Insertion site dynamics and histology in a rabbit model after conventional or suspension rectus recession combined with ipsilateral antagonist resection

Securing extraocular muscles in strabismus surgery: biomechanical analysis of muscle imbrication and knot tying technique

An experimental study was performed to quantitatively evaluate the tensile strength implications of two important steps in extraocular muscle surgery: muscle imbrication and knot configuration. The study was conducted in a controlled fashion using fresh ex vivo pig eyes with extraocular muscles attached and a precision digital force gauge. The study provides clinically translatable data to inform optimal surgical technique. The results suggest that imbrication of the muscle edge is most secure when the suture is looped around itself in a manner that allows it to be tightly cinched and locked and that granny knots possess similar tensile strength to square knots.

Securing extraocular muscles in strabismus surgery: laboratory analysis of biomechanical parameters related to the suture

PURPOSE

To investigate the tensile properties of several components used to secure extraocular muscle to sclera in strabismus surgery to determine potential failure points.

METHODS

A digital force gauge measured the tensile strength of intact or damaged 6-0 Vicryl suture (Ethicon, Somerville, NJ), as well as threads tied in a 2-1-1 or 2-1-1-1 surgeon's knot configuration. Human sclera was used to test the resistance to drag of knotted and unknotted 6-0 Vicryl suture thread through partial thickness sclera. Mean values were compared using a t test.

RESULTS

The mean tensile strength of 6-0 Vicryl suture was 623.5 g, but it was markedly reduced by damage from the needle (P < 0.0001) or ophthalmic needle holder (P < 0.0001). The 2-1-1 knots broke at a mean force of 307.6 g, compared with 292.8 g for 2-1-1-1 knots (P = 0.84). Drag through a 2 mm scleral tunnel was 4.6 g, compared to 13.6 g for a 4 mm tunnel (P = 0.011). The force required to pull a knotted suture through a 4 mm scleral tunnel was 254 g for a 2-1-1 knot and 367 g for a 2-1-1-1 knot (P < 0.015).

CONCLUSIONS

Although 6-0 Vicryl possesses adequate tensile strength for muscle fixation, thread damage from a needle or needle holder may cause serious losses in tensile strength. Knot-breaking strength is not significantly increased by adding a fourth throw. Frictional forces of the scleral tunnel are not sufficient to provide muscle stabilization, but the presence of a knot can provide substantial resistance to suture slip into the scleral tunnel.

Securing extraocular muscles in strabismus surgery: biomechanical analysis of muscle imbrication

An experimental study was performed to quantitatively evaluate the tensile strength of extraocular muscle imbrication as it relates to the positioning of the imbricating suture. The study was conducted in a controlled fashion using fresh ex vivo pig eyes with extraocular muscles attached and a precision digital force gauge. The study provides clinically translatable data to inform surgical technique regarding secure muscle imbrication. Results suggest that imbrications performed 0.5 mm or less from the cut muscle edge or 0.5 mm or less from the lateral margin may be prone to tensile failure.

Securing extraocular muscles in strabismus surgery: biomechanical analysis of knot-tying technique

BACKGROUND

The safe and precise reattachment of extraocular muscles requires a technical approach that minimizes any opportunity for the muscle to slip intraoperatively or postoperatively while minimizing surgical risk. Biomechanical testing can provide important quantitative information about the tensile properties of different knot configurations that may inform surgical technique.

METHODS

A precision digital force gauge was used to assess the tensile strength created by different knot tying techniques and configurations in human sclera using 6-0 polyglactin 910 suture.

RESULTS

The mean tensile strengths of the first knot throw formed with either one, two, or three loops, with widely separated scleral tunnels, were 5 g, 10 g, or 27 g, respectively. When the scleral tunnels are closely spaced in a "cross-swords" fashion, the mean strength of a first throw made with two loops increased to 385 g. If a first throw with two conventional loops was cinched against one of the scleral tunnels or a reversed first loop is used, the mean tensile strength increased to 112 g or 381 g, respectively, even with widely spaced scleral tunnels.

CONCLUSIONS

Proper cinching or minor modification of the first knot throw provides excellent tensile strength, even with short, widely spaced scleral tunnels, comparable to that achieved with the technically more demanding crossed swords technique. Conventional, noncinched first throws are prone to slip at low force when scleral tunnels are widely separated, though the resistance increases as the number of loops increases.

Effects of solid hyaluronic acid film on postoperative fibrous scar formation after strabismus surgery in animals

PURPOSE

The purpose of this study was to investigate the inhibitory effect of solid hyaluronic acid-carboxymethylcellulose film on the formation of wound adhesion after strabismus surgery on rabbit eyes.

METHODS

The authors performed strabismus surgery on rabbit eyes with hyaluronic acid film applied under and above the muscles. Histological examination was performed 90 days postoperatively using Masson trichrome staining. The length of adhesion tissues in the operated area was quantitatively compared between film-treated and control eyes.

RESULTS

Hyaluronic acid film significantly prevented the formation of adhesions between muscle, conjunctiva, and sclera after strabismus surgery (t test, P < .05).

CONCLUSION

The current results indicate that hyaluronic acid film can inhibit the formation of postoperative adhesion around conjunctiva, muscle, and sclera to some extent. The authors conclude that this substance offers potential benefits for ophthalmic surgery, not only with strabismus surgery but also procedures such as scleral buckle.

Scar remodeling after strabismus surgery

PURPOSE

We sought to investigate abnormal scar lengthening after strabismus surgery.

METHODS

Patients with overcorrection after strabismus surgery or undercorrection after extraocular muscle resection underwent exploration of previously operated muscles. Abnormal findings were documented by inspection and photography, and repair was undertaken at first with absorbable sutures and later with nonabsorbable sutures.

RESULTS

Lengthened scars, consisting of amorphous connective tissue, were repaired on 198 muscles in 134 procedures by excision of the scar and reattachment of the muscle to sclera; absorbable sutures were used in 64 procedures, and nonabsorbable sutures were used in 70 procedures. Thirty-one procedures were followed by partial recurrence of the original overcorrection; 7 of these had documented restretching. The use of nonabsorbable sutures decreased the recurrence of strabismus from 42% to 6%. Factors that distinguished patients with stretched scars from patients with classic slipped muscles included minimal or no limitation of versions, less separation of the tendons from sclera, and thicker appearance of the scar segments.

CONCLUSIONS

A lengthened or stretched remodeled scar between an operated muscle tendon and sclera may contribute to variability of outcome after strabismus repair, even years later. Definitive repair requires firm reattachment of tendon to sclera with nonabsorbable suture support.

Evaluation of mitomycin to limit postoperative adhesions in strabismus surgery

BACKGROUND

Ocular motility dysfunction following strabismus surgery may be the result of postoperative scarring or the formation of adhesions. Mitomycin C (MMC) has been used with encouraging results as an adjunct to standard treatment of hypertrophic conjunctival scars after strabismus surgery. It has been demonstrated that MMC does not inhibit muscle reattachment and might inhibit adhesions and scar formation in the rabbit. We investigated in a rabbit model effectiveness of MMC in reducing the formation of postoperative adhesions following reoperations and the tensile strength of the new musculo-scleral junction.

METHODS

A prospective, masked-observer, controlled study was performed in rabbits. Symmetrical bilateral recessions of the superior and inferior rectus muscles were performed on each rabbit. A reoperation was performed 6 weeks later, in which the muscles were advanced back to their original insertion. During the reoperation, one eye served as the control while the other was treated with a 5-minute intraoperative exposure to topical mitomycin.

RESULTS

Mitomycin reduced the formation of adhesions and the amount of postoperative scarring. The tensile strength of the musculo-scleral junction was reduced in the mitomycin-treated eyes but exceeded the force generated during extraocular ductions.

CONCLUSION

MMC may be an effective adjunctive therapy in the treatment of strabismus associated with pre-existing adhesions or scarring.

Application of the potassium-titanyl-phosphate laser during extraocular muscle surgery: technique and histopathology

We determined laser parameters and delivery system requirements for successful use of the potassium-titanyl-phosphate (KTP) laser for strabismus surgery and its histopathologic effect on extraocular muscle, tendon, sclera, and cornea of human and rabbit eyes. Enucleated cadaver eyes and exenterated rabbit orbital contents were used. Using a 200-microns fiberoptic tip delivery system, varying laser energies were used to perform muscle insertion site and corneal damage, tenotomies, and myotomies. Pulse durations of 0.5 second and energies above 0.8 watt were needed for tenotomy or myotomy. No damage to the surrounding tissues or sclera was observed with laser tenotomy or myotomy performed 0.5 mm from the insertion site. Energy above 0.8 watt applied directly caused full thickness disruption. In comparison to scissor myotomy, the laser provided charring of the superficial tissues. This study shows that the KTP laser can be safely and accurately used for extraocular muscle tenotomy or myotomy.