Helsinki-born Nykänen fought as part of a commando unit during the war. Commander-in-Chief Carl Gustaf Emil Mannerheim, after whom the medal is named, awarded Nykänen his Mannerheim Cross on 1 August 1943 on the recommendation of divisional commander Uno Fagernäs.
Nykänen had led a commando unit that obtained valuable information from the enemy. After the war he worked for a mechanical engineering firm until his retirement in 1981. He wrote a wartime memoir in 1983.
The last surviving holder of a Mannerheim Cross is Tuomas Gerdt, who is 89 years of age and lives in the eastern town of Lappeenranta.
The award has been given to 191 soldiers for acts of bravery during the Second World War. Four recipients were recognized for more than one act, and the cross has been awarded on a total of 197 occasions.