**10. Complications of distraction osteogenesis**

The complication associated with a DO include muscular contractures, subluxations, vascular and nerve lesions, premature or delayed consolidation, and even bone non-union. The placement of intramedullary pins near a nerve or large caliber blood vessel can lead to damage on those structures during the lengthening [1].

Neuromuscular lesions are rarely associated with lengthening phases unless they exceed 30% of the limb size [33, 82, 83]. Subluxations are associated with muscular contractures and can occur in substantially excessive lengthening. Premature consolidations can be prevented with an adequate DR and DRy. Delayed consolidations are multifactorial but are more commonly reported cases where an excessive DR was applied. Bone non-union is on its own associated to an infectious process. A strict radiographic protocol allows a control, assessment, and readjustment in order to avoid these complications [1].

One of the limitations of this technique is the long period necessary for the newly formed bone to mature, mineralize, and consolidate. The external fixators must be kept until the end of the consolidation period in order to confer the stability necessary to obtain better quality bone [3].

*Clinical Implementation of Bone Regeneration and Maintenance*

mesenchymal stem cells and osteoinductive signals [63, 64].

conditions should not be considered as favorable candidates [63].

After the tumor resection, BTO is similar to a conventional DO, a latency period

of 3 days is sufficient unless the dog is receiving chemotherapy treatment. In those cases, a longer latency period of up to 7 days should be applied. Afterwards, the distraction should consist on a DR of 1 mm/day and DRy of 2–4 times a day. Immediately after a chemotherapy session, distraction should be ceased for 3 days before being restarted. This waiting period can be eliminated if the patient shows signs of premature consolidation. Radiographic reassessment should be made every 10–14 days during bone transport and every 3–4 weeks after docking. Some animals may require higher DR to prevent premature consolidation, while other may require occasional "resting" period of 2–5 days. If the regenerated bone begins to be progressively thinning, ductile, and with "hourglass" shape in radiographs, it is

amputation [66–68].

an adaption of the DO technique, is used to preserve limb function after resection of large segmental bone defects. Briefly, after the tumor excision, an osteotomy is performed on the proximal bone segment, creating a distraction focus and resulting on a small portion of healthy bone which will act as the transport segment. Then using an external ring fixator, this segment is slowly distracted in the defect direction, creating regenerated tissue resulting in bone union and a bridged effect. The distraction should continue until 3 days after the segments touch in order to compress the distal healthy bone, turning it metabolically active, this process is called docking. Successful docking is achieved when the transport segment heals with the adjacent bone. It is possible to predict the timing of docking by measuring the distance between the two bones on radiographs and calculating the number of days required to achieve contact based upon the DR. The surgeon should consider grafting when the transport segment is approximately less than 0.5 cm from contact with the docking site. When owners strongly wish to avoid further surgery, autologous bone marrow graft, obtained from the patient, could be mixed with canine demineralized bone matrix (DBM) into the docking site, acting as a vehicle of

BTO surged as an alternative to cadaveric allograft bone transports, which was seen as the main limb salvage procedure in alternative to amputation; however, complications such as non-union, graft fracture, and infection are referred in the literature. One study reported that nearly one half of the patients develop infection may be associated with the lack of intrinsic blood supply surrounding the allograft and tumor resection area [65]. This high complication rate could lead to soft tissue lost, chronic pain, non-weight-bearing lameness, multiple surgeries, and even

The extent of the needed tissue resection can be planned based on detailed radiographs, scintigraphy, or ideally, a preoperative magnetic resonance imaging (MRI) which will be essential to help build the fixator frame, and assess the extent of the tumor involvement within the bone marrow, as it commonly exceeds the extent detected on radiographs. The surgeon should plan to excise at least 2 cm of bone proximal to the most proximal extent of tumor identified [63]. The patients with better outcome in DO upon oncologic surgery are those whose tumors are located in the distal radius or ulna, due to bigger pancarpal arthrodesis success [64]. The best candidates for limb salvage are those whose tumors involve less than 50% of the bone and have minimal soft tissue involvement. In theory, the extension of tumor treatable with this technique is limited to by the ability to achieve appropriate margins. There must be at least enough bone remaining in the proximal radius to create a transport segment and to place three wires above the transport segment. Dogs with infected allografts after prior limb salvage surgery are suitable candidates for bone transport, unless they have had recent radiation therapy. Patients with pathologic fracture, multicentric neoplasia, metastasis or severe intercurrent health

**100**

During a femoral lengthening, the muscles inserted therein are responsible for the majority of the complication that may occur. The quadriceps, glutes, and abductors can influence the lengthening progression, and the tension exercised on the soft tissues causes pain, reduces the articular mobility, and deforms the regenerated bone column. To achieve a successful lengthening, it is imperative that one understands this concept and adjust the surgical technique and patient management to minimize its impact [5].

Stogov and collaborators showed, in dogs, that a high frequency (120 DRy) of 3 mm/day does not only produce viable bone, but also produce compensatory alterations to the muscle tissue that would prevent catabolic alterations on the anterior tibial muscle during a tibia elongation. These authors referred that a high frequency lengthening amount that does not exceed 15% of the initial tibial length, does not result in considerable damage to the anterior tibial muscle. Using a DR of 3 mm/day while increasing the DRy (180 automated distractions per day) can produce a consistent regenerated bone [84].

As mentioned before, the soft tissues are a limitation factor for the procedure [34, 82, 85]. Lengthening exceeding 20% the original bone measure is reported to damage peripheral nerves, muscular, and tendon structures. Thus, physical rehabilitation during the procedures could decrease the severity of the muscular contractures and prevents articular diseases. The double-level or bi-level lengthening, which consist on creating two fracture focus and therefore two focus of bone distraction can reduce by half the distraction period duration, dispersing the distraction forces applied at the soft tissues and reducing the degenerative effects [1]. The correction of biapical radial deformities in dogs has been described with success using bi-level hinged external fixators as posterior distraction [86].

Taking into consideration that the DO can also occur along a transverse axis, perpendicular to the longitudinal bone axis, it is also possible to perform a widening of bone tissue. Some authors have already successfully preformed bone transports, in order to correct a defect on a long bone they perform a DO on the contralateral bone and use the regenerated tissue as graft to the affected limb. It has been performed in the same bone tibia-tibia but also in ipsilateral ulnar and radial bone transports, tibial-humeral and fibular-tibial, and this procedure is also performed in human medicine [87].

It is worth referring a recent study in humans, which applied a multidirectional DO device, a new technique with the goal of correcting cranial deformities in children [88].
