May 16, 2018
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A 12-year-old boy with a 1-month history of left hip pain

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A 12-year-old boy with a past medical history of left iliac crest bone graft for pharyngoplasty/cleft palate repair performed 5 years prior to presentation arrived at our clinic with anterior left hip pain, which has been waxing and waning since the bone graft procedure. He denies any new or recent trauma. During the past month, he noted significant worsening of his pain. The pain was severe enough to keep him out of school for the past 2 weeks. When asked to localize the pain, he demonstrated the ‘C’ sign, cupping his lateral hip with his hand in a ‘C’ shape. He stated the pain does not radiate nor does he endorse mechanical symptoms. The pain is worse at night and it has now limited his weight-bearing to the point of needing crutches to ambulate. He has tried physical therapy (PT), NSAIDs and narcotics without relief of his symptoms. He denied any constitutional symptoms.

On exam, he has a coxalgic gait. His lumbar spine, sacroiliac joints and greater trochanters are not tender to palpation. When compared to the right hip, his left hip lacks 10° terminal flexion, 5° internal rotation and has a significant decrease in external rotation with flexion, abduction and external rotation testing secondary to pain. The flexion, adduction, internal rotation exam and the extension, abduction, external rotation exam were positive.

Radiographs (Figure 1) were obtained which demonstrated Risser 0 and early erosive changes along the radiographic teardrop of the left hip. MRI (Figure 2) that was dated 3 days prior to presentation demonstrated no evidence of fracture, stress reaction, labral pathology or other soft tissue pathology. The significant finding was a hypointense 10-mm by 10-mm nodular lesion on both T1-weighted and T2-weighted imaging in the cotyloid fossa.

Preoperative radiograph and MRI
Figure 1. Preoperative anteroposterior radiograph of the pelvis of a skeletally immature patient (Risser 0) demonstrates early erosive changes of the radiographic teardrop of the left hip.
Figure 2. Preoperative MRI of the left hip is shown. Images 2a and 2b are coronal cuts demonstrating a hypointense 10-mm x 10-mm lesion on both T1-weighted and T2-weighted sequences. 2c is an axial cut demonstrating the position of the lesion in the cotyloid fossa.

Source: Allston J. Stubbs IV, MD

What is your diagnosis?

See answer on next page.

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Pigmented villonodular synovitis

The exam and MRI findings are consistent with localized pigmented villonodular synovitis (PVNS) vs. another nodular lesion. The patient underwent arthroscopic synovectomy, foreign body excision and intraoperative biopsy to address the lesional pathology.

Surgical technique

The hip was gently distracted under fluoroscopic guidance. Diagnostic arthroscopy was performed via the anterolateral and modified-anterior portals with 6-mm microcapsulotomies. Initial focus was on the nodular lesion in the central compartment, which was noted to be in the cotyloid fossa. It was excised using a grasper and shaver and sent to pathology (Figure 3). Frozen section demonstrated hemosiderin and giant cells consistent with PVN. Final pathology confirmed a diagnosis of PVNS.

Once the lesion was excised, mild chondromalacia of the acetabulum secondary to mechanical damage was seen and addressed via chondroplasty. Within the central compartment, there was tearing and partial detachment of the labrum which was repaired with retrograde suture anchors. After completion of work in the central compartment, the peripheral compartment pathology was addressed. Osteoplasty across the anterior head-neck junction of the femur was performed for the patient’s femoroacetabular impingement. Once the procedures were complete, the instruments were removed, and the capsule was not closed.

Postoperatively, immediate continuous passive range of motion (ROM) was initiated with PT. He was maintained at 20-pound flat foot weight-bearing for 2 weeks and passive ROM exercises. He progressed to weight-bearing as tolerated, active ROM exercises and hip strengthening. At the 4-month follow up, the patient was pain-free and progressing in ROM and strengthening. He was returned to activity without restriction.

nodular PVNS lesion
Figure 3. Intraoperative arthroscopic images show the nodular PVNS lesion as seen from the modified anterior portal during excision.

Discussion

PVNS is a mono-articular disease process that presents in diffuse or localized forms. Both forms have similar histologic appearance, however diffuse type is notorious for a greater risk of recurrence. PVNS most commonly affects the knee, which occurs in up to 80% of cases, followed by the hip, ankle, shoulder and elbow. The prevalence is documented at one case in 1.8 million people. It has a higher predilection for female patients than male patients. The etiology is unknown, but it is thought to be a neoplastic process leading to uncontrolled villous growth of the synovium. Support for the neoplastic theory lies in the rare case reports of malignant transformation of PVNS. Additionally, there is a genetic component which has been tied to the CTS1 gene, encoding for a ligand of a tyrosine kinase receptor.

The typical presentation of PVNS often includes a painful, swollen joint that may have mechanical symptoms or recurrent atraumatic hemarthroses. The differential diagnosis will include synovial chondromatosis, inflammatory synovitis or hemophilia. Determining a correct diagnosis begins with imaging. Initial radiographs may show cystic erosions on both sides of the joint with a sclerotic rim or joint space narrowing depending on the duration, size and aggressiveness of the lesions. MRI shows a characteristic low-signal intensity on T1-weighted and T2-weighted sequences that is attributed to hemosiderin deposits.

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Biopsy is the gold standard to establish a definitive diagnosis. Gross pathology typically has a yellowish or reddish-brown appearance secondary to the hemorrhagic nature of the condition and resultant hemosiderin deposits. Grossly, diffuse type will demonstrate villous projections as compared with a pedunculated lesion as occurs in the localized type. Histology includes hemosiderin-laden multinucleated giant cells, foamy histiocytes and mononuclear cells.

PVNS of the pediatric hip is rare, thus there is a paucity of data regarding treatment and outcomes in the literature. However, there is a recent systematic review from Rush University Medical Center looking at treatment and outcomes of PVNS of the hip. It analyzed the three common treatment options for PVNS: open synovectomy; arthroscopic synovectomy; or open synovectomy with arthroplasty. The mean age of patients included in these studies was 33.2 years with a standard deviation of 12.6 years. The studies were comprised of pediatric and adult patients. Pediatric patients made up a significant minority of the study population. Findings demonstrated a similar rate of revision surgery for synovectomy alone vs. synovectomy with arthroplasty, however the mean time to revision surgery was significantly longer for the group that underwent synovectomy with arthroplasty (11.8 years vs. 6.5 years). There were fewer cases of arthroscopic synovectomy compared to open cases. However, based on the limited data, it seemed results of arthroscopic intervention were better with localized PVNS as opposed to diffuse type. Lastly, the efficacy of adjuvant external beam radiation is unproven in PVNS. Thus, there are no recommendations for or against its use.

Due to our patient’s history and physical exam, there was a wide differential diagnosis. Once MRI was obtained and characteristic findings of hypointense intra-articular lesions were identified on T1 and T2 imaging, our differential diagnosis list was narrowed. The diagnosis of nodular PVNS was confirmed arthroscopically with biopsy and excision. Due to inconclusive long-term outcome data in the literature and concerns of radiation, particularly near reproductive organs of a 12-year-old boy, we did not pursue adjuvant radiation therapy for this patient.

Disclosures: Stubbs reports he receives publishing royalties from Thieme Medical and serves on various boards and committees. Teske reports no relevant financial disclosures.