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Osteoarthritis is one of the oldest recorded diseases that can impair movement and cause pain—affecting over half of the elderly community, osteoarthritis of the acromioclavicular joint is one of the most common sources of shoulder pain due to its ability to break down tissues within a joint due to repeated mechanical loadings. These loading repetitions eventually begin to form osteophytes at the articulating surfaces of the joint effectively increasing the stress at the joint and decreasing the spacing. Due to this decrease of space, the clinical physical examinations done involve moving the arm into positions that decrease the space further causing acute pain at the joint. One of the current standard clinical physical examination tests is the Cross Body Adduction test which has been shown to close the joint spacing a significant enough amount to cause irritation and signal the presence of osteoarthritis. However, a new test involving placing the hand behind the back, called the Reverse Shoulder Internal Rotation Test—also referred to as the Hand Behind the Back test—has been proposed after it was observed clinically to provide a more accurate osteoarthritis diagnosis than the Cross Body Adduction test for some patients. Through this work, both the Cross Body Adduction and Hand Behind the Back tests were modeled in order to determine if there is merit for the Hand Behind the Back test to be used as a diagnostic tool for clinicians.Both tests were modeled using the Zygote Solid 3D 50th Percentile Male Human Anatomy model (ZYGOTE, American Fork, UT) for the bone 3D models and MSC.ADAMS (MSC Software, Newport Beach, CA) to compile and run the simulations. Within MSC.ADAMS the bones were given compact bone material properties and were outfitted with joints, single-component forces for muscles, springs for ligaments, and normal to the rib’s tangent springs to simulate the scapulothoracic articulation. Once the models were completed, the simulations were ran and it was found that the distance between the acromioclavicular joint articulating surfaces decreased by 0.3 mm for the Cross Body Adduction test and the Hand Behind the Back test demonstrated a spacing decrease of 1.65 mm—5.5x greater decrease than the Cross Body Adduction test. These results indicate that the Hand Behind the Back test may be a better diagnostic test for early stage osteoarthritis of the acromioclavicular joint due to the greater stress and irritation it places upon the joint. In order to validify these findings, further studies are required.