SUBACUTE KNEE PAIN IS NOT ALWAYS WHAT IT SEEMS

Steven R. Sabo, MDSports Medicine Fellow 2011-2012University of South Florida and

Morton Plant Mease / BayCare Health System

History of Present Illness

• 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 Pain @ deep popliteal fossa,Moderate size joint effusion without warmthNo joint line tendernessROM decreased (only 10 to 130 degrees)Equivocal Thessaly testNo ligament defect noted on stress tests

Differential Diagnosis:

• Meniscal tear with effusion

• Baker’s 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 Baker’s 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

• Normal PVNS

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 effusion @ 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).

Take Home Messages:

• Relatively rare (incidence 1.8 cases/ million people), usually benign intra-articular and peri-articular hyperproliferation of synoviumCause 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, MDOrthopedic Specialties of Clearwater FL

Sean Bryan, MD

USF / MPM Sports Medicine Fellowship andFamily Medicine Residency Program Director

Ted Farrar, MDUSF / MPM Sports Medicine Fellowship Associate Director

Jonathan Squires, MDRadiology Associates of Clearwater FL

Robert Schoer MD and Pathology DepartmentMorton Plant Mease Medical Center Clearwater FL