Longitudinal Change of Medial and Lateral Patellar Stiffness After Reconstruction of the Medial Patellofemoral Ligament for Patients with Recurrent Patellar Dislocation.

BACKGROUND: Longitudinal changes in patellar stiffness following reconstruction of the medial patellofemoral ligament for recurrent patellar dislocation at full extension are unknown. METHODS: Fifteen consecutive patients (three men and twelve women, with a mean age of twenty-two years) with seventeen knees were matched by sex and age to thirty-two reference subjects in this prospective study. The follow-up period was a minimum of twenty-four months. The medial patellofemoral ligament reconstruction used an autograft semitendinosus tendon and an interference screw system with or without lateral release under 10 N of laterally directed force. The medial patellar stiffness and lateral patellar stiffness were measured in 0° of knee extension using the Patella Stability Tester preoperatively; postoperatively at three, six, twelve, and eighteen months; and at the time of the latest follow-up. Before and after the surgical procedure, patients were evaluated for apprehension and Kujala and Lysholm scores; radiographic examinations were performed to evaluate changes, including osteoarthritic changes. RESULTS: The medial stiffness of the affected side before the surgical procedure was significantly lower than the lateral stiffness (p = 0.004) and the stiffness for healthy reference knees (p = 0.004). Medial stiffness three months after the surgical procedure was significantly elevated compared with lateral values (p = 0.027), preoperative values (p < 0.001), and reference group values (p = 0.002); reached the reference level by six months; and was maintained for up to two years. Furthermore, medial stiffness and lateral stiffness were well balanced after six months and this balance was sustained for up to two years postoperatively. No recurrent dislocation occurred during the follow-up period; one patient experienced apprehension. Postoperative radiographic findings and clinical scores were significantly improved at the time of the latest follow-up (p < 0.05). One knee progressed to patellofemoral osteoarthritis. CONCLUSIONS: The value for medial stiffness was significantly improved three months after medial patellofemoral ligament reconstruction compared with the preoperative and lateral values and returned to the reference level by six months. Medial stiffness and lateral stiffness of the patella were well balanced by six months and retained that balance for up to two years, with good clinical results. LEVEL OF EVIDENCE: Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

Measurement characteristics of a force-displacement curve for chronic patellar instability.

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.