When and how much does the muscle strength recover after arthroscopic superior capsular reconstruction?

BACKGROUND

Recently, arthroscopic superior capsular reconstruction (SCR) has been performed for irreparable large to massive rotator cuff tears and excellent clinical results have been reported. Although the muscle strength is reported to recover, it has not yet been clarified when and how much it recovers. The purpose of this study was to determine the recovery pattern of muscle strength after SCR.

METHODS

We retrospectively reviewed 35 patients (mean age, 65 years) who met the following inclusion criteria: (1) patients with large to massive irreparable tears of the rotator cuff including the supraspinatus and infraspinatus tendons; (2) those with severe muscle atrophy and fatty change; (3) those who underwent assessment of muscle quality and strength by magnetic resonance imaging and dynamometry at 6 months, 1 year, and 2 years; (4) those with a minimum follow-up period of 2 years; and (5) those without severe osteoarthritis. The isometric muscle strength of scaption (ie, scapular-plane elevation), internal rotation, and external rotation in adduction was measured twice for each motion by a dynamometer.

RESULTS

Relative to the muscle strength on the uninvolved side, the involved side showed 61% ± 21% in scaption, 63% ± 20% in external rotation, and 103% ± 29% in internal rotation at 2 years after surgery. Whereas no significant differences were observed between the 1-year and 2-year follow-up assessments, a significant difference in muscle strength of scaption was found between 6 months and 1 year (P = .0174). Graft retear was seen in 5 cases (14%). There was a trend that the muscle strength of scaption and external rotation in the no-retear group was greater than that in the retear group despite no significant difference (P = .0717 and P = .0824, respectively).

CONCLUSION

The recovery of the muscle strength after SCR was observed until 1 year after surgery, and the muscle strength of scaption and external rotation returned to 60% of that on the uninvolved side at 2 years.

Electromyographic analysis of the supraspinatus and deltoid muscles during 3 common rehabilitation exercises

CONTEXT

Investigators have observed electromyographic (EMG) activity of the supraspinatus muscle and reported conflicting results.

OBJECTIVE

To quantify EMG activity of the supraspinatus, middle deltoid, and posterior deltoid muscles during exercises commonly used in rehabilitation.

DESIGN

One-factor, repeated-measures design.

SETTING

Controlled laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty-two asymptomatic subjects (15 men, 7 women) with no history of shoulder injury participated.

MAIN OUTCOMES MEASURE(S)

The dominant shoulder was tested. Fine-wire EMG electrodes were inserted into the supraspinatus, middle deltoid, and posterior deltoid muscles. The EMG data were collected at 960 Hz for analysis during maximal voluntary isometric contraction (MVIC) and 5 repetitions of 3 exercises: standing elevation in the scapular plane ("full can"), standing elevation in the scapular plane with glenohumeral internal rotation ("empty can"), and prone horizontal abduction at 100 degrees with glenohumeral external rotation ("prone full can"). We calculated 1-way repeated-measures analysis of variance (P < .05) and post hoc 2-tailed, paired t tests to detect significant differences in muscle activity among exercises.

RESULTS

No statistical difference existed among the exercises for the supraspinatus. The middle deltoid showed significantly greater activity during the empty-can exercise (77 +/- 44% MVIC) and prone full-can exercise (63 +/- 31% MVIC) than during the full-can exercise (52 +/- 27% MVIC) (P = .001 and .017, respectively). The posterior deltoid showed significantly greater activity during the prone full-can exercise (87 +/- 53% MVIC) than during the full-can (P = .001) and the empty-can (P = .005) exercises and significantly greater activity during the empty-can exercise (54 +/- 24% MVIC) than during the full-can exercise (38 +/- 32% MVIC) (P = .012).

CONCLUSIONS

While all 3 exercises produced similar amounts of supraspinatus activity, the full-can exercise produced significantly less activity of the deltoid muscles and may be the optimal position to recruit the supraspinatus muscle for rehabilitation and testing. The empty-can exercise may be a good exercise to recruit the middle deltoid muscle, and the prone full-can exercise may be a good exercise to recruit the posterior deltoid muscle.