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Biomedical subjects

J P Arokoski

Publications and source records attributed to J P Arokoski.

14 recordsLinked to original sources
PubMed2001

Back and abdominal muscle function during stabilization exercises.

OBJECTIVES: To assess the paraspinal and abdominal muscle activities during different therapeutic exercises and to study how load increment produced by varying limb movements and trunk positions could affect these muscle activities. DESIGN: A cross-sectional study comparing muscle activities between men and women. SETTING: Rehabilitation clinic in university hospital. PARTICIPANTS: Twenty-four healthy volunteers (14 women, 10 men) aged 21 to 39 years. INTERVENTIONS: Subjects performed 16 different therapeutic exercises commonly used to treat low back pain. MAIN OUTCOME MEASURES: Surface electromyography was recorded from the paraspinal (T9, L5) and abdominal (rectus abdominis, obliquus externus) muscles during these exercises. Average electromyographic amplitudes obtained during the exercises were normalized to the amplitude in maximal voluntary contraction (% MVC) to produce interindividually comparable muscle activity assessments. RESULTS: Mean average normalized electromyographic amplitudes (% MVC) of the exercises were below 50% MVC. At L5 level, the multifidus muscle activities were significantly higher (p <.05) in women than in men, whereas no significant difference was found at T9 level. Similarly, rectus abdominis and obliquus externus activities were significantly higher (p <.001, p <.05) in women than in men. Load increment in hands or unbalanced trunk and limb movements produced higher paraspinal and abdominal muscle activities (p <.05). CONCLUSIONS: Simple therapeutic exercises are effective in activating both abdominal and paraspinal muscles. By changing limb and trunk positions or unbalancing trunk movements, it is possible to increase trunk muscle activities. Women were better able to activate their stabilizing trunk muscles than men; but it is also possible that men, having a much higher degree of strength on maximal contraction, only need to activate a smaller amount of that maximum to perform a similar activity.

Abdominal Muscles↗
PubMed2001

Age matters: collagen birefringence of superficial articular cartilage is increased in young guinea-pigs but decreased in older animals after identical physiological type of joint loading.

OBJECTIVE: To compare responses of the collagen network and glycosaminoglycans (GAGs) of articular cartilage to physiological type of joint loading in young growing and adult mature guinea-pigs. DESIGN: 10- and 44-week-old guinea-pigs were accustomed to treadmill running for 3 weeks. Thereafter the animals ran 2500 m/day, 5 days a week, for 15 weeks. Articular cartilage specimens from knee joints were collected at 28 and 62 weeks. Osteoarthritis (OA) prevalence and severity was evaluated by aid of light microscopy. The degree of collagen fibril network organization and content was analyzed with quantitative polarized light microscopy. The local concentration of GAGs was determined from cartilage sections with digital densitometry after safranin-O staining. RESULTS: In the young guinea-pigs, running increased up to 24% the optical retardation of polarized light by collagen in the superficial articular cartilage of femur, indicating either a higher degree of fibril assembly and organization or increased amount of collagen, or both. In contrast, in the adult mature animals the optical retardation decreased almost 50% after joint loading (P< 0.01-0.001). Running did not increase cartilage fibrillation. Significant changes in GAG content of cartilage were not found either in the young or adult mature runners. CONCLUSIONS: Increased birefringence of the superficial articular cartilage after joint loading in young guinea-pigs can be interpreted to be a sign of improved and decreased birefringence in older animals a sign of worsened property of the collagen network. It can be suggested therefore that joint loading strengthened the collagen network in the young runners. It can be hypothesized further that with time the inferior property of the collagen network predisposes the older runners to earlier OA than in controls.

Aging↗
PubMed2001

Decline after immobilisation and recovery after remobilisation of synovial fluid IL1, TIMP, and chondroitin sulphate levels in young beagle dogs.

OBJECTIVE: To monitor the concentration of markers of cartilage and synovium metabolism in the knee (stifle) joint synovial fluid of young beagles subjected to immobilisation and subsequent remobilisation. METHODS: The right hind limb of 17 dogs was immobilised in flexion for 11 weeks. Simultaneously, the contralateral left knee was exposed to increased weight bearing. The remobilisation period lasted 50 weeks. Litter mates served as controls. The concentration in joint lavage fluid of interleukin 1alpha (IL1alpha) was measured by immunoassay, the activity of phospholipase A(2) (PLA(2)) was determined by an extraction method, chondroitin sulphate (CS) concentration by precipitation with Alcian blue, hyaluronan (HA) by an ELISA-like assay using biotinylated HA-binding complexes, matrix metalloproteinase 3 (MMP-3), and tissue inhibitor of metalloproteinases 1 (TIMP-1) by sandwich ELISA, and synovitis was scored by light microscopy. RESULTS: Synovitis or effusion was absent in all experimental and control groups. Immobilisation decreased the joint lavage fluid levels of IL1alpha (p<0.05), TIMP (p< 0.05), and the concentration of CS down to 38% (p<0.05) in comparison with untreated litter mates with normal weight bearing. Immobilisation did not affect the activity of PLA(2), or the concentration of MMP-3 or HA in synovial fluid. Joint remobilisation restored the decreased concentrations of markers to control levels. Increased weight bearing did not change the concentrations of markers in comparison with the control joints with normal weight bearing. CONCLUSIONS: 11 weeks' joint immobilisation decreased the concentration of markers of cartilage and synovium metabolism in the synovial fluid, and remobilisation restored the concentrations to control levels. The changes in joint metabolism induced by immobilisation, as reflected by the markers, are thus different from those found in osteoarthritis, where increased levels of these markers are associated with enhanced degradation and synthesis. These findings suggest that the change induced in joint metabolism by immobilisation is reversible in its early stages.

Animals↗
PubMed2000

Topographical variation of the elastic properties of articular cartilage in the canine knee.

Equilibrium response of articular cartilage to indentation loading is controlled by the thickness (h) and elastic properties (shear modulus, mu, and Poisson's ratio, nu) of the tissue. In this study, we characterized topographical variation of Poisson's ratio of the articular cartilage in the canine knee joint (N=6). Poisson's ratio was measured using a microscopic technique. In this technique, the shape change of the cartilage disk was visualized while the cartilage was immersed in physiological solution and compressed in unconfined geometry. After a constant 5% axial strain, the lateral strain was measured during stress relaxation. At equilibrium, the lateral-to-axial strain ratio indicates the Poisson's ratio of the tissue. Indentation (equilibrium) data from our prior study (Arokoski et al., 1994. International Journal of Sports Medicine 15, 254-260) was re-analyzed using the Poisson's ratio results at the test site to derive values for shear and aggregate moduli. The lowest Poisson's ratio (0.070+/-0.016) located at the patellar surface of femur (FPI) and the highest (0.236+/-0.026) at the medial tibial plateau (TMI). The stiffest cartilage was found at the patellar groove of femur (micro=0.964+/-0.189MPa, H(a)=2.084+/-0. 409MPa) and the softest at the tibial plateaus (micro=0.385+/-0. 062MPa, H(a)=1.113+/-0.141MPa). Comparison of the mechanical results and the biochemical composition of the tissue (Jurvelin et al., 1988. Engineering in Medicine 17, 157-162) at the matched sites of the canine knee joint indicated a negative correlation between the Poisson's ratio and collagen-to-PG content ratio. This is in harmony with our previous findings which suggested that, in unconfined compression, the degree of lateral expansion in different tissue zones is related to collagen-to-PG ratio of the zone.

Analysis of Variance↗
PubMed2000

Normal and pathological adaptations of articular cartilage to joint loading.

Joints are functional units that transmit mechanical loads between contacting bones during normal daily or specialized activities, e.g., sports. All components of the joint, i.e. articular cartilage, bone, muscles, ligaments/tendons and nerves, participate in load transmission. Failure in any of these components can cause joint malfunction, which, in turn, may lead to accumulation of damage in other joint components. Mechanical forces have great influence on the synthesis and rate of turnover of articular cartilage molecules, such as proteoglycans (PGs). Regular cyclic loading of the joint enhances PG synthesis and makes cartilage stiff. On the other hand, loading appears to have less evident effects on the articular cartilage collagen fibril network. Continuous compression of the cartilage diminishes PG synthesis and causes damage of the tissue through necrosis. The prevailing view is that osteoarthrosis (OA) starts from the cartilage surface through PG depletion and fibrillation of the superficial collagen network. It has also been suggested that the initial structural changes take place in the subchondral bone, especially when the joint is exposed to an impact type of loading. This in turn would create an altered stress pattern on joint surfaces, which leads to structural damage and mechanical failure of articular cartilage. The importance of the neuromuscular system to the initiation and progression of OA is still poorly understood. Many surgical extra- and intra-articular procedures have been used for the treatment of OA. Although some of the new methods, such as autologous chondrocyte transplantation and mosaicplasty, have given good clinical results, it is reasonable to emphasize that the methods still are experimental and more controlled studies are needed.

Animals↗
PubMed1999

Biomechanical and structural characteristics of canine femoral and tibial cartilage.

To analyze the interrelationships between the structure, composition, and mechanical properties of articular cartilage, canine knee (n = 10) femoral and tibial cartilages were used as experimental tissues. The biomechanical properties, instant shear modulus (IM), and equilibrium shear modulus (EM) of articular cartilage were investigated using an in situ indentation creep technique. The local variations in the concentration of glycosaminoglycans (GAGs) in the cartilage were measured with a microspectrophotometer after safranin-O staining of histological sections. Using a computer-based quantitative polarized light microscopy method, area-specific measurements of the optical path difference were performed to quantitate collagen-related optical retardation (gamma) of cartilage zones. The IM and EM were 131.3 and 51.2% higher (p < 0.001) in the femoral cartilage than in the tibial cartilage, respectively. The mean thickness of the superficial zone and the relative proportion of the superficial zone from the total uncalcified cartilage was 107.1 and 155.3% higher (p < 0.001) at the femoral test points than in the tibial ones, respectively. The mean thickness of the tibial uncalcified cartilage was 21.1% higher (p < 0.001) than the thickness of the femoral cartilage. The GAG concentration of the tibial cartilage was higher (14.8%, p < 0.001) than that of the femoral cartilage, especially in the superficial zone (50.0%, p < 0.05), whereas the gamma of the collagen network in the superficial zone of the femoral cartilage was 64.7% higher (p < 0.001) than in the tibial cartilage. The percent relative thickness and retardation gamma of the superficial zone correlated positively with the indentation stiffness of the canine knee articular cartilage. These observations indicate that cartilage is structurally inhomogenous and layered tissue and the local organization of collagen and GAG concentration of the articular cartilage regulate the biomechanical properties of the tissue. The structure and composition of the superficial articular cartilage significantly affects the indentation response of the canine knee articular cartilage.

Animals↗
PubMed1999

Back and hip extensor muscle function during therapeutic exercises.

BACKGROUND: Therapeutic exercises are widely used in the treatment of low back problems. Clinical knowledge about targeting the load in these exercises, however, is insufficient. This study assessed the L2 and L5 level paraspinal and gluteus maximus muscle activities in different therapeutic exercises. Intramuscular and surface electromyography (EMG) measurements were obtained to study whether surface EMG measurements can be used in the assessment of multifidus muscle function. METHODS: Eleven healthy subjects (5 men, 6 women) 21 to 38 years of age volunteered for the study. The subjects performed 18 different therapeutic exercises. During the exercises paraspinal EMG was recorded using fine wire and surface electrodes. The normalized peak and average muscle EMG activities (percentage of amplitude in maximal voluntary contraction [MVC]) during each task were determined. RESULTS: The correlations between the average intramuscular and surface activities of the normalized EMG (% of MVC) at the L2 and L5 levels were .928 and .950, respectively. The peak and average EMG amplitudes of the exercises were below 50% and 25% of MVC, respectively. At the L5 level, the multifidus peak and average EMG amplitudes (% MVC) were higher in women than in men, whereas no significant difference was found at the L2 level. In women, the normalized multifidus EMG amplitude was higher at the L5 level than at the L2 level, whereas no significant difference was found in men. In both sexes, the normalized EMG amplitude was higher in the multifidus than in the longissimus muscle. CONCLUSION: Surface EMG measurements may be used in the assessment of multifidus muscle function. Simple therapeutic exercises are effective in activating the lumbar paraspinal muscles.

Adult↗
PubMed1999

Experimental validation of arthroscopic cartilage stiffness measurement using enzymatically degraded cartilage samples.

In order to evaluate the ability of the arthroscopic indentation instrument, originally developed for the measurement of cartilage stiffness during arthroscopy, to detect cartilage degeneration, we compared changes in the stiffness with the structural and constitutional alterations induced by enzymes on the tissue in vitro. The culturing of osteochondral plugs on Petri dishes was initiated in Minimum Essential Medium with Earle's salts and the baseline stiffness was measured. Then, the experimental specimens were digested using 50 microg ml(-1) trypsin for 24 h, 0.1 U ml(-1) chondroitinase ABC or 30 U ml(-1) purified collagenase (type VII) for 24 h or 48 h (n = 8-15 per group). The control specimens were incubated in the medium. After the enzyme digestion, the end-point stiffness was measured and the specimens for the microscopic analyses were processed. The proteoglycan (PG) distribution was analysed using quantitative microspectrophotometry and the quantitative evaluation of the collagen network was made using a computer-based polarized light microscopy analysis. Decrease (p < 0.05) of cartilage stiffness was found after 24 h trypsin (36%) and 48 h chondroitinase ABC (24%) digestion corresponding to a decrease (p < 0.01) of up to 80% and up to 30% in the PG content respectively. Decrease of the superficial zone collagen content or arrangement (78%, p < 0.001) after 48 h collagenase digestion also induced a decrease (30%, p < 0.001) in cartilage stiffness. We conclude that our instrument is capable of detecting early structural and compositional changes related to cartilage degeneration.

Animals↗
PubMed1999

Remobilization does not fully restore immobilization induced articular cartilage atrophy.

The recovery of articular cartilage from immobilization induced atrophy was studied. The right hind limbs of 29-week-old beagle dogs were immobilized for 11 weeks and then remobilized for 50 weeks. Cartilage from the immobilized knee was compared with tissue from age matched control animals. After the immobilization period, uncalcified articular cartilage glycosaminoglycan concentration was reduced by 20% to 23%, the reduction being largest (44%) in the superficial zone. The collagen fibril network showed no significant changes, but the amount of collagen crosslinks was reduced (13.5%) during immobilization. After remobilization, glycosaminoglycan concentration was restored at most sites, except for in the upper parts of uncalcified cartilage in the medial femoral and tibial condyles (9% to 17% less glycosaminoglycans than in controls). The incorporation of 35SO4 was not changed, and remobilization also did not alter the birefringence of collagen fibrils. Remobilization restored the proportion of collagen crosslinks to the control level. The changes induced by joint unloading were reversible at most sites investigated, but full restoration of articular cartilage glycosaminoglycan concentration was not obtained in all sites, even after remobilization for 50 weeks. This suggests that lengthy immobilization of a joint can cause long lasting articular cartilage proteoglycan alterations at the same time as collagen organization remains largely unchanged. Because proteoglycans exert strong influence on the biomechanical properties of cartilage, lengthy immobilization may jeopardize the well being of articular cartilage.

Amino Acids↗
PubMed1998

Articular cartilage superficial zone collagen birefringence reduced and cartilage thickness increased before surface fibrillation in experimental osteoarthritis.

OBJECTIVES: To investigate articular cartilage collagen network, thickness of birefringent cartilage zones, and glycosaminoglycan concentration in macroscopically normal looking knee joint cartilage of young beagles subjected to experimental slowly progressive osteoarthritis (OA). METHODS: OA was induced by a tibial 30 degree valgus osteotomy in 15 female beagles at the age of 3 months. Fifteen sisters were controls. Cartilage specimens were collected seven (Group 1) and 18 months (Group 2) postoperatively. Collagen induced optical path difference and cartilage zone thickness measurements were determined from histological sections of articular cartilage with smooth and intact surface by computer assisted quantitative polarised light microscopy. Volume density of cartilage collagen fibrils was determined by image analysis from transmission electron micrographs and content of glycosaminoglycans by quantitative digital densitometry from histological sections. RESULTS: In the superficial zone of the lateral tibial and femoral cartilage, the collagen induced optical path difference (birefringence) decreased by 19 to 71% (p < 0.05) seven months postoperatively. This suggests that severe superficial collagen fibril network deterioration took place, as 18 months postoperatively, macroscopic and microscopic OA was present in many cartilage areas. Thickness of the uncalcified cartilage increased while the superficial zone became thinner in the same sites. In operated dogs, glycosaminoglycan content first increased (Group 1) in the lateral tibial condyle and then decreased (Group 2) (p < 0.05). CONCLUSION: In this OA model, derangement of the superficial zone collagen network was the probable reason for birefringence reduction. This change occurred well before macroscopic OA.

Animals↗
PubMed1997

Specimen preparation and quantification of collagen birefringence in unstained sections of articular cartilage using image analysis and polarizing light microscopy.

To establish an optimal method for analysis of the collagen structures from unstained tissue sections, a computerized image analysis system using a charge coupled device camera coupled to a polarizing light microscope was used. Retardation values of birefringence, which are proportional to the content and fibril orientation of collagen in the extracellular matrix of articular cartilage, were determined from sections prepared in different ways. In the superficial zone of articular cartilage, the highest retardation values were recorded from sections cut parallel to the so-called split lines indicating the anisotropic arrangement of collagen. Complete digestion of glycosaminoglycans reduced the retardation value by approximately 6.0%, suggesting a minor, but not insignificant, contribution of glycosaminoglycans to the birefringence of the matrix. The use of a mounting medium with a refractive index close to that of the collagen (e.g. DPX) increased the specificity of the method, since the optical anisotropy of collagen derives predominantly from the intrinsic (structural) birefringence. In conclusion, analysis of unstained sections after careful removal of paraffin and glycosaminoglycans from the tissues provides a sensitive and rapid quantitative assessment of oriented collagen structures in articular cartilage.

Animals↗
PubMed1996

Decreased birefringence of the superficial zone collagen network in the canine knee (stifle) articular cartilage after long distance running training, detected by quantitative polarised light microscopy.

OBJECTIVE: To investigate the effects of a one year programme of running training (up to 40 km/day for 15 weeks) on the spatial orientation pattern of collagen and glycosaminoglycans in articular cartilage in different parts of the knee (stifle) and shoulder joints of young beagle dogs. METHODS: Area specific measurements of the optical path difference (= retardation, gamma) and the cartilage zone thickness were performed using conventional procedures and a new computer based quantitative polarised light microscopy method. Transmission electron microscopy was used to determine the zonal volume density of collagen fibrils. The concentrations of collagen and hydroxypyridinium crosslinks were investigated biochemically. RESULTS: Running training decreased gamma by 24-34% (p < 0.05) in the superficial zone of the lateral femoral condyle articular cartilage and at the centre of the tibial condyles. Gamma of glycosaminoglycans decreased by 26% (p < 0.05) in the superficial zone of the lateral condyle of the femur, but at the same site the volume density of collagen fibrils was unchanged. Neither the collagen concentration nor the concentration of hydroxypyridinium crosslinks was altered as a result of running. In both control and runner dogs, the thickness and gamma values of the superficial zone were greater in the humerus and the femur than in the tibia. CONCLUSION: Endurance type running exercise in beagles caused a reduction in the superficial zone birefringence of the articular cartilage, which indicates either a disorganisation or a reorientation of the superficial zone collagen network. Articular cartilage showed marked variability of collagen network organisation over the different knee (stifle) joint articular surfaces.

Amino Acids↗