Avulsive Achilles Tendon Rupture in a Patient With Alkaptonuria: A Case Report.

Alkaptonuria is a rare autosomal recessive disease caused by a mutation in the homogentisate 1,2-dioxygenase (HGO) gene, leading to the accumulation of homogentisic acid (HGA). HGA polymerizes to form a black pigment that accumulates in connective tissue and joints (ochronosis), causing their destruction. In this work, we report a case of Achilles tendon rupture in a patient with a prior diagnosis of alkaptonuria. A 71-year-old man presented to the emergency department reporting pain in his posterior right ankle and dysfunction, evolving over three weeks after falling down a short flight of stairs. He had previously been diagnosed with alkaptonuria and had undergone five joint prostheses and an aortic valve replacement. A physical examination revealed right ankle edema, pain upon palpation, a palpable gap at the insertion of the tendon, and a positive Thompson test. An MRI confirmed an avulsive rupture at the insertion of the Achilles tendon. During surgical exploration, black pigmentation was observed in the tendon, which was reinserted using a double-row system reinforced with a percutaneous Bunnel stitch. The patient was discharged the following day with a cast splint, maintaining the foot in physiological plantar flexion for two weeks. In the subsequent two weeks, he used a non-weight-bearing walker boot, and finally, in the following two weeks, he began weight-bearing. Two months post-operation, he was walking without support. Twelve months after the intervention, the patient regained their previous functional status, being able to walk on tiptoes without difficulty. Spontaneous Achilles tendon rupture without associated trauma in patients with ochronosis is rare, with limited literature demonstrating successful outcomes post-surgery. Since the tendon becomes more fragile due to pigment accumulation, it was reinserted using a double-row system, increasing the contact area and more effectively distributing the load. There is no standard technique for treating these patients, but the patient's previous functional capacity was restored, with no new ruptures to date. The significant morbidity of alkaptonuria and potential complications, such as tendon ruptures, warrant future studies to discover and develop new prophylactic and therapeutic treatments.