Patellar instability

Abstract

Lateral patellar dislocation (PD) has multifactorial origin. Its treatment will depend on the physical demands of the patient, triggering event and injury mechanism of PD, number of dislocation episodes, patellofemoral joint morphology, and concomitant injuries. After primary PD, despite the risk of recurrence being 33-77%, first treatment option is mostly conservative, except if an osteochondral fragment needs to be refixed or removed. This practice has been questioned lately by the Patella Instability Severity Score that determines the risk for recurrent PD in function of age, bilaterality, and anatomical risk factors. Risk behavior in relation to sports activity seems to be an additional risk factor. The treatment of recurrent PD is surgical with only low recurrent rate (2-4%). Medial patellofemoral ligament (MPFL) reconstruction is the most widely used technique. The ideal candidates are subjects with painless intervals between PD and without major trochlear dysplasia (TD) or patella alta. However, postoperative pain and loss of flexion might be observed if the graft is overtensioned or its fixation point malpositioned. Trochleoplasty is the only technique that aims at improving containment with the risk to increase peak forces due to incongruence. Due to the demanding technique its superiority over isolated MPFL reconstruction has been described only in grotesque TD and PD in higher knee flexion (>60°). Tibial tubercle osteotomy can be distalized in case of patella alta or medialized in case of lateralized tibial tubercle. Indication should be considered carefully, since patellar tracking will be influenced almost throughout the full range of motion and might therefore induce discomfort or pain.