Ultrasound image of model C immersed in water.Model C made of nylon PA 12 using an EOS Formiga P100 printer and selective laser sintering printing technology. Note the characteristic hyperechoic appearance created by the strong reflection of the ultrasound beam by the model, simulating bone (*). The joint space is visible as a gap between the cranial (left) and caudal (right) articular processes (white arrow).