Alain Meunier

Distribution of Intracortical Porosity in Human Midfemoral Cortex by Age and Gender

The purpose of this study was to describe the age‐specific distribution of midfemoral intracortical porosity throughout the cortical width in males and females. Microradiography and an automated image analysis system were used to study midfemoral cortical bone specimens from 163 white people, including 77 males and 86 females, in a recent anthropological collection covering a broad age range. In each specimen, porosity (percentage of the cortical bone area occupied by pores), pore number, and pore size were measured throughout the entire cortex and in three cortical subregions of equal width labeled the periosteal, midcortical, and endosteal subregions. For each gender, relationships linking age to porosity, pore number, and mean pore size were assessed using regression analysis. In addition, age‐ and site‐related changes in these three variables were tested for significance using two‐way analysis of variance (ANOVA). Age explained 52% of the porosity variance in females and 13.5% in males. In each gender, there were significant age‐ and site‐related differences in porosity, pore number, and pore size. In adults aged 60 years or younger, both pore size and pore number increased with increasing age, whereas in adults older than 60 years, pore size continued to increase but pore number decreased. In males, the age‐related changes in pore size and pore number were proportionally similar in the three cortical subregions. In females, in contrast, the changes predominated in the endosteal subregion and resulted in significant cortical thinning.

Fractures of ceramic bearings: history and present status.

During a period of 25 years (1977 to 2001), 13 fractures of an alumina component were recorded retrospectively. During the same period, approximately 5500 alumina components were implanted (3300 with all-alumina bearings and 1200 with alumina-on-polyethylene). These events occurred in seven women and six men, with a mean age of 59 years and a mean weight of 71 kg. There were eight fractures of the femoral head and five fractures of the socket component. Three fractures clearly were related to trauma (two fractures of the socket and one fracture of the head) and two were related to an abnormal design (one 22-mm head and one extra-long neck). Five fractures occurred without any rational explanation, but two fractures that occurred in the early phase could have been caused by a weaker alumina material. Finally three recent fractures of the liner were related to a change in the design of the material. This has been corrected and no additional fractures were observed. Although this dramatic event is of concern, it is infrequent and easy to solve by a limited revision procedure if done emergently. This rare complication should be balanced with the other complications of THR, including mechanical failures and osteolysis, often described with metal-on-polyethylene prostheses.

Ten-year survivorship of cemented ceramic-ceramic total hip prosthesis.

In the first 187 consecutive alumina-alumina combination hip arthroplasties performed from 1977 to 1979, both components were cemented with conventional techniques. At ten-year follow-up evaluation, 87 patients were reviewed or interviewed by telephone, 37 were dead, 39 were lost to follow-up evaluation, and 24 failures were reoperated on before the end of ten years. The major cause of failure was aseptic loosening of the acetabular component (15 failures). Fracture of the socket and of the femoral head occurred in five patients in this series. However, these complications were not seen with components manufactured after 1979. At the end of ten years, survivorship analysis depicted a 82.59% survival rate when reoperation was considered as failure and a 88.57% rate when reoperation for aseptic loosening was considered as failure. The femoral component had a 99.16% survival rate and the acetabular component had an 88.57% survival rate when reoperation for aseptic loosening was considered as failure. Age, appearance of a two- or three-zone demarcation at the intermediate follow-up evaluation, and outer diameter of the acetabular component were the major parameters influencing the results. Better results observed in the population younger than 50 years of age may be related to the small amount of wear debris produced by the alumina-alumina combination. This combination in hip prosthesis is secure, but should be implanted in young and active patients; the outer diameter of the acetabular component must be at least 50 mm. The major problem that remains is the sockets fixation. It could be improved by a design modification, by choosing another mode of fixation, or both.

The Effects of Remodeling on the Elastic Properties of Bone

SummaryCortical bone can be modeled as a complex hierarchical composite interrelating both structure and material properties on four levels of structural organization: molecular, ultrastructural, microscopic, and macroscopic. In young animals, the microstructural systems are long parallel lamellar units, plexiform bone, which in older or more mature animals converts by internal remodeling into multiple concentric lamellar units, secondary osteons, forming haversian bone. Ultrasonic wave propagation measurements performed on both plexiform and haversian bone clearly show a definitive relationship with microstructure; haversian bone can be described as a transversely symmetric material whereas plexiform bone appears to be orthotropic in nature. The anisotropy of the elastic constants are found to reflect the tissue symmetry; moreover, plexiform bone is stiffer and more rigid in all directions than is haversian bone. Similar experiments were performed on osteoporotic and osteopetrotic bone. While the results for osteoporotic bone are understandable in terms of the increased porosity, the results for the osteopetrotic bone are anomalous with respect to its density. Since Wolff, the remodeling of bone has been interpreted as a way of altering the mechanical properties to suit some need. For haversian remodeling from plexiform bone, the argument that adaptation occurs to optimize properties requires additional clarification since haversian bone appears to have inferior mechanical properties to plexiform bone.

The elastic anisotropy of bone.

In modeling the anisotropic properties of hydroxyapatite (HAp), Katz found that two kinds of phenomenological relationships held among the elastic stiffness coefficients. Firstly, there are three linear combinations--(c11 + c22 + c33), (c44 + c55 + c66), (c12 + c13 + c23)--which arise naturally when computing the isotropic averages of anisotropic crystal systems over all possible spatial orientations. Secondly, the degree of elastic anisotropy in such crystal systems is characterized by two specific factors: (a) the ratio of the linear compressibility along the unique axis to that perpendicular to it, (c11 + c12 - 2c23)(c33 - c13); and (b) the ratio of the two shear moduli, c44/c66. There have been a number of experiments in recent years which have used either mechanical methods or ultrasonic techniques to measure the anisotropic elastic properties of bovine and human cortical bone. Analyses of data from these experiments show that the above relationships also play a significant role in characterizing the elastic anisotropy in bone.

Long-term in vivo bioactivity and degradability of bulk sol-gel bioactive glasses

Melt-derived bioactive glasses have been used with success in various clinical applications for over 10 years. Recently, particles of sol-gel-derived bioactive glasses with an initial high specific surface area have been shown to exhibit excellent osteoconductive properties as well as significant degradability. In this work, we explored the long-term in vivo bioactivity and degradability of bulk sol-gel-derived glasses in a rabbit model. Two sol-gel compositions (58S and 77S Bioglass) were used. Bulk 45S5 Bioglass was used as a control. Both sol-gel-derived glasses demonstrated osteoconductive properties similar to 45S5 Bioglass. In addition, absorbability was observed for both sol-gel-derived glasses starting after 12 weeks of implantation. Total absorption reached 40% after 52 weeks. No degradation could be measured in the case of bulk 45S5 melt-derived Bioglass within 1 year of implantation. The degradation process was highly time dependent, as demonstrated by regression analysis. New bone formation was found to fill in areas that had been resorbed, similar to bone remodeling. This absorbability can be assumed to be at least partially related to an osteoclastic resorption as viable osteoclasts-like cells were found to be in direct contact with the glass surfaces.

Measurement of anisotropic vertebral trabecular bone loss during aging by quantitative image analysis

SummaryAge-dependent variations in the architecture of vertebral trabeculae in both the vertical and horizontal planes were characterized by quantitative image analysis. Images were obtained from autopsy specimens of the third lumbar vertebrae in 61 subjects (30 men and 31 women) whose ages ranged between 33 and 89 years). All subjects had died acutely either after trauma or illnesses unrelated to the skeleton. Using mathematical morphology techniques, we measured total bone area and perimeter, and the width of trabecular particles and medullary spaces in each slice. Between the age intervals 33–49 and 80–89 years: total bone loss in the vertical and horizontal planes was 51 and 64% for women, and 38 and 29% for men, respectively. Mean trabecular width (MTW) in the vertical plane decreased from 172 to 128 μm in women and from 181 to 144 μm in men; MTW in the horizontal plane fell from 144 to 112 μm in women and remained at 114 μm in men. Maximum trabecular width decreased with age in both planes in both sexes. The mode for trabecular width was 111 μm in both sexes for all ages and in both planes. The total number of trabeculae decreased only for women in the vertical plane. Intertrabecular spaces enlarged reciprocally as the trabeculae became thinner, but the widening of spaces was much greater than that expected with trabecular thinning alone. We conclude that age-related bone loss is comprised of two processes: reduction of MTW and fragmentation and complete loss of some trabeculae. We found no evidence of vertical trabeculae thickening during normal aging.

Scanning Acoustic Microscope Studies of the Elastic Properties of Osteons and Osteon Lamellae

Scanning acoustic microscopy (SAM) provides the means for studying the elastic properties of a material at a comparable level of resolution to that obtained by optical microscopy for structural studies. SAM is nondestructive and permits observation of properties in the interior of materials which are optically opaque. Two modes of ultrasonic signals have been used in a Model UH3 Scanning Acoustic Microscope (Olympus Co., Tokyo, Japan) as part of a continuing study of the microstructural properties of bone. The pulse mode, using a single narrow pulse in the range of 30 MHz to 100 MHz, has been used to survey the surface and interior of specimens of human and canine femoral compact cortical bone at resolutions down to approximately 30 microns. To obtain more detailed information at significantly higher resolution, the burst mode, comprised of tens of sinusoids, has been used at frequencies from 200 MHz to 600 MHz. This has provided details of both human and canine single osteons (or haversion systems) and ostenoic lamellae at resolutions down to approximately 1.7 microns, well within the thickness of a lamella as viewed in a specimen cut transverse to the femoral axis.

In vitro acoustic waves propagation in human and bovine cancellous bone.

The acoustic behavior of cancellous bone with regard to its complex poroelastic nature has been investigated. The existence of two longitudinal modes of propagation is demonstrated in both bovine and human cancellous bone. Failure to take into account the presence of these two waves may result in inaccurate material characterization.

Wear of alumina-on-alumina total hip arthroplasties at a mean 11-year followup

The surface topography of 11 alumina-onalumina hip arthroplasties retrieved for aseptic loosening at a mean 11-year followup was investigated. Macroscopic wear was assessed using a coordinate measuring machine. Microscopic wear features were evaluated by Talysurf analysis. Scanning electron microscopy was used to look at the alumina microstructure. Components were classified into three groups: (1) low wear with no sign of wear and average arithmetic roughness values below 0.05 μm; (2) stripe wear with a visible oblong worn area on the femoral heads and penetration rates below 10 μm/year; and (3) severe wear with a visible loss of material on both components, showing total roughness values as much as 4 μm and maximum penetrations higher than 150 μm. Alumina quality assessed by grain size measurements and porosity percentages improved progressively from 1977 to 1988. This resulted in a correlated decrease of the microscopic wear magnitude. However, on a macroscopic scale, factors responsible for either a load increase (weight, young age, and male gender) or impairment in the load distribution over the component surfaces (large grain size, nonoptimal initial cup inclination, and cup migration and/or tilting) increased the penetration rates.