Early failures of porous tantalum osteonecrosis implants: a case series with retrieval analysis

Porous tantalum osteonecrosis implants have been used in femoral head necrosis for several years, while the clinical outcomes were mixed. As a joint-preserving surgery, early necrosis deterioration and conversion to total hip arthroplasy failed our expectation. We hence investigate an observational study with retrieval analysis to find out the underlying reasons. Thirteen patients were treated with core decompression and implantation of a tantalum rod. The cases were evaluated both functionally and radiologically. We retrieved and analyzed the micro-structural changes and the histopathologic features of four early failed femoral heads with scanning electron microscopy, histopathologic examination, and micro-CT scaning. All implants were placed in proper positions. One-year survival rate was 64.29 % with a HSS score of 81.11 +/- 15.62. Four patients converted to arthroplasty in a mean time of 305 days (0.84 years), with a HSS score of 43.75 +/- 7.5 at the last follow-up. A liquid layer surrounded the tantalum implant was noted on MRI in all four failed cases. Volume render CT remodeling revealed interspace between the metal and bone. Scanning electron microscopy and histopathologic examination indicated sparse and isolated bone ingrowth into the implants. The remodeled trabecular bone and the increased density around the peri-implant area were illustrated with micro-CT scaning. The deterioration of early failed tantalum implant exceeds the nature of osteonecrosis progression. Rather than insufficient mechanical support resulting in improper position and invalid bone ingrowth, nullification of core decompression and consequential intra-osseous pressurization probably led to early failure of porous tantalum osteonecrosis implants.