Anatomy Slings and Their Relationship to Low Back Pain

 Introduction Stability in the Lumbo-Pelvic Region Myofascial Slings Anterior Oblique Sling Posterior Oblique Sling Evolution has seen human beings develop from quadrupedal into bipedal creatures. This adaptation has allowed us to carry out tasks at a more advanced level than we would have done previously, however, has also brought about changing demands upon the body. This has meant that the body has had to adapt in order to cope with different stresses. With the transformation of humans into upright-functioning beings, the demand upon the posterior structures of the body has changed dramatically, and these have had to adapt accordingly. For example, the gluteus maximus has evolved from a relatively small muscle (as observed in chimpanzees) to being the largest muscle in the body (Vleeming 2012). It has become part of a system which is specialised and integral in supporting functional control in movements such as human gait – the posterior oblique muscle sling (POS). This sling system consists of the latissimus dorsi (LD), the gluteus maximus (GM), and the inter-connecting thoracolumbar fascia (TLF) (Lee 2011). The POS, otherwise known as the back functional line, crosses approximately at the level of the sacro-lumbar junction. The lower portion of the sling, consisting of the distal GM fibres, passes underneath the iliotibial tract to attach to the posterolateral edge of the femur, thus this system becomes linked with the lateral sling (Myers 2013). Within recent decades’ clinicians have begun to identify that stability is a complex phenomenon, and “a system of assisting movement whilst stabilising” exists (Vleeming 1995). The POS is fundamental to this method of functioning.
The role of the POS is most distinguished during the single support (stance) phase of gait. Prior to heel strike, the ipsilateral hamstring muscle contracts in order to prepare the limb for weight-bearing. During this, the proximal hamstring also carries the role of stabilising the ipsilateral pelvis against the activity of the quadriceps, in order to prevent excessive anterior rotation of the ilium. However, once heel strike occurs, hamstring activity diminishes and its role of limiting ilium movement is largely undertaken by the GM. At this point the muscle is in a lengthened position. Simultaneously, counter-rotation of the trunk also begins to takes place. During this process, the arm contra-lateral to the stance leg is ante-flexed, undergoing an eccentric contraction of the LD in order to control the forward momentum of the limb, whilst taking the LD also into a lengthened position (Vleeming 2007; Chek 2011). The propulsive phase of gait then follows, with both the GM and contralateral LD concentrically contracting from a lengthened to shortened position, resulting in extension of the arm with the opposite propelling leg. When these two simultaneously occurring mechanisms are coupled, a contraction of GM alongside its contralateral LD is observed (Chek 2011). As discussed previously, this causes an increase in tension within the TLF, eliciting stabilisation of the SIJ and lumbar spine (Lee). This theory also adds credence to the remark that weakening of the GM aspect of the POS often results in hamstring dysfunction, due to the compensatory activity in order to stabilise the ilium (Sahrmann 2012). As well as the SIJ compressional stability that this system produces through the TLF, some authors also believe that the mechanism acts a ‘smart spring’, using phasic contractions to release and store energy during gait. Vleeming (2007) theorises that kinetic energy is built up in the GM and LD as they lengthen prior to and during heel strike, respectively. This energy is then released as these muscles shorten immediately following the lengthening phase, causing this kinetic energy to be released. A similar response is observed when a finger rapidly returns to a neutral position, when it is released following passive full extension. There is debate surrounding whether this kinetic energy is stored within the muscles or the TLF (Dorman 1992). Regardless of this, it is widely believed that this mechanism reduces energy expenditure of surrounding muscles of locomotion, thus reducing the metabolic cost of gait (Vleeming 2007; Chek 2011). Traditional exercise training to stabilise the SIJ focuses on ‘core’ units, often with the aim of isolating muscles in order to strengthen them. As discussed in the section “Stability in the Lumbo-Sacral Region” the demands upon human beings suggest that strengthening techniques should be incorporated into dynamic movements. Thus, in order to train the POS, the GM and LD should not be viewed in isolation, rather utilised in synergy with each other to promote efficient gait as described previously. A good example of an exercise that can be used for treating POS dysfunction is the reverse lunge. A therapist should utilise this once a patient can achieve pain-free hip motion and satisfactory static stability (Nickelston 2013). A demonstration of this exercise is shown in the video below:
As alluded to previously, it is vital that the muscle slings of the body function harmoniously in order to facilitate efficient movement and prevent injury. This is especially pertinent between the anterior oblique sling (AOS) and the POS. These systems can be viewed similarly to a muscle pair, with an antagonist and an agonist: whilst one is contracting, the other may work to control the movement being produced. An example of this in the AOS and POS is during the swing of a tennis racket. The movement and power is produced by the AOS which causes a rotation and forward movement of the pelvis, trunk and arm. However, the POS is also crucial during this action in order decelerate the movement when appropriate, using eccentric control. This helps to aid an individual in maintaining their balance during a highly dynamic movement such as this, whilst stabilising the lumbo-pelvic hip complex. Deep Longitudinal Sling Lateral Sling How Do These Link to Low Back Pain? Conclusion