Hypothesis

1. Biomechanical Comparision of Locking Plates With and Without Cement for Internal Fixation of Proximal Humerus FracturesLaura M. Decker, RET Fellow 2009Kenwood Academy High SchoolRET Mentor: Dr. Farid Amirouche, PhDNSF- RET Program Introduction Abstract • Motivation • Proximal humerus fractures are the • second most common fracture of the upper • extremities1. • 75% of these injuries are in • individuals over the age of 602. • These patients may be predisposed to these injuries due to lowered bone densities and osteoporosis2. In the upper extremities, proximal humerus fractures are the second most common type of fracture. 75% of these injuries occur in patients over the age of 60. This study’s objective is to compare the stability of the Synthes 3.5mm LCP Proximal Humerus Plate with and without Norian SRS calcium phosphate cement. 9 human humerus bones were dissected of all soft tissue and given a simulated 2 part fracture. Each specimen was repaired with a 3.5mm LCP plate and tested in vitro, (4 without cement, 5 with cement) using an Instron 5569 universal testing machine. Each bone is fitted with 4 LVDT sensors, and tested using varying forces ranging from 40-350 N. Data from each sensor was collected using LabView 8. Data analysis shows that the calcium phosphate cement does improve the stability of the implant and may improve the density of the bone around the fracture site. cerebral artery Hypothesis Figure 1: A: Showes a 2-part proximal fracture, (B) showes the same fracture repaired with a 3.5mm LCP proximal humerus plate. Hypothesis • If Norian SRS calcium phosphate cement is injected into the screw holes of a 3.5mm LCP proximal humerus plate, then there will be an increase in the stability of the implant. Figure 2: Proximal end of human humerus bone fitted with the 3.5mm Proximal Humerus Plate after testing. Figure 1: Proximal end of human humerus bone fitted with the 3.5mm Proximal Humerus Plate before testing. Materials and Methods A B Testing Protocol Surgical Protocol • Surgical plate fixation • 9 human humerus bones were x-rayed to determine bone quality. • Each bone is surgically given a simulated proximal humerus fracture at the surgical neck just below the head and the distal part of the bone is removed. • All 9 bones were then repaired using a 3.5mm LCP Proximal Humerus Plate. • 5 of the 9 bones were injected at the screw holes with Norian SRS injectable calcium phosphate cement. • Mechanical bone testing • The bone is anchored on a custom made aluminum plate using 2 screw-down U-brackets. • The bone shaft is fitted with 2 sets of LVDT sensors that measure displacement of the bone at 2 points. Each set has a sensor that measures bone displacement in the X and Y direction. • A specific force is applied to the head of the bone and displacement is measured. Figure A: Humerus that has been repaired with a 3.5mm LCP humerus plate. Figure B: Humerus bone attached to aluminum base plate fitted with LVDT sensors. Conclusion Acknowledgements • NSF Grant EEC-0743068 • Prof. A. Linninger, RET Program Director • Dr. Gerardo Ruiz, RET Program Managing Director • Dr. Farid Amirouche, Research Mentor • University of Illinois- Chicago Calcium phosphate cement does increase the stability of the LCP Plate by reducing displacement. References • Source: Two-Part Surgical Neck Fractures of the Proximal Humerus1 • Source: Biomechanical Comparision of a unique locking plate versus a standard plate for internal fixation of proximal humerus fractures in a cadaveric model.2 • Image Source: Displacement/Screw Cutout after Open Reduction and Locked Plate Fixation of Humeral Fractures2 Figure 4A (Left) Overall average displacement in mm for each bone at each sensor. Figure 4B (Right) Graph of overall average displacement in mm at each sensor.