Ossicular Chain Dislocation - An Overview

Introduction:

During any head injury, in the hustle of finding severe head injuries, one of the often missed conditions leads to hearing loss. This is because hearing loss after a head injury is of delayed onset, showing its occurrence after a few days to a few months. The hearing loss can be sensorineural conductive or mixed, depending on its origin. Here, the ossicular chain is a part of the ear that consists of three bones: the malleus, incus, or stapes. All these three bones are joined by the synovial joint, where the entire structure of the ossicular chain is enclosed within the temporal bone in the middle ear. Although the temporal bone is a support system in protecting the ossicular bones, the structure is still vulnerable to damage depending on the injury type.

What Causes Ossicular Chain Dislocation?

Ossicular chain dislocation occurs due to medical conditions like congenital diseases or cholesteatoma due to erosion of the ear ossicles or trauma. The most common causes of ossicular chain dislocation are:

• Injuries due to blast impact.

• Injuries due to changes in air pressure, typically affecting the lungs and ear.

• Indirect blow on the side.

• Injury due to any instrumentation in the ear.

How Commonly Is Ossicular Dislocation Seen?

The incidence of ossicular dislocation is uncommon, although the exact reason for the condition is unknown. Almost fifty percent of the temporal bone fractures occur due to injury to the ossicles. Seventy-five percent of the cases seen of head injury occur in patients associated with hearing loss, with 37 percent of cases with ossicular dislocation. Ossicular chain dislocation is often seen in young men between the ages of 16 and 30 years, but it is commonly seen in people of all ages and genders.

What Are the Events That Occur During an Ossicular Dislocation?

Ossicular dislocation is a condition that occurs due to fracture or dislocation of the bones in the ear. The injuries of ossicular dislocation are seen involving dislocation of the incudomalleolar and incudostapedial bones, subluxation of stapedio vestibular and incudomalleal, and slight dislodgement of the incus bone. However, the most common area leading to dislocation of the ossicles is found only by exploring it in the incudostapedial joint. Although these events occur in the ear during ossicular dislocation, the exact happenings can be identified only by using diagnostic methods.

How Is Ossicular Dislocation Seen Clinically?

Most of the patients following a head trauma often show complaints like an inability to hear. Here, in such cases, conducting a thorough ear test for the patients is highly essential, as it may show if there is the presence of any amount of blood filled in the ear canal, blood-stained tympanic membrane (hemotympanum), any perforation occurring in the tympanic membrane or presence of leakage of the cerebrospinal fluid. Other clinical signs associated with ossicular dislocation are palsy of the face, constant ringing sound in the ear (tinnitus), lightheadedness, and any breach in the tympanic membrane.

What Are the Ways to Identify Ossicular Dislocation?

As ossicular dislocation occurs after a head injury, most of the time, a thorough examination of the head is done following the injury. Some of the investigations preferred are:

• Computed Tomography (CT scan): Computed tomography is a two-dimensional imaging technique that gives multiple slicing of a particular part under examination to have multiple perspectives on it. A computed tomography of the head is done to detect any fracture associated with ossicular dislocation.

• Audiogram: This test is done in patients once the stability clearance is given. It is a metric test to assess the hearing capacity of the individual's ears. Here, in this condition, an audiogram is performed to detect the presence of any hearing loss.

• Magnetic Resonance Imaging (MRI): An MRI is a three-dimensional imaging technique that is used to assess the ligaments and the soft tissues associated with a particular area of interest. Here, an MRI is performed to rule out any tear in the tympanic membrane or soft tissues surrounding the ear.

How Is Ossicular Dislocation Treated?

The treatment of ossicular dislocation is given to people who show signs of hearing loss within six months of injury. Treatment options can be done with both medical and surgical management. However, surgery is not preferred in patients in whom surgery cannot be performed or considered medically unstable. In the case of surgical treatment, the procedure can be delayed even up to five years after a traumatic incident. However, the surgical procedure is done under general anesthetic to identify and locate disruption of the ossicular chain, especially the middle ear, to know if the surgery is really necessary. The surgery to treat the fracture or tear in the ossicular chain is called ossiculoplasty and involves several techniques.

What Are the Conditions That Resemble Ossicular Dislocation?

Many conditions or etiology can cause loss of hearing after an injury, and this hearing inability can be differentiated into two different types broadly, namely:

Conductive Hearing Loss: This hearing loss occurs when the sound cannot conduct itself or travel from the middle ear to the outer ear. This type of hearing loss can also occur due to the following conditions and they are:

• Perforation in the tympanic membrane.

• Hemotympanum.

• Ossicular chain dislocation.

Sensorineural Hearing Loss: This type of hearing loss occurs when there is damage to the inner ear. The conditions that may cause the hearing loss are:

• Usage of endolymphatic hydrops.

• Fistula of the peri lymphatics (fluid in the ear).

• Bleeding in the ear after any injury.

• Subluxation of stapedio vestibular subluxation.

What Are the Complications Associated With Ossicular Dislocation?

As ossicular dislocation often occurs along with head injuries, several complications are seen conjoint with this. The complications associated with ossicular dislocation are:

• Progressively increasing hearing loss.

• Injury to the facial nerve.

• Vertigo (lightheadedness).

• Tinnitus - Hearing of a ticking sound in the ear.

• Dislodgement of any ear prosthesis that has been placed.

Conclusion:

With the treatment provided, many patients show a major improvement, where the space closure between the bone and the gap formed is also seen to be reduced drastically, around 20 dB (decibels) in 70 percent of the cases and 10dB (decibels) in 30 percent of the cases, from around a decibel gap of 35dB. Also, in the case of these ossicular injuries, most of the time, patients are treated by doctors of multiple specialties, including brain surgeons, ear, nose, and throat specialists (ENT), doctors in emergency medicine, and rehabilitative specialists like hearing and speech therapists, etc. However, many cases of ossicular dislocation are seen commonly, and these cases differ. A proper customized strategic treatment plan should be executed for a better outcome.