Bone Stress Injuries 101
What is a bone stress injury?
A bone stress injury by definition is an imbalance between the microdamage formation from loading and its removal. When we load a bone beyond its capacity to remodel, the microdamage becomes too great and it is left vulnerable and susceptible to fracture. BSIs occurs along a pathology continuum, beginning with a stress reaction, which can progress to a stress fracture, which can progress to a complete fracture.
Because of the nature of repetitive mechanical loading, long distance runners are at an increased risk for developing a BSI.
An athlete’s biomechanics, training stimulus, and muscle strength can all affect how bone are loaded, but genetics, diet, hormone levels, physical activity, and medications can affect how well your bones resist load. While there are many factors that can contribute to the development of a BSI, energy availability (EA) is a HUGE one. Low EA occurs when there isn’t enough caloric intake to meet energy demands. Even short time periods (5 days where you aren’t fueling enough for your runs) can negatively alter bone metabolism. If you aren’t eating enough to fuel your workouts AND recovery, you are leaving your bones very vulnerable to breakdown. While women and men are both susceptible, women are at a greater risk due to the relationship between EA, bone mass, and menstrual function. In fact, menstrual dysfunction (absence of a period) can increase a female runner’s risk fo developing a BSI almost six fold!
Studies are even showing that EA may be more important than calcium or Vitamin D levels. Hence, if you’re taking your vitamins but STILL aren’t eating enough, you aren’t doing much to reduce your BSI risk.
While MRI is the gold standard for BSI detection, it’s important to correlate those findings to your physical exam. In fact, a recent study showed that 43% of collegiate runners exhibited signs of a tibial stress reaction on MRI, but none went on to develop a BSI over the next two years.
Bone Stress Injury Grading
Grade I : mild to moderate periosteal edema
Grade II : moderate to severe periosteal edema
Grade III : moderate to severe periosteal edema on T1 ND T2 weighted images
Grade IV: moderate to severe edema + clearly visible fracture line
Low Risk Stress Injuries - Posteromedial tibia, fibula/lateral malleolus, femoral shaft, pelvis, calcaneus, Diaphysis of 2nd to 4th metatarsals
High Risk Stress Injuries - Femoral neck, anterior cortex of tibia, medial malleolus, talus, navicular, proximal diaphysis of 5th metatarsal, Base of 2nd metatarsal, Great toe sesamoid bones
Bone stress injury symptoms differ from sources of pain generated by other soft tissues like muscles or tendons. Typically bone pain can be classified as a gradual onset of diffuse and predictable pain that does not “warm-up” with activity (aka it does not improve). The pain can progressively worsen with increased loading from walking or running and improve when the bone loading ceases. On physical examination, there can often be localized bony tenderness depending on the location and accessibility of the injury. Occasionally redness, swelling and warmth can be present from an associated inflammatory reaction. Symptoms and clinical presentation and MRI findings, as well as a thorough subjective history all go into the diagnosis of a BSI.
Managing Bone Stress Injuries
When we unload bone, its quality changes and it becomes weaker. After a bone stress injury (especially if the bone has been immobilized, surgically fixated, or offloaded) , it is absolutely critical that an athlete take part in a progressive loading program to improve the strength and adaption of the bone and other soft tissues BEFORE returning to run. It is not enough to simply start running again after you are pain-free.
Return-to-sport timelines are dependent upon the location of the BSI (high risk or low risk) and the grade of severity (Grades 1, 2, 3 or 4). High risk sites need to be carefully monitored throughout due to their risk of delayed union and progression to complete fracture. Low risk/low grade BSIs have a return to sport timeline as soon as 8.7 weeks while high risk/low grade + high risk/high grade BSIs may need up to 22 weeks. Risk is determined by blood flow and how easily the bone can be offloaded. Grade (1-4) is determined by MRI - the amount of swelling in the bone and/or presence of a fracture line.
Bones should only be offloaded until an athlete can walk pain-free. Once an athlete is able to walk and perform daily activities without pain, a progressive exercise program should begin.
To improve bone remodeling, shorter and more frequent sessions (with ample recovery) are recommended over long, less frequent sessions. Why? Bone quickly becomes desensitized to loading and fully saturated after only 40 repetitions (think 40 hops or 40 squats). The absolute maximum amount of bone pain tolerated with activity is 0/10. The presence of pain during or after activity signals that the bone is being loaded beyond its capacity.
For example, a runner may have a strength program broken down into three short sessions a day with two exercises in each session and ample recovery in between.
Exercises should be progressed to include plyometrics BEFORE starting to run again. My patients have a return-to-run protocol they need to pass before I will let them start running. An athlete MUST improve muscular strength and endurance as well as bone integrity before returning to run.
So when can you start running again? Rule of thumb for my patients - if they have been pain-free for AT LEAST 7 consecutive days AND have passed my return-to-run test, they may initiate a return-to-run program, starting with a walk/run progression.
When returning to run after a BSI, a couple form tips can help reduce the magnitude of bone loading with each step. Adapting a slightly higher cadence will decrease ground contact time and therefore the amount of time the tissue is loaded. Decreasing overstriding (landing closer to the body’s center of mass) will also decease the amount of shock being absorbed by the bone.
Preventing Bone Stress Injuries
Contrary to popular belief, distance running is not a great bone-building sport. The repetitive, unidirectional loading with distance runners does not stimulate bone adaptation. The best type of loading for bones is variable and unpredictable. And the best time to build strong bones is before puberty. In fact, participation in ball sports as a youth decreased the risk of stress fracture by almost half!
The biggest risk factor for a bone stress injury is a history of bone stress injury. Here are a few tips I’ve compiled to help you build strong bones safely and reduce your risk for developing a bone stress injury:
EAT. I cannot stress this enough. Our bones are constantly breaking down and remodeling - replacing old bone with new. You HAVE to be eating enough calories for this to happen successfully. If you’re not, don’t even bother reading the rest of this.
Track your training! If you go out and do a long, hard run, you aren’t going to get a bone stress injury that day. It usually takes 3-4 weeks for BSIs to present. If you’ve been diagnosed with a BSI, look back 3-4 weeks from onset of symptoms to figure out if there was some training load error.
Increase volume before increasing intensity. AN increase in training volume increases BSI risk in a 1:1 ratio. An increase in intensity increases BSI risk exponentially. The thing that loads bones MOST is muscle contraction (not impact). The body can tolerate increases in loading cycles pretty well (duration, mileage, etc.), but increases in magnitude (intensity) increase your BSI risk exponentially.
Keep loading cycles short but frequent! After 100 back to back loading cycles (steps if running, squats in the gym), your bone cells become deaf and shut down to the stimulus. You can get better bone adaptation if you keep sessions short and break them up into bouts - 1 cycle in the morning, 1 at lunch, 1 in the evening (with at least 4-6 hours between). If you’re introducing plyometrics, reduce running workload simultaneously. As you build tolerance, increase running workload back up again.
References:
Barrack MT, Gibbs JC, De Souza MJ, Williams NI, Nichols JF, Rauh MJ, Nattiv A. Higher incidence of bone stress injuries with increasing female athlete triad-related risk factors: a prospective multisite study of exercising girls and women. Am J Sports Med. 2014 Apr;42(4):949-58.
Bergman AG, Fredericson M, Ho C, Matheson GO. Asymptomatic tibial stress reactions: MRI detection and clinical follow-up in distance runners. AJR Am J Roentgenol. 2004 Sep;183(3):635-8.
Fredericson M, Jennings F, Beaulieu C, Matheson GO. Stress fractures in athletes. Top Magn Reson Imaging. 2006 Oct;17(5):309-25.
Ruohola JP, Laaksi I, Ylikomi T, et al. Association between serum 25(OH)D concentrations and bone stress fractures in Finnish young men. J Bone Miner Res. 2006;21:1483-1488.
Santos-Rocha, R. A., Oliveira, C. S., & Veloso, A. P. (2006). Osteogenic index of step exercise depending on choreographic movements, session duration, and stepping rate. British Journal of Sports Medicine, 40(10), 860-866.
Van Langendonck L, Lefevre J, Claessens AL, Thomis M, Philippaerts R, Delvaux K, Lysens R, Renson R, Vanreusel B, Vanden Eynde B, Dequeker J, Beunen G. Influence of participation in high-impact sports during adolescence and adulthood on bone mineral density in middle-aged men: a 27-year follow-up study. Am J Epidemiol. 2003 Sep 15;158(6):525-33.
Warden SJ, Davis IS, Fredericson M. Management and prevention of bone stress injuries in long-distance runners. J Orthop Sports Phys Ther. 2014 Oct;44(10):749-65. doi: 10.2519/jospt.2014.5334. Epub 2014 Aug 7.
