Fusion Sign of Tendon-to-Bone Healing on X-Ray after Rotator Cuff Repair

Purpose: In clinical practice, increased radiolucency at the insertion site of a repaired tendon on the humerus on postoperative radiographs of patients following rotator cuff repair is often observed. Separately, magnetic resonance imaging (MRI) revealed tendon-to-bone healing in conjunction with this finding. Thus, we suspected that such radiographic changes are associated with tendon-to-bone healing, a phenomenon we labeled as the “fusion sign.” This study sought to investigate the diagnosis rate of the fusion sign in relation to tendon-to-bone healing after rotator cuff repair. Methods: Patients who underwent open rotator cuff repair (ORCR) or arthroscopic rotator cuff repair (ARCR) at two centers from 2010 to 2018 and who underwent MRI more than 6 months postoperatively were included in this study. The presence of radiolucency of the humeral footprint on a radiograph (the fusion sign) was investigated and checked for the concurrent presence of tendon-to-bone healing on MRI. Results: In total, 187 shoulders after ARCR and 55 shoulders after ORCR were included in this study. Among these, SH repair was performed in 202 shoulders and suture-bridging repair was performed in 40 shoulders. The fusion sign was positive in 67.8% of cases and negative in 32.3%. The positive predictive value (PPV) of the total population was 0.963 and did not differ according to the suture method used, reported as 0.964 in ARCR, 0.962 in ORCR, 0.966 in the surface-holding technique, and 0.938 in the suture-bridging technique. The intraobserver reliability was ĸ = 0.4478 (p < 0.001). The interobserver reliability for all observers was ĸ = 0.408 (p < 0.001). Conclusion: Postoperatively, the presence of the fusion sign at the footprint of the humerus strongly suggests that tendon-to-bone healing has occurred.