Premature failure of Kinemax Plus total knee replacements

Abstract

We describe a cohort of patients with a high rate of mid-term failure following Kinemax Plus total knee replacement inserted between 1998 and 2001. This implant has been recorded as having a survival rate of 96% at ten years. However, in our series the survival rate was 75% at nine years. This was also significantly lower than that of subsequent consecutive series of PFC Sigma knee replacements performed by the same surgeon. No differences were found in the clinical and radiological parameters between the two groups. At revision the most striking finding was polyethylene wear. An independent analysis of the polyethylene components was therefore undertaken. Scanning electron microscopy revealed type 2 fusion defects in the ultra-high molecular weight polyethylene (UHMWPE), which indicated incomplete boundary fusion. Other abnormalities consistent with weak UHMWPE particle interface strength were present in both the explanted inserts and in unused inserts from the same period. We consider that these type 2 fusion defects are the cause of the early failure of the Kinemax implants. This may represent a manufacturing defect resulting in a form of programmed polyethylene failure.

Polyethylene thickness is a risk factor for wear necessitating insert exchange

“…A recent study has shown the catastrophic consequences of increased PE wear, leading to a high failure rate in a contemporary TKA design [23, 24]. Therefore, the problems of excessive wear are not only a problem of the past [25, 26].…”

Effectiveness of anti‐oxidant polyethylene: What early retrievals can tell us

“…Some free radicals remain and initiate an oxidation cascade that occurs in air during shelf‐storage, and during in vivo use . Oxidation causes chain scissioning and embrittlement leading to reduced toughness, increasing the possibility of fatigue fracture during in vivo use, especially in knees . Manufacturers have employed post‐irradiation thermal treatments to reduce or eliminate these free radicals by annealing below the melt temperature or remelting the irradiated UHMWPE.…”

“…6 Oxidation causes chain scissioning and embrittlement leading to reduced toughness, 7,8 increasing the possibility of fatigue fracture during in vivo use, especially in knees. 9,10 Manufacturers have employed post-irradiation thermal treatments to reduce or eliminate these free radicals by annealing below the melt temperature 11,12 or remelting 13 the irradiated UHMWPE. Neither method has proved to be without associated problems.…”

Wear-pattern analysis in retrieved tibial inserts of mobile-bearing and fixed-bearing total knee prostheses

“…[1][2][3][4][5] Premature wear of UHMWPE tibial inserts is one of the major causes of failure of TKRs. 6,7 Moreover, particulate wear debris released from polyethylene may also trigger a biological response resulting in osteolysis and/or aseptic loosening of the implant. [8][9][10][11][12] The contemporary tibial component in a TKR can either be a fixed-or a mobilebearing design.…”