Pain and Opioid use Following Total Knee Arthroplasty: Psycho-Social Factors are More Predictive Than Pharmacogenomics

BACKGROUND

This prospective, observational study was designed to assess the phenotype variation of the genes associated with pain and opioid use following total knee arthroplasty (TKA) in comparison to psycho-social elements.

METHODS

Preoperative demographic data and Patient-Reported Outcomes Measurement Information System-43 scores were obtained on 305 elective TKA patients. Patient visual analog scale pain scores and opioid use were extracted from the hospital record. Following discharge, participants completed a daily log of visual analog scale pain score, and medications used over 30 days. Pharmacogenomic testing was performed for three genes, CYP2D6, COMT, and OPRM1, which are involved in the opioid pathway and pain modulation.

RESULTS

Other than increased pain seen in the COMT high activity group while in the hospital, none of the phenotype variations of the three genes were significantly associated with the participants' pain or opioid use. The Patient-Reported Outcomes Measurement Information System-43 domains of pain interference and anxiety were significantly associated with pain and opioid use using multiple logistic regression.

CONCLUSIONS

Pharmacogenomic testing in this study was not predictive of pain and opioid use following TKA compared with psycho-social variables.

Predicting chronic postsurgical pain: current evidence and a novel program to develop predictive biomarker signatures

ABSTRACT

Chronic pain affects more than 50 million Americans. Treatments remain inadequate, in large part, because the pathophysiological mechanisms underlying the development of chronic pain remain poorly understood. Pain biomarkers could potentially identify and measure biological pathways and phenotypical expressions that are altered by pain, provide insight into biological treatment targets, and help identify at-risk patients who might benefit from early intervention. Biomarkers are used to diagnose, track, and treat other diseases, but no validated clinical biomarkers exist yet for chronic pain. To address this problem, the National Institutes of Health Common Fund launched the Acute to Chronic Pain Signatures (A2CPS) program to evaluate candidate biomarkers, develop them into biosignatures, and discover novel biomarkers for chronification of pain after surgery. This article discusses candidate biomarkers identified by A2CPS for evaluation, including genomic, proteomic, metabolomic, lipidomic, neuroimaging, psychophysical, psychological, and behavioral measures. Acute to Chronic Pain Signatures will provide the most comprehensive investigation of biomarkers for the transition to chronic postsurgical pain undertaken to date. Data and analytic resources generatedby A2CPS will be shared with the scientific community in hopes that other investigators will extract valuable insights beyond A2CPS's initial findings. This article will review the identified biomarkers and rationale for including them, the current state of the science on biomarkers of the transition from acute to chronic pain, gaps in the literature, and how A2CPS will address these gaps.

Adverse local tissue reaction arising from corrosion at the femoral neck-body junction in a dual-taper stem with a cobalt-chromium modular neck

BACKGROUND

Femoral stems with dual-taper modularity were introduced to allow additional options for hip-center restoration independent of femoral fixation in total hip arthroplasty. Despite the increasing availability and use of these femoral stems, concerns exist about potential complications arising from the modular neck-body junction.

METHODS

This was a multicenter retrospective case series of twelve hips (eleven patients) with adverse local tissue reactions secondary to corrosion at the modular neck-body junction. The cohort included eight women and three men who together had an average age of 60.1 years (range, forty-three to seventy-seven years); all hips were implanted with a titanium-alloy stem and cobalt-chromium-alloy neck. Patients presented with new-onset and increasing pain at a mean of 7.9 months (range, five to thirteen months) following total hip arthroplasty. After serum metal-ion studies and metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) revealed abnormal results, the patients underwent hip revision at a mean of 15.2 months (range, ten to twenty-three months). Tissue specimens were examined by a single histopathologist, and the retrieved implants were studied with use of light and scanning electron microscopy.

RESULTS

Serum metal levels demonstrated greater elevation of cobalt (mean, 6.0 ng/mL) than chromium (mean, 0.6 ng/mL) or titanium (mean, 3.4 ng/mL). MRI with use of MARS demonstrated adverse tissue reactions in eight of nine patients in which it was performed. All hips showed large soft-tissue masses and surrounding tissue damage with visible corrosion at the modular femoral neck-body junction. Available histology demonstrated large areas of tissue necrosis in seven of ten cases, while remaining viable capsular tissue showed a dense lymphocytic infiltrate. Microscopic analysis was consistent with fretting and crevice corrosion at the modular neck-body interface.

CONCLUSIONS

Corrosion at the modular neck-body junction in dual-tapered stems with a modular cobalt-chromium-alloy femoral neck can lead to release of metal ions and debris resulting in local soft-tissue destruction. Adverse local tissue reaction should be considered as a potential cause for new-onset pain in patients with these components, and early revision should be considered given the potentially destructive nature of these reactions. A workup including serologic studies (erythrocyte sedimentation rate and C-reactive protein), serum metal levels, and MARS MRI can be helpful in establishing this diagnosis.

Limitations of imageless computer-assisted navigation for total hip arthroplasty

We prospectively evaluated acetabular cup placement in total hip arthroplasty with an imageless computer navigation system or using conventional manual technique. The achieved cup orientation in the manual group had substantially larger variances and greater placement error than the navigation cases. The use of navigation was abandoned in 3 cases because of excessive pelvic tilt and unreliable registration of the pelvis. Computer navigation system helped improve the accuracy of the acetabular cup placement for total hip arthroplasty in this study. The variation between the intraoperative navigation readings and the computed tomographic values suggests that relying on palpation of bony landmarks through drapes and tissue is a limitation of this method. Further, the variation in pelvic tilt has an effect on cup placement that requires further studies.

Validation of a computer navigation system and a CT method for determination of the orientation of implanted acetabular cup in total hip arthroplasty: a cadaver study

BACKGROUND

Successful hip reconstruction to restore the normal hip biomechanics requires precise placement of implants. Computer assisted navigation in total hip arthroplasty has been proposed to have the potential to help achieve a high accuracy in implant placement. The goal of the study was to evaluate the accuracy of an imageless computer navigation system on cadavers and to validate a non-invasive computed tomography method for post-operative determination of acetabular cup orientation.

METHODS

Total hip arthroplasty was performed on seven cadaver hips with the aid of an imageless computer navigation system. The achieved cup orientation were recorded using three methods, (1) intra-operatively using the imageless computer navigation system, (2) post-operatively with direct bone digitization and (3) with a computed tomography based three dimensional model interpreted by three raters. Measurement from the direct bone digitization was taken as the gold standard to evaluate the other two methods. The intra-rater and inter-rater consistency of the computer tomography-model method were assessed by Cronbach's alpha determination.

FINDINGS

Compared with the cup orientation obtained from the direct bone digitization, the average difference for anteversion and abduction were 3.3 (3.5) degrees (P=0.045) and 0.6 (3.7) degrees , respectively, for navigation reading. The average differences for computer tomography-model for three raters were 0.5 (2.1) degrees , 0.8 (1.5) degrees and 3.2 (3.3) degrees (P=0.043) for anteversion and 0.4 (1.6) degrees , 0.3 (1.6) degrees and 2.1 (2.7) degrees for abduction. The intra-rater consistency ranged from 0.626 for a novice rater to over 0.97 for experience raters. The inter-rater consistency (including novice and experienced raters) was over 0.90.

INTERPRETATION

While the values for cup orientation determined with imageless computer navigation were comparable to those from direct bone and implant digitization, the measurement for anteversion obtained was not as accurate as that for abduction. The proposed computer tomography-model method has an excellent intra-rater consistency for experienced raters, as well as an excellent overall inter-rater consistency. The study confirms that a non-invasive computed tomography based model analysis can be used in clinical practice as a valid method for post-operatively evaluating the orientation of the acetabular component.

Computer-assisted total hip navigation

Accurate implant placement in total hip replacement is important in avoiding dislocation, impingement, and edge-loading throughout the patient's postoperative functional range of motion. Current implants and bearing surfaces now provide the potential for prolonged longevity of the reconstruction, which can be compromised by malposition of the components outside of designated "safe zones." Computer-assisted hip navigation offers the potential for more accurate placement of hip components and control of leg length and offset. Systems are now available that allow registration of the bony anatomy based on preoperative CT images, intraoperative fluoroscopic images, or imageless techniques based on palpation of the landmarks. In each of these approaches, cup position has been based on coordinate systems formed by identification of the anterior pelvic frontal plane. All systems have shown improved accuracy of acetabular cup placement compared with conventional manual techniques. Cup anteversion is less accurate than cup abduction with the imageless approach. Measurements made with the use of navigation systems also have shown a large variation in pelvic tilt or pelvic flexion-extension in series of cases, which can affect the appropriate cup position for each patient. The results of computer-assisted navigation in the future may be improved by incorporation of measurements of each patient's pelvic tilt, femoral stem position, and hip kinematics.

Computed tomographic follow-up evaluation of operative intervention for periacetabular lysis

Computed tomography (CT) accurately evaluates periacetabular lytic lesions. The purpose of this study is to determine the fate of osteolytic lesions after treatment with liner exchange and bone grafting. Fifteen patients who had undergone liner exchange with grafting for progressive lytic lesions, as demonstrated by preoperative CT scans, were identified. Postoperative CT scans were performed at a minimum of 2 years post revision. The largest cross sectional lytic area was compared with the postoperative scan to determine the fate of the lesion. The mean size of the measured lytic lesions preoperatively was 6.38 cm(2). Postoperatively, lesions decreased to 2.94 cm(2) (P = .000). Modular liner exchange with grafting is effective in treating osteolytic lesions in the pelvis, as demonstrated by CT.

Total hip arthroplasty with the porous-coated anatomic hip prosthesis: results at 11 to 18 years

The authors had previously reported good results with apparent fixation of a series of porous-coated anatomic hips at 2 to 4 years. In a larger series of 133 hips with porous-coated anatomic uncemented components, 91 hips in 82 patients were available for a follow-up of 11 years or greater. Although 3.1% of acetabular cups had migrated or had been revised at 2 to 4 years; at 11 to 18 years, there was 37% lysis, 21.7% migration, and 32.3% revision. For the femur at 2 to 4 years, there was 3.1% migration and 1.5% revision. At 11 to 18 years, there was 27.2% lysis (proximal only), 6.6% migration, and 3.2% revision. Survival analysis for migration or revision for the femoral was 94%, and for the acetabular component, 63%, deteriorating markedly after 10 years.

Computer assisted navigation in total knee arthroplasty: improved coronal alignment

The use of a computer navigation system is intended to optimize implant positioning. This study compares prospectively followed total knee arthroplasty (TKA) done with imageless computer-assisted navigation with a cohort of TKA done with manual instruments. Primary TKAs were performed on 147 knees, with 78 in the manual group and 69 in the navigated group. Coronal alignment was determined by postoperative full-length standing radiographs. The 2 groups had similar mean values for radiographic mechanical axis at 0.4 degrees . There was a larger variation in alignment in the manual group, with 58% of the manual group within 2 degrees of neutral compared with 78% of the navigated group (P = .008). The navigation system reproducibly resulted in a more reliable reproduction of the mechanical axis.

Total hip arthroplasty through a minimal posterior approach using imageless computer-assisted hip navigation

With decreased exposure in a minimal posterior hip incision, navigation with computer assistance provides an alternative method to accurately place the components. This study compares the results of a series of 82 navigated total hips to a retrospective cohort of 50 hips done with conventional instruments. The surgical incision split the gluteus maximus but did not extend distally into the fascia. The goal of cup placement was 40 degrees to 45 degrees of abduction (ABD) and 17 degrees to 23 degrees of flexion (FLX). Postoperative radiographs were digitized and analyzed. In the study group, 82 hips were done with computer assistance and compared with 50 done with conventional methods (manual) through the same incision. Radiographic analysis showed that there were significantly fewer cases inside the desired range of ABD and FLX in the manual group (6%) compared with the navigation group (30%), P = .001, with significant differences in the variances of ABD and FLX (P = .011 and .028). Improved accuracy of cup placement was found with increased experience in the use of navigation by the surgeon over the time of the series. The use of a computer-assisted surgery navigation system with a minimal posterior incision for a total hip arthroplasty results in significantly more reproducible acetabular component placement.

A prospective, randomized study of preoperative autologous donation for hip replacement surgery

BACKGROUND

Preoperative autologous blood donation is commonly performed to meet potential perioperative transfusion needs and is a common practice prior to total hip arthroplasty. Using standardized transfusion guidelines, we prospectively analyzed the effectiveness of preoperative autologous donation as a method for decreasing allogeneic transfusion among patients undergoing unilateral primary total hip replacement who were eligible to donate autologous blood.

METHODS

Patients who were scheduled for primary total hip replacement surgery and who had a preoperative baseline hemoglobin level >or=120 g/L were randomized either to donate two units of blood (autologous donors) or not to donate any blood (nondonors). The donors and nondonors were compared with regard to demographic data, blood-loss volumes, hemoglobin measurements, and transfusion rates. Randomization continued until data were obtained from at least forty patients per treatment group.

RESULTS

Of the ninety-six patients who completed the study, forty-two were autologous donors and fifty-four were nondonors. There were no significant differences between the donors and nondonors with regard to age, male:female ratio, estimated blood volume, baseline physical condition, or operative blood loss. The hemoglobin values at the time of enrollment (baseline), at the time of hospital discharge, and six weeks postoperatively were not significantly different between the two groups, although values at the time of admission (129 +/- 13 g/L versus 138 +/- 12 g/L) and in the recovery room (104 +/- 12 g/L versus 115 +/- 13 g/L) were significantly lower in the autologous donor group (p < 0.05). No patient in either group required an allogeneic transfusion. Twenty-nine (69%) of the forty-two donors received an autologous transfusion. Thirty-four (41%) of eighty-two autologous units were wasted. At a charge of $379 per autologous unit, there was an additional cost of $758 for each patient in the donor group.

CONCLUSIONS

Preoperative autologous donation provided no benefit for nonanemic patients undergoing primary total hip replacement surgery. Preoperative autologous donation increased the likelihood of autologous transfusion, wastage of predonated units, and costs.

Linezolid treatment for osteomyelitis due to vancomycin-resistant Enterococcus faecium

The incidence of nosocomial infections caused by vancomycin-resistant enterococci has risen substantially during the past 15 years. We report the use of linezolid for the successful treatment of hip prosthesis infection associated with osteomyelitis due to vancomycin-resistant Enterococcus faecium.

Use of helical computed tomography for the assessment of acetabular osteolysis after total hip arthroplasty

BACKGROUND

Acetabular osteolysis is a major problem affecting long-term survival of total hip prostheses. Since lytic lesions may be asymptomatic until extensive bone loss has occurred, early detection of lytic lesions is important. The purposes of this study were to determine the efficacy and potential role of high-resolution helical (or spiral) computed tomography with metal-artifact minimization in the early detection of osteolysis of the pelvis and to use the method to determine if there was a relationship between the extent of osteolysis and the amount of polyethylene wear.

METHODS

Forty patients (fifty hips) who had undergone primary cementless total hip arthroplasty between 1988 and 1994 were evaluated as part of an ongoing prospective study. These patients had a history of high-level activity that was believed to place them at increased risk for accelerated polyethylene wear. The most recent follow-up radiographs were compared with the three-month postoperative radiographs. Helical computed tomography scans with metal-artifact minimization were made, and evidence of osteolytic lesions on these scans was compared with that on the radiographs. Two-dimensional wear analysis was performed with use of digitized radiographs, and the results were compared with loss of bone volume as calculated from the computed tomography scans.

RESULTS

Acetabular lysis was identified on the radiographs of sixteen hips and on the computed tomography scans of twenty-six hips. Radiographs underestimated the extent of the lysis in thirteen of the sixteen hips. There was no correlation (r = 0.036) between linear wear and the measured volume of bone loss, with the numbers available. On the basis of the amount of lysis seen on the computed tomography scans, one patient underwent a revision procedure.

CONCLUSIONS

Helical computed tomography with metal-artifact minimization is more sensitive for identifying and quantifying osteolysis after total hip arthroplasty than is plain radiography. Since computed tomography scans show both the extent and the location of lytic lesions, they are useful to guide treatment decisions as well as to assist in planning for surgical intervention, when needed, in patients with suspected osteolysis.

Effect of initiation chemistry on the fracture toughness, fatigue strength, and residual monomer content of a novel high-viscosity, two-solution acrylic bone cement

Porous-free, two-solution bone cements have been developed in our laboratory as an alternative to commercial powder/liquid formulations. Each pair of solutions consist of poly(methyl methacrylate) (PMMA) powder dissolved in methyl methacrylate (MMA) monomer, with benzoyl peroxide (BPO) added to one solution as the initiator and N,N-dimethyl-p-toluidine (DMPT) added to the other as the activator. When mixed, the solutions polymerize via a free radical reaction, which is governed by the concentrations of initiator and activator and their molar stoichiometry. Previous work by the authors has demonstrated that these two-solution cement compositions are comparable to Simplex P bone cement in polymerization exotherm, setting time, and flexural mechanical properties. This study was designed to evaluate the effect of BPO and DMPT concentrations, along with their molar ratio, on the fracture toughness, fatigue strength, and residual monomer content of the experimental compositions. The results showed that fracture toughness and fatigue strength for the solution cements were comparable to Simplex P and were not significantly affected by the BPO concentration or the BPO:DMPT molar ratio; however, the highest DMPT concentration yielded significantly lower values for both variables. Residual monomer content was significantly affected by both the individual concentrations of BPO and DMPT and their molar ratios. The two-solution cements had significantly higher residual monomer contents versus Simplex P; however, this can be attributed to their higher initial monomer concentration rather than a lower degree of conversion.

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 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.

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.

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.

The rationale, design characteristics, and preliminary results of a primary custom total hip prosthesis

Seventy-three primary custom-made uncemented hip implants have been inserted since July 1987. The initial clinical results are equivalent to those of conventionally made components, but there has been less residual and recurrent thigh pain with the custom devices. The custom implants have achieved 20% greater canal fill with much less variation than conventionally made devices. Custom components have been particularly useful in patients with significant anatomic deformity and associated arthritis.

Cancellous bone material properties in osteoarthritic and rheumatoid total knee patients

One hundred and thirty-four cancellous bone biopsy specimens were taken from the proximal tibias and distal femurs of 55 patients undergoing total knee replacement for analysis of their area fraction and mechanical testing to determine their strength and stiffness. The purpose of the study was to measure the material properties of cancellous bone taken from arthritic patients and compare these with bone from normal subjects. The results showed a wide variation of strength (0.5-18.1 MPa, mean 5.6 MPa) and stiffness (11-504 MPa, mean 152 MPa). These values are in the same range or less than those reported for bone from normal tibias.

Rigidity of initial fixation with uncemented tibial knee implants

This study quantifies the in vitro motion occurring between bone and cemented and noncemented tibial components. Liquid metal strain gauges were used to measure the motion between the tibial component and bone at four locations in eight cadaver tibia at near-point cyclic loads ranging from 10 to 2,000 N. Two types of motion were observed: inducible displacement, which is reversible, followed the oscillating load and occurred in both cemented and uncemented tests, and liftoff or separation of the component and bone, which occurred only for the noncemented cases and remained even after removal of the load. For both motion types, noncemented tests exhibited significant (P less than .05) and dramatic increased interface motion compared to the cemented cases for all load types. The results suggest that the magnitudes of implant-bone interface separation at loads in the low physiologic range for noncemented implants can be sufficiently large to inhibit bony ingrowth into a prosthesis with an average pore size of 300 microns.

Vacuum mixing of acrylic bone cement

A partial-vacuum (500-550 mmHg), slow-speed (2 Hz) system for optimal blending of the liquid and powder components of Simplex-P acrylic bone cement was developed to eliminate five different sources of porosity observed with x-ray during the course of cement preparation and specimen fabrication. The vacuum mixing system produces set specimens of less than 1% porosity that have significant improvements over specimens prepared with conventional mixing in the mechanical properties of tensile and compressive strength and uniaxial tensile fatigue life. Hence, a much stronger cement can be available in surgery without any change in original chemical composition.

The influence of prosthetic stem stiffness and of a calcar collar on stresses in the proximal end of the femur with a cemented femoral component

We used three-dimensional finite-element models of the proximal end of the femur to examine the influence of stem material, stem geometry, and the use of a calcar collar on the stresses in and around implanted total hip-replacement femoral components. Anatomical bone geometries and realistic prosthetic geometries were considered. A slender titanium-alloy stem with a collar allows creation of calcar stresses of approximately 80 per cent of the anticipated normal levels. A similar stem of cobalt-chromium alloy creates calcar stresses of 67 per cent of these normal values. Stem designs without a collar were shown to generate no more than 40 per cent of normal values while larger, stiffer stems were seen to create less than 30 per cent of normal values, with or without a collar. Proximal cement stresses were increased by the use of titanium-alloy stems, but were reduced to low levels by a functioning collar. The highest cement stresses in the system were found near the tip of the stem, where titanium-alloy stems create lower stresses than do corresponding cobalt-chromium-alloy stems. The achievability of calcar loading with a titanium prosthesis was demonstrated in in vitro strain-gauge tests.

CLINICAL RELEVANCE

Loosening of the femoral stem and calcar resorption are problems that are seen in many long-term clinical series of total hip prostheses. In order to reduce the incidence of these problems, the goal of the designer of a prosthesis is to reduce cement and cement interface stresses around the femoral stem and to create stress distributions in the bone that will prevent resorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cement pressure and bone strength on polymethylmethacrylate fixation

The effect of the quality of the bone and of the cement pressurization magnitude and duration on the fixation achieved with polymethylmethacrylate (PMMA) bone cement is studied in vitro. Seventy-one cement-bone interface specimens, prepared under various conditions of pressurization of low-viscosity bone cement, are tested in tension. The load at failure and the maximum cement penetration are measured to assess the fixation achieved, and the quality of the bone is assessed by determining the compressive strength of each of the bone specimens. Statistical analysis of the data indicates that the pressure magnitude is the most influential of the factors considered in the cement penetration behavior and in the development of failure load capacity. The duration of the pressure does not appear to be a significant factor. The cement penetration is a decreasing function of the bone strength, reflecting a decrease in the porosity and an increase in the area fraction. Although not directly measured in these tests, these latter bone properties are indirectly measured by the bone compressive strength. The effect of increasing bone strength on the failure load is nonlinear. The development of adequate failure load capacity is the result of a balance between the cement penetration allowed by the porosity of the bone and the inherent strength of the cancellous bone itself. Weak bone, although adequately penetrated by cement, cannot provide strong fixation. Stronger, denser bone limits cement penetration, but pressurization enhances development of failure load capacity through more complete infusion and interlocking of the cement in the available pore space. The strength of the fixation achievable for any bone is limited by the intrinsic strength of the bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of fat admixture on the strengths of conventional and low-viscosity bone cements

The diametral tensile and compressive strengths of both conventional doughy and low-viscosity (LVC) bone cements were tested with sequential admixtures of up to 50% (by weight) liquified fat. The addition of as little as 5% (by weight) fat caused a significant reduction (p = 0.05) in the strengths of both cements. The LVC appeared to be affected to a greater degree by fat contaminations than did the conventional cement, although the strengths of the LVC were generally equal to or higher than those of the conventional cement. The enhanced effect of fat contamination on the LVC was thought to be due to the more fluid, tacky nature of this material during administration.

Arthrography after total hip arthroplasty: a modified technique used in the diagnosis of pain

The results of plain film radiography and arthrography in diagnosing loosening of a prosthetic component after total hip arthroplasty were correlated with surgical findings in 31 patients who required surgery because of hip pain. The accuracy of arthrography in diagnosing component loosening using 5 ml of contrast material was 51%, and the accuracy of plain radiography was 69%. An accuracy of 92% was achieved using a modified arthrographic technique in which the pressure in the joint was recorded after injection of contrast material and while the patient walked to ensure that it was comparable with the pressure that caused the patient's pain prior to the study. Three per cent of the arthrographic studies using this technique were false negative and 5% were false positive.