Impaction bone grafting in revision hip surgery. A high incidence of complications.

We have reviewed retrospectively 68 revisions of the femoral component in arthroplasties of the hip in 65 patients, using impaction bone grafting, at a median of three years (1 month to 6 years). We employed the cemented Exeter X-Change technique in 36 patients and the uncemented Bi-Metric allografting method in 32. The 37 bone defects were grade 3 or grade 4 on the Endo-Klinik classification. The Mayo hip score improved from a mean of 32 (SD +/- 18) to 62 (SD +/- 15). Most (25) of the 34 complications occurred in grade-3 and grade-4 defects; nine were intraoperative diaphyseal fractures and eight fractures of the greater trochanter. All the fractures united. The risk of intraoperative fracture was prevented by supporting the bone with wires in 16 hips, with reinforcement mesh in 18 and by a plate in six. Early migration of the stem of more than 10 mm during the first year indicated rotational instability; it occurred in three cases. In difficult revision cases with large defects of the femoral bone, bone-impaction techniques carry a high risk of complications.

Recovery of sciatic nerve injuries in association with total hip arthroplasty in 27 patients.

We analyzed 27 sciatic nerve injuries associated with total hip arthroplasty (THA). The patients were 23 women and 4 men, and their median age was 55 years (range, 28-75 years). In 1987 to 1995, 4,339 THAs were performed. Primary arthroplasties accounted for 3,471 and 868 were revisions. Nine patients had developmental dysplasia of the hip. Six operations were revisions. Radiologic lengthening was median 1.4 cm (range, -1 to 4.1 cm); in 8 cases, lengthening was greater than 2 cm. The median follow-up period was 58 months (range, 24-110 months). Eight patients recovered fully, the recovery of 7 patients was fair, and 12 patients had a considerable permanent disability. The risk of nerve injury was not related to the extent of lengthening. The recovery of the nerve injury was only weakly correlated to its primary postoperative extent. The sciatic nerve injury rate was 0.6%.

Noise, impulse noise, and other physical factors: combined effects on hearing.

In most of the epidemiologic studies conducted during the last 20 years, impulse noise caused increased risk of hearing loss in comparison to continuous noise with the same acoustical energy. The interaction between noise exposure (broadband at 100 dB(A)) and hand-arm vibration (125 Hz at 2 ms-2 acceleration level) has been proven for people having vibration-induced white finger symptoms. This interaction is evidenced as a permanent hearing loss. However, why the interaction is seen only in people with VWF is not known. The mechanisms may be related to individual susceptibility, and hypotheses are given on the role of the autonomous nervous system regulating the peripheral vascular reaction. Whole-body vibration (2-10 Hz, at 10 ms-2 level) seems to increase the TTS when noise (broadband at 90 dB(A)) is present. This effect is more pronounced at higher temperatures. The hypothermia protects hearing against the effects of noise in animal studies. The interaction between noise and temperature decrease seems obvious in animal studies. Exercise has both increased and decreased the TTS during noise exposure. The effects have been successfully explained as the depression of the stapedius reflex. Thus, less protection against noise is provided for the inner ear in exercise conditions. The increase of the blood temperature also has been suggested to increase noise-induced TTS during exercise. Electromagnetic fields have been found to cause acoustical interactions in the inner ear. Animal studies and human studies have given contradictory results on the effects of magnetic coil devices on hearing. The MR imaging devices produce noise levels of 82-93 dB, which is not sufficient to produce the risk of permanent hearing loss when short exposure durations are taken into consideration. More systematic research is needed with accurately defined electromagnetic characteristics to reveal the potential interactions. The interactions seem to exist, but relatively high levels and durations of exposure are needed to produce an observable effect on hearing. More investigations are still needed on the permanent hearing loss in humans caused by simultaneous long-term exposures to interacting environmental factors.

Physical characteristics of gunfire impulse noise and its attenuation by hearing protectors.

The peak sound pressure level (SPL), spreading of pressure wave and other physical characteristics of the impulse noise from weapons were studied in actual shooting conditions for assessment of gunfire noise exposure. Additionally, the attenuation of SPL by hearing protectors was measured with miniature microphones to evaluate protection efficiency in real shooting conditions. The peak SPLs at the shooter's ear ranged from 132 dB (miniature rifle) to 183 dB (howitzer). The spectral content of the main part of the acoustic energy was less than 400 Hz (peak 16-100 Hz) for large-caliber weapons and 150-2,500 Hz (peak 900-1,500 Hz) for small-caliber weapons (rifles). The safe distances from the noise source (less than 140 dB peak SPL) were 50-200 m for large-caliber weapons. Rifle impulses (assault rifle, caliber 7.62) had a peak SPL of 154 dB at a distance of 4 m from the muzzle. The peak SPLs of different explosives ranged from 125 to 185 dB at distances of 10 to 300 m. In rifle shooting, the attenuation efficiency of earplugs (16dB) or small-volume (thin) earmuffs (17 dB) was not sufficient and their use as sole protectors cannot be recommended. Instead, large-volume earmuffs should be used. Impulses from pistol and shotgun were fairly effectively attenuated both by small-volume and large-volume earmuffs. All kinds of earmuffs appeared to be ineffective (attenuation less than 15 dB) against impulses from large-caliber weapons with energy content at very low frequencies. Therefore, the combined use of earmuffs and earplugs is recommended for the most noisy operations. On the basis of the present data, wider safety zones were adopted in the Finish Defence Forces at shooting with different weapons.

Effect of hand-arm vibration on inner ear and cardiac functions in man.

To evaluate distant effects of hand-arm vibration we studied Finnish forestry workers using chain saw during the years 1972 through 1990. The hearing was tested annually and individual regression curves for sensorineural hearing loss (SHL) were calculated. Robinson's model was used in prediction of SHL. The heart rate variation (HRV) indexes at rest and during deep breathing test were analyzed to measure autonomic nervous function. In Robinson's model the measured SHL (17.8 dB) respected the predicted SHL (17.2 dB). The subjects with VWF had on average, 10 dB greater hearing loss than those who did not have VWF. The regression model based increase of hearing loss during follow up correlated with ageing, not to VWF. The intercept differed significantly in those with VWF from those without VWF. We found a significant difference between HRV indexes during deep breathing test in those with the shortest and those with the longest vibration exposure. The HRV decreased with age, but multiple regression analysis showed that the total exposure time to vibration had an independent negative association with HRV indexes. Our results suggest that prolonged exposure to vibration caused by chain saw has negative effects an autonomic functions. The aggravated hearing loss in subjects with VWF may be due to vibration induced changes in the autonomic nervous system or internal factors of the blood vessels.

Vibration exposure and prevention in Finland.

The number of annually compensated occupational diseases due to exposure to hand-arm vibration (HAV) has decreased during the last 15 years. The number of exposed workers has been declining in Finland, especially in forestry work, as harvesters have increasingly replaced manual chain saw operations. During the entire 1970s, forest work caused more cases of vibration-induced occupational diseases than all industrial branches together. The decrease is mainly due to the technical development of chain saws, but also to the effective health care services in Finland. Other factors such as warm transport, warm rest cabins in which to take pauses at work, warm meals, adequate protective clothing, and vocationally adjusted early medical rehabilitation have helped to cut down health hazards, especially in forest work. The number of new cases has been decreasing in Finland not only in forestry but also in other industries. In Finland a considerable amount of research has been conducted to hand-arm vibration, resulting in the increased awareness of the health risks related to certain occupations. This has helped to carry out the Primary Health Care Act (1972) followed by the Occupational Health Care Act (1979) which obligates employers to arrange occupational health care for their employees. We believe that the research activity has contributed significantly to achieving the present health in Finnish work places. The purpose of the present paper is to describe the cases of occupational exposure to HAV, and the effectiveness of different preventive measures in Finland.

Hearing loss risk from exposure to shooting impulses in workers exposed to occupational noise.

The effect of shooting impulses on hearing was analysed in 150 professional forest workers exposed to noise from chain saws. The exposure to shooting impulses (Lesi) was designed to take into account the peak levels of shooting impulses, their number and use of hearing protectors. Hearing loss was dependent on Lesi even after allowing for the age of subjects and their exposure to chain saw noise. Hearing threshold levels were compared between pairwise matched groups with high and low Lesi. Proper matching was achieved for age, chain saw noise, salicylate consumption, blood pressure, cholesterol, smoking and vibration-induced white finger symptoms. The workers with high Lesi had 9 dB greater hearing loss at 4 kHz and 10 dB greater hearing loss at 8 kHz than those with low Lesi, the difference being significant at P < 0.05 level. In evaluation of noise-induced hearing loss the exposure to shooting impulses from different calibre weapons should be determined since they increase the extent of hearing loss. The present study describes the Lesi method which more accurately evaluates the harmful effects of shooting noise impulses on hearing.

Measurements of postural stability: development of a force platform and some excitation systems.

Technical data are given for the construction of a low cost transportable force platform to measure postural stability. The measuring elements in the platform are placed between two rigid metal plates to give information about the movements of the center point of force of a standing subject. The system utilizes a microcomputer for data collection, and data analysis routines are used to calculate the movement of the center point of force. Postural perturbation was excited with a vibrating platform, a low frequency noise source and a vibration stimulator for the calf muscles.

Hearing protection against high-level shooting impulses in relation to hearing damage risk criteria.

The earmuff attenuation of acoustic impulses produced by large-caliber weapons was measured with a high-speed microcomputer controlled unit. The estimated accuracy was +/- 1 dB in peak sound-pressure level measurements. The peak levels outside earmuffs were 184 dB for the heavy bazooka and 172 dB for the hand-held bazooka (re: 20 microPa). Heavy bazooka impulse peak levels were attenuated from 7 to 19 dB by the earmuffs depending on the mass and volume of the measured three types of earmuffs. Hand-held bazooka impulse peak levels were attenuated by the earmuffs from 9 to 15 dB. The risk limits for hearing loss from a single impulse were exceeded in spite of the use of earmuffs when the criteria of CHABA (USA) or Pfander (Germany) were applied. The unexpectedly low attenuation was due to the low-frequency waveform of the high-level impulses. The earmuffs were found to prolong the impulse duration, which may reduce the benefit otherwise achieved by attenuation of the peak levels.

Transmission of vibration from tool handle to wrist and to head.

Transmission of vibration from the handle of the tool to the handarm system was investigated by measuring vibration in pairs from the source and from the wrist and head. The frequency response function was applied to describe the transmission properties. The measurements were taken at work places to evaluate the effect of different work-related factors on the transmission. Laboratory measurements were conducted to evaluate the effect of different grip forces and the use of protective gloves on the transmission. The field measurements comprised five different groups of workers whose exposure to vibration was evaluated and whose observed symptoms of vibration-induced white finger (VWF) was compared to the predicted ones based on the exposure data and on ISO 5349. The comparison of the prevalence data was in good agreement for the forest workers. The ISO method seemed to underestimate the genesis of VWF in workers who had to use high grip forces and for whom the vibration comprised high values of impulsiveness. The present results suggest that the frequency response function as independent of the input signal may thus describe factors important to the transmission of vibration.

[A comparison of hearing losses in the workers of a shipyard and in loggers in relation to individual risk factors]. / Sravnenie poter' slukha u rabochikh sudoverfi i lesorubov v sviazi s individual'nymi faktorami riska.

It is suggested that, within the same energy level, an impulse noise is more hazardous to hearing than a permanent noise. To justify this hypothesis, a study was performed with groups of wood-cutters and shipyard workers to investigate different characteristics of noise load (noise levels, noise impulsivity from the outside and under the ear-flaps, noise emission levels with regard to the length of work and using ear-flaps), and hearing losses (both real and forecasted on the Robinson model). To avoid individual factors, a computerized assessment of 38 pairs of workers from both teams was performed (with regard to similar noise emission levels, diastolic pressures, smoking habits, their military service backgrounds as to the service in heavy artillery units, absence of otic diseases, low consumption of salicylates). The results showed that, within the same energy level, the noise in the shipyard was three times as impulsive and more otic disorders inducing than the noise in the wood-cutters' working conditions.

Risk factors in the genesis of sensorineural hearing loss in Finnish forestry workers.

A detailed analysis of risk factors for the development of sensorineural hearing loss (SNHL) was carried out in 199 forest workers. The hearing threshold of both ears at 4000 Hz was measured, and the effect of age, exposure to noise, blood pressure, presence of vibration induced white finger (VWF), tobacco smoking, plasma LDL-cholesterol concentration, and consumption of drugs were evaluated by multiple linear regression analysis. Aging was the major risk factor, followed by exposure to occupational noise and the presence of VWF. Plasma LDL-cholesterol concentration and the use of antihypertensive drugs also correlated significantly with SNHL. These main factors were able to explain about 28% of the SNHL variance. Additional factors in the analysis, including smoking, systolic and diastolic blood pressure, and consumption of salicylates did not significantly contribute to the genesis of SNHL.

Impulse noise and hand-arm vibration in relation to sensory neural hearing loss.

The present study was carried out to determine whether impulse noise and simultaneous exposure to noise and vibration can aggravate sensory neural hearing loss (SNHL) among forest (N = 199) and shipyard (N = 171) workers. The average level of exposure to noise outside the used earmuffs and the average exposure over time were nearly equal for the two groups. The impulsiveness of the noise and the average exposure level inside the earmuffs were measured with a miniature microphone. The hearing threshold of the workers was measured at 4 kHz and then estimated according to Robinson's model to compare the observed and expected hearing loss. The impulsiveness of the noise was greater both outside and inside the earmuffs in shipyard work than in forest work. The average SNHL was higher than predicted for the shipyard workers and about the same as predicted for the forest workers. The total exposure level inside the earmuffs was influenced by the total wearing time. The low frequencies of the chain-saw noise were not attenuated sufficiently by the earmuffs to protect the workers' hearing. The present study suggests that exposure to impulse noise increases the risk of SNHL, but that simultaneous exposure to hand-arm vibration and noise does not.

Evaluation of factors affecting sensory neural hearing loss.

A detailed analysis of risk factors in the development of sensory-neural hearing loss (SNHL) was carried out in 199 forest workers. The mean hearing threshold of both ears at 4000 Hz was measured and the effect of age, exposure, blood pressure, presence of vibration induced white finger (VWF), tobacco smoking and plasma lipid concentrations on SNHL were evaluated by multiple linear regression analysis. A part of aging the major risk factors were presence of VWF, elevation of LDL-cholesterol level and usage of antihypertensive agents. Additional factors in the analysis, e.g. smoking and diastolic and systolic blood pressure did not significantly contribute to the genesis of SNHL.

Industrial impulse noise, crest factor and the effect of earmuffs.

Noise measurements were taken inside and outside earmuffs worn by 238 workers at 21 industrial plants in order to evaluate exposure to noise and to measure the attenuation by earmuffs used at workplaces. The means of the equivalent noise levels were 93 dB outside the earmuffs and 76 dB inside them. The mean earmuff attenuation was 17 dB. The standard deviations of each of these three values was 6 dB. Thus 90% of the employees wearing earmuffs experienced equivalent noise levels of lower than 85 dB(A) inside the earmuffs. In addition to equivalent noise level, the impulsiveness of the noise was determined based on the cumulative distribution of the crest factor of the signal. The impulse percentage F15 denotes the percentage of the total measurement time when the peak level exceeds the rms level by at least 15 dB. The mean impulse percentage F15 was 1.6% outside earmuffs and 0.8% inside earmuffs. The results showed that earmuffs also attenuated the impulsiveness of noise. The shipyard noise had the highest impulse percentage; the noise in printing plants and papermills had the lowest impulse percentage.

Sensory-neural hearing loss during combined noise and vibration exposure. An analysis of risk factors.

A detailed analysis of risk factors for the development of sensory-neural hearing loss (SNHL) was carried out on 122 forest workers. These forest workers were selected from a larger group (n = 217) by restricting the age range to 30-55 years. The hearing threshold of the left ear at 4000 Hz was measured and the effect of age, exposure, systolic and diastolic blood pressure (DBP), presence of vibration-induced white finger (VWF), tobacco smoking and use of earmuffs were evaluated in multiple linear regression analysis. Robinson's nonlinear model was used to evaluate the rate of hearing loss. Aging was the major risk factor and it explained 15.4% of the variance of the SNHL. The presence of VWF was the second most important single risk factor and explained a further 5.2% of the SNHL. Elevation of DBP correlated significantly with SNHL and explained an additional 4.1% of the SNHL. These main factors were able to explain about 26% of the spread of SNHL. Additional factors in the analysis, e.g. smoking, systolic blood pressure, did not significantly contribute to the genesis of SNHL. When Robinson's model was applied to the SNHL data, on a group basis, we did not observe any exaggerated risk of hearing loss due to combination of noise and vibration. In combined exposure subjects with VWF as well as subjects with enhanced DBP will run a higher risk for SNHL.

The efficiency of earmuffs against impulse noise from firearms.

Young men conscripted into the armed forces still run a risk of suffering hearing damage during their military service. This risk could be reduced by effective personal hearing protectors. The standard tests to determine the attenuation values of hearing protectors cannot be applied to high-intensity impulse noise from firearms, but the protectors should be evaluated under actual firing conditions. The attenuation values of the hearing protectors (earmuffs) most commonly used in the Finnish Army were tested for impulse noise from different weapons. The attenuation was found to be good for pistol shots, moderate for rifle shots and very poor for cannonfire. The tested earmuffs gave only minimal protection against low-frequency impulse energy.

Further evidence of a relation between noise-induced permanent threshold shift and vibration-induced digital vasospasms.

The relation between noise-induced permanent threshold shift (NIPTS) and vibration-induced dysfunction in the digital circulation was examined in a longitudinal survey among forest workers. The survey was based on annual examinations done between 1972 and 1983. Thirty-two forest workers with digital vasospasms were compared with referents matched for age, exposure, and use of ear protectors. No significant differences between the groups were observed at 1,000 or 2,000 Hz. The forest workers with digital vasospasms had significantly greater NIPTS at 4,000 and 8,000 Hz than the symptom-free referents. During the follow-up period, the gap in NIPTS between the two groups did not increase. Vibration measurements from chain saws manufactured in different years indicated that chain saws manufactured after 1970 had a tenfold reduction in vibration, whereas the reduction in noise levels was only slight. The results suggest that vibration-induced activation of the autonomic nervous system, which is thought to elicit digital vasospasms, may also contribute to the development of NIPTS.

Digital high-speed sampling of combined exposure to noise and vibration.

The digital high-speed sampling technique was applied to simultaneous measurements of exposure to noise and vibration among workers who used hand-held power tools in a shipyard. The transducers were two accelerometers and two microphones which measured the transmission of vibration acceleration from the handle of the tool to the wrist and the attenuation of noise by the earmuffs. The measurements were taken by a microcomputer-controlled digital multichannel sampling unit. An analogue-digital converter was used with a 100-kHz scanner for multichannel signal acquisition in the 10 kHz bandwidth. The sound pressure was A-weighted, and the vibration acceleration was both unweighted and weighted according to the guidelines of the International Organization for Standardization. Impulsiveness was determined as the difference between the peak and root-mean-square levels. The noise exposure was 81 dB during grinding and 85 dB during hammering. The earmuffs provided protection against impulse noise at least when the impulses contained high frequencies. The transmission loss of vibration acceleration between the tool handle and wrist was 45 dB for grinding and 29 dB for hammering. The transmission of noise and vibration was affected by the frequency content and impulsiveness of the signals.