Magnetic resonance imaging evaluation of oblique injuries: Introduction of the deadrise sign

Abstract

Oblique injuries are a common sports-related injury to the lateral abdominal wall, most commonly caused by forceful trunk rotation, which tears the internal oblique from the undersurface of the lower ribs. Despite increased awareness and prevention efforts, these injuries remain a significant contributor to missed playing time. A single institution retrospective cohort review of oblique injury magnetic resonance images (MRIs) was performed, followed by a comprehensive review including relevant anatomy, grading considerations, and introduction of the deadrise sign, interpretation pearls, case examples, MRI protocols, and treatment algorithms.

INTRODUCTION

Oblique injuries are a common sports-related injury to the lateral abdominal wall.^[1-3] Most injuries are diagnosed clinically and resolve in a few weeks with conservative management. However, a small subset of high-level athletes exists that are referred for imaging evaluation to direct treatment regimens and optimize recovery time.

The most common cause of oblique injury is forceful trunk rotation, which tears the internal oblique from the undersurface of the lower ribs.^[1-4] Baseball and cricket are the most well-documented in the literature, though any activity involving forceful trunk rotation can result in oblique injuries.^[1-3] Oblique injuries are more common on the non-dominant side in baseball players (leading side), as opposed to the dominant or trailing side, due to increased rotational force on the contralateral trunk necessary for optimizing performance metrics.^[1,2,4] The incidence of oblique injuries in professional baseball has been a target of research in the past several years. Despite increased awareness and prevention efforts, these injuries remain a significant contributor to missed playing time.^[1,2] To date, no qualitative radiology signs related to oblique tears have been published in the literature.

Learning objectives

• Importance of oblique injuries in sports imaging

• Anatomy of the lateral abdominal wall musculature

• Primary muscle involved and location of injuries

• Common injury magnetic resonance imaging (MRI) findings, the deadrise sign, and proposed injury grading system

• Basic MRI protocol and treatment algorithm.

SINGLE INSTITUTION RETROSPECTIVE REVIEW

Subjects and methods

Our patient population was obtained by searching the PowerScribe reporting database for abdominal MRIs ordered by orthopedic/sports medicine providers for the past 10 years. After exclusions detailed in the flowchart [Figure 1], our final population was obtained.

Figure 1:

Flowchart demonstrating excluded exclusion criteria. MRI: Magnetic resonance imaging. *Nondisplaced rib fractures and subcutaneous contusion, ** 29 MRIs from 23 patients due to a few patients having multiple exams.

Twenty-nine MRIs were interpreted from 23 patients. All patients with multiple examinations had injuries that were separated temporally and by muscle involvement, without follow-ups of the same injury. The demographics are outlined in Table 1, and exclusion criteria are outlined in Figure 1. MRI examinations were reviewed from August 2013 to October 2022 by two fellowship-trained radiologists documenting consensus findings: primary muscle involved and injury severity; side and location of injury; surrounding muscular injuries; surrounding myofascial fluid; and greatest extent of injury (measured in the long-axis anteroposterior dimension on axial or sagittal images).

Table 1:

Patient demographics.

Variable	Value
Total MRIs	29
Number of patients evaluated (n)	23
Age at first MRI, years mean (range)	27.9 (22–58)
Sex, n (%)
Male	22 (95.7)
Female	1 (4.3)
Ethnicity, n (%)
Non-Hispanic	12 (52.2)
Hispanic	2 (8.7)
Unknown	9 (39.1)
Sport, n (%)
Baseball	17 (73.9)
Football	4 (17.4)
Golf	1 (4.3)
N/A	1 (4.3)
Dominant hand, n (%)
Right	13 (56.5)
Left	4 (17.4)
N/A	6 (26.1)

MRI: Magnetic resonance imaging, N/A: Not Applicable

Results

The most common location of injuries was the costochondral junction of the 10–12^th ribs (91–21/23): 21% involved the 10^th rib, 75% involved the 11^th rib, and 4% involved the 12^th rib. One patient had an injury at the 8^th costochondral junction, while another had multiple injuries separated in time and space at the iliac attachment.

The average length of injury along the long axis of the rib was 3.2 cm. Surrounding myofascial fluid without muscle injury abutted the external oblique in 66% of cases and the transverse abdominis in 59% of cases. Surrounding muscular injury involved the external oblique in 52% of cases, the transverse abdominis in 24% of cases, and the intercostal musculature in 10% of cases. This is outlined in Table 2.

Table 2:

Injury characteristics.

Variable	n (%)
Internal oblique	29 (100)
Iliac attachment	4 (13.8)
Rib undersurface	25 (86.2)
8th rib	1 (3.4)
10th rib	5 (17.2)
11th rib	18 (62.1)
12th rib	1 (3.4)
Surrounding myofascial fluid location
External oblique	19 (65.5)
Transverse abdominis	17 (58.6)
Surrounding muscular injury involvement location
External oblique	15 (51.7)
Transverse abdominis	7 (24.1)
Intercostal musculature	3 (10.3)
Severity
Grade 1	7 (24.1%)
Grade 2	22 (75.9%)

Discussion

The internal oblique was the primary muscle injured in 100% of our population without isolated injuries to the external oblique or transversus abdominis muscles. When these muscles were involved, their injuries were less severe than those of the internal oblique.

Since most internal oblique injuries occur at the undersurface near the costochondral junction of the lower ribs, the single most important image is a short-axis view of the rib/cartilage at the level of the tear to evaluate for undercutting fluid. We deemed this the “deadrise sign,” and it was present in 100% of the MRIs that demonstrated macroscopic tearing (grade 2 injuries) at the costochondral attachments. The deadrise sign is a novel qualitative imaging characteristic that confirms the presence of a true tear from the undersurface of the rib and assists with directing treatment strategies [Figure 2].

Figure 2:

(a) Illustration of the deadrise sign. In nautical terms, the deadrise is the angle between the hull of a ship and its apex, which affects ship balance. Like how water undercuts a ship, fluid can undercut the rib at the costochondral junction, which indicates at least partial-thickness stripping/avulsion of the internal oblique. We refer to this as the deadrise sign. (b) Best visualized on a short-axis STIR image of the rib at the level of the injury (red arrows).

Deadrise sign

The average length of injury along the long axis of the rib (often AP dimension) is the single most relevant measurement clinically, representing the length of stripping/avulsion from the undersurface of the rib. However, this measurement is also highly variable and subjective. It can be over-measured by including surrounding muscular strain and myofascial fluid and undermeasured by being unable to visualize the full extent on a single axial or sagittal slice. Assuming adequate images were obtained, the deadrise sign is an easily reproducible imaging finding indicating a tear rather than strain. The conventional tear length measurement can be used as a quantitative tool to further characterize the overall severity of the injury.

Surrounding myofascial fluid without muscle injury is common, abutting the external oblique and the transverse abdominis in over half of the cases. Surrounding muscular injury was slightly less common, most commonly involving the external oblique.

ANATOMY OF THE LATERAL ABDOMINAL WALL

Broadly, abdominal wall muscular injuries can involve the rectus abdominis muscle (rarely imaged), the rectus abdominis-adductor aponeurosis (core muscle injury or athletic pubalgia), or the oblique muscles [Figure 3].

Figure 3:

(a) Virtual model demonstrating the types and locations of abdominal wall muscular injuries. Oblique injuries involve the lateral abdominal wall musculature, most commonly at the attachment of the lower ribs, and less commonly in the muscle belly or at the iliac attachment. (b) Axial T2-weighted injury magnetic resonance imaging and (c) non-contrast CT images demonstrating the three layers of the lateral abdominal wall musculature: external oblique (superficial, yellow), internal oblique (middle, green), and transversus abdominis (deep, purple). (d) Coronal oblique STIR image of the lateral abdominal wall demonstrating the 3 layers of the lateral abdominal wall musculature: external oblique (superficial, yellow), internal oblique (middle, green), and transversus abdominis (deep, purple).

The lateral abdominal wall musculature is composed of three layers, from superficial to deep: External oblique [Figure 4], internal oblique [Figure 5], and transverse abdominis [Figure 6].

Figure 4:

(a) Virtual model and T2-weighted axial injury magnetic resonance image (b) demonstrating the external oblique muscle. The external oblique (yellow) is the most superficial muscle layer of the lateral abdominal wall. Its fibers run in an anteroinferior trajectory. (c) Sagittal T1-weighted and (d) STIR images of the external oblique muscle. Notice the normal anatomic striations of the muscle and anteroinferior trajectory (yellow arrows), which become more evident with intramuscular edema.

Figure 5:

(a) Virtual model and (b) T2-weighted axial injury magnetic resonance image demonstrating the internal oblique muscle. The internal oblique (green) is the middle muscle layer of the lateral abdominal wall. (c) Sagittal T1-weighted image of the internal oblique muscle and diagram demonstrating anterosuperior fiber trajectory (green arrows).

Figure 6:

(a) Virtual model and T2-weighted axial injury magnetic resonance image (b) demonstrating the transverse abdominis muscle. The transverse abdominis (purple arrow) is the deepest and thinnest muscle layer of the lateral abdominal wall. (c) Sagittal STIR image of the transverse abdominis muscle demonstrating transverse fiber trajectory, more visible with muscular edema related to strain (purple circle).

Since the internal oblique is always involved in oblique injuries, more detailed anatomy is crucial for image interpretation [Figure 7]. The inferior attachment of the internal oblique is referred to as the origin. It predominantly involves the anterior 2/3 of the iliac crest and extends to the lateral aspect of the iliopectineal arch (immediately deep to the inguinal ligament). The medial attachment contributes to the linea alba, and the posterior attachment contributes to the thoracolumbar fascia. The superior attachment is referred to as the insertion and involves the undersurface of the 10^th–12^th ribs posteriorly and the undersurface of the costal cartilages anteriorly. It becomes aponeurotic at approximately the level of the 9^th costal cartilage, and its aponeurosis continues superiorly to higher rib levels, at least to the ^7th costal cartilage.^[3,5,6] The internal oblique is the abdominal continuation of the thoracic internal intercostal muscle (which is also the middle muscle of the three intercostal muscles, mirroring lateral abdominal wall anatomy).^[6]

Figure 7:

(a) Virtual 3D model indicates the most common location of internal oblique tears, which involve the undersurface of the costochondral junction of the lower ribs, most notably the floating 11^th and 12^th ribs (yellow circle). (b) Coronal and (c) sagittal STIR images demonstrate full-thickness undersurface tear at the costochondral junction of the floating left 11^th rib (red arrow = positive deadrise sign). Notice the change in signal intensity from the end of the ossified rib to the hypointense costochondral cartilage on STIR sequences (yellow arrow). The floating ribs have cartilage along their rib ends despite no direct or indirect connection with the sternum.

The 11^th and 12^th ribs (and sometimes the 10^th) are floating ribs with no sternal attachment. The 8^th–10^th ribs are false ribs with an indirect attachment to the sternum through a common costal cartilage confluence. The 1^st–7^th ribs are considered true ribs with direct cartilaginous sternal attachment.^[6]

By convention, muscle tears are described using thickness and width [Figure 8]. Thickness is the transverse diameter and can be either partial or full thickness. Width (interchangeable with length) represents the AP dimension. The internal oblique never completely avulses from the long axis of the rib; thus, it is essentially all partial width.

Figure 8:

(a) Axial T2 and (b) oblique coronal STIR sequences demonstrating dimensional terminology of thickness, width, and length when describing internal oblique injuries. Oblique muscle injuries are often full-thickness, although never full-width. For this reason, full-thickness/width injuries (grade 3) with functional loss do not occur.

INJURY GRADING CONSIDERATIONS

There is controversy regarding the grading of oblique injuries due to differences between imaging and clinical grading systems. Traditional grade I/II/III nomenclature works well for many muscle groups. For example, complete tears of the Achilles or biceps brachii tendons (imaging grade 3) correspond to concordant loss of function (clinical grade 3).

However, oblique musculature has a multilayer composition with redundant functionality. Injuries often result in partial or full-thickness avulsion from the undersurface of a rib (imaging grade 2) with discordant loss of function (clinical grade 1) [Figure 9]. In addition, research demonstrates that the traditional imaging grading system lacks accuracy in predicting functional loss.^[7] Several newer grading systems have been proposed that demonstrate greater functional accuracy at the cost of increased complexity, limiting applicability. Subjective review at our institution demonstrates both inter- and intra-reader variability in adherence to numerical grading systems when interpreting oblique muscle injuries.

Figure 9:

The difference between strain, partial-thickness tear, and full-thickness tear. Notice the current grading scheme, where the strain is considered grade 1, while the partial-thickness and full-thickness tears are considered grade 2. STIR: Short tau inversion recovery, PD: Proton Density

The most accurate way to communicate findings to ordering providers and training staff is a concise and accurate description of the tear length, location, and amount of surrounding edema, without strict adherence to the numerical grading system. For the purposes of this article, oblique injuries will be described conventionally. While this approach is technically less accurate in predicting functional loss, it avoids complex grading systems and discordant imaging-clinical findings.

Imaging reports should include any injuries to the internal oblique, their location, and surrounding muscular injuries. A measurable hematoma and surrounding myofascial fluid may or may not be present. The approximate width of the tear may assist the clinician in developing a timeline for return to activity, as width has a high correlation with recovery time.^[8] This measurement is subjective and difficult to reproduce, although it can be achieved by providing the extent of stripping along the undersurface of the rib on the long-axis view. However, this can underestimate the full length of the tear due to the convex curvature of the rib, preventing visualization of the entire tear on a single slice.

Finally, it is important to be aware that muscle edema on imaging is abnormal. It is possible to have transient physiologic muscle edema on MR after strenuous workouts due to both increased muscle recruitment of water and the microscopic tearing necessary for subsequent hypertrophy.^[9] However, it is assumed that the clinician has ruled out this possibility, and the pain is unusually excessive or abrupt in onset. Muscle edema in athletes is almost always related to injury/trauma. In other patient populations, it could be related to infectious, inflammatory, neurologic, neoplastic, or iatrogenic etiologies.^[10,11]

LOCATION OF TEARS

Oblique injuries are managed conservatively, so precise localization is often not necessary. Palpation and tissue markers at the presumed rib level are encouraged to help with clinical follow-up, direct potential therapies, and optimize imaging.^[12,13]

CASE EXAMPLES

Strain (no tear)

Case 1 Figure 10.

Figure 10:

(a) Axial STIR and (b) sagittal STIR sequences demonstrate focal low-grade strain with muscular edema of the left internal oblique near the iliac attachment (red arrows). No fluid signal or architectural distortion to indicate a tear. STIR: Short tau inversion recovery.

Partial-thickness tears

Case 1 Figure 11.

Figure 11:

(a) Coronal STIR (b) sagittal STIR. Images show a partial-thickness tear of the internal oblique at the undersurface of the costochondral junction at the floating 11^th rib with positive deadrise sign (red arrow). Thin STIR hyperintense signal along the rib undersurface on sagittal long-axis views (yellow arrows) represents intercostal vasculature and should not be confused with tear extension. STIR: Short tau inversion recovery.

Case 2 Figure 12.

Figure 12:

(a) Axial STIR and (b) coronal STIR images show partial-thickness tears of the internal oblique and deeper fibers of the external oblique muscles involving the undersurface of the floating left 12^th rib with surrounding myofascial fluid (red arrow = positive deadrise sign). (c) Coronal CT with bone windows from an unrelated examination performed 14 months later, demonstrating tiny fragments of dystrophic calcification at the site of prior injury (yellow arrow). STIR: Short tau inversion recovery ,CT: Computed tomography.

Case 3 Figure 13.

Figure 13:

(a) Coronal STIR and (b) sagittal STIR sequences show a partial-thickness tear of the internal oblique at the undersurface of the costochondral junction of the floating 11^th rib (red arrow = positive deadrise sign). Notice the costal cartilages of the 8^th–10^th ribs converging before their sternal attachment, which is why these are known as “false ribs” (yellow arrow). STIR: Short tau inversion recovery.

Full-thickness tears

Case 1 Figure 14.

Figure 14:

(a) Coronal short-axis STIR and (b) sagittal STIR images demonstrate a positive deadrise sign (red arrow) with a full-thickness tear of the internal oblique at the undersurface of the 11^th rib costochondral junction. The defect measures 2.2 cm along the long axis of the rib. Retraction and surrounding strain of the internal oblique muscle are evident by the fiber trajectory on the sagittal long-axis view.

Case 2 Figure 15.

Figure 15:

(a) Axial STIR, (b) axial PDfs, and (c) coronal PDfs sequences demonstrating a full-thickness tear of the right internal oblique from the undersurface of the 11^th rib with a positive deadrise sign (red arrow). Surrounding muscle strain involves the internal oblique, as well as the overlying external oblique and the deeper transversus abdominis fibers. Notice the improved fluid sensitivity but increased image noise of (a) STIR compared to (b) PDFS. STIR: Short tau inversion recovery. PDfs: Proton-density fat saturated

Iliac attachment tears

Case 1 Figure 16.

Figure 16:

(a) Axial T2 FS and (b) coronal STIR images demonstrate a large full-thickness, partial-width tear of the right internal oblique muscle just proximal to the iliac wing attachment (red arrows). STIR: Short tau inversion recovery. FS: Fat saturated

Case 2 Figure 17.

Figure 17:

(a) Axial T2 FS, (b) coronal STIR, and (c) sagittal T2 FS images depict a partial-thickness tear of the right internal oblique at the iliac attachment (red arrows). STIR: Short tau inversion recovery. FS: Fat saturated

DIFFERENTIAL DIAGNOSIS

In our athletic population, the most common mimickers of oblique injuries are rib/costochondral fractures and subcutaneous contusions. (MRI of a rib fracture in a baseball player) has no body text citation. Nondisplaced rib fractures in athletes can be related to either stress or trauma [Figure 18]. Core muscle injuries usually present differently and are rarely a diagnostic mimicker.

Figure 18:

(a) Axial T2, (b) axial STIR, and (c) sagittal STIR injury magnetic resonance imaging performed on a baseball player to evaluate for suspected oblique strain reveals an acute non-displaced fracture of the left 12^th rib at the costochondral junction (red arrows). This patient was excluded from the data analysis. STIR: Short tau inversion recovery.

Oblique injuries less commonly involve the iliac attachment. In the skeletally mature population, you can also have avulsion fractures from the iliac crest. In the skeletally immature population, iliac apophyseal avulsion injuries or iliac apophysitis may occur. The apophysis usually fuses around ages 14–16 but can fuse as late as ages 18–20.^[14,15]

Previous articles have gone into much greater detail regarding additional abdominal wall injuries, such as traumatic abdominal wall hernias (lumbar or spigelian) and MorelLavallée fascial degloving injuries.^[14,16] Other diagnostic mimickers include nephrolithiasis, although these lack the inciting forceful trunk rotation and usually do not pose a diagnostic dilemma.

MRI PROTOCOL CONSIDERATIONS

Base protocol

The use of tailored and standardized protocols is ideal for MRI. Tailored protocols reduce table time and scanner throughput. Patient positioning, accessory coil usage, and receiver bandwidth are paramount for image optimization. The delicate balance between signal-to-noise ratio (SNR), spatial resolution, and duration varies by scanner and sequence and can often be optimized by working closely with your technologists and physicists.^[17]

Below is an example protocol [Table 3]:

Table 3:

Scanning parameter table summary. All sequences are fast spin echo; parameters are for a 1.5T magnet with targeted skin markers. The spine coil that is integrated into the injury MRI table is often used. When surface coils are used, a 4-channel large flex coil or a 6-channel flex body coil is utilized. Contrast administration is not indicated. Protocol is adapted from the KUMC institutional protocol and the European Society of Musculoskeletal Radiology Sports Subcommittee open-access guidelines.

Sequence	FOV (cm2)	TR/TE (ms)	Slice thickness & Interslice gap	Matrix	Signals acquired (# of excitations)	Echo train length and Inversion time (ms)	Receiver bandwidth (Hz/pixel)	Scanning time (min)
Axial T1	17–24 cm2	TR 500 TE 10-15	4 mm slices 5 mm gap	256×212	1	ETL 3	150–200	2–4
Axial STIR	17–24 cm2	TR 3000–4200 TE 30	4 mm slices 5 mm gap	256×212	1	ETL 8 TI 160	150–200	3–6
Coronal STIR	17–24 cm2	TR 3000–4200 TE 30	4 mm slices 5 mm gap	256×212	1	ETL 8 TI 160	150–200	3–6
Sagittal STIR	17–24 cm2	TR 3000–4200 TE 30	4 mm slices 5 mm gap	256×212	1	ETL 8 TI 160	150–200	3–6
KUMC: University of Kansas Medical Center, FOV: Field of View, TR: Repetition Time, TE: Echo Time, ETL: Echo train length, TI, MRI: Magnetic resonance imaging, #Number of excitations, STIR: Short tau inversion recovery.								Total: 20 min

The axial T1 and axial STIR sequences optimize anatomy and injury localization. Short-axis STIR (coronal) best identifies the fluid cleft along the undersurface of the rib/cartilage compatible with stripping/avulsion of the internal oblique (deadrise sign). Long-axis STIR (sagittal) best identifies the extent of the tear along the length of the rib [Figures 19 and 20].

Figure 19:

Axial CT, bone window. Due to the predominantly anterior trajectory of ribs, short-axis views of internal oblique tears are often obtained in the coronal plane (yellow, A). However, the costochondral junction of the lower ribs is located more posteromedially, which can occasionally result in short-axis views obtained in the sagittal plane (blue, B).

Figure 20:

(a and b) Image acquisition with scan planes. Initial images are acquired with T1 and axial STIR through the level of the injury with skin markers, which demonstrate myofascial fluid and incomplete visualization of the undersurface tear. (c) Oblique coronal STIR images provide a true short-axis view to better evaluate the full-thickness tear (red arrow = positive deadrise sign). (d) Oblique sagittal STIR images provide a long-axis view with measurable AP extent of injury, including the high-grade internal oblique tear (red arrow). Notice the internal oblique fiber orientation (anterosuperior, green arrow), external oblique fiber orientation (anteroinferior, yellow arrow), and intercostal vasculature, which can be mistaken for edema (blue arrow). STIR: Short tau inversion recovery.

Our institution utilizes a STIR heavy protocol due to its high sensitivity for fluid detection and more homogenous fat suppression, which is often needed in technically challenging cases. Any fluid-sensitive sequence with fat suppression could be interchanged (such as Proton-Density Fat Saturated or T2 FS) at the expense of inhomogeneous fat suppression and fluid sensitivity. All sequences are obtained by fast/turbo spin echo (FSE). Due to longer T2-weighted scan times, additional imaging techniques can be used to decrease scan time or reduce motion, such as Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER), Siemens-proprietary motion-reduction technique equivalent to generic PROPELLER (BLADE), Single-shot Fast Spin Echo (SSFE), or Half-Fourier Acquisition Single-shot Turbo spin Echo (HASTE).^[17-22] Common artifacts include motion, wraparound, and incomplete fat suppression.^[17-21]

Common artifacts

Figures 21 and 22.

Figure 21:

(a) Axial T1 and (b) axial STIR images. The most common artifact encountered is motion. This is usually involuntarily related to cardiac motion or respiration near the diaphragm (a) or bowel peristalsis lower in the abdomen (b). Motion artifact occurs in the phase encoding gradient (PEG), which is appropriately positioned along the Y-axis in the first image (a). PEG is incorrectly positioned along the X-axis in the second image (b), which is suboptimal due to the obscuration of the oblique musculature and site of injury (as denoted by the red arrow). Motion artifact can be limited using fast scanning techniques, shallow breathing instructions, prone positioning, passive restraints (such as tape, sandbags, and foam/rubber), and anxiety reduction techniques (such as music headphones and minimal sedation).

Figure 22:

(a) Axial T1 and (b) axial STIR images demonstrate a near full-thickness tear of the internal oblique muscle with associated intramuscular hematoma and surrounding strain (red arrow). In addition, the images remain of diagnostic quality despite several artifacts. The most striking artifact is the wrap-around or aliasing artifact (blue arrows). The technologist appropriately flipped the phase and frequency encoding gradients between sequences, resulting in the artifact being repositioned into a non-contributory portion of the image. An additional artifact includes incomplete fat suppression (inhomogeneity) in the right posterior perirenal space (orange arrow). This should not be mistaken for retroperitoneal extension of injury. Finally, notice the slightly T2 hyperintense rings anterior and posterior to the gallbladder (yellow arrows), which likely represent motion/ghosting artifacts. Like wrap-around, motion artifact also occurs in the phase encoding gradient. Finally, note the layering of the T1 isointense signal in the gallbladder, which is not an artifact and likely represents concentrated bile in this young athlete, although sludge could appear similar if the patient was pregnant, ill, on octreotide, or experienced recent rapid weight loss.

Localization pearl

Figure 23.

Figure 23:

(a) Coronal STIR image demonstrates a near full-thickness tear of the left internal oblique along the undersurface of the costochondral junction (green arrow). The exact rib level was difficult to determine, although presumed to be the 11^th rib. The skin marker (red arrow) was noted to overly one rib level above the tear. (b) After magnetic resonance imaging, the technologist replaced the skin marker with a radiopaque BB (orange arrow). A standard chest radiograph was performed to confirm 12 rib pairs (not shown), followed by targeted radiographs of the BB for rib localization. The BB was shown to extend over the 10^th rib, which confirmed the tear at the 11^th rib level (yellow arrow). While this is often an unnecessary step since exact localization will not change management, it could easily be built into a protocol if referring clinicians request such precision.

Treatment algorithm

MRI injury grade affects an athlete’s return to play. Figure 24 illustrates a treatment algorithm. Grade 0 and grade 1 injuries are treated conservatively with physical therapy. Grade 2 injuries may potentiate orthobiologic treatments such as the injection of platelet-rich plasma.^[18]

Figure 24:

Flowchart illustrating the presence or absence of the deadrise sign, injury severity, and treatment pathways. MRI: Magnetic resonance imaging.

CONCLUSION

Oblique injuries are common, particularly in baseball, although they are usually only imaged at the elite level. Oblique injuries primarily involve the internal oblique muscle, usually at the undersurface of the lower rib costochondral junctions. Obtaining short-axis and long-axis views of the rib/cartilage site of injury is essential for diagnosis. The deadrise sign is an easily reproducible imaging finding indicating at least partial-thickness tearing (grade 2 or higher), rather than strain. Imaging plays an important role in athlete return to play protocols.

Funding Statement

Financial support and sponsorship: Nil.

Ethical approval:

Institutional Review Board approval is not required.

Declaration of patient consent:

Patient’s consent is not required as patient’s identity is not disclosed or compromised.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.