The influence of expansion on intraoperative bone blood flow in multisegmental maxillary osteotomies: an experimental study

Abstract

The aim of the presented study was to investigate the effect of maxillary expansion in multisegmental Le Fort I osteotomies on bone blood flow. Five sheep underwent a three-piece total maxillary osteotomy. Bone blood flow was measured intraoperatively by laser Doppler flowmetry in the premaxilla, the lateral segments and the mandible before osteotomy, after osteotomy and segmentation as well as after 4 mm, 8 mm and 12 mm expansion with a Hyrax screw. A significant reduction in blood flow was seen after osteotomy and segmentation with a factor of 3.10 and between 4 mm and 8 mm expansion with a factor of 1.81. No significant differences could be found between 0 mm and 4 mm widening or between 8 mm and 12 mm widening. These results suggest that expansion of more than 4 mm in multisegmental osteotomies enhances the risk of avascular sequelae. As greater maxillary widening has been carried out in many cases without avascular complications, further research on additional factors, influencing the recovery of perfusion, is needed.

Surgical correction of severe dentofacial deformities often requires segmental maxillary osteotomy. A possible sequela of this technique is aseptic necrosis due to compromised blood supply of the maxilla . Expansion of the segmented maxilla seems to be the highest risk for this complication . Basic research into bone blood flow after different osteotomies of the maxilla was carried out by N elson et al. and B ell et al. in animal studies . In Nelson’s study with radioactive microspheres on macaque monkeys the perfusion of the alveolar bone decreased by 57% in the animals with intact descending palatine artery and by 89% when the artery was cut . Owing to early recovery, avascular sequelae were not seen. No study has been performed on the effect of expansion on the bone blood flow in osteotomized segments. In contrast to the technique with radioactive microspheres, measurement of perfusion with a laser Doppler allows continuous recording without immediate death of the animal. Studies using laser Doppler flowmetry have shown the effects of segmented maxillary osteotomies on pulpal blood flow 1–7 days postoperatively . Expansion of the maxilla was not reported.

The current study was designed to evaluate the effect of intraoperative expansion on the bone blood flow of the premaxilla and lateral segments during multisegmental Le Fort I osteotomies.

Material and methods

Five healthy adult sheep were used. The surgical procedures were performed in the operating theatre of the University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca.

Anaesthesia

All animals initially received 0.2 mg atropine. Anaesthesia was introduced giving Xylazin Bio 2% 3 mg/kg and ketamin 0.2 mg/kg as an i.v. bolus. According to the depth of anaesthesia, the i.v. boluses were repeated. Local anaesthesia with articain 4% was administered above the trachea, the cheeks and the maxilla. Tracheostomy was performed with an 8.5 Charrière preshaped tube. Crystalloid solutions were used for fluid maintenance.

Surgical technique

To facilitate the surgical approach, the cheeks were incised on both sides. After circumvestibular incision, a complete Le Fort I osteotomy was performed as described by B ell et al. for humans . A 12 mm hyrax screw (Dentaurum Maxi, Ispringen, Germany) was adapted individually to the palate ( Fig. 1 ). Segmentation was done between the second and third premolar through the infraorbital foramen on both sides and paramedially to achieve a three-piece maxilla ( Figs 2 and 3 ). For the measurement of blood flow, two small holes were drilled anteriorly and distally to the vertical osteotomy on both sides in the cortical bone next to the apex of the adjacent tooth. As a reference point, an additional hole was drilled after a small vestibular incision in the anterior mandible ( Fig. 2 ). For intrasurgical widening of the maxilla the adapted hyrax screw was fixed with a custom-made splint to the teeth of each lateral segment.

Fig. 1
Individually adapted hyrax screw (Dentaurum Maxi, Ispringen, Germany).

Fig. 2
Osteotomy lines and measurement sites. PM, premaxilla; LS, maxillary lateral segment; M, mandible.

Fig. 3
(a) Intraoperative view after maxillary segmentation. IN, infraorbital nerve. (b) Osteotomy lines marked with arrows.

Blood flow measurement

A laser Doppler flowmeter (Periflux PF 5001, Perimed, Järfälla, Sweden) was used to assess the bone blood flow in the maxilla and the mandible. Light with a wavelength of 780 nm is produced by a 1 mW He–Ne laser. A straight probe (PF 407, Perimed, Järfällä, Sweden) was used to conduct the light to the measurement site in the cancellous bone and to return the backscattered light to the flowmeter. The probe has a diameter of 1 mm. The optical fibre has a diameter of 125 μm, the fiber-to-fiber distance is 500 μm. According to the Doppler effect, the amount of backscattered light is recorded by the flowmeter. The voltage of the produced output signal has a linear relation to the flow of the red blood cells (number of cells × average velocity). The perfusion units (PU) shown by the laser Doppler are a relative measurement of the blood flow. The data were collected on a wide band setting. A computer was connected to the RS-232 port of the laser Doppler for storage of the date and later analysis with the specific software (PeriSoft for Windows, Perimed, Järfällä, Sweden). To ensure reproducibility of the measurements, a probeholder (Perimed, Järfällä, Sweden) for the specific demands of the bone blood flow measurement was used ( Fig. 4 ). The probe was calibrated before surgery with a plastic bloc (Perimed, Järfällä, Sweden) for zero voltage and a motility standard (Perimed, Järfällä, Sweden) for 250 PU.

Fig. 4
Probe (PF 407, Perimed, Järfällä, Sweden) with probe holder.

Procedure

After incision of the upper and lower vestibule, the first measurements were taken at all five sites (T1). The next blood flow recording was made after Le Fort I osteotomy and segmentation of the maxilla (T2). Having adapted the hyrax screw after the second measurement, perfusion data were collected with 4 mm widening (T3), 8 mm widening (T4) and 12 mm widening (T5) of the lateral segments. For each site, the data were registered continuously until at least 2 min of stable values were seen on the screen.

Data analysis

The mean perfusion was calculated for each session during the phase of stable values. Peaks due to movement artefacts were excluded. As the circulation in sheep during general anaesthesia is not as stable as in humans , the perfusion values of the upper jaw were also calculated as percentage of the actual perfusion of the mandible for statistical analysis. The perfusion of the left and the right maxilla and of the premaxilla and the lateral segments were compared with an analysis of variance. The factors of reduction of the perfusion between recording sessions T1 to T5 are given together with their 95% confidence intervals (CI). A probability of P < 0.05 was considered significant.

Results

All animals survived until the end of the surgical procedures. The descending palatine artery was preserved in all cases. Medians and ranges of all measurement sites and time points are given in Table 1 . To reduce the effect of blood pressure and depth of anaesthesia all data were calculated as the ratio between the observed perfusion value of the maxilla and the respective value of the mandible. The ratio showed no significant differences between the left and right sides ( F = 1.61, P = 0.2077) ( Fig. 5 ). No significant difference could be found between premaxilla and lateral segments ( F = 2.06, P = 0.1552) ( Fig. 6 ). The geometric means of the overall perfusion of the maxilla as ratio to the respective mandibular perfusion were 0.508 at T1, 0.164 at T2, 0.169 at T3, 0.097 at T4 and 0.087 at T5 ( Fig. 7 ). The reduction of perfusion from T1 to T2 had a factor of 3.10 and was highly significant ( P = 0.0012). Between T2 and T3 and between T4 and T5 no significant reduction of the perfusion could be found. Pooling the data of T2/T3 and T4/T5, this factor was 1.81 with a high level of significance (95% CI 1.22–2.70; P = 0.0099).

Table 1
Bone blood flow (medians and ranges) in perfusion units (PU).
Site T1 T2 T3 T4 T5
Mandible 68.3 (52–105.5) 46.4 (25.7–90) 61.2 (29.9–72.1) 78.4 (39.3–114.1) 67.9 (39–129.9)
Left premaxilla 23.8 (20.1–38.3) 6.6 (4.2–21) 9.6 (3.3–36.3) 5.3 (3.4–12.5) 5.6 (3.1–11.7)
Right premaxilla 52.2 (18.9–87.1) 6.5 (2.4–33) 9.4 (3.3–24.4) 3.1 (1.6–15.7) 7.7 (2.3–14.1)
Left lateral segment 23.7 (20.1–117.7) 13.4 (12.7–15.4) 12.1 (2.2–14.6) 12.2 (5.3–14.5) 8 (3.6–14.4)
Right lateral segment 35.8 (13.9–106.8) 6.9 (2.5–14.5) 6.6 (6–17.4) 6.2 (2.7–14.9) 9.5 (1.3–16.3)
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Feb 8, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on The influence of expansion on intraoperative bone blood flow in multisegmental maxillary osteotomies: an experimental study
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