Thomas P. Schmalzried

Bio: Thomas P. Schmalzried is an academic researcher from UCLA Medical Center. The author has contributed to research in topics: Arthroplasty & Osteolysis. The author has an hindex of 24, co-authored 36 publications receiving 4771 citations. Previous affiliations of Thomas P. Schmalzried include Harvard University.

Periprosthetic Bone Loss in Total Hip Arthroplasty: Polyethylene Wear Debris and the Concept of the Effective Joint Space

Abstract: Thirty-four hips in which there had been prosthetic replacement were selected for study because of the presence of linear (diffuse) or lytic (localized) areas of periprosthetic bone loss. In all hips, there was careful documentation of the anatomical location of the material that had been obtained for histological analysis, and the specific purpose of the removal of the tissue was for examination to determine the cause of the resorption of bone. Specimens from twenty-three hips were retrieved during an operation and from eleven hips, at autopsy. The area of bone loss was linear only in sixteen hips, lytic only in thirteen, and both linear and lytic in five. In all thirty-four hips, intracellular particulate debris was found in the macrophages that were present in the area of bone resorption. All thirty-four had intracellular particles of polyethylene, many of which were less than one micrometer in size. Thirty-one hips had extracellular particles of polyethylene as well. Twenty-two of the thirty-four hips had intracellular metallic debris; in ten, metallic debris was found extracellularly as well. Ten of the sixteen cemented specimens had intracellular and extracellular polymethylmethacrylate debris. In the mechanically stable prostheses--cemented and uncemented--polyethylene wear debris was identified in areas of bone resorption far from the articular surfaces. The number of macrophages in a microscopic field was directly related to the amount of particulate polyethylene debris that was visible by light microscopy. Although the gross radiographic appearances of linear bone loss and lytic bone loss were different, the histological appearance of the regions in which there was active bone resorption was similar. Regardless of the radiographic appearance and anatomical origin of the specimen, bone resorption was found to occur in association with macrophages that were laden with polyethylene debris. In general, the number of macrophages present had a direct relationship to the degree of bone resorption that was seen. We believe that these findings indicate that joint fluid penetrates far more extensively than previously thought, even in a well fixed component, along the interface between the prosthesis and bone and in the periprosthetic tissues; it is often more extensive than is shown by arthrography. We therefore suggest the concept of the effective joint space to include all periprosthetic regions that are accessible to joint fluid and thus accessible to particulate debris.(ABSTRACT TRUNCATED AT 400 WORDS)

Assessing activity in joint replacement patients.

Abstract: Outcome evaluations of lower extremity joint reconstructions should include an assessment of patient activity. In vivo wear assessments of total joint prostheses should be based on a measure of use, not time in situ or a proxy such as age or gender; however, clinicians lack a simple method to reliably assess the activity of patients with joint replacement. The modern pedometer can be a satisfactory means of quantifying the use of lower extremity joints. The pedometer, however, requires special effort on the part of the physician or evaluator and the patient. Therefore, we compared the quantitative assessment of walking activity of 100 total joint replacement patients, as measured with a pedometer, to the UCLA activity score and a simple visual analog scale that can easily be employed during a routine office evaluation. Both the UCLA activity rating (P = .002) and the visual analog scale rating of the investigator (P = .00001) had a strong correlation with the average steps per day as recorded by the pedometer. There was, however, up to a 15-fold difference in the average steps per day for individual patients with the same UCLA score. The visual analog scale as rated by the patients of their own activity did not have as strong a correlation with the pedometer data (P = .08) as did patient age (P = .049). For practical reasons, the pedometer is probably best reserved for the evaluation of extreme cases of activity (or inactivity). This study indicates that both the UCLA activity rating and the investigator visual analog scale are valid for routine activity assessment in a clinical setting. Adjustments of the UCLA activity score for the frequency and intensity of activity, as can be done with the investigator visual analog scale, increase the accuracy of the activity rating.

The mechanism of loosening of cemented acetabular components in total hip arthroplasty : analysis of specimens retrieved at autopsy

Abstract: Late aseptic loosening of cemented acetabular components is governed by the progressive, three-dimensional resorption of the bone immediately adjacent to the cement mantle. This process begins circumferentially at the intraarticular margin and progresses toward the dome of the implant. Evidence of bone resorption at the cement-bone interface was present even in the most well-fixed implants before the appearance of lucent lines on standard roentgenographic views. The mechanical stability of the implant was determined by the three-dimensional extent of bone resorption and membrane formation at the cement-bone interface. The leading edge of the membrane is a transition zone from regions of membrane interposition between the cement and the bone to regions of intimate cement-bone contact. Histologic analysis revealed that progressive bone resorption is fueled by small particles of high density polyethylene (HDP) migrating along the cement-bone interface and bone resorption occurs as a result of the macrophage inflammatory response to the particulate HDP. Evidence in support of a mechanical basis for failure of fixation was lacking. The mechanism of late aseptic loosening of a cemented acetabular component is therefore biologic in nature, not mechanical. This is exactly opposite to the mechanism of loosening on the femoral side of a cemented total hip replacement, which is mechanical in nature.

The origin of submicron polyethylene wear debris in total hip arthroplasty.

Abstract: The microscopic morphology of worn polyethylene surfaces was compared with that of the associated polyethylene particles for acetabular cups tested in a wear simulator and for cups worn in vivo, using scanning electron microscopy. In the absence of significant third-body abrasive damage, the articulation of the ball in the cup produced a visually polished surface on the polyethylene. On a micron scale, the morphology of the worn polyethylene from in vitro and in vivo wear included nodules and fibrils consistent with adhesive, abrasive, and microfatigue wear mechanisms. Larger wear features, such as deep scratches or pits measuring in 10s of microns, that were seen in the in vivo cups were attributed to third-body wear. The polyethylene particles isolated from the serum lubricants of the wear tests and from the periprosthetic tissues were primarily submicron in size, were either rounded or elongated, and were consistent with the submicron wear features seen on the cup surfaces. It is the submicron particles that are associated with inflammatory periprosthetic bone loss in total hip replacement. Although the mean dimensions of the particles generated in vitro were slightly smaller than those of the in vivo particles, the overall morphologies were very comparable, suggesting that the same lubrication and wear processes were acting in the simulator as in vivo.

Isolation of predominantly submicron-sized UHMWPE wear particles from periprosthetic tissues

Abstract: A method of tissue digestion using sodium hydroxide was applied to the isolation and recovery of ultra-high-molecular-weight polyethylene (UHMWPE) particles from tissues around failed total hip replacements. Density gradient ultracentrifugation of the digested tissues was performed to separate the UHMWPE from cell debris and other particulates. Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC) verified that the recovered particles were UHMWPE. When viewed by scaning electron microscopy, individual particles were clearly observed and were either rounded or elongated. The majority were submicron in size. The application of this method to the study or particles from periprosthetic tissues may elucidate aspects of biomaterial particles size and shape that are important to the biologic response to, and clinical outcome of, total joint replacement. © 1995 John wiley & Sons, Inc.

Primary total hip replacement surgery: a systematic review of outcomes and modelling of cost-effectiveness associated with different prostheses.

Abstract: Objectives- T identify the literature on primary total hip replacement(THR) surgery that is relevant to the question of whether prostheses differ in their medium to longer term outcomes, and to synthesise this evidence. To use evidence regarding both costs and outcomes of primary THR to model how much more effective newer prostheses must be to justify higher costs

The problem is osteolysis

Abstract: Recent studies have generated considerable information that reveals substantial support for major change in the understanding of total hip arthroplasty and its current state. Although some of these observations appear unrelated at first glance, they can be drawn together to support the thesis that osteolysis is the dominant problem in total hip arthroplasty. These observations are as follows: (1) Five-year followup data are required for a minimum assessment of a new concept in total hip design and material because osteolysis is uncommon before that time. (2) Excellent fixation can be achieved on the femoral side with good cementing and good cementless techniques. Thus, femoral component loosening is less of an issue currently. (3) Many acetabular components become loose because of the ingress of particulate debris that leads to linear bone loss at the interface with the pelvis, a process that is biologically akin to the more florid forms of osteolysis. Thus, much acetabular component loosening represents a form of osteolysis. (4) Many cementless femoral reconstructions have developed a high incidence of femoral osteolysis. (5) Many cementless sockets have developed a high incidence of pelvic osteolysis. Taken in conjunction, these observations suggest that periprosthetic osteolysis is the leading problem in contemporary total hip replacement.

Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: A CONSEQUENCE OF EXCESS WEAR

Abstract: Early failure associated with adverse reactions to metal debris is an emerging problem after hip resurfacing but the exact mechanism is unclear. We analysed our entire series of 660 metal-on-metal resurfacings (Articular Surface Replacement (ASR) and Birmingham Hip Resurfacing (BHR)) and large-bearing ASR total hip replacements, to establish associations with metal debris-related failures. Clinical and radiological outcomes, metal ion levels, explant studies and lymphocyte transformation tests were performed. A total of 17 patients (3.4%) were identified (all ASR bearings) with adverse reactions to metal debris, for which revision was required. This group had significantly smaller components, significantly higher acetabular component anteversion, and significantly higher whole concentrations of blood and joint chromium and cobalt ions than asymptomatic patients did (all p < 0.001). Post-revision lymphocyte transformation tests on this group showed no reactivity to chromium or cobalt ions. Explants from these revisions had greater surface wear than retrievals for uncomplicated fractures. The absence of adverse reactions to metal debris in patients with well-positioned implants usually implies high component wear. Surgeons must consider implant design, expected component size and acetabular component positioning in order to reduce early failures when performing large-bearing metal-on-metal hip resurfacing and replacement.