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.