SUBACUTE KNEE PAIN IS NOT ALWAYS WHAT IT SEEMS Steven R. Sabo, MD Sports Medicine Fellow University of South Florida and Morton Plant Mease / BayCare Health System

History of Present I llness 36 y.o. male softball player and auto mechanic c/o right knee pain, stiffness, and swelling x 3 months Twisted right knee walking down stairs. Posterior knee joint 6/10 pain, increases with any knee flexion. No giving way, locking, or prior Hx of trauma.

R knee Injury x 3 months MHX/SHX: Prior left knee sprain 1 yr ago resolved. No chronic injuries or diseases. Meds: None Allergies: Pen causes rash. Exam: 6/10 deep popliteal fossa, Moderate size joint effusion without warmth No joint line tenderness ROM decreased (only 10 to 130 degrees) Equivocal Thessaly test No ligament defect noted on stress tests

Differential Diagnosis: Meniscal tear with effusion Bakers cyst partial ACL/PCL ligament injury with effusion Osteoarthritis, loose body, Stress fracture. infectious arthritis, gout or pseudogout RA autoimmune arthritis, psoriatic or seronegative arthritis, amyloidosis, SLE

Imaging and Special Studies: X-rays revealed mild osteoarthritis CBC, ESR, CRP, RF and ANA ordered by PCM and were normal Aspiration of knee = 10 ml of blood tinged rusty colored synovial fluid without evidence of crystals, infection, or malignant cells. Stiffness and effusion recurred rapidly before the next day Sports Med / Ortho ordered an MRI.

MRI of Right Knee Diffuse non-calcified nodular synovial thickening 8.5 cm diameter Bakers popliteal cyst Chondromalacia Patella, mild diffuse No ligament derangement, meniscal tear, fracture, or bone contusion.

New Differential Diagnosis: Synovial Chondromatosis Chronic Hemarthrosis Rheumatoid Arthritis Pigmented Villonodular Synovitis Benign fibroblastic tumors

Surgery and Pathology Results: Exploratory open arthrotomy with synovectomy done because of MRI findings. Dark Red 16 x 12 x 6 cm large lobulated mass immediately extruded from the surgical wound as if under pressure. Multiple lesions had eroded partially into the undersurface and margins of the patella. Pathology: hypervascular proliferative synovium containing multinucleated giant cells, macrophages, and hemosiderin.

Normal Synovium vs. Pigmented Villonodular Synovitis NormalPVNS

Final Diagnosis: Pigmented Villonodular Synovitis (PVNS) Treatment: Synovectomy for complete removal of lesion, post-op hinged knee brace, then physical therapy. Outcome: Patient had return of normal joint function. Normal ROM and strength. No recurrence of pain or 6 months PX: Diffuse PVNS recurs up to 46%, Localized PVNS recurs at 8%

Tx options for recurrence Repeat Synovectomy XRT Radiation Therapy 4000 cGy If enough of joint is destroyed: bone grafting or total joint replacement Tumor Necrosis Factor α inhibitor (class of drugs): off label use to decrease inflammatory response for refractory PVNS, reported in Rheumatology case studies. Examples: etanercept (Enbrel), infliximab (Remicade), adalimumab (Humira).etanercept infliximabadalimumab

Take Home Messages: Relatively rare (incidence 1.8 cases/ million people), usually benign intra-articular and peri- articular hyperproliferation of synovium Cause debated: malignant transformation vs. chronic inflammatory Removal of the lesion is usually curative Repeat imaging is prudent since it recurs Important to occasionally widen your DDX for knee pain.

Special Thanks: Our patient (written consent given to allow this case report) Allen Hughes, MD Orthopedic Specialties of Clearwater FL Sean Bryan, MD USF / MPM Sports Medicine Fellowship and Family Medicine Residency Program Director Ted Farrar, MD USF / MPM Sports Medicine Fellowship Associate Director Jonathan Squires, MD Radiology Associates of Clearwater FL Robert Schoer MD and Pathology Department Morton Plant Mease Medical Center Clearwater FL