Given the lack of predictive models to identify patients who are at risk for persistent pain after joint replacement, this study is a welcome start as it has identified a primary, though not surprising, risk factor: Diabetes.
Strong relationships have already been established between arthritis and high blood sugar. High glucose concentrations even below the diabetic level have been associated with tibial cartilage volume loss and bone lesions in women, and poor blood sugar control is known to contribute to the catabolic joint stew which breaks down joint bone and cartilage in arthritis in general. At a deeper level, a hormone called Osteocalcin which is a chemical messenger secreted only by the osteoblasts (bone stem cells) within your bones, has been demonstrated to be a crucial part of the blood sugar control system. A Columbia study back in 2010 established that your pancreas produces insulin, the insulin talks to your bone osteoblasts which in turn talk back through Osteocalcin, to help keep blood sugar in check.
This study set out to establish, or rule out, an association between persistent pain after joint replacement and disorders of glucose metabolism, metabolic syndrome and obesity. For the purpose of the study, persistent pain was defined as pain lasting 3 or more months in the operated joint. One hundred and ninety three Osteoarthritis patients, of which 74 were total hip, and 119 total knee, were surveyed 1-2 years after surgery. All patients’ blood sugar levels had been established and recorded prior to their surgery. After excluding participants for additional surgeries, 134 were actually studied. Various metrics were applied to account for age, sex and which joint operated. The results were 37% of the patients had painful joints and 14% had persistent pain, knee patients being more affected than hip patients. Of the three conditions considered, only previously diagnosed Diabetes was strongly associated with persistent pain (5/19 with diabetes, only 13/115 without), concluding that Diabetes is a risk factor for persistent pain 1-2 years post surgery for primary total hip and knee replacement patients.
The upshot? Though this was the obvious first place to look given the established relationship between blood sugar and arthritis, the results were significant. Optimistically, these findings will inspire additional research into identifying all the risk factors for post surgical persistent pain after joint replacement. While at some point injectable biologics will replace most orthopedic surgeries and joint replacements will be reserved for cases in which all other options have failed, at present, hip and knee replacements continue to be done routinely. Hopefully, this type of research will give physicians the opportunity to work on the risk factors BEFORE surgery, rather than the patients dealing with the consequences after the fact!