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Flexion Deformity of the Knee in CP

- Discussion:
    - most thoroughly analyzed joint in cerebral palsy has been knee;
    - most common deformity of the knee involves flexion contractures and decreased range of motion;
    - early changes:
           - short stride gait and reduced popliteal angle;
           - knee flexed at the initiation of stance phase and throughout gait cycle;
    - late changes:
           - knee flexion and hip extension contracture;
           - patellae alta;
    - role of quadriceps:
           - although knee-flexed postures are most easily conceived of as being due to spastic hamstring muscles, spasticity of the quadriceps 
                  (co-spasticity) is often associated with this deformity;
           - spasticity of the quadriceps (most often the rectus) limits the 35 degrees of initial flexion and the 70 degrees of total flexion of the 
                  knee during the swing phase of gait and results in a less-than-optimum, energy-consuming, stiff-legged gait;
    - crouched gait:
           - gait pattern characterized by hip-flexion, knee-flexion, and ankle-dorsiflexion posture throughout stance phase;
           - either the psoas or the hamstrings may be responsible for the flexion posture of the hip and knees;
           - in some cases crouched gait pattern is precipitated by lengthening of the Achilles tendon, without addressing hamstring contractures;

- Hamstring Lengthening:
    - hamstring lengthening is helpful to relieve excessive contractures, esp when they have a significant effect on gait;
    - hamstring lengthening is often performed along with Achilles tendon lengthening (in order to avoid crouched gait)
    - the threshold for performing hamstring lengthening varies, but many surgeons use a popliteal angle of 90-100 deg as a threshold for 
           performing lengthening in non ambulating patients and an angle of 135 deg as a threshold in ambulators;
    - distal hamstring lengthening is preferred (over proximal lengthening) for ambulatory patients;
    - complications:
           - may result in knee recurvatum if distal lengthening is performed in the face of uncorrected equinus;
           - may increase lumbar lordosis (if hamstring lengthening is performed proximally);

- Rectus Transfer:
    - transfer of the distal part of the rectus femoris tendon may be indicated in order to partially reduce the spasticity of the quadriceps;
    - rectus transfer (to the gracilis) allows better knee function and foot clearance in the swing phase of gait;
    - distal part of rectus femoris tendon is freed from vastus lateralis and medialis muscles, and the flat tendon is separated from underlying 
           vastus intermedius tendon and is sectioned distally;
           - resultant free rectus femoris tendon is then transferred to belly of the sartorius muscle so that it can act as initial flexor of the knee 
                  and external rotator of the hip

Rectus femoris surgery in children with cerebral palsy. Part I: The effect of rectus femoris transfer location on knee motion.

Rectus femoris surgery in children with cerebral palsy. Part II: A comparison between the effect of transfer and release of the distal rectus femoris on knee motion.

Common gait abnormalities of the knee in cerebral palsy.

The effect on gait of lengthening of the medial hamstrings in cerebral palsy.

Distal lengthening of the hamstrings in patients who have cerebral palsy. Long-term retrospective analysis.