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Skin Integrity and Pressure Injuries

SCI vs. Able-Bodied Participants

Concern has been raised regarding the use of data from studies where able-bodied subjects are used and results are generalized to a disabled population, particularly in relation to the use of pressure mapping. The use of able-bodied subjects is often seen in the pressure mapping data provided by support surface manufacturers. Several studies have looked at pressure mapping comparisons between disabled and non-disabled subjects to determine if there is a difference in pressure data. Drummond (1985) compared pressure mapping values of 16 subjects with paraplegia (14 with spina bifida cystica; 2 traumatic) with 15 normal subjects. The paraplegia group was divided further into those who developed ulcers (n=10) and those who did not (n=6). In subjects with ulcerations, the posterior distribution of high pressure under the IT and coccyx areas were an average of 60% of the body weight compared to 40% in the normal group. The majority of subjects (8/10) with ulcers showed asymmetrical IT loading with greater than 30% of body weight on one IT, in contrast to 0 subjects in both the non-ulcerated and normal subjects. Further, the majority of subjects (8/10) with ulcers had greater than 11% of the weight distributed to sacral and coccyx regions compared to 2/6 non-ulcerated and 0 normal subjects (Drummond 1985).

Results of a study by Stinson et al. (2003), in which the relationship between interface pressure and body mass index, gender and seating positions were evaluated in 63 volunteer students, indicated that there was no significant relationship between average pressures and height, weight or gender. This was confirmed by a study by Karatas et al. (2008) where these same parameters were compared between 16 subjects with SCI and 18 healthy volunteer subjects. Comparing average pressure and body mass index, Stinson et al. (2003) showed significance (p<0.01), whereas the study by Karatas did not (p>0.05). Karatas et al. (2008) also used pressure mapping to examine centre of pressure displacement. Centre of pressure displacement in patients with SCI was significantly smaller in all directions than in healthy volunteers (p<0.05).

Author Year
Country
Research Design
Sample Size

Methods

Outcome

Hobson 1992
USA
Prospective Controlled
Trial
N=22
Population:
SCI group (n=12): Mean Age=40.9 yr; Gender: males=10, females=2; Level of injury: paraplegia=7, tetraplegia=5; Severity of injury: complete; Mean time since injury=19.5 yr. Able-Bodied group (n=10): Mean age=39.3 yr; Gender: males=6, females=4.
Intervention: Comparison of Pressure mapping and shear measurements from midline neutral posture to eight typical wheelchair-sitting postures (trunk bending left and right, forward trunk flexion 30 and 50 degrees, back recline 110 and 120 degrees and tilt 10 and 20 degrees).
Outcome Measures: Tangentially induced shear (TIS) measuring shear forces; Pressure distribution – Oxford Pressure Monitor Device measuring average and maximum pressure and peak pressures gradient.
1. Mean maximum pressure was on average 26% higher in the SCI group versus the able-bodied group.
2. Forward trunk flexion reduced the average pressure for both groups; however, SCI group encountered a 10% increase in pressure at the initial 30° of forward flex before a reduction occurred.
3. SCI subjects had a mean peak pressure gradient that was 1.5-2.5 greater than able-bodied subjects. Maximum decrease of pressure gradient from a neutral position happened after the backrest reclined to 120°.
4. When a sitting position change occurred, a similar shift to the anterior/posterior midline location of maximum pressure was experienced in both groups. From neutral, a forward trunk flexion at 30° and 50° produced a 2.4 and 2.7 cm posterior shift. When the backrest reclined to 120°, the greatest posterior shift occurred at 6 cm.
Gutierrez et al. 2004
Sweden
Case Control
N=33
Population:
SCI group: Gender: males=25; Level of injury: paraplegia=25; Severity of injury: AIS A=25.Able-bodied group: Gender: males=8.
Intervention: Posture changes as related to pressure, contact area and symmetry of loading, on a standardized hard surface and for SCI, in their wheelchair as well.
Outcome Measures: Pressure distribution via Tekscan Pressure Mat.
1. Significant differences were found between the groups. SCI group had increased pressure (p<0.01), decreased contact area (p<0.01), and increased asymmetry (p<0.05).
2. Sitting in their own wheelchair improved pressure distribution, as compared to the hard surface. Although total seating area force increased (p<0.01), the pressure reduced, and the contact area increased (p<0.01).
3. No improvements occurred when comparing relaxed and upright position in their own wheelchair.

Discussion

Hobson (1992) evaluated the pressure distribution differences between able-bodied and SCI populations. The results indicated that the SCI population had, on average, 26% higher maximum pressure in all nine postures evaluated. Gutierrez et al. (2004) found a significant difference between their SCI group and control group, with the SCI group having increased pressure, decreased contact area, and increased asymmetry. Gutierrez et al. (2004) indicated that subjects with SCI were supporting the same weight as the able-bodied subjects, but on a smaller area of surface contact with asymmetries, resulting in a higher maximum pressure; therefore, it is important to assess loading asymmetries for the SCI population. Gutierrez et al. (2004) found no significant differences in sitting configurations for high versus low thoracic SCI.

Conclusions

There is level 2 evidence (from one prospective controlled trial: Hobson 1992) and level 4 evidence (from one case control study: Gutierrez et al. 2004) to support not generalizing pressure mapping data from able-bodied subjects to SCI subjects.

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