Internal Fixation of a Standard Joint Depressed Intraarticular (Sanders IIb) Calcaneus Fracture: Biomechnical Analysis of a Novel Techique.
Orthopedic Research Center - Dr. J. Nelson

An ideal calcaneal construct would include minor hardware prominence, sturdy posterior facet fixation and nomial soft tissue disruption. The purpose of this study was to develop such a novel construct for fixation of the calcaneous and undertake a quality biomechanical analysis which will compare our new techique to the standard calcaneus fixation. Resutls show that the novel screw fixation technique had significantly less movement compared to the standard plate fixation.

Compression Strength and Porosity of Single-Antibiotic Cement Vacuum-Mixed with Vancomycin
Orthopedic Research Center - Dr. H. Brock

The addition of antibiotics to cement allows the theoretical benefit of providing high local drug concentrations with less risk of systemic complications. A major drawback of this combination is the detrimental effect antibiotics have on the mechanical properties of bone cement. The study was designed to determine how much Vancomysin can be added while maintaining at least 70 MPa of compressive strength. Results showed that up to 6 grams of Vancomysin can be added without have a determintal effect. Amounts larger than 6 grams could possible effect the bonds the cement needs to maintain its stiffness.

Comparision of Different Implants for Fixation of Posterior Malleolus Fractures
Orthopedic Research Center - Dr. S. Schutt

The aim of the study was to present an alternative way of fixating a posterior malleolus fracture.  We believed that the Tight Rope system will allow for equal to better fixation than compression screws during a static load and fatigue testing.  Results showed that the there was no significant difference between the Tight Rope system and the screw fixation technique. Clinicially the smaller the posterior fragment of the tibia the more likely a tight rope sytem could be used.

Identify site-specific molecular targets regulating cartilage cell differentiation
Harrington Laboratory for Molecular Orthopedics
Principal Investigator: J. Wang --- funded by NIH

Bone morphogenetic proteins (BMPs) play an important role in skeletal development and postnatal bone repair. Our previous studies have demonstrated that BMPs and demineralized bone matrix (DBM)-induced repair of rat calvarial bone defects occurs initially by the proliferation and differentiation of resident cells directly to osteoblasts and the direct formation of bone tissue. Utilizing special experimental models that separate DBM from the host bone, we have demonstrated that DBM-induced osteoblasts are primarily derived from the dura (Figures A-B), which are spatially distinct from the later formation of cartilage derived from cells in the overlying skin flap. In contrast, implantation of BMP/DBM into rat thoracic subcutaneous sites first induces cartilage cells followed by an endochondral sequence of ossification (Figure C). The molecular and cellular mechanisms of site-specific responses to BMP/DBM are unknown. The major goal of this project is to identify site-specific molecular targets regulating cartilage cell differentiation in adult rodents.

Implantation of DBM into rat cranial defects initially induces the proliferation and differentiation of dura-derived mesenchymal cells directly to osteoblasts (A-B), while implantation of DBM into rat thoracic subcutaneous sites first induces cartilage cells (C).

Bone Sialoprotein and Osteogenesis
Harrington Laboratory for Molecular Orthopedics
Principal Investigator: J. Wang

Bone sialoprotein (BSP) is one of the major non-collagenous extracellular matrix (ECM) phosphoproteins in bone and dentin. BSP is highly expressed in developing and postnatal regenerating bone, but its precise function is largely unclear. Previous in vitro studies suggest that BSP may be involved in cell attachment, cell migration, and calcium-phosphate mineral deposition. We have recently investigated the function of BSP in more complex in vivo environments by implanting BSP with type-I collagen as a carrier into surgically created 8-mm rat cranial defects. The results show that BSP-collagen, but not collagen alone, stimulates differentiation of resident responding cells into osteoblasts followed by synthesis of new bone in the mid-portion of the cranial defects. The bioactivity of BSP, a non-growth factor protein, in stimulating osteoblast differentiation and bone regeneration in a bone defect model is an unprecedented result. However, the mechanisms of BSP-mediated osteogenesis are unknown. The major goal of this project is to explore the mechanisms for BSP action in osteogenesis and bone regeneration.

Dynamic Gait Simulator
Ryan Farmer, Kelly Hendricks, Terence McIff

The Dynamic Gait Simulator or Hip Simulator is a custom designed machine, built for the hip stem initial stability study. Through its integration with an 858 Mini Bionix materials testing machine, femoral components used in hip replacement surgery may be dynamically tested in three dimensions with four degrees of freedom. Two rotary actuators turn the distal end of the femur around the X' and Y' axes while the linear actuator applies a downward force through the centroid of the head of the femoral component. The rotations of the femur and the dynamic loading patterns used are correlated to together to replicate the gait cycles of a person walking normal, going up stairs, going down stairs, sitting down, and standing up. The correlation of the input data is achieved through a feedback system in which optical encoders tell the computer the position of each rotary actuator, and a load cell relays information back to the system to measure how much force is being applied to the femoral component.