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[Quadriceps dysplasia and patellar tilt in objective patellar instability]
1Service Professeur H. Dejour, Centre Hospitalier Lyon-Sud, Pierre-Bénite.
Summary
Patellar tilt measured on CT scans can identify patellar instability, even in asymptomatic knees. A threshold of 20 degrees reliably indicates pathological tilt, aiding diagnosis and treatment planning.
Area of Science:
- Orthopedics
- Radiology
- Biomechanics
Background:
- Vastus medialis dysplasia is a known indicator of patellar instability.
- Pre-operative identification of this dysplasia can be challenging.
Purpose of the Study:
- To evaluate patellar tilt measurement on CT scans as a method for assessing patellar instability.
- To determine if patellar tilt is an indicator of underlying functional abnormalities.
Main Methods:
- CT scans were used to measure patellar tilt in extension.
- Measurements were taken with the quadriceps relaxed and contracted.
- Three groups were studied: operated knees (n=143), asymptomatic contralateral knees (n=67), and control knees (n=54).
Main Results:
- Patellar tilt was significantly increased in both operated and asymptomatic contralateral knees compared to controls.
- Quadriceps contraction exacerbated patellar tilt in instability groups but not controls.
- A threshold of 20 degrees for patellar tilt demonstrated 90% sensitivity and 91% specificity for pathological cases.
Conclusions:
- Patellar tilt in extension reflects a functional disorder of the entire quadriceps, not just the vastus medialis.
- Measuring patellar tilt with relaxed and contracted quadriceps helps identify borderline functional abnormalities.
- A pathological patellar tilt is reliably identified at or above 20 degrees.