yes that is partly true Joanne, however-
Quadricep weakness is not the impairment, Hamsrtings are the impairment.
Per the research as well as studies performed by Vladamir Janda and NSCA, the quadriceps are STRONGER not weaker. The hamstrings are phasic weaker muscles in numerous studies not only on OA of the knee, but on contributing factors for ACL injuries, meniscal, etc,
The main causes based on SCIENCE and EVIDENCED Based Research are:
1-Obesity or increase in amount of adipose tissue loading the weighttbearing joints
2-Inactivity or lack thereof by most americans
3-Imbalanced diet which compliments #1 where there has been a surgence of Americans eating processed foods, fried foods, enormous amounts of sugar, soda, etc
4-Lack of flexibility of quadriceps and hip flexors. Increased tissue density creates increased compression, load to the tibiofemoral and patello femoral joint
Remember look at the research!