How does patient-specific unicompartmental knee arthroplasty influence squatting biomechanics at mid-term follow up?

The potential advantages of patient-specific (PS) compared with off-the-shelf (OTS) unicompartmental knee arthroplasty (UKA) in terms of knee function remain unclear. Therefore, the aim of this study was to determine whether PS-UKA implant leads to superior improvement in terms of knee joint function compared with an OTS-UKA while performing a deep squat.

Twenty-two patients and 22 healthy individuals, matched for age and height, were recruited. Eight patients were operated with PS-UKA, and 14 patients with OTS-UKA. All patients were evaluated at a minimum follow up of 3 years post-surgery. Participants were instructed to squat as deeply as possible. Sagittal, frontal and transverse kinematics and kinetics were calculated for hip, knee and ankle joints. Co-contraction index was calculated for knee flexor and extensor muscles. Statistical Parametric Mapping was used to compare dependant variables.

PS-UKA and OTS-UKA showed no significant differences in spatiotemporal, kinematic, or kinetic outcomes. Compared with controls, OTS-UKA displayed reduced knee flexion, lower hip and knee sagittal range of motion, decreased hip contribution, and increased ankle contribution to total support moment.

The personalization of the implant did not demonstrate superior knee function compared with off-the-shelf UKA during squatting. The decrease in maximum knee flexion compared with the control group may be associated with fear of movement for both designs. In addition, PS-UKA and OTS-UKA patients adopted an ankle dominant strategy during squatting compared with the control group. Further analyses are required to validate these findings in other, more challenging functional tasks such as sit-to-stand and stairs negotiation.