The relation between muscle force and functional movement performance in patients one year after knee replacement surgery: a pilot study

Purpose: Limited evidence exists on the clinical use of the forward lunge (FL) and the squat in rehabilitation protocols following knee replacement surgery. The aim of this study is to compare the squat and FL performance between patients with unicondylar (UKA), total knee arthroplasty (TKA) and controls. The second aim will be to investigate the relation between muscle force and the performance of these functional movements. Methods: Sixteen one-year post knee replacement surgery patients and 9 control subjects were recruited for this study. Subjects performed three FL and squat trials. A visual rating (good or bad) at knee, hip and ankle level was performed while subjects executed the functional movements. A physical examination and functionality assessment was performed. An ANOVA test followed by a Bonferroni correction was used to assess differences between groups. A chi-square test was used to compare differences based on the performance of the functional movements at different body levels. An unpaired T-test was used to assess differences in muscle force and knee joint mobility between subjects with a ‘good’ or ‘bad’ performance Results: No statistical differences were demonstrated between groups regarding squat performance. Patients with TKA performed significantly worse at trunk and knee level during the FL. A bad performance of the FL at knee level was associated with reduced muscle strength of the gluteus medius, maximus and hamstrings across groups. Conclusion: The FL is a challenging task for patients with a knee replacement, especially for those with reduced muscle force at hip stabilizers and knee prime movers.