Akdeniz University Medical School Department of Ophthalmology SLIPPED or LOST MUSCLE DURANOGLU Yasar; MD Akdeniz University Medical School Department of Ophthalmology Antalya/TURKEY 2012

One of most catastrophic events in performing extraocular muscle surgery is to lose a muscle. *Philip KNAPP, Transactions of the New Orleans Academy of Ophthalmology,1978

Slipped muscle is one of most serious potential complication of strabismus surgery. Parks, Bloom and Plager defined the entity of a ‘slipped’ muscle as a disinserted rectus muscle that, after reattachment to the globe, retracts posteriorly within its capsule while the empty capsule remains attached to the sclera. *Parks MM, Bloom JN, The ‘slipped muscle’, Ophthalmology 1979; 86:1389-96 *Bloom JN, Parks MM, The aetiology, treatment and prevention of the’ slipped muscle’, J Pediatr Ophthalmology Strabismus 1981; 18:6-11. *Plager DA, Parks MM, Recognition and repair of the slipped rectus muscle. J Pediatr Ophthalmology Strabismus 1988; 25:270-4.

A slipped muscle should be considered in the differential diagnosis of a patient presenting with a marked limitation of duction and suspected when there is an early or late unexpected postoperative overcorrection with a large angle of deviation.

As expected, the medial rectus muscle had the greatest incidence of slippage. Because the medial rectus muscle does not have fascial attachments to the oblique muscles.

Murray, Mac Ewan et al. reported their patients all with slipped medial rectus muscle and each was successfully relocated with one procedure. Murray ADN, Slipped and lost muscles and other tales of the unexpected AAPOS 1998; 2:133-43. Mac EwanCJ,Lee JP,Fells P. Aetiology and management of the ‘detached’ rectus muscle.Br J Ophthalmol 1992;76:131-6.

Reduced saccadic velocity measurements, The widening of the palpebral fissure (grater than 1 mm) on attempted eye movement to the side of action of the slipped muscle. Reduced saccadic velocity measurements, The active forced generation test, Dynamic Orbital Imaging studies, Oculo-cardiac reflex during surgery, Ultrasonic biomicroscopy, The different intraocular pressure measurements; support the diagnosis but are conclusive. Mac EwanCJ,Lee JP,Fells P. Aetiology and management of the ‘detached’ rectus muscle.Br J Ophthalmol 1992;76:131-6.

A definitive diagnosis is made intraoperatively; The hallmark of the diagnosis of a slipped muscle is the empty muscle capsule attached to the sclera. The thin and less vascular capsule must be distinguished from the bulkier, more solid tendon and its highly vascular capsule.

Excessive muscle recession, Hemorrhage and edema around the muscle, The differential diagnosis for slipped muscle includes; Excessive muscle recession, Hemorrhage and edema around the muscle, A severed nerve to the extraocular muscle, A- crushed or entrapped muscle, Muscle fibrosis or contracture. Inferior oblique muscle inclusion syndrome can mimic a slipped muscle Lenart TD, Lambert SR, Slipped and lost extraocular muscles. Ophthalmol Clin North Am 2001:14:433–42.

ETIOLOGY

If the suture is passed only through the thin capsule before disinsertion, it retracts itself posteriorly within the capsule after reattachment to sclera, leaving the empty sheath attached to the recession site on the sclera. If the whole width of the muscle tendon is not included in the sutures before disinsertion, it could result in partial recession of the muscle tendon. *Lenart TD, Lambert SR, Slipped and lost extraocular muscles. Ophthalmol Clin North Am 2001:14:433–42.

PREVENTION

Proper surgical techniques that can help minimize the incidence of slipped muscle include obtaining a full thickness locking bite at the edge of the muscle as well as a full-thickness suture loop placed through the central third of the muscle or tendon secured with a surgeons knot.

Anterior tenon’s capsule overlying the muscle tendon should be carefully removed so that the surgeon can clearly visualize the full-thickness tendon, thus ensuring that the tendon secured and not just the overlying tenon’s capsule. The majority of the posterior intermuscular septum and check ligaments should be left intact.

Visualization through the operation microscope offers enhanced control, particularly during the placement of the sutures and routine microscopic control of strabismus surgery has been suggested by several authors.

The suture in a recession should be placed at least 1mm from the insertion. This can be accomplished if the suture is placed just behind a thin 8mm-10mm or 12mm muscle hook.

The scleral bite should be at least 1. 5mm long and at least 0 The scleral bite should be at least 1.5mm long and at least 0.2mm deep using 6/0-vicryl suture or equivalent*. * The numbers were established in invitro studies by Coats and Paysse.

Because of unpredictable outcome of slipped muscle surgery, Murray and Sebastian advise surgeons to perform adjustable suture surgery in cooperative patients. Sebastian RT, Marsh IB, Adjustment of the surgical nomogram for surgery on slipped extraocular muscle.J AAPOS 2006; 10:573-6.

Murray pointed that the management of the slipped muscle is early and carefully exploration. Contracture of the ipsilateral antagonist can occur as early as 2 weeks after initial surgery. If explored early, the muscle should be found 5 to 6 mm from the intended insertion, but with time it will have retracted even further.

SURGICAL TECHNIQUE

Slipped muscle has been found using traditional conjonctival approach.

The diagnostic translucent empty capsule is usually identified with following careful dissection of the fibrous tissue surrounding the capsule.

After measured the length empty muscle sheath, the muscle should be imbricated with a nonabsorbable synthetic suture.

Securely reattached to the original site of insertion.

Resection of empty capsule

Loss of a rectus muscle may occur as a rare complication of strabismus surgery. In addition,extraocular muscle may become traumatically detached from the globe when they rupture or are transected as the result of an injury or during the course of retinal detachment or paranasal sinus or orbital surgery.

In differentiating between a lost and slipped muscle, Parks and Plager characterized a lost muscle by the absence of any attachment of the muscle or its capsula to the sclera, adding that the muscle became detached either during surgery or shortly thereafter.

Although slipped and lost muscles are different with their respect to their etiology, prevention and surgical repair, their clinical presentation may be similar. Nevertheless, a loss muscle is usually associated with a large angle of strabismus and marked limitation of excurtion in its field of action.

High resolution dynamic MRI has been regarded as the investigation of choice for determining the exact position of a lost muscle and the presence or absence of its attachment to the eye.

Any muscle lost during the course of a strabismus operation should be retrived during that operation. This applies both to cut and snapped muscles.

Adequate illumination, good exposure and appopriate magnification are essential. Ideally, a zoom operating microscope should be used and two experienced assistants should be present to assist with the exploration.

The microscope should be fitted with an attachment for each assistant, who is then able to view the same operation field as the surgeon, thereby ensuring good exposure throughout the procedure.

MUSCLE AFTER HANG BACK RECESSION SURGERY THE SURGICAL RESULTS OF THE SLIPPED MEDIAL RECTUS MUSCLE AFTER HANG BACK RECESSION SURGERY DURANOGLU Yasar; MD Akdeniz University Medical School Department of Ophthalmology Antalya/TURKEY 2012 This study was presented in 32nd European Strabismological Association Meeting, 7-10th September 2008, Munich, Germany

This study introduced the results of the surgical therapy to correct the slippage of medial rectus muscle after hang back recession surgery for esotropia. The records of 15 patients who underwent re- exploration for slipped muscle by a single consultant (D.Y.) were included in this study.

Before corrective surgery Forced ductions, Active force generation, Gaze-dependent clinical tests; Squint magnitude, Eye movement range, Palpebral fissure widening, Proptozis, Intraocular pressure change were recorded.

Dynamic Orbital Imaging studies was performed to identify slipped medial rectus muscle.

RESULTS The antagonist muscle was recessed only in one patient who had a tight (positive) forced duction test. The resected part of the slipped muscle was examined. Fibrovascular connective tissue was found in all specimen with no muscle fibers in it.

Table I. Descriptive clinical data for the patients The Mean Age 5-50 (17.4) years Average score of preoperative medial rectus muscle underaction -1 - -4 (-2.26) Average length of empty muscle sheath (mm) (5-9) 6.3 Average duration between the time of first operation and that lead to the slipped muscle 1-3 (2.1) years Average Follow up Time 2.3 years Preoperative horizontal deviation degree (Prism Dioptres) 15-50(Average 30.8) Postoperative horizontal deviation degree   Orthophoria-10 (Average 4)

After this second procedure large widening the lid fissure and mild exophthalmos resolved.

Although more experience would be needed to evaluate long term results, we concluded that an approximate 3.20 PD change in angle of deviation was observed for every mm of muscle of advancement. For very large and very small deviations, surgeons should modify their experience.

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