415

ORIGINAL
Differences in incidence rate and onset timing of undiagnosed
finger symptom among shoulder surgeries related tocomplex regional pain syndrome
Jun Kawamataa, Naoki Suenagab, Naomi Oizumib, Hisashi Matsumotoc, Akira Kikuchid, and Masataka Inouee
Department of Orthopaedic Surgery, Kaisei Hospital, Hokkaido, Japan, bUpper Extremity Center of Joint Replacement and Endoscopic Surgery, Hokushin Orthopaedic Hospital, Hokkaido , Japan, cDepartment of Rehabilitation, Hokushin Orthopaedic Hospital, Hokkaido, Japan,dDepartment of Rehabilitation, Koga Hospital, Hokkaido, Japan, eFaculty of Nursing, University of Kochi, Kochi, Japana

Abstract : The purpose of this study was to clarify the difference in onset timing and incidence of undiagnosed
finger symptom (UDFS) between various shoulder surgical procedures. In this study, UDFS symptoms included
the following four symptoms in the fingers ; edema, limited range-of-motion, skin color changes, and abnormal
sensations. UDFS cases were defined as those presenting with at least one UDFS. In result, the incidence rate of
UDFS cases was 7.1% overall (58 / 816 shoulders), 7.4% (32 / 432) in arthroscopic rotator cuff repair (ARCR), 9.0%
(11 / 122) in open rotator cuff repair (ORCR), 1.4% (2 / 145) in arthroscopic subacromial decompression (ASD), 13.2%(5 / 38) in open reduction and internal fixation (ORIF), 11.1% (3 / 27) in humeral head replacement, 4.8% (1 / 21) inanatomical total shoulder arthroplasty, and 12.9% (4 / 31) in reverse total shoulder arthroplasty cases. The Ratewas significantly higher with ARCR compared to ASD (p < .01). About onset timing in weeks postoperatively, theORIF group had a statistically earlier symptom onset than the Rotator cuff repair (ARCR + ORCR) group (2.4
weeks vs. 6.0 weeks, p < .01). When classifying the onset timing into before and after the removal of the abduction
pillow, the ORIF group showed a statistically higher rate of onset before brace removal than the Rotator cuff
repair groups (p < .01). Differences in UDFS among shoulder surgeries were demonstrated in this study. J. Med.
Invest. 70 : 415-422, August, 2023
Keywords : Complex regional pain syndrome (CRPS), Perioperative complications, Shoulder surgery, edema

INTRODUCTION
Complex regional pain syndrome (CRPS) is a serious complication of orthopedic surgeries that could lead to permanent
disability in the extremities. However, even now, details about
the pathophysiology, methods of prevention, and other aspects of
CRPS remain unknown. Several reports have shown high incidence rates of CRPS following shoulder surgeries (1-3).
However, only a few in depth studies have so far been conducted on CRPS after shoulder surgeries, and the target ofthese studies was limited to a single surgical procedure, suchas arthroscopic rotator cuff repair (ARCR) (3, 4) or subacromial
surgery (5).
Several factors are reportedly related to the onset of CRPS,
such as fracture (6), immobilization (7), joint contracture (3), andendothelial damage caused by the surgical incision (8). These
factors vary considerably among the different shoulder surgicalprocedures.
Therefore, we hypothesized that the onset timing and incidence rate might be different among different shoulder surgeries. To the best of our knowledge, however, no report has
indicated differences in incidence rates and onset timings of
CRPS among different surgical procedures.
Early diagnosis and treatment are important in the clinicalcourse of CRPS. However, to improve diagnostic specificity, theReceived for publication December 8, 2022 ; accepted June 16, 2023.
Address correspondence and reprint requests to Jun Kawamata, MD,
Department of Orthopaedic Surgery, Kaisei Hospital, 16-27 Minami2chome, Nishi23jo, Obihiro City, Hokkaido 080-2473, Japan andFax : +81-155-37-7202. E-mail : junkawamata@hotmail.com

current major diagnostic criteria for CRPS are based on thepresence of two or more suggestive symptoms (9, 10). In addition, the edema of the fingers also contributes to insufficiencyof activities of daily living in patients, and some cases result todevelop finger contracture. To detect CRPS at an early phase,
we defined undiagnosed finger symptom (UDFS) cases by thepresence of ≥ 1 of four UDFS (include edema, limited ROM, skincolor changes, and abnormal sensations) that are present at highrates in CRPS (11). The purpose of this study was to investigate
differences in onset timing and incidence rate of UDFS among
the various shoulder surgeries to verify our hypothesis.

MATERIALS AND METHODSThis research was approved by the institutional review boardsof the authors’ affiliated institutions. A prospective cohort study
was conducted at four private orthopedic hospitals. The included surgeries were ARCR, open rotator cuff repair (ORCR),
arthroscopic subacromial decompression (ASD), open reduction
and internal fixation (ORIF) for proximal humeral fracturewith intramedullary nailing, humeral head replacement (HHR),
anatomical total shoulder arthroplasty (TSA), and reverse total
shoulder arthroplasty (RSA). In consideration of the similarityof the surgical procedures, surgery for nonunion was treated as
ORIF in this study.
Between January 2018 and December 2019, these surgeries were performed on 922 shoulders in 877 patients by five
surgeons who had at least 20 years of experience in shoulder
surgery. Unified indications for each surgery were used by thesurgeons. We did not include surgeries for shoulder instability
because most of these patients were much younger than those

The Journal of Medical Investigation Vol. 70 2023

J. Kawamata, et al. UDFS in shoulder surgeries

416

who underwent other surgeries.
The patients were followed for 3 months after surgery toevaluate for the occurrence of UDFS, as described below. The
3-month follow-up period was based on a previous prospective
study that reported that the incidence rate of CRPS diminishedafter the first 3 months postoperatively (12). Among these 922
shoulders, we excluded 106 shoulders from the study for the following reasons : inadequate follow-up duration (< 3 months) in 90
shoulders, simultaneous wrist fracture on the same side in two,
severe general postoperative complications in four, and postoperative surgical site infection in one shoulder. We also excluded
nine cases with the preoperative presence of UDFS. None of the
816 included cases had a previous history of CRPS.
As a result, this study evaluated 816 shoulders in 783 patients.
The mean age at surgery was 65.9 years (range, 16–92 years).
The patients included 406 men and 410 women. Details about
their preoperative diagnoses and surgeries are presented inTable I.
In arthroscopic surgeries, we additionally performed capsularrelease if contractures were found by evaluation under anesthesia. In prosthetic surgeries for rotator cuff tear arthropathy(CTA), cuff reconstruction with muscle tendon transfers werealso performed (13). A systematic postoperative rehabilitation
program was conducted in all the patients according to theirdiagnosis and surgical procedure. In the program, the abduction
pillow fixation period was also defined by each surgery, as shownin Table II. In all the cases, finger, elbow, and scapular range-ofmotion (ROM) exercises were started on the day after surgery.
We defined UDFS by referencing Veldman’s report (11). On thebasis of the results of this report, we chose four objective finger
symptoms that present high incidence rates in the early phaseof CRPS, namely edema, limited ROM, skin color changes, andabnormal sensations. UDFS cases were defined as those presenting at least one UDFS.

Table I. The number of Patients’ diseases and surgical procedures
diseasen(shoulders)Surgicalproceduren(shoulders)

RCT

579

ARCR

432

IM

131

ORCR

122

Fracture

41

ASD

145

CTA

38

ORIF

38

OA

14

HHR

27

LOOSE

5

TSA

21

RA

4

RSA

31

NU

2

ON

1

CAD

1

Data are expressed as the number of shoulders. RCT, rotator cuff
tear. IM, impingement syndrome.
Fracture, fracture of proximal humerus. CTA, cuff tear arthritis.
OA, osteoarthritis of glenohumeral joint.
LOOSE, component loosening of prosthesis of shoulder joint. RA,
rheumatoid arthritis. NU, nonunion of proximal humerus fracture.
ON, osteonecrosis of humeral head. CAD, chronic anterior dislocation
ARCR, arthroscopic rotator cuff repair. ORCR, open rotator cuff
repair. ASD, arthroscopic subacromial decompression. ORIF, open
reduction and internal fixation for proximal humeral fracture withintramedullary nailing. HHR, humeral head replacement. TSA,
anatomical total shoulder arthroplasty. RSA, reverse total shoulder
arthroplasty.

Table II. Postoperative rehabilitation programs
Surgical procedurestartshoulder ROM

Abduction pillow
fixation period

ASD

1 day

2 days

ARCR / ORCR

1 day-2 weeks

6-8 weeks

HHR

2-4 weeks

8 weeks

ORIF

1-2 weeks

4-6 weeks

TSA

1 day

2 weeks

RSA

2-4 weeks

4-6 weeks

ARCR, arthroscopic rotator cuff repair. ORCR, open rotator cuff
repair. ASD, arthroscopic subacromial decompression. ORIF, open
reduction and internal fixation for proximal humeral fracture withintramedullary nailing. HHR, humeral head replacement. TSA,
anatomical total shoulder arthroplasty. RSA, reverse total shoulder
arthroplasty.

All the cases were observed for the occurrence of UDFS for
3 months postoperatively. In the UDFS cases, the number andonset timing of positive symptoms were recorded. Patient factors(age, sex, history of previous shoulder surgeries, and fracture or
non-fracture) were investigated in all the cases. In the fracture
cases, the interval between the fracture and surgery was also
investigated. The preoperative Constant score for pain (graded,
No ; 15 pts, Mild pain ; 10 pts, Moderate ; 5 pts, Severe or permanent ; 0.) and ROM of the shoulder (active flexion and externalrotation) was also evaluated in all the cases except those with afracture, chronic anterior dislocation, and traumatic rotator cuff
tear, because these patients could not move their shoulder due tothe presence of severe pain.

Statistical analysis
The individual factors were statistically evaluated between
the UDFS cases (group U) and non-UDFS cases (group N). In
the fracture cases, the time period between the fracture andsurgery was evaluated as a risk factor. In the arthroscopic surgeries (ARCR + ASD), the addition of capsule release was also
evaluated as a risk factor.
To clarify the factors affecting the incidence rate of UDFS,
incidence rates were compared among several subgroups of thesurgical procedures. The ARCR and ASD groups were compared
to determine the difference between arthroscopic surgeries, and
the ARCR and ORCR groups were compared to determine thedifference between the two rotator cuff repair procedures. The
TSA, RSA, and HHR groups were compared to determine thedifference in terms of the various prosthetic replacements performed ; acute fracture cases were excluded from the comparison
to eliminate the effects of the fracture, as already reported (14).
For assessment of the onset timing of the UDFS, patientswere grouped as the ORIF group, rotator cuff repair (RCR)
group (ARCR + ORCR), and prosthesis replacement group(TSA + HHR + RSA) for comparison.
The Mann–Whitney U test was used for analysis of quantitative data and Fisher’s exact probability test was used for categorical data. A multi-group comparison and Bonferroni correction
were used for comparison of the results in ≥ 3 groups. We set 5%
as the level of significance. Logistic regression analysis was usedin the comparison between groups C and N, to determine thecorrelation between individual factors and UDFS.
All the statistical analyses were performed with EZR (Saitama
Medical Center, Jichi Medical University, Saitama, Japan),which is a graphical user interface for R (The R Foundation for
Statistical Computing, Vienna, Austria).

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The Journal of Medical Investigation Vol. 70 August 2023
RESULTSThe overall incidence rate of UDFS cases was 7.1% (58 / 816
shoulders). Table III shows the incidence rates of each surgery.
A high rate of UDFS cases was observed in the ORIF and RSA
groups, which included relatively many fracture cases.
The symptoms appeared at a median of 5.5 weeks (range,
1.7–10.0 weeks) after surgery. Edema was present in almost all
the cases. In contrast, skin color changes and abnormal sensations were present in only a few patients (Figure 1). Except for
the two patients who were lost to follow-up before attaining cure,complete disappearance of the symptoms was confirmed in all

the patients who presented with UDFS, although the timing ofsymptom resolution was not clarified in some patients with along interval between follow-up visits to the hospital.
Regarding individual risk factors, no statistically significant
differences were found between groups U and N (Table IV). The
mean (± SD) preoperative interval between the injury and surgery in fracture cases did not differ significantly between UDFS
and non-UDFS cases (22.3 ± 29.4 days vs. 12.1 ± 16.9 days, p= .09). In arthroscopic surgeries, addition of capsule release did
not prove to be a risk factor for UDFS (odds ratio (OR), 1.51 ; 95%
confidence interval (CI), 0.57–3.57 ; p = .35). In the comparison of incidence rates between the different procedures, theTable III. Incidence rate and onset timing of UDFS
fracture case UDFS cases(shoulders)(shoulders)

onset timing(weeks)

ARCR (n = 432)-

32 (7.4%)

6.0 (2.0-10.0)

ORCR (n = 122)-

11 (9.0%)

7.6 (2.0-10.0)

ASD (n = 145)-

2 (1.4%)2.7 (1.7-3.7)

ORIF (n = 38)

36

5 (13.2%)

2.4 (2.0-3.7)

HHR (n = 27)-

3 (11.1%)

8.0 (2.0-8.0)

TSA (n = 21)-

1 (4.8%)

2.6

RSA (n = 31)

5

4 (12.9%)

3.65 (1.7-6.7)

total (n = 816)41

58 (7.1%)

5.5 (1.7-10.0)

ARCR, arthroscopic rotator cuff repair. ORCR, open rotator cuff
repair. ASD, arthroscopic subacromial decompression. ORIF, open
reduction and internal fixation for proximal humeral fracturewith intramedullary nailing. HHR, humeral head replacement.
TSA, anatomical total shoulder arthroplasty. RSA, reverse total shoulder arthroplasty. fracture case and UDFS cases wereexpressed as the number of shoulders (%). Onset timing were expressed as the number of post operative weeks of median (range).

Figure 1. Incidence rates of the four UDFS

ROM, range of motion. The data represent the number of shoulders.

Table IV. Multivariable analysis of preoperative epidemiologic data within each group (Group U vs. Group N)
VariableGroup U(n = 58)

Group N(n = 763)

OR(95%CI)

P valueAge (yr)67.7 ± 9.5

65.8 ± 11.0

0.99
(0.97-1.02)

.64

1.01
(0.64-2.09)

.62

sex
Male

29 (50.0%)377 (49.7%)

Female29 (50.0%)381 (50.3%)

Constant pain score (points)

4.7 ± 4.2

6.1 ± 4.0

1.04
(0.96-1.11).34

Active flexion

137.0 ± 28.5

137.2 ± 30.7

1.00
(0.99-1.01).64

External rotation

44.4 ± 18.0

46.5 ± 19.7

1.01
(0.99-1.02).52

History of shoulder surgery

10 (17.2%)

129 (17.0%)

1.02(0.48-2.18).96

fracture case

7 (12.0%)34 (4.5%)120000(0-inf).99

ROM (degrees)OR, odds ratio. CI, confidence interval.
Data are expressed as the number of shoulders (%) or as the mean ± standard deviation. (*P < .05) No individual
risk factor detected (even in the method of forward-backward stepwise selection method).

J. Kawamata, et al. UDFS in shoulder surgeries

418

incidence rate of UDFS was significantly higher in the ARCR
group than the ASD group (ARCR, 32 shoulders (7.4%) ; ASD,
2 (1.4%) ; OR, 5.7 ; 95%CI, 1.4-49.8 ; p = .007) (Table V). No significant differences were found between the ARCR and ORCR
groups (Table VI). Further, no significant differences were foundbetween the HHR, TSA, and RSA groups (Table VII).
Regarding the onset timing of UDFS, the ORIF group hada statistically significantly earlier onset of symptoms than the
RCR group (ARCR + ORCR) (Figure 2 ; Table VIII). Whenclassifying the onset timing into before and after brace removal,
the ORIF group showed a statistically higher rate of symptom
onset before brace removal than the RCR group. The onset timeof UDFS was not significantly different between the prosthetics
group as compared to the other two groups (Table VIII).

Table V. Preoperative epidemiologic data and incidence rate within each group (ARCR vs ASD)
Variable

ARCR(n = 432)

ASD(n = 145)

P valueAge (yr)65.3 ± 9.8

60.6 ± 11.8

< .001*

sex

.56

Male

221 (51.1%)

70 (48.3%)

Female211 (48.9%)

75 (51.7%)

6.5 ± 3.7

5.1 ± 4.2.001*

Active flexion

144.4 ± 25.5

128.9 ± 29.0

< .001*

External rotation

50.6 ± 17.3

39.7 ± 20.2

< .001*

History of shoulder surgery

75 (17.4%)

21 (15.3%).60

Variable

ARCR(n = 432)

ASD(n = 145)

OR(95%CI)

P value

UDFS cases (%)

32 (7.4%)

2 (1.4%)5.7(1.4-49.8).007*

Constant pain score (points)
ROM (degrees)CI, confidence interval
ARCR, arthroscopic rotator cuff repair.
ASD, arthroscopic subacromial decompression.
Data are expressed as the number of shoulders (%) or as the mean ± standard deviation. (*P < .05)

Table VI. Preoperative epidemiologic data and incidence rate within each group (ARCR vs ORCR)
Variable

ARCR(n = 432)

ORCR(n = 122)

P valueAge (yr)65.3 ± 9.8

67.1 ± 0.9

.07

sex

.01*

Male

221 (51.1%)

84 (68.9%)

Female211 (48.9%)

38 (31.1%)

6.5 ± 3.7

6.5 ± 0.4.79

Constant pain score (points)
ROM (degrees)
Active flexion

144.4 ± 25.5

135.2 ± 3.0.006*External rotation

50.6 ± 17.3

46.0 ± 1.7.02*

History of shoulder surgery

75 (17.4%)

19 (15.6%).67

Variable

ARCR(n = 432)

ORCR(n = 122)

OR(95%CI)

P value

UDFS cases (%)

32 (7.4%)

11 (9.0%)0.80 (0.38-1.83).56

CI, confidence interval. SMD, standardized mean difference
ARCR, arthroscopic rotator cuff repair.
ORCR, open rotator cuff repair.
Data are expressed as the number of shoulders (%) or as the mean ± standard deviation. (*P < .05)

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The Journal of Medical Investigation Vol. 70 August 2023
Table VII. Multiple comparison of preoperative epidemiologic data and incidence rate within each group (HHR vs. TSA vs. RSA)
Variable

HHR (n = 27) TSA (n = 21)

Age (yr)

P value

RSA (n = 26)
HHR vs TSA

HHR vs RSA

TSA vs RSA.12< .001*

.008*

.07

.57

.33

.40

.23

68.9 ± 1.5

73.0 ± 2.4

81.6 ± 6.7

Male

12 (44.4%)

4 (19.0%)

9 (34.6%)

Female15 (55.6%)

17 (81.0%)

17 (65.4%)

Constant painscore (points)

5.7 ± 0.8

3.1 ± 0.8

4.8 ± 4.7

.02

sex

ROM (degrees)
Active flexion

135.9 ± 4.7

108.3 ± 7.6

105.8 ± 44.0

.004*

.008*

.94

External rotation

45.0 ± 3.9

33.1 ± 5.3

30.4 ± 21.1

.08

.008*

.56

History of shoulder
surgery

5 (18.5%)

9 (42.9%)

12 (46.2%)

.11

.04

1.00

Variable

HHR (n = 27) TSA (n = 21)

UDFS cases (%)

3 (11.1%)

1 (4.8%)

RSA (n = 26)

2 (7.7%)

HHRvsTSA
OR(95%CI)
0.41(<  0.01-5.53)

HHRvsRSAP valueOR(95%CI).62

0.67(0.05-6.42)

TSAvsRSAP valueOR(95%CI)

P value

1.00

1.65(0.08-103.11)

1.00

CI, confidence interval. SMD, standardized mean difference. HHR, humeral head replacement. TSA, anatomical total shoulder arthroplasty.
RSA, reverse total shoulder arthroplasty. Data are expressed as the number of shoulders (%) or as the mean ± standard deviation. (*P < .0167
after Bonferroni correction)

Figure 2. Box-and-whisker plot depicting the onset times of UDFS
RCR, rotator cuff repair. ORIF, open reduction and internal fixation.
(*P < .0167 after Bonferroni correction).

Table VIII. Onset timing of each group of UDFS
Variable

Postoperative weeks

RCR (n = 43)

6.0 (2.0-10.0)

ORIF (n = 5)

2.4 (2.0-3.7)

P value

Prosthesis (n = 8)

3.8 (1.7-8.0)

Relation to brace removal
Before brace removal

14 (32.6%)

5 (100%)4 (50.0%)

After brace removal

29 (67.4%)

04 (50.0%)

RCRvsORIF

RCRvs
Prosthesis

ORIFvs
Prosthesis

.002*

.11

.38

< .001*.43.11

RCR, rotator cuff repair. ORIF, open reduction and internal fixation.
Data are expressed as the number of weeks of median (range).
Incidence rate are expressed the number of shoulders (%). (*P < .0167 after Bonferroni correction)

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J. Kawamata, et al. UDFS in shoulder surgeries

DISCUSSION
In this study, we clarified the differences in incidence rates
and onset timings of UDFS among various shoulder surgeries.
The incidence rate of CRPS has been reported in several studies
as 0.9%–2.9% in upper extremity surgeries (15-17), 1%–8.2% following ARCR (1, 18), and 13.7% following subacromial shoulder
surgery (5). Tanesue reported that the incidence rate of CRPS
after ARCR was 0.5-24.2% in Japanese people (4).
Many reports used the criteria for diagnosis of CRPS as thepresence of > 2 of the four UDFS assessed in our study (2, 9, 10).
These criteria have been shown to have a high specificity formaking a diagnosis of CRPS. On the other hand, use of these criteria might lead to a delay in diagnosis because patients usuallyshow only one symptom in the early stages of CRPS.
Regarding the clinical course of CRPS, Varitimidis et al.
reported that the acute phase of the syndrome was reversed(19). De Mos reported a poor outcome in a patient with CRPS
who presented a high number of symptoms (20). These reportssuggest that early detection and therapeutic intervention are
obviously important to improve the clinical course of CRPS.
Therefore, in this study, we defined UDFS cases as the presence of at least one symptom, to facilitate the early detectionof UDFS cases. Using the current, more sensitive criteria, theoverall incidence rate of UDFS cases in this study was 7.1%,
although this would probably have been lower if we had applied
other criteria of ≥ 2 positive symptoms.
The reason for the lower incidence rate of UDFS cases in ourstudy is not clear, but our systematic postoperative care could
have affected this result. We typically use cryotherapy with anicing machine for pain relief during the early postoperative period (21). We also use interscalene brachial plexus block to control
pain, adding dexamethasone to prolong the duration of the nerve
block to > 24 hours after surgery (22). As part of the rehabilitation program, we start ROM exercises of the scapula, elbow,
and finger soon after surgery. These interventions could havecontributed to preventing UDFS in the majority of our patients.
Previous studies reported that the individual factors related to
CRPS were age (23), female sex (10, 24), preoperative pain (25),preoperative contracture (3), and fracture (6). In our investigation, none of these factors was statistically significantly different
between groups U and N. Further, although the odds ratio fordeveloping UDFS was extremely high in patients with fractures,no significant difference was found in logistic regression analysis, probably because the sample size was too small.
Guo reported that tibial fractures with 4 weeks of cast immobilization induced CRPS-like changes in rats (7). This suggeststhat preoperative immobilization might be a risk factor for
CRPS, which could be one of the causes of the high incidence
rate of CRPS in fracture cases. Moreover, we hypothesized thatthe waiting period in fracture cases might relate to the onset of
CRPS ; however, we found no significant correlation between
the duration of the preoperative period and the development of
CRPS.
In the present study, ARCR cases had a higher incidence rateof UDFS than ASD cases. In a previous study, preoperative contracture was reported to be a risk factor for CRPS (3) ; however,no significant differences in preoperative ROM and the additionof a capsule release procedure were found between the two surgical procedures. Other factors that would likely be different
between the two surgical methods would be operation time,
postoperative pain due to rotator cuff traction, etc. ; however,
the most considerable difference observed between ARCR and
ASD cases in our study was the brace fixation duration (Table
II), which might explain the high percentage of ARCR cases thatshowed UDFS after brace removal.

During the brace fixation period, mechanical stimulation of
the bone by the skeletal muscle might decrease, resulting in neuropathy of the extremity. Terkelsen et al. reported that immobilization of healthy upper extremities for 4 weeks induced increases
in the levels of inflammatory mediators (IL-1β, IL-6, and TNF-α)and similar clinical changes (allodynia, temperature changes,
and edema) as those elicited by limb fracture with casting (26).
Therefore, the longer immobilization period might have induced
the UDFS in the ARCR group.
In contrast, the incidence rate of UDFS did not differ significantly between ARCR and ORCR patients. Regarding the pathophysiology of CRPS, Groeneweg et al. reported that endothelial
damage caused by surgical incision triggers vasoconstrictionthat induces CRPS (7, 8). On the other hand, Mertz et al. reported
no significant difference in the incidence rate of CRPS between
endoscopic and open release procedures for carpal tunnel release (24). In their retrospective cohort study on distal radial
fractures, Wang et al. reported that use of a volar locking plate
lowered the incidence rate of CRPS as compared with external
fixation (27). These reports indicate that skin incision is notnecessarily related to the development of CRPS type1. However,cutaneous nerve injury generates CRPS type 2. Therefore, we
make a skin incision from the acromion to the outside of thecoracoid process when performing shoulder surgeries to reduce
the risk of cutaneous neuropathy.
Moreover, we found no significant difference between thethree arthroplasties. In other words, no association was foundbetween the process of glenoid component insertion and UDFS.
Mortazavi et al. reported that compression damage to the maintrabecular structure, osteotomy, and hematoma formation
associated with the component caused an increase in the levelof inflammatory mediators, which might be involved in the development of CRPS (28). However, no previous studies compared
the incidence of CRPS between prosthetic surgeries with andwithout glenoid surfacing. We also could not deny the influenceof glenoid component insertion on the occurrence of CRPS due tothe small number of cases evaluated.
Amongst the various prosthetic surgical procedures, RSA has
a higher potential risk than TSA of causing nerve stretching
during surgery, which can induce CRPS (29). However, the present study showed no significant difference among the prosthetic
surgeries after exclusion of fracture cases. Additionally, theoverall incidence rate of UDFS was high in the ORIF and RSA
groups. This might indicate that the higher occurrence of UDFS
in these patients was due to the presence of fractures rather than
to the surgical procedure itself.
Considering the difference in onset timing between UDFS
following RCR and ORIF, the pathophysiology of CRPS might
have affected the difference. A longer period of brace fixation was
required in the postoperative treatment of RCR than ORIF. As
described earlier, postoperative immobilization might be one of
the causes of UDFS occurring immediately after brace removal.
However, the reason for the onset of symptoms after brace removal is still unclear. It is possible that brace removal with theshoulder in the drooping position leads to traction on the brachial
plexus and blood vessels, which in turn leads to poor circulationin the upper extremity, as is seen in thoracic outlet syndrome.
On the other hand, in fracture healing, the hematoma in theearly phase contains hematopoietic and immune cells (30), andcauses the local release of inflammatory mediators. The consequent local inflammation might induce UDFS in the early stage
after surgery. In addition, preoperative fracture immobilization
could be related to the onset of CRPS, as already stated (6). As
the pathophysiology of CRPS is still unknown, our discussion
about the onset timing of CRPS remains a hypothesis, andfurther studies are necessary to clarify the pathology of each

The Journal of Medical Investigation Vol. 70 August 2023
symptom. Our results might enable earlier diagnosis and therapeutic intervention for UDFS, especially after high-risk shoulder
surgeries, which will improve the prognosis and prevent progression to severe CRPS.

Limitations
The present study has several limitations. First, the numberof cases in each surgery group was small, although some of theresults were proved to be statistically significant. Second, because the study involved subjective evaluation by each surgeon,
the diagnosis of UDFS might have involved some bias. In the
future, symptoms should be diagnosed more objectively, for example, by thermographic recording of skin temperature (31) andthe pain-to-heat test with an air-pressure-controlled thermode(31). Third, this study included surgeries performed by multiple
surgeons. Lastly, there is a possibility that we did not accurately
detect the onset timing of UDFS because the patients were examined by the surgeons at certain intervals after surgery.
Future studies with longer follow-up will be useful for providing data on the correlation between the recovery period andfactors such as the surgical procedure, number of symptoms, andindividual characteristics of the patients.

CONCLUSION
In the present study, UDFS were observed in 7.1% of the cases
after various shoulder surgeries. The incidence rate of UDFS
was significantly higher following ARCR than ASD. ORIF wasassociated with a statistically earlier onset of UDFS than RCR.
These findings will be useful when considering the start ofphysiotherapy after shoulder surgeries from the perspective ofprevention of CRPS, and could contribute to the early detectionof and therapeutic intervention for CRPS.

CONFLICT OF INTEREST
All authors declare no conflicts of interests.

ACKNOWLEDGEMENT
The authors thank Shintaro Yamane, Chika Yoshioka, andTomoya Matsuhashi for contributing their cases to this study.
And authors would like to thank Yukiyoshi Hisada for his technical advices.

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