Recurrent total knee arthroplasty aseptic loosening in a patient with hypophosphatasia: are they related? A case report

Hypophosphatasia (HPP) is a rare metabolic bone disease caused by deficient alkaline phosphatase activity, leading to impaired mineralization. While total knee arthroplasty (TKA) is a common treatment for end-stage knee arthritis, its outcomes in patients with metabolic bone disorders like HPP are poorly documented. We describe a 49-year-old woman with genetically confirmed adult-onset HPP who underwent primary and revision TKA due to persistent joint pain and mechanical symptoms. Both procedures failed due to aseptic loosening despite appropriate surgical technique and implant positioning. Intraoperative findings revealed highly porous, fragile bone with poor vascularization. Although a direct causal relationship cannot be established, HPP-related bone fragility may impair osseointegration and predispose to early implant failure. This case highlights the need to consider underlying metabolic bone disorders in TKA candidates. To our knowledge, this is the first reported case of recurrent aseptic TKA loosening in a patient with HPP. Further research is needed to clarify the role of HPP in prosthetic failure.