Research Review By Dr. Jeff Muir©

Audio:

Download MP3

Date Posted:

March 2020

Study Title:

Differential movement of the sciatic nerve and hamstrings during the straight leg raise with ankle dorsiflexion: Implications for diagnosis of neural aspect to hamstring disorders

Authors:

Bueno-Gracia E, Pérez-Bellmunt A, Estébanez-de-Miguel E, López-de-Celis C, Shacklock M, Caudevilla-Polo S, González-Rueda V

Author's Affiliations:

Faculty of Health Sciences, University of Zaragoza, Spain; Faculty of Medicine and Health Sciences, International University of Catalonia, Barcelona, Spain; Neurodynamic Solutions, Adelaide, Australia.

Publication Information:

Musculoskeletal Science and Practice 2019; 43: 91–95.

Background Information:

Hamstring injuries are a common sports-related injury and are prevalent across a variety of sports (e.g. soccer and athletics) (1, 2). One perhaps underappreciated aspect of hamstring injuries is the involvement of the sciatic nerve, owing to its close proximity to the biceps femoris, near its attachment at the ischial tuberosity. The resulting hip and thigh pain, which may occur with or without sciatic nerve involvement (3-5), is a common presentation of injuries of the proximal hamstring (4, 6, 7). Specifically, conditions such as deep gluteal syndrome (DGS) (i.e. compression of the nerve by the piriformis, gluteus or hamstring muscles) are often overlooked causes of chronic buttock and lower extremity pain (5).

The straight leg raise (SLR) test is the most commonly performed physical test for sciatic nerve or lumbar nerve root irritation in patients with low back pain (8-11) and is also commonly used to evaluate hamstring muscle flexibility (12, 13). The addition of ankle dorsiflexion to the SLR is thought to help differentiate between sciatic nerve and hamstring pain (11, 14-16). Animal and cadaver studies have demonstrated distal movement of the tibial nerve at the knee with ankle dorsiflexion during SLR, although little is known about the effect of this combined test on the proximal sciatic nerve.

As such, the purpose of this study was to evaluate the mechanical behaviour of the sciatic nerve and biceps femoris muscle in the proximal thigh during SLR with ankle dorsiflexion. More specifically, both strain (elongation) and excursion (displacement) of the muscle and nerve were tested in a cadaver model to investigate the specificity of ankle dorsiflexion for the sciatic nerve and hamstrings at different ranges of hip flexion during the SLR test.

Pertinent Results:

Strain Measurements:
Ankle dorsiflexion at all hip angles resulted in statistically significant strain on the sciatic nerve at the proximal hamstrings (0 degrees = 1.26% ± 1.60%, p < 0.001; 30 deg = 2.25% ± 1.94%, p < 0.001; 90 deg = 3.06% ± 1.94%, p < 0.001) with the greatest strain noted at 60 degrees of hip flexion (3.66% ± 2.40%, p < 0.001). Ankle movement did not affect the level of strain in the biceps femoris at any hip position.

Excursion Measurements:
Excursion of the sciatic nerve higher than the minimal detectable difference was noted in all hip flexion positions. At the proximal hamstrings, consistent distal movement of the sciatic nerve was noted, with maximal excursion observed at 30 degrees of hip flexion (2.19 ± 0.96mm, p > 0.001). The biceps femoris was not affected by ankle movement.

Clinical Application & Conclusions:

This study demonstrated that ankle dorsiflexion during SLR at varying degrees of hip flexion induces changes in the strain and excursion of the sciatic nerve at the proximal hamstring. Conversely, the biceps femoris at the same location was not affected by ankle dorsiflexion during SLR. The authors suggest that this difference may form the basis of a differential diagnosis test when considering upper hamstring disorders and posterior hip and thigh pain. In other words, if dorsiflexing the ankle reproduces posterior upper thigh pain or causes distal neural pain or symptoms during the SLR, the sciatic nerve is likely involved. A simple, clinical take-home from this study!

Study Methods:

The study was a cross-sectional study using six fresh, frozen human cadavers. A total of 11 lower extremities were utilized (1 was excluded).

Experimental Procedures:
Cadavers were placed in a contralateral side-lying position. Strain and excursion measurements were made at 0, 30, 60 and 90 degrees of hip flexion, in random order. The knee was placed in full extension and the ankle in full plantar flexion prior to testing. Hip and knee positions were maintained manually through testing. For each testing position, the ankle was manually moved from full plantar flexion to full dorsiflexion. Testers were blinded to the effects of each maneuver on the nerve and muscle. Each movement was repeated five times at each level of hip flexion.

Strain Measurements:
Strain gauges were inserted into the biceps femoris and sciatic nerve with two barbed pins, at 4 and 6 cm distal to the ischial tuberosity. Differential variable reluctance transducers (DVRTs) were used to monitor and measure strain. The percentage change in strain was used as the main outcome, calculated as [(end length – start length)/start length] x 100.

Excursion Measurements:
A metal screw was inserted into the ischial tuberosity to act as a reference point. Longitudinal excursion was defined as the distance from this reference marker to the distal barb of the DVRT within each of the sciatic nerve and biceps femoris muscle. A digital caliper was used to measure this distance.

Study Strengths / Weaknesses:

Strengths:
  • Use of cadavers allowed for experimental procedures that would not be feasible in live human subjects.
  • Clinically relevant testing lead to clinically useful conclusions regarding differential diagnosis testing.
Weaknesses:
  • Use of cadavers may be associated with movements not representative of natural human movement.
  • Tension, excursion and torsion of the sciatic nerve and biceps femoris were not measured through the entire SLR range.

Additional References:

  1. Van Dyk N, Bahr R, Burnett AF et al. A comprehensive strength testing protocol offers no clinical value in predicting risk of hamstring injury: a prospective cohort study of 413 professional football players. Br J Sports Med 2017; 51(23): 1695–1702.
  2. Edouard P, Branco P, Alonso JM. Muscle injury is the principal injury type and hamstring muscle injury is the first injury diagnosis during top-level international athletics championships between 2007 and 2015. Br J Sports Med 2016; 50(10): 619–630.
  3. McCrory P, Bell S. Nerve entrapment syndromes as a cause of pain in the hip, groin and buttock. Sport Med 1999; 27(4): 261–274.
  4. Martin HD, Khoury A, Schröder R, Palmer IJ. Ischiofemoral impingement and hamstring syndrome as causes of posterior hip pain: where do we go next? Clin Sports Med 2016; 35(3): 469–486.
  5. Jackson TJ. Endoscopic sciatic nerve decompression in the prone position—an ischial-based approach. Arthrosc Tech 2016; 5(3): e637–e642.
  6. Martin RRL, Schröder RG, Gomez-Hoyos J et al. Accuracy of 3 clinical tests to diagnose proximal hamstrings tears with and without sciatic nerve involvement in patients with posterior hip pain. Arthrosc J Arthrosc Relat Surg 2018; 34(1): 114–121.
  7. Haus BM, Arora D, Upton J, Micheli LJ. Nerve wrapping of the sciatic nerve with acellular dermal matrix in chronic complete proximal hamstring ruptures and ischial apophyseal avulsion fractures. Orthop J Sport Med 2016; 4(3): 1–7.
  8. Hall T, Zusman M, Elvey R. Adverse mechanical tension in the nervous system? Analysis of straight leg raise. Man Ther 1998; 3(3): 140–146.
  9. Sierra-Silvestre E, Torres Lacomba M, de la Villa Polo P. Effect of leg dominance, gender and age on sensory responses to structural differentiation of straight leg raise test in asymptomatic subjects: a cross-sectional study. J Man Manip Ther 2017; 25(2): 91–97.
  10. Capra F, Vanti C, Donati R et al. Validity of the straight-leg raise test for patients with sciatic pain with or without lumbar pain using magnetic resonance imaging results as a reference standard. J Manip Physiol Ther 2011; 34(4): 231–238.
  11. Boyd BS, Villa PS. Normal inter-limb differences during the straight leg raise neurodynamic test: a cross sectional study. BMC Muscoskelet Disord 2021; 13(1): 245.
  12. Feland JB. Effect of submaximal contraction intensity in contract-relax proprioceptive neuromuscular facilitation stretching. Br J Sports Med 2004; 38(4): e18–e18.
  13. Baltaci G, Un N, Tunay V et al. Comparison of three different sit and reach tests for measurement of hamstring flexibility in female university students. Br J Sports Med 2003; 37(1): 59–61.
  14. Boyd BS, Wanek L, Gray AT, Topp KS. Mechanosensitivity of the lower extremity nervous system during straight-leg raise neurodynamic testing in healthy individuals. J Orthop Sport Phys Ther 2009; 39(11): 780–790.
  15. Gadjosik R, Barney F, Bohannon R. Effects of ankle dorsiflexion on active and passive unilateral straight leg raising. Phys Ther 1985; 65: 1478–1482.
  16. Boland R, Adams R. Effects of ankle dorsiflexion on range and reliability of straight leg raising. Aust J Physiother 2000; 46: 191–200.