Foot Loading Symmetry is Improved after Unicompartmental Knee Arthroplasty

Abstract

Category: Basic Sciences/Biologics; Midfoot/Forefoot Introduction/Purpose: Unicompartmental Knee Arthroplasty (UKA) is a surgical option for osteoarthritis in a single compartment of the knee. Compared to Total Knee Arthroplasty (TKA), UKA is less expensive, retains the cruciate ligaments and results in lower post-operative morbidity.[1] It has been reported that about 10 percent of UKAs require revision to TKA for multiple reasons. In TKA, ankle alignment has demonstrated a significant effect on outcomes and function. [2] Plantar pressure, a measure of foot and ankle loading, changes after TKAs but has yet to be evaluated in UKAs. The purpose of this study is to evaluate the effects of medial UKA on plantar pressure which may be a variable that contributes to revisions in these patients. Methods: Following IRB approval and informed consent, we evaluated 7 adults (14 Feet) (average age 62; range: 54 to 68 years old; 4F/ 3M). All participants walked at a self-selected speed pre surgery and 7 months post-surgery. The Pedar insole pressure system (Novel), with 99 sensors per insole, was used to collect bilateral plantar pressure during gait at 100 Hz. All participants wore the same type of shoes (Nike Zoom) for the test. The insole was divided into 9 regions for analysis2 (Figure 1). The maximum pressure (MP) within each foot region was calculated for each step and averaged over all steps. Paired and unpaired t- tests were performed to identify differences in the MP from pre to post-op and between operated and contralateral sides, respectively. Results: An average of 24 steps were recorded from each patient pre and post operatively. MP became more symmetrical between feet post-operatively, with significant improvements in bilateral symmetry observed in the medial heel, medial and lateral forefoot regions (all p<0.01). The MP in the lateral midfoot region of the operative side increased during ambulation post- operatively (p<0.05). The MP in the lateral forefoot region of the non-operative side decreased post-operatively (p<0.01). Conclusion: Our results indicate that foot loading, as assessed through plantar pressure, becomes more symmetrical after unilateral UKA and may also affect non-operative foot loading. Although our sample size is small, our data is comparable with a similar study done in TKA patients which reported changes forefoot and lateral midfoot loading.