[The treatment of patellar dislocation: a systematic review]

The diagnosis and treatment of patellar dislocation is very complex. The aim of this study is to give an overview of the biomechanics of the patellofemoral joint and to point out the latest developments in diagnosis and treatment of patellar dislocation.

The authors electronically searched Medline, Cochrane and Embase for studies on the biomechanics of the patellofemoral joint and for conservative and surgical treatments after patellar dislocation. We extracted baseline demographics, biomechanical, conservation and surgical details.

Understanding the biomechanics of the patellofemoral joint is necessary to understand the pathology of patellar dislocation. The patellofemoral joint consists of a complex system of static, active and passive stabilising factors. Patellar instability can result from osseous and soft-tissue abnormalities, such as trochlear dysplasia, patella alta, a high tibial tuberosity trochlear groove (TTTG) distance, weaknesses of the vastus medialis obliquus or a lesion of the medial retinaculum. Recent studies have focused on the medial patellofemoral ligament (MPFL) and have shown that the MPFL is the most significant passive stabiliser of the patella. Following patellar dislocation, an MRI should be standard practice to detect an MPFL rupture, osteochondral lesions or other risk factors for redislocation. An acute first-time patellar dislocation without osteochondral lesions and without severe risk factors for a redislocation should follow a conservative treatment plan. If surgical treatment is required, the best postoperative results occur when the MPFL is reconstructed, leading to a redislocation rate of 5%, this includes cases that have a dysplastic trochlea. Duplication of the medial retinaculum show very inconsistent results in the literature, possibly due to the fact that the essential pathomorphology of patellar dislocation is not addressed. Addressing the exact location of the rupture of the MPFL with a suture is possibly more convenient, especially after first-time dislocation with associated risk factors for a redislocation. Recent literature does not encourage the use of lateral release, since this can increase patellar instability. Indications for lateral release include persistent patellar instability or pain reduction in an older arthritic subject. For correcting a patellofemoral malalignment, the TTTG distance should be measured and a medial transposition of the anterior tibial tubercle hinged on a distal periosteal attachment should be considered. Cartilage lesions on the medial facet of the patella are a contra-indication for medial tubercle transposition. For cartilage lesions of the lateral facet, antero-medialization of the tibial tubercle can be successful. A tubercle osteotomy can be efficiently combined with MPFL reconstruction. We believe that patients with open epiphyseal plates should be treated with duplication of the medial retinaculum. In the presence of patellar maltracking, an additional subperiostal soft tissue release with medialisation of the distal part of the patellar tendon can be performed.

It seems that the predominating factors for patellar dislocation are heterogenic morphology in combination with individual predisposition. Non-surgical treatment is typically recommended for primary patellar dislocation without any osteochondral lesions and in the absence of significant risk factors for redislocation. If surgical treatment is deemed necessary, addressing the essential pathomorphology has become the primary focus.