Harry A. McKellop

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.

Functional range of motion of the joints of the hand

Active ranges of motion of the joints of the hand are well documented, but there is little data reporting the functional ranges of motion required to perform activities of daily living. Electrogoniometric and standard methods were used to measure both active and functional ranges of motion of the metacarpalphalangeal and interphalangeal joints during 11 activities of daily living. In the fingers, only a small percentage of the active range of motion of the joints was required for functional tasks. Functional flexion postures averaged 61 degrees at the metacarpalphalangeal joint, 60 degrees at the proximal interphalangeal joint, and 39 degrees at the distal interphalangeal joint. In the thumb, functional flexion postures averaged 21 degrees at the metacarpalphalangeal joint and 18 degrees at the interphalangeal joint using only 32% of the available flexion. Active thumb metacarpalphalangeal joint motion was found to be bimodal in the study group.

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.

Effect of protein lubrication on the wear properties of materials for prosthetic joints.

The effects of pre-dilution and other modifications of bovine serum lubricants on the wear properties of UHMW polyethylene acetabular cups were evaluated in a hip joint simulator. The wear rate increased, and a nonphysiological type of surface-pitting occurred, when the serum was pre-diluted to 40% or lower concentration. During the wear test, the equilibrium temperature and the precipitation of proteins were substantially greater with zirconia balls than with cobalt-chromium. Protein precipitation, a potential modulator of in vitro wear, was shown to be temperature, concentration, and time-dependent in water-bath tests, which indicated that ball-cup interface temperatures in the simulator must be above 60 degrees C, i.e., well above the bulk lubricant temperature, to account for wear test protein precipitation. Several modifications of serum that were, in part, intended to decrease the tendency for protein precipitation were found to markedly affect the wear properties of the two combinations of materials. In particular, modified serum, which lacked some of the higher molecular weight proteins, produced a much higher wear rate than a control serum with the same initial protein concentration. The results indicated directions for further research to clarify the lubricating properties of serum, and for developing a universal standard test lubricant.

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.

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.

The effect of simulated fracture-angulations of the tibia on cartilage pressures in the knee joint.

The effects of angular deformities of the tibia on the contact areas and pressures on cartilage in the knee were measured with use of pressure-sensitive film. Six cadaver knees were mounted in a test-frame, such that the offset and tilt of the knee relative to the load-axis simulated that due to angular deformities of the tibia of 5, 10, 15, or 20 degrees of varus or valgus at the levels of the proximal, middle, and distal thirds. Angulation had little effect on the contact area. The change in pressure was least for fractures of the distal third and greatest for fractures of the proximal third. For example, a 20-degree angulation of the distal third increased the maximum contact pressure by an average of 26 per cent in the compartment toward the load-axis and reduced it by 32 per cent in the opposite compartment. With an angulation of 20 degrees at the level of the proximal third of the tibia, the increase in pressure averaged 106 per cent and the decrease averaged 89 per cent. The changes in pressure with fractures at the middle third were between these extremes.

Irradiation of chemically crosslinked ultrahigh molecular weight polyethylene

Acetabular cups for artificial hip joints were prepared by compression molding of ultrahigh molecular weight polyethylene in the presence of peroxide. Peroxide crosslinking led to a decrease in the degree of crystallinity, peak melting temperature, and recrystallization temperature, as well as decreased crystal perfection and size. Peroxide crosslinked cups were sterilized with gamma rays at room temperature in air atmosphere to an average dose of 3.4 Mrad. Irradiation produced further crosslinking in amorphous regions plus extensive chain scission of taut tie molecules and led to increased crystallinity and crystal perfection. A significant increase in carbonyl concentration was determined for irradiated specimens. In general, peroxide crosslinking reduces the effect of irradiation on the crosslinked network, because chemical crosslinking stabilizes chain fragments resulting from radiolytic scission and suppresses recrystallization of broken chains from amorphous regions. Wear rates were much lower for chemically crosslinked cups, which showed about one-fifth of the wear of control cups for the period from 0.5 to 1.0 million cycles.

Profile of oxidation in irradiated polyethylene

Following gamma irradiation in air which causes bond scission and yields large concentrations of peroxy radicals, maximum oxidation and an increase in crystallinity occurs on the surface of ultrahigh molecular weight polyethylene. Here, bimolecular reactions of peroxy radicals generate carbonyls, mostly ketones. On the polymer surface, peroxy radicals continue to react over time periods of years to generate carbonyls and chain scission. Peroxy radicals in the interior of the polymer abstract hydrogens and form hydroperoxides, inducing chain reactions and a slow but continue increase of ketone. Within the polymer sample, to a decreasing depth with increasing dose, a reduced concentration of oxygen is available to react with radiolytic radicals, so that more efficient crosslinking and a low level of hydroperoxide chain reaction occur. After long periods of time a surface maximum in carbonyl concentration is produced. Heating polyethylene in high pressures of oxygen accelerates the oxidative process.

A biomechanical evaluation of a cannulated compressive screw for use in fractures of the scaphoid

The compressive force generated by a 3.5 mm ASIF cannulated cancellous screw with a 5 mm head was compared with that generated by a standard 3.5 mm ASIF screw (6 mm head), a 2.7 mm ASIF screw (5 mm head), and a Herbert screw. The screws were evaluated in the laboratory with the use of a custom-designed load washer (transducer) to the maximum compressive force generated by each screw until failure, either by thread stripping or by head migration into the specimen. Testing was done on paired cadaver scaphoids. To minimize the variability that occurs with human bone, and because of the cost and difficulty of obtaining human tissue specimens, a study was also done on polyurethane foam simulated bones. The 3.5 cannulated screw generated greater compressive forces than the Herbert screw but less compression than the 2.7 mm and 3.5 mm ASIF cortical screws. The 3.5 mm cannulated screw offers more rigid internal fixation for scaphoid fractures than the Herbert screw and gives the added advantage of placement over a guide wire.