Ring Removal Device Team: Evan Rogers, Sujan Bhaheetharan, Tyler Allee, Steve Noel BME 301 February 24, 2006

Client: Scott Springman, M.D. Anesthesiologist UW - Hospital Advisor: William Murphy, Ph.D. Professor Dept. of Biomedical Engineering University of Wisconsin

Overview Current Ring Removal Techniques Current Problems Background Product Specifications Proposed Designs Future Work Questions

Problem Statement An improved method is needed to remove rings from a patient’s swollen finger. Currently, it is necessary to push, prod, and hurt patients while trying to remove rings. Removal is necessary because some surgeries have a high risk of inducing generalized body edema, including fingers. If the finger swelling is too great, the blood supply to fingers may stop and potentially lead to gangrene. When is necessary to cut off the ring, an instrument that severs one part of the ring exists. We will create a mechanical device that will allow the ring to spread open easily without pinching the patient’s fingers. Traditional "tricks" exist to try to reduce tissue water in the finger to help remove an un-cut ring. We will develop a process that may include these, while creating a new device to aid in ring removal.

Background Ring Cutter –Ring is cut at one end –Pried open –Ring can be later soldered back together Common Methods –Reducing finger tissue temperature to reduce swelling –Lubrication –Elevation Destructive MethodRemoval Method String method –Wrap string from distal end toward the ring to push excess fluid out of finger to reduce size –String fed under the ring; start unwrapping it. –Unwrapping of string forces ring off Surgical Glove Method –Feed glove under ring –Over lap ring, and remove ring

Problems with Current Methods String Method Requires high degree of skill Time-consuming Uncomfortable Limited by arthritis Surgical Glove Method Hard to feed glove under ring High probability of glove failure Limited by arthritis Destructive Difficulty removing ring after severed – Prying Ring apart Ring destroyed Common Methods Low rate of success Limited by arthritis

Finger Physiology Upper limit Shear Strength of bone 68 MPa Lower Limit Therapy treatment for patient with leg edema 6.67 kPa Finger Edema Also called dropsy Fluid accumulation in intercellular spaces

Finger Physiology Finger Arthritis Nodules develop around knuckles Made up of bone spurs (osteophytes) Become swollen and inflamed Reasons for removal Prevent fluid buildup Prevent lack of circulation to distal end of finger MRI

Product Specifications Device does not require high degree of skill Minimizes discomfort for patient Expedites current process Inexpensive Factors in permanent swelling (arthritis of the knuckle) Factors in removable swelling

Design 1: Shape Memory Alloy Non-Destructive Method Nitinol - Mix of Nickel and Titanium of equal weights Mechanics -Two Phases: Superelastic and Rigid Memory -Phase transform temp range 41º to 64º F -Force generation during phase change, recovering elastic deformation Design -Cylindrical design -Two design - Compression of finger - Expansion of ring

Design 2: Polyurethane Compression Sheath Non-destructive Method Material –High Poisson’s Ratio –Higher Ultimate and shear strength –Elastic –Varying thickness due to different stress concentrations Threading System –Ads in threading sheath between ring and finger Tension in long axis of finger cause compression of swollen tissue Lubricated, Elevation, Cold compress Finger sheath Plastic hook Sheath overlaps ring Pull overlapped sheath to remove ring

Design 3: Ring Spreader Destructive Method Used in conjunction with ring cutter Adds in spreading ring after cutting Hand crank design Force output 6.5 times force input Ratchet safety system Grip Spreader Knob ( Side View ) ( Top View) Spreader Gear Box

Design Matrix PolyurethaneNitinolRing Spreader Safety (10)979 Cost (5)442 Ease Of Use (8)657 Effectiveness (10)679 Adaptability (7)746 Total (40)322833

Future Work Finalize designs Build Prototype Test Destructive/Non-Destructive Prototypes and make necessary changes Develop step by step procedure to be use in conjunction with device

Questions?