Purpose: Cervical arthroplasty is an emerging technology with the potential of motion preservation and reduced adjacent level disease. However, the factors that influence postoperative range of motion (ROM) and patient satisfaction is not fully understood. The aim of this study was to evaluate the influence of disk height on the postoperative motion as well as clinical outcomes.

Method: 167 patients from a multi-center prospective randomized FDA trial with single level ProDisc-C arthroplasty performed were evaluated radiographically utilizing Medical Metrics (QMATM, Medical Metrics, Inc.). Preoperative and postoperative disk height and ROM were measured from standing lateral and flexion-extension radiographs. Of these 167 patients, 19 patients from a single center had clinical outcomes based on ODI and VAS scores evaluated pre and postoperation with a mean follow-up of 22 months. Two-tailed student’s T-test and Spearman’s Rho tests were performed in order to find out if there was any correlation or “threshold” effect between the disk height and ROM.

Results: Patients with less than 4 mm of preoperative disc height had a 1.8° increase in their flexion-extension ROM after TDA as compared to no change in ROM in patients with more than 4 mm of preoperative disc height (p=0.04). Patients with more than 5mm of postoperative disc height have significantly higher postoperative flexion-extension ROM (10.1°) than those with less than 5mm disc height (8.3°, p=0.014). However, patients with more than 7mm of postoperative disc height have significantly lower postoperative lateral bending ROM (4.1°) than those with less than 7mm disc height (5.7°, p=0.04). It appears that the optimal postoperative disc height is between 5 to 7 mm for increased ROM on flexion-extension and lateral bending. No correlation could be found between clinical outcomes and disc height. Similarly, no threshold effect could be found between any specific disc height and ODI or VAS.

Conclusion: Patients with greater disc collapse benefit more in ROM from a TDR. The optimal range to maximize ROM for postoperative disc height is between 5 to 7mm. This optimal range did not translate into better clinical outcome at 2 year follow-up. A longer follow-up will yield if less ROM ultimately leads to worse clinical outcomes.

Purpose: Facet joint arthrosis is an entity that can have a key role in the etiology of low back pain, especially with hyperextension, and is a key component of surgical planning, especially when considering disc arthroplasty. Plain films and MRI are most commonly utilized as the initial imaging of choice for low back pain, but these methods may not truly allow an accurate assessment of facet arthosis. Our purpose was to observe the inter- and intraobserver reliability of utilizing CT and MRI to evaluate facet arthrosis, the inter- and intraobserver reliability of the facet grading system, and the agreement of surgeons as to when to perform disc arthroplasty after the lumbar facets are evaluated.

Method: A power analysis was performed which showed we would need 6 reviewers and 43 images to have 80% power to show excellent reliability. 102 CT and the corresponding MRI images of lumbar facets were obtained from patients who were to undergo lumbar spine surgery of any type. 10 spine surgeons and 3 spine fellows reviewed the randomized images at 2 time points, 3 months apart, graded the facet arthosis as well as indicated whether they would chose to perform a disc arthroplasty based on the amount of facet arthrosis. Both interobserver and intraobserver kappa values were calculated by result comparison between observers at the two time points and between CT and MRI images from the same patient.

Results: interobserver reliability for MRI was 0.21 and 0.07(fair to slight agreement), and for CT was 0.33 and 0.27(fair agreement), for the spine surgeons and spine fellows respectively. The mean intraobserver reliability for MRI was 0.36 and 0.26 (fair agreement) and for CT was 0.52 and 0.51 (moderate agreement). The kappa value for agreement of whether to perform a disc arthroplasty after grading the facet arthrosis utilizing MRI was 0.22 (fair agreement) and utilizing CT was 0.33 (fair agreement) among the senior spine surgeons.

Conclusion: The existing grading system for facet arthrosis and of whether to perform a disc arthroplasty utilizing the grading system has at best only fair agreement. CT is more reliable for grading facet arthrosis.