Knee joint line related to bony landmarks of the knee: a radiologic study in a Thai population

BACKGROUND: During revision total knee arthroplasty (TKA), knee joint line restoration may be difficult due to bone loss or structural changes. Although bony landmarks are consistent and can be used as references, there are limited data in Asian patients. We studied the knee joint line related to bony landmarks of the knee in a Thai population. MATERIALS AND METHODS: Magnetic resonance imaging (MRI) of 140 healthy knees of Thai patients (70 males, 70 females) were investigated. In all knees, a perpendicular line from knee joint line to the medial epicondyle (distance A) and the lateral epicondyle (distance B) in the coronal plane were measured. In the sagittal plane, a perpendicular line from the knee joint line to the fibular head (distance C), the tibial tubercle (distance D), and the inferior patellar pole (distance E) were measured. The femoral transepicondylar width (FW) was measured along the transepicondylar axis. The ratios of distances A, B, C, D, and E related to FW were evaluated (epicondylar ratio). RESULTS: The mean and standard deviation (SD) of distances A, B, C, D, E, and FW were 27.1 ± 2.7 mm, 21.7 ± 2.5 mm, 12.6 ± 3 mm, 21.3 ± 3.6 mm, 7.6 ± 4.8 mm, and 76.7 ± 3.99, respectively. There was wide variation of measured values, with statistically significant differences between genders in distances A, B, C, and FW. The mean and SD of epicondylar ratios A/FW, B/FW, C/FW, D/FW, and E/FW were 0.35 ± 0.02, 0.29 ± 0.02, 0.16 ± 0.05, 0.28 ± 0.04, and 0.09 ± 0.04, respectively. All epicondylar ratios demonstrated less variation than all measured distances, with statistical differences between genders in the A/FW and D/FW ratios. However, the B/FW ratio had the highest consistent mean value. In addition, it had narrower SD than the rest (0.29 ± 0.02; range, 0.22–0.33). CONCLUSIONS: In Thai knees, the measured distances from bony landmarks to the knee joint line had higher variation than the epicondylar ratio. Among all studied epicondylar ratios, the ratio between lateral epicondyle to joint line distance (distance B)/FW demonstrated the narrowest range of mean and SD values; therefore, this could be the most reliable landmark for intraoperative knee joint line verification by multiplying the FW of the patient by 0.29 to get distance B in that patient.