Knee arthrodesis with the Wichita Fusion Nail: an outcome comparison.

UNLABELLED: The Wichita Fusion Nail (WFN) is a knee arthrodesis stabilization system that employs compression via an intramedullary rod. It was designed for use in the salvage of the irretrievably failed total knee arthroplasty and other severe knee pathologies. Questionnaires covering the fusion success rate, fusion time, and complication rate were obtained from 33 surgeons who were among the first to use the device. Data from these questionnaires were analyzed to determine if the rate of successful fusion was close to 100%, which was the primary hypothesis of this study. The average time required to achieve fusion and the rate of complications were also calculated and compared to similar results available in the literature. The results for 44 selected patients were included and it was determined that all achieved fusion for a success rate of 100%. This compared favorably with reported success rates in the range of 54% to 96%. The average fusion time was 15.5 weeks. Complications included: six delayed unions, three deep infections, and two periimplant fractures for a major complications rate of 20.4%. Both the fusion times and complication rate compared favorably with other reported results. Surgeons using the device for the first time had outcomes equal to those of more experienced users. Our results demonstrated that a rate of successful arthrodesis close to 100% could be consistently achieved with the WFN. Overall, the WFN facilitated an improved outcome for a previously difficult procedure. LEVEL OF EVIDENCE: Therapeutic study, level IV (case series). See the Guidelines for Authors for a complete description of level of evidence.

Effect of bone block removal and patellar prosthesis on stresses in the human patella.

Thermoelastic stress analysis was used to examine stresses on the anterior surface of patellae after patellar bone block excision for autogenous graft anterior cruciate ligament reconstruction. Complications of anterior cruciate ligament injury often lead to degenerative changes in the knee that can require total knee joint replacement. It was hypothesized that stresses in a bone block-compromised patella may be increased even further by insertion of a patellar prosthesis. All patellae were first tested intact and then were retested after a sequence of surgical modifications including patellar prosthesis implantation, tapered bone block excision, square bone block excision, and both shapes of excised bone blocks with a patellar prosthesis in place. Stresses in patellae with bone blocks excised were significantly greater than stresses in intact patellae. The anterior surface stress pattern in the loaded patella was significantly altered by excision of a bone block. There were no significant differences between maximum stress in patellae with tapered and square bone blocks excised. A finite element analysis showed that excision of a larger trapezoid-shaped bone block greatly increased maximum stress levels. Insertion of a patellar prosthesis did not significantly alter stress patterns or maximum stress levels in the patella.

External fixation of unstable Malgaigne fractures: the comparative mechanical performance of a new configuration.

An external fixator has been designed that is rigid enough to eliminate the need for skeletal traction in patients with unstable pelvic-ring fractures. This Wichita frame is similar to the Pittsburgh frame but is stiffened by the use of locked crossbars connecting the side triangles. The frame was tested in cadaveric specimens by techniques previously reported. In addition, finite-element modeling of the various frame designs was performed to ensure that the frame configuration was optimal and to supplement in vitro test results. Multiple variables that can influence frame failure loads were examined.

Ceramics in orthopedic surgery.

Ceramics are stable compounds of metals with oxygen or other anions. They have been considered for orthopedic implant applications for nearly three decades because of their wear resistance and biochemical inertness. After numerous efforts to realize this promise, ceramics have not achieved wide acceptance because of their brittleness that carries the risk of unpredictable catastrophic failure in load-bearing applications. Perhaps the brightest prospects for ceramics lie in their use as reinforcing fibers in composite implants and as calcium hydroxylapatite coatings on metal implants where it can induce direct bonding with bone.

Stress enhancement and fatigue susceptibility of porous coated Ti-6Al-4V implants: an elastic analysis.

An elastic stress analysis of porous-coated implant surfaces was performed using the finite element method. Three-hundred-microns-diameter metal beads sinter bonded onto an implant surface were modeled with sinter neck radii of 5, 10, 20, and 50 microns. Smooth-surface, single-bead, single-layer, and double-layer systems were analyzed. The finite element models were loaded to simulate bone-bead contact forces and lateral hip implant tensile forces. Results showed that, for a single bead sinter-bonded onto an implant surface, concentration of stress occurs either at the base of the sinter neck or within the neck itself, depending on the type of load applied. Under lateral hip implant tensile loads, a maximum stress concentration factor of 1.97 was obtained for a single bead sinter-bonded onto a implant surface. Addition of a single layer of beads onto the implant surface resulted in a significant increase in stress at the most proximal and distal ends of the porous layer, with a maximum stress concentration factor of 4.3. Addition of a second layer of beads did not significantly increase the magnitude of the stress concentration occurring at the ends of the porous layer. The results of this study provide stress concentration factors for porous coatings with sinter necks of known dimensions under loading conditions similar to those present along the lateral surface of a hip prosthesis.

Titanium-coated Dacron velour: a study of interfacial connective tissue formation.

Polyethylene terephthalate in textile form (Dacron) has been used extensively as a surgical implant material for applications such as vascular grafts and percutaneous access devices. It is moderately histocompatible eliciting a chronic inflammatory reaction predominately in tissue which has grown into the pores of the fabric. Titanium implants on the other hand, induce only the slightest inflammatory response and connective tissue adhesion to the titanium oxide surface is excellent. It was, therefore, hypothesized that a titanium coating on Dacron fabric might improve its histocompatibility while leaving its desirable mechanical properties unaffected. To test this idea, Dacron velour specimens were coated with titanium by vacuum deposition and were implanted together with uncoated controls in rabbits subcutis. After various implantation times, the specimens were recovered and the associated tissue was examined histologically. Qualitative and semiquantitative analysis revealed that tissue ingrowth quantity and quality was highly variable, not only between test and control specimens, but also between animals and even between specimens within the same animal. This indicated that there may be a number of factors influencing tissue ingrowth that were not adequately controlled in this study. The titanium coating which was undoubtedly highly oxidized had a profound qualitative and quantitative effect on fibroblast activity (ground substance formation) and fibroblast adhesion to the Dacron fibers. The results obtained after these short-term implantation periods indicate that titanium coating affects the quality of the interfacing tissue and may actually improve long-term histocompatibility. Long-term studies will have to confirm these preliminary data.

Growth inhibition of cultured fibroblasts by cobalt and nickel.

It is known that tissues surrounding the site of an implanted prosthetic alloy are exposed to increased concentrations of the metals comprising the alloy. However, the exact identity and concentration of such metallic products are usually unknown, thus limiting the possibilities for quantifying any observed toxicological response to the metals. This report describes some of the effects of increased concentrations (7.5-30 microgram/ml; 1-5 x 10(-4)M) Of cobalt (as CoCl2.6H2O) and of nickel (NiCl2.6H2O) on the growth and morphology of cultured mouse fibroblasts. Ultrafiltration experiments indicated that much of the total Co or Ni present in cell culture medium could become bound to macromolecular serum components of the medium. Morphological changes and depressions in the cell growth rate were found to result from high concentrations (15-30 microgram/ml) of either Co or Ni. However, lower concentrations of nickel may have produced some stimulation of cell growth, whereas all concentrations of Co studied were found to depress the rate of cell growth. The growth rate of actively proliferating fibroblasts was quite sensitive to variations in the concentration of either cobalt or nickel. Increased concentrations of cobalt or nickel, therefore, might also affect the normal reconstructive activity of fibroblasts in vivo.

An evaluation of porous alumina ceramic dental implants.

The fabrication, characterization, and clinical results of porous rooted alumina dental implants in animals are presented. Failures of all implants occurred in less than six months and were attributed to the presence of microporosity on the crown and cervical portion of the implant which prevented the establishment of an effective biological seal between the oral cavity and the alveolus.