Papers by Author: Juan C. Hermida

Abstract: The Success of Hydroxyapatite-Coated Acetabular Components Has Not Been Consistent. Plasma-Sprayed Hydroxyapatite Coatings Work Well on Nonporous Substrates but Do Not Coat the Inner Surfaces of Open-Porous Substrates. Solution Deposition Can Generate Consistent Bioceramic Coats on Porous Surfaces that More Closely Mimic the Trabecular Pattern and Biochemistry at the Bone Interface. we Compared Bone Response to the Following Implants: Porous-Coated Ti6al4v Cylinders with 1 of 3 Treatments: Plasma Sprayed with Hydroxyapatite (HA), Coated with a Solution-Deposited Biomimetic Apatite Coating (BA), and Untreated (Control). Bilateral Femurs in 36 Rabbits Were Implanted with One of the above Implants. Bone Ingrowth for HA and BA Surfaces Was Significantly Higher than that for Control Surfaces. No Fragmentation or Debris Production Was Evident in the Apatite Coat of the BA Group. A Biomimetic Coat of Solution-Deposited Apatite May Be Resistant to Coating Delamination and Particle Generation.

Abstract: Hydroxyapatite (HA) coatings for femoral stems have been successful in short- to intermediate-term follow up. However, the outcomes of HA-coated cups have not been as successful as comparable non-HA-coated designs. This has been attributed to component design and to poor quality HA-coating processes. This is a clinical outcome study of a newer generation acetabular design with an improved plasma-sprayed HA-coat. Ninety consecutive primary total hip replacements implanted with a HA-coated metal-backed cup were prospectively followed up for 2–5 years after surgery. Mean age was 69 years, male:female ratio was 36:47; mean-weight was 77 kg. Polyethylene wear was measured on digitized images. Component position, component migration, and implant-bone interface radiolucent lines were analyzed by computerized image analysis. Hip-scores improved from preoperative mean 59(±12) to a final follow-up mean of 91(±12). One hip was revised for recurrent dislocation. No hips were revised for aseptic loosening. Mean acetabular abduction angle was 46°(±8.5) and anteversion was 18°(±8.7). Incomplete lucent lines were noted on early postoperative radiographs in 5% of the cases. With ongoing follow up radiolucent line thickness decreased by mean 13% and radiolucent line density increased by 11%. No cup had complete continuous radiolucent lines or lysis. Mean polyethylene linear and volumetric wear rates were 0.14(± 0.15) mm/year and 73(± 70) mm3/year respectively. Wear rates were higher in males (p<0.03). No other factor (age, body weight, cup abduction or anteversion angle) correlated significantly with wear rate. This study presents encouraging short-term results. The improvement in radiolucent lines suggests a beneficial effect of the HA-coat on bone ingrowth. None of the cups loosened or migrated. Wear rates were comparable to published reports of successful non-HA-coated cups. Long-term follow up is ongoing to corroborate these early findings.

Abstract: Implants with a highly porous coating of Tritanium Dimensionalized MetalÔ have the advantage of simulating the trabecular structure of bone to provide maximum available porous space for bone ingrowth. Plasma-sprayed hydroxyapatite coatings work well on non-porous substrates but do not coat the inner surfaces of open-porous substrates. Solution deposition can produce a consistent bioceramic coating of precise thickness on porous surfaces. This report compares bone response to a highly porous titanium surface with a solution deposited coating of hydroxyapatite. Ti6AL4V rods were implanted bilaterally in the intramedullary canals of 40 rabbit femurs. The implants had a 1.5 mm CPTi coating, which was >65% porous with pore sizes of 250-400 microns. (Tritanium Dimensionalized MetalÔ). Twenty implants (T-HA) were coated with hydroxyapatite by a solution deposition method (Peri-ApatiteÒ). The other 20 implants (T) had no hydroxyapatite coating. Implants were provided with a final diameter of 5 mm and length of 23 mm (Howmedica Osteonics, Mahwah, NJ). Rabbit femurs were harvested at 6 and 12 weeks after surgery sectioned at two levels: in the diaphyseal and metaphyseal portion of the femoral canal. Scanning electron images (SEM) in backscattered mode were digitally captured. Osseointegration was measured by automated computerized histomorphometry of the SEM images. Mean bone ingrowth at both time points was significantly different between hydroxyapatite-coated and non-hydroxyapatite coated implants (p<0.01). The hydroxyapatite coating had a significant benefit on the bone growth into porous titanium surfaces. Bone ingrowth was substantially higher at all time points in the hydroxyapatite-coated surface relative to the uncoated surface and in both diaphyseal and metaphyseal cross-section levels. The finding of a higher percentage of bone growth deeper in the pores of the surface is encouraging. This signifies that the solution deposited Peri-Apatite coating is capable of depositing a bioactive coat of hydroxyapatite in the depths of the porous surface. This depth of penetration is not achievable by conventional plasma-sprayed deposition of hydroxyapatite. Implants with a Tritanium Dimensionalized MetalÔ surface and a solution deposited Peri-Apatite coating have the potential to develop into attractive alternatives for noncemented total hip arthroplasty.

Abstract: Typical plasma-sprayed hydroxyapatite coatings work well on non-porous substrates but do not coat the inner surfaces of open-porous substrates. Solution deposition can produce consistent bioceramic coats of precise thickness on porous surfaces. The resultant “biomimetic” surface more closely mimics the trabecular pattern and biochemistry at the bone interface. This report compares bone response to porous surfaces with biomimetic hydroxyapatite coatings. Implants were manufactured as Ti6Al4V cylinders (5-mm diameter, 41-mm long) coated with c.p-Ti PorocoatÒ porous layer with a thickness of 750 (± 250 µm). Implants were divided into three groups based on surface treatments. The porous surfaces of control group implants did not receive any treatment. The porous surfaces of HA group implants were plasma sprayed with hydroxyapatite. The porous surfaces of BAp group implants were coated with a biomimetic apatite (BAp) coating using a lowtemperature solution-based process that mimics bone mineralization. BAp coating is pure apatite coating of uniform structure and composition, with a thickness of approximately 15 µm on the outer beads. Because of the reduced thickness, the BAp coating does not block the pores or alter the porous structure. Bilateral femurs in thirty-six rabbits were implanted with one of the above groups. Twelve rabbits each were euthanized at 2, 4, and 12 weeks. Osseointegration was measured by automated computerized histomorphometry of scanning electron microscopy images of sections taken through the implant. Bone ingrowth on the Control surface was 45 % at 2 weeks and 47% at 12 weeks. Bone ingrowth on the PS surface increased from 51% at 2 weeks to 67% at 12 weeks. Bone ingrowth on the BAp surface increased from 45 % at 2 weeks to 71% at 12 weeks. At both time points mean bone ingrowth on PS and BAp coated implants was significantly higher than the control uncoated implants (p < 0.01). By 12 weeks the PS hydroxyapatite coat began showing evidence of fragmentation and debris production on SEM. This was not evident in the BAp coat. This study supports the hypothesis that apatite coating benefits osseointegration. A biomimetic coat of solution deposited apatite may not show the disadvantages of coating delamination and particle generation. Biomimetic apatite coatings may be attractive alternatives for noncemented total hip arthroplasty.