Final answer:
The prefix a paramedic would use when describing any condition within a patient's musculoskeletal joints is 'arthro-'.
Step-by-step explanation:
The prefix a paramedic would use when describing any condition within a patient's musculoskeletal joints is arthro-. This prefix is derived from the Greek word 'arthros', which means joint. For example, if a patient has inflammation in their knee joint, a paramedic might use the term 'arthritis', which refers to inflammation in the joints.