we examined the ratio of patients who require tubercle transfer by employing various factors to review the lateral displacement of TT in patients with patellar dislocations
Although the lateral displacement of the tibial tubercle (TT) is considered one of the predisposing factors to recurrent patellar dislocation, there have been few reports on the morphology and attachment site abnormalities of the proximal tibia. Moreover, the degree to which tubercle transfer can be considered for tubercle displacement is seldom discussed in the literature. In this study, we examined the ratio of patients who require tubercle transfer by employing various factors to review the lateral displacement of TT in patients with patellar dislocations.
Study groups were formed as follows: 60 knees in 60 patients with patellar dislocation (Group P) and 60 knees in 60 patients who were sex and age matched as a control group (Group C). The degree of lateral displacement for TT was evaluated by three measurement methods, including the TT-PCL distance, TT-PCL-ratio (TT-PCL/transverse diameter of tibial plateau), and lateral displacement ratio (LDR) of the TT obtained by CT axial imaging. Measurements were compared between the two groups, and the AUC of the ROC curve was determined for each method to evaluate for patellar dislocation. Furthermore, we implemented a cut-off value for the minimum value of each measurement permitting 10mm of medial TT transfer in Group C, and we calculated the ratio of patients who are indicated for medial TT transfer in Group P.
The mean value for TT-PCL distance (Group C, 19.8±2.7mm, range13.9-25.5; Group P, 21.0±3.2mm, range 12.8-29.9; p=0.02), TT-PCL ratio(Group C, 27.9±3.4 %, range 19.9-35.7; Group P, 30.1±3.7%, range 20.1-41.4; p=0.001), and LDR (Group C, 64.8±2.8%, range 56.8-72.4; Group P, 66.4±2.6%, range 60.7-71.7; p=0.001) were all significantly greater in Group P than Group C. The AUC of the ROC curve for LDR, TT-PCL distance, and TT-PCL ratio was 0.6, 0.65, and 0.67, respectively. If the cut-off values for the minimum value of each measurement permitting 10mm of medial TT transfer in Group C were 24mm, 34% and 70%, the number of patients in Group P who satisfy such conditions were 9 (15%), 7 (11.6%), and 5 (8.3%), respectively.
Significant difference was found in the mean value of all measurement methods used in this study; however, these differences were clinically small. Additionally, the AUC of the ROC curve for each measurement method showed low values. In cases that did not allow for an excessively medialized TT position compared to the control, the ratio of patients indicated for 10mm of medial TT transfer were very small. Thus, we extrapolated that the individual difference in the position of TT at the proximal tibia is even small in Group P and that patients with excessively lateral TT positions are limited to a small fraction of cases. The indication and amount of medial TT transfer should both be determined upon the degree of lateral TT displacement at the proximal tibia.