Genetic or acquired collagen and healing disorders cause several difficulties during strabismus surgery. Sutures may not hold well in tissue and pull through. Tissues may tear during surgery and require delicate technique. Muscle paths may be displaced due to weak pulley support, causing complex strabismus patterns.
Weak wound healing after previous strabismus surgery may lead to stretched and/or migrated scars, with recurrent or consecutive strabismus. Repair techniques are presented in this chapter. Pulled-in-two syndrome with tear of the muscle at the musculotendinous junction is also discussed.
27 Stretched Scar Repair and Management of Other Weak Collagen Abnormalities
Weak collagen can cause difficulty during strabismus surgery. Conjunctiva can tear easily in the elderly as well as younger patients with underlying collagen abnormalities. When weak connective tissue is encountered during routine strabismus surgery, it may be wise to use nonabsorbable sutures for tendon reattachment to prevent healing difficulties such as stretched scar and scar migration. Weak primary collagen and weak wound healing 1 , 2 may be seen in combination, or as isolated phenomena. Patients with weak collagen may be prone to pulley displacements, which should be identified and corrected (Chapter 19, Chapter 30).
27.2 Stretched Scar Repair
Stretched scar patients have always had previous strabismus surgery, by definition. 2 , 3 Prior surgical records are helpful, and will allow targeted exploration of only the previously operated muscles. If records are unavailable, then all four rectus muscles on each eye may be inspected with two small fornix incisions, such as an inferomedial incision to inspect the inferior and medial recti, and a superotemporal incision to inspect the superior and lateral rectus muscles. If the history is clear and the strabismus pattern straightforward, then complete inspection of all the muscles is not necessary. The first clue to the possibility of a stretched or lengthened scar is usually the ease of dissection and isolation of the muscle. 2 As the problem is one of weak scar tissue, conjunctival scarring is usually mild. The muscle is isolated on the Stevens tenotomy hook in normal fashion, and then placed on the larger Green hook. Retraction of the conjunctiva over the hook is usually surprisingly easy for a reoperation case due to the weak scar formation. Two other clues to the presence of stretched scar are the rolling of the muscle over the hook when the hook is pulled anteriorly (Fig. 27‑1), and the ease of lifting of the hook away from the sclera (Fig. 27‑2) due to the weak scar between tendon and sclera (Video 27.1, Video 27.2).
27.2.1 Recognizing the Stretched Scar Margins
With experience, the surgeon is usually able to identify the edge of the healthy tendon (Fig. 27‑3). If the margin is not clear, then a helpful trick is to place a 6–0 polyglactin suture through scar tissue at the insertion site on the sclera and disinsert the muscle (Fig. 27‑4). Flip the muscle over and view the undersurface (Fig. 27‑5). The demarcation between tendon and scar is usually clearer from underneath (Video 27.3). When the original muscle surgery was a resection, the scar tissue is seen to emanate directly from muscle tissue rather than tendon (Fig. 27‑6)
27.2.2 Measuring and Calculating Muscle Reattachment Position
Two measurements are taken: (1) the distance between the original insertion and the found position of attachment to sclera and (2) the length of the stretched/lengthened scar segment between the sclera and tendon. The standard surgical tables are usually effective in predicting the amount of tendon advancement needed, by adding the millimeters of excised scar tissue to the advancement of insertion toward the original insertion (Fig. 27‑7). The formula for this is T = (A + S) – X. For example, in a patient with consecutive exotropia due to previous bilateral medial rectus recessions, the standard surgical table (Table 27.1, Table 27‑2) might recommend bilateral medial rectus resections of 6 mm (X in formula). If the left medial rectus is found 7 mm from the original insertion (A), with a 4-mm segment of amorphous scar tissue between the true tendon and sclera (S), then it should be advanced 2 mm from the found position (F) to position T to obtain the effect of a 6-mm resection. If measuring from the original insertion, that distance would be A – T, which is 5 mm in this example. If the right medial rectus is found 6 mm from the original insertion (A) with a 3-mm segment of stretched scar (S), it will be reattached at the 3-mm position to obtain a 6-mm effect.
These tables were developed empirically by Dr. Parks over years of clinical experience. The numbers here were those in actual use at the height of his career and are slightly higher than those he published. They have served well in this author’s practice for many years, with occasional adjustments. This author prefers smaller resections to create less bulk over the insertions and will sometimes reduce the resection by 1 or 2 mm and increase the recession by the same amount. For recess/resect procedures on one eye, read across the table on each line for the numbers.