Osteoblast differentiation onto different biometals with an endoprosthetic surface topography in vitro.

In this in vitro study, we compared the cytocompatibility and osteoblast promoting potency on human bone marrow cell culture with three different alloys (surgical steel, CoCr, Ti6Al4V) and three different surface structures (polished, sandblasted, porous coated). These biometals were specifically chosen because of their current applications in clinical orthopedic practices. Human mononuclear bone marrow cells were cultivated onto the surface of the different biomaterials and stimulated by dexamethasone, L-ascorbic-acid-2-phoshpate and beta-glycerolphosphate over a 3-week period. Immunofluorescent stainings against several antigens (ALP, RANKL, osteopontin, collagen I), mRNA-expression of collagen (Col) I/II, BSP, osteopontin, osteocalcin, TRAP, light and scanning electron microscopy evaluation were used to evaluate cellular growth and osteoblast differentiation. For surface roughness and energy analysis of the specimen, roughness profile (Ra, Rz) and contact angle (CA) measurements were performed. We found differences between the different biometals and surface structures. Steel showed potential cytotoxic effects whereas CoCr and more Ti6Al4V showed an excellent cytocompatibility. There were no qualitative differences in mRNA expression between each of the tested biomaterials. In terms of antigen expression, a sandblasted Ti6Al4V surface showed enhanced osteoblastic differentiation. A porous-coated surface improved the osteoconductivity of CoCr when compared to a polished surface. In contrast to controls all cells cultivated with biometals induced a RANKL expression. Cells increased the implant roughness with the exception of sandblasted Ti6Al4V. Our data show that surface topography and physicochemical properties of biometals influence osteoblast differentiation in vitro.

The influence of surface roughness on stem-cement gaps.

We have compared the interface morphology at the stem-cement interface of standard Charnley stems with a satin finish (Ra = 0.75 microm) with identical stems which had been grit-blasted over their proximal third (Ra = 5.3 microm) to promote a proximal bond. The stems were cemented into cadaver femora using conventional contemporary cementing techniques. After transverse sectioning, we determined the percentage of the perimeter of the stem which had a gap at the interface. There were substantial gaps (mean 31.4 +/- 17.1%) at the stem-cement interface in the grit-blasted region. This fraction was significantly (paired t-test, p = 0.0054) higher than that found around the contralateral satin-finished stems (mean 7.7 +/- 11.7%). Although studies of isolated metal-cement interfaces have shown that the bond strength can increase with surface roughness it cannot be assumed that this effect will be observed under clinical conditions.

Maximizing ultra high molecular weight polyethylene performance in total knee replacement.

The etiology of polyethylene wear following TKR is multifactorial. Factors such as surgical technique, patient selection, and choice of implant design directly impact the polyethylene wear rate. Surgical technique is directly associated with polyethylene wear; particularly the thickness of the polyethylene insert, the postoperative mechanical axis of the limb, and the alignment of the tibial component in the coronal plane. Patient selection is an important determinant of polyethylene wear, as patient body weight and activity level have been shown to correlate with wear rate. Prosthetic design plays a role in polyethylene wear as femoral-tibial contact areas, peak contact forces, and surface topography of the polyethylene are important considerations. The method by which the polyethylene is manufactured and the method of sterilization are also important determinants of polyethylene wear. Wear of polyethylene is one source of particulate debris following TKR. Phagocytosis of the particulate debris by macrophage occurs at the prosthesis-bone interface. The macrophage produces inflammatory mediators in response to the particulate debris. Inflammatory mediators act at the failed interface to effect bone resorption and produce osteolysis. In summary, the surgeon can play a major role in maximizing polyethylene performance in TKR by understanding the multiple factors that contribute to polyethylene wear and taking steps to lessen their effect.

Mixed-mode failure response of the cement-bone interface.

Mechanical failure of the cement-bone interface can contribute to clinical loosening of cemented total hip replacements. The conditions that cause loosening are poorly understood, in part, due to a lack of information on the mechanical behavior of the cement bone interface. The purpose of this study was to determine the mechanical behavior of the cement-bone interface due to mixed-mode (combined tension and shear) loading and to develop a failure model for the cement bone interface. Laboratory tests of machined cement-bone test specimens were performed with mixed-mode loading conditions (loading angles of 22.5 degrees, 45 degrees, and 67.5 degrees) to determine the mechanical response in the pre-yield and post-yield state. After accounting for the quantity of interdigitated bone as a covariate, the mixed-mode data were combined with previous tension (0 degrees) and shear data (90 degrees) to develop a failure model for the cement bone interface. The strength of the interface was positively correlated with the quantity of interdigitated bone (r2 = 0.70, 0.53, 0.49, for 22.5 degrees, 45 degrees, and 67.5 degrees, respectively). There was a significant increase in failure strength (P < 0.001) with increasing mixed-mode angle. When all data were incorporated into an elliptical failure criterion, the average error between the actual and predicted strength was 33%. These results can now be incorporated into constitutive models of the cement bone interface to determine the initiation and progression of interface failure in cemented total hip replacements.

Mechanical strength of the cement-bone interface is greater in shear than in tension.

The objective of this study was to determine the relative mechanical properties of the cement-bone interface due to tensile or shear loading. Mechanical tests were performed on cement-bone specimens in tensile (n = 51) or shear (n = 55) test jigs under the displacement control at 1 mm/min until complete failure. Before testing, the quantity of bone interdigitated with the cement was determined and served as a covariate in the study. The apparent strength of the cement-bone interface was significantly higher (p < 0.0001) for the interface when loaded in shear (2.25 MPa) when compared to tensile loading (1.35 MPa). Significantly higher energies to failure (p < 0.0001) and displacement before failure (p < 0.01) were also determined for the shear specimens. The post-yield softening response was not different for the two test directions. The data obtained herein suggests that cement-bone interfaces with equal amounts of tensile and shear stress would be more likely to fail under tensile loading.

Pre-yield and post-yield shear behavior of the cement-bone interface.

Aseptic loosening of cemented total hip replacements is thought to involve mechanical failure of the cement-bone interface. However, the mechanical response of the interface, particularly the post-yield behavior, is not well understood. The purpose of this study was to determine the constitutive behavior of the cement-bone interface for loading in shear using a combination of experimental and finite element methods. A total of 55 cement-bone specimens (5 x 10 x 15-20 mm) from the proximal femur of human cadavers were loaded to failure under displacement control with use of a custom shear test jig. Finite element models of the test specimens were made and included provision for a two-parameter nonlinear interface model at the cement-bone interface. The experimental tests revealed a complicated load versus displacement response with an initial linear region and a reduction in slope until the ultimate strength (2.25+/-1.49 MPa) was reached, followed by an exponential decrease in load with increasing displacement until the entire interface debonded. Failure most often occurred at the cement-bone interface, where the cement penetrated into the bone with bone remaining in the cement in 30 specimens and with bone remaining in the cement and cement spicules remaining in the bone in 22 specimens. The adjacent bulk bone and cement did not appear to be permanently deformed. Finite element models of the test specimens revealed that failure initiated at the base of the test specimen before the peak load had been reached. The two interface parameters, interface strength (2.71+/-1.90 MPa) and interface-softening exponent (4.96+/-3.47 1/mm), could be determined directly from the experimental data and provided a good fit with the experimental structural response for a wide range of interface strengths. These results show that the cement-bone interface does not fail abruptly when the shear strength is reached but absorbs a substantial amount of energy with post-yield strain-softening behavior.

Prevention of deep-vein thrombosis after total hip arthroplasty. Comparison of warfarin and dalteparin.

The effectiveness and safety of warfarin were compared with those of a low-molecular-weight heparin (dalteparin) for the prevention of deep-vein thrombosis after total hip arthroplasty in a prospective, randomized, multi-institutional trial. Patients who were older than eighteen years of age and were scheduled to have an elective primary or revision total hip arthroplasty were eligible; 580 patients were randomized, 550 had the operation and received prophylaxis, and 382 had evaluable venograms. Prophylaxis was provided either with warfarin beginning the night before the operation or with dalteparin beginning two hours before the operation and was continued until venography was performed. Bleeding was assessed on the basis of intraoperative blood loss, transfusion requirements, a decrease in hematocrit, and clinically identified bleeding complications. The prevalence of deep-vein thrombosis was found to be significantly lower in the patients who had received dalteparin than in those who had received warfarin (twenty-eight [15 per cent] of 192 patients compared with forty-nine [26 per cent] of 190 patients; p = 0.006). Deep-vein thrombosis occurred in the calf veins of twenty-one patients (11 per cent) who had received dalteparin and of forty-three patients (23 per cent) who had received warfarin; this difference was significant (p = 0.003). Proximal deep-vein thrombosis occurred in ten patients (5 per cent) who had received dalteparin and in sixteen patients (8 per cent) who had received warfarin; however, with the numbers available, no significant difference could be detected (p = 0.185). We also could not detect a significant difference with regard to the intraoperative and postoperative blood loss, the decrease in hematocrit, and the prevalence of major bleeding complications between the two groups; however, the patients who had received dalteparin had a significantly higher prevalence of bleeding complications involving the operative site (p = 0.03), and a significantly greater percentage required postoperative transfusions (p = 0.001). We concluded that preoperative prophylaxis with dalteparin is significantly more effective than that with warfarin in preventing deep-vein thrombosis after total hip arthroplasty. The greater effectiveness of dalteparin must be considered, however, in light of an increased need for postoperative transfusions and an increase in the prevalence of wound-related bleeding complications.

Modeling the tensile behavior of the cement-bone interface using nonlinear fracture mechanics.

The tensile mechanical behavior of the cement-bone interface where there was a large process (plastic) zone at the interface was modeled using a nonlinear fracture mechanics approach. A finite element method was employed, which included a piecewise nonlinear interface, to investigate the behavior of experimental cement-bone test specimens and an idealized stem-cement-bone (SCB) structure. The interface model consisted of a linear elastic region with high stiffness until the yield strength was reached, followed by an exponential softening region, until zero stress. The yield strength and rate of exponential softening after yielding at the cement-bone interface were shown to have a marked effect on the structural stiffness of the SCB model. The results indicate that both yield strength and postyield behavior should be included to characterize the mechanics of the cement-bone interface fully.

Tensile strength of the cement-bone interface depends on the amount of bone interdigitated with PMMA cement.

An experimental investigation was performed to (1) determine the general mechanical behavior and in particular, the post-yield behavior of the cement-bone interface under tensile loading, (2) determine where interface failure occurs, and (3) determine if the mechanical properties of the interface could be related to the density of bone at the interface and/or the amount of cement-bone interdigitation. Seventy-one cement-bone test specimens were machined from human proximal femurs that had been broached and cemented using contemporary cementing techniques. The amount of cement-bone interdigitation was documented and the quantitative computed tomography equivalent mineral density (QCT density) of the bone with cement was measured. Specimens were loaded to failure in tension under displacement control and exhibited linear elastic behavior with some reduction in stiffness until the peak tensile stress was reached (1.28 +/- 0.79 MPa). A substantial amount of strain softening (negative tangent stiffness) with an exponential-type decay was found after the peak stress and continued until there was complete debonding of the specimens (at 0.93 +/- 0.44 mm displacement). Interfacial failure most often occurred at the extent of cement penetration into the bone (56% of specimens) or with small spicules of cement left in the bone (38% of specimens). The results showed that the post-yield tensile behavior contributes substantially to the energy required to cause failure of the cement-bone interface, but the post-yield behavior was not well correlated with the amount of interdigitation or density of bone. Linear regression analysis revealed a moderate (r2 = 0.499, p < 0.0001) positive relationship between the tensile strength of the cement-bone interface and the quantity of bone interdigitated with the cement.

Effects of stem length on mechanics of the femoral hip component after cemented revision.

Bone loss in the proximal femur at the time of revision hip arthroplasty for a failed primary cemented femoral component can substantially reduce the stability of the revision stem. Use of an extended-length femoral component has been suggested to aid in achieving long-term fixation; however, the optimal stem length is unknown. A three-dimensional finite element model of a Charnley-type revision femoral component in a sclerotic shell of cortical bone devoid of cancellous bone was developed, and five different stem lengths ranging from 140 to 273 mm were used. The interface between the sclerotic bone and cement mantle consisted of fibrous tissue. Distal to the sclerotic bone, bonding was allowed between the cement and bone. Relative motion between the cement and bone was reduced substantially when the stem extended beyond the original defect. Maximum principal stresses in the proximal cement mantle decreased from 7.7 to 5.5 MPa, but cement stresses near the distal tip increased from 7.9 to 10.7 MPa when the stem just bridged the defect. Further increases in stem length reduced the distal cement stresses. Increases beyond two femoral diameters had a minor effect on changes in relative motion, cement mantle stresses, and stresses across the cement-bone interface. The results suggest that a femoral component that extends beyond the area of cancellous bone defect by two femoral diameters will be most effective in minimizing stresses and motion that could be associated with clinical loosening of the cemented revision. A shorter stem that just bridges the cancellous bone defect left from the primary procedure may not provide adequate distal fixation due to high cement-bone shear stresses.

Influence of stem geometry on mechanics of cemented femoral hip components with a proximal bond.

Nonlinear, three-dimensional, finite element models of cemented femoral hip components with a proximal stem-cement bond were developed with use of a Charnley stem geometry and a modified Charnley stem geometry that had a cylindrical cross section over the distal two-thirds of the stem (Distal-Round). Peak tensile stresses in the proximal cement mantle increased 63 and 74% for the Charnley and Distal-Round stems, respectively, when the proximal stem-cement interface was debonded. The shear stresses over the stem-cement interface with a proximal bond were 29% larger for the Distal-Round stem than for the Charnley stem. After the proximal stem-cement interface was debonded, the peak tensile stresses in the cement mantle were 15% larger for the Distal-Round stem than for the Charnley stem. The results illustrate that stresses within the proximal cement mantle could be substantially reduced for both Charnley and Distal-Round stems through use of a proximal stem-cement bond. However, the risk of debonding may be higher for the Distal-Round stem because of increased shear stresses, and once debonded the risk of further loosening due to failure of the cement mantle would also be higher for the Distal-Round stem.

Early failure of the femoral component in unicompartmental knee arthroplasty.

Unicompartmental knee arthroplasty has been proposed as treatment for unicompartmental arthritis. Overall, results have been satisfactory, with occasional failures of tibial component fixation. Short-term loosening of the femoral components in unicompartmental knee arthroplasty that required revision to total knee arthroplasty is reported. All patients presented with pain and instability of the knee, with loosening confirmed radiographically and at revision surgery. The Porous-Coated Anatomic femoral component (Howmedica, Rutherford, NJ) was biomechanically tested after being implanted in cadaver limbs. Cyclic loading in flexion and extension under physiologic loads resulted in implant failure. The mode of failure was rocking in the sagittal plane, which corresponds to the clinical findings. The femoral implant design consists of an angled bone-implant interface with straight arms, which causes shear at the bone-prosthesis interface did not loosen under identical biomechanical testing in paired knees. It was concluded that the Porous-Coated Anatomic femoral component has an unacceptably high early clinical loosening rate, confirmed by comparative biomechanical testing.

Blood salvage after total hip arthroplasty.

We performed a prospective, randomized study to determine the effect of postoperative collection and reinfusion of unwashed, filtered, salvaged blood on the transfusion requirements of 232 patients managed with a total hip replacement. Patients who were scheduled to have a primary or revision procedure were advised to predeposit two or four units of autologous blood, respectively, before the operation. In addition, intraoperative blood salvage was performed for all patients who had a revision procedure. The patients were randomly assigned to one of two groups: the first group was managed with postoperative blood salvage with use of the Autovac Postoperative Orthopaedic Autotransfusion Canister and the second, with closed suction drainage with use of the Hemovac system. In the first group, blood was collected from wound drains for four hours postoperatively; if at least 300 milliliters of blood was collected, the unwashed blood was reinfused through a microaggregate filter during a two-hour period. A maximum of 1000 milliliters of salvaged blood was reinfused; any blood that had not been reinfused within six hours after the beginning of collection was discarded. No complications or episodes of hypotension, confusion, cardiac or pulmonary compromise, febrile reaction, or coagulopathy were observed during or after the reinfusion of the unwashed, filtered, salvaged blood. No reinfusions were interrupted or discontinued. We found that postoperative reinfusion of unwashed, filtered, salvaged blood was associated with a decreased prevalence of homologous transfusion after a total hip replacement among patients for whom preoperatively donated autologous blood was not available.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential distribution of insulin-like growth factors and their binding proteins within bone: relationship to bone mineral density.

To evaluate the possibility that insulin-like growth factors (IGFs) and their binding proteins (BPs) in bone play a role in regulating cortical bone formation in growing animals, we compared changes in IGF and IGF BP levels with changes in bone mineral density (BMD) at three different regions (proximal, middle, and distal) along the rabbit femoral shaft. BMD measured by dual-energy x-ray absorptiometry decreased progressively from proximal to distal regions of the shaft, from 0.449 +/- 0.005 to 0.354 +/- 0.002 g/cm2 (mean +/- SEM; n = 9), respectively; total protein concentrations also decreased toward the distal region. We extracted the IGFs and their BPs from bone by demineralization in 10% EDTA and 4 M guanidine-HCl (pH 4.5). The IGFs were then separated from their BPs by size exclusion HPLC. The pH of the extraction buffer profoundly influenced the recoveries of the IGFs and, to a lesser extent, the total protein; at least 100% more IGFs were recovered at acid (4.5) pH than at neutral (7.5) or basic (10.5) pH. The levels of IGF-I decreased markedly from proximal to distal regions, from 273 +/- 27 to 100 +/- 38 ng human IGF-I equivalent/g bone (or 103 +/- 10 to 52 +/- 11 ng human IGF-I equivalent/mg protein), respectively. IGF-II was uniformly distributed (385 +/- 17 ng human IGF-II equivalent/g bone; mean of all three regions). Levels of the predominant 28-32 kD IGF BP doublet increased by about 100% from proximal to distal segments, regardless of whether the data were expressed per unit mass or protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissociation of bone mineral density from age-related decreases in insulin-like growth factor-I and its binding proteins in the male rat.

We evaluated the possibility that age-related decreases in circulating and/or bone-associated insulin-like growth factor-I (IGF-I) and its binding proteins (BPs) were associated with the development of osteopenia in 8-, 16-, and 24-month-old specific pathogen-free Brown Norway/Fischer 344 male rats. We measured bone mineral densities (BMD) of femurs by dual-energy x-ray absorptiometry. IGFs and IGFBPs were extracted from bone and separated by molecular exclusion HPLC before quantitation by specific radioligand assays. BMD did not change significantly between 8 and 24 months of age. IGF-I levels decreased by about 30% between 8 and 24 months in both serum and bone. Similarly, both circulating and bone-derived IGFBPs also declined (30% and 60%, respectively) with age. Thus, maintenance of femoral BMD throughout most of the adult rat life span was dissociated from the age-related decline in circulating and bone-associated IGF-I and IGFBPs.

Dialysis arthropathy of the hip.

Beta 2-microglobulin amyloid deposition is associated with a destructive arthropathy in the hip of chronic hemodialysis patients. Twenty-five hips from 18 patients were assessed for the presence and immunohistochemical type of amyloid. The hemodialysis group was compared with an age- and disease-matched control group that had no evidence of renal failure. Beta 2-microglobulin amyloid deposits were present in all patients who had been on hemodialysis for 18 months or more. Beta 2-microglobulin amyloid deposits were not found in patients who had been on hemodialysis for less than 18 months. Amyloid deposits were seen first in the articular cartilage and later involved the synovial membrane, joint capsule, and subchondral bone as well. The presence and amount of amyloid deposition correlated to the duration of hemodialysis. Severely affected hip roentgenographically had a concentric loss of joint space, periarticular erosions, and cystic lesions in the femoral head and acetabulum. These pathologic and roentgenographic changes suggest that amyloid deposition leads directly to the erosive hip arthropathy occurring in hemodialysis patients.

Prevention of heterotopic ossification in high-risk patients by radiation therapy.

Heterotopic ossification (HO) is a frequent occurrence after cemented and cementless total hip arthroplasty (THA). Patients at risk for this complication include those with preexisting ipsilateral or contralateral HO, diffuse idiopathic skeletal hyperostosis, hypertrophic osteoarthrosis, posttraumatic arthritis, and ankylosing spondylitis. Low-dose radiation therapy effectively prevents HO in this high-risk group when treatment is begun early in the postoperative period. A prospective evaluation has established the efficacy of fractionated and single-dose radiation therapy protocols. Limited radiation portals are used in patients receiving cementless prostheses. A rectangular radiation portal obliquely oriented to the prosthesis enables radiation treatment of the periarticular soft tissues while avoiding exposure of the bone-prosthesis interface. Radiation therapy to this interface may inhibit or delay bony ingrowth. Radiation therapy is the only treatment used to prevent HO that is delivered locally and not systemically. Low-dose radiation therapy using a limited radiation portal is the treatment of choice to prevent HO in high-risk patients after cementless THA.