Internal consistency and factor structure of Jenkins Sleep Scale: cross-sectional cohort study among 80 000 adults.

OBJECTIVES: To assess the internal consistency and construct validity of the Finnish translation of the Jenkins Sleep Scale (JSS) in a large healthy working-age population with diverse work characteristics. DESIGN: Survey-based cross-sectional cohort study. SETTING: Survey conducted by an institute of occupational health. PARTICIPANTS: Employees of 10 towns and 6 hospital districts. PRIMARY AND SECONDARY OUTCOME MEASURES: The internal consistency defined by a Cronbach's alpha. Exploratory and confirmatory factor analyses to evaluate the construct structure of the JSS. RESULTS: Of 81 136 respondents, 14 890 (18%) were men and 66 246 (82%) were women. Their average age was 52.1 (13.2) years. Of the respondents, 41 823 (52%) were sleeping 7 or less hours per night. The mean JSS total score was 6.4 (4.8) points. The JSS demonstrated high internal consistency with an alpha of 0.80 (lower 95% confidence limit 0.80). Exploratory factor analysis supported a one-factor solution with eigenvalue of 1.94. Confirmatory factor analysis showed that all four items were positively correlated with a single common factor explaining 44%-61% of common factor's variance. CONCLUSIONS: The Finnish translation of JSS was found to be a unidimensional scale with good internal consistency. As such, the scale may be recommended as a practicable questionnaire when studying sleep difficulties in a healthy working-age population.

Intertester and intratester reliability of a movement control test battery for patients with knee osteoarthritis and controls.

OBJECTIVES: To develop a test battery of movement control (MC) tests and assess its intertester and intratester reliability. METHODS: 29 subjects with knee OA with mean age of 64.7 (SD 8.7) years and 12 controls without either knee pain or previous diagnosis of OA (mean age 36.6 (SD 16.2) years) were included. Two experienced physiotherapists rated the filmed test performance of six MC tests blinded to the patients and to each other on 3-point scale as correct, incorrect or failed. Weighted kappa coefficient (wK) with 95% confidence interval (95%CI) and the percentage of agreement were calculated for each test. RESULTS: One-leg stance, one-leg squat 30 degrees and step down tests showed moderate to excellent inter- and intratester reliability with wK ranging between 0.43-0.85 for intertester and 0.51-0.80 for intratester reliability. The reliability of the 90 degrees squat test, small squat and step up tests was poor (wK ranging between 0.09-0.50). CONCLUSIONS: One-leg stance test, one-leg squat 30 degrees and step down test are reliable in the subjects with knee OA and controls. Further studies are needed to evaluate the discriminative validity of the reliable tests.

Magnetic resonance imaging (MRI)-defined cartilage degeneration and joint pain are associated with poor physical function in knee osteoarthritis - the Oulu Knee Osteoarthritis study.

OBJECTIVE: The main aim was to investigate the associations between Magnetic Resonance Imaging (MRI)-defined structural pathologies of the knee and physical function. DESIGN: A cohort study with frequency matching on age and sex with eighty symptomatic subjects with knee pain and suspicion or diagnosis of knee osteoarthritis (OA) and 57 asymptomatic subjects was conducted. The subjects underwent knee MRI, and the severity of structural changes was graded by MRI Osteoarthritis Knee Score (MOAKS) in separate knee locations. WOMAC function subscores were recorded and physical function tests (20-m and 5-min walk, stair ascending and descending, timed up & go and repeated sit-to-stand tests) performed. The association between MRI-defined structural pathologies and physical function tests and WOMAC function subscores were evaluated by linear regression analysis with adjustment for demographic factors, other MRI-features and pain with using effect size (ES) as a measure of the magnitude of an association. RESULTS: Cartilage degeneration showed significant association with poor physical performance in TUG-, stair ascending and descending-, 20-m- and 5-min walk-tests (ESs in the subjects with cartilage degeneration anywhere between 0.134 [95%CI 0.037-0.238] and 0.224 [0.013-0.335]) and with increased WOMAC function subscore (ES in the subjects with cartilage degeneration anywhere 0.088 [0.012-0.103]). Also, lateral meniscus maceration and extrusion were associated with poor performance in stair ascending test (ESs 0.067 [0.008-0.163] and 0.077 [0.012-0.177]). CONCLUSIONS: After adjustments cartilage degeneration was associated with both decreased self-reported physical function and poor performance in the physical function tests. Furthermore, subjects with lateral meniscus maceration and extrusions showed significantly worse performance in stair ascending tests.

Associations between MRI-defined structural pathology and generalized and localized knee pain - the Oulu Knee Osteoarthritis study.

OBJECTIVE: To determine the associations between multi-feature structural pathology assessed using magnetic resonance imaging (MRI) and the presence of knee pain, and to determine the associations between the locations of structural changes and different knee pain patterns. METHOD: Eighty symptomatic subjects with knee pain and suspicion or diagnosis of knee OA and 63 asymptomatic subjects underwent knee MRI. Severity of structural changes was graded by MRI Osteoarthritis Knee Score (MOAKS) in separate knee locations. The associations between cartilage damage, bone marrow lesions (BMLs), osteophytes, Hoffa's synovitis, effusion-synovitis, meniscal damage and structural pathologies in ligaments, tendons and bursas and both the presence of pain and the knee pain patterns were assessed. RESULTS: The presence of Hoffa's synovitis (adjusted RR 1.6, 95% CI 1.2-1.3) and osteophytes in any region (2.07, 1.19-3.60) was significantly associated with the presence of pain. Any Hoffa's synovitis was associated with patellar pain (adjusted RR 4.70, 95% CI 1.19-3.60) and moderate-to-severe Hoffa's synovitis with diffuse pain (2.25, 1.13-4.50). Medial knee pain was associated with cartilage loss in the medial tibia (adjusted RR 2.66, 95% CI 1.22-5.80), osteophytes in the medial tibia (2.66, 1.17-6.07) and medial femur (2.55, 1.07-6.09), medial meniscal maceration (2.20, 1.01-4.79) and anterior meniscal extrusions (2.78, 1.14-6.75). CONCLUSIONS: Hoffa's synovitis and osteophytes were strongly associated with the presence of knee pain. Medial pain was associated most often with medially located structural pathologies.

Repeatability of knee impulsive loading measurements with skin-mounted accelerometers and lower limb surface electromyographic recordings during gait in knee osteoarthritic and asymptomatic individuals.

OBJECTIVES: To determine the repeatability of knee joint impulsive loading measurements with skin-mounted accelerometers (SMAs) and lower limb surface electromyography (EMG) recordings during gait. METHODS: Triaxial SMA and EMG from 4 muscles during level and stair walking in nine healthy and nine knee osteoarthritis (OA) subjects were used. The initial peak acceleration (IPA), root mean square (RMS), maximal acceleration transient rate (ATRmax) and mean EMG activity (EMGact) were calculated. The coefficient of variation (CV) and the intraclass correlation coefficient (ICC) were calculated to measure repeatability. RESULTS: The CV and ICC of RMS accelerations ranged from 4.9% to 10.9% and from 0.69 to 0.96 in both study groups during level walking. The CV and ICC of IPA and ATRmax varied from 7.7% to 14.2% and from 0.85 to 0.99 during level and stairs up walking in healthy subjects. The CV and ICC of EMGact ranged from 8.3% to 31.7% and from 0.16 to 0.97 in both study groups. CONCLUSIONS: RMS accelerations exhibited good repeatability during walking in healthy and knee OA subjects. The repeatability of EMG measurements was acceptable in healthy subjects depending on the measured muscles.

Physical function and properties of quadriceps femoris muscle after bariatric surgery and subsequent weight loss.

OBJECTIVES: To investigate the effects of bariatric surgery-induced weight loss on physical function, the properties of quadriceps femoris muscle (QFM), and the subjective disabilities of the subjects with excessive weight. METHODS: Thirteen female and three male subjects were studied before and 8.8 months after Roux-en-Y gastric bypass (RYGP) operation. The health-related quality of life (RAND-36) and the self-reported disease-specific joint symptoms (WOMAC) were estimated. The objective physical function was evaluated with sock, repeated sit-to-stand, 6-minute walk, stair ascending and descending and timed up and go tests and the properties of the QFM were measured with ultrasound. RESULTS: The average weight loss was 27.3 kg. Objectively measured physical function improved after RYGP operation. Physical functioning, physical role functioning and general health domain scores of the RAND-36 were significantly improved. The stiffness and function scores were lower after RYGP operation in knee OA subjects. The subcutaneous fat thickness and the absolute muscle thickness of QFM decreased, but the ratio of muscle cross sectional area/total body weight did not change. The fat and connective tissue proportion in the QFM muscle were significantly increased. CONCLUSIONS: The RYPG-surgery-induced weight loss exerts a positive impact on physical function but a negative impact on a muscle structure.

Risk factors for the development of hip osteoarthritis: a population-based prospective study.

OBJECTIVES: Potential risk factors and their roles in the aetiology of hip OA are poorly understood. We analysed several alleged risk factors predisposing to hip OA in a 22-yr prospective study. METHODS: A comprehensive health survey was carried out in 1978-80 in a nationally representative sample of adult Finns. In 2000-01, 1286 participants in that survey were invited for re-examination, and 909 agreed to participate. After excluding those with hip OA at the baseline and those who were no longer working, a total of 840 subjects constituted the present study population. Hip OA was diagnosed on the basis of a standardized clinical examination by physicians who applied uniform criteria both at the baseline and at the re-examination phase. RESULTS: After 22 yrs of follow-up, hip OA was diagnosed in 41 subjects (4.9%). Heavy manual labour predicted the risk of developing hip OA [adjusted odds ratio (OR) 6.7; 95% CI 2.3, 19.5]. Permanent damage as a consequence of any musculoskeletal injury was also an independent predictor of hip OA (adjusted OR 5.0; 95% CI 1.9, 13.3). BMI, smoking, alcohol intake and leisure time physical activity were not factors which were predictive for hip OA. CONCLUSION: Heavy physical stress at work and major musculoskeletal injuries are associated with an increased risk of developing clinically diagnosed hip OA.

Relative bone mineral density measured by metacarpal index (MCI) and chronic spinal syndromes: an epidemiological study.

OBJECTIVES: The results of previous studies on the association between bone mineral density (BMD) and chronic spinal syndromes have been contradictory. Therefore, we studied relative BMD measured by the metacarpal index (MCI) and its associations with chronic neck and low-back syndromes and diffuse idiopathic skeletal hyperostosis (DISH). METHODS: A population sample of 8000 Finns aged 30 years and over was invited to a comprehensive health examination in 1978-1980; 90% complied. In the clinical phase, a trained physician diagnosed chronic neck and low-back syndromes. Hand and chest radiographs were taken from 3568 participants to determine the MCI and to diagnose DISH. Of these, 340 subjects were re-examined clinically in 2000. RESULTS: After adjusting for potential confounding factors, a high MCI showed a significant cross-sectional association with chronic neck syndrome and DISH. The odds ratio (OR) per increment of one standard deviation (0.1) of MCI for chronic neck syndrome was 1.33 [95% confidence interval (CI) 1.21-1.47] and for DISH 1.29 (95% CI 1.04-1.60). No association was found between MCI and chronic low-back syndrome. In the follow-up setting, however, baseline MCI did not predict the incidence of chronic neck or low-back syndromes. CONCLUSIONS: Relative BMD is directly proportional to the prevalence of chronic neck syndrome. Further studies are needed to clarify the mechanisms of the association. The close association found between high relative BMD and DISH suggests a joint metabolic factor, which needs to be studied further to determine its effects on bones and intervertebral discs.

Agreement between clinical and radiological methods of diagnosing knee osteoarthritis.

OBJECTIVE: To determine the agreement between clinical diagnosis and different radiological grading scales of knee osteoarthritis (OA) in an epidemiological study. METHODS: Health 2000 Survey is an extensive population study focusing on major health problems in a representative sample of 8028 Finns over 30 years of age. In the survey, physicians diagnosed knee OA on the basis of physical status, symptoms, and medical history. A total of 130 participants (mean age 60 years, 68% female) were re-examined 1 year later (Kuopio OA 2000 Study) to determine the agreement between clinical and radiological diagnosis as well as between three different radiological grading scales (Kellgren and Lawrence, Ahlbäck, and Piperno). Weight-bearing knee radiographs were taken and graded by a radiologist in Kuopio University Hospital. The history of knee symptoms was obtained using the Western Ontario MacMaster (WOMAC) and Lequesne questionnaires. RESULTS: Knee OA was diagnosed clinically in 17.7% and radiologically in 24.6-30% of participants. The strength of agreement was moderate (kappa values 0.34-0.54) between the clinical and the radiological diagnosis and substantial (0.62-0.78) between the different radiological scales. Those subjects identified by any diagnostic method as having OA in either knee reported significantly more symptoms and disability than the other subjects. CONCLUSION: The agreement between the clinical diagnosis performed in a large population study and radiological grading scales was only moderate. By contrast, the agreement between different radiological scales was substantial.

Association of radiological hand osteoarthritis with bone mineral mass: a population study.

OBJECTIVES: A number of previous studies have reported an inverse relationship between osteoarthritis and osteoporosis. However, the association has remained controversial because osteoarthritis in hand joints seems to associate differently from osteoarthritis in weight-bearing joints with bone mineral mass. We studied osteoarthritis in distal interphalangeal (DIP) joints and osteoarthritis in the base of the thumb (CMC-1) for their cross-sectional associations with metacarpal cortical bone mineral mass, and for their prediction of calcaneal broadband ultrasound attenuation. METHODS: A population sample of 8000 Finns aged 30 yr and over was invited to a comprehensive health examination in 1978-1980; 90% complied. Hand radiographs were taken from 3568 participants to diagnose osteoarthritis in various hand joints, and to determine two indicators of cortical bone mineral mass, the combined cortical thickness (CCT) and the metacarpal index (MCI). Calcaneal broadband ultrasound attenuation was measured 20 yr later in 340 of these participants with the Sahara sonometer. RESULTS: In the cross-sectional setting, osteoarthritis in the DIP joints and osteoarthritis in the base of the thumb (CMC-1) were significantly associated with low CCT and low MCI. These associations were proportional to the radiological severity of osteoarthritis. In the follow-up setting, symmetrical DIP osteoarthritis adjusted for age, sex, body mass index, smoking, education, workload and MCI significantly predicted low values of broadband ultrasound attenuation. CONCLUSIONS: Our results indicate a direct relation of both radiological DIP osteoarthritis and CMC-1 osteoarthritis with low cortical bone mineral mass, in proportion to the severity of osteoarthritis. The presence of symmetrical DIP osteoarthritis, a possible indicator of generalized osteoarthritis, suggests an increased risk of osteoporosis over time.

Physical therapy and rehabilitation programs in the management of hip osteoarthritis.

Nonpharmacological treatment programmes are as important as drug treatment in hip osteoarthritis (OA). Drugs (analgesic and nonsteroidal anti-inflammatory drugs) should not be used as sole treatments in hip OA. Patient education and weight reduction are the primary therapeutic approaches. Different types of exercises are beneficial for patients with hip OA. Occupational therapy plays a central role in the management of hip OA patients with functional limitations. More and better-designed trials are needed to evaluate the efficacy of nonpharmacological treatment programmes used in hip OA.

Osteoarthritis of finger joints in Finns aged 30 or over: prevalence, determinants, and association with mortality.

BACKGROUND: Prevalence and risk factors of osteoarthritis (OA) in finger joints have been amply explored in previous studies. However, no study has focused on finger joint OA as a predictor of mortality. OBJECTIVE: To investigate finger joint OA for its associations with alleged risk factors and with life expectancy in an extensive health survey. METHODS: From 1978 to 1980 a representative population sample of 8000 Finns aged 30 years or over was invited to participate in a comprehensive health examination; 90% accepted. Hand radiographs were taken from 3595 subjects. By the end of 1994, 897 of these had died. RESULTS: The prevalence of OA of Kellgren's grade 2 to 4 in any finger joint and in at least two symmetrical pairs of distal interphalangeal joints (DIPs) was 44.8% and 16.0%, respectively. Age and body mass index were significant determinants for OA both in any finger joint and in symmetrical DIP OA. The history of physical workload in women showed a positive association with OA in any finger joint. Smoking in men seemed to protect against symmetrical DIP OA. As adjusted for the determinants above, symmetrical DIP OA predicted mortality in women (relative risk (RR), 1.23; 95% confidence interval (95% CI) 1.01 to 1.51), but not in men (RR 0.89; 95% CI 0.68 to 1.16). In men, however, OA in any finger joint significantly predicted cardiovascular deaths (RR 1.42; 95% CI 1.05 to 1.92). CONCLUSION: OA in any finger joint and symmetrical DIP OA have different risk factor profiles and predict mortality in different patterns between men and women.

Use of health-care services, work absenteeism, leisure-time physical activity, musculoskeletal symptoms and physical performance after vocationally oriented medical rehabilitation-description of the courses and a one-and-a-half-year follow-up study with farmers, loggers, police officers and hairdressers.

The aim of this study was to evaluate the effectiveness of vocationally oriented medical rehabilitation (VOMR) carried out in institutions with regard to the use of health-care services, work absenteeism, leisure-time physical activity, musculoskeletal symptoms and physical performance during 112 years of follow-up. The prospective cohort study consisted of 265 patients from four different occupational groups (loggers, hairdressers, police officers and female farmers) who took part in VOMR courses in three inhouse phases, financed by the Finnish Social Insurance Institution, and who had chronic musculoskeletal symptoms in their back and neck. The subjective physical and mental strain of work, subjective neck-shoulder and low-back pain, use of health-care services and leisure-time physical activity were assessed with a questionnaires. The muscle strength of the upper and lower extremities and trunk was determined and maximal VO2 was measured using the direct maximal bicycle ergometer test. The subjective physical and mental strain of work, subjective neck-shoulder and low-back pain and physical performance showed positive significant development and improvement. The changes in the use of health-care services and work absenteeism were minor or insignificant. The general finding was that the results from the second phase of the VOMR courses did not differ from those of the third phase. VOMR courses had a beneficial effect on physical performance and subjective pain caused by neck and back musculoskeletal diseases of farmers, loggers, police officers and hairdressers within 112 years of follow-up, but VOMR courses did not decreased the use of health-care services.

Increased bone mineral content and bone size in the femoral neck of men with hip osteoarthritis.

OBJECTIVES: Even though clinical findings support the idea that hip osteoarthritis (OA) is associated with increased bone mineral density (BMD), the subject remains controversial. This study was therefore initiated to investigate the relation between the severity of hip OA and femoral and calcaneal BMD. METHODS: On the basis of the American College of Rheumatology criteria on classification of OA of the hip, 27 men (aged 47-64 years) with unilateral or bilateral hip OA and 30 age matched randomly selected healthy men were studied. Plain radiographs were graded using Li's scale from 0 (no OA) to 4 (severe OA). According to the side of the highest radiographic score from the patients with clinical hip OA, 29.6% had grade 1, 29.6% grade 2, and 40.8% grade 3 OA. Bone mineral content (BMC), areal BMD (BMD(areal)), and bone dimensions (area and width) were measured by dual x ray absorptiometry at the proximal femur. BMD(areal) of the calcaneus was measured from the central area of the bone. Volumetric measurements from magnetic resonance images of the femoral neck were used to create a BMD measure that was corrected for the femoral neck volume (BMD(mri)). RESULTS: There were no differences in weight, or body mass index between the study groups. There were no significant BMD(areal) differences in any of the subregions of the proximal femur (femoral neck and trochanter) or calcaneus between the OA and control groups. Neither did the BMD(mri) of the femoral neck differ between the groups. However, the BMC of the femoral neck was 18% higher (p<0.01) in patients with OA than in controls. Similarly femoral neck bone width and volume were 9% and 18% respectively higher (p<0.001) in patients with OA. CONCLUSIONS: The results suggest that men with hip OA have larger femoral neck size and consequently higher BMC than healthy controls matched for age and sex. There is no significant difference in femoral neck BMD (BMD(areal) or BMD(mri)) between the groups. Furthermore, increased BMD(areal) was not found in the peripheral skeleton. These findings suggest that hip OA is not associated with an increase in BMD(areal) in the femoral neck. However, the increase in BMC and bone size in patients with hip OA may play a part in the pathogenesis of the disease.

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.

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.

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.

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.