About this post: Understanding
Spinal Line of Gravity.
Viewing the body from the side, (in the Sagittal view) the standard spinal curves are clearly visible. The head is situated above the pelvis and hips, which in turn, is located above the feet. The Thoracic curve toward the back of the body in the chest region is in stark contrast to the Lumbar curve in the lower back curved to the front of the body. This alignment allows for a comfortable posture while the person is standing.
In this side or sagittal view, a line can be drawn from the head to the feet. This is called the “Spinal Line of Gravity”.
The Spinal Line of Gravity runs from behind the outer ear canal straight down through the femoral heads until they reach the feet just in front of the heel bone. On the journey from head to foot, this line passes through the middle of C7 (last cervical vertebra) and then through the back portion of S1.
Often overlooked, and seldom checked by X-Rays, this vertical line (we may compare it to a plumb line) originates from the middle of C7. It continues downwards and may pass well in front of, or to the rear, of the S1 vertebra. This is a cause of significant strain on the spine and a causing factor in severe back pain.
An experimental test you can do.
Try standing upright, relaxed. Now tilt your torso forward at the hips, say 10-20°. Hold this position for 5 minutes. You will experience significant strain developing in your lower back muscles. Should this posture be held for more extended periods of time, considerable muscle pain and spasm will be experienced.
Spinal Line of Gravity in Lumbar Spinal Fusion surgery.
When lumbar spinal fusion surgery is done, the surgeon needs to ensure the lumbar curve is maintained carefully. The Spinal Line of Gravity may not be disturbed, either to the front or to the rear of the plumbline. This biomechanical principle remains one of the significant challenges facing spinal surgeons. This is especially important when fusing the last lumbar vertebrae to the sacrum.
Spinal Line of Gravity in Obese Patients.
In an obese patient the increased fat deposit of the body as is seen in the abdominal region, further compromised by increased breast size in the obese female patient, is found in front of the spinal line of gravity.
Imagine a person strapping a 10 kg (or more) bag of potatoes to the front of their body. There will be an undeniable force negatively impacting the spinal alignment, pulling the upper torso forward. To accommodate the excess weight and resultant changed posture, the person carrying this extra weight will curve their lower back ( increasing the lumbar lordosis) to get underneath the weight they have to manage. The patient is actually trying to restore the perpendicular line from C7 down to S1.
Spinal Line of Gravity in the Pregnant Patient.
The same happens in the pregnant patient, although the medical advice in these patients would always be to shed the excess weight as soon as possible after delivery. (see back pain in pregnancy)
Patients with Sagittal Structural Malalignment.
Sagittal malalignment may develop because of structural deformities of the spine.
Examples may be Vertebral fractures, Ankylosing Spondylitis, deforming disease like infections to the spine and the dreaded Failed back syndrome after fusion surgery.
These entities will not be corrected by postural improvement, muscle strengthening and stretching exercises.
In many cases, depending on the severity of the condition, additional deformities may develop.
These include Flexion contracture deformity of the hips, Anterior pelvic tilting, knee flexion during standing with the inability to straighten the knees when lying down, even leading to knee flexion contractures.
Such postural changes all contribute to strain on the lumbar spine and if severe enough, be responsible for significant and even crippling pain. Corrective surgery may be required.
Also Read: “Normal and Abnormal Curves“
Credit of Featured Image: florian-van-duyn-383221-unsplash.