Hip and knee replacements are now a common surgical procedure with more than 700,000 total joint arthroplasties (TJAs) performed in the US every year. Due to the reduction in pain and increases in mobility experienced after having a TJA, it could be expected that weight loss may occur as a by-product of the surgery. But is this the case? This is the question posed by Maria Inacio, a doctoral candidate from the San Diego State University/University of California, San Diego, who is employed at Kaiser Permanente, and her colleagues at those institutions. They conducted a review of the current literature to find out.

Their results appear online in the journal Clinical Orthopaedics and Related Research®, published by Springer.

Obesity itself is one of the major risk factors leading to the need for a hip or knee replacement. Activity can be severely restricted by joint pain in these individuals and one might presume weight loss would occur postoperatively as mobility improves with increased activity levels. Such weight loss could reduce the risk of complications such as prosthetic loosening, thus reducing the chances of requiring further surgery.

The authors conducted a review of twelve studies meeting their criteria. They considered the studies thus far in this area to be of generally low quality with small sample sizes and poor methods, leading to a risk of bias. Overall the studies reported between 14 percent to 49 percent of patients had lost weight a year after having a TJA. However, the ranges of weight loss suggested inconsistent loss and the differences in the study designs meant that overall there was no conclusive pattern. In fact, the studies showed that more patients gained weight than lost.

In a CORR Insights® commentary on the manuscript, Stuart B. Goodman, MD, PhD, of Stanford University said, "Obese patients frequently tell clinicians that they are overweight because their painful hips or knees limit their physical activities and their capability to 'burn calories.' Unfortunately, after a comprehensive analysis of the data, the answer to this important question is still unknown."

Inacio and colleagues believe that since TJAs are such a common surgery, further research in this field is warranted and a large representative national study would be desirable. Weight loss, either to prevent the development of osteoarthritis or to reduce long-term morbidity after a hip or knee replacement is extremely desirable in this population. Current evidence is not sufficiently robust to provide an accurate picture, and clinically effective measures cannot be put into place unless the present situation is understood.