患者男25岁。以“右膝疼痛2年加重1个月”入院。患者2年前右膝关节有轻度扭伤史,当时感疼痛,但负重活动均正常,疼痛也逐渐好转,未加重视。此后,右膝每轻碰硬物即感疼痛,近1个月来负重行走也感膝前疼痛。X线片示右髌骨内有一密度减低区,以“右髌骨良性肿瘤,性质待定”收住入院。体 The patient is 25 years old. With “right knee pain for 2 years aggravated 1 month” admitted to hospital. The patient had a history of mild sprains in the right knee joint two years ago. At that time, he felt pain, but his weight-bearing activities were normal, and the pain gradually improved and he did not pay attention. Since then, the right knee feels painful with each touch of a hard object, and walking in the last month has also caused pain before the knee. The X-ray film showed a region of reduced density in the right sacrum, and was admitted to the hospital with a “benign tumor of right sacrum, whose nature was to be determined.” body