Correction of coronal alignment correlates with reconstruction of joint height in unicompartmental knee arthroplasty

Objectives Because there have been no standard methods to determine pre-operatively the thickness of resection of the proximal tibia in unicompartmental knee arthroplasty (UKA), information about the relationship between the change of limb alignment and the joint line elevation would be useful for pre-operative planning. The purpose of this study was to clarify the correlation between the change of limb alignment and the change of joint line height at the medial compartment after UKA. Methods A consecutive series of 42 medial UKAs was reviewed retrospectively. These patients were assessed radiographically both pre- and post-operatively with standing anteroposterior radiographs. The thickness of bone resection at the proximal tibia and the distal femur was measured radiographically. The relationship between the change of femorotibial angle (delta FTA) and the change of joint line height, was analysed. Results The mean pre- and post-operative FTA was 180.5 degrees (172.2 degrees to 184.8 degrees) and 175.0 degrees (168.5 degrees to 178.9 degrees), respectively. The mean delta FTA was 5.5 degrees (2.3 degrees to 10.1 degrees). The joint line elevation of the tibia (JLET) was 4.4 mm (2.1 to 7.8). The delta FTA was correlated with the JLET (correlation coefficient 0.494, p = 0.0009). Conclusions This study indicated that there is a significant correlation between the change of limb alignment and joint line elevation. This observation suggests that it is possible to know the requirement of elevation of the joint line to obtain the desired correction of limb alignment, and to predict the requirement of bone resection of the proximal tibia pre-operatively.