Polyethylene contact stresses, articular congruity, and knee alignment.

Increased conformity at the tibiofemoral articulation increases contact area and reduces contact stresses in total knee arthroplasty. Malalignment, however, can increase polyethylene contact stresses. The effect of knee alignment and articular conformity on contact stresses was evaluated in a finite element model.

Quadriceps moment arm and quadriceps forces after total knee arthroplasty.

Knee prosthetic designs that increase quadriceps moment arm can reduce quadriceps tension and patellofemoral compressive forces. Six knees from cadavers were tested on the Oxford knee rig, which simulates closed chain knee extension under load. Three conditions were tested sequentially for each knee: Normal, Control (implanted with the Osteonics 7000 knee design), and Scorpio (implanted with the Osteonics Scorpio design).

Polyethylene wear and variations in knee kinematics.

A six-station knee wear simulator was used to test a posterior cruciate-retaining total knee arthroplasty design. Six implants each were tested in three groups; low intensity, high intensity, and malalignment using kinematic inputs from normal gait data, more severe loading conditions, and 3 degrees varus malalignment, respectively. For each group, gravimetric wear of the polyethylene inserts was measured for 5,000,000 cycles.

Patellar tracking in total knee arthroplasty: inset versus onset design.

Patellar components come in onset and inset designs. Kinematic differences between these designs were studied in a cadaver model of closed kinetic chain knee extension. Seven frozen knees were implanted with a standard posterior cruciate-retaining design.

Impact of mechanical trauma on matrix and cells.

Posttraumatic arthritis is one of the most common causes of secondary osteoarthritis. The contribution of cell death to matrix degradation has not been characterized fully. The current study was designed to determine the effect of mechanical injury on chondrocyte viability and matrix degradation.

In vivo changes after mechanical injury.

Chondrocytes undergo apoptosis in response to mechanical injury in vitro. The current clinical study correlates arthroscopic and magnetic resonance imaging results with biopsy specimens of cartilage from patients with knee injury. Twenty patients were evaluated at a mean 2.

The Harris-Galante Porous acetabular component at intermediate follow-up.

Outcome of the acetabular component in 90 consecutive primary noncemented total hip arthroplasties (THAs) was prospectively studied. The acetabular cup consisted of a hemispherical titanium alloy shell with a titanium fiber-mesh porous coating and a modular polyethylene liner (Harris-Galante Porous-1, Zimmer, Warsaw, Ind). The cup was implanted using line-to-line reaming with adjunctive dome screw fixation.

Tibiofemoral conformity and kinematics of rotating-bearing knee prostheses.

Increasing tibiofemoral articular conformity theoretically increases articular contact area and reduces contact stresses in total knee arthroplasty. Fixed-bearing knee designs possess relatively low tibiofemoral conformity, in part to allow tibiofemoral rotation without generating excessive stresses at the articulation or the implant-bone interface. This study analyzed knee kinematics of mobile-bearing designs in a closed chain dynamic knee extension model in posterior cruciate-retaining design with high- and low tibiofemoral conformity and posterior cruciate-substituting designs with and without rotational constraint.

Throat carriage of pneumococci in healthy school children in the Union Territory of Pondicherry.

Background & Objectives: Colonisation of Streptococcus pneumoniae in the throat is common among children the world over. Little is known about the relationship of nasopharyngeal carriage and invasive disease or the way it spreads within the households and close confines. There is a paucity of data on the colonization of Strep.

Comparison between the kinematics of fixed and rotating bearing knee prostheses.

Rotating platform mobile bearing knee implants allow for increased tibiofemoral articular conformity without restricting axial rotation. In the current study, the effect of rotating platform knee replacement with and without posterior cruciate ligament substitution on knee kinematics was investigated. Five knees were implanted sequentially implanted with standard (fixed) bearings and then with rotating platform prostheses, each in posterior cruciate retaining and substituting designs.

The press-fit condylar total knee system: 8- to 10-year results with a posterior cruciate-retaining design.

A total of 108 consecutive Press-Fit Condylar total knee arthroplasties were performed in 94 patients. All patients had implantation with a cemented posterior cruciate-retaining design, which included resurfacing of the patella. Mean age at surgery was 70 years (range, 35-87 years).

The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios.

Background: Prosthetic impingement due to poor positioning can limit the range of motion of the hip after total hip arthroplasty. In this study, a computer model was used to determine the effects of the positions of the acetabular and femoral components and of varying head-neck ratios on impingement and range of motion.

Methods: A three-dimensional generic hip prosthesis with a hemispherical cup, a neck diameter of 12.

Omnifit-HA stem in total hip arthroplasty. A 2- to 5-year followup.

Outcomes of the first 60 noncemented Omnifit-HA total hip arthroplasties in 56 patients were studied prospectively for 2 to 5 years. The femoral prosthesis had a proximal third circumferential hydroxyapatite coated surface treatment. The acetabular component was a hemispheric modular, porous, nonhydroxyapatite press fit cup, supplemented with screw fixation.

Venous thromboembolic disease after hybrid hip arthroplasty with negative duplex screening.

Postoperative duplex ultrasonography screening after total hip arthroplasty has been shown to identify patients who may require treatment or additional monitoring for venous thromboembolic disease. The potential for manifestation of venous thromboembolic disease subsequent to screening remains a concern. The objective of this study was to determine the prevalence of symptomatic venous thromboembolic disease after total hip arthroplasty and after inhospital prophylaxis, inhospital screening with negative results for proximal deep venous thrombosis, and no posthospitalization venous thromboembolic disease prophylaxis.

Late deep venous thrombosis and delayed weightbearing after total hip arthroplasty.

One hundred ninety-nine patients who underwent primary total hip arthroplasty and used in hospital pneumatic compression stockings and aspirin as thromboembolic prophylaxis were screened for deep venous thrombosis using duplex ultrasonography on the fourth postoperative day. Of the initial 98 patients, 21 underwent noncemented arthroplasty, maintained touchdown weightbearing for 6 weeks after surgery, and then began progressive partial weightbearing. Of the subsequent 101 patients, 28 underwent noncemented arthroplasty and began progressive weightbearing immediately after surgery.

Blood loss and transfusion rate in noncemented and cemented/hybrid total hip arthroplasty. Is there a difference? A comparison of 25 matched pairs.

A common assumption among orthopedic surgeons is that cemented/hybrid total hip arthroplasty (THA) results in lower transfusion requirements than noncemented THA. The hypothesized mechanism to account for transfusion differences is that cement application, after polymerization, decreases perioperative blood loss. To evaluate this theory, a retrospective matched-pair study was performed to quantify perioperative, intraoperative, postoperative blood loss, and transfusion requirements among patients undergoing cemented/hybrid and noncemented THA.

Bone response to implant surface morphology.

This study was designed to measure implant osseointegration using different surface treatments. Bilateral distal intramedullary implantation of titanium cylinders 25 mm x 5 mm was performed in 60 rabbits. The 3 surfaces tested were fiber mesh, mean pore size 400 microns; grit-blasted, mean surface roughness 6 microns; and acid-etched, mean surface roughness 18 microns.

Polyethylene wear after total hip arthroplasty: the effect of a modular femoral head with an extended flange-reinforced neck.

The use of modular components in total hip arthroplasty has been thought to contribute to accelerated polyethylene wear. Specifically, a modular femoral head with a flange extension and a longer neck may cause increased wear. The purpose of the current study was to evaluate the effect of a flange extension on polyethylene wear.

Fatigue model to characterize cement-metal interface in dynamic shear.

This study evaluated the interface shear strength between vacuum mixed polymethyl-methacrylate and two types of surface enhancements under static and dynamic shear loading. Cobalt chrome coupons with grit blasted or light plasma sprayed surfaces were tested. For each test, two coupons were mounted in a stainless steel chamber such that they were bonded with a 2-mm cement mantle for each test.