(Radiographics. 1999;19:655-672.)
© RSNA, 1999
Imaging Features of Avulsion Injuries1
Max A. Stevens, MD,
Georges Y. El-Khoury, MD,
Mary H. Kathol, MD,
Eric A. Brandser, MD and
Shirley Chow, MD
1 From the Department of Radiology, Musculoskeletal Division, University of Iowa Hospitals and Clinics, 200 Hawkins Dr, Iowa City, IA 52242. Recipient of a Certificate of Merit award for a scientific exhibit at the 1997 RSNA scientific assembly. Received April 13, 1998; revision requested June 1 and final revision received October 5; accepted October 6. Address reprint requests to G.Y.E.
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Abstract
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Avulsion injuries are common among participants in organized sports, especially among adolescent participants. Imaging features of both acute and chronic avulsion injuries of the pelvis, knee, ankle and foot, shoulder, and elbow were evaluated to help distinguish these injuries from more serious disease processes such as neoplasm and infection. At radiography, acute injuries (ie, those resulting from extreme, unbalanced, often eccentric muscular contractions) may be associated with avulsed bone fragments, whereas subacute injuries have an aggressive appearance that may include areas of mixed lysis and sclerosis. Chronic injuries (ie, those resulting from repetitive microtrauma or overuse) or old inactive injuries may be associated with a protuberant mass of bone and may bear a striking resemblance to a neoplastic or infectious process. Although not usually required, computed tomography is helpful in the diagnosis if radiographic findings are equivocal or if the injury is not in the acute phase. MR imaging is best suited for the evaluation of injuries to muscles, tendons, and ligaments. Recognition of characteristic imaging features and familiarity with musculotendinous anatomy will aid in accurate diagnosis of avulsion injuries.
Index Terms: Ankle, fractures, 46.4191 • Elbow, fractures, 42.4191 • Extremities, CT, 40.1211 • Extremities, MR, 40.1214 • Foot, fractures, 46.4191 • Fractures, stress • Knee, fractures, 45.4191 • Pelvis, fractures, 44.4191 • Shoulder, injuries, 41.4191
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INTRODUCTION
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Sports play a large part in many people's lives. With the excitement and enthusiasm that accompany athletic endeavors, however, frequently comes injury. More and more people are either participants in organized sports or "weekend warriors" (1,2). Such people are prone to avulsion injuries. Adolescent participants, because of the inherent weakness of the apophysis, are especially vulnerable to such fractures (3). Most often the injury is abrupt and a clear history is available, which makes clinical and radiographic diagnosis easy. Sometimes, however, there is no history of a specific traumatic event and radiographic findings are confusing. Such findings can lead to excessive imaging, biopsy, and incorrect diagnosis because posttraumatic bone changes can simulate osteomyelitis or even malignancy at radiography (4). Therefore, an understanding of musculotendinous anatomy is crucial in the diagnosis of avulsion injuries.
Muscles produce movement at joints. They attach directly to bone or indirectly by means of tendons. Excessive tensile forces can result in muscle strain, tendon rupture, or avulsion fracture. When eccentric muscular contraction occurs in adults as a result of landing after a jump or falling from a height, for example, the musculotendinous junction is particularly vulnerable to injury. In adolescents, muscles and tendons commonly insert on apophyses, which are more susceptible to injury until patients reach their middle twenties (5). Therefore, the age of the patient is an important factor in evaluation of the injury site (6).
Acute avulsion injuries result from extreme, unbalanced, and often eccentric muscular contractions, and patients with such injuries present with severe pain and loss of function (6). In contrast, chronic avulsion injuries are the result of repetitive microtrauma or overuse and usually occur during organized sports activities (7,8). Sometimes, multiple avulsions are seen in different stages of healing. Cheerleaders, sprinters, and gymnasts as well as football, baseball, and track athletes are especially prone to these injuries (4,8).
In this article, we discuss and illustrate the radiographic, computed tomographic (CT), and magnetic resonance (MR) imaging appearances of a variety of acute and chronic avulsion injuries of the pelvis, knee, ankle and foot, shoulder, and elbow.
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PELVIC INJURIES
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In the pelvis, avulsion injuries primarily occur at six sites (Fig 1). The ischial tuberosity is the most common site. It is the insertion site of the hamstring muscle group, and avulsions usually occur before closure of the apophysis (9,10). Avulsion is caused by extreme active contraction of the hamstrings during, for example, sprinting by runners or sudden and excessive passive lengthening in cheerleaders or dancers (11). Patients typically present with pain in the buttock region, an antalgic gait, or inability to walk (6,10). In acute cases, a nondisplaced avulsion of the ischial tuberosity appears as a curved, sharply marginated piece of bone adjacent to its origin (ischial epiphysiolysis) (Fig 2). Patients with injuries of this type tend to respond well to conservative treatment such as several days of bed rest, restricted activity, and a return to normal activity over the next 6–12 weeks (6). If the fragment is displaced more than 2 cm, however, fibrous union may occur, resulting in extended disability (10). Development of sciatica may be related to irritation of the sciatic nerve either when exuberant callus formation occurs during healing or when the avulsed fragment directly impinges on the nerve (5). At radiography, healing avulsions can have an aggressive appearance, including lysis and destruction. These changes can mimic those seen with osteomyelitis or Ewing sarcoma (4,11). Chronic avulsion injuries frequently result in prominent bone formation (Fig 3). Sometimes only a remote history of minor trauma exists, which makes the clinical diagnosis difficult. In such cases, CT may be helpful in diagnosis (12). In cases of impingement on the sciatic nerve, CT may also aid in management planning (13).
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Figure 1. Diagram shows characteristic sites of avulsion injury in the pelvis. AIIS = anterior inferior iliac spine, ASIS = anterior superior iliac spine. (Modified and reprinted, with permission, from reference 6.)
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Figure 2a. Acute avulsion of the ischial tuberosity in a young football player who experienced sudden onset of pain in the right gluteal region. (a) Anteroposterior radiograph shows an acute avulsion of the ischial tuberosity (arrows). The bone fragment is sharply defined and displaced inferiorly. (b) Coronal T1-weighted MR image reveals a hematoma at the site of the avulsion (arrows).
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Figure 2b. Acute avulsion of the ischial tuberosity in a young football player who experienced sudden onset of pain in the right gluteal region. (a) Anteroposterior radiograph shows an acute avulsion of the ischial tuberosity (arrows). The bone fragment is sharply defined and displaced inferiorly. (b) Coronal T1-weighted MR image reveals a hematoma at the site of the avulsion (arrows).
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Figure 3a. Chronic avulsion of the ischial tuberosity in a college football player who had experienced pain in each gluteal fold region on separate occasions several months earlier. (a) Low anteroposterior radiograph of the pelvis shows bilateral chronic avulsions of the ischial tuberosity. Protuberant bone (solid arrows) and a large, smooth fragment (open arrows) are seen. (b) Sagittal proton-density–weighted MR image shows irregularity and bony protuberance of the left side of the ischial tuberosity (arrows), findings that are consistent with the chronic nature of the injury.
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Figure 3b. Chronic avulsion of the ischial tuberosity in a college football player who had experienced pain in each gluteal fold region on separate occasions several months earlier. (a) Low anteroposterior radiograph of the pelvis shows bilateral chronic avulsions of the ischial tuberosity. Protuberant bone (solid arrows) and a large, smooth fragment (open arrows) are seen. (b) Sagittal proton-density–weighted MR image shows irregularity and bony protuberance of the left side of the ischial tuberosity (arrows), findings that are consistent with the chronic nature of the injury.
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Another common avulsion injury involves the anterior superior iliac spine, which is the attachment site for the sartorius muscle and the tensor muscle of the fascia lata. This type of injury occurs in sprinters during forceful extension at the hip (Fig 4). Patients present with pain just below the most anterior aspect of the iliac crest. Sometimes the avulsion fragment can be palpated (6). Such injuries usually heal quickly and without sequelae after simple restriction of activity.
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Figure 4. Avulsion of the anterior superior iliac spine in a 16-year-old sprinter who had experienced sudden onset of pain above the right hip. Anteroposterior radiograph shows an acute avulsion of the anterior superior iliac spine (arrow). The sharp, distinct margins of the fracture indicate the acute nature of the injury.
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Avulsion fracture of the anterior inferior iliac spine is less common than that of the anterior superior iliac spine. The anterior inferior iliac spine is the origin of the straight head of the rectus femoris muscle. Avulsion of the anterior inferior iliac spine also results from forceful extension at the hip (Figs 5, 6). Avulsion of the anterior superior iliac spine can simulate this injury if the fragment is retracted inferior to the level of the anterior inferior iliac spine. Avulsions of both the anterior superior and anterior inferior iliac spines tend to be less symptomatic and disabling than avulsions of the ischial tuberosity, and recovery time is relatively short (5). Injuries of the iliac spine are first treated with bed rest with the hips and knees flexed, then with progressive ambulation (6). Full athletic potential is regained in about 5–6 weeks.
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Figure 5. Figures 5, 6. (5) Avulsion of the anterior inferior iliac spine in a 16-year-old football player who had experienced sudden onset of pain above the right hip 3 months earlier. Anteroposterior radiograph of the pelvis shows a chronic avulsion of the anterior inferior iliac spine (arrow), the site of attachment for the rectus femoris. The smooth margins and bony protuberance indicate the chronic nature of the injury. (6) Avulsion of the left anterior inferior iliac spine and ischial tuberosity in a 17-year-old track star who presented with a 3-week history of hip pain. Anteroposterior radiograph of the left hip shows a subacute avulsion of the left anterior inferior iliac spine (open arrow) and ischial tuberosity (solid arrows). The margins are somewhat ill-defined, but protuberant bone is lacking. These findings suggest a subacute injury in the healing phase but may be mistaken for a more aggressive process.
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Figure 6. Figures 5, 6. (5) Avulsion of the anterior inferior iliac spine in a 16-year-old football player who had experienced sudden onset of pain above the right hip 3 months earlier. Anteroposterior radiograph of the pelvis shows a chronic avulsion of the anterior inferior iliac spine (arrow), the site of attachment for the rectus femoris. The smooth margins and bony protuberance indicate the chronic nature of the injury. (6) Avulsion of the left anterior inferior iliac spine and ischial tuberosity in a 17-year-old track star who presented with a 3-week history of hip pain. Anteroposterior radiograph of the left hip shows a subacute avulsion of the left anterior inferior iliac spine (open arrow) and ischial tuberosity (solid arrows). The margins are somewhat ill-defined, but protuberant bone is lacking. These findings suggest a subacute injury in the healing phase but may be mistaken for a more aggressive process.
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The symphysis pubis and inferior pubic ramus are the origin for the long adductor, short adductor, and gracilis muscles. Avulsion injuries here are virtually always due to chronic overuse, although they are occasionally acute in athletes such as soccer players, in whom there is forceful contraction against resistance when, for example, two players kick the ball simultaneously (Fig 7). Discrete bone fragments are not seen in these injuries, in contrast to injuries at other sites in the pelvis (14). Pain is localized to the groin. It is difficult to discern exactly which muscle is involved at clinical examination or radiography. MR imaging might aid in identification of the specific muscle involved but is not indicated for treatment. Furthermore, its use is usually not justified because of the expense involved. Chronic or overuse avulsion injury at the pubis leads to rarefaction or lysis and may be confused with infection or Ewing sarcoma (Fig 8) (8). Such avulsions are usually unilateral and may be associated with a soft-tissue mass in the upper medial thigh and with a patient history and physical examination findings that support the diagnosis (14). Therefore, when based on clinical history and characteristic radiographic appearance, the proper diagnosis may be made with confidence. Treatment is conservative and includes rest and decreased weight bearing for several weeks (6).
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Figure 7. Chronic avulsion in an athlete with a long history of groin pain but no specific injury or time of onset. Anteroposterior radiograph reveals a chronic avulsion at the insertion of the adductor muscle group to the left symphysis pubis (arrows).
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Figure 8. Chronic avulsion at the pubis in a male athlete with a long history of groin pain. Findings on an anteroposterior radiograph (not shown) were consistent with chronic avulsion of the right symphysis pubis. Coronal T2-weighted MR image shows edema in the marrow and reactive change in the surrounding soft tissues (arrows) caused by chronic repetitive microtrauma. Patient history, radiography, and follow-up are generally all that are required to determine the traumatic pathogenesis. In this case, however, MR imaging was performed because of persistent clinical suspicion for a tumor. The patient was treated with rest, and later at follow-up his pain had resolved.
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There have been a few reports of iliac crest avulsion at the insertion of the abdominal musculature, but these injuries are uncommon (11). The acute form of this injury is associated with abrupt directional changes during motion or with repetitive microtrauma as seen in long-distance runners. Radiographs may show asymmetry of the iliac crest apophyses. Treatment should be conservative, and an excellent outcome may be expected (6).
Avulsion of the lesser trochanter at the insertion of the iliopsoas muscles may occur in young athletes but is rare (15). Although not as common as other avulsions in the pelvis, it causes considerable pain and decreased function. Patients respond well to conservative therapy (4,6). In adults, however, it has been our experience that such avulsions are rare and are virtually always due to metastatic disease (Fig 9).
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Figure 9. Avulsion fracture of the lesser trochanter in a 65-year-old patient who experienced a sudden pop and pain in the left side of the groin. Anteroposterior radiograph shows a lesser trochanter avulsion fracture (solid arrow). A lytic defect is seen at the femur attachment site (open arrow). This case proved to be metastatic squamous cell carcinoma at histologic analysis.
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The greater trochanter is the attachment site for the hip rotators, including the middle and least gluteal, internal obturator, gemellus, and piriform muscles. Avulsion of the greater trochanter occurs when there is a sudden directional change (6,16). At radiography, the greater trochanter is displaced from its origin (Fig 10). Sometimes displacement is minimal, which makes visualization difficult.
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Figure 10a. Avulsion fracture of the greater trochanter in an 80-year-old man who had twisted his hip. (a) Anteroposterior radiograph shows an avulsion fracture of the greater trochanter with minimal displacement (arrow). (b) Coronal T1-weighted MR image shows the greater trochanter fracture to better advantage (arrows).
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Figure 10b. Avulsion fracture of the greater trochanter in an 80-year-old man who had twisted his hip. (a) Anteroposterior radiograph shows an avulsion fracture of the greater trochanter with minimal displacement (arrow). (b) Coronal T1-weighted MR image shows the greater trochanter fracture to better advantage (arrows).
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MR imaging of the pelvis and hip is generally not required. It is best suited for the evaluation of injuries to muscles, tendons, and ligaments. At MR imaging, avulsion injuries have an aggressive appearance and can mimic processes such as tumor or infection. History and conventional radiography are usually all that are needed to make a proper diagnosis.
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KNEE INJURIES
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The knee is another site at which avulsion injuries may occur (Fig 11). Segond fracture is a cortical avulsion fracture involving the meniscotibial portion of the middle third of the lateral capsular ligament (17) that is caused by forceful internal rotation and varus stress. Patients present with pain at the lateral joint line and with anterolateral rotational instability (rotational subluxation) (17). The avulsed fragment in Segond fracture lies immediately distal to the lateral tibial plateau and appears as an elliptic piece of bone parallel to the tibia (Fig 12). Segond fracture should be differentiated from avulsion of the Gerdy tubercle at the insertion of the iliotibial band, which lies more anterior and distal.
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Figure 11a. Diagrams show common avulsion sites in the knee as seen from an anteroposterior (a) and lateral (b) perspective. ACL = anterior cruciate ligament, LCL = lateral collateral ligament, PCL = posterior cruciate ligament.
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Figure 11b. Diagrams show common avulsion sites in the knee as seen from an anteroposterior (a) and lateral (b) perspective. ACL = anterior cruciate ligament, LCL = lateral collateral ligament, PCL = posterior cruciate ligament.
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Figure 12a. Segond fracture in a patient who had sustained rotational injury to the knee. (a) Anteroposterior radiograph shows a piece of bone adjacent to the lateral cortex of the tibia (arrows). (b) Coronal T1-weighted MR image shows the avulsed bone fragment (arrow) attached to the medial aspect of the lateral capsular ligament.
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Figure 12b. Segond fracture in a patient who had sustained rotational injury to the knee. (a) Anteroposterior radiograph shows a piece of bone adjacent to the lateral cortex of the tibia (arrows). (b) Coronal T1-weighted MR image shows the avulsed bone fragment (arrow) attached to the medial aspect of the lateral capsular ligament.
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Segond fractures can be subtle but are usually visible on anteroposterior or tunnel-view radiographs. The thin arc of bone on radiographs has been designated the lateral capsular sign (18). MR imaging shows marrow edema in the lateral tibial rim (19). More important, MR imaging is often performed because of the close association between these fractures and other injuries, including tears of the anterior cruciate ligament (75%–100% of cases) and meniscal tears (66%–70%) (19,20). Segond fracture may also be associated with avulsions of the fibular head at the insertion of the biceps muscle of the thigh and the fibular collateral ligament (20). Therefore, it is important that this avulsion be identified because it indicates significant injury to the knee.
Disruption of the arcuate complex is associated with posterolateral instability (8,21,22) and occurs when force is directed at the anteromedial tibia with the knee extended. The arcuate complex supports the posterolateral corner of the knee. Its main components are the fabellofibular ligament, the arcuate ligament, and the popliteal muscle and tendon (Fig 13). Also important are the coronary ligament, the oblique popliteal ligament of Winslow, and the lateral (fibular) collateral ligament (21). Clinical findings include posteromedial subluxation of the tibia. The fibular head is the attachment for most of these ligaments and tendons and consequently is often avulsed. The size of the resulting fragment is variable (Figs 14, 15). Associated injuries include tears of the anterior cruciate ligament and damage to the peroneal nerve (8).
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Figure 13. Diagram shows major posterolateral stabilizers of the knee. The site of bone avulsion is usually the fibular head, which is the anchor for many of these ligaments and tendons. (Modified and reprinted, with permission, from reference 22.)
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Figure 14. Figures 14, 15. (14) Avulsion fracture of the fibular head in a woman who twisted her knee while running. Anteroposterior radiograph shows a displaced avulsion fracture of the fibular head (arrow). This finding indicates injury of the arcuate complex and posterolateral instability. (15) Knee injury and posterolateral instability. Coronal T1-weighted MR image demonstrates an avulsion of the fibular head (arrow).
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Figure 15. Figures 14, 15. (14) Avulsion fracture of the fibular head in a woman who twisted her knee while running. Anteroposterior radiograph shows a displaced avulsion fracture of the fibular head (arrow). This finding indicates injury of the arcuate complex and posterolateral instability. (15) Knee injury and posterolateral instability. Coronal T1-weighted MR image demonstrates an avulsion of the fibular head (arrow).
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Avulsion of the tibial eminence can occur in adults but is more common in children (Fig 16). Patients present with an aching, flexed knee with signs of hemarthrosis and anterior instability (18). In children, avulsion of the tibial eminence is the result of forced flexion of the knee with internal rotation of the tibia (Fig 17) and is usually not associated with other knee injuries. In adults, the injury is more often secondary to a motor vehicle accident in which the leg is hyperextended at impact (23). Adults also have a higher prevalence of associated injuries, including medial collateral ligament tears and focal bone contusions (24,25). Diagnosis at radiography can be difficult and often requires additional tunnel-view and oblique imaging. CT and MR imaging can display the fracture site to greater advantage (Figs 18, 19) (5).
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Figure 17. Figures 17–19. (17) Avulsion of the tibial eminence in a young patient who presented with acute pain and anterior instability. Anteroposterior radiograph of the right knee shows avulsion of the tibial eminence (arrow) at the attachment site for the anterior cruciate ligament. This injury has the same functional features as any other tear of this ligament. (18) Avulsion of the tibial eminence in a young athlete with anterior instability. Coronal T2-weighted MR image shows edema of the tibial eminence (arrows), which on sagittal T2- and proton-density–weighted MR images (not shown) proved to be a nondisplaced avulsion. (19) Avulsion of the tibial eminence in a patient who had sustained a knee injury about 2 weeks earlier. Coronal T1-weighted MR image shows an avulsion of the tibial eminence (large arrow) with contusion of the medial tibial plateau (small arrow). T1 lengthening (edema) of the tibial eminence is relatively limited, suggestive of a subacute injury.
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Figure 18. Figures 17–19. (17) Avulsion of the tibial eminence in a young patient who presented with acute pain and anterior instability. Anteroposterior radiograph of the right knee shows avulsion of the tibial eminence (arrow) at the attachment site for the anterior cruciate ligament. This injury has the same functional features as any other tear of this ligament. (18) Avulsion of the tibial eminence in a young athlete with anterior instability. Coronal T2-weighted MR image shows edema of the tibial eminence (arrows), which on sagittal T2- and proton-density–weighted MR images (not shown) proved to be a nondisplaced avulsion. (19) Avulsion of the tibial eminence in a patient who had sustained a knee injury about 2 weeks earlier. Coronal T1-weighted MR image shows an avulsion of the tibial eminence (large arrow) with contusion of the medial tibial plateau (small arrow). T1 lengthening (edema) of the tibial eminence is relatively limited, suggestive of a subacute injury.
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Figure 19. Figures 17–19. (17) Avulsion of the tibial eminence in a young patient who presented with acute pain and anterior instability. Anteroposterior radiograph of the right knee shows avulsion of the tibial eminence (arrow) at the attachment site for the anterior cruciate ligament. This injury has the same functional features as any other tear of this ligament. (18) Avulsion of the tibial eminence in a young athlete with anterior instability. Coronal T2-weighted MR image shows edema of the tibial eminence (arrows), which on sagittal T2- and proton-density–weighted MR images (not shown) proved to be a nondisplaced avulsion. (19) Avulsion of the tibial eminence in a patient who had sustained a knee injury about 2 weeks earlier. Coronal T1-weighted MR image shows an avulsion of the tibial eminence (large arrow) with contusion of the medial tibial plateau (small arrow). T1 lengthening (edema) of the tibial eminence is relatively limited, suggestive of a subacute injury.
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Avulsion fractures of the posterior cruciate ligament of the tibia are rare and are difficult to visualize at radiography. They result from forceful displacement in a flexed knee or from hyperextension. Findings can be subtle and confusing, particularly if the fragment is not significantly displaced (Fig 20). CT or MR imaging may be helpful in the diagnosis (Figs 21, 22).
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Figure 20. Figures 20–22. Avulsion fracture of the posterior cruciate ligament due to hyperextension of the knee. (20) Lateral radiograph shows an avulsed bone fragment at the site of attachment of the posterior cruciate ligament (arrow). (21) Axial CT scan demonstrates an avulsion fracture with minimal displacement of the avulsed fragment (arrows). (22) Sagittal proton-density–weighted MR image demonstrates an avulsion fracture with displacement of the avulsed fragment (arrow).
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Figure 21. Figures 20–22. Avulsion fracture of the posterior cruciate ligament due to hyperextension of the knee. (20) Lateral radiograph shows an avulsed bone fragment at the site of attachment of the posterior cruciate ligament (arrow). (21) Axial CT scan demonstrates an avulsion fracture with minimal displacement of the avulsed fragment (arrows). (22) Sagittal proton-density–weighted MR image demonstrates an avulsion fracture with displacement of the avulsed fragment (arrow).
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Figure 22. Figures 20–22. Avulsion fracture of the posterior cruciate ligament due to hyperextension of the knee. (20) Lateral radiograph shows an avulsed bone fragment at the site of attachment of the posterior cruciate ligament (arrow). (21) Axial CT scan demonstrates an avulsion fracture with minimal displacement of the avulsed fragment (arrows). (22) Sagittal proton-density–weighted MR image demonstrates an avulsion fracture with displacement of the avulsed fragment (arrow).
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Avulsions of the tibial tuberosity are uncommon and are associated with sports activities that require jumping. They occur with violent active extension of the knee or passive flexion against contracted quadriceps muscles (26,27). Three types of fractures are described in the Watson-Jones classification scheme on the basis of extent of involvement of the proximal tibial epiphysis and degree of displacement of the fracture fragment (Fig 23) (26,28). In type 1 injuries, there is avulsion of the apophysis without injury to the tibial epiphysis (Fig 24). In type 2 injuries, the epiphysis is lifted cephalad and incompletely fractured. Type 3 injuries show displacement of the proximal base of the epiphysis with the fracture line extending into the joint (Fig 25). Type 1 and 2 fractures tend to occur in younger adolescents (12–14 years of age), whereas type 3 fractures occur in older adolescents (15–17 years of age). Although an acute injury, tibial tuberosity avulsion is most frequently seen in young adolescents with ongoing Osgood-Schlatter disease (28).
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Figure 24. Figures 24, 25. (24) Avulsion fracture of the tibial tuberosity in a basketball player who experienced acute, intense pain on landing after a jump. Lateral radiograph of the knee shows a type 1 tibial tuberosity avulsion fracture that involves the center of ossification (arrows) without injury to the tibial epiphysis. (25) Avulsion fracture of the tibial tuberosity in a young male athlete. The patient had sustained a knee injury while pole vaulting. Lateral radiograph shows a type 3 tibial tuberosity avulsion fracture with displacement of the proximal base of the epiphysis and extension into the joint (arrows).
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Figure 25. Figures 24, 25. (24) Avulsion fracture of the tibial tuberosity in a basketball player who experienced acute, intense pain on landing after a jump. Lateral radiograph of the knee shows a type 1 tibial tuberosity avulsion fracture that involves the center of ossification (arrows) without injury to the tibial epiphysis. (25) Avulsion fracture of the tibial tuberosity in a young male athlete. The patient had sustained a knee injury while pole vaulting. Lateral radiograph shows a type 3 tibial tuberosity avulsion fracture with displacement of the proximal base of the epiphysis and extension into the joint (arrows).
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Osgood-Schlatter disease is a chronic avulsion injury thought to result from repetitive microtrauma and traction on the tibial tubercle. Some believe the cause to be trauma to the patellar tendon at its insertion to the tibial tubercle (Fig 26) (29,30). Osgood-Schlatter disease is typically seen in active adolescents, particularly those who participate in sports that require jumping, squatting, and kicking, and can be bilateral in up to 50% of patients (30,31). Boys tend to be affected more often than girls. Patients present with localized pain, swelling, and tenderness. Diagnosis is most often made clinically. When used, radiography shows fragmentation of the tibial tubercle, although this finding alone may represent a normal ossification center. Therefore, the most important diagnostic criteria are seen at MR imaging and include (a) soft-tissue swelling anterior to the tibial tuberosity, (b) loss of the sharp inferior angle of the infrapatellar fat pad and surrounding soft tissues, (c) thickening and edema of the inferior patellar tendon, and (d) infrapatellar bursitis (5,29,31). On occasion, the disease along with associated radiographic findings persist into adulthood. This phenomenon is known as unresolved Osgood-Schlatter disease (Fig 27).
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Figure 26. Figures 26, 27. (26) Osgood-Schlatter disease in a young basketball player known for his jumping ability who presented with chronic knee pain. Lateral radiograph shows protuberant bone tissue of the inferior pole of the patella, "jumper's knee" (arrowhead), and irregularity of the tibial tuberosity (arrow). (27) Chronic unresolved Osgood-Schlatter disease in a 28-year-old male athlete who presented with pain in the tibial tuberosity. The disease had been diagnosed when the patient was an adolescent. Sagittal T2-weighted MR image shows several bone fragments adjacent to the tibial tuberosity (solid arrows) and proximate to edema in the tibia (open arrow). These findings, together with the patient's history, were consistent with Osgood-Schlatter disease.
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Figure 27. Figures 26, 27. (26) Osgood-Schlatter disease in a young basketball player known for his jumping ability who presented with chronic knee pain. Lateral radiograph shows protuberant bone tissue of the inferior pole of the patella, "jumper's knee" (arrowhead), and irregularity of the tibial tuberosity (arrow). (27) Chronic unresolved Osgood-Schlatter disease in a 28-year-old male athlete who presented with pain in the tibial tuberosity. The disease had been diagnosed when the patient was an adolescent. Sagittal T2-weighted MR image shows several bone fragments adjacent to the tibial tuberosity (solid arrows) and proximate to edema in the tibia (open arrow). These findings, together with the patient's history, were consistent with Osgood-Schlatter disease.
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Jumper's knee is a syndrome that is characterized by pain at the distal or proximal insertion of the patellar tendon (32,33). It is seen most often in basketball, football, or volleyball players and is caused by repetitive microtrauma. Jumper's knee occurs during the adolescent years and is seen more often in boys. Typical MR imaging findings include thickening of the tendon with increased signal intensity on T1- and T2-weighted images (Fig 28). In chronic cases, protuberant bone may project from the inferior aspect of the patella. A similar entity associated with repetitive microtrauma is Sinding-Larsen-Johansson syndrome, which involves the distal patellar pole at the insertion of the patellar tendon. It usually occurs in the preadolescent or early adolescent years and has a male predilection. As in Osgood-Schlatter disease, fragmentation can occur at the inferior patellar pole. Some patients with recalcitrant patellar tendinitis may benefit from surgical intervention (34).
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Figure 28. Jumper's knee in a volleyball player who presented with anterior knee pain. Sagittal proton-density–weighted MR image shows a thickened patellar tendon with abnormally increased signal intensity, especially at insertion sites on the tibial tuberosity and patella, findings that are consistent with patellar tendinitis (arrows). The high signal intensity persisted on T2-weighted images.
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Patellar sleeve fractures are acute cartilaginous avulsion fractures of the lower pole of the patella (35). Radiographs demonstrate one or more bone fragments adjacent to the lower pole of the patella (Fig 29). However, damage to the cartilage may be underestimated at radiography and MR imaging may be required for better visualization of the cartilage and identification of joint involvement. Treatment for a widely displaced fragment involves open surgical reduction and realignment of the articular surface as well as reconstruction of the extensor apparatus (35).
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Figure 29. Patellar sleeve fracture associated with hyperextension injury in an 11-year-old boy. Lateral radiograph shows an area of hyperlucency in the inferior patellar pole (arrows).
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ANKLE AND FOOT INJURIES
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Calcaneal insufficiency avulsion fracture is an extraarticular fracture in the posterior third of the calcaneus that is seen almost exclusively in diabetic patients (Fig 30) (36). This injury is probably related to osteopenia and superimposed neuropathic changes, and it usually begins at the calcaneal tuberosity and extends superiorly. The avulsed fragment is displaced cephalad owing to the pull of the Achilles tendon (36). Calcaneal insufficiency avulsion fracture can be differentiated from typical stress fractures in that the latter have normal bone density and do not become displaced.
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Figure 30. Calcaneal insufficiency avulsion fracture in a 52-year-old patient with diabetes. Lateral radiograph shows a calcaneal insufficiency avulsion fracture (arrow), probably due to osteopenia and neuropathic changes because such a fracture occurs almost exclusively in diabetic patients.
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Posterior capsular avulsion of the ankle that involves the distal tibia is rare (37). The presumed mechanism is forced dorsiflexion of the foot. Radiographs show a curvilinear calcification adjacent to the posterior aspect of the ankle joint (Fig 31). Anterior capsular avulsion occurs in basketball players and is a chronic injury caused by microtrauma at the insertion of the capsule to the talus, which results in a bony protuberance (Fig 32).
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Figure 31. Posterior capsular avulsion of the ankle in a woman who had sustained an injury 5 weeks earlier. Lateral radiograph shows curvilinear calcification adjacent to the posterior tibial margin (arrow). This finding is consistent with posterior capsular avulsion but is not often seen; clinically, the injury amounts to a sprained ankle and there is no need for follow-up imaging. The patient usually recovers fully with conservative treatment.
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Figure 32. Anterior capsular avulsion in a basketball player with chronic pain in the proximal anterior foot. Lateral radiograph shows protuberance of the anterior talus where the joint capsule is inserted, which indicates chronic avulsion (arrow). As with posterior capsular avulsion, this type of injury usually goes unrecognized because radiographic follow-up is not required (cf Fig 31).
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Avulsions of the base of the fifth metatarsal bone are common and are caused by forceful contraction of the short peroneal tendon against an inverted foot, as when stepping off a curb or tripping. Some suggest that the firmly attached lateral band of the plantar aponeurosis is the structure most likely responsible (38). This fracture should be differentiated from (a) a true Jones fracture, which is a transverse fracture through the junction of the diaphysis and metaphysis, and (b) a stress fracture of the diaphysis that results from repetitive cyclic forces applied to the foot (Fig 33) (38). Jones fractures and diaphyseal stress fractures may require aggressive treatment because of the high prevalence of complications due to nonunion or refracture (38–42).
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SHOULDER INJURIES
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Isolated humeral avulsion fractures of the greater tuberosity are uncommon (43). The greater tuberosity is the attachment site of the supraspinatus, infraspinatus, and teres minor tendons. Patients present with a history of falling on an outstretched hand with the elbow extended and often with anterior dislocation (44). They have reduced abduction strength similar to that resulting from a rotator cuff tear. It is difficult to distinguish between isolated humeral avulsion fractures of the greater tuberosity and rotator cuff tears at clinical examination. The distinction is crucial, however, because treatment of the two injuries is different. At radiography, the fracture may not be readily apparent and may be seen only on delayed images (Fig 34a). MR imaging is often requested in cases of suspected rotator cuff tear in which marrow edema is incidentally seen surrounding the greater tuberosity and denoting the margins of the occult avulsion fracture (Fig 34b) (6). In some cases, ultrasound may be helpful in identification of a cortical step-off, which should prompt further radiographic investigation (43). In rotator cuff tears, outcome of prompt surgical repair has been shown to be superior to that of nonsurgical management. In contrast, nondisplaced avulsion fractures of the greater tuberosity are best treated conservatively with immobilization followed by a gradual increase in activity (43).
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Figure 34a. Avulsion fracture of the greater tuberosity in a patient who had fallen from a horse onto her outstretched arm. (a) Anteroposterior radiograph shows a nondisplaced avulsion fracture of the greater tuberosity (arrows). (b) Coronal oblique T1-weighted MR image shows the fracture to greater advantage (arrow). The rotator cuff was intact.
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Figure 34b. Avulsion fracture of the greater tuberosity in a patient who had fallen from a horse onto her outstretched arm. (a) Anteroposterior radiograph shows a nondisplaced avulsion fracture of the greater tuberosity (arrows). (b) Coronal oblique T1-weighted MR image shows the fracture to greater advantage (arrow). The rotator cuff was intact.
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Isolated avulsion of the lesser tuberosity at the insertion of the subscapularis muscle is rare. It is thought to occur most frequently when the arm is abducted 60°–90° and the subscapularis muscle forcefully contracts to resist further external rotation. Patients are typically involved in strenuous sports (eg, wrestling) in which there is contraction of the subscapularis muscle against forced abduction, but they may not recall a specific traumatic event. They present with loss of motion, pain with resistive internal rotation, and dead-arm syndrome (45). The avulsed lesser tuberosity may retract and lie inferior and medial to the glenoid (46,47). The avulsion may be associated with posterior glenohumeral dislocation and dislocations of the biceps tendon (48).
Anteroposterior radiographs obtained with the patient's arm rotated internally will usually demonstrate a large fragment, but a small, minimally displaced fragment may be seen only on an axillary view (Fig 35). Sometimes the abnormality is misinterpreted as calcific tendinitis of the biceps or of the subscapularis tendons; however, both of these conditions are uncommon. Their radiographic appearance is fluffy and lacks the trabeculation seen with an avulsed fragment of bone (45,46). Although MR imaging is not necessary, it does allow evaluation of the entire rotator cuff and better visualization of a minimally displaced fragment.
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ELBOW INJURIES
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In the elbow, most avulsion injuries are caused by medial tension stresses. In children, relatively lax ligaments make the flexor pronator muscle group, which attaches to the medial epicondyle, the main stabilizer of the elbow against valgus strain. In adults, the ulnar collateral ligament (which inserts on the coronoid and olecranon processes) and the joint capsule are the main stabilizers. Because the apophysis is the weakest link, a force that will cause ligamentous sprain in adults causes apophyseal avulsion in children (49,50). This basic but important difference results in different radiographic appearances.
The most common avulsion injury in the elbow involves the medial epicondyle. This injury is seen in adolescents and may be acute or chronic. "Little League elbow" is associated with recurrent contraction of the flexor pronator group of muscles during the acceleration phase of throwing. If avulsion occurs suddenly, radiographs show soft-tissue swelling and separation of the medial epicondyle. Avulsion of the medial epicondyle is treated with closed reduction and immobilization. If the injury is chronic, there may be fragmentation and roughening of the medial epicondyle. Discontinuation of the inciting activity serves as effective treatment (49,50).
The most common cause of medial epicondylar avulsion is a fall onto an outstretched hand with the elbow in full extension (6). With valgus stress, the medial joint space is momentarily opened and sometimes the avulsed fragment becomes trapped within the joint (Fig 36). Medial epicondylar avulsion is also frequently seen with posterolateral dislocation of the elbow (50). In either case, the entrapped fragment may simulate the trochlear ossification center and, if not recognized, lead to disabling degenerative osteoarthritis (51). Therefore, the entrapped fragment must be removed.
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Figure 36. Medial epicondylar avulsion in an 8-year-old boy who had fallen onto his outstretched arm. Anteroposterior radiograph shows a displaced, avulsed medial epicondylar apophysis between the ulna and the as yet unossified trochlear epiphysis (arrow), which could be mistaken for the trochlear ossification center. The avulsed fragment was reduced and surgically affixed to its site of origin at the medial epicondyle.
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Avulsion of the long head of the biceps tendon is usually seen in the elderly. Patients feel a snap with associated pain in the anterior elbow and, with complete avulsion, a palpable mass in the anterior upper arm. Sometimes there is only partial avulsion (3). This injury is generally treated conservatively, but in athletes it may be treated with tenodesis.
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SUMMARY
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Avulsion injuries are common in young athletes. Moreover, avulsion injuries are common in children but are also seen to a lesser extent in adults. Radiographs of acute injuries reveal avulsed pieces of bone. Subacute injuries have an aggressive radiographic appearance (eg, mixed lytic and sclerotic areas). Chronic or old inactive injuries may be associated with a protuberant mass of bone and may bear a striking resemblance to a neoplastic or infectious process. Although not usually required, CT is helpful in the diagnosis if radiography is nondiagnostic or if the injury is not in the acute phase. MR imaging is best suited for the evaluation of injuries to muscles, tendons, and ligaments. Recognition of characteristic radiographic patterns and familiarity with musculotendinous anatomy will aid in accurate diagnosis.
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Abstract
INTRODUCTION
