Value of CT scan-assessed tibial tuberosity-trochlear groove distance in identification of patellar instability.

Purpose: Tibial tuberosity-trochlear groove (TTTG) distance is currently considered as one of the main factors in decision-making for surgical intervention in patients with patellar instability. The current study aimed to provide a valid comparison of TTTG distance in the healthy knees with those with patellar instability.
Materials and Methods: Patients with a history of two or more episodes of patellar dislocation in the same knee who were referred to our department for the assessment of TTTG distance were included. Asymptomatic knees of patients as well as both knees of 21 healthy individuals were used as controls.
Results: A total number of 42 patients, including 14 (33.3 %) male and 28 (66.7 %) female, with a mean age of 28.6 ± 12.3 years were included. Twenty-one controls with no significant difference of personal characteristics with patients were also enrolled. The mean TTTG distance in symptomatic and asymptomatic knees of patients were 18.71 ± 3.96 mm and 17.35 ± 4.39 mm with no significant difference (P = 0.298). The mean TTTG distances of both symptomatic and asymptomatic knees of patients were significantly higher than in knees of controls (P < 0.001).
Conclusion: The findings of the current study are not in favor of considering TTTG distance independently in decision-making for surgical interventions. However, greater TTTG in both asymptomatic and symptomatic knees of patients compared to controls indicates that this measure could still be considered as an indicator of knee instability and even the need for surgery if considered in addition to other factors.