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Biomedical subjects

J L Cunningham

Publications and source records attributed to J L Cunningham.

At least 37 records · Page 2Linked to original sources
PubMed1998

A portable monitoring system for measuring weight-bearing during tibial fracture healing.

An ambulatory monitoring system has been developed to measure the weight-bearing achieved by a patient on their fractured leg. The system is lightweight, portable, and can monitor weight-bearing continuously over an extended period of time. In addition to mean weight-bearing, the system can also determine temporal parameters associated with the patients' gait. This system was used to measure the weight-bearing achieved during the course of fracture healing in a small number of patients being treated by a variety of fixation methods for a tibial fracture. In general, weight-bearing was observed to increase with time post fracture, and the fixation method employed appeared to influence the rate of increase of loading of the fractured limb, more rigid methods of fixation enabling full-weight-bearing to be achieved sooner.

Adolescent↗
PubMed1998

Strain rate and timing of stimulation in mechanical modulation of fracture healing.

Fracture of the long bones results in a repair process that has the potential to restore the anatomic morphology and mechanical integrity of the bone without scar tissue. The repair process can occur in two patterns. In the first, under conditions of rigid stabilization, direct osteonal remodeling of the fracture line can occur with little or no external callus, a process known as direct bone repair. The second pattern of repair involves bridging of the fragments with external callus and formation of bone in the fracture site by endochondral healing. This type of repair is known as indirect bone healing and occurs under less rigid interfragmentary stabilization. The rate of healing and the extent of callus in this type of repair can be modulated by the mechanical conditions at the fracture site. Applying cyclic interfragmentary micromotion for short periods has been shown to influence the repair process significantly, and characteristics of this stimulus influence the healing response observed. In the current study, a short term interfragmentary cyclic micromovement applied at a high strain rate induced a greater amount of periosteal callus than the same stimulus applied at a low strain rate. This high strain rate stimulus applied later in the healing period significantly inhibited the progress of healing. The beneficial effect of this particular biophysic stimulus early in the healing period may be related to the viscoelastic nature of the differentiating connective tissues in the early endochondral callus. In the early endochondral callus, high rates of movement induce a greater deformation of the fracture fragments because of the stiffening of the callus. Alternatively, the transduction pathway may involve streaming potentials as a result of the high movement rate.

Animals↗
PubMed1997

A survey of the pre-bonding preparation of denture teeth and the efficiency of dewaxing methods.

OBJECTIVES: Denture tooth debonding remains a significant problem, with the surface condition of the tooth playing a pivotal role. The purpose of this investigation was to determine the methods used in tooth preparation. The efficiency of wax removal from teeth using a range of water temperatures was also investigated. METHODS: (a) A postal survey on the methods of denture tooth preparation, prior to denture processing, was conducted amongst dental instructors in prosthodontic departments of dental schools in Great Britain and Ireland. (b) Tooth surfaces contaminated with fluorescence wax were subjected to agitation in water at a range of temperatures and the surfaces examined under ultraviolet radiation. RESULTS: (a) The majority of operators did not use a solvent for the removal of the wax film from the teeth. Modification of the tooth ridge lap surface was carried out by 52% of the respondents on initial processing but increased to 85% when rebonding teeth. (b) Dewaxing denture teeth at a range of water temperatures showed wax retention on the tooth surfaces up to 90 degrees C. Rough surfaces retained more wax than smooth surfaces. Wax eliminator was shown to be necessary for complete wax removal. CONCLUSIONS: No standard technique exists amongst dental instructors for the preparation of denture teeth prior to acrylic resin polymerization. The use of a wax solvent is to be recommended.

Acrylic Resins↗
PubMed1997

Bone mineral changes during tibial fracture healing.

The traditional assessment of fracture healing by manipulation and viewing of radiographs is subjective and qualitative. Dual energy x-ray absorptiometry by contrast provides an accurate, precise, and minimally invasive quantitative measure of bone mineral density, a property that shows strong correlations with various mechanical properties of bone. Fourteen patients with unilateral tibial shaft fractures stabilized by external fixation were monitored with dual energy x-ray absorptiometry at monthly intervals after fracture. Fractured and contralateral unfractured bones (controls) were scanned on each occasion. Changes in mineralization with time over the whole length of the fractured bone could be seen. The most pronounced effects were visible in the area of the fracture, with a minimum recorded fracture site bone mineral density of 38 +/- 13% of contralateral values, but often more long term alterations in bone mineral density affected regions at some distance from this zone. Significantly, in four patients who had scans 5 or more months after fracture, the mineralization at the fracture site had returned to control levels, whereas bone mineral density in a region proximal to the fracture showed evidence of persisting posttraumatic osteoporosis.

Absorptiometry, Photon↗
PubMed1997

Development of a six station knee wear simulator and preliminary wear results.

In order to assess the wear performance of different designs of total knee replacements (TKR), a six station multi-axis knee simulator has been designed, built and commissioned. The most important features of a knee simulator are representative angles of flexion-extension synchronized with a dynamically applied load, and a combination of rolling and sliding motion. The simulator typically applies flexion-extension of 0-65, anterior-posterior translation of up to 15 mm, a dynamic load of up to 5.0 kN, and operates at 1.0 Hz. The loads and motions are applied using computer controlled servohydraulic actuators and hence their profiles are easily modified. A preliminary wear test has been conducted using a Kinemax (Howmedica, United Kingdom) TKR. The test was conducted in 30 per cent bovine serum which was changed every 150,000 cycles, at which time the bearing surfaces were examined and the UHMWPE tibial component was weighed. Over eight million cycles, a tibial wear rate of 2.62 mg/10(6) cycles was measured. The mild wear observed was characterized by burnishing and slight scratching in the anterior posterior direction. These observations are broadly in line with both in vitro and ex vivo studies reported in the literature for this type of prosthesis. Delamination wear sometimes observed in vivo was not seen.

Animals↗
PubMed1997

Factors contributing to the wear of polyethylene in clinical practice.

Wear of polyethylene is a major contributor in the failure of total joint replacement. A number of different factors may predispose to increased wear of polyethylene. These can be broadly categorized as (i) material polymorphism, (ii) poor design features and (iii) three-body wear. Many of these factors contribute to the wear encountered in clinical practice. These mechanisms are reviewed and examples identified in which they have resulted in increased wear.

Biocompatible Materials↗
PubMed1997

The pathogenesis of osteolysis in two different cementless hip replacements.

Wear of ultra-high molecular weight polyethylene has been incriminated in the osteolysis associated with aseptic loosening of hip implants. A variety of different factors can contribute to accelerated patterns of polyethylene wear and subsequent osteolysis. This paper examines the incidence of osteolysis observed in two different well-matched cohorts of cementless total hip arthroplasties. The patterns of osteolysis observed, which are ascribed to the generation of polyethylene debris, are interpreted with reference to the design of the individual prostheses.

Biocompatible Materials↗
PubMed1996

Simultaneous bilateral tibial stress fractures in a 15-year-old milkman--a case report.

Although stress fractures are well recognized, their frequency, sequelae and complex aetiology are often under-rated. In this case report, we describe an unusual case of simultaneous bilateral stress fractures of the proximal tibial shaft in a young man, exposed to a sudden increase in unaccustomed joint loading due to his part-time occupation. The pathogenesis is discussed.

Adolescent↗
PubMed1996

Dual-energy X-ray absorptiometry as a measure of healing in fractures treated by intramedullary nailing.

The conventional qualitative techniques of manual manipulation and plain radiography do not give a quantifiable measurement of healing. With internal fixation, manual manipulation is not usually possible, and conventional radiographs may not give much useful information, particularly if only a small amount of callus is formed. Dual-energy x-ray absorptiometry (DXA) provides an accurate method of quantifying the changes in bone mineral density (BMD) which occur during fracture healing. Preliminary work showed that the presence of a highly attenuating metal implant in the scan area did not affect the reliability of BMD data obtained from scans. On this basis, we have assessed the use of DXA in the clinical situation to monitor fractures treated by intramedullary nailing. Five fractures of the mid-shaft of the tibia stabilized by interlocked intramedullary nails have been monitored by DXA at monthly intervals through healing. DXA improves on radiography in giving a quantitative measure of fracture site mineralization. However, it is concluded that, because of the relatively small changes in callus BMD encountered with the rigid fixation provided by interlocked intramedullary nailing, DXA offers no significant diagnostic advantages over plain radiography.

Absorptiometry, Photon↗
PubMed1996

A new technique for determining the denture tooth bond.

Defective bonds between resin teeth and denture base material remain a continuing source of failure. Findings from the limited number of studies on this topic are diminished by the numerous experimental approaches adopted. National and international standard specifications also adopt different methods of specimen preparation and physical straining. A critical appraisal of the various standards is carried out and a new procedure for determining the denture tooth to acrylic resin bond is described. A study using this technique found that physical modification and alginate contamination of the tooth had no significant effect on the bond strength. Ineffectual wax elimination was the main cause of failure.

Acrylic Resins↗
PubMed1996

Ultrasound velocity and attenuation at different skeletal sites compared with bone mineral density measured using dual energy X-ray absorptiometry.

Measurements of ultrasound velocity were performed in the tibia in a group of 89 female subjects (mean age 50.6 years). Velocity and broadband ultrasound attenuation (BUA) measurements were performed in the os-calcis in a group of 100 male and female subjects (mean age 55.8 years). Dual energy X-ray absorptiometry (DEXA) scans were also performed on all of these subjects enabling measurements of lumbar spine and femoral neck bone mineral density (BMD) to be obtained. In two small subgroups of the above groups, each comprising 20 subjects, measurements of tibial BMD and os-calcis BMD were also performed. Tibial BMD and ultrasound velocity were found to be well correlated (r = 0.71), although both spine and femoral neck BMD were poorly correlated with ultrasound velocity in the tibia (r = 0.299 and 0.072, respectively). BUA of the os-calcis was moderately correlated with BMD at the same site (r = 0.44) and showed similar or slightly better correlations with BMD measurements of the lumbar spine and femoral neck (r = 0.410 and 0.537, respectively). Ultrasound velocity in the os-calcis was well correlated with os-calcis BMD (r = 0.729) but only moderately correlated with spine and femoral neck BMD (r = 0.470 and 0.498, respectively). This study suggests that BUA and ultrasound velocity measurements of the os-calcis are better predictors of BMD at the critical skeletal sites of the lumbar spine and femoral neck than ultrasound velocity in the tibia. Ultrasound velocity in the tibia and the os-calcis was found to be a good predictor of the BMD in the measured bone.

Absorptiometry, Photon↗
PubMed1996

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

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.

Adult↗
PubMed1995

The assessment of fracture healing using dual x-ray absorptiometry: a feasibility study using phantoms.

Tissue substitute materials of water and Perspex for soft tissue and aluminium and hydroxyapatite for bone have been combined into phantoms to simulate tibial fractures and have been used to assess the viability of using dual x-ray absorptiometry to quantitatively measure changes in bone density during fracture healing. It was found that it was possible to detect small gaps created in the aluminium phantoms to simulate a tibial fracture down to a gap size of 0.95 mm with the gap oriented both parallel and perpendicular to the x-ray beam. The mass and area density of small samples of calcium hydroxyapatite were found to be closely correlated with the values of bone mineral content (r2 = 0.97) and density (r2 = 0.99) given by the scanner, and low values of bone mineral content and density, which might be expected around a healing fracture, could be precisely measured. Reproducibility of the results was found to be good with a coefficient of variation of less than 1.5%.

Absorptiometry, Photon↗
PubMed1995

Influence of metallic implants adjacent to the measurement site on DEXA measurements: a phantom study.

The use of dual-energy x-ray absorptiometry (DEXA) to measure changes in bone mineral density (BMD) at a healing fracture may be limited by the presence of a steel implant, such as an intramedullary nail or internal fixation plate. To determine the effect of steel implants adjacent to the measurement site on BMD measurements, tests were conducted on three geometries of steel and aluminium phantom. Analysis of variance performed on the BMD data from scans of the aluminium phantoms with and without steel present indicated that the steel had no effect on the results obtained at the 5% significance level. These results imply that the presence of a steel implant adjacent to an area of interest, for example a healing fracture, would not affect the reliability of DEXA scans, and that this method of monitoring healing could therefore be used with fractures stabilized by internal fixation.

Absorptiometry, Photon↗
PubMed1994

Measuring stiffness can define healing of tibial fractures.

We measured fracture stiffness in 212 patients with tibial fractures treated by external fixation. In the first 117 patients (group 1) the decision to remove the fixator and allow independent weight-bearing was made on clinical grounds. In the other 95 patients (group 2) the frames were removed when the fracture stiffness had reached 15 Nm/degree. In group 1 there were eight refractures and in group 2 there was none (p = 0.02, Fisher's exact test). The time to independent weight-bearing was longer in group 1 (median 24 weeks) than in group 2 (21.7 weeks, p = 0.02). The greater precision of our objective measurement was associated with a reduction in refracture rate and in the time taken to achieve independent weight-bearing. We consider that a stiffness of 15 Nm/degree in the sagittal plane provides a useful definition of union of tibial fractures.

Biomechanical Phenomena↗
PubMed1993

Bond strength of denture teeth to acrylic bases.

The literature relating to the determination of the bond strength of plastic denture teeth to acrylic resin denture material is reviewed. The papers are presented in chronological order with information on specimen preparation, batch sizes and methods of testing. The lack of uniformity in experimental techniques and the diverse range of products assessed makes recommendations for laboratory practice difficult to formulate. One consistent observation is that tooth surface contamination with wax decreases the bond strength between the teeth and the denture base material. A universal testing method needs to be formulated to replace the various techniques now employed.

Acrylic Resins↗
PubMed1993

Skeletal accelerations measured during different exercises.

Exercise is often suggested as a means of reducing the effects of osteoporosis in post-menopausal women. In response to an increase in physical activity, bone mass can be increased and several studies have investigated the effectiveness of different exercises in increasing bone mass. In this study we have attempted to quantify the effect of different exercises by measuring the accelerations produced during various exercises. Accelerations have been measured at the ankle of normal subjects during a series of impulsive (walking, running and walking up and down stairs) and non-impulsive (cycling) exercises. Accelerations were measured using an accelerometer attached to a stiff cuff which straps around the ankle. Signals from the accelerometer are amplified and recorded using a specially developed portable data-logging system. THe principal parameters measured were the maximum change of acceleration (peak to peak) and the rate of change of acceleration. From the results it was observed that running and walking up and down stairs produced the highest peak-to-peak change (running = 8.08 g; walking downstairs = 8.11 g) and rate of change of acceleration (running = 2.14 g/s; walking downstairs = 2.07 g/s). By contrast, a non-impulsive exercise such as cycling produced relatively low values of peak-to-peak change (2.24 g) and rate of change (0.23 g/s) of acceleration.

Adult↗