Tibial Tubercle-Posterior Cruciate Ligament Distance Fails to Capture Pathologic Patellar Lateralization in Trochlear Dysplasia.

PURPOSE: To compare tibial tubercle-trochlear groove (TT-TG) and tibial tubercle-posterior cruciate ligament (TT-PCL) distances across grades of trochlear dysplasia (TD) in patients with patellofemoral instability, to evaluate their relations with knee rotation angle (KRA) and patellar lateralization, measured as patellar tendon-lateral trochlear ridge (PTLTR), and to determine its influence on surgical indications for realignment procedures.

METHODS: Patients with patellofemoral instability treated between 2017 and 2024 were retrospectively reviewed. Magnetic resonance imaging measurements included TT-TG, TT-PCL, TTdiff (TT-TG - TT-PCL), KRA, and PTLTR. TD was graded by Dejour classification and grouped as normal/low grade (normal-A) or high grade (B-D). Pathologic thresholds were defined as TT-TG ≥ 15 mm, TT-PCL ≥ 24 mm, and PTLTR ≥ 5.6 mm. Independent-samples t-tests, Mann-Whitney U tests, Pearson correlation coefficients, Fisher's exact tests, and receiver operating characteristic curve analysis were used as appropriate.

RESULTS: A total of 153 patients were included. Mean TT-TG and TT-PCL were 17.3 ± 5.6 and 21.7 ± 4.1 mm, respectively. High-grade TD showed significantly greater TT-TG (18.7 ± 6.3 vs 16.0 ± 5.6 mm, P = .002), KRA (4.4 ± 6.8° vs 1.9 ± 8.0°, P < .001), and PTLTR (18.2 ± 8.5 vs 12.6 ± 8.1 mm, P < .001), whereas TT-PCL did not differ between groups (P = .387). TT-TG correlated positively with KRA (r = 0.47, P < .001), whereas TT-PCL showed a weak inverse correlation (r = -0.18, P = .027); TTdiff showed the strongest association (r = 0.56, P < .001). PTLTR correlated with TT-TG (P < .001) but not TT-PCL. Threshold analysis revealed discordance: 39.2% of normal/low-grade and 44.6% of high-grade TD patients were pathologic by TT-TG despite normal TT-PCL, whereas only 26.8% met TT-PCL criteria overall (P = .004).

CONCLUSIONS: TT-PCL underestimates functional patellar lateralization and surgical candidacy for realignment, particularly in high-grade TD where rotational malalignment is prominent. TT-TG shows stronger associations with rotational alignment and patellar engagement.

LEVEL OF EVIDENCE: Level III, retrospective cohort study.