Rheumatoid Arthritis-Associated Shoulder Rice Body Bursitis: Arthroscopic Management and Mechanistic Implications

Introduction

Rice body formation in bursae represents a rare synovial pathological phenomenon characterized by the presence of numerous white, smooth, rice-grain-shaped free bodies within the bursal cavity [1]. Although its precise incidence remains difficult to quantify because of nonspecific clinical manifestations and limited epidemiological data, existing literature consistently classifies this condition as rare [2–4]. The subacromial-subdeltoid bursa is the most frequently affected anatomical site, likely due to chronic inflammatory stimulation of synovial tissue in this region [3–6].

Two complementary hypotheses currently dominate the discourse regarding the pathogenic mechanism of rice body formation. The synovial shedding hypothesis proposes that chronic inflammation or ischemia induces necrosis and shedding of synovial villi, which form the core of free bodies [3]. In contrast, the fibrin deposition hypothesis emphasizes fibrinogen exudation, aggregation, and organization secondary to inflammation or microcirculatory disturbances within joints or bursae, rather than detached synovial tissue [4]. The results of recent studies suggest that these mechanisms represent stages of a continuous pathological process: fragments generated by synovial inflammation, proliferation, and necrosis serve as seeds, which become progressively encapsulated by fibrin layers and undergo organization within synovial fluid [3,4,7].

Qi et al. [8] provided critical evidence supporting the synovial shedding hypothesis through a multimodal imaging-pathological correlation study of a recurrent case. Their observations included: (1) magnetic resonance imaging (MRI) showing massive effusion with floating necrotic synovium in the subacromial-subdeltoid bursa; (2) ultrasound revealing synovial shedding that resembled “floating aquatic weeds”; and (3) secondary arthroscopy confirming intra-articular partially encapsulated necrotic synovial tissue. This chain of evidence validated the pathological progression of “chronic synovitis → microinfarction → synovial necrosis and shedding → fibrin encapsulation → rice body formation” in clinical settings, establishing a reproducible observational paradigm for subsequent experimental research. In contrast, Pertea et al [9] challenged the synovial origin hypothesis through histological analysis. Their findings demonstrated that rice body cores consist of eosinophilic amorphous material lacking cellular components, without a physical connection to synovial tissue. The characteristic T2-weighted hypointensity on MRI reflected dense avascular structures consistent with fibrin clots, supporting the fibrin deposition hypothesis. This ongoing debate underscores the likelihood that these mechanisms function at distinct pathological stages.

This report presents a case of subacromial bursitis with rice body formation secondary to rheumatoid arthritis (RA). By integrating multimodal imaging features with pathological evidence, it provides a novel clinical perspective to understand the pathogenesis of this uncommon entity.

Case Report

CASE PRESENTATION:

A 55-year-old Han Chinese woman (body mass index 23.1 kg/m²) presented with progressive right shoulder swelling, pain, and restricted range of motion for more than 1 month. She had a 7-year history of seropositive RA (rheumatoid factor 46 IU/mL, normal reference range <14 IU/mL; anti-cyclic citrullinated peptide [CCP] antibody >300 U/mL) that was managed with tofacitinib (5 mg twice daily) and methotrexate (10 mg weekly). Systemic assessment indicated clinical remission in the bilateral hands (swollen joint count=1), although isolated right shoulder inflammation persisted (C-reactive protein [CRP] 8.2 mg/L). The patient had no history of smoking, alcohol consumption, or other known health hazards. Infectious etiologies were considered and excluded. Tuberculosis was ruled out by a negative Mantoux tuberculin skin test, absence of pulmonary lesions on chest radiography, and negative acid-fast bacilli staining and culture.

PHYSICAL AND IMAGING FINDINGS:

Physical examination of the right shoulder revealed noticeably restricted active range of motion: flexion limited to 95° (versus 170° contralaterally) and abduction limited to 50° (versus 160° contralaterally), with passive motion improving by 15–20°. MRI with proton density-weighted imaging with fat saturation sequences demonstrated multiple hypointense nodules within the subacromial-subdeltoid bursa (Figure 1).

TREATMENT COURSE:

Under general anesthesia, a standard posterior portal (approximately 5 mm) was created, and a 30° arthroscope was introduced to explore the subacromial-subdeltoid bursa. Intraoperatively, hundreds of white loose bodies (diameter 0.4–1.1 cm) with well-defined borders and a characteristic “rice grain” appearance were identified within the bursa. Capillary networks were observed surrounding some rice body clusters (Figure 2A, 2B), but no vessels penetrated individual rice bodies. Intraoperative safety monitoring confirmed: (1) blood loss less than 20 mL according to gravimetry, and (2) absence of instrument-related cartilage damage. After complete debridement of the bursal rice bodies (Figure 3A), synovectomy was performed using a radiofrequency plasma ablation system. Postoperative pathological examination confirmed fibrous hyperplasia with chronic inflammatory cell infiltration (Figure 3B, hematoxylin-eosin staining, magnification 400×).

A phased rehabilitation protocol was implemented: cryotherapy was applied for 20 min per session every 2 h during waking hours (6–8 sessions/day), initiated within 24 h postoperatively; passive range-of-motion exercises commenced at 72 h postoperatively and were performed 3 times daily (morning, afternoon, evening) within pain-free limits (flexion up to 90°, abduction up to 80°); and progressive resistance training with elastic bands (initial resistance ~1–2 kg) was introduced at 1 week. Postoperative evaluation at 6 weeks confirmed (1) absence of surgical site infection (Additional treatment, Serous discharge, Erythema, Purulent exudate, Separation of deep tissues, Isolation of bacteria, and duration of inpatient Stay [ASEPSIS] score=0) and (2) normalization of inflammatory markers (erythrocyte sedimentation rate [ESR]: 12 mm/h; CRP: 0.3 mg/dL).

At the 6-month follow-up, the patient demonstrated clinically significant functional recovery: active shoulder flexion improved to 165° (preoperative 95°), abduction improved to 160° (preoperative 50°), and Constant-Murley score increased from 42 to 86. Subjective pain relief was reflected by a decrease in visual analog scale score from 7/10 to 1/10.

Discussion

PATHOGENESIS: OBSERVATIONAL FINDINGS AND MECHANISTIC HYPOTHESES:

The pathogenesis of rice bodies remains controversial, with the central debate focused on 2 hypotheses. The fibrin deposition hypothesis posits that inflammation or microcirculatory disturbances within joints or bursae initiate fibrin aggregation [4]. In contrast, the synovial shedding hypothesis proposes that rice bodies arise from the shedding of ischemic necrotic synovial villi [3]. Key intraoperative observations revealed a capillary network surrounding aggregated clusters of rice bodies (Figure 3A, red arrow), but no blood vessels were observed penetrating the internal structure of individual rice bodies. Such findings are rare in acellular fibrin clots and more consistent with the features of active inflammatory tissues, such as synovium, which are capable of inducing angiogenesis. Therefore, these observations support a central role for synovial inflammation: synovial tissue may undergo necrosis and shedding under conditions of chronic inflammation and ischemia; the shed material could subsequently be enveloped by surrounding vascularized inflammatory synovium. This process aligns with the pathological model presented in the synovial shedding hypothesis. Notably, this finding can be correlated with the typical synovial pathological changes observed in RA: activated synovial fibroblasts exhibit abnormal angiogenesis driven by pro-inflammatory factors [10,11], and histopathological examination confirms chronic inflammation and fibrin deposition in bursal tissue (Figure 3B). The observed vascularization phenomenon can be regarded as a morphological manifestation of local abnormal vascular proliferation and activation of the inflammatory response within the pathological synovial microenvironment of RA.

ADVANTAGES OF ARTHROSCOPIC TREATMENT:

Although arthroscopic treatment for rice body bursitis lacks direct evidence-based validation from randomized controlled trials, retrospective case series and comparative studies [5,12,13] indicate clear advantages over open bursectomy and conservative management. Through minimally invasive incisions up to 5 mm, arthroscopic treatment permits complete removal of a large number of rice bodies in a single operation (Figure 3A), substantially reducing the risk of complications from large wounds caused by deltoid muscle detachment in open surgery [4,5]. Under direct visualization, the procedure allows simultaneous differential diagnosis of lesions (excluding tumors and infections) and radiofrequency plasma synovial ablation, thereby preventing residual lesions and reducing recurrence risk associated with the limited visual fields of open surgery [14]. In terms of safety, the overall complication rate for arthroscopic procedures is approximately 1.0% (based on general arthroscopic data) [15–17]; most minor complications are self-limiting. These safety results sharply contrast with the 1–3% infection rate reported for open shoulder surgery [17,18], as well as the significantly higher risks of nerve injury and joint stiffness associated with open procedures.

DIFFERENTIAL DIAGNOSIS OF RICE BODIES ACROSS DISEASES:

Rice bodies are not pathognomonic for RA and require multimodal diagnostic distinction from other conditions. Tuberculous arthritis demonstrates caseous necrosis with Langhans giant cells on pathology, periarticular osteoporosis and marginal bone erosion on imaging, and tuberculosis-polymerase chain reaction positivity (62.5–90% sensitivity). It is distinguished from RA by central bone erosion and negative tuberculosis-polymerase chain reaction results [19,20]. Idiopathic synovitis lacks RA-like vascular proliferation (pannus) and typically manifests with normal or mildly elevated CRP and ESR, whereas RA is characterized by polyarticular involvement and pronounced elevation of inflammatory markers [9,21]. Systemic lupus erythematosus demonstrates fibrin-dominant deposits without synovial hyperplasia, non-erosive joint changes, and anti-dsDNA positivity (>95% specificity), in contrast to RA, which requires anti-CCP antibodies and demonstrates erosive arthritis [22,23]. Prosthetic joint infection is characterized by biofilm-associated bacterial colonies, periprosthetic radiolucent zones larger than 2 mm, and positive Gram stain or culture results; it warrants surgical debridement, rather than RA-directed therapy [24–26]. In the present case, RA was confirmed by histopathological evidence of vascularized synovium adjacent to rice bodies (exhibiting a peripheral capillary network without direct encapsulation of the lesions) and by serological elevation of anti-CCP antibody, CRP, and ESR levels. Infectious causes, particularly tuberculosis, were definitively excluded through a negative Mantoux test, normal chest radiography, and negative acid-fast bacilli staining and culture. These findings underscore the importance of integrating histopathology, imaging, serology, and microbiological testing for accurate diagnosis.

DIAGNOSTIC STRATEGY: IDENTIFICATION OF ATYPICAL RA MANIFESTATIONS AND AN INTEGRATED IMAGING APPROACH:

Even when systemic symptoms of RA are well controlled (e.g., low disease activity in hand joints), clinicians should maintain a high index of suspicion for bursitis in patients who present with isolated, refractory symptoms in large joints, such as shoulder swelling accompanied by restricted mechanical movement. Conventional X-ray examinations may lead to missed diagnoses because of their inability to visualize the bursa and rice bodies (Figure 4C). Therefore, a stepwise integrated imaging strategy is required. First, dynamic ultrasound monitoring can detect the floating movement of multiple hypoechoic particles within the bursa (Figure 4A) and confirm the absence of blood flow signals within the rice bodies (Figure 4B), a feature validated as a reliable diagnostic marker [27]. Subsequently, MRI using proton density-weighted imaging with fat saturation/T2-weighted imaging sequences can capture low-signal filling defects within the hyperintense bursal fluid and confirm the core characteristic of rice bodies, which exhibit isointense signals on both T1- and T2-weighted images [28]. This imaging feature serves as a key differential diagnostic criterion distinguishing rice bodies from pigmented villonodular synovitis and synovial chondromatosis. By combining the complementary strengths of ultrasound and MRI, this approach substantially improves the early identification of atypical RA manifestations.

REHABILITATION AND PROGNOSIS: MANAGEMENT STRATEGIES FOR EXTENDED FOLLOW-UP AND RECURRENCE RISK CONTROL:

Although the patient in our case demonstrated clinically significant recovery of shoulder function at 6 months postoperatively, with a Constant-Murley score of 86, extended follow-up beyond 6 months is essential to assess the long-term prognosis of RA-associated bursitis. As a common complication of RA, the recurrence risk of bursitis is strongly correlated with disease activity and primarily driven by 2 core factors. The first is persistent high disease activity, with a 1-year recurrence rate of 32.7% when disease activity score using 28 joint counts (DAS28) is above 3.2, compared with 4.1% when DAS28 is below 2.8 [29]. The second is inadequate treatment adherence, given that the remission rate with up to 12 weeks of triple disease-modifying antirheumatic drug therapy is 18.7% and increases to 54.1% with extension to 36 weeks; patients who reduce medication dosage without achieving deep remission face a 35% higher recurrence risk [30]. Based on these findings, a dual-track strategy is recommended for long-term management. First, a stepwise rehabilitation program involving cryotherapy, passive joint mobilization, and progressive resistance training should be utilized to restore biomechanical function of the shoulder. Concurrently, a treat-to-target approach should be implemented to maintain DAS28 below 2.8 and normalize CRP and ESR levels, combined with quarterly Doppler ultrasound monitoring to guide medication adjustments and control recurrence risk at its inflammatory source.

LIMITATIONS AND FUTURE DIRECTIONS:

The single-case design limits generalizability and long-term assessment, particularly with regard to histopathological validation of vascularization around rice bodies. Future studies should: (1) establish multicenter cohorts (n ≥50) to identify recurrence predictors (e.g., DAS28 >3.2) through serial power Doppler ultrasound and DAS28-CRP monitoring; (2) quantify synovial fibrinogen/vascular endothelial growth factor/tumor necrosis factor-α ratios using liquid chromatography-tandem mass spectrometry to define diagnostic thresholds (>1.5) and clarify mechanisms of fibrin deposition versus angiogenesis; and (3) establish tumor necrosis factor-α transgenic models with microvascular ligation to track synovial shedding (≥3×baseline) and fibrin expansion (≥50%) both spatially and temporally. These approaches will link mechanistic insights to therapeutic targets and advance personalized management of RA-associated rice body bursitis.

Conclusions

This report describes successful treatment of RA-associated shoulder rice body bursitis using arthroscopic debridement. Six-month postoperative follow-up demonstrated restoration of shoulder range of motion to 165° forward flexion and 160° abduction, improvement of Constant-Murley score from 42 to 86, and reduction of visual analog scale score for pain from 7 to 1. Intraoperative findings revealed a capillary network surrounding rice body clusters without vascular penetration into individual rice bodies, providing potential morphological evidence in support of the synovial shedding hypothesis. These observations suggest that rice bodies develop through synovial necrosis and shedding induced by chronic inflammation, followed by secondary fibrin encapsulation.