A 29-year-old G7P2315 woman gave birth to a girl at 37 weeks via spontaneous vaginal delivery. APGAR scores were 9 and 9. Birth weight was 2760 g. Cardiovascular and pulmonary examinations were normal (heart rate, 154 beats/min; respiratory rate, 52 breaths/min). Following delivery, the neonate appeared healthy, had a lusty cry, and had no visible craniofacial or cutaneous abnormalities; however, the bilateral knees were hyperextended to 90° to 110° (FIGURE 1A).
The mother had started prenatal care at 7 weeks with 10 total visits to her family physician (JD) throughout the pregnancy. Routine laboratory screening and prenatal ultrasounds (including an anatomy scan) were normal. She had a history of 3 preterm deliveries at 35 weeks, 36 weeks, and 36 weeks, respectively, and had been on progesterone shots once weekly starting at 18 weeks during the current pregnancy. She had no history of infections or recent travel. Her family history was remarkable for a sister who gave birth to a child with thrombocytopenia absent radius syndrome.
The neonate tolerated passive flexion of the knees to a neutral position. Hip examination demonstrated appropriate range of movement with negative Ortolani and Barlow tests. The infant’s feet aligned correctly, with toes in the front and heels in the back, and an x-ray of the bilateral knees showed no fractures or dislocation.
Based on the clinical examination and x-ray findings, we made a diagnosis of congenital genu recurvatum. A pediatric orthopedics consultation was obtained, and the knees were placed in short leg splints in comfortable flexion to neutral on Day 1 of life. She was discharged the next day.
Congenital genu recurvatum, also known as congenital dislocation of the knee, is a rare condition involving abnormal hyperextension of the unilateral or bilateral knees with limited flexion.1 Reports in the literature are limited, but there seems to be a female predominance among known cases of congenital genu recurvatum.2 The clinical presentation varies. Finding may be isolated to the knee(s) but also can present in association with other congenital abnormalities, such as developmental dysplasia of the hip, clubfoot, and hindfoot and forefoot deformities.3,4
Diagnosis is made clinically with radiographic imaging
Diagnosis of congenital genu recurvatum is made clinically and can be confirmed via radiographic imaging of the knees.5 Clinical diagnosis requires assessment of the degree of hyperextension and palpation of the femoral condyles, which become more prominent as the severity of the hyperextension increases.6 X-rays help assess if a true dislocation or subluxation of the tibia on the femur has occurred. Based on the clinical and radiographic findings, congenital genu recurvatum typically is classified according to 3 levels of severity: grade 1 classification only involves hyperextension of the knees without dislocation or subluxation, grade 2 involves the same characteristic hyperextension along with anterior subluxation of the tibia on the femur, and grade 3 includes hyperextension with true dislocation of the tibia on the femur.1 Grades 1 and 2 on this spectrum technically are diagnosed as congenital genu recurvatum while grade 3 is diagnosed as a congenital dislocation of the knee,7 although the 2 terms are used interchangeably in the literature. We classified our case as a grade 1 congenital genu recurvatum based on the clinical and radiographic findings.
Congenital knee hyperextension has intrinsic and extrinsic causes
Hyperextension of the knees at birth may be caused by various intrinsic or extrinsic factors. Intrinsic causes may include breech position, lack of intrauterine space, trauma to the mother, quadriceps contracture or fibrosis, absence of the suprapatellar pouch, deficient or hypoplastic anterior cruciate ligament, pathological tissues, arthrogryposis, or genetic disorders such as Larsen syndrome or achondroplasia.6
Continue to: Extrinsic causes...