What is Ossicular-Chain Dislocation?
It’s common for people to experience hearing loss after a head injury, but this often isn’t evident right away because doctors are focused on treating more serious injuries. There are three types of hearing loss: conductive (sound isn’t reaching the inner ear), sensorineural (damage to the inner ear or nerves), or a mix of these two. If conductive hearing loss lasts for over six weeks after an injury, it’s possible that there’s been a displacement of the ossicular chain.
The ossicular chain is made up of three bones—the malleus, incus, and stapes—connected by two joints. These bones collect sound vibrations from the eardrum and pass them to the inner ear. They also naturally amplify sound, and if they couldn’t perform their function, it could reduce hearing by about 50-60 decibels.
The ossicular chain lies within the part of the skull bone in the middle ear. While the skull provides good protection, these tiny bones can still get damaged. The positions of the malleus and stapes make them less likely to move about compared to the incus. This might be why displacement of these bones happens more often than fractures.
What Causes Ossicular-Chain Dislocation?
Ossicular chain dislocation, or a disruption in the three tiny bones in your ear, usually happens because of an injury. This could also happen due to a type of skin cyst called cholesteatoma or because of a disease present at birth. However, this is typically the result of these bones being worn away or necessary steps during surgery for the skin cyst. This is a separate condition and won’t be covered in this particular discussion.
The majority of ossicular chain dislocations are often a result of injury to the temporal bone – the bone which surrounds the ear. However, it’s important to remember that this dislocation can also occur even if there’s no fracture in the temporal bone.
There have been other reported injuries which can lead to this dislocation including:
- A blow to the opposite side
- Injuries from explosive blasts
- Damages from tools used in the external ear canal
- Injuries due to significant changes in air or water pressure, also known as barotrauma
The most common situations that can lead to this condition include road traffic collisions, falls, and instances of physical conflict.
Risk Factors and Frequency for Ossicular-Chain Dislocation
Ossicular chain dislocation, or the displacement of the small bones in the ear, is not very common, and we don’t know exactly how often it happens. It’s been suggested that about half of all fractures to the temporal bone, an area in your skull, lead to injuries of these small ear bones. In the week after a head injury, about 75% of people report hearing loss. As time goes on, this number decreases to about 37%, 3 to 6 weeks after the injury. However, if the hearing loss is still present 6 weeks later, it’s likely because of an ossicular chain dislocation. This situation accounts for about 4% of all head injury cases.
Most people who experience an ossicular chain dislocation are young men between the ages of 16 and 30, but it can happen to anyone, regardless of their age or sex.
Signs and Symptoms of Ossicular-Chain Dislocation
Most people seek medical treatment after experiencing a head injury, having concerns primarily about hearing loss. During the examination, the doctor will perform a thorough ear review. Findings might include blood in the ear canal, a buildup of blood behind the eardrum, a ruptured eardrum, or a leak of the clear fluid that surrounds the brain and spinal cord. The doctor will also rule out other potential causes of hearing loss.
Alongside hearing loss, some people might experience:
- Facial paralysis or weakness
- A ringing sensation in the ear (tinnitus)
- Dizziness or loss of balance (vertigo)
- A hole or tear in the eardrum (Perforated tympanic membrane)
Testing for Ossicular-Chain Dislocation
If a person has suffered a traumatic injury that might have disrupted the small bones in the ear, the first step is usually to check for more serious head injuries. To do this, a type of scan called a CT head scan is usually ordered. If this scan shows a fracture in the part of the skull near the ear, it’s essential to determine if this fracture has affected the small, vital structures inside the ear. This evaluation will give clues about potential damage to the middle and inner ear.
Once the person is medically stable, a test called an audiogram should be carried out as soon as possible. This test measures how well they can hear and provides a starting measurement for any hearing loss. It might be hard at this stage to tell if any hearing loss they have is due to disruption of the bones in the ear or due to blood in the ear, which is a common result of a traumatic injury. That’s why it’s recommended to do another audiogram after at least 6 weeks have passed since the injury. By this time, any blood should have cleared up, and any hearing loss that’s still present – assuming the ear drum itself is intact – is likely due to disruption of the bones in the ear. Another test, called tympanometry, might show increased movement in the ear, which can suggest a disruption in the chain of bones.
An ordinary CT head scan, typically used for trauma cases, isn’t enough to get a good look at the ear bones, so a CT temporal bone scan should be requested for more detailed imaging. However, not all disruptions of the ear bones can be seen on CT scans, and sometimes the diagnosis can only be confirmed by surgically exploring the middle ear.
Treatment Options for Ossicular-Chain Dislocation
In situations where a person has had hearing loss for over six months, there are a few options for treatment. These include non-invasive treatments, which could involve using a hearing aid, or undergoing surgery. However, surgery may not be an option if the person only has hearing in one ear or if they are not physically strong enough for the procedure.
There is no immediate urgency for surgery. The typical duration between the time of injury and the surgery is more than five years. Surgery would involve examining the middle ear while the patient is under general anesthesia to find and fix the damaged chain of tiny bones in the ear, a procedure is known as ossiculoplasty. There are various methods of ossiculoplasty, which are discussed in other articles in this series.
What else can Ossicular-Chain Dislocation be?
There are several health conditions that can lead to hearing loss after a person experiences trauma. These conditions either cause a “conductive” type of hearing loss, a “sensorineural” type of hearing loss, or a combination of both in the case of a condition called stapediovestibular subluxation. It’s also possible for a person to have more than one of these conditions at the same time.
Conductive hearing loss is caused by issues related to the following:
- Blood buildup in the eardrum (Hemotympanum)
- A tear in the eardrum (Tympanic membrane perforation)
- Dislocation of the tiny bones in the ear (Ossicular chain dislocation)
Sensorineural hearing loss happens due to problems like:
- Bleeding in the inner ear after trauma (Post-traumatic inner ear hemorrhage)
- A leak of inner ear fluid (Perilymphatic fistula)
- An abnormal buildup of a particular type of inner ear fluid (Endolymphatic hydrops)
- Displacement of a tiny bone in the ear and the inner ear’s balance organ (Stapediovestibular subluxation)
What to expect with Ossicular-Chain Dislocation
Ossiculoplasty, a surgery to repair the tiny bones in the ear, usually leads to better hearing for most patients. After the operation, it’s been found that most people experience an average improvement of 35dB in what’s known as the air-bone gap, which can vary between 8-60dB. The air-bone gap is a measure of hearing loss. Over 70% of patients see this gap reduced to less than 20dB, while over 30% of patients reduce the gap to less than 10dB. This means the majority of patients see a significant improvement in their hearing after the surgery.
Possible Complications When Diagnosed with Ossicular-Chain Dislocation
There can be several complications after undergoing an ossiculoplasty surgery. These may include:
- Hearing getting worse
- The prosthesis coming out
- Injury to the facial nerve
- Dizziness
- Constant ringing or noise in ear
Preventing Ossicular-Chain Dislocation
Guidance from public health experts to avoid head injuries could also decrease cases of ossicular chain dislocation, a condition affecting the ear. People need to understand the importance of wearing proper head protection when biking, motorcycling, or engaging in extreme sports. They should also always use seatbelts while in cars.
Additionally, people should be warned about messing with their ear canals. It’s best to follow the old saying, ‘never stick anything smaller than your elbow in your ear.’ This advice can protect the ear from potential injury.
