|Year : 2015 | Volume
| Issue : 2 | Page : 189-195
Rapid magnetic resonance imaging protocol for detecting femoral head avascular necrosis: A case series-it's utility in the general population in developing countries
M Sanjay Khaladkar1, Shubreet Randhawa1, Guneet Singh1, Gujarathi Aditi1, Kuber Rajesh1, Sidhu Rajeshwar2
1 Department of Radiodiagnosis Dr. D.Y. Patil Medical College and Research Centre, Pune, Maharashtra, India
2 Department of Orthopaedics, Jawaharlal Nehru Medical College, K.L.E. University, Belgaum, Karnataka, India
|Date of Web Publication||13-Mar-2015|
M Sanjay Khaladkar
Flat No. 5, Plot No. 8, S.No. 26/A, Tejas Building, Sahawas Society, Karve Nagar, Pune - 411 052, Maharashtra
Source of Support: None, Conflict of Interest: None
Introduction: Osteonecrosis of the femoral head is an increasing cause of musculoskeletal disability, common among the younger population, between the third and fifth decade of life, affecting mainly men, thereby requiring prompt diagnosis and early intervention. Aims and Objectives: The aim was to formulate a limited magnetic resonance imaging (MRI) examination protocol for detection of avascular necrosis (AVN) in clinically suspected cases that can be performed rapidly and will be inexpensive. Materials and Methods: Forty-five patients suspected clinically and or on conventional radiography for AVN of the femoral head were referred for MRI hip. MRI hip was done on 1.5 T Siemens Avanto. Of 45, 36 were detected to have AVN (total 58 hips), whereas 9 did not have AVN on MRI. Initially, coronal T1-weighted image (T1WI) sequence was obtained as limited MRI protocol, followed by complete MRI examination. Results: Maximum patients belonged to age group 31-40 (30.5%). 32 (88.88%) patients were males and 4 (11.11%) were females. Bilateral AVN was detected in 44 (61.1%) and unilateral in 14 patients (38.8%). Pre collapsed stage (Stages I and II) was detected in 18 hips (31.03%), collapsed stage (Stages III and IV) was detected in 40 hips (68.9%). Peripheral low-intensity rim was seen on T1WI in all 58 cases of AVN. Double line sign on T2-weighted image was seen in 33/58 (56.8%). Conclusion: Our study concluded that coronal T1W sequence is an easy, rapid and cost-effective method of detecting unilateral or bilateral AVN.
Keywords: Avascular necrosis, femoral head, magnetic resonance imaging, ostoenecrosis, rapid magnetic resonance imaging protocol
|How to cite this article:|
Khaladkar M S, Randhawa S, Singh G, Aditi G, Rajesh K, Rajeshwar S. Rapid magnetic resonance imaging protocol for detecting femoral head avascular necrosis: A case series-it's utility in the general population in developing countries. Med J DY Patil Univ 2015;8:189-95
|How to cite this URL:|
Khaladkar M S, Randhawa S, Singh G, Aditi G, Rajesh K, Rajeshwar S. Rapid magnetic resonance imaging protocol for detecting femoral head avascular necrosis: A case series-it's utility in the general population in developing countries. Med J DY Patil Univ [serial online] 2015 [cited 2019 Mar 25];8:189-95. Available from: http://www.mjdrdypu.org/text.asp?2015/8/2/189/153156
Avascular necrosis (AVN) of the femoral head is an increasing cause of musculoskeletal disability. The disease is common among the younger population, especially between the third and fifth decade of life, affecting mainly men. Due to the higher occurrence in young adults, early diagnosis and treatment is of utmost importance as delay in diagnosis and treatment increases cost of treatment and morbidity. AVN in initial stages is asymptomatic and progresses to destruction of the hip joint in a relatively short time, requiring hip arthroplasty as the treatment. Hence, a quick and early detection can lead to the formulation of timely therapeutic methods, which are less debilitating for patients. Data in developed countries are known. Every year in the USA there are between 10,000 and 20,000 new cases diagnosed with AVN of the femoral head. About 5-18% of a total of 500,000 hip replacement surgeries performed in a year are performed on patients diagnosed with AVN of the femoral head. Cost estimated is about 1 billion dollars annually.  Evidence-based data on incidence and prevalence, and costs of diagnosing and treating this disease are poorly known in India. The disease occurrence is more in men than in women.
The existing magnetic resonance imaging (MRI) protocol for detection of AVN of the femoral head is taking T1-weighted image (T1WI), T2WI, T2-gradient-echo (GRE) sequences in the coronal plane, T2WI sequence in the sagittal plane and T1WI and T2WI sequences in the axial plane. Limited MRI examination protocol followed in this study involved T1WI sequence in the coronal plane.
In private diagnostic centers, charges for radiograph of pelvis with both hips is Rs. 300/ and full MRI examination of hips is Rs. 6500/. The charges for screening of MRI hips with coronal T1 are Rs. 500/. Time taken for full MR examination of hips and limited examination (coronal T1) is approximately 15-18 min and 3 min 26 s respectively. Due to reduced cost of the examination, lesser time taken for the MR examination and early diagnosis of AVN of the femoral head, orthopedicians and clinicians maybe more willing to obtain MR examination. In addition to diagnosis of AVN on MRI, extent of osteonecrosis can also be predicted. Percentage of involvement of femoral head weight-bearing surface area can be calculated by software. However, this was not done in our study due to unavailability of software. The objective of this study was to formulate and evaluate a limited MRI examination protocol for detection of AVN in clinically suspected cases that can be performed rapidly and will be inexpensive.
| Materials and Methods|| |
A total of 45 patients residing in of Pimpri-Chinchwad area, an industrial township in Pune, India, who were suspected clinically and or on conventional radiography for AVN of the femoral head were referred for MRI hip to Radiology Department of Padmashree D.Y. Patil Medical College from February, 2013 to July, 2013. Limited MRI protocol, followed by complete MRI protocol was carried out. Comparison of limited MRI examination protocol and detailed MRI examination of hips for detecting AVN was done with respect to detection, cost and time taken. All patients who were suspected clinically and or on conventional radiography for AVN of femoral head were included in this study. Patients with acute trauma suspected infective arthritis, rheumatoid arthritis, or age <10 years (Perthe's disease) were excluded. MR examination of hips was performed with a Siemens Magnetom Avanto 1.5 Tesla. Our technicians were trained to position patients by palpating greater trochanter and obtaining the images at that level. Initially, only coronal T1WIs were obtained. This was labeled as the limited examination protocol. Pulse sequence parameters were repetition time (TR)-623 ms, echo time (TE)-23 ms, time of acquisition 3.26 min, field of view (FOV) 300 mm, slice thickness 4 mm, interslice gap 10% (0.4 mm), flip angle 180, matrix 320 × 270. A total of 20-25 images were obtained in 3 min 26 s. Body coil was used for radiofrequency transmission and reception. This was followed by full examination in axial, coronal and sagittal-oblique planes using T1W, T2W and GRE-T2 and short tau inversion-recovery (STIR) sequences. Coronal T1WI (as described above), coronal T2-weighted image (T2WI) (parameters were TR-4010 ms, TE 81 ms, time of acquisition 1.30 min, FOV 300 mm, slice thickness 4 mm, interslice gap 10% (0.4 mm), flip angle 150, matrix 448 × 378), coronal STIR (pulse sequence parameters were TR-3000 ms, TE 23 ms, time of acquisition 2.05 min, FOV 300 mm, slice thickness 4 mm, interslice gap 10% (0.4 mm), flip angle 150, matrix 320 × 268), coronal GRE T2 (pulse sequence parameters were TR-500 m s, TE 12.70 ms, time of acquisition 2.0 min, FOV 300 mm, slice thickness 4 mm, interslice gap 10% (0.4 mm), flip angle 20, matrix 320 × 270), axial T1WI (pulse sequence parameters were TR-598 ms, TE 12 ms, time of acquisition 3.16 min, FOV 280 mm, slice thickness 3 mm, interslice gap 50% (1.5 mm), flip angle 90, matrix 384 × 270), axial T2WI (pulse sequence parameters were TR-3500 ms, TE 78 ms, time of acquisition 4.35 min, FOV 300 mm, slice thickness 3 mm, interslice gap 50% (1.5 mm), flip angle 150, matrix 384 × 268 ), T2WI oblique-sagittal (pulse sequence parameters were TR-3800 ms, TE 79 ms, time of acquisition 2.26 min, FOV 200 mm, slice thickness 3 mm, interslice gap 20% (0.6 mm), flip angle 100, matrix 256 × 256). The total time taken for complete MRI scan varied between 15 and 18 min. This imaging protocol was applied prospectively in patients referred to our department who were suspected clinically of having AVN hip referred by clinicians and orthopedicians.
| Results|| |
A total of 45 patients who were suspected clinically and or on conventional radiography for AVN of the femoral head were referred for MRI hip [Table 1]. Out of 45, 36 were detected to have AVN on MR, while 9 did not have AVN on MRI.
Age group varied from 11 to 70 years. Maximum belonged to age group 31-40 (30.5%), followed by 21-30 (25%) and 41-50 (22.2%) [Table 2]. Out of 36 cases of AVN, 32 (88.88%) were males and 4 (11.11%) were females [Table 3]. AVN was bilateral in 22 patients (61.1%) [Figure 1] and unilateral in 14 patients (38.8%) [Table 4]. Out of 58 hips, left hip was involved in 33 cases (56.8%) and right hip was involved in 25 (43.1%).
|Figure 1: Coronal T1-weighted image-bilateral Ficat and Arlet Stage I avascular necrosis. Also noted old healed fracture at junction of right femoral head and neck|
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Stage I AVN was detected in 4/58 (6.8%) [Figure 1], Stage II AVN was detected in 14/58 (24.1) [Figure 2], Stage III AVN in 18/58 (31%) [Figure 2] and Stage IV AVN was detected in 22/58 (37.9%) hips [Figure 3] and [Figure 4] [Table 5].
|Figure 2: Coronal T1-weighted image sequence-bilateral avascular necrosis demarcated by serpigenous hypointense line. Right femoral head and neck shows bone marrow edema appearing hypointense. (Ficat and Arlet Grade III on the right and Grade II on the left)|
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|Figure 3: Coronal T1-weighted image-bilateral avascular necrosis Stage IV on right with reduction in joint space, Stage III on left with preserved joint space with loss of normal rounded contour of femoral heads on both sides|
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|Figure 4: Coronal T1-weighted image-bilateral avascular necrosis femoral head with secondary osteoarthritis (left more|
than right showing resorption of femoral head — Ficat and Arlet Grade IV)
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Stage I AVN was detected in 4 hips (right hip-3 and left-hip 1). Stage II AVN was detected in 14 hips (right hip-6 and left-hip 8). Stage III AVN was detected in 18 hips (right hip-8 and left-hip 10). Stage IV AVN was detected in 22 hips (right hip-8 and left-hip 14) [Table 6].
Out of 58 cases of AVN, pre collapsed stage (Stages I and II) were detected in 18 hips (31.03%), collapsed stage (Stages III and IV) were detected in 40 hips (68.9%) [Figure 4] and [Table 7].
Peripheral low-intensity rim was seen on T1WI in all 58 cases of AVN (100%) as seen in [Figure 2]. Double line sign on T2WI was seen in 33/58 (56.8%) [Figure 5]. Bone marrow edema was seen in 30/58 (51.7%) [Figure 6]. Synovial effusion was noted in 49/58 (84.4%) [Figure 6]. Flattening of the femoral head was seen in 40/58 hips (68.9%). Joint space narrowing was seen in 22/58 hips (37.9%). Periarticular muscle atrophy was seen 40/58 cases (68.9%) [Table 8].
|Figure 5: Coronal T2-weighted image sequence-bilateral Ficat and Arlet Stage IV avascular necrosis with Double line sign|
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|Figure 6: Coronal short tau inversion-recovery sequence-bilateral Ficat and Arlet Stage II avascular necrosis with double line sign. Also noted bone marrow edema in bilateral femoral necks with synovial effusion|
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In our study, AVN was detected in all 58 cases with limited MRI protocol (coronal T1WI sequence). Thus, sensitivity and specificity of detecting AVN with coronal T1W sequence was 100%. This may be due to small and highly selective sample size in our case series (as most of the patients were detected to have Stage III and Stage IV AVN). A larger sample size with better case-mix, including subjects with early AVN is suggested to know the efficacy of this limited MRI protocol in detecting sensitivity and specificity of AVN.
Comparison of our findings was done with a detailed examination of hips. Detailed MRI examination of the hip showed additional findings like synovial effusion and bone marrow edema. Double line sign detected on T2WI, contour flattening and thinning of articular cartilage were better-evaluated on detailed MRI examination when compared with limited MRI protocol. However, in view of advantages of limited hip MR examination protocol (low technical requirements with easy availability of body coil, reduced time taken and low cost), it can be implemented in early detection of AVN of the femoral head, especially in developing countries in low socioeconomic population, who may not be able to afford detailed MRI examination.
| Discussion|| |
Avascular necrosis (aseptic necrosis, osteonecrosis, and ischemic necrosis) is due to compromise of the bone vasculature and subsequent death of bone and marrow cells.  It leads to mechanical failure and secondary osteoarthritis. Male to female ratio is 5-8:1, with an average age of onset between 30 and 40 years. It contributed to 10% of total hip replacements.
Causes of AVN are-traumatic (which includes fractures, dislocation, fracture dislocation, minor blunt trauma) and nontraumatic (in which pancreatitis, pregnancy, systemic lupus erythematosis, alcohol, idiopathic, infection, Caissons disease, radiation, arteritis, Gaucher's disease, sickle cell disease, chronic renal failure, leukemia/lymphoma, gout, hyperlipidaemia, thrombophlebitis, smoking and iatrogenic play a role). On an average, 60-90% cases are due to steroids or alcohol. , Whereas hyperlipidemia contributes to 80% of idiopathic AVN's. The main pathophysiologic event of AVN is vascular compromise of sinusoids of trabecular bone leading to necrosis. AVN develops in fatty marrow that happens to be less vascular. Epiphyses of bones have predominantly fatty marrow and hence is affected in AVN. The collateral vascular supply of the femoral head is relatively limited. After the initial insult, marrow elements and cortex die. Inflammatory response develops to necrosis (in weeks to months), cuff of hyperemia, inflammatory cell infiltrate and fibrosis (granulation tissue) surrounds the necrosed area creating a reactive interface. Clinically, patients present with insidious onset weight-bearing or motion induced pain with limited range of movement. 
Technicians can easily position patients for MR examination of hips by palpating the greater trochanter. Scout images are not necessary. Diagnostic coronal T1WIs of both hips can readily be obtained without obtaining scout images. AVN is diagnosed on T1W coronal images as a band of low signal intensity in antero-superior portion of involved femoral head. This appearance is characteristic.  Furthermore on T2WIs, characteristic double line sign is seen with an inner high-intensity band due to hypervascular granulation tissue, hyperemic response adjacent to thickened trabeculae and an outer low-intensity band due to adjacent sclerotic bone (junction of viable and nonviable bone). Double line sign is specific for AVN diagnosis.  However, this sign is uncommon with the use of the fast spine echo sequences with or without fat suppression and is not necessary for diagnosis of AVN. Subsequently grading of AVN was done in our study using the Ficat and Arlet staging modified in 1985. 
Use of rapid screening MR for detection of AVN of the femoral head is not widespread. Although some references for similar limited MR examination are given in the literature. Medina et al. showed that a 5 min brain examination could be used to detect intracranial tumor in children and adolescents.  Similarly, Robertson et al. used a 2.5 min pulse sequence to detect lumbar spondylosis.  In another study of fast MR imaging screening protocol for occult lumbosacral dysraphism in children and young adults turned out to be unsuccessful relative to a full MR examination. 
Limited hip MR examination protocol can be readily performed with the easily available body coils as femoral heads are relatively large structures. Hence successful body coil imaging has proven to be diagnostically successful. , Technical requirements of this limited protocol are low with coronal T1WI pulse sequence being the optimal sequence. These factors along with reduced cost and reduced time requirement could gain acceptance by radiologists and clinicians in early detection of AVN of the femoral head.
Avascular necrosis of the femoral head is characterized by ischemia of bone marrow followed by death of trabecular bone pathologically. Optimal management of AVN femoral head is early treatment prior to onset of damaging events like subchondral fracture and cartilage damage.  In a study core decompression was successful in 84% of patients with Stage I, 65% of patients with Stage II, and only 47% of patients with Stage III disease, thus highlighting the effectiveness and relationship between the choice of treatment and pathological stage of the symptomatic hip. 
Early effective treatment needs timely diagnosis, and this cannot be made clinically and on conventional radiographs alone. Conventional radiography does not detect AVN until a substantial portion of femoral head weight-bearing surface is involved. MR is highly sensitive in detecting AVN of femoral heads in early stages. Favorable outcome with less debilitating effects is seen in early stage AVN of the femoral head when percentage of involvement of the femoral head is low. Beltran et al. demonstrated that femoral head collapse did not occur when less than 25% of the weight-bearing surface was involved occurred in 43% of hips when 25-50% of the surface was involved, and occurred in 87% of hips when more than 50% of the surface was involved.  MR examination can detect both AVN in early stages as well as calculate percentage of involvement of femoral head weight-bearing surface and thus giving an insight into the prognosis of the disease. 
Bone marrow histologically is composed of hematopoietic cells, osteocytes (osteoclasts, osteoblasts) and marrow fat cells. These cells when exposed to ischemic insult die at a different rate. Hematopoietic cells die within 6-12 h, osteocytes live up to 12-48 h, while fat cells live up to 5 days after an ischemic insult.  Normal marrow appearance is high signal intensity on T1 images and intermediate signal intensity on T2W images. MR imaging of AVN depicts these changes in marrow signal. Though histological definition of osteonecrosis means death of osteocytes, MR imaging changes of AVN reflect death and replacement of normal fat cells. The most common MR appearance of AVN on T1W images is a band of low signal intensity in antero-superior portion of the femoral head which is characteristic.  T1WI alone in the coronal plane is highly effective in diagnosing AVN. This site represents most peripheral site in intraosseous circulation of the proximal femur. Associated findings like bone marrow edema in femoral head and neck and synovial effusion in the hip joint are commonly seen with a peak incidence in Stage III. Bone marrow edema when compared to synovial effusion has a stronger association with pain in AVN. 
Early asymptomatic AVN do not need surgical treatment and should be closely monitored with serial examination. Surgical treatment of AVN is aimed to retard the progression of AVN in pre collapsed stage (core decompression).  Reconstruction procedure (arthroplasty) is done in collapsed stages. 
| Limitations|| |
There are several limitations to this study. Our study was performed at high field strength (1.5 T) so applicability of this method to magnets of lower fields strength is not known. Full MR study was used as a reference standard for disease state determination. The patient population and risk factors for disease may affect the usefulness of a limited MR examination, for e.g., patients with steroid-induced AVN may have hip pain due to fracture or infection which may not be detected using limited MR sequence. Similarly, patients with sickle cell anemia with extensive bone infarcts may develop new onset of hip pain due to osteomyelitis or septic arthritis, which again may not be detected by limited MR imaging protocol. In our study, AVN was detected in all 58 cases with limited MRI protocol (coronal T1WI sequence). This may be due to small and highly selective sample in our case series (as most of the patients were detected to have Stage III and Stage IV AVN). A larger sample size with better case-mix, including subjects with early AVN is recommended to validate this limited MRI protocol in terms of sensitivity, specificity, positive and negative predictive values.
| Conclusion|| |
Coronal T1WI sequence can be used as limited MRI protocol for diagnosis of AVN of the femoral head (unilateral or bilateral). It reduces the time needed for imaging and proved to be cost effective. It should be included as protocol to diagnose AVN in developing countries especially in lower socioeconomic population. In doubtful cases, it may be followed by complete MRI examination.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]