BACKGROUND: The superior oblique frenulum is a fascial membrane that prevents substantial separation of the superior rectus muscle and SO tendon. METHODS: In three patients, the superior rectus muscle was disinserted and temporarily suspended 6, 8, 10, 12, and 14 mm in random order from its insertion. The change in position of the anterior edge of the superior oblique tendon from the superior rectus muscle insertion was measured before and after severing the frenulum structure. In four other patients undergoing superior oblique recession, the superior oblique tendon was disinserted at its insertion temporally. The amount of recession that spontaneously occurred was measured before and after severing the frenulum. RESULTS: In the first group, there was essentially a one-to-one correlation between the posterior movement of the superior oblique tendon and the amount of superior rectus recession for recessions up to 10 mm. After severing the frenulum, the anterior portion of the superior oblique tendon was positioned less posteriorly. It measured less than 1.2 mm for superior rectus recessions up to 14 mm. For the second group, the mean suspension distance of the cut end of the disinserted superior oblique tendon was 2.4 +/- 0.4 mm before stripping the frenulum as compared with 8.5 +/- 0.7 mm after stripping the frenulum (Student's t-test, p = 0.0011). CONCLUSIONS: The frenulum pulls the superior oblique tendon posteriorly as the superior rectus muscle is recessed and constrains the superior oblique tendon after disinsertion. How this connection is handled at the time of surgery may have implications for superior rectus recessions and superior oblique tendon surgery.
BACKGROUND: The superior oblique frenulum is a fascial membrane that prevents substantial separation of the superior rectus muscle and SO tendon. METHODS: In three patients, the superior rectus muscle was disinserted and temporarily suspended 6, 8, 10, 12, and 14 mm in random order from its insertion. The change in position of the anterior edge of the superior oblique tendon from the superior rectus muscle insertion was measured before and after severing the frenulum structure. In four other patients undergoing superior oblique recession, the superior oblique tendon was disinserted at its insertion temporally. The amount of recession that spontaneously occurred was measured before and after severing the frenulum. RESULTS: In the first group, there was essentially a one-to-one correlation between the posterior movement of the superior oblique tendon and the amount of superior rectus recession for recessions up to 10 mm. After severing the frenulum, the anterior portion of the superior oblique tendon was positioned less posteriorly. It measured less than 1.2 mm for superior rectus recessions up to 14 mm. For the second group, the mean suspension distance of the cut end of the disinserted superior oblique tendon was 2.4 +/- 0.4 mm before stripping the frenulum as compared with 8.5 +/- 0.7 mm after stripping the frenulum (Student's t-test, p = 0.0011). CONCLUSIONS: The frenulum pulls the superior oblique tendon posteriorly as the superior rectus muscle is recessed and constrains the superior oblique tendon after disinsertion. How this connection is handled at the time of surgery may have implications for superior rectus recessions and superior oblique tendon surgery.