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

Abstract

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.

Keywords: Bony landmarks; Joint line restoration; Knee arthroplasty; Revision.

Fig. 1

Demonstration of the measurement technique in coronal view of MRI. The knee joint line connects the most distal point of medial femoral condyle and lateral femoral condyle. Line A is the distance from the most prominent point of medial femoral epicondyle (ME, arrow) perpendicular to the knee joint line. Line B is the distance from the most prominent point of lateral femoral epicondyle (LE, arrowhead) perpendicular to the knee joint line

Fig. 2

Demonstration of the measurement technique in sagittal view of MRI. The knee joint line was identified by the line between the highest points of cartilage of the anterior and the posterior tibial plateau. Line C is the distance from the highest point of fibular head perpendicular to the knee joint line. Line D is the distance from tibial tubercle to the knee joint line. It is measured from the most proximal point where the patella tendon is inserted into the tibial tubercle to the knee joint line. Line E is the distance from the most inferior point of inferior pole patella perpendicular to the knee joint line

Fig. 3

Demonstration of the measurement technique in axial view of MRI. The femoral transepicondylar width (FW) is the distance from the most prominent point of medial femoral epicondyle (ME, arrow) to the most prominent point of the lateral femoral epicondyle (LE, arrowhead)

Fig. 4

Graph comparing the mean and standard deviation among investigated distances to the knee joint line. There are significant variations between genders in distances A, B, C, and D

Fig. 5

Graph comparing the mean and standard deviation among ratios between investigated distances and the femoral width. The ratio of distance B/FW provides a similar mean, with narrower standard deviation than the others