Journal Club: The distance between two limbs of stapes can give indication on how far the round window is located.

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Today's journal article

McMenomey S, Tubbs RS, Kveton J, Cottrell J. Evaluating the Stapes as a Landmark for Round Window Identification in Cochlear Implantation. 

Why I picked this article

The cochlear implant surgery can restore the sense of hearing in those with profound hearing loss. During the surgery, the cochlear implant is inserted into the cochlea through an anatomical opening called the round window, or through an opening made next to the round window. The surgical approach to ensure the successful insertion of the cochlear implant to achieve good contact with auditory neurons is critical for good patient outcomes. 

This research used some CT data from human patients to understand if the Stapes can be used as a landmark to predict the round window location. 

Some of the research findings

Patient data:

  • 102 ears (51 left and 51 right temporal bones)
  • Preoperative 
Key findings:
  • The researchers first measured the intercrural width of the stapes. 
  • This is the distance between the two limbs of the stapes bone - presumably, the maximum distance was measured in a plane parallel to the stapes. 
  • The average was 2.1 mm, with a maximum of 2.6 and a minimum of 1.7 mm. 
  • The posterior limb was used as the landmark. 
  • From the posterior limb, if you move inferiorly by the same distance as the intercrural width, it generally lands close to the round window niche. 

Haruna's takeaway

It's interesting to see the variability measured for the stapes footplate. Compared to how much the round window niche size and shape vary, the stapes seem very consistent in my view. 

The angle relationship between the stapes and the round window, particularly in vivo, is very hard to visualise with an endoscope. Visually, the intercrural distance may be quite easy to visualise, and at least it gives some distance expectation on how far the round window should be from the limb of the stapes. As sometimes, the round window is not visible due to overhanging mucosa or a big bony overhang on the niche, it may be helpful to know the approximate distance as the "radius to look for" where the round window "should be". 

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This is Haruna's 75/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.