Challenging Implantation of Hip Prosthesis in a 32-year-old Patient with Kniest Syndrome.

INTRODUCTION: Kniest dysplasia is associated with short body stature (dwarfism) and impairment of the musculoskeletal system due to a mutation in the COL2A1 gene coding for a protein that forms type II collagen. Hip endoprosthesis for patients with Kniest system requires a specific femoral shaft design since the medullar space is limited due to the underlying dysplasia. The Wagner cone stem has shown excellent results. It is especially suitable for patients with small or dysplasic femur. However, no data exist regarding hip endoprosthesis in a patient with Kniest syndrome.

CASE REPORT: A 32-year-old female patient with Kniest syndrome presented at our department with a painful pseudarthrosis after femoral valgisation osteotomy 8 years ago. A Wagner cone stem and acetabular roof cup with a cemented Ecofit cup 2M (dual-articulation acetabular cup system) were implanted due to a dysplastic femur with a small medullary space. The Ecofit cup itself is associated with a reduced risk of dislocation. The patient was satisfied with the range of motion after hip endoprosthesis and reported a significant increase in quality of life. The patient is still comfortable with the hip prosthesis at the most recent follow-up 4 years after implantation. Follow-up radiographs over 4 years have not revealed any signs of loosening or migration, and no Trendelenburg sign was reported for the affected side.

CONCLUSION: The Wagner cone stem provides a good solution in challenging femora caused by previous osteotomies, fractures, or dysplasia. Additional stability of hip prosthesis can be achieved using a dual articulation acetabular cup system. Furthermore, we applied an attachment tube based on the concept of tumorprosthesis where the abductor muscle group got reattached.