The majority of uncemented femoral components used in total hip arthroplasty (THA) are of a monoblock design. This monoblock design has been around for many years and has a very low complication rate (McLaughlin and Lee 1997). Once the stem has been seated in the femur, the version of the neck cannot be altered, and the leg length and hip offset can only be changed slightly with a modular head. A modular neck-stem design (also known as a femoral stem with an exchangeable neck) has been introduced over the last few years by a number of different companies. This allows the surgeon to alter neck version, leg length and hip offset after the stem has been seated with the aim of more accurately recreating hip biomechanics to that of the native hip (Cheal et al. 1992; Ovesen et al. 2010). This should reduce the risk of impingement and dislocation after THA. This theoretical advantage has seen the modular neck-stem design grow in popularity over recent years; however, concerns are now being raised regarding their clinical results.
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