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The implantation of a hip prosthesis is one of the most common operations in Germany. There isn’t such thing as the one ideal implant. Currently, both monoblock and modular cups are being used. This work deals with the question whether both cups are equally recommendable.
Ten years after surgery, 533 implants were evaluated based on survivorship, clinical, ra-diographic, and patient satisfaction. 396 RM Classic monoblock cups (Mathys) were compared to 137 modular cups, 69 Reflection acetabular cup systems (Smith & Nephew) and 68 trilogy acetabular systems (Zimmer). All cups were uncemented primary im-plantats with ceramic-polyethylene bearings.
The data for this retrospective cohort study were collected using patient and investigator sheets during a 10-year follow-up. In order, to draw conclusions from non-randomized patient groups, a detailed group comparison was performed. There was no difference in gender, diagnosis and risk factors, as well as in activity, preoperative Harris Hip Score and the Charnley classification. However, there were dissimilarities in age and femoral head size. Patients with a monoblock cup showed an average age of 62 years and were therefore 5 years older than the comparison group. In addition, RM cups were more often combined with a 28 mm head. In order to avoid a falsification due to the different age, further analysis was made, in which a subdivision into younger (<55 years) and older patients (≥ 55 years) was carried out. In addition, the head diameter was considered in the evaluation of the revisions and radiological analysis.
Implant survivorship was performed with the Kaplan-Meier curve and the long-rank test. Patient satisfaction was assessed using a Chi-Square test. A t-test was used for the evalu-ation of the Harris hip score and the radiographic wear. An ethics vote for the OKK data-base was existent.
After ten years, 97% oft the modular implants were still containing the initial cups. The RM cups had 2% lees. However, there was no significant difference (p = 0.282) to the comparison group. In the modular cups, the reason for a revision was not attributed to the modularity. In two cases, a single inlay change was performed with good long-term re-sults. In the clinical evaluation of patient satisfaction (p = 0.507) and Harris hip score (p = 0.326), no significant difference was found in both groups. 96% of patients with an unrevised monoblock cub were satisfied by the operation. In the comparison group, the subjective satisfaction was 94%.
The mean Harris Hip Score of all unrevised cases was 84 points. Patients with a modular cub achieving better scores. In all radiography, no significant differences were found. The wear of the monoblock cup was 0.087 mm per year and 0.002 mm per year over that of the modular systems. Increased osteolysis in the sense of a backside wear occurred in the modular cabs in not significant. The lysis in the area of the proximal shaft stayed almost the same.
Even after considering the age and head size differences, the implants were equivalent in all evaluations. So far it cannot be determined in which cases modularity could be an advantage. Replacement of the inlay, however, seems very promising for revisions after a short time. Nevertheless, it remains questionable whether the long-term result are just as good.
In summary, both modular and monoblock cubs achieved good results in survivorship, clinical, radiological results and patient satisfaction in the 10-year follow-up and showed no significant differences. Based on this evaluation and the results found in the literature, both cubs can be equally recommended. Therefore, the choice which implant suits the patient best remains an individual decision.