lower extremity, risk model, work-related musculoskeletal disorder, risk factor, occupational disorder, knee disorder


Introduction: Lower extremity (LE) work-related musculoskeletal disorders (WMSDs) are known to occur with cumulative exposure to occupational and personal risks. The objective of this dissertation study was to find if creating a quantifiable risk detection model for the LE was feasible. The primary product of the literature review conducted for this study resulted in focusing the attention of the model development process onto creating the initial model of the LE for assessing knee disorder risk factors. Literature Review: LE occupational disorders affect numerous industries and thousands of people each year by affecting any one of the musculoskeletal systems deemed susceptible by the occupational and personal risk factors involved. Industries known to be affected tend to have labor intensive job descriptions. Some of the numerous industry examples include mining, manufacturing, firefighting, and carpet laying. Types of WMSDs noticed by the literature include bursitis, osteoarthritis, stress fractures, tissue inflammation, and nerve entrapment. In addition to the occupationally related disorders that may develop, occupationally related discomforts were also taken into consideration by this study. Generally, both the disorders and the discomforts can be traced to either a personal or occupational risk factor or both. Personal risk factors noted by the literature include a person's physical fitness and health history (such as past injuries). Meanwhile, occupational risks can be generalized to physical postures, activities, and even joint angles. Prevalence data over a three year interval (2003-2005) has found that LE WMSDs make up on average approximately 7.5% of all the WMSD cases reported to the US Occupational Safety and Health Administration (OSHA). When the literature is refined to the information pertaining to occupational knee disorders, the mean prevalence percentage of the same three year range is about 5%. Mean cost for knee injuries were found to be $18,495 (for the year between 2003 and 2004). Methodology: Developing a risk model for the knee meant using groups of subject matter experts for model development and task hazard analysis. Sample occupational risk data also needed to be gathered for each of a series of tasks so that the model could be validated. These sample data were collected from a sample aircraft assembly plant of a US aerospace manufacturer. Results: Based on the disorder and risk data found in the literature, a knee risk assessment model was developed to utilize observational, questionnaire, and direct measure data collection methods. The final version of this study's knee model has an inventory of 11 risk factors (8 occupational and 3 personal) each with varying degrees of risk exposure thresholds (e.g., high risk, moderate risk, or minimal risk). For the occupational risk assessment portion of the model, the results of task evaluations include both an occupational risk resultant score (risk score) and a task risk level (safe or hazardous). This set of results is also available for a cumulative (whole day) assessment. The personal risk assessment portion only produces a risk resultant score. Validation of the knee risk model reveals statistically (t (34) = 1.512, p = 0.156), that it is functioning as it should and can decide between hazardous and safe tasks. Additionally, the model is also capable of analyzing tasks as a series of cumulative daily events and providing an occupational and personal risk overview for individuals. Conclusion: While the model proved to be functional to the given sample site and hypothetical situations, further studies are needed outside of the aerospace manufacturing environment to continue testing both the model's validity and applicability to other industrial environments. The iterative adjustments generated for the occupational risk portion of the model (to reduce false positives and negatives) will need additional studies that will further evaluate professional human judgment of knee risk against this model's results. Future investigations must also make subject matter experts aware of the minimal risk levels of this knee risk assessment model so that task observational results are equally comparable. Additional studies are moreover needed to assess the intimate nature between variable interactions; especially multiple model defined minimal risks within a single task.


If this is your thesis or dissertation, and want to learn how to access it or for more information about readership statistics, contact us at

Graduation Date



McCauley-Bush, Pamela


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Industrial Engineering and Management Systems

Degree Program

Industrial Engineering








Release Date

May 2009

Length of Campus-only Access


Access Status

Doctoral Dissertation (Open Access)