May 2015

Popliteal Angle – A Measurement of Hamstring Tightness

Hamstring tightness and lack of flexibility is a common source of increased stresses on the anterior knee, low back, and pelvis and has been associated with problems and diagnoses in all of those systems.  It is important to assess hamstring flexibility as part of an overall comprehensive knee, low back, or pelvic examination.

We tend to think in terms of structural lesions-what we can fix. We tend to rely on the evaluation of the musculoskeletal system for forming diagnoses on things such as muscle strength, ROM, joint mobility, special tests, and a more local approach.  This approach is useful in acute conditions. Movement however, is dependent on the interaction of structural and functional components. Neuromuscular interactions and causative factors are important when diagnosing functional problems which requires a more comprehensive examination approach to better identify the cause of the pain.

Functional problems we see include chronic LBP, SI joint dysfunction, patellofemoral pain syndrome, shoulder impingement, and various hip pathologies which all involve posture, postural stability, muscle tone, and movement patterns.

An enhanced physical examination allows determination of the functional deficits and mechanical flaws within the sensorimotor system leading to structural failure – identify the cause (which could be structural, functional, or both), and not just the source. Identifying the cause allows for the potential elimination or improvement of the problem rather than just treating the symptoms. This is important preoperatively as well as postoperatively and should not just be left up to the physical therapist to identify.

Hamstring flexibility is usually assessed by measuring the hamstring-popliteal angle.  In this measurement, the hip is flexed to 90°and the knee is extended to a point where it becomes tight.  This should be done passively and not actively for measurement purposes.  The hamstring-popliteal angle is measured in relation to a line drawn parallel to the femur and the angle that forms between another line drawn parallel to the tibia.  In this manner, the patient that can only have the knee extended to a right angle before the hamstrings become tight would be noted to have a hamstring-popliteal angle of 90°and would be considered to have very tight hamstrings.  Intraobserver reliability with this measurement is reliable with less interobserver reliability, particularly in cerebral palsy patients as compared to a control group.  The popliteal angle seems to be more reliable than a modified straight leg test to check hamstring flexibility.  Start checking and measuring this angle as part of your examination and you will begin to see tightness problems causative effects on various problems and diagnoses and improvement in hamstring flexibility associated with improved function and less pain in your patients.  Posterior chain exercises improving flexibility and strength are an important component of rehabilitation, balance, and athletic performance.

Submitted by:

James A. Slough, MD
Buffalo, New York