Purpose: To report the clinical and radiographic prospective results of a consecutive series of patient with a minimum two year follow-up with the Charite Total Disc Arthroplasty (TDA).

Methods: Between 2001 and 2005 sixty patients underwent a Charite TDA (Depuy Spine, Raynham, MA) at either L4–5 or L5-S1. The primary indication for surgery was discogenic low back pain confirmed by provocative discography. Clinical assessment was carried out preoperatively and postoperatively at 3, 6, 12 months, and once a year thereafter using the Oswestry Disability Index (ODI), Visual Analogue Scale (VAS) for back and leg pain, and SF-36. Radiographic analysis included: angle of sagittal rotation, translation of the rostral vertebra onto the caudal vertebra, anterior vertical motion (AVM), middle vertical motion (MVM), posterior vertical motion (PVM), pre- and post-operative lumbar lordosis, disc height and subsidence of the TDA. The radiographic measurements were performed using the GE Medical Systems Centricity PACS Software Version 1.0.

Results: There were 36 female and 24 male patients with a mean age of 39 (range 21–59). The mean duration of low back pain was 70 months. Twenty-five percent claimed work compensation status. The mean post-operative hospital stay was 4.8 days. A statistical significant improvement was demonstrated between the mean pre-operative ODI (50) and all post-operative intervals (p< 0.0001) which had declined to 27.7 by one year. Similarly, pre-operative VAS back pain (8.0), leg pain (6.1), SF-36 physical component summary score (33.5) and mental component summary score (41.8) remained improved (p< 0.0001) by three months (4.1, 3.1, 51.7, 62.0 respectively).

The mean pre and post-operative lumbar lordosis was 34.58 and 53.48 respectively. The mean sagittal rotation was 6.5 degrees at 5 year follow-up, while the mean translation was 0.83 mm. The mean AVM, MVM and PVM were 0.59 mm, −3.96 mm and 3.69 mm respectively at 5 year follow-up.

Conclusion: This study demonstrates satisfactory clinical results in carefully selected patients. The radiographic assessment confirmed preservation of movement at the replaced disc during flexion and extension of the lumbar spine.

Interest Statement: No financial benefits or funding has been received for the completion of this study.

Purpose: To investigate subsidence of the Charite total disc arthroplasty (TDA) and to identify if a discrepancy between vertebral endplate and the Charite footprint predispose to subsidence.

Methods: Between July 2001 and May 2008 64 patients underwent a Charite TDA (DePuy Spine, Raynham, MA). They were prospectively followed at 3, 6, 12 months, and once a year thereafter.

The following measurements were performed on the replaced motion segment using a lateral radiograph:

The anterior-posterior (AP) dimension of the end plates.

The ratio between the actual and radiographic AP length of the metal endplate was calculated and utilized as the correction factor for the error of magnification on all other radiographic measurements.

Results: At L5-S1 the mean subsidence was 1.87 mm and occurred exclusively at the posterior part of the inferior end plate of L5. The mean posterior uncoverage was 3.5 mm (L5) and 0.27 mm (S1).

At L4–L5 the mean subsidence was 1.48 mm (L4) and 0.56 mm (L5). Posterior uncoverage of L4 and L5 vertebrae were 4.81 and 2.22 mm, respectively.

Subsidence of more than 1 mm was present in all cases where the posterior uncoverage of the end plate with the TDA was more than 2 mm (odds ratio: 5.7). Subsidence was non – progressive in all cases.

An anatomic mismatch exists between L5 and S1 endplates in the AP dimension; in more than half the patients S1 is shorter than L5.

Conclusion: The radiographic measurements suggest an increased likelihood of subsidence with more than 2 mm of posterior uncoverage of the end plate by the TDA. The endplate AP length of S1 is frequently less than that of L5. Implant selection based on the smaller S1 endplate may produce worrisome uncoverage of the L5 inferior endplate leading to an increased risk of subsidence and possible catastrophic failure. TDA design should afford modularity to compensate.

No financial benefits or funding has been received for the completion of this study.

Preliminary results suggest that a new rhBMP-2 formulation may provide an alternative for autologous bone graft in two-level posterolateral fusions

The purpose of this study was to compare the success of instrumented two level fusions using a new rhBMP-2 formulation versus iliac crest bone graft (ICBG). In this formulation, rhBMP-2 was at a concentration of 2mg/cc in a Biphasic Calcium Phosphate (60% hydroxyapatite/40% tricalcium phosphate) ceramic granule carrier. Twenty-nine patients were enrolled in this multicentered, prospective, randomized study. Either 30cc of rhBMP-2/BCP or fresh ICBG were used. Clinical evaluations were done preoperatively, at discharge and 1.5, three, six, twelve and twenty-four months including Oswestry Disability Index SF36, back pain and leg pain questionnaires. CT scan and xrays were independently assessed at six, twelve, and twenty-four months. Fusion criteria included bilateral bridging trabecular bone on each level, less than 3mm translation, less than five degrees angulation . Seventeen patients received ICBG and twelve received rhBMP-2/BCP. With the use of rhBMP-2 average OR time was reduced from 3.8 to 2.9 hours. Twenty-nine patients (100%) have reached twenty-four month followup. Clinical improvements were similar in both groups, however, fusion success was much improved with the use of rhBMP-2. At twenty-four months all patients receiving rhBMP-2/BCP were fused versus 58% of ICBG patients. These results suggest that rhBMP-2/BCP may have improved fusion success in challenging two level posterolateral fusions as compared to ICBG.