Stemless / Short-Stem Shoulder Arthroplasty

Three lengths of humeral component. Anatomic total shoulder arthroplasty can use a standard-length stem, a short-stem or a stemless humeral component, and the trend is towards shorter components. A stemless implant fixes entirely in the proximal humeral metaphysis, the cut humeral surface, with no diaphyseal stem; a short-stem keeps a shortened metaphyseal stem.

Why go shorter. Shorter and stemless components preserve humeral bone stock, which eases any later revision, and they decrease operative time. They also avoid the complications of a diaphyseal stem:

• Periprosthetic humeral fracture
• Difficult stem extraction at revision
• Stress shielding, where a stiff diaphyseal stem unloads the proximal humerus and causes proximal bony adaptation and radiolucent lines

The price. Because fixation is metaphyseal, a stemless implant depends on adequate proximal humeral bone quality. That is the one judgement that decides the implant, and how it is made is set out below.

Outcomes. Across stem lengths, motion, patient-reported outcomes, complication and revision rates are broadly equivalent at short-to-mid term, and the shorter components have the practical advantage of shorter operative time. They also show fewer humeral radiolucent lines, a difference weighed against the registry revision data further down the page.

Metaphyseal, press-fit fixation raises the obvious question of how the implant actually holds.

The central anchor. A stemless humeral component anchors entirely in the proximal humeral metaphysis through a central fixation element seated in the cancellous bone of the cut surface. Designs vary:

• A porous-coated cage or anchor
• A finned central peg or corolla
• Some designs add peripheral fins or a small central screw

Primary and secondary stability. Primary stability comes from a cementless press-fit and impaction into the cancellous bone, together with engagement of the strong cortical rim of the humeral neck cut. Secondary stability comes from bony on-growth and ingrowth (osseointegration) onto the porous surface; the general biology of bone ingrowth is developed in Osseointegration.

When not to use one. A stemless implant is contraindicated or avoided where the proximal humeral metaphyseal bone is inadequate, and a stemmed implant is used to gain diaphyseal fixation instead:

• Severe osteoporosis
• Large subchondral cysts
• Avascular necrosis with collapse
• Significant deformity

Before surgery. Suspect poor metaphyseal bone in severe osteoporosis, inflammatory arthritis, avascular necrosis, large subchondral cysts and deformity, and assess the proximal humerus on imaging. General assessment of bone quality is developed in Osteoporosis.

In theatre. After the humeral head cut, assess the exposed metaphyseal cancellous bone directly. Either of two findings signals that it will not hold a stemless anchor:

• The thumb test: cancellous bone that compresses or indents easily under thumb pressure is too soft
• Trial stability: a stemless trial that toggles or lacks rotational purchase signals inadequate fixation

Revision. Because the diaphysis and bone stock are preserved, a failed stemless or short-stem implant can be converted relatively straightforwardly to a stemmed anatomic or reverse arthroplasty. The trade-off is the dependence on bone quality, so selection, the right implant for the right bone and patient, is the key to using these designs well.

Seven-Year Registry Survivorship

Registry data now reach seven years, further than the short-to-mid-term comparative series. A New Zealand Joint Registry study of the 12 most-used anatomic total shoulder arthroplasty implants followed 3,952 patients (3,114 conventional stems, 360 short stems and 478 stemless) for revision up to seven years.

There was no significant difference between the three, and that held irrespective of patient age or surgeon volume. There were no cases of humeral loosening in any group up to seven years, and no intra-operative humeral fractures in the stemless group, which directly supports one of the stated reasons to avoid a diaphyseal stem.

The Radiolucent Lines Are Radiographic, Not Yet Clinical

The difference. The most quoted advantage of the shorter components is radiographic: in a series of 825 patients, humeral radiolucent lines were seen in 1.6% of stemless and 1.7% of short-stem against 11.9% of standard stems. That difference is real, substantial and explained by loading the metaphysis rather than bypassing it.

What it has not changed. In the same comparative series, range of motion, patient-reported outcomes, complications and revision rates did not differ by stem length, and in the registry revision rates were equivalent. A radiolucent line is currently a marker of altered load transfer, not a demonstrated cause of failure, and quoting the 1.6%-versus-11.9% contrast as though it were a survivorship advantage overstates it.

The honest position. Stress shielding may matter over a longer horizon than has yet been observed, which is why standardised radiographic description of it has been called for. Durability beyond seven years is still being established.

A Statistically Significant Difference That Is Not a Clinically Important One

The registry also found a better six-month Oxford Shoulder Score for stemless than conventional stems, 40.7 versus 39.4, p = 0.023. The p-value is real, but the gap is 1.3 points on a 48-point scale, which no patient would notice; with nearly 4,000 patients a trivial difference reaches significance easily. It is a worked example of the distinction between a significant result and an important one, and should not be offered as a functional argument for the implant.