Knee Dislocation: A Rare Congenital Condition in an Infant
A girl was born at 40 weeks and 5 days of gestation via spontaneous vaginal delivery to a 24-year-old, gravida 1, para 1 woman who had received regular prenatal care. The newborn’s Apgar score was 8 at 1 minute and 9 at 5 minutes. There were no delivery complications.
Maternal prenatal serologic test results were negative with the exception of rubella, the results of which were equivocal. The mother denied the use of illicit drugs, tobacco, or other medications during the pregnancy. The mother’s medical history was significant for seizures that had been treated successfully with divalproex sodium, which had been stopped 6 months before conception.
At 5 hours of age, the newborn’s vital signs were all within normal limits. Her birth weight, length, and head circumference were all between the 10th and 90th percentiles. Physical examination findings included significant molding of the head with caput succedaneum, as well as right lower extremity abnormality. Her right knee was positioned such that, when flexed, the foot touched the abdomen (Figure 1). Her right foot was in correct anatomic position with respect to the ankle, and the ankle had full range of motion.
Ortolani and Barlow maneuvers were negative for hip dysplasia. The girl had full range of motion in the knees bilaterally, but in opposite directions. All other joints were intact and without deformity. No polydactyly, syndactyly, or contractures were noted. No obvious pain was elicited on palpation or movement of the right knee. No swelling or erythema of the extremities was present, with 2+ dorsalis pedis and posterior tibial pulses and good capillary refill. Mild plantar cyanosis was observed bilaterally. No sacral dimple or sacral hair tuft were present. The rest of the physical examination findings were within normal limits. Bilateral hip ultrasonography results were negative for dysplasia.
Orthopedics was consulted, and they confirmed the diagnosis of congenital knee dislocation. They reduced the knee at the bedside, placed the newborn in an anterior blocking splint, and recommended outpatient follow-up in 1 week.
Lateral view radiographs (Figures 2 and 3) revealed the approximately 2-cm anterior placement of the proximal tibia in relation to the distal portion of the femur. No fractures or bony lesions were present.
Discussion
Congenital dislocation of the knee (CDK) is a rare malformation marked by hyperextension of the knee with concurrent limitation of flexion. It is diagnosed at birth and can be confirmed by radiography or ultrasonography.
CDK generally occurs sporadically, and the incidence is estimated at 1 case per 100,000, with incidence in girls greater than in boys.
Several classification systems have been developed to describe congenital hyperextension of the knee, all of which are based on the relative positioning of the tibia to the femur. Grade 1 CDK is a simple genu recurvatum, or congenital hyperextension of the knee; grade 2 is congenital hyperextension of the knee with anterior subluxation of the tibia on the femur; and grade 3 is congenital hyperextension of the knee with anterior dislocation of the tibia on the femur.1-5
CDK can occur as an isolated deformity or it can be associated with other skeletal anomalies. Associated skeletal anomalies are relatively common in infants with congenital hyperextension or dislocation of the knee.
Although CDK can be caused by a variety of factors, it traditionally has been classified into either extrinsic or intrinsic etiologies.6 Extrinsic causes, or factors that mechanically disrupt the normal range of motion of the knee joint, include the congenital absence of the cruciate ligaments, contracture or fibrosis of the quadriceps, and “packaging disorders” such as breech positioning with the feet being locked under the mandible.2,6-9 Intrinsic factors, or genetic abnormalities, include Larsen syndrome, Desbuquois syndrome, and gPAPP deficiency.1,10 CDK also can be related to both intrinsic and extrinsic causes, such as arthrogryposis multiplex congenita or as part of a paralytic condition such as myelomeningocele. Additional associated anomalies include clubfoot, spina bifida, scoliosis, coxa valga, dislocation of the elbow, anomalies of the toes, cleft palate, Down syndrome, hydrocephalus, facial paralysis, and cryptorchidism.11
The goal of treatment is to provide a functioning limb that allows ambulation. Most cases of CDK can be treated nonsurgically and achieve good results when initiated immediately after birth.10,12 Nonsurgical management includes early manipulation and serial long leg casting/splinting on a weekly basis in an attempt improve the range of motion at the knee.
Operative management usually is reserved for refractory cases in which casting and splinting fails to reach 30 degrees of flexion after 3 months. The goal of surgery is to obtain 90 degrees of flexion at the knee via a V-Y quadricepsplasty or Z-lengthening. An anterior joint capsule release or a collateral ligaments mobilization also might need to be performed.
R. David Graham is a fourth-year medical student at the Morsani College of Medicine at the University of South Florida in Tampa.
Lana Soylu, MD, is an assistant professor of pediatrics at the Morsani College of Medicine at the University of South Florida.
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