Long-term behaviour of the Charnley
offset-bore acetabular cup
Theologos T. Ioannidis, Nikolas Zacharakis,
Evangelos A. Magnissalis, George Eliades, George Hartofilakidis
From the University of Athens and the Research Centre for Biomaterials, Athens,
Greece
e report the long-term radiological results of 58
total hip arthroplasties (THA) using the
Charnley offset-bore acetabular socket. Wear was
measured at four sites and radiolucent lines and
possible migration were recorded. Four cups were
retrieved at revision and were examined using light
microscopy, SEM and X-ray microanalysis.
At a mean follow-up of seven years the mean wear
in the DeLee and Charnley zone I was 0.4 mm and in
zone II 0.26 mm. The wear rate was 0.06 and
0.04 mm/year, respectively. Progression of radiolucent
lines was seen in five cases (8.6%). Three sockets
(5.2%) were revised because of aseptic migration at a
mean follow-up of 9.8 years and one socket for
infection at two years.
The offset-bore acetabular cup had excellent wear
behaviour and a low migration and revision rate. We
recommend that it should be considered in THA since
the use of small cups is increasing, particularly in
revision cases.
W
J Bone Joint Surg [Br] 1998;80-B:48-53.
Received 12 June 1997; Accepted 5 August 1997
The Charnley extra small socket with a face diameter of
1
35 mm has an offset bore so that the cavity for the femoral
head is placed eccentrically. The thickness of ultra-highmolecular-weight polyethylene (UHMWPE) is approximately 10 mm in the upper weight-bearing part, equal to
that of conventional sockets, and then decreases to a few
millimetres in the lower part (Fig. 1).
We have used this acetabular component since 1976,
T. T. Ioannidis, MD, Associate Professor
N. Zacharakis, MD, Registrar
G. Hartofilakidis, MD, FACS, Emeritus Professor of Orthopaedics
Department of Orthopaedics, University of Athens, KAT Hospital, Kifissia
14561, Greece.
E. A. Magnissalis, PhD, Bioengineer, Quality Control Section
G. Eliades, DDS, D Odont, Head, Quality Control Section
Research Centre for Biomaterials, Athens 16562, Greece.
Correspondence should be sent to Professor G. Hartofilakidis at 21 Fotiou
Patriarchou Street, Athens 11471, Greece.
©1998 British Editorial Society of Bone and Joint Surgery
0301-620X/98/18057 $2.00
48
mainly in patients with neglected high and low dislocations
undergoing primary total hip arthroplasty (THA) as well as
in a few revision cases. We now report the long-term results
regarding acetabular wear, radiolucent lines, cup migration
and the rate of loosening. Four retrieved acetabular sockets
have also been examined by light microscopy and SEM and
by X-ray microanalysis.
Patients and Methods
Between 1973 and 1992 a total of 702 THAs were performed by the senior authors (GH and TTI) using the
1
Charnley low-friction arthroplasty (LFA) technique. Since
1976, 72 offset-bore sockets have been used in 54 patients.
Seven cases have been lost to follow-up. In six hips (four
patients) the immediate postoperative radiographs were
either missing or of very poor quality and they were
excluded. One Girdlestone procedure, performed because
of infection in the second postoperative year, was also
excluded. This left 58 hips (42 patients) in the study with a
mean follow-up of seven years (3 to 19). Most of the cases
2,3
were high dislocations (Table I). All the patients were
women with a mean age of 48.4 years (23 to 68).
In 44 hips (75.9%) offset-bore sockets had been used in
combination with the cotyloplasty technique which has
2,3
been previously reported. This entails fracture of the
floor of the original acetabulum, bone grafting, and controlled medialisation of the cemented cup.
The current and immediate postoperative radiographs
were evaluated independently by two examiners using a
Vernier micrometer calliper with the 22.25 mm LFA femoral head as a guide for the correction of magnification.
There were almost no interobserver differences in the
measurements. When there were such differences they were
small and the mean value was used. The thickness of
the UHMWPE was measured according to Charnley and
4
5
Halley and Wroblewski at 30, 45, 90 and 150° from the
upper rim of the cup. The mean value of wear at 30° and
45° was adopted as the zone-1 measurement so that the
results corresponded to the three radiological zones of
6
DeLee and Charnley. The annual wear rate was
calculated.
We recorded the presence of radiolucent lines in the three
6
7
zones of DeLee and Charnley according to McCoy et al
THE JOURNAL OF BONE AND JOINT SURGERY
LONG-TERM BEHAVIOUR OF THE CHARNLEY OFFSET-BORE ACETABULAR CUP
49
Results
Clinically, all 42 patients (58 hips) had well-functioning
THAs and were rated high on the Merle d’Aubigné and
1
Postel scale as modified by Charnley (Figs 2 and 3).
Radiological analysis showed no wear in five (8.6%) and
minimal wear in three (5.2%) of our acetabular cups. In the
rest, the mean wear in zone I was 0.4 mm and in zone II
0.26 mm. In zone III it was not possible to calculate wear
since any wear in the other two zones results in enlargement of the apparent radiological ‘thickness’ of this area.
The annual wear rate was 0.06 mm in zone I and 0.04 mm
in zone II. There was a significant wear rate (> 0.13 mm/
annum) in only 12 THAs (20.7%). The most common site
for maximal penetration in a single socket was the zone at
90° (44.8% of the sockets) followed by that at 45° (24.1%)
and at 30° (17.2%). Details are given in Tables III to V.
Table I. Details of the underlying pathology of the 58 THAs
Fig. 1
The offset-bore acetabular socket.
with grades from 0 to 4. Migration in the horizontal and
vertical direction was measured using the interteardrop line
as a guide and 2 mm as the lower limit. Progression of the
lines was also noted.
Analysis of the articular surface of the four retrieved
implants included macroscopic inspection using a magnifying lens, light microscopy, SEM and wavelength-dispersive
X-ray microanalysis (JXA 733 Super probe, Jeol Ltd,
Tokyo, Japan). Table II gives the details of the retrieved
implants.
Congenital hip disease
High dislocation
Low dislocation
Dysplasia
Revision THA
44
8
3
3
Table II. Details of the examined retrieved acetabular sockets
Number
Months in situ
Side
Age at first
operation (yr)
1
2
3
4
187
63
28
81
L
L
L
L
40
30
41
66
Anteroposterior radiographs of a 37-year-old woman
with high dislocation of the right hip preoperatively
(a) and 19 years after THA with an offset-bore acetabular component (b). The clinical and radiological
results were satisfactory and there was no migration.
The direction of maximum penetration was found at
90° with total penetration of 1.46 mm (0.076 mm per
annum).
Fig. 2a
VOL. 80-B, NO. 1, JANUARY 1998
Fig. 2b
50
T. T. IOANNIDIS,
N. ZACHARAKIS,
E. A. MAGNISSALIS,
Fig. 3b
Fig. 3c
Table III. The mean wear (mm) in all three
DeLee and Charnley zones for 58 TKAs at
a mean follow-up of 84.4 months
Wear
I
II
III
G. HARTOFILAKIDIS
Anteroposterior radiographs of a 47-year-old woman
with bilateral high dislocation. Figure 3a – Before
operation. Figure 3b – Six years and four months after
THA of the right hip with an offset-bore acetabular
component combined with cotyloplasty. There was no
migration. The direction of maximum penetration was
found at 30°, with total penetration of 0.12 mm
(0.018 mm per annum). Figure 3c – Six years and five
months after THA of the left hip with an offset-bore
acetabular component and a cotyloplasty. There was no
migration. The direction of maximum penetration was
found at 90°, with total penetration of 0.32 mm
(0.049 mm per annum).
Fig. 3a
Zone
G. ELIADES,
Mean
Table V. Incidence of maximum penetration
in the measured sites for 58 TKAs
Number
%
10
14
26
17.2
24.1
44.8
Minimal wear*
3
5.2
No wear
5
8.6
SD
-0.4
-0.26
0.09*
0.58
0.68
0.66
* apparent thickening
Table IV. The mean annual wear rate (mm
per annum) for all three zones for 58 TKAs
Zone
Mean wear rate
I (30° to 45°)
II (90°)
III (150°)
-0.06
-0.04
-0.02*
Location (degrees)
30
45
90
* both the actual wear and the intersite differences were very small and undiscernible
* apparent increase
THE JOURNAL OF BONE AND JOINT SURGERY
LONG-TERM BEHAVIOUR OF THE CHARNLEY OFFSET-BORE ACETABULAR CUP
Table VI. Acetabular demarcation
7
according to McCoy et al
Grade
Number
%
0
1
2
3
4
19
27
4
3
5
32.8
46.6
6.9
5.2
8.6
51
abular cup with the longest follow-up (187 months). There
were scratches, gouges, shredding and pitting mainly at the
upper load-bearing regions. Lower regions had polishing of
the machining marks. SEM and X-ray microanalysis findings revealed crystalline formations in the lower region of
the articular surfaces (Fig. 4). These crystals differed in
appearance and composition from the adjacent area and
were characterised by the presence of calcium and
phosphorus.
There was no significant demarcation around the cup; 46
7
(79.4%) were in grades 0 to 1 according to McCoy et al,
(Table VI). Only five hips (8.6%) showed migration; in
three it was progressive and they were subsequently
revised. Two others were revised because of aseptic loosening of the stem. In both, the well-fixed acetabular cup
showed excessive wear (> 1.13 mm). Revisions were performed at a mean of 9.8 years postoperatively (4 to 16).
Macroscopic and microscopic changes in the retrieved
8,9
implants were similar to those previously reported. Discoloration and plastic deformation of the UHMWPE were
observed macroscopically along the upper rim of the acet-
The longevity of a THA depends on many factors, some of
which are ‘surgeon-dependent’. Since UHMWPE debris
has now been recognised to be a major factor in loosening
of the prosthesis the acetabular part of an implant has
10-12
recently become the focus of attention.
The thickness
of the UHMWPE also plays an important role in its wear. It
has been reported that thickness of 5 mm or less in metal13
backed sockets could lead to catastrophic results. This
can be regulated by choosing the appropriate acetabular cup
Fig. 4a
Fig. 4b
Discussion
SEM and X-ray area scan images of crystalline formations observed at the
lower region of retrieved components. Figure 4a – Backscattered electron
image for composition (BEI-COMPO) showing crystalline formations of
different composition from the surrounding polyethylene area. Figure 4b –
Calcium area scan of image in Figure 4a. Figure 4c – Phosphorus area
scan of image in Figure 4a (magnification 200; scale bar 100 m).
Fig. 4c
VOL. 80-B, NO. 1, JANUARY 1998
52
T. T. IOANNIDIS,
N. ZACHARAKIS,
E. A. MAGNISSALIS,
and head diameter. In certain conditions and in some
revision situations, a ‘shallow’ cup of a small diameter
must be used, but even with a 22.2 mm head, the thickness
of UHMWPE becomes critical. The offset cup gives almost
standard thickness of UHMWPE in the upper weight1
bearing part of the socket.
14
Dennis and Halley have presented a preliminary report
of nine cases in which this design of small acetabular cup
was used and, recently, the first well-documented study on
15
54 THAs was reported from Wrightington Hospital. This
gives a rate of 35% for no wear in a mean follow-up of 8.1
years which differs from our figure of 8.6, with a mean
follow-up of seven years (or 13.7% if minimal wear is
included). Our finding, however, of an annual wear rate of
0.06 and 0.04 mm per annum for zones I and II, respectively,
is comparable with the Wrightington figure of 0.04 mm per
annum overall. Many of our patients have the common
underlying pathology of congenital hip disease and are a
young and active group with a mean age of 48.4 years.
Wear of UHMWPE depends on many factors such as the
16
mechanical roughness finish of the femoral head, the
surface preparation of the UHMWPE, the method of sterilisation, the shelf life of the implant and finally the thick10
ness of the plastic. Implants of the non-conforming
designs have been found to be more susceptible to
10,17-19
wear,
but fatigue wear is unusual owing to the
conformity of the two contacting surfaces.
Our findings add to the evidence that conformity plays a
very important role in the wear behaviour of UHMWPE
15
and agree with those of Izquierdo-Avino et al . The wear
rates are considerably lower than the historically reported
figures for the conventional Charnley acetabular cup which
G. ELIADES,
G. HARTOFILAKIDIS
4,5,7,20-25
range from 0.07 to 1.15 mm per annum.
Another important aspect is the effect of cup thickness
on the surrounding mantle of acrylic cement (PMMA).
26
Oh showed that the strain in the cement mantle rose in
model sockets when the thickness fell from 5 to 2 mm and
27
Pedersen et al reported an increase of 400% in tension
and 200% in compression stresses in the cement mantle
when the UHMWPE thickness was reduced from 14.5 to
3.5 mm as the simulated head diameter changed from 22 to
44 mm.
The fact that our group of patients is relatively young,
active and that their common pathology requires a technically demanding operation makes these findings more
significant.
Crystalline calcium-phosphorus formations observed in
the analysed retrieved sockets may be related to the deposition of bone debris or to some interaction with biological
fluids on the unloaded lower region of the sockets. While
their origin is still under investigation, their limited area is
believed to be indicative of an enhanced articular
conformity.
Our follow-up is relatively short and therefore we are
unable to guarantee the long-term advantage of the offset
cup, but so far we have had no evidence of deterioration in
performance in cups that have been reviewed at 15 years.
The use of small cups is increasing not only in neglected
cases of congenital hip disease but also in revision cases
with problems of bone loss. The offset-bore socket should
be considered as an excellent alternative.
No benefits in any form have been received or will be received from a
commercial party related directly or indirectly to the subject of this
article.
References
1. Charnley J. Low friction arthroplasty of the hip: theory and practice.
Berlin, etc: Springer-Verlag, 1979:20-5.
2. Hartofilakidis G, Stamos K, Ioannidis TT. Low friction arthroplasty
for old untreated congenital dislocation of the hip. J Bone Joint Surg
[Br] 1988;70-B:182-6.
3. Hartofilakidis G, Stamos K, Karachalios T, Ioannidis TT, Zacharakis N. Congenital hip disease in adults: classification of acetabular
deficiencies and operative treatment with acetabuloplasty combined
with total hip arthroplasty. J Bone Joint Surg [Am] 1996;78-A:
683-92.
4. Charnley J, Halley DK. Rate of wear in total hip replacement. Clin
Orthop 1975;112:170-9.
5. Wroblewski BM. Direction and rate of socket wear in Charnley lowfriction arthroplasty. J Bone Joint Surg [Br] 1985;67-B:757-61.
6. DeLee JG, Charnley J. Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop 1976;121:20-32.
7. McCoy TH, Salvati EA, Ranawat CS, Wilson PD Jr. A fifteen-year
follow-up study of one hundred Charnley low-friction arthroplasties.
Orthop Clin North Am 1988;19:467-76.
8. Rostoker W, Chao EYS, Galante JO. The appearances of wear on
polyethylene: a comparison of in vivo and in vitro wear surfaces.
J Biomed Mat Res 1978;12:317-35.
9. McKellop HA, Campbell P, Park SH, et al. The origin of submicron
polyethylene wear debris in total hip arthroplasty. Clin Orthop 1995;
311:3-20.
10. Bartel DL, Bicknell VL, Wright TM. The effect of conformity,
thickness and material on stresses in ultra-high molecular weight
components for total joint replacement. J Bone Joint Surg [Am] 1986;
68-A:1041-51.
11. Collier JP, Mayor MB, Surprenant VA, et al. The biomechanical
problems of polyethylene as a bearing surface. Clin Orthop 1990;
261:107-13.
12. Harris WH. The problem of osteolysis. Clin Orthop 1995;311:
46-53.
13. Berry DJ, Barnes CL, Scott RD, Cabanela ME, Poss R. Catastrophic failure of the polyethylene liner of uncemented acetabular
components. J Bone Joint Surg [Br] 1994;76-B:575-8.
14. Dennis DA, Halley DK. Use of the Charnley mini-offset bore
acetabular component in severe acetabular dysplasia: a preliminary
report. Clin Orthop 1996;211:140-7.
15. Izquierdo-Avino RJ, Siney PD, Wroblewski BM. Polyethylene wear
in the Charnley offset bore acetabular cup: a radiological analysis. J
Bone Joint Surg [Br] 1996;78-B:82-4.
16. Saikko VO. Wear of the polyethylene acetabular cup: the effect of
head material, head diameter, and cup thickness studied with a hip
simulator. Acta Orthop Scand 1995;66:501-6.
17. Wright TM, Bartel DL. The problem of surface damage in polyethylene total knee components. Clin Orthop 1986;205:67-74.
18. Collier JP, Mayor MB, McNamara JL, Suprenant VA, Jensen RE.
Analysis of the failure of 122 polyethylene inserts from uncemented
tibial knee components. Clin Orthop 1991;273:232-42.
THE JOURNAL OF BONE AND JOINT SURGERY
LONG-TERM BEHAVIOUR OF THE CHARNLEY OFFSET-BORE ACETABULAR CUP
19. Wright TM, Rimnac CM, Stulberg SD, et al. Wear of polyethylene
in total joint replacement: observations from retrieved PCA knee
implants. Clin Orthop 1992;276:126-34.
20. Griffith MJ, Seidenstein MK, Williams D, Charnley J. Socket wear
in Charnley low friction arthroplasty of the hip. Clin Orthop 1978;
137:37-47.
21. Cupic Z. Long-term follow-up of Charnley arthroplasty of the hip.
Clin Orthop 1979;141:28-43.
22. Salvati EA, Wilson PD, Jolley MN, et al. A ten-year follow-up study
of our first one hundred consecutive Charnley total hip replacements.
J Bone Joint Surg [Am] 1981;63-A:753-66.
23. Wroblewski BM. 15-21-year results of the Charnley low-friction
arthroplasty. Clin Orthop 1986;211:30-5.
VOL. 80-B, NO. 1, JANUARY 1998
53
24. Wroblewski BM, McCullagh PJ, Siney PD. Quality of the surface
finish of the head of the femoral component and the wear rate of the
socket in long-term results of the Charnley low-friction arthroplasty.
Proc Inst Mech Eng H 1992;206:181-3.
25. Isaac GH, Wroblewski BM, Atkinson JR, Dowson D. A tribological
study of retrieved hip prostheses. Clin Orthop 1992;276:115-25.
26. Oh I. A comprehensive analysis of the factors affecting acetabular cup
fixation and design in total hip replacement arthroplasty: a series of
experimental and clinical studies. In: Hungerford DS, ed. The Hip.
Proceedings of the Open Scientific Meeting of the Hip Society, St
Louis, etc: CV Mosby 1983:129-77.
27. Pedersen DR, Crowninshield RD, Brand RA, Johnston RC. An
axisymmetric model of acetabular components in total hip arthroplasty. J Biomech 1982;15:305-15.