Subchondral damage after acute transarticular loading: an in vitro model of joint injury

Effects of and Response to Mechanical Loading on the Knee

Mechanical loading to the knee joint results in a differential response based on the local capacity of the tissues (ligament, tendon, meniscus, cartilage, and bone) and how those tissues subsequently adapt to that load at the molecular and cellular level. Participation in cutting, pivoting, and jumping sports predisposes the knee to the risk of injury. In this narrative review, we describe different mechanisms of loading that can result in excessive loads to the knee, leading to ligamentous, musculotendinous, meniscal, and chondral injuries or maladaptations. Following injury (or surgery) to structures around the knee, the primary goal of rehabilitation is to maximize the patient's response to exercise at the current level of function, while minimizing the risk of re-injury to the healing tissue. Clinicians should have a clear understanding of the specific injured tissue(s), and rehabilitation should be driven by knowledge of tissue-healing constraints, knee complex and lower extremity biomechanics, neuromuscular physiology, task-specific activities involving weight-bearing and non-weight-bearing conditions, and training principles. We provide a practical application for prescribing loading progressions of exercises, functional activities, and mobility tasks based on their mechanical load profile to knee-specific structures during the rehabilitation process. Various loading interventions can be used by clinicians to produce physical stress to address body function, physical impairments, activity limitations, and participation restrictions. By modifying the mechanical load elements, clinicians can alter the tissue adaptations, facilitate motor learning, and resolve corresponding physical impairments. Providing different loads that create variable tensile, compressive, and shear deformation on the tissue through mechanotransduction and specificity can promote the appropriate stress adaptations to increase tissue capacity and injury tolerance. Tools for monitoring rehabilitation training loads to the knee are proposed to assess the reactivity of the knee joint to mechanical loading to monitor excessive mechanical loads and facilitate optimal rehabilitation.

Operative Treatment of Intra-Articular Distal Radius Fractures With versus Without Arthroscopy: study protocol for a randomised controlled trial

Background

In the past several years, an increase in open reduction and internal fixation (ORIF) for intra-articular distal radius fractures has been observed. This technique leads to a quicker recovery of function compared to non-operative treatment. However, some patients continue to have a painful and stiff wrist postoperatively. Arthroscopically assisted removal of intra-articular fracture haematoma and debris may improve the functional outcomes following operative treatment of intra-articular distal radius fractures. The purpose of this randomised controlled trial is to determine the difference in functional outcome, assessed with the Patient-Rated Wrist Evaluation (PRWE) score, after ORIF with and without an additional wrist arthroscopy in adult patients with displaced complete articular distal radius fractures.

Methods

In this multicentre trial, adult patients with a displaced complete articular distal radius fracture are randomised between ORIF with an additional wrist arthroscopy to remove fracture haematoma and debris (intervention group) and conventional fluoroscopic-assisted ORIF (control group). The primary outcome is functional outcome assessed with the PRWE score after three months. Secondary outcomes are wrist function assessed with the Disability of the Arm, Shoulder and Hand (DASH) score, postoperative pain, range of motion, grip strength, complications and cost-effectiveness. Additionally, in the intervention group, the quality of reduction, associated ligamentous injuries and cartilage damage will be assessed. A total of 50 patients will be included in this study.

Discussion

Although ORIF of intra-articular distal radius fractures leads to a quicker resume of function compared to non-operative treatment, some patients continue to have a painful and stiff wrist postoperatively. We hypothesise that, due to the removal of fracture haematoma and debris by an additional arthroscopy, functional outcomes will be better compared to the non-arthroscopically treated group.

Trial registration

ClinicalTrials.gov, NCT02660515. Registered on 13 January 2016.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2409-2) contains supplementary material, which is available to authorized users.

The acetabular labrum

The acetabular labrum is a soft-tissue structure which lines the acetabular rim of the hip joint. Its role in hip joint biomechanics and joint health has been of particular interest over the past decade. In normal hip joint biomechanics, the labrum is crucial in retaining a layer of pressurised intra-articular fluid for joint lubrication and load support/distribution. Its seal around the femoral head is further regarded as a contributing to hip stability through its suction effect. The labrum itself is also important in increasing contact area thereby reducing contact stress. Given the labrum’s role in normal hip joint biomechanics, surgical techniques for managing labral damage are continuously evolving as our understanding of its anatomy and function continue to progress. The current paper aims to review the anatomy and biomechanical function of the labrum and how they are affected by differing surgical techniques.

Take home message: The acetabular labrum plays a critical role in hip function and maintaining and restoring its function during surgical intervention remain an essential goal.

Cite this article: Bone Joint J 2016;98-B:730–5.

Focal cartilage defect compromises fluid-pressure dependent load support in the knee joint

A focal cartilage defect involves tissue loss or rupture. Altered mechanics in the affected joint may play an essential role in the onset and progression of osteoarthritis. The objective of the present study was to determine the compromised load support in the human knee joint during defect progression from the cartilage surface to the cartilage-bone interface. Ten normal and defect cases were simulated with a previously tested 3D finite element model of the knee. The focal defects were considered in both condyles within high load-bearing regions. Fluid pressurization, anisotropic fibril-reinforcement, and depth-dependent mechanical properties were considered for the articular cartilages and menisci. The results showed that a small cartilage defect could cause 25% reduction in the load support of the knee joint due to a reduced capacity of fluid pressurization in the defect cartilage. A partial-thickness defect could cause a fluid pressure decrease or increase in the remaining underlying cartilage depending on the defect depth. A cartilage defect also increased the shear strain at the cartilage-bone interface, which was more significant with a full-thickness defect. The effect of cartilage defect on the fluid pressurization also depended on the defect sites and contact conditions. In conclusion, a focal cartilage defect causes a fluid-pressure dependent load reallocation and a compromised load support in the joint, which depend on the defect depth, site, and contact condition.

[Bone marrow edema and joint injuries]

BACKGROUND

The development of bone marrow edema in body regions adjacent to joints can have many causes and a differentiation is not possible using magnetic resonance imaging (MRI).

DEFINITION

Bone marrow edema is not necessarily an indication for microfractures. The definition of bone marrow edema is a purely radiological description. There is no uniform classification of bone marrow edema. The clinical significance, therapy and course are heterogeneous; therefore, there are no uniform recommendations for therapy.

DIAGNOSTICS

A bone marrow edema visible in MRI does not always lead to certain inferences regarding the pathogenesis. In order to be able to detect fractures it is necessary to carry out a biopsy and a histological examination.

CONCLUSION

The interpretation of MRI results and the derivation of a therapy in every case need a balanced assessment of the MRI results, medical history, clinical investigations and clinical symptoms.

Subchondral bone in osteoarthritis: insight into risk factors and microstructural changes

Osteoarthritis (OA) is a major cause of disability in the adult population. As a progressive degenerative joint disorder, OA is characterized by cartilage damage, changes in the subchondral bone, osteophyte formation, muscle weakness, and inflammation of the synovium tissue and tendon. Although OA has long been viewed as a primary disorder of articular cartilage, subchondral bone is attracting increasing attention. It is commonly reported to play a vital role in the pathogenesis of OA. Subchondral bone sclerosis, together with progressive cartilage degradation, is widely considered as a hallmark of OA. Despite the increase in bone volume fraction, subchondral bone is hypomineralized, due to abnormal bone remodeling. Some histopathological changes in the subchondral bone have also been detected, including microdamage, bone marrow edema-like lesions and bone cysts. This review summarizes basic features of the osteochondral junction, which comprises subchondral bone and articular cartilage. Importantly, we discuss risk factors influencing subchondral bone integrity. We also focus on the microarchitectural and histopathological changes of subchondral bone in OA, and provide an overview of their potential contribution to the progression of OA. A hypothetical model for the pathogenesis of OA is proposed.

Subchondral bone sclerosis in osteoarthritis: not just an innocent bystander

Abstract  Osteoarthritis (OA) is considered to be a complex illness in which the tissues of the joint play a significant role in the initiation and/or progression of the pathophysiology. We still do not completely understand what initiates the degradation and loss of cartilage. However, it has been suggested that increased catabolism due to elevated cytokines and growth factors in OA joints plays a significant role. Recent evidence suggests a key role for the subchondral bone tissue in the progression and/or initiation of OA. Indeed, the subchondral bone tissue produces a number of similar proinflammatory cytokines, and growth factors are involved in cartilage tissue remodeling. Interestingly, studies have shown the presence of clefts or channels in the tidemark that appears early in OA, indicating a possible way to traffic cytokines and growth factors from the subchondral compartment to the overlying cartilage. Therefore, it is possible that certain bone-derived products drive cartilage metabolism. Potential candidates include insulin-like growth factor-1 (IGF-1), transforming growth factor-β (TGF-β) interleukin 1β (IL-1β), and interleukin-6 (IL-6). Demonstrating that the subchondral bone plays a role in the initiation of OA would greatly contribute to furthering our knowledge of this pathology and provide new insights for therapeutic approaches.

Evaluation of knee joint muscle forces and tissue stresses-strains during gait in severe OA versus normal subjects

Osteoarthritis (OA) is the leading cause of pain and disability in the elderly with the knee being the most affected weight bearing joint. We used a musculoskeletal biomechanical model of the lower extremity including a detailed validated knee joint finite element model to compute lower extremity muscle forces and knee joint stresses-strains during the stance phase of gait. The model was driven by gait data on OA patients, and results were compared with those of the same model driven by data on normal controls. Additional analyses were performed with altered cartilage-menisci properties to evaluate the effects of deterioration during OA. In OA patients compared to normal subjects, muscle forces dropped at nearly all stance periods except mid-stance. Force in the anterior cruciate ligament remained overall the same. Total contact forces-stresses deceased by about 25%. Alterations in properties due to OA had negligible effects on muscle forces, but increased contact areas and cartilage strains and reduced contact pressures. Reductions in contact stresses and increases in tissue strains and transfer of load via menisci are partly due to the altered kinetics-kinematics of gait and partly due to deterioration in cartilage-menisci properties in OA patients.

Biphasic finite element contact analysis of the knee joint using an augmented Lagrangian method

Biphasic contact analysis is essential to obtain a more complete understanding of soft tissue biomechanics; however, only a limited number of studies have addressed these types of problems. In this paper, a theoretically consistent biphasic finite element solution of the 2D axisymmetric human knee was developed, and an augmented Lagrangian method was used to enforce the biphasic continuity across the contact interface. The interaction between the fluid and solid matrices of the soft tissues of the knee joint, the stress and strain distributions within the meniscus, and the changes in stress and strain distributions in the articular cartilage of the femur and tibia after complete meniscectomy were investigated. It was found that (i) the fluid phase carries more than 60% of the load, which reinforces the need for the biphasic model for knee biomechanics; (ii) the inner third and outer two-thirds of the meniscus had different strain distributions; and (iii) the distributions of both maximum shear stress and maximum principal strain in articular cartilage changed after complete meniscectomy - with peak values increasing by over 350%.

Altered knee joint mechanics in simple compression associated with early cartilage degeneration

The progression of osteoarthritis can be accompanied by depth-dependent changes in the properties of articular cartilage. The objective of the present study was to determine the subsequent alteration in the fluid pressurization in the human knee using a three-dimensional computer model. Only a small compression in the femur-tibia direction was applied to avoid numerical difficulties. The material model for articular cartilages and menisci included fluid, fibrillar and nonfibrillar matrices as distinct constituents. The knee model consisted of distal femur, femoral cartilage, menisci, tibial cartilage, and proximal tibia. Cartilage degeneration was modeled in the high load-bearing region of the medial condyle of the femur with reduced fibrillar and nonfibrillar elastic properties and increased hydraulic permeability. Three case studies were implemented to simulate (1) the onset of cartilage degeneration from the superficial zone, (2) the progression of cartilage degeneration to the middle zone, and (3) the progression of cartilage degeneration to the deep zone. As compared with a normal knee of the same compression, reduced fluid pressurization was observed in the degenerated knee. Furthermore, faster reduction in fluid pressure was observed with the onset of cartilage degeneration in the superficial zone and progression to the middle zone, as compared to progression to the deep zone. On the other hand, cartilage degeneration in any zone would reduce the fluid pressure in all three zones. The shear strains at the cartilage-bone interface were increased when cartilage degeneration was eventually advanced to the deep zone. The present study revealed, at the joint level, altered fluid pressurization and strains with the depth-wise cartilage degeneration. The results also indicated redistribution of stresses within the tissue and relocation of the loading between the tissue matrix and fluid pressure. These results may only be qualitatively interesting due to the small compression considered.

Does prior sustained compression make cartilage-on-bone more vulnerable to trauma?

BACKGROUND

This study investigated how varying levels of prior creep deformation in cartilage-on-bone samples influences their mechanical response and vulnerability to structural damage following a single traumatic impact.

METHODS

Bovine patellae were subjected to varying intervals of prior creep loading at a constant stress of 4MPa. Immediately following removal of this stress the samples were impacted with a pendulum indenter system at a fixed energy of 2.2J.

FINDINGS

With increasing prior creep, the peak force on impact rose, the duration of impact and time to reach peak force both decreased, and both the energy dissipated during impact and the magnitude of impulse were both unchanged by the level of prior creep. With increasing prior creep, the severity of impact-induced osteochondral damage increased: articular cartilage cracks penetrated to a greater depth, extending to the calcified cartilage layer resulting in hairline fractures or articular cartilage delamination and associated secondary damage to the vascular channels in the subchondral bone.

INTERPRETATION

The study shows that exposure of the cartilage-on-bone system to prior creep can significantly influence its response to subsequent impact, namely force attenuation and severity of damage to the articular cartilage, calcified cartilage and vascular channel network in the subchondral bone.

Relationship between cartilage and subchondral bone lesions in repetitive impact trauma-induced equine osteoarthritis

OBJECTIVE

To correlate degenerative changes in cartilage and subchondral bone in the third carpal bone (C3) of Standardbred racehorses with naturally occurring repetitive trauma-induced osteoarthritis.

DESIGN

Fifteen C3, collected from Standardbred horses postmortem, were assessed for cartilage lesions by visual inspection and divided into Control (CO), Early Osteoarthritis (EOA) and Advanced Osteoarthritis (AOA) groups. Two osteochondral cores were harvested from corresponding dorsal sites on each bone and scanned with a micro-computed tomography (CT) instrument. 2D images were assembled into 3D reconstructions that were used to quantify architectural parameters from selected regions of interest, including bone mineral density and bone volume fraction. 2D images, illustrating the most severe lesion per core, were scored for architectural appearance by blinded observers. Thin sections of paraffin-embedded decalcified cores stained with Safranin O-Fast Green, matched to the micro-CT images, were scored using a modified Mankin scoring system.

RESULTS

Subchondral bone pits with deep focal areas of porosity were seen more frequently in AOA than EOA but never in CO. Articular cartilage damage was seen in association with a reduction in bone mineral and loss of bone tissue. Histological analyses revealed significant numbers of microcracks in the calcified cartilage of EOA and AOA groups and a progressive increase in the score compared with CO bones.

CONCLUSION

The data reveal corresponding, progressive degenerative changes in articular cartilage and subchondral bone, including striking focal resorptive lesions, in the third carpal bone of racehorses subjected to repetitive, high impact trauma.

Biological aspects of early osteoarthritis

PURPOSE

Early OA primarily affects articular cartilage and involves the entire joint, including the subchondral bone, synovial membrane, menisci and periarticular structures. The aim of this review is to highlight the molecular basis and histopathological features of early OA.

METHODS

Selective review of literature.

RESULTS

Risk factors for developing early OA include, but are not limited to, a genetic predisposition, mechanical factors such as axial malalignment, and aging. In early OA, the articular cartilage surface is progressively becoming discontinuous, showing fibrillation and vertical fissures that extend not deeper than into the mid-zone of the articular cartilage, reflective of OARSI grades 1.0-3.0. Early changes in the subchondral bone comprise a progressive increase in subchondral plate and subarticular spongiosa thickness. Early OA affects not only the articular cartilage and the subchondral bone but also other structures of the joint, such as the menisci, the synovial membrane, the joint capsule, ligaments, muscles and the infrapatellar fat pad. Genetic markers or marker combinations may become useful in the future to identify early OA and patients at risk.

CONCLUSION

The high socioeconomic impact of OA suggests that a better insight into the mechanisms of early OA may be a key to develop more targeted reconstructive therapies at this first stage of the disease.

LEVEL OF EVIDENCE

Systematic review, Level II.

Pathophysiology and diagnosis of third carpal bone disease in horses: A review

Third carpal bone (C3) disease is a significant cause of lameness in Standardbred and Thoroughbred horses. The bone density of C3 increases as a result of exercise, reducing the compliance of the bone and predisposing it to injury. Currently, the most widely used method of diagnosis is subjective radiography using the tangential view. Radiographically, increases in bone mineral density (BMD) appear as sclerosis but it is not known at what point increases in sclerosis indicate the onset of disease or increased risk of C3 fracture. A quantitative assessment of the BMD of C3 in horses would improve understanding of the changes that occur within this bone and guide athletic management, as it is thought that BMD changes precede articular cartilage damage. Methods of non-invasive bone-mineral analysis used for the detection of osteoporosis in humans include single photon absorptiometry (SPA), dual x-ray absorptiometry (DXA), computed tomography (CT), radioabsorptiometry (RA), quantitative ultrasonography (QU) and magnetic resonance imaging (MRI). To date, DXA and RA are the most commonly used methods of quantitative non-invasive bone-mineral analysis in horses. The cost of equipment and difficulties in performing DXA in live animals preclude the routine use of this technique for diagnostic purposes. RA may become clinically applicable to C3 analysis in horses, but small variations in x-ray beam angle when taking the tangential view significantly affect results, making this technique clinically inapplicable at this time. Currently, methods of quantitative non-invasive bone-mineral analysis of C3 in horses are not suited to clinical application.

The OARSI histopathology initiative - recommendations for histological assessments of osteoarthritis in the dog

The dog is a common model for study of osteoarthritis (OA). Subjective histologic scoring systems have often served as the reference standard for presence and severity of OA. However, these scoring systems have perceived shortcomings. The system developed for this report attempts to address these shortcomings by providing a standardized methodology for global assessment of the joint, versatility and the potential for relative weighting of pathology, allowing for comparison among time points, studies, and centers, and critical analysis of the system's reliability. The proposed system for assessment of canine tissues appears to provide an effective method for global assessment of articular pathology in OA. The system is versatile, comprehensive, and reliable and appears to have advantages over conventional scoring systems.

Two-dimensional strain fields on the cross-section of the human patellofemoral joint under physiological loading

The objective of this study was to provide a detailed experimental assessment of the two-dimensional cartilage strain distribution on the cross-section of the human patellofemoral joint (PFJ) subjected to physiological load magnitudes and rates. The medial side of six human PFJs sectioned along their mid-sagittal plane was loaded up to the equivalent of two body weights on a whole joint, and strain measurements obtained from digital image correlation are reported at 0.5s. Normal strains tangential to the articular surface and shear strains in the plane of the cross-section showed consistent patterns among all specimens, whereas normal strains perpendicular to the articular surface exhibited some variability that may be attributed to subject-specific variations in material properties through the depth of the articular layers. Elevated tensile and compressive principal normal strains were observed near the articular surface, around the center of the contact region, with additional locations of elevated compressive strains occurring at the bone-cartilage interface. Under an average contact stress of approximately 3.3MPa, the peak compressive principal normal strains for the patella and femur averaged -0.158+/-0.072 and -0.118+/-0.051, respectively, magnitudes that are significantly greater than the relative changes in cartilage thickness, -0.090+/-0.030 and -0.072+/-0.038 (p<0.005). These experimental results provide a detailed description of the manner by which human PFJ articular layers deform in situ under physiological load conditions.

Exercise-induced metacarpophalangeal joint adaptation in the Thoroughbred racehorse

Repetitive bone injury and development of stress fracture is a common problem in humans and animals. The Thoroughbred racehorse is a model in which adaptive failure and associated development of stress fracture is common. We performed a histologic study of the distal end of the third metacarpal bone in two groups of horses: young Thoroughbreds that were actively racing (n = 10) and a group of non-athletic horses (n = 8). The purpose of this study was to determine whether development of articular microcracks was associated with specific alterations to subchondral plate osteocytes. Morphometric measurements were made in five regions of the joint surface: lateral condyle, lateral condylar groove, sagittal ridge, medial condylar groove, and medial condyle. The following variables were quantified: hyaline cartilage width; calcified cartilage width; the number of tidemarks; microcrack density at the articular surface; blood vessel density entering articular cartilage; the presence of atypical bone matrix in the subchondral plate; bone volume fraction; and osteocyte density. Adaptation of articular cartilage was similar in both groups of horses. Vascularization of articular cartilage was increased in the group of non-athletic horses. Microcracks, which typically had an oblique orientation to the joint surface, were co-localized with blood vessels, and resorption spaces. Microcracking was increased in the condylar grooves of athletic horses compared with the other joint regions and was also increased compared with the condylar groove regions of non-athletic horses. Coalescence of microcracks also led to development of an intracortical articular condylar stress fracture in some joints and targeted remodeling of affected subchondral plate. The subchondral plate of the condyles in athletic horses was sclerotic, and contained atypically stained bone matrix with increased numbers of osteocytes with atypical morphology. However, osteocyte numbers were not significantly different between groups. We conclude that differences in site-specific microdamage accumulation and associated targeted remodeling between athletic and non-athletic horses are much greater than differences in subchondral osteocyte morphology. However, the presence of atypical subchondral bone matrix in athletic horses was associated with extensive osteocyte loss. Although osteocyte mechanotransduction is considered important for functional adaptation, in this model, adaptation is likely regulated by multiple mechanotransduction pathways.

Etiopathogenesis of osteoarthritis

Because of the implications for prevention and treatment, how a clinician views osteoarthritis (OA) matters. We view OA as an attempt to contain a mechanical problem in the joint and as failed repair of damage caused by excessive mechanical stress on the joint. OA is organ failure of the synovial joint. Because of insufficient focus on reduction of the habitually loaded contact area of the joint and on aberrant loading, we believe that therapeutic efforts aimed at pathogenetic mechanisms in OA have been misdirected: neither the large role that a reduction of excessive levels of mechanical stress plays in promoting the healing response in OA nor the evidence that relief of joint pain and improvement in function, rather than the appearance of the articular surface, are the most important outcomes of the healing process have been sufficiently emphasized. Various mechanical abnormalities can trigger the processes involved in repair and attempts by the joint to contain the mechanical insult, but without a return to mechanical normality, attempts at healing will fail. In our view, drugs may be helpful symptomatically, but cannot accomplish this. In our view, as long as the joint remains in the same adverse mechanical environment that got it into trouble in the first place, it is unlikely that a drug that inhibits a specific enzyme or cytokine in the pathways of cartilage breakdown, or further stimulates the already increased synthesis of cartilage matrix molecules will solve the problem of OA. Also, because the subchondral bone is critically important in containing the mechanical abnormalities that damage the cartilage, emphasis on cartilage repair alone is likely to be futile. On the other hand, if the abnormal stresses on the joint are corrected, intervention with a structure-modifying drug may be superfluous.

Role of cartilage collagen fibrils networks in knee joint biomechanics under compression

Collagen fibrils networks in knee cartilage and menisci change in content and structure from a region to another. While resisting tension, they influence global joint response as well as local strains particularly at short-term periods. To investigate the role of fibrils networks in knee joint mechanics and in particular cartilage response, a novel model of the knee joint is developed that incorporates the cartilage and meniscus fibrils networks as well as depth-dependent properties in cartilage. The joint response under up to 2000N compression is investigated for conditions simulating the absence in cartilage of deep fibrils normal to subchondral bone or superficial fibrils parallel to surface as well as localized split of cartilage at subchondral junction or localized damage to superficial fibrils at loaded areas. Deep vertical fibrils network in cartilage play a crucial role in stiffening (by 10%) global response and protecting cartilage by reducing large strains (from maximum of 102% to 38%), in particular at subchondral junction. Superficial horizontal fibrils protect the tissue mainly from excessive strains at superficial layers (from 27% to 8%). Local cartilage split at base disrupts the normal function of vertical fibrils at the affected areas resulting in higher strains. Deep fibrils, and to a lesser extent superficial fibrils, play dominant mechanical roles in cartilage response under transient compression. Any treatment modality attempting to repair or regenerate cartilage defects involving partial or full thickness osteochondral grafts should account for the crucial role of collagen fibrils networks and the demanding mechanical environment of the tissue.

Knee joint biomechanics in open-kinetic-chain flexion exercises

BACKGROUND

Different rehabilitation exercises such as open-kinetic-chain flexion and extension exercises are currently employed in non-operative and post-operative managements of joint disorders. The challenge is to strengthen the muscles and to restore the near-normal function of the joint while protecting its components (e.g., the reconstructed ligament) from excessive stresses.

METHODS

Using a validated 3D nonlinear finite element model, the detailed biomechanics of the entire joint in open-kinetic-chain flexion exercises are investigated at 0 degrees, 30 degrees, 60 degrees and 90 degrees joint angles. Two loading cases are simulated; one with only the weight of the leg and the foot while the second considers also a moderate resistant force of 30 N acting at the ankle perpendicular to the tibia.

FINDINGS

The addition of 30 N resistant force substantially increased the required hamstrings forces, forces in posterior cruciate and lateral collateral ligaments and joint contact forces/areas/stresses.

INTERPRETATION

At post-anterior cruciate ligament reconstruction or injury period, the exercise could safely be employed to strengthen the hamstrings muscles without a risk to the anterior cruciate ligament. In contrast, at post-posterior cruciate/lateral collateral ligaments reconstructions or injuries, the open-kinetic-chain flexion exercise should be avoided under moderate to large flexion angles and resistant forces.

Computational biomechanics of knee joint in open kinetic chain extension exercises

Open kinetic chain (OKC) extension exercises are commonly performed to strengthen quadriceps muscles and restore joint function in performance enhancement programs, in exercise therapies and following joint reconstruction. Using a validated 3D nonlinear finite element model, the detailed biomechanics of the entire joint in OKC extension exercises are investigated at 0, 30, 60 and 90 degrees joint angles. Two loading cases are simulated; one with only the weight of the leg and the foot while the second considers also a moderate resistant force of 30 N acting at the ankle perpendicular to the tibia. The presence of the 30 N markedly influences the results both in terms of the magnitude and the trend. The resistant load substantially increases the required quadriceps, patellar tendon, cruciate ligaments and joint contact forces, especially at near 90 degrees angles with the exception of ACL force that is increased at 0 degrees angle. At post-ACL reconstruction period or in the joint with ACL injury, the exercise should preferably be avoided at near full extension positions under large resistant forces.

Role of endochondral ossification of articular cartilage and functional adaptation of the subchondral plate in the development of fatigue microcracking of joints

The mechanisms that regulate functional adaptation of the articular ends of long bones are poorly understood. However, endochondral ossification of articular cartilage and modeling/remodeling of the subchondral plate and epiphyseal trabeculae are important components of the adaptive response. We performed a histologic study of the distal end of the third metacarpal/metatarsal bone of Thoroughbreds after bones were bulk-stained in basic fuchsin and calcified sections were prepared. The Thoroughbred racehorse is a model of an extreme athlete which experiences particularly high cyclic strains in distal limb bones. The following variables were quantified: microcrack boundary density in calcified cartilage (N.Cr/B.Bd); blood vessel boundary density in calcified cartilage (N.Ve/B.Bd); calcified cartilage width (Cl.Cg.Wi); duplication of the tidemark; and bone volume fraction of the subchondral plate (B.Ar/T.Ar). Measurements were made in five joint regions (lateral condyle and condylar groove; sagittal ridge; medial condylar and condylar groove). N.Cr/B.Bd was site-specific and was increased in the condylar groove region; this is the joint region from which parasagittal articular fatigue (condylar) fractures are typically propagated. Formation of resorption spaces in the subchondral plate was co-localized with microcracking. N.Ve/B.Bd was also site-specific. In the sagittal ridge region, N.Ve/B.Bd was increased, Cl.Cg.Wi was decreased, and B.Ar/T.Ar was decreased, when compared with the other joint regions. Multiple tidemarks were seen in all joint regions. Cumulative athletic activity was associated with a significant decrease in B.Ar/T.Ar in the condylar groove regions. N.Cr/B.Bd was positively correlated with B.Ar/T.Ar (P < 0.05, r(s) = 0.29) and N.Ve/B.Bd was negatively correlated with B.Ar/T.Ar (P < 0.005, r2 = 0.14) and Cl.Cg.Wi (P < 0.05, r2 = 0.07). We conclude that endochondral ossification of articular cartilage and modeling/remodeling of the subchondral plate promote initiation and propagation of site-specific fatigue microcracking of the joint surface, respectively, in this model. Microcracking of articular calcified cartilage likely represents mechanical failure of the joint surface. Propagation of microcracks into the subchondral plate is a critical factor in the pathogenesis of articular condylar fatigue (stress) fracture. Functional adaptation of the joint likely protects hyaline cartilage from injury in the short-term but may promote joint degeneration and osteoarthritis with ongoing athleticism.

The role of computational models in the search for the mechanical behavior and damage mechanisms of articular cartilage

Articular cartilage plays a vital role in the function of diarthrodial joints. Due to osteoarthritis degeneration of articular cartilage occurs. The initial event that triggers the pathological process of cartilage degeneration is still unknown. Cartilage damage due to osteoarthritis is believed to be mechanically induced. Hence, to investigate the initiation of osteoarthritis the stresses and strains in the cartilage must be determined. So far the most common method to accomplish that is finite element analysis. This paper provides an overview of computational descriptions developed for this purpose, and what they can be used for. Articular cartilage composition and structure are discussed in relation with degenerative changes, and how these affect mechanical properties.

Results of arthroscopic reduction and percutaneous fixation for acute displaced scaphoid fractures

PURPOSE

This study used percutaneous techniques augmented by simultaneous wrist arthroscopy to visualize the fracture and thus confirm the fracture alignment and reduction and also to assesses the concurrent associated ligament injuries.

TYPE OF STUDY

Retrospective study.

METHODS

Arthroscopy was used to help to reduce scaphoid fractures and assess soft-tissue injuries in 15 acute cases (13 male and 2 female patients). The fractures were treated by reduction under arthroscopic control and percutaneous fixation with the cannulated interosseous compression screw. Soft-tissue lesions were also treated at the same time using debridement, suture repair, or K-wire transfixation. The average age of the patients was 29.2 years (range, 19 to 48 years).

RESULTS

Two patients (13.3%) had scapholunate (SL) ligament injuries, and both exhibited partial tear of the SL ligament. Four patients (26.7%) suffered lunotriquetral (LT) ligament injuries and received ligament debridement, K-wire fixation of the LT joint, and splinting. Six patients (40%) had chondral fractures. Additionally, the triangular fibrocartilage complex (TFCC) was torn in 5 patients (33%). Finally, 5 patients (33%) suffered radioscaphocapitate ligament or long radiolunate ligament injuries. All fractures healed without malunion or nonunion and, at follow-up of 24 to 28 months, 11 patients had excellent results and 4 had good results based on Mayo Modified Wrist Scores.

CONCLUSIONS

We believe that arthroscopic reduction may be considered for scaphoid fractures because this approach can use a single procedure to achieve acceptable restoration of fractures as well as assessment and management of soft-tissue lesions.

LEVEL OF EVIDENCE

Level IV Therapeutic Study, case series with no, or historical, control group.

Cartilage tolerates single impact loads of as much as half the joint fracture threshold

We hypothesized that one mechanical insult could affect cellular proliferation, matrix turnover, and the structural integrity of cartilage, and that these effects would be dose dependent and time dependent. One impact load of low impact (14.4 MPa +/- 2.1 MPa), medium impact (22.8 MPa +/- 5.8 MPa), or high impact (55.5 MPa +/- 12.6 MPa) was administered to the posterior aspect of the medial femoral condyle of New Zealand White rabbits using a previously validated pendulum device. Animals were euthanized at 2, 6, and 12 weeks after impact, and the impacted and sham (contralateral limb) cartilage were harvested. Each specimen was assessed by light microscopy and by immunohistochemical methods. Although impacted specimens had greater loss of proteoglycan staining than sham cartilage, these changes were neither dose dependent nor time dependent. No structural damage, enzymatic proteoglycan or collagen breakdown, or cellular proliferation was identified in the different impact groups. Articular cartilage is a resilient tissue, particularly in situ, and can tolerate single impact loads of as much as 45% of the joint fracture threshold without considerable disruption or degradation.

Stresses in the local collagen network of articular cartilage: a poroviscoelastic fibril-reinforced finite element study

Osteoarthritis (OA) is a multifactorial disease, resulting in diarthrodial joint wear and eventually destruction. Swelling of cartilage, which is proportional to the amount of collagen damage, is an initial event of cartilage degeneration, so damage to the collagen fibril network is likely to be one of the earliest signs of OA cartilage degeneration. We propose that the local stresses and strains in the collagen fibrils, which cause the damage, cannot be determined dependably without taking the local arcade-like collagen-fibril structure into account. We investigate this using a poroviscoelastic fibril-reinforced FEA model. The constitutive fibril properties were determined by fitting numerical data to experimental results of unconfined compression and indentation tests on samples of bovine patellar articular cartilage. It was demonstrated that with this model the stresses and strains in the collagen fibrils can be calculated. It was also exhibited that fibrils with different orientations at the same location can be loaded differently, depending on the local architecture of the collagen network. To the best of our knowledge, the present model is the first that can account for these features. We conclude that the local stresses and strains in the articular cartilage are highly influenced by the local morphology of the collagen-fibril network.

The quantitative assessment of photodensity of the third carpal bone in the horse

AIM

To determine whether variation in x-ray-beam angle significantly affected photodensity of the third carpal bone (C3) in the horse using the tangential radiographic view, and indirectly determine whether radioabsorptiometry (RA) could be used to assess differences in bone mineral density (BMD) of C3 between exercised and non-exercised horses.

METHODS

The left distal carpal row was isolated post-mortem from 2-year-old Thoroughbred horses that had been either exercised (n=7) for up to 14 weeks using a standard training regimen for racehorses, or not exercised (n=7). The effect of variation in x-ray-beam angle on photodensity was determined on these isolated carpal bones in vitro. Image analysis was used to assess photodensity (compared to a known thickness of aluminium) of four regions of interest (ROI) in C3 and one ROI in the fourth carpal bone (C4) of 14 isolated distal rows of carpal bones of the horse. The isolated carpal bones were placed fl at on a x-ray cassette and radiographed at 90 degrees (i.e. with the x-ray beam perpendicular to the cassette). The x-ray-beam angle was varied in the dorsal sagittal plane by 5 degrees increments to a total of 15 degrees from 90 degrees and from a base angle of 60 degrees (the x-ray-beam angle at which the tangential view is taken in clinical cases).

RESULTS

Variation in beam angle of <10 degrees from 90 degrees significantly affected photodensity, and photodensity was significantly affected when the angle was varied <5 degrees from 60 degrees . When taken at an x-ray-beam angle of 60 degrees , the abaxial aspect of the radial facet of C3 had a consistently higher photodensity than the rest of C3 and C4. The photodensity of the third and fourth carpal bones was higher in exercised horses than in non-exercised horses.

CONCLUSION

As variation in x-ray-beam angle significantly affected photodensity, RA using the tangential view is not considered clinically applicable for assessing BMD of C3 and the accuracy of subjective assessment of BMD of C3 using the tangential view in horses is questionable.

Microfractures and microcracks in subchondral bone: are they relevant to osteoarthrosis?

The existing data are consistent with the view that reactivation of the secondary center of ossification and not the stiffening of the metaphyseal trabecular bone is a mechanism of cartilage loss in idiopathic OA. The stiffening of the subchondral calcified structures would appear to be etiologically incidental and, as the arthrotic process progresses, sometimes locally transient. It is also now clear that although the apparent density of the subchondral cortical plate increases because of thickening of the plate as the OA process progresses, the elastic modulus of the bone might be reduced locally because of increases in vascularization and in the rate of bony remodeling subjacent to the cartilage. Microcracks in the subchondral mineralized tissues might contribute to degeneration of the hyaline cartilage by initiating vascular invasion of the calcified cartilage, leading to reactivation of the tidemark and enchondral ossification with subsequent thinning of the overlying articular cartilage. The thinning would tend to increase shear stresses at the base of the articular cartilage [38], overwhelming the ability of the cartilage to repair itself, resulting in cartilage degeneration. The pathogenesis of cartilage breakdown in OA is a biological and a mechanical process. OA can be understood only if the relationship between the mechanics and the biology is fully appreciated. Failure to properly absorb impact leads to microdamage in the subchondral plate and calcified cartilage. The authors believe that this action causes the secondary center of ossification at the tidemark to advance by enchondral ossification, leading to thickening of the mineralized tissues and thinning of the overlying hyaline articular cartilage. Microcracks will cause the initiation of targeted remodeling, accounting for the increased turnover and reduced material density of the subchondral plate. The resultant thinning of the articular cartilage might lead to initiation of further microdamage in bone and cartilage through a positive feedback mechanism, which can ultimately lead to complete loss of the articular cartilage. In this view, the mechanical overload that initiates microdamage of the subchondral bone provokes a biological response that potentiates the progression of articular cartilage damage in OA.

Subchondral bone in osteoarthritis: a biologic link with articular cartilage leading to abnormal remodeling

PURPOSE OF REVIEW

This review deals with new findings highlighting the concept of cross-talk between subchondral bone tissue and articular cartilage that may be crucial for the initiation and/or progression of osteoarthritis. In this review, new factors either produced by subchondral bone tissue or modifying osteoblast metabolism, yet implicated in osteoarthritis, are discussed.

RECENT FINDINGS

The development of cartilage degeneration is concomitant with subchondral bone thickness in osteoarthritis, whereas it is related to higher subchondral bone activity and dysregulation in the synthesis of bone proteins. As an immediate consequence, homotrimers of type 1 collagen are formed that could lead to undermineralization of this tissue. This dysregulation also leads to abnormal production of different factors by osteoblasts such as prostaglandins, leukotrienes, and growth factors. Because microcracks or neovascularization provide a link between the subchondral bone tissue and articular cartilage, these factors could contribute to the abnormal remodeling of osteoarthritic cartilage.

SUMMARY

These findings have an immediate implication for research because new tools need to be developed to study the subchondral bone-cartilage functional unit. Moreover, it could lead to a possible cure for osteoarthritis because this pathology should be considered both a bone and cartilage disease.

Approach to cartilage injury in the anterior cruciate ligament-deficient knee

The treatment of articular cartilage lesions remains one of the great challenges facing orthopedic surgeons today. The technique of chondrocyte transplantation has opened the door for the application of biologic solutions to difficult problems. These techniques will prove the keystone of further advances into biologic joint repair and replacement. Enthusiasm, however, must be tempered by the numerous gaps in cartilage science and the overwhelming need for further long-term data to demonstrate the efficacy of these techniques in thwarting the presumed eventual progression of these lesions toward osteoarthritis. The status of the articular cartilage is of paramount importance in ACL decision-making. Every effort must be made to protect the existing hyaline articular cartilage during ACL reconstruction. Though current cartilage repair techniques are in their infancy, they remain stepping-stones to future developments. It is hoped that we will one day be able to regenerate normal hyaline cartilage without great morbidity. At present, the ACL surgeon must accept techniques that diminish symptoms and do not burn bridges to future advances. The orthopedic surgeon must increase his knowledge of the basic science of articular cartilage in order to best choose from the various cartilage treatments that evolve.

A method for delivering variable impact stresses to the articular cartilage of rabbit knees

OBJECTIVE

To develop a method by which a single impact force of controlled magnitude and rate could be applied uniformly to an area on the posterior aspect of the medial femoral condyle of adult rabbits.

DESIGN

An in-vivo animal model using a pendulum device, designed and manufactured to supply the kinetic energy necessary to apply different impact loads to the posterior aspect of the medial femoral condyle of a rabbit.

SETTING

Biomechanical laboratory, University Medical Center.

SUBJECTS

A total of thirty-six femoral condyles from 3-kilogram New Zealand White (NZW) rabbits were used during this evaluation.

INTERVENTION

An aluminum impactor was made based on the sagittal and coronal radii of curvature of six matched pairs (n = 12) of femurs from three-kilogram NZW rabbits. This impactor was coupled with the pendulum and used to apply different impact loads to both of the medial femoral condyle of the knees of NZW rabbits (n = 24).

MAIN OUTCOME MEASUREMENTS

Peak impact force, time to peak impact force, and average contact area between impactor and medial femoral condyle, were measured for each group of animals tested.

RESULTS

The pendulum delivered a consistent impact force to the rabbit condyle of 120.0 N (+/-18.1; coefficient of variance, 15 percent) with 400 grams attached to the pendulum arm, at an average time to peak force of 0.021 seconds (+/-0.001, co. var. 4.8 percent). The peak impact force was significantly different for each of the three impact mass groups of animals (p < 0.001). By contrast, time to peak force for each mass group averaged approximately 0.020 seconds and the average contact area was 6.26 mm2 (+/-0.51). Quantitative assessment of the exposed medium pressure-sensitive film confirmed uniform impact force intensity within each specimen.

CONCLUSIONS

An in-vivo animal model was developed to deliver a controlled and rapid impact force to a specific area of the weight-bearing surface of the adult rabbit knee. These loads were applied at a rate comparable to the clinical setting of falling onto an outstretched hand, thus simulating a common clinical scenario by which cartilage is often injured. This model can be used in future experiments to investigate mechanism by which posttraumatic arthritis develops after articular injuries.

Chondrocyte death precedes structural damage in blunt impact trauma

Joint impact trauma has been shown to cause fissures, fibrillation, and other structural damage of the cartilage or subchondral bone. Previous studies used impact energies sufficient to fracture the underlying bone. Under these circumstances, the initial influence of impact trauma on cellular components and cartilage structure is unknown. The goal of this study was to determine whether an impact trauma first causes cellular or structural damage to a cartilage layer. Such damage might be the starting point of degenerative changes found in osteoarthrosis. Porcine patellas (n = 12) were subjected to standardized low-impact loading of three magnitudes with a spherical impactor attached to a drop tower device (0.06, 0.1, and 0.2 J). India ink staining and scanning electron microscopic analysis were used for analysis and showed no evidence of gross structural disruption. Chondrocyte viability assessed with thiazole blue staining and propidium iodide counterstaining was reduced significantly in the tangential and middle zones with increasing impact energy. These results indicate that chondrocyte death may precede excessive structural damage reported in earlier studies and might be a crucial factor in posttraumatic osteoarthrosis.

Arthroscopically-assisted reduction of intra-articular fractures and soft tissue management of distal radius

Arthroscopy was used to help to reduce intra-articular fractures of the distal radius and treat soft tissue injuries in 33 acute cases. The fractures were treated by reduction under arthroscopic control and percutaneous fixation either with or without external fixation. The triangular fibrocartilage complex (TFCC) was torn in 18 of 33 patients (54%). All tears were peripheral and were repaired with arthroscopic procedures. Scapholunate (SL) ligament injuries prevailed in six (18%) patients; most of them exhibited instability in the SL joint. They received SL ligament debrided and transfixed with K-wires. Four (12%) of the patients suffered lunotriquetral (LT) ligament injuries; three of them also received transfixation with K-wires. Six (18%) of the patients exhibited chondral fractures. All fractures healed without measurable incongruity of joint surface and at follow-up (24 to 36 months), 11 patients displayed excellent results and 22 patients displayed good results according to the Mayo modified wrist score.

Effect of contact stress in bones of the distal interphalangeal joint on microscopic changes in articular cartilage and ligaments

OBJECTIVE

To examine articular cartilage of the distal interphalangeal (DIP) joint and distal sesamoidean impar ligament (DSIL) as well as the deep digital flexor tendon (DDFT) for adaptive responses to contact stress.

SAMPLE POPULATION

Specimens from 21 horses.

PROCEDURE

Pressure-sensitive film was inserted between articular surfaces of the DIP joint. The digit was subjected to a load. Finite element models (FEM) were developed from the data. The navicular bone, distal phalanx, and distal attachments of the DSIL and DDFT were examined histologically.

RESULTS

Analysis of pressure-sensitive film revealed significant increases in contact area and contact load at dorsiflexion in the joints between the distal phalanx and navicular bone and between the middle phalanx and navicular bone. The FEM results revealed compressive and shear stresses. Histologic evaluation revealed loss of proteoglycans in articular cartilage from older horses (7 to 27 years old). Tidemark advancement (up to 14 tidemarks) was observed in articular cartilage between the distal phalanx and navicular bone in older clinically normal horses. In 2 horses with navicular syndrome, more tidemarks were evident. Clinically normal horses had a progressive increase in proteoglycans in the DSIL and DDFT.

CONCLUSIONS AND CLINICAL RELEVANCE

Load on the navicular bone and associated joints was highest during dorsiflexion. This increased load may be responsible for microscopic changes of tidemark advancement and proteoglycan depletion in the articular cartilage and of proteoglycan production in the DSIL and DDFT Such microscopic changes may represent adaptive responses to stresses that may progress and contribute to lameness.

The process of lubrication impairment and its involvement in temporomandibular joint disc displacement: a theoretical concept

PURPOSE

This article re-evaluates the chain of events leading to temporomandibular joint (TMJ) disc displacement. The joint lubrication system and the process of its breakdown are clarified and an attempt is made to evaluate the possible effect of increased friction between the disc and fossa on the anterior displacement of the disc.

MATERIALS AND METHODS

The study is based on the author's accumulated clinical data and results obtained from laboratory investigations regarding TMJ lubrication and its possible breakdown, coupled with pertinent information culled from the literature.

RESULTS

Translation of the disc in the TMJ is enabled due to the presence of phospholipids and hyaluronic acid, which constitute an efficient lubrication system. This system may break down in the presence of uncontrolled free radicals. In the absence of lubricants, the articular surfaces are smooth, elastic in texture, and possess strong surface energy. Such opposing planes, especially in the presence of a thin fluid film (sub-boundary lubrication) tend to generate high friction while the disc is sliding against the fossa. Such friction is probably the prime mover in loosening the disc attachments to the condyle, with subsequent disc displacement.

CONCLUSIONS

Increased friction of the contiguous parts may well be a major causative factor in displacement of the articular disc. This should be taken into account in considering the appropriate treatment approach. It also raises some doubts regarding the validity of using repositioning techniques.

Effect of impact load on articular cartilage: cell metabolism and viability, and matrix water content

Significant evidence exists that trauma to a joint produced by a single impact load below that which causes subchondral bone fracture can result in permanent damage to the cartilage matrix, including surface fissures, loss of proteoglycan, and cell death. Limited information exists, however, on the effect of a varying impact stress on chondrocyte biophysiology and matrix integrity. Based on our previous work, we hypothesized that a stress-dependent response exists for both the chondrocyte's metabolic activity and viability and the matrix's hydration. This hypothesis was tested by impacting bovine cartilage explants with nominal stresses ranging from 0.5 to 65 MPa and measuring proteoglycan biosynthesis, cell viability, and water content immediately after impaction and 24 hours later. We found that proteoglycan biosynthesis decreased and water content increased with increasing impact stress. However, there appeared to be a critical threshold stress (15-20 MPa) that caused cell death and apparent rupture of the collagen fiber matrix at the time of impaction. We concluded that the cell death and collagen rupture are responsible for the observed alterations in the tissue's metabolism and water content, respectively, although the exact mechanism causing this damage could not be determined.

Contact analysis of biphasic transversely isotropic cartilage layers and correlations with tissue failure

Failure of articular cartilage has been investigated experimentally and theoretically, but there is only partial agreement between observed failure and predicted regions of peak stresses. Since trauma and repetitive stress are implicated in the etiopathogenesis of osteoarthritis, it is important to develop cartilage models which correctly predict sites of high stresses. Cartilage is anisotropic and inhomogeneous, though it has been difficult to incorporate these complexities into engineering analyses. The objectives of this study are to demonstrate that a transversely isotropic, biphasic model of cartilage can provide agreement between predicted regions of high stresses and observed regions of cartilage failure and that with transverse isotropy cartilage stresses are more sensitive to convexity and concavity of the surfaces than with isotropy. These objectives are achieved by solving problems of diarthrodial joint contact by the finite-element method. Results demonstrate that transversely isotropic models predict peak stresses at the cartilage surface and the cartilage-bone interface, in agreement with sites of fissures following impact loading; isotropic models predict peak stresses only at the cartilage-bone interface. Also, when convex cartilage layers contacted concave layers in this study, the highest tensile stresses occur in the convex layer for transversely isotropic models; no such differences are found with isotropic models. The significance of this study is that it establishes a threshold of modeling complexity for articular cartilage that provides good agreement with experimental observations under impact loading and that surface curvatures significantly affect stress and strain within cartilage when using a biphasic transversely isotropic model.

Damage to rabbit femoral articular cartilage following direct impacts of uniform stresses: an in vitro study

OBJECTIVE

To determine the acute gross and histologic damage resulting to femoral cartilage from an in vitro direct impact of uniform stress.

DESIGN

Gross and histologic evaluations were performed on rabbit femoral condyles impacted by a drop-tower device.

BACKGROUND

It is thought that impacts above a given threshold stress may initiate post-traumatic arthritis. The extent of damage following impacts of specific stress has not been previously studied.

METHODS

12 New Zealand White rabbit medial femoral condyles were divided into three groups by impact type and magnitude. A drop tower was used to strike the femoral condyle with a flat impactor, or with a custom contoured impactor. Gross and histological grades were given depending on the depth and number of fissures and cracks in the impacted condyle.

RESULTS

The degree of damage correlated best with the type of impactor used and with the impact force; correlation between damage and impact stress was less significant. Contoured impactors tended to produce superficial fibrillation, while flat impactors tended to produce deep cracks. Impact forces above 500 N tended to create more severe damage than impact forces below 500 N. Subchondral bone remained intact in all cases and deep cartilage damage did not occur without disruption of more superficial layers. Poor correlation was found between damage as graded by gross examination versus damage graded histologically.

CONCLUSIONS

Acute damage corresponds best with type of impactor and impact force, and not as well with impact stress. Micro structural injuries may be present in the absence of gross findings.

RELEVANCE

Post-traumatic arthritis is a disabling disease thought to occur when a blow of stress above a given threshold is delivered to articular cartilage. Current animal models of post-traumatic arthritis are unable to characterize the impact stress applied to an articular surface. This study examines grossly and histologically the structural damage occurring as a result of impacts of given stress and force.

Detection of experimentally produced occult microfractures at the bone-cartilage interface in decalcified sections

We compared three histological preparation methods to detect experimentally produced occult microfractures in decalcified human patellae: a paraffin tape-transfer technique, a paraffin slab-cut method, and a paraffin method with methyl salicylate as the clearing agent. Microfractures were observed at the bone-cartilage interface and were oriented either parallel or perpendicular to the tidemark. Both types of microfractures were documented with each preparation method. The slab-cut method was time-consuming, but the section thickness allowed detailed analysis of the architecture of microcracks as they passed into the depth of the section. The methyl salicylate method was efficient and produced thin, serial sections with good morphological detail and minimal cutting artifact. Reliable histological data were also derived from the tape-transfer technique, but this method was inconsistent. The methods summarized here for processing decalcified human joint tissues provide a basis for future orthopaedic studies investigating occult microfractures at the bone-cartilage interface.

A method to increase the sensitive range of pressure sensitive film

Pressure-sensitive film is frequently used in biomechanics to document intra- and extra-articular contact pressures. This often involves the contact of two surfaces of varying curvature producing non-uniform pressure distributions. The purpose of this study was to determine the feasibility of using multiple films in such experiments to yield accurate pressure and contact area data. A composite arrangement of film was dynamically loaded using cylindrical indenters of five radii. An analytical model of each indentation was constructed to provide a standard for error analysis. The study showed that several ranges of pressure sensitive film can be used simultaneously to accurately transduce contact pressures arising from loading scenarios that produce contact pressure gradients and contact pressures that involve suprathreshold loading of a given film range.

Relationship between articular cartilage damage and bone density in the first metatarsal

It is well known that bone changes occur in relationship to the articular cartilage damage seen in osteoarthritis. Numerous studies have shown a relationship between bone density and articular cartilage damage in knee and hip joints, but it is controversial as to whether or not an increased subchondral bone density results in greater cartilage damage. We studied 49 pairs of cadaveric first metatarsals in an attempt to correlate the level of cartilage damage seen on the distal articular surface with areal and volumetric density and other parameters such as bone geometry. A positive correlation was detected between articular cartilage damage and bone density by peripheral quantitative computed tomography in five of eight frontal slices in the head of the left metatarsal in the male sample only. The more extensive subchondral cysts found in the right male metatarsal may have contributed to the lack of correlation between the two variables on the right side. In addition, females displayed significantly greater osteophytosis than males at a given grade of cartilage damage, thus, possibly leading to a painful, apropulsive gait and a disuse osteopenia which would neutralize any subchondral bone density increase associated with cartilage damage. Microscopic investigations are, therefore, warranted to detect bone changes on a more discreet level, particularly within the subchondral plate.

Bone bruise of the knee: histology and cryosections in 5 cases

We evaluated the histopathologic and cryosectional appearance of bone bruise injuries of the knee detected on MRI. Histologic evaluation of bone biopsies from 3 patients revealed microfractures of cancellous bone, edema and bleeding in the fatty marrow. Between intact lamellar bone trabecules, fragments of hyaline cartilage mixed with highly fragmented bone trabecules were found. Postmortem specimens were obtained from 2 more patients, killed in motor vehicle accidents. MRI revealed bone bruise injuries of the lateral femoral condyle and of the lateral tibial plateau in 1 knee and anterior cruciate ligament disruption, a medial meniscus tear and bone bruise injury of the tibial plateau and of the lateral femoral condyle in the other specimen. The specimens were embedded in physiologic saline solution and frozen to -30 degrees C. By rotationcryotomy, 1 mm slices were removed from the surface of the specimens and documented on photographs. Subchondral lesions and bleeding were found, corresponding to the MR images.

Effects of osteochondral fragmentation and intra-articular triamcinolone acetonide treatment on subchondral bone in the equine carpus

To determine the effects of osteochondral fragmentation and intra-articular corticosteroid treatment on dynamics of bone remodelling and fragility, 12 horses each had a unilateral, 8 mm osteochondral fragment created in the distal aspect of one radiocarpal bone. Six of the horses were treated in the fragmented joint, and the other 6 were treated in the nonfragmented joint with 12 mg of triamcinolone acetonide (TA) 14 and 28 days after surgery. All horses were exercised on a high-speed treadmill starting 15 days, and ending 72 days after surgery. Horses treated with TA in the fragmented joints were significantly less lame than those treated in the nonfragmented joints. Third carpal bones from joints with fragments showed significantly more vascularity, single labelled surface, total labelled surface and mineralising surface in subchondral and subjacent trabecular bone. Trends were also seen towards higher vascular canal volume and osteochondral junction remodelling sites in third carpal bones from fragmented joints. No significant differences were seen in microdamage density or size between fragmented and nonfragmented joints. No significant influence of TA treatment was seen on any parameter measured. The results from this study show that osteochondral fragmentation induces significant changes in remodelling of opposing bones, and that the administration of corticosteroids into joints with fragmentation does not significantly alter bone remodelling or fragility.