Innovative prostheses to restore hearing

Posted on May 28, 2015

Many of us take for granted things such as the ability to hear and enjoy music, the sound of children laughing or the simple joy of being part of a conversation with good friends. We usually don’t even think about how privileged we are in being able to hear.

Despite the many advances that have been made in medicine, a large proportion of the population is still affected by hearing loss. According to the South African Hearing Institute, hearing loss is a natural part of growing older, meaning that our hearing ability declines naturally from age 30 or 40. By the time we reach our 80s, more than half of us suffer from significant hearing loss. Hearing loss may, however, also occur as a result of disease, infections or drugs. It may be inherited or result from physical damage to the ears or serious head injuries.

One cause of hearing loss is a condition called otosclerosis. It is commonly believed to be congenital and occurs when abnormal bone material grows around the tiny stirrup bone (stapes) in the middle ear. Otosclerosis usually originates at the foot of the stapes, where it attaches to the cochlea. The abnormal bone growth inhibits movement of the stapes which, in turn, reduces the intensity of sound that is transferred to the cochlea. Eventually the stapes can become fixed, or fused, with the bone of the cochlea. In some cases, the other bones of the middle ear – the anvil (incus), and the hammer (malleus) – may also be affected. This condition can lead to either conductive hearing loss –where sounds reach the eardrum but are incompletely transferred through the tiny bones (ossicles) of the middle ear; or, in some cases, over time, to sensorineural hearing loss, which occurs when there is damage to the inner ear (cochlea), or to the nerve pathways from the inner ear to the brain.

There are two primary treatment options available to those who suffer from otosclerosis, namely hearing aids (more recently including bone-conduction hearing aids) and a surgical procedure called a stapedectomy. Hearing aids are usually very effective in the early stages of the disease, but eventually a stapedectomy may be required to try to restore hearing to some extent. According to the Encyclopedia of Surgery, a stapedectomy is a very safe procedure with a relatively low rate of complications.

During the procedure the innermost bone (stapes) of the three tiny bones of the middle ear is removed, and replaced with a small plastic tube surrounding a short length of stainless steel wire (a prosthesis). This extremely delicate operation is performed using an operating microscope, with the patient under local or general anaesthesia. If more than one ossicle is affected, the patient often undergoes total ossicle replacement (ossiculoplasty), in which even the unaffected ossicles are replaced.

Prof Mashudu Tshifularo, Head of the Department of Otorhinolaryngology (ear, nose and throat (ENT)) at the University of Pretoria (UP), believes that ‘innovate or perish’ are words to live by when it comes to clinical procedures, teaching, research and medical devices. He feels that academics have a responsibility to come up with solutions that benefit the communities around them. His commitment to this philosophy of innovation in the health sciences is evidenced by the fact that he has designed and patented several medical devices and procedures that are widely used in the ENT field today.

According to him, the complete removal of the stapes (including its suprastructure, stapedial tendon and incostapedial joint) or the complete removal of all ossicles (in cases where the malleus and/or incus may also have been affected), is not ideal, as parts of the structures may still be healthy and functioning properly. He believes that the removal of all the components interferes with the delicate amplification and loud sound dampening system of the inner ear, and that the prosthetics that have been in common use to date do not take the normal anatomy and function of the human ossicles into account.  

To address this problem, Prof Tshifularo has patented a prosthesis that allows the surgeon to replace only the ossicle (or ossicles) that are not functioning properly. The patent includes separate replacement prostheses for each of the ossicles - the stirrup (stapes), the hammer (malleus) and the anvil (incus). Each of these prosthetics are shaped and configured to resemble the natural ossicle it represents.   

Prof Tshifularo’s invention also aims to simplify the stapedectomy procedure itself and increase its chances of success with minimal intrusion trauma. He says that by only replacing the ossicles that are not functioning properly, the procedure carries significantly less risk than known prosthetics and their associated surgical procedures. His procedure also reduces the chance of facial paralysis, which can occur if the facial nerve that passes through the middle ear space is damaged accidentally during traditional surgery.

Helen Keller said, ‘When you lose your eyesight you lose touch with things. When you lose your hearing you lose contact with people.’ Hearing is a primary human sense and its loss severely diminishes quality of life. Innovative advances in medical devices and surgical procedures such as the one discussed above, along with the dedication of medical professionals like Prof Tshifularo and his team at UP, will ensure that the precious gift of hearing is restored to many people all over the world. 

- Author Ansa Heyl

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