Healthesystems' semi-annual RxInformer clinical journal tackles the issue of degenerative conditions in workers' compensation, and cites two WCRI studies:

Degenerative comorbid conditions are present in 19% of claims and can drive up claim costs and disability duration. Many of these degenerative conditions are more common in older workers, a fact compounded by the continued aging of the workforce.
Degenerative conditions can be defined as illnesses that cause a progressive breakdown of cells, tissues, or organs over time, leading to a decline in function. These conditions can affect various parts of the body, but when discussed in the context of workers’ comp, “degenerative conditions” often refers to such conditions of the musculoskeletal variety...

The Workers’ Compensation Research Institute (WCRI) found that degenerative comorbid conditions are present in 18.7% of workers’ comp claims. This includes:

Osteoarthritis, found in 9.7% of claims
Spondylosis (with or without nerve involvement), found in 6.2% of claims
Degenerative disc disease, found in 5.6% of claims

You can read the full article here.  

The WCRI studies that they cite are Degenerative and Comorbid Conditions in Workers’ Compensation and Patterns and Trends of High-Cost Claims Involving Back and Shoulder Injuries.  Click the links for information on how to download a copy!