The site of pressure sore development will depend on several factors such as patient’s mobility, body mass index, positioning, and local anatomy. However, the most common overall site is the sacrum (28–36%). This occurs most frequently in bed-bound patients, particularly those with spinal cord injuries and other individuals such as frail, elderly patients with decreased mobility who spend long periods of time in a lying position. Other common anatomic sites are the ischial tuberosity (17–20%) in seated patients who spend long periods in wheelchairs, for example. The heels are also quite commonly affected (9%) in bed-bound patients lying supine. The greater trochanter is at risk in individuals lying in a lateral position for extended periods. The posterior scalp (occiput) is at risk for patients in intensive care for extended periods due to immobility.1
Causal factors in the development of pressure sores can be classified as intrinsic or extrinsic. Key extrinsic factors are the forces of shear, friction, and pressure (compression). However, moisture is also an extrinsic factor, and this increases the risk of pressure sore development in incontinent patients. Intrinsic factors include ischemia, infection, sensory loss, vascular disease, altered consciousness, decreased autonomic control, anemia, and malnutrition. Management of pressure sores is based on addressing both intrinsic and extrinsic factors.1–4
is one example. It has subscales, including sensory perception, skin moisture, activity, mobility, nutrition, and local mechanical forces that act on wounds. Composite scores range from 6 to 23, with lower scores indicating an increased risk for pressure sore development.1,2 Other systems include the Waterlow score, which places patients in different risk categories (low, medium, and high) based on factors such as body mass index (BMI), skin type, sex, malnutrition, continence, mobility, and age.3 Although the assessment and scoring of a pressure sore are typically undertaken by the nursing team, understanding the workings of these systems is highly relevant to the surgical team both for delivery of high- quality, safe patient care and for the preparation for clinical exams. Assessment of pressure areas now forms part of the surgical check listing process before starting and after completing surgery. This is particularly important in longer procedures and in high-risk patients.
4. Enis JE, Sarmiento A. The pathophysiology and management of pressure sores. Orthop Rev 1973;2:25–34
Capillary blood pressure ranges from 12 mm Hg at the venous end to 32 mm Hg at the arterial end. If external pressure exceeds the capillary opening pressure, then perfusion is reduced. For short time periods, this will have no detrimental effect. However, if it is continued for an extended time, ischemia and tissue damage will occur. An inverse relationship exists between the amount of pressure and the duration required to cause pressure necrosis. Animal studies have shown that a pressure of 70 mm Hg applied over 2 hours was sufficient to cause pathologic changes in dogs. In a porcine model, pressure of 100 mm Hg for only 10 minutes caused muscle necrosis. Changes in the skin occur later than those in muscle, suggesting that pressure sores begin deep and the skin changes are late signs. Lindan et al1 performed a landmark study in 1965. They observed pressures of up to 60 mm Hg in the sacral area of humans who were in a supine position (Fig. 66.2). Pressure in the heels, occiput, and buttocks was approximately 40 mm Hg. Measurements of patients in the seated position were greatest at the ischial tuberosities and were in the order of 100 mm Hg. This helps explain the high incidence of ischial pressure sores. A B C D Fig. 66.2 Pressure-distribution maps (in mm Hg) of a male figure. A, Supine. B, Prone. C, Sitting with feet hanging freely. D, Sitting with feet supported. (Adapted from Lindan O, Greenway RM, Piazza JM. Pressure distribution on the surface of the human body. I. Evaluation in lying and sitting positions using a bed of springs and nails. Arch Phys Med Rehabil 46:378, 1965.)
All of the choices are vital components of prevention and nonsurgical management of pressure sores. However, according to the Kosiak’s principle, tissues tolerate increased pressure if it is interspersed with pressure-free periods.1 Seated patients should therefore be lifted every 10 minutes for 10 seconds, and supine patients should be turned every 2 hours. Kosiak2 first demonstrated the principle in 1959 by applying varying loads to the trochanters and ischial tuberosities of dogs. He found that high loads for short periods or low loads for long periods caused pressure ulcers. He later used a rat model to show that removal of pressure for short periods of time provided relief and resulted in less tissue damage.3 Tissues are more susceptible to a constant load as opposed to an intermittent load. Similarly, Dinsdale4 showed prevention of injury when pressure was relieved for short durations, for example, 5 minutes of relief from a pressure of more than 400 mm Hg.
The benchmark test for diagnosis of osteomyelitis within a deep pressure area is a positive bone biopsy. However, this is not always technically possible unless the patient is in the OR. Routine microbiology swabs from pressure sores will show growth of multiple organisms and interpretation of these results needs to be combined with a clinical evaluation to assess for evidence of local infection. The best noninvasive option for patients with suspected osteomyelitis would be an MRI. Plain radiographs and CT may be useful but are less accurate. The clinical importance of osteomyelitis is that if the extent is unknown or underappreciated, then any reconstruction is destined to fail.1–3
MRI has a high sensitivity and specificity for evaluation of the extent of osteomyelitis. Huang et al1 conducted a study to assess the accuracy and utility of MRI for diagnosing osteomyelitis in pressure sores, using histologic/ microbiologic results as the standard of reference. They compared the extent of infection using MRI and surgical margins. The overall accuracy of MRI was high with only one false-negative MRI study. MRI for the diagnosis of osteomyelitis yielded a sensitivity of 97% and a specificity of 89%. A total of 21 patients underwent limited surgical resection guided by MRI findings in which only the enhancing area was resected. Osteomyelitis recurred only once, at the surgical margins. The authors concluded that MRI is accurate in the diagnosis of osteomyelitis and associated soft tissue abnormalities in spinal cord–injured patients. It can delineate the extent of infection and help to guide limited surgical resection and preserve viable tissue.
Dakin’s solution can be useful for cleaning wounds such as pressure sores that have Pseudomonas growth, but should be used cautiously and for limited periods because of its toxicity to healthy tissue. It contains sodium hypochlorite and boric acid, not silver sulfadiazine. It should be diluted to quarter strength and used for a few days only (not 14 days). Wounds with Pseudomonas typically appear green and have a characteristic malodor. Other popular dressings for pressure sores include hydrogels if there is black eschar, hydrocolloids if there is granulation tissue, and an alginate and absorbent foam in wounds with high exudate. Manuka honey has also become popular for chemical debridement of pressure sores and this works in a number of ways which include antibacterial as well as debriding. The use of a dressing containing silver is particularly useful in cases of Pseudomonas infection. Irrespective of dressing used, the propensity for a pressure sore to heal will be dependent on the vascularity of the wound itself and removal of the instigating cause.1–3
Although any nonviable or infected bone should be fully debrided, healthy bony prominences should not be routinely excised. If healthy bony prominences are excised to relieve pressure at the site of the sore, this can have unintended consequences from pressure transfer to other sites. An example is perineal ulceration following over-resection of the ischial tuberosity. Coating the bursa with methylene blue dye before excision can help verify that all bursal tissue has been completely excised. Infiltration of the peribursal area with a liposuction solution can help reduce/control bleeding during debridement. During reconstruction, any dead space must be obliterated with the chosen flap. Flaps should always be designed to allow for further revision surgery. For this reason, advancement and rotation flaps are generally preferred.1–3
series. Several authors have assessed recurrence rates after reconstruction of pressure sores. The overall rates range from 19% at 3.7 years (Kierney et al1) to 69% at 9.3 months (Disa et al2). Disa et al indicated that young posttraumatic paraplegics had a particularly high recurrence rate of 79% at 11 months. In a meta-analysis of pressure sore recurrence rates from 55 studies, Sameem et al3 identified similar recurrence rates with myocutaneous (8.9%) and fasciocutaneous (11.2%) flaps. Perforator flaps appeared to fare best overall with a 5.6% recurrence rate, but the differences between the three flap types were not statistically significant.