Varus Morphology And Its Surgical Implication In Osteoarthritic Knee And Total Knee Arthroplasty

Background Knee varus alignment represents a notorious cause of knee osteoarthritis. It can be caused by tibial deformity, combined tibial-femoral deformity and/or ligament imbalance. Understanding malalignment is crucial in total knee arthroplasty (TKA) to restore frontal plane neutral mechanical axis. The aim of this study was to determine which factor contributes the most to varus osteoarthritic knee and its related surgical implications in performing a TKA. Methods We retrospectively evaluated 140 patients operated for TKA due to a varus knee. Full-leg hip to ankle preoperative X-rays were taken. Radiological parameters recorded were: mechanical axis deviation (MAD), hip-knee-ankle (HKA), anatomical-mechanical Angle (AMA), medial neck-shaft angle (MNSA), mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA), lateral proximal femoral angle (LPFA), lateral distal tibial angle (LDTA), femoral bowing and length of tibia and femur. We also determined ideals tibial and femoral cuts in mm according to mechanical alignment technique. A R2 was calculated based on the linear regression between the predicted values and the observed data. Results The greatest contributor to arthritic varus (R=0,444) was MPTA. Minor contributors were mLDFA (R= 0.076), JLCA (R = 0,1554), LDTA (R = 0.065), Femoral Bowing (R= 0,049). We recorded an average of 7,6 mm in lateral tibial cut thickness to restore neutral alignment. Conclusions The radiological major contributor to osteoarthritic varus knee alignment is related to proximal tibia deformity. As a surgical consequence, during performing TKA, the majority of the correction should therefore be made on tibial cut.

Effect of Tibial Slope on Coronal Alignment in Total Knee Arthroplasty

Malalignment of total knee arthroplasty (TKA) components affects function and survivorship. Common practice is to set coronal alignment prior to adjusting slope. With improper jig placement, adjustment of the slope may alter coronal alignment. The purpose of this study was to quantify the change in coronal alignment with increasing posterior tibial slope while comparing two methods of jig fixation. A prospective consecutive series of 100 patients underwent TKA using computer navigation. Fifty patients had the extramedullary cutting jig secured proximally with one pin and 50 patients had the jig secured proximally with two pins. Coronal alignment (CA) was recorded with each increasing degree of posterior slope (PS) from 0 to 7 degrees. Mean CA and change in CA were compared between cohorts. Utilizing one pin, osteotomies drifted into varus with an average change in CA of 0.34 degrees per degree PS. At 4 degrees PS, patients started to have >3 degrees of varus with 12.0% having >3 degrees of varus at 7 degrees PS. Utilizing two pins, osteotomies drifted into valgus with an average change of 0.04 degrees in CA per degree PS. No patients in the two-pin cohort fell outside 3 degrees varus/valgus CA. CA was significantly different at all degrees of PS between the cohorts. Changes in PS influenced CA making verification of tibial cut intraoperative critical. Use of >1 pin and computer navigation were beneficial to prevent coronal plane malalignment. This relationship may explain why computer navigation has been shown to improve alignment as well as survivorship and outcomes in some patients, especially those <65 years.

Tibial Cut Accuracy in Mechanically Aligned Total Knee Arthroplasty Using Extensor Hallucis Longus Tendon to Determine Extramedullary Tibial Guide Position

This study aimed to determine the tibial cut (TC) accuracy using extensor hallucis longus (EHL) tendon as an anatomical landmark to position the total knee arthroplasty (TKA) extramedullary tibial guide (EMTG), and its impact on the TKA mechanical alignment (MA). We retrospectively studied 96 TKA, performed by a single surgeon, using a femoral tailored intramedullary guide technique. Seventeen were prior to the use of the EHL and 79 used the EHL tendon to position the EMTG. We analyzed preoperative and postoperative standing total lower extremity radiographs to determine the tibial component angle (TCA) and the correction in MA, comparing pre-EHL use and post-EHL technique incorporation. Mean TCA was 88.89 degrees and postoperative MA was neutral in 81% of patients. Pre- and postoperative MAs were not correlated. As a conclusion of this study, using the EHL provides a safe and easy way to determine the position of EMTG.

Tibial tray rotation and posterior slope increase risk for outliers in coronal alignment

Aims The extensive variation in axial rotation of tibial components can lead to coronal plane malalignment. We analyzed the change in coronal alignment induced by tray malrotation. Methods We constructed a computer model of knee arthroplasty and used a virtual cutting guide to cut the tibia at 90° to the coronal plane. The virtual guide was rotated axially (15° medial to 15° lateral) and with posterior slopes (0° to 7°). To assess the effect of axial malrotation, we measured the coronal plane alignment of a tibial tray that was axially rotated (25° internal to 15° external), as viewed on a standard anteroposterior (AP) radiograph. Results Axial rotation of the cutting guide induced a varus-valgus malalignment up to 1.8° (for 15° of axial rotation combined with 7° of posterior slope). Axial malrotation of tibial tray induced a substantially higher risk of coronal plane malalignment ranging from 1.9° valgus with 15° external rotation, to over 3° varus with 25° of internal rotation. Coronal alignment of the tibial cut changed by 0.07° per degree of axial rotation and 0.22° per degree of posterior slope (linear regression, R2 > 0.99). Conclusion While the effect of axial malalignment has been studied, the impact on coronal alignment is not known. Our results indicate that the direction of the cutting guide and malalignment in axial rotation alter coronal plane alignment and can increase the incidence of outliers. Cite this article: Bone Joint J 2020;102-B(6 Supple A):43–48.

A Technical Tip to Avert Meniscal Rotation and Dislocation in a Mobile Bearing Unicompartmental Knee Arthroplasty

The Oxford (Oxford® partial knee; Biomet) mobile bearing medial unicondylar knee replacement (OUKR) is a preferred choice by surgeons due to minimal blood loss, reduced pain, and better range of motion. Commonly observed complications include aseptic loosening, polyethylene wear, bearing dislocation, and periprosthetic fractures. A bearing dislocation can be prevented by ensuring that there is correct tracking of bearing during the trial reduction as well as no loss of entrapment. We present a case report in a 50-year-old patient undergoing bilateral OUKR wherein it was observed that the meniscal bearing upon the flexion of the knee joint had the tendency to dislocate. Upon revising the vertical tibial recut according to the anterior superior iliac spine, the meniscus was found to have a normal excursion. Mobile bearing dislocation is a unique complication of mobile bearing OUKR. Surgical technique is of paramount importance in ensuring a successful OUKR. The vertical tibial cut is made to accommodate the vertical wall of the tibial component. Meniscal displacement is quite a common complication and can occur due to multiple causes. Inaccurate vertical tibial cut may be one such reason leading to tibial dislocation.

Morphometric analysis of medial and lateral tibia plateau and adaptability with Oxford partial knee replacement in a Japanese population

Aims: In unicompartmental knee arthroplasty (UKA), tibial components must be correctly sized and positioned so that tibial cut surfaces are well covered without marked under- or overhang with impingement of the surrounding soft tissue. We used morphometric data of both medial and lateral tibial plateaus separately to plan UKA and evaluated the compatibility of the measurement data to the dimensions of six currently available tibial prostheses in a Japanese population. Materials and Methods: Using computed tomography, we preoperatively examined 60 patients (30 medial and 30 lateral osteoarthritis (OA)) scheduled for primary UKA at our hospital between 2013 and 2017. Each tibial cutting surface was measured in the transverse plane at 2 mm below the respective joint line. We used anteroposterior and mediolateral length to calculate the mediolateral length/anteroposterior ratio of both medial and lateral compartments. We then compared measurements across six current UKA systems: Oxford fixed tibia and fixed lateral tibia, Triathlon, TRIBRID, JOURNEY UNI, and HLS Uni Evolution. Results: We found no significant differences in morphometric data between the medial and the lateral OA. The cutting surface of lateral plateau, however, had smaller anteroposterior dimensions, greater mediolateral length, and higher mediolateral length/anteroposterior ratio than those of medial plateau. Therefore, in this Japanese population-based study, Oxford lateral tibia had good compatibility with the measurement data of lateral compartments. Conclusions: Lateral compartments had lower anteroposterior length, greater mediolateral length, and higher mediolateral length/anteroposterior ratio than those of medial compartments. We, therefore, strongly recommend using Oxford fixed lateral tibia for lateral OA over other current tibial prostheses because of superior coverage.