Delamination of a highly cross-linked polyethylene liner associated with titanium deposits on the cobalt-chromium modular femoral head following dislocation.

Retrieval studies of total hip replacements with highly cross-linked ultra-high-molecular-weight polyethylene liners have shown much less surface damage than with conventional ultra-high-molecular-weight polyethylene liners. A recent revision hip replacement for recurrent dislocation undertaken after only five months revealed a highly cross-linked polyethylene liner with a large area of visible delamination. In order to determine the cause of this unusual surface damage, we analysed the bearing surfaces of the cobalt-chromium femoral head and the acetabular liner with scanning electron microscopy, energy dispersive x-ray spectroscopy and optical profilometry. We concluded that the cobalt-chromium modular femoral head had scraped against the titanium acetabular shell during the course of the dislocations and had not only roughened the surface of the femoral head but also transferred deposits of titanium onto it. The largest deposits were 1.6 microm to 4.3 microm proud of the surrounding surface and could lead to increased stresses in the acetabular liner and therefore cause accelerated wear and damage. This case illustrates that dislocations can leave titanium deposits on cobalt-chromium femoral heads and that highly cross-linked ultra-high-molecular-weight polyethylene remains susceptible to surface damage.

Relationship between gravimetric wear and particle generation in hip simulators: conventional compared with cross-linked polyethylene.

Hip-simulator studies have shown reduced gravimetric wear rates for inert-gas gamma-irradiated ultra-high molecular weight polyethylene when compared with conventional ethylene-oxide-sterilized ultra-high molecular weight polyethylene. Analysis shows a greater number of particles generated from inert-gas gamma-irradiated ultra-high molecular weight polyethylene. This study was undertaken to examine particle-generation rates of polyethylene with different levels of cross-linking and to correlate them with gravimetric wear data. Particle-generation rates did not correlate with gravimetric wear rates. Particle analysis should be performed to predict the in vivo behavior of bearing surface materials. Cross-linked ultra-high molecular weight polyethylene subjected to 10 Mrad (100,000 Gy) of gamma irradiation generated significantly fewer particles than ethylene-oxide-sterilized ultra-high molecular weight polyethylene; it also demonstrated a 96% reduction in the volume of particles.

Vancomycin-resistant Enterococcus infected total knee arthroplasty.

Use of vancomycin to treat infections and hospital colonization with methicillin-resistant Staphylococcus aureus has contributed to the development of vancomycin resistance in Enterococcus. Postoperative infection with vancomycin-resistant Enterococcus developed in 2 patients after total knee arthroplasty, indicating that the infections were nosocomial. Both patients required multiple procedures. The infections were controlled with serial open débridements. One knee was fused successfully, and the other was managed with resection arthroplasty.

Infection after total joint arthroplasty in patients with human immunodeficiency virus or intravenous drug use.

Patients with intravenous drug use (IVDU) and patients with human immunodeficiency virus (HIV) with painful joint arthrosis present a difficult treatment decision. The purpose of this study was to determine the rate of deep periprosthetic infection in patients with HIV or IVDU after total joint arthroplasty (TJA). Twenty-nine patients with HIV or a history of IVDU or both underwent TJA. Of 28 HIV-positive patients undergoing TJA, 4 (14%) developed infections. Two of 8 joints (25%) in the IVDU group developed an infection. Two of 5 joints (40%) with both IVDU and HIV developed a deep infection. Patients with HIV or a history of IVDU are more likely to develop a deep infection compared with other patients undergoing TJA. The decision to proceed with TJA in HIV-positive and IVDU patients should be made only after weighing the ratio of risks and benefits.

Arthrofibrosis after total knee arthroplasty.

Six total knee arthroplasties in five patients were revised because of persistent limited motion after the primary arthroplasty. All of the revised implants were of an appropriate size and not malpositioned. No cause of stiffness was identified other than soft tissue contracture. Four of the components were posterior cruciate retaining and two were posterior cruciate substituting. Heterotopic bone formation was observed in two knees before the revision surgery and five knees after the revision surgery. Arc of motion was increased from 36 degrees (range, 20 degrees-70 degrees) before revision surgery to 86 degrees (range, 70 degrees-110 degrees) after revision surgery. What triggers the proliferation of extensive scar tissue formation in patients with arthrofibrosis is not clear. Some patients may be predisposed to this condition or may have it develop as a response to the surgical trauma and postoperative rehabilitation. However, when arthrofibrosis does develop after total knee arthroplasty, some improvement in motion and pain can be achieved with revision surgery.

Management of contained medial [protrusiol] acetabular defects in revision total hip arthroplasty.

Medial migration of the acetabular cup and protrusio of the medial wall is a well recognized failure mechanism of acetabular fixation in cemented total hip arthroplasty. In the protruded acetabulum, a medialized position of the acetabular component is associated with increased medial cortical bone stresses, while more lateral positioning reduces the medial stresses. Use of a protrusio ring or medial wire mesh may limit medial migration. However, late failure of acetabular revision reconstructions can occur when cemented protrusio rings or wire mesh reinforcement are used without bone grafting.

Photoelastic analysis of stresses produced by different acetabular cups.

Porous-coated acetabular components can provide long-term biologic fixation to bone. However, the periacetabular stress patterns and mechanisms by which different types of cementless acetabular cups obtain initial stability is not clear. In the current study, periacetabular stresses produced by different cementless acetabular cup geometries were quantitated using a three-dimensional photoelastic model. The cup geometries consisted of trispiked, finned, hemispherical, and nonhemispherical (wider than a hemisphere at the periphery) geometries. The cup models were loaded incrementally in the photoelastic material to simulate periacetabular stress distributions at the time of implantation during surgery rather than under physiologic weightbearing loads. The peripheral stress distributions and their magnitudes induced by the trispiked and oversized hemispherical cups were similar, but the trispiked cup induced localized high stress regions where the spikes penetrate the bone model. The fins separated the periacetabular material into quadrants, which was associated with decreased peripheral stresses. A nonhemispherical geometry with a wider diameter at the rim than a hemisphere increased peripheral stresses more than an oversized hemispherical geometry and required less force to seat the implant. Although various cementless acetabular cups can perform well clinically, they produce different periacetabular stresses and appear to obtain initial fixation by different mechanisms.

An inexpensive molding method for antibiotic-impregnated cement spacers in infected total hip arthroplasty.

Placement of an antibiotic-impregnated cement endoprosthesis facilitates patient mobilization and treatment of infection complicating total hip arthroplasty. Molds, particularly to form the spherical head of the cement endoprosthesis, are not readily available, however. We have found that the rubber bulb portion of an irrigation syringe can be conveniently used as a mold to shape the proximal end of a cement endoprosthesis during surgery.

Failure of a metal-on-metal total hip arthroplasty from progressive osteolysis.

Ultra-high-molecular weight polyethylene (UHMWPE) wear, debris-induced osteolysis is a frequent cause of failure of total hip arthroplasty. Metal-on-metal total hip arthroplasty eliminates the generation of UHMWPE particulate debris. Although the volumetric wear of a metal-on-metal articulation may be lower than a metal-UHMWPE articulation, the number of particles may be higher. Osteolysis can develop in response to metallic and UHMWPE debris. The following case of massive osteolysis associated with large amounts of cobalt-chrome wear debris shows adhesive and abrasive wear mechanisms, as well as wear caused by third-body cobalt-chrome debris and impingement of the femoral component against the rim of the acetabular cup, which led to failure of a metal-on-metal total hip arthroplasty.

Simultaneous primary and contralateral revision total knee arthroplasty.

Seven patients underwent primary and contralateral revision total knee arthroplasty (TKA) under one anesthetic in a sequential fashion. The average patient age was 67.6+/-6.9 years. Average blood loss was 764+/-568 cc, average operative time was 269+/-107 minutes, and average length of hospital stay was 9.6+/-3.4 days. One patient with a history of hypertension, diabetes, and coronary heart disease died from pulmonary embolism 7 days after surgery. Deep infection with enterococcus developed in the revised knee of another patient 3 months after surgery. For the six surviving patients, knee pain and function were improved by surgery. However, in this small series of patients, two major complications occurred. These results indicate that if this procedure is considered at all, it should be reserved for only healthy patients with relatively uncomplicated knee reconstructions.

Prophylactic intramedullary femoral rodding during total knee arthroplasty with simultaneous femoral plate removal.

Removal of a plate from the distal femur creates a risk of fracture through the screw holes. This is a particular concern when a total knee arthroplasty is present because supracondylar fracture may occur with minimal trauma. A patient who presents after prior plating of a distal femur fracture with osteoporosis, retained hardware associated with pain, and gonarthrosis severe enough to warrant total knee arthroplasty is often difficult to manage. Prophylactic intramedullary rodding is a well-accepted method of treating pathologic stress risers in the femur. An intramedullary rod can be inserted into the femur at the time of total knee arthroplasty. This method permits simultaneous plate removal and total knee arthroplasty while protecting the femur from postoperative fracture.

Endosteal referencing in revision total knee arthroplasty.

A method of orienting the femoral and tibial bone cuts relative to the endosteal cortex of the femur and tibia was used in 32 patients who underwent revision total knee arthroplasty. The mean orientation of the femoral component was 96.74 degrees +/- 1.03 degrees, mean orientation of the tibial baseplate was 90.71 degrees +/- 1.10 degrees, mean anatomic tibiofemoral alignment was 7.42 degrees +/- 1.69 degrees of valgus, and mean mechanical tibiofemoral alignment was 1.09 degrees +/- 1.83 degrees of valgus. Mean tibial bowing was 1.63 degrees +/- 1.57 degrees of valgus, and mean femoral bowing was 0.58 degrees +/- 1.53 degrees of varus. Valgus tibial bowing was correlated with valgus orientation of the tibial component (r = .86, P < .000001), and varus femoral bowing was correlated with orientation of the femoral component (r = .54, P = .0054). Referencing the implant position from the endosteal cortex of the intramedullary canals provides a reliable method of achieving satisfactory alignment in most revision total knee arthroplasties; however, bowing of the femur or tibia can affect alignment.

Intramedullary pressure and pulmonary function during total knee arthroplasty.

Twenty-eight patients who underwent unilateral total knee arthroplasty and 20 patients who underwent simultaneous bilateral total knee arthroplasties participated in this study and were randomized to have either a fluted or round 10-mm diameter femoral intramedullary alignment rod used during surgery. The intramedullary rods were cannulated and connected with pressure tubing to a monitor which provided measurements of pressure at the tip of each rod. Arterial blood gas measurements on room air were obtained before and on the morning after surgery. An arterial line was placed and an arterial blood gas measurement was obtained at the time of skin incision and again after tourniquet release. Pulmonary shunt was calculated from the arterial blood gas measurements. Intramedullary pressure during rod insertion was significantly higher for the groups of patients having the round compared with the fluted rod. The change in pulmonary shunt during surgery was lowest for the patients in the unilateral group having the fluted rod and highest for the patients in the bilateral group having the round rod. A fluted rather than a round intramedullary alignment rod should be used to minimize intramedullary pressure and pulmonary shunting during unilateral and bilateral total knee arthroplasties.

Factors affecting stability of press fit acetubular cups.

Press fitting cementless porous coated acetabular components without screw fixation is desirable to minimize debris-related problems. Compression between the bone and periphery of an acetabular component which is slightly larger than the reamed acetabulum provides implant fixation while oversizing at the dome may adversely affect stability. In most primary total hip arthroplasties, the acetabulum can be reamed to a hemispherical cavity and assessed using acetabular sizing trials prior to implanting the cup. Use of an implant with a hemispherical dome and gradual transition to a wider peripheral dimension maximizes peripheral bone strains and implant stability with less impaction force and overall deformation than a larger oversized hemispherical cup.

Distribution of orthopaedic surgeons, lawyers, and malpractice claims in New York.

The New York State Department of Health Medical Malpractice Insurance Database was used to determine the number and location of malpractice claims filed by residents of New York State against board certified orthopaedic surgeons between 1979 and 1993. The numbers of board certified orthopaedic surgeons, lawyers, law firms doing medical malpractice work, and malpractice claims per capita for each county were calculated. Stepwise linear regression analysis was used to determine whether the per capita rate of malpractice claims was predicted by the population density of board certified orthopaedic surgeons, law firms filing malpractice claims, or total population of lawyers. Three thousand one hundred eighty-two malpractice claims were filed during the period of interest. The per capita rate of malpractice claims did not correlate with the population density of board certified orthopaedic surgeons. The per capita malpractice claim rate, however, was significantly correlated with the population density of law firms filing malpractice claims and with the overall population density of lawyers. Orthopaedic practices located in areas with high concentrations of lawyers involved in medical malpractice litigation appear to have a higher risk of having malpractice claims filed against them than practices located in other areas.