A combination of extrinsic factors, such as training errors and environmental factors, and intrinsic or anatomical factors, such as bony alignment of the extremities, flexibility deficits, and ligamentous laxity, predisposes athletes to develop overuse injuries. Hubbard et al. [25] established that the factors most influencing MTSS development were previous history of MTSS and stress fracture, years of running experience, and orthotic use (Fig. 43.2). Running injury rates increase significantly when weekly mileage extends beyond 40 miles cumulatively [26]. Common causes of running injuries include overuse, lack of rest, and activities that aggravate biomechanical predisposers of specific injuries [27]. Female gender, previous history of MTSS, fewer years of running experience, orthotic use, increased body mass index, increased navicular drop (ND), and increased external rotation hip range of motion in males are all significantly associated with an increased risk of developing MTSS [28].

A variety of physical characteristics of athletes has been proposed to be related to the risk in sustaining a sports injury [29]. Yagi et al. [30] found in females that body mass index (BMI) significantly increased the risk of MTSS and also a higher BMI was associated with a longer recovery time [11]. No significant differences were found in anthropometric parameters (thigh length, leg length, foot length, and leg circumference) and body composition (the amount of minerals and body fat percentage) in a MTSS patient group [31].

Overuse injuries develop when repetitive stress to bone and musculotendinous structures damage tissue at a greater rate than that at which the body can repair itself [32], and MTSS often results when bone remodelling processes adapt inadequately to repetitive stress [33]. For Devas et al. [34] and Jackson et al. [35], between pain and stress fracture, athletes may show a variety of features including periostitis, cortical demineralisation, cortical hypertrophy, or mixed patterns.

The pathogenesis is explained by increased pressure in the fascial compartment of the deep flexor muscles due to prolonged exercise. In patients susceptible to MTSS, the fascial compartments are too small to accommodate the associated 20% increase in muscle mass that typically occurs with heavy exercise [36]. The pathology of the compartment syndrome is that with exercise, a muscle retains fluid and increases bulk. Authors have demonstrated that elevated muscle compartment pressure in athletes may cause either medial-sided shin pain [16, 37] or lateral-sided shin pain [4], but this is highly contentious [10, 38]. It may be concluded that the body of evidence supports the idea that increased compartment pressure may cause shin splint pain, but not all shin splint pain is due to increased compartment pressure and that fasciotomy not only decreases the compartment pressure but decreases the muscle traction effect on the periosteum.

Biomechanical studies indicate why certain athletes are predisposed to get shin splints and may explain the pathophysiology behind elevated compartment pressure or musculotendinous tears in the aetiology of shin splints.

Malalignments of the lower extremities (average prevalence 18% and only minor deviations) did show some inconsistent relationships with the number of (specific) injuries. For pelvic obliquity, it was positive as predicted, but for malalignment of the rearfoot and a deviant footprint, it appeared to be negative. Runners with medial shin pain displayed greater frontal plane pelvic tilt excursion, peak hip internal rotation, and decreased knee flexion while running compared to a control group [13]. Leg length inequality and malalignment of the knees were not related to injuries [29]. Sommer and Vallentyne [39] found that a standing foot angle of <140° and a varus alignment of the hindfoot and/or forefoot were predictive of a previous history of MTSS.

Malalignment has also been implicated in iliotibial band syndrome, MTSS, lower extremity stress fractures, and plantar fasciitis (Fig. 43.3). Muscle inflexibility aggravates and predisposes someone to the development of a variety of overuse injuries, especially those occurring in children and adolescents, including the traction apophysitis. Flexibility deficits may be improved by an appropriate stretching protocol. Unfortunately, lower extremity malalignment is less amenable to intervention.

Foot overpronation is thus a well-documented cause of shin splints. These include tibia vara – because the foot hits the ground in an exaggerated, inverted position, therefore it must “roll over” further to make adequate ground contact and forefoot varus – because the rearfoot must “roll over” further (pronate) to compensate for the inverted forefoot and internal femoral torsion [40], because the foot may pronate to increase abduction and therefore make someone walk straighter. Increased internal rotation of the hip significantly increased the risk of MTSS [30]. Other causes of overpronation include plantarflexed fifth metatarsal, limb length inequality, various neuromuscular conditions, and tibial torsion [40]. An imbalance in foot pressure with greater pressure on the medial side than on the lateral side was the primary risk factor.

The combination of female gender and ND test measures provides an accurate prediction for the development of MTSS. Several studies [28, 41–44] have demonstrated that excessive static ND is related to the diagnosis.

Football players with MTSS have an abnormal structural deformation of their feet during the support (or stance) phase of running. This abnormal motion could be a risk factor for the development of MTSS [45].

Orthotics is often prescribed to improve lower extremity alignment. However, studies have not shown that orthotics has any effect on knee alignment, and, while they can alter subtalar joint alignment, the clinical benefit of this remains unclear. Awareness of anatomical factors that may predispose overuse injuries allows the clinician to develop individual rehabilitation programmes designed to decrease the risk of overuse injury. In addition, the clinician can advise the athlete on the importance of avoiding extrinsic factors that may also predispose overuse injury [32].

It is believed that overused, fatigued muscles can cause or exacerbate the condition of shin splints. Certainly it is widely held that shin splints are most frequently seen in the underconditioned athlete trying to do too much too soon [35, 46]. Clement et al. [46] noted that earlier scientific work had suggested that muscles were able to act as “shock absorbers’ and therefore absorb some of the stress of movement that would otherwise go directly to the bone. They therefore suggested that the athlete that asked his body to do too much too soon would fatigue his muscles and may decrease the shock absorption function of the muscle. Consequently, all stress would be transmitted direct to the bone, hence bone overload and periostitis. Taunton et al. [47] supported this and pointed out that biomechanical abnormality would make muscle overstress occur earlier.