Concept of Balance

It is a peculiarity of humans that they walk upright. For this to be possible without undue stress on the muscles and ligaments of the body, the axis of gravity must fall within a surface defined by the position of the feet and called the polygon of support.

"Balance" is a property of the body that keeps the axis of gravity within the polygon of support. It is closely related to the shapes and functions of the spine and pelvis. For that purpose, on could consider the pelvis to be part of the spine, a concept called the "pelvic vertebra".

A distinction is made between sagittal and coronal balance. “Sagittal” means the plane seen when looking at the body from its side. “Coronal” means the plane seen when looking at the body from the front or back.

“Sagittal balance” is usually dependent on the concave backward shape of the lumbar spine (the lumbar lordosis).

It can be lost with decrease of the intervertebral disc spaces (as seen with advanced disc degeneration), compression fractures of the vertebras (as seen with osteoporosis), abnormal curves of the spine (as seen in some forms of scoliosis and kyphosis) or with slippage of one vertebra over another (as seen in spondylolisthesis). What happens is that the body leans progressively forward, placing it constantly off-balance (fig. 1).

fig.1

Coronal balance is more forgiving as it would take a significant scoliosis to place the axis of gravity out of the polygon of support sideways. However, lesser degrees of imbalance may place sustained undue stress on the ligaments, muscles and joints, ultimately causing pain. Sacroiliac instability (i.e. sacroiliac dysfunction) relates to coronal balance. Normally, in the coronal (or frontal) plane, the axis of gravity should fall along the axis of the spine, right on the midline of the body (separating right from left), and is at right angle with the axis of the hip joints when the individual is standing straight up (perpendicular with the midline sagittal plane). This ideal situation is called "coronal balance".

fig. 2

Sacroiliac instability causes asymmetry of the pelvic girdle which disrupts the alignment of the hip axis in comparison to the spine axis. This results in undue stress on the ligaments and muscles of the low back with ambulation, causing pain (fig. 2).

Our surgical technique of sacroiliac stabilization aims to optimize the “alignment” of the pelvic girdle in order to maximize coronal balance to the extent possible. This reduces the stress on the ligaments, muscles and other joints of the low back to ultimately reduce or cure the pain.

“Pelvic obliquity” refers to the differential development (from birth) of the sacrum and/or other bones of the pelvis on each side of the midline (i.e. everyone is slightly different from one side of the body to the other). This is not infrequently associated with some degree of scoliosis. Lesser degrees of pelvic obliquity (pelvic asymmetry) may however exist. There may also be some variation (from birth) of the external bony landmarks of the pelvis, making true “alignment” difficult or impossible to detect without x-rays. In fact, x-rays cannot assess ilio-sacral symmetry because of the factors just mentioned and also because a slight variation in posture (due to the presence of pain, spasm and/or posturing) may make the pelvis look uneven. However, x-rays can show how close one is to true coronal balance, which is the ultimate aim of surgery (making one as close to true coronal balance as possible).

It is difficult to assess coronal balance in an un–anesthetized individual whose sacroiliac joint has not been stabilized (by surgical means or other). On the other hand, a stabilized pelvis (with stabilized sacroiliac joints) where the axis of the hip joints is perpendicular (or nearly perpendicular) to the midline sagittal plane of the sacrum and spine (with the individual under anesthesia to avoid spasm and posturing), must necessarily be optimally “aligned” for coronal balance.

Does this tell us anything about what form of treatment might be better for sacroiliac instability?

If the sacroiliac pain is infrequent (maybe occurring weekly or less) and disappears with therapeutic manipulations, one can assume that coronal balance is present when pain-free. In this situation, prolotherapy may be adequate to treat the problem. Prolotherapy (also called regenerative spine injections) consists of injecting an irritant substance (such as Dextrose) in the ligaments of a joint causing an inflammatory reaction followed by healing and tightening. It is similar to the sclerotherapy used for varicose veins for example.

On the other hand, if sacroiliac pain is present all the time, it may be difficult to assess whether or not sacroiliac alignment by manipulations does or does not re-establish coronal balance (as there may be variations in the external bony landmarks as mentioned). In this situation, it is unclear whether or not the legs remain even when standing. Under those circumstances, a surgical stabilization may be preferable.