The effects of manual pelvic compression on trunk motor control during an active straight leg raise in chronic pelvic girdle pain subjects

Abstract

A sub-group of pelvic girdle pain (PGP) patients with a positive active straight leg raise (ASLR) responds positively to the application of external pelvic compression during the test. This study investigated the effect of this phenomenon on electromyographic (EMG) activity of the trunk muscles and intra-abdominal and intra-thoracic pressures in subjects with a unilateral sacroiliac joint (SIJ) pain disorder (n = 12). All subjects reported reduced difficulty ratings during an ASLR with pelvic compression (paired t-test: p < 0.001), yet no statistically significant changes in the muscle activation or pressure variables were found. However, visual inspection of the data revealed two divergent motor control strategies with the addition of compression. Seven subjects displayed characteristics of a decreased EMG profile, while in the other five subjects the EMG profile appeared to increase. As such this study provides preliminary evidence of two disparate patterns of motor control in response to the addition of pelvic compression to an ASLR. The findings may reflect different mechanisms, not only in the response to pelvic compression, but also of the underlying PGP disorder.

Introduction

Compression of the pelvis via a pelvic belt is commonly used in the management of subjects with pelvic girdle pain (PGP) (Ostgaard et al., 1994b, Mens et al., 2000, Nilsson-Wikmar et al., 2005, Haugland et al., 2006). The major benefit of compression from a treatment perspective appears to be the provision of symptomatic relief (Ostgaard et al., 1994b, Mens et al., 1999, Mens et al., 2006a). In some subjects though compression may negatively influence symptoms (Ostgaard et al., 1994b, Mens et al., 1999). An interesting aspect of this dichotomy is reflected in the situation where on one hand compression with a belt can provide symptomatic relief, while on the other hand manual compression is used as a provocation test for sacroiliac joint (SIJ) pain (Laslett et al., 2005). Additionally, it has been proposed that these contrasting responses to compression can be helpful in the identification of sub-groups of patients with PGP (O'Sullivan and Beales, 2007b, O'Sullivan and Beales, 2007c).

A number of studies have investigated mechanisms by which pelvic compression may alleviate PGP symptoms. Compression across the ilium with a belt has been shown to increase SIJ stiffness, as measured by Doppler imaging of vibration, in both pain free (Damen et al., 2002) and PGP subjects (Mens et al., 2006a). Similarly pelvic compression using a belt results in decreased sagittal SIJ rotation in cadaver specimens of the pelvis (Vleeming et al., 1992). These findings suggest that pelvic compression can increase intra-articular compression in the SIJs, augmenting stability of the pelvis and subsequently relieve symptoms by decreasing the load on pain sensitive structures.

Altered motor patterns could also potentially create a mechanism for PGP by abnormally loading pain sensitive pelvic structures. Altered motor control patterns have been detailed in chronic PGP subjects during the active straight leg raise (ASLR) test (O'Sullivan et al., 2002, Beales et al., 2009a). The ASLR is a valid and reliable tool used to assess load transfer through the pelvis (Mens et al., 1999, Damen et al., 2001, Mens et al., 2001, Mens et al., 2002a, O'Sullivan et al., 2002), and is well suited to investigation of both motor control and the effects of pelvic compression. Pelvic floor (PF) descent, diaphragmatic splinting and aberrant respiratory patterns during the ASLR can all be positively influenced with the addition of manual pelvic compression through the ilia during the ASLR (O'Sullivan et al., 2002). These findings suggest that the mechanisms for symptom reduction with pelvic compression may result from augmentation of the active components of pelvic stability (force closure).

We have recently documented motor control patterns in subjects with chronic PGP during an ASLR (Beales et al., 2009a). Subjects in that study demonstrated a predominant motor control pattern of bracing through the abdominal wall and the chest wall (CW), that was associated with increased intra-abdominal pressure (IAP) and depression of the PF when lifting the leg on the affected side of the body. The purpose of this study was to investigate the effect of manual pelvic compression during the ASLR on the patterns observed in those subjects. It was hypothesised that compression would result in a reduced electromyographic (EMG) profile and a reduction in IAP associated with maintaining the ASLR.