Abstract
Internal distraction devices for severe midface hypoplasia are often criticized for their distraction at a single pivot point, resulting in “mid-face tipping,” a phenomenon which is in part related to the differential resistance of the soft tissues at orbital and maxillary levels. To address this deficiency, we present our early experience with an internal bi-level midface distraction system. Four patients underwent midface advancement with an internal bi-level distraction system. The specifics of design, application, distraction, and removal are detailed. Hospital records were reviewed to capture patient demographics, length of stay, OR times, and complications. Relevant cephalometry was performed pre- and post-operatively, and compared. In 2015, 4 patients with severe mid-face hypoplasia were treated with an internal bi-level mid-face distraction system. The mean age was 13.5 ± 1.7 years. The mean operative time was 269.7 ± 67.4 min. The mean LOS was 10 ± 7.4 days. The on-table distraction was 5 mm. Distraction subsequently proceeded at a variable rate of 0.5 to 1.0 mm daily with a maximal distraction of 20 and 30 mm at orbital and maxillary levels, respectively. Mean time to distractor removal was 11.2 ± 1.1 weeks. Device design allowed facile removal through minimally invasive incisions. Cephalometry was seen to progress towards age-matched norms. There were no major complications. Minor complications included breakage of the vertical component of the maxillary arm at the time of device removal in 1 patient. By allowing real-time adjustment at the orbital and maxillary levels to combat differential resistance, early experience with our device maximizes occlusal advancement without overcompensating orbital translation.
Introduction
The Le Fort III osteotomy has been applied to restore facial projection, rectify malocclusion, increase vertical facial dimension, rectify pathologic upper airway anatomy and correct significant exorbitism for select midface craniofacial dysostoses since 1967. 1 The interval 50 years has seen an increase in surgeon experience, procedural comfort, advances in pediatric anesthesia, and the advent of distraction osteogenesis (DO). 2
Since the introduction of DO of the midface by Cohen et al 3 in 1993, a number of internal and external distraction devices have been manufactured and trialed. There are 2 commercially available external halo devices (External Mid-face Distractor, manufactured by Synthes, Oberdorf, Switzerland and the Rigid External Distractor, manufactured by KLS Martin, Tuttlingen, Germany). The primary advantage of the external device is the ability to perform real-time modification of the vectors of force during distraction. Secondary benefits include the technical ease of device application and removal, as well as a decreased risk of unfavorable fracture patterns in areas of thin cortical zygomatic bone stock. The major d`dvantages are patient non-compliance related to the psychosocial stigma of the device as well as frame- and hardware-related complications such as pin loosening and pin site scarring.4,5
In an effort to improve patient compliance, a number of internal distraction devices have been developed. Until now, most have consisted of 2 parallel bone-anchored elements spanning either the temporal skull to lateral orbit, or zygoma to zygoma following osteotomy. 6 This design is often criticized for its distraction at a single pivot point with the inability to adjust the vector of force during the distraction phase. The consequent vector may result in a clockwise rotation of the entire midface during distraction, lending to an anteroinferior over-translation of the inferior orbital rims, hollow-appearing orbits with increased vertical dimension, and an under- or un-corrected class III malocclusion with a posterior open bite.7-9 Furthermore, such “midface tipping,” is a phenomenon not only influenced by a single non-modifiable distraction vector, but is at least in part owed to the differential resistance of the soft tissues at orbital and maxillary levels. Other groups have previously attempted to address this clockwise rotation of the midface during distraction by application of concomitant dental appliances. To this end, Francis et al developed a technique using orthodontic temporary anchorage devices (TADs) or microimplants to hold interarch Class III relationship elastics. A review of the technique revealed correction of malocclusion and improved midface projection without a significant increase in vertical orbital dimension when trialed in both cadavers and a series of 17 syndromic patients with severe midface hypoplasia undergoing monobloc or Le Fort III osteotomies. 10
In an effort to attain ideal cephalometric mid-face advancement in plane with the Frankfort horizontal vector and thus obviating the midface rotation associated with the application of current internal distraction devices following Le Fort III osteotomy, while simultaneously addressing the inherent differential soft tissue resistance at orbital and maxillary levels, we present our early experience with an internal bilevel midface distraction system. We show that the independently controlled, bilevel nature of our design allows real-time adjustment of distraction vectors and thereby serves to maximize occlusal advancement while obviating excessive orbital translation.
Materials and Methods
Four patients aged 11-15 underwent midface advancement by a single surgeon with a KLS Martin internal bilevel distraction system (KLS Martin Inc, #51-410-30-09) following Le Fort III osteotomy in 2015. Pre-operative virtual surgical planning (VSP) was utilized in all patients. The specifics of design, technical application and distraction are detailed. Hospital and clinic records were reviewed for patient demographics, length of stay (LOS), operative times, distraction rates, and major and minor complications. Post-operative computed tomography was performed in all patients following the consolidation phase and removal of the device. Analysis of the relevant cephalometric parameters was performed both pre- and post-distraction and ultimately compared for interval deltas and progression toward facial norms.
Device
Figures 1 and 2 illustrate device design in both conception and when affixed to a VSP model, respectively. The device is modular, with bilevel bone-anchoring elements at the lateral orbit and upper maxilla. Posteriorly, the device is fabricated with a 4 cm × 4 cm titanium cranial mesh for fixation to the temporal bone. A 51 mm (81 mm with activators at maximum distraction) horizontal rotary arm connects to the lateral orbital rim pivot serving as the upper or orbital level of the bilevel system. The lateral orbital rim pivot is designed as a basket and hook with 2 spikes on the posterior aspect of the pivot and 2 screw holes on the anterior aspect to stabilize the pivot at the orbital rim if desired. A second 37 mm (67mm with activators at maximum distraction) horizontal rotary arm lies directly inferior and parallel to the orbital arm of the device. This arm terminates in an upper spindle through which a 55 mm vertical bar slides when introduced from an oral approach. A 1.0 mm profile 12-hole maxillary plate is attached to a fixed lower spindle. Together, the latter serves as the lower or maxillary level of the bilevel device. Each of the individual rotary arms is capped posteriorly at the temporal level with a male hex, which can be independently activated by a standard patient screwdriver. Maximal distraction of the device at both orbital and maxillary levels is 30 mm.
Bi-level mid-face distractor design and conception.
Modular distractor design.
The device design allows for easy assemblage and ultimate removal. The orbital component is affixed following exposure of bony landmarks via a traditional bicoronal incision. The maxillary component is attached to the orbital arm via an intraoral approach. Following the consolidation phase, 2 design features allow for facile removal of the bilevel hardware: (1) the simple basket and hook design of the lateral orbital pivot (as opposed to screw fixation) and (2) an access arm that remains in the mouth allowing 1 to simply turn and activate the vertical bar through the upper spindle until detached. These modifications allow the surgeon to make only limited access incisions in the temporal and buccal areas at the time of device removal.
Technique
Pre-operative virtual surgical planning was performed in all patients (3D Systems, Littleton, CO). Le Fort III osteotomies were performed following exposure of relevant anatomic landmarks via a bicoronal approach. The maxilla was exposed via bilateral gingivobuccal incisions. The devices were anchored to the temporal bones proximally via the cranial mesh and distally to 1 of 2 separate landing zones. The first is the lateral orbit (illustrated in Figure 3a with 5 mm of intraoperative advancement) and the second is the upper maxilla (Figure 3b). Maxillary plates were placed above the level of unerupted dentition. Orbital level hardware was fixed prior to the maxillary hardware such that the upper spindle was in place to receive the maxillary arm once delivered via the intraoral approach. A latency interval of 48 h was utilized. Independent distraction at both the orbital and maxillary levels was initiated and adjusted as needed based on aesthetic and occlusal relationships. In general, the majority of the advancement was completed at the maxillary level, where most of the soft tissue resistance is typically found, while more minimal distraction is performed at the orbital level to prevent an exaggerated correction. The rate of distraction ranged from 0.5 to 1 mm daily. Following the completion of distraction, a minimum of 8 weeks’ consolidation was allowed.
Device application in vivo. The device was bone anchored to the temporal bone proximally and distally to 2 separate landing zones: (a) the lateral orbit as illustrated here with 5 mm of intraoperative distraction and (b) the maxillary antrum where the plates are designed to be placed above the level of unerupted dentition.
Results
In 2015, 4 patients with class III skeletal relationships and severe midface hypoplasia were treated with an internal bilevel mid-face distraction system. Two patients were syndromic (Apert). The mean age was 13.5 ± 1.7 years. The mean operative time was 269.7 ± 67.4 min. The mean LOS was 10 ± 7.4 days, which was prolonged due to a single patient who developed post-operative ventilator-associated pneumonia. The on-table intraoperative distraction was 5 mm. Distraction proceeded at a variable rate of 0.5 to 1.0 mm daily with a maximal distraction of 20 mm at the orbital level and 30 mm at the maxillary level. Mean time to distractor removal was 11.2 ± 1.1 weeks. Cephalometric analysis was performed in both pre- and post- distraction intervals utilizing CT imaging, and parameters were compared to age-matched norms (Table 1).
Cephalometric Analysis.
Interval cephalometric deltas in SNA and ANB illustrate that the advancement was successful, while the parameter of primary interest, the occlusal plane to Frankfort Horizontal angle as a measure of mid-face pitch, trends towards normalization when compared to age-matched controls.
There were no major complications. Minor complications included an unfavorable fracture at the lateral buttress in 1 patient at the time of osteotomy, and a second patient with over-distraction of the maxillary arm, which was successfully compensated for in the clinic setting. There were no instances of early relapse (<3 months) in any of the patients following consolidation and device removal. Pre- and post-operative results photographs are shown in Figures 4 to 6.
(a) A 14 years old female, Apert’s syndrome and classic stigmata of mid-face hypoplasia (pre-op views) and (b) post-operative frontal, lateral and occlusive views following distraction.
(a) A 12 years old female with severe mid-face hypoplasia (pre-op) and (b) post-operative views following distraction.
(a) A 14 years old male, Apert’s syndrome and classic stigmata of mid-face hypoplasia (pre-op views) and (b) post-operative views following distraction.
Discussion
Distraction osteogenesis has revolutionized treatment of patients with severe syndromic and nonsyndromic midface hypoplasia who, due to their symptom profiles, often require midface advancement prior to skeletal maturity. This may be timed from the first few years of life through adolescence for those patients with absolute indications for intervention such as obstructive sleep apnea or those with a significant risk of exorbitism-related corneal complications.11-13 With an increase in specialized training, advances in anesthesia, and a familiarity with distraction hardware for cranial vault and mandibular pathologies, the last decade has seen an rapid increase in the utility of DO for aesthetic improvement in adolescents and teenagers who suffer the significant psychosocial burden of craniofacial dysmorphism at school-age. Furthermore, with evidence in the literature supporting decreased operative times, intraoperative blood loss, post-operative pain and LOS as well the potential to decrease the number of secondary procedures required after skeletal maturity, craniofacial surgeons can expect to see only a broadening of indications for DO utility and an interest in improving device design.14,15
External halo devices have the advantage of multilevel force vector control, though psychosocial stigma of the device is not insignificant. By contrast, current internal devices reduce the associated psychosocial burden, but remain criticized for their single non-modifiable vector advancement.16-18 Additionally, the presently marketed internal designs have been shown to promote an unfavorable clockwise rotation of the midface during advancement. The result is an unfavorable increase in vertical dimension of the orbit with subsequent hollowing, poor central projection, and an under- or un-corrected class III malocclusion with posterior open bite.7-9 The etiology of the latter malrotation with internal devices is at least two-fold: (1) device distraction around a single-pivot point and (2) the inherent differential soft tissue resistances at orbital and maxillary levels (i.e., orbital < maxillary level soft tissue resistance). To this end, we sought to alter the current distractor design to address these associated shortcomings.
With the ultimate goal of providing mid-face advancement parallel to the Frankfort horizontal line and overcoming potential post-distraction asymmetries, we designed a bilevel construct. This bilevel design with both lateral orbit and maxillary fixation points addresses the tendency of previous midface distractor systems to rotate around a single pivot point at or above the zygoma-zygomatic arch interface. Additionally, the independent rotary components, which allow for the real-time adjustment of distraction rates at orbital and maxillary levels, serve to: (1) compensate for the influence of intrinsic differential soft tissue resistances at these levels and (2) allow for control over the mid-face pitch during advancement.
As described, the modular design allows for facile assemblage via bicoronal and gingivobuccal access points without a significant learning curve for the practitioner already familiar with current fundamental concepts and techniques. Similarly, the device can be easily removed via limited-access incisions with minimal soft tissue dissection at a secondary procedure. The temporal cranial location of both rotary activators obviates the discomfort of previous intraoral activation designs and facilitates distraction at home for parents with a standard hexagonal screwdriver.
Results of our early experience illustrate that the device is safe, with no major procedural or device related complications. Review of relevant cephalometric deltas (Table 1), illustrates significant improvement in facial projection while obviating midface rotation. This can be seen by progression of SNA, ANB, vertical maxillary height, and occlusal plane-to-Frankfort horizontal vectors toward the norms reported for age-matched controls. Post-operative photographs further support early favorable results for the device, revealing significant improvement in facial projection, vertical maxillary dimension, exorbitism and occlusal balance.
The authors recognize several potential limitations of the design. First, an additional procedure and anesthetic is required for hardware removal. This is an inherent limitation of internal devices. Second, the potential exists for injury to unerupted dentition when fixing the maxillary plates. To address the latter issue, we have adopted virtual surgical planning for our patients with the preparation of 3-D models for precise plate bending. These models can be prepared with coloring of the unerupted dentition and sterilized for use in the operating room To improve safety in younger patients with mixed dentition undergoing the procedure, our next generation device will be designed with the ability to couple to an intraoral splint.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.