Isolated posterior cruciate ligament tears in monozygotic twins: A case report

Posterior cruciate ligament (PCL) tears are not as frequent as anterior cruciate ligament (ACL) tears. They are rare as an isolated injury and more commonly occur in a multi-ligament-injured knee. We reported a case of rupture of PCL in monozygotic twins.

A 19-year-old female presented with giving away of her left knee since 4 months ago. She fell from stairs previously. Physical examination demonstrated positive posterior drawer test. Magnetic resonance imaging showed ruptured PCL and lateral meniscal tear. Two months later, her identical twin, also a 19-year old-female, fell from the stairs and complained of giving away. Physical examination showed positive posterior drawer test. Magnetic resonance imaging demonstrated ruptured PCL and lateral meniscal tear. Both patients underwent arthroscopic-assisted PCL reconstruction using gracilis, semitendinosus, and peroneus tendon graft. At one year of follow-up, there were no graft failures. The twins had satisfactory outcome measured by Osteoarthritis Outcome Score (KOOS) and visual analogue scale (VAS). Both were athletes prior to their injury and they returned to sport.

Although it has never been reported before, this report shows that patients may have genetic predisposition to the incidence of PCL rupture. This is likely because of heritable factors, such as biomechanical, anatomic, anthropometric, and neuromuscular traits. A family history of PCL tear may increase the risk of a PCL tear. Further studies are recommended to examine genetic variants as a risk factor for PCL tears and other knee disorders.

Multiple variables may lead to the increased risk of these twins: the combination of improper neuromuscular control, genetic factors, and possibly hormonal factors contributed to their PCL injuries. Further history exploration, lab tests, and genetic analysis should be done to determine the variables. Both patients returned to sports protocol testing and returned to sports one year postoperatively.