2017 ISAKOS Biennial Congress ePoster #2214

 

Biomechanical Advantage of a Superior Lateral Placed Anchor for Subscapularis Footprint Reconstruction

Felix Dyrna, MD, Münster GERMANY
Leo Pauzenberger, MD, Vienna AUSTRIA
Elifho Obopilwe, ME, BSc, Farmington, CT UNITED STATES
Cory Dwyer, BSc., Farmington, CT UNITED STATES
Elmar Herbst, MD, PhD, Münster GERMANY
Knut Beitzel, MD, MA, Cologne GERMANY
Augustus D. Mazzocca, MS, MD, Farmington, CT UNITED STATES
Sepp Braun, MD, PhD, Munich, Bavaria GERMANY

TU Munich, Munich, GERMANY

FDA Status Cleared

Summary

In order to restore the cranial aspect of the subscapularis tendon and therefore prevent tear progression it is recommended to place a superior lateral anchor.

Abstract

Background

The subscapularis (SSC) tear commonly merges from the cranial aspect of the tendon and progresses inferiorly. Additionally, the superolateral aspect of the subscapularis is part of the medial pulley sling that stabilizes the biceps pointing out the relevance of the cranial tendon portion. Several studies demonstrate a significant improvement of shoulder function after SSC repair but do also show a partial re-tear rate and progressive atrophy especially of the superior aspect of the muscle, demonstrating an unsatisfactory footprint restoration. The purpose of this study was to evaluate contact pressure, displacement, and pressurized footprint area differences between double-row and single-row repair techniques for full thickness SSC defects focusing on the superior lateral (leading) edge.

Methods

The native footprint was measured on fifteen pairs of human cadaveric shoulders mean age 67.2 years. According to the Fox/Romeo classification a A) 25% and a B) 50% defect in a superior inferior direction was created. A pressure sensitive sensor was placed between the bone and tendon. After placement of digital position markers, specimens were mounted onto a servo-hydraulic test system to analyze contact variables at 0º and 20º of abduction with a force controlled ramped program up to 50N. Additionally each specimen was cyclic loaded (10N-100N, 300 cycles) natively, with defect, and repaired. The tears were repaired with one of three constructs: A two anchor based conventional single row (SR) or lateral row construct (LR) or a three anchor based double row (DR). Outcome variables were displacement, pressurized footprint coverage, contact pressure and ultimate tensile load.

Results

The mean native footprint area among all groups was 476.1mm2 ± 69.5 and did not show a significant difference (p=0.31). The 25% defect equaled a mean area of 117.1mm2 ± 32.2 and could equally be restored with either a SR or LR construct revealing adequate load to failure stability (SR 511N ± 120 versus LR 461N ± 145) and a pressurized reconstruction of the footprint of SR 84% ± 8.9 / LR 95.1% ±7.9. If focusing on the superior lateral edge, creating a 10% region of interest (ROI) of the total defect size, the SR could reconstruct 25.5%±14.8 whereas the LR repair restored 100% ± 0 pressurized contact area (p=0.01). The created 50 % defect (mean 276.4mm2 ± 58.2) could be restored with the SR construct up to 72.8% ± 14.2, LR 93.5% ± 10.6 (p=0.02) and DR 90.6% ± 11.8 (p=0.04). With significant differences on the superior lateral edge ROI SR covered 38.9% ± 31.4, LR 76.8% ± 24.4 (p=0.04) and DR 70.2% ± 26.1..All repair groups achieved satisfactory ultimate stress results SR 451N ± 124.74, LR 548N ± 228.37 (p= 0.4), DR 508N ± 170.13.

Conclusion

The biomechanical advantage of a superior lateral placed anchor increases with defect size. In order to restore the leading edge of the subscapularis muscle and therefore prevent tear progression it is recommended to add a superior lateral anchor. Clinical trials are needed to proof the results of this study.