There are four types of flap tear: longitudinal, lamellar, beveled, and retracted. Recognition and repair requires familiarity with the normal anatomy of the rectus muscle as well as its surrounding capsular layers and adjacent pulley tissues. Repair of associated pulley displacement and rupture of posterior Tenon’s capsule and muscle capsule are all necessary components of complete flap tear repair. Muscle displacement may coexist with flap tear, and may need to be addressed separately, if flap tear repair does not restore the muscle path.
Slipped muscles, which are iatrogenic due to improper technique during strabismus surgery, are repaired with the same methods used to repair stretched scars, although the pathologic mechanisms are different. Lost muscles may be traumatic or iatrogenic and are defined as a muscle that has lost all connection to the globe. Some are relatively straightforward to locate and repair, if pulley sleeve connections to other muscles remain and allow the muscle to be traced. Many are located in the same layer where flap tear is found, and familiarity with flap tear repair improves success in locating lost muscles. The most difficult lost muscle to repair is the medial rectus, which lacks attachments to any oblique muscle and tends to retract deep into the orbit. Meticulous technique may allow direct retrieval, but if this is not possible, an imaging-guided orbital wall approach is usually successful.
29 Traumatic Strabismus Repair (Flap Tear, Slipped and Lost Muscles)
29.1 Flap Tear Repair
Forced duction testing usually shows restriction toward the field of action of the torn muscle. Torsional forced duction is also frequently abnormal into excylcorotation and incyclorotation due to adhesions between the intra- and extraconal spaces. 1 , 2 , 3 The muscle is approached through a fornix incision opposite the expected direction of flap attachment. For example, when an inferior rectus (IR) flap tear is suspected in an exotropia case, it is best to use an inferonasal fornix incision to isolate the IR. This avoids disturbing the possible outward-pulling flap and pulley tissue. The incision should be as small as possible, and the rectus muscle is placed on a Green muscle hook in standard fashion. The Desmarres retractor is then placed over the muscle without dissection, so the landmarks can be inspected (Fig. 29‑5, Fig. 29‑6). In severe flap tear cases the adhesions may be so dense that the retractor cannot be placed, so some minimal dissection is required in order to place the retractor. Dissection should be kept as anterior as possible to avoid disturbing the perimuscular tissues. If the anatomy is unclear, a brief view of the uninvolved muscle of the fellow eye can be helpful for comparison (Fig. 29‑7, Video 20.1, Video 29.1, Video 29.2).
29.1.1 Longitudinal Flap Tear
Once the missing section of muscle has been identified, a Stevens tenotomy hook is placed over the intact capsule of the attached portion of muscle and then passed over the avulsed section of muscle and drawn forward (Fig. 29‑1, Fig. 29‑8). This allows one to feel the pull from the point of scarring between the flap edge and the surrounding orbital tissues. The flap edge is dissected free, and a nonabsorbable suture is placed through the flap, with locking bites (Fig. 29‑8a, b). The flap is then reattached at its normal anatomical position, either to sclera or into the muscle itself, depending upon the nature of the tear. The capsule is repaired with a fine absorbable or nonabsorbable monofilament suture (Fig. 29‑8c). There is usually a rent in the posterior Tenon’s capsule, which is also repaired (Fig. 29‑9, Video 29.1, Video 29.2, Video 29.3, Video 29.4, Video 29.5, Video 29.6, Video 29.7). Sometimes the muscle belly is observed to be displaced at the outset, but it usually returns to its normal anatomical position once the layers are restored. If it is still out of position at the completion of flap tear repair, a myopexy suture 4 may be added.
29.1.2 Lamellar Flap Tear
When the entire width of the muscle is avulsed in lamellar fashion, the tenotomy hook is used to tease the flap layer from the orbital tissues (Fig. 29‑2). This type of tear is more difficult to see than a longitudinal flap and is more easily located by feel. (Longitudinal flaps have some remaining intact capsule visible on the muscle surface, and are easier to see than lamellar flaps, in which the muscle seems intact but is simply devoid of capsule.) There is no resistance to passing the hook between the flap and the orbital tissues, as the capsule prevents scarring. The only adhesions are at the distal edge of the flap. Once the flap has been freed, the repair is the same as outlined above (Fig. 29‑10, Video 20.3, Video 29.8, Video 29.9). Lamellar flaps are generally under less tension than longitudinal flaps, and repair with a finer suture is possible. Some may be due to a congenital malformation (Video 29.10). This author usually uses 7–0 polypropylene to suture lamellar flaps.
29.1.3 Beveled Flap Tear
Repair of a beveled tear is much the same as that of a longitudinal tear (Fig. 29.3). The repair should attempt to restore the natural anatomy as accurately as possible, angling the suture placement to match the defect (Video 29.3, Video 29.6, Video 29.11).
29.1.4 Retracted Flap Tear (Turtleneck)
To repair a retracted flap tear, a toothed forceps is placed within the capsule, and the retracted muscle tissue is pulled forward. This is done by feel. The repair then proceeds similarly to the longitudinal flap tear repair (Video 29.6). Retracted flaps usually originate from the insertion rather than the musculotendinous junction (Fig. 29‑4).