Transposition Surgeries in Strabismus
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The history of transposition surgeries in squint dates back to 1908, when Hummelsheim first described the transposition procedure for the correction of esodeviation in sixth nerve palsy. A large number of modifications further took place with time resulting in a large number of variations in the procedure. These procedures however must be avoided in patients with vascular insufficiency, or when there is stiffness of the antagonist resulting into restriction.
Indications for transposition surgeries include Paralytic squint: The most common indication for transposition surgeries in squint is paralytic squint. Transposition surgeries must be planned only when the forced duction test is free and active force generation test reveals absence of any active force generation.(Figure1)
Duane’s Retraction Syndrome
Lost or slipped muscle
Mechanism of Action
The main aim of transposition surgeries is to realign the eyes in primary position,(1) although the results of transposition procedure are usually good but patients must understand that the ductions in the direction of action of paralyzed muscle might not improve much, further addition of posterior fixation sutures can improve the results. The mechanism of action of transposition procedure is still controversial, some authors believe that improvement in the primary position can be due to transfer of function of transposed muscle in the direction of action paralyzed muscle through the change in the direction in vector forces of the transposed muscle. Other hypothesis states it to be due to the passive restraint to hold the eye in primary position. In augmented procedures with posterior fixation sutures, it has been suggested that rectus muscle pulley are diverted posteriorly in the direction of transposition while translating the centre of the globe. Probably more than one mechanism act together to achieve alignment in the primary position.
Transposition procedures for Sixth nerve palsy
Full tendon transposition
Full tendon transposition involves full tendon transposition of vertical recti, after dis inserting them.(2) To prevent the risk of anterior segment ischemia the vertical recti must be carefully dissected to conserve the anterior ciliary artery branches. Extensive dissection should be avoided. (Figure2a)
The transposed vertical rectus muscles are passed beneath the lateral rectus muscle and attached at the respective opposite corners of the lateral rectus muscle insertion.also increases the transposed muscle path length while avoiding resection of the transposed muscles.In the original description for abducens nerve palsy, it reduced the need for simultaneous ipsilateral medial rectus weakening more than twofold.(3)(Figure2b)
After making a limbal based incision superiorly and inferiorly the temporal halves of superior and inferior rectus are secured, disinserted and further transposed towards the lateral rectus. The transposed halves of both the vertical recti are further inserted near the insertion of the lateral rectus. While splitting and disinserting the vertical recti, care must be taken to protect the anterior ciliary circulation.(4) (Figure3)
To increase the effectiveness of Hummelscheim procedure, resection of the transposed tendon can be added along with recession of medial rectus. (Figure4)
Effectiveness of Hummelsheim procedure Modified Hummelsheim procedure has been reported to correct a preoperative deviation of 43 Δ ± 5 Δ to postoperative 6 Δ ± 7 Δ .(5)
Jensen’s procedure is indicated in sixth nerve palsy, and was first described by Jensen et al in 1964.(6) In this procedure the muscle belly is not dis-inserted and therefore does not predispose to anterior segment ischemia, however anterior segment ischemia has been reported with the Jansen’s procedure.
When performing Jensen’s procedure for lateral rectus palsy, limbal base incision is made to expose the bellies of lateral, superior and inferior rectus, intermuscular septa of all the three muscles is dissected to expose 12-15 mm of the muscle belly behind its insertion. Muscle bellies of each of the exposed recti are split with the help of a muscle hook, utmost care must be taken to preserve at least one anterior ciliary artery undisturbed. A 5-0 ethibond suture is then used to form a loop around each of the muscle belly. The sutures are then tied to bring the muscle bellies close approximately 12 mm behind the insertion. (Figure 5) Effectiveness of Jensen Procedure Cline et al in their study on 26 patients who underwent Jansen’s procedure with medial rectus recession found that at 6 months follow up 18 eyes had less than 20% of normal abduction saccadic velocity; 9 eyes had 20% to 40%, and 2 patients could not be assessed with saccadic velocities.(7)
Modifications of Jensen's Procedure
Vessel sparing modification: In this modification instead of looping the suture around the entire rectus muscle segments, the suture can be passed beneath the anterior ciliary vessels present on the orbital surface of each muscle
Technique The technique was described by Nishida et al in 2003.(8) In this technique after making a limbal based conjunctival peritomy the vertical recti are hooked. Intermuscular septum and fascia along the lateral margin of each of the vertical recti are carefully dissected and the vertical muscle belly is then longitudinally split from the centre of the muscle insertion for about 15 mm with a short muscle hook. Following this 8 to 10mm posterior to the insertion of each of the vertical recti 6-0 nylon monofilament sutures are passed. These sutures are further passed through the sclera 8mm posterior to the insertion of lateral rectus beside the superior or inferior margin. One scleral suture can be added on the inside edge of each transposed muscle to the sclera.(Figure6)
Effectiveness of Nishida According to Nishida et al, the surgery resulted in an average correction of 42.4PD.
Modification Of Nishida's Procedure
Indications Besides abducens nerve palsy, modified Nishida’s technique has been used in patients of monocular elevation deficit(9) and in cases of transected and lost medial rectus(10,11) Nishida et al further modified the procedure and omitted the step of muscle splitting to prevent further damage during the surgical manipulation. (12) Technique A limbal based incision is made which helps in better exposure of the vertical recti. 6-0 polypropylene or ethibond sutures are passed through the temporal margins of the vertical recti at a distance of 8 to 10 mm behind the insertion points of the vertical recti. The sutures can be tied there to avoid muscle breakage due to tension during transposition. The same suture is then passed through each scleral wall at a distance of 10 to 12 mm behind the supero-temporal and infero-temporal limbus, following this temporal margin of each vertical rectus is transposed and anchored onto the sclera. (Figure7)
Superior Rectus transposition (SRT)
SRT was described by Jhonston et al.(13) The procedure involves transposing only the superior rectus muscle to the insertion of lateral rectus. This helps to preserve ciliary circulation and simpifies the procedure. The procedure has been found to improve the mean angle of esotropia, abduction limitation, and head turn, with recovery of stereopsis in 80% of patients with no clinically significant induced vertical or torsional diplopia.(14) Jhonston et al in their orignal description also had similar results. However, theoretical concerns with the procedure include vertical misalingnment and induced torsion. But in practice there are a very few cases dealing with these complications.(15)(Figure8)
Inferior Rectus Transposition (IRT)
IRT is a logical alternative to SRT. When combined with an augmentation suture, either with or without simultaneous adjustable medial rectus recession, IRT was shown to significantly improve the esotropia, abduction, and head turn in a small group of patients who were deemed at risk of hypothetical exacerbation by SRT due to preoperative hypertropia or intorsion of the operative eye. IRT can also achieve a small downward shift in the operative eye that can help correct a preexisting hypertropia.(16)
Transposition Procedures for Third Nerve Palsy
Superior oblique tendon transfer
Technique The procedure was initially described by Peter in 1934.(17) A limbal based peritomy is performed in the superonasal quadrant which is sufficient to provide exposure to both medial and superior recti. The superior oblique is isolated and dissected free of surrounding fascial attachments along the tendon, following underneath and along the nasal side of the superior rectus. The superior oblique tendon is engaged on a small muscle hook on the nasal side of the superior rectus muscle and is secured with a double-armed 6-0 absorbable suture The tendon is disinserted and brought down toward the superior edge of the medial rectus insertion. The tendon is then sutured to the sclera at the superior border of the medial rectus insertion at the point on the tendon thus bringing the eye to a centred position. (Figure9)
Lateral rectus to Medial Rectus transposition
Technique Limbal based peritomy is performed over the lateral, superior, and medial rectus muscles. The attachments and intermuscular septa of lateral rectus muscle is dissected, the muscle is secured with 6/0 vicryl suture and disinserted The lateral rectus muscle suture is then passed beneath the superior rectus muscle in the direction of the medial rectus muscle, thus pulling the lateral rectus muscle in that direction. Lateral rectus is then sutured neat the superior margin of the medial rectus insertion. (Figure10) Effectiveness The procedure was initially described by Taylor(18) and was found to be effective, later Morad et al described the procedure in a case of combined third and fourth nerve palsy.(19)
Full tendon medial transposition of lateral rectus with augmentation sutures
Saxena R et al introduced a modification of full tendon transposition, in cases with hypertropia along with exotropia, the disinserted lateral rectus was passed under the inferior oblique, inferior rectus muscle and was reattached just below the insertion of the medial rectus muscle. Augmentation sutures with 5–0 Ethibond were placed 8mm behind the new insertion of transposed lateral rectus muscle which included at least a third of the muscle fibres in each bite On the other hand in their series patients with hypotropia, lateral rectus muscle was passed under superior rectus, superior oblique after posterior tenectomy of the muscle and reattached at the upper border of the medial rectus along with augmentation sutures.(20)
Medial transposition with Y splitting of lateral rectus
Technique Limbal based peritomy is performed, lateral rectus is hooked and intermuscular septa is dissected 15mm posterior to the insertion. Muscle is then split 15mm posterior to the insertion, towards the posterior septum. The split portions of the lateral rectus are than secured with the help of 6-0 polyester suture, and disinserted. The upper half of the muscle is then passed beneath the superior oblique, and inferior half is moved beneath the inferior rectus and inferior oblique. The two halves of lateral rectus are then inserted near the insertion of medial rectus. (Figure11) Effectiveness of the procedure Gokyigit et al, inserted the lateral rectus 1mm posterior to medial rectus found a success rate of 90 per cent with the procedure with the mean pre-op deviation being 73.7Δ ± 8.9Δ and post-op deviation being 11.8Δ ± 1.0Δ.(21)
Augmentation of the split lateral rectus
Indications The procedure has been used in third nerve palsy and synergistic divergence in Duane’s retraction syndrome.(22) Technique The surgery is undertaken through four fornix conjunctival incisions in each quadrant after performing a forced duction test to confirm a free lateral rectus muscle. The lateral rectus is hooked, split in half up to at least 15 mm posteriorly after placing 6-0 Vicryl sutures. Superior oblique is hooked and posterior tenectomy is done as in conventional surgeries. Posterior tenectomy of superior oblique helps in free movements of the transposed muscle under it, reduces the abduction effect and hence brings out greater correction. The superior half of the split In this modification, in addition to the above surgical steps, equatorial fixation sutures are put 8 mm behind the new insertion of the split muscles with 5-0 Ethibond passing them through the transposed ends incorporating 25℅ of the muscle.(23)
Transposition Procedures for Duane's Retraction Syndrome
Indications of surgery for Duane's Retraction Syndrome
- Presence of a compensatory head posture towards the affected side causing neck discomfort,
- Cosmesis in primary gaze due to the horizontal deviation
- Severe co-contraction
Transposition procedures help in improving abduction in cases of Duane's retraction syndrome, although there has always been a concern about the increase in severity of co-contaction after transposition surgery.(24)
Various transposition procedures advocated for Duane's Retraction Syndrome include:(25)
- Full Vertical Rectus transposition
- Full Vertical Rectus transposition with cross suture approach
- Jensen's procedure
- Nishida's procedure
- Superior Rectus Transposition
- Inferior Rectus Transposition
Vertical Muscle Palsy
Knapp’s procedure is indicated in patients of monocular elevation deficit, the horizontal recti (both medial and lateral recti are disinserted and transposed superiorly.(26)(Figure12)
In modified Knapp’s procedure, both the horizontal recti are split into two halves. The lower half is used for correction of horizontal deviation and the superior half is transposed superiorly.(27)(Figure13)
Augmented Knapp’s procedure is similar to Knapp’s the addition involves a foster suture Transposition procedure for double depressor palsy.(28)
The procedure is relatively less commonly performed, the common indications include double depressor palsy and congenital absence of inferior rectus. In this procedure, the horizontal recti are transposed to the level of inferior rectus. (29) (Figure10) V.Maurino et al in their study found Inverse Knapp's to correct the vertical deviation in primary position and down gaze from 16.06 prism dioptres (PD) to 7.35 PD and 26.45 PD to 6.66 PD respectively.(30)
- Anterior segment ischemia: Circulation to the anterior segment is provided by seven anterior ciliary arteries and two posterior ciliary arteries. One anterior ciliary artery supplies the lateral rectus muscle and two supply each of the other extraocular muscles. The vertical rectus muscle in particular has a major impact on anterior segment circulation. Disinsertion of the recti leads to disruption of blood supply to the anterior segment increasing the risk for Anterior segment ischemia (ASI). Old age, atherosclerotic changes in the blood vessels, hyperviscosity, buckle surgery for retinal detachment and simultaneous disinsertion of two or more recti increase the risk for anterior segment ischemia. ASI is associated with lid edema, conjunctival congestion and chemosis, cataractous changes in the lens, corneal edema, anterior chamber cells and flare. Vertical transposition surgeries along with recession of a horizontal muscle carries the highest risk for ASI. Jensen's procedure although was reported to be relatively safe initially, but ASI has also been reported with the procedure. (31)The risk of ASI is maximum in the first six months, hence a repeat surgery should be planned after 6 months of the initial surgery, providing sufficient time for the development of collaterals.
- Undercorrection: Undercorrection in strabismus surgeries is far more common than overcorrection. The second surgery to be done depends upon the cause of residual deviation. If the forced duction test (FDT) is still tight then further recession of the antagonist can be planned, but if FDT is free then further addition of foster sutures can be helpful. In third nerve palsy medial periosteal fixation of globe can be planned.
- Induced Vertical deviation: Induced vertical deviations have been observed in 6-30% patients undergoing vertical rectus transposition for lateral rectus palsy.(32) Vertical deviations can be minimized by meticulous surgical dissection of the attachments between inferior rectus muscle, capsulopalpebral fascia, and Lockwood’s ligament. Induced vertical or cyclotropias from altered tension or direction of action of the superior oblique muscle can also occur; thus dissection of the attachments between the superior rectus muscle and the superior oblique tendon are also important. Intraoperative forced ductions can help identify patients at risk for a new-onset hypotropia
- Other complications of squint surgery include tenon's prolapse, conjunctival prolapse, conjunctival cyst, corneal dellen formation, surgery on wrong eye, wrong muscle, scleral perforation, slipped muscle, bradycardia and secondary infections may occurin any patient undergoing squint surgery.
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