We provided an evidence-based review of scapular notching, a novel complication unique to reverse TSA. This study addressed key questions relating to the etiology and incidence of scapular notching, radiographic progression and the effect on implant stability, the relationship between scapular notching and clinical outcomes, and the identification of preoperative and intraoperative risk factors for the development of this complication. We also emphasized strategies aimed at recognizing risk factors for scapular notching and described both technique-related and implant design-related ways to minimize or avoid scapular notching.
The limitations of this review parallel the deficiencies in the current body of literature on scapular notching. There are only a handful of clinical studies addressing this problem. The majority are short or medium term, nonrandomized, and noncontrolled and involve heterogeneous patient populations, a variety of implant types, and differing surgical techniques. Despite this lack of standardization, much headway has been made with regard to defining the scope of the problem, its root causes, and its effect on patient outcome. The highlights of the current body of knowledge are summarized below.
Scapular notching after reverse TSA describes the erosion of bone of the scapular neck secondary to mechanical abutment of the humeral implant with adduction of the upper extremity [7
]. With repetitive mechanical contact between the polyethylene cup of the humeral component and the inferior scapular neck, wear of the polyethylene may compound a notch by provoking a biologic response, leading to chronic inflammation of the joint capsule, local osteolysis, and the potential for implant loosening [13
]. Additionally, this may lead to loss of joint constraint, creating the potential for joint instability [1
]. The Nerot-Sirveaux classification has been developed to characterize scapular notching. A Grade 1 notch describes a defect contained within the inferior pillar of the scapular neck. A Grade 2 notch involves erosion of the scapular neck to the level of the inferior fixation screw of the glenosphere baseplate. A Grade 3 scapular notch indicates extension of the bone loss over the lower fixation screw, while a Grade 4 defect describes progression to the undersurface of the baseplate.
Scapular notching tends to first appear in the early postoperative period, with most reports describing radiographic evidence of scapular neck erosion between 6 weeks and 14 months postoperatively [7
]. The reported incidence ranges from 44% to 96% of cases [1
]. Simovitch et al. [16
] noted postoperative scapular notching in 44% of cases. In that series, notching was radiographically evident at a mean of 4.5 months postoperatively, with no cases demonstrating scapular erosion after 14 months of followup. Clinical series published by Levigne et al. [11
], Sirveaux et al. [18
], and Boileau et al. [1
] reported scapular notching with a slightly higher incidence, 62%, 63.6%, and 74%, respectively. Another series by Werner et al. [22
] demonstrated a near-universal presence of notching, finding evidence of inferior scapular neck erosion in 96%, with 54% of the notches classified as either Grade 1 or 2 and 46% as Grade 3 or 4.
Radiographic progression of scapular notching remains controversial in the literature. Studies by Werner et al. [22
] and Simovitch et al. [16
] demonstrate the extent of the scapular notching plateaus over time, while Levigne et al. [11
] report contradictory results. Werner et al. [22
] noted 79% of patients had no evidence of progression at 1 year of followup, with the remainder increasing by a maximum of one grade at the time of final evaluation at a mean of 38 months. Simovitch et al. [16
] similarly reported stabilization at a mean of 18 months postoperatively, with no evidence of progression at 24 months of followup. However, other studies have demonstrated scapular notching can increase with the length of followup. Levigne et al. [11
] reported radiographic evidence of notch progression between 1 and 2 years of followup and between 2 and 3 years of followup, with increases in the percentage of cases with Grades 3 and 4 inferior scapular neck erosion over time. Further clinical studies are necessary to evaluate this controversial topic.
To date, only case reports describe a negative impact of scapular notching on implant survivorship. Delloye et al. [4
] and Vanhove and Beugnies [20
] report progression of scapular notching leading to glenosphere loosening in small series of patients. Short-term followup in larger clinical studies precludes any meaningful conclusions with regard to the impact of notching on implant stability. Levigne et al. [11
] did show a correlation between the presence and size of a notch with the development of radiolucencies around both the humeral and glenoid components as followup time increased. It is likely, with longer followup, the precise impact of scapular notching on the clinical outcome and survival of reverse TSA will be better understood.
The clinical relevance of scapular notching is similarly controversial in the literature, with some authors reporting no impact on postoperative function [1
] and overall outcome and others describing a negative correlation between a scapular notch and the results after reverse TSA [16
]. Studies by Levigne et al. [11
], Werner et al. [22
], and Boileau et al. [1
] reported there was no correlation between the presence or grade of scapular notching and any objective or subjective clinical measure or postoperative complication. Other clinical studies noted a direct association between the presence and extent of scapular notching and lower Constant-Murley and subjective shoulder scores. Sirveaux et al. [18
] found cases with more extensive notching (Grades 3 and 4) had lower postoperative Constant-Murley scores. Simovitch et al. [16
] similarly found lower mean Constant-Murley scores, lower subjective shoulder score, inferior shoulder strength, and worse postoperative ROM in patients with scapular notches compared with those without this complication. Further research is needed to clarify the conflicting results from these clinical series.
There are known predictors of scapular notching that can be categorized into several different groups. Patient-specific risk factors for scapular notching include rotator cuff tear arthropathy with a narrowed acromiohumeral distance (incidence of 76% compared to 38% in posttraumatic cases), glenoids with superior erosion (Type E2 glenoid wear), and MRI evidence of Grade 3 or 4 fatty infiltration of the infraspinatus muscle [11
]. Surgical technique is also a risk factor, with the anterosuperior approach having a higher incidence of scapular notching than those approached through the deltopectoral interval (86% versus 56%) [11
]. Neutral or superiorly tilted baseplates increase the risk of scapular notching compared with inferior glenoid tilt. Several studies demonstrate allowing inferior overhang of the glenosphere improved impingement-free adduction and abduction angles [9
]. It has also been shown baseplates implanted with a slight (15°) inferior tilt had the most compressive forces under the baseplate during loading with the least amount of tensile forces and the smallest amount of micromotion [9
]. Other predictive factors relating specifically to implant design will be described in a later section.
In an effort to avoid or minimize the development of a postoperative notch, surgeons should take these predictors of notching into account during the preoperative workup, operative procedure, and postoperative followup. Preoperatively, a diagnosis of rotator cuff arthropathy should prompt the surgeon to evaluate the condition of the glenoid, looking for evidence of superior wear (Type E2 or E3 glenoid) and the condition of the patient’s infraspinatus on MRI. In cases where the preoperative workup indicates the potential for scapular notching, a deltopectoral surgical approach may be warranted to ensure appropriate implant positioning. Intraoperatively, during exposure and preparation of the glenoid, an effort can be made to ensure the glenosphere baseplate is implanted as inferior on the native glenoid as possible to foster inferior overhang of the glenosphere component. Superior glenoid wear can be visually confirmed and preferential reaming can be performed to promote a slight inferior tilt to the implanted glenosphere baseplate (10°–20°). The senior author (GPN) uses hand reamers on the glenoid, reaming until a “subchondral smile” of cancellous bone can be seen on the inferior aspect of the glenoid (Fig. ). Superior defects that remain subsequent to hand reaming can be bone grafted, ensuring the glenosphere baseplate is not placed with a superior tilt. The glenosphere can be sized appropriately to allow for 2 to 3 mm of inferior overhang, which will promote postoperative ROM, stability, and minimization of notch development with humeral adduction. Additionally, the surgeon should be aware of the implant options available with respect to their system of choice, such as humeral component neck-shaft angle, lateral offset of the center of rotation, glenosphere sizes, and depth of the polyethylene cup. Postoperatively, the surgeon should be vigilant in his or her assessment of followup radiographs, evaluating the inferior aspect of the scapula for evidence of notch development and progression. By noting the position of the glenosphere relative to the inferior aspect of the glenoid and its tilt on postoperative radiographs, patients at risk for notch development can be identified and followed closely.
Fig. 4 The glenoid is reamed by hand until a “subchondral smile” of cancellous bone is seen on the inferior aspect of the glenoid. Once this level is reached, any superior glenoid defects that remain can be bone grafted to ensure the glenosphere (more ...)
With recent clinical and biomechanical studies proposing alterations in implant design and surgical technique in an effort to reduce the incidence and impact of scapular notching, the question arises whether we can respect Grammont’s main principles while at the same time provide improved outcomes in the absence of notching. A new reverse TSA was recently designed incorporating the Grammont principles of medialization and inferiorization of the center of rotation of the glenoid component while incorporating some design initiatives to minimize potential abutment of the medial aspect of the humeral component against the inferior scapular neck. These design and surgical technique issues were in response to what had been clinically seen and what had been learned by basic studies discussed in this paper. The senior author (GPN) is a designer and received royalties for this implant. First utilized in March 2006, the design of the Trabecular Metal™ Reverse Shoulder System (Zimmer, Inc, Warsaw, IN) respects the proven Grammont principles of inferiorization and medialization of the glenoid center of rotation while incorporating certain design characteristics to prevent scapular notching. The metallic neck-shaft angle is 143° and the polyethylene component has a 7° angle, thus creating a total neck-shaft angle of 150°. This 5° difference from other reverse TSA designs allows for better adduction of the arm without mechanical abutment. Additionally, this implant design is low profile with no metallic material above the humeral osteotomy. The Trabecular Metal™ glenosphere baseplate has a 3-mm pad on its back surface, creating a small lateral offset when implanted onto the glenoid surface (Fig. ). These design characteristics coupled with operative technique improvements focusing on inferior glenosphere placement with an inferior tilt have shown radiographically a decreased incidence of scapular notching at 6 months (0%) and at 14 months (8%) in an ongoing clinical series.
Fig. 5A–B (A) An immediate postoperative AP radiograph shows a TSA using the Trabecular Metal™ Reverse Shoulder System implanted into the right shoulder for treatment of rotator cuff tear arthropathy. Implant design characteristics of the differing neck-shaft (more ...)
While the results of reverse TSA continue to improve and the indications for its use are expanding, there is clearly a need for better understanding of the complication of scapular notching. At this time, the effects of scapular notching on patient function, radiographic progression, and implant stability remain controversial. It is our hope this review has raised clinical awareness about this important entity, exposed the limitations of the current body of literature, and helped to promote further clinical investigation.