P Mertl, JF Lardanchet, E Havet, J Vernois, (Amiens)
Introduction
Modular necks used during primary or revision total hip arthroplasties permit to restor the ideal femoral offset and arm of abductors muscles, to ajust leg length and to reduce impingment between the neck and the socket with good hip balancing.
Material and methods
Modular necks are titanium implants manufactured with a double Morse taper: one cylindrical for the junction with the head, and one flat for the junction with the stem. They are avalaible in 2 lengths (short and long) with 6 different geometries: straight (CCD:135°), antevreted of 8° or 15°, 8° and 15° of varus (CCD: 127° and 120°), and a combination of anteverted and varus neck.
122 primary THA were performed with a minimal of 5 years follow-up in the Orthopaedic Department of Amiens University Hospital with modular necks.
Results
7 patients died and none were lost of follow-up. None rupture was deplored. Femoral offset was restored in 97% of these cases even in the revision surgery, end equalization of leg length
was obtained in 98% of the patients. Residual Trendelemburg sign was noted in 3 patients, always after reduction of the offset. The rate of dislocation was low with 2% because of the absence of impingment.
Discussion
Because proximal femoral geometry is different for each patient and femoral offset independent from the IM canal diameter, modular neck is one easy solution to restor independent parameters. In addition, the per-operative trials permit to choose the best implant to avoid any impingment, reducing the risk of dislocation and increasing the range of motion. It’s ideal now for the use of hard bearings. Laboratory analysis have demonstrated very good resistance in assembly-distraction, deep flexion and rupture tests. No corrosion was noted and retrieved weight loss was minimal.