Westley Hayes

MICROHARDNESS OF BI-ANTIBIOTIC-ELUTING BONE CEMENT SCAFFOLDS

Bi-antibiotic-impregnated bone cements (BIBCs) are widely used in orthopaedics as a prophylactic agent (depot) to address post-surgical infections. Although hardness is widely considered a viable index to measure the integrity of the cement structure, there are few specific studies involving changes in hardness characteristics of BIBCs post elution of high doses of two widely used antibiotics: tobramycin and gentamicin. Increased doses of antibiotics and increased duration of elution may also decrease the hardness of polymethyl methacrylate (PMMA) bone cement, thus increasing the chances of shattering, scratching, and deformation.In this project, we have investigated the changes in surface hardness of five different antibiotic-loaded specimens: 0.5 g tobramycin and 0.5 g gentamicin together, 1 g tobramycin, 1 g gentamicin, 5 g tobramycin and 5 g gentamicin together, and 10 g tobramycin (each added to 40 g of PMMA), post elution for various time periods (1, 3, and 21 days). The effect of hydration on the hardness of bone cement was studied to replicate in vivo conditions. The micro-indentation tester (Buehler m5103) was utilized to determine if the increased antibiotic loads would compromise the integrity of the bone cement matrix.The results demonstrated that the amount of drug initially incorporated determined the hardness of the cement post elution. As compared to the control (no antibiotic), specimens containing 1 and 10 g of antibiotic exhibited over 50% and 73% decrease in hardness, respectively. The different treatment durations (post 1 day) as well as the hydration conditions had insignificant effect on the hardness of the cement.

Regional Variations in Shear Strength and Density of the Human Thoracic Vertebral Endplate and Trabecular Bone

Background Previous studies investigated the overall mechanical strength of the vertebral body; however, limited information is available on the biomechanical properties of different regions within the vertebral endplate and cancellous bone. In addition, the correlation between mechanical strength and various density measurements has not been studied yet. Methods Thoracic (T10) vertebrae were harvested from fifteen human cadaveric spines (average age: 77 years old). Twelve cylindrical cores of 7.2 mm (diameter) by 3.2 mm (height) were prepared from each vertebral body. Shear was produced using a stainless steel tubular blade and measured with a load cell from a mechanical testing machine. Optical and bulk densities were calculated before mechanical testing. Apparent, material, and ash densities were measured after testing. Results Material density and shear strength increased from anterior to lateral regions of both endplate and cancellous bone. Endplate shear strength was significantly lower in the anterior (0.52 ± 0.08 MPa) than in the lateral region (2.72 ± 0.59 MPa) (p=0.017). Trabecular bone maximum load carrying capacity was 5 times higher in the lateral (12 ± 2.74 N) (p=0.09) and 4.5 times higher in the central (10 ± 2.24 N) (p=0.2) than in the anterior (2 ± 0.60 N) regions. Mechanical strength positively correlated with ash density, and even moreso with material density. Conclusion Shear strength was the lowest at the anterior region and highest at the lateral region for both endplate and cancellous bone. Material density had the best correlation with mechanical strength. Newer spinal implants could optimize the loading in the lateral aspects of both endplate and cancellous bone to reduce the likelihood of screw loosening and the subsidence of disc replacement devices. This study was reviewed by the SUNY Downstate Medical Center IRB Committee; IRB#: 533603-2.

A biomechanical analysis of tibial ACL reconstruction with graft length mismatch

Introduction: The incidence of graft length mismatch (GLM) during anterior cruciate ligament (ACL) reconstruction is reported to be up to 13%, with a rate of 20% when using bone-patellar tendon-bone (BPTB) allografts. Multiple techniques have been described to accommodate for the longer BPTB graft. As no study has compared the biomechanical properties of these methods (with cyclic loading), we evaluated the strength of four different surgical techniques used to accommodate for GLM during ACL reconstruction. Methods: A total of 32 fresh-frozen bovine tibiae and patellar tendons were divided into four groups based on the method of tibial graft fixation: (1) sutures tied over a post, (2) bone staples, (3) screws and washers, and (4) soft-tissue conversion with interference screw. Biomechanical testing was performed comparing the tensile properties of graft fixation techniques under cyclic loading. Ability to withstand 1500 cycles of load, the maximum tensile strength at load-to-failure, and the mode-of-failure were evaluated. Results: Only group 4 had all grafts intact after 1500 loading cycles, while the other groups had one graft failure at 338 (group 1), 240 (group 2), and 309 (group 3) cycles. The highest mean load-to-failure was observed in group 3 at 762 ± 173 N, which was found to be significantly higher than the other groups. The mean loads to failure in groups 1–4 were 453 ± 86 N, 485 ± 246 N, 762 ± 173 N, and 458 ± 128 N. Conclusion: While there are multiple viable techniques for fixation of a BPTB graft in the case of GLM, this study demonstrated that direct screw fixation offers the strongest construct.

Systematic Review of All Smart Phone Applications Specifically Aimed For Use As a Scoliosis Screening Tool

The scoliometer is an inclinometer commonly used in scoliosis screening. The device is used during an Adams forward bend test, in which a patient bends forward at the hips to measure deformity of the rib cage and spinal column. If a sufficient angle of rotation is measured, then the appropriate referrals and x-rays can be made and taken. This ubiquitous screening tool allows for a quick and simple scoliosis screening and is a mainstay of scoliosis management. With the advent and rapid improvement of smart phone technology, many scoliometer applications have become readily accessible. Our study was designed to test the accuracy, precision, and calibration of several scoliometer applications available on both the Apple iPhone and Samsung Galaxy platforms. Application cost was also analyzed to assess the plausibility of using a smartphone scoliometer application in place of a traditional scoliometer in a traditional scoliosis screening. Our data show that available smart phone applications can be used effectively and that, in a controlled environment, some applications performed better than a traditional scoliometer. Application price was not correlated with effectiveness; the cost-free application performed better than the for-purchase application.

Acromioclavicular joint reconstruction using a tendon graft: a biomechanical study comparing a novel “sutured throughout” tendon graft to a standard tendon graft

Background: With a recurrence rate of over 30%, techniques that offer stronger acromioclavicular (AC) joint reconstruction through increased graft strength may provide longevity. The purpose of our study was to determine the biomechanical strength of a novel tendon graft sutured throughout compared to a native tendon graft in Grade 3 anatomical AC joint reconstruction. Methods: For this in vitro experiment, nine paired (n = 18) embalmed cadaveric AC joints of three males and six females (age 86 years, range 51–94 years) were harvested. Anatomic repair with fresh bovine Achilles tendon grafts without bone block was simulated. Specimens were divided into two groups; with group 1 using grafts with ultra-high molecular-weight polyethylene (UHMWPE) suture ran throughout the entire length. In group 2, reconstruction with only native allografts was performed. The distal scapula and humerus were casted in epoxy compound and mounted on the mechanical testing machine. Tensile tests were performed using a mechanical testing machine at the rate of 50 mm/min. Maximum load and displacement to failure were collected. Results: The average load to failure was significantly higher for group 1 compared to group 2, with mean values of 437.5 N ± 160.7 N and 94.4 N ± 43.6 N, (p = 0.001). The average displacement to failure was not significantly different, with 29.7 mm ± 10.6 mm in group 1 and 25 mm ± 9.1 mm in group 2 (p = 0.25). Conclusion: We conclude that a UHMWPE suture reinforced graft can provide a 3.6 times stronger AC joint reconstruction compared to a native graft.

A Biomechanical Comparison of Different Tendon Repair Techniques

Previous studies have examined multiple suture techniques for the repair of ruptured tendons. In this study, we investigated how the two- and four-stranded Krackow suture weave techniques compared with a novel Krackow/Bunnell suture technique. Our hypothesis was that the Krackow/Bunnell suture would have greater strength compared with the two- and four-stranded Krackow suture in terms of resistance to pullout from the muscle tendon. Thirty fresh bovine Achilles tendons were assigned randomly to three groups: (1) two-stranded Krackow, (2) fourstranded Krackow, and (3) the Krackow/Bunnell combination. After suture placement, all specimens were subjected to initial cyclic loading (0-200 N for 200 cycles) and then the tension to failure force defined as the pullout through the muscle tendon was evaluated. Significantly greater deformation before suture failure was seen in the Krackow/Bunnell group compared with the four-stranded Krackow construct (36.2 vs. 28.7 mm, p = 0.009), as well as greater energy required to rupture the suture (4635 vs. 3346 N/mm; p = 0.016). There was no significant difference with regard to the force to failure between the two groups (four-stranded Krackow vs. Krackow/Bunnell). The two-stranded Krackow was found to be inferior to both the four-stranded Krakow and the Krakow/Bunnell techniques with regard to load to failure. We have found that the Krackow/Bunnell suture technique is at least comparable to, if not superior to, the four-stranded Krackow technique with regard to deformation before suture failure and energy required to rupture the tendon. Therefore, the Krackow/Bunnell technique may be an optimal construct if the surgeon is concerned about suture pullout through the tendon; however, future studies evaluating this technique in the clinical setting are required before making any final conclusions for patient use.

Strength of Syndesmosis Fixation: Two TightRope versus One TightRope with Plate-and-Screw Construct

Injuries involving the distal tibiofibular syndesmosis can lead to critical destabilization of the ankle mortise. Although specific indications for operative fixation remain unclear, accurate reduction of the syndesmosis has been correlated with the best functional outcomes. The purpose of this study was to evaluate the maximum torque and rotation to failure after fixation with a novel construct. Seven pairs (14 ankles) of embalmed cadaveric lower legs, disarticulated at the knee, were obtained. Each pair was randomly assigned to receive either two TightRopes (Arthrex) or a plate-and-screw construct with one TightRope. All samples were mechanically tested in torsion to determine peak torque, torsional stiffness, and the maximum rotation angle at which failure occurred. Differences between the groups were compared using paired Students t test. The maximum torque to failure after fixation was not significantly different between the two TightRopes (28.8 N*m; range, 7.3-49.7 N*m) and the one TightRope group (29.5 N*m; range, 9.2-44.9 N*m; p = 0.92). The maximum rotation to fracture after fixation was not significantly different between the two TightRopes (33.3 degrees; range, 21.6-57.0 degrees) and one TightRope group (38.6 degrees; range, 23.0-73.9 degrees). All specimens failed with the fracture of the fibula at the level of the inferior syndesmotic screw. The similar load to failure of the two TightRope and the one TightRope and plate-and-screw plate suggested similar stiffness between the two constructs. The addition of the plate may improve distribution of forces at the level of syndesmosis, reducing stress risers and decreasing the risk of failure, as demonstrated by a lower rotation to failure of the one TightRope with plate-and-screw construct. In addition, this construct is not likely to not be associated with any substantial cost increase. Further clinical studies may further elucidate the role of plate and/or TightRope augmentation to syndesmosis fixation.

Variations in Density and Shear Strength within the Human Thoracic Vertebral Endplate and Trabecular Bone

We assessed the regional variations in density and shear strength within the human thoracic vertebral body using donated cadaveric tissues. Shear strength was significantly lower in the anterior than in the lateral region. From the inferior to the superior endplates, shear strength and maximum load to failure decreased by 23% and 33%, respectively. Trabecular bone maximum load carrying capacity was 5 times higher in the lateral and 4.5 times higher in the central than in the anterior regions. Mechanical strength positively correlated with ash density and most closely with material density.

Influences of the vertebral endplate microvasculature on the development of degenerative disc diseases: A preliminary study

An average of 70% of all Americans will suffer from one episode of low back pain (LBP) in their lifetime [1]. Senescence of the avascular nucleus pulposus with decreased transport of nutrients is thought to lead to degenerative disc diseases (DDD) and low back pain [2-5]. We investigated the relationship between aging, cartilage endplate microvasculature, and the level of disc degeneration. Lumbar discs with adjacent endplates were harvested from three fresh young bovine and three embalmed human cadaveric spines. After tissue processing, histology, and staining, microscopic features of endplate vascular channels were visualized under light microscopy and measured using ImageJ. Our preliminary data showed a 15% decrease in the vascular channel count at the interface between subchondral bone and cartilage endplate from the bovine to the elderly human specimens. Moreover, we observed a 67% increase in endplate thickness and a 70% decrease in cross sectional vascular area in the human subjects.

Biomechanical Evaluation of Osteoporotic Sheep Long Bones

The objective of this research was to develop a calcium phosphate-based synthetic bone mineral (SBM) that will have a potential for osteoporosis therapy and prevention. The goal of this study was to test the efficacy of SBM in preventing loss of strength in long bones of osteoporotic sheep. The animals were divided into four groups: sham-operated; ovariectomized (OVX); OVX supplemented with SBM without fluoride; OVX supplemented with SBM containing fluoride. The bones were scanned by CT and tested mechanically in 4-point-bending from which the mechanical properties and fracture behavior were evaluated. The load at 1mm deformation for the OVX sheep tibias was significantly lower than the sham operated group and groups with special diets. The sheep given the SBM (+F) showed the highest load carrying capacity. Similarly, the stiffness and energy to fracture of the OVX sheep was also significantly lower than the group given SBM (+F). The ultimate stress and the elastic modulus did not show any statistically significant difference among the four groups. SBM was partially successful at preventing loss of bone strength in osteoporotic sheep.