Genu Recurvatum or Knee Hyperextension

Genu recurvatum is a deformity in the knee  where the knee angulates backwards because of hyperextension occurs in the tibiofemoral joint [the knee goes further into extension beyond the neutral]

Genu recurvatum is also called knee hyperextension and back knee.

Depending upon hyperextension, the recurvatum could be mild, moderate or severe.

The normal range of motion of the knee joint is from 0 to 135 degrees in an adult. Genu recurvatum is operationally defined as knee extension greater than 5°[Also labeled as -5 and implies 5 degrees beyond zero.]

Genu recurvatum may cause knee pain, an extension pattern gait and have poor proprioceptive control of terminal knee extension.

The condition can be congenital or acquired.

Congenital genu recurvatum is apparent at birth. It can occur as an isolated entity or can be associated with other musculoskeletal anomalies, or part of a syndrome. [see the list of causes]

Isolated congenital genu recurvatum is thought to be associated with include breech positioning and oligohydramnios.

Congenital dislocation of the knee is the major cause of  pathological genu recurvatum and some authors consider them entities in the continuum.

Factors Causing Genu Recurvatum

The following factors may be involved in causing this deformity

• Laxity of the knee ligaments
• Muscle Weakness

• • Biceps femoris muscle
  • Hip extensor muscles
  • Gastrocnemius muscle
  • Popliteus muscle weakness

• Malalignment of the tibia and femur as in malunion
• Instability of the knee joint due to ligaments and joint capsule injuries
• Deficit in joint proprioception
• Lower limb length discrepancy

Conditions Associated with knee recurvatum

• Spastic lesions
• Lower motor neuron lesions like Polio
• Congenital genu recurvatum
• Cerebral palsy
• Multiple sclerosis
• Muscular dystrophy
• Plantar flexion contracture
• Arthrogryposis multiplex congenita
• Congenital knee dislocation
• Connective tissue disorders (e.g. Ehlers-Danlos disease, Larsen syndrome)
• Connective tissue disorders
  • • Marfan syndrome
    • Ehlers-Danlos syndrome
    • Benign hypermobile joint syndrome
    • Osteogenesis imperfecta disease
• Proximal growth plate injury
• Osgood-Schlatter disease
• osteomyelitis)
• Ligament injury as in sports
  • Cruciate ligament injury
  • Posterolateral corner injury
  • Superficial medial collateral knee
  • Posterior oblique ligament.

Clinical Presentation

Knee recurvatum may be asymptomatic or may cause

• Knee giving way into hyperextension
• Difficulty with endurance activities
• Pinching in the front of the knee

An assessment of a patient for ligament hypermobility should be made.

Imaging

X-rays rule out bony injuries or subluxation.

Assessment of knee alignment must be performed via a long leg x-ray. Their posterior tibial slope must also be calculated on a lateral knee x-ray.

Patients who have a decreased posterior tibial slope tend to have more problems with knee hyperextension.

Treatment for Genu Recurvatum

Positional congenital knee recurvatum gets resolved spontaneously.

For other types of congenital recurvatum treatment may include watchful waiting, flexion exercises, splinting, casting, or surgery. The treatment is guided by severity.

Treatment of acquired genu recurvatum would depend on the cause. Not all causes would be curable though and treatment may aim at functional improvement.

For example, ligament reconstruction should be done in cases of ligament injury and osteotomy may improve the knee in case of malalignment.

Proximal tibial osteotomy in cases where the tibial slope is increased may be done.