Abstract
The proximal modular neck in total hip arthroplasty is not a new concept, but there has been resurgence in interest with multiple companies offering proximal modularity.
The proposed advantages of proximal modularity are 1) reduced impingement and subsequent reduced risk of ceramic liners, 2) reduced risk of dislocation and 3) fine tuning of leg length and offset. All of these surgical goals can be accomplished with careful surgical planning and technique, without introducing the risks associated with new technologies. Further, according to the Australian Orthopaedic Association 2014 Joint Replacement Registry annual report, the dislocation rate for components with femoral neck modularity is actually higher than fixed necks. As such, there are no advantages to modular necks.
Modular necks introduce new problems and risks. Modular necks introduce an additional source of corrosion and fretting, and specific systems have been recalled over such concerns. There are numerous case reports of dissociation and fracture at the junction. Fracture appears to be a significant issue in some systems. Retroversion of the neck to reduce the chance of dislocation is not necessarily benign with respect to implant fixation and stability, with RSA and registry data suggesting caution in the application of retroverted necks. Modular necks are difficult to dissociate when in vivo, negating the long-term benefit of modular conversion. Finally, proximal neck modularity significantly increases the cost of the implant, without any documented improvement in long-term outcome.
Modular necks offer limited advantages with significant potential downside. On balance of the evidence, the routine use of modular necks in primary total hip arthroplasty is difficult to justify.
