(K-429) Comparison of design feature geometry to inform surgical instrument reprocessing risk

Medical instrument reprocessing is an essential practice in healthcare delivery. Reprocessing involves preparing medical instruments for re-use and includes removal of biological debris and pathogens through cleaning and disinfection or sterilization. U.S. FDA regulations require surgical instrument manufacturers to develop reprocessing procedures and validate their efficacy. However, the increasing complexity of medical device designs and their use environments can increase the risks of inadequate reprocessing and associated device malfunctions and potential patient injury. While FDA and other organizations (e.g., AAMI and ISO) have published lists of design features that present known difficulties for reprocessing, information needed to define relative risks or feature-specific parameters that increase/decrease risks of inadequate reprocessing is lacking. These defined lists of design features include crevices, which are a common feature found on both reusable instruments that are commonly reprocessed, and single-use instruments that are perceived as more challenging to reprocess. Quantifying geometric data of difficult-to-clean features such as crevices may help further the understanding of the effect of design parameters on cleaning difficulty. There is an urgent need to quantify reprocessing risks associated with certain design features. The goal of this project is to measure crevice geometry across a variety of instrument designs and assess differences in crevice geometric data between collections of reusable and single-use instruments.

This study included 42 handheld surgical instruments, consisting of 14 stainless steel reusable instruments and 28 single-use instruments having both stainless steel and plastic components. Crevices were visually identified by two independent observers and classified as one of three types (i.e., boundless, through, and blind) using common descriptors for shape and cross-section (Figure 1). Crevices were measured using calibrated images captured with a reflected light inspection microscope (Omni-Core, Ash Technologies) and a hand-held caliper when needed for larger dimensions. Crevice dimension was defined by length, width, and depth. Generally, length and width were defined based on crevice feret diameters parallel to the surface of the instruments - length was assigned to the larger feret diameter and width was assigned to the smaller feret diameter. Depth was measured as a recession perpendicular to the instrument surface. A total of 641 crevices were measured, which includes all identified crevices on all instruments. Two independent observers measured a subset of 22 crevices to determine inter-observer variability (reliability). For statistical analysis, the median values and ranges of the length, width, and depth were calculated for each crevice type for all reusable instruments and all single-use instruments. 

There were 261 crevices measured on reusable instruments and 380 measured on single-use instruments. Of the 261 crevices measured on reusable instruments, 83% were boundless, 11% were through, and 6% were blind. Of the 375 crevices measured on single-use instruments, 46% were boundless, 9% of them were through, and 45% were blind (Table 1). Performing a chi-square test for independence indicated that crevice type and instrument type are dependent (χ2=116.5, p=5.11*10-26).

The median length, width, and depth of crevices on reusable instruments were 6.78 mm, 1.41 mm, and 0.84 mm, respectively, compared to the median length, width, and depth of crevices on single-use instruments, which were 14.1 mm,1.12 mm, and 1.12 mm (Table 2).

Median length, width, and depth of crevices found on reusable instruments were shorter, higher, and higher, respectively, than the median length, width and depth found on single-use instruments. None of the measured sample populations followed a normal distribution (Jarque-Bera test, ɑ=0.05, χ2=5.99). Sample distributions were compared using a Mann-Whitney U test, in which comparison between reusable and single-use instrument crevice length and width demonstrated significantly different medians (Z=-5.7, Z=-4.4, respectively, 95% confidence interval). Depth comparison did not demonstrate significantly different medians between the two groups (Z=-0.88).

Thin, long spaces provide more difficulty for removal of bioburden than shorter, wider spaces. Therefore, based on observed geometric data, crevice parameters on single-use instruments are likely more conducive to harboring bioburden than crevice parameters on reusable instruments. Longer lengths and smaller widths on single-use instrument crevices may provide an environment more challenging for cleaning procedures during reprocessing. Although statistical analysis did not show a significant difference between median depths, single-use instruments have a larger range of depths than reusable instruments, which is true of length and width as well. Reusable instruments were designed with a higher proportion of boundless crevices while single-use instruments were designed with a higher proportion of blind crevices. Blind crevices are similar to dead-end holes, which also present known risks for harboring bioburden. This dimensional analysis suggests that reusable and single-use instruments have different design features and further work is needed to evaluate whether that difference impacts ease and effectiveness of reprocessing.