Achilles tendon ossification: pathology, imaging and aetiology

Elemental and Structural Characterization of Heterotopic Ossification during Achilles Tendon Healing Provides New Insights on the Formation Process

Heterotopic ossification (HO) in tendons can lead to increased pain and poor tendon function. Although it is believed to share some characteristics with bone, the structural and elemental compositions of HO deposits have not been fully elucidated. This study utilizes a multimodal and multiscale approach for structural and elemental characterization of HO deposits in healing rat Achilles tendons at 3, 6, 12, 16, and 20 weeks post transection. The microscale tomography and scanning electron microscopy results indicate increased mineral density and Ca/P ratio in the maturing HO deposits (12 and 20 weeks), when compared to the early time points (3 weeks). Visually, the mature HO deposits present microstructures similar to calcaneal bone. Through synchrotron-based X-ray scattering and fluorescence, the hydroxyapatite (HA) crystallites are shorter along the c-axis and become larger in the ab-plane with increasing healing time, while the HA crystal thickness remains within the reference values for bone. At the mineralization boundary, the overlap between high levels of calcium and prominent crystallite formation was outlined by the presence of zinc and iron. In the mature HO deposits, the calcium content was highest, and zinc was more present internally, which could be indicative of HO deposit remodeling. This study emphasizes the structural and elemental similarities between the calcaneal bone and HO deposits.

Acute fracture of an extensively ossified segment of the Achilles tendon

Extensive tendon ossification is thought to be rare and is hypothesised to occur due to cell-mediated tissue remodelling. Literature outlining risk factors for the development of an ossified segment, and then a consequent fracture is limited to case reports and case series. A woman in her fifties with a background of several autoimmune disorders presented to a sports and exercise medicine clinic with posterior ankle pain following a bout of brisk walking a month prior. CT and MRI imaging demonstrated a fractured extensively ossified segment of the corresponding Achilles tendon. Conservative treatment was trialled for six months, however, was unsuccessful. Surgical excision of the calcified fragment and flexor hallucis longus tendon transfer were suggested as a potential solution. This case is compared with and builds on current literature surrounding pathophysiology and optimal treatment of extensively ossified segments of the Achilles tendon.

Inhibition of PI3K/AKT signaling pathway prevents blood-induced heterotopic ossification of the injured tendon

Objective

It is a common clinical phenomenon that blood infiltrates into the injured tendon caused by sports injuries, accidental injuries, and surgery. However, the role of blood infiltration into the injured tendon has not been investigated.

Methods

A blood-induced rat model was established and the impact of blood infiltration on inflammation and HO of the injured tendon was assessed. Cell adhesion, viability, apoptosis, and gene expression were measured to evaluate the effect of blood treatment on tendon stem/progenitor cells (TSPCs). Then RNA-seq was used to assess transcriptomic changes in tendons in a blood infiltration environment. At last, the small molecule drug PI3K inhibitor LY294002 was used for in vivo and in vitro HO treatment.

Results

Blood caused acute inflammation in the short term and more severe HO in the long term. Then we found that blood treatment increased cell apoptosis and decreased cell adhesion and tenonic gene expression of TSPCs. Furthermore, blood treatment promoted osteochondrogenic differentiation of TSPCs. Next, we used RNA-seq to find that the PI3K/AKT signaling pathway was activated in blood-treated tendon tissues. By inhibiting PI3K with a small molecule drug LY294002, the expression of osteochondrogenic genes was markedly downregulated while the expression of tenonic genes was significantly upregulated. At last, we also found that LY294002 treatment significantly reduced the tendon HO in the rat blood-induced model.

Conclusion

Our findings indicate that the upregulated PI3K/AKT signaling pathway is implicated in the aggravation of tendon HO. Therefore, inhibitors targeting the PI3K/AKT pathway would be a promising approach to treat blood-induced tendon HO.

Identification of Heterotopic Mineralization and Adjacent Pathology in the Equine Fetlock Region by Low-Field Magnetic Resonance Imaging, Cone-Beam and Fan-Beam Computed Tomography

Heterotopic mineralization in equine distal limbs has been considered an incidental finding and little is known about its imaging features. The study aimed to identify heterotopic mineralization and adjacent pathology in the fetlock region with cone-beam (CB) computed tomography (CT), fan-beam (FB) CT, and low-field magnetic resonance imaging (MRI). Images from 12 equine cadaver limbs were examined for heterotopic mineralization and adjacent pathology and verified by macro-examination. Retrospective review of the CBCT/MR images from 2 standing horses was also included. CBCT and FBCT identified twelve mineralization's with homogeneous hyperattenuation: oblique-sesamoidean-ligament (5) without macroscopic abnormality; deep-digital-flexor-tendon (1) and suspensory-branch (6) with macroscopic abnormalities. MRI failed to identify all mineralization's, but detected suspensory branch splitting, and T2 and STIR hyperintensity in 4 suspensory-branches and 3 oblique-sesamoidean-ligaments. Macro-examination found corresponding disruption/splitting and discoloration. All modalities identified 7 ossified fragments showing cortical/trabecular pattern: capsular (1), palmar sagittal ridge (1), proximal phalanx (2) without macroscopic abnormality, and proximal sesamoid bones (3). On MRI, fragments were most identifiable on T1 images. All abaxial avulsions had suspensory-branch splitting on T1 images with T2 and STIR hyperintensity. Macro-examination showed ligament disruption/splitting and discoloration. Suspensory-branch/intersesamoidean ligament mineralization's were identified by CBCT in standing cases; 1 had associated T2 hyperintensity. Both CT systems were generally superior in identifying heterotopic mineralization's than MRI, while MRI provided information on soft tissue pathology related to the lesions, which may be important for management.

Heterotopic mineral deposits in intact rat Achilles tendons are characterized by a unique fiber-like structure

Heterotopic mineralization entails pathological mineral formation inside soft tissues. In human tendons mineralization is often associated with tendinopathies, tendon weakness and pain. In Achilles tendons, mineralization is considered to occur through heterotopic ossification (HO) primarily in response to tendon pathologies. However, refined details regarding HO deposition and microstructure are unknown. In this study, we characterize HO in intact rat Achilles tendons through high-resolution phase contrast enhanced synchrotron X-ray tomography. Furthermore, we test the potential of studying local tissue injury by needling intact Achilles tendons and the relation between tissue microdamage and HO. The results show that HO occurs in all intact Achilles tendons at 16 weeks of age. HO deposits are characterized by an elongated ellipsoidal shape and by a fiber-like internal structure which suggests that some collagen fibers have mineralized. The data indicates that deposition along fibers initiates in the pericellular area, and propagates into the intercellular area. Within HO deposits cells are larger and more rounded compared to tenocytes between unmineralized fibers, which are fewer and elongated. The results also indicate that multiple HO deposits may merge into bigger structures with time by accession along unmineralized fibers. Furthermore, the presence of unmineralized regions within the deposits may indicate that HOs are not only growing, but mineral resorption may also occur. Additionally, phase contrast synchrotron X-ray tomography allowed to distinguish microdamage at the fiber level in response to needling. The needle injury protocol could in the future enable to elucidate the relation between local inflammation, microdamage, and HO deposition.

Disruption of the mouse Bmal1 locus promotes heterotopic ossification with aging via TGF-beta/BMP signaling

INTRODUCTION

Heterotopic ossification of tendons and ligaments is a painful and debilitating disease with no effective treatment. Although aging has been reported to be correlated with the occurrence and development of this disease, the mechanism remains unknown.

MATERIALS AND METHODS

In the present study, we generated Bmal1-/- mice, which disrupted the circadian clock and displayed premature aging, as an aging model to explore the role of Bmal1 in TGF-beta (β)/BMP signaling in progressive heterotopic ossification of tendons and ligaments with aging.

RESULTS

We first confirmed that BMAL1 expression is downregulated in human fibroblasts from ossification of the posterior longitudinal ligament using online datasets. Bmal1 deficiency in mice caused significantly progressive heterotopic ossification with aging starting at week 6, notably in the Achilles tendons and posterior longitudinal ligaments. Ossification of the Achilles tendons was accompanied by progressive motor dysfunction of the ankle joint. Histology and immunostaining showed markedly increased endochondral ossification in the posterior longitudinal ligaments and Achilles tendons of Bmal1-/- mice. Ligament-derived Bmal1-/- fibroblasts showed an osteoblast-like phenotype, upregulated osteogenic and chondrogenic markers, and activated TGFβ/BMP signaling, which was enhanced by TGFβ1 stimulation. Furthermore, Bmal1-/- mouse embryonic fibroblasts had a stronger potential for osteogenic differentiation with activation of TGFβ/BMP signaling.

CONCLUSIONS

These findings demonstrated that Bmal1 negatively regulates endochondral ossification in heterotopic ossification of tendons and ligaments with aging via TGFβ/BMP signaling, thereby identifying a new regulatory mechanism in age-related heterotopic ossification of tendons and ligaments.

Intrafascicular chondroid-like bodies in the ageing equine superficial digital flexor tendon comprise glycosaminoglycans and type II collagen

The superficial digital flexor tendon (SDFT) is considered functionally equivalent to the human Achilles tendon. Circular chondroid depositions scattered amongst the fascicles of the equine SDFT are rarely reported. The purpose of this study was the detailed characterization of intrafascicular chondroid-like bodies (ICBs) in the equine SDFT, and the assessment of the effect of ageing on the presence and distribution of these structures. Ultrahigh field magnetic resonance imaging (9.4T) series of SDFT samples of young (1-9 years) and aged (17-25 years) horses were obtained, and three-dimensional reconstruction of ICBs was performed. Morphological evaluation of the ICBs included histology, immunohistochemistry and transmission electron microscopy. The number, size, and position of ICBs was determined and compared between age groups. There was a significant difference (p = .008) in the ICB count between young and old horses with ICBs present in varying number (13-467; median = 47, mean = 132.6), size and distribution in the SDFT of aged horses only. There were significantly more ICBs in the tendon periphery when compared with the tendon core region (p = .010). Histological characterization identified distinctive cells associated with increased glycosaminoglycan and type II collagen extracellular matrix content. Ageing and repetitive strain frequently cause tendon micro-damage before the development of clinical tendinopathy. Documentation of the presence and distribution of ICBs is a first step towards improving our understanding of the impact of these structures on the viscoelastic properties, and ultimately their effect on the risk of age-related tendinopathy in energy-storing tendons.

Extensive Ossification of the Achilles Tendon with and without Acute Fracture: A Scoping Review

Extensive Ossification of the Achilles Tendon (EOAT) is an uncommon condition characterized by the presence of heterotopic ossification within the substance of the Achilles Tendon and is distinct from other tendinopathies associated with tendon mineralization. The purpose of this scoping review of the literature on EOAT is to describe the pathogenesis, patient population, presentation, management, and outcomes of this rare condition. Fifty-four articles were included in the scoping review after screening and selection. According to the literature, EOAT often presents with pain and swelling around the Achilles Tendon and is frequently associated with acute trauma. EOAT is more common in men, and although the exact mechanisms of the pathology are not fully understood, EOAT may demonstrate specific molecular signaling patterns. The lack of knowledge regarding the molecular mechanism may be a significant hindrance to the management of the condition. Even though a standard treatment regimen for EOAT does not exist, conservative management for six months in patients without complications is recommended. Those who have an acute fracture of the ossification should be managed more aggressively and will often require surgical repair with autograft, although there is no standardized procedure at this time. Clinicians should be aware of the typical presentation, risk factors, and management options of patients with EOAT. Additionally, they should be cautious when selecting treatment strategies and conduct a thorough evaluation of long-term outcomes with various treatment modalities, which this review provides. Most important, this review highlights the need for further research to determine the best course of clinical treatment of EOAT injuries, in order to establish a standard treatment regimen.

Reduction of mechanical loading in tendons induces heterotopic ossification and activation of the β-catenin signaling pathway

Background

Tendons are the force transferring tissue that enable joint movement. Excessive mechanical loading is commonly considered as a primary factor causing tendinopathy, however, an increasing body of evidence supports the hypothesis that overloading creates microdamage of collagen fibers resulting in a localized decreased loading on the cell population within the damaged site. Heterotopic ossification is a complication of late stage tendinopathy, which can significantly affect the mechanical properties and homeostasis of the tendon. Here, we the examine the effect of mechanical underloading on tendon ossification and investigate its underlying molecular mechanism.

Method

Rabbit Achilles tendons were dissected and cultured in an underloading environment (3% cyclic tensile stain,0.25 ​Hz, 8 ​h/day) for either 10, 15 or 20 days. Using isolated tendon-derived stem cells (TDSCs) 3D constructs were generated, cultured and subjected to an underloading environment for 6 days. Histological assessments were performed to evaluate the structure of the 3D constructs; qPCR and immunohistochemistry were employed to study TDSC differentiation and the β-catenin signal pathway was investigated by Western blotting. Mechanical testing was used to determine ability of the tendon to withstand force generation.

Result

Tendons cultured for extended times in an environment of underloading showed progressive heterotopic ossification and a reduction in biomechanical strength. qPCR revealed that 3D TDSCs constructs cultured in an underloading environment exhibited increased expression of several osteogenic genes: these include RUNX2, ALP and osteocalcin in comparison to tenogenic differentiation markers (scleraxis and tenomodulin). Immunohistochemical analysis further confirmed high osteocalcin production in 3D TDSCs constructs subject to underloading. Western blotting of TDSC constructs revealed that β-catenin accumulation and translocation were associated with an increase in phosphorylation at Ser552 and decrease phosphorylation at Ser33.

Conclusion

These findings unveil a potential mechanism for heterotopic ossification in tendinopathy due to the underloading of TDSCs at the damage sites, and also that β-catenin could be a potential target for treating heterotopic ossification in tendons.

The Translational potential

Tendon heterotopic ossification detrimentally affect quality of life especially for those who has atheletic career. This study reveals the possible mechanism of heterotpic ossification in tendon related to mechanical loading. This study provided the possible to develop a mechanical stimulation protocol for preventive and therapeutic purpose for tendon heterotopic ossification.

Fracture of ossified Achilles tendons: A review of cases

Fracture of an ossification of the Achilles tendon (OAT) is a rare entity, and its etiology, pathology, and treatment remain unclear. We reviewed and scrutinized 18 cases (16 articles) of the fracture of an OAT. The most common etiologies of the ossifications include previous surgery and trauma. The fractures often occur without any trigger or with minimal trigger. The long, > 5 cm, ossification in the body of the Achilles tendon may have a higher risk of fracture. The OAT itself is often asymptomatic; however, its fracture causes severe local pain, swelling, and weakness of plantar flexion, which forces patients to undergo aggressive treatments. Regarding the treatments of the fractures, nonoperative treatment by immobilizing ankle joint could be an option for elderly patients. However, because it often cannot produce satisfactory results in younger patients, surgical treatment is typically recommended. Excision of the fractured mass and repairing the tendon is applicable if the remnant is enough. If there is a defect after the excision, reconstruction with autologous grafts or adjacent tendon transfer is performed. Gastrocnemius fascia turndown flap, hamstring tendon and tensor fascia lata are used as autologous grafts, whereas peroneus brevis and flexor hallucis longus tendons are used for the tendon transfer. If the fracture of an OAT is treated properly, the functional result will be satisfactory.

Genetic and Acquired Heterotopic Ossification: A Translational Tale of Mice and Men

Heterotopic ossification is defined as an aberrant formation of bone in extraskeletal soft tissue, for which both genetic and acquired conditions are known. This pathologic process may occur in many different sites such as the skin, subcutaneous tissue, skeletal muscle and fibrous tissue adjacent to joints, ligaments, walls of blood vessels, mesentery and other. The clinical spectrum of this disorder is wide: lesions may range from small foci of ossification to massive deposits of bone throughout the body, typical of the progressive genetically determined conditions such as fibrodysplasia ossificans progressiva, to mention one of the most severe and disabling forms. The ectopic bone formation may be regarded as a failed tissue repair process in response to a variety of triggers and evolving towards bone formation through a multistage differentiation program, with several steps common to different clinical presentations and distinctive features. In this review, we aim at providing a comprehensive view of the genetic and acquired heterotopic ossification disorders by detailing the clinical and molecular features underlying the different human conditions in comparison with the corresponding, currently available mouse models.

Extensive Achilles tendon ossification: Repair using a fascia lata graft

Ossification of the Achilles tendon is a relatively common finding. However, a large ossification covering more than two third of the tendon is rarely seen. A 70 year old patient with a 12 cm long Achilles tendon ossification is discussed. The ossification was surgically removed and the tendon was subsequently reconstructed using a fascia lata autograft. Postoperatively the ankle was immobilised for 3 months. One year postoperatively the patient was completely recovered with the ability to stand on his toes, and minimal loss in range of motion. LEVEL OF CLINICAL EVIDENCE: 4.

Heterotopic Ossification After an Achilles Tendon Rupture Cannot Be Prevented by Early Functional Rehabilitation: A Cohort Study

BACKGROUND

Tendon loading might play a role in the development of heterotopic ossification after Achilles tendon ruptures. Early heavy loading on a healing tendon in animals has been shown to prolong the proinflammatory response, and inflammatory cells are thought to drive heterotopic ossification formation. Taken together, this suggests that early rehabilitation might influence heterotopic ossification development.

QUESTIONS/PURPOSES

The purposes of this study were to investigate (1) whether the presence of heterotopic ossification after Achilles tendon ruptures influences clinical outcome and (2) whether early mobilization or weightbearing prevents the development of heterotopic ossification.

METHODS

This was a retrospective analysis of 69 patients from a previous clinical trial. All patients were treated surgically, but with three different early rehabilitation protocols after surgery: late weightbearing and ankle immobilization, late weightbearing and ankle mobilization, and early weightbearing and ankle mobilization. Plain radiographs taken 2, 6, 12, 26, and 52 weeks postoperatively were analyzed for heterotopic ossification, which was detected in 19% of patients (13 of 69) at 52 weeks. Heterotopic ossification was measured, scored, and correlated to clinical outcomes; heel-raise index (HRI), ankle joint ROM, tendon strain, Achilles tendon rupture score (ATRS), and Victorian Institute of Sport Assessment-Achilles (VISA-A) questionnaire scores at 26 and 52 weeks postoperatively.

RESULTS

Heterotopic ossification had no adverse effects on patient-reported outcomes (ATRS or VISA-A), tendon strain, or ROM. In fact, patients with heterotopic ossification tended to have a better HRI at 52 weeks compared with patients without (mean difference 14% [95% CI -0.2 to 27]; p = 0.053). Neither the occurrence (heterotopic ossification/no heterotopic ossification) nor the heterotopic ossification severity (ossification score) differed between the three rehabilitation groups. Seventeen percent of the patients (four of 24) with early functional rehabilitation (early weightbearing and ankle joint mobilization exercise) had heterotopic ossification (score, 2-3) while late weightbearing and immobilization resulted in heterotopic ossification in 13% of the patients (score, 3-4).

CONCLUSIONS

Heterotopic ossification occurs relatively frequently after Achilles tendon ruptures but appears to have no adverse effects on functional outcomes. Furthermore, heterotopic ossification develops during the first 6 weeks after rupture, and weightbearing or ankle-joint mobilization does not prevent this from occurring.

LEVEL OF EVIDENCE

Level III, prognostic study.

Extensive Atraumatic Heterotopic Ossification of the Achilles Tendon in an Adolescent with Metabolic Syndrome: A Case Report

CASE

A 15-year-old boy with type 1 diabetes mellitus, hypertension, and obesity presented with atraumatic posterior ankle pain and stiffness due to extensive heterotopic ossification (HO) of the Achilles tendon. The ossification was successfully surgically resected and tendon primarily repaired. Wound dehiscence was noted at the first preoperative visit, managed conservatively by local wound care, and healed uneventfully by secondary intention. One-year follow-up showed no recurrence of HO, return to baseline activities, yet low Oxford scores.

CONCLUSION

HO of the Achilles tendon is a rare clinical entity. We report an atraumatic case in an adolescent patient with metabolic syndrome, which may demonstrate systemic inflammation because of metabolic syndrome as a risk factor for HO.

Effects of Pulsed Electromagnetic Field Therapy on Rat Achilles Tendon Healing

The Achilles tendon is frequently injured. Data to support specific treatment strategies for complete and partial tears is inconclusive. Regardless of treatment, patients risk re-rupture and typically have long-term functional deficits. We previously showed that pulsed electromagnetic field (PEMF) therapy improved tendon-to-bone healing in a rat rotator cuff model. This study investigated the effects of PEMF on rat ankle function and Achilles tendon properties after (i) complete Achilles tendon tear and repair with immobilization, (ii) partial Achilles tendon tear without repair and with immobilization, and (iii) partial Achilles tendon tear without repair and without immobilization. We hypothesized that PEMF would improve tendon properties, increase collagen organization, and improve joint function, regardless of injury type. After surgical injury, animals were assigned to a treatment group: (i) no treatment control, (ii) 1 h of PEMF per day, or (iii) 3 h of PEMF per day. Animals were euthanized at 1, 3, and 6 weeks post-injury. Joint mechanics and gait analysis were assessed over time, and fatigue testing and histology were performed at each time point. Results indicate no clear differences in Achilles healing with PEMF treatment. Some decreases in tendon mechanical properties and ankle function suggest PEMF may be detrimental after complete tear. Some early improvements were seen with PEMF after partial tear with immobilization; however, immobilization was found to be a confounding factor. This body of work emphasizes the distinct effects of PEMF on tendon-to-bone healing and supports trialing potential treatment strategies pre-clinically across tendons before applying them clinically. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:70-81, 2020.

Quantitative comparison of three rat models of Achilles tendon injury: A multidisciplinary approach

The Achilles tendon, while the strongest and largest tendon in the body, is frequently injured. Inconclusive evidence exists regarding treatment strategies for both complete tears and partial tears. Well-characterized animal models of tendon injury are important for understanding physiological processes of tendon repair and testing potential therapeutics. Utilizing three distinct models of rat Achilles tendon injury, the objective of this study was to define and compare the effects and relative impact on tendon properties and ankle function of both tear severity (complete tear versus partial tear, both with post-operative immobilization) and immobilization after partial tear (partial tear with versus without immobilization). We hypothesized that a complete tear would cause inferior post-injury properties compared to a partial tear, and that immediate loading after partial tear would improve post-injury properties compared to immobilization. All models were reproducible and had distinct effects on measured parameters. Injury severity drastically influenced tendon healing, with complete tear causing decreased ankle mobility and tendon mechanics compared to partial tears. One week of plantarflexion immobilization had a strong effect on animals receiving a partial tear. Tendons with partial tears and immobilization failed early during fatigue cycling three weeks post-injury. Partial tear without immobilization had no effect on ankle range of motion through dorsiflexion at any time point compared to the pre-surgery value, while partial tear with immobilization demonstrated diminished function at all post-injury time points. All three models of Achilles injury could be useful for tendon healing investigations, chosen based on the prospective applications of a potential therapeutic.

Mkx-Deficient Mice Exhibit Hedgehog Signaling-Dependent Ectopic Ossification in the Achilles Tendons

Heterotopic ossification is the abnormal formation of mineralized bone in skin, muscle, tendon, or other soft tissues. Tendon ossification often occurs from acute tendon injury or chronic tendon degeneration, for which current treatment relies heavily on surgical removal of the ectopic bony tissues. Unfortunately, surgery creates additional trauma, which often causes recurrence of heterotopic ossification. The molecular mechanisms of heterotopic ossification are not well understood. Previous studies demonstrate that Mkx is a transcription factor crucial for postnatal tendon fibril growth. Here we report that Mkx^-/- mutant mice exhibit ectopic ossification in the Achilles tendon within 1 month after birth and the tendon ossification deteriorates with age. Genetic lineage labeling revealed that the tendon ossification in Mkx^-/- mice resulted from aberrant differentiation of tendon progenitor cells. Furthermore, tissue-specific inactivation of Mkx in tendon cells postnatally resulted in a similar ossification phenotype, indicating that Mkx plays a key role in tendon tissue homeostasis. Moreover, we show that Hedgehog signaling is ectopically activated at early stages of tendon ossification and that tissue-specific inactivation of Smoothened, which encodes the obligatory transducer of Hedgehog signaling, in the tendon cell lineage prevented or dramatically reduced tendon ossification in Mkx^-/- mice. Together, these studies establish a new genetic mouse model of tendon ossification and provide new insight into its pathogenic mechanisms. © 2018 American Society for Bone and Mineral Research.

Heterotopic Ossification: A Comprehensive Review

Heterotopic ossification (HO) is a diverse pathologic process, defined as the formation of extraskeletal bone in muscle and soft tissues. HO can be conceptualized as a tissue repair process gone awry and is a common complication of trauma and surgery. This comprehensive review seeks to synthesize the clinical, pathoetiologic, and basic biologic features of HO, including nongenetic and genetic forms. First, the clinical features, radiographic appearance, histopathologic diagnosis, and current methods of treatment are discussed. Next, current concepts regarding the mechanistic bases for HO are discussed, including the putative cell types responsible for HO formation, the inflammatory milieu and other prerequisite “niche” factors for HO initiation and propagation, and currently available animal models for the study of HO of this common and potentially devastating condition. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Magnolol prevents ossified tendinopathy by inhibiting PGE2-induced osteogenic differentiation of TDSCs

Magnolol is a compound that is extracted from magnolia, is used in Chinese medicine and is a type of lignan. Magnolol has various anti-inflammation, anti-proliferation and pro-autophagy effects. Ossified tendinopathy affects many athletes and people with repetitive tendon injuries. Ossified tendinopathy is a tremendous economic burden, and no effective and safe drugs are available to prevent the pathogenesis of ectopic ossification. In this study, we aimed to study how magnolol affects ossified tendinopathy by evaluating its effects on osteogenic differentiation of tendon-derived stem cells (TDSCs). Our data suggested that magnolol attenuated ectopic ossification in the Achilles tendon caused by Achilles tenotomy. Magnolol inhibited PGE2-induced ALP activity and prevented calcium deposits in TDSCs in vitro. Magnolol also exerted inhibitory effects on expression of osteogenic factors, such as Runx2, OCN, and BMP2 in vivo. Further investigation revealed the underlying mechanism by which magnolol prevents PGE2-induced ectopic ossification. Specifically, magnolol inhibits PGE2-induced PI3K/AKT/β-catenin pathway activation in TDSCs. Our findings demonstrated that magnolol inhibited ossified tendinopathy through preventing osteogenic differentiation of TDSCs via downregulation PGE2-induced PI3K/AKT/β-catenin pathways.

Imaging Features of Soft-Tissue Calcifications and Related Diseases: A Systematic Approach

Soft-tissue calcification refers to a broad category of lesions. Calcifications are frequently identified by radiologists in daily practice. Using a simple algorithm based on the distribution pattern of the lesions and detailed clinical information, these calcified lesions can be systematically evaluated. The distribution pattern of the calcific deposits enables initial division into calcinosis circumscripta and calcinosis universalis. Using laboratory test results (serum calcium and phosphate levels) and clinical history, calcinosis circumscripta can be further categorized into four subtypes: dystrophic, iatrogenic, metastatic, and idiopathic calcification. This pictorial essay presents a systematic approach to the imaging features of soft-tissue calcifications and related diseases.

Achilles Tendinopathy

Achilles tendinopathy is a common cause of disability. Despite the economic and social relevance of the problem, the causes and mechanisms of Achilles tendinopathy remain unclear. Tendon vascularity, gastrocnemius-soleus dysfunction, age, sex, body weight and height, pes cavus, and lateral ankle instability are considered common intrinsic factors. The essence of Achilles tendinopathy is a failed healing response, with haphazard proliferation of tenocytes, some evidence of degeneration in tendon cells and disruption of collagen fibers, and subsequent increase in noncollagenous matrix. Tendinopathic tendons have an increased rate of matrix remodeling, leading to a mechanically less stable tendon which is more susceptible to damage. The diagnosis of Achilles tendinopathy is mainly based on a careful history and detailed clinical examination. The latter remains the best diagnostic tool. Over the past few years, various new therapeutic options have been proposed for the management of Achilles tendinopathy. Despite the morbidity associated with Achilles tendinopathy, many of the therapeutic options described and in common use are far from scientifically based. New minimally invasive techniques of stripping of neovessels from the Kager's triangle of the tendo Achillis have been described, and seem to allow faster recovery and accelerated return to sports, rather than open surgery. A genetic component has been implicated in tendinopathies of the Achilles tendon, but these studies are still at their infancy.

A silent massive ossification of Achilles tendon as a suspected rare late effect of surgery for club foot

We report the case of a 66-year-old male patient with massive ossification of the distal portion of the Achilles tendon, as a late consequence of a surgical release for club foot conducted in his childhood. The singularity of the case report derives from its clinical features: the bone mass was of abnormal dimensions, almost substituting the entire tendon; the condition had always been asymptomatic, without deficits in range of motion, in absence of either pain or biomechanical defects with age. In fact, the condition was diagnosed just recently as a consequence of a tear. Despite an ultrasound diagnosis after the injury, only during the surgical treatment, a proper evaluation of the entity of the pathology was possible. Although the ossification of Achilles tendon is a rare clinical condition with a complex multifactorial etiology, in our case report, some of the elements in the patient's medical history could be useful for the pathogenesis and early diagnosis of the disease. The aim of this case report is to emphasize the importance both of a correct evaluation of clinical history and of an accurate diagnosis, in order to conduct a proper management of this pathology.

Achilles Pain, Stiffness, and Muscle Power Deficits: Midportion Achilles Tendinopathy Revision 2018

The Orthopaedic Section of the American Physical Therapy Association (APTA) has an ongoing effort to create evidence-based practice guidelines for orthopaedic physical therapy management of patients with musculoskeletal impairments described in the World Health Organization's International Classification of Functioning, Disability, and Health (ICF). The purpose of these revised clinical practice guidelines is to review recent peer-reviewed literature and make recommendations related to midportion Achilles tendinopathy. J Orthop Sports Phys Ther 2018;48(5):A1-A38. doi:10.2519/jospt.2018.0302.

The metalloproteinase-proteoglycans ADAMTS7 and ADAMTS12 provide an innate, tendon-specific protective mechanism against heterotopic ossification

Heterotopic ossification (HO) is a significant clinical problem with incompletely resolved mechanisms. Here, the secreted metalloproteinases ADAMTS7 and ADAMTS12 are shown to comprise a unique proteoglycan class that protects against a tendency toward HO in mouse hindlimb tendons, menisci, and ligaments. Adamts7 and Adamts12 mRNAs were sparsely expressed in murine forelimbs but strongly coexpressed in hindlimb tendons, skeletal muscle, ligaments, and meniscal fibrocartilage. Adamts7-/- Adamts12-/- mice, but not corresponding single-gene mutants, which demonstrated compensatory upregulation of the intact homolog mRNA, developed progressive HO in these tissues after 4 months of age. Adamts7-/- Adamts12-/- tendons had abnormal collagen fibrils, accompanied by reduced levels of the small leucine-rich proteoglycans (SLRPs) biglycan, fibromodulin, and decorin, which regulate collagen fibrillogenesis. Bgn-/0 Fmod-/- mice are known to have a strikingly similar hindlimb HO to that of Adamts7-/- Adamts12-/- mice, implicating fibromodulin and biglycan reduction as a likely mechanism underlying HO in Adamts7-/- Adamts12-/- mice. Interestingly, degenerated human biceps tendons had reduced ADAMTS7 mRNA compared with healthy biceps tendons, which expressed both ADAMTS7 and ADAMTS12. These results suggest that ADAMTS7 and ADAMTS12 drive an innate pathway protective against hindlimb HO in mice and may be essential for human tendon health.

Stem cells and heterotopic ossification: Lessons from animal models

Put most simply, heterotopic ossification (HO) is the abnormal formation of bone at extraskeletal sites. HO can be classified into two main subtypes, genetic and acquired. Acquired HO is a common complication of major connective tissue injury, traumatic central nervous system injury, and surgical interventions, where it can cause significant pain and postoperative disability. A particularly devastating form of HO is manifested in the rare genetic disorder, fibrodysplasia ossificans progressiva (FOP), in which progressive heterotopic bone formation occurs throughout life, resulting in painful and disabling cumulative immobility. While the central role of stem/progenitor cell populations in HO is firmly established, the identity of the offending cell type(s) remains to be conclusively determined, and little is known of the mechanisms that direct these progenitor cells to initiate cartilage and bone formation. In this review, we summarize current knowledge of the cells responsible for acquired HO and FOP, highlighting the strengths and weaknesses of animal models used to interrogate the cellular origins of HO.

MR imaging as a problem solving tool in posterior ankle pain: A review

Posterior ankle pain is a cause of chronic pain and disability, afflicting a wide range of individuals. While proper identification of the cause is essential for timely and adequate treatment, identifying the cause and excluding mimickers is often challenging for the physician due to the complex nature of the joint. In addition, pathology that can cause posterior ankle pain may occur on their own or in co-existence. Clinical conditions that can present as posterior ankle pain include: posterior ankle impingement, Achilles tendon pathology, medial flexor tendon pathology, peroneal pathology, retrocalcaneal bursitis, posterior subtalar tarsal coalition, sinus tarsi, and tarsal tunnel syndrome. In this review we introduce current concepts of pathophysiology in the main conditions involved in posterior ankle pain, and review the role of MR in the diagnosis and management of each condition. When pathology can be detected earlier and with more specificity, appropriate and time-sensitive treatment can be commenced, thus improving clinical outcomes.

Ten weeks of treadmill running decreases stiffness and increases collagen turnover in tendons of old mice

Increased tendon stiffness in response to mechanical loading is well established in young animals. Given that tendons stiffen with aging, we aimed to determine the effect of increased loading on tendons of old animals. We subjected 28-month-old mice to 10 weeks of uphill treadmill running; sedentary 8- and 28-month-old mice served as controls. Following training, plantaris tendon stiffness and modulus were reduced by approximately half, such that the values were not different from those of tendons from adult sedentary animals. The decrease in plantaris tendon stiffness was accompanied by a similar reduction in the levels of advanced glycation end-product protein adducts in tibialis anterior tendons of trained compared with sedentary old mice. In Achilles tendons, elevated mRNA levels for collagen type 1, matrix-metalloproteinase-8, and lysyl oxidase following training suggest that collagen turnover was likely also increased. The dramatic mechanical and structural changes induced by training occurred independent of changes in cell density or tendon morphology. Finally, Achilles tendon calcification was significantly reduced following exercise. These results demonstrate that, in response to exercise, tendons from old animals are capable of replacing damaged and dysfunctional components of extracellular matrix with tissue that is mechanically and structurally comparable to adult tissue.

Tendon mineralization is progressive and associated with deterioration of tendon biomechanical properties, and requires BMP-Smad signaling in the mouse Achilles tendon injury model

Ectopic tendon mineralization can develop following tendon rupture or trauma surgery. The pathogenesis of ectopic tendon mineralization and its clinical impact have not been fully elucidated yet. In this study, we utilized a mouse Achilles tendon injury model to determine whether ectopic tendon mineralization alters the biomechanical properties of the tendon and whether BMP signaling is involved in this condition. A complete transverse incision was made at the midpoint of the right Achilles tendon in 8-week-old CD1 mice and the gap was left open. Ectopic cartilaginous mass formation was found in the injured tendon by 4weeks post-surgery and ectopic mineralization was detected at 8 to 10weeks post-surgery. Ectopic mineralization grew over time and volume of the mineralized materials of 25-weeks samples was about 2.5 fold bigger than that of 10-weeks samples, indicating that injury-induced ectopic tendon mineralization is progressive. In vitro mechanical testing showed that max force, max stress and mid-substance modulus in the 25-weeks samples were significantly lower than the 10-weeks samples. We observed substantial increases in expression of bone morphogenetic protein family genes in injured tendons 1week post-surgery. Immunohistochemical analysis showed that phosphorylation of both Smad1 and Smad3 was highly increased in injured tendons as early as 1week post-injury and remained high in ectopic chondrogenic lesions 4-weeks post-injury. Treatment with the BMP receptor kinase inhibitor (LDN193189) significantly inhibited injury-induced tendon mineralization. These findings indicate that injury-induced ectopic tendon mineralization is progressive, involves BMP signaling and associated with deterioration of tendon biomechanical properties.

Successful treatment of a fracture of a huge Achilles tendon ossification with autologous hamstring tendon graft and gastrocnemius fascia flap: a case report

Background

Fracture of an ossified Achilles tendon is a rare entity, and no standard treatment has been established. This is the first report to describe the use of a hamstring tendon graft and gastrocnemius fascia flap for Achilles tendon reconstruction.

Case presentation

We present the case of a 50-year-old woman with fracture of an ossified Achilles tendon. She presented to our clinic with acute right hindfoot pain, which started suddenly while going up the stairs. Plain radiography and magnetic resonance imaging revealed a massive ossification on the right Achilles tendon extending over 14 cm in length; the ossification was fractured at 5 cm proximal to the calcaneus insertion. Surgical treatment included removal of the ossified tendon and reconstruction with an autologous hamstring tendon graft and gastrocnemius fascia flap. One year after surgery, she was able to walk with little pain or discomfort and to stand on her right tiptoe.

Conclusion

Our novel surgical procedure may be useful in the treatment of fractured ossified Achilles tendons and large Achilles tendon defects.

Ossification of the bilateral Achilles tendon: a rare entity

Ossification of the Achilles tendon is a rare clinical entity comprising of one or more segments of variable sized ossified masses in the fibrocartilaginous substance of the tendon. The etiology of ossification of the Achilles tendon is multifactorial with recurrent trauma and surgery comprising major predisposing factors, with others being metabolic, systemic, and infectious diseases. The possibility of a genetic predisposition towards this entity has also been raised, but has not yet been proven. We present a rare case of ossification of the bilateral Achilles tendons without any history of trauma or surgery in a 48-year-old female patient.

IL-1β irreversibly inhibits tenogenic differentiation and alters metabolism in injured tendon-derived progenitor cells in vitro

Tendon injuries are common, and the damaged tendon often turns into scar tissue and never completely regains the original biomechanical properties. Previous studies have reported that the mRNA levels of inflammatory cytokines such as IL-1β are remarkably up-regulated in injured tendons. To examine how IL-1β impacts tendon repair process, we isolated the injured tendon-derived progenitor cells (inTPCs) from mouse injured Achilles tendons and studied the effects of IL-1β on the inTPCs in vitro. IL-1β treatment strongly reduced expression of tendon cell markers such as scleraxis and tenomodulin, and also down-regulated gene expression of collagen 1, collagen 3, biglycan and fibromodulin in inTPCs. Interestingly, IL-1β stimulated lactate production with increases in hexokinase II and lactate dehydrogenase expression and a decrease in pyruvate dehydrogenase. Inhibition of lactate production restored IL-1β-induced down-regulation of collagen1 and scleraxis expression. Furthermore, IL-1β significantly inhibited adipogenic, chondrogenic and osteogenic differentiation of inTPCs. Interestingly, inhibition of tenogenic and adipogenic differentiation was not recovered after removal of IL-1β while chondrogenic and osteogenic differentiation abilities were not affected. These findings indicate that IL-1β strongly and irreversibly impairs tenogenic potential and alters glucose metabolism in tendon progenitors appearing in injured tendons. Inhibition of IL-1β may be beneficial for maintaining function of tendon progenitor cells during the tendon repair process.

Multiple intratendinous ossified deposits of the Achilles tendon: Case report of an unusual pattern of ossification

True ossification of the Achilles tendon is a rare condition as compared to calcification. The etiology of ossification is multifactorial, however, previous surgery, trauma and degenerative changes have been attributed to be the major causes. Three different patterns of ossification have been described within the Achilles tendon based on their location. We present a case of multiple discrete deposits of ossification within the main substance of the Achilles tendon in a young male with a previous history of clubfoot surgery in childhood. The pattern of ossification was different than all the previously reported cases. Pain was the predominant symptom. He was investigated by using plain radiographs, ultrasonography, computed tomography and magnetic resonance imaging. Surgical excision of all the bony lumps lead to satisfactory outcome without any complications.

An atraumatic case of extensive Achilles tendon ossification

BACKGROUND

Ossification of the Achilles tendon is rare with most cases of ossification or calcification consisting of small, focal lesions. This pathology is usually predisposed by surgery, trauma, or other factors.

CASE DESCRIPTION

A case of extensive Achilles ossification and calcification, without prior surgery or trauma, is reported. Following removal of one of the largest ossific masses reported in the literature, measuring 11.0cm×2.5cm×2.0cm with additional 6.5cm calcifications, surgical reconstruction was required.

PURPOSE AND CLINICAL RELEVANCE

The objective of this report was to describe an unusual case of Achilles tendon ossification and calcification that occurred without the presence of predisposing factors. When a large gap is present after removal of the ossification, direct repair may be impossible and V-Y lengthening plus flexor hallucis longus (FHL) transfer is a viable option for pain relief and return to function.

Ossifying tendinitis of the rotator cuff after arthroscopic excision of calcium deposits: report of two cases and literature review

Ossifying tendinitis (OT) is a type of heterotopic ossification, characterized by deposition of hydroxyapatite crystals in a histologic pattern of mature lamellar bone. It is usually associated with surgical intervention or trauma and is more commonly seen in Achilles or distal biceps tendons, and also in the gluteus maximus tendon. To our knowledge, there is no description of OT as a complication of calcifying tendinitis of the rotator cuff. In this report, we describe two cases in which the patients developed an OT of the supraspinatus after arthroscopic removal of calcium deposits. The related literature is reviewed.

The effect of decellularized matrices on human tendon stem/progenitor cell differentiation and tendon repair

It is reported that decellularized collagen matrices derived from dermal skin and bone have been clinically used for tendon repair. However, the varying biological and physical properties of matrices originating from different tissues may influence the differentiation of tendon stem cells, which has not been systematically evaluated. In this study, the effects of collagenous matrices derived from different tissues (tendon, bone and dermis) on the cell differentiation of human tendon stem/progenitor cells (hTSPCs) were investigated, in the context of tendon repair. It was found that all three matrices supported the adhesion and proliferation of hTSPCs despite differences in topography. Interestingly, tendon-derived decellularized matrix promoted the tendinous phenotype in hTSPCs and inhibited their osteogenesis, even under osteogenic induction conditions, through modulation of the teno- and osteolineage-specific transcription factors Scleraxis and Runx2. Bone-derived decellularized matrix robustly induced osteogenic differentiation of hTSPCs, whereas dermal skin-derived collagen matrix had no apparent effect on hTSPC differentiation. Based on the specific biological function of the tendon-derived decellularized matrix, a tissue-engineered tendon comprising TSPCs and tendon-derived matrix was successfully fabricated for Achilles tendon reconstruction. Implantation of this cell-scaffold construct led to a more mature structure (histology score: 4.08 ± 0.61 vs. 8.51 ± 1.66), larger collagen fibrils (52.2 ± 1.6 nm vs. 47.5 ± 2.8 nm) and stronger mechanical properties (stiffness: 21.68 ± 7.1 Nm m(-1) vs.13.2 ± 5.9 Nm m(-1)) of repaired tendons compared to the control group. The results suggest that stem cells promote the rate of repair of Achilles tendon in the presence of a tendinous matrix. This study thus highlights the potential of decellularized matrix for future tissue engineering applications, as well as developing a practical strategy for functional tendon regeneration by utilizing TSPCs combined with tendon-derived decellularized matrix.

Investigating tendon mineralisation in the avian hindlimb: a model for tendon ageing, injury and disease

Mineralisation of the tendon tissue has been described in various models of injury, ageing and disease. Often resulting in painful and debilitating conditions, the processes underlying this mechanism are poorly understood. To elucidate the progression from healthy tendon to mineralised tendon, an appropriate model is required. In this study, we describe the spontaneous and non-pathological ossification and calcification of tendons of the hindlimb of the domestic chicken (Gallus gallus domesticus). The appearance of the ossified avian tendon has been described previously, although there have been no studies investigating the developmental processes and underlying mechanisms leading to the ossified avian tendon. The tissue and cells from three tendons - the ossifying extensor and flexor digitorum longus tendons and the non-ossifying Achilles tendon - were analysed for markers of ageing and mineralisation using histology, immunohistochemistry, cytochemistry and molecular analysis. Histologically, the adult tissue showed a loss of healthy tendon crimp morphology as well as markers of calcium deposits and mineralisation. The tissue showed a lowered expression of collagens inherent to the tendon extracellular matrix and presented proteins expressed by bone. The cells from the ossified tendons showed a chondrogenic and osteogenic phenotype as well as tenogenic phenotype and expressed the same markers of ossification and calcification as the tissue. A molecular analysis of the gene expression of the cells confirmed these results. Tendon ossification within the ossified avian tendon seems to be the result of an endochondral process driven by its cells, although the roles of the different cell populations have yet to be elucidated. Understanding the role of the tenocyte within this tissue and the process behind tendon ossification may help us prevent or treat ossification that occurs in injured, ageing or diseased tendon.

Could ossification of the achilles tendon have a hereditary component?

Ossification of the Achilles tendon (OTA) is an unusual clinical condition. It is characterized by the presence of an ossified mass within the fibrocartilaginous substance of the Achilles tendon. The etiology of the ossification of the Achilles tendon is unknown. Review of the literature suggests that its etiology is multifactorial. The major contributing factors are trauma and surgery with other minor causes such as systemic diseases, metabolic conditions, and infections. To our knowledge, no previous reports suggest any genetic/hereditary predisposition in OAT. We report 3 siblings who have OAT with no history of any of the aforementioned predisposing factors. Could OAT have a hereditary component as one of its etiologies?

Heterotopic mineralization (ossification or calcification) in tendinopathy or following surgical tendon trauma

Heterotopic tendon mineralization (ossification or calcification), which may be a feature of tendinopathy or which may develop following surgical trauma (repair or graft harvest), has not received much attention. The purpose of this article is to review the prevalence, mechanisms and consequences of heterotopic tendon mineralization and to identify the gaps in our current understanding. We focus on endochondral heterotopic ossification and draw on knowledge of the mechanisms of this process in other tissues and conditions. Finally, we introduce a novel murine Achilles tendon needle injury model, which will enable us to further study the mechanisms and biomechanical consequences of tendon mineralization.

Neurogenic heterotopic ossification: epidemiology and morphology on conventional radiographs in an early neurological rehabilitation population

OBJECTIVE

To retrospectively evaluate neurogenic heterotopic ossification in an early neurological rehabilitation population (phases B and C) with respect to epidemiology and morphology on conventional radiographs.

MATERIALS AND METHODS

Over a 4-year period, 1,463 patients treated at a clinic for early neurological rehabilitation were evaluated for clinical symptoms of neurogenic heterotopic ossification. In case of clinical suspicion, plain radiographs of the expected sites were obtained. If heterotopic ossification was detected, the initial and subsequent radiographs were retrospectively analyzed for sites, size, and morphology. Immature lesions were categorized as small (<10 mm) or large (10-100 mm).

RESULTS

The prevalence rate of neurogenic heterotopic ossification was 2.05%. The condition was most common in young male adults. The hip was the most common site accounting for more than half of the cases. Two or more ossifications were seen in 56.7% of the affected patients with approximately two-thirds showing bilateral symmetric involvement of corresponding joint regions. The size of ossifications strongly varied interindividually. Small immature lesions demonstrated less progression in size than large lesions during maturation (P < 0.05).

CONCLUSION

Standard radiographs, as a fast and inexpensive technique, allow the expected size progression of heterotopic ossifications during maturation to be estimated, which is relevant in terms of therapeutic decisions, patient mobilization, and neurological rehabilitation.