We retrospectively reviewed 2869 patients who had 3346 THAs with hard-on-hard bearing surfaces implanted between January 1996 and March 2009; 1757 (53%) were COC components and 1589 (47%) were MOM components (Table ). During that time, we treated 13,073 patients, between two institutions, with THA using all implants. The indications for the use of a hard-on-hard bearing surface were (1) patients with end-stage arthritis, (2) active patients, (3) patients younger than 60 years, and (4) patients at high risk for instability (MOM cohort). The contraindications for surgery were patients with (1) infection, (2) severe bone loss, (3) compromised soft tissue envelope, (4) neurovascular deficiency, and (5) preexisting conditions prohibiting induction of anesthesia. The average age of the patients in the COC cohort was 50 years (range, 15–80 years), with 1017 patients (60%) being men. The mean height and weight of this cohort were 1.7 m (range, 1.2–2.2 m) and 100 kg (range, 37.2–214.5 kg), respectively. The average age of the patients in the MOM cohort was 58 years (range, 19–89 years), with 628 (52%) patients being men. The mean height and weight in this cohort were 1.7 m (range, 1.2–1.9 m) and 92.5 kg (range, 45.5–205 kg), respectively. No patients were recalled specifically for this study; all data were obtained from medical records and radiographs. We had prior Institutional Review Board permission.
Summary of results of COC and MOM THA
For the COC cohort, we used one of six different acetabular shell types between 2002 and 2009, with the two most common types being Trident®
(806 of 1757 patients, 45%) and Trident®
(692 of 1757, 39%) (Stryker Orthopaedics, Mahwah, NJ, USA). Between 2002 and 2009, we used 10 types of femoral stems, with the most common being Accolade®
(1338 of 1757 patients, 76%) (Stryker Orthopaedics). Femoral head sizes ranged from 28 to 36 mm. Minimum followup was 6 months (mean, 50.4 months; range, 6–96 months) in the COC cohort, with 1697 records (97%) available. Six different surgeons performed the procedures, each utilizing a modified Hardinge approach [10
] while the patient was in a supine position. Patients in the COC cohort returned for followup visits at 6 weeks, 6 months, and 1 year. Afterwards, we followed up with patients at either 1- or 2-year intervals to assess for component failure. At each postoperative visit, the surgeons evaluated patients and obtained radiographs. Sixty patients from the COC cohort were lost to followup at an average of 65 days (range, 0–179 days).
Between 1996 and 2006, the surgeons at one center performed 1589 MOM primary THAs, of which a minimum 2-year followup (mean, 60.2 months; range, 24–178 months) was available for 1210 (76%). The surgeons utilized three systems of acetabular construct: a modular titanium shell with a CoCr insert and a 28- or 32-mm inner diameter (351 patients, 22%), a CoCr monoblock shell of increasing thickness mated with a 38-mm CoCr head (750, 47%), and a solid “resurfacing style” CoCr monoblock thin (3-mm) shell with anatomic heads of increasing diameter (40–60 mm) (488, 31%). Four surgeons performed the procedures, all utilizing a modified direct lateral approach (modified Hardinge) with the patient in the lateral decubitus position. Patients were followed at 6 weeks and then seen yearly thereafter. At each postoperative visit, the surgeons evaluated patients and obtained radiographs. Three hundred seventy-nine patients from the MOM cohort were lost to followup at an average of 234 days (range, 3–690 days). From the medical records, we determined whether the patient had a revision and those lost to followup.
We used a two-tailed unpaired t-test to assess differences in continuous variables (age, height, weight, BMI) and a two-tailed Fisher exact test to determine differences in sex proportions between revised and unrevised hips. We used a univariate regression analysis for the MOM design type data. We analyzed all data using SPSS® (SPSS Inc, Chicago, IL, USA).