UW Shoulder and Elbow Academy

Glenoid erosion is a recognized cause of inferior clinical results in humeral hemiarthroplasty.

While there is much current interest in the use of a pyrocarbon joint surface to reduce glenoid erosion, as the x-ray above demonstrates, glenoid erosion can take place with pyrocarbon as well as with metal humeral heads.

Here we present some approaches to reducing the risk of glenoid erosion that apply no matter what type of joint surface is used.

The gleonoid.

In the great majority of arthritic shoulders, there is loss of the congruency between the humeral and glenoid articular surfaces. Thus, rather than having the load distributed evenly across the joint (below left), the load is concentrated on a reduced area at the back of the joint. The resulting pressure (load/area) causes progressive posterior bone loss and decentering.

If a hemiarthroplasty is performed without addressing this force maldistribution, the posterior bone erosion will continue.

On the other hand, if conservative glenoid reaming is used to create a single concavity, even load distribution can be achieved.

Experience suggests that a 2 mm diametral mismatch between the humeral head and the reamed glenoid is optimal.

If glenoid erosion is to be minimized, the maximum amount of the best quality bone (arrows) needs to be preserved.

by conservative reaming

This can be accomplished by accepting, rather than correcting, glenoid retroversion.

The diagrams below show the preservation of quality bone with accepting the glenoid retroversion (left) in comparison to the greater amount of bone removed with correcting glenoid retroversion (right)

In reaming the glenoid, sharp reamers and irrigation can help minimize the risk of thermal injury to the glenoid bone (see Thermal effects of glenoid reaming during shoulder arthroplasty in vivo).

While some surgeons advocate drilling holes in the reamed glenoid surface

it is apparent that this can weaken the glenoid surface making it more prone to erosion. Perhaps this "docking" is more appropriate when making a pie.

Finally, when possible it is desirable to preserve the glenoid labrum recognizing its load bearing and stabilization functions.

Overstuffing: Soft tissues

As pointed out in How to Overstuff an Anatomic Arthroplasty and Overstuffing is not a radiographic diagnosis, overstuffing is a condition in which the size and position of the shoulder arthroplasty implants result in excess tightening of the soft tissues encapsulating the joint. Thus, a shoulder with a chronically tight capsule and rotator cuff may be overstuffed by normally sized implant.

As pointed out in Practical Evaluation and Management of the Shoulder, overstuffing can not only restrict the range of glenohumeral motion

but it can also increase the force necessary to move the joint,

which increases pressure on the glenoid joint surface when vigorous stretching is carried out.

Thus for that reason, soft tissue releases are important for reducing the pressure on the glenoid and the risk of glenoid erosion.

180 degree releases if there is excessive posterior translation

360 releases if the shoulder is tight all around

The adequacy of the releases can be verified while the trial components are in place, verifying that the shoulder can be easily flexed to at least 150 degrees

and that the shoulder meets the 40, 50, 60 rules (40 degrees of external rotation with the subscapularis approximated, 50% posterior translation, and 60 degrees of internal rotation with the arm abducted).

Overstuffing: Implant size and positioning.

While much attention is being paid to pyrocarbon as an alternative bearing surface, glenoid erosion can be seen with humeral heads of any type of material.

Common implant related causes of overstuffing.

(1) Inadequate head cut, leaving a too long neck.

(2) Too large humeral component

(3) Head too medial

(4) Head too high

When the head is high, it acts like a cam (click here), excessively tightening the inferior capsule when the arm is elevated because the center of rotation is malpositioned. This tightening results in increased pressure on the glenoid surface when the arm is raised.

(5) Head high and medial

From the above it is noted that humeral head malposition can occur with pyrocarbon and with metal heads; humeral head malposition can occur with stemless, short stem and standard length stems.

To avoid overstuffing related to the humeral component, careful attention needs to be paid to the neck cut, head size and component position.

Conclusion

The risk of glenoid erosion can be reduced by preserving and protecting the best bone in the glenoid, balancing the soft tissues to optimize glenoid laxity, along with careful selection and positioning of the humeral component.

Avoiding glenoid erosion appears to depend more on surgical technique than on technology.

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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).

Shoulder arthroplasty using a pyrocarbon articulating surface has attracted the attention of surgeons and implant companies. We reviewed a dozen articles on the clinical application of pyrocarbon hemiarthroplasty.

Pyrocarbon hemiarthroplasty of the shoulder: a systematic review and meta-analysis of clinical results These authors reviewed 12 studies with a total of 536 patients having pyrocarbon hemiarthroplasty. Radiographically, 22.8% of patients (n = 536, 8 studies) had evidence of glenoid erosion, 10.4% had changes in implant positioning, and 9.9% had tuberosity thinning. In addition, 1.5% of patients had radiographic subacromial space reduction, whereas 0.7% had an increase in tuberosity thickness. Across all studies, there was an 8.6% complication rate, with the most common cause being glenoid erosion (2.6%, n = 14). There was an overall 7.7% revision rate (n = 41), with 63% of revisions (n = 26) undergoing conversion to reverse or total shoulder arthroplasty. The reasons for revision included glenoid erosion, subscapularis failure, periprosthetic fracture, glenoid loosening, instability, subluxation, infection, greater tuberosity fracture, stiffness, pain, impingement, rotator cuff tear, and implant breakage.

Comparing revision rates and survival of pyrocarbon and non-pyrocarbon heads in total- and hemi- shoulder arthroplasty found that 6 of 47 metal hemiarthroplasties were revised while 1 of 43 pyrocarbon hemiarthroplasties were revised. The reasons for revision were not provided. It is of note, as shown below, that the followup period for the non-pyrocarbcn (metal) humeral hemiarthroplasties was longer than for the pyrocarbon humeral heads and that most of the revisions for the metal heads occurred after 7 years; 7 year data was not available for the pyrocarbon heads.

Short-term outcomes following 159 stemmed pyrolytic carbon shoulder hemiarthroplasties and how they compare with conventional hemiarthroplasties and total shoulder arthroplasties in patients younger than 60 years with osteoarthritis: results from the New Zealand National Joint Registry These authors found that revision rate (calculated as rate per 100 component-years) in patients aged <60 years with osteoarthritis was 1.275, 2.654, and 1.613 for pyrocarbon hemiarthroplasties (PyCHA), conventional hemiarthroplasties (HA), and anatomic total shoulders (aTSA), respectively. Although there was a trend toward a lower revision rate in the PyCHA group compared with the HA and aTSA groups, the differences did not reach the level of statistical significance (P > .05).

In total, 5 revisions were performed in the PyCHA group, with patients ranging in age from 37 to 66 years. The time from index surgery to revision ranged from 0.03 to 3.58 years. Three patients underwent revision owing to ‘‘overstuffing’’ of the glenohumeral joint due to oversized implants, and the other 2 patients underwent revision owing to rotator cuff failure.

The differences in the total OSS and the pain and function subcategory scores were not statistically significant between the PyCHA and HA groups.

The hypothesis of a lower revision rate and superior OSS in the PyCHA group compared with the HA and aTSA groups was not supported.

Pyrocarbon humeral heads for hemishoulder arthroplasty grant satisfactory clinical scores with minimal glenoid erosion at 5-9 years of follow-up These authors retrieved the records of 45 consecutive patients who underwent HSA with pyrocarbon humeral heads from 2013 to 2017.

Glenoid erosion at two years and five years after surgery are shown below.

Glenoid erosion was not associated with clinical outcome

From the examples shown in the article, there was a consistent problem with overstuffing.

and bone resorption (adaptive changes) in the metaphysis.

Short-term outcomes and survival of pyrocarbon hemiarthroplasty in the young arthritic shoulder

Because of the fragility of pyrocarbon a metal plate (lower row) is used to obviate the risk of fracture of the unprotected pyrocarbon head (upper row)

This results in a thicker head than that for a metallic head of the same diameter of curvature.

The authors concluded that "the severity of glenoid bone erosion or the association with glenoid reaming does not affect functional outcomes and failure risk. By contrast, nonanatomic reconstruction of the proximal humerus after HA-PYC (see below) is not rare (one-third of the cases) and is associated with lower functional outcomes, as well as higher risks of complications (subscapularis insufficiency and/or symptomatic glenoid erosion) and revision (see below). Surgeons should be aware of the increased thickness of the pyrocarbon heads, related to the addition of a metallic plate (+1.5 mm in thickness) under the bearing surface to prevent any breakage of the pyro- carbon head plus the void (+0.5 mm) needed to accommodate the double Morse taper."

Survivorship of shoulder arthroplasty in young patients with osteoarthritis: an analysis of the Australian Orthopaedic Association National Joint Replacement Registry These authors studied patients aged <55 years, of which 70 (4.5%) were stemmed hemiarthroplasty with a metal head (HSMH) and 159 (10.2%) were stemmed hemiarthroplasty with a pyrocarbon head (HSPH). Glenoid erosion was the most common cause of revision for HSMH (50%). Instability/dislocation was the leading cause of revision for HSPH (28.6%).

Pyrocarbon hemiprostheses show little glenoid erosion and good clinical function at 5.5 years of follow-up These authors performed a single-center consecutive cohort study of 31 of 34 patients (91%) who underwent pyrocarbon hemiarthroplasty (PyC HA) between September 2013 and June 2018. In 11 of these patients, concentric glenoid reaming was additionally performed. The mean follow-up period was 5.5 years (range, 3.5-7 years). . Anteroposterior radiographs were analyzed according to an established method by 2 independent observers: A line parallel to the superior and inferior glenoid rim was translated to the most medial point of the glenoid surface. A further parallel line was placed on the spinoglenoid notch. The distance between these 2 lines was measured. Measurements were scaled using the known diameter of the implanted humeral head component.

Mean medial glenoid erosion measured 1.4 mm at an average of 5.5 years of follow-up. In the first year, 0.8 mm of erosion was observed, significantly more than the average erosion per year of 0.3 mm (P < .001).

Mean erosion per year was 0.4 mm in patients with glenoid reaming vs. 0.2 mm in those without reaming (P = .09).

The prosthesis survival rate was 100%.

There was no correlation between erosion and change in Constant score (r = 0.06) and a weak correlation (r = 0.37) between erosion and pain improvement (P = .039).

In this study there were some examples of overstuffing as shown below.

Pyrocarbon Hemi-Shoulder Arthroplasty Provides Satisfactory Outcomes Following Prior Open Latarjet

These authors reviewed 9 shoulders with arthritis after previous Latarjet procedures that was treated with a pyrocarbon hemiarthroplasty.

One shoulder required conversion to reverse shoulder arthroplasty, 3 years after HSA. The remaining 8 shoulders were assessed at 6.1 years after the index HSA. Glenoid erosion only progressed in 1 shoulder from mild to moderate. The Constant score was 79.6, pain on VAS was 1.0, and SSV was 80.0. The active forward elevation improved from 96 degrees to 151 degrees.

As before, overstuffing was observed.

Pyrolytic carbon head shoulder arthroplasty: CT scan glenoid bone modeling assessment and clinical results at 3-year follow-up these authors reported the radiological glenoid modifications and clinical outcomes in 41 patients at 3 years mean follow-up of hemi shoulder arthroplasty (HA) with pyrocarbon (PYC) humeral head at an average follow-up of 36.3 months. No glenoid reaming was performed. Preoperative and postoperative computed tomography scans at the last follow-up were performed to achieve 3-dimensional reconstructions of the scapulae. Deformities of the glenoid surface were analyzed as a distance differential between postoperative and preoperative to investigate potential bone remodeling vs. glenoid erosion.

Ten of the 13 patients with posterior head subluxation had recentered the humeral head.

Glenoid wear was less than 0.6 mm at 3 years mean follow-up. The authors reported no revisions

Mean humeral head center of rotation (COR) deviation was 2.8 ± 1.1 mm. Eight patients had excessive COR deviation (>3 mm) in superior and medial direction. Reasons for these nonanatomical reconstructions were: oversized implant for 1 patient; inadequate cut (insufficient or vertical) for 7. In addition, 3 other patients had an oversized implant without affecting COR. These 8 patients presented no complications at the last follow-up.

Mid-term outcomes of pyrolytic carbon humeral resurfacing hemiarthroplasty compared with metal humeral resurfacing and metal stemmed hemiarthroplasty for osteoarthritis in young patients: analysis from the Australian Orthopaedic Association National Joint Replacement Registry

These authors analyzed data from the Australian Orthopaedic Association National Joint Replacement Registry for patients aged <55 years who had undergone a primary shoulder replacement for osteoarthritis from April 16, 2004, to December 31, 2019: 163 were pyrocarbon hemi-resurfacing procedures, 163 were metal hemi-resurfacing procedures, and 67 were metal stemmed hemiarthroplasties.The cumulative percentage of revision at 6 years was 8.9% for pyrocarbon hemi-resurfacing, 17.1% for metal hemi-resurfacing, and 17.5% for metal stemmed hemiarthroplasty.

Pain, prosthesis fracture, and infection were the key reasons for revision. No pyrocarbon hemi-resurfacing cases were revised for glenoid erosion.

In male patients, pyrocarbon humeral resurfacing had a lower cumulative percentage of revision compared with metal stemmed hemiarthroplasty

Fracture of pyrocarbon humeral head resurfacing implant: a case report

The authors report a case of a pyrocarbon humeral head resurfacing implant fracture, occurring 6 years after its implantation, without any obvious trauma or dislocation.

B2 and B3 glenoid osteoarthirtis: outcomes of corrective and concentric (C2) reaming of the glenoid combined with pyrocarbon hemiarthroplasty

These authors hypothesized that corrective and concentric reaming of the glenoid associated with pyrocarbon hemiarthroplasty (HA-PYC) could improve the centering of the humeral head and decrease the risk of persistent painful glenoid erosion in 41 shoulders of young and active patients with B2 and B3 glenoids. At a mean follow-up of 4.5 years the prosthesis survival was 95% (39 of 41). No patient has been reoperated for painful glenoid erosion. The mean glenoid retroversion decreased from 17.1 degrees preoperatively to 8.3 degrees at last follow-up with improvement in humeral alignment with the glenoid from 59.9% to 50.3%. The humeral head was recentered on the glenoid surface in 97%. CT scan measurements showed that the average total medialization was 3.7 mm due to reaming and 1.7 mm due to erosion). The adjusted Constant Score increased from 43% to 97% and the Subjective Shoulder Value from 38% to 84% Overall, 84% of active patients returned to work, and all patients returned to sports.

At a mean follow-up of 4.5 years, the prosthesis survival rate was 95% (39/41), and no patient has been reoperated for painful glenoid erosion. Two shoulders required revision to reverse total shoulder arthroplasty because of subscapularis insufficiency.

The authors caution that there is a risk of overstuffing the GH joint with HA-PYC because of the presence of a metallic tray under the pyrocarbon head that increases the global thickness of the humeral head by about 2 mm.

They present a diagram showing the increased amount of bone removed with corrective reaming (B) in comparison to the non-corrective reaming used in the typical ream and run procedure (A).

They also demonstrate the difference between the measurement of humeral centering on the glenoid (left) and the relationship between the humeral head and the plane of the scapula (right). As is pointed out by the graph below, the relationship between the humeral head and the plane of the scapula is primarily determined by the degree of retroversion and is not a true measure of "subluxation".