Mechanical Interactions - Preventive Biomechanics - page 247

incidence rate of 1.3 % during inpatient health care. Prevalence is especially high
among the bedridden elderly and those who suffer impaired sensation. Once a sore
has developed it represents a trauma for the patient and treatment is elaborate and
costly. As a result, total annual costs are estimated to be 1-2 billion Euros in the
Federal Republic of Germany alone (Leffmann et al. 2002) similar figures apply
for the UK (Bennet et al. 2004).
Lesion severity ranges from superficial skin irritation in patients with tran-
siently impaired sensation to deep sores in long-term immobilized patients. Life-
threatening infections and/or the necessity for surgical treatment may ensue. Thus,
pressure sores contribute considerably to morbidity and mortality in immobilized
patients. Figure 6.1 shows body regions prone to sore formation.
Different classification guidelines grade pressure ulcers according to severity,
cf. e.g. Dealey and Lindholm (2006). These include numerous stages each defining
a different grade of tissue damage. Pressure ulcer grading helps provide risk
assessment of potential pressure ulcer development and helps determine the extent
of tissue damage. It furthermore permits prevalence and incidence surveys which,
as additional information, help judge effectiveness of body support devices.
Although there have been several grading systems introduced, up to 14 as reported
in Halboom (2005), probably the most widely used is that developed by the
NPUAP and the European pressure ulcer advisory panel (EPUAP), the European
counterpart, cf. Table 6.1 . Historically, the first well-documented pressure ulcer
grading system was introduced by Shea (1975), defining each stage by the extent
of tissue damage. As a common feature, all classification systems focus on visible
examination of the skin and signs of skin breakdown.
Clinical observation shows that pressure ulcer development is progressive and
can either begin in superficial skin layers or may originate from deep subdermal
layers, spreading to superficial dermal and then epidermal layers (Daniel et al.
1981; Quintavalle et al. 2006; Bliss 1993). The NPUAP has recently redefined the
definition and the stages of pressure ulcers, and defined deep tissue injuries (DTI)
as ''a pressure related injury to subcutaneous tissues under intact skin''. This
revision was initially accompanied by the debate about whether these injuries are
truly pressure ulcers. In fact, DTI is a very severe form of pressure ulcer which
progresses more quickly and involves more extensive ulceration than superficial
ulcers. Due to the fact that the skin is most often intact, DTI is commonly mistaken
for a grade-I pressure ulcer or even a bruise. This misjudgement can have a
profound impact on patient outcome, liability, and reimbursement. Often, by the
time the ulcer is detected, clinical intervention is complicated and the prognosis
uncertain.
Deep tissue injury is not a new discovery. Shea's early grading system referred
to DTI using the term 'closed pressure sores'. A century earlier, in 1873, Sir Paget,
who was the first to officially relate pressure ulcers to local external loading, noted
a form of ulcer erupting from intact skin.
Due to the DTI phenomenon it is not sufficient to investigate the mechanical
tissue situation under body weight loading exclusively at the skin level, but also in
deeper

tissue layers. Mechanical evaluation tools, however, like a pressure