Why does the upper buttock step form — this concern is a cosmetic challenge that often persists no matter how slim a person becomes or how much weight they lose. A horizontal depression just below the waist, over the sacrum, can make the entire back view appear “flat” and make the hip line look as though it is sagging. At our clinic, the number of patients visiting with the upper buttock step as their chief complaint has been rising year after year. In this column, Dr. Moriwaki explains the true causes in medical detail, from the anatomy of the lumbo-sacral junction to the way subcutaneous fat is distributed.

The True Identity of the Upper Buttock Step — Anatomy of the Lumbo-Sacral Junction

This depression is anatomically located in what is called the lumbo-sacral junction. It sits at the boundary between the 5th lumbar vertebra and the 1st sacral vertebra, just above the posterior superior iliac spine (PSIS) of the pelvis.

This region is also an anatomical “seam” where the insertion of the erector spinae muscles (multifidus and longissimus) meets the origin of the gluteal fascia. Skeletally, the sacrum tilts slightly backward, and the lumbar spine above it curves forward (lumbar lordosis). In other words, the skeletal architecture itself makes this area prone to surface irregularities from the start.

Skeletal Factor — Sacral Tilt and Lumbar Lordosis

In patients with strong pelvic anterior tilt, lumbar lordosis is exaggerated and the inflection point at the lumbo-sacral region deepens. In such cases the upper buttock step is structurally accentuated and cannot be fully erased by removing fat alone. Skeletally derived depressions must be understood as something that will remain to some degree, since the bones themselves cannot be repositioned.

Fat Distribution Factor — The Thickness of the Superficial Layer of the Lower Back

On the other hand, when the superficial fat over the lumbar back becomes thick, the “bulge above the step” is exaggerated and the depression becomes more visible. Asian women in particular tend to accumulate fat across the lumbar back and over the sacrum, and are anatomically more prone to this kind of irregularity than their Western counterparts.

Can the Upper Buttock Step Be Improved by Liposuction?

In short, many cases of the upper buttock step can be improved by liposuction, but not every case can be erased completely. Poor surgical design can even accentuate the depression instead of softening it.

In lumbar liposuction, the “bulge above the step” must be aspirated as a sheet from the superficial layer, while fat should be preserved — or actively reinjected as a fat graft — into the upper hip area below the step. This combination of subtraction and addition is essential. At our clinic we refer to this design as “lumbo-sacral line formation.”

Suitable Cases

· Patients with a thick superficial fat layer over the lumbar back, with a pinchable fat thickness of 2 cm or more

· Patients whose pelvic tilt is not extreme and whose dominant cause is fat-based

· Patients in their 20s to early 40s with preserved skin elasticity

Cases With Limited Indication

· Patients with a strong congenital sacral tilt and a skeletally deep depression

· Patients whose skin has overstretched after repeated weight fluctuations

· Patients with extremely thin lumbar back fat that cannot be pinched

Our Clinic’s Surgical Design for the Lumbo-Sacral Region

At our clinic, we take a composite approach to the upper buttock step. First, VASER liposuction is used to three-dimensionally aspirate the superficial fat over the lumbar back and the lower lateral abdomen, eliminating the bulge above the step. Then, if needed, fat is grafted into the upper hip area to reinforce the volume below the step. This creates a three-dimensional, feminine lumbo-sacral line that traces a beautiful S-curve when viewed from the side.

For patients with reduced skin elasticity, we add post-operative skin tightening treatments such as RF or Morpheus8 Burst to promote skin contraction and prevent residual irregularities. The degree to which we can three-dimensionally design “where to aspirate, where to preserve, and where to add” largely determines the final result.

Self-Care and Cautions to Avoid Worsening the Step

Patients with strong pelvic anterior tilt may reduce the visual impact of the step by incorporating iliopsoas stretching and gluteal training (such as hip lifts). In daily life, it is important to avoid prolonged sitting and to keep the pelvis upright.

However, self-care alone cannot fully erase a lumbo-sacral depression, so for those with significant concerns, consultation with a specialist is recommended. For standards of safety in aesthetic surgery, please refer to the Japan Society of Aesthetic Surgery.

For more detailed articles on liposuction and breast augmentation, please see our related liposuction column index.

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Medical Supervisor: Shin Moriwaki, MD

Member, Japan Society of Aesthetic Surgery (JSAS) / Member, American Academy of Aesthetic Medicine

ECFMG Certificate (US Medical License Qualification)

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