In the first of a two-part series, David Joyce explains how injury causes lumbopelvic instability
For the spine and legs to work efficiently, the body needs a stable base. It is estimated that the sacral base has to bear 60% of the body’s weight in standing(1). The body therefore requires an efficient system to absorb and transfer this load across the mobile joints of the pelvis, ie the two sacroiliac joints (SIJs) and the symphysis pubis.
The need for stable shock absorption is even greater among athletes, where shearing loads are much bigger: just think of the vertical forces shooting up the leg and across the sacroiliac joint (SIJ) as the fast bowler hits the popping crease, or the massive vertical loads involved in tasks such as serving in tennis, hurdling or landing from a vault.
The sacroiliac joint (SIJ) derives the necessary stability for these formidable loads through ‘form closure’ and ‘force closure’. Form closure refers to the ‘anatomical fit’ of the unfused joints in the pelvis; force closure is the sum of the compression provided by gravity, muscular and connective tissue systems.
The sacroiliac joint is formed by the wedgeshaped sacrum articulating with its neighbouring pelvic bones (the ‘innominate’). Its relatively flat joint surfaces are optimally adapted for the transfer of large loads. The joint surface alignment, however, is close to vertical, a precarious position under vertical shearing load. The joint therefore needs specialised adaptations in order to properly transfer load without damage. These come by way of a series of ridges and complimentary depressions, plus thick and coarse articular cartilage, which increase joint friction to augment form closure.
Perfect form closure would mean that the sacroiliac joints (SIJs) were incapable of movement. Yet the pelvis needs to be able to make small degrees of movement, so supplementary stability is provided where necessary through active compression: force closure.
The muscular elements of force closure can be divided into the inner and outer muscular units(2). The inner unit is made up of transversus abdominis, multifidus and the pelvic floor. The outer unit is comprised of four muscular slings:
* posterior oblique
* deep longitudinal
* anterior oblique
The muscles contribute to force closure, and thereby the safe transfer of load through the pelvis, in two ways:
1. They augment the compressive forces across the symphysis pubis and sacroiliac joints (SIJs) to reduce the amount of unrestrained joint movement (ie the joint’s neutral zone)
2. They change the position of the joint, producing increased tension in the surrounding ligamentous structures.
The third unit of force closure is provided by connective tissue. Ligaments restrict pelvic mobility to those positions in which the joint can bear weight. For this purpose the most important are thought to be the sacrotuberous, sacrospinous, interosseous, long dorsal sacroiliac and iliolumbar ligaments. Beyond this it is thought that the thoracodorsal fascia (TDF), a connective tissue bridge between the inner and outer muscle units, increases joint compression by transferring muscular contraction forces to the rear part of the pelvis(3).
Motor control is the term used to describe the pattern of timing of muscle contraction and release coordinated by the nervous system. Good dynamic stability is dependent on effective feedback and feed-forward loop interaction between the afferent input and efferent output motor neurons, the aim of which is to control the path of movement (4,5). The body deploys precise muscle-firing sequences in the pelvis to help it transfer load, particularly in tasks that have high vertical shear forces, such as jumping and running.
Injury and load transfer
It is now accepted that active control of vertebral movement at individual intervertebral levels (for example L4/5) is affected by lumbopelvic pain. There is a growing body of evidence that suggests that muscular interplay is also disrupted in people with pelvic dysfunction.
O’Sullivan et al (2002)(6) showed that when patients with sacroiliac joint (SIJ) dysfunction performed an active leg loading test, they had altered breathing patterns and increased downward excursion of the pelvic floor muscles. The corollary is that pelvic injury reduces the amount of load the local stability systems can transfer effectively, causing the body to find aberrant, compensatory motor control strategies to augment force closure.
Hungerford et al (2003)(1) provided further evidence of alterations in muscle recruitment in the presence of sacroiliac joint (SIJ) dysfunction, in particular delayed firing of the internal obliques, lumbar multifidus and gluteus maximus, and premature activation of biceps femoris. The delay in obliques and multifidus activity occurred on the stance limb during hip flexion on both the symptomatic and asymptomatic sides. The authors suggest that the earlier onset of biceps femoris activity may be a compensatory mechanism to augment force closure through its connections on to the sacrotuberous ligament and TDF.
Vogt et al (2003)(7) found a similar delay in gluteus maximus activation during locomotion in subjects with lumbopelvic pain. An aberrant motor control pattern, with the tonic pelvic stabilisers becoming phasic, is thought to be a major reason why the vertical shear forces in activities such as walking, lunging and landing from a jump are commonly seen as aggravating activities in people with pelvic pain.
While there is a paucity of evidence-based diagnostic tests for pelvic dysfunction overall, several features of a disrupted ability to transfer load can be assessed clinically, the most widely reported test being the active straight leg raise (ASLR).
The ASLR examines for a reduced ability to provide enough force closure to raise a leg against gravity, and whether this deficiency can be overcome by means of manual compression. The patient lies supine and they are asked to raise one leg (with knee straight) about 20cm off the bed. They are asked about the effort required to lift the leg compared to the other side. The assessor should pay attention to discrepancies in movement strategies or neuromuscular compensations between sides. If there is a difference (commonly reported as feeling heavier or harder to lift), the assessor can provide some manual compression through the pelvis and the patient is asked to lift their leg again.
A positive test indicates a loss of ability to perform compressive closure. If the patient then ‘braces’ their abdominals (eg by doing a half sit-up) before lifting their leg, and it feels easier or lighter, it indicates that there is a force closure problem and this provides the clinician with the direction for treatment, ie improve lumbopelvic stability and strength.
A second test of the ability of the pelvis to safely withstand vertical loading is the stork (aka Gillet) test. The patient stands on one leg and flexes the knee and hip on the other side. The posterior superior iliac spine (PSIS) of the support leg should remain level with the second sacral spinous process. If the PSIS migrates upwards, this is thought to be attributable to a failure in load transfer. The clinician should also pay attention to the motor strategy used when the client performs this test, by examining the timing and holding capacity of internal obliques, multifidus and gluteus maximus.
The clinician can also make use of other indirect clues to determine a loss of motor control in load transfer. A reduced ability to stand on the affected leg and a positive Trendelenburg sign may indicate inefficient lumbopelvic and hip stabilising strategies; reduced hamstring and hip adductor muscle length and trigger points throughout these muscle groups may point to their excessive use as compensatory pelvic stabilisers(1).
Load transfer is a key role of the pelvis. It is achieved through a combination of form and force closure, conducted by an efficient motor control programme. The neural pattern is altered in patients with pelvic injuries resulting in a decreased ability to transfer loads. This can be assessed using the ASLR test, the stork test and a variety of indirect clinical signs.
Next month: sacroiliac joint (SIJ) dysfunction treatment strategies
1. Hungerford B, Gilleard W and Hodges P (2003) ‘Evidence of altered lumbopelvic muscle recruitment in the presence of sacroiliac joint pain’ Spine 28, 1593-1600
2. Lee D and Vleeming A (2000) ‘Current concepts on pelvic impairment’ In Singer KP (Ed) Proceedings of the 7th Scientific Conference of the IFOMPT (pp118-123) The University of Western Australia, Perth, Australia
3. Vleeming A, Pool-Goudzwaard AL, Stoeckart R, van Wingerden JP and Snijders CJ (1996) ‘The posterior layer of the thoracolumbar fascia. Its function in load transfer from spine to legs’ Spine 20, 753-758
4. Hodges P and Richardson C (1997a) ‘Feedforward contraction of transversus abdominis is not influenced by the direction of arm movement’ Experimental Brain Research 114, 362-370
5. Hodges P and Richardson C (1997b) ‘Contraction of the abdominal muscles associated with movement of the lower limb’ Physical Therapy 77, 1132-1144
6. O’Sullivan PB, Beales DJ, Beetham JA, Cripps J, Graf F, Lin IB et al (2002) ‘Altered motor control strategies in subjects with sacroiliac joint pain during the active straightleg- raise test’ Spine 27, E1-E8
7. Vogt L, Pfeifer K and Banzer W (2003) ‘Neuromuscular control of walking with chronic low-back pain’ Manual Therapy 8, 21-28