Bone Stress Injuries: Intro

I spend my days in an outpatient orthopedic physical therapy clinic primarily serving trainees in Basic Combat Training (aka BCT, basic training, or boot camp). We see what most expect from a high-tempo training environment consisting of physical training, obstacle courses, combatives training, ruck marches, and field training: ankle sprains, knee pain, shoulder dislocations, etc. However, the MOST COMMON injuries we see and manage in physical therapy are bone stress injuries (BSIs). This post’s purpose is simply to review BSIs while future posts will dive further into diagnosing and management.

As the name implies, BSIs are stressed bones resulting in physiological changes to the bone itself. In the disease-free population without underlying metabolic disorders, BSIs are overuse injuries caused by repetitive stress to the bones, most often to the lower extremities. The “stress” is from high-impact activities like running, jumping, rucking, and marching. Even prolonged standing can create stress. The stress is cumulative and starts as mild inflammation and swelling within the bones. However, as the stress accumulates, the inflammation and swelling increases inside the bone and can ultimately lead to a fracture to the bone’s cortex (outer shell).

It’s common to see radiologists use a four-level grading system when diagnosing BSIs. Grade one through three are stress reactions without a discrete fracture line. To keep it simple, we can classify grades one, two, and three as mild, moderate, and severe stress reactions, respectively. A grade four BSI is commonly referred to as a “stress fracture” and occurs when a fracture line is detected. Again, grades one through three are stress reactions without a fracture, and grade four is a stress fracture with a present fracture line.

So why does this happen? Well, it’s normal for bones to breakdown some each day, especially with high impact activities, then to rebuild themselves with proper rest and nutrition. This is actually how the body gets stronger over time. Each time the body restores itself, it makes the involved bones a little bit stronger. This process allows us to go from couch potato to marathon runner without destroying ourselves. The same goes for muscle building and turns the scrawny to “jacked”. With proper programming and balanced lifestyle, this process takes significant time which explains why normal people can’t increase running mileage quickly or make instant huge “gainz” in the gym. However, when the level of activity is too much and the amount of recovery time between training events is too little, the bones breakdown quicker than they can rebuild. This combination leads to BSIs.

Let’s look at my patient population specifically to see why BSIs are the most common injuries we evaluate. First, the physical demands of basic training are usually far more than trainees are used to prior to military service. Everyday, these individuals are running, marching, rucking, jumping, and standing for significant periods. The combination of daily high impact activities and lack of recovery brews BSIs. Second (and unfortunately), the general fitness level a lot of trainees prior to basic training is oftentimes low. Heard of the running program Couch to 5k? Well, this is Couch to Army for many. So, not only are they experiencing a high level of impact with inadequate recovery, they arrive to training predisposed to stress injuries simply due to poor fitness and, consequently, bone health (one benefit of physical activity is increased bone strength). Other risk factors include being female and a shorter stature, and my military installation graduates the most female trainees than any other basic training location. Lastly, we are also the home of the largest basic training program with over 50,000 trainees coming through annually. The combination of sheer trainee volume alongside the other identified reasons above explain why BSIs are the most common injury our physical therapy team evaluate and manage.

BSIs are not exclusively experienced in the military population. The same is true for the average person looking to start running or increase their mileage in hopes of conquering their first marathon. The sport of running appears to have the highest rate of bone stress injuries compared to other sports, which makes sense based on the repetitive high-impact nature of running. However, with its increase in popularity, I would not be surprised to see a “large” incidence of BSIs in rucking events.

So, that is BSIs in a nutshell. In summary, BSIs are physically stressed bones as a result of high-impact activities and inadequate recovery. Severity of injury can range from a mildly irritated bone to a large stress fracture. I will continue expanding on this topic in future posts to include diagnosing and management.

Thanks for reading and hope you got something out of this. Please share your experience or feel free to drop a question in the comments section!

- Pat

Psalm 18:32

It is God who arms me with strength and makes my way perfect.

**Note: Comments made in this post are original to the author and do not represent the official view/opinion of the United States Army**

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