Summary

If planned carefully, crKA-TKA can be reproducible and repeatable without sophisticated tools and instrumentations. Intra-operatively varus tibial cuts can be checked using the long alignment rod pointing towards the third meta-tarsal.

Abstract

Introduction

An area of contemporary research on knee arthroplasty has seen a focus towards restoring natural knee kinematics by various alignment techniques, thereby improving the gait parameters and targeting better patient-reported outcomes. However, it has also been considered that correcting the full varus may lead to more stress on the medial tibial insert in severe varus-aligned knees, increasing the chances of early failure. The restricted kinematic alignment (rKA) technique principle thus highlights a middle-path between true bony kinematic and conventional mechanical alignment. This study aims at validating an intra-operative method of restoring the tibial varus cut by using a long alignment rod pointing towards the third meta-tarsal (MT) when using restricted Kinematically Aligned (rKA-TKA) protocol while performing TKA. Secondarily the study aims to also establish whether callipered rKA can be performed with pre-operative planning on weightbearing long film radiographs and quantifying the achievement of radiological target post-operatively. Methodology: A prospective observational study was conducted among 25 patients (25 knees) undergoing TKA. The institutional ethics board approved the study, and all patients consented to participate in the present study before enrolling. All patients were operated following crKA-TKA by a single arthroplasty trained surgeon. We used MediCAD Hectec Gmbh (Germany) software for pre-operative planning for all our patients. A single orthopedic trainee resident doctor performed all pre-operative planning. Post-operatively radiographs were studied whether target range were achieved, by two residents two weeks apart. Tibial cuts and femoral alignments were planned using this software so that coronal angular alignment can be achieved post-operatively according to rKA protocol. All patients received Attune Cemented PS knee implants (Depuy Synthes) without patellar resurfacing. Pre-operative tibial cuts were planned and intra-operative callipered technique was used to check cartilage wear and taking the planned cuts so that target angular alignment could be achieved. MPTA was targeted to 87 degrees for all patients. Femoral cuts were taken using intramedullary zig according the native femoral axis angle, compensating the medial articular cartilage wear. The cutting block was kept at 0 degree of rotation verified with equal posterior condylar cuts so that native LDFA could be reconstructed. Intra-operatively we aimed to verify the tibial varus cut by using the a long alignment rod pointing to the third meta-tarsal. Target was to achieve planned MPTA and LDFA within 1 degree of error margin. Post-operatively weight bearing long-film radiographs were procured after 1 month of surgery. Results: Native varus for all patients were within a range of 5-10 degrees. Intra-operatively under-correcting the tibial varus was confirmed after taking the tibial cuts with the long alignment rod pointing towards the 3rd MT. We could achieve target values of tibial varus (MPTA), LDFA reconstruction with overall limb alignment under-corrected, in all patients post-operatively. All patients were in the target range of angular measurements with good Intra-class correlation 0.982 with good intra-observer and interobserver reliability. Conclusion: The study proves that crKA-TKA can be planned using templating software and replicated without sophisticated tools like computer navigation systems or patient-specific zigs. If planned carefully, crKA-TKA can be reproducible and repeatable without sophisticated tools and instrumentations.