The Change of Rectus Muscle Length Caused by Traction with Muscle Hooks in Strabismus Surgery: The Second Report

PURPOSE: To investigate the influence of the change in medial rectus resection amount caused by traction with muscle hooks on surgical results in exotropia. METHODS: In this prospective study 38 exotropia patients underwent unilateral lateral rectus recession-medial rectus resection (R & R). After isolation of the medial rectus muscle, the length of the muscle was measured with a muscle hook, and the portion to be resected was marked using gentian violet stain with calipers. After the medial rectus was retracted with two muscle hooks in either direction, its length was measured again with the calipers. Group 1 includes the patients with the planned resection amount changed to a more 0.5-1.0 mm when the rectus muscle was retracted, while group 2 did not change with the second muscle hook. The surgical results were compared between the 2 groups at postoperative 6 months. RESULTS: Mean resection amount was changed from 5.07 +/- 0.76 mm to 5.36 +/- 0.73 mm after pulling the second muscle hook. Sixteen patients (42.1%) were included in group 1 and 22 patients (57.9%) in group 2. There was no significant statistical difference in mean preoperative and postoperative deviated angle between the two groups. Success rates defined as the ocular alignment within +/- 10 PD in the primary position at postoperative 6 months were 75.0% in group 1 and 86.3% in group 2, which is not stastistically different (p > 0.05). CONCLUSIONS: Medial rectus resection amounts can be changed with the muscle traction with two muscle hooks, which induced the planned amount of resection less than first measured resection amount. However, there was little influence on surgical outcomes from the change occurred to a maximum 1 mm in resection measurement due to traction with two muscle hooks.

The Change of Rectus Muscle Length Caused by Traction With Muscle Hooks in Strabismus Surgery-the First Report

PURPOSE: To evaluate changes in muscle length when retracting the extraocular rectus muscle with muscle hooks during strabismus surgery. METHODS: Forty-four rectus muscles of 42 patients consecutively resected in two hospitals (A, B) were included in this study. After isolation of the rectus muscle, the length of the muscle was recorded and the portion to be resected was marked using gentian violet stain on the tip of calipers. After the rectus muscle was retracted with two muscle hooks in either direction, its length was measured again with the calipers. RESULTS: The length of the rectus muscle was not changed by retraction in 25 of 44 muscles (56.8%). The length of the muscle was changed by 0.5 mm in 13 muscles (29.5%) and by 1mm in six muscles (13.6%). Changes of rectus muscle length over 0.5 mm were observed in 15 of 27 muscles of patients treated at hospital A (55.5%) and four of 17 muscles of patients treated at hospital B (23.5%). The results for the two hospitals were significantly different (p=0.037). CONCLUSIONS: Small errors in measurement can occur when muscle resections are performed during strabismus surgery. Institutional or clinician related factors may explain variations in error rates between hospitals.