Congenital Absence of the Anterior Cruciate Ligament

Abstract

Congenital absence of the anterior cruciate ligament (ACL) is a rare condition, with a reported prevalence of 0.017 per 1000 live births, and most commonly appears in association with other congenital lower extremity abnormalities such as knee dislocation, proximal focal femoral deficiency, and fibular hemimelia. The Manner classification system is used to describe three types of congential deficiency of the cruciate ligaments. The most common, Type I, is hypoplasia or aplasia of the ACL with a normal posterior cruciate ligament (PCL). Type II describes absence of the ACL with hypoplasia of the PCL. In Type III, the femoral intercondylar arch and tibial eminence are absent, with dysplasia in both cruciate ligaments. Clinical presentation varies based on degree of deformity and the associated congenital conditions present. It is normally obvious at birth but in some cases is not recognized until a patient presents with what is assumed to be an injury. There is no consensus regarding management of this condition. Treatment will depend upon whether the condition is symptomatic and what other congenital abnormalities are present. The main indication for ACL reconstruction is symptomatic instability of the knee, despite conservative treatment.