Arthrogenic muscle inhibition: A prevalent issue in knee arthroplasty

Flexion contracture is a multifactorial complication after knee osteoarthritis and knee arthroplasty. Among the causes, arthrogenic muscle inhibition (AMI) has never been studied. It is a failure to achieve proper quadriceps motor activation, which can lead to flexion contracture due to hamstring contracture. In this study, we hypothesised that AMI is present in patients with knee osteoarthritis and after knee arthroplasty. The aims were to assess: (1) the prevalence of preoperative AMI, for patients without preoperative AMI, (2) the incidence of post-operative AMI at 2 weeks, (3) its associated factors at 2 weeks and (4) the incidence 90 days after surgery.

An international, prospective study enroled 341 patients undergoing knee arthroplasty across three centres. 316 patients met the inclusion criteria: symptomatic knee requiring unicompartmental, total or revision arthroplasty. Twenty-five patients undergoing simultaneous bilateral procedures were excluded. Among the included patients, 275 patients without preoperative AMI were analysed for post-operative incidence and associated factors. AMI was assessed using the SANTI classification on the day of surgery, at 15 days, and at 3 months. One patient was lost to follow-up at 3 months.

Preoperative AMI ≥  1 was observed in 13% (95% confidence interval [CI] = 9-17). At 2 weeks post-operatively, AMI ≥  1 occurred in 36% (95% CI = 30-42), with 13% showing AMI ≥  2, characterised by quadriceps inhibition and flexion contracture. Female gender (odds ratio [OR] =  2.81; p < 0.002), early post-operative flexion contracture attitude such as keeping the knee bent, placing a pillow under the knee, or folding the hospital bed (OR =  5.89; p < 0.001), and high pain scores (OR = 13.57; p < 0.001) were significantly associated with AMI ≥  1 at 2 weeks. At 3 months, AMI ≥ 1 occurred in 12.4% (95% CI = 8.7-16.9).

AMI is a prevalent issue both pre- and post-operatively. Its incidence underscores the relevance of this condition; it should be considered in the management of post-operative flexion contracture in knee arthroplasty.

Level III, observation cohort study.