Age

The age of an athlete can affect both the type of injury that may occur and the healing mechanisms that follow. Younger and older athletes tend to be more injury prone for a variety of reasons. There is generally less muscle mass and muscle strength in both of these groups compared with older adolescents and young adults. This can result in greater injury risk both in contact and endurance sports. Less protective sports equipment is available for children than adults, which can lead to greater injury risk from ground reaction forces and physical contact. The quality of coaches in children’s teams is often lower than their adult counterparts, which may cause injury due to improper training and coaching supervision (Dalton 1992). Some studies have found that 70% of all sports injuries occur in children under 18 years (Hergenroeder 1998).

In children of all ages fractures are more common than ligamentous disruptions. Even the location of fractures varies with the age of the child. Adolescents tend to have fractures in the physeal areas, whereas preadolescents have more fractures in the diaphysis (Cantu & Micheli 1991). Certain bony injuries, such as the osteochondritides, can only occur in the young athlete. Also traction apophysitis of the calcaneus (Sever’s disease), the fifth metatarsal (Iselin’s disease), and of the tibial tubercle (Osgood–Schlatter’s disease) only occur in children and adolescents, although rarely the symptoms may persist into adulthood in the case of Osgood–Schlatter’s disease. Both traction apophysitis in the young athlete and musculotendinous injuries in the older athlete have been linked with reduced flexibility. It is known that reduced flexibility is more common in both groups (Anderson & Burke 1994, Gerrard 1993). Assessment of flexibility is therefore a key area when examining both children and older athletes with sports injuries.

Musculotendinous injuries are the commonest injury in the older athlete (over 40 years). This is due to a number of cellular changes which occur with increasing age. Changes in collagen cross-linking cause an increase in tendon stiffness and reduce the elasticity of the tendon. Similar change have also been seen in ligaments. This can result in a muscle being subject to earlier and prolonged loading in a movement cycle and being unable to undergo normal stretching, resulting in damage to the musculotendinous unit. The diameter, density and cellularity of the collagen fibrils are also diminished with advancing age, which results in reduced muscle mass and strength. Finally, the blood supply to tendons reduces with age, resulting in an increased risk of tendonitis, tendinosis or rupture (Sassmannshausen 2006, Strocchi et al 1991).

Overuse injuries in the older athlete may also develop due to a delayed physiological response to exercise. When a person starts an exercise programme there are gradual positive changes to the cardiovascular, neurological, endocrine and musculoskeletal systems. As a person becomes fitter the muscles become stronger and there is an increase in bone density. These normal adaptive changes are delayed in the older athlete and may cause musculotendinous injuries if the athlete increases their training volume too quickly. Older males are almost twice as likely to develop a sports injury as older females (Gerson & Stevens 2004).

Gender

Physiological differences between the sexes result in differences in athletic performance. For comparative body sizes women have a reduced cardiac output, blood volume, vital capacity and mean muscle mass when compared with males. Whether this increases the risk of injury in female athletes is uncertain. Studies involving civilian populations have not shown significant differences in injury rates between the sexes (Hootman et al 2002, Knowles et al 2006), except in children, where boys are twice as likely to be injured as girls (Bruns & Maffulli 2000). McQuillan & Campbell (2006) attributed this to football and found that if football was excluded from the analysis the rates of injury were the same for boys and girls. This is in contrast to studies involving military personnel in which injury rates among female recruits are between two and four times higher than among their male counterparts (Jones et al 1988, Ross & Woodward 1994, Yates & White 2004).

Perhaps of more significance than injury rates are the differences in the types of injury seen between males and females. Certain injuries are associated with certain sporting activities, for example posterior ankle impingement, which is most commonly seen in females participating in either dance or gymnastics. Pain from existing structural deformity or natural alignment may also occur in the female athlete. Hallux valgus is far more common in females and the joint or prominence can become painful due to the increased ground reaction and frictional forces of sporting activity. A valgus alignment of the knee is more common in females, and this can increase the strain on the medial soft-tissue structures of the knee during sport involving excessive knee flexion and rotation, for example, medial collateral ligament injuries in skiing. Patellofemoral syndrome is undoubtedly more common in females than in males, and this is probably due to a wider pelvis decreasing the mechanical efficiency and altering the muscle mechanics of the patellofemoral joint.

The incidence of stress fractures has also been reported to be higher in females. Early studies showed the female incidence to be 10 times greater than men (Protzman & Griffis 1977). Although more recent studies have not shown such a significant difference between the sexes it is generally accepted that female athletes are more prone to stress fracture than males, especially in the military. There are three common aetiological factors which may be responsible for this greater relative risk of stress fracture. These interlinking factors are known as the female athlete triad or unhappy triad and usually present as a combination of:

Although any of these factors can be present in the non-athletic female population, both amenorrhoea and eating disorders are more common among athletes. Some prospective studies have also demonstrated that stress fractures occurred more frequently in female athletes with low bone density (Bennell et al 1996) and also those with menstrual irregularities (Brukner & Bennell 2001, Rauh et al 2006).

It is generally agreed that females are more flexible than males. Whether this should affect injury rates between the sexes is unclear, but it has been reported that greater flexibility may predispose ligament injuries whereas inflexibility may predispose musculotendinous injuries. This would result in females being more prone to ligament injuries and males to musculotendinous injuries. Some evidence would appear to support this theory, as both anterior cruciate knee ligament injuries and lateral collateral ankle ligament injuries have been reported to be higher in females than in males undertaking the same activity (Almeida et al 1999, Griffin 1994) while Achilles tendon injuries are more common in males (Kannus & Jozsa 1991).

Previous injury

History of previous injury is a common finding when assessing the injured athlete. The relative risk of developing an injury when a history of a previous injury is present is two to three times greater than with a history of no injury. The majority of studies in this area have involved military subjects or runners. It is not surprising that a previously traumatised structure may be re-injured, as the athlete may frequently return to exercise too quickly or the underlying cause of the injury has not been addressed. The subsequent injury is often more severe than the previous injury. An example of this is seen in tibial stress fractures, where there is a history of previous exercise-induced shin pain in up to 50% of cases.

The subsequent injury does not necessarily occur at the same location as the previous injury. This may suggest compensatory changes have occurred due to the injury or its treatment. These changes may be in proprioception or neuromuscular coordination resulting in excessive strain on adjacent or distant structures (Case history 15.2).

Structural alignment

The assessment of structural alignment must include an overall impression of the whole body, with a specific focus on the lower limbs and the injured area. The purpose is to assess and determine if the body’s structure and function has caused or contributed to the injury. Biomechanical abnormalities may be identified, but their relevance to injury must be determined. It is also important to determine if any abnormality has occurred due to the injury rather than causing it (cause and effect). Although many studies have identified a biomechanical link with common overuse injuries there are also many studies which could not. It is therefore essential that the practitioner keeps an open mind when assessing a biomechanical causation for the patient’s injury and explores all aspects of potential aetiology of the injury.

Structural alignment should be assessed with the patient non-weightbearing, weightbearing and dynamically. A thorough examination in all three components is essential if the practitioner is to gain a complete picture of the athlete’s structure and function as it relates to the injury. This assessment should include examination of the joints, muscles and osseous alignment (Ch. 10, section A). The majority of podiatric interventions in sports injuries are related to the assessment and treatment of structural alignment and function that has caused or contributed to the injury.

Chronic or overuse sports injuries are usually due to the presence of one or both of the following situations:

Although this is a rather simplistic view, it can be seen to be true in the majority of cases. If we consider two runners with patellofemoral syndrome: runner A runs over 160 km/week, running every day; runner B runs 32 km/week, running 3 times per week with 4 rest days. Apart from their injuries, they are both healthy and have taken 6 months to get to this weekly mileage. It should be clear that runner A is doing too much, too soon, and too frequently:

Other aetiological factors may also be present in runner A, but treatment will fail unless the errors of the training schedule are addressed. In the case of runner B, the aetiology of his injury is likely to be due to abnormal structure and function which has resulted in excessive patellofemoral joint reaction forces. His structural assessment should include examination of factors such as:

The presence or absence of these factors should assist the practitioner in identifying the aetiological factors and planning the most effective treatment (Witvrouw et al 2000).

Asymmetries between limbs may represent the obvious cause of a unilateral overuse injury. However, it is important to consider the role of other factors such as the type of activity, exercise surface, unilateral trauma and injury history. Any of these factors may cause a unilateral injury. If structural asymmetry is identified, then the practitioner must determine a biomechanical mechanism by which the asymmetry could have caused the overuse injury. If we consider stress fractures as an example, there is a strong association between stress fractures and limb-length inequality (Brukner et al 1999). Stress fractures tend to occur in the longer limb, and the greater the inequality the greater the incidence (Friberg 1982). The reasons for this are thought to be due to the biomechanical consequences of the limb-length difference, which results in a longer stance phase, skeletal realignment, greater osseous torsion and increased muscle activity of the longer limb. However, other studies have not shown any increase in injury risk when a limb-length inequality of >5 mm is present (Goss et al 2006).

Flexibility

Hypermobility due to increased muscle flexibility and ligamentous laxity has been associated with a greater risk of injury. Hypermobility is often determined by the Beighton score, which is based on a nine-point test designed to measure excessive joint movement (Ch. 14). This test has been used in a number of studies on flexibility and injury, which have generally shown that hypermobility is associated with a greater incidence of ligamentous injury. Rossiter & Galbraith (1996) found that hypermobility was present in 34% of military recruits with ankle and knee ligament injuries compared with 19% of control subjects. Increased flexibility, measured by the sit and reach test, in the absence of ligamentous laxity has not been shown to be a significant factor in injury prediction.

Generalised inflexibility due to muscle tightness has been linked to musculotendinous injury: while this is likely to be true, it has only been proved in one long-term prospective study to date (Witvrouw et al 2003). However, if a theoretical causal link can be made between the muscle inflexibility and the injury, then stretching of those muscles should be included in the treatment programme. Likewise, if hypermobility is present, then stretching should be avoided and athletes encouraged to perform specific stabilising exercises.

Stretching prior to activity in an attempt to reduce the risk of lower limb injury is contentious. Some large randomised controlled trials involving military recruits (Pope et al 1998, 2000) have shown no benefit in stretching while others have (Amako et al 2003). In two large systematic reviews of the literature neither set of authors could conclude on any significant benefit of stretching prior to sports participation (Fradkin et al 2006, Thacker et al 2004). This does not mean that injured athletes with muscle inflexibility should not be instructed to stretch, as this is an effective treatment modality. However, athletes are often questioned as to whether they stretch before and after activity and encouraged to do so if they do not. There seems little evidence to support this premise and failure to stretch before exercise should not necessarily be viewed as a risk factor to injury.

Physical fitness

Physical fitness is known to lower the risk of injury, as shown in a number of studies based on military and civilian populations (Neely 1998). This protective mechanism not only applies to practising a known sport but also to learning a new sport or athletic skill. The level of reduced risk varies among the studies, and is dependent upon the activity being undertaken and the fitness test used. Pope et al (2000) were able to demonstrate that the least-fittest group of their army recruits were 14 times more likely to sustain a lower limb injury than the fittest group. The fitness method used was the progressive 20 m shuttle run test, also known as the bleep test. This test is one of the most popular fitness tests used today.

When assessing injured athletes it is important to gauge their fitness level, as you may need to offer advice on a more appropriate training regimen. This is often the case for the novice athlete who enthusiastically embarks on an over-ambitious fitness programme. This will result in injury, as the musculoskeletal system is not prepared for such strenuous exercise. When an injury occurs, the athlete should be advised to modify their exercise regimen to prevent recurrence or further injury to other structures. This advice may include changing the method of exercise or reducing the intensity, frequency or duration of the exercise.

Physical build

The relationship of physical strength to injury is unknown. To avoid injury the musculoskeletal system must be able to cope with the physical demand of the sporting activity. Some evidence suggests that stronger athletes are more injury prone (Knapik et al 1992). The reasons for this are unclear, but it may be that the muscular forces generated by stronger athletes damage their joint structures and even the muscles themselves. It may also be that stronger athletes exercise at greater intensity or duration than weaker athletes, resulting in higher injury rates.

There is a correlation between strength imbalance and injury that is most frequently seen in the knee joint, where differences between hamstring and quadriceps strengths have been associated with cruciate ligament injuries. The role of strength differences between limbs has also shown a greater injury incidence on the weaker side. There is general agreement that strength differences greater than 10% can increase the injury risk to the weaker limb. These injuries may be acute, as with cruciate ligament injuries, or chronic, due to fatigue, for example tendinopathy, muscle strains and stress fractures. The role of limb dominance in injury incidence is less certain. Limb dominance in racket or ball sports is associated with different injury patterns. However, in sports that require equal stresses through both limbs there is no evidence to suggest limb dominance is a risk factor. Herring (1993) did not find any difference in injury incidence based on limb dominance in elite runners.

Anthropometric data such as height, weight, body mass index (BMI) and total body fat have also been examined as injury risk factors. In general, it is only the BMI that has been shown to be a positive indicator for injury risk. The BMI is determined by dividing the body weight in kilograms by the height of the patient in metres squared (kg/m²). The normal BMI range is 20–25 with above 25 representing clinically overweight, above 30 clinically obese and below 20 representing underweight. As a general rule, the injury risk doubles for individuals who fall outside the normal BMI range.