Ординатура / Офтальмология / Английские материалы / Strabismus Surgery and Its Complications_Coats, Olitsky_2007

Slipped and Lost

Muscles

23

Other than an intraocular infection or a retinal detachment with loss of vision, a lost muscle is one of the most devastating complications that a strabismus surgeon can face in the intraoperative or postoperative period. This chapter will discuss the various causes of slipped and lost muscles along with the stretched scar syndrome.

It is useful to consider slipped muscles, lost muscles and muscle with stretched scars as occurring in three distinct categories (>Table 23.1). These categories are helpful for the purpose of the discussion of etiology, diagnosis, evaluation and treatment, as well as prevention. Differences in the approach to diagnosing and treating slipped muscle versus lost muscle will be reviewed. In addition, while a muscle that has developed a stretched scar at its new insertion is technically not a slipped or lost muscle, this condition is said to often be confused with a slipped muscle and its diagnosis and management will also be reviewed in this chapter.

A slipped muscle is a disinserted rectus muscle, which, after reattachment to the globe, retracts posteriorly within its muscle capsule, while the empty capsule remains attached to the sclera at the intended new insertion site. A slipped muscle should be differentiated from a lost muscle in which no portion of the muscle, including its capsule, remains attached to the sclera. There are four causes of lost muscles, three of which occur as a result of surgery, including inadvertent severing of a muscle from the globe, a surgically snapped or torn muscle, and late detachment of the muscle from the globe. The fourth type is a nonsurgical traumatic muscle detachment from the globe.

I.Slipped muscle

II.Lost muscle

A.Intraoperative loss

i.Inadvertent disinsertion

ii.Snapped or torn

B.Late loss

C.Loss secondary to trauma

III.Stretched scar syndrome

Chapter

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23.1 The Slipped Muscle

The term slipped muscle generally refers to a disinserted rectus muscle, which, after reattachment to the globe, retracts posteriorly within its muscle capsule, while the empty muscle capsule remains attached to the sclera [1–3]. A slipped muscle should be differentiated from a lost muscle in which no portion of the muscle remains attached to the sclera (>Fig. 23.1).

The incidence of slipped muscles is unknown. Several series in the literature discuss both slipped and lost muscles as a single entity. It is beneficial, however, to consider these conditions as two separate entities because their cause, treatment and prevention may vary significantly. Plager and Parks [3] reported 52 patients with 62 slipped rectus muscles. Murray [4] reported 16 cases of slipped muscles and Knapp [5] described more than 60 cases of slipped and/or lost muscles.

23.1.1 Presentation and Diagnosis

A common theme is present in most reports on slipped muscles. Typically, the patient presents shortly after strabismus surgery with a moderate to large consecutive deviation and

Fig. 23.1. Slipped muscle. Note thin pseudotendon (muscle capsule) on hook

a small to medium duction deficit (>Fig. 23.2). The duction deficit is often subtle. In most series, the medial rectus muscle was the most commonly involved muscle and in some series it represented the only muscle involved [4, 6]. It is unclear if this is because the problem is more prone to occur with a medial rectus muscle, or if the medial rectus muscle is operated on more frequently than other extraocular muscles, and thus may be over represented. Often, the initial diagnosis of a slipped muscle is not made by the referring ophthalmologist. Instead, the patient is referred after a second strabismus surgery has been performed to correct the consecutive deviation and fails to achieve satisfactory alignment.

Usually, the distinction between a slipped versus a lost muscle can be made during standard clinical examination. Although the patient may have a large consecutive deviation, the duction deficit is usually less than would be expected if the muscle was completely detached from the globe. A neuroimaging study, such as computed tomography (CT) scanning or magnetic resonance imaging (MRI), can be helpful in

confirming the diagnosis of a slipped muscle (or ruling out a lost muscle) by demonstrating that the muscle tendon itself is not attached to the globe but rather is in near proximity to the globe [6, 7] (>Fig. 23.3). At the time of surgical exploration, the surgeon should anticipate finding the muscle capsule at­ tached to the globe at or near the intended location for muscle placement during the previous surgery. Once the muscle capsule is identified, it is carefully followed posteriorly where the muscle/tendon itself will be found attached to muscle capsule (>Fig. 23.4). The entire muscle insertion may slip in the cap­ sule evenly, or one pole of the insertion may slip asymmetrically compared to the other.

A slipped rectus muscle is often suspected because of the presence of a consecutive deviation, a duction limitation, and a negative spring-back test (>Table 23.2). A spring-back test is performed intraoperatively prior to making a conjunctival incision. The test depends on intact elastic forces of the rectus muscles to briskly restore the eye near to the primary position following a large passive duction in the direction opposite the

Fig. 23.3. CT scan with bottom arrow showing slipped left medial rectus. The top arrow shows the muscle capsule still attached to the sclera. {Reprinted from Murray AD (1998) Slipped and lost muscles and other tales of the unexpected. Philip Knapp Lecture. J AAPOS 2:133–143, with permission from American Association for Pediatric Ophthalmology and Strabismus [4]}

Fig. 23.4. Slipped muscle after detachment of the pseudotendon from the globe. Note pseudotendon held in forceps with attachment of muscle to the capsule posteriorly

suspected slipped muscle (>Fig. 23.5). A muscle that has significantly slipped will often, but not always, fail to briskly return toward the primary position, and instead will remain near the position of maximum passive duction (>Fig. 23.6).

In addition to simple visual inspection of the muscle, two simple tests, the see-through test (as taught by Jampolsky) and the step test [8], can help to confirm the diagnosis of a slipped muscle (>Table 23.2). Both tests are performed after surgical exposure and isolation of the muscle on a muscle hook. The see-through test is generally performed first. A muscle hook is generally not readily visible behind an intact rectus muscle or tendon (>Fig. 23.7). A muscle hook is generally readily visible behind the pseudotendon (muscle capsule) of a slipped muscle (>Fig. 23.1). The step test is performed by placing mild traction with a muscle hook on the global surface of the muscle and then sliding the muscle hook posteriorly. A step can usu-

ally be palpated during this maneuver at the junction between the pseudotendon and the rectus muscle or tendon if the muscle has slipped (>Fig. 23.8). This is in contrast to the smooth transition that occurs between the junction of a normal rectus muscle and its tendon.

Table 23.2. Signs of a slipped rectus muscle

Consecutive deviation

Duction limitation

Positive spring-back test

Positive see through test

Positive step test

Fig. 23.6. Abnormal spring-back test. With a lost or severely slipped muscle the eye fails to recoil back to the primary position after being displaced. In this case, the medial rectus muscle has been surgically detached from the globe

Fig. 23.7. The see-through test for a slipped muscle. A muscle hook is generally not readily visible behind a rectus muscle tendon, compared with visibility behind the pseudotendon of a slipped muscle as in Fig. 23.1

Fig. 23.8a,b. The step test for a slipped muscle. Mild traction is placed on the global surface of the muscle as the hook is moved posteriorly. a A step can usually be palpated at the junction between the pseu-

dotendon and the rectus muscle/tendon if the muscle has slipped, b compared to the smooth transition at the junction between a normal rectus muscle and its tendon

23.1.2 Treatment

Once the muscle/tendon has clearly been identified as attached to the muscle capsule, it should be isolated, secured with sutures (>Fig. 23.9a), and brought back in contact with the globe (>Fig. 23.9b). If a significant amount of time has elapsed since the original surgery, the muscle will generally be very contracted. Advancing a significantly contracted muscle to its previously intended new insertion on the sclera may lead to a significant overcorrection, necessitating modification of the original surgical plan.

In general, during the repair of a long-standing slipped muscle, we place mild anterior traction on the muscle while holding the eye in the primary position (>Fig. 23.10a). The muscle is reattached to the globe with temporary sutures at the position where it makes contact with the globe in the primary position (>Fig. 23.10b). Forced traction testing is then done. We prefer to find the point at which we begin to note resistance to forced traction testing at approximately three-quarters full duction in the direction of the slipped muscle’s antagonist. The muscle position is adjusted and the sutures finally converted to a permanent knot once this is achieved (>Fig. 23.10c). We do not usually place slipped muscles on adjustable sutures, but rather place the antagonist on an adjustable suture if this is

deemed necessary. The vast majority of the time we do not use adjustable sutures in the repair of a slipped muscle.

Because accurate alignment may be impossible in this setting due to difficulties in deciding where to attach the muscle, patients and parents should be advised that further surgery may be needed after the muscle has been reattached and ocular rotations improved. Once recognized, abnormal ocular alignment due to a slipped muscle can virtually always be corrected with surgery. The success rate is high in most series.

23.1.3 Prevention

In theory, a slipped muscle should be a preventable event. Full thickness locking bites which incorporate the muscle, and not just the muscle capsule, should prevent the muscle from slipping within its muscle capsule (>Fig. 23.11). If the muscle capsule is thick, making clear identification of the muscle difficult, the anterior portion of the muscle tendon should be cleaned of fascial attachments to allow more precise placement of sutures in the muscle tendon. Surgeons who do not regularly perform strabismus surgery are typically most concerned about making the scleral needle passes deep enough to prevent complete detachment of the muscle. While this is obviously also critical to

Fig. 23.12. Producing a true locking bite on the muscle border

the success of the surgery, the importance of the full thickness locking bites to secure both the muscle and the muscle capsule to the sclera at the time of muscle reattachment should not be overlooked. Mims [9] has described a technique to ensure that a true locking bite is achieved (>Fig. 23.12). Some surgeons make use of a double locking bite to provide additional security. We do not generally find it necessary to place a second locking bite if the first is made correctly, except when operating on severely restricted muscles, such as those commonly seen in patients with thyroid-related ophthalmopathy.

23.2 The Lost Rectus Muscle

A lost extraocular muscle can occur following any ophthalmic surgical procedure. The complication most commonly occurs following strabismus surgery or retina surgery and generally involves rectus muscles. It can also occur as a result of trauma

or surgery on adjacent structures, such as endoscopic sinus surgery [10] (>Fig. 23.13). Unlike a slipped muscle, when an extraocular muscle is lost, no direct attachment remains between the muscle tendon and the globe. The muscle and its capsule both retract posteriorly into the orbit. The term “lost” muscle is technically incorrect since the location of the muscle is known to be in the posterior orbit. The term “detached” muscle is probably superior, but the term lost muscle is so widely used in the ophthalmologic literature that the term will be used in this discussion.

A patient with a lost rectus muscle almost always presents within hours or days after surgery. At the time of presentation, a large consecutive strabismus is seen, typically with an associated large duction deficit. Though most patients present for evaluation within hours or days after surgery, late loss of a muscle has been reported up to 5 weeks after the surgery [5]. This scenario may be particularly likely following retinal surgery where an encircling element such as a silicone buckle gradually erodes through the rectus muscle insertion (>Fig. 23.14).

23.2.1 Clinical Presentation and Diagnosis

The clinical presentation is usually helpful in differentiating between a slipped and a lost muscle. A patient with a slipped muscle may have straight appearing eyes in the immediate postoperative period until full muscle function returns and gradually pulls the muscle posteriorly into the muscle capsule. A patient with a lost muscle will generally, though not always, present with a large consecutive deviation in the immediate postoperative period. In addition, the duction deficit seen in a patient with a lost muscle is almost always very large, in contrast to the smaller duction deficit usually seen with a slipped muscle. As with a slipped muscle, the medical rectus muscle is the most commonly involved muscle to experience this complication. Plager and Parks [11] reported 25 cases of lost extraocular muscles: 21 occurred during strabismus surgery; of

Fig. 23.13a,b. Lost medial rectus muscle following endoscopic sinus surgery. a The patient developed an acute exotropia with inability to adduct the involved eye past midline. b CT scan of a second patient demonstrating disruption of the medial orbital wall and medial rectus muscle

those, 6 muscles were lost due to unintentional transection of an adjacent muscle at the time of surgery. Murray [4] reported 37 cases of lost extraocular muscles. In his series, 32 occurred as a result of trauma and only 2 occurred during strabismus surgery. The management of a lost extraocular muscle depends largely on the mechanism by which the muscle has been lost and the timing of recognition and intervention.

Fig. 23.14. Lost (detached) right inferior rectus muscle due to erosion by a scleral buckle that occurred several weeks after surgery. See Fig. 27.14 for slitlamp photo of the involved eye

23.2.1.1 Intraoperative Muscle Loss

Inadvertent detachment of an extraocular muscle can occur with almost any ophthalmologic surgical procedure, including pterygium surgery (>Fig. 23.15). If an extraocular muscle is lost during an ophthalmic surgical procedure, it should be retrieved immediately, if possible. Generally, exposure of the surgical site is better at the time of the initial surgery and the newly exposed tissue planes may make identification and retrieval of a lost muscle easier than if surgical repair is attempted hours or days later. The surgeon should avoid purposeless exploration in search of a lost muscle, a practice that can significantly worsen the situation, resulting in hemorrhage, fat intrusion into the surgical site, and other complications. If the operating surgeon is not familiar with the techniques of exploration to locate a lost extraocular muscle, it is best to terminate the intended surgical procedure and refer the patient to a skilled strabismus surgeon as soon as possible. Though optimal to make the repair during the initial operation, later repair is far superior to the damage that may occur during aimless exploration. If the muscle is lost during a nonstrabismus procedure, the surgeon

Fig. 23.15. Lost medial rectus muscle following pterygium surgery

should consider consulting a strabismus surgeon to assist with retrieval and repair while the patient is in the operating room, if the lost muscle is not identified with minimal, careful exploration. While this represents the optimal scenario, it is rarely practical and the repair is often done later when the strabismus surgeon is available. The technique of retrieval and repair of a lost muscle is reviewed below.

In most cases, intraoperative loss of an extraocular muscle can be avoided with proper surgical technique. Careful identification and isolation of rectus muscle in the vicinity of the surgical field during strabismus and nonstrabismus procedures is an important step in the prevention of accidental detachment or transaction of a muscle. An important preventive measure in reducing the risk of a lost muscle during rectus muscle recession surgery is to limit dissection of the posterior intermuscular septum, muscle capsule, and muscle pulley. Excessive dissection of these structures does not enhance the effect of recession surgery [12] but increases the chance that the muscle

Chapter 23

will retract into the posterior orbit if control of the distal aspect of the muscle is lost. Sutures used during strabismus surgery should be handled carefully, preferably with smooth instruments, as instruments with teeth and rough edges can result in damage to the suture material, causing weakness of the suture, reducing its tensile strength with resulting reduction in the strength of the new muscle attachment to the sclera.

23.3 The Snapped or Torn Extraocular Muscle

Snapping or tearing an extraocular muscle apart can occur during strabismus and during other ophthalmologic surgical procedures and can involve any of the extraocular muscles. The muscle will usually rupture at the muscle–tendon junction during manipulation that exceeds the breaking point of the muscle [13–15] (>Fig. 23.16). Most cases of intraoperative

Fig. 23.17a,b. Repair of a ruptured muscle. a, b End-to-end anastomosis if the distal aspect of the muscle is intact, or c suturing the proximal aspect of the muscle directly to the sclera and performing a double

muscle rupture reported in the literature have occurred in adult patients, many with serious underlying systemic illnesses. The muscle is often reported to pull apart with mild traction and has been referred to as the pulled in two syndrome (PITS) [13, 15]. This condition most commonly involves the medial and inferior rectus muscles. Because the muscle rupture typically occurs well posterior to the muscle insertion into the sclera, retrieval of the proximal, lost aspect of the muscle is rendered more difficult, and is often impractical.

Exploration in an attempt to locate the proximal end of the muscle should be carried out in a manner similar to that described for retrieval of a muscle which has been lost intraoperatively, as described below. If the proximal end of the muscle can be retrieved, it may be possible to perform an end- to-end anastomosis of the proximal and distal segments of the muscle, assuming that the distal muscle segment is still intact and attached to the globe (>Fig. 23.17). In most cases, this will provide acceptable alignment in primary position though the action of the damaged muscle will usually be significantly reduced [4]. If the distal aspect of the muscle is inadequate for an end-to-end anastomosis, the proximal muscle segment can usually be sutured directly to the sclera. A double marginal myotomy (Chap. 15) may be required to allow the muscle to be sutured anterior to the equator of the globe, a position usually required to minimize the risk of a primary position deviation and a severe duction limitation (>Fig. 23.17). Temporary mechanical fixation of the globe to reduce tension on this tenuous union may be helpful in some cases (Chap. 15)

In some cases, it may be possible to retrieve the muscle from within the orbit through an orbitotomy at a late date. In most cases, the outcome is likely to be alignment in the primary position and limited function of the involved muscle. If the muscle cannot be retrieved, a transposition procedure is required [15] (Chap. 11).

marginal myotomy, if needed to allow the muscle to be placed anterior to the equator

23.4 Delayed Loss of an Extraocular Muscle

For purposes of this discussion, delayed loss of an extraocular muscle is considered to be one in which loss of the muscle is recognized at some point following the completion of a surgical procedure. This definition includes cases in which the muscle truly does lose its attachment to the globe after surgery and cases where the loss occurs at the time of surgery, but is not recognized until a later date. Affected patients generally present with a large consecutive strabismus and a pronounced duction deficit. The diagnosis is usually readily apparent.

Imaging studies may be helpful in selected cases to confirm the diagnosis, but is not always required if the clinical diagnosis is clear. Magnetic resonance imaging is considered to be superior in most cases as it allows better visualization of the muscle [7] (>Fig. 23.18). In addition, dynamic magnetic resonance imaging allows visualization of the globe in different gaze positions in cooperative patients [16] which can be

helpful in diagnosis and surgical planning. Magnetic resonance imaging may also help in the differentiation between a muscle which has been lost due to detachment from the globe versus a muscle that has been lacerated or ruptured. In the latter case, the proximal portion of the muscle may be visualized within the orbit while the distal portion of the muscle may be seen still attached to the sclera. Magnetic resonance imaging can help to rule out a muscle paralysis, a condition that can rarely be confused with a lost or lacerated muscle if it occurs shortly after an ophthalmologic surgical procedure. Generally, this is not a source of confusion but in cases where the preoperative history is questionable or unknown, it may be helpful.

Exploration with definitive surgical repair should be undertaken as soon as practical. Earlier surgical exploration may allow identification of suture material that is still partially attached to the lost extraocular muscle, greatly simplifying repair. Timely repair also minimizes contracture of both the antagonist and the lost muscle, which, when present, increases the complexity of treatment. Treatment options are discussed in Sect. 23.6.

23.5Traumatic Disinsertion of an Extraocular Muscle

Both blunt and penetrating trauma can result in extraocular muscle detachment from the globe (>Fig. 23.19). In some reported series, trauma represents the overwhelming majority of cases of lost muscles. The patient generally presents with an acute onset, large angle strabismus and a large duction deficit. The differential diagnosis includes muscle paralysis and restrictive strabismus due to muscle entrapment in an orbital fracture. Initial evaluation should include careful assessment to rule out serious associated systemic and/or ocular injuries. Treatment of visionand/or life-threatening injuries obviously takes precedence over repair of a traumatically detached

Fig. 23.19. Computed tomography scan demonstrating a traumatic rupture of the right medial rectus muscle

Chapter 23

extraocular muscle. Once these more serious problems have been managed and the patient is considered medically stable, detailed evaluation of the cause of the patient’s ocular motility disturbance is appropriate and may include forced duction testing, forced generation testing, and neuroimaging studies of the orbit.

The timing of surgical exploration and repair depends on several variables. Early exploration and treatment should be considered to prevent contracture of both the detached muscle and the antagonist muscle. If there is significant concurrent hemorrhage and/or edema, a delay in surgical exploration may allow for better assessment of the motility disturbance, altering surgical planning. Furthermore, resolution of hemorrhage and/or edema usually makes surgical repair less complex because it allows better visualization of the affected muscle.

23.6Surgical Treatment

of the Lost Extraocular Muscle

23.6.1 Retrieval and Reattachment

If the muscle capsule and intermuscular septum have undergone extensive dissection prior to the muscle being lost, the muscle will commonly retract through Tenon’s capsule to enter the posterior orbit. The surgeon should identify the potential space within Tenon’s capsule through which the muscle has retracted. Repair is optimally carried out through a large limbal incision, and the surgeon may wish to convert to a limbal incision if surgery was initiated through a fornix incision (Chap. 8). The basic steps required to locate a lost muscle in this situation involve retraction of the conjunctival flap and Tenon’s capsule anteriorly to expose the global surface of Tenon’s capsule. The global surface of Tenon’s capsule is visually inspected and delicately manipulated with fine toothed forceps in an attempt to locate the potential space representing the ruminants of the muscle capsule passing through Tenon’s capsule.

A common mistake is to attempt to locate the lost muscle along the surface of the globe posteriorly. Rather, the surgeon should recognize that the paths of the extraocular muscles are guided and restrained by the rectus muscle pulley system and, instead of coursing along the globe, the rectus muscles course posteriorly and toward the adjacent orbital wall to enter the pulley mechanism. Exploration should proceed along the adjacent orbital wall, rather than adjacent to the globe (>Fig. 23.20). If the surgeon is unable to locate the lost muscle during the course of the exploration, a decision must be made whether to proceed with alternative treatment, such as a muscle­ transposition procedure, or to defer surgery to another day when further evaluation and other treatment modalities may be available to assist in the repair.

Deferring definitive repair, such as a transposition procedure, when the muscle cannot be located may offer some significant benefits in many situations, and the surgeon must make this determination on a case-by-case basis. There are no rules on when to proceed with a transposition and when other