Previous studies reported the following important factors determining the repair integrity after rotator cuff repair: tear size [15
], location, presence/absence of atrophy and fatty degeneration in the muscles [16
], repair tension, tendon quality, and patient age [2
]. Gerber et al. [16
] and Goutallier et al. [14
] reported that the most significant risk factors for retear are the presence of atrophy and fatty degeneration.
Recent biomechanical studies have demonstrated that the elements for successful repair of a rotator cuff tear are achievement of strong fixation [19
], a high interface pressure, a wide interface area between the tendon and the bone [22
], and minimization of stress concentration inside the tendon [7
]. Some new suture techniques allowing achievement of all of these elements have been devised [1
]. Therefore, the reported retear rate after open and arthroscopic repair surgeries has improved [1
]. Then, improvement of rotator cuff repair techniques is also expected to facilitate recovery of the muscle atrophy and fatty degeneration.
However, in some basic studies, Matsumoto et al. found neither reversal of atrophy nor reversal of fatty infiltration after delayed repair in rabbits [26
]. Burkhead et al. reported that successful repair may partially reverse muscular atrophy but not fatty infiltration in sheep [19
]. In a previous clinical study, Gerber et al. reexamined the records of 57 of 63 patients who underwent postoperative CT and were followed up for a mean duration of 17.7 months [18
]. They found no regression of infraspinatus fatty degeneration even after a watertight repair, and improvement of supraspinatus fatty degeneration was noted in only 6 cases [14
]. Thomazeau et al. reported more optimistic results of evaluation of supraspinatus muscle atrophy: in one half of the 22 patients who underwent continuous cuff repair, the atrophy improved by more than 10% [27
] (mean followup, 21.1 months).
In this study, we found higher rate of improvement of atrophy and no significant correlation between the grade of preoperative atrophy and the repair integrity. And we also found higher rate of improvement of fatty degeneration and no significant correlation between preoperative fatty degeneration and repair integrity. We consider that the reasons for this result are due to our higher rate of successful repair and longer follow-up period, giving enough time for atrophy and fatty degeneration to improve.
Several limitations must be considered when changes in the rotator cuff muscles are analyzed by determining crossed-sectional areas on one MRI plane. One crossed-sectional area may not represent the total muscle volume, especially as muscles change in shape along their length. Furthermore, we did not investigate time-dependent changes in this study, and there is some possibility that the measured area was not exactly same before and after surgery because of the influence of retraction of the cuff muscles on MRI [28
]. In the future study, sequential postoperative MRI must be performed to investigate under what circumstances the fatty degeneration might be irreversible and clinical point at which cuff muscles may not be able to return to nearly normal function despite successful surgical repair as evaluated by MRI.
In conclusion, we indicate that successful repair of chronic massive cuff tears may allow arrest or recovery of severe fatty degeneration and atrophy of the torn muscles. Furthermore, in massive cuff tears, successful repair is the key to long-term functional improvement not only for pain relief and stabilizing.