The reverse-ball-and-socket implant has been approved for use in the United States since 2004 for patients older than 70 years of age with an irreparable rotator cuff tear accompanied by arthritis. For most patients, shoulder pain is reduced and function is improved, allowing improved forward elevation of the shoulder. It is, however, linked to a relatively high risk (about 15 to 30 percent) of post-surgical complications, including dislocation and loosening of the implants.
When introducing orthopaedic residents to performing this complex procedure, April Armstrong, M.D. shares her own clinical tips and pearls that she believes have benefited her patients and reduced the need for revision surgery.
First and foremost, adequate exposure of the glenoid with appropriate releases of the soft tissue and the capsule are critical. Armstrong says, “The key is to have the inferior aspect of the glenosphere implant flush or slightly lower than the inferior aspect of the native glenoid surface. In order to do this, one must have full exposure of the inferior glenoid which is difficult since the axillary nerve and often scar tissue are there to contend with. Use the “tug test” to confirm the location of the axillary nerve when performing this exposure. This is where the axillary nerve is palpated as it runs anterior to the subscapularis and then gently tug on the undersurface of the deltoid, confirming the location of the nerve. Complete release of the inferior capsule is necessary to feel the neck of the glenoid.” Appropriate position of the glenosphere is important for the humerus to be able to clear the inferior aspect of the ball implant when adducting the arm. Otherwise the medial aspect of the humerus will impinge on any remaining native inferior glenoid bone when the patient adducts the arm and this leads to polyethylene wear and early failure of the implants. Also, it is important to avoid superior tilting of the glenosphere, it should be neutral or slightly inferiorly angulated relative to the glenoid. Often since the humeral head rides superiorly on the glenoid there is superior wear of the glenoid which can misguide tilting of the glenosphere. It is important to recognize this and be sure that the glenosphere is tilted appropriately.
Armstrong notes that “The natural inferior lip of the glenoid is prominent as the glenoid has a concave surface. I found that this natural inferior lip would make it harder to position the guide so that it was flush with the inferior surface of the glenoid or slightly tilted inferiorly and it would tend to push the orientation more superiorly. As a result, I have taken to minimally burring or ronguering down the natural inferior native lip so that it is flush with the inferior half of the glenoid, being careful not to compromise the subchondral bone, in order to avoid this tendency.” Glenoid exposure is difficult and takes time. It is best to not allow the deformity of the shoulder joint to dictate where the glenosphere is positioned, but rather pay close attention to the principles so that the implant is positioned optimally. Of course there are times where there is significant bone loss of the glenoid and other bone grafting and implant techniques may be required. Optimal glenosphere position is still a hot topic of discussion, let alone glenosphere design and fixation techniques.
“The reverse ball and socket concept continues to be an area of focused research and I am sure that the principles will continue to evolve overtime,” says Armstrong.
April Armstrong, M.D.
Orthopaedic surgeon, shoulder and elbow, associate professor, orthopaedics and rehabilitation
- Fellowship: Orthopaedic surgery- shoulder and elbow, Washington University Barnes-Jewish Hospital, St. Louis, Missouri
- Fellowship: Orthopaedic surgery- hand and upper extremity, London Health Sciences Centre, London, Ontario
- Residency: Orthopaedic surgery, London Health Sciences Centre, London, Ontario
- Medical School: University of Western Ontario Schulich School of Medicine and Dentistry, London, Ontario