SEGOND FRACTURE
• Most common avulsion described in the knee joint .
• Cortical avulsion of the middle third of the lateral capsular ligament
Mechanism- Internal rotation of knee and Varus stress.
Imaging-
Lateral capsular sign
Associations:
• Anterior cruciate ligament and meniscal tear
• Avulsion of the fibular attachment of the long head of the biceps femoris tendon and the fibular collateral ligament
• Rarely can be seen with avulsion of the ACL from its insertion anterior to the tibial eminence.
Diagrammatic representation of structures involved in segond fracture- Refer image 3.
Case of Segond fracture- Refer image 4
REVERSE SEGOND FRACTURE
• Location and mechanism are opposite to segond fracture – External rotation and valgus stress.
• Represents injury to deep capsular component of medial collateral ligament.
Associations:
• Midsubstance tears of PCL and avulsions of the PCL from the posterior tibial plateau.
• Medial meniscus tear.
Case of Reverse Segond fracture- Refer image 5.
AVULSIONS AROUND FIBULAR HEAD
Avulsions around fibular head include Arcuate complex avulsion fracture and biceps tendon avulsion.
Refer image 6 for diagrammatic representation of Avulsions around fibular head
ARCUATE COMPLEX AVULSION FRACTURE
- Simplified description of the arcuate complex to include just the fabellofibular,
popliteofibular,
and arcuate ligament.
- These insert on to the fibular styloid process.
- Mechanism-Trauma to the anteromedial tibia while the knee is in extension,
varus force to the externally rotated tibia or sudden hyperextension.
Associations:
• Damage to stabilising structures of knee including the ACL and PCL,
lateral capsular ligament,
medial and lateral collateral ligaments,
iliotibial band,
popliteus muscle,
and menisci.
• In severe cases,
damage to the peroneal nerve resulting into lateral compartment syndrome.
Case of Arcuate complex avulsion fracture- Refer image 7.
Case of biceps femoris tendon avulsion fracture- Refer image 8.
QUADRICEPS TENDON AVULSION
Avulsion fracture of the quadriceps tendon from the upper pole of the patella.
Mechanism- strong deceleration in young athletes and sudden contraction of the quadriceps muscle with the knee flexed during athletic activities such as jumping and kicking.
It occurs mostly as an isolated finding.
Case of quadriceps tendon avulsion- Refer image 9.
ACL AVULSION FRACTURE
• Fragment seen medial and anterior to the tibial eminence
• Mechanism differs in children and in adults.
IMAGING-
• Conventional radiograph- Tiny bone fragment in the intercondylar notch with cortical irregularity of the adjacent tibial eminence suggesting a donor site for the fragment.
• MR imaging is useful to confirm that the fragment does arise from the tibia.
• The Meyers and McKeever classification system describes four subtypes of tibial spine fractures.
Type I injury - minimally displaced fragment.
Type II injury - anterior elevation of the fracture fragment
Type III and IV injuries demonstrate complete separation of the fragment from the tibia.
Type IV injury includes a rotational component or comminution of the fragment as well.
Case of ACL avulsion in children- Refer image 10.
Case of ACL avulsion in adults- Refer image 11.
POSTERIOR CRUCIATE LIGAMENT AVULSION
§ Bony avulsion of the posterior cruciate ligament
Associations
§ Disruption of the medial and lateral collateral ligament complexes,
medial and lateral meniscal tears,
and focal bone contusions of the anterior tibia and lateral femoral condyle.
Case of Posterior cruciate ligament avulsion- Refer image 12.
PATELLAR SLEEVE AVULSION FRACTURE
Patellar sleeve avulsion is bone avulsion at the proximal patellar tendon insertion along with underlying cartilaginous injury which can be seen on MRI,
whereas Sinding-Larsen-Johansson syndrome is only a bone avulsion at the proximal patellar insertion.
Differentiation between the two entities is important as patellar sleeve avulsion requires open reduction whereas Sinding-Larsen-Johansson syndrome is managed conservatively.
Case of patellar sleeve avulsion fracture - Refer image 13.
SEMIMEMBRANOUS TENDON AVULSION
• Avulsion fracture of the semimembranosus tendon is difficult to detect at conventional radiography.
It is appreciated only on the lateral view and appears as a tiny avulsed bone fragment displaced posterosuperiorly from its insertion on the tibia.
• Proposed mechanism- external rotation and abduction of a flexed knee,
varus force applied to the flexed knee,
and valgus force applied to the tibia.
• Associations- ACL injury,
the posterior horn of the medial meniscus tear and posterior meniscocapsular separation.
Diagrammatic representation of Semimembranous tendon avulsion- Refer image 14.
OSGOOD-SCHLATTER DISEASE
• Osgood-Schlatter disease is suspected to be a chronic avulsion injury related to repetitive microtrauma and traction on the tibial tubercle by the patellar tendon.
• Almost always occurs in adolescent male athletes performing activities that require jumping and kicking.
• Bilateral in up to 50% of cases.
• Proposed mechanism- Avulsion of a portion of the tibial tuberosity secondary to forceful contraction of the quadriceps muscle and subsequently the patellar tendon.
• No associated injuries.
Diagrammatic representation Osgood-schlatter disease- Refer image 15.
ILIOTIBIAL BAND AVULSION FRACTURE
- The proposed mechanism of injury involves a pure varus force.
- At MR imaging,
avulsion and retraction of the iliotibial band from its distal insertion on the Gerdy tubercle are visualized.
- Associated injury to the ACL is a common finding in this entity.
- Isolated tears of the iliotibial band are infrequent.
Diagrammatic representation Iliotibial band avulsion fracture- Refer image 16.
Images 17 and 18 summarizes the avulsion fractures around the knee.