subchondral insufficiency fracture of the knee
Morbus
Ahlbäck. Zusätzlich sklerosierte Zone medial an der proximalen Tibia als möglicher Rest eines nicht ossifizierenden Fibroms.
Morbus
Ahlbäck mediale Femurkondyle mit (untere Bilder) sekundärer Verlagerung des Dissekates in den suprapatellaren Recessus in der Planungsaufnahme unmittelbar präoperativ.
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Radiological pattern of a “mobile” subchondral fracture, pathognomonic for necrosis. a On CT arthrography, a very thin fracture/separation in the subchondral trabecular bone appears as a radiolucent line (“eggshell dissection”) (arrow). b A few months later, a radiograph shows a collapse of the condyle lower pole (arrow) with breaks in the continuity of the subchondral bone plate (arrowheads). c An additional radiograph performed by fluoroscopy and with traction on the leg shows a slight opening of the subchondral bone dissection (arrow)
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Evolution of an early subchondral insufficiency fracture with osteonecrosis. a Initial radiograph shows a slight hyperostosis near a discrete depression of the lower pole of the condyle (arrow). b Additional radiograph tangent to the posteroinferior pole of the condyle and performed with traction on the leg shows a typical subchondral bone dissection (arrow). c Three months later, this necrotic area shows a focal collapse (arrows), already complicated by a complete narrowing of the adjacent joint space (arrowhead)
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Enhancement pattern of a presumed subchondral insufficiency fracture with osteonecrosis. a T1-weighted MR image shows low signal intensity predominating near the condylar surface, extending deep in the epiphysis, and gradually attenuating with blurred outlines (asterisk). b, c On fat-suppressed T2-weighted image (b), this area (asterisk) shows high signal intensity and enhances after intravenous contrast injection (asterisk on post-contrast T1-weighted sequence in c). In this case, the subchondral area immediately adjacent to the bone plate (arrows) shows low signal intensity with fat-suppressed T2-weighting (in b) and no enhancement with post-contrast T1-weighting (in c). This pattern corresponds to an area of degraded subchondral fatty marrow, suggestive of a SIF-ON
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Visibility of subchondral insufficiency fracture (SIF) in a BME-like area. a–c On T1-weighted MR images (a), the fracture can be masked by the neighboring low signal intensity, while on fat-suppressed T2-weighted (b) or T2-weighted images (c) the fracture is apparent (arrowheads), contrasting with the surrounding high signal. In this case of SIF, BME-like high signal intensity is present on both sides of the fracture, including the area between the latter and the articular surface, corresponding to the area with infiltrated but a not degraded fatty marrow. Note that the fracture line does not completely isolate this subchondral area. The potential for this SIF to heal was confirmed by a follow-up study a few months later showing normalization (d)
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Modified diagram from Yamamoto and Bullough. Based on the authors’ concept, this modified diagram (adapted from Fig. 2) proposes that a SIF (subchondral insufficiency fracture) has the potential to heal provided that there is continuity between the area located between the fracture plane and the articular surface and the rest of the medullary epiphyseal space. Conversely, a SIF-ON would occur in case this continuity is lost
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Microvascularization of the subchondral bone of a condyle (from Reddy and Frederick [41]). The subchondral area has multiple anastomoses between terminal arterioles
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Subchondral insufficiency fracture complicated with osteonecrosis (SIF-ON) and early subchondral collapse. a T2-weighted MR image shows a wide subchondral low signal intensity area (arrow). On T1-weighted images without (b) and after contrast injection (c) a large portion of this area does not enhance after intravenous contrast injection (arrows in c). Note also a thin line with high fluid-like signal intensity in dissected subchondral fracture on T2-weighted image (arrowhead in a)
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Example of a pejorative evolution of a SIF to a SIF-ON. a, b At the initial stage, the BME-like high intensity on fat-suppressed T2-weighted MR image and a small fissure line (black arrow in a) are suggestive of a SIF. However, the subchondral bone adjacent to the cartilage shows a thick and extensive low signal-intensity area (white arrows in a and b). c, d Five months later (c, d) the marrow abnormalities persist, with the appearance of small geode-like images (arrows) and a small break in the subchondral bone plate (arrowhead in d). e, f Three months later, radiograph (e) still shows heterogeneous density of the lower condylar pole, and CT arthrography (f) shows a subchondral geode and bone resorption (arrowheads), associated with a focal collapse of the subchondral bone surface (arrow)
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Negative prognostic value of low signal bone marrow on T2-weighted MR image. a The subchondral bone of the two medial femorotibial joint surfaces shows marked low signal intensity on a T1-weighted MR image. b, c Coronal and sagittal fat-suppressed T2-weighted MR images (b, c) show relatively wide and thick subchondral areas adjoining the articular surface, with low signal intensity (arrows), suggestive of SIF-ON. d–f Three months later, a significant bone marrow low signal intensity persists on T1-weighted image (d) and coronal and sagittal fat-suppressed T2-weighted images show pejorative evolution with a collapse of the tibial plateau and a wide subchondral bone dissection and chondral fracture in the lower pole of the condyle (e, f)
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Early subchondral insufficiency fracture with osteonecrosis (SIF-ON) and collapse. a T1-weighted MR image shows an area of low signal intensity in the inferior pole of the medial condyle (arrow). b T2-weighted image (b) shows an immediate subchondral low signal intensity area longer than 14 mm (arrowheads), suggestive of early SIF-ON. Note also several fissure lines away from the surface (arrow), which is also a risk factor for an evolution towards a SIF-ON. c A few years later, a radiograph shows an irregular collapsed articular surface, confirming the initial suspicion of SIF-ON
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Evolution in two stages of subchondral insufficiency fracture (SIF). a, b Coronal T1-weighted (a) and sagittal T2-weighted (b) MR images show BME-like signal intensities in medial condyle (asterisks), except for a very thin (< 4 mm in thickness) subchondral low signal intensity area on the T2-weighted image (arrowhead in b). c MRI follow-up three years later with T2-weighted image (c) shows a small deformation of the lower pole of the condyle with thickening of the subchondral low signal intensity area, now exceeding 4 mm in thickness (arrows), suggesting the evolution of the SIF towards osteonecrosis (SIF-ON). d Nine years after the initial examination, a radiograph confirms an irreversible lesion, with deformation of the epiphyseal surface (arrowhead), which is moderate in this case and clinically well tolerated
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Diagram summarizing the prognostic value of typical subchondral signal intensity on T2-weighted sequences in SIF and SIF-ON. Note that in some cases, a very limited area with subchondral low T2 signal intensity is of doubtful prognosis and may progress either to healing or to SIF-ON. Without a particular event (meniscectomy or rapid cartilage degeneration for example), the evolution of a typical SIF towards a SIF-ON is very rare
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Evolution of subchondral osteonecrosis related to insufficiency fracture (SIF-ON) according to the size of the necrosis. a Radiograph of this SIF-ON shows a collapse of the inferior pole of a condyle, which extends to more than 50% of its width (64%). Its pejorative evolution led to the placement of prosthesis a few months later (b)
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Evolution of subchondral osteonecrosis related to insufficiency fracture (SIF-ON) according to the size of the necrosis. a, b Fat-suppressed T2-weighted MR coronal images (a) and T2-weighted sagittal image (b) show a very small heterogeneous signal intensity area (arrow). c, d Ten months later, CT arthrography images show very limited collapse (arrows)
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Early-stage subchondral insufficiency fracture (SIF). a Radiograph shows no significant finding apart from very subtle flattening of the condylar surface (arrowhead). b T1-weighted MR image shows moderate low signal intensity within the condyle (asterisk). c Fat-suppressed T2-weighted image shows BME-like high signal intensity more intense near the articular surface and extending to a part of the condyle without clear limits (asterisk). Note that the thin fracture line with low signal intensity is poorly visible with T1-weighting, and that with T2-weighting, high signal intensity extends within the area between the fracture and the articular surface (arrowheads). The high signal intensity in this area of the subchondral bone is an important finding to differentiate a SIF from a SIF-ON
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Diagram depicting the histopathologic classification of the two types of subchondral lesions, by Yamamoto and Bullough (with authorization of the author T.Y. [23]). In lesions previously considered as “spontaneous osteonecrosis of the knee (SONK),” the authors showed that the area located between fracture line and the articular contour contains either normal bone marrow (in subchondral insufficiency fractures (SIFs)), or focal osteonecrosis (in SIF complicated with osteonecrosis (SIF-ON))
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. SIF in a patient with osteomalacia. T2-weighted MR image shows a low signal intensity band corresponding to a particularly thick trabecular fracture (arrow). The bone marrow of this portion of the condyle shows BME-like high signal intensity (asterisk). Note that the BME-like signal extends between the fracture and the bone-cartilage interface (arrowheads). That area of the subchondral bone is in continuity with the rest of the epiphyseal area
Subchondral
insufficiency fracture of the knee • Spontaneous osteonecrosis of the knee - Ganzer Fall bei Radiopaedia
Aseptische
Knochennekrose der Femurkondyle (in diesem Fall lateral) bei einem 28-jährigen Mann nach längerer Kortisoneinnahme. Morbus Ahlbäck.
Morbus
Ahlbäck. Zusätzlich sklerosierte Zone medial an der proximalen Tibia als möglicher Rest eines nicht ossifizierenden Fibroms.
Morbus
Ahlbäck. Bei dem Patienten bestand gleichzeitig eine ausgeprägte Hüftkopfnekrose.
Subchondral
insufficiency fracture of the knee • Subchondral insufficiency fracture of the knee - Ganzer Fall bei Radiopaedia
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Subchondral insufficiency fracture (SIF) and subchondral insufficiency fracture complicated with osteonecrosis (SIF-ON). a Bone scan in a woman who presented with sudden onset of pain for several weeks, showing intense uptake in the medial femorotibial compartment. b Two months later, radiograph shows focal collapse of the inferior pole of the medial condyle (arrow) with sclerosis of the adjacent cancellous bone, and a sclerotic horizontal band parallel to the medial tibial plateau (arrowhead). c MR shows a focal very low signal intensity on coronal T1-weighted image in the medial condyle lower pole (arrow) and a thin low signal intensity horizontal band under the medial tibial plateau (arrowhead). Fat-suppressed T2-weighted image (d), showing heterogeneous signal in the condylar lesion (arrow) and a bone marrow moderate high signal under the tibial plateau (asterisk). e A T2-weighted MR posterior coronal image shows a wide radial rupture of the medial meniscus (arrow), causing extrusion of the meniscus middle portion (arrowhead in d). f Sagittal T2-weighted image shows low signal intensity in a thick and extended subchondral bone marrow area adjacent to the condylar surface (arrow), corresponding to an area of degraded bone marrow. Under the tibial plateau, the thin horizontal band with a low signal intensity (arrowhead) is surrounded by an almost normal marrow signal intensity. These aspects are typical of a SIF for the tibial plateau and a SIF-ON for the condyle
Subchondral
insufficiency fracture of the knee • Spontaneous osteonecrosis of the knee (SONK) - Ganzer Fall bei Radiopaedia
Subchondral
insufficiency fracture of the knee • Spontaneous osteonecrosis of the knee - Ganzer Fall bei Radiopaedia
Subchondral
insufficiency fracture of the knee • Spontaneous osteonecrosis of the knee - Ganzer Fall bei Radiopaedia
Subchondral
insufficiency fracture of the knee • Spontaneous osteonecrosis of the knee (SONK) - Ganzer Fall bei Radiopaedia
Subchondral
insufficiency fracture of the knee • Subchondral insufficiency fracture of the knee - Ganzer Fall bei Radiopaedia
Subchondral
insufficiency fracture of the knee • Subchondral insufficiency fracture of the knee - Ganzer Fall bei Radiopaedia
Subchondral
insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee—pathogenesis and diagnosis at imaging. Pejorative evolution of SIF related to cartilage degradation. a, b Initial T1-weighted MR image shows a typical subchondral insufficiency fracture in the medial tibial plateau on T1-weighted image (arrow in a) with a BME-like high-signal intensity on fat-suppressed T2-weighted image (asterisk in b). c The lesion is associated with a radial tear of the posterior horn of the medial meniscus (arrow). d–f Six months later, T1-weighted (d) and fat-suppressed T2-weighted (e) images show various signal intensities in bone on both sides of a severe chondral loss (arrows in f). The initial examination already showed a clear thinning of the cartilage of the medial condyle (arrowhead in b), which could have indicated a pejorative evolution
Subchondral insufficiency fracture of the knee (SIF/SIFK) are stress fractures in the femoral condyles or tibial plateau that occur in the absence of acute trauma, typically affecting older adults.
Terminology
The entity subsumes that previously known as spontaneous osteonecrosis of the knee (SONK/SPONK) or Ahlbäck disease. Recognizing that spontaneous osteonecrosis of the knee was a misnomer and actually represents a subchondral insufficiency fracture that progressed to subchondral collapse with secondary osteonecrosis, the Society of Skeletal Radiology Subchondral Bone Nomenclature Committee recommended that "subchondral insufficiency fracture" be the preferred term .
Epidemiology
Subchondral insufficiency fracture of the knee is seen more frequently in women (M:F 1:3) and affects older patients, typically over the age of 55.
Clinical presentation
Patients often recall an acute onset of severe pain without significant trauma.
Pathology
By definition, secondary osteonecrosis of the knee occurs secondary to an insult. Subchondral insufficiency fracture of the knee is not thought to be caused by bone death but instead by osteoporosis and insufficiency fractures, with histopathologically proven origins in weakened trabeculae and applied microtraumatic forces .
Radiographic features
It is almost always unilateral, usually affects the medial femoral condyle (but can occasionally involve the tibial plateau ) and is often associated with a meniscal tear.
Plain radiograph
In the later stages features seen include:
- flattening of the medial femoral condyle
- subchondral radiolucent focus
- complicating subchondral fracture with periosteal reaction
MRI
Features can vary depending on the stage and are best characterized on T2-weighted and proton density-weighted sequences. The following criteria apply to lesions without overlying cartilage abnormalities:
- subchondral bone plate fracture
- in the weight-bearing area of the involved condyle
- subtle flattening or a focal depressive deformity
- an irregular, discontinuous hypointense line in the subarticular marrow, representing callus and granulation tissue
- there may be a fluid-filled cleft within the subchondral bone plate (poor prognostic factor)
- excavated defect of the articular surface (advanced cases)
- focal subchondral area of low signal intensity subjacent to the subchondral bone plate representing local ischemia (considered most important in early lesions and a specific MRI finding)
- this area shows no enhancement on post-contrast; if it is thicker than 4 mm or longer than 14 mm, the lesion may be irreversible and may evolve into irreparable epiphyseal collapse and articular destruction
- appears as a thickened subchondral bone plate, which represents a fracture with callus and granulation tissue and secondary osteonecrosis in the subarticular region
- ill-defined bone marrow edema and a lack of peripheral low signal intensity rim as seen in osteonecrosis and bone infarcts
Associated features that may predict prognosis include:
- associated meniscal tear and degree of extrusion
- chondrosis severity
Treatment and prognosis
Prognosis varies from complete recovery to total joint collapse . Treatment can either be operative or non-operative, with initial treatment often conservative and consisting of analgesia and protected weight bearing. Subchondral hypointense fracture lines tend to resolve with conservative therapy. In more advanced cases, subchondroplasty (where a bone substitute is injected) may be considered.
Differential diagnosis
Possible considerations include:
- osteochondritis dissecans of the knee
- subchondral stress/fatigue fracture: overuse injuries in patients without associated risk factors
History and etymology
It was first systematically described by Ahlbäck in 1968 .
Siehe auch:
- Aseptische Knochennekrose
- Morbus Sudeck
- Insuffizienzfraktur
- Osteochondrosis dissecans des Kniegelenks
- Knochenmarködem-Syndrom des Knies
und weiter:
Assoziationen und Differentialdiagnosen zu subchondrale Insuffizienzfraktur des Knies:
