Research Review by Dr. Shawn Thistle©

Date:

Sept. 2008

Study Title:

Do “sliders” slide and “tensioners” tension? An analysis of neurodynamic techniques and considerations regarding their application

Authors:

Coppieters MW; Butler DS

Authors’ Affiliations:
  • Coppieters - Division of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland, Australia
  • Butler - Neuro-Orthopedic Institute, Adelaide, Australia

Publication Information:

Manual Therapy 2008; 13: 213-221.

Summary:

Peripheral nerve entrapment disorders such as carpal tunnel syndrome (CTS) or cubital tunnel syndrome are becoming more widely recognized and treated by manual therapists. Despite this, current clinical research regarding non-invasive treatment for these conditions is sparse, and treatment modalities are often poorly documented.

Anecdotally, many therapists successfully treat a variety of peripheral nerve entrapment disorders with soft tissue techniques such as Active Release Techniques®, Trigenics®, and the like. The goal of this cadaveric, biomechanical study was to attempt to quantify longitudinal excursion and strain in the median and ulnar nerves at the wrist and elbow during different nerve gliding exercises. Such exercises are often used in the treatment of nerve entrapments, and it would be clinically useful to know which techniques are the most effective.

In a recently published Cochrane review on conservative treatments for CTS (1), the efficacy of traditionally used modalities for CTS was brought into question. Of note, this review did not include most of the studies published on nerve gliding exercises, which have been favorably included in other reviews on the topic (2, 3). Overall, the literature is controversial – some authors recommend the use of nerve gliding, while others do not.

Nerve Gliding

The nerve gliding/sliding exercises studied to date attempt to induce sliding of the median nerve relative to its surrounding structures by performing joint movements that elongate the nerve bed. It has been suggested that lengthening the nerve bed elongates the nerve, which in turn increases nerve tension and intraneural pressure. With sustained increases in nerve tension, it is reasonable that intraneural blood flow may be reduced.

With a dynamic variation in the pressure (as with nerve gliding exercises which alternate joint positions to “slide” the nerve), evacuation of intraneural edema may be facilitated, which in theory should reduce symptoms. Alternatively, increased nerve strain may cause ectopic discharges from mechanoreceptors, theoretically increasing symptoms. Thus, a proper balance must be achieved, which is the goal of nerve gliding.

This can be accomplished by elongating the nerve bed at one joint while simultaneously counterbalancing that with a reduction in nerve bed length at an adjacent joint (i.e. a “sliding” technique). These techniques aim to mobilize the nerve with minimal increase in tension. Alternatively, a “tensioning” technique would apply tension to either end of a nerve bed simultaneously.

Study Methods:

  • two embalmed male cadavers were utilized
  • a digital Vernier caliper was used to measure longitudinal excursion of the median and ulnar nerves in relation to surrounding structures
  • a fixed marker was screwed into the humerus, while a mobile marker (a suture) was placed around each nerve
  • linear displacement transducers (1.5 micro-meter resolution) measured strain in both nerves
Median Nerve:
  • Starting position for the median nerve: arm in 10° of shoulder abduction, elbow in submaximal extension (170°), forearm supinated, and wrist in neutral position (0°)
  • Tensioning Technique: consisted of simultaneous wrist extension (from 0-60°) and elbow (from 90° to 165°), followed by a return to the starting position (full elbow extension was defined as 180°)
  • Sliding Technique: consisted of alternating elbow extension (loads the nerve) and wrist flexion (unloads the nerve) with elbow flexion and wrist extension (ROM identical to tensioning technique)
Ulnar Nerve:
  • Starting position for the ulnar nerve: 90° shoulder abduction, 90° elbow flexion, neutral wrist position
  • Tensioning Technique: with the wrist in 60° of extension, the elbow was flexed from (150° to 65°) and the shoulder abducted (from 60° to 100°), with the forearm supinated)
  • Sliding Technique: consisted of elbow extension (unloads the nerve) and shoulder abduction (loads the nerve) with elbow flexion and shoulder adduction (ROM identical to tensioning technique and wrist was in 60° of extension)
Pertinent results of this study include:

Median Nerve:
  • longitudinal excursion at the wrist was nearly twice as large for the sliding technique (12.6 mm) versus the tensioning technique (6.1 mm)
  • paradoxically, longitudinal excursion at the humerus was larger for the tensioning technique (16.1 mm) versus the sliding technique (11.1 mm)
  • strain in the median nerve at the wrist remained constant during the sliding technique (0.8%) whereas it varied strongly during the tensioning technique (6.8%)
  • peak strain was significantly larger in the tensioning technique (+ 4.7%) compared to the sliding technique (+ 2.7%)
Ulnar Nerve:
  • excursion of the ulnar nerve with the sliding technique was approximately double that of the tensioning technique (8.3 vs. 3.8 mm)
  • changes in strain were minimal with the sliding technique (similar to the median nerve)
  • due to buckling of the nerve in the relaxed position of the tensioning technique, accurately determining the strain during this motion was not possible

Conclusions & Practical Application:

This study clearly demonstrates that different types of nerve gliding exercises have largely different mechanical effects on peripheral nerves. Longitudinal motion and strain were both largely influenced by particular joint movements, and positions at adjacent joints.

To illustrate, wrist extension resulted in a nearly 9mm excursion of the median nerve at the wrist, which was increased to over 12mm if accompanied by elbow flexion. Further, this study showed that large amounts of nerve movement can occur with very little nerve strain. These finding was consistent between the two cadavers, and make intuitive sense. As suspected, strain was larger during the tensioning techniques, where simultaneous lengthening of the nerve beds occurred at adjacent joints.

These findings, when taken together, suggest that sliding techniques may be appropriate for post-surgical cases, acute injuries, and cases where the nerve may be entrapped or surrounded by bleeding or inflammation.

What this study cannot clarify is the contention that nerve sliding exercises can dynamically “pump” or “milk” the nerves, thus reducing intraneural inflammation; nor whether these exercises can prevent fibroblastic activity or scar tissue formation around nerves. Although in theory nerve gliding exercises could affect both of these parameters, further study is required.

Nerve sliding techniques involve large amplitude movements, can be performed actively or passively, are non-aggressive and generally do not provoke symptoms, and can be easily incorporated into active home care for patients. They can also have the added benefit of reducing fear of movement in patients with peripheral nerve conditions. Clinicians should become familiar with these techniques, and use them as simple additions in their treatment plans.

An obvious limitation of this study is that only two cadavers were used. It should be noted however, that similar trends were observed for both nerves in both cadavers, with no indication that the findings are not representative. Future research on this interesting aspect of manual medicine will further clarify the benefits of this type of intervention.

Additional References:
  1. O’Connor D, Marshall S, Massy-Westropp N. Non-surgical treatment (other than steroid injection) for carpal tunnel syndrome. The Cochrane Database of Systematic Reviews 2003; 1: CD003219.
  2. Michlovitz SL. Conservative interventions for carpal tunnel syndrome. JOSPT 2004; 34(10): 589-600.
  3. Muller M et al. Effectiveness of hand therapy interventions in primary management of carpal tunnel syndrome: A systematic review. Journal of Hand Therapy 2004; 17(2): 210-218.