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

University of MichiganDepartment of Radiology

Corresponding Author:Brian Sabb

briansabb@gmail.com