Exploring Long-Term Results of Shoulder Replacement Surgery
Hip and knee joint replacements have been around long enough now to have the results of long-term studies. But total shoulder replacements (TSR) are still new enough that the first 10- to 15-year follow-up studies are just coming out. In this report, surgeons from the Rochester, Minnesota Mayo Clinic present the longest duration study on shoulders with cemented metal-backed glenoid components.
Every joint replacement has two sides. In the case of the shoulder, there's the humeral component to replace the round head of the upper arm bone (the humerus). And there's the socket or glenoid side of the joint. The socket replacement can be made of all plastic called polyethylene, all metal, or a combination of both. The implants can be press-fitted (pressed into the bone without cement) or cemented in place.
The 100 patients in this study all received a cemented Neer-II metal-backed component (manufactured by Kirschner Medical in New Jersey). The patients were carefully selected for the study. They had to have a diagnosis of osteoporosis without a history of trauma. Follow-up had to be for at least two years. Anyone with a different kind of glenoid implant was not included in the study.
There is no real guideline for when to use the Neer-II metal-backed component. Studies have not shown one implant type has an advantage over the others. Some surgeons choose the metal-backed implant for patients who are large. The reason for this is because the metal-backed component is larger than the all-polyethylene implant. Smaller patients are given the all-polyethylene part because it is smaller and fits better.
The Mayo has a unique advantage in doing studies like this. They have a large number of patients whose information has been downloaded into their computer. Researchers can use the computer database to pull up specific patients and pertinent information.
In this case, all the computer files of patients who had a shoulder joint replacement could be collected. If the patients met the study criteria, then they received several surveys to fill out. Records on range-of-motion before and after the procedure were checked. And the results of X-rays were also included.
The outcome measures used to determine results included pain, shoulder range-of-motion, and function. Function was assessed based on a combination of pain, motion, and activity level. Activity was usually limited by the presence of pain and loss of motion. X-rays were examined by two independent shoulder surgeons. They didn't know the patients what the patients looked like clinically.
Suspicious or alarming X-rays findings included periprosthetic lucency (thinning of the bone around the implant), subluxation (partial dislocation of the implant), and erosion (wearing away) of the bone underneath the implant.
There were some complications that required a revision procedure. Loosening of the implant was the biggest problem. Other problems included polyethylene wear and bone fracture of the humerus (upper arm bone). The biggest concern was for the high rate of periprosthetic lucency.
Anyone with subluxation had decreased and painful motion. There were no such symptoms with bone changes (erosion or lucency). Patient results were rated as excellent in about half the group. The remaining half alternated between satisfactory and unsatisfactory in rating their results.
Most of the unhappiness with the outcomes were related to a loss of motion, presence of pain, or need for revision surgery. Men and women responded the same to questions about satisfaction, so the results weren't linked with gender (male versus female).
The main author of this study had previously done a study on patients receiving an all-polyethylene glenoid implant. The results of those patients were also compared to these patients. There was no indication that one type (polyethylene versus metal) was better than the other.
Most studies end the report by giving a list of limitations with the study. There were quite a few possible problem areas with this study. These limitations can sometimes affect how reliable or valid the study results are.
For example, there were three shoulder surgeons involved instead of one surgeon doing all the procedures in a consistent way. And even though patients with rotator cuff tears were screened out, there were still a few that were discovered at the time of surgery. The presence of a rotator cuff tear changes how the surgery is done.
Follow-up with X-rays wasn't always possible for patients who had moved or died. Range-of-motion was measured by different surgeons (again, instead of one surgeon consistently measuring everyone). And they did not use a special tool called a goniometer to get objective motion readings. And there wasn't consistency in deciding which patients should get the metal-backed implant.
But despite all the ifs, ands, or buts, the results represent an important step forward in tracking the results of shoulder replacement surgery using a specific component part. The authors suggest further follow-up is needed and especially further study on why there was such a high rate of bone lucency (thinning) around the implant in so many patients. For now, it can be said that using the cemented metal-backed glenoid implant provides pain relief and improved motion for patients with osteoarthritis.
Nattapol Tammachote, MD, et al. Long-Term Results of Cemented Metal-Backed Glenoid Components for Osteoarthritis of the Shoulder. In The Journal of Bone & Joint Surgery. January 2009. Vol. 91A. No. 1. Pp. 160-166.