Benign acquired subluxation of the knee

To describe several cases of recurrent femorotibial subluxation episodes in pediatric patients, to review the existing literature about this rare entity, and to characterize its different clinical presentations.

The study included a series of three cases seen at our center. All patients underwent a structured anamnesis and complete physical examination, as well as a basic radiological study. One underwent magnetic resonance imaging. A literature search was performed in the main databases under the terms "Snapping knee" and "Femorotibial subluxation in child" to consult previous studies.

Clinical onset was between 6 and 14 months of age, with episodes of femorotibial subluxations associated with irritability or fever. Examination showed increased joint laxity and a discrete genu valgum. Imaging studies showed no anatomical alterations. The symptoms gradually decreased in intensity and frequency. Two of the patients were treated with extension splints with no differences between them or with respect to the patient in whom therapeutic abstention was chosen.

There are two independent presentations of the pathology that have not been well differentiated so far. The first (patients described from our clinical practice) is in initially healthy children who begin with episodes of subluxation in relation to febrile episodes or irritability, with an anodyne physical examination, and benign evolution with progressive reduction of the episodes even without treatment. The second presents as episodes of anterior subluxation since birth in patients with associated pathologies (usually spinal), anterior cruciate ligament instability, and need for surgical treatment to reduce the number of episodes.