An introduction to the anatomy of pelvic pain

2.1 An introduction to the anatomy of pelvic pain

The anatomy of pelvic pain can conveniently be divided into the clinical anatomy and biomechanics of the pelvis (see Chapter 2.2) and the anatomy of the pelvic floor (Chapter 2.3). However, the human body operates as a system (Ahn et al. 2006, Reeves et al. 2007) and cannot be divided quite so simplistically. Each component of the movement system is likely to influence distal and proximal regions, it is modulated by many factors from across somatic, psychological and social domains (Moseley 2007, Fall et al. 2010) and ultimately it is controlled by the central nervous system (CNS). It is therefore important always to remind ourselves not to focus solely on the end organ that we may perceive to be ‘at fault’, particularly as the relationship between pain and the state of the tissues becomes weaker as pain persists (Moseley 2007).

The lumbopelvic spine is encompassed by a dense ligamentous connective tissue stocking (Willard 2007) containing five lumbar vertebrae, sacrum, coccyx and two innominates, which are joined by strong ligamentous attachments posteriorly at the sacroiliac joints and anteriorly at the symphysis pubis. Furthermore, the thoracolumbar junction (T10–L2) can, when stimulated, result in pain perceived in the pelvis, and will also need to be evaluated in patients with chronic pelvic pain (CPP). The stiffness of the spine will be the result of reaction forces acting across it, and is modified by gravity, the shape of the articular surfaces, the actual joint position, proprioceptive muscle reflexes, the level of muscle (co)contractions and increased ligament tension.

European guidelines proposed the following functional definition of joint stability:

To emphasize the importance of muscle and neural control when the muscles of the spine are removed, the spine can buckle with compressive loads of just 90 N (Crisco et al. 1992). The nervous system is therefore likely to coordinate muscle activity to match the internal and external forces placed on the spine in order to meet the demands for stable movement (for a review see Hodges & Cholewicki 2007). Simultaneous co-activation of many muscle groups will increase the stiffness of the spine, but the relative contribution will vary with the task, posture, movement direction and potentially the high real or perceived risk of injury (Cholewicki et al. 1997, 2000, Reeves & Cholewicki 2003). In situations of high real or perceived risk, the CNS may opt to limit the possibility of error and utilize a strategy to stiffen the spine, thus increasing the safety margin; conversely if the threat is low, the CNS could opt to use a more versatile strategy (Hodges & Cholewicki 2007). The lumbopelvic spine therefore forms a key role in the transfer of load from the upper body to the lower limbs, and the stability of the spine and pelvis is a complex, dynamic system with feedback control involving the bony architecture, muscles, connective tissue and the CNS. All anatomical structures that influence the thoracolumbar junction, the lumbopelvic spine and lower limbs may therefore need to be evaluated in patients with CPP. Further details can be found in Chapters 11.1 and 11.2.

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