Paul C. McAfee

A Prospective, Randomized, Multicenter Food and Drug Administration Investigational Device Exemptions Study of Lumbar Total Disc Replacement With the CHARITE^ Artificial Disc Versus Lumbar Fusion : Part I : Evaluation of Clinical Outcomes

Study Design. A prospective, randomized, multicenter, Food and Drug Administration-regulated Investigational Device Exemption clinical trial. Objectives. The purpose of this study was to compare the safety and effectiveness of lumbar total disc replacement, using the CHARITÉ™ artificial disc (DePuy Spine, Raynham, MA), with anterior lumbar interbody fusion, for the treatment of single-level degenerative disc disease from L4-S1 unresponsive to nonoperative treatment. Summary of Background Data. Reported results of lumbar total disc replacement have been favorable, but studies have been limited to retrospective case series and/or small sample sizes. Methods. Three hundred four (304) patients were enrolled in the study at 14 centers across the United States and randomized in a 2:1 ratio to treatment with the CHARITÉ™ artificial disc or the control group, instrumented anterior lumbar interbody fusion. Data were collected pre- and perioperatively at 6 weeks and at 3, 6, 12, and 24 months following surgery. The key clinical outcome measures were a Visual Analog Scale assessing back pain, the Oswestry Disability Index questionnaire, and the SF-36 Health Survey. Results. Patients in both groups improved significantly following surgery. Patients in the CHARITÉ™ artificial disc group recovered faster than patients in the control group. Patients in the CHARITÉ™ artificial discgroup had lower levels of disability at every time interval from 6 weeks to 24 months, compared with the control group, with statistically lower pain and disability scores at all but the 24 month follow-up (P < 0.05). At the 24-month follow-up period, a significantly greater percentage of patients in the CHARITÉ™ artificial disc group expressed satisfaction with their treatment and would have the same treatment again, compared with the fusion group (P < 0.05). The hospital stay was significantly shorter in the CHARITÉ™ artificial disc group (P < 0.05). The complication rate was similar between both groups. Conclusions. This prospective, randomized, multicenter study demonstrated that quantitative clinical outcome measures following lumbar total disc replacement with the CHARITÉ™ artificial disc are at least equivalent to clinical outcomes with anterior lumbar interbody fusion. These results support earlier reports in the literature that total disc replacement with the CHARITÉ™ artificial disc is a safe and effective alternative to fusion for the surgical treatment of symptomatic disc degeneration in properly indicated patients. The CHARITÉ™ artificial disc group demonstrated statistically significant superiority in two major economic areas, a 1-day shorter hospitalization, and a lower rate of reoperations (5.4% compared with 9.1%). At 24 months, the investigational group had a significantly higher rate of satisfaction (73.7%) than the 53.1% rate of satisfaction in the control group (P = 0.0011). This prospective randomized multicenter study also demonstrated an increase in employment of 9.1% in the investigational group and 7.2% in the control group.

The incidence of complications in endoscopic anterior thoracolumbar spinal reconstructive surgery. A prospective multicenter study comprising the first 100 consecutive cases.

Study Design A prospective multicenter study on 100 consecutive surgical procedures. Objectives A prospective multicenter study was performed to evaluate the early perioperative complications in 100 endoscopic spinal procedures-78 videoassisted thoracic surgical procedures and 22 laparoscopic lumbar instrumentation and fusion procedures. Summary of Background Data Endoscopic procedures have been widely applied in general surgery for appendectomy, cholecystectomy, liver resection, Nissen fundoplication, colon resection, and hernia repairs. Video-assisted thoracic surgery is widely used for pleural biopsy, lung resection, and sympathectomy. This is the first large series to date investigating the safety and potential complications using endoscopic surgery for anterior decompression or fusion of the thoracolumbar spine. Methods Video-assisted thoracic surgical procedures included multilevel anterior thoracic releases for deformity, 27 patients; anterior thoracic discectomies with spinal canal decompression, 41 patients; pyogenic vertebral osteomyelitis decompression, 2 patients; and vertebral corpectomy for neurologic decompression, 8 patients. Mean operative time was 2 hours, 34 minutes (range, 45 minutes to 6 hours), and mean length of stay was 4.97 days (range, 2–21 days). Anterior laparoscopic interbody stabilization and fusion at L4–5 or L5-S1 was performed in 22 patients. The mean operative time was 4 hours, 17 minutes (range, 2 hours, 40 minutes to 9 hours), and the mean length of stay was 5.6 days (range, 1–23 days). Results The most common video-assisted thoracic surgical complications were transient intercostal neuralgia (six patients) and atelectasis (five patients). The most common laparoscopic complication was bone graft donor site infection (two patients). There were two endoscopic cases that were converted to open procedures, one for extensive pleural adhesions and one for a common illac vein laceration. Conclusions The endoscopic spinal approaches proved to be safe operative procedures in 100 consecutive cases. There were no permanent latrogenic neurologic injuries and no deep spinal infections.

The value of computed tomography in thoracolumbar fractures. An analysis of one hundred consecutive cases and a new classification.

We studied 100 consecutive patients with potentially unstable fractures and fracture-dislocations by multiplane computed tomography. The mechanism of failure of the middle osteoligamentous complex of the spine (posterior longitudinal ligament, posterior part of the vertebral body, and posterior annulus fibrosus) was determined by three-dimensional analysis. Three modes of middle-column failure were used to classify the injuries: axial compression (seventy-three patients), axial distraction (fifteen patients), and translation within the transverse plane (twelve patients). Fifty of eighty-six patients who were evaluated in the acute phase of injury underwent operative stabilization, and the mechanism of middle-column disruption determined the type of instrumentation that was used. Compression and distraction injuries of the middle complex could be appropriately treated by Harrington distraction and compression instrumentation, respectively. However, in translational injuries (torn posterior longitudinal ligament) routine Harrington instrumentation was contraindicated due to the risk of overdistraction. Translational injuries were associated with the greatest degree of instability and often had complete ligament discontinuity at the level of the affected vertebrae. Patients with a translational injury had the most severe neural deficits (six of eleven patients studied acutely having a complete spinal cord lesion). Translational injuries of the middle column were treated by segmental spinal instrumentation to provide strong fixation with minimum risk of neural sequelae from passing sublaminar wires. Moreover, postoperative use of a cast over insensate skin was not required. Computed tomography was more sensitive than any other modality in the diagnosis of disruption of the posterior elements in unstable burst fractures, and computer-reconstructed sagittal images were accurate in evaluating the nature of facet-joint failure in distraction injuries. Computed tomography with metrizamide proved superior to either conventional tomography or myelography alone in localizing the site of neural canal compromise in acute thoracolumbar injuries. The mode of failure of the middle osteoligamentous complex as visualized by computed tomography determined the pattern of spinal injury, the severity of the neural deficit, the degree of instability, and the type of instrumentation required.

Biomechanical analysis of cervical stabilization systems : an assessment of transpedicular screw fixation in the cervical spine

Study Design The biomechanical stability of seven cervical reconstruction methods including the transpedicular screw fixation was evaluated under four instability patterns. These four modalities, based on the range and grade of instability, allowed a reproducible biomechanical assessment to establish the in vitro role of internal fixation in the cervical spine. Objectives This study biomechanically investigated the stability of seven reconstruction methods in the cervical spine as influenced by four instability patterns and assessed whether three-column fixation for the cervical spine using transpedicula screw fixation for the cervical spine using transpedicular screw fixation would provide increased stability over that of conventional cervical fixation systems. Methods A total of 24 calf cervical spine specimens were divided into four experimental groups. The spinal constructs including seven reconstruction techniques-the posterior AO titanium reconstruction plate, Bohlmans posterior triple-wiring, transpedicular screw fixation, anterior illac bone graft, anterior AcroMed plate, anterior AO titanium locking plate, and combined fixation with the AO anterior plate and posterior triple-wir-ing—were tested under four loading modes. Results Anterior plating methods provided less stability than that of posterior constructs under axial, torsional, and flexural loading conditions. Exclusive posterior procedures provided increased stability compared with the intact spine in one level fixation, however, did not sustain the torsional stability when the anterior and middle column was eliminated in two-level fixation. The stabilizing capabilities of both the combined fixation and transpedicular screw fixation were clearly demonstrated in all loading modes, however, those of the latter were superior in multilevel fixation. Conclusion Front and back approaches, employing the anterior plate and posterior triple-wiring, and transpedicular screw fixation demonstrated clear biomechanical advantages when the extent of instability increased to three-column or multilevel. Three-column fixation for the cervical spine using transpedicular screw fixation offers increased stability over that of conventional cervical fixation systems, particularly in multiple level constructs

Influence of bone mineral density on the fixation of thoracolumbar implants. A comparative study of transpedicular screws, laminar hooks, and spinous process wires.

Posteriorly directed load to failure testing of four different types of spinal implants was performed in individual T5 to S1 vertebra harvested from seven fresh-frozen human cadaveric spines. The implants tested were: 1) Drum-mond spinous process wires, 2) Harrington laminar hooks, 3) Cotrel-Dubousset transpedicular screws, and 4) Steffee VSP transpedicular screws. The ultimate failure of each implant was compared with the bone mineral density of each vertebra to determine which implants, if any, were particularly advantageous in osteoporotic vertebrae. Before biomechanical testing, the spines were analyzed in vitro by dual photon absorptiometry to determine the bone mineral densities (gm/cm2) of each vertebra. The mean tensile loads to failure for each of the implants tested were as follows: Cotrel-Dubousset transpedicular screws: 345 Newtons; spinous process wire/button: 382 Newtons; Steffee transpedicular screws: 430 Newtons; and laminar hooks: 646 Newtons. The difference between the loads to failure for laminar hooks and the, other implants was significant (P < 0.05) using oneway analysis of variance. The overall correlation coefficient for bone mineral density with ultimate load to failure was 0.30 (P < 0.001). The correlation coefficients were 0.47 (P < 0.001) for spinous process wires alone; 0.096 (not significant) for laminar hooks alone; 0.37 (P < 0.001) for Cotrel-Dubousset pedicle screws; and 0.48 (P < 0.001) for Steffee pedicle screws. Of the four different implants tested, laminar hooks were most resistant to failure from posteriorly directed forces. In contrast to spinous process wires and transpedicular screws, loads to failure for laminar hooks did not correlate with bone mineral density. The increased resistance to failure from posteriorly directed forces and independence from variations in bone mineral density may indicate that laminar hooks are superior to spinous process wires and pedicle screws for spinal fixation in patients with decreased bone mineral density due to osteoporosis, osteomalacia, or other forms of metabolic bone disease.

Anterior decompression of traumatic thoracolumbar fractures with incomplete neurological deficit using a retroperitoneal approach.

Between 1973 and 1981, seventy patients with a spinal cord injury secondary to a thoracolumbar fracture were treated by anterior spinal-canal decompression through a retroperitoneal approach. All of these patients had an incomplete neurological deficit caused by retropulsed vertebral-body fragments and intervertebral disc material in the spinal canal. Forty-eight patients have been followed for an average of 3.4 years (range, two to 8.6 years). Either computed tomography or lateral tomography, or both, was performed after surgery on these forty-eight patients, and confirmed the successful removal of the cause of compression in all of them. No patient lost further cord or cauda equina function after the anterior decompression. Thirty-seven of the forty-two patients who had a motor deficit improved by at least one class in motor strength. Fourteen of the thirty patients whose quadriceps and hamstrings were too weak to permit walking regained full independent walking ability. Twelve of the thirty-two patients who had a conus medullaris injury demonstrated neurogenic bowel and bladder recovery. The degree of neurological recovery of spinal cord injury after anterior spinal decompression of thoracolumbar fractures appears more favorable than after other, previously reported techniques that do not decompress the spinal canal.

Stability of posterior spinal instrumentation and its effects on adjacent motion segments in the lumbosacral spine.

Study Design. An in vitro biomechanical analysis of three anterior instability patterns was performed using calf lumbosacral spines. Stiffness of the constructs was compared, and segmental motion analyses were performed. Objectives. To clarify the factors that alter the stability of the spinal instrumentation and to evaluate the influence of instrumentation on the residual intact motion segments. Summary of Background Data. Recently, many adverse effects have been reported in fusion augmented with rigid instrumentation. Only few reports are available regarding biomechanical effects of stability provided by spinal instrumentation and its effects on residual adjacent motion segments in the lumbar‐lumbosacral spine. Methods. Eighteen calf lumbosacral spine specimens were divided into three groups according to instability patterns‐one‐level, two‐level, and three‐level disc dissections. Six constructs were cyclically tested in rotation, flexion‐extension, and lateral bending of intact spines, of destabilized spine, and of spines with four segmental posterior instrumentation systems used to extend the levels of instability (Cotrel‐Dubousset compression hook and three transpedicular screw fixation systems). During each test, stiffness values and segmental displacements were measured. Results. The rigidity of the instrumented construct increased as the fixation range became more extensive. Although application of the instrumentation effectively reduced the segmental motion of the destabilized vertebral level, the motion at the destabilized level tended to increase as the number of unstable vertebral levels increased, and the fixation range of the instrumentation became more extensive. Instrumented constructs produced higher segmental displacement values at the upper residual intact motion segment when compared with those of the intact spine. In contrast, the instrumented constructs decreased their segmental displacement values at the lower residual intact motion segment with higher magnitude of the translational (shear) motion taking place compared with the intact spine in flexion‐extension and lateral bending. These changes in the motion pattern became more distinct as the fixation range became more extensive. Conclusions. As segmental spinal instrumentation progresses from one level to three levels, the overall torsional and flexural rigidity of the system increases. However, segmental displacement at the site of simulated instability becomes more obvious. Application of segmental instrumentation changes the motion pattern of the residual intact motion segments, and the changes in the motion pattern become more distinct as the fixation range becomes more extensive and as the rigidity of the construct increases.

Adjacent Level Intradiscal Pressure and Segmental Kinematics Following A Cervical Total Disc Arthroplasty : An In Vitro Human Cadaveric Model

Study Design. In vitro investigation of cervical adjacent level intradiscal pressures (IDPs) following a total disc replacement arthroplasty. Objectives. The current in vitro study was undertaken to compare adjacent level IDPs and operative level kinematics following a cervical arthroplasty versus an arthrodesis procedure. Summary of Background Data. Clinical data indicate the incidence of symptomatic transition syndrome to be as high as 3% annually following a cervical interbody arthrodesis. Recent developments in the motion preservation technology should, in theory, minimize transition syndrome at the adjacent levels. Methods. A total of 10 human cadaveric cervical spines were used in this investigation. Following intact analysis, all specimens were sequentially reconstructed at C5–C6 with 1) total disc replacement (TDR), 2) allograft dowel, and 3) allograft dowel + anterior cervical plate. Testing was performed in displacement control under axial rotation, flexion/extension, and lateral bending loading modes. IDPs were recorded at C4–C5 and C6–C7 whereas peak range of motion (ROM) and NZ were monitored at C5–C6 level. Results. Similar IDPs were recorded between the intact condition and a TDR reconstruction at both adjacent levels under all loading modes (P > 0.05). However, the C4–C5 IDP values produced under flexion/extension testing for both arthrodesis treatments were significantly higher than the means obtained for the intact and disc replacement groups (P < 0.05). Similar intergroup differences were observed at the C6–C7 level; however, statistical significance was achieved during all three loading methods (P < 0.05). C5–C6 ROM analysis indicated a significantly lower ROM for both arthrodesis constructs compared with intact and TDR groups during flexion/extension testing (P < 0.05). No differences were recorded between the intact and the total disc replacement group under any loading conditions (P > 0.05). Conclusion. This is a first study to document that a cervical disc replacement arthroplasty procedure maintains adjacent level IDPs and reconstruction level kinematics near the preoperative values. Consequently, total disc replacement may provide an alternative to conventional surgical management of cervical discogenic pathology decreasing the incidence of symptomatic transition syndrome.

Biomechanical evaluation of total disc replacement arthroplasty: an in vitro human cadaveric model.

Study Design. This in vitro biomechanical study was undertaken to quantify the multidirectional intervertebral kinematics following total disc replacement arthroplasty compared to conventional stabilization techniques. Objective. Using an in vitro human cadaveric model, the primary objective was to compare the multidirectional flexibility properties and map the center of intervertebral rotation of total disc arthroplasty versus conventional threaded fusion cages and cages augmented with transpedicular fixation for single-level spinal instrumentation. Summary of Background Data. The utilization of motion-preserving implants versus instrumentation systems, which stabilize the operative segments, necessitates improved understanding of their comparative biomechanical properties. Methods. A total of eight human cadaveric lumbosacral spines (L2 to sacrum) were utilized in this investigation and biomechanically evaluated under the following L4–L5 reconstruction conditions: 1) intact spine; 2) SB Charitè disc prosthesis; 3) BAK cages; and 4) BAK cages + ISOLA pedicle screw/rod fixation (anteroposterior). The superior (L3–L4) and inferior (L5–S1) intervertebral levels remained uninstrumented to quantify adjacent level properties. Multidirectional flexibility included pure, unconstrained moments (±8 Nm) in axial rotation, flexion–extension, and lateral bending, with quantification of the operative and adjacent level range of motion and neutral zone, which were normalized to the intact spine condition. Results. The SB Charitè prosthesis indicated an average percentage increase in axial rotation range of motion by 44% compared to the intact condition (P < 0.05), whereas the BAK and anteroposterior reconstructions decreased range of motion by 29% and 80%, respectively (P < 0.05). The SB Charitè was significantly different from BAK and combined anteroposterior reconstructions (P < 0.05). Flexion–extension indicated a minor increase in range of motion for the SB Charitè (3%) versus the intact disc (P > 0.05), whereas the BAK and anteroposterior stabilization groups resulted in significant decreases in range of motion (BAK = 57%, anteroposterior = 93%) (P < 0.05) when compared to the intact and SB Charitè conditions. Based on flexion–extension radiographs, the intervertebral centers of rotation were in the posterior one-third of the operative intervertebral disc only for the SB Charitè reconstruction and intact spine condition, with definitive evidence of physiologic intervertebral translation (intact 2.06 ± 77 mm; SB III = 1.9 ± 0.98 mm). Conclusions. Total disc arthroplasty serves as the next frontier in the surgical management of discogenic spinal pathology. The SB Charitè restored motion to the level of the intact segment in flexion–extension and lateral bending and increased motion in axial rotation. The anterior annular resection necessary for device implantation and unconstrained design of the prosthesis account for this change in rotation. The normal lumbar flexion–extension axis of rotation is an ellipse rather than a single point. Only disc replacement rather than pedicle instrumentation or BAK interbody instrumentation preserves the kinematic properties and normal mapping of segmental motion at the operative and adjacent intervertebral disc levels.

Prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the CHARITÉ artificial disc versus lumbar fusion: Five-year follow-up

BACKGROUND CONTEXT The CHARITE artificial disc, a lumbar spinal arthroplasty device, was approved by the United States Food and Drug Administration in 2004 based on two-year safety and effectiveness data from a multicenter, prospective, randomized investigational device exemption (IDE) study. No long-term, randomized, prospective study on the CHARITE disc or any other artificial disc has been published to date. PURPOSE The purpose of this study was to compare the safety and effectiveness at the five-year follow-up time point of lumbar total disc replacement using the CHARITE artificial disc (DePuy Spine, Raynham, MA) with that of anterior lumbar interbody fusion (ALIF) with BAK cages and iliac crest autograft, for the treatment of single-level degenerative disc disease from L4 to S1, unresponsive to nonoperative treatment. STUDY DESIGN/SETTING Randomized controlled trial-five-year follow-up. PATIENT SAMPLE Ninety CHARITE patients and 43 BAK patients. OUTCOME MEASURES Self-reported measures: visual analog scale (VAS); validated Oswestry disability index (ODI version 1.0); Short-Form 36 Questionnaire, and patient satisfaction. Physiologic measures: radiographic range of motion, disc height, and segmental translation. Functional measures: work status. METHODS Of the 375 subjects enrolled in the CHARITE IDE trial, 277 were eligible for the five-year study and 160 patients thereof completed the five-year follow-up. The completers included 133 randomized patients. Overall success was defined as improvement> or =15 pts in ODI vs. baseline, no device failure, absence of major complications, and maintenance or improvement of neurological status. Additional clinical outcomes included an ODI questionnaire as well as VAS, SF-36, and patient satisfaction surveys. Work status was tracked for all patients. Safety assessments included occurrence and severity of adverse events and device failures. Radiographic analyses such as index- and adjacent-level range of motion, segmental translation, disc height, and longitudinal ossification were also carried out. RESULTS Overall success was 57.8% in the CHARITE group vs. 51.2% in the BAK group (Blackwelders test: p=0.0359, Delta=0.10). In addition, mean changes from baseline for ODI (CHARITE: -24.0 pts vs. BAK: -27.5 pts), VAS pain scores (CHARITE: -38.7 vs. BAK: -40.0), and SF-36 questionnaires (SF-36 Physical Component Scores [PCS]: CHARITE: 12.6 pts vs. BAK: 12.3 pts) were similar across groups. In patient satisfaction surveys, 78% of CHARITE patients were satisfied vs. 72% of BAK patients. A total of 65.6% patients in the CHARITE group vs. 46.5% patients in the BAK group were employed full-time. This difference was statistically significant (p=0.0403). Long-term disability was recorded for 8.0% of CHARITE patients and 20.9% of BAK patients, a difference that was also statistically significant (p=0.0441). Additional index-level surgery was performed in 7.7% of CHARITE patients and 16.3% of BAK patients. Radiographic findings included operative and adjacent-level range of motion (ROM), intervertebral disc height and segmental translation. At the five-year follow-up, the mean ROM at the index level was 6.0 degrees for CHARITE patients and 1.0 degrees for BAK patients. Changes in disc height were also similar for both CHARITE and BAK patients (0.7 mm for both groups, p=0.9827). Segmental translation was 0.4 and 0.8mm in patients implanted with CHARITE at L4-L5 vs. L5-S1, respectively, and 0.1mm in BAK patients. CONCLUSIONS The results of this five-year, prospective, randomized multicenter study are consistent with the two-year reports of noninferiority of CHARITE artificial disc vs. ALIF with BAK and iliac crest autograft. No statistical differences were found in clinical outcomes between groups. In addition, CHARITE patients reached a statistically greater rate of part- and full-time employment and a statistically lower rate of long-term disability, compared with BAK patients. Radiographically, the ROMs at index- and adjacent levels were not statistically different from those observed at two-years postsurgery.