Many time it is but a person can have wear and tear OA without an accident
but with heavy use over a long time.

Here is a post from the past on  glucosamine.

Glucosamine is Associated with Improved Osteoarthritis Outcomes

Gillian A. Hawker1, Michal Abrahamowicz2, Roxane du Berger3, Annette
Wilkins4, Elizabeth Badley4. 1Women's College Campus of SWCHSC, Toronto,
ON, Canada; 2Department of Epidemiology and Biostatisitics, McGill
University, Montreal, PQ, Canada; 3Division of Clinical Epidemiology,
The Montreal General Hospital, Montreal, PQ, Canada; 4Arthritis
Community Research & Evaluation Unit, UHN, Toronto, ON, Canada

Purpose: To prospectively examine the effect of osteoarthritis (OA)
therapies on changes in OA pain and disability.

Methods: A prior study ('96-'98) established a population cohort of
2,411 individuals aged 55+ years with disabling hip/knee arthritis
(baseline). In '99, the cohort was invited to participate in a 5-year
follow-up study. Information was collected at baseline and annually:
age, sex, education, income, living circumstances, self-reported
comorbidity, use of therapies (NSAIDs, pain killers, steroid injection,
glucosamine, walking aids and devices), hip/knee joint replacement,
visits to arthritis health care professionals, and OA pain and
disability (WOMAC).

Three mixed regression models were used estimate associations between
current use of different therapies and repeated measurements of the
WOMAC, adjusting for sociodemographics, comorbidity and concurrent use
of other therapies. Model 1 assessed if individuals currently on a
therapy have better WOMAC scores across the repeated assessments than
those not using the therapy. Model 2 adjusted additionally for baseline
WOMAC values while Model 3 adjusted for the prior year WOMAC value to
investigate if change from last year is associated with recent use of
the therapy.

Results: 1,376 patients contributed a total of 4,119 assessments.
Baseline mean age was 72 years; 72% were female. The proportion using
glucosamine increased from 9% to 17% during the follow-up period.
Adjusting for sociodemographics and concurrent use of other therapies,
current glucosamine use was associated with lower WOMAC scores in all
models.

Across the repeated assessments, individuals taking glucosamine had a
mean WOMAC score 1.8 points lower than individuals with the same
characteristics and treatments who were not taking this therapy (95% CI:
0.5 to 3.0, p=0.005). This effect remained significant after adjusting
for baseline and final year WOMAC scores, which were on average lower by
1.5 (95% CI: 0.3 to 2.7, p=0.014) and 1.1 (95% CI: 0 to 2.3, p=0.05),
respectively.

No other therapy showed any association with improved outcomes. Other
significant predictors of lower WOMAC scores at follow-up were: younger
age, higher education and income, and male gender. Males had, on
average, WOMAC scores 4 points lower than women with the same
sociodemographics and treatments (mean 4 points lower; 95% CI: 2.6 to
5.4, p<0.0001).

Conclusion: Of the therapies considered, only glucosamine was associated
with an improvement in OA pain and disability providing support for the
benefits of this therapy in OA. The absence of an effect with other
therapies is likely due to confounding by indication, which is less
likely to impact non-physician-prescribed glucosamine use.

Dug,,, here is a site where most of your questions will be answered from a
person who has battled with his knees for many years up in Alaska.
http://home.gci.net/~cushman4/oa-gcs.htm

Harv