The snapped inferior rectus.

Purpose: To evaluate the management and possible aetiology of the snapped inferior rectus muscle in strabismus surgery.

Methods: Three patients are described whose inferior rectus muscle broke across its width some 8-10mm behind the insertion while being held on a squint hook without excessive force during strabismus surgery. The proximal part of the muscle was not found. The distal part of the snapped muscle was excised for pathological examination. Transposition of the inferior halves of the adjacent horizontal muscles to the insertion of the inferior rectus (a modified inverse-Knapp procedure) was performed in all cases.

Results: After the transposition surgery, one patient was orthotropic in the primary position, one patient required a prism correction to produce a range of single vision and the third patient was orthotropic after a further operation. There was good depression in one case and the other two had a limitation of depression. In all cases, horizontal movements remained intact and there were no signs of anterior segment ischaemia.

Conclusions: The unique relations of the inferior rectus to the surrounding tissues may be a factor in causing the breaking of this muscle. Two of the patients were elderly and this may be a factor also. Transposition surgery is the appropriate management when the proximal part of the snapped muscle cannot be located and has satisfactory but imperfect results.