FEB 18, 2011
By Shimon Rumelt, MD
This randomized controlled study compared implant and prosthetic movement after myoconjunctival enucleation followed by polymethyl methacrylate (PMMA) implantation with two other techniques: traditional enucleation with muscle imbrication using a PMMA implant, and enucleation and porous polyethylene implantation. The results demonstrated statistically and clinically significantly better implant and prosthesis movement with the myoconjunctival PMMA technique than with traditional PMMA implantation and better prosthesis movement than with the more expensive porous polyethylene implant, with reduced risk of implant displacement and exposure.
The authors randomized 150 patients undergoing unilateral primary enucleation between July 2004 and June 2007 to one of the three treatments. In the traditional PMMA group, the implant was placed behind the posterior Tenon's capsule in the intraconal space. The posterior Tenon's capsule was sutured, as well as the lateral to the medial rectus and the superior to the inferior rectus. Then the anterior Tenon's capsule and the conjunctiva were sutured separately. In the myoconjunctival PMMA group, the procedure was identical except that the recti muscles were sutured to the anterior Tenon and conjunctiva near the fornices. In the porous polyethylene group, the implant was placed within the Tenon's capsule with a scleral cap over it, and the muscles were sutured to the cap.
Acrylic prostheses custom made by a trained ocularist were fitted six weeks after surgery in all patients. A masked observer measured implant and prosthesis movement six weeks after surgery using a slit-lamp device with real-time video and still photographic documentation.
The authors found that prosthesis movement was significantly better with the myoconjunctival PMMA implant than with either the traditional PMMA (P = 0.001) or porous polyethylene (P = 0.002) implants. Implant movement with the myoconjunctival PMMA implant was better than the traditional PMMA implant (P = 0.001) but similar to that of the porous polyethylene implant.
The authors suggest that the reason for the superior implant and prosthesis movement with the myoconjunctival PMMA is that the attachment of the muscles to the fornices allow better movement because of changes in fornice depth. However, another explanation might be a difference in the muscle lever, which is longer and in closer to optimal position with myoconjunctival PMMA implantation than when the muscles are sutured to a scleral cap or to each other. Thus an optimum position should be reached without compromising the location of the implant while achieving better prosthesis and implant motility.
The authors also note the higher cost of the porous polyethylene implant of around $300 compared with $2 for the PMMA implant. Given that the PMMA implant is relatively inexpensive and myoconjunctival enucleation easy to master and time efficient, the authors recommend myoconjunctival enucleation followed by PMMA implant insertion as the procedure of choice in primary enucleation when implant pegging is not a consideration.