Ossifying tendinitis of the rotator cuff after arthroscopic excision of calcium deposits: report of two cases and literature review
© The Author(s) 2014
Received: 8 February 2014
Accepted: 23 June 2014
Published: 15 July 2014
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.
Subacromial calcium deposits and calcifications in the tendons of the rotator cuff (RC), with histologic presence of chondrocytes along tenocytes, were identified as a cause of scapulohumeral periarthritis in the early 1900s [1–3]. Later, the term calcifying tendinitis (CT) was coined, denoting an evolutionary process tending towards spontaneous healing . Prevalence of CT was reported to be 2.7 % in asymptomatic individuals and it seems to be more common in females between their fourth and sixth decades, and sedentary workers . Uhthoff and Sarkar  noted that CT evolves through a typical cycle in three distinct stages: pre-calcific, calcifying and post-calcific. The pre-calcific stage is characterized by metaplasia of tenocytes into chondrocytes that can be stimulated by multiple factors including hypoxia, microtrauma, disuse and hormonal action. The calcific stage can be divided into three phases: formation, resting and resorption; the process evolves from deposition of amorphous calcium phosphate followed by vascularisation to absorb the calcium deposits. The phase of resorption is associated with significant clinical pain experienced by the patient. The post-calcific stage marks collagenisation of the lesion by fibroblasts, thus ending the cycle of calcifying tendinitis.
It is usually associated with surgical intervention or trauma  and is more commonly seen in the Achilles tendon  or following repair of ruptured distal biceps . 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 patients developed an OT of the supraspinatus after arthroscopic removal of calcium deposits, and we review the literature.
In April 2005 the patient came to our outpatient office, complaining of severe pain and discomfort in the right shoulder for 1 year. After radiological and ultrasound (US) examination, he was diagnosed with calcific tendinitis of the rotator cuff and he underwent two cycles of extracorporeal shock wave (ESW) therapy. At 1 year follow-up he had not had any improvement in pain and shoulder function and therefore was advised to undergo shoulder arthroscopy.
After 1 year of moderate postoperative pain, the patient asked to be reassessed again due to severe disability during work and daily living activities Several attempts at conservative therapies (rehabilitation, laser therapy, NSAID, steroid injections) failed and he was therefore prescribed shoulder MRI that revealed slight changes in signal intensity (T1 weighted) of the supraspinatus insertion due to degenerative alterations of the tendon (Fig. 4d). A third arthroscopic approach in May 2009 showed a subacromial bursitis with fibrous adhesions and a complete tendon healing. We performed a S/A bursectomy, removal of adhesions and tendon stimulation with low radiofrequency (Fig. 5e, f).
The patient followed the standard postoperative program and he had slight pain for 3 years, especially during work activity. At the last FU examination in December 2013 (8 years) the CS was 87 and SST had 10/12 “yes” responses.
CT of the shoulder is a widespread clinical condition with a significant impact on patient’s quality of life. Although several treatments have been proposed, the best option to choose is still controversial [12–16]. Extracorporeal shock wave therapy (ESWT) has been described to be effective [13, 14], but a long-term follow-up study showed that about 20 % of the patients treated have required surgery . US-guided needling, irrigation and aspiration may reduce pain and stimulate calcium resorption , while a surgical approach is suggested in cases with persistent disabling symptoms for at least 6 months . Some case-series studies reported good results with partial removal of the calcific deposits, so as to preserve the integrity of the tendon [17, 18]. However, in cases with arthroscopic removal of large and deep calcific deposits, it is recommended to repair the defect with side-to-side sutures or anchors [16, 18]. Recurrence is a known complication following surgical excision of calcific deposits of the shoulder with an incidence reported between 16 % and 18 % , but to our knowledge, there is no description of recurrence in the form of OT. Tendon involvement by HO was found in 26.7 % of patients after shoulder surgery and 80 % of these occurred after RC repair and acromioplasty, but the presence of ossifications seemed to be of minor clinical impact [7, 8, 20, 21].
In a case series of 892 patients treated with acromioplasty and distal clavicle resection, Berg et al.  reported 5 % with ectopic bone formation, including sites like S/A space, acromio-clavicular joint, coraco-acromial ligament and coraco-clavicular ligament: around 3.2 % of them were symptomatic.
HO of the deltoid muscle  and supraspinatus tendon  has also been described following open RC repair. The first was managed with resection of pathologic bone and soft tissue contracture by open interval release and manipulation followed by radiation therapy; in the second case the authors did not perform any additional surgery but they described the association with axillary nerve palsy and they highlighted that there were several risk factors present, including two operations within 2 months, smoking and chronic pulmonary disease. In fact, it has been postulated that hypoxia may drive metaplasia in bone-forming cells in patients who are chronic smokers and continue smoking in the peri-operative period and in patients suffering from chronic pulmonary diseases [22, 23].
The mechanism of origin of bone metaplasia in the RC tendon with calcium deposits is unknown, but some aspects of this phenomenon can be interpreted through the findings already known to us. The presence of resident progenitor cells with multi-differentiation potential in the human tendon  and local release of bone morphogenic proteins (BMP) which helps in differentiation of pluripotent mesenchymal cells into osteoblasts [25, 26] has been noted after acromioplasty and in cases with degenerated cuff tissue; these biologic changes may thus induce ectopic bone formation [22, 27]. Ectopic chondrogenesis and ossification have been reported in the patellar calcific tendinopathy rat model and to a lesser extent, in the traumatic patellar tendon injury model . The authors detected BMP-2 protein in the chondrocyte-like cells and calcific deposits in both injury models but not in control samples, indicating that BMP-2 might be involved in the pathogenesis of ectopic chondrogenesis and ossification. HO is common after traumatic injuries requiring prolonged immobilization and rigorous passive physiotherapy  or can be associated with other specific rheumatic conditions . An additional predisposing factor for HO is an altered balance within the autonomic nervous system, as seen in brain, spinal cord or peripheral nerve injury . Finally, it can develop after minimally invasive surgery and arthroscopy, but the incidence is less common than after open shoulder surgery . The dilution of osteoinductive marrow elements with irrigation fluid and also its continuous washout may be implicated in its formation . We accurately investigated overall features of both our patients but we didn’t find any of the supposed risk factors which are implicated in HO. Both patients were non-smokers with no history of any chronic neurological or internal diseases, and surgeries were performed arthroscopically without pre- or postoperative nerve involvement. The patients followed a protocol of physiotherapy as standardized for all our cases of CT arthroscopically managed. No significant anthropometric difference was found comparing the two patients, nor did they have a family history of inflammatory osteoarthritis, connectivitis or other rheumatic or metabolic disorders; both were employed with no potential habits (smoking, alcohol, drugs, dietary behaviour) or work-related risk factors.
In both cases the RC was involved with severe pain and functional impairment that required an arthroscopic second look to ascertain the origin and the characteristics of the mass.
During the surgical procedure of case 1 we found a formation of hard consistency above and partly within the supraspinatus tendon at the same site the first calcific deposit was removed from; in case 2 we found similar macroscopic characteristics of the ossification, with a tendency to infiltrate the tendon. The histologic features showed in both cases areas of chondrometaplasia and ossification that were diagnosed as a particular form of OT, without supposing such a kind of evolution before the intraoperative assessment.
The ossifications found above and within the substance of the tendon may be the result of a transformation of mesenchymal cells to bone-forming cells in response to the surgical excision of the calcium deposit and suturing of the tendon during the arthroscopic procedure.
Our preference for complete, meticulous excision of the mass might help avoid further recurrence of the ossifying mass. The long-term follow-up of the two cases described in this study showed no clinical or radiological recurrence of the deposits. Although the surgical approach may have been the trigger event inducing the chondrometaplasia, we have not enough data to support this speculative hypothesis, nor can we rule out that the ossification and cartilaginous metaplasia could be the natural evolution of the case. The surgical findings described in this study led us to consider with caution arthroscopic excision of calcium deposits and to be meticulous during the subacromial debridement of calcific foci to minimize the risk of recurrence. We do believe that the description of these two rare cases of OT will be useful to include this condition as a further complication of CT and also to consider the shoulder as an additional potential site of OT.
Conflict of interest
Both patients provided informed consent to the publication of their clinical cases.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
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