Tibia Lengthening and Deformity Correction With a Multiplanar External Fixator



Tibia Lengthening and Deformity Correction With a Multiplanar External Fixator


Collin J. May



Operative Indications

The use of a multiplane external fixator for distraction osteogenesis is a powerful tool to address limb deformity and limb-length differences in pediatric patients.


Preoperative Planning/General Considerations



  • The goal of corrective surgery for limb deformity is a normal mechanical axis (of the involved bone and the limb overall) with joint lines that are parallel to the floor and limb lengths that are equal


  • Determining the osteotomy level, the degree of correction, the timing and rate of correction, and avoidance of injury to vital structures are all key aspects of the preoperative plan


  • Principles of external fixator stability are of critical importance in distraction osteogenesis. Stability increases with larger pin diameters, greater pin spread (on each side of osteotomy), increased pin number, and pins in multiple planes. Fine wires should be spread as close to 90° as anatomically possible, and at least 60° is preferable


  • Proper pin/wire insertion technique is critical to minimize the risk of postoperative infection. This includes placement of half-pins on subcutaneous bone borders (if possible), adequate skin incisions for pin placement, use of sharp drill bits (flutes of drill should be cleaned between uses) and irrigation to prevent thermal necrosis, and use of soft tissue protector when drilling to prevent soft tissue injury


  • Pins/wires should remain 15 mm from knee joint and 10 mm from ankle joint to avoid intracapsular placement


  • Half-pin diameters of 5 mm or 6 mm are preferred in the lower limb (but pin diameter should not exceed 1/3 the diameter of the bone). Pins with hydroxyapatite (HA) coating adhere better to bone and may lead to less frequent loosening and pin-site infection


Analysis of Deformity



  • A standing hips-to-ankles radiograph with patellas forward is the workhorse image for assessing coronal plane deformity and limb-length. Full-length lateral images of the limbs with the knee in maximal extension is helpful for assessment of sagittal plane deformity if present


  • Radiographs are assessed for mechanical axis, joint angles (mechanical or anatomic), magnitude of deformity or length difference, localization of the apex of the deformity, and visualization of any planned correction (Figure 25.1)










Examination



  • A comprehensive physical examination should be performed, including neurologic assessment, Gait evaluation, and limb examination standing, supine, and prone for rotational and angular limb deformity as well as limb-length discrepancy. Presence of joint contractures should be noted, as these will impact radiographic assessment of limb-length differences


Positioning



  • Supine


  • Bump under ipsilateral hip to prevent leg from externally rotating


  • Leg elevated a few centimeters on folded sheets or blanket platform to raise above other lower limb for easier access to medial side


  • Nonsterile tourniquet applied to thigh (for use during approach to osteotomy but lowered before drilling bone to avoid thermal necrosis)


  • C-arm and fluoroscopic image intensifier should be placed on the opposite side of the patient as the operative limb (surgeon will need to place initial fine wire(s) from lateral to medial)


Surgical Approach

Osteotomy of the tibia is performed through a midline longitudinal incision overlying the metadiaphyseal crest of the tibia, approximately 4 to 5 cm in length. Osteotomy of the fibula is typically performed in the distal 1/3 of the fibula, and at least 8 to 10 cm above the tibiofibular syndesmosis through a 2 to 3 cm lateral longitudinal incision.


Technique in Steps

This procedure is performed under general anesthesia. Careful consideration should be given regarding use of regional anesthesia due to the potential risk of postoperative compartment syndrome and the need to intraoperatively monitor for nerve stimulation during placement of fine wires. Similarly, paralytic agents should be avoided (or should have worn off) when placing fine wires around the knee to monitor for peroneal nerve stimulation



  • Ring selection



    • Ring size can be preoperatively templated, based on the soft tissue shadow of the anteroposterior (AP) and lateral x-rays of the leg (Figure 25.2)


    • Appropriate size rings should be confirmed intraoperatively prior to placement to ensure that rings do not impinge on soft tissue around the full circumference of the leg (ring should remain at least 2 cm from the skin surface to account for postoperative swelling)


    • A two-thirds ring is typically chosen at the proximal tibia to allow knee flexion beyond 90° (due to posterior opening), and full rings are used in the tibial shaft and distal tibia


    • Proximal and distal rings can be different sizes


  • Fibula osteotomy



    • Osteotomy of the fibula is necessary to allow for appropriate tibial lengthening and deformity correction. For most proximal tibial osteotomies, the fibula osteotomy is distal to the tibial osteotomy in the middle to distal 1/3 of the bone. Osteotomy should be performed at least 8 to 10 cm above the syndesmosis








    • Osteotomy should be performed in an oblique plane. Orientation of this plane is important when rotational or angular correction is planned. For correction of external tibial torsion, the cut orientation is proximal-anterior to distal-posterior. For correction of internal tibial torsion, the obliquity should be proximal-posterior to distal-anterior (Figure 25.3)

    Steps



    • Longitudinal incision 2 to 3 cm in length overlying the course of the fibula


    • Blunt dissection onto lateral compartment is performed, paying close attention to avoid injury to either superficial peroneal or sural nerves (depending on relative anterior or posterior location of incision, respectively)


    • Fascia is opened, and peroneal musculature is retracted anteriorly. Fibula periosteum is exposed and incised longitudinally. Periosteum is elevated, and small blunt Hohmann retractors are placed in the subperiosteal plane anterior and posterior to the bone (adequate protection of the soft tissue is critical; as significant bleeding can occur from the interosseous veins or arteries if injured)


    • A 2.5 mm drill is utilized to make a series of drill holes laterally, which are fanned in the appropriate plane posteriorly, anteriorly, and medially


    • An osteotome is utilized to complete the cut


    • Mobility of the proximal and distal fragments must be confirmed by visualizing translation under fluoroscopy (Figure 25.4)


    • The wound is irrigated and closed in layers


  • Syndesmosis screw



    • In cases of limb-lengthening or significant limb deformity correction, fixation of the fibula proximally and distally is necessary. Proximal fixation is provided by initial fine wire through the
      fibula head attached to the proximal ring of the fixator. Distal fixation is through the syndesmosis screw












    • For most adolescent and adult patients, we prefer to use a single 4.5 mm cannulated screw through three cortices (for small children, smaller cannulated screws or fine wire attached to the distal ring can be utilized)

    Steps

Jun 9, 2022 | Posted by in Reconstructive surgery | Comments Off on Tibia Lengthening and Deformity Correction With a Multiplanar External Fixator
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