Thomas P. Schmalzried

Periprosthetic bone loss in total hip arthroplasty. Polyethylene wear debris and the concept of the effective joint space.

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

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.

Wear is a function of use, not time

Polyethylene wear (linear penetration) in 37 hip replacements was assessed from digital images using a validated two-dimensional, edge detection-based computer algorithm. Patient activity was assessed with a pedometer, a step activity monitor and a simple visual analog scale. Joint use was related to wear at the 90% confidence level. Without three recognized outliers, wear was highly correlated to use. The visual analog scale activity rating was significantly related to wear for the 24 hip replacements with standard polyethylene. Univariate regression analysis indicated that male gender, height, weight (which were both highly correlated to male gender) and hip center of rotation were significantly correlated to wear. Multivariate regression analysis indicated that male gender, femoral off-set, and Hylamer® were significantly correlated to wear. Based on the wear and activity data from the 24 hip replacements with standard polyethylene, the average volumetric wear rate per million cycles with a 70 kg patient weight was 30 mm3. This unique in vivo result can be considered a target wear rate for standard polyethylene in hip simulator studies.

Cobalt and chromium concentrations in patients with metal on metal total hip replacements.

There has been a resurgence of interest in the use of metal on metal bearings in total hip arthroplasty. Although the use of metal on metal bearing couples would eliminate or substantially reduce particulate polyethylene generation (depending on the presence or absence of polyethylene in the implant system), there is concern about the potential for increased particulate and ionic metal generation in comparison with polyethylene on metal bearings. These metallic degradation products may be transported away from the implant site and distributed systemically. Chromium concentrations in the serum and urine and cobalt concentrations in the serum were measured in subjects with cobalt chromium alloy metal on metal total hip replacements and in controls without implants. Eight subjects with long term (> 20 years) McKee-Farrar total hip replacements had 9-fold elevations in serum chromium, 35-fold elevations in urine chromium, and at least 3-fold elevations in serum cobalt concentrations in comparison with controls. Six subjects with short term (< 2 years) metal on metal surface replacement arthroplasties had 3-fold elevations in serum chromium, 4-fold elevations in urine chromium, and 4-fold elevations in serum cobalt concentrations in comparison with subjects with McKee-Farrar implants. Although the toxicologic importance of these trace metal elevations has not been established, serum and urine metal concentrations may be useful markers for the tribologic performance of metal on metal bearings.

Current Concepts Review - Wear in Total Hip and Knee Replacements*

Before the advent of total joint replacement, patients who had end-stage arthritis of the lower extremities had unremitting pain and a greatly decreased functional capacity. In addition, they often were confined to a wheelchair and were dependent on the care of others. Today, the outcomes of primary total hip and knee replacement are predictable and usually excellent35,45,57,64,212,221. Prosthetic joint replacement has dramatically improved the lives of millions of people worldwide. As the fixation of total joint implants has become more reliable and durable and as the technology of total joint replacement has been applied to younger and more active patients, the current limitations of total joint arthroplasty are related to the wear of the components248. Wear is the removal of material, with the generation of wear particles, that occurs as a result of the relative motion between two opposing surfaces under load. In complex mechanical-biological systems such as total hip and knee replacements, there can be many types of wear. Although the mechanical consequences of wear, such as progressive thinning of polyethylene components, can limit the functional life of a joint replacement, the clinical problems from wear more frequently are due to the release of an excessive number of wear particles into a biological environment. When particles within a certain size-range are phagocytized in sufficient amounts, the macrophages enter into an activated state of metabolism, releasing substances that can result in periprosthetic bone resorption. Progressive loss of periprosthetic bone can necessitate a reoperation, which is the definitive measure of clinical failure of a joint arthroplasty. It is important to distinguish among the fundamental mechanisms of wear (adhesion, abrasion, and fatigue); the changes in the appearance (the morphological characteristics) of the bearing surfaces, which are referred to …

The relationship between the design, position, and articular wear of acetabular components inserted without cement and the development of pelvic osteolysis.

Between 1983 and 1987, an acetabular component with a unique chamfered-cylinder design was inserted without cement in 134 hips. With use of this design, initial stability is achieved through a cylindrical interference fit with the peripheral rim of the acetabulum, without the need for pegs, spikes, or screws. At an average of sixty-four months (range, forty to ninety-six months) after implantation, follow-up data were available for 113 hips (ninety-three patients). No component had been revised for loosening or was radiographically loose. However, the prevalence of balloon-like osteolysis of the pelvis was 17 per cent (nineteen hips). This bone loss was generally not associated with pain or other symptoms. Ten of the nineteen hips that were associated with pelvic osteolysis (including six of the nine that were associated with osteolysis of the ilium) had been reconstructed with use of an acetabular component that had no holes in the shell (that is, the shell was completely solid). This finding indicates that, while elimination of holes through the acetabular shell may have advantages, it will not prevent pelvic osteolysis. The osteolysis of the ilium was associated with a lateral opening of the acetabular component of more than 50 degrees (p < 0.0001). All of the hips in this series had insertion of a porous-ingrowth femoral resurfacing component made of titanium alloy. These components are no longer used. Revision of the femoral side due to osteolysis provided a unique opportunity to inspect directly forty-two clinically well functioning acetabular components. All of the polyethylene liners and acetabular shells were found to be rigidly fixed. Inflammatory tissue at the periphery of the implant-bone interface resulted in circumferential resorption of periacetabular bone despite rigid fixation of the component. This is direct evidence that a process of bone resorption similar to that reported at the cement-bone interface of cemented acetabular components can occur at the implant-bone interface of components inserted without cement. At the reoperation, a communication that had led to the pelvic osteolysis was found through areas of bone resorption at the periphery of the implant-bone interface. These areas were essentially cystic and were filled with a mixture of fluid and friable, yellow-tan tissue. It appeared that the osteolytic process had expanded into the soft cancellous bone and marrow while being contained by the denser cortical shell of the pelvic bones.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanism of loosening of cemented acetabular components in total hip arthroplasty. Analysis of specimens retrieved at autopsy.

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.

Wear in total hip and knee replacements.

Before the advent of total joint replacement, patients who had end-stage arthritis of the lower extremities had unremitting pain and a greatly decreased functional capacity. In addition, they often were confined to a wheelchair and were dependent on the care of others. Today, the outcomes of primary total hip and knee replacement are predictable and usually excellent. Prosthetic joint replacement has dramatically improved the lives of millions of people worldwide. As the fixation of total joint implants has become more reliable and durable and as the technology of total joint replacement has been applied to younger and more active patients, the current limitations of total joint arthroplasty are related to the wear of the components. Wear is the removal of material, with the generation of wear particles, that occurs as a result of the relative motion between two opposing surfaces under load. In complex mechanical-biological systems such as total hip and knee replacements, there can be many types of wear. Although the mechanical consequences of wear, such as progressive thinning of polyethylene components, can limit the functional life of a joint replacement, the clinical problems from wear more frequently are due to the release of an excessive number of wear particles into a biological environment. When particles within a certain size-range are phagocytized in sufficient amounts, the macrophages enter into an activated state of metabolism, releasing substances that can result in periprosthetic bone resorption. Progressive loss of periprosthetic bone can necessitate a reoperation, which is the definitive measure of clinical failure of a joint arthroplasty.

The Harris-Galante porous-coated acetabular component with screw fixation. Radiographic analysis of eighty-three primary hip replacements at a minimum of five years.

The results of eighty-three consecutive primary total hip arthroplasties in which a Harris-Galante porous-coated acetabular component had been used were reviewed after a minimum of five years. In all patients, the stated diameter of the acetabular component (the diameter printed on the packaging for the implant) used was equal to the stated diameter of the reamer (the diameter printed on the reamer) that had been used last in the preparation of the acetabulum. As there was little or no press-fit stability, stability was obtained initially with multiple transfixing screws. No component was revised because of loosening, and none were radiographically loose at an average of sixty-eight months and a maximum of seven years after the operation. There was no evidence of disruption of the titanium porous mesh, and no screw had bent or broken. Two sockets, however, had been revised because of failure of the liner-locking mechanism as well as disassociation of the polyethylene liner from the titanium-alloy shell. Lysis of bone occurred in only one patient, around one screw. Areas of non-contact (gaps) between the porous mesh at the periphery of the acetabular component and the bone were seen on the immediate postoperative radiographs of nearly half of the patients. New areas of radiolucency, which had not been seen immediately postoperatively, were identified at two years in forty-nine hips. These radiolucent lines were never wider than one millimeter and were most frequently located in zone 3 and, less frequently, in zone 1. At the time of the most recent follow-up evaluation, a progressive radiolucent line was identified around twenty-two components and a discontinuous radiolucent line was present in all three zones around eleven components. No continuous radiolucent line was identified at the mesh-bone interface of any component. These results are superior to our results with cemented acetabular components after a similar period of follow-up. A longer period of follow-up is needed before the importance of these thin radiolucent lines can be determined, but experience with cemented acetabular components indicates that progressive or extensive radiolucent lines, or both, may represent resorption of bone at the porous mesh-bone interface and this can lead to loosening of the component. Our data suggest that the technique used for implantation may be important not only for the initial fixation and ingrowth of bone, but also for the long-term durability of the fixation of a porous-coated acetabular component.(ABSTRACT TRUNCATED AT 400 WORDS)

Nerve palsy associated with total hip replacement. Risk factors and prognosis.

We reviewed the results of 3126 consecutive total hip replacements and identified postoperative neuropathy in the ipsilateral lower extremity after fifty-three (1.7 per cent) over-all and after 1.3 per cent of the primary arthroplasties. The prevalence was 5.2 per cent after the primary arthroplasties that had been done for congenital dislocation or dysplasia of the hip and 3.2 per cent after the revisions (all diagnoses). Thus, these two types of operations were risk factors (p less than 0.01). Limb-lengthening only partially accounted for the increased prevalence of neuropathy after these procedures. The sciatic nerve was involved in all but five extremities. The cause of the palsy was unclear or unknown in thirty (57 per cent) of the extremities. When the patients were last seen, at a minimum of one year and a maximum of sixteen and one-half years after the operation, seven extremities were normal neurologically, thirty-three had a mild neurological deficit, and thirteen had a major deficit. All patients who had complete recovery of neurological function had it by twenty-one months. Of thirty-six extremities that were evaluated at a minimum of twenty-four months after the operation, seven were neurologically normal, twenty-three had a mild persistent deficit, and six had a major persistent deficit. The ability to walk decreased for all patients who had a nerve palsy. The greatest disability was in the patients who had been forty-eight years old or less and had had a primary total hip replacement (p = 0.037). The prognosis for neurological recovery was related to the degree to which the nerve was damaged.(ABSTRACT TRUNCATED AT 250 WORDS)