FUNCTIONAL-ANATOMY OF THE LEVATOR PALPEBRAE SUPERIORIS MUSCLE AND ITSCONNECTIVE-TISSUE SYSTEM

Aims/background - The connective tissue system of the levator palpebra e superioris muscle (LPS) consists of the septa surrounding its muscle sheath, the superior transverse ligament (STL) commonly referred to a s 'Whitnall's ligament' and the common sheath which is the fascia betw een the LPS and the superior rectus muscle (SRM), The anterior band-li ke component of the common sheath is called transverse superior fascia l expansion (TSFE) of the SRM and LPS. It mainly extends from the conn ective tissue of the trochlea to the fascia of the lacrimal gland. A d etailed description of the relation between the LPS and its connective tissue is presented. Furthermore, the course of the LPS in the orbit is described. The study was conducted to provide a morphological basis for biomechanical and clinical considerations regarding ptosis surger y Methods - Postmortem dissections were performed in 16 orbits from ei ght cadavers. The microscopical anatomy was demonstrated in six formal in preserved orbits fi om six cadavers which had been sectioned in the frontal and sagittal plane and stained with haematoxylin and azophlox in. Surface coil magnetic resonance imaging in the sagittal and corona l plane was pet-formed in five orbits from five normal volunteers usin g a T1 weighted spin echo sequence. Results - The STL and the TSFE sur round the LPS to form a fascial sleeve around the muscle which has att achments to the medial and lateral orbital wall, The TSFE, which is th icker than the STL, blends with Tenon's capsule. The STL and the fasci al sheath of the LPS muscle are suspended from the orbital roof by a f ramework of radial connective tissue septa. MR images show that the TS FE is located between the anterior third of the superior rectus muscle and the segment of the LPS muscle where it changes its course from up wards to downwards. In this area, the LPS reaches its highest point in the orbit (culmination point). The culmination point is located a few millimetres posterior to the equator and superior to the globe. Concl usion - Whitnall's ligament can be considered to consist of two distin ct parts - the TSFE inferior to the LPS and the STL superior to the LP S. Since the medial and lateral main attachments of Whitnall's ligamen t are situated inferior to the level of the culmination point of the L PS, the ligament itself is unlikely to suspend the levator muscle. How ever, a suspension of the LPS may be achieved by the radial connective tissue septa of the superior orbit. The TSFE in connection with the g lobe may have an additional supporting function. The elasticity of Whi tnall's ligament and its connections with highly elastic structures in cluding Tenon's capsule, may provide the morphological substrate for t he previously proposed passive (that is, without orbicularis action) l owering of the lid during downward saccades.