Purpose: Magnetic resonance imaging (MRI) and Computerized tomography (CT) are commonly used for the diagnosis and assessment of lumbar spinal stenosis. The available literature has not identified which modality is superior. We compared the reliability and accuracy of CT and MRI in the assessment of lumbar spinal stenosis.

Method: We performed a prospective review of CT and MRI scans of 54 patients referred for surgical consultation. One orthopaedic spine fellow and one neuro-radiologist reviewed the CTs and MRIs. A qualitative and quantitative analysis was performed. Intra-observer and inter-observer reliability was determined using Kappa coefficient. The patient’s official reports were correlated with analysis performed by the two reviewers. Owsestry and SF-36 data was correlated with the qualitative and qualitative assessment of stenosis on CT, MRI using the Pearson’s R coefficient.

Results: MRI – substantial inter-observer agreement was achieved between surgeon and neuro-radiologist as well as between surgeon and reporting radiologist (κ= 0.74 and κ=0.64 respectively). Moderate agreement was found between neuro-radiologist and reporting radiologist (κ=0.57). Almost perfect intra-observer reliability for MRI was achieved by the two expert reviewers (κ=0.91 for surgeon and κ=0.92 for neuro-radiologist). CT – moderate inter-observer agreement (κ=0.58) was found between surgeon and neuro-radiologist. Fair agreement was found between neuro-radiologist and reporting radiologist and between surgeon and reporting radiologist (κ=0.30 and 0.32 respectively). Substantial intra-observer agreement was found for the surgeon (κ=0.77) while the neuro-radiologist achieved almost perfect agreement (κ=0.96).

Conclusion: This study directly demonstrates that MRI is likely a more reliable tool than CT, but neither correlates with functional status.

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.

Method: Between July 2001 and May 2008, 69 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 0.27mm (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.

Purpose: Bone mineral density (BMD) is an important factor in the performance of orthopaedic instrumentation both in and ex-vivo, and until now, there has not existed a reliable technique for determining BMD at the precise location of such hardware. This paper describes such a technique using cadaveric human sacra as a model.

Method: Nine fresh-frozen sacra had solid and hollow titanium screw placed into the S1 pedicles from a posterior approach. High-resolution micro-computed tomography (CT) was performed on each specimen before and after screw placement. All images were reconstructed with an isotropic spatial resolution of 0.308 mm, reoriented, and the pre-screw and post-screw scans were registered and transformed using a six-degree rigid-body transformation matrix. Once registered, two points, corresponding to the center of the screw at the cortex and at the screw tip, were determined in each scan. These points were used to generate cylindrical regions of interest (ROI) with the same trajectory and dimensions as the screw. BMD measurements were obtained within each of the ROI in the pre-screw scan. To examine the effect of artefact on BMD measurements around the titanium screws, annular ROI of 1 mm thickness were created expanding from the surface of the screws, and BMD was measured within each in both the pre-and post-screw scans.

Results: The registration process was accurate, with an error of 0.2 mm. Four specimens were scanned five times with repositioning, and error in BMD measurements was ± 2%. BMD values in the cylindrical ROI corresponding to screw trajectories were not statistically different from side to side of each specimen (p = 0.23). Artefact-related differences in BMD values followed an exponential decay curve as distance from the screws increased, approaching a low value of approximately 20 mg HA/cc, but not disappearing completely.

Conclusion: CT in the presence of metal creates artefact, making measured BMD values near implants unreliable. This technique is accurate for determination of BMD, non-destructive, and eliminates the problem of this metal artefact through the use of co-registration of a pre- and post-screw scan. This technique has applications both in-vitro and in-vivo.

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).

Method: 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 postoperative 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). One patient with an L5-S1 TDA has since undergone a posterolateral instrumented fusion. The mean pre- and post-operative lumbar lordosis was 34.58 and 53.48 respectively. The mean saggital 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.