Australian and New Zealand Journal of Ophthalmology 1985: 13: 67-69

DIAGNOSIS AND MANAGEMENT OF LOST MUSCLE FOLLOWING STRABISMUS SURGERY

F. BILLSON FRACO, FRACS professor of Ophthalmology, The University of Sydney

A. FlTZGERALD DipAppSci (Ortho), DOBA Department of Clinical Ophthalmology, Sydney €ye Hospital

Abstract Of all the complications of strabismus surgery, the lost muscle IS one of the most alarming, and yet with patience and careful management it may be one of the most amenable to treatment.

This paper reports seven cases of lost muscle following strabismus surgery. In six of the seven cases referred to the Department of Clinical Ophthalmology there had been delay in diagnosis tor periods varying from SIX weeks to 17 years. All the lost muscles were successfully retrieved.

With good illumination and magnification and a careful search of the sub-Tenon’s capsule space it is unusual to need to explore the orbital fat to retrieve the muscle.

Key words: Lost muscle, strabismus surgery, slipped muscle, oculo-cardiac reflex, medial rectus, lateral rectus, inferior rectus, overcorrection, undercorrection.

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Of all the complications of strabismus surgery, the lost muscle is one of the most alarming, and yet with patience and careful management, it may be one of the most amenable to treatment. Helvston et al.’ report successful recovery of 59 out of 60 cases of muscle lost at strabismus surgery. The lost muscle in strabismus surgery occurs in one of three situations. It may occur at the time of surgery if the muscle is lost before it is reattached to the globe. It may occur following surgery if the sutures loosen, allowing the muscle and its sheath to detach from the globe. Alternatively the sheath may remain attached to the globe and the muscle may slip within the sheath.

The purpose of this paper is to report seven cases of lost or slipped muscle. A higher index

of suspicion of this condition should result in earlier recognition and surgical intervention.

MATERIALS AND METHODS The surgical approach used (Billson) makes use of a fornix-based conjunctival and Tenon’s capsule flap. Tenon’s capsule and conjunctiva are held back with 6.0 catgut sutures. A fixation suture into the sclera is placed at the limbus along the line of the rectus muscle. Dissection is carried out in the sub-Tenon’s capsule space approach- ing the site of muscle with caution. If there is evidence of the sheath still present at the insertion it forms a guide along which exploration can take place to identify the slipped muscle within the sheath.

Reprint requests: Prof. F. Billson, The University of Sydney Department of Clinical Ophthalmology, Sydney Eye Hospital, Sir John Young Crescent, Woolloomooloo, New South Wales 201 1, Australia.

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TABLE 1 Seven Patients with Lost or Slipped Muscles After Surgery

Case No.

Age at surgery on lost muscle

(years: sex) Lost

muscle Slipped muscle

Time to secondary surgery

1 21/2:F - Medial rectus 2 years 2 3%:F Medial rectus - 2 years

6 months 3 6 :F Lateral rectus - 4 13 :F Medial rectus - 18 months 5 5 :M Medial rectus - 1 day 6 22 :F Medial rectus - 17 years (adj. suture) 7 11 :M Inferior rectus - 3 months

The dissection is carried out with good magnification and illumination and where necessary the operating microscope is introduced.

RESULTS Seven patients (Table 1) were referred to the University Department of Clinical Ophthalm- ology with disturbances of ocular rotation and a lost muscle was found to be the cause. In Case 1, the medial rectus was found to have slipped within the sheath. In Cases 2, 4, 5 , and 6 , the medial rectus was found to have slipped together with the sheath. In Case 3, the lateral rectus had slipped together with the sheath. In Case 7, the inferior rectus had been lost together with the sheath. In every case the lost muscle was identified and reattached to the globe.

All seven patients with lost muscles had limited ocular movement. In Cases 5 and 7, seen within six weeks of diagnosis, the forced duction test was negative, confirming the suspicion of a lost muscle as the cause. In Cases 1, 2, 3 , 4, and 6 , seen later than six months, a forced duction test showed a tight antagonist to the lost muscle. In each case the suspected lost muscle together with its antagonist was explored. Surgery in every case was tedious and took at least an hour of patient searching to locate the muscle. There was a need to explore extensively deep within Tenon’s capsule.

In two cases the attachment at surgery was found to be in juxtaposition to the optic nerve. In both these cases the slipped muscle was the medial rectus.

The oculo-cardiac reflex2 was helpful in locating the lost muscle. At surgery (in Case I), pulling on the muscle or tissues adjacent to the lost muscle caused slowing of the heart.

DISCUSSION The most important factor in the successful management of a lost muscle is having a high index of suspicion.

If muscle movements are checked after operation, inappropriate movement accomp- anied by unexpected over or undercorrection should alert the clinician to the possibility of a lost muscle. For example, in the case of detachment of the medial rectus, the globe may be voluntarily abducted beyond the midline and a mild exophthalmos accompanied by a marked limitation of ocular rotation seen in attempted gaze into the field of action of the disinserted muscle.

In addition to the clinical observation of limitation of movement, observation of the saccadic velocity of the eye in the direction of movement gives further information and may be confirmed using electro-oculography to monitor the saccadic v e l o ~ i t y . ~ . ~ Further information can be obtained by a forced duction test in the fully conscious patient, although not in small children.

In the case of the infant, a forced duction test under anaesthesia is warranted. In the early postoperative period, a forced duction test will distinguish between restrictions due to excessive resection and lost muscle where, in the latter, there will be no evidence of restriction when the

68 AUSTRALIAN AND NEW ZEALAND JOURNAL OF OPHTHALMOLOGY

eye is passively rotated in the direction of the limited muscle action.

When there is marked reduction of eye movement after operation, and a lost muscle is suspected, the patient should be taken to theatre without delay for exploration. The diagnosis of a lost muscle will become obvious at that time. If days or weeks have elapsed before the diagnosis is confirmed, the antagonist muscles become tight and contractured. This significantly limits forced duction in the field of action of the hisinserted muscle. This, in turn, significantly increases the chance of misdiagnosis and subsequent inappropriate secondary corrective surgery.

If the muscle is not found to be attached to the anticipated insertion and no sign of the sheath is present, the possibility that both the muscle and the sheath have slipped must be considered. A careful search in the sub-Tenon’s capsule space extending back even to near the optic nerve should be carried out. Failure to identify the muscle in the sub-Tenon’s capsule space should be followed by careful dissection with good illumination and magnification in an endeavour to find the muscle even into the orbital tissue. In some cases the operating micro- scope needs to be resorted to, to permit adequate illumination and magnification.

Breaching Tenon’s capsule and allowing orbital fat to get into the wound involves the serious risk of causing unsightly scarring and adhesion syndromes, which in themselves form a strong reason for not breaching Tenon’s capsules until a careful search of the sub-Tenon’s capsule aspace has been completed.

With careful dissection, the majority of muscles can be successfully recovered, as this report indicates. In the rare case, when the muscle cannot be recovered, it would be necessary to give thought to weakening procedures of the antagonist combined in some

cases with a Faden operation and transposition of muscles, taking care to avoid anterior segment ischaemia.

CONCLUSION Distinguishing a lost muscle as a cause of over- correction or undercorrection is less a problem if at the conclusion of every strabismus operation a forced duction test is performed. If the ductions are normal, and marked early post- operative limitation of eye rotations are noted, the possibility of a lost muscle exists. Surgery and recovery of the muscle is easier in the early postoperative period. Therefore, if there is any possibility that the muscle has slipped, reoperation should be performed immediately.

Clearly the muscle capsule must be distinguished from the muscle tendon, which is thicker and more vascular. Careful dissection and identification of the capsule is a useful guide to finding the muscle.

Even in cases where overcorrection is suspected, particularly if reoperation is resorted to, the muscle with limited action should be exposed to determine if it is appropriately inserted. Although the lost muscle can be relied upon to be retrieved in the majority of cases, the problem of the contracted antagonist must still be dealt with and may prove an important element in the final result achieved.

References 1 .

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Helvston EM, Jampolsky A, Knapp P, et al. Symposium on strabismus. Transactions of the New Orleans Academy of Ophthalmology. 1st ed. St Louis: CV Mosby, 1978:

Apt L, lsenberg SJ. The oculo-cardiac reflex as a surgical aid in identifying slipped or lost extra-ocular muscles. Br J Ophthalmol 1980; 64: 362-5. Rosenbaum AL, Mentz HS. Diagnosis of lost or slipped muscle by saccadic velocity measurements. Am J Ophthalmol 1974; 77: 215-222. Mentz HS. The role of slipped or lost muscle in overcor- rections in strabismus. Am Orthopt J 1976; 26: 20-4. Parkes MM. Ocular motility and strabismus. 1st ed. Maryland: Harper & Rowe, 1975: 175-176.

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