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Appropriate pressure during the application of a cast is critical to provide adequate stabilization of fractures. Force-sensing resistors (FSR) were used to measure pressure during cast placement and removal. The data demonstrated a signature pattern of skin pressure during the different steps of cast placement and removal. This reproducible signal provides validity evidence for our model.
Cast placement is a widely used method for the treatment of fractures; however, complications can arise if the cast is placed loosely (abrasions, friction blisters) or too tight (compartment syndrome, ischemia and pressure sores) . Changes in fracture management practice and work hour restrictions have decreased orthopedic surgery residents’ exposure to cast application hindering their ability to practice . Our prior work showed sensor enabled medical simulation allows for quantitative evaluation of hands-on clinical skills . Additional research has demonstrated the feasibility of measuring casting pressures . The goal of this project is to develop a casting simulation model that provides immediate, reliable feedback regarding skin pressure during cast placement and removal.
A plastinated arm model created from PlatSil Gel-10 (Polytek Development Corp) was utilized in the simulated experiment. A single person’s right forearm was used as a comparison. Data were collected from seven force-sensing resistors (FSR) (Interlink Electronics FSR™): six on the dorsal and ventral surface of the forearm and one on the palm (Figure 1). Sensor inputs were sampled at a rate of 15 Hz using in-house hardware and software. The experimental protocol involved seven steps of cast placement and removal by the same experienced provider with pressure recordings taken throughout. The steps are as follows: 1) placement of cotton undercast padding; 2) placement of two layers of fiberglass casting tape; 3) cast sawing down the dorsal longitudinal midline of the cast; 4) cast spreading through the dorsal cut (univalve); 5) cast sawing down the ventral longitudinal midline of the cast; 6) cast spreading through the ventral cut (bivalve); 7) cast removal. Pressure sensor data were collected and plotted over time for each of the sensors using Matlab. The data from FSR #2 were representative of the sample, and therefore, it was used for further analysis.
Results are presented from FSR #2 located on the dorsal mid-forearm (Figures 2 & 3). After application of the cotton undercast padding, the average skin pressure of the plastinated arm (20.46 mmHg (SD 0.76)) was similar to that of the human arm (20.60 mmHg (SD 0.37)). Again, following application of the fiberglass cast, the average skin pressure of the plastinated arm (42.20 mmHg (SD 2.52)) was similar to the human arm (45.58 mmHg (SD 2.71)). During the cast application process, the maximum and minimum skin pressures tended to be higher for the human arm (59.49 mmHg and 39.68 mmHg) than the plastinated arm (49.07 mmHg and 34.63 mmHg). With the human model, recordings were taken during hand movement. This data showed increased variability of pressures with a maximum pressure of 71.51 mmHg and minimum skin pressures of 33.57 mmHg. The average skin pressure in the human arm model after hand movement was much lower (26.67 mmHg (SD 4.06)) than prior to hand movement (45.58 mm Hg (SD 2.71)).
Application and removal of the cast on both the plastinated and human forearm demonstrated a signature pattern of changes in skin pressure (Figures 2 & 3) giving validity to use of FSR’s to monitor pressure changes during the task. The plastinated and human arm had similar pressures following placement of the cotton undercast padding and fiberglass cast indicating the materials used to create the plastinated model are a good simulation for human tissue. There were some areas of difference between the human and plastinated skin pressures likely related to muscle contraction and skin movement intrinsic to the human model. These factors will be important to consider when developing an effective teaching simulation model for cast placement.
This project demonstrated an innovative strategy for monitoring skin pressure during cast application in the process of developing a simulation model that provides immediate, reliable feedback during cast placement. Further research is needed to establish an expert standard of cast application pressures for our simulation model.