Sacrum: Definition and What it is

Medically and clinically reviewed by Jonathan Lee, MD and Dylan Peterson, PT, DPT

Sacrum Definition and Meaning

The sacrum is a triangular-shaped bone located at the base of the vertebral column, connecting the spine to the pelvis. The sacrum forms the back wall of the pelvis, protecting and supporting vital body parts, such as the bladder, rectum, and reproductive organs.

Anatomy of the Sacrum

The sacrum is formed by the fusion of five vertebrae, labeled S1 to S5. It’s located between the lumbar spine (low back) and the coccyx (tailbone). 

Function of the Sacrum

The sacrum’s primary function is to transfer the weight of the upper body to the lower limbs by distributing the forces generated during activities like standing, walking, and running. The sacrum also serves as an anchor point for several muscles and ligaments that aid in movement. The sacroiliac (SI) joints, located where the sacrum connects to the pelvis on each side of the body, provides stability to the lower back and pelvis. Muscles, such as the gluteus maximus and piriformis, attach to the sacrum, contributing to posture, movement, and overall spinal support.

If any of the muscles or ligaments that attach to the sacrum get injured, irritated, or inflamed, it can lead to conditions that affect the sacrum, causing discomfort, pain, and changes in mobility. Common conditions include: sacroiliac (SI) joint pain, which often results in low back and butt pain that can make even sitting and walking uncomfortable; and piriformis muscle pain (or syndrome), which can occur when the piriformis muscle becomes tight or inflamed, irritating the nearby sciatic nerve and causing pain that radiates down the leg (similar to sciatica).

Sacral Pain: A Hinge Health Perspective

Musculoskeletal conditions that affect the sacrum, particularly those that contribute to back pain, can feel frustrating, upsetting, or even a little hopeless, especially if the pain persists or interferes with your daily activities. No matter how bad your back pain is, or how long it’s been going on, you can always do something to help improve it. 

If you’re reluctant to move because you think you’ll cause more damage or injury to your back and lower body, know this: Movement is often the fastest way to healing. As our Hinge Health care team says, movement is medicine. Movement helps rehab the muscles, tendons, and ligaments that connect to the sacrum by increasing blood flow and gradually improving strength and flexibility.

Physical therapy can aid in the treatment and recovery of many sacrum-related conditions. A physical therapist (PT) can show you specific stretching and strengthening exercises for your low back, buttocks, hips, and legs that may help relieve pain, improve mobility, and restore function. You can see a physical therapist in person or use a program like Hinge Health to access a PT via telehealth/video visit.

How Hinge Health Can Help You 

If you have joint or muscle pain that makes it hard to move, you can get the relief you’ve been looking for with Hinge Health’s online exercise therapy program.

The best part: You don’t have to leave your home because our program is digital. That means you can easily get the care you need through our app, when and where it works for you. 

Through our program, you’ll have access to therapeutic exercises and stretches for your condition. 

Additionally, you’ll have a personal care team to guide, support, and tailor our program to you. See if you qualify for Hinge Health and confirm free coverage through your employer or benefit plan here.

This article and its contents are provided for educational and informational purposes only and do not constitute medical advice or professional services specific to you or your medical condition.


  1. Sattar, M. H., & Guthrie, S. T. (2020). Anatomy, Back, Sacral Vertebrae. PubMed; StatPearls Publishing. 

  2. Vorvick, L. J. (2023, April 27). Sacrum. MedlinePlus. 

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