Corrective Supracondylar Humeral Osteotomies Using the Small AO External Fixator

Traditional methods of correcting malunited distal humeral fractures in children involve complex wedge osteotomies held with pins or internal fixation devices. These require a large exposure and challenging fixation. We elected to perform simple transverse osteotomies, without wedges, using a lateral incision. These were maintained by the small AO external fixator. Between 1987 and 2004, five children with malunited distal humeral fractures were treated. Angular and rotational correction was obtained in each case. Bony union occurred at an average of 8 weeks. A simple osteotomy held by the small AO external fixator provides accurate correction, precise adjustability, and solid stability. J Pediatr Orthop B 15:194-197
c 2006 Lippincott Williams & Wilkins.

Introduction

The surgical correction of malunited distal humeral fractures in children is challenging and complex. Traditional methods require exact wedge resections [1-4]. The osteotomy is typically maintained with pin fixation [2,4] or with internal hardware [5-7]. Internal devices are usually removed surgically once osteotomy healing is complete. Pin fixation requires extended periods of casting to protect the osteotomy until bony union has occurred [2]. Loss of fixation with pins is a known complication [8,9].

We elected to perform osteotomies of the distal humerus through a limited lateral approach using a single transverse osteotomy. On the basis of our experience with the small AO external fixator in other locations [10- 15], we believed that this device would allow us to maintain an osteotomy with a rigid construct that is both precisely adjustable and light in weight. The stability of the small AO external fixator would permit immediate active range of motion. In addition, the fixator and pins can be removed in the office setting, avoiding a second operative procedure. We therefore selected the small AO external fixator to maintain osteotomies in the distal humerus.

Methods

Between 1987 and 2004, five children with malunited distal humeral fractures presented at our institution. The average age was 6 years (range: 4-10 years). There were four boys and one girl. The four boys presented with malunited supracondylar fractures. They demonstrated cubitus varus angulation measuring an average of 201 (range: 16-281) and internal rotation of the distal humerus. The girl presented with a lateral condyle fracture with cubitus valgus angulation of 331 and external rotation of the distal humerus. In each case, these deformities affected both function and cosmesis. Each child had an intact neurovascular examination at presentation.

Distal humeral osteotomy was performed after informed consent had been obtained. The child was placed supine with both upper extremities draped free. Proximal and distal pin clusters consisting of 2.5mm end-threaded AO Schanz pins were inserted before the osteotomy. The distal pin cluster consisted of two or three pins placed laterally, parallel to and 1 cm proximal to the distal humeral growth plate. The proximal pin cluster consisted of two or three pins placed laterally, in line with the humeral shaft (Fig. 1a).

A small longitudinal incision was made laterally, between the pin clusters. The distal humerus was exposed and the periosteum was elevated. A right-angle osteotomy was performed just above the distal pin cluster, using a drill and osteotome. This technique allowed a complete bony cut while protecting the ulnar nerve on the medial side (Fig. 1b).

Correction of the rotational deformity was addressed first. Angular deformity was then corrected by minimal distal fragment displacement, locking the proximal cortex into the distal medulla (Fig. 1c).

Stabilization of the osteotomy by the external fixator required connecting the proximal and distal pin clusters with at least three 4mm carbon fiber rods. The pins in each cluster were subsequently interconnected for additional stability (Fig. 2a and b). The elbow was then flexed and extended intraoperatively to confirm the stability of the osteotomy and to help locate and relieve pin tethering in the skin or fascia. Correction was assessed by intraoperative radiographic visualization and by comparison with the free draped contralateral arm, with particular attention to rotational alignment.

Postoperatively, pin sites were cleaned twice daily with a 50/50 solution of normal saline/hydrogen peroxide applied with a spray bottle. The pin sites were not manipulated. After 1 week, daily showering substituted for 1 daily pin care session. This protocol was taught to the patient's family before discharge. Half-dose cephalosporin (cephalexin, 25 mg/kg, divided three times daily) was given orally while the pins were in situ. This antibiotic protocol has been successful in avoiding pin tract infections in osteotomies elsewhere using the small AO external fixator [10-15] and was therefore continued in this series.

Physical therapy was started immediately. This protocol consisted of an active range of motion of elbow and forearm rotation. Isometric muscle strengthening exercises were also performed.

Results

Distal humeral osteotomies were successfully performed in all five children (Fig. 3a and b). Rotation and angulation matched the parameters of the uninjured contralateral extremity. No neurovascular deficits occurred in the immediate or extended postoperative period. The small AO external fixator was well-tolerated. A full range of motion was achieved in all patients while the pins were in situ. No superficial or deep pin tract infections occurred. Loss of fixation did not occur. The osteotomies healed at an average of 8 weeks. All pins were removed in the office setting.

At a mean follow-up of 12 years (range: 1-18 years), the correction was maintained in each child. No growth disturbances occurred. Avascular necrosis did not occur in any of the children. Full strength and range of motion was preserved, as compared with the contralateral extremity. The minor surgical scarring was considered acceptable by the patient in each case.

Discussion

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