vulsion Injuries of the Pelvis Ricki Shah, M.D., Nirav Shelat, D.O., Georges Y. El-Khoury, M.D., D. Lee ennett, M.., M..., M.D. Division of Musculoskeletal Radiology, University of Iowa Hospitals & linics, Iowa ity, I thletic injuries are a common cause of avulsion injuries in the pelvis, apophyseal or otherwise. Early and accurate imaging diagnosis of this group of injuries is necessary for appropriate management. Using the classical understanding of the muscle-tendon-bone unit, injuries occur at variable locations that can be predicted based on patient age and risk factors. Injuries in most adults typically occur within the tendon due to chronic tendinopathy and degeneration. In younger adults, injuries typically occur at the myotendinous junction, which usually presents as a muscle strain pattern. The injury pattern in the pediatric population is unique, as the weakest link in the chain is the unfused apophysis. vulsion injuries most often occur with either concentric or eccentric muscle contraction. Excessive passive stretching has also been described as a mechanism for avulsions. ctivities requiring running and kicking, as well as rapid directional change, can cause apophyseal avulsions. Patients often describe a pop at the time of injury, followed by pain, swelling, and muscle weakness. 1 On physical examination, patients often have point tenderness at the site of the apophyseal avulsion. 2 Radiographic imaging is usually adequate for the diagnosis of an apophyseal avulsion if there is at least partial ossification of the involved apophysis. MR imaging is often required in suspected cases of avulsion when radiographs are inconclusive or when the apophysis has yet to ossify. Ultrasound can be technically challenging, requiring a skilled operator, but can be particularly useful for assessing myotendinous injuries. The predominant locations of apophyseal avulsion injuries in the pelvis and, therefore the focus of this review article, include the ischial tuberosity, anterior inferior iliac spine (IIS), anterior superior iliac spine (SIS), and pubic symphysis, in descending order of frequency (Figure 1). 3 Iliac crest avulsions can also occur, but are rare. 4 Ischial Tuberosity The ischial tuberosity is the site of origin of the hamstring muscles and adductor magnus (Figure 2) and represents the most common location for avulsion injuries in the pelvis. 3 The tendinous attachments of the hamstrings include the semimembranosus and the conjoined tendon of the semitendinosus and biceps femoris. Ossification of the ischial apophysis is variable. It usually begins to ossify at 14-16 years of age and fully ossifies by 22-24 years of age. Following a hamstring avulsion injury, patients describe buttock pain and weakness. Pain is often exacerbated by walking, and patients may have an antalgic gait. vulsion at the ischial tuberosity often occurs due to forceful flexion of the hip with the knee extended, or due to eccentric overload of the hamstring muscles with forceful contraction against resistance, which places strain at the hamstring origins. ccurate diagnosis can be made with radiographs if the apophysis is ossified. Typically with an acute injury, a curved osseous fragment is seen adjacent to the ischial tuberosity, morphologically similar to the ischial tuberosity (Figure 3). MRI can be used J m Osteopath oll Radiol 2016; Vol. 5, Issue 4 Page 5
FIGURE 1. 3-D pelvic T reconstruction illustrating muscle/tendon attachment sites in the pelvis most commonly associated with avulsion injuries. Red anterior superior iliac spine; blue anterior inferior iliac spine, green ischial tuberosity; cyan pubic symphysis; purple iliac crest. FIGURE 2. 3-D pelvic T denoting the origin of the hamstring muscles at the ischial tuberosity. The right-sided ischial tuberosity is annotated (green) with the musculature overlaid on the contralateral side. The conjoined tendon of the biceps femoris and semitendinosus originate at the posteromedial aspect of the ischial tuberosity, and the semimembranosus originates at the posterolateral aspect of the ischial tuberosity. The adductor magnus originates medially. D FIGURE 3. 15-year-old boy with bilateral buttock pain and ischial tuberosity avulsion fractures. P view of the pelvis () and left hip () show irregularity (arrows) at the bilateral ischial tuberosities with widening of the curved apophysis, consistent with avulsive injury. xial T1 () and T2 fat-suppressed MR images (D) show widening of the ischial tuberosity physis bilaterally (dashed arrows, ), underlying irregularity of the osseous structure, and associated edema (curved arrows, D) within the ischial tuberosities. Page 6 J m Osteopath oll Radiol 2016; Vol. 5, Issue 4
FIGURE 4. Young patient with displaced ischial tuberosity avulsion fracture. P pelvic radiograph () reveals a right ischial tuberosity avulsion fragment (arrow) displaced >2 cm, increasing risk of symptomatic nonunion. Subsequent coronal T1 () and T2 fat-suppressed MR images () further delineate the avulsion fracture (arrow, ) and associated fluid signal, suggesting nonfusion (curved arrow, ). FIGURE 5. Subtle ischial tuberosity avulsion injury. P view of the pelvis demonstrates a subtle case of chronic left ischial tuberosity avulsion with asymmetric cortical irregularity of the left ischial tuberosity (curved arrow). omparison with the asymptomatic side is beneficial, especially in subtle cases. when radiographs are inconclusive to evaluate for myotendinous injury or avulsion of a nonossified apophysis. pophyseal avulsions displaced < 2 cm often heal with conservative management. 1 vulsion fragments displaced > 2 cm may not fuse and can predispose to a fibrous union 4 (Figure 4). Exuberant callus formation may cause impingement on adjacent structures, including the sciatic nerve. Injuries are more commonly unilateral, and therefore, comparison with the asymptomatic side is helpful, particularly in subtle cases (Figure 5). nterior Inferior Iliac Spine The direct head of the rectus femoris originates at the anterior inferior iliac spine (IIS) (Figure 6). Ossification begins between 13-14 years of age, with complete ossification by 16-18 years of age. Similar to the other avulsion injuries, patients often describe a pop followed by pain and weakness, particularly with flexion. Injury typically occurs from eccentric contraction of the rectus femoris. This most commonly occurs with forceful extension of the hip while the knee is flexed, 5 a pattern often seen in sprinters and athletes involved in kicking. 2 FIGURE 6. 3-D pelvic T reconstruction showing origin of the direct head rectus femoris at the anterior inferior iliac spine (IIS). The rightsided IIS is annotated (blue) with the musculature overlaid on the contralateral side. The adjacent reflected head of the rectus femoris originates at the superior acetabular groove and ridge (curved arrow). J m Osteopath oll Radiol 2016; Vol. 5, Issue 4 Page 7
FIGURE 7. IIS avulsion injury. P view of the right hip shows an osseous fragment (arrow) at the IIS, consistent with avulsion injury. FIGURE 8. IIS avulsion injury with donor site. P pelvis shows unilateral right IIS avulsion (arrow) with donor site at the IIS. areful evaluation of the IIS to look for a donor site is recommended as an avulsed anterior superior iliac spine (SIS) fragment may displace far enough to appear as an IIS avulsion injury. FIGURE 9. IIS avulsion injury with edema. xial T1 () and T2 fat-supressed MR images () show osseous avulsion (arrow, ) of the IIS with associated edema (curved arrow, ) On radiographs, an osseous fragment is seen adjacent to the IIS (Figure 7). The fragment is usually unilateral with a corresponding donor site evident on the underlying iliac bone (Figure 8). MRI is useful in cases of a nonossified apophysis or when the diagnosis is unclear based on radiographs. On MRI (Figure 9) the avulsed fragment is identified with varying levels of associated soft-tissue edema. The reflected head of the rectus femoris originates at the superior acetabular ridge. vulsion injuries can occur at this location; however, they are uncommon. superior acetabular ridge avulsion has similar findings to an IIS avulsion, including an avulsed fragment, which can be best seen on the frog-leg lateral view (Figure 10). pophyseal injuries of the IIS are usually managed conservatively. Page 8 J m Osteopath oll Radiol 2016; Vol. 5, Issue 4
FIGURE 10. 23-year-old man with acetabular-indirect head of the rectus femoris avulsion injury after kicking a football. Frog-leg lateral view of the right hip () performed approximately 7 months following the injury shows calcifications (arrow) adjacent to the right superior acetabulum. Differential considerations include an IIS vs. superior acetabular avulsion. xial T2 fat-supressed MR image () shows normal insertion of the direct head of the rectus femoris at the IIS (curved arrow) and fluid signal (arrowhead) at the expected location of the origin of the reflected head, consistent with avulsion injury of the indirect head of the rectus femoris. FIGURE 11. 3-D pelvic T reconstruction showing the origin of the sartorius and portions of the tensor fascia lata at the SIS. The left-sided IIS is annotated (red) with the musculature overlaid on the contralateral side. nterior Superior Iliac Spine The anterior superior iliac spine (SIS) is an osseous protuberance at the anterior margin of the iliac crest (Figure 11). The sartorius and portions of the tensor fascia lata (TFL) originate at the SIS and are the primary muscles that can cause avulsion injuries at the SIS. The sartorius courses medially in the anterior compartment to insert on the proximal medial tibia at the pes anserine aponeurosis. This oblique course of the muscle allows for hip and knee flexion as well as hip abduction and external rotation. The SIS begins to ossify between 13-15 years of age and fuses with the underlying anterior margin of the iliac crest in the early 20s. The SIS is the third most common site of apophyseal avulsion fractures in the pelvis. pophyseal avulsion of the SIS results from sudden forceful contraction of the sartorius with the hip in extension and the knee flexed. 2 Therefore, this is most common in running athletes. Injuries may also occur with kicking. 2 n avulsion injury of an ossified SIS apophysis is seen typically as a small osseous fragment adjacent to the SIS (Figures 12, 13). However, in rare circumstances, severe avulsion of the anterior superior iliac spine (SIS) apophysis may cause the apophysis to displace inferiorly, projecting over the IIS, simulating avulsion of the IIS (Figure 13). Evaluating the underlying IIS and SIS for a possible donor site can be helpful. Morphologic changes to the underlying iliac bone are often seen at the avulsion site. These injuries are often unilateral, and therefore, comparison with the asymptomatic side is recommended. The majority of SIS avulsion injuries heal with conservative management. It is imperative that these injuries be diagnosed appropriately with medical imaging, as the high osteoblastic activity on biopsy specimens may be mistaken for osteosarcoma. Symphysis Pubis The primary musculotendinous origins at the symphysis pubis include the J m Osteopath oll Radiol 2016; Vol. 5, Issue 4 Page 9
FIGURE 12. Young gymnast with SIS avulsion injury. P view of the pelvis () shows an avulsion of the left SIS (arrow). P radiograph 5 months later () shows progressive healing with callus formation (arrow). Following an additional injury 13 months after the initial injury, P radiograph of the pelvis () now shows a new avulsion of the right SIS (curved arrow) with the prior left-sided avulsion injury healed (arrow). D rectus abdominis, gracilis, adductor brevis and adductor longus (Figure 14). vulsion injuries at the symphysis pubis are uncommon and are usually from chronic overuse, although acute avulsions do occur rarely. cute avulsions in young athletes usually occur with forceful contraction against resistance. 2 vulsion injuries at the symphysis pubis are usually seen within the spectrum of athletic pubalgia. s discrete osseous fragments are rarely seen, particularly in acute cases, radiographs may be negative. However, secondary changes may be seen at the symphysis pubis including widening, lysis and cortical irregularity, particularly in chronic cases (Figure 15). These injuries can be better evaluated by MRI, which can allow for identification of specific muscular involvement (Figure 16). lthough the rectus abdominus also inserts at the pubic symphysis, frank avulsion is rare. More commonly, partial avulsions or tears of the rectus-adductor aponeurosis are seen with fluid undermining the attachment site. This injury is commonly seen with athletic pubalgia, and is also known as a sports hernia. 6,7 FIGURE 13. 14-year-old girl with SIS avulsion following a motor vehicle collision and subsequent development of heterotopic ossification. P view of the right hip () shows a subtle small avulsion fracture of the right SIS (arrow). Imaging 3 years later () shows the avulsed fragment with heterotopic ossification (arrow) and inferior displacement to the level of the IIS. This is confirmed on MRI (coronal T1, ; coronal T2 with fat suppression, D) with the sartorius originating from the avulsed fragment (arrow, ) and the direct head of the rectus femoris originating from the IIS (dashed arrow, D). Iliac rest vulsions of the iliac crest are rare. The iliac crest is where components of the abdominal wall musculature insert. Radiographs are typically adequate to make the diagnosis and findings include irregularity of the apophysis of the iliac crest (Figure 17). MRI can confirm findings, which would show corresponding edema on the fluid-sensitive sequences. Page 10 J m Osteopath oll Radiol 2016; Vol. 5, Issue 4
FIGURE 14. 3-D pelvic T reconstruction showing the adductor and rectus aponeurotic attachment at the pubic symphysis. The right-sided pubic symphysis is annotated (cyan) with the musculature overlaid on the contralateral side. FIGURE 15. Secondary changes of pubic symphysis avulsion injury. P radiograph of the pelvis in this patient with chronic injury shows widening and lysis at the pubic symphysis (arrow). Radiographic findings are often not identified in cases of acute avulsive injury at the symphysis pubis. FIGURE 16. Pubic symphysis avulsion injury on MRI. Sagittal T2 fat-suppressed MR image of the pelvis shows acute avulsion of the adductor tendons with associated retraction (arrow) and fluid gap (arrowhead). onclusion pophyseal avulsion injuries in the pelvis are not uncommon in clinical practice, especially in the setting of athletic injuries. Since the clinical presentation of avulsion injuries overlaps with numerous additional musculoskeletal injuries, imaging plays a key role in establishing the correct diagnosis. Understanding the underlying myotendinous and bony anatomy, mechanisms of injury, and characteristic imaging features associated with avulsion injuries will FIGURE 17. Iliac crest avulsion injury. P view of the pelvis shows asymmetric irregularity of the right iliac crest apophysis, consistent with avulsion injury (arrow). Incidentally, a healing left anterior superior iliac spine avulsion injury (curved arrow) is also seen. allow for prompt diagnosis and treatment, ultimately improving outcomes. lthough radiographs often allow for confident diagnosis, MR imaging is helpful in cases when radiographs are inconclusive or not definitive. References 1. Giordano D. ssessment and treatment of hip pain in the adolescent athlete. Pediatr lin N m 2014;61(6):1137-1154. 2. oyd KT, Peirce NS, att ME. ommon hip injuries in sport. Sports Med 1997;24(4):273-288. 3. Rossi F, Dragoni S. cute avulsion fractures of the pelvis in adolescent competitive athletes: prevalence, location and sports distribution of 203 cases collected. Skeletal Radiol 2001;30(3):127-131. 4. Stevens M, El-Khoury GY, Kathol MH, randser E, how S. Imaging features of avulsion injuries. Radiographics 1999;19(3):655-672. 5. Reina N, ccadbled F, de Gauzy JS. nterior inferior iliac spine avulsion fracture: a case report in soccer playing adolescent twins. J Pediatr Orthop 2010;19(2):158-160. 6. Zoga, Kavanagh E, Omar IM, et al. thletic pubalgia and the sports hernia : MR imaging findings. Radiology 2008;247(3):797-807. 7. Omar IM, Zoga, Kavanagh E, et al. thletic pubalgia and sports hernia : optimal MR imaging technique and findings. Radiographics 2008;28(5):1415-1438. J m Osteopath oll Radiol 2016; Vol. 5, Issue 4 Page 11