Popliteal Angle Test

The popliteal angle test is used very commonly for the assessment of hamstring contracture in patients with cerebral palsy.

How do you measure the Popliteal Angle?

The child lies supine, and the examiner flexes the hip joint to 90° while the contralateral hip is in neutral position and the limb is extended at the knee. The examiner gradually extends the knee with hip flexed at 90°.

When the examiner feels a substantial resistance to knee extension, the acute angle formed between the long axis of the femur and tibia is measured.

See Also: Knee Muscles Anatomy

Popliteal Angle Assessment

The value of the Popliteal Angle tends to increase with age and normally is less than 30–40° in adolescent children. The values in cerebral palsy children tend to be between 37° and 66° (mean being 51.9°).

The popliteal angle normal values may differ from the mean reported in the literature, which is 26° in children of 4 years and more. When it crosses 50°, it is considered abnormal.

The straight leg raise angle is also reduced in patients with tight hamstrings. When the hamstrings are significantly tight, hip flexion gets constrained.

It is very important to identify and address concomitant hip flexion contractures as the correction of hamstring tightness without managing hip flexion contractures leads to an exaggeration of hip flexion deformity and an increase in the anterior pelvic tilt during gait (hamstrings being extensors of the hip).

In a study to measure the normal Popliteal Angle values, the values were as following:

• Between the ages of 1 and 3 years, the mean angle was 6 degrees (range, 0-15).
• At age 4, the angle rose to 17 degrees in girls and 27 degrees in boys (range, 5-45).
• At greater than or equal to 5 years the mean angle was 26 degrees with little change (range, 0-50).
• A popliteal angle of greater than 50 degrees in the above age groups indicates abnormal hamstring tightness.

See Also:

• Thomas Test
• Hamstring Flexibility

Reliability of Popliteal Angle measurement

A study to assess the Reliability of popliteal angle measurement found that because of poor interobserver reliability of popliteal angle measurement, this should not be the only variable in clinical decision making in CP patients.

Modified Popliteal Angle Test

The modified Popliteal Angle Test is the bilateral popliteal angle (PAB) test. Here, after assessment of the Popliteal Angle in the standard way and maintaining the position of the limb, the examiner flexes the child’s contralateral hip to align the anterior superior iliac spine (ASIS) and posterior superior iliac spine (PSIS) vertically.

The value (acute angle between the femur and long axis of the tibia) changes now and is noted, and the difference between the two measurements is defend as the hamstring shift, which indicates the amount of hip flexion contracture in CP patients.

The PAB was an attempt to eliminate the ambiguity in measuring the PA by aligning the pelvis in a way to simulate the upright posture adapted while walking. The PA is considered to reflect functional hamstring muscle contractures, whereas the PAB reflects the true hamstring contracture.

In the bilateral popliteal angle test, there is posterior tilting of the pelvis due to the relaxation of the hip flexors on the opposite limb. This leads to a distal shift of the shortened hamstrings on the ipsilateral limb leading to a smaller PA compared to the standard measurement technique. A hamstring shift more than 20° denotes excessive anterior pelvic tilt due to tight hip flexors or weak hip extensors.

It is important to differentiate capsular contracture of the knee joint from hamstring contracture in a child with cerebral palsy. In capsular contracture, the position of the hip will not alter the knee extension, and in hamstring contracture, the knee extension will improve with hip extension/ankle plantarflexion and reduces with hip flexion to 90°.

References

1. Manikowska F, Chen BP, Jóźwiak M, Lebiedowska MK. The popliteal angle tests in patients with cerebral palsy. J Pediatr Orthop B. 2019 Jul;28(4):332-336. doi: 10.1097/BPB.0000000000000579. PMID: 30550510.
2. Katz K, Rosenthal A, Yosipovitch Z. Normal ranges of popliteal angle in children. J Pediatr Orthop. 1992 Mar-Apr;12(2):229-31. doi: 10.1097/01241398-199203000-00014. PMID: 1552027.
3. Ten Berge SR, Halbertsma JP, Maathuis PG, Verheij NP, Dijkstra PU, Maathuis KG. Reliability of popliteal angle measurement: a study in cerebral palsy patients and healthy controls. J Pediatr Orthop. 2007 Sep;27(6):648-52. doi: 10.1097/BPO.0b013e3180dca15d. PMID: 17717465.