In Vivo Graft Elongation After Arthroscopic Dermal Superior Capsular Reconstruction

Abstract

Background: Superior capsular reconstruction (SCR) is a procedure purported to restore stability of the glenohumeral joint after an irreparable rotator cuff tear, but the in vivo behavior of the graft is unknown. Previous work has not evaluated the relationship between graft deformation, kinematics, and healing. Purpose: To (1) determine regional graft elongation after SCR, (2) determine if graft elongation is related to graft healing, and (3) identify associations between graft elongation and changes in kinematics from presurgery to postsurgery. Study Design: Case series; Level of evidence, 4. Methods: Ten patients who underwent SCR performed abduction and shoulder rotation with the arm at 90° of humerothoracic abduction before and 1 year after surgery while biplane radiographs were collected at 50 images per second. Kinematics was determined with submillimeter accuracy by matching patient-specific digitally reconstructed radiographs of the humerus and scapula to the biplane radiographs using a validated volumetric tracking technique. Graft elongation was calculated using motion of the graft anchors that were identified on postoperative magnetic resonance imaging. Differences in elongation between anterior and posterior regions of the graft, as well as associations between graft elongation, graft healing, and kinematics, were analyzed. Results: Peak graft elongation ranged from a 3% decrease in the anterior region during rotation to up to a 171% increase in the anterior region during abduction and the posterior region during rotation. Grafts that were healed at both anterior anchors reached the intraoperative length at lower abduction angles (60°) than grafts that were not healed at 1 or both of the anterior anchors (87°) ( P = .005). The posterior anchor graft origin to insertion distances were 2.1 mm farther apart after surgery compared with before surgery during both abduction and rotation. Conclusion: SCR dermal allografts are stretched well beyond their intraoperative length in vivo. Graft healing appears to be associated with less graft elongation. The posterior portion of the SCR graft does not appear to improve glenohumeral joint stability 1 year after surgery. Improved clinical outcomes after dermal allograft SCR may be because of the spacer effect of the graft rather than improved glenohumeral joint stability 1 year after surgery.