Posterior Fixation Sutures
Charles J. Bock Jr, MD
PREOPERATIVE CONSIDERATIONS
In strabismus where a strengthening procedure is contraindicated or not possible, weakening of the contralateral yoke muscle may be considered. Posterior fixation employs four mechanisms of action: (1) limiting maximal ocular rotation of the operated muscle, (2) decreasing total strength of the operated muscle by effectively shortening the muscle, (3) increasing innervation to the weak (paired yoke) muscle by Herring’s Law of Equal Innervation, and similarly, (4) increasing relaxation of the contralateral antagonist via Sherrington’s Law of Reciprocal Innervation.
Greater surgical effect is generally possible on the medial and inferior rectus muscles due to the shorter arc of contact of these muscles with the globe compared to the lateral rectus muscle; therefore, it is easier to achieve more weakening effect on the medial and inferior rectus muscles without being as far posterior. Care must be taken when considering surgery on the superior rectus muscle due to the presence of the superior oblique tendon in the field of operation.
Indications for posterior fixation in incomitant strabismus:
Paretic:
Sixth nerve palsy.
Internuclear ophthalmoplegia.
Restrictive:
Orbital fracture or other trauma.
Prior surgery with orbital hardware: scleral buckle, glaucoma implant.
Potentially combined etiology:
Duane syndrome.
Monocular elevation deficiency.
Esotropia:
High AC/A resistant to weaning bifocal.
Convergence excess.
Other potential indications:
Dissociated vertical deviation.
Nystagmus with head position.
SURGICAL PROCEDURE
Adequate exposure is critical. The fixation suture is generally placed 15-20 mm posterior to the limbus. Suture selection is important.
While 6-0 Mersilene on an S-28 needle (Ethicon) or 5-0 Mersilene on an S-14 needle (Ethicon) can be used, a shorter spatulated needle is preferred, due to exposure concerns. The 5-0 polyester suture on an R-5 needle (Alcon) is excellent for this, though the suture material often drags Tenon tissue. Another choice is the CV-8 Gore-Tex, TTc-9 needle (Gore Medical); this needle is tapered, rather than spatulated, but short and easily maneuvered.
Posterior Fixation without Recession
With the muscle on the muscle hook, the sutures are placed on an equal distance posterior to the limbus. Retract orbital tissue with a Desmarres or Fison retractor, using a neurosurgical sponge if necessary. Use a small hook to gently lift the edge of the muscle so that the suture pass through the sclera is at the muscle edge. Incorporate 1/4-1/3 of the muscle in the pass. Repeat on the opposite side, and tie both sutures securely (Figs. 49.1 and 49.2).
Posterior Fixation with Recession
Once the muscle has been disinserted from the globe, retract it gently with orbital tissue. Here, there are two options: (1) place two sutures through the sclera at locations corresponding to the edges of the muscle as above, reattach the muscle, then pass the needles through the edge of the muscle (Figs. 49.3 and 49.4), or (2) pass a single double-armed suture through the sclera at a position corresponding to the center of the muscle, reattach the muscle, and then bring each needle up through the muscle and tie on top and in the center of the muscle (Figs. 49.5 and 49.6).
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