Stephanie Muh, MD
The use of press-fit humeral components for reverse shoulder arthroplasty has become more common in shoulder replacement surgery. Historically, humeral fixation was achieved with cementation techniques. However, due to increased operating time for cementation and added difficulty with higher complications in revisions during humeral component removal, surgeons have increasingly transitioned to press-fit humeral stems.
This article is a retrospective review of primary reverse shoulder replacements implanted with a modular diaphyseal press-fit humeral stem. Total hip literature has shown that distal press-fit stems obtain control through the medullary canal. The torsional stress is then transferred to proximal fixation and leads to increased stress shielding proximally with corresponding bone loss. This seems to be demonstrated in this study as well. With only a short-term follow-up, the authors found minimal radiolucent lines around distal fixation. However, 97% of radiographs demonstrated radiolucent lines around the smooth metaphyseal component. Additionally, the authors found progression of these radiolucent lines during the first two years. The authors claim the radiolucent line progression stabilizes after two years, however their mean follow up was 42 months (three and a half years). I do not believe this is sufficient time to truly access whether evidence of radiolucent lines has stabilized.
The evidence of proximal humeral bone loss is concerning and brings up an interesting clinical question. How do we revise shoulders with massive proximal bone loss? While the long-term outcomes are not known, the potential of revision surgery with extensive proximal bone loss will be a challenge. As a young fellowship-trained shoulder surgeon, I will have to be prepared to treat these difficult cases. Currently there are few options available for extensive proximal bone loss. Historically allografts have been used to reconstruct the proximal humerus. However, there are concerns with graft resorption, nonunion at graft-host junction, and de novo infection. In my opinion, an implant that proximally recreates the proximal bone allowing for increased humeral lateralization and deltoid wrapping and improved joint mechanics and stability is critical. Additionally, the distal fixation should provide immediate stability with decreased torsional stress to avoid additional proximal stress shielding.
In my experience, the Equinoxe Humeral Reconstruction Prosthesis provides a modular implant that recreates the humeral bone loss proximally while allowing for both intramedullary and extramedullary distal fixation.
This is a case of a 75 year old male who had a revision reverse TSA with traditional Grammont-style humeral prosthesis in 2013 for a failed cemented hemiarthroplasty. He presented four years out with worsening pain and function. X-rays demonstrated a loose humeral component with extensive proximal bone loss.
The implant proximally demonstrates appropriate humeral lateralization with the contour of the proximal body lateral to the acromion. Distal fixation was achieved with intramedullary cemented stem and extramedullary hydroxyapatite coated collar.
Stephanie Muh, MD, is deputy chief of service in the department of orthopaedics at Henry Ford Hospital West Bloomfield where she specializes in shoulder and elbow reconstruction, rotator cuff repair and arthritis. Dr. Muh completed her residency in orthopaedic surgery at the Henry Ford Hospital and shoulder and elbow fellowship at Case Western Reserve University/University Hospitals of Cleveland.