Rounding of the Inferior Rectus Muscle as an Indication of Orbital Floor Fracture with Periorbital Disruption

Abstract

IObjective: To determine if rounding of the inferior rectus muscle on coronal computed tomographic (CT) scans predicts disruption of the periorbita in orbital floor fractures and therefore predicts delayed enophthalmos.Design: Cadaveric study with CT scan analysis. I Setting: Cadaveric laboratory and CT scanner at a tertiary care hospital in London, Ontario.Methods: Each orbit of each cadaveric head was randomly assigned to have either intact or disrupted periorbita. Progressively larger orbital floor fractures were made and CT scans were taken before fractures and after each fracture to assess the shape of the inferior rectus muscle. Measurements were made of the length of the long and short axis of the inferior rectus muscle using CT analysis software. The short to long axis ratio was then compared.Main Outcome Measures: Change in the short to long axis ratio of the inferior rectus muscle and correlation of the ratio with intact and disrupted periorbita.Results: Orbital floor fractures measuring 1 x 1 cm show an increase in the short to long axis ratio (rounding) of the inferior rectus muscle only if the periorbita is disrupted. Orbital floor fractures measuring 2 x 2 cm show rounding of the inferior rectus muscle regardless of whether the periorbita is intact or disrupted; however, the degree of rounding is greater if the periorbita is disrupted.Conclusions: For small orbital floor fractures, rounding of the inferior rectus muscle predicts periorbital disruption. This may therefore represent an indication for early surgical repair to prevent delayed enophthalmos. SOMMAIREObjectif: Determiner si un arrondissement du muscle droit inferieur a la tomodensitometrie predit une interruption de la periorbite dans une fracture du plancher orbitaire ce qui pourrait signer une enophtalmie retardee.Devis: Etude sur cadavres avec analyse des tomodensitometries. Localisation: Hopital de soins tertiaires a London, Ontario.Methodes: Chaque orbite de chaque tete a ete assigne au hasard entre le groupe avec periorbite intacte ou celul avec interruption. Nous avons cree des fractures de plus en plus grandes dans le plancher en prenant une tomodensitometrie avant et apres chaque fracture pour evaluer la forme du muscle droit inferieur. Nous avons mesure la longueur des axes longs et courts du muscle droit inferieur grace a un logiciel d'analyse. Nous avons ensuite compare les ratios des deux axes.Variable Evaluees: Changement dans le ratio des deux axes et correlation entre le ratio et I'etat de la periorbite. Resultats: Les fractures du plancher mesurant 1 x 1 cm montrent une augmentation du ratio (arrondissement du muscle droit inferieurl seulement quand la periorbite est interrompue. Par contre les fractures mesurant 2 • 2 cm montre toutes un arrondissement que la periorbite soit intacte ou non, mais le degre augmente quand la periorbite est interrompue.Conclusion: Pour les petites fractures du plancher orbitaire, un arrondissement du muscle droit inferieur predit une interruption de la periorbite. Cela peut representer une in...

Facial Fractures

“…29 Some authors have advocated evaluating this by examining the shape of the inferior rectus by means of coronal computed tomographic scans. 30,31 It is felt that rounding of the relatively flat inferior rectus is an indication of loss of ligamentous support and, subsequently, a higher likelihood of enophthalmos developing (Fig. 4).…”

Muscle Shape as a Predictor of Traumatic Enophthalmos

“…Levine et al proposed that soft tissue edema alone or together with intramuscular and perimuscular hemorrhage could cause the shape of the inferior rectus muscle to change from elliptical to round on coronal CT. 21 Alternatively, others have hypothesized that rounding occurs because of disruption of orbital periosteum, which subsequently leads to periorbital herniation into the maxillary sinus. 5,8,9 These opposing theories were tested by Banerjee et al in a cadaveric study. 8 They showed that progressively larger orbital floor defects resulted in ptosis of orbital soft tissue into the maxillary sinus.…”

Evidence-Based Medicine

“…This finding has been shown to be predictive of post operative enophthalmos. 55,56 Moreover, Matic et al have shown that a heighttowidth ratio greater than 1.00 in the inferior rectus muscle is predictive of late enophthalmos but not per sistent diplopia. 57…”