Flexion Deformity of the Knee
Original Editor - Jentel Van De Gucht
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. 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.The deformity is either temporary or permanent.
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
2) Contracture with joint anatomy and mobility are preserved:
- After knee operations(Total arthroplasty)
- Tendon transfers
- Stiffness post fractures of Femur,Tibia,Patella,or the whole knee joint
- Scar tissue
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 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.
- 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 contacture less than 15 degrees of extensor lag and toe walking where contacture 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
- A progressive crouch gait and limping while walking leads to shortening of stride length,
- 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 poplitial 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 persons personal and social life.
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. 
The main aim of the treatment is:
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.