J Korean Ophthalmol Soc.  2010 Aug;51(8):1121-1128.

Muscle Weakening Effect After Superior Rectus Z-myotomy in Rabbits

• Ku HC
• Park YG
• Lee SY
• Lee YC

Abstract

PURPOSE
To experimentally investigate the effect for muscle weakness after superior rectus Z-myotomy and histological changes.
METHODS
Superior rectus muscle fibers of rabbits (16 rabbits, 32 eyes) were cut transversely with scissors across 75% of the muscle in two different positions on opposite sides. In group 1 (16 eyes), myotomies were performed at 2 and 7 mm from the muscle insertion (5 mm gap) and in group 2, performed at 2 and 5 mm (3 mm gap). The change of mark, eyeball position, and muscle tension after myotomy and 4 weeks postoperatively was evaluated, the location of the mark was examined, and muscle tissue biopsy was performed.
RESULTS
After Z-myotomy, the marks of the two groups moved significantly posteriorly from insertion within groups (p<0.05), with no significant differences between groups (p=0.469). Eyeball positions of the two groups moved significantly inferiorly (p<0.05); the amount of position change of group 1 was greater than group 2 (p<0.05). When the globe was pulled in opposite directions for muscle action, the degree of change decreased with significant difference within groups (p<0.05), but there were no significant differences between groups (p=0.32).
CONCLUSIONS
Z-myotomy of the superior rectus muscle affected the recession of eyeball position and weakened the muscle action. Muscle weakening affected by the different gaps between myotomies did not show consistent results.

Keyword

Eyeball position; Muscle tension; Muscle weakness; Z-myotomy

MeSH Terms

Biopsy
Muscle Tonus
Muscle Weakness
Muscles
Rabbits

Figure

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  Figure 1. Procedures of superior rectus Z-myotomy. (A) Superior rectus muscle is exposed with muscle hooks after conjunctival dissection. (B) Marking with 5-0 black silk on the superior rectus muscle 9.0 mm from the muscle insertion site. (C) The hemostat is placed to grasp the muscle that will be cut. (D) The muscle is cut along the crushed area using small snips with scissors. (E)(F) Noticeable lengthening of the muscle is achieved.

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  Figure 2. This diagram depicts the position of the mark and Z-myotomy in the superior rectus muscle.

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  Figure 3. This diagram illustrates the method for measuring the eyeball position.

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  Figure 4. Histologic findings of Z-myotomy site of a group 1 rabbit at 4 weeks after surgery (Masson's trichrome stain). (A-1, A-2, A-3) Proximal portion from the mark, injured muscle by myotomy. This muscle tissue showed vague margin between the orbital layer and global layer, collagen fiber proliferation among muscle fibers, and severely distorted EOM structure. (B-1, B-2, B-3) Distal portion from the mark, intact muscle. This intact muscle showed well defined orbital layer (small sized muscular fibers, surround global layer) and global layer (large sized muscular fibers, surrounded by orbital layer).

Reference

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