Edward Ebramzadeh

The cement mantle in total hip arthroplasty. Analysis of long-term radiographic results.

The correlation between the thickness of the cement mantle, the medullary canal fill, and the orientation of the stem and the long-term radiographic outcome of 836 cemented femoral components in patients who had a primary total hip replacement was assessed with use of survival analysis over a twenty-one-year follow-up period. The femoral stems of hips that had a two to five-millimeter-thick cement mantle in the proximal medial region had a better outcome than stems implanted with a thicker or thinner cement mantle. Stems in femora with less than two millimeters of proximal medial cancellous bone had a better outcome than stems in femora with thicker cancellous bone. Stems that filled more than half of the medullary canal had better radiographic results than those that filled half or less. Progressive loosening, fracture of the cement, and radiolucent lines at the stem-cement or bone-cement interfaces were more likely to develop in stems that were oriented in more than 5 degrees of varus than in those in neutral or valgus. The noted correlations were true whether the stem was made of titanium alloy or of stainless steel. The results of this study emphasize the importance of careful preoperative planning in total hip arthroplasty done with cement and provide guidelines for the selection of the shape, size, and position of the stem.

Total hip arthroplasty with cement. A long-term radiographic analysis in patients who are older than fifty and younger than fifty years.

The long-term performance of a total of 712 Charnley and STH prostheses was evaluated as a function of the patients age (older than fifty years or younger than fifty years) and of the underlying disease (osteoarthrosis, rheumatoid arthritis, or avascular necrosis). In patients who were older than fifty years, there were lower incidences of continuous cement-bone radiolucency about the acetabular component (p = 0.04), wear of the polyethylene acetabular cup (p = 0.03), and resorption of the calcar (p = 0.03). However, larger percentages of younger patients had rheumatoid arthritis or avascular necrosis. In the cohort of patients who had osteoarthrosis, the performance of the prosthesis did not differ significantly between older and younger patients; therefore we attributed the differences that were observed to the disease--that is, to rheumatoid arthritis or avascular necrosis.

In vivo wear of titanium-alloy hip prostheses.

We examined samples of tissue and components that had been removed during twenty revisions of total hip arthroplasties in which a titanium-alloy femoral component had been used. Minute amounts of metallic debris were detected in the tissues from two patients. The amounts of polyethylene and methylmethacrylate debris and the histological reactions in the tissues corresponded closely with those reported in earlier studies of total hip prostheses made of stainless steel or cobalt-chromium alloy.

Lessons learned from loosening of the McKee-Farrar metal-on-metal total hip replacement

Clinical and radiographic data for 15 McKee-Farrar hip replacements that had failed because of aseptic loosening (4 stem loosening, 9 cup loosening, and 2 loosening of both components) between 0.6 and 21 years (average, 8.3 years) were compared with 15 hips in which the McKee-Farrar total hip replacement has survived between 21 and 26 years. Hips that loosened were biomechanically disadvantaged compared with those that demonstrated long-term survival. Radiographic evaluation demonstrated that in hips that were revised for aseptic femoral loosening, the offset was decreased by a mean of 1.4, whereas it was increased by a mean of 4.9 mm in the surviving hips (P = .04). Further, in hips revised for aseptic loosening, the center of rotation was medialized by a mean of only 1.4 mm, whereas the center of rotation was medialized by a mean of 6.4 mm in the surviving hips (P = .1). Unfavorable biomechanics results in increased joint reaction forces that could contribute to loosening of these prostheses. Five of 6 McKee-Farrar stems revised for aseptic loosening compared with 7 of 15 surviving stems were in varus (P = .1) and, as a result, had cement mantle defects in zones III and VII. Thus, in the McKee-Farrar, similar to what has been seen in hips with metal-on-plastic bearings, curved stems are associated with varus positioning, cement mantle defects, and loosening. Wear of the metal-on-metal articulation does not appear to be the cause of failure in these cases. Wear could not be detected radiographically. At revision surgery, there was no indication of excessive bearing wear or gross metal staining of periprosthetic tissues. Microscopic analysis of tissue sections demonstrated both metal and polymethylmethacrylate particles of variable size and shape. The variability of the particles suggests that they are likely the result of loosening and that they were not generated by bearing surface wear that could cause loosening. Although it is hoped that improvements in the wear resistance of the bearing will increase survivorship, this experience and analysis of the McKee-Farrar total hip replacement illustrates the importance of the implant design, biomechanics of the reconstruction, and role of surgical implantation technique.

Cup containment and orientation in cemented total hip arthroplasties

We reviewed the radiographs of 864 Charnley and STH (Zimmer) cemented total hip arthroplasties with a mean follow-up of seven years (maximum 16 years). Survivorship analysis was used to assess the correlation between radiographic performance and the bony containment or the coronal orientation of the acetabular cup. The cup orientation and containment were interrelated; all vertically oriented cups were completely contained, whereas 25% of more horizontal cups were only partially contained. Completely contained cups had significantly lower incidences of complete cement-bone radiolucency (p = 0.02) and of wear (p = 0.09). Vertically oriented cups had a lower incidence of continuous radiolucency than neutrally oriented cups, but this was not statistically significant (p = 0.25). Our results confirm the importance of complete bony containment, and also indicate that it is better to accept vertical orientation and obtain full bony coverage than to have a more horizontal orientation with partial containment.

Control of motion of tibial fractures with use of a functional brace or an external fixator. A study of cadavera with use of a magnetic motion sensor.

A computer-linked magnetic motion transducer was used to monitor and record the six components of motion of the bone fragments in eight cadaveric tibiae in which a simulated, oblique fracture of the middle of the shaft had been stabilized with a functional brace. The limbs were mounted in a servo-hydraulic testing frame, and a cyclic load of 150 newtons was applied along the axis of the tibia. Motion sensors, attached to each side of the fracture, measured and displayed the values of the three translations (axial, anterior-posterior, and medial-lateral), the axial rotation, and the two angulations (anterior-posterior and varus-valgus) as they occurred. Although only an axial load was applied, the off-axis motions were comparable in magnitude with the motion along the axis. The elastic (recoverable) translations of the fragments ranged from 0.5 to 1.9 millimeters, about four to ten times larger than the corresponding motions that were recorded in an earlier study of such fractures that had been stabilized with two types of external fixators. The recoverable rotation and angulations of the fragments of the limbs in the functional brace ranged from 0.7 to 1.2 degrees, about ten times those recorded when the external fixators were used.

Total hip replacement after failed hemiarthroplasty or mould arthroplasty. Comparison of results with those of primary replacements

We compared the radiographic results of secondary total hip replacements, 99 following failed uncemented hemiarthroplasties and 21 following failed mould arthroplasties, with those of 825 primary cemented total hip replacements. The probability of occurrence of a number of radiological changes over time was calculated using survival analysis. The mean follow-up was 7.6 years (range one month to 20 years). The performance of the secondary total hip replacements varied with the preceding implant and was different for acetabular and femoral components. The incidence of radiological loosening was higher for femoral components implanted after failed hemiarthroplasties and for acetabular components after failed mould arthroplasties. However, the incidence of continuous radiolucent lines was lower for the acetabular components of converted hemiarthroplasties than for the primary replacements.

The Influence of the Acromioclavicular Joint Degeneration on Supraspinatus Outlet Impingement and the Acromion Shape

Purpose. To assess the anatomic association of acromioclavicular joint degeneration to supraspinatus outlet impingement and the acromion shape. Methods. Sagittal oblique magnetic resonance images of 49 shoulders in 49 patients were reviewed. 29 of them (mean age, 59 years) underwent surgery for impingement with or without rotator cuff tear (group 1), whereas the 20 controls (mean age, 27 years) were treated for shoulder instability without rotator cuff disease or acromioclavicular joint derangement (group 2). The supraspinatus outlet and the acromion shape of the 2 groups were compared. Results. The difference in the mean supraspinatus outlet between groups 1 and 2 was 11% (514 vs 577 mm2, p=0.095) and between the subgroup (of group 1) with full thickness rotator cuff tears and group 2 was 17% (481 vs 577 mm2, p=0.036). Six of the acromions in group 1 were type III (hooked) compared to none in group 2. Conclusion. In severe acromioclavicular degeneration, distal clavicular excision is recommended, even in cases with an asymptomatic acromioclavicular joint, so as to prevent further osteophyte formation.

Wear of Titanium 6–4 Alloy in Laboratory Tests and in Retrieved Human Joint Replacements

During the period from 1975 to 1985, a variety of joint replacement prostheses were introduced clinically that included a bearing surface of titanium-6% alumi-num-4% vanadium alloy (Ti-6A1-4V) articulating against an acetabular component of ultra-high molecular weight (UHMW) polyethylene. Hip prostheses included the STH, the DF-80, the Six Ti-28 and the Six Ti-32 (Zimmer, Inc. Warsaw, IN), the Stanmore (Zimmer GB), the ES-30 (Biomet, Inc., Warsaw, IN) and the APR (Intermedics, Inc., Austin, TX). Titanium alloy knee prostheses included the Miller/Galante (Zimmer) and the Natural Knee (Intermedics). The suitability of this combination of bearing materials was initially questioned because, in some laboratory wear tests, titanium alloy underwent severe abrasive-corrosive wear, characterized by extensive scoring of the metal surface and the release of large amounts of finely divided metallic particles that blackened the opposing polymer and the lubricant [1-8].

Skeletal muscle contractions uncoupled from gravitational loading directly increase cortical bone blood flow rates in vivo

The direct and indirect effects of muscle contraction on bone microcirculation and fluid flow are neither well documented nor explained. However, skeletal muscle contractions may affect the acquisition and maintenance of bone via stimulation of bone circulatory and interstitial fluid flow parameters. The purposes of this study were to assess the effects of transcutaneous electrical neuromuscular stimulation (TENS)‐induced muscle contractions on cortical bone blood flow and bone mineral content, and to demonstrate that alterations in blood flow could occur independently of mechanical loading and systemic circulatory mechanisms. Bone chamber implants were used in a rabbit model to observe real‐time blood flow rates and TENS‐induced muscle contractions. Video recording of fluorescent microspheres injected into the blood circulation was used to calculate changes in cortical blood flow rates. TENS‐induced repetitive muscle contractions uncoupled from mechanical loading instantaneously increased cortical microcirculatory flow, directly increased bone blood flow rates by 130%, and significantly increased bone mineral content over 7 weeks. Heart rates and blood pressure did not significantly increase due to TENS treatment. Our findings suggest that muscle contraction therapies have potential clinical applications for improving blood flow to cortical bone in the appendicular skeleton.