Subject-specific registration of bony landmarks in the rat hindlimb. (A) shows an example for one animal at one configuration, showing the registration between measured landmarks (red) and landmarks on the model’s skeletal surface (green). (B) summarizes the registration accuracy across animals. The bars show the registration error with no joint constraints, the error using the subject-independent joint centers and axes from the model template, and the error using the subject-specific joint centers and axes. The subject-specific error was obtained through cross-validation, fitting the joint model parameters at N-1 configurations and evaluating the error for the remaining configuration, then repeating for all N configurations.