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Estimation of the Recovery of Physiological Genu Varum With Linear Mixed Model

Akhmedov, Bekhzad MD*; Ahn, Soyeon PhD; Chung, Chin Youb MD*; Lee, Kyung Min MD*; Sung, Ki Hyuk MD*; Kim, Tae Won MD*; Lee, Seung Yeol MD*; Choi, In Ho MD; Cho, Tae-Joon MD; Yoo, Won Joon MD; Park, Moon Seok MD*

Journal of Pediatric Orthopaedics: June 2013 - Volume 33 - Issue 4 - p 439–445
doi: 10.1097/BPO.0b013e318277093d
Knee/Tibia

Background: Although previous studies have provided reference values for the lower limb alignment in children with physiological genu varum, those often have methodologic flaws, including problems with assumptions of statistical independence. In this study we intend to use appropriate statistical methods to determine reference values of the recovery of physiological genu varum by using a linear mixed model (LMM).

Methods: The database of our institution was searched and teleroentgenograms of patients up to 5 years of age with clinical diagnosis of physiological genu varum were selected. The mechanical tibiofemoral angle (mTFA), mechanical lateral distal femoral angle (mLDFA), and mechanical medial proximal tibial angle (mMPTA) were measured from each radiograph. These measures were then incorporated in LMM. The reference values for mTFA, mLDFA, and mMPTA were calculated by LMMs with age, sex, and side of the limbs, as the fixed effects with each subject as random effects.

Results: A total of 425 teleroentgenograms were evaluated from 161 patients with physiological genu varum. Age, sex, and limb side terms were found to be significant contributing factors to the measures. In the LMM, with the age as quadratic, mTFA was equal to −0.3-degree varus [95% confidence interval (CI), −5.9 to 5.3 degrees] at the age of 3 years. The mLDFA was equal to 87.8 degrees (95% CI, 82.8-92.8 degrees) at the age of 4.5 years. The mMPTA was equal to 88.8 degrees (95% CI, 80.4-97.2 degrees) at the age of 2.5 years.

Conclusions: An LMM fitted well to estimate the natural recovery of physiological genu varum. Age, sex, and side of the limbs were found to be significant factors in the estimation of mTFA, and age and side of limbs were significant in estimation of mLDFA and mMPTA.

Level of Evidence: Level III—diagnostic study.

*Department of Orthopaedic Surgery

The Medical Research Collaborating Center, Seoul National University Bundang Hospital, Kyungki

Department of Orthopaedic Surgery, Seoul National University Children’s Hospital, Seoul, Korea

Bekhzad Akhmedov, MD and Soyeon Ahn, PhD are co-first authors.

No commercial support in any form including pharmaceutical and industry backing have been received or will be received from any commercial party related directly or indirectly to the subject of this article. None of the authors received financial support for this study. There was no external funding source for this study.

The authors declare no conflict of interest.

Reprints: Moon Seok Park, MD, Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, 300 Gumi-Dong, Bundang-Gu, Sungnam, Kyungki 463-707, Korea. E-mail: pmsmed@gmail.com.

© 2013 by Lippincott Williams & Wilkins