Tendon elongation: a new surgical technique for convergent squint after three wall orbital decompression in thyroid associated ophthalmopathy

Introduction: Large convergent squint angles can occur after three wall orbital decompression in patients with thyroid associated ophthalmopathy and compressive optic neuropathy. These squint angles can be too large to be corrected by a simple recession of the medial rectus muscles. Resection of the lateral rectus muscles is not recommendable, because the medial rectus muscles are trapped in the ethmoid sinus. A new surgical procedure will be introduced.

Methods: Large convergent squint angles have been corrected in 18 patients with a medial rectus muscle tendon elongation using a 10mm wide Tutoplast® interponate. The length was preoperatively determined. Monocular excursions and squint angles in primary position were evaluated preoperatively and 7 months after the operation.

Results: The median preoperative squint angle in primary position was +25.1° (max: 40°; min 10°). Seven months after surgery the median squint angle was 2.6° (max: 0°; min +10°). 14 of 18 patients had no double vision in primary position postoperatively. The dose-effect- coefficient (improvement of the squint angle [°]/amount of recession (R) of the muscle [mm]) was lower for the tendon elongation (1.0°/mm R) in comparison to bilateral recession of the medial rectus muscles (in patients without prior orbital decompression: 1.58°/mm R). Abduction improved on average about 14.1° (±9.6°) to 21.8° and adduction deteriorated on average about 15.9° (±6.4°) to 17.8°. A fixation of the interponate 3mm behind the original insertion of medial rectus muscle resulted in better conjunctival appearance.

Discussion: The results of the trial revealed that medial rectus muscle tendon elongation with a Tutoplast® interponate is a safe method to correct large convergent squint angles after orbital decompression. The low dose-effect-coefficient might be a result of the tendon fixation close to the original insertion which preserves normal leverage due to normal arc of contact. A significant convergence insufficiency did not occur.