Saturday, July 29, 2017

Short-stemmed humeral components - do they 'preserve more bone'?

These authors evaluated the short-term clinical outcomes of an anatomic short-stem humeral
component in total shoulder arthroplasty. They hypothesized that the implant would lead to significant functional improvement with low rates of radiographic loosening at a minimum follow-up of 2 years. 

This is the implanted used.

After an anatomic head cut was made, the canal of the humerus was sequentially broached until optimal fit was achieved and rotational stability of the implant was obtained. All humeral implants were impacted with a press-fit technique without the use of cement.

Sixty-four patients with a mean age of 64.1 years were available for follow-up at a mean of 25 months postoperatively. There were significant improvements in the Visual Analog Scale (6 to 2; P < .001), Simple Shoulder Test (4 to 10; P < .001), Single Assessment Numeric Evaluation (32 to 84; P < .001), and American Shoulder and Elbow Surgeons (37 to 80; P < .001) scores. Forward flexion improved from 116° to 148° (P < .001), external rotation improved from 30° to 57° (P < .001), and internal rotation improved from an average spinal level of S1 to L2 (P < .001). 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 one 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.


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