Influence of Severity and Duration of Anterior Knee Pain on Quadriceps Function and Self-Reported Function

Abstract

Context Little is known about how the combination of pain severity and duration affects quadriceps function and self-reported function in patients with anterior knee pain (AKP). Objective To examine how severity (low [≤3 of 10] versus high [>3 of 10]) and duration (short [<2 years] versus long [>2 years]) of AKP affect quadriceps function and self-reported function. Design Cross-sectional study. Setting Laboratory. Patients or Other Participants Sixty patients with AKP (mean pain severity = 4 of 10 on the numeric pain rating scale, mean pain duration = 38 months) and 48 healthy control individuals. Patients with AKP were categorized into 3 subdivisions based on pain: (1) severity (low versus high); (2) duration (short versus long); and (3) severity and duration (low and short versus low and long versus high and short versus high and long). Main Outcome Measure(s) Quadriceps maximal (maximal voluntary isometric contraction) and explosive (rate of torque development) strength, activation (central activation ratio), and endurance (average peak torque) and self-reported function (Lower Extremity Functional Scale score). Results Compared with the healthy control group, (1) all AKP subgroups showed less quadriceps maximal strength (P < .005, d ≥ 0.78) and activation (P < .02, d ≥ 0.85), except for the AKP subgroup with low severity and short duration of pain (P > .32); (2) AKP subgroups with either high severity or long duration of pain showed less quadriceps explosive strength (P < .007, d ≥ 0.74) and endurance (P < .003, d ≥ 0.79), but when severity and duration were combined, only the AKP subgroup with high severity and long duration of pain showed less quadriceps explosive strength (P = .006, d = 1.09) and endurance (P = .0004, d = 1.21); and (3) all AKP subgroups showed less self-reported function (P < .0001, d ≥ 3.44). Conclusions Clinicians should be aware of the combined effect of severity and duration of pain and incorporate both factors into clinical practice when rehabilitating patients with AKP.