Setting, participants, and implants
This was a retrospective cohort study of consecutive cases performed at a single institution (Kuopio University Hospital, Finland). A total of 101 patients who had primary (n = 70/101 ([70%]) or revision (n = 31/101 [30%]) THA at a university teaching hospital between April 1, 2018, and June 30, 2020, were included. A minimum of 2 years of follow-up was set, ending on June 30, 2022, or following the death of the patient. At our institution, we are used to perform THA rather than hemiarthroplasty for (a) active patients who were independently mobile before a displaced FNF and for (b) patients who have other well-known risk factors (e.g., hip dysplasia, post-traumatic arthrosis, AVN, or degenerative neurological disease) for dislocation. These 101 MDMCs THAs were the first ones operated at our institution and none of the patients were excluded from this study.
We evaluated how introduction of MDMC at our institution in year 2018 has affected the yearly number of hip dislocations following THA. The annual number THA patients treated for dislocation at our institution was harvested from the Finnish Hospital Discharge Register (FHDR) provided by the Finnish Institute for Health and Welfare [
22]. From FHDR data, we screened the annual number of all primary THA patients operated at our institution and (a) who had undergone primary THA due to any reason (including hip fracture), (b) who had undergone THA with any kind of implant due to hip fracture and (c) had a hospitalization period due to hip dislocation during one-year follow-up after implantation of primary THA between years 2008 and 2020.
Patient data, including age, gender, operation side, operation indication, and such as surgical details, were collected from the hospital’s medical records. Complications were defined as minor (no need for revision) and major (revision surgery or other serious adverse event). The major complications were defined as dislocation, prosthetic joint infection (PJI), loosening of the implant, periprosthetic fracture, nerve damage, and other serious events. Major complications with and without revision surgery were analyzed separately. Other complications, like superficial infection, were considered minor. The time from the primary surgery to complication was evaluated.
All patients received a hemispherical MDMC implant (Novae® E TH, SERF, Décines-Charpieu, France). An acetabular titanium shell with a cementless or cemented porous interface was used, and the mean diameter of the MDMC was 51 (range 29–62) mm in both groups (Table
1). The metallic head size was either 22 or 28 mm. The femur stem was cemented in 57/101 (56%) of the cases (Table
1). The femur components were Lubinus SPII® (Link, Hamburg, Germany), Summit® (Johnson & Johnson, Warsaw, Indiana, USA), Taperloc® (Biomet, Warsaw, Indiana, USA), Biomet Reach® (Biomet, Warsaw, Indiana, USA), Corail® (Johnson & Johnson, Warsaw, Indiana, USA), and Spectron® (Smith & Nephew, Watford, UK). In one revision case, the stem was changed due to loosening in addition to revision of the acetabulum component.
Table 1
Patients’ demographic characteristic
Gender | | | 0.50✢ |
Female | 39 (56) | 15 (48) | |
Male | 31 (44) | 16 (52) | |
Operation indication | | | < 0.001✢ |
Hip fracture | 47 (67) | 0 | |
Primary osteoarthrosis | 11 (16) | 0 | |
Dislocation | 0 | 13 (42) | |
Component instability | 0 | 12 (39) | |
Avascular necrosis | 7 (10) | 0 | |
Infection | 0 | 4 (13) | |
Post-traumatic arthrosis | 4 (6) | 0 | |
Pain | 0 | 2 (6) | |
Hip dysplasia | 1 (1) | 0 | |
Operation side | | | 0.31✢ |
Left | 37 (53) | 13 (42) | |
Right | 33 (47) | 18 (58) | |
Surgical approach | | | |
Posterolateral | 68 (97) | 27 (87) | |
Lateral hardinge | 2 (3) | 4 (13) | |
Acetabulum component fixation | | | < 0.001✢ |
Cementless | 50 (71) | 7 (23) | |
Cemented | 20 (29) | 24 (77) | |
MDM metallic head size | | | 0.02✢ |
22 mm | 2 (3) | 5 (16) | |
28 mm | 68 (97) | 26 (84) | |
Radiological analysis | Mean (SD, range) | Mean (SD, range) | |
Acetabulum component position | | | |
Inclination angle° | 48 (9, 31–71) | 47 (9, 27–68) | 0.73◇ |
Anteversion angle° | 23 (9, 4–43) | 19 (9, 1–35) | 0.03◇ |
Acetabular component position at Lewinnek safe zone* | | | 0.41✢ |
Yes | 31 (44) | 11 (65) | |
No | 39 (56) | 20 (35) | |
Surgical technique and follow-up
The operations were performed by consultant orthopedic surgeons or by orthopedic residents with supervision of a consultant orthopedic. Overall, 64/101 (63%) of the operations were done by four experienced consultant orthopedic surgeons. All the revision cases were performed by these four experienced consultant orthopedic surgeons. The posterolateral approach was used in all cases. Spinal anesthesia was given for 76/101 (76%) of the patients; the remaining patients (25/101, 24%) received general anesthesia. A single dose of antibiotic prophylaxis (cefuroxime 3.0 g or clindamycin 900 mg) was given preoperatively and routine postoperatively anticoagulation was prescribed for 4 weeks in all cases. Free range of motion and full-weight bearing was allowed immediately after operation for all patients. A routine outpatient follow-up visit was scheduled 3 months after THA.
Retrospective radiological evaluation was done by authors M.R. and S.M. from the radiographs taken at the 3 months postoperative control. Inclination and anteversion of the acetabulum component were measured from anteroposterior (AP) and mediolateral (M/L) native plain radiographs. The evaluation was carried out using a picture archiving and communication system (PACS).
Statistical analysis
Kaplan–Meier survivorship analysis was performed to calculate survivorship and freedom from revision for any reason. Categorical variables are expressed as frequencies and percentages, and continuous variables are presented as the mean and standard deviation (SD). Continuous data were compared using the Mann–Whitney U-test. Categorical data were compared with the Chi-square test and
t-test. Cox regression analysis was used to evaluate common risk factors for revision (age [≤ 75 and > 75 years], gender, acetabulum component position [Lewinnek safe zone, 5°–25° anteversion and 30°–50° inclination] [
8], and operation type [primary or revision]). Fisher’s exact test was used to analyze operation diagnosis as a risk factor for revision. The hazard ratios (HR) with their respective 95% confidence intervals (CI) were specified for each estimate of the model parameters. A
p-value < 0.05 were considered statistically significant. The data was analyzed using SPSS Statistics Version 27.0 (IBM Corp., Armonk, NY, USA).