Significance of tibial-tubercle trochlear groove distance and adjunctive radiological parameters in patients with recurrent patellar instability.

PURPOSE

Magnetic resonance imaging (MRI) is often used to evaluate patients with patellar dislocations to facilitate diagnosis and management strategies. Many radiological parameters have been described in the literature. The aim of this study was to assess the significance of tibial-tubercle trochlear groove distance (TT-TG) distance and other MRI measurements in patients with and without patellar instability.

METHODS

This case-control study included 41 patients with recurrent patellar instability and 50 patients with stable knees, all of whom underwent MRI scans. A total of 19 radiological parameters were measured in both groups.

RESULTS

All measured MRI parameters had statistically significant differences between both groups (p < 0.05) apart from trochlear cartilage length. TT-TG distance. 20 mm had the strongest association with patellar instability (OR 53.3, p = 0.006, 95%CI [3.1- 927.4]) and the highest specificity (100%) but had the lowest sensitivity (34%) out of all the measured parameters. TT-TG. 13 mm had a higher sensitivity (68%) but lower specificity (72%) and weaker association with patellar instability (OR 5.5, p < 0.001, 95%CI [2.2. 13.7]). TT-TG/trochlear articular cartilage width ratio also had a strong association with patellar instability (OR 14.7, p < 0.001, 95%CI [4.5. 48.5]) with high specificity (92%) but lower sensitivity (56%).

CONCLUSION

The cut-off values for TT-TG distance at 13 mm and 20 mm both had advantages and disadvantages which supports the concept of using patient-individualised ratios. Patellar instability is associated with many radiological abnormalities demonstrated on MRI scans. Selection of the most appropriate measurement is dependent on the philosophy and preference of the treating clinician.