Animal models of degenerative joint disease

Experimentally induced cam impingement in the sheep hip

Sheep hips have a natural non-spherical femoral head similar to a cam-type deformity in human beings. By performing an intertrochanteric varus osteotomy, cam-type femoro-acetabular impingement (FAI) during flexion can be created. We tested the hypotheses that macroscopic lesions of the articular cartilage and an increased Mankin score (MS) can be reproduced by an experimentally induced cam-type FAI in this ovine in vivo model. Furthermore, we hypothesized that the MS increases with longer ambulatory periods. Sixteen sheep underwent unilateral intertrochanteric varus osteotomy of the hip with the non-operated hip as a control. Four sheep were sacrificed after 14, 22, 30, and 38-weeks postoperatively. We evaluated macroscopic chondrolabral alterations, and recorded the MS, based on histochemical staining, for each ambulatory period. A significantly higher prevalence of macroscopic chondrolabral lesions was found in the impingement zone of the operated hips. The MS was significantly higher in the acetabular/femoral cartilage of the operated hips. Furthermore, these scores increased as the length of the ambulatory period increased. Cam-type FAI can be induced in an ovine in vivo model. Localized chondrolabral degeneration of the hip, similar to that seen in humans (Tannast et al., Clin Orthop Relat Res 2008; 466: 273-280; Beck et al., J Bone Joint Surg Br 2005; 87: 1012-1018), can be reproduced. This experimental sheep model can be used to study cam-type FAI.

Evaluation of chondrocyte death in canine osteochondral explants exposed to a 0.5% solution of bupivacaine

OBJECTIVE

To evaluate chondrocyte death in canine articular cartilage exposed in vitro to bupivacaine with and without methylparaben and to compare viability for cartilage with intact or mechanically debrided surfaces.

SAMPLE POPULATION

Both glenohumeral joints from 10 adult canine cadavers.

PROCEDURES

10 osteochondral cores were harvested from each of the 20 humeral heads; synovium and 1 core from each joint were examined to verify joint health, and the other 9 cores were exposed to canine chondrocyte culture medium (CCCM), a 0.5% solution of bupivacaine, or 0.5% solution of bupivacaine with methylparaben for 5, 15, or 30 minutes.

RESULTS

For the superficial zone of surface-intact chondrocytes, bupivacaine with methylparaben caused a significantly higher percentage of chondrocyte death at 5 minutes (47.7%) than did bupivacaine (23.6%) or CCCM (25.4%). Bupivacaine (53.8%) and bupivacaine with methylparaben (62.5%) caused a significantly higher percentage of chondrocyte death at 30 minutes than did CCCM (20.0%). For the superficial zone of chondrocytes with debrided surfaces, bupivacaine with methylparaben caused a significantly higher percentage of chondrocyte death at 30 minutes (59%) than it did at 5 minutes (37.7%). Bupivacaine with methylparaben caused a significantly higher percentage of chondrocyte death at 30 minutes (59.0%) than did CCCM (28.9%). For middle and deep zones of chondrocytes, treatment solution and surface debridement had minimal effects on percentage of chondrocyte death.

CONCLUSIONS AND CLINICAL RELEVANCE

Bupivacaine and bupivacaine with methylparaben were cytotoxic to canine articular chondrocytes in vitro. Intra-articular administration of bupivacaine is not recommended for clinical use until additional studies are conducted.

Distribution of lactate dehydrogenase in healthy and degenerative canine stifle joint cartilage

In dogs, degenerative joint diseases (DJD) have been shown to be associated with increased lactate dehydrogenase (LDH) activity in the synovial fluid. The goal of this study was to examine healthy and degenerative stifle joints in order to clarify the origin of LDH in synovial fluid. In order to assess the distribution of LDH, cartilage samples from healthy and degenerative knee joints were investigated by means of light and transmission electron microscopy in conjunction with immunolabeling and enzyme cytochemistry. Morphological analysis confirmed DJD. All techniques used corroborated the presence of LDH in chondrocytes and in the interterritorial matrix of healthy and degenerative stifle joints. Although enzymatic activity of LDH was clearly demonstrated in the territorial matrix by means of the tetrazolium-formazan reaction, immunolabeling for LDH was missing in this region. With respect to the distribution of LDH in the interterritorial matrix, a striking decrease from superficial to deeper layers was present in healthy dogs but was missing in affected joints. These results support the contention that LDH in synovial fluid of degenerative joints originates from cartilage. Therefore, we suggest that (1) LDH is transferred from chondrocytes to ECM in both healthy dogs and dogs with degenerative joint disease and that (2) in degenerative joints, LDH is released from chondrocytes and the ECM into synovial fluid through abrasion of cartilage as well as through enhanced diffusion as a result of increased water content and degradation of collagen.

Pathophysiology and Management of Arthritis

This article primarily reviews the pathophysiology, diagnosis, and therapy of osteoarthritis but also briefly discusses immune-mediated arthritides. Given the frequency of occurrence of arthritis in veterinary patients, it is crucial that clinicians be aware of the mechanisms of the disease and be comfortable with diagnosis and treatment. Unfortunately,there is a great deal of information still to be learned in regards to management of these cases. Because of the rapid and continuing research gains, it behooves clinicians to maintain a current awareness of the related literature.

Early changes in experimental osteoarthritis using the Pond-Nuki dog model: technical procedure and initial results of in vivo MR imaging

The purpose of this study was to prove the feasibility of combining in vivo MR imaging with the Pond-Nuki animal model for the evaluation of osteoarthritis. In an experimental study, 24 beagle dogs underwent transection of the anterior cruciate ligament of the left leg (modified Pond-Nuki model). The dogs were randomly assigned into four groups and examined by MRI after 6, 12, 24 and 48 weeks. MR imaging of both knees was performed under general anesthesia with the contralateral joint serving as control. In group 1 (6 weeks postoperatively), the first sign detected on MRI was subchondral bone marrow edema in the posteromedial tibia. After 12 weeks, erosion of the posteromedial tibial cartilage could be observed, followed by meniscus degeneration and osteophytosis after 24 and 48 weeks. The contralateral knee joint showed transient joint effusion, but no significant signs of internal derangement (P<0.001). By combining in vivo MR imaging with the Pond-Nuki model, it is possible to detect early signs of osteoarthritis. The first sign was posteromedial subchondral bone marrow edema in the tibia followed by progressive cartilage degeneration and joint derangement. The in vivo model therefore seems to be suitable for longitudinal studies or monitoring the therapeutic effects of osteoarthritis.

Spontaneous and experimental osteoarthritis in dog: similarities and differences in proteoglycan levels

The unilateral canine model is the most commonly used model of experimental osteoarthritis (OA). In this model, the anterior cruciate ligament (ACL) of one knee is transected and the contralateral joint is usually used as a control. However, dogs, similar to humans, can develop OA spontaneously with old age. Additionally, certain breeds of dogs are genetically predisposed to OA and can develop symptoms at a young age. The goal of this study was to compare the pathological changes of proteoglycans in OA cartilage from dogs that developed OA spontaneously to those that underwent ACL transection. For this reason, biglycan, decorin and fibromodulin levels and degradation patterns were compared by Western blot hybridization, and aggrecan contents were quantified by dimethylmethylene blue assay. The changes in proteoglycan levels in the cartilage of dogs with spontaneous OA, regardless of their age, were very similar to those published for human OA cartilage. However, when OA developed as a result of ACL-surgery, the changes in proteoglycans were different from those of slowly developing spontaneous OA. Therefore, these differences should be taken into consideration when the ACL-transection model is used.

Regional quantification of cartilage type II collagen and aggrecan messenger RNA in joints with early experimental osteoarthritis

OBJECTIVE

Accurate assessment of chondrocyte metabolism is a potentially valuable indicator of cartilage health in osteoarthritis (OA). This study was conducted to explore the anabolic metabolism of chondrocytes early in the natural history of an experimental canine model of OA.

METHODS

Competitive reverse transcription-polymerase chain reaction was used to calculate the copy number of type II collagen and the messenger RNA (mRNA) levels of aggrecan core protein in articular cartilage samples obtained from different regions of the femorotibial joint 12 and 39 weeks after cruciate transection.

RESULTS

Gene expression of both type II collagen and aggrecan in cartilage samples obtained from experimental joints at both intervals after surgery was elevated significantly compared with that in samples from contralateral control joints. The number of mRNA copies per microgram of DNA of aggrecan exceeded that of type II collagen in control cartilage, but the copy number of type II collagen mRNA exceeded that of aggrecan in OA cartilage. Thus, the ratio of type II collagen-to-aggrecan mRNA copy number (normalized to DNA) was shown to be characteristically altered in cartilage with experimental OA.

CONCLUSION

Accurate assessment of multiple gene products in small samples of cartilage taken from focal areas of a joint can be used diagnostically for monitoring chondrocyte metabolism and possibly for staging at least the early phases of this joint disease.

Changes in the canine femoropatellar joint space in the postsurgical, cruciate-deficient stifle joint

In this study, we investigate the factors that influence changes in articular cartilage thickness in naturally occurring osteoarthritis of the canine stifle joint. Fifty-eight dogs with QA secondary to cranial cruciate ligament deficiency were examined radiographically at 0, 7, and 13 months using 90 degree flexed mediolateral radiographs of both stifle joints. The femoropatellar joint space widths were measured using a computer-assisted video image analysis system. The femoropatellar joint space widths were found to be significantly increased in index joints as compared to contralateral joints. In addition, there was a significant increase in femoropatellar joint space (FPJS) width over the course of the study, particularly between entry and 7 months. Factors that might influence the degree of femoropatellar joint space increase (bodyweight, age, sex, disease duration, radiographic score) were investigated using regression analysis. Body weight at baseline showed a moderate to strong relationship with change in FPJS between 0 and 7 months (Pearson's partial correlation r = 0.417, p = .006). This relationship was less strong for change in femoropatellar joint space between 7 and 13 months (r = 0.324, p = .036).

Articular cartilage lesions of the knee following immobilisation or destabilisation for 6 or 12 weeks in rabbits

Eighty mature female New Zealand White rabbits were sacrificed 6 or 12 weeks after either section of the medial collateral and the anterior cruciate ligaments with removal of the anterior third of the medial meniscus of one knee, or immobilisation of one knee, using the contralateral non-treated knee as the control. The area of degenerated joint surface of the distal femur, and water and proteoglycan content were measured, and the articular cartilage stained using haematoxylin and eosin and safranin O. Destabilisation resulted in a significantly larger time-dependent degenerated joint surface area. Water content significantly increased after 6 weeks with no significant differences between immobilisation and destabilisation. Destabilisation resulted in a significantly greater decrease in proteoglycan content. At 12 weeks, the control knees of the animals undergoing destabilisation showed significant degenerative changes. There were more extensive lesions in destabilisation, while 6 weeks of immobilisation produced moderate degenerative joint disease.

Clinical natural history of the postsurgical cruciate deficient canine stifle joint: year 1

The aims of this prospective study were to investigate the associations and correlations between individual clinical features of osteoarthritis of the cruciate deficient stifle joint and to document the temporal changes in these features over a 13-month period following surgical treatment. Fifty-eight dogs with osteoarthritis of the stifle joint, secondary to cranial cruciate ligament deficiency, were examined before surgical treatment for cruciate deficiency and at one and a half, seven and 13 months after surgery. At each visit, clinical features were graded using four-point, discontinuous, ordinal grading (Likert) scales and intra-articular pathology was also scored in a similar fashion at arthrotomy. No attempt was made to construct an aggregate score because the relative importance of different disease features and the relationships between them were not understood at the time of writing. At entry, the relationships between background disease variables and clinical parameters were investigated as well as the relationships between clinical parameters and intra-articular pathology scores. Longitudinal analysis was performed to test for those features which showed significant change over the 13-month follow-up period. At entry, periarticular thickening and degree of crepitus were significantly correlated with disease duration. Several features showed significant change over the study period. Notably, the degree of quadriceps atrophy showed significant decrease from baseline scores at seven and 13 months while remaining different from normal, suggesting that a measure of quadriceps atrophy may be a useful measure of long-term outcome in this disease.

Winner of the AlbertTrillat Young Investigator Award. The effects of aggressive notchplasty on the normal knee in dogs

We assessed the possible association between an aggressive intercondylar notchplasty and histopathologic, radiographic, and gait changes to the knee. Three groups of six adult greyhounds were observed for 6 months. Group I dogs had a sham operation. Group II dogs had a 4-mm notchplasty of the lateral femoral condyle where it articulates with the lateral tibial spine. Group III dogs had a 7- to 8-mm notchplasty of the lateral femoral condyle to simulate the long-term effects of an overly aggressive notchplasty. Force plate gait analyses were not significantly different for any dogs at 3 and 6 months. Histopathologic studies (hematoxylin and eosin and safranin O stains) revealed notchplasty area remodeling with a thin layer of lamellar bone covered by fibrous connective tissue. Both Group II and III dogs had significant loss of lateral femoral condyle and trochlear groove articular surface proteoglycans. The radiographic notch width index remained unchanged throughout the study for Group I; the indexes increased immediately after surgery in Groups II and III because of the notchplasty, but after 6 months these values returned to near-preoperative measurements. An aggressive intercondylar notchplasty caused articular cartilage histopathologic changes at 6 months consistent with those found in knees with early degenerative arthritis. Significant refilling of a non-impinged notchplasty occurred by 6 months after surgery. Our results raise concern about the effects of aggressive intercondylar notch widening in humans.

Ultrastructural immunolocalization of bone sialoprotein in guinea-pig osteoarthritis

In diarthrodial joints, bone and cartilage are structurally and functionally inseparable as shown in osteoarthritis (OA), where subchondral bone changes are integral in the disease process. By ultrastructural immunohistochemistry using polyclonal antibodies against guinea-pig bone sialoprotein (BSP), we investigated the distribution of this matrix protein at the osteocartilaginous interface in Hartley guinea-pig knees at different stages of primary osteoarthritis. Between 6 and 12 months they developed moderate osteoarthritic changes predominantly in the medial condyle, progressing to severe OA at 30 months. In all age groups BSP labeling was concentrated to the osteocartilaginous interface at a 1 micron narrow zone at the interface. In the medial osteoarthritic condyle, BSP was increased as compared with the lateral nonosteoarthritic condyle, but only at 30 months, when cartilage fibrillation correlated to BSP. Our observations suggest that altered BSP abundance may be a potential bone marker for late stage OA, while early events in bone cannot be monitored. BSP is expressed early in osteogenesis and may have a role in biological mineralization and growth. Since a sharp zone of intense BSP labeling remains at a remarkably constant level throughout life in guinea-pigs, BSP may have an important structural and/or regulating role at the interface. The protein may act as an anchor of calcified articular cartilage to subchondral bone or by regulating mineralization at the osteocartilaginous interface.

Correlation of morphologic and biochemical changes in the natural history of spontaneous osteoarthrosis in guinea pigs

OBJECTIVE

To study how the concentrations of proteoglycans (PGs) and collagen change in various parts of tibial articular cartilage during aging, and to evaluate the development of spontaneous osteoarthrosis (OA) in guinea pigs.

METHODS

PGs were extracted from guinea pig cartilage samples using 4M guanidine hydrochloride, and the amount of hydroxyproline was determined in the extraction remainder. The molecular size and aggregation of PGs were analyzed by electrophoresis, and the glycosaminoglycan composition was assessed by high-performance liquid chromatography.

RESULTS

The PG concentration was proportional to the load distribution. However, when OA became histologically manifest, the PG concentration decreased by 50% (from a mean of 44 microg to 22 microg per mg fresh tissue) and the collagen level decreased by 40% (from a mean of 17 microg to 10 microg per mg fresh tissue), while the proportion of water increased by 13% (from a mean of 710 mg to 800 mg per mg fresh tissue).

CONCLUSION

Unmineralized cartilage can, within physiologic load limits, respond to increased mechanical demands by increasing the PG and collagen concentrations. Beyond a certain limit, however, the cartilage can no longer compensate for further increases in stress, which results in cartilage degeneration and losses of matrix constituents. These losses seemed to appear earlier in the disease process than has been described in previous animal models of secondary OA.

Focal destruction and remodeling in guinea pig arthrosis

We investigated the proximal tibiae in adult, middle-aged and old (6,12, and 30 months) guinea pigs with spontaneous arthrosis by quantitative morphometry. Since the cartilage destruction develops predominantly in the medial tibial plateau, the lateral side may serve as an internal control, In established lesions, cartilage destructions were focal, surrounded by a brim of thickened cartilage that was grossly intact, but showed cell clustering, hypertrophy and increased metachromasia. Peripherally, there was a distinct transition to normal-appearing cartilage. Subjacent to the cartilage ulcerations, subchondral bone was thickened. Compared to the lateral plateau the height of the calcified cartilage increased and the surface density of the osteocartilaginous interface decreased. Marrow depletion and cysts developed below the cartilage ulcerations. Cysts seem to develop through fibrous tissue partially undergoing cartilage metaplasia in tiny noduli that subsequently coalesce, liquefy centrally and expand. Superficially, similar fibrocartilaginous proliferations result in incomplete resurfacing and small areas of subchondral resorption; in the periphery of the joint, they form osteophytes. In the guinea pig, arthrosis tissue destruction is thus accompanied by local tissue proliferation.

Experimental osteoarthritis in dogs: a comparison of the Pond-Nuki and medial arthrotomy methods

Lesions induced by transecting the cranial cruciate ligament in two surgical models of osteoarthritis (OA) in mature, male, cross-bred dogs were compared by using an established grading system and alternatives. Previously, we relied on evaluations of lesions in articular cartilage on femurs alone. No statistically significant differences were found between grades for lesions in cartilage when either treated or control joints were compared by surgical method. Because the Pond-Nuki method yielded statistically significant differences between grades for lesions affecting treated and control femurs or tibias, and for some parameters indicative of synovitis, we preferred this method of surgery. Although by using the medial arthrotomy method of surgery, we were able to destabilize the joint in a more consistent manner, significant differences between treated and control joints were found for lesions on tibias, but not femurs, a frequent site for OA in humans. Suggestions are made for enhancing the surgical models and for a more holistic approach to evaluating joints morphologically.

Perspectives: applications of a biomechanical model of the endochondral ossification mechanism

A biomechanical model of endochondral ossification (Frost and Jee, 1994. Anat. Rec., 240:435-446) can help to explain: (1) some differences in fracture patterns in children and adults, (2) increased fractures during the human adolescent growth spurt, (3) localization of stress fractures and pseudofractures to cortical instead of trabecular bone, (4) increased bone mass in adult-acquired and childhood obesity, (5) subchondral bone densification and osteopenia in some arthroses, (6) why and where mammals lose spongiosa with aging, (7) why, as percents of the original bone stock, metaphyseal trabecular bone losses with aging usually exceed cortical bone losses, (8) why osteochondritis dissecans and aseptic necroses of bone localize in epiphyses instead of metaphyses, (9) some features of growth plate histology in rickets and the chondrodystrophies, (10) why spontaneous fractures in osteoporotic patients affect vertebral more than metaphyseal spongiosa, (11) why osteopenias develop in most chronic, debilitating diseases, and (12) why histomorphometric values can differ in iliac bone biopsies obtained by the "vertical" Jamshidi and "horizontal" Bordier-Meunier techniques.

Perspectives: a biomechanical model of the pathogenesis of arthroses

This model views the common, initiating cause of arthroses as excessive articular cartilage microdamage. If so, understanding it would become a central problem for understanding the pathogenesis of arthroses. The model proposes the microdamage can stem from: (1) Excessive total loads on normal joints; (2) underadaptations in a joint's size or shape that leave its momentarily loaded area too small for normal loads; (3) impaired microdamage repair in subchondral bone or articular cartilage; (4) abnormal composition or structure that makes a tissue develop excessive microdamage under normal loads. (5) (2)-(4) above could stem from changed set points or "lead times" for a joint's adaptations and maintenance, which in turn could stem from (6) genetic influences, some drugs, toxins, diseases, and "X," and (7) from combinations of the above. In the pathogenesis of arthroses this model assigns special importance to the stiffness of joint tissues (as distinguished from their strength), to the typical largest unit loads they carry as a result of a subject's usual physical activities, and to microdamage in those tissues.

Animal models for osteoarthritis: processes, problems and prospects

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An experimental model of osteoarthrosis in the temporomandibular joint of the rabbit

Degenerative changes in the temporomandibular joint were induced in 24 rabbits by surgical perforation of the disk. The incongruence obtained between the joint surfaces caused a gradual increase in macroscopic and microscopic changes, including gross remodeling, loss of tissue volume, and altered cell morphology within a 16-week observation period. These changes occurred concurrently with major alterations in the composition of the matrix, as demonstrated by increase in the glycosaminoglycan content of both condylar cartilage and disk and by loss of hydroxyproline in the disk. The lesions in the disk tissue were clearly discernible, whereas those in the condylar cartilage were less extensive. The described method is concluded to give alterations in the temporomandibular tissues, as seen in degenerative joint disease of an early stage.

Osteoarthrosis induced by intra-articular hydrogen peroxide injection and running load

Osteoarthrosis of the rat knee joint was induced successfully by intra-articular injection of 2% hydrogen peroxide (H2O2) and running load. In the group receiving two injections of physiological saline with running load, no histological osteoarthrotic knees were developed up to 8 weeks after the injection. In the group receiving two 2% H2O2 injections and running load, advanced osteoarthrosis occurred in all knees 8 weeks after the first injection, and the Mankin's score of osteoarthrotic knees appeared to be higher than the group receiving two 2% H2O2 injections without running load (p less than 0.004, Kruskal-Wallis H test). In the rats receiving a single 2% H2O2 injection with running load and a vitamin E-enriched diet, the inhibitory effect of vitamin E on the development of osteoarthrosis was statistically significant compared to the regular diet group (p less than 0.05, Wilcoxon rank test).

Osteoarthritis research: animal models

Although limited in scope and detail, the current review has sought to highlight the contribution of animal models in the study of OA. Further use of these and other models should provide information that may lead to methods for the early detection and successful treatment of human OA.

The early response of articular cartilage to ACL transection in a canine model

Ten outbred dogs underwent unilateral transection of the anterior cruciate ligament of the knee (stifle) joint with sacrifice from 6 to 27 weeks post-operatively. On the operated side were found mild degenerative changes histologically and evidence of increased proteoglycan synthesis with no net loss of uronic acid. Water content was increased in the medial femoral condyle. Contralateral knees showed evidence of increased proteoglycan synthesis and uronic acid content without histologic cartilage lesions.

A preconditioned arthritic hip model

The authors describe a reproducible, inexpensive, large animal model of a preconditioned arthritic hip that can be subjected to various types of surgical reconstructions to assess, compare, and improve their efficacy. In 76 sheep the right hip was denuded of articular cartilage and followed clinically, radiologically and histologically for up to 2 years. In 15 sheep the cartilage was removed and the subchondral bone penetrated, and in 61 the cartilage alone was removed. By 3 months all sheep had developed arthritic changes similar to those seen in humans, with osteophytes, cysts, bone erosions, and periarticular inflammation. The sheep in which the cartilage was removed and the subchondral bone penetrated developed a severe, rapidly destructive arthropathy. These sheep provide a good model for future projects to assess complex methods of surgical reconstruction in cases of deficient bone stock. The sheep in which the cartilage alone was removed developed a moderate, more gradual type of arthritis. These sheep provide a good model for future projects to assess various types of arthroplasties as they might apply to the majority of less destructive arthritic hips, as seen in clinical practice.

Joint reaction to polyethylene implantation: a method for inducing osteoarthritic change and osteophyte formation in the rabbit knee joint

Joint lesions were induced by implantation of a rigid piece of polyethylene sutured under the patella and quadriceps tendon of the rabbit's right knee. Compared to the left sham-operated knee, follow-up studies revealed progressive changes that consisted of early and transient synovial hyperemia and proliferation and late osteoarthritis. By day 7 after surgery, soft synovial-like tissue proliferated around the implant and the articular margins of the femoral trochlea indicating primitive "osteophytic" protuberances (synoviophytes). By day 15 after surgery, the synoviophytes had acquired a more solid consistency and were composed mostly of fibrocartilage covered by a fibro-cellular synovial lining (chondrophytes). By that time, this tissue was invaded with vascular channels; signs of ossification were already present in the deepest layer adjacent to bone. Between the 2nd and 12th weeks, this fibro-cartilaginous tissue, except for the surface fibrous or fibrocartilaginous layer, was progressively replaced by immature bone (osteophyte). Secondary bone remodeling started soon after the first lamellae of immature bone were deposited. Complete integration of the osteophyte into the distal femur occurred during the 2nd and 3rd month.

Transection of the canine anterior cruciate ligament: a concise review of experience with this model of degenerative joint disease

Transection of the anterior cruciate ligament in dogs is probably the most widely used model for degenerative articular disease. Two techniques, the percutaneous stab and arthrotomy, are currently employed. Reported results of the degree of cartilage damage and the time of onset of lesions vary considerably in the literature. Several papers described overt fibrillation as early as 6 weeks post-operatively while others found only mild changes up to nearly 4 years. Critical analysis of the model revealed that parameters such as the breed of dog, its age, weight, amount of exercise and technique of surgery may influence the onset and severity of lesions. Further research is essential to define the relative importance of each.

Enzymic heterogeneity of normal canine articular cartilage

Articular cartilage is generally considered to be an homogeneous tissue. It has now been shown that, although different regions of the medial tibial cartilage of the dog have very similar oxidative enzymic activities, each region is heterogeneous with respect to these activities. The conventional histological delineation of this cartilage has been modified, to take into account a narrow band (designated zone 2a), just below the most superficial spindle-shaped cells, that has higher oxidative enzymic activity than any other. Changes in the activity in this zone might be diluted by the lack of change in other zones if measured by conventional biochemical procedures which could not measure the activities of the different zones separately.

Low temperature and conventional scanning electron microscopic observations of dog femoral condylar cartilage surface after anterior cruciate ligament division

The left stifle joints of 16 beagle dogs were subjected to surgical division of the anterior cruciate ligament (ACL). The femoral condyles showed surface alterations and damage after 14 days when examined by low temperature (LTSEM) and conventional scanning electron microscopy (SEM). The first change was an increase in the fibrous texture of the articular cartilage surface. Folds and surface roughening were later recognised. After 112 days deformation and disruption gave way to cracking or fracture of the surface layers. Superficial damage was focal in distribution and accompanied by a decrease in the frequency of tertiary elevations. The affected areas of cartilage increased in frequency and size with time and surgery. The observations obtained from LTSEM, in which the tissue remains fully hydrated during examination, may be caused by alterations in water content and a loss of proteoglycan at the surface, together with changes in cell shape and size. Surface cracks may be the en face appearance of histological fibrillation.

X-ray diffraction studies of tibial plateau cartilage using synchrotron radiation

X-ray diffraction studies of articular cartilage have been performed using X-rays from two sources: a conventional generator and synchrotron radiation. Blocks of tissue from the tibial plateaux of pigs and dogs were examined to find the orientations of collagen fibrils throughout their depth. Analysis of the resulting diffraction patterns revealed a zonal arrangement of fibrils in both pig and dog tissue. At the articular surface the preferred orientation of fibrils was parallel to the surface, below this was a zone with no obvious preferred orientation and the remaining tissue had fibrils oriented mainly perpendicular to the surface. Using a conventional source of X-rays the exposure time for a single diffraction pattern was a number of days but this was reduced to about 10 min using the more intense synchrotron radiation. This improvement in exposure time facilitates the examination of small areas of tissue. X-ray diffraction using the synchrotron source offers a quick method of determining collagen fibril orientations in small areas of articular cartilage.