- Email: [email protected]
Intellijoint HIP: A 3D Minioptical, Patient-Mounted, Sterile Field Localization System for Orthopedic Procedures
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Intellijoint HIP: A 3D Minioptical, Patient-Mounted, Sterile Field Localization System for Orthopedic Procedures Andre Hladio, Richard Fanson and Jeffrey Muir Intellijoint Surgical, Waterloo, ON, Canada
ABSTRACT The Intellijoint HIP system is a minioptical navigation system used to make accurate and real-time positional measurements during total hip arthroplasty (THA). Measurements of acetabular implant angle and change in leg length and offset are provided relative to the patient’s anatomy; these measurements are critical to patient outcomes. The Intellijoint HIP system is enabled through a novel and proprietary minioptical navigation technology, involving a patient-mounted camera and a tracker for positional detection by the camera when mounted on surgical instruments or anatomical locations. The Intellijoint HIP system is optimized for accessibility, usability, and integration with orthopedic workflows. There are no preoperative imaging requirements (i.e., it is an “imageless” system), and the device is fully surgeon controlled from the sterile field. Opportunities exist to apply the core minioptical technology outside of THA procedures. Handbook of Robotic and Image-Guided Surgery. DOI: https://doi.org/10.1016/B978-0-12-814245-5.00024-4 © 2020 Elsevier Inc. All rights reserved.
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24.1
Background
Correct implant positioning is critical to the success of orthopedic procedures. For example, in total hip arthroplasty (THA), the alignment of the acetabular component is critical to postoperative hip stability, as a malaligned acetabular component is known to lead to hip dislocations requiring medical intervention [1 3]. In another example with respect to THA, improper femoral and/or acetabular sizing or placement may cause leg length discrepancy leading to postoperative complications. As value-based healthcare models and patient expectations continue to rise, issues such as postoperative dislocation and leg length inequality are more and more highly scrutinized. Fig. 24.1 illustrates a patient before/ after THA. Prior to surgery, the hip joint is diseased (most commonly osteoarthritis), causing the mating articulating surfaces of the acetabulum and the femoral head not to function correctly, which induces pain and decreased patient mobility. After a hip replacement, the new articulating interface is formed by an acetabular implant and a femoral implant; the diseased bone is removed and replaced by artificial components. Surgical navigation systems were developed to increase spatial precision in surgery, as well as to decrease the invasiveness of surgical procedures. A surgical navigation system functions by measuring relative pose between trackers, wherein the trackers are attached to anatomical structures and surgical instruments, and provide the measured relative pose to the surgeon to achieve a spatial goal during surgery. These systems were originally developed for neurosurgical and spinal applications. For example, in a neurosurgical procedure, a location within a patient’s brain, preidentified on a brain scan, could be accessed through a small coin-sized craniotomy with the use of surgical navigation. In a spine surgery, a pedicle screw could be inserted within a vertebra along a safe trajectory, avoiding the spinal cord with use of surgical navigation. Some surgical navigation systems are compatible with preoperative or intraoperative imaging, and involve an “image registration” process, wherein the coordinate frame of the trackers is mapped to the coordinate frame of a medical image. Surgical navigation systems are “imageless” if they do not rely on pre- or intraoperative imaging. Various sensing modalities may be used for pose measurement, including stereoscopic infrared optical detection of active or passive trackers, inertial sensing, and electromagnetic tracking. Most commonly, surgical navigation systems rely on a stereoscopic infrared camera, locating either active or passive markers attached to anatomical structures or instruments, and executing a software workflow on a computer coupled to the camera. As surgical navigation systems demonstrated success in neuro and spinal surgery applications in the late 1990s, many were researching its utility in orthopedic arthroplasty applications. Surgical navigation systems were commercially introduced for orthopedic arthroplasty applications in the United States in the early 2000s [4], applying the same technology base as was used in neuro and spinal navigation. Initially, many systems were image-based (requiring a computed tomography (CT) scan); however, as CT scans were not the standard of care for routine arthroplasty procedures, many systems transitioned to be imageless. Examples of some of the original commercially available orthopedic navigation systems for hip arthroplasty procedures include: G G G G
BrainLab Hip Unlimited (BrainLab, Munich, Germany); Stryker Versatile Hip (Stryker Corp, Kalamazoo, MI, United States); Orthosoft Hip Universal (Zimmer CAS, Montreal, QC, Canada); NaviPro Hip (Kinamed Inc., Camarillo, CA, United States).
Shortly after their commercial introductions, some surgical navigation systems were augmented with robotic manipulators. For example, the Mako robotic system (Mako Surgical Corp, Ft Lauderdale, FL) comprises a traditional navigation system based on a stereoscopic, infrared, passive tracking modality. A tracker is attached to a “passive” robot manipulator with surgical tools (e.g., saws, high-speed burrs, reamers) coupled to its end-effector. A closed-loop control FIGURE 24.1 A patient’s hip before and after THA. THA, Total hip arthroplasty.
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FIGURE 24.2 Fixed alignment guides on acetabular implant inserter.
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Cost [10,11]; Sterility concerns: Some systems require a pseudo-sterile registration procedure to be conducted with the patient supine, prior to positioning them laterally for surgery and establishing the sterile field; Line of sight: The stereoscopic infrared optical modality is most common, in which the camera needs an unobstructed view of the multiple trackers in the sterile field. Operating room (OR) personnel must adjust their positions to allow the camera to see the trackers; OR layout: In addition to line-of-sight issues, most systems have a large OR footprint, making them intrusive during OR set-up. In smaller ORs, these systems may not fit at all; Additional procedure time: Initially, tools and techniques were ported into arthroplasty navigation from neurosurgical or spinal applications, and would cause 20 30 minutes of additional procedure time. Though not significant where neuro and spinal surgeries would last for 5 1 hours, arthroplasty procedures generally last 1 hour, in which case 20 30 minutes is significant [12,13]; Personnel training requirements: Many systems require a dedicated operator running the computer system. Training hospital staff to run the navigation system computer is burdensome; Portability: Most hospitals have multiple surgeons running multiple ORs simultaneously. Robotic and navigation systems for arthroplasty lack portability to facilitate efficient transitions from OR to OR.
The genesis of the Intellijoint minioptical technology was at the University of Waterloo (Waterloo, ON, Canada) in 2007. In an undergraduate mechatronics design course, the Intellijoint design group was inspired to address the
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system is implemented in which the pose of the robotic manipulator is tracked, and control signals restrict the movements of the surgical tools so that bone removal is according to a surgical plan. This system relies on a segmented CT scan and a preoperatively developed surgical plan, and may be used for partial knee arthroplasty, total knee arthroplasty, and THA. Despite demonstrating increased accuracy and outlier reduction [5 8], surgical navigation and robotic systems have yet to gain widespread market adoption. As a result, surgeons continue to rely on manual techniques and mechanical instrumentation for implant positioning. One common exemplary manual technique is the use of fixed alignment guides on an acetabular implant inserter, as shown in Fig. 24.2. The fixed alignment guides provide the surgeon with a visual cue of the alignment of the acetabular implant inserter relative to the operating table. The numerous drawbacks of using fixed alignment guides include: the guide only provides a fixed, static target (the surgeon cannot effect a patient-specific target); and, the patient’s position on the operating table may shift during the procedure (causing alignment relative to the operating table to result in incorrect alignment relative to the patient). Although the success rate of orthopedic surgery is high [9], implant positioning-related complications still occur when using manual and mechanical techniques. Some commonly cited reasons that surgical navigation and robotic systems have experienced low adoption within orthopedics include:
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challenges faced by one of their fathers—a rural community orthopedic surgeon, who wanted access to assistive technology to allow him to align hip implants accurately and reproducibly. In his surgical setting, traditional orthopedic navigation technologies were prohibitive for many of the reasons outlined above. The Intellijoint minioptical technology was developed to overcome these barriers. In 2013, the Intellijoint minioptical technology was commercially introduced in Canada, and subsequently in the United States for controlled release of a minimally featured system (measurements of intraoperative leg length and offset change). In late 2015, a fully featured system based on the Intellijoint minioptical technology was introduced commercially in Canada and the United States, which included leg length, offset, and cup angle measurement capability.
24.2 24.2.1
Intellijoint minioptical technology System overview
The Intellijoint minioptical technology comprises a patient-mounted tracking camera within the surgical sterile field, as shown in Fig. 24.3. The camera is rigidly fixed to the bone via patient mounting hardware, and connected to a computer workstation (not shown) via universal serial bus (USB). The camera provides buttons so that a sterile user can control the computer workstation. The computer workstation runs image processing and computer vision algorithms to calculate and display implant positioning data, based on a video feed of the tracker. The tracker is shown attached to an acetabular inserter tool (with an acetabular implant on the distal end of the tool). The acetabular inserter is a part of the instrumentation associated with the acetabular implant, and the tracker interfaces with this tool across a variety of implant vendors via a magnetic v-block adaptor. An animation video illustrating the use of the Intellijoint minioptical technology in an anterior THA procedure is provided. Advantages of this system architecture, relative to the previously commercialized surgical navigation systems, include: G
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Minimal line-of-sight disruptions—as long as the line of sight between the camera and the tracker is unbroken, the system is expected to function; Sterile field control—the sterile user can interact with the computer workstation via buttons on the camera, without compromising sterility or requiring additional staff to run the computer; High portability and flexibility in OR configuration—with the exception of the computer workstation, the entire minioptical system operates within the sterile field; there is no large, bulky equipment to manage. Fig. 24.4 illustrates an OR in which a patient is positioned for hip arthroplasty surgery, along with the Intellijoint technology, comprising a minioptical camera (located on a standard sterile Mayo stand, prior to being mounted to the patient), FIGURE 24.3 Intellijoint minioptical technology for acetabular implant alignment in THA, including a camera (attached to the bone), and a tracker (attached to a surgical acetabular inserter). THA, Total hip arthroplasty.
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FIGURE 24.4 Operating room configuration including the Intellijoint system.
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FIGURE 24.5 Photograph of the camera.
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the workstation coupled to the camera via a wired connection (outside of the sterile field), and a tray with sterile instruments for coupling the camera and tracker to anatomical structures and instruments, respectively; The system is universally compatible with implant instrumentation via the tracker adaptor (many of the previous surgical navigation systems are designed for compatibility with a single implant vendor’s products).
24.2.2
Camera
The most novel aspect of the Intellijoint minioptical technology is the camera. The camera is the primary sensor for generating spatial tracking measurements (i.e., the position and orientation of the tracker component, described below). The camera also provides a three-button interface (green circle, x, and square) to send commands to the computer workstation, to which is it connected via USB. A photograph of the camera is provided in Fig. 24.5.
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The optical technology includes a single camera with a wide field of view lens, an infrared filter, a global shutter imager, and infrared illumination from light emitting diodes (LEDs) surrounding the lens. The camera is designed to be patient-mountable within a surgical sterile field, and/or handheld during use. A size comparison between the camera and a Polaris Optical Tracking System (Northern Digital Inc., Waterloo, ON, Canada)—a market leader in supplying the surgical navigation and robotic surgery industry—is provided in Fig. 24.6. The camera is designed to be enclosed within a sterile drape before being introduced into the sterile field. The sterile drape is a custom design for the Intellijoint minioptical camera, and comprises a long tubular section terminating in an optical window. The system is designed to compensate for the optical effects of the optical window, so as not to introduce measurement inaccuracies. The sterile drape and optical window are held in alignment with the camera via a shroud component; the shroud snaps onto features of the camera without risking puncture to the sterile drape. Fig. 24.7 illustrates a user snapping the shroud over a draped camera. For patient mounting, the ability to aim the camera in a desired direction (i.e., at the surgical site), as well as remove the camera when not in use are important design requirements. A camera clamp is used to rigidly hold the shroud/camera/sterile drape assembly. The camera clamp has a spherical inner-surface profile, and the shroud has a spherical outer surface profile; hence, when loosely engaged, the clamp forms a moveable ball joint assembly with the shroud/camera/ sterile drape. The camera may be aligned by moving the ball joint based on visual cues or on software guidance, and
FIGURE 24.6 Size comparison between Intellijoint minioptical technology and the Polaris system.
FIGURE 24.7 Applying the shroud over a draped camera.
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FIGURE 24.8 Clamp/Shroud/Camera assembly for camera aiming and quick attachment and detachment during use.
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Detecting movement of a patient during a surgical procedure, by monitoring their orientation with respect to gravity; Measuring an inertial vector (based on the direction of gravity), where optical measurements are not feasible; Detecting vibrations or unwanted movement of the camera that could compromise optical measurement integrity.
24.2.3
Software framework
The Intellijoint minioptical technology includes a software framework, which receives USB camera data, and outputs pose (for use by the clinical application software). The software framework implements an image-processing pipeline to take a raw image, and compute a pose of a tracker within that image, based on a camera calibration and an expected tracker geometry. The high-level steps for determining pose are described below and illustrated in Fig. 24.9: G G
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A raw image 2D image is received into computer memory from the camera; Segment detection: Segments that may correspond to a tracker sphere are identified using segment detection techniques based on pixel intensity; Segment rejection: Since the tracker has four retroreflective spheres, four valid segments are expected. In this step, invalid segments are rejected based on various criteria, including size, shape, and relative spacing; Centroid detection: The 2D pixel centroids of the four valid segments are calculated (i.e., four sets of segment centroid coordinates); Point correspondence: The centroids are associated with the tracker sphere they represent. Heuristics based on expected relative spacing are used. The result is an ordered list of centroid coordinates; Pose calculation: A six degrees of freedom pose (x, y, z, roll, pitch, yaw) is calculated via a nonlinear optimization that receives the ordered list of centroid coordinates and camera and tracker models as inputs; This process is repeated for each image in a video stream running at 30 fps.
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when in the desired alignment, the clamp may be locked. To facilitate temporarily removing the camera (e.g., during a surgical step to avoid the camera being in the way), the clamp provides a magnetic kinematic mount interface. The kinematic mount interface is highly repeatable, so that the camera returns to the same location between attach/detach cycles. A photograph of the clamp/shroud/camera assembly (sterile drape not shown) is provided in Fig. 24.8. The camera interfaces with a computer workstation via a wired USB connection. The camera system is powered by the USB connection, without the need for any additional dedicated power supply. A 5-m USB cable is used, to ensure adequate length for any OR configuration, as well as to ensure that the workstation is out of the sterile field. This length is at the upper limit of the current USB standard. In addition to optical sensing, the camera includes an integrated three-axis accelerometer that is coregistered to the optical system, and calibrated to measure the camera’s orientation with respect to the direction of gravity. The resulting inertial measurements are provided in real time along with the optical camera feed. There are several possible use cases for inertial sensor measurements, including:
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FIGURE 24.9 Image processing pipeline.
The process for determining the inclination of the camera (based on accelerometer measurements) follows a similar method. The software framework sets limits on the optical tracking volume, to ensure accuracy. The validated tracking volume is illustrated in Fig. 24.10. In this figure, standard and extended tracking volumes are illustrated. In the extended tracking volume, angular constraints are added (in software) on the working volume, so that when in regions susceptible to pose calculation error (i.e., long distances away, at the edge of the imager), pose measurements of the tracker will not be generated.
24.2.4
Tracker
The Intellijoint minioptical system generates pose measurements between the camera and the tracker (shown in Fig. 24.11). The tracker provides four mounting posts at precisely known positions for attaching sterile retroreflective spheres (such as those marketed by Northern Digital Inc, Waterloo, ON, Canada). The retroreflective spheres reflect infrared illumination back toward the source (i.e., the camera), causing the spheres to appear brightly in the camera image. The tracker interfaces with various components (such as surgical tools) via a magnetic kinematic mount. The Intellijoint minioptical system may be deployed as a single-tracker system.
24.3
Minioptical system calibration
The Intellijoint minioptical system is designed to be “calibration-free,” in the sense that there are no field or preoperative calibration steps required. Other navigation systems (such as the Orthosoft Hip navigation system, marketed by Zimmer CAS, Montreal, QC, Canada) require surgical instruments to be calibrated preoperatively. The minioptical camera only requires factory calibration to consistently function correctly in the field, including when enclosed in the sterile drape. The monocular nature of the camera reduces the opto-mechanical complexity of the system, which enables robust, consistent adherence to the factory calibration. Conversely, for example, in a large-baseline
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FIGURE 24.10 Validated tracking volume.
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FIGURE 24.11 Tracker with retroreflective spheres.
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stereo camera system, the exact distance between both cameras is required to be precisely known, and is subject to various mechanical disturbances such as thermal deformation. Should a minioptical camera become compromised for any reason (e.g., damage to the lens), causing the calibration to no longer match the actual camera’s behavior, a software-implemented error metric will prevent inaccurate measurements, and prompt a potential replacement or servicing of the camera. The error metric is based on the optimization residual of the pose estimation operation, previously described. Trackers are not required to be calibrated, but rather rely on mechanical design and manufacturing processes that facilitate a robust adherence to a nominal model, known by the software. Similar to the minioptical camera, should a tracker ever become compromised for any reason (e.g., physical damage), the software-implemented error metric, based on the pose optimization residual, will prevent inaccurate measurements and prompt a potential replacement of the tracker component.
24.4 24.4.1
Clinical applications Intellijoint HIP
Intellijoint HIP is an imageless, portable, streamlined hip navigation system that provides measurements of acetabular implant inclination and anteversion, as well as change in leg length and offset. Intellijoint HIP is compatible with lateral, posterior, anterior, and revision THA workflows. The camera is mounted to the patient’s pelvis during the procedure, and the tracker can be mounted (at various points in time during the procedure) to the patient’s femur, registration instruments, and the acetabular implant inserter. Intellijoint HIP includes a set of sterile instruments used to mount the minioptical camera and the tracker to their respective objects. The sterile instruments are reusable, and autoclavable. Fig. 24.4 illustrates the sterile instruments within an OR configured for a THA procedure. Intellijoint HIP is a calibration-free system. The calibration of the minioptical system has been previously described. Additionally, no surgical instruments require preoperative calibration. This is primarily achieved through a magnetic v-block interface between the tracker and the acetabular implant inserter. The v-block is designed and manufactured to provide a known and repeatable angle with respect to any shaft (e.g., the shaft of an acetabular inserter tool) to which it is mounted. Fig. 24.3 shows the magnetic v-block component, coupling the tracker to the acetabular inserter tool. Intellijoint HIP does not require specific preoperative planning. Surgeons may plan their surgeries according to their standard methods, and use Intellijoint HIP intraoperatively to execute their plans. In some THA surgeries, there is a reliance on fluoroscopy to confirm acetabular implant inclination and anteversion, as well as change in leg length and offset. Intellijoint HIP is compatible with procedures using fluoroscopy (i.e., the system does not interfere with fluoroscopic imaging equipment), and has the potential to decrease the amount of fluoroscopy for a given procedure, since the surgeon may rely on Intellijoint HIP for measurements that would otherwise be captured via fluoroscopy. Fluoroscopy involves irradiating the patient and hospital staff; decreasing radiation is beneficial for those present in the OR. An example display screen, showing acetabular implant inclination and anteversion, is shown in Fig. 24.12, and a photograph of the sterile field corresponding to the display screen is shown in Fig. 24.13, in which a surgeon is holding the acetabular inserter with a tracker coupled thereto, and the camera is coupled to the patient’s pelvis.
24.4.2
Other applications
The Intellijoint minioptical technology may be applied to other procedures. It is well suited for patient-mounted, handheld or body worn, or robot-mounted applications, where sterile usage is required. Some example procedures include: G
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Total knee arthroplasty, where the technology could be used to make accurate bony cuts to ensure correct implant alignment; Cranial surgery, where the technology could be used to stereotactically access regions within a patient’s brain, for example, to take a biopsy; Ear, nose, and throat surgery, where the technology could be used to insert surgical tools into a particular cavity within a patient’s skull through their nose; Spinal surgery, where the technology could be used to drill a hole through the pedicle of a vertebra without risking breaching the spinal column.
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FIGURE 24.12 Acetabular implant alignment screen.
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FIGURE 24.13 Photograph of intellijoint HIP in use for acetabular implant inclination and anteversion measurement.
24.5
Accuracy performance
To quantify the accuracy performance of the Intellijoint minioptical technology, a standard protocol was applied (ASTM 2554-10 Standard Practice for Measurement of Positional Accuracy of Computer Assisted Surgery Systems). A calibrated phantom with precisely known divot locations (see Fig. 24.14) is used as a ground truth. This phantom is specified by the standard, and includes an array of divots at known spatial locations [measured by a coordinate measurement machine (CMM)]. The Intellijoint minioptical system generates 3D measurements of the phantom divot locations by attaching a ball-tipped probe to the end of the tracker, and mating the probe tip with any divot. Those measurements are compared to the known spatial locations to quantify accuracy. The phantom divots are measured with a CMM to an accuracy of 0.1 mm. Divots are arranged at various heights throughout a 20 3 20 cm volume, grouped into sets of five. A photograph of the phantom set up for use, including a tracker with a ball-tipped probe attached thereto is provided in Fig. 24.15.
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FIGURE 24.14 Accuracy phantom used to perform positional accuracy testing according to ASTM 2554-10.
FIGURE 24.15 Accuracy phantom in use by a user.
The results of design verification testing demonstrated that the Intellijoint minioptical system is capable of localizing a single point with a precision of 0.54 mm (RMS), and the distance between any two points with worst-case accuracy of 0.28 mm (RMS) [note: the accuracy between two points (0.28 mm RMS) is less than the precision of a single point (0.54 mm RMS), since the accuracy metric utilizes an average measured position at each of the two points]. The significance of these results is that the Intellijoint minioptical system should be expected to normally measure with submillimetric accuracy in space. This is sufficient for many clinical applications.
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Conclusion
The Intellijoint minioptical technology enables accurate surgical navigation via a patient-mounted camera directly within the sterile field, and overcomes many of the barriers to adoption of traditional arthroplasty navigation systems (e.g., cost, line-of-sight issues, portability, etc.). Its utility in THA has been demonstrated via Intellijoint HIP, a commercially available system for providing a surgeon with measurements of acetabular implant angles and positional changes to leg length and offset.
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Challenges and further development
The Intellijoint minioptical technology has not been proven outside of THA. It is speculated that this technology would be well suited for a variety of clinical applications, such as knee, cranial, spinal, and ear, nose, and throat surgery; however, further development should be conducted to confirm this hypothesis. Further, the Intellijoint minioptical technology has only been used in an “imageless” context (i.e., no registration to a 3D medical image dataset). Further development focus may include image-based applications. Although already much smaller than other optical navigation technologies, another area of development may include further miniaturization of the camera and tracker, to enable different types of surgery. Another potentially advantageous application for this technology is integration with robotics. The camera is sufficiently small so as to be mountable directly to a robotic manipulator. It is speculated that the camera may be used as a pose measurement sensor in a closed-loop robotic control system.
[1] Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am 2007;89(8):1832 42. [2] Masaoka T, Yamamoto K, Shishido T, Katori Y, Mizoue T, Shirasu H, et al. Study of hip joint dislocation after total hip arthroplasty. Int Orthop 2006;30(1):26 30. [3] Nishii T, Sugano N, Miki H, Koyama T, Takao M, Yoshikawa H. Influence of component positions on dislocation: computed tomographic evaluations in a consecutive series of total hip arthroplasty. J Arthroplasty 2004;19(2):162 6. [4] FDA. 510(k) Premarket notification. US Food and Drug Administration; 2017 [cited December 19, 2017]. Available from: ,https://www. accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm.. [5] Gurgel HM, Croci AT, Cabrita HA, Vicente JR, Leonhardt MC, Rodrigues JC. Acetabular component positioning in total hip arthroplasty with and without a computer-assisted system: a prospective, randomized and controlled study. J Arthroplasty 2014;29(1):167 71. [6] Lass R, Kubista B, Olischar B, Frantal S, Windhager R, Giurea A. Total hip arthroplasty using imageless computer-assisted hip navigation: a prospective randomized study. J Arthroplasty 2014;29(4):786 91. [7] Lin F, Lim D, Wixson RL, Milos S, Hendrix RW, Makhsous M. Limitations of imageless computer-assisted navigation for total hip arthroplasty. J Arthroplasty 2011;26(4):596 605. [8] Najarian BC, Kilgore JE, Markel DC. Evaluation of component positioning in primary total hip arthroplasty using an imageless navigation device compared with traditional methods. J Arthroplasty 2009;24(1):15 21. [9] Shan L, Shan B, Graham D, Saxena A. Total hip replacement: a systematic review and meta-analysis on mid-term quality of life. Osteoarthritis Cartilage 2014;22(3):389 406. [10] Slover JD, Tosteson AN, Bozic KJ, Rubash HE, Malchau H. Impact of hospital volume on the economic value of computer navigation for total knee replacement. J Bone Joint Surg Am 2008;90(7):1492 500. [11] Brown ML, Reed JD, Drinkwater CJ. Imageless computer-assisted versus conventional total hip arthroplasty: one surgeon’s initial experience. J Arthroplasty 2014;29(5):1015 20. [12] Manzotti A, Cerveri P, De Momi E, Pullen C, Confalonieri N. Does computer-assisted surgery benefit leg length restoration in total hip replacement? Navigation versus conventional freehand. Int Orthop 2011;35(1):19 24. [13] Kalteis T, Handel M, Bathis H, Perlick L, Tingart M, Grifka J. Imageless navigation for insertion of the acetabular component in total hip arthroplasty: is it as accurate as CT-based navigation? J Bone Joint Surg Br 2006;88(2):163 7.
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References
Intellijoint HIP: A 3D Minioptical, Patient-Mounted, Sterile Field Localization System for Orthopedic Procedures Andre Hladio, Richard Fanson and Jeffrey Muir Intellijoint Surgical, Waterloo, ON, Canada
ABSTRACT The Intellijoint HIP system is a minioptical navigation system used to make accurate and real-time positional measurements during total hip arthroplasty (THA). Measurements of acetabular implant angle and change in leg length and offset are provided relative to the patient’s anatomy; these measurements are critical to patient outcomes. The Intellijoint HIP system is enabled through a novel and proprietary minioptical navigation technology, involving a patient-mounted camera and a tracker for positional detection by the camera when mounted on surgical instruments or anatomical locations. The Intellijoint HIP system is optimized for accessibility, usability, and integration with orthopedic workflows. There are no preoperative imaging requirements (i.e., it is an “imageless” system), and the device is fully surgeon controlled from the sterile field. Opportunities exist to apply the core minioptical technology outside of THA procedures. Handbook of Robotic and Image-Guided Surgery. DOI: https://doi.org/10.1016/B978-0-12-814245-5.00024-4 © 2020 Elsevier Inc. All rights reserved.
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24.1
Background
Correct implant positioning is critical to the success of orthopedic procedures. For example, in total hip arthroplasty (THA), the alignment of the acetabular component is critical to postoperative hip stability, as a malaligned acetabular component is known to lead to hip dislocations requiring medical intervention [1 3]. In another example with respect to THA, improper femoral and/or acetabular sizing or placement may cause leg length discrepancy leading to postoperative complications. As value-based healthcare models and patient expectations continue to rise, issues such as postoperative dislocation and leg length inequality are more and more highly scrutinized. Fig. 24.1 illustrates a patient before/ after THA. Prior to surgery, the hip joint is diseased (most commonly osteoarthritis), causing the mating articulating surfaces of the acetabulum and the femoral head not to function correctly, which induces pain and decreased patient mobility. After a hip replacement, the new articulating interface is formed by an acetabular implant and a femoral implant; the diseased bone is removed and replaced by artificial components. Surgical navigation systems were developed to increase spatial precision in surgery, as well as to decrease the invasiveness of surgical procedures. A surgical navigation system functions by measuring relative pose between trackers, wherein the trackers are attached to anatomical structures and surgical instruments, and provide the measured relative pose to the surgeon to achieve a spatial goal during surgery. These systems were originally developed for neurosurgical and spinal applications. For example, in a neurosurgical procedure, a location within a patient’s brain, preidentified on a brain scan, could be accessed through a small coin-sized craniotomy with the use of surgical navigation. In a spine surgery, a pedicle screw could be inserted within a vertebra along a safe trajectory, avoiding the spinal cord with use of surgical navigation. Some surgical navigation systems are compatible with preoperative or intraoperative imaging, and involve an “image registration” process, wherein the coordinate frame of the trackers is mapped to the coordinate frame of a medical image. Surgical navigation systems are “imageless” if they do not rely on pre- or intraoperative imaging. Various sensing modalities may be used for pose measurement, including stereoscopic infrared optical detection of active or passive trackers, inertial sensing, and electromagnetic tracking. Most commonly, surgical navigation systems rely on a stereoscopic infrared camera, locating either active or passive markers attached to anatomical structures or instruments, and executing a software workflow on a computer coupled to the camera. As surgical navigation systems demonstrated success in neuro and spinal surgery applications in the late 1990s, many were researching its utility in orthopedic arthroplasty applications. Surgical navigation systems were commercially introduced for orthopedic arthroplasty applications in the United States in the early 2000s [4], applying the same technology base as was used in neuro and spinal navigation. Initially, many systems were image-based (requiring a computed tomography (CT) scan); however, as CT scans were not the standard of care for routine arthroplasty procedures, many systems transitioned to be imageless. Examples of some of the original commercially available orthopedic navigation systems for hip arthroplasty procedures include: G G G G
BrainLab Hip Unlimited (BrainLab, Munich, Germany); Stryker Versatile Hip (Stryker Corp, Kalamazoo, MI, United States); Orthosoft Hip Universal (Zimmer CAS, Montreal, QC, Canada); NaviPro Hip (Kinamed Inc., Camarillo, CA, United States).
Shortly after their commercial introductions, some surgical navigation systems were augmented with robotic manipulators. For example, the Mako robotic system (Mako Surgical Corp, Ft Lauderdale, FL) comprises a traditional navigation system based on a stereoscopic, infrared, passive tracking modality. A tracker is attached to a “passive” robot manipulator with surgical tools (e.g., saws, high-speed burrs, reamers) coupled to its end-effector. A closed-loop control FIGURE 24.1 A patient’s hip before and after THA. THA, Total hip arthroplasty.
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FIGURE 24.2 Fixed alignment guides on acetabular implant inserter.
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Cost [10,11]; Sterility concerns: Some systems require a pseudo-sterile registration procedure to be conducted with the patient supine, prior to positioning them laterally for surgery and establishing the sterile field; Line of sight: The stereoscopic infrared optical modality is most common, in which the camera needs an unobstructed view of the multiple trackers in the sterile field. Operating room (OR) personnel must adjust their positions to allow the camera to see the trackers; OR layout: In addition to line-of-sight issues, most systems have a large OR footprint, making them intrusive during OR set-up. In smaller ORs, these systems may not fit at all; Additional procedure time: Initially, tools and techniques were ported into arthroplasty navigation from neurosurgical or spinal applications, and would cause 20 30 minutes of additional procedure time. Though not significant where neuro and spinal surgeries would last for 5 1 hours, arthroplasty procedures generally last 1 hour, in which case 20 30 minutes is significant [12,13]; Personnel training requirements: Many systems require a dedicated operator running the computer system. Training hospital staff to run the navigation system computer is burdensome; Portability: Most hospitals have multiple surgeons running multiple ORs simultaneously. Robotic and navigation systems for arthroplasty lack portability to facilitate efficient transitions from OR to OR.
The genesis of the Intellijoint minioptical technology was at the University of Waterloo (Waterloo, ON, Canada) in 2007. In an undergraduate mechatronics design course, the Intellijoint design group was inspired to address the
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system is implemented in which the pose of the robotic manipulator is tracked, and control signals restrict the movements of the surgical tools so that bone removal is according to a surgical plan. This system relies on a segmented CT scan and a preoperatively developed surgical plan, and may be used for partial knee arthroplasty, total knee arthroplasty, and THA. Despite demonstrating increased accuracy and outlier reduction [5 8], surgical navigation and robotic systems have yet to gain widespread market adoption. As a result, surgeons continue to rely on manual techniques and mechanical instrumentation for implant positioning. One common exemplary manual technique is the use of fixed alignment guides on an acetabular implant inserter, as shown in Fig. 24.2. The fixed alignment guides provide the surgeon with a visual cue of the alignment of the acetabular implant inserter relative to the operating table. The numerous drawbacks of using fixed alignment guides include: the guide only provides a fixed, static target (the surgeon cannot effect a patient-specific target); and, the patient’s position on the operating table may shift during the procedure (causing alignment relative to the operating table to result in incorrect alignment relative to the patient). Although the success rate of orthopedic surgery is high [9], implant positioning-related complications still occur when using manual and mechanical techniques. Some commonly cited reasons that surgical navigation and robotic systems have experienced low adoption within orthopedics include:
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challenges faced by one of their fathers—a rural community orthopedic surgeon, who wanted access to assistive technology to allow him to align hip implants accurately and reproducibly. In his surgical setting, traditional orthopedic navigation technologies were prohibitive for many of the reasons outlined above. The Intellijoint minioptical technology was developed to overcome these barriers. In 2013, the Intellijoint minioptical technology was commercially introduced in Canada, and subsequently in the United States for controlled release of a minimally featured system (measurements of intraoperative leg length and offset change). In late 2015, a fully featured system based on the Intellijoint minioptical technology was introduced commercially in Canada and the United States, which included leg length, offset, and cup angle measurement capability.
24.2 24.2.1
Intellijoint minioptical technology System overview
The Intellijoint minioptical technology comprises a patient-mounted tracking camera within the surgical sterile field, as shown in Fig. 24.3. The camera is rigidly fixed to the bone via patient mounting hardware, and connected to a computer workstation (not shown) via universal serial bus (USB). The camera provides buttons so that a sterile user can control the computer workstation. The computer workstation runs image processing and computer vision algorithms to calculate and display implant positioning data, based on a video feed of the tracker. The tracker is shown attached to an acetabular inserter tool (with an acetabular implant on the distal end of the tool). The acetabular inserter is a part of the instrumentation associated with the acetabular implant, and the tracker interfaces with this tool across a variety of implant vendors via a magnetic v-block adaptor. An animation video illustrating the use of the Intellijoint minioptical technology in an anterior THA procedure is provided. Advantages of this system architecture, relative to the previously commercialized surgical navigation systems, include: G
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Minimal line-of-sight disruptions—as long as the line of sight between the camera and the tracker is unbroken, the system is expected to function; Sterile field control—the sterile user can interact with the computer workstation via buttons on the camera, without compromising sterility or requiring additional staff to run the computer; High portability and flexibility in OR configuration—with the exception of the computer workstation, the entire minioptical system operates within the sterile field; there is no large, bulky equipment to manage. Fig. 24.4 illustrates an OR in which a patient is positioned for hip arthroplasty surgery, along with the Intellijoint technology, comprising a minioptical camera (located on a standard sterile Mayo stand, prior to being mounted to the patient), FIGURE 24.3 Intellijoint minioptical technology for acetabular implant alignment in THA, including a camera (attached to the bone), and a tracker (attached to a surgical acetabular inserter). THA, Total hip arthroplasty.
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FIGURE 24.4 Operating room configuration including the Intellijoint system.
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FIGURE 24.5 Photograph of the camera.
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the workstation coupled to the camera via a wired connection (outside of the sterile field), and a tray with sterile instruments for coupling the camera and tracker to anatomical structures and instruments, respectively; The system is universally compatible with implant instrumentation via the tracker adaptor (many of the previous surgical navigation systems are designed for compatibility with a single implant vendor’s products).
24.2.2
Camera
The most novel aspect of the Intellijoint minioptical technology is the camera. The camera is the primary sensor for generating spatial tracking measurements (i.e., the position and orientation of the tracker component, described below). The camera also provides a three-button interface (green circle, x, and square) to send commands to the computer workstation, to which is it connected via USB. A photograph of the camera is provided in Fig. 24.5.
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The optical technology includes a single camera with a wide field of view lens, an infrared filter, a global shutter imager, and infrared illumination from light emitting diodes (LEDs) surrounding the lens. The camera is designed to be patient-mountable within a surgical sterile field, and/or handheld during use. A size comparison between the camera and a Polaris Optical Tracking System (Northern Digital Inc., Waterloo, ON, Canada)—a market leader in supplying the surgical navigation and robotic surgery industry—is provided in Fig. 24.6. The camera is designed to be enclosed within a sterile drape before being introduced into the sterile field. The sterile drape is a custom design for the Intellijoint minioptical camera, and comprises a long tubular section terminating in an optical window. The system is designed to compensate for the optical effects of the optical window, so as not to introduce measurement inaccuracies. The sterile drape and optical window are held in alignment with the camera via a shroud component; the shroud snaps onto features of the camera without risking puncture to the sterile drape. Fig. 24.7 illustrates a user snapping the shroud over a draped camera. For patient mounting, the ability to aim the camera in a desired direction (i.e., at the surgical site), as well as remove the camera when not in use are important design requirements. A camera clamp is used to rigidly hold the shroud/camera/sterile drape assembly. The camera clamp has a spherical inner-surface profile, and the shroud has a spherical outer surface profile; hence, when loosely engaged, the clamp forms a moveable ball joint assembly with the shroud/camera/ sterile drape. The camera may be aligned by moving the ball joint based on visual cues or on software guidance, and
FIGURE 24.6 Size comparison between Intellijoint minioptical technology and the Polaris system.
FIGURE 24.7 Applying the shroud over a draped camera.
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FIGURE 24.8 Clamp/Shroud/Camera assembly for camera aiming and quick attachment and detachment during use.
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Detecting movement of a patient during a surgical procedure, by monitoring their orientation with respect to gravity; Measuring an inertial vector (based on the direction of gravity), where optical measurements are not feasible; Detecting vibrations or unwanted movement of the camera that could compromise optical measurement integrity.
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Software framework
The Intellijoint minioptical technology includes a software framework, which receives USB camera data, and outputs pose (for use by the clinical application software). The software framework implements an image-processing pipeline to take a raw image, and compute a pose of a tracker within that image, based on a camera calibration and an expected tracker geometry. The high-level steps for determining pose are described below and illustrated in Fig. 24.9: G G
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A raw image 2D image is received into computer memory from the camera; Segment detection: Segments that may correspond to a tracker sphere are identified using segment detection techniques based on pixel intensity; Segment rejection: Since the tracker has four retroreflective spheres, four valid segments are expected. In this step, invalid segments are rejected based on various criteria, including size, shape, and relative spacing; Centroid detection: The 2D pixel centroids of the four valid segments are calculated (i.e., four sets of segment centroid coordinates); Point correspondence: The centroids are associated with the tracker sphere they represent. Heuristics based on expected relative spacing are used. The result is an ordered list of centroid coordinates; Pose calculation: A six degrees of freedom pose (x, y, z, roll, pitch, yaw) is calculated via a nonlinear optimization that receives the ordered list of centroid coordinates and camera and tracker models as inputs; This process is repeated for each image in a video stream running at 30 fps.
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when in the desired alignment, the clamp may be locked. To facilitate temporarily removing the camera (e.g., during a surgical step to avoid the camera being in the way), the clamp provides a magnetic kinematic mount interface. The kinematic mount interface is highly repeatable, so that the camera returns to the same location between attach/detach cycles. A photograph of the clamp/shroud/camera assembly (sterile drape not shown) is provided in Fig. 24.8. The camera interfaces with a computer workstation via a wired USB connection. The camera system is powered by the USB connection, without the need for any additional dedicated power supply. A 5-m USB cable is used, to ensure adequate length for any OR configuration, as well as to ensure that the workstation is out of the sterile field. This length is at the upper limit of the current USB standard. In addition to optical sensing, the camera includes an integrated three-axis accelerometer that is coregistered to the optical system, and calibrated to measure the camera’s orientation with respect to the direction of gravity. The resulting inertial measurements are provided in real time along with the optical camera feed. There are several possible use cases for inertial sensor measurements, including:
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FIGURE 24.9 Image processing pipeline.
The process for determining the inclination of the camera (based on accelerometer measurements) follows a similar method. The software framework sets limits on the optical tracking volume, to ensure accuracy. The validated tracking volume is illustrated in Fig. 24.10. In this figure, standard and extended tracking volumes are illustrated. In the extended tracking volume, angular constraints are added (in software) on the working volume, so that when in regions susceptible to pose calculation error (i.e., long distances away, at the edge of the imager), pose measurements of the tracker will not be generated.
24.2.4
Tracker
The Intellijoint minioptical system generates pose measurements between the camera and the tracker (shown in Fig. 24.11). The tracker provides four mounting posts at precisely known positions for attaching sterile retroreflective spheres (such as those marketed by Northern Digital Inc, Waterloo, ON, Canada). The retroreflective spheres reflect infrared illumination back toward the source (i.e., the camera), causing the spheres to appear brightly in the camera image. The tracker interfaces with various components (such as surgical tools) via a magnetic kinematic mount. The Intellijoint minioptical system may be deployed as a single-tracker system.
24.3
Minioptical system calibration
The Intellijoint minioptical system is designed to be “calibration-free,” in the sense that there are no field or preoperative calibration steps required. Other navigation systems (such as the Orthosoft Hip navigation system, marketed by Zimmer CAS, Montreal, QC, Canada) require surgical instruments to be calibrated preoperatively. The minioptical camera only requires factory calibration to consistently function correctly in the field, including when enclosed in the sterile drape. The monocular nature of the camera reduces the opto-mechanical complexity of the system, which enables robust, consistent adherence to the factory calibration. Conversely, for example, in a large-baseline
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FIGURE 24.10 Validated tracking volume.
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FIGURE 24.11 Tracker with retroreflective spheres.
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stereo camera system, the exact distance between both cameras is required to be precisely known, and is subject to various mechanical disturbances such as thermal deformation. Should a minioptical camera become compromised for any reason (e.g., damage to the lens), causing the calibration to no longer match the actual camera’s behavior, a software-implemented error metric will prevent inaccurate measurements, and prompt a potential replacement or servicing of the camera. The error metric is based on the optimization residual of the pose estimation operation, previously described. Trackers are not required to be calibrated, but rather rely on mechanical design and manufacturing processes that facilitate a robust adherence to a nominal model, known by the software. Similar to the minioptical camera, should a tracker ever become compromised for any reason (e.g., physical damage), the software-implemented error metric, based on the pose optimization residual, will prevent inaccurate measurements and prompt a potential replacement of the tracker component.
24.4 24.4.1
Clinical applications Intellijoint HIP
Intellijoint HIP is an imageless, portable, streamlined hip navigation system that provides measurements of acetabular implant inclination and anteversion, as well as change in leg length and offset. Intellijoint HIP is compatible with lateral, posterior, anterior, and revision THA workflows. The camera is mounted to the patient’s pelvis during the procedure, and the tracker can be mounted (at various points in time during the procedure) to the patient’s femur, registration instruments, and the acetabular implant inserter. Intellijoint HIP includes a set of sterile instruments used to mount the minioptical camera and the tracker to their respective objects. The sterile instruments are reusable, and autoclavable. Fig. 24.4 illustrates the sterile instruments within an OR configured for a THA procedure. Intellijoint HIP is a calibration-free system. The calibration of the minioptical system has been previously described. Additionally, no surgical instruments require preoperative calibration. This is primarily achieved through a magnetic v-block interface between the tracker and the acetabular implant inserter. The v-block is designed and manufactured to provide a known and repeatable angle with respect to any shaft (e.g., the shaft of an acetabular inserter tool) to which it is mounted. Fig. 24.3 shows the magnetic v-block component, coupling the tracker to the acetabular inserter tool. Intellijoint HIP does not require specific preoperative planning. Surgeons may plan their surgeries according to their standard methods, and use Intellijoint HIP intraoperatively to execute their plans. In some THA surgeries, there is a reliance on fluoroscopy to confirm acetabular implant inclination and anteversion, as well as change in leg length and offset. Intellijoint HIP is compatible with procedures using fluoroscopy (i.e., the system does not interfere with fluoroscopic imaging equipment), and has the potential to decrease the amount of fluoroscopy for a given procedure, since the surgeon may rely on Intellijoint HIP for measurements that would otherwise be captured via fluoroscopy. Fluoroscopy involves irradiating the patient and hospital staff; decreasing radiation is beneficial for those present in the OR. An example display screen, showing acetabular implant inclination and anteversion, is shown in Fig. 24.12, and a photograph of the sterile field corresponding to the display screen is shown in Fig. 24.13, in which a surgeon is holding the acetabular inserter with a tracker coupled thereto, and the camera is coupled to the patient’s pelvis.
24.4.2
Other applications
The Intellijoint minioptical technology may be applied to other procedures. It is well suited for patient-mounted, handheld or body worn, or robot-mounted applications, where sterile usage is required. Some example procedures include: G
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Total knee arthroplasty, where the technology could be used to make accurate bony cuts to ensure correct implant alignment; Cranial surgery, where the technology could be used to stereotactically access regions within a patient’s brain, for example, to take a biopsy; Ear, nose, and throat surgery, where the technology could be used to insert surgical tools into a particular cavity within a patient’s skull through their nose; Spinal surgery, where the technology could be used to drill a hole through the pedicle of a vertebra without risking breaching the spinal column.
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FIGURE 24.12 Acetabular implant alignment screen.
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FIGURE 24.13 Photograph of intellijoint HIP in use for acetabular implant inclination and anteversion measurement.
24.5
Accuracy performance
To quantify the accuracy performance of the Intellijoint minioptical technology, a standard protocol was applied (ASTM 2554-10 Standard Practice for Measurement of Positional Accuracy of Computer Assisted Surgery Systems). A calibrated phantom with precisely known divot locations (see Fig. 24.14) is used as a ground truth. This phantom is specified by the standard, and includes an array of divots at known spatial locations [measured by a coordinate measurement machine (CMM)]. The Intellijoint minioptical system generates 3D measurements of the phantom divot locations by attaching a ball-tipped probe to the end of the tracker, and mating the probe tip with any divot. Those measurements are compared to the known spatial locations to quantify accuracy. The phantom divots are measured with a CMM to an accuracy of 0.1 mm. Divots are arranged at various heights throughout a 20 3 20 cm volume, grouped into sets of five. A photograph of the phantom set up for use, including a tracker with a ball-tipped probe attached thereto is provided in Fig. 24.15.
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FIGURE 24.14 Accuracy phantom used to perform positional accuracy testing according to ASTM 2554-10.
FIGURE 24.15 Accuracy phantom in use by a user.
The results of design verification testing demonstrated that the Intellijoint minioptical system is capable of localizing a single point with a precision of 0.54 mm (RMS), and the distance between any two points with worst-case accuracy of 0.28 mm (RMS) [note: the accuracy between two points (0.28 mm RMS) is less than the precision of a single point (0.54 mm RMS), since the accuracy metric utilizes an average measured position at each of the two points]. The significance of these results is that the Intellijoint minioptical system should be expected to normally measure with submillimetric accuracy in space. This is sufficient for many clinical applications.
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Conclusion
The Intellijoint minioptical technology enables accurate surgical navigation via a patient-mounted camera directly within the sterile field, and overcomes many of the barriers to adoption of traditional arthroplasty navigation systems (e.g., cost, line-of-sight issues, portability, etc.). Its utility in THA has been demonstrated via Intellijoint HIP, a commercially available system for providing a surgeon with measurements of acetabular implant angles and positional changes to leg length and offset.
24.7
Challenges and further development
The Intellijoint minioptical technology has not been proven outside of THA. It is speculated that this technology would be well suited for a variety of clinical applications, such as knee, cranial, spinal, and ear, nose, and throat surgery; however, further development should be conducted to confirm this hypothesis. Further, the Intellijoint minioptical technology has only been used in an “imageless” context (i.e., no registration to a 3D medical image dataset). Further development focus may include image-based applications. Although already much smaller than other optical navigation technologies, another area of development may include further miniaturization of the camera and tracker, to enable different types of surgery. Another potentially advantageous application for this technology is integration with robotics. The camera is sufficiently small so as to be mountable directly to a robotic manipulator. It is speculated that the camera may be used as a pose measurement sensor in a closed-loop robotic control system.
[1] Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am 2007;89(8):1832 42. [2] Masaoka T, Yamamoto K, Shishido T, Katori Y, Mizoue T, Shirasu H, et al. Study of hip joint dislocation after total hip arthroplasty. Int Orthop 2006;30(1):26 30. [3] Nishii T, Sugano N, Miki H, Koyama T, Takao M, Yoshikawa H. Influence of component positions on dislocation: computed tomographic evaluations in a consecutive series of total hip arthroplasty. J Arthroplasty 2004;19(2):162 6. [4] FDA. 510(k) Premarket notification. US Food and Drug Administration; 2017 [cited December 19, 2017]. Available from: ,https://www. accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm.. [5] Gurgel HM, Croci AT, Cabrita HA, Vicente JR, Leonhardt MC, Rodrigues JC. Acetabular component positioning in total hip arthroplasty with and without a computer-assisted system: a prospective, randomized and controlled study. J Arthroplasty 2014;29(1):167 71. [6] Lass R, Kubista B, Olischar B, Frantal S, Windhager R, Giurea A. Total hip arthroplasty using imageless computer-assisted hip navigation: a prospective randomized study. J Arthroplasty 2014;29(4):786 91. [7] Lin F, Lim D, Wixson RL, Milos S, Hendrix RW, Makhsous M. Limitations of imageless computer-assisted navigation for total hip arthroplasty. J Arthroplasty 2011;26(4):596 605. [8] Najarian BC, Kilgore JE, Markel DC. Evaluation of component positioning in primary total hip arthroplasty using an imageless navigation device compared with traditional methods. J Arthroplasty 2009;24(1):15 21. [9] Shan L, Shan B, Graham D, Saxena A. Total hip replacement: a systematic review and meta-analysis on mid-term quality of life. Osteoarthritis Cartilage 2014;22(3):389 406. [10] Slover JD, Tosteson AN, Bozic KJ, Rubash HE, Malchau H. Impact of hospital volume on the economic value of computer navigation for total knee replacement. J Bone Joint Surg Am 2008;90(7):1492 500. [11] Brown ML, Reed JD, Drinkwater CJ. Imageless computer-assisted versus conventional total hip arthroplasty: one surgeon’s initial experience. J Arthroplasty 2014;29(5):1015 20. [12] Manzotti A, Cerveri P, De Momi E, Pullen C, Confalonieri N. Does computer-assisted surgery benefit leg length restoration in total hip replacement? Navigation versus conventional freehand. Int Orthop 2011;35(1):19 24. [13] Kalteis T, Handel M, Bathis H, Perlick L, Tingart M, Grifka J. Imageless navigation for insertion of the acetabular component in total hip arthroplasty: is it as accurate as CT-based navigation? J Bone Joint Surg Br 2006;88(2):163 7.
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References