A 53-year-old man was addressed to the orthopedic clinic for a knee replacement surgery.

The patient complained of pain in several joints starting at age 30, mostly affecting the lumbar spine. Over several years, he developed non-inflammatory arthritis of the hips and knees, leading to the indication of total replacement of the right knee joint. Upon opening of the joint capsule, the surgeon was startled to observe a striking brown-black discoloration of the cartilage. This unexpected finding led to the suspension of the surgery pending clarification of the etiology. Clinical examination revealed ochronosis of the ear cartilage bilaterally, sclera and teeth, together with a hyperpigmented postoperative scar (Figure 1). Urine organic acid analyses unveiled homogentisic acid elevation. Molecular analysis showed two pathogenic variants in the HGD gene [c.133delT, p.(Ser45GInfsTer66); c.1078G>C, p.(Gly360Arg)], hence confirming the diagnosis of Alkaptonuria (AKU; OMIM #203500).¹ Joint replacement surgery was rescheduled and performed successfully with uncomplicated postoperative follow-up (Figure 2).

一名 53 岁男子被送往骨科诊所进行膝关节置换手术。

患者从 30 岁开始主诉多个关节疼痛，主要影响腰椎。几年来，他患上了髋关节和膝关节的非炎症性关节炎，导致需要完全更换右膝关节。打开关节囊后，外科医生惊讶地观察到软骨显着的棕黑色变色。这一意外发现导致手术暂停，等待病因明确。临床检查显示双侧耳软骨、巩膜和牙齿的黄褐斑，以及色素沉着的术后疤痕（图 1）。尿液有机酸分析揭示了尿黑酸升高。分子分析显示HGD基因中有两个致病变异 [c.133delT, p.(Ser45GIn fs第 66 节）；c.1078G>C, p.(Gly360Arg)]，因此确认了碱尿症的诊断 (AKU; OMIM #203500)。¹关节置换手术被重新安排并成功进行，术后随访不复杂（图 2）。