Bilateral Patellar Tendon Rupture Following Total Knee Arthroplasty in a Patient With Alkaptonuria: A Case Report

Alkaptonuria (AKU) is a rare hereditary disorder of tyrosine degradation. The disorder is characterized by the accumulation of a pigment called homogentisic acid. Its accumulation can lead to the breakdown of connective tissue, including tendons. This report presents a 46-year-old male with a history of bilateral total knee arthroplasty (TKA) who sustained bilateral patellar tendon rupture after an acute injury. A single-stage bilateral knee revision with direct repair of the extensor mechanism augmented with Achilles allograft was performed. The procedure was successful, and the patient had an excellent post-operative outcome at one year post-operatively. This case attempts to highlight the possible complications from AKU in order to better counsel patients with this condition who are undergoing TKA.

Alkaptonuria with extensive ochronotic degeneration of the Achilles tendon and its surgical treatment: a case report and literature review

Background

Alkaptonuria is a rare genetic metabolic disorder due to deficiency of homogentisate 1,2-dioxygenase (HGD), an enzyme catalyzing the conversion of homogentisate to 4-maleylacetoacetate in the pathway for the catabolism of phenylalanine and tyrosine. HGD deficiency results in accumulation of homogentisic acid and its pigmented polymer. Ochronosis is a bluish-black discoloration due to the deposition of the polymer in collagenous tissues. Extensive ochronotic involvement of the Achilles tendon in alkaptonuria and its surgical treatment is rarely reported.

Case report

A 43-year-old man presented to our clinic in March 2019 with sudden onset of left Achilles tendon pain with no history of prior trauma. Surgical exploration revealed a complete disruption of the tendon at its attachment to the calcaneus. Black pigmentation was extensive and reached the calcaneal tuberosity, extending about 7 cm from the insertion.

Discussion

Achilles reconstruction was performed using flexor hallucis longus tendon transfer. The patient experienced uncomplicated healing with satisfactory functional results.

Conclusion

Orthopedic surgeons should be aware of the progressive nature of alkaptonuria. Extensive degenerative changes of the ruptured tendon should be suspected so that physicians can plan tendon repair and facilitate prompt surgical intervention.