Top 100 Biomechanical Guidelines #25: Understand the 3 Measurements taken on a Standing AP Pelvic Xray

Standing AP Pelvis Xray with shoes and orthotic devices

     Look at: Heights at the Acetabulum, Sacral Base, Heights at the Iliac Crests

     As you review this xray, you will see that the the left hip at the acetabulum (hip joint) is higher than the right. This is the true leg length difference if the foot is in its neutral subtalar position (why it is best to take this xray with stable shoes and stable orthotic devices in the shoes). The symbol marked UPRIGHT means standing and is on the left side. The base of the spine where L5 vertebrae rests on the sacrum, also called the sacral base, drops to the right side. One of the last posts discuss how to measure sacral base unleveling. Many feel that getting a level sacral base is more important than correcting the hip height difference.The highest point on the iliac crest, not even seen on the left since it is higher than the right side, is a summation of the pelvic difference. When you look at many points of the pelvis, comparing right to left, you will see how the left is higher all around. However, one of the major problems we face is one of trying to take xrays only when crucial (due to the radiation). I would love to xray after very change I make, but I must be conservative due to the radiation exposure.

     Common Xray Findings Example:

• Hip Height at Acetabulum 10 mm short right (TRUE STRUCTURAL)
• Iliac Crest 17 mm short right (further pelvic and Sacro-Iliac joint collapse)
• Sacral Base 13 mm short right (amount spine needs for leveling)

With these findings, it is easy to start with 1/8th inch lift (3.3mm) for 2 weeks, another 1/8th inch for 2 weeks, and then 3rd 1/8th inch lift for the final 2 weeks. I start with tie-on shoes that take the full 3/8th of an inch. I would then have the patient wear this amount for two months to get use to them. Some time with a physical therapist to work out the predictable muscle soreness that will ensue would be great during this time. After the 2 months, if there is still limb dominance, still some symptoms, then I would go up another 1/8th to correct for the sacral base (the extra 3 mm the xrays showed). Of  course, many stop the correct at lower levels if the symptoms are resolved. Patients can fight you alot during lift therapy since they do want lifts. Who would?? It is important to stay focused, and the xrays really help in this regard. The xrays tell us what is the short side, and by how much. Treatment can be gradual, but complete correction of a short leg is usually obtainable.