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Patellar instability

Patellar instability refers to recurrent or persistent tendency of the patella to subluxate or dislocate from the trochlear groove, most commonly in the lateral direction. It is usually related to a combination of traumatic injury and anatomical risk factors such as trochlear dysplasia, patella alta, increased TT–TG distance, and abnormal limb alignment. Patients typically present with anterior knee pain, apprehension, recurrent giving way, or episodes of patellar dislocation.

Patellar instability is a disorder of the patellofemoral joint in which the patella fails to remain centrally contained within the trochlear groove during knee motion. It most commonly presents as lateral patellar subluxation or dislocation, particularly in adolescents and young adults. The condition may follow an acute traumatic dislocation or occur because of predisposing anatomical abnormalities. Important risk factors include trochlear dysplasia, patella alta, increased tibial tubercle–trochlear groove (TT–TG) distance, rotational malalignment, genu valgum, and ligamentous laxity. Injury to the medial patellofemoral ligament (MPFL) is common after a lateral patellar dislocation. Patients may complain of recurrent dislocation, a sensation of the patella slipping laterally, anterior knee pain, swelling, or apprehension during knee flexion. Examination includes assessment of patellar tracking, the patellar apprehension test, J-sign, patellar glide, limb alignment, and generalized ligamentous laxity. Imaging includes plain radiographs to assess patellar height, trochlear morphology, and associated osteochondral injury. CT or MRI may be used to evaluate TT–TG distance, trochlear dysplasia, MPFL injury, cartilage damage, and rotational alignment. A first-time uncomplicated dislocation is often managed with brief immobilization followed by early rehabilitation, focusing on quadriceps and hip strengthening. Recurrent instability or significant anatomical abnormalities may require surgery such as MPFL reconstruction, tibial tubercle osteotomy, trochleoplasty, or corrective osteotomy, depending on the underlying pathology. The aim of treatment is to restore stable patellar tracking, prevent recurrent dislocation, protect the patellofemoral cartilage, and improve pain and function.

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Patellar instability

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