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 (fully discussed in the SCIRE Wheeled Mobility chapter). 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).
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. Hamanami et al. (2004) identified the highest pressures were at the IT. 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.
There is level 2 evidence (from one prospective controlled trial; Hobson 1992) to support not generalizing pressure mapping data from able-bodied subject to SCI subjects.
There is level 4 evidence (from one case control study; Gutierrez et al. 2004) to support the typical locations for high pressure in the SCI population being the ischial tuberosities and the coccyx.
Pressure mapping studies using able-bodied subjects should not be generalized to the SCI population because pressure differences exist between the two groups.
Typical areas of high pressure for the SCI population include sacrum, coccyx and/or ischial tuberosities.