Approach Considerations

Radiography is the principal study used in the diagnosis of patellofemoral arthritis. Computed tomography can also be used to determine patellar tilt and articular damage. Arthroscopy can be used for both diagnosis and therapy.

No laboratory tests are usually required for the initial workup for knee pain. However, if clinical suspicion arises, a workup for systemic causes of polyarticular arthritis may be appropriate. This workup includes but is not limited to an evaluation for Lyme disease, rheumatoid arthritis, psoriatic arthritis, and gout.

Radiography

Radiographic views of the knee include standing anteroposterior (AP), lateral, and axial (Merchant view, 45° flexion).^[21]These radiographic views should be examined closely for narrowing of the joint space, osteophytes, articular degeneration, and patella alignment. Congruence of the patella and patella tilt can be assessed on the axial view. Specific measurements, which can be obtained from the radiographs, include the sulcus angle, the congruence angles, and the Insall-Salvati ratio (described below).

A sulcus angle is the angle between the medial and lateral condyles and the sulcus. It normally averages 138°. (See the image below.)

Patellofemoral arthritis. The sulcus angle is the angle formed by the condyles and the sulcus. This is a measurement of trochlear depth. A finding greater than 138° indicates the presence of patellofemoral dysplasia.

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A congruence angle is the angle between a line bisecting the sulcus angle and the articular ridge. It normally averages 6° and is a measurement of subluxation.

The Insall-Salvati ratio is the ratio of the length of the patella ligament to patella length as measured on the lateral view. The ratio should be 1:1; a ratio of more than 1:2 indicates the presence of patella alta. (See the image below.)

Patellofemoral arthritis. The Insall-Salvati ratio is used to assess the position of the patella and determine if the patella alta or patella baja is present. The ratio of the height of the patella to the length of the patella tendon should be 1:1.

View Media Gallery

The patellofemoral index is a distance ratio of the articular ridge and medial condyle to the articular surface and the lateral condyle. (See the image below.)

Patellofemoral arthritis. The patellofemoral index is the ratio of M, the closest distance between the articular ridge and the medial condyle, and L, the closest distance between the lateral facet and condyle.

View Media Gallery

With radiography, the presence of osteophytes at the lateral femoral trochlea combined with narrowing of the joint has 90% sensitivity in diagnosing arthritic changes, as compared with MRI.^[22]

Diagnostic Arthroscopy

Arthroscopy is an excellent tool for diagnosing patellofemoral arthritis.^[22]The surface of the patellofemoral and tibiofemoral joints can be evaluated under direct visualization to assess the size, severity, and location of articular degeneration. The motion of the patella with flexion and extension can be observed to determine whether subluxation is present. Arthroscopy can also be used for therapy.

Histologic Findings

Normal articular cartilage is smooth and glistening. Degenerative changes observed in the articular cartilage of the patella are similar to those observed in other joints. In one of the earliest descriptions of the pathology of the patellofemoral joint, Outerbridge described dulling of the color and softening of the cartilage as the earliest changes in chondromalacia patellae.^[3]With progressive degeneration, osteoarthritis develops, and fissures and erosion of the cartilage occur. These changes are typically more pronounced on the medial patellar facet than elsewhere, but eventually extend throughout the patella.

Treatment & Management

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Media Gallery

Patellofemoral arthritis. The sulcus angle is the angle formed by the condyles and the sulcus. This is a measurement of trochlear depth. A finding greater than 138° indicates the presence of patellofemoral dysplasia.
Patellofemoral arthritis. The patellofemoral index is the ratio of M, the closest distance between the articular ridge and the medial condyle, and L, the closest distance between the lateral facet and condyle.
Patellofemoral arthritis. The lateral patellofemoral angle is the angle between the intercondylar line and the lateral facet.
Patellofemoral arthritis. The Insall-Salvati ratio is used to assess the position of the patella and determine if the patella alta or patella baja is present. The ratio of the height of the patella to the length of the patella tendon should be 1:1.
Patellofemoral arthritis. Anteroposterior, lateral, and patellar views of an arthritic knee demonstrate severe patellofemoral arthritis. This patient subsequently underwent total knee arthroplasty.
Patellofemoral arthritis. Poor bone quality of the patella made a patella resurfacing procedure impossible in this patient who underwent total knee arthroscopy for severe arthritis.
Patellofemoral arthritis. This patient had severe medial compartment arthritis but a relatively normal patellofemoral joint. Therefore, patellofemoral resurfacing was not performed at the time of surgery.
Patellofemoral arthritis.

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Author

Dinesh Patel, MD, FACS Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital

Dinesh Patel, MD, FACS is a member of the following medical societies: American Academy of Orthopaedic Surgeons

Disclosure: Nothing to disclose.

Coauthor(s)

Kathleen A Hogan, MD Fellow in Arthroplasty, Department of Orthopedics, Brigham and Women's Hospital

Kathleen A Hogan, MD is a member of the following medical societies: Sigma Xi, The Scientific Research Honor Society

Disclosure: Nothing to disclose.

H Del Schutte, Jr, MD Associate Professor of Orthopedic Surgery, Department of Orthopedic Surgery, Medical University of South Carolina

H Del Schutte, Jr, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Medical Association, American Orthopaedic Association, California Medical Association, South Carolina Medical Association, Southern Medical Association, Southern Orthopaedic Association, Orthopaedic Research Society, American Association of Hip and Knee Surgeons

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Thomas M DeBerardino, MD, FAAOS, FAOA Professor of Orthopaedic Surgery, University of Texas Health Science Center at San Antonio, Joe R and Teresa Lozano Long School of Medicine; Professor of Orthopaedic Surgery and Faculty of Sports Medicine Fellowship, Baylor College of Medicine; Sports Medicine Orthopaedic Surgeon, Department of Orthopaedics, UT Health San Antonio; Consulting Surgeon, Sports Medicine, Arthroscopy and Reconstruction of the Knee, Hip and Shoulder

Thomas M DeBerardino, MD, FAAOS, FAOA is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Orthopaedic Association, American Orthopaedic Society for Sports Medicine, Arthroscopy Association of North America, Clinical Orthopaedic Society, Herodicus Society, International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Arthrex, Inc.; MTF; Aesculap; Conmed; JRF<br/>Received research grant from: Arthrex, Inc.; MTF.

Additional Contributors

Charles T Mehlman, DO, MPH Professor of Pediatrics and Pediatric Orthopedic Surgery, Division of Pediatric Orthopedic Surgery, Director, Musculoskeletal Outcomes Research, Cincinnati Children's Hospital Medical Center

Charles T Mehlman, DO, MPH is a member of the following medical societies: American Academy of Pediatrics, American Fracture Association, Scoliosis Research Society, Pediatric Orthopaedic Society of North America, American Medical Association, American Orthopaedic Foot and Ankle Society, American Osteopathic Association, Arthroscopy Association of North America, North American Spine Society, Ohio State Medical Association

Disclosure: Nothing to disclose.