Inter-Operative BIOmechanical Surgical Splint By: Nick Schlewitz Department of Biomedical Engineering Vanderbilt University Advisors: Dr. Paul King, Vanderbilt University; Dr. Edward Glaser, D.P.M BIOSS

What’s a Bunion? A bunion is calcium deposit which occurs at the head of the first metatarsal. The extra calcium causes a separation of the first and second metatarsals. The big toe commonly crosses over the second toe if left untreated. The greater the separation, the more severe the operation to correct it.

Fix My Bunion There are more than 171,000 bunion surgeries performed each year, and nearly 20,000 of those are so severe they require restructuring of the first metatarsal. This is called a closing wedge osteotomy. Closing wedge osteotomies are major operations and carry severe complications, sometimes crippling the patient. Radiograph of a patient’s first metatarsal following a closing wedge osteotomy. A pin has been inserted to align the first metatarsal in the correct position.

Complications? The most common complication resulting from a closing wedge osteotomy is called Metatarsus Primus Elevatus (MPE). MPE is best described as an elevation of the big toe. The toe becomes fixated in this position and becomes rigid or completely immobile. This condition can be crippling and/or lead to future operations. MPE, the big toe is clearly raised as a result of a closing wedge osteotomy

Why MPE? How do we treat it? MPE is caused by one of two reasons: 1.Surgical technique, which involves the precision of the cut in the bone. 2.Post-operative weight bearing Both causes can be addressed during the healing stages, when the foot is bandaged, with a splint that holds the toe in the correct position and sustains its mobility. This is precisely what BIOSS is designed to do.

BIOSS: How it Works BIOSS is designed to alleviate MPE by two mechanisms: 1.By providing arch support, the plantar fascia tendon will act to pull the big toe down, eliminating elevatus. This mechanism is called the windlass effect. 2.By incorporating a continuous passive motion device (CPM), the big toe will be well nourished, causing it will heal faster, and will not stick to the healing bone.

The Design The arrow indicates the arch support which is unique to each persons foot. The entire foot bed and toe guard are made of a low density polyethylene plastic and connected with a locking nut and bolt. BIOSS prototype showing the arch support

Continuous Passive Motion In order to continuously move the toe, a 3 RPM geared motor BIOSS prototype emphasizing the CPM feature