The limping child due to transient synovitis of the hip joint (toxic synovitis)
The limping child – where to begin?
The approach to a limping child is complex and difficult to summarize.
There are many possible causes, each stemming from a different origin—orthopedic, infectious, inflammatory, or even neurological.
However, there is one diagnosis that is relatively common in pediatrics and worth knowing about: transient synovitis of the hip.
It’s important for parents to be familiar with its characteristics.
This condition is also known by other names, such as “toxic synovitis,” even though there’s nothing actually toxic about it.
So, read on—and learn.
What is synovitis and what does it have to do with the hip joint?
The synovia is a tissue that lines some of the body’s joints, including the hip joint.
Its purpose is to cover the joint and produce nourishing and lubricating substances.
Synovitis is inflammation of this tissue, which causes secretion of inflammatory fluid into the joint, leading to pain.
What is transient synovitis of the hip joint in children?
In pediatric textbooks, this disease is described in the Rheumatology chapter (diseases of the joints), under ‘Reactive and post-infectious arthritis’.
Thus, it can be inferred that transient synovitis is caused by a reaction following exposure to certain infections.
For example, a child might catch a virus causing a common cold and recover.
The body fights the virus and produces antibodies, but sometimes these antibodies mistakenly cause inflammation in a joint.
This is called ‘Reactive and post-infectious arthritis’.
If we aspirate the joint fluid and analyze it, we will not find the virus itself, but rather evidence of the immune system’s response to the infection that caused the cold about two weeks earlier.
What are the main pathogens that begin this chain reaction in children?
Usually, these are pathogens that cause mild upper respiratory viral infections in the two weeks preceding the limp.
In many cases, parents may not have noticed or may not remember that such an infection occurred.
What is the typical clinical manifestation?
The typical ages affected are three to eight years, and the disease is more common in boys than girls.
Children usually complain of pain in the hip joint area or the hip itself, and the child starts to limp abruptly on the affected leg.
Note that the leg still carries weight, which contrasts with conditions where the child stands in a “stork” position.
Usually, there is no history of injury and no fever of 38 degrees Celsius or above.
The pain and limp may be more noticeable at some times of the day and almost disappear at others.
At times, symptoms may worsen in the evening after a day of activity.
Sometimes, it’s hard for parents to decide which leg is problematic.
You can ask the child to walk and observe which leg the child “lingers” on less (i.e., moves quickly over).
For example, if the inflammation is in the left hip, the child will limp and make a quicker movement when stepping on the left foot compared to a full, longer step on the right foot.
This disease typically lasts several days, about a week on average, but may continue longer.
If lab tests are performed in a child with transient synovitis, they usually show low inflammatory markers.
X-rays or ultrasounds may sometimes reveal excess fluid in the joint capsule, indicating inflammation.
More important than blood tests or imaging is to refer to the pediatrician for a thorough examination.
How will the pediatrician diagnose transient synovitis?
Truthfully? Almost at the early stage of describing the history of the present illness.
A child in the typical age range with a mild to moderate limp, no high fever, and no other red flags.
On examination, there is a limp on one leg but no swollen joints or painful areas on bones that may suggest injury.
During the physical exam, with the child lying face up, the physician examines the lower body including both legs.
Customarily, the exam begins with the non-painful limb to minimize pain and resistance.
At the end, the physician will assess the hip joint by performing a movement called “internal rotation,” which often causes the child to startle.
Internal rotation means rotating the hip joint inward.
Sometimes the pain is so mild it requires close observation of the child’s facial expressions to detect a small grimace.
Lab tests are not required in most cases.
X-rays or referral to a pediatric orthopedic surgeon are reserved for unclear diagnoses.
However, your pediatrician must be professional and experienced in diagnosing this condition, as other diseases should not be missed.
What should not be missed in the limping child?
Of course, other important diagnoses should be considered:
Injuries – mainly fractures or sprains.
There are fractures in children, such as greenstick fractures, that are difficult to diagnose and require experience to suspect.
Read more here on signs of fractures in children.
Infections – mainly deep infections of bone or joint.
Children with bacterial joint infections usually appear sicker and have fever.
However, not all children show typical signs.
A bacterial infection must never be overlooked because appropriate and timely treatment is essential.
Other diseases – there are many rarer diseases that may cause limping.
An experienced physician will consider these alternative diagnoses and rule them out one by one until only transient synovitis remains.
What is the treatment of transient synovitis?
As this is an inflammatory process, anti-inflammatory drugs are appropriate, mainly NSAIDs such as ibuprofen.
I recommend treatment twice a day for three days, followed by gradual reduction.
Improvement is usually immediate, although the limp may return slightly after stopping treatment.
Rest? Yes and no.
If the child is in pain and limping, rest is better.
On the other hand, children (and their muscles and bones) need to move, so I might advise avoiding strenuous activities like track and field, but there is no reason to avoid school or kindergarten.
Most importantly, diagnose this condition with your pediatrician and trust their expertise to rule out other serious conditions.
Be patient, and the child will recover.
If symptoms persist beyond two weeks, return to your physician for reevaluation.
Good luck!
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