SAMIR S.SHAHMDALBERT C.YANMD
Copyright 2008 American Medical Association. All Rights Reserved. Applicable FARS/DFARS Restrictions Apply to Government Use.2008
Congenital dislocation of the knee is characterized by forward displacement of the proximal tibia on the femoral condyles, with hyperextension of the knee joint. It was first described by a Swiss physician Chatelain in 1822, as noted by Shattock.1 Congenital dislocation of the knee is a relatively rare condition with an incidence of about 1:100 000 or about 1% of the incidence of development dislocation of the hip.1,2 Most cases are sporadic, with a few familial reports.3
Various etiologies have been suggested, including intrinsic (genetic or dysplastic) and extrinsic (mechanical) causes, though both may occur in a given patient.1,4 Intrinsic causes include Ehlers-Danlos syndrome, Larsen syndrome, arthrogryposis multiplex congenita, and multiple chromosomal abnormalities, like trisomies of chromosomes 9 and 21, partial monosomies, partial trisomy, partial tetrasomy 9p, and ring chromosomes 13, 14, and 18. Extrinsic causes include abnormal fetal position, like extended breech, and quadriceps muscles fibrosis. Associated conditions include congenital dislocations of the hip, elbows, and radial head; clubfoot; and coxa valga.5
Congenital dislocation of the knee is easily diagnosed at birth by the upwards posterior rotation of the tibia over the knee joint. It can be confirmed by radiography. Prenatal ultrasonography has also shown potential for diagnosis as it shows the quadriceps fibrosis as a focal thinning with a hyperechoic abnormal area at the distal end of the quadriceps muscle.6 Congenital dislocation of the knee is classified depending on the severity of the deformity as group 1, genu recurvatum; group 2, anterior subluxation; or group 3, anterior dislocation.7 In group 1, the knee hyperextends more than 15° but flexes fully. In group 2, the knee hyperextends more than 15° but there is some restriction of flexion or the knee feels unstable. In group 3, the knee is unstable and extension or flexion is variable.
Treatment depends on the severity of the knee dislocation, age of patient, and presence of associated deformities. Immediate reduction or serial casting should be tried when the patient is seen early after birth, especially when younger than 2 days. If the patient is seen late and serial casting proves to be unsuccessful, traction in the Bryant position or in a prone position may be used for 1 to 2 weeks, followed by closed reduction. In a recalcitrant case, an arthrogram may be performed with open reduction.8 Surgical treatment has also been suggested for patients in whom 3 months of casting fails, without reduction of the subluxation or without obtaining 45° of flexion.1 Surgery involves lengthening of the quadriceps tendon with a V-Y–shaped plasty, enlarging the suprapatellar pouch by anterior capsulotomy, and reducing the dislocation. Operative findings show quadriceps muscle fibrosis; abnormal anterior cruciate ligament; hypoplastic, dislocated patella; and anteriorly dislocated hamstrings and iliotibial band.5
In the presence of associated deformities, the knee should be treated first, followed by the foot and then the hip. Conservative treatment is likely to fail in patients with genetic or dysplastic causes like Larsen syndrome or arthrogryposis multiplex congenita.9 Nonoperative treatment has a better prognosis.
Return to Quiz Case.
Correspondence: Nirav J. Shastri, MD, Department of Pediatrics, Children's Mercy South Urgent Care Center, Children's Mercy Hospital and Clinic, 5808 W 110th St, Overland Park, KS 66211 (firstname.lastname@example.org).
Accepted for Publication: August 1, 2007.
Author Contributions:Study concept and design: Shastri. Acquisition of data: Shastri and Winners. Analysis and interpretation of data: Shastri. Drafting of the manuscript: Shastri and Winners. Critical revision of the manuscript for important intellectual content: Shastri. Administrative, technical, and material support: Shastri and Winners. Study supervision: Shastri and Winners.
Financial Disclosure: None reported.
Picture of the Month—Diagnosis. Arch Pediatr Adolesc Med. 2008;162(8):788. doi:10.1001/archpedi.162.8.788