Robert J. Nobilini, Ph.D., Biomechanical Engineer

Case Summary:   A paraplegic patient was undergoing exercise therapy on a Functional Electrical Stimulation (FES) bicycle at a physical therapy clinic when she incurred a supracondylar fracture of her left distal femur.

Expert Analysis:  The incident bike used electrodes that were connected to leads from a microprocessor; which, in turn, stimulated the muscles of the legs to crank the pedals and turn a weighted flywheel.  During the setup, the therapist applied electrodes to the muscles of the upper legs and connected leads from the microprocessor.  Once complete, the therapist hand-cranked the pedals until the patient’s legs took over.  During the session, the therapist made several attempts to hand-crank the pedals but could not get the patient to pedal the bike for any length of time.  The patient’s riding was characterized as “jerky.” 

The firing sequence of the muscles in each leg was determined by the microprocessor based on feedback from a position sensor on the crank.  When the left leg was in the down position, past bottom dead center, it should have been pulling up on the pedal while the right leg was pushing down.  However, if the electrodes on the hamstring and quadriceps of the left leg were reversed, the left leg would have been fighting against the force of the right leg and the momentum of the flywheel.  Under these conditions, the patient’s ride would have been “jerky” and the loading on the patient’s left leg would have been consistent with the fracture that she incurred.  

It was reported that during the subject session, the therapist was training the patient’s mother on how to setup the incident FES bicycle.  The therapist testified that she had intentionally reversed the leads on the patient’s left hamstring and quadriceps muscles in order to test the patient’s mother but had corrected the leads prior to the exercise session.  However, the mechanics of the patient’s injuries were consistent with the leads being in the reversed order during the exercise session.

Because it was foreseeable that the leads could be misplaced, it was therefore warranted that the manufacturer have a system in place that would verify that the proper muscles were being stimulated.  This system could have been as simple as having the microprocessor sequentially stimulate each muscle while requiring the therapist to palpate and confirm that the proper muscle was being stimulated.  Had such a system been in place, the subject incident would have been prevented.  

Result:  Expert analysis revealed that the FES bicycle was defective and a direct cause of the patient’s injuries. Case settled.

Robert J. Nobilini, Ph.D., Biomechanical Engineer with DJS Associates, Inc., can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.

Categories: Case Studies | Engineering

Tags: Bicycle | Biomechanical Engineering | Physical Therapy