Kinematics Of Total Knee Arthroplasty Research Articles

Comparison of Kinematics in Cruciate Retaining and Posterior Stabilized for Fixed and Rotating Platform Mobile-Bearing Total Knee Arthroplasty with respect to Different Posterior Tibial Slope.

Reconstructed posterior tibial slope (PTS) plays a significant role in kinematics restoration after total knee arthroplasty (TKA). However, the effect of increased and decreased PTS on prosthetic type and design has not yet been investigated. We used a finite element model, validated using in vitro data, to evaluate the effect of PTS on knee kinematics in cruciate-retaining (CR) and posterior-stabilized (PS) fixed TKA and rotating platform mobile-bearing TKA. Anterior-posterior tibial translation and internal-external tibial rotation were investigated for PTS ranging from -3° to 15°, with increments of 1°, for three different designs of TKA. Tibial posterior translation and external rotation increased as the PTS increased in both CR and PS TKAs. In addition, there was no remarkable difference in external rotation between CR and PS TKAs. However, for the mobile-bearing TKA, PTS had less effect on the kinematics. Based on our computational simulation, PTS is the critical factor that influences kinematics in TKA, especially in the CR TKA. Therefore, the surgeon should be careful in choosing the PTS in CR TKAs.

Wear properties of poly-ether-ether-ketone bearing combinations under zero and cross shear kinematics in total knee arthroplasty.

Poly-ether-ether-ketone (PEEK), having shown favorable biocompatibility in spinal applications is being considered as an alternative biomaterial in orthopaedics, either as part of an all-polymer bearing couple, or a replacement for the metallic component in hard-on-soft bearings. Throughout the literature ultra-high molecular weight polyethylene exhibits a range of wear behavior dependent upon the amount of cross shear (CS) present in the bearing motion; in comparison, the behavior of PEEK bearing combinations subject to cross shear conditions is less understood. The aim of this study was to investigate the effect of cross shear on PEEK-on-PEEK and PEEK-on-Metal bearing couples. Wear tests were conducted using a four station pin-on-plate rig capable of uni-directional motion (zero cross shear) and multidirectional motion (cross shear); reciprocation (1 Hz), rotation (0 or 1 Hz), with gravimetric wear analysis used to determine the wear factors. The combined wear factors from the PEEK pins articulating on either PEEK or metal plates in this study suggest that it is preferable to use PEEK-on-Metal bearing couples under zero cross shear kinematic conditions and PEEK-on-PEEK for high cross shear applications. PEEK appears to demonstrate a CS dependency when articulating on hard surfaces. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 445-453, 2019.

The Relationship between Soft-Tissue Balance and Intraoperative Kinematics of Guided Motion Total Knee Arthroplasty.

A new design of the so-called "guided-motion" total knee arthroplasty (TKA) is expected to produce normal-like kinematics. The implant behaves strictly as a mechanically constraint-guided motion system. However, no previous reports have demonstrated the most appropriate surgical technique or soft-tissue balance that would reproduce ideal kinematics. The purpose of this study was to clarify the relationship between soft-tissue balance and the intraoperative kinematics of guided-motion TKA. In this study, intraoperative kinematics of 95 patients whose TKA was performed with a guided-motion prosthesis (Journey II BCS Smith and Nephew) were measured using the computed tomography (CT)-free navigation system. All procedures were performed via the same soft-tissue balancing technique, which focused on the medial compartment because guided-motion TKA must acquire medial stability to induce medial pivot motion. We measured the extension and flexion osteotomy gaps using a force-controlled compartment-specific ligament tensioner with a distraction force of 80 N for each compartment and divided patients into three groups based on the relationship between extension and flexion joint osteotomy gaps of the medial compartment: group1- loose flexion gap, group 2-equal joint gap, and group 3-tight flexion gap. We compared the preoperative demographic characteristics, implant alignment, and intraoperative kinematics among the three groups. There was no difference between the preoperative demographic characteristics and postoperative implant alignment in the three groups. The relative tibial internal rotational angles in groups 1 and 2 were significantly larger than that in group 3 at 60°, 90°, and maximum flexion (p < 0.05). The appropriate soft-tissue balance of the medial compartment for guided-motion TKA was an equal joint osteotomy gap or a larger flexion than extension gap. A tight flexion gap should be avoided.

The Mobile-bearing TKA: Is There Still a Place?

During the 1980s, fixed-bearing total knee arthroplasty (TKA) became a reliable, reproducible procedure with about 95% implant survival after 10 years. However, implant loosening and polyethylene wear became recognized as long-term causes of late failure. If loosening is related to abnormal strains at the bone-implant interface, polyethylene wear is mainly caused by the lack of congruency during implant motion, and thus surgeons tried to improve TKA’s kinematics by introducing a second degree of freedom in their implants. Mobile-bearing knee replacements are based on a mobile polyethylene insert that articulates with a metallic femoral component and a metallic tibial tray. Those TKA designs have sought to increase congruency without increasing the stresses on the implant fixation. In vitro kinematic studies have shown reduced polyethylene wear in mobile bearings because of increased implant conformity and reduced polyethylene contact. In vivo kinematic analysis tends to confirm that mobile-bearing implants allow more natural knee movement. Despite several prospective, randomized studies having been performed, there is no clinical evidence supporting mobile bearing superiority over fixed-bearing designs. Studies focusing on gait parameters, clinical scores, or implant survival failed to confirm in vitro substantial advantage of mobile-bearing implants. More, recent improvement in polyethylene materials might solve wear issues: the last generation of cross-linked polyethylene, associated with a more morphometric design will probably provide superior implant survivorship and more physiological knee biomechanics.

Posterior tibial slope impacts intraoperatively measured mid-flexion anteroposterior kinematics during cruciate-retaining total knee arthroplasty

Posterior tibial slope (PTS) for cruciate-retaining (CR) total knee arthroplasty (TKA) is usually pre-determined by the surgeon. Limited information is available comparing different choices of PTS on the kinematics of the CR TKA, independent of the balancing of the extension gap. This study hypothesized that with the same balanced extension gap, the choice of PTS significantly impacts the intraoperatively measured kinematics of CR TKA. Navigated CR TKAs were performed on seven fresh-frozen cadavers with healthy knees and intact posterior cruciate ligament (PCL). A custom designed tibial baseplate was implanted to allow in situ modification of the PTS, which altered the flexion gap but maintained the extension gap. Knee kinematics were measured by performing passive range of motion (ROM) tests from full extension to 120° of flexion on the intact knee and CR TKAs with four different PTSs (1°, 4°, 7°, and 10°). The measured kinematics were compared across test conditions to assess the impact of PTS. With a consistent extension gap, the change of PTS had significant impact on the anteroposterior (AP) kinematics of the CR TKA knees in mid-flexion range (45°-90°), but not so much for the high-flexion range (90°-120°). No considerable impacts were found on internal/external (I/E) rotation and hip-knee-ankle (HKA) angle. However, the findings on the individual basis suggested the impact of PTS on I/E rotation and HKA angle may be patient-specific. The data suggested that the choice of PTS had the greatest impact on the mid-flexion AP translation among the intraoperatively measured kinematics. This impact may be considered while making surgical decisions in the context of APkinematics. When using a tibial component designed with "center" pivoting PTS, a surgeon may be able to fine tune the PTS to achieve proper mid-flexion APstability.

Distal Femoral Rotation Correlates With Proximal Tibial Joint Line Obliquity: A Consideration for Kinematic Total Knee Arthroplasty

BackgroundWe hypothesized that there is a correlation between the distal femoral rotation and proximal tibial joint line obliquity in nonarthritic knees. This has significance for kinematic knee arthroplasty, in which the target knee alignment desired approximates the knee before disease. MethodsFifty computed tomography scans of nonarthritic knees were evaluated using three-dimensional image processing software. Four distal femoral rotational axes were determined in the axial plane: the transepicondylar axis (TEA), transcondylar axis (TCA), posterior condylar axis (PCA), and a line perpendicular to Whiteside's anterior-posterior axis. Then, angles were measured relative to the TEA. Tibial joint line obliquity was measured as the angle between the proximal tibial plane and a line perpendicular to the axis of the tibia. ResultsThere was a strong positive correlation between PCA-TEA and tibial joint line obliquity (r = 0.68, P < .001) as well as TCA-TEA and tibial joint line obliquity (r = 0.69, P < .001). In addition, the tibial joint line obliquity and TCA-TEA angles were similar, 3.7° ± 2.2° (mean ± standard deviation) and 3.5° ± 1.7°, respectively (mean difference, 0.2° ± 0.2°; P = .369). ConclusionBoth PCA-TEA and TCA-TEA strongly correlated with proximal tibial joint line obliquity indicating a relationship between distal femoral rotational geometry and proximal tibial inclination. These findings could imply that the native knee in flexion attempts to balance the collateral ligaments toward a rectangular flexion space. A higher tibial varus inclination is matched with a more internally rotated distal femur relative to the TEA.

Preoperative knee deformity and kinematics impact postoperative knee kinematics in total knee arthroplasty

BackgroundThe purpose of this study was to evaluate the relationship between the preoperative knee deformity/kinematic pattern and the postoperative knee kinematic pattern in posterior cruciate ligament substituting (PS)-total knee arthroplasty (TKA). MethodsThis study involved 39 patients with medial osteoarthritis who underwent a primary PS-TKA using a computed-tomography-based navigation system. All the operations were performed by a single surgeon using a subvastus approach, modified gap technique and the same PS type of prosthesis (Genesis II™ total knee system, Smith & Nephew, Memphis, TN, USA). Knee deformity, kinematic pattern after capsule incision (preoperative knee kinematics), and kinematic pattern after implantation (postoperative knee kinematics) in PS-TKA were measured. Kinematic patterns were divided into two groups: a medial pivot group and a non-medial pivot group. ResultsPreoperative varus knee deformity was significantly larger in the non-medial pivot group than in the medial pivot group (femorotibial angle: 184.7±6.4° vs. 180.8±3.9°, P<0.05). In addition, preoperative knee kinematics were conserved postoperatively, at a rate of 82% (P<0.01). ConclusionsThe severity of varus knee deformity and the preoperative knee kinematic pattern might have affected the postoperative knee kinematics in PS-TKA. This must be confirmed with a randomized controlled trial on a large population study. Level of evidence: case control study, Level III.

Surgical Techniques for Total Knee Arthroplasty: Measured Resection, Gap Balancing, and Hybrid.

Total knee arthroplasty (TKA) is effective in managing end-stage degenerative joint disease. Achieving favorable clinical outcomes is predicated on proper implant alignment, sizing, and rotation as well as adequate soft-tissue balancing. Modern TKA implants are designed to address the fundamental needs of attaining stability in both flexion and extension and of optimizing patellar tracking. Measured resection and gap balancing are the two different techniques used to implant the TKA components used today. Both techniques have been validated as durable and successful, and each has unique advantages and disadvantages. A hybrid technique has been developed that combines the benefits of measured resection and gap balancing and minimizes the limitations associated with both techniques. This hybrid approach has the potential for achieving improved TKA kinematics and refined surgical technique.

Total knee replacement: intraoperative and postoperative kinematic assessment.

The main goals of the total knee arthroplasty (TKA) is to reduce the perceived pain and restore knee mobility and function in case of osteoarthritic knees joints. Literature shows how the three major causes of TKA failures are related to wear, loosening and instability and this is due to a problem of imbalance and malalignment. Intraoperative and postoperative kinematics analysis could be of benefit for improving surgery outcome. The aim of the present paper is to give an overview of the two set-up with the highest accuracy for intraoperative and postoperative TKA kinematics evaluation, currently in use at Istituto Ortopedico Rizzoli. Introperative and Postoperative Evaluation: For intraoperative evaluation it has been presented a navigation system with a specifically developed software, while for the postoperative it has been presented the roentgen stereophotogrammetric analysis (RSA). The navigation system consists in a laptop connected with an optoelectronic localizer (Polaris, Northern Digital Inc, Canada). Two reference arrays with passive optical markers and a marked probe are used to localize the knee joint in the 3D space and track the joint kinematics. The RSA is a radiographic technique used in orthopaedic field for measuring micromotion at bone/prosthesis interface or for joint kinematics evaluation. The RSA uses two X-ray sources synchronized with two digital flat-panels. The present paper shows that using the navigation system allows the surgeon to easily perform kinematic and alignment evaluation during TKA surgery while the RSA allows a quantitative evaluation of the joint kinematics during the recovery time.

Case series report of navigation-based invivo knee kinematics in total knee arthroplasty with a gradually reducing femoral radius design.

BackgroundSimulations show that paradoxical anterior femoral slide in conventional dual radius total knee arthroplasty (TKA) is initiated by sudden reduction of the femoral radius from distal to posterior. Therefore, we hypothesized that a new TKA prosthesis design with a gradually reducing femoral radius may minimize the anterior slide in navigation-based in vivo knee kinematics. The purpose of this study was to compare the kinematics of TKA in vivo using a prosthesis with a gradually reducing radius, in comparison with the conventional dual radius design.MethodsA retrospective case series report was performed for 12 knees with osteoarthritis using a CT-free navigation system. Six knees received TKA using a prosthesis with a gradually reducing femoral radius (Attune CR) and the other 6 knees underwent TKA using a conventional dual radius design (PFCΣ CR). Anterior-posterior (AP) displacement of the medial and lateral femoral condyles relative to the tibia, and kinematic patterns of the femur throughout the range of motion were compared between the groups.ResultsThe average AP displacement in the Attune CR group indicated no paradoxical anterior movement of both condyles, and kinematic data showed a medial pivot pattern. In contrast, AP displacement in the PFCΣ CR group indicated that both condyles showed paradoxical anterior movement, and kinematically both condyles moved in the same manner, showing a parallel motion pattern.ConclusionTKA using a prosthesis with a gradually reducing radius minimized paradoxical anterior slide in navigation-based in vivo knee kinematics.

Can intraoperative kinematic analysis predict postoperative kinematics following total knee arthroplasty? A preliminary.

The preliminary study analyzed the relationship between intraoperative navigation-based kinematics and postoperative 2-dimensional/3-dimensional (2D/3D) image registration-based kinematics in total knee arthroplasty (TKA). Six knees in 5 patients were analyzed. All TKA procedures were performed using an image-free knee navigation system. Tibial internal rotation was assessed by intraoperative knee kinematics. At 1 year after surgery, tibial internal rotation was evaluated using a 2D/3D image registration technique under loaded and unloaded conditions. The correlation between intraoperative and postoperative data for the tibial internal rotation angle at 10 increments of knee flexion was then assessed. Difference in the knee flexion angle between the intraoperative and postoperative evaluations was adjusted to account for the sagittal cutting angle of the distal femur and proximal tibia. A correlation was found between the intraoperative and postoperative data for loaded knee flexion with this adjustment (Pearson's r = 0.725, p = 0.012). However, intraoperative kinematics was not significantly correlated with postoperative kinematics in the absence of loading. Larger adequately powered prospective studies are now needed to confirm our preliminary finding that postoperative loaded kinematics can be predicted by intraoperative evaluation. J. Med. Invest. 65:21-26, February, 2018.

Peer review report 1 on “Case series report of navigation-based in vivo knee kinematics in total knee arthroplasty with a gradually reducing femoral radius design”

Peer review report 1 on “Case series report of navigation-based in vivo knee kinematics in total knee arthroplasty with a gradually reducing femoral radius design”

The utility of bicruciate-retaining total knee arthroplasty.

BackgroundWe describe the features of modern and historical bicruciate-retaining (BCR) total knee arthroplasty (TKA) implants compared with other TKA implant designs, reviewing kinematics, proprioception, operative technique, and clinical results.MethodsWe performed a review based on PubMed, Embase, CINAHL Plus, and Cochrane databases from January 1990 to April 2016 using combinations of the following keywords: “bicruciate-retaining arthroplasty,” “bicruciate-retaining total knee arthroplasty,” “bicruciate-retaining TKA,” “kinematics,” “knee kinematics,” and “TKA kinematics.”ResultsFour studies have supported the notion that preservation of both cruciate ligaments in TKA preserves more “normal” knee kinematics. BCR implants provide greater proprioceptive performance when compared with posterior cruciate-retaining (CR) TKA implants. However, the operative implantation is more challenging with BCR TKAs, requiring the surgeon to take additional precautions. Overall, there did not seem to be a significant difference in short-term clinical outcomes between the BCR and CR implants.ConclusionsThe utility of BCR TKA is still debatable. The literature has not shown clear indications and guidelines for the value and use of this implant. Although kinematics have been shown to mirror the native knee more closely, the clinical outcomes of BCR vs CR TKAs do not differ significantly. Moreover, additional care must be taken when inserting a BCR implant. The anterior cruciate ligament exploration and preservation is more challenging and certain preparation and precautions must take place. Overall, we have not found that BCR implants are significantly superior to CR implants with regards to short term clinical outcomes despite the BCR TKA having improved kinematics and proprioception.

In vitro and in vivo kinematics of total knee arthroplasty—a review of the research at the Orthopaedic Bioengineering Laboratory of the Massachusetts General Hospital (MGH)

Quantitative data of total knee arthroplasty (TKA) kinematics is vital for understanding component failure and to provide guidelines for improvement of the component design. Our lab started studying TKA kinematics in 1998. First, we developed an in vitro robotic experimental setup to test knee kinematics after TKA surgery under various simulated physiological loading conditions. Second, we developed a dual fluoroscopic imaging system (DFIS) to analyze the in vivo knee kinematics after TKA surgery during functional activities. Using these in vitro and in vivo approaches, we have extensively investigated the kinematics of typical posterior cruciate retaining (CR) and posterior substituting (PS) TKAs. Analyses included six degrees-of-freedom (DOF) tibiofemoral joint kinematics, tibiofemoral articular contact locations, posterior cruciate ligament (PCL) function in CR TKAs and cam-post contact in PS TKAs. In addition we have studied the biomechanical factors that may affect flexion capabilities of the knee by comparing the biomechanics of conventional, high-flexion TKA designs with normal knees and knees with osteoarthritis (OA). In this review, we will briefly describe the in vitro and in vivo testing systems developed at our lab for TKA kinematics analyses followed by a summary of our research results on various TKA components.

Characterizing fluoroscopy based kinematic accuracy as a function of pulse width and velocity

Fluoroscopic imaging has become increasingly popular to investigate total knee arthroplasty kinematics non-invasively − 3D implant models are aligned with 2D image projections, and optimized via an edge-contour alignment technique. Previous studies have quantified the accuracy of this approach, however they do not always adequately address the impact of image collection parameters. A particularly sensitive parameter is the pulse width, or exposure time per frame. At longer pulse widths, more motion is captured in a single frame; this can lead to image blur and subsequent degradation to image edge quality. Therefore, the comparative accuracy of relative joint kinematics as a function of pulse width and joint velocity needs to be defined. A limits of agreement approach was taken to define the mean differences between optoelectric kinematic measures (gold standard) and fluoroscopic methods at various pulse widths (1, 8 and 16ms) and knee velocities (50, 100 and 225°/s). The mean absolute differences between the optoelectric and fluoroscopic methods for 1ms pulse width were less than 1.5° and 0.9mm. Comparable rotational differences (1.3°) were observed for the 8ms pulse width but had larger translational differences (1.4mm). The 16ms pulse width yielded the greatest mean differences (2.0° and 1.6mm), which increased with knee flexion velocity. The importance of pulse width and velocity should not be overlooked for future studies – this parameter has proven to be a sensitive metric in the quantification of joint motion via fluoroscopy and must be identified and reported in future studies.

Prediction of in-vivo kinematics and contact track of total knee arthroplasty during walking

In vivo kinematics of total knee arthroplasty (TKA) are essential to investigate the articular surface wear of the knee implant. However, the prediction of in vivo knee kinematics and contact track during walking remains challenged. In this study, a previously developed subject-specific musculoskeletal multibody dynamics model was utilized to predict the in vivo kinematics of TKA during the straight gait and right-turn cycles, and the contact position as described by the center of pressure (COP). The predicted in vivo knee motions of the straight gait cycle were found with similar kinematic patterns and ranges of motion to clinical studies. The main internal-external rotations of the femoral component relative to the tibial insert occurred at the stance phase of the straight gait cycle with a lateral rotational pivot point; while the remaining changes in the contact positon mainly exhibited the anterior or posterior translation. For the right-turn cycle, the major changes in the contact positon were the internal-external rotations, and the rotational pivot points were mostly located at the medial compartment. These predictions further demonstrate that in vivo kinematics and contact track are gait pattern-dependent and are important considerations to further investigate the in vivo wear mechanisms of TKA bearings.

Influence of Medial Collateral Ligament Release for Internal Rotation of Tibia in Posterior-Stabilized Total Knee Arthroplasty: A Cadaveric Study

BackgroundPrevious studies suggested that changes in kinematics in total knee arthroplasty (TKA) affected satisfaction level. The aim of this cadaveric study was to evaluate the effect of medial collateral ligament (MCL) release by multiple needle puncture on knee rotational kinematics in posterior-stabilized TKA. MethodsSix fresh, frozen cadaveric knees were included in this study. All TKA procedures were performed with an image-free navigation system using a 10-mm polyethylene insert. Tibial internal rotation was assessed to evaluate intraoperative knee kinematics. Multiple needle puncturing was performed 5, 10, and 15 times for the hard portion of the MCL at 90° knee flexion. Kinematic analysis was performed after every 5 punctures. After performing 15 punctures, a 14-mm polyethylene insert was inserted, and kinematic analysis was performed. ResultsThe tibial internal rotation angle at maximum knee flexion without multiple needle puncturing was significantly larger (9.42°) than that after 15 punctures (3°). Negative correlation (Pearson r = −0.715, P < .001) between tibial internal rotation angle at maximum knee flexion and frequency of puncture was observed. The tibial internal rotation angle with a 14-mm insert was significantly larger (7.25°) compared with the angle after 15 punctures. ConclusionTibial internal rotation during knee flexion was reduced by extensive MCL release using multiple needle puncturing and was recovered by increasing of medial tightness. From the point of view of knee kinematics, medial tightness should be allowed to maintain the internal rotation angle of the tibia during knee flexion which might lead to patient satisfaction.

Changes in knee kinematics following total knee arthroplasty.

Total knee arthroplasty (TKA) changes the knee joint in both intentional and unintentional, known and unknown, ways. Patellofemoral and tibiofemoral kinematics play an important role in postoperative pain, function, satisfaction and revision, yet are largely unknown. Preoperative kinematics, postoperative kinematics or changes in kinematics may help identify causes of poor clinical outcome. Patellofemoral kinematics are challenging to record since the patella is obscured by the metal femoral component in X-ray and moves under the skin. The purpose of this study was to determine the kinematic degrees of freedom having significant changes and to evaluate the variability in individual changes to allow future study of patients with poor clinical outcomes. We prospectively studied the 6 degrees of freedom patellofemoral and tibiofemoral weightbearing kinematics, tibiofemoral contact points and helical axes of rotation of nine subjects before and at least 1 year after total knee arthroplasty using clinically available computed tomography and radiographic imaging systems. Normal kinematics for healthy individuals were identified from the literature. Significant differences existed between pre-TKA and post-TKA kinematics, with the post-TKA kinematics being closer to normal. While on average the pre-total knee arthroplasty knees in this group displayed no pivoting (only translation), individually only five knees displayed this behaviour (of these, two showed lateral pivoting, one showed medial pivoting and one showed central pivoting). There was considerable variability postoperatively as well (five central, two lateral and two medial pivoting). Both preop and postop, flexion behaviour was more hinge-like medially and more rolling laterally. Helical axes were more consistent postop for this group. An inclusive understanding of the pre-TKA and post-TKA kinematics and changes in kinematics due to total knee arthroplasty could improve implant design, patient diagnosis and surgical technique.

Normal Femorotibial Rotational Alignment and Implications for Total Knee Arthroplasty: an MRI Analysis.

Rotational alignment of prosthetic components in total knee arthroplasty (TKA) is important to successful outcomes. Component malrotation is a known cause of revision and understanding normal rotational alignment may help recreate normal joint kinematics. To date, no large MRI study assessing femorotibial rotational alignment in nonarthritic knees has been undertaken. Is Insall's tibial axis a reliable rotational landmark against common femoral rotational axes in the nonarthritic patient population? We reviewed 544 knee MRI scans performed for suspected soft tissue pathology and identified Insall's tibial rotational axis as well as the femoral clinical trans-epicondylar axis (TEAc), femoral surgical trans-epicondylar axis (TEAs), posterior condylar articular axis (PCA), and a modified Eckhoff's cylindrical axis. The perpendiculars of these axes were superimposed on Insall's tibial axis, and the angular differences were measured. Insall's axis was internally rotated to the TEAc by 1.4°, externally rotated to Eckhoff's cylindrical axis by 1.8°, externally rotated to the TEAs by 2.7°, and externally rotated to the PCA by 3.5°. The mean deviation from 0° (optimal alignment for each femoral axis) was significantly greater for the PCA relative to all other femoral axis. Insall's axis is a reliable landmark for rotational positioning of the tibial component and may optimize femorotibial kinematics in fixed-bearing TKA.

Computer Assisted Mechanical Axis and Kinematic TKA

Introduction:Total knee arthroplasty (TKA) has traditionally been and largely continues to be aligned mechanically, that being with a neutral coronal plane mechanical tibiofemoral axis and a joint line orientated at 900 to this axis. Femoral component rotation is set by gap balancing or by externally rotating 30 from any of a number femoral reference lines. This produces a rectangular flexion gap and relaxes patellar tracking. Kinematic alignment (KA) is an alternative technique that aims to restore premorbid alignment, joint orientation and ligament tension. The basic premise for this technique is based on evidence that the medial and lateral femoral condyles consistently equate to cylinders of equal or near equal size and that therefore with a fixed radius, cruciate retaining implant, matched distal femoral, posterior femoral and proximal tibial resections, accounting for bone and cartilage already lost will reproduce the premorbid joint line and restore native premorbid kinematics. Femoral rotation is therefore referenced off the prearthritic posterior condylar axis (PCA) that is on average internally rotated to the AP axis. Kinematic alignment therefore has the potential to challenge patellar tracking, increase patellar load and potentially increase patellar complications.Method:Case control study – level of evidence III-2. Between November 2012 and June 2013 the senior author completed 104 consecutive computer assisted (CAS) kinematically aligned total knee arthroplasties (TKA) with a cruciate retaining, fixed bearing, single radius implant. The results of these surgeries were compared with the results of 91 consecutive CAS mechanically aligned TKA done between November 2011 and October 2012 using the same navigation system and implant Implant sizing and positioning as well as gap measurement and ligament balance was done with computer assistance in all cases. Data was collected prospectively and analysed retrospectively.Results:The Oxford Knee Score improved from 22.2 preoperatively to 42.3 postoperatively in the kinematic group and from 21.5 to 42.1 in the mechanical group. Improvements in the KOOS domains were similar between the two groups except for the sport domain that favoured the kinematic group. Postoperative range of motion was slightly better in the mechanical group. On average there was a difference of femoral component rotation of 4.50. In the kinematic group femoral position was 2.30 internally rotated relative to the AP axis (range 10.50 IR to-6.50 ER) whereas in the mechanical group femoral position was 1.20 externally rotated (range 50 IR to 90 ER. There were six patellofemoral complications in five patients in the kinematic group requiring four additional procedures. Complications included patellar stress fracture / AVN in four patients, one acute patellofemoral dislocation and one chronic patellofemoral dislocation. There were no patellofemoral complications in the mechanical group.Conclusions:The overall results of CAS kinematic and mechanical TKA are similarly excellent but patellofemoral complications occur at an unacceptably high rate with strict kinematic positioning. Patellar resurfacing should be undertaken with caution in kinematic TKA. In the context of kinematic conflict between the posterior condylar and AP axes the femoral component should be externally rotated to reduce load on the patella.