Summary

Anatomical variation in the patellofemoral joint that contribute to patella instability can be characterised radiographically. Identifying patients with these risk factors can potentially help with early intervention and potentially delay the progression of patellofemoral osteoarthritis

Abstract

Background

The patellofemoral joint (PFJ) is a complex structure with high functional and biomechanical requirements, predisposing it to frequent and recurrent injury. Patella instability is a spectrum of conditions including symptomatic patella instability, patella subluxation and patella dislocation. This can result in debilitating symptoms such as anterior knee pain and a feeling of knee instability.

Multiple studies have been done to identify radiological parameters that account for patella instability. While most studies have been conducted on the Western population, few have looked at these parameters in an Asian population. However, the knee anatomy between the Western and Asian population has been shown to be different. This study aims to identify structural risk factors through radiological parameters that would predispose patients to patella subluxation and/or dislocation in the Asian population.

Methods

A retrospective study was conducted, including 50 knees from 46 patients who had symptoms of patella instability. Nine radiological parameters (sulcus angle, congruence angle, lateral patellofemoral (PF) angle, crossing sign, Caton-Deschamp index, trochlear depth, lateral trochlear inclination, tibial tuberosity-trochlear groove (TT-TG) distance, trochlear facet symmetry) were recorded from plain radiographs and MRI studies. These were compared with a control group of 50 asymptomatic knees from 46 patients.

Results

All the radiological parameters showed significant differences (P < 0.05) between the instability group and control group. Patients with patella instability tend to have a dysplastic femoral trochlear groove characterized by greater sulcus angles and reduced trochlear depth and lateral trochlear inclination angle, along with trochlear facet asymmetry. The crossing sign was seen in patients with patella instability; however, this was absent in the control group. Signs of abnormal patellofemoral alignment were also evident in the instability group, with greater congruence angles and reduced lateral PF angles. The instability group also had greater Caton-Deschamp index values and TT-TG distances.

Conclusion

This study showed there are anatomical factors that potentially contribute to the risk of patella instability in Asian patients, key of which is trochlear dysplasia. Identifying patients with these risk factors may allow early intervention to delay the progression of patellofemoral osteoarthritis.