Stress analysis of a total hip acetabular component: an FEM study.

A stress analysis of a total hip acetabular component was performed using three-dimensional finite element modeling. The model consisted of 548 four-noded quadrilateral shell elements with 582 nodes. A worst-case support condition was assumed in which bony contact with small areas of the ilium, ischium, and pubis was represented by three-point support. Loads corresponding to the peak pressures developed in the hip when rising from a seated position--the activity contributing most to the fatigue of a prosthesis--were applied to the model. Peak stresses of 490 MPa are predicted around a screw hole in the region of greatest loading; according to the fatigue curve for porous-coated Ti-6Al-4V alloy, this translates into a component life of three years. When the area of bony support for the prosthesis is increased by a factor of 1.5, the fatigue life is more than doubled to seven years. The addition of restraints around the loaded hole to represent the placement of a screw extends the lifetime dramatically to 65 years. Substituting the material properties of cobalt-chromium alloy increases the predicted lifetime of the component to twelve years. We conclude that poor bone support can compromise the service life of titanium alloy acetabular components. Furthermore, we suggest that screw fixation be used to secure the prosthesis in the anterior-superior region if the prosthesis is not well supported by bone in the acetabulum.

Body fat distribution, plasma lipoproteins and the risk of coronary heart disease of male subjects.

Recent studies have related waist to hip ratio (WHR) to the incidence of coronary heart disease (CHD), but the causes underlying this relation are not fully known. The purpose of this study was to determine if waist to hip ratio is associated with the concentration of plasma lipids and apolipoproteins (apoproteins) that predispose individuals to a higher CHD risk. Plasma lipids and apoprotein concentrations were determined in 100 male volunteers, ranging in age from 19-68 yr, and WHR ranging from 0.89-1.09. Significant positive associations were found between WHR, plasma glucose (r = 0.25, P = 0.01), cholesterol (r = 0.21, P = 0.04), LDL cholesterol (r = 0.22, P = 0.03), triglycerides (r = 0.25, P = 0.01) and the ratio of total cholesterol to HDL-cholesterol (r = 0.30, P = 0.002). Negative associations were found between WHR and HDL-cholesterol (r = -0.19, P = 0.05), plasma apoprotein A-I (4 = -0.28, P = 0.005) and the ratio of plasma apoprotein A-I to apoprotein B (r = -0.26, P = 0.01). To determine the extent to which these correlations were independent of age and body fat content, a subsample of 15 pairs matched on age and percent body fat, but differing in WHR was selected from the larger sample. In the group with high WHR (1.06) HDL-cholesterol and apo A-I levels were lower and apo B higher than in the group with low WHR (0.96). Total cholesterol, triglycerides and LDL cholesterol levels in the group with high WHR were also higher but marginally significant statistically. These results show that WHR is associated with plasma lipid and apolipoprotein concentrations that are more predisposing to CHD and that males with male type obesity may be at a higher risk of CHD development than those with female type, regardless of age or degree of obesity.

Cefoxitin antibiotic concentration in bone and synovial fluid.

A single intravenous 2 g dose of cefoxitin, a broad spectrum antibiotic, was administered prophylactically just prior to operation on 60 patients undergoing total joint replacement (30 total hip replacements, 30 total knee replacements). Specimens of blood, bone, and synovial fluid were obtained during the operative procedure and assayed for cefoxitin concentration. Peak serum levels drawn five minutes after completion of antibiotic administration showed an average of 191 mcg/ml. Synovial fluid specimens were obtained an average of 33 minutes following antibiotic administration with a mean cefoxitin concentration of 72 mcg/ml. Bone samples from either the femoral condyle or femur head were taken an average of 65 minutes after the antibiotic was given and showed a mean cefoxitin concentration of 12 mcg/g. Simultaneous serum concentration was 63 mcg/ml. No allergic reactions occurred despite a history of skin rash after penicillin in eight patients. One patient developed deep infection caused by poor healing of the skin over the surgical site, thus leading to infection and involvement of the joint well after prophylaxis ended.

Computerized tomography in assessment of acetabular fractures.

Computerized tomography (CT) can be a useful adjunct to conventional radiography in assessment of acetabular fractures and fracture-dislocations of the hip. Owing to the complex bony architecture of the acetabulum, CT affords better definition of fracture patterns in this region than roentgenography, including special views and tomography. The cross-sectional views of CT offer improved definition of the characteristics of a complex acetabular fracture, including integrity of the weight-bearing dome, congruity of joint surfaces, degree of comminution, size and spatial relationship of fragments, and presence of intra-articular fragments. Computerized reconstruction of sagittal and coronal views at desired levels duplicates polytomography and renders standard tomography unnecessary. Radiation exposure required for a CT examination of the pelvis is equal to or less than that required for a polytomography study. CT can be utilized as a valuable diagnostic aid in the assessment of selected acetabular fractures and fracture-dislocations of the hip, providing often otherwise unobtainable information to the choice of treatment for these difficult injuries.

Cephalothin and cefamandole penetration into bone, synovial fluid, and wound drainage fluid.

UNLABELLED: Concentrations of cephalothin or cefamandole were measured in serum, bone, synovial fluid, and wound drainage fluid in fifty-seven patients undergoing total hip or knee replacement after a two-gram intravenous bolus injection. The concentrations were similar in serum and synovial fluid for both antibiotics; however, in bone and drainage fluid the concentration of cefamandole was higher by a factor of three. Concentrations of the same antibiotic at the hip and knee were not significantly different even though a tourniquet was used for the knee replacement procedures. CLINICAL RELEVANCE: The antibiotics penetrate bone and enter synovial fluid so rapidly that it is unnecessary to administer prophylactic antibiotics prior to the time of surgery.

Frequency of hydronephrosis in Wistar rats.

Kidneys from 1806 Wistar rats were examined grossly for hydronephrosis and ureteral dilation. Hydronephrosis was seen more often on the right side (11%) than the left (0.3%). Overall frequency of hydronephrosis in males (181/1305) was greater than in females (23/501), and the frequency was statistically greater in male rats aged 5,6,8 and 9 weeks than in age-matched females.

Compartment syndrome of the interosseous muscles: early recognition and treatment.

A compartment syndrome of the interosseous muscles can be a challenging diagnosis as there is generally no neurovascular compromise to the digits involved. The most sensitive clinical sign is pain with passive motion at the metacarpal phalangeal joint of the involved digit. In this report, a 31-year-old man developed a compartment syndrome of the first, second, and third dorsal interosseous muscles following an injection of heroin in the "snuffbox" area. Compartmental tissue pressure measurements were 80, 75, and 55 mmHg respectively, and were a significant aid in the early diagnosis as well as management.

Cefazolin concentrations in bone and synovial fluid.

A single intravenous dose of one gram of cefazolin was administered prophylactically to forty-eight patients undergoing total joint replacement. The serum half-life of the antibiotic was 1.8 hours, the same value found in normal volunteers. The mean concentration in bone during surgery was 5.7 micrograms per gram of bone. The mean concentration in synovial fluid during surgery was 24.4 micrograms per milliliter of fluid.

Total hip arthroplasty in the cardiac transplant patient.

Osteonecrosis of the femoral head following cardiac transplantation has led to bilateral total hip arthroplasties in 2 patients. The clinical course and rejections of these patients are outlined. The pathological changes in the femoral heads suggested that the process leading to osteonecrosis in the cardiac transplant patient is the same as that following renal transplantation, both being due to immunosuppression probably related to steroid dosage. Successful joint replacement can be carried out in the cardiac transplant with careful monitoring of anesthesia. Both patients have done well, being followed for 14 and 6 months respectively.

ASA-dipyridamole prophylaxis in elective total hip replacement.

A prospective, double-blind clinical study was performed to evaluate the combination of dipyridamole 225 mg/day and acetylsalicylic acid 1 gm/day prophylaxis of postoperative venous thromboembolism in elective total hip replacement. Patients were stratified according to age, and randomly assigned to receive drug or placebo. All patients were followed with 125I-labeled fibrinogen scanning for one week postoperatively, or until fully mobile. Venography was performed in 79/132 patients; in 36 patients the venogram was obtained to confirm a positive fibrinogen scan, in 43 patients an elective venogram was obtained on the seventh postoperative day to evaluate the operated thigh (a blind area for scanning). Thrombosis (by scan or venogram) was found in 17/68 (25%) in the control group, and in 23/64 (36%) in the treated group. Overall incidence was 40/132 (30%). Correlation of scan with venography was 90%. There were no clinically significant pulmonary emboli in either group. The combination of acetylsalicylic acid (ASA) and dipyridamole as given in this study is not effective prophylaxis in elective total hip replacement.

The dashboard knee injury.

An in-depth study of 74 motor vehicle accidents involving 222 people revealed that 57 of the 153 people injured sustained 69 knee injuries from contact with the instrument panel. There were 51 mild, 10 moderate, and 8 severe knee injuries. Low force contact caused bruising, and more serious injuries occurred when a greater magnitude of force was applied. Injury was most severe when this force was concentrated in a small area and caused lacerations, fractured patella, and open wounds of the joint. Legs trapped under the dashboard with simultaneous rotational, varus, valgus, or frontal forces by the inertial motion of the body produced serious injuries similar to those recieved in sports. Degenerative arthritis was more likely to occur in the seriously injured knees, but generally was not predictable. Long-term disability might be mitigated by early diagnosis and treatment of the specific injury.

Salvage of infected total joint replacements.

Among 424 total joint replacement (362 hip and 62 knee replacements) since 1971, eight deep infections have occurred (two primary and six late) in six patients. Removal of the prosthesis has been necessary in only one patient to date. Our follow-up experience, extending over a maximum period of 20 months, indicates that successful salvage of infected total joint arthroplasties without bone involvement may be accomplished without removal of the prosthesis if there is adequate surgical debridement and proper antibiotic therapy.

Selective arterial embolization for hemorrhage following hip arthroplasty.

A case is presented in which selective embolization of gelfoam was used to control late postoperative bleeding, developing in a patient following hip arthroplasty. Although primarily used in gastrointestinal bleeding, diagnostic and therapeutic angiography, selective embolization is clearly applicable to postoperative bleeding encountered in orthopedics.

The current status of hip replacement.

Total hip arthroplasty, since the release of methylmethacrylate, is being performed in this country at the rate of about 15,000 per year. For the older patient, virtual absence of pain, improved function, and a short-term rehabilitative effort, make total hip arthroplasty the procedure of choice in the treatment of severe noninfected hip disease. For other patients, successful salvage of previously failed hip surgeries is now possible. Finally, there are those younger patients for whom no other form of therapy is possible to provide pain-free function. Although not a panacea for all hip disease, the total hip arthroplasty has provided pain-free existence with improved function and a return to a useful life for patients with previously inoperable hip disease, no matter what the etiology.