Does component malposition lead to revision of shoulder arthroplasty?

Humeral and glenoid component malposition in patients requiring revision shoulder arthroplasty: a retrospective, cross-sectional study lists instability: 32% (most common in RSA cases (40%). rotator cuff tear: 32% — predominantly in TSA (45%), loosening: 25% (highest in RSA (34%), infection: 11%, periprosthetic fracture: 5%. 

This commercially-funded investigation concluded: "The data from this study suggest that component malposition is frequently present among patients requiring revision arthroplasty." and "Improved component positioning is needed, including the development of more effective intra-operative techniques to ensure proper humeral and glenoid component position to minimize the risk of revision surgery." However, this study did not demonstrate that the rate of malposition was more frequent in revised than in unrevised shoulders. To conclude that malposition causes revision, we need to know how often well-functioning, unrevised shoulders also exceed defined thresholds.

Here are some details: component position was measured on pre-revision radiographs. "Thresholds for Malposition" were based on values found in prior publications.

From the above and the figure below it can be seen that the definition of acceptable component position is quite narrow.

The authors note that using narrower thresholds dramatically increases "malposition" rates. For example, lowering the threshold for the change in humeral center of rotation from >5mm to  >3mm increased the rate of "malpositioned" components from 45% to 58% of TSA cases. It seems likely that there are many unrevised shoulder arthroplasties with a change in humeral center of rotation exceeding the 5mm or the 3mm thresholds.

This is akin to having the distance between field goal uprights being 3 feet (below right) rather than the regulation 18.5 feet (below left).  Narrowing the goal posts does not change the quality of the kicker.

To understand the nature of thresholds, we need scatter plots including both revised and unrevised shoulders that show the relationship between component position and outcomes across the full spectrum of both variables. Such plots would reveal the true clinical significance of positioning variations. These data are not included in this study.

The value of scatter plots is shown by four hypothetical examples illustrating different possible relationships between component positioning and outcomes. Each represents a fundamentally different clinical reality with different implications for the value of precision positioning technology.

Figure 1. Scenario A: Hard Threshold Pattern

This pattern shows a clear inflection point at 5 mm deviation. Below this threshold, outcomes remain excellent with minimal variation. Above it, outcomes deteriorate sharply.  The blue dots represent cases without revision, while red dots indicate cases that required revision surgery.

Figure 2. Scenario B: Soft Threshold Pattern (Gradual Decline)

This pattern demonstrates a linear relationship where each degree of deviation causes proportional outcome deterioration. There is no sharp inflection point. Note the increasing concentration of revisions (red dots) as deviation increases, but many poorly-positioned components still function adequately.

Figure 3. Scenario C: No Clear Relationship (Zone of Indifference)

This pattern shows outcomes scattered across the full range regardless of positioning. The flat trend line suggests that within the measured range, this particular positioning parameter has minimal impact on outcomes. Other factors (soft tissue management, patient selection, surgical technique) dominate. The random distribution of revisions (red dots) across all positioning values supports this interpretation.

Figure 4. Scenario D: Inverted U-Shaped Relationship (Optimal Zone)

This pattern demonstrates that extremes in either direction cause poor outcomes, with an optimal zone in the middle. This could represent parameters like humeral version where both excessive anteversion and retroversion are problematic. The concentration of revisions (red dots) at both extremes supports the concept of an optimal middle zone.

Scatter plots such as these reveal (1) the percentage of "well-positioned" implants failed and (2) the percentage of "malpositioned" implants that function successfully and (3) whether it is likely that deviations caused failure, or whether failures have occurred for other reasons, such as instability from poor soft tissue balancing, poor bone quality, infection, or periprosthetic fracture.

Conclusion

The modes of shoulder arthroplasty failure and revision are well established.

Why do primary anatomic total shoulder arthroplasties fail today? A systematic review and meta-analysis  identified implant loosening (26.1%), particularly of the glenoid component, as the most common cause of contemporary aTSA failure, followed by rotator cuff insufficiency (17.3%), instability (10.4%), and infection (10.2%)

Revision of reverse total shoulder arthroplasty: a scoping review of indications for revision, and revision outcomes, complications, and rerevisions found the primary reasons for revision were dislocation or instability (30%), baseplate complications (25%), infection (23%),  acromial/scapular fractures and humeral component issues (10%).

 Notice that the leading causes of failure — loosening, instability, infection — are not primarily positioning problems. Precision technology addresses none of them.

The critical unanswered question is the dose-response relationship between positioning deviation and clinical outcome - four possible patterns are shown by the hypothetical examples above. 

Each surgeon needs to ask, "are the complications experienced by my patients likely to be addressed by component positioning between tight goal posts or are they more likely to be addressed by better patient selection, better component seating, better soft tissue balancing, better prophylaxis against infection, or different component selection?".

Keeping Cool

Dark Eyed Junco

Matsen Backyard

2020

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). 

Humeral and glenoid component malposition in revised shoulder arthroplasty - Part I - what might have been done differently?

The authors of Humeral and glenoid component malposition in patients requiring revision shoulder arthroplasty: a retrospective, cross-sectional study explored 234 cases of revised shoulder arthroplasty and reported "quantitative analysis demonstrated that the majority of glenoid components in these revision cases were malpositioned in both TSA (51%) and RSA (93%) when all measures were considered. Similarly, there was humeral component malposition in 57% of TSA cases, 62% of RSA cases, and 54% of hemiarthroplasty cases when all measures were considered. When asked if there was glenoid component malposition, the independent reviewer considered 17% of glenoid components to be malpositioned in TSA cases and 54% in RSA cases. The investigative institutions reported similar rates. For the humeral side, the independent reviewer felt that 71% of TSA cases, 24% of RSA cases, and 74% of hemiarthroplasty implants were malpositioned in some direction. The investigative institutions reported similar rates."

This article is very thought provoking: it merits two posts. Here's the first.

The authors conclude:  "Improved component positioning is needed, including the development of more effective intra-operative techniques to ensure proper humeral and glenoid component position to minimize the risk of revision surgery." 

The authors' examples of malposition are shown below, providing an opportunity to consider what might have been done differently in each case to avoid the malpostion (see Of successful mammoth hunting and glenoid component failure - modeling causation).

Knowing full well that many of this blog's readers would consider a high-tech approach (e.g.robotics, navigation systems, patient specific instrumentation), here's how we'd try to avoid these malpositions in my practice.

A. Humeral head too high

The "head high" problem may be avoided by assuring that the humeral head is placed just below the berm. 

Note also in both of these cases the diaphysis of the humeral component was too large, causing stem incarceration, preventing full seating of the component. Stem incarceration may be prevented by using a smaller diameter humeral component with impaction grafting, 

using a short stem, or using a stemless component.

B. Insufficient humeral resection

The "long neck" problem may be avoided by full exposure of the anatomic neck for the cut.

C. Too high baseplate

The "Baseplate High" problem may be avoided by making preoperative measurements on a plain preoperative Grashey view. Below left, a line segment equal to half the baseplate diameter is drawn from the inferior glenoid to the articular surface perpendicular to the supraspinatus fossa line. A second line segment is drawn from the inferior glenoid lip to the intersection of the first line segment with the articular surface. This distance can me measured at surgery. This intersection indicates the starting point for the drill.

D. Superior tilt of baseplate. 

The "baseplate looking up" problem may be avoided by making preoperative measurements on a plain preoperative Grashey view. Below left a line (yellow) is drawn from the drill insertion point (see "C" above) parallel to the supraspinatus fossa line. This is the drill trajectory. Below right the angle between the drill trajectory and the superior face of the glenoid is noted and used to define the tilt of the drill for insertion of the baseplate.

Looking forward to your comments!

Northern Flicker

Matsen Backyard

2022

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). 

Does subscapularis sparing = subscapularis sparing?

Clinically important subscapularis failure is reported in approximately 5% of patients following anatomic total shoulder arthroplasty. For example, Functional and radiographic results of anatomic total shoulder arthroplasty in the setting of subscapularis dysfunction: 5-year outcomes analysis found that patients who develop subscapularis dysfunction after TSA have worse patient reported outcome, range of motion, functional tasks of internal rotation, and radiographic outcomes, as well as increased rates of revision. In spite of subscapularis dysfunction, these patients maintained clinically significant improvement for pain and function at a mean 5-year follow-up.

Some surgeons have advocated a "subscapularis-sparing" approach to shoulder arthroplasty, with the goal of improving patient outcomes. The theoretical advantages of the subscapularis-sparing approach include earlier rehabilitation, reduced risk of subscapularis failure, and preservation of anterior shoulder stability.  See for example, The subscapularis-sparing windowed anterior technique for total shoulder arthroplasty which reviewed 47 cases performed by an individual experienced surgeon. 

However a recent article, Safety and Efficacy of Subscapularis-Sparing Shoulder Arthroplasty Approaches: A Systematic Literature Review considered 15 studies (1573 patients) reporting subscapularis-sparing shoulder arthroplasty. Eight studies directly compared subscapularis-sparing and standard techniques. The authors concluded "subscapularis-sparing" shoulder arthroplasty is a safe and effective technique with comparable patient outcomes, range of motion, pain and revision to nonsparing techniques." - i.e. they did not find evidence of greater clinical value with the "subscapularis-sparing" approach.

Two articles directly compared the two techniques (both by the same authors):

Total shoulder arthroplasty using a subscapularis-sparing approach: A radiographic analysis concluded "Although anatomic restoration of the shoulder can be accomplished using subscapularis-sparing TSA, retained osteophytes and significant mismatch of the HHD raise concerns regarding long-term outcomes."

Subscapularis-Sparing Total Shoulder Arthroplasty: A Prospective, Double-Blinded, Randomized Clinical Trial reported "At short-term follow-up, the outcome of TSA using the SSC-sparing surgical approach was similar to the outcome of TSA using the standard approach."

Concerns

(1) Like all new techniques, subscapularis-sparing has a learning curve to be negotiated by each surgeon using it. Even in experienced hands, in certain cases the technique may need to be abandoned in favor of a subscapularis takedown. See The subscapularis-sparing windowed anterior technique for total shoulder arthroplasty. 

(2) Risk of subscapularis distruption. Ultrasound assessment after a subscapularis-sparing approach to total shoulder arthroplasty found that rate of subscapularis disruption using a subscapularis-sparing approach for aTSA by was 14% (32 (86%) of 37 were intact)- thus, the risk of tendon injury is not eliminated with the subscapularis-sparing approach. As is the case for the failures with the standard approach, those with disrupted tendons had reasonable patient-reported outcomes but demonstrated decreased strength in forward flexion, abduction, and external rotation. 

(3) Limited exposure (See The subscapularis-sparing windowed anterior technique for total shoulder arthroplasty.)

    a. Restricted visualization may result in suboptimal component positioning, with 31.8% of patients showing center-of-rotation differences >3 mm. Additionally, humeral head diameter mismatch >4 mm occurs more commonly in the subscapularis-sparing group compared to traditional approaches.

    b. Incomplete osteophyte removal occurs more frequently with the subscapularis-sparing technique, achieved in only 75% of cases compared to more complete removal with traditional approaches. 

(4) Complications

    Complication profiles were similar between subscapularis-sparing and standard approaches in the randomized trial, with 3 patients in the sparing group and 2 in the standard group requiring revision surgery. See: Subscapularis-Sparing Total Shoulder Arthroplasty: A Prospective, Double-Blinded, Randomized Clinical Trial 

[2]Incomplete osteophyte removal occurs more frequently with the subscapularis-sparing technique, achieved in only 75% of cases compared to more complete removal with traditional approaches. 

Comment:

The subscapularis-sparing approach is being explored to minimize clinically significant subscapularis dysfunction after shoulder arthroplasty. 

We have not adopted the subscapularis-sparing approach at this point; instead we prioritize surgical exposure to optimize glenoid component seating and complete osteophyte resection. We have not conducted a head to head comparison of our method to the subscapularis-sparing technique.

We also recognize that all shoulders and all subscapularis tendons are not the same.  Thus, as the protocol below emphasizes (steps 1, 2 and 3), assessing in each patient the risk factors for subscapularis failure - regardless of the technique used - is essential to surgical decision making.

As Johnathan Swift (author of Gulliver's Travels) pointed out in 1750:

Our approach for anatomic arthroplasty is based on several key steps:

(1) Assess preoperative stiffness. Shoulders with limited external rotation when the arm is adducted are at higher risk of repair failure.

(2) Assess preoperative strength. Shoulders with weak internal rotation may have poor quality subscapularis tendons increasing risk of postoperative failure.

(3) Assess other risk factors for subscapularis failure: inflammatory arthropathy, malutrition, steroid use, prior surgery

(4) In shoulders at high risk for subscapularis failure, consider a reverse rather than an anatomic total shoulder (aTSA).

(5) For patient having aTSA , release subscapularis tendon and subjacent capsule completely from lesser tuberosity, retaining capsule on the tendon's deep surface.

(6) Perform a 360 degree release of the subscapularis from the coracoid, glenoid, and inferior capsule to optimize excursion of tendon

(7) Perform glenoid arthroplasty

(8) If necessary, trial undersized humeral head component so that the lateral border of the subscapularis reaches the reattachment site at the lesser tuberosity with the arm in external rotation.

(9) Pass six FiberWire sutures through quality bone at the lesser tuberosity

(10) Insert humeral component sized per trialing (#5 above)

(11) Place additional FiberWire sutures in the rotator interval to reinforce the repair.

(12) Tie repair sutures

(13) Verify satisfactory motion before skin closure.

(14) Start assisted flexion in recovery room (note: our practice is to avoid plexus blocks for shoulder arthroplasty to allow sensory feedback during these exercises).

(15) Allow use of arm for activities with elbow at side. Gradually transition to active elevation starting at six weeks after surgery.

(16) Allow progressive increase in resistance over the first postoperaive year, making sure that 20 repetitions are easy and comfortable before adding additional weight.

Conclusion

Current evidence suggests that standard and subscapularis-sparing approaches produce similar outcomes. We prefer subscapularis peel and secure repair because in our hands it provides excellent exposure for osteophyte resection and glenoid component positioning and seating. At the same time we recognize that other surgeons may be equally comfortable with the subscapularis-sparing approach.

Making Choices

Cliff Swallows

Kalaloch Lodge, Washington

2021

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). 

Intraoperative navigation for shoulder arthroplasty - where are we going?

Computer-assisted navigation systems for shoulder replacement surgery are - like robotics (see What should be the role of robotics in shoulder arthroplasty?) - commercially advocated to aid surgeons in positioning components to match a preoperative plan based on a static preoperative CT scan.

Opinions vary among expert surgeons regarding which component positions (e.g. glenosphere position, lateralization, inclination; humeral distalization and lateralization) optimize patient reported comfort and function on one hand and minimize the risk of important complications (such as instability/dislocation and acromial/spine stress fractures) on the other. Furthermore the preoperative plan is formed in the absence of important intraoperative findings (such as soft tissue balance and bone characteristics) that are observed after the shoulder is surgically exposed and that often require the surgeon to modify the preoperative plan.

Let's consider a recent systematic review, The Role of Intraoperative Navigation in Reverse Total Shoulder Arthroplasty and its Impact on Clinical Outcomes: which assessed five studies with nearly 2,000 patients having reverses total shoulder carried out using ExactechGPS Navigation.

Three studies directly compared navigated versus conventional non-navigated reverse shoulder replacement. All three showed the same result: no clinically significant differences in functional outcomes.

Short-term clinical and radiologic outcomes of reverse total shoulder arthroplasty with navigation system in the Asian population: a retrospective comparative study found "the use of a navigation system in rTSA showed no significant difference in clinical outcomes and complications compared to conventional implantation."

Early clinical outcomes following navigation-assisted baseplate fixation in reverse total shoulder arthroplasty: a matched cohort study found: "navigated and non-navigated RSAs yielded similar rates of improvement in range of motion and functional outcome scores"

 Intraoperative navigation system use increases accuracy of glenoid component inclination but not functional outcomes in reverse total shoulder arthroplasty: a prospective comparative study. found "There were no statistically significant differences in ROM, PROMs, and satisfaction between patients receiving computer-navigated and standard RSA at a short-term follow-up. "

The review paper (The Role of Intraoperative Navigation in Reverse Total Shoulder Arthroplasty and its Impact on Clinical Outcomes) does not report comparative cost, surgical time, revision rates, or complication rates for patients receiving navigated and non-navigated reverse total shoulders. Furthermore, the article does not address the learning curve for this technology and whether this is a reasonable undertaking for the many surgeons who perform  relatively few reverse total shoulders per year.

Notably absent from all published studies is a comparative cost analysis. The proprietary nature of navigation system pricing—where capital equipment, disposables, software, and per-case fees create opaque total costs—prevents the field from conducting basic cost-effectiveness evaluation. 

There is yet another issue: that of complications related to the navigation system itself, such as problems with fixation of the device to the coracoid. Coracoid fracture represents an uncommonly reported but specific complication of navigation-assisted shoulder arthroplasty, with an overall reported incidence of approximately 0.05% in experienced hands but significantly higher rates (up to 30%) during the learning curve. 

High intraoperative accuracy and low complication rate of computer-assisted navigation of the glenoid in total shoulder arthroplasty analyzed 16,723 navigated shoulder arthroplasty cases reported 9 coracoid fractures.

GPS NAVIGATION SYSTEM ALLOWS THE SURGEON TO PREPARE THE IMPLANT SITE AS PLANNED ON PREOPERATIVE SOFTWARE IN REVERSE SHOULDER ARTHROPLASTY: 3 coracoid fractures in the first 10 cases

THE USE OF NAVIGATION IN REVERSE SHOULDER ARTHROPLASTY: PRELIMINARY REPORT OF 11 CASES: 1 fracture in the first case.

Safety and Efficacy of Intraoperative Computer-Navigated Versus Non-Navigated Shoulder Arthroplasty at a Tertiary Referral: 2 cases (5.5%) of coracoid fracture.

If you are curious, here's some detail about the ExactechGP Navigation system.  You might like by looking at this video

The Basic Technology -  

The Components:

1. Preoperative Planning

    * Patient gets a CT scan of their shoulder

    * Surgeon uploads CT to Equinoxe Planning App software

    * Surgeon creates a 3D virtual plan: glenoid component position, version, inclination, depth, screw trajectories

    * Within days, the plan is uploaded to GPS workstation

2. Intraoperative Hardware

GPS Workstation:

    * Compact mobile unit within sterile field

    * Has an infrared camera that tracks the LED markers

    * Screen displays real-time surgical guidance

Three Active Trackers (reusable, battery-powered with IR LEDs):

    * Probe Tracker: Hand-held pointer for registration

    * Glenoid Tracker: Attached to coracoid process (bone stabilizer)

    * Tool Tracker: Attached to surgical instruments (reamers, drill guides)

3. The Workflow

Step 1: Registration (Mapping CT to Patient)

    * Surgeon attaches Glenoid Tracker to coracoid process with a pin

    * Using the Probe Tracker, surgeon touches specific anatomic landmarks on the scapula

    * System matches these physical points to the CT scan

    * Creates a "coordinate system" linking the patient's real anatomy to the virtual plan

Step 2: Real-Time Guidance

    * Surgeon attaches Tool Tracker to reamer/drill/guide instruments

    * Camera tracks all three trackers simultaneously via their IR LEDs

    * Screen shows:

        o Current instrument position vs. planned position

        o Version and inclination in real-time

        o Reaming depth

        o Screw trajectories and lengths

Step 3: Verification

    * After component placement, system verifies final position

    * Compares achieved vs. planned placement

Conclusion:

The question each surgeon must ask is whether intraoperative navigation addresses problems experienced by patients in their own practice having reverse total shoulder arthroplasty.

The question the field of shoulder surgery must ask is which specific patient problems (instability? fracture? stiffness? pain?) occur due to positioning errors that: (a) surgeons using standard techniques cannot adequately control, and (b) navigation systems would prevent. 

Finding the way

Snow Geese 

Skagit, Washington

202

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).