Summary

Analysis of the lateralization of the Tibial Tubercle in Patellar instability, found to be only 59% present in altered TT-TG pathologic distance

Abstract

Background

In patients with Patellar instability, a pathologic increase in TT-TG distance represent a risk factor. This measure is not validated as a determinant causal factor, nor provides information on the location of the malformation. The purpose of this study is to propose that not every patient with an increased TT-TG distance (>20mm) has a tibial tubercle, and that in that cases, the increase in TT-TG distance is caused by trochlear alterations.

Method

Observational retrospective study, with 62 knees in 52 patients (cases) with 1 or more patellar dislocation episodes, and 60 knees in 30 patients (controls) with patellar dysfunction study with no story of dislocation, which had a standardized protocol for patellofemoral measurements in CT scan. Tibial Tubercle lateralization (TT-L) with respect to tibia, was measured as the distance between Tibial tubercle mid point, and the center of tibial plateaus. This distance was measured parallel to tibial posterior condylar line. Significate differences between TT-L in patients and controls where estimated whith an unpaired t test.

Results

Statistically significant difference (p<0.05) was found between TT-L distance in control group (mean 8.6mm) and patients (mean 12.3mm). TT-TG average in control group was 12.6mm and in patients group 18.4mm (p<0.05). In control group, TT-L <10mm was found in 96%. 36 of 64 knees in patients group where found to have >10mm of TT-L. 41% of patients with >20mm TT-TG distances had a <10mm TT-L.
Conclusions. Not all patients with an altered TT-TG distance have an altered Tibial Tubercle. Only 59% with a pathologic TT-TG distance (>20mm) had an altered Tibial Tubercle lateralization, with respect to the tibia.