n Feature Article
Comparison of Specific Femoral Short Stems
and Conventional-Length Stems in Primary
Cementless Total Hip Arthroplasty
Young-Soo Shin, MD; Dong-Hun Suh, MD; Jong-Hoon Park, MD; Jeong-Lae Kim, MD;
Seung-Beom Han, MD
abstract
There are several reported disadvantages with conventional-length femoral
stems in cementless total hip arthroplasty (THA). Therefore, various efforts
have been made to develop a specific femoral short stem to improve physiologic bone remodeling at the femoral aspect of a cementless THA. However, there are potential disadvantages with specific femoral short stems, such
as malalignment, inadvertent subsidence, and potential proximal femoral
fracture. Therefore, the authors quantitatively compared radiographic and
clinical outcomes as well as component-specific complications between 2
groups of patients following primary cementless THA. A matched comparison was made between specific femoral short stems (n=50) and conventional-length femoral stems (n=50) in cementless THA procedures performed
between January 2008 and January 2012. Patients were matched for age,
sex, body mass index, height, surgical approach, and surgeon. No significant differences were found between the 2 groups in mean postoperative
radiographic outcomes, functional outcomes, or complications. Both groups
showed satisfactory performance at 5-year follow-up. Specific femoral short
stems resulted in a higher incidence of malalignment and subsidence and a
lower incidence of thigh pain and proximal bone resorption compared with
conventional-length femoral stems. Although longer follow-up is required,
specific femoral short stems may have clinical and radiographic advantages
with equivalent perioperative complications relative to conventional-length
femoral stems. However, this technique requires proper patient selection in
combination with careful preoperative planning and meticulous surgical
technique. [Orthopedics. 2016; 39(2):e311-e317.]
O
ver the past several decades, conventional femoral fixation with
tapered stems has been used in
cementless total hip arthroplasty (THA)
MARCH/APRIL 2016 | Volume 39 • Number 2
in an effort to provide reliable long-term
fixation in patients with functional improvement. Recent studies showed overall
survivorship of greater than 94% for sev-
eral conventional-length tapered femoral
components at 20-year follow-up.1-3 However, conventional-length femoral stems
in cementless THA have several reported
disadvantages, including challenges with
proximal-distal femoral mismatch, preservation of the osseous femoral neck, and
optimal proximal load transfer.4,5 There
has been a recent surge of interest in the
use of shorter stems for younger, more active patients undergoing cementless THA.
Pain relief, improved function, and the
radiographic stability of short stems of
various designs were shown with followup of 2 to 8 years.6,7 Various efforts have
been made to develop a femoral neck-preserving short stem to improve physiologic
bone remodeling at the femoral aspect of
a cementless THA. In addition, femoral
neck-preserving short stems have several
proposed advantages, including their inThe authors are from the Veterans Health Service Medical Center (Y-SS), Korea University Ansan Hospital (D-HS), and Korea University Anam
Hospital (J-HP, J-LK, S-BH), Seoul, South Korea.
The authors have no relevant financial relationships to disclose.
Correspondence should be addressed to:
Seung-Beom Han, MD, Korea University Anam
Hospital, Anamdong 5 ga, Seoul, South Korea
(oshan@korea.ac.kr).
Received: April 6, 2015; Accepted: September
1, 2015.
doi: 10.3928/01477447-20160222-04
e311
n Feature Article
clinical outcomes as well as componentspecific complications in 2 groups of patients after primary cementless THA. It
was hypothesized that the results with the
specific femoral short stems would be at
least equivalent to those with the currently
available conventional-length femoral
stems.
Materials and Methods
Figure 1: Photograph of the specific femoral short
stem prosthesis (METHA, Aesculap, Tuttlingen,
Germany) analyzed in the current study.
herent bone-preserving nature wherein
a more oval-shaped stem is fixed to the
proximal femur. This allows more rotational stability and prevents distal migration, and the absence of the distal portion
of the stem helps to avoid stress shielding and thigh pain.8-12 However, femoral
neck-preserving short stems also have
potential disadvantages. First, they tend to
have a higher incidence of malalignment;
therefore, they have been associated with
poor functional outcomes and survivorship.12 Second, incorrect stem sizing may
cause inadvertent subsidence; therefore,
precise stem sizing of short stems is difficult compared with conventional stems.13
Third, there are concerns about potential
proximal femoral fracture.12 To the best
of the authors’ knowledge, no studies
have simultaneously compared specific
femoral short stems with conventionallength femoral stems in patients undergoing primary cementless THA. This study
quantitatively compared radiographic and
e312
Patient Selection and Study Design
Starting in January 2008, THA with
BiCONTACT (Aesculap, Tuttlingen, Germany) was performed predominantly at
the study institution, along with METHA
(Aesculap). During the study period, the
stem type was selected by the surgeon in
a nonsystematic manner, with the typical
process of trial and implementation. The 2
stems were compared in patients who had 5
years of follow-up. The authors were aware
that the BiCONTACT stem had good longterm results compared with other contemporary femoral stems.14 A total of 237
THA procedures were performed at the
study institution between January 2008 and
January 2012. The current study included
patients with indications for primary THA.
The use of specific femoral short stems
was begun at the institution in June 2008.
Exclusion criteria for METHA treatment
were radiographically noticeable osteoporosis with T-score of less than 2.5 and
dysplastic hips with abnormal deviation of
the femoral neck or metaphyseal deformity
secondary to fracture that would exclude
insertion of the specific model of short
stem that was used. Simple radiographs,
dual-energy x-ray absorptiometry, and intraoperative bone stock findings were used
to assess bone quality because inadequate
bone structure may lead to poor fixation,
even in patients with good bone quality.
The authors evaluated 54 consecutive THA
procedures performed with specific femoral short stems between June 2008 and January 2012. Four patients declined to participate in follow-up for reasons unrelated
to the THA. After these patients were excluded, 50 patients who had specific femo-
ral short stems were included in the current
study, with a minimum 5-year follow-up.
These patients underwent THA with specific femoral short stems (METHA) with
a modular acetabular component consisting of a hemispherical titanium cup
(PLASMACUP SC; Aesculap) with an
outer coating of plasma-sprayed pure titanium (Plasmapore; Aesculap) and a 36mm delta ceramic femoral head and liner.
This stem was composed of monoblock
with 120°, 130°, and 135° head-neck-shaft
angles and had a proximal rough titanium,
plasma-sprayed, microporous coating with
a thin 20-μm layer of pure calcium phosphate (Figure 1). Digital templating is considered an essential step before METHA
implantation and is commonly used to determine the head-neck-shaft angle preoperatively and to ensure the femoral resection
level and the anatomy of the femoral neck
intraoperatively. Patients receiving the
short stem THA were classified as group
A and were reviewed in a case-matched
analysis with 133 consecutive THA procedures performed with conventional-length
femoral stems (BiCONTACT; Aesculap).
In these patients, THA was performed
with conventional-length femoral stems
(BiCONTACT) with a modular acetabular component consisting of a hemispheric
titanium cup (PLASMACUP SC) with an
outer coating of plasma-sprayed pure titanium (Plasmapore) and a 36-mm delta
ceramic femoral head and liner. This is a
straight, collarless stem made of titanium
alloy with plasma spray (pore size, 50-200
μm). Patients who underwent THA with
the conventional-length stem were classified as group B. For every patient who was
treated with a specific femoral short stem,
a matched patient who was treated with a
conventional-length stem was identified
from the database by age (±5 years), sex,
body mass index (±2 kg/m2), height (±5
cm), surgical approach, and surgeon in a
1:1 ratio. Matching in a 1:2 ratio was not
possible because of the limited sample
size. All procedures were performed by a
single surgeon (S.-B.H.) using a postero-
Copyright © SLACK Incorporated
n Feature Article
lateral surgical approach. All patients were
administered prophylactic antibiotics perioperatively to prevent postoperative infection. This study was approved by the ethics committee at the study institution, and
informed consent was obtained from all
patients.
Clinical Evaluation
A simple questionnaire was completed, and clinical outcomes were determined using the Harris Hip Score (HHS)
and the Western Ontario and McMaster
Universities Arthritis Index (WOMAC)
score at each visit. Data were recorded
preoperatively and at 6 weeks, 6 months,
1 year, and annually thereafter. Preoperative demographic and clinical data for the
2 groups were evaluated (Table 1). Preoperative HHS and WOMAC score were
not significantly different between the 2
groups.
Radiographic Evaluation
Each patient had regular evaluation
preoperatively and at 6 weeks, 6 months,
1 year, and annually thereafter by analyzing radiographic outcomes for implant
alignment and stability as assessed by 2
independent radiographic reviewers. The
patients were placed in the supine position, with the affected leg in 20° internal
rotation. The foot was fixed by an assistant
to inhibit measurement errors. Stem position was defined as angulation along the
stem relative to the femoral shaft. Varus or
valgus positioning (>5° from neutral) was
measured. Subsidence was analyzed by
measuring the change in distance from the
superior tip of the greater trochanter to the
distal tip of the implant and was defined as
greater than 2 mm.15,16 Radiographic findings in the femur were evaluated in the
conventional 7 zones for bony ingrowth
or resorption, including proximal bone
resorption, defined as loss of trabecular
bone density or loss of definition between
the cortical and cancellous bone, blending into a uniform density; endosteal spot
welds, defined as local deposition of new
MARCH/APRIL 2016 | Volume 39 • Number 2
Table 1
Preoperative Demographic and Functional Data
Variable
Group A (n=50)
Sex, M/F, No.
Group B (n=50)
P
35/15
32/18
.211
48.45 (30-68)
49.91 (40-67)
.472
Body mass index, mean (range),
kg/m2
23.4 (19.5-34.2)
23.8 (18.4-38.1)
.337
Height, mean (range), m
1.73 (1.53-1.82)
1.71 (1.50-1.79)
.281
56.5 (36-77)
59.5 (36-83)
.255
Neck
0.785 (0.542-0.935)
0.711 (0.527-0.910)
.207
Trochanter
0.732 (0.530-0.851)
0.776 (0.541-0.816)
.809
Intertrochanter
1.210 (0.883-1.336)
1.058 (0.776-1.280)
.439
Ward’s triangle
0.635 (0.437-0.912)
0.666 (0.432-0.953)
.664
Total
0.999 (0.607-1.108)
0.974 (0.684-1.211)
Age, mean (range), y
Follow-up, mean (range), mo
Bone mineral density, mean
(range), g/cm2
Diagnosis, No. (%)
.373
>.999
Osteoarthritis
5 (10)
8 (16)
Avascular necrosis
39 (77)
36 (71)
6 (13)
6 (13)
Harris Hip Score, mean±SD
(range)
Septic hip sequelae
55.0±10.4 (29-76)
53.0±8.4 (25-75)
.316
Western Ontario and McMaster
Universities Arthritis Index,
mean±SD (range)
53.0±14.6 (40-64)
49.5±12.3 (32-78)
.359
Abbreviations: F, female; M, male.
bony trabeculae bridging the cortex and
the implant surface; and cortical hypertrophy, defined as new bone of cortical density that resulted in an increase in cortical
thickness.17 Additionally, heterotopic ossification was observed and classified according to the Brooker grading system.18
Component-specific complications, such
as subsidence, fracture, and malalignment, were evaluated.
Statistical Analysis
Statistical analysis was performed
with SPSS statistical software, version
20 (IBM Corp, Armonk, New York).
P<.05 was considered statistically significant. The HHS, WOMAC score, and
radiographic data in the 2 groups at final
follow-up were compared with an independent samples t test for continuous vari-
ables. Chi-square (Fisher’s exact) test was
used for categorical variables to determine
whether the incidence of complications
and sex were different in the 2 groups.
Results
Clinical Outcomes
In group A, mean preoperative HHS
and WOMAC score of 55.0 and 53.0, respectively, improved to mean postoperative values of 98.6 and 3.3, respectively,
at an average follow-up of 37.2 months.
Therefore, HHS and WOMAC score
improved by 43.6 and 49.7 points, respectively, in group A. In group B, mean
preoperative HHS and WOMAC score of
53.0 and 49.5, respectively, improved to
mean postoperative values of 97.8 and 4.4,
respectively, at an average follow-up of
35.3 months. Therefore, in group B, HHS
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n Feature Article
Table 2
Valgus Position of Implants (Group A)
Mean±SD (Range)
Variable
Patients in Valgus
Position (n=2)
Patients in Neutral
Position (n=48)
Pa
Preoperative Harris Hip Score
Preoperative Western Ontario and
McMaster Universities Arthritis Index
41.5±13.4 (32-51)
55.9±9.7 (29-74)
.056
51.9±1.4 (50-52)
52.7±15.1 (24-79)
.875
Postoperative Harris Hip Score
98.5±2.1 (97-100)
98.6±2.0 (93-100)
.935
5.0±4.2 (2-8)
3.2±2.8 (0-8)
.404
Postoperative Western Ontario and
McMaster Universities Arthritis Index
a
Independent samples t test.
Table 3
Incidence of Complications
No. (%)
Group A (n=50)
Group B (n=50)
Pa
Subsidence
1 (2)
0 (0)
.313
Periprosthetic fracture
1 (2)
1 (2)
1.000
Malalignment
2 (4)
1 (2)
.554
Leg length discrepancy
1 (2)
0 (0)
.313
Thigh pain
0 (0)
2 (4)
.151
Heterotopic ossification
1 (2)
2 (4)
.554
Infection
0 (0)
1 (2)
.313
Dislocation
1 (2)
1 (2)
1.000
Complication
a
Fisher’s exact test.
and WOMAC score improved by 44.8 and
45.1 points, respectively. In addition, no
significant differences in mean postoperative HHS (P=.168) or WOMAC score
(P=.158) were observed in the 2 groups,
according to an independent samples t test.
Table 2 shows 2 stems (4%) located in
valgus position (>5° from neutral). Mean
preoperative and postoperative HHS and
WOMAC score were similar to those for
stems located neutrally in group A.
Radiographic Findings
All stems in group A showed bone
bridging and endosteal spot welds distributed in Gruen zones 2 and 6 as evidence
of bony ingrowth with no radiolucencies
e314
(Figure 2). Two patients in group B had
a slight decrease in bone density, mostly
in Gruen zones 1 and 7. No radiographic
evidence of osteolytic lesions, cortical
hypertrophy, or acetabular fractures was
detected in either group, and no patient
required revision surgery for aseptic loosening.
Complications
Chi-square (Fisher’s exact) test showed
no significant difference in patient complications in the 2 groups (Table 3). One
patient in group A with a head-neck-shaft
angle of 135° had subsidence (>2 mm,
P=.313) that showed bony ingrowth, with
no further progression of subsidence at fi-
Figure 2: Radiograph showing well-fixed acetabular and femoral components in an ideal position in
the right hip without osteolysis. Bone trabeculae
are seen streaming toward the METHA stem (Aesculap, Tuttlingen, Germany) (spot welds) in Gruen
zones 2 and 6.
nal follow-up. Two patients (1 in group A
and 1 in group B) had intraoperative minor femur neck fracture (P=1.00). These
patients were treated with cerclage wires
without further incident. Three patients (2
in group A, valgus and head-neck-shaft
angle of 135°; 1 in group B, varus) had
malalignment (P=.554) that was not associated with loosening. One patient in
group A with a head-neck-shaft angle of
135° had leg length discrepancy of greater
than 1 cm (shortening, P=.313). Two patients in group B had thigh pain (P=.151)
that disappeared after a few months. Three
patients (1 in group A and 2 in group B)
had heterotopic ossifications (P=.554)
that were categorized as Brooker class I
in 2 patients and class II in 1 patient and
did not limit their activities. One patient in
group B had a superficial wound infection
that was treated with local debridement
and antibiotics. Early dislocation occurred
Copyright © SLACK Incorporated
n Feature Article
in 2 patients (1 in group A and 1 in group
B). Two patients reported postoperative
falls at the bedside, and both were treated
with closed reduction without further procedures. No hips had deep venous thrombosis or pulmonary embolism.
Discussion
The most important finding of the current study was that no significant differences in clinical or radiographic outcomes
or component-specific complications were
observed between the 2 groups. Additionally, valgus alignment after insertion of
METHA stems did not negatively affect
clinical outcomes at short- to midterm follow-up. Although no significant differences were observed in thigh pain or proximal
bone resorption in the 2 groups, patients
in group B had a higher incidence of thigh
pain (4%) and proximal bone resorption
(4%) than patients in group A. Additionally, although no significant difference in
malalignment or subsidence was found
between the 2 groups, patients in group A
who had a head-neck-shaft angle of 135°
had a higher incidence of malalignment
(4%) and subsidence (2%) than those in
group B.
One of the most common complications
of conventional-length stems in cementless THA is the potential risk of proximal
stress shielding.19 Therefore, many studies investigated patients who underwent
treatment with a femoral neck-preserving
short stem to allow more proximal load
transfer and reduction of the stress shielding effect. However, there have been no
direct in vivo simultaneous comparisons
of specific femoral short stems (METHA)
and conventional-length femoral stems
(BiCONTACT) after primary cementless
THA. Only 1 biomechanical study of strain
patterns with 2 synthetic femora showed
that both stems apparently decreased strain
in the greater trochanter region; furthermore, the BiCONTACT stem dramatically decreased strain around the calcar
with a combination of metaphyseal and
diaphyseal load transfer.10 These earlier
MARCH/APRIL 2016 | Volume 39 • Number 2
results indicated that both stems similarly
decreased fundamental strain and the risk
of stress shielding in the proximal femur;
however, the anchorage location of the femur may be different. In contrast, a study
of clinical and radiographic outcomes in
177 patients who underwent THA with a
BiCONTACT stem reported that proximal bone resorption was 6% at long-term
follow-up.20 This discrepancy was likely
due to the use of synthetic bone, which
may have affected the measurement of
proximal bone resorption as a result of altered stress in the proximal femur. In the
current study, patients in group B had a
higher incidence (4%) of proximal bone
resorption than those in group A, even with
a short follow-up period. This proximal
bone resorption may have occurred because there was no primary goal to achieve
press-fit and maximal canal filling, including less reproducible insertion with a surgical technique because of an initial learning
curve. In addition, all patients who had
proximal bone resorption had thigh pain. In
general, thigh pain is related to a stem design that occupies the diaphysis, although
BiCONTACT stems are designed to
achieve proximal load transfer.5,21 This
may explain the current finding that the
METHA stem minimized stress shielding as a result of proximal bone resorption
and thigh pain and provided more successful bone remodeling, according to Wolff’s
law.22
With the METHA stem, it is necessary
to avoid any valgus position that could
lead to subsidence without proximallateral support, whereas other short stems
may be prone to the varus position when
encountering osteoporotic bone with a
widened intramedullary canal.23,24 One
study showed that the level of neck resection with a short metaphyseal stem affects
the stem position, the head-neck-shaft
angle, femoral offset, and leg length, indicating that a lower neck resection causes
a more vertical stem position, which decreases offset and leg length and increases
the head-neck-shaft angle.25 This was
similar to previous findings that showed
that the final position of the METHA
stem and the head-neck-shaft angle were
significantly higher with lower neck resection and that the offset was in a lower
position compared with more proximal resections.26 The current study showed that
1 of 2 patients in group A who had a valgus stem position with a head-neck-shaft
angle of 135° simultaneously had subsidence and leg length discrepancy. This
finding suggested that an unintentionally
lower neck resection could change stem
position and offset, leading to subsidence.
Interestingly, the current findings showed
no difference in HHS and WOMAC score
in the valgus position of implants compared with the neutral position of implants
in group A. Discrepancies between clinical and radiographic outcomes may be the
result of the lack of standardized scoring
systems based on a relatively arbitrary
patient report. Other differences may be
the result of unexpectedly complicated
biomechanics of the hip between various tissues and bony structures. Together,
clinically, these studies suggest that preservation of a 5- to 10-mm cortical ring
around the femoral neck and osteotomy at
an angle of 50° to the femoral shaft axis
may have advantages during METHA
stem implantation, including more accurate neck resection and better control of
the stem position (Figure 3).
Many studies have investigated the factors that predispose patients to periprosthetic fractures of the femur and found
that they may include stem design and
individual parameters, such as body mass
index and bone mineral density.27,28 However, the current study showed no significant differences in periprosthetic fractures
between the 2 groups in body mass index,
bone mineral density, age, sex, preoperative diagnosis, or stem design, although
the very specific tapered nature of the
stemless implant caused significant hoop
stress, increasing the likelihood of femoral neck fracture. It is possible that most
of the periprosthetic fractures were seen
e315
n Feature Article
Figure 3: Radiographic templates showing a 5- to
10-mm–thick ring of cortex around the femoral
neck that provides considerable anchorage. Osteotomy of the femoral neck is performed at an angle
of 50° to the femoral shaft axis, measuring the distance from the lesser trochanter.
in the initial learning period. This could
be the result of an inaccurate implantation technique, most likely involving intentionally high neck resection and the
use of a bigger rasp than planned to avoid
undersizing.
This study had several limitations. First,
although the data were collected prospectively, the study design was retrospective
and not randomized. Second, all THA
procedures were performed by a single
surgeon. Although the authors attempted to
standardize the surgical techniques, it may
be difficult to distinguish clearly between
the 2 procedures and to avoid the potential drawback of selecting patients who
are satisfactory candidates. However, the
surgeon who performed these procedures
was highly experienced with these techniques, especially with respect to femoral
neck resection. Additionally, the authors attempted to minimize selection bias resulting from the inclusion of a single surgeon
through case-matched analysis. Third, the
study did not compare reliability between
2 implants with completely different stems
in analyzing clinical and radiographic out-
e316
comes because the specific femoral short
stem was not just a shorter design of the
conventional-length stem. Furthermore, the
design of this particular stemless implant
allows subsidence in the short term, and
unlike most cementless stems, subsidence
of greater than 2 mm is consistent with
ingrowth because of the tapered stem design.29,30 However, no consensus has been
reached on specific criteria for comparison
of 2 implants. Finally, the median followup of 5 years was relatively short to allow a
conclusion regarding implant safety. However, the current study provides baseline
comparison data, especially in terms of
functional scores and complication rates.
Despite these limitations, to the authors’
knowledge, this in vivo study is the first to
simultaneously compare specific femoral
short stems with conventional-length femoral stems in patients undergoing primary
cementless THA.
Conclusion
No significant differences in clinical
and radiographic outcomes or componentspecific complications were observed between the 2 groups, showing satisfactory
performance at 5-year follow-up. Group
A had a higher incidence of malalignment
and subsidence and a lower incidence of
thigh pain and proximal bone resorption
than group B. Although longer follow-up
is required, specific femoral short stems
may have clinical and radiographic advantages and equivalent perioperative complications compared with conventionallength femoral stems. In addition, specific
femoral short stems provide a step toward
a specific design that more closely resembles the physiologic joint, and they appear
to be a viable treatment option for active
patients. However, their effective use requires proper patient selection in combination with careful preoperative planning
and meticulous surgical technique.
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