L'absence congénitale du LCA est une affection rare, quelques séries seulement sont rapportées par la littérature et concerne des cas sporadiques, tous associés à des malformations diverses. Nous rapportons une série comportant 8 genoux ayant une laxité congénitale chez 5 patients. Cette série est particulière car tous les patients étaient issus d'une même famille, posant ainsi la question de l'origine génétique de cette affection et faisant toute la particularité de cette étude.

La série comportait 4 hommes et une femme dont l'âge moyen était de 46 ans. La douleur fémoro-tibiale médiale et fémoro-patellaire était le maître symptôme retrouvé chez tous les patients. L'examen physique retrouvait les signes majeurs de la laxité antérieure du genou (ressaut rotatoire, manœuvre de Trillat Lachman) avec atteinte des structures capsulo-ligamentaires postérieures et une saillie anormale de la tubérosité tibiale antérieure. Le bilan radiologique standard mettait en évidence quelques particularités sémiologiques évocatrices d'agénésie du LCA. L'IRM et l'arthroscopie confirmaient le diagnostic dans 5 cas.

La confrontation de nos résultats avec ceux de la littérature a permis de retirer quelques particularités propres à notre série.

The purpose of this work was to present a descriptive analysis of eight cases of congenital agenesia of the anterior cruciate ligament (ACL). Congenital absence of the ACL is rare. The few series reported in the literature have been limited to sporadic cases all associated with diverse malformations. We report a series of eight cases knees in five patients presenting congenital knee laxity. These patients were all members of the same family, raising the question of an inherited condition. We describe the characteristic features and natural history of ACL agenesia compared with post-traumatic loss of the ACL.

This descriptive study included five patients (eight knees) with agenesia of the ACL. There were four men and one woman, mean age 46 years. All five patients had a common ancestor.

The main symptom was medial femorotibial and patellofemoral pain, present in all patients. Physical examination revealed major anterior laxity (positive pivot test, Trillat Lachman test) involving the posterior capsule and ligament structures and an abnormal knob on the anterior tibial tubercle. Plain x-rays demonstrated an abnormal aspect of the tibial spines, suggestive of ACL agenesia. The spines were flat in three knees, smooth in three, and dome shaped in two. On the lateral view, the femoral condyles presented an abnormal rounded posterior curvature in all of the affected knees. The tibial slope was increased in all knees, 20.6° on average. MRI and arthroscopy confirmed the diagnosis in three knees.

Examining our cases and the data in the literature led to the following remarks. The family pedigree in our patients suggested autosomal dominant inheritance. Episodes of serious laxity are rare in subjects with congenital absence of the ACL compared with posttrauma patients, probably due to adaptation since infancy. Hypoplasia of the tibial spine and the lateral femoral condyle are characteristic consequences of ACL agenesia. In comparison with posttrauma cases, the natural history of ACL agenesia is characterized by better functional tolerance and inevitable progression to osteoarthritis due to the permanent anterior laxity. Degenerative disease may develop late and more slowly than after traumatic injury of the ACL. Unlike common arthrosis, the lateral femorotibial and patellofemoral compartments are preserved longer

Though rare, congenital absence of the ACL should be evoked as a possibility in patients with chronic anterior laxity without trauma. The radiological aspect is highly suggestive of the diagnosis which can be confirmed by MRI or arthroscopy. Study of the present series enabled a description of the natural history of ACL agenesia, which is different from that of traumatic ACL tears because of the lack of secondary meniscal lesions and the later progression of osteoarthritic degeneration.