Minimally invasive plate osteosynthesis after osteotomy for deformity correction
Introduction
The correction of axial deformity and rotational malalignment of lower extremities resulting from congenital malformation, trauma, or cerebral palsy remains a challenge for orthopaedic surgeons. Although various complex angular deformities are usually treated by gradual correction with external fixators, the considerable time for which external fixators must be applied interferes with the patient‘s daily activities and causes many complications, such as pin-track infection and joint contractures. In case of simple types of deformity, surgeons may prefer correction using an open osteotomy with internal fixation. Rotational osteotomies are frequently performed for torsional deformities of the femur and tibia in children with cerebral palsy. A pin and plaster technique is an acceptable method for tibial osteotomy, but is not recommended for a femoral deformity. Although open osteotomy and plating can be used, there is the risk of infection and impaired healing because the surgery requires a long incision and extended exposure to fix the plate. Intramedullary nailing with percutaneous osteotomy is a good alternative to solve this problem, as it does not need cast immobilization and permits early weight bearing. However, IM nailing is not recommended for skeletally immature children with open physis due to the possibility of growth disturbance and the potential for causing osteonecrosis of the femoral head.
Minimally invasive plate osteosynthesis is a well-accepted technique in the treatment of fractures especially when used in combination with the locking compression plate (LCP). This technique has been used for pediatric femoral and tibial fractures with an excellent union rate and minimal complications. The locking plate provides fixed angle stability, strong enough to provide sufficient stability throughout the process of achieving bone union after osteotomy. Minimally invasive plate osteosynthesis after osteotomy is an effective method of treating deformity correction. It reduces the need for external fixation, promotes early rehabilitation, and return to daily life activities.
Indications
The indication for corrective osteotomy is an excessive angulation or rotation that interferes with gait and function. A plate is recommended in children where intramedullary fixation may injure the epiphyseal plate, and also in moderate, simple deformities where there is no advantage in using external fixators. Complex angular deformities, which require bone lengthening, or which may lead to neurological problems for patients after the procedure, are good indications for applying a ring external fixator.
Operative procedure
The preoperative plan needed to correct the deformity must be very precise. Measuring the thigh-foot angle assesses the rotational deformity of the tibia. The middle of the femur or tibia is chosen for the rotational osteotomy. The malalignment test is used to determine the joint alignment and joint orientation based on standing anteroposterior and lateral x-rays reaching from hip to ankle. X-rays of the tibia and femur are obtained on both sides. Then, the surgeon determines the center of rotation of angulation of angular deformity based on these x-rays. The femoral rotational deformity is clinically evaluated on the basis of the range of the internal and external rotation of the hip, comparing the normal with the abnormal side.
After choosing the location for the osteotomy, the transverse osteotomy is performed through a 2 cm incision thus protecting the periosteum. Multiple drill holes are made with a 2.5 mm drill bit and a chisel is used to complete the procedure. After the osteotome is performed, rotational deformities and/or some of the angular deformities are corrected manually to achieve the desired angle determined by the preoperative plan.
The plate must be long enough to be fixed with at least three bicortical screws in each segment. Two separate incisions are made over the proximal and distal segments and a sub-muscular tunnel is prepared for plate insertion. The precontoured plate is slipped percutaneously under the muscle. Once the plate is in the correct position, a K-wire is placed in the most proximal and most distal holes of the plate to maintain its position. Using small stab incisions, screws are positioned to engage at least three bicortical screws on either side of the osteotomy.
In cases of complex deformities, the external fixator may be applied before the osteotomy is performed. Wires or Schanz screws are fixed at locations which will not interfere with future plating. After correcting the deformity by adjusting the external fixator to achieve correct alignment, MIPO can be performed as previously described and the external fixator removed.
Rehabilitation
In most cases there is no need for external immobilization after fixation. Patients are encouraged to start range-of-motion exercises in the hospital and advised to use crutches for toe-touch weight bearing for approximately 8 weeks. Once x-ray control shows good healing the patient is allowed to engage in full weight bearing.
Advantages and disadvantages
The MIPO technique after osteotomy is a minimally invasive procedure which provides adequate stability and is convenient for the patient, since the internal fixation reduces the pin-related problems of external fixation and allows for early rehabilitation. A traditional closed- or open-wedge osteotomy with plate fixation is the standard technique for correction of varus or valgus deformity. However, this technique often requires a large incision with soft-tissue damage, considerable bleeding, and a bone graft. These disadvantages can be overcome by using a MIPO technique because the periosteal blood supply is preserved. This eliminates the necessity for a bone graft, and enhances fracture healing. This technique can also be used in small children with an open physis or narrow medullary canals.
However, the surgeon should note that this method is technically more demanding, and it may increase radiation exposure. In addition, the correction may not be as perfect as that obtained by gradual correction using an external fixation technique.
Further reading
Gugenheim JJ Jr, Brinker MR (2003) Bone realignment with use of temporary external fixation for distal femoral valgus and varus deformities. J Bone Joint Surg Am; 85-A(7):1229–1237. Ilizarov GA (1988) The principles of the Ilizarov method. Bull Hosp Joint Dis Orthop Instr; 48(1):1–11. Oh CW, Song HR, Kim JW, et al (2010) Deformity correction with submuscular plating technique in children. J Pediatr Orthop B; 19(1):47–54.Case 3: Femur, shaft: varus malunion
Case description
A 6-year-old girl presented with a femoral malunion. Her parents brought her to the hospital because she had a limp caused by limb shortening. Her femoral shaft fracture had been treated initially by external fixation.
Indication for MIPO
The osteotomy of the malunion site can be performed through a small incision. Once the osteotomy is performed plate fixation using a MIPO technique is recommended to provide adequate stability. It is difficult to control the correct alignment of the limb following osteotomy using nonoperative treatment with a cast.
Preoperative planning
When a corrective osteotomy is to be performed the deformity has to be defined in all planes, including the amount of shortening that requires correction. The preoperative plan should include a graphic representation of the osteotomy site and the fracture fragments after osteotomy, the surgical approach, the reduction technique, the most appropriate implant, and the steps required to insert it. In this case, the lateral callus formation may require the plate to be precontoured to allow satisfactory reduction of the fracture ( Fig 25-25 ).
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