Development of a Depth Gage Instrument for Orthopedic Surgery Brian Cost 1, Justin Johnson 1, Tyler Kibbee 1 Advisor: Derek Lewis 2, Director of Engineering Vanderbilt University Engineering School, Biomedical Engineering Department OrthoHelix Surgical Designs, Inc. RESULTS & DISCUSSION (cont.) MATERIALS & METHODS CONCLUSIONCONCLUSION REFERENCESREFERENCES Market Analysis: Projected Development Cost: - Expended $10, Future Dev. $10, Total$21, NPV for 20 yr. Horizon$413, Production Cost (per gage)$ MSRP (per gage) $ Profit (per gage)$73.00 Safety Issues Silicon tip unexpected disassembly Wire/switch joint wear FDA Classification: Class I Sec Depth gauge for clinical use. (a) Identification. A depth gauge for clinical use is a measuring device intended for various medical purposes, such as to determine the proper length of screws for fastening the ends of a fractured bone. (b) Classification. Class I (general controls). The device is exempt from the pre-market notification procedures Market Analysis: Projected Development Cost: - Expended $10, Future Dev. $10, Total$21, NPV for 20 yr. Horizon$413, Production Cost (per gage)$ MSRP (per gage) $ Profit (per gage)$73.00 Safety Issues Silicon tip unexpected disassembly Wire/switch joint wear FDA Classification: Class I Sec Depth gauge for clinical use. (a) Identification. A depth gauge for clinical use is a measuring device intended for various medical purposes, such as to determine the proper length of screws for fastening the ends of a fractured bone. (b) Classification. Class I (general controls). The device is exempt from the pre-market notification procedures Design Motivation: Improve accuracy of screw hole measurements to prevent patient discomfort and device failure Improve surgeons ability to easily measure hole depth Conclusions: The design currently meets all of the specifications that we had set out to accomplish. Future Directions: Refine hollow shaft design Improve switch design Contract prototype manufacturing Verification/Validation testing for FDA approval Design Motivation: Improve accuracy of screw hole measurements to prevent patient discomfort and device failure Improve surgeons ability to easily measure hole depth Conclusions: The design currently meets all of the specifications that we had set out to accomplish. Future Directions: Refine hollow shaft design Improve switch design Contract prototype manufacturing Verification/Validation testing for FDA approval Materials SolidWorks, Computer SLA printer, SLA devices Saw bone models, Plates, Screws, Drill Bits, Drivers Medical-grade Silicon, Stainless Steel Design Reverse-engineered the existing depth gage to obtain a 3D model Developed five potential ideas to expandable tip revision Resulted in using a medical-grade silicon tip that expands similar to a wine bottle stopper In order for tip to expand, the center of the gage body was hollowed out to make room for a pull stick Materials SolidWorks, Computer SLA printer, SLA devices Saw bone models, Plates, Screws, Drill Bits, Drivers Medical-grade Silicon, Stainless Steel Design Reverse-engineered the existing depth gage to obtain a 3D model Developed five potential ideas to expandable tip revision Resulted in using a medical-grade silicon tip that expands similar to a wine bottle stopper In order for tip to expand, the center of the gage body was hollowed out to make room for a pull stick R.D. Guyer. "United States Patent # 5,928,243: Pedicle probe and depth gage". Spinal Concepts Inc. July 27, D.A. Fischer. "United States Patent # 4,450,834: External fixation device". Ace Orthopedic Manufacturing Inc. May 29, M. Dace, B. Wilfong. United States Patent # 7,293,364: Measurement device". Warsaw Orthopedic, Inc. November 13, 2007 MSC Industrial Supply Company Website, Material Property Information. Silicon Azom.com The A to Z of Materials. Grade 420 Stainless Steel R.D. Guyer. "United States Patent # 5,928,243: Pedicle probe and depth gage". Spinal Concepts Inc. July 27, D.A. Fischer. "United States Patent # 4,450,834: External fixation device". Ace Orthopedic Manufacturing Inc. May 29, M. Dace, B. Wilfong. United States Patent # 7,293,364: Measurement device". Warsaw Orthopedic, Inc. November 13, 2007 MSC Industrial Supply Company Website, Material Property Information. Silicon Azom.com The A to Z of Materials. Grade 420 Stainless Steel BACKGROUNDBACKGROUND The pull stick binds the silicon to the depth gage shaft. Ppull stick motion forces the silicon to compress and expand laterally. Millimeter pull stick displacement requires great sensitivity. To prevent operator overextension, we added a switch. The switch design ensures repeatable specified displacement to obtain desired expanded silicon. Our switch design optimizes ease of use. Circular switch motion allows individualized positioning for operator comfort. This way, the surgeon could use any desired finger to engage the switch. Testing I. Material TestingII. Failure Testing a. Strength of silicon a. Pull-out Strength b. Stainless steelb. Material Deformation The pull stick binds the silicon to the depth gage shaft. Ppull stick motion forces the silicon to compress and expand laterally. Millimeter pull stick displacement requires great sensitivity. To prevent operator overextension, we added a switch. The switch design ensures repeatable specified displacement to obtain desired expanded silicon. Our switch design optimizes ease of use. Circular switch motion allows individualized positioning for operator comfort. This way, the surgeon could use any desired finger to engage the switch. Testing I. Material TestingII. Failure Testing a. Strength of silicon a. Pull-out Strength b. Stainless steelb. Material Deformation Project Description Design, build and test an improved depth gage instrument for a variety of orthopedic surgeries - Achieve bi-cortical fixation using a compression stopper Achieve Ergonomic Grip - Ease of use for surgeons Design for Accuracy - Proper depth and correct size screw used Existing Industry Design Inadequate measurements, poor repeatability Unable to engage far cortex of bone consistently Shaft warps with repeated use and abuse Surgeons bend shaft in attempt to engage far cortex Permanent damage to gage renders it useless Company Background: OrthoHelix Surgical Designs, Inc. Small biotech company started by Orthopedic surgeon - 4 specialized product trays MaxLock™ CalcLock™ MaxTorque™ DRLock™ Serves Niche Market - Small bone surgery - Hand and Foot specialists Project Description Design, build and test an improved depth gage instrument for a variety of orthopedic surgeries - Achieve bi-cortical fixation using a compression stopper Achieve Ergonomic Grip - Ease of use for surgeons Design for Accuracy - Proper depth and correct size screw used Existing Industry Design Inadequate measurements, poor repeatability Unable to engage far cortex of bone consistently Shaft warps with repeated use and abuse Surgeons bend shaft in attempt to engage far cortex Permanent damage to gage renders it useless Company Background: OrthoHelix Surgical Designs, Inc. Small biotech company started by Orthopedic surgeon - 4 specialized product trays MaxLock™ CalcLock™ MaxTorque™ DRLock™ Serves Niche Market - Small bone surgery - Hand and Foot specialists Comparison: Prototype vs. Existing Design Testing Results Comparison: Prototype vs. Existing Design Testing Results MATERIALS & METHODS (cont.) Fig. 1 (left): The tip in the unexpanded position. Fig. 2 (right): The tip in the expanded position. Fig. 3: Section view of depth gage depicting pull stick and switch mechanism. Fig. 4 (left): Switch in the disengaged position, allowing tip to relax. Fig. 5 (right): Switch in the engaged position, compressing tip into engaged position Fig. 7 (left): Prototype gage being tested on sawbone model in unexpanded position. Fig. 8 (right): Prototype gage in expanded position. Silicon Tip Material Properties Minimum Temp. (ºF)-60 Maximum Temp. (ºF)500 Tensile Strength (MPa)700/650 Durometer Thickness1/4" Grade 420 Stainless Steel Properties Tensile Strength (MPa)1620 Yield Strength (MPa)1420 Density (kg/m 3 )7750 Elastic Modulus (GPa)200 Specific Heat (J/kg-K)460 RESULTS & DISCUSSION Fig. 6: From top to bottom; 30 mm, 50 mm existing gages, our prototype Fig. 9 (left): Overview of depth gage inserted in sawbone. Fig. 10 (below): Close-up of prototype shaft and silicon tip (NOTE: not to scale)