A Novel Anatomic Landmark to Assess Adequate Decompression in Anterior Cervical Spine Surgery: The Posterior Endplate Valley (PEV).

STUDY DESIGN: A retrospective study. OBJECTIVES: (1) To assess the reliability of using the posterior endplate valley (PEV) to predict the cranial-caudal location of the cervical pedicle intraoperatively; (2) to assess the impact of age on the cervical PEV-pedicle relationship, interpedicular distance, and foraminal height. SUMMARY OF BACKGROUND DATA: The cervical pedicle, which is the anatomic landmark defining the boundaries of the foramen, is hidden from view intraoperatively in the anterior cervical approach, potentially leading to incomplete foraminal decompression. An intraoperative landmark which heralds the location of the pedicle and therefore can be relied upon as a guide for decompression has not been previously described. METHODS: We retrospectively reviewed cervical computed tomography images of younger (<50 y) and older (>50 y) patients. Using the coronal reconstructed image taken at the posterior margin of the vertebral body, we constructed a line between the superior aspect of the pedicles and measured the distance from this line to the PEV. Interpedicular distance and foraminal height were also measured. RESULTS: One hundred patients were included in the final analysis. The mean distance (mm) from the pedicular line to the PEV from C3 to C7 respectively was 1.0±0.99, 0.01±0.76, 0.09±0.70, 0.20±0.71, and 0.27±0.79. No significant difference between young and elderly patients was noted (P<0.05). Intervertebral foraminal size was significantly greater in younger compared with elderly patients at all levels except C2-C3. The mean interpedicular distance was 23.05±1.76 mm. CONCLUSIONS: This study demonstrates, for the first time, that the PEV is an accurate surgical landmark that is consistently at most 1 mm from the superior aspect of the cervical pedicle in the subaxial spine. Furthermore, this study demonstrated that foraminal height was significantly larger in younger compared with elderly patients at all cervical levels below C3. LEVEL OF EVIDENCE: Level 3.

Comparison of Kinematics and Tibiofemoral Contact Pressures for Native and Transplanted Lateral Menisci.

BACKGROUND: Lateral meniscus transplantation is a proven treatment option for the meniscus-deficient knee, yet little is known about meniscal kinematics, strain, and tibiofemoral contact pressure changes after transplantation or the effect of altered root position in lateral meniscus transplantation. PURPOSE: To compare the native lateral meniscal kinematics, strain, and tibiofemoral contact pressures to a best-case scenario meniscus transplant with perfectly matched size and position and to determine how sensitive these factors are to subtle changes in shape and position by using a nonanatomic meniscus transplant position. STUDY DESIGN: Controlled laboratory study. METHODS: The lateral menisci of 8 cadaveric knees were circumferentially implanted with radiopaque spherical markers. They were mounted to a testing apparatus applying muscle and ground-reaction forces. The meniscus was evaluated at 0°, 30°, 90°, and 115° of knee flexion using Roentgen stereophotogrammetric analysis (RSA), with a pressure sensor affixed to the lateral tibial plateau. Measurements were recorded for 3 states: the native lateral meniscus, an anatomic autograft transplant, and a nonanatomic autograft transplant with an anteriorized posterior root position. RESULTS: After transplantation, there was less posterior displacement in both the anatomic and nonanatomic transplant states compared with the native meniscus, but this was not significant. The largest lateral translation in the native state was 2.38 ± 1.58 mm at the anterolateral region from 0° to 90°, which was increased to 3.28 ± 1.39 mm (P = .25) and 3.12 ± 1.18 mm (P = .30) in the anatomic and nonanatomic transplant states, respectively. Internal deformations of the transplant states were more constrained, suggesting less compliance. The native meniscus distributed load over 223 mm2, while both the anatomic (160 mm2) and nonanatomic (102 mm2) states concentrated pressure anteriorly to the tibial plateau centroid. CONCLUSION: This study is the first to characterize kinematics in the native lateral meniscus compared with a transplanted state utilizing RSA. Results demonstrate increased meniscal constraint and pressure concentrations even after an ideal size and position matched transplantation, which further increased with a nonanatomic posterior root position. CLINICAL RELEVANCE: The results show that kinematics are similar in both transplanted states when compared with the native meniscus at various flexion angles. Because both transplanted states were more constrained with less deformation compared with the native state, this should allow for relatively safe postoperative range of motion. However, in the transplanted states, peak pressures were distributed over a smaller area and shifted anteriorly. This pattern was exacerbated in the nonanatomic state compared with anatomic. This could have detrimental effects with regard to articular cartilage degeneration, and ultimately result in a failed transplantation.