Gene expression analysis of subchondral bone, cartilage, and synovium in naturally occurring equine palmar/plantar osteochondral disease.

Osteoarthritis (OA) is a disease of the entire joint but the relationship between pathological events in various joint tissues is poorly understood. We examined concurrent changes in bone, cartilage, and synovium in a naturally occurring equine model of joint degeneration. Joints (n = 64) were grossly assessed for palmar/plantar osteochondral disease (POD) in racehorses that required euthanasia for unrelated reasons and assigned a grade of 0 (n = 34), 1 (n = 17), 2 or 3 (n = 13) using a recognized grading scheme. Synovium, cartilage, and subchondral bone were collected for histological and gene expression analysis. Relations between POD grade, cartilage histological score, and gene expression levels were examined using one-way analysis of variance or Kruskal-Wallis test and Spearman's correlation coefficient with corrections for multiple comparisons. Cartilage histological score increased in joints with POD grade 1 (p = 0.002) and 2 or 3 (p < 0.001) compared to 0. At grade 1, expression of COL1A1, COL2A1, and MMP1 increased and BGN decreased in subchondral bone while expression of BGN and ACAN decreased in cartilage. These changes further progressed at grades 2 and 3. POD grades 2 and 3 were associated with decreased expression of osteoclast inhibitor OPG and increased markers of cartilage degeneration (MMP13, COL1A1). Expression of the vascular endothelial growth factor decreased with POD grade and negatively correlated with cartilage histological score. Synovium showed no histological or transcriptomic changes related to pathology grade. Cartilage degeneration in POD is likely to be secondary to remodeling of the subchondral bone. Limited activation of proinflammatory and catabolic genes and moderate synovial pathology suggests distinct molecular phenotype of POD compared with OA.

Osteochondritis dissecans (OCD) in Horses - Molecular Background of its Pathogenesis and Perspectives for Progenitor Stem Cell Therapy.

Osteochondrosis (osteochondrosis dissecans; OCD) is a disease syndrome of growing cartilage related to different clinical entities such as epiphysitis, subchondral cysts and angular carpal deformities, which occurs in growing animals of all species, including horses. Nowadays, these disorders are affecting increasing numbers of young horses worldwide. As a complex multifactorial disease, OCD is initiated when failure in cartilage canals because of existing ischemia, chondrocyte biogenesis impairment as well as biochemical and genetic disruptions occur. Recently, particular attention have been accorded to the definition of possible relations between OCD and some metabolic disorders; in this way, implication of mitochondrial dysfunctions, endoplasmic reticulum disruptions, oxidative stress or endocrinological affections are among the most considered axes for future researches. As one of the most frequent cause of impaired orthopaedic potential, which may result in a sharp decrease in athletic performances of the affected animals, and lead to the occurrence of complications such as joint fragility and laminitis, OCD remains as one of the primary causes of considerable economic losses in all sections of the equine industry. It would therefore be important to provide more information on the exact pathophysiological mechanism(s) underlying early OC(D) lesions, in order to implement innovative strategies involving the use of progenitor stem cells, which are considered nowadays as a promising approach to regenerative medicine, with the potential to treat numerous orthopaedic disorders, including osteo-degenerative diseases, for prevention and reduction of incidence of the disease, not only in horses, but also in human medicine, as the equine model is already widely accepted by the scientific community and approved by the FDA, for the research and application of cellular therapies in the treatment of human conditions.

Clinical and Biological Signature of Osteochondritis Dissecans in a Cross-Sectional Study.

The healing potential of knee osteochondritis dissecans (OCD) focal lesions is not well defined. We performed a cross-sectional study correlating local and systemic biological characteristics with the patients' characteristics. We evaluated both local tissue markers (CD34, CD146, CD166, and tartrate-resistant acid phosphatase (TRAP)) and systemic serum biomarkers (fragments or propeptide of type II collagen: C2C, CTX-II, CPII, and TRAP5b) on histologically scored osteochondral fragments or serum from OCD patients. These biological features were associated with the patients' characteristics (IKDC subjective score, age, and body mass index (BMI)). Histological cartilage tissue score correlated with patients' IKDC and C2C and CPII biomarkers. CPII correlated also with histological bone tissue score. The percentage of CD146 positive cells in cartilage and CD34 positive cells in bone highly correlated with the patient's age and BMI, respectively. The percentage of TRAP in bone was directly correlated with both IKDC and age. Multivariate statistical analysis evidenced that only four parameters significantly predicted IKDC. In conclusion, a complete picture of OCD knee characteristics, defined by local and systemic markers of cartilage and bone remodeling, together with the patients' characteristics, might help to better understand the healing potential of each patient and to target and improve current OCD treatments.

Cartilage and Bone Serum Biomarkers as Novel Tools for Monitoring Knee Osteochondritis Dissecans Treated with Osteochondral Scaffold.

Knee osteochondritis dissecans (OCD) is a focal disease of the joint characterized by modifications of bone and cartilage tissues. Biomimetic osteochondral scaffolds are used to restore these tissues. The aim of this prognostic prospective cohort study was to evaluate serum biomarkers of cartilage (fragments or propeptide of type II collagen: CTXII, C2C, and CPII) and bone (tartrate-resistant acid phosphatase (TRAP) 5b and osteocalcin (OC)) turnover during follow-up of patients treated with an osteochondral scaffold, to identify which were related to healing outcome and clinical score. We found that cartilage (CPII) and bone (OC) synthetic biomarkers were significantly increased during the first-year follow-up, while the respective degradative markers (CTXII, C2C, and TRAP5b) were not modulated. Only CTXII/CPII and C2C/CPII cartilage ratios were significantly modulated, evidencing a higher remodeling of cartilage compared to bone tissue. Cartilage and bone single biomarkers or ratios at one-year follow-up showed values close to or similar to those of healthy subjects. International Knee Documentation Committee (IKDC) score significantly increased from T0 to T2, while the Tegner score did not. Taking into consideration an IKDC score > 70 as clinical success, we found that all OCD cases with both CPII (> 300 pg/ml) and C2C/CPII (<0.35) presented IKDC scores of clinical success. OCD patients treated with an osteochondral scaffold showed an improvement at one-year follow-up, evidenced by both clinical and serum cartilage biomarkers. These data confirmed that cartilage and bone remodeling took place and showed that systemic biomarkers represent a sensitive tool for monitoring OCD patients during the follow-up.

Focal Defects of the Knee Articular Surface: Evidence of a Regenerative Potential Pattern in Osteochondritis Dissecans and Degenerative Lesions.

The surgical treatment of knee articular focal lesions may offer heterogeneous clinical results. Osteochondritis dissecans (OCD) lesions showed to heal better than degenerative lesions (DL) but the underlying biological reasons are unknown. We evaluated the basal histological and immunohistochemical characteristics of these lesions analyzing a series of osteochondral fragments from young patients with similar age but presenting different etiology. Osteochondral tissue samples were stained with Safranin O and graded using a histological score. Markers of mesenchymal progenitor cells (CD146), osteoclasts (tartrate-resistant acid phosphatase, TRAP), and vessels (CD34) were evaluated. Histological score showed a higher degeneration of both cartilage and bone compartments in OCD compared to DL fragments. Only CD146-positive cells were found at the same percentage in cartilage compartment of both DL and OCD patients. By contrast, in the bone compartment a significantly higher percentage of CD146, TRAP, and CD34 markers was found in OCD compared to DL patients. These data showed distinct histological characteristics of osteochondral focal lesions located in the same anatomical region but having a different etiology. The higher percentages of these markers in OCD than in DL, mainly associated with a high bone turnover, could help to explain the higher clinical healing potential of OCD patients.

Chondrocytes Derived From Mesenchymal Stromal Cells and Induced Pluripotent Cells of Patients With Familial Osteochondritis Dissecans Exhibit an Endoplasmic Reticulum Stress Response and Defective Matrix Assembly.

UNLABELLED: : Familial osteochondritis dissecans (FOCD) is an inherited skeletal defect characterized by the development of large cartilage lesions in multiple joints, short stature, and early onset of severe osteoarthritis. It is associated with a heterozygous mutation in the ACAN gene, resulting in a Val-Met replacement in the C-type lectin domain of aggrecan. To understand the cellular pathogenesis of this condition, we studied the chondrogenic differentiation of patient bone marrow mesenchymal stromal cells (BM-MSCs). We also looked at cartilage derived from induced pluripotent stem cells (iPSCs) generated from patient fibroblasts. Our results revealed several characteristics of the differentiated chondrocytes that help to explain the disease phenotype and susceptibility to cartilage injury. First, patient chondrogenic pellets had poor structural integrity but were rich in glycosaminoglycan. Second, it was evident that large amounts of aggrecan accumulated within the endoplasmic reticulum of chondrocytes differentiated from both BM-MSCs and iPSCs. In turn, there was a marked absence of aggrecan in the extracellular matrix. Third, it was evident that matrix synthesis and assembly were globally dysregulated. These results highlight some of the abnormal aspects of chondrogenesis in these patient cells and help to explain the underlying cellular pathology. The results suggest that FOCD is a chondrocyte aggrecanosis with associated matrix dysregulation. The work provides a new in vitro model of osteoarthritis and cartilage degeneration based on the use of iPSCs and highlights how insights into disease phenotype and pathogenesis can be uncovered by studying differentiation of patient stem cells. SIGNIFICANCE: The isolation and study of patient stem cells and the development of methods for the generation of iPSCs have opened up exciting opportunities in understanding causes and exploring new treatments for major diseases. This technology was used to unravel the cellular phenotype in a severe form of inherited osteoarthritis, termed familial osteochondritis dissecans. The phenotypic abnormalities that give rise to cartilage lesions in these patients were able to be described via the generation of chondrocytes from bone marrow-derived mesenchymal stromal cells and iPSCs, illustrating the extraordinary value of these approaches in disease modeling.

Early intra-articular complement activation in ankle fractures.

Cytokine regulation possibly influences long term outcome following ankle fractures, but little is known about synovial fracture biochemistry. Eight patients with an ankle dislocation fracture were included in a prospective case series and matched with patients suffering from grade 2 osteochondritis dissecans (OCD) of the ankle. All fractures needed external fixation during which joint effusions were collected. Fluid analysis was done by ELISA measuring aggrecan, bFGF, IL-1 ß, IGF-1, and the complement components C3a, C5a, and C5b-9. The time periods between occurrence of fracture and collection of effusion were only significantly associated with synovial aggrecan and C5b-9 levels (P < 0.001). Furthermore, synovial expressions of both proteins correlated with each other (P < 0.001). Although IL-1 ß expression was relatively low, intra-articular levels correlated with C5a (P < 0.01) and serological C-reactive protein concentrations 2 days after surgery (P < 0.05). Joint effusions were initially dominated by neutrophils, but the portion of monocytes constantly increased reaching 50% at day 6 after fracture (P < 0.02). Whereas aggrecan and IL-1ß concentrations were not different in fracture and OCD patients, bFGF, IGF-1, and all complement components were significantly higher concentrated in ankle joints with fractures (P < 0.01). Complement activation and inflammatory cell infiltration characterize the joint biology following acute ankle fractures.

Association between intraarticular cytokine levels and clinical parameters of osteochondritis dissecans in the ankle.

BACKGROUND: Reliable data about in vivo regulation of cytokines in osteochondritis dissecans (OCD) of the ankle are still missing. Disease-specific regulation patterns were hypothesized. METHODS: 28 patients with a mean age of 30.7 ± 14.8 years undergoing an arthroscopy of the ankle because of OCD were prospectively included in a clinical trial. Lavage fluids were analyzed by ELISA for levels of aggrecan, BMP-2, BMP-7, IGF-1, IGF-1R, bFGF, endoglin, MMP-13, and IL-1ß. Additionally, clinical parameters and scores (FFI, CFSS, AOFAS) were evaluated and supplemented by the Kellgren Lawrence Score (KLS) for conventional X-rays and the Ankle Osteoarthritis Scoring System (AOSS) for MRI. RESULTS: Grading of OCD lesions statistically significant increased with age and was higher in case of previously performed operations (p<0.03). A worse clinical function reflected by low AOFAS and CFSS scores or high FFI was associated with high grading of cartilage damage or OCD (p<0.03). Similarly, high radiological scores (KLS and AOSS) indicating progress of OA positively correlated with grading of cartilage damage and OCD. The concordance between the MRI and arthroscopic classification was overall moderate (κ=0.52). Biochemically, only IGF/IGF-1R levels were consistently negatively associated with OCD grading, ICRS score, FFI and KLS (p<0.05). Correlation data is supported by post hoc statistics. CONCLUSIONS: Radiological and clinical parameters in association with synovial IGF-1/IGF-1R levels indicated an increasing joint degeneration with rising OCD stage. TRIAL REGISTRATION: German Clinical Trials Register DRKS00000365, 11/03/2008.

Synovial fluid D-dimer concentration in horses with osteochondritis dissecans and osteoarthritis.

OBJECTIVE: To assess the synovial fibrinolytic pathway activation in adult horses with developmental and degenerative arthropathies such as osteochondritis dissecans (OCD) and osteoarthritis (OA) by measuring synovial D-dimer concentrations. METHODS: Prospective observational clinical study of horses admitted for OCD or OA. Synovial fluid was collected during lameness examination or prior to the surgical procedure, and D-dimer concentration and routine synovial fluid analysis were performed. RESULTS: Fifty-eight horses (14 with OCD, 10 with OA and 34 controls) were included in this study. Synovial D-dimer concentrations of horses with OCD and OA were both higher when compared with controls, but were only significantly different in horses with OCD (p = 0.005). However, no statistical differences were observed when comparing synovial D-dimer concentrations from the OCD horses with the OA-affected horses (p = 0.444). CLINICAL SIGNIFICANCE: Activation of coagulation and fibrinolysis play a role in the pathophysiology of equine OCD and OA.

Comparison between normal and loose fragment chondrocytes in proliferation and redifferentiation potential.

PURPOSE: Loose fragments in osteochondritis dissecans (OCD) of the knee require internal fixation. On the other hand, loose fragments derived from spontaneous osteonecrosis of the knee (SONK) are usually removed. However, the difference in healing potential between OCD- and SONK-related loose fragments has not been elucidated. In this study, we investigated proliferative activity and redifferentiation potential of normal cartilage-derived and loose fragment-derived chondrocytes. METHODS: Cells were prepared from normal articular cartilages and loose fragment cartilages derived from knee OCD and SONK. Cellular proliferation was compared. Redifferentiation ability of pellet-cultured chondrocytes was assessed by real-time PCR analyses. Mesenchymal differentiation potential was investigated by histological analyses. Positive ratio of a stem cell marker CD166 was evaluated in each cartilaginous tissue. RESULTS: Normal and OCD chondrocytes showed a higher proliferative activity than SONK chondrocytes. Chondrogenic pellets derived from normal and OCD chondrocytes produced a larger amount of safranin O-stained proteoglycans compared with SONK-derived pellets. Expression of chondrogenic marker genes was inferior in SONK pellets. The CD166-positive ratio was higher in normal cartilages and OCD loose fragments than in SONK loose fragments. CONCLUSIONS: The OCD chondrocytes maintained higher proliferative activity and redifferentiation potential compared with SONK chondrocytes. Our results suggest that chondrogenic properties of loose fragment-derived cells and the amount of CD166-positive cells may affect the repair process of osteochondral defects.

In vitro phenotypic modulation of chondrocytes from knees of patients with osteochondritis dissecans: implications for chondrocyte implantation procedures.

We attempted to characterise the biological quality and regenerative potential of chondrocytes in osteochondritis dissecans (OCD). Dissected fragments from ten patients with OCD of the knee (mean age 27.8 years (16 to 49)) were harvested at arthroscopy. A sample of cartilage from the intercondylar notch was taken from the same joint and from the notch of ten patients with a traumatic cartilage defect (mean age 31.6 years (19 to 52)). Chondrocytes were extracted and subsequently cultured. Collagen types 1, 2, and 10 mRNA were quantified by polymerase chain reaction. Compared with the notch chondrocytes, cells from the dissecate expressed similar levels of collagen types 1 and 2 mRNA. The level of collagen type 10 message was 50 times lower after cell culture, indicating a loss of hypertrophic cells or genes. The high viability, retained capacity to differentiate and metabolic activity of the extracted cells suggests preservation of the intrinsic repair capability of these dissecates. Molecular analysis indicated a phenotypic modulation of the expanded dissecate chondrocytes towards a normal phenotype. Our findings suggest that cartilage taken from the dissecate can be reasonably used as a cell source for chondrocyte implantation procedures.

Evaluation of reparative cartilage after autologous chondrocyte implantation for osteochondritis dissecans: histology, biochemistry, and MR imaging.

BACKGROUND: The aim of this study was to investigate the biochemical properties, histological and immunohistochemical appearance, and magnetic resonance (MR) imaging findings of reparative cartilage after autologous chondrocyte implantation (ACI) for osteochondritis dissecans (OCD). METHODS: Six patients (mean age 20.2 +/- 8.8 years; 13-35 years) who underwent ACI for full-thickness cartilage defects of the femoral condyle were studied. One year after the procedure, a second-look arthroscopic operation was performed with biopsy of reparative tissue. The International Cartilage Repair Society (ICRS) visual histological assessment scale was used for histological assessment. Biopsied tissue was immunohistochemically analyzed with the use of monoclonal antihuman collagen type I and monoclonal antihuman collagen type II primary antibodies. Glycosaminoglycan (GAG) concentrations in biopsied reparative cartilage samples were measured by high performance liquid chromatography (HPLC). MR imaging was performed with T1- and T2-weighted imaging and three-dimensional spoiled gradient-recalled (3D-SPGR) MR imaging. RESULTS: Four tissue samples were graded as having a mixed morphology of hyaline and fibrocartilage while the other two were graded as fibrocartilage. Average ICRS scores for each criterion were (I) 1.0 +/- 1.5; (II) 1.7 +/- 0.5; (III) 0.6 +/- 1.0; (IV) 3.0 +/- 0.0; (V) 1.8 +/- 1.5; and (VI) 2.5 +/- 1.2. Average total score was 10.7 +/- 2.8. On immunohistochemical analysis, the matrix from deep and middle layers of reparative cartilage stained positive for type II collagen; however, the surface layer did not stain well. The average GAG concentration in reparative cartilage was 76.6 +/- 4.2 microg/mg whereas that in normal cartilage was 108 +/- 11.2 microg/mg. Common complications observed on 3D-SPGR MR imaging were hypertrophy of grafted periosteum, edema-like signal in bone marrow, and incomplete repair of subchondral bone at the surgical site. Clinically, patients had significant improvements in Lysholm scores. CONCLUSIONS: In spite of a good clinical course, reparative cartilage after ACI had less GAG concentration and was inferior to healthy hyaline cartilage in histological and immunohistochemical appearance and on MRI findings.

Cartilage-derived biomarkers and lipid mediators of inflammation in horses with osteochondritis dissecans of the distal intermediate ridge of the tibia.

OBJECTIVE: To assess whether reported alterations in metabolism of cartilage matrix in young (0 to 24 months old) horses with osteochondritis dissecans (OCD) may also be found in older (24 to 48 months old) horses with clinical signs of OCD and to investigate the role of eicosanoids in initiating these clinical signs. SAMPLE POPULATION: Synovial fluid was collected from 38 tarsocrural joints of 24 warmblood horses with (22 joints of 16 horses) or without (16 joints of 8 horses) clinical signs and a radiographic diagnosis of OCD of the distal intermediate ridge of the tibia. PROCEDURES: Turnover of type II collagen was investigated by use of specific immunoassays for synthesis (carboxypropeptide of type II collagen [CPII]) and degradation (collagenase-cleaved fragments of type II collagen [C2C]) products. Furthermore, glycosaminoglycan (GAG), leukotriene (LT) B(4), cysteinyl LTs, and prostaglandin (PG) E(2) concentrations were determined, and concentrations in joints with OCD were compared with those in joints without OCD. RESULTS: Concentrations of CPII, C2C, and GAG did not differ significantly between affected and nonaffected joints. Fluid from joints with OCD had significantly higher LTB(4) and PGE(2) concentrations than did fluids from nonaffected joints. CONCLUSIONS AND CLINICAL RELEVANCE: Altered collagen or proteoglycan turnover was not detected in 24- to 48-month-old horses at the time they developed clinical signs of OCD of the distal intermediate ridge of the tibia. However, increased concentrations of LTB(4) and PGE(2) in fluid of joints with OCD implicate these mediators in the initiation of clinical signs of OCD.

Microscopic localization of active gelatinases in equine osteochondritis dissecans (OCD) cartilage.

OBJECTIVE: To investigate the relationship between matrix metalloproteinase (MMP) activity and osteochondritis dissecans (OCD) in the equine joint. METHODS: Equine articular cartilage was obtained from normal (N = 8) and osteochondrotic (OCD) (N = 6) femoropatellar joints from horses at necropsy. The activity of gelatinase MMPs was determined in sections of cartilage by in situ gelatin zymography. RESULTS: Gelatinase activity was markedly increased in articular cartilage obtained from OCD samples and was particularly prominent in the deep cartilage zone. Activity was only seen in the pericellular area of chondrocytes. In addition, in OCD cartilage there were vertical lines of activity, starting from the deep zone and radiating towards the articular surface. In contrast, normal cartilage showed only a very small amount of gelatinolytic activity, which was not restricted to specific cartilage zones. Gelatin zymography of culture supernatants from isolated chondrocytes demonstrated increased production of MMP-2 and MMP-9 from OCD chondrocytes. CONCLUSIONS: Sections of articular cartilage from OCD lesions revealed MMP activity, especially in the deep zone adjacent to the calcified subchondral bone. This MMP activity could account for the loss of cartilage integrity in the deep cartilage zone and the vertical lines of activity could represent areas of mechanical weakness, likely to result in fissures and the release of cartilage fragments into the joint space.

Biochemical characterization of cartilage affected by osteochondritis dissecans in the humeral head of dogs.

OBJECTIVE: To determine glycosaminoglycan (GAG) concentration and immunohistochemical staining characteristics of type-I, -II, and -X collagen from cartilage affected by osteochondritis dissecans (OCD) in dogs. ANIMALS: 31 dogs with OCD and 11 clinically normal purpose-bred dogs. PROCEDURE: Cartilage samples were evaluated microscopically, and GAG content was determined. Immunohistochemical staining was performed for type-I, -II, and -X collagen. Sections were subjectively evaluated for location and intensity of staining. RESULTS: Cartilage affected by OCD had a variety of pathologic changes and significantly lower GAG concentrations than did normal cartilage. Normal cartilage had no detectable type-I collagen. For dogs < 9 months of age, cartilage affected by OCD had significantly more type-I collagen but significantly less type-X collagen than did control cartilage. For dogs > 12 months of age, cartilage affected by OCD contained significantly more type-I collagen than did control cartilage. There was a significant negative correlation between immunoreactivity of type-I collagen and that of type-II and -X collagen. A significant positive correlation was found between immunoreactivity of type-II and -X collagen. CONCLUSIONS AND CLINICAL RELEVANCE: Cartilage affected by OCD contains less GAG, more type-I collagen, and less type-X collagen, compared with normal cartilage. A direct correlation between these changes and the etiopathogenesis of OCD was not established.

[Lesions of the growth plate caused by sports stress]. / Störungen der Wachstumsfugen durch sportliche Uberbelastung.

Besides the positive physiological, psychological and social aspects, sports activities in adolescents bear the risk of injuries and overuse of the locomotor system. Previous examinations have shown that increased stress to the growth plates by sports activities, in relation to the intensity of strain during growth spurts, can influence normal growth. In female gymnasts, hormonal changes can decrease the growth speed and long-term growth. On the other hand, during more intensive phases of growth the column cartilage of the growth plate is the weakest part of the locomotor system because of the influence of somatotropin and low levels of testosterone. This can cause subchondral stress fractures in the growing cartilage that later on, if missed or not sufficiently treated, can cause osteochondrosis dissecans. The apophysis of tendons of big muscle groups can show loosening of the apophysis caused by increased muscle strength and acute or chronic microtrauma. Male adolescents show an incidence of lesions in the relation of 9:1 to female adolescents. The therapy for apophyseal lesions is generally nonoperative. Due to the persistent growth possibility, pseudotumors can occur, which can cause problems in differential diagnosis among skeletal tumors. Too high pressure, pushing and tearing forces can influence growth. Later examinations of previous high-level sportsmen and patients with coxarthrosis with and without a sports history show that blockage of the rotation of the foot during growth, for example caused by soccer shoes, can cause high pushing forces on the femoral epiphysis, which can lead to epiphyseolysis cap. fem. lenta and thereby to pre-arthritic deformities. This is overcorrection of the "physiological" epiphyseolysis, described by Morscher. Knowledge of the reduced strength of the growth plate indicates better adaptation of training and supervision of the adolescent high-level sportsman. A regular check-up of the growing athlete and a reduction in sports intensity during the growth spurts, prohibition of negative training parts and sometimes even prohibition of sports at all, if there is a lesion of the growth plate or hormonal disorders, are sometimes necessary to minimize late defects. In addition to this, a reduction of strain in some sports and, for example, prohibition of rotation-blocking soccer shoes in the adolescent soccer player is necessary.

Experimentally induced cartilaginous fractures (osteochondritis dissecans) in foals fed low-copper diets.

Four Thoroughbred foals were weaned from their dams when they were 1 day old and were fed a liquid milk-replacer diet containing approximately 1.7 micrograms of copper/g from plastic buckets for 4 to 7 months. They were kept in stalls with fiberglass walls and asphalt floors covered with rubber pads. Serum copper and zinc concentrations were determined 3 times/week by atomic absorption spectrophotometry, and liver copper and zinc concentrations were determined similarly after acid digestion of tissues taken at necropsy. The amount of soluble collagen in articular cartilage and aortic tissue was determined after necropsy. Clinical signs of illness, particularly evidence of lameness, were monitored daily. The foals were weighed weekly, and growth rate was monitored by measurement of height at the withers. Packed cell volumes and total and differential WBC counts were measured each time blood was drawn for copper and zinc concentration determinations. The foals were examined by necropsy at the end of the experiment, and the tissues were examined histologically. The foals developed intermittent, but nondebilitating, diarrhea with the onset of low serum copper concentrations. Considering the totally liquid diet, the foals grew well. Serum copper concentrations decreased to less than 0.1 micrograms/ml in 13 to 16 weeks. Lameness was evident 2 to 6 weeks after serum copper concentrations decreased to their lowest value (less than 0.1 micrograms/ml). All foals developed stilted gaits and ultimately walked on the front of their hooves. Major hematologic changes and alterations of hair color were not evident. Soluble collagen of articular cartilage and aortic tissue increased from 340 to 600% greater than that of control foals.(ABSTRACT TRUNCATED AT 250 WORDS)