John T. Ruth

The effect of implant overlap on the mechanical properties of the femur.

BACKGROUND The most biomechanically stable relationship between the side plate of a compression hip screw (CHS) and retrograde intramedullary (IM) femoral nail has not been described in the literature. This becomes a clinical issue when treating supracondylar femur fractures with a retrograde nail in patients with a history of compression hip screw fixation of intertrochanteric fractures. The proximal end of the nail and the interlocking screws may act as a stress riser in the femoral diaphysis. The purpose of this study is to determine the biomechanical consequences of the amount of implant overlap between a CHS plate and retrograde IM femoral nail. METHODS Nine paired fresh-frozen cadaver femora from elderly donors were cleaned of soft tissue and fixed with uniaxial strain gauges. Each femur was loaded three times in a fall-loading configuration to 50 kg at a rate of 1 Hz. The study consisted of two phases. In phase 1, six pair were randomly divided into a control and test femur from each pair. Three states were compared on each test femur: uninstrumented, instrumented with CHS, and instrumented with CHS and retrograde nail. The control femur consisted of the matched femur tested in two states: uninstrumented and instrumented with a CHS. The femora were then loaded to failure. The tests were performed with the retrograde nail and CHS gapped 3 cm, kissing, and overlapping by two screw holes (two pair for each state). In phase 2, each of the remaining three pair were instrumented with a CHS and retrograde nail overlapping in one femur and gapped in the matched femur and tested in the same manner. Data analysis was performed using Pearsons correlation coefficients between groups. Paired samples t tests were used to compare differences within test states and independent samples t tests were used to compare differences between femora. Mean strain at 50-kg load, load-versus-strain patterns, failure patterns, and load and strain at failure were recorded. RESULTS; Correlation coefficients were greater than 0.98 within and between pairs (p < 0.001). There were statistically significant differences (p < 0.05) in strain patterns between the uninstrumented, CHS, and CHS/IM test states. The addition of a side plate significantly (p < 0.05) increased lateral compressive strains in the femoral diaphysis. Mean strain at 50-kg load was significantly (p < 0.05) altered by the addition of the retrograde nail in all three implant orientations. Gapped implants failed at lower loads and strains than femurs with kissing and overlapping implants. Gapped constructs failed at lower loads than control states. Overlapped constructs tolerated the highest loads and strains before failure. CONCLUSION Strain patterns are altered by the degree of implant overlap in the proximal femoral diaphysis. Femora with uninstrumented intervals between retrograde nails and side plates fail at lower loads than femora without retrograde nails and those with kissing or overlapping implants. Kissing or overlapping instrumentation increases load to failure and creates a more biomechanically stable construct than gapped implants. The findings of this study suggest an overlapping implant orientation in the femur increases failure load at the implant interface.

A novel biomimetic polymer scaffold design enhances bone ingrowth

There has been recent interest in treating large bone defects with polymer scaffolds because current modalities such as autographs and allographs have limitations. Additionally, polymer scaffolds are utilized in tissue engineering applications to implant and anchor tissues in place, promoting integration with surrounding native tissue. In both applications, rapid and increased bone growth is crucial to the success of the implant. Recent studies have shown that mimicking native bone tissue morphology leads to increased osteoblastic phenotype and more rapid mineralization. The purpose of this study was to compare bone ingrowth into polymer scaffolds created with a biomimetic porous architecture to those with a simple porous design. The biomimetic architecture was designed from the inverse structure of native trabecular bone and manufactured using solid free form fabrication. Histology and muCT analysis demonstrated a 500-600% increase in bone growth into and adjacent to the biomimetic scaffold at five months post-op. This is in agreement with previous studies in which biomimetic approaches accelerated bone formation. It also supports the applicability of polymer scaffolds for the treatment of large tissue defects when implanting tissue-engineering constructs. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009.

Bilateral asymmetric hip dislocation: case report and literature review

Simultaneous anterior and posterior hip dislocation is an unusual injury. A unique case is presented, consisting of bilateral asymmetric hip dislocation with associated femoral head, femoral shaft, and acetabular fractures resulting from a motorcycle collision. The mechanisms of injury, management, role of imaging, and complications of this injury complex are discussed, with a review of the relevant literature.

In vivo telemetric determination of shear and axial loads on a regenerative cartilage scaffold following ligament disruption

Recent interest in repair of chondral and osteochondral cartilage defects to prevent osteoarthritis caused by ligament disruption has led to the research and development of biomimetic scaffolds combined with cell-based regeneration techniques. Current clinical focal defect repair strategies have had limited success. New scaffold-based approaches may provide solutions that can repair extensive damage and prevent osteoarthritis. This study utilized a novel scaffold design that accommodated strain gauges for shear and axial load monitoring in the canine stifle joint through implantable telemetry technology. Loading changes induced by ligament disruption are widely implicated in the development of injury-related osteoarthritis. Seeding the scaffold end with progenitor cells resulted in higher shear stress than without cell seeding and histology showed significantly more bone and cartilage formation. Biomechanically, the effect of transecting the anterior cruciate ligament was a significant reduction in braking load in shear, but no change axially, and conversely a significant reduction in push-off load axially, but no change in shear. This is the first study to report shear loads measured directly in knee joint tissue. Further, advances of these measurement techniques are critical to developing improved regeneration strategies and personalizing reliable rehabilitation protocols.

Olecranon Osteotomy Repair: The Tensioned Locking Plate Technique

The tensioned locking plate technique takes advantage of two fracture healing modalities. A direct healing effect from osteon bridging due to lag screw compression is combined with axial and angular stability provided by a locking plate construct.

Determination of joint loads using new sensate scaffolds for regenerating large cartilage defects in the knee

Two complete unicondylar surface replacement scaffold designs to support tissue-engineered cartilage growth that utilized adult endogenous stem cells were 3D printed and tested in a dog stifle model. Integrated rosette strain gauges were calibrated and used to determine shear loading within stifle joints for up to 12 months. An activity index that compared extent of daily activity with tissue formation showed differences in the extent and quality of new tissue with the most active animal having the most new tissue formation. Shear loads were highest early and decreased with time indicating that cartilage tissue formation begins while tissues experience high shear loads and continues as the loads decrease toward normal physiological levels. Scaffolds with biomimetic support pegs facilitated the most rapid bone ingrowth and were noted to have more cartilage formation with better quality cartilage as measured using both indentation testing and histology. Comparison of implant placement depth to previous studies suggested that placement depth affects the amount of tissue formation. This study provides measurements of loading patterns and cartilage regeneration on a complete medial condylar surface replacement that can be used for preclinical testing of a tissue engineering approach for the most common form of early stage osteoarthritis, unicondylar disease.

Analysis of Musculoskeletal Injuries Sustained in Falls From the United States–Mexico Border Fence

Injuries sustained by unauthorized individuals who jump or fall from the United States-Mexico border fence are frequently treated by trauma centers in border states. The authors investigated patterns of musculoskeletal injury occurring in these individuals to improve emergency department assessment and to identify strategies to prevent future injuries. A retrospective chart review was performed for patients presenting to an urban, level I trauma center with musculoskeletal injuries sustained in a jump or fall from the United States-Mexico border fence between February 2004 and February 2010. Frequency of fracture by site, frequency of open fracture, and associated patterns of injury were recorded. The population was stratified by age and sex to identify disparity in injury pattern. Average length of stay and number of surgical interventions were also recorded. During the study period, 174 individuals who had jumped or fallen from the United States-Mexico border fence were identified. The population contained 93 (53%) women and 81 (47%) men with an average age of 31.5 years (range, 11-56 years). On average (±standard error), men sustained slightly more fractures than women (1.77±0.12 vs 1.43±0.07; P=.015). There were no significant differences in the number of fractures sustained between age groups. Average length of stay for patients admitted to the hospital was 3.5 days. Patients underwent an average of 0.75 surgical interventions during admission. Falls from the United States-Mexico border fence are a significant cause of morbidity among unauthorized immigrants. [Orthopedics. 2017; 40(3):e432-e435.].

213 POROUS POLYBUTYLENE TEREPHTHALATE IMPLANTS ALLOW FOR BONE INGROWTH AND PROVIDE A WELL-ANCHORED SCAFFOLD THAT CAN BE USED TO DELIVER TISSUE-ENGINEERED CARTILAGE.

While joint pain and loss of mobility are common causes of impairment, there are few procedures that can consistently restore the long-term function of damaged articular cartilage. One approach that offers a potential solution for articular cartilage repair is replacement of the damaged cartilage using a tissue-engineered scaffold. The goal of this study was to measure loading and bone attachment in sensate, porous, calcium phosphate ceramic (CPC) coated polybutylene terephthalate (PBT) scaffolds that have been implanted in the medial compartment of the knees of 6 canines. In addition histology, histomorphometry, and scanning electron microscopy (SEM) were used to characterize bone growth into and around the PBT scaffold. In vivo measurements from the calibrated scaffolds indicated that peak loads in the dog knees ranged from 80-120N. Post-sacrifice biomechanical testing indicated that these loads correlated to pressures of 11 ± 1.54 MPa in the medial compartment of the knees. Histology demonstrated a bone volume of 6.8 ± 8.8% within the scaffold pores and an osteoid volume of 64.9 ± 17.2%. Histomorphometry indicated an increased bone formation rate within the scaffold pores, 8.2E-5 ± 5.9E-5 μm3 /μm2 /day, compared to 1.3E-5 ± 0.8E-5 mm3 /μm2 /day in control knees. SEM demonstrated less bone within the scaffold pores compared to the extensive amount of bone surrounding the scaffold and in intimate contact with the CPC particles. These results demonstrate that the scaffold is mechanically coupled to the bone. In addition, the increased bone formation rate and osteoid within the PBT pores demonstrate that bone formation is still occurring 6 months post-op. Currently studies are focused on the integration of PBT scaffolds containing a tissue-engineered cartilage covering into damaged articular cartilage.