Preventing Acromial/Scapular Spine Fractures in Reverse Shoulder Arthroplasty: Defining what the surgeon can control.

I'll start out with a few conclusions:

(1) Acromial and scapular spine stress fractures are clinically important complications of reverse total shoulder arthroplasty (RSA), occuring in 3-11% of cases and often resulting in poor functional outcomes such as persistent pain and limited active motion. 

(2) The principal risk factors - female sex, advanced age, poor bone quality, inflammatory arthropathy, cuff deficiency, corticosteroid use, thinned acromion from prior surgery or erosion, proximal humeral migration - are not under the control of the surgeon, except as they affect the decision to proceed with RSA surgery. 

(3) Surgeons do control humeral and glenosphere component selection and positioning. However the evidence guiding practice is not robust due to the lack of standardized nomenclature and what parameters should be measured in future clinical research. 

Here are a set of four easy to make measurements the importance of which is supported by the review below. These address the problem of uncertainty and inconsistency found in published studies regarding RSA geometry. Such measurements will be important in answering the key questions surgeons have: what component positions provide the best function and which minimize the risk of complications such as scapular stress fractures for my patients?

(1) Acromio-humeral distance measured from the acromion to the greater tuberosity along a line parallel to the bony glenoid face (both post-op and pre-op to post-op change).

(2) The perpedicular distance between the glenosphere center of rotation (COR yellow dot) and the glenoid bony face (yellow line)

(3) The perpendicular distance between the lateral extent of the glenosphere and the glenoid bony face (blue line)

(4) The perpendicular distance between the tuberosity and the glenoid bony face (long black line).

Consistent use of these measurements would address much of the current ambiguity in the literature, as illustrated by the following review.

Glenosphere lateralization 

One of the issues in reviewing the literature on "glenosphere lateralization" is a failure of many articles to define the term. Are the authors talking about lateralization of the center of rotation in relation to the glenoid bone (yellow line) or lateralization of the lateral aspect of the glenosphere in relation to the glenoid bone (blue line)? The former affects the deltoid moment arm and the range of impingement-free range of motion, while the latter contributes to the global lateralization of the humeral tuberosity (black line) which affects the soft tissue tension that is important for stabilizing the articulation through concavity compression. As seen in Know Your Glenospheres these two dimensions can be varied independently by changing the diameter of curvature of the glenosphere. The effect of the humerus on the global lateralization is the difference between the black and blue lines. 

Biomechanical studies

Implant positioning in reverse shoulder arthroplasty has an impact on acromial stresses and The effect of load and plane of elevation on acromial stress after reverse shoulder arthroplasty found that glenosphere lateralization, but not humeral lateralization, increased acromial stress.

Factors Influencing Acromial and Scapular Spine Strain after Reverse Total Shoulder Arthroplasty: A Systematic Review of Biomechanical Studies found glenoid lateralization was consistently associated with increased acromial and scapular spine strain. 

In addition, transection of the coracoacromial ligament resulted in significantly increased strains. Although preserving the integrity of the CAL is not an implant-related factor, it is a surgeon-controlled variable. Its importance is demonstrated in two basic science papers: Scapular Ring Preservation: Coracoacromial Ligament Transection Increases Scapular Spine Strains Following Reverse Total Shoulder Arthroplasty and Coracoacromial ligament integrity influences scapular spine strain after reverse shoulder arthroplasty and finally the clinical study Does Preservation of Coracoacromial Ligament Reduce the Acromial Stress Pathology Following Reverse Total Shoulder Arthroplasty? Transection of the coracoacromial ligament consistently increased scapular spine strain in biomechanical studies and was associated with higher clinical fracture rates in the 265-patient study (29.4% vs 13.2% with CAL section vs. preservation).

Clinical evidence

There is a lack of clinical studies that have actually measured the radiographic glenosphere COR lateralization and correlated it with acromial fracture risk.  

Up to 8 mm of glenoid-sided lateralization does not increase the risk of acromial or scapular spine stress fracture following reverse shoulder arthroplasty with a 135° inlay humeral component examined RSA patients categorized based on implant specifications (metallic offset from baseplate and glenosphere selection). The amount of glenoid-sided lateralization varied from 0 to 8 mm in 2-mm increments. The actual glenosphere COR lateralization with respect to the glenoid bone was not measured radiographically. 

Does isolated glenosphere lateralization affect outcomes in reverse shoulder arthroplasty? compared shoulders with the COR 2 mm lateral to the glenoid bone to those with the COR 6 mm lateral to the glenoid bone. Acromion and spine fractures were found it 3% of the 2 mm group and in 1% in the 6 mm group.

Lateralized versus nonlateralized glenospheres in reverse shoulder arthroplasty: a systematic review with meta-analysis found no difference in acromion/ spine fracture rates between RSAs catagorized as "lateralized" and "nonlateralized". Data on the difference in COR to glenoid bone distance for the two groups are not presented.

The risk of postoperative scapular spine fracture following reverse shoulder arthroplasty is increased with an onlay humeral stem did not find a fracture rate difference between lateralized and non-lateralized glenospheres. Data on the difference in COR to glenoid bone distance for the two groups are not presented

Implant-Positioning and Patient Factors Associated with Acromial and Scapular Spine Fractures After Reverse Shoulder Arthroplasty found that "excessive" glenoid-sided and global lateralization were associated with higher fracture rates; "excessive" is not defined. "Total glenoid lateral offset" was defined as the sum of lateralization contributed by the glenosphere, baseplate, and bone graft if present. Data on the relation of the glenosphere COR to the humeral bone are not presented.

Humeral position

The humerus can be moved distally by the glenosphere (inferior positioning on the glenoid bone, inferior tilt, inferior offset) and by the humerus (using an onlay component, high positioning of an inlay component). Humerus distalization can be documented in terms of postoperative position or as the change in preoperative to postoperative position. 

Different methods have been used to characterize humeral distalization making it difficult to compare studies. It seems most intuitive to directly measure acromiohumeral distance: the distance from the lateral acromion to the lateral prominence of the tuberosity along a line parallel to the glenoid face. This approach can be used both before and after RSA.

Influence of implant design and parasagittal acromial morphology on acromial and scapular spine strain after reverse total shoulder arthroplasty: a cadaveric and computer-based biomechanical analysis found that lengthening above 25 mm produced large strains in the acromion and scapular spine.

Up to 8 mm of glenoid-sided lateralization does not increase the risk of acromial or scapular spine stress fracture following reverse shoulder arthroplasty with a 135° inlay humeral component found that the change in acromiohumeral distance (delta AHD) was significantly higher in the stress fracture group. For every 1cm increase in delta AHD, there was a 121% increased risk for fracture. For every 1mm increase in inferior glenosphere overhang, there was a 19% increase in fracture risk.

The risk of postoperative scapular spine fracture following reverse shoulder arthroplasty is increased with an onlay humeral stem found "Increased postoperative distalization is associated with an increased risk of SSF after RSA." While the authors also concluded that  "An onlay stem resulted in a 10 mm increase in distalization compared with an inlay stem, and a 2.5 times increased risk of SSF. " it is apparent that what's important is not only the component design (inlay vs onlay) but also on the amount of distalization, which is influenced by both design and implant position. An onlay component can be inset in the humerus while an inlay component can be placed high with respect to the tuberosity.

Acromial Fractures in Reverse Shoulder Arthroplasty: A Clinical and Radiographic Analysis  greater arm lengthening was more common in the fracture group 

Predictive factors of acromial fractures following reverse total shoulder arthroplasty: a subgroup analysis of 860 shoulders  showed that a significant association of higher postoperative lateralization (by lateralization shoulder angle), lower distalization (by distalization shoulder angle), a lower acromiohumeral distance, and higher age were predictive only for Levy type III fractures. These result are  contradictory to other data, possibly because of small numbers (only 16 Levy III fractures) and the confounder of older age. Notably among the 860 shoulders the fracture types most clearly related to deltoid tension (Levy I and II) showed no association with any measured parameter.

The data on the effect of humeral component lateralization on acromial/spine fractures is inconclusive.

Summary: The current data are incomplete and, in many cases, inconclusive. Humeral distalization beyond 20-25mm appears to increase fracture risk (biomechanical threshold ~25mm; clinical data showing 121% increased risk per 10mm increase in delta acromiohumeral distance). Transection of the coracoacromial ligament consistently increased scapular spine strain in biomechanical studies and was associated with higher clinical fracture rates in the 265-patient study (29.4% vs 13.2% acromial pathology with CAL section vs. preservation).

Basic science data suggest that glenosphere COR lateralization may increase fracture risk, but clinical studies using categorical classifications ('lateralized' vs 'non-lateralized') without actual measurements are inconclusive. 

The effect of humeral lateralization remains unclear. 

Thus for high-risk patients (elderly women, inflammatory arthropathy, prior acromioplasty, thin acromion), limiting the change in acromiohumeral distance (delta AHD) to <20mm,  preserving the CAL, and avoiding excessive glenoid lateralization may be prudent pending better evidence—which will require standardized measurements such as those proposed above.

See also Preventing Scapular Spine Fractures: The Superior Baseplate Screw Question

Fractures

Mt. Rainier National Park

July 2024

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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).

Know your glenospheres

The geometry of reverse total shoulder (RSA) implants along with the soft tissue tension and balance are important determinants of the outcome for patients having this procedure. Surgeons need to understand the characteristics of the implants they use so they can made good decisions for each of their patients. While humeral component design and placement, soft tissue management, and the preoperative to postoperative change in acromio/humeral distance are critical variables in RSA, here we'll zone in on the glenosphere.

The nomenclature used to describe the geometry of the glenosphere can be confusing and differs among the manufacturing companies. 

Here's a simplified approach to characterizing three key elements of glenosphere anatomy that can be applied to any make of glenosphere

(1) Glenosphere diameter of curvature (blue line) 

2) Distance from center of rotation (COR) to glenoid bone (yellow line)

Note that this distance needs to include the thickness of the baseplate lying between the glenosphere and the bone, which varies by manufacterer and with the use of augments.

The "names" of the glenospheres may not be accurate descriptions their geometry. For example for the 32 mm diameter implants in one company's system, there are 32 "neutral", 32 -4, and 32 -6. Including a 3 mm thick baseplate, the distances from the COR to the glenoid bone surface are, respectively 13 mm, 9 mm, and 7 mm (not 0, -4 and -6).

The COR lateralization from bone for the 32, 36 and 40 diameter of curvature glenospheres in this system are shown below.

Note that the COR to bone distance is the same for the 32 -6 and the 40 "neutral"

3) The glenosphere's contribution to the lateralization of the humerus. This is equal to the COR lateralization from the glenoid bone + the radius of the glenosphere (shown by the blue line in the figure below). 

These values for the 32, 36, and 40 mm glenospheres are shown in the right column of the chart below.

Note that the distance from glenoid bone to the lateral aspect of the glenosphere is the same for the 32 -6, the 36 -4 and the 40 -4. 

Since even the most sophisticated preoperative planning software cannot predict which glenosphere will provide the best mobility and stability, we have to rely on intraoperative trialing to determine the best glenoid component geometry. A chart like the above is handy to guide our component trialing by pointing out the COR lateralization (which affects deltoid moment arm and range of motion) and total lateralization (which affects soft tissue tension and stability thorough concavity compression) for the different options. 

During trialing the surgeon can assess shuck when the humerus is pulled laterally, unwanted bone contact, range of motion (including extension), and stability using a variety of tests including the two hand lever test.  

A 32 -6 may be a reasonable starting point in a small patient with a tight shoulder. An average sized patient with cuff tear arthropathy might merit starting with a 32 -4. A large patent needing stability may need a 36 neutral or 40 -4.

There are many important elements of a good reverse total shoulder arthroplasty. Selecting the best glenosphere for the patient is one of them.

Making good choices

Lewis' Woodpecker

Tualatin

2020

Follow on twitter/X: https://x.com/RickMatsen
Follow on facebook: https://www.facebook.com/shoulder.arthritis
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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).

Preoperative planning for reverse total shoulder using plain films.

A major component of the success of reverse total shoulder arthroplasty is the position and orientation of the base plate on the glenoid bone. While many different planning systems are available, the challenge is transferring the plan to the patient without relying on expensive and time-consuming approaches, such patient specific instrumentation or augmented reality.

Our usual target is to have the inferior edge of the baseplate at the inferior aspect of the reamed glenoid and tilted inferiorly with the central screw or peg inclined so that it is parallel to the floor of the supraspinous fossa. 

For routine cases, we plan for rTSA using plain x-rays obtained in the plane of the scapula (Grashey view). The scaled image is uploaded to the universally available PACS (Picture Archiving and Communication System). PACS tools are used to find the location of insertion point and the inclination of the drill for the central screw or post. These scaled measurements are then used to position and orient the drill on the patient's glenoid in the operating room. This generic approach does not encourage the surgeon to select implants from any particular company.

Here's an example: a 70 year old man with a massive irreparable cuff tear and pseudo paralysis. 

On the PACS screen a line segment (yellow) with a length equal to the radius of the base plate is drawn perpendicular to the floor of the supraspinatus fossa (red line) from the glenoid articular surface to the glenoid neck. The upper end of this line is the insertion point (yellow dot)

The distance of this point along the glenoid articular surface (green line) from the inferior glenoid lip is measured on the scaled PACS image. The insertion point can be found at surgery by measuring this distance using a flexible ruler.

The angle of drill insertion (dotted gold line) relative to the joint surface at the insertion point (black line) is noted on PACS and duplicated at surgery.

 

Favard et al have described four types of glenoid pathoanatomy in cuff tear arthropathy.  

For some cases, such as types E1 and E3, this planning approach may indicate that excessive reaming of inferior glenoid bone would be necessary to achieve the desired baseplate position and orientation. In such cases superior bone grafting or an augmented baseplate may be called for.

While more sophisticated proprietary systems can be used for more complex pathoanatomy, this generic approach can be effective for a large percentage of rTSA cases.

We use a similar plain films/PACS approach to planning a stemless anatomic arthroplasty - see this link.

Sometimes a convenient solution is staring right at us

Sooty Grouse

Mt. Rainier

July 4, 2025

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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).

Reverse total shoulder revisions and glenosphere size - are we asking the right questions?

 Effect of glenosphere size on reverse shoulder arthroplasty revision rate: an analysis from the Australian Orthopaedic Association National Joint Replacement Registry

These authors sought to investigate the relationship between glenosphere size and revision rates among 28,817 primary reverse total shoulder arthroplasty (RTSA). 

They concluded that glenosphere sizes <38mm had a higher revision rate compared to 38-40mm glenospheres (HR =1.28)) and >40mm sizes (HR=1.35). 

Males with  <38mm and 38-40mm glenospheres had significantly higher revision rates compared to >40mm glenospheres (HR = 1.49 and HR = 1.28). 

Females with <38mm and >40mm glenospheres had higher revision rates compared to females with 38-40mm glenospheres (HR 1.38 and HR 1.41). 

For patients aged 65-74 years, glenospheres >40mm had a significantly lower revision rate than both the <38mm glenospheres and 38-40mm glenospheres.

The Delta Xtend with 38-40mm glenospheres had higher revision rates compared to >40mm glenospheres (HR=1.49). 

The SMR L1, 38-40mm glenospheres had a lower rate of revision compared to <38mm (HR= 0.50) and >40mm glenospheres (HR=0.60).

They concluded that revision rates were lower for females with 38-40mm glenospheres and lower for males with >40mm glenospheres.

Comment: The Australian Orthopaedic Joint Replacement Registry is an invaluable resource in that it is centrally administered and that systematically captures data from essentially all of the joint replacements in the country, avoiding the problem of transfer bias and selection bias that confounds many case series. The AOAJRR provides important information on rates of revision and factors associated with revision arthroplasty. It does not, however, enable analysis of the relationship between factors - such as glenosphere size - and patient-reported measures of comfort and function.  

In this study the authors recorded over twenty different reasons for revision of RTSA ("revision diagnoses") ranging from dislocation to heterotopic bone formation. The strategies for preventing glenohumeral dislocation are surely different than those for preventing infection, implant loosening, dissociation of the glenosphere from the baseplate, glenoid implant breakage, or heterotopic bone formation.  Is glenosphere size really the primary determinant of each of these reasons for revisions?

The registry contains a number of important variables: patient age, sex, diagnosis, and  prosthesis manufacturer in addition to glenosphere size. The large numbers of patients in the registry provides a unique opportunity to perform a multivariate analysis (MVA) for each of the major RTSA revision diagnoses. In contrast to previously published case series where the number of revisions is low, they have the numbers to do this: 339 cases of instability, 231 cases of infection, 179 cases of loosening, and 123 cases of fracture. 

The question to be asked with a MVA is, "what factors (including but not confined to glenosphere size) are independently associated with each of the major revision diagnoses?"

The answers will be be interesting if not surprising.

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How you can support research in shoulder surgery Click on this link.

Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link)

Shoulder arthritis - x-ray appearance (see this link)

The smooth and move for irreparable cuff tears (see this link)

The total shoulder arthroplasty (see this link).

The ream and run technique is shown in this link.

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).

Reverse total shoulder - effects of bony and prosthetic glenoid lateralization

Finite element analysis of glenoid-sided lateralization in reverse shoulder arthroplasty

These authors conducted a 3D finite element analysis (FEA) to evaluate glenoid-sided lateralization in reverse shoulder arthroplasty and compared bony and prosthetic approaches to lateralization. Bony lateralization was accomplished by the insertion of a bone graft between the baseplate and the glenoid. Prosthetic lateralization was accomplished by either increasing the thickness of the base plate or increasing the thickness of the glenosphere.

Stress and displacement were evaluated at baseline and following 5, 10, and 15 mm of bony or prosthetic lateralization. 

Maximum stress for a 36 mm glenosphere without bone graft increased by 137% for the 5 mm graft, 187% for the 10 mm graft, and 196% for the 15 mm graft. Displacement also increased progressively with increasing graft thickness. 

Stress and displacement were reduced with a smaller glenosphere, inferior tilt of the baseplate, and divergent peripheral screws. 

Compared to bony lateralization, stress was lower with prosthetic lateralization through the glenosphere or baseplate. 

Displacement with 5 mm of bony lateralization reached recommended maximal amounts for osseous integration, whereas, this level was not reached until 10–15 mm of prosthetic lateralization. 

Baseplate stress and displacement in this FEA model was lower with a smaller glenosphere, inferior tilt, and divergent screws. 

Bony lateralization increased stress and displacement to a greater degree than prosthetic lateralization.

The authors concluded that at least 10 mm of prosthetic lateralization is mechanically acceptable during RSA, but that only 5 mm of bony lateralization is advised. 

Comment: There seems to be a trend away from the original Grammont design of reverse total shoulder

because of concerns about (1) scapular notching, (2) neurologic consequences of lengthening the arm, and (3) external rotator weakness from medialization of the humerus. With the advent of secure baseplate fixation, surgeons can reduce the notching and neurologic risks with a more anatomic reconstruction that includes East-West tensioning of the residual external rotators and other soft tissues. This lateralization can be accomplished by interposing a bone graft between the baseplate and the glenoid bone 

or by having a lateral offset built into the prosthesis. While bone graft has shown a high healing rate, there is concern about the possibility of compression of the graft with loss of the intended amount of lateralization. Our preference is for an implant system that allows variable lateral prosthetic offset combined with secure baseplate fixation. 

 

This article provides additional support for the use of prosthetic lateralization.

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Click here to see the new Shoulder Arthritis Book.

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Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

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Reverse total shoulder - is the glenosphere completely seated?

Since we posted on this article in April, we have checked the number of turns of the set screw in the fully seated glenosphere of the DJO reverse shoulder prosthesis. In each case 4.5 turns were necessary to fully tighten this screw. Should it not be possible to turn the screw 4.5 times, we would be concerned about incomplete seating of the glenosphere. This check is now a routine part of our procedure.

The April post is reproduced below

A nondestructive method to verify the glenosphere-baseplate assembly in reverse shoulder arthroplasty

These authors point to the uncommon but important risk of glenophere dissociation reverse shoulder arthroplasty.  A mechanically compromised Morse taper is thought to be the main cause of this complication, with bony abutment and soft tissue interposition being cited as the most important problems along with cantilevered engagement of the glenosphere due to impaction under a slight angle and incomplete engagement due to proud or cross-threaded baseplate screws.

They suggest that current methods for assessing the security of the Morse taper assembly require applying considerable torque to the glenosphere which may damage the quality of the taper. They proposed measuring the implant-specific angular rotation–torque curve while engaging the Morse taper by tightening the central locking screw. 

As can be seen from their graph below, in comparison to the desired (baseline) seating, the torque increase with screw tightening occurs with fewer rotations of the screw driver when there is interposition or abutment.

This is shown diagrammatically below; note that the insertion of the screw was blocked with fewer turns of the screw in cases B and C when the glenosphere is incompletely seated.

Although small interpositioning and impingement defects are difficult to detect without using an instrumented tool, such as the one presented in this study, large defects could probably be detected without an instrumented tool. The 1000-μ m and 2000-μ m defects locked the screw for both tested implants more than 1 full turn before their normal angular rotation end point. Thus the authors propose the following:  By applying moderate pressure on the glenosphere central screw while screwing in a counterclockwise direction before the start of engagement, a “click” can be sensed that indicates the starting point. From that point on, the number of turns can be counted before a considerable amount of torque needs to be applied to the screw to further tighten it. If the screw begins to tighten 1 or more full turns less than the number of turns known to completely seat the screw (approximately 6.4 full turns for the Delta CTA or Delta Xtend implant), it is time to check for peripheral bony abutment or soft tissue interposition. Note that the number of full rotations before reaching the angular rotation end point is prosthesis specific.

Comment: By virtue of its constrained kinematics, the reverse total shoulder transmits loads directly from the humeral component to the glenoid component, without the suppleness of a normal or an anatomic arthroplasty. Thus, the fixation and integrity of reverse total shoulder components may be challenged by impacts that would be unlikely to affect a conventional total shoulder. Because the reverse total shoulder components are often modular and held together by Morse tapers and because they can be loaded in directions that can challenge the Morse taper, there is a risk of dissociation with impact loading.

Glenoid component dissociation has been reported with various designs of reverse total shoulders (Sirveaux 2004)(Ekelund 2011) (Zumstein 2011) (Middernacht 2008)(Farshad 2010)(Kempton 2011)(Clark 2012).

A recent article on Glenosphere dissociation after reverse shoulder arthroplasty is of interest. These authors reviewed their reverse total shoulder arthroplasty database and identified 13 patients with glenosphere dissociation between 1999 and 2013; dissociation occurred 0.5 months to 7 years postoperatively.Incidence of dissociation was correlated to glenosphere size (p < .001). Dissociated glenosphere size distribution was as follows: 32 mm (n = 1), 36 mm (n = 4), 40 mm (n = 6), and 44 mm (n = 2).The authors noted that improper taper engagement reduced the torsional capacity of the glenosphere-baseplate interface.

The risk of dissociation can be reduced by considering the geometry of the specific implant and the instruments, by specific surgical steps, by vigorous intraoperative testing and by cautioning the patient to avoid impact loading after surgery. 

As is the case with any Morse taper, incomplete seating - even by a fraction of a millimeter - can reduce the security of the cold weld between the two parts assembled by the taper. Complete seating can be prevented by fluid in the well of the female aspect of the assembly, by tissue or bone that block complete seating, or by insufficient force applied to impact the two components together.

In the design shown below, the glenoid head (glenosphere) fits over the baseplate but does not completely cover it. thus it may be difficult to see whether or not the glenoid head is completely seated. 

Instruments, such as the rim reamer shown below help remove potentially interfering bone that may prevent the glenoid head from being completely seated.

This works well for the small glenoid head, because the outside diameter of the rim reamer is greater than that of the collar of the small glenoid head.

The rim reamer may be less effective when the collar of the glenoid head has an outside diameter greater than that of the rim reamer.

The principal method by which the seating can be verified is to pull vigorously on the glenoid head after it has been impacted into position, attempting to dissociate it from the baseplate. With some designs, vigorous traction can be applied using a t-handled instrument. An even better test can be performed by attempting to twist the glenosphere using the t-handle: if it twists on the base plate, it is not securely seated. 

After the glenosphere has been securely impacted into position, the retaining screw is inserted. The retaining screw should be tightened to the maximum number of turns that the Torque Driver allows. The Torque Driver will limit the torque to 22.5 in-lbs +/- 2.5 in-lbs. It will typically be about four full turns for all glenospheres.
After surgery, patients need to be reminded that impact loading is to be avoided.

Our current reverse total shoulder technique is shown in this link.


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Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

To see the topics covered in this Blog, click here

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'


See from which cities our patients come.

See the countries from which our readers come on this post.