Tibial Stress Fracture
Tibial stress fractures are common in athletes in running and jumping sports, as well as in military recruits. The choice of treatment depends on the location of the stress fracture.
Lower extremity stress fractures (also known as fatigue fractures) are common in athletes participating in sports that involve running and jumping. The tibia (shinbone) is the most commonly affected bone, making up 19-60 % of all stress fractures in humans (1,2).
Distance runners are at increased risk of developing a stress fracture, with annually reported incidences of up to 15-20 % (1,3). Military recruits are also at increased risk (2,4). Tibial stress fractures also frequently occur in track and field athletes, football players, basketball players, gymnasts, ballet dancers, and more (2,4,5). A considerable proportion develops stress fractures in both tibias (6).
Women have twice the risk of developing tibial stress fractures than men (7,8). While the etiology of this is multifactorial, it has partially been attributed to the female athlete triad (7).
Stress fractures usually present with a gradual onset of pain during exercise over the course of weeks or months, and the physical examination reveals tenderness at the site of the stress fracture, with or without swelling. The pain is alleviated by rest and worsens with impact activity, and may persist after exercise. Jumping on one leg often reproduces the pain (3,9).
Symptoms of a stress fracture in the posteromedial tibial border are similar to that of medial tibial stress syndrome (MTSS) (commonly known as «shin splints»); however, the pain is more focal, and the area of point tenderness is less than 5 cm, usually around 2-3 cm. Some experience a sudden increase in pain during activity, which may be a sign that a bone stress reaction progressed to a complete stress fracture (5).
Etiology of tibial stress fractures
Stress fractures usually presents when there has been an increase in training load. Increases in the duration, intensity and/or frequency of exercise without adequate rest, will lead to a buildup of microscopic lesions inside the cortical bone that are not allowed to heal (3,10).
Cells that demineralize the bone (osteoclasts) outpaces the cells that remineralize it, which reduces bone mineral density (BMD) in the area that has been subjected to increased stresses, thereby weakening the bone. Studies have shown that the tibia is at its weakest after 3-4 weeks of increased training loads, and that it is relatively weaker during the first 8 weeks (11). It is during this time that most stress fractures occur (12).
The majority of tibial stress fractures occur in the cortical (compact) bone (3,9). Stress fractures occur less frequently in cancellous (trabecular) bone which undergo more rapid turnover and remodeling than cortical bone (9). Stress fracture of cancellous bone often correlates with low BMD (3,9).
Low-risk stress fractures (LRSFs)
90-94 % of all tibial stress fractures occur on the inside/backside of the tibial shaft, and are termed posterior tibial diaphysis stress fractures (posterior TDSFs). They are considered as low-risk stress fractures (LRSFs) because they heal well with conservative treatment (6).
Whenever we walk, run or jump, the tibia is subjected to bending stress in addition to compressive and shear stresses. LRSFs are located at the compression side during tibial bending, making nonunion (fracture that does not heal) unlikely since the surfaces are not separating when the tibia is subjected to loads, and compression stimulates bone growth (3). I addition, this area is highly vascularized (has more blood vessels), giving the bone appropriate conditions for healing (3).
High-risk stress fractures (HRSFs)
Stress fractures in the middle third of the front part of the tibial shaft, termed anterior tibial diaphysis stress fractures (anterior TDSFs), comprise 5-10 % of all tibial stress (13). Anterior TDSFs typically occur in athletes who perform repetitive jumping, such as basketball players.
Anterior TDSFs are located at the tension side of the tibia, in an area which has poor vascular (blood) supply. It is therefore vulnerable to displacement, delayed union, nonunion, and complete fracture, making it a high-risk stress fracture (HRSF) that often requires surgical intervention (3,14). Individuals with a confirmed HRSF should always be referred to an orthopedist or orthopedic surgeon.
Stress fractures of the medial malleolus are rare, making up less than 1 % of all tibial stress fractures. These are also categorized as HRSFs because they often require surgical intervention in order to heal (3).
Stress fractures develops because of abnormal loading on normal bone. Another type of fracture that is called insufficiency fracture is common in elderly populations and postmenopausal women, secondary to osteopenia/osteoporosis (9). These fractures are the result of normal or traumatic loading on abnormal bone (2).