Low back pain (LBP), the most common musculoskeletal disease, is the leading cause for disabilities among the elderly. Existing techniques for LBP diagnosis such as invasive bone pins or X-Ray imaging have problems of being invasive, radiative, or requiring bulky equipment. Patients cannot move freely when being monitored with these techniques. Piezoelectric micromachined ultrasonic transducer (PMUT) based wearable sensors, form a promising alternative for vertebra kinetics monitoring as they do not cause exposure to ionizing radiation, have low power consumption, and a small form factor. This paper demonstrates a linear PMUT array designed for this purpose and its imaging of vertebra phantoms.