Sunday, October 26, 2025

The three faces of pyrocarbon shoulder arthroplasty

I suspect that few of you have seen the 1957 Oscar Award winning movie the three faces of Eve, based on the true story of a woman with three distinct personalities.

We now have three faces of pyrocarbon shoulder arthroplasty, which - as in the case of Eve - can be confusing.

(1) The pyrocarbon interposition shoulder arthroplasty (PISA). In this application a pyrocarbon sphere is inserted between the glenoid and the reamed proximal humerus. There is no fixation of the implant to the humerus.

The outcomes for this implant have been recently summarized:Long-term (minimum 10 years) survival and outcomes of pyrocarbon interposition shoulderarthroplasty

(2) The pyrocarbon hemiarthroplasty In this application a pyrocarbon humeral is supported by a short humeral stem. Because pyrocarbon is brittle and cannot bear high bending or shear loads directly, a metal disc is used to provide rigid structural support, distributing stresses evenly from the pyrocarbon head to the humeral stem to prevent fracture or delamination of the pyrocarbon–graphite composite under load.

The outcomes for this implant have been recently summarized: Pyrocarbon hemiarthroplasty for the treatment of shoulder osteoarthritis in young, active patients: survival and risk factors for revision

and

(3) The pyrocarbon resurfacing arthroplasty. In this application, the implant consists of a pyrocarbon shell (the articulating surface) that’s bonded to a graphite or carbon–carbon substrate. On the deep (bone) side, this substrate is attached to a small metal fixation post or peg, made of titanium alloy. The peg fits into a reamed cavity in the humeral head, providing press-fit fixation.The pyrocarbon layer is relatively thin (≈1–2 mm) and brittle. The bone itself provides the primary structural support, i.e. the implant relies on the intact humeral head bone stock. If the humeral head bone is weak (osteopenic, cystic, or osteonecrotic) or irregular, the peg may not be fully supported, leading to subsidence or breakage. The implant is press-fit, not stemmed, so the peg can loosen if the bone does not integrate well. Pyrocarbon is brittle compared to metal, so if there is malalignment, eccentric loading, or joint incongruity, it can chip, break or wear at the edges.

The outcomes for this implant have been recently summarized: Outcomes of pyrolytic carbon humeral resurfacing hemiarthroplasty compared to best in class total shoulder arthroplasty in young patients with osteoarthritis: analysis from the Australian Orthopaedic Association National Joint Replacement Registry.

We'll spend a bit of time on this "face" of pyrocarbon in that it is relatively less familiar to most of us.

The authors of the above referenced study compared the survivorship and reasons for revision between pyrocarbon resurfacing and the best performing anatomic total shoulder arthroplasty prostheses. The included included all primary shoulder arthroplasty procedures undertaken for osteoarthritis (OA) in patients aged < 65 years and reported to the Australian Orthopaedic Association Joint Replacement Registry between September 2004 and December 2022. Two cohort groups were compared; 403 pyrolytic carbon (pyrocarbon) humeral hemi-resurfacing (PHR) and 1,952 anatomic total shoulder prostheses (five different designs with polyethylene glenoid components selected for their low cumulative percent revision at 5 years).

There were 20 (5.0%) PHR and 123 (6.3%) aTSR revised.

The predominant reason for revision in the aTSAs was loosening (34%).

The predominant reason for revision was implant breakage (35%) for PHR.

As discussed above, the lack of metal support for the resurfacing implant leaves it vulnerable to fracture from eccentric loading. The pyrocarbon layer is typically only 1–2 mm thick. Unlike metal-backed implants, there’s no broad metal support, so any concentrated stress can propagate cracks.

With this resurfacing implant there also may be a risk of overstuffing of the joint. Here's an illustration from the paper:

Note the lateralization of the humerus and the overstuffing by the surface-mounted implant.

In contrast, when the head cut is made in conventional hemiarthroplasty (see below), the surgeon has the opportunity to adjust head position and thickness, balancing joint laxity and stability.

Comment: These innovations (along with countless others) represent attempts to improve outcomes for patients having shoulder arthroplasty. However, as George Athwal pointed out in his memorable Neer Lecture at the 2025 meeting of the American Shoulder Elbow Surgeons, we may be reaching the limit of what can be accomplished with "innovative" changes in implants, rather improvement is more likely to come from attention to surgeon education, patient selection and surgical technique.

It's about making wise choices

Great Horned Owl

Washington Part Arboretum

2023

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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).

Saturday, October 25, 2025

Napoleon and how to use graphics effectively - a lesson from 1869. NB: post ends with cannon fire.

Not infrequently we see a graphic like this

that consumes a huge amount of space in comparison to a simple sentence: "45% of the patients were male and 55% female". That picture is surely not worth 1,000 words.

By contrast in 1869 Charles Joseph Minard set the standard for the most content-rich graphic.

Let me first sent the scene.

In the summer of 1812, Emperor Napoleon Bonaparte

launched his most ambitious and disastrous military campaign: the invasion of Russia. At its height, his Grande Armée numbered over 600,000 soldiers, drawn from across Europe — French, German, Italian, Polish, and others.

His goal was to force Tsar Alexander I of Russia back into compliance with the Continental System, a blockade designed to isolate Britain economically

On June 24, 1812, Napoleon’s army crossed the Niemen River, entering Russian territory. He expected a swift victory — perhaps a single decisive battle leading to Russian surrender. Instead, the Russians under Generals Barclay de Tolly and later Kutuzov refused to give battle. They retreated steadily eastward, employing a scorched-earth policy: burning crops, villages, and supplies to deny resources to the invaders.

As Napoleon advanced deeper into Russia, the vast distances, poor roads, heat, and disease took a terrible toll. Thousands of horses died; supply lines stretched thin. Yet Napoleon pressed forward, hoping for a decisive engagement.

The Russians finally made a stand at Borodino, about 70 miles west of Moscow, on September 7, 1812. It was one of the bloodiest single-day battles of the Napoleonic Wars.The French attacked fiercely, using artillery and infantry in massive assaults.The Russians, entrenched behind earthworks, resisted stubbornly. By the day’s end, about 70,000 men were dead or wounded. The Russians withdrew in good order, but the path to Moscow lay open.

Napoleon entered Moscow on September 14, 1812, expecting Tsar Alexander to sue for peace. Instead, the city was nearly deserted — and soon fires broke out, destroying much of it. The French occupation turned hollow and desperate. With winter approaching, no peace offer came, and supplies were dwindling.

After five weeks in the ruined city, Napoleon realized he could not remain. On October 19, 1812, he began the retreat which was a catastrophe. Temperatures dropped rapidly, roads turned to ice, and snowstorms struck the exhausted troops. The Grande Armée, already weakened by hunger and disease, disintegrated under the strain. Cossack cavalry and Russian regulars harried the retreating columns. Starvation, frostbite, and exhaustion killed tens of thousands. At the crossing of the Berezina River in late November, only desperate improvisation saved a fraction of the army from total destruction.

Napoleon returned to Paris ahead of his shattered army, arriving in December 1812. The disaster marked the turning point of his empire. His aura of invincibility was broken; within two years, a coalition of European powers had driven him from power.

The campaign became a symbol of hubris and overreach, and its horrors were immortalized in literature, art, and one of the most famous data visualizations in history — Charles Joseph Minard’s 1869 diagram of the army’s advance and retreat, showing both the route and the dwindling number of survivors as the temperature dropped.

In this action-packed illustration, Napolean's advance into Russia is shown in tan, while his retreat is shown in black. The width of the tan and black reflect the number of troops. Of the more than 600,000 men who had entered Russia, fewer than 25,000 returned. At the bottom of the chart is a plot of the temperature the troops experienced on the way home: 43 degrees F when leaving Moscow on October 19, 1812 dropping to -15 degrees F at the crossing of the Berezina River on November 29, 1812.

For the history buffs, the story is told in detail here.

To bring this post to a close, click on this celebration of Napolean's defeat.

Full performance w/ pyrotechnics! | Tchaikovsky | 1812 Overture

complete with canon fire.

This post was inspired by an article in today's New York Times:

Friday, October 24, 2025

When should we consider anatomic total shoulder arthroplasty in patients under 50 years of age?

It is well recognized that patients under the age of 50 often have risk factors for inferior clinical outcomes from shoulder arthroplasty:

(1) more complex arthritis (avascular necrosis, capsulorrhaphy arthropathy, chondrolysis, rheumatoid arhritis, anchor arthropathy, post traumatic arthritis, failed non-arthroplasty surgery, post infectious arthritis, etc.),

(2) higher activity levels,

(3) higher expectations,

(4) increased longevity,

(5) increased risk of cutibacterium periprosthetic infection.

The arthroplasty options for managing arthritis in younger patients include: hemiarthroplasty, ream and run, total shoulder arthroplasty and reverse total shoulder arthroplasty. The choice among these options needs to be made by shared patient-surgeon decision making. Because of the many factors that weigh on this decision, it is unlikely that randomized controlled trials or propensity matching will yield patient-specific guidelines on "the best" approach for young patients with arthritis. Because the surgeon is the method, different surgeons will lean toward certain options based on their experience and training.

The authors of Anatomic Total Shoulder Arthroplasty Indications, Outcomes, and Survivorship in Patients Younger Than 50 Years of Age: A Systematic Review reviewed articles published in last 44 years and found 9 that met their inclusion criteria representing 184 shoulders in 173 patients with a mean age ranging from 33 to 44 years of age. As indicated above, a minority (38%) had primary osteoarthritis, while 35% had rheumatoid arthritis, 9% post-traumatic arthritis, 7% chondrolysis, 6% avascular necrosis, and 5% other. This spectrum is quite different from that of patients over the age of 50.

While patient reported outcomes were improved on average, the improvements were substantially less than those reported by older patients having primary osteoarthritis.

Implant survivorship ranged from 95 to 100% at 0 to 10yrs, 71% to 84% at 11 to 15yrs, and 61% to 84% at > 15yrs postoperatively. These data suggest that over one-third of patients having had an anatomic TSA at the age of 40 years of age had a revision for failure by the time they were over 55 years of age.

Revision rates and followup durations varied widely: 1/26 at 2.3yrs to 7/17 at 14.5yrs. The indications for revision are shown in this table below drawn from the data in the paper.

Comment: As is the case in all reviews and longer term followup studies, it is likely that the implants and techniques used in these papers do not represent current practice. Longer term data on what is being done today will become available a decade from now, but at that time techniques and implants will be different than those used in current practice. As pointed out in Objective ignorance - a problem in predicting outcomes in climbing and in orthopaedic surgery we can't predict future outcomes from past data.
The one element that we do not expect to change is that, as pointed out by the authors of Comparison of patients undergoing primary shoulder arthroplasty before and after the age of fifty, younger patients have more complex pathological conditions, such as capsulorrhaphy arthropathy, rheumatoid arthritis, and posttraumatic arthritis. Only 21% of the younger patients had primary degenerative joint disease, whereas 66% of the older patients had that diagnosis.
With some of these diagnoses, such as rheumatoid and other inflammatory arthropathies, a glenoid component is commonly indicated. However when a glenoid component fails it typically leaves a large, difficult to manage defect in the glenoid bone.

Therefore, for diagnoses such as capsulorrhapy arthropathy, secondary arthritis, AVN and primary osteoarthritis in patients with increased longevity and higher desired activity levels, there is a rise in interest in bone-preserving procedures that do not involve insertion of a glenoid component. Such procedures include a hemiarthroplasty alone or a ream and run (hemiarthroplasty with non-prosthetic glenoid arthroplasty).

Sometimes simpler is better

American Avocet

Malheur

May 2025

Thursday, October 23, 2025

Reverse total shoulder stability and instability - the role of concavity compression

As is the case for the normal shoulder and the anatomic total shoulder, the stability of the reverse total shoulder (rTSA) depends on concavity compression. In the rTSA the concavity of the humeral liner is compressed onto the glenosphere by soft tissue tension and active muscle constraction.

The authors of Computational Analysis of Compressive Joint Stability and Acromial StressAssociated with Varied Rotator Cuff Integrity after Reverse Shoulder Arthroplasty used finite element analysis (FEA) to evaluate changes in joint compressive stability and acromial stress with varied rotator cuff integrity, glenoid component lateralization, and humeral distalization after rTSA.

Glenohumeral contact force (compression) decreased with progressive cuff removal. Compared to the intact rotator cuff state, compression decreased 59% when the subscapularis was absent, 11% when the infraspinatus was absent, and 67% when both subscapularis and infraspinatus were absent.

Compression increased with progressive levels of glenoid lateralization. The table below shows compression (Newtons) for various degrees of cuff integrity and various amounts of glenosphere lateralization.

Six mm lateralization increased compression by two-fold when the subscapularis was intact (red arrow).

Six mm lateralization with an inlay stem resulted in a small (0.2% to 1.8%) increase in the proportion of acromial and scapular spine cortical bone regions exceeding the yield stress threshold.

Addition of an onlay humeral stem, though resulting in larger improvements in joint compressive stability, had a considerable (23.0% to 30.4%) increase in the acromial and scapular spine cortical bone regions exceeding the yield stress threshold compared to inlay humeral configurations.

This study illustrates the important role that compression from the rotator cuff plays in the stability from concavity compression with the rTSA.

It also points out that when the rotator cuff is compromised, joint compression can be recovered by increasing glenoid lateralization and humeral distalization. However, the improvement in joint stability comes at the cost of increases in acromial/scapular spine stress.

----

I'm taking the liberty of reposting a post from April so that the reader has much of the rTSA stability/instability story in one spot.

Instability and dislocation are major complications of reverse total shoulder arthroplasty (RSA) and are not easily solved by revision.

To help understand reverse shoulder stability and instability I will use some diagrams by Steve Lippitt from the 5th Edition of The Shoulder. Steve was also critical to the understanding of concavity compression and describing the stability ratio. See Glenohumeral stability from concavity-compression: A quantitative analysis

The reverse total shoulder is stabilized by conconcavity compression in which the concavity of the humeral polyethylene is pressed onto the glenosphere by the vector sum of muscle action, gravity and other forces (red arrow).

Dislocation can result when the compressive forces or the concavity of the humeral cup are insufficient to manage a displacing load, such as that from pushing one's self up from an armchair.

Dislocation can result when the vector sum of the forces acting on the humerus is not aligned with the glenosphere,

When unwanted contact occurs between the scapula and humeral component, displacing forces can misalign the compressive force required for stability.

To start, I'd like to direct the reader to several classic articles on this topic:

2011 Complications in reverse total shoulder arthroplasty

2015 Results of closed management of acute dislocation after reverse shoulder arthroplasty

2016 Revision for a failed reverse: a 12-year review of a lateralized implant

2018 Classification of instability after reverse shoulder arthroplasty guides surgical management and outcomes

2023 Revision for instability following reverse total shoulder arthroplasty: outcomes and risk factors for failure

I'll pick up the story from 2024 to the time of this writing (April 2025).

*Dislocation of the reverse total shoulder continues to be a major and prevalent issue for patients and surgeons

Mitigating the Risk of Instability After Reverse Shoulder Arthroplasty: A Critical Analysis Review of Patient and Surgical Factors Instability and dislocation after reverse shoulder arthroplasty may occur in up to 31% of patients. Clinical risk factors for instability include younger age, male sex, increased body mass index, preoperative diagnosis of proximal humerus fracture or rotator cuff pathology, history of instability of the native shoulder or after surgery, and a medical history of Parkinson's disease. In patients at a high risk of instability, surgeons should consider a more lateralized prosthesis (particularly in patients with an incompetent rotator cuff), repairing the subscapularis (particularly when using a medialized prosthesis), and upsizing the glenosphere (>40 mm in male and 38-40 mm in female patients). While potentially useful, less evidence exists for the use of a constrained liner.

Midterm outcomes of primary reverse shoulder arthroplasty: a systematic review of studies with minimum 5-year follow-up The rate of shoulder dislocation was 3.7% (0%-20.4%),

Instability after reverse shoulder arthroplasty: a retrospective review of thirty one cases The most frequent etiology for RSA instability was loss of compression, followed by impingement and loss containment.

Revision of reverse total shoulder arthroplasty: A scoping review of indications for revision, and revision outcomes, complications, and re-revisions 22% of the complications were dislocations or instability. 30% of the revisions were for dislocation or instability.

Predictors of dislocations after reverse shoulder arthroplasty: a study by the ASES complications of RSA multicenter research group. Patients with a primary diagnosis of glenohumeral osteoarthritis with an intact rotator cuff had an overall lower rate of dislocation than patients with other diagnoses (0.8% vs. 2.5%. Patient-related factors independently predictive of dislocation, in order of the magnitude of effect, were a history of postoperative subluxations before radiographically confirmed dislocation (odds ratio [OR]: 19.52), primary diagnosis of fracture nonunion (OR: 6.53), revision arthroplasty (OR: 5.61), primary diagnosis of rotator cuff disease (OR: 2.64), male sex (OR: 2.21), and no subscapularis repair at surgery (OR: 1.95).

Complications following reverse total shoulder arthroplasty for proximal humeral fractures: a systematic review The most common postoperative complication was prosthetic instability/dislocation: 2.3%

Complications after reverse shoulder arthroplasty for proximal humerus nonunion The most common postoperative complication was prosthetic instability/dislocation: 12%

Poor clinical outcomes and high rates of dislocation after modular reverse shoulder arthroplasty for proximal humeral oncologic resection Dislocations occurred in 40%

Intraoperative repair of functional subscapularis during RSA by deltopectoral approach could improve internal rotation but does not prevent anterior dislocation. In the functional repair group, three shoulders (1.2%) reported subjective instability and 1 (0.4%) dislocated.None occurred in in either the non-functional repair or non-repair groups.

Reverse shoulder arthroplasty with a 155 degrees neck-shaft angle inlay implant design without reattachment of the subscapularis tendon results in satisfactory functional internal rotation and no instability: a cohort study. One out of 210 prostheses was revised for dislocation within the first month after primary surgery.

Impact of morbid obesity on postoperative outcomes in reverse total shoulder arthroplasty: A national inpatient sample analysis Morbid obesity (BMI >/=40 kg/m(2)) was associated with a periprosthetic dislocation rate of 2.60 % in comparison to 1.59 % in controls

Impact of accumulating risk factors on the incidence of dislocation after primary reverse total shoulder arthroplasty using a medial glenoid-lateral humerus onlay prosthesis. 1.4% of the patients experienced dislocation with a medialized glenoid-lateralized humerus onlay rTSA prosthesis. The greatest risk factors for dislocation were male sex, age <68 years at the time of surgery, patients with body mass index >30, patients who received glenospheres having a diameter >40 mm, and patients who received expanded or laterally offset glenospheres.

Low success rate of closed reductions when treating dislocations after reverse shoulder arthroplasty: a study by the ASES Complications of RSA Multicenter Research Group. a closed reduction was initially attempted in the majority of patients, but only about one-third were successful and required no further intervention. Unsuccessful closed reductions were associated with higher patient BMI. Revision surgery for dislocations was complicated by a high rate of recurrent dislocations and rerevision surgery.

*The diameter, depth and orientation of the humeral cup affect stability of the reverse total shoulder. However, it must be remembered that the ability of the RSA to resist dislocation depends not only on the shape and orientation of the cup, but also on the direction and magnitude of the net force as shown by the red arrows in the first two diagrams at the start of this post.

From Grammont to a New 135 degrees Short-Stem Design: Two-Hand Lever Test and Early Superior-Lateral Dislocations Reveal Critical Role of Liner Stability Ratio and Stem Alignment

Illustration of a reverse total shoulder arthroplasty: radius (r) of the glenosphere and concavity depth (d) or jump height of the liner are required to calculate the liner stability ratio (LSR). Yellow area: the extent of the glenosphere covered by the liner; yellow striped line: angle of coverage (degree of glenosphere coverage by the liner).

Patients having receiving RSA had an 8% dislocation rate for standard liners and a 0% dislocation rate for retentive liners. The authors attribute this difference to the jump height for the 36 mm standard implant of 8.1 and a linear stability ratio (LSR) of 152%; whereas the 36 mm retentive liner had a jump height of 10.1 and linear stability ratio of 195 to 202%

For this design, the most stable liner type was the 36 retentive:

They also found that the mean effective neck-shaft angle was 133 degrees (127-144 degrees) for short stems and 135 degrees (129-143 degrees) for long stems. Long stems significantly reduced varus outliers

which may have an increased risk for instability.

Varus-valgus alignment of humeral short stem in reverse total shoulder arthroplasty: does it really matter? The utilization of short humeral stems in reverse total shoulder arthroplasty has gained attention, however, concerns exist regarding the risk of misalignment with implant insertion. In this cadaver study, anterior dislocation forces were considerably lower in the varus group compared to the neutral group. Valgus positioning did not significantly impact instability compared to the neutral position.

*Know the implants you're using

Large variability in degree of constraint of reverse total shoulder arthroplasty liners between different implant systems There were variations in jump height between rTSA systems at a given size, resulting in large differences in stability ratio. Standard liners exhibited a stability ratio range from 126% to 214% (mean 158% (SD 23%)) and constrained liners a range from 151% to 479% (mean 245% (SD 76%)). The angle of coverage showed a range from 103 degrees to 130 degrees (mean 115 degrees (SD 7 degrees) for standard liners and a range from 113 degrees to 156 degrees (mean 133 degrees (SD 11 degrees )) for constrained liners.

Four arthroplasty systems had constant stability ratios for standard liners (within 5%) across different sizes, while one system showed slight inconsistencies (within 10%), and ten arthroplasty systems showed large inconsistencies (range 11% to 28%). The stability ratio of constrained liners was consistent across different sizes in two arthroplasty systems and inconsistent in seven systems (range 18% to 106%).

Impact of constrained humeral liner on impingement-free range of motion and impingement type in reverse shoulder arthroplasty using a computer simulation The humeral liner may be changed to a constrained type when stability does not improve by increasing glenosphere size or lateralization with implants, and patients, particularly women with obesity, have risks of periprosthetic instability that may be secondary to hinge adduction on the thorax. This RSA computer simulation model demonstrated that constrained humeral liners led to decreased impingement-free ROM.

From Dr Stefan Bauer I received the most interesting response below.

Maintaining Stability

Harlequin Duck Stabilized Against the Surf

Rosario Beach

2021

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