Higher pathologic threshold of increased tibial tuberosity–trochlear groove distance should be considered for taller patients

Abstract

PurposeThe aim of this study was to evaluate the correlation between tibial tuberosity–trochlear groove distance (TT–TG) and body height or knee size, and to find height‐related pathologic thresholds of increased TT–TG. MethodsOne‐hundred and fifty‐three patients with recurrent patellar instability and 151 controls were included. The TT–TG was measured on axial computed tomography (CT) images. Femora width and tibial width were selected to represent knee size. The correlation of TT–TG and gender, body height, femora width, and tibial width was evaluated. The height‐related pathologic threshold of increased TT–TG was produced according to Dejour’s method. To combine TT–TG with body height and knee size, three new indexes were introduced, ratio of TT–TG to body height (RTH), ratio of TT–TG to femoral width (RTF), and ratio of TT–TG to tibial width (RTT). The ability to predict patellar instability was assessed by the receiver‐operating characteristic (ROC) curve, odds ratios (ORs), sensitivity, and specificity. ResultsIn patients with patellar instability, TT–TG showed significantly correlation with patient height, femoral width, and tibial width respectively (range r = 0.266–0.283). This correlation was not found in the control group. The pathologic threshold of TT–TG was 18 mm in patients < 169 cm (53%), and the mean TT–TG was 21 mm in patients ≥ 169 cm (54%). There was significant difference in RTH, RTF, and RTT between the two groups. RTH, RTF and RTT have similar large area under the curve (AUC) with TT–TG. ConclusionsTT–TG showed significant correlation with body height and knee size, respectively. The pathologic threshold of increased TT–TG was suggested to be 21 mm for patients ≥ 169 cm and 18 mm for patients < 169 cm. Body height‐related pathologic threshold provided a supplement for indications of tibial tuberosity medialization. Level of evidenceIV.

Increased tibial tuberosity torsion has the greatest predictive value in patients with patellofemoral instability compared to other commonly assessed parameters

“…However, as the TT-TG distance represents a bare length measurement of the distance between the TT and trochlear groove, it does not account for any rotational differences in the TT, which also likely affects patellar stability. Several other drawbacks have been identified in the assessment of the TT-TG distance, such as compromised measurements in patients with trochlear dysplasia, dependency on body height and knee size and influence of trochlear groove medialization, tibiofemoral rotation, tibial tubercle lateralisation or femoral version in the measurements [1,12,24,27,28,30,31]. Hence, further measurements for patellofemoral instability have been developed over time to overcome these obstacles [5,17,23].…”

“…However, the TT-TG distance measurement represents a simple length measurement of the distance between the tibial tuberosity (TT) and the trochlear groove, which does not account for rotational differences in the TT that may potentially impact patellofemoral instability. Furthermore, several studies have shown that the TT-TG distance is influenced by numerous individual factors [1,12,24,27,28,30,31]. Therefore, several parameters have been proposed to overcome these impairments [5,17,23].…”

Clinical outcomes of derotational femoral osteotomy combined with medial patellofemoral ligament reconstruction in patients with patellar dislocation and increased femoral anteversion unaffected by the pattern of distribution of femoral torsion

“…The CA is defined as the angle formed by the angle bisector of the trochlear groove angle and the line of the lower pole of the patella (Figure 2b). The tibial tuberosity–trochlear groove distance (TT‐TG) was measured as previously described by Wang et al [21]. The Caton–Deschamps index was used to measure patellar height [24].…”

“…Many authors have reported morphological changes in the femoral trochlea and posterior femoral condyle in patients with patellar dislocation [17–20]. Yang et al also reported a correlation between anterior and posterior femoral condyle composite deformity and increased FA in patients with patellar instability [21]. A distal derotational femoral osteotomy does not change the abnormal femoral condyle morphology; only the overall femoral torsional deformity does.…”

Medial patellofemoral ligament reconstruction combined with derotational distal femoral osteotomy yields better outcomes than isolated procedures in patellar dislocation with increased femoral anteversion

“…The tibial torsion angle was measured between a tangent line of the posterior margin of the tibial plateau and a line connecting the midpoints of the medial and lateral malleoli [24]. The TT–TG distance was measured as previously described by Wang et al [33].…”