MRI is a common tool in the evaluation of musculoskeletal injury that allows the clinician to pinpoint specific pathologies. The patient's history and physical exam play a critical role in the diagnosis of sports injuries, however, complementary imaging can play an important role in determining the nature and extent of injury. With the widespread use of MRI, attention has focused on the signals generated following injury. In particular, bone marrow oedema (BME) patterns can be used to aid in the diagnosis of musculoskeletal injury. In this pictorial essay, the authors will demonstrate common patterns of BME that accompany a wide range of musculoskeletal injuries. It is expected that by the end of this article, the reader will be able to (1) recognise BME is a phenomenon observed on MRI following sports injury; (2) recognise typical patterns of BME; (3) understand the relationship of oedema to the type of injury and (4) in the presence of oedema, understand other co-existing injuries that ultimately may have an impact on management.
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Musculoskeletal injuries often lead to bone marrow oedema (BME) which is optimally detected by T1-weighted and fat-suppressed T2-weighted MRI. Although the histopathological changes observed on MRI are not clearly defined, alterations in MRI signal intensity following injury may include disruption of cellular elements, necrosis, haemorrhage, trabecular bone microfractures and oedema (reviewed in1). Although there is much research to be done on the consequences of BME, from a clinical perspective, unique patterns of BME serve as an important tool in elucidating the mechanism and type of musculoskeletal injury. Furthermore, the pattern of oedema can prompt the clinician to focus attention on associated areas of injury, which may be overlooked otherwise. There are several general categories of BME including oedema as a result of impaction, avulsive forces or stress (discussed in1). In this review, BME patterns associated with 10 diverse musculoskeletal pathologies in the upper and lower limb will be presented.
Pathology and imaging findings
Impaction-type BME is the result of bone-on-bone injury or direct impact to the bone by an external force. Typically, the resulting BME is extensive and is intimately associated with the overlying cortical bone that has been impacted.
Anterior shoulder dislocation
Anterior shoulder dislocation is a common sport injury and occurs when force is applied to an abducted and externally rotated shoulder.2 Many abnormalities can result from dislocation. On MRI, BME is found in the posterolateral humeral head superiorly secondary to impaction of the humeral head on the glenoid or coracoid process (figure 1). This pattern of oedema prompts one to look for several associated injuries, such as osteochondral compression fractures of the posterolateral humeral head (Hill-Sachs lesion) secondary to impaction against the glenoid rim (figure 2). Anterioinferior labral abnormalities in the setting of Hill-Sachs lesions include the following: Bankart, anterior labral periosteal sleeve avulsion, Perthes lesion and glenolabral articular defect. Less commonly, osteochondral fracture of the underlying glenoid can occur in anterior dislocation.3
Ulnar impaction syndrome (ulnar abutment syndrome)
Ulnar impaction syndrome results from increased ulnar loading due to relative lengthening of the ulna (congenital positive ulnar variance, malunion of distal radius fracture, radial head resection) or excessive intermittent ulnar carpal loading with otherwise normal anatomy.4 It can also occur less commonly with neutral or negative ulnar variance.4 This injury is commonly workplace related, secondary to repetitive microtrauma, however, it is known to occur in gymnasts. There is a spectrum of findings including, tears of the radial attachment of the triangular fibrocartilage complex, chondromalacia of the distal ulna, lunate and triquetrum, lunotriquetral ligament tear and osteoarthritis (oedema of the distal ulna and proximal medial lunate, sclerosis, subchondral cysts) of the distal ulnocarpal and distal radioulnar joints (figure 3).4
CAM type femoroacetabular impingement (FAI)
CAM type FAI occurs due to repetitive abutment between the femur and acetabulum related to the non-spherical shape of the femoral head–neck junction and often becomes symptomatic in young male athletes especially with flexion, adduction and internal rotational movements.5 ,6 An osseous excrescence is often seen in this region on plain film imaging (figure 4). BME is frequently present in this region as is oedema within the superolateral acetabulum. CAM type FAI can lead to anterosuperior labral and chondral damage and premature osteoarthritis (figures 4–6). Early identification and surgical treatment may prevent or delay end-stage osteoarthritis in younger patients.5 ,6
Patellar dislocation occurs most commonly in young female adults and is known to occur in sports such as dancing, gymnastics, when swinging a baseball bat and occasionally with direct trauma. Some patients are predisposed to dislocation due to a developmentally shallow trochlea, hypoplastic patella or malalignment of the trochlea groove and tibial tuberosity. The patella most frequently dislocates laterally due to a forceful contraction of the quadriceps in valgus position, pulling the patella out of the femoral trochlear groove.7 Anterolateral femoral condyle and inferomedial patella BME are virtually diagnostic MR findings (figure 7). Associated injuries include sprain or disruption of medial retinaculum (with avulsive type BME) and patellofemoral ligament, as well as medial patella and anterolateral femoral osteochondral fractures (figure 8).8
Posterior cruciate ligament (PCL) tear
The most common mechanism for an isolated PCL tear is a dashboard injury where an anterior force is applied to a flexed knee resulting in posterior tibial translation.7 ,8 Such an injury may also occur in the setting of a bicycle accident or baseball player colliding with a catcher. Impaction type BME is located to the anteromedial tibia (figures 9 and 10), and associated injuries include rupture of posterior joint capsule, patellar fracture or osteochondral injury and hip injury.8
Anterior cruciate ligament (ACL) tear
ACL tears occur commonly in sports that involve cutting motions such as soccer, basketball and skiing. The mechanisms of injury involves a pivot shift mechanism with valgus flexion and external rotation.7 Impaction type BME occurs in the lateral femoral condyle and posterolateral tibial plateau (figures 11 and 12), where compression fractures are not uncommon. Associated soft tissue injuries include posterior horn meniscal tears, medial collateral ligament damage and posterior capsule injury (figure 13).7,–,9 BME secondary to semimembranosus attachment avulsion7 or a Segond avulsion fracture of posterolateral tibia can also be seen.7
Avulsive type injuries
Avulsive injuries result in a focal area of BME related to disruption at the attachment site. The injures described in this section have an avulsive BME component. Given that most sports injuries are complex, impaction type BME is also shown in the presented examples.
Posterior superior impingement of the shoulder (internal impingement)
Subacromial impingement of the rotator cuff tendons is a common clinical presentation. While the aetiology of the less common posterior superior shoulder impingement is multifactorial, it is known that excessive contact can occur between the posterior supraspinatus and anterior infraspinatus tendon undersurface and the posterior superior glenoid during the late cocking phase in overhead throwing athletes.10,–,12 This condition may be exacerbated by anterior microinstability.12
MRI is useful in the evaluation of internal impingement. In this condition, both avulsive and impaction type BME occurs in the posterolateral humeral head (figure 14). Other imaging findings include humeral subcortical cysts or cortical irregularity deep to infraspinatus insertion. This is accompanied by posterior superior labral fraying, tears or detachment as well as articular partial thickness tears of the supraspinatus or infraspinatus tendons (figure 14).10,–,12
Posterolateral corner injury
A common mechanism for posterolateral corner injury is direct force applied to the anteromedial proximal tibia with knee near full extension. Other mechanisms include non-contact external rotation hyperextension injury or knee dislocation.13 Avulsive type BME in the fibular styloid process raises concern for injury to the posterolateral corner structures, including the fibular collateral ligament, biceps femoris tendon as well as the popliteofibular, fabellofibular and arcuate ligaments (figures 15–17).13 Typical associated injuries include both cruciate ligament injury and meniscal tears. Unrecognised and untreated posterolateral corner injury can lead to chronic knee instability, development of significant osteoarthritis and predispose to cruciate graft failure.13 Treatment remains controversial, however, surgical repair following an acute injury is thought to have a better outcome than surgery for chronic injuries, and is best accomplished within 3 weeks of an acute injury.13
BME due to repetitive stress
The significance of BME due to chronic stress is not well understood, however, in these types of injuries, the BME is usually in the subcortical region. The following examples illustrate two conditions where oedema occurs, one in the setting of avascular necrosis and the other due to repetitive strain.
Osteochondritis dissecans (OCD) of the capitellum
OCD arises in adolescents and young adults when a portion of subchondral bone undergoes avascular necrosis. The aetiology of OCD is unknown but may be due to repetitive microtrauma to the poorly vascularised capitellum.14 OCD can occur with repetitive valgus overload such as in baseball pitchers and gymnasts.14 Imaging findings include BME in the anterior capitellum with or without lesion stability (figure 18). One must be careful not to interpret a pseudodefect of the capitellum (located posteriorly at the junction of capitellum and lateral epicondyle) as OCD.15 Stability of the osteochondral lesion determines the treatment options, with conservative management being indicated for stable lesions and surgical management reserved for those with unstable lesions or failed conservative management.14
Osteitis pubis forms part of ‘athletic pubalgia’ spectrum, with oedema occurring at the symphysis pubis (figure 19). It frequently coexists with adductor muscle group dysfunction, including microtears of the pubic insertion of the rectus abdominis aponeurosis or at the adductor longus tendinoperiosteal junction (figure 20).16 It occurs in sports with excessive truncal rotation, such as with soccer and hockey, which amplify the biomechanical strain on symphysis pubis and its associated support structures.16
Unique patterns of BME serve as fingerprints in the evaluation and diagnosis of a multitude of musculoskeletal injuries, thereby prompting the investigator to evaluate important associated structures, and ultimately significantly impact patient management.
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Contributors All authors contributed to the conception, drafting and revising of this essay.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.