Knee moments after unicompartmental knee arthroplasty during stair ascent

Abstract

Background: For unicompartmental knee arthroplasty (UKA), abnormal loading on the tibiofemoral joint could exacerbate knee osteoarthritis or implant wear. Joint moments are an indirect measure of such loading. However, little is known about knee moments of patients with UKA, tempering enthusiasm for its use.

Questions/purposes: In patients with UKAs performing stair ascent, we (1) determined whether interlimb differences for knee moments are demonstrated, (2) described the knee kinetics of patients with medial and lateral UKAs, and (3) investigated possible factors that might influence the knee abductor moments.

Methods: In our cross-sectional study, we recruited 26 patients with UKA with nondiseased contralateral limbs who performed stair ascent. Seventeen patients had medial UKAs and nine had lateral UKAs. Paired t-tests and CIs were applied to determine interlimb differences within each UKA group for peak knee moments and times to peak moments.

Results: During stair ascent, the medial UKA group displayed greater peak extensor moments for the nondiseased compared to the UKA limb (p = 0.030), whereas the lateral UKA group did not (p = 0.087). For both medial and lateral UKA groups, the UKA limb demonstrated greater internal peak abductor moments (p = 0.005 and 0.013, respectively). Both UKA groups exhibited knee moments similar to those in the literature. Limb dominance and postoperative time were correlated for both UKA groups.

Conclusions: Reduced knee extensor moments of limbs with UKA displayed by some participants may indicate less compressive loading on the tibiofemoral joint surfaces, whereas the increased abductor moments suggest increased compression on the medial compartment. These findings suggest UKA knees may not be subjected to excessive loads regardless of the side reconstructed.

Figures

Fig. 1A–C

Two representative knee moment patterns are displayed by the two groups in (A) extensor moment, (B) abductor moment, and (C) internal rotator moment during stair ascent. Dots indicate peak moments tested. BM = body mass; LL = leg length.

Fig. 2A–C

Graphs show peak knee moments of UKA and non-UKA limbs for the medial (MED) and lateral (LAT) UKA groups during stair ascent: (A) extensor moment, (B) abductor moment, and (C) external rotator moment. Asterisks indicate significant interlimb differences within a group (p < 0.05, paired t-test). BM = body mass; LL = leg length.

Fig. 3A–D

Scatter plots compare peak abductor moments during stair ascent to (A, C) postoperative time and (B, D) postoperative mechanical alignment (valgus = positive) in the (A, B) medial and (C, D) lateral UKA groups. Regression lines and Pearson’s correlation r are noted in all graphs. BM = body mass; LL = leg length.