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Genu recurvatum, or "back knee," is hyperextension of the knee to greater than 5 degrees. The three types of genu recurvatum are external rotary deformity (ERD) recurvatum, internal rotary deformity (IRD) recurvatum and nonrotary deformity (NRD) recurvatum. Knee hyperextension is sometimes the result of misalignment of the ankle joint; it can also result from knee injury, excess laxity in the knee joint or postural habits. Hyperextension of the knee can cause stress in the anterior cruciate ligament (ACL) and posterior knee structures and lead to permanent damage of the joint. Physical therapists often tape or brace the knee in patients who have genu recurvatum, and therapists provide proprioceptive training, muscle imbalance correction and gait training.
Genu recurvatum occurs more often in females than in males. Abnormal foot and ankle position during walking or injuries that involve hyperextension of the knee can cause genu recurvatum. Symptoms include pain in the medial tibiofemoral joint, which is the inner-leg portion of the knee, or in the posteriolateral ligamentous structures in the outer back portion of the knee. Untreated genu recurvatum leads to increased tissue damage and can cause permanent deformity, so timely diagnosis and treatment are important.
External rotary deformity recurvatum occurs when the foot remains in an equinovarus position during walking, with the heel elevated and the forefoot pointed inward, which causes hyperextension of the knee. ERD usually is seen in stroke patients whose foot movements become abnormal because of an abnormal pattern of muscle tone. Internal rotary deformity recurvatum starts with an abnormal gait in which the forefoot is rotated outward, which causes the person to compensate by overextending the knee, leading to a recurvatum deformity. In the case of nonrotary deformity recurvatum, the foot and ankle are positioned normally, and the knee is the primary abnormality. An injury that forces hyperextension of the knee is usually the cause of NRD.
All three types of genu recurvatum place strain on the knee and will cause increasing joint deformity if not corrected. Untreated ERD leads to increasing soft tissue damage as well as permanent recurvatum and genu valgum deformities of the knee. IRD produces a less-severe recurvatum deformity, along with genu varum, or "bow legs." NRD causes increasing stress to the posterior soft tissue structures of the knee, which leads to increasing recurvatum deformity.
Physicians use X-rays or magnetic resonance imaging (MRI) along with gait analysis to diagnose and classify genu recurvatum. Patients who suffer from ERD or IRD usually require foot orthotics to correct their ankle positioning. Physical therapists might tape the knee for support in mild cases. Patients who have more severe recurvatum might require knee braces.
Gait training, balance exercises and proprioceptive exercises can help improve mild to moderate recurvatum, as can exercises to strengthen the quadriceps and gastrocnemius muscles. The treatment depends on the type and severity of recurvatum. Some cases require surgery to repair damage to the knee.