In community-dwelling women frailty is associated with imminent risk of osteoporotic fractures.

Frailty reflects an accelerated health decline. Frailty is a consequence of fracture and contributes to fracture. Greater frailty was associated with higher fracture risk. Frail women were at immediate risk (within 24 months) of a hip or major fracture. Fracture prevention could be improved by considering frailty status. INTRODUCTION: Frailty encompasses the functional decline in multiple systems, particularly the musculoskeletal system. Frailty can be a consequence of and contribute to fracture, leading to a cycle of further fractures and greater frailty. This study investigates this association, specifically time frames for risk, associated fracture types, and how grade of frailty affects risk. METHODS: The study is performed in the OPRA cohort of 1044, 75-year-old women. A frailty index was created at baseline and 5 and 10 years. Women were categorized as frail or nonfrail and in quartiles (Q1 least frail; Q4 most frail). Fracture risk was assessed over short (1 and 2 years) and long terms (5 and 10 years). Fracture risk was defined for any fracture, major osteoporotic fractures (MOFs), and hip and vertebral fracture, using models including bone mineral density (BMD) and death as a competing risk. RESULTS: For women aged 75, frailty was associated with higher risk of fracture within 2 years (Hip SHRadj. 3.16 (1.34-7.47)) and MOF (2 years SHRadj. 1.88 (1.12-3.16)). The increased risk continued for up to 5 years (Hip SHRadj. 2.02 (1.07-3.82)); (MOF SHRadj. 1.43 (0.99-2.05)). Grade of frailty was associated with increased 10-year probability of fracture (p = 0.03). Frailty predicted fracture independently of BMD. For women aged 80, frailty was similarly associated with fracture. CONCLUSION: Frail elderly women are at immediate risk of fracture, regardless of bone density and continue to be at risk over subsequent years compared to identically aged nonfrail women. Incorporating regular frailty assessment into fracture management could improve identification of women at high fracture risk.

Kidney function and its association to imminent, short- and long-term fracture risk-a longitudinal study in older women.

Reduced kidney function is associated with an increased fracture risk, although the relationship between an age-related decline and fractures needs further investigation. We followed kidney function and fracture risk for 10 years. A mild-moderate decline in kidney function was associated with fracture, but not in advanced age. INTRODUCTION: With age, kidney function declines. Though well known that chronic kidney disease is associated with increased fracture risk, the extent to which the typical age-related decline contributes is unclear. In the OPRA cohort, a longitudinal study of older non-selected women, we investigated the association between kidney function and fracture. METHODS: Cystatin C-based kidney function estimates were available at age 75 (n = 981) and 80 (n = 685). Women were categorized by kidney function: normal (CKD stages 1 and 2), mild-moderate (3a), poor (3b-5), and imminent, short- and long-term fracture risk investigated. BMD measurements and kidney function for risk prediction were also evaluated; women were categorized by both reduced kidney function (stages 3-5) and osteoporosis status. RESULTS: In the short term, 2-3 years, mild-moderate kidney dysfunction was associated with the highest risk increase: osteoporotic fractures (2 years HRadj 2.21, 95% CI 1.27-3.87) and also up to 5 years (between 75 and 80 years) (HRadj 1.51, 1.04-2.18). Hip fracture risk was similarly increased. This association was not observed from age 80 nor for women with poorest kidney function. Reduced kidney function was associated with higher risk even without osteoporosis (osteoporotic fracture; HRadj 1.66, 1.08-2.54); risk increased by having both osteoporosis and reduced function (HRadj 2.53, 1.52-4.23). CONCLUSION: Older women with mild-moderate reduction of kidney function are at increased risk of fractures, but not those with the worst function. Our findings furthermore confirm the value of osteoporosis assessment and it is possible that in this age group, age-related decline of kidney function has limited contribution compared with BMD.

Reduced kidney function is associated with BMD, bone loss and markers of mineral homeostasis in older women: a 10-year longitudinal study.

Kidney function decreases with age; however, the long-term influence on bone density (BMD) in older women already at risk of osteoporosis is unknown. We followed kidney function and bone loss for 10 years. Declining kidney function was adversely associated with bone loss and mineral homeostasis in old women, though it attenuated with advanced aging. INTRODUCTION: Existing studies do not fully address the relationship between kidney function and bone metabolism with advanced aging in Caucasian women. This study describes the association between kidney function, BMD, bone loss and bone metabolism in older women and provides a review of the available literature for context. METHODS: We studied participants from the OPRA cohort with follow-up after 5 and 10 years. Using plasma cystatin C (cysC), estimated glomerular function rate (eGFR) was evaluated at age 75 (n = 981), 80 (n = 685) and 85 (n = 365). Women were stratified into "normal" function (CKD stages 1-2), "intermediate" (stage 3a) and "poor" (stages 3b-5), and outcome measures-BMD, bone loss and markers of mineral homeostasis-were compared. RESULTS: Femoral neck (FN) BMD positively associated with kidney function at 75 years old ([Formula: see text] = 0.001, p = 0.028) and 80 years old ([Formula: see text] = 0.001, p = 0.001), although with small effect size. Prevalence of osteoporosis (FN T-score ≤ - 2.5) did not differ with kidney function. Measured at age 75, women with poor kidney function had higher annual percentage bone loss over 5 years compared to those with normal function (2.3%, 95% CI 1.8-2.8 versus 1.3%, 95% CI 1.1-1.5, p = 0.007), although not when measured from age 80 or 85. Additionally, markers of mineral homeostasis (PTH, phosphate, vitamin D, calcium), CRP and osteocalcin differed by kidney function. CONCLUSIONS: In old women, kidney function is associated with BMD, bone loss and altered mineral homeostasis; probably, a relationship attenuated in the very elderly.

C-reactive protein, bone loss, fracture, and mortality in elderly women: a longitudinal study in the OPRA cohort.

SUMMARY: This longitudinal study investigates the association between C-reactive protein (CRP), osteoporosis, fractures, and mortality in 1044 elderly women. CRP was not an indicator for low bone mineral density (BMD), bone loss, or fracture in elderly women; however, women with elevated CRP levels over a prolonged period lost more bone over the 10-year follow-up, although fracture risk was not increased. INTRODUCTION: Inflammation may contribute to the pathophysiology underlying impaired bone metabolism. This study investigates the association between CRP, BMD, bone loss, fracture risk, and mortality in women aged 75 and above. METHODS: This longitudinal study is based on 1044 women, all age 75 at inclusion, reassessed at ages 80 and 85, with a mean follow-up time of 11.6 years (maximum 16.9 years). RESULTS: Women in the lowest CRP quartile (mean 0.63 mg/L) had lower BMD compared to those in the highest CRP quartile (mean 5.74 mg/L) at total hip (TH) (0.809 vs. 0.871 g/cm2, p<0.001) and femoral neck (FN) (0.737 vs. 0.778 g/cm2, p=0.007). A single measurement of CRP was not associated with bone loss; however, women with persistently elevated CRP, i.e., ≥3 mg/L at ages 75 and 80 had significantly higher bone loss compared to women with CRP<3 mg/L (TH -0.125 vs. -0.085 g/cm2, p=0.018 and FN -0.127 vs. -0.078 g/cm2, p=0.005) during 10 years of follow-up. Women in the highest CRP quartile had a lower risk of osteoporotic fractures (hazard ratios (HR) 0.76 (95% confidence intervals (CI) 0.52-0.98)) compared to those in the lowest, even after adjusting for weight and BMD. Mortality risk was only increased among women with the highest CRP levels. CONCLUSION: CRP was not an indicator for low BMD, bone loss, or fracture in elderly women in this study. Persistently elevated CRP however seemed to be detrimental to bone health and may be associated with a higher rate of bone loss. Only the highest CRP levels were associated with mortality.

Longitudinal Measurements of FGF23, Sarcopenia, Frailty and Fracture in Older Community Dwelling Women.

BACKGROUND: FGF23 has been associated with frailty and functional performance in older individuals, but the association to sarcopenia is unknown. OBJECTIVES: To investigate the association between FGF23, frailty, sarcopenia and fractures in older community dwelling women. DESIGN: Prospective longitudinal cohort study. SETTING: Malmö, Sweden. PARTICIPANTS: 995 75-year-old women, followed prospectively for ten years, with re-investigations after five (n=667) and ten (n=324) years. MEASUREMENTS: C-terminal levels of FGF23 were measured and a frailty index of 'deficits in health' created. Sarcopenia was defined by low muscle mass and strength and "probable sarcopenia" by low muscle mass only. Incident fractures were continuously registered for 10-years. Based on tertiles of FGF23, odds ratio for frailty, sarcopenia and probable sarcopenia was investigated using logistic regression models adjusted for: eGFR, PTH, calcium, vitamin D and phosphate. Fracture-free survival during 10-year follow-up was depicted using Kaplan Meier curves. RESULTS: While fracture-free survival did not differ between tertiles, women in the highest tertile of FGF23 had lower muscle strength and gait speed, and higher proportion with impaired mobility at baseline. At age 75, these women had higher odds of also being frail (ORadj 1.6 (95% CI 1.1-2.4)) and suffering from probable sarcopenia (ORadj 1.8 (95% CI 1.1-3.1)), but not sarcopenia. At follow-up the association between FGF23 and probable sarcopenia was not evident. While the association with frailty was attenuated at age 80 after adjustment (ORadj 1.6 (95% CI 1.0-2.5)), women in the highest tertile had higher odds of being frail at age 85 (ORadj 3.4 (95% CI 1.7-6.6)). CONCLUSIONS: FGF23 may be a promising clinical marker for muscle strength, functional performance, and frailty in older women, but not for future fragility fractures. Whether FGF23 is also associated with sarcopenia requires further investigation.

Differences between the peripheral and the central nervous system in permeability to sodium fluorescein.

Sodium fluorescein (SF) was used as a very small tracer (mol wt 376; 5 A diameter) to examine diffusion barriers in peripheral nerves and to compare them to those in other regions of the nervous system. The technique involved immobilization of the tracer by rapid freezing, followed by freeze-drying and vacuum embedding in paraffin. The localization of the SF was then determined in tissue secretions using fluorescence microscopy. Even at the highest doses of intravenously (IV) injected tracer, no extravasation could be detected in the cerebral cortex. On the other hand, SF penetrated very rapidly into peripheral ganglia and into the epineurium and perineurium of large peripheral nerves. The penetration of SF into the endoneurium of large nerves was, however, much more restricted with tracer detectable within the endoneurium only at high doses and long survival times. Even in such cases, the level of SF fluorescence was much lower within nerve fascicles than in the epineurium and the perineurium, and a sharp gradient in fluorescence intensity persisted at the inner border of the perineurium. The extent of extravasation into the endoneurium varied markedly betwen different fascicles of the same nerve and between different nerves in the same animal. Experiments involving injection of high doses of SF adjacent to the nerve indicated relatively little movement of SF across the perineurium, which indicates that the observed accumulation of tracer within the endoneurium was the result of direct extravasation of SF from the endoneural blood vessels. Small nerve branches (< 100 mu diameter) showed an earlier and more extensive penetration of SF into the endoneurium than large nerves like the sciatic, hypoglossal, or ventral tail nerve. This may be due to a diffusion of SF along the extracellular space of the endoneurium from nerve terminals where the perineurial barrier is open-ended. In experiments involving IV injection of a solution containing both green fluorescent SF and red fluorescent Evans Blue (Evans Blue-serum albumin conplex, EBA = mol wt. 69,000), the distribution of SF could be directly compared at various sites and sacrifice times to that of EBA, a much larger tracer. SF appeared more rapidly and extensively than EBA in the various compartments in ganglia and peripheral nerve. The distribution of EBA was the same as is typically seen when this tracer is injected alone, indicating that there was no change in vascular permeability associated with IV injection of SF. Since SF is of very small size, freely diffusible, nontoxic, and detectable at very low concentrations, it should be a useful complement to existing tracers. When tissues are processed according to the indicated procedure, one can obtain a very sensitive and reliable localization of this tracer which should be of value for studies in the nervous system concerning various pathological conditions associated with permeability alterations.

A sensitive method for histochemical demonstration of horseradish peroxidase in neurons following retrograde axonal transport.

A study was made on the effects of various fixatives and some other histochemical parameters used in the procedure for demonstrating labeled neurons following retrograde axonal transport of horseradish peroxidase (HRP). The enzyme was injected into the tongue of adult mice and the results were obtained by counting labeled hypoglossal neurons following certain variations in the procedure. Paraformaldehyde in the fixative should be avoided since it reduces the number of labeled neurons as compared to glutaraldehyde in a concentration of 1.5-2.5% Fixation for about 4 h is recommended followed by a wash in 5% sucrose buffer overnight. Variables in the histochemical procedure were systematically studied in order to determine optimal pH, buffer type, buffer concentration and substrate concentration. The effect of using a "preincubation" in buffer containing only diaminobenzidine tetrahydrochloride (DAB) was also examined. These results were used to develop a modified histochemical procedure which produced a substantial increase in the number of detectable HRP-labeled neurons as compared to equivalent sections that were reacted in the incubation medium described by Graham and Karnovsky. The modified histochemical procedure involves incubation (no preincubation with DAB only) of sections in the dark for 30 min in a solution consisting of 10 ml cacodylate buffer (pH 5.1;0.1 M), 20 mg DAB and 0.1 ml of 1% hydrogen peroxide. The Kodak Wratten no. 46 filter is recommended for light-microscopical identification of labeled neurons since it is closely matched to the absorption spectrum of the DAB reaction product and consequently greatly increases the contrast of HRP-labeled neurons.

Uptake and retrograde axonal transport of various exogenous macromolecules in normal and crushed hypoglossal nerves.

Macromolecular tracers were injected into the tongue or around a crush in mouse hypoglossal nerves. At various times thereafter, the tracers were histochemically localized on the basis of peroxidase activity. The distribution of reaction product was then examined using light microscopy in order to study the influence of molecular charge and size on uptake and retrograde axonal transport from the periphery or from the crushed axon. Of various proteins with peroxidase activity, horseradish peroxidase and cytochrome-c showed the greatest penetration into axons proximal to the crush. Following injection into the tongue, intra-axonal cytochrome-c was detectable in some of the peripheral branches but not any of the other proteins. Retrograde transport to the nerve cell bodies was demonstrated for horseradish peroxidase and cytochrome-c, both from the tongue and from the axonal crush but not for microperoxidase, myoglobin, hemoglobin, lactoperoxidase and catalase. The number of neuronal cell bodies having detectable reaction product was higher for peroxidase-injected than for cytochrome-c-injected animals. Ferritin and iron-dextran (Imferon) also accumulated in hypoglossal neurons, but this could be detected only after repeated injections into the tongue. Uptake and retrograde transport from the tongue or from the crush occurred both for anionic and for cationic horseradish peroxidase. This is interpreted as evidence against absolute specificity in the uptake and transport of macromolecules on the basis of electrical charge.

Early influx of horseradish peroxidase into axons of the hypoglossal nerve during Wallerian degeneration.

Horseradish peroxidase (HRP) was applied around mouse hypoglossal nerves which were damaged by a crush or a ligature. HRP was then visualized distal to the lesions by light- and electron microscopic histochemistry. At the injury the enzyme entered axons and could also be detected several millimetres down in the distal segment. By 24 h reaction product (r.p.) was either diffusely distributed in the axoplasm or present in various vesicular organelles. Our results indicate that there is a rapid influx of macromolecules into axons after a lesion to a nerve. A similar uptake of 'wound substances' into axons distal to an injury might well have some relation to the process by which axonal breakdown is initiated during Wallerian degeneration.

Axonal uptake of horseradish peroxidase isoenzymes during Wallerian degeneration.

Horseradish peroxidase isoenzymes were applied around crushed mouse hypoglossal nerves to study the influence of electrical charge on the uptake and ultrastructural distribution of macromolecules in axons distal to an injury. Both isoenzymes tested (Sigma type IX, cationic and type VII, anionic) were readily taken up into axons and moved in a distal direction along the nerve. Samples taken 1-3 mm below the crush showed that reaction products from both enzymes covered the inner surface of the axonal plasma membrane and were attached to organelles, particularly microtubules and neurofilaments. However, reaction product in the Schwann cell basement lamina and in the endoneurial collagen was much more dense with cationic peroxidase than with the anionic isoenzyme. Our study shows that both cationic and anionic macromolecules can move into axons distal to a nerve lesion. It can be assumed that also other agents can be taken up into axons and that 'wound substances' in this way may influence the processes by which axons are destroyed during Wallerian degeneration.

Central projection of the sensory component of the rat recurrent laryngeal nerve.

The central projection from the sensory components in the rat recurrent laryngeal nerve was studied using WGA-HRP. Sensory terminals were found bilaterally in the nuclei of the tractus solitarius, although they were very sparse contralaterally. In the ipsilateral nucleus, most of these terminals were located in the interstitial subnucleus extending, from the most rostral area, near the obex, caudally for a distance of 1.5 mm.

Comparison between retrospective gating and ECG triggering in magnetic resonance velocity mapping.

ECG-triggered cinematographic studies of the cardiovascular system are hampered by several technical restrictions such as the inability to image end-diastole, ghosting, varying signal intensity, and phase contributions from eddy currents. Retrospective gating may solve these problems, but involves signal manipulation such as interpolating raw data from a time window. In this study, the performance of the two gating strategies was compared in quantitative MR velocity mapping on the abdominal aorta in eight healthy volunteers and on a pulsatile flow phantom. The results were compared to a one-dimensional velocity mapping technique and Doppler ultrasound. Finally, the consequence of decreasing the time window in the raw data interpolation used for retrospective gating was also examined. With retrospective gating, a low-pass filtering was seen, causing significantly prolonged duration and decreased amplitude of flow pulses. However, by reducing the time window retrospectively gated flow measurements were in good agreement with those that are ECG triggered. When fulfilling the demand of a narrow time window for interpolation, retrospective gating offers several advantages in MR velocity mapping.

Age-related changes in the neuromuscular junctions in the human posterior cricoarytenoid muscles: a quantitative study.

The posterior cricoarytenoid muscle is unique histochemically, ultrastructurally, and functionally. It has been suggested that the posterior cricoarytenoid muscle undergoes early aging. Aging in peripheral nerves has been reported to resemble a "dying back" neuropathy in that the most severe and earliest age-related changes occur at the most distal levels of the nerve fibers. The lengths and terminal axonal branching of neuromuscular junctions in 17 human posterior cricoarytenoid muscles aged 4 days to 95 years were determined. Both neuromuscular junction lengths and the numbers of axonal terminal branches in the very young group differed significantly from values in two older groups. In contrast to results reported for some other muscles, there was no significant age-related change in these parameters in the posterior cricoarytenoid muscle during adult life. This difference may be related to the repetitive contraction of the posterior cricoarytenoid muscle.

Three-dimensional computer reconstruction of the neuromuscular junction distribution in the human posterior cricoarytenoid muscle.

Recent studies have indicated that in a denervated muscle highly specific interactions occur between regenerating axons and the basal lamina of the myofiber precisely at the original synaptic sites. Since these findings suggest that synapse regeneration is facilitated at the original synaptic sites, a knowledge of the distribution of neuromuscular junctions in the human posterior cricoarytenoid (PCA) muscle may guide reinnervation procedures in this muscle. We, therefore, have used histochemical and computer graphics techniques to reconstruct the three-dimensional distribution of neuromuscular junctions in the human PCA taken fresh at autopsy. The results indicated a more localized pattern of neuromuscular junctions as compared to the human thyroarytenoid muscle. The results will be discussed with respect to their implications for procedures for reinnervation of the posterior cricoarytenoid muscle.

The effect of tracheostomy on posterior cricoarytenoid muscle.

It has been reported previously that the amount of electromyographic (EMG) potential of the posterior cricoarytenoid (PCA) decreases after prolonged tracheostomy. It is, therefore, reasonable to assume that a significant alteration of the biochemical characteristics of this muscle would also occur. In addition to histochemical analysis, endoscopic and EMG data were recorded to give a direct comparison in each subject. Seven male beagles were used for this study. Four were tracheostomized and three served as controls. They were examined immediately before and after surgery and again after 4 weeks by EMG and endoscopic techniques. Histochemical staining was performed on each subject. All three modalities failed to demonstrate a substantial difference between the controls and the experimental dogs.

Muscle fiber types in the cat middle ear muscles. II. Tensor tympani.

Using quantitative histochemical techniques, it was determined that the tensor tympani muscle of the cat consists of three muscle fiber types: type 1, type 2A (staining characteristics similar to the type 1 and type 2A muscle fibers found in the control tibialis anterior muscles), and a third unclassified fiber type (type 3) similar to the 2A fiber type except that it had extremely dense alkaline actomyosin adenosine triphosphatase staining (mean transmittance, type 2A = 33.6%; type 3 = 17.3%), as well as dense staining for periodic acid-Schiff, menadione-linked alpha-glycerolphosphate dehydrogenase, nicotinamide-adenine dinucleotide tetrazolium reductase, and succinic dehydrogenase. The type 1 fiber population was smaller in diameter (mean +/- SD, 14 +/- 4 microns) than the type 2A fiber (mean +/- SD, 21 +/- 5 microns) and the type 3 fiber (mean +/- SD, 22 +/- 6 microns) populations. In all muscles, intrafascicular and extrafascicular fat accumulations were found, with the majority being extrafascicular. Calculations indicate that the tendon occupies approximately 41% of the total muscle volume, while the muscle fibers constitute 59% of the volume.

Age-related changes in the internal branch of the rat superior laryngeal nerve.

This investigation was initiated to provide data on the ultrastructural basis for neurologic age-related changes in laryngeal sensory function. In the present study, an animal model (female Wistar rats: age range: young [Y], 3 to 5 months; old [O], 25 months; and very old [VO], 29 to 30 months) was used to examine systematically changes in the internal branch of the superior laryngeal nerve with age using electron microscopic morphometric techniques. Total fiber counts, fiber populations (size categories), and mean fiber size for myelinated and unmyelinated fibers did not change with age. Qualitative changes were consistent with segmental demyelination and axonal degeneration in the older animals. There was also a significant age-related increase in the volume fraction of adaxonal Schwann cell cytoplasm (Y, 0.019; O, 0.041; and VO, 0.042). Ultrastructural correlates of intracellular support and axonal transport showed a significant decrease in the numerical density of neurofilaments (Y, 0.126/micron2; O, 0.073/micron2; and VO, 0.078/micron2) in the older animals, but no change in the numerical density of microtubules. Energy metabolism correlates in the form of mitochondrial volume fraction did not change with age. There was a significant increase in the volume fraction of the intrafascicular extracellular space (Y, 0.224; O, 0.271; and VO, 0.301), indicating a late, age-related change in the extracellular environment. These changes could lead to decreased conduction velocity or complete fiber dysfunction. A number of these changes resembled those of aged human peripheral nerves already examined.

Motor end-plate distribution in the human lateral cricoarytenoid muscle.

Knowledge of the neuromuscular junction distribution in the intrinsic laryngeal muscles has potential clinical application in directing procedures that affect the function of these muscles through their neuromuscular junctions. We used histochemical techniques and computer graphics to determine the three-dimensional distribution of the motor end-plates in the human lateral cricoarytenoid muscle. In contrast to the results that have been reported for the human thyroarytenoid, cricothyroid, and posterior cricoarytenoid muscles, where end-plates are more diffusely distributed, the results of our study indicate that in the human lateral cricoarytenoid muscle, the neuromuscular junctions are generally found within a broad band at the midlength of the muscle. This more focused distribution should be advantageous clinically in facilitating the manipulation of the motor end-plates in this muscle.

Motor end-plate distribution in the human interarytenoid muscle.

Histochemical and computer graphic techniques were used to determine the distribution of neuromuscular junctions in the human interarytenoid (IA) muscle. The motor end-plates of four IA specimens obtained from normal postmortem larynges were visualized using an acetylcholinesterase stain. The three-dimensional distribution of motor end-plates was later reconstructed using computer graphics. The motor end-plates in the IA were found to be distributed in an inverted "Y" configuration. A broad band of end-plates was found at the midpoint of the muscle fibers in the superior and middle aspect of the muscle. This band divided obliquely in a lateral direction toward the inferior border of the muscle. This pattern of motor end-plate distribution is possibly consistent with the bilateral innervation of the IA by the recurrent laryngeal nerves.

Age-related changes in muscle fiber regeneration in the human thyroarytenoid muscle.

BACKGROUND: Muscle fiber regeneration is essential to maintain normal muscle fiber populations and muscle mass by continuous replacement of fibers lost to acute muscle injury or overuse. However, the extent of ongoing muscle fiber regeneration in the laryngeal muscles is unknown. OBJECTIVE: The present study provides statistically unbiased, quantitative estimates of the content of regenerating fibers in the human thyroarytenoid muscle over the adult lifespan. DESIGN: In the adult, only regenerating muscle fibers express the developmental myosin isoform. Therefore, regenerating fibers were identified using immunohistochemical techniques. The content of regenerating muscle fibers in the entire muscle volume was then estimated using stereological techniques. Through the use of a computer-automated sampling protocol, stereological data were collected from sets of isotropic uniform random cryostat sections. Overprojection error was minimized by using a confocal laser-scanning microscope to image thin optical sections for use as sample fields. SUBJECTS: Eight autopsy cases, subjects ranging in age from 19 to 81 years. RESULTS: The summed length of fibers expressing developmental myosin increased significantly (P=.02) with age when compared with the overall muscle fiber length. CONCLUSIONS: This finding indicates that muscle fibers maintain the capability for spontaneous regeneration, and that the proportion of regenerating fibers increases as the thyroarytenoid muscle ages. This increase is possibly a compensatory response to an age-related increase in muscle fiber injury or death.