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Instrumented measurement of patellar mobility
D C Fithian1, D K Mishra, P F Balen
1Department of Orthopaedic Surgery, University of California at San Diego, USA.
The American Journal of Sports Medicine
|September 1, 1995
Summary
This study introduces a new instrument to objectively measure patellofemoral laxity, revealing significant differences in knee joint stability between healthy and dislocated knees. The findings aid in diagnosing peripatellar soft tissue imbalance.
Area of Science:
- Orthopedic biomechanics
- Sports medicine
- Knee joint instability research
Background:
- Patellofemoral laxity is a key factor in knee injuries, particularly lateral patellar dislocation.
- Objective measurement of medial and lateral patellar restraints is crucial for understanding knee stability.
Purpose of the Study:
- To objectively analyze medial and lateral patellofemoral laxity using a novel measurement instrument.
- To assess the diagnostic accuracy of this instrument in identifying peripatellar soft tissue imbalance.
Main Methods:
- Developed and utilized an instrument to measure the force-displacement relationship of medial and lateral patellar restraints.
- Examined 94 uninjured athletic subjects and 22 patients with unilateral lateral patellar dislocation.
- Calculated peripatellar soft tissue balance by subtracting medial from lateral patellar displacement.
Main Results:
- Significant differences in patellar laxity were found between control, affected, and contralateral knees.
- Control knees showed medial displacement exceeding lateral displacement (mean -2.1 mm at 5 lbs).
- Affected knees demonstrated lateral displacement exceeding medial displacement (mean +3.2 mm at 5 lbs), with 91% sensitivity and 81% specificity for imbalance.
Conclusions:
- The developed instrument provides an objective measure of patellofemoral laxity and peripatellar soft tissue balance.
- This method effectively differentiates between healthy and unstable knees, aiding in the diagnosis of patellar instability.
- Findings highlight the utility of this tool in clinical settings for evaluating knee joint stability.