Surgeons propose ‘slipperiness score’ for winter weather reports

Dr. Kevin Chung

Dr. Kevin Chung

The plethora of meteorological indexes — wind chill factor, humidex, UV index, air quality index, pollen counts — may have to make room for a new “slipperiness score” proposed by clinicians at the University of Michigan.

The researchers, led by two surgeons, analyzed a sample of U.S. Medicare claims from 2007 for distal radius fracture (a cohort of 21,507 patients, or 25% of all of Medicare beneficiaries with distal radius fractures that year) and correlated the diagnoses with weather data for the date and location of each injury in the cohort.

From that analysis, they devised a novel “slipperiness score,” from zero to seven, for the severity of slippery weather conditions.

The scoring calculator, below, shows the incremental contribution of each weather condition to the risk of slipping:

Weather Condition                                                                                           Added to Score

  • 1. Temperature ≤32°F                                                                                            +1
  • 2a. Presence of mild weather events* (e.g., rain, drizzle) OR           +1
  • 2b. Presence of harsh weather events† (e.g., snow, freezing rain)      +2
  • 3. Presence of snow/ice on ground at start of day                                     +1
  • 4a. Precipitation on ground that day with water
  • equivalent ≤0.01 inch OR                                                                                    +1
  • 4b. Precipitation on ground that day with water
  • equivalent >0.01 inch                                                                                            +2
  • 5. Max wind speed ≥24 mph                                                                               +1
  • Total‡ 0–7
  • *Mild weather events: rain, mist, drizzle, showers, thunderstorms.
  • †Harsh weather events: freezing drizzle, freezing fog, freezing rain, hail, snow pellets, ice pellets, snow grains, snow, glaze, drifting snow, thunderstorm hail, thunderstorms with snow pellets, thunderstorm snow.
  • ‡Total = slipperiness score (0–7).

Risky slippery days were deemed to be those with a slipperiness score of 5 or higher, the researchers reported in the February issue of Plastic and Reconstructive Surgery, noting that the risk of sustaining a distal radius fracture was increased 21% on days with a slipperiness score above 4.

Dichotomizing the slipperiness score with 5 and above being a “slippery” day, the incidence rate ratio for a slippery day is 1.14, indicating that the risk of sustaining a distal radius fracture in an elderly population is increased by 14% on a slippery day. The findings applied only to minor distal radius fractures, which the researchers said are more likely caused by slip and fall accidents,  but major fractures did not increase significantly based on slipperiness score.

“Although the concept that slippery footing increases your risk of falling isnʼt new, what weʼve been able to show is that these dangerous conditions result in more fractures in this already vulnerable population of adults,” lead  author Dr. Aviram Giladi, a  resident in the department of surgery, said in a university news release.

“Understanding the risk of these injuries can help inform prevention and preparation efforts, especially on days where the weather is bound to result in more slippery conditions,” added senior  author and hand surgeon Dr. Kevin Chung.

“We hope to help people prepare for risky conditions and adjust where and when they walk outdoors,” said Dr. Chung, who is also professor of plastic surgery and orthopedic surgery and the Charles B. G. de Nancrede Professor of Surgery.

The score “allows our results to be more transferrable to public health and prevention domains by providing an easily reproducible scale that helps predict fracture risk attributable to weather,” they said in the report of the study.

They acknowledged that  factors other than weather conditions affect walking safety and fracture risk, including footwear, distance walked and sidewalk maintenance — making pavement safety modeling more “challenging” than road safety modeling.

But “considering the ease with which a daily weather report could be translated into this slipperiness score, identifying and publicizing high-risk-weather days can be implemented similar to air quality, ultraviolet light, and icy road warning systems,” they added. “Although the results from these warning systems have been mixed, when used properly, they can effect change and health improvements for individuals.”

Other studies have shown that a major limitation to the success of fall risk prevention in the elderly is that many of those with the highest risk — who are more mobile and athletic for their age — do see themselves as being at risk of falling. They also prefer “messages of health and independence,” the Michigan group wrote.

“Using a slipperiness index to relay hazardous conditions might inform timely behavior change and have success in fall and fracture prevention where other educational efforts have thus far been unsuccessful.”~TM

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