Symptomatic Aseptic Loosening of a Short Humeral Stem Following Anatomic Total Shoulder Arthroplasty
These authors point out that the rate of aseptic humeral component loosening with standard-length stems is low (0.3%) and that presence of humeral loosening gives rise to concern for periprosthetic shoulder infection.
They conducted a retrospective multi-institutional review of anatomic total shoulders performed with a grit-blasted, rectangular short humeral stem without ingrowth coating.
The average patient age was 62 and 57% were male. Three of the four surgeons used a lesser tuberosity osteotomy (LTO) and one preferred the subscapularis peel. Due to the metaphyseal fit and proximal geometry of this implant, careful attention had to be paid to the size of the LTO during the approach to ensure adequate bone stock for circumferential press-fit placement of the stem. Patients for whom the surgeon did not achieve rigid press-fit were converted to long-stem fixation or were cemented and were excluded from this analysis. The number of patients excluded because of inability to use the short stem is not provided.
One-year radiographs were available in 65%.
All patients with concern for clinically significant humeral loosening underwent work-up for periprostheticshoulder infection. Immediate post-operative films were reviewed to identify any differences in prosthetic canal fit. The authors found no differences in canal fit between patients with concern for symptomatic loosening and those with pain-free, stable implants.
Twenty-three (12.5%) patients presented with a painful shoulder and met the authors' criteria for humeral loosening at a mean follow-up of 1.5 years (range: 1.5 months – 3.4 years); half had gross humeral subsidence. Thirteen (7.1%) of these underwent revision shoulder arthroplasty where a loose stem was confirmed.
All revisions underwent tissue culture and three cases were thought to have probable or possible periprosthetic infections.
The rate of symptomatic aseptic humeral loosening in this series was 10.9% (20/184) with 5.4% undergoing revision surgery. Patients with symptomatic aseptic humeral loosening were more likely to be male (90.5%) than those patients without symptoms (52.8%; p<0.001). Of the 105 male shoulders included in this cohort, 19 (18.0%; 19/105) developed symptoms and radiographic findings concerning for aseptic loosening. Ten (9.5%; 10/105) had a revision for aseptic loosening.
The authors concluded that the early humeral loosening rate for this stem design "far outpaces previously reported rates and this study likely under-reports the true incidence of clinically-significant loosening as it only contains limited short-term follow-up".
Comment: Perceived shortcomings of conventional long-stemmed diaphyseal-fitting humeral components (e.g.difficulty with stem extraction at the time of revision surgery, management of periprosthetic fractures, and metaphyseal osteolysis from stress-shielding) has driven an interest humeral implants with a short-stem. However, this study and other similar studies have not demonstrated an advantage of short stemmed humeral components over standard stems. Standard stem fixation with impaction grafting avoids the problems of "diaphysial fitting" and minimizes stress shielding, fracture risk, and difficulties in stem removal should it become necessary.
