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Measurement characteristics of a force-displacement curve for chronic patellar instability
Norimasa Egusa1, Ryuji Mori, Yuji Uchio
1Departments of Rehabilitation, Faculty of Medicine, Shimane University, Izumo, Shimane, Japan.
Objective:
The clinical diagnosis of patellar instability is subjective, depending on the patient's apprehension. We hypothesized that a subjective diagnosis could be supported by a numerical evaluation of the slope, or compliance, of the early phase of a force-displacement curve.
Design:
Cross-sectional control group comparison.
Setting:
A university-based sports clinic.
Participants:
Healthy volunteers (n = 21; 16-40 years old) and patients (n = 21; 15-34 years old) who had a clearly definable diagnosis of unilateral dislocation, followed by chronic anterior knee pain, and positive apprehension signs for more than 6 months, without patella alta or abnormal limb alignment.
Intervention:
Lateral displacement and reactive forces were measured with a Patella Stability Tester.
Main Outcome Measures:
Sensitivity in detecting injured knees was defined, with the 95% confidence interval of healthy subjects determined as the normal range.
Results:
Compliance at 5 mm in displacement showed the highest reproducibility (plot difference of 4.7%) and the highest sensitivity (95%). Among injured knees, compliance was significantly correlated with the activity-related symptoms of the Kujala score (correlation coefficient, -0.61; P = 0.004). Compliance at 5 mm of displacement showed the highest sensitivity (95%) and significant correlation with the activity-related symptoms of the Kujala score among injured knees (coefficient of determination, 0.37; P = 0.004).
Conclusions:
It is a novel finding that early compliance at 5 mm of displacement showed a correlation with the subjective diagnosis and symptoms.
