Showing papers by "Nuffield Orthopaedic Centre published in 1996"

Questionnaire on the perceptions of patients about shoulder surgery

Abstract: We developed a 12-item questionnaire for completion by patients having shoulder operations other than stabilisation. A prospective study of 111 patients was undertaken before operation and at follow-up six months later. Each patient completed the new questionnaire and the SF36 form. Some filled in the Stanford Health Assessment Questionnaire (HAQ). An orthopaedic surgeon assessed the Constant shoulder score. The single score derived from the questionnaire had a high internal consistency. Reproducibility, examined by test-retest reliability, was found to be satisfactory. The validity of the questionnaire was established by obtaining significant correlations in the expected direction with the Constant score and the relevant scales of the SF36 and the HAQ. Sensitivity to change was assessed by analysing the differences between the preoperative scores and those at follow-up. Changes in scores were compared with the patients' responses to postoperative questions about their condition. The standardised effect size for the new questionnaire compared favourably with that for the SF36 and the HAQ. The new questionnaire was the most efficient in distinguishing patients who said that their shoulder was much better from all other patients. The shoulder questionnaire provides a measure of outcome for shoulder operations which is short, practical, reliable, valid and sensitive to clinically important changes.

An evaluation of the constant-murley shoulder assessment

Abstract: We have analysed the Constant-Murley (1987) assessment for 25 patients with shoulder pathology. We found the score easy to use, with low inter- and intraobserver errors, but sufficiently imprecise in repeated measurements to give concern in its use for clinical follow-up of patients. We have calculated 95% confidence limits for a single assessment to be within 16 to 20 points in most cases. In addition, we found that all our subjects with instability as their main problem scored within five points of the maximum; this suggests that the scoring method may need to be revised for use on these patients.

Cloning and characterization of an IGF-1 isoform expressed in skeletal muscle subjected to stretch.

Abstract: To ascertain if IGF-1 is a regulator of local muscle growth, total RNA was extracted from rabbit muscle induced to undergo rapid hypertrophy using active stretch and from control muscles. This was analysed by Northern hybridization with a 280 base pair probe containing sequences derived from exons 3 and 4 of the insulin-like growth factor 1 gene. Two types of insulin-like growth factor 1 mRNA were shown to be strong expressed in the stretched muscles. In situ hybridization using the same probe (280 base pair) showed that IGF-1 is strongly expressed in muscle that is induced to grow rapidly and is expressed in the muscle fibres themselves. Using RT-PCR a single insulin-like growth factor 1 isoform cDNA (IGF-1Ea) could be cloned from the normal resting muscles. However, an additional isoform of insulin-like growth factor 1 (insulin-like growth factor 1Eb) was found to be expressed in stretched muscle undergoing hypertrophy. The E domain sequence of the additional isoform differs from the liver insulin-like growth factor 1Ea by the presence a 52 base pair insert. This changes the reading frame of the derived carboxyl-terminal resulting in a different precursor insulin-like growth factor 1 isoform. This insulin-like growth factor 1 mRNA probably encodes the precursor insulin-like growth factor 1 isoform that is responsible for local muscle growth regulation in response to mechanical stimulation. To confirm that alternative splicing of the insulin-like growth factor 1 gene occurs in muscle in response to physical activity, oligonucleotide primers were made which specifically amplify the cDNAs of two isoforms (insulin-like growth factors 1Ea and Eb) in the human as well as the rabbit. Following altered physical activity for 2 h to 6 days, appreciable levels of insulin-like growth factor 1Eb (in human the Ec) isoform were detected in skeletal muscle by using RT-PCR. In contrast very little if any of this splice variant could be detected in control muscle not subjected to stretch or extra physical activity.

Thromboprophylaxis and death after total hip replacement

Abstract: The recommendation that patients having a total hip replacement should receive pharmacological thromboprophylaxis is based on the belief that fatal pulmonary embolism is common, and that prophylaxis will decrease the death rate. To investigate these assumptions we performed a meta-analysis of all studies on hip replacement which included information about death or fatal pulmonary embolism. A total of 130 000 patients was included. The studies were so varied in content and quality that the results of our analysis must be interpreted with some caution. The fatal pulmonary embolism rate was 0.1% to 0.2% even in patients who received no prophylaxis. This is an order of magnitude lower than that which is generally quoted, and therefore the potential benefit of prophylaxis is small and may not justify the risks. To balance the risks and benefits we must consider the overall death rate. This was 0.3% to 0.4%, and neither heparin nor any other prophylactic agent caused a significant decrease. Our study demonstrates that there is not enough evidence in the literature to conclude that any form of pharmacological thromboprophylaxis decreases the death rate after total hip replacement. For this reason guidelines which recommend their routine use to prevent death after hip replacement are not justified.

Cellular biology of bone-resorbing cells

Abstract: Resorption of bone occurs continuously throughout life, first as part of skeletal growth and modeling and, later, in the process of bone-remodeling in the adult skeleton. Since the 1970's, considerable progress has been made in unraveling the basic cellular mechanisms that regulate the formation and activity of the osteoclast, the main cellular agent of bone resorption. These recent advances have resulted mainly from the introduction of new methods of isolation and culture of osteoclasts and evaluation of resorptive activity; techniques have also been developed for the generation of osteoclasts in long-term culture of precursor cells found in hematopoietic tissues and peripheral blood. Although reports have suggested that other cells (such as tumor cells or macrophages) are capable of degrading bone matrix48,104,152 and releasing local factors that contribute to resorption of bone45,102,105,113, the osteoclast is the only cell specialized for this function. The purpose of this review is to integrate new knowledge regarding the formation of osteoclasts and the regulation of their activity within a general view of the cellular biology of normal and pathological bone resorption. After a review of the criteria by which osteoclastic cells are defined, the origin and formation of osteoclasts will be considered, along with mechanisms governing their recruitment, activation, and function. The manner in which these mechanisms contribute to osteoclastic bone resorption under various pathological conditions as well as the possible roles of other cells (both skeletal and extraskeletal in origin) in this process will be discussed. Studies on the biology of bone-resorbing cells can be properly evaluated only if the criteria for the recognition of osteoclasts are clearly defined. On histological sections, osteoclasts are readily identified as large multinucleated cells that lie in apposition to a bone surface undergoing lacunar resorption …

Theory and Practice of Meniscal Knee Replacement: Designing against Wear:

Abstract: This paper attributes the high rate of high-density polyethylene (HDP) wear in many knee prostheses to incongruity of their articular surfaces. The authors discuss the anatomical and kinematic features of the knee which have led most designers to choose incongruous surfaces and review the reasons for employing free bearings, analogues of the natural menisci, to provide congruity without restriction of movement. There are theoretical reasons against employing freely mobile bearing in the absence of a functioning anterior cruciate ligament (ACL) and the authors' experience has confirmed this limitation in practice. It is concluded that, in bicompartmental replacement, the movements of the meniscal bearing should be limited in the anteroposterior direction. For unicompartmental arthritis, an unconstrained bearing can be employed if, as is usually the case, all ligaments are intact.

Isolation and culture of bone-forming cells (osteoblasts) from human bone.

Abstract: The most conspicuous function of the osteoblast is the formation of bone. During phases of active bone formation, osteoblasts synthesize bone matrix and prime it for subsequent mineralization. Active osteoblasts are plump, cuboidal cells rich in organelles involved in the synthesis and secretion of matrix proteins. Unlike fibroblasts, they are obviously polarized, secreting matrix onto the underlying bony substratum which consequently grows by apposition. Some osteoblasts are engulfed in matrix during bone formation and are entombed in lacunae. These cells are described as osteocytes and remain in the bone matrix in a state of low metabolic activity. At the completion of a phase of bone formation, those osteoblasts which avoided entombment in lacunae lose their prominent synthetic function and become inactive osteoblasts, otherwise known as bone-lining cells. In mature bone, lining cells cover most of the bone surfaces. Osteocytes and bone-lining cells should not be considered as inactive cells since they play a major role in the regulation of bone modeling and remodeling and in calcium homeostasis (1).

A placebo controlled double blind trial to evaluate the effectiveness of pulsed short wave therapy for osteoarthritic hip and knee pain

Abstract: The aim of this study was to investigate the effectiveness of pulsed short wave (PSW) in the relief of pain in osteoarthritis of the hip and knee. Ninety-two patients, mean age 63 years, (34 men and 58 women) were randomly allocated to one of three groups: (1) Active PSW, using the dosage found in a pilot study to be non-significantly most effective, (2) Placebo PSW, (3) No treatment control group. Nine sessions of treatment were provided over a 3-week period, each application lasting for 15 min. The machine was modified by the manufacturers so that the therapist was able to administer the treatment and carry out assessments without being aware of the treatment allocation. Outcome measures included sensory and affective pain diary reports averaged over days and weeks, self-reported benefit and the General Health Questionnaire. Analysis of variance with repeated measures over time was used to find out if the active treatment had a specific effect, incremental to the placebo effect. There were no significant differences between the active and placebo groups over time. According to the pain diary reports, both active and placebo groups tended to improve slightly during treatment, but worsened after its withdrawal. Patients who were given the placebo application tended to report more benefit than those who had the active treatment, although this did not quite reach statistical significance (P < 0.06). Patients who were not on a waiting list for surgery did significantly better over time than those who were (P < 0.03). There were no significant differences between the groups over time for the other outcome variables. Any treatment effect on this patient population appears to have been largely placebo-mediated. No evidence was found therefore for the specific effectiveness of PSW for treatment of osteoarthritic hip or knee pain.

Long-term comparison of charnley and stanmore design total hip replacements

Abstract: We reviewed the records of the long-term outcome of 208 Charnley and 982 Stanmore total hip replacements (THR) performed by or under the supervision of one surgeon from 1973 to 1987. The Stanmore implant had a better survival rate before revision at 14 years (86% to 79%, p = 0.004), but the difference only became apparent at ten years. The later Stanmore implants did better than the early ones (97% to 92% at ten years, p = 0.005), the improvement coinciding with the introduction of a new cementing technique using a gun. Most of the Charnley implants were done before most of the Stanmore implants so that the difference between the results may in part be explained by improved methods, but this is not the complete explanation since a difference persisted for implants carried out during the same period of time. We conclude that improved techniques have reduced failure rates substantially. This improvement was much greater than that observed between these two designs of implant. Proof of the difference would require a very large randomised controlled trial over a ten-year period.

MRI diagnosis of partial tears of the anterior cruciate ligament.

Abstract: In an attempt to define the magnetic resonance imaging (MRI) features of partial tears of the anterior cruciate ligament (ACL) we retrospectively analysed the MRI scans of 30 patients with a recent arthroscopic finding of a normal, a partial or a completely torn ACL. On review of the original reports MRI correctly predicted 9/9 (100 per cent) complete ACL tears, 11/12 (92 per cent) normal ACLs but only 1/9 (11 per cent) partial ACL tears. On analysis of the MRI there were four features which helped to differentiate partial ACL tears from either complete ACL tears or normal ligaments. These were the appearance of some intact fibres, thinning of the ligament, a wavy or curved ligament and the presence of an inhomogeneous mass posterolateral to the ACL. We propose that these findings may be indicators of partial ACL tear.

The Problem of ‘Noise’ in Monitoring Patient-Based Outcomes: Generic, Disease-Specific and Site-Specific Instruments for Total Hip Replacement:

Abstract: OBJECTIVES To compare the performance of three types of patient-based health status instrument--generic, disease-specific and site-specific--in assessing changes resulting from total hip replacement (THR). METHODS A two-stage prospective study of patients undergoing surgery for THR involving an assessment at a pre-surgical clinic and a follow-up clinic at 6 months. 173 patients with a diagnosis of arthritis and being admitted for unilateral THR were recruited in the outpatient departments of a specialist orthopaedic hospital and peripheral clinics within Oxfordshire. Patients' health status was assessed using the 12-item Oxford Hip Score, the Arthritis Impact Measurement Scales (AIMS) and SF-36 general health questionnaire together with their surgeons' assessment using Charnley hip score obtained before and 6 months after surgery. RESULTS Effect sizes, used to compare change scores, revealed that pain and function domains changed most following THR on both the AIMS and the SF-36. 71 patients (41%) were assessed as having symptoms or problems currently affecting lower limb joints other than the hip recently replaced. Change scores were compared between these patients and all other patients who reported no current problems with other joints. The Oxford Hip Score found no significant difference between change scores for these two groups of patients while both AIMS and SF-36 physical and pain dimensions recorded significant differences of similar magnitude (physical P < 0.01, pain P < 0.05). Likely reasons for this were apparent on closer inspection of the item content of each instrument. CONCLUSIONS Assessment of outcomes in THR is necessarily long-term. Within studies of this kind, a hip-specific instrument (Oxford Hip Score) is likely to be more able to distinguish between symptoms and functional impairment produced by the index joint, as compared with other joints and conditions, than either a disease-specific instrument (AIMS) or a generic health status measure (SF-36). This is important given the high probability of existing and subsequent co-morbidity affecting such populations of patients. This consideration is likely to be relevant to any long-term assessment programme following treatment for a condition which threatens bilateral expression over time.

Fibrodysplasia (myositis) ossificans progressiva: clinicopathological features and natural history

Abstract: Patients with fibrodysplasia (myositis) ossificans progressiva (FOP) (n = 28) were studied for up to 24 years. All had characteristic short big toes potentially recognizable at birth; there were radiographic changes in the toes, thumbs, cervical spine and metaphyses of the long bones, including exostoses. Ossification in the large skeletal muscles began from birth to 16 years (mean age 4.6 years) initially in 25 patients in the neck and upper spinal muscles, and later around the hips, major joints and jaw. The rate and extent of disability was unrelated to the time of onset. There was no evidence that any form of treatment produced consistent benefit. Despite the unique combination of skeletal abnormalities and ectopic ossification, the first diagnosis in patients with FOP was often wrong and usually delayed after ectopic ossification began (mean 2.7 years, range 0-14). Except where presentation was unusual, such as progressive stiffness, this delay was mainly due to failure to recognize the significance of the abnormal toes. The most frequent erroneous histological diagnoses were soft tissue sarcoma or fibromatosis. This series emphasizes the usually incorrect initial diagnosis, the misinterpretation of the histology, the unpredictable prognosis and the failure of current treatment. Despite its extreme rarity, there is a need for wider knowledge of this condition both to avoid clinical errors and to stimulate research.

Cells of the mononuclear phagocyte series differentiate into osteoclastic lacunar bone resorbing cells

Abstract: Although the osteoclast shares several features with other cells of the mononuclear phagocyte system (MPS), its precise cellular ontogeny is unknown, and its membership of the MPS is controversial. This study examined whether various cells of the MPS can be induced to differentiate into cells capable of the highly specialized osteoclastic function of lacunar bone resorption. We isolated mouse and rat monocytes, mouse (liver, peritoneal, alveolar, brain) tissue macrophages, and spleen and marrow haemopoietic cells, as well as foreign body macrophages and macrophage polykaryons derived from subcutaneous granulomas formed by implantation of latex beads and coverslips in mice. When these cells were incubated with UMR106 osteoblast-like cells on glass coverslips and human cortical bone slices in the presence of 1,25-dihydroxy vitamin D3 [1,25(OH)2D3] for 7 and 14 days, numerous tartrate-resistant acid phosphatase-positive cells formed in these co-cultures and scanning electron microscopy revealed extensive lacunar resorption of the bone surface. Bone resorption was seen as early as 4 days after monocytes were co-cultured with UMR106 cells. With the exception of bone marrow-derived cells, lacunar resorption was not seen in the absence of UMR106 cells. These findings show that a bone-derived stromal cell element is necessary for differentiation of monocytes and tissue and inflammatory macrophages into osteoclast-like cells capable of extensive lacunar bone resorption, and would argue in favour of osteoclast membership of the MPS.

The development of adolescent idiopathic scoliosis

Abstract: There are many conflicting actiological theories for adolescent idiopathic scoliosis. We present a simple new model of scoliosis and a mechanism by which it is initiated and progresses. This mechanism provides a final common pathway for the multiple aetiological factors. A simple model of the spine, incorporating its fundamental mechanical features, was constructed. The model consisted of interconnected anterior compression and posterior tension columns. It allowed normal spinal movements, with flexion limited by the posterior column and rotation centred around the anterior column. It also allowed deformities to develop. The ends of the model were fixed in the position of the vertebrae they represented. Overgrowth of the anterior column relative to the posterior column caused the model to take up the shape of an idiopathic scoliosis. The greater the overgrowth, the more marked the deformity. Normally anterior and posterior column growth are coupled. During the growth spurt the thoracic kyphosis flattens indicating that anterior growth temporarily exceeds posterior growth. If this overgrowth is marked a scoliosis will develop, as demonstrated by the model. Once this occurs the coupling is lost, anterior growth further outstrips posterior growth and the deformity progresses. Not all scolioses worsen, as the tendency to progress is balanced by neuromuscular factors and remodelling. Factors that increase the growth rate, induce asymmetry or decrease the inherent stability of the spine all encourage the development and progression of a scoliosis. This explains the complex biomechanics of scoliosis and provides a final common pathway by which the multiple aetiological factors can induce idiopathic scoliosis. It has important implications for the understanding and treatment of this condition.

The forces which develop in the tissues during leg lengthening. A clinical study

Abstract: Axial forces were measured during limb lengthening in a series of ten patients with varying pathologies in order to assess the mechanical characteristics of the distracted tissues and the levels of axial force to which soft tissues are subjected during leg lengthening. The pattern of force was found to vary according to the underlying pathology. For post-traumatic shortening in adults both the peak and the resting forces rose steadily during lengthening reaching maximum forces of the order of 300 N. Patients with congenitally short limbs developed very high peak forces (in some cases over 1000 N) and also showed large amounts of force relaxation (typically 400 to 500 N). When very high levels of force were recorded, there was a higher complication rate. In particular, there was a high instance of angular deformity. This occurred because the loads encountered resulted in failure of some of the external fixation frames.

Increased osteoclastic differentiation by PMMA particle-associated macrophages. Inhibitory effect by interleukin 4 and leukemia inhibitory factor.

Abstract: To determine the influence of polymethylmethacrylate (PMMA) wear particles on macrophage-osteoclast differentiation, PMMA particles were added to mouse monocytes which were cocultured with UMR 106 osteoblast-like cells in the presence of 1, 25 di-hydroxy vitamin D3 [1, 25(OHJ2D3 for up to 7 days on glass coverslips and for up to 14 days on human cortical bone slices.An increase in osteoclast differentiation, as evidenced by the expression of the osteoclast-associ-ated enzyme tartrate-resistant acid phosphatase (TRAP) and the extent of lacunar bone resorption, was observed in monocyte cultures to which PMMA had been added. Interleukin 4 (IL-4) and Leukemia Inhibitory Factor (LIF) added to these cocultures caused considerably less expression of TRAP and significant inhibition of lacunar bone resorption. This inhibitory effect was reversed by the addition of specific neutralizing antibodies to LIF and IL-4. These findings show that PMMA-wear particle-associated macrophages exhibit an enhanced capacity for di...

Migration of cemented femoral components after THR. Roentgen stereophotogrammetric analysis.

Abstract: We studied the migration of 58 cemented Hinek femoral components for total hip replacement, using roentgen stereophotogrammetric analysis over four years. The implants migrated faster during the first year than subsequently, and the pattern of migration in the second period was very different. During the first year they subsided, tilted into varus and internally rotated. After this there was slow distal migration with no change in orientation. None of the prostheses has yet failed. The early migration is probably caused by resorption of bone damaged by surgical trauma or the heat generated by the polymerisation of bone cement. Later migration may be due to creep in the bone cement or the surrounding fibrous membrane. The prosthesis which we studied allows the preservation of some of the femoral neck, and comparison with published migration studies of the Charnley stem suggests that this decreases rotation and may help to prevent loosening.

Transmission of Rapidly Applied Loads Through Articular Cartilage Part 2: Cracked Cartilage

Abstract: A model of articular cartilage suffering rapidly applied loads and containing splits and fissures is presented. The possibility of cracks propagating through the cartilage collagen network is analysed using elastic fracture mechanics. Cracks are modelled using the distributed dislocation technique and the crack tip stress intensity factors are thereby evaluated. The mode I (tensile) stress intensity factors are generally much larger than the mode II (shearing) factors for cracks at the articular surface and close to, and at oblique angles to, the cartilage-bone interface, two regions where cartilage cracks have been observed. This suggests an opening, tensile mode of failure. The mode II factors are larger for cracks running along the interface. The rapidly loaded cracked cartilage model may explain the splits observed in osteoarthrotic cartilage.

Bone growth and remodelling after fracture

Abstract: We used a rabbit model to investigate the mechanism by which the angulation of fractures is corrected in children. We produced a transverse proximal tibial fracture in one leg of 12 eight-week-old New Zealand white rabbits and measured bone alignment and length and the patterns of bone growth and remodelling. The angle between the joint surfaces changed rapidly to correct the alignment of the limb as a result of asymmetrical growth of epiphyseal plates. In an adult with closed plates, the angle between the joint surfaces cannot therefore improve. The angle at the fracture itself showed slow improvement because of bone drift and the asymmetrical growth of the epiphyseal plates. Remodelling corrected the shape of the bone in the region of the fracture. Periosteal division on the convex side increased the growth of the epiphyseal plate on that side, thus slowing the correction. The effect was relatively small, providing an indication that factors other than the periosteum are important in inducing correction. External torsional deformities developed because of helical growth at the plate. This was probably caused by abnormal posture which induced a torque at the growth plate. Helical growth is the mechanism by which rotational deformities can occur and correct.

Bisphosphonate Inhibition of bone resorption induced by particulate biomaterial-associated macrophages

Abstract: Aseptic loosening of total joint replacements is associated with bone resorption. A heavy infiltrate of foreign body macrophages in response to biomaterial wear particles is commonly found in the fibrous membrane surrounding loose components. It has recently been shown that foreign body macrophages can differentiate into osteoclastic cells. To determine whether pharmacological inhibitors of bone resorption have a role to play in controlling the osteolysis of aseptic loosening, we analyzed the effect of a bisphosphonate, disodium ethane-1 , 1 -diphosphonate (EHDP) on this process. Murine monocytes and foreign body macrophages (derived from granulomas formed by subcutaneous implantation of particles of prosthetic biomaterials) were co-cultured with UMR106 osteoblast-like cells in the presence of 1,25 dihydroxyvitamin D, for 14 days on glass coverslips and bone slices. EHDP significantly inhibited bone resorption in these co-cultures. There was little or no expression of the osteoclast-associated enzyme, tartrate-resistant acid phosphatase (TRAP) in EHDP-treated co-cultures. Addition of EHDP to monocyte-UMR106 co-cultures after the appearance of TRAP-positive cells did not abolish bone resorption, indicating that EHDP, in addition to its known inhibitory effect on osteoclast function, suppresses differentiation of osteoclast precursors. EHDP inhibition of the osteolysis induced by particulate biomaterial-associated macrophages shows that pharmacological inhibition of bone resorption might be used to control the osteolysis of aseptic loosening.

Hay fever treatment in general practice: a randomised controlled trial comparing standardised Western acupuncture with Sham acupuncture

Abstract: Summary The effect of standardised, Western acupuncture on hay fever symptoms was investigated in a randomised, controlled, single-blind trial in comparison with “sham” acupuncture. Three general practices, in Oxfordshire (rural), Lincolnshire (semi-rural), and Peterborough (urban), recruited 102 patients aged 16 or over with long-standing, moderate or severe hay fever symptoms that had required continuous therapy for at least one month of the year for three or more consecutive years. The patients were asked to keep a diary to record: the amount of medication used daily; a daily symptom score (using a ten-point scale), from which was derived a weekly remission of symptoms score; and their assessment of the effect of acupuncture on the hay fever symptoms. Symptom scores and use of medication were similar in the two groups. In the four-week period following each patient9s first treatment, remission of symptoms was reported by 39.0% in the active treatment group and 45.2% in the sham group; mean weekly symptom scores were 18.4 and 17.6 respectively; and mean units of medication used were 4.1 and 5.0 respectively. Sixteen out of 43 patients in the active treatment group and 14 out of 43 in the sham group felt that the acupuncture had had an excellent or very good effect on their hay fever. The treatments were simple, safe, reproducible and perceived as equally effective. Whether this represented an acupuncture effect, a placebo effect, or natural variation in a fluctuating condition, is not clear.

Muscular Activity and the Biomechanics of the Hip

Abstract: The interactions between the forces transmitted by the muscles and by the bones are central to the understanding of load transmission in the musculoskeletal system. A reasonable concept of the biom...

Fibre Recruitment and Shape Changes of Knee Ligaments during Motion: As Revealed by a Computer Graphics-Based Model

Abstract: A computer graphics-based model of the knee ligaments in the sagittal plane was developed for the simulation and visualization of the shape changes and fibre recruitment process of the ligaments during motion under unloaded and loaded conditions. The cruciate and collateral ligaments were modelled as ordered arrays of fibres which link attachment areas on the tibia and femur. Fibres slacken and tighten as the ligament attachment areas on the bones rotate and translate relative to each other. A four-bar linkage, composed of the femur, tibia and selected isometric fibres of the two cruciates, was used to determine the motion of the femur relative to the tibia during passive (unloaded) movement. Fibres were assumed to slacken in a Euler buckling mode when the distances between their attachments are less than chosen reference lengths. The ligament shape changes and buckling patterns are demonstrated with computer graphics. When the tibia is translated anteriorly or posteriorly relative to the femur by muscle forces and external loads, some ligament fibres tighten and are recruited progressively to transmit increasing shear forces. The shape changes and fibre recruitment patterns predicted by the model compare well qualitatively with experimental results reported in the literature. The computer graphics approach provides insight into the micro behaviour of the knee ligaments. It may help to explain ligament injury mechanisms and provide useful information to guide the design of ligament replacements.

An instrumented spacial linkage for monitoring relative three-dimensional motion between fracture fragments.

Abstract: A mechanical linkage with electro-magnetic sensors (a displacement transducer) is described, which may be used to measure accurately the relative motion at a bony junction such as a fracture. The linkage may be fixed to bone screws of externally-fixated fractures during routine patient activity, to measure three-dimensional inter fragmentary displacements arising from dynamic loading. Movements of the linkage are monitored by six Hall Effect devices for the six degrees of freedom (three orthogonal translations and three rotations about the translating axes). Measurements are made within error bounds of +/- 0.025 mm and +/- 0.025 deg over a range of 5 mm for the two orthogonal transverse translations, 8 mm for axial translation and 8 deg for the three rotations. Movements at the linkage, remote from the fracture, are then translated mathematically to the fracture site, assuming rigid screw contact with the bone. Displacements of the distal fragment in relation to the proximal, at the fracture center, can then be expressed anatomically through anterior, medial, and distal translations, and rotations in the sagittal, coronal, or transverse planes.

Effect of HLA type and hypocomplementaemia on the expression of parvovirus arthritis: one year follow up of an outbreak.

Abstract: OBJECTIVES--To determine the effect of HLA type and hypocomplementaemia on the duration and severity of joint involvement in parvovirus infection (HPV). METHODS--Forty seven patients were selected on a geographical basis from 83 with proven HPV infection during an outbreak that occurred in Oxfordshire in 1993. They were contacted by questionnaire a year later. Thirty five patients were available for examination and blood sampling. Subjects were typed for HLA-DRB1 alleles and HLA-B27 status. Immunological profiles, including C3 and C4 complement components, were determined. RESULTS--Joint symptoms occurred in all patients. They resolved within a week in 12 patients and persisted beyond one year in 19. On review, none had a picture of rheumatoid arthritis, but three patients had developed carpal tunnel syndrome. Decreased C4 was found in four. The HLA frequencies were similar to those in controls; however, joint symptoms persisted for more than one week in all HLA-DR4 positive patients (p = 0.009). There was no relation between the severity of joint symptoms and either HLA type, or hypocomplementaemia. CONCLUSIONS--Joint symptoms are common in parvovirus infection and the presence of HLA-DR4 may be associated with persistence of joint symptoms beyond one week. This study revealed no evidence of progression to rheumatoid arthritis.

Distributed Dislocation Fundamentals

Abstract: The whole of this book is concerned with the exploitation of Bueckner’s theorem and the modelling of cracks by the distribution of strain nuclei of various kinds along crack lines in otherwise perfect bodies. In order to introduce the technique in the simplest possible way we will first consider plane problems. Figure 2.1(a) shows a plane crack opened by a tensile field. From Bueckner’s theorem the solution to this problem can be obtained by a superposition of the problems shown in Figures 2.1(b,c). These are the stresses arising in the uncracked body, as shown in Figure 2.1(b), and the stresses induced in the unloaded body, Figure 2.1(c), due to the application of equal and opposite tractions to those present along the line of the crack in problem Figure 2.1(b). The strategy we will adopt to generate the corrective tractions shown in Figure 2.1(c) is to make a fine slit along the line of the crack; the two sides of the cut are then separated by inserting material to fill ‘the crack’, as shown. The interior of the real open crack is, of course, empty; the inserted material is simply a mathematical device — a means of generating the corrective tractions, and at the same time simulating separation of the crack faces.