Seven phenotypes of varus osteoarthritic knees can be identified in the coronal plane

Abstract

Purpose Recommendations for resecting distal femur and proximal tibia in mechanical and anatomical alignment techniques are standardized. Kinematic alignment propagates individualizing resection planes. Whether significant variation exists, to warrant departure from standardized resection planes, has not been shown thus far in a large cohort of knees and with a wide range of varus deformity. The null hypothesis of this study was that there was no phenotypic variation in varus osteoarthritic knees. The aim of this paper was to determine whether distinct phenotypes could be identified, based on variations in coronal femoral and tibial morphology, which could aid in surgical planning and categorizing varus knees for future studies. Methods 2129 full-leg weightbearing radiographs were analyzed (1704 preoperative; 425 of contralateral arthritic knee). Measurements made were of HKA (hip-knee-ankle angle), VCA (valgus correction angle), mLDFA (lateral mechanical distal femoral angle), aLDFA (lateral anatomical distal femoral angle), MPTA (medial proximal tibial angle), MNSA (medial neck shaft angle), TAMA (angle between tibial mechanical and anatomical axes), and TPDR (percentage length of tibia proximal to extra-articular deformity). Results Seven distinct types were identified covering 2021 knees, reducible to 4 broad phenotypes: 11% were Type 1 'Neutral' knees showing values close to reported normal knees (mean VCA 5.5°, mLDFA 87°, aLDFA 81°). 38% were Type 2 'Intra-articular varus' with medial intra-articular bone loss (mean mLDFA 90.9°, MPTA 85.4°, VCA of 5.7°). 41% were Type 3 'Extra-articular varus' with extra-articular deformity (EAD). Type 3a had proximal tibial EAD; Type 3b had tibial diaphyseal EAD; Type 3c had femoral EAD (mean VCA 8.7°, HKA 166°), and severe medial bone loss (mean mLDFA 92°, MPTA 83°). 9% were Type 4 'Valgoid type' with features of valgus knees: Type 4a had medial femoral bowing (mean VCA 2.9°); Type 4b had significant distal femoral valgus (mean mLDFA 85.3°, aLDFA 78.6°). Conclusions The null hypothesis that there was no phenotypic variation in varus osteoarthritic knees was rejected as considerable variation was found in coronal morphology of femur and tibia. Four broad phenotypic groups could be identified. Plane of the knee joint articular surface was quite variable. This has relevance to planning and performance of corrective osteotomies, unicompartmental and total knee arthroplasty. Level of Evidence III, retrospective cohort study.

Valgus arthritic knees can be classified into nine phenotypes

“…A recent study in a large series of varus osteoarthritic knees has shown an analogous classification with 7 phenotypes which could be broadly classified into 4 groups – neutral, intra‐articular varus, extra‐articular varus, and a ‘valgoid’ type [15]. The present study also has shown 4 broad phenotypes corresponding to the ones reported [15], except that the valgoid type among varus knees was replaced by ‘varus’ type for the valgus knees, and there were two additional subtypes within type 4.…”

“…From the above measurements, the entire range of values of VCA were segregated into 4 groups, those of mLDFA, aLDFA and TBA into 5 groups each and TBA into 3 groups in accordance with previously reported methods [15].…”

“…Variations in coronal alignment in healthy knees have been described by Lin et al [10], Hirschmann et al [5], and Micicoi et al [13]. A recent study has reported 7 phenotypes of varus osteoarthritic knees [15] and another study has looked at a combined cohort of osteoarthritic varus and valgus knees [22]. However, there are very few morphologic studies specifically of valgus arthritic knees.…”

How Do the Morphological Abnormalities of Femoral Head and Neck, Femoral Shaft and Femoral Condyle Affect the Occurrence and Development of Medial Knee Osteoarthritis

“…10 Mullaji et al use measurement of the alignment of the lower limbs to classify KOA and explore the similarities and differences between different types. 11 However, the above researchers focused more on the influence of the anatomy of the hip or proximal femur on KOA. Other researchers have measured angles that reflect anatomic abnormalities in the hip and tried to look for correlations with changes in the alignment of lower limb.…”

“…Mullaji et al . use measurement of the alignment of the lower limbs to classify KOA and explore the similarities and differences between different types 11 . However, the above researchers focused more on the influence of the anatomy of the hip or proximal femur on KOA.…”