Summary

Estimation of normative values for radiographic parameters of coronal lower limb alignment in the general Japanese population showed that constitutional varus based on MPTA were observed in men and women, and these radiographic parameters were not correlated with age, BMI or BMD.

Abstract

Purpose

While the recent interest for the coronal plane lower limb alignment for considering etiology of developing knee osteoarthritis (KOA) or planning for osteotomy and arthroplasty, there have been few large-sample epidemiological study regarding normative values of these parameters in people without osteoarthritic changes in radiographs. The purpose of this study was to estimate normative values of radiographic parameters in lower limb alignment and investigate its age-related changes in Japanese general population.

Methods

A total of 1474 knees in 737 volunteers (307 men and 430 women) who participated in the Iwaki cohort study were enrolled. Standing anterior-posterior radiographs were evaluated with Kellgren Lawrence (KL) grade, and KL grade 2 and more were defined KOA. Radiographic parameters; hip knee ankle angle (HKAA), femorotibial angle (FTA), mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA), weight bearing line ratio (WBLR) were measured. And their normative values were estimated as mean ± 2 standard deviations for non-KOA group aged 18-39 years, and associations with age were analyzed. Also, to investigate related factors for radiographic parameters in non-KOA group and KOA group, regression analysis was performed with HKAA, FTA, mLDFA and MPTA as dependent variables, and age, sex, BMI, and BMD as independent variables, respectively.

Results

The overall prevalence of radiological KOA was 31.2%, with 18.7% in men and 39.8% in women (p<0.001). Normative values in overall young healthy participants were 1.8 ± 5.1° in HKAA, 175.7 ± 6.5° in FTA, 86.4 ± 3.4° in mLDFA, 85.8 ± 4.1° in MPTA, 1.2 ± 2.7° in JLCA and 39.7 ± 23.7% in WBLR. There was significant difference in HKAA, FTA, MPTA and WBLR between men and women. Correlation analyses in non-KOA group revealed that, while age and BMD were correlated with HKAA, FTA, MPTA and WBLR, their correlation coefficients were very low (r=-0.220 to 0.189) in men. In women, while HKAA was correlated with age, and HKAA and MPTA were correlated with BMD, correlated coefficients were very low (r=-0.054 to 0.096). Regarding the correlation among age, BMI, BMD and radiographic parameters in KOA group, correlation coefficients were very low. Regression analysis in non-KOA group showed that sex was significantly related with HKAA (p<0.001), FTA (p=0.003), mLDFA (p=0.043) and MPTA (p<0.001). Age was correlated with only FTA (p=0.002) and MPTA (p=0.046). In contrary, BMD was significantly correlated with FTA (p<0.001) in KOA group, and sex was correlated with FTA (p=0.042) and MPTA (p=0.002).

Conclusions

Normative values of radiographic parameters in coronal plane lower limb alignment were estimated, and they were different between men and women. Furthermore, radiographic parameters were not correlated with age, BMI and BMD. These data might be useful to consider the etiology and therapeutic strategy for knee osteoarthritis.