Flexion Deformity of the Knee
Original Editor - Jentel Van De Gucht
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Definition/Description:[edit | edit source]
A flexion deformity of the knee is the inability to fully straighten or extend the knee, also known as flexion contracture. Normal active range of motion (AROM) of the knee is 0° extension and 140° flexion. An accurate definition of this would be limited knee extension range, both actively and passively. It develops as a result of failure of knee flexors i.e Hamstring muscle to lengthen in tandem with the bone, especially when there is inadequate physical therapy to provide active and passive mobilization of the affected joint. It is usually a combination of bony deformity, capsular and ligamentous deformity. They often require extensive rehabilitation.  In most cases, flexion deformities occur bilaterally. The deformity is either temporary or permanent.
Epidemiology/Aetiology:[edit | edit source]
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, like,
- Rheumatoid arthritis
- Cerebral Palsy or congenital deformity
- Hip joint injuries
- Ankle pathologies
- Other degenerative conditions
- Osteogenesis Imperfecta
- Pterygium Syndrome
2) Contracture with joint anatomy and mobility are preserved:
- After knee operations(Total Knee arthroplasty)
- Tendon transfers
- Stiffness post fractures of Femur, Tibia, Patella or the whole knee joint
- Scar tissue
Pathology[edit | edit source]
In osteoarthritis or rheumatoid arthritis, swelling is due to synovial inflammation leading to fluid in joint subsequently resulting in assuming of position maximum accommodation i.e. flexion. Chronic posterior femoral and tibial osteophytes tent upon the capsule resulting in further flexion at the knee and sometimes mechanical block to extension. Other factors like hamstring shortening and ligament contracture also contribute to flexion at the knee. This can lead to increased abnormal forces at the joint while standing, walking, etc and thus lead to abnormal gait pattern which can further lead to limb length discrepancy. Due to these forces and compensatory action of the body to walk, pathological changes may start ascending upwards towards the pelvis and spine and worsen the condition in severe flexion deformities of knee.It is usually associated with either genu varus or valgus.
Characteristics/Clinical Presentation:[edit | edit source]
Patients with flexion contractures often walk with a bent-knee gait. Patients often report sleeping with a pillow under their knee or in the fetal position. All of these activities exacerbate the flexion contracture. This provides increasing strain on the quadriceps and increasing strain contact forces in the patellofemoral joint and Tibiofemoral joint when the flexion deformity is more than 15 degress of extensor lag.
There is early joint degradation that includes cartilage erosion, meniscal injury, ligament strains, associated tightness of TFL and the main muscles around the hip and ankle joint like iliopsoas, hamstrings, Gastrosoleus, Quadriceps and adductors or abductors of hip depending upon if there is a secondary deformity of either genu varum or genu valgum and patella alta.
Grades of flexion deformity by Lombardi et al -
Grade I - mild contracture with deformity limited to less than 15°
Grade II - moderate contracture with deformity between 15° and 30°
Grade III - severe contracture with deformity greater than 30°
Gait Changes:[edit | edit source]
- Flexed position of the knee at the initiation of the stance phase and throughout the gait cycle. Heel strike is absent, the foot is placed flat on the floor when contracture less than 15 degrees of extensor lag and toe walking where contracture more than 15 degrees of extensor lag. The popliteal angle is reduced.
- The body is propelled forward with increased flexion at hip in swing phase
- Other symptoms of flexion contractures are anterior knee pain, compensatory movements such as hip flexion deformity accompanied by lumbar lordosis. 
- Changes which appear later are severe contracture of knee and hip and patella alta. Knee flexion contracture significantly influences three-dimensional trunk kinematics during relaxed standing and level walking, and will lead to spinal imbalance. Due to continuous pressure on the popliteal fossa there may be pressure generated on the common peroneal nerve and tibial nerve and the other contents of fossa.
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. It interferes with the patient's personal and social life.
In CP, for individuals who are ambulatory, Gross Motor Function Classification System (GMFCS) I–III, limited ability for full knee extension can lead to significant disability with a flexed knee gait posture called crouch gait.
Special Tests[edit | edit source]
- Thomas Test: Rule out iliopsoas tightness
- Tripod sign: Hamstring Contracture
- Clarke's test: Patellofemoral pain syndrome
Physiotherapy Management:[edit | edit source]
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. 
The main aim of the treatment is:
- Co-activation of Hamstrings and Quadriceps
- Improve eccentric hamstring strength
- Improve concentric quadriceps strength
- Patellar mobility
- Hip and ankle joint movements
- Gait training
- Return to normal life.
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[edit | edit source]
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 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. 
There are specific situations in which the best option is gradual distraction and extension employing an external fixator (Illizarov). This may best serve those patients who have neglected or teratologic deformities, such as pterygium syndrome, or have reached skeletal maturity.
Contraindications for surgery -
There are few contraindications for surgical correction of FKFD (Flexed Knee Flexion Deformity).
Contraindications for osteotomy include the following:
Contraindications for guided growth include the following:
- Closed physes
- Stiff or unstable knee
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