Minimally invasive plate osteosynthesis and limb lengthening
Introduction
Limb lengthening by distraction osteogenesis has been widely used since first introduced by Ilizarov. However, due to the complications associated with a long period of external fixation and increased patient discomfort, refinements in techniques of lengthening have been developed: lengthening over an intramedullary (IM) nail reduces the duration of external fixation and protects the distracted bone during the consolidation phase. The method also allows patients to regain movement faster and earlier return to daily life activities. However, IM nails are difficult to use when there is a narrow medullary canal or the medullary canal is deformed. Joint contracture and open physes are further contraindications to IM nailing. Furthermore, IM nailing of the femur may result in osteonecrosis of the femoral head, especially in children.
Today, minimally invasive plate osteosynthesis (MIPO) is an accepted technique in the treatment of fractures especially in combination with the locking compression plate (LCP). This procedure protects the periosteal blood supply which promotes good formation of the distraction callus. Because of its fixed angle stability, the locking plate is strong enough to provide sufficient stability throughout bone consolidation after removal of the fixator. Minimally invasive plate osteosynthesis combined with distraction osteogenesis in limb lengthening is an effective method, since it reduces the duration of application of the external fixation, prevents refracturing, and allows for early rehabilitation.
Limb-lengthening process
The classical limb-lengthening process can be divided into three phases:
Initial operation: To accomplish lengthening, an external fixator is inserted using either a ring or a monolateral fixator. The usual method of leg lengthening is gradual distraction (callotasis) of a fracture callus created after a low-energy corticotomy of the long bone. This requires careful preservation of the soft-tissue envelope.
Distraction phase: After a latent period of 7–10 days when fracture callus develops at the corticotomy site, gradual distraction begins. The distraction period continues until the desired amount of lengthening or the maximal amount of lengthening, dependent on soft-tissue constraints, has been achieved. Lengthening should proceed at a rate that is tolerable to the fracture callus and soft tissues, and which does not interfere with their blood supply. This is usually 1 mm per day. The limb is maintained in the lengthened state by the external fixator until adequate consolidation of the new bone has been established to minimize the risk of fracture after removal of the apparatus.
Consolidation phase: After the desired lengthening or deformity correction has been achieved, no further adjustment is required. Newly regenerated bone is not strong enough to resist shortening or breakage without the continued support of the external fixation device. When lengthening is performed with external fixator alone, the external device remains in place until the consolidation phase is completed. Typically, this consolidation period is approximately twice as long as the distraction period. However, its duration is influenced by many factors. The “healing index” comprises the total amount of time in external fixation per centimeter of lengthening, which usually amounts to about 30 days/cm.
A significant disadvantage associated with gradual lengthening of fracture callus is the prolonged consolidation phase spent with the external fixator in situ while the lengthened segment develops enough strength to allow removal of the fixator. To reduce this period it has been proposed to lengthen the femur or tibia using intramedullary rods, with locking of the fragments to the rod when distraction is complete allowing earlier removal of the external fixator. Minimally invasive plate osteosynthesis with a locking plate is a recent advance in limb-lengthening management and is an alternative to the IM nail.
Principle and concept
Various diseases or injuries may cause limb-length discrepancies, which are indications for limb lengthening using distraction osteogenesis. The main reason for limb lengthening with MIPO technique after distraction osteogenesis is to reduce the time of external fixation after gaining the desired length. Indications for MIPO are: limbs not indicated for lengthening over an IM nail, such as those with an open physis, bone deformity, or a narrow intramedullary canal.
Operative two-step technique
Procedure for limb lengthening
Tibial lengthening
With the patient lying supine on a radiolucent table, a 3–4 cm incision is made in the area of the Gerdy tubercle at the proximal tibia. A precontoured lateral plate is chosen, which is long enough to place at least three bicortical screws within 5–6 holes plus the proposed amount of lengthening distal to the planned osteotomy. After preparing a submuscular tunnel, the plate is inserted extraperiosteally along the lateral surface of the tibia. Four or five locking screws are inserted proximally without damaging the physis. Through a second incision, using multiple drill holes and a handheld osteotome, a metaphyseal corticotomy is performed 1 cm below the distal screw of the proximal segment. The monolateral lengthening frame or ring fixator is fixed to the medial side of each segment with three half pins, avoiding contact with plate and screws. A 3.5 mm cortex screw distally from the tibia to fibula is then inserted to hold the distal tibiofibular joint after osteotomy of the distal fibula in order to maintain ankle stability.
Femoral lengthening
A narrow plate, long enough to allow the required lengthening, is chosen. With the patient positioned supine or in the lateral decubitus position, an incision 3–4 cm long is made along the lateral aspect of the greater trochanter. After preparing the submuscular tunnel, the plate is inserted along the lateral surface of the femur. Three or four locking screws are used to fit the plate to the proximal segment. Then, a metaphyseal corticotomy is performed 1 cm below the distal screw. In some cases, a flexible nail may be inserted to stabilize the distal segment during lengthening. The monolateral frame is fixed to the lateral side of each segment with three half pins, which are placed carefully to avoid possible damage to the growth plate, causing growth arrest. At the same time, the position of the pin should not be in the way of plate application.
After 7–10 days, distraction is started at a rate of 1 mm/day, while partial weight bearing is allowed. Physical therapy should start as soon as possible to maintain range of motion in adjacent joints. Additionally, x-rays are obtained to monitor progress.
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