Keywords bone remodeling - femur - hip prosthesis - prosthesis design
Introduction
Total hip arthroplasty is one of the most common orthopedic surgical procedures. As
the number of surgeries increased, the stem design became one of the most important
factors affecting overall prosthesis longevity and patient satisfaction. One of the
stems that provide good results and long-term outcomes is the cementless one, invented
in 1950.[1 ] Several studies have reported early loosening and instability associated with the
initial design, which may be caused by proximal femoral osteopenia resulting from
the stress shielding effect.[2 ] Many modern stems have been developed by promoting proximal engagement, using hydroxyapatite
porous coating, which is more compatible with the patient proximal femoral dense bone.
By utilizing taper and anatomical designs, they can decrease the distal stem engagement
and employ shorter stems, which can reduce proximal bone loss by up to 14%.[3 ] Moreover, many studies have shown that the stem design revolution reduced stem subsidence,
thigh pain, and loosening.[4 ]
[5 ] Nevertheless, no previous research has compared the progression of bone integration
and proximal bone loss between a double-tapered wedge stems (Accolade II, Stryker,
Portage, MI, USA) and anatomical stems (ABGII, Stryker). Therefore, this study compares
proximal femoral filling differences between such stem designs, using immediate postoperative
imaging and proximal bone loss utilizing follow-up X-ray. The results will provide
a better choice of stem, decrease early complications, and increase satisfaction with
the total hip replacement operation.
Materials and Methods
Study Design
This study is a retrospective descriptive-cohort study of immediate and postoperative
follow-up imaging from total hip arthroplasty surgery performed from 2017 to 2019.
The hospital's Ethics Committee (ID: 62133) approved the research protocol and waived
the requirement for informed consent for this study. All patients' collected data
and identifiers were made fully anonymous.
Samples
Inclusion Criteria
With permission from the radiology department of Rajavithi, patients aged between
18 and 80 years who received primary total hip arthroplasty using both types of stems
between 2017 and 2019 and had follow-up imaging for up to a year were included in
this study.
Exclusion Criteria
Patients who were under 18 years of age, received revision hip arthroplasty, had prior
hip dysplasia, had any postoperative complication, and with follow-up imaging of less
than 1 year were excluded.
Data Collection and Measurement
We obtained immediate and postoperative follow-up imaging from the radiology department
for patients who underwent total hip arthroplasty, covering a period of up to 1 year.
Data analysis was based on the femoral canal filling ratio method, used by the orthopedic
surgeon responsible for adult hip and knee reconstruction.[6 ] The data included measurements of the proximal femoral and stem diameter in the
anteroposterior view at three levels: lesser trochanter (LT), 2 cm proximal to the
LT, and 6 cm distal to the LT ([Fig. 1 ]).
Fig. 1 Measurement of canal filling ratios at the lesser trochanter (LT), 2 cm proximal
to LT, and 6 cm distal to LT.
The follow-up imaging was analyzed for proximal femoral bone density changes using
the optimal densitometry method,[7 ] employing Image J (public domain), a digital optical image analysis software for
windows, which measured bone changes in zones 1, 4, and 7 according to the Gruen fixation
zone[8 ] ([Fig. 2 ]).
Fig. 2 Measurement of the proximal femoral bone density using optimal densitometry method.
Statical Analysis
Descriptive statistics (number, percentage, mean, median, standard deviation, as well
as minimum and maximum values) were used to describe the characteristics of the samples.
The Chi-squared test was employed to compare categorical data. The paired t test was utilized to compare independent data such as stem and femoral types. Furthermore,
the t test was employed to compare dependent data such as postoperative imaging. The level
of significance was defined as a p -value < 0.05. All statistical analyses were performed using the IBM SPSS Statistics
for Windows (IBM Corp., Armonk, NY, USA) software, version 20.0.
Results
Demographics Data
A total sample of 92 patients (22 males and 70 females) was included in this study.
The mean age was of 53.86 ± 13.00 years. There were 34 patients in the anatomical
stem group (ABGII) and 58 patients in the double-tapered wedge stem group (Accolade
II).
When comparing canal filling ratios between both stems, the canal filling ratio in
the double-tapered wedge stem was significantly higher than that in the anatomical
stem group at all 3 measurement levels (p < 0.001, p < 0.001, and p = 0.013), as shown in [Table 1 ].
Table 1
Level
Anatomical stem (n = 34)
Double-tapered wedge stem (n = 58)
Difference (95% confidence interval)
p -value
Lesser trochanter
81.56
88.13
−6.57 (−9.74 to −3.39)
< 0.001*
2 cm above the lesser trochanter
85.98
93.49
−7.51 (−10.07 to −4.95)
< 0.001*
6 cm below the lesser trochanter
78.58
85.64
−7.06 (−12.56 to −1.56)
0.013*
[Table 2 ] presents the femoral bone density changes in each stem type in Gruen zones 1, 4,
and 7. Both stems showed a femoral proximal bone loss from the baseline to every time
point.
Proximal bone density changes in anatomical stem
At 6-months postoperatively, there were significant differences in femoral bone loss
in zones 1, 4, and 7 (p = 0.024, p < 0.001, and p = 0.006, respectively); the highest femoral bone loss was observed in zone 4 (5.74%).
At 1-year postoperatively, there was a significant difference in femoral bone loss
in zones 1, 4, and 7 (p < 0.001); the highest femoral bone loss was found in zone 7 (20.65%). At 2 years
postoperatively, significant differences in femoral bone loss were observed in zones
1 (p < 0.001), 4 (p = 0.004), and 7 (p < 0.001); the highest femoral bone loss was seen in zone 1 (34.48%).
Proximal bone density changes in double-tapered wedge stem
At 6-months postoperatively, there was a significant difference in femoral bone loss
in zones 1, 4, and 7 (p < 0.001); the highest femoral bone loss was observed in zone 1 (8.28%). At 1-year
postoperatively, there was a significant difference in femoral bone loss in zones
1, 4, and 7 (p < 0.001); the highest femoral bone loss was seen in zone 1 (12.48%). At 2-years postoperatively,
a significant difference in the femoral bone loss was found in zones 1, 4, and 7 (p < 0.001); the highest femoral bone loss was seen in zone 1 (22.37%).
Table 2
Femur
Anatomical stem (n = 34)
Double-tapered wedge stem (n = 58)
Postoperative (baseline)
6 months
1 year
2 years
Postoperative (baseline)
6 months
1 year
2 years
Zone 1
FBD (%; mean ± SD)
Change (%)
(135.59 ± 12.20)
(131.15 ± 10.53)
−4.44
(117.35 ± 14.19)
−13.79
(84.74 ± 7.29)
−34.48
(130.33 ± 13.30)
(122.05 ± 15.14)
−8.28
(109.57 ± 12.09)
−12.48
(91.63 ± 9.06)
−22.37
p -value
0.024*
< 0.001*
< 0.001*
< 0.001*
< 0.001*
< 0.001*
Zone 4
FBD (%; mean ± SD)
Change (%)
(164.03 ± 16.41)
(158.29 ± 17.11)
−5.74
(145.74 ± 16.92)
−12.56
(135.39 ± 12.74)
−13.65
(152.86 ± 29.44)
(148.14 ± 24.19)
−4.72
(138.64 ± 18.49)
−9.50
(129.77 ± 11.34)
−16.23
p -value
0.001*
< 0.001*
0.004*
0.098
< 0.001*
< 0.001*
Zone 7
FBD (%; mean ± SD)
Change (%)
(157.85 ± 13.84)
(152.71 ± 11.31)
−5.15
(132.06 ± 12.33)
−20.65
(107.83 ± 19.79)
−29.57
(152.29 ± 13.11)
(144.29 ± 14.85)
−8.00
(135.12 ± 14.89)
−9.17
(126.87 ± 10.59)
−11.13
p -value
0.006
< 0.001*
< 0.001*
< 0.001*
< 0.001*
< 0.001*
Comparing proximal femoral bone loss between both designs, the double-tapered wedge
stem demonstrated significantly less proximal femoral bone loss in the Gruen zone
7 ([Fig. 3 ]). However, there was no significant difference in proximal femoral bone loss in
zones 1 and 4, as shown in ([Figs. 4 ]
[5 ]) and [Table 3 ].
Fig. 3 Comparison of the proximal femoral bone density changes in the Gruen zone 7 of both
stems (A, anatomical stem; B, double-tapered wedge stem).
Fig. 4 Comparison of the proximal femoral bone density changes in the Gruen zone 1 of both
stems (A, anatomical stem; B, double-tapered wedge stem).
Fig. 5 Comparison of the proximal femoral bone density changes in the Gruen zone 4 of both
stems (A, anatomical stem; B, double-tapered wedge stem).
Table 3
Femoral bone density
Stem type
p -value
Anatomical stem (n = 34)
Double-tapered wedge stem (n = 58)
Zone 1
Postoperative (baseline)
135.59 ± 12.20
130.33 ± 13.30
0.062
6 months
131.15 ± 10.53
122.05 ± 15.14
0.003*
1 year
117.35 ± 14.19
109.57 ± 12.09
0.006*
2 years
84.74 ± 7.29
91.63 ± 9.06
0.004*
Change (1-year postoperatively)
−18.24 ± 20.48
−20.76 ± 9.36
0.501
Zone 4
Postoperative (baseline)
164.03 ± 16.41
152.86 ± 29.44
0.022*
6 months
158.29 ± 17.11
148.14 ± 24.19
0.021*
1 year
145.74 ± 16.92
138.64 ± 18.49
0.070
2 years
135.39 ± 12.74
129.77 ± 11.34
0.096
Change (1-year postoperatively)
−18.29 ± 14.79
−14.22 ± 24.22
0.320
Zone 7
Postoperative (baseline)
157.85 ± 13.84
152.29 ± 13.11
0.058
6 months
152.71 ± 11.31
144.29 ± 14.85
0.005*
1 year
132.06 ± 12.33
135.12 ± 14.89
0.314
2 years
107.83 ± 19.79
126.87 ± 10.59
< 0.001*
Change (1-year postoperatively)
−25.79 ± 15.85
−17.17 ± 13.23
0.010*
[Table 3 ] showed that only zone 7 had significant differences in femoral bone density changes
between both stems (p = 0.01).
Discussion
Cementless total hip arthroplasty is a popular procedure, particularly for younger
patients,[9 ] with a good long-term outcome. However, it was reported to have proximal femoral
osteopenia and early aseptic loosening in early designs[4 ] due to the stress shielding effect and proximal micromotion of the stem. Later,
the stem was refined by improvement in surface and coating material, decrease in the
material's stiffness, and variants of the femoral stem length all greatly improve
the survival and lessens chance of complications in the procedure.[10 ]
For canal filling of femoral canal, our study found the canal filling ratio in the
double-tapered wedge stem was significantly higher than that in the anatomical stem
group at all levels (LT, 2 cm above LT, and 6 cm below LT). It is worth noting that
the higher femoral canal filling and canal filling ratio observed in our study may
increase the risk of failure of osteointegration, as suggested by the study by Cooper
et al.,[11 ] who noted that an increase in the mid and distal filling, as well as and canal-flare
index, are the most important risk factors for osteointegration failure.
According to our study on changes in periprosthetic bone density, the immediate postoperative
bone mineral density on the operated side should be used as the baseline value to
exclude bone loss due to the operation procedure.[12 ] Despite this method, our study found bone density loss in both stems from the baseline,
which we attribute to stress-shielding in the area. This finding is consistent with
the Venesmaa et al.[13 ] study, which reported a general decrease in all regions of interest until 6 months,
particularly in the Calcar region, and only minor changes after this time period.
However, our study observed a decrease in bone density up to 1 year postoperatively.
We found that in zone 7, the anatomical stem had a significantly higher femoral bone
density loss than that the double-tapered wedge stem (−25% versus −17%, p = 0.010). Nevertheless, no significant femoral bone density loss was observed in
zones 1 and 4.
The main strength of this study is that it was conducted by a single surgeon in a
single center, which minimized confounding factors from surgical technique and postoperative
patient care. However, this study has limitations. First, its retrospective nature,
which limited data collection on all factors that may have influenced bone loss in
our patient population. Additionally, the sample size was relatively small, which
prevented us from conducting a meaningful subgroup analysis to investigate the impact
of various factors on bone loss. Second, the follow-up period was short (12 months),
although we believe it was adequate, as periprosthetic bone density loss was most
pronounced in the first postoperative year, with minimal changes thereafter. This
finding is consistent with previous studies that highlighted the initial periprosthetic
bone remodeling process occurring within the first 12 postoperative months.[14 ]
Conclusion
Double-tapered wedge stem design had a significantly higher canal filling ratio than
the anatomical stem at all levels, with a lower femoral bone density loss identified
in the follow-up postoperative imaging at zone 7. However, in zones 1 and 4, no significant
difference in femoral bone density loss was observed.
