Component malalignment in unicompartmental knee arthroplasty (UKA) has been associated with contact stress concentration and poor clinical outcomes. However, there is a paucity of data regarding UKA component alignment and in vivo articular contact in weight-bearing position. This study aims to (1) quantify three-dimensional UKA component alignment and (2) evaluate the association between the component alignment and in vivo articular contact in standing position.
Seventy-seven UKAs in 68 consecutive patients were imaged in standing position using a biplanar X-ray imaging acquisition system. The UKA models were imported into a virtual imaging environment and registered with component silhouette on X-ray image for determination of component position and contact location. Anatomic bony landmarks of the lower limb were digitized for quantification of the bone alignment.
The femoral component (FC) showed 1.6° ± 3.3° valgus, 6.5° ± 6.4° external rotation, and 2.4° ± 4.6° flexion. The tibial component (TC) showed 3.9° ± 4.5° varus, 4.4° ± 6.7° internal rotation, and 10.1° ± 4.6° tibial slope. The average contact point was located medially and posteriorly by 7.8 ± 7.6% and 0.7 ± 7.7% of TC dimensions to its center. Multiple regression analysis identified FC flexion as a significant variable affecting UKA anterior and/or posterior contact position (R = 0.549, P < .001).
This study demonstrated the highest variability of UKA component positioning in axial plane rotation for FC and TC. The association between FC flexion and anterior contact position suggests accurate implant positioning may be important in optimizing in vivo UKA contact behavior. Further studies are required to gain understanding of the influence of axial rotation variability on in vivo UKA contact kinematics during functional activities.