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Award Winning Anterior Knee Pain Educational Exhibit at The American Roentgen Ray Society (ARRS)Annual Meeting
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University of MichiganDepartment of Radiology
Anterior Knee Pain:A Diagnostic Conundrum
Brian Sabb, DOJ. David Blaha, MD
Department of Orthopaedic Surgery
Disclosure of Commercial Interest
Neither I nor my immediate family members have a financial relationship with a commercial organization that may have a direct or indirect interest in the content.
Objectives
• Improve the participant’s understanding of the radiologic diagnosis of anterior knee pain
• The participant will know specific imaging findings of anterior knee pathology
• Understand the biomechanics and pathophysiology of the patellofemoral joint and how they should be applied to the imaging evaluation
Anterior Knee PainAnatomical Categorization
• Prepatellar Soft Tissues
• Quadriceps Fat Pad
• Infrapatellar Fat Pad of Hoffa
• Extensor Mechanism
• Patellofemoral Joint
• Patella
Prepatellar Bursitis
• Inflammation of the prepatellar bursa
• In more severe cases one will see formation of a discrete fluid collection
• Can become infected, i.e. septic bursitis
• In chronic cases, may contain multiple calcified bodies
• US may show hyperemia; suggesting inflammation, infection, or acute trauma
Prepatellar Bursitis
PD PD FAT SAT
Prepatellar Bursitis
PD PD FAT SAT
T2 FAT SAT
Quadriceps Fat Pad Edema
• Shown in a recent study to clinically mimic meniscal tear in 55% of patients and to present with anterior knee pain in 28% of patients
• Present in about 4-12 % of knee MRIs
• Edema may be present with or without mass effect
Shabshin, Skeletal Radiology. 2006 May; 35(5): 269-74 Roth, AJR. 2004 Jun;182(6):1383-7
Quadriceps Fat Pad Edema
PD PD FAT SAT T2 FAT SAT
Infrapatellar Fat Pad of Hoffa
• Hoffa’s disease
• Localized nodular synovitis
• Pigmented villonodular synovitis (PVNS)
• Intraarticular chondroma
• Infrapatellar plica syndrome
Hoffa’s Disease
• A syndrome of fat pad impingement
• Acute or repetitive trauma causes inflammatory changes in the infrapatellar fat
• The resulting pain, swelling, and fat hypertrophy limits range of motion
• Over time, fibrotic tissue is formed
Hoffa’s Disease
PD PD FAT SAT
Localized Nodular Synovitis
• Benign proliferative disease
• Most commonly affects the tendon sheaths of the hands, e.g. giant cell tumor of tendon sheath
• MRI demonstrates a well defined mass in Hoffa’s fat pad
• Typically low SI on T1 and variable SI on T2
Localized Nodular Synovitis
PD PD FAT SAT T2 FAT SAT
Pigmented Villonodular Synovitis (PVNS)
• Benign proliferative disorder of the synovium
• Usually involves large joints
• 80% of cases affect the knee
• Synovial deposition of hemosiderin results in irregular synovial masses that show a significant amount of hypointensity on all sequences
Pigmented Villonodular Synovitis (PVNS)
PD PD FAT SAT T2 FAT SAT
Intraarticular Chondroma
• Although a rare lesion; they overwhelmingly occur around the knee, typically the infrapatellar fat pad
• May calcify and even ossify
• May erode the lower pole of the patella
• May displace the patellar tendon
Intraarticular Chondroma
PD PD FAT SAT
T2 FAT SAT
Infrapatellar Plica Injury
• A thin fold of synovial tissue, extending from the inferior pole of the patella through Hoffa’s fat to the intercondylar notch anterior to the anterior cruciate ligament
• High signal along the course of the plica indicates injury to the plica
• Thickening of the plica even in the absence of edema or fluid suggests a chronic injury
Cothran, AJR 2003; 180(5): 1443-1447
Infrapatellar Plica Injury
PD PD FAT SAT T2 FAT SAT
Extensor Mechanism Pathology
• Traumatic– Tendinosis– Patellar tendon tear– Quadriceps tendon tear
• Intrinsic patellar tendon lesions, e.g. gout
• Patellar enthesopathy
• Osteochondroses, e.g. Osgood-Schlatter Disease
Patellar Tendinosis
• Pain in the infrapatellar region
• Commonly seen in athletes
• MRI demonstrates thickening of the patellar tendon with intermediate T1 or PD signal and increased signal on T2 especially with fat suppression
• Ultrasound demonstrates thickening, hypoechogenicity, and increased color flow
Patellar Tendinosis
PD PD FAT SAT T2 FAT SAT
Patellar Tendon Tear
• MRI– Fluid signal is seen at site of tear;
decreased T1 and increased T2 signal– A tendon gap is seen along with diastasis
of tendon fibers in full thickness tear• US
– Hypoechoic foci– Posterior shadowing is seen at ends of
the retracted tendon in full thickness tear– Patella alta
Complete Patellar Tendon Tear
PD FAT SAT
Longitudinal Ultrasound
Quadriceps Tendon Tear
• MRI– Partial thickness tear reveals small
pockets of fluid indicating tear often superimposed on the more diffuse increased T2 signal of tendinosis
• Ultrasound– Partial thickness tears demonstrate
hypoechogenicity and swelling• By both modalities, tendon retraction and
discontinuity of fibers indicates full thickness tear
Quadriceps Tendon Tear
Full thickness tear by MR with diastasis of fibers filled by high T2 fluid and and by longitudinal US with hypoechoic fluid
PD FAT SAT
PD FAT SAT
Complete Quadriceps Tendon Tear
PDNote: patella baja
Intrinsic Patellar Tendon Lesion: Gout
• MRI reveals low T1 and mildly high T2 signal. There is an infiltrating mass present
• Ultrasound reveals hyperechogenicity, acoustic shadowing, and calcifications. Employing color flow imaging is important since peripheral hyperemia is expected
Gout of The Patellar Tendon
PD PD FAT SAT
T2 FAT SAT
T2 FAT SAT
T2 FAT SAT
Gout of The Patellar Tendon by US
Intratendinous Crystals
Peripheral hyperemia
Shadowing
Enthesopathy of The Patella
• May be related to a degenerative process
• One must also consider inflammatory arthropathies
– Psoriasis
– Ankylosing spondylitis
– Reactive arthritis
Psoriasis
PD PD FAT SAT PD FAT SAT
Ankylosing Spondylitis
Ankylosing Spondylitis
PD PD FAT SAT T2 FAT SAT
T1
Extensive bone marrow edema and associated enthesitis
Reactive Arthritis
Osgood Schlatter Disease
• An osteochondrosis of the tibial tubercle manifesting as anterior knee pain in adolescents
• The fragmentation can persist into adulthood and cause continued or recurrent symptoms
Sequela of Osgood Schlatter
PD PD FAT SAT
T2 FAT SAT
T1
Note the irregularity and edema causing recurrent and chronic pain
Patellar Malalignment
• Transient Patellar Dislocation
• Excessive Lateral Pressure Syndrome (ELPS)
• Patellar Tendon Lateral Femoral Condyle Friction Syndrome
Transient Patellar Dislocation
• The medial patellar facet impacts against the lateral femoral condyle, producing bone bruises or microfractures. The pattern is nearly pathognomonic
• Injury to the medial patellar retinaculum is very common
• Predisposing factors include dysplastic trochlea, patella alta, lateralized tibial tubercle, and tight lateral retinaculum
• Treatment for recurrent dislocation often includes lateral retinacular release to decrease lateralization force on the patella
Transient Patellar Dislocation
Lateral femoral condyle
T2 FAT SAT
Medial patella
Excessive Lateral Pressure Syndrome (ELPS)
• Classically categorized as tilt without subluxation. Look for narrowing at the lateral aspect of the patellofemoral joint, especially in young patients with anterior knee pain
• However, only rarely see advanced tilt without subluxation
• Surgical treatment includes lateral retinacular release to decrease the translational force on the patella
• Attempt to make the diagnosis before advanced osteoarthritis (OA) ensues
January 2001
at 27 years old
August 2005
at 31 years old
Excessive Lateral Pressure Syndrome
T2 FAT SAT T2 FAT SAT
The OA renders treatment/surgery less effective
Suggest the diagnosis based on the tilt; prior to OA
Images courtesy of Mark Schweitzer, MD
Chung, Skeletal Radiology 2001 Nov; 39: 694-697
Patellar Tendon-Lateral Femoral Condyle Friction Syndrome
• Presents as anterior knee pain exacerbated by hyperextension
• MRI reveals edema in the superolateral aspect of Hoffa’s fat pad between the patellar tendon and the lateral femoral condyle
• Likely related to, or a form of patellar malalignment
• Associated with patella alta
Patellar Tendon Lateral Femoral Condyle Friction Syndrome
PD FAT SAT Cor FAT SAT T2 FAT SAT
The alta allows for the contact between the tendon and the femoral condyle
Patellar Abnormalities
• Bipartite patella
• Multipartite patella
• Patellar fracture
Bipartite Patella
• Painful bipartite patella is a cause of anterior knee pain
• Any bipartite or multipartite bone can develop a pseudarthrosis
• The pseudarthrosis is manifested on MRI as bone marrow edema and as fluid between the osseous fragments
• Initial treatment includes physical therapy, rest, and pain control
• When initial therapy fails, surgery is often performed
• Surgical options include:– Resection of the painful fragment– Lateral retinacular release– Detachment of the insertion site of the vastus lateralis
Bipartite Patella
PD FAT SAT T2 FAT SAT
Cor T2 FAT SAT
Note the accessory ossicle is typically superolateral
Bone marrow edema and cystic changes correlate with pain
Cor T1
Multipartite Patella
T2 FAT SAT
Cor T2 FAT SAT
Cor T2 FAT SAT
T1
Note the typical superolateral fragments
Patellar Fracture
• Susceptible to fracture because of its superficial location and lack of protection
• Two-thirds are horizontal fractures
• Next most frequent are comminuted and vertical fractures
• Look for sharp fracture lines, joint effusion, and location of fracture lines away from the typical superolateral location of an accessory ossicle
Patellar Fracture
Patellar Fracture
Axial CT showing a lipohemarthrosis