Simultaneous pigmented villonodular synovitis and synovial chondromatosis of the knee joint: case report

Abstract

Background:

Pigmented villonodular synovitis (PVNS) and synovial chondromatosis (SC) are rare joint diseases. Their coexistence within the same joint is exceedingly rare, and understanding such overlapping joint pathologies is crucial for improving diagnosis and treatment strategies.

Materials and methods:

This case has been reported in accordance with the SCARE criteria. A patient presenting with knee pain and swelling underwent arthroscopic examination. Arthroscopic findings suggested the presence of both PVNS and SC. To confirm the diagnosis, post-operative histopathological analysis was performed on synovial tissue samples obtained during arthroscopy.

Results:

Histopathological examination confirmed the simultaneous presence of PVNS and SC in the knee joint. To our knowledge, this is the first reported case of these two conditions coexisting within an adult knee joint. Arthroscopic examination provided key visual findings that guided the collection of samples, while histopathology validated the overlapping diagnoses.

Conclusion:

We report a detailed case of simultaneous PVNS and SC in an adult knee joint. The affected synovium and loose bodies were removed arthroscopically, although long-term follow-up is still required. In summary, this case provides valuable clinical insight into a rare presentation, while the underlying cellular and molecular mechanisms warrant further investigation.

Background

Pigmented villonodular synovitis (PVNS), reclassified by the World Health Organization in 2013 as diffuse tenosynovial giant cell tumor (TGCT)[1], is a subtype of TGCT. It is characterized by hemosiderin deposition and synovial inflammation. Although PVNS is typically benign and locally invasive^[2,3^], cases of distant metastasis to the lungs and lymph nodes have been reported^[4,5^]. This condition is relatively rare, with an incidence of approximately four cases per million, and it predominantly affects females more than males[6].

HIGHLIGHTS

• Pigmented villonodular synovitis (PVNS) coexisting with synovial chondromatosis (SC) is an exceptionally rare synovial disorder.

• Imaging alone may not reliably distinguish PVNS from SC.

• Arthroscopy identified proliferative synovium and multiple loose bodies.

• Histopathology confirmed the coexistence of PVNS and SC.

• Recognition of dual pathology may affect surgery and recurrence surveillance.

Synovial chondromatosis (SC), in contrast, is marked by the formation of cartilaginous or osteochondral bodies within the synovium[7]. SC can occur in both intra-articular and extra-articular structures and has an incidence of 1.8 cases per million per year in England, affecting males 1.8–3 times more frequently than females^[8,9^]. Patients with PVNS or SC often present with joint pain, swelling, stiffness, and limited range of motion (ROM), with magnetic resonance imaging (MRI) being an effective diagnostic tool[10].

While both PVNS and SC are rare joint disorders, their coexistence within the same joint is exceedingly uncommon. Histopathological examination remains the gold standard for definitive diagnosis of both conditions. A literature review shows that concurrent PVNS and SC have been documented in the hip[11], elbow[12] (PVNS of the elbow developed first; SC of the same elbow was diagnosed 6 years later after debridement), and temporomandibular joint (TMJ)[13]. Recently, a case of coexistence of the two diseases was reported in the knee of a pediatric patient[14] (Table 1); however, to our knowledge, no detailed cases have been documented in the adult knee joint. This report describes the case of a 50-year-old woman with chronic pain of the left knee due to combined SC and PVNS, to highlight that these two rare conditions can occur concurrently and emphasize the need for thorough preoperative evaluation.

Table 1.

Summary of previously reported cases of concurrent PVNS and SC across different joints.

Study	Age	Sex	Site	Symptom duration (months)	Follow-up (months)	Recurrence
Cai et al[13]	21	Female	Temporomandibular joint	3	13	No
Efrima et al[11]	37	Female	Hip joint	156	12	No
Ekman et al[12]	57	Male	Elbow joint	6	72	Yes
Beauchamp et al[14]	4	Female	Knee joint	/	3	No

Presentation of case

This case has been reported in accordance with the SCARE criteria[15]. A 50-year-old woman was admitted to the Department of Orthopedic with a complaint of chronic traumatic pain in her left knee persisting for over 30 years. She initially injured her knee in a fall while running, resulting in a sprain that led to left knee pain, swelling, and restricted ROM, and conservative treatments were administered at that time. Throughout the course of the disease, she experienced recurrent episodes of left knee pain, and multiple intra-articular injections were administered prior to this inpatient admission. One year ago, a benign tumor in the left parathyroid gland was surgically removed. Physical examination revealed no positive signs, such as joint swelling, joint line tenderness, limited ROM, a positive McMurray test, or a floating patella test, among others. Radiographs revealed narrowing of the medial tibiofemoral joint space and osteophyte formation in the intercondylar region and along the joint margins; two small loose osteochondral bodies were identified in the lateral joint space. On the lateral view, calcification was observed in the patellar tendon area (Fig. 1A). MRI revealed extensive synovial inflammation and effusion in the left knee joint, with numerous loose bodies dispersed in the intercondylar area and even extending outside the joint into the popliteus muscle, where proliferative soft tissue encapsulated some of the loose bodies. Figure 1B-E show characteristic MRI images with soft tissue encasing some of the loose bodies. MRI raised a differential diagnosis that included PVNS, SC, gout, joint infection, and synovial sarcoma, but the findings were not definitive prior to arthroscopic examination.

Figure 1.

Pre-operative images of the left knee. (A) Anteroposterior and lateral radiographs of the left knee joint. (B and D) Sagittal views of the left knee. (C) Coronal view of the left knee. (E) Axial view of the left knee. White arrows indicate loose bodies encased within soft tissue.

Arthroscopic knee surgery was performed using standard anterolateral, anteromedial, posterolateral, and posteromedial portals for observation and intervention. Hypertrophic red-brown synovium, along with multiple loose bodies, was observed in the medial and lateral compartments, as well as the posterior aspect of the joint (Fig. 2). Some loose bodies were embedded within the proliferative synovium. An arthroscopic shaver, grasping forceps, and Kocher forceps were used to debride the inflamed synovium and remove the loose bodies. The guiding principle of this procedure is to inspect all compartments of the knee joint and to debride all suspicious synovium until normal tissue is exposed; all loose bodies must be removed arthroscopically. Typical brown synovium and loose bodies were collected for pathological examination (Fig. 3A-B). A vacuum drainage bottle was placed in the joint cavity. Postoperatively, once the drainage bottle was removed, the patient was allowed immediate full weight-bearing and encouraged to perform active knee extension and flexion exercises through the full ROM as tolerated, with the assistance of crutches. Histological images show the characteristic features of PVNS and SC, including hemosiderin deposition, hemosiderin-laden macrophages, chondrocytes, and cartilage matrix (Fig. 3C-F). In Figure 3E, the coexistence of PVNS and SC is clearly observed.

Figure 2.

Arthroscopic images. (A) Typical PVNS synovium and a loose body. (B–D) Loose bodies located within the joint and extending outside the joint.

Figure 3.

Samples collected during arthroscopic surgery alongside histological sections. (A) Typical PVNS synovium. (B) Numerous loose bodies. (C) Hematoxylin and eosin (HE) staining of PVNS. (D) HE staining of SC. (E) HE staining of PVNS-encased SC, a well-circumscribed nodule of hyaline cartilage surrounded by proliferative synovial tissue. The cartilage nodule contains chondrocytes embedded in lacunae with mild nuclear atypia and basophilic matrix calcification. The surrounding synovium exhibits villous proliferation with hyperplastic synoviocytes, hemosiderin deposition, and chronic inflammatory cell infiltration, consistent with pigmented villonodular synovitis; 100× magnification; (F) higher magnification (200×) of (E).

Discussion

From this case, we learned that PVNS can coexist with SC, reminding us to consider multiple synovial pathologies when evaluating atypical joint lesions and to rely on pathology for definitive diagnosis. Simultaneous PVNS and SC have previously been reported in the hip[11], TMJ[13], elbow[12], and pediatric knee joint[14]; the occurrence of these conditions across multiple joints suggests that simultaneous PVNS and SC may develop in any synovial joint, though it remains rare. However, this represents the most detailed case of PVNS and SC in the adult knee, with distinct radiological, gross, and histological evidence confirming their coexistence. The preoperative, intraoperative, and postoperative findings may help arthroscopic surgeons better understand this condition and facilitate comprehensive preoperative planning to improve patient outcomes.

The etiology of PVNS remains undetermined. Some scholars consider it a chronic inflammatory process associated with trauma and abnormal metabolic activities; however, increasing evidence suggests that PVNS is neoplastic in nature^[5,16,17^], with DNA rearrangements identified in many patients, primarily involving regions 1p11-13^[18^], 2q35-37^[19^], and chromosomes 5 and/or 7[20]. Recently, the CSF-1 and COL6A3 genes have been identified at the breakpoints 1p13 and 2q35, respectively, and are thought to play a critical role in the development^[21,22^]. CSF-1 is involved in the proliferation and differentiation of monocytes and macrophages, while COL6A3 encodes a type IV alpha-3 collagen chain. Additionally, O’Keefe et al[23] reported that PVNS is closely associated with IL-1β, IL-6, TNF-α, and MMP-9, all of which may contribute to synovitis and cartilage degradation.

SC can be classified into primary and secondary types[24]. Primary SC, also known as idiopathic SC, has an unclear etiology, and the loose bodies are typically uniform in size. Secondary SC, on the other hand, is associated with osteoarthritis, trauma, and osteochondritis dissecans and is characterized by loose bodies of varying sizes^[25,26^]. Recently, chromosomal aberrations on chromosome 6[25] have been identified in some patients and may be related to the progression of SC. The varied sizes of loose bodies in this study classify the condition as secondary SC. Considering the etiology of both rare diseases, the coexistence of PVNS and SC in this patient may be attributed to a long history of trauma, which appears to have affected structures outside the joint as well. Trauma likely caused initial damage to intra-articular structures, leading to the persistent production of inflammatory cytokines that irritated the synovium and promoted cartilage degradation. This may have initiated a vicious cycle, continuously altering the joint’s original structure. However, whether the coexistence of these two diseases results from trauma requires further exploration.

Notably, our intraoperative findings revealed that most of the loose bodies were irregular in shape, unlike the typical loose bodies of SC, which are usually regular with smooth margins. However, histological analysis demonstrated a typical loose body encapsulated within hypertrophic synovium. We speculate that this condition may be attributable to degeneration and wear within the knee joint, particularly given that this patient had severe osteoarthritis. Both diseases have significant recurrence rates, reported at 10–56%[27] for PVNS and 0–31%[28] for SC. Arthroscopic removal of loose bodies in SC is recommended to prevent cartilage wear, though the necessity of synovectomy remains debated. Arthroscopic treatment is also the standard approach for PVNS globally, though its recurrence rate is higher than that of SC. To reduce recurrence, radiation therapy[29] has been applied to PVNS treatment, but optimal dosing and long-term safety require further validation. Pexidartinib[30], an oral tyrosine kinase inhibitor that selectively targets CSF-1 receptors, has shown some efficacy in preventing recurrence after diffuse PVNS surgery, although studies indicate an effectiveness rate of only about 30%. Overall, the high recurrence rates of PVNS and SC remain unresolved, and future advances may rely on uncovering their underlying cellular and molecular mechanisms.

This study also has limitations. Although the patient was scheduled for outpatient follow-up at 6 and 12 months postoperatively, she declined to return after discharge. Consequently, critical postoperative data – including recurrence, ROM, and functional outcomes – are lacking. Nevertheless, this report documents a rare coexistence of PVNS and SC within the same knee joint. Because these two entities share overlapping clinical and imaging features, recognizing the possibility of their concurrence is important for accurate diagnosis and complete synovial resection. This case may heighten surgeons’ awareness and inform the management of comparable presentations.

Conclusion

We report a detailed case of simultaneous PVNS and SC in an adult knee joint. The affected synovium and loose bodies were removed arthroscopically, although long-term follow-up is still required. In summary, this case provides valuable clinical insight into a rare presentation, while the underlying cellular and molecular mechanisms warrant further investigation.

Ethical approval

This work has been approved by the Chongqing Songshan General Hospital (CSGWEC20210782).

Consent

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal upon request.

Sources of funding

Not applicable.

Author contributions

P.Z. performed the surgery and collected the clinical data. P.Z. drafted the manuscript. W.A.-M. reviewed the imaging and prepared the figures. P.Z. critically revised the manuscript. All authors read and approved the final manuscript.

Conflicts of interest disclosure

The authors have no conflicts of interest to declare.

Research registration unique identifying number (UIN)

Not applicable.

Guarantor

Ping Zhou.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Data availability statement

All data generated or analyzed during this study are included within this manuscript.

Assistance with the study

None.

Presentation

None.