The purpose of this study was to determine the efficacy of ultrasonography (USG) for the evaluation of bone formation in the mandibular distraction wound and to compare this with radiographic evaluation, which is currently the standard modality. Twenty-two patients underwent mandibular distraction (30 sides) with a variety of distraction devices. The wounds were assessed with plain radiographs and USG at established time intervals. Estimates of bone formation using a semiquantitative bone fill score were made for radiographs and USG. USG bone fill scores were correlated with radiography scores. At week 4 the difference between the scores was statistically significant ( P = 0.01); at all other time points, USG and radiography scores were comparable. At week 4, USG scores were significantly higher than the corresponding radiography scores, indicating that USG is an earlier indicator of calcification in the distraction zone as compared to radiography. USG evaluation of the distraction osteogenesis (DO) zone has many inherent advantages over conventional methods. The results of this study indicate that USG is an accurate non-invasive technique that may prove to be useful in assessing the mandibular DO regenerate in patients.
Distraction osteogenesis (DO) is a process of new bone formation between the surfaces of bone segments gradually separated by incremental traction, as described by Ilizarov who has pioneered distraction since the 1950s.
Presently no fixed protocol exists for the assessment of the distraction regenerate, which could aid in modifying the distraction protocol according to the needs of each patient. Ultrasonography (USG) promises to give an accurate assessment of not only the mandibular regenerate, but also the surrounding soft tissues.
The current commonly used methods for assessment of the clinical DO zone consist of serial physical examinations, plain radiographs, dual energy X-ray absorptiometry (DEXA), and computed tomography (CT). In contrast to these, USG is an inexpensive and efficient method of imaging that provides detailed assessment of bone formation across a defect. It has previously been proved useful for the evaluation of long bone DO healing.
The healing DO zone does not contain cortex, hence it can be penetrated by USG waves. This phenomenon is presumed to allow the surgeon or radiologist to evaluate the quantity, distribution, and density of the regenerate. Standard radiographic imaging poorly defines the regenerate as compared to the high accuracy of USG. It has been observed that the presence of bone union on radiographs is difficult to evaluate and not reliable during the first 4 weeks of fixation. Various superimpositions in the postero-anterior (PA) view and panoramic radiographs of the skull have a limited application in patients with a distraction device in situ . In contrast, USG can easily be adjusted to the area of interest in the mandible. The application is non-invasive, safe, simple, and reproducible.
There is a need to evaluate USG as a diagnostic tool in the evaluation of distraction regenerate, osteogenesis, and soft tissue growth (histiogenesis). The aim of this study was to evaluate the efficacy of USG as an accurate, non-invasive tool for the evaluation of bone formation in patients undergoing mandibular DO. The objective was to evaluate and compare the USG findings vis-à-vis results of assessment with radiographs.
Patients and methods
Twenty-two patients (12 males and 10 females) underwent DO of 30 mandibular sites, which included bilateral ( n = 8) and unilateral ( n = 14) procedures. The unilateral DO cases included four bimaxillary DO. Patient age ranged between 10 and 28 years (mean age 19.18 years). Patients from the oral and maxillofacial outpatient treatment department were included, as well as patients referred from allied specialities of the institute on the basis of having existing mandibular hypoplasia (congenital/acquired). The principles of DO were used to correct the existing mandibular skeletal deformities in this group of patients. Patients with neuropsychiatric disorders, on immunosuppressive medication, and those at the extremes of age were excluded from the study.
Evaluation of the regenerate of mandibular DO was carried out; the state of mineralization was evaluated with radiographs and USG at weeks 1, 4, 8, and 24 post distraction by rating on a 4-point semiquantitative scale and comparing the results obtained. A non-parametric test (Wilcoxon signed ranks test) was used to compare the USG and radiograph scores.
A variety of distraction devices were used, which were placed intraorally ( n = 28 sites) or extraorally ( n = 2 sites). The distractors were placed at various mandibular sites, according to the needs of each case. The various sites used were: mandibular body ( n = 8 sites), ramus ( n = 9 sites), ramus–condyle unit (RCU) ( n = 4 sites), mandibular midline ( n = 4 sites), and simultaneous maxillomandibular distraction ( n = 5 sites) in which the mandible was distracted at the ramus segment. Standard surgical steps with necessary modifications were undertaken.
After a latency period of 4 days (based on the site of DO), distraction was performed at the rate of 1 mm/day in 0.5-mm twice a day increments, as per the treatment plan and requirements of each case. In the present study of mandibular distractions, a minimum of 6 mm to a maximum of 23 mm (mean 13.25 mm) of distraction was achieved.
The protocol followed post distraction consisted of clinical evaluation, radiography, and USG examinations using a 7 MHz transducer (SONOLINE Adara; Siemens AG, Germany) at 1, 4, 8, and 24 weeks.
Clinical examination included evaluation of mandibular symmetry, occlusion, and stability by bimanual palpation, and observation for signs of infection and wound dehiscence. Occlusion was examined to document the progression of the planned mandibular movement.
USG images were rated on a 4-point semiquantitative scale based on definition of the gap margins, through-transmission of the ultrasonographic waves, and the presence of echogenic material.
For this study, digital panoramic radiographs and occlusal radiographs (for patients undergoing mandibular midline DO) were scored by an experienced radiologist, who reviewed a series of unlabelled radiographs.
Assessment criteria for radiographs
The radiographs obtained for each patient (22 patients, 30 mandibular sites) were evaluated for distraction gap and radiographic bone fill, which was estimated using a 4-point semiquantitative score in which: 0 = no bone; 1 = 0% to <50% bone fill; 2 = >50% to <100% bone fill; 3 = complete bone fill. The scores obtained were averaged.
USG is defined as the morphologic or descriptive analysis of ultrasonographic images. The patients underwent serial USG examinations throughout the neutral fixation period. An experienced radiologist performed the USG examinations. The USG beam was oriented perpendicular to the bone surface and a real-time survey was performed of the DO zone producing axial slices. First the distractor was detected. This was easily achieved due to the typical metal echoes. Starting from the anterior part of the device, the upright scanner was moved back following the inferior margin of the mandible. The frame, the axis, and the carriage of the device can easily be detected. The most valuable picture can be obtained if the scanner is applied perpendicularly to the osteotomy gap.
Assessment criteria for ultrasonography
The USG images obtained for each patient (22 patients, 30 mandibular sites) were rated using a 4-point semiquantitative score: 0 = complete through-transmission of USG waves, clear gap margins, and no echogenic material; 1 = partial through-transmission of the USG waves, identifiable gap margins, and <50% echogenic material; 2 = partial through-transmission of the USG waves, partially obscured gap margins, and >50% echogenic material; 3 = no through transmission of the USG waves, invisible gap margins, and 100% echogenic material.
All patients completed the treatment successfully. The desired/planned distraction was achieved in all patients, as observed intraoperatively at the time of distractor removal. One patient had the distraction devices removed prematurely (post distraction) due to infection and an implant reaction. There was partial bone fill in the gap and miniplates were used to stabilize the mandible. All other distraction devices remained stable until the time of removal. In general, none of the patients reported marked discomfort during the treatment phase. The patients reported regularly for distractor activation as well as postoperative follow-up.
The magnitude of lengthening was measured on radiographs during distraction, at the end of DO, and at the end of neutral fixation. The minimum lengthening of the mandible achieved was 6 mm and the maximum lengthening was 23 mm (range 6–23 mm). The radiographic bone fill in the distraction gap was evaluated using a 4-point semiquantitative score assigned to each site at weeks 1, 4, 8, and 24 ( Table 1 ) from the time of initiation of DO ( Figs 1a, 2a, 3a, and 4a ). The distraction gap was maintained during the neutral fixation period. The median bone fill score just before distractor removal was 2.0 (range 0–3) ( Table 2 ).
|Patient no.||Distraction, mm||USG