When Tyler Pennel revealed, a few weeks after his brave effort in the OT marathon, that he had joined the sacral stress fracture “club” (Emily Infeld, Emma Coburn, Ryan Vail, Gabe Grunewald, Kara Goucher…to name just a few) we decided to seek an expert’s analysis of this injury.

We hit a home run when Emily Kraus, MD (Clinical Assistant Professor and PM&R Sports Medicine Physician, Department of Orthopaedic Surgery, Stanford University) and Michael Fredericson, MD (Director, PM&R Sports Medicine,; Professor, Orthopaedic Surgery; Director, Non-Operative Sports Medicine Fellowship Program, Stanford University) agreed to step up.

by Emily Kraus, MD & Michael Fredericson, MD for AthleteBiz

As a runner, given the diagnosis of a “stress fracture” is a disheartening moment, because you know it typically means a huge shift in that season’s training and goals. As one might expect, the diagnosis usually happens in the heat of training, just when an athlete is finding his or her rhythm. When the stress fracture is located in the tailbone (or sacrum), it can be even more shocking and confusing for the athlete. Sacral stress fractures have plagued the most elite of runners. Below are just a few of the many examples:

Kara Goucher was sidelined by the injury in 2014 and it took months before she was back to running and even longer before she felt she had returned to her pre-injury level of fitness.

Emily Infeld experienced two sacral stress fractures over two years, but was able to bounce back and clinch the bronze medal at the 2015 IAAF World Championships.

Mario Fraioli, a successful running coach, former elite athlete and experienced sports writer sustained several sacral stress fractures (three to be exact) during the peak of his training. His earlier blog entries share his initial symptoms and then eventual diagnosis.

Stress fractures of the foot or leg bones are somewhat understandable, but why are runners getting fractures in their tailbone? In this article, I will define sacral stress fractures; discuss risk factors, symptomatic presentation, diagnostic work-up, management, and finally prevention strategies.

“Insufficiency” versus “Fatigue” Fractures

A stress fracture occurs when a bone fails to withstand repetitive forces (such as the impact experienced when running) over time. This can be divided further into insufficiency fractures and fatigue fractures. Insufficiency fractures usually occur when an elderly patient (usually with osteoporosis) sustains a normal stress on a weak bone, such as during a fall. A fatigue fracture is when abnormal stress is placed on a normal, healthy bone. Interestingly, many athletes who develop sacral stress fractures demonstrate qualities of both insufficiency and fatigue fractures, highlighting the importance of addressing both.

The Anatomy

The sacrum (or tailbone) is a triangular, wedge-shaped bone, adding stability to the pelvis (figure 1).

Stress fractures can occur in 3 zones (figure 2). Most fractures occur in Zone 1, which includes the sacral ala (wing). Zone 2 involves the sacral foramina (openings where the spinal nerves exit). Zone 3 involves the central sacral canal and can cause more severe neurologic injury.

Risk Factors

Sacral insufficiency fractures are often seen in osteoporotic elderly females or in males or females with chronic diseases which impair bone formation. It can also be seen in pregnant and lactating women.

Sacral fatigue fractures usually occur in younger, active athletes. Potential causes are listed in table 1

Table 1 – Causes of Sacral Stress Fractures Leg length discrepancy Repetitive stress or weight-bearing exercise Weak supporting muscles of the hips, glutes, low back Changes in physical demands, environment, footwear, training intensity Increased stress on the sacrum from pelvic anteversion (i.e., a forward rotated pelvis) Female athlete triad*

* The female athlete triad consists of low bone mineral density, low energy availability with or without disordered eating, and menstrual irregularities (absent or infrequent menstrual cycle or delayed onset of first period)

Symptoms and Making the Diagnosis

One of the challenges with a rapid diagnosis (and earlier start to rehab) is the vague presentation. Athletes may report low back, buttock, or hip pain, usually worse with weight-bearing activity. Depending on the fracture location within the sacrum, there could be a pinched nerve with symptoms of shooting pain down the leg. Because of the nonspecific presentation, the stress fracture diagnosis may be delayed or misdiagnosed as a back or hip problem.

Diagnosis of a sacral stress fracture almost always requires more advanced imaging such as magnetic resonance imaging (MRI) or a bone scan, as x-rays are often negative (don’t assume you’re in the clear if you had a normal x-ray).

But, why?

After the bad news is confirmed, runners may wonder, “why” and “why me” two important questions which need to be addressed. Because the sacral bone is not commonly injured in healthy female athletes, it is recommended that any female with this injury be evaluated for risk factors related to the female athlete triad and low bone density. The first step is a comprehensive nutrition screen, evaluating for energy deficiency or a frank eating disorder. It is also important to consider menstrual history, including if the athlete is on oral contraceptives. Having regular periods while on oral contraceptives does not always ensure normal hormonal regulation and can provide a false sense of reassurance to an athlete at risk. Additional work-up includes checking bone health biomarkers, such as vitamin D, calcium, and thyroid function. A DEXA scan is indicated to accurately measuring bone mineral density.

First Steps to Take Before You Run

All athletes should be taking in around 1,200 mg – 1,500 mg of calcium per day via diet, and if needed, the use of supplements. Vitamin D intake is recommended at 600 IU per day via diet, moderate sun exposure, and again, when needed, the use of supplements. If there’s concern about low energy because of underfueling, athletes should meet with a dietitian to screen for adequate calorie intake.

Finally, a referral to an endocrinologist may also be warranted to address causes of low bone mineral density. In severe cases, athletes may need to be on hormone replacement or other prescription medications to improve bone health.

Back to Running

Because of the many factors which can lead to these frustrating injuries, the timeline for return to running should be individualized for each athlete. The team involved in this decision should consist of the physician, athlete, physical therapist, coach, and trainer. Athletes should avoid weight bearing until able to walk without pain and then transition to nonimpact training (i.e., stationary bike, pool running). Throughout this time, strength training exercises are essential to help support and optimize running mechanics.

It may take six to twelve weeks from initial injury before initiation of a return to run protocol. An anti-gravity treadmill is one option to ensure a safe transition back to sport. A case study by Tenforde et al reported a return-to-run protocol using an anti-gravity treadmill in a 21-year-old collegiate female runner with a pelvic stress fracture. Ten weeks from initial injury, she successfully returned to running and competed in a 10k at the NCAA championships. Studies show athletes may not return to pre-injury training level for three to six months from initial injury. Much of this variability is dependent on severity of injury, underlying risk factors (female athlete triad, etc) and the type of return-to-run-protocol. Those initial weeks are a great time to address potential underlying causes which may have contributed to the injury so the runner can return to sport stronger and wiser.

Prevention

For those readers who are currently injury-free (congrats!), you may be asking how you can avoid a sacral stress fracture or a stress fracture at any location for that matter. Below are some tips to help keep you on the track, roads, or trails:

Disclaimer: This blog is for informational purposes only. Doctors cannot provide a diagnosis or individual treatment advice via e-mail or online. Please consult your physician about your specific health care concerns.

References

Chen Y, Tenforde A S, Fredericson M. 2013. Update on stress fractures in female athletes: epidemiology, treatment, and prevention. Current Reviews in Musculoskeletal Medicine 6 (2): 173-181.

Eller D J, Katz D S, Bergman A G, Fredericson M, Beaulieu C F. 1997. Sacral stress fractures in long-distance runners. Clinical journal of sport medicine 7 (3): 222-225.

Fredericson M, Salamancha L, Beaulieu C. 2003. Sacral stress fractures: tracking down nonspecific pain in distance runners. The Physician and sportsmedicine 31 (2): 31-42.

Tenforde AS, Watanabe LM, Moreno TJ, Fredericson M. Use of an antigravity treadmill for rehabilitation of a pelvic stress injury. PMR. 2012;4:629–31.

Zaman F M, Frey M, Slipman C W. 2006. Sacral stress fractures. Current sports medicine reports 5 (1): 37-43.

Tips from Tyler

(My) recovery is going well. I think it is good to tell people to get a full blood profile, especially vitamin D. I was fortunate in that mine was only a level 3 fracture, and we caught it early. I really only ran two days on it. Some advice I would give is be cautious with the diagnosis. If you feel some pain coming on that might be a Sacral SF, stop running immediately. Get an MRI/Bone Scan as soon as possible. If the scan turns out to be negative, hopefully it would only about a week or two of missed training. If the scan turns out to be positive, then you started your recovery process a week or two early and did not do any additional damage to the Sacrum.

Update from Tyler: Breaking the Cycle on tylerpennelrunning.com