Heat Generation during Minimally Invasive First Metatarsal Osteotomy: A Cadaveric Study

Abstract

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: Bunions are one of the most common pathologies treated by orthopedic foot and ankle surgeons. The usage of minimally invasive and percutaneous surgical techniques continues to rise due to evidence of less pain, improved functional outcomes and low recurrence rates. Still, concern regarding heat generation during these procedures, osteonecrosis of bone, and nonunion persists. Literature suggests cool irrigation is superior to room temperature irrigation, but the question remains if irrigation is needed at all. This study evaluates the heat generation during percutaneous bunion surgery and analyzes the use of cooled irrigation compared to no irrigation at all. This study tested the hypothesis that cool irrigation would lead to overall lower heat generation compared to no irrigation at all. Methods: 5 matched paired cadavers (10 legs) were used to simulate MIS first metatarsal distal transverse osteotomy for all trials. Prior to osteotomy, 4 temperature probes were inserted as to the border where the Shannon burr would travel along the osteotomy site (Image 1). Probes were secured by suture and temperature was recorded using K-type thermocouples. All trials were completed using a pulse technique of 20 seconds on, 5 seconds off with a Shannon Burr and fluoroscopic guidance. Trials were complete with continuous cold irrigation (N=5) and without any irrigation at all (N=4). Temperatures were evaluated at baseline, during burring, and after burring to assess total heat generation and dissipation. A two-tailed t-test was used to analyze differences in heat generation and dissipation between procedures completed with irrigation and without irrigation (P < 0.05). Results: 5 cadavers with a mean age of 86.2 were evaluated (10 total simulations, 9 analyzed). Cadavers underwent 1 trial with irrigation, and 1 without on opposite feet. 88.9% of patients showed heat generation below the level of bone necrosis (50 oC). One trial with irrigation temperature rose to 79.1oC. Matching specimen without irrigation had probe failure and no temperature was obtained. Average burr time was 51.2±2.4 seconds with irrigation, and 35±0.5 seconds without. Irrigation was associated with a significant increase in burr time (P=0.002). Average temperature change was 13.62±11.9 and 0.7±0.5 during burring, 7.1±1.8 and 5.8±0.3 after burring in procedures with and without irrigation, respectively. No significant difference was detected between heat generation in irrigated vs non-irrigated procedures (P = 0.371, 0.548). Conclusion: This study found that in a cadaveric model the use of cooled irrigation, compared to no irrigation, did not lead to a significant difference in the heat generation during MIS first metatarsal distal transverse osteotomy. However, 1 out of the 9 samples used in this study showed a heat generation above 50 oC. Additionally, to our surprise the use of irrigation led to a significant increase in burring time. This may be useful information for a surgeon when considering the usage of cooled irrigation to reduce the potential risk of osteonecrosis when performing a MIS first metatarsal distal transverse osteotomy.