A proposed safety angle for dual bundle MPFL reconstruction: an observational magnetic resonance imaging study.

ABSTRACT

INTRODUCTION: The anatomical dual bundle medial patellofemoral ligament (MPFL) reconstruction technique is one of the surgical techniques used to treat lateral patellar instability. This commonly involves the creation of two patella bone tunnels through which the limbs of the grafts are inserted. The surgical risks include patellar fracture and penetration of patellofemoral articular surface. Thus, an easily reproducible intra-operative guiding parameter is useful to reduce such complications. PURPOSE: The aim of this study is to demarcate a safe working zone in the axial plane for the patella tunnels. METHODS: In this pilot study, we projected patella bone tunnels on the MRI knee images of 201 male patients with intact MPFLs. Two tunnel projections, superior and inferior, are made from the medial to the lateral sides of the patella. The projection of each superior and inferior tunnel is subdivided into three different angles in the axial plane. The tunnel length, thickness of the bone anterior to each tunnel and safety angle are measured. The safety angle refers to the angle between the longitudinal axis of each tunnel and the horizontal plane of the patella. RESULTS: Our current study population consisted of 201 male patients (104 Wiberg type 1, 97 Wiberg type 2, no type 3 or 4). For the superior tunnels, the tunnel lengths are 14.8 mm, 24.3 mm and 27.2 mm. The respective safety angles are 24.9 degrees, 24.5 degrees and 8.8 degrees. The thickness of the bone anterior to the tunnels are 5.9 mm, 2.5 mm and 6.2 mm. For the inferior tunnels, the tunnel lengths are 18.4 mm, 21.9 mm and 34.9 mm. The respective safety angles are 23.5 degrees, 22.5 degrees and 8.5 degrees. The thickness of the bone anterior to the respective tunnels are 5.9 mm, 3.1 mm and 6.0 mm. CONCLUSION: The proposed safety angle of 8.8 degree for the superior tunnel, and 8.5 degrees for the inferior tunnel is a potentially useful intra-operative guide for the surgeon and can potentially reduce the risks of fracture and articular cartilage injury in patellae with Wiberg 1 and 2 morphologies. LEVEL OF EVIDENCE Level II, retrospective study.