Bone Morphing: 3D Morphological Data for Total Knee Arthroplasty

Imageless robotic total knee arthroplasty determines similar coronal plane alignment of the knee (CPAK) parameters to long leg radiographs

BACKGROUND

The coronal plane alignment of the knee (CPAK) classification was first developed using long leg radiographs (LLR) and has since been reported using image-based and imageless robotic total knee arthroplasty (TKA) systems. However, the correspondence between imageless robotics and LLR-derived CPAK parameters has yet to be investigated. This study therefore examined the differences in CPAK parameters determined with LLR and imageless robotic navigation using either generic or optimized cartilage wear assumptions.

METHODS

Medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were determined from the intraoperative registration data of 61 imageless robotic TKAs using either a generic 2 mm literature-based wear assumption (Navlit) or an optimized wear assumption (Navopt) found using an error minimization algorithm. MPTA and LDFA were also measured from preoperative LLR by two observers and intraclass correlation coefficients (ICCs) were calculated. MPTA, LDFA, joint line obliquity (JLO), and arithmetic hip-knee-ankle angle (aHKA) were compared between the robotic and the average LLR measurements over the two observers.

RESULTS

ICCs between observers for LLR were over 0.95 for MPTA, LDFA, JLO, and aHKA, indicating excellent agreement. Mean CPAK differences were not significant between LLR and Navlit (all differences within 0.6°, P > 0.1) or Navopt (all within 0.1°, P > 0.83). Mean absolute errors (MAE) between LLR and Navlit were: LDFA = 1.4°, MPTA = 2.0°, JLO = 2.1°, and aHKA = 2.7°. Compared to LLR, the generic wear classified 88% and the optimized wear classified 94% of knees within one CPAK group. Bland-Altman comparisons reported good agreement for LLR vs. Navlit and Navopt, with > 95% and > 91.8% of measurements within the limits of agreement across all CPAK parameters, respectively.

CONCLUSIONS

Imageless robotic navigation data can be used to calculate CPAK parameters for arthritic knees undergoing TKA with good agreement to LLR. Generic wear assumptions determined MPTA and LDFA with MAE within 2° and optimizing wear assumptions showed negligible improvement.

Accuracy of intraoperative bone registration and stereotactic boundary reconstruction during total knee arthroplasty surgery

BACKGROUND

The intraoperative registration of the bones play a crucial role in image-based computer-assisted knee arthroplasty to achieve accurate implant placement and to create reliable stereotactic bone boundaries for robot-assisted surgical systems.

METHOD

This study assessed the intraoperative registration accuracy on six intact fresh frozen cadavers.

RESULTS

Rotational errors around the mechanical axis were the largest, with a standard deviation of 1.2° and outliers up to 3.7°. The mean translational errors were lower than 1 mm, with outliers up to 1.5 mm. These errors were amplified to 2 mm for the registration-based reconstruction of the posterior bone surface at the resection levels.

CONCLUSION

Given the cumulative behaviour of surgical errors, registration errors can affect the final implant positioning. Furthermore, inaccuracies in the reconstructed bone boundary directly affect the virtual stereotactic boundaries used in robotic-assisted surgery and can result in an incomplete resection or inadvertent soft tissue damage.

Mechanical Alignment in Knee Replacement Homogenizes Postoperative Coronal Hip-Knee-Ankle Angle in Varus Knees: A Navigation-Based Study

After knee replacement, postoperative lower limb alignment is influenced by the geometry of the prosthesis position and surrounding soft tissue that contributes to the hip-knee-ankle (HKA) angle. The purpose of this study is to determine the dynamic coronal HKA angle after mechanical alignment in total knee replacement using computer navigation. We conducted a pre-post design study of 71 patients with varus osteoarthritic knees on which total knee arthroplasty was performed. The HKA was measured before and at the end of the surgical procedure with the patient in the supine position using a navigation system at 30, 60, and 90 degrees of knee flexion. Postoperative implant position and flexion and extension gaps were assessed. HKA was clustered in three preoperative dynamic patterns (PDPs; Varus-Neutral, Varus-Valgus, and Varus-Varus). There were statistically significant differences in the dynamic coronal HKA between the preoperative and postoperative statuses after mechanically aligned knee replacement (with p < 0.0001) Before the surgical procedure, statistically significant differences were found between patterns at any angle of flexion confirming a well-differentiated preoperative dynamic behavior between the three groups. Postoperatively, 98.6% (71 out of 72) of the knees were within ± 3 degrees of the HKA at full extension. Fifty-eight knees (80.6%) were assessed to a "within-range" postoperative dynamic alignment at any grade of flexion considered. There are differences between the preoperative and postoperative status of the dynamic coronal HKA angle after mechanically aligned knee replacement. We proposed that an excellent dynamic HKA alignment is achieved not only at full extension within the range of 0 ± 3 degrees but also when this alignment is maintained at 30, 60, and 90 degrees.

Robotic-assisted total knee arthroplasty with the OMNIBot platform: a review of the principles of use and outcomes

INTRODUCTION

Technology that enables the orthopaedic surgeon to deliver a surgical plan with precision and reproducibility continues to evolve. Robotic TKA represents the next phase of technological development in knee arthroplasty. Multiple propriety robotic platforms are now available for use in TKA, and one such system is the OMNIBotics platform. We conducted a review of this system, reporting its history and principles of use, published outcomes and our own personal experience performing OMNI robotic-assisted TKAs.

MATERIALS AND METHODS

A literature review was conducted using the PRISMA guidelines. Thirteen papers were included for the final review.

RESULTS

The OMNIBot is an accurate and consistent delivery tool in TKA surgery and compares favourably to instrumented, navigation-assisted and patient-specific cutting guides. The OMNIBot has been shown to be a reliable tool for delivering different alignment philosophies as well as planning and achieving tibio-femoral coronal balancing. The utility of the system is increased when the robot is used in conjunction with a soft-tissue tensioning device-the BalanceBot. Data regarding PROM's are limited, however results to date show reliable outcomes. Survival analysis of RATKA using the OMNIBot is limited to one study which reported 99.26% survivorship at 3 years. We report our own outcomes using the OMNIBot, having performed 766 TKA's using the OMNIBot, since 2014 with 99.48% survivorship at 6 year follow-up.

CONCLUSION

The OMNIBot platform is an imageless, passive robotic system available since 2007, with over 30,000 TKA's being performed with its assistance. It has a small physical footprint, is relatively inexpensive and time efficient. Our review demonstrates a high level of precision of the surgical planning, with a modestly improved accuracy compared to conventional and navigation technology. Published outcomes are limited, however demonstrate good short-term PROM's and survivorship data that compare favourably to other robotic TKA cohorts.

Contemporary Robotic Systems in Total Knee Arthroplasty: A Review of Accuracy and Outcomes

The success of total knee arthroplasty (TKA) depends on restoration of the stability and biomechanical efficiency of the native knee. The emergence of robotic surgical technologies has greatly increased the precision and reproducibility. We discuss contemporary robotic TKA systems by reviewing the features of the individual platforms, their accuracy, and the clinical outcomes. While early results suggest significant gains in patient outcomes, long-term evidence is still awaited from multicenter prospective clinical trials. Moreover, advances in this technology are needed to address knee laxity while individualizing the functional performance of each patient's new joint.

Computer assisted orthopaedic surgery: Past, present and future

Computer technology is ubiquitous and relied upon in virtually all professional activities including neurosurgery, which is why it is surprising that it is not the case for orthopaedic surgery with fewer than 5% of surgeons using available computer technology in their procedures. In this review, we explore the evolution and background of Computer Assisted Orthopaedic Surgery (CAOS), delving into the basic principles behind the technology and the changes in the discussion on the subject throughout the years and the impact these discussions had on the field. We found evidence that industry had an important role in driving the discussion at least in knee arthroplasty-a leading field of CAOS-with the ratio between patents and publications increased from approximately 1:10 in 2004 to almost 1:3 in 2014. The adoption of CAOS is largely restrained by economics and ergonomics with sceptics challenging the accuracy and precision of navigation during the early years of CAOS moving to patient functional improvements and long term survivorship. Nevertheless, the future of CAOS remains positive with the prospect of new technologies such as improvements in image-guided surgery, enhanced navigation systems, robotics and artificial intelligence.

Clinical relevance of augmented statistical shape model of the scapula in the glenoid region

OBJECTIVE

To illustrate (a) whether a statistical shape model (SSM) augmented with anatomical landmark set(s) performs better fitting and provides improved clinical relevance over non-augmented SSM and (b) which anatomical landmark set provides the best augmentation strategy for predicting the glenoid region of the scapula.

METHODS

Scapula SSM was built using 27 dry bone CT scans and augmented with three anatomical landmark sets (16 landmarks each) resulting in three augmented SSMs (aSSM_proposed, aSSM_set1, aSSM_set2). The non-augmented and three augmented SSMs were then used in a non-rigid registration (regression) algorithm to fit to six external scapular shapes. The prediction error by each type of SSM was evaluated in the glenoid region for the goodness of fit (mean error, root mean square error, Hausdorff distance and Dice similarity coefficient) and for four anatomical angles (critical shoulder angle, lateral acromion angle, glenoid inclination, glenopoar angle).

RESULTS

Inter- and intra-observer reliability for landmark selection was moderate to excellent (ICC>0.74). Prediction error was significantly lower for SSM_{non-augmented} for mean (0.9 mm) and root mean square (1.15 mm) distances. Dice coefficient was significantly higher (0.78) for aSSM_proposed compared to all other SSM types. Prediction error for anatomical angles was lowest using the aSSM_proposed for critical shoulder angle (3.4°), glenoid inclination (2.6°), and lateral acromion angle (3.2°).

CONCLUSION AND SIGNIFICANCE

The conventional SSM robustness criteria or better goodness of fit do not guarantee improved anatomical angle accuracy which may be crucial for certain clinical applications in pre-surgical planning. This study provides insights into how SSM augmented with region-specific anatomical landmarks can provide improved clinical relevance.

Total knee arthroplasties from the origin to navigation: history, rationale, indications

Since the early 1970s, total knee arthroplasties have undergone many changes in both their design and their surgical instrumentation. It soon became apparent that to improve prosthesis durability, it was essential to have instruments which allowed them to be fitted reliably and consistently. Despite increasingly sophisticated surgical techniques, preoperative objectives were only met in 75% of cases, which led to the development, in the early 1990s, in Grenoble (France), of computer-assisted orthopaedic surgery for knee prosthesis implantation. In the early 2000s, many navigation systems emerged, some including pre-operative imagery ("CT-based"), others using intra-operative imagery ("fluoroscopy-based"), and yet others with no imagery at all ("imageless"), which soon became the navigation "gold standard". They use an optoelectronic tracker, markers which are fixed solidly to the bones and instruments, and a navigation workstation (computer), with a control system (e.g. pedal). Despite numerous studies demonstrating the benefit of computer navigation in meeting preoperative objectives, such systems have not yet achieved the success they warrant, for various reasons we will be covering in this article. If the latest navigation systems prove to be as effective as the older systems, they should give this type of technology a well-deserved boost.

Strain-Initialized Robust Bone Surface Detection in 3-D Ultrasound

Three-dimensional ultrasound has been increasingly considered as a safe radiation-free alternative to radiation-based fluoroscopic imaging for surgical guidance during computer-assisted orthopedic interventions, but because ultrasound images contain significant artifacts, it is challenging to automatically extract bone surfaces from these images. We propose an effective way to extract 3-D bone surfaces using a surface growing approach that is seeded from 2-D bone contours. The initial 2-D bone contours are estimated from a combination of ultrasound strain images and envelope power images. Novel features of the proposed method include: (i) improvement of a previously reported 2-D strain imaging-based bone segmentation method by incorporation of a depth-dependent cumulative power of the envelope into the elastographic data; (ii) incorporation of an echo decorrelation measure-based weight to fuse the strain and envelope maps; (iii) use of local statistics of the bone surface candidate points to detect the presence of any bone discontinuity; and (iv) an extension of our 2-D bone contour into a 3-D bone surface by use of an effective surface growing approach. Our new method produced average improvements in the mean absolute error of 18% and 23%, respectively, on 2-D and 3-D experimental phantom data, compared with those of two state-of-the-art bone segmentation methods. Validation on 2-D and 3-D clinical in vivo data also reveals, respectively, an average improvement in the mean absolute fitting error of 55% and an 18-fold improvement in the computation time.

A novel 3D approach for determination of frontal and coronal plane tibial slopes from MR imaging

BACKGROUND

The proximal tibia is geometrically complex, asymmetrical, and variable, is heavily implicated in arthrokinematics of the knee joint, and thus a contributor to knee pathologies such as non-contact anterior cruciate ligament injury. Medial, lateral, and coronal tibial slopes are anatomic parameters that may increase predisposition to knee injuries, but the extent to which each contributes has yet to be fully realized. Previously, two-dimensional methods have quantified tibial slopes, but more reliable 3D methods may prove advantageous.

AIMS

(1) to explore the reliability of two-dimensional methods, (2) to introduce a novel three-dimensional measurement approach, and (3) to compare data derived from traditional and novel methods.

METHODS

Medial, lateral, and coronal tibial slope geometry from both knees (left and right) of one subject were obtained via magnetic resonance images and measured by four trained observers from two-dimensional views. The process was repeated via three-dimensional approaches and data evaluated for intra- and inter-rater reliability.

RESULTS

The conventional method presented a weaker Intraclass Correlation Coefficient (ICC) for the measured slopes (ranging from 0.43 to 0.81) while the resultant ICC for the proposed method indicated greater reliability (ranging from 0.84 to 0.97). Statistical analysis supported the novel approach for production of more reliable and repeatable results for tibial slopes.

CONCLUSIONS

The novel three-dimensional method for calculating tibial plateau slope may be more reliable than previously established methods and may be applicable in assessment of susceptibility to osteoarthritis, as part of anterior cruciate ligament injury risk assessment, and in total knee implant design.

Computer-Assisted Orthopedic Surgery: Current State and Future Perspective

Introduced about two decades ago, computer-assisted orthopedic surgery (CAOS) has emerged as a new and independent area, due to the importance of treatment of musculoskeletal diseases in orthopedics and traumatology, increasing availability of different imaging modalities, and advances in analytics and navigation tools. The aim of this paper is to present the basic elements of CAOS devices and to review state-of-the-art examples of different imaging modalities used to create the virtual representations, of different position tracking devices for navigation systems, of different surgical robots, of different methods for registration and referencing, and of CAOS modules that have been realized for different surgical procedures. Future perspectives will also be outlined.

A Three-Dimensional Statistical Average Skull: Application of Biometric Morphing in Generating Missing Anatomy

PURPOSE

The utilization of three-dimensional modeling technology in craniomaxillofacial surgery has grown exponentially during the last decade. Future development, however, is hindered by the lack of a normative three-dimensional anatomic dataset and a statistical mean three-dimensional virtual model. The purpose of this study is to develop and validate a protocol to generate a statistical three-dimensional virtual model based on a normative dataset of adult skulls.

METHOD

Two hundred adult skull CT images were reviewed. The average three-dimensional skull was computed by processing each CT image in the series using thin-plate spline geometric morphometric protocol. Our statistical average three-dimensional skull was validated by reconstructing patient-specific topography in cranial defects. The experiment was repeated 4 times. In each case, computer-generated cranioplasties were compared directly to the original intact skull. The errors describing the difference between the prediction and the original were calculated.

RESULTS

A normative database of 33 adult human skulls was collected. Using 21 anthropometric landmark points, a protocol for three-dimensional skull landmarking and data reduction was developed and a statistical average three-dimensional skull was generated. Our results show the root mean square error (RMSE) for restoration of a known defect using the native best match skull, our statistical average skull, and worst match skull was 0.58, 0.74, and 4.4  mm, respectively.

CONCLUSIONS

The ability to statistically average craniofacial surface topography will be a valuable instrument for deriving missing anatomy in complex craniofacial defects and deficiencies as well as in evaluating morphologic results of surgery.

A novel registration method for computer-assisted total knee arthroplasty using a patient-specific registration guide

Total knee arthroplasty (TKA) is a surgical method for replacing a degenerated or diseased knee joint that can no longer perform daily functions with an artificial knee implant. In TKA, the artificial knee implant should be inserted such that it aligns well with the mechanical axis of the leg. Thus, precise bone cutting is essential. To improve TKA outcomes, a registration process is performed to locate the predetermined bone cutting area by calculating the position and posture of the femur and tibia. In this article, we propose a patient-specific registration guide that is able to significantly reduce registration time and effort without loss of accuracy. Furthermore, the patient-specific registration guide can be implemented with real-time registration, allowing continuous surgical information to be provided without the insertion of any tracking devices. The precision and accuracy of the proposed registration guide were confirmed through animal tests with a digitizer, stereo camera, and linear motion generator. The error of our registration method, including measurement and guide attachment errors, reached a maximum of 0.321 mm for one pair of cow legs.

Recutting the distal femur to increase maximal knee extension during TKA causes coronal plane laxity in mid-flexion

BACKGROUND

The aim of this study was to quantify the effects of distal femoral cut height on maximal knee extension and coronal plane knee laxity.

METHODS

Seven fresh-frozen cadaver legs from hip-to-toe underwent a posterior stabilized TKA using a measured resection technique with a computer navigation system equipped with a robotic cutting guide. After the initial femoral resections were performed, the posterior joint capsule was sutured until a 10° flexion contracture was obtained with the trial components in place. Two distal femoral recuts of +2mm each were then subsequently made and the trials were reinserted. The navigation system was used to measure the maximum extension angle achieved and overall coronal plane laxity [in degrees] at maximum extension, 30°, 60° and 90° of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee.

RESULTS

For a 10 degree flexion contracture, performing the first distal recut of +2mm increased overall coronal plane laxity by approximately 4.0° at 30° of flexion (p=0.002) and 1.9° at 60° of flexion (p=0.126). Performing the second +2mm recut of the distal femur increased mid-flexion laxity by 6.4° (p<0.0001) at 30° and 4.0° at 60° of flexion (p=0.01), compared to the 9 mm baseline resection (control). Maximum knee extension increased from 10° of flexion to 6.4° (± 2.5° SD, p<0.005) and to 1.4° (± 1.8° SD, p<0.001) of flexion with each 2mm recut of the distal femur.

CONCLUSIONS

Recutting the distal femur not only increases the maximum knee extension achieved but also increases coronal plane laxity in midflexion.

The effect of proximal tibial slope on dynamic stability testing of the posterior cruciate ligament- and posterolateral corner-deficient knee

BACKGROUND

Proximal tibial slope has been shown to influence anteroposterior translation and tibial resting point in the posterior cruciate ligament (PCL)-deficient knee. The effect of proximal tibial slope on rotational stability of the knee is unknown.

HYPOTHESIS

Change in proximal tibial slope produced via osteotomy can influence both static translation and dynamic rotational kinematics in the PCL/posterolateral corner (PLC)-deficient knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Posterior drawer, dial, and mechanized reverse pivot-shift (RPS) tests were performed on hip-to-toe specimens and translation of the lateral and medial compartments measured utilizing navigation (n = 10). The PCL and structures of the PLC were then sectioned. Stability testing was repeated, and compartmental translation was recorded. A proximal tibial osteotomy in the sagittal plane was then performed achieving either +5° or -5° of tibial slope variation, after which stability testing was repeated (n = 10). Analysis was performed using 1-way analysis of variance (ANOVA; α = .05).

RESULTS

Combined sectioning of the PCL and PLC structures resulted in a 10.5-mm increase in the posterior drawer, 15.5-mm increase in the dial test at 30°, 14.5-mm increase in the dial test at 90°, and 17.9-mm increase in the RPS (vs intact; P < .05). Increasing the posterior slope (high tibial osteotomy [HTO] +5°) in the PCL/PLC-deficient knee reduced medial compartment translation by 3.3 mm during posterior drawer (vs deficient; P < .05) but had no significant effect on the dial test at 30°, dial test at 90°, or RPS. Conversely, reversing the slope (HTO -5°) caused a 4.8-mm increase in medial compartment translation (vs deficient state; P < .05) during posterior drawer and an 8.6-mm increase in lateral compartment translation and 9.0-mm increase in medial compartment translation during RPS (vs deficient state; P < .05).

CONCLUSION

Increasing posterior tibial slope diminished static posterior instability of the PCL/PLC-deficient knee as measured by the posterior drawer test but had little effect on rotational or dynamic multiplanar stability as assessed by the dial and RPS tests, respectively. Conversely, decreasing posterior slope resulted in increased posterior instability and a significant increase in the magnitude of the RPS.

CLINICAL RELEVANCE

These results suggest that increasing posterior tibial slope may improve sagittal stability in the PCL/PLC-deficient knee. Moreover, a knee with diminished posterior tibial slope may demonstrate greater multiplanar instability in this setting. Consequently, proximal tibial slope should be considered when treating combined PCL/PLC injuries of the knee.

Profile of the distal femur anterior cortex--a computer-assisted cadaveric study

INTRODUCTION

Accurate positioning and sizing of the femoral component in total knee arthroplasty is important for stability and functional outcome. The purpose of the study was to evaluate the bony profiles of the distal anterior femoral cortex (AFC).

MATERIALS AND METHODS

Anatomical bony landmarks on 50 adult cadaveric femora were collected. Critical points were used to identify the distal AFC surface.

RESULTS

There were four anterior cortex profiles: (1) lateral side highest and medial side lowest (56%); (2) lowest height in median area (26%); (3) highest height in median area (14%); (4) medial side highest and lateral side lowest (4%).

DISCUSSION

Anterior referencing in TKA needs to represent the anterior shape of the distal femoral cortex to prevent notching, femoro-patellar overstuffing or flexion gap mismanagement. Due to the variability of the AFC, surgeons have to carefully select the AFC landmark to be sure of avoiding complications.

Effect of meniscal loss on knee stability after single-bundle anterior cruciate ligament reconstruction

PURPOSE

The menisci are known to be important secondary constraints to anterior translation of the tibia in the ACL-deficient knee. The effect of meniscal loss on knee stability as measured by the magnitude of the pivot shift following ACL reconstruction is unknown. The objective of this investigation was to determine the effect of meniscectomy on knee stability following two single-bundle ACL reconstruction strategies.

MATERIALS AND METHODS

A mechanized pivot shift was performed on cadaveric specimens in the ACL-intact and ACL-deficient state. Tibiofemoral translation was recorded using a surgical navigation system. The ACL was reconstructed utilizing a nonanatomic graft (n = 10) extending from the posterolateral tibial footprint to the anteromedial femoral footprint, or an anatomic anteromedial single-bundle graft extending from the anteromedial tibial footprint to the anteromedial femoral footprint (n = 10) and testing repeated. The medial or lateral meniscus was sectioned and the examination repeated. The other meniscus was sectioned and the examination subsequently repeated.

RESULTS

Lateral compartment translation during the pivot shift was significantly reduced following anatomic ACL reconstruction. In the nonanatomic group, lateral compartment translation increased by 9.1 mm (P < 0.001) after unicomparmental meniscectomy and 11.5 mm (P < 0.001) after bicompartmental meniscectomy. In the anatomic reconstruction group, lateral compartment translation increased by 7.6 mm (P < 0.001) after bicompartmental meniscectomy.

CONCLUSION

With isolated ACL injury, anatomic single-bundle ACL reconstruction controlled the pivot shift during time zero testing. However, significant increases in lateral compartment translation during the pivot shift are seen following bicompartmental meniscectomy. Nonanatomic ACL reconstruction was less effective in controlling the pivot shift at time zero testing, and significant increases in lateral compartment translation during the pivot shift were seen following both unicomparmental and bicompartmental meniscectomy.

Intra-operative navigation of knee kinematics and the influence of osteoarthritis

Intra-operative assessment of knee kinematics should optimise implantation of total knee arthroplasties. The purpose of this work was to validate the data delivered by an adapted navigation system in 10 healthy cadaver knees and to investigate the kinematics of 10 osteoarthritic (OA) knees in patients undergoing total knee replacement. The system displayed the magnitude of axial rotation, the position of the instantaneous centre of axial rotation and the displacements of the condyles. Successive cycles from full extension to 140° of flexion in the same knee produced a mean external rotation of 20° ± 10°, which was correlated to knee flexion (r=0.6 ± 0.2 in healthy knees, r=0.8 ± 0.2 in OA knees). The centre of axial rotation migrated posteriorly an average of 8.2mm in both groups. The posterior displacements were 4 mm ± 5 mm in healthy and 5 mm ± 6 mm in OA knees for the medial condyle, and 21 mm ± 9 mm in healthy and 21 mm ± 10 mm in OA knees for the lateral condyle. The medial condyle lifted off beyond 110° of flexion. Results in healthy knees were consistent with those reported in the current literature. The kinematics of healthy and of OA knees with an intact anterior cruciate ligament did not differ significantly.

Influence of femoral malrotation on knee joint alignment and intra-articular contract pressures

INTRODUCTION

The standard treatment of femoral diaphyseal fractures is intramedullary nailing. Torsion error remains a largely unsolved problem. We hypothesized that femoral malrotation would change the coronal alignment of the lower extremity and the center of force (COF) in the tibiofemoral joint as compared to the native state.

METHOD

Ten cadaveric legs were used. Intraarticularly placed sensor foil was used to measure contact pressures for each condyle. The resultant pressure of this two-force measurement was calculated as the COF for the joint. Mechanical axis was defined by the navigation system. Two novel devices were used: (1) to simulate bodyweight with leg attachment and fixation to the anterior pelvis and (2) to fix the femur at various degrees of malrotation. A mid-diaphyseal osteotomy was performed and the distal fragment was rotated both internally and externally in 5° increments to a maximum of 25°. COF and axial alignment were assessed at each step with application of a half-bodyweight specific to each specimen.

RESULTS

Internal rotation resulted in valgus deviation of the mechanical axis and a shift in COF towards the lateral condyle (P < 0.05). External rotation caused varus deviation and switched COF towards the medial condyle (P < 0.05). This study shows that femoral malrotation has a significant effect on mechanical axis alignment and force vectors within the knee. Correlation with clinical outcomes is necessary and further research into minimizing such errors of torsion is warranted.

CONCLUSION

Torsion errors are not merely cosmetic issues, but may result in further morbidity, such as varus or valgus deformity and shifting of the COF, which may lead to joint arthrosis.

Comparison between computer-assisted-navigation and conventional total knee arthroplasties in patients undergoing simultaneous bilateral procedures: a randomized clinical trial

BACKGROUND

Total knee arthroplasty has been increasingly used for young and active patients, and prosthesis durability is important in these patients. The accuracy of implant placement has been one of the major factors that determine the long-term survival of the prosthesis. The purpose of this study was to compare the accuracy of prosthetic alignment between computer-assisted-navigation and conventional total knee arthroplasties.

METHODS

From March 2007 to June 2008, thirty-two patients with bilateral knee osteoarthritis underwent simultaneous bilateral total knee arthroplasty with the same type of implant in each knee. The subjects included seven men and twenty-five women, with an average age of sixty-three years. For each patient, the bilateral total knee arthroplasty was performed with computer-assisted navigation in one knee and a conventional technique in the other. The operative technique and the order of the surgical procedures were randomized. The patients and surgeons conducting the follow-up study and performing the imaging measurements were blinded to the type of surgical procedure.

RESULTS

There was a significant difference between the two groups with regard to the alignment of the knee prosthesis in the coronal and sagittal planes. Nine knee implants (28%) in the conventional group, compared with no knee implants in the computer-navigation group, deviated >3° from the mechanical axis in the coronal plane. The coefficient variation of data in the conventional group was three times greater than that in the computer-navigation group. There was no significant difference in the rotational angle of the femoral component between the two groups. The Hospital for Special Surgery (HSS) scores at six months postoperatively were substantially increased compared with the preoperative scores in both groups.

CONCLUSIONS

Computer-assisted navigation consistently provided coronal plane alignment within 3° of the mechanical axis, which was significantly better than the alignment obtained with conventional total knee arthroplasty.

A mechanized and standardized pivot shifter: technical description and first evaluation

PURPOSE

The pivot shift test (PST) is a complex, multiplanar maneuver used to assess rotatory instability of the knee. The grading is subjective due to the broad range of examination techniques and lack of tibiofemoral motion quantification. The goal of this study was to develop and evaluate a mechanized device for quantitative assessment of the PST.

METHODS

We constructed a mechanized pivot shifter (MPS). In five cadaveric hip-to-toes specimens, the anterior cruciate ligament was resected. We used a surgical navigation system for acquisition of the tibiofemoral motion path during the PST. Two sets of measurements were obtained for the MPS and for two examiners performing the manual technique.

RESULTS

Mean lateral compartment translation magnitudes for each MPS measurement were 13.5 mm (σ = 6.7) and 13.6 mm (σ = 6.7). For examiner 1, 14.9 mm (σ = 6.5) and 15.7 mm (σ = 6.3). For examiner 2, 16.9 mm (σ = 6.3) and 16.1 mm (σ = 5.2). Differences were not significant (n.s.). The MPS had narrower limits of agreement than both examiner 1 and examiner 2.

CONCLUSION

The MPS demonstrated no significant differences in the tibiofemoral translation magnitudes compared to the manual technique. It resulted in better test-retest reliability and more consistent measurements of tibiofemoral translation when compared to manual PST. The high repeatability factor conferred by the MPS is a clinical advantage.

Adjustable cutting blocks for computer-navigated total knee arthroplasty: a cadaver study

Computer-navigation in total knee arthroplasty has been reported to increase accuracy but also procedure duration. We compared surgical time and precision using a novel adjustable cutting block vs freehand navigation with conventional blocks on 12 bilateral cadaver tibiae. The mean time required was significantly less to position the adjustable block than the conventional block (2 minutes 10 seconds vs 6 minutes 35 seconds, P = .006). Guide positioning precision (standard deviation) for the adjustable block vs conventional block was as follows: varus/valgus, 0.24 degrees vs 1.16 degrees (P = .015); posterior slope, 0.35 degrees vs 0.74 degrees (P = .13); and cut height, 0.37 vs 1.41 mm (P = .010). There were no significant differences in the final bone cut accuracy between the 2 groups. The use of adjustable cutting blocks simplifies navigated procedures and may reduce the time required to perform a navigated total knee arthroplasty.

The effect of medial versus lateral meniscectomy on the stability of the anterior cruciate ligament-deficient knee

BACKGROUND

The pivot shift is a dynamic test of knee stability that involves a pathologic, multiplanar motion path elicited by a combination of axial load and valgus force during a knee flexion from an extended position.

PURPOSE

To assess the stabilizing effect of the medial and lateral meniscus on anterior cruciate ligament-deficient (ACL-D) knees during the pivot shift examination.

STUDY DESIGN

Controlled laboratory study.

METHODS

A Lachman and a mechanized pivot shift test were performed on 16 fresh-frozen cadaveric hip-to-toe lower extremity specimens. The knee was tested intact, ACL-D, and after sectioning the medial meniscus (ACL/MM-D; n = 8), lateral meniscus (ACL/LM-D; n = 8), and both (ACL/LM/MM-D; n = 16). A navigation system recorded the resultant anterior tibial translations (ATTs). For statistical analysis an analysis of variance was used; significance was set at P < .05.

RESULTS

The ATT significantly increased in the ACL-D knee after lateral meniscectomy (ACL/LM-D; P < .05) during the pivot shift maneuver. In the lateral compartment of the knee, ATT in the ACL-D knee increased by 6 mm after lateral meniscectomy during the pivot shift (16.6 +/- 6.0 vs 10.5 +/- 3.5 mm, P < .01 for ACL/LM out vs ACL out). Medial meniscectomy, conversely, had no significant effect on ATT in the ACL-D knee during pivot shift examination (P > .05). With standardized Lachman examination, however, ATT significantly increased after medial but not lateral meniscectomy compared with the ACL-D knee (P < .001).

CONCLUSION

Although the medial meniscus functions as a critical secondary stabilizer to anteriorly directed forces on the tibia during a Lachman examination, the lateral meniscus appears to be a more important restraint to anterior tibial translation during combined valgus and rotatory loads applied during a pivoting maneuver.

CLINICAL RELEVANCE

This model may have implications in the evaluation of surgical reconstruction procedures in complex knee injuries.

An application of principal component analysis to the clavicle and clavicle fixation devices

Background

Principal component analysis (PCA) enables the building of statistical shape models of bones and joints. This has been used in conjunction with computer assisted surgery in the past. However, PCA of the clavicle has not been performed. Using PCA, we present a novel method that examines the major modes of size and three-dimensional shape variation in male and female clavicles and suggests a method of grouping the clavicle into size and shape categories.

Materials and methods

Twenty-one high-resolution computerized tomography scans of the clavicle were reconstructed and analyzed using a specifically developed statistical software package. After performing statistical shape analysis, PCA was applied to study the factors that account for anatomical variation.

Results

The first principal component representing size accounted for 70.5 percent of anatomical variation. The addition of a further three principal components accounted for almost 87 percent. Using statistical shape analysis, clavicles in males have a greater lateral depth and are longer, wider and thicker than in females. However, the sternal angle in females is larger than in males. PCA confirmed these differences between genders but also noted that men exhibit greater variance and classified clavicles into five morphological groups.

Discussion And Conclusions

This unique approach is the first that standardizes a clavicular orientation. It provides information that is useful to both, the biomedical engineer and clinician. Other applications include implant design with regard to modifying current or designing future clavicle fixation devices. Our findings support the need for further development of clavicle fixation devices and the questioning of whether gender-specific devices are necessary.

Detection of the center of the hip joint in computer-assisted surgery: An evaluation study of the Surgetics algorithm

OBJECTIVE

The aim of this paper is to assess the accuracy of an algorithm implemented by PRAXIM in the SURGETICS navigation station for detection of the hip center. This study will assess the robustness and accuracy of the algorithm in various clinical situations such as those involving non-sphericity of the femoral head, motion of the pelvis during hip center detection, and restricted range of motion.

MATERIALS AND METHODS

The localization of the hip center, based on kinematics, relies on the recording of n successive positions of the femoral rigid body in the localizer reference system during a passive circumduction motion of the hip joint. Therefore, the shape of the clouds of points acquired may vary from one acquisition to the next. To allow a comprehensive study of the consequences of these variations for hip center detection, we developed a simulator to generate numerous clouds of points. Results given subsequently for each test are the values of the difference between the femoral mechanical axis computed with C(c), the computed hip center, and the same axis computed with C(o), the reference hip center.

RESULTS

Test 1: Sensitivity to noise. The errors ranged from 3.33 E - 12 (SD 3.29E - 12) for a noise of 0 mm to 8.18E - 1 (SD - 7.05E - 1) for a noise of 15 mm. Test 2: Sensitivity to the shape of the acquisition motion. All trajectories gave an error < 1 degrees . Test 3: Sensitivity to restricted range of motion. No value > 1 degrees was found during this test. Test 4: Sensitivity to the distance between two points of the cloud. No value > 0.5 degrees was found during this test. Test 5: Sensitivity to the number of points included in the cloud. No value > 1 degrees was found during this test.

CONCLUSIONS

The Surgetics algorithm is robust to noise, can compensate for pelvic motion, and can be used even in the case of restricted range of motion.

Computer aided surgery system for shoulder prosthesis placement

The aim of this research is to provide a light and easy-handling shoulder model for surgeons in order to ease the preoperative and peroperative work required when replacing the shoulder joint with a prosthesis. The digital mock-up of the shoulder is simplified according to the criteria of the surgeon, allowing easy manipulation of the model for a virtual operation. The model can be parameterized from X-rays or CT images. This paper describes the method used to obtain a virtual mock-up that is useful for preoperative simulation. Furthermore, it is shown that a real-time augmented reality system could be achieved for peroperative application.

A navigated 8-in-1 femoral cutting guide for total knee arthroplasty technical development and cadaveric evaluation

The goals of this study were to determine the precision of femoral component placement using a novel computes assisted surgery (CAS)-enabled 8-in-1 cutting guide in cadaver limbs and to identify errors generated at various stages of the cutting process. The cutting guide placement was on average within 1 degrees or millimeter of the target position in the varus/valgus, axial rotation, and cut height directions and within 2 degrees or millimeters, in all other directions. The difference between the desired femoral component and the impacted trial component position, defined as the execution error, averaged 0.9 degrees +/- 1.7 degrees of varus rotation, 0.8 +/- 2.3 mm of lateral translation, and 0.3 +/- 1 mm of proximal translation in the coronal plane (+/-SD). In the sagittal and axial planes, the execution error averaged 2.8 degrees +/- 2.5 degrees of flexion, 3.4 +/- 1.3 mm of anterior translation, and 0.7 degrees +/- 2.7 degrees of external rotation. CAS permits accurate placement of 8-in-1 jigs for valgus/varus, axial rotation, and cut height but is less accurate in the sagittal plane. Care should be taken when executing the cuts, which can affect precision in the sagittal plane more than actual positioning of the jig.

Full-scale 3D preoperative planning system for calcaneal osteotomy with a multimedia system

This study presents a new computer-assisted surgical planning and simulating system that employs a multimedia environment for calcaneal osteotomy surgery. The system uses a full-scale computer-assisted engineering technique for designing and developing preoperative planning modules. The planning system not only presents a real-sized 3-dimensional (3D) image of the calcaneus, but also provides detailed interior measurements of the calcaneus from various cutting planes. The multimedia user interface integrates the function of different software programs in order to plan and simulate the operation. These functions include 3D image model capturing, sectioning, translocation, rotating, and measuring relevant foot anatomy, all of which can be integrated and used for surgical planning, as well as for future study and discussion. Furthermore, because the system is computer based with a multimedia user interface, surgeons can use it to explore the optimal operative procedure. The system also has a databank that can be updated and expanded, and can be used to provide clinical cases to different users for education and training.

LEVEL OF CLINICAL EVIDENCE

5.

Reliability of image-free navigation to monitor lower-limb alignment

Proper alignment of the mechanical axis of the lower limb is the principal goal of a high tibial osteotomy. A well-accepted and relevant technical specification is the coronal plane lower-limb alignment. Target values for coronal plane alignment after high tibial osteotomy include 2 degrees of overcorrection, while tolerances for this specification have been established as 2 degrees to 4 degrees. However, the role of axial plane and sagittal plane realignment after high tibial osteotomy is poorly understood; consequently, targets and tolerance for this technical specification remain undefined. This article reviews the literature concerning the reliability and precision of navigation in monitoring the clinically relevant specification of lower-limb alignment in high tibial osteotomy. We conclude that image-free navigation registration may be clinically useful for intraoperative monitoring of the coronal plane only. Only fair and poor results for the axial and sagittal planes can be obtained by image-free navigation systems. In the future, combined image-based data, such as those from radiographs, magnetic resonance imaging, and gait analysis, may be used to help to improve the accuracy and reproducibility of quantitative intraoperative monitoring of lower-limb alignment.

Reliability of navigated lower limb alignment in high tibial osteotomies

BACKGROUND

Navigation allows for determination of the mechanical axis of the lower extremity during high tibial osteotomy (HTO) procedures. The objectives of this study were to (1) evaluate the reliability of noninvasive registration with an image-free navigation system for HTO and (2) determine the accuracy of the navigation system to monitor changes in lower limb alignment as compared with alignment measured with a novel 3-dimensional computed tomography method.

HYPOTHESIS

Navigated limb alignment demonstrates good reliability and accuracy in all 3 planes.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Thirteen cadaver legs were used to examine the intra- and interobserver registration reliability of 3 observers. Initial coronal, sagittal, and axial alignment was measured on 6 legs, 3 times each, at intervals >36 hours. Navigated HTOs were then performed on all 13 legs, pre- and postoperative alignment was recorded, and data were compared with equivalent measures obtained by 3-dimensional computed tomography. Reliability and accuracy data were both analyzed using intraclass correlation coefficients with the following established thresholds: good, >0.75; fair, 0.4 to 0.75; and poor, <0.4.

RESULTS

Intraclass correlation coefficients for intraobserver reliability were categorized as follows: varus-valgus, good; flexion-extension, fair; and femoral-tibial rotation, poor. For interobserver reliability, results were varus-valgus, fair; flexion-extension, fair; and femoral-tibial rotation, poor. Intraclass correlation coefficients for navigation accuracy were varus-valgus, good; tibial slope, good; and tibial torsion, poor. Maximum differences in navigation-computed tomography measurements were Delta varus-valgus angle, 4.5 degrees; Delta tibial slope, 8.8 degrees; and Delta tibial torsion, 16.5 degrees.

CONCLUSION AND CLINICAL RELEVANCE

Navigation may be reliable and clinically useful for dynamic monitoring of coronal leg alignment but has limits in determination of sagittal and axial plane alignment.

Computer assisted orthopedic surgery; its influence on prosthesis size in total knee replacement

Improvement of alignment and position of the components in TKAs using Computer Assisted Orthopaedic Surgery (CAOS) has been described. However, much less is known about the accuracy of CAOS in determining the size of the components. The purpose of this study was to evaluate the size of the femoral and tibial component using the CAOS system from Brainlab. The component sizes were compared to pre-operative templating and post-operative scoring the adequateness of size. Forty TKAs (NexGen) were evaluated: 20 using CAOS and 20 conventional. Statistical analysis of the templated and implanted size indicated a fair agreement for the femur (kappa 0.38) and the tibia (kappa 0.35). In the CAOS group significantly more oversizing occurred for the femoral component (p=0.020). No significant difference was found for the tibial component. We conclude there is a risk of oversizing the femoral component of the NexGen system when using CAOS.

The use of ultrasound in acquisition of the anterior pelvic plane in computer-assisted total hip replacement: a cadaver study

We have evaluated in vitro the accuracy of percutaneous and ultrasound registration as measured in terms of errors in rotation and version relative to the bony anterior pelvic plane in computer-assisted total hip replacement, and analysed the intra- and inter-observer reliability of manual or ultrasound registration. Four clinicians were asked to perform registration of the landmarks of the anterior pelvic plane on two cadavers. Registration was performed under four different conditions of acquisition. Errors in rotation were not significant. Version errors were significant with percutaneous methods (16.2 degrees; p < 0.001 and 19.25 degrees with surgical draping; p < 0.001), but not with the ultrasound acquisition (6.2 degrees, p = 0.13). Intra-observer repeatability was achieved for all the methods. Inter-observer analysis showed acceptable agreement in the sagittal but not in the frontal plane. Ultrasound acquisition of the anterior pelvic plane was more reliable in vitro than the cutaneous digitisation currently used.

New visualization tools: computer vision and ultrasound for MIS navigation

BACKGROUND

A versatile image acquisition method called echo surgetics has been developed for minimally invasive computer-assisted orthopaedic procedures. The principle of echo surgetics is to use freehand three-dimensional (3D) ultrasound to acquire relevant 3D bone surface and point data transcutaneously, eliminating access problems associated with conventional digitizers. The concept has been implemented in three technologies: Echo Point, Echo Matching and Echo Morphing.

METHODS

Cadaver experiments were carried out to evaluate the accuracy of (a) Echo Point for digitization of the anterior pelvic plane (APP) in total hip arthroplasty, and (b) Echo Morphing for reconstructing the distal femur in minimally invasive knee surgery.

RESULTS AND CONCLUSIONS

Echo Point provided significantly improved results (p < 0.001) over conventional digitization where mean tilt errors exceeded 20 degrees . The Echo Morphing experiments demonstrated that with a reasonable number of points (ca. 1000) and initial attitude (IA) error (ca. 5-10 mm and 5-10 degrees ) we can obtain an average accuracy of approximately 1 mm that is sufficient for most of clinical applications.

Sagittal alignment of the lower extremity while standing in Japanese male

There is little information available regarding the sagittal mechanical axis of the lower extremity of normal subjects under weight-bearing conditions. The purpose of this study was to determine the sagittal alignment of the lower extremity under such conditions. Anteroposterior and lateral radiographs were taken of the 20 lower extremities of 10 healthy male Japanese volunteers (mean age, 27 years) while standing. The coronal mechanical axis passed through 33.9% medial to the proximal tibial articulating surface. The sagittal mechanical axis passed through 38.0% anterior to the distal femoral condyle and 27.9% anterior to the proximal tibial articulating surface, and also passed 5.2 mm anterior to the intercondylar notch. Our study therefore showed that the coronal and sagittal mechanical axes of the lower extremity do not always pass through the center of the knee. This has important implications for alignment in surgery of lower extremities such as total knee arthroplasty and osteotomy.

[Confrontation of the radiographic preoperative planning with the postoperative data for uncemented total hip arthroplasty]

PURPOSE OF THE STUDY

For hip prosthesis surgery, the challenge is to obtain optimal function of the instrumented hip but also to eliminate any limb length discrepancy, correct the femur offset and guarantee the center of rotation of the hip joint. Preoperative planning for total hip arthroplasty (THA) enables determination of the appropriate length for the prosthetic neck and the size and eventually the type of implants to use. From a prospective series of 86 patients who underwent first-intention THA for implantation of a noncemented prosthesis, we studied the precision of the outcome as function of the preoperative planning. We also ascertained whether the preoperative planning was sufficient to provide the measurements necessary for correct implant position.

MATERIAL AND METHODS

We analyzed a prospective series of patients who underwent first-intention THA from January 2004 through January 2006. To be eligible for inclusion, patients could not have a THA of the contralateral hip. The series was composed of 58 females and 28 males, mean age 70.2 years (range 45-93). The reasons for THA were primary degenerative disease (n=76) and aseptic osteonecrosis (n=10). The contalateral hip was intact and free of osteoarthritis with an anatomic presentation considered to be normal. The standard X-ray protocol included an anteroposterior view of the pelvis in the upright position and 10 degrees internal rotation obtained preoperatively and three months postoperatively. All radiographic measurements were made by the same investigator using a manual nondigitalized technique. We compared planning parameters (pivot size and type, length of the neck, and size of the cup) with the final outcome in order to determine the compliance with the preoperative planning. All operations were performed in the lateral supine position under general anesthesia and by the same surgeon. The posterolateral Moore approach was used. All implants were press fit without cement, both for the cup and for the femoral piece.

RESULTS

All planning parameters selected for study (offset, size of the head and the cup, length of the neck) were available for 32 hips, giving an overall conformity of 37%. The length of the neck was as planned in 75% of hips, the size of the cup in 62% and the size of the femoral stem in 64%. The offset defined preoperatively was never changed during the operation. Ideal implantation (+/- 5mm for all criteria selected for study) was obtained in 60% of hips; the height of the center of rotation was reproduced in 81% and the lateralization in 84%. Femur lateralization was reproduced in 75% of the hips and hip offset in 66%. Leg length discrepancy was avoided in 85% of the patients.

DISCUSSION AND CONCLUSION

Preoperative planning reliably predicts the final offset of the implanted femoral stem. It is more difficult to predict the size of a press fit cup but in our experience the difference does not greatly affect restitution of the hip anatomy. We readily changed the length of the neck during the operation if necessary and have found that the leg length has been better with this approach. This leads to the observation that all of the planning parameters are not fully accurate because of the magnification effect, anatomic conditions, or possible defective execution. While the overall rate of conformity was low, looking at the results for each element separately provided a useful element for each phase of the operation. We recommend planning a medium length neck so it can be easily changed during the operation. The availability of offset measurements is particularly important to control hip lateralization and leg length. Current advances in computer-assisted surgery should be helpful in improving the imperfections of preoperative planning.

Accurate and robust reconstruction of a surface model of the proximal femur from sparse-point data and a dense-point distribution model for surgical navigation

Constructing a 3-D surface model from sparse-point data is a nontrivial task. Here, we report an accurate and robust approach for reconstructing a surface model of the proximal femur from sparse-point data and a dense-point distribution model (DPDM). The problem is formulated as a three-stage optimal estimation process. The first stage, affine registration, is to iteratively estimate a scale and a rigid transformation between the mean surface model of the DPDM and the sparse input points. The estimation results of the first stage are used to establish point correspondences for the second stage, statistical instantiation, which stably instantiates a surface model from the DPDM using a statistical approach. This surface model is then fed to the third stage, kernel-based deformation, which further refines the surface model. Handling outliers is achieved by consistently employing the least trimmed squares (LTS) approach with a roughly estimated outlier rate in all three stages. If an optimal value of the outlier rate is preferred, we propose a hypothesis testing procedure to automatically estimate it. We present here our validations using four experiments, which include 1) leave-one-out experiment, 2) experiment on evaluating the present approach for handling pathology, 3) experiment on evaluating the present approach for handling outliers, and 4) experiment on reconstructing surface models of seven dry cadaver femurs using clinically relevant data without noise and with noise added. Our validation results demonstrate the robust performance of the present approach in handling outliers, pathology, and noise. An average 95-percentile error of 1.7-2.3 mm was found when the present approach was used to reconstruct surface models of the cadaver femurs from sparse-point data with noise added.