What is the popliteal angle in a child with cerebral palsy?

What is the Popliteal Angle?

The popliteal angle is a clinical measurement used to assess hamstring muscle tightness by measuring the angle formed when the knee is extended while the hip is held at 90 degrees of flexion. 1

Measurement Technique

• The test is performed with the hip positioned at 90 degrees of flexion, and the knee is then passively extended until resistance is felt from the hamstring muscles. 1
• A 360-degree goniometer is used to measure the angle between the femur and tibia at the point of maximum knee extension. 2
• Both unilateral and bilateral measurement techniques exist, with good interrater reliability (ICC 0.80-0.86 for unilateral, 0.82-0.83 for bilateral measurements). 3

Normal Values in Children

• Between ages 1-3 years, the mean popliteal angle is 6 degrees (range 0-15 degrees). 2
• At age 4 years, the angle increases to 17 degrees in girls and 27 degrees in boys (range 5-45 degrees). 2
• At age 5 years and older, the mean angle is 26 degrees with minimal subsequent change (range 0-50 degrees). 2
• A popliteal angle greater than 50 degrees indicates abnormal hamstring tightness in children. 2

Clinical Application in Cerebral Palsy

• The popliteal angle is specifically used to assess hamstring contracture in children with cerebral palsy, particularly those with spastic diplegia where lower limbs are more affected. 1, 2
• Extremity tone can be monitored during maturation by documenting popliteal angles after the first year of life. 1
• The measurement helps guide treatment decisions, including consideration for proximal hamstring lengthening in severe cases affecting sitting ability and positioning. 4

Important Clinical Caveats

• Muscle activation during testing is a significant confounding factor—knee flexors show fivefold increase in activation during the test, particularly in the ipsilateral hamstring. 5
• The popliteal angle should not be relied upon as the sole criterion for treatment selection in cerebral palsy due to high inter- and intraobserver variability (74% of observed variability is observer-related with conventional testing). 6, 5
• The modified popliteal angle demonstrates an inverse relationship with maximum hamstring length during gait (p<0.01), making it more clinically relevant than conventional measurement. 6
• Only 10 of 32 limbs in one study actually had short medial hamstrings despite abnormal popliteal angles, highlighting that the test may not accurately reflect true hamstring length in all cases. 6