Achieving the correct inclination angle for the acetabular component in total hip arthroplasty (THR) can be technically challenging. The aim of this study is to validate the use of a simple, laser-guided system to address the acetabular cup inclination angle intraoperatively and quantify its accuracy and repeatability across users. A simple inclinometer system was manufactured, consisting of a laser that snaps into both the inclinometer and the handle of a standard trial cup impacter. The system functions as follows:
desired inclination angle is set on the inclinometer, inclinometer is positioned on the acetabulum, laser beam is projected onto and marked on a screen outside of the surgical exposure, the impacter is reoriented in the acetabulum until the laser beam aligns with the recorded mark on the screen. A validation study was performed on this system using intact cadavers (N=4). A THR-specific. Trial acetabular components were installed unilaterally in each donor using both the laser inclinometer system with an in-line mounted intraoperative navigation system (NaviVision, Vector Vision Hip 3.1, BrainLab) serving as the measurement standard. Three orthopaedic surgeons participated in the study, two experienced with the device (“experts”) and one “novice”, and each surgeon performed two sequential validation experiments:
10 trials at a set device inclination angle, and 5 trials of matching the trial cup placement to this set angle. Using the laser-guided system, the inclination angle of the trial cup deviated from the desired orientation by 1.1±0.9° (mean st. dev; range: 0–3°) for all specimens across all operators. The corresponding error in anteversion angle was 1.4±1.3° (range: 0–5°). There was no difference in inclination angle between expert and novice surgeons (1.0±0.8° versus 1.1±1.2°, respectively; p>
0.10 for unpaired t-test). To set the desired inclination angle on the trial cup, original and final laser target positions were within 4.1±2.5 cm at 1 m screen placement. Results suggest that the laser-guided system has sufficient accuracy and repeatability for use intra-operatively. Inclination angles differed from prescribed angles by 1° on average, and malalignment in anteversion was subclinical, ≤5° for all cases. Furthermore, the tolerance for laser re-alignment sufficiently large (5–10 cm) to make the device functional intraoperatively. Future work will focus on expanding the sample size and correcting simple design limitations in the device.
While the early period of distraction osteogenesis has been extensively investigated, there are very few data describing the long-term morphology of the regenerate. We performed magnetic resonance scans in ten adults (men age 35+− 11 yr), seven of whom had bone transport for an iatrogenic osseous defect while further three had tibial lengthening for limb length discrepancy. Follow-up ranged between 14 and 43 months (mean : 28 + − 10 months) following the removal of the external fixator. The perimeter, cross- sectional area, volume and the mean signal intensity was calculated from the obtained T1 weighted axial images. Values were compared with the contralateral tibia that acted as control. All cases that had bone transport increased the volume of the tibia from 15.3% up to 50.8%. The regenerated segment was noted to have expanded significantly (p<
0.0001) in all cases. Mean signal intensity in the regenerate decreased in seven cases significantly (p<
0.0001) suggesting increase content of unhydrated tissue such as bone and collagen. The cross-sectional surface of the transported segment was increased in all cases (p<
0.008). Finally in cases that underwent bone transport, the docking site was noted to be obstructed by unhydrated tissue. Contrary to previous claims, the post-distraction osteogenesis tibia is far from normal, consisting of areas with potentially different biomechanical properties. Recognition of these changes is essential not only for appropriate pre-operative counselling but also for considering treatment modalities in case of a fracture.