Histologic changes in ruptured canine cranial cruciate ligament

Prevalence of lymphoplasmacytic synovitis in dogs with naturally occurring cranial cruciate ligament rupture

OBJECTIVE

To determine the prevalence of lymphoplasmacytic synovitis (LPS) in dogs with naturally occurring cranial cruciate ligament (CCL) rupture and compare clinical, radiographic, cytologic, and histologic findings in dogs with and without LPS.

DESIGN

Cross-sectional study.

ANIMALS

110 dogs with naturally occurring CCL rupture.

PROCEDURES

Histologic examination of synovial biopsy specimens obtained at the time of surgical treatment was used to identify dogs with LPS. Clinical, radiographic, cytologic, and histologic findings were compared between dogs with and without LPS.

RESULTS

56 (51%) dogs had histologic evidence of LPS. There were no significant differences in age, body weight, duration of lameness, severity of lameness, severity of radiographic signs of degenerative joint disease, extent of CCL rupture (partial vs complete), or gross appearance of the medial meniscus between dogs with and without LPS. Mean tibial plateau angle was significantly lower in dogs with LPS than in dogs without LPS, and dogs with LPS were significantly more likely to have neutrophils in their synovial fluid. Lymphocytes were seen in synovial fluid from a single dog with LPS.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that LPS was common in dogs with naturally occurring CCL rupture. However, only minor clinical, radiographic, cytologic, and histologic differences were identified between dogs with and without LPS.

Morphometric characteristics of the pelvic limbs of Labrador Retrievers with and without cranial cruciate ligament deficiency

OBJECTIVE-To evaluate skeletal characteristics of pelvic limbs with and without cranial cruciate ligament (CCL) deficiency in Labrador Retrievers. ANIMALS-30 adult purebred Labrador Retrievers. PROCEDURES-Pelvic limbs (n = 28) of 14 dogs without CCL deficiency were classified as control limbs, whereas the limbs of 16 dogs with CCL deficiency were considered affected by (18 limbs) or predisposed to (10 contralateral limbs of dogs with 1 affected limb) CCL deficiency. Skeletal characteristics were evaluated via physical examination, radiography, and computed tomography. Radiographic and computed tomographic variables were compared among limb groups by use of a mixed-model ANOVA. RESULTS-The tibial plateau slope was steeper in CCL-deficient limbs but not in predisposed limbs, compared with the slope in control limbs. The angle between diaphyseal and proximal tibial axes was increased in both CCL-deficient and predisposed limbs. The relative width of the proximal portion of the tibia and the inclination of the patellar ligament did not differ among limb groups. The overall and distal femoral anteversion angles were greater in CCL-deficient and predisposed limbs, whereas the femoral condyle trochanteric angle was decreased in those limb groups, compared with findings in control limbs. CONCLUSIONS AND CLINICAL RELEVANCE-Cranial angulation of the proximal portion of the tibia, excessive steepness of the tibial plateau, and distal femoral torsion appeared more likely to be associated with CCL deficiency than femoral angulation, tibial torsion, intercondylar notch stenosis, and increased inclination of the patellar ligament.

Characterization of normal canine anterior cruciate ligament-associated synoviocytes

This study was designed to identify and quantify synoviocyte phenotypes enveloping the canine anterior cruciate ligament (ACL) to test the hypothesis that there are at least two synoviocyte phenotypes, each with distinct quantities and topographical distributions. CD18 and HSP25 epitopes were colocalized in the synovium of 10 normal canine ACLs. Sagittal sections were prepared from medial, central, and lateral aspects of each ACL and phenotypes were quantified in the proximal, middle, and distal aspects of each section. Distinct synoviocyte populations stained positive for CD18 (CD18+) or HSP25 (HSP25+), and a small population of cells stained for both epitopes (DS+). The proportion (mean +/- SEM) of HSP25+ synoviocytes (57% +/- 7.5%) was significantly greater than the proportion of CD18+ synoviocytes (27% +/- 8.2%), which was significantly greater than the proportion of DS+ synoviocytes (16% +/- 3.5%). Reverse transcriptase polymerase chain reaction (RT-PCR), Western blot analysis, and immunoelectron microscopy confirmed the presence of CD18 and HSP25 epitopes in the canine ACL. Identification and quantification of ACL synoviocytes may serve as the foundation for future studies involving ACL disease or reconstruction.

Gene expression profiling of normal and ruptured canine anterior cruciate ligaments

OBJECTIVE

To identify genes which may be involved in the development of anterior cruciate ligament (ACL) laxity and rupture in a naturally occurring canine osteoarthritis (OA) model.

DESIGN

Three groups of dog were studied: (1) dogs with ACL rupture; (2) dogs with intact ACLs from a breed predisposed to ACL rupture; (3) dogs with intact ACLs from a breed at very low risk of rupture. The transcriptomes of the ACLs from each group were compared using a whole genome microarray and quantitative reverse transcriptase polymerase chain reaction. Differential gene expression in ruptured canine ACLs was compared with that published in the literature for ruptured human ACLs.

RESULTS

No significant differences were identified between the gene expression profiles of normal ACLs of a breed predisposed to ACL rupture when compared to a breed relatively resistant to ACL rupture. A general pattern of increased protease and extracellular structural matrix gene expression was identified in the ruptured ACLs when compared to intact ACLs. The gene expression profiles of ruptured canine ACLs demonstrate similar patterns to those previously reported for ruptured human ACLs.

CONCLUSIONS

A transcriptomic basis to breed specific risk for the development of canine ACL rupture was not identified. Although changes in matrix associated gene expression in the ruptured ACL are similar between humans and dogs, the molecular events which may predispose to ACL laxity and rupture were not defined.

Strategies to improve anterior cruciate ligament healing and graft placement

Recent improvements in anterior cruciate ligament (ACL) reconstruction have been notable for strategies to improve ACL healing and to improve graft placements. The controversial choice of 1-bundle or 2-bundle grafts requires an advanced knowledge of native ACL insertional anatomy and an appreciation for the kinematic effects of graft placements. Understanding the limitations of surgical techniques to place tunnels is important. Once grafts are placed, new biologic strategies to promote intra-articular and intraosseous healing are evolving. Although these biologic engineering strategies are currently experimental, they are projected for clinical application in the near future.

Expression of immune response genes in the stifle joint of dogs with oligoarthritis and degenerative cranial cruciate ligament rupture

Dysregulation of immune responses within joints plays an important role in development of inflammatory arthritis. We determined expression of a panel of immune response and matrix turnover genes in synovial fluid collected from a group of dogs with stifle oligoarthritis and associated degenerative cranial cruciate ligament (CCL) rupture (n=27). We also studied synovial fluid gene expression in dogs affected with other forms of degenerative arthritis (n=9) and in the stifle joint of healthy dogs with intact CCL (n=14). After collection, synovial cells were pelleted and RNA was isolated. Relative expression of cathepsin K, cathepsin S, tartrate-resistant acid phosphatase (TRAP), matrix metalloproteinase-9 (MMP-9), invariant chain (li), toll-like receptor-2 (TLR-2), and TLR-9 was determined using real-time quantitative RT-PCR. Data were normalized to peripheral blood mononuclear cells (PBMC) as an internal control. Relative expression of cathepsin K, MMP-9, TRAP, and li was increased in the stifle synovial fluid of dogs with oligoarthritis, when compared with the stifles of healthy dogs (P<0.05). In contrast, relative expression of all of the genes-of-interest in synovial fluid from joints affected with other forms of arthritis was not significantly different from the stifles of healthy dogs. TRAP expression was also significantly increased in the stifle joints of dogs with oligoarthritis, when compared to joint expression of TRAP in dogs with other forms of degenerative arthritis (P<0.05). In the dogs with stifle oligoarthritis, expression of both matrix turnover and immune response genes was increased in stifle synovial fluid, when compared with the internal PBMC control, whereas in healthy dogs and dogs with other forms of arthritis, only expression of matrix turnover genes was increased in synovial fluid, when compared with the internal PBMC control (P<0.05). Taken together, these findings suggest that antigen-specific immune responses within the stifle joint may be involved in the pathogenesis of persistent synovitis and associated joint degradation in dogs with oligoarthritis and degenerative CCL rupture.

Detection and distribution of apoptotic cell death in normal and diseased canine cranial cruciate ligaments

One of the possible initiating factors in canine cranial cruciate ligament (CCL) rupture could be an abnormal pattern of ligament cell death. This study compared apoptotic cell death in sections of ruptured CCLs and normal controls, and examined nitric oxide (NO) production in joint tissues and correlated this to apoptosis. CCLs and cartilage from the lateral femoral condyle were harvested from 10 healthy dogs and 15 dogs with CCL rupture and ligaments were further processed to detect cleaved caspase-3 and to determine supernatant NO production in explant cultures. Apoptotic activity was greater in ruptured ligaments compared to controls. NO in ligaments showed a moderate but significant positive correlation with caspase-positive cells. The results suggest that increased apoptosis has a role in CCL rupture and that apoptosis may be influenced by local NO production.

Expression profiling of select cytokines in canine osteoarthritis tissues

The objective of this study was to investigate the level of expression of five cytokines in four different articular tissues from the joints of dogs with and without osteoarthritis (OA). Articular tissues were harvested from the stifle (fat, cranial cruciate ligament, synovial membrane) or hip (articular cartilage) from eight dogs with OA secondary to cranial cruciate ligament disease (stifle) or hip dysplasia (hip), undergoing routine surgical treatment for the condition, and from five dogs euthanatized without orthopaedic disease. The mRNA transcript numbers for interleukin-1beta (IL-1beta), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10) and interleukin-17 (IL-17) were determined by quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR). Increased expression of IL-1beta, IL-6 and IL-10 in OA synovial membrane, increased expression of IL-1beta and IL-6 in ruptured (OA) ligament, and reduced expression of IL-8 in OA synovial membrane were identified. Cytokine expression was detected in multiple tissues within the articular joint, but differential expression in OA was detected primarily in the synovial membrane and cranial cruciate ligament.

Relationship of Tibial Plateau Slope to Limb Function in Dogs Treated with a Lateral Suture Technique for Stabilization of Cranial Cruciate Ligament Deficient Stifles

OBJECTIVE

To evaluate the effect of a lateral suture technique (LST) on tibial plateau angle (TPA) measurement and to compare TPA with functional outcome in dogs treated for cranial cruciate ligament (CrCL) rupture with LST.

STUDY DESIGN

Prospective clinical study.

SAMPLE POPULATION

Dogs (n=34) with unilateral CrCL instability.

METHODS

All dogs had lameness examination, survey stifle radiographs, and force plate analysis before and at 6, 12, 24, and 48 weeks after surgery. Radiographic osteoarthritis (OA) scores and lameness scores were assigned using previously reported methods. Preoperative radiographs were performed in all dogs, and postoperative serial radiographs were performed in 6 dogs for measurement of TPA. Differences in TPA measurements were evaluated with a random effects repeated measures model. The significance of LST on TPA measurement was established in 6 dogs and the effect of TPA on vertical impulse, peak vertical force, progression of radiographic scores, and lameness score were analyzed by general linear models in all dogs. Differences were considered significant if P<.05.

RESULTS

Significant differences were not noted between pre- and serial postoperative measurements of TPA. A significant correlation was not established between TPA and postoperative vertical impulse, peak vertical force, lameness score, or radiographic OA scores.

CONCLUSIONS

TPA values were unchanged after LST and TPA does not affect outcome measures in dogs treated with LST.

CLINICAL RELEVANCE

TPA has no predictive value on clinical outcome in dogs treated with LST for stabilization of CrCL deficient stifles.

Morphologic and functional features of the canine cruciate ligaments

OBJECTIVE

To review the gross, microscopic, and functional anatomy of the cranial cruciate ligament (CCL) in dogs.

STUDY DESIGN

Literature review.

METHODS

Reports of the anatomy and function of the cruciate ligaments in dogs were retrieved by search of the 1975-2005 PubMed database.

RESULTS

The CCL has an important biomechanical function resisting cranial drawer, hyperextension, and internal rotation and acts to fine tune and guide the stifle through its rolling and sliding motion. It has a complex architecture, and distinct geographic regions within the ligament have different functional roles depending on the angle and loading conditions. Collagen type I is the main component of the extracellular matrix; the fibrils have a crimped structure. The cruciate ligaments are almost completely covered by synovium, protecting them from synovial fluid. Cruciate blood supply is mainly of soft tissue origin. The intraligamentous network is relatively limited whereas the core of the middle third of the CCL is even less well vascularized. Neurohistologic studies are very limited in the dog. Various mechanoreceptors and proprioceptive receptors have been identified within the substance of the cruciate ligaments.

CONCLUSIONS

CCL structural characteristics play an important part in its complex behaviour with the crimped pattern of the collagen fibrils being an important determinant of its biomechanical properties. In contrast to reports of managing CCL rupture, there are few reports describing the microanatomy and neurovascular morphology of the cruciate ligaments.

CLINICAL RELEVANCE

Cruciate disease is likely multi-factorial. Improved understanding of CCL degradation leading to CCL rupture is critical to development of new diagnostic tests for cruciate disease in dogs. Appropriate intervention during the early stages of disease process might preserve CCL structural properties by preventing further collagen degradation. Accurate knowledge of functional and fiber bundle anatomy is imperative for reconstruction and restoration of normal stifle joint physiology. Reconstructive goals should alleviate existing instability and mimic normal kinematics. Knowledge of the exact function of the CCL in the neuromuscular control around the stifle joint could possibly explain osteoarthritis progression after CCL damage.

Collagen fragmentation in ruptured canine cranial cruciate ligament explants

Collagen fragmentation in cranial cruciate ligament (CCL) explants and stifle synovial fluid was investigated in dogs with ruptured and intact CCL. Cathepsin K and tartrate-resistant acid phosphatase (TRAP) activities were determined in CCL explant supernatants. Formation of collagen fragments was determined in explant supernatants and stifle synovial fluid. Cathepsin K(+) and TRAP(+) cells were stained specifically in histological sections of CCL. Formation of telopeptide collagen fragments was increased in ruptured CCL explants and stifle synovial fluid from dogs with ruptured CCL. In ruptured CCL explants, release of collagen fragments was associated with extracellular release of TRAP and the presence of cathepsin K(+) cells within CCL tissue. Cathepsin K(+) and TRAP(+) cells were only seen in ruptured CCL. It was concluded that infiltration of the CCL with TRAP(+) cells in dogs with CCL rupture is associated with increased collagenolysis. It is hypothesized that recruitment and activation of TRAP(+) mononuclear cells within the synovium and CCL precipitates CCL rupture through upregulation of collagenolytic enzymes and collagen degradation.

Morphometric assessment of the proximal portion of the tibia in dogs with and without cranial cruciate ligament rupture

Based on the clinical observation that dogs with a steep tibial plateau slope had variable tibial morphology, we hypothesized that these dogs could be further characterized using measurements developed by examining computer generated models of specific proximal tibial malformations. A 3D tibial model was created from a normal canine tibia. The model was manipulated to reproduce two specific proximal tibial anomalies representing deformities originating from the tibial plateau or the proximal tibial shaft. Data from these models were used to create specific measurements that would characterize the shape of these anomalies. These measurements included the diaphyseal tibial axis (DTA)/proximal tibial axis (PTA) angle, which defined the orientation of the proximal portion of the shaft in relation to the tibial mid-shaft. These measurements were then made on radiographs of dogs with and without cranial cruciate ligament (CCL) rupture. Models with tibial plateau and proximal shaft deformities had a steep tibial plateau slope (TPS). Models with proximal shaft deformity had a markedly increased DTA/PTA angle. The model with a 10 degree proximal shaft deformity had a DTA/PTA angle of 11.23 degrees. Six dogs (9.0%) had a DTA/PTA angle larger than 11.23 degrees (range, 11.4-13.9 degrees). Dogs in this group had ruptured CCL and a steep TPS. Dogs with CCL rupture had higher TPS (mean, 31.8 +/- 4.1 degrees) and DTA/PTA angle (mean, 6.0 +/- 3.3 degrees) than dogs without CCL rupture (means, 23.6 +/- 3.4 degrees and 4.1 +/- 2.2 degrees, respectively). Dogs with proximal shaft deformity represented a distinct group, which could not be identified using the magnitude of the TPS alone. Characterizing more precisely the shape of the proximal portion of the tibia in dogs contributes to our understanding of the pathogenesis of steep TPS and may facilitate the optimization of the surgical management of dogs with CCL rupture.

Collagenolytic protease expression in cranial cruciate ligament and stifle synovial fluid in dogs with cranial cruciate ligament rupture

OBJECTIVE

To determine expression of collagenolytic genes and collagen degradation in stifle tissues of dogs with ruptured cranial cruciate ligament (CCL).

ANIMALS

Six dogs with CCL rupture and 11 dogs with intact CCL.

PROCEDURES

Gene expression in CCL tissue and synovial fluid cells was studied using reverse transcriptase-polymerase chain reaction (RT-PCR). Collagen degradation was studied using CCL explant cultures and a synovial fluid bioassay.

RESULTS

Expression of matrix metalloproteases (MMP) was not found in young Beagles with intact CCL; however, increased expression of MMP-3 was found in CCL tissue from older hounds with intact CCL, when compared with young Beagles. In dogs with ruptured CCL, expression of MMP-2 and -9 was increased in stifle tissues, when compared with dogs with intact CCL. Similar to MMP-9, expression of tartrate-resistant acid phosphatase (TRAP) and cathepsin S was only found in stifle tissues from dogs with ruptured CCL; in contrast, expression of cathepsin K was found in all ruptured and intact CCL. Collagen degradation was increased in ruptured CCL, when compared with intact CCL.

CONCLUSION

Rupture of the CCL is associated with up-regulation of expression of MMP-2 and -9 (gelatinase A and B), TRAP, and cathepsin S, and increased degradation of collagen.

CLINICAL RELEVANCE

These findings suggest that MMP-2, -9, cathepsin S, and TRAP may be important mediators of progressive joint destruction in dogs with CCL rupture. These genes are markers for macrophages and dendritic cells. MMP and cathepsin S pathways may offer novel targets for anti-inflammatory medical therapy aimed at ameliorating joint degradation associated with inflammatory arthritis.

Inflammatory changes in ruptured canine cranial and human anterior cruciate ligaments

OBJECTIVE

To compare expression of tartrate-resistant acid phosphatase (TRAP) and cathepsin K and histologic changes in canine cranial cruciate ligaments (CCLs) and human anterior cruciate ligaments (ACLs).

STUDY POPULATION

Sections of cruciate ligaments from 15 dogs with ruptured CCLs, 8 aged dogs with intact CCLs, 14 human beings with ruptured ACLs, and 11 aged human beings with intact ACLs.

PROCEDURE

The CCLs and ACLs were evaluated histologically, and cells containing TRAP and cathepsin K were identified histochemically and immunohistochemically, respectively.

RESULTS

The proportion of ruptured CCLs that contained TRAP+ cells was significantly higher than the proportion of intact ACLs that did but similar to proportions of intact CCLs and ruptured ACLs that did. The proportion of ruptured CCLs that contained cathepsin K+ cells was significantly increased, compared with all other groups. Numbers of TRAP+ and cathepsin K+ cells were significantly increased in ruptured CCLs, compared with intact ACLs. The presence of TRAP+ cells was correlated with inflammatory changes, which were most prominent in ruptured CCLs.

CONCLUSION AND CLINICAL RELEVANCE

Results suggest that synovial macrophage-like cells that produce TRAP are an important feature of the inflammation associated with CCL rupture in dogs. Identification of TRAP and cathepsin K in intact CCLs and ACLs from aged dogs suggests that these enzymes have a functional role in cruciate ligament remodeling and repair. We hypothesize that recruitment and activation of TRAP+ macrophage-like cells into the stifle joint synovium and CCL epiligament are critical features of the inflammatory arthritis that promotes progressive degradation and eventual rupture of the CCL in dogs.

Localization of Cathepsin K and Tartrate-Resistant Acid Phosphatase in Synovium and Cranial Cruciate Ligament in Dogs with Cruciate Disease

OBJECTIVE

To localize cathepsin K and tartrate-resistant acid phosphatase (TRAP) in synovium and cranial cruciate ligament (CCL) of dogs with cruciate disease.

ANIMALS

Dogs (n=15) with cruciate disease and ruptured CCL, and 12 dogs with intact CCL.

METHODS

Synovium and CCL were examined histologically and cells containing cathepsin K or TRAP were identified immunohistochemically and histochemically, respectively.

RESULTS

Increased cellular localization of cathepsin K and TRAP was detected in synovium and ruptured CCL in dogs with cruciate disease, when compared with tissues from dogs with intact CCL. Inflammation of synovium with TRAP+ macrophage-like cells was seen in 73% of dogs with CCL disease, but was not seen in dogs with intact CCL. The presence of cathepsin K and TRAP protein in synovium and CCL tissues was significantly correlated in dogs with CCL rupture.

CONCLUSION

Inflammation of the epiligament of ruptured CCL with cathepsin K+ and TRAP+ macrophage-like cells forms part of a similar, more generalized chronic inflammatory change within the periarticular tissues of the stifle of a large proportion of dogs with CCL rupture.

CLINICAL RELEVANCE

Production of matrix-degrading enzymes by the synovium may induce progressive pathologic rupture of the CCL. Therefore, these collagenolytic pathways may offer a novel target for medical therapy of joint inflammation in canine patients with cruciate disease.

Relationship Between Age and Tibial Plateau Angle in Dogs With Cranial Cruciate Rupture

The pathogenesis of cranial cruciate ligament (CCL) rupture remains controversial, and its relationship to tibial plateau angle is unknown. In this study, the tibial plateau angle was measured in 200 large-breed dogs diagnosed with CCL rupture. Correlation analyses were performed to determine whether the age at the time of CCL rupture and the tibial plateau angle were related. While these two values were inversely correlated, the relationship was not strong enough to explain the frequency of CCL rupture in young, large-breed dogs. There was no statistically significant correlation between age at the time of CCL rupture and tibial plateau angle.

Cranial Cruciate Ligament Pathophysiology in Dogs With Cruciate Disease: A Review

Cruciate disease is a common cause of chronic lameness in dogs. Midsubstance rupture of the cranial cruciate ligament (CCL) arises from progressive pathological failure, often under conditions of normal loading in adult dogs with CCL instability. A high risk of rupture is associated with inflammation of the synovium and adaptive or degenerative changes in the cells and matrix of the CCL. In contrast, CCL rupture in puppies is usually associated with traumatic injury and avulsion of the CCL from its sites of attachment.

Evaluation of ligament fibroblast viability in ruptured cranial cruciate ligament of dogs

OBJECTIVE

To determine fibroblast viability, assess development of apoptosis, and evaluate tissue hypoxia via histochemical, in-situ hybridization, or immunohistochemical staining in ruptured and intact cranial cruciate ligaments (CCLs) of dogs.

ANIMALS

32 dogs with ruptured CCLs, and 8 aged and 19 young dogs with intact CCLs.

PROCEDURE

Markers of cell viability (lactate dehydrogenase [LDH]), apoptosis (terminal deoxynucleatidyl transferase-mediated deoxyuridine triphosphate-nick end labeling [TUNEL] method), and hypoxia (hypoxia-inducible factor-1alpha [HIF-1alpha] monoclonal antibody) were applied to CCL specimens; positive cells were assessed objectively (LDH) and subjectively (TUNEL and HIF-1alpha) in the main axial tissue component (core) and synovial intima and subintima (epiligamentous tissue).

RESULTS

Viable fibroblasts were seen in all intact and ruptured CCLs. More nonviable cells were found in the core regions of ruptured CCLs and intact CCLs of young dogs than in the epiligamentous regions. Number of nonviable cells in the core region of ruptured CCLs was greater than that in intact CCLs of young and aged dogs, whereas the number in the epiligamentous region was similar in all specimens. The TUNEL and HIF-1alpha staining was only found in the epiligamentous region of ruptured CCLs.

CONCLUSIONS AND CLINICAL RELEVANCE

Ruptured CCLs contained a high number of nonviable cells but not a great number of apoptotic cells. Repair processes in the epiligamentous region of the CCL include a metabolic response to hypoxia, suggesting that necrosis of ligament fibroblasts and transformation of surviving cells to a spheroid phenotype may be a response to hypoxia cause by microinjury or inadequate blood flow.