Stress-Related Injuries Around the Lesser Trochanter in Long-Distance Runners

Musculoskeletal Imaging Clinical Observations Nguyen et al. Stress Injury Around Lesser Trochanter Musculoskeletal Imaging Clinical Observations Josephine T. Nguyen 1 Jeffrey S. Peterson 2 Sandip Biswal 3 Christopher F. Beaulieu 3 Michael Fredericson 4 Nguyen JT, Peterson JS, Biswal S, Beaulieu CF, Fredericson M Keywords: femoral neck, iliopsoas, MRI, musculoskeletal, stress injuries DOI:10.2214/AJR.07.2513 Received May 4, 2007; accepted after revision December 4, 2007. 1 Magnetic Resonance Imaging, Radiology, Long Beach Memorial Medical Center, Long Beach, CA. 2 Innovative Sports Medicine, Mountain View, CA. 3 Department of Radiology, Stanford University Medical Center, Stanford, CA. 4 Division of Physical Medicine and Rehabilitation, Department of Orthopaedic Surgery, Stanford University Medical Center, 300 Pasteur Dr., Edwards Bldg. R107A, Stanford, CA 94305-5336. Address correspondence to M. Fredericson. AJR 2008; 190:1616 1620 0361 803X/08/1906 1616 American Roentgen Ray Society Stress-Related Injuries Around the Lesser Trochanter in Long-Distance Runners OBJECTIVE. Imaging abnormalities around the lesser trochanter are occasionally found in long-distance runners, yet little research has been conducted concerning this area of the hip. In addition, the relation between iliopsoas insertional abnormalities at the lesser trochanter and femoral neck stress injuries has not been examined, to our knowledge. We report MRI findings at the lesser trochanter in nine long-distance runners with hip or groin pain and a consistent constellation of the following findings: abnormalities associated with the iliopsoas tendon and its insertion, including marrow edema at the lesser trochanter; periostitis around the lesser trochanter; and bone marrow edema in the femoral neck. One case involved temporal progression to a cortical fracture. CONCLUSION. Long-distance runners with hip or groin pain and abnormal MRI findings involving the insertion of the iliopsoas tendon and marrow edema in the lesser trochanter may be at risk of stress injuries at the femoral neck. S ymptoms of groin or hip pain in long-distance runners can indicate stress reactions at the femoral diaphysis or neck, but we are aware of only one study [1] of the incidence of injury at the lesser trochanter. Those investigators found this injury to be quite common. The subjects were 71 athletes (89% of whom were runners with hip, groin, or thigh pain) with 74 stress injuries to the femur. Using bone scintigraphy, the authors detected abnormal radiotracer uptake isolated to the lesser trochanter in 20% of the patients. MRI was not used in that study. Bony stress injuries to the proximal femur can manifest with vague groin, hip, or anterior thigh pain that worsens with continued weightbearing. Physical examination is challenging owing to difficulty in palpating the deeper bones in this area. The findings include limited range of motion of the hip, pain on forced rotation or axial loading, and tenderness over the involved bone, but these findings are nonspecific. A positive result of a hop test, in which the patient reproduces the pain by hopping on the involved extremity, occurs in as many as 70% of patients with femoral neck stress fractures but also is not specific [1]. The fulcrum test may help in the early detection of femoral shaft stress fractures and in guiding follow-up treatment [2]. Because of the limitations of physical examination, imaging is always indicated when a patient has symptoms of stress injury to the hip joint. Compared with radiography, bone scintigraphy, and CT, MRI is the most accurate imaging technique for early diagnosis of bony stress injury [3, 4]. MRI can help guide management by defining the exact anatomic location and facilitating grading of the degree of stress injury. For example, a stress injury to the femoral neck with a cortical fracture necessitates abstention from weightbearing and close monitoring for progression of the damage and the need for internal fixation [5]. On the other hand, isolated periostitis at the lesser trochanter or abnormalities limited to the iliopsoas tendon may necessitate only a short period of modification of activity. The aim of this study was to assess the MRI findings associated with symptomatic stress injuries at the lesser trochanter in long-distance runners to develop guidelines for clinical management. Materials and Methods Retrospective MRI evaluation was performed in the cases of nine long-distance runners (seven women, two men; mean age, 28.8 years; range, 19 38 years) consecutively registered with MRI evidence of stress injury at the lesser trochanter. All patients presented with anterior hip, thigh, or 1616 AJR:190, June 2008

Stress Injury Around Lesser Trochanter groin pain aggravated by weightbearing activity. The pain had developed during training for marathons or competition for club or university running teams. The primary imaging criterion for inclusion in the study was bone marrow edema at the lesser trochanter. All patients underwent MRI with a 1.5-T system (Signa, GE Healthcare) and a torso phasedarray coil. T1-weighted spin-echo imaging was performed at a TR of 800 milliseconds and a minimum TE, typically 15 18 milliseconds. Fatsuppressed proton-density or T2-weighted imaging was performed at a TR/TE of 4,000/54 72 and a matrix size of 512 192 for coronal images and 256 192 for axial images. Two signal averages were performed. The imaging planes were coronal and axial; sup plementary sagittal images were obtained in some cases. Each imaging study was evaluated by consensus by two board-certified radiologists specialized in reading musculoskeletal MR images. The criteria for a diagnosis of bone marrow edema were intramedullary low signal intensity on T1-weighted images and intramedullary high signal intensity on T2-weighted images that were significantly different from the surrounding signal intensity in the medullary cavity. A fracture was diagnosed when a line of low signal intensity was surrounded by abnormal signal intensity in the medullary cavity. Periostitis was diagnosed when a thin band of high signal intensity was seen adjacent to the cortex on T2-weighted images. Criteria for iliopsoas insertional tendinopathy included thick ening or abnormal signal intensity in the tendon or abnormal signal intensity around the tendon. MRI was performed at initial presentation of all patients. One patient, a 36-year-old woman who was a marathon runner, underwent follow-up MRI 6 weeks after the initial study. She had not followed activity restrictions, and the symptoms had worsened. The other patients did not need additional MRI; they had followed treatment recommendations, and the symptoms had not progressed. Results The following findings were seen in all patients: abnormalities associated with the iliopsoas tendon at its insertion, periostitis near the lesser trochanter, and varying degrees of marrow edema extending from the lesser trochanter into the medial inferior aspect of the femoral neck (Table 1). Examples of lesser trochanters with normal MRI features are shown in Figures 1 and 2. The center of the lesser trochanter was identified as a protuberance where the thick, low-signal-intensity psoas tendon inserts. It is important to recognize that at this level, a low-signal-intensity strut of bone projecting TABLE 1: Summary of MRI Findings at Lesser Trochanter Sex Femoral Neck Marrow Edema Lesser Trochanter into the medullary cavity represents the normal calcar femorale, which should not be mistaken for a fracture line. Bone marrow edema was represented by high signal intensity in the medullary space of the lesser trochanter on fat-suppressed T2- weighted images (Figs. 3 and 4). In all patients, varying degrees of bone marrow edema extended to the medial inferior aspect of the femoral neck immediately superior to the lesser trochanter. Periosteal reaction at the lesser trochanter was represented by fluid Iliopsoas Findings a Fracture Line Contralateral Hip F b Present, present Present, present Present, present Absent, present Normal, normal F Present Present Present Present Normal F Present Present Present Absent Normal F Present Present Present Absent Not depicted F Present Present Present Absent Not depicted M Present Present Present Absent Not depicted F Present Absent Present Present Normal M Present Present Present Absent Normal M Present Present Present Absent Normal a Iliopsoas findings were thickening of the tendon or peritendinous edema near its attachment to the lesser trochanter. b Patient was the only one to undergo follow-up imaging. The first finding was made at the initial MRI examination and the second at follow-up. Fig. 1 36-year-old man with normal lesser trochanter. Axial fat-suppressed T2-weighted MR image shows no decrease in marrow signal intensity at lesser trochanter compared with elsewhere in medullary space. Normal calcar femorale (arrow) should not be mistaken for a fracture line. Fig. 2 27-year-old man with normal lesser trochanter. Coronal fat-suppressed T2-weighted MR image shows no decrease in marrow signal intensity at lesser trochanter compared with elsewhere in medullary space. signal intensity along the periosteal surface of bone in this region (Figs. 3 and 4). On long-t2-weighted images abnormalities associated with the iliopsoas muscle and tendon included thickening of the tendon and high signal intensity around the tendon at its insertion on the lesser trochanter. This finding represented fluid or soft-tissue edema at the enthesis (Figs. 3 and 4). Three of nine patients had visible fracture lines. The lines were approximately 1 cm long, extended slightly obliquely in the medial AJR:190, June 2008 1617

Nguyen et al. A D G Fig. 3 36-year-old woman marathon runner with groin pain after long run. A and B, Coronal (A) and axial (B) T2-weighted fat-suppressed MR images through lesser trochanter obtained at initial presentation show thickening of right iliopsoas tendon and surrounding soft-tissue edema near insertion of tendon on lesser trochanter (solid arrow) and marrow edema at anterior aspect of lesser trochanter (dashed arrow, A). C and D, Coronal (C) and axial (D) T2-weighted MR images through femoral neck obtained at initial presentation show soft-tissue edema surrounding distal right iliopsoas tendon (straight solid arrow) slightly proximal to its insertion and marrow edema extending to inferomedial femoral neck (dashed arrow, C). High signal intensity represents elevation of periosteum (curved arrow, D) off cortex of inferomedial femoral neck. E and F, Two months after A D, patient, who had not restricted weightbearing, returned with worsened hip and groin pain. Coronal (E) and axial (F) T2-weighted MR images show area of bone marrow edema in right lesser trochanter (dashed arrow) has enlarged. Abnormal high signal intensity of soft tissues surrounding iliopsoas tendon (solid arrow) has progressed slightly. G, Coronal T2-weighted MR image shows small line of low signal intensity in inferomedial femoral neck (dashed arrow) representing fracture line. Abnormal high signal intensity of soft tissues surrounding iliopsoas tendon (solid arrow) has progressed slightly. H, T2-weighted MR image shows abnormally high signal intensity of soft tissues surrounding iliopsoas tendon (solid straight arrow) has progressed slightly. Periosteal edema (curved arrow) is more prominent than in D. Dashed arrow indicates line of low signal intensity in inferomedial femoral neck. femoral neck, and were visible on both T1- and T2-weighted images (Fig. 3G). One patient had follow-up imaging findings that showed progression from an initial presentation of only marrow edema and iliopsoas insertion findings to cortical fracture 6 weeks later (Figs. 3E 3H). No patient had evidence of bony avulsion of the lesser trochanter. In the cases of six of the patients (seven sets of images), the contralateral asymptomatic hip was included in the imaging field of view (Table 1). In none of these cases were abnormalities, such as peritendinous edema or bone marrow edema, present around the contralateral lesser trochanter. B E H Discussion The most notable observation in the runners in this study was a consistent constellation of findings that accompanied marrow edema at the lesser trochanter: abnormalities associated with the iliopsoas tendon and its insertion, including marrow edema at the lesser trochanter; periostitis around the lesser trochanter; and bone marrow edema in the femoral neck. Each of these findings in isolation is nonspecific and can occur in both stress reactions and enthesopathy, hence the potential for confusing one diagnosis for the other. The enthesis is defined as the site of attachment of tendons and ligaments to bone. It includes the adjacent inserting tendon, the periosteum, and the bone at the attachment site [6]. Periostitis occurs in enthesopathy but also has been described as an early-grade bone stress reaction at several sites in the body [7, 8]. Bone marrow edema is often found at many sites of tendon and ligamentous avulsion injury (enthesopathy) [9, 10] but also occurs in stress injury. Stress reactions are caused by undue stresses that lead to an imbalance in bone remodeling, local osteopenia, and microfractures, which manifest on MRI as bone marrow edema. Unchecked, this microscopic damage can accumulate and result in a macroscopic fracture visible on MRI as a line of low signal intensity [7, 8]. We believe that when these abnormalities are found together, especially at the lesser trochanter, bony stress injury should be suspected. The extension of marrow edema from the lesser trochanter to the inferior medial femoral neck is particularly worrisome for a femoral neck stress reaction. It is important to differentiate iliopsoas insertional tendinopathy or enthesopathy from a bone stress reaction because of the marked differences in management. Initial therapy for musculotendinous injuries typically consists of stretching, strengthening exercises, and in some cases, local corticosteroid injection [11]. By contrast, protected weightbearing is indicated for bony stress injuries of the femoral C F 1618 AJR:190, June 2008

Stress Injury Around Lesser Trochanter A Fig. 4 21-year-old man on university cross country team presented after 2-week history of right hip pain, which had worsened since patient stopped running. Threephase bone scan (not shown) depicted increased uptake at insertion of distal iliopsoas muscle and tendon. A, Coronal fat-suppressed T2-weighted image shows marrow edema in lesser trochanter (solid arrow) extending to inferomedial femoral neck (dashed arrow). B and C, Axial fat-suppressed T2-weighted images through lesser trochanter (B) and inferior femoral neck (C) show marrow edema in lesser trochanter (dashed arrow, B) and inferior femoral neck (dashed arrow, C), thickening of iliopsoas tendon (solid arrow), and soft-tissue edema surrounding tendon. Periosteal edema (arrowhead, B) is evident along femoral neck and lesser trochanter. neck [12]. We believe that in runners, the location of marrow edema at the lesser trochanter signifies the earliest phase of a bony stress reaction and not merely enthesopathy. Several potential explanations exist for the tendency of iliopsoas enthesopathy and femoral basocervical stress reactions to occur together in runners. We postulate that during long-distance running, chronic traction forces from the iliopsoas muscle, a powerful hip flexor, place undue stress on the femoral neck [9, 10]. Endorsing this theory are results with biomechanical models showing that contraction of the iliopsoas muscle increases axial bending strain on the medial aspect of the femoral neck to produce femoral neck fractures [13, 14]. A second potential mechanism involves decreased shielding of bone related to muscle fatigue. With extensive training or long runs, muscle fatigue is thought to result in more load transmission to bone, thereby increasing the risk of osseous injury [15, 16]. Because musculotendinous units are prone to injury, the iliopsoas musculotendinous unit can be injured by repetitive, excessive, or unbalanced contraction of the iliopsoas muscle during running [17]. The flexor musculotendinous unit acts as a shock-absorbing spring during running [18], and injury to this structure can expose the femoral neck to injury during running, especially at push-off. Injury to the tendon near its insertion can cause reactive marrow edema at the lesser trochanter and place forces at the inferomedial femoral neck that expose this site to stress injury, giving rise to the constellation of findings found in our patients. That findings at the lesser trochanter can precede a stress fracture of the inferomedial femoral neck is supported by the visualization of temporal progression to a stress fracture in one patient who did not follow recommendations for activity restriction and had worsening of symptoms, for which follow-up imaging was performed. The relation to femoral neck fracture is further suggested by identification of two other patients who had a fracture line in the medial femoral neck. Although these patients did not have previous images to show temporal progression from findings isolated to the lesser trochanter from a femoral neck fracture, femoral neck fracture was shown to coexist with other abnormalities at the lesser trochanter, as for other patients in this series. In previously devised MRI-based schemes for grading bone stress injury, the sole presence of periostitis is assigned grade 1. The addition of bone marrow edema constitutes grades 2 and 3, depending on severity. The B presence of a fracture line without displacement constitutes grade 4. To our knowledge, such a grading system has been applied to the femoral shaft [4, 7, 8] and tibial shaft [7] but not to the lesser trochanter or basocervical femoral neck fracture. On the basis of the findings in our limited case series, we recommend that patients with evidence of marrow edema (grade 2 and greater) in the lesser trochanter be treated as if they have a stress injury and be required to refrain from any running or impact activities until symptoms subside. If there is any significant extension of the edema into the inferior femoral neck, the patient should be treated with a period of protected weightbearing and close monitoring for assessment of progression. Stress injuries are increasing in frequency owing to the increasing popularity of marathon training and other endurance sports. Because MRI can show subtle periosteal edema, marrow edema, and fracture lines not seen on radiographs, MRI is probably the most valuable tool for detecting symptomatic stress reactions in distance runners. Although it is well known that early stress injuries can pro gress to frank fractures, to our knowledge, such progression around the lesser trochanter has not been previously documented. The potential relation C AJR:190, June 2008 1619

Nguyen et al. between abnormalities at the lesser trochanter and basocervical femoral neck stress fractures has not been previously described, to our knowledge. We conclude that abnormalities at the lesser trochanter can indicate impending femoral neck stress injury in runners. Conservative treatment recommendations are indicated along with a period of activity restriction and possibly protected weightbearing. References 1. Clement DB, Ammann W, Taunton JE, et al. Exercise-induced stress injuries to the femur. Int J Sports Med 1993; 14:347 352 2. Johnson AW, Weiss CB Jr, Wheeler DL. Stress fractures of the femoral shaft in athletes more common than expected: a new clinical test. Am J Sports Med 1994; 22:248 256 3. Shin AY, Morin WD, Gorman JD, Jones SB, Lapinsky AS. The superiority of magnetic resonance imaging in differentiating the cause of hip pain in endurance athletes. Am J Sports Med 1996; 24:168 176 4. Arendt EA, Griffiths HJ. The use of MR imaging in the assessment and clinical management of stress reactions of bone in high-performance athletes. Clin Sports Med 1997; 16:291 306 5. Bergman AG, Fredericson M. MR imaging of stress reactions, muscle injuries, and other overuse injuries in runners. Magn Reson Imaging Clin N Am 1999; 7:151 174 6. Resnick D, Niwayama G. Entheses and enthesopathy: anatomical, pathological, and radiological correlation. Radiology 1983; 146:1 9 7. Fredericson M, Bergman AG, Hoffman KL, Dillingham MS. Tibial stress reaction in runners: correlation of clinical symptoms and scintigraphy with a new magnetic resonance imaging grading system. Am J Sports Med 1995; 23:472 481 8. Anderson MW, Kaplan PA, Dussault RG. Adductor insertion avulsion syndrome (thigh splints): spectrum of MR imaging features. AJR 2001; 177:673 675 9. Huang GS, Yu JS, Munshi M, et al. Avulsion fracture of the head of the fibula (the arcuate sign): MR imaging findings predictive of injuries to the posterolateral ligaments and posterior cruciate ligament. AJR 2003; 180:381 387 10. Stevens MA, El-Khoury GY, Kathol MH, Brandser EA, Chow S. Imaging features of avulsion injuries. RadioGraphics 1999; 19:655 672 11. Adler RS, Buly R, Ambrose R, Sculco T. Diagnostic and therapeutic use of sonography-guided iliopsoas peritendinous injections. AJR 2005; 185:940 943 12. Johnston CA, Wiley JP, Lindsay DM, Wiseman DA. Iliopsoas bursitis and tendinitis: a review. Sports Med 1998; 25:271 283 13. Yang KH, Shen KL, Demetropoulos CK, et al. The relationship between loading conditions and fracture patterns of the proximal femur. J Biomech Eng 1996; 118:575 578 14. Simoes JA, Vaz MA, Blatcher S, Taylor M. Influence of head constraint and muscle forces on the strain distribution within the intact femur. Med Eng Phys 2000; 22:453 459 15. Miller C, Major N, Toth A. Pelvic stress injuries in the athlete: management and prevention. Sports Med 2003; 33:1003 1012 16. Pentecost RL, Murray RA, Brindley HH. Fatigue, insufficiency, and pathologic fractures. JAMA 1964; 187:1001 1004 17. Moore JS. Function, structure, and responses of components of the muscle-tendon unit. Occup Med 1992; 7:713 740 18. Arendt EA. Stress fractures and the female athlete. Clin Orthop Relat Res 2000; Mar:131 138 1620 AJR:190, June 2008