Genu recurvatum loosely translates as “backward-bending knee.” It is also known as congenital dislocation of the knee (CDK) or congenital dislocation of the patella (CDP), and sometimes as congenital hyperextension. CDK is a rare condition with an incidence rate of approximately 1 per 100,000 live births. It is characterized by congenital hyperextension of the knee and marked limitation of flexion. Patients with this condition present with a patella that is dislocated laterally, permanently, and irreducibly. However, there is some disagreement with this description. Some suggest obligatory patella dislocation is a separate condition where the dislocation is hypoplastic to start and becomes fixed into the lateral position as the child grows. Some physicians believe this condition should be renamed “developmental dysplasia and dislocation disorder (DDDP)” to more accurately reflect it as a wide-spectrum disorder.
There are 3 classical morphologies associated with this condition: congenital hyperextension, congenital hyperextension with anterior subluxation of the tibia on the femur, and congenital hyperextension with anterior dislocation of the knee joint on the tibia. Bilateral dislocation does occur but it is even rarer. The etiology of CDK is not fully understood. There have been multigenerational families afflicted with this condition but the majority of cases are sporadic. It has been associated with breech deliveries, and other contributing factors include quadriceps contracture and hypoplasia of the anterior cruciate ligament.
CDK was relatively unheard of prior to 1880. Occasionally one could find an obscure reference cited in the medical literature of the day. One of the first accounts of this condition is accredited to Chatelain in 1822. However, it was Guenoit who called attention to CDK and made it a mainstream diagnosis. In 1880, following a communication in front of the Société de Chirurgie, where Guenoit detailed 2 cases, the number of reports increased. In 1888, there were 25 documented reports in the medical literature, but by 1900, that number grew to 127.
This video was taken on the streets of Marseilles, France. This poor soul has a severe form of CDK. Due to the extent of his affliction, he is forced to walk on all fours, and his gait resembles that of an insect.
(The exact nature of this individual’s affliction cannot be independently confirmed, but it appears to be consistent with an untreated severe form of CDK.)
Watch it and draw your own conclusions.
Patients with CDK often have other comorbidities, including developmental hip dysplasia, club foot, and arthrogryposis. It has also been reported in patients with Larsen syndrome, Down syndrome, nail-patella syndrome, congenital vertical talus, and Rubinstein-Taybi syndrome. Early non-operative reduction therapy seems to offer some hope to afflicted children. A literature search of treatments resulted in the following: serial casting, Pavlik harness, skin traction, and skeletal traction. Mayer concluded that 81% of patients achieved treatment success when a procedure was performed prior to 3 months of age, but the procedure only had a 33% success rate when completed between the ages of 3 to 6 years. Some children may not respond to non-operative reduction therapy; in those cases, surgery is necessary and these patients often have “true” congenital malformations. Either way, once diagnosed, a treatment course should be considered.