Introduction

What is Klippel-Feil syndrome?

Klippel-Feil syndrome (KFS) is a rare condition in which two or more bones in the neck (cervical vertebrae) are abnormally fused from birth. This fusion leads to a shortened neck, with limited and restricted range of motion, and muscular pain. Other signs include asymmetries of the face, a low hairline, and chronic headaches. This condition can lead to more serious issues such as spinal canal narrowing (spinal stenosis), problems associated with the brain, spinal cord or nerves, and even instability in the spine.¹

Clinically, KFS is classified into three subtypes using the Samartzis classification system. These subtypes (Type I, II, and III) are classified depending on the number and pattern of cervical vertebrae fusions. Classification is important for clinicians to understand the severity of the syndrome and risks of complications, in order to guide management strategies and prevent the risk of progression and complications.²

Development of Klippel-Feil syndrome

Normal spinal development and Klippel-Feil syndrome

The spine is made up of 33 bones, called vertebrae. The first seven bones in the neck are called the cervical vertebrae and are labelled as C1-C7, from top to bottom. The spine begins to develop early in pregnancy, with each vertebra developing separated by discs of cartilage, called intervertebral discs, providing a cushioning support between them.³

In KFS, a fault in the segmentation of the cervical vertebrae occurs during the first three to eight weeks of pregnancy, when the embryo is developing. It results in an abnormal fusion of some or all of the cervical vertebrae, causing them to stick together as a single piece.

The exact mechanism by which this faulty development occurs is not well known. Most cases are sporadic, meaning they happen randomly with no obvious genetic or environmental trigger. However, there are some genetic, less frequent forms of KFS. In the genetic form of the syndrome, abnormalities in genes involved in the normal development of the bone and spinal cord are inherited, resulting in the development of KFS.⁴

Classification and diagnosis

Classification of Klippel-Feil syndrome

Feil’s classification (1919)

The original classification of KFS was proposed in 1919 by Andre Feil, dividing the syndrome into three subgroups, and accounts for anomalies in the cervical, as well as the lower regions of the spine, called the thoracic and lumbar regions. These subtypes are:

• Type I: fusion of many of the vertebrae, spread throughout the cervical and upper thoracic region of the spine
• Type II: fusion of two or three vertebrae, with other associated abnormalities in the cervical spine
• Type III: fusion in the cervical vertebra, with lower thoracic or lumbar vertebrae anomalies

This system had limited clinical relevance to predict severity and how a person would experience symptoms based on the type they had.⁵

Samartzis' classification (modern clinical use)

This classification uses imaging techniques to focus on the fusion patterns at the cervical vertebrae of the spine and the development of symptoms associated with this region. Hence, KFS is divided into three subtypes:

• Type I: a single fusion between two vertebrae in the cervical spine region
• Type II: multiple, separate fusions between the cervical vertebrae
• Type III: multiple, continuous fusions between more than two cervical vertebrae 

This classification system allows clinicians to predict the severity of the syndrome, the clinical signs and symptoms, and progression of disease depending on the type they have.²

Diagnosis of Klippel-Feil syndrome 

Klippel-Feil syndrome often presents with other conditions at birth, such as Duane syndrome, Sprengel deformity and other spinal, heart, kidney and hearing abnormalities. Therefore, during diagnosis, it is essential to use a combination of clinical examinations and imaging techniques of the spine, but also to assess multiple body parts such as the heart and ears.^6,7

Clinical examinations

• Medical and family history
• Physical examination: they will look for signs, such as a shortened neck and low hairline, and symptoms such as signs of pinching of the nerves, which is called radiculopathy, and poor nerve reflexes

Imaging techniques 

Imaging techniques are used to look at the spine when diagnosing KFS. These are usually X-rays, however, they can include a computed tomography (CT) and magnetic resonance imaging (MRI) scan as well. The differences are:⁸

• X-rays: images the entire spine, showing fusion of the spinal vertebrae and any other abnormalities in the spine  
• CT scans: images the entire spine, and can provide more detailed imaging of the fusion patterns and structure of the spine
• MRI scans: images the soft tissue structures in the spinal area, such as the intervertebral discs, spinal cord, nerve roots and ligament structures supporting the vertebrae

Clinical implications and management of Klippel-Fiel syndrome

Correctly determining the specific type of KFS a person has is crucial for directing clinical management. The majority of people can be managed without surgical intervention, except in cases of sudden changes in nerve function, brain activity, and movement, as well as spinal instability and prolonged symptoms that may pose risks. 

The Samartzis classification is essential in identifying the best management strategy. Individuals with Type I KFS tend to have more symptoms associated with restricted movement, while those with Type II and III are more likely to have nerve and muscle symptoms.

KFS can have multiple presentations affecting different parts of the body. Collaborative care is important with various specialised doctors for the heart, kidneys and abdomen.^2,8

Non-surgical management

Non-surgical treatments are often used to alleviate symptoms. This typically applies to people with one or two fusions (Type I). When fusions are situated below the C3 spinal vertebrae, individuals can often participate in contact sports if they receive proper education. Conversely, if fusions are located above C3, the risk is greater, making contact sports inadvisable due to the heightened chance of spinal injury.^8,9

Surgical management

Surgery is required in patients who have ongoing nerve pain, weakness in muscles, and instability in their spine. If the spine is unstable, surgery usually involves fusion of the cervical vertebrae.¹⁰

Complications

Timely and appropriate management is necessary, as these cervical fusions can predispose a person to fractures, intervertebral disc regeneration, narrowing of the spinal cord and intervertebral disc herniation (bulging disc). Therefore, management needs to be timely to reduce the risk of complications and improve outcomes.^11,12

Summary

Klippel-Feil Syndrome is a complex condition in which an individual is born with an abnormal fusion of the cervical vertebrae in their spine. Most cases occur randomly, although there are certain genes that can be inherited, which increase the chance of being born with KFS. KFS typically presents with a short neck, a low hairline at the back of the head, and limited movement of the neck. Given variable presentations, assessment is thorough, involving physical examination, history taking, and spinal imaging, to classify people using the Samartzis classification system, dividing it into subtypes I, II and III depending on the number of cervical vertebrae which are fused, and the pattern of their fusions. Classification is important as it can help guide appropriate treatment, whether it can be treated nonoperatively or require surgical operations to prevent or treat complications such as sudden nerve and muscle weakness or instability in the spine. Surgical procedures can have variable outcomes, therefore, comprehensive care between various medical professionals is required to prevent severe progression and optimise the outcome.