Negative biomechanical effects of large grade nuclectomy in the transforaminal endoscopic discectomy increased the risk of adjacent segment diseases: A finite element study

•A large grade of nuclectomy leading to poor prognosis, but the underlying biomechanical mechanism was unclearly illustrated.•Biomechanical deterioration is a significant initial trigger for ASD, but no published studies clearly illustrated that a large grade of nuclectomy causes mechanical environment deterioration and is seen as a risk factor for ASD.•Significant biomechanical deterioration, both in the adjacent disc and zygapophyseal joints, is observed in the caudal side after the in-out TED with large nuclectomy.•A large grade of nuclectomy is regarded as an independent risk factor of adjacent segment disease in the caudal functional spinal unit after the in-out TED.