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Original Report |
1
Department of Radiology, University of Virginia Health Sciences Center, Box
170, Charlottesville, VA 22908.
2
Department of Orthopaedic Surgery, University of Virginia Health Sciences
Center, Charlottesville, VA 22908.
3
Present address: Department of Bone and Joint Radiology, Massachusetts General
Hospital, 15 Parkman St., WACC 515, Boston, MA 02114-3117.
Received December 11, 2000;
accepted after revision March 14, 2001.
Address correspondence to M. W. Anderson.
Abstract
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CONCLUSION. Symptoms of vague hip, groin, or thigh pain may be associated with stress-related changes in the proximal to mid femoral shaft (thigh splints). When interpreting MR imaging studies of the pelvis in patients presenting with these symptoms, careful attention should be directed to this portion of the femur. This is especially important because the findings may be subtle, and this region is often at the distal edge of most MR imaging studies of the pelvis and hip.
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Stress-related injuries are one source of hip pain and commonly involve the bones of the pelvis or the femoral neck. Stress fractures involving the femoral shaft are less common. Another stress-related injury in the femoral region is the adductor insertion avulsion syndrome, also known as "thigh splints" [1, 2]. This syndrome is thought to represent an avulsive injury of the proximal femoral shaft related to one or more of the adductor muscles that insert in this region. Radiographic and bone scan findings in patients with this syndrome have been reported previously. We present five cases of this femoral injury identified using MR imaging.
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Conventional radiography and MR imaging studies were performed within 10 days of each other in all patients. MR scanning was performed on a 1.5-T magnet (Vision and Symphony; Siemens, Erlangen, Germany). We used a body coil to obtain coronal T1-weighted images and turbo spin-echo inversion recovery images in the coronal plane. The parameters for T1-weighted images included TR range/TE range, 500-760/12-20. Turbo spin-echo inversion recovery images included the following parameters: 4000-8000/30-60; inversion time, 150 msec; echo train length, 7; field of view, 300-400 mm; imaging matrix, 287-484 x 512; and number of signal acquisitions, 1. Radiographs and MR images were reviewed by one of three musculoskeletal radiologists. In one patient, follow-up radiographs and MR images were obtained 6 months after the original studies.
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Initial radiographs of the pelvis or affected femur revealed normal findings in all five patients.
A thin rim of high signal intensity on turbo spin-echo inversion recovery images was observed along the medial periosteum of the proximal to mid femoral shaft in all five patients. The length of involvement varied from 4 to 9 cm (mean, 5.6 cm), but the abnormalities were consistently present along the posteromedial aspect of the femoral shaft at the level of the adductor muscle insertions (Fig. 1).
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Abnormally increased signal intensity was identified in the underlying marrow in four of the five patients at the level of the periosteal signal abnormality (Fig. 2A,2B,2C). In three of these four patients, abnormal signal intensity was also seen in the adjacent cortex, consistent with developing stress fractures (Fig. 3A,3B,3C). One of the patients presented with bilateral groin pain and was found to have abnormal periosteal, medullary, and cortical signal intensity involving the proximal to mid portions of both femurs.
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All patients were instructed to rest and were treated with conservative therapy; their symptoms resolved in 1-2 months. Follow-up radiographs of the femur were obtained in one patient 6 months after the initial imaging studies and showed mild cortical thickening along the medial femoral shaft at the site of the prior MR imaging abnormalities (Fig. 2A,2B,2C). A follow-up MR examination performed at that time revealed complete resolution of the periosteal, cortical, and medullary signal intensity abnormalities that were identified on the original scan.
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A different type of stress injury is thought to be related to repetitive avulsive stresses at tendinous insertions on a bone, leading to a traction periostitis at these sites. The most well-known example is the shin splints syndrome that affects the tibia at the attachment of the soleus muscle, also known as the posteromedial tibial stress syndrome. Radiographs often reveal normal findings but may also reveal areas of periosteal new bone formation. The classic scintigraphic appearance is that of elongated foci of increased uptake along the tibia on delayed images without evidence of a stress fracture [3]. MR imaging of patients presenting with acute shin splints shows a spectrum of findings ranging from periosteal edema or fluid to abnormal signal intensity in the medullary cavity or cortex, which correspond to stress reactions and stress fractures, respectively [4].
Similar to shin splints, the adductor insertion avulsion syndrome, or thigh splints, has been described in the proximal to mid femur [1, 2]. These patients present with activity-related groin pain that is relieved with rest. Findings on physical examination include increased adductor tone and tenderness over the adductor muscles, as well as severe pain with active resistance to hip adduction and external rotation. Radiographs may show periosteal reaction along the proximal third of the medial femoral shaft near the insertions of the adductor brevis and longus muscles. Bone scan findings include abnormal, elongated, linear uptake along the medial and, to a lesser degree, lateral cortexes of the proximal to mid femur, without evidence of a focal stress fracture. In one report, the length of involvement ranged from 15% to 44% of the femoral shaft [1].
The periosteal changes along the proximal to mid femur in patients with thigh splints are thought to be related to the pull of the adductor longus and brevis tendons that insert along the femur at these levels. This hypothesis is supported by the linear high signal intensity, compatible with periostitis, that was present in all our patients along the medial femoral cortex on turbo spin-echo inversion recovery images.
Stress fractures have also been described in this portion of the femur and often display an oblique orientation [5,6,7]. The abnormal signal intensity in the underlying marrow in four of our patients is compatible with an area of stress reaction rather than a traction periostitis, and the cortical signal abnormality seen in two patients is consistent with a developing stress fracture. This suggests that thigh splints are likely in the early stage of a developing osseous stress reaction or fracture and therefore may carry a more ominous prognosis for an athlete who wants to continue training. This also highlights the importance of completely imaging the abnormal area to provide accurate staging of the abnormality with MR imaging [8].
The location of this disorder places it at the edge of the field of view for a typical MR imaging study of the pelvis or hips. An awareness of this entity should lead to the use of a larger field of view when performing a screening MR study in a patient with hip or thigh pain. Also, when analyzing the images, careful attention should be directed to the medial periosteum of the proximal to mid femoral shaft, because the thin line of high signal intensity can easily be missed or misconstrued for a vessel.
The differential diagnosis for this MR appearance includes tumor and osteomyelitis. However, the absence of an abnormal signal intensity in the medullary cavity in many cases, especially on T1-weighted images, and the absence of a soft-tissue mass, argue against these entities. The MR imaging findings described in our patients should prompt a provisional diagnosis of a stress-related injury, and a trial of conservative therapy should be instituted before a biopsy is performed. These injuries usually respond relatively quickly to rest, which is evidenced by the resolution of symptoms in all our patients after 1-2 months. Short-term follow-up imaging can also be useful, because the radiologic visualization of a fracture line is diagnostic.
In conclusion, we have described the MR imaging findings of the adductor insertion avulsion syndrome (thigh splints). Although MR imaging shows some features of a traction periostitis, we believe this syndrome represents an early phase along the continuum of osseous fatigue damage that may lead to a frank stress fracture if not recognized.
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