# Radiographic classification of osteoarthritis

Radiographic systems to classify osteoarthritis vary by which joint is being investigated. In osteoarthritis, the choice of treatment is based on pain and decreased function, but radiography can be useful before surgery in order to prepare for the procedure.

## Vertebral column

There are many grading systems for degeneration of intervertebral discs and facet joints in the cervical and lumbar vertebrae, of which the following radiographic systems can be recommended in terms of interobserver reliability:
* Kellgren grading of cervical disc degeneration
* Kellgren grading of cervical facet joint degeneration
* Lane grading of lumbar disc degeneration
* Thompson grading of lumbar disc degeneration (by magnetic resonance imaging)
* Pathria grading of lumbar facet joint degeneration (by computed tomography)
* Weishaupt grading of lumbar facet joint degeneration (by MRI and computed tomography)
Kellgren grading of cervical disc degeneration :
| I | Minimal anterior osteophytosis |
| II | Definite anterior osteophytosis Possible disc space narrowing Some endplate sclerosis |
| III | Moderate disc space narrowing Definite endplate sclerosis Osteophytosis |
| IV | Severe disc space narrowing Endplate sclerosis Multiple large osteophytes. |
Lane grading of lumbar disc degeneration :
| Grade | Joint space narrowing | Osteophytes | Sclerosis |
| 0 | None | None | None |
| 1 | Definite but mild narrowing | Small | Present |
| 2 | Moderate | Moderate | – |
| 3 | Severe (complete joint space loss) | Large | – |
The Thomson grading system is regarded to have more academic than clinical value.
Thomson grading of lumbar disc degeneration :
| Grade | Nucleus | Anulus | Endplate | Vertebral body |
| I | Bulging gel | Discrete fibrous laminae | Hyaline, uniform thickness | Rounded margins |
| II | Peripheral white fibrous tissue | Mucinous material between laminae | Irregular thickness | Pointed margins |
| III | Consolidated fibrous tissue | Extensive mucinous infiltration; loss of annular-nuclear demarcation | Focal defects in cartilage | Small chondrophytes or osteophytes at margins |
| IV | Horizontal clefts parallel to endplate | Focal disruptions | Fibrocartilage extending from subchondral bone; irregularity and focal sclerosis in subchondral bone | Osteophytes smaller than 2 mm |
| V | Clefts extended through nucleus and annulus | | Diffuse sclerosis | Osteophytes greater than 2 mm |

## Shoulder

The Samilson–Prieto classification is preferable for osteoarthritis of the glenohumeral joint.
Samilson–Prieto classification :
| Grade | Description |
| Mild | Exostosis of inferior humerus and/or glenoid measuring less than 3 mm |
| Moderate | Exostosis of inferior humerus and/or glenoid measuring 3–7 mm, and slight irregularity of the joint |
| Severe | Exostosis of inferior humerus and/or glenoid measuring more than 7 mm in height as well as sclerosis and narrowing of the joint space (normal joint space is 4–5 mm). |

## Hip

The most commonly used radiographic classification system for osteoarthritis of the hip joint is the Kellgren–Lawrence system (or KL system). It uses plain radiographs.
Kellgren–Lawrence system :
| Grade | Description |
| 0 | No radiographic features of osteoarthritis |
| 1 | Possible joint space narrowing (normal joint space is at least 2 mm at the superior acetabulum) and osteophyte formation |
| 2 | Definite osteophyte formation with possible joint space narrowing |
| 3 | Multiple osteophytes, definite joint space narrowing, sclerosis and possible bony deformity |
| 4 | Large osteophytes, marked joint space narrowing, severe sclerosis and definite bony deformity |
Osteoarthritis of the hip joint may also be graded by Tönnis classification. There is no consensus whether it is more or less reliable than the Kellgren-Lawrence system.
Tönnis classification :
| Grade | Description |
| 0 | No osteoarthritis signs |
| 1 | Mild: increased osteosclerosis minor joint space narrowing (normal joint space is at least 2 mm at the superior acetabulum) no or minor loss of head sphericity |
| 2 | Moderate: small bone cyst moderate joint space narrowing moderate loss of head sphericity |
| 3 | Severe: large bone cysts severe joint space narrowing, or joint space obliteration severe deformity of the head |

## Knee

For the grading of osteoarthritis in the knee, the International Knee Documentation Committee (IKDC) system is regarded to have the most favorable combination of interobserver precision and correlation to knee arthroscopy findings. It was formed by a group of knee surgeons from Europe and America who met in 1987 to develop a standard form to measure results of knee ligament reconstructions.
The Ahlbäck system has been found to have comparable interobserver precision and arthroscopy correlation to the IKDC system, but most of the span of the Ahlbäck system focused at various degrees of bone defect or loss, and it is therefore less useful in early osteoarthritis. Systems that have been found to have lower interobserver precision and/or arthroscopy correlation are those developed by Kellgren and Lawrence, Fairbank, Brandt, and Jäger and Wirth.
International Knee Documentation Committee (IKDC) system :
| Grade | Findings |
| A | No joint space narrowing, defined in this system as at least 4 mm joint space |
| B | At least 4 mm joint space, but small osteophytes, slight sclerosis, or femoral condyle flattening |
| C | 2–4 mm joint space |
| D | < 2 mm joint space |
Ahlbäck classification :
| Grade | Findings |
| I | Joint space narrowing, with or without subchondral sclerosis. Joint space narrowing is defined by this system as a joint space less than 3 mm, or less than half of the space in the other compartment, or less than half of the space of the homologous compartment of the other knee. |
| II | Obliteration of the joint space |
| III | Bone defect/loss < 5 mm |
| IV | Bone defect/loss between 5 and 10 mm |
| V | Bone defect/loss > 10 mm, often with subluxation and arthritis of the other compartment |
For the patellofemoral joint, a classification by Merchant 1974 uses a 45° "skyline" view of the patella:
Merchant system :
| Stage | Description |
| 1 (mild) | Patellofemoral joint space > 3 mm |
| 2 (moderate) | Joint space < 3 mm but no bony contact |
| 3 (severe) | Bony surfaces in contact over less than one quarter of the joint surface |
| 4 (very severe) | Bony contact throughout the entire joint surface |

## Other joints

* In the temporomandibular joint, subchondral sclerosis of the mandibular condyle has been described as an early change, condylar flattening as a feature of progressive osteoarthritis, and narrowing of the temporomandibular joint space as a late stage change. A joint space of between 1.5 and 4 mm is regarded as normal.
* For the ankle, the Kellgren–Lawrence scale, as described for the hip, has been recommended. The distances between the bones in the ankle are normally as follows:
   * Talus - medial malleolus: 1.70 ± 0.13 mm
   * Talus - tibial plafond: 2.04 ± 0.29 mm
   * Talus - lateral malleolus: 2.13 ± 0.20 mm