Congenital Dislocation of Knee

This condition is also called congenital genu recurvatum. It was first described by Chatelain as congenital dislocation of knee.

Congenital knee dislocation occurs in children with myelomeningocele arthrogryposis and Larsen’s syndrome. This condition is  often associated with developmental dysplasia of the hip, clubfoot, and metatarsus adductus.

Congenital dislocation of knee is  100 times less common than congenital hip dislocation. Developmental dysplasia of hip and clubfoot are the commonly associated anomalies.

50% of patients with congenital knee dislocations will have hip dysplasia affect one or both hips and about 70% would have associated clubfoot.

Bilateral congenital dislocation of knee is almost always associated with syndromes, most commonly with laxity syndromes, Ehlers-Danlos syndrome, Larson’s syndrome, or Beal’s syndrome.

The congnital dislocation of knee occurs in less than 1 in 1000 live births.

Bilateral congenital dislocation of knee with clubfoot in Larsen Syndrome, Image credit: JCONWEB

Causes of Congenital Dislocation of Knee

Various causative factors factors have been proposed for congenital dislocation of knee. These are

• Abnormal fetal positioning
• Quadriceps fibrosis/atrophy
• Patellar hypolasia
• Contracture of iliotibial band
• Lack of formation or atrophy of suprapatellar pouch
• Hypoplasia of cruciate ligaments
• Ligament laxity syndrome
• Arthrogryposis
• Spinal dysraphism

Congenital knee dislocation is mainly of three types

Traumatic Developmental Type.

This type of dislocation is most common and considered to result because of malposition of limb in uterus. The knee is in extension and gets further compressed into recurvatum by uterine compression which also is responsible for prevention of flexion.

Primary Embryonic Defect

The dislocation of the knee is part of the spectrum of disorders occurring due to embryonic defect.

There could be other defects present. This type is usually accompanied by other defects, such as hare-lip cardiac defects, spina bifida and congenital dislocation of the hip. This type of congenital dislocation of knee is uncommon. It is also most  difficult to treat.

Quadriceps Contracture

This theory says that there is quadriceps muscle contracture that drags knee into a deformed position similar to that found in arthrogryposis.

Presentation of Congenital Knee Dislocation

At birth, the knee is found  fixed hyperextension with a varying degree of subluxation or dislocation forwards of the tibia on the femoral condyles, and the skin cover the anterior aspect of the joint shows several transverse creases. The patella is small or absent.

On the posterior aspect of the joint, the hamstring muscles are palpable as tense cords, and the femoral condyles are felt projecting in the popliteal fossa. The joint is relatively fixed.

When attempts are made to flex the dislocated knee, an elastic resistance is felt because of quadriceps tendon.

Tight collateral ligament and anteriorly subluxated hamstring could also be resisting factors.

Broadly speaking, depending on the position of the tibia and femur, knee dislocation could be

• Proximal tibia in relation to distal femur, but the knee is markedly hyperextended.
• Proximal tibia dislocated forwards in relation to the distal femur.

Treatment of Congenital Dislocation of Knee

Most of the cases of congenital dislocation of knee can be treated non-operatively. The treatment is done by reduction with manual manipulation and casting  with long leg casting.

Treatment is begun at birth of shortly thereafter and the casts are repeated at 2 to 3 day intervals until flexion beyond 90 degree is obtained. Thereafter a bivalve cast is used for 3 months.

The cast is  removed twice a day for 30 minute intervals and active flexion and extension is carried out. An x- ray check-up is obtained during correction to make certain that the proximal tibia a maintaining a normal anatomical relationship to the distal femur.

Cast is generally removed after about 3 month period  and a removable cast or brace is applied to counter any tendency to return to a hyperxtended position.

Sometimes, due to capsular adherence and anterior subluxation of hamstring, the reduction becomes difficult.

If the reduction is not accomplished surgery is  indicated as soon as the difficult is recognized at 3-6 months

[If  both knee and hip dislocated, then knee needs to be treated first as Pavlik harness which is used for treatment of congenital hip dislocation cannot be applied if the knee is dislocated.]

Surgery for Congenital Knee Dislocation

Surgery consists of  soft tissue release which is indicated if there is a failure to gain 30 degrees of flexion after 3 months of casting.

Goal of surgery is to obtain 90 degrees of flexion. It is accomplished by following surgical procedures as needed

• Quadriceps tendon lengthening
• anterior joint capsule release
• Posterior transposition of hamstring tendon
• Mobilization of collateral ligaments

Postoperatively, the limb is kept in cast in 45 to 60 degrees of flexion for 3 to 4 weeks.