Introduction

Calcific tendinopathy is a common condition related to deposition of calcium, mostly hydroxyapatite crystals, within the tendons. More rarely the pathology can affect also other anatomical structures as the ligaments. The condition is unique and distinct from degenerative tendons disease, and indeed calcium deposition in degenerative tendinopathy has a different chemical composition than in calcific tendinitis. The shoulder and the hip are the most commonly affected joints [1], but calcific tendinitis may occur in any tendons of the body [2, 3]. In many cases asymptomatic, it can sometimes be a cause of severe pain. The pathogenesis is not completely understood, but it seems related to areas of hypoxia in tendons, which lead to fibrocartilaginous metaplasia, followed by the formation of a calcium deposit, typically in healthy tendons with no pathologic findings.

Calcific tendinopathy is a dynamic process that evolves through successive stages, characterized by distinct imaging, pathologic and clinical features. Four stages of disease are described in the Uhthoff Cycle [4]: pre-calcific, in which fibrocartilaginous transformation occurs within tendon fibers, usually asymptomatic (Stage 1); formative, in which calcifications are formed, usually poorly symptomatic and including sub-acute low-grade pain, increasing at night (Stage 2); resorptive, in which the tendon develops increased vasculature and calcium deposits are usually removed by phagocytes, but calcifications may migrate into the adjacent structures (Stage 3); and post-calcific, in which there is self-healing and repair of the tendon fibers over several months, which may be associated with pain and restricted function (Stage 4).

While there is an extensive literature on the ultrasound diagnosis of the calcific tendinopathy of the shoulder and its therapies [5,6,7,8,9,10], there are only sporadic reports on the other sites. This article aims to provide a systematic review of the literature to highlight the localizations of calcific tendinopathy beyond the rotator cuff, its ultrasound characteristics and the therapeutic possibilities.

This review is generated from the combined experience of our centers, as indicated by the references in the text, and a thorough analysis of the literature from the last 45 years (1972–2017). A systematic search of the literature was performed in PubMed and included original studies and review articles. Case reports and case series were selected according to clinical relevance. Of the 192 selected articles on PubMed animal and cadaver studies were excluded (8 articles), so 184 articles were evaluated (Tables 1, 2, 3).

Table 1 Articles reporting neck calcific tendinopathy
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Table 2 Articles reporting upper extremities calcific tendinopathy
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Table 3 Articles reporting lower extremities calcific tendinopathy
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Neck

The neck, despite being a rare site of calcific tendinopathy, is the most frequently reported site in the literature, with 157 patients in 79 different articles. Calcific deposits tend to occur anteriorly to C1 and C2, near the insertion of the longus colli muscle, in two cases anteriorly to C4–C5 and, only in one, to C5–C6. Calcific tendinopathy may manifest with cervical and shoulder pain [75], neck stiffness, dysphagia or odynophagia, sore throat, fever and mild leukocytosis. Clinical findings of calcific retropharyngeal tendonitis are similar to the retropharyngeal abscess that represents a medical emergency [46]. Other conditions, like meningitis, pharyngitis, epiglottitis, infectious spondylitis, traumatic injury, cervical disk herniation, muscle spasm, foreign body aspiration and neoplasm, must be excluded [23, 39].

Standard latero-lateral radiographs of the cervical spine, showing calcification at the insertion of the longus colli muscle, are usually adequate for a diagnosis. Computed tomography may be useful for a differential diagnosis with retropharyngeal abscess. Magnetic resonance imaging can identify prevertebral edema [77]. There are no descriptions of ultrasound evaluations of calcific tendinopathy of the neck muscles, most likely because they are rarely examined using ultrasound.

Shoulder and arm

The shoulder is the joint most commonly affected by calcific tendinopathy, mostly the rotator cuff tendons [3, 10, 187], rarely the other tendons (pectoralis major, trapezius, biceps brachii) (Fig. 1). Pectoralis major calcific tendinopathy was described in four articles. Radiographs all showed a lithic area of the lateral humeral cortex with periosteal reaction. Second-level examinations (computed tomography and magnetic resonance imaging) and, in one case biopsy, were necessary for the aspecific findings of the radiographs. A single case of calcific tendinopathy is reported in the trapezius tendon. Biceps brachii calcific tendinopathy has been reported in both the proximal and the distal insertions (Fig. 2), except of the brief head. Calcific tendinopathy was also reported concomitant in the biceps tendon and in the rotator cuff tendon [98]. One of the five cases of calcific distal biceps tendinitis affected a 3-year-old boy [114]. Physical examination shows pain, tenderness, swelling and functional limitation, without a history of traumatic events. The differential diagnoses of extra-articular calcific tendinopathy are with calcific bursitis and loose bodies in the biceps tendon recess and synovial osteochondromatosis [98]. Radiography and ultrasound are sufficient for diagnosis.

Fig. 1
figure 1

Long head of the biceps tendon calcific tendinopathy at mid-arm level. a Long axis; b, c short axis. Ultrasonography shows calcifications (a calipers, b arrows) with absence of posterior acoustic shadowing (resorptive phase)

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Fig. 2
figure 2

Distal biceps tendon calcific tendinopathy at the level of the elbow, proximal to the insertion on the radial tubercle. a Long axis, b short axis. Ultrasonography shows calcifications (arrows) with absence of posterior acoustic shadowing (resorptive phase)

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Elbow and forearm

Two cases of calcific tendinopathy of the common extensor tendon of the elbow were described in two young women exhibiting pain, swelling and functional limitation. Radiograph and ultrasound showed soft-fluid calcification near the muscle insertion [90]. To our knowledge, the common flexor tendon has not been reported in the literature as affected.

Hand and wrist

Tendons of the hand and wrist [188, 189] are rarely reported as affected by calcific tendinopathy (incidence of 2%) [116], but more often the flexor tendons than the extensors (flexor carpi ulnaris four cases, flexor digitorum profundus two cases, flexor digitorum superficialis two cases, abductor pollicis brevis 2). Authors have described calcific tendinopathy in the flexor carpi radialis, abductor digiti minimi, extensor pollicis longus, abductor pollicis longus, flexor pollicis longus and the tendons of the intrinsic muscles. Two cases of calcific tendinopathy of the carpal tunnel tendons have been reported in literature, both with carpal tunnel syndrome.

The differential diagnosis includes soft-tissue infection, bone fracture, metabolic disorder (hyperparathyroidism, gout, pseudogout, hypervitaminosis D, hypercalcemia), degenerative or inflammatory or autoimmune conditions. Clinical presentation, ultrasound and radiographs can differentiate calcific tendinopathy from other etiologies [121].

Hip

The hip [190] is the second most common site of calcific tendinopathy, after the shoulder [158]. The tendons of the rectus femoris are the most commonly involved (Fig. 3) described in 56 patients in 14 different articles. Both direct and indirect tendon components may be affected by this pathology, with prevalence, in our experience, of the direct tendon. But it is also necessary to distinguish the tendinous calcifications from calcifications of their insertional bursae, just beneath the direct and indirect tendon, that may occur quite frequently. The second most common group are the gluteal tendons (42 cases of the gluteus medius and 36 cases of the gluteus maximus reported). Adductor magnus, adductor longus and adductor brevis calcific tendinopathy have been described in six cases (1 magnus, 1 brevis and 4 unknown). Other rare sites are the piriformis (2 cases), the iliopsoas (2 cases), the ischiococcygeus (1 case) and the sartorius (1 case).

Fig. 3
figure 3

Direct tendon of rectus femoris calcific tendinopathy at the level of the anteroinferior iliac spine. a Long axis, b short axis. Ultrasonography shows calcifications (arrows) with absence of posterior acoustic shadowing (resorptive phase). AIIS anteroinferior iliac spine

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Usually occurring in middle-age, patients have functional limitation, tenderness, pain and a positive Patrick’s test [183]. Depending on the affected tendon, the differential diagnosis includes infection [124, 180], arthritis, lumbar radiculopathy [126, 140, 168], os acetabuli, avulsion fracture, insertional calcified bursitis, sesamoid bones, myositis ossificans and chondrosarcoma [146]. Sonography and standard radiographs can be used for diagnosis, showing the calcification. Sometimes computed tomography is useful for bone evaluation, and MRIs to show soft-tissue edema and bone marrow edema.

Thigh, knee and leg

Thigh, knee and leg are rarely affected by calcific tendinopathy, and only a few cases involving the quadriceps tendon, patellar tendon (Fig. 4) and iliotibial band (Fig. 5) [191] are described. In many articles [125, 162] there is no distinction between calcific tendinopathy and calcifications of tendinous tendons, but the majority are calcifications in tendinous tendons. As usual, patients have functional limitations, tenderness and pain. The articles confirm the main role of ultrasound in the diagnosis and in the management of calcific tendinopathy, even of the less common ones.

Fig. 4
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Iliotibial band calcific tendinopathy at the level of the Gerdy’s tubercle. Ultrasonography shows calcifications (arrows) with absence of posterior acoustic shadowing (resorptive phase)

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Fig. 5
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Patellar tendon calcific tendinopathy at the level of the tibial tuberosity. Ultrasonography shows calcifications (arrows) with absence of posterior acoustic shadowing (resorptive phase)

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Foot and ankle

Calcific tendinopathy of the ankle [192] and foot is frequently misdiagnosed because of its rare occurrence and a clinical presentation that is similar to other entities. Achilles tendon calcific tendinopathy was described in eight articles, in both sexes, but more commonly in males. The second most commonly involved tendons are the peroneus longus (3 cases) and the flexor hallucis brevis (2 cases). Single cases have been described in other tendons (extensor hallucis longus, tibialis posterior and flexor of the forefoot).

Motion restriction secondary to pain, erythema, swelling and tenderness are the most frequent symptoms, in the absence of acute trauma [108]. The differential diagnosis is broad and includes gout or pseudogout, avulsion fractures, sesamoid bones, myositis ossificans and infection [156]. Ultrasonography and radiography can be used to make a diagnosis of calcific tendinopathy of the ankle and the foot, while computed tomography and MRI have few indications [136].

Ligaments

Calcifications of the ligaments, that can produce an important pain symptomatology like the calcific tendinopathy of the rotator cuff, are more frequent in the medial collateral ligament (proximal insertion) of the knee, where they can also become of considerable size [193, 194]. Other ligaments less frequently affected by the pathology are the lateral collateral ligament, the anterior or posterior cruciate ligament of the knee and sometimes Wrisberg ligament [195, 196].

Differential diagnosis

Depending on the affected tendon the differential diagnosis includes many diseases. Among the idiopathic ones the most known is the diffuse idiopathic skeletal hyperostosis (DISH) which predominantly affects the spine while ligaments and tendons of the appendicular skeleton are rarely involved [197]. In these cases, the US differential diagnosis is not possible and is generally related to the distribution and site of the calcifications.

The differential diagnosis with the calcification in a degenerative tendinopathy is more easy even with the ultrasound because the affected tendon appear as normal in calcific tendinopathy while shows diffuse signs of degeneration (e.g., hypoechogenicity, loss of the fibrillar aspect) around the calcification in a degenerative tendinopathy. In the most challenging cases, CT and MRI may be necessary.

Non-surgical treatment (or conservative, or minimally invasive treatments)

Calcific tendinopathy is usually a self-limited condition, so the initial management of pain is conservative, with physical therapy and oral administration of NSAIDs. If these treatments fail, other non-surgical therapeutic options may be considered: extra-corporeal shock wave therapy (ESWT), steroid injection (ultrasound-guided or unguided) and US-guided percutaneous aspiration of calcific tendinopathy (US-PICT). ESWT is based on the application of repetitive pulses over the affected site. The results are variable and the exact underlying mechanism of the therapeutic effect on calcific tendinopathy is still debated. It seems to be related to the phagocytosis of calcium deposition induced by the neovascularization response and leukocyte chemotaxis [198]; ESWT therapy is painful, expensive and not widely available. The use of conservative treatment or ESWT in patients with acute pain from calcific tendinopathy in resorption seems to be suboptimal, and often fails. The symptoms in this phase significantly impact quality of life [9, 199]. Minimally invasive interventional techniques (steroid injection of calcific tendinitis) may be used in these cases (US-guided or unguided) and/or US-guided percutaneous aspiration of calcific tendinopathy (US-PICT) [200]. A study by de Witta et al. reports that US-PICT is a superior method compared to steroid injection in the calcific tendinitis of the rotator cuff [201]. In cases of hard calcifications in mildly symptomatic patients, elective treatments should be considered [202]. Percutaneous treatment is not indicated when patients are asymptomatic, and calcification is very small (≤ 5 mm) [203]. Different approaches have been reported in recent studies and all include the use of a fluid: local anesthetic or saline solution to dissolve calcium deposits; one needle or two needles are used to inject and retrieve the fluid to dissolve calcium deposits. Recent evidence has suggested that a double-needle approach might be more appropriate for treating harder deposits, while one needle may be more useful in treating fluid calcifications. Some advantages of US-PICT are that the procedure does not require any hospitalization, is performed under local anesthesia, the patient can return home about 30 min after the procedure is complete, there is no need for post-procedural immobilization, and the patient can return to work sooner [10].

Surgical treatment

Arthroscopic treatment of calcific tendinitis involves selected cases in which conservative or less invasive approaches have failed. Calcification removal techniques vary according to the type of tendon incision and the instrumentation used to remove the calcium deposit. The surgery allows the removal of calcification and a thorough cleaning of the joint of interest. Surgery requires hospitalization, general anesthesia or sedation, however, and a relatively long rehabilitation period after treatment.

Conclusion

Calcific tendinopathy is commonly found in non-rotator cuff tendons. It is easily diagnosed using ultrasound, although ultrasound is rarely used in some anatomic sites, such as neck muscles. Depending on the affected tendon the differential diagnosis includes many diseases, and CT and MRI may be necessary. Usually occurring in middle-age, it can however affect patients of all ages, and a case was reported in a 3-year-old boy. Patients with calcific tendinopathy have functional limitation, tenderness and pain.

Resorption of deposits generally occurs spontaneously, although some patients show persistent clinical symptoms and require therapy. Various therapies can be used, although ultrasonographic guided therapeutic procedures (steroid injection or percutaneous aspiration) seem to be the most effective, particularly for calcific tendinopathy in resorption. Surgery remains an option in cases where other approaches have failed.