[Screw Angle and Condylar Ratio as Possible Parameters to Monitor the Treatment of Idiopathic Axial lower Limb Deformities Using Eight-Figure Plates].

Purpose of the study: Temporary hemiepiphyseodesis using figure-eight plates is currently one of the main surgical techniques to correct axial deformities of lower limbs in paediatric patients. Comprehensive analysis, correct indication and monitoring of treatment are the basic prerequisites for successful therapy. The aim of the study was to analyse parameters that could become an alternative to standard parameters used nowadays, namely the inserted screw angle (SA), and a new parameter - condylar ratio (CR).

Material and methods: The study included 47 patients treated at the Department of Paediatric Surgery, Orthopaedics and Traumatology at the University Hospital in Brno between 2014 and 2021 and diagnosed with idiopathic bilateral axis deviation of lower limbs, namely genu valgum. After having met the inclusion criteria, the patients underwent a clinical check-up, and long leg radiographs were also obtained. Anthropometric parameters (age, sex, BMI, intermalleolar distance (IMD)), duration of treatment as well as radiographic parameters - mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA), SA and CR, and their derived parameters expressing the change per unit time and defined as a rate of correction (r-mLDFA, r-mMPTA, r-SA, r-CR) were recorded. The obtained values were subsequently statistically analysed, namely by comparing the pretreatment and posttreatment values and through correlation analysis.

Results: The mean age of the population was 11.4 years, BMI 26.9 and IMD 14.1. The mean duration of treatment in the study population was 13.9 months. A significant difference was established between the pretreatment and posttreatment values of all measured radiographic parameters (p<.05). A significant correlation was identified between r-mLDFA and r-SA (p=.002), while no significant correlation was found between r-mLDFA and r-CA or between r-CA and r-SA (p=.650; p=.884).

Discussion: Comprehensive evaluation of the treatment of axial deformities of lower limbs and its optimization are crucial for successful therapy. In addition to the standard mechanical or even anatomical parameters assessing the axis deviation of lower limbs, the authors seek to evaluate also other parameters that may provide a new insight into the deformity or offer additional benefits such as reduced radiation exposure. Such a parameter is for instance the angle of inserted screws in the eight-figure plate system, although there is a difference in opinion among the authors. In our study, we concluded that it is the change in the screw angle that significantly correlates with the mechanical axis of the femur, and thus, under certain circumstances, can become a monitoring parameter. Contrarily, the condylar ratio is a newly introduced quantity which in our study did not show any significant correlation with the mechanical axis of the femur, although a significant change before and after therapy was observed.

Conclusions: A significant correlation was established between the rate of change in screw angle and r-mLDFA, which may, under certain circumstances, serve as a parameter for treatment evaluation, with the advantage of reduced radiation exposure since the assessment requires one scan of the knee joints under loading only. On the other hand, though, no significant correlation was established between the CR as the newly defined parameter and r-mLDFA, which is why it can only be considered as a complementary parameter rather than a decisive one.

Key words: temporary hemiepiphysiodesis, growth plate, genua valga, screw angle, correlation.