Flexion Deformity of the Knee

Original Editor - Jentel Van De Gucht

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Definition/Description

A flexion deformity of the knee is the inability to fully straighten the knee, also known as flexion contracture. Normal active range of motion (AROM) of the knee is 0° extension and 140° flexion. In people with a flexion deformity, AROM of one or both knees is reduced. It develops as a result of failure of knee flexors to lengthen in tandem with the bone, especially when there is inadequate physical therapy to provide active and passive mobilization of the affected joint. They often require extensive rehabilitation.  In most cases, flexion deformities occur bilaterally.

Epidemiology/Etiology

Flexion deformities can arise by different causes. Two types of flexion contracture of the knee can be distinguished: 1) contracture associated with joint destruction and ankylosis and 2) contracture with joint anatomy and mobility are preserved. They can be caused by a piece of bone or other tissue getting in the way and blocking movement, knee replacement components in the wrong position or scar tissue restricting that cannot further straightening an extreme tightness in the hamstring muscles. Flexion deformities are common complications following trauma, inflammatory conditions, immobilization, burns and congenital deformities.

A few examples in which flexion contractures of the knee can occur are: burn scars, intra-articular fractures, septic arthritis, juvenile rheumatoid arthritis, cerebral palsy and many others.

Characteristics/Clinical Presentation

Patients with flexion contractures often walk with a bent-knee gait. This provides increasing strain on the quadriceps and increasing strain contact forces in the patellofemoral joint. Walking distance is reduced and increased strain during bent-knee gait may lead to quadriceps weakness and early onset of quadriceps fatigue. Other symptoms of flexion contractures are anterior knee pain, a progressive crouch gait and limping while walking. They often lead to compensatory movements such as hip flexion deformity accompanied by lumbar lordosis.

Short-term and long-term changes can be distinguished. Early changes are shortening of stride gait, reduced popliteal angle and a flexed position of the knee at the initiation of the stance phase and throughout the gait cycle. Changes which appear later are severe contracture of knee and hip and patella alta.

Knee flexion contractures have a lot of functional consequences such as weight-bearing activities and difficulties with bed or chair positioning. Normal daily activities become more difficult because more energy is required to perform them.

Physical Therapy Management

Depending on etiology and severity of the deformity, different management programs are necessary. Treatment of knee flexion contractures includes non-surgical and surgical methods. In both cases, physiotherapy is necessary. Conservative treatments include physical therapy, home exercise programs, and home mechanical therapy. These are used to treat and minimize the occurrence of flexion contractures. In some cases, such as with cerebral palsy, spasticity management is also necessary.

Physical therapy may include manual stretching, prolonged stretching using a tilt table, prolonged stretching using a sandbag/weight over the distal femur, mechanical traction, passive range of motion exercises and joint mobilization The effectiveness of a given treatment to reduce flexion contractures is a function of the applied torque, as well as the duration and frequency of the treatment.

Medical Management

For patients who have failed standard conservative treatment for two or more months, focused treatment protocols including physical therapy and the use of custom knee devices have been demonstrated to effectively treat flexion contractures. Other treatment methods include orthoses, casting and bracing. Some types of splits have been marketed as another method of applying low stretching forces over prolonged periods. They provide a resistance to flexion so the knee is at rest in maximum extension. The resistance can be inflated. They are easy to apply, mobile and comfortable for patients. In most cases, splints and orthoses are used to prevent deformities or maintain range of motion after stretching but not for increasing motion.

In more severe cases, surgical treatment such as soft-tissue release, osteotomies (removing a part of the bone), femoral shortening, hamstring lengthening and rectus transfer may be necessary.  Hamstring lengthening is helpful to relieve excessive contractures, especially when they have a significant effect on gait. Rectus transfer may be indicated to partially reduce the spasticity of the quadriceps, especially in patients with cerebral palsy.