Tibial tubercle to trochlear groove distance versus tibial tubercle to posterior cruciate ligament distance for predicting patellar instability: a systematic review

Correlation Between Radiological Measurements for Patellar Instability and Patient-Reported Outcome Measurements in Adolescents: A Study From the Faroese Knee Cohort

BACKGROUND

Radiological measurements can predict patellar dislocation and are used to plan patella-stabilizing surgery in patients who have patellofemoral instability. However, it is unclear whether these measurements can predict subjective symptoms in patients without previous stabilizing surgery.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

HYPOTHESIS/PURPOSE

The purpose was to investigate the correlation between radiological measurements and subjective symptoms in individuals with previous patellar dislocation without previous patella-stabilizing surgery. It was hypothesized that this correlation would be negative.

METHODS

A national cohort of patients with previous patellar dislocation was created by inviting all inhabitants of the Faroe Islands aged 15 to 19 years to answer an online survey. All patients with previous patellar dislocation and no previous surgery to the knee were invited to undergo radiography and magnetic resonance imaging of both knees. The radiological measurements were the Dejour classification, lateral trochlear inclination angle, trochlear depth, Caton-Deschamps index, and tibial tubercle-trochlear groove distance. The participants completed patient-reported outcome measures (PROMs), which were the Banff Patellar Instability Score 2.0, Kujala score, Marx score, and EQ-5D-5L score. Continuous data from each radiological measurement were plotted against each PROM to create scatter plots for visual inspection and analysis.

RESULTS

A total of 1714 (46%) invited individuals responded to the survey invitation, of whom 595 were excluded because of not answering at least 1 PROM. After exclusion of participants with previous knee surgery, 102 participants reported a history of patellar dislocation. Of these, 75 participants underwent radiography and magnetic resonance imaging of their knees and were included in the study for further analysis. Scatter plots and R2 values showed no correlation between radiological measurements and PROM scores.

CONCLUSION

This study found no correlation between the most used radiological measurements in patellar instability and PROM scores. The results imply that radiological measurements are not indicative of subjective health and well-being of patients undergoing nonoperative management of patellar dislocations.

Impact of sex and age on the lateralisation of the tibial tubercle in normal paediatric and adolescent populations

PURPOSE

Numerous methods have been proposed to characterise tubercle lateralisation. However, their normal values and related changes remain unclear. Accordingly, it was aimed to determine the potential sex and age effects and determined the optimal individualised method of diagnosing lateralisation of the tibial tubercle in patients with recurrent patellar dislocation (RPD).

METHODS

Measurements included the tibial tubercle-trochlear groove (TT-TG) distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance and tibial tubercle lateralisation (TTL); and the proximal tibial width (PTW), trochlear width (TW) and trochlear dysplasia index (TDI), for adjustment. A two-way analysis of variance was used to determine the effect of age, sex and their interaction within the normal group. When the age effect was statistically significant, a nonlinear regression was created. Areas under the receiver-operating characteristic curve (AUCs) were calculated to assess diagnostic accuracy.

RESULTS

A total of 277 normal participants (mean [SD] age, 13.5 [2.6] years; 125 [45.1%] female) and 227 patients with RPD (mean [SD] age, 13.5 [2.6] years; 161 [58.1%] female) were analysed. It was found that in the normal group, in patients aged 7-10, TT-PCL distance (p = 0.006), TTL (p = 0.007) and TT-PCL/PTW (p < 0.001) were significantly larger in females than in males. A significant sex effect was also detected on TT-TG/TW (p = 0.014). TT-TG distance, TT-PCL distance, TTL and TT-PCL/PTW (in male patients) approached an established normal adult value of 12.3 mm, 20.9 mm, 0.64 and 0.28, respectively, with increasing age (p < 0.001). The AUC was greater for TT-TG/TDI and TT-TG/TW (p ≤ 0.01) and TT-TG/TDI outperformed TT-TG/TW in patients aged 15-18 (p = 0.004).

CONCLUSIONS

Tubercle lateralisation increased with age and was affected by sex, with the exception of TT-TG distance and TT-TG/TDI. TT-TG/TDI is the optimal method of diagnosing a lateralized tibial tubercle in patients with RPD. These findings assist with the evaluation of tubercle lateralisation in that they provide a proper protocol for paediatric and adolescent populations with RPD; and thus, will help determine whether medial tubercle transfer should be included among the tailored surgical procedures considered for the treatment of patients with RPD.

LEVEL OF EVIDENCE

Level III.