The technique of limb lengthening as developed by llizarov encompasses 3 principles: gradual distraction, use of a ring fixator to produce symmetrical distraction force, and preservation of the endosteal blood supply by means of a low energy corticotomy.12-14 The principle of gradual distraction is universally accepted; the other 2 principles have been breached without compromising the results. Off axis unilateral fixators, such as the Orthofix (Orthofix SRL, Verona, Italy) and Wagner (Synthes USA, Paoli, PA) devices, have proved suitable for limb lengthenings as well.8,11,19 In addition, several reports of animal studies and a few case reports have indicated that destruction of the endosteal blood supply by placement of an intramedullary device is compatible with successful lengthening.2-4,10,11,15,16,20
Because the external fixation devices are often poorly tolerated by patients and because pin tract problems are common, the authors sought to develop a technique that would minimize the duration of external fixation. Lengthening was performed over an intramedullary nail that is statically locked when the desired length is achieved, thereby permitting early removal of external fixation. Reported here are the results of a study using goats to show the feasibility of this approach and an initial study of patients for whom the technique was used.
MATERIALS AND METHODS
Eight minigoats weighing 60 to 110 pounds were used. Each goat underwent osteotomy and lengthening of the tibia. In 4 goats, the tibial canal was reamed and an intramedullary nail was placed at the time of the initial surgery for lengthening. In the remaining 4 goats, lengthening was performed without disturbing the medullary canal.
Surgery was performed with the goats under general anesthesia. Through an anterolateral approach, a transverse osteotomy of the tibia was made at the midshaft level with use of a water cooled power saw. Two parallel Schanz transfixation pins were placed in the distal segment in the anterolateral plane. For goats in which a nail was to be inserted, the proximal tibia was exposed through a midline incision lateral to the patellar tendon. An inlet hole was created at the level of the tibial tuberosity, and the canal was reamed with a power reamer to a diameter of 5 mm. A solid stainless steel rod 5 mm in diameter by 10 cm in length was then inserted into the canal past the osteotomy site until it reached the distal Schanz pins. Two additional Schanz pins were placed in the proximal segment proximal to the intramedullary rod and parallel to the distal pins. Unilateral external fixator frame (Orthofix) with distraction apparatus was assembled and mounted on the 4 pins. The osteotomy gap was reduced and compression applied through the fixator, and the surgical wounds were closed.
Animals were caged separately for 1 week after surgery; thereafter, they were pastured together. Analgesic injections were given on the first 2 postoperative days for pain control. On postoperative day 3, distraction was initiated at a rate of 1 mm per day in 3 divided doses and continued to Day 22, for an expected lengthening of 2 cm. When the distraction was completed, all articulations on the fixator were tightened. Regular radiographs were taken biweekly. The external fixator remained in place until the animals were euthanized. One animal from each treatment group (nail or no nail) was euthanized at 2, 4, 8, or 12 weeks after completion of lengthening, at which time the tibiae were removed for mechanical testing.
The explanted tibiae (both the lengthened bone and the normal contralateral) were potted proximally and distally in methylmethacrylate and torqued to failure in internal rotation by means of a Frankel-Burstein apparatus driven by a stepper motor.6 The metal rod was left in the canal during testing. The rate of torsional loading was 100 ° per minute. After mechanical testing, the specimen was reassembled, fixed in 40% alcohol, dehydrated, and embedded in polymethyl-methacrylate. Transverse and longitudinal sections were cut and milled to a finished thickness of 50 μm. Sections were stained with either Villanueva stain or Toluidine blue or were used for contact microradiography.
From June 1992 to September 1993, 20 limb lengthening procedures involving use of conventional Ilizarov distraction techniques combined with intramedullary nailing were performed at the National Taiwan University Hospital in Taipei. The origins of the limb length deficiency were congenital (4 patients), sequelae of poliomyelitis (9 patients), trauma (6 patients), and osteomyelitis (1 patient). Of these 20 procedures, 15 involved a minimum followup of 1 year from the time of removal of the external fixator; these 15 are the subject of the current analysis. There were 11 male and 4 female patients with an average age of 27.4 years (range, 18-37 years). Lengthening was done on the tibia for 11 patients and on the femur for 4. Average preoperative length discrepancy was 5.4 cm (range, 3.2-8.8 cm) on the scanograms.
The primary surgery started with creation of a proximal inlet for insertion of a guide pin into the medullary canal. Antegrade reaming was done over the guide pin to enlarge the canal to a size 2 mm greater in diameter than the nail to be used. In all tibias, 9-mm Grosse-Kempf nails were used; in the femurs, 2 were 9 mm and 2 were 10 mm. After reaming, the bone was divided by a careful corticotomy while the guide pin remained in place. The nail was then driven into the canal until it reached the distal metaphysis, and the proximal end was locked with 2 cross locking screws. Crossed transfixation wires were then placed proximally and distally, with care taken to avoid the nail. Ilizarov ring frames were assembled to the wires and joined by 4 longitudinal distraction columns.
After surgery, the subjects were allowed to ambulate with partial weightbearing. After 1 week of rest, distraction was started at a rate of 1 mm per day in 4 divided doses on the eighth day; this was continued until the desired correction was reached. The second surgery took place within 1 month after completion of lengthening, when sufficient callus was seen on radiographs. It consisted of removal of the external fixation frame and cross locking of the distal holes of the intramedullary nail. To speed the progression of the callus, most patients (11) received supplementary autogenous marrow injection into the gap during the second procedure. Partial weightbearing continued and serial radiographs were taken to observe progression of healing. The level of weightbearing was increased accordingly in the following 3 to 6 months, and then full weightbearing was allowed. Autogenous bone grafting with slabs of cancellous bone from the iliac crest was further applied for 2 patients with delayed callus progression during their late course. The pretreatment and posttreatment function of knee motion in the femoral lengthening group and ankle motion in the tibial lengthening group were investigated. Consolidation index was estimated from the total period needed for full ossification of the distraction callus divided by the length gained for the limb.
All minigoats completed 2 cm of lengthening on 1 side of the limbs. Most of the goats suffered from pin tract drainage problems, especially in the proximal segment, but the drainage problems did not progress to bone infection. The last 2 goats were euthanized at 10 weeks instead of at the scheduled 12 weeks from the date of completion of lengthening. The animals could not bear full weight on the leg that had been operated on, even though their activity was unrestricted. (In a subsequent study, pin tract problems were eliminated with use of larger and more docile dairy goats and with medial rather than anterolateral placement of the external fixator.)
Two weeks after completion of lengthening, the gap remained radiolucent in the control goats and in the goats that had intramedullary nailing. At 4 weeks, radiodense callus was evident on radiographs in both groups in the posterior region on the opposite side of the external fixator (Fig 1). At this time, the volume and density of callus appeared to be greater in goats in which nails were not used compared with those with nails. The difference between the 2 groups became insignificant by 8 weeks after completion of lengthening. The callus began to expand toward the anterior side of the gap at this time (Fig 2). At 10 weeks, the entire gap was filled with callus, though its density was notably less than the opposite normal cortex. Radiolucent crack lines were observed in some of the regenerative callus (Fig 3).
Torsional testing of explanted tibiae was performed on the goats euthanized 4, 8, and 10 weeks after completion of lengthening. Energy to failure of the tibiae with intramedullary nails, normalized to the intact contralateral tibia, was 7.3% ± 0.3% (6.8%-7.6%) at 4 weeks, 24.4% ± 0.5% (23.8%-24.9%) at 8 weeks, and 33.8% ± 0.6% (33.2%-34.5%) at 10 weeks.
In histologic sections 2 weeks after completion of lengthening, the distraction gap was full of collagen fibers intermingled with some vascular channels corresponding to areas of radiolucency in the same site on the radiograph. At 4 weeks, bundles of bone trabeculae were evident within the fibrous network. Parallel trabeculae also were found contiguous to the cut ends of the bones. The collagen fibers and trabeculae were oriented parallel to the axis of distraction. At this time, less callus was evident in the tibiae with nails compared with those without nails. The activity of the callus progression was restricted primarily to the posterior portion of the gap early in the course (Fig 4). By 8 weeks, further maturation of the callus was evident and bridging of new bone trabeculae was present in the intermediate fibrous zone of the gap. At 10 weeks, the posterior callus continued to mature, demonstrating lamellar bone, haversian systems, and marrow elements. Simultaneously, bone formation was found to be expanding anteriorly in the gap.
Lengthening among the human subjects proceeded uneventfully. The procedure was terminated when the length of the operated limb equaled that of the opposite side. The average gain in length was 4.0 cm (range, 3.0-6.5 cm), which was far less than the discrepancy of 5.4 cm (range, 3.2-8.8 cm) measured from the scanograms. Because there was concern about potential delay in callus formation, the external devices were kept in place 1 month after completion of lengthening. When the fixator was shifted to a locked intramedullary nail, the radiographic sign of distraction callus was positive in most of the cases (13 of 15 subjects). For the next several months, new callus continued to increase in volume, progress in mineralization, and remodel into lamellar bone. The preference of callus initiation in the femurs was eccentric, as it was in tibial lengthening in the goat study, but was located in the medial site of the gap rather than in the posterior site. The location of callus initiation in the tibia was variable. Mostly, it was present in the posterior site but sometimes was found in the anterior aspect of the gap (Fig 5). By 6 months after completion of lengthening, most patients could bear full weight, although the distraction callus had not yet fully ossified. Within 1 year, 12 of the 15 subjects had fully consolidated bone filling the distraction gap (Fig 6); the remaining 3 had incomplete ossification, although they could perform activities of daily living. Two of the latter cases (1 femur and 1 tibia) accepted additional autogenous cancellous bone graftings and achieved full bony consolidation in an additional 6 months. The average consolidation index for the femur was 55 days per cm and 49 days per cm for the tibia. The average knee function in femur lengthenings at final followup was 118 ° (range, 90 °-150 °), compared with 138 ° (range, 110 °-150 °) before treatment, whereas the average ankle function in the tibial group was 28.5 ° (range, 0 °-70 °), compared with 39.5 ° (15 °-70 °) before the procedures. Two patients had pin tract drainage and 1 subsequently developed infection at the osteotomy site, which resolved with antibiotic treatment without interrupting the lengthening. All of the subjects tolerated the entire treatment course well and were satisfied with the results and the avoidance of prolonged embarrassment of the bulky external device.
Despite various technical difficulties and a limited number of subjects for the animal study, this lengthening model in goats showed the feasibility of successful distraction osteogenesis over a reamed intramedullary device. Because of the small sample size, the authors did not attempt to quantitate in detail the volume or strength of distraction callus between the groups treated with and without nails, but this study provides good background for the subsequent clinical trial. Other researchers have reported successful lengthening over a nonreamed intramedullary rod as well.2-4,20 Although nonreamed nails are accepted in the management of long bone fractures, particularly in the tibia, and also have been tried in clinical lengthening procedures,2,20 a reamed nail was used in the current series. Reaming allowed use of a larger, stronger nail and made lengthening smoother, without nail inpingement in the canal. It is also likely that as fully internalized intramedullary lengthening devices are developed, they will require reaming to accommodate the bulkiness of the driving mechanism.1,9,16,24 However, reaming of the bone canal may severely disrupt the endosteal vasculature.17 The ability of the bone to generate callus after reaming and insertion of a nail challenges 1 of Ilizarov's assertions, that is, that the medullary cavity must be disturbed as little as possible.12
Some clinical studies have shown that an osteotomy, which may interrupt the medullary circulation, is as effective as corticotomy in creating the initial division of the bone in lengthening.5,22 In their studies involving rabbits, Kojimoto et al18 showed that the medullary canal could be scraped out without adverse consequences but that periosteum was critical for formation of a regenerate callus. Delloye et al,7 in a dog study, found that plugging the medullary canal with cement after osteotomy seriously interfered with regeneration and reported that regeneration from the periosteum alone was insufficient. These apparently contradictory findings may reflect in part the high reconstitutive ability of the endosteal vasculature. Rhinelander21 noted that reconstitution of the medullary vasculature might be complete within 2 weeks after reaming. Medullary callus may contribute to regeneration despite reaming, whereas plugging the canal with cement would prevent this response.
With the use of Ilizarov's corticotomy technique and with preservation of the medullary tissues, distraction is begun the day after surgery.14 Rashke et al,20 who used nonreamed nails to lengthen the tibias of 4 patients, waited 5 to 10 days after osteotomy before initiating distraction. In the goats used in the present study, lengthening was initiated with a reamed nail after a 3-day delay. In human patients, however, the authors waited 7 days before initiating distraction. The waiting period varies according to the subjects and surgeons. These results suggest that distraction osteogenesis is possible after 3 days of rest in bone in which a nail has been placed for lengthening. This time interval may have allowed the medullary cavity to regain a significant blood supply by the time of distraction.23
Elasticity of the eccentrically placed fixation device in the goats used in the current study resulted in unequal loads around the distraction gap and may in part be responsible for the eccentric development of callus, which in all cases was initiated in the posterior region opposite the fixator. Enrichment of circulation in this region in which major blood vessels are located also may play an important role in the initiation of distraction callus. In the human subjects, the ring fixator provided coaxial symmetric forces, and callus initiation in the tibias occurred evenly throughout the gap. However, in the femurs it was initiated in the medial aspect of the gap. This may have been caused by the eccentric placement of fixation for the proximal femur in the ring fixator system. It also reflects the superior vascularity in the medial aspect of the thigh, which has major neurovascular structures that provide blood supply to the distraction gap in the early stages before regeneration of endosteal circulation.
The primary clinical motivation for these studies was to decrease the time that patients must endure external fixation, which they tolerate poorly. In this respect, the concept was successful; all fixators were removed within 30 days of lengthening. Although the consolidation index was slightly longer than in conventional lengthening with a simple external fixator, the patients experienced more rapid and unencumbered rehabilitation than would have been possible with the external fixators in place. The slight increase in duration of the initial surgery required to place the nail and the second surgery required to statically lock the nail are minimal disadvantages compared with the greatly facilitated rehabilitation permitted by early removal of external fixation. The pin tract problem is limited to the period in lengthening so that the the incidence of infection is reduced and function of the lengthened limb is comparable with function before treatment. The results of the animal study and those of the 15 patients indicate that reaming and nailing is compatible with successful lengthening at an acceptable rate. For the potential delay of the consolidation period in nailed bone, the external fixator was originally kept in place 1 month after the expected length had been gained. Considering the positive result in progression of the distraction callus, this 1 month prolongation appears unnecessary, which may further reduce the external fixation period.
The current study highlighted the healing potential of distraction callus in a reamed and nailed bone. The positive findings support the use of a similar technique involving conventional lengthening along with an interlocking nail in patients. Minimal complications and the short period of external fixation with this method are appreciated by patients. This study provides an improved technique for limb lengthening and proves that reaming and nailing are compatible with successful lengthening. Furthermore, it establishes a prerequisite for a fully internal lengthening device, that is, that reaming and nailing are necessary for such instrumentation.
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