No difference in clinical outcome, bone density and polyethylene wear 5-7 years after standard navigated vs. conventional cementfree total hip arthroplasty

The purpose of this investigation was to compare clinical outcome, component loosening, polyethylene cup wear and periprosthetic bone mineral density between "cup first" navigated and conventional cementless total hip arthroplasty (THA) 5-7 years after surgery. Fifty patients who received THA with (n = 25) or without (n = 25) the use of an image-free navigation system by a single surgeon were investigated after a mean follow-up of 6.4 (4.8-7.4) years. The Hip Osteoarthritis Outcome Score (HOOS) and the Harris Hip Score (HHS) were obtained; range-of-motion (ROM) was evaluated by a blinded examiner. Radiographic cup inclination, signs of radiographic loosening and polyethylene wear were analysed with the help of digital analysis software on anterio-posterior radiographs by a blinded examiner. Acetabular and femoral periprosthetic bone density was evaluated with the help of dual-energy X-ray absorptiometry. We were unable to find any statistical significant or clinically relevant difference for the HOOS, HHS, ROM and polyethylene wear between the navigated and the conventional THA group 5-7 years after surgery. Cup inclination was more precise in the navigated THA group in relation to the target value of 45A degrees. Standard "cup first" THA navigation does not improve mid-term functional outcome, bony ingrowth and/or polyethylene wear. New concepts in computer-assisted THA, considering cup and stem as coupled biomechanical partners are needed to justify the effort of navigation in routine operations.