UW Shoulder and Elbow Academy: Stemless humeral component for anatomic total shoulder

Like all arthroplasty systems, the stemless humeral arthroplasty has its own challenges, for example with respect to component placement

and avoiding overstuffing

The authors of Stress shielding following stemless anatomic total shoulder arthroplasty point out that "failure following total shoulder arthroplasty (TSA) is most commonly related to the glenoid component. Humeral component failure is rare and is usually related to infection." One of the arguments put forward for stemless humeral components is that they are bone preserving and avoid issues of stress shielding. These authors conducted a retrospective review of 152 total shoulder arthroplasties (TSA) performed with the Sidus Stem-Free System (Zimmer/Biomet) to assess the radiographic proximal humeral bone adaptations seen following stemless anatomic total shoulder arthroplasty.

They found that at 2 years postoperatively, stress shielding was noted in 61 (41%) shoulders. A total of 11 (7%) shoulders demonstrated severe stress shielding with 6 occurring along the medial calcar. There was one instance of greater tuberosity resorption. At the final follow-up, no humeral implants were radiographically loose or migrated. There was no statistically significant difference in clinical and functional outcomes between shoulders with and without stress shielding. Patients undergoing a lesser tuberosity osteotomy had lower rates of stress shielding.

Here are some examples from the manuscript:

(Top) sequential axillary radiographs (L to R: 6 weeks, 6 months, 12 months, and 24 months postoperatively) demonstrating severe stress shielding along the anterior zone.

(Bottom) Sequential anteroposterior (AP) radiographs (L to R: 6 weeks, 6 months, 12 months, and 24 months postoperatively) demonstrating moderate stress shielding along the medial calcar and greater tuberosity regions. Note the thinning of the cortex along the medial calcar.

(Left) Three-month postoperative anteroposterior (AP) radiograph and

(Right) 2-year postoperative AP radiograph demonstrating severe stress shielding along the medial calcar.

Anchor fins are seen to be in contact with the lateral cortex of the proximal humerus. This is confirmed on multiple views at multiple time points. Complete 2 mm radiolucent lines are observed as well around the glenoid component indicating a potentially loose implant. Glenoid radiolucent lines were noted in 28 (18%) patients.

Comment: As the authors point out at the start, the humeral component is not a common cause of failure in anatomic total shoulder arthroplasty. In this paper they pointed to a substantial rate of proximal humeral bone loss at two years after insertion of a particular stemless component. Other outcomes may pertain to other designs.

While this study did not document worse clinical outcomes in shoulders with stress shielding, it is not known if these adaptive changes progress over time. Furthermore it is not known whether the bone loss might predispose the proximal humerus to fracture should revision be necessary.

It is worth comparing this study to another that assessed stress shielding after an impaction grafted standard length humeral stem. Note that the amount of humeral bone resected for insertion of the standard stem is the same as that for the stemless implant. Thus it is not clear that a stemless humeral component is truly "bone preserving" in comparison.

Radiographic outcomes of impaction-grafted standard-length humeral components in total shoulder and ream-and-run arthroplasty: is stress shielding an issue?

These authors evaluated humeral stress shielding after shoulder arthroplasty performed with a smooth, standard-length humeral stem fixed with impaction autografting.

Prior to placement of the final component, cancellous autograft harvested from the humeral head was placed in the humeral canal and pressed into place using a humeral impactor with the same stem geometry as the implant. Autograft was progressively inserted until the impactor fit tightly within the humerus. The final uncoated, smooth, stemmed, fixed-angle humeral component with the desired head geometry was then driven into the prepared canal.

At two years after surgery, the radiographic appearances were evaluated by an independent experienced shoulder surgeon from another institution not involved in the care of these patients. The metaphysical and diaphysial filling ratios were measured as shown below.

The filling ratios were small, showing a substantial preservation of bone stock.

The overall radiographic results are shown below

The 48 ream-and-run procedures showed partial calcar osteolysis in 9 cases (19%) and the 78 TSAs showed partial calcar osteolysis in 19 cases (24%) and complete calcar osteolysis in 2 (3%).

The Simple Shoulder Test score improved from 3.9±2.5 to 9.9±2.4.

Humeral component subsidence or component shift was observed in 3 ream-and-run procedures (6%) and in 8 TSAs (10%). These radiographic findings were not significantly associated with patient demographic characteristics, canal-filling ratios, or clinical outcomes.

The authors concluded that this independent assessment of the 2-year radiographic and clinical outcomes of a conventional smooth humeral stem inserted with impaction autografting demonstrates the clinical utility of this bone-preserving approach to humeral component fixation with minimal complications; good clinical outcomes; and low rates of bone loss, component subsidence, and shift in position.

After three decades of use, impaction autografting of a smooth standard-length stem remains our preferred method for bone-preserving humeral component fixation.

Impaction allografting also remains our preferred method for addressing failed prior humeral component fixation with a short stem - no additional bone is removed