PEDIATRIC LIMB DEFORMITY AND LIMB LENGTH DISCREPANCY

Jill Flanagan, M.D.

 

Introduction: Pediatric limb deformity and limb length issues truly represent the differences of pediatric orthopaedics from its adult counterpart.  To understand pediatric deformity and limb length issues requires the understanding of growth and development of children’s bones.  To help sort out this broad topic, it helps to break down the deformity and limb length issues into their most common causes.

  • Congenital: there are certain types of abnormalities that a child may be born with leading to different limb lengths.  The three most common of these include congenital femoral deficiency, fibular deficiency, and/or tibial deficiency.  These deficiencies can lead to major differences in limb lengths.
  • Trauma: if a child breaks a bone through a growing  center (physis), he/she may be at risk for a limb length difference.  Two of the more common types of trauma leading to limb length differences are breaks through the bottom (distal) growth area of the femur bone or the top (proximal) growth area of the tibia bone.
  • Infection: If a child suffers an infection in a bone or joint, especially when he/she is very young, there is a chance that the growth area itself may become damaged and may not grow properly, or the body’s reaction to the infection can cause the bone to overgrow and become longer than the other side.
  • Treatment Principles: In general, a person of average adult size can tolerate limb length differences of ¾” (2 cm) or less.  When a child is still growing the limb length discrepancy is expected to continue to increase, and the difference at full growth (at skeletal maturity) can be predicted. When differences are projected to be greater than 2 cm, the discussion regarding treatment begins.  The option to address the LLD is either to shorten the long leg or lengthen the short leg. For the growing child, if the difference at maturity is projected to be between 2-5 cm (up to 2 inches), then often shortening of the other limb is recommended via a surgery known as an epiphysiodesis.  In this surgery, the growth area of the longer side is surgically stopped .  The shorter side then continues to grow and catch up in length to the longer side.  This kind of surgery may affect the ultimate height of the individual at skeletal maturity. There are certain situations that may direct toward lengthening surgery. These include:
  1. If differences are projected to be greater than 5 cm in the growing child
  2. A child is already fully grown but has a limb length difference greater than 2 cm
  3. There happens to be deformities of the short limb that also need to be corrected
  4. If there is a concern about maintaining a longer ultimate height.

Nonoperative Treatment:

  • For small differences, less than ¾”, no treatment may be needed, although treatment is considered if the child has symptoms.
  • For slightly larger differences, approximately 1” – if someone is not a surgical candidate, or for whatever reason is against any type of surgery, a shoe lift is always an option. Lifts less than ½” can be placed in a shoe, but lifts larger than this will need to be placed outside the shoe.  While in theory, someone with a 5-inch limb length difference could have a 5” lift, this is not a practical option as a long-term solution.  Shoe wear options are extremely limited, and the risk of ankle injuries and other problems are higher with the larger lifts.  The shoe would also be extremely heavy and often unsightly.

Surgical Treatment:

  • Epiphysiodesis: “Shortening” via epiphysiodesis of the longer side is typically recommended for projected limb length differences between 2-5 cm (3/4”-2”). This procedure can be achieved by a variety of techniques. In this procedure, the growth area (physis) is drilled surgically. The growth area is made of cartilage, and after the surgery, the cartilage hole heals itself, but fills in with bone.  Once bone fills up this hole, the bone no longer can grow.  Some surgeons will also implant metal (screws or plates) to help prevent any further growth at the site. This is a simple, very predictable and outpatient procedure, however it is not a good for big LLD.
  • Limb lengthening:
    • General Lengthening Principals: In general, limb lengthening surgeries are performed by surgically breaking the bone, waiting for certain amount of time for the healing process to start (callus formation) and then stretching the bone daily until the goal length is desired. If the bone is lengthened too fast, it may not heal, and it places the surrounding muscles, nerves, and joints at risk for permanent damage. If the bone is lengthened too slow, then it may heal too quickly, and the bone may not be able to reach its actual length.  This procedure involves lengthening of the bones/ muscles and other structures. Muscles contractures or stretching of the nerves may happening during the treatment.  It is a very specialized surgical skill, and only surgeons who are trained in limb lengthening should be performing the operation.

There are two basic types of devices that are utilized at this time to perform a limb lengthening surgery- either some type of external fixator or an internal lengthening nail.  Only after a thorough discussion with a lengthening surgeon will one understand more about limb lengthening and then which device is most appropriate to lengthen someone’s bone.

Limb lengthening should only be performed by surgeons trained in limb lengthening.  The process is intricate and time consuming, and success is highly dependent on the skill and knowledge of the surgeon, the ability of the surgeon and the family to communicate regularly, and aggressive physical therapy – both during and after lengthening.

  • Lengthening with External Fixators: There are two basic types of external fixators – a monolateral external fixator (attached from one side to the bone like a rail), and a hexapod external fixator. A surgeon will opt for the fixator that is best suited for a patient’s problems. In general, a limb lengthening performed in conjunction with a deformity correction is typically performed with a circular hexapod external fixator, while a pure lengthening, especially in the femur bone, is performed with a monolateral external fixator (a rail).

A hexapod (circular) external fixator is made of two circular metal rings connected with six telescopic struts.  Each of the struts can be individually lengthened or shortened relative to each other. This allows for movement in six different axes and affords these hexapod external fixators the ability to correct very severe and extreme limb deformities.

  • Lengthening with an Internal Lengthening Nail: When using an internal lengthening nail, basic lengthening principles still apply.  The bone is broken and stretched at a specific rate.  Rather than having a fixator outside the body, the lengthening nail is placed inside the bone.  Some nails have a magnet to help enable them to lengthen, while others use an electric motor.  Not every lengthening can be performed with an internal lengthening nail.  Restrictions may be due to:
    • The patient’s size
    • Whether the bone is crooked
    • If the lengthening is on a young child.

Further details of who is a lengthening candidate with a lengthening nail should be discussed with a limb lengthening surgeon

  • Limb Deformity Surgeries: Simply put, limb deformity surgeries are performed to take a crooked limb (such as the leg bone, the thigh bone or arm bone) and make it straight again.  Straight bones allow the joints to be loaded evenly to avoid early joints arthritis and improve walking ability. There are a wide variety of fixation techniques but can essentially be narrowed down to several specific criteria.
  • Acute Correction: as the name applies, acute correction surgeries are performed at the time of surgery, “one and done” so to speak.  Typically, deformities can be fixed acutely if the crookedness is not too severe, and/or if the deformity is limited to one direction rather than multiple directions.  In addition, the acute correction cannot cause undue stress on the surrounding nerves, arteries, and joints.  Acute corrections can essentially be performed one of two ways – either with a plate and/or wires or with a nail.  Below are some examples of how crooked bones can be straightened acutely.  Acute correction is not without limitations, and can result in over or under correction and may stretch the surrounding nerves.
Here is a mature young man with inherited rickets. Due to his bone disease, his femur bone bowed. In this example, his deformity was acutely corrected by breaking the bone in two places, and then fixing the deformity acutely with the use of a nail.
Here is a young boy with a skeletal dysplasia who has corrected acutely both at the top of the femur and bottom of the femur with a plate at the top and wires on the bottom.

 

Gradual Correction: gradual correction surgeries are performed with the use of an external fixator.  There can be several reasons why a surgeon would opt to perform a gradual correction.  The most common four reasons are the following:

  • The deformity is too complex (too big deformity, affecting multiple directions, bad surrounding soft tissues) to “fix” at one time with accuracy
  • Acute correction will result in compromise to surrounding structures (typically nerves and blood vessels)
  • The deformity is too large to correct at a single setting
  • The limb is also short, and so lengthening is desired

Gradual correction of a limb deformity with an external fixator utilizes similar principles and techniques as limb lengthening with an external fixator.