Overuse injury occurs when repeated mechanical loading exceeds the threshold that the body tissue is able to withstand without disruption. Many tissues of the body are susceptible to overuse injury but the two most commonly affected are bones and tendons.
Stress fractures are overuse injuries to bones caused by repetitive loading that can be tensile or compressive. Bone is constantly remodeling in response to mechanical stress. Over a 7 -10 year period every bone has completely new cells compared to the decade prior. This remodeling occurs as an ongoing process of bone resorption and new bone formation performed by specific cells at the microscopic level. Bone stress injuries and stress fractures occur during an abrupt increase in the load applied to the bone, when bone resorption occurs quicker than the new bone can be formed. This increased load is often due to an increase in duration, intensity or frequency of physical activity without adequate rest periods. The bone responds to the stress of overload with oedema, which can be picked up on MRI (bone stress injury) before there is a break in the architecture of the bone (stress fracture).
Stress fractures can occur in any bone that is subject to mechanical overload. Some sites of the body are more common (such as stress fracture of the tibia (shin bone) in runners) and some are rare. Some sites are low risk and heal well as long as the mechanical load is decreased for a period of time and some sites are high risk for complications of healing due to particularly poor blood supply. These sites need to have specific offloading and sometimes complete non-weight-bearing for a period of time in order for the bone to heal (for example navicular stress fractures in the foot).
Stress fracture management is not just about resting the bone for long enough so that it heals. There needs to be an assessment of all the contributing causes and all modifiable risk factors need to be addressed. This includes biomechanical factors relating to the athlete and strength and weakness imbalances in the kinetic chain, evaluation of training loads, equipment and surfaces and attention to nutrition and contributors to bone health including macronutrient intake and bone density. Prevention of bone stress injury is much better than cure.
When a tendon is subject to high loads over time, pain and dysfunction can occur. Tendon overload was originally called tendonitis because it was thought that the cause of the pain was inflammation, however research in the area has shown an absence of inflammatory cells in tendons that are symptomatic from repetitive loading and the preferred term is tendinopathy. Tendinopathy occurs when there is a failed healing response in the tendon at the microscopic level.
Increased participation in recreational sporting activities, particularly in middle-aged adults, has led to an increase in tendinopathy but the condition can also occur in elite athletes when their regular training volumes are suddenly increased. Risk factors can be related to the properties of the tendon and other attributes of the athlete (intrinsic factors) and also related to the loads on the tendon, playing surfaces and other external factors such as footwear (extrinsic factors). As tendons age, they lose some of their energy storage capacity and therefore the risk of tendinopathy increases with age.
Tendinopathy presents as pain in the tendon with load and on palpation of the tendon. The pain is often worse first thing in the morning and after periods of rest during the day. It has a warm up effect, where the pain is present for the initial stages of activity but then it may go away completely in the later stages and then returns while at rest after the activity or few hours later or the next day. Once present, tendinopathies are often refractory to treatment and get worse if they are ignored. They often don’t heal just with rest and as soon as the activity that caused the pain is resumed, the pain returns.
Tendinopathies need to be managed carefully. Tendons require optimal loading for the microstructure to adapt and heal. This means that they need some load, as complete offloading doesn’t promote tissue adaptation, but too much loading (if sport or other inciting activity is continued) doesn’t allow healing to occur. They are often slow to resolve, requiring many months for full resolution of symptoms. Patience is needed and adherence to a progressive, active rehabilitation program is needed after predisposing factors are assessed and addressed. Symptoms may worsen initially during the performance of rehabilitation exercises but this should settle once the exercise is stopped. This mechanical loading is important to stimulate healing.
Rehabilitation programs usually start with isometric exercises (static muscle squeezes), which can be pain relieving for the tendon. Then there is a progression to both concentric and eccentric exercises (the muscle lengthens while under load), which are the mainstay of tendon rehabilitation programs. Progressive resistance training specific for the injured tissues, with relatively slow movements at fairly heavy loads, lead to the best outcomes in tendon rehabilitation. Injection therapies are occasionally needed to help facilitate a rehabilitation program in recalcitrant cases. Surgery is rarely indicated for tendinopathy.
If you have an overuse injury, or pain that is worse with activity or afterwards, a consultation at Shire Sports Medicine can be beneficial for you to get an accurate diagnosis, to help guide management of your condition and to ensure the prevention of further complications.