- Email: [email protected]
Femoroacetabular impingement: bone marrow oedema associated with fibrocystic change of the femoral head and neck junction
Clinical Radiology (2007) 62, 472e478
Femoroacetabular impingement: bone marrow oedema associated with fibrocystic change of the femoral head and neck junction S.L.J. Jamesa,b,*, D.A. Connella, P. O’Donnella, A. Saifuddina a
Department of Radiology, RNOH Stanmore, Stanmore, Middlesex, UK, and Department of Radiology, The Royal Orthopaedic Hospital, Birmingham, UK
b
Received 29 August 2006; received in revised form 24 October 2006; accepted 8 November 2006
AIM: To describe the association of bone marrow oedema adjacent to areas of fibrocystic change at the femoral head and neck junction in patients with femoroacetabular impingement. MATERIALS AND METHODS: The clinical and imaging findings in six patients with bone marrow oedema adjacent to an area of fibrocystic change at the femoral head and neck junction are presented. There were five males and one female (age range 19e42 years, mean age 34.5 years). Three patients were referred with a clinical suspicion of femoroacetabular impingement, two with suspected osteoid osteoma and one with a clinical diagnosis of sciatica. The volume of bone marrow oedema (grade 1: 0e25%, grade 2: 26e50%, grade 3: 51e75% and grade 4: 76e100% of the femoral neck width), presence of labral and articular cartilage abnormality, joint effusion, and femoral head and neck morphology were recorded. RESULTS: Magnetic resonance imaging (MRI) identified fibrocystic change in the anterolateral aspect of the femoral head and neck junction in all cases (mean size 9 mm, range 5e14 mm, three multilocular and three unilocular cysts). The volume of oedema was variable (one grade 1, two grade 2, one grade 3 and two grade 4). All patients had abnormality of the anterosuperior labrum with five patients demonstrating chondral loss. An abnormal femoral head and neck junction was identified in five patients. CONCLUSION: The radiological finding of fibrocystic change at the anterosuperior femoral neck with or without bone marrow oedema should prompt the search for femoroacetabular impingement. Bone marrow oedema may rarely be identified adjacent to these areas of cystic change and should be considered in the differential diagnosis of bone marrow oedema in the femoral neck. ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction Femoroacetabular impingement is recognized as a cause of intermittent hip or groin pain that may be exacerbated by physical activity in young adults.1 It has been suggested that certain abnormal morphological features of the femoral head or acetabulum lead to abnormal abutment between the proximal femur and acetabular rim in terminal hip motion.1 Clinical examination is directed towards the demonstration of impingement, particularly in flexion, * Guarantor and correspondent: S.L.J. James, Department of Radiology, RNOH Stanmore, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK. Tel.: þ44 208 9542300; fax: þ44 208 9095281. E-mail address: [email protected] (S.L.J. James).
adduction and internal rotation. Imaging studies may identify a variety of findings, including anterosuperior labral and chondral abnormality and abnormal bony prominence and fibrocystic change at the femoral head and neck junction.2e5 It is important to recognize the presence of femoroacetabular impingement as it has been postulated that early intervention may prevent the development of premature osteoarthritis.1 The diagnosis of femoroacetabular impingement is therefore made using a combination of clinical examination and imaging. Arthroscopy confirms the diagnosis and allows therapeutic intervention to be undertaken. Six patients are described who had fibrocystic change in the anterolateral femoral head with
0009-9260/$ - see front matter ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2006.11.022
Bone marrow oedema associated with femoroacetabular impingement
a clinical assessment and magnetic resonance imaging (MRI) features consistent with femoroacetabular impingement. In the present cases, extensive marrow oedema was identified adjacent to these areas of fibrocystic change. Fibrocystic change has been identified in the asymptomatic population and is frequently termed a ‘‘herniation pit’’.6 To the authors’ knowledge, there have been no previous reports of bone marrow oedema identified on MRI in association with fibrocystic change of the femoral head and neck junction in patients with femoroacetabular impingement.
473
of fibrocystic change at the femoral head and neck junction, volume of bone marrow oedema (grade 1: 0e25%, grade 2: 26e50%, grade 3: 51e75% and grade 4: 76e100% of the femoral neck width), labral abnormality, acetabular cartilage abnormality, femoral head abnormal morphology and the presence of a joint effusion. Only cases encountered in routine clinical practice with femoroacetabular impingement that demonstrated bone marrow oedema adjacent to an area of fibrocystic change were included in the study.
Results Materials and methods Six cases were collected over a 1-year period from a number of institutions at which the authors practise. There were five males and one female, age range 19e42 years, mean age 34.5 years. Three of the patients were referred with a clinical suspicion of femoroacetabular impingement, and subsequent imaging confirmed this initial impression. Two of the patients were referred to our tertiary referral centre for orthopaedic oncology with a clinical suspicion of an osteoid osteoma after imaging at other institutions. The final patient presented with a short history of right-sided sciatica. The initial suspected diagnosis was of a disc prolapse, but MRI of the lumbar spine was entirely normal. In the latter three cases, imaging review and further clinical consultation allowed the correct diagnosis to be reached. Approval from our institutional review board was not required for the retrospective review of case notes and imaging studies used in this study. As imaging was performed at a number of institutions, a combination of radiographs, computed tomography (CT) and MRI was available for review. Four of the patients were imaged using the preferred protocol for MRI of the hip. This involved a surface coil strapped over the hip and centred over the region of the femoral head. An axial localizing image was obtained followed by: (1) axial and coronal proton density fast spin-echo (FSE) imaging [repetition time (TR)/echo time (TE) 4000 ms/34 ms]; (2) sagittal oblique fast spinecho sequence plotted from the axial images 10 oblique from the midline (TR/TE 4000 ms/34 ms); (3) coronal short tau inversion recovery (STIR) imaging (TR/TE 4500 ms/24 ms). The two patients who underwent MRI at outside institutions had a combination of T1, STIR and T2 weighted sequences. MR arthrography was available in one patient. Retrospective image review allowed the following information to be included: the presence
The clinical features and imaging findings of the patients are listed in Table 1. The patients consisted of predominantly young men, with symptoms exacerbated by a variety of sporting activities. Clinical examination revealed findings consistent with femoroacetabular impingment, although this was only apparent on repeat clinical examination in two of the cases. Fibrocystic change was identified in all cases on MRI in the anterolateral aspect of the femoral head and neck junction and CT correlation was available in two cases (Fig. 1a,b). The mean size of the cysts was 9 mm, range 5e14 mm. Three of the cystic regions were unilocular (Fig. 1a,b) and three were multilocular (Fig. 2a,b). Variable amounts of bone marrow oedema were identified (Fig. 3a,b). The size of the cystic alteration and presence of multiple cysts did not correlate with greater amounts of bone marrow oedema. All patients demonstrated an abnormal cleft at the labral chondral transitional zone in the anterosuperior region with adjacent cartilage loss in five of the six patients (Fig. 4). Abnormal bony prominence of the femoral head and neck junction (Fig. 5) was present in five patients, and abnormal acetabular morphology was not evident in any of the cases.
Discussion Femoroacetabular impingement usually affects young adults who describing intermittent hip or groin pain, frequently exacerbated by sporting activity.1 Examination reveals pain on flexion, internal rotation and adduction as the femoral head abuts the acetabular rim.1 Two types of femoroacetabular impingement have been proposed, the ‘‘cam’’ and ‘‘pincer’’ type. The ‘‘cam’’ impingement, more commonly seen in young males, refers to an abnormally prominent femoral head and neck junction that causes a shearing force at
474
Table 1 Age
Sex
Clinical features and imaging findings of patients with bone marrow oedema adjacent to an area of fibrocystic change at the femoral head and neck junction Side
42
M
R
30
M
L
39
M
R
19
M
L
35
F
R
42
M
R
Clinical history
Clinical examination
CT and MRI findings Fibrocystic change
Bone marrow oedema
Labral abnormality
Cartilage abnormality
Femoral head and neck junction abnormality
Joint effusion
Discomfort exacerbated by running Pain exacerbated by sporting activity, particularly rowing Pain radiating from hip to thigh on exercise Groin pain exacerbated by cycling Hip pain exacerbated by dancing Groin pain exacerbated by squash
Pain on flexion, internal rotation and adduction Pain on internal rotation and adduction Pain on hip flexion
Anterolateral Solitary 7 mm maximum dimension Anterolateral Multiloculated 11 mm maximum dimension Anterolateral Solitary 5 mm maximum dimension Anterolateral Multiloculated 12 mm maximum dimension Anterolateral Solitary 6 mm maximum dimension Anterolateral Multiloculated 14 mm
Grade 3
Anterosuperior labral lesion
Anterosuperior cartilage thinning
Nil
Grade 2
Anterosuperior labral lesion
Anterosuperior cartilage thinning
Grade 4
Anterosuperior labral lesion
Anterosuperior cartilage thinning
Grade 4
Anterosuperior labral lesion
Anterosuperior cartilage thinning
Grade 2
Anterosuperior labral lesion
Nil
Bony prominence head and neck junction Bony prominence head and neck junction Bony prominence head and neck junction Bony prominence head and neck junction Nil
Grade 1
Anterosuperior labral lesion
Full-thickness loss anterosuperior cartilage
Bony prominence head and neck junction
Pain on flexion, internal rotation and adduction Pain on flexion, internal rotation and adduction Pain on internal rotation
Nil
Nil
Mild
Mild
Mild
S.L.J. James et al.
Bone marrow oedema associated with femoroacetabular impingement
475
Figure 1 (a) Axial T2-weighted MRI image demonstrating the unilocular cyst involving the femoral head and neck junction (arrow). (b) Axial CT through the femoral neck demonstrating an anteriorly unilocular cyst at the femoral head and neck junction (arrow).
the acetabular labral chondral transitional zone in flexion. It has been postulated by a number of authors that this may be related to a variety of causes, including subclinical slipped capital femoral epiphysis, previous traumatic injury, postsurgical osteotomy, reduced antetorsion of the femoral head, and post-Perthes disease.7e10 The ‘‘pincer’’ type, more frequently encountered in middle-aged women, describes an abnormal acetabular shape that may also reduce femoral head
clearance and provide a source of impingement.1 Potential causes of the pincer type impingement include acetabular retroversion, protrusio acetabulae and coxa profunda.2 Fibrocystic change at the anterosuperior femoral head and neck junction is described in patients with femoroacetabular impingement.2e4 However, there is some controversy as to whether the cystic change is due to impingement, or whether it represents a separate, more indolent process, as in its
Figure 2 (a) Coronal STIR MRI image demonstrating a multiloculated cyst in the proximal femur with some adjacent bone marrow oedema. (b) Coronal CT reformat confirming the multilocular nature of the fibrocystic change.
476
S.L.J. James et al.
Figure 3 (a) Coronal STIR MRI image demonstrating intense bone marrow oedema at the femoral head and neck junction (arrow). The bone marrow oedema surrounded the cystic lesion illustrated in Fig. 1. (b) Coronal STIR MRI image demonstrating intense bone marrow oedema at the femoral head and neck junction (arrowhead). Prominence of the femoral head and neck junction is evident (black arrow) and a high signal cleft is identified at the base of the acetabular labrum (white arrow).
original description as a herniation pit.6 Pitt and co-workers6 described the cystic alterations at the anterosuperior femoral head and neck junction and proposed that synovial tissue may herniate through defects in the cortical bone of the femoral neck. Furthermore, the pressure of the iliofemoral ligament on the anteromedial joint capsule has been implicated as a possible cause for this herniation. These herniation pits have been considered
a normal variant with an incidence of between 5 and 12%.6,11 Leunig and co-workers3 describe the high prevalence of juxta-articular fibrocystic change at the anterosuperior femoral head and neck junction. They found 33% of the patients included in their series demonstrated this radiographic finding and suggest that femoroacetabular impingement may be causal in the development of this cystic change.3 This group also studied a cohort
Figure 4 Coronal fat-suppressed T1-weighted MR arthrogram image demonstrating contrast extending into a cleft at the base of the acetabular labrum (arrow).
Figure 5 Axial proton density FSE image demonstrating abnormal osseous prominence at the femoral head and neck junction.
Bone marrow oedema associated with femoroacetabular impingement
of patients with developmental hip dysplasia and found none of the 132 hips had evidence of herniation pits. They concluded that this supported their hypothesis that herniation pits may be caused by the repetitive contact between the femoral head and acetabular rim.3 Subsequently, further workers have shown a 24% incidence of fibrocystic change at the femoral head and neck junction in femoroacetabular impingement.2 However, Kassarjian et al.4 identified synovial herniation pits in only 5% of their series, an equivalent incidence to that previously quoted in the normal population.4 A number of series do not describe cystic change at the femoral head and neck junction as being present or a feature in their cases of femoroacetabular impingement.5,7,8,12 However, it is important to note that morphological changes of the femoral head and neck are frequently identified in patients with femoroacetabular impingement,7,8 and that the original descriptions of herniation pits also describe alterations at the femoral head and neck junction.11 Leunig and co-workers3 also studied the spatial relationship between the fibrocystic change and the acetabular rim using a combination of dynamic MRI and intra-operative observations. They found intra-operative evidence of bony contusions at the anterosuperior femoral head and neck junction close to the areas of fibrocystic change. This contact occurred in flexion and internal rotation and they hypothesized that the pressure induced in flexion may produce the fibrocystic change. Of particular relevance to the current study, they found no cases of marrow oedema in the 39 of 117 hips with fibrocystic change in the femoral head. They hypothesized that this may relate to a slow repetitive process rather than forceful impaction as the mechanism of fibrocystic change.3 In the cases included in this series, marrow oedema was demonstrated in the femoral neck adjacent to the areas of cystic change. This may relate to ongoing impaction between the femoral head and acetabulum sufficient to cause bone marrow oedema in these patients with femoroacetabular impingement. This may support the hypothesis proposed by Leunig and co-workers that herniation pits may be caused by the repetitive contact between the femoral head and acetabular rim. However, their assumption that the process relates to a slow repetitive process may not be entirely true. MRI is the technique of choice in the identification of the labral and chondral abnormality demonstrated in patients with femoroacetabular impingement. A number of workers have described the MR arthrographic findings,4,5,11 and more
477
recently James and co-workers reported the noncontrast enhanced MRI appearances in femoroacetabular impingement using a high-resolution technique.2 If an arthrographic technique is used, it is important that a water-sensitive sequence is included in the protocol as well as fat-suppressed T1-weighted imaging. This facilitates the identification of bone marrow oedema, either related to fibrocystic change at the femoral head and neck junction or in the acetabulum in association with advanced chondromalacia. Both arthrographic and non-arthrographic techniques demonstrate labral and chondral abnormality, most frequently located in an anterosuperior position. In femoroacetabular impingement, an abnormal cleft is typically identified at the labral chondral transitional zone. The repetitive impingement between the femoral head and acetabulum causes a shearing force to be applied at the junction of the labrum and the adjacent acetabular articular cartilage. This is often termed a labral tear; however, this term is frequently used to describe labral diseases that relate to a number of differing aetiologies. True traumatic labral tears are rare, and in patients with acetabular dysplasia, the labrum is elongated and demonstrates abnormal intrasubstance change. Previous workers have recognized anterosuperior acetabular cartilage abnormality in between 78e95%, anterosuperior labral tear in 64e100% and abnormal femoral head and neck shape in 93% of patients.4,5,11 Two of the cases in the present series were referred with a clinical suspicion of osteoid osteoma after initial imaging at other institutions. A combination of CT and MRI characterized the lesion and allowed other diagnoses to be excluded. CT may provide further diagnostic information, demonstrating the nidus in patients with osteoid osteoma or a fracture line. Marrow oedema in the femoral neck may be observed in a number of differing pathological processes including osteoid osteoma, occult fracture or focal areas of avascular necrosis.13e15 The present series suggests that femoroacetabular impingement should be considered in the differential diagnosis of lateral femoral neck bone marrow oedema when this is adjacent to an area of cystic change. There are a number of limitations of this study. A small sample of individuals with femoroacetabular impingement and bone marrow oedema is included. In the senior author’s experience, most patients with fibrocystic change in the anterolateral femoral head do not demonstrate bone marrow oedema on MRI. However, the six cases that are presented do indicate that it may occasionally be identified in femoroacetabular
478
impingement, but it is not known whether this is symptomatic or not. It is noteworthy that in one of the patients included in the present series, MRI of both hips was performed. The patient demonstrated anterosuperior labral and chondral abnormality and fibrocystic change bilaterally. The patient was symptomatic on the right side, which demonstrated bone marrow oedema on MRI. Second, histological correlation of the nature of the cystic alterations identified in the femoral head was not obtained. The term fibrocystic change has been adopted by previous workers to describe these cystic alterations in the femoral head,2e4 but histological correlation of the fibrous component has not been performed in these studies. It may therefore be slightly misleading to use a pathological term to describe an imaging feature. In this article, the clinical presentation and imaging findings were described in six patients with femoroacetabular impingement who demonstrate bone marrow oedema adjacent to areas of fibrocystic change in the femoral head and neck junction. The presence of marrow oedema adjacent to areas of cystic change in the femoral neck should prompt the search for further evidence of femoroacetabular impingement. Marrow oedema may also give further support to the theory that these fibrocystic alterations relate to ongoing impaction between the femoral head and acetabulum.
References 1. Ganz R, Parvizi J, Beck M, et al. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res 2003;417:112e20.
S.L.J. James et al.
2. James SLJ, Ali K, Malara F, et al. MR imaging findings of femoroacetabular impingement. AJR Am J Roentgenol 2006; 187:1412e9. 3. Leunig M, Beck M, Kalhor M, et al. Fibrocystic changes at anterosuperior femoral neck: prevalence in hips with femoroacetabular impingement. Radiology 2005;236:237e46. 4. Kassarjian A, Yoon LS, Belzile E, et al. Triad of MR arthrographic findings in patients with cam-type femoroacetabular impingement. Radiology 2005;236:588e92. 5. Schmid MR, Notzli HP, Zanetti M, et al. Cartilage lesions in the hip: diagnostic effectiveness of MR arthrography. Radiology 2003;226:382e6. 6. Pitt MJ, Graham AR, Shipman JH, et al. Herniaton pit of the femoral neck. AJR Am J Roentgenol 1982;138:1115e21. 7. Notzli HP, Wyss TF, Stoecklin CH, et al. The contour of the femoral headeneck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br 2002;84:556e60. 8. Jager M, Wild A, Westhoff B, et al. Femoroacetabular impingement caused by a femoral osseous headeneck bump deformity: clinical, radiological, and experimental results. J Orthop Sci 2004;9:256e63. 9. Snow SW, Keret D, Scarangella S, et al. Anterior impingement of the femoral head: a late phenomenon of LeggeCalveePerthes’ disease. J Pediatr Orthop 1993;13: 286e9. 10. Eijer H, Ganz R. Anterieur femoro-acetabulair impingement na een mediale collumfractuur. Een casus. Ned Tijdschr Trauma 1999;2:50e2. 11. Daenen B, Preidler KW, Padmanabhan S, et al. Symptomatic herniation pits of the femoral neck: anatomic and clinical study. AJR Am J Roentgenol 1997;168:149e53. 12. Leunig M, Podeszwa D, Beck M, et al. Magnetic resonance arthrography of labral disorders in hips with dysplasia and impingement. Clin Orthop Relat Res 2004;418:74e80. 13. Ehara S, Rosenthal DI, Aoki J, et al. Peritumoral edema in osteoid osteoma on magnetic resonance imaging. Skeletal Radiol 1999;28:265e70. 14. Kim YM, Oh HC, Kim HJ. The pattern of bone marrow oedema on MRI in osteonecrosis of the femoral head. J Bone Joint Surg Br 2000;82:837e41. 15. Theodorou DJ, Theodorou SJ, Haghighi P, et al. Distinct focal lesions of the femoral head: imaging features suggesting an atypical and minimal form of bone necrosis. Skeletal Radiol 2002;31:435e44.
Femoroacetabular impingement: bone marrow oedema associated with fibrocystic change of the femoral head and neck junction S.L.J. Jamesa,b,*, D.A. Connella, P. O’Donnella, A. Saifuddina a
Department of Radiology, RNOH Stanmore, Stanmore, Middlesex, UK, and Department of Radiology, The Royal Orthopaedic Hospital, Birmingham, UK
b
Received 29 August 2006; received in revised form 24 October 2006; accepted 8 November 2006
AIM: To describe the association of bone marrow oedema adjacent to areas of fibrocystic change at the femoral head and neck junction in patients with femoroacetabular impingement. MATERIALS AND METHODS: The clinical and imaging findings in six patients with bone marrow oedema adjacent to an area of fibrocystic change at the femoral head and neck junction are presented. There were five males and one female (age range 19e42 years, mean age 34.5 years). Three patients were referred with a clinical suspicion of femoroacetabular impingement, two with suspected osteoid osteoma and one with a clinical diagnosis of sciatica. The volume of bone marrow oedema (grade 1: 0e25%, grade 2: 26e50%, grade 3: 51e75% and grade 4: 76e100% of the femoral neck width), presence of labral and articular cartilage abnormality, joint effusion, and femoral head and neck morphology were recorded. RESULTS: Magnetic resonance imaging (MRI) identified fibrocystic change in the anterolateral aspect of the femoral head and neck junction in all cases (mean size 9 mm, range 5e14 mm, three multilocular and three unilocular cysts). The volume of oedema was variable (one grade 1, two grade 2, one grade 3 and two grade 4). All patients had abnormality of the anterosuperior labrum with five patients demonstrating chondral loss. An abnormal femoral head and neck junction was identified in five patients. CONCLUSION: The radiological finding of fibrocystic change at the anterosuperior femoral neck with or without bone marrow oedema should prompt the search for femoroacetabular impingement. Bone marrow oedema may rarely be identified adjacent to these areas of cystic change and should be considered in the differential diagnosis of bone marrow oedema in the femoral neck. ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction Femoroacetabular impingement is recognized as a cause of intermittent hip or groin pain that may be exacerbated by physical activity in young adults.1 It has been suggested that certain abnormal morphological features of the femoral head or acetabulum lead to abnormal abutment between the proximal femur and acetabular rim in terminal hip motion.1 Clinical examination is directed towards the demonstration of impingement, particularly in flexion, * Guarantor and correspondent: S.L.J. James, Department of Radiology, RNOH Stanmore, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK. Tel.: þ44 208 9542300; fax: þ44 208 9095281. E-mail address: [email protected] (S.L.J. James).
adduction and internal rotation. Imaging studies may identify a variety of findings, including anterosuperior labral and chondral abnormality and abnormal bony prominence and fibrocystic change at the femoral head and neck junction.2e5 It is important to recognize the presence of femoroacetabular impingement as it has been postulated that early intervention may prevent the development of premature osteoarthritis.1 The diagnosis of femoroacetabular impingement is therefore made using a combination of clinical examination and imaging. Arthroscopy confirms the diagnosis and allows therapeutic intervention to be undertaken. Six patients are described who had fibrocystic change in the anterolateral femoral head with
0009-9260/$ - see front matter ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2006.11.022
Bone marrow oedema associated with femoroacetabular impingement
a clinical assessment and magnetic resonance imaging (MRI) features consistent with femoroacetabular impingement. In the present cases, extensive marrow oedema was identified adjacent to these areas of fibrocystic change. Fibrocystic change has been identified in the asymptomatic population and is frequently termed a ‘‘herniation pit’’.6 To the authors’ knowledge, there have been no previous reports of bone marrow oedema identified on MRI in association with fibrocystic change of the femoral head and neck junction in patients with femoroacetabular impingement.
473
of fibrocystic change at the femoral head and neck junction, volume of bone marrow oedema (grade 1: 0e25%, grade 2: 26e50%, grade 3: 51e75% and grade 4: 76e100% of the femoral neck width), labral abnormality, acetabular cartilage abnormality, femoral head abnormal morphology and the presence of a joint effusion. Only cases encountered in routine clinical practice with femoroacetabular impingement that demonstrated bone marrow oedema adjacent to an area of fibrocystic change were included in the study.
Results Materials and methods Six cases were collected over a 1-year period from a number of institutions at which the authors practise. There were five males and one female, age range 19e42 years, mean age 34.5 years. Three of the patients were referred with a clinical suspicion of femoroacetabular impingement, and subsequent imaging confirmed this initial impression. Two of the patients were referred to our tertiary referral centre for orthopaedic oncology with a clinical suspicion of an osteoid osteoma after imaging at other institutions. The final patient presented with a short history of right-sided sciatica. The initial suspected diagnosis was of a disc prolapse, but MRI of the lumbar spine was entirely normal. In the latter three cases, imaging review and further clinical consultation allowed the correct diagnosis to be reached. Approval from our institutional review board was not required for the retrospective review of case notes and imaging studies used in this study. As imaging was performed at a number of institutions, a combination of radiographs, computed tomography (CT) and MRI was available for review. Four of the patients were imaged using the preferred protocol for MRI of the hip. This involved a surface coil strapped over the hip and centred over the region of the femoral head. An axial localizing image was obtained followed by: (1) axial and coronal proton density fast spin-echo (FSE) imaging [repetition time (TR)/echo time (TE) 4000 ms/34 ms]; (2) sagittal oblique fast spinecho sequence plotted from the axial images 10 oblique from the midline (TR/TE 4000 ms/34 ms); (3) coronal short tau inversion recovery (STIR) imaging (TR/TE 4500 ms/24 ms). The two patients who underwent MRI at outside institutions had a combination of T1, STIR and T2 weighted sequences. MR arthrography was available in one patient. Retrospective image review allowed the following information to be included: the presence
The clinical features and imaging findings of the patients are listed in Table 1. The patients consisted of predominantly young men, with symptoms exacerbated by a variety of sporting activities. Clinical examination revealed findings consistent with femoroacetabular impingment, although this was only apparent on repeat clinical examination in two of the cases. Fibrocystic change was identified in all cases on MRI in the anterolateral aspect of the femoral head and neck junction and CT correlation was available in two cases (Fig. 1a,b). The mean size of the cysts was 9 mm, range 5e14 mm. Three of the cystic regions were unilocular (Fig. 1a,b) and three were multilocular (Fig. 2a,b). Variable amounts of bone marrow oedema were identified (Fig. 3a,b). The size of the cystic alteration and presence of multiple cysts did not correlate with greater amounts of bone marrow oedema. All patients demonstrated an abnormal cleft at the labral chondral transitional zone in the anterosuperior region with adjacent cartilage loss in five of the six patients (Fig. 4). Abnormal bony prominence of the femoral head and neck junction (Fig. 5) was present in five patients, and abnormal acetabular morphology was not evident in any of the cases.
Discussion Femoroacetabular impingement usually affects young adults who describing intermittent hip or groin pain, frequently exacerbated by sporting activity.1 Examination reveals pain on flexion, internal rotation and adduction as the femoral head abuts the acetabular rim.1 Two types of femoroacetabular impingement have been proposed, the ‘‘cam’’ and ‘‘pincer’’ type. The ‘‘cam’’ impingement, more commonly seen in young males, refers to an abnormally prominent femoral head and neck junction that causes a shearing force at
474
Table 1 Age
Sex
Clinical features and imaging findings of patients with bone marrow oedema adjacent to an area of fibrocystic change at the femoral head and neck junction Side
42
M
R
30
M
L
39
M
R
19
M
L
35
F
R
42
M
R
Clinical history
Clinical examination
CT and MRI findings Fibrocystic change
Bone marrow oedema
Labral abnormality
Cartilage abnormality
Femoral head and neck junction abnormality
Joint effusion
Discomfort exacerbated by running Pain exacerbated by sporting activity, particularly rowing Pain radiating from hip to thigh on exercise Groin pain exacerbated by cycling Hip pain exacerbated by dancing Groin pain exacerbated by squash
Pain on flexion, internal rotation and adduction Pain on internal rotation and adduction Pain on hip flexion
Anterolateral Solitary 7 mm maximum dimension Anterolateral Multiloculated 11 mm maximum dimension Anterolateral Solitary 5 mm maximum dimension Anterolateral Multiloculated 12 mm maximum dimension Anterolateral Solitary 6 mm maximum dimension Anterolateral Multiloculated 14 mm
Grade 3
Anterosuperior labral lesion
Anterosuperior cartilage thinning
Nil
Grade 2
Anterosuperior labral lesion
Anterosuperior cartilage thinning
Grade 4
Anterosuperior labral lesion
Anterosuperior cartilage thinning
Grade 4
Anterosuperior labral lesion
Anterosuperior cartilage thinning
Grade 2
Anterosuperior labral lesion
Nil
Bony prominence head and neck junction Bony prominence head and neck junction Bony prominence head and neck junction Bony prominence head and neck junction Nil
Grade 1
Anterosuperior labral lesion
Full-thickness loss anterosuperior cartilage
Bony prominence head and neck junction
Pain on flexion, internal rotation and adduction Pain on flexion, internal rotation and adduction Pain on internal rotation
Nil
Nil
Mild
Mild
Mild
S.L.J. James et al.
Bone marrow oedema associated with femoroacetabular impingement
475
Figure 1 (a) Axial T2-weighted MRI image demonstrating the unilocular cyst involving the femoral head and neck junction (arrow). (b) Axial CT through the femoral neck demonstrating an anteriorly unilocular cyst at the femoral head and neck junction (arrow).
the acetabular labral chondral transitional zone in flexion. It has been postulated by a number of authors that this may be related to a variety of causes, including subclinical slipped capital femoral epiphysis, previous traumatic injury, postsurgical osteotomy, reduced antetorsion of the femoral head, and post-Perthes disease.7e10 The ‘‘pincer’’ type, more frequently encountered in middle-aged women, describes an abnormal acetabular shape that may also reduce femoral head
clearance and provide a source of impingement.1 Potential causes of the pincer type impingement include acetabular retroversion, protrusio acetabulae and coxa profunda.2 Fibrocystic change at the anterosuperior femoral head and neck junction is described in patients with femoroacetabular impingement.2e4 However, there is some controversy as to whether the cystic change is due to impingement, or whether it represents a separate, more indolent process, as in its
Figure 2 (a) Coronal STIR MRI image demonstrating a multiloculated cyst in the proximal femur with some adjacent bone marrow oedema. (b) Coronal CT reformat confirming the multilocular nature of the fibrocystic change.
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Figure 3 (a) Coronal STIR MRI image demonstrating intense bone marrow oedema at the femoral head and neck junction (arrow). The bone marrow oedema surrounded the cystic lesion illustrated in Fig. 1. (b) Coronal STIR MRI image demonstrating intense bone marrow oedema at the femoral head and neck junction (arrowhead). Prominence of the femoral head and neck junction is evident (black arrow) and a high signal cleft is identified at the base of the acetabular labrum (white arrow).
original description as a herniation pit.6 Pitt and co-workers6 described the cystic alterations at the anterosuperior femoral head and neck junction and proposed that synovial tissue may herniate through defects in the cortical bone of the femoral neck. Furthermore, the pressure of the iliofemoral ligament on the anteromedial joint capsule has been implicated as a possible cause for this herniation. These herniation pits have been considered
a normal variant with an incidence of between 5 and 12%.6,11 Leunig and co-workers3 describe the high prevalence of juxta-articular fibrocystic change at the anterosuperior femoral head and neck junction. They found 33% of the patients included in their series demonstrated this radiographic finding and suggest that femoroacetabular impingement may be causal in the development of this cystic change.3 This group also studied a cohort
Figure 4 Coronal fat-suppressed T1-weighted MR arthrogram image demonstrating contrast extending into a cleft at the base of the acetabular labrum (arrow).
Figure 5 Axial proton density FSE image demonstrating abnormal osseous prominence at the femoral head and neck junction.
Bone marrow oedema associated with femoroacetabular impingement
of patients with developmental hip dysplasia and found none of the 132 hips had evidence of herniation pits. They concluded that this supported their hypothesis that herniation pits may be caused by the repetitive contact between the femoral head and acetabular rim.3 Subsequently, further workers have shown a 24% incidence of fibrocystic change at the femoral head and neck junction in femoroacetabular impingement.2 However, Kassarjian et al.4 identified synovial herniation pits in only 5% of their series, an equivalent incidence to that previously quoted in the normal population.4 A number of series do not describe cystic change at the femoral head and neck junction as being present or a feature in their cases of femoroacetabular impingement.5,7,8,12 However, it is important to note that morphological changes of the femoral head and neck are frequently identified in patients with femoroacetabular impingement,7,8 and that the original descriptions of herniation pits also describe alterations at the femoral head and neck junction.11 Leunig and co-workers3 also studied the spatial relationship between the fibrocystic change and the acetabular rim using a combination of dynamic MRI and intra-operative observations. They found intra-operative evidence of bony contusions at the anterosuperior femoral head and neck junction close to the areas of fibrocystic change. This contact occurred in flexion and internal rotation and they hypothesized that the pressure induced in flexion may produce the fibrocystic change. Of particular relevance to the current study, they found no cases of marrow oedema in the 39 of 117 hips with fibrocystic change in the femoral head. They hypothesized that this may relate to a slow repetitive process rather than forceful impaction as the mechanism of fibrocystic change.3 In the cases included in this series, marrow oedema was demonstrated in the femoral neck adjacent to the areas of cystic change. This may relate to ongoing impaction between the femoral head and acetabulum sufficient to cause bone marrow oedema in these patients with femoroacetabular impingement. This may support the hypothesis proposed by Leunig and co-workers that herniation pits may be caused by the repetitive contact between the femoral head and acetabular rim. However, their assumption that the process relates to a slow repetitive process may not be entirely true. MRI is the technique of choice in the identification of the labral and chondral abnormality demonstrated in patients with femoroacetabular impingement. A number of workers have described the MR arthrographic findings,4,5,11 and more
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recently James and co-workers reported the noncontrast enhanced MRI appearances in femoroacetabular impingement using a high-resolution technique.2 If an arthrographic technique is used, it is important that a water-sensitive sequence is included in the protocol as well as fat-suppressed T1-weighted imaging. This facilitates the identification of bone marrow oedema, either related to fibrocystic change at the femoral head and neck junction or in the acetabulum in association with advanced chondromalacia. Both arthrographic and non-arthrographic techniques demonstrate labral and chondral abnormality, most frequently located in an anterosuperior position. In femoroacetabular impingement, an abnormal cleft is typically identified at the labral chondral transitional zone. The repetitive impingement between the femoral head and acetabulum causes a shearing force to be applied at the junction of the labrum and the adjacent acetabular articular cartilage. This is often termed a labral tear; however, this term is frequently used to describe labral diseases that relate to a number of differing aetiologies. True traumatic labral tears are rare, and in patients with acetabular dysplasia, the labrum is elongated and demonstrates abnormal intrasubstance change. Previous workers have recognized anterosuperior acetabular cartilage abnormality in between 78e95%, anterosuperior labral tear in 64e100% and abnormal femoral head and neck shape in 93% of patients.4,5,11 Two of the cases in the present series were referred with a clinical suspicion of osteoid osteoma after initial imaging at other institutions. A combination of CT and MRI characterized the lesion and allowed other diagnoses to be excluded. CT may provide further diagnostic information, demonstrating the nidus in patients with osteoid osteoma or a fracture line. Marrow oedema in the femoral neck may be observed in a number of differing pathological processes including osteoid osteoma, occult fracture or focal areas of avascular necrosis.13e15 The present series suggests that femoroacetabular impingement should be considered in the differential diagnosis of lateral femoral neck bone marrow oedema when this is adjacent to an area of cystic change. There are a number of limitations of this study. A small sample of individuals with femoroacetabular impingement and bone marrow oedema is included. In the senior author’s experience, most patients with fibrocystic change in the anterolateral femoral head do not demonstrate bone marrow oedema on MRI. However, the six cases that are presented do indicate that it may occasionally be identified in femoroacetabular
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impingement, but it is not known whether this is symptomatic or not. It is noteworthy that in one of the patients included in the present series, MRI of both hips was performed. The patient demonstrated anterosuperior labral and chondral abnormality and fibrocystic change bilaterally. The patient was symptomatic on the right side, which demonstrated bone marrow oedema on MRI. Second, histological correlation of the nature of the cystic alterations identified in the femoral head was not obtained. The term fibrocystic change has been adopted by previous workers to describe these cystic alterations in the femoral head,2e4 but histological correlation of the fibrous component has not been performed in these studies. It may therefore be slightly misleading to use a pathological term to describe an imaging feature. In this article, the clinical presentation and imaging findings were described in six patients with femoroacetabular impingement who demonstrate bone marrow oedema adjacent to areas of fibrocystic change in the femoral head and neck junction. The presence of marrow oedema adjacent to areas of cystic change in the femoral neck should prompt the search for further evidence of femoroacetabular impingement. Marrow oedema may also give further support to the theory that these fibrocystic alterations relate to ongoing impaction between the femoral head and acetabulum.
References 1. Ganz R, Parvizi J, Beck M, et al. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res 2003;417:112e20.
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2. James SLJ, Ali K, Malara F, et al. MR imaging findings of femoroacetabular impingement. AJR Am J Roentgenol 2006; 187:1412e9. 3. Leunig M, Beck M, Kalhor M, et al. Fibrocystic changes at anterosuperior femoral neck: prevalence in hips with femoroacetabular impingement. Radiology 2005;236:237e46. 4. Kassarjian A, Yoon LS, Belzile E, et al. Triad of MR arthrographic findings in patients with cam-type femoroacetabular impingement. Radiology 2005;236:588e92. 5. Schmid MR, Notzli HP, Zanetti M, et al. Cartilage lesions in the hip: diagnostic effectiveness of MR arthrography. Radiology 2003;226:382e6. 6. Pitt MJ, Graham AR, Shipman JH, et al. Herniaton pit of the femoral neck. AJR Am J Roentgenol 1982;138:1115e21. 7. Notzli HP, Wyss TF, Stoecklin CH, et al. The contour of the femoral headeneck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br 2002;84:556e60. 8. Jager M, Wild A, Westhoff B, et al. Femoroacetabular impingement caused by a femoral osseous headeneck bump deformity: clinical, radiological, and experimental results. J Orthop Sci 2004;9:256e63. 9. Snow SW, Keret D, Scarangella S, et al. Anterior impingement of the femoral head: a late phenomenon of LeggeCalveePerthes’ disease. J Pediatr Orthop 1993;13: 286e9. 10. Eijer H, Ganz R. Anterieur femoro-acetabulair impingement na een mediale collumfractuur. Een casus. Ned Tijdschr Trauma 1999;2:50e2. 11. Daenen B, Preidler KW, Padmanabhan S, et al. Symptomatic herniation pits of the femoral neck: anatomic and clinical study. AJR Am J Roentgenol 1997;168:149e53. 12. Leunig M, Podeszwa D, Beck M, et al. Magnetic resonance arthrography of labral disorders in hips with dysplasia and impingement. Clin Orthop Relat Res 2004;418:74e80. 13. Ehara S, Rosenthal DI, Aoki J, et al. Peritumoral edema in osteoid osteoma on magnetic resonance imaging. Skeletal Radiol 1999;28:265e70. 14. Kim YM, Oh HC, Kim HJ. The pattern of bone marrow oedema on MRI in osteonecrosis of the femoral head. J Bone Joint Surg Br 2000;82:837e41. 15. Theodorou DJ, Theodorou SJ, Haghighi P, et al. Distinct focal lesions of the femoral head: imaging features suggesting an atypical and minimal form of bone necrosis. Skeletal Radiol 2002;31:435e44.