OPN: Can you summarise your biomechanical findings presented at the International Congress on Shoulder and Elbow Surgery (ICSES) in April?
HR: This is an incredibly exciting time in the history of shoulder arthroplasty. We are beginning to discover that the two complications seen most often in reverse shoulder patients can be addressed with implant design improvements. Our team has seen scapular notching and instability decline dramatically2,3 with the use of the Equinoxe Shoulder System. And while I do believe we are excellent surgeons, there is no doubt that the implant design positions us for success.
To put a finer point on it, our published multi-centered scapular notching rate has been 13% with minimum two-year follow-up2 with a very low rate of instability.3 I was privileged to present a comparison of different reverse shoulder designs at the ICSES in Nagoya, Japan.4,5,6 We believe this may establish the biomechanical nomenclature to better understand the impact of different implant designs.
JZ: I agree, and what impresses me the most is the range of motion that we’re seeing with Equinoxe patients. Because we have such low rates of instability with the Equinoxe implant,3 it’s given us the latitude to assess the subscapularis’ impact on range of motion.
Our team has found that because the humerus is distally shifted with the reverse, the subscapularis acts primarily as an adductor during abduction and causes the deltoid to have to work harder to elevate the arm.6,7 So, if the implant is inherently stable by design, as we have found ours to be, repairing the subscapularis may be unnecessary, and it can limit a patient’s ability to lift the arm. In fact, Dr. Routman has submitted this analysis as an abstract at the upcoming British Elbow and Shoulder Society (BESS) annual scientific meeting.
OPN: Please tell us about the Equinoxe design parameters that have improved implant stability.
HR: Because the Equinoxe builds on top of the humerus, we are able to lateralise the humerus while maintaining the center of rotation only 2mm off the face of the glenoid. This increases the deltoid wrapping angle (illustrated in the image below) and allows the deltoid to compress the humerus into the glenoid, thereby improving stability.4,5,6
OPN: You mentioned building on top of the humerus. Does that feature of the Equinoxe Platform System really improve patient outcomes?
JZ: While intuitively we knew that a revision-friendly platform stem would be better for the patient, the clinical data collected by Lynn Crosby, MD and Tom Wright, MD quantified the significance of it.1
Specifically, 67 patients underwent revision to reverse total shoulder arthroplasties at two different academic institutions. The patients were separated into two groups. Patients in Group 1 had a traditional stem that had to be removed during the revision. Patients in Group 2 had a platform stem that was retained during the revision.
The data from that study is quite impressive. Additionally, when calculating the cost of the replacement stem as well as additional OR time, there are significant savings that come with a platform stem ($8-$15k in the United States).
OPN: What’s next for the Equinoxe?
HR: On a practical level, one of the things I find most helpful in the operating theatre is the new Equinoxe augmented glenoid solutions that help me preserve bone and overcome challenging glenoids. A significant portion of cuff tear arthropathy patients have superior wear. Historically we’ve had to ream down the bone to correct this wear, but with the new augmented glenoids, we can preserve the patient’s native bone8 and address the defect with the implant.
- Crosby LA, Wright TW. Revision Total Shoulder Arthroplasty with and without Humeral Stem Removal: How Much of a Difference Does it Make? In: Transactions of the 23rd Annual British Elbow and Shoulder Society Scientific Meeting. Torquay, United Kingdom; 2012.
- Roche, C. et al. Scapular Notching and Osteophyte Formation after Reverse Shoulder Replacement: Radiological Analysis of Implant Position in Male and Female Patients. The Bone and Joint Journal. Vol. 95-B, #4:530-535. 2013.
- Flurin, P. et al. A Correlation of Five Commonly Used Clinical Metrics to Measure Outcomes in Shoulder Arthroplasty. Trans. of the 58th Annual ORS Meeting. 2012.
- Roche, C. et al. Asymmetric Tensioning of the Rotator Cuff by Changing Humeral Retroversion in Reverse Shoulder Arthroplasty. Trans. of the International Shoulder and Elbow Congress. 2013.
- Roche, C. et al. Biomechanical Analysis of 3 Commercially Available Reverse Shoulder Designs in a Normal and Medially Eroded Scapula. Trans. of the International Shoulder and Elbow Congress. 2013.
- Hamilton, M. et al. The Effect of Reverse Shoulder Design on the Moment Arms of Muscles Surrounding the Joint During External Rotation. Trans. of the International Shoulder and Elbow Congress. 2013.
- Onstott, E. et al. Consequences of Concomitant Subscapularis Repair with Reverse Total Shoulder Arthroplasty. Trans. of the 58th Annual ORS Meeting. 2012.
- Roche, C. et al. Computer Assessment of Scapula Cortical and Cancellous Bone Removal When Correcting a Posterior Defect Using Three Different Glenoid Prosthesis Designs. Trans. of the 59th Annual ORS Meeting. 2013.