Farmers have a high risk of developing hip osteoarthritis (OA) due to the physical demands of their occupation. Nearly all farmers (87%) report joint pain while 22% have a prior diagnosis of OA (Webber et al. 2021). Farmers are at an approximately 9 times higher risk to develop hip OA compared to the general population (Croft et al. 1992). Farmers are at a 60% higher risk of developing severe hip OA within the first five years of their agricultural career (Croft et al. 1992; Andersen et al. 2012), which may be associated with the harsh terrains that farmers ambulate through on a daily basis (Services 2001). This increased risk is associated with a diminished work capacity (Webber et al. 2021) leading to a financial burden of approximately $167 million in lost productivity (Davis and Kotowski 2007). Although occupational tasks such as excessive standing and lifting heavy loads are associated with increased odds of developing symptomatic hip OA (Allen et al. 2010), there is little known about the potential biomechanical factors associated with hip joint degeneration in the farming population. This lack of information has led to ineffective non-operative treatments for both the clinical- (pain and dysfunction) and structural- (cartilage degeneration) symptoms associated with hip OA in the farming community.

Optimal joint loading during activity is essential in maintaining adequate articular cartilage health (Griffin and Guilak 2005) yet people with hip OA exhibit altered hip joint loading patterns during walking. More specifically, when compared to people without hip OA, people with hip OA exhibit lower peak hip extension angles as well as a higher peak hip extensor moments during walking and these altered sagittal plane hip joint mechanics are associated with hip joint cartilage degeneration and poor hip-related outcomes.(Kumar et al. 2015; Liao et al. 2019) These altered hip joint loading patterns may also be associated with the higher bone mineral density (BMD) within the femoral neck, which leads to a 57% higher risk of developing hip OA (Bergink et al. 2019). This multi-factorial pathomechanism of altered hip joint mechanics and impaired bone health observed in the non-agricultural population, may be similar to the pathomechanism of hip OA in the agricultural population, who’s job demands increase the exposure to this abnormal joint loading. However, the gait mechanics in farmers with hip OA has yet to be investigated.

Current non-operative treatments for hip OA used in the non-agricultural population include exercise (Zhang et al. 2008; Bannuru et al. 2019; Kolasinski et al. 2020) yet these exercise-based guidelines are based on clinical opinion (Kolasinski et al. 2020) and may not be generalizable to the farming population. Understanding the biomechanical etiology of hip OA in farmers will lead to the development of effective treatment programs for hip OA in the farming population. More specifically, an assessment of the gait-related deficits that may lead to hip OA in farmers is warranted and will provide the biomechanical targets needed to develop effective multi-disciplinary, exercise and movement re-training programs for treatment of hip-related clinical- and structural-disease within the farming community. Therefore, the purpose of this exploratory study was to assess gait mechanics in farmers compared to matched asymptomatic, non-farming individuals. It was hypothesized that farmers would exhibit altered lower extremity joint mechanics during walking when compared to the control group.

There were no between group differences in demographics, walking speed or total stance time (p>0.05; Table 1). Hip and knee joint kinematics were similar between the farmers and the controls (p>0.05; Figure 1) yet farmers exhibited statistical trends of lower peak ankle plantarflexion angles (p=0.08, d=1.28). Despite similar hip joint moments, the farmers ambulated with a significantly higher knee extensor moment (p=0.04, d=1.52) and moment impulse (p=0.05, d=1.66) during the first half of stance as well as statistical trends (p=0.08, d=1.46) of higher knee flexion moment impulse during the second half of stance (Figure 2). Farmers also walked with statistical trends of a higher ankle plantarflexor moment (p=0.08, d=1.48) and a significantly higher ankle plantarflexion moment impulse (p=0.04, d=1.56) when compared to the control group (Table 2). Farmers exhibited statistical trends of higher peak vGRF during the first (p=0.07, d=1.56) and second (p=0.07, d=1.53) halves of stance yet similar vGRF loading rates (p=0.15) as the control group (Figure 3).

This exploratory study assessed lower extremity gait mechanics in farmers to develop a preliminary understanding of the potential biomechanical factors related to hip joint OA in the agricultural community. The results of this study demonstrate a multi-joint gait alteration in farmers compared to non-farmers and may suggest a compensatory gait pattern to optimize hip joint mechanics in these farmers. More specifically, these results may suggest that farmers ambulate with altered knee and ankle joint mechanics in order to potentially absorb the large vGRF that are transferred through the lower extremity in a more optimal manner.

The farmers ambulated with higher peak vGRF during the first and second half of stance, suggesting that the farmers tended to apply a larger amount of force to the ground while walking. Although there were no differences in hip or knee kinematics, these higher vGRF may require a larger amount of absorption by the foot/ankle complex and may lead to the more dorsiflexed (i.e. less plantarflexed) ankle joint exhibited by the farmers during loading response. The more dorsiflexed ankle joint may require a proximal joint compensation to help support the lower extremity during the early stance phase. This study results indicate that the farmers ambulate with a higher knee extensor moment and moment impulse. This suggests farmers require a larger demand on the quadriceps to support the lower extremity.

Similar to the first half of stance, the farmers ambulated with a higher peak vGRF compared to the control group. In order to potentially provide for a more optimal strategy to absorb the higher vGRF through the lower extremity, the farmers ambulated with a higher knee flexor moment impulse compared to the control group in order to utilize the knee flexor musculature to help absorb the larger vGRF. These altered knee joint mechanics may have placed a larger demand on the ankle plantarflexors during terminal stance. More specifically, the farmers ambulated with a higher ankle plantarflexion moment and moment impulse during the second half of the stance phase, which may have potentially assisted farmers with push off of the lower extremity during terminal stance. In addition, prior work in the femoroacetabular impingement syndrome (FAIS) population, a pre-arthritic hip disease, demonstrated that individuals with FAIS ambulate with higher ankle plantarflexion moments and moment impulses compared to healthy individuals (Samaan et al. 2017). The farmers in this study demonstrated similar ankle joint mechanics during terminal stance as individuals with FAIS and may suggest that altered ankle joint mechanics in farmers may be a biomechanical marker associated with pre-arthritic hip joint disease.

This study is not without limitations and therefore, the results should be interpreted with caution. The main limitation of this study is the small sample size, yet the intention in this exploratory study was to provide an assessment of gait mechanics in farmers compared to a non-farming population. Although the small sample size is a limitation, the effect sizes of these results were large and suggests practical significance of the findings. The cross-sectional design of this study does not allow the determinization of whether or not these altered gait mechanics in farmers are a causative or compensatory mechanism of hip joint degeneration or hip pain in the farming population. Additionally, the design of this study has farmers walking on a flat treadmill despite previous work showing that there are other occupational specific tasks such as excessive standing and lifting heavy loads (Allen et al. 2010) that may be associated with development of lower extremity joint pain. Farmers also tend to wear work boots while performing their daily agricultural tasks, which may help to explain the large vGRF observed in this farmer cohort. This study’s experimental protocol required these farmers to ambulate with standardized athletic shoes, which may be considered a limitation of this study. It is also important to mention that despite the relatively large effect sizes for the statistically significant results, this study may be underpowered and therefore, future studies should include a larger cohort of farmers. The study results should be interpreted with caution as four crop farmers and one cattle farmer were included, and due to the small sample size, the authors are unable to directly understand occupation specific factors related to altered gait patterns. Although the overall intent of this paper was to assess gait mechanics in farmers, the cohort of farmers all self-reported lower extremity pain prior to the study, yet it should be noted that pain was not an inclusionary criterion for this study. Despite these limitations, the study provides a preliminary understanding of the impact that agricultural occupations have on joint mechanics that may be associated with the increased prevalence of hip OA in the agricultural population.

This study provides an initial assessment of lower extremity joint mechanics during walking in farmers. The farmer cohort in this study ambulated with altered lower extremity joint mechanics compared to an asymptomatic, non-farming population. As farmers are at an elevated risk of developing hip osteoarthritis, larger scale studies should be conducted to obtain a more conclusive understanding of the potential impact of altered gait mechanics on hip joint health in agricultural populations. In addition, future work should utilize a larger and more diverse sample of farmers in order to perform sub-group analyses to quantify gait patterns between different farming occupational groups. Further biomechanics-related research in farmers can provide the data needed to develop a multidisciplinary-based exercise program for conservative treatment of hip OA in the farming community.