Wednesday, January 1, 2003

The Sacral Base Angle (SBA) Verifying Data To Prove Chiropractic

© 2003 by Dr. Tim Maggs

Chiropractic has built a reputation on the chiropractor's ability to both locate and eliminate spinal subluxations. While this claim makes our profession unique, we also must respect the fact that there are many different methods used to both locate and correct these spinal distortions.

Just as chiropractic throughout the years has fought for the privilege to be different from the mainstream, it seems necessary at this time of diversity in our profession to allow all clinically acceptable methods and let each and every chiropractor choose the method most suited for them.

The downside in this effort, however, is with the educational and marketing of our profession to the mis-informed public. We live in a society that is subtly educated through many marketing and advertising means, societal pressures and quick and easy, palliative methods. For chiropractic to ever become a force in the healthcare community, it seems imperative for us to find common ground with sound clinical evidence-based protocols that all chiropractors use to educate their patients and their communities. When this can be achieved, a powerful momentum will help to elevate our message in a very positive way.

Currently, our profession has practitioner's who use muscle testing to locate subluxations. Others use x-rays, while still others use palpation. Some prefer leg-length checks while others base their decision on location of pain. There are still more means used today, but the point is that we have no uniformity. We'd impress ourselves if we could ever get 10 random chiropractors to agree on what constitutes a subluxation on an x-ray. And, until we find this uniformity, we will continue to be our worst enemies in helping our profession to grow.

The Sacral Base Angle

Standing x-rays provide a wealth of information for both diagnostic and educational purposes. One of the more important measurements a chiropractor can use in their practice is the sacral base angle. This is the angle formed with a line drawn along the top of the sacrum and intersecting with another line parallel to the ground (Fig. 1). A normal sacral base angle is 36°-42°. Of course, this should only be measured when the subject is x-rayed in the standing position with shoes off.

The importance of the sacral base angle is huge when considering your patient from an engineering, or architectural perspective. When the angle is increased or decreased from normal, there will be a significantly reduced capacity of the low back over the life of that patient. Secondly, imbalances and abnormal weight distribution have been shown to accelerate degenerative changes in the over-burdened joints. The sacral base angle is also important when determining the extent of work needed on a patient. Regardless of the location of the spinal condition a patient is suffering with, the sacral base angle will play an important role in insuring maximum recovery for the patient. If this angle doesn't become part of the initial examination, it's impossible to know what the accurate prognosis and recommendations should be. Thirdly, it's critically important to collect data for the verification of the benefits of chiropractic care, and this measurement provides a solid reference point to measure benefits of treatment. If an abnormal sacral base angle can be found on the initial exam and the patient is put through a corrective treatment/conditioning program and improvements can be seen on re-x-rays, that becomes powerful evidence-based protocols that will get the attention of the medical community. And if this protocol can be duplicated and shown to be directly associated with pain relief and improved capacity, then chiropractic will have a much stronger stance in the medical community, as well as with the eyes of the general public.

What Influences the Sacral Base Angle

First of all, there are many, many factors that influence the exact angle of a person's sacral base. What we now know is that the efficiency of the low back architecture in a person is much greater from an engineering point of view when the sacral base falls between 36°-42°. If the angle is outside this range, the efficiency of the supportive joints and tissues goes down proportionately, and increases the vulnerability of the individual with regard to injury and degenerative potentials in their life.

The most influencing factors affecting the sacral base angle are heredity, prior injuries, poor conditioning, foot imbalances, leg length differences, weight problems, bad habits, poor posture, job, mattress, shoe style and quality, diet and frequency of getting adjusted. There certainly are many other influencing factors, but from a practical point of view, we must efficiently work with those we know and can improve upon.

One of the greatest influences of the sacral base angle is the biomechanics of the feet. If there is bilateral pronation, bilateral supination or imbalances in the arches of the feet, then correction of an abnormal sacral base angle becomes more difficult. A thorough foot evaluation (Fig. 2) will highlight any of the possible contributing factors from the feet. If an abnormal sacral base angle is present, any abnormal findings found on the foot exam would indicate the need for custom-fitted orthotics. These will allow the foundation of the body, the feet, to provide a balanced support for the re-education and improvement of the supportive structures that will encourage improvement in the sacral base angle.

Further evaluation would consist of a visual exam in the standing position, active range of motion of the lumbo-sacral spine, muscle testing for strength and flexibility, Lasegue's, Bilateral Leg Lowering, Patrick-Fabere, Gaenslen's and leg length measurement. Of all tests performed, the most valuable is the standing x-ray. The lateral view will provide the exact measurement we're looking for. This measurement becomes impossible to determine when there is a sacralization or lumbarization present.

Abnormal Sacral Base Angle

When an abnormal sacral base angle is found on x-ray, it usually accompanies some low back symptoms. The correction of this condition, not just the elimination of symptoms, becomes the objective. As seen in (Fig. 3), there is a 56° angle. This young athlete went through a 6 month corrective program, consisting of 40 chiropractic adjustments, a detailed strength and flexibility program, a muscle management program allowing him to increase blood flow to involved muscles with the Intracell Stick® (Fig. 4) and was fitted for custom-fitted orthotics, which he wore full time. The result is a significant improvement in his follow-up x-ray 6 months after beginning the program. The sacral base angle was reduced to 43° (Fig. 5) and the patient improved greatly from a symptomatic and functional point of view.

Medical Research

The importance and value of the SBA might be seen in a medical study1 performed on 40 members of a cycling club who had experienced low back pain. Serial fluoroscopic studies were performed on the lumbo-sacral region of 30 club cyclists who did not have back pain to assess baseline parameters while they cycled on different types of bicycles.

Forty members (both male and female with no ages given) with intermediate intensity low-back pain were divided into 2 groups (20 members each) and cycled with seats that had an anterior angle of inclination of between 10°-15°. (An angle of greater than 15° caused discomfort and slipping from the seat). The cyclists were seen again after 6 months of cycling and questioned about back pain.

72% reported improvement in the incidence and magnitude of pain, and 20% reported major improvement. No statistically significant correlation was found in the type of bicycle, gender, age, distance cycled per week or the angle of the inclination. The authors of this study claim that anterior angling of the saddle represents one step that the general public can take to reduce the incidence and severity of low-back pain.

Comment on the study from medical authority

"The authors devote relatively little explanation to why depressing (or, for that matter, elevating) the seat angle takes pressure off the sacral promontory, and why decreased pressure should benefit nonspecific low-back pain. Thus assessing the plausibility and validity of the results is difficult. Given the study's lack of blinding or a control, the results should be viewed as preliminary; however, they do provide some concrete advice for physicians to prescribe for recreational cyclists with back pain: Depress the front edge of the seat 10°-15° from the level position. Explaining to the patient why this works is another matter. In addition, the authors note the inevitable trade-off between comfort and performance: Although an anterior tilt may not be optimal for performance, it may offer relief for cyclists with back pain. This study provides an intriguing clinical observation with a potential biomechanical explanation and is worthy of further study and preliminary clinical use."

Thomas Schwenk, M.D.
Ann Arbor, Michigan


It's important to recognize that no other healthcare profession uses biomechanical information, such as the SBA, to assess patient status or to use the information in constructing a corrective program. Chiropractors would do well to standardize the use of this finding on all exams, as this finding provides valuable architectural information when talking about protecting a structure over the life of any patient. It also becomes a starting point that can be measured against in the future.

The above medical study is almost in conflict with the body of knowledge that medicine lives by, as they primarily look for pathology and treat pharmaceutically or surgically. Nowhere in their procedures do they look for structural imbalances or do they allow for structural rehabilitation, while that is exactly what chiropractic professes. With these types of findings, chiropractors can begin the process of standardizing the tests that we use and the findings we get in an effort to educate and help many more people. This is just the beginning.

1Salia M., Brosh T, Blankstein A, et al; Effect of changing the saddle angle on the incidence of low back pain in recreational bicyclists. Br J Sports Med 1999; 33(5): 398-400

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