Taper corrosion: a complication of total hip arthroplasty

Abstract

The focus on taper corrosion in modular hip arthroplasty increased around 2007 as a result of clinical problems with large-head metal-on-metal (MoM) bearings on standard stems. Corrosion problems with bi-modular primary hip stems focused attention on this issue even more.Factors increasing the risk of taper corrosion were identified in laboratory and retrieval studies: stiffness of the stem neck, taper diameter and design, head diameter, offset, assembly force, head and stem material and loading.The high variability of the occurrence of corrosion in the clinical application highlights its multi-factorial nature, identifying the implantation procedure and patient-related factors as important additional factors for taper corrosion.Discontinuing the use of MoM has reduced the revisions due to metal-related pathologies dramatically from 49.7% (MoM > 32 mm), over 9.2% (MoM ⩽ 32 mm) to 0.8% (excluding all MoM).Further reduction can be achieved by omitting less stiff Ti-alloys and large metal heads (36 mm and above) against polyethylene (PE).Standardized taper assembly of smaller and ceramic heads will reduce the clinical occurrence of taper corrosion even further. If 36 mm heads are clinically indicated, only ceramic heads should be used.Taper-related problems will not comprise a major clinical problem anymore if the mentioned factors are respected. Cite this article: EFORT Open Rev 2020;5:776-784. DOI: 10.1302/2058-5241.5.200013.

Keywords: assembly; contamination; corrosion; design; loading; metal; taper.

Fig. 1

Definition of the head-stem taper connection. The male stem taper geometry is defined by the proximal and distal diameters and its length. The ‘12/14’ taper is defined with a proximal diameter of 12 mm, a distal diameter of 14 mm and a length of 20 mm, resulting in a male stem taper angle of 5.725° or 5°43’30’’ (the same angle as in the original ‘14/16’ taper). The female taper angle of ceramic heads is always by 1’ to 6’ larger, in order to achieve initial proximal engagement between female and male taper. Most metal heads are designed similarly but some are manufactured with the same nominal female taper angle as the stem. The true contact length depends on the assembly force and the taper angle difference (indicated in green). All these values are not standardized and vary between manufacturers.

Fig. 2

Number of peer-reviewed journal publications for the search terms ‘(taper OR trunnion) AND hip AND corrosion’ in PubMed. The number of publications started to increase from the few anecdotal reports published before 2009 and peaked in 2016 with continuing high interest since.

Fig. 3

(a) X-ray of a stem taper fracture in a Ti-alloy primary stem with a large MoM bearing after four years in situ. This design utilizes a Ti-alloy adapter sleeve to assemble the CoCr-bearing surface to the stem. (b) The explanted components with the broken stem taper inside the adapter sleeve inside the head (courtesy H. Ettema, Isala).

Fig. 4

(a) Female head taper corrosion after seven years in situ. The overlay shows the depth of the female head taper wear (material loss 6.7 mm³). (b) The male stem taper did not show signs of corrosion but slight marks from the revision surgery.

Fig. 5

(a) X-ray after fracture of of a Ti-Ti Revision stem after seven years in situ (courtesy M. Rudert, Würzburg). (b) Fracture surfaces of the broken taper showing the typical split lines of a fatigue fracture.

Fig. 6

(a) X-ray of a male patient (76 years) prior the 4th isolated right cup revision in 2019 after original stem implantation with a 32 mm metal XXXL head in 1984. (b) The stem taper showed only light corrosion and minor damage from the multiple revision surgeries. (c) X-ray after the revision with a 36 mm ceramic option XXXL head on the original stem.