Restoring the femoral offset prevent early migration of the stem in total hip arthroplasty: an EBRA-FCA study

The use of modular stems is still debated and controversial. Some authors have highlighted a number of disadvantages of modular prostheses including high costs, the tendency to fracture, the fretting and corrosion and the increased production of debris. Other authors have emphasized several advantages to adapt the prosthesis to the morphometric differences of patients, to allow better accuracy in restoring the anatomy and biomechanics of hip joint. The advantages of the modular devices appear to be more evident in patients with developmental dysplasia of the hip (DDH). In our study we compared 96 patients, operated for arthritis of the hip with 55 modular neck prostheses (PROFEMUR®, Wright® Arlington, Tennesse, USA) and 41 standard femoral stems (SYMAX®, Striker® Kalamazoo, Michigan, USA). The precision of restoring the natural offset during surgery was correlated with the clinical outcome and the radiological early migration of each stem measured using the computer-assisted EBRA-FCA method. The average preoperative HHS (Harris Hip Score) was 44 (23-66); the postoperative 86.56 in the 55 patients operated with modular prostheses and 81.70 in the 41 patients with monoblock stem. The worst HH Scores were seen in patients in whom the offset was not restored properly. On the contrary, the best scores have been reached in patients in which that value is closer to the “target” value (offset value of the contralateral hip). Restoring the proper offset seems to determine an appropriate tension of the abductor muscles of the hip and implies a better functioning of the joint and a better primary stability of the implant, with less early migration. This has to be a primary objective of THA surgery.