What are the bias, imprecision, and limits of agreement for finding the flexion-extension plane of the knee with five tibial reference lines?

Intraoperative Challenges of the Kinematic Knee

Total knee arthroplasty (TKA) is a widely accepted surgical procedure for managing end-stage knee osteoarthritis. Among the various TKA techniques, kinematic alignment has gained increasing popularity as it can potentially restore a more natural joint function. However, despite its theoretical advantages, kinematic total knee replacement presents several operative challenges that necessitate a thorough understanding and analysis of patient-specific anatomy during surgical planning and execution. This review article aims to critically evaluate the operative challenges associated with kinematic TKA and explore potential strategies to optimize surgical outcomes. The challenges encompass multiple aspects including patient selection, preoperative planning, bone cuts, soft tissue balancing, and component positioning.

Reference Axes for Tibial Component Rotation in Total Knee Arthroplasty: Computed Tomography-Based Study of 1,351 Tibiae

BACKGROUND

Many anatomic landmarks have been described for setting tibial component rotation intraoperatively. There is no consensus as to which axis is best for reducing outliers and preventing malrotation.

METHODS

The SOMA (Stryker Orthopaedic Modeling and Analytics) database (Stryker) was used to identify 1,351 computed tomography (CT) scans of the entire tibia. Several reference axes for the tibia (including the Mayo axis, Akagi line, Insall line, anterior condylar axis [ACA], posterior condylar axis [PCA], lateral tibial cortex [LTC], Cobb axis, tibial crest line [TCL], and transmalleolar axis [TMA]) were constructed according to published guidelines. The Berger method served as the reference standard.

RESULTS

The Mayo method (involving a line connecting the medial and middle one-thirds of the tibial tubercle and the geometric center of the tibia) and the Insall line (involving a line connecting the posterior cruciate ligament [PCL] insertion and the intersection of the middle and medial one-thirds of the tibial tubercle) both had low variability relative to the Berger method (7.8° ± 1.0° and 5.1° ± 2.2°, respectively) and a low likelihood of internal rotation errors (0.7% and 1.8%, respectively). No clinically significant gender-based differences were found (<0.7° for all). The same was true for ethnicity, with the exception of consistently greater tibial intorsion in Asian versus Caucasian individuals (mean difference in TCL position, +4.5° intorsion for Asian individuals; p < 0.001).

CONCLUSIONS

This CT-based study of 1,351 tibiae (which we believe to be the largest study of its kind) showed that the Mayo and Insall methods (both of which reference the medial and middle one-thirds of the tibial tubercle) offer an ideal balance of accuracy, low variability, and a reduced likelihood of internal rotation errors. Setting rotation on the basis of distal landmarks (tibial shaft and beyond) may predispose surgeons to substantial malrotation errors, especially given the differences in tibial torsion found between ethnic groups in this study.

LEVEL OF EVIDENCE

Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

Automated Artificial Intelligence-Based Assessment of Lower Limb Alignment Validated on Weight-Bearing Pre- and Postoperative Full-Leg Radiographs

The assessment of the knee alignment using standing weight-bearing full-leg radiographs (FLR) is a standardized method. Determining the load-bearing axis of the leg requires time-consuming manual measurements. The aim of this study is to develop and validate a novel algorithm based on artificial intelligence (AI) for the automated assessment of lower limb alignment. In the first stage, a customized mask-RCNN model was trained to automatically detect and segment anatomical structures and implants in FLR. In the second stage, four region-specific neural network models (adaptations of UNet) were trained to automatically place anatomical landmarks. In the final stage, this information was used to automatically determine five key lower limb alignment angles. For the validation dataset, weight-bearing, antero-posterior FLR were captured preoperatively and 3 months postoperatively. Preoperative images were measured by the operating orthopedic surgeon and an independent physician. Postoperative images were measured by the second rater only. The final validation dataset consisted of 95 preoperative and 105 postoperative FLR. The detection rate for the different angles ranged between 92.4% and 98.9%. Human vs. human inter-(ICCs: 0.85−0.99) and intra-rater (ICCs: 0.95−1.0) reliability analysis achieved significant agreement. The ICC-values of human vs. AI inter-rater reliability analysis ranged between 0.8 and 1.0 preoperatively and between 0.83 and 0.99 postoperatively (all p < 0.001). An independent and external validation of the proposed algorithm on pre- and postoperative FLR, with excellent reliability for human measurements, could be demonstrated. Hence, the algorithm might allow for the objective and time saving analysis of large datasets and support physicians in daily routine.

The value of postoperative prosthesis alignment and patellar height measurements on standard X-rays after Total Knee Arthroplasty: Does it relate to knee function after 5 years?

BACKGROUND

The purpose of this retrospective cohort study was to investigate the influence of parameters of malalignment on knee function 5 years post TKA and, additionally, to explore alterations in patellar height after TKA.

METHODS

All 661 patients undergoing TKA between 2010 and 2011 were considered for inclusion. Preoperative and 1-year postoperative short-leg radiographs were assessed for malalignment parameters: coronal tibial angle (cTA), sagittal tibial angle (sTA), femoral flexion angle (FFA) and mediolateral tibial mismatch. Patellar height was measured using the modified Insall-Salvati ratio. We determined improvements in knee function utilizing the Knee Society Score (Function score, KSS-F), Oxford Knee Score (OKS) and Algofunctional index (AI). Influences of malalignment parameters were analyzed univariate and selected (p < 0.10) for multivariate linear regression analysis. Inter-observer reproducibility was assessed by test-retest analysis of 30 randomly selected radiographs and calculation of an intra-class correlation coefficient (ICC) for all radiographic parameters.

RESULTS

Three-hundred and four patients were included. Multivariate regression showed degrees of cTA malalignment to be significantly associated with only the KSS-F (β = -3.52). Correction of coronal deformity was stronger associated with knee function (KSS-F β = 2.81; AI β = -0.36). Patellar height was significantly reduced after TKA (1.51 vs 1.44). Decrease of patellar height was weakly associated with the OKS (β = 10.69). ICC scores were: cTA 0.81, sTA 0.57, IS 0.72, FFA 0.75.

CONCLUSION

Postoperative coronal tibial plate alignment and correction of preoperative coronal deformity are associated with improved knee function 5 years post TKA. Decrease in patellar height was weakly associated with knee function. Short-leg radiography can be a sufficient screening tool for prosthesis alignment.

Increases in tibial force imbalance but not changes in tibiofemoral laxities are caused by varus-valgus malalignment of the femoral component in kinematically aligned TKA

PURPOSE

The purposes of this study were to quantify the increase in tibial force imbalance (i.e. magnitude of difference between medial and lateral tibial forces) and changes in laxities caused by 2° and 4° of varus-valgus (V-V) malalignment of the femoral component in kinematically aligned total knee arthroplasty (TKA) and use the results to detemine sensitivities to errors in making the distal femoral resections. Because V-V malalignment would introduce the greatest changes in the alignment of the articular surfaces at 0° flexion, the hypotheses were that the greatest increases in tibial force imbalance would occur at 0° flexion, that primarily V-V laxity would significantly change at this flexion angle, and that the tibial force imbalance would increase and laxities would change in proportion to the degree of V-V malalignment.

METHODS

Kinematically aligned TKA was performed on ten human cadaveric knee specimens using disposable manual instruments without soft tissue release. One 3D-printed reference femoral component, with unmodified geometry, was aligned to restore the native distal and posterior femoral joint lines. Four 3D-printed femoral components, with modified geometry, introduced V-V malalignments of 2° and 4° from the reference component. Medial and lateral tibial forces were measured during passive knee flexion-extension between 0° to 120° using a custom tibial force sensor. Eight laxities were measured from 0° to 120° flexion using a six degree-of-freedom load application system.

RESULTS

With the tibial component kinematically aligned, the increase in the tibial force imbalance from that of the reference component at 0° of flexion was sensitive to the degree of V-V malalignment of the femoral component. Sensitivities were 54 N/deg (medial tibial force increasing > lateral tibial force) (p < 0.0024) and 44 N/deg (lateral tibial force increasing > medial tibial force) (p < 0.0077) for varus and valgus malalignments, respectively. Varus-valgus malalignment did not significantly change varus, internal-external rotation, anterior-posterior, and compression-distraction laxities from 0° to 120° flexion. At only 30° of flexion, 4° of varus malalignment increased valgus laxity 1° (p = 0.0014).

CONCLUSION

At 0° flexion, V-V malalignment of the femoral component caused the tibial force imbalance to increase significantly, whereas the laxities were relatively unaffected. Because tibial force imbalance has the potential to adversely affect patient-reported outcomes and satisfaction, surgeons should strive to limit errors in resecting the distal femoral condyles to within ± 0.5 mm which in turn limits the average increase in tibial force imbalance to 68 N. Because laxities were generally unaffected, instability resulting from large increases in laxity is not a clinical concern within the ± 4° range tested.

LEVEL OF EVIDENCE

Therapeutic, Level II.

Internal-external malalignment of the femoral component in kinematically aligned total knee arthroplasty increases tibial force imbalance but does not change laxities of the tibiofemoral joint

PURPOSE

The purposes of this study were to quantify the increase in tibial force imbalance (i.e. magnitude of difference between medial and lateral tibial forces) and changes in laxities caused by  2° and 4° of internal-external (I-E) malalignment of the femoral component in kinematically aligned total knee arthroplasty. Because I-E malalignment would introduce the greatest changes to the articular surfaces near 90° of flexion, the hypotheses were that the tibial force imbalance would be significantly increased near 90° flexion and that primarily varus-valgus laxity would be affected near 90° flexion.

METHODS

Kinematically aligned TKA was performed on ten human cadaveric knee specimens using disposable manual instruments without soft tissue release. One 3D-printed reference femoral component, with unmodified geometry, was aligned to restore the native distal and posterior femoral joint lines. Four 3D-printed femoral components, with modified geometry, introduced I-E malalignments of 2° and 4° from the reference component. Medial and lateral tibial forces were measured from 0° to 120° flexion using a custom tibial force sensor. Bidirectional laxities in four degrees of freedom were measured from 0° to 120° flexion using a custom load application system.

RESULTS

Tibial force imbalance increased the greatest at 60° flexion where a regression analysis against the degree of I-E malalignment yielded sensitivities (i.e. slopes) of 30 N/° (medial tibial force > lateral tibial force) and 10 N/° (lateral tibial force > medial tibial force) for internal and external malalignments, respectively. Valgus laxity increased significantly with the 4° external component with the greatest increase of 1.5° occurring at 90° flexion (p < 0.0001).

CONCLUSION

With the tibial component correctly aligned, I-E malalignment of the femoral component caused significant increases in tibial force imbalance. Minimizing I-E malalignment lowers the increase in the tibial force imbalance. By keeping the resection thickness of each posterior femoral condyle to within ± 0.5 mm of the thickness of the respective posterior region of the femoral component, the increase in imbalance can be effectively limited to 38 N. Generally laxities were unaffected within the ± 4º range tested indicating that instability is not a clinical concern and that manual testing of laxities is not useful to detect I-E malalignment.

Reliability evaluation of inter-eminence line, Akagi and Dalury lines for intraoperative tibial rotation: An osteology-based study

BACKGROUND

This large osteology study examined the reliability, reproducibility and correlation between previously described tibial tray rotation alignment lines (including Akagi and Dalury lines). In addition, it described a novel inter-eminence line utilising the tibial plateau inter-condylar eminences as a landmark.

METHODS

A total of 214 post-medieval (18-19th centuries) skeletal tibia were examined. The inter/intra-observer variation and correlation between reference lines were measured.

RESULTS

Inter-observer reproducibility was excellent and there were no differences between Akagi, Dalury, and inter-eminence lines. Similarly, intra-observer reliability was excellent for Akagi, Dalury, and inter-eminence lines. Qualitative review of tibial inter-condylar eminences suggested that these could be easily identifiable. When taking the medial angle from a medial-lateral reference line, the Akagi line showed a mean of 96.90° (±10.27), inter-eminence line 94.52° (±12.84), and Dalury line 88.06° (±11.75). The angle produced by the Dalury line was significantly different from both the Akagi and inter-eminence lines (P≤0.001). The Akagi line and inter-eminence line showed a strong correlation (r=0.74). The Dalury line showed a weaker correlation with both the Akagi line (r=0.69) and inter-eminence line (r=0.40).

CONCLUSION

This study suggested that tibial rotation lines showed excellent intra/inter-observer reliability and reproducibility. The novel and easily drawn inter-eminence line showed strong correlation with the Akagi line and could be used for tibial tray rotational alignment in total knee arthroplasty.

Alignment options for total knee arthroplasty: A systematic review

In spite of improvements in implant designs and surgical precision, functional outcomes of mechanically aligned total knee arthroplasty (MA TKA) have plateaued. This suggests probable technical intrinsic limitations that few alternate more anatomical recently promoted surgical techniques are trying to solve. This review aims at (1) classifying the different options to frontally align TKA implants, (2) at comparing their safety and efficacy with the one from MA TKAs, therefore answering the following questions: does alternative techniques to position TKA improve functional outcomes of TKA (question 1)? Is there any pathoanatomy not suitable for kinematic implantation of a TKA (question 2)? A systematic review of the existing literature utilizing PubMed and Google Scholar search engines was performed in February 2017. Only studies published in peer-reviewed journals over the last ten years in either English or French were reviewed. We identified 569 reports, of which 13 met our eligibility criteria. Four alternative techniques to position a TKA are challenging the traditional MA technique: anatomic (AA), adjusted mechanical (aMA), kinematic (KA), and restricted kinematic (rKA) alignment techniques. Regarding osteoarthritic patients with slight to mid constitutional knee frontal deformity, the KA technique enables a faster recovery and generally generates higher functional TKA outcomes than the MA technique. Kinematic alignment for TKA is a new attractive technique for TKA at early to mid-term, but need longer follow-up in order to assess its true value. It is probable that some forms of pathoanatomy might affect longer-term clinical outcomes of KA TKA and make the rKA technique or additional surgical corrections (realignment osteotomy, retinacular ligament reconstruction etc.) relevant for this sub-group of patients. Longer follow-up is needed to define the best indication of each alternative surgical technique for TKA. Level I for question 1 (systematic review of Level I studies), level 4 for question 2.

Does a positioning rod or a patient-specific guide result in more natural femoral flexion in the concept of kinematically aligned total knee arthroplasty?

PURPOSE

Flexion of the femoral component in 5° increments downsizes the femoral component, decreases the proximal reach and surface area of the trochlea, delays the engagement of the patella during flexion, and is associated with a higher risk of patellar-femoral instability after kinematically aligned TKA. The present study evaluated flexion of the femoral component after use of two kinematic alignment instrumentation systems. We determined whether a distal cutting block attached to a positioning rod inserted perpendicular to the distal femoral joint line in the axial plane and 8-10 cm into the distal femur anterior and posterior to the distal cortex of the femur in the sagittal plane or a femoral patient-specific cutting guide sets the femoral component in more natural flexion.

METHODS

Flexion of the femoral component was measured with respect to the sagittal femoral anatomic axis of the distal diaphysis and the sagittal femoral axis on rotationally controlled long-leg lateral computer scanograms. Measurements were performed on 53 consecutive patients treated with a kinematically aligned TKA performed with a distal cutting block attached to a positioning rod, and 53 consecutive patients treated with a kinematically aligned TKA performed with a femoral patient-specific cutting guide.

RESULTS

The average flexion and variability (±standard deviation) of the femoral component of patients treated with a positioning rod was 1° ± 2° and 7° ± 4° with respect to the anatomic and mechanical axes, respectively, which was 5° less than the average flexion of the femoral component of patients treated with a femoral patient-specific cutting guide of 6° ± 4° and 12° ± 5° (p = 0.0001, p = 0.0001, respectively).

CONCLUSIONS

Because a distal cutting block attached to a positioning rod sets the femoral component in 5° less flexion and with less variability than a femoral patient-specific cutting guide, we prefer this instrumentation system when performing kinematically aligned TKA to reduce the risk of patellar-femoral instability. Each surgeon should determine the repeatability of setting the flexion of the femoral component with this instrumentation system.