Diseases of the middle ear often affect the ossicles leading to bony erosions and discontinuity of the ossicular chain.
Congenital ossicular chain abnormalities are usually a result of abnormal embryological development of the ossicles and middle ear. These may or may not be associated with external ear abnormalities like microtia and vice versa. They present with poor hearing that is detected with newborn hearing screening or speech and language delay.
Acquired causes of ossicular chain disruptions are more varied. The most common causes are recurrent otitis media and otomastoiditis as well as cholesteatomas that result in erosion of the ossicles, especially involving the long and lenticular processes of the incus. Other causes like temporal bone fractures and benign tumours like glomus tympanicums can also disrupt the ossicular chain.
Patients would have conductive hearing loss with Tuning Fork tests showing better Bone Conduction hearing than Air Conduction hearing. Rinne’s Tuning Fork would be negative and the Weber’s Tuning Fork test would lateralise to the affected side. If a surgery is required to treat the underlying middle ear disease, an ossiculoplasty to restore continuity of the ossicular chain can be performed at the same time. An ossiculoplasty would be to afford natural acoustic hearing 24 hours a day without the need to use any hearing device.
Ossiculoplasty is a surgical procedure to restore the continuity of the ossicular chain. The incision is a small end-aural incision, located between the tragus and root of the helix of the pinna. New techniques like the Endoscopic Transcanal approach allows for potentially no visible incisions and better visualization of the middle ear. The tympanic membrane is lifted, the deficit examined and measured and surgery performed to surgically reconnect the ossicular chain. Hearing restoration success rates of this operation can be as high as 90%.
The missing or dislocated portions of the ossicular chain can be replaced by autologous materials including any remnant ossicles, cartilage from the tragus or pinna, or cortical bone harvested from the temporal bone. These materials are reshaped and carefully inserted to connect the remaining ossicles. Alternatively, we can use synthetic prostheses made of metallic alloys or fluoroplastics known as Total or Partial Ossicular Replacement Prosthesis (TORP/PORP) that are specially designed to replace either the entire or part of the ossicular chain.
