Background
It is important to ensure a hip replacement that has no complications and lasts for a reasonable length of time especially in young active patients. The ideal articulation should have good lubrication with minimal wear, should be hard enough to resist fractures, and should be highly biocompatible and available in different head sizes. The use of ceramics as bearing surfaces has had a long and successful history. Ceramic-on-ceramic (C.o.C) is a very wear-resistant, versatile articulation with different neck lengths and head diameters (28–32 mm, with large ceramic heads with a diameter of 36–40 mm now available).
Aim
The aim of the study was to investigate a possible effect of different ceramic head sizes on early clinical results in patients treated with C.o.C total hip replacement (THR), with special concern on postoperative hip range of motion (ROM) and stability.
Patients and methods
This study included 40 cases in 35 patients with end-stage arthritis. All cases were treated with C.o.C THR. Cases were divided into three groups according to the size of the ceramic head. Group I included 13 cases with 28-mm heads. Group II included 12 cases with 32-mm heads. Group III included 15 cases with 36-mm heads. Results were assessed according to the Harris Hip Score (HHS).
Results
There was significant improvement in the HHS at 6 weeks postoperatively in all the three groups compared with the preoperative HHS; this improvement became much more significant at 6 months postoperatively. At 6 weeks postoperatively, there was a statistically nonsignificant difference in the mean postoperative hip ROM scores between group I and group II cases and also between group II and group III cases, whereas there was a statistically significant difference in the mean postoperative hip ROM scores only between group I and group III cases. At 6 months postoperatively, the difference in mean postoperative hip ROM scores between all the three groups of cases became statistically nonsignificant. Although dislocation occurred in only one case (representing 2.5% of all the studied cases) with a 28-mm head, no sharp correlation between the head size and dislocation was detected.
Conclusion
Increasing the head size can safely improve the ROM especially in the early postoperative period but the term ‘large head’ could be a relative or a nonspecific term when considering the clinical (true) but not the technical (theoretically possible) ROM or if the relation between the head diameter to the size of the ceramic liner/cup construct and the head/neck ratio are not considered. The head size is critical for stability in THR but dislocation is multifactorial. Although C.o.C articulation is a marvelous bearing surface for young active patients, especially women in the child-bearing period, the 36-mm heads could not be used in most female cases (being restricted by the size of the native bony acetabulum), and therefore male patients have a better scope of being treated with 36-mm heads.