2004 Abstract : CS 1

Authors: Sean M. Hassinger, MD, Gordon Harding, Montri D. Wongworawat, MD

Title: Effects of Lavage on Bacterial Penetrance and Retention in Soft Tissue

Addresses: Loma Linda University School of Medicine, Department of Orthopaedic Surgery and Department of` Microbiology, 11234 Anderson Street, Suite A521, Loma Linda, CA, 92354

Purpose: To compare the depth of penetration and retention of bacteria in soft tissue after lavage.

Methods :Fresh ovine muscle specimens were harvested at the time of euthanasia and divided into control, low pressure lavage (LPL), and high pressure pulsatile lavage (HPPL) groups. The lavage groups were divided into subgroups (n = 10 each): lavage directed in-line (IL) with and across (AC) the muscle fibers.
Staphylococcus aureus bacteria were labeled using carboxyfluorescein diacetate, succinimidyl ester (CDFA/SE). The cells were washed in phosphate buffered saline and prepared at 5 x 108 cells/ml.
HPPL (Surgilav Plus, Stryker) and LPL (standardized to 3 psi) were held 5 cm from the muscle surface. After 200 ml lavage, each section was fixed in formaldehyde, embedded in paraffin, and mounted. Fluorescent images were obtained, and 50 µm x 50 µm grids were superimposed for referenced counting.
The bacteria were counted by two blinded independent observers, and inter- and intra-observer reliability was calculated using the Pearson correlation coefficient. Comparisons of bacterial penetration and retention were performed using analysis of variance, followed by Tukey post hoc (confidence interval: 95%, p < 0.05).

Results: Inter- and intra-observer reliabilities were good (r = 0.73) and excellent (r = 0.93), respectively. Average depth of bacterial penetration (depth where 50th percentile of bacteria were present for each specimen) and the total number of bacteria counted in a 50 µm wide column of tissue were determined. Results are summarized.

Depth (µm) with 50th percentile 850 ± 690 * 1680 ± 233 * 2095 ± 970 ** 3835 ± 409 ** 4220 ± 272
Number of bacteria in 50 µm column 94.4 ± 32.8 93.9 ± 27.9 * 39.7 ± 8.5 ** 197.4 ± 22.4 ** 187.6 ± 38.2
* significant when compared with the control group; ** significant when compared with the control, LPL-AC, and LPL-IL groups

Discussion: Recent evidence shows that HPPL damages bone, delays fracture healing, disrupts soft tissue, and drives particulate debris deeper. While bacterial size and adhesion characteristics present as new variables, similar findings were noted in this study, which demonstrated that HPPL was less effective at removing bacteria from muscle tissue. In-line irrigation may be more effective because fluid can more easily pass along fiber planes, while low pressure may enable better egress of contamination. In this study, the number of bacteria in the control group may be an underestimation, because the surface bacterial layer was likely partially washed off during fixation.

Significance: HPPL results in significantly deeper penetration and greater retention of bacteria in contaminated soft tissue. LPL is more effective in cleansing wounds contaminated with bacteria.