Trabecular bone strain changes associated with cartilage defects in the proximal and distal tibia

Raccoons Reveal Hidden Diversity in Trabecular Bone Development

Trabecular bone, and its ability to rapidly modify its structure in response to strain exerted on skeletal elements, has garnered increased attention from researchers with the advancement of CT technology that allows for the analysis of its complex lattice-like framework. Much of this research has focused on adults of select taxa, but analysis into trabecular development across ontogeny remains limited. In this paper, we explore the shift in several trabecular characteristics in the articular head of the humerus and femur in Procyon lotor across the entirely of the species' lifespan. Our results show that while body mass plays a role in determining trabecular structure, other elements such as bone growth, increased activity, and puberty result in trends not observed in the interspecific analysis of adults. Furthermore, differences in the trabeculae of the humerus and femur suggest combining distinct boney elements in meta-analysis may obfuscate the variety in the structures. Finally, rates at which fore and hindlimb trabeculae orient themselves early in life differ enough to warrant further exploration to identify the currently unknown causes for their variation.

Ontogenetic Patterning of Human Subchondral Bone Microarchitecture in the Proximal Tibia

High-resolution computed tomography images were acquired for 31 proximal human tibiae, age 8 to 37.5 years, from Norris Farms #36 cemetery site (A.D. 1300). Morphometric analysis of subchondral cortical and trabecular bone architecture was performed between and within the tibial condyles. Kruskal−Wallis and Wilcoxon signed-rank tests were used to examine the association between region, age, body mass, and each morphometric parameter. The findings indicate that age-related changes in mechanical loading have varied effects on subchondral bone morphology. With age, trabecular microstructure increased in bone volume fraction (p = 0.033) and degree of anisotropy (p = 0.012), and decreased in connectivity density (p = 0.001). In the subchondral cortical plate, there was an increase in thickness (p < 0.001). When comparing condylar regions, only degree of anisotropy differed (p = 0.004) between the medial and lateral condyles. Trabeculae in the medial condyle were more anisotropic than in the lateral region. This research represents an innovative approach to quantifying both cortical and trabecular subchondral bone microarchitecture in archaeological remains.

Experimental mechanical strain measurement of tissues

Strain, an important biomechanical factor, occurs at different scales from molecules and cells to tissues and organs in physiological conditions. Under mechanical strain, the strength of tissues and their micro- and nanocomponents, the structure, proliferation, differentiation and apoptosis of cells and even the cytokines expressed by cells probably shift. Thus, the measurement of mechanical strain (i.e., relative displacement or deformation) is critical to understand functional changes in tissues, and to elucidate basic relationships between mechanical loading and tissue response. In the last decades, a great number of methods have been developed and applied to measure the deformations and mechanical strains in tissues comprising bone, tendon, ligament, muscle and brain as well as blood vessels. In this article, we have reviewed the mechanical strain measurement from six aspects: electro-based, light-based, ultrasound-based, magnetic resonance-based and computed tomography-based techniques, and the texture correlation-based image processing method. The review may help solving the problems of experimental and mechanical strain measurement of tissues under different measurement environments.

Functional imaging in OA: role of imaging in the evaluation of tissue biomechanics

Functional imaging refers broadly to the visualization of organ or tissue physiology using medical image modalities. In load-bearing tissues of the body, including articular cartilage lining the bony ends of joints, changes in strain, stress, and material properties occur in osteoarthritis (OA), providing an opportunity to probe tissue function through the progression of the disease. Here, biomechanical measures in cartilage and related joint tissues are discussed as key imaging biomarkers in the evaluation of OA. Emphasis will be placed on the (1) potential of radiography, ultrasound, and magnetic resonance imaging to assess early tissue pathomechanics in OA, (2) relative utility of kinematic, structural, morphological, and biomechanical measures as functional imaging biomarkers, and (3) improved diagnostic specificity through the combination of multiple imaging biomarkers with unique contrasts, including elastography and quantitative assessments of tissue biochemistry. In comparison to other modalities, magnetic resonance imaging provides an extensive range of functional measures at the tissue level, with conventional and emerging techniques available to potentially to assess the spectrum of preclinical to advance OA.

Quantification of the effect of osteolytic metastases on bone strain within whole vertebrae using image registration

The vertebral column is the most frequent site of metastatic involvement of the skeleton with up to 1/3 of all cancer patients developing spinal metastases. Longer survival times for patients, particularly secondary to breast cancer, have increased the need for better understanding the impact of skeletal metastases on structural stability. This study aims to apply image registration to calculate strain distributions in metastatically involved rodent vertebrae utilizing µCT imaging. Osteolytic vertebral lesions were developed in five rnu/rnu rats 2-3 weeks post intracardiac injection with MT-1 human breast cancer cells. An image registration algorithm was used to calculate and compare strain fields due to axial compressive loading in metastatically involved and control vertebrae. Tumor-bearing vertebrae had greatly increased compressive strains, double the magnitude of strain compared to control vertebrae (p=0.01). Qualitatively strain concentrated within the growth plates in both tumor bearing and control vertebrae. Most interesting was the presence of strain concentrations at the dorsal wall in metastatically involved vertebrae, suggesting structural instability. Strain distributions, quantified by image registration were consistent with known consequences of lytic involvement. Metastatically involved vertebrae had greater strain magnitude than control vertebrae. Strain concentrations at the dorsal wall in only the metastatic vertebrae, were consistent with higher incidence of burst fracture secondary to this pathology. Future use of image registration of whole vertebrae will allow focused examination of the efficacy of targeted and systemic treatments in reducing strains and the related risk of fracture in pathologic bones under simple and complex loading.

The effect of tibial lengthening on immature articular cartilage of the ankle joint

Is the articular cartilage of the immature ankle joint damaged by tibial lengthening? Sixteen immature rabbits underwent a 30% diaphyseal lengthening by tibial callotasis. Damage was assessed by scanning electronic microscopy and histomorphometry at the completion of distraction and after an additional 5 weeks. Despite joint contracture, little damage in the articular cartilage was observed in contrast to the knee joint. The findings show that the immature ankle joint is more resilient to stress than the knee and implies that reduced weight bearing and decreased joint movement alone are not sufficient to cause cartilage damage, at least in the ankle.

Basic science of intra-articular fractures and posttraumatic osteoarthritis

Intra-articular fractures represent the primary etiologic factor leading to posttraumatic osteoarthritis. The pathomechanisms linking intra-articular fractures to end-stage cartilage destruction are poorly understood. However, fracture-related chondrocyte death has been linked to posttraumatic osteoarthritis. Researchers have made significant progress in understanding the pathomechanical link between injury and chondrocyte death. This article reviews recent basic scientific progress investigating intraarticular fractures and fracture-related chondrocyte death and dysfunction.

Whole Bone Strain Quantification by Image Registration: A Validation Study

Quantification of bone strain can be used to better understand fracture risk, bone healing, and bone turnover. The objective of this work was to develop and validate an intensity matching image registration method to accurately measure and spatially resolve strain in vertebrae using μCT imaging. A strain quantification method was developed that used two sequential μCT scans, taken in loaded and unloaded configurations. The image correlation algorithm implemented was a multiresolution intensity matching deformable registration that found a series of affine mapping between the unloaded and loaded scans. Once the registration was completed, the displacement field and strain field were calculated from the mappings obtained. Validation was done in two distinct ways: the first was to look at how well the method could quantify zero strain; the second was to look at how the method was able to reproduce a known applied strain field. Analytically defined strain fields that linearly varied in space and strain fields resulting from finite element analysis were used to test the strain measurement algorithm. The deformable registration method showed very good agreement with all cases imposed, establishing a detection limit of 0.0004 strain and displaying agreement with the imposed strain cases (average R2=0.96). The deformable registration routine developed was able to accurately measure both strain and displacement fields in whole rat vertebrae. A rigorous validation of any strain measurement method is needed that reports on the ability of the routine to measure strain in a variety of strain fields with differing spatial extents, within the structure of interest.

Autologous chondrocyte transplantation for the treatment of massive cartilage lesion of the distal tibia: a case report with 8-year follow-up

We report on the 8-year follow-up outcome after autologous chondrocyte transplantation in a case of massive cartilage lesion of the distal tibia in a young patient after intraarticular fracture. To our knowledge, this is the first case report in which autologous chondrocyte transplantation was performed in the distal tibial chondral lesion. Long-term clinical success was achieved by this method of treatment in a patient too young to be treated with arthrodesis.

Contact stress transients during functional loading of ankle stepoff incongruities

Cartilage deformation demonstrates viscoelastic behavior due to its unique structure. However, nearly all contact studies investigating incongruity-associated changes in cartilage surface stresses have been static tests. These tests have consistently measured only modest increases in contact stresses, even with large incongruities. In this study, an experimental approach measuring real-time contact stresses in human cadaveric ankles during quasi-physiologic motion and loading was used to determine how stepoff incongruities of the distal tibia affected contact stresses and contact stress gradients. Peak instantaneous contact stresses, in ankles with stepoffs between 1.0 and 4.0mm of the anterolateral articular surface, increased by between 2.3 x and 3.0 x compared to the corresponding intact ankle values. Peak instantaneous contact stress gradients in stepoff configurations increased by between 1.9 x and 2.6 x the corresponding intact configuration values. Anatomic reduction of the displaced fragment restored intact contact stresses and contact stress gradients. Intact and anatomic configurations demonstrated a heterogeneous population of low-magnitude, randomly oriented contact stress gradient vectors in contrast to high-magnitude, preferentially oriented gradients in stepoff configurations. Peak instantaneous contact stresses may be important pathomechanical determinants of post-traumatic arthritis. Abnormal contact stress gradients could cause regional pathological disturbances in cartilage stress and interstitial fluid distribution. Measuring contact stresses and contact stress gradients during motion allowed potential incongruity-associated pathologic changes in loading that occur over the complete motion cycle to be investigated.

A cadaveric investigation into the links between macroscopic and microscopic osteoarthritic changes at the hip

Our objective was to investigate the frequency and distribution of osteoarthritic changes at the hip, including the relationship between osteoarthritic lesions on the femoral head surface and histological changes in articular cartilage, in 12 cadavers. Twelve embalmed cadavers (five males and seven females) were dissected, and the femoral head was removed from both sides (24 femoral heads). Any gross osteoarthritic changes were noted and graded (on a scale of 1-3). A circular disc was then removed from the equator of the femoral head and divided into nine regions. Out of 192 segments, 54 underwent sectioning and staining with haematoxylin and eosin to assess histological changes in cartilage. Osteoarthritis of the hip was present in all cadavers, with all males having bilateral OA and 50% having grade 2 or higher lesions (50% were grade 1), and four of the seven female specimens having bilateral OA and only 7% with grade 2 lesions (with 71% grade 1 and 21% normal). Chondrocyte clustering was most commonly observed in the deep layer of cartilage followed by the intermediate and superficial layers respectively, as the grade of the macroscopic lesion increased. Cartilage injury at the histological level precedes any visible denudation of the femoral head articular cartilage. This study supports the hypothesis that early osteoarthritic changes occur in the deep layer of cartilage near the tide mark and progress superficially concomitant with an overall increase in the osteoarthritic lesion size on the femoral head surface.

The impact of osteoarthritis: implications for research

Osteoarthritis, the clinical syndrome of joint pain and dysfunction caused by joint degeneration, affects more people than any other joint disease. There are no consistently effective methods for preventing osteoarthritis or slowing its progression, and symptomatic treatments provide limited benefit for many patients. Osteoarthritis disables about 10% of people who are older than 60 years, compromises the quality of life of more than 20 million Americans, and costs the United States economy more than $60 billion per year. The incidence of osteoarthritis rises precipitously with age; as a result, the prevalence and burden of this disorder is increasing rapidly. Study of the patterns osteoarthritis incidence and prevalence shows that it occurs frequently in the hand, foot, knee, spine and hip, but rarely in the ankle, wrist, elbow, and shoulder, and the most important universal risk factors are age, excessive joint loading, and joint injury. Analysis of the impact of osteoarthritis raises questions that include: Why does the incidence increase progressively with age? Why are some joints rarely affected? How do mechanical forces cause joint degeneration? What biologic and mechanical factors slow or accelerate the rate of joint degeneration? Answering these questions could lead to effective methods of preventing osteoarthritis and slowing its progression.

Incongruity versus instability in the etiology of posttraumatic arthritis

The etiology of posttraumatic arthritis is understood poorly but it clearly has a pathomechanical component. Posttraumatic arthritis likely results from irreversible cartilage damage sustained at the time of injury and chronic cartilage overloading resulting from articular incongruity and instability. However, the relative importance of instability and incongruity is unknown. Clinical studies show that the hip, knee, and ankle tolerate incongruity differently. However, all three joints poorly tolerate instability. Basic mechanical studies have shown that static loading of articular surface incongruities have caused relatively modest increases in contact pressure. However, static testing poorly replicates normal viscoelastic properties of cartilage, which may mask important transient stress elevations that occur during motion. Static tests also ignore potential abnormal loads that may accumulate throughout a motion cycle. We review the clinical and basic scientific evidence linking incongruity and instability to posttraumatic arthritis. Preliminary data from a newly developed dynamic ankle testing device are presented. Dynamic testing allows measurement of transient contact loads and loading rates that occur through the entire motion cycle and it opens the door to measure mechanical abnormalities associated with instability.

Outcomes after treatment of high-energy tibial plafond fractures

BACKGROUND

Although a number of investigators have documented clinical outcomes and complications associated with tibial plafond, or pilon, fractures, very few have examined functional and general health outcomes associated with these fractures. Our purpose was to assess midterm health, function, and impairment after pilon fractures and to examine patient, injury, and treatment characteristics that influence outcome.

METHODS

A retrospective cohort analysis of pilon fractures treated at two centers between 1994 and 1995 was conducted. Patient, injury, and treatment characteristics were recorded from patient interviews and medical record abstraction. Study participants returned to the initial treatment centers for a comprehensive evaluation of their health status. The primary outcomes that were measured included general health, walking ability, limitation of range of motion, pain, and stair-climbing ability. A secondary outcome measure was employment status.

RESULTS

Eighty (78%) of 103 eligible patients were evaluated at a mean of 3.2 years after injury. General health, as measured with the Short Form-36 (SF-36), was significantly poorer than age and gender-matched norms. Thirty-five percent of the patients reported substantial ankle stiffness; 29%, persistent swelling; and 33%, ongoing pain. Of sixty-five participants who had been employed before the injury, twenty-eight (43%) were not employed at the time of follow-up; nineteen (68%) of the twenty-eight reported that the pilon fracture prevented them from working. Multivariate analyses revealed that presence of two or more comorbidities, being married, having an annual personal income of less than 25,000 US dollars, not having attained a high-school diploma, and having been treated with external fixation with or without limited internal fixation were significantly related to poorer results as reflected by at least two of the five primary outcome measures.

CONCLUSIONS

At more than three years after the injury, pilon fractures can have persistent and devastating consequences on patients' health and well-being. Certain social, demographic, and treatment variables seem to contribute to these poor outcomes.