NATHAN Grima has been forced into retirement by injury, with the North Melbourne key defender requiring a third operation on his troublesome back.

North announced on Wednesday morning that Grima, 29, had decided to hang up his boots after 86 games in eight seasons at Arden Street.

Grima had surgery in February to remove a section of damaged disc from his back, having had surgery on the same area in late 2010.

The defender suffered a setback in rehabilitation recently and specialists recommended surgery to fuse a disc in his spine that should alleviate the pain and symptoms of his back condition. Grima has been an almost automatic senior selection since 2010 when fit, but his horror run of injuries meant he never played more than 17 games in a season. North's lack of genuine key defenders in recent seasons meant Grima, 192cm and 94kg, was often required to stand bigger and stronger opponents. But the Tasmanian was usually up to the task and North came to have such faith in him he was often sent to the opposition's most dangerous forward. In addition to his ongoing back problems, Grima was also troubled by knee problems during his career, having undergone an anterior cruciate ligament reconstruction at the end of his first pre-season while still on North's rookie list. His 2014 season was plagued by a navicular injury, while he also had operations on his ankles, fingers and hands. Grima was recruited as a 22-year-old by North at the end of 2007 at pick No.14 in the rookie draft. Overlooked in several earlier drafts, he had come to North's attention as a key member of Central District's 2007 SANFL premiership team. Grima had previously played with South Launceston but moved to Adelaide to reinvigorate his football career. Nathan Grima's career Games: 86 Disposals average: 16.7 Marks average: 5.4 Career highs: - 29 disposals (21 kicks, 8 handballs), 12 marks and 4 tackles in round 12 against Gold Coast at Metricon Stadium, 2012 - 27 disposals (16 kicks, 11 handballs), 8 marks in round 19 against Fremantle at Etihad Stadium, 2010 - 26 disposals (14 kicks, 12 handballs), 10 marks in round 20 against St Kilda at Etihad Stadium, 2010

• Who's hanging up the boots? 2015's retirements and delistings