1. Engineering Objectives
Surgical Cube Attachment for Leg-Length Equalization (S.C.A.L.E.)
Andrew Bell1, Evan Blair1, Andrew Lewis1, Jake Smithey1
1Mississippi State University Bagley College of Engineering - Department of Agricultural and Biological Engineering
Introduction
Market and Design
Concept
Conclusions
Abstract
Leg length inequality after hip replacement procedures can cause mechanical problems for patients. Currently, there is no standard measurement method to ensure pre- and post-op leg length equality. The construction of a device to aid surgeons in eliminating this risk would be of great practical value for both doctors and patients. We constructed a simple, easy to use method for enabling surgeons to repeatably capture a critical length during hip replacement.
Market
Surgeons, especially inexperienced
Between 2010 and 2020, approximately 168,300 Americans will become physicians
4% will go on to become orthopedic surgeons
Translates to approximately 6,700 new surgeons in this time frame [3]
Estimated that 332,000 hip replacements are performed each year
Many inexperienced surgeons performing numerous THRs
MRS spectral data (ppm)
Figure 2. Measurement of critical length used to ensure prosthesis is positioned ideally
Figure 3. SolidWorks rendering of device. Steinmann pin slots and fastening screw threads can be seen.
Slot for Steinmann pin
Threaded holes for fastening screws
Procedure
Step 1. Insert Steinmann pin in ilium directly above the greater trochanter. Make sure pin is securely in place.
Step 2. Slide attachment over Steinmann pin and position vertically over tip of greater trochanter
Step 3. Insert Steinmann pin (shorter pin ideal) into attachment so that the tip is touching the greater trochanter. Marking contact point on greater trochanter helpful. Fasten all screws.
Step 4. Flip construct up and out of the way, conduct hip replacement as normal, then when positioning the new femoral head, flip construct back down and use the point of the pin as a guide to correctly position the prosthetic femoral head.
Figure 4. Device standard use diagrams
Results
The stainless steel construct can be autoclaved, while the aluminum construct can be sterilized using other means (gas sterilization).
The small size and dynamic fastening ensure maneuverability.
The sturdy grips on the Steinmann pins provide accurate measurement.
Conclusions
Device improves leg length and offset equality during THR surgery.
Useful for patients of all sizes, especially older/larger patients (spacious bone structure improves ease of use).
Proof of concept confirmed through testing demonstration.
Background
Figure 1. Details standard hip replacement procedure
332,000 people undergo total hip replacement surgery every year in the United States of America [1]
Critical length from pelvic ilium to greater trochanter can be used to predict leg length. (See Figure 2.)
Engineering Objectives
Sterility takes the first priority, as the device needs to be used intra-operatively. Next, the device should have maneuverability and be quickly executable in a cluttered surgical environment. Lastly, the measurement accuracy of the device is a key engineering objective.
Budget
Item
Cost
Sawbones (Pelvis & Femur)
$111
Steinmann Pins
*Acquired free of charge from Mississippi Bone and Joint Clinic
Device base
*Produced free of charge by ABE Shop
TOTAL
Design
Utilizes the ilium of the pelvis and the greater trochanter of the femur as reference points, taking advantage of their stationary position before and after implantation.
Holds two commonly used orthopedic Steinmann pins (Figure 5) in place: one to be inserted horizontally into the ilium, and one to extend down vertically and touch the greater trochanter, marking it position (Figure 2 & 4).
The pins can be fixed into place using the screws that extend into the pinholes.
1 in x 1 in cube with two 2mm pinholes and four 2mm screw holes (Figure 3)
Constructed of aluminum, although stainless steel also an option.
Problem
3 to 4% of total hip replacement (THR) patients may experience leg length discrepancy (LLD) following surgery [2]. Even, very small discrepancies in leg length can lead to serious mechanical issues in the body, such as back pain, hip instability, paresthesia, and lack of balance.
Current leg length measurement procedures are rudimentary and improvised, and a more accurate, reliable procedure is needed in the field of orthopedics.
Design of a system that enables surgeons to measure leg length in the most accurate and convenient way possible is needed.
Acknowledgements
We would like to thank Taylor Haltom, E.I., Dr. Filip To,
Dr. Steven Elder, Dr. Lakiesha Williams, Dr. Allen Butler M.D., the Mississippi Bone and Joint Clinic, and the Agricultural and Biological Engineering shop.
Figure 5. (Left) Final prototype construct of device (Middle) Steinmann Pins (Right) Metal Hip Replacement
References
[1] “Questions and Answers about Hip Replacement.” National Institute of Arthritis and
Musculoskeletal and Skin Diseases. July 2013.
[2] Wylde V, Bannister G, Blom A, Whitehouse S, Taylor A, Pattison G. Prevalence and functional impact of patient-perceived leg length discrepancy after hip replacement. International Orthopaedics [serial on the Internet]. (2009, Aug 1), [cited April 20, 2014]; 33(4): Available from: Scopus®.
[3] “Physicians and Surgeons.” U.S. Bureau of Labor Statistics, Employment Projections Program. March 29, 2012.
The authors declare no conflicts of interest. © Bell, Blair, Lewis and Smithey 2014