The hypermobile lateral meniscus (HLM) is one of the causes of lateral knee pain and a locking sensation. In children the cause tends to be due to congenital absence of posterior capsular attachments, whilst in adults it is more likely traumatic.
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Epidemiology
There is a bimodal age distribution pattern of patients with hypermobile lateral meniscus. In children, the onset is in older preteens and teenagers. The majority of pediatric patients cannot recall a traumatic event and most cases are bilateral.
In adults, on the other hand, a remembered history of trauma is usually present.
Clinical presentation
The main symptoms are lateral knee pain and intermittent locking and catching of the joint. On physical examination, a provocative maneuver known as the Figure-4 test which places the affected knee in flexion, varus and external rotation may reproduce locking in patients with a hypermobile lateral meniscus 3.
Pathology
In pediatric population, it is thought to be secondary to the congenital absence of the meniscotibial ligament or meniscocapsular attachments.
In adults, the disruption of the popliteomeniscal fascicles is usually secondary to trauma which may lead to hypermobility of the lateral meniscus.
In cases of hypermobile lateral meniscus, the posterior portion of the lateral meniscus shows paradoxical excessive forward translation with knee flexion and posterior translation with knee extension 4.
Radiographic features
High incidence of abnormal posterosuperior and anteroinferior popliteomeniscal fascicles is present in patients with recurrent lateral meniscal subluxation. Posterosuperior fascicle abnormality can be seen in asymptomatic patients, but an abnormal anteroinferior popliteomeniscal fascicle is essential to allow lateral meniscal subluxation, and is consistently seen in hypermobile lateral meniscus.
Treatment and prognosis
Meniscal preservation and stabilization by fixation of the meniscus to the posterior capsule, usually via an arthroscopic approach is the treatment of choice 3,5.
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