A pilot study of the manual force levels required to produce manipulation induced hypoalgesia

Abstract

Objective. A pilot investigation of the influence of different force levels on a treatment technique's hypoalgesic effect.

Design. Randomised single blind repeated measures.

Background. Optimisation of such biomechanical treatment variables as the point of force application, direction of force application and the level of applied manual force is classically regarded as the basis of best practice manipulative therapy. Manipulative therapy is frequently used to alleviate pain, a treatment effect that is often studied directly in the neurophysiological paradigm and seldom in biomechanical research. The relationship between the level of force applied by a technique (e.g. biomechanics) and its hypoalgesic effect was the focus of this study.

Methods. The experiment involved the application of a lateral glide mobilisation with movement treatment technique to the symptomatic elbow of six subjects with lateral epicondylalgia. Four different levels of force, which were measured with a flexible pressure-sensing mat, were randomly applied while the subject performed a pain free grip strength test.

Results. Standardised manual force data varied from 0.76 to 4.54 N/cm, lower–upper limits 95 CI, respectively. Pain free grip strength expressed as a percentage change from pre-treatment values was significantly greater with manual forces beyond 1.9 N/cm (P=0.014).

Conclusions. This study, albeit a pilot, provides preliminary evidence that in terms of the hypoalgesic effect of a mobilisation with movement treatment technique, there may be an optimal level of applied manual force.
Relevance

This study indicates that the level of applied manual force appear to be critical for pain relief.

Introduction

Despite an emerging evidence base for manual therapy in the treatment of musculoskeletal disorders, little is known about the mechanisms through which manual therapy achieves its clinically beneficial effects [1]. Research of the effects and mechanisms of manual therapy appears to be compartmentalised into two paradigms: biomechanical or neurophysiological [2], [3]. Manual therapy is frequently sought and provided for relief of musculoskeletal pain [4]. Interestingly, the direct pain relieving effects have been largely studied in the neurophysiological paradigm and not in the biomechanical.

The biomechanical approach to studying manual therapy has followed two discrete paths, one for high velocity thrust techniques and the other for mobilisation treatment techniques. In brief, the biomechanical study of high velocity thrust techniques has focused on quantifying the forces used by practitioners during the execution of the treatment technique, and investigating the relationship between the applied manual forces and various outcomes of the treatment technique [2], [5], [6]. For example, this research has shown that there is significant variation in the forces that are used when manipulating the different regions of the spine; that the audible release (i.e., joint cracks and pops) that occurs with high velocity thrust techniques is inconsistently related to the applied forces; and that electromyographic activity of a muscle was increased during manipulation [2], [7], [8], [9]. In contrast to research on high velocity thrust techniques, and with few exceptions, biomechanical analysis of mobilisation therapy has used a mechanised treatment technique applicator [10], [11]. Although the use of a mechanical treatment technique provides a consistent standardised force, which is desirable in the study laboratory, its application has been restricted to posteroanterior mobilisation techniques of the thoracic and lumbar spines. Some examples of the findings of this research to date are that induced motions occur at spinal regions beyond that of the treatment segment and that with higher rates of application there is a considerably increased stiffness at the local motion segment being treated [10]. To date, the relationship between the biomechanics of a manual therapy treatment technique and its direct initial pain relieving effects has not been investigated [3].

Biomechanical research to date has focused on spinal techniques. Peripheral treatment techniques have largely been ignored. This is somewhat surprising since it would seem that peripheral joints would appear easier to visualise and measure biomechanically.

Recently, a new type of treatment technique, mobilisation with movement, has been developed [12]. Mobilisation with movement treatment techniques are particularly remarkable because they exert strong hypoalgesic effects as demonstrated by several single case studies, case reports and clinical trials [13], [14], [15], [16], [17]. The lateral glide treatment technique of the elbow in subjects who had chronic lateral epicondylalgia has been the focus of these studies. The lateral glide treatment technique involves the application of a lateral glide across the elbow joint complex, which is then held while the patient performs a pain-provoking manoeuvre such as a gripping action or movement of the elbow. Technically, in its clinical application, the success of the mobilisation with movement treatment technique appears to depend upon the accurate localisation of the manual contact, the amount of force application and the direction of the force application.

Classically, lateral epicondylalgia is characterised as pain over the lateral epicondyle, a painfully weak gripping action, and tenderness to palpation over the lateral epicondyle [18]. Grip strength testing invariably reveals the reproduction of pain and weakness and identifies the predominant functional impediment of this condition.

The aim of this pilot study was to test the assertion that the amount of manual force applied during the mobilisation with movement of the elbow was a critical factor in the technique's ability to produce hypoalgesia.