John G. Skedros

Implications of reference axes used for rotational alignment of the femoral component in primary and revision knee arthroplasty

A careful review of the literature revealed that no data had been reported on the angular difference or similarity between the posterior condylar axis used by many surgeons for primary total knee arthroplasty and the transepicondylar axis, which has been considered a useful anatomical landmark for femoral component placement in revision total knee arthroplasty. The purpose of this study was to determine whether measurable differences exist between the posterior condylar axis and the transepicondylar axis of the human femur. Nineteen pairs of human donor femora were measured. This study demonstrated that when the posterior condylar axis was taken as 0 degrees of rotation, the transepicondylar axis was found to be approximately 5 degrees externally rotated for both right and left femora, a significant difference (P < .05). However, there was no statistically significant difference in the angle measured between the posterior condylar axis and the transepicondylar axis when comparisons were made between matched right and left femora (P > .05). It is suggested that this information can be applied to improving the techniques currently used in the placement of both primary and revision femoral knee components.

Determining mineral content variations in bone using backscattered electron imaging

The mechanical properties of bones are greatly influenced by the ratio of organic constituents to mineral. Determination of bone mineral content on a macroscopic scale is straightforward, but microscopic variations, which can yield new insights into remodelling activities, mechanical strength, and integrity, are profoundly more difficult to measure. Measurement of microscopic mineral content variations in bone material has traditionally been performed using microradiography. Backscattered electron (BSE) imaging is a technique with significantly better resolution than microradiography with demonstrated consistency, and it does not suffer from projection-effect errors. We report results demonstrating the applicability of quantitative BSE imaging as a tool for measuring microscopic mineral content variations in bones representing a broad range of mineralization. Bones from ten species were analyzed with Fourier-transformed infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectrometry, ash measurements, and BSE imaging. BSE image intensity (graylevel) had a very strong positive correlation to mineral (ash) content. Compositional and crystallographic variations among bones had negligible influence on backscattered electron graylevels. The present study confirms the use of BSE imaging as a tool to measure the microscopic mineral variability in a broad range of mineralized tissues.

Evidence of structural and material adaptation to specific strain features in cortical bone

Functionally induced strains provide epigenetic signaling for bone modeling and remodeling activities. Strain gauge documentation of the equine third metacarpal reveals a neutral axis passing through the craniolateral cortex, resulting in a narrow band of cortex loaded predominantly in tension, with the remainder of the cortex experiencing a wide range of compression strain magnitudes that are maximal in the caudomedial cortex. This predictable strain pattern provides a model for examining the hypothesis that strain mode, magnitude, and strain energy density are potential correlates of compact bone structural and material organization.

Measurement of femoral anteversion by biplane radiography and computed tomography imaging: comparison with an anatomic reference.

Kuo T, Skedros J, Bloebaum R. Measurement of femoral anteversion by biplane radiography and computed tomography imaging: comparison with an anatomic reference. Invest Radiol 2003;38:221–229. Rationale and Objectives.The ability of biplane radiography and standard computed tomography (CT) imaging techniques to measure accurately the human femoral anteversion was evaluated and compared with an anatomic reference: the osteometric method. Methods.Femoral anteversion of 10 normal adult cadaveric human femora were determined using a standardized anatomic measurement method (the anatomic reference) and the 2 selected common imaging techniques (biplane radiography and CT). Results.On average, anteversion measurements using biplane radiography were 21/2 times greater in magnitude than measurements using the anatomic reference (absolute mean difference, 13.5°;P = 0.004). In contrast, the discrepancy between CT and anatomic reference measurements was notably less and not statistically significant (absolute mean difference, 2.8°;P = 0.351). In addition, biplane radiography demonstrated greater inter- and intrarater variability than CT imaging for repeated measurements of the same bone specimens. Conclusions.Compared with the anatomic reference, CT imaging was an accurate and valid technique for measuring the femoral anteversion. In contrast, biplane radiography demonstrated significant inconsistencies in the measurement of this anatomic parameter.

Biomechanical Implications of Mineral Content and Microstructural Variations in Cortical Bone of Horse, Elk, and Sheep Calcanei

Artiodactyl and perissodactyl calcanei have been recently introduced as models for examining bone for mechanically mediated adaptation. We have reported substantial regional variations in cortical bone microstructure and mineral content within the same cross‐section of mule deer calcanei. In part, these variations may be adaptations accommodating the customary presence of predominantly tension, compression, and shear strain modes in mutually exclusive cortical locations. Calcanei from skeletally mature horses, elk, and sheep were examined in order to corroborate these previous findings.

Modeling and remodeling in a developing artiodactyl calcaneus: A model for evaluating Frost's Mechanostat hypothesis and its corollaries

The artiodactyl (mule deer) calcaneus was examined for structural and material features that represent regional differences in cortical bone modeling and remodeling activities. Cortical thickness, resorption and formation surfaces, mineral content (percent ash), and microstructure were quantified between and within skeletally immature and mature bones. These features were examined to see if they are consistent with predictions of Frosts Mechanostat paradigm of mechanically induced bone adaptation in a maturing “tension/compression” bone (Frost, 1990a , b , Anat Rec 226:403–413, 414–422). Consistent with Frosts hypothesis that surface modeling activities differ between the “compression” (cranial) and “tension” (caudal) cortices, the elliptical cross‐section of the calcaneal diaphysis becomes more elongated in the direction of bending as a result of preferential (> 95%) increase in thickness of the compression cortex. Regional differences in mineral content and population densities of new remodeling events (NREs = resorption spaces plus newly forming secondary osteons) support Frosts hypothesis that intracortical remodeling activities differ between the opposing cortices: 1.) in immature and mature bones, the compression cortex had attained a level of mineralization averaging 8.9 and 6.8% greater (P < 0.001), respectively, than that of the tension cortex, and 2.) there are on average 350 to 400% greater population densities of NREs in the tension cortices of both age groups (P < 0.0003). No significant differences in cortical thickness, mineral content, porosity, or NREs were found between medial and lateral cortices of the skeletally mature bones, suggesting that no modeling or remodeling differences exist along a theoretical neutral axis. However, in mature bones these cortices differed considerably in secondary osteon cross‐sectional area and population density. Consistent with Frosts hypothesis, remodeling in the compression cortex produced bone with microstructural organization that differs from the tension cortex. However, the increased remodeling activity of the tension cortex does not appear to be related to a postulated low‐strain environment. Although most findings are consistent with predictions of Frosts Mechanostat paradigm, there are several notable inconsistencies. Additional studies are needed to elucidate the nature of the mechanisms that govern the modeling and remodeling activities that produce and maintain normal bone. It is proposed that the artiodactyl calcaneus will provide a useful experimental model for these studies. Anat Rec 263:167–185, 2001.

Knowledge and Opinions of Orthopaedic Surgeons Concerning Medical Evaluation and Treatment of Patients with Osteoporotic Fracture

BACKGROUND With the exponential increase in osteoporotic fractures, orthopaedic surgeons are in a logical position to become more involved in the medical treatment of this disease. However, it has been hypothesized that surgeons may not be inclined to initiate such treatment if they do not view medical interventions as an extension of their surgical opportunities. The objective of this study was to determine the knowledge and opinions of orthopaedic surgeons with regard to their opportunities for initiating medical treatment of patients with an osteoporotic fracture. METHODS A survey consisting of twenty-two questions was administered to 171 orthopaedic surgeons in Utah, Idaho, and Wyoming. RESULTS Of the 171 surveys that were mailed, 107 usable surveys were returned (a 63% response rate). A majority of the orthopaedic surgeons thought that it was appropriate to expand their orthopaedic practice to include prescribing pharmacological treatments for osteoporosis (68% agreed or strongly agreed with that statement). However, 47% were concerned enough about adverse events related to some conventional pharmacological treatments that they would rather avoid prescribing them. Of the surgeons who were willing to prescribe these treatments, 74% felt most comfortable prescribing bisphosphonates and >77% felt most comfortable prescribing calcium and vitamin-D supplements. Fifty-one percent considered an apparent osteoporotic fracture and several other clinical risk factors for osteoporosis as sufficient evidence for initiating pharmacological treatments, whereas 72% thought that a bone-density scan should be made before initiating treatment. Although 32% thought that all nonoperative treatment should be the responsibility of a primary care provider, 63% thought that the orthopaedic surgeon should initiate a workup to look for secondary causes of the osteoporosis and should begin medical treatment of patients with an osteoporotic fracture before referring them. CONCLUSIONS Although a majority of orthopaedic surgeons believe that they should expand their role in the medical treatment of patients with an osteoporotic fracture, many do not institute medical treatment and think that the patients primary care providers should be responsible for medical care.

The rotator cuff-deficient arthritic shoulder: diagnosis and surgical management.

&NA; The symptomatic rotator cuff‐deficient, arthritic glenohumeral joint poses a complex problem for the orthopaedic surgeon. Surgical management can be facilitated by classifying the disorder in one of three diagnostic categories: (1) rotator cuff‐tear arthropathy, (2) rheumatoid arthritic shoulder with cuff deficiency, or (3) degenerative arthritic (osteoarthritic) shoulder with cuff deficiency. If it is not possible to repair the cuff defect, surgical management may include prosthetic arthroplasty, with the recognition that only limited goals are attainable, particularly with respect to strength and active motion. Glenohumeral arthrodesis is a salvage procedure when other surgical measures have failed. Arthrodesis is also indicated in patients with deltoid muscle deficiency. Humeral hemiarthroplasty avoids the complications of glenoid loosening and is an attractive alternative to arthrodesis, resection arthroplasty, and total shoulder arthroplasty. The functionally intact coracoacromial arch should be preserved to reduce the risk of anterosuperior subluxation. Care should be taken not to “overstuff” the glenohumeral joint with a prosthetic component. In cases of significant internal rotation contracture, subscapularis lengthening is necessary to restore anterior and posterior rotator cuff balance. If the less stringent criteria of Neers “limited goals” rehabilitation are followed, approximately 80% to 90% of patients treated with humeral hemiarthroplasty can have satisfactory results.

Does the degree of laminarity correlate with site-specific differences in collagen fibre orientation in primary bone? An evaluation in the turkey ulna diaphysis

de Margerie hypothesized that preferred orientations of primary vascular canals in avian primary cortical bone mediate important mechanical adaptations. Specifically, bones that receive habitual compression, tension or bending stresses typically have cortices with a low laminarity index (LI) (i.e. relatively lower cross‐sectional areas of circularly (C) orientated primary vascular canals, and relatively higher areas of canals with radial (R), oblique (O) or longitudinal (L) orientations. By contrast, bones subject to habitual torsion have a high LI (i.e. relatively higher C‐orientated canal area) [LI, based on percentage vascular canal area, = C/(C + R + O + L)]. Regional variations in predominant collagen fibre orientation (CFO) may be the adaptive characteristic mediated by LI. Using turkey ulnae, we tested the hypothesis that site‐specific variations in predominant CFO and LI are strongly correlated. Mid‐diaphyseal cross‐sections (100 ± 5 µm) from subadult and adult bones were evaluated for CFO and LI using circularly polarized light images of cortical octants. Results showing significant differences between mean LI of subadult (40.0% ± 10.7%) and adult (50.9% ± 10.4%) (P < 0.01) bones suggest that adult bones experience more prevalent/predominant torsion. Alternatively, this relationship may reflect differences in growth rates. High positive correlations between LI and predominant CFO (subadults: r = 0.735; adults: r = 0.866; P < 0.001) suggest that primary bone can exhibit potentially adaptive material variations that are independent of secondary osteon formation.

Comparison of human, primate, and canine femora : Implications for biomaterials testing in total hip replacement

The canine model remains an animal of choice for determining the efficacy and safety of various materials and designs used in human total hip replacement (THR). The primate also is used in orthopedic-related research for studying limb anatomy, gait, and age-related bone loss. In order to better understand the appropriateness of these animal models for human THR, external morphologies of thirty-three adult Caucasian human, sixteen adult chimpanzee, and forty-two adult greyhound femora were compared using osteometric methods. Measured parameters included anteversion angle, cervico-diaphyseal angle, femoral head offset in the frontal plane, and anterior bow profiles along the femoral diaphysis. Although some of the measured parameters were approximately similar between species (e.g., mean cervico-diaphyseal angle of humans and chimpanzees), the majority demonstrated morphologic differences that may be biomechanically significant for interpreting stress transfer across the hip (e.g., mean anteversion angle and mean normalized femoral head offset between species). Additionally, age-related changes in proximal femoral morphology and gait pattern, as well as species-related differences in local muscle and inertial forces, may result in notably different loading conditions across the hip joint of each species. Therefore, discretion must be exercised when evaluating canine or primate THR materials and designs for potential use in the human hip.