INTRODUCTION
Critical size tibial bone defects are a difficult problem frequently encountered in orthopaedic trauma and limb reconstruction situations. These defects can be caused by a multitude of conditions including bone loss from trauma and bone resection secondary to tumor or infection. Numerous treatment algorithms for dealing with these large segment bone defects have been reviewed in the supplement and the work horse for these being bone transport by a circular ring fixator.1–4 5
CASE 1
A 28-year-old man with a medical history of psoriasis and hypothyroidism was involved in a motor vehicle accident in which he sustained a type III-A open tibia fracture. He was treated in an outside hospital with irrigation and debridement with application of an external fixator. The patient subsequently returned to the operating room approximately 48 hours after presentation and underwent intramedullary nailing of his left tibia fracture. He subsequently developed a poor healing wound and was initially treated with a short course of intravenous antibiotics. A chronic draining sinus tract developed over a period of 4 months and then was referred for further evaluation and treatment. On referral, the patient was found to have a chronically infected nonunion of the left tibia with draining sinus tract over the anteromedial aspect of the lower leg. At this time, he underwent deep bone biopsy of the left tibia nonunion with radical debridement of the sinus tract as well as hardware removal and debridement of the nonviable bone with insertion of antibiotic intramedullary nail with intercalary antibiotic cement spacer. After debridement and antibiotic intramedullary nail placement, the patient underwent free flap coverage with anterolateral thigh free flap. He was treated with 6 weeks of intravenous antibiotic therapy for culture-positive methicillin-sensitive Staphylococcus aureus . After serial debridement and conclusion of the patients' antibiotic therapy, the patient was left with a diaphyseal segmental bone defect measuring 4 centimeters in length (Fig. 1 ).
FIGURE 1.: Anteroposterior and lateral x-rays of 4-cm defect with antibiotic intramedullary nail and intercalary antibiotic spacer.
Risks and benefits of surgical options for tibial defect reconstruction were discussed with the patient at length, including treatment with internal bone transport using a magnetic-powered bone transport nail (Precice Bone Transport Nail, NuVasive Specialize Orthopedics Inc, Aliso Viejo, CA). The patient was taken to the operating room where the pervious antibiotic-impregnated intramedullary nail was removed. A femoral distractor was placed to maintain length and alignment. The free flap was elevated, where heterotopic ossification was resected along with the intercalary antibiotic spacer at the bone defect site to prevent impedance of bone transport. At this time, the predetermined corticotomy site was identified, and an incision was made over the anterior cortex of the proximal metadiaphyseal region of the tibia distal to the tibial tubercle. The periosteum was incised vertically, and subperiosteal dissection was performed medially and laterally to protect the periosteum at the corticotomy site. A fresh 2.5-mm drill bit was used to score the predetermined corticotomy site (Fig. 2 ). Subsequently, a ball-tipped reamer was then placed in the medullary canal, and the canal was sequentially reamed to a 13.5-mm side cutting reamer as the desired nail diameter was an 11.5 mm bone transport nail. Before insertion of the intramedullary nail, the corticotomy was completed using an osteotome (Fig. 3 ). Placement of the Shantz pin into the bone transport segment was used to perform an osteoclasis maneuver assuring the corticotomy was completed. The bone transport nail was then inserted in the usual fashion with 3 proximal static interlocking screws drilled, measured, and placed followed by a proximal posterior blocking screw to prevent an apex anterior deformity of the proximal tibia during transport. Two statically placed distal interlocking screws were placed using the perfect circle technique. Subsequent to this, a single transport segment screw was drilled, measured, and placed from a medial to lateral direction. The external remote controller was used to test the nail intraoperatively to assure the transport section was working appropriately by transporting 1 mm checking under fluoroscopic image intensification.
FIGURE 2.: Intraoperative fluoroscopy showing subperiosteal retractors protecting the periosteum while drilling the corticotomy site.
FIGURE 3.: Intraoperative fluoroscopy during corticotomy completion with osteotome and vice grip assuring completion and freely mobile transport segment.
Postoperatively, the patient was limited to touch down weight-bearing after a latency period of 8 days. The patient began bone transport at 0.75 mm per day divided into 0.25 mm increments 3 times per day. Seven weeks after placement of the intramedullary bone transport nail, a docking procedure was performed. Before the docking site procedure, the patient had approximately 5 mm of transport until bone contact at the docking site. The patient returned to the operating room for free flap was elevation with the nonunion ends at the docking site decorticated using a high-speed bur with placement of autologous anterior iliac crest bone graft at the docking site. The posterior cortex was closer than the anteromedial and lateral cortices at the docking site, and thus, this portion of the docking site was preferentially burred back to achieve good transverse cortical contact at the docking site during compression. A second locking screw was drilled, measured, and placed into the transport segment to improve stability during compression of the docking site. After decortication of the docking site, there was approximately 8 mm of transport remaining, and thus, the transport was programmed for this additional remaining segment with the addition of 2 mm to allow compression at the docking site by the nail (Fig. 4 ). At 7 months after intramedullary nail insertion, the patient had sufficient regenerate to be considered healed (Fig. 5 ).
FIGURE 4.: Progression of bone transport from initiation of transport (A), during transport before docking (B) with final docking, and early consolidation of regenerate (C).
FIGURE 5.: Healed regenerate with complete defect reconstruction.
CASE 2
An otherwise healthy 46-year-old man sustained a Gustilo–Anderson type IIIB diaphyseal tibia fracture with an associated distal fibula fracture in a high-speed jet-ski collision with gross freshwater contamination. At the index procedure, the fracture sites were debrided, and the tibia was stabilized with an external fixator, and a one-third tubular plate was used to fix the fibula. He underwent 3 additional debridements as the zone of injury evolved in the days after injury with extensive necrotic skin and soft tissue. The patient also developed intermittent fevers, and intraoperative wound cultures produced Aeromonas hydrophilia and Eggerthella lenta for which he received 6 weeks of oral ciprofloxacin and metronidazole based on sensitivity analysis. Thirteen days after the injury and at the fifth surgery, the wound no longer seemed grossly contaminated, and the tibia fracture was reduced and stabilized with a medullary nail from an infrapatellar approach (Fig. 6 ).
FIGURE 6.: A, Anteroposterior and (B) lateral radiographs after debridement of the infected fracture site and segmental fibula resection to facilitate soft-tissue coverage with free vascularized latissimus dorsi flap and local rotational flaps for anterior and posterior wounds, respectively.
After definitive stabilization, he received a free latissimus dorsi myocutaneous flap to cover an anterior soft-tissue defect and a rotational gastrocnemius myocutaneous flap for a posterior soft-tissue defect. After 6 months of persistent pain at the fracture site, a computed tomography scan confirmed nonunion. Subsequent debridement at the fracture site resulted in a segmental bone defect of 6 cm.
The patient was presented with multiple surgical options to address his large segmental bone defect and elected for internal bone transport using a magnetic-powered medullary transport nail (PRECICE Bone Transport nail, NuVasive Specialized Orthopedics Inc, Aliso Viejo, CA). Alignment of the proximal and distal segments was maintained with the use of an external fixator. The prior medullary nail was extracted, and the necrotic bone was excised with flat cuts at the anticipated docking sites. The planned corticotomy was created with multiple passes of a fresh drill bit before reaming the canal; this was completed just before inserting the nail. The medullary canal was over-reamed by 2 mm using a guide wire to maintain concentric reaming, and a 11.5-mm nail was passed down the canal. Interlocking screws were placed proximally, distally, and in the transport segment (Fig. 7 ). Finally, the function of the magnetic-powered external remote control (ERC) was tested intraoperatively.
FIGURE 7.: A, Anteroposterior and (B) lateral radiographs immediately after placement of the motorized medullary implant with a 5-cm defect.
Postoperatively, the patient was permitted weight-bearing as tolerated. The postoperative defect was 50 mm; after a 1-week latency, transport began at 0.75 mm day in 3 0.25-mm increments. Eleven weeks after placement of the nail, a docking procedure was performed. When the patient was approximately 1 cm away from docking, the bone ends were debrided of fibrous tissue, and the regenerate was injected with concentrated bone marrow aspirate. An additional 2 mm of compression was performed in the office after docking. At 9 months postoperative, the patient was determined to achieve union at the docking site and sufficient ossification of the regenerate to be considered healed (Fig. 8 ).
FIGURE 8.: A, Anteroposterior and (B) lateral radiographs 1 year postoperatively from the bone transport procedure.
SURGICAL TECHNIQUE
Patient Selection
Patient selection is critical to the success of intramedullary bone transportation. Critical factors such as location of the defect, size of defect, soft-tissue envelope, angular and rotational deformities, and patient compliance should be taken into consideration when selecting a patient as a candidate for intramedullary bone transport. Critical-sized bone defects greater than 4 cm in length should be considered for reconstruction by distraction osteogenesis . A healthy robust soft-tissue envelope often requiring rotational or free flap coverage is paramount to the success of intramedullary bone transport. Finally, the ability of the patient to comply with a complex reconstruction process requires the ability to adhere to the weight-bearing precautions and being able to perform serial applications of the external remote controller to drive the bone transport process.
Preoperative Planning
Preoperative evaluation begins with high-quality calibrated radiographs to allow accurate measurement of preoperative bone defects and angular deformities. Standing hip to ankle alignment films with full-length anteroposterior and lateral calibrated radiographs of the tibia are required for adequate preoperative planning. Angular deformities can be evaluated on the radiographs and should be supplemented with a good physical examination for evaluation of any rotational deformities that may need to be addressed at the time of bone transport. In addition, a thorough physical examination evaluating the neurovascular status of the patient is important as many patients with large segmental defects may have preoperative deficits that should be documented before proceeding with bone transport. Physical examination will reveal any preoperative soft-tissue coverage issues that may require plastic and reconstructive surgical evaluation as well as help with planning for any needed rotational or free flap elevation during the surgical procedure.
Calibrated radiographs will allow the determination of the preoperative defect length, which should be measured to assist with surgical planning. Pre-existing implants such as prior intramedullary nails should also be evaluated as this may affect the desired bone transport nail diameter selected for reconstruction. Other pre-existing implants, including plates, screws, or prior knee ligament reconstruction implants, should also be reviewed for the need for possible removal during the reconstructive process. Once the medullary canal diameter and pre-existing intramedullary nail diameters are calculated, the desired diameter of the bone transport nail may then be selected. Next, the length of the bone defect should be evaluated as well as desired stroke length (length of transport that the bone transport nail is able to accomplish during a cycle). Stroke lengths vary from 60 to 100 mm depending on desired length of the nail.
Once the appropriate diameter and length of nail as well as length of transport has been determined, the appropriate corticotomy site should be evaluated. Corticotomy sites should be planned whenever possible in metaphyseal or metadiaphyseal regions because these areas have better blood supply and regenerative capacity. A more diaphyseal located corticotomy may necessitate a slower distraction rate. Furthermore, preoperative evaluation of patients' age, comorbidities, and prior bony and soft-tissue injuries should be considered as increased age, and associated comorbidities may degrade the patient's regenerative capacity. Patients with comorbidities may necessitate a slower rate of bone transport and a longer latency period after corticotomy to assure optimal regenerate formation.
Intraoperative Technique
Intraoperative technique is broken up into 5 distinct phases. Phases include maintenance of length and alignment with removal of pre-existing implants, developing corticotomy site and scoring the corticotomy site before reaming, reaming of the medullary canal, followed by completion of the corticotomy site with placement of the intramedullary nail and any needed blocking screws, and finally, intraoperative testing of the bone transport nail to assure transport mechanism is working.
Pre-existing implants may have to be removed before proceeding with reaming of the medullary canal depending on the size, location of the defect, and location of pre-existing hardware. Length and overall alignment should be maintained. External fixation, femoral distractor, or manual traction may be used to maintain length and alignment. Pre-existing external fixation or intramedullary nails should then be removed as needed. Any pre-existing implants from prior fixation or pre-existing knee ligament reconstruction implants that requires removal should be performed at this time as well.
The next step is to intraoperatively determine the appropriate corticotomy site based on preoperative planning. Preoperative planning makes every attempt to create a corticotomy site in a more metaphyseal or metadiaphyseal region if possible. Any free flap elevation should also be planned at this time. Sharp knife dissection is performed at the planned corticotomy site of the proximal tibia distal to the tibial tubercle. The authors' preferred method (J.W.S. and G.S.M.) is then to prepare the corticotomy site with multiple 2.5-mm drill holes to assure a transverse oriented corticotomy site. Once multiple drill holes have been performed preparing the corticotomy site attention may then be turned to intramedullary reaming.
The approach to the anterior knee should then be performed with the surgeons' preferred parapatellar or transpatellar tendon approach for intramedullary nailing. A guide wire should be used to ensure that the correct trajectory with start point just medial to the lateral tibial spine and parallel to the anterior tibial cortex is used. Once the entry portal is performed, a guide wire should then be placed in the medullary canal across the deformity with any antibiotic spacer removed before this step. A flexible reamer is used without a tourniquet during the reaming process to prevent thermal necrosis. The canal is reamed increasing in half millimeter increments until the canal is over-reamed 2 mm above the predetermined bone transport nail diameter.
Once intramedullary reaming has been completed, a sharp osteotome is then placed into the corticotomy site protecting the periosteum, and a wrench can then be used to torque the osteotome to complete the corticotomy. With the corticotomy completed, the intramedullary nail may then be inserted. Proximal interlocking screws are then placed through the proximal aiming device in the usual technique. Blocking screws may then be placed proximally and/or distally to prevent deformity during subsequent bone transport. The nail is then locked distally as well. The bone transport slot is identified, and 1 or 2 medial to lateral bone transport interlocking screws are then placed. Once the transport segment interlocking screw(s) are placed, then the ERC is positioned over the magnet, which is located in the distal aspect of the tibial nail. Intraoperative assessment of motor function is performed with attention focused at the corticotomy site with an intraoperative transport of 1 mm being performed. Alternatively, before nail overdistraction technique as described by Quinnan in this supplement can also be used to confirm nail function.
Postoperative Details
One of the most critical steps in postoperative planning is establishing when the patient must return to the operating room. Patients may require return for screw exchange if the intercalary slot is used; the ERC should be programmed accordingly and a surgical date booked to facilitate timely exchange. If the defect allows, use of the slot should be avoided.
Patients may also need to return to the operating room for docking site management. Many “personalized” docking site protocols exist; however, 2 main strategies are common and have been reviewed in this supplement. The authors' preference is to add graft at the time of docking site preparation. The transport should be uninterrupted or minimally interrupted by the docking site procedure. It is advantageous to program the ERC to stop at the time of desired prep (ie, set for 40 mm for a 50 mm defect). The patient must bring the ERC to the hospital for the procedure to have it reprogrammed for the additional transport and docking protocol.
Compression across the docking site will facilitate union. Achieving the desired amount of compression is nuanced and requires observation. Generally, deformation of the interlocking bolts of the transport segment suggests that sufficient compression has been achieved. With accurate measurement of the remaining defect at the time of docking prep/grafting, one can program the ERC for an additional 2–5 mm beyond the length of the defect. The surgeon should determine if this has resulted in deformation of the interlocking bolts; if not, an additional 1–2 mm of transport can be performed in the office until deformation has occurred. If compression is lost, additional transport can be performed in the office at subsequent visits.
Frequent office visits are mandatory during the transport phase to ensure adequate regenerate formation and progress. The authors' preference is a visit at 10–14 days postoperatively to begin the distraction phase and every 2 weeks thereafter during distraction. Additional visits may be necessary for screw exchange or docking prep.
Patients should receive physical therapy throughout the recovery period to maintain range of motion. Postoperative weight-bearing status is dependent on the size of the nail. When using the NuVasive partially threaded screws, the 10.0 mm nail has a maximum load of 11 kg (25 lb). The 11.5 and 13.0 mm nails have weight limits of 87 kg (190 lb) and 114 kg (250 lb), respectively. When using the NuVasive fully threaded screws, the 10.0 mm nail has a maximum load of 11 kg (25 lb). The 11.5 mm and 13.0 mm nails have weight limits of 57 kg (125 lb). The preoperative plan and ultimate weight-bearing status will be dependent on the patient's weight and ability to modulate weight-bearing.
DISCUSSION
Ring external fixator frames have been shown to be effective; however, they are cumbersome and are associated with a high risk (up to 100%) of pin site infection.4 distraction osteogenesis . However, it is imperative that deformity be corrected before implantation and prevented throughout transport with appropriate blocking screws.
Large segmental bone defects present significant challenges for the patient and surgeon, but many options are available. Further study is warranted to define indications for each technique. The best treatment plan can only be identified after thorough discussion with the patient to identify their goals and resources for postoperative recovery.
REFERENCES
1. El-Rosasy MA. Acute Shortening and re-lengthening in the management of bone and soft tissue loss in complicated fractures of the tibia. J Bone Joint Surg Br. 2007;89:80–88.
2. Schemitsch E. Size matters: defining critical in bone defect size!. J Orthop Trauma. 2017;31(suppl 5):S20–S22.
3. Nauth A, Schemitsch E, Norris B, et al. Critical-size bone defects: is there a consensus for diagnosis and treatment? J Orthop Trauma. 2018;32(suppl 1):S7–S11.
4. Kazmers N, Fragomen AT, Rozbruch R. Prevention of pin site infection in external fixation: a review of the literature. Strateg Trauma Limb Reconstr. 2016;11:75–85.
5. Sampaio FMB, Marcal LP, Reis DGD, et al. Clinical evaluation of patients submitted to osteogenic distraction in the lower limb at a university hospital. Rev Bras Orthop. 2016;51:521–526.
