Faculty Bibliography

STUDY DESIGN: Biomechanical study. OBJECTIVE: To evaluate the cervical facet loading profile of an intervertebral cervical disc prosthesis incorporating a unique saddle-shaped articulation and to determine the effect of implantation of the prosthesis on both the loading curve and area distribution of facet loading, when compared with that of an intact specimen. SUMMARY OF BACKGROUND DATA: This is the first study that examines the effect of implantation of a cervical disc replacement on the loading of the facet joints. METHODS: Fresh-frozen ovine cervical spine specimens were used. Specimens were prepared and disarticulated to yield 6 functional spinal units, which were secured and mounted in a custom fixture on a material testing apparatus. A novel pressure sensor was constructed by combining a resistive ink thin film sensor with Fuji pressure-sensitive film. The sensor was calibrated before unilateral insertion into the cervical facet joint via a small arthrotomy. Specimens were tested in both intact condition and after surgical intervention consisting of discectomy and implantation of an intervertebral cervical disc prosthesis (CerviCore, Stryker Spine, Allendale, NJ). Specimens were tested in flexion, extension, and lateral bending to 3 Nm and in torsion to 2.5 Nm. At the termination of each loading profile, the load was maintained for 30 seconds to permit full exposure of the Fuji film. For each configuration, the maximum resultant load, load rate, and contact area pressure at the endpoint of the loading profile were determined. A paired Student t test was used to determine the differences between the intact specimen and the specimen with an implanted intervertebral disc prosthesis. RESULTS: There were no statistically significant differences in mean or maximum pressures between the intact specimen and the specimen with an intervertebral disc in all loading configurations. Similarly, there was no significant difference in the total measured force between the groups in all loading configurations. There was no significant difference in contact areas between the groups in flexion, lateral bending, and torsion. When evaluated in extension, the intact specimen had a mean contact area of 0.8 cm compared with 0.5 cm for the intervertebral disc (P<0.02). CONCLUSIONS: Biomechanical testing in an ovine model demonstrated no significant difference in measured facet pressures and forces between an intact native cervical disc specimen and a cervical intervertebral disc prosthesis using a saddle-shaped articulation. Peak and mean pressures were not demonstrated to be significantly different between the implanted and intact disc conditions. Implantation of the prosthesis resulted in a significant reduction of contact area under extension moments

STUDY DESIGN.: Technique tips and retrospective review of prospectively collected data. OBJECTIVE.: To describe a technique for centralizing cervical plates using the center of the manubrium as a primary external guide and its alignment with the mandible as a secondary guide. SUMMARY OF BACKGROUND DATA.: Proper alignment of cervical plates is desirable to avoid improper placement of screws and possibly altered biomechanical performance. Large body habitus may portend suboptimal exposure, a limited utility of skin surface landmarks for level determination, and may make it difficult to reliably centralize plates in the coronal plane during anterior cervical surgery. METHODS.: We describe a technique that uses the center of the manubrium to determine the midline of the cervical spine and align a line drawn through the manubrium with the center of the mandible to provide a central axis for placing cervical plates along the entire cervical spine. We used anteroposterior fluoroscopy to validate that a line from the middle of the manubrium to the mandible bisected the spinous processes and midline of the vertebral bodies. We prospectively collected data on 39 consecutive patients undergoing anterior cervical discectomy and fusion with cervical plates using this technique. RESULTS.: The mean amount of angulation and translation about a midline axis were 2.24 degrees +/- 1.49 degrees and 1.04 +/- 0.86 mm, respectively. There were no statistical differences among 1-level, 2-level, and 3-level fusions (P > 0.05). The intraobserver correlation coefficient for the measurement technique was R = 0.90 (P = 0.0016). CONCLUSION.: We validated that the midline of the cervical spine is in line with a straight bovie cord connecting the midline of the manubrium to the midline of the mandible using anteroposterior fluoroscopy. Using this line, we prospectively centered cervical plates with no significant difference between levels. These data may also serve as a benchmark for assessing cervical plate alignment

STUDY DESIGN: Prospective inter-rater and intrarater reliability analysis. OBJECTIVE: To compare the inter-rater and intrarater reliability of magnetic resonance imaging (MRI) and computed tomography (CT) for grading of facet arthropathy as well as determining whether there is a contraindication to total disc replacement (TDR). SUMMARY OF BACKGROUND DATA: Several classifications attempted to evaluate lumbar facet joints and their degree of arthropathy. The Fujiwara-MRI and Pathrea-CT classifications remain the most commonly used. METHODS: A total of 10 fellowship-trained orthopedic spine surgeons and 3 orthopedic spine fellows evaluated 50 levels from L3-L4 through L5-S1 on parallel axial MRI (T1 and T2) and CT images. The degree of osteoarthritis was graded on a 4-point scale (Fujiwara-MRI and Pathrea-CT). Surgeons evaluated whether the degree of facet disease represented a contraindication to TDR. Grading was performed during 2 sessions. Weighted kappa statistics were used to describe inter- and intraobserver agreement. RESULTS: The inter-rater reliability for MRI was 0.21 and 0.07 (fair to slight) among attendings and fellows, respectively. inter-rater reliability for CT was 0.33 and 0.27 (fair), respectively. The mean intrarater reliability for MRI was fair, 0.36 (attendings) and 0.26 (fellows). The mean intrarater reliability for CT was moderate, 0.52 (attendings) and 0.51 (fellows). For possible TDR contraindication, the inter-rater reliability for MRI was 0.22 and 0.01 (fair to slight) among attendings and fellows, respectively. Inter-rater reliability for CT was 0.33 and 0.45 (fair), respectively. The mean intrarater reliability for MRI was fair, 0.36 (attendings) and 0.26 (fellows). The mean intrarater reliability for CT was moderate, 0.52 (attendings) and 0.51 (fellows). CONCLUSION: The current grading system for facet arthropathy has only fair agreement. CT is slightly more reliable for grading. Intrarater reliability was only fair for MRI and moderate for CT. Only limited agreement existed between surgeons as to the extent of facet disease that would pose as a contraindication for TDR

Stress fractures of the lower extremities are a known risk of intense physical activity. Femoral stress fractures represent a small subset of lower extremity stress fractures but can have grave consequences if undetected, resulting in a displaced fracture. If detected prior to displacement, conservative treatment of these fractures is highly successful. However, displacement frequently makes surgical treatment necessary. Unfortunately these fractures are often difficult to detect. Symptoms of stress fractures are frequently vague, particularly in femoral stress fractures. Specific physical examination techniques can assist in diagnosis but require a very high index of suspicion. Plain radiographs are also frequently negative in early stress fractures, further confounding diagnosis, and bone scan or magnetic resonance imaging studies are frequently needed. We present a case of an otherwise healthy 15-year-old male athlete with bilateral femoral stress fractures. The patient reported bilateral knee pain of 2 months' duration with physical activity, but had not curtailed his activities. His pain had been evaluated with plain radiographs, which were interpreted as normal. Immediately prior to presentation, while playing lacrosse, he sustained a displaced right supracondylar femur fracture. On further evaluation with bone scan he was found to have a contralateral nondisplaced supracondylar femoral stress fracture. His displaced fracture was managed with a retrograde intramedullary nail and his nondisplaced fracture was treated conservatively.