Low back pain is a common problem in active populations, but I rarely see runners with back pain—and when I do, it’s often a bone stress injury (BSI).
When a runner reports a gradual onset of unilateral back pain, I’m immediately concerned about a potential sacral stress fracture (SSF). Although rare in the general public, these often occur in endurance athletes — and they’re a bit more complicated than other stress fractures due to the sacrum’s unique nature.
Your sacrum is a wedge-shaped bone forming the backside of your pelvis. When standing, the weight of your body is transferred from your sacrum to your hips, all the way down to your feet. Whether running, picking up your kid, or carrying something overhead, your sacrum and pelvis keep you from toppling over. This load spreads across your sacrum and pelvic bones like a trampoline stretching as a child preps to fly in the air. This coordination is likely why 78% of runners with a sacral stress fracture also have a pubic rami fracture1.
The sacrum (and other pelvic bones) are unique.
These more central bones are much more meshy and web-like internally. This porous nature creates a higher surface area exposed to blood flow2, meaning what’s pumping through your blood vessels has a greater opportunity to influence your bones.
Let’s head to your metaphorical kitchen to highlight why this is important.
Grab your favorite pan, click on a burner and throw a bit of oil into the frying pan. Toss an entire clove of garlic in your pan then a second clove that’s finely diced. Due to the higher surface area, the chopped garlic will cook quicker (and may be more likely to burn). The heat, the oil, and the pan have a quicker influence on the diced garlic versus the whole clove.
Spongy bones act the same way. The inner, meshed network is influenced to a greater degree by your overall health. That’s likely why athletes who’ve sustained stress fractures in bones with more trabecular bone (spine, pelvis, sacrum, hips) were more likely to exhibit disordered eating, menstrual dysfunction and lower bone mineral density3,4.
It’s crucial to understand these deficits may exist if the goal is to return to pain-free running. You can have the best rehab plan in the world, but if it doesn’t investigate these areas it will fall short. When diagnosed with a SSF these areas must be assessed to determine the right course of rehab. A skilled sports medicine physician, endocrinologist, and dietitian can assist with this testing.
There are three different zones of sacral fractures, with runners generally developing the injury throughout zone one.
Runners often report a gradual onset of unilateral low-back pain that worsens with running, jumping, or other weight-bearing activities. They also might report popping, clicking, and audible sounds through the area. Symptoms often feel better when non-weight bearing or with rest. SSFs aren’t the only cause of unilateral back pain, so these conditions should be in your differential diagnosis.
It’s important to understand that many SSFs will be misdiagnosed as SI joint dysfunction. Runners regularly spend frustrated rehab sessions on correcting faulty sacral positions and twisted innominates when their sacrum is broken!
They don’t need muscle energy techniques and exercises. They need crutches.
Laura Opstedal has a great tweet on this topic below. I echoed many of the same sentiments when trying to memorize these confusing charts in school.
So glad this stuff is bullshit bc I didnt understand it anyway 💅🏻 pic.twitter.com/myXmOs4ATo— Laura Opstedal (@LauraOpstedal) June 13, 2017
Clinically, SSFs regularly present with
- Pain with sacral palpation
- A positive FABERs test
- A positive Gaenslen’s test
- A positive squish test
- Painful open chain hip flexion (i.e. marching or ascending stairs)
- Impact (running, plyometrics, etc.)
The only way to diagnose a SSF is with an MRI. Imaging can also help determine the fracture’s severity and your expected timeline for returning to running.
Following diagnosis, the first step is eliminating painful activities, which may include using crutches for ten days to six weeks. Non-impact cross-training is often allowed between 6-8 weeks and finally progresses into a return to run progression5,7.
These injuries are tough! Understanding the role of the sacrum and the importance of a multidisciplinary team in stress fracture management is crucial to get you back to 100%.
Thanks for taking the time to read. If you found this blog helpful I’d love it if you signed up for my monthly newsletter. I’ll write you once a month and keep you up to date on all the latest in running-related injuries and the life of a solopreneuer!
-Nathan Carlson PT, DPT, USATF
- Aretxabala I, Fraiz E, Pérez-Ruiz F, et al. Sacral Insufficiency Fractures High association with pubic rami fractures. Clin Rheumatol. 2000;19:399–401.
- Dalstra M, Huiskes H, Odgaard A et al. Mechanical and Textural Properties of Pelvic Trabecular Bone. Journal of Biomechanics, 26(4-5), 523-535.
- Rizzone K, Ackerman K, Roos K et al. The Epidemiology of Stress Fractures in Collegiate Student-Athletes, 2004–2005 Through 2013–2014 Academic Years. Journal of Athletic Training 2017;52(10):966–975
- Nattiv A, Kennedy G, Barrack M et al. Correlation of MRI Grading of Bone Stress Injuries with Clinical Risk Factors and Return to Play a 5-Year Prospective Study in Collegiate Track and Field Athletes. Am J Sports Med. 2013 Aug;41(8):1930-41.
- Longhino V, Bonora C, and Sansone V. The Management of Sacral Stress Fractures: Current Concepts. Clinical Cases in Mineral and Bone Metabolism 2011; 8(3): 19-23 19.
- Harris C, Vincent H, Vincent K et al. Sacral Stress Fractures: They See You, But Do You See Them? Current Sports Medicine Reports
- Zaman F, Frey M, Slipman C. Sacral Stress Fractures. Current Sports Medicine Reports 2006, 5:37–43.