Traditional anatomic total shoulder replacements have been shown to aid in reducing pain and improving motion and function in very obese patients. But when compared with adults who are not obese (and who also receive an anatomic total shoulder replacement), results are definitely not as good. The obese patient is more likely to have problems and complications and less likely to be happy with the results.
The “normal” or anatomic shoulder replacement was designed to copy our real shoulder. The glenoid component (the socket) was designed to replace our anatomic shoulder socket with a thin, shallow plastic cup. The humeral head component was designed to replace the ball of the humerus with a metal ball that sits on top of the glenoid.
A different type of implant has been developed for use with older adults who need a shoulder replacement but who have a severe tear of the rotator cuff tendons. The four muscles and their tendons that make up the rotator cuff fit around the shoulder joint and help hold the joint stable yet provide full range-of-motion at the same time. This alternate replacement device is called a reverse total shoulder arthroplasty (RTSA).
But without an intact rotator cuff, the implant often loosens and/or the shoulder dislocates. This can be prevented by reversing the socket and the ball, placing the ball portion of the shoulder where the socket used to be and the socket where the ball or humeral head used to be. This new design provides a much more stable shoulder joint that can function without a rotator cuff. How well does it work with people who have an intact rotator cuff but have a different problem: they are obese.
To find out, the reverse total shoulder arthroplasty (RTSA) was used in three separate groups and results compared in this study. The three groups included 17 obese patients, 36 patients who are overweight, and 23 patients in the normal weight category. The patients were placed in each group according to height and weight using the World Health Organization’s well-known Body Mass Index or BMI measurements.
Patients ranged in age from 51 to 88 years old. Follow-up was started two weeks after surgery and continued at six weeks, three months, one year, and then every two years for up to five years. The study is ongoing but the mid-term results are published here.
Data collected and used to compare results included surgical time, amount of blood loss during the procedure, and length of stay in the hospital. They also compared postoperative complications (type and rate). And, indeed, they found that obese patients were able to regain significant amounts of lost motion but they also had significantly more complications than the other two groups. The obese patients lost more blood during the procedure, but surgical time and length of hospital stay were the same among all three groups.
Complications were greater in the obese group for several reasons. Surgical difficulties occur just due to the amount of adipose tissue (fat) that must be cut through to get to the shoulder joint. Fatty tissues tend to have less blood flow to them (they are said to be poorly vascularized). This lack of blood flow can delay or impair healing.
Many more patients in the obese group also had diabetes, a known factor in decreased circulation and delayed wound healing. And the infection rate of 18 per cent in the obese group was clearly much higher than for the nonobese group who had no (zero per cent) infections.
The authors concluded that obesity is NOT a contraindication to reverse total shoulder replacement. But patients should be warned of the high complication rate, especially for the risk of infection. Of course, they can also expect the same improvements in motion and reductions in pain obtained by nonobese patients. Time will tell if other changes (positive or negative) will occur in the long-term results. This study will continue with additional reports published in the future.