In recent years, the plantaris tendon has been implicated in the development of chronic painful mid-portion Achilles tendinopathy. In some cases, a thickened plantaris tendon is closely associated with the Achilles tendon, and surgical excision of the plantaris tendon has been reported to be curative in patients who have not derived benefit following conservative treatment and surgical interventions. The aim of this review is to outline the basic aspects of, and the recent research findings, related to the plantaris tendon, covering anatomical and clinical studies including those dealing with histology, imaging and treatment. Cite this article: Bone Joint J 2016;98-B:1312–19

Aims. Functional rehabilitation has become an increasingly popular treatment for Achilles tendon rupture (ATR), providing comparably low re-rupture rates to surgery, while avoiding risks of surgical complications. Limited evidence exists on whether gap size should affect patient selection for this treatment option. The aim of this study was to assess if size of gap between ruptured tendon ends affects patient-reported outcome following ATR treated with functional rehabilitation. Methods. Analysis of prospectively collected data on all 131 patients diagnosed with ATR at Royal Berkshire Hospital, UK, from August 2016 to January 2019 and managed non-operatively was performed. Diagnosis was confirmed on all patients by dynamic ultrasound scanning and gap size measured with ankle in full plantarflexion. Functional rehabilitation using an established protocol was the preferred treatment. All non-operatively treated patients with completed Achilles Tendon Rupture Scores (ATRS) at a minimum of 12 months following injury were included. Results. In all, 82 patients with completed ATRS were included in the analysis. Their mean age was 51 years (standard deviation (SD) 14). The mean ATRS was 76 (SD 19) at a mean follow-up of 20 months (SD 11) following injury. Gap inversely affected ATRS with a Pearson’s correlation of -0.30 (p = 0.008). Mean ATRS was lower with gaps > 5 mm compared with ≤ 5 mm (73 (SD 21) vs 82 (SD 16); p = 0.031). Mean ATRS was lowest (70 (SD 23)) with gaps > 10 mm, with significant differences in perceived strength and pain. The overall re-rupture rate was two out of 131 (1.5%). Conclusion. Increasing gap size predicts lower patient-reported outcome, as measured by ATRS. Tendon gap > 5 mm may be a useful predictor in physically demanding individuals, and tendon gap > 10 mm for those with low physical demand. Further studies that control for gap size when comparing non-operative and operative treatment are required to assess if these patients may benefit from surgery, particularly when balanced against the surgical risks. Cite this article: Bone Joint J 2020;102-B(11):1535–1541

Introduction. Flexor Hallucis Longus (FHL) tendon transfer is a well-recognised salvage operation for irreparable tendon Achilles (TA) ruptures and intractable Achilles tenonopathy. Several case series describes the technique and results of arthroscopic FHL tendon transfers. We present a comparative case series of open and arthroscopic FHL tendon transfers from Southmead Hospital, Bristol, UK. Methods. For the arthroscopic FHL transfers in most cases the patients were positioned semi prone with a tourniquet. A 2 or 3 posterior portal technique was used and the tendon was secured using an RCI screw. The rehabilitation was similar in both groups with 2 weeks in an equinus backslab followed by gradual dorsiflexion in a boot over the following 6 weeks. Anticoagulation with oral aspirin for 6 weeks was used. A retrospective case note review was performed. Results. There were 12 arthroscopic (8 males, 4 female) and 16 open procedures (9 male, 7 female). Both had a mean age of 56. 1 arthroscopic FHL was lost to follow up. There were no concomitant procedures in the arthroscopic group. In the open group the TA was repaired in 7 cases (3 of these involved z-shortening). There was 1 plantaris interposition, 1 V-Y advancement and 1 gastrocnemius advancement. Degenerate tendon was excised in 1 severe re-rupture of a calcified tendinopathic achilles. There was no difference in tourniquet time between the groups (arthroscopic 69mins vs open 64 mins, p=0.64). There were no complications in the arthroscopic group. In the open group there was 1 superficial wound infection, 1 nerve injury & 1 delayed DVT at 3 months. Conclusion. Arthroscopic FHL transfer is a safe and effective surgical option when no other achilles procedures are required. The soft tissue insult is minimal, making it a good option for patients with poor soft tissues or neurovascular compromise

Introduction:. Peroneal muscle weakness is a common pathology in foot and ankle surgery. Polio, charcot marie tooth disease and spina bifida are associated with varying degrees of peroneal muscle paralysis. Tibialis Posterior, an antagonist of the peroneal muscles, becomes pathologically dominant, causing foot adduction and contributes to cavus foot posture. Refunctioning the peroneus muscles would enhance stability in toe off and resist the deforming force of tibialis posterior. This study determines the feasibility of a novel tendon transfer between peroneus longus and gastrocnemius, thus enabling gastrocnemius to power a paralysed peroneus tendon. Method:. 12 human disarticulated lower limbs were dissected to determine the safety and practicality of a tendon transfer between peroneus longus and gastrocnemius at the junction of the middle and distal thirds of the fibula. The following measurements were made and anatomical relationships quantified at the proposed site of the tendon transfer: The distance of the sural nerve to the palpable posterior border of the fibula; the angular relationship of the peroneus longus tendon to gastrocnemius and the achilles tendon; the surgical field for the proposed tendon transfer was explored to determine the presence of hazards which would prevent the tendon transfer. Results:. The mean angle between the tendons of peroneus longus and gastrocnemius/achilles tendon was 3°. The sural nerve lies on average 30 mm posterior to the palpable posterior border of the fibula. There were no significant intervening structures to prevent the proposed tendon transfer. Conclusion:. The line of action of peroneus longus and gastrocnemius are as near parallel as to be functionally collinear. The action of gastrocnemius may be harnessed to effectively power a paralysed peroneus longus tendon, without significant loss of force owing to revectoring of forces. The surgical approach to effect such a tendon transfer is both safe and practical

Introduction. The exact action of the Peroneus Longus muscle on the foot is not fully understood. It is involved in a number of pathological processes like tendonitis, tenosynovitis, chronic rupture and neurological conditions. It is described as having a consistent insertion to the base of the first metatarsal, but there have also been reports of significant variations and additional slips. Our aim was to further clarify the anatomy of the main insertion of the Peroneus Longus tendon and to describe the site and frequency of other variable insertion slips. Methods and Materials. The course of the distal peroneus longus tendon and its variable insertion was dissected in 12 embalmed, cadaveric specimens. The surface area of the main insertion footprint and angle of insertion was measured using an Immersion Digital Microscribe and 3D mapping software. The site and frequency of the other insertion slips is also presented. Results. There was a consistent, main insertion to the infero-lateral aspect of the first metatarsal in all specimens. The only additional slip was to the medial cuneiform. This did not increase the total footprint. Discussion. The main footprint of the Peroneus Longus tendon is on the first metatarsal. There was an additional slip to the medial cuneiform in 33% of our specimens. Although we are unsure about the significance of this additional slip, we hope it will lead to a better understanding of the mechanism of action of this muscle and its role both in the normal and pathological foot

Operative and non-operative treatment regimens for Achilles tendon ruptures vary greatly but commonly involve rigid casting or functional bracing. The aim of our study was to investigate the extent of tendon apposition following such treatments. Twelve fresh-frozen, adult below knee lower-extremity cadaveric specimens with intact proximal tibiofibular joints were used. Each was prepared by excising a 10cm × 5cm skin and soft tissue window exposing the Achilles tendon. With the ankle in neutral position, the tendon was transfixed with a 2mm k-wire into the tibia, 8cm from its calcaneal insertion. A typical post-rupture gap was created by excising a 2.5cm portion of tendon between 3.5cm and 6cm from its calcaneal insertion. The specimens were then placed into a low profile walker boot (SideKICK. TM. , Procare) without wedges and a window cut into the back. The distance between the proximal and distal Achilles tendon cut edges was measured and repeated with 1, 2 and 3 (10mm) wedges. Subsequently the specimens were placed into a complete below knee cast in full equinus which was also windowed. The Achilles tendon gap (mean +/− SD) measured: 2.7cm (0.5) with no wedge, 2.3cm (0.4) with 1, 2.0cm (0.4) with 2, 1.5cm (0.4) with 3 wedges and 0.4cm (0.3) in full equinus cast. The choice of treatment had a significant effect on tendon gap (p< 0.0001 – repeated measures ANOVA), and all pairwise comparisons were significantly different (Bonferroni), with all p< 0.001, apart from 0 wedge vs. 1 wedge (p< 0.01) and 1 wedge vs. 2 wedges (p< 0.05). Our results showed that each wedge apposed the tendon edges by approximately 0.5cm with the equinus cast achieving the best apposition. Surgeons should consider this when planning appropriate immobilisation regimes for Achilles tendon ruptures

Introduction:. Although dislocation of the peroneal tendons (PT's) in association with calcaneal fractures has been described over 25 years ago, it frequently passes unrecognised by radiologists and orthopaedic surgeons. This retrospective study aims to determine the prevalence of PT dislocation in association with calcaneal fractures at a single institution and describe systematic steps to avoid missed diagnosis at each stage of management. Methods:. CT scans of all patients with calcaneal fractures from the Picture Archiving and Communications System (PACS) from 2010 were systematically reviewed. The senior author and a Musculoskeletal Radiologist analysed the images for concomitant dislocation or subluxation of the PT's, utilizing criteria as defined by Ho et al. Further to this we included patients who sustained calcaneal fractures with associated PT dislocation prior to June 2010 and were referred either for primary open reduction or later with post-traumatic osteoarthrosis of the subtalar joint. Results:. Over three years and nine months beginning in June 2010, 71 calcaneal fractures were identified on PACS. 15 of those had associated subluxation or dislocation of the peroneal tendons either on CT scan or at surgery (21%). 10 of our 71 patients exhibited a fleck sign on plain anteroposterior ankle x-ray (14.1%) suggesting potential avulsion of the superior peroneal retinaculum. The combined cohort comprised 28 patients, 23 men and 5 women, aged 21 to 82 years (average, 46.3 years). 22 (79%) of PT dislocations were not recognised at the original injury. In six patients undergoing operative fixation, five (83.3%) had dislocated PT's noted on CT scan. In one case (16.7%) the peroneal tendons were clinically dislocated. Conclusion:. The PT dislocation rate in this paper is comparable with the literature. Patients should undergo careful clinical examination, radiological assessment with x-ray and CT followed by probing at surgery to ensure the diagnosis is not missed

Introduction. The mainstay of treatment in non-insertional Achilles tendinopathy is non-operative, however between 1/4 and 1/3 of patients fail this. The main symptom is pain which appears to be related to new nerve endings that grow into the tendon with the neovessels from the paratenon. Treatments which strip the paratenon from the tendon are showing promise including formal paratenon stripping via Achilles tendinoscopy. The pain and swelling in Achilles tendinopathy is usually on the medial side leading to the postulation that the plantaris tendon may have a role to play. Methods. We report a consecutive series of 11 patients who underwent Achilles tendinoscopy with stripping of the paratenon and division of the plantaris tendon, above the level of the tendinopathic changes in the Achilles. All patients had failed conservative treatment for at least 6 months and requested surgical intervention. The patients were scored with the SF-36, AOS and AOFAS hindfoot questionnaires pre-operatively and at a minimum of 2 years post operatively. They also recorded their level of satisfaction with the treatment at final follow up. Results. The mean AOFAS scores significantly improved from 68 pre-op to 92 post op (p = 0.0002) as did the AOS scores for both pain (28% pre-op to 8% post op (p=0.0004)) and disability (38% pre-op to 10% post op (p=0.0005). The mean SF-36 scores also improved but were not statistically significant (pre-op 76 post op 87 (P = 0.059). There were no complications. 8 of the 11 patients were satisfied, the other 3 somewhat satisfied. Conclusion. The results of Achilles tendinoscopy and division of the plantaris tendon are encouraging but further studies are required to compare it to other treatments. It is minimally invasive and low risk so should not affect the ability to perform a formal open procedure if unsuccessful

We studied a cohort of 26 diabetic patients with chronic ulceration under the first metatarsal head treated by a modified Jones extensor hallucis longus and a flexor hallucis longus transfer. If the first metatarsal was still plantar flexed following these two transfers, a peroneus longus to the peroneus brevis tendon transfer was also performed. Finally, if ankle dorsiflexion was < 5° with the knee extended, a Strayer-type gastrocnemius recession was performed. The mean duration of chronic ulceration despite a minimum of six months’ conservative care was 16.2 months (6 to 31). A total of 23 of the 26 patients were available for follow-up at a mean of 39.6 months (12 to 61) after surgery. All except one achieved complete ulcer healing at a mean of 4.4 weeks (2 to 8) after surgery, and there was no recurrence of ulceration under the first metatarsal. We believe that tendon balancing using modified Jones extensor hallucis longus and flexor hallucis longus transfers, associated in selected cases with a peroneus longus to brevis transfer and/or Strayer procedure, can promote rapid and sustained healing of chronic diabetic ulcers under the first metatarsal head

Introduction. The attachment of the plantar aponeurosis to the proximal phalanx of the toe, through the plantar plate (PP), forms the main flexor of the toe during gait by the reversed windlass mechanism. Disruption of the plantar plate is a common cause of pain, instability and toe deformity. Surgical techniques have recently been described to repair tears but long term results are awaited. This study aims to review the results of a technique designed to reconstruct and reinforce the failed plantar plate and restore the reversed windlass. Methods. Through a dorsal extra-articular approach the EDL tendon of the affected toe is used to restore the mechanical link between the proximal phalanx and the plantar aponeurosis on the plantar aspect of the joint. 42 PP reconstructions in 39 patients (36 female) aged 44–72 were undertaken, most frequently on the 2. nd. toe. 25 required correction of hallux valgus and four had undergone this previously. Follow up was 2–81 months. Results. Normal alignment and joint stability was obtained in 33 toes (81%). These patients reported no pain and were completely satisfied with the final result. Recurrence of the deformity with an unstable joint occurred in 8 toes, requiring revision surgery. Failure was more likely with pre-operative dislocation, lateral subluxation, or multiple toe involvement. Minor complications occurred in 5 patients. Conclusions. Repair or reconstruction of the plantar plate for lesser claw toe deformity is a logical option for correcting the deformity, and restoring toe function and the reversed windlass mechanism. The extra-articular approach may reduce the risk of joint stiffness, avoid scarring of the plantar tissues, and avoid toe elevation associated with metatarsal shortening. This approach is designed to reinforce the weakened plantar plate and may be a satisfactory alternative and more durable technique than direct plantar plate repair

This study assessed if transfer of the extensor hallucis longus is a valid alternative treatment to split transfer of the tibialis anterior tendon in adult hemiplegic patients without overactivity of the tibialis anterior. One group of 15 patients had overactivity of tibialis anterior in the swing phase, and underwent the split transfer. A further group of 14 patients had no overactivity of tibialis anterior, and underwent transfer of extensor hallucis longus. All patients had lengthening of the tendo Achillis and tenotomies of the toe flexors. All were evaluated clinically and by three-dimensional gait analysis pre- and at one year after surgery. At this time both groups showed significant reduction of disability in walking. Gait speed, stride length and paretic propulsion had improved significantly in both groups. Dorsiflexion in the swing phase, the step length of the healthy limb and the step width improved in both groups, but only reached statistical significance in the patients with transfer of the extensor hallucis longus. There were no differences between the groups at one year after operation. When combined with lengthening of the tendo Achillis, transfer of the extensor hallucis longus can be a valid alternative to split transfer of the tibialis anterior tendon to correct equinovarus foot deformity in patients without overactivity of tibialis anterior

Recurrent dislocation of peroneal tendons is uncommon and there are few reports of the long-term results after repair. The Singapore operation, first described in 1985, is an anatomical repair based on the Bankart-like lesion seen in the superior peroneal retinaculum. We reviewed 21 patients after a mean follow-up of 9.3 years, and found no recurrence. Eighteen had good functional results and had returned to their previous levels of vocational and sports activities. The three fair results were due to painful scars or neuromas

Introduction. The delayed presentation of Achilles tendon rupture is common, and is a difficult problem to manage. A number of surgical techniques have been described to treat this problem. We describe the use of Flexor Hallucis Longus (FHL) transfer to augment the surgical reconstruction of the delayed presentation of achilles tendon rupture. Materials and Methods. Fourteen patients with chronic tendo-Achilles rupture, presenting between April 2008 and December 2010, underwent surgical reconstruction and FHL transfer. Surgery was performed employing standard operative techniques, with shortening of the Achilles tendon and FHL transfer into the calcaneum with a Biotenodesis screw (Arthrex). VISA-A scores were performed preoperatively and six months postoperatively. Complication data was collected by review of the electronic patient record and direct patient questioning. Results. One patient died of an unrelated cause shortly before outcome scoring, and another patient was excluded because casting in the preoperative period prevented accurate scoring, although he achieved a good post-treatment score. Analysis was therefore carried out on twelve patients. Eleven of the twelve patients had significant improvement in their VISA-A score, with a mean improvement in score of 30 (p < 0.05). There were no significant complications in any of the patients. Conclusion. Our results show that FHL transfer in the management of chronic Achilles tendon rupture is a good, safe and reliable technique. There is excellent improvement in the mean VISA-A score, with no significant complications. Our results support the use of FHL tendon transfer for patients with chronic tendo-Achilles rupture

Aims

To determine whether the findings from a landmark Canadian trial assessing the optimal management of acute rupture of the Achilles tendon influenced the practice patterns of orthopaedic surgeons in Ontario, Canada.

Tendinopathy can commonly occur around the foot and ankle resulting in isolated rupture, debilitating pain and degenerative foot deformity. The pathophysiology and key cells involved are not fully understood. This is partly because the dense collagen matrix that surrounds relatively few resident cells limits the ability of previous techniques to identify and target those cells of interest. In this study, we apply novel single cell RNA sequencing (CITE-Seq) techniques to healthy and tendinopathic foot/ankle tendons. For the first time we have identified multiple sub-populations of cells in human tendons. These findings challenge the view that there is a single principal tendon cell type and open new avenues for further study. Healthy tendon samples were obtained from patients undergoing tendon transfer procedures; including tibialis posterior and FHL. Diseased tendon samples were obtained during debridement of intractable Achilles and peroneal tendinopathy, and during fusion of degenerative joints. Single cell RNA sequencing with surface proteomic analysis identified 10 sub-populations of human tendon derived cells. These included groups expressing genes associated with fibro-adipogenic progenitors (FAPs) as well as ITGA7+VCAM1- recently described in mouse muscle but, as yet, not human tendon. In addition we have identified previously unrecognised sub-classes of collagen type 1 associated tendon cells. Each sub-class expresses a different set of extra-cellular matrix genes suggesting they each play a unique role in maintaining the structural integrity of normal tendon. Diseased tendon harboured a greater proportion of macrophages and cytotoxic lymphocytes than healthy tendon. This inflammatory response is potentially driven by resident tendon fibroblasts which show increased expression of pro-inflammatory cytokines. Finally, identification of a previously unknown sub-population of cells found predominantly in tendinopathic tissue offers new insight into the underlying pathophysiology. Further work aims to identify novel proteins targets for possible therapeutic pathways

Aims. The Chopart joint complex is a joint between the midfoot and hindfoot. The static and dynamic support system of the joint is critical for maintaining the medial longitudinal arch of the foot. Any dysfunction leads to progressive collapsing flatfoot deformity (PCFD). Often, the tibialis posterior is the primary cause; however, contrary views have also been expressed. The present investigation intends to explore the comprehensive anatomy of the support system of the Chopart joint complex to gain insight into the cause of PCFD. Methods. The study was conducted on 40 adult embalmed cadaveric lower limbs. Chopart joint complexes were dissected, and the structures supporting the joint inferiorly were observed and noted. Results. The articulating bones exhibit features like a cuboid shelf and navicular beak, which appear to offer inferior support to the joint. The expanse of the spring ligament complex is more medial than inferior, while the superomedial part is more extensive than the intermediate and inferoplantar parts. The spring ligament is reinforced by the tendons in the superomedial part (the main tendon of tibialis posterior), the inferomedial part (the plantar slip of tibialis posterior), and the master knot of Henry positioned just inferior to the gap between the inferomedial and inferoplantar bundles. Conclusion. This study highlights that the medial aspect of the talonavicular articulation has more extensive reinforcement in the form of superomedial part of spring ligament and tibialis posterior tendon. The findings are expected to prompt further research in weightbearing settings on the pathogenesis of flatfoot. Cite this article: Bone Jt Open 2024;5(4):335–342

Insertional Achilles tendinitis with considerable degeneration that failed non-operative treatment typically requires tendon debridement and reattachment to bone. It is common practice for tendons to be reattached back with anchor sutures, but this poses a challenge to patients who are not able to afford them. Bony anchorage of tendons may be performed by passing sutures through tunnels, but the strength of repair compared to by using anchors is not known. We investigated the load at clinical and catastrophic failure of these two methods of reattachment. Sixteen paired Achilles tendons along with the calcaneus were harvested from eight fresh frozen cadavers. Paired randomization was done. For the anchor suture group, two 5’0 anchors with polyethylene #2 sutures were used for reattachment whereas for the suture only group, tendons were reattached to bone using braided polyester #2 sutures via two bony tunnels. All samples were mounted on a materials testing system and preloaded at 50N for 60sec before load to failure at a rate of 1mm/sec. With the assumption that preloading has removed tendon crimp and any subsequent extension is a result of gapping at the repair site, loads at 5mm, 10mm, 15mm, and 20mm of extension were noted as well as the maximal load at failure. We found higher loads were needed to cause an extension of 5 to 20mm in the suture only group compared to the anchor suture group but these data were not significant. On the other hand, the anchor suture group required higher loads before catastrophic failure occurred compared to the suture only group, but this again is not significant. We conclude that suture only reattachment of the Achilles tendon is comparable in strength with anchor suture reattachment, and this method of reattachment can be considered for patients who do not have access to anchor sutures

Background. Weightbearing computed tomography scans allow for better understanding of foot alignment in patients with Progressive Collapsing Foot Deformity. However, soft tissue integrity cannot be assessed via WBCT. As performing both WBCT and magnetic resonance imaging is not cost effective, we aimed to assess whether there is an association between specific WBCT and MRI findings. Methods. A cohort of 24 patients of various stages of PCFD (mean age 51±18 years) underwent WBCT scans and MRI. In addition to signs of sinus tarsi impingement, four three-dimensional measurements (talo-calcaneal overlap, talo-navicular coverage, Meary's angle axial/lateral) were obtained using a post processing software (DISIOR 2.1, Finland) on the WBCT datasets. Sinus tarsi obliteration, spring ligament complex and tibiospring ligament integrity, as well as tibialis posterior tendon degeneration were evaluated with MRI. Statistical analysis was performed for significant (P<0.05) correlation between findings. Results. None of the assessed 3D measurements correlated with spring ligament complex or tibiospring ligament tears. Age, body mass index, and TCO were associated with tibialis posterior tendon tears. 75% of patients with sinus tarsi impingement on WBCT also showed signs of sinus tarsi obliteration on MRI. Of the assessed parameters, only age and BMI were associated with sinus tarsi obliteration diagnosed on MRI, while the assessed WBCT based 3D measurements were, with the exception of MA axial, associated with sinus tarsi impingement. Conclusion. While WBCT reflects foot alignment and indicates signs of osseous impingement in PCFD patients, the association between WBCT based 3D measurements and ligament or tendon tears in MRI is limited. Partial or complete tears of the tibialis posterior tendon were only detectable in comparably older and overweight PCFD patients with an increased TCO. WBCT does not replace MRI in diagnostic value. Both imaging options add important information and may impact decision-making in the treatment of PCFD patients

Background. Iatrogenic hallux varus is a rare complication after hallux valgus surgery. Operative treatment comprises a wide variety of techniques, of which the reversed transfer of the abductor hallucis tendon is the most recent described technique. Methods. This paper will present the long-term clinical results of the reversed transfer of the abductor hallucis longus. Therefore, we performed a prospective clinical observational study on 16 female patients. Our hypothesis is that the tendon transfer will persist in a good alignment and patient satisfaction on long term. There is a 100% follow-up rate with a range from 10 to 101 months. Patients were subjected to a clinical examination, three questionnaires and their general satisfaction. Results. Out of 16 patients, at time of follow-up, we found a positive correlation between the subjective outcome score and alignment (r = 0.59), and between the general satisfaction and alignment (r = 0.77). Based on the general satisfaction we achieved a success satisfaction rate of 69% (11 patients). The other 31% (5 patients) patient group was only satisfied with major reservations or not satisfied at all. The two most invalidating complications were a coronal or sagittal malalignment or the combination of both. Conclusion. Our results suggest that the reverse abductor hallucis tendon transfer is a good technique to treat a supple iatrogenic hallux varus with an observed success satisfaction rate of 69% at a mean follow-up time of 48 (range 10–101) months. However, patients should be informed that on the long-term loss of correction is possible

Aims. In the context of tendon degenerative disorders, the need for innovative conservative treatments that can improve the intrinsic healing potential of tendon tissue is progressively increasing. In this study, the role of pulsed electromagnetic fields (PEMFs) in improving the tendon healing process was evaluated in a rat model of collagenase-induced Achilles tendinopathy. Methods. A total of 68 Sprague Dawley rats received a single injection of type I collagenase in Achilles tendons to induce the tendinopathy and then were daily exposed to PEMFs (1.5 mT and 75 Hz) for up to 14 days - starting 1, 7, or 15 days after the injection - to identify the best treatment option with respect to the phase of the disease. Then, 7 and 14 days of PEMF exposure were compared to identify the most effective protocol. Results. The daily exposure to PEMFs generally provided an improvement in the fibre organization, a decrease in cell density, vascularity, and fat deposition, and a restoration of the physiological cell morphology compared to untreated tendons. These improvements were more evident when the tendons were exposed to PEMFs during the mid-acute phase of the pathology (7 days after induction) rather than during the early (1 day after induction) or the late acute phase (15 days after induction). Moreover, the exposure to PEMFs for 14 days during the mid-acute phase was more effective than for 7 days. Conclusion. PEMFs exerted a positive role in the tendon healing process, thus representing a promising conservative treatment for tendinopathy, although further investigations regarding the clinical evaluation are needed. Cite this article: Bone Joint Res 2020;9(9):613–622