2.1.1 Length deficiency can occur in one or both legs, and may be acquired (for example, secondary to trauma or infection) or, more rarely, be congenital (for example, due to hypoplasia or dysplasia). The femur, tibia or both can be involved. Deficiency or inequality in leg length can result in a limp and may limit functional ability.
2.1.2 Lengthening of the shorter leg can be attempted using external fixation devices. However, these devices are associated with significant morbidity, including infection of the pin tracts, pain, hip and knee subluxation or dislocation, and angulation deformity of the bone. External fixation devices may also be impractical or aesthetically unacceptable to some patients.
2.2.1 Intramedullary distraction devices are similar to the intramedullary nails used in the management of fractures of the femur and tibia. They have two interlocking sections, allowing controlled movement between the two pieces. The device is implanted into the intramedullary space under general anaesthesia. An osteotomy is performed, avoiding damage to the periosteum and blood supply. The proximal and distal sections of the distraction system are then fixed to the relevant sections of the bone with locking screws. The device exerts a force along the long axis of the bone, which stimulates new bone formation and lengthening. This process occurs very slowly. Different devices achieve distraction in different ways.
2.3.1 The evidence reviewed was based on case series only. The reported mean values for lengthening achieved were 46 mm (n = 48 patients), 50 mm (n = 23) and 63 mm (n = 10) in the femur, and 49 mm (n = 18) in a mixed tibial and femoral case series. The rate of lengthening achieved ranged from 0.82 mm to 1.11 mm per day.
2.3.2 In a case series, the range of knee movement in 21 patients treated with unilateral lengthening was not significantly altered following the procedure. Average knee extension was 2.5 ± 5.9° at baseline and 2.5 ± 6.1° at follow-up. Knee flexion was 155 ± 19.2° at baseline and 145 ± 19° at follow-up.
2.3.3 In one series, results described as 'excellent' (evaluated using a composite outcome that included criteria of joint movement, gait, pain and functional ability) were achieved in 75% (18/24) of patients. Full weight bearing was achieved at a mean of 67 days after the intervention in 48 patients in one case series. For more details, refer to the 'Sources of evidence' section.
2.3.4 The Specialist Advisers considered the procedure to be novel and stated that it was still being refined. They also stated that, compared with external fixation devices, there is a lack of control, which may lead to premature or delayed consolidation.
2.4.1 Few studies reporting safety outcomes were identified. One case series (n = 52) reported femoral fissure and spontaneous bony section (not otherwise defined) during bone reaming in one patient. A second case series reported transient palsy of the peroneal nerve in 9% (2/23) of patients, which resolved within 3 months.
2.4.2 The most common postoperative adverse event reported was pain during limb lengthening. In one case series, all 31 patients experienced some degree of pain or discomfort during the lengthening process, and 39% (12/31) required readmission and general anaesthesia to allow ratcheting (the motion that delivers extension of the nail). In two other series, analgesia was required for ratcheting in 4% (2/48) and 9% (2/23) of patients. In a case series that reported pain outcomes quantitatively, pain during ratcheting was rated as between 1.5 and 2.4 on a four-point scale among 48 patients undergoing lengthening of one or both femurs, and 1.5 points during bone-consolidation periods. However, in two case series of 18 and 12 patients, no patient required pain control during lengthening.
2.4.3 Bone fractures (either during lengthening or after removal of the nail) were reported in 1 out of 52 (2%) and 2 out of 31 (6%) patients. The reported incidence of mechanical failure of the lengthening nail ranged between 4% (1 out of 24 treated bones) and 16% (4 out of 25 patients). Mechanical failures included nail bending, failure or locking, broken wire, motor failure and ratchet wear. For more details, refer to the 'Sources of evidence' section.
2.4.4 The Specialist Advisers stated that potential complications include poor bone formation, bone lengthening at an inappropriate rate (resulting in either bone weakness or premature consolidation), fat embolisation, deep vein thrombosis, respiratory distress syndrome and equinus ankle deformity.