Pressure pain threshold and temporal summation in patients after musculoskeletal trauma in the upper limb: a cross-sectional study

Jéssica Xavier de Sá Morais¹, Luciane Fernanda Rodrigues Martinho Fernandes¹, Laura Vitória Sousa Silva¹, Laura Evangelista¹, Andrea Licre Pessina Gasparini¹, Marco Aurélio Sertório Grecco², Denise Martineli Rossi^1*

¹Institute of Health Sciences, Department of Applied Physiotherapy, Federal University of Triângulo Mineiro, Uberaba, MG, Brazil

²Department of Orthopedics and Traumatology, Federal University of Triângulo Mineiro, Uberaba, MG, Brazil.

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Abstract

Objective: This cross-sectional study aimed to compare pressure pain threshold and temporal summation in patients following acute musculoskeletal trauma at different sites of the upper limb and to investigate the association of these variables with a neuropathic component of pain.

Methods: Adults of both sexes with musculoskeletal trauma in the upper limb were included. Pain intensity, injury type and causes, and pain medication were collected. The pressure pain threshold assessment by a digital algometer in the upper trapezius and anterior tibial muscles, bilaterally, and Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) questionnaire were used.

Results: A total of 82 patients were evaluated, 24 with proximal injuries (proximal and shaft humerus, clavicle, scapula), 25 with elbow and forearm injuries, and 33 with distal injuries (distal forearm, wrist and hand). Injuries causes were traffic (45%), work (30%), domestic (17%, including falls from height) and others (8%). The pressure pain threshold was (F=7.71; p<0.01) lower in the proximal compared to elbow (p = 0.04; effect size = -0.76) and distal injuries (p =<0.01, effect size = -1.11) for the upper trapezius ipsilaterally to the injury side. There was a negative and weak correlation between this pressure pain threshold and LANSS (p = 0.03; r = -0.22).

Conclusion: Pressure pain threshold in the upper trapezius ipsilaterally to the affected side was lower in the proximal injuries compared to elbow, distal forearm, wrist and hand injuries. Decreased values of pressure pain threshold were associated to increased neuropathic component.

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Introduction

Musculoskeletal trauma, including fractures, has shown a 69% increase in prevalence from 1900 to 2019 across all ages groups, according to the Global Burden of Disease study^1. It is estimated that 973 million sustained injuries requiring medical attention, and among them, 38.5% experienced fractures^2. The growing prevalence of trauma-related musculoskeletal conditions has led to increase demand for rehabilitation services, raising public health costs and contributing to sick leave and disability.¹ Post-traumatic stress, pain distribution across the body map and pain intensity have been identified as important indicators of poor prognosis for chronic post-traumatic pain³. The incidence of chronic pain following musculoskeletal trauma may reach up to 86% within 84 months (7 years), and in approximately 30% of cases, it is associated with moderate to severe neuropathic pain⁴.

Assessing pain thresholds and temporal summation can provides insights into the underlying mechanisms of the pain experience^5. The pressure pain threshold (PPT), defined as the point at which a mechanical stimulus is perceived as painful, has demonstrated good to good to excellent reliability in participants with acute musculoskeletal trauma⁶.  Temporal summation, characterized by a progressive increase in pain response to repetitive stimuli (thermal or mechanical), also shows good to excellent reliability in this population⁶.

Lower heat pain thresholds and reduced pressure pain tolerance in areas such as the forearm, fingers, knee or calf, measured preoperatively, have been associated with greater postoperative analgesic consumption. ⁵  Additionally, lower pain thresholds uninjured tissues distal to the lesion may reflect increased sensitivity of the central nervous system to nociceptive stimuli, and acute global hypersensitivity, placing patients’ greater risk for developing persistent pain^7. However, it has also been suggested that pain sensitivity assessment alone may not capture the complex emotional and psychological dimensions of postoperative pain, since anxiety and psychological stress are also significant predictors of postoperative pain and increased analgesic use^5. It is well established that variables such as sex, age and sleep quality can influence PPT in patients with whiplash-associated disorders^7, as can anxiety, pain expectation and pain catastrophizing, particularly in the postoperative period of elective orthopedic surgery in children aged 6 and 16 years⁸.

Recent studies highlight the importance of evaluating pain mechanisms and screening for hypersensitivity components^9. As nociceptive pain (evoked by noxious stimulation of peripheral nociceptors (chemical, thermal or mechanical), pain perception proportional to nociceptive input; neuropathic pain that represents a neuroanatomical distribution in the face of injuries or diseases of the nervous system central or peripheral; and nociplastic pain associated with altered nociception, in which even without any clear evidence of real or potential tissue damage, there is activation of peripheral nociceptors in the absence of disease or injury to the somatosensory system¹⁰.

In a study with 1.000 patients, the neuropathic pain component was present in 43% of cases, significantly increasing pain intensity at rest and during movement, analgesics consumption (68% versus 54%), sleep disturbance (55 % vs. 35%) and sick leave. ⁹ Another study reported the presence of neuropathic pain in 8% to 13% of patients with chronic pain 3 and 6 months after total knee arthroplasty¹¹.

Fractures and musculoskeletal injuries often result in not only localized tissue damage but also alterations in pain processing that can extend beyond the site of injury. However, clinical assessment tools typically focus on structural damage and pain intensity, neglecting underlying alterations in pain modulation that may predispose individuals to chronic pain. The evaluation of PPT and temporal summation offers a window into this altered pain processing mechanisms, providing objective markers of peripheral and central sensitization. These measures are especially warranted in individuals with fractures, as this population is at increased risk for developing persistent pain due to both physical trauma and psychological stressors. Identifying changes in pain sensitivity early in the acute phase may allow for stratification of patients at risk for poor recovery and guide more targeted pain management and rehabilitation strategies. Given the complexity of the functional outcomes following musculoskeletal trauma and the involvement of different pain mechanisms (nociceptive and neuropathic), there remains a need to better understand the factors and mechanisms associated with pain perception in patients who experienced upper limb trauma. This cross-sectional study aimed to compare pressure pain threshold and temporal summation in patients following acute musculoskeletal trauma at different sites of the upper limb and to investigate the association of these variables with a neuropathic component of pain. We hypothesized that lower pressure pain thresholds in the upper trapezius would be observed in patients with injuries closer to the upper limb, and that lower thresholds and greater temporal summation responses would be associated with a higher LANSS scores, indicating a greater contribution of the neuropathic pain component.

Methods

Study design and participants

This cross-sectional study evaluated 82 patients at University Hospital between June 2023 and June 2024. All participants signed the written informed consent before data collection, and the Ethics Committee Committee of the Federal University of Triângulo Mineiro (protocol number: CAAE: 45528821.6.0000.5154) approved this study.

Inclusion criteria consisted of adults who were admitted to the hospital due to musculoskeletal trauma in different locals of the upper limb. Exclusion criteria were: central nervous system injury, polytrauma and previous long-term diseases as cancer.

Variables

Sociodemographic variables as age, sex (categorized as a biological attribute), body mass index, occupation. Clinical variables included: pain intensity measured by Numeric Pain Rating Scale (NPRS) ranging from 0 (no pain) and 10 (worst possible pain), injury cause as traffic, work, domestic (including falls from height) and sports, and injury type as fractures or complex injuries (including tendon, nerve and dislocations). Pain medication was also collected as non-steroidal anti-inflammatory drugs (NSAIDs) and opioids.

The Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) scale consists of 7 items in total containing a five-item domain on pain symptoms and two items involving sensory testing. The total score ranges from 0 to 24 points, where scores below 12 suggest pain with nociceptive predominance, while scores above 12 suggest pain with neuropathic predominance¹².

The Pittsburgh Sleep Quality Index (PSQI) was applied to assess sleep quality)^13. The questionnaire consists of 19 self-reported questions. The sum of the 7 component scores produces a global score, which varies from 0 to 21, where the highest score indicates worse sleep quality (Buysse et al., 1989). PSQI global score greater than 5 indicates great difficulties in at least 2 components or moderate difficulties in more than 3 components¹³.

Depression and anxiety were measured by the Hospital Anxiety and Depression Scale (HADS) has 14 items ranging from 0 to 21 points (15). This scale was validated and demonstrated reliability, with the intraclass correlation coefficient (ICC) for anxiety (0.46) and for depression (0.43)¹⁴. The kinesiophobia was assess by the Tampa Scale for Kinesiophobia (TSK) consisting of 17 items, with final score ranging from 17 to 68 points which higher scores reflect a greater level of kinesiophobia. This scale has been validated and shows excellent reliability¹⁵.

The pressure pain threshold assessment was carried out using a digital algometer (Wagner Instrument) in the upper trapezius and the anterior tibialis muscle, bilaterally. The pressure pain threshold was defined as the minimum amount of pressure that caused the onset of pain reported by the patient. Three measurements were taken at each point with an interstimulus interval of 30 seconds¹⁶.

The temporal summation assessment was performed through mechanical stimulation of the digital algometer in the region of the upper trapezius of the affected side for 10 times the average pressure previously measured, with an interesting interval of 1 second. Participants rated the pain intensity of the first and tenth stimulus using the NPRS. The temporal sum was measured after the assessment of the pressure pain threshold and the assessments had an interval of at least 2 minutes to ensure that there was no interference between tests.

Statistical analysis

The variables were presented as median (standard deviation) for continuous variables and frequency and percentage for categorical variables for descriptive purposes. The Shapiro-Wilk test was used to verify the normal distribution of continuous variables. Kruskal-Wallis was used to compare age, body mass index, LANSS, NPRS, PSQI and HADS among the groups. Chi-square Test or Fisher's exact Test (if the minimum expected value in any cell was < 5) were used to determine if there was statistically significant difference in proportions among groups. The Analysis of covariance (ANCOVA) was used to compare the pressure pain threshold among the groups considering sex, LANSS, PSQI and HADS variables. Spearman’s rank correlation coefficient (ρ) was used to assess the strength and direction of the association between variables. The magnitude of the correlation was interpreted as follows: values between 0.00–0.39 weak, 0.40–0.79 moderate, and 0.80–1.00 strong. Negative values indicated inverse relationships. Statistical significance was set at p < 0.05.

Results

A total of 82 patients were evaluated in this study (Table 1): 24 had proximal injuries (proximal humerus, humerus shaft, clavicle, scapula), 25 patients had injuries around the elbow joint and 33 patients had distal injuries, including distal forearm, wrist and hand injuries. Fractures were the most common injury type. A statistically significant difference was found for complex injuries (involving tendons, nerves, or dislocations), which were more prevalent in distal upper limb injuries (χ²= 0.03) (Table 1). Regarding occupation, 69% of the sample were handyman, 16% administrative workers, 8% housewives, and 7% classified as others (including retiree, students, unemployed). Regarding injury cause, 45% were related to traffic accidents, 30% to work incidents, 17% to domestic accidents (including falls from height), and 8% to other causes (e.g., sports and violence). Psychological variables were not different among the groups (Table 1).

Table 1: Sociodemographic and clinical characteristics (n = 82).

Variables	Proximal (n=24)	Elbow (n = 25)	Distal (n = 33)	p value
Age (years)	42.4 (14.32)	41.7 (16.9)	41.1 (15.2)	0.83
BMI (kg/m2)	27.4 (6.7)	27.7 (5.6)	27.1 (7.0)	0.77
Sex:
Men, n (%)	16 (67%)	23 (92%)	28 (85%)	0.14
Women, n (%)	8 (33%)	2 (8%)	5 (15%)
Injuries type:
Fracture	20 (83%)	23 (92%)	21 (64%)	0.03
Complex injuries	4 (17%)	2 (8%)	12 (36%)*
Pain intensity by NPRS (0-10)	4.6 (2.9)	3.2 (2.3)	4.1 (3.1)	0.25
LANSS (0-24)	16.7 (11.4)	13.4 (11.0)	14.6 (11.3)	0.66
PSQI (0-21)	8.3 (3.4)	9.7 (3.8)	9.0 (4.2)	0.48
HADS (0-21)	11.2 (6.1)	10.5 (5.8)	11.6 (6.2)	0.81
TSK	40.5 (7.4)	38.2 (5.2)	40.4 (7.9)	0.42
Pain medication
NSAIDs	3 (16%)	0 (0%)	2 (10%)	0.07
Opioids: Tramadol	2 (10%)	0 (0%)	4 (21%)
Opioids: Morphine	3 (16%)	0 (0%)	2 (10%)
NSAIDs + Tramadol	4 (21%)	8 (40%)	4 (21%)
NSAIDs + Morphine	7 (37%)	12 (60%)	7 (37%)

Values presented in mean (standard deviation) and frequency (percentage); BMI, Body Mass Index; NPRS, Numeric Pain Rating Scale; LANSS, Leeds Assessment of Neuropathic Symptoms and Signs; PSQI, The Pittsburgh Sleep Quality Index; HADS, Hospital Anxiety and Depression Scale; TSK, Tampa Scale of Kinesiophobia; NSAIDs, Non-steroidal anti-inflammatory drugs. The Kruskal-Wallis and Chi-Square (χ2) or Fisher exact tests were used to compare the groups. *p < 0.05

Pressure pain threshold was significantly (F = 7.71; p<0.01) lower in the proximal injuries in the upper limb compared to elbow joint and distal injuries, but not between elbow and distal, considering only the measurement in the upper trapezius ipsilateral to the injury side with strong effect sizes (Table 2). Other variables were not different among groups (Table 2).

Table 2. Pressure pain threshold and temporal summation in patients after acute musculoskeletal trauma in different local of the upper limb (n = 82). Values presented in estimated mean and 95% Confidence Interval.

Variables	Proximal (n=24)	Elbow (n = 25)	Distal (n = 33)	ANCOVA p value	Prox. vs Elb. p value (ES)	Prox. vs Distal p value (ES)	Elb. Vs Distal p value (ES)
UT- Ips. (kgf)	2.5 (1.5; 3.4)	4.1 (3.0; 5.2)	4.9 (4.0; 5.8)	<0.01*	0.04 (-0.76)*	<0.01 (-1.11)*	0.44 (0.3)
UT- Cont. (kgf)	3.5 (2.4; 4.5)	4.6 (3.3; 5.8)	4.7 (3.7; 5.7)	0.18	0.33 (-0.45)	0.18 (-0.50)	0.97 (-0.06)
AT- Ips. (kgf)	6.5 (4.9; 8.1)	5.1 (3.3; 6.9)	6.8 (5.2; 8.3)	0.24	0.43 (0.39)	0.95 (-0.08)	0.23 (-0.47)
AT- Cont. (kgf)	6.4 (4.9; 7.8)	5.8 (4.1; 7.5)	6.6 (5.1; 8.0)	0.70	0.84 (0.17)	0.97 (-0.06)	0.68 (-0.23)
TS	0.6 (-0.4; 1.7)	0.8 (-0.4; 1.9)	1.3 (0.4; 2.3)	0.51	0.98 (-0.05)	0.54 (-0.31)	0.66 (-0.25)

Values presented in estimated mean (standard error) and frequency (percentage); UT: upper trapezius muscle; Ips: ipsilateral; Cont: Contralateral; TS: temporal summation; AT: anterior tibialis muscle; ES: effect size; Prox: Proximal; Elb: Elbow. ANCOVA: covariables: sex, LANSS, PSQI and HADS variables. * p< 0.05.

There were weak negative correlations between pressure pain threshold and LANSS, PSQI and TSK (Table 3 and Figure 1). Moderate positive correlations were also observed between HADS and LANSS, and between HADS and PSQI (Table 3). Additionally, moderate positive correlations were found between TSK and LANSS, and between TSK and HADS (Table 3). These findings suggest that higher levels of neuropathic pain symptoms and kinesiophobia were associated with increased anxiety and depression symptoms, and decreased pressure pain threshold.

Table 3: Correlation among psychological questionnaires and pressure pain threshold.

Pearson correlation
Variables			PPT-UT-Ips	LANSS	PSQI		HADS			TSK
PPT-UT-Ips	p value	-
	R	-
LANSS	p value	0.03*		-
	R	-0.24		-
PSQI	p value	0.02*		0.06		-
	R	-0.26		0.22		-
HADS	p value	0.09		<0.01*		<0.01*		-
	R	-0.20		0.65		0.47		-
TSK	p value	0.02*		<0.01*		0.31		<0.01*			-
	R	-0.25		0.43		0.12		0.35			-

Legend: PPT-UT-Ips: Pressure pain threshold of the ipsilateral upper trapezius muscle; LANSS, Leeds Assessment of Neuropathic Symptoms and Signs; PSQI, The Pittsburgh Sleep Quality Index; HADS, Hospital Anxiety and Depression Scale; TSK, Tampa Scale of Kinesiophobia. * p< 0.05.

Figure 1: Scatterplot between pressure pain threshold (kgf) of the ipsilateral upper trapezius muscle to the injury and the Leeds Assessment of Neuropathic Symptoms and Signs (A) and the Tampa Scale of Kinesiophobia (B).

 Discussion

Our study demonstrated that patients with proximal upper limb injuries presented lower pressure pain threshold in the ipsilateral upper trapezius compared to those with more distal injuries (elbow, forearm, wrist and hand). Additionally, reduced PPT values of the ipsilateral upper trapezius were significantly associated with a higher neuropathic component, kinesiophobia and worst sleep quality. Higher levels of neuropathic pain symptoms and kinesiophobia were also associated with increased anxiety and depression symptoms and kinesiophobia, suggesting that psychological factors may play a relevant role in pain perception and related outcomes in this population.

A study conducted with pediatric patients undergoing orthopedic surgery observed a reduction in PPT even before the surgical intervention, suggesting that anticipatory anxiety and catastrophic thoughts may influence pain perception independently of tissue damage^8. Although our sample involved adults with trauma, a similar mechanism could be considered. The observed association between low PPT and higher kinesiophobia in our sample supports the idea that psychological factors may amplify pain sensitivity, possibly through descending modulatory pathways. This emphasizes the relevance of including psychosocial assessments in the clinical evaluation of trauma patients.

Patients with temporomandibular dysfunction have also been shown to exhibit lower pressure pain thresholds, poorer sleep quality, and higher levels of anxiety when compared to healthy controls. ¹⁷ These findings highlight the importance of addressing biopsychosocial factors in the evaluation and management of pain, given their substantial impact on patients' overall quality of life. In individuals with acute whiplash-associated disorders⁷, low pressure pain thresholds in areas distal to the neck, i.e., regions not directly affected by the injury, have been identified as an important factor of worse short-term neck-related disability in a longitudinal cohort study, supporting the notion that the nociceptive input from the injury site may lead to generalized hypersensitivity. In contrast, our cross-sectional study analysis did not revealed differences in PPTs measured in the anterior tibialis among injury groups, suggesting that the sensitization observed in our sample may be more regionally restricted, particularly affecting areas anatomically closer to the site of trauma, such as the upper trapezius. Peripheral sensitization is a key mechanism underlying the amplification of deep tissue pain, particularly in musculoskeletal conditions. It occurs when muscle nociceptors become hyperresponsive due to the release of inflammatory mediators triggered by tissue damage or inflammation¹⁸. This heightened activity lowers the threshold needed to activate these receptors, making even mild stimuli sufficient to induce pain. As a result, pain perception becomes intensified, contributing to hyperalgesia in deeper tissues. Over time, this hyperexcitability may alter nerve function and exacerbate the response to mechanical stimuli, reinforcing a cycle of persistent and amplified pain¹⁸.

In our study, we focused on the acute phase of upper limb trauma suggesting reduced pressure pain thresholds especially in patients with proximal injuries. However, even after clinical recovery, previous fractures can lead to long-lasting changes in pain processing, as demonstrated by a study comparing individuals without current pain but with a history of distal radius fracture to those with no fracture history found that the previous group exhibited a significantly larger area of referred pain and a greater number of painful regions on the affected side compared to the contralateral side^19.

The temporal summation method is used to assess pain amplification through the "wind-up" phenomenon, which reflects the increased excitability of afferent neurons following repeated noxious stimuli²⁰. This process enhances pain perception and is associated with neuronal plasticity, playing a critical role in the pathophysiology and progression of chronic pain ^20. In our study, however, no significant differences were found between groups for this variable, suggesting that peripheral sensitization associated with the acute traumatic event was the predominant pain mechanism involved.A strength of this study is the inclusion of relevant covariates known to influence pressure pain threshold, such as sex, presence of neuropathic pain components, sleep quality, and levels of anxiety and depression. Additionally, the focus on patients with upper limb traumatic injuries addresses a population that is comparatively underrepresented in the literature, as most research tends to focus on lower limb trauma.
A primary limitation is the cross-sectional design, which precludes the ability to assess causal relationships or the longitudinal development of chronic pain and its associated factors. Another limitation of our study was the unexpected difference in injury types among the groups. Specifically, there was a higher incidence of more complex injuries—such as tendon, nerve, and joint dislocations—in the distal upper limb group, which might have influenced our results.

Conclusion

Patients with traumatic injuries in different locations along the upper limb exhibited distinct pressure pain threshold profiles relative to the trauma site. Specifically, pressure pain threshold in the upper trapezius were significantly lower in individuals with proximal injuries near this region, compared to those with more distal injuries involving the elbow, distal forearm, wrist and hand, even after controlling for covariates such as neuropathic pain component, sleep quality, and sex. Moreover, reduced pressure pain threshold values in the ipsilateral upper trapezius were correlated with higher neuropathic pain scores, kinesiophobia and worse sleep quality.

Funding

This study was supported by Fundação de Amparo à Pesquisa do Estado de Minas Gerais - FAPEMIG (grant number: APQ 00444/21 - EDITAL 001/2021 – DEMANDA UNIVERSAL).

Acknowledgment

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

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