Reverse total shoulder - how to fix the stem

Radiographic changes and clinical outcomes associated with an adjustable diaphyseal press-fit humeral stem in primary reverse shoulder arthroplasty

These authors evaluated the minimum two year radiographic and clinical outcomes of an adjustable diaphyseal press-fit humeral stem in 232 primary reverse total shoulders.

Radiographic evidence of loosening was identified in 1 RSA (0.4%) associated with deep infection. Aseptic loosening was not observed. No stems were identified as being at high risk for loosening.
Internal stress shielding was observed proximal to the coated diaphyseal component in 226 shoulders (97.4%). This finding was often visible at 3 months (92.7%) and predictably progressed on subsequent radiographs. Progression beyond the 2-year period was rarely seen (4.4%). No external stress shielding or osteolysis was observed. Example post operative films are show below. Arrows added to show the progressive change in the bony increased offset bone graft used between the glenoid component and the glenoid bone. 

Immediate post op

3 months post op

22 mo post op

46 mo post op

At an average follow-up of 36.6 months, significant improvements were identified in all measured clinical outcomes (P < .001).

Thirty-six complications occurred in 33 patients (15.1%). These complications included acromial/scapular spine stress fracture (n = 7), deep infection (n = 7), baseplate failure (n = 6), dislocation (n = 5), transient neuropathy (n = 4), superficial infection (n = 3), postoperative periprosthetic Vancouver C humeral shaft fracture (n = 1), humeral shaft fracture during implant removal (n = 1), baseplate malposition (n = 1), and retained drill fragment (n = 1). 

Failures, defined as requiring revision surgery, were documented in 17 RSAs. In 11 of these shoulders, the diaphyseal component was retained and used for revision RSA. These included 6 baseplate failures and 1 baseplate malposition that required revision. In some of these revisions, the metaphyseal component was exchanged without the need for humeral stem removal. Segmental stacking inserts were available to adjust component height in the management of instability.

One stem was left in place during stage 1 of a 2-stage revision RSA for treatment of a deep infection.

Six stems were removed for treatment of deep infection. One of these stems was loose and was easily removed. The other 5 stems were well fixed and were explanted using various stem removal techniques. An iatrogenic humeral shaft fracture occurred in 1 patient. No other complications occurred during stem removal.

Comment: This is a large and interesting series of primary reverse total shoulders performed by an individual highly experienced surgeon. The overall good patient results are presented along with a candid report of the complications. It is of note that this series did not include patients treated for failed primary arthroplasty - a cohort in which the complication rate is predictably higher.

With respect to the management of infection, it is always a challenge to decide if a well fixed stem needs to be removed (to increase the chance that the biofilm has been eliminated). Here one stem was retained and six were removed.

With this implant the goal is to customize the implant to fit the diaphysis.

We use an alternative approach that fits the internal anatomy of humerus to the implant.

The goal is to achieve secure fixation without creating a stress riser at the tip of the component and to reduce the risk of stress shielding. Impaction grafting enables us to use a prosthetic humeral stem that is smaller in diameter than the humeral diaphysis so that diaphyseal loading is avoided. The medullary canal is conservatively reamed to remove cancellous but retain cortical bone. The humeral metaphysis is reamed to 42 mm to accommodate the metaphyseal aspect of the humeral component 

A trial component is inserted to assure that reduction can be accomplished, that the joint is stable, and that there is no unwanted contact between the prosthesis and the scapula. Impaction grafting is carried out with an impactor of the same size and shape of the monoblock humeral component.

Drill holes are placed in the lesser tuberosity for reattachment of the subscapularis if sufficient tendon is available. The wound is thoroughly irrigated. The humeral prosthesis is driven into the impaction grafted canal, assuring a snug fit and rotational stability.

The joint is reduced; range of motion and stability are again verified. The subscapularis is repaired to the previously placed sutures. A standard wound closure is followed by the application of dry sterile dressings. 

Postoperative rehabilitation consists of the use of a sling for comfort and support for 6 weeks. Gentle activities of daily living are allowed during this period. After six weeks progressive increase in active use of the shoulder is encouraged; stretching exercises are usually unnecessary.

Here are the post operative radiographs from two case examples of the technique. 

 




Note also the use of a glenosphere with a short neck on it rather that the use of bone graft to offset the glenosphere.

 

This approach is bone preserving. By using a single piece (monoblock) component) and avoiding a tight diphyseal fit, ingrowth surfaces, cement, and modularity, the technique is simplified and revision is facilitated.

====

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

Information about shoulder exercises can be found at this link.

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.

Reverse total shoulder components - the price of modularity

Fatigue failure of reverse shoulder humeral tray components of a single design

These authors suggest that modularity in reverse shoulder arthroplasty provides surgical flexibility and facilitates less-complex revision surgery, but that the potential for fatigue fracture is higher with modular components. 

They studied 8 humeral trays of nearly identical designs: 4 made of Ti-6Al-4V (Ti) and 4 made of CoCrMo (CoCr),

Both types of implant are still on the market.

Some of the results of this retrieval study are shown here.

As shown above, two Ti devices were revised for in vivo fracture.

Scanning electron microscopy showed cracking in the other 2 Ti trays and no evidence of cracking in the CoCr components. A geometric difference in the CoCr devices resulted in a 25% decreased stress under simulated activities of daily living. Accounting for the tray material properties, the fatigue failure envelope ranged from 1000 to 1 million cycles for Ti and from 30,000 to >10 million cycles for CoCr. Finite element and fatigue analyses predict a 10-fold lifetime increase for the CoCr devices compared with the Ti devices.

They concluded that fatigue failure is possible for some reverse shoulder components and is likely exacerbated by fillet radius, tray thickness, and material choice.

Comment: This report shows how important it is for the surgeon to understand the material and the geometry of the components he or she plans to use.

We've actually put up a post previously on this exact topic; it is reproduced below

Here's an instructive case that came to us for revision.

Three years ago a patient had a reverse total shoulder. Post operative films shown below

Within the first month the glenosphere dissociated from the baseplate requiring revision as shown below.

With a year or so, he developed pain and clunking in his shoulder and had these radiographic findings (problem is subtle, can you see it?)

 He came to see us at which time we obtained these films.

 Did you notice the dissociation of the humeral tray from the stem. It turns out that this tray was made of Titanium.

 In this cases, the stem of the tray had fatigued and fractured.

We were able to obtain a Chrome-Cobalt humeral tray and used it in our revision, shown below. We also resected the heterotopic bone and cultured the wound for Propionibacterium. There was no growth on these cultures.

In the current wave of enthusiasm for implanting reverse total shoulders, it is important to recognize that this is a technically demanding procedure and that each implant system has its own nuances for fixation of the glenoid base plate, glenosphere, humeral stem, humeral tray and humeral poly. This case also demonstrates that the forces at the articulation are large - enough to result in fatigue fracture of the stem of the tray. It also points out the importance of understand the metallurgy of the implant.

Our practice is to use an impaction grafted non-modular monoblock prosthesis , which avoids the risk of tray failure
                                                     

===

Consultation for those who live a distance away from Seattle.

Check out the new Shoulder Arthritis Book - click here.

Click here to see the new Rotator Cuff Book

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.

Conversion of anatomic arthroplasty to reverse total shoulder: what is the place for modular stems?

Conversion of Stemmed Hemi- or Total to Reverse Total Shoulder Arthroplasty: Advantages of a Modular Stem Design

These authors point out that revision of a well-fixed humeral stem has the potential risk of loss of humeral bone stock, nerve injury, periprosthetic fracture, and malunion or nonunion of a humeral osteotomy with later humeral component loosening.

They conducted a retrospective study of 48 hemiarthroplasties and eight total shoulder arthroplasties that were converted to a reverse total shoulder arthroplasty system. 19 of the stems were modular and 37 were non-modular. The incremental cost of a modular stem design over a standard implant are not stated.

The commonest reasons for conversion to a reverse shoulder arthroplasty was rotator cuff lesion with instability/loss of function (29), aseptic stem loosening (8), stem malposition with functional deficit (8), failure of glenoid component (6), and glenoid erosion (5). 

In 13 cases (all with modular stems) the surgeon elected to retain the humeral stem and in 43 (6 with modular stems and 37 without modular seems) the surgeon elected to change the stem because of stem loosening in 10 cases, stem malposition in 8, and difficulty in conversion of a non modular stem to a reverse in 25. In 12 cases a longitudinal humeral osteotomy was required for stem removal.

Blood loss, surgical time, the rate of complications (principally fractures) and revision rate were greater in the cases where the surgeon chose to perform a full stem exchange. 

Comment: It is of interest that most of the anatomic hemiarthroplasties and total shoulder arthroplasties in this series that were revised to reverse total shoulders were for diagnoses (proximal humeral fractures, post traumatic arthritis and cuff tear arthropathy) that today may well be treated with primary reverse total shoulders rather than an anatomic arthroplasty with a modular stem.

While the authors conclude that "..modularity of a shoulder arthroplasty system has proven and substantial advantages if conversion to reverse total shoulder arthroplasty becomes necessary and might be considered as prerequisite for stemmed shoulder arthroplasty systems", it is unclear for which patients they recommend the modular stem.  It would be important to know whether the number of cases of primary arthroplasty with modular stems that need revision and which can be successfully revised without stem removal offsets the incremental cost of the general use of modular stem designs.

See related posts here and here.

===
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'

Modular reverse total shoulder components - if it can be put together, it can come apart

Unscrewing instability of modular reverse shoulder prosthesis increases propensity for in vivo fracture: a report of two cases

This relatively hidden article has an important message: modular components can come apart. This is particularly the case for reverse total shoulder components in that the loading in modes other than compression is more likely than in anatomic arthroplasty.

The authors point out that reverse total shoulder complications are reported increasingly and include dislocations, infections, hematomas, glenoid loosening, glenosphere unscrewing, scapular notching, polyethylene wear, metallosis, and dissociation of modular humeral components at the proximal metaphysis and distal diaphysis. Importantly in the two cases they reported, both had proximal humeral bone loss, which, of course, removes a substantial amount of protection from the humeral component. In both of these cases the modular parts of the humeral component became unscrewed with extensive metallosis, suggesting that even before fracture, fretting wear at the unstable screw joint was occurring. 

They suggest that a possible mechanisms for in vivo unscrewing was abutment of the tuberosity against the glenoid (see below). Another is simply that the loading of the reverse humeral component by the glenosphere can exert torque on the component that can lead to failure. Interestingly they point out that ASTM International and International Organization for Standardization standards for cyclic fatigue and fretting corrosion of modular joints only exist for hip prostheses; no testing standards exist specifically for reverse total shoulder components. 

Steps to avoid humeral component failure of this type include (1) the use of a single piece (monoblock) component, (2) use of a well fixed proximal humeral allograft in cases of proximal humeral deficiency, and (3) care at surgery to avoid unwanted contact between the humeral component and the glenoid. While monoblock components may seem attractive, they have the disadvantage of reducing the versatility in restoring bone length and soft tissue tension that modular implants provide. 

The true rate of these complications is not known, but as we say here, 'if it has happened once, it can happen again'. 

====

Click here to see the new Rotator Cuff Book

Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis 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.