Saturday, October 21, 2017

Short humeral stems, is there a case to be made?

Clinical and radiographic outcomes after total shoulder arthroplasty with an anatomic press-fit short stem

These authors identified 118 TSAs completed with press-fit short stem and minimum 2-year follow-up; 85 of these patients had a grit-blasted (GB) short stem placed, whereas 33 patients had short stems with proximal porous coating (PPC).
Three female patients with GB stems had gross loosening of their humeral components before 1 year, 2 requiring revision. Radiolucent lines around the humeral component were found in 5.9% without evidence of loosening. Osseous resorption at the medial cortex was noted in 9.3%. 

Of patients with PPC stems, none were observed to have radiolucent lines compared with 8.2% in the GB group (P = .09).

The figures from this article show some of the issues with short humeral stems

This article can be considered along with a recent post on a similar topic:

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) 

(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.

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.

Compare the amount of bone preserved with this method (seen below) in comparison to that with the short stemmed component (shown above).


Additional thoughts on humeral components can be found here.

The reader may also be interested in these posts:

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