American Shoulder and Elbow Surgeons Journal Club on Reverse Total Shoulder Arthroplasty - a reflections on the articles. Part 1

ASES will provide a Virtual Journal Club on Reverse Total Shoulder, Tuesday, January 27th at 7pm CST, featuring moderators Drs. Christopher Klifto and Eric Wagner and panelists: Drs. Emilie Cheung, Larry Gulotta and Joaquin Sanchez-Sotelo (click on this link).

Here are some thoughts on two of the articles to be discussed.

(1) Scapulothoracic orientation has a significant influence on the clinical outcome after reverse total shoulder arthroplasty reported a retrospective analysis of 681 primary rTSA patients from a single-center registry. Patients were classified into three posture types based on scapular internal rotation measured on preoperative cross-sectional imaging:

• Type A: ≤36° scapular internal rotation (n=225)

• Type B: >36° to 46° (n=326)

• Type C: >46° (n=130) - represents poorest posture with increased kyphosis. At two years after surgery these patients had a few degrees (6 to 10 degrees) worse range of motion than type A. While the SPADI scores were 9 points worse, the difference did not exceed the MCID. Similarly the pain scores and complication rates were not clinically significantly different between types A and C.

The study is limited by (1) the  fact that posture was measured in a static supine position not during function while standing and confounded because (2) the types differed with respect to patient sex (more females in type C) and type of implants (more Grammont types used in type C).  While it is speculated that type C patients would benefit from increased distalization and potentially more lateralized constructs, this was not demonstrated in this paper.

(2) The relationship between design-based lateralization, humeral bearing design, polyethylene angle, and patient-related factors on surgical complications after reverse shoulder arthroplasty: a machine learning analysis considered 3,837 primary rTSA procedures using machine learning to predict surgical complications. Complications occurred in one out of eight patients, with superficial infections (2.1%), acromial/scapular fractures (2%), and instability (1.6%) being most common.

Patient factors (younger age, tobacco use, prior surgery, diagnosis of instability sequelae or nonunion) were stronger predictors of complications than implant design (inlay humeral component, medialized glenoid, medialized humerus, minimal global lateralization, lateralized glenoid-medialized humerus).

The machine learning model achieved an AUC-ROC of 0.61 (the value for random change would be 0.5).

This study reinforces that patient selection and optimization are paramount, with surgical technique and implant design playing less important roles. The findings appear to favor lateralized constructs (glenoid and humeral components) and onlay designs. However, the modest predictive accuracy suggests complications are multifactorial and not easily predicted.

The authors carefully describe the limitations of the study:

(1) the study retrospectively analyzed patients from an institutional registry

(2) glenoid, humeral, and global lateralization were measured on digitized templates as opposed to radiographic measures (thus, surgeon technique may have had a major impact on the final implant position different than the manufacturer specifications).

(3) the case volume of the individual surgeons was not analyzed with respect to complication rate.

(4) the medialized designs were the only implants available during the learning period of rTSA at this institution; thus it is unclear whether the increased complications associated with this design were related to the design itself or due to surgeon inexperience. In this registry, lateralized constructs were associated with fewer complications, but this may reflect their use in later years by more experienced surgeons in better-selected patients.

(5) the implants with lower proportions in the study led to more statistical fragility regarding design parameters

(6) it is not clear whether complications with certain designs (for example, the lateralized glenoid-medialized humerus (LGMH) combination) were due to the implant or to differences in the patient populations receiving the different implants

(7) the modest AUC-ROC of 0.61 suggests that the model did not include additional important predictive factors (e.g. surgical technique, other patient factors).

(8) this study looks at associations, but we cannot determine whether the associations imply causation  (i.e. does the use of certain implants cause an increased risk of complications?). See Surgical failures: what causes them and how can we do better for our patients.

We might wonder if in the future natural language processing of the entire records of these patients might lead to a model with greater predictive capacity by capturing such potentially important variables as:

• Intraoperative findings (bone quality, soft tissue (subscapularis) condition, unexpected anatomic variants)
• Surgeon operative notes describing technical challenges
• Rehabilitation compliance and early recovery patterns
• Social determinants of health (support systems, living situation)
• Detailed medication histories and comorbidity severity
• Patient expectations and psychological factors

In the end we must ask: Are complications in rTSA fundamentally predictable, or are there elements (e.g., subclinical infections, individual healing variability, unpredictable trauma) that limit any model's ceiling? 

Is the modest AUC of 0.61 due to insufficient data or to irreducible uncertainty (inherent biological variability among patients, intraoperative details, postoperative course)? 

See Objective ignorance - a problem in predicting outcomes in climbing and in orthopaedic surgery

Here's how a conversation with a prospective patient about complications might go.

What we know: "Your age, tobacco use, overall health, nutrition and whether you've had prior surgery influence your risk of complications. We can't change some of these, but we can optimize your nutrition and help with smoking cessation if relevant. At your surgery, we'll use proven techniques and appropriate implants based on the best available evidence."

What we don't know: "Even with sophisticated analysis of thousands of cases, we can only weakly predict who will experience a complication. Much depends on factors we cannot measure or control—how your body responds to surgery, healing variability, and events after you leave the hospital."

What this means for you: "We focus our efforts where evidence shows they matter most: optimizing your health before surgery, using proven surgical approaches, and supporting your recovery afterward. We avoid expensive technologies that claim precision but haven't been shown to improve outcomes that matter to patients."

Follow on twitter/X: https://x.com/RickMatsen
Follow on facebook: https://www.facebook.com/shoulder.arthritis
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link)
The total shoulder arthroplasty (see this link)
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link)

Shoulder rehabilitation exercises (see this link).