Tool parameters to minimize temperature changes in bone drilling.

BACKGROUND: Drilling is a common technique used in orthopedic surgery procedures but causes increases in temperature that can lead to cell damage and death. The extent of this depends largely on the magnitude of the increase in temperature. The commonly accepted limit to prevent osteonecrosis is less than 47 °C for 60 s. There is controversy when it comes to the optimal drilling parameters that limit temperature increases and cell death. In addition to this, less research has been done on the drilling effects in the osteochondral area of joints. Osteochondral tissue damage can interfere with the daily lives of patients and if severe enough will need to be treated. We hypothesize that increasing tool speed and drill bit size will increase temperature that could be above the osteonecrosis limit. METHODS: Ex-vivo experiments were conducted on porcine shoulder joints that tested the thermal effects of different tool speeds and drill bit sizes. A thermal camera was used to record and measure real time temperature changes while drilling. Three drill bit sizes and five tool speeds were used. Statistical analyses includes Welch's ANOVA with Games-Howell Post Hoc analyses, multivariate linear regression, and surface response regression were used to explore the association of tool speeds and drill bit size on temperature. RESULTS AND CONCLUSIONS: All the tool speed and drill bit size combinations lead to an increase in temperature that were under the commonly accepted limit. The highest temperature reached was 44 °C with a tool speed of 1150 RPM and 3070 RPM and drill bit size 5.159 mm. It was found that increasing the tool speed increased the temperature change and increasing the drill bit size increased the temperature change.

Microencapsulation of Stem Cells for Therapy.

An increasing demand to regenerate tissues from patient-derived sources has led to the development of cell-based therapies using autologous stem cells, thereby decreasing immune rejection of scaffolds coupled with allogeneic stem cells or allografts. Adult stem cells are multipotent and are readily available in tissues such as fat and bone marrow. They possess the ability to repair and regenerate tissue through the production of therapeutic factors, particularly vasculogenic proteins. A major challenge in cell-based therapies is localizing the delivered stem cells to the target site. Microencapsulation of cells provides a porous polymeric matrix that can provide a protected environment, localize the cells to one area, and maintain their viability by enabling the exchange of nutrients and waste products between the encapsulated cells and the surrounding tissue. In this chapter, we describe a method to produce injectable microbeads containing a tunable number of stem cells using the biopolymer alginate. The microencapsulation process involves extrusion of the alginate suspension containing cells from a microencapsulator, a syringe pump to control its flow rate, an electrostatic potential to overcome capillary forces and a reduced Ca++ cross-linking solution containing a nutrient osmolyte, to form microbeads. This method allows the encapsulated cells to remain viable up to three weeks in culture and up to three months in vivo and secrete growth factors capable of supporting tissue regeneration.

Alginate microencapsulation technology for the percutaneous delivery of adipose-derived stem cells.

BACKGROUND: Autologous fat is the ideal soft-tissue filler; however, its widespread application is limited because of variable clinical results and poor survival. Engineered fillers have the potential to maximize survival. Alginate is a hydrogel copolymer that can be engineered into spheres of <200 µm, thus facilitating mass transfer, allowing for subcutaneous injection, and protecting cells from shearing forces. METHODS: Alginate powder was dissolved in saline, and adipose-derived stem cells (ADSCs) were encapsulated (1 million cells/mL) in alginate using an electrostatic bead generator. To assess effects of injection on cell viability, microspheres containing ADSCs were separated into 2 groups: the control group was decanted into culture wells and the injection group was mixed with basal media and injected through a 21-gauge needle into culture wells. Microbeads were cultured for 3 weeks, and cell number and viability were measured weekly using electron and confocal microscopy. To assess effects of percutaneous injection in vivo, twenty-four male nude mice were randomly separated into 2 groups and injected with either empty microcapsules or ADSC-laden microcapsules. Mice were harvested at 1 and 3 months, and the implants were examined microscopically to assess bead and cell viability. RESULTS: A flow rate of 5 mL/h and an electrostatic potential of 7 kV produced viable ADSC-laden microbeads of <200 µm. There were no differences in bead morphology and ADSC viability between microcapsules placed versus injected into tissue culture plates for up to 3 weeks. Microspheres implanted in a nude mouse model show durability up to 3 months with a host response around each individual sphere. ADSCs remained viable and showed signs of mitosis. CONCLUSIONS: ADSCs can be readily cultured, encapsulated, and injected in alginate microspheres. Stem cells suspended in alginate microspheres survive in vivo and are seen to replicate in vitro.

Sub-muscular plating of the humerus: an emerging technique.

OBJECTIVE: The purpose of the present study was to evaluate percutaneous sub-muscular internal fixation using a locked screw methodology for treatment of diaphyseal humeral fractures. METHODS: Inclusion criteria were multiple extremity fractures, open fractures, neurovascular injuries,additional ipsilateral upper extremity fractures, the inability to obtain a satisfactory closed reduction and isolated fractures with circumstances that prevented effective bracing. Exclusion criteria were immaturity, neoplasm, infection and intra-articular extensions in the same bone. Outcome measures included clinical and radiographic healing, complications, elbow and shoulder symptoms, range of motion (ROM) and Constant­Murley (CM) scores. RESULTS: Thirty-one patients with 32 fractures were evaluated with a mean follow-up of 16 months (3­38 months). There was radiographic healing in 31 out of the 32 fractures; the non-union was revised to open plating at 6 months and healed uneventfully. Hardware complications included two construct disengagements; one patient was revised and healed, and the other achieved union with bracing.Neurovascular complications included one preoperative nerve palsy that recovered by 3 months, two partial to complete postoperative nerve palsies that recovered by 6 months, and one intact-to-complete nerve palsy due to a bone fragment that required decompression with full recovery by 3 weeks. All patients had functional ROM with a mean CM score of 88. There were no elbow complaints and minor shoulder dysfunction occurred in two patients with ipsilateral shoulder injuries. The rate of neurovascular complications was comparable to open plating techniques and all patients had full recovery. CONCLUSION: We feel sub-muscular anterior plating of the humerus using locking screw technology is a viable and useful method for diaphyseal humeral fractures.