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Why Lumbar Artificial Discs Fail (Home Run or Strike Out) Pettine K, Megpara, M, Techy F

Abstract Purpose:  To  determine  why  A.D.R.’s  fail  by  examining  results  of  91  patients  in  F.D.A.  studies  performed  at  a  single  I.D.E.  site  with  minimum  two-­‐year  follow-­‐up.  

Methods:  To  minimize  variables,  every  patient  undergoing  A.D.R.  at  one  I.D.E.  site  by  two  surgeons  were  evaluated  for  clinical  success.  Failure  was  defined  as  less  than  50%  improvement  in  O.D.I.  and  V.A.S.  or  any  additional  surgery  at  index  or  adjacent  spine  motion  segment.  This  criterion  for  success  was  more  stringent  than  F.D.A.  guidelines,  which  require  only  a  25%  improvement  in  O.D.I.  and  V.A.S.  for  clinical  success.    

Three  A.D.R.’s  were  evaluated:  Maverick™  (M)  25  patients,  Charité™  (C)  31  patients,  Kineflex  ™(K)  35  patients.  All  procedures  were  one  level  performed  at  L4-­‐5  or  L5-­‐S1.  Demographics  and  inclusion/exclusion  criteria  were  similar  and  will  be  discussed.  Facet  pain  was  diagnosed  by  facet  block  and  significant  clinical  improvement  after  facet  rhizotomy.    

Results:  Overall  clinical  failure  occurred  in  26%,  (24  of  91  patients)  at  two-­‐year  follow  up.  Clinical  failure  occurred  in:  (M)  28%,  (7  of  25  patients);  (C)  39%,  (12  of  31  patients);  (K)  14%,  (5  of  35  patients).      The  type  of  A.D.R.  makes  a  difference.  Causes  of  failure  included:  facet  pathology  50%  of  failure  patients,(12  of  24).  Implant  complications  occurred  in  5%  of  the  total  patients  and  21%  of  the  failure  patients,  (5  of  24).  Patients  with  additional  orthopedic  or  medical  pathology  or  disability/narcotic  issues  making  them  unable  or  unwilling  to  fill  out  follow-­‐up  forms  specific  to  their  A.D.R.  occurred  in  29%  (7  of  24),  of  the  failure  group.  Despite  the  fact  these  patients  were  considered  failures  based  on  O.D.I.  and  V.A.S.,  they  reported  a  92%  satisfaction  with  the  A.D.R.  and  would  repeat  the  surgery  for  the  same  result.  Interestingly,  A.D.R.  patients  are  often  either  a  clinical  success  at  three-­‐month  follow-­‐up  (home  run)  or  a  possible  failure  (strike  out).  Only  five  patients  went  from  a  success  to  failure  after  three  months.  One  was  an  infection  one  year  after  A.D.R.  and  four  patients  developed  additional  pathology  unrelated  to  their  A.D.R.  Only  one  patient  went  from  a  failure  to  success  after  a  facet  rhizotomy  one  year  after  A.D.R.  

Conclusions:  Seventy-­‐four  percent  of  patients  after  A.D.R.  met  strict  clinical  success  after  two-­‐year  follow-­‐up.  The  clinical  success  verses  failure  rate  did  not  change  from  their  three-­‐month  follow-­‐up  in  85  of  the  91  patients  (93%).  Home  run  verse  strike  out  can  be  determined  early.  Failures  occurred  due  to:  facet  pain,  50%  of  the  time;  implant  complications  in  21%;  and  additional  unrelated  pathology  or  disability/narcotic  issues  resulting  in  form  filling  not  specific  to  their  ADR  in  29%  of  patients.  Implant  type  appears  to  impact  clinical  success.  These  results  indicate  overall  clinical  success  can  be  improved  most  by  patient  selection  and  implant  type.    

 

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Introduction The purpose of this study is an attempt to ascertain the reason patients undergoing lumbar artificial disc replacement (LADR) do not meet FDA definitions of clinical success or do not meet a more stringent definition of success. The lumbar spine motion segment is a three-joint complex. The two vertebrae of a motion segment are connected via a disc anteriorly and two facet joints posteriorly. Any of these structures can cause chronic low back pain. The FDA indication for LADR is discogenic low back pain.10,11 Biomechanical studies have shown an annular tear can result in a decrease in rotational constraints resulting in increased stress on the facet joints.5-8 In addition, as a disc space collapses secondary to dehydration, more compressive forces occur across the facet joints. The exact etiology of a patient’s low back pain remains difficult to specifically identify. MRI scanning, discography and facet blocks can be used in an attempt to identify a specific pain generator. Patients undergoing LADR are generally diagnosed via history and physical examination indicating severe midline pain aggravated with activities and relieved typically in a supine position. Symptoms may be aggravated by sitting, lifting, twisting, bending and stooping. Review of the IDE clinical data reveals overall clinical success of 63.5% in the ProDisc-L IDE study18,19,33 and 63.6% in the Charité IDE study.12-17 Reoperations occurred in six patients in the ProDisc-L IDE study. Four patients had reoperation secondary to migration of either the ultra-high molecular weight polyethylene (UHMWPE) inlay or entire implant migration. Two additional patients required reoperation secondary to a technical error of inserting the UHMWPE inlay in one patient and a second patient was converted to a fusion due to unresolved pain after the ADR. Eleven patients (5.4%) in the Charité group required reoperation. The authors did not detail the reasons. In neither study is there any discussion or explanation for the patients who did not meet FDA clinical success. This would amount to 36.5% of the patients in the ProDisc IDE and 36.4% of patients in the Charité IDE. Several studies have concluded the interesting observation that patients following LADR generally achieve their 24-month follow-up results at three months post operative.47 In general, a patient’s improvement in oswestry disability index (ODI) and visual analogue scale (VAS) are present by their three-month follow-up. The vast majority of patients do not significantly change from what their clinical result is at this early follow-up. Patients generally are either a “home run” or “strike out” by their three-month follow-up. Material and Methods This study involves an analysis of every patient in an FDA IDE study undergoing a LADR by the senior author at a single FDA IDE site. Every patient was part of two different FDA IDE studies. The first study involved a prospective randomized study comparing the results of the Maverick LADR versus LT cage with BMP. FDA clinical success was defined as a 20% improvement in oswestry disability index (ODI) from pre-op to two-year follow-up with no reoperations and no neurologic deterioration. There were 25 patients in this study. The second FDA study involved a prospective randomized comparison of the Charité versus Kineflex LADR. Clinical success in this study required a 15-point improvement in ODI from

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pre-op to two-year follow-up with no deterioration of neurologic status or reoperation. This study consisted of 35 patients with a Kineflex artificial disc and 31 patients with a Charité artificial disc. These 91 FDA IDE patients from two studies provide the basis for this paper. The cases were consecutively performed. The follow up at 2 years is 100%.

Chart 1

Methods

91 Patients in F.D.A. I.D.E Lumbar A.D.R. StudiesThree A.D.R.’sn Maverick: 25 patientsn Charite: 31 patientsn Kineflex: 35 patients

Single site with the same two surgeons, surgical staff and clinical staffMinimum 2 year follow-up

Maverick™ (M)

Charité™ (C)

Kineflex ™(K)

Kineflex versus Charité versus Maverick Kineflex Disc Charité Maverick Disc Number of Subjects 35 31 25 Male 15 13 17 Female 18 18 8 Age, mean (SD), years 40.1 (10.01) 40.8 (7.68) 37 Body Mass Index, mean 26.6 (3.39) 26.0 (3.40) 27 Surgery Level: L4-5 6 (18%) 4 (12.9%) 6 (24%) Surgery Level: L5-S1 27 (81.8%) 27 (87.1%) 19 (76%) Definition of Clinical Success The definition of clinical success for the basis of this paper required a 50% improvement in ODI from pre-operative through two-year follow-up. This is more stringent than the 15-point improvement required for the FDA IDE trials. In addition, any patient undergoing a reoperation or showing signs of neurologic deterioration were considered a failure. This more stringent definition of clinical success was utilized to provide more patients for critical evaluation and a 50% improvement in ODI was felt to be a reasonable stringent definition of success. Glassman, et al.49 published a study determining the level where patients perceive clinical success. They determined a patient required a 20% improvement in SF36 and an approximate 40% decrease in

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ODI and VAS before the patient perceived lumbar fusion as a success. This more stringent definition of success was thus felt reasonable. Facet Pain Facet pain was diagnosed in patients who complained of continued pain after LADR. These patients typically had pain worse with extension and often unilateral off midline. These patients underwent intra-articular injection of the facet joint under fluoroscopic control. Each facet joint was anesthetized with 0.25ml of 0.25% Marcaine and 0.25ml of Depo-Medrol. These patients required at least an 80% improvement in their symptoms following this injection. In those patients achieving at least an 80% improvement in their symptoms after the first facet injection, if their pain returned, a second injection was performed. Again, if they achieved an 80% reduction in their pain, they were considered to have continued pain secondary to facet pathology. Results Based on a strict definition requiring at least a 50% improvement in ODI at two-year follow-up with no reoperations or deterioration in neurologic status, overall clinical failure occurred in 27% (24 of 89 patients) at two-year follow-up. Clinical failure occurred in 28% (7 of 25) of the Maverick patients, 39% (12 of 31) of the Charité patients and 15% (5 of 35) of the Kineflex patients.

Chart 2

Utilizing A Strict Definition of Failure 26% (24 of 91 patients)

Maverick: 28% (7 of 25 patients)Charite: 39% (12 0f 31 patients)Kineflex: 15% (5 of 35 patients)

Cause of Failure Facet pathology was the etiology of failure in 50% (12 of 24) of the failure patients. All of these patients were diagnosed as having facet pain based on two separate injections as defined in the methods section. Nine of these patients went on to have percutaneous facet rhizotomy performed. None of these 12 patients have gone on to any additional surgery. Presently, they are living with their symptoms.

Chart 3

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Reasons for Failure

Failure Due to Facet Pain: n 50% (12 out of 24 patients)n Facet pain diagnosed by >80% relief from 2 facet

blocks and relief with rhizotomy

Charite: 7Kineflex: 3Maverick:2

Implant complications occurred in five of the total 91 patients and 21% (5 of 24) of the failure patients. These five patients had the following complications. One Maverick patient became infected 18 months after the initial surgery requiring surgical debridement and fusion. One Charité patient underwent revision of the implant within 24 hours post initial operation to a more midline position. One Charité patient underwent a posterior fusion secondary to bilateral pedicle fractures occurring six weeks post operatively. One Charité patient underwent a posterior fusion secondary to an implant invaginating into the L4 vertebral body at six weeks post op. One Kineflex patient subluxed the sacral endplate anteriorly approximately 4mm and underwent conversion to an anterior lumbar interbody fusion within 24 hours of the index operation.

Chart 4 Failure Due To Implant Complications

21% of overall failures (5 out of 24 patients)1 Infection: 18 months post-op

4 Re-operations: 2 within 24 hours All Charite/Kineflex 2 within 6 weeks

Patients with additional orthopedic or medical pathology or disability/narcotic issues making them unable or unwilling to fill out follow-up forms specific to their artificial disc replacement occurred in 29% (7 of 24) of the failure group. Despite the fact these patients were considered failures based on ODI and visual analog scale (VAS), they reported a 92% satisfaction rate with the artificial disc and would repeat the surgery for the same result.

Chart 5 Chart 6

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Reasons for Failure

Failure Due to Additional Orthopedic Pathology:n 29% (7 out of 24 patients)n These 7 patients were failures due to <50%

improvement in O.D.I. yet 92% reported satisfaction with A.D.R. and would repeat surgery for same result.

Overall Cause of Clinical Failure

n Facet Pain = 50%n Implant Complications = 21%n Complex Patients = 29%

Chart 7

Implant Comparison

Implant Comparison:n Facet Pain:

n Charite: 7n Kineflex: 3n Maverick: 2

n Re-operations:n Maverick: 1 (Infection)n Charite: 3 (Pedicle fracture, collapse, mal-position)n Kineflex: 1 (Subluxation)

n Failure Rate:n Maverick: 28%n Charite: 39%n Kineflex: 14%

Interestingly, ADR patients are either a clinical success at three-month follow-up (home run) or possible failure (strike out). Only five patients in the entire group of 91 patients went from a success to failure after three months. One patient had an infection 18 months after the initial artificial disc replacement, and four patients developed additional pathology unrelated to their artificial disc replacement. These patients did not have additional surgery but were considered failures due to the ODI scores. Only one patient went from failure to success after facet rhizotomy one year after artificial disc replacement. Discussion The lumbar spine motion segment is a three-joint complex. The two vertebrae of a motion segment are connected via a disc anteriorly and two facet joints posteriorly. Any of these structures can cause chronic low back pain. The FDA indication for LADR is discogenic low back pain.10,11 Biomechanical studies have shown an annular tear can result in a decrease in rotational constraints resulting in increased stress on the facet joints.5-8 In addition, as a disc space collapses secondary to dehydration, more compressive forces occur across the facet joints.

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The exact etiology of a patient’s low back pain remains difficult to specifically identify. MRI scanning, discography and facet blocks can be used in an attempt to identify a specific pain generator. Patients undergoing LADR are generally diagnosed via history and physical examination indicating severe midline pain aggravated with activities and relieved typically in a supine position. Symptoms may be aggravated by sitting, lifting, twisting, bending and stooping. Generally, patients have desiccation on a sagittal T2 weighted MRI scan. Discography has been shown to be helpful in diagnosing patients with discogenic back pain.41-46 Nevertheless, most authors would agree today that the discogram presents inconsistent results in most studies and cannot solely and reliably indicate the pain generator in back pain syndrome 50. General contraindications to LADR are severe disc space collapse, moderate to severe facet degeneration or severe symptomatic facet pain.10,31,34,38,39

Review of the IDE clinical data reveals overall clinical success of 63.5% in the ProDisc-L IDE study18,19,33 and 63.6% in the Charité IDE study.12-17 Reoperations occurred in six patients in the ProDisc-L IDE study. Four patients had reoperation secondary to migration of either the ultra-high molecular weight polyethylene (UHMWPE) inlay or entire implant migration. Two additional patients required reoperation secondary to a technical error of inserting the UHMWPE inlay in one patient and a second patient was converted to a fusion due to unresolved pain after the ADR. Eleven patients (5.4%) in the Charité group required reoperation. The authors did not detail the reasons. In neither study is there any discussion or explanation for the patients who did not meet FDA clinical success. This would amount to 36.5% of the patients in the ProDisc IDE and 36.4% of patients in the Charité IDE. Several studies have concluded the interesting observation that patients following LADR generally achieve their 24-month follow-up results at three months post operative.47 In general, a patient’s improvement in oswestry disability index (ODI) and visual analogue scale (VAS) are present by their three-month follow-up. The vast majority of patients do not significantly change from what their clinical result is at this early follow-up. Patients generally are either a “home run” or “strike out” by their three-month follow-up. Siepe6,31 reported on 99 patients who underwent either non-segmental TDR at L4-5 (group A = 22 patients), mono-segmental TDR at L5-S1 (group B = 57 patients) or bi-segmental TDR at L4-5 and L5-S1 (group C = 20 patients). The follow-up was 12 months. All patients underwent pre-operative facet joint injections to rule out facet pain prior to TDR. They reported an overall revision rate of 8.1%. Sixteen patients (16.2%) underwent fluoroscopically guided facet injections post operatively with significant relief. Most of the patients with post operative ongoing facet pain had a TDR at L5-S1. A wide range of complication rates from 1-40% has been reported in the literature following LADR with most reports ranging between 10-20%.4,9,20,24,27-29

McAfee, et al.25 reported a reoperation rate of 8.8% (52 of 589 patients) with the Charité.25 Complications reported include access related complications with sympathectomies, retrograde ejaculation, hematomas or seromas. Post operative complications reported include heterotopic ossification, persisting facet joint problems, sub-optimal placement of the implant, adjacent segment disc herniation, superficial wound infection.

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An increasing number of clinical, radiographic and biomechanical studies suggest posterior motion segment structures, primarily facet joints, are a major etiology of continuing pain or development of pain following LADR.22,30-32,35,36 Sagittal imbalance following LADR is an important factor to developing facet pain.23 Implant position within the motion segment has been reported to have profound effects on posterior joint pain. A posterior center of rotation of the LADR emulates normal spinal motion kinematics. An anterior center of rotation of the LADR increases facet forces. Removing the anterior longitudinal ligament in the process of insertion of LADR has been shown in numerous studies to increase stresses on the facet joints.1-3,5,7,22,30,35,37,40 This study indicates the type of artificial disc replacement in terms of its kinematics appears to influence the incidence of post operative facet pain. Three artificial discs are reported in this study. Biomechanically, the Kineflex and Maverick discs both have a posterior center of rotation and would be considered more constrained than the Charité. The Charité has a central center of rotation with a center core which allows 2mm of translation. Thus, flexion, extension and side bending are all associated with a coupled motion.8,20,21,26 This unconstrained design may result in increased strain on the facet joints resulting in the higher incidence of facet pain reported in the study with the Charité. Five of the 91 patients in this study had additional surgery at the index level. Four of these occurred within eight weeks of the index surgery and one patient had a late (18 months) infection. This is consistent with previously reported revision rates. Clinical result issues specific to patients in an FDA IDE study are the seven of 24 patients (29%) in the failure group who did not have facet pain or device problems. These seven patients were considered failures because they reported on their FDA IDE follow-up forms additional orthopedic, medical pathology or disability/narcotic issues resulting in a lack of adequate improvement in ODI or VAS. These patients were clinical failures only because of their failure to report at least 50% improvement in ODI and VAS at two-year follow-up. When specifically asked about their LADR, 92% of these patients were highly satisfied with the disc replacement and would do the surgery again for the same result. When specifically questioned as to why they did not report significant improvement in ODI or VAS, their explanations related to their additional orthopedic, medical pathology or psychosocial issues. These results should caution FDA IDE investigators to possibly exclude complex orthopedic patients or any patient with disability/narcotic issues who may not be able to accurately fill out forms specific to the results of their LADR. Conclusions: Seventy-­‐four  percent  of  patients  after  A.D.R.  met  strict  clinical  success  after  two-­‐year  follow-­‐up.  The  clinical  success  verses  failure  rate  did  not  change  from  their  three-­‐month  follow-­‐up  in  85  of  the  91  patients  (93%).  Home  run  verse  strike  out  can  be  determined  early.  Failures  occurred  due  to:  facet  pain,  50%  of  the  time;  implant  complications  in  21%;  and  additional  unrelated  pathology  or  disability/narcotic  issues  resulting  in  form  filling  not  specific  to  their  ADR  in  29%  of  patients.  Implant  type  appears  to  

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impact  clinical  success.  These  results  indicate  overall  clinical  success  can  be  improved  most  by  patient  selection  and  implant  type.    

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13Guyer RD, McAfee PC, Hochschuler SH, et al. Prospective randomized study of the Charité artificial disc: data from two investigational centers. Spine J 2004 Nov-Dec;4(6 Suppl):252S-9S. 14Guyer RD, McAfee PC, Banco RJ, et al. Prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: Five-year follow-up. Spine J 2008a Sept 18. 15Blumenthal S, McAfee PC, Guyer RD, et al. A prospective, randomized, multicenter Food and Drug Administration investigational device exemptions study of lumbar total disc replacement with the Charité™ artificial disc versus lumbar fusion. Part I: evaluation of clinical outcomes. Spine 2005;30(14):1565-75. 16Blumenthal SL, Ohnmeiss DD, Guyer RD, et al. Prospective study evaluating total disc replacement: preliminary results. J Spinal Disord Tech 2003 Oct;16(5):450-4. 17Charité Artificial Disc: About our disc. Updated 2007. Accessed November 13, 2009. Available at URL address: http://www.charitedisc.com/charitedev/domestic

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disc versus lumbar fusion. Part II: Evaluation of radiographic outcomes and correlations of surgical technique accuracy with clinical outcomes. Spine 2005;30(14):1576-83. 26Panjabi M, Malcomson G, Teng E, et al. Testing of lumbar CHARITÉ discs versus fusions. Spine 2007;32(9):959-66. 27Punt IM, Visser VM, van Rhijn LW, et al. Complications and reoperations of the SB Charité™ lumbar disc prosthesis: experience in 75 patients. Eur Spine J 2008 Jan;17(1):36-43. Epub 2007 Oct 10. 28Regan JJ. Clinical results of Charité lumbar total disc replacement. Orthop Clin N Am 2005;36:323-40. 29Ross R, Mirza AH, Norris HE, et al. Survival and clinical outcome of SB Charite III disc replacement for back pain. J Bone Joint Surg Br 2007 Jun;89(6):785-9. 30SariAli E, LeMaire JP, Pascal-Mousselard H, et al. In vivo study of the kinematics in axial rotation of the lumbar spine after total intervertebral disc replacement: long-term results: a 10-14 years follow up evaluation. Eur Spine J 2006 Jan 21;:1-10. 31Siepe CJ, Korge A, Grochulla F, et al. Analysis of post-operative pain patterns following total lumbar disc replacement: results from fluoroscopically guided spine infiltrations. Eur Spine J 2008 Jan;17(19):44-56.

32Siepe CJ, Zelenkov P, Sauri-Barraza JC, et al. The fate of facet joint and adjacent level disc degeneration following total lumbar disc replacement: a prospective clinical, x-ray, and magnetic resonance imaging investigation. Spine (Phila Pa 1976) 2010 Oct 15;35(22):1991-2003. 33Zigler J, Delamarter R, Spivak JM, et al. Results of the prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of the ProDisc-L® total disc replacement versus circumferential fusion for the treatment of 1-level degenerative disc disease. Spine 2007;32(11):1155-62. 34Zindrick MR, Tzermiadianos MN, Voronov LI, et al. An evidence-based medicine approach in determining factors that may affect outcome in lumbar total disc replacement. Spine 2008 May 15;33(11):1262-9. 35Park CK, Ryu KS, Jee WH. Degenerative changes of discs and facet joints in lumbar total disc replacement using ProDisc II: minimum two-year follow-up. Spine 2008 Jul 15;33(16):1755-61. 36Shim CS, Lee S-H, Shin H-D, et al. CHARITÉ versus ProDisc: A comparative study of a minimum 3-year follow-up. Spine 2007;32(9):1012-8. 37vanOoij A, Oner FC, Verbout AJ. Complications of artificial disc replacement: A report of 27 patients with the SB Charite disc. J Spinal Disord Tech. 2003;16(4):369-83.

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38Caspi I, Levinkopf M, Nerubay J. Results of lumbar disk prosthesis after a follow-up period of 48 months. Is Med Assoc J. 2003;5(1):9-11.

39Bertagnoli R, Yue JJ, Fenk-Mayer A, et al. Treatment of symptomatic adjacent-segment degeneration after lumbar fusion with total disc arthroplasty by using the ProDisc prosthesis: a prospective study with 2-year minimum follow up. J Neurosurg Spine 2006[a];4:91-7.

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