Assessing Hip Strength...Validity and Reliability

Clinically we are expected to assess all aspects of a patient’s musculoskeletal condition, but often we neglect to specifically assess muscle strength of an affected joint. In particular, muscles surrounding the hip, pelvis and groin are often assumed, or based on functional tests, without specific testing. Unfortunately it is challenging in the clinic to use valid and reliable measures to test the strength, so what reliable clinical tests are available to test hip muscle strength?

Starting with functional tests, Crossley and colleagues (2011) determined a single leg (SL) squat was sufficiently reliable in diagnosing those with hip muscle weakness. The study looked at dividing patient’s SL Squat performance into the categories of good, fair or poor. There was strong agreement between assessors, with the ‘good’ group then displaying higher hip abduction and trunk muscle torque. There was no difference in external rotation between ‘good’ and ‘poor’ groups, however this will be discussed later. Also, no hip extension strength measures were taken. A more recent study looked at a step-down task, again with physiotherapists assessing movement quality. Those with moderate or poor control had significantly less hip abduction strength, as well as reduced knee flexion and hip adduction range (quadriceps and ITB/tensor fascia latae shortening) (Park, Cynn, & Choung, 2013). Again no hip extension measures were taken and no difference in external rotation was found.

  Crossley et al (2009): Examples of Single Leg Squat. A) good performance; B) poor overall and trunk performance; C) poor pelvis and hip performance; D) poor hip and knee performance.

Crossley et al (2009): Examples of Single Leg Squat. A) good performance; B) poor overall and trunk performance; C) poor pelvis and hip performance; D) poor hip and knee performance.

In both these studies, hip external rotation was tested in sitting or prone with the knees strapped together, and the force exerted against the tibia. The clamshell is also a hip external rotation movement, but possibly more clinically relevant. Selkowitz (2013) showed the clamshell has double the gluteus maximus torque compared to gluteus medius, with gluteus maximus being a primary extensor and eternal rotator of the hip. Although the hip external rotation assessment was performed according to the validated literature, possibly a between groups difference would have occurred if external rotation was assessed in the clam position. With no evidence to support this, clinically I use sitting or prone external rotation to assess the deep hip rotators with clamshells, prone hip extension or single leg bridge used to assess gluteus maximus. I find the biggest contributor to a dynamic knee valgus (hip adduction, internal rotation) is a weak gluteus maximus and often discover a specific weakness in this muscle, yet the patient can present strong on isolated hip external rotation. Again, there is no evidence for this distinction, just what I have seen clinically.

Given those with anterior knee pain, who typically display poor SL Squat technique, show deficits in hip abductor, extensor and external rotator strength (Prins & van der Wurff, 2009), the assessment of hip extension strength in both these studies would have been enlightening. This again highlights the need to assess all muscles around the hip, not just the abductors.

  Selkowitz et al (2013) – clamshell movement, with blue resistance band, pelvis and feet touching wall, leg positioned in 45° hip, 90° knee flexion.

Selkowitz et al (2013) – clamshell movement, with blue resistance band, pelvis and feet touching wall, leg positioned in 45° hip, 90° knee flexion.

Moving from functional assessment into specific muscle testing, various positions are required to assess hip muscle strength. Sidelying abduction is described as the most valid assessment for hip abduction strength, compared to supine and standing (Widler et al., 2009). Prone hip extension and supine hip extension (from 30° hip flexion, pushing against manual resistance towards the bed) are both shown to be valid and reliable in assessing hip extension, when using dynamometers (Perry, Weiss, Burnfield, & Gronley, 2004). There is strong reliability in assessing hip adductors in supine with resistance placed against the knees, pushing into abduction (Malliaras, Hogan, Nawrocki, Crossley, & Schache, 2009). The same authors show moderate intra-rater and inter-rater reliability when assessing internal and external rotation. The patient lays supine with the foot hanging over the bed, with the hip in neutral and knee in 90° flexion, then exerting force against the medial or lateral malleolus. I am not aware of any studies with stronger reliability, for testing hip rotation, than this.

  Wilder et al (2009) – sidelying abduction, assessing hip abduction strength

Wilder et al (2009) – sidelying abduction, assessing hip abduction strength

  Malliaras et al (2009) – assessing hip internal & external rotation strength

Malliaras et al (2009) – assessing hip internal & external rotation strength

When assessing hip strength, a perceived exertion or repetitions to fatigue may be more clinically relevant. If the patient displays Grade 5/5 hip extension strength but had poor control on left single leg squat, it may be more appropriate to measure prone hip extension repetitions to fatigue. This prevents a ceiling effect and allows a more specific reassessment asterisk for future sessions. Alternatively, you may ask the patient to rate their perceived exertion, during the prone hip extension, on a numerical rating scale (0-10 or 0-100 etc). This may assist in patient involvement and ownership of their condition, as they recognise a difference between sides. This is based on clinical experience, however it provides an objective asterisk sign to reassess in subsequent treatments, which is more relevant than Grade 4+/5 hip flexion. 

Conclusion:

  • Functional assessment – a poor single leg squat or step down highlights poor hip control, most likely hip abduction, extension and external rotation weakness
  • Specific testing –
    • hip flexion – supine, resistance at 45° hip flexion
    • extension – prone, knee 90° flexed
    • abduction – sidelying (see picture above)
    • adduction – supine, adduct against resistance
    • internal/external rotation – hip neutral with knee 90° flexed over edge of bed (see picture above)
  • Use number of repetitions to fatigue, perceived exertion if patient achieves Grade 5/5 on manual muscle testing

Alicia

References:

Crossley, K. M., Zhang, W.-J., Schache, A. G., Bryant, A., & Cowan, S. M. (2011). Performance on the single-leg squat task indicates hip abductor muscle function. The American journal of sports medicine, 39(4), 866-873.

Malliaras, P., Hogan, A., Nawrocki, A., Crossley, K., & Schache, A. (2009). Hip flexibility and strength measures: reliability and association with athletic groin pain. British journal of sports medicine, 43(10), 739-744.

Park, K.-M., Cynn, H.-S., & Choung, S.-D. (2013). Musculoskeletal predictors of movement quality for the forward step-down test in asymptomatic women. The Journal of orthopaedic and sports physical therapy, 43(7), 504-510.

Perry, J., Weiss, W. B., Burnfield, J. M., & Gronley, J. K. (2004). The supine hip extensor manual muscle test: a reliability and validity study. Archives of physical medicine and rehabilitation, 85(8), 1345-1350.

Prins, M. R., & van der Wurff, P. (2009). Females with patellofemoral pain syndrome have weak hip muscles: a systematic review. The Australian journal of physiotherapy, 55(1), 9-15.

Selkowitz, D. M., Beneck, G. J., & Powers, C. M. (2013). Which exercises target the gluteal muscles while minimizing activation of the tensor fascia lata? Electromyographic assessment using fine-wire electrodes. The Journal of orthopaedic and sports physical therapy, 43(2), 54-64.

Widler, K. S., Glatthorn, J. F., Bizzini, M., Impellizzeri, F. M., Munzinger, U., Leunig, M., & Maffiuletti, N. A. (2009). Assessment of hip abductor muscle strength. A validity and reliability study. The Journal of bone and joint surgery. American volume, 91(11), 2666-2672.