Editors’
ChoiceORIGINAL PAPER

Nagoya J. Med. Sci. 85. 223–232, 2023
doi:10.18999/nagjms.85.2.223

Hook plate fixation versus locking plate fixation
for distal clavicle fracture:a multicenter propensity score-matched study
Hiroshi Takahashi1, Yasuhiko Takegami1, Katsuhiro Tokutake2,
Yujiro Katayama1 and Shiro Imagama1
Department of Orthopedic Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan2
Department of Hand Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan

1

ABSTRACTHook plate fixation and locking plate fixation are two standard internal fixation implants for treating
distal clavicle fractures. We aimed to clarify the following: 1) Does the locking plate offer better clinicaloutcomes than the hook plate? 2) Is bone union better with a locking plate than hook plate? and 3) Are
complications different between the locking plate and hook plate? We conducted a retrospective multicenter
study of 338 patients who underwent surgery from 2014 to 2018 in our 10 hospitals, which comprise the
TRON group. Of them, 208 patients treated using any plates were eligible. After 30 patients were excluded
for various reasons, 178 patients were included. We classified them into two groups, locking plate group(Group L) and hook plate group (Group H), using propensity score matching. We confirmed bone unionwith an X-ray, evaluated the UCLA shoulder score, and compared the frequency of complications. After
matching, Group L and Group H included 49 patients each. The UCLA score was higher in Group L
than in Group H at each follow-up point. We confirmed bone union in all patients in Group L, but it was
not confirmed in three patients (6.1%) in Group H. No statistically significant differences were observed
except for plate migration, which was observed in nine patients (18.4%) in Group H but in no patients inGroup L. The postoperative UCLA score was significantly better in Group L. We recommend the locking
plate as a surgical treatment for distal clavicle fractures.
Keywords: distal clavicle fracture, locking plate, hook plate, clavicle, propensity score matching
Abbreviations:
AC: acromioclavicular
ASA: American Society of Anesthesiologists
UCLA: University of California, Los Angeles
This is an Open Access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
License. To view the details of this license, please visit (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Received: January 5, 2022; accepted: April 12, 2022
Corresponding Author: Yasuhiko Takegami, MD, PhD
Department of Orthopedic Surgery, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho,Showa-ku, Nagoya 466-8550, Japan
Tel: +81-52-741-2111, Fax: +81-52-744-2460, E-mail: takegami@med.nagoya-u.ac.jp223

Hiroshi Takahashi et al

INTRODUCTION
Although distal clavicle fractures are relatively rare, representing only 15–28% of all clavicle
fractures, they constitute 30–45% of the cases of nonunion.1-3 Nonunion of a distal clavicle
fracture causes pain and dysfunction. Various implants for fixation of distal clavicle fracture havebeen developed to prevent nonunion, including coracoclavicular fixation, tension band wiring,hook plates, and clavicular locking plates.4,5 Hook plate fixation and locking plate fixation are
two standard internal fixation implants for treating clavicle fractures. Recent systematic reviews
have shown that both the hook plate and locking plate offer excellent bone union rates andprovide comparative functional outcomes,6,7 although hook plate fixation had higher complication
rates.6-12 However, these reviews were based on case series with relatively small sample size. In
addition, only a few papers directly compare the two fixation methods. We hypothesized thatclinical outcome with the clavicular locking plate would be better than that with hook platefixation for distal clavicle fracture. The purpose of this multicenter study was to compare 1)
the clinical outcomes of hook plate fixation to those of locking plate fixation for distal clavicle
fracture, 2) bone union with the two devices, and 3) the incidence of complications.

MATERIALS AND METHODS
Study design and settingThis multicenter retrospective study used data obtained from the TRON (Trauma ResearchGroup of Nagoya) database in which member hospitals have registered orthopedic trauma surgery
cases annually since 2014. The hospitals participating in the database are all hospitals associatedwith the Department of Orthopedic Surgery of our university. Orthopedic surgeons perform thesurgery at these hospitals in Central Japan. We collected cases of clavicle fractures from thisdatabase that were treated surgically.
Participants
From January 2014 to December 2018, 338 patients with distal clavicle fractures were admitted and underwent surgery in our 10 hospitals. Of them, 208 patients treated using any plates,
clavicular locking plates, or clavicular hook plates were eligible. We excluded 19 patients lost tofollow-up at six months after surgery, 10 patients with no University of California at Los Angeles(UCLA) shoulder score or follow-up X-ray, and one patient who received additional treatment ofcoracoclavicular fixation. Thus, 178 patients were included in this study group (Figure 1). We
classified the patients into two groups according to the kind of treatment received: the locking
plate group (Group L) and the hook plate group (Group H).
Demographics
After applying the inclusion and exclusion criteria, the study sample contained 178 patientswith distal clavicle fractures. Background and operative procedures of the patients are describedin Table 1. We obtained patient characteristics data from the electronic records in each hospital.
We extracted sex, age, body mass index, American Society of Anesthesiologists (ASA) PhysicalStatus Classification System, operation time, surgical method, and the implant used.
Surgical procedure
Indications for surgical treatments were Neer type II with displacement or type V fracture.
Patients were operated on under general anesthesia and in the standard beach chair position.
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Fixation for distal clavicle fractures

Fig. 1 Flow diagram showing the number of patients included in this study
BMI: body mass index
ASA: American Society of Anesthesiologists Physical Status Classification
CC: coracoclavicular

Table 1

Patients demographics (n=178)

Characteristic

Value

Implant (Locking plate/Hook plate), n114/64Sex (M/F), n (%)

159 (89.3)/19 (10.7)

Age, years (SD)46.3 (14.4)

BMI, kg/m (SD)22.5 (3.05)

ASA (I/II/III/IV), n (%)

130 (73.0)/39 (21.9)/8 (4.5)/1 (0.6)

Neer type (II/V), n (%)

154 (86.5)/24 (13.5)

Dislocation, mm (range)

9.0 (0-32)

Fragment size, mm (SD)20.3 (9.78)

2

BMI: body mass index
ASA: American Society of Anesthesiologists Physical Status Classification System

We used a standard anterosuperior approach to the clavicle. Electrocautery was used to control
superficial bleeding and dissection directly to the clavicle. Care was taken not to damage thesupraclavicular nerve and the superior acromioclavicular joint ligaments. After identifying thefracture site, all hematoma and debris were removed. Then, we used a tenaculum bone clamp
to provide an efficacious reduction. The surgical methods are as follows.
Locking plate. We used an LCPTM (DePuy Synthes) or VariAx (Stryker) plate. The plate was
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secured to the clavicle once the reduction was confirmed. We filled the medial holes with both
locking and non-locking screws. Because the lateral fragment was often small and vulnerable,
as much as possible, we inserted screws into the distal fragment. We confirmed proper hardware
placement in that the plate did not cross over the acromioclavicular joint and that all screws
remained extra-articular on the fluoroscopic image.
Hook plate. We used an LCP (DePuy Synthes) plate. Without opening the acromioclavicular(AC) joint, the joint’s location was marked with a needle and confirmed by fluoroscopy. We
removed the dorsal soft tissue of the AC joint. An appropriate depth of plate was used and passed
below the acromion. The shaft of the plate was placed on the superior aspect of the clavicle andchecked for alignment. A deeper hook was used in case of difficulty lowering the plate shaft
onto the clavicle. The clavicle portion of the plate was slightly bent to ensure central placementof the plate on the clavicle. The plate was then secured to the shaft with 3.5-mm cortical screws
approximating the clavicle’s plate. For either surgical method, once we were satisfied with the
reduction and hardware placement, the wound was closed in layers. Drains were not used.
Aftercare
Patients were treated for about two weeks by use of a sling to allow for range-of-motion
exercises. In both groups, active mobilization was allowed postoperatively. In Group L, full rangeof motion was allowed from 4 weeks postoperatively. In Group H, the postoperative elevation
was limited to 90°, and full range of motion was allowed after plate removal. The implant wasremoved from all patients after bone union was confirmed.
Data evaluation
We evaluated the UCLA score at three and six months after surgery and at the final follow-up.
The UCLA score system mainly grades five aspects: pain, function, active forward flexion, manualmuscle testing, and patient satisfaction. The scoring standard has a maximum of 35 points (bestpossible outcome). There is no reported minimum clinically important difference for the UCLA
score for clavicle fractures. However, the minimum clinically important difference for proximal
humerus fractures was reported to be 2–2.4 points.13
We defined contracture, impingement, superficial and deep infections, scar problems, nonunion,
reduction-loss, migration, and screw back-out as complications referring to previous reports.6-12,14
Complications were collected from the electronic medical charts. We also compared the frequency
of complications. Plate migration is defined as an obvious loss of reduction or plate breakage.
As for hook plates, complications include radiographic evidence of osteolysis of the acromion
around the hook.15
Radiographic analysis
Radiographic data were obtained by reading the computerized radiographic images available
in the computer system of each institution. All patients underwent an X-ray before surgery for
determination of the type of fracture according to the Neer classification. The radiographic evaluation comprised the analysis of conventional radiographic frontal views. We defined dislocation
as the distance between the inferior rim of the proximal end and the superior rim of the distal
end of the clavicle.16 We defined the inferior cortex length of the distal fragment as the fragment
size.17 We obtained an X-ray at three and six months after surgery and at the final follow-up
to confirm bone union.
Each measurement was taken twice at a two-week interval by one orthopedic surgeon (HT),and the final measurement was the average of the two values. Intraobserver reliability wasmeasured using Cohen’s kappa value and intraclass correlation coefficient. Intraobserver reliability
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Fixation for distal clavicle fractures

was found to be good (Cohen’ kappa = 0.90, 95% confidence interval = 0.88–0.92, intraclasscorrelation coefficient = 0.931, 95% confidence interval = 0.88–0.97).
Statistical analysis
We used propensity score matching to mitigate the effects of confounding. When using
propensity scores, we selected sex, age, body mass index, ASA Physical Status Classification
System, Neer type, displacement, and fragment size as confounding factors referred to in previous studies.18,19 We evaluated differences between the two groups using the Student t-test andMann-Whitney U test for the continuous variables and Fisher’s exact test for the categoricalvariables. P <0.05 was considered to indicate significance. We used EZR software version 1.40
(Jichi Medical School, Tochigi, Japan) for statistical analysis.
We used the results from a prior study to assume sample size using power analysis, whichsuggested a 3-point difference in the UCLA score. The standard deviation was 3.0. This resulted
in 22 patients being required in each group.20

RESULTSGroup L included 114 patients, and Group H included 64 patients (Table 1). After propensity
score matching, Group L and Group H included 49 patients each (Figure 1; Table 2). There wereno statistically significant differences between the two groups. Plate removal was performed in
all cases, and the average hardware removal period was shorter for Group H than for Group L.
There was no statistically significant difference in the operation time for open reduction andinternal fixation between the two groups (Group L, 92 min vs Group H, 85 min; P = 0.15).
Figure 2 shows the values of the UCLA score at three and six months and at the last follow-up.
The UCLA score in Group L was higher than that in Group H at each follow-up point (median

Table 2

Study group demographics

Characteristic

Group LGroup HP Value

Number, n

49

49

Sex (M/F), n (%)

44 (89.8)/5 (10.2)

43 (87.8)/6 (12.2)

1Age, years (SD)43.4 (12.7)

45.9 (15.1)

0.379

BMI, kg/m (SD)22.0 (3.4)

21.9 (2.5)

0.951

ASA (I/II/III/IV),n (%)

38 (77.6)/7 (14.3)/3 (6.1)/1 (2.0)

33 (67.3)/14 (28.6)/2 (4.1)/0 (0)0.226Neer type (II/V),n (%)

42 (85.7)/7 (14.3)

42 (85.7)/7 (14.3)

1

Operative time,min (SD)

92 (32.2)

85 (34.4)

0.147

Follow-up period,
months (range)

12.9 (6–22)

9.0 (6–23)

2

Hardware removal, 13.0 (6.4–15.1)
months (range)

8.9 (6.4–12.4)

BMI: body mass index
ASA: American Society of Anesthesiologists Physical Status Classification System
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Hiroshi Takahashi et al

Fig. 2

Box plots of UCLA score at 3 and 6 months after surgery andat the final follow-up visit for both groups
Each box represents the 25th and 75th percentiles, and lines within the boxes represent the median. Crosses inthe boxes represent the mean, and whisker bars represent the 10th and 90th percentiles.
*P <0.05

Table 3
Score
Category Group L
Pain

UCLA shoulder scores at three and six months and at last follow-up

3 months
Group H

6 months
P value Group L

8.00
8.00
0.076
[4.00, 10.00] [1.00, 10.00]

Group H

Last follow-up
P value Group L

Group HP value

10.00
10.00
0.008*[6.00, 10.00] [2.00, 10.00]

10.00
10.00
0.067
[8.00, 10.00] [2.00, 10.00]

Function 10.00
8.00<0.001* 10.00
10.00
0.001*[6.00, 10.00] [4.00, 10.00][8.00, 10.00] [4.00, 10.00]

10.00
10.00
0.021*[8.00, 10.00] [8.00, 10.00]

Activeforwardflexion

5.00[2.00, 5.00]

3.00[2.00, 5.00]<0.001* 5.00
[3.00, 5.00]

4.00[2.00, 5.00]<0.001* 5.00
[4.00, 5.00]

5.00[3.00, 5.00]

0.212

Manualmuscletesting

5.00[4.00, 5.00]

5.00[2.00, 5.00]

0.007*

5.00[4.00, 5.00]

5.00[3.00, 5.00]

0.001*

5.00[4.00, 5.00]

5.00[3.00, 5.00]

0.044*

Satisfac- 5.00
tion
[0.00, 5.00]

5.00[0.00, 5.00]<0.001* 5.00
[0.00, 5.00]

5.00[0.00, 5.00]

0.004*

5.00[0.00, 5.00]

5.00[0.00, 5.00]

0.156*Indicates statistical significance (p <0.05)

at 3 months, 6 months, and last follow-up: 33 vs 27, P <0.001; 35 vs 30.5, P <0.001; and 35
vs 35, P = 0.03, respectively). Table 3 shows the UCLA subscale scores for pain, function,
active forward flexion, manual muscle testing, and patient satisfaction in both groups. All values
except the pain subscale in Group L were significantly better than those in Group H up to 6
months after surgery. Group L values for the subscales of function and manual muscle testing
were higher than those in Group H to the last follow-up.
We confirmed bone union in all patients in Group L. However, we could not confirm bone
union in three patients (6.1%) in Group H (P = 0.24), and these fractures were all Neer classification type II.
Table 4 shows the incidence of complications related to the two implant types. No statisticallysignificant differences were observed except for plate migration between the two groups. Plate
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Table 4Complications in the two groups

Complication

Group LGroup H

Number, n

49

49

P value

Impingement, n (%)

0 (0.0)4 (8.2)

0.117

Infection, n (%)

4 (8.2)3 (6.1)

1

Scar problem, n (%)

0 (0)1 (2.0)

1

Reduction loss, n (%)

0 (0)3 (6.1

0.242

Plate migration, n (%)

0 (0)9 (18.4)

0.003*

Screw backout, n (%)

1 (2.0)2 (4.1)

1

Re-operation, n (%)

2 (4.1)1 (2.0)1

L: locking plate
H: hook plate*Indicates statistical significance (p <0.05)

migration was observed in nine patients (18.4%) in Group H but in no patients in Group L.

DISCUSSION
The ideal surgical management of distal clavicle fractures continues to be controversial. We
compared the postoperative results of the locking plate and the hook plate for distal clavicle
fracture repair in terms of clinical outcomes, bone union, and the incidence of complications.
Clinical outcomes
As for clinical outcomes, as shown in Figure 2, the UCLA scores indicated that the hook plategroup performed worse than the locking plate group at three months, six months, and at the last
follow-up. A meta-analysis reported that compared with the locking plate, the hook plate for thetreatment of distal clavicle fractures was associated with worse recovery of shoulder function.6
We showed that the clinical outcomes in the patients with hook plates were worse than thosein the patients with locking plates. We assume that the irritation of bone and soft tissue by
the hooks affects the clinical outcome. In a morphometric analysis study, the hook penetrated
the synovial bursa in 89% of the specimens, was in contact with the supraspinatus muscle in
60%, and came into contact with the acromion after inserting the hook plate in 60%. The space
under the scapula narrowed, causing an increase in synovial bursa pressure.21 The presence ofthe hook plate restricts rotation of the large tuberosity of the humerus, and direct collision withthe large tuberosity can stimulate and damage the supraspinatus muscle, resulting in pain andweakness.22 A finite element analysis also showed that the force generated by the hook plate
was concentrated on the acromion’s lower surface.23 In addition, the compression force can leadto local inflammatory stimulation of soft tissue.24
Rehabilitation progress was slower in the hook plate group. We speculated that rehabilitation
might not proceed as expected due to the reduced opportunity for the patient to move the shoulder joint, causing contracture of the shoulder joint and, eventually, dysfunction. Therefore, we
considered that the pain remained, range of motion was impaired, and muscle strength decreased,
which eventually led to the decrease in patient satisfaction. In contrast, locking plates provide
excellent fixation of bone fragments but do not contribute to AC joint stability. The treatment
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Hiroshi Takahashi et alof Neer type II distal clavicle fractures with a titanium cable plus a locking plate has a good
curative effect, few complications, and good postoperative recovery.25 Further studies are required
to evaluate the efficacy of additional ligament reconstruction.
Bone union
Our results regarding bone union were similar to those of several previous studies. No
significant difference was found between the locking plate and hook plate groups in the rate ofbone union.24 Another systematic review showed there to be no statistically significant difference
between the groups in terms of the occurrence of delayed union.25 Further, a biomechanicalstudy showed no significant difference in the strength of fixation between the locking plate andhook plate.26
Complications between the two plate types
Among the complications, only plate migration was significantly more common in Group
H. The nonunion present in the 3 patients (6.1%) in Group H may have been due to slightly
inferior fixation. The design of the hook plate maintains the typical stability of the AC joint,
which means that the stability of the hook plate depends on the stability of the AC joint. The
movement of the AC joint causes rotation of the scapula and clavicle. Biomechanical studies
have shown that scapular and clavicular rotations are relatively small until the humerus reaches
approximately 90° of elevation. However, when the upper humerus reaches 150°, the clavicle’s
posterior rotation increases to 27°, and the elevation increases to 21°.27 The rotation and elevation
occurring during arm elevation cause subacromial hook movement. However, shoulder arthroscopy
has shown that the subacromial hook appears to move under the acromion at the same time thatthe shoulder joint raised.28 When the scapula and clavicle rotate, movement of the hook occurs.
Strengths and limitations
The strength of this study was the use of propensity score matching, by which the patient
backgrounds were matched for sex, age, body mass index, ASA Physical Status Classification
System and Neer type. Our study had several limitations. First, there remained unmeasured
confounding factors after using the propensity score-matching method. Second, our subjects
included only a single race, Asians, whose average height and weight are relatively small. Third,
we did not evaluate rotator cuff injuries with imaging, ultrasonography, or magnetic resonanceimaging. Fourth, we did not evaluate conservative treatment. Asymptomatic nonunion does notappear to adversely affect the functional outcome in the medium term.28 Fifth, assessment of the
AC joint including instability is not available at all institutions. Sixth, we obtained the informationon complications only from the medical chart; thus, observer bias may be present. Seventh, toinclude the effect of implant removal in this study, the timing of removal of the implant may
have affected the clinical results.

CONCLUSION
We compared postoperative results between the locking plate and hook plate for distal clavicle
fractures after propensity score matching. The postoperative UCLA score was significantly worsein the hook plate group than the locking plate group. We recommend the locking plate as asurgical treatment for distal clavicle fractures.

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Fixation for distal clavicle fractures

ACKNOWLEDGMENTS
We thank Dr Yuki Saito, Dr Ryosuke Sugimoto, Dr Takuya Sugimoto, Dr Yujiro Kagami,
Dr Toshifumi Omichi, Dr Hidenori Inoue, Dr Tokumi Kanemura, Dr Masahiro Hanabayashi, Dr
Osamu Ito, Dr Yasuhide Kanayama, Dr Koji Maruyama, Dr Hiroaki Yoshida, Dr Nobuyuki Okui,
Dr Tadahiro Sakai and Dr Toshihiro Ando for data collection.

CONFLICT OF INTEREST
The authors declare no conflicts of interest.

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