Biomedical subjects

G Kotzar

Publications and source records attributed to G Kotzar.

5 recordsLinked to original sources

PubMed1994

A six-degree-of-freedom transducer for in vitro measurement of patellofemoral contact forces.

A satisfactory design of the patellar component used in total knee arthroplasty and a general understanding of the effects of orthopedic procedures require, in part, an accurate description of patellofemoral contact forces. Experimental determination of the contact stress distribution requires integration to estimate the contact forces. Due to complex patellar geometry, the determination of the components of the resultant load is difficult. Current techniques for the direct measurement of contact loads either report a single load component or require sequential experiments to fully describe the contact force. The present study describes the development of a six-degree-of-freedom patellofemoral force transducer. This transducer allows the simultaneous determination of the three components of the contact force with an increase in accuracy over available devices. The contact forces components are accurate to 1% of full scale (900 N anterior-posterior, +/- 200 N medial-lateral and inferior-superior). The location on the patella where the resultant force acts is determined to within 1 mm. Relative movement of this point as a function of either normal change in knee flexion angle or as a result of a typical orthopedic procedure is determined to within 0.1 mm. A protocol is presented that allows the contact forces to be determined for either the anatomically normal patella or a patella following total knee arthroplasty.

Calibration↗

PubMed1993

A biomechanical analysis of atlantoaxial stabilization methods using a bovine model. C1/C2 fixation analysis.

The reliability and initial postoperative stability of six widely used C1-C2 surgical constructs were evaluated by nondestructive biomechanical testing of ten fresh bovine upper cervical spine segments. The six fixation techniques were the simple midline sublaminar C1 wiring (SMW), the modified Gallie wiring (MGW), the Brook wedge arthrodesis (BWA), the bilateral lateral mass screw (LMS), and the Clark arthrodesis without (CWO) and with (CW) the adjunctive use of polymethylmethacrylate (PMMA) cement. Instability was produced by resection of the base of the dens. Intact, destabilized, and instrumented constructs were tested in unconstrained flexion, extension, torsion, anterior, and posterior shear forces. The LMS and CW techniques proved the most effective in achieving C1-C2 stability. Sublaminar C2 wiring methods tended to have greater torsional and shear stiffness. Less rigid fixation techniques frequently loosened. All non-PMMA-enhanced wired constructs failed to restore the ability to adequately resist the posterior translation of C1 on C2. Stabilization of an unstable atlantoaxial articulation is best accomplished by a lateral mass screw or sublaminar C1-C2 PMMA-enhanced technique. Other techniques provided less consistent and reliable surgical fixation. Because of the inadequacy of wired constructs to resist posterior shear in patients with this instability pattern, the usual treatment may need to be modified to include more prolonged or protective external immobilization or more rigid fixation techniques. Although less rigid, the SMW and the MGW techniques are safer because they require less-frequent passage of sublaminar wires, avoid potential problems with PMMA, and obviate the hazards of further lateral dissection and insertion of the transarticular screws.

Animals↗

PubMed1987

Femoral component loosening in hip arthroplasty. Cadaver study of subsidence and hoop strain.

To aid in understanding loosening following cemented total hip arthroplasty, we conducted a cadaver study of the proximal femur with implanted cobalt-chromium and titanium femoral components of recent design, loaded through the head of the prosthesis. Stem subsidence and strain in the proximal femur were measured. After proximal support of the implant collar was removed, we found that cobalt-chromium implants had a greater tendency to subside than titanium implants. Subsidence of a femoral component within the cement mantle caused an increase in tensile hoop strain measured in the proximal cortex. When implants were loaded until failure of the cortex, a direct relationship between increase in subsidence and increase in cortical hoop strain was demonstrated. Our data show that implants that resist subsidence into the cement mantle tend to decrease hoop strains in the proximal femoral cortex.

Bone Cements↗

PubMed1987

Effects of repetitive loading on the integrity of porous coatings.

In spite of the increasing numbers of porous coated total hip femoral components implanted each year, little is known about the shear strength or fatigue performance of the interface between coating and implant substrate. The appearance of loose beads in clinical follow-up roentgenograms suggests that shear failure of bead welds does occur and that the coating could be a weak link in the implant-bone or implant-cement-bone system. In this study, a test specimen design and test regimen for quasistatic and fatigue testing of implant-porous coating shear properties was developed. Both cobalt-chromium (CoCr) alloy and titanium (Ti) bead-substrate interfaces of various surface designs were studied. Results showed that static bead-substrate interface properties for both titanium and CoCr specimens were superior to published values of bone-bead shear strengths. By comparison, fatigue tests showed that the strength of bead welds on a smooth substrate was inadequate, with a preferential failure site being between beads and substrate rather than between beads and cement or beads and bone. However, implant surface contours or a bead recess were found to protect the bead welds, and specimens with those features successfully withstood ten million dynamic loading cycles.

Chromium Alloys↗

PubMed1983

Contrast bone cement.

The effects of adding 1.0 cc of aqueous methylene blue dye as a visual contrast agent to a standard 40 g pack of acrylic bone cement are determined. These cements are evaluated: Simplex P (Radiopaque), Zimmer Bone Cement, and Zimmer LVC Bone Cement. Seven tests were performed. Leach out is less than 2.0% and was undetectable after day 8. Biocompatibility using a rabbit model shows contrast and white cement to be equivalent. Tension, compression, and 3- and 4-point bending strengths are not significantly altered except for a slight increase in 4-point bending strength for contrast Zimmer (regular) bone cement. Dough, set, and working times are decreased by 30-150 s. The ASTM F451 intrusion standards are met for all three contrast cements. Viscosity increases more rapidly for contrast cement, but remains sufficiently low (less than 100 N-s/m2) early after mixing to allow good penetration into bone. Ease of removal and visualization of contrast cement are shown by revision of cemented femoral total hip components in synthetic and cadaver femurs and by debriding cement particles from a soft tissue background coated with blood. The use of contrast bone cement appears to be both safe and efficacious for use in initial and revision total joint replacements. Because of the decreased working times, its use is recommended only by experienced surgeons.

Animals↗