Factors associated with contralateral limb knee pain in unilateral lower limb amputees: a cross-sectional analysis of 531 patients

Background: Lower limb amputation results in substantial biomechanical alterations during gait, frequently leading to asymmetrical loading of the contralateral limb. Chronic overloading of the sound extremity has been implicated in the development of secondary musculoskeletal complications, including knee pain and osteoarthritis. However, the factors associated with contralateral joint pain among amputees remain incompletely understood. The objective of the study was to estimate the prevalence of patient-reported contralateral knee pain among unilateral lower limb amputees and identify demographic and clinical factors associated with its presence. Methods: A cross-sectional observational study was conducted using a clinical database of 531 adult unilateral lower limb amputees undergoing prosthetic rehabilitation from 2016 to 2021. Contralateral knee pain was recorded as a patient-reported binary outcome (yes/no) during clinical assessment. Demographic variables, amputation characteristics, time since amputation, time to first prosthetic fitting, body weight, and walking distance were analysed. Continuous variables were compared between pain and no-pain groups using independent-samples t-tests, and categorical variables using chi-square tests where applicable. Results: Contralateral knee pain was reported by 64 of 531 participants, giving an overall prevalence of 12.1% (95% CI 9.6-15.1%). Participants with knee pain were older than those without pain (54.9 versus 48.9 years; p=0.009) and had a longer duration since amputation (20.1 versus 13.5 years; p=0.018). Body weight (p=0.48), daily walking distance (p=0.26), and time to prosthetic fitting (p=0.25) were not significantly different between groups. Conclusions: Contralateral knee pain was present in approximately one in eight unilateral lower limb amputees in this cohort. Increasing age and longer duration since amputation were associated with the presence of contralateral knee pain. Because this cross-sectional study used a patient-reported binary pain outcome and did not include a validated knee functional score, the findings should be interpreted as associations rather than causal or independent predictive effects.