FACTORS THAT AFFECT THE MAGNITUDE OF TIBIAL TUBERCLE-TROCHLEAR GROOVE DISTANCE IN PATIENTS WITH PATELLAR INSTABILITY
Figure 1 - Method of calculation for (A) tibial tubercle–trochlear groove distance, measured as the medial-lateral distance between the deepest cartilaginous point of the trochlear groove and the midpoint of the patellar tendon insertion at the tibial tubercle; (B) patellar width, the widest distance from the medial to lateral articular borders of the patella in a line parallel to the posterior femoral condylar axis; and (C) trochlear width, the width of the trochlear cartilage from the medial articular border of the patella to the lateral edge of the trochlear cartilage in a line parallel to the posterior femoral condylar axis.
Background: Tibial tubercle-trochlear groove (TT-TG) distance is a risk factor for recurrent patellar dislocation and is often included in algorithmic treatment of instability. The underlying factors that determine TT-TG have yet to be clearly described in orthopaedic literature.
Purpose/hypothesis: The purpose of our study was to determine the underlying anatomic factors contributing to TT-TG distance. We hypothesized that degree of tubercle lateralization and knee rotation angle may substantially predict TT-TG.
Study design: Cross-sectional study; Level of evidence, 3.
Figure 2 - Method of calculation for (A) knee rotation angle and (B) tibial tubercle lateralization based on axial magnetic resonance imaging scans. Knee rotation angle (α) was measured as the angle between a line tangent to the posterior-most aspect of the femoral condyles and a line tangent to the posterior tibial condyles. Tibial tubercle lateralization was measured as the distance from the center of the tibial tubercle to the medial edge of the tibial plateau (β1) as a percentage of the total tibial width (β2).
Methods: All patients evaluated for patellar instability at a single institution between 2013 and 2021 were included. Patients with previous knee osseous procedures were excluded. TT-TG and its anatomic relationship to patellofemoral measures, including dysplasia, femoral anteversion, tibial tubercle lateralization, knee rotation angle, and tibial torsion, were measured and subsequently quantified using univariate and multivariable analysis.
Figure 3 - Method of calculation for (A) femoral anteversion, demonstrating measurement of the angle between the femoral neck axis and an axis parallel to the posterior aspect of the femoral condyles, and (B) external tibial torsion, the angle between the previously determined posterior condylar axis and the bimalleolar axis on axial magnetic resonance imaging scans.
Results: In total, 76 patients met the inclusion criteria (46 female, 30 male; mean ± SD age, 20.6 ± 8.6 years) and were evaluated. Mean TT-TG was 16.2 ± 5.4 mm. On univariate analysis, increasing knee rotation angle (P < .01), tibial tubercle lateralization (P = .02), and tibial torsion (P = .01) were associated with increased TT-TG. In dysplastic cases, patients without medial hypoplasia (Dejour A or B) demonstrated significantly increased TT-TG (18.1 ± 5.4 mm) as compared with those with medial hypoplasia (Dejour C or D; TT-TG: 14.9 ± 5.2 mm; P = .02). Multivariable analysis revealed that increased knee rotation angle (+0.43-mm TT-TG per degree; P < .01) and tubercle lateralization (+0.19-mm TT-TG per percentage lateralization; P < .01) were statistically significant determinants of increased TT-TG distance. Upon accounting for these factors, tibial torsion, trochlear width, and medial hypoplasia were no longer significant components in predicting TT-TG (P≥ .54). Of note, all patients with TT-TG ≥20 mm had tibial tubercle lateralization ≥68%, a knee rotation angle ≥5.8°, or both factors concurrently.
Conclusion: TT-TG distance is most influenced by knee rotation angle and tibial tubercle lateralization.
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Published November 22, 2022 in the American Journal of Sports Medicine.