Recommended design and surgical technique modifications to reduce scapular notching

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 notching^10-19. 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 glenoid^20,21. 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 impingement^20,21. 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 much glenosphere overhang is achievable; implant positioning should take a particular patient’s soft tissue laxity into account. The primary limitation of this study is the degree that the study population represents the global reverse shoulder patient population; this concern is mitigated by the large sample size (n=226) and wide distribution of surgery sites (seven institutions: three teaching and four private hospitals; two different countries).

References

1. Roche, C. et al. Scapular Notching Radiographic Analysis: Recommendations for Glenoid Plate Positioning and Glenosphere Overhang in Male and Female Patients. Trans. of the 58th Annual ORS Meeting. 2012.
2. Sirveaux, F. et al. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive rupture of the cuff. JBJS 86-B: 388-395. 2004.
3. Werner, C. et al. Treatment of painful pseudoparaesis due to irreparable rotator cuff dysfunction with the Delta III reverse ball and socket total shoulder prosthesis. JBJS. Vol. 87-A. #7: 1476-1486. 2005.
4. Boileau, P. et al. The Grammont reverse shoulder prosthesis: results in cuff tear arthritis, fracture sequelae, and revision arthroplasty. JSES. 15(5):527-40. 2006.
5. Simovitch, R. et al. Predictors of scapular notching in patients managed with the Delta III reverse total shoulder replacement. JBJS. 89:588-600. 2007.
6. Karelse, A. et al. Prosthetic component relationship of the reverse Delta III total shoulder prosthesis in the transverse plane of the body. JSES. #14 (4): 602-607.2008.
7. Levigne, C. et al. Scapular notching in reverse shoulder arthroplasty: is it important to avoid it and how? CORR. Published online Nov 30. 2010.
8. Stechel, A. et al. Reversed shoulder arthroplasty in cuff tear arthritis, fracture sequelae, and revision arthroplasty. Acta Orthopaedica. 81 (3)367–372. 2010.
9. Kempton, L. et al. A radiographic analysis of the effects of prosthesis design on scapular notching following reverse total shoulder arthroplasty. JSES. #20: 571-576. 2011.
10. Nyffeler, R.W. et al. Biomechanical Relevance of Glenoid Component Positioning in the Reverse Delta III Total Shoulder Prosthesis. JSES. Vol. 14. #5: 524-528. 2005.
11. Roche, C. et al. Geometric analysis of the Grammont reverse shoulder prosthesis: an evaluation of the relationship between prosthetic design parameters and clinical failure modes. Proceedings of the 2006 ISTA Meeting. 2006.
12. Roche, C. et al. Geometric Analysis of the Grammont Reverse Shoulder Prosthesis: an evaluation of the relationship between prosthetic design parameters and clinical failure modes. Trans. of 53rd Annual ORS Meeting, 2007.
13. Kelly, J. et al. Optimizing Glenosphere Position and Fixation in Reverse Shoulder Arthroplasty, Part One: The 12mm rule. JSES. Vol. 17: 589-594. 2008.
14. Middernacht, B. et al. Consequences of Scapular Anatomy for Reversed Total Shoulder Arthroplasty. CORR. Vol. 466, #6: 1410-1418. 2008.
15. Roche, C. et al. An Evaluation of the Relationships between Reverse Shoulder Design Parameters and Clinical Failure Modes. JSES. Vol. 18: 734-741. 2009.
16. Kontaxis, A. The biomechanics of reverse shoulder replacement – a modeling study. Clinical Biomechanics. #24: 254-260. 2009.
17. Roche, C. et al. Anterior and Posterior Scapular Impingement Associated with Two Different Reverse Shoulder Designs. Trans. of the 56th Annual ORS Meeting. 2010
18. De Wilde, L.F. et al. Prosthetic Overhang is the Most Effective Way to Prevent Scapular Conflict in a Reverse Total Shoulder Prosthesis. Acta Orthopaedica. Vol. 81, #6: 719-726. 2010.
19. Nicholson, G.P. et al. Scapular Notching: Recognition and Strategies to Minimize Clinical Impact. CORR. Vol. 469, #9: 2521-2530. 2011. #9: 2521-2530. 2011.

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