Modular femoral stems for total hip arthroplasty (THA) were introduced to allow additional options for surgeons in controlling leg lengths, offset and implant stability. This option is widely used in our Region, where the study was conducted, having a modular neck stem nearly 35% of primary THA in 2013. Great majority of modular neck is made of Titanium alloy. The study was designed as a retrospective descriptive case series of 67 hips in patients who underwent revision of a THA. All had a Titanium modular neck. In 44 cases revision was due to breakage of the neck, in the remaining 23 it was due to different reasons unrelated to modular neck such as bone fracture, breakage of a ceramic component, cup loosening. Mean follow up was 3.5 yrs. For all patients excised capsule and surrounding tissue were graded for presence of necrosis, inflammatory exudate, lymphocytes, and wear particles using light microscopy of routine paraffin sections stained with hematoxylin and eosin. The retrieved modular neck-body and head-neck junctions were examined for evidence of fretting and corrosion. For some patient dosage of circulating Titanium was obtained. Approval was obtained from institutional review board. It resulted that a variable amount of wear was observed in the first group of patients, with no evidence of lymphocytic reaction, but with variable notes of necrosis. Broken necks showed different patterns of damage, with different degree of corrosion, beside the fatigue fracture. In the second group wear was less evident or absent and negativity of lymphocyte reaction was substantially confirmed. Circulating Titanium ions were one order of magnitude higher in first group (mean 35 micrograms /liter). It can be concluded that fracture of Titanium modular necks occurs progressively, wear does not induce lymphocytic reaction and circulating ions increase.
After a few years from its introduction, the limits of the THA became evident, mainly due to high rates of mobilization for polyethylene wear and to the release of metal ions from MOM and MOP couplings. Ceramic bearings were thus introduced in surgery to obtain lower levels of friction and wear. These issues have now been well recognized by several studies, which show that ceramic-on-ceramic joint has the lowest wear rate among various articulations and that ceramic particles induce less macrophage reaction and decrease cytokine secretion, allowing to have little periprosthetic osteolysis. After the first results in the late 70′s and early 80′s, the mechanical reliability was improved due to the manufacturers' efforts to reduce the ceramic fragility evolving average grain microstructure and lowering the degree of impurity. Betterment and standardization of production have led to 3rd generation alumina, Biolox Forte in 1994, that achieved a lower incidence of fracture. The purpose of our study has been to assess long-term follow-up results of alumina-on-alumina 3rd generation ceramic total hip cementless arthroplasty performed at our institution from January 1995 to December 2000. We prospectively followed more than 200 patients operated of THA for primary or secondary hip osteoarthritis analyzing clinical and radiographs features. In this period, the total hip replacement were performed by a single surgeon, who is the senior author (A.T.) in our Institution. All patients were clinically examined to confirm the diagnosis and all of them were checked with a standard plain radiographs in two projections and, when necessary, the radiographic examination was completed by CT scans. The same prosthesis was used in all patients, a 3rd generation alumina COC articulation, composed of a hemispherical titanium alloy cup and a 28-mm alumina ceramic femoral head. The modular ceramic head was fixed to a 12/14 taper cone. Proximally plasma-spray hydroxyapatite coated Ti alloy stems completes the implant features. Modular necks were used in retro or anteversion and varus or valgus offset, allowing changes in neck-shaft angle and giving a perfect intraoperative stability. Clinical assessment was performed using the Merle-D'Aubigne and Postel hip score. Each patient was assessed before surgery, after 30 days, afterwards at 4 months and annually after surgery. The mode of femoral component fixation was radiographically classified as bone ingrowth fixation, stable fibrous fixation or unstable fixation, according to the criteria Engh-Bobyn. Osteolysis was evaluated on the femoral side at each Gruen zone. Osteolysis on the acetabular side was evaluated by DeLee and Chanley zone. Our study has concluded that cementless modular hip arthroplasty with 3rd generation ceramic-on-ceramic bearing, with a 13 to 18 years follow-up, shows an excellent survivorship, in particular for the very low volume release of microparticles during friction, which consequently reduction of cytokine release, thus diminishing the risk of periprosthetic osteolysis and loosening of implant components.
