The relationship between joint hypermobility and patellar instability: A systematic review.

Introduction: Hypermobility describes the movement of joints beyond normal limits. Whether hypermobility predisposes to patellar instability is yet to be established. We aimed to determine if joint hypermobility leads to an increased risk of patellar instability, and to evaluate outcomes of treatment for patellar instability in those who exhibit hypermobility. Methods: Published and unpublished literature databases were searched to September 7, 2023. Studies comparing prevalence of patellar dislocation/differences in treatment outcomes in patients with and without hypermobility were included. Results: We identified 18 eligible studies (4,391 patients). The evidence was low in quality. A case series on 82 patients found that there was a relationship between generalised joint laxity and patellar instability. This was corroborated by a study comparing 104 patients with patellar dislocation to 110 patients without. Prevalence of generalised joint laxity was six time higher in the former (64.4% vs 10.9%, p < 0.001).Five studies found surgical intervention aimed at correcting patellar dislocation in patients with idiopathic hypermobility led to satisfactory outcomes. There was conflicting evidence regarding if hypermobile patients have worse outcomes than non-hypermobile patients following medial patellofemoral ligament reconstruction (MPFLR) in two studies. In addition, this procedure had a 19.1% failure rate in patients with Ehlers Danlos Syndrome (EDS), with hypermobility associated with a higher failure rate (p = 0.03). One study showed the type of graft used made no difference in outcome scores or re-dislocation rates (p > 0.5). Another study had 7/31 (22.6%) autografts which failed, compared to 2/16 allografts (12.5%) (p = 0.69). Conclusion: Joint hypermobility is a risk factor for patellar instability. Identification of at-risk groups may aid prevention of dislocations and allow for appropriate treatment. Patients with EDS experience poor outcomes following patellar stabilization surgery, with post-operative monitoring required.