Summary

The Patellar Tendon to Lateral Trochlear Ridge (PT-LTR) measurement may be a useful tool in predicting which patients with patellofemoral instability may benefit from a bony realignment procedure in addition to a soft tissue stabilization procedure.

Abstract

Introduction

The purpose of this study was to assess the PT-LTR in patients with instability with and without concomitant malalignment to explore the hypothesis that PT-LTR may be a significant measurement of patients who exhibit patellar maltracking in addition to patellar instability. We also sought to explore the relationship between patellar height and TT-TG (Tibial Tubercle to Trochlear Groove) to PT-LTR.

Methods

The groups were: patients who underwent 1) anterior cruciate ligament (ACL) reconstruction (control), 2) isolated medial patellofemoral ligament reconstruction (MPFL-R) for patellofemoral instability and 3) combined MPFL-R and tibial tubercle transfer (TTT). Group 3 patients included those excluded from a prospective study for patellar instability treatment with isolated MPFL-R and met one of four previously defined exclusion criteria. Intraclass correlation coefficients were generated to determine level of agreement in PT-LTR measurement between raters. Continuous variables were analyzed using one-way ANOVA or Kruskal-Wallis test and categorical variables were analyzed using chi-square or Fisher's exact test, as appropriate. PT-LTR was compared by surgery type using the Kruskal-Wallis test. Post-hoc pairwise comparisons were produced, and Tukey adjustment was utilized to account for multiple comparisons. PT-LTR was compared by alta and TT-TG cut-offs using independent two-sample t-test or Wilcoxon Mann-Whitney test, as appropriate. Stratified analyses were then conducted to compare patients with both alta and TT-TG at defined cut-offs. Spearman correlations were calculated between Caton-Deschamps Index (CDI) and PT-LTR, TT-TG and PT-LTR.

Results

Patients in each group differed significantly by age (p < .0001). The oldest group was ACL (29.31 ± 13.79 years), followed by MPFL-R+TTT (26.65 ± 9.68 years), and the youngest group was isolated MPFL-R (18.82 ± 6.55 years). There were no significant differences in sex between each group, though the study sample was majority female. The groups (listed in order) differed significantly by their CDI (1.07 ± 0.17, 1.18 ± 0.16, 1.29 ± 0.24, p=0.0009), incidence of patella alta defined as CDI>1.2 (n=6, 13 and 18, p=0.0065), TT-TG (10.99 ± 3.00, 16.23 ± 3.78, and 19.36 ± 3.46, p < .0001), TT-TG > 15 (n=3, 18 and 29 p < .0001)., TT-TG > 20 (n=0, 5, and 13 p < .0001), patella alta with TT-TG >15 (1, 10 and 17, p < .0001) and patella alta with TT-TG >20 (0, 2 and 7, p=0.0081). Interclass correlation coefficients were 0.93 (highly correlated) for the full cohort and 0.67 for the ACL group, 0.80 for the MPFL-R group and 0.93 for the MPFL-R+TTT group. Therefore, the senior author’s measurements were used. The mean PT-LTR differed significantly between groups (p<0.0001). Measurements for ACL, isolated MPFL-R, and MPFL-R+TTT were 1.15 ± 3.71mm, 6.06 ± 6.58mm, and 12.72 ± 8.43mm respectively.

Conclusion

This study demonstrates that mean PT-LTR is significantly higher in patients who underwent MPFL-R+TTT compared to controls and patients who underwent isolated MPFL-R, which may reflect its role as a measurement of patellar maltracking in the setting of patellar instability. PT-LTR may be a useful tool in predicting which patients may benefit from a bony realignment procedure in addition to a soft tissue stabilization procedure.