Exposure to risk factors for the development of lower limb osteoarthritis during Army infantry training

Background: Osteoarthritis (OA) is a degenerative musculoskeletal condition which affects the joints. Rates of lower limb OA in military personnel have been increasing over time and are becoming more prevalent in younger personnel. This has the potential to lead to personnel discharge and losses in, and impacts on, military capability. Therefore, the purpose of this study was two-fold: (1) to determine the exposure of Army trainees qualifying as infantry soldiers to occupational tasks associated with the development of lower limb OA, and (2) to compare the cumulative exposure to such tasks to minimum exposure thresholds set by the Australian Repatriation Medical Authority (RMA) for the development of lower limb OA.Methods: Exposure to occupational tasks undertaken by Army trainees who completed the initial basic training (12 weeks) followed by initial infantry training (16 weeks) were determined. Cumulative magnitudes of exposure to activities known to be associated with increased risk of OA development were calculated using a desktop analysis of both training programs. For example, threshold values relating to durations in various body positions, loads lifted and carried, and stair-climbing tasks were calculated using a desktop analysis and validated by direct observations and surveys. The physically demanding occupational tasks reported by the RMA’s Statements of Principles to be associated with increased risk of developing lower limb OA in this population of interest were kneeling/squatting >1hour, lifting or carrying loads >20kg, and climbing >150 stairs. Findings were extrapolated into a Job Exposure Matrix.Results: Following both training programs required to qualify as an infantry soldier, projected annual cumulative kilograms of all lifted loads while weight bearing through the lower limbs was 140,647 kg. Under the RMA’s ‘reasonable hypothesis’ scenario for increased risk of lower limb OA due to service reasons of lifting loads over 20 kg to a cumulative total of 100,000 kg within a 10-year service period, trainees in this training program were estimated to meet this threshold in 2 years, 26 weeks following commencement of service; if these exposures continued at the same level as those during the 28 weeks of training. Additionally, the ‘balance of probabilities’ scenario for having carried loads over 20 kg for a cumulative total of 3,800 hours within a 10-year period of service, would be met after 4 years, 45 weeks.Discussion: The exposures threshold levels associated with an increased risk of developing lower limb OA in Infantry soldiers for lifting and carrying of loads of over 20 kg are likely to be reached within approximately 2.5 and 5 years, respectively, if the cumulative loads continue from those experienced during trade training. This is a highly probable scenario given the load carriage requirements of these personnel.Impact: Infantry personnel are known to lift and carry heavy occupational loads. While load carriage is an essential occupational task, it may concomitantly increase infantry personnel’s risk of developing lower limb OA. Means of mitigating cumulative exposures and musculoskeletal recovery techniques should be developed to reduce the risk and increasing burden of lower limb OA within Army infantry personnel.Conflict of interest statement: This research was funded by the Department of Veterans’ Affairs.