Congenital Dislocation of the Knee

Definition

Congenital dislocation of the knee is a condition characterised by hyperextension deformity of knee with varying degrees of pathological anterior displacement of the tibia present at birth.

History

• First described by Chenssier in 1812.
• Subsequently reported by Chatelaine in 1822 and by Bord in 1834.

Aetiology

• Three theories have been proposed about the causation. (Elmadag 2013)
  • Mechanical theory – Due to abnormal intrauterine position
  • Primary embryologic theory – Due to embryonic defect
  • Mesenchymal theory – Due to quadriceps contracture
• The primary cause can be extrinsic or intrinsic.
• Intrinsic causes are genetic or developmental and extrinsic factors are mechanical factors.
• Extrinsic causes can be oligohydramnios, multiple pregnancy, intrauterine fetal malposition, quadriceps contracture and birth trauma.

Epidemiology

• Majority of cases are sporadic.
• Incidence is 1 in 100,000 live births. Seen in 1% of patients with DDH
• Associations
  • Breech presentation – 30%
  • CTEV- 47%
  • DDH- 50%
  • Syndromes
    • Arthrogryposis multiplex
    • Larsen syndrome
    • Ehlers Danlos syndrome
    • Beals syndrome
    • Myelodysplasia

Classification

Leveuf and Pais Classification

Simple hyperextension – 15-20⁰hyperextension, passive flexion up to 90⁰.

Anterior subluxation – 25-40⁰hyperextension and no flexion.

Anterior dislocation – No contact between distal femoral and proximal tibial articular surfaces.

Finder’s Classification (Finder 1964)

Type I– Physiological hyperextension up to 20⁰is considered normal. Usually disappears by the age of 8 years.

Type 2– Simple hyperextension that persist into adult life.

Type 3– Anterior subluxation with hyperextension up to 90⁰. Flexion only to neutral position.

Type 4– Dislocation of knee with anterior and proximal migration of proximal tibia.

Type 5– Complex variants associated with syndromes and other congenital deformities. 

Tarek CDK grading system (Tarek 2011)

G1– Simple recurvatum. Passive flexion >90⁰. Manage by serial casting.

G2– Subluxation. Passive flexion 30-90⁰. Manage by percutaneous quadriceps release

G3– Dislocation. Passive flexion <30⁰. Manage by V-Y Quadricepsplasty.

Pathology

• Quadriceps fibrosis and contracture.
• Tight anterior capsule.
• Hypoplastic or absent patella.
• Hypoplastic suprapatellar bursa.
• Anterior subluxation or dislocation of knee.
• Transverse anterior skin crease.
• Round condyles.
• Increased tibial plateau.
• Rotatory or valgus deformity of tibia.
• Hamstrings may be displaced anteriorly and become extensors of knee.
• Absent or elongated anterior cruciate ligaments (Katz 1967).
• Lax or displaced cruciate ligaments.

Clinical features

• Child born with varying degrees of hyperextension deformity of the knee.
• Passive flexion of knee limited to varying degrees depending on the severity.
• May be associated with other musculoskeletal anomalies like developmental dysplasia of hip or congenital talipes equinovarus.
• Varying degrees of anterior displacement of the tibia in relation to the femur present.

Diagnosis

• Prenatal ultrasound may help in diagnosis.
• X-ray shows deformity with angulation in hyperextension type, anterior translation with variable amount of contact between femur and tibia in subluxation type and total loss of contact between femur and tibia with hyperextension deformity in dislocation type.
• Ultrasound shows obliteration of  suprapatellar pouch.
• Arthrogram may be necessary to identify intra-articular pathology.

How to treat these children?

When to treat?

How to do closed reduction?

How to do a surgical correction?

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