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Total knee arthroplasty in a patient with Hardcastle syndrome.

Diaphyseal medullary stenosis is a rare skeletal dysplasia of unknown etiology with potential autosomal dominant genetic inheritance. A variant of diaphyseal medullary stenosis has been associated with a high risk of malignant transformation, specifically in the form of malignant fibrous histiocytoma. This potential combination of diaphyseal medullary stenosis and malignant fibrous histiocytoma is known as Hardcastle syndrome. This article presents a case of a 32-year-old man with osteoarthrosis of the knee as a consequence of Hardcastle syndrome for which he underwent a total knee arthroplasty (TKA) with a satisfactory outcome. Our case demonstrates pathological and radiological signs of skull involvement, which has not previously been reported in the literature as a manifestation of this condition. We discuss the differential diagnoses of diaphyseal dysplasia that should be considered in such cases and advocate the use of a triad of preoperative radiological investigations, including early thallium isotope bone, magnetic resonance imaging, and computed tomography. We also discuss the use of long-stemmed prostheses, extramedullary femoral alignment, and the concerns of using Computer Assisted Surgery for total knee arthroplasty in patients with diaphyseal medullary stenosis.With the short-term success of TKA in Hardcastle syndrome, we found that TKA could be considered as an alternative treatment option in symptomatic patients. However, due to the fact that the potential for malignant transformation in this syndrome is unchanged by a TKA, the patient should remain under close clinical and radiological follow-up.