Limb Lengthening
Limb lengthening is a surgery which is performed to increase the length of a bone. Shortening of a bone may be secondary to the following:
- Injury to growth plate during childhood
- Malunited fractures
- Bone infections- Osteomyelitis
- Tumours around growth plate
- Congenital or by Birth- like CFFD Congenital Focal Femoral Deficiency Brachymetatarsia or brachymetacarpia.
- Certain genetic disorders
Whatever may be the cause, limb length discrepancy especially in the lower limbs is functionally and cosmetically disabling. The bone is lengthened at a maximum rate of 1mm per day with the help of external fixator. The lengthening involves three stages:
- Application of frame Surgery is usually done under spinal or general anesthesia. It involves cutting the bone and application of an external fixator for lengthening the bone. After surgery a latency period of 2-3 weeks is kept before lengthening is started. During this time hematoma and immature bone formation starts at the osteotomy site. Pain in the post op period is managed by appropriate analgesics. During the latency period soft tissue also recover from the trauma of surgery and pain settles down gradually
- Lengthening phase: lengthening is done at the rate of 1 mm per day maximum. During this phase the patient is taught to adjust the struts of the hexapod or the Ilizarov frame to achieve lengthening. As bone is being lengthened the soft tissue including muscles, ligaments, tendons, and Neurovascular structures also lengthen. One of the most important aspects of this phase is aggressive and appropriate physiotherapy, so that the soft tissue is in sync with the bone during lengthening. In case the soft tissue lags behind it can lead to development of secondary contractures due to tightening of muscles- equinus at the ankle with tibia lengthening and flexion at the knee with femur lengthening are usually the result of this. In such a scenario the rate of lengthening may be decreased for some time or lengthening may have to be stopped completely for some time, so that the muscles can be stretched out with physiotherapy. Pin tract infections are common during this phase as the pins cut through the skin and other soft tissues. These are usually managed with appropriate pin site care and may occasionally warrant short term antibiotics course.
- Consolidation phase: During the consolidation phase the immature and soft lengthening regenerate consolidates into mature, hard and solid bone. Pin tract infections usually settle and are less common. Soft tissue including muscles become progressively adaptive and minor residual secondary deformities like ankle equinus are more easily addressed. Duration of the consolidation phase is usually 2-3 times that of lengthening phase. Once X rays confirm that bone has adequately healed, the external fixator is removed usually on a day care basis.
Devices used for limb lengthening
Limb lengthening involves application of an external fixator or frame after cutting the bone (osteotomy). External fixator may be circular (Conventional Ilizarov or Hexapods like Taylor spatial frame) or linear (Monorail LRS system) . The External fixators are fixed to the bone using wires and pins. Lengthening can also be achieved with internally fixed devices like the Precise nail. The nail is lengthened by an externally placed magnetic device. They are more convenient and patient friendly. However, they are extremely expensive and have a complication set of their own. Another method which is used is known as Lengthening over Nail (LON) or Lengthening and then Nailing (LATN) . Both the procedures involve lengthening with and external fixator which is removed as soon as the desired length is achieved. Stability during the Consolidation phase is provided by the Interlock nail which is either put at the time when External fixator is applied or at the time external fixator removal. Both LON and LATN aim to decrease the duration of time for which the external fixator is on. It aims to decrease the complications associated with prolonged fixator application and promises an easier rehab and earlier return to function. Deep infection due to contaminated pin tracts remains one of the potential pitfalls of this technique.
Amount of lengthening
The amount of lengthening depends upon many factors including age, the bone being lengthened and the cause of shortening. In general, legs can be lengthened up to 25 percent of their original length per cycle and arms can be lengthened up to 40 percent of their original length per cycle. In cases with post traumatic shortening the bone is lengthened till its equal to the opposite side. Typically, a bone can be lengthened around 5-6 cm during a single lengthening cycle
