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

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 subdivi-sions 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.