Plasticity in Human Tissue

PLASTICITY IN HUMAN TISSUE

Plasticity refers to a quality associated with being plastic, malleable, and capable of being shaped or formed (OED 2007). Although the term plasticity tends to be most frequently applied in the field of neurology it is important to recognise that it is a characteristic of all human tissue. Human tissues have the capacity to adapt to the nature and extent of the forces applied to them. For example, if we consider the practice of lifting weights. Over a period of time, within a progressive lifting programme, an individual will be able to progressively lift larger weights. The skeletal muscles and tendons loaded by lifting weights adapt over time as the individual progressively lifts more weight. These adaptations affect all components of the musculotendinous apparatus. The contractile component of the muscle gets larger and stronger (Kraemer and Ratamess, 2004) and capable of producing increased force. In parallel with this process the non-contractile components get correspondingly stronger and thicker to accommodate the extra loading (Benjamin 2002). In addition,adaptations occur at the interface between the tendon and the bone so that the bony prominences also develop to withstand the increased force exerted. Consider an individual who suddenly lifts a weight or engages in an activity where the force generated with the musculotendinous apparatus exceeds that which the muscle, tendon or bone can withstand. In this situation the tissue fails to withstand the force applied and injury occurs. For example, excessive load generated in the quadriceps muscle may lead to muscle damage, patellar tendon damage or avulsion fracture of the tibial tubercle. Human tissues undergo reversal of these adaptations during the periods of immobilisation or reduced activity which occur frequently following trauma. In these situations the effect of immobilisation causes the reverse of the processes identified above. This reduces the ability of the damaged tissues to withstand loading. Physiotherapeutic management of these patients focusses on trying to restor the affected tissues’ capacity to withstand normal loading therefore enabling the individual to return to normal function. It is important to remember that these soft tissue adaptation processes occur in both the injured and the uninjured tissues. Physiotherapeutic approaches are therefore fundamentally aimed at capitalising on this plastic property of human tissue so that therapy works alongside, and enhances, the normal healing and repair processes.

PLASTICITY IN HUMAN TISSUE


FACTORS INFLUENCING THE RATE OF HEALING IN THE STAGES OF PROLIFERATION AND REMODELLING

An important consideration is that the processes of tissue proliferation and remodelling take place over significant periods of time (Watson 2004). The period of time for the completion of these pathophysiological processes can run into years and is dependent on a number of factors including:

severity of initial trauma, e.g. a severe second-degree ligament sprain of the lateral ligament complex at the ankle will have a more prolonged proliferation and remodelling period than a first degree ligament sprain affecting the same structure;

early management where the approach taken has laid the necessary foundations for proliferation and repair, e.g. an appropriate approach has been taken to rest/protect traumatised tissues (see earlier sections in this chapter). This has the potential to reduce the onset of chronic inflammation where an agent is responsible for the ongoing irritation of an injury and therefore perpetuates the period of the stages of bleeding and inflammation;

tissue vascularity, e.g. skeletal muscle, which is highly vascular, has more potential for repair than a relatively avascular tendon;

age, e.g. a similar grade of injury is likely to take longer in the repair process in an older individual than one who is younger (Myer 2000);

nutrition – adequate nutrition (also related to blood flow) is required for healing to take place;

medication, e.g. NSAIDs and steroidal drugs slow down proliferation and remodelling processes;

temperature;

biochemical factors;

appropriate loading of healing tissue during rehabilitation.

It is very important that the physiotherapist has a depth of understanding of the pathophysiological processes involved in proliferation and remodelling, as well as the clinical reasoning skills required to make the appropriate professional decisions. In addition to this knowledge, the ability to apply this knowledge of the clinical effects of a number of physiotherapeutic treatment modalities, as well as the psychological and sociological theory in order that treatments are effective, is also required. In this section, short case studies will be used to illustrate the main points.

It is very important that the physiotherapist has a depth of understanding of the pathophysiological processes involved in proliferation and remodelling, as well as the clinical reasoning skills required to make the appropriate professional decisions. In addition to this knowledge, the ability to apply this knowledge of the clinical effects of a number of physiotherapeutic treatment modalities, as well as the psychological and sociological theory in order that treatments are effective, is also required.

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