A perfect body movement requires a symmetrical musculoskeletal system. Some people suffer with difficulty in doing physical activities because of the asymmetry in their musculoskeletal system. This condition is medically termed as limb length discrepancy.

What is limb length discrepancy?

Limb length discrepancy or anisomelia is a medical condition where there is a difference in the length of the arms or legs. This orthopedic problem usually appears in childhood or from a serious injury or illness that affects the growth plate (the area of growing tissue near the ends of the long bones in children and adolescents). In exception to extreme conditions, the differences in arm length do not usually impact the arm functions. Limb length discrepancy have high impact on leg functions; the bones that are affected by a leg length discrepancy are the femur (thighbone) and tibia (shinbone).

Small differences in limb length are common and less noticeable. When the limb length difference measures more than 1.5 to 2.0 cm (5/8 of an inch), it will affect the patient's well-being and have significant impact on the physical movements, which requires treatment.

What are the symptoms of limb length discrepancy?

Signs and symptoms of a leg length discrepancy depend on the cause and difference in the length measurements. The common symptoms includes:

• Walking difficulties like limping, walking with shorter steps, or walking on the tip-toes of the shorter leg.
• Feeling pain and fatigue when one takes extra effort to move.
• Adults may have conditions like low-back pain, osteoarthritis and scoliosis (sideways curvature of the spine).

What causes limb length discrepancy?

Limb length discrepancy has many causes, which can be divided into four main groups:

• Congenital: This type of limb length discrepancy is present by birth. In this case, the baby may be born with short or missing limb bones or one side of the body may grow larger than the other. Generally, the length difference will be too small to be detected during the early stages, but increases progressively over time.
  
  
• Developmental: This type of limb length discrepancy happens in infants. It is caused by any childhood illness or injury to the growth plate, resulting in a discrepancy that appears over time.
  
  
• Post-traumatic: Incorrect healing of any fractures and other traumatic injuries to the bone can cause one leg to be shorter than the other, in turn resulting in limb discrepancy. This happens when the skin and muscle tissue around the bone are severely injured and exposed, as in case of open fractures.
  
  
• Idiopathic: In this type of limb length discrepancy, the exact cause of the condition is unknown.

Some risk factors that are associated with limb length discrepancy are:

• Bone tumors and its related treatments
• Some diseases like Neurofibromatosis, Ollier disease
• Certain neurologic conditions and other causes of inflammation of the joints during growth like juvenile idiopathic arthritis

How limb length discrepancy is diagnosed?

A discrepancy in leg length in children can be easily observed by the parents as they grow and begin to crawl and walk. Your doctor will conduct a detailed physical examination and imaging tests to confirm or diagnose a discrepancy in length.

• Physical examination and visual evaluation: The physician will observe the sitting, walking and standing patterns of the child. To measure the extent of the limb-length difference, physician may ask the patient to stand barefoot and place a series of wooden blocks under the shorter leg until the child’s hips are level. The blocks used are then measured to find out the difference between the two legs.
  
  
• Imaging tests: Doctor will recommend imaging studies to confirm the diagnosis, create baseline measurements of both legs for proper treatment recommendations. This may include the following:
  • X-rays will produce dense images of bones which helps to determine the skeletal maturity (size, shape and the growth pattern of bones).
    
    
  • EOS imaging or scanograms will create 3-dimensional models to measure the length of the bones in the legs. EOS images are taken while the child is in an upright or standing position.
    
    
  • Computed tomography (CT) scans create cross-sectional images of the bones and its tissues by using a combination of X-rays and computer technology.
    
    
  • Magnetic resonance imaging (MRI) will produce detailed images of organs, soft tissues, muscles, ligaments and other structures within the body without exposing any radiations.

In growing children, your doctor will take repeated physical examination and imaging tests to determine if the discrepancy is increasing or is the same. A limb length discrepancy can also be detected on a screening tests for scoliosis (curvature of the spine).

What are the treatment options for limb length discrepancy?

Before planning for the treatment, doctor will consider the child’s age, the length of the discrepancy and the cause if known. The non-surgical and surgical treatment options for limb length discrepancy are discussed below:

• Non-surgical treatment: This treatment is recommended for those patients whose length discrepancies are mild i.e., less than an inch. This method includes:
  • Orthotics: A supportive wear is fitted inside or outside the shoes. Wearing a shoe lift will adjust the difference between the two legs. It can also relieve back pain associated with this condition. These are inexpensive and can be easily removed if not effective.
    
    
  • Observation (every six to12 months): At routine intervals, doctor may recommend a physical examination for children who have not reached skeletal maturity. Regular measurement can determine the discrepancy pattern of the limb.
• Surgical treatment: Surgical treatment is recommended for those patients whose limb length difference measures more than an inch. This method will equalize small differences in leg length by:
  
  • Slowing down or stopping the growth of longer limb
  • Lengthening the shorter limb
  • Shortening the longer limb,

The surgical treatment procedures include:

• Epiphysiodesis or guided growth surgery: It is a simple surgical procedure recommended for those patients who are still growing (children). This method will slow down or stop growth at one or two growth plates in the longer leg. Epiphysiodesis can be performed in one of two ways:
  
  1. The growth plate may be destroyed to stop further growth by drilling or scraping it.
     
     
  2. Metal staples, or a metal plate with screws are placed around the sides of the growth plate in order to slow or stop growth. These inserts are removed when the shorter limb matches with the longer one.
     
     
• Limb lengthening: This is a preferred method to treat limb-length discrepancies as it allows your child to grow to their normal height. Here, surgeon will cut the bone of the shorter leg and use either an external fixator or internal device to slowly lengthen the bone and to correct the length difference. As the surgical procedure is complicated, this is recommended only for those patients who have significant difference in limb length. Both internal and external lengthening will take several months to complete and require frequent follow ups.
  
  In external fixation, surgeon will cut the bone in the shorter leg into two segments and externally insert a platform-like frame to connect to the bones with pins. Lengthening begins about a week after surgery and is performed by turning the dial on the fixator. The dial will increase the space between the cut bones, allowing new bone to slowly form which will lengthen it. The bone may lengthen 1 mm per day i.e., approximately 1 inch per month. The procedure has some potential risk like infection and stiffness of adjacent joints, as the fixator is placed externally.
  
  In internal fixation, surgeon will cut the bone of the shorter leg and surgically implant an expandable metal rod in the bone. This rod will lengthen gradually in response to the normal movements of the patient's limb. As the rod lengthens, it will create space for new bone to grow. This procedure has less risk compared to external fixation method.
  
  
• Limb shortening: This procedure is recommended for those patients who have reached skeletal maturity and have mild or moderate limb-length difference. During the process, the surgeon will remove a bone section from the longer limb, insert a metal rod or plate and screw it to keep the bone in place while healing.
  
  As a major shortening occurs, it can weaken the muscles of the leg and should not be used for significant limb-length discrepancies.
  
  
• Amputation and prosthetic fitting: In some cases, where the limb length is very long (8 inch or more), the doctors may recommend an amputation or prosthetic fittings like mechanical knee or below-the-knee prosthetics to correct the condition.

What is the outlook or prognosis for limb length discrepancy?

With proper treatment, children with limb-length discrepancies can live long and perform normal physical activities. Understand the treatment plan for each stage as it will help you to adhere to the plans.

Sources

1. Limb Length Discrepancy. https://orthoinfo.aaos.org/en/diseases--conditions/limb-length-discrepancy/. Accessed on: 26-02-2020.
2. Leg Length Discrepancy (Pediatric). https://www.columbiadoctors.org/condition/leg-length-discrepancy-pediatric. Accessed on: 26-02-2020.
3. Limb-length Discrepancy. https://www.chop.edu/conditions-diseases/limb-length-discrepancy. Accessed on: 26-02-2020.
4. Limb-length Discrepancy https://kidshealth.org/en/parents/leg-length-discrepancy.html. Accessed on: 26-02-2020.