Aims and Objectives:
To develop a dynamic physical examination test that functionally simulates actual patellar instability events and that mimics the range of patellar stabilizer insufficiency in an individual patient.
Materials and Methods:
Seventy-four consecutive patients (male/female 33/41; mean age 22±7 years) with recurrent lateral patellar instability and thirty controls (male/female 16/14; mean age 31±14 years) were prospectively evaluated using the reversed dynamic patellar apprehension test (ReDPAT). The examination starts with the knee flexed at 120°. The knee is then extended while the patella is translated laterally. The maneuver is stopped at first onset of a subjective apprehensive reaction, and the ReDPAT result is considered positive according to this knee joint flexion angle. Anatomical predisposition was assessed according to Dejour’s classification of trochlear dysplasia, tibial tuberosity-trochlear groove distance, tibial tuberosity-posterior cruciate ligament distance, patellar height, and varus/valgus malalignment.
Results:
The study group had an average of 3.4 ± 1.0 (1-6) anatomical risk factors for lateral patellar dislocation. Severe trochlear dysplasia (84%) and patella alta (49%) were the most common. Test sensitivity, specificity, and accuracy reached 97.3%, 90%, and 95.2%, respectively, and test-retest reliability was good (Pearson’s r 0.84; p<0.0001). The ReDPAT results became positive at a mean knee flexion angle of 58°±17° (20°-90°). Knee flexion angle correlated significantly with the severity of trochlear dysplasia (p=0.018), valgus deformity (p=0.011), and the total number of anatomical risk factors (p=0.02).
Conclusion:
This study introduced the reversed dynamic patellar apprehension test as a reliable clinical examination tool in the assessment of lateral patellar instability. The results of this study indicate that the degree of knee joint flexion at which the provocative sense of apprehension becomes positive correlates with severity of trochlear dysplasia, valgus deformity and the total number of anatomical risk factors for patellar instability.