Scapular notching is the most common reported complication of reverse shoulder arthroplasty, occurring in 44 to 96% of patients having a reverse shoulder designed with a medialised glenoid center of rotation (CoR) (Table 1)2-9.
Reported Scapular Notching Rates for Grammont-Style Reverse Shoulder Prostheses
Recent work has recommended design modifications for Grammont reverse shoulder manufacturers and surgical technique modifications for surgeons to improve range of motion and stability and reduce scapular notching10-19. A radiographic analysis of 226 patients who received the Exactech Equinoxe® Reverse Shoulder reported a 9.7% scapular notching rate with a reverse shoulder prosthesis whose CoR is slightly lateralised (2mm) relative to the glenoid. At a mean follow up of 21.2 months1, 2.7% of patients had a grade 2 notch and no grade 3 or 4 notches were observed.
Minimised Scapular Notching
The Equinoxe Reverse is designed to minimise scapular notching and enhance glenoid fixation. Its components build off the Equinoxe platform primary and fracture humeral stems, which provide intra-operative flexibility and enable surgeons to convert a well-fixed stem to a reverse without stem removal. The Equinoxe Reverse lateralises the humerus, which addresses the scapular notching challenge, by using larger diameter glenospheres (38, 42 and 46mm) and decreasing the humeral neck angle to 145 degrees. Additionally, placing the humeral tray on top of the resection eliminates the need to conically ream the proximal humerus, improves exposure and allows for larger glenospheres to be implanted (i.e., the size of the proximal humerus does not dictate the size of the glenosphere).
Reported Scapular Notching Rates for Grammont-Style Reverse Shoulder Prostheses
These radiographic results for scapular notching are very favorable (~7x reduction in the overall scapular notching rate) relative to other published complications rates: as described in Table 1, the weighted average scapular notching rate reported for medialised glenoid CoR reverse shoulder designs is 68.2%, where 20.9% have a notch greater than grade 22-9. These results confirm the conclusions of previous work that demonstrated that subtle prosthesis designs changes (i.e., inferiorly shifted glenosphere/superiorly shifted baseplate peg, curved back glenoid plate, 145° humeral neck, 2mm lateralised CoR) can dramatically reduce impingement and improve range of motion(Table 2)11,12,15,17.
Greater Range of Motion
The innovative Equinoxe glenoid baseplate design has a built-in offset that distally shifts the glenosphere to a position that decreases the likelihood of humeral liner impingement on the inferior glenoid20,21. This offset negates the need for additional bone-consuming implantation techniques (i.e., inferiorly tilting the baseplate or pre-notching the bone)11, 12, 15, 17. The increased stability provided by the larger diameter glenospheres enable the humeral liners to be less constrained relative to other systems and thereby permits greater range of motion prior to impingement20,21. The extended glenosphere articular surface and chamfered sides maximise inferior overhang to minimise the potential for scapular notching and improve range of motion.
The results of this study1 also demonstrate significant differences in both the glenoid plate position and glenosphere overhang between males and females and between patients with and without a notch. Gender differences result from differences in bone size, reflected by the larger percentage of males who received a 42 or 46mm glenosphere (73.2% vs 24.5% of females who received a 42 or 46mm glenosphere). Given this implant size distribution, this study identifies differences and makes recommendations for optimal implant placement to reduce notching in males and females. These recommendations are specific to the Equinoxe reverse shoulder; care should be made when extrapolating these results to other reverse shoulder devices due to differences in design parameters. Additionally, there is a functional limit to how