Pettibon Treatment in Lakewood
Normal vs. Abnormal
Like any physiologic process, the spine and posture must also possess a normal measurement. Just as blood pressure, serum cholesterol, body temperature, and blood pH have normal values, so too must static spinal structure. The spine serves two distinct functions:
1) provide protection for the spinal cord, and
2) provide structural support for the bony frame.
In providing this structural support, one common denominator exists for all upright bipedal mammals: gravity. Given that gravity is a constant on Earth, a corollary to the second spine function is that it also serves to adapt to gravity, while allowing for a balance between support and flexibility. Various authors have attempted to identify a normal spinal model.5,9,10,11 Most recently, Harrison et al.5,17,20,26 and Troyanovich et al.44 outlined their definition of a normal sagittal spine by using elliptical shell modeling. They conclude that the normal cervical curve should be a 42.5º arc of a circle from C2-C7, the thoracic kyphosis should be a 44.2º ellipse when measured from T1-T12, and the lumbar spine should be a 39.7º ellipse from L1-L5. According to Kapandji27, each of these three areas should measure 45º arcs of a circle. The inherent problem with an ellipse is the fact that an ellipse contains a stress point. The arc of a circle, on the other hand, is radially loaded, meaning that an arc does not contain stress points. When modeling the lumbar spine as an arc instead, as Kapandji27 does, each of the lumbar segments bears the weight of the trunk uniformly. Therefore, it seems logical to use the Kapandji spinal model as a clinical goal compared to sagittal ellipses. The spinal model proposed by Pettibon,38 adapted from the parameters identified by Kapandji,27 is pictured in Figure 1.
In discussing the concept of a normal spine, it is also important to address the idea of clinical symptoms in spine correction. Although clinical trials have not been conducted, theoretical models have attempted to demonstrate the inevitable result of chronic abnormal spinal loading. For example, a forward head posture can reverse the stresses placed upon the cervical spine. This causes degenerative changes at the anterior portion of the mid and lower cervical spine due to increased compressive force at these areas.19,21 It also creates traction stress along the posterior longitudinal ligament, thereby promoting traction spur development. This concept is supported in a recent study by Wiegand et al.,45 where abnormal changes in cervical spine configuration correctly predicted cervical pathology 79% of the time. A significant relationship has also been shown between cervical spine pathology and symptoms. Ironically, although cervical pathology may be present with abnormal cervical spine structure, the relationship between an altered cervical spinal structure and clinical symptoms is tenuous at best.36 However, it could be postulated, as in the case of scoliosis progression,48 that because the cervical spine pathology may develop slowly over time, the body continuously adapts to the abnormal position and advancing pathology. Therefore, symptoms do not develop until a critical point has been reached, such as neuroforaminal stenosis or spinal canal stenosis, eg. cauda equina syndrome.
The ultimate purpose of identifying a normal spine and posture is simply to provide a reference point from which a clinical goal can be developed. Spinal correction as a clinical goal and outcome is becoming more important and necessary in a society where musculoskeletal complaints total nearly $50 billion in health care spending annually.6 With the growing interest occurring in spinal correction, consensus on a normal sagittal spine is desirable so that randomized trials and outcome assessments in the clinical setting can be designed and tested.