Tendon Injury and Risk

In general, tendon injury can be described as damage caused by physical trauma sustained by the tendon, and the severity of injury depends to the amount of damage sustained (Whitting, et al., 2008b). Furthermore, in mild and moderate injuries, the tendon structure is partially disrupted, but although damaged, it is still able to accept load with a smaller magnitude than before the injury (Whitting, et al., 2008b). Complete failure of the tendon structure leads to inability to transmit load. Injuries that are minor and are ignored, with repeated loading may progress to more

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severe injuries. Improper and inadequate treatment may also contribute to a more severe injury. This has an obvious implication for a range of activities ranging from normal activities that require movement to athletic performance where high levels of force and rate of force development are required (Pearson, 2010).

Tendon injury can result from a single insult (acute injury) or long-term abuse due to repeating loads (chronic injury) (Whitting, et al., 2008b). There are two factors leading to these injuries, referred to as either intrinsic or extrinsic (Lee, et al., 2008b, Pearson, 2010). Intrinsic is an injury caused by forces generated within the body such as tendonitis, muscle tears, ligament strains and stress fractures, while extrinsic is a type of injury caused by forces outside the body such as impact or contact caused by another person, inadequate equipment or training, or some other environmental factor (Sharma, et al., 2006, Seitz, et al., 2011).

2.1.3.1 Acute Tendon Injury

A complete or partial rupture of the tendon structure gives rise to an acute tendon injury. The injury usually occurs when a sudden force or torque applied to the tendon, resulting in a partial or complete tear to the tissue structure (Sharma, et al., 2006, Pearson, 2010). However, it has also been reported that there may be an intrinsic factor when strenuous activity is routinely carried out as cumulative damage may occur leading to a catastrophic failure to the tissue (Pearson, 2010).

Study reported that tendon injuries occurred more often to males than females (Clayton, et al., 2008). However, it is unclear if this is due to more participation in sport by males, which may explain a higher risk exposure to tendon injuries. A comparison between male and female showed that with similar strain limits, for a given force, females show a higher musculoskeletal injury risk with respect to the lower limb (Onambele, et al., 2007). This increase in injury risk may be associated with differences in stiffness of lower limb between the genders (Onambele, et al., 2007). It is also reported that certain classes of drugs can affect the collage tissue directly, leading to weakened structures that may rupture under high loading

conditions (Sode, et al., 2007). Anabolic steroids are also shown to have an affect on the collagen matrix, which increased the abnormality and function of the connective tissue and tendon simply cannot keep pace and succumbs to injury. Recent evidence has indicated that certain specific gene polymorphisms may relate to tendon injuries. Each gene code plays specific roles to the structural component of the tendon and may be the cause for tendon injury rates (Mokone, et al., 2005, Mokone, et al., 2006). There has been no agreement about the optimal method for repair and subsequent rehabilitation treatment of tendon ruptures (Pearson, 2010). However, there is increasing evidence to suggest that surgery treatment for active and able individuals may provide better functional capacity over non-operative options while, for less active individuals, non-invasive treatment may be encouraged (Pearson, 2010). Rehabilitation protocols may help for optimal healing after surgery, and with the use of ultrasound and magnetic resonance imaging (see Figure 2.5), an insight into the mechanical property of the injured tendon can be observed in vivo, and further rehabilitation can be planned and carried out.

Figure 2.5: Example of tendon rupture with arrow indicating the rupture area (from http://www.ultrasoundcases.info/).

2.1.3.2 Chronic Tendon Injury

Chronic tendon injury is usually associated with overuse or degeneration of tendon. An overloaded tendon may become inflamed and lead to tendonitis, where the tendon is experiencing short-term inflammation and responds to treatments such as ice, reduction of activity, anti-inflammatory medications and physical treatment. If an injured tendon is repeatedly by overloaded, tendinopathy may develop where the tendon structure begins to minor rupture or tear, but becomes thickened and weakened with a range of chemicals released, which causes the inflammation. At this time, the blood supply required to provide necessary healing components is insufficient, and so the tendon may fail to recover from the trauma.

Some tendinopathy shows a high concentration of blood supply to the tendon with no association to a healing response (Sharma,et al., 2005). Previous study suggested that overuse injuries to the patella may be caused by tensile loading which affected the performance of the patella tendon and the angle of the knee for maximal loading, indicating localised tendon strain (Almekinders, et al., 1994, Almekinders, et al., 2002). Classically, tendinopathy pain has been attributed to inflammation; however, a recent study showed (Sharma, et al., 2006) that chronically painful Achilles and patella tendons show no indication of inflammation and many of the damaged tendon that are detectable on MRI or ultrasound are not painful. The pain, however, may originate from the mechanical breakdown of collagens (Sharma et al., 2006).

Medical imaging techniques such as MRI and ultrasound allow for the quantification of tendinopathy diagnosis, and these are typically used to determine tendon anomalies. Ultrasound has been used to characterise three different levels of tendinopathy (Archambault et al. 1998) (see Figure 2.6).

Figure 2.6: Different levels of tendinopathy illustrating (a) normal tendon, (b)

enlarged tendon areas, and (c) Hypoechoic areas (Archambault et al. 1998).

To summarise, the tendon plays key roles for body motion, enabling the use of the muscle to transmit forces. However, the tendon can be injured either by external forces disrupting the mechanical behaviour of the tendon or internally due to excessive or sudden force to the tendon structure which leads to complete tendon rupture. Diagnosis with the aid of medical imaging has been utilised to observe tendon healing and to detect inflammation or damage for further rehabilitation. However, understanding of the aetiology of Tendinopathy is poor and as such treatment and rehabilitation modalities are not well defined.