Kristian Kley completed his medical training at Hannover Medical School in 2006 and then started a residency in orthopaedic trauma in Hannover with Prof Philipp Lobenhoffer. He is now working as fellow in a group practice in Hannover (Gelenkchirurgie Orthopädie Hannover) with Prof. Lobenhoffer. Kristian Kley early developed a strong interest in osteotomy around the knee. He is an active member of the Hannover team treating 300 patients per year with osteotomy around the knee and developing new techniques and instruments to ease these procedures. He has been active on national and international meetings and is also guest member of the Joint Preservation Expert Group of AO Foundation. Kristian Kley has developed unique techniques of minimal-invasive osteotomy of femur and tibia which are now used clinically in Hannover on a regular basis.