The FDA approved the use of the reverse shoulder prosthesis in the United States in 2004, nearly 25 years following its re-debut in France. Combined, there are 40 years of experience addressing varying shoulder conditions once treated with non-prosthetic or unconstrained shoulder arthroplasty solutions. Surgical techniques and prosthetic designs have evolved over the years, leading to improvements in clinical outcomes, implant longevity and lower rates of complications. The earliest design, the Grammont-style reverse shoulder arthroplasty (RSA), was built on the engineering premise of a medialized center of rotation, as measured at the center of the glenosphere, in reference to the native glenoid face. While a medialized center of rotation increases the mechanical efficiency of the deltoid, it tends to result in mechanical impingement between the humeral polyethylene insert and the scapula neck. Cadaveric and biomechanical studies as well as computer simulation models have demonstrated the increased risk of the following complications: scapular notching, decreased rotation and prosthetic instability; whereas a lateralized center of rotation has demonstrated superiority in maximizing overall passive arc of motion and preventing scapular notching. In addition, the tensioned soft tissues (remaining rotator cuff and deltoid) effectually improve implant stability.1,2
Surgical lateralization can be achieved via metal or bone. Using a thicker baseplate and/or glenosphere achieves glenoid sided lateralization while increasing joint loading. The increased compressive and shearing forces increases the potential for glenoid loosening.3 To offset the torque forces seen in metallic increase offset (MIO-RSA), bone graft can be placed under the baseplate; and once healed, theoretically, the center of rotation is lateralized and remains at the bone-implant interface.
In a study by Boileau et al, a retrospective case series of 143 shoulders were treated with a BIO-RSA for rotator cuff deficiency.4 It was a multicenter retrospective study with a minimum of five years’ follow-up. All patients in the study had a Grammont-style RSA with the use of autograft harvested from the humerus for bony lateralization. The mean follow-up period was 75 months, the preoperative diagnosis varied, the average age was 72 years, and 72% were women. Patients undergoing revisions or those with insufficient humeral head autograft were excluded. From a technical standpoint, a cylinder of cancellous bone was harvested from the humeral head of 7mm and 10mm thickness, for 42mm sphere and 36mm sphere, respectively, and placed on the baseplate. All baseplates were implanted with a lengthened central peg in 10° of inferior tilt.
Instability and scapular stress fractures remain two of the most common complications after reverse Total Shoulder Arthroplasty (rTSA),1 both of which may compromise outcomes and require further surgery. Each is conversely related to the soft tissue tension in the deltoid and remaining rotator cuff which are affected by implant configuration, including glenosphere diameter, glenosphere offset, humeral tray, and liner thickness. These parameters may also affect the resting tension in the remaining cuff which can thereby impact postoperative active shoulder rotation.2
To date, surgeon determination of the optimal construct tension after reduction of rTSA remains largely qualitative and may be based on individual experience derived from ease of reduction, passive range of motion on the table, presence or absence of boney impingement, and “shuck tests” for dislocation. The integrity and repairability of the subscapularis may also play a role. Currently, there remain no quantitative methods to measure soft tissue tension intraoperatively and how it may change during different arm positions that correlate with desired patient function after rTSA.
The reverse shoulder prosthesis was introduced in France in the 1980s and was FDA-approved for use in the United States in 2004. Since that time, it has revolutionized the field of shoulder replacement. The reverse shoulder prosthesis has a proven track record of providing predictable and sustainable pain relief and functional improvement for patients with a host of shoulder pathologies, ranging from osteoarthritis to rotator cuff arthropathy. The stability and functional improvements afforded by the reverse shoulder prosthesis are achieved, in part, by transitioning the large outer deltoid muscle of the shoulder into a mechanically advantaged motor of the arm. As a result of the forces generated by the deltoid muscle, high loads are transmitted to the site of origin of that muscle on the scapula leading to fractures in a rare cohort of patients. These so-called acromial fractures are not widely studied due to their infrequency and the relative heterogeneity of reverse shoulder prosthesis designs on the market. Improvements in understanding acromial fractures is important as their occurrence can impair the clinical outcome of the reverse shoulder prosthesis. A recent study by Routman et al.is, to date, the largest cohort of patients reported, which sheds light on the patient risk factors and prosthesis-related factors leading to this unfortunate and uncommon complication of reverse shoulder replacement.
When Dr. Paul Grammont introduced the reverse total shoulder arthroplasty (rTSA) in the late 1980s/early 1990s, it was a revolutionary treatment for a previously unsolved clinical condition, rotator cuff tear arthropathy. The original design had an unfortunately high complication rate which limited its use. Modern designs have significantly improved the complication rate as well as the success of the operation, and indications for rTSA have significantly increased. This increasing utilization has led some to coin the phrase “reversomania”, suggesting it is being done too often or perhaps too soon.
Clearly, complication rates for rTSA have decreased,1 and the rate of rTSAs performed have significantly increased with more rTSAs now being performed than anatomic shoulder arthroplasty (aTSA).2 The authors of the study, “A 10-year experience with reverse shoulder arthroplasty: are we operating earlier?”, sought to determine if, due to increased comfort and success with rTSA, surgeons are performing rTSA earlier in the disease process. In other words, has the “tipping point”, the point at which the patient’s symptoms are severe enough that the patient and surgeon elect to undergo rTSA changed, or has the threshold for performing surgery moved?
In 2013, Dr. Carlo Romano presented clinical evidence for InterSpace via a systematic review of globally accumulated literature. Five years later, in 2018, the data was updated to include new publications and 28 peer-reviewed papers found from more than 20 different sites. The review excluded case reports, clinical series with less than 10 patients, duplicate studies, and series with a mean follow-up of less than 24 months. The inclusion criteria left 19 papers for a total of 732 spacers implanted at 18 centers. This systematic review of the literature demonstrates the safe and effective use of InterSpace in overcoming complications associated with Periprosthetic Joint Infection (PJI).
Only 43 patients (5.9 percent) had a persistent infection that required a spacer exchange or resection arthroplasty
Seven hundred and nine (709) patients underwent the second-stage procedure
Of the 709, only 44 patients (6.2 percent) had an infection at the mean follow-up of 55 months.1
Today, the updated clinical results continue to show that the routine use of the InterSpace antibiotic spacers are validated. As a recent example of published clinical results, Patrick et al. from the University of Florida published “Management of infected shoulder arthroplasty: a comparison of treatment strategies” in the Journal of Shoulder and Elbow Surgery. Among the reviewed treatment modalities for infected shoulder arthroplasty, the InterSpace Shoulder was found to be an effective tool across various treatment strategies.
There is ample support in the literature that superior inclination of the glenoid baseplate in reverse total shoulder arthroplasty (rTSA) can lead to a higher risk of instability and premature implant failure. This is because a superiorly inclined baseplate experiences a greater shear vector imparted by the action of the deltoid muscle. Because cuff deficient arthritic shoulders often develop superior glenoid erosion, shoulder surgeons must carefully assess preoperative glenoid inclination when planning rTSA to avoid implant malposition. Preoperative planning platforms now allow surgeons virtually correct glenoid deformity while also optimizing implant fixation, backside contact with host bone, and avoidance of bone impingement such as scapular notching.
Boileau et al recently described a new measurement of glenoid inclination called the Reverse Shoulder Angle (RSA). Their contention is that referencing the more traditional ß-angle (the angle formed by a line connecting the superior and inferior glenoid face with a perpendicular to a line along the floor of the supraspinatus fossa) may inadvertently cause surgeons to superiorly incline small, flat-backed reverse baseplates when placed on the inferior half of the glenoid. Therefore, the RSA angle measures only the inferior half of the glenoid rather than the full glenoid face. This results in an average measured inclination of 25° + 8°, which is a 10° + 5° compared to the ß-angle. The authors note that Favard E1 glenoids with central erosion are at risk for baseplate malposition.
Accurate placement of the glenoid component in reverse total shoulder arthroplasty (rTSA) is important to reduce component loosening, scapular notching, instability and to maximize impingement-free range of motion. Initial stability of the implant is critical for bony in-growth and is dependent upon optimal screw placement and maximizing screw length. Glenoid exposure and anatomy can be difficult, and in the presence of glenoid wear or deformity, placement of the implant and screws may be challenging.
Computer navigation has been shown to improve the ability to place the central glenoid post/cage fully within the glenoid vault and to optimize screw placement and length (Nashikkar et al). Computer navigation has also been shown to improve accuracy in achieving correct version and inclination of the glenoid component (Nguyen et al; Verborgt et al; Kircher et al). Some surgeons may be concerned about the perception of increased surgical time associated with computer navigation as well as any learning curve that comes with adopting a new procedure. This study by Wang et al investigated the learning curve of computer navigated rTSA, the accuracy of implant placement, and the effect on surgical time.
This well-designed study was a prospective case-series of a single experienced shoulder surgeon evaluating his first 24 consecutive navigated rTSAs. Although he had extensive experience with the arthroplasty system, his only prior experience with this navigation system was a sawbone workshop, a single cadaveric case, and a single clinical case to allow himself and his surgical team to be familiar with the setup and workflow. All cases underwent preoperative planning using Blue Ortho CT protocol (Blue Ortho, Grenoble, France). The goal of planning was to attain a glenoid implant version as close to 00 as possible using reaming or augments, attain 00 of inferior inclination, maximize bone-implant contact, and keep the glenoid central cage fully contained in the glenoid vault. Preoperative planning took 3-5 minutes per patient, a step I would argue should be done whether navigation is planned or not.
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 occur1,2 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.
The incidence of shoulder arthroplasty continues to increase, and this has brought continued innovation in preoperative planning and implant design. Concurrently, with improved imaging techniques, our understanding of pathologic changes that affect the joint have begun to elucidate strategies to address glenoid wear. Durability of the glenoid implant remains the weak link of shoulder arthroplasty,2,10 and both clinical and biomechanical studies have demonstrated that excessive residual retroversion or inclination,7,9 excessive corrective reaming,4,5 recurrent humeral subluxation6 and insufficient implant contact1 with bone are all risk factors for component loosening or failure. While augmented anatomic and reverse glenoid implants are now widely available, their use remains fairly limited relative to the frequency of pathologic wear. Guidelines on their use have also yet to be established, and a surgeon’s ability to accurately place such implants in cases with significant to extreme glenoid wear are uncertain. Prior cadaveric studies examined surgeon accuracy in recreating a preoperative plan using conventional instruments with free-hand techniques. The studies demonstrated significant variability and an average error of + 6-10° relative to the planned correction.11 This indicates that “eyeballing” glenoid implant placement may lead to significant variation from the plan. Particularly in cases of moderate to severe pathologic wear, such as the Walch B2 or B3 glenoid. This inaccuracy can be the difference between long-term durability and mid-term failure.
CT-based preoperative planning is now widely available and increasingly popular as it allows surgeons to virtually plan implant selection and placement and optimize parameters such as correction of inclination and version, peg placement in the glenoid vault, backside contact and amount of corrective reaming. While this can provide a very quantitative method of glenoid reconstruction, planning alone does not guarantee proper bone preparation or implant placement without additional technology to assist surgeons in replicating the plan. While patient-specific instrumentation (PSI) can improve the accuracy of implant placement over free-hand techniques, it still has a margin of error of + 4° on average.3,12 As studies have shown increased stresses in the cement mantle over 10° of residual version, this amount of error could potentially lead to pathologic implant malposition. Furthermore, PSI does not allow surgeons to adjust the plan intraoperatively if needed.