Arithmetic hip-knee-ankle angle and stressed hip-knee-ankle angle: equivalent methods for estimating constitutional lower limb alignment in kinematically aligned total knee arthroplasty

Abstract

Purpose Kinematically aligned total knee arthroplasty (KA TKA) relies on precise determination of constitutional alignment to set resection targets. The arithmetic hip-knee-ankle angle (aHKA) is a radiographic method to estimate constitutional alignment following onset of arthritis. Intraoperatively, constitutional alignment may also be approximated using navigation-based angular measurements of deformity correction, termed the stressed HKA (sHKA). This study aimed to investigate the relationship between these methods of estimating constitutional alignment to better understand their utility in KA TKA. Methods A radiological and intraoperative computer-assisted navigation study was undertaken comparing measurements of the aHKA using radiographs and computed tomography (CT-aHKA) to the sHKA in 88 TKAs meeting the inclusion criteria. The primary outcome was the difference in the paired means between the three methods to determine constitutional alignment (aHKA, CT-aHKA, sHKA). Secondary outcomes included testing agreement across measurements using Bland-Altman plots and analysis of subgroup differences based on different patterns of compartmental arthritis. Results There were no statistically significant differences between any paired comparison or across groups (aHKA vs. sHKA: 0.1°, p = 0.817; aHKA vs. CT-aHKA: 0.3°, p = 0.643; CT-aHKA vs. sHKA: 0.2°, p = 0.722; ANOVA, p = 0.845). Bland-Altman plots were consistent with good agreement for all comparisons, with approximately 95% of values within limits of agreement. There was no difference in the three paired comparisons (aHKA, CT-aHKA, and sHKA) for knees with medial compartment arthritis. However, these findings were not replicated in knees with lateral compartment arthritis. Conclusions There was no significant difference between the arithmetic HKA (whether obtained using CT or radiographs) and the stressed HKA in this analysis. These findings further validate the preoperative arithmetic method and support use of the intraoperative stressed HKA as techniques to restore constitutional lower limb alignment in KA TKA. Level of evidence III.

Knees with anteromedial osteoarthritis show a substantial phenotypic variation prior and following medial unicompartmental knee arthroplasty

“…The present findings are in accordance with previous studies demonstrating that either CPAK phenotypes I or II were the most commonly observed knee phenotypes in both healthy knees [12, 18, 21] and arthritic patients undergoing TKA [14, 18, 21, 31, 37, 40]. A recent study evaluating the CPAK phenotype distribution among 8739 osteoarthritic knees, identified CPAK phenotype I and II as the predominant phenotypes, with incidences of 28.1% and 27.3% respectively [14].…”

Reliability and validity of OpenPose for measuring hip-knee-ankle angle in patients with knee osteoarthritis

“…The HKA angle is defined as the angle between the mechanical axes of the femur and tibia in the coronal plane 1 . Based on this angle, lower extremity alignment is classified as varus, neutral or valgus 2 – 4 . Many reports have shown that varus or valgus alignment increases the risk of incidence and progression of knee OA 5 – 9 .…”

The language of knee alignment

“…this narrowing results in a fundamentally altered mhka, meaning estimation of the constitutional alignment is no longer possible using mechanical axis referencing. nevertheless, constitutional (or prearthritic) alignment can be approximated using the "arithmetic HKA" (aHKA = MPTA − LDFA), an especially useful tool when considering individualized surgical techniques, [13][14][15][16] provided the arthritic process has not yet caused significant bone wear.…”