Final answer:
The term 'open scissors syndrome' is not commonly recognized, but based on provided details, the primary side effect might be 'Altered joint mechanics,' due to changes in muscle balance or skeletal posture.
Step-by-step explanation:
The term 'open scissors syndrome' is not a widely recognized medical term; therefore, it is important to clarify that this question might refer to a specific, perhaps less known, condition or concept. Based on the provided information, if we consider an analogy with the listed options, the primary side effect of 'open scissors syndrome' could be theorized as C) Altered joint mechanics. This option seems to correspond with the rotation of the femur and humerus to point to the side, suggesting an impact on the way joints move and function, potentially due to abnormal muscle balance or skeletal posture. An altered state of joint mechanics can lead to various complications, including pain, reduced range of motion, and an increased risk for injury.