A Biomechanical Investigation of Shape Memory Staples

Parker P. Duncan, MD1 Clayton C. Bettin, MD1 James T. Reagan, MD2 Denis J. DiAngelo, PhD1 PJ Johnson, BS1

1 University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery & Biomedical Engineering Memphis, Tennessee 2 Tennessee Orthopaedic Clinics

Knoxville, Tennessee

Purpose

The use of shape memory alloys, specifi cally nitinol staples, has gained popularity in orthopedic osteosynthesis applications secondary to their inherent simplicity and ease of use as well as their biomechanical compressive ability. The key objectives of this pilot study were to determine the e ect on staple leg and bridge length and unicortical versus bicortical fi xation on compression, bending sti ness, and torsional rigidity as well as to investigate how staple position and construct confi guration would altered these values.

Methods

Transverse osteotomies were made using a sagittal saw in identical bicortical sawbones blocks to simulate an osteosynthesis site. This site was fi xed with a single staple of varying bridge and leg length with unicortical or bicortical purchase. Tekscan sensors were used to determine compressive force before and after cyclic loading with a four-point bender and biaxial mechanical testing frame to determine bending sti ness and torsional rigidity of each construct. Also tested were anatomic sawbones 1st metatarsal and metacarpal models which were fi xed with di erent staple products and constructs from multiple di erent manufacturers including: orthogonal and parallel placed two staple constructs, multiple four-leg staples, and a staple plate.

Results

This study is currently underway at the UTHSC Orthopedic Biomechanics Lab (DiAngelo). All materials have been obtained, but await fi nal protocol testing prior to formal testing runs.

Conclusions

We hypothesize that staples placed with bicortical technique, perpendicular to a potential osteosynthesis site will produce the most compression, bending sti ness, and torsional rigidity. Also, we hypothesize that orthogonally placed staples will produce the most bending sti ness and torsional rigidity among staple constructs with each producing similar compressive ability.

Corresponding Author

Clayton C. Bettin, MD

1211 Union Avenue, Suite 500 Memphis, TN 38104 P: 901-759-5422 F: 901-435-5639 cbettin@campbellclinic.com

PARKER P. DUNCAN, MD

Hometown: Johnson City, TN Undergraduate Institution: University of Memphis Medical School: University of Tennessee Health Science Center College of Medicine Dr. Duncan is the oldest of three children. He follows in the footsteps of his father, an orthopaedic spine surgeon, in choosing a career in medicine. Dr. Duncan met his wife August at the University of Memphis, and they were married in 2014. August is an Executive Assistant and recently earned her MHA. When asked why he chose medicine as a career: Growing up, I enjoyed science (biology and chemistry) and enjoyed studying physiology and anatomy. I shadowed my dad and his partners as well for job experience, and seeing the good they could do for their patients through medicine was inspiring to me to pursue a career in it. And why he chose orthopaedics as a specialty: In medical school, my favorite subject was gross anatomy, and I really enjoyed working in the gross lab. I spent four semesters teaching anatomy to other med students as a tutor throughout med school. Orthopaedics is all about anatomy, so naturally it was a fi t for me, as I knew I would go into surgery. Plans After Campbell: Dr. Duncan will complete a Foot and Ankle Fellowship at Steadman Clinic in Vail, Colorado. Dr. Duncan adds: Thank you to all of my staff for allowing me to take care of your patients. Thank you, as well, for your time and resources that make our training at Campbell Clinic the best orthopaedic training in the world.