Background:​ Total knee arthroplasty (TKA) is a successful surgical treatment for people with end-stage knee osteoarthritis (OA) ^1,2. More than 700,000 TKAs are performed annually in the United States ³, and that number is estimated to reach 3.5 million TKAs by 2030 ⁴. Despite the success rate of this surgery, many individuals who get TKA develop a rapid onset (3.2 years ⁵) of OA on the contralateral knee after the initial surgery ⁶. Individuals after TKA are known to move asymmetrically ^7,8 and have residual physical impairments in strength and range of motion ^9,10, but it is not clear how these deficits contribute to contralateral OA progression. Abnormal joint biomechanics predict primary knee OA progression ^11,12, but there is a lack of evidence about which biomechanical and clinical factors predict contralateral knee OA progression after unilateral TKA. Even though clinically meaningful information can be obtained through the use of motion analysis, the complexity of laboratory equipment and the associated costs are a major obstacle for clinicians when evaluating movement patterns for individuals with musculoskeletal disorders. There has been an increasing interest in using commercially available wireless shoe insoles for kinetic assessments in the clinical setting to measure the real-life performance ¹³.

Aims:​ Therefore, the overall goals of this project were to 1) quantify the influence of contralateral knee OA on movement patterns and movement symmetry and 2) identify biomechanical and clinical predictors of radiographic knee OA progression in the contralateral knee after unilateral TKA. We also developed methods to quantify force asymmetry in a clinical setting using vertical ground reaction force acquired through commercially available shoe insoles. This will provide researchers and clinicians with more realistic estimates of asymmetry that may occur during actual activities of daily living.

Results:​ Results from our studies revealed that patients who have structural evidence of contralateral knee OA after TKA, even without contralateral symptoms, have altered walking patterns. Specifically, these individuals move more symmetrically, albeit more abnormally, in both limbs. In our predictive analyses, we found that the majority of individuals (62.5-78%) had radiographic progression of contralateral knee OA at multi-year follow-up. We did not identify any biomechanical predictors of contralateral OA progression, but contralateral quadriceps strength was significantly higher in the non-progressor group (25.4+7.5 Nm/kg/m² ;​ p=0.033) and greater contralateral quadriceps strength was protective against OA progression (odds ratio=1.117;​ p=0.047;​ Table 3). For every one unit increase in quadriceps strength, the likelihood of being a non-progressor increased by 11.7%.

Conclusions:​ Participants with contralateral knee OA have more symmetrical gait, although they adopt a more abnormal and stiff-legged gait pattern bilaterally. Symmetrical movement patterns between limbs after surgery should not be the sole factor upon which movement recovery is based. Although abnormal biomechanics are known risk factors for primary knee OA, it is possible that the mechanisms that result in OA progression of the contralateral limb are different than primary knee OA progression. Quadriceps strength is a prognostic indicator for knee OA progression in the contralateral limb and should remain to be a primary focus of rehabilitation after unilateral TKA. These findings will help clinicians better educate patients and develop targeted strengthening interventions for improving contralateral joint health post-TKA. uture work should evaluate other objective measures of OA progression and determine if cumulative measures of joint loading are related to OA worsening.