Jørgen Mørup Jørgensen

Tensile and compressive properties of cancellous bone

The relationship between the mechanical properties of trabecular bone in tension and compression was investigated by non-destructive testing of the same specimens in tension and compression, followed by random allocation to a destructive test in either tension or compression. There was no difference between Youngs modulus in tension and compression, and there was a strong positive correlation between the values (R = 0.97). Strength, ultimate strain and work to failure was significantly higher in tensile testing than in compressive testing.

The avian inner ear

No systematic investigations and only two pilot studies have been published on cytokinetics in cadaveric skin [1, 2]. Many findings, however, have been reported on the kinetics of epidermal cells in live humans (for review, see [3]). We took single or repeated biopsies from a total of 45 human cadavers at different postmortal intervals (PMI). The cadavers were stored at 4 ~ for a PMI of 4 to 75 h. The biopsy specimens were incubated in vitro with radioactively labeled DNA precursors, 3H-thymidine only as well as 3H-thymidine and 14C-thymidine consecutively, exposed at a temperature of 37 ~ and 2.2 bar 02 [4]. The following results were obtained: Even though the single values were broadly scattered, no statistically relevant change in the kinetic data was observed under the described storage conditions of the cadavers. The labeling index (LI) was 2.7 + 0.8 ~ (approx. 20 h PMI) or 2.8 _+ 0.9~ (approx. 40 h PMI); the DNA synthesis time (ts) was 4.7 _ 1.4 h (approx. 30 h PMI) or 3.2 + 1.1 h (approx. 40 h PMI); and the potential doubling time (tpot) was 181.3 +_ 57.2 (approx. 30 h PMI) or 137.7 +_ 40.4 h (approx. 40 h PMI). No indications of biorhythmic changes were observed. For the female cadavers, mean LI was 2.6 + 0 .8%, t S 3.9 -!-0.2, and tpot 168.5 + 34.3 h. For the male cadavers, mean LI was 2.5 + 0.8 %, t s 5.0 + 1.6, and tpo t 183.9 + 27.2 h. No statistically relevant differences were established. Age dependency was investigated by determining LI in the epidermis of thigh and knee. No statistically relevant age-dependent differences were established for either region. Finally, the cytokinetic data were evaluated with respect to their dependency on topography. Epidermis f rom the following regions was examined: temple, anterior part of neck, mamma (upper outer quadrant), lateral chest wall, lower abdomen, thigh (extensor side), knee (extensor side), upper arm (flexor side), and elbow. The LI was highest in the elbow (3.1 + 1.0) and lowest in the lower abdomen (2.1 + 0.8%). The tpo t was shortest in the elbow (109.3 + 72.5 h) and comparatively long in the lower abdomen (183 +_ 38.7 h). No statistically relevant differences were established for these two biopsy sites; roughly the same proliferative behavior was observed in the other sites. Our findings indicate an extremely short t s and a decrease of t s and too t dependent on the storage time of the cadavers. The question arises whether the calculated ts and tpo t correspond to a real DNA synthesis time or a real potential doubling time. The double-labeling method for determining t s might be influenced by the increasing PMI leading to a change of the cell flux through the cycle. Since the calculated tpo t depends on t s, tvot tends to decrease with t s. In spite of these considerations, the LI as well as the/pot (up to a storage time of 30 h) of cadavers are comparable with those reported for live humans [3]. Differentiation according to sex, age, and site revealed no statistically relevant differences in LI, ts, and /pot-

Mechanical strength of tibial trabecular bone evaluated by X-ray computed tomography

The prospects for the use of quantitative computed tomography (QCT) for evaluation of mechanical properties of tibial trabecular bone were investigated. Computed tomography (CT) data from the proximal tibial epi- and metaphysis of six human cadaver knees were correlated with mechanical data obtained from compression tests and penetration strength measurements. In addition CT and intraoperative penetration data were compared in 20 patients. If spatial agreement between CT and mechanical measurement sites is optimized, close correlations are found between the relative linear attenuation coefficient determined by CT and the ultimate strength (r = 0.84), the yield strength (r = 0.85), the elastic modulus (r = 0.78), the ultimate energy absorption (r = 0.83), the yield energy absorption (r = 0.81), and the penetration strength (r = 0.82). It is concluded that these correlations are sufficient to make QCT a valuable tool for non-invasive evaluation of the spatial distribution of bone properties in several clinical applications.

Morphology of Electroreceptive Sensory Organs

The morphology of electroreceptive organs in lampreys and their larvae, different fishes, aquatic amphibians, and monotreme mammals is described. The sense organs vary from superficial end buds in lampreys, to ampullary organs and tuberous organs in many fishes and amphibians, to specialized mucous glands in the monotremes. The sensory cells are quite different. Some have a bundle of apical microvilli, as in lampreys and many teleost fishes. Cartilaginous and non-teleost fishes have a single apical cilium that in some species is surrounded by a few microvilli. Caecilian and urodele amphibians may have both a cilium and microvilli. Only the monotremes lack specialized sensory cells, possessing instead naked nerve endings connected to mucous glands. In all electroreceptive organs examined, only afferent nerve endings have been identified.

The Inner Ear of the Lungfish Protopterus

The sensory end organs of the inner ear of the lungfish, Protopterus, were examined using scanning and transmission electron microscopy. The utricle has a structure and hair cell orientation pattern that are typical for vertebrates, although the hair cells are unusually large. There are the typical three semicircular canals extending from the utricle, with the typical hair cell orientations, but the lateral canal sensory crista looks like the “hemicrista” of some amphibians and amniotes, lacking a saddle‐shaped flare on one wall of the ampulla. Unlike most vertebrates that have the saccule and lagena as two separate pouches ventral to the utricle, the lungfish has a single large ventral pouch that contains a single large pasty otoconial mass. This mass covers two hair cell patches, each like a striola with prominent hair cell ciliary bundles, that are presumed to represent saccular and lagenar maculae. However, these two major sensory patches are not completely separate maculae because they lie within a less densely populated field of smaller hair cells, which forms an extrastriolar region that surrounds and fills the region between the two striolae of higher hair cell density. The more caudal lagenar striola is a vertically elongated stripe with hair cell orientation vectors facing antiparallel on either side of a midline drawn vertically along the macula, resembling the macula lagena of some bony fishes but not of tetrapods. The more rostral saccular striola is a curving band with hair cell orientation vectors facing away from its midline, but because this macula curves in three dimensions, the vectors at the rostral end of this striola are oriented mediolaterally, whereas the vectors on the caudal half of this striola are oriented dorsoventrally. The presence of a macula neglecta was confirmed near the posterior canal as a tiny single patch of a few dozen hair cells with all the cell orientations directed caudally. The ciliary bundles on the cells in the striolar‐like regions of all of three otolithic organs average over 80 cilia, a number far greater than for any other fish studied to date. The features of the single sacculolagenar pouch with separate striolar‐like regions, the cellular orientation in the otolith organs, and the large cells and ciliary bundles in Protopterus also were observed in specimens of the other extant lungfish genera, Lepidosiren and Neoceratodus. J. Comp. Neurol. 471:277–288, 2004.

Isotherm mapping in hyperthermia using subtraction X-ray computed tomography

The prospects for the use of X-ray computed tomography (CT) for isotherm mapping were investigated. The spatial distribution of CT changes was obtained by digital subtraction of images taken before and during heating of a 200 mm diameter cylindrical 4% agar phantom. Due to a rather unfavourable signal-to-noise ratio, the noise level in the resulting image had to be reduced by low-pass filtering using the 2-dimensional Fast Fourier Transform followed by spatial averaging. The resulting isotherms showed a resolution of 0.5 degree C at a spatial resolution of 4.2 mm. Isotherms so obtained are presented and the possibility of using the method in clinical hyperthermia is discussed.

Remodeling of the tibial plateau after knee replacement. CT bone densitometry.

We measured the changes of bone density by computed tomography of the proximal tibia after total knee replacement in 18 patients, 9 with arthrosis and 9 with rheumatoid arthritis. All the patients had good results after 1 and 2 years. There were no significant radiolucencies at the cement-bone interface. At the early postoperative measurements, we found abnormal mediolateral distributions of density, closely related to the preoperative tibiofemoral angle (r = -0.67). This distribution was within normal limits after 3 months in knees with preoperative valgus and after 2 years in knees with preoperative varus. The mean tibial density did not differ between patients with arthrosis and rheumatoid arthritis at the early postoperative examination, but the density in rheumatoid patients decreased by one third during the 2-year period. Although the overall change after knee replacement was loss of density, the preoperatively less loaded condyles had a slight tendency towards increasing density with time, a response that was considerable in some cases.

Structure and Growth of the Utricular Macula in the Inner Ear of the Slider Turtle Trachemys scripta

In general, postembryonic production of inner ear vestibular hair cells (HCs) is believed to occur in all nonmammalian vertebrates. However, no study on this topic has been published on reptiles and, consequently, it is not known whether this also applies to these vertebrates. Therefore, the present study applied stereological methods in order to estimate the total number of HCs in turtles of varying sizes. The findings are that in prehatchlings the utricular macula (UM) contains ˜4000 HCs as compared to ˜5000 in juveniles, ˜8000 in medium-sized turtles, and ˜12,000 in large, sexually mature turtles. Scanning electron microscopy (SEM) reveals that presumably newly generated HCs with small surface areas and thin stereovilli are found in all regions of the UM. Furthermore, it reveals that utricular HCs can be classified as belonging to a specific region from the morphology of their apical structure. Striolar HCs have a large free oval-to-ovoid surface, a hair bundle with numerous stereovilli, and a short kinocilium. Rampary and cotillary HCs have smaller and slimmer free surfaces, comparatively fewer stereovilli, but much longer kinocilia. In conclusion, the current study demonstrates that postembryonic production of HCs does occur in reptiles and thereby supports the general view that this is a common trait in all nonmammalian vertebrates.In general, postembryonic production of inner ear vestibular hair cells (HCs) is believed to occur in all nonmammalian vertebrates. However, no study on this topic has been published on reptiles and, consequently, it is not known whether this also applies to these vertebrates. Therefore, the present study applied stereological methods in order to estimate the total number of HCs in turtles of varying sizes. The findings are that in prehatchlings the utricular macula (UM) contains ˜4000 HCs as compared to ˜5000 in juveniles, ˜8000 in medium-sized turtles, and ˜12,000 in large, sexually mature turtles. Scanning electron microscopy (SEM) reveals that presumably newly generated HCs with small surface areas and thin stereovilli are found in all regions of the UM. Furthermore, it reveals that utricular HCs can be classified as belonging to a specific region from the morphology of their apical structure. Striolar HCs have a large free oval-to-ovoid surface, a hair bundle with numerous stereovilli, and a short kinocilium. Rampary and cotillary HCs have smaller and slimmer free surfaces, comparatively fewer stereovilli, but much longer kinocilia. In conclusion, the current study demonstrates that postembryonic production of HCs does occur in reptiles and thereby supports the general view that this is a common trait in all nonmammalian vertebrates.

The inner ear macular sensory epithelia of the Daubenton's bat.

The inner ear macular sensory epithelia of the Daubentons bat were examined quantitatively to estimate the area and total number of hair cells. Ultrastructural examination of the sensory epithelium reveals two main types of hair cells: the chalice‐innervated hair cell and the bouton‐innervated hair cell. The existence of an intermediate type, with a nerve ending covering the lateral side of the hair cell, indicates that the chalice‐innervated hair cells are derived from bouton‐innervated hair cells. Thus, at least a part of the bouton‐innervated hair cells forms a transitional stage. A number of immature as well as apoptotic hair cells were observed. It is suggested that a continuous production of new hair cells takes place in mature individuals, probably based on transdifferentiation of supporting cells. J. Comp. Neurol. 438:433–444, 2001.

Continuous Hair Cell Turnover in the Inner Ear Vestibular Organs of a Mammal, the Daubenton's Bat (Myotis daubentonii)

Abstract In both humans and mice the number of hair cells in the inner ear sensory epithelia declines with age, indicating cell death (Park et al. 1987; Rosenhall 1973). However, recent reports demonstrate the ability of the vestibular sensory epithelia to regenerate after injury (Forge et al. 1993, 1998; Kuntz and Oesterle 1998; Li and Forge 1997; Rubel et al. 1995; Tanyeri et al. 1995). Still, a continuous hair cell turnover in the vestibular epithelia has not previously been demonstrated in mature mammals. Bats are the only flying mammals, and they are known to live to a higher age than animals of equal size. The maximum age of many species is 20 years, with average lifespans of 4–6 years (Schober and Grimmberger 1989). Further, the young are fully developed and able to fly at the age of 2 months, and thus the vestibular organs are thought to be differentiated at that age. Consequently, long-lived mammals such as bats might compensate for the loss of hair cells by producing new hair cells in their postembryonic life. Here we show that the utricular macula of adult Daubentons bats (more than 6 months old) contains innervated immature hair cells as well as apoptotic hair cells, which strongly indicates a continuous turnover of hair cells, as previously demonstrated in birds.