Evaluating axial alignment and knee phenotypes in a young Indian population, using X-rays converted to three-dimensional bone models, and their relevance in total knee arthroplasty

Purpose: The standard principle of total knee arthroplasty (TKA) targeted by most orthopaedicians is the alignment of the lower limb in a neutral mechanical axis. However, for several patients the neutral mechanical alignment is not normal. Aligning these patients to a neutral mechanical axis may not result in desirable outcomes as it may feel unnatural. This study aimed to discover what percentage of the young healthy Indian population have a neutral hip-knee-ankle angle (HKA = 180 degrees) and what percentage of this population have a deviation from the neutral HKA. We also studied the distribution of knee phenotypes in this non-arthritic population. Subjects and methods: A total of 196 lower limbs were evaluated from 100 subjects, between the ages of 20 and 35 years, without any history of lower limb pathology, of which 50 were males and 50 were females. All volunteers were subjected to full-leg standing anteroposterior and lateral digital radiographs on which various alignment parameters were analysed. Three-dimensional bone models were generated using a validated software. Results: 125 limbs (63.7%) from the total population lay in the range of 180 +/- 3 degrees; 7.14% (14/196) of the total limbs had an HKA angle of 180 degrees; 29.5% (58/196) of the total population had a varus alignment, i.e., HKA angle of <= 176 degrees and 6.6% (13/196) had knees in valgus alignment, i.e., HKA angle of >= 184 degrees. Thirty-four percent (33/96) of limbs in men and 25% (25/100) of limbs in women had constitutional varus knees with an alignment of <= 176 degrees; 5.2% (5) of limbs in men and 8% (8) of limbs in women had constitutional valgus knees with an alignment of >= 184 degrees; 67/96 knees in males and 58 knees in females were in the range of 180 +/- 3 degrees. Conclusions: A significant portion of the normal population had limbs that deviated from the neutral HKA. If these subjects were to need TKA in the future, it would not be desirable to restore their alignment to its neutral. O 2024 Elsevier B.V. All rights reserved.