PEDIATRIC/CRANIOFACIAL Documentation of the Incidents Associated with Mandibular Distraction: Introduction of a New Stratification System Pradip R. Shetye, D.D.S., M.D.S. Stephen M. Warren, M.D. Daniel Brown, M.D. Judah S. Garfinkle, D.M.D. Barry H. Grayson, D.D.S. Joseph G. McCarthy, M.D. New York, N.Y.
Background: This article aims to assess the spectrum of unfavorable events or incidents encountered during mandibular distraction and to evaluate the difference in the incident rates among the following treatment groups: (1) native bone distraction using an external device, (2) native bone distraction using an internal device, and (3) grafted bone distraction using an external device. Methods: This retrospective study examined the records of 141 patients treated by mandibular distraction over a 16-year period. Of the total 141 patients, 56 underwent unilateral mandibular distraction and 85 underwent bilateral mandibular distraction, contributing to a total of 226 sided distraction procedures. The number of procedures performed on native bone using external devices was 149, versus 41 internal devices. There were 36 distractions performed on grafted bone with external devices. Incidents were broadly classified into three groups based on a severity index. A minor incident was one that resolved satisfactorily with minimal or no invasive intervention. A moderate incident was one that resolved satisfactorily with moderate clinical intervention. A major incident was one that did not resolve or could not be resolved with surgical intervention, and compromised treatment outcome. Results: The major incident rate was 5.31 percent (total of 226 distraction procedures). A higher rate of major incidents was observed when distracting grafted bone. The overall minor incident rate was 26.99 percent and the moderate incident rate was 20.35 percent. Conclusion: Mandibular distraction can be considered a safe and predictable procedure for lengthening/augmenting the mandible in patients with lower jaw deficiencies. (Plast. Reconstr. Surg. 123: 627, 2009.)
istraction osteogenesis has become a widely used technique to reconstruct the hypoplastic mandible since the report of McCarthy and colleagues in 1992.1 The technique has subsequently been applied to the maxilla and cranium to correct various craniofacial anomalies. Distraction osteogenesis has been established as the preferred technique in many clinical situations because of the relative safety of the procedure, reduced hospital stay, lower incidence of blood transfusion, elimination of the harvest of bone graft, and a concomitant expansion of the associated soft tissue.2 Over the years, the biology of the distraction zone has been studied extenFrom the Institute of Reconstructive Plastic Surgery, New York University Medical Center. Received for publication August 3, 2008; accepted August 12, 2008. Copyright ÂŠ2009 by the American Society of Plastic Surgeons DOI: 10.1097/PRS.0b013e3181956664
sively in the laboratory and the technique has been refined.3 These advances have been characterized by an improved surgical procedure and modifications of the distraction devices, including transformation from more bulky externally placed devices to small internally buried devices. As is true of all procedures, distraction osteogenesis is not without its incidents. Surgical incidents are not necessarily the result of an error in surgical technique or management.4 Several authors have reported the incident rates associated with mandibular distraction. These reports vary from a rate as low as 2.5 percent to as high as 35 percent.2,5,6 The large variation in the reporting of
Disclosure: None of the authors has a financial interest to disclose in relation to the content of this article.
Plastic and Reconstructive Surgery • February 2009 incident rate is primarily attributable to the often ambiguous and sometimes arbitrary definition of surgical complications/incidents as traditionally reported by surgeons. During any surgical procedure and the associated perioperative period, the surgeon may encounter various events that range in severity from cardiac arrest to a localized suture infection. The management (and outcome) of such clinical problems can differ widely. Some of the unintended events may not lead to adverse outcomes but do merit documentation to be able to assess the overall potential risk of the surgical procedure and the associated increase in health care expenses. In addition, one report5 was based on a survey of many authors, an inaccurate method of documenting perioperative incidents. Several authors have endeavored to classify surgical incidents based on different grading systems.7–9 Many of the reported classification system are elaborate and complex and ultimately difficult to apply in the day-to-day clinical setting. In this article, the authors aim to assess the spectrum of incidents encountered during mandibular distraction and to evaluate the difference in the incident rates between distraction osteogenesis in the following treatment subgroups: (1) native mandibular bone distraction using an external device, (2) native bone distraction using an internal device, and (3) grafted bone distraction using an external device. This article also addresses the management of these problems and precautions that are necessary to prevent them.
Table 1. Diagnoses of the 141 Patients Included in the Study Diagnoses Craniofacial microsomia Treacher Collins syndrome Robin sequence Nager syndrome Developmental micrognathia TMJ ankylosis Femoral hypoplasia Cerebrocostomandibular syndrome Tumor Total
No. of Patients 77 22 16 4 13 4 3 1 1 141
TMJ, temporomandibular joint.
After surgical osteotomy and fixation of the device, there was a latency period of 6 days (0 to 7 days). The device was activated at a rate of 1 mm/day: 0.5 mm in the morning and 0.5 mm in the evening. The patient’s parents were instructed to activate the device and the activation was supervised periodically. With the multiguided device, the force vector angulation was changed to achieve the desired direction when necessary. The mean activation period was 30.2 days, with a mean distraction length of 25.45 mm (as calibrated on the device). Activation of the device was terminated when the clinical objective was achieved.2 The mean consolidation period of 60.4 days (range, 45 to 75 days) was followed by device removal. The progress of distraction was evaluated with periodic radiographs. All incidents encountered during the distraction process were documented in the patient’s record.
PATIENTS AND METHODS This retrospective study examined records of patients treated for mandibular distraction at the New York University Institute of Reconstructive Plastic Surgery over a 16-year period (1989 to 2005). All patients with unilateral and bilateral mandibular distraction were included, but patients treated for mandibular midline and transport distraction were excluded from this study. One hundred forty-one patients formed the sample for this study; there were 81 men and 60 women. The mean age was 6.3 years, with a range of 0.1 years to 41.9 years. The diagnoses of all patients were recorded (Table 1 ). Of the total 141 patients, 56 underwent unilateral mandibular distraction and 85 underwent bilateral mandibular distraction, for a total of 226 sided (56 ⫹ 85 ⫻ 2) distraction procedures. The number of procedures that were performed on native bone using external devices was 149 versus 41 with internal devices. There were 36 distractions performed on grafted bone (external devices only).
Stratification of Surgical Incidents: The Severity Scale We designed a stratification system, based on the severity of the event, to classify incidents observed during any surgical intervention and the associated perioperative period. The three broad categories of incidents are minor, moderate, and major. The key to understanding and using this stratification scheme is based on the basic terminology. Incidents are defined as an unintended event, however trivial or commonplace, that could have harmed or did harm a patient.10 An adverse outcome is defined as an unintended and unwanted event or state occurring during or following medical care, that is so harmful to a patient’s health that (adjustment of) treatment is required or that permanent damage results.11 The perioperative period is defined as that interval period beginning at the commencement of the surgical procedure and ending up to 60 days postoperatively (extended in this study to the conclusion of the con-
Volume 123, Number 2 â€˘ A New Stratified Reporting System solidation period or removal of the distraction device).We propose the following stratification method (Table 2) to report all incidents encountered during and following any surgical procedure. Minor Incident A minor incident is defined as a perioperative event that does not lead to an adverse outcome and can be resolved with or without noninvasive therapy. An example of such an event could be the resulting difficulty in opening the mouth during the mandibular distraction procedure or a temporary mechanical problem faced in the activation of the device. Both problems will not lead to an adverse outcome and can be resolved without invasive intervention. Moderate Incident A moderate incident is defined as a perioperative event that could result in an adverse outcome but can be resolved with invasive therapy or return to the operating room. An example of such an incident would be a mechanical failure of a distraction device during activation. To avoid compromising the clinical outcome, the patient should be returned to the operating room to replace the device. Major Incident A major incident is defined as a perioperative event that results in an adverse outcome and did not resolve or could not be resolved with invasive therapy. An example of such a incident would be premature consolidation of the distraction bony segments, fibrous nonunion, or nerve injury (e.g., neurotmesis). All of these incidents have a significant impact on the patients. The severity scale can be applied easily to any surgical procedure. The potential qualifications for admission to each category are listed in Table 3.
RESULTS The rate of minor incidents, moderate incidents, and major incidents observed in all the
Table 3. Subcategories of Minor, Moderate, and Major Incidents I. Minor incident A. Hardware related 1. Difficulty in device activation 2. Device backup 3. Improper vector 4. Inadequate device length B. Hard- and soft-tissue related 1. Pain at bony generate site 2. Hypertrophic scar 3. Cyst caused by pins 4. Psychological problem 5. Neurapraxia 6. Infection 7. Trismus during treatment or device removal 8. Parotid gland injury II. Moderate incident A. Hardware related 1. Inadequate device length 2. Improper vector 3. Device backup 4. Unstable device 5. Unstable device following trauma 6. Device deformation or breakage B. Hard- and soft-tissue related 1. Premature ossification 2. Scar requiring revision III. Major incident A. Hardware related 1. Unstable device 2. Device deformation breakage B. Hard- and soft-tissue related 1. Tooth follicle perforation and dislodgement 2. Premature consolidation 3. Fibrous union 4. TMJ ankylosis and degenerative changes 5. Fracture 6. Nerve injury (e.g., neurotmesis) C. Medical 1. Systemic infection/sepsis 2. Embolism 3. Cardiac event 4. Anoxia/airway problem 5. Death TMJ, temporomandibular joint.
categories of mandibular distraction is presented in Table 4. Minor incidents were observed in 26.99 percent of all procedures, and moderate incidents were reported in 20.35 percent of distraction procedures. The overall rate of major incidents was
Table 2. Perioperative* Incident Stratification Event Minor incident Moderate incident Major incident
Definitions Event that does not lead to adverse outcomes and can be resolved with or without noninvasive therapy Event that could result in an adverse outcome but can be resolved with invasive therapy Event that results in an adverse outcome and did not or could not be resolved with invasive therapy
Examples Pin-site infection, trismus, hypertrophic scarring Premature ossification, device breakage, improper vector Tooth injury, fibrous nonunion, device failure
*The perioperative period extends from the date of surgical procedure until removal of device.
Plastic and Reconstructive Surgery • February 2009 Table 4. Number and Percentage of Incidents by Severity Index Type of Events (n ⴝ 226) No incidents Minor incidents Moderate incidents Major incidents
No. (%) 107 (47.3) 61 (26.99) 46 (20.35) 12 (5.31)
5.31 percent. Table 5 lists the types of events documented for the three subgroups of mandibular distraction. Figures 1 through 3 depict the percentage of minor, moderate, and major incidents.
DISCUSSION It has been 18 years since the distraction technique was first applied to reconstruct a human mandible. Over the intervening years, there has been significant development and refinement of the distraction process, making it one of the most widely used and effective reconstructive techniques in craniofacial surgery. It has proven
uniquely useful in reconstructing the hypoplastic mandible, especially in growing children. Because of our long-term and ongoing clinical experience, we decided to present this review of our perioperative incidents as a part of a clinical outcome study. A comprehensive literature review on the reporting of surgical incidents demonstrated the lack of a suitable classification system that could encompass all of the events encountered during the associated perioperative period. Most reports ignore minor events/incidents and note only severe complications. This has led to a generalized underreporting of incidents that could greatly affect both the patient and clinician experience with the procedure and ultimate clinical outcome.12 We believe that it is vitally important to report all minor and moderate incidents encountered during the perioperative period for all surgical procedures. The reporting of minor and moderate incidents helps the clinician to be aware of all possible events and to focus on improving the
Table 5. Percentage of Minor, Moderate, and Major Incidents in Three Mandibular Distraction Groups
Minor incident Difficulty in device activation Device backup Improper vector Inadequate device length Pain at bony regenerate site Hypertrophic scar Cyst caused by pins Psychological problem Neurapraxia (inferior alveolar nerve) Infection Trismus during treatment or device removal Parotid gland injury Moderate incident§ Improper vector Device backup Loose device Loose device following trauma Device deformation breakage Premature ossification Scar requiring revision Major incident兩兩 Unstable device Tooth follicle or damaged teeth Premature consolidation Fibrous union TMJ ankylosis and degenerative changes Fracture
Native Bone External Devices (n ⴝ 95)* (%)
Native Bone Internal Devices (n ⴝ 25)† (%)
Bone Graft External Devices (n ⴝ 21)‡ (%)
2.68 0.00 0.67 0.67 4.70 0.67 0.67 0.00 0.00 8.05 0.00 1.34
4.88 14.63 0.00 4.88 9.76 0.00 0.00 2.44 2.44 7.32 9.76 2.44
8.33 0.00 0.00 0.00 11.11 0.00 0.00 0.00 0.00 8.33 0.00 0.00
2.01 0.67 6.71 4.70 0.67 2.68 2.01
2.44 4.88 2.44 0.00 2.44 2.44 0.00
0.00 0.00 11.11 11.11 5.56 0.00 2.78
0.67 0.67 0.67 0.00 1.34 0.67
0.00 0.00 0.00 2.44 0.00 0.00
5.56 0.00 2.78 0.00 5.56 0.00
TMJ, temporomandibular joint. *Distraction, n ⫽ 149. †Distraction, n ⫽ 41. ‡Distraction, n ⫽ 36. §Inadequate device length, a moderate incident, did not occur with any of the procedures. 兩兩Device deformation breakage, nerve injury (e.g., neurotmesis), medical infection, embolism, cardiac event, anoxia/airway problems, and death did not occur with any of the procedures.
Volume 123, Number 2 â€˘ A New Stratified Reporting System
Fig. 1. Percentage of minor incidents observed in three mandibular distraction groups.
Fig. 2. Percentage of moderate incidents observed in three mandibular distraction groups.
Plastic and Reconstructive Surgery â€˘ February 2009
Fig. 3. Percentage of major incidents observed in three mandibular distraction groups.
technique to minimize the occurrence of such events. The absence of a classification system that addresses and reports minor and moderate incidents prompted us to develop a new stratified reporting system, the severity scale. We have used the new stratification system to report the incidents rates associated with mandibular distraction. Minor Incidents The incidences of minor incidents observed in all three patient subgroups are listed in Table 5 and Figure 1. In patients treated with internal distraction devices, higher incidences of distraction device backup (14.63 percent) and trismus (9.76 percent) were reported. The device backup or reverse slippage during activation was the most common problem associated with the first generation of buried or internal distraction devices. This problem could be attributed to the sleeker device design that does not withstand the reciprocal rebound forces of soft tissue and the muscle pull as the device is being activated. These findings have also been well documented when using palatal expanders, such as those used routinely in orthodontic therapy to correct a narrow maxillary dentoalveolar arch. Device backup could lead to a
failure of the osteotomized segments to move apart with subsequent premature consolidation. It is critical to monitor the activation of the device and to confirm activation by taking serial radiographs (not a simple undertaking in the young patient) to ensure that the bony segments are being distracted. This problem can be compensated for by adding additional turns when activating the device. Recognition of this internal distraction device problem, however, has resulted in the addition of a ratchet mechanism in the second generation of buried devices to prevent backing up. A high incidence of trismus was also evident with the internal distraction device. We speculate that these patients had trismus secondary to the distraction device interfering with temporomandibular joint function. From previous work, we know that the condyle and disk undergo reversible changes when loaded during distraction.13 Because the internal distraction devices can deliver distraction vectors as steep as 70 degrees relative to the maxillary occlusal plane angle, the internal device may drive the condyle into the temporomandibular joint with greater force than the external distraction devices, causing more trismus.14 This hypothesis, however, remains to be proven.
Volume 123, Number 2 • A New Stratified Reporting System In the group of patients undergoing grafted bone distraction, pain at the bony generate site (11.11 percent) and difficultly in activation (8.33 percent) were common problems encountered. The rate of infections was similar in all three groups of patients. The most common site of infection was the pin site. Inadequate device length occurred in nearly 5 percent of patients treated with an internal distraction device. Since we treated growing children, we included an overcorrection in our treatment plan. Even when we achieved our desired overcorrection, nearly all patients will require either a second distraction osteogenesis or a mandibular orthognathic procedure at skeletal maturity to achieve centric occlusion. Therefore, if our treatment plan estimated 10 mm of overcorrection, but the device length limited us to 7 mm, we would classify this as “inadequate device length”—a minor incident. It is important to note that we have also listed inadequate device length under the moderate incident category, even though this event never occurred. How could inadequate device length be categorized as a moderate incident? If, for example, we estimated that 10 mm of overcorrection would achieve satisfactory retroglossal space for tracheostomy decannulation following distraction but we achieved only 7 mm and the tracheostomy could not be removed, we would classify this as a moderate incident because of inadequate device length and perform a second procedure to obtained the desired advancement and remove the tracheostomy. This did not occur in the 226 distraction procedures reported here. Moderate Incidents The incidence of moderate events reported in all three of the patient groups was 20.35 percent (Table 5). Improper vector occurred in 2 percent of patients treated with external devices, and improper vector selection occurred in 2.44 percent of patients treated with internal semiburied devices. We hypothesize that improper vector trajectory occurred in patients treated with an external distraction device because the muscles of mastication prevented the mandible from responding to the change in vector direction. For example, if the patient had a large preexisting anterior open bite and little masseter function, as the distracted mandible moved anteriorly, the tight strap muscles and absence of masseter activity prevented the mandible from following the external distraction device vector change as we attempted to close the
anterior open-bite. In contrast, the vector of mandibular trajectory is fixed once the internal semiburied devices is placed and has been described mathematically by Dec et al. and Vendittelli et al.14,15 Therefore, inaccuracies in internal device vector may be the result of inaccurate vector selection. A higher incidence of external device instability was observed in the grafted bone group (11.11 percent) compared with the native bone distraction group (6.71 percent). The distraction of grafted bone presents challenges, as the bone varies in volume and density when compared with the native bone of the mandible. Inadequate retention of the pins in the grafted bony segments was the main problem. Because of small bone volume and inherent instability of the pins when placed in grafted bone, alternate methods of anchorage must be explored. Dislodgment of external devices because of trauma was also reported to be higher in grafted bone (11.11 percent) when compared with native bone (4.70 percent). Projection of the external device makes it prone to trauma, especially in children. Most traumas occurred as a result of rough play. A loose device at the end of the consolidation period does not pose any threat, but device loosening during the activation phase necessitates returning the patient to the operating room for reapplication of the device. Major Incident The major incident rate was 5.31 percent. In grafted bone, loosening of distraction devices and temporomandibular joint ankylosis each had the highest major incident rate (5.56 percent), followed by premature consolidation (2.78 percent). Temporomandibular joint ankylosis is attributable primarily to a lack of adequate cartilaginous interface between the grafted bone and the reconstructed glenoid fossa. The compressive forces resulting from the distraction technique lead to a bone-to-bone contact in the area of the reconstructed temporomandibular joint space, resulting in bony fusion. In patients who had native bone distraction by internal devices, fibrous union was the major incident (2.44 percent). This may be attributed to device instability or internal device backup.
CONCLUSIONS Mandibular distraction osteogenesis can be considered a safe and predictable procedure for lengthening the mandible in patients with cranio-
Plastic and Reconstructive Surgery • February 2009 facial anomalies. Grafted bone has a higher rate of major incidents than distraction of native bone. Internal buried devices have a higher rate of minor events but a lower rate of major incidents compared with external devices. The newly stratified reporting system, the severity scale, is a simple and efficient method of documenting all of the incidents observed during mandibular distraction. Because of stratification, the incidents having a negative impact on clinical outcome can be easily identified. In addition to reporting major incidents, documenting minor and moderate incidents helps the clinician to be aware of all possible events that can occur during distraction, and the clinician can then focus on improving the technique to minimize the occurrence of such events. This system of classification can be modified easily and adapted to any surgical procedure; it should be particularly helpful in the development of surgical outcome studies. Joseph G. McCarthy, M.D. Institute of Reconstructive Plastic Surgery New York University Medical Center 560 First Avenue New York, N.Y. 10016 firstname.lastname@example.org
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