CAOS 2016: 16TH ANNUAL MEETING OF THE INTERNATIONAL SOCIETY FOR COMPUTER ASSISTED ORTHOPAEDIC SURGERY
PROGRAM FOR SATURDAY, JUNE 11TH
Days:
previous day
all days

View: session overviewtalk overview

08:00-09:10 Session 24: Total Hip Arthroplasty
Location: Hall B
08:00
Noise After Total Hip Arthroplasty: A Comparison Between Navigated Ceramic-on-Ceramic, Conventional Ceramic-on-Ceramic, and Conventional Metal-on-Polyethylene Groups
SPEAKER: Kamal Deep

ABSTRACT. Introduction: It is not known whether computer navigation can help reduce the incidence of hip noise after ceramic- on- ceramic (CoC) total hip arthroplasty (THA). Our first aim was to compare the incidence of hip noise between navigated and conventional CoC THA. Little is known about the incidence of noise after metal- on- polyethylene (MoP) THA. Our second aim was to compare the incidence of noise between CoC and MoP groups.

Methods: Incidence of noise after THA was compared between 202 hips in the navigated CoC group, 128 hips in the conventional CoC group, and 106 hips in the conventional MoP group. Data was collected through a telephone or postal interview using a questionnaire.                  Results: Incidence of any noise was significantly greater in the conventional group (21.9%) as compared to navigated group (6.4%; p<0.0001). Squeaking specifically, was also significantly greater in the conventional group as compared to navigated group (10.9% vs. 4%; p=0.02). Odds ratios for squeak and any noise in the conventional vs. navigated groups were 3 (p=0.02) and 4.1 (p=0.0001) respectively. The incidence of noise in the MoP group (2.8%) was similar to navigated CoC group (6.4%, p=0.28) but was significantly lower as compared to conventional CoC group (21.9%, p<0.0001).                  Discussion: Navigated CoC THAs are 3 times less likely to squeak and 4 times less likely to have any noise as compared to conventional CoC THAs. Incidence of any noise after MoP THA was similar to navigated CoC THA but significantly lower as compared to conventional CoC THA.

08:10
Effect of different pelvic horizontal references on leg length measurement in navigated THA

ABSTRACT. Introduction: There exist several methods to measure leg length of patient. The shape of the pelvis is often not symmetric, which might cause significant discrepancies between navigation measured leg length and radiographic leg length. The purpose of the present study was to evaluate the effect of differences of pelvic horizontal references (inter-ASIS line and the inter- ischial tuberosity line) on leg length measurement.

Methods: A total of eighty-one consecutive patients who underwent CT between November 2010 and November 2012 were the subjects of this study (except who had previous surgeries were excluded). To calculate the differences of leg length measurements by different pelvic horizontal references, the horizontal position of anatomic hip centers was determined 30mm lateral to the teardrop on the inter-tear drop line, where the differences of leg length was measured using trigonometric function.

Results: The absolute mean difference between the inter-teardrop line and the inter- ASIS line was 3.5mm (SD 2.8mm, range 0 to 13.1mm), eighteen cases (22.2%) showed leg length discrepancy of more than 5mm only by using the inter-ASIS line as a pelvic horizontal reference. The absolute mean difference between the inter-teardrop line and the inter- ischial tuberosity line was 2.7mm (SD 2.1mm, range 0 to 9.7mm), ten cases (12.3%) showed leg length discrepancy of more than 5mm only by using the inter-ischial tuberosity line as a pelvic horizontal reference.

Discussion: In conclusion, pelvic asymmetry caused significant difference in leg length measurement. It is necessary to use the same horizontal pelvic reference in preoperative planning, navigation surgery, and postoperative measurement of leg length in THA.

08:20
A Cadaveric Validation Study Of The Custom−Made Acetabular Prosthesis Produced By Additive Manufacturing

ABSTRACT. Introduction: The number of total hip arthroplasties has been increasing worldwide, and it is expected that revision surgeries will increase significantly in the near future. Although reconstructing normal hip biomechanics with extensive bone loss and massive acetabular defect in the revision surgery remains challenging, various reconstructive materials have been developed. The custom−made acetabular component produced by additive manufacturing (rapid prototyping), which can be fitted to a patient’s anatomical and bone defect, is expected to be a predominant reconstruction material. The purpose of this study was to validate the custom−made acetabular component regarding three−dimensional positioning and alignment with fresh cadaveric hip joints.

Methods: Based on computed tomography data, after making the bone defect, two types of custom−made acetabular components (augmented type and tri−flanged type), which adapted to the bone defect substantially, were produced by an additive manufacturing machine.

Results & Discussion: The present study demonstrated that preoperative planning of the center of the hip joint was successfully reproduced after the implantation of both types of custom−made acetabular components. However, there was some degree of variation in terms of component alignment in the augmented type. There is scope for further improvement, but the custom−made acetabular component produced by additive manufacturing may become very useful reconstruction material in hip revision surgeries.

08:30
The Rom Simulation Study Of Bone Impingement In Normal Hip Joints
SPEAKER: Takeshi Ogawa

ABSTRACT. Introduction: We have developed the range of motion (ROM) simulation software (THA analyzer) to measure ROM by collision detection in multi-directional positions of the hip. The purpose of this study was to measure the bony ROM in normal hip bone models using this software and to clarify the factors affecting the bone impingement pattern.

Methods: The subjects were 15 normal hips. Three dimensional surface models of the pelvis and femur were reconstructed from preoperative CT images. We performed virtual hip implantation with the same center of rotation, femoral offset, and leg length as the original hips. Subsequently, we create the bony ROM mapping with THA analyzer. According to the borderline of impingement at the flexion-internal rotation corner, the hips were classified into two groups; group-A showed more than 45° of the borderline slope and the remaining hips were group-B. We measured the neck shaft angle, the femoral offset, femoral anteversion, pelvic tilt, acetabular anteversion, sharp angle, and CE angle. These factors were compared between the two groups. Statistical analysis was performed with Mann-Whitney U test, and statistical significance was set at P<0.05.

Results: There were 7 hips in group-A and 8 hips in group-B. Femoral offset was 38 mm ±2.2 mm in group-A and 30mm ±2.7 mm in group-B. Femoral anteversion was 32°±6.4° in-group A and 43° ±4.8° in group-B. There were statistically significant differences in the femoral offset and femoral anteversion between the groups.

Discussion: The increase of femoral offset or decrease of femoral anteversion revealed an early impinge in internal rotation.

08:40
Is Patient Positioning Reliable In Total Hip Arthroplasty?

ABSTRACT. Introduction: To our knowledge, no study has assessed the ability of rigid patient positioning devices to afford arthroplasty surgeons with ideal pelvic positioning throughout surgery. The purpose of this study is to utilize robotic-arm assisted computer navigation to assess the reliability of pelvic position in total hip arthroplasty performed on patients positioned with rigid positioning devices.

Methods: 100 hips (94 patients) prospectively underwent total hip Makoplasty in the lateral decubitus position from the posterior approach; 77 stabilized by universal lateral positioner, and 23 by peg board. Prior to reaming, CT-templated computer software generated true values of pelvic anteversion and inclination based on the position of the robot arm registered to the patient’s preoperative pelvic CT.

Results: Mean alteration in anteversion and inclination values were 1.7 degrees (absolute value 5.3 degrees, range -20 - 20 degrees) and 1.6 degrees (absolute value 2.6 degrees, range -8 - 10 degrees) respectively. 22% of anteversion values were altered by >10 degrees; 41% by > 5 degrees. There was no difference between positioners (p=0.36) and regression analysis revealed that anteversion differences were correlated with BMI (p=0.02).

Discussion: Despite the use of rigid patient positioning devices - a lateral hip positioner or peg board – our data reveals clinically important malposition of the pelvis in many cases, especially with regards to anteversion. These results show a clear need to pay particular attention to anatomic landmarks or computer assisted techniques to assure accurate acetabular cup positioning. Patient positioning by should not be solely trusted.

08:50
The Novel Imageless Hip Navigation System, Brainlab Hip 6.0, Should Not Be Used For Japanese Patients With Pelvic Deformities

ABSTRACT. CT-based navigation systems provide clinically acceptable accuracy to place acetabular cup even for Japanese patients with pelvic deformities due to DDH. However, CT-based navigation system was avoided because of its expensiveness, radiation exposure, and complex procedures and companies shifted to develop imageless navigation system. The novel imageless navigation for THA, Brainlab hip 6.0 (BH6.0) (Brainlab AG, Munich) uses the new coordinate based on the references on the acetabulum and the spinous process of lumbar spine. We investigate the accuracy of this new registration in BH6.0 for Japanese patients. Plaster 3D pelvic models were created based on the preoperative CT images of patients with bony deformities of Crowe’s type I, II, III, and IV. Each pelvic model has holes to insert guide wires which indicated inclination at 45 degrees and anteversion at 20 degrees in the APP coordinate. After registrations using BH6.0, the angles measured by the BH6.0 were recorded when the navigation pointer was aligned to the guide wires. We compared the angles of the wires and the measured angles by BH6.0. The average differences and 95% confidence intervals were not acceptable for clinical use. The differences were not small even in models with Crowe’s type I and II whose acetabulum also showed deformities such as double floors. Main reason for these errors was to use references around the acetabulum for registration. The previous CT-based navigation systems already overcame these problems by using references on the pelvis except for acetabular regions. In conclusion, we Japanese need CT-based computer assisted orthopaedic surgeries for accurate acetabular cup positioning.

09:00
Robot-Assisted Primary Cementless Total Hip Arthroplasty with A Short Bone-Conserving Stem: A Prospective Randomized Short-Term Outcome Study
SPEAKER: Seung-Jae Lim

ABSTRACT. Introduction: Recently, two topical issues in total hip arthroplasty (THA) can be a robot-assisted surgery and use of a short bone-conserving stem. However, there is a potential risk of stem malalignment, stem subsidence leading to unstable fixation, and the possibility of intraoperative femoral fracture when short bone-conserving stems are used. To address these limitations, robot-assistance could provide be a solution. The purpose of this study was to evaluate the effects of robotic milling on the accuracy of short bone-conserving stem positioning and on the short-term clinical outcome in THA using a prospective, randomized design.

Methods: From November 2011 to June 2012, a total of 54 patients scheduled for primary THA using a short bone-conserving femoral stem were randomised into two groups, either robotic milling group or manual rasping group. Three patients (3 hips) in the robotic milling group and two patients in the manual rasping group were lost to follow-up, leaving 24 patients (24 hips) in the robotic milling group and 25 patients (25 hips) in the manual rasping group. The Tri-Lock Bone Preservation Stem was used in all hips and all operations were performed through an anterolateral approach by one surgeon in the lateral decubitus position. New femoral fixator clamp attached to the femoral head was used to decrease soft tissue dissection and nerve injury (Fig. 1). A pinless version of the ROBODOC system using a MicroScribe 3D digitizer for femoral registration was used. The patients were assessed clinically and radiographically at 8 weeks, 5 months, 12months, and 24 months.

Results: Robotic milling group had a significantly longer operation time, requiring on average 8.9 minutes for registration and 11.2minutes for milling. On the other hand, robotic milling group showed superior results in terms of stem alignment and leg length equality. Two intraoperative femoral fractures occurred only in manual rasping group. Harris hip scores and WOMAC scores at 24 months postoperatively were similar in both groups. No complications including stem loosening, infection, nerve palsy, or dislocation encountered in either group during the follow-up period.

Discussion: The present study suggested that robot-assisted short bone-conserving THA could increase the accuracy of stem alignment, improve leg length equality, and help reduce the risk of intraoperative femoral fracture as compared with manual rasping. However, the clinical outcome scores did not differ between the two groups at the time of short-term follow-up. Long-term follow-up is needed to determine whether there will be a long-term clinical relevance of robot-assisted implantation of short bone-conserving stems in THA.

09:10-10:20 Session 25: Spine and Osteotomies
Location: Hall B
09:10
An Electronic Conductivity Device Is A Safe Option Of Cervical Pedicle Screw Placement
SPEAKER: Jun Ouchida

ABSTRACT. Introduction: Cervical pedicle screw (CPS) provides strong immobilization for cervical fixation. However, for anatomical character it has a potential risk of neurovascular complication during the surgical procedure. Although many surgical techniques to prevent surgical complications reported, safe and accurate screw insertion is still challenging. An electronic conductivity device (ECD) has been reported its high sensitivity and specificity for detecting pedicle perforations in thoracolumbar spine. The purpose of this study is to evaluate the usefulness of an electronic conductivity device in CPS placement.

Methods: Thirty five CPS (C2:4, C3:4, C4:10, C5:9, C6:5, C7:3) for eight patients (mean age 78.3 years, range 73-82 years) inserted using ECD between April 2015 and November 2015 were retrospectively enrolled. To evaluate the accuracy and safety of the screw insertion, the axial and sagittal view on pre- and postoperative reconstructed computed tomography (CT) were analyzed for anatomical character of cervical pedicle, screw position and screw breach of the pedicle. Screw breach was classified into four grades (grade0-3) according to a previously established grading system. Neurovascular complications were also surveyed using motor evoked potential (MEP) monitoring during surgical procedure and postoperative neurological deterioration.

Results: The mean outer pedicle width was 5.4±1.0 mm, for outer pedicle height 7.0±1.5 mm. The mean pedicle axial angle was 41.3±6.3 degree, for pedicle sagittal angle was 90.5±13.4 degree, for screw axial angle was 35.9±5.9 degree, for screw sagittal angle was 87.4±13.7 degree. In this study, 5 screws were noted to breach (C3: 1, C4: 2, C5: 1, C6: 1) in postoperative CT. All screw breach were classified into grade1. There were found neither MEP deterioration during surgical procedure, nor neurovascular complications due to screw placement occurred in this series.

Discussion: In this series, CPS insertion using ECD showed high accuracy, and there were no neurovascular complications. ECD can be a useful option of safe insertion of cervical pedicle screws.

09:20
Clinical Accuracy Of Cervical Pedicle Screw Placement Using O-Arm Navigation: Evaluation Of Difference Between Correctly Positioned And Malpositioned Screws
SPEAKER: Naoki Segi

ABSTRACT. Introduction: Cervical pedicle screw (CPS) fixation has become popular enough to publish good clinical results, however, it has the potential for serious complications. Despite little number of misplacements leads to complications, these events can result in catastrophic outcome. The aim of this study is to assess the reliability of CPS placement using O-arm navigation and to clarify the features of CPS malposition.

Methods: Between 2009 and 2014, 101 consecutive patients underwent posterior instrumentation with CPS (454 CPSs) at our institute. We evaluated pre- and postoperative CT scans so that we measured pedicle angles and screw angles (the angle formed by a screw axis and sagittal plane), and classified CPS breaches into 4 grades (0 – 3) and 5 directions (lateral, medial, superior, inferior, anterior).

Results: Of the all 454 CPSs, 385 (85%) were assessed as Grade 0 (no breach); 56 (12%) as Grade 1 (<2mm breach); 10 (2%) as Grade 2 (<4mm breach); and none as Grade 3. Of the malpositioned 66 CPSs, 54 screws were lateral deviation. From C2 to C5, the differences between two angles of a CPS and the pedicle that the screw implanted in were significant between correct and malpositioned CPSs.

Discussion: Because computer-assisted navigation is one of useful options in order to increase the safety of CPS insertion, we apply O-arm navigation. However, the latest generation of intraoperative navigation technology cannot ensure complete safety of CPS placement. From C2 to C5, smaller screw angle made a CPS malposition and breach lateral wall of pedicle.

09:30
Can the Use of 3D Intraoperative Imaging Optimize Per-Cutaneous Pedicle Screw Placement?

ABSTRACT. Introduction: In recent years internal fixation of the spine by using posterior approach with minimal-invasive and/or percutaneous technique were increasingly used in trauma surgery. Navigation is supposed to provide better data because percutaneous pedicle screw placement lost of direct visual and anatomical control on the back part of the vertebra. We hypothesize that a percutaneous - minimal invasive - dorsal procedure using 3D intra-operative imaging for vertebral fractures allows short operating times with correct screw positioning and does not increase radiation exposure.

Methods: 59 patients were included in this prospective, single center and randomized study. 29 patients (108 implants) were operated on by using percutaneous technique and conventional (Conv) OR imaging (conventional 2D C-arm) and 30 patients (72 implants) were operated on by using the same percutaneous technique, but with the help of a 3D fluoroscopy-based navigation system (3D fluo). In the two groups, a percutaneous approach was performed for transpedicular vertebroplasty or percutaneous pedicle screws insertion. In the two groups, surgery was done from T4 level to L5 levels. Patients (54 years old on average) suffered trauma fractures and/or fragility fractures. Evaluation of screw placement was done by using post-operative CT with two independent radiologists that used Youkilis criteria. Operative and radiation running time were also evaluated.

Results: With percutaneous surgery, the navigation technique (3D fluoro) was less accurate with 13.88% of misplaced pedicle screws (10/72) compared with 11.11% (12/108) observed with conventional 2D C-arm (Conv). The radiation running time for each vertebra level (two screws) reached on average 0.56 mSv with the navigated group (3D fluoro) compared to 1.57 mSv with the conventional 2D C-arm group (Conv). The time required for instrumentation (one vertebra, two screws) with the navigated group (3D fluoro) was 19.75 minutes compared to 9.19 minutes with the conventional 2D C-arm group (Conv). The results were statistically significant in terms of radiation dose and operative running time (p < 0.05), but not in terms of accuracy (p= 0.24).

Discussion: With percutaneous procedures, 3D fluoroscopy-based navigation (3D fluo) system has no superiority in terms of operative running time and to a lesser degree in terms of accuracy, as compared to 2D conventional procedure (CP), but the benefit in terms of radiation dose is important. Other advantages of the 3D fluo system are twofold: up-to-date image data of patient anatomy and immediate availability to assess the anatomical position of the implanted screws.

09:40
Accuracy of pedicle screw insertion using a new intraoperative cone-beam CT imaging technique: retrospective analysis of 586 screws

ABSTRACT. Introduction: To assess accuracy of pedicle screw placement using a novel intraoperative cone-beam computed tomography (CBCT) imaging technique, and to compare the efficacy of this technique with conventional postoperative computed tomography (CT) scans for pedicle breach determination.

Methods: In 102 patients, 2 orthopaedic surgeons inserted 586 pedicle screws over a 21 month period. In all patients, intraoperative CBCT scans were acquired after all screws were inserted, and retrospectively reviewed by the same orthopaedic surgeons for pedicle breach determination and grading according to recognized classification systems. Of the 586 inserted screws, placement assessment of 239 screws were also carried out in conventional postoperative CT scans using the same grading system. Agreement on screw placement assessment carried out in intraoperative CBCT and in conventional postoperative CT was measured.

Results: Of the 586 inserted pedicle screws, 496 (84.6%) were placed within the pedicle without any breach, 24 (4.1%) were in-out-in screws with a lateral breach but with the screw tip inside the vertebral body, 21 (3.6%) had a medial breach of less than 2 mm, 10 (1.7%) had a medial breach between 2 mm and 4 mm, 4 (0.7%) had a medial breach of more than 4 mm, 5 (0.9%) had a lateral breach, and 26 (4.4%) had an anterior breach. Seventeen screws (2.9%) were revised intraoperatively. Kappa and Gwet’s coefficients on screw placement assessment carried out in intraoperative CBCT and in conventional postoperative CT scans were 0.80 and 0.93, respectively.

Discussion: Intraoperative CBCT allows for accurate assessment of pedicle screw placement and might render postoperative CT imaging unnecessary.

09:50
Screw Perforation Features in 148 Consecutive Patients Performed Computer-Guided Cervical Pedicle Screw Insertion

ABSTRACT. Introduction: Cervical pedicle screw (CPS) fixation has been criticized for the potential risk of serious injury to neurovascular structures. To avoid such serious risks, computed tomography (CT)-based navigation has been used during CPS insertion, but screw perforation can occur even with the use of a navigation system. This study aimed to clarify screw perforation features in 148 consecutive patients treated with computer-assisted CPS insertion and to determine important considerations for computer-assisted CPS insertion. Materials and Methods: The records of 148 consecutive patients who underwent CPS insertion using a CT-based navigation system were reviewed. Postoperative CT images were used to evaluate the accuracy of screw placement. The screw insertion status was classified as grade 1, indicating that the screw was accurately inserted in pedicle; grade 2, indicating perforation of less than 50% of the screw diameter; and grade 3, indicating perforation of 50% or more of the screw diameter. We analyzed the direction and rate of screw perforation according to the vertebral level. Results: Of the screws showing grade 3 perforation, 70.5% screws were laterally perforated. Furthermore, we evaluated screw perforation rates according to the vertebral level. Grade 3 pedicle screw perforation occurred in 4.8% of C2 screws; 6.5% of C3 screws; 12.8% of C4 screws; 7.1% of C5 screws; 2.8% of C6 screws; and 4.5% of C7 screws. Grades 2 and 3 pedicle screw perforations occurred in 11.9% of C2 screws, 21.0% of C3 screws, 31.2% of C4 screws, 23.0% of C5 screws, 14.6% of C6 screws, and 13.5% of C7 screws. C3-5 screw perforation rate was significantly higher than C6-7 (p<0.01). Conclusions: Careful insertion of CPS is necessary, especially at C3 to C5, even when using a CT-based navigation system. Pedicle screws tend to be laterally perforated.

10:00
Does Navigation Assist Less-Experienced Surgeons In Performing Pericetabular Osteotomy Through A Mini-Incision?
SPEAKER: Masaki Takao

ABSTRACT. Introduction: Rotational acetabular osteotomy (RAO) is a periaceabular osteotomy used to treat developmental hip dysplasia (DDH). It requires detailed anatomical knowledge of the pelvic anatomy and three-dimensional cognitive skills. We addressed whether a computer navigation system combined with a preoperative computed tomography (CT)-based plan enabled surgeons to perform RAO safely and reliably through a mini-incision regardless of their level of experience.

Methods: We enrolled 24 patients (25 hips) with DDH (radiographic grade 0 or 1 osteoarthritic changes: Tönnis classification). Using the navigation system, four surgeons performed RAO via a mini-incision transtrochanteric approach. Two experienced surgeons treated 15 patients (16 hips). Two less-experienced surgeons treated 9 patients (9 hips). Operative data and clinical and radiographic outcomes were compared. Average follow-up was 2.1 years.

Results: There were no significant differences in the (1) incision length, operation time, or intraoperative blood loss; (2) numerical pain rating scale score and Western Ontario and McMaster Universities Osteoarthritis Index Scale score at 1 year postoperatively or at the latest follow-up; (3) preoperative and postoperative coverage of the femoral head by the acetabulum, postoperative joint congruency, postoperative medial and distal displacement of the femoral head, or acetabular thickness. One patient treated by a less-experienced surgeon developed a deep infection postoperatively that was successfully treated by single irrigation and debridement.

Discussion: The navigation system combined with the preoperative CT-based plan enabled less-experienced surgeons to perform RAO through a mini-incision as safely and reliably as experienced surgeons.

10:10
Reduced Bony Hip Range of Motion Associated with ADL Impairment Related To Hip Flexion After Rotational Acetabular Osteotomy

ABSTRACT. Introduction: The purpose of this study was to study the relationship between postoperative bony ROM and ADL impairment related to hip flexion at 2 years after RAO.

Methods: We reviewed 20 patients with symptomatic DDH who underwent RAO. With the questionnaires, we assessed whether the subjects could perform clipping toenails and putting on and taking off socks, and defined the ADL impairment as difficult for these two activities. We investigated the relationship between the ADL impairment at 2 years after RAO and postoperative bony ROMs measured by 3D surface models of the pelvis and femur.

Results: Mean bony flexion ROM in these 3 subjects with ADL impairment at 2 years was significantly smaller than that in the remaining 17 subjects (97º and 109.8º, respectively, p=0.013). Mean bony internal rotation ROM at 90º of flexion in subjects with ADL impairment was significantly smaller than that without ADL impairment (10.3º and 37.4º, respectively, p=0.019). The prevalence of ADL impairment was significantly higher in subjects with both 105º or less of bony flexion and 20º or less of bony internal rotation ROM at 90º flexion than that in the remaining subjects (75% (3/4 hips) and 0% (0/16hips), p=0.03). The postoperative femoral head coverage such as lateral CEA and anterior CEA didn’t associate with ADL impairment.

Discussion: This may indicate that subjects can avoid postoperative ADL impairment related to hip flexion if the subject obtain bony flexion was 105º or more, or bony internal rotation ROM at 90º of flexion was 20º or more after RAO. Because bony ROM after reorientation of the acetabulum can be influenced by the femoral head coverage, the morphology of proximal femur, and the morphology of the pelvis close to the acetabular rim, preoperative planning considering not only the femoral head coverage but also postoperative bony ROM is desirable to avoid postoperative ADL impairment related to hip flexion.

10:50-12:00 Session 26: Procedure Planning
Location: Hall B
10:50
3D Surgical Planning And Patient Specific Intsruments (PSIs) Can Replicate Accurate Bone Resections And Reconstructions In Bone Sarcoma Surgery

ABSTRACT. Introduction: Navigation-assisted surgery has been reported to enhance resection accuracy in bone sarcoma surgery. However, the technique requires additional facilities and setup time. Patient specific instruments (PSIs) have been used as a simpler alternative in assisting joint arthroplasty and limb deformity correction. We determine 1) the accuracy of bone resections using 3D surgical planning and PSIs; 2) the time required for performing the bone resections using PSIs; 3) the problems of using PSIs; 4) the recurrences, function and complications.

Methods: Among 26 surgically treated bone sarcoma patients, nine patients had resection with the assistance of PSIs with 3D planning. The procedure was planned using engineering software. The resection accuracy was accessed by comparing CT images of resected specimens with the planned in seven patients. Mean age was 30.9 (9 – 64). Mean followup was 2.8 year (1.4 – 4.3).

Results: The mean time required for placing PSIs was 5.8 minutes (1 – 10) and performing bone osteotomies with assistance of PSIs was 4.4 minutes (2 – 6). The mean maximum deviation error was 1.6mm (0.5 – 3.9). One PSI was broken during bone resection and one patient needed re-resection using the same PSI. One pelvic patient died of local recurrence and lung metastases 6 months postoperatively. One patient developed a solitary lung metastasis at 20 months after surgery. The mean Musculoskeletal Tumor Society score was 27.6 (21 – 30). There were no complications related to 3D planning and PSIs.

Discussion: In selected patients, 3D surgical planning and PSIs replicate complex bone resections and reconstructions in bone sarcoma surgery. Comparative studies with conventional or navigation-assisted resections are required.

11:00
What Is The Correct Patient-Specific Safe Zone For Cup Orientation In Total Hip Arthroplasty?
SPEAKER: Juliana Hsu

ABSTRACT. Introduction: During total hip arthroplasty (THA), malpositioning of the acetabular cup can lead to accelerated wear, impingement, and dislocation. Often, the Lewinnek safe zone, which suggests an inclination of 40° +/-10° and an anteversion of 15° +/- 10°, is considered as the optimal cup orientation. Depending on the technique for cup positioning guidance, either the operating table or the anterior pelvic plane (APP) is used as the reference frame. However, changes in pelvic tilt result in altered functional cup orientations in the standing position. Due to great interindividual variations of pelvic tilt in the standing position as well as changes between the standing and the supine position, the same safe zone defined with respect to the APP or the operating table cannot be applied to all patients. Numerous studies have been published regarding the optimal cup orientation. They can be divided into clinical outcome studies and biomechanical studies. In clinical outcome studies, the cup orientations of THA patients with and without dislocations are measured and a zone with high probability of no dislocation is identified. Since dislocation occurred also inside the safe zone and stable hips were outside the safe zone, a cup orientation optimal for a group might not suit each individual patient. The general idea of the biomechanical approach is to find a cup orientation which allows either a certain predefined desired range of motion (ROM) or certain motion sequences. The results highly depend on the chosen ROM or the motion data which were mostly representative data instead of patient-individual data.

Discussion: The individual hip motion during typical daily activity (stair climbing, binding shoes, deep seating, walking, etc.) as well as dislocation-prone manoeuvres should be considered based on motion analysis in order to derive an optimal patient-specific cup position and orientation.

11:10
Patient Specific Instrument Can Achieve Same Accuracy With Less Resection Time Than Navigation Assistance In Periacetabular Pelvic Tumor Surgery: A Cadaveric Study

ABSTRACT. Introduction: Inaccurate resection in pelvic tumors can lead to compromised margins with increase local recurrence. Navigation-assisted and patient-specific instrument (PSI) techniques have recently been reported in assisting pelvic tumor surgery with the tendency of improving surgical accuracy. We compared the accuracy of transferring a virtual pelvic resection plan to actual surgery using navigation-assisted or PSI technique in a cadaver study.

Methods: CT scans were performed in twelve cadaveric bodies including whole pelvic bones. Either supraacetabular or partial acetabular resection was virtually planned in bilateral hemipelvis using MIMICS software. The virtual resection plan was either transferred to a CT-based navigation system (OrthoMap 3D, version 2.0, Stryker) or was used for the design and fabrication of PSI. Pelvic resections were performed using navigation assistance in six cadavers and PSI in another six. Post-resection images were co-registered with preoperative planning for comparative analysis of resection accuracy in the two techniques.

Results: The mean average deviation error from the planned resection was no different (p = 0.19) for the navigation and the PSI groups: 1.9 (95% CI, 1.5-2.2mm) versus 1.4mm (95% CI, 0.6-2.1mm), respectively. The mean time required for the bone resection was greater (p = 0.0006) for the navigation group than for the PSI group: 16.2 (95% CI, 11.0-21.3 min) versus 1.1 min (95% CI, 0.5-1.7min), respectively.

Discussion: In simulated periacetabular pelvic tumor resections, PSI technique enabled surgeons to replicate the virtual surgical plan with similar accuracy but with less bone resection time when compared with navigation assistance. Further studies are required to determine the exact role of the techniques and investigate their clinical benefits in pelvic tumor surgery.

11:20
The Safe Zone of Component Orientation of Dual Mobility Bearing THA for Withstanding Postoperative 20° Pelvic Posterior Tilting Change

ABSTRACT. Introduction: Pelvic posterior tilting change (PPTC) after THA increases cup anteversion and inclination and results in a risk of prosthesis impingement (PI) and edge loading (EL). However, dual mobility bearing (DM) have a large oscillation angle and potential to withstand EL on high cup inclination such as 60~65°. The purpose of this study was to investigate the optimal orientation of DM-THA for avoiding PI and EL against postoperative 20°PPTC.

Methods: Our study was performed with CT -based 3D simulation software (ZedHip. LEXI co. Japan). The CT data was derived from an asian typical woman with normal hips. Prosthesises were 42mm outer head of MDM system and AccoladeⅡ 127°(Stryker). Cup orientation was described as anatomical definition. The safe zone was calculated by the required hip range of motion which was defined as 130°flexion, 40°extension, 30°external rotation, and 50°internal rotation with 90°flexion and the maximum inclination of DM cup which was 60°in consideration of withstanding EL. The optimal cup orientations withstanding 20°PPTC were defined as the primary cup orientation which changes consistently within the safe zone with the match of 20°PPTC and have lowest inclination

Results: The optimal orientations could be identified only within stem anteversion from 15°to 40°. The relationship between the optimal cup orientation and stem anteversion could be automatically identified. The correlation between stem anteversion and cup anteversion was linearly distributed and could be expressed as an approximated line of the formula that (stem anteversion)+(cup anteversion)=36.8. And likewise the relationship between stem anteversion and cup inclination was curved-linerly distributed and could be expressed as an approximated curved line of the formula that (cup inclination)=0.04(stem anteversion)2-2.18(stem anteversion)+74.8.

Discussion: Cup orientation calculated by the Widmer’s combined anteversion theory is easily deviated from the safe zone by PPTC. The optimal cup orientation calculated in this study could be set more inclination and retroversion than it calculated by the Widmer’s theory in contribution of large oscillation angle and admissibility of high inclination cup setting of DM. Therefore it could be possible to withstand 20°PPTC. Performing THA with considering postoperative PPTC is necessary for good long term outcome without dislocation and PE wear. The solution for 20°PPTC after THA is to apply dual mobility bearing and the formula of combined orientation theory calculated in this study.

11:30
Increase in Safe Zone Area of the Acetabular Cup Using Dual Mobility Cups in Total Hip Arthroplasty: A Simulation Study

ABSTRACT. Introduction: Dual mobility cup (DMC) inserts reduce the risk for dislocation after total hip arthroplasty by increasing the area of the safe zone, defined as the area within the acetabular cup over which movement between the femoral and acetabular components is controlled without impingement. The aim of our study was to use an anatomical model to evaluate the area of the safe zone for a DMC insert, compared to a fixed insert, and to calculate the change in area for both types of inserts for different anteversion angles of the femoral component.

Methods: A model of the pelvis and femur were developed from computed tomography images. The safe zone was defined as the area in the acetabular cup component over which conditions for stable range of motion were satisfied. The safe zone was calculated for both a fixed and a DMC insert over pre-determined range of three-dimensional motion, and the effect of increasing the anteversion position of the femoral component from 5° to 35° quantified.

Results: The ratio of the area of the safe zone for the DMC insert to of the fixed insert increased from 4.8 at 5° anteversion of the femoral component to 14.8 with 35° of anteversion. This represents an increase in stability of 10°~15° in both vertical and horizontal directions, compared to the fixed insert.

Discussion: A 4~15 fold expansion of the safe zone can be expected with the use of DMC insert. DMC insert would be favored with a large anteversion of the stem.

11:40
Atlas-Based Scaphoid Fixation Planning
SPEAKER: Randy Ellis

ABSTRACT. Introduction: The scaphoid is the most commonly injured carpal bone. The management of these fractures is often complicated by this bone's unique anatomy and geometry, and its a tenuous blood supply. Scaphoid non-union can be a debilitating condition that results in persistent wrist pain, stiffness and scaphoid non-union advanced collapse.

Methods: We proposed using a Lie group statistical shape atlas to plan scaphoid fixation surgery. An atlas was constructed using a population of samples with a base sample planned by expert surgeons. The base shape was then deformed to approximate new samples. The base plan was carried to the deformed base, to become the plan for the new sample.

The method was validated using a dataset of 19 human scaphoids. The study showed that, for this a small dataset, the Lie group model outperformed the linear model by a factor of 2. The computed plans were also compared to plans devised by three expert surgeons. The automatic plans were indistinguishable from adding a fourth surgeon.

Discussion: This work used a Lie group shape atlas in computer-assisted planning of scaphoid fixation. The method enhanced manual methods by accurately and automatically planning a clinically acceptable drilling path. The drilling path determined the location of the implant with respect to the anatomy. Manifold methods, including Lie groups, are promising for shape representation and surgical planning.

11:50
Fully Automated Measurement Of The Change In Pelvic Sagittal Inclination From The Supine To The Standing Position In 373 Cases Before Total Hip Arthroplasty

ABSTRACT. Introduction: Cup anteversion and inclination are usually planned by referring to the supine position of the pelvis. However, functional cup anteversion and cup inclination also change as the pelvic sagittal inclination (PSI) changes. The change in PSI from the supine to the standing position has been reported in some reports, but these reports required considerable manual input and great effort for measurements. We developed a fully automated computational method to measure PSI in both the supine and standing positions to easily investigate PSI. The purposes of this study were to evaluate the reliability of this method to measure PSI and to analyse the factors that relate to a greater than 10° change in PSI from supine to standing in a large cohort.

Methods: A total of 373 patients who underwent THA were the subjects of the study. PSI in the supine position was measured using the preoperative CT images, and the radiographs taken in the standing position were used to measure the PSI in the standing position. PSI in the supine position was measured as the angle between the anterior pelvic plane and the horizontal line of the body. PSI in the standing position was measured using a 2D-3D registration method. To analyze the factors related to a greater than 10° change in PSI from supine to standing, sex, age, existence of OA in the contralateral hip, Crowe classification of the operated hip, and the PSI in the supine position were also measured. To verify accuracy, the PSIs of 100 cases were measured with the manual method, and the intra-class correlation coefficient (ICC) was calculated.

Results: The median PSI in the supine position was 5.2°, and the median PSI in the standing position was -1.2°. The median change in the PSI from supine to standing was -5.9°. On the other hand, PSI changed more than 10° posteriorly in 69 cases (18%). On logistic regression analysis that set change of PSI greater than 10° as the dependent variable, age and PSI in the supine position under 5.2° were the significant factors (odds ratio: 1.05, 23.4). The ICC of PSI measurement in the both positions were more than 0.98.

Discussion: The fully automated system to measure the PSI in the supine and standing positions contributed greatly to increasing the number of subjects and facilitating the analysis of the factors. By expanding this automated method to postoperative radiographs, postoperative changes and longitudinal changes in the PSI can also be measured in a larger number of subjects. In conclusion, the ICCs of the automated PSI measurement were very high, the odds ratio of a greater than 10° change of PSI from supine to standing increased 5% as patient age increased one year, and the odds ratio was very high if PSI in the supine position was less than 5.2°.