Thomas J.J. Maal

Predictability in orbital reconstruction: A human cadaver study. Part I: Endoscopic-assisted orbital reconstruction.

In the treatment of orbital defects, surgeon errors may lead to incorrect positioning of orbital implants and, consequently, poor clinical outcomes. Endoscopy can provide additional visualization of the orbit through the transantral approach. We aimed to evaluate whether endoscopic guidance during orbital reconstruction facilitates optimal implant placement and can serve as a convenient alternative for navigation and intra-operative imaging. Ten human cadaveric heads were subjected to thin-slice computed tomography (CT). Complex orbital fractures (Class III/IV) were created in all eligible orbits (nxa0=xa019), which were then reconstructed using the conventional transconjunctival approach with or without endoscopic guidance. The ideal implant location was digitally determined using pre-operative CT images, and the accuracy of implant placement was evaluated by comparing the planned implant location with the postoperative location. There were no statistically significant differences (pxa0>xa00.05) in the degree of implant dislocation (translation and rotation) between the transconjunctival orbital reconstruction and the endoscopic-assisted orbital reconstruction groups. Endoscopic-assisted orbital reconstruction may facilitate the visualization of orbital defects and is particularly useful for training purposes; however, it offers no additional benefits in terms of accurate implant positioning during the anatomical reconstruction of complex orbital defects.

Orbital volume analysis: validation of a semi-automatic software segmentation method.

PurposeThe purpose of this study was to validate a quick, accurate and reproducible (semi-) automatic software segmentation method to measure orbital volume in the unaffected bony orbit. Precise volume measurement of the orbital cavity is a useful addition to pre-operative planning and intraoperative navigation in orbital reconstruction.MethodsIn 21 CT scans, one unaffected orbit was selected to compare manual segmentation (gold standard) with three segmentation methods using iPlan software (version 3.0.5; Brainlab, Feldkirchen, Germany): automatic (method A), automatic minus bone/air masks (method SA) and automatic minus masks followed by manual adjustments (method SAA). First, validation of the manual segmentation and a newly described method for the anterior boundary was performed. Subsequently the accuracy, reproducibility and time efficiency of the methods were examined. Measurements were performed by two observers.ResultsThe intraclass correlation for the interobserver agreement of the anterior boundary was 0.992, and the intraobserver and interobserver agreement for the manual segmentation were 0.997 and 0.994, respectively. Method A had an average volumetric difference of 0.49xa0cc (SD 0.74) in comparison with the gold standard; this was 0.24xa0cc (SD 0.27) for method SA and 0.86xa0cc (SD 0.27) for method SAA. The average time for each method was 38 (SD 5.4), 146 (SD 16.0) and 327 (SD 36.2) seconds per orbit.ConclusionThe built-in automatic method A is quick, but suboptimal for clinical use. The newly developed method SA appears to be accurate, reproducible, quick and easy to use. Manual adjustments in method SAA are more time-consuming and do not improve volume accuracy. The largest volume discrepancy is located near the inferior orbital fissure.

Predictability in orbital reconstruction. A human cadaver study, part III: Implant-oriented navigation for optimized reconstruction

Navigation-assisted orbital reconstruction remains a challenge, because the surgeon focuses on a two-dimensional multiplanar view in relation to the preoperative planning. This study explored the addition of navigation markers in the implant design for three-dimensional (3D) orientation of the actual implant position relative to the preoperative planning for more fail-safe and consistent results. Pre-injury computed tomography (CT) was performed for 10 orbits in human cadavers, and complex orbital fractures (Class III/IV) were created. The orbits were reconstructed using preformed orbital mesh through a transconjunctival approach under image-guided navigation and navigation by referencing orientating markers in the implant design. Ideal implant positions were planned using preoperative CT scans. Implant placement accuracy was evaluated by comparing the planned and realized implant positions. Significantly better translation (3.53 mm vs. 1.44 mm, p = 0.001) and rotation (pitch: -1.7° vs. -2.2°, P = 0.52; yaw: 10.9° vs. 5.9°, P = 0.02; roll: -2.2° vs. -0.5°, P = 0.16) of the placed implant relative to the planned position were obtained by implant-oriented navigation. Navigation-assisted surgery can be improved by using navigational markers on the orbital implant for orientation, resulting in fail-safe reconstruction of complex orbital defects and consistent implant positioning.

Quantitative Assessment of Orbital Implant Position – A Proof of Concept

Introduction In orbital reconstruction, the optimal location of a predefined implant can be planned preoperatively. Surgical results can be assessed intraoperatively or postoperatively. A novel method for quantifying orbital implant position is introduced. The method measures predictability of implant placement: transformation parameters between planned and resulting implant position are quantified. Methods The method was tested on 3 human specimen heads. Computed Tomography scans were acquired at baseline with intact orbits (t0), after creation of the defect (t1) and postoperatively after reconstruction of the defect using a preformed implant (t2). Prior to reconstruction, the optimal implant position was planned on the t0 and t1 scans. Postoperatively, the planned and realized implant position were compared. The t0 and t2 scans were fused using iPlan software and the resulting implant was segmented in the fused t2 scan. An implant reference frame was created (Orbital Implant Positioning Frame); the planned implant was transformed to the reference position using an Iterative Closest Point approach. The segmentation of the resulting implant was also registered on the reference position, yielding rotational (pitch, yaw, roll) as well as translational parameters of implant position. Results Measurement with the Orbital Implant Positioning Frame proved feasible on all three specimen. The positional outcome provided more thorough and accurate insight in resulting implant position than could be gathered from distance measurements alone. Observer-related errors were abolished from the process, since the method is largely automatic. Conclusion A novel method of quantifying surgical outcome in orbital reconstructive surgery was presented. The presented Orbital Implant Positioning Frame assessed all parameters involved in implant displacement. The method proved to be viable on three human specimen heads. Clinically, the method could provide direct feedback intraoperatively and could improve postoperative evaluation of orbital reconstructive surgery.

3-Dimensional CBCT analysis of mandibular asymmetry in unilateral condylar hyperplasia

PURPOSEnThree-dimensional quantification of asymmetry in UCH has not been reported yet, but would be useful for diagnosing and evaluating the degree of deformity in this disease. It enables profound decision-making and timing of surgery. Unilateral condylar hyperplasia (UCH) can subjectively be classified in hemimandibular elongation (HE), hemimandibular hyperplasia (HH) and a combination of these two (hybrid form). The main purpose of this study was to quantify mandibular asymmetry in UCH patients with a reliable and reproducible method. Secondly, it was evaluated whether the existing classification can be confirmed.nnnMATERIALS AND METHODSn37 UCH-patients with progressive mandibular asymmetry, supported by a positive bone scan and/or such clinical progression that condylectomy was performed, were included in this retrospective study. A group of healthy subjects, matched for age and gender, was used as the control group. Cone-beam computed tomography (CBCT) scans were imported in Maxilim® software. Each mandibular half was divided into three skeletal segments (condyle, ramus, and body). Linear and volumetric measurements were calculated for these skeletal units on the affected and unaffected side, for both patients and controls.nnnRESULTSnSignificant differences between affected and unaffected sides in the patient group were found in condylar, ramus, and body segments for linear (pxa0<xa00.01) as well as for volumetric quantitative measurements (pxa0<xa00.0040). A mean linear difference between affected and unaffected sides in the condylar region of the UCH patient group was found of 3.6xa0mm (sd 2.9) versus 0.2xa0mm (sd 1.5) in controls. For volumetric measurements there was a mean difference between the left and right condyle of 718xa0mm3 (sd 638) in the patient group versus 8xa0mm3 (sd 225) difference in the control group. The condyle was the most affected segment. Differences between sides were significantly larger in the patient group than in the control group (pxa0<xa00.001). It was not possible to objectify differences between HE and HH.nnnCONCLUSIONnCBCT is a useful and accurate modality for quantification and evaluation of mandibular asymmetry in UCH. It enables objective monitoring. The existing classification in HE and HH could not be confirmed.

The orbit first! A novel surgical treatment protocol for secondary orbitozygomatic reconstruction

A novel surgical treatment sequence for secondary orbitozygomatic complex (OZC) reconstruction is described. Orbital reconstruction is performed before OZC repositioning. A surgical plan is made: the affected OZC is virtually osteotomized and aligned with a mirrored model of the unaffected OZC. A patient-specific implant (PSI) is designed for orbital reconstruction. Screw holes from the primary reconstruction are used for fixation. Primary screw hole positions at the repositioned OZC are embedded in the design, to guide OZC repositioning. A second patient-specific design is made for guidance at the zygomaticomaxillary buttress. The workflow was utilized in two patients. The PSI was positioned using navigation feedback. After repositioning of the zygomatic complex, the screw hole positions at the infraorbital rim and zygomaticomaxillary buttress seemed to align perfectly: no screw hole adjustments were necessary. Minor deviations were seen between planned and acquired PSI position; the mean errors between planned and acquired OZC position were 1.5 and 1.2xa0mm. Orbital reconstruction with a PSI before OZC repositioning ensures true-to-original orbital reconstruction. The use of old screw hole positions enables the PSI to be used as a static guide for OZC repositioning. The combination of static and dynamic guidance increases predictability in secondary OZC reconstruction.

Implant-oriented navigation in orbital reconstruction. Part 1 : technique and accuracy study

Intraoperative navigation is frequently used to assess the position of the implant in orbital reconstruction. Interpretation of the feedback from the navigation system to a three-dimensional position of the implant needs to be done by the surgeon, and feedback is only gathered after the implant has been positioned. An implant-oriented navigation approach is proposed, with real-time intuitive feedback during insertion. A technical framework was set up for implant-oriented navigation, with requirements for planning, implant tracking, and feedback. A dedicated navigation instrument was designed and a software tool was developed in order to meet the technical requirements. An accuracy study was performed to investigate the accuracy of the method in comparison to the regular navigation pointer. A proof of concept was provided. The results showed a translation error of 1.12-1.15mm for implant-oriented navigation with regular registration (pointer 0.71-0.98mm) and 0.81mm with accurate registration (pointer 0.54mm). Rotational error was found to be small (<3°). Quantitative and intuitive qualitative feedback could be provided to the surgeon in real-time during insertion of an orbital implant. Following this proof of concept and accuracy study, the implications for the clinical workflow should be evaluated. An implant-oriented approach may form the foundation for augmented reality or robotic-aided implant insertion.

Measuring zygomaticomaxillary complex symmetry three-dimensionally with the use of mirroring and surface based matching techniques

OBJECTIVEnThe study aim was to validate a new method for measuring zygomaticomaxillary complex (ZMC) symmetry, which can be helpful in analyzing ZMC fractures.nnnMETHODSnThree-dimensional virtual hard-tissue models were reconstructed from computed tomography (CT) datasets of 26 healthy individuals. Models were mirrored and superimposed. Absolute average distance (AD) and 90th percentile distance (NPD) were used to measure overall and maximal symmetry. The Intraclass Correlation Coefficient (ICC) was calculated to measure interobserver consistency. In order to determine whether this technique is applicable in ZMC fracture cases, 10 CT datasets of individuals with a unilateral ZMC fracture were analyzed.nnnRESULTSnFor the unaffected group the mean AD was 0.84xa0±xa00.29xa0mm (95% CI 0.72-0.96) and the mean NPD was 1.58xa0±xa00.43xa0mm (95% CI 1.41-1.76). The ICC was 0.97 (0.94-0.98 as 95% CI), indicating almost perfect interobserver agreement. In the affected group the mean AD was 2.97xa0±xa01.76xa0mm (95% CI 1.71-4.23) and the mean NPD was 6.12xa0±xa03.42xa0mm (95% CI 3.67-8.57). The affected group showed near-perfect interobserver agreement with an ICC of 0.996 (0.983-0.999 as 95% CI).nnnCONCLUSIONSnThe method presented is an accurate instrument for evaluation of ZMC symmetry, which can be helpful for advanced diagnostics and treatment evaluation.

Autologous Bone Is Inferior to Alloplastic Cranioplasties: Safety of Autograft and Allograft Materials for Cranioplasties, a Systematic Review

BACKGROUNDnCurrently, various materials are routinely used for cranioplasty after decompressive craniectomy, each with their own features, potential benefits, and harms.nnnOBJECTIVESnTo systematically review available literature about safety (infection, resorption, and removal) of different materials used for cranioplasty for any indication.nnnMETHODSnA comprehensive search in MEDLINE, EMBASE, and the Cochrane library was performed for relevant studies published up to January 2017. Study quality was assessed according to the Cochrane Collaboration risk of bias assessment tool, and a set of 27 predetermined parameters was extracted by 2 investigators independently for further analysis.nnnRESULTSnThe search yielded 2 randomized, 14 prospective, and 212 retrospective studies, totaling 10,346 cranioplasties in which 1952 (18.9%) complications were reported in patients between 0 and 90 years old. Overall, study quality was low and heterogeneity was large. Graft infections and resorption were most prevalent: overall infection rate was 5.6%. Autologous cranioplasties showed an infection rate of 6.9% versus 5.0% in combined alloplastic materials, including poly(methyl methacrylate) with 7.8%. Resorption occurred almost exclusively in autologous cranioplasties (11.3%). The greatest removal rate was reported for autologous cranioplasties (overall: 10.4%), which was significantly greater than that of combined alloplastic materials (overall: 5.1%; risk differencexa0= 0.052 [95% confidence interval: 0.039-0.066]; NNTxa0= 19 [95% confidence interval: 15-25]).nnnCONCLUSIONSnAvailable evidence on the safety of cranioplasty materials is limited due to a large diversity in study conduct, patients included, and outcomes reported. Autografts appear to carry a greater failure risk than allografts. Future publications concerning cranioplasties will benefit by a standardized reporting of surgical procedures, outcomes, and graft materials used.

The use of cranial resection templates with 3D virtual planning and PEEK patient-specific implants: A 3 year follow-up

PURPOSEnThe aim of this study was to evaluate the accuracy of resection templates in cranioplasties in order to facilitate a one-stage resection and cranial reconstruction.nnnPATIENTS AND METHODSnIn three cases, cranial resections were combined with direct reconstructions using the principles of computer-aided design, manufacturing, and surgery. The precision of the resection template was evaluated through a distance map, comparing the planned and final result.nnnRESULTSnThe mean absolute difference between the planned and actual reconstructed contour was less than 1.0xa0mm. After 3 years, no clinical signs of infection or rejection of the implants were present. The computed tomography scans showed no irregularities, and the aesthetic results remained satisfactory.nnnCONCLUSIONnOne-stage resection and cranial reconstruction using a resection template, control template, and a prefabricated patient-specific implant of poly(ether-ether-ketone) (PEEK) proved to be a viable and safe method.