Acta Orthopaedica 2012; 83 (6): 599–603 599
Good short-term outcome of primary total hip arthroplasty
with cementless bioactive glass ceramic bottom-coated
109 hips followed for 3–9 years
Kazutaka So1, Kumiko T Kanatani2, Yutaka Kuroda1, Takashi Nakamura1, Shuichi Matsuda1, and
1Department of Orthopaedics, Kyoto University; 2Department of Health Informatics, School of Public Health, Kyoto University Graduate School of
Medicine, Kyoto, Japan.
Submitted 12-03-31. Accepted 12-08-14
Open Access - This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use,
distribution, and reproduction in any medium, provided the source is credited.
Background and purpose Cementless total hip arthroplasty is
currently favored by many orthopedic surgeons. The design of the
porous surface is critically important for long-term fixation. We
examined the clinical and radiographic outcome of the cementless
titanium hip implant with a bottom coating of apatite-wollaston-
ite containing bioactive glass ceramic.
Methods We retrospectively reviewed 109 hips (92 patients)
that had undergone primary cementless total hip arthroplasty
with bioactive glass ceramic bottom-coated implants. The mean
follow-up period was 7 (3–9) years. Hip joint function was evalu-
ated with the Merle d’Aubigné and Postel hip score, and radio-
graphic changes were determined from anteroposterior radio-
Results The mean hip score improved from 9.7 preoperatively
to 17 at the final follow-up. The overall survival rate was 100% at
9 years, when radiographic loosening or revision for any reason
was used as the endpoint. 3 stems in 2 patients subsided more than
3 mm vertically within 1 year after implantation. Radiographs
of the interface of the stem and femur were all classified as bone
Conclusions The short-term results of this study show good
outcome for cementless implants with a bottom coating of apatite-
wollastonite containing bioactive glass ceramic.
The use of cementless implants in total hip arthroplasty is
increasing in many countries. A great deal of effort has gone
into the development of new implants that are designed for
better cementless fixation. Press-fit total hip implants obtain
initial stability by maximum contact with the bone surface
of the acetabulum and the internal cortical bone surface of
the femoral metaphysis. To achieve long-term fixation of the
implant to the host bone by osteointegration into the implant,
a variety of surface textures for the implants have been devel-
oped; these include plasma-sprayed, grit-blasted, or bead-
sintered surfaces (Ryan et al. 2006). Once bone apposition to
anchor the implant is complete, the implant is stabilized in
bone. The addition of a biologically active coating, including
a hydroxyapatite (HA) coating, accelerates osteointegration of
the implant into the bone and leads to inhibition of subsidence,
prevention of proximal stress shielding, resistance to wear
particle migration, and reduction of thigh pain (Maheshwari
et al. 2008).
A glass ceramic containing apatite and wollastonite (AW-
GC) was reported to have high mechanical strength and the
capability of forming a strong chemical bond with osseous
tissue (Kokubo et al. 1985, Nakamura et al. 1985). Ido et
al. (1993) produced 2 types of cementless implants in dogs.
One was coated with titanium plasma spray and the other was
coated further with AW-GC in the deep layer of the pores and
showed better cementless fixation in the early phase. Based
on these results, the Q Hip System H6 cementless stem and
QPOC Porous Cup (Japan Medical Materials, Osaka, Japan)
were produced in 1999 (Figure 1). This stem is a proximal
press-fit uncollared cementless design made from a titanium
alloy (Ti6Al2Nb1Ta0.8Mo), with an AW-GC bottom-coated
porous surface applied by pure titanium plasma spray, which
accepts a 22.2-mm or 26.0-mm zirconia ceramic head (yttria-
stabilized tetragonal zirconia containing 0.25 wt% Al2O3;
ISO13356) or a CoCr head. We retrospectively examined the
clinical and radiographic outcome of the cementless uncol-
lared AW-GC bottom-coated titanium hip implants after a
minimum follow-up of 3 years.
600 Acta Orthopaedica 2012; 83 (6): 599–603
All operations were performed with a direct lateral
approach and a partial trochanteric osteotomy, as reported
by Dall (1986). The cementless AW-GC bottom-coated ace-
tabular component (QPOC Porous Cup) was placed, and an
acetabular autogenous bulk or chip bone graft with a resected
femoral head was performed at the superolateral aspect of the
acetabular roof in 82 hips. The bulk bone graft was fixed with
1 or 2 bioresorbable poly(L-lactide)-HA screws (Superfixorb;
Takiron, Osaka, Japan). The cementless acetabular liner was
made of γ-irradiated, highly cross-linked, ultra-high-molecu-
lar-weight polyethylene (CLQC liner; Japan Medical Mate-
rials). The femur was prepared using reamers and broaches.
Broaches of increasing size were used until an appropriate fit
was achieved, and the corresponding stem was the same size
as the last broach. The H6 cementless stem was implanted.
The stem size ranged from 7 mm to 14 mm (median 11 mm)
in width at a point 100 mm distal to the medial edge of the
calcar. 88 femoral heads had a diameter of 22.2 mm and 21
had a diameter of 26 mm. All femoral heads were made of
zirconia ceramic. All patients received intravenous antibiotics
30 min preoperatively and for 2 days postoperatively. Heparin
calcium was used as routine thromboprophylaxis for 7 days.
Standard radiographs were taken after surgery, at 2, 4, 6, and
8 weeks, at 3, 6, and 12 months, and at 6-monthly or yearly
intervals thereafter. The prevalence, location, and extent of
osteolytic lesions, reactive lines, calcar resorption, pedestal
formation, and cortical hypertrophy were determined from
anteroposterior radiographs taken at the time of the last follow-
up. Calcar resorption (defined as rounding of the calcar) was
distinguished from calcar osteolysis (defined as a punched-
out, expansive area with a concave shape) (Engh et al. 1987).
The distance between the most proximal point of the greater
trochanter and the proximal apex of the shoulder of the pros-
thesis along the axis of the femoral stem on anteroposterior
digital images of the hip joint was measured for identification
of the stem subsidence. Fixation of femoral components was
categorized using the criteria described by Engh et al. (1990)
as bone ingrowth fixation, stable fibrous fixation, or unstable
fixation. Radiographic loosening of the acetabular component
was defined as a continuous reactive line at the bone-implant
interface or any change in the position of the component over
time. Radiographic changes were described with the Gruen
zones for the proximal femur and with the DeLee and Charn-
ley zones for the acetabulum. Ossification of the femoral stem
was graded according to the Brooker ectopic ossification grad-
Hip joint function was rated according to the scoring system
of Merle d’Aubigné and Postel.
Linear mixed model with random effects for subjects was used
to evaluate the effect of operation on the Merle d’Aubigné and
Postel hip score using the statistical software package R ver-
sion 2.13.0 (http://www.r-project.org/). Linear mixed model
allows inclusion of correlated observations. We used com-
pound symmetry pattern for covariance structures. Signifi-
cance was set at p < 0.01. Kaplan-Meier survivorship analysis
was used to study the implant survival.
The mean operating time was 109 (64–203) min and mean
intraoperative blood loss was 360 (30–1140) mL. The hip
score improved from 9.7 (SD 1.8) preoperatively to 16.5 (SD
1.5) postoperatively (p = 0. 001). No postoperative compli-
cations occurred. None of the patients had an infection or a
13 hips showed thickening of the femoral cortex near the
tip of the stem. 3 hips showed initial stem subsidence of > 3
mm within 1 year after the operation (Table), but there was
no progressive subsidence after this time and this result did
not significantly alter the clinical outcome. Grafted bone was
remodeled in all cases. There was no reactive line at the bone-
implant interface or any change in the position of the acetabu-
lar component. Radiographic evaluation of the interface of the
stem and femur (Engh’s classification) showed that all 109
hips were classified as bone ingrowth fixation and none were
Figure 1. The Q Hip System
H6 cementless stem and
QPOC Porous Cup.
Patients and methods
From February 2002 through
December 2007, 102 consecu-
tive patients underwent 121 pri-
mary THAs in which cement-
less uncollared circumferential
AW-GC bottom-coated porous-
coated titanium hip implants
were used. We failed to trace
10 patients (12 hips) for fol-
low-up of more than 3 years,
and the remaining 92 patients
(78 women, 109 hips) were
retrospectively reviewed after
obtaining institutional board
approval. The mean age at oper-
ation was 50 (20–75), height
158 (SD 7.6) cm, and weight 57
(SD 9.9) kg. The diagnosis was
secondary osteoarthritis caused
by developmental dysplasia or
congenital dislocation of the
hip in 83 hips, osteonecrosis of
the femoral head in 19, rheuma-
toid arthritis in 3, posttraumatic
osteoarthritis in 2, and primary
osteoarthritis in 2. The mean
follow-up period was 6.8 (3.0–
Acta Orthopaedica 2012; 83 (6): 599–603 601
classified as stable fibrous ingrowth. Overall, there was no
loosening of either the acetabular or the femoral component
(Figure 2). At the latest follow-up, no femoral or acetabular
components had been revised for aseptic loosening or for any
other reason. The Kaplan-Meier survivorship analysis, with
radiographic loosening or revision as the endpoint, revealed
a rate of survival of the femoral and acetabular component
of 100% at 9 years. In the worst-case scenario Kaplan-Meier
survival analysis, assuming that all 12 hips in 10 patients who
were lost to follow-up failed, revealed a 9-year implant survi-
vorship of 90% (95% CI: 85–95) using failure as the endpoint.
Intraoperative crack or fracture of the femur occurred in 6
hips, which were fixed by wiring. 3 postoperative fractures
occurred in the greater trochanter, but no additional surgery
was needed. Heterotopic ossification was observed in 35 hips,
and this was classified as grade 1 in 20, grade 2 in 13, and
grade 3 in 2; none required any operation. At the latest follow-
up, 4 hips were causing the patient mild thigh pain, and 1 hip
caused moderate thigh pain. Neither infection nor implant
Clinical and radiographic outcomes of uncemented THA have
been improving, and uncemented implants are increasingly
used, although they are still being developed further. Long-
term success depends partly on the initial mechanical stability
of the implants used to improve overall fixation by osteoin-
tegration. Titanium and its alloys are used widely because of
their biocompatibility, high corrosion resistance, and low elas-
tic modulus, which is close to that of bone. To provide a high
friction surface for physical interlocking at the implant-bone
interface and to enhance bone-bonding activity of the titanium
implants, porous structures on the surface of the implant have
been developed with the use of plasma-sprayed, grid-blasted,
fiber-metal or bead-sintered methods. HA is now coated on the
porous implant surface. HA promotes direct bonding between
the implant and the bone because of its good osteoconductiv-
ity. Previous studies have reported on the effectiveness of HA
coating of total hip implants regarding early bone-bonding
ability (Geesink et al. 1987, Cook et al. 1988). HA coating
contributes to early implant stability and reduction of subsid-
ence risk and thigh pain, and inhibition of distribution of wear
particles through the bone-implant interface (Kroon and Free-
man 1992, Rahbek et al. 2001, Chambers et al. 2007, Epi-
nette and Manley 2008). However, a number of concerns have
been raised about the use of this coating on porous-surfaced
implants. These include a reduction in the space available for
bone ingrowth, relatively poor bonding between the substrate
and the HA coating layer, and relatively rapid degradation of
HA, which produces HA debris and induces third-body wear
(Bloebaum et al. 1994, Morscher et al. 1998, Liu et al. 2000).
A recent report by Lazarinis et al. (2011) showed that the use
of HA coating did not enhance 10-year implant survival.
AW-GC is a bioactive glass ceramic containing wollaston-
ite and oxyapatite as the major components. This ceramic has
excellent biocompatibility and a great ability to form tight
Radiographic results in 109 hips
Bone ingrowth fixation
Stable fibrous fixation
Figure 2. A 60-year-old woman with secondary osteoarthritis of the right hip. A. The preoperative Merle
d’Aubigné and Postel score was 10 points. B. AW-GC bottom-coated acetabular and femoral com-
ponents were implanted. C. The Merle d’Aubigné and Postel score improved to 16 points, and bone
ingrowth fixation was achieved 9 years after surgery.
A B C
602 Acta Orthopaedica 2012; 83 (6): 599–603
chemical bonds with living bone (Nakamura et al. 1985).
Analysis of the bone-bonding ability of AW-GC coated on
titanium alloy by the plasma-spray technique and implan-
tation into the tibial bones of mature rabbits showed that
AW-GC had earlier bone-bonding ability and greater mechan-
ical strength through the formation of the Ca-P-rich layer.
Kitsugi et al. (1989) reported an increase in the load to failure
of specimens containing AW-GC in segmental replacement
of the rabbit tibia under load-bearing conditions. Yamamuro
and Takagi (1991) studied the effect of AW-GC coating on
titanium plasma spray-coated implants under loading condi-
tions and found that AW-GC coating only on the bottom of the
porous surface had greater bonding strength than fully AW-
GC-coated and uncoated implants. A study of cementless total
hip implants coated with titanium plasma spray followed by
AW-GC bottom coating in dogs showed that bone had grown
in the deepest part of the porous layer 1 month after implanta-
tion, which was earlier than in those without AW-GC bottom
coating (Ido et al. 1993).
Titanium and its alloys are currently used in a variety of
orthopedic implants. Ti6Al4V has good mechanical proper-
ties, but vanadium has been proven to be cytotoxic (Sabbioni
et al. 1991). The Ti6Al2Nb1Ta0.8Mo alloy has been adopted
for the K-MAX Q Hip System H6 stem and QPOC socket.
This titanium alloy has 870 MPa in tensile strength, 790 MPa
in yield strength, and 108 MPa in Young’s modulus, values
that are similar to those of Ti6Al4V (860 MPa, 795 MPa, and
110 MPa, respectively). By contrast, the fatigue strength (490
MPa) of Ti6Al2Nb1Ta0.8Mo is greater than that of Ti6Al4V
(410 MPa), allowing reduction of the neck diameter to 9 mm.
Reduced neck diameter may contribute to an increased oscil-
lation angle, which should prevent dislocation and reduce the
generation of polyethylene wear particles. Further studies will
be needed to evaluate the effect of reduced neck diameter on
the clinical and radiographic outcomes.
The K-MAX Q Hip System H6 stem is a cementless
metaphyseal-fitting device that was designed to fit into the
Japanese femur and to minimize stress shielding and abnormal
bone reaction. The stem has a proximal circumferential pure
titanium plasma-sprayed porous coating with AW-GC bottom
coating, and the acetabular component (QPOC socket) has the
same coating. The pore size of this coating is 350–450 μm,
which is suitable for osteointegration (Bram et al. 2000, 2006,
Xue et al. 2007). It can be expected that rapid bony ingrowth
into the porous layer will lead to early mechanical anchor-
ing between the bone and the porous layer. In our study, we
observed neither progressive subsidence nor osteolysis. To our
knowledge, our study is the first to evaluate the clinical and
radiographic results associated with AW-GC bottom-coated
THA prostheses implanted in humans. The clinical outcome
after a mean follow-up of 7 years was excellent. Radiographs
showed good osteointegration and implant fixation in the
proximal stem and acetabular regions and no progressive
radiolucency or osteolysis. However, calcar resorption was
found in 102 of 109 hips and cortical hypertrophy was found
in 13 hips. Further improvement of the stem design and shape
is required for optimal load distribution.
The present study had some limitations. First, a substantial
number of patients were lost, and the follow-up period was
relatively short. Secondly, the influence of AW-GC bottom
coating on implant fixation in the early period after implanta-
tion has not been studied in retrieved implants.
In conclusion, we found that a proximal circumferential
porous-coated femoral prosthesis and an acetabular prosthesis
with AW-GC bottom coating were stable after implantation.
AW-GC may give early bone bonding and may be of advan-
tage for initial stability. The optimal combination of surface
structure and surface chemistry is promising for improvement
of the initial and long-term stability of cementless implants.
KS, YK, TN, and SM analyzed the data, and participated in the writing of the
manuscript. KTK analyzed the data statistically. HA coordinated the study,
analyzed the data, and participated in the writing of the manuscript.
No competing interests declared.
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