UW Shoulder and Elbow Academy: Short stemmed humeral components

Radiographic changes differ between two different short press-fit humeral stem designs in total shoulder arthroplasty

These authors compared the radiographic changes of the humerus in the short term after total shoulder arthroplasty using two different short-stem humeral components,

(1) a collarless humeral stem with an oval geometry and curved stem (Ascend or Ascend Flex;Wright Medical, Memphis, TN, USA) (42 patients)

and

(2) a humeral stem with a metaphyseal collar, rectangular geometry, and straight stem (Apex; Arthrex, Inc., Naples, FL, USA) (35 patients).

At a minimum of 2 years postoperatively the authors determined that there were greater radiographic changes seen with the Ascend (classified as low in 38% and high in 62%, medial calcar osteolysis in 71% than with the

Apex (classified as low in 77% and high in 23%, medial calcar osteolysis in 28.5%).

The examples they present show a stress shielding effect with both designs.

Comment: This study, along with others highlighted in prior posts, point out that humeri with short stems often demonstrate a stress shielding effect. This is in contrast to the findings with smooth, impaction grafted standard stems (see below) that appear to preserve at least as much bone as a short stemmed prosthesis.

Secure fixation may also become an issue with short stemmed components as shown by this case we saw last week. Here is the x-ray soon after surgery

and here is the x-ray one year after surgery, showing humeral component loosening.

Here is another recent post on the topic of short stems.

Short-term clinical outcome of an anatomic short-stem humeral component in total shoulder arthroplasty

This is the implanted used in that study:

Sixty-four patients with a mean age of 64.1 years were available for follow-up at a mean of 25 months postoperatively. On radiographic examination, 9% of stems were deemed "at risk" for loosening (defined as the presence of any stem subsidence, varus or valgus tilt, or radiolucent lines ≥2 mm in 3 or more radiographic zones), but there was no gross loosening in any patient.

They reviewed a recent report (see this link) evaluating the clinical and radiographic outcomes of 73 TSAs performed with a collarless press-fit short stem which demonstrated a 71% rate of radiolucent lines. The overall revision rate at a mean of 33 months was 12%, and 8.7% of the remaining stems were considered at risk for loosening. They reviewed another recent report (see this link) that reported radiolucencies in 22% of 49 short-stem TSAs with a press-fit collared design.

Comment: Short stemmed humeral components are usually described as 'bone preserving". We agree that bone preservation is important, but find that this objective can be achieved with a standard humeral component inserted with impaction grafting - an approach that is at least as bone preserving as with the use of short stemmed implants. Because impaction grafting distributes interface forces over a broad area, a standard length stem without ingrowth surfaces minimizes problems with stress shielding and achieves additional stability through greater bone-prosthesis contact.