GTS (Global Tissue Sparing)
Femoral Hip Stem: Design validation
through initial clinical results
Optimal implant stability
Immediate post operative implant axial stability is
attained in the GTS design by the incorporation of
a 9.6° tapered stem. Rotational stability is attained
by the stems elliptica-octoagonal cross section and
longitudinal fins which cut through the compacted
femoral bone (Fig. 2).
Fig. 1:
GTS femoral stem: standard and varized option
Introduction
The GTS (Global Tissue Sparing) stem was developed
by Professor Guido Grappiolo to address the demands
for primary cementless stem for use in tissue sparing
total hip arthroplasty. The benefits and potential
complications of this surgical philosophy being
summarised in the review article1 by Malik, A. and
Dorr, L.D referenced below.
The femoral stem design aims to provide the
critical features of tissue preservation and optimal
implant stability which contribute towards good
clinical efficacy and implant longevity:
Tissue Preservation
The GTS stem is designed to allow implantation
during which the greater trochanter is preserved with
limited disruption to the gluteus medius muscle thus
enabling a minimally invasive surgical approach2–5
with maximum bone preservation. This is enabled by
using a relative short stem (93.4 mm – 139 mm) with
a pronounced reduced lateral shoulder which allows
for a curved insertion of the stem into the metaphysis.
The tapered wedge design of the stem provides
a metaphyseal press-fit limiting the invasion into
the femoral canal, reducing distal load transfer and
potentially eliminating post operative thigh pain.6 The
limited destruction of proximal femoral bone during
implantation of the GTS stem thus preserves bone stock
making any subsequent revision arthroplasty easier.
Fig. 2:
GTS Implant cross section in relation to prepared
femoral canal
These longitudinal fins differ to conventional
fin design in that they have an almost organic
appearance. This unique design not only helps
enhance rotational stability, but may also improve
compression of the cancellous bone while also
maximizing bone contact.
The stem geometry, together with the use of
compression rasps, produces a tight interference
fit with the bone which in the proximal portion of
the stem can produce between 0.3 mm to 0.6 mm
anterior/posterior and 1.8 mm of lateral press fit.
In this manner bone can be conserved due to the
compaction of the cancellous bone,7 which in other
stem designs would be removed. Cancellous bone
compaction in addition to providing primary stability8
preserves the intramedullary blood supply.
The in-vitro stability of the GTS stem has been
evaluated9 against several cementless stems. The
rotational stability at the proximal 2/3 anchorage
being comparable to VerSys® E.T® and CLS® (Zimmer
Inc.) designs. The CLS® stem has longitudinal ribs
on its surface designed to enhance primary implant
stability and provide fixation into cancellous bone.
Although there is clinical evidence that these ribs
do not contribute toward bone ingrowth,10 other
information11 would suggest that they are of assistance
in attaining primary implant fixation and the
maintaining bone mineral density in the proximal
femur for significant periods post operatively.
The GTS stem an Interloc grit blasted surface
to encourage bone apposition and facility secondary
fixation. Evidence12 of bone on-growth exists from the
use of this surface on other Biomet stems (Bi-Metric).
The Interloc surface also provides a periarticular seal13
which, if polyethlyene wear debris is present, provides
a barrier to its transmission along the implant/
bone surface interface and, therefore reducing the
potential for polyethylene induced osteolysis.
Grit blast surface finishes have successfully been
used in other press-fit stem designs with document14–16
excellent long-term implant survivorship. However,
the surface finish on the GTS stem is coarser that the
micro-porous surface treatment17 used on the CLS®
stem.
Initial Clinical results
To date there have been two presentations/
publications on the early clinical results from the
use of the GTS stem. An immediate post operative
radiographic evaluation by Professor Alessandro
Massé 18 and 1 year clinical results19 have been
evaluated by Professor Guido Grappiolo.
Radiographic Evaluation.
The aim of this study was to determine whether the
GTS stem was able to:
1.Reconstruct femoral offset
2.Restore the cervico-diaphyseal angle.
3.Minimise/eliminate leg length discrepancy.
All patients had a total hip arthroplasty surgery,
utilizing the GTS stem, at Istituto Clinico Humanitas
di Rozzano, Milan, Italy. The etiopathology at the time
of surgery was predominantly (81.5%) idiopathic
osteoarthritis but also include patients who presented
with developmental dysplasia of the hip, femoral head
osteonecrosis, perthes, post traumatic arthritis and a
previous hip resurfacing.
Preoperative radiographs were reviewed to
measure:
• Offset – femoral offset is the distance from
the centre of rotation of the femoral head to
a line bissecting the long axis of the femur
• Diaphysis/neck angle
• Leg length discrepancy
• Flare index - The ratio of the endosteal canal
diameter 2 cm below the lesser trochanter
and the endosteal canal diameter 10 cm
below the lesser trochanter.
• Cortico-Medullary index – The ratio of the
cortical bone diameter 10 cm below the lesser
trochanter and the medullary canal diameter
at the same level.
• Post operative radiographs were examined
to measure the above parameter plus the
metaphyseal filling rate and any signs of bone
resorption.
• Metaphyseal filling rate – The ratio of the
medullary canal dimension 2 cm above the
lesser trochanter and the prosthesis dimension
at the same level.
Clinical Results
Typical early post operative anterior/posterior and
lateral radiographs from patients who received the
GTS stem are shown in Figure 4.
The study involved reviewing radiographs from
54 patients with less than 5 months follow up. The
average age of the patients was 59 years, but included
those from >70 and <30 years (Figure 3.)
Age distribution
20
15
10
5
Fig. 4:
Radiograph at 1 year follow-up
0
>70 <80
years
>60 <70
years
>50 <60
years
>40 <50
years
>30 <40 <30 years
years
Fig. 3:
Age distribution of the 54 patients, whose X-rays were
reviewed for the radiographic evaluation
2 • GTS (Global Tissue Sparing) Femoral Hip Stem: Design validation through initial clinical results
Following the use of the GTS stem the
reconstructed mean femoral offset was 50.23 mm
compared with the mean preoperative value of 51.0
mm. A similar reconstruction of the native cervicaldiaphyseal angle was attained, from a mean 130.7°
before surgery to a mean 128.3° after surgery.
The use of the GTS stem produced no
discernible increase in leg length. Pre-operatively the
patient population had a mean leg length discrepancy
of -1.2 cm. Post-operatively the mean discrepancy was
reduced to 0.2 cm.
The flare index and cortical-medullary index
measured preoperatively were 3.48 (S.D ±1.89) and
2.28 (S.D. ±1.2), respectively. The metaphyseal filling
rate, an indication of how well the implant fits the
proximal femur, was 1.44.
The post operative radiographs were also
examined for signs of radiolucency or resorption. At a
maximum of 6.7 months post-op. there were no signs
of either radiolucency or resorption.
Clinical Evaluation
In early published clinical results, the use of the use
of the stem is described in 570 total hip arthroplasties
and the clinical and radiological results from 100
patients who had attained 1 year or more follow up is
provided. The patient demographics, implants used
and assessment methods used were as follows:
Implants utilized:
Femoral Stems:
485 procedures (85%) used Standard stems with 133°
cervico-diaphyseal (CD) angle, 84 (17.3%) of which
were size 0. The stem size distribution for standard
and varus stems is provided in Figure 5 and Figure 6.
Size distribution – Standard
100
80
60
40
20
0
-6
-5
-4
-3
-2
-1
0
+1
+2
+3
+4
+5
+6
Fig. 5:
GTS standard stem (133°) – size distribution for the first
570 implanted stems.
Patient demographics:
Five hundred and seventy GTS stems were implanted
in 539 patients. The average age of the patients was
57.8 years (range 17.3 – 88.1) and 283 (52.5%) were
male.
The patient’s aetiology was predominantly
(61%) idiopathic osteoarthritis but also included
congenital dysplasia, aseptic necrosis of the femoral
head and sequelae resulting from perthes disease and
trauma. Posterior lateral surgical approach was used
on all patients
Size distribution – Varus
15
12
9
6
3
0
-6
-5
-4
-3
-2
-1
0
+1
+2
Fig. 6:
+3
+4
+5
GTS varized stem (122°) – size distribution for the first
570 implanted stems.
3 • GTS (Global Tissue Sparing) Femoral Hip Stem: Design validation through initial clinical results
+6
Acetabular Cups
Femoral head/acetabular liner articulation materials:
Cementless acetabular cups were used in all surgeries.
They included Exceed ABT (Biomet UK Ltd), M2aMagnum (Biomet UK Ltd), Regenerex (Biomet
Orthopaedics), Avantage (Biomet France) and
others. The percentage of cup types used is shown in
Figure 7.
The Femoral head size used was either 32 mm or in
the cases of larger cups 36 mm diameter. The majority
(57%) of surgical procedures used ceramic on
polyethylene articulating bearings of which 234 (77%)
cases utilised vitamin E stabilized (E1) polyethylene.
Other articulations included ceramic-on-ceramic,
metal-on-metal and metal-on-polyethylene. The
distribution of articulating surfaces used is given in
Figure 8.
Acetabular Cups
Regenerex
1%
M2a-Magnum
17%
Other
41%
Articulating Surfaces
Avantage
0%
Exceed ABT
41%
Ceramic/Poly
57%
Ceramic/
Ceramic
17%
Metal/Metal
17%
Metal/ Poly
9%
Fig. 7:
Shell distribution for the first 570 cases.
Fig. 8:
Tribology distribution for the first 570 cases
4 • GTS (Global Tissue Sparing) Femoral Hip Stem: Design validation through initial clinical results
Method of clinical assessment:
The clinical efficacy of the GTS stem seen in the first
100 patients (all of whom were at least 12 months from
surgery) was assessed by the use of Oxford Hip, Harris
Hip scores and the incidence of adverse events. The
hip scores were measured at 45 days, 3 months, 6
months and 1 year following surgery.
Results:
Pre-operative and post-operative scores were available
for only 84 of the 100 patients documented in the
publication .The Oxford hip score, undertaken by a
patient administered questionnaire, increased from
a mean pre-operative value of 24.85 (range 0-45)
to a 12 month mean of 47.7 (range 44-48). As this
score has a highest attainable value of 48 from patient
and function questions, the scores obtained would
indicate that GTS patients are attaining low pain and
high hip function at 12 months post-op. Similarly, the
Harris Hip Score in these same patients increased
from a pre-operative mean of 53.9 (range 24-90) to a
12 month mean of 99.2 (range 93-100).
Adverse events:
The incidence of intra-operative complication in
this series was small. Intra-operatively there were 5
cases (0.9%) of spitting of the femur above the lesser
trochanter these complications occurring early on in
the learning curve associated with this new system. All
the implants were stable, however in 3 cases circlage
wiring was used and in the other 2 cases transverse
screws were used to close the split.
Postoperatively there was one adverse event
(traumatic fracture) due to a patient falling in the
rehabilitation phase. This patient subsequently had
revision surgery. Three further required wound
debridement due to suspected sepsis.
Planned studies
RSA evaluation:
In order to verify the in vitro stability studies and
provide evidence for regulatory agencies, an in vivo
stability/motion study is planned for the GTS stem.
The evaluation will compare the stability (both
primary and secondary) of the GTS against that of
the HA coated Taperloc stem in patients undergoing
primary uncemented total hip arthroplasty.
In the planned 50 patient randomised
controlled trial the stability and motion of both
implants will be determine via the model based RSA
method, all patients will receive the uncemented
Regenerex cup.
The study will be undertaken at the MC
Haaglanden Hospital, Netherlands and RSA
measurements will be taken pre-operatively and at 3
months, 6 months, 1 year, 2 years and 5 years intervals.
Bone mineral density measurements will so be taken
via DEXA at the same time intervals to determine
the effect on the imposition of the stems on bone
remodelling in the proximal femur.
Using the RSA technique the study will be able
to measure stem position translation in the x, y and z
directions with an accuracy of between 0.05 and 0.5
mm and rotational changes to an accuracy of between
0.15° and 1.15°. The hypotheses for the study being
that the implant stability for the GTS is equal to that
of the well documented, clinically proven Taperloc
stem in the initial two years and also thereafter.
Multicentre clinical evaluation:
To date all the clinical data on the GTS stem has
results from its use by Professor Grappiolo and his
colleagues. To confirm the initial promising clinical
results and verify that the GTS stem is capable of
providing excellent performance in the hands of
other clinicians, a multi-centre clinical study is being
initiated.
This prospective study will determine long-term
implant efficacy for both standard and varus versions
of the GTS stem. 250 patients will be recruited from
5 clinical centres (50 patients each). This will include
125 patients with standard stems and 125 patients with
varized stems. These hospitals will be in Germany(2),
Italy, Spain and France.
Patients will be included if they present with the
following eitiologies:
• Primary and secondary coxarthritis
• Inflammatory (Rheumatoid) arthritis
• Avascular necrosis of the femoral head
• Sequelae from previous operations to the hip
• Congenital hip dysplasia.
5 • GTS (Global Tissue Sparing) Femoral Hip Stem: Design validation through initial clinical results
The primary outcome measure for this
evaluation will be the mean Harris Hip score at 2 years
post operative. The secondary outcome measures
include:
• Radiographic evaluation
• Patient satisfaction , measured using EQ5-D
• Incidence and nature of adverse events and
complications
• Implant survivorship.
Patients will have a follow-up examined at 3
months, 1 year, 2 year, 3 year, 5 year, 7 year and at 10
years.
Conclusion
Several design features incorporated in the GTS stem
have been validated and documented in peer reviewed
publications. These include tissue preservation, bone
conservation and the use of a grit-basted surface
finish.
The initial stability of the stem has been
evaluated against other documented brands via in
vitro mechanical testing, the stability of the GTS stem
being equivalent to stems with long-term clinical
results.
Early results from its clinical use confirms that
the GTS stem is able to reconstruct the native hip
anatomy in terms of the restoration of the cervicodiaphyseal angle and femoral neck offset
Initial clinical outcomes, although of very shortterm nature, indicate that the GTS stem is capable
of providing patients with pain relief and good hip
function. A low incidence of complications associated
with the use of the GTS has been documented. The
majority of which occurred intra-operatively and may
be associated with the learning curve present with the
introduction of any new implant system.
Provision has been made to quantify the stability
of the stem in an RSA investigation and determine
its clinical outcome in other non-designer clinical
centres by the use of a multi-centre study.
References
1.Malik, A. and Dorr, L.D. The Science of Minimally Invasive
Total Hip Arthroplasty. Clinical Orthopaedics and Related
Research. 463: 74–84, 2007.
2.Berry, D.J. et al. Symposium: Minimally Invasive Total Hip
Arthroplasty. Development of Early Results and a Critical
Analysis. Journal of Bone and Joint Surgery (Am.) 85: 2235–
46, 2003.
3.Ranawat, C.S. et al. Minimally Invasive Total Joint
Arthroplasty: Where are we going?. Journal of Bone and
Joint Surgery (Am.). 85:2070–1, 2003.
4. Scuco, T.P. Is Small Necessarily Better? American Journal of
Orthopedics. 32: 169, 2003
5.Kappe, T. et al. Minimally Invasive Total Hip Arthroplastytrend or State of the Art?: A Meta-analysis. Ortopade
Journal. Apr 10, 2011 [Epub ahead of print].
6. Robinson, R. P. et al. Hip Arthroplasty Using the Cementless
CLS stem: A 2-4 Year Experience. Journal of Arthroplasty.
9(2): 177–192, 1994.
7.Swanson, T.V. The Tapered Press-fit Total Hip Arthroplasty.
Journal of Arthroplasty. 20(4): 63–7, 2005.
8.Green, J.R. et al. The Effect of Bone Compaction on Early
Fixation of Porous Coated Implants. Journal of Arthroplasty.
14: 91, 1999.
9.Laboratory report. Standardized in vitro characterisation
of the initial fixation behaviour and medio-lateral bending
behaviour of the GTS stem in composite femurs. Laboratory
of Biomechanics and Implant Research. Heidelberg
University Hospital. Data on file at Biomet.
10.Sportono, L. et al. The CLS System: Theorectical Concept
and Results. Act Orthopaedica Belgica. 59(1): 144–8, 1993.
11.Aldinger, P.R. and Sabo, D. et al. Pattern of Periprosthetic
Bone Remodelling Around Stable Uncemented Tapered
Hip Stems: A Prospective 84 Month Follow-up Study and
a Median 156 Month Cross-sectional Study with DEXA.
Calcified Tissue International. 73: 115–21, 2003.
12.Coathup, M.J. et al. A Comparison of Bone Remodelling
Around Hydroxyapatite Coated, Porous Coated and Grit
Blasted Hip Replacements Retrieved at Post Mortem.
Journal of Bone and Joint Surgery (Br). 82-B: 118–23, 2001.
13.Robinson, P.R. and Gaston, R. et al. Uncemented Total Hip
Arthroplasty using the CLS stem: A Titanium Alloy Implant
with a Corundum Blast Finish. Journal of Arthroplasty. 11(3):
286–92, 1996.
14.Delaunay, C. and Kapandji, A.I. Survival Analysis of
Cementless Grit-blasted Titanium Total Hip Arthroplasties.
Journal of Arthroplasty. 19:151, 2004.
15.Delaunay, C. et al. Grit Blasted Titanium Femoral Stem in
Cemented Primary Total Hip Arthroplasty: A 5 to 10 Year
Multicentre Study. Journal of Arthroplasty. 16:47, 2001.
16.Pieringer, H. et al. Long-term Results with the Cementless
Alloclassic Brand Hip Arthroplasty System. Journal of
Arthroplasty. 18: 321, 2003.
6 • GTS (Global Tissue Sparing) Femoral Hip Stem: Design validation through initial clinical results
17.Robinson, P.R., Lovell, T. and Green, T.M. Hip Arthroplasty
Using the Cementless CLS Stem: A 2-4 Year Experience.
Journal of Arthroplasty. 9(2) :177–84, 1994.
18.Massè, A. et al. GTS user group meeting. Milan. April, 2011.
19.Grappiolo, G. et al. Short GTS Stem with Trochanteric
Preservation: Preliminary Clinical and Radiological Results.
GIOT. 37(1); 19–22, 2011.
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7 • GTS (Global Tissue Sparing) Femoral Hip Stem: Design validation through initial clinical results
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