[Correction of Valgus Knee Deformity by Hemiepiphyseodesis: a Restrospective Analysis]

PURPOSE OF THE STUDY Hemiepiphyseodesis is commonly used to correct a coronal plane knee deformity during childhood. Since 2007 Blount staple method has been replaced by the eight-Plate Guided Growth System. We retrospectively analysed the indications, results and complications of the older Blount staple method so as to compare them with the newer eight-Plate Guided Growth system. MATERIAL AND METHODS In the period from 2009 to 2019, a total of 98 lower extremities of 54 patients were treated by hemiepiphyseodesis. Lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA) and mechanical axis deviation (MAD) were measured before and after the correction. We focused on the location of hemiepiphyseodesis (distal femur/proximal tibia/both), the operative time and compared the results of implanting 2 or 3 Blount staples. RESULTS The primary correction of valgus knee deformity was achieved in 97%, of which only partial correction was observed in 9.2% and slight overcorrection in 6.1%. A total of 4 patients (4.1%) underwent subsequent corrective osteotomy. The mean LDFA increased from 80° to 86°, while the mean MPTA decreased from 94° to 92°. The mean MAD decreased from 23 mm to 3 mm. The reported complication rate was 5.1%, including four cases of loosening of staples and one case of superficial infection. DISCUSSION It has been verified that the LDFA reduction correlates with staple implantation into the distal femur, conversely the increase in the MPTA correlated with the implantation of staples into the proximal tibia or into both locations. The number of implanted staples (2 or 3) did not affect the size of the resulting correction, but the operative time was statistically significantly shorter when 2 instead of 3 staples were implanted. CONCLUSIONS Blount staple hemiepiphyseodesis is an older method, but it still gives very good results with a low rate of complications. The operating time can be shortened by using 2 staples only, with the same correction effect. The LDFA and MPTA parameters are helpful in identifying the location of hemiepiphyseodesis. The key to success of treatment still remains in correct timing of the implantation of staples with sufficient growth potential. Key words: hemiepiphyseodesis, guided growth, valgus knee deformity, Blount staple.