THE SNAPPED INFERIOR RECTUS

Purpose: To evaluate the management and possible aetiology of the snap ped inferior rectus muscle in strabismus surgery. Methods: Three patie nts are described whose inferior rectus muscle broke across its width some 8-10 mm behind the insertion while being held on a squint hook wi thout excessive force during strabismus surgery. The proximal part of the muscle was not found. The distal part of the snapped muscle was ex cised for pathological examination. Transposition of the inferior halv es of the adjacent horizontal muscles to the insertion of the inferior rectus (a modified inverse-Knapp procedure) was performed in all case s. Results: After the transposition surgery, one patent was orthotropi c 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 t o the surrounding tissues may be a factor in causing the breaking of t his muscle. Two of the patients were elderly and this may be a factor also. Transposition surgery is the appropriate management when the pro ximal part of the snapped muscle cannot be located and has satisfactor y but imperfect results.