Biomedical subjects

J D DesJardins

Publications and source records attributed to J D DesJardins.

8 recordsLinked to original sources

PubMed2006

Effect of lubricant composition on the fatigue properties of ultra-high molecular weight polyethylene for total knee replacement.

Ultrahigh molecular weight polyethylene (UHMWPE) fatigue is a critical factor affecting the longevity of total knee replacement (TKR) bearings. With the increased need for laboratory studies to mimic near in vivo conditions for accurate characterization of material performance, the present study investigated the role of hyaluronic acid (HA) in testing lubricant on the crack growth response of UHMWPE. It was hypothesized that the change in lubricant viscosity as a result of HA would affect the fatigue life of the polymer. A fracture mechanics approach as per ASTM E 647 was adopted for this study. Surface micrograph and surface chemistry analyses were employed to study the micromechanisms of fatigue failure and protein adsorption of the specimen surfaces. Rheological analysis indicated that the addition of HA to diluted bovine serum increased testing lubricant viscosity. HA concentrations of 2.22, 0.55, and 1.5 g/l closely matched the viscosity ranges reported for osteoarthritis, rheumatoid arthritic diseased joint fluid, and periprosthetic fluids respectively. Results showed that the addition of HA to standard diluted bovine serum lubricants, in concentrations similar to that of periprosthetic fluid, delayed crack initiation and crack growth during fatigue testing.

Animals↗

PubMed2002

Effect of stair descent loading on ultra-high molecular weight polyethylene wear in a force-controlled knee simulator.

A loading protocol approximating forces, torques and motions at the knee during stair descent was developed from previously published data for input into a force-controlled knee simulator. A set of total knee replacements (TKRs) was subjected to standard walking cycles and stair descent cycles at a ratio of 70: 1 for 5 million cycles. Another set of implants with similar articular geometry and the same ultra-high molecular weight polyethylene (UHMWPE) resin (GUR 415), sterilization and packaging was tested with standard walking cycles only. Implant kinematics, gravimetric wear and surface roughness of the UHMWPE inserts were analysed for both sets of implants. Contact stresses were calculated for both loading protocols using a Hertzian line contact model. Significantly greater weight loss (p < 0.05) and more severe surface damage of UHMWPE inserts resulted with the walking + stair descent loading protocol compared to walking cycles only. Anterior-posterior (AP) tibiofemoral contact point displacements were lower during stair descent than walking, but not significantly different (p = 0.05). Contact stresses were significantly higher during stair descent than walking, owing to higher axial loads and the smaller radius of curvature of the femoral components at higher flexion angles. High contact stresses on UHMWPE components are likely to accelerate the fatigue of the material, resulting in more severe wear, similar to what is observed in retrieved implants. Thus the inclusion of loading protocols for activities of daily living in addition to walking is warranted for more realistic in vitro testing of TKRs.

Activities of Daily Living↗

PubMed2001

Effects of in vitro wear of machined and molded UHMWPE tibial inserts on TKR kinematics.

The effect of manufacturing process on the wear and mechanical performance of a total knee replacement (TKR) design was investigated with the use of a force-controlled knee joint simulator. Ultra-high molecular weight polyethylene (UHMWPE) tibial inserts processed by direct compression molding from 1900H resin were compared to UHMWPE tibial inserts machined from a compression-molded sheet of GUR 1050. Both sets of components had the same posterior-cruciate-retaining geometry, and were identically aligned with cobalt-chromium-molybdenum alloy femoral components. Wear tests were conducted at a frequency of 1 Hz for 4 million cycles with the use of a standard walking cycle pattern. Implant kinematics, including anterior-posterior (AP) displacement and internal-external (IE) rotation in response to applied loads were monitored. Gravimetric wear, surface roughness, and surface morphology were used to characterize the wear process of the UHMWPE inserts. Results showed that the molded UHMWPE inserts exhibited less gravimetric wear over time than the machined inserts of the same design. Both the machined and molded components exhibited scratching, pitting, and burnishing over their wear areas. The AP displacement distance per cycle of the molded tibial inserts decreased over the course of testing, resulting in a shorter total testing displacement for this group compared to machined tibial inserts. Although AP displacement distance per cycle for machined tibial inserts did not change significantly over the course of testing, their position relative to the femoral components shifted posteriorly over time, resulting in an elongated wear track.

Arthroplasty, Replacement, Knee↗

PubMed2000

The use of a force-controlled dynamic knee simulator to quantify the mechanical performance of total knee replacement designs during functional activity.

The experimental evaluation of any total knee replacement (TKR) design should include the pre-implantation quantification of its mechanical performance during tests that simulate the common activities of daily living. To date, few dynamic TKR simulation studies have been conducted before implantation. Once in vivo, the accurate and reproducible assessment of TKR design mechanics is exceedingly difficult, with the secondary variables of the patient and the surgical technique hindering research. The current study utilizes a 6-degree-of-freedom force-controlled knee simulator to quantify the effect of TKR design alone on TKR mechanics during a simulated walking cycle. Results show that all eight TKR designs tested elicited statistically different measures of tibial/femoral kinematics, simulated soft tissue loading, and implant geometric restraint loading during an identical simulated gait cycle, and that these differences were a direct result of TKR design alone. Maximum ranges of tibial kinematics over the eight designs tested were from 0.8mm anterior to 6.4mm posterior tibial displacement, and 14.1 degrees internal to 6.0 degrees external tibial rotation during the walking cycle. Soft tissue and implant reaction forces ranged from 106 and 222N anteriorly to 19 and 127N posteriorly, and from 1.6 and 1.8Nm internally to 3.5 and 5.9Nm externally, respectively. These measures provide valuable experimental insight into the effect of TKR design alone on simulated in vivo TKR kinematics, bone interface loading and soft tissue loading. Future studies utilizing this methodology should investigate the effect of experimentally controlled variations in surgical and patient factors on TKR performance during simulated dynamic activity.

Biomechanical Phenomena↗

PubMed1999

Size and position of a single condyle allograft influence knee kinematics.

An optimal match for size and shape between the donor femur and the host knee is considered a critical factor influencing the outcome of a knee allograft implantation. An in vitro allograft model was developed to determine the influence of the size and position of a lateral distal femoral condylar allograft on knee kinematics. Functional knee motion was simulated in a cadaver host knee in the intact state after removing and reimplanting the native lateral condyle of the distal femur and after serially replacing the native condyle with eight donor allografts. Each allograft was first tested in an optimal position and subsequently shifted 3 mm proximal and 3 mm distal to the joint line to quantify changes in joint kinematics due to the position of the allograft. The intact knee and the knee with the ideally implanted native allograft followed similar kinematic trends. Decreasing the width of the allograft increased the valgus knee orientation at full flexion, translated the tibia posteriorly at full extension, and externally rotated the tibia throughout knee flexion. The proximal shift in allograft position increased the valgus orientation at full extension, translated the tibia posteriorly at mid-flexion, and externally rotated the tibia throughout flexion. The distal shift in position had the opposite effect on the kinematics of the proximal shift. These results indicate that improving techniques for preoperative size-matching and intraoperative allograft placement may help to reduce biomechanical complications following implantation of the allograft.

Biomechanical Phenomena↗

PubMed1999

Hamstrings cocontraction reduces internal rotation, anterior translation, and anterior cruciate ligament load in weight-bearing flexion.

Strengthening of the hamstrings is often recommended following injury and reconstruction of the anterior cruciate ligament. It has been suggested that hamstrings activity stabilizes the knee and reduces anterior cruciate ligament load during weight-bearing flexion; however, the effects of hamstrings cocontraction on the kinematics and mechanics of the normal knee have not been assessed at physiological load levels. The aim of this study was to determine whether the addition of hamstrings force affects knee rotations, translations, and joint and quadriceps force during flexion with loads at physiological levels applied to the muscles and joints. Eight cadaveric knee specimens were tested with a servohydraulic mechanism capable of applying controlled dynamic loads to simulate quadriceps and hamstrings muscle forces throughout a physiological range of motion. A constant vertical load of physiologic magnitude was applied to the hip, and quadriceps force was varied to maintain equilibrium throughout flexion. Two conditions were tested: no hamstrings force and a constant hamstrings force equivalent to the vertical load. Hamstrings force significantly reduced internal rotation (p<0.0001) and anterior translation (p<0.0001), increased quadriceps force (p<0.0001) and normal resultant force on the tibia (p<0.0001), and reversed the direction of the shear force on the tibia (p<0.0001). These results suggest that hamstrings strengthening following anterior cruciate ligament injury may benefit anterior cruciate ligament-deficient and reconstructed knees by reducing the load in the ligament; however, they also imply that this comes at the expense of efficiency and higher patellofemoral and joint forces.

Aged↗

PubMed1998

A repeatable alignment method and local coordinate description for knee joint testing and kinematic measurement.

A method for aligning cadaver knee specimens to a mechanical testing rig and determining local anatomical coordinate systems using landmarks identifiable on plane X-rays is introduced. Three sequential rotational alignments arc used to position the femur and tibia relative to the coordinate system of the testing mechanism. To validate this methodology five independent observers aligned the same knee specimen. The maximum error in the alignment orientations of the tibia and femur was 2.2 from the mean. These small misalignments produced variations of up to 4.7 in tibio-femoral rotations measured during knee flexion. Kinematic measurements of 15 specimens aligned using this procedure indicate that knee alignment is reproducible and physiologically relevant.

Biomechanical Phenomena↗

PubMedDate not supplied

The effect of intercondylar notchplasty on the patellofemoral articulation.

Using pressure-sensitive film, we measured the patellofemoral contact areas and pressures after increasing degrees of notchplasty in eight fresh-frozen cadaveric knee specimens. Each specimen was stabilized on an axial loading frame with physiologic loads applied through the quadriceps tendon at varying flexion angles. The patellofemoral joint was loaded at 90 degrees, 105 degrees and 120 degrees of knee flexion. The same measurements were then obtained after serial notchplasties of 3, 6, and 9 mm. The film was analyzed for contact areas and for contact pressures by densitometry. There was no statistical significance between contact area or pressure after notchplasties of 3, 6, or 9 mm at 90 degrees, 105 degrees, and 120 degrees of knee flexion. These data suggest that routine notchplasty does not affect the patellofemoral articulation.

Cadaver↗