ISAKOS Congress 2021

2021 ISAKOS Biennial Congress Paper

 

What Is The Ideal Position Of The Shoulder For Graft Fixation In Arthroscopic Superior Capsular Reconstruction? A Computational Analysis.

Madalena João Antunes, MsC, Lisboa, Lisboa PORTUGAL
Carlos Quental, PhD, Prof., Lisboa PORTUGAL
João Folgado, PhD, Prof., Lisboa PORTUGAL
Clara Azevedo, MD, Lisbon PORTUGAL
Catarina Ângelo 515904945, MD, Lisbon PORTUGAL

IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, PORTUGAL

FDA Status Not Applicable

Summary

A computational analysis was designed to determine the role of the fascia lata graft in restoring shoulder stability in arthroscopic superior capsular reconstruction for irreparable rotator cuff tears. Shoulder stability was better restored when the graft was fixed with the shoulder at 5º to 10º of abduction, and in 10º of internal rotation, and when the long head of the biceps was preserved.

Abstract

Background

Arthroscopic superior capsular reconstruction (ASCR) for the treatment of irreparable rotator cuff tears (IRCTs) has been shown to produce excellent functional outcomes. However, the graft tear rate ranges from 4.2% to 75%. The position of the shoulder during graft fixation may be a key factor impacting the outcome of ASCR, and biomechanical evidence regarding the effect of initial graft positioning on the stability of the shoulder, and on the functional role of the graft is lacking. This study aimed to determine whether the position of the shoulder during graft fixation influences the stability of the shoulder and graft tear risk. The hypotheses were that ASCR would increase the stability of the shoulder after an IRCT, and different positions of the shoulder during graft fixation would influence shoulder stability and graft tear risk.

Methods

A musculoskeletal model of the upper limb was modified to account for the fixation of the graft. A total of 126 shoulder positions of fixation were simulated to improve shoulder stability. The material properties of the graft were defined based on experimental data that the authors had collected previously from 20 cadaveric fresh fascia lata grafts. The rotator cuff tear was modelled assuming a full-thickness tear of the supraspinatus tendon. The effect of concomitant long head of the biceps (LHB) tenotomy was also studied. The biomechanical parameters evaluated included the strain of the graft and the glenohumeral joint reaction force, to estimate the integrity of the graft and shoulder stability, respectively. The positions of high risk of tear were defined as those for which the strain of at least one segment of the graft exceeded the strain failure of 15%. Analysis of variance (ANOVA) and Tuckey’s test were used to compare the shoulder stability index among shoulder positions of fixation. The significance level was set to p < 0.05.

Results

Fixation at abduction angles of >15º resulted in a high risk of graft tear when the arm returned to the resting position. For this reason, the stability of the shoulder, for these positions, was not evaluated. Shoulder stability significantly improved compared with the preoperative condition, regardless of the shoulder position of fixation (95% confidence intervals, p<0.001). Fixation of the graft with the shoulder at 5º to 10º of abduction and in 10º of internal rotation correlated with the most significant improvement in shoulder stability compared to the preoperative condition (p<0.001). Concomitant tenotomy of the LHB significantly decreased shoulder stability of ASCR (p=0.007).

Conclusion

ASCR for IRCTs increases the stability of the shoulder compared to the preoperative condition. Fixing the superior capsular graft with the shoulder at 5º to 10º of abduction, and in 10º of internal rotation, and without concomitant LHB tenotomy, improves shoulder stability. Abduction angles >15º increase the graft tear risk.
This study supports the relevance of the position of the shoulder during graft fixation both for the stability of the shoulder, and for graft integrity after ASCR. New studies should investigate the role of LHB tenodesis as an alternative to tenotomy to preserve the LHB’s stabilizing effect in ASCR.

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