Teaching Case

A 31-year-old woman was examined for pain in the right knee after intense walking. There was no history of trauma to the knee joint, or instability. Posterior drawer sign was positive. The patient underwent MR imaging of the knee. The pain subsided with analgesics, rest and local ice application.

MRI of the right knee showed absence of the posterior cruciate ligament. Coronal proton density-weighted (TR/TE 2800/40) spin echo MR image showed fibres of the anterior cruciate ligament coursing from the lateral femoral condyle to the anterior portion of the tibia. The femoral and tibial insertion sites of the posterior cruciate ligament were not identified, except from the insertion site of the posterior meniscofemoral ligament of Wrisberg (arrowhead) (Fig. 1). Both menisci were normal. The femoral intercondylar notch and femoral condyles were well developed. Tibial spines appeared normal. Sagittal proton density-weighted (TR/TE 2800/40) spin echo MR image again showed aplasia of the posterior cruciate ligament. The posterior meniscofemoral ligament of Wrisberg (arrows) adjacent to the site of the posterior cruciate ligament was identified extending from the posterior horn of the lateral meniscus to the lateral aspect of the medial femoral condyle (Fig. 2).

Dysplasia of one or both cruciate ligaments can be associated with congenital longitudinal deformity of the lower limb [1]. Deficiency of the cruciate ligaments can occur traumatically or congenitally. Congenital aplasia or hypoplasia of the cruciate ligaments is a very rare anomaly with a prevalence of 0.017 per 1,000 live births [2]. Common associated abnormalities may include various congenital longitudinal deficiencies of the lower limb (short femur, aplasia of the fibula or patella), hypoplasia of the lateral femoral condyle, and changes involving the tibial eminence and/or menisci [3]. It has been suggested that the development of the tibial spines ceases when no traction from the absent anterior cruciate ligament exists. Furthermore, the association of cruciate ligament agenesis and meniscal pathology is related to their common embryological origin. Cruciate ligament malformations may be responsible for instability of the knee joint.