bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission of the Load in the Knee Joint with Special Reference to the Role of the Menisci
Authors: Seedhom B B
Published: February 2007

The menisci of the knee joint transmit a considerable fraction of the total load acting on the joint. This paper describes an investigation into the load carrying capacity of the individual meniscus. Interest is also directed to an examination of the function of the degenerate meniscus and that of the meniscus with different kinds of tears. Quantifying the meniscal loads is based on a four-spring model representing the load bearing areas in the knee with intact menisci. The assumptions underlying the model are discussed and the problems of loading associated with the four-spring model are described. These problems called for careful consideration of the methods of loading and aligning the joint. A loading machine with a special aligning device was built for the experimental work.

The experimental procedure is described in Part II. The intact individual meniscus was shown to transmit 70-99 per cent of the load acting on the respective side. The load carrying capacity of the meniscus was shown to decrease following the removal of a simulated ‘bucket-handle’ tear but in some cases it remained virtually unaltered. The stresses in the knee with redundant menisci were shown to increase by three to five fold their magnitude in the knee with intact menisci. Following removal of a simulated bucket-handle' tear, the stresses increased, but much less dramatically. The clinical implications of total and partial meniscectomy are discussed.
Hydrophilic Polyurethane Elastomers for Hemiarthroplasty: A Preliminary in Vitro Wear Study
Authors: Medley J B , Pilliar R M , Wong E W , Strong A B
Published: February 2007

Polyurethane surface layers with visco-elastic properties similar to natural articular cartilage are proposed for use with single component joint replacement prostheses in which the implant is intended to bear against a natural cartilage surface. Preliminary in vitro experiments were performed to study the effect of fluid film lubrication on the wear of the polyurethane. The results suggest the possibility of designing a metallic prosthesis with a polyurethane surface layer for hemiarthroplasty such that a fluid film will be formed to protect both surfaces during implant functioning.
A Study of the Interface between Resilient Denture Liners and Polymethylmethacrylate
Authors: Amin Wala M , Fletcher A M , Ritchie G M
Published: February 2007

Four of the commonly used resilient denture lining materials were investigated, they were of different chemical composition, physical forms and processing cycles.

Scanning electron microscope examinations of the interface between the liners and the regular acrylic resin base material were carried out in an attempt to assess the bonding of these materials to the denture base, and to evaluate the reliability of their use.

The effect of water on the liner/denture base interface was also investigated, and the validity of roughening the tissue surface of the denture base prior to processing the liner was assessed.

The findings point to the advisability of using the acrylic type of soft liners whenever resilient liners are indicated. Roughening the fitting surface of the denture base to which the resilient lining materials is to be applied has a weakening effect on the bond between the lining and the denture base.

Long term exposure of the liners to water has a destructive effect. The infused water into the material leads to swelling and stresses build up at the denture base interface and these tend to promote distortion and reduction in bonding.
Air Flow Patterns in the Operating Theatre
Authors: Howorth F H
Published: February 2007

Bacteria-carrying particles and exhaled anaesthetic gases are the two contaminants found in the air flow patterns of operating rooms. Their origin, direction and speed were illustrated by a motion picture using Schlieren photography and smoke tracers.

Compared with a conventionally well air conditioned operating theatre, it was shown that a downward flow of clean air reduced the number of bacteria-carrying particles at the wound site by sixty times. The Exflow method of achieving this without the restriction of any side panels or floor obstruction was described. The total body exhaust worn by the surgical team was shown to reduce the bacteria count by a further eleven times. Clinical results show that when both these systems are used together, patient infection was reduced from 9 per cent to between 0.3 per cent and 0.5 per cent, even when no pre-operative antibiotics were used.

Anaesthetic gas pollution was measured and shown to be generally 1000 p.p.m. at the head of the patient, in induction, operating and recovery rooms, also in dental and labour rooms. A high volume low pressure active scavenging system was described together with its various attachments including one specially for paediatric scavenging. Results showed a reduction of nitrous oxide pollution to between zero and 3 p.p.m. The economy and cost effectiveness of both these pollution control systems was shown to be good due to the removal of health hazards from patients and theatre staff.
Finite Element Analysis of a Simulated Total Hip Replacement
Authors: Svensson N L , Valliappan S , McMahon R
Published: February 2007

This paper presents the results of a finite element analysis of a Stanmore prosthesis cemented into a titanium alloy tube. The problem was analysed since a reliable set of experimental data was available for comparison with the results of analysis. The results achieved demonstrate the importance of using joint elements which permit slip between the prosthesis and cement.
A Monitor for Plotting Pressure Contours inside a Plaster Cast
Authors: Pratt D J , Bowker P , Wardlaw D , McLauchlan J
Published: February 2007

An instrument is described which has been developed for making multi-point pressure measurements inside the thigh portion of a femoral fracture brace. The construction of pneumatic sensing elements, which could be used in various forms in a range of applications, is described together with a comparator circuit which allows pressure monitoring over a period of time.
An Interface Pressure Sensor for Routine Clinical Use
Authors: Robertson J C , Shah J , Amos H , Druett J E , Gisby J
Published: February 2007

The art of fitting the environment to the patient is sadly lacking. There are at least 24 000 patients in Great Britain suffering from pressure sores. The art will not improve until relevant parameters of tissue viability are measured routinely wherever patients are cared for. Disorders of temperature and blood pressure were not understood until standard measurements were widely taken. What are the relevant parameters for disorders of tissue viability? The authors single out pressure and movement, and note that pressure recorded with time will also monitor movement. They offer their flanged 28 mm electro-pneumatic pressure sensor as a possible standard instrument for most clinical purposes whether research or routine.

The discussion covers the theoretical objections to interface pressure measurement, analyses the sources of error in their electro-pneumatic technique and compares its accuracy to that of other transducers.
A New Approach to Elbow Arthroplasty
Authors: Souter W A
Published: February 2007

The development of a two component endoprosthesis, the articular surfaces of which are modelled very closely on those of the normal trochlear joint, is described. Fixation is achieved through the use of methyl methacrylate cement around a keel and stem on the ulnar side and around a supracondylar metal stirrup with projecting flanges in the capitellum and medial epicondyle in the humerus. In vitro studies suggest that this fixation should be adequate to resist the forces normally transmitted across the elbow, these forces ranging according to the activity from half to three times body weight.

Early clinical results have proved very satisfactory with regard to relief of pain and recovery of flexion, pronation, supination, power and function as a whole. The recovery of lost extension has proved more elusive. A much longer follow-up of two to five years will be required in order to ascertain whether the problem of loosening has been solved.
A Discrete Step Goniometer for the Human Elbow
Authors: Roth P J , Unsworth A , Haslock I
Published: February 2007

A discrete step goniometer has been developed which measures the total integrated angle of elbow flexion and extension movements. It is compact, comfortable and convenient to wear and use. Preliminary results have shown that it is sufficiently accurate for most clinical applications if calibration is carried out prior to the experiments and it should prove to be a useful device in diagnosis, evaluation of treatment and normal data collection.
Synthesis of a Knee Joint Endoprosthesis is Based on Pure Rolling
Authors: Elad D , Seliktary R , Mendes D
Published: February 2007

One of the major contributing factors to the life of knee endoprostheses is wear resulting from sliding of the mating surfaces. Although this is not considered the primary cause for failure of the prosthesis, the importance of reducing wear becomes more pronounced with the increase of life expectancy of the patients. Sliding mechanisms are subjected to wear significantly more than rolling mechanisms. It was therefore suggested to develop a prosthetic knee joint in which the mating surfaces will roll one on top of the other. For this purpose an experimental study was carried out aimed at the investigation of the natural knee centrodes. Rolling of the natural centrodes on each other is bound to retain the natural kinematics of the knee elements and that of the soft tissues. Since the natural centrodes were found mechanically inadequate for reproduction, synthetic surfaces were postulated and examined. The various surfaces were subjected to kinematic optimization and the optimal surfaces from structural and kinematic reproduction aspects were selected. Finally, a conceptual configuration of the joint is suggested taking into account the necessary constraints for the performance of the rolling function.
Wear of Artificial Joint Materials III
Authors: Treharne R W , Young R W , Young S R
Published: February 2007

This paper describes a new method for testing total knee prostheses under simulated in vivo conditions. Previous knee simulator work has been summarized and described. The major variables of testing are also described in detail. The results of wear testing five types of knee prostheses were that the wear rate was nearly an inverse relationship with contact area— knees with a higher contact area had lower wear rates.
Modular Concept in a Multi-Functional above Knee Prosthesis
Authors: Chaudhry K K , Guha S K , Verma S K
Published: February 2007

Conventional designs of above knee prostheses do not permit squatting and sitting cross-legged (SCL) on the floor. These postures are commonly adopted in India and other Afro-Asian countries. A new prosthesis design permitting these postures has been evolved. Further, a modular system has been prepared to fit into a number of different leg sizes. As a result of the new technology, the ankle remains fixed in normal walking and automatically flexes during squatting. Also for SCL, the thigh rotation is automatic. Thus, no hand manipulations are needed and the movements, both going down and arising are similar to normal movements.
Choosing a Wheelchair Cushion
Authors: Robertson J C , Shah J
Published: February 2007

A preliminary survey of twelve cushions on the standard 8L chair suggests that sheepskin and ministry cushions compare favourably with commercial cushions in respect to pressure and displacement characteristics. Ripple and water cushions were best.
In Vivo Hip Joint Forces Recorded on a Strain Gauged ‘English’ Prosthesis Using an Implanted Transmitter
Authors: Kilvington M , Goodman R M F
Published: February 2007

This paper describes the results obtained from implanting a strain gauged version of an ‘English’ hip joint replacement together with a totally implantable FM radio transmitter. The implant is based upon a new concept in the design of femoral hip components having a diminished head offset to reduce head load and improved stem shape permitting alignment of the neck along the theoretical axis of peak load transmitted during the gait cycle.

The implant was inserted using the ‘English’ trochanteric approach (English, 1975) which further reduces the load on a prosthetic hip joint with the use of a spacer out from the redundant femoral head to rearrange the trochanteric muscle lever arms.

The resulting axial load is detected by four strain gauges mounted on a ‘piston in cylinder’ arrangement contained within the thickened neck of the prosthesis.

The single channel FM transmitter relays the gauge output to a signal processing unit to give a direct output of activity for recording on a UV recorder. Recordings were taken during implantation, recovery, walking (at three days) physiotherapy, stair climbing and walking over a period of forty days.
The Effect of Posture on the Strength of the Lumbar Spine
Authors: Adams M A , Hutton W C
Published: February 2007

Experiments were performed on cadaveric lumbar intervertebral joints in order to assess the effects of heavy lifting on the lumbar spine. It was found that in the simulated erect lordotic posture, the apophyseal joints can resist a significant proportion of the intervertebral compressive force. Slightly flexed lumbar joints have a compressive strength that comfortably exceeds the forces generated by heavy lifting. Hyperflexion just beyond the normal limit of motion can render lumbar intervertebral discs vulnerable to posterior prolapse when compressed by physiological loads. It is concluded that no injury should be sustained by the osteoligamentous lumbar spine as a result of a single heavy lift provided that the lumbar spine is kept slightly flexed.
Methods of Impact Absorption When Landing from a Jump
Authors: Lees A
Published: February 2007

The vertical reaction force was measured during impact landings following a vertical jump. It was observed that variations between subjects occurred in the magnitude of the peak force over the first 150-200 ms after impact. This period of the landing is termed the impact absorption phase. Two extreme cases of impact landings are taken for analysis. These are referred to as ‘hard’ and ‘soft’ landings, describing the magnitude of the vertical force peak during impact absorption. These differences are produced as a result of the interactions which occur between the individual segments of the human body. The segmental contribution to the total force curve was derived by film analysis techniques. The specific influence of each segment on the total force curve was isolated and made comparable with other segments by using the relative acceleration of the segment mass centre to the lower joint about which it rotates. By using this variable to compare hard and soft landings, it was established that a soft landing was produced by a phased and controlled deceleration of body segments.
Spinal and Pelvic Movement during Walking—A New Method of Study
Authors: Thurston A J , Whittle M W , Stokes I A F
Published: February 2007

A non-invasive method of measuring pelvic and lumbar spinal movement during walking has been developed. Targets attached to the subject reflect light from stroboscopic lamps mounted near to each of three television cameras which are interfaced to a computer. The targets' locations are identified by the interface and stored as coordinate pairs. From the two-dimensional data from two cameras, three-dimensional data are derived and the relative movements of the lumbar spine and pelvis can be calculated.

The ranges of spinal and pelvic movements in a group of twenty-two normal males have been measured. The mean values of spinal motion were 5.1° in the sagittal plane, 9.3° in the coronal plane and 8.3° axial rotation. The corresponding pelvic movements were 4.0° in the sagittal plane, 7.7° in the coronal plane and 11.2° axial rotation.

The system is useful to document abnormalities and to record the effects of treatment.
A Finite Element Study of the Human Hip Joint
Authors: Afoke N Y P , Byers P D , Hutton W C
Published: February 2007

A finite element study of human hip joint is described. The results show that the articular cartilage is well able to distribute the applied load. Values for the compressive radial stress were calculated and compare favourably with published results. Values for compressive hoop stress and shear stress are also given.
The Response of Human Skin to Small Tensile Loads in Vitro
Authors: Abas W A B Wan , Barbenel J C
Published: February 2007

The mechanical properties of excised strips of human skin were investigated in the initial high compliant phase. The specimens showed preconditioning on repeated load cycling. The preconditioned specimen displayed a reproducible response, and a region of linear load-extension behaviour. The value of the tensile modulus and Poisson's ratio, both referred to the dimensions of the preconditioned specimens, are reported and the tissues shown to be anisotropic. Stress relaxation tests showed the properties of the tissues to be time dependent.
A Study of Corrosion Fatigue in Cast Cobalt-Chrome-Molybdenum Alloys
Authors: Bolton J D , Hayden J , Humphreys M
Published: February 2007

Fatigue crack growth rates in Ringer's solution have been shown to be significantly higher than in air, and the crack growth threshold level reduced by the presence of a corrosive environment. This demonstrates that cast cobalt alloys are susceptible to corrosion fatigue effects in the human body, at least during crack propagation, and the proposed mechanism for this involves the synergistic effect of crack tip corrosion and the effects of cyclic stress which produce a ‘true corrosion fatigue’ phenomenon.
Ligament Function and Joint Stability Elucidated by a New Technique
Authors: Rasmussen O , Andersen K
Published: February 2007

For analysing the ligaments of the ankle joint, their function, and the traumatic mechanisms which cause them to rupture, an apparatus was developed which enables graphic registration of rotatory movements in the ankle joint in two planes simultaneously, when a given torque is applied to the talus. In a modified form, this apparatus is applicable also for other joints. A lever with strain gauges and potentiometers is fixed in the talus of an osteoligamentous preparation. The lever is moved manually, and signals from the strain gauges and potentiometers are collected by a microcomputer for later transfer to a computer service centre where the mobility at the chosen torque is calculated and plotted as mobility patterns. The appearance of these patterns depends upon which ligaments are intact. The patterns plotted in any situation are reproducible, provided that the state of the ligaments is unchanged. In cutting experiments it was possible to demonstrate that rupture of the anterior talofibular ligament may occur simultaneously with partial rupture of the posterior talofibular ligament, although the calcaneofibular ligament remains intact. This occurs if the distortion trauma causing the rupture consists of an internal rotation of the talus, not if it consists mainly of a tilting of the talus in the ankle mortise.
A Load Cell System in Foot Pressure Analysis
Authors: James W V , Orr J F , Huddleston T
Published: February 2007

A method of displaying discrete areas of pressure beneath the foot has been produced. The device employs a pressure sensitive elastomer which gives quantitative readings of the pressure developed. The 512 load cells are enclosed in a low profile platform only one inch in depth which provides a low-cost system that can be employed in clinical situations.
A Clinical Electrogoniometry System
Authors: James W V , Orr J
Published: February 2007

To answer a clinical need, a simple goniometry system for the measurement of the lower limb joints has been devised. By means of a low-cost microprocessor the results are provided in printout, in a clinically useful form.
The History and Development of Artificial Limbs
Authors: Orr J F , James W V , Bahrani A S
Published: February 2007

The loss of a limb is a tragic event and artificial limbs are used to substitute for this loss. Early artificial limbs were crude, consisting of peg legs and hook hands. However, with the developments in surgery and technology better limbs became available. In the sixteenth century, surgeons who carried out the amputations recruited the help of craftsmen to provide their patients with artificial limbs which were functionally useful and resembled the shape of normal limbs.

Significant advances in the development of limb fitting services have been prompted by the two World Wars. Rapid progress has been made since the 1940s. This is due to the collaboration of surgeons, engineers and prosthetists to employ new developments in technology and materials to the rehabilitation of amputees.
Alloys for Orthopaedic Implant Use
Authors: Dobbs H S , Robertson J L M
Published: February 2007

The paper compares four alloys in orthopaedic implant use on the basis of their performance in laboratory tests. The alloys compared were cast Co–Cr–Mo, powder metallurgy (PM) Co–Cr–Mo, Ti 318 and Ti 550. Tensile, corrosion fatigue, and corrosion tests were carried out and the effect of heat treatment and of surface treatment was investigated. The corrosion fatigue tests ranked the alloys in the following order of merit (1) Co–Cr–Mo (PM), (2) Ti 550, (3) Ti 318, and (4) cast Co–Cr–Mo. The corrosion tests demonstrated for cast Co–Cr–Mo the effect of passivation, steam sterilization, and texturing, and for Ti 318 the effect of oxidizing, anodizing, and acid etch/shot peening. It was concluded that for joint replacement applications requiring the highest corrosion fatigue strength regardless of cost and neglecting the possible importance of elastic modulus, Co–Cr–Mo (PM) was best. For applications requiring ease of manufacture and allowing a lower corrosion fatigue strength, cast Co–Cr–Mo was the material of choice. For most other applications and in particular where high corrosion fatigue strength at a reasonable cost was required, the Ti alloys offered worthwhile advantages.
A Proposed Design for an Expanding Hip Nail
Authors: Raftopoulos D , Baril J D
Published: February 2007

Hip fractures are a common problem and many devices have been utilized in the fixation of these fractures. The fixation of hip fractures is reviewed. A new expanding, sliding, compression nail is described. The nail's unique feature is its ability to be expanded within the femoral head providing secure fixation to the proximal fragment.
Disc Pressure Measurements when Rising and Sitting down on a Chair
Authors: Andersson G B J , Örtengren R , Nachemeson A
Published: February 2007

Disc pressures were measured in the third lumbar disc whilst sitting down on a chair and rising. Three methods of rising and sitting down were studied; unsupported, using thigh support and using armrest support. Pressure increases always occurred. The use of arm support was found to reduce significantly the maximum pressure measured, and the armrests were particularly effective for that purpose.
The Application of Optimization Methods for the Calculation of Joint and Muscle Forces
Authors: Barbenel J C
Published: February 2007

An analysis is presented of the force actions at the temporomandibular joint and in the muscles of mastication during biting. The resulting equations cannot be solved in order to determine the muscle and joint forces because the number of unknown quantities exceeds the number of equations. Solutions are obtained which minimize either the total force produced by the muscles of mastication or the force at the temporo-mandibular joint. It is shown that the predictions of muscle action obtained from these solutions are at variance with the muscles shown to be active experimentally. The limitations of the application of optimization procedures to redundant problems associated with muscle and joint force analyses are discussed.
In Vivo Measurement of the Mechanical Properties of Bone Tissue. Preliminary Results
Authors: Burny F , Saric O , Bourgois R , Donkerwolcke M , Andrianne Y
Published: February 2007

The paper is a preliminary report on the possibility of measuring the mechanical characteristics of the bone at the time of the anchorage of the osteosynthesis.

The measurement of the maximum torque of a screw could be representative for the strength of the material.
Spinal Fixator for the Management of Spinal Injury (the Mechanical Rationale)
Authors: Rezaian S M , Dombrowski E T , Ghista D N
Published: February 2007

The goal of successful treatment of spinal injury is to achieve a stable pain-free spine with no deformity and also the complete anterior decompression of the cord for maximum neurological recovery, the minimum bed-ridden time and hospitalization, and reduction of complications and expenses. A special ‘spinal fixator’ has been developed to fulfill these aims. It is a small apparatus with two components: a stabilizer to fix the adjacent vertebrae and a turn-buckle part to produce compression. Extensive biomechanical tests on cadavers confirmed that this appliance produced secure stability on the broken spine. It will simply replace the broken bodies through an anterolateral approach, restore the height of the body vertebrae for normal weight-bearing, and securely stabilize the broken spine for early mobility and rehabilitation; and finally, it will provide the chance to decompress the cord anteriorly for a better recovery. In this way the patient will be able to sit one day after the operation, to stand (with or without brace) in two to three weeks, and leave the hospital in three to six weeks after the operation. Details of engineering rational bases of this technique are described.
Partial Immobilization of the Ankle and Talar Joints Complex and its Effect on the Ground-Foot Force Characteristics
Authors: Seliktar R , Mizrahi J
Published: February 2007

A combined qualitative–quantitative approach towards the analysis of the ground reaction forces is suggested so as to detect deficiencies and predict hazards in human locomotion. The population studied is a group of patients who have undergone partial or full arthrodesis of the ankle–subtalar joint complex. The various ways in which the effects of ankle fusion are reflected on the force characteristics are discussed. The non-uniformity of reflection suggests an elaborate compensatory mechanism which is also being considered. As a conclusion it is suggested that surgical corrections such as immobilization of joints may be hazardous to the skeletal elements unless adequate compensatory walking habits are developed. The reduced flexibility of the system has to be compensated either by involving other joints, such as the knee, in the force attenuation process or by provision of flexible footware.
Cancellous Bone Strength at the Proximal Human Tibia
Authors: Hvid Ivan , Jensen Jørn
Published: February 2007

Machined specimens from ten cadaver proximal tibiae were tested in compression to study the variation of mechanical strength with the distance from the joint surface. There was a statistically significant reduction of stiffness and strength with increasing distance from the joint beneath the lateral condyle and the intercondylar area; at the medial condyle no such reduction could be demonstrated. Linear regression analysis showed that the tangent modulus may be used to predict yield strength ( r = 0.92) and ultimate strength ( r = 0.91) when destruction of the specimen is undesirable.

One important limitation of the technique employed is that the length of test specimens determines the resolution that can be obtained.
Liquid Repellency and Surgical Fabric Barrier Properties
Authors: Olderman G M
Published: February 2007

Those who are responsible for controlling the surgical environment require a technically sound, practical, valid, and consistent means of evaluating the barrier properties of surgical drapes and apparel. While many laboratories have, by necessity, agreed upon a limited number of test procedures to evaluate the liquid penetration resistance or repellency of a barrier material, there is no uniform code or guideline that defines the preferred method or methods of evaluation. Assuming wet bacterial transmission through a barrier material is related to the liquid penetration resistance of that material, the following paper attempts to outline the physicochemical basis of repellency in terms of a word equation, define the terminology and relevance to surgical barriers, and suggest the optimum choices of tests from among those in common usage including the group that had been under consideration by the Association for the Advancement of Medical Instrumentation (AAMI) Aseptic Barrier Materials Committee.

Because the liquid penetration resistance of a barrier material is a function of both permeability and surface wettability, comprehensive evaluation must include tests for both properties. No single test has been shown to do this reproducibly.

Two tests, used by a number of industrial labs, are recommended because, while each test reflects predominantly the degree of either porosity or wetting, together they have been shown to yield information on both properties reliably with results that can be reproduced. These two tests, the fixed liquid pressure test and the dynamic impact test, are simple, non-destructive, and require little special equipment, so they can be performed relatively rapidly on both linens and single-use non-wovens.
A Study of the Wear Characteristics of Ultra-High Molecular Weight Polyethylene Sliding against Glass
Authors: Randall J E , Dowson D
Published: February 2007

Investigations of the wear of ultra high molecular weight polyethylene in unidirectional sliding against a range of glass counterfaces of various initial surface roughnesses are described. The tests were carried out either with the wear specimens under dry conditions of contact or lubricated by distilled water. Comparative tests under rarified atmosphere were also carried out. A single sliding speed of 0.24 m/s and two constant loads of 20 N and 80 N per test pin were used.

The initial wear factors measured were often low, but the onset of a second, more severe, wear regime commonly occurred at an early stage in the testing. This phenomenon produced overall wear factors which were higher than those previously reported for this polymer sliding against both ceramic and stainless steel counterfaces of similar roughnesses after the same distances of sliding under equivalent conditions of testing.
The Bond Strength and Ageing of Plasma-Sprayed Coatings of Alumina on Metal Substrates
Authors: Randall J E , Dowson D
Published: February 2007

Changes in the bond strength of alumina coatings after soaking in deionised water have been studied in conjunction with investigations of the wear characteristics of ultra-high molecular weight polyethylene against ceramics coated onto metal substrates.

The results reported in this paper concern plasma sprayed alumina coatings, applied both directly and using an intermediate bonding layer, onto medical grade stainless steel or titanium alloy.

The bond strength was measured in tension both before immersion and at various intervals over a period of up to eighteen months (13 000 hours) soaking in water. After about four months a significant deterioration in bond strength was noted. This deterioration continued for the duration of the investigation and the reductions in the bond strengths observed were often greater than 75 per cent of the original values.

A white powdery deposit was found in the containers in which the ageing was carried out and a similar deposit was also seen on some of the fracture surfaces. Analysis identified Al(OH)3 and an amorphous phase of alumina. A complex diffusion mechanism appeared to have taken place which resulted in a deterioration in the properties of the ceramic coatings.
Cancellous Bone Strength Measurements with the Osteopenetrometer
Authors: Hvid Ivan , Andersen Kurt , Olesen Svend
Published: February 2007

An instrument designed to measure cancellous bone strength at the tibial and femoral condyles during total knee replacement is described and evaluated with respect to the relationship of measurements to conventional compression tests on machined specimens in a material testing machine.

The instrument, referred to as an osteopenetrometer, indirectly measures the force and depth of penetration of a needle that is advanced into the cancellous bone at constant speed. A small computer controls the measuring procedure and corrects the force readings for resistance in the hydraulic system.

The relationship between osteopenetrometer measurements and compression tests is best described by a power law, with correlation coefficients of approximately 0.90 when ultimate stress data were compared. A 2.5 mm pointed needle with the shaft milled to 2.3 mm to avoid friction along the needle shaft is favoured for clinical measurements since readings from different depths beneath the resection surface may then be directly compared.

The error of measurement was assessed by comparison of observed and smoothed data from measurements across tibial and femoral condylar resection surfaces. Ninety-nine per cent tolerance limits of ± 3.0 MPa (compared to a range of 0–40 MPa in units peculiar to the osteopenetrometer) were found.
Wear Tests on Alumina for Application in Heart Valve Prostheses
Authors: Gentle C R , Juden H
Published: February 2007

Medical grade alumina in a porous form, as well as the normal dense form, have been tested in a crossed-cylinder wear machine under conditions which reproduce those to be found in heart valves. The results show steady wear rates. For dense alumina pairs this rate is 9.9 × 10–7 mm3 (Nm)–1; for porous pairs it is about 10 times higher. A dense alumina valve prosthesis using a hinge mechanism is estimated from this data to have a useful life of about 45 years.
Some Time Dependent Properties of the Intervertebral Joint when under Compression
Authors: Smeathers J E
Published: February 2007

The experimental technique reported here was developed to provide data for mathematical models simulating the mechanical properties of the human lumbar spine. Dynamic compression tests on intervertebral joints from the lumbar region of sheep (body mass 50–70 kg) were used to assess the technique as human cadaveric material was not readily available. The loading pattern on the human spine during walking was simulated by exposing each joint to dynamic compression loads of 750 ± 250 N at a frequency of 1 Hz. The joints were tested at body temperature in Tyrode's solution. In order to detect the dominant viscoelastic properties of each joint the energy dissipation, spring stiffness, and creep response were monitored for twenty-eight hours.

The results of these long term axial compression tests on lumbar intervertebral joints from sheep show that the joint rapidly loses its capacity to dissipate strain energy. After quarter of an hour the energy dissipation (hysteresis) of the joint has dropped from 37 per cent to less than 10 per cent. The spring stiffness of the joint under these compressive loads starts at 6 MN m–1 increasing to 12 MN m–1 by the end of the test. The characteristic time for the creep response (retardation time) occurs after two and a quarter hours.
An Evaluation of Total Hip Replacement Cementing Technique Using Sonic Resonance
Authors: Poss R , Jr G W Pratt , Chung J K
Published: February 2007

The feasibility of assessing the quality of the bond achieved by cement fixation of implants by their sonic characteristics was examined by theoretical and experimental models. Mechanical excitation of implants in the audio sonic range in vitro produced experimental results that were in close agreement with computer predicted values. The sonic technique was utilized to evaluate certain aspects of current surgical technique using in vitro models. By sonic criteria, steady state polymerization of surgical simplex cement occurs approximately eleven minutes after hand held cement has cured. The value of meticulous preparation of bone surfaces prior to cement introduction is confirmed. Differences in the quality of bond obtained by variations in cement technique, or recementing to old cement, can be distinguished by this method. These results suggest that sonic assessment may provide a more sensitive measure of the quality of bond achieved than does roentgen examination. In clinical use, both intra-operatively and post-operatively, application of this technique may yield an immediate assessment of the quality of cement fixation.
The Influence of Environmental Factors on Evaporation and Heat Loss from Burned Tissue
Authors: Martin C J , Muir I F K
Published: February 2007

Destruction of skin by severe burning leads to substantial loss of fluid. Increased evaporative heat loss in addition to energy demands for tissue repair causes hypermetabolism in a severely burned patient, placing a large stress on the body. The dependence of evaporation rate and energy supply on environmental variables has been studied using a phantom in which a free water surface simulated burned tissue. Vapour diffusion resistances have been derived from the experiments, and compared with values calculated from data obtained from other studies of burned tissue. These can be used to predict rates of evaporation and heat loss for burned tissue, and their dependence on different environmental factors. Experiments have shown that energy in the form of radiant heat or warm air blown over the water surface can be supplied to reduce heat losses without significantly affecting evaporation rate.
A Static Experimental Stress Analysis of a Single Plateau of the Geomedic® Knee Joint Using Embedded Strain Gauges
Authors: Little E G
Published: February 2007

The tibial component of the Geomedic® knee joint is subject to a non-uniform stress distribution which tends to cause loosening from the substrate. An experimental stress analysis was carried out to establish the nonuniform stress distribution by embedding three dimensional strain rosettes into epoxy plugs and fitting them into a large epoxy model of the tibial component. The strain data caused by loading the model of the tibial component in compression was analysed and was compared with results from a finite element analysis on a similar model of the prosthesis.
Measuring Devices for Studying Joint Mobility in the Normal Population
Authors: Haskard D O , Silman A J
Published: February 2007

Fixed torque screwdrivers were used to develop instruments for measuring joint mobility for epidemiological studies. The composite movements of forearm and lower limb rotation were measured by such devices and the results compared with a previously described similar device for index finger hyperextension. The magnitude of the intra-observer variation for all movements was very low and thus highlighted the potential value of these devices for population studies.
Bone Mineral Assay: Its Relation to the Mechanical Strength of Cancellous Bone
Authors: Hvid I , Jensen N C , Bünger C , Sølund K , Djurhuus J C
Published: February 2007

Photon absorptiometric (125I) bone mineral assay and low strain-rate axial compression tests were carried out on cylindrical cancellous bone specimens from the proximal tibial epiphysis of large, skeletally mature mongrel dogs. Bone mineral assay was reproducible within ±5.0 per cent (99 per cent tolerance limits). Linear regression analysis with the bone mineral concentration as the independent variable showed a strong correlation towards the ultimate strength ( r = 0.92) and the yield strength ( r = 0.89), somewhat weaker towards the elastic modulus ( r = 0.82), the ultimate energy absorption ( r = 0.79), and the yield energy absorption ( r = 0.73), and insignificant towards the ultimate strain ( r = −0.14) and the yield strain ( r = −0.18). The power relationships between trabecular bone density and compressive strength and modulus suggested by Carter and Hayes (1977) were not statistically superior to linear relationships in the relatively narrow density range reported here. The quadratic relationship between bone mineral content and energy absorption suggested for cortical bone (Currey, 1969) could not be confirmed for trabecular bone. Linear regression analysis with the elastic modulus as the independent variable showed that the regression coefficients to predict ultimate strength and yield strength are statistically indistinguishable from those found in studies on human material. It is concluded that non-destructive techniques to measure bone density and mineralization may be suitable for clinical bone strength assay.
Compressive Creep Behaviour of Irradiated Ultra High Molecular Weight Polyethylene at 37° C
Authors: Little E G
Published: February 2007

Compressive creep tests were carried out on samples of irradiated ultra high molecular weight polyethylene at 37°C to establish the modulus of the material for stress analysis of prostheses.
A Model for the Function and Failure of the Meniscus
Authors: Aspden R M
Published: February 2007

The meniscus has been modelled as a toroid of constant wedge-shaped cross-section resting on a compliant base and loaded in compression from above. This simple model allows the cross-sectional shape and the mechanical properties of the fibrocartilage to be varied systematically in order to determine the essential features of the response of the meniscus to compressive load. A finite element representation of this model shows that a circumferential tensile strain is developed, irrespective of the cross-sectional shape or the elastic moduli of the fibrocartilage, to balance the applied load. A horizontal boundary between regions of positive and negative shear strains and a region of radial tensile strain are also developed. These regions coincide with the locations of horizontal and longitudinal tears which are the most commonly observed lesions of the meniscus. The model shows that the posterior segment of the medial meniscus is most vulnerable to injury.
An Experimental Study of Femoral Cement Stress in Total Hip Replacement — Influence of Structural Stiffness of the Femoral Stem
Authors: Miles A W , Dall D M
Published: February 2007

This paper describes the measurement of femoral cement stresses in model femora using embedded strain gauges. In particular the influence of the elastic modulus of the stem material is examined. The study showed that while compressive stresses in the proximal cement are increased quite markedly with lower modulus materials, the important circumferential tensile stresses in this area are only marginally affected. Furthermore, the stresses were all well below the quoted failure levels for bone cement.
The Influence of Spine Geometry on the Coupling between Lateral Bending and Axial Rotation
Authors: Scholten P J M , Veldhuizen A G
Published: February 2007

A biomechanical model study was undertaken to examine to what extent facet joint orientation and inclination of the motion segments influence the coupling between lateral bending and axial rotation that occurs in the human spine. The results show that there is an opposite influence of the inclination of the motion segments and the orientation of the facet joints on the axial rotation associated with lateral bending. As one moves in a rostrocaudal direction along the spine there is a decrease of the axial rotation associated with lateral bending. At the upper part of the thoracic spine there is a reinforcement of the axial rotation due to the ventrally inclined orientation of the vertebrae. In the lower thoracic and upper lumbar spine the axial rotation during lateral bending will oppose that due to the dorsally inclined orientation of the vertebrae. In a flexed position of the spine, this coupling is stronger than in an extended spine.
Measurement of Movement in Hip Joint Disease
Authors: Gore T A , Higginson G R , Stevens J
Published: February 2007

In earlier papers (Gore et al., 1979; 1984) an electrogoniometer for measuring hip movement was described, and measurement of normal hip movement was reported for both sexes over a wide age range. Against that background this paper describes the patterns of movement for a number of pathological conditions examined: the progression of osteo-arthrosis through four examples covering the range from early diagnosis to a severe case; bilateral Charnley arthroplasty; a left osteotomy coupled with a McKee total replacement of the right hip; and bilateral congenital dislocation of the hips.
A Microcomputer Controlled Hand Assessment System Used for Clinical Measurement
Authors: Jones A R , Unsworth A , Haslock I
Published: February 2007

To improve the objectivity of clinical assessment of hand function, a microcomputer controlled system of force transducers has been developed and used to study twenty normal subjects and thirty-eight patients suffering from rheumatoid arthritis. The parameters measured were grip and individual finger forces, pan and kettle handle grip and lift force, key twist torque, lateral pinch force, and individual finger pulp pinch forces.

‘Power’ grip forces were found to be remarkably similar in the left and right hands as indeed was the contribution made by each finger to the total force. Pan grip and lift forces were also similar in left and right hands, but the grip force was far greater than the lift force in both normals and patients. Kettle grip forces were much less than the lift force in normal subjects, while patients gripped the kettle with almost as much force as they used to lift it.

Patients were weaker than normals exerting roughly one third of the forces of normals in all modes of measurement. There were different styles of lifting demonstrated by the patient group.
The Role of Cement in the Long Term Performance and Premature Failure of Charnley Low Friction Arthroplasties
Authors: Isaac G H , Atkinson J R , Dowson D , Wroblewski B M
Published: February 2007

A number of polyethylene acetabular cups (59) and femoral stems (38) of Charnley hip prostheses were obtained following revision surgery and examined by scanning electron microscopy. In many cases, acrylic cement particles were embedded in the articulating surface of the cups. These particles caused surface pitting. The appearance of the articulating surfaces suggested that some cement had been present from the time of arthroplasty. In other cups there was evidence of cement ingress during the service life. Failure to use sufficient cement at arthroplasty resulted in cavities on the backs of the cups. Many femoral heads had become scratched in vivo, the surface roughness increasing from an initial value less than 0.02 μm Ra to a value on removal of 0.07 μm Ra. The increased roughness increases the amount of wear in the polyethylene sockets. Laboratory tests show that retrieved acrylic cement particles will scratch stainless steel, and it is our conclusion that entrapped cement will damage both components of the prosthesis and may cause premature failure.
Dynamic Assessment of Knee Joint Function
Authors: Whittle M W
Published: February 2007

Clinical research into the pathology and treatment of knee disorders is greatly enhanced by the availability of objective data on knee function. A three-dimensional measurement system, using television cameras and force platforms interfaced to a computer, is used to make a combined kinetic and kinematic assessment of the knee. Information is provided on the standing knee alignment, the general gait parameters, and the knee angle and moment when walking, in both sagittal and coronal planes. An example is given of the use of these data in the assessment of unicompartmental knee replacement arthroplasty.