Abstract
OBJECTIVES:
Peripherally directed treatments (targeted exercise, surgery) can reduce, but not fully eliminate, pain for up to 40% of patients with Achilles tendinopathy. The objectives of the present study were (1) to identify indicators of altered central processing in participants with Achilles tendinopathy compared to controls, and (2) to determine which indicators of altered central processing would persist after a local anesthetic injection in patients with Achilles tendinopathy.
DESIGN:
Mechanistic clinical trial.
METHODS:
Forty-six adults (23 with chronic Achilles tendinopathy, 23 matched controls) repeated (1) a movement-evoked pain rating, (2) motor performance assessment, (3) pain psychology questionnaires, and (4) quantitative sensory testing. Participants with Achilles tendinopathy received a local anesthetic injection before repeat testing and controls did not. Mixed-effects analyses of variance examined the effects of group, time, and group by time.
RESULTS:
The Achilles tendinopathy group had movement-evoked pain, motor dysfunction, and higher pain psychological factors (pain catastrophizing, kinesiophobia) compared to controls (P<.05). The Achilles tendinopathy group did not have indicators of nociplastic pain with quantitative sensory testing (P>.05). In those with Achilles tendinopathy, local anesthetic injection eliminated pain and normalized the observed deficits in heel-raise performance and pain catastrophizing (group-by-time effect, P<.01), but not in kinesiophobia (P = .45). Injection did not affect measures of nociplastic pain (P>.05).
CONCLUSION:
People with Achilles tendinopathy had elevated pain psychological factors and motor dysfunction but no signs of nociplastic pain with quantitative sensory testing. Removal of nociceptive input normalized movement-evoked pain and some indicators of altered central processing (motor dysfunction, pain catastrophizing), but not kinesiophobia.
Keywords: central sensitization, kinesiophobia, kinetics, movement-evoked pain, nociceptive
People with Achilles tendinopathy report activity limitations and demonstrate motor dysfunction, particularly of the plantar flexors.1-7,11,12,16-18,23,26-29,31,36,37,46,47 Peripheral nociceptive input can cause motor dysfunction. In healthy volunteers experimentally induced Achilles tendon pain reduces muscle activation20 and experimentally induced knee pain intensity correlates with strength.21 Pain and motor dysfunction can be perpetuated by psychological factors. To date, only 1 study has examined pain psychology in Achilles tendinopathy.25-35 Participants with Achilles tendinopathy and higher fear of movement (ie, kinesiophobia) regained less calf muscle endurance (fewer heel raises) with a progressive Achilles tendon loading program than participants with lower kinesiophobia.35 Nociplastic pain is driven by sensitization of the central nervous system and, despite resolution of the initial cause(s),22 may contribute to persistent Achilles tendinopathy, although there are conflicting findings.33,41
Our aims were (1) to identify indicators of altered central processing in participants with Achilles tendinopathy compared to control participants without chronic pain, matched by age, sex, and body mass index (BMI); and (2) to determine which indicators of altered central processing persist after a local anesthetic injection to the Achilles tendon in patients with Achilles tendinopathy.
A secondary analysis examined correlations between indicators of altered central processing in participants with Achilles tendinopathy that changed with an anesthetic injection.
METHODS
In this mechanistic, nonrandomized controlled trial, all participants repeated testing twice in the following order within a single laboratory-based testing session: (1) movement-evoked pain ratings, (2) motor performance, (3) pain psychology questionnaires, and (4) sensory testing. The Achilles tendinopathy group received an anesthetic injection after the first set of tests. For participants with bilateral Achilles tendinopathy, the more painful side was designated the involved side for testing and injection.
Injection
A sports medicine physician performed an ultrasound examination to determine the presence of tendinosis, enthesophytes, and/or bursitis. The participant’s reported area of maximum pain within the insertion or midportion of the Achilles tendon was used to individualize the location of the injection (FIGURE 1). The on-set for ropivacaine was 10 to 20 minutes, and pain relief lasted for 6 to 8 hours. Repeat testing began 30 minutes after the injection. Participants with Achilles tendinopathy were contacted 1 day and 1 week following testing to ask about any injection-related adverse events.
FIGURE 1.
Sonographic guidance was used to inject 4 mL of 0.5% ropivacaine deep (A) and superficial (B) to the tendon to ensure coverage of the painful region. The needle was first inserted between the AT and the calcaneus to administer ropivacaine. The needle was then redirected posterior to the AT to administer more anesthetic. Abbreviations: AT, Achilles tendon; C, calcaneus; N, needle.
Participants
Participants were recruited from January 2016 to May 2018. The flow of participants from enrollment to analysis is reported using a Consolidated Standards of Reporting Trials diagram (FIGURE 2). Participants with Achilles tendinopathy were recruited at university-based orthopaedic surgery foot and ankle clinics and sports medicine tendinopathy clinics when scheduling notes indicated evaluation for pain that could be related to Achilles tendinopathy. Participants with Achilles tendinopathy were also recruited with a university-wide mass e-mail and chart review of patients seeking care for Achilles-related pain at university-affiliated clinics. Screening was completed in person (recruitment in the clinic) and by phone (mass e-mail or chart review recruitment). Controls were recruited through a university-wide mass e-mail and www.researchmatch.org, and screened via an online survey to identify persons who best matched the participants with Achilles tendinopathy based on age, sex, and BMI. Eligibility criteria are listed in TABLE 1. All participants consented to participate in this study, which was approved by the University of Iowa Institutional Review Board (IRB-01 Biomedical) and registered at www.clinicaltrials.gov (Achilles Pain Block, NCT03316378). Study data were collected and managed using the REDCap electronic data-capture tools hosted at the University of Iowa.
FIGURE 2.
Flow chart of participants from enrollment through analysis. Among participants excluded from participation, “lost to follow-up” and “declined” were most common (59/149 screened), with fear of an injection or lack of time being commonly reported reasons. Fifty-four individuals screened did not meet the criteria for chronic AT due to their AT pain being too acute/infrequent (less than 3 months in duration or no current symptoms), or they did not have AT pain but rather a differential diagnosis. Abbreviations: AT, Achilles tendinopathy; BMI, body mass index.
TABLE 1.
Eligibility Criteria for All Participants and Specific Criteria Per Group
| Inclusion Criteria | Exclusion Criteria | ||
|---|---|---|---|
| AT Group | Control Group | AT Group | Control Group |
|
|
|
|
Abbreviations: AT, Achilles tendinopathy; BMI, body mass index.
Baseline Sample Characteristics
The Patient-Reported Outcomes Measurement Information System (PROMIS) short form 8b (depression) assessed self-reported depression.32 The Brief Pain Inventory (BPI) quantified global pain intensity and interference with activity participation.40 The Victorian Institute of Sport Assessment-Achilles (VISA-A) questionnaire measured symptom severity.34 The International Physical Activity Questionnaire (IPAQ) short form quantified participant-reported physical activity in metabolic equivalents of task minutes over the past week.14 The numeric pain-rating scale was used to quantify pain over the past week and monitor movement-evoked pain during study participation.49
Repeated Measures
All of the following repeated measures demonstrated good test-retest reliability in the control group (intraclass correlation coefficient of 0.8 or greater), except for temporal summation (TS) measures (intraclass correlation coefficient of 0.43 to 0.76) (APPENDIX TABLE 1, available at www.jospt.org).
Motor Control Performance
Plantar flexor endurance was assessed by the maximum number of single-limb heel raises on each side. For balance, participants were permitted to use a railing at elbow height to support themselves with their fingertips. Participants were encouraged to do as many repetitions as possible until they could not do any more with proper form (heel-raise height at least 50% of first repetition, knee straight, trunk upright) or until the task became too painful (greater than 4/10).
Routine (stair ascent) and novel (waltz box step) activities were collected with 3-D motion analysis. Stair ascent represented a rhythmic task, which may not be as susceptible to changes in peripheral nociception due to established brain activation patterns and locomotor central pattern generators.24 The waltz box step represented a novel task, which may be more susceptible to change. As previously described,13 the transitional step from the ground to the stairs was analyzed. Cadence was standardized using a metronome at 100 beats per minute.24 For the waltz task, the push-off from the supporting limb onto the contralateral side during a lateral sidestep was analyzed (APPENDIX FIGURE). Speed was standardized with the auditory cue of music at 80 beats per minute.
A minimum of 3 trials per task were normalized to stance phase and averaged to create one representative trial. Digitized points defined the ankle joint center as the midpoint between the malleoli, using Visual3D software (C-Motion, Inc, Germantown, MD). The ankle was modeled as the calcaneus relative to the tibia. A 9-camera Optotrak 3-D motion-analysis system (Northern Digital Inc, Waterloo, Canada) tracked motion at a rate of 60 Hz. A force plate embedded in the floor provided 3-D ground reaction forces (Kistler Group, Winterthur, Switzerland). Kinematic data were smoothed using a fourth-order, zero-phase-lag Butterworth filter with a cutoff frequency of 6 Hz.
Pain Psychology Questionnaires
Controls were instructed to think about any pain/discomfort during the motor tasks when completing the Tampa Scale of Kinesiophobia (TSK)44 and the Pain Catastrophizing Scale (PCS).39 Participants with Achilles tendinopathy were given the same instruction, except to specifically think about any pain/discomfort in their Achilles tendon. To explore the potential short-term effect of an anesthetic injection on pain psychology, participants also completed the PCS during a 1-week follow-up phone call.
Quantitative Sensory Testing
The pressure pain threshold (PPT) was used to detect primary hyperalgesia at the (more) involved Achilles and widespread hyperalgesia (heel and hamstring on the contralateral side; near the elbow at the muscle belly of the wrist extensors bilaterally). A pressure algometer (Somedic SenseLab AB, Sösdala, Sweden) was applied perpendicular to the skin at a rate of 50 kPa/s with a 1-cm2 tip. Participants pressed a button when the sensation of pressure first became painful (greater than 0/10). The mean of 3 trials per area represented the PPT. After the anesthetic injection, the Achilles PPT on the involved side was greater than 600 kPa, which confirmed adequate anesthesia and absence of peripheral nociceptive input.
For conditioned pain modulation (CPM), the conditioning stimulus was a 120-second cold-water bath of the hand. Pressure pain thresholds were assessed at the hamstring and heel on the contralateral Achilles tendinopathy side after the hand was in the cold-water bath for at least 20 seconds. An increase in PPT during the conditioning stimulus indicated CPM.
We used 2 methods to assess TS to cold and heat. For cold, participants rated their hand pain at 5 and 20 seconds during a 120-second cold-water bath, with the hand submerged up to the wrist crease. An increase in hand pain from 5 to 20 seconds during the cold-water bath indicated TS. Because of variable reliability, heat TS was not analyzed (APPENDIX TABLE 1).
Statistical Analysis
Changes in Achilles tendon pain from preinjection to postinjection were compared with Wilcoxon signed-rank tests. Mixed-effects analyses of variance were used to examine group, time, and group-by-time interaction effects for motor performance, pain psychology, and sensory testing. The type I error rate for the analyses of variance was maintained at .05 by using a Bonferroni adjustment for multiple comparisons (3 comparisons for motor performance, 2 comparisons for pain psychology, and 4 comparisons for sensory testing). The elbow PPTs for the left and right sides were averaged because there were no side-to-side differences (paired t test; first repetition, P = .116; second repetition, P = .932). Post hoc comparisons examined significant interaction effects, and P values were Bonferroni adjusted for the number of time points. We used sensitivity analysis to check whether our results were consistent across Achilles tendinopathy subtypes (midportion/insertional) and laterality (unilateral/bilateral). This study was not sufficiently powered to detect changes in the primary outcomes with smaller subgroups (n = 7-16), so statistical significance was defined as P<.05 (unadjusted) for this exploratory post hoc analysis. We used Pearson correlations to examine relationships between the magnitudes of change after an anesthetic injection of identified indicators of altered central processing in the Achilles tendinopathy group.
A priori power analysis determined that a sample size of 20 per group was needed to detect effect sizes (between groups, >0.91; over time, >0.68) less than or equal to published results for ankle power (mean difference, 0.9 ± 0.9 W/kg),13 kinesiophobia (minimal detectable change, 5.6 ± 5.7 points),19 and PPT (group difference, 171.8 ± 174.8 kPa),30 with a power of at least 80% and statistical significance defined as P≤.05. Because 3 participants with Achilles tendinopathy had insufficient movement-evoked pain relief from the anesthetic injection, an additional 3 participants were recruited per group.
RESULTS
Sample Characteristics
The groups were matched by age, sex, and BMI (P>.05) (TABLE 2). Additional participant characteristics are reported in TABLE 2. Most participants with Achilles tendinopathy had had symptoms for at least a year (median, 1.3 years; interquartile range, 0.8-2.8 years). Many had seen a physical therapist (52%), and all had tried some form of treatment for Achilles tendinopathy symptoms (TABLE 3). Of participants with Achilles tendinopathy, 70% had unilateral pain (TABLE 4). Insertional Achilles tendinopathy (70%) was more frequent in this sample than midportion Achilles tendinopathy (30%). The majority of participants had signs of tendinosis, and participants with insertional Achilles tendinopathy often had enthesophytes and/or bursitis on ultrasound imaging (TABLE 4).
TABLE 2.
Baseline Characteristics of the Control and Achilles Tendinopathy Groupsa
| Controls (n = 23) | AT (n = 23) | Group Comparisonb | P Value | |
|---|---|---|---|---|
| Age, y | 49.2 ± 10.6 | 49.5 ± 10.3 | 0.3 (−5.9, 6.6) | .930 |
| Sex (female), n (%) | 15 (65) | 15 (65) | … | 1.000 |
| Body mass index, kg/m2 | 31.3 ± 5.7 | 33.7 ± 7.8 | 2.5 (−1.6, 6.5) | .229 |
| PROMIS-depression | 46.4 ± 7.6 | 46.7 ± 8.2 | 0.2 (−4.6, 5.1) | .921 |
| BPI-intensity | 0.1 (0.0-0.8)c | 2.5 (1.7-3.6c | 2.1 (1.5, 2.8d | <.001 |
| BPI-interference | 0.0 (0.0-1.0)c | 1.9 (1.1-3.7)c | 1.6 (0.7, 2.4)d | .002 |
| VISA-A | 100 (100-100)c | 39.0 (33.0-59.0)c | −61.0 (−64.0, −54.0d | <.001 |
| IPAQ-total physical activity, MET-min/wk | 2508 (759-3984)c | 2220 (798-3920)c | 53 (−1110, 1112)d | .910 |
Abbreviations: AT, Achilles tendinopathy; BPI, Brief Pain Inventory; IPAQ, International Physical Activity Questionnaire; MET, metabolic equivalent; PROMIS, Patient-Reported Outcomes Measurement Information System; VISA-A, Victorian Institute of Sport Assessment-Achilles.
Values are mean ± SD unless otherwise indicated.
Values are mean difference (95% confidence interval) unless otherwise indicated. Sample characteristics were compared between groups using independent-samples t tests for parametric data, the Mann-Whitney U test for nonparametric data, or the chi-square test for categorical data.
Values are median (interquartile range).
Values are median group difference (Hodges-Lehmann statistic).
TABLE 3.
Types of Treatment and Treatment Providera
| Sample, % | |
|---|---|
| Treatment provider | |
| Physical therapist | 52 |
| Other care provider (chiropractor, massage therapist, orthopaedic surgeon, podiatrist, primary care provider, sports medicine physician) | 57 |
| Treatment | |
| Stretching | 70 |
| Tendon-loading exercise | 61 |
| Shoe insert (eg, heel lift, arch support) | 57 |
| Night splints | 39 |
| Pain medication (NSAID, acetaminophen) | 26 |
| Modalities (ice, heat) | 22 |
| Corticosteroid injection | 13 |
| Nitroglycerine patch over Achilles tendon | 7 |
| Iontophoresis | 7 |
| Soft tissue instrument-assisted mobilization | 4 |
Abbreviation: NSAID, nonsteroidal anti-inflammatory drug.
All participants had seen a care provider and/or tried at least 1 form of treatment. Many participants had seen multiple care providers and tried multiple treatments for Achilles tendinopathy pain.
TABLE 4.
Frequency of Pathology Assessed Using Ultrasound Imaging in Participants With Achilles Tendinopathy, by Subtype
| Type/Laterality | Tendinosis | Enthesophytes | Bursitis |
|---|---|---|---|
| Insertional (n = 16) | |||
| Unilateral (n = 11) | 8/11 (73%) | 9/11 (82%) | 8/11 (73%) |
| Bilateral (n = 5) | 5/5 (100%) | 5/5 (100%) | 5/5 (100%) |
| Midportion (n = 7) | |||
| Unilateral (n = 5) | 4/5 (80%) | 0/5 (0%) | 0/5 (0%) |
| Bilateral (n = 2) | 2/2 (100%) | 0/2 (0%) | 0/2 (0%) |
Achilles Tendinopathy Pain
Prior to the anesthetic injection, all participants with Achilles tendinopathy reported movement-evoked pain (TABLE 5). After the injection, movement-evoked pain reduced (P<.01 for all comparisons), although some participants reported a mild sensation of discomfort during activity. One participant had increased pain after the injection due to pressure in retrocalcaneal space, and 2 participants had partial pain relief (movement-evoked pain of at least 1/10). The Achilles tendinopathy group reported no injection-related adverse events.
TABLE 5.
Achilles Tendinopathy Pain Ratings on a 0-to-10 Verbal Numeric Pain-Rating Scalea
| Pain Rating | Total AT (n = 23) | Insertional AT (n = 16) | Midportion AT (n = 7) | Unilateral AT (n = 16) | Bilateral AT (n = 7) |
|---|---|---|---|---|---|
| Highest in past week | 7.0 (5.0-8.0) | 8.0 (5.5-90) | 5.0 (4.0-6.0) | 5.5 (4.3-8.0) | 8.0 (70-9.0) |
| Lowest in past week | 0.0 (0.0-1.0) | 0.0 (0.0-1.0) | 1.0 (0.0-1.0) | 0.0 (0.0-1.0) | 0.0 (0.0-1.0) |
| Standing, time 1 | 1.0 (0.0-2.0) | 0.5 (0.0-1.0) | 1.0 (0.5-3.0) | 1.0 (0.5-2.0) | 0.3 (0.0-1.8) |
| Standing, time 2 | 0.0 (0.0-0.1) | 0.0 (0.0-0.4) | 0.0 (0.0-0.0) | 0.0 (0.0-0.0) | 0.1 (0.0-1.0) |
| Stairs, time 1 | 2.0 (1.0-3.0) | 2.0 (1.0-3.0) | 2.0 (1.0-3.0) | 2.0 (1.0-2.8) | 3.0 (1.5-4.0) |
| Stairs, time 2 | 0.0 (0.0-1.0) | 0.0 (0.0-1.0) | 0.0 (0.0-0.5) | 0.0 (0.0-09) | 0.0 (0.0-1.0) |
| Waltz, time 1 | 1.8 (1.0-2.3) | 1.5 (1.0-3.0) | 2.0 (1.0-2.0) | 1.3 (1.0-2.0) | 2.5 (1.1-3.5) |
| Waltz, time 2 | 0.0 (0.0-0.0) | 0.0 (0.0-0.0) | 0.0 (0.0-0.0) | 0.0 (0.0-0.0) | 0.0 (0.0-1.3) |
| Heel raise, time 1 | 2.0 (0.3-4.0) | 2.5 (0.8-4.0) | 2.0 (0.0-5.0) | 2.0 (0.0-3.0) | 4.0 (1.5-5.5) |
| Heel raise, time 2 | 0.0 (0.0-0.5) | 0.0 (0.0-1.5) | 0.0 (0.0-0.0) | 0.0 (0.0-0.0) | 1.5 (0.0-3.3) |
Abbreviation: AT, Achilles tendinopathy.
Values are median (interquartile range). Participants rated their AT pain over the past week, pain during standing, and movement-evoked pain (stairs, waltz, heel raise). For the last 4 activities, participants rated their pain at 2 time points: prior to the anesthetic injection (time 1) and after the anesthetic injection (time 2).
Motor Control Performance Measures
Prior to the anesthetic injection, the Achilles tendinopathy group performed fewer heel raises than controls (post hoc group effect at time 1, P = .006). After the anesthetic injection, the Achilles tendinopathy group was able to complete a similar number of heel raises to that completed by controls (group-by-time effect, P = .036; post hoc group effect at time 2, P = .272) (TABLE 6). A sensitivity analysis indicated a consistent improvement in heel-raise number for all Achilles tendinopathy subgroups (insertional, midportion, unilateral, bilateral) after the anesthetic injection compared to controls (group-by-time effect, P<.05) (APPENDIX TABLES 2 through 5). Although the sensitivity analysis also indicated an effect of group, this was driven by between-group differences prior to the injection (control versus insertional, P = .018 and versus unilateral, P = .012), not after the injection (control versus insertional, P = .09 and versus unilateral, P = .200). There were no differences between groups (Achilles tendinopathy versus control) and no effect of injection in the Achilles tendinopathy group on motor performance in the low-level activities of stair ascent and the waltz (P>.05 for all group, time, and group-by-time effects) (TABLE 6).
TABLE 6.
Measures of Altered Central Processing, Including Motor Dysfunction, Heightened Pain Psychology Factors, and Nociplastic Pain, in Participants With Achilles Teninopathy
| Bonferroni-Adjusted P Value | |||||
|---|---|---|---|---|---|
| Domain/Test/Time Pointa | AT Groupb | Control Groupb | Group | Time | Group by Time |
| Motor performance | |||||
| Maximum single-limb HRs, n | .054 | .708 | .036 | ||
| Time 1 | 13.5 (9.4, 17.6) | 22.5 (18.5, 26.6) | |||
| Time 2 | 17.0 (12.8, 21.1) | 21.3 (17.3, 25.3) | |||
| Peak plantar flexor power during stair ascent, W/kg | 1.000 | 1.000 | .369 | ||
| Time 1 | 2.7 (2.3, 3.0) | 3.0 (2.6, 3.3) | |||
| Time 2 | 2.8 (2.4, 3.2) | 2.8 (2.4, 3.2) | |||
| Peak plantar flexor power during the waltz, W/kg | 1.000 | .327 | 1.000 | ||
| Time 1 | 0.8 (0.6, 1.0) | 0.7 (0.5, 0.9) | |||
| Time 2 | 0.7 (0.5, 0.9) | 0.6 (0.5, 0.8) | |||
| Pain psychology questionnaires | |||||
| Tampa Scale of Kinesiophobia | <.001 | .012 | .450 | ||
| Time 1 | 37.2 (34.7, 39.7) | 29.6 (27.1, 32.1) | |||
| Time 2 | 34.9 (32.5, 37.3) | 28.7 (26.2, 31.1) | |||
| Pain Catastrophizing Scale | <.001 | <.001 | <.001 | ||
| Time 1 | 12.6 (9.2, 15.9) | 1.9 (−1.5, 5.2) | |||
| Time 2 | 2.5 (1.2, 3.7) | 1.3 (0.0, 2.6) | |||
| Time 3 | 8.3 (5.5, 11.2) | 0.9 (−1.9, 3.7) | |||
| Quantitative sensory testing | |||||
| PPT at the wrist extensors, kPac | 1.000 | .136 | 1.000 | ||
| Time 1 | 330.6 (270.9, 390.4) | 303.2 (243.4, 362.9) | |||
| Time 2 | 314.8 (260.6, 368.9) | 280.3 (226.1, 334.5) | |||
| CPM: PPT at hamstrings contralateral to AT pain, kPa | .664 | <.001 | 1.000 | ||
| Before CPM: time 1 | 463.5 (375.2, 551.8) | 383.6 (297.4, 469.8) | |||
| During CPM: time 1 | 596.5 (475.5, 717.5) | 501.0 (382.9, 619.1) | |||
| Before CPM: time 2 | 425.7 (345.3, 506.0) | 358.0 (280.0, 436.4) | |||
| During CPM: time 2 | 530.3 (448.7, 611.8) | 432.0 (352.3, 511.6) | |||
| CPM: PPT at heel contralateral to AT pain, kPa | 1.000 | <.001 | 1.000 | ||
| Before CPM: time 1 | 789.6 (650.2, 929.1) | 729.4 (597.9, 860.9) | |||
| During CPM: time 1 | 960.3 (804.2, 1116.4) | 842.9 (695.8, 990.1) | |||
| Before CPM: time 2 | 731.3 (609.3, 853.3) | 653.5 (538.5, 768.5) | |||
| During CPM: time 2 | 837.0 (707.0, 967.1) | 766.5 (643.9, 889.2) | |||
| Temporal summation: verbal numeric pain rating during ice bath of the hand | 1.000 | <.001 | .418 | ||
| 5 s: time 1 | 3.2 (2.5, 3.9) | 2.9 (2.2, 3.6) | |||
| 20 s: time 1 | 5.2 (4.2, 6.1) | 4.9 (4.1, 5.8) | |||
| 5 s: time 2 | 3.1 (2.2, 3.9) | 3.1 (2.3, 3.9) | |||
| 20 s: time 2 | 5.3 (4.3, 6.2) | 5.8 (4.9, 6.7) | |||
Abbreviations: AT, Achilles tendinopathy; CPM, conditioned pain modulation; HR, heel raise; PPT, pressure pain threshold.
Time point 1, prior to the anesthetic injection/first repetition (controls); time point 2, after the anesthetic injection/second repetition (controls); time point 3, at 1-week follow-up (Pain Catastrophizing Scale only).
Values are mean (95% confidence interval).
Measured bilaterally as the average of the left and right sides.
Pain Psychology Questionnaires
The Achilles tendinopathy group had higher TSK and PCS scores than controls (group effect, P<.001 for both comparisons) (TABLE 6). The anesthetic injection had no effect on TSK score (group-by-time interaction effect, P = .450), and the TSK score was slightly lower in both groups with repeat testing (time effect, P = .012) (TABLE 6). The anesthetic injection lowered the PCS score in participants with Achilles tendinopathy to levels similar to those of controls. Participants with Achilles tendinopathy had a higher PCS score prior to the anesthetic injection (P<.001) and at 1 week (P<.001) than that of controls, but there was no difference between groups immediately after the injection (post hoc testing, P = .582). The sensitivity analysis yielded the same results for all subgroups (APPENDIX TABLES 2 through 5).
Quantitative Sensory Testing
Localized
The Achilles tendinopathy group had a lower Achilles tendon PPT than that of controls (Achilles tendinopathy, 423.0 ± 196.1; control, 645.1 ± 250.3; mean difference, 222.1; 95% confidence interval: 88.5, 355.7; P<.01).
Widespread
The PPTs on the contralateral heel and hamstring increased during CPM, and there were increases in pain over time during TS in both groups (time effect, P<.001) (TABLE 6). There were no differences between groups for any of the indicators of nociplastic pain (group effect and group-by-time effect, P>.05 for all comparisons) (TABLE 6). The sensitivity analysis yielded the same group and group-by-time effects for all subgroups (APPENDIX TABLES 2 through 5). There was a reduction of less than 30 kPa between the first and second repetitions of PPT at the elbow for certain subgroups (control versus insertional, P = .016 and control versus unilateral, P = .045) (APPENDIX TABLES 2 and 4). The sensitivity analysis also detected a group-by-time interaction (P = .046) for TS, where participants with midportion Achilles tendinopathy (n = 7) had a smaller increase in pain rating prior to the injection (1.5-point increase in numeric pain-rating scale) compared to after (2.2-point increase) and to the control group (2- to 2.7-point increase) (APPENDIX TABLE 3).
Relationship Between Motor Control, Pain, and Pain Psychology
In the Achilles tendinopathy group, there were correlations between improved heel-raise performance and reduced TSK score (r = −0.57, P = .01) and decreased pain (r = −0.46, P = .04) (FIGURE 3). Reduction in pain was not significantly correlated with a reduction in TSK score (r = 0.32, P = .16). Change in PCS score was not correlated with heel-raise performance, pain, or TSK score (r<0.2, P>.05). To fulfill the assumptions of parametric testing, 2 outliers (increases of 18 and 25) for the change in the maximum number of heel raises after an anesthetic injection were capped at the third highest value in the sample (increase of 9).
FIGURE 3.
Pearson correlations between (A) an indicator of altered central processing (motor dysfunction using the number of heel raises) and heightened pain psychology (using the TSK) (r = −0.57, P = .01), (B) number of heel raises and changes in pain (reported during the single-limb heel raise using the NPRS) (r = −0.46, P = .04), and (C) heightened pain psychology and changes in pain (r = 0.32, P = .16) after an anesthetic injection in participants with Achilles tendinopathy. Abbreviations: NPRS, numeric pain-rating scale; TSK, Tampa Scale of Kinesiophobia.
DISCUSSION
We detected motor dysfunction and elevated pain catastrophizing and fear of movement in participants with Achilles tendinopathy. We did not detect nociplastic pain with measures of widespread sensitivity, TS, and CPM. An anesthetic injection at the site of Achilles tendon pain immediately improved heel-raise performance and reduced pain catastrophizing, yet kinesiophobia remained elevated.
Altered Processing in the Central Nervous System of Participants With Achilles Tendinopathy
Participants with Achilles tendinopathy, compared to controls, had altered central processing on some indicators, including motor dysfunction with single-limb heel raises, higher pain catastrophizing, and higher kinesiophobia. Consistent with Plinsinga et al,33 who showed no alterations in pain thresholds outside the Achilles tendinopathy site, we failed to detect signs of nociplastic pain. The lack of widespread reductions in PPT or enhanced TS suggests that there was not a general increase in central excitability. However, the enhanced pain catastrophizing and motor dysfunction, reversed by local anesthetic, suggests enhanced central excitability. However, it was localized and maintained by continued nociceptive input. There may be a localized, not widespread, loss of central inhibition in individuals with Achilles tendinopathy.41
Nociceptive Input Drives Movement Pain, Motor Dysfunction, and Pain Catastrophizing
Eliminating nociceptive input nearly eliminated movement-evoked pain, motor dysfunction, and pain catastrophizing. Our findings suggest that heel-raise performance was impaired by peripheral nociceptive input, yet expectation of pain relief could influence outcomes.8 Also, it remains unknown whether motor dysfunction with high-level plyometric tasks (eg, running, jumping) would similarly resolve with pain relief. Interpretation of clinical examination findings in some individuals could be altered if Achilles tendinopathy pain provokes motor dysfunction and/or elevates pain psychological factors, rather than the reverse. Future studies should consider the potential interplay of pain, motor function, and psychological factors identified in this study with other factors such as tendon pathology, altered mechanical properties of the tendon, and neuromuscular control measures.10,48
Kinesiophobia Was Linked to Motor Dysfunction and Was Independent of Nociceptive Input
Unlike pain catastrophizing, kinesiophobia did not resolve with an anesthetic injection. Severity might explain the differential effect on psychological factors. Participants with Achilles tendinopathy had elevated kinesiophobia (37.2 ± 6.2; high TSK score, 37 or greater44), while pain catastrophizing was well below the clinical cutoff (12.6 ± 10.6; high PCS score, 30 or greater39). In patients with knee pain, interventions that reduce pain can also greatly reduce catastrophizing, indicating that the PCS may reflect a more dynamic state than a stable trait.15,45 Our data suggest that pain relief alone may be sufficient to address low levels of pain catastrophizing in patients with chronic Achilles tendinopathy—but not kinesiophobia, at least acutely.
Improvement in motor dysfunction (heel-raise performance) was moderately associated with pain relief and reduced kinesiophobia. Absence of a significant correlation between changes in pain and kinesiophobia indicates that peripheral nociceptive input and kinesiophobia may both independently contribute to motor dysfunction in moderate-level tasks involving the foot and ankle. These findings underscore the importance of using psychologically informed physical therapy to evaluate any relationship between pain, motor dysfunction, and kinesiophobia.
Limitations
This mechanistic study modeled the immediate effect of a treatment targeting peripheral nociceptive input, which was confirmed by an absence of sensation to pressure in the Achilles tendinopathy group. An injection can also have central effects that reduce pain, such as the expectation of pain relief.38,42,43 Yet prior studies support anesthetic injection to reduce pain ratings more than saline injection when the pain condition is localized.9,38,50 More research is needed to understand how pain mechanisms may differ in acute Achilles tendinopathy and subtypes of Achilles tendinopathy (insertional, midportion, unilateral, bilateral).
CONCLUSION
Participants with Achilles tendinopathy had signs of altered central processing, including motor dysfunction and pain psychology (elevated pain catastrophizing and kinesiophobia). We did not detect other signs of nociplastic pain, like widespread sensitivity, enhanced TS, or reduced CPM. Heelraise performance immediately improved with pain relief. Elevated kinesiophobia did not resolve with removal of nociceptive input.
KEY POINTS.
FINDINGS:
People with chronic Achilles tendinopathy had movement-evoked pain, motor dysfunction, elevated pain catastrophizing, and elevated fear of movement. A local anesthetic injection eliminated pain and normalized the observed deficits in motor performance and pain catastrophizing, but not in fear of movement.
IMPLICATIONS:
Peripheral nociceptive input drives localized movement-evoked pain and some signs of altered central processing (motor dysfunction, pain catastrophizing), but not fear of movement. To address all Achilles tendinopa–thy-associated deficits identified in this study, patients may benefit from psychologically informed physical therapy to evaluate any relationship between pain, motor dysfunction, and kinesiophobia.
CAUTION:
Although we found that peripheral nociceptive input was a mechanism for motor dysfunction, evaluation of all factors contributing to motor dysfunction is needed to tailor care to the individual.
ACKNOWLEDGMENTS:
The authors would like to thank Dr John Yack for his contributions to the study design, as well as Dr Phinit Phisitkul for his input to study design and participant recruitment. The authors thank Tarek Karam, Rebecca Torres, Evan Streeby, and Grace Weiland for their assistance. We thank all participants for their time, effort, and interest in clinical science. Results of the study will be e-mailed to all participants who requested a copy of published findings.
This study was registered at www.clinicaltrials.gov as “Achilles Pain Block” (NCT03316378) and was funded by National Institutes of Health grants K99AR071517, T32 NS045549-12, and 54TR001013 (for REDCap electronic data-capture tools). Preliminary data were collected with the support of an Academy of Orthopaedic Physical Therapy grant from the American Physical Therapy Association.
APPENDIX
Table 1.
Within-Session Test-Retest Reliability in Controls, Who Did Not Receive an Anesthetic Injection Between Repeat Tests
| ICCa | |
|---|---|
| Motor performance measures | |
| Plantar flexor endurance: maximum number of single-limb heel raises | 0.83 (0.63, 0.92) |
| Stair ascent biomechanics, peak motion, and plantar flexor kinetics | |
| Dorsiflexion | 0.82 (0.57, 0.92) |
| Moment | 0.91 (0.78, 0.96) |
| Power | 0.83 (0.61, 0.93) |
| Waltz biomechanics, peak motion, and plantar flexor kinetics | |
| Dorsiflexion | 0.91 (0.79, 0.96) |
| Moment | 0.93 (0.84, 0.97) |
| Power | 0.97 (0.92, 0.99) |
| Pain psychology questionnaires | |
| Tampa Scale of Kinesiophobia | 0.89 (0.75, 0.95) |
| Pain Catastrophizing Scale | 0.90 (0.78, 0.96) |
| Quantitative sensory testing | |
| Pressure pain threshold | |
| Heel | 0.93 (0.79, 0.97) |
| Hamstring | 0.95 (0.89, 0.98) |
| Elbow | 0.93 (0.81, 0.97) |
| Conditioned pain modulation | |
| Hamstring pressure pain threshold | 0.86 (0.65, 0.94) |
| Heel pressure pain threshold | 0.93 (0.78, 0.97) |
| Temporal summation with constant cold stimulus (NPRS) | |
| Hand: 5 s | 0.76 (0.52, 0.89) |
| Hand: 20 s | 0.71 (0.29, 0.88) |
| Heat pain threshold | |
| Hand | 0.80 (0.64, 0.89) |
| Temporal summation with constant heat stimulus (NPRS)b | |
| Hand: first repetition | 0.43 (0.11, 0.66) |
| Hand: fifth repetition | 0.72 (0.50, 0.85) |
| Hand: 10th repetition | 0.58 (0.32, 0.77) |
Abbreviations: ICC, intraclass correlation coefficient; NPRS, numeric pain-rating scale.
Values in parentheses are 95% confidence interval. The ICC estimates were calculated based on absolute agreement with a 2-way mixed-effects model. The ICCs for ankle biomechanics and pressure pain thresholds were based on a mean rating (k = 3); those for heel raises, pain psychology questionnaires, and temporal summation were based on a single measure.
Due to poor reliability, temporal summation to a constant heat stimulus was not further analyzed. For temporal summation to heat, the stimulus intensity was the temperature that the participant rated 4/10 from a series of 10 randomly ordered pulses from 40°C to 49°C (TSA 2 neurosensory analyzer; Medoc Ltd, Ramat Yishai, Israel). A 4/10 pain stimulus was delivered 10 times to the thenar eminence. The temperature started at 2°C below the 4/10 pain intensity stimulus and increased at a rate of 8°C/s; there were 2.5 seconds between stimuli. Pain was reported after the first, fifth, and 10th repetitions. Temporal summation was defined as the peak pain rating minus the initial pain rating. For test-retest reliability, the ICCs were examined in the control group.
Table 2.
Measures of Altered Central Processing, Including Motor Dysfunction, Heightened Pain Psychology Factors, and Nociplastic Pain, in Participants With Insertional AT
| P Value | |||||
|---|---|---|---|---|---|
| Domain/Test/Time Pointa | Insertional AT Groupb | Control Groupb | Group | Time | Group by Time |
| Motor performance | |||||
| Maximum single-limb HRs, n | .027c | .734 | .049 | ||
| Time 1 | 14.2 (9.2, 19.2) | 22.5 (18.5, 26.6) | |||
| Time 2 | 16.0 (11.4, 20.6) | 21.3 (17.3, 25.3) | |||
| Peak plantar flexor power during stair ascent, W/kg | .804 | .637 | .264 | ||
| Time 1 | 2.8 (2.4, 3.2) | 3.0 (2.6, 3.3) | |||
| Time 2 | 2.9 (2.4, 3.3) | 2.8 (2.4, 3.2) | |||
| Peak plantar flexor power during the waltz, W/kg | .816 | .019c | .13 | ||
| Time 1 | 0.8 (0.6, 1.0) | 0.7 (0.5, 0.9) | |||
| Time 2 | 0.6 (0.4, 0.8) | 0.6 (0.5, 0.8) | |||
| Pain psychology questionnaires | |||||
| Tampa Scale of Kinesiophobia | .001 | .030 | .484 | ||
| Time 1 | 36.5 (33.8, 39.2) | 29.6 (27.1, 32.1) | |||
| Time 2 | 34.8 (31.8, 37.7) | 28.7 (26.2, 31.1) | |||
| Pain Catastrophizing Scale | <.001 | <.001 | .001 | ||
| Time 1 | 13.1 (8.9, 17.2) | 1.9 (0.0, 5.2) | |||
| Time 2 | 2.8 (1.2, 4.4) | 1.3 (0.0, 2.6) | |||
| Time 3 | 7.4 (4.6, 10.3) | 0.9 (0.0, 3.7) | |||
| Quantitative sensory testing | |||||
| PPT at the wrist extensors, kPad | .502 | .016c | .881 | ||
| Time 1 | 333.9 (260.7, 407.2) | 303.2 (242.1, 364.3) | |||
| Time 2 | 308.2 (243.9, 372.5) | 280.3 (226.7, 334.0) | |||
| CPM: PPT at hamstrings contralateral to AT pain, kPa | .435 | <.001 | .388 | ||
| Before CPM: time 1 | 422.8 (318.9, 526.6) | 383.6 (297.4, 469.8) | |||
| During CPM: time 1 | 579.1 (427.2, 731.1) | 501.0 (382.9, 619.1) | |||
| Before CPM: time 2 | 379.0 (285.9, 472.0) | 358.0 (280.0, 436.4) | |||
| During CPM: time 2 | 503.2 (401.5, 604.9) | 432.0 (352.3, 511.6) | |||
| CPM: PPT at heel on side contralateral to AT pain, kPa | .861 | <.001 | .811 | ||
| Before CPM: time 1 | 710.0 (535.6, 884.3) | 729.4 (597.9, 860.9) | |||
| During CPM: time 1 | 903.0 (700.3, 1105.7) | 842.9 (695.8, 990.1) | |||
| Before CPM: time 2 | 648.6 (496.0, 801.2) | 653.5 (538.5, 768.5) | |||
| During CPM: time 2 | 800.1 (627.0, 973.2) | 766.5 (643.9, 889.2) | |||
| Temporal summation: verbal numeric pain rating during ice bath of the hand | .84 | <.001 | .673 | ||
| 5 s: time 1 | 3.0 (2.1, 3.9) | 2.9 (2.2, 3.6) | |||
| 20 s: time 1 | 5.2 (4.0, 6.3) | 4.9 (4.1, 5.8) | |||
| 5 s: time 2 | 3.4 (2.3, 4.5) | 3.1 (2.3, 3.9) | |||
| 20 s: time 2 | 5.6 (4.4, 6.8) | 5.8 (4.9, 6.7) | |||
Abbreviations: AT, Achilles tendinopathy; CPM, conditioned pain modulation; HR, heel raise; PPT, pressure pain threshold.
Time point 1, prior to the anesthetic injection/first repetition (controls); time point 2, after the anesthetic injection/second repetition (controls); time point 3, at 1-week follow-up (Pain Catastrophizing Scale only).
Values are mean (95% confidence interval).
Change in statistical significance compared to the primary analysis.
Measured bilaterally as the average of the left and right sides.
Table 3.
Measures of Altered Central Processing, Including Motor Dysfunction, Heightened Pain Psychology Factors, and Nociplastic Pain, in Participants With Midportion AT
| P Value | |||||
|---|---|---|---|---|---|
| Domain/Test/Time Pointa | Midportion AT Groupb | Control Groupb | Group | Time | Group by Time |
| Motor performance | |||||
| Maximum single-limb HRs, n | .103 | .067 | .009 | ||
| Time 1 | 12.1 (5.1, 19.1) | 22.5 (18.6, 26.5) | |||
| Time 2 | 18.9 (11.4, 26.3) | 21.3 (17.6, 24.9) | |||
| Peak plantar flexor power during stair ascent, W/kg | .374 | .565 | .096 | ||
| Time 1 | 2.4 (1.8, 3.0) | 3.0 (2.6, 3.3) | |||
| Time 2 | 2.7 (2.0, 3.5) | 2.8 (2.5, 3.1) | |||
| Peak plantar flexor power during the waltz, W/kg | .673 | .217 | .022c | ||
| Time 1 | 0.7 (0.3, 1.0) | 0.7 (0.5, 0.9) | |||
| Time 2 | 0.8 (0.4, 1.2) | 0.6 (0.5, 0.8) | |||
| Pain psychology questionnaires | |||||
| Tampa Scale of Kinesiophobia | .004 | .002 | .061 | ||
| Time 1 | 38.7 (33.7, 43.7) | 29.6 (27.2, 31.9) | |||
| Time 2 | 35.3 (31.1, 39.5) | 28.7 (26.3, 31.0) | |||
| Pain Catastrophizing Scale | <.001 | <.001 | <.001 | ||
| Time 1 | 11.4 (7.9, 15.0) | 1.9 (0.0, 5.0) | |||
| Time 2 | 1.7 (0.0, 4.1) | 1.3 (0.0, 2.7) | |||
| Time 3 | 10.4 (6.2, 14.7) | 0.9 (0.0, 3.6) | |||
| Quantitative sensory testing | |||||
| PPT at the wrist extensors, kPad | .568 | .517 | .242 | ||
| Time 1 | 323.2 (212.1, 434.2) | 303.2 (241.9, 364.4) | |||
| Time 2 | 329.8 (220.7, 439.0) | 280.3 (220.1, 340.5) | |||
| CPM: PPT at hamstrings on contralateral AT pain side, kPa | .108 | .001 | .973 | ||
| Before CPM: time 1 | 539.1 (385.6, 692.6) | 383.6 (304.3, 463.0) | |||
| During CPM: time 1 | 628.8 (415.0, 842.6) | 501.0 (388.8, 613.2) | |||
| Before CPM: time 2 | 512.3 (369.2, 655.5) | 358.0 (280.7, 435.3) | |||
| During CPM: time 2 | 580.6 (433.1, 728.1) | 432.0 (345.2, 518.7) | |||
| CPM: PPT at heel on side contralateral to AT pain, kPa | .147 | .012 | .607 | ||
| Before CPM: time 1 | 922.4 (680.2, 1164.6) | 729.4 (590.7, 868.1) | |||
| During CPM: time 1 | 1055.9 (781.0, 1330.8) | 842.9 (682.8, 1003.0) | |||
| Before CPM: time 2 | 869.2 (656.2, 1082.1) | 653.5 (521.8, 785.2) | |||
| During CPM: time 2 | 898.5 (665.8, 1131.2) | 766.5 (618.6, 914.5) | |||
| Temporal summation: verbal numeric pain rating during ice bath of the hand | .734 | <.001 | .046c | ||
| 5 s: time 1 | 3.6 (2.3, 4.8) | 2.9 (2.2, 3.6) | |||
| 20 s: time 1 | 5.1 (3.7, 6.6) | 4.9 (4.1, 5.8) | |||
| 5 s: time 2 | 2.4 (1.0, 3.9) | 3.1 (2.3, 3.9) | |||
| 20 s: time 2 | 4.6 (3.2, 5.9) | 5.8 (5.0, 6.5) | |||
Abbreviations: AT, Achilles tendinopathy; CPM, conditioned pain modulation; HR, heel raise; PPT, pressure pain threshold.
Time point 1, prior to the anesthetic injection/first repetition (controls); time point 2, after the anesthetic injection/second repetition (controls); time point 3, at 1-week follow-up (Pain Catastrophizing Scale only).
Values are mean (95% confidence interval).
Change in statistical significance compared to the primary analysis.
Measured bilaterally as the average of the left and right sides.
Table 4.
Measures of Altered Central Processing, Including Motor Dysfunction, Heightened Pain Psychology Factors, and Nociplastic Pain, in Participants With Unilateral AT
| P Value | |||||
|---|---|---|---|---|---|
| Domain/Test/Time Pointa | Unilateral AT Groupb | Control Groupb | Group | Time | Group by Time |
| Motor performance | |||||
| Maximum single-limb HRs, n | .037c | .457 | .047 | ||
| Time 1 | 14.1 (9.3, 18.9) | 22.5 (18.5, 26.6) | |||
| Time 2 | 16.8 (11.8, 21.8) | 21.3 (17.3, 25.3) | |||
| Peak plantar flexor power during stair ascent, W/kg | .555 | .837 | .098 | ||
| Time 1 | 2.6 (2.2, 3.0) | 3.0 (2.6, 3.3) | |||
| Time 2 | 2.8 (2.3, 3.3) | 2.8 (2.4, 3.2) | |||
| Peak plantar flexor power during the waltz, W/kg | .332 | .142 | .498 | ||
| Time 1 | 0.9 (0.6, 1.1) | 0.7 (0.5, 0.9) | |||
| Time 2 | 0.7 (0.5, 1.0) | 0.6 (0.5, 0.8) | |||
| Pain psychology questionnaires | |||||
| Tampa Scale of Kinesiophobia | .005 | .025 | .544 | ||
| Time 1 | 35.2 (32.3, 38.1) | 29.6 (27.1, 32.1) | |||
| Time 2 | 33.6 (30.8, 36.5) | 28.7 (26.2, 31.1) | |||
| Pain Catastrophizing Scale | <.001 | <.001 | <.001 | ||
| Time 1 | 10.8 (7.6, 14.0) | 1.9 (0.0, 5.2) | |||
| Time 2 | 1.6 (0.2, 3.0) | 1.3 (0.0, 2.6) | |||
| Time 3 | 6.7 (4.3, 9.0) | 0.9 (0.0, 3.7) | |||
| Quantitative sensory testing | |||||
| PPT at the wrist extensors, kPad | .406 | .045c | .856 | ||
| Time 1 | 338.9 (264.9, 413.0) | 303.2 (242.1, 364.3) | |||
| Time 2 | 319.8 (251.3, 388.2) | 280.3 (226.7, 334.0) | |||
| CPM: PPT at hamstrings on contralateral AT pain side, kPa | .053 | <.001 | .536 | ||
| Before CPM: time 1 | 512.1 (400.2, 624.1) | 383.6 (297.4, 469.8) | |||
| During CPM: time 1 | 678.3 (523.0, 833.7) | 501.0 (382.9, 619.1) | |||
| Before CPM: time 2 | 462.9 (362.6, 563.2) | 358.0 (280.0, 436.4) | |||
| During CPM: time 2 | 573.3 (475.4, 671.2) | 432.0 (352.3, 511.6) | |||
| CPM: PPT at heel on side contralateral to AT pain, kPa | .172 | <.001 | .770 | ||
| Before CPM: time 1 | 876.7 (712.9, 1040.5) | 729.4 (597.9, 860.9) | |||
| During CPM: time 1 | 1004.6 (811.7, 1197.5) | 842.9 (695.8, 990.1) | |||
| Before CPM: time 2 | 768.8 (625.7, 911.8) | 653.5 (538.5, 768.5) | |||
| During CPM: time 2 | 866.2 (715.6, 1016.7) | 766.5 (643.9, 889.2) | |||
| Temporal summation: verbal numeric pain rating during ice bath of the hand | .911 | <.001 | .440 | ||
| 5 s: time 1 | 3.5 (2.6, 4.4) | 2.9 (2.2, 3.6) | |||
| 20 s: time 1 | 5.0 (3.9, 6.1) | 4.9 (4.1, 5.8) | |||
| 5 s: time 2 | 3.2 (2.1, 4.4) | 3.1 (2.3, 3.9) | |||
| 20 s: time 2 | 5.2 (4.0, 6.5) | 5.8 (4.9, 6.7) | |||
Abbreviations: AT, Achilles tendinopathy; CPM, conditioned pain modulation; HR, heel raise; PPT, pressure pain threshold.
Time point 1, prior to the anesthetic injection/first repetition (controls); time point 2, after the anesthetic injection/second repetition (controls); time point 3, at 1-week follow-up (Pain Catastrophizing Scale only).
Values are mean (95% confidence interval).
Change in statistical significance compared to the primary analysis.
Measured bilaterally as the average of the left and right sides.
Table 5.
Measures of Altered Central Processing, Including Motor Dysfunction, Heightened Pain Psychology Factors, and Nociplastic Pain, in Participants With Bilateral AT
| P Value | |||||
|---|---|---|---|---|---|
| Domain/Test/Time Pointa | Bilateral AT Groupb | Control Groupb | Group | Time | Group by Time |
| Motor performance | |||||
| Maximum single-limb HRs, n | .072 | .121 | .013 | ||
| Time 1 | 12.2 (4.5, 19.8) | 22.5 (18.6, 26.5) | |||
| Time 2 | 17.3 (10.4, 24.3) | 21.3 (17.6, 24.9) | |||
| Peak plantar flexor power during stair ascent, W/kg | .810 | .490 | .545 | ||
| Time 1 | 2.8 (2.2, 3.4) | 3.0 (2.6, 3.3) | |||
| Time 2 | 2.8 (2.2, 3.4) | 2.8 (2.5, 3.1) | |||
| Peak plantar flexor power during the waltz, W/kg | .453 | .098 | .695 | ||
| Time 1 | 0.6 (0.2, 0.9) | 0.7 (0.5, 0.9) | |||
| Time 2 | 0.5 (0.1, 0.8) | 0.6 (0.5, 0.8) | |||
| Pain psychology questionnaires | |||||
| Tampa Scale of Kinesiophobia | <.001 | .003 | .058 | ||
| Time 1 | 41.7 (37.5, 45.9) | 29.6 (27.2, 31.9) | |||
| Time 2 | 37.9 (33.7, 42.1) | 28.7 (26.3, 31.0) | |||
| Pain Catastrophizing Scale | <.001 | <.001 | <.001 | ||
| Time 1 | 16.6 (10.9, 22.2) | 1.9 (0.0, 5.0) | |||
| Time 2 | 4.4 (1.9, 7.0) | 1.3 (0.0, 2.7) | |||
| Time 3 | 12.1 (7.3, 17.0) | 0.9 (0.0, 3.6) | |||
| Quantitative sensory testing | |||||
| PPT at the wrist extensors, kPac | .786 | .191 | .542 | ||
| Time 1 | 311.7 (202.6, 420.8) | 303.2 (241.9, 364.4) | |||
| Time 2 | 303.3 (202.2, 404.4) | 280.3 (220.1, 340.5) | |||
| CPM: PPT at hamstrings on contralateral AT pain side, kPa | .880 | <.001 | .747 | ||
| Before CPM: time 1 | 373.2 (235.8, 510.7) | 383.6 (304.3, 463.0) | |||
| During CPM: time 1 | 444.7 (250.3, 639.0) | 501.0 (388.8, 613.2) | |||
| Before CPM: time 2 | 356.4 (222.6, 490.3) | 358.0 (280.7, 435.3) | |||
| During CPM: time 2 | 450.3 (300.1, 600.5) | 432.0 (345.2, 518.7) | |||
| CPM: PPT at heel on side contralateral to AT pain, kPa | .845 | .015 | .219 | ||
| Before CPM: time 1 | 598.1 (335.0, 861.2) | 729.4 (590.7, 868.1) | |||
| During CPM: time 1 | 863.0 (559.2, 1166.8) | 842.9 (682.8, 1003.0) | |||
| Before CPM: time 2 | 648.9 (399.0, 898.7) | 653.5 (521.8, 785.2) | |||
| During CPM: time 2 | 772.9 (492.2, 1053.7) | 766.5 (618.6, 914.5) | |||
| Temporal summation: verbal numeric pain rating during ice bath of the hand | .859 | <.001 | .247 | ||
| 5 s: time 1 | 2.7 (1.5, 4.0) | 2.9 (2.2, 3.6) | |||
| 20 s: time 1 | 5.4 (3.9, 7.0) | 4.9 (4.1, 5.8) | |||
| 5 s: time 2 | 2.7 (1.3, 4.1) | 3.1 (2.3, 3.9) | |||
| 20 s: time 2 | 5.3 (3.9, 6.7) | 5.8 (5.0, 6.5) | |||
Abbreviations: AT, Achilles tendinopathy; CPM, conditioned pain modulation; HR, heel raise; PPT, pressure pain threshold.
Time point 1, prior to the anesthetic injection/first repetition (controls); time point 2, after the anesthetic injection/second repetition (controls); time point 3, at 1-week follow-up (Pain Catastrophizing Scale only).
Values are mean (95% confidence interval).
Measured bilaterally as the average of the left and right sides.
FIGURE.
Participant with Achilles tendinopathy performing the waltz box step. A set of 3 infrared diodes on a thermoplastic molded platform were taped to the skin of each segment. The images demonstrate the participant stepping forward onto the left leg (A), and then pushing off from the left leg with a lateral sidestep onto the right leg (B). The ankle power generated by the left leg during the lateral sidestep was used for analysis.
Footnotes
This clinical trial was approved by the University of Iowa Institutional Review Board (IRB-01 Biomedical).
The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article.
PATIENT AND PUBLIC INVOLVEMENT: There was no patient or public involvement in this study.
DATA SHARING:
Individual participant data that underlie the results reported in this article, after deidentification, will be available immediately following publication and up to 5 years following publication. These data will be shared with researchers who provide a methodologically sound proposal and will use the data to achieve aims specified in the proposal. Proposals should be directed to the corresponding author. To gain access, data requestors will need to sign a data-access agreement.
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