Specific Design of a Press Fit Humeral Stem Provides low Stress Shielding in Reverse Shoulder Arthroplasty at minimum 5 Years FU

Abstract

Press fit fixation is becoming more popular in RSA to preserve, in theory, bone capital. Several studies report that bone resorption can be very high around humeral stems depending on their size, shape and mode of fixation. The aim of the current study is to mid-term follow-up clinical and radiological result of a press fit ovoid regular stem RSA in non acute trauma cases.

Materials and methods: We performed a retrospective monocentric study of patients continuously implanted with the Humeris® stem RSA for degenerative change of the shoulder. Nineteen shoulders, in eighteen patients (74.6 y.o (from 69 to 81)), were available at minimum five years follow-up.

Results: The mean final adjusted Constant score was 111.9 (65 to 130), and the mean ASES score was 49.82 (10 to 60). Humeral resorption was observed in 21% of cases. We found a statistically significant (p = .014) lower adjusted Constant score in patients presenting with resorption on post-operative X-rays compared to those without resorption (115.6 vs. 98.25). Half cases of patients presenting a resorption underwent L'Episcopo procedure during surgery. Humeral resorption occurs the first year after surgery and do not increase even 8 years after surgery. Analysis demonstrated no correlation between the value of filling ratios and bone resorption.

Conclusion: The current study confirms a low rate of stress shielding around the studied stem, with rare bony resorption and no osteopenia around the humeral stem. This study highlights the importance of choosing the appropriate proximal shape and length of the humeral stem for press fit fixation in RSA.

Keywords: bone resorption; humeral stem; long follow up; pressfit; reverse Shoulder Arthroplasty.

Figure 1.

Humeris ® is a press fit, ovoid, stem that can be used for anatomic and reverse shoulder arthroplasty. An asymmetric 135/145 polyethylene / metal backed humeral cup allows to have a 145° cervico-diaphysal angle even with an anatomic cut of the humeral head.

Figure 2.

Measurements of the filling ratio on AP (proximal and distal) and lateral (distal) X-Rays. The blue line materializes the shaft axis (SA) of the humerus. At the level of the humeral baseplate and at the level of the junction between the second and the distal third of the stem, two lines are drawn perpendicular to the SA. The green lines illustrate the measurements of the stem width, and the red lines illustrate the measurements of the endocortical width. The filling ratio is calculated by dividing at each level the stem width by the endocortical width.

Figure 3.

Xray AP view at 1 month, 1 year and 8 years after RSA. Resorption appears at 1 year, at the location of the latissimus dorsi tendon transfer. No progression of the resorption occurs over time.

Figure 4.

Xray AP view at 1 month, 1 year and 8 years after RSA. No resorption appears over time. Distal filling ratio changes but no impact is seen on proximal aspect of the humerus.