James E. Moody

Functional pelvic orientation measured from lateral standing and sitting radiographs.

We prospectively obtained preoperative and 3-month postoperative lateral pelvic radiographs in the standing and sitting positions from 84 patients who underwent total hip arthroplasty. We measured pelvic orientation (flexion extension) using the anterior pelvic plane as defined by the anterior superior iliac spines and pubic tubercles as references. There was a trend towards upright pelvic alignment when standing, with a mean anterior pelvic plane angle of 1.2° (range, −22°-+27°). In the sitting position the pelvis tended to extend posteriorly, with a mean anterior pelvic plane angle of −36.2° (range, −64°-+4°). There was a wide variation in the arc of pelvic flexion extension as patients moved from standing to sitting, with arc of pelvic motion in some patients as mobile as 70° and in others as stiff as 5°. There was no significant variation between males and females or between preoperative and postoperative pelvic flexion extension. There were substantial variations in pelvic orientation when comparing standing and sitting for an individual patient and between different patients. This variation can be unpredictable, and may influence implant alignment and stability after total hip arthroplasty.Level of Evidence: Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Surgical navigation for total hip replacement with the use of hipnav

HipNav, an image-guided surgical navigation system, is presented. The system was developed to measure and guide the placement of prosthetic components in total hip replacement surgery (THR), it incorporates a 3-dimensional preoperative planner with a simulator and an intraoperative surgical navigator. Coupling optimized preoperative planning with accurate surgical navigation will assist the surgeon in properly orienting the components, minimizing the risk of impingement and dislocation. Intraoperatively, the system uses image-guided tools to assist in accurate placement of the acetabular cup. The acetabular implant is placed in the planned position with the aid of a simple “aim-and-shoot” interface. The actual measurements of version and abduction are also provided. The use of this new class of operative sensors has been incorporated into a regular surgical routine. There are few additional steps necessary, therefore, for the image-guided procedure, which does not add significantly to the total time of surgery. We expect that these tools will lead to less invasive and more accurate THR surgery and directly relate patient outcomes to measured surgical practice.

Computer evaluation of kinematics of anterior cruciate ligament reconstructions.

Current clinical and instrumented outcome measurements of knee instability lack accuracy, especially when multiplanar instability is considered. The aim of our cadaveric study was to describe the kinematics in the intact, double bundle, and anteromedial bundle reconstructed anterior cruciate ligament knee by applying a protocol for computer-assisted evaluation of knee kinematics. An optical navigation system was used to acquire knee motion (n = 5) during clinical evaluations by tracking markers rigidly attached to the bones. The protocol included acquisition of anteroposterior translations and internal-external rotations and evaluation of three clinical knee laxity tests (anterior drawer, manual, and instrumented Lachman). Our anteroposterior translation data showed the double-bundle technique and anteromedial bundle technique could restore anteroposterior stability comparable to the intact state. For internal-external laxity, the double-bundle technique demonstrated overcorrection at 15°, 60°, 75°, and 90°. The anterior drawer and manual Lachman knee laxity tests showed improved stability for the double-bundle compared to the anteromedial bundle technique. This pilot study suggests the computation of knee laxity with a high precision method might be a step toward a more precise kinematic test of knee stability for evaluating different reconstruction methods.Level of Evidence: Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Surgical Navigation for THR: A Report on Clinical Trial Utilizing HipNav

Computer-assisted Total Hip Replacement (THR) surgery using the HipNav surgical navigational system was evaluated. This summary reports on the first 100 HipNav clinical trial patients and focuses on: 1) patient demographics, 2) post-operative clinical outcomes, 3) incision length measurements, 4) mechanical guide measures, and 5) functional pelvic tilt measurements. Results from this clinical trial have shown no system-related complications, an improvement in post-operative clinical outcomes, reductions in soft tissue dissection, an unreliability of traditional mechanical alignment guides, and a variability of pelvic orientation during functional activity.

Calibration Method for Determining the Physical Location of the Ultrasound Image Plane

This paper describes a calibration method for determining the physical location of the ultrasound (US) image plane relative to a rigidly attached 3D position sensor. A calibrated US probe can measure the 3D spatial location of anatomic structures relative to a global coordinate system. The calibration is performed by aiming the US probe at a calibration target containing a known point (1 mm diameter sphere) in physical space. This point is repeatedly collected at various locations in the US image plane to produce the calibration dataset. An idealized model of the collection process is used to eliminate outliers from the calibration dataset and also to examine the theoretical accuracy limits of this method. The results demonstrate accurate and robust calibration of the 3D spatial relationship between the US image plane and the 3D position sensor.

Post-Operative Measurement of Acetabular Cup Position Using X-Ray/CT Registration

This paper describes a system for measuring acetabular implant orientation following total hip replacement surgery. After a manual initialization procedure, the position of the pelvis is established relative to a pair of nearly orthogonal radiographs by automatically registering to pre-operative pelvic CT data. The pose of the cup is then recovered by projecting a 3D surface model into the two images. A phantom study is presented in which this pose is expressed relative to well defined anatomical landmarks and compared to measurements obtained using an image-guided surgery system.

Gauging Clinical Practice: Surgical Navigation for Total Hip Replacement

HipNav is a hip implant navigation and guidance system which helps surgeons plan acetabular implant orientation preoperatively, and guides them intraoperatively to achieve this intended plan. Through this process, these technologies are used to measure, gauge, and quantify current clinical practice. With HipNav, surgeons plan and execute the procedure in the 3-D realm with accurate patient models, taking advantage of anatomic information normally lost through traditional planning methods. During surgery HipNav tracks the alignment tool with respect to the pelvis, compensating for any pelvic motion, thereby ensuring an accurate measurement of alignment and placement according to the plan.

Computer-assisted evaluation of kinematics of the two bundles of the anterior cruciate ligament.

Abstract The aim of this cadaveric study was to describe the kinematics of the anterior cruciate ligament (ACL)-intact, posterolateral (PL) bundle-deficient and ACL-deficient knee by applying a protocol for computer-assisted evaluation of knee kinematics. The hypothesis that the PL bundle functions mainly at low knee flexion angles was tested. An optical tracking system was used to acquire knee joint motion on 10 knees during clinical evaluations by tracking markers rigidly attached to the bones. The protocol included acquisition of anterior-posterior (AP) translations and internal-external (IE) rotations, and evaluation of three clinical knee laxity tests (anterior drawer, manual and instrumented Lachman). The data demonstrated no significant contribution to AP translation and IE laxity from the PL bundle over the entire range of motion. The clinical knee laxity tests showed no significant differences between the ACL-intact and PL bundle-deficient states. The hypothesis could not be proven. Current clinical knee laxity measurements may not be suited for detecting subtle changes such as PL bundle deficiency in the ACL anatomy. The computation of knee laxity might be a step towards a more precise kinematic test of knee stability not only in the native and torn ACL state of the knee but also in the reconstructed knee. Zusammenfassung Ziel der Kadaverstudie war, die Kinematik von Kniegelenken mit intaktem, PL-Bündel-defizientem und defizientem VKB mit Hilfe eines Protokolls für Computer-assistierte Beurteilung von Gelenkkinematiken zu untersuchen. Die Hypothese war, dass das PL-Bündel primär bei niedrigen Flexionsgraden das Kniegelenk stabilisiert. Ein optisches Positionsmesssystem wurde benutzt, um Bewegungen von 10 verschiedenen Kniegelenken während der klinischen Tests zu dokumentieren. Das Protokoll beinhaltete die Erfassung von anteriorposteriorer Translation, Innen- und Außenrotation, manuellem und instrumentiertem Lachman-Test sowie vorderer Schublade. Die Daten zeigten keinen signifikanten Anteil des PL- Bündels für anteriorposteriore Translation und Innen- und Außenrotation über das gesamte Bewegungsausmaß des Kniegelenkes. Die klinischen Tests zeigten ebenso keine signifikanten Unterschiede zwischen VKB-intakten und PL-Bündel-defizienten Kniegelenken. Die Hypothese konnte somit nicht bestätigt werden. Gegenwärtige klinische Knietests sind möglicherweise nicht geeignet, um kleine Unterschiede in der VKB-Anatomie wie PL-Bündel-Läsionen zu beurteilen. Die Dokumentation der Kniegelenklaxizität mit dem Computer mag ein Schritt für eine präzisere kinematische Gelenkbeurteilung, nicht nur bei intaktem und defizientem VKB, sondern auch bei verschiedenen Rekonstruktionen sein.