Problems in the musculoskeletal system

• Genu Varum is more common than genu valgus in achondroplasia. Knock-knees do not need treatment because they do not progress. Bowlegs however can result in symptoms around the knee such as pain and restricted walking ability. Pain around the knee due to bowing should be distinguished from knee pain due to spinal stenosis. A child with achondroplasia and genu varum with associated x-rays is shown below.

• Some experts believed that relative overgrowth of the fibula compared to the tibia causes the knee to bend inwards. Therefore, surgery in the past relied on stopping growth in the fibula (epiphyseodesis) or removing a portion of the fibula.
• A more recent analysis of this problem has shown that the bend occurs in the lower part of the femur and the upper part of the tibia. In addition, the tibia is twisted along its axis (internal tibial torsion). A few questions need to be answered through long-term studies before treatment can be advocated for genu varum.
  • Does genu varum in achondroplasia affect long-term function?
  • Does it pose an increased risk for knee arthritis in future?
  • How does surgical correction influence natural history?
• We are still in the process of addressing these issues and definite answers may not be available immediately. Symptomatic knee arthritis is not a frequent problem in adults with achondroplasia and this is perhaps a reassuring fact for parents. The current recommendation is to undergo surgery only in the presence of bothersome symptoms or if there is severe deformity. Bracing is not advocated because it is difficult to exert enough corrective forces on the bones in the presence of ligamentous laxity.
• Spinal stenosis in the lumbar spine is very common in young adults with achondroplasia, though it can occur at any age. The narrow spinal canal found in achondroplasia and the normal size of the spinal cord and cauda equina (nerve bundle at the base of the spine) mean that there is less room for the spinal cord in the achondroplastic spine. In some patients, this narrowing of the vertebral canal results in compression of the nerves. Symptoms include activity-related leg pain that is relieved on squatting down, tingling, pins and needles, or numbness in the feet (paraesthesias), weakness of the legs or rarely, disturbances in control of bladder or bowel function (incontinence). X-rays, CT and MRI scans of the lower spine, confirm the diagnosis. We believe that obesity greatly increases the risk of this problem developing.
• Fixed TLK- As mentioned above, most infants with achondroplasia have a TLK and this is normal. In the vast majority of patients, as the child begins to walk, the TLK will spontaneously resolve without treatment. In some children however, the TLK will become fixed or permanent. Prolonged un-supported sitting likely predisposes this to occur. Bracing can be done to treat this problem and if severe enough, surgery may be required. Typically when a child is laid on their belly, the thoraco-lumbar region will flatten and indicate that the TLK is flexible. When however a child is placed face down and a hump in the spine is seen, as pictured below, the TLK is said to be fixed and treatment will be required (5).

• What are the physical characteristics of Achondroplasia?
• How is the diagnosis made?
• What are the associated medical problems?
• Problems in the musculoskeletal system
• Problems elsewhere in the body
• What are things to watch out for?
• References