Screw Length and Quantity in rTSA

Jay J. King, MD

Read complete study: Impact of screw length and screw quantity on reverse total shoulder arthroplasty glenoid fixation for 2 different sizes of glenoid baseplates

Even though reverse total shoulder arthroplasty (rTSA) is becoming an increasingly commonly performed procedure throughout the world, studies are still needed in order to understand how we can maximize outcomes and minimize complications. While lack of glenoid baseplate fixation is not a common problem, loosening can occur^1,2  and can lead to inferior outcomes and revision surgery.  In addition, scapular spine stress fractures have been associated with glenoid screw placement in rTSA and also lead to inferior clinical outcomes.^3,4  Understanding complications such as these are important for future surgeons so that they can be avoided.

Roche et al in their recent article in JSES Open Access entitled “Impact of screw length and screw quantity on reverse total shoulder arthroplasty glenoid fixation for 2 different sizes of glenoid baseplates” evaluated how the number and length of screws affect baseplate fixation in an osteoporotic bone-substitute model using the Exactech standard and the Exactech small glenoid baseplates. They evaluated shear and compressive cyclic loading in a biomechanical model looking at constructs with two, four, and six screws with different screw lengths (18, 30, 46mm). All scenarios tested showed that the baseplates remained well-fixed after cyclical loading of 10,000 cycles without catastrophic failure, but there was a difference in displacement between the constructs. Baseplate displacement was less for the constructs with four screws compared to the constructs with two screws. The addition of six screws in the large baseplate did not make a difference in displacement. In addition, constructs with the longest screws had the lowest amount of baseplate displacement after cyclical loading. Short screws (18mm) showed the most displacement in both the small and standard baseplates.

This study is important for two main reasons.  First, it demonstrates the importance of long screws when attempting adequate glenoid fixation in osteoporotic bone. While none of the constructs failed, displacement is a concern for long-term fixation. The better the constructs can withstand displacement, the less chance of loosening they will have. Obtaining longer screws with good fixation in rTSA can be difficult due to lack of intraoperative visualization of the glenoid vault. While preoperative planning and association with bony landmarks is critical for baseplate and screw placement, the ability to place the screws exactly where they are desired (to maximize length and fixation) is difficult. ExactechGPS intraoperative computer navigation (Guided Personalized Surgery) gives surgeons the ability to place the screws intraoperatively exactly where they want within the glenoid vault to maximize screw length and fixation.

Secondly, this study also shows that increasing the number of screws decreases the risk of baseplate displacement. The downside of increasing the number of screws is that it increases the risk of scapular spine stress fracture⁴ as well as injury to the suprascapular nerve.⁵ In addition, just placing four screws, even though one or two may not have good fixation, does not likely add much to a construct in which two or three long screws with good fixation are present. This study showed that longer screws may substitute for more screws in regard to initial baseplate fixation in osteoporotic bone. In my experience, intraoperative computer navigation allows me to place screws in the best bone available and in the appropriate trajectory to have longer screws which, therefore, leads to better fixation with less screws. The screw orientation that I use with computer navigation differs from my preoperative plan commonly, especially in glenoids with severe wear or when baseplate augments are used. In addition, I avoid any screws or screw orientations that exit anywhere near the spinoglenoid notch to avoid contact with the suprascapular nerve or its branches.

Decreasing the number of screws by optimizing the screw trajectory and fixation can lower total implant cost, potentially decrease injury to branches of the suprascapular nerve, and potentially decrease scapular spine fracture stress risers. This study validates what I suspected about the number and length of screws used in baseplate fixation.  Currently, I commonly use two or three long screws with excellent fixation placed with the assistance of computer navigation. Gaining knowledge regarding baseplate fixation is important to understand how surgeons can minimize complications regarding baseplate placement. More research is necessary to understand how increasing the length of screws and decreasing the number of screws affects the long-term rTSA clinical outcomes and complication rates.

 

Jay J. King, MD, is an assistant professor at the University of Florida College of Medicine Department of Orthopaedics for general orthopaedics, shoulder and elbow surgery. He earned his medical degree at Drexel University in 2006 before completing his residency in orthopaedic surgery there, followed by a clinical research fellowship in orthopaedic oncology at the University of Pennsylvania in Philadelphia. He has published various works in national and international journals and is a member of various national and state orthopaedic organizations. He currently practices at the UF Health Orthopaedics and Sports Medicine Institute.

References:

1. Bitzer A, Rojas J, Patten IS et. al. Incidence and risk factors for aseptic baseplate loosening of reverse total shoulder arthroplasty.  J Shoulder Elbow Surg. 2018; 27(12): 2145-52.
2. Rojas J, Choi K, Joseph J, Srikumaran U, McFarland EG. Aseptic glenoid baseplate loosening after revers total shoulder arthroplasty. J Bone Joint Surg Reviews.    7(5)?: e7.
3. Kennon JC LuC, McGee-Lawrence ME, Crosby LA. Scapula fracture incidence in reverse total shoulder arthroplasty using screws above or below metaglene central cage: clinical and biomechanical outcomes. J Shoulder Elbow Surg. 2017; 26: 1023e30.
4. Otto RJ, Virani NA, Levy JC, Nigro PT, Cuff DJ, Frankle MA. Scapular fractures after reverse shoulder arthroplasty: evaluation of risk factors and the reliability of a proposed classification. J Shoulder Elbow Surg. 2013; 22: 1514e21.
5. Molony DC, Cassar Gheiti AJ, Kennedy J, Green C, Schepens A, Mullett HJ. A cadaveric model for suprascapular nerve injury during glenoid component screw insertion in reverse-geometry shoulder arthroplasty. J Shoulder Elbow Surg. 2011; 20: 1323e7.