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A limb length difference or discrepancy may occur in an individual from birth (congenital) or may occur due to trauma (acquired). Limb length discrepancies in the upper limb are usually well tolerated. However, a difference or anticipated difference of more than 2cm in the lower limb typically necessitates surgical intervention to improve the gait pattern and reduce the risk of unwanted sequelae such as mechanical back pain or early onset arthritis.
Limb lengthening surgery offers a potential strategy to equalise the limb lengths. It involves a process called distraction osteogenesis. The bone is intentionally broken and then slowly stretched as it is healing to lengthen the bone. Typically, the stretching starts after a period of 5-10 days. Thereafter, the bone is lengthened no more than 1mm a day divided into 3 or 4 intervals. The length of time required to achieve the initial length is multiplied by a factor of 3-4 before the bone fully solidifies. On average, it takes 50-60 days to get 1cm of healed bone. This is called the bone healing index. The time may be increased in smokers or individuals with poor diet resulting in low calcium or vitamin D. Also, the use of pain medications in the class of non-steroidal anti-inflammatory drugs (NSAIDs) may prolong healing of the bone.
Surgery to achieve limb lengthening usually involves one of two methods: external fixation or internal fixation.
1. External fixation involves the application of a device that sits on the outside of the skin with wires or screws attaching it to the bone. It may be on one side of the limb (monolateral fixator) or encircle the limb (circular fixator). Of the circular fixators, some offer greater accuracy and ease of correcting concomitant deformity. These are called hexapods and utilise a computer program to aid the lengthening/deformity correction. There are a variety of hexapods available on the market. The one with the longest history is the Taylor Spatial Frame (TSF).
2.Internal lengthening devices have become more popular as they have been refined over the years. As the name suggests, the implant called a ‘nail’ is embedded in the centre of the bone after its broken. Thereafter, it is activated to achieve the same rate of lengthening as when using an external fixator. The most popular brand currently on the market is called ‘Fitbone’. It involves lengthening the bone by activating a motor in the nail via impulses sent to it through an antenna.
The post operative period following application of either an external or internal lengthening device involves regular x ray check-ups and physiotherapy input to maintain strength and joint movement during the lengthening process. Thereafter, there is a phased return to full weight bearing whilst the bone solidifies.
There are pros and cons to either lengthening strategy.
The internal devices are usually more expensive but convenient with less intervention required in the outpatient department and a lesser risk of infection. However, they have reduced ability to correct deformities when compared to external fixators.
On the other hand, external fixators are more labour intensive for the patient and in the clinic. There is a higher rate of infection and more discomfort. But they are normally more inexpensive and more versatile.
At Fracture and Orthopaedic Clinic, we are happy to assess your limb-length discrepancy and/or deformity and give you advice regarding the options available to correct the limb length discrepancy and/or deformity to improve your quality of life.