Albert H. Burstein

Studies of the mechanism by which the mechanical failure of polymethylmethacrylate leads to bone resorption.

The purpose of this study was to examine the relationship between the mechanical failure of polymethylmethacrylate and bone resorption at the bone-cement interface of a prosthesis. Evaluation of tissue that had been retrieved from the cement-bone interface of eighteen femoral components of total hip prostheses that were loose without associated infection revealed that a critical factor associated with bone resorption was the presence of particles that were small enough (one to twelve micrometers) to be phagocytized by macrophages. To study this phenomenon in vitro, macrophages in tissue culture were exposed to three preparations of polymethylmethacrylate cement. A novel method of cement preparation was used with control for solid and soluble contaminants, which provided a sensitive and specific technique for the determination of which mediators were released from the macrophages. Electron microscopy demonstrated phagocytosis of particles of less than twelve micrometers in size, regardless of the type of cement preparation. Exposure to all three cement preparations resulted in toxicity, as reflected by inhibition of 3H-thymidine incorporation. Exposure also led to increased release of tumor necrosis factor, but none of the three preparations resulted in release of prostaglandin E2. Division of the cement preparations into two groups on the basis of the size of the particles demonstrated that exposure to particles that were small enough to be phagocytized led to inhibition of 3H-thymidine incorporation and release of tumor necrosis factor, while exposure to particles that were too large to be phagocytized did not. Neither exposure to small particles nor exposure to large particles of cement led to release of prostaglandin E2. Our results show that when the mechanical failure of cement produces particles that are small enough to be phagocytized, phagocytosis of the particles results in the increased production of tumor necrosis factor by the macrophages, which may in turn lead to bone resorption and prosthetic loosening. These small particles also decrease 3H-thymidine uptake by the macrophages.

COULOMB FRICTIONAL INTERFACES IN MODELING CEMENTED TOTAL HIP REPLACEMENTS: A MORE REALISTIC MODEL

Loosening of cemented femoral hip stems could be initiated by failure of the cement mantle due to high cement stresses. The goals of this study were to determine if realistic stem-cement interface characteristics could result in high cement stresses when compared to a bonded stem-cement interface and to determine if stem design parameters could be chosen to reduce peak cement stresses. Three-dimensional finite-element models of cemented femoral hip components were studied with bonded or realistic Coulomb friction stem-cement interfaces. The results showed that the use of a non-bonded, non-linear Coulomb friction interface resulted in substantially different stress fields in the cement when compared to a bonded stem-cement interface. Tensile stresses in the proximal cement mantel for the Coulomb friction interface case (10.8 MPa) were greater than the fatigue strength of the cement. In contrast, the tensile stresses in the cement mantle were not greater than the fatigue strength for the bonded case (7.5 MPa). Failure of the cement mantle in the proximal femur could therefore be initiated by a lack of a bond at the stem-cement interface. The effect of different cross-sectional stem geometries (medial radii of 3.0, 4.9 and 5.5 mm and antero-posterior widths of 9.8 and 13.7 mm) and different elastic moduli (cobalt chromium alloy and titanium alloy) for the stem material were also evaluated for models with a Coulomb friction interface. Changes in the stem cross-section and elastic modulus had only limited effects on the stress distributions in the cement. Of the parameters evaluated in this study, the characteristics of the stem-cement interface had the largest effect on cement mantle stresses.

The interaction of the macrophage and the osteoblast in the pathophysiology of aseptic loosening of joint replacements

Macrophage phagocytosis of cement particles with production of inflammatory mediators is a component of the underlying mechanism of aseptic loosening of joint prostheses. Prostaglandin E2 (PGE2), a bone resorbing mediator, has been implicated in the loosening process. Investigations have shown that macrophage phagocytosis of cement particles leads to production of bone-resorbing mediators other than PGE2. In this study, conditioned medium from macrophages exposed to crushed simplex cement particles stimulated osteoblasts to release radiolabeled arachidonic acid and metabolites. Incubation of osteoblasts in conditioned medium from macrophages exposed to cement particles small enough to be phagocytized increased PGE2 release 80-fold over unexposed osteoblasts (P<0.001). Incubation of osteoblasts in conditioned medium from macrophages exposed to particles too large to be phagocytized, or to bone cement filtrate, did not stimulate PGE2 release. We propose that the role of the macrophage in aseptic loosening is primarily to recognize the mechanical failure of the cement mantle by phagocytosis of cement particles and subsequent production of small amounts of specific mediators. These mediators stimulate surrounding osteoblasts to secrete PGE2, which then amplifies the inflammatory response and ultimately results in bone resorption and aseptic loosening.

Custom-designed femoral prostheses in total hip arthroplasty done with cement for severe dysplasia of the hip

A custom-designed femoral prosthesis was implanted with cement and a standard acetabular component was used to treat nineteen severely dysplastic hips in fourteen consecutively managed patients. Components that had been custom-designed with the use of plain radiography were used because the anatomical reconstructive goals could not be achieved with commercially available implants. These goals were to match the offset of the femoral head and the length of the lower limb with those on the normal side for patients who had unilateral involvement and to provide an average (thirty to forty-millimeter) offset with equal limb lengths for patients who had bilateral involvement. A retrospective clinical and radiographic analysis was performed. The diagnoses included coxa vara (one hip), congenital dislocation (twelve hips), achondroplasia (three hips), and spondyloepiphyseal dysplasia (three hips). The mean age at the time of the reconstruction was forty-nine years (range, twenty-two to seventy-three years), and the mean duration of follow-up was fifty-seven months (range, twenty-seven to 108 months). In five hips, bone-grafting of the acetabulum was needed to obtain superolateral coverage. The clinical result was excellent in eighteen hips and good in one. No revisions have been performed to date. Two femoral components were possibly loose radiographically. One was associated with a definite loosening of the acetabular cup. In addition, one other cup was possibly loose. There was a 100 per cent rate of survival if only a revision procedure was considered as a failure.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of an experimental immune synovitis on the failure mode and strength of the rabbit anterior cruciate ligament.

The strength and failure mode of a fresh femur-anterior cruciate ligament-tibia complex was studied in normal rabbits and after the induction of an experimental immune synovitis. Five modes of failure were observed: (1) through the anterior cruciate ligament alone; (2) through a small piece of bone with the anterior cruciate ligament attached; (3) through a condyle; (4) through the metaphysis; and (5) through the diaphysis. In the normal complex, failure always occurred through the anterior cruciate ligament. In the controls, the average ratio of failure-load to body weight was seventy-four newtons per kilogram. After induction of an immune synovitis this ratio was significantly reduced, to twenty-two newtons per kilogram. Synovial cathepsin-D enzyme activity in these knees was 5.27 micromoles per hour per milligram of protein, which was significantly elevated when compared with the control level of 0.26. Histological examination of the anterior cruciate ligament after induction of the immune synovitis but before strength-testing demonstrated loss of the normal undulating fiber orientation, disorganization of the normal cellular pattern, and a decrease in the staining of the interstitial matrix with Mallory trichrome. There was a moderate infiltration of mononuclear and polymorphonuclear inflammatory cells in the body of the ligament. Histological studies of the ligament after strength-testing showed that the failure resulted in a mop-like appearance and morphological characteristics similar to those observed before testing.

Custom total shoulder arthroplasty in inflammatory arthritis. Preliminary results.

Twenty-three patients with inflammatory arthritis and rotator cuff deficiency have undergone 27 custom-fit total shoulder arthroplasties. The design used included a short-stem humeral component and a metal-backed glenoid component with an offset keel. The glenoid component was custom-fit to provide maximum coverage of the glenoid surface. The average age of the patients at the time of surgery was 55 years (range, 20-75 years). All patients had inflammatory arthritis, 16 were on steroids, and all had some degree of rotator cuff involvement ranging from small to complete tears. The average length of follow-up study was 5 years (range, 3-7 years). The average preoperative shoulder score was 36 points (range, 15-50 points) with an average pain score of 7 (of 30) points. Postoperatively, the shoulder score improved to 85 points with a pain score of 28 points. Twenty-one shoulders scored a good to excellent result. Two patients required reoperation, both for recurrent rotator cuff tears, one of which occurred after a fall. Radiographic analysis revealed no incidence of humeral radiolucency and six cases of glenoid radiolucency. Only two of these were progressive and both were associated with irreparable rotator cuff tears. Thus, in the early follow-up, this design of glenoid has decreased the incidence of glenoid radiolucency in this difficult patient population.

Telemetering in vivo loads from nail plate implants

A system of multi-channel telemetry capable of broadcasting in vivo loading from orthopaedic implants is presented. Its use to monitor the two orthogonal bending moments about the nail plate junction of three implanted hip nails is described. Typical results from these cases in which the telemeterized implant was employed to treat proximal femoral fixation and osteotomy are given.

A clinical and radiographic analysis of loosening of total knee arthroplasty components using a bilateral model

Patients undergoing bilateral, simultaneous total knee replacement provide a unique opportunity to study the role of operative techniques in the development of radiolucent lines because variables such as age, sex, weight, diagnosis, and bone quality are internally matched when the result on one side is compared with that of the other. This allows more conclusive examination of operative factors, such as component alignment, level of tibial bone resection, and cement handling. With this as the objective, the clinical and radiographic results of the first 50 bilateral total knee replacements performed by the senior author were studied. Postoperative alignment was found to influence significantly the incidence of tibial radiolucent lines. Use of cement to reconstruct defects in the proximal tibia resulting from preoperative deformity consistently led to the development of radiolucent lines in the area of the defect. There was also indirect evidence that failure to achieve an intimate microinterlock at the bone-cement interface may play a major role in the development of tibial radiolucent lines.

Geometrical properties of bone sections determined by laminography and physical section

Abstract The cortical bone areas and second moments of area were calculated for five human tibias using both physical sections and laminograms. Calculations based upon the laminograms tended to slightly overestimate second moments of area about the principal axes, but average error was less than 6% for both maximum and minimum values, demonstrating that laminography is an effective noninvasive technique for the determination of geometrical properties of long bones.