الفهرس 
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Abstract
OA is the most prevalent joint disease worldwide and one of the most crucial health problems in modern industrial societies. It is the foremost cause of disability in elder adults, as high as that for cardiovascular disease.
KOA is categorized as either primary or secondary, depending on its cause. Primary KOA is the consequence without any recognised reason of articular cartilage degeneration. While, secondary KOA is due to degeneration of articular cartilage due to a well-known reason.
Diagnosis of KOA can be established on the basis of; clinical symptoms, radiological features and/or arthroscopic examination. Radiographic OA definitions are depending mainly on the Kellgren-Lawrence classification which classify the extent of OA into grades from zero to four, relying on the presence and severity of radiographic features of the case. Arthroscopy considered as a typical diagnostic procedure and one of four most acceptable types of imaging examinations, based on modified Outerbridge classification system graded from 0 - 4. Clinical/symptomatic diagnosis was based on the American College of Rheumatology (ACR) criteria for KOA.
Risk factors leading to KOA development can be substantially varied, which may be modifiable or non-modifiable factors. Modifiable could be articular trauma, occupational (standing for long time and frequent knee bending), muscle weakness or imbalance, weight or health related (metabolic syndrome). While non-modifiable factors are more limited to be gender (females more common than males), age, genetics or ethnic. These factors could be also categorized into intrinsic factors or extrinsic factors.
Occupations which require repetitive bending have been demonstrated to be related with higher risk of radiographic KOA. Occupational kneeling and/or squatting are the main primary risk factors in correlation with knee conditions and also heavy lifting.
Methods:
Setting:
This study was conducted in orthopedic clinics and physical medicine clinic in Alexandria University Main Hospital and private orthopedic clinics.
Study design:
It is a hospital-based case control study.
Sample size:
This study included a sample of 440 individuals were recruited and divided into two groups. They were 220 cases and 220 controls, 213 males and 227 females, aged from 24 years to 75 years and randomly selected through random sampling.
Data collection:
Data was collected in two stages; an interviewer-administered questionnaire stage and a clinical examination stage. The questionnaire includes 28 items in four domains: personal data (12 items), medical history (6 items), pain assessment (5 items) and physical activity/workload (5 items).
Informed consent was signed by all participants after a simple and clear explanation of the research objectives and the study procedures.
Statistical analysis:
Collected data were analysed using the Statistical Package for Social Sciences (SPSS ver.20 Chicago, IL, USA). Pearson Chi square test was used to detect association between categorical variables and Spearman correlation coefficient used to correlate between quantitative variables. Student t-test for normally distributed variables, to compare between cases and controls. Mann Whitney test and Kruskal Wallis test were used to compare between cases group and controls group for quantitative not normally distributed data. Logistic regression analysis models were used to estimate OR of the most significant risk factors. Population attributable risks (PAR%) were tested for the risk factors and for both physical workload/activities; squatting/kneeling and lifting / carrying within cases. PAR% calculations were based on the adjusted OR in the final model of regression analysis.
Interaction analysis was performed to measure the impact of combination between potential risk factors that developing osteoarthritis on aside and physical workloads/activities; kneeling/squatting and lifting/carrying on the other side.
Accordingly, mode of interaction that was described by Saracci and Boffetta (1994) was figured out to quantify the combination effect.
Results:
Study results revealed that about half of participants were males (48.4%) while females (51.6%) with a mean age of 50.69 years. Regarding BMI, 46.8% of cases were overweight and about 30% were workers. Comparing cases and controls indicated significant difference between the two groups regarding family history of osteoarthritis and number of working weekly days. Osteoarthritic cases presented with pain (100%); two thirds of them had moderate intermittent pain, Heberden’s nodes (54%) and without knee joint previous surgeries (81%). OA diagnosed clinically/symptomatic and radiological in 35% of cases while radiological diagnosis only in 41% having grade III based on K-L scale and about half of cases bilaterally affected.
There was significant association between physical workload/activities tasks (lifting/carrying and walking) and the time practicing; whether it is less than ten years or ten years and more.
Logistic regression analysis was applied for four parameters; occupation, BMI, family history of osteoarthritis and number of working days per each week, as significant and common risk factors based on literature review and previous studies. Final models were done including occupation, family history of osteoarthritis and number of working days per each week, as risk factors to estimate their odds ratios accordingly in developing OA, BMI only was excluded. Odds ratio were (OR= 2.2, 95% CI [1.2 – 4.2]), (OR= 2.7, 95% CI [1.8 – 4.2]) and (OR= 2, 95% CI [1.2 – 3.4]), respectively.
Also, logistic regression analysis was applied for most common physical activities/workload tasks which were squatting/kneeling and lifting / carrying. Final model verified the significant difference for both, with (OR= 222, 95% CI [49.5 – 1000]) and (OR=2.5, 95% CI [1.2 – 5]), respectively. Multivariate analysis was adjusted for the previous four risk factors.
PAR% was estimated based on proportion of OA within population that could be attributed to workers category to be 18.94 %, family history of OA to be 33.8% and seven working days per week to be 19.2%.
About 82% of KOA of study population may be attributed to physical workload requiring squatting/kneeling, while 87.3% was the proportion of experiencing KOA in the study population that could be attributed to the lifting/carrying activity.
Interaction analysis was performed to measure the impact of combination between different risk factors and the two physical activities workload. Moderate and vigorous squatting/kneeling in any occupation category were significant and put the individual at high risk of developing KOA (p < .001). This was totally true as its mode of interaction was more than multiplicative. The same effect was concluded with lifting/carrying, with the same mode of interaction.
Also, measuring the effect of interaction between family history of OA and both physical activities workload, confirmed the same effect as occupation but with different mode of interaction. It was near multiplicative in the relation between family history and squatting/kneeling (OR=1726, 95% CI [197 – 15110]), while it was intermediate between family history and lifting/carrying (OR=42.7, 95% CI [16 – 114]).
The last interaction was measured between number of weekly working days and lifting/carrying activity, showing intermediate mode of interaction as an effect of this combination in developing KOA (OR=24, 95% CI [9 – 62]).