Modular hip stems offer many advantages in revision arthroplasty. However, the region of modularity is prone to failure. Fracture of the non-cemented fluted tapered titanium Modular Prosthesis (MP) stem is relatively rare. We present here a case of a distal non-traumatic fracture of the MP stem and review the previously reported cases. A 53-years old, relatively active, male patient with a body mass index (BMI) of 37 kg/m 2 had a fracture of the non-cemented MP stem on the left side after five years without complaints. The BMI was 45 at the time of implantation of the MP stem. His weight was significantly reduced, but the stem failed and fractured at an atypical site, quite distal to the modular junction. The broken stem with a relatively small diameter had been exchanged to a larger one. Fracture of the non-cemented fluted proximally-modular distally-tapered titanium MP stem might occur after years. Even in cases of good bone quality of the proximal femur, patient BMI and activity level should be considered when selecting the stem diameter. Furthermore, proximal bone loss of the femur should be considered as a potential cause of failure.

The treatment of severe acetabular defects in revision total hip arthroplasty (Paprosky type IIIa and IIIb) is demanding and choosing the appropriate surgical technique remains controversial. The introduction of trabecular metal augments has led to a variety of new treatment options. The authors present a case of a Paprosky Type IIIb acetabular defect due to eight subsequent revisions of the left hip. The patient was treated with an alternative treatment option using multiple tantalum wedges. Anatomical reconstruction was achieved and at 12 months follow-up, the patient was pain free and was able to walk without walking aids.

Complete knee dislocation is a rare and severe injury and usually follows high-energy trauma. Non-traumatic knee dislocations are exceedingly rare, while severe overweight appears to be the main cause of the knee dislocation. We here report on a spontaneous knee dislocation in a patient with severe osteoarthritis of the left knee. A 68-year-old woman was admitted to our hospital for an elective total knee replacement. One year prior to admission, a planned joint replacement was not performed due to an existing ulcus cruris. After healing of the ulcus cruris, the patient presented with progressive pain and instability of the left knee without any trauma. The clinical examination showed a multidirectional instability of the left knee with a restricted range of motion (ROM) with 0-0-40 degrees for extension and flexion. The performed radiological examination revealed an anterior knee dislocation of the left knee. Intraoperative findings suggest a non-traumatic aetiology. We suspect that osteoarthritis of the left knee has caused the dislocation. Therefore, we recommend, even in usually "harmless" osteoarthritis, close clinical and radiological follow-up examinations to detect and treat possible complications.

Reconstruction of a large acetabular bone defect is a complex problem in revision hip arthroplasty. The authors report a novel method of reconstructing an uncontained acetabular defect (Paprosky type IIIb) using multiple tantalum augments. A 73-year-old female patient presented to our institution with a chronically dislocated primary left total hip arthroplasty with radiographs demonstrating migration of acetabular component and formation of pseudoarthrosis within the left ilium. Extensive arthrolysis and anatomic reconstruction of the acetabular bone defect were performed using the novel method of multiple tantalum augments. Postoperatively, recovery was initially complicated by multiple dislocations requiring an exchange to an elevated liner, however subsequently achieved good function.