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Overcorrection In Rigid External Distraction: Quantifying Skeletal Distraction And Long-term Outcomes In Maxillary Hypoplasia
Pranav Rajaram, B.S.1, Makenna K. Ley, B.S.
2, Steven R. Buchman, M.D.
3, Christian J. Vercler, M.D., M.A.
3, Hannes Prescher, M.D.
3.
1University of Michigan Medical School, Ann Arbor, MI, USA,
2College of Medicine - Tucson, University of Arizona, Tucson, AZ, USA,
3Section of Plastic & Reconstructive Surgery, Department of Surgery, University of Michigan, Ann Arbor, MI, USA.
PURPOSE: Rigid external distraction (RED) for cleft-related maxillary hypoplasia requires deliberate overcorrection to overcome soft-tissue resistance (biological boundaries) and skeletal relapse. The translation of distraction distance to skeletal advancement is poorly defined. We aimed to quantify the skeletal translation coefficient, describe complications, and report long-term outcomes.
METHODS: A single-institution retrospective review of 24 patients (ages 9-20) undergoing Lefort 1 maxillary advancement with RED was performed. Data included demographics, distraction protocol, cephalometrics, overjet, and need for orthognathic surgery. Primary outcome was the skeletal translation coefficient (k = Δoverjet/distraction distance) at first and latest follow-up. Secondary outcomes included relapse, cephalometric change, and reoperation.
RESULTS: Twenty-four patients (58% bilateral CLP; mean age 15.3 years) underwent RED. Mean distraction was 20.8 mm with overjet improvement of 14.8 mm (-10.7 to +4.1) at 175 days (k=0.71) and relapse of 1.3 mm at 1,203 days (k=0.65). Actual distraction rate was 0.62 vs 1.0 mm/day planned. Adjustments were required in 62.5% and premature consolidation occurred in 16.7%. Cephalometrics normalized (Table 1). Five patients (20.8%) required secondary orthognathic surgery.
CONCLUSION: In this large single-center, long-term study of RED outcomes, about two-thirds of distraction distance translates into skeletal advancement, underscoring the need to plan device-level overcorrection to achieve the desired overjet. Only 20.8% of severely retrognathic patients required secondary orthognathic surgery, supporting overcorrection as a mainstay of RED.
Table 1: Distraction parameters, cephalometric outcomes, and secondary surgical interventions| Category | Parameter | Results |
| Patient Characteristics | N (patients) | 24 |
| Bilateral CLP (%) | 58 % |
| Mean age (years) | 15.3 |
| Distraction & Consolidation | Device travel, mm (range) | 20.8 (15-35) |
| Duration distraction, days (range) | 38.3 (17-79) |
| Distraction rate, mm/day (range) | 0.62 (0.25-1.15) |
| Consolidation duration, days (range) | 70.1 (37-122) |
| Total device time, days (range) | 108.4 (71-154) |
| Adjustments required, n (%) | 15/24 (62.5%) |
| Premature consolidation, n (%) | 4/24 (16.7%) |
| Dental Outcomes | | Pre-op | Post-op | Notes |
| Mean overjet (mm) | -10.7 | 4.1 at 175 d | k=0.71 at 175 d |
| 2.8 at 1203 d | k=0.65 at 1203 d |
Cephalometric Outcomes
(n=17 pre-op, 13 post-op) | ANB (°) | -10.5 | 6.3 | Δ+16.8 |
| SNA (°) | 78.9 | 90.0 | Δ +11.1 |
| SNB (°) | 89.4 | 83.7 | Δ -5.7 |
| Wits (mm) | -13.4 | 3.1 | Δ +16.5 |
| Secondary Surgeries | Reoperation, n (%) | 5 pts (20.8 %) |
| BSSO | 3 pts (12.5 %) |
| Midface advancement | 2 pts (8.3 %) |
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