Differences in the surface composition of seemingly similar F75 cobalt-chromium micron-sized particulates can affect synovial fibroblast viability.

We present data and analyses concerning the cytotoxicity and bioreactivity associated with the surface composition of fine metal particulates that are similar to those commonly released in the body by prostheses used in total joint replacement surgery. Here we study the bulk and surface compositions of three separately procured cobalt-chromium-molybdenum (CoCrMo) micron-sized particulate powders, each identified by their corresponding vendor as being ASTM F75 grade material. We use energy dispersive spectroscopy (EDS) to verify the bulk metallic composition and X-ray photoelectron spectroscopy (XPS) to examine the surface metallic composition of each CoCrMo powder. Cultured synovial fibroblasts were then exposed to the particulate powders to see how the metallic surfaces might affect cellular viability. Results indicate that while the bulk metallic composition of each CoCrMo powder was similar, the surface metallic compositions were found to be dramatically different and yielded equally dramatic differences in terms of cytotoxicity and bioreactivity of synovial fibroblast in culture.

Dietary aluminium and renal failure in the koala (Phascolarctos cinereus).

The study investigated the link between the potentially nephrotoxic levels of aluminium ingested in the natural diet of eucalypt leaves by koalas in the Adelaide Hills, South Australia, and the high incidence of renal failure in koalas within this habitat. Routine histology of kidney specimens revealed no pathologies at the light microscopic level and contrasted sharply with the clinical signs of renal failure. However staining with solochrome azurine and Perl's Prussian blue showed aluminium was present in some proximal convoluted tubules in all specimens. Aluminium was also found in bone samples. The presence of aluminium in bone and kidney tissues was confirmed using electron dispersive x-ray analysis with transmission and scanning electron microscopy. Ultrastructural changes, including a decrease in lysosomal numbers, were seen in proximal convoluted tubules and these changes were shown to coincide with the presence of aluminium. No aluminium was found in koalas that died from causes other than renal failure. It was concluded that renal failure in the koalas of the Adelaide Hills is characterised by the presence of aluminium in the kidneys and bone and it is probably related to the high levels of aluminium in their restricted diet of eucalypt leaves. However, it is not known if the presence of aluminium is the cause or effect of the renal failure. The study is the first account where aluminium ingested as part of the natural diet of mammals has been shown to accumulate in the animal and be implicated with nephrotoxicity.

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)

A comparative evaluation of tibial component designs of total knee prostheses.

UNLABELLED: Three-dimensional finite-element stress analyses were used to compare the fixation of tibial component configurations of surface-replacement-type total knee prostheses, bases on the stresses in the cancellous bone, in the polymethylmethacrylate, and at the bone cement-bone interface. The results indicate that, in general, metal components provide lower system stresses than polyethylene components, particularly in the methacrylate and the cancellous bone, and that one-piece designs give lower bone cement-bone interface stresses compared with those with separated condylar components. Of the designs considered, a single-post, metal-backed design provided the lowest system stresses over-all. CLINICAL RELEVANCE: a great and confusing variety of tibial component design exists today, with more in the process of development. Short of long term clinical trials, there are few objective methods by which these designs can be evaluated and long-term performance predicted. There is evidence from clinical results that excessively high stresses in the systems can lead to loosening of the tibial component. The finite-element method provides a method for comparing prosthetic designs using system stresses a s a design criterion. On this basis, we analyzed the stress distribution for several types of tibial components and discuss the advantages and disadvantages of their designs.

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.

UNLABELLED: 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)

An in vitro simulation study of impulsive force transmission along the lower skeletal extremity.

Several investigators have revealed that a relationship exists between articular cartilage deterioration and the mechanical stress that results from transient impulsive forces created in the lower extremity during gait. This study is an investigation of the transmission of impulse waves through the lower extremity and the effect of knee pathology and prosthetic knee replacement on their transmission. An in vitro experiment is performed using human cadaver specimens that are instrumented with accelerometers. The distal end of the tibia is impacted with a vibration shaker to simulate heel strike. The results indicate that the normal knee joint is able to attenuate 59% of the transient peak force applied to it by the tibia. This attenuation capacity is reduced by knee pathology and decreases further with implantation of a knee prosthesis. The results indicate that abnormalities at the knee may increase the risk of degenerative changes at the ankle, hip and in the spine due to increased transient impulsive forces.

Myoelectric activity and sequencing of selected trunk muscles during isokinetic lifting.

Trained weight lifters lift heavy loads without a concomitant degree of acute low-back injuries. To study the process by which large loads are lifted with minimal injury, integrated electromyographic signals were recorded from four large muscle groups: gluteus maximus, quadriceps, latissimus dorsi, and erector spinae in 4 weight lifters and 11 asymptomatic control subjects. These signals were recorded during a floor-to-knuckle-height isokinetic lift (dead lift) at 30.5 and 45.7 cm/sec. The signals were normalized for the height of the lift and the maximal isokinetic integrated electromyographic activity. The weight lifters achieved maximal force at 50% of maximal lift height, whereas the control subjects achieved it at 67%. Although not statistically significant, the weight lifters used the gluteus maximus more during the early stages of the lift, perhaps contributing to earlier development of force. This process would stabilize the pelvis and permit the erector spinae to extend the trunk more efficiently. The weight lifter then completed the lift with prolonged and increasing activity in the quadriceps. This technique may minimize the required force in the erector spinae and the forces on the low-back structures. Clinical implications include more effective strength training of lifting muscle groups other than spinal extensors and the teaching of lifting strategies employed by weight lifters in low-back rehabilitation and work-hardening programs.

In vitro comparison of over-the-top and through-the-condyle anterior cruciate ligament reconstructions.

Knee kinematics, during standard knee examination maneuvers, were measured on 15 fresh cadaveric knees in their normal state and after isolated sectioning of the anterior cruciate ligament using a six degree of freedom electrogoniometer. Proximal iliotibial band autografts were used to perform two anterior cruciate ligament reconstructions on the cadaveric knees: an over-the-top reconstruction and a through-the-condyle procedure. Both of these reconstructions reduced the abnormal anterior translation of the anterior cruciate ligament-deficient knee seen in Lachman testing. However, neither reconstruction restored the normal anterior translation. In addition, other motions remained uncorrected: 1) the internal rotation due to internal torque at full extension; 2) coupled anterior translation during internal rotation at full extension; and 3) coupled medial translation with anterior translation in Lachman testing. There were no statistical differences noted in the joint kinematics created by either reconstruction.

Kinematic in-vitro comparison between the normal knee and two techniques for reconstruction of the anterior cruciate ligament.

The influence of anterior cruciate ligament sectioning and the results of its reconstruction on joint kinematics were studied using eight cadaver knees and a computerized system for analysis of three-dimensional motions. A Dacron(®) prosthesis was used in a transcondylar isometric drill-guide-determined route, and in an over-the-top route. After sectioning of the anterior cruciate ligament, the tibial motion increased in several passive laxity tests including anterior/posterior translation as well as varus/valgus and internal/external rotation. Increased valgus rotation was also seen during a simulated active extension manoeuvre. The effect of anterior cruciate ligament reconstruction was seen only on anterior/posterior translation, where the drill-guide technique restored, and the over-the-top technique partially restored, normal sagittal play at 90° of knee flexion. At 30° of knee flexion both methods reduced, but did not normalize, anterior/posterior translation. An adverse effect of both techniques, more prominent with the drill-guide technique which involved an extensive notchplasty, was abnormal external tibia[ rotation in 90° of knee flexion with the tibia in a gravity-determined position. Both techniques resulted in less than normal external rotation in the screw-home mechanism.

A technique for quantitative assessment of three-dimensional motion with applications to human joints.

A technique is developed for quantitative measurement of general three-dimensional motion, and this technique is applied to the kinematics of anatomical joints. The spatial locations of three orthogonal points representing coordinate frames on each member of the joint are measured during motion of the joint by photo encoders of a three-dimensional mechanical pointer. Kinematic calculations are used to derive, from the experimentally collected data, the six orthogonal components of the motion of one member relative to the other. The accuracy of this technique is presented. Applications to the knee and ankle are discussed.

A comparison of the effects of prosthetic and commercially pure metals on retrieved human fibroblasts: the role of surface elemental composition.

The most common clinical cause of long-term failure in total joint replacement surgery is inflammatory aseptic osteolysis; a condition in which bone surrounding the prosthetic implant, and to which the implant is attached, is resorbed, rendering the artificial device loose and painful. Historically, the severity of this bone resorptive process has been thought to be predominately attributed to the size and shape of wear-debris particles, particularly the metallic particulates that interact biologically/immunologically with cells in the joint. Because the cytotoxic reactions are the result of interactions between the cells and the surfaces of the particulates, it is not clear in the realm of orthopedics to what extent different surface stoichiometric ratios contribute to instigating bioreactive or cytotoxic cellular responses that can lead to aseptic osteolysis. Using energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), this study presents data and analyses concerning the respective bulk and surface stoichiometric ratios of two commercially pure metal micro-particulates (tantalum and titanium), two prosthetic F75 cobalt-chromium-molybdenum alloy micro-particulates, and prosthetic F136 titanium-aluminum-vanadium alloy micro-particulates, each containing elements common to total joint replacement surgery. Cell culture viability data from four volunteer donors are also presented, which suggest that micro-particulates containing large percentages of surface titanium and aluminum can cause moderate cellular toxicity, and micro-particulates containing large percentages of surface cobalt can result in extremely severe cellular toxicity. This work further suggests that surface analysis techniques, such as XPS, are essential to determine surface elemental characterization of metallic materials prior to interpreting cellular response results.

Analysis of model variables and fixation post length effects on stresses around a prosthesis in the proximal tibia.

A two-dimensional, finite element model of a single-posted, metal, tibial prosthetic component implanted with PMMA in the proximal tibia is developed. The effects upon the stresses at the PMMA-bone interface and in the cancellous bone around the component due to the inclusion in the model of the cortical shell and the heterogeneity and anisotropy of the cancellous bone, are demonstrated. Various lengths of the fixation post are considered. The cortical shell adds support and stiffness to the bone structure, and allows generation of significant stresses proximally. The heterogeneity of the cancellous bone, as assumed here, dictates the form of the stress distributions and the magnitudes and locations of the peak stress values around the post of the component. Peak stress values can occur at locations proximal to the post tip. The anisotrophy of the cancellous bone significantly alters the magnitudes of the stresses. Lower stresses along the post interface and higher stresses beneath the plate of the prosthesis are seen in the anisotropic models. Lengthening of the fixation post reduces stresses proximally, but the effects of post lengthening upon the maximum stress values around the post are highly dependent upon the assumed properties of the cancellous bone.

Polyisobutylene-toughened poly(methyl methacrylate): III. PMMA-l-PIB networks as bone cements.

A series of novel polyisobutylene (PIB)-toughened poly(methyl methacrylate) (PMMA) networks consist of rubbery PIB domains covalently bonded to a glassy PMMA matrix. Materials containing 8.5-17 wt.% PIB (Mn = 18,000 g/mol) in a PMMA matrix (PIB/PMMA) were evaluated to assess their feasibility as the powder component along with methyl methacrylate (MMA) as the liquid component in a standard powder/liquid bone cement formulation. A standard ISO four-point bend test, commonly used for testing bone cements, was employed to investigate flexural properties. The mixing time and powder/liquid (P/L) ratio were studied to formulate novel PIB/PMMA cements for optimum toughness. Appropriate formulations led to improved toughness while adequate flexural strength and modulus were maintained. An experimental PIB/PMMA-system exhibited approximately 57 MPa flexural strength and approximately 2000 MPa flexural modulus.

Fracture of a fenestrated metal backing of a tibial knee component. A case report.

The case of a metal-backed tibial component that failed by metal fracture is reported. Fracture occurred through fenestrations in the metal plate surrounding the central metal stem. The fracture followed loss of bony support beneath the medial tibial plateau, which had allowed varus deformity of the replaced joint. A high tibial osteotomy procedure had preceded replacement of the joint.

Alkyl cyanoacrylates as space filling bone adhesives.

Higher chained alkyl cyanoacrylates have potential to function efficiently as space filling, hydrophobic, viscoelastic, biocompatible, and rapidly polymerizing bone adhesives. Hence they may be useful in applications where a void has to be filled, such as replacement of the intervertebral disc. To assess their applicability as space filling material in such an application, three alkyl cyanoacrylates; methoxyethyl cyanoacrylate, isobutyl cyanoacrylate, and isoamyl cyanoacrylate have been evaluated in this study. The bonding strength of these cyanoacrylates to bone in a space filling situation have been measured. The results indicate the bond strength of isoamyl cyanoacrylate (0.13 MPa) to be significantly (p less than 0.05) lower compared with methoxyethyl cyanoacrylate (0.33 MPa) and isobutyl cyanoacrylate (0.37 MPa). There was no significant difference in the bond strengths of isobutyl cyanoacrylate and methoxyethyl cyanoacrylate.

Accuracy assessment of a technique for contact point determination from planar radiographs.

The purpose of this study was to determine the accuracy, precision and repeatability of a simple radiographic method which might be used in in-vivo determination of joint contact points following total joint replacement (TKA). A model of a TKA was constructed from which the anterior/posterior location of the contact point could be mathematically calculated. A radiograph was taken of the model and two observers repeatedly determined the contact point using a parallel rule. The measured locations were compared to the calculated values. The accuracy and precision of the measurement locations in comparison to the calculated values were 1.6 mm and 0.4 mm, respectively. The mean inter-observer error was 0.2 mm.

Evaluation of the preovulatory rise of follicle stimulating hormone and progesterone in normally ovulating women of reproductive age.

Sixteen normally ovulating women of reproductive age were evaluated to determine the extent of the preovulatory FSH and progesterone rise in association with the LH surge. Highly significant differences were demonstrated between the baseline and peak preovulatory levels of both FSH and progesterone (P less than .0005). These significant peak ovulatory differences of FSH and progesterone were associated with a 2.5-fold rise (mean difference of 9.06 mIU/mL) of FSH and a 3.0-fold rise (mean difference of 1.94 ng/mL) of progesterone. These small, yet very significant, preovulatory increments of FSH and progesterone are important in the ovulatory process and the formation of an adequate corpus luteum.

Computational stress analysis of cup replacement hip arthroplasty.

A two-dimensional finite element model of a total surface replacement hip arthroplasty was utilized to study the performance characteristics of the prosthesis by means of stress analysis. No significant changes occur in stress field distribution following resurfacing arthroplasty in the proximal femur. Local bending phenomena appear to occur in the femoral component under static loading. Prosthesis-cortical bone continuity at the femoral neck does not affect stress field distribution. Finally, trochanteric osteotomy causes a change in the stress field distribution of the proximal femur that may be a significant factor in femoral neck fracture.