Alex Johnson

Comparison of optical see-through head-mounted displays for surgical interventions with object-anchored 2D-display

PurposeOptical see-through head-mounted displays (OST-HMD) feature an unhindered and instantaneous view of the surgery site and can enable a mixed reality experience for surgeons during procedures. In this paper, we present a systematic approach to identify the criteria for evaluation of OST-HMD technologies for specific clinical scenarios, which benefit from using an object-anchored 2D-display visualizing medical information.MethodsCriteria for evaluating the performance of OST-HMDs for visualization of medical information and its usage are identified and proposed. These include text readability, contrast perception, task load, frame rate, and system lag. We choose to compare three commercially available OST-HMDs, which are representatives of currently available head-mounted display technologies. A multi-user study and an offline experiment are conducted to evaluate their performance.ResultsStatistical analysis demonstrates that Microsoft HoloLens performs best among the three tested OST-HMDs, in terms of contrast perception, task load, and frame rate, while ODG R-7 offers similar text readability. The integration of indoor localization and fiducial tracking on the HoloLens provides significantly less system lag in a relatively motionless scenario.ConclusionsWith ever more OST-HMDs appearing on the market, the proposed criteria could be used in the evaluation of their suitability for mixed reality surgical intervention. Currently, Microsoft HoloLens may be more suitable than ODG R-7 and Epson Moverio BT-200 for clinical usability in terms of the evaluated criteria. To the best of our knowledge, this is the first paper that presents a methodology and conducts experiments to evaluate and compare OST-HMDs for their use as object-anchored 2D-display during interventions.

Towards clinical translation of augmented orthopedic surgery: from pre-op CT to intra-op x-ray via RGBD sensing

Pre-operative CT data is available for several orthopedic and trauma interventions, and is mainly used to identify injuries and plan the surgical procedure. In this work we propose an intuitive augmented reality environment allowing visualization of pre-operative data during the intervention, with an overlay of the optical information from the surgical site. The pre-operative CT volume is first registered to the patient by acquiring a single C-arm X-ray image and using 3D/2D intensity-based registration. Next, we use an RGBD sensor on the C-arm to fuse the optical information of the surgical site with patient pre-operative medical data and provide an augmented reality environment. The 3D/2D registration of the pre- and intra-operative data allows us to maintain a correct visualization each time the C-arm is repositioned or the patient moves. An overall mean target registration error (mTRE) and standard deviation of 5.24 ± 3.09 mm was measured averaged over 19 C-arm poses. The proposed solution enables the surgeon to visualize pre-operative data overlaid with information from the surgical site (e.g. surgeon’s hands, surgical tools, etc.) for any C-arm pose, and negates issues of line-of-sight and long setup times, which are present in commercially available systems.

Multi-modal imaging, model-based tracking, and mixed reality visualisation for orthopaedic surgery

Orthopaedic surgeons are still following the decades old workflow of using dozens of two-dimensional fluoroscopic images to drill through complex 3D structures, e.g. pelvis. This Letter presents a mixed reality support system, which incorporates multi-modal data fusion and model-based surgical tool tracking for creating a mixed reality environment supporting screw placement in orthopaedic surgery. A red–green–blue–depth camera is rigidly attached to a mobile C-arm and is calibrated to the cone-beam computed tomography (CBCT) imaging space via iterative closest point algorithm. This allows real-time automatic fusion of reconstructed surface and/or 3D point clouds and synthetic fluoroscopic images obtained through CBCT imaging. An adapted 3D model-based tracking algorithm with automatic tool segmentation allows for tracking of the surgical tools occluded by hand. This proposed interactive 3D mixed reality environment provides an intuitive understanding of the surgical site and supports surgeons in quickly localising the entry point and orienting the surgical tool during screw placement. The authors validate the augmentation by measuring target registration error and also evaluate the tracking accuracy in the presence of partial occlusion.

Plan in 2-D, execute in 3-D: An augmented reality solution for cup placement in total hip arthroplasty

Abstract. Reproducibly achieving proper implant alignment is a critical step in total hip arthroplasty procedures that has been shown to substantially affect patient outcome. In current practice, correct alignment of the acetabular cup is verified in C-arm x-ray images that are acquired in an anterior–posterior (AP) view. Favorable surgical outcome is, therefore, heavily dependent on the surgeon’s experience in understanding the 3-D orientation of a hemispheric implant from 2-D AP projection images. This work proposes an easy to use intraoperative component planning system based on two C-arm x-ray images that are combined with 3-D augmented reality (AR) visualization that simplifies impactor and cup placement according to the planning by providing a real-time RGBD data overlay. We evaluate the feasibility of our system in a user study comprising four orthopedic surgeons at the Johns Hopkins Hospital and report errors in translation, anteversion, and abduction as low as 1.98 mm, 1.10 deg, and 0.53 deg, respectively. The promising performance of this AR solution shows that deploying this system could eliminate the need for excessive radiation, simplify the intervention, and enable reproducibly accurate placement of acetabular implants.

On-the-fly augmented reality for orthopedic surgery using a multimodal fiducial

Abstract. Fluoroscopic x-ray guidance is a cornerstone for percutaneous orthopedic surgical procedures. However, two-dimensional (2-D) observations of the three-dimensional (3-D) anatomy suffer from the effects of projective simplification. Consequently, many x-ray images from various orientations need to be acquired for the surgeon to accurately assess the spatial relations between the patient’s anatomy and the surgical tools. We present an on-the-fly surgical support system that provides guidance using augmented reality and can be used in quasiunprepared operating rooms. The proposed system builds upon a multimodality marker and simultaneous localization and mapping technique to cocalibrate an optical see-through head mounted display to a C-arm fluoroscopy system. Then, annotations on the 2-D x-ray images can be rendered as virtual objects in 3-D providing surgical guidance. We quantitatively evaluate the components of the proposed system and, finally, design a feasibility study on a semianthropomorphic phantom. The accuracy of our system was comparable to the traditional image-guided technique while substantially reducing the number of acquired x-ray images as well as procedure time. Our promising results encourage further research on the interaction between virtual and real objects that we believe will directly benefit the proposed method. Further, we would like to explore the capabilities of our on-the-fly augmented reality support system in a larger study directed toward common orthopedic interventions.

Lesions of Ligamentum Teres: Diagnostic Performance of MRI and MR Arthrography—A Systematic Review and Meta-Analysis

OBJECTIVE The purpose of this study is to determine the diagnostic performance of MRI and MR arthrography for depicting ligamentum teres lesions. MATERIALS AND METHODS A literature search was performed. Original studies reporting the diagnostic accuracy of MRI examinations for the depiction of ligamentum teres lesions were included. RESULTS Eight studies entailing 1456 MRI examinations were included (frequency of median ligamentum teres injury, 25.9%; interquartile range, 14.1-45.3%). Two studies reported the results of unenhanced MRI examinations, and their diagnostic performance could not be estimated. Sensitivity, specificity, and diagnostic odds ratio (DOR) of all MRI examinations were 64.7%, 86.9%, and 12.2, respectively, whereas the sensitivity, specificity, and DOR of MR arthrography examinations were 82.2%, 88.6%, and 35.9, respectively. The heterogeneity (I2) for all MRI and MR arthrography examinations was 92.3% and 88.2%, respectively. Five blinded MR arthrography studies with 643 MR arthrography examinations found an appropriate threshold effect for summary ROC construction (AUC, 0.95). The summary estimate of these studies yielded a sensitivity of 87.8%, a specificity of 91%, and DOR of 73.1. The heterogeneity (I2) for this group was 64.3%. In patients with low pretest probability (25%), MR arthrography enabled the exclusion of ligamentum teres lesion (postprobability for a negative result, 4%; negative likelihood ratio, 0.13). CONCLUSION MR arthrography can depict ligamentum teres lesions with high accuracy. However, its diagnostic performance for differentiating various types of ligamentum teres lesions (partial, complete ligamentum teres tears, and hypertrophic ligamentum teres), as well as the diagnostic performance of unenhanced MRI for the depiction of ligamentum teres lesions, is yet to be determined because of the paucity of reported data in the literature.

Complications of Tibial Tuberosity Osteotomy

It is important to understand potential complications of tibial tuberosity osteotomies (TTOs) and how to avoid them. TTO is associated with a 1% to 3% rate of tibial fracture and 1% rate of nonunion. Early weight-bearing and complete detachment of the distal tuberosity may increase these risks. Painful screws requiring removal occur in 3% to 77% of cases. Use of small (3.5- mm diameter), countersunk screws reduces this risk. Recurrent instability occurs in ∼5% of cases at 5 years. The risk of deep-vein thrombosis (4%) after TTO is higher than that associated with other sports surgeries (1% to 2%). The risk of wound complications is ∼1% and can be reduced with meticulous handling of soft tissues and avoidance of large medial incisions. The risk of deep infection is <1%. Severe complications such as compartment syndrome and pulmonary embolism are rare.

Diagnostic injections about the shoulder

Injections about the shoulder serve diagnostic as well as therapeutic purposes. Diagnosis of shoulder conditions, such as rotator cuff tears, acromioclavicular joint pathology, subacromial impingement or anterolateral pain syndrome, glenohumeral joint pathology, suprascapular nerve entrapment, and biceps tendon pathologies, is often complicated by concomitant conditions with overlapping symptoms and by inconclusive physical examination and imaging results. Injections of anesthetic agents can often help clinicians locate the source of pain. However, technique and accuracy of needle placement can vary by route. Accuracy is often improved with the use of ultrasonography guidance, although studies differ on the benefits of guided versus unguided injection.

Complications After Tibial Tuberosity Osteotomy: Association With Screw Size and Concomitant Distalization

Background: Tibial tuberosity osteotomy (TTO) is a versatile procedure commonly used to treat patellar instability as well as to unload cartilage lesions. TTO with concomitant distalization (TTO-d) may be performed in patients with patella alta to stabilize the patella by helping it to engage in the trochlea earlier during flexion. Purpose: To identify and compare perioperative complications in patients who underwent TTO and those who underwent TTO-d and to analyze risk factors associated with these complications. Study Design: Cohort study; Level of evidence, 3. Methods: We retrospectively identified perioperative complications and associated factors from medical records for 240 patients who underwent TTO with or without distalization performed by 2 surgeons at 2 institutions between 2009 and 2015. A musculoskeletal radiologist at each institution determined osteotomy union using a published grading system. Significance was set at P < .01. Results: Of the 240 patients, 153 (122 TTO, 31 TTO-d) had clinical and radiographic follow-up of at least 90 days or evidence of osseous union. Eighty-eight complications were identified in 71 of 153 (46%) patients: delayed union (n = 35); painful hardware (n = 32); deep vein thrombosis (n = 4); clinical nonunion, delayed range of motion, sensory deficit, and wound breakdown (n = 3 each); and broken screw, fascial hernia, hematoma, quadriceps dysfunction, and tibial fracture (n = 1 each). Thirteen of 35 delayed unions occurred in the TTO-d group (P = .005). Painful hardware was more frequent in patients who received 4.5-mm screws (31/115) than in those who received 3.5-mm screws (1/38) (P = .001). A reoperation was required in 38 of 153 patients (37 patients using 4.5-mm screws vs 1 patient using 3.5-mm screws; P < .001), primarily for screw removal (32/38). Conclusion: Minor complications, including delayed union and painful hardware, were common, but major complications such as tibial fracture, deep vein thrombosis, and clinical nonunion were rare. Delayed union was more frequent in the TTO-d group. The 3.5-mm screws were less painful and less likely to need removal than the 4.5-mm screws.

Automatic intraoperative stitching of nonoverlapping cone‐beam CT acquisitions

PURPOSE Cone-beam computed tomography (CBCT) is one of the primary imaging modalities in radiation therapy, dentistry, and orthopedic interventions. While CBCT provides crucial intraoperative information, it is bounded by a limited imaging volume, resulting in reduced effectiveness. This paper introduces an approach allowing real-time intraoperative stitching of overlapping and nonoverlapping CBCT volumes to enable 3D measurements on large anatomical structures. METHODS A CBCT-capable mobile C-arm is augmented with a red-green-blue-depth (RGBD) camera. An offline cocalibration of the two imaging modalities results in coregistered video, infrared, and x-ray views of the surgical scene. Then, automatic stitching of multiple small, nonoverlapping CBCT volumes is possible by recovering the relative motion of the C-arm with respect to the patient based on the camera observations. We propose three methods to recover the relative pose: RGB-based tracking of visual markers that are placed near the surgical site, RGBD-based simultaneous localization and mapping (SLAM) of the surgical scene which incorporates both color and depth information for pose estimation, and surface tracking of the patient using only depth data provided by the RGBD sensor. RESULTS On an animal cadaver, we show stitching errors as low as 0.33, 0.91, and 1.72 mm when the visual marker, RGBD SLAM, and surface data are used for tracking, respectively. CONCLUSIONS The proposed method overcomes one of the major limitations of CBCT C-arm systems by integrating vision-based tracking and expanding the imaging volume without any intraoperative use of calibration grids or external tracking systems. We believe this solution to be most appropriate for 3D intraoperative verification of several orthopedic procedures.