I know someone who says they had to have 2 discs replaced in their spine....the scar from the surgery however is just below their bellybutton, going down in a straight line....Now I know nothing about disc replacement surgery...but wouldn't they go in through your back...
To anyone who's had disc replacement/problems
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Total Disc Replacement ? St. Mary's Experience
Vikram Parmer MD, James Zucherman MD, Ken Hsu MD, Paul Fuchs MD
Functions of the intervertebral disk
Mobility
Weight Bearing
Provide stability
What happens to the diseased intervertebral disk?
Limitations of current treatments for the diseased intervertebral disk
Goals of intervertebral disk replacement
Contraindications
Designs
Components of the modern disk replacement
Prospective randomized double blind trial of the ProDisc intervertebral disk prosthesis versus interbody fusion
Inclusion and exclusion criteria
Surgical Technique
Results
Complications
Future Goals
It is classically taught that the lumbar spine is designed to provide axial rigidity to the lower trunk, to sustain axial compression loads exerted from the trunk and upper limbs and to permit movements between the trunk and pelvis. A functional spinal motion segment has three articulations ? the intervertebral disk and the two posterior facet joints. The intervertebral disk is responsible for transmission and stabilizing a combination of compressive, torsional and bending forces subjected to the trunk of the body. The hydrostatic pressures in the inner gel like nucleus pulposus resist compressive and bending forces while torsional forces are mainly resisted by the outer annular fibers. The facets joints provide a posterior articulation between adjacent vertebrae and limit mobility of the motion segment. There is a close relationship between the intervertebral disk and the posterior facet joints. Facet arthrosis and degeneration do not occur without the presence of adjacent disk degeneration.
During the degenerative process, changes occur in the nucleus and annulus. In the nucleus, chemical changes decrease proteoglycan content, thereby impairing its ability to bind water and bear axial loads. This results in abnormal loading of the motion segment with the annular fibers being subjected to excessive stresses. Deterioration of the annulus results. This allows stimulation of the pain fibers in the annulus leading to back pain symptoms. The combination of degenerative disk changes and accompanying facet deterioration are hallmarks of the degenerative cascade. In addition to axial back pain, end stage consequences of the degenerative cascade may include symptomatic spinal stenosis, degenerative spondylolisthesis and degenerative scoliosis.
Current surgical treatments for degenerative spinal problems do not restore normal spinal function. Diskectomy and laminectomy violate the three joint complex and often increase segmental instability. The instability may require fusion. Fusion itself is not without problems. Fusion procedures have been shown to accelerate the degenerative process and lead to adjacent instability and spinal stenosis. Other problems with fusion include chronic bone donor site pain and the need for further procedures such as implant removal.
In reviewing the literature, spinal fusion has varied success rates. A 65% to 93% success rate has been described in the current literature. Even when one attains "successful" lumbosacral arthrodesis or fusion, there are still long-term sequelae that must be considered. Additionally, there are inherent drawbacks. Kostuik in Orthopaedic Clinics of North America 1998, estimated that approximately 30% of patients who underwent fusion had long-term sequelae. He did state, though, that fusion was successful in the majority of patients. The main issue with spinal fusion is adjacent segment degeneration. After spinal fusion, motion segments are removed from function, and as a result spinal levels adjacent to the fusion have additional stress placed upon them. Premature disc degeneration, instability, and premature arthritis are all potential issues at the adjacent segments after a fusion. Authors such ask C.K. Lee in Spine in 1988 and T.R. Lehman in Spine in 1987 have confirmed the phenomenon of adjacent segment degeneration. Additionally, Hsu and Zucherman at the NASS meeting in 1988 presented their experience. They showed that the addition of rigid instrumentation commonly used during fusion procedures can lead to even further stress upon the adjacent segments. There are still further concerns, such as pseudarthrosis, graft site pain, stress shielding, disuse osteoporosis, and instrument failure in association with fusion procedures.
Because of concerns with fusion procedures, there is a significant amount of interest in total disc replacement (TDR). Proponents of TDR state that total disc replacement would potentially relieve symptoms, prevent long-term issues associated with fusion, and also remove the diseased disc, commonly known as the "pain generator." In addition, other major goal of disk replacement surgery includes maintaining and restoring normal segmental spinal motion. It would restore the disk space height and therefore restore the segmental lordosis. It would allow indirect decompression of foraminal stenosis and protect adjacent levels from iatrogenically accelerated degeneration.
Fernstrom is credited with the first disc replacement in 1966 (See Fig. 1 and 2). The disc replacement consisted of essentially a ball bearing that was placed between the vertebral bodies in the spine. This failed because of subsidence into the vertebral body over time, as well as loosening and expulsion. Since that time, other physicians have invented their own form of disc replacement. While the literature is somewhat sparse, Lee, Ray, Steffee, Buttner-Jans (Charite) (Fig. 3), and Marnay (ProDisc) (Fig. 4) have documented their individual experiences with their respective disc replacements. These authors have proposed disc replacement as a substitution for fusion in order to treat back pain and at the same time preserve vertebral motion.
Today, both in Europe and the United States, there has been great success with total joint arthroplasty, specifically in the knee and hip (Fig. 5 and 6), and to a somewhat lesser extent in the shoulder. Prior to total hip arthroplasty, for example, a patient had to deal with decreased function as well as long-term pain. Their options for treatment were essentially limited. Some patients were told just to "deal with their pain." Others tried bracing, pain medicines, therapy, and activity modification. Unfortunately, they had to refrain from activities they enjoyed. Fusion was an option, and it provided significant pain relief, but at the expense of motion. Additionally, these patients underwent premature wear and tear of the surrounding joints, most notably the contralateral hip, the knees, the feet, and the spine. At this time, total joint arthroplasty of knees and hips has surpassed fusion as the standard of care. The reason for this is that the long-term results are excellent. The patients sustain significant functional improvement. Additionally, the indications for this procedure are straightforward. On the other hand, spinal fusion is still widely performed for many etiologies. Very commonly in the United States, spinal fusion is performed for discogenic back pain as well as instability.
From a clinical standpoint general indications for disk replacement surgery include: (1) patients with back and leg pain not responsive to appropriate nonsurgical treatment, (2) symptomatic 1 or 2 level disk changes associated with collapse, (3) symptomatic early stage disk changes identified by MRI and/or diskogram in the absence of facet arthritis, (4) and patients without prior history of back surgery at the affected level.
Major contraindications include facet joint arthrosis, spinal instability, altered posterior elements secondary to prior surgery (such as laminectomy, and facetectomy), infection and metabolic bone diseases (osteoporosis).
Kostuik in Orthopaedic Clinics of North America reviewed his prerequisites and criteria for biomechanically and functionally successful disc replacement. First, disc replacements would need to be durable. As disc replacements would be placed in patients in the age range of 30 to 50 years of age, they should be able to last 40 years. He estimated that during this time period, a motion segment would undergo 85 million cycles, and as a result testing should be performed at 1 million cycles. Also, the materials must be compatible, and we must be conscientious of the volume of wear particles. It is known from the total joint literature that the body responds to wear particles and osteolysis is the result. Osteolysis is a major concern because of bone loss and loosening of implants. Additionally, there are corrosion issues. Implants with dissimilar metals can potentially cause corrosion and premature wear of the implant. The implant must also have a long fatigue life so that fracture and breakage do not occur. Geometry of the disc placement prosthesis needs to be such that neurovascular structures are not impinged upon or put at risk. There also needs to be the ability to implant the disc replacement at contiguous levels. The kinematics of the disc replacement should ideally match those of the healthy disc. Numerous studies have been performed, which have determined the range of motion of the native discs, and the disc replacements should emulate these ranges of motion. The disc replacements need to have dynamics which are equal to the inherent disc as well. The disc has a natural stiffness about it. The disc replacement should duplicate the native disc stiffness in order to transmit physiologic stresses. Without the transmission of physiologic stresses, there could be bone resorption, which would lead to implant loosening, or with too much stress there would be bone deposition. Bone deposition could cause decreased range of motion of the prosthesis, or impinge upon neurovascular structures. Finally, bone fixation is critical. The implant has to have immediate and long-term bone fixation to maintain its function. The disc replacement needs to be fail-safe so it can resist catastrophic failure and maintain its integrity in the case of a major trauma to the spine.
There have been numerous prototypes and models invented.
The Fernstrom, as stated, was essentially a ball bearing, but failed because of settling, loosening, and expulsion. (Fig. 1 and 2)
The Lee disc replacement was a polymer combination in order to replicate the consistencies of the natural disc. There was a central portion of the disc which was a soft polymer in order to replicate the soft nucleus pulposus of the inherent disc. On the outer portion of the disc replacement, the polymer had a moderate hardness in order to emulate the annulus fibrosus. The endplates had a significant hardness to them so that they would be more similar to the bony endplates in the native spine. (Fig. 7)
Froning developed a disc replacement that had implant anchoring pins and an inflatable bladder, which could be inflated to desired pressures. (Fig. 8)
Edland had a disc replacement that looked similar to a tire with spokes. This disc replacement could be folded and then inserted into the disc space. (Fig. 9)
Khvisyuk developed a disc replacement with metal endplates and spikes for anchoring. There was a silicone cushion between the two endplates, and it was "pinned" into place. (Fig. 10)
Kuntz developed a disc replacement that resembled a "clothespin" and had a central hinge to allow for flexion and extension. (Fig. 11)
Patil developed a disc replacement that resembled a box with springs. Unfortunately, the main limitation was scar formation, which filled in the spaces and inhibited the spring action. (Fig. 12)
The Steffee disc had metal endplates with porous coating to allow for bone ingrowth as well as an elasteromeric cushion between the two endplates. (Fig. 13) The early versions of this disc replacement failed because of separation of the elasteromeric cushion from the endplates. Additionally, there were concerns about toxicity of the intervening material.
The Downey disc replacement looked similar to a top with anchoring pins as well as an elasteromeric wafer, which was bonded to and over the plates. (Fig. 14)
Ray had a disc replacement that was slightly different than the previous ones. (Fig. 15) The native annulus was left intact, but the nucleus was replaced. These were "bags" that were semipermeable with a core made of hyaluronic acid, which imbibed water and allowed the disc replacement to swell. These devices were inserted posteriorly after disc removal. Problems experienced with this disc replacement included expulsion of the prosthesis.
Kostuik invented a disc replacement that was all metal. (Fig. 16 and 17) The endplates were made of cobalt-chrome, and the springs were made of titanium. There was a posterior hinge as well as screws that allowed the replacement to be secured for early fixation.
Buttner-Jans invented the Charite disc replacement. (Fig. 18, 19, and 20) This disc replacement has metal endplates with spikes, as well as a high molecular weight polyethylene spacer. These endplates are porous coated for bone ingrowth. The polyethylene insert does not lock into place, and there is motion on both the superior portion of the polyethylene and the inferior portion of the polyethylene on the respective metal endplates.
There is a paucity in the literature today concerning total disc replacement. The Charite has the most data. The Charite has gone through three generations, and it dates back to 1984. There have been device failures with earlier designs, but no device failures with the most recent model. The Charite comes in three sizes, and still maintains the cobalt-chromium endplates and the ultra high molecular weight polyethylene sliding core. It is inserted through an anterior transabdominal approach. There are three sizes of the polyethylene core, which allow for customization of disc height. During implantation, it is anchored to the bony endplates in the vertebral bodies and inserted with special intervertebral spreader tools.
Several authors have reviewed their experiences of the Charite device. Buttner-Jans in 1988 reviewed his initial clinical experience of 62 patients, and he submitted that there were 83% very satisfactory or "better-than-before" operation results. T. David in the European Spine Journal in 1993 reviewed his results with the Charite in 22 patients. He had a minimum of a one-year follow-up and 65% excellent or good results. He concluded that the disc replacement procedure had a very narrow application, and artificial disc replacement, in his opinion, was not a routine procedure. Griffith et al in Spine in 1994 had the first multi-center, multi-surgeon, retrospective review of the Charite. There were 93 patients in which the Charite 3 device was inserted. The most common diagnosis was degenerative disc disease in 52%, and the most common level implanted was the L4-5 level. The follow-up was 11.5 +/- 8.4 months. He reported a significant functional and pain improvement, although there was no work status change in the patients evaluated. There was a 6.5% incidence of migration, subsidence, and dislocation. He concluded that prospective randomized studies were needed to compare artificial disc replacement versus fusion procedures. Cinotti et al in Spine in 1996 also performed a one-surgeon retrospective review of 46 Charite 3 devices. He had a minimum of a two-year follow-up. The diagnoses were approximately 50% degenerative disc disease and 50% failed disc excision. They had a 69% satisfactory result for one-level procedures, and a 40% satisfactory result with two-level procedures. He determined that central and posterior placement of the prosthesis allowed more motion postoperatively. Additionally, they determined that patients who were allowed to undergo early exercise (versus three months of corset wear) had significant improvement in range of motion at the implanted level. They hypothesized that their poorer results in two-level procedures were because of the following: this device was difficult (in their experience) to implant at two levels because of excessive distraction that had to be performed at the second level; additionally, at the second level, a smaller device needed to be inserted, and this device needed to be inserted more anteriorly, very likely contributing to decreased range of motion at that second level. They concluded that in their hands, success was less than seen in fusion cases. The poor outcome was possibly due to their poor patient selection. The Charite in their opinion was not suitable for two levels, and they also determined that prospective randomized studies were needed to evaluate disc replacement versus fusion procedures.
The ProDisc total disk prosthesis utilizes total joint replacement knowledge in its design. The goal for the prosthesis is to restore anatomy and motion, and at the same time relieve pain and improve outcome. The ProDisc has a modular design with a superior and inferior cobalt-chrome endplate. (Fig. 21) The surfaces are porous (titanium plasma spray) to allow for bone ingrowth. Additionally, the inferior endplate allows for a polyethylene insert to be snapped into place utilizing a locking mechanism. (Fig. 22) The superior and inferior endplates have keels and two pegs on them, which allow for initial stability. (Fig. 23) Long-term fixation is afforded by bony ingrowth into the porous coating on the superior and inferior endplates. The ProDisc implant offers 6° or 11° of lordosis, and has heights of 10, 12, or 14 mm. Also, the design of the ProDisc is modeled closely after the morphology of the inherent disc. (Fig. 24) The ProDisc allows 13° of flexion and 7° of extension, closely following the normal range of motion of 10° of flexion and 5° of extension documented in the literature. Lateral bending is slightly more than the native disc. The ProDisc allows 10° of right and left lateral bending, compared to the inherent motion segment with left and right lateral bending of 5°. The axial rotation of the ProDisc is unconstrained as compared to the inherent motion segment, which allows 3°. The potential concern in this case is that excess stress will be placed upon the posterior elements. This could possibly cause premature stress upon the articular cartilage and resulting arthritis. This is speculative, though. There has been mechanical testing of the ProDisc to assess the "creep" of the ultra high molecular weight polyethylene, and to assess motion of the implant into the vertebral bodies. Also, the implant's response to shear stresses and wear of the ultra high molecular weight polyethylene has been evaluated. The ProDisc representatives, through their research, report that the ProDisc has a minimum of 22% less creep that the Charite device. Also, the ProDisc has less progressive increase in creep deformation at increasing load than the Charite. The ProDisc has a minimum 10% less permanent deformation than the Charite as well. The ProDisc inlay shows no loss of the snap-in function of the polyethylene. Migration of the implant starts at 12 KN without any evidence of tilting. The ProDisc results in a smoother pressure transition at the implant rim because of the radius of the implant. Compared to the Charite, the ProDisc shows fixation strength in shear without sudden failure. In mechanical testing, dislocation starts at 450 newtons of shear force and 0.3 mm displacement without any evidence of tilting. Wear fatigue testing shows the ProDisc to have a 30% less wear factor compared to total knee and total hip replacements. The ProDisc model shows minimal ultra high molecular weight polyethylene (UHMWP) cold flow. Finally, the ProDisc in biomechanical testing shows no signs of fatigue, breakage, or delamination under microscopic evaluation.
The earlier ProDisc results have been evaluated by their inventor, Dr. Marnay. He had an outside organization perform a prospective review of 61 of his cases. 95% were available for follow-up at seven to eleven years. 33% of these procedures were performed at two levels. At follow-up, all of the prostheses were intact and functioning, and there was no evidence of subsidence or migration. Additionally, there were no revisions or removals, and there were 92.7% of the patients who were satisfied or entirely satisfied. They concluded that there was no difference in results in one- or two-level implantations, and there were no device-related safety issues. Weichert et al reported a 6 month followup of 16 ProDisc patients where the mean Visual analog scale (VAS) score improved from 7.0 to 1.9 and the Oswestry Pain Score improving from 23.3 to 10.2. Bertagnoli and Kumar published results of a 108 patient series with a followup period of 3-24 months. They reported that 91% of the patients have excellent outcome, 8% with a good outcome and 1% with a fair outcome. The obvious drawback was that the specific criteria used to make the classification system were not clearly defined.
The St. Mary's Spine Center (San Francisco, California) is involved in a multi-center prospective randomized controlled clinical trial, evaluating the ProDisc total disc replacement. The study consists of 510 cases. 340 cases utilize the ProDisc, and these will be compared to 170 fusion cases. The follow-up will be a minimum of 24 months, and the goal is to assess the safety and effectiveness of the disc replacement. The inclusion criteria include: (1) Back and/or leg pain and radiographs (CT,MRI, plain films or myelograms) showing any one of the following: (i) instability (> 3mm translation, ,> 5 mm angulation), (ii) decreased disk height > 2mm, (iii) scarring/thickening of the annulus fibrosis, (iv) herniated nucleus pulposus, (v) vacuum phenomenon, (2) age range 19 to 59 years old, (3) failed 6 months conservative treatment, (4) Oswestry low back pain disability questionnaire score at least 20 out of 50 and a (5) signed informed consent.
Exclusion criteria include: (1) greater than 2 levels of degenerative disk disease, (2) known allergy to titanium, polyethylene, cobalt, chromium and molybdenum, (3) prior fusion at any lumbar level, (4) clinically compromised vertebral bodies at affected levels secondary to current or past trauma , (5) radiographically documented evidence of facet joint disease, (6) lytic spondylolisthesis or spinal stenosis, (7) degenerative spondylolisthesis greater than grade one, (7) back or leg pain of unknown etiology, (8) osteoporosis, (9) Paget's disease, (10) morbid obesity (Body Mass Index > 40, weight > 100 pounds over ideal body weight, (11) pregnant or plan pregnancy within 3 years, (12) taking medications that interfere with bone/soft tissue healing, (13) presence of rheumatoid arthritis or autoimmune disease, (14) active malignancy.
Spinal fusion was chosen as the randomized control in the study. A circumferential fusion was performed in all the patients randomized to receive a fusion. The fusion was either an anterior lumbar interbody fusion (ALIF) or a posterior lumbar interbody fusion (PLIF) using a commercially available femoral ring allograft along with a posterior lateral fusion with autogenous iliac crest autograft. Pedicle screw instrumentation using the Ti alloy CD system from Medtronic Sofamor Danek was placed in each patient receiving a fusion.
The surgical technique for the disk replacement in all patients consisted of 8 reproducible steps. All cases were performed with the patient in a supine position on a standard radiolucent operative table. The surgical approach was an anterior retroperitoneal approach for each patient. Once the appropriate disk level was exposed, a complete diskectomy was performed including removal of the cartilage from the superior and inferior endplates and removal of the posterior longitudinal ligament. Next trial implants were inserted to determine the size of the prosthesis. After, trialing for the size of the final component, a chisel was used under fluoroscopic guidance to prepare the position of the keel of the superior and inferior components. Next, the two plate components, pre-assembled on a back table were inserted in the determined position. Under fluoroscopic guidance, the surgical goal was to place the prosthesis in the midline in the frontal plane and as posterior as possible in the sagittal plane without entering the spinal canal. Distraction was next performed with a distractor instrument and the polyethylene inlay component was inserted and locked into the inferior plate component. Finally, the insertion instruments were removed and water tight closure was performed. The patients were ambulated with the assistance of a physical therapist on post operative day one. Post-operative follow up data will be recorded at 6 weeks and then at 3,6,9,12,18, and 24 months.
Outcome measures recorded during the study include four patient self-assessments: (1) Oswestry Low Back Pain disability questionnaire, (2) SF-36 Health Survey, (3) Overall Pain on a 10 cm Visual Analog Scale, (4) Satisfaction on a 10 cm Visual Analog Scale. In addition, the primary investigator performed a physical and neurological examination checking for range of motion, bone graft donor site, root tension signs, reflexes, muscle strength, and sensory deficits. Radiographic examination consisting of standing AP and lateral films, flexion/extension films and lateral bending films were also obtained. The above outcome measures were recorded pre-operatively and during each post-operative visit.
The series at St Mary's Spine center currently consists of 29 patients who have received 40 intervertebral disk arthroplasties. In addition, 12 patients were randomized to fusion. Three patients who received a total of 4 disk arthroplasties have 18 month follow-up. Five patients who received 5 disk arthroplasties have 12 to 18 month follow up. Seven patients who received 11 disk arthroplasties have 6 to 12 month follow up and 13 patients who received 19 disk replacements have 3 to 6 month follow-up. One patient has currently been followed for two months. For the 29 patients, the average pre-op Oswestry pain score was 25.2 and the average score at the most recent follow-up was 19.8, a 22 percent decrease. In patients with 18 month follow up, the average Oswestry score has fallen from 29.6 (range 29-31) to 19.3(range 14-24), a 35 percent decrease. In the 12-18 month group, the average score fell from 31.8 (range 24-39) to 22.4 (range 11 to 30), a 30 percent decrease. In the 6 to 12 month group, the average score has dropped from 26 (range 20 to 31) to 22 (range 16-31), a 15 percent decrease. In the three to six month follow up group, the average Oswestry score fell from 21 (range 21-40) to 17 (range 0 to 36) , a 20 percent decrease. As would be expected, the further out from the replacement procedure the patients get, the greater the decrease in the Oswestry score. This allows for the patients' surgical sites to heal and for the patients to complete the appropriate post-op rehabilitation regimen.
The pre-op range of motion average at the operated levels in the group followed for at least 18 months included 8.25 degrees on the flexion/extension and 10.75 degrees on the lateral bending. The range of motion at the most recent follow-up averaged 8 degrees on the flexion/extension views and averaged 6.5 degrees on the lateral bending views. In the group with 12-18 month follow up, the pre-op and most recent post-op visit range of motions on flexion/extension views were 6.8 and 6.2 degrees respectively. On the lateral bending views, the pre-op and most recent post-op visit range of motions was 4 and 2 degrees respectively. In the group with 6-12 month follow-up, the pre-op and post-op range of motions on the flexion/extension views were 4.2 and 4.2 degrees respectively. On the lateral bending views, the pre-op and post-op range of motions was 3.0 and 4.2 degrees respectively. In the group with 3-6 month follow up, the pre-op and post-op range of motions on the flexion/extension views averaged 5.2 and 7 degrees respectively while on the lateral bending views, the pre-op and most recent post-op visit wee 2.2 and 3.3 degrees respectively. The above values suggest that range of motion was maintained at the operated levels. The long term effect of preserving the range of motion in preventing the degenerative cascade requires further follow up. Of the 40 cases 16 disk replacements involved the L4-L5 level. The pre-op range of motions of flexion/extension and lateral bending were 9.2 and 4.8 degrees respectively. The post-op range of motion in flexion/extension and lateral bending averaged 7.14 and 5 degrees respectively. The other 24 replacements were at the L5-S1 level. The pre-op range of motions for flexion/extension and lateral bending were 5.25 and 2.7 degrees while the post-op range of motions were 5.4 and 3.3 degrees respectively.
Further review of the radiographs revealed no patient who received an arthroplasty had implant migration and subsidence (> 3mm). No patient had extensive radiolucency along the implant/bone interface (> 25% of the interface's length for each endplate). There has been no loss of disk height in any operated disk arthroplasty and no arthroplasty has evidence of bony fusion.
Commonly associated post-operative complications associated with lumbar disk replacement procedures include: (1) abdominal wall hematomas, (2) vascular injury, (3) dural tears, (4) Nerve injury, (5) Retrograde ejaculation in males, (6) Migration of the prosthesis. In our series of 40 disk replacements, there has been one incident of a common iliac artery tear discovered intra-operatively and repaired. The patient's post-operative course proceeded without incident. There have been no re-operations in either the disk arthroplasty group or the fusion group.
Total disk replacement is essentially in its infancy. The early studies of Marnay and the ProDisc are encouraging. There is no doubt further randomized prospective trials are needed to evaluate total disc replacement versus fusion as a viable option in degenerative lumbar disk disease. The advantage of this study is that in addition to being a prospective, randomized double blind trial, outcomes are being measured using standard assessments such as the Oswestry low back pain questionnaire and visual analog scale. As spine surgeons learn more about total disk replacement, it is imperative that strict indications are developed.
References
Bertagnoli R, Kumar S. Indications for full prosthetic disc arthroplasty: A correlation of clinical outcome against a variety of indications. Eur Spine J. 11(suppl. 2): S124-30. 2002
Bogduk N: The artificial disc. In Churchill Clinical Anatomy of the Lumbar Spine and Sacrum, 3rd ed. Edinburgh, Livingstone, 1997
Buttner-Janz K, Scheilnack K, Zippel H: Biomechanics of the SB Charite lumbar intervertebral disc endoprosthesis. Int Orthop 13: 173-176. 1989
Cinotti G, David T, et al.: results of disc prosthesis after a minimum follow up period of 2 years. Spine 21: 995-1000. 1996
David T: Lumbar Disc prosthesis. Eur Spine J. 1: 254-259. 1993
Edeland HG: Some additional suggestions for an intervertebral disc prosthesis. J Biomech Eng. 7: 7-62, 1985
Fairbank JCT, Couper Mbaot J, Davies, et al: The Oswestry Low Back Pain Questionnaire. Physiotherapy. 66: 271-272. 1980
Fernstrom U: Arthroplasty with intercorporal endoprosthesis in herniated disc and in painful disc. Acta Chir Scand (Suppl) 357: 154-159, 1966
Froming N: Artificial Intervertebral Disc. United States Patent File. 1974
Griffith S, et al.: A multicenter retrospective study of the clinical results of the Link SB Charite intervertebral prosthesis. The Initial European Experience. Spine 19: 1842-1849. 1994
Haher TR, et al: The role of the lumbar facet joints in spinal stability. Identification of alternative paths of loading. Spine 19: 2667-2670, 1994
Hsu KY, Zucherman J, et al.: Deterioration of motion segments adjacent lumbar spinal fusion. Presented at the annual meeting of the North American Spine society. Colorado Springs, Colorado, July 24-27, 1988
Kostiuk JP: Alternatives to Spinal Fusion, Orthop Clin North Am 29: 701-715, 1998
Lee CK: Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine. 13:475-477. 1988
Lee CK, Langrana NA, Parsons JR, et al.: Functional Disc prosthesis. Transactions of the 45th annual meeting of the orthopaedic research society: Las Vegas, Nevada, February.
Marnay T: Lumbar disc arthroplasty, 8-10 year results using titanium plates with a polyethylene inlay component. Presented at the annual meeting of the American Academy of Orthopaedic Surgeons, March 2001, San Francisco, California
Patil AA: Artificial Intervertebral Disc. United States Patent File. 1982
Ray C: Artificial disc. Present at the Challenge of the Lumbar Spine 1988 Meeting. San Antonio, Texas, November 9-14, 1988.
Steffee A: Artificial disc. Presented at the Challenge of the Lumber Spine 1988 Meeting. San Antonio, Texas, November 9-14, 1988.
Wiechert K, Mayer HM, Marnay et al: ProDisc. Preliminary results of a multicenter prospective clinical trial. Presented at the Spine Arthroplasty Conference, May 2001, Munich, Germany.
Total Disc Replacement ? St. Mary's Experience
Vikram Parmer MD, James Zucherman MD, Ken Hsu MD, Paul Fuchs MD
Functions of the intervertebral disk
Mobility
Weight Bearing
Provide stability
What happens to the diseased intervertebral disk?
Limitations of current treatments for the diseased intervertebral disk
Goals of intervertebral disk replacement
Contraindications
Designs
Components of the modern disk replacement
Prospective randomized double blind trial of the ProDisc intervertebral disk prosthesis versus interbody fusion
Inclusion and exclusion criteria
Surgical Technique
Results
Complications
Future Goals
It is classically taught that the lumbar spine is designed to provide axial rigidity to the lower trunk, to sustain axial compression loads exerted from the trunk and upper limbs and to permit movements between the trunk and pelvis. A functional spinal motion segment has three articulations ? the intervertebral disk and the two posterior facet joints. The intervertebral disk is responsible for transmission and stabilizing a combination of compressive, torsional and bending forces subjected to the trunk of the body. The hydrostatic pressures in the inner gel like nucleus pulposus resist compressive and bending forces while torsional forces are mainly resisted by the outer annular fibers. The facets joints provide a posterior articulation between adjacent vertebrae and limit mobility of the motion segment. There is a close relationship between the intervertebral disk and the posterior facet joints. Facet arthrosis and degeneration do not occur without the presence of adjacent disk degeneration.
During the degenerative process, changes occur in the nucleus and annulus. In the nucleus, chemical changes decrease proteoglycan content, thereby impairing its ability to bind water and bear axial loads. This results in abnormal loading of the motion segment with the annular fibers being subjected to excessive stresses. Deterioration of the annulus results. This allows stimulation of the pain fibers in the annulus leading to back pain symptoms. The combination of degenerative disk changes and accompanying facet deterioration are hallmarks of the degenerative cascade. In addition to axial back pain, end stage consequences of the degenerative cascade may include symptomatic spinal stenosis, degenerative spondylolisthesis and degenerative scoliosis.
Current surgical treatments for degenerative spinal problems do not restore normal spinal function. Diskectomy and laminectomy violate the three joint complex and often increase segmental instability. The instability may require fusion. Fusion itself is not without problems. Fusion procedures have been shown to accelerate the degenerative process and lead to adjacent instability and spinal stenosis. Other problems with fusion include chronic bone donor site pain and the need for further procedures such as implant removal.
In reviewing the literature, spinal fusion has varied success rates. A 65% to 93% success rate has been described in the current literature. Even when one attains "successful" lumbosacral arthrodesis or fusion, there are still long-term sequelae that must be considered. Additionally, there are inherent drawbacks. Kostuik in Orthopaedic Clinics of North America 1998, estimated that approximately 30% of patients who underwent fusion had long-term sequelae. He did state, though, that fusion was successful in the majority of patients. The main issue with spinal fusion is adjacent segment degeneration. After spinal fusion, motion segments are removed from function, and as a result spinal levels adjacent to the fusion have additional stress placed upon them. Premature disc degeneration, instability, and premature arthritis are all potential issues at the adjacent segments after a fusion. Authors such ask C.K. Lee in Spine in 1988 and T.R. Lehman in Spine in 1987 have confirmed the phenomenon of adjacent segment degeneration. Additionally, Hsu and Zucherman at the NASS meeting in 1988 presented their experience. They showed that the addition of rigid instrumentation commonly used during fusion procedures can lead to even further stress upon the adjacent segments. There are still further concerns, such as pseudarthrosis, graft site pain, stress shielding, disuse osteoporosis, and instrument failure in association with fusion procedures.
Because of concerns with fusion procedures, there is a significant amount of interest in total disc replacement (TDR). Proponents of TDR state that total disc replacement would potentially relieve symptoms, prevent long-term issues associated with fusion, and also remove the diseased disc, commonly known as the "pain generator." In addition, other major goal of disk replacement surgery includes maintaining and restoring normal segmental spinal motion. It would restore the disk space height and therefore restore the segmental lordosis. It would allow indirect decompression of foraminal stenosis and protect adjacent levels from iatrogenically accelerated degeneration.
Fernstrom is credited with the first disc replacement in 1966 (See Fig. 1 and 2). The disc replacement consisted of essentially a ball bearing that was placed between the vertebral bodies in the spine. This failed because of subsidence into the vertebral body over time, as well as loosening and expulsion. Since that time, other physicians have invented their own form of disc replacement. While the literature is somewhat sparse, Lee, Ray, Steffee, Buttner-Jans (Charite) (Fig. 3), and Marnay (ProDisc) (Fig. 4) have documented their individual experiences with their respective disc replacements. These authors have proposed disc replacement as a substitution for fusion in order to treat back pain and at the same time preserve vertebral motion.
Today, both in Europe and the United States, there has been great success with total joint arthroplasty, specifically in the knee and hip (Fig. 5 and 6), and to a somewhat lesser extent in the shoulder. Prior to total hip arthroplasty, for example, a patient had to deal with decreased function as well as long-term pain. Their options for treatment were essentially limited. Some patients were told just to "deal with their pain." Others tried bracing, pain medicines, therapy, and activity modification. Unfortunately, they had to refrain from activities they enjoyed. Fusion was an option, and it provided significant pain relief, but at the expense of motion. Additionally, these patients underwent premature wear and tear of the surrounding joints, most notably the contralateral hip, the knees, the feet, and the spine. At this time, total joint arthroplasty of knees and hips has surpassed fusion as the standard of care. The reason for this is that the long-term results are excellent. The patients sustain significant functional improvement. Additionally, the indications for this procedure are straightforward. On the other hand, spinal fusion is still widely performed for many etiologies. Very commonly in the United States, spinal fusion is performed for discogenic back pain as well as instability.
From a clinical standpoint general indications for disk replacement surgery include: (1) patients with back and leg pain not responsive to appropriate nonsurgical treatment, (2) symptomatic 1 or 2 level disk changes associated with collapse, (3) symptomatic early stage disk changes identified by MRI and/or diskogram in the absence of facet arthritis, (4) and patients without prior history of back surgery at the affected level.
Major contraindications include facet joint arthrosis, spinal instability, altered posterior elements secondary to prior surgery (such as laminectomy, and facetectomy), infection and metabolic bone diseases (osteoporosis).
Kostuik in Orthopaedic Clinics of North America reviewed his prerequisites and criteria for biomechanically and functionally successful disc replacement. First, disc replacements would need to be durable. As disc replacements would be placed in patients in the age range of 30 to 50 years of age, they should be able to last 40 years. He estimated that during this time period, a motion segment would undergo 85 million cycles, and as a result testing should be performed at 1 million cycles. Also, the materials must be compatible, and we must be conscientious of the volume of wear particles. It is known from the total joint literature that the body responds to wear particles and osteolysis is the result. Osteolysis is a major concern because of bone loss and loosening of implants. Additionally, there are corrosion issues. Implants with dissimilar metals can potentially cause corrosion and premature wear of the implant. The implant must also have a long fatigue life so that fracture and breakage do not occur. Geometry of the disc placement prosthesis needs to be such that neurovascular structures are not impinged upon or put at risk. There also needs to be the ability to implant the disc replacement at contiguous levels. The kinematics of the disc replacement should ideally match those of the healthy disc. Numerous studies have been performed, which have determined the range of motion of the native discs, and the disc replacements should emulate these ranges of motion. The disc replacements need to have dynamics which are equal to the inherent disc as well. The disc has a natural stiffness about it. The disc replacement should duplicate the native disc stiffness in order to transmit physiologic stresses. Without the transmission of physiologic stresses, there could be bone resorption, which would lead to implant loosening, or with too much stress there would be bone deposition. Bone deposition could cause decreased range of motion of the prosthesis, or impinge upon neurovascular structures. Finally, bone fixation is critical. The implant has to have immediate and long-term bone fixation to maintain its function. The disc replacement needs to be fail-safe so it can resist catastrophic failure and maintain its integrity in the case of a major trauma to the spine.
There have been numerous prototypes and models invented.
The Fernstrom, as stated, was essentially a ball bearing, but failed because of settling, loosening, and expulsion. (Fig. 1 and 2)
The Lee disc replacement was a polymer combination in order to replicate the consistencies of the natural disc. There was a central portion of the disc which was a soft polymer in order to replicate the soft nucleus pulposus of the inherent disc. On the outer portion of the disc replacement, the polymer had a moderate hardness in order to emulate the annulus fibrosus. The endplates had a significant hardness to them so that they would be more similar to the bony endplates in the native spine. (Fig. 7)
Froning developed a disc replacement that had implant anchoring pins and an inflatable bladder, which could be inflated to desired pressures. (Fig. 8)
Edland had a disc replacement that looked similar to a tire with spokes. This disc replacement could be folded and then inserted into the disc space. (Fig. 9)
Khvisyuk developed a disc replacement with metal endplates and spikes for anchoring. There was a silicone cushion between the two endplates, and it was "pinned" into place. (Fig. 10)
Kuntz developed a disc replacement that resembled a "clothespin" and had a central hinge to allow for flexion and extension. (Fig. 11)
Patil developed a disc replacement that resembled a box with springs. Unfortunately, the main limitation was scar formation, which filled in the spaces and inhibited the spring action. (Fig. 12)
The Steffee disc had metal endplates with porous coating to allow for bone ingrowth as well as an elasteromeric cushion between the two endplates. (Fig. 13) The early versions of this disc replacement failed because of separation of the elasteromeric cushion from the endplates. Additionally, there were concerns about toxicity of the intervening material.
The Downey disc replacement looked similar to a top with anchoring pins as well as an elasteromeric wafer, which was bonded to and over the plates. (Fig. 14)
Ray had a disc replacement that was slightly different than the previous ones. (Fig. 15) The native annulus was left intact, but the nucleus was replaced. These were "bags" that were semipermeable with a core made of hyaluronic acid, which imbibed water and allowed the disc replacement to swell. These devices were inserted posteriorly after disc removal. Problems experienced with this disc replacement included expulsion of the prosthesis.
Kostuik invented a disc replacement that was all metal. (Fig. 16 and 17) The endplates were made of cobalt-chrome, and the springs were made of titanium. There was a posterior hinge as well as screws that allowed the replacement to be secured for early fixation.
Buttner-Jans invented the Charite disc replacement. (Fig. 18, 19, and 20) This disc replacement has metal endplates with spikes, as well as a high molecular weight polyethylene spacer. These endplates are porous coated for bone ingrowth. The polyethylene insert does not lock into place, and there is motion on both the superior portion of the polyethylene and the inferior portion of the polyethylene on the respective metal endplates.
There is a paucity in the literature today concerning total disc replacement. The Charite has the most data. The Charite has gone through three generations, and it dates back to 1984. There have been device failures with earlier designs, but no device failures with the most recent model. The Charite comes in three sizes, and still maintains the cobalt-chromium endplates and the ultra high molecular weight polyethylene sliding core. It is inserted through an anterior transabdominal approach. There are three sizes of the polyethylene core, which allow for customization of disc height. During implantation, it is anchored to the bony endplates in the vertebral bodies and inserted with special intervertebral spreader tools.
Several authors have reviewed their experiences of the Charite device. Buttner-Jans in 1988 reviewed his initial clinical experience of 62 patients, and he submitted that there were 83% very satisfactory or "better-than-before" operation results. T. David in the European Spine Journal in 1993 reviewed his results with the Charite in 22 patients. He had a minimum of a one-year follow-up and 65% excellent or good results. He concluded that the disc replacement procedure had a very narrow application, and artificial disc replacement, in his opinion, was not a routine procedure. Griffith et al in Spine in 1994 had the first multi-center, multi-surgeon, retrospective review of the Charite. There were 93 patients in which the Charite 3 device was inserted. The most common diagnosis was degenerative disc disease in 52%, and the most common level implanted was the L4-5 level. The follow-up was 11.5 +/- 8.4 months. He reported a significant functional and pain improvement, although there was no work status change in the patients evaluated. There was a 6.5% incidence of migration, subsidence, and dislocation. He concluded that prospective randomized studies were needed to compare artificial disc replacement versus fusion procedures. Cinotti et al in Spine in 1996 also performed a one-surgeon retrospective review of 46 Charite 3 devices. He had a minimum of a two-year follow-up. The diagnoses were approximately 50% degenerative disc disease and 50% failed disc excision. They had a 69% satisfactory result for one-level procedures, and a 40% satisfactory result with two-level procedures. He determined that central and posterior placement of the prosthesis allowed more motion postoperatively. Additionally, they determined that patients who were allowed to undergo early exercise (versus three months of corset wear) had significant improvement in range of motion at the implanted level. They hypothesized that their poorer results in two-level procedures were because of the following: this device was difficult (in their experience) to implant at two levels because of excessive distraction that had to be performed at the second level; additionally, at the second level, a smaller device needed to be inserted, and this device needed to be inserted more anteriorly, very likely contributing to decreased range of motion at that second level. They concluded that in their hands, success was less than seen in fusion cases. The poor outcome was possibly due to their poor patient selection. The Charite in their opinion was not suitable for two levels, and they also determined that prospective randomized studies were needed to evaluate disc replacement versus fusion procedures.
The ProDisc total disk prosthesis utilizes total joint replacement knowledge in its design. The goal for the prosthesis is to restore anatomy and motion, and at the same time relieve pain and improve outcome. The ProDisc has a modular design with a superior and inferior cobalt-chrome endplate. (Fig. 21) The surfaces are porous (titanium plasma spray) to allow for bone ingrowth. Additionally, the inferior endplate allows for a polyethylene insert to be snapped into place utilizing a locking mechanism. (Fig. 22) The superior and inferior endplates have keels and two pegs on them, which allow for initial stability. (Fig. 23) Long-term fixation is afforded by bony ingrowth into the porous coating on the superior and inferior endplates. The ProDisc implant offers 6° or 11° of lordosis, and has heights of 10, 12, or 14 mm. Also, the design of the ProDisc is modeled closely after the morphology of the inherent disc. (Fig. 24) The ProDisc allows 13° of flexion and 7° of extension, closely following the normal range of motion of 10° of flexion and 5° of extension documented in the literature. Lateral bending is slightly more than the native disc. The ProDisc allows 10° of right and left lateral bending, compared to the inherent motion segment with left and right lateral bending of 5°. The axial rotation of the ProDisc is unconstrained as compared to the inherent motion segment, which allows 3°. The potential concern in this case is that excess stress will be placed upon the posterior elements. This could possibly cause premature stress upon the articular cartilage and resulting arthritis. This is speculative, though. There has been mechanical testing of the ProDisc to assess the "creep" of the ultra high molecular weight polyethylene, and to assess motion of the implant into the vertebral bodies. Also, the implant's response to shear stresses and wear of the ultra high molecular weight polyethylene has been evaluated. The ProDisc representatives, through their research, report that the ProDisc has a minimum of 22% less creep that the Charite device. Also, the ProDisc has less progressive increase in creep deformation at increasing load than the Charite. The ProDisc has a minimum 10% less permanent deformation than the Charite as well. The ProDisc inlay shows no loss of the snap-in function of the polyethylene. Migration of the implant starts at 12 KN without any evidence of tilting. The ProDisc results in a smoother pressure transition at the implant rim because of the radius of the implant. Compared to the Charite, the ProDisc shows fixation strength in shear without sudden failure. In mechanical testing, dislocation starts at 450 newtons of shear force and 0.3 mm displacement without any evidence of tilting. Wear fatigue testing shows the ProDisc to have a 30% less wear factor compared to total knee and total hip replacements. The ProDisc model shows minimal ultra high molecular weight polyethylene (UHMWP) cold flow. Finally, the ProDisc in biomechanical testing shows no signs of fatigue, breakage, or delamination under microscopic evaluation.
The earlier ProDisc results have been evaluated by their inventor, Dr. Marnay. He had an outside organization perform a prospective review of 61 of his cases. 95% were available for follow-up at seven to eleven years. 33% of these procedures were performed at two levels. At follow-up, all of the prostheses were intact and functioning, and there was no evidence of subsidence or migration. Additionally, there were no revisions or removals, and there were 92.7% of the patients who were satisfied or entirely satisfied. They concluded that there was no difference in results in one- or two-level implantations, and there were no device-related safety issues. Weichert et al reported a 6 month followup of 16 ProDisc patients where the mean Visual analog scale (VAS) score improved from 7.0 to 1.9 and the Oswestry Pain Score improving from 23.3 to 10.2. Bertagnoli and Kumar published results of a 108 patient series with a followup period of 3-24 months. They reported that 91% of the patients have excellent outcome, 8% with a good outcome and 1% with a fair outcome. The obvious drawback was that the specific criteria used to make the classification system were not clearly defined.
The St. Mary's Spine Center (San Francisco, California) is involved in a multi-center prospective randomized controlled clinical trial, evaluating the ProDisc total disc replacement. The study consists of 510 cases. 340 cases utilize the ProDisc, and these will be compared to 170 fusion cases. The follow-up will be a minimum of 24 months, and the goal is to assess the safety and effectiveness of the disc replacement. The inclusion criteria include: (1) Back and/or leg pain and radiographs (CT,MRI, plain films or myelograms) showing any one of the following: (i) instability (> 3mm translation, ,> 5 mm angulation), (ii) decreased disk height > 2mm, (iii) scarring/thickening of the annulus fibrosis, (iv) herniated nucleus pulposus, (v) vacuum phenomenon, (2) age range 19 to 59 years old, (3) failed 6 months conservative treatment, (4) Oswestry low back pain disability questionnaire score at least 20 out of 50 and a (5) signed informed consent.
Exclusion criteria include: (1) greater than 2 levels of degenerative disk disease, (2) known allergy to titanium, polyethylene, cobalt, chromium and molybdenum, (3) prior fusion at any lumbar level, (4) clinically compromised vertebral bodies at affected levels secondary to current or past trauma , (5) radiographically documented evidence of facet joint disease, (6) lytic spondylolisthesis or spinal stenosis, (7) degenerative spondylolisthesis greater than grade one, (7) back or leg pain of unknown etiology, (8) osteoporosis, (9) Paget's disease, (10) morbid obesity (Body Mass Index > 40, weight > 100 pounds over ideal body weight, (11) pregnant or plan pregnancy within 3 years, (12) taking medications that interfere with bone/soft tissue healing, (13) presence of rheumatoid arthritis or autoimmune disease, (14) active malignancy.
Spinal fusion was chosen as the randomized control in the study. A circumferential fusion was performed in all the patients randomized to receive a fusion. The fusion was either an anterior lumbar interbody fusion (ALIF) or a posterior lumbar interbody fusion (PLIF) using a commercially available femoral ring allograft along with a posterior lateral fusion with autogenous iliac crest autograft. Pedicle screw instrumentation using the Ti alloy CD system from Medtronic Sofamor Danek was placed in each patient receiving a fusion.
The surgical technique for the disk replacement in all patients consisted of 8 reproducible steps. All cases were performed with the patient in a supine position on a standard radiolucent operative table. The surgical approach was an anterior retroperitoneal approach for each patient. Once the appropriate disk level was exposed, a complete diskectomy was performed including removal of the cartilage from the superior and inferior endplates and removal of the posterior longitudinal ligament. Next trial implants were inserted to determine the size of the prosthesis. After, trialing for the size of the final component, a chisel was used under fluoroscopic guidance to prepare the position of the keel of the superior and inferior components. Next, the two plate components, pre-assembled on a back table were inserted in the determined position. Under fluoroscopic guidance, the surgical goal was to place the prosthesis in the midline in the frontal plane and as posterior as possible in the sagittal plane without entering the spinal canal. Distraction was next performed with a distractor instrument and the polyethylene inlay component was inserted and locked into the inferior plate component. Finally, the insertion instruments were removed and water tight closure was performed. The patients were ambulated with the assistance of a physical therapist on post operative day one. Post-operative follow up data will be recorded at 6 weeks and then at 3,6,9,12,18, and 24 months.
Outcome measures recorded during the study include four patient self-assessments: (1) Oswestry Low Back Pain disability questionnaire, (2) SF-36 Health Survey, (3) Overall Pain on a 10 cm Visual Analog Scale, (4) Satisfaction on a 10 cm Visual Analog Scale. In addition, the primary investigator performed a physical and neurological examination checking for range of motion, bone graft donor site, root tension signs, reflexes, muscle strength, and sensory deficits. Radiographic examination consisting of standing AP and lateral films, flexion/extension films and lateral bending films were also obtained. The above outcome measures were recorded pre-operatively and during each post-operative visit.
The series at St Mary's Spine center currently consists of 29 patients who have received 40 intervertebral disk arthroplasties. In addition, 12 patients were randomized to fusion. Three patients who received a total of 4 disk arthroplasties have 18 month follow-up. Five patients who received 5 disk arthroplasties have 12 to 18 month follow up. Seven patients who received 11 disk arthroplasties have 6 to 12 month follow up and 13 patients who received 19 disk replacements have 3 to 6 month follow-up. One patient has currently been followed for two months. For the 29 patients, the average pre-op Oswestry pain score was 25.2 and the average score at the most recent follow-up was 19.8, a 22 percent decrease. In patients with 18 month follow up, the average Oswestry score has fallen from 29.6 (range 29-31) to 19.3(range 14-24), a 35 percent decrease. In the 12-18 month group, the average score fell from 31.8 (range 24-39) to 22.4 (range 11 to 30), a 30 percent decrease. In the 6 to 12 month group, the average score has dropped from 26 (range 20 to 31) to 22 (range 16-31), a 15 percent decrease. In the three to six month follow up group, the average Oswestry score fell from 21 (range 21-40) to 17 (range 0 to 36) , a 20 percent decrease. As would be expected, the further out from the replacement procedure the patients get, the greater the decrease in the Oswestry score. This allows for the patients' surgical sites to heal and for the patients to complete the appropriate post-op rehabilitation regimen.
The pre-op range of motion average at the operated levels in the group followed for at least 18 months included 8.25 degrees on the flexion/extension and 10.75 degrees on the lateral bending. The range of motion at the most recent follow-up averaged 8 degrees on the flexion/extension views and averaged 6.5 degrees on the lateral bending views. In the group with 12-18 month follow up, the pre-op and most recent post-op visit range of motions on flexion/extension views were 6.8 and 6.2 degrees respectively. On the lateral bending views, the pre-op and most recent post-op visit range of motions was 4 and 2 degrees respectively. In the group with 6-12 month follow-up, the pre-op and post-op range of motions on the flexion/extension views were 4.2 and 4.2 degrees respectively. On the lateral bending views, the pre-op and post-op range of motions was 3.0 and 4.2 degrees respectively. In the group with 3-6 month follow up, the pre-op and post-op range of motions on the flexion/extension views averaged 5.2 and 7 degrees respectively while on the lateral bending views, the pre-op and most recent post-op visit wee 2.2 and 3.3 degrees respectively. The above values suggest that range of motion was maintained at the operated levels. The long term effect of preserving the range of motion in preventing the degenerative cascade requires further follow up. Of the 40 cases 16 disk replacements involved the L4-L5 level. The pre-op range of motions of flexion/extension and lateral bending were 9.2 and 4.8 degrees respectively. The post-op range of motion in flexion/extension and lateral bending averaged 7.14 and 5 degrees respectively. The other 24 replacements were at the L5-S1 level. The pre-op range of motions for flexion/extension and lateral bending were 5.25 and 2.7 degrees while the post-op range of motions were 5.4 and 3.3 degrees respectively.
Further review of the radiographs revealed no patient who received an arthroplasty had implant migration and subsidence (> 3mm). No patient had extensive radiolucency along the implant/bone interface (> 25% of the interface's length for each endplate). There has been no loss of disk height in any operated disk arthroplasty and no arthroplasty has evidence of bony fusion.
Commonly associated post-operative complications associated with lumbar disk replacement procedures include: (1) abdominal wall hematomas, (2) vascular injury, (3) dural tears, (4) Nerve injury, (5) Retrograde ejaculation in males, (6) Migration of the prosthesis. In our series of 40 disk replacements, there has been one incident of a common iliac artery tear discovered intra-operatively and repaired. The patient's post-operative course proceeded without incident. There have been no re-operations in either the disk arthroplasty group or the fusion group.
Total disk replacement is essentially in its infancy. The early studies of Marnay and the ProDisc are encouraging. There is no doubt further randomized prospective trials are needed to evaluate total disc replacement versus fusion as a viable option in degenerative lumbar disk disease. The advantage of this study is that in addition to being a prospective, randomized double blind trial, outcomes are being measured using standard assessments such as the Oswestry low back pain questionnaire and visual analog scale. As spine surgeons learn more about total disk replacement, it is imperative that strict indications are developed.
References
Bertagnoli R, Kumar S. Indications for full prosthetic disc arthroplasty: A correlation of clinical outcome against a variety of indications. Eur Spine J. 11(suppl. 2): S124-30. 2002
Bogduk N: The artificial disc. In Churchill Clinical Anatomy of the Lumbar Spine and Sacrum, 3rd ed. Edinburgh, Livingstone, 1997
Buttner-Janz K, Scheilnack K, Zippel H: Biomechanics of the SB Charite lumbar intervertebral disc endoprosthesis. Int Orthop 13: 173-176. 1989
Cinotti G, David T, et al.: results of disc prosthesis after a minimum follow up period of 2 years. Spine 21: 995-1000. 1996
David T: Lumbar Disc prosthesis. Eur Spine J. 1: 254-259. 1993
Edeland HG: Some additional suggestions for an intervertebral disc prosthesis. J Biomech Eng. 7: 7-62, 1985
Fairbank JCT, Couper Mbaot J, Davies, et al: The Oswestry Low Back Pain Questionnaire. Physiotherapy. 66: 271-272. 1980
Fernstrom U: Arthroplasty with intercorporal endoprosthesis in herniated disc and in painful disc. Acta Chir Scand (Suppl) 357: 154-159, 1966
Froming N: Artificial Intervertebral Disc. United States Patent File. 1974
Griffith S, et al.: A multicenter retrospective study of the clinical results of the Link SB Charite intervertebral prosthesis. The Initial European Experience. Spine 19: 1842-1849. 1994
Haher TR, et al: The role of the lumbar facet joints in spinal stability. Identification of alternative paths of loading. Spine 19: 2667-2670, 1994
Hsu KY, Zucherman J, et al.: Deterioration of motion segments adjacent lumbar spinal fusion. Presented at the annual meeting of the North American Spine society. Colorado Springs, Colorado, July 24-27, 1988
Kostiuk JP: Alternatives to Spinal Fusion, Orthop Clin North Am 29: 701-715, 1998
Lee CK: Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine. 13:475-477. 1988
Lee CK, Langrana NA, Parsons JR, et al.: Functional Disc prosthesis. Transactions of the 45th annual meeting of the orthopaedic research society: Las Vegas, Nevada, February.
Marnay T: Lumbar disc arthroplasty, 8-10 year results using titanium plates with a polyethylene inlay component. Presented at the annual meeting of the American Academy of Orthopaedic Surgeons, March 2001, San Francisco, California
Patil AA: Artificial Intervertebral Disc. United States Patent File. 1982
Ray C: Artificial disc. Present at the Challenge of the Lumbar Spine 1988 Meeting. San Antonio, Texas, November 9-14, 1988.
Steffee A: Artificial disc. Presented at the Challenge of the Lumber Spine 1988 Meeting. San Antonio, Texas, November 9-14, 1988.
Wiechert K, Mayer HM, Marnay et al: ProDisc. Preliminary results of a multicenter prospective clinical trial. Presented at the Spine Arthroplasty Conference, May 2001, Munich, Germany.
dude wtf is that bullshit. I asked a simple question. SO to anyone who's not a douche, can you answer my question?
So someone takes a moment to help and YOU are the one being a douche about it. I am not surprised:roll:
Slew Foot
Lifer
- Sep 22, 2005
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Either or, it depends on how much needs to be replaced. If they need to do work on the lamina or pedicles they'll go through the back. If they need to take out the whole disk theyll go through the front. If they only need to take out a samll part of disk in the back, theyll go through the back.
alright, cool...I was curious, I just thought it sounded odd to go through the stomache, but apparently that can be normal
Its normal for full disc fusion to go through front and back, I have 3 scars, one below stomach, one on my hip (they take a bit of bone from your hip if you want to use your own bone for the graph, or you can use a cadavore for donor bone) and one big one on your back.
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