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Executive Summary

Which is the best bearing surface for primary total hip replacement? A New Zealand Registry study

Sharplin P., Wyatt M. C., Rothwell A., Frampton C., Hooper G.
Hip Int. 2017 Dec 1:0. doi: 10.5301/hipint.5000585.
Level of Evidence:
Not indicated. Retrospective clinical study.


Sharplin et al. extracted from the New Zealand Registry (NZJR) the data of primary hip arthroplasty procedures (106,139) and 4,960 revisions (4.7 %) performed from January 1, 1999 and December 31, 2015 with the aim to identify the best performing bearing surface.

The sixteen years outcomes of Metal-on-Polythylene (MoP; 35,647), Metal-on-Crosslinked Polyethylene (MoXPE; 31,579), Ceramic-on-Polythylene (CoP; 6,833), Ceramic-on-Crosslinked Polyethylene (CoXPE; 14,382), Ceramic-on-Ceramic (CoC; 11,235), Metal-on-Metal (MoM; 5,989) and Ceramic-on-Metal (CoM; 474) were analysed by calculating the Kaplan-Meier estimates and adjusting them with Cox-proportional hazards regression models by age at surgery, gender, surgical approach, surgeon volume, fixation and head size.

The cementless implants were the most common used implants (39.1 %), followed by hybrid (38,6 %) and cemented fixations (22.3 %). In 64.0 % of the CoC cases the head size was equal or larger than 36 mm. The 28 mm head size was predominantly used with CoP (92.9 %) and MoP (85.7 %) bearing surfaces, whereas larger heads (≥32 mm) were preferred with CoXPE (70.4 %) and MoXPE (56.5 %). The posterior surgical approach was the most common (68.3 %) followed by the lateral (27.8 %). The patients in the ceramic group were almost a decade younger than the metal counterpart. The Hardon-Hard combinations were preferred by high volume surgeons (≥ 100 procedures per year), whereas the Hard-on-Soft bearings were mostly used by surgeons performing between 25 and 49 procedures per year.

The most common reasons for revisions were acetabular loosening (22.2 %) followed by femoral loosening (16.7 %). The lowest revision rate for acetabular loosening was associated with CoXPE and MoXPE and the lowest rate of revision for femoral loosening with CoC. All Hard-on-Hard bearings had a lower revision rate for dislocation when compared with Hard-on-Soft combinations. The revisions for infection were most common with MoXPE and least common with CoC. Of the 12 reported fractured ceramic heads 11 were 28 mm diameter heads. The fracture rate of ceramic heads larger than 28 mm resulted to be 0.005 %. In CoC bearings, 5 heads and 29 insert fractures (0.26 %) were reported. All the fractured ceramic liners fractured were from the third ceramic generation (BIOLOX®forte, CeramTec GmbH). 185 (23.2 %) of the MoM revisions were for adverse local reaction for metal debris. 18 (8.2 %) of the CoC revisions were due to noise-related issues.

CoXPE bearing surfaces showed the lowest revision rate, but when the revision rate were adjusted by age, gender, approach, fixation and surgical volumes CoC resulted to be superior followed by CoXPE. However, when looking to the last 10 years and considering the 32 mm and 36 mm head sizes only, CoXPE resulted to be significantly superior than CoC solution. In the conclusion, the authors indicate the CoXPE as the most promising option for young and active patients undergoing primary THR.

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