Abstract
Background: Lateral epicondylitis (LE), commonly known as tennis elbow, is an enthesopathy involving the insertion of the common extensor tendon (CET), frequently associated with overuse and degenerative changes. While several conservative therapies exist-including NSAIDs, corticosteroids, PRP, and physiotherapy-none have proven uniformly effective, and some carry undesirable side effects. Recently, collagen peptides have emerged as a promising therapeutic option due to their regenerative and anti-inflammatory properties. Objective: To evaluate the efficacy and safety of ultrasound-guided injections of low-molecular-weight peptides (LWPs) derived from hydrolyzed collagen in patients with LE and partial-thickness CET tears. Methods: This retrospective study included 13 patients with persistent epicondylar pain and ultrasonographic evidence of partial CET tears. Patients received two US-guided injections of collagen peptides, at baseline and at two weeks. Clinical outcomes were assessed using the Numeric Rating Scale (NRS) for pain, while structural changes were monitored via greyscale (GS) and Power Doppler ultrasound at predefined follow-up points. Results: Pain scores improved significantly as early as three days post-injection (mean NRS reduction from 7.5 to 4.8; p<0.05), with continued improvement to 2.5 at one month. Doppler signal decreased significantly, indicating reduced inflammation. Tendon lesions resolved in 8/13 patients and decreased in size in 3. Only two patients experienced mild, transient post-injection pain. Conclusion: Collagen peptide injections appear to be safe and effective treatment for LE, offering significant pain relief and tendon healing. These preliminary findings support further prospective, controlled trials to validate long-term efficacy and positioning in clinical practice.
Keywords: Lateral epicondylitis , ultrasound , ultrasound-guided injections , low-molecular weight peptides
Introduction
Lateral epicondylitis (LE), or tennis elbow, is an enthesopathy affecting the pre-insertional tract of the common extensor tendon (CET) to the lateral epicondyle of the humerus [1].
Overuse injuries, particularly involving the extensor carpi radialis brevis (ECRB) tendon, contribute to the development of this condition [1].
The repetitive strain on the tendon insertion leads to reduced blood supply and formation of microtears, ultimately resulting in degenerative lesions [2].
LE is prevalent among middle-aged individuals, affecting approximately 1-3% of the general population, with no notable gender disparities [3, 4].
While many cases resolve within a year without intervention, persistent or severe forms of LE often require conservative treatment or even surgery.
Currently, non-surgical interventions are prioritized in the absence of standardized therapies for LE.
These interventions include physiotherapy, shock-wave treatment, nonsteroidal anti-inflammatory drugs (NSAIDs), and local injections with corticosteroids (CSs), platelet-rich plasma (PRP), and botulinum toxin (BT) [5, 6, 7].
However, these available treatments have limitations in terms of efficacy and long-term outcomes.
Physiotherapy may not provide adequate pain relief or full recovery, NSAIDs offer temporary relief without addressing degenerative changes, and PRP can be very effective but may yield inconsistent outcomes due to device heterogeneity [8].
Additionally, corticosteroids can induce local tissue atrophy, impairing tendon healing and regenerative potential [9].
Recently, the local administration of collagen peptide injections has emerged as a promising therapeutic approach for acute and chronic musculoskeletal disorders [10].
Collagen peptides, derived from collagen hydrolysis, consist of short amino acid chains with remarkable properties such as high biocompatibility and low immunogenicity.
Collagen, an essential structural component of connective tissue, is abundantly present in various anatomical structures including bones, tendons, muscles, ligaments, cartilage, teeth, and skin.
In tendinopathies, excessive and repetitive mechanical loading triggers a cascade of events leading to tissue damage, inflammation, and impaired healing [11].
This process disrupts collagen synthesis, organization, and turnover, ultimately contributing to tendon degeneration and weakening.
By supplying the necessary building blocks in the form of short amino acid chains, collagen peptides act as precursors for the synthesis of new collagen fibers.
This promotes the remodeling and strengthening of the tendon structure, restoring its mechanical properties and improving its resistance to further damage [12].
Additionally, collagen peptides modulate inflammation and cellular signaling pathways, creating a favorable microenvironment for tissue regeneration and healing [13].
Some studies have explored the benefits of oral collagen peptide supplementation.
In a randomized, placebo-controlled study, 40 healthy males received a daily dosage of 5g collagen peptides or a placebo supplement.
The collagen peptides supplementation resulted in a significant increase in tendon cross-sectional area and muscle thickness compared to the placebo group [14].
In another placebo-controlled cross-over study, oral supplementation of specific collagen peptides improved symptoms and tendon vascularization in patients with chronic mid-portion Achilles tendinopathy, in combination with structured exercise [15].
However, local injection of collagen peptides may be more effective in healing tendinopathies than oral supplementation due to its direct delivery and targeted action at the site of injury, bypassing potential limitations of systemic absorption and distribution.
A case report described a patient with a partial-thickness tear of the supraspinatus tendon who was treated with four type I porcine collagen ultrasound-guided injections at weekly intervals.
Along with exercises, the patient exhibited almost complete resolution of shoulder symptoms and functional limitations [16].
Recently a paper addressing the efficacy of collagen peptides injection in supraspinatus tears in 21 patients has been published [17] but there is a lack of literature investigating the use of collagen peptide intra-tendinous injection specifically for the treatment of LE.
Therefore, this study aimed to assess the efficacy and safety of collagen peptide solution intra-tendinous injection in patients with LE.
Objective
The main aims of the present study were:
-to evaluate the clinical efficacy of US-guided injections with low-molecular weight peptides (LWPs) derived from hydrolyzed collagen at elbow level in patients with pain due to enthesopathy and partial thickness tear of the CET detected by ultrasound (US) at the insertion on the epicondyle
-to record side effects of LWPs of collagen injections
-to investigate the ability of musculoskeletal US in identifying the pathological findings responsible for treatment failure
Materials and Methods
Study design
This is a retrospective study involving consecutive patients with elbow lateral epicondylar pain due to enthesopathy with partial thickness tear of the CET diagnosed by US.
Patients have been enrolled in the outpatient clinic of the Rheumatology section of the Interdisciplinary Pain medicine Unit of Santa Maria Maddalena Hospital in Occhiobello, Italy, Emergency County Hospital Craiova, Rheumatology Department, Romania and Ecomed Research Clinic, Craiova, Romania between July 2021 and February 2023.
Patients eligible for US-guided collagen injections were those over 18 years old with persistent elbow pain for at least one month and an US diagnosis of CET pathology with at least a partial tear.
Exclusion criteria were previous surgery, known hypersensitivity to drug’s substances and a known diagnosis of inflammatory arthritis.
Moreover, the presence of concomitant fibromyalgia and cervical spine disease has been investigated and recorded.
According to our routine follow-up protocol, patients have been evaluated four times: before the first injection of LWPs (baseline visit, t0), 3 days after baseline visit (telephonic follow-up, t1), 2 weeks after baseline visit (first follow up visit, t2, coinciding with the second injection) and 1 month after second injection (second follow-up visit, t3).
During each visit, the following data were recorded: the Numeric Rating Scale (NRS 0-10) for pain and both Grey Scale (GS), and Power Doppler (PD) US findings indicative of entheseal pathology.
During the telephonic follow-up, only the Numeric Rating Scale (NRS 0-10) and any side effects were recorded.
Ultrasound examination
Patients have been examined with an Alpinion xcube90 ultrasound machine using a 5-25 MHz linear transducer according to a standardized scanning protocol, with the elbow in flexed and neutral position.
The enthesis was assessed in both long and short-axis with the probe perpendicular to the tendon [18, 19]
All the US examinations were carried out by an expert rheumatologist (F.P. or F.V.) to detect US findings reported in the inclusion and exclusion criteria.
US assessment aimed to confirm the presence of CET enthesis pathology, detecting B-mode alterations (thickening, hypoechogenicity, tears) (Figure 1) and Doppler signal according to OMERACT guidelines [18].
Figure 1.
Ultrasound images of the common extensor tendon in longitudinal (A) and transverse (B) planes, showing the tendon (T), humerus (H), collateral ligament (L), and humeroradial joint capsule (C).
A heterogeneous appearance of the tendon is noted, with a hypoechoic area suggestive of a lesion (arrow).
Particular attention was given to probe positioning in order to avoid anisotropy-induced artifacts that could interfere with the accurate diagnosis of tendon tears [12].
Only partial full-thickness tears with a maximum diameter of less than 8mm were included in the study.
A 0 to3 semiquantitative scoring system for entheseal hypervascularization was adopted in accordance with the OMERACT criteria, where 0 indicates absence of Doppler signal, 1 indicates presence of <2 punctiform Doppler signals with no confluent Doppler signal, 2 indicates presence of 2-4 punctiform Doppler signals or 1 confluent Doppler signal and 3 indicates presence of >4 punctiform Doppler signals or >1 confluent Doppler signal) [20, 21, 22].
No scoring was applied for B-mode enthesopathy while lesions’ dimensions have been recorded.
During follow-up visits, US examination was carried out to identify any changes of CET tendon.
Ultrasound-guided injection
All the patients underwent two US-guided injections with LWPs: at baseline visit (t0) and at first follow-up visit (t2).
US-guided injections were performed using a standardized protocol.
Patient were seated with the arm in neutral position, the elbow flexed at 90 degrees, and the forearm in a prone position on the bed.
A rheumatologist (F.P. or F.V.) with more than 10 years of experience injected all the tendons using a free-hand US-guided in-plane approach (real-time visualization of the needle tip during its progression from the skin to the target) visualizing the tendon in transverse view (Figure 2).
Figure 2.
Short-axis ultrasound image of the common extensor tendon, with visualization of the needle (needle) advancing toward the hypoechoic lesion (arrow), H-Humerus
A specific preparation (5 mg/dl 1 ml LWPs, Peptys-Horizon Lab Company, Italy) has be injected into the intra-tendinous lesion whenever possible or in the peritendinous area, using a 25-Gauge needle.
Data Analysis
Changes over time were assessed using a one-way repeated-measures ANOVA (within-subject factor: time, T0-T3).
When the overall effect was significant, pairwise post-hoc comparisons were performed using Bonferroni correction.
A two-sided p value <0.05 was considered statistically significant.
Changes in Power Doppler scores over time were analyzed using the Wilcoxon signed-rank test.
Given the small sample size and the ordinal nature of pain scores, Spearman’s rank correlation was used to analyze the effect of age on pain reduction.
Results
Thirteen patients have been included in the study (mean age 51,3 years, 6 females).
According to inclusion criteria all the patients presented US signs of enthesopathy (9/13 had thickening, 11/13 hypoechogenicity, 4/13 enthesophytes, 13/13 hypervascularization).
All patients showed at least 1 partial tendon lesion usually between 2 and 5 mmm of width; only one patient had a larger lesion of 7mm.
Baseline characteristics of patients are showed in Table 1.
Table 1.
Baseline demographic and clinical characteristics of the study population
Baseline characteristics
Age (mean, SD)
51,3±10,5
Female sex (%)
46%
Pain NRS (mean, SD)
7,5±1,7
PD signal (median,
2 (1-3)
Tendon lesion (%)
100%
NRS: Numeric Rating Scale; PD: Power Doppler; SD: Standard Deviation
Efficacy
The majority of patients (10) achieved the minimal clinically detectable improvement (2 points of pain NRS) as early as T1 and the result was maintained during the further follow-up.
Pain, measured by NRS (mean±SD), showed a significant decrease after the first injection (7.5±1.7 vs 4.8±2.7, p<0.05), with continued improvement throughout the follow-up period (T3: 2.5±1.1) (Table 2).
Table 2.
Evolution of clinical and ultrasound parameters at baseline and follow-up (T1-T3).
Baseline
T1
T2
T3
p
Pain NRS
(mean, SD)
7,5±1,7
4,8±2,7
3,6±2,5
2,5±1,1
<0,05
(repeated-measures ANOVA, post-hoc Bonferroni)
PD signal
(median, range)
2 (1-3)
N.D.
1(0-2)
1 (0-2)
<0,05
(Wilcoxon)
Tendon lesion (%)
100%
N.D.
50%
38%
N.A.
NA: Not Available; ND: Not Done; NRS: Numeric Rating Scale; PD: Power Doppler; SD: Standard Deviation
A repeated-measures ANOVA showed a statistically significant effect of time on the outcome NRS-pain, indicating that scores changed significantly across follow-up visits.
The effect size was large (Partial eta-squared 0.619), suggesting that the effect of time on pain change is not only statistically significant but also relevant.
Post-hoc testing (Bonferroni-corrected) showed that scores decreased significantly from baseline (T0) to T1, T2, and T3.
More specifically, T1 was significantly higher than T3, while T1 vs T2 and T2 vs T3 did not reach statistical significance after correction.
Overall, the data are consistent with an early drop from baseline followed by a more gradual change over subsequent follow-up (Figure 3).
Figure 3.
Changes in NRS pain score over time (T0-T3). Data are presented as mean±SD. Differences across time points were analyzed using a repeated-measures ANOVA. When the overall effect was significant, pairwise post-hoc comparisons with Bonferroni correction were performed. Horizontal brackets indicate statistically significant differences between time points (p <0.05; p <0.01; p <0.001).
Overall, these findings indicate a rapid and clinically meaningful response to ultrasound-guided collagen peptide injections, with sustained pain reduction over time.
The early improvement observed at T1 suggests a fast onset of action, while the progressive changes in Power Doppler signal and tendon morphology support a continuing biological effect beyond short-term analgesia.
The magnitude of pain reduction from baseline to T3 (ΔT0-T3) was compared between males and females.
Although male patients showed a numerically greater improvement (5.14±2.42) than females (3.50±2.81), this difference did not reach statistical significance (t-test p=0.33; Mann-Whitney p=0.25).
These findings indicate that long-term pain reduction was comparable between sexes.
Exploratory analyses were performed to investigate the relationship between age and pain outcomes.
Spearman correlation analyses showed a significant inverse correlation between age and pain scores at T2 (ρ=−0.56, p=0.049), while correlations at T1 and T3 were not statistically significant.
Age was positively correlated with early pain reduction from baseline to T1 (ρ=0.61, p=0.028), indicating greater early improvement in older patients.
The correlation between age and pain reduction from baseline to T3 did not reach statistical significance, indicating and effect of age in the speed of the response but not on the magnitude.
PD signal decreased progressively during follow up with a significant decrease between T0 and T2 and between T2 and T3 (Wilcoxon, p<0,05 and 0,005 respectively) (Table 2).
In 8 out of 13 patients, no lesions were detectable at T3, in 2 patients they remained unchanged while in the 3 patients there have been a decrease in the size of the lesion.
No data were recorded for the other B-mode features of enthesopathy (Table 2).
Taken together, the ultrasound findings suggest that inflammatory changes tend to improve earlier than structural tendon abnormalities, highlighting different timelines for biological response and tissue repair.
Safety
Out of 13 patients, 2 patients experienced a short duration (1 day) exacerbation of pain after the injection.
One patient took a tablet of paracetamol while the other one reported pain being not so intense to need any treatment.
Predictors of failure
Due to the limited number of patients, especially among non-responders-it was not possible to identify determinants of treatment response.
Discussions
The results of this study suggest that ultrasound-guided injection of LWPs derived from hydrolyzed collagen represents a promising therapeutic option for the management of LE, particularly in patients with US signs of enthesopathy and partial-thickness tears of the CET.
The significant and rapid reduction in pain, as measured by the NRS, was evident as early as the first follow-up (T1), sustained and further enhanced throughout the follow-up period.
The maintenance of the positive result with progressive improvement over time argues against a predominant placebo effect, which is known to be frequent after interventional procedures, and typically transient in nature.
From a clinical perspective, this pattern is particularly relevant, as early pain relief may facilitate patient adherence to conservative management strategies and reduce the need for more invasive interventions.
The rapid analgesic effect may be attributed not only to the regenerative properties of collagen peptides but mainly to their modulatory role in local inflammation.
This hypothesis is supported by the significant reduction in intra-tendinous PD signal, indicative of decreased hyperaemia and inflammatory activity, with statistically significant differences observed between T0 and T2 (p<0.05) and between T2 and T3 (p<0.005).
These findings align with previous studies suggesting that collagen peptides modulate inflammation and cellular signaling pathways, creating a favorable environment for tissue regeneration and healing [13].
Moreover, in chronic tendinopaties, intratendinous PD may reflect not only active inflammation but also advanced stages of tendon degeneration as described in the continuum model proposed by Cook and Purdam [23].
In our patients, the reduction of PD signal concomitant with lesion improvement/resolution, is probably a positive sign of tissue remodeling and restoration toward a healthier tendon structure.
From an ultrasonographic perspective, the reduction in the size of tendon lesions and the complete resolution of these lesions in 8 out of 13 patients at T3 indicate a positive effect on the tendon healing process.
However, in 2 patients, the lesions remained unchanged, while in 3 others, only a reduction in lesion size was observed.
These results seem to confirm what has already be shown by Latini et al about the efficacy of US-guided injection of (LWPs) derived from hydrolyzed collagen in supraspinatus tendon tears [17].
This variability in response may be related to individual factors such as the chronicity of the lesion, patient comorbidities, or the extent of tendon degeneration, which were not extensively analyzed in this study.
Moreover, due to the retrospective nature of this study, it has been impossible to determine if patients respected a rest period after the injection or if they went on with their usual activities possibly worsening the already present lesion.
In this context, musculoskeletal ultrasound should not be regarded solely as a diagnostic tool, but also as an instrument for treatment selection and follow-up, allowing a more personalized and pathophysiology-driven approach to lateral epicondylitis.
A particularly relevant finding is the favorable safety profile of the procedure.
Only 2 patients reported transient pain exacerbation after the injection, which resolved spontaneously or with the intake of a single dose of paracetamol.
No severe adverse events or local complications were reported, confirming the safety of collagen peptide injections.
This contrasts with corticosteroid injections, which are associated with potential adverse effects such as local tissue atrophy and impaired tendon healing [9].
However, this study has several limitations.
The small sample size (13 patients) limits the generalizability of the findings and reduces the statistical power to identify predictors of treatment response.
Additionally, the absence of a control group or a direct comparison with other established therapies, such as platelet-rich plasma (PRP) or corticosteroids, prevents definitive conclusions regarding the relative efficacy of collagen peptides.
The retrospective nature of the study and the lack of complete ultrasonographic data on certain B-mode features of enthesopathy further constrain the interpretation of the results.
Another critical limitation is the relatively short follow-up period, which does not allow for the assessment of long-term outcomes.
Given that LE often presents as a chronic condition with potential for recurrence, future studies should include extended follow-up periods to evaluate the durability of clinical improvements and the prevention of relapses.
Conclusion
Although preliminary, the present findings suggest that collagen peptide injections may represent a valuable addition to the therapeutic armamentarium for lateral epicondylitis, particularly in patients with ultrasound-confirmed enthesopathy and partial-thickness tendon tears.
In conclusion, ultrasound-guided injection of low-molecular-weight collagen peptides demonstrated efficacy in reducing pain and improving PD findings at entheseal level in patients with lateral epicondylitis, with a favorable safety profile.
Despite methodological limitations, these encouraging results warrant further prospective, randomized controlled trials to confirm efficacy, explore long-term outcomes, and establish the role of this therapy in clinical practice.
Conflict of interests
The authors declare no competing interests.
Acknowledgments
None to declare.
Author Contributions
Conceptualization, F.P., E.F. and F.A.V.; Methodology, F.P., E.F., X.B. and F.A.V.; Ultrasonography, F.P. and F.A.V.; Data analysis, X.B., S.C.D.; Manuscript writing and initial draft preparation, F.P. and F.A.V.; Manuscript review and editing, F.P., E.F. and F.A.V.; All authors read and approved the final manuscript.
Funding
This research received no specific funding.
Institutional Review Board
The study was conducted according to the guidelines of the Declaration of Helsinki; the study and the protocols used therein were approved by the Ethics Committee of the Emergency County Hospital of Craiova, Romania (reg. NR 22763/09.05.2023).
Consent Statement
All human subjects involved in this study provided a written informed consent before participation, including the consent of publishing their anonymized data.
Data availability
All data presented in the manuscript are available from the authors upon request.
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