University of Pennsylvania, 1 Cupp Pavilion, 39th and Market Streets, Philadelphia, PA, 19104, USA.
Clin Orthop Relat Res. 2014 Jan;472(1):155-61. doi: 10.1007/s11999-013-2946-2.
Restoration of posterior condylar offset (PCO) during total knee arthroplasty is essential to maximize range of motion, prevent impingement, and minimize flexion instability. Previously, PCO was determined with lateral radiographs, which could not distinguish the asymmetries between the femoral condyles. MRI can independently measure both medial and lateral PCO.
QUESTIONS/PURPOSES: The purpose of this study is to determine the normal PCO of the knee, to establish the differences in medial and lateral PCO, and to compare PCO measurements obtained from radiographs versus those obtained from MRI.
We identified 32 patients without a history of prior knee pathology who had both plain radiographs and MRI scans of the same knee performed. The PCO was measured on lateral radiographs and compared with MRI measurements using a novel three-dimensional protocol.
By MRI, the mean medial PCO was 29 (± 3) mm and the mean lateral PCO was 26 (± 3) mm; both values were greater (p < 0.001 and p = 0.03, respectively) than the mean radiographic PCO of 25 (± 2) mm. The medial PCO, as measured by MRI, was significantly greater than the lateral PCO (p < 0.001).
Plain radiographs underestimate PCO as well as the asymmetry of the medial and lateral PCO compared with MRI. This discrepancy is the result of both articular cartilage thickness and the anatomic differences between medial and lateral condyles. Designers of knee prostheses and instrumentation should take these differences into account.
在全膝关节置换术中，恢复后髁偏心距（PCO）对于最大限度地增加活动范围、防止撞击和最小化屈曲不稳定性至关重要。此前，PCO 是通过侧位 X 线片确定的，而该方法无法区分股骨髁之间的不对称性。MRI 可以独立测量内侧和外侧 PCO。
问题/目的：本研究旨在确定膝关节的正常 PCO，确定内侧和外侧 PCO 的差异，并比较 X 线片和 MRI 测量的 PCO 值。
我们确定了 32 例无膝关节病史的患者，这些患者的同一条膝关节同时进行了普通 X 线片和 MRI 扫描。在侧位 X 线片上测量 PCO，并使用新的三维方案与 MRI 测量值进行比较。
MRI 测量的平均内侧 PCO 为 29（±3）mm，平均外侧 PCO 为 26（±3）mm；与 X 线片测量的平均 PCO（25（±2）mm）相比，这两个值均更大（p<0.001 和 p=0.03）。MRI 测量的内侧 PCO 明显大于外侧 PCO（p<0.001）。
与 MRI 相比，普通 X 线片低估了 PCO 以及内侧和外侧 PCO 的不对称性。这种差异是由于关节软骨厚度和内侧与外侧髁之间的解剖差异造成的。膝关节假体和器械的设计者应考虑到这些差异。
