Bone cutting errors in total knee arthroplasty

Reproducibility of a new device for robotic-assisted TKA surgery

Purpose

Enhancing implant placement to achieve optimal gap balance is crucial in total knee arthroplasty (TKA). Given the limited precision of traditional instrumentation, tools like computer-assisted surgery and robotic-assisted TKA have emerged. This experimental cadaveric study aimed to evaluate the accuracy and reproducibility of the collaborative image-free Robin robotic system to support its future clinical application.

Methods

Fifteen cadaveric specimens were treated by eight experienced TKA surgeons. All surgeons, experts in computer-assisted TKA but new to the Robin system, received standardized training. The Robin system uses a robotic arm to position and hold a universal cutting jig, while surgeons perform osteotomies. The indicator for registration repeatability was the alignment of the cutting block position with the previous pin placement. Bony resection, angles and axes were evaluated by comparing the preoperative planning values to the ones obtained with the Robin system with a validated navigation system.

Results

There were no statistically significant differences between the planned and measured values for most resection angles, except for femoral and tibial orientation on sagittal plane (0.6 ± 0.8° and 0.6 ± 1.0°, respectively). Similarly, no statistically significant differences were recorded for resection thickness values, except for the distal medial femoral cut (0.8 ± 0.7 mm). Moreover, these results showed consistency among the different first-time users.

Conclusions

The study found that the Robin robotic system closely matched the preoperative plan for TKA, demonstrating high accuracy and consistency among first-time users. This allows surgeons to easily achieve their planned targets without having to adapt their surgical technique, potentially improving both efficiency and outcomes even when handling complex cases.

Level of Evidence

Not applicable.

Are all robotic technologies created equal? Comparing one of the latest image-free robotic technologies to all other robotic systems for total knee arthroplasty

BACKGROUND

Robotic-assisted technologies have been developed to increase surgical precision and reduce surgical variability in total knee arthroplasty (TKA). Several different robotic systems have been introduced in the last decade for TKA. The DePuy Synthes VELYS™ Robotic-Assisted Solution (VRAS) is an imageless system designed to eliminate the need for preoperative CT scans and is one of the latest entrants in the rapidly evolving field of robotic technology in TKA. This study compared the clinical and economic outcomes associated with VRAS and other robotic-assisted technologies for primary TKA.

METHODS

A retrospective cohort study using the Premier Healthcare Database included patients who underwent primary TKA with VRAS or other robotic-assisted technologies from January 1, 2022, to April 30, 2023. The primary outcome for the study was hospital follow-up visits (revisits) within 90 days post-TKA. Secondary outcomes included readmission and revision rates within 90 days post-TKA, operating room time, length of stay, discharge status and hospital costs. Cohorts were balanced using propensity score fine stratification, and generalized linear models were constructed to evaluate outcomes.

RESULTS

This study included 827 VRAS TKA patients and 16,428 TKA patients treated with other robotic-assisted technologies. The 90-day all-cause and knee-related revisit rates were significantly lower for VRAS than for other robotic-assisted technologies (all-cause 13.9% vs. 22.8% and knee-related 2.8% vs. 5.4%, respectively; p value < 0.01). The all-cause and knee-related 90-day readmission rates were also lower for VRAS, although the differences were not statistically significant. The 90-day revision rates were similar for VRAS and other robotic-assisted technologies (0.48% vs. 0.45%), as was the operating room time (138 vs. 137 min). The 90-day knee-related cost for the VRAS cohort was $15,048 compared to $16,867 for other robotic technologies.

CONCLUSIONS

This database study demonstrated that early postoperative revisit rates and total cost of care are lower for VRAS than for all other robotic-assisted technologies for TKA, while operating room time and discharge status were similar. These are important findings in ever-evolving healthcare systems that are increasingly cost conscious and cognizant of principles associated with value-based care.

Mechanical Performance of Cellulose Nanocrystal and Bioceramic-Based Composites for Surgical Training

This study evaluated the mechanical performance of a cellulose nanocrystal (CNC)-based composite, consisting of hydroxyapatite and natural fibers, mimicking the mechanical properties of real bone. The effect of natural nanofibers on the cutting force of the composite was evaluated for suitability in surgical training. Although hydroxyapatite has been extensively studied in bone-related applications, the exploration of epoxy-based composites incorporating both hydroxyapatite and CNC represents a novel approach. The evaluation involved a load cell with an oscillating saw. The uniform distribution of CNCs within the composite was assessed using 3D X-ray imaging. The cutting force was found to be 4.005 ± 0.5469 N at a feed rate of 0.5 mm/s, comparable to that required when cutting real bone with the osteon at 90°. The 90-degree orientation of the osteon aligns with the cutting direction of the oscillating saw when performing knee replacements on the tibia and femur bones. The addition of CNCs resulted in changes in fracture toughness, leading to increased material fragmentation and surface irregularities. Furthermore, the change in the cutting force with depth was similar to that of real bone. The developed composite material enables bone-cutting surgeries using bioceramics and natural fibers without the risks associated with cadavers or synthetic fibers. Mold-based computed tomography data allows for the creation of various bone forms, enhancing skill development for surgeons.

Accuracy and Outcomes of a Novel Cut-Block Positioning Robotic-Arm Assisted System for Total Knee Arthroplasty: A Systematic Review and Meta-Analysis

Background

The primary objective of this study was to determine the accuracy and precision of component positioning of the ROSA Robotic System for total knee arthroplasty (TKA).

Methods

A Preferred Reporting Items for Systematic Reviews and Meta-Analysis systematic review was conducted using 4 electronic databases (MEDLINE, EMBASE, Pubmed, and Cochrane Library) to identify all clinical and radiological studies reporting information about the use and results of the ROSA system. The criteria for inclusion were published research articles evaluating the accuracy of component positioning, learning curve, component alignment, complications, and functional outcomes in adults who underwent robotic-assisted TKA. The National Institutes of Health Quality Assessment Tool was used to evaluate the quality of all the included studies.

Results

A total of 26 studies were assessed for eligibility, and 17 met the inclusion criteria. Nine studies reported on the accuracy and precision of component positioning. The ROSA platform for TKA had a cutting error of less than 0.6° for all coronal and sagittal parameters. Pooled analysis demonstrated accuracy within 0.61-1.87° and precision within 0.97-1.34° when the final intraoperative plan was compared to postoperative radiographs with fewer outliers. Four studies reported improved functional scores with ROSA-assisted TKA than conventional TKA within 1 year of surgery. There was no difference in overall complication rates when compared to conventional TKA.

Conclusions

The ROSA system is both highly accurate and precise, with fewer outliers when analyzed at various time points, including postoperative standing radiographs. Future studies with robust methodology and longer follow-up are required to demonstrate whether these findings have any clinical benefits in the long term.

Angle Accuracy of Intramedullary Bone Resection Guides for Total Knee Arthroplasty

The importance of proper prosthetic placement has been confirmed in numerous studies. The objective of this study was to compare the planned resection angles to the verified intraoperative angles of femoral and tibial varus/valgus, tibial slope, and femoral flexion for each total knee performed using intramedullary (IM) cut guides for both distal femur and proximal tibia cuts. A total of 1,000 total knee arthroplasties (TKAs) were evaluated for this study. Intraoperative cut-check technology was used to show real-time validation of these resection angles. Assuming an acceptable range of within 2° of the planned cuts, results show the femoral varus/valgus angles were 75% accurate, the femoral flexion angles were 50.8% accurate, the tibial cuts were 95.2% accurate in the coronal plane, and the tibial slope was the least accurate with only 50.3% within the acceptable range. This showed that IM guides are reasonably accurate in producing desired angles in the coronal plane but less accurate in the sagittal plane, with a greater number of outliers in femoral flexion and posterior slope. Surgeons need to be aware of potential cutting errors when using IM guides as they affect the overall alignment of the implant, and real-time verification technology is available to verify the accuracy of the cuts.

Total knee replacement with an accelerometer-based, hand-held navigation system improves knee alignment: reliable in all patients

BACKGROUND

Achieving adequate alignment has traditionally been an important goal in total knee arthroplasty to achieve long-term implant survival. While accelerometer-based hand-held navigation systems (ABN) has been introduced as a way to achieve alignment, there is a limited body of evidence on its accuracy, especially in patients under 65 years with differing etiologies for knee arthritis. This study aimed to assess the precision of a specific ABN system in restoring the mechanical axis and report surgical variables and complications, with particular attention to younger patients.

METHODS

We conducted a retrospective review of 310 primary TKA performed with ABN from May 2016 to February 2021. The mean patient age was 67.4 (SD 8.9) years, with 43% under 65 years and mean body mass index of 33.2 (SD 6.8). The average surgical time was 96.8 min (57-171) and the average follow-up was 3.3 years (1.9-6.7). Data regarding length of stay, pain, range of motion (ROM), complications, and reinterventions were collected from the institutional joint arthroplasty registry and the medical records. Preoperative mechanical axis measurements and postoperative radiological data, including mechanical axis, component alignment and mechanical alignment outliers were analyzed.

RESULTS

The mean preoperative mechanical axis was 175.4° (SD 7.6), with 248 knees (80%) in preoperative varus. The mean postoperative mechanical axis was 179.5° (SD 1.96) with 98% of knees falling within ± 3° of the neutral mechanical axis. Only 6 knees (2 varus, 4 valgus) fell outside the ± 3° range. And 3 knees (1 varus, 2 valgus) fell outside the ± 5° range. In the sagittal plane, 296 knees (95.5%) knees were within ± 3° of goal of 3 degrees of femoral flexion and 302 (97.4%) knees were within ± 2° of goal 1° of slope for tibial component. Far outliers (alignment outside ± 5° of targeted position) were found in 3 knees. Factors such as posttraumatic arthrosis, previous surgery, presence of retained hardware, and age below 65 years were not associated with increase in alignment outliers and far outliers. No complications related to the navigation system were observed. There were 22 complications and 20 reoperations, including 2 revisions for periprosthetic joint infection and 1 revision for flexion instability. Patients that required knee manipulation achieved an ultimate flexion of 110° (SD 14.1).

CONCLUSIONS

The ABN system proved to be user-friendly and accurate in reducing alignment outliers in both coronal and sagittal planes in all patient populations. It offers a straightforward navigation solution while preserving surgeon autonomy and the use of traditional surgical tools. These findings advocate for the integration of this navigation system as a valuable tool to enhance the precision of TKA surgery in all patient groups.

Robots on the Stage: A Snapshot of the American Robotic Total Knee Arthroplasty Market

» Computer-assisted robots aid orthopaedic surgeons in implant positioning and bony resection. Surgeons selecting a robot for their practice are faced with numerous options. This study aims to make the choice less daunting by reviewing the most commonly used Food and Drug Administration-approved robotic total knee arthroplasty platforms in the American arthroplasty market.» Modern total knee arthroplasty (TKA) robots use computer guidance to create a virtual knee model that serves as the surgeon's canvas for resection planning.» Most available robotic TKA (rTKA) systems are closed semiactive systems that restrict implant use to those of the manufacturer.» Each system has distinct imaging requirements, safety features, resection methods, and operating room footprints that will affect a surgeon's technique and practice.» Robots carry different purchase, maintenance, and equipment costs that will influence patient access across different socioeconomic groups.» Some studies show improved early patient-reported outcomes with rTKA, but long-term studies have yet to show clinical superiority over manual TKA.

Two- and three-dimensional evaluations following handheld robot-assisted total knee arthroplasty

Robot-assisted total knee arthroplasty (TKA) has proven to be successful in improving the accuracy of component positioning and reducing radiographic outliers. This study aimed to evaluate and compare the alignment of the components using two- and three-dimensional (2D and 3D) measurements following handheld imageless robot-assisted TKA. Seventy consecutive patients underwent primary TKA at our institution using a handheld robot-assisted system. Full-length standing anteroposterior and lateral radiographs were obtained 2 weeks after surgery for assessment of 2D component alignments. Pre- and postoperative computed tomography (CT) images were obtained to assess 3D component alignment. The reference points defined on preoperative CT images were transferred to the postoperative CT images. The absolute errors in the 2D and 3D component alignments from the planned, validated cutting, and validated implantation angles were calculated. Outliers of >  ± 3° of femoral and tibial component alignments in the coronal and sagittal planes were also investigated. All absolute errors in the 2D and 3D component alignments were < 1°, except for the planned and validated cutting angles of the femoral sagittal alignment. No outliers were observed in the femoral or tibial component in the coronal plane. Significant differences between the 2D and 3D measurements were observed for the mean absolute value from the planned and validated cutting angles in the femoral sagittal plane and from the validated implantation angle in the tibial coronal plane. The handheld robot-assisted system demonstrated a high accuracy for component alignment using 2D and 3D evaluations.

Comparison of accuracy and early outcomes in robotic total knee arthroplasty using NAVIO and ROSA

This study aimed to compare the cutting and component placement accuracies and early outcomes after total knee arthroplasty (TKA) between an image-free handheld robotic system (NAVIO) and a radiography-based robotic system (ROSA). This retrospective study included 88 patients (88 knees) who underwent TKA using the NAVIO (40 patients) or ROSA (48 patients) robotic systems. The accuracies of the robotic systems were compared. Clinical scores were evaluated using the Knee Society Score 2011 (KSS 2011) and the forgotten joint score (FJS)-12 at 1 year postoperatively. The femoral sagittal cutting error was smaller in the NAVIO group than in the ROSA group. The other cutting errors were not statistically different in both groups. Implantation errors did not differ between the groups. Regarding the clinical outcomes of the KSS 2011 subscales, the symptoms score was higher in knees operated using ROSA than in those using NAVIO. The other KSS 2011 subscales and the FJS-12 showed no differences between the two groups. In conclusion, the femoral sagittal cutting error was smaller in the NAVIO group than in the ROSA group, and the KSS 2011 symptom score subsection at one year was higher in the knees operated using ROSA than in those using NAVIO.

Improving alignment in total knee arthroplasty: a cadaveric assessment of a surgical navigation tool with computed tomography imaging

PURPOSE

To investigate the accuracy of an imageless, optical surgical navigation tool to assist with femoral and tibial bone cuts performed during TKA.

PATIENTS AND METHODS

Six board-certified orthopedic surgeons participated in a laboratory cadaver investigation, performing femoral and tibial bone cuts with the assistance of a computer navigation tool. Femoral and tibial varus/valgus, tibial slope, femoral flexion, and both femoral and tibial rotation measurements from the device were compared with angular measurements calculated from computed tomography (CT) images of the knees.

RESULTS

Measurements with the navigation tool were highly correlated with those obtained from CT scans in all three axes. For the distal femoral cut, the absolute mean difference in varus/valgus was 0.83° (SD 0.46°, r = 0.76), femoral flexion was 1.91° (SD 1.16°, r = 0.85), and femoral rotation was 1.29° (SD 1.01°, r = 0.88) relative to Whiteside's line and 0.97° (SD 0.56°, r = 0.81) relative to the posterior condylar axis. For the tibia, the absolute mean difference in varus/valgus was 1.08° (SD 0.64°, r = 0.85), posterior slope was 2.78° (SD 1.40°, r = 0.60), and rotation relative to the anteroposterior axis (posterior cruciate ligament to the medial third of the tibial tuberosity) was 2.98° (SD 2.54°, r = 0.79).

CONCLUSION

Utilization of an imageless navigation tool may aid surgeons in accurately performing and monitoring femoral and tibial bone cuts, and implant rotation in TKA and thus, more accurately align TKA components.

Augmented Reality Navigation Can Achieve Accurate Coronal Component Alignment During Total Knee Arthroplasty

Background Computer-navigated knee arthroplasty has been shown to improve accuracy over conventional instruments. The next generation of computer assistance is being developed using augmented reality. The accuracy of augmented reality navigation has not been established. Methods From April 2021 to October 2021, a prospective, consecutive series of 20 patients underwent total knee arthroplasty utilising an augmented reality-assisted navigation system (ARAN). The coronal and sagittal alignment of the femoral and tibial bone cuts was measured using the ARAN and the final position of the components was measured on postoperative CT scans. The absolute difference between the measurements was recorded to determine the accuracy of the ARAN. Results Two cases were excluded due to segmentation errors, leaving 18 cases for analysis. The ARAN produced a mean absolute error of 1.4°, 2.0°, 1.1° and 1.6° for the femoral coronal, femoral sagittal, tibial coronal and tibial sagittal alignments, respectively. No outliers (absolute error of >3°) were identified in femoral coronal or tibial coronal alignment measurements. Three outliers were identified in tibial sagittal alignment, with all cases demonstrating less tibial slope (by 3.1°, 3.3° and 4°). Five outliers were identified in femoral sagittal alignment and in all cases, the component was more extended (3.1°, 3.2°, 3.2°, 3.4° and 3.9°). The mean operative time significantly decreased from the first nine augmented reality cases to the final nine cases by 11 minutes (p<0.05). There was no difference in the accuracy between the early and late ARAN cases. Conclusion Augmented reality navigation can achieve accurate alignment of total knee arthroplasty with a low rate of component malposition in the coronal plane. Acceptable and consistent accuracy can be achieved from the initial adoption of this technique, however, some sagittal outliers were identified and there is a clear learning curve with respect to operating time. The level of evidence was IV.

Impact of patient, surgical, and implant design factors on predicted tray-bone interface micromotions in cementless total knee arthroplasty

Micromotion magnitudes exceeding 150 µm may prevent bone formation and limit fixation after cementless total knee arthroplasty (TKA). Many factors influence the tray-bone interface micromotion but the critical parameters and sensitivities are less clear. In this study, we assessed the impacts of surgical (tray alignment, tibial coverage, and resection surface preparation), patient (bone properties and tibiofemoral kinematics), and implant design (tray feature and surface friction) factors on tray-bone interface micromotions during a series of activities of daily living. Micromotion was estimated via three previously validated implant-bone finite element models and tested under gait, deep knee bending, and stair descent loads. Overall, the average micromotion across the tray-bone cementless contact interface ranged from 9.3 to 111.4 µm, and peak micromotion was consistently found along the anterior tray edge. Maximizing tibial coverage above a properly sized tibial tray (an average of 12.3% additional area) had minimal impact on micromotion. A 1 mm anterior tray alignment change reduced the average micromotion by an average of 16.1%. Two-degree tibial angular resection errors reduced the area for bone ingrowth up to 48.1%. Differences on average micromotion from ±25% changes in bone moduli were up to 75.5%. A more posterior tibiofemoral contact due to additional 100 N posterior force resulted in an average of 79.3% increase on average micromotion. Overall, careful surgical technique, patient selection, and controlling kinematics through articular design all contribute meaningfully to minimizing micromotion in cementless TKA, with centralizing the load transfer to minimize the resulting moment at the anterior tray perimeter a consistent theme.

Is Valgus Cut Angle Based on Radiographic Measurements in Total Knee Arthroplasty Really Inaccurate? A Comparison of Two- and Three-Dimensional Measurements

Radiographs are widely used to measure distal femoral valgus cut angle (VCA) in total knee arthroplasty (TKA), but its accuracy is controversial. This study used three-dimensional (3D) reconstruction models to verify the accuracy of VCA measurements on radiographs, and explore the correlation of VCA with hip-knee-ankle (HKA) angle and lateral femoral bowing angle (FBA). A total of 444 osteoarthritis knees of 444 patients from August 2016 to June 2018 was included retrospectively. On radiographs, two-dimensional VCA (VCA-2D) was measured between the femoral mechanical axis and the distal femoral anatomical axis, and HKA was measured between the femoral mechanical axis and the tibial mechanical axis. On the coronal projection of computed tomography 3D models, the anatomical landmarks used for VCA-3D measurements were the same as those on the radiographs, FBA was measured between the proximal and distal femoral anatomical axis. The distributions of VCA-2D and VCA-3D were evaluated by means and variances. The correlation between HKA and VCA and between FBA and VCA was explored. There was a statistical difference between VCA-2D and VCA-3D (p < 0.001), but the deviation was very small (0.15 ± 0.69 degrees), 83.3% of the deviations were less than 1 degree. VCA would increase both in 2D and 3D with increasing of FBA and HKA varus. There was no statistically significant difference between VCA-2D and VCA-3D in patients with moderate varus knees (0-8 degrees of varus) and mild bowing femurs (FBA <5 degrees). Overall, the deviation caused by using radiography to measure VCA was negligible. VCA measurements using radiographs were accurate in patients with moderate varus knees and mildly bowed femurs. This study reflects level of evidence III.

Influence of Machining Parameters on Cutting and Chip-Formation Process during Cortical Bone Orthogonal Machining

Cortical bone machining is commonly used in craniofacial surgery. The shaping of bone surfaces requires a precise determination of the process’s complexity due to the cutting tool’s defined or undefined geometry. Therefore, research was carried out to assess the impact of the rake angle (γ), clearance angle and depth of cut (d) on the cortical bone machining process. Analysis was carried out based on the orthogonal cutting in three directions. The cutting tool shape was simplified, and the cutting forces and the chip-formation process were monitored. The highest values of the resultant cutting force and shear force were recorded for γ < 0. The specific cutting force decreases with the increase of d. Cutting in the transverse direction is characterized by the highest values of resultant cutting force and shear force. The coefficient of friction depends primarily on the d and takes a constant value or increases with the increase of γ. The tests showed that the chips are formed in the entire range of d ≥ 0.5 µm and create regular shapes for d ≥ 10 µm. The research novelty confirms that even negative cutting angles guarantee controlled cutting and can find wider application in surgical procedures.

The use of imageless navigation to quantify cutting error in total knee arthroplasty

PURPOSE

Navigated total knee arthroplasty (TKA) improves implant alignment by providing feedback on resection parameters based on femoral and tibial cutting guide positions. However, saw blade thickness, deflection, and cutting guide motion may lead to final bone cuts differing from planned resections, potentially contributing to suboptimal component alignment. We used an imageless navigation device to intraoperatively quantify the magnitude of error between planned and actual resections, hypothesizing final bone cuts will differ from planned alignment.

MATERIALS AND METHODS

A retrospective study including 60 consecutive patients undergoing primary TKA using a novel imageless navigation device was conducted. Device measurements of resection parameters were obtained via attachment of optical trackers to femoral and tibial cutting guides prior to resection. Following resection, optical trackers were placed directly on the bone cut surface and measurements were recorded. Cutting guide and bone resection measurements of both femoral and tibial varus/valgus, femoral flexion, tibial slope angles, and both femoral and tibial medial and lateral resection depths were compared using a Student's t-test.

RESULTS

Femoral cutting guide position differed from the actual cut by an average 0.6 ± 0.5° (p = 0.85) in the varus/valgus angle and 1.0 ± 1.0° (p = 0.003) in the flexion/extension angle. The difference between planned and actual cut measurements for medial and lateral femoral resection depth was 1.1 ± 1.1 mm (p = 0.32) and 1.2 ± 1.0 mm (p = 0.067), respectively. Planned cut measurements based on tibial guide position differed from the actual cut by an average of 0.9 ± 0.8° (p = 0.63) in the varus/valgus angle and 1.1 ± 1.0° (p = 0.95) in slope angle. Measurement of medial and lateral tibial resection depth differed by an average of 0.1 ± 1.8 mm (p = 0.78) and 0.2 ± 2.1 mm (p = 0.85), respectively.

CONCLUSIONS

Significant discrepancies between planned and actual femoral bone resection were demonstrated for flexion/extension angle, likely the result of cutting error. Our data highlights the importance of cut verification postresection to confirm planned resections are achieved, and suggests imageless navigation may be a source of feedback that would allow surgeons to intraoperatively adjust resections to achieve optimal implant alignment.

After 25 years of computer-navigated total knee arthroplasty, where do we stand today?

Background

Limb and implant alignment along with soft tissue balance plays a vital role in the outcomes after total knee arthroplasty (TKA). Computer navigation for TKA was first introduced in 1997 with the aim of implanting the prosthetic components with accuracy and precision. This review discusses the technique, current status, and scientific evidence pertaining to computer-navigated TKA.

Body

The adoption of navigated TKA has slowly but steadily increased across the globe since its inception 25 years ago. It has been more rapid in some countries like Australia than others, like the UK. Contemporary, large console-based navigation systems help control almost every aspect of TKA, including the depth and orientation of femoral and tibial resections, soft-tissue release, and customization of femoral and tibial implant positions in order to obtain desired alignment and balance. Navigated TKA results in better limb and implant alignment and reduces outliers as compared to conventional TKA. However, controversy still exists over whether improved alignment provides superior function and longevity. Surgeons may also be hesitant to adopt this technology due to the associated learning curve, slightly increased surgical time, fear of pin site complications, and the initial set-up cost. Furthermore, the recent advent of robotic-assisted TKA which provides benefits like precision in bone resections and avoiding soft-tissue damage due to uncontrolled sawing, in addition to those of computer navigation, might be responsible for the latter technology taking a backseat.

Conclusion

This review summarizes the current state of computer-navigated TKA. The superiority of computer navigation to conventional TKA in improving accuracy is well established. Robotic-assisted TKA provides enhanced functionality as compared to computer navigation but is significantly more expensive. Whether robotic-assisted TKA offers any substantive advantages over navigation is yet to be conclusively proven. Irrespective of the form, the use of computer-assisted TKA is on the rise worldwide and is here to stay.

Temperature Distribution Simulation, Prediction and Sensitivity Analysis of Orthogonal Cutting of Cortical Bone

Bone cutting plays an important role in spine surgical operations. The power devices with high speed employing in bone cutting usually leads to high cutting temperature of the bone tissue. This high temperature control is important in improving cutting surface quality and optimizing the cutting parameters. In this paper, the bone-cutting model was appropriately simplified for finite element (FE) based modeling of 2D orthogonal cutting to discuss the change law of cutting temperature of cortical bones for cervical vertebra, and to study the orthogonal cutting mechanism of the anisotropic cortical bone, a 3D FE simulation model had been also established in which longitudinal, vertical, and transversal cutting types were accomplished to investigate the effect of osteons orientation. Secondly, this response surface method was used to regress the simulation results, and establishes the prediction model of maximum temperature on cutting depth, cutting speed, and feed speed. Then, the Sobol method was used to analyze the sensitivity of the milling temperature prediction mathematical model parameters, in order to clarify and quantitatively analyze the influence of input milling parameters on the output milling temperature. Finally, the cutting temperatures obtained with the simulations were compared with the corresponding experimental results obtained from the bone milling tests. This study verifies the influence of key variables and the cutting parameters on thermo mechanical behavior of the bone cutting. The obtained cutting temperature distribution for the bone surfaces could be employed to establish a theoretical foundation for research on thermal damage control of bone tissues.

The use of augmented reality for limb and component alignment in total knee arthroplasty: systematic review of the literature and clinical pilot study

PURPOSE

A systematic review of the literature has been carried out to assess the actual evidence of the use of augmented reality in total knee arthroplasty (TKA). We then conducted a pilot clinical study to examine the accuracy of the Knee + augmented reality navigation in performing TKA. The present augmented reality (AR) system allows the surgeon to view the tibial and femur axis superimposed on the surgical field through the smart glasses. It provides real-time information during surgery and intraoperative feedback.

METHODS

A systematic review of the PubMed, MEDLINE, and Embase databases up to May 2021 using the keywords "augmented reality", "knee arthroplasty", "computer assisted surgery", "navigation knee arthroplasty" was performed by two independent reviewers. We performed five TKAs using the Knee + system. Patients were 4 females, with mean age of 76.4 years old (range 73-79) and mean Body Max Index (BMI) of 31.9 kg/m2 (range 27-35). The axial alignment of the limb and the orientation of the components were evaluated on standardized pre and postoperative full leg length weight-bearing radiographs, anteroposterior radiographs, and lateral radiographs of the knee. The time of tourniquet was recorded. The perception of motion sickness was assessed by Virtual Reality Sickness Questionnaire (VRSQ) subjected to surgeon immediately after surgery.

RESULTS

After duplicate removal, a total of 31 abstracts were found. However, only two studies concerned knee arthroplasty. Unfortunately, both were preclinical studies. Knee + system is able to perform a cutting error of less than 1° of difference about coronal alignment of femur and tibia and less than 2° about flexion/extension of femur and posterior tibial slope. The absolute differences between the values obtained during surgery and the measurement of varus femur, varus tibia, posterior slope, and femur flexion angle on post-operative radiographs were 0.6° ± 1.34°, 0.8° ± 0.84°, 0.8° ± 1.79°, and 0.4 mm ± 0.55 mm, respectively.

CONCLUSIONS

On light of our preliminary results, the Knee + system is accurate and effective to perform TKA. The translation from pilot study to high-level prospective studies is warranted to assess accuracy and cost-effective analysis compared to conventional techniques.

LEVEL OF EVIDENCE

IV.

A clinical review of robotic navigation in total knee arthroplasty: historical systems to modern design

Robotic-assisted total knee arthroplasty (RA-TKA) has shown improved reproducibility and precision in mechanical alignment restoration, with improvement in early functional outcomes and 90-day episode of care cost savings compared to conventional TKA in some studies. However, its value is still to be determined.Current studies of RA-TKA systems are limited by short-term follow-up and significant heterogeneity of the available systems.In today's paradigm shift towards an increased emphasis on quality of care while curtailing costs, providing value-based care is the primary goal for healthcare systems and clinicians. As robotic technology continues to develop, longer-term studies evaluating implant survivorship and complications will determine whether the initial capital is offset by improved outcomes.Future studies will have to determine the value of RA-TKA based on longer-term survivorships, patient-reported outcome measures, functional outcomes, and patient satisfaction measures. Cite this article: EFORT Open Rev 2021;6:252-269. DOI: 10.1302/2058-5241.6.200071.

The Functionality of a Novel Robotic Surgical Assistant for Total Knee Arthroplasty: A Case Series

Conventional total knee arthroplasty and soft tissue balancing is based on a subjective unquantified assessment, which can lead to imperfect balancing and poor patient outcomes. Five case studies were used to present the functionality of a novel robotic system in allowing intraoperative adjustments based on objective measures for several primary total knee arthroplasty cases. The robotic system allows the surgeon to drive every step of the case, turning the subjective nature of conventional knee replacement into a more objective and scientific approach for restoration of alignment, gap balancing, joint space restoration, femoral rotation, and Q-angle restoration. The robotic system allowed precise intraoperative adjustments, as demonstrated by these cases, and is a promising step towards more personalized total knee arthroplasty made possible by utilizing real-time objective measures.

Accuracy in the Execution of Pre-operative Plan for Limb Alignment and Implant Positioning in Robotic-arm Assisted Total Knee Arthroplasty and Manual Total Knee Arthroplasty: A Prospective Observational Study

AIM

The objective of the study is to compare the accuracy of implant positioning and limb alignment achieved in robotic-arm assisted total knee arthroplasty(RATKA) and manual total knee arthroplasty(MTKA) to their respective preoperative plan.

PATIENTS AND METHODS

This was a prospective observational study conducted in a tertiary care centre between August 2018 and January 2020. 143 consecutive RATKA(105 patients) and 151 consecutive MTKA(111 patients) performed by two experienced arthroplasty surgeons were included. Two independent observers evaluated the accuracy of implant positioning by measuring the radiological parameters according to the Knee-Society-Roentgenographic-Evaluation-System and limb alignment from postoperative weight-bearing scanogram. Outcomes were defined, based on the degree of deviation of measurements from the planned position and alignment, as excellent(0-1.99°), acceptable(2.00-2.99°) and outlier(≥ 3.00°).

RESULTS

There were no systematic differences in the demographic and baseline characteristics between RATKA and MTKA. Statistically significant outcomes were observed favouring robotic group for postoperative mechanical axis (p < .001), coronal inclination of the femoral component (p < 0.001), coronal inclination of tibial component (p < 0.001), and sagittal inclination of tibial component (p < 0.001). There was no significant difference in the sagittal inclination of the femoral component (p = 0.566). The percentage of knees in the 'excellent' group were higher in RATKA compared to MTKA. There was absolutely no outlier in terms of limb alignment in the RATKA group versus 23.8% (p < 0.001) in the MTKA group. All the measurements showed high interobserver and intraobserver reliability.

CONCLUSION

Robotic-arm assisted TKA executed the preoperative plan more accurately with respect to limb alignment and implant positioning compared to manual TKA, even when the surgeons were more experienced in the latter.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43465-020-00324-y.

Comparison of Tip- Versus Hub-Oscillating Saw Blade Control in a Total Knee Arthroplasty Model

BACKGROUND

Oscillating saws are commonly used for bone preparation in total knee arthroplasty but can cause injury to the posterior neurovascular bundle during tibial resection. Tip-oscillating saw blades are a recent innovation that could improve saw control due to decreased excursion; however, the tactile feedback to the surgeon is different.

METHODS

To compare traditional hub and new tip-oscillating saw blades, 16 participants of varying levels of experience were video-recorded during composite tibial bone model resections to measure posterior saw blade plunge. Subjective perceptions of saw control and preference were also surveyed.

RESULTS

Saw blade design and level of surgical experience did not produce a significant difference in posterior saw blade plunge (P > .05). Independent of saw blade design, subjects with no previous saw experience had significantly decreased posterior tibial plunge over subsequent resections. Tip-oscillating saw blades were perceived to be easier to use and control by less experienced participants (P = .0163).

CONCLUSION

Tip-oscillating saw blades do not alter the risk of posterior tibial saw plunge compared with traditional saw blades.

Improving Tibial Component Coronal Alignment During Total Knee Arthroplasty with the Use of a Double-Check Technique

Objective

To compare the efficacy of the restoration of tibial component coronal alignment with a double‐check technique and the conventional surgical technique during total knee arthroplasty (TKA) in knee osteoarthritis patients, and to investigate the distribution of the medial proximal tibial angle (MPTA) after TKA.

Methods

A retrospective review was performed of 151 patients (179 knees) with knee osteoarthritis undergoing primary TKA in Beijing Chaoyang Hospital, Capital Medical University from February 2013 to January 2015 to evaluate the differences in MPTA in patients undergoing the conventional TKA and those undergoing a modified TKA with a double‐check technique after the surgery. All patients were evaluated by MPTA, range of motion (ROM), Knee Society Clinical Rating System (KSS) clinical scores, and KSS functional scores. An MPTA deviation of 3° or greater was considered malalignment.

Results

A total of 130 TKA procedures in 119 patients were included in the study: 64 knees treated with conventional TKA and 66 knees treated with the double‐check technique TKA. The mean postoperative MPTA was 88.6° ± 2.2° in the conventional TKA group and 89.1° ± 1.5° in the double‐check TKA group. The mean postoperative MPTA between the two groups was not significantly different. In the conventional TKA group, 79.7% (51 knees) had a postoperative MPTA deviation within 3° and 20.3% (13 knees) had a MPTA deviation greater than 3°. In the double‐check TKA group, 93.9% (62 knees) had a postoperative MPTA deviation within 3°and 6.1% (4 knees) had a MPTA deviation greater than 3°. The postoperative MPTA deviation within 3° showed a statistically significant difference between the two groups. In the double‐check TKA group, a 21.2% (14 knees) tibial malalignment was detected after the first check and a 9.1% (6 knees) tibial malalignment was detected after the second check. The mean postoperative ROM was 118.1° ± 9.2° in the conventional TKA group and 115.7° ± 10.1° in the double‐check TKA group. The mean postoperative KSS clinical score was 89.3 ± 3.5 in the conventional TKA group and 89.0 ± 3.7 in the double‐check TKA group. The mean postoperative KSS functional score was 84.8 ± 10.0 in the conventional TKA group and 84.9 ± 9.0 in the double‐check TKA group. The mean postoperative ROM, KSS clinical scores, and KSS functional scores between the two groups were not statistically significantly different.

Conclusion

Malalignment of the tibial component can occur after conventional TKA, and the double‐check technique is an effective method to improve tibial component coronal alignment.

Design of a Three-Dimensional-Printed Surgical Glove for Minimal-Incision Podiatric Surgery

BACKGROUND

Precision in minimal-incision surgery allows surgeons to achieve accurate osteotomies and patients to avoid risks. Herein, a surgical guide for the foot is designed and validated in vitro using resin foot models for hallux abducto valgus surgery.

METHODS

Three individuals with different experience levels (an undergraduate student, a master's student, and an experienced podiatric physician) performed an Akin osteotomy, a Reverdin osteotomy, and a basal osteotomy of the first metatarsal.

RESULTS

The average measurements of each osteotomy and the angle of the basal osteotomy do not reveal significant differences among the three surgeons. A shorter deviation from the planned measurements has been observed in variables corresponding to the Akin osteotomy (the maximum deviation in the measurement of the distance from the proximal medial end of the Akin osteotomy to the first metatarsophalangeal joint interline was 1.67 mm, and the maximum deviation from the proximal lateral end of the Akin osteotomy to the first metatarsophalangeal joint interline was 1.00 mm). As for the Reverdin osteotomies, the maximum deviations in the measurement of the distance from the proximal medial end of the osteotomy to the first metatarsophalangeal joint interline were 3.60 and 3.53 mm in the expert and undergraduate surgeons, respectively. All of the osteotomies were precise among the groups, reducing the learning curve to the maximum.

CONCLUSIONS

The three-dimensional-printed prototype has been proven effective in guiding surgeons to perform different types of osteotomies. Minimal deviations from the predefined osteotomies were found among the three surgeons.

No correlation between rotation of femoral components in the transverse plane and clinical outcome after total knee arthroplasty

PURPOSE

It was hypothesized that malrotation of femoral component in total knee arthroplasty (TKA) will significantly impact clinical outcome.

METHODS

Eighty-eight consecutive patients with primary osteoarthritis of the knee were prospectively evaluated. They received a cemented posterior stabilized TKA (NexGen, Zimmer/Biomet^® Inc., Warsaw, IN, USA). The femoral component was placed in 3° of external rotation referenced to the posterior condylar line. Postoperatively, a CT scan was performed to evaluate rotation of femoral component in the transverse plane. SF-36, KSS, and WOMAC, as well as their range of motion was assessed prior to surgery, after 6 and 24 months. Data are presented as mean and standard deviation (SD), as well as range if applicable. Correlation analysis was performed between the placement of the femoral component in the transverse plane and the clinical outcome.

RESULTS

Femoral component placement was on average 0.1° [SD 2.5°, range - 6.5° to + 6.5°] referenced to the surgical transepicondylar line showing a wide range between the two landmarks after surgery. After 6 months, WOMAC category 'physical function' correlated significantly with femoral component rotation (r = - 0.28, p = 0.007). After 24 months, WOMAC categories 'physical function' and 'pain' correlated significantly with femoral rotation (r = - 0.41, p < 0.001; and r = - 0.33, p = 0.001). No significant correlations were found between femoral component rotation and range of motion (r = 0.04), WOMAC category "stiffness", KSS, as well as SF-36 questionnaires. These reported formally significant correlations were without any clinical relevance.

DISCUSSION

The study showed that there is a significant patients specific femoral component placement in the transverse plane. Internal or external malrotation of the femoral component does not correlate automatically with poor knee function. The lack of correlation between femoral component position and clinical as well as functional outcome underlines complexity and significant individuality of each patient. The surgeon should be aware of the finding and attention should be paid during surgery when significant divergency is seen between the two landmarks. Soft tissue balancing might be very crucial in these specific patients, which needs to be studied in depth in the future.

LEVEL OF EVIDENCE

II.

Accuracy of medial-side cutting guide compared to anterior cutting guide in distal femoral osteotomy of total knee arthroplasty

INTRODUCTION

Minimally invasive surgery (MIS) in total knee arthroplasty has the benefits of less postoperative pain and a faster recovery time. An MIS instrument was designed to help surgeons perform this procedure under reduced visualization conditions. A medial cutting guide of the distal femur is used to cut the distal femoral bone without patella subluxation. This study aimed to compare the accuracy of the distal femoral bone cut between the medial and standard anterior cutting guides.

MATERIALS AND METHODS

Two orthopedic surgeons, who specialize in total knee arthroplasty and are familiar with both of these cutting guides, performed the procedures. Forty-eight synthetic saw bones were used, and five-degree valgus medial and anterior cutting guides were randomly assigned to the surgeons. After the osteotomies were performed, the synthetic saw bones were investigated via plain radiographs. Two independent radiologists measured the medial distal femoral angle (MDFA) and the posterior distal femoral angle (PDFA).

RESULTS

The MDFA in the medial cutting group was statistically significantly different from that of the anterior cutting group (94.18° ± 1.47° vs. 94.98° ± 1.14°, P = 0.041). However, the PDFA was not different between the two groups. Likewise, the number of outliers was not different between the groups when a ± 2° error was defined as an outlier (P = 0.609 for MDFA and P = 0.359 for PDFA). Moreover, a high degree of reliability was found in both MDFA and PDFA measurements (intraclass correlation coefficients = 0.813 and 0.824, respectively).

CONCLUSIONS

In this experimental study, the MIS medial cutting guide was less accurate than the standard cutting guide in the distal femoral cut.

Risk factors and outcomes in asymmetrical femoral component size for posterior referencing bilateral total knee arthroplasty: a matched pair analysis

Background

Theoretically, potential errors in femoral component (FC) sizing can affect postoperative functional outcomes after total knee arthroplasty (TKA), including range of motion (ROM), anterior knee pain, and flexion stability. Incidences of asymmetrical femoral components (AFC) in bilateral TKA have been reported; however; there is a lack of data on exactly why AFC size selection may differ in patients who have had posterior referencing system bilateral TKA. Therefore, this study was conducted to determine risk factors of AFC size selection in patients specifically undergoing posterior referencing bilateral TKA and to compare clinical outcomes between those with AFC or symmetrical femoral component (SFC) sizes.

Methods

We conducted a retrospective matched-pair study comparing thirty-four patients who had undergone simultaneous and staged bilateral TKA using AFC size (Group I) and thirty-five patients with SFC size (Group II). Patients were matched according to gender, body mass index, prosthesis type, and operative technique. Preoperative radiographic morphology of both distal femurs including anteroposterior/mediolateral diameters, anterior-posterior femoral offset, and postoperative radiographic data of FC comprising flexion and valgus angle were recorded. The postoperative functional outcomes including ROM, anterior knee pain, knee society score, and functional score at 6 weeks, 3, 6, 12 and 24 months were compared.

Results

There were no differences in morphology between left and right distal femurs from preoperative radiographic data in both groups. The postoperative radiograph showed a significantly greater FC flexion angle difference in Group I vs. Group II (2.18° ± 1.29° and 1.36° ± 1.08° P = 0.007), while the other parameters were the same. The postoperative clinical outcomes displayed no distinction between groups.

Conclusion

The factor primarily associated with AFC size selection in bilateral TKAs is the difference in FC flexion angle but not the morphological diversity between sides. The postoperative functional outcomes were not inferior in AFC patients in comparison with SFC patients.

Deviation of femoral intramedullary alignment rod influences coronal and sagittal alignment during total knee arthroplasty

BACKGROUND

An intramedullary (IM) rod is used to resect the distal femur vertically to the femoral mechanical axis in the coronal plane in many cases of total knee arthroplasties (TKA). The valgus angle between the mechanical axis and the anatomical axis of the distal femur is estimated preoperatively. It is known the deviation of the IM rod in the femoral canal could influence the femoral component alignment. However, there is no published data regarding how many degrees of deviation to make with the IM rod. The purpose of this study is to measure each deviation of the IM rod using three-dimensional (3D) computer simulations.

METHODS

Preoperative CT scans on 30 knees undergoing TKA were studied. The line connecting central points at 10 and 20 cm proximal from the intercondylar notch was defined as the anatomical axis and the point at which the anatomical axis intersects the surface of the distal femur was considered as the entry point of the IM rod. The medio-lateral (ML) and antero-posterior (AP) deviations between the anatomical axis and the IM rod were measured.

RESULTS

The ML and AP deviations were 0.8 and 1.1° on average. The IM rod was deviated medio-laterally more than 1.0° in three knees (10%).

CONCLUSION

Surgeons should note the ML difference of the resection thickness of the distal femur for coronal alignment. If the ML difference varies greatly from the preoperative planning, they need to adjust at most 1.0° of valgus angle to achieve the appropriate coronal alignment. Level of evidence III, Therapeutic.

Case-related factors affecting cutting errors of the proximal tibia in total knee arthroplasty assessed by computer navigation

PURPOSE

The aim of this study was to determine factors that contribute to bone cutting errors of conventional instrumentation for tibial resection in total knee arthroplasty (TKA) as assessed by an image-free navigation system. The hypothesis is that preoperative varus alignment is a significant contributory factor to tibial bone cutting errors.

METHODS

This was a prospective study of a consecutive series of 72 TKAs. The amount of the tibial first-cut errors with reference to the planned cutting plane in both coronal and sagittal planes was measured by an image-free computer navigation system. Multiple regression models were developed with the amount of tibial cutting error in the coronal and sagittal planes as dependent variables and sex, age, disease, height, body mass index, preoperative alignment, patellar height (Insall-Salvati ratio) and preoperative flexion angle as independent variables.

RESULTS

Multiple regression analysis showed that sex (male gender) (R = 0.25 p = 0.047) and preoperative varus alignment (R = 0.42, p = 0.001) were positively associated with varus tibial cutting errors in the coronal plane. In the sagittal plane, none of the independent variables was significant.

CONCLUSION

When performing TKA in varus deformity, careful confirmation of the bone cutting surface should be performed to avoid varus alignment. The results of this study suggest technical considerations that can help a surgeon achieve more accurate component placement.

LEVEL OF EVIDENCE

IV.

Increased precision of coronal plane outcomes in robotic-assisted total knee arthroplasty: A systematic review and meta-analysis

BACKGROUND

Inaccuracy of component alignment in total knee arthroplasty adversely impacts outcomes. Robotic systems improve translation of pre-operative planning to intra-operative steps, theoretically resulting in greater accuracy and precision. In this study we systematically review literature data of alignment outcomes and apply meta-analysis methods to assess whether robotic-assisted knee arthroplasty provides superior outcomes when compared to conventional knee prostheses.

METHODS

A PRISMA compliant search comparing alignment outcomes in robotic vs conventional knee arthroplasty was performed. Primary outcome measures were; number of three degree outliers and mean deviation from a neutral post-operative mechanical axis.

RESULTS

In total, from five studies reporting upon 402 knees, a post-operative mechanical axis malalignment of >3° occurred in 1/181 (0.006%) of robotic knees, and 42/159 (26.4%) of conventional knees with a meta-analysis odds ratio of 0.04 (95% CI 0.01-0.14), p < 0.00001 favouring robotic-assisted instrumentation. Meta-analysis also demonstrated weighted mean differences of post-operative mechanical axis alignment to be significantly more accurate in the robotic knee group: mean difference -0.63 (95% CI: -1.18,-0.08), z = 2.25, p = 0.02. Sensitivity analysis with inclusion of only Level 1 studies showed similar findings.

CONCLUSIONS

This systematic review and meta-analysis demonstrates clear evidence of increased accuracy of alignment in robotic-assisted knee arthroplasty with specific regard to reconstituting a neutral mechanical axis and minimising number of outliers in the coronal plane. Further studies and long term data is required in order to conclude on survivorship and functional outcomes.

THINK surgical TSolution-One® (Robodoc) total knee arthroplasty

THINK Surgical TSolution-One^® is an active-autonomous, image-based, robotic milling system which enables the surgeon to attain a consistently accurate implant component positioning. The TSolution-One^® system is capable of achieving this through an image-based preoperative planning system which allows the surgeon to create, view and analyse the surgical outcome in 3D. The accuracy and precision of component positioning have been attributed to the following factors: customized distal femoral resection, accurate determination of the femoral rotational alignment, minimization of errors and maintenance of bone temperature with robotic milling. Despite all these advantages, there is still a paucity of long-term, high-quality data that demonstrates the efficacy of robotic-assisted total knee arthroplasty (TKA). Questions regarding radiation risks, prolonged surgical duration and cost-effectiveness remain unanswered. This paper aims to describe: (1) TSolution-One^® surgical technique; (2) limitations and complications; (3) clinical and radiological outcomes.

Computational modelling of motion at the bone-implant interface after total knee arthroplasty: The role of implant design and surgical fit

BACKGROUND

Aseptic loosening, osteolysis, and infection are the most commonly reported reasons for revision total knee arthroplasty (TKA). This study examined the role of implant design features (e.g. condylar box, pegs) and stems in resisting loosening, and also explored the sensitivity of the implants to a loose surgical fit due to saw blade oscillation.

METHODS

Finite element models of the distal femur implanted with four different implant types: cruciate retaining (CR), posterior stabilising (PS), total stabilising (TS) with short stem (12mm×50mm), and a total stabilising (TS) with long stem (19mm×150mm) were developed and analysed in this study. Two different fit conditions were considered: a normal fit, where the resections on the bone exactly match the internal profile of the implant, and a loose fit due to saw blade oscillation, characterised by removal of one millimetre of bone from the anterior and posterior surfaces of the distal femur. Frictional interfaces were employed at the bone-implant interfaces to allow relative motions to be recorded.

RESULTS

The results showed that interface motions increased with increasing flexion angle and loose fit. Implant design features were found to greatly influence the surface area under increased motion, while only slightly influencing the values of peak motion. Short uncemented stems behaved similarly to PS implants, while long canal filling stems exhibited the least amount of motion at the interface under any fit condition.

CONCLUSION

In conclusion, long stemmed prostheses appeared less susceptible to surgical cut errors than short stemmed and stemless implants.

Accuracy of the Precision Saw versus the Sagittal Saw during total knee arthroplasty: A randomised clinical trial

BACKGROUND

The aim of this study was to compare the accuracy of the oscillating tip saw system (Precision Saw=PS) with the more conventional fully oscillating blade system (Sagittal Saw=SS) during computer-assisted total knee arthroplasty (CAS-TKA).

METHODS

A prospective, randomised, controlled trial included 58 consecutive patients who underwent primary CAS-TKA and were randomly assigned in the PS group or the SS group to compare the accuracy of both blades. The primary outcome was the difference between the intended cutting planes and the actual cutting planes in degrees (°) in two planes of both the femur and the tibia. The secondary outcome was total surgery time.

RESULTS

Tibia: In the VV-plane no significant differences were registered for the mean absolute deviation (p=0.28). The PS was more accurate in the AP-plane (p=0.03). Femur: The PS showed significantly fewer mean absolute deviations in the VV-plane (p=0.03); however, the SS revealed better accuracy in the FE-plane (p=0.04). The difference in the surgery time between the groups was not statistically significant (p=0.45). Two outliers were measured using the SS, while seven outliers were detected using the PS.

CONCLUSION

The Precision Saw is not proven to be overall more accurate than the Sagittal Saw. Significantly better accuracy was shown with the PS in the two cutting planes, with the exception of one cutting plane that favoured the SS. Greater number of outliers were found using the PS.

LEVEL OF EVIDENCE

II.

Three-dimensional analysis of the tibial resection plane relative to the arthritic tibial plateau in total knee arthroplasty

Background

Kinematically aligned total knee arthroplasty strives to correct the arthritic deformity by restoring the native tibial joint line. However, the precision of such surgical correction needs to be quantified in order to reduce recuts of the resection and to design assisting instrumentation. This study describes a method for novel three-dimensional analysis of tibial resection parameters in total knee arthroplasty. Pre-operative versus post-operative differences in the slopes of the varus-valgus and flexion-extension planes and the proximal-distal level between the tibia resection and the arthritic tibial joint line can reliably be measured using the three-dimensional models of the tibia and fibula. This work uses the proposed comparison method to determine the parameters for resecting the tibia in kinematically aligned total knee arthroplasty.

Methods

Three-dimensional shape registration was performed between arthritic surface models segmented from pre-operative magnetic resonance imaging scans and resected surface models segmented from post-operative computed tomography scans. Mean, standard deviation and 95% confidence intervals were determined for all measurements. 

Results

Results indicate that kinematically aligned total knee arthroplasty consistently corrects the varus deformity and restores the slope of the flexion-extension plane and the proximal-distal level of the arthritic tibial joint line. The slope of the varus-valgus plane is most precisely associated with the overall arthritic slope after approximately 3° of correction and the posterior slope is biased towards the overall arthritic plateau, though less precisely than the varus correlation.

Conclusions

Use of this analysis on a larger population can quantify the effectiveness of the tibial resection for correcting pathologies, potentially reduce imprecisions in the surgical technique, and enable development of instrumentation that reduces the risk of resection recuts. The kinematic alignment technique consistently corrects varus deformities.

Computed navigated total knee arthroplasty compared to computed tomography scans

BACKGROUND

Successful total knee arthroplasty (TKA) includes accurate alignment. Controversy remains as to whether computer-navigated TKA improves the overall result and clinical outcome. Our aim is to compare the limb alignment and prosthesis positioning according to the pre- and postoperative computed tomography (CT) scans with the data collected from the navigation system.

METHODS

We compared the pre- and postoperative limb alignments and prosthesis alignment provided by the Orthopilot navigation system, Aesculap®, with CT scans measured by the Traumacad® software of 70 TKAs.

RESULTS

A positive correlation with statistical significance (P=0.00001, r=0.874) between the navigation system data and the CT images was found. Mean femoral cut was five degrees (valgus), and mean tibial cut was one degree (varus). Our study revealed that the navigation system assisted the surgeon to implant the prosthesis at a good acceptable alignment.

CONCLUSION

We found that the navigation system is accurate and correlates to the pre- and postoperative CT scans. Furthermore, the navigation system can assist the surgeon to achieve good limb alignment and cutting planes of the prosthesis.

A modified technique to reduce tibial keel cutting errors during an Oxford unicompartmental knee arthroplasty

PURPOSE

Bone cutting errors can cause malalignment of unicompartmental knee arthroplasties (UKA). Although the extent of tibial malalignment due to horizontal cutting errors has been well reported, there is a lack of studies evaluating malalignment as a consequence of keel cutting errors, particularly in the Oxford UKA. The purpose of this study was to examine keel cutting errors during Oxford UKA placement using a navigation system and to clarify whether two different tibial keel cutting techniques would have different error rates.

METHODS

The alignment of the tibial cut surface after a horizontal osteotomy and the surface of the tibial trial component was measured with a navigation system. Cutting error was defined as the angular difference between these measurements. The following two techniques were used: the standard "pushing" technique in 83 patients (group P) and a modified "dolphin" technique in 41 patients (group D).

RESULTS

In all 123 patients studied, the mean absolute keel cutting error was 1.7° and 1.4° in the coronal and sagittal planes, respectively. In group P, there were 22 outlier patients (27 %) in the coronal plane and 13 (16 %) in the sagittal plane. Group D had three outlier patients (8 %) in the coronal plane and none (0 %) in the sagittal plane. Significant differences were observed in the outlier ratio of these techniques in both the sagittal (P = 0.014) and coronal (P = 0.008) planes.

CONCLUSION

Our study demonstrated overall keel cutting errors of 1.7° in the coronal plane and 1.4° in the sagittal plane. The "dolphin" technique was found to significantly reduce keel cutting errors on the tibial side. This technique will be useful for accurate component positioning and therefore improve the longevity of Oxford UKAs.

LEVEL OF EVIDENCE

Retrospective comparative study, Level III.

Individual valgus correction angle improves accuracy of postoperative limb alignment restoration after total knee arthroplasty

PURPOSE

The purpose of the current study was to compare and investigate the effect of fixed and individual valgus correction angle (VCA) on postoperative alignment restoration. It is hypothesized that individual VCA would be more accurate than fixed VCA in postoperative limb alignment restoration.

METHODS

Four hundred and fifty-two patients with 546 consecutive uncomplicated primary total knee arthroplasties performed by a single surgeon, with 302 knees that had individual VCA (group A) and 244 knees that had fixed 5° VCA (group B), were enroled in this study. Preoperative and postoperative full-length standing hip-to-ankle radiographs were used to assess limb alignment. Postoperative hip-knee-ankle angle (θ), femoral component angle (α) and tibial component angle (β) were measured and compared between the two groups.

RESULTS

Mean postoperative θ angle and α angle were 178.9° (SD 1.3°) and 89.1° (SD 1.1°) in the group A, whereas they were 177.8° (SD 1.9°) and 87.9° (SD 1.5°) in the group B. There were significant differences in both parameters between the two groups (p = 0.021 and 0.016, respectively). Mean postoperative β was 89.8° (SD 1.2°) in the group A and 89.7° (SD 1.3°) in the group B, and no significant difference was detected. There were 114 (37.7 %), 221 (73.2 %) and 265 (87.7 %) knees that had restoration of mechanical axis to ±1°, ±2°, ±3° of neutral, respectively, and 37 (12.3 %) outliers (>±3°) in the group A, whereas there were 48 (19.7 %), 122 (50.0 %) and 170 (69.7 %) knees that had restoration of mechanical axis to ±1°, ±2°, ±3° of neutral, respectively, and 74 (30.3 %) outliers in the group B. Group A had a higher percentage of restoration of limb alignment and fewer outliers than those in the group B, and this difference was statistically significant (p < 0.001).

CONCLUSIONS

The results from the present study demonstrated that individual VCA for distal femoral resection could enhance the accuracy of postoperative limb alignment restoration compared with fixed VCA. For clinical relevance, individual VCA should be recommended for routine use in all patients in order to achieve the expected postoperative neutral limb alignment and reduce the risk of postoperative malalignment due to the planning error of a fixed VCA.

LEVEL OF EVIDENCE

Prospective comparative study, Level II.

Patient-specific instrumentation for total knee arthroplasty

PURPOSE

To assess the accuracy of total knee replacements (TKRs) performed using CT-based patient-specific instrumentation by postoperative CT scan.

METHOD

Approval from the Ethics Committee was granted prior to commencement of this study. Fifty prospective and consecutive patients who had undergone TKR (Evolis, Medacta International) using CT-based patient-specific instrumentation (MY KNEE, Medacta International) were assessed postoperatively using a CT scan and the validated Perth protocol measurement technique. The hip-knee-ankle (HKA) angle of the lower limb in the coronal plane; the coronal, sagittal, and rotational orientation of the femoral component; and the coronal and sagittal orientation of the tibial component were measured. These results were then compared to each patient's preoperative planning. The percentage of patients found to be less than or equal to 3° of planned alignment was calculated. One patient was excluded as the femoral cutting block did not fit the femur as predicted by planning and therefore underwent a conventional TKR.

RESULTS

Ninety-eight percent of patients were within 3° of planned alignment in the coronal plane reproducing the predicted HKA angle. Predicted coronal plane orientation of the tibial and femoral component was achieved in 100% and 96% of patients, respectively. The sagittal orientation of the femoral component was within 3° in 98% of patients. The planned sagittal positioning of the tibial component was achieved in 92% of patients. Furthermore, 90% of patients were found to have a femoral rotation within 3° of planning. Eighty-six percent of patients achieved good-to-excellent outcome at 12 months (Oxford Knee Score > 34).

CONCLUSION

We have found that TKR using this patient-specific instrumentation accurately reproduces preoperative planning in all six of the parameters measured in this study.

Femoral sizer design can increase anterior notching during total knee arthroplasty

BACKGROUND

The anteroposterior (AP) portions of the distal femur are generally resected externally rotated relative to the posterior condylar line (PCL) in non-navigated/measured-resection total knee arthroplasty (TKA). Some femoral sizing devices allow rotational adjustment before sizing (rotation-modified sizing devices), while others do not (rotation-unmodified sizing devices). When rotation-unmodified sizing devices are used, the stylus attached to the sizing device identifies the proximal/anterior flange cut assuming the femoral component is aligned parallel to the PCL. However, if the AP cutting device is externally rotated then unexpected notching of the anterior cortex can occur.

METHODS

We simulated TKA surgery in 100 Japanese varus osteoarthritic knees using three-dimensional planning software. The femoral component was aligned parallel to the PCL and the AP component position was determined so proximal anterior flange was just touching the anterior cortex. Next, the femoral component was externally rotated parallel to the surgical epicondylar axis (SEA). If the proximal anterior flange penetrated femoral bone, the length and thickness of anterior notching were measured.

RESULTS

The proximal anterior flange rested on the anterior cortex or penetrated the femoral bone in all knees. There was a strong positive correlation between PCA and length of anterior notching. Anterior notching more than 10mm length or one-millimeter thickness occurred in most cases (82.4% and 70.6%, respectively) where the posterior condylar angle (PCA) was more than four degrees.

CONCLUSIONS

Anterior femoral notching is influenced by the design of the femoral sizing guide and subsequent rotation of cutting blocks, especially in knees with a large PCA.

Twice cutting method reduces tibial cutting error in unicompartmental knee arthroplasty

BACKGROUND

Bone cutting error can be one of the causes of malalignment in unicompartmental knee arthroplasty (UKA). The amount of cutting error in total knee arthroplasty has been reported. However, none have investigated cutting error in UKA. The purpose of this study was to reveal the amount of cutting error in UKA when open cutting guide was used and clarify whether cutting the tibia horizontally twice using the same cutting guide reduced the cutting errors in UKA.

METHODS

We measured the alignment of the tibial cutting guides, the first-cut cutting surfaces and the second cut cutting surfaces using the navigation system in 50 UKAs. Cutting error was defined as the angular difference between the cutting guide and cutting surface.

RESULTS

The mean absolute first-cut cutting error was 1.9° (1.1° varus) in the coronal plane and 1.1° (0.6° anterior slope) in the sagittal plane, whereas the mean absolute second-cut cutting error was 1.1° (0.6° varus) in the coronal plane and 1.1° (0.4° anterior slope) in the sagittal plane. Cutting the tibia horizontally twice reduced the cutting errors in the coronal plane significantly (P<0.05).

CONCLUSION

Our study demonstrated that in UKA, cutting the tibia horizontally twice using the same cutting guide reduced cutting error in the coronal plane.

No evidence of superiority in reducing outliers of component alignment for patient-specific instrumentation for total knee arthroplasty: a systematic review

Patient-specific instrumentation (PSI) technology has been developed to improve alignment when implanting total knee arthroplasty (TKA) and is a new focus in the orthopaedic community. Current controversial data concerning PSI are discussed. A systematic review to compare PSI with conventional instrumentation and assess the radiographic outcomes was performed. Electronic databases (including PubMed, Medline, Embase, the Cochrane Library and the Science Citation Index database) and conference proceedings from 1950 to 2014 in the English language were searched. Data, including relevant patient characteristics, sample size, radiographic method, PSI system manufacturer and outliers of implant positioning and alignment on radiography were independently extracted from all eligible studies by two of the authors. A total of 2739 TKAs were included (1410 performed with PSI and 1329 with conventional instrumentation). There were more TCA outliers (malalignment >3°) and tibial slope outliers (malalignment >3°) in the PSI group than in the conventional group. The other radiographic outcomes assessed, including coronal, sagittal or rotational alignment outliers did not differ between the two groups. With regard to radiographic outcomes, our findings indicate that PSI technology is not superior in reducing outliers of component alignment.

Robotic-assisted knee arthroplasty

Robotics in total knee arthroplasty (TKA) has undergone vast improvements. Although some of the systems have fallen out of favor due to safety concerns, there has been recent increased interest for semi-active haptic robotic systems that provide intraoperative tactile feedback to the surgeon. The potential advantages include improvements in radiographic outcomes, reducing the incidence of mechanical axis malalignment of the lower extremity and better tissue balance. Proponents of robotic technology believe that these improvements may lead to superior functional outcomes and implant survivorship. We aim to discuss robotic technology development, outcomes of unicompartmental and total knee arthroplasty and the future outlook. Short-term follow-up studies on robotic-assisted knee arthroplasty suggest that, although some alignment objectives may have been achieved, more studies regarding functional outcomes are needed. Furthermore, studies evaluating the projected cost-benefit analyses of this new technology are needed before widespread adoption. Nevertheless, the short-term results warrant further evaluation.

Retrospective Clinical and Radiological Outcomes after Robotic Assisted Bicompartmental Knee Arthroplasty

Purpose. Bicompartmental knee arthroplasty (BiKA) is a favorable alternative to total knee arthroplasty for degenerative disease limited to two knee compartments. Recently developed robotic-assisted systems improved the clinical efficacy of unicompartmental knee arthroplasty by providing enhanced component positioning with dynamic ligament balancing. The purpose of this study was to evaluate the short-term outcomes of patients, undergoing bicompartmental knee arthroplasty at a single institution by a single surgeon using a robotic-assisted system. It was hypothesized that robotic assisted BiKA is a prevailing choice for degenerative disease limited to two knee compartments with good functional results. Methods. A search of the institution's joint registry was conducted to identify patients that underwent robotic-assisted BiKA of the patellofemoral compartment and the medial or lateral compartment. Results. A total number of 29 patients (30 BiKA) with a mean age of 63.6 years were identified who received a patellofemoral resurfacing in combination with medial or lateral compartment resurfacing. Twenty-four out of 29 patients had good to excellent outcome. Conclusion. Robotic assisted bicompartmental arthroplasty using broad indications and only excluding patients with severe deformity and those that have less than 4 mm of joint space in the surviving compartment demonstrated 83% good to excellent results.

The role of complex clinical scenarios in the failure of modular components following revision total knee arthroplasty: A finite element study

Modular prostheses are increasingly applied in complex revision knee arthroplasty scenarios due to the greater intraoperative flexibility they provide to the surgeon, for example, accurate placement of stem in canal while maintaining a good fit distally for complex femoral geometry. However, growing evidence indicates that these modular devices often fail at the stem junction. Modular prostheses are generally applied to provide enhanced fixation in poor quality bone or in the presence of condylar defects. From the literature, it is unclear which of these patient scenarios contribute the most to modular component failure. The present study uses finite element (FE) models to answer this question. The findings of this study indicate that the most significant increase in stem junction stress occurs in the presence of large condylar defects. However, taking into account standard clinical practice (large F3 defects typically result in distal femoral replacement), the most significant factor is then found to be compromised bone quality, these findings are particularly evident at higher flexion angles. Based on the findings of this study, it can be concluded that patients with large femoral defects or severely compromised bone quality are particularly vulnerable to implant failure when a modular approach is adopted.

A new method for calculating femoral anterior cortex point location and its effect on component sizing and placement

BACKGROUND

Variation in anterior femoral cortex morphology can cause improper component placement and alignment. When surgical inaccuracies occur, the mechanical properties of the distal femur may be altered, which could result in lower surgical success rates and an increased chance of postoperative complications.

QUESTIONS/PURPOSES

The purpose of the study is to come up with a reproducible computational algorithm to simulate what the surgeon does in the operating room. This method could help in surgical preplanning, patient-specific instruments, and implant design. From there, we evaluated (1) the angular difference between reference alignment axes; and (2) whether the location of the anterior cortex point and alignment axes had an effect on implant placement and amount of bone resected in seven implant systems.

METHODS

We analyzed 470 femurs from white and black individuals. Two points were defined using automatic three-dimensional landmarking: sizing point and femoral resection anterior cortex (FRAC) point. Alignment axes including the transepicondylar, posterior condylar, distal anatomical (DAA), and mechanical axes (MAs) were automatically calculated and used along with the resection point to define the anterior reference plane. Two mechanical axes were defined for the purpose of this study: MA-1 is a virtual construct used in navigated surgeries defined as the axis joining the center of the femoral head and the knee center and MA-2 was calculated as the axis joining the center of the femoral head and distal exit point of the DAA. Amounts of anterior, posterior, and distal resected bone were calculated along with the difference in orientation between the alignment axes.

RESULTS

The mean angular difference between transepicondylar axis and posterior condylar axis (PCA) was 5.44°±2.99°. All seven implant families showed more total bone resection on both the lateral and medial sides when the implants were aligned using MA-2 and PCA+3 of external rotation (PCA+3) when compared with using MA-1 and PCA+3 (p<0.01). Using MA-2 and PCA+3 as an alignment method reduced the amount of bone resection on both medial and lateral anterior surfaces from 1 to 2 mm.

CONCLUSION

The FRAC point is a key landmark in the placement and sizing of the femoral component. Improper sizing, notching, undercutting, or overstuffing can occur based on selecting the highest or lowest cortex point.

CLINICAL RELEVANCE

Balanced placement, prevention of notching, and anterior and posterior cut balancing were accomplished when using the suggested cortex point.