Acta Med. Okayama, 2023
Vol. 77, No. 4, pp. 407‑414
CopyrightⒸ 2023 by Okayama University Medical School.

Original Article

http://escholarship.lib.okayama-u.ac.jp/amo/

Usefulness of Force-Controlled Pelvic Stress Radiograph in the Evaluation
and Treatment of Fragility Fractures of the Pelvis in Geriatric Patients:
A Pilot Study
Kensuke Hottaa,b＊, and Takaomi Kobayashib,c＊aDepartment of Orthopaedic Surgery, Amagi Chuo Hospital, 667 Amagi, Asakura, Fukuoka 838-0068, Japan,b
Department of Orthopaedic Surgery, Karatsu Red Cross Hospital, Karatsu, Saga 847-8588, Japan,c
Department of Orthopaedic Surgery, Faculty of Medicine, Saga University, Saga 849-8501, Japan

This study aimed to investigate the usefulness of force-controlled pelvic stress radiographs in the evaluation andtreatment of fragility fractures of the pelvis (FFP) using a functional treatment strategy. We conducted a retrospective study of 55 geriatric patients with FFP who underwent pelvic stress radiographs on admission. The
differences in the sacral width, pelvic ring width, and medial femoral head width between the radiographs withand without the Sam Sling II M size were defined as Δ sacral width, Δ pelvic ring width, and Δ medial femoral
head width, respectively. We used Pearson’s correlation test to assess the relationship between the degree ofradiographic instability and the Johns Hopkins highest level of mobility scale (JH-HLM) at 10-days postadmission. Conventional receiver-operating-characteristic curve analysis was used to identify cases requiring surgery
using the best cutoff value for radiographic instability. The JH-HLM was significantly correlated with Δ sacral
width (r = −0.401, p = 0.017), but not with Δ pelvic ring width (r = −0.298, p = 0.080) nor with Δ medial femoral
head width (r= −0.261, p = 0.128). The best cutoff value of Δ sacral width in identifying surgical cases was
10.7 mm (sensitivity 75.0%, specificity 98.0%). Force-controlled pelvic stress radiographs could be helpful inassessing the need for surgery on admission.
Key words: fragility fracture of the pelvis, functional treatment strategy, Sam Sling, stress radiograph, Johns
Hopkins highest level of mobility scaleFragility fractures of the pelvis (FFP) have been
increasing in aging societies [1 , 2] and are caused
by a low-energy pelvic trauma in geriatric patients who
have osteoporosis. There has been an ongoing debate
regarding the best treatment strategies for FFP [3-9].
First, Rommens et al. [3-6] proposed through radiographic management that conservative therapy is recommended for FFP types I (anterior lesions only) and II
Received August 5, 2022 ; accepted March 31, 2023.
Corresponding authors. Phone : +81-955-72-5111; FAX : +81-955-73-9530
E-mail : kensukehotta@hotmail.co.jp (K. Hotta); Phone : +81-952-34-2343;
FAX : +81-952-34-2059
E-mail : takaomi_920@yahoo.co.jp (T. Kobayashi)＊
The authors equally contributed to this work.
＊(nondisplaced posterior lesions), and minimally invasive surgical treatment (e.g., navigated percutaneous
screw fixation [10]) is efficacious for FFP types III (displaced unilateral posterior lesions) and IV (displaced
bilateral posterior lesions). In contrast, it was recently
found that radiographic instability detected by pelvic
static radiographs is not necessarily related to functional
mobility [9], with some researchers going further bysuggesting that functional instability on admission [7]or at 7-14 days postadmission could also pose as a surgical indication [7-9].
Conflict of Interest Disclosures: No potential conflict of interest relevantto this article was reported.

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Acta Med. Okayama Vol. 77, No. 4

More importantly, radiographic instability of thepelvis can be determined more accurately by pelvic
stress radiographs taken under anesthesia (e.g., Pelvic
rock test [11] and internal rotation, external rotation,and push-pull maneuvers of both lower extremities[12 , 13]) or awake (e.g., the lateral decubitus position[14], Chamberlain technique [15], and Thigh lever technique [15]) than by static pelvic radiographs in patientswith pelvic fractures caused by high-energy trauma [16].
These pelvic stress radiographs in geriatric patientswith FFP can, however, result in anesthesia-related andother types of complications, as well as fracture progression. In this context, a force-controlled circumferential pelvic belt in the awake condition could improve
the safety and efficacy of pelvic stress radiographs inpatients with FFP. Therefore, the present study aimed
at investigating the usefulness of these force-controlled
pelvic stress radiographs in the awake condition in theevaluation and treatment of FFP.

Methods
Study design. We conducted a retrospective studyof geriatric patients with FFP who had undergone evaluation and received treatment for FFP using a functional treatment strategy [9]. As shown in Table 1,
which summarizes the patients’ characteristics, 55
geriatric patients out of 75 consecutive patients with
FFP between January 2018 and January 2020 were considered eligible for this study; of the remaining
20 patients, 16 lacked evaluable data and 4 patientswere younger than 65 years.
All procedures performed in studies involving humanparticipants were in accordance with the ethical standards of the institutional review board of Karatsu Red
Cross Hospital (registration number: 2021-13-1) andwith the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Treatment strategy.
All subjects who underwent
evaluation and received treatment for FFP according to
the functional treatment strategy [9] had also undergone conservative therapy that included full-weightbearing exercises (within pain limits). In this regard, arehabilitation therapy program typically consisted of
40 min of therapy per day at least 5 days a week.
Patients with swallowing ability took 60-mg loxoprofen
orally whereas those without it took 25-mg diclofenac
sodium as a suppository. Patients for whom nonsteroi-

dal anti-inflammatory drugs were contraindicated took
200-400 mg acetaminophen orally while analgesics wereadministered upon request every 6-8 h. The level offunctional mobility (i.e., difficulty with auxiliary standing on one leg and/or two legs due to permanent pelvicpain) registered 10 days after diagnosing a patient with
FFP would determine the continuity of conservative
therapy or the shift toward surgical stabilization.
Radiographic study. The author (KH) of thisstudy assessed the radiographs of all subjects. The
instability was evaluated upon admission by anteroposterior supine radiographs with and without stress,
which were obtained without the use of anesthesia (i.e.,under awake condition) using the Sam Sling II M size
(Sam Medical Products, Wilsonville, OR, USA), which
had an auto stop at 150 N and was placed at the level ofthe greater trochanters (Fig. 1). The sacral width, thepelvic ring width and the medial femoral head width oneach radiograph were measured (Fig. 2) [17 , 18]. The
value obtained by subtracting the sacral width, the pelvic ring width, and the medial femoral head width in
the radiographs with stress from those without stress isdefined as delta (Δ) sacral width, Δ pelvic ring width,

Fig. 1

Usage of the Sam Sling.

Pelvic Stress Radiograph for FFP

August 2023

A

409

B

Fig. 2A best-ﬁt plumb line was drawn from the midline of the lumbar spine through the pubic symphysis. The sacral width, pelvic ringwidth, and medical femoral head width for each hemi-pelvis in relation to the plumb line were measured on anteroposterior supine
radiograph (A) without and (B) with the Sam Sling.

and Δ medial femoral head width, respectively.
We performed Rommens FFP classification [3-6] on
computed tomography (CT) or magnetic resonanceimaging (MRI) during the first examination using thefollowing categories: unilateral anterior pelvic ring disruption (FFP type Ia), bilateral anterior pelvic ring
disruption (FFP type Ib), dorsal nondisplaced posterior
injury only (FFP type IIa), sacral crush with anterior
disruption (FFP type IIb), nondisplaced sacral, sacroiliac, or iliac fracture with anterior disruption (FFP typeIIc), displaced unilateral ilium fracture and anterior
disruption (FFP type IIIa), displaced unilateral sacroiliac disruption and anterior disruption (FFP type IIIb),
displaced unilateral sacral fracture together with anterior disruption (FFP type IIIc), bilateral iliac fracturesor bilateral sacroiliac disruptions together with anterior
disruption (FFP type IVa), spinopelvic dissociation
together with anterior disruption (FFP type IVb), and a
combination of various posterior instabilities together
with anterior disruption (FFP type IVc). Others were
judged to be unclassifiable.
Study of functional mobility and instability.
The
author (KH) of this study assessed the functional
mobility of all subjects, while the functional instability
was assessed both upon admission and at 10-days postadmission by the Johns Hopkins highest level of mobility scale (JH-HLM), which is a 1-item scale with eightordinal responses scored based on patient’s observed

highest level of activity as follows: 1, only lying; 2, bed
activities; 3, sitting at edge of bed; 4, transferring tochair; 5, standing for greater than or equal to 1 min;6, walking 10 or more steps; 7, walking approximately
7.5 min or more; and 8, walking approximately 75 min
or more [19 , 20].
Statistical analysis. To assess the relationshipbetween the degree of radiographic instability (i.e.,
Δ sacral width, Δ pelvic ring width, and Δ medial femoral
head width on admission) and the functional mobility(i.e., JH-HLM on admission and at 10 days postadmission) we used Pearson’s correlation test. Correlation
coefficients of 0.00-0.10, 0.10-0.39, 0.40-0.69, 0.700.89, and 0.90-1.00 were defined as having negligible,
weak, moderate, strong, and a very strong correlation,
respectively [21]. Conventional receiver operating
characteristic curve (ROC) analysis was used to calculate the best cutoff value for the degree of radiographic
instability (i.e., Δ sacral width, Δ pelvic ring width, andΔ medial femoral head width on admission) necessary
to identify the FFP cases requiring surgery. The discriminative ability of the model was assessed based on
the area under the ROC (AUC), where values of 0.500.59, 0.60-0.69, 0.70-0.79, 0.80-0.89, and 0.90-1.00
were respectively classified as failure, poor, fair, good,and excellent [22] with the level of significance(p-value) set at 0.05. These analyses were performed
using JMP® pro 14 (SAS Institute, Cary, NC, USA).

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Acta Med. Okayama Vol. 77, No. 4

Results
Patients’ characteristics.
Table 1

Patients’ demographic

data are shown in Table 1. Among 55 patients, 51
underwent conservative treatment, and 4 received surgical intervention. The average age of patients who

Patient characteristics

Characteristics
Age＊, years
Gender, men/women
Body mass index＊, kg/m2
Δ sacral width> 10 mm, n (%)
0-10 mm, n (%)< 0 mm, n (%)Δ pelvic ring width> 10 mm, n (%)
0-10 mm, n (%)< 0 mm, n (%)Δ medical femoral head width> 10 mm, n (%)
0-10 mm, n (%)< 0 mm, n (%)
JH-HLM on admission
1, n (%)
2, n (%)
3, n (%)
4, n (%)
5, n (%)
6, n (%)
7, n (%)
8, n (%)
JH-HLM at 10-days postadmission
1, n (%)
2, n (%)
3, n (%)
4, n (%)
5, n (%)
6, n (%)
7, n (%)
8, n (%)
FFP types on admission
Ia, n (%)
Ib, n (%)
IIa, n (%)
IIb, n (%)
IIc, n (%)
IIIa, n (%)
IIIb, n (%)
IIIc, n (%)
IVa, n (%)
IVb, n (%)
IVc, n (%)
Unclassiﬁable, n (%)

Overall (n = 55)

Conservative treatment (n = 51)

Surgical intervention (n = 4)

85.7 ± 8.1 (69 to 101)
6/49
19.7 ± 3.1 (13.4 to 29.3)

85.5 ± 8.1 (69 to 101)
5/46
19.8 ± 3.2 (13.4 to 29.3)

88.7 ± 9.7 (78 to 97)
1/3
18.4 ± 2.4 (16.7 to 21.1)

5 (9.1)27 (49.1)
23 (41.8)

2 (3.9)26 (51.0)
23 (45.1)

3 (75.0)
1 (25.0)0 (0)6 (10.9)30 (54.5)
19 (34.5)5 (9.8)27 (52.9)
19 (37.3)

1 (25.0)
3 (75.0)0 (0)6 (10.9)35 (63.6)
14 (25.5)

5 (9.8)32 (62.7)
14 (27.5)

1 (25.0)
3 (75.0)0 (0)6 (10.9)
11 (20.0)
8 (14.5)
11 (20.0)
7 (12.7)
8 (14.5)
3 (5.5)
1 (1.8)2 (3.9)11 (21.6)
8 (15.7)
11 (21.6)
7 (12.7)
8 (15.7)
3 (5.9)1 (2.0)4 (100.0)
0 (0)
0 (0)
0 (0)
0 (0)
0 (0)
0 (0)
0 (0)

4 (7.3)0 (0)1 (1.8)12 (21.8)
7 (12.7)
13 (23.6)
14 (25.5)
4 (7.3)

0 (0)
0 (0)
1 (2.0)12 (23.5)
7 (12.7)
13 (25.5)
14 (27.5)
4 (7.8)4 (100.0)
0 (0)
0 (0)
0 (0)
0 (0)
0 (0)
0 (0)
0 (0)

13 (23.6)
0 (0)1 (1.8)17 (30.9)
0 (0)3 (5.5)
0 (0)
0 (0)
0 (0)
11 (20.0)
3 (5.5)7 (12.7)

13 (25.5)0 (0)1 (2.0)15 (29.4)
0 (0)2 (3.9)
0 (0)
0 (0)
0 (0)
10 (19.6)
3 (5.9)7 (13.7)

0 (0)
0 (0)
0 (0)
2 (50.0)0 (0)1 (25.0)
0 (0)
0 (0)
0 (0)
1 (25.0)
0 (0)
0 (0)

JH-HLM, the Johns Hopkins highest level of mobility scale; FFP, fragility fracture of the pelvis
Values are expressed as the mean ± standard deviation (range)＊Pelvic Stress Radiograph for FFP

August 2023

received conservative treatments and surgical intervention were 85.5 years and 88.7 years, respectively.
JH-HLM scoring of 1 on admission in patients who
received conservative treatments and surgical intervention were 2/51 (3.9%) and 4/4 (100.0%), respectively.
JH-HLM scoring of 1 at 10-days postadmission inpatients who received conservative treatments and surgical intervention were 0/51 (0%) and 4/4 (100.0%),
respectively. FFP type III/IV on admission in patients
who received conservative treatments and surgical intervention were 22/51 (43.1%) and 2/4 (50.0%), respectively.
Correlation analysis results. The JH-HLM measured at 10-days postadmission was moderately correlated with Δ sacral width (r = −0.401, p = 0.017), but it
was not significantly associated with either Δ pelvic ringwidth (r = −0.298, p = 0.080) or Δ medial femoral headwidth (r = −0.261, p = 0.128). There were no significant
associations between the JH-HLM upon admission and
the Δ sacral width (r = −0.165, p = 0.340), the Δ pelvic
ring width (r = −0.134, p = 0.437) or the Δ medial femoral head width (r = −0.110, p = 0.525) (Table 2).

411

ROC analysis results.
The AUC values of the
Δ sacral width, the Δ pelvic ring width, and the Δ
medial femoral head width for discriminating surgicalcases were 0.86, 0.82, and 0.79, respectively; thus, thediscriminative ability of these models was fair to good.
The best cutoff value of Δ sacral width, Δ pelvic ringwidth, and Δ medial femoral head width in identifying
surgical cases with difficulty standing at a 10-days postadmission were 10.7 mm (sensitivity 75.0%, specificity
98.0%), 6.5 mm (sensitivity 75.0%, specificity 86.3%),
and 8.6 mm (sensitivity 75.0%, specificity 84.3%),
respectively (Fig. 3).

Discussion
Our main findings were the following: (1) the Δ sacral
width upon admission was moderately correlated withthe functional mobility measured at 10-days postadmission; (2) the degree of radiographic instability uponadmission was non-significantly correlated with functional mobility upon admission; finally, (3) the best

Table 2
The relationships between the Johns Hopkins highest level of mobility scale (JH-HLM) on admission and at 10-days
postadmission and the Δ sacral width, Δ pelvic ring width, and Δ medial femoral head width on admission
JH-HLM
On admission
At 10-days postadmission

Δ Sacral width

Δ Pelvic ring width

Δ Medical femoral head width

Pearsonʼs r

P-value

Pearsonʼs r

P-value

Pearsonʼs r

P-value－0.165－0.401

0.340
0.017

－0.134－0.298

0.437
0.080

－0.110－0.261

0.525
0.128

JH-HLM, the Johns Hopkins highest level of mobility scale

A

B

C

Fig. 3
Receiver-operating-characteristic (ROC) curve to determine the best cutoﬀ value for the (A) Δ sacral width, (B) Δ pelvic ringwidth, and (C) Δ medial femoral head width in identifying the surgical cases in functional treatment strategy for fragility fracture of thepelvis.

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Hotta et al.

cutoff value of the Δ sacral width for identifying surgical cases with difficulty standing at 10-days postadmission was 10.7 mm (sensitivity 75.0%, specificity
98.0%).
We found a significant correlation between the
degree of radiographic instability (i.e., Δ sacral width)when assessed by the Sam Sling on admission and thefunctional mobility at 10-days postadmission. In contrast, a past report [9] found no statistically significant
association between radiographic instability on a staticradiograph upon admission and the functional mobility
measured at 10-days postadmission. It seems therefore
likely that stress radiographs of the pelvis can represent
the functional instability more accurately than staticradiographs. There are two explanations for theseresults. First, stress radiographs are able to assess not
only static skeletal structures but also the displacement
history, which includes large muscle-tendon units that
attach to the pelvis [23 , 24]. Even though muscles andligaments that attach to the pelvis are considered intact
in most patients with FFP [23], a low-energy pelvic
trauma might still cause injuries. Second, the reliabilityof the FFP classification on a static radiograph involving
a complete nondisplaced or displaced sacral fracture isreported to be relatively poor [25]. Further investigation may be required to clarify whether stress radiographs help improve the reliability of the FFP classification on a static radiograph.
In this study, a non-significant correlation wasobserved between the degree of radiographic instability(i.e., Δ sacral width, Δ pelvic ring width, and Δ medial
femoral head width) assessed by the Sam Sling uponadmission and the functional mobility upon admission.
To support this, there was also no statistically significant association between radiographic instability on a
static radiograph on admission and the functional
mobility on admission in past literature [9]. This ispartly explained by the fact that functional mobility on
admission is influenced not only by structural problems(i.e., skeletal structures, muscles, and ligaments) but
also by acute pain [7 , 9]. The pain does subside overhospitalization, at which point functional instability
due to the structural problems may then become apparent. From the treatment viewpoint, which focuses onfunctional instability caused by structural problems,
functional mobility at 7-14 days postadmission may be
more suitable in determining surgical interventions
than that detected on admission [7-9].

Acta Med. Okayama Vol. 77, No. 4

The best cutoff value of the Δ sacral width for identifying surgical cases with difficulty standing at 10-days
postadmission was found to be roughly 11 mm, while
the AUC, the sensitivity and the specificity were 0.86,
75.0%, and 98.0%, respectively. Force-controlled stressradiographs on admission are thus helpful in determining the need for surgery, but they have not been recommended in the screening for surgical indications within
the functional treatment strategy for FFP due to their
low sensitivity and their high specificity. Although
10 days of bed rest has little effect on the physical performance of geriatric populations [26], prolonged hospital stays can increase in-hospital complications [27],the patients’ and their families’ burden, and the use of
medical expenses and resources. Furthermore, prolonged posttraumatic pelvic pain negatively impacts thequality of life [28]. Therefore, although the gold standard consideration in determining when a patient with
FFP should receive surgery is the pain and associatedmobility at 10-days postadmission, force-controlled
stress radiographs upon admission could be an option
within the functional treatment strategy for FFP.
Our study has some limitations. First, even though
our study provides the first insight (pilot study) on this
topic, the number of subjects was small due to the low
incidence of FFP, which might have affected the results.
The number of patients with FFP has been increasing in
aging societies and is expected to triple between 2020
and 2030 [1], warranting further investigations on this
topic with sufficient statistical power. Second, a pelvic
stress radiograph with the Sam Sling does not assessvertical instability but rather rotational instability.
However, weight bearing was found to have little impact
on the fracture displacement in FFP (0.2-0.8 mm) [17],so this limitation might not have much influence on theassessment of radiographic instability. Third, plain
anteroposterior radiographs (i.e., stress radiographs)
used for the measurement could potentially have magnification errors, which might affect the differencesfrom CT- or MRI-based measurements. However, it
would be somewhat difficult to conduct CT or MRI several times in clinical field. Fourth, intra-class correlation coefficients of the stress radiographs were unclear.
The location of the buckle and elevation of the belt havebeen reported to influence fracture reduction and exacerbation [29 , 30]. Indeed, both positive and negativevalues were detected in Δ sacral width, Δ pelvic ringwidth, and Δ medial femoral head width as shown inPelvic Stress Radiograph for FFP

August 2023

Table 1. These may have influenced the results. Finally,
temporarily increased dislocation during the stressradiographs was detected in some cases. Notably, theuse of pelvic circumferential compression devices inlateral compression mechanisms could lead toover-compression of the fracture and associated further
injury [31]. Furthermore, the other adverse effects
from the use of pelvic circumferential compression
devices (e.g., bladder rupture, external iliac vein compression, and skin disorders) have been reported in past
literature [32]. However, no such adverse events wereobserved in this study.
In conclusion, the Δ sacral width upon admission
was significantly correlated with functional mobility
10-days postadmission. The best cutoff value of the
Δ sacral width for identifying surgical cases with difficulty standing in a period of 10 days after admission
was roughly 11 mm (sensitivity 75%, specificity 98%).
Although the fundamental consideration in determining when a patient with FFP should receive surgery is
pain and the associated mobility at 10-days postadmission, prolonged hospital stays can increase in-hospitalcomplications, patients’ and their families’ burden,
medical expenses, and the resource utilization.
Furthermore, prolonged posttraumatic pelvic pain negatively impacts the quality of life. Force-controlled
pelvic stress radiographs under awake conditions could
be helpful in establishing the need for surgery on
admission as part of the functional treatment strategy
for FFP. Further studies are needed on this topic.

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