Novel technique for achieving the under-correction of native tibial varus in calipered restricted kinematically aligned total knee arthroplasty - A validation study

Purpose: Restricted kinematic alignment (rKA) TKA is relatively newer technique for achieving an overall under-corrected limb alignment. The present study aims to provide an easy and reproducible technique for achieving calipered rKA-TKA (crKA-TKA) using routine instrumentation.

Method: A prospective study was conducted including 30 patients (30 knees). All patients underwent crKA-TKA by the same surgeon. Pre-operatively all patients underwent long film standing radiographs, and coronal angles were measured to plan tibial bony cuts and the femoral axis angle (FAA) to restore tibial varus under correction and native distal femoral anatomy, respectively. Intra-operatively while taking tibial cuts, the alignment rod was noted to be always pointing towards the "third metatarsal" of the ipsilateral foot.

Results: 30 patients underwent total knee replacement with crKA technique. Angular corrections were satisfactory with all patients reaching the target MPTA of 87.48 ± 0.78 and LDFA of 90.301 ± 2.66 as planned, with an overall under-corrected limb alignment. HKA was achieved within a target of < ± 3 degrees of the native knee (3.56 ± 1.29). Post-operative radiological parameters were checked by two separate observers with excellent intra-class correlation coefficients.

Conclusion: The present study validates a novel intra-operative technique of confirming an under-corrected native tibial varus while performing crKA-TKA. The radiological outcomes of the study confirm that with careful pre-operative planning, coronal angular targets were easily achievable with very less outliers. Study further establishes that this method of calipered technique in rKA-TKA using routine digital templating software and standard instrumentations is an alternative method of executing rKA.

Level of evidence: IV, Prospective case series.