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In our article, we investigated indications that football as a competitive sport in adolescents increases the risk of developing genu varum (bowlegs). Leisure time sport is explicitly excluded, and the great importance of sport for the development of adolescents was emphasized (1). In accordance with the article’s topic and the timing of its publication, immediate reporting in the media was extensive, as expected. Lively (we hope) scientific discussion will take its time to run its course. We therefore wish to express our particular thanks for the feedback from specialists and would respond to our correspondents as follows.

We thank Prof. Lahm for his additions to our article. It is correct that the longitudinal axis of the leg constitutes the central topic of our article. It is the most important parameter in the context of deformities close to the knee joint in the clinical/anatomical and radiological contexts. The terms (mechanical) leg axis or Mikulicz line are used synonymously, alongside other terms. A long standing radiograph is the gold standard for determining the leg’s mechanical axis (2). But this is not an option for studies of healthy adolescents. We therefore evaluated only clinical studies in our article. We were not able to give “much space” to the “radiological criteria” for reasons of restricting ourselves to include the essentials: in only one sentence on page 403 and in a paragraph on page 406. The mechanical axis of the leg was not shown/labeled in Figure 2 for reasons of clarity. It could have been mentioned in the described clinical case on page 406. But here, too, the positive late result after bilateral realignment (with a clinically and radiologically centered longitudinal axis in both legs) fell victim to space restrictions.

We also thank Prof. Schiltenwolf for his comments. Our article does indeed include a cautious warning. Cautious, because the literature on the topic is scarce, warning because the meta-analysis indicates a clear direction. When discussing the relevance of genu varum, we cautiously explained the hypothesis that, on the basis of the existing evidence, deviations of the leg axis encourage knee osteoarthritis. A reference not cited in the article for reasons of space supports this hypothesis also on the basis of long standing radiographs (3). If a clear contradiction to this hypothesis is supported merely by the cited 2007 article “Knee alignment does not predict incident osteoarthritis,” then methodological weaknesses of this article should be mentioned. A limitation of the so-called Framingham osteoarthritis study lies in the determination of the leg axis by using focused views of the knee joint only. We wish to reiterate that in contrast to the long standing radiograph (2), focused views of unilateral knee joints are less appropriate for determining the leg’s mechanical axis (4).

In conclusion, further, high quality studies are needed.

DOI: 10.3238/arztebl.2018.0684

On behalf of the authors

Dr. med. Peter Helmut Thaller
Arbeitsgruppe 3D-Chirurgie
Klinik für Allgemeine, Unfall- und Wiederherstellungschirurgie
Klinikum der Ludwig-Maximilians-Universität München
Campus Innenstadt, pthaller@med.lmu.de

Conflict of interest statement

The authors of all contributions declare that no conflict of interest exists.

1.
Thaller PH, Fürmetz J, Chen F, Degen N, Manz KM, Wolf F: Bowlegs and intensive football training in children and adolescents—a systematic review and meta-analysis. Dtsch Arztebl Int 2018; 115: 401–8 VOLLTEXT
2.
Thaller PH, Baumgart R, Burghardt R, Knuellig S, Buerklein D, Mutschler W: Digital imaging in lower limb bone deformities—standards and new perspectives. ELSEVIER International Congress Series 2005; 1281: 154–8 CrossRef
3.
Sharma L, Song J, Felson DT, Cahue S, Shamiyeh E, Dunlop DD: The role of knee alignment in disease progression and functional decline in knee osteoarthritis. JAMA 2001; 286: 188–95 CrossRef
4.
Zampogna B, Vasta S, Amendola A, et al.: Assessing lower limb alignment: comparison of standard knee xray vs long leg view. Iowa Orthop J 2015; 35: 49–54 MEDLINE PubMed Central
1.Thaller PH, Fürmetz J, Chen F, Degen N, Manz KM, Wolf F: Bowlegs and intensive football training in children and adolescents—a systematic review and meta-analysis. Dtsch Arztebl Int 2018; 115: 401–8 VOLLTEXT
2.Thaller PH, Baumgart R, Burghardt R, Knuellig S, Buerklein D, Mutschler W: Digital imaging in lower limb bone deformities—standards and new perspectives. ELSEVIER International Congress Series 2005; 1281: 154–8 CrossRef
3.Sharma L, Song J, Felson DT, Cahue S, Shamiyeh E, Dunlop DD: The role of knee alignment in disease progression and functional decline in knee osteoarthritis. JAMA 2001; 286: 188–95 CrossRef
4.Zampogna B, Vasta S, Amendola A, et al.: Assessing lower limb alignment: comparison of standard knee xray vs long leg view. Iowa Orthop J 2015; 35: 49–54 MEDLINE PubMed Central

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