What do we know about taper corrosion in total hip arthroplasty?

Mechanically assisted crevice corrosion (MACC) at metal/metal modular junctions in which at least one of the components is fabricated from cobalt-chromium alloy, has reemerged as a potential clinically significant complication in total hip arthroplasty. The clinical manifestation of MACC may include the development of an adverse local tissue reaction (ALTR), similar to what has been described in association with metal-on-metal bearing total hip and resurfacing arthroplasty. The clinical presentation of MACC-associated ALTRs may include pain and possibly late recurrent dislocations. Abnormal metal artifact reduction sequence magnetic resonance images and elevated serum metal levels (cobalt elevations out of proportion to chromium elevations) can be helpful in the diagnosis of these MACC-associated ALTRs.

Short-term results of the M2a-taper metal-on-metal articulation.

A polyethylene-free, metal-on-metal acetabular system (M2a-taper [Biomet, Inc., Warsaw, IN]) was designed in an effort to improve total hip arthroplasty (THA) longevity. Minimum 2-year follow-up results involving 72 polyethylene liner THAs and 78 metal liner THAs from a multicenter, randomized, controlled, investigational device exemption study are reported. Mean Harris hip scores of 95.54 (polyethylene liner group) and 95.23 (metal liner group) were reported at mean follow-up intervals of 3.29 and 3.23 years. Radiographic evaluation revealed no evidence of early failure. No acetabular components have been revised or are pending revision. No statistically significant differences in the data were calculated between liner types except for the immediate postoperative (P=.0415) and minimum 2-year follow-up (P=.0341) angles of inclination. The M2a-taper metal-on-metal articulation may represent a viable alternative for THA in younger, higher demand patients.

A theoretical and experimental analysis of polymerization shrinkage of bone cement: A potential major source of porosity.

A theoretical basis for understanding polymerization shrinkage of bone cement is presented based on density changes in converting monomer to polymer. Also, an experimental method, based on dilatometry and the Archimedes' principle is presented for highly precise and accurate measurement of unconstrained volumetric shrinkage of bone cement. Furthermore, a theoretical and experimental analysis of polymerization shrinkage in a constrained deformational state is presented to demonstrate that porosity can develop due to shrinkage. Six bone-cement conditions (Simplex-Ptrade mark vacuum and hand mixed, Endurancetrade mark vacuum mixed, and three two-solution experimental bone cements with higher initial monomer levels) were tested for volumetric shrinkage. It was found that shrinkage varied statistically (p< or = 0.05) from 5.1% (hand-mixed Simplex-Ptrade mark) to 6.7% (vacuum-mixed Simplex-Ptrade mark) to 10.5% for a 0.6:1 (polymer g/monomer mL) two-solution bone cement. Shrinkage was highly correlated with initial monomer content (R(2) = 0.912) but with a lower than theoretically expected rate. This discrepancy was due to the presence of residual monomer after polymerization. Using previously determined residual monomer levels, the theoretic shrinkage analysis was shown to be predictive of the shrinkage results with some residual monomer left after polymerization. Polymerization of a two-solution bone cement in a constrained state resulted in pores developing with volumes predicted by the theory that they are the result of shrinkage. The results of this study show that shrinkage of bone cement under certain constrained conditions may result in the development of porosity at the implant-bone cement interface and elsewhere in the polymerizing cement mantle.

Comparison of acute normovolemic hemodilution and preoperative autologous blood donation in clinical practice.

STUDY OBJECTIVE: To compare, by model simulation, acute normovolemic hemodilution (ANH) and preoperative autologous blood donation (PABD) to predict their efficacy in current clinical practice. To discuss their similarities and offer guidelines based on expected operative blood loss. DESIGN: Model simulation using data obtained from total hip arthroplasty procedures. SETTING: University medical center. PATIENTS: 91 patients who participated in PABD undergoing single, primary, total hip replacement surgeries from January to December 1997. INTERVENTIONS: A nonanemic (Hb baseline 14 g/dL), average-sized patient (estimated blood volume 5,000 mL) who donated two units by either PABD or ANH was assumed for model simulation. The Hb-final, as a function of 250-mL blood loss increments after retransfusion of two autologous units, was calculated for each technique and compared to a control (nondonor) to predict the effectiveness of PABD and ANH in conserving red cell mass. Data from hip arthroplasties over a 12-month period were used to determine the parameters for the model. Results were subjected to regression analysis and tested for parallelism of slopes, with p < 0.05 accepted to indicate a statistical difference. MAIN RESULTS: The difference in Hb-final between PABD and ANH was not statistically different over a wide range of blood loss. When compared to control, there was no difference in Hb-final measurements in the estimated blood loss (EBL) range of less than 1,000 mL. ANH and PABD provide some benefit when EBL is greater than 1,500 mL in nonanemic, average-sized patients. As blood loss increases, the benefit of autologous collection becomes more clinically evident. CONCLUSION: PABD exemplifies a "chronic" form of ANH in current clinical practice and offers little advantage over ANH as a blood conservation technique for high-blood-loss operations. When surgical blood loss is predictably mild to moderate (range 250 to 1,000 mL), neither blood conservation technique is necessary.

Evaluation of the safety and efficacy of enoxaparin and warfarin for prevention of deep vein thrombosis after total knee arthroplasty.

Of 263 patients who underwent total knee arthroplasty, 122 received adjusted low-dose warfarin and 141 received enoxaparin as deep vein thrombosis (DVT) prophylaxis. Three patients in the warfarin group and 3 in the enoxaparin group developed ultrasound-detectable DVT (P > .05). Although the amount of perioperative blood transfused was equivalent in both groups, the overall hemoglobin drop was greater (P < .005) in the enoxaparin group (2.9 g/dL) as compared with the warfarin group (2.3 g/dL). Five patients (4.6%) in the warfarin group and 16 (11.3%) in the enoxaparin group had bleeding complications (P < .05). Our data support earlier published reports suggesting that reductions, if any, in the incidence of DVT associated with enoxaparin are offset by a significant increase in bleeding complications as compared with adjusted-dose warfarin. We continue to use adjusted-dose warfarin as primary thromboembolic prophylaxis after total knee arthroplasty.

Efficacy of preoperative autologous blood donation: analysis of blood loss and transfusion practice in total hip replacement.

STUDY OBJECTIVE: To determine the frequency of allogeneic transfusion for total hip replacement (THR) surgery and to examine the efficacy of preoperative autologous blood donation (PABD) under specified, standardized blood transfusion guidelines. DESIGN: Prospective, nonrandomized study. SETTING: University medical center. PATIENTS: All ASA physical status I, II, III, and IV patients undergoing single, primary, THR surgery from April 1998 to March 1999. INTERVENTIONS: All patients received standardized transfusion and anticoagulation therapy. Demographic, blood loss, and transfusion data were collected and compared between all patients participating in PABD (donors) and patients not participating in PABD (nondonors). Overall allogeneic blood exposure was established. Since most anemic patients could not participate in PABD, allogeneic transfusion frequency was also examined in a subset of nonanemic patients (hemoglobin > or =12 g/dL) who were potentially able to participate in PABD. MEASUREMENTS AND MAIN RESULTS: n = 231 patients, 142 donors and 89 nondonors. Mean estimated blood volume (EBV) of donors was 4991 +/- 1042 mL versus nondonors 4631 +/- 1108 mL (p < 0. 01). ASA physical status I-II/III-IV among donors was 118/24 versus nondonors 61/28 (p < 0.01). Overall allogeneic blood exposure was 22% (51/231). Allogeneic transfusion frequency for all donors was 15% (22/142) versus nondonors 33% (29/89) (p < 0.05). Among nonanemic patients, donor versus nondonor EBV and ASA physical status I-II/III-IV were 5074 +/- 1019 mL versus 4743 +/- 1172 mL and 107/20 versus 48/15 (p = NS); allogeneic transfusion frequency reduced to 13% (16/127) versus 17% (11/63) (p = NS), respectively. CONCLUSIONS: Allogeneic blood exposure was >10% despite the use of PABD. The efficacy of PABD has been obscured by the fact that donors of autologous blood tend to be larger and healthier than nondonors. After exclusion of anemic patients, autologous donors and nondonors were clinically comparable and the difference in allogeneic blood exposure was not statistically significant. PABD offers only a modest, if any, benefit for THR surgery.

A novel high-viscosity, two-solution acrylic bone cement: effect of chemical composition on properties.

Solutions of poly(methyl methacrylate) (PMMA) powder predissolved in methyl methacrylate (MMA) have been developed as an alternative to current powder/liquid bone cements. They utilize the same addition polymerization chemistry as commercial cements, but in mixing and delivering via a closed system, porosity is eliminated and the dependence of material properties on the surgical technique is decreased. Twelve different sets of compositions were prepared, with two solutions of constant polymer-to-monomer ratio (80 g of PMMA/100 mL of MMA) and all combinations of four benzoyl peroxide (BPO) initiator levels added to the first solution and three N, N-dimethyl-p-toluidine (DMPT) activator levels added to the second. These compositions were tested, along with Simplex-P bone cement, for effects of BPO and DMPT concentrations on polymerization exotherm, setting time, flexural strength, modulus, and maximum strain. The results show that each of these dependent variables was affected significantly by the individual concentrations of BPO and DMPT and their interactions. The flexural strength, modulus, and polymerization exotherm reached their maximums at about a 1:1 molar ratio of BPO to DMPT. Most compositions had exotherms, setting times, and maximum strains within the range of commercial cements and flexural strengths and moduli up to 54 and 43% higher than Simplex-P, respectively.

Maintenance of proximal bone mass with an uncemented femoral stem analysis with dual-energy x-ray absorptiometry.

Bone ingrowth into uncemented femoral implants with proximal porous coatings has been designed to avoid proximal stress shielding and preserve femoral strength. Dual-energy x-ray absorptiometry allows repeated quantitative analysis of anteroposterior scans of the proximal femur. By use of dual-energy x-ray absorptiometry and qualitative radiographic changes, 31 total hip arthroplasties with an individually designed, proximally porous-coated prosthesis were evaluated after surgery and at intervals up to 2 years. All implants appeared to achieve successful bone ingrowth and subsequent remodeling. At the most proximal level around the neck osteotomy, the postoperative loss of bone density at 6 months was -14.5%, which persisted at 24 months with -11.6%. At the level of the distal portion of the porous coating in the lower metaphysis, the density change was -8.7%, but bone had remodeled at 24 months with a change in density of only -1.0% compared with the immediate postoperative scan. With a design that results in reliable proximal ingrowth, this study predicts that after an initial decline in bone density, a positive bone remodeling response occurs that could lead to long-term stable fixation of the femoral implant.

Functional outcome and patient satisfaction in total knee patients over the age of 75.

Seventy-four patients, age 75 or older, who had undergone 98 primary total knee arthroplasties were evaluated in a retrospective cohort study, with validated questionnaires that assessed self-reported pain, physical function, mental health, and satisfaction. Average follow-up period was 34 months (range, 12-67 months). Overall, 90.8% reported improvement, 88.8% were satisfied with the results of surgery, and 91.8% felt they had made the right decision. Dissatisfaction with the results correlated with poorer mental health scores, decreased physical function, and increased bodily pain scores (P < .05). Satisfaction was correlated with better pain scores on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and SF-36 (P < .05) but not with Hospital for Special Surgery scores (P = .328). Poor surgical results leading to revision surgery (5%) were associated with preoperative deformity greater than 20 degrees. Based on this patient-assessed outcome analysis, total knee arthroplasty is a worthwhile and beneficial procedure in the elderly.

How superior placement of the joint center in hip arthroplasty affects the abductor muscles.

This study examines the effects of a superiorly placed hip center on the strength of the abductor muscles. A 3-dimensional computer model of the hip and the surrounding musculature was used to calculate the moment arms, forces, and moments generated when the hip abductor muscles are maximally activated. A representation of a hip prosthesis was implanted into the computer model with altered hip center positions and a range of prosthetic neck lengths. Analysis of these simulated hip replacements demonstrated that superolateral placement of the hip center (2 cm superior and 2 cm lateral) decreases the moment arms of the hip abductor muscles by an average of 28%. This decrease in moment arm cannot be restored by increasing prosthetic neck length, resulting in an unrecoverable loss of abduction strength with superolateral displacement. By contrast, a 2-cm superior displacement of the hip center changes the moment arms and force generating capacities of the abductors by less than 10% if prosthetic neck length is increased to compensate for decreased muscle length. The results of this study suggest that superior positioning of the hip center, without lateral placement, does not have major, adverse effects on abduction moment arms or force generating capacities when the neck length is appropriately increased.

Effect of ketorolac tromethamine on bleeding and on requirements for analgesia after total knee arthroplasty.

The effect of ketorolac tromethamine, a non-steroidal anti-inflammatory drug, on postoperative blood loss and on the requirement for morphine was assessed after total knee arthroplasty, an operation in which blood loss is mainly measured rather than estimated. The purpose of this prospective, randomized, double-blind clinical trial was to determine whether administration of ketorolac in the perioperative period would increase bleeding related to the operation. Fifty-nine patients who had a total knee arthroplasty received either thirty milligrams of ketorolac or a placebo consisting of saline solution, intravenously, every six hours, in four doses. The first dose was administered about an hour before the end of the operation. Blood loss and use of morphine for pain control were measured for the first twenty-four hours postoperatively. The per cent change in the hematocrit and the amount of transfused blood were also recorded. The patients who received ketorolac used 27 per cent less morphine than those who received the placebo (40.0 +/- 23.4 milligrams compared with 55.1 +/- 23.5 milligrams [mean and standard deviation]); this difference was significant (p < 0.05). On the first day after the operation, the hematocrit decreased from 0.364 +/- 0.043 preoperatively to 0.278 +/- 0.032 in the patients who received ketorolac and from 0.363 +/- 0.046 to 0.298 +/- 0.030 in the patients who received the placebo. The 6 per cent greater decrease in the group that received ketorolac was significant (p < 0.05) but not clinically important.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety of 1-stage bilateral total knee arthroplasty.

Bilateral total knee replacements during a single operation with intramedullary femoral guide rods have been associated with the possible development of a fat embolism syndrome. To assess the safety of this procedure, in which the femoral canal was decompressed by the use of an overdrilled entrance hole and fluted guide rod, 17 unilateral and 18 bilateral consecutive total knee patients were evaluated. There were no differences between the groups on the basis of changes in chest radiographs, percentage of estimated pulmonary shunting, mental status changes, or fat and bone marrow elements drawn from a central venous catheter in the right atrium. Although no patient had free fat in the blood, bone marrow elements were found in 3 bilateral and 2 unilateral cases. No patient had clinical manifestations of a fat emboli syndrome. With appropriate femoral canal decompression, bilateral 1-stage total knee replacement appears to be a safe procedure.

Superior displacement of the hip in total joint replacement: effects of prosthetic neck length, neck-stem angle, and anteversion angle on the moment-generating capacity of the muscles.

The purpose of this study was to determine the effects of superior displacement of the hip center and changes in three prosthetic parameters (neck length, neck-stem angle, and anteversion angle) on the capacity of muscles to generate force and moment about the hip. A three-dimensional model that calculates the maximum isometric forces and moments generated by 25 muscles crossing the hip over a wide range of body positions was used to evaluate the effects of a 2 cm elevation of the hip center and changes in the prosthetic parameters. After superior displacement of the hip center, the neck length was increased from 0 to 3 cm, the neck-stem angle was varied between 110 and 150 degrees, and the anteversion angle was varied between 0 and 40 degrees. Our analysis showed that a 2 cm superior displacement of the hip center would decrease the moment-generating capacity of the four muscle groups studied (abductors, adductors, flexors, and extensors) if neck length were not increased to compensate for decreased muscle length. In the computer model of an adult man that we used, a 2 cm increase in neck length restored the moment-generating capacity of the muscles by increasing muscle length and force-generating capacity. However, a 3 cm increase in neck length increased passive muscle forces substantially, which potentially could limit joint motion. An increased neck-stem angle (i.e. a valgus neck) decreased the abduction moment arm but increased the moment-generating capacity of the other muscle groups. A change in the anteversion angle from 0 to 40 degrees had a relatively small effect on the isometric moment-generating capacity of the muscles studied.

The hemostatic effects of desmopressin on patients who had total joint arthroplasty. A double-blind randomized trial.

The effects of desmopressin on postoperative bleeding and postoperative transfusion requirements were studied in ninety-two hemostatically normal patients who had had an elective primary total hip or total knee arthroplasty. The patients were randomized into either a placebo or a desmopressin group in a double-blind prospective clinical trial. During closure of the wound, desmopressin (0.03 microgram per kilogram of body mass) or the placebo was infused into a peripheral vein over a twenty-minute period. Compared with the placebo, desmopressin did not significantly decrease blood loss or transfusion requirements, and it did not affect the postoperative platelet or fibrinogen levels or the bleeding time. The results were no different even when the treatment and control groups were matched according to surgeon, use of cement for the femoral and knee components, preoperative use of non-steroidal anti-inflammatory agents, or performance of a lateral release for total knee arthroplasty. We concluded that desmopressin does not reduce blood loss or transfusion requirements after total joint arthroplasty.

Reinfusion of postoperative wound drainage in total joint arthroplasty. Red blood cell survival and coagulopathy risk.

Fifty patients with total joint arthroplasties (28 total hip arthroplasties, 11 total knee arthroplasties, and 11 bilateral total knee arthroplasties) received autotransfusions from their postoperative wound drainage. The blood was collected in a closed sterile drainage system without any additional anticoagulant. Pre- and postoperative measurements were made of the patient's hemoglobin, platelets, fibrinogen, haptoglobin, fibrin degradation products, and D-dimer (a specific type of fibrin degradation product). Red blood cell survival was assessed in 16 of the patients by labeling the shed blood with 51Cr sodium chromate prior to reinfusion. To control for fluid shifts, continued bleeding, and dilution effects of further transfusions in the immediate postoperative period, 10 patients also had their native blood labeled with 111In oxime. In this study, the mean estimated blood loss was 1,062 mL (+/- 1,247) with a mean wound drainage of 836 mL (+/- 338). Of this, a mean of 450 mL (+/- 261) of blood was was given back to the patient in addition to routine, preoperative autologous donated blood. Six (12%) patients experienced transient fevers at the time of retransfusion. Detailed hematologic studies were performed on the shed blood in 19 patients. The collected blood was completely defibrinated, but did contain fibrin degradation products, as indicated by the D-dimer level, and hemolyzed blood as the haptoglobin was reduced. Even though the blood containing the above breakdown products was reinfused to the patients, there were no clinical manifestations of disseminated intravascular coagulation. Both the hemolyzed and defibrinated products were subsequently cleared by the body.(ABSTRACT TRUNCATED AT 250 WORDS)

Progressive subluxation and polyethylene wear in total knee replacements with flat articular surfaces.

One hundred eighty-six Microloc tricompartmental, cruciate-sparing, primary total knee replacements in 136 patients were performed between 1983 and 1987. Femoral components were made of cobalt-chrome-molybdenum alloy. The tibial component baseplates were made of titanium-aluminum-vanadium alloy. The baseplates were made with three small porous-coated pegs for fixation with or without cement, or with a central stem for fixation with cement. The polyethylene was affixed to the baseplate by a mechanical locking mechanism that was nonmodular. The articular surfaces of both components were flat mediolaterally and anteroposteriorly. The patellar components were dome shaped and metal backed with titanium-aluminum alloy. Seventy-three percent of the femoral components, 26% of the tibial components, and 48% of the patellar components were inserted without bone cement. The average time to maximum follow-up examination was 6.1 years (range, four to nine years). Of implants that had not been revised, 84.4% had good or excellent results (using the Hospital for Special Surgery scoring system) at final follow-up examination. The average range of motion of functioning implants at final follow-up examination was 108 degrees. Revisions for failure only of the metal-backed patellar component were performed in 22 knees (11.8%). Forty knees (21.5%) required revision for failure of the femoral-tibial articulation. Reasons for failure in this group included: polyethylene wear (57.5%); loosening (15.0%); tibial tray fracture (10.0%); sepsis (12.5%); and dislocation or ligament laxity (5.0%). An additional 15 functioning knees (8.1%) have radiographic evidence of progressive femoral-tibial subluxation. Future failure of these devices is considered likely. Polyethylene wear requiring revision was not statistically associated with patient age, gender, preoperative diagnosis, height, weight, or component size. Polyethylene failure leading to revision was related to the radiographic appearance of femoral-tibial component subluxation. This subluxation was most likely to occur after five years of component implantation. The development of progressive femoral-tibial subluxation was statistically associated with postoperative extremity malalignment, excessive varus positioning of the tibial component, bone grafting of the tibial plateau, the use of the small-pegged tibial component, and the use of this component without cement. Polyethylene wear associated with progressive femoral-tibial subluxation occurred at the periphery of the tibial plateau and along the raised portion of the tibial spine. The metal baseplate at the edge of the plateau was frequently exposed and worn. Bone lysis associated with the presence of polyethylene, metal, and cement debris was frequently observed.

Do we need to vacuum mix or centrifuge cement?

In total hip surgery, the goal of porosity reduction techniques in the preparation of acrylic bone cement is to provide a stronger, more fatigue resistant material between the implant and bone. Conventional mixing of polymethylmethacrylate bone cement produces porosity of 5% to 16%, whereas vacuum mixing or centrifugation reduces the porosity to a range of 0.1% to 3.4%. Multiple studies have demonstrated that this results in a cement that has a significant increase in static and dynamic testing to failure. Fracture of the cement mantle has been found as a part of the failure pattern in many total hip prostheses requiring revision for loosening. Vacuum mixing or centrifugation produces a stronger cement to resist the component of loosening caused by fracture of the cement mantle. Where failure occurs at the bone-cement interface, as in cemented acetabular migration, no improvements from porosity reduction would be expected. Along with enhanced femoral designs, improvements in cement technique with modern methods of bone preparation and administration of the cement have resulted in a marked improvement in clinical and roentgenographic loosening rates in cemented femoral components at medium-term follow-up periods of five to ten years. Intact total hip prostheses, retrieved for reasons other than loosening, at longer-term follow-up periods, have shown intact bone-cement interfaces. However, these specimens have also shown incipient cracks in the acrylic cement that emanate from and connect defects in the cement mantle and at the metal-cement interface. The use of a void-free, structurally stronger material is expected to improve the stability and longevity of the cement supporting femoral implants.

A computer-based biomechanical analysis of the three-dimensional motion of cementless hip prostheses.

A computer-based mathematical technique was developed to measure and completely describe the migration and micromotion of a femoral hip prosthesis relative to the femur. This technique utilized the mechanics of rigid-body motion analysis and apparatus of seven linear displacement transducers to measure and describe the complete three-dimensional motion of the prosthesis during cyclic loading. Computer acquisition of the data and custom analysis software allowed one to calculate the magnitude and direction of the motion of any point of interest on the prostheses from information about the motion of two points on the device. The data were also used to replay the tests using a computer animation technique, which allowed a magnified view of the three-dimensional motion of the prosthesis. This paper describes the mathematical development of the rigid-body motion analysis, the experimental method and apparatus for data collection, the technique used to animate the motion, the sources of error and the effect of the assumptions (rigid bodies) on the results. Selected results of individual test runs of uncemented and cemented prostheses are presented to demonstrate the efficacy of the method. The combined effect of the vibration and electrical noise resulted in a resolution of the system of about 3-5 microns motion for each transducer. Deformation effects appear to contribute about 3-15 microns to the measurement error. This measurement and analysis technique is a very sensitive and powerful means of assessing the effects of different design parameters on the migration and micromotion of total joint prostheses and can be applied to any other case (knee, dental implant) where three-dimensional relative motion between two bodies is important.

Total hip replacement with cemented, uncemented, and hybrid prostheses. A comparison of clinical and radiographic results at two to four years.

One hundred and thirty-one patients who had 144 cemented or uncemented hip prostheses were followed prospectively for two to four years. A cemented or a hybrid prosthesis (consisting of a cemented femoral component and an uncemented acetabular component) was used in men older than seventy years, in women older than sixty years, and in younger patients in whom adequate initial fixation could not be obtained without cement. Uncemented, porous-surfaced implants were used in all other patients. The over-all clinical results were similar for the three groups. For the fifty-two hips that had a cemented prosthesis, the mean total Harris hip rating was 91 points and the score for pain, 42 points; for the twenty-seven hips that had a hybrid prosthesis, 90 and 43 points; and for the sixty-five hips that had an implant allowing ingrowth of bone in both the acetabulum and the femur, 95 and 43 points. Two prosthetic stems that were designed to allow ingrowth of bone had aseptic loosening; one was revised. Pain in the thigh, usually slight and not disabling, occurred at one year in 24 per cent of the patients in whom a femoral component allowing ingrowth had been used; the prevalence of pain then declined. The incidences of migration of the components and of radiolucent lines were greater in the acetabula that had a cemented component than in those that had a cup allowing ingrowth of bone.