Sacral Stress Fracture in Runners: A Sneaky Cause of Low Back Pain?

Zone 1 (most common) - Involves the sacral wings or ala without extension to the foramina or central sacral canal. Can affect the lumbosacral nerve roots.

Zone 2 - Involves the sacral foramina but no impingement on the central sacral canal.

Zone 3 - Involves the central sacral canal. Often presents with saddle anesthesia and loss of sphincter tone. High incidence of cauda equina. Not to be missed!

What is the best way to diagnose?

Diagnosis can be challenging due to difficulty differentiating pathologies with common symptoms. Similarly, published case reports of sacral stress fracture describe a wide range of symptoms^{(2, 4, 9)}. The most common, however, are as follows:

• Diffuse pain located at the sacrum, lower back, or pelvis/ buttock area
• Posterior hip and buttock pain in unilateral cases
• Localized tenderness on palpation
• Antalgic gait
• Normal ROM of hip
• Normal lumbar spine ROM
• More pronounced with training, and may prevent running
• Relieved by rest and then returns with impact
• Night pain
• Radiculopathy

As well as a detailed patient history, special tests that may also help the diagnosis include:

1. Single leg hop test ^{(2, 10)}
2. Flexion-abduction and external rotation (FABER) test ^{(6, 10)}
3. Gaenslen’s test⁽⁶⁾
4. SIJ distraction and compression tests⁽⁶⁾

Imaging is useful in conjunction with patient history and physical examination. MRI for stress fractures is currently the gold standard, largely due to the ability to display soft tissue and bone edema. Radiographs lack the ability to determine acute stress fractures since it may take three weeks for cortical irregularities and periosteal reactions to become evident⁽²⁾. Computer tomography (CT) scanning is useful in diagnosis but lack the sensitivity of MRI to provide a concurrent evaluation of soft tissue⁽²⁾. Bone scans (scintigraphy) are highly sensitive; however, the incur undesirable radiation exposure.

Sacral fracture treatment

Once a firm diagnosis has been established, load modification should be the initial intervention^{(2, 9, 10)}. This may entail simply ceasing running. However, it may also mean more drastic off-loading with the use of crutches, if pain continues with weight bearing.

Sacral stress fractures can take 7-12 weeks to allow sufficient healing^{(2, 10)}. This process is vital to prevent non- or delayed-union, which is the only time when surgical intervention is necessary⁽²⁾. Anti-inflammatory medication should be avoided as it is associated with non-union due to the impact on prostaglandin (E₂ specifically) activity during the initial stages of healing^{(2, 6)}.

Minimal-impact cardiovascular exercise should be initiated to maintain cardiovascular conditioning, such as cycling, pool running, antigravity treadmill running, and swimming^{(2, 9-11)}. These should be guided by symptoms and can help promote the ideology of ‘mechanotherapy’ where relative load accelerates healing⁽⁸⁾.

Although research is limited, it seems logical to consider a biomechanical cause of sacral stress fractures. There are suggestions that treatment should include rehabilitation, targeting trunk, and pelvic girdle stability, muscle endurance training, balance/ proprioception training, flexibility, and gait retraining ^{(2, 9, 10)}. However, specific examples are not given.

Therapeutic exercises

The following exercises target common areas (trunk, pelvis, hip, knee, and ankle positional control as well as load), and are therefore useful to consider when rehabilitating a runner back to impact tolerance. They should be completed 3-4 times per week:

1. Single-leg squat off a box (Figure 3)
2. Split squat with or without step (Figure 4)
3. Single-leg soleus heel raise (Figure 5)
4. Cable pallof press (Figure 6)
5. Bird dog with resistance band (Figure 7)

Given the healing time frames mentioned above, the progression of returning to running should be gradual and guided by pain provocation. A walk-to-run (4mins:1mins) program should be instilled initially, or progressive tolerance to load using an Anti-gravity treadmill. Once continual running is tolerated, mileage and intensity should increase by no more than 10% per week⁽²⁾. Re-imaging is not necessary unless pain exceeds expected time-frames. Any concerns regarding intrinsic and extrinsic risk factors should be tackled for future prevention.

References

1. Wright, A.A et al. Br J Sports Med 2015; 49:1517-1523
2. Kahanov, L. et al. J Sports Med 2015; 6: 87-95
3. Liong, S.Y. & Whitehouse, R.W. Br J of Radiology 2012, 85: 1148-1156
4. Boissonnault, W.G. & Thein-Nissenbaum, J.M. J Orthop Sports Phys Ther 2002, 32(12): 613-621
5. Tenforde, A.S. et al. Med Sci Sports Exerc 2013; 45: 1843-51
6. Longhino, V. et al. Clin Cases Mineral Bone Metabolism 2011; 8)3):19-23
7. Zaman, F.M. et al. Curr Sports Med Reports 2006; 5(1): 37-43
8. Kahn, K. M. & Scott, A. Br J Sports Med 2009; 43: 247-251
9. Liimatainen E. et al. J Research Sports Med 2016; 1(1): 20-26
10. Harris, C.E. et al. Curr Sports Med Reports 2016; 73
11. Tenforde, A.S. et al. J Injury Function Rehab 2012; 4(8): 629-31