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

Abstract

ObjectivesBecause 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.MethodsA 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 (δFTA) and the change of joint line height, was analysed.ResultsThe mean pre- and post-operative FTA was 180.5° (172.2° to 184.8°) and 175.0° (168.5° to 178.9°), respectively. The mean δFTA was 5.5° (2.3° to 10.1°). The joint line elevation of the tibia (JLET) was 4.4 mm (2.1 to 7.8). The δFTA was correlated with the JLET (correlation coefficient 0.494, p = 0.0009).ConclusionsThis 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.Cite this article: Bone Joint Res 2015;4:128–133

Interpreting regression models in clinical outcome studies

“…For example, when comparing radiographic parameters or associating surgical technical factors, values of R 2 are reported in the 0.2 to 0.4 range. 8,9 Whereas, comparing data between separate (but intrinsically similar) outcome assessment questionnaires can yield higher values in excess of 0.7. 10 …”

Importance of joint line preservation in unicompartmental knee arthroplasty: Finite element analysis

“…However, unlike TKA, the joint line change in medial UKA affects not only the anatomical position of the patella but also the joint line of the lateral compartment. Kuwashima et al investigated the effect of mechanical alignment, which is correlated with the joint line elevation, following medial UKA of the tibial compartment . To preserve the joint line, the surgeon should generally resect the tibial bone 4 mm from the bony surface of the tibia compartment .…”

“…The PE insert was modeled as an elastoplastic material, and the implant components were modeled as linear elastic isotropic materials (Table ). In developing the joint line FE model, we referred to a previous study . The femoral component and tibial tray were fully bonded to the femur and tibia bone models, respectively.…”

“…Preserving the joint line in TKA implantation, especially during revision surgery, is essential in post‐operative prognosis . The correction of mechanical alignment is mainly determined by the elevation (restoration) of the joint line at the tibia and femur, especially in medial OA . Hopgood et al investigated the change in joint line at the tibial side, which is affected by the difference between the depth of resection at the proximal tibia and the thickness of the polyethylene (PE) insert .…”

“…Weber et al introduced the method that allows to measure the joint line shift reliably on a standard anterior–posterior radiograph . Kuwashima et al found that the change in mechanical alignment is correlated with the joint line height at the medial proximal tibia and distal femur in UKA . However, the effect of the joint line in UKA has not been investigated from a biomechanical perspective.…”