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Biomedical subjects

W G Kernohan

Publications and source records attributed to W G Kernohan.

At least 37 records · Page 2Linked to original sources
PubMed1993

Deep venous thrombosis in orthopaedic patients. Improving the specificity of diagnosis.

The diagnosis of deep vein thrombosis after total joint arthroplasty is difficult. The most widely used method of detection is physical examination and selective venography, which are unreliable and expensive even when symptoms and signs are prominent. This study employed computerized strain gauge plethysmography (CSGP) to select symptomatic patients for venography. The incidence of detection by CSGP was increased from 16% to 81.7%. Repeated CSGP also was investigated, but although specificity was further enhanced, it was at the expense of sensitivity. The negative predictive value of the CSGP screening was high and comparable to that of venography and indicates that CSGP is useful in the management of patients with symptoms suggestive of deep vein thrombosis. Computerized strain gauge plethysmography results emphasize the low specificity and poor feasibility of clinical examination and venography. Computerized strain gauge plethysmography is strongly advocated as a selection procedure for invasive venography in total joint arthroplasty patients.

Hip Prosthesis↗
PubMed1993

Low-frequency vibration emitted from unstable hip in human neonate.

Developmental dysplasia of the hip (DDH) continues to be an orthopedic enigma. Some authors still believe it is a purely birth phenomenon. Even with widespread birth screening, however, DDH continues to become evident later than three months of age, long after a satisfactory outcome can be guaranteed. In an effort to reduce the number of late manifestations, the authors have developed a noninvasive form of screening for DDH called vibration arthrometry. Five hundred neonates were examined in local maternity hospitals, according to the guidelines of Ortolani and Barlow. The new method involves the attachment of miniature accelerometers around the infant's pelvis. Using this method, it was possible to elicit vibration events from approximately one fourth (255 hips) of the hips tested; vibrations were recorded from normal hips (125), from "clicky" hips (128), and from unstable hips (two). Differences between "nil-felt" (clinically silent) and "click-felt" (palpable clicking on testing) were significant. Vibration testing can be seen as an aid in the manual palpation necessary to detect this crippling condition.

Female↗
PubMed1993

What do orthopaedic surgeons tell patients?

Surgical patients have the right to clear communication regarding diagnosis, treatment and prognosis including risks and likelihood of success. In order to ascertain the level of consensus which exists among orthopaedic surgeons about what patients should be told, a short questionnaire comprising a fictitious case history of a candidate for total hip replacement and a list of sample statements was mailed to all orthopaedic surgeons in Northern Ireland; 86% replied. Surgeons were in general agreement about what the patient should and should not be told prior to operation. This approach may be adapted for other procedures.

Hip Prosthesis↗
PubMed1992

A computerised system of screening for deep venous thrombosis.

We have developed a computer controlled system of strain gauge plethysmography for use as a screening tool for proximal segment venous thrombi which is simple to use, well tolerated by patients and extremely accurate. The computerised test was evaluated in 171 limbs of 163 symptomatic patients by comparison with subsequent ascending venography. Each of twenty occlusive proximal segment thrombi were identified, one non occlusive thrombus screened normal giving an overall sensitivity of 95.2%. The specificity of the test was 80% with a negative predictive value of 99.0%. The computerised system allows accurate screening for proximal segment venous thrombosis, and may permit more selective use of venography in the symptomatic post-operative limb.

Acute Disease↗
PubMed1992

A prospective randomized trial of chemonucleolysis and conventional disc surgery in single level lumbar disc herniation.

The role of chemonucleolysis as an alternative to disc surgery is still disputed. The authors conducted a prospective randomized controlled trial of chemonucleolysis and conventional disc surgery involving 92 patients with L4-5 or L5-S1 disc herniation who failed to respond to conservative treatment. There were 46 patients in each group, matched for demographic, clinical characteristics, and co-interventions. Independent examiners assessed patients before treatment, at 6 weeks after, 3 months after, and 1 year after treatment. A comprehensive method of outcome assessment involving physiological outcome, functional outcome, cost outcome, and psychological outcome was employed. Nine chemonucleolysis patients and one disc surgery patient required additional surgery for failure of initial treatment (P less than 0.02). The outcomes at 6 weeks and at 3 months were better in the surgical group, but at 1 year the differences were not significant. The authors conclude that chemonucleolysis as a minimally invasive technique produces inferior short-term results and offers no advantage over conventional discectomy.

Adult↗
PubMed1992

Total joint replacement: implication of cancelled operations for hospital costs and waiting list management.

OBJECTIVE: To identify aspects of provision of total joint replacements which could be improved. DESIGN: 10 month prospective study of hospital admissions and hospital costs for patients whose total joint replacement was cancelled. SETTING: Information and Waiting List Unit, Musgrave Park Regional Orthopaedic Service, Belfast. PATIENTS: 284 consecutive patients called for admission for total joint replacement. MAIN MEASURES: Costs of cancellation of operation after admission in terms of hotel and opportunity costs. RESULTS: 28(10%) planned operations were cancelled, 27 of which were avoidable cancellations. Five replacement patients were substituted on the theatre list, leaving 22(8%) of 232 operating theatre opportunities unused. Patients seen at assessment clinics within two months before admission had a significantly higher operation rate than those admitted from a routine waiting list (224/232(97%) v 32/52(62%), x2 = 58.6, df = 1; p < 0.005). Mean duration of hospital stay in 28 patients with cancelled operations was 1.92 days. Operating theatre opportunity costs were 73% of the total costs of cancelled total joint replacements. CONCLUSION: Patients on long waiting lists for surgery should be reassessed before admission to avoid wasting theatre opportunities, whose cost is the largest component of the total costs of cancelled operations.

Data Collection↗
PubMed1992

The Belfast hip screener: from infancy to maturity.

Hip dislocation remains the most significant childhood orthopaedic abnormality despite the efforts of neonatal screening, first described in 1910. A new method of enhancing the performance of screening, the Belfast hip screener, is a non-invasive device developed to detect and interpret the vibrations ("clicks" and "clunks") which are emitted as the hips are physically tested. A progress report is presented covering ten years' work from early records made with tape recorders to modern methods of digital signal processing.

Diagnosis, Computer-Assisted↗
PubMed1991

Vibration arthrometry in assessment of knee disorders: the problem of angular velocity.

A knee joint that has sustained a painful injury will typically require skillful examination, by an orthopaedic surgeon, for signs of internal damage. These signs include characteristic sounds and vibrations, which are produced by the knee when it is stressed. The technique of vibration arthrometry is being developed to assist the clinical examiner in identifying these vibrations and to improve diagnostic accuracy. To detect and record the knee vibrations, small lightweight accelerometers are positioned on various bony prominences around the knee. These produce electronic signals which permit objective analysis of the vibration characteristics. It has been found that varying the investigative procedure can affect the magnitude of some parameters of the vibration signal. If these parameters are to be used in evidence of knee pathology, the effect of the investigative procedure must be normalized. The effect of speed of joint movement has been quantified in a pilot study involving 24 patients with internal knee damage. Custom-designed hardware was used to measure joint speed as the rate of change of joint angle, which was measured by an electrogoniometer. It was found that the energy content of the vibration, reflected by the peak amplitude and root mean square value was strongly affected by joint speed. However, the characteristic shape of the vibration, reflected by the peak frequency in the harmonic spectrum of the signal, remained similar for the range of joint speed in the investigation.

Adult↗
PubMed1991

Optical measurements of physiological patellofemoral crepitus.

An optical method to measure directly small displacements of the patella has been developed. Light from a helium-neon laser was reflected from a plane mirror taped to the skin over the patella to a glass plate which generated a set of fringes by interference of light reflected from the front and rear surfaces of the plate. The movement of the fringe system was detected using a photodiode. The optical measurements of displacement were compared with those deduced from an accelerometer attached to the same joint. The method was found to be capable of detecting patellar displacements in the range from 20 microns to 180 microns.

Femur↗
PubMed1991

Serum keratan sulphate level following chemonucleolysis.

In chemonucleolysis, accuracy of injection can be in doubt if the patient fails to respond. Discography preceding chemonucleolysis is associated with increased neurologic complications. Biplane fluoroscopy may fail to provide a clear picture on many occasions. The serum keratan sulphate levels were estimated in patients undergoing chemonucleolysis to ascertain if this could be used as a biochemical indicator to confirm accurate needle placement and to predict outcome. Serum keratan sulphate levels rose significantly following chemonucleolysis during the first 3 days (P less than 0.01). The rise was not significantly different, however, in patients who had improvement in their leg pain from those who did not improve (P = 0.35). Serum keratan sulphate level estimation before chemonucleolysis and at 24 or 48 hours following the procedure can be used to confirm accuracy of needle placement, but the rise in keratan sulphate is not predictive of the clinical outcome of the procedure.

Adult↗
PubMed1991

Non-invasive diagnosis and prophylaxis in orthopaedics.

In this paper some ten years of work in bioengineering is described. The central theme is non-invasive diagnosis and prophylaxis. This theme is exemplified in several interrelated sections of work which are described. The work is categorized into: modest beginnings, hip and knee vibration papers, deep venous thrombosis and cavitation in human joints. The philosophy is straightforward--to benefit patients by making harmless measurement.

Biomechanical Phenomena↗
PubMed1991

Vibration arthrometry in congenital dislocation of the hip.

Three hundred six neonates referred to a research clinic for vibration arthrometry were studied to determine whether the application of objective methods could enhance the accuracy of hip examinations. A total of 629 vibration episodes (hip "clicks" and "clunks") were detected using miniature accelerometers and recorded during testing for congenital dislocation of the hip. Five categories of congenital dislocations of the hip (CDH) were defined: normal (53 cases), safe click (201 cases), click associated with later CDH (16 cases), unstable (14 cases), and late CDH (22 cases). Follow-up examinations were performed over a four-year period. Detailed measurement of vibration signals was possible and resulted in the resolution of eight variables for each episode. Two variables, pulse area and peak frequency, were selected for their power to discriminate between the five clinical groups. The pulse area values were higher for the late and unstable groups. In addition, the vibrations were examined using Fourier analysis, and the safe click group demonstrated higher frequency components than any other group. Vibration arthrometry is proposed as a possible adjunct in screening for CDH, as it may pick up cases that would be missed by an average examiner and it could monitor clicks, thus avoiding nonessential splintage.

Diagnosis, Computer-Assisted↗
PubMed1990

Osteoarthritis.

Explore the source record for details and available documents.

Adult↗
PubMed1990

Fourier analysis of ventricular fibrillation of varied aetiology.

Fast Fourier Transform analysis was used to study ventricular fibrillation induced by several different methods in 43 greyhounds anaesthetized with sodium pentobarbitone. The dominant frequency at the body surface of ventricular fibrillation induced electrically in non-ischaemic hearts was initially 9.9 +/- 0.7 Hz, remained above 9 Hz for 70 s and then rapidly fell to 5 Hz. The dominant frequency of ventricular fibrillation induced by acute occlusion (initially 12.3 +/- 0.2 Hz), or by reperfusion (12.2 +/- 0.4 Hz) of the anterior descending branch of the left coronary artery, showed a similar time-course. However, ventricular fibrillation induced by administration of potassium (4.8 +/- 0.8 Hz) or ouabain (7.1 +/- 1.1 Hz) was significantly slower. Fibrillation recorded from the endocardium of the heart initially showed a similar dominant frequency to that recorded at the body surface, but there was no significant fall in frequency over 3.3 mins. There was little difference in the time-course of fibrillation in the non-ischaemic heart recorded directly from the epicardium or from a surface lead. These findings may be of relevance to the poor response to DC countershock after prolonged ventricular fibrillation, hyperkalaemia or cardiac glycosides.

Animals↗
PubMed1990

Pharmacological analysis of established ventricular fibrillation.

1. The effects of anti-arrhythmic drugs on the power spectrum of established ventricular fibrillation induced by endocardial electrical stimulation, have been studied in greyhounds anaesthetized with sodium pentobarbitone (35 mg kg-1, i.v.). 2. In dogs receiving no drug, initial recording of ventricular fibrillation showed a dominant frequency of 9.9 +/- 0.7 Hz (lead II) and 10.0 +/- 0.6 Hz (endocardium). After 3.3 min the frequency had fallen to 4.0 +/- 0.4 Hz in lead II, but remained high in the endocardium (10.7 +/- 0.5 Hz). 3. Lignocaine significantly reduced the dominant frequency for fibrillation recorded from lead II at (0-80 s), and for endocardial fibrillation at (0-200 s). 4. Pretreatment with propranolol or bretylium had little effect on the time course of the dominant frequency of fibrillation in lead II or the endocardium. 5. Verapamil prevented the fall in frequency seen in lead II after 80 s in the no drug group. A significantly higher frequency was maintained in both lead II (14.7 +/- 0.9 Hz) and the endocardium (14.8 +/- 0.9 Hz) for 3.3 min, compared with the no drug group (P less than 0.01). 6. Activation of fast sodium channels may determine the rapid frequency of the initial stages of ventricular fibrillation. The rapid fall in dominant frequency in lead II after fibrillation for 80 s can be prevented by calcium channel blockade and may be due to intracellular accumulation of calcium.

Animals↗
PubMed1990

Vibration arthrometry. A preview.

Throughout the ages, physicians have listened to sounds and felt vibrations from human joints in their attempts to diagnose pathology. They have used a wide vocabulary to describe these phenomena, but technology has been slow to provide recording and analytic equipment. Lately, accelerometers have been used with considerable success in a new noninvasive method now known as vibration arthrometry (formerly "arthrography"). The technique has been used in early detection of congenital dislocation of the hip and also in diagnosis of meniscal pathology. More recently, patellar vibration has been used to assess the mechanical properties of articular cartilage. Vibration arthrometry has also yielded new information on a possible damage mechanism associated with shock vibration that arises during cavitation of synovial fluid. Joint vibrations are therefore useful aids to diagnosis and may even be etiologic in orthopedic disease.

Hip Dislocation, Congenital↗
PubMed1989

A study of the cracking sounds from the metacarpophalangeal joint.

The familiar cracking sounds produced by distraction of the metacarpophalangeal joints were studied using accelerometers and a computerized signal analysis system. The joints were distracted in a controlled manner using a motorized device which simultaneously monitored the load on the joint and its extension. The load and extension parameters and those from the signal analysis were used to examine diurnal variation, the effects of multiple distractions, distraction speed, hand temperature and loading between distractions, and to show that in many cases, the energy contained in a crack signal, expressed as a ratio of the articular cartilage volume, exceeded a known level needed to produce articular cartilage damage.

Adult↗