Preliminary Application Of Percutaneous Guide Template In Drilling Decompression Of Osteonecrosis Of The Femoral Head

Objectives: To evaluate the feasibility and effects of 3D printing percutaneous guide template in drilling decom-pression of ONFH.Methods: Between November 2011 and September 2015,20 patients(27 symptomatic hips)that agreed to accept the operation of drilling decompression were included in this study.They were randomly allocated to two treatment groups,the template guiding group and the traditional fluoroscopy group.Patients were clinically evaluated using Harris hip score(based on pain,range of motion,and ambulatory ability)at preoperation.The diagnosis of ONFH was confirmed with plain radiographs,computed tomography examinations and magnetic resonance imaging.In templete,at first,several mark points were selected on the skin around affected hip.Hemispheric markers of diameter 1cm which can display in CT image were attached to mark points of skin.Circles were drawn on the skin around the markers using a mark pen.Then,CT scan of hips was performed with 0.625 mm slice thickness on patients lying in supine position same with intraoperative position.In order to keep the position of patient,we used vacuum cushion and mark on patient and cushion.The images were stored in DICOM format and transferred to a workstation running MIMICS 10.01 software(Materialise,Belgium)to generate 3D reconstruction model of the targeted hip.A surgical plan was performed,including finding the optimal puncture position,and confirming direction,diameter and depth of the virtual pins according to the position and size of the ischemic area.Three virtual pins were drilled though the femoral neck into the different site of lesion of the femoral head.The ideal pins we planed can be drilled through the top,the middle and the bottom of the ischemic area,respectively,and arrive at the proximal ischemic area of the femoral head.Then,the model was exported in STL format to the reverse engineer software,Geomagic Studio 7(Geomagic,US).Using this software,the drill guide template with three trajectories was constructed with a surface designed to be the inverse of the skin and markers,thus potentially enabling a near-perfect fit.Once this had been done,the virtual template model was exported in STL format to a 3D printer,SLA600,and the real drill template was manufactured in resin using the stereolithography rapid prototyping technique.The image of preoperative design can be printed out and taken into the operation room for reference.Drill guide template and skin markers were sterilized by low temperature plasma sterilization.Surgery was performed under either general or epidural anesthesia and patients were placed in supine position same as CT scan position.After routine disinfection and sterile towers cover,markers were attached to the skin coincided with marked circles.Drill guide template was placed on the skin surface slightly and perfectly fit with skin surface and markers on a lock-and-key principle.So,the proper insert point,drill direction were confirmed.Three guide pins were drilled through the trajectories according to the planed length and diameter.Introperative anteroposterior and lateral fluoroscopies were used to ensure the pins' direction coincided with preoperative planed direction.At last,the pins were drilled out,and the incisions were sewn up.In the same period,the 10 patients of control group were performed drill decompression according to experience and spatial imagination of surgeon in the free-hand technique under C-arm supervision.We also did three passes through the top,the middle and the bottom of the ischemic area.Anteroposterior and lateral fluoroscopic views were necessary while advancing the pin to ensure that the pin was advanced through the femoral neck into the lesion of femoral head.The evaluation parameters included operation time,radiation time,the times of drilling correction and Harris hip score.Results: we can draw the conclusion that the characteristics of patients and ONFH at baseline are similar as listed and just the type of treatment was different in two groups.In control group,one pin penetrated the femoral head cartilage.In template group,there were no operative complications including damage of femoral cartilage,fracture,infection and hematoma,and no pins were broken.In both groups,symptoms of hip pain were relieved in different degree after operation.The mean operation time in the template group is 27.8 min,while 44.4 min in the control group.The radiation times needed in template group 11.2 times was significantly lower in the control group 34.4 times.The times of drilling correction was 1.2 compared to 3.4,respectively,with significant difference.Before operation,the groups has similar scores(71.1 to 71.7).At three months followup,the mean Harris hip score of each group differed significantly from the preoperative score,respectively.Mean score of template group(85.2)was higher than control group(82.4),but there was no significant difference.Conclusion: This percutaneous template guide technique is a promising and well-planned,solution to safely perform drilling decompression with clear reduction of intraoperative radiation exposure time,operation time and times of drilling correction.