Critical hip disorders show upon spinal imaging studies

When patients are suffering from back pain and radiating pain in their lower extremities, it is usual to suspect that the symptoms are caused by a spinal disorder. The symptoms could, however, be due to one of many extraspinal disorders. Differentiating these from spinal pathology requires precise clinical and radiological examinations.

One of the most important extraspinal lesions that can mimic spinal problems is peripheral vascular stenos is in the lower extremities.¹ Vascular Doppler ultrasound or angiography can be performed when vascular disorders are suspected. Attention must also be directed to etiologies such as facet joint arthrois, sacroiliac joint arthritis, pelvic insufficiency fractures, gynecologic disorders, malignancies, and neuropathies.²

Low back pain is one of the most common musculoskeletal complaints and is frequently accompanied by hip and thigh pain. Hip osteoarthritis is another common cause of pain and disability, particularly in the geriatric population.² The true diagnostic dilemma in some patients is to determine whether chronic low back or leg pain is attributable to a spinal disorder, a hip/ leg disorder, or both.^3,4

Although a careful history and physical examination may often distinguish radicular pain from pain originating in the joint, separating the two can be difficult.⁵ Clinical symptoms of lumbar spinal stenosis or radiculopathy may be similar to symptoms originating from the hip and pelvic region.^5,6 One problem in diagnosing patients with lower extremity pain is identifying the cause as originating in the spine, hip, or both.⁷ Failure to recognize concurrent disease of both hip and spine may lead to misdiagnosis and possibly to erroneous treatment.⁸

Few studies describe hip and spine disorders coexisting in the same patient. Some patients in our own study (described below) reported persistent symptoms after spinal surgery. Their chief complaints originated from hip disorders. Several patients had hip pathology rather than a spinal lesion. Imaging examinations should be performed to exclude hip and pelvic disorders, even though this requires more time and incurs more expense.

Our imaging protocol when investigating spinal pathology usually comprises plain-film radiography, CT, and MRI. We tend to use only the routine sagittal and axial images when interpreting spine MRI examinations and to focus solely on spinal structures. Anteroposterior views in a plain radiograph sometimes show us the hip pathology,⁹ but this approach is relatively limited, and it is difficult to get more precise information.

We previously used coronal scout images to localize sagittal and axial images when performing spine MRI. When interpreting coronal spine images, however, we noted that abnormal signal intensity and/or contours of the femoral head, neck, and hip joint structures were identified. This led us to modify the localization images so that the hip joints and femoral heads could be visualized as well as possible. That allowed us to detect several hip abnormal ities more clearly without additional scans.

Lumbar spine MR images from more than 17,000 consecutive patients have been evaluated at our institution since Nove mber 2004. Coronal scout images were acquired for localization purposes be fore each routine lumbar spine MRI examination. A protocol was established for the coronal scout images that included the hip joints and proximal femurs. Five to seven images were acquired with 10-mm or 12-mm slice thickness (Figure 1). We interpreted the scout images as well as the routine spine images. The patients' clinical symptoms were then considered to determine which lesion(s) could be the cause of the pain. Images were interpreted by an experienced radiologist, neurosurgeon, and orthopedic surgeon.

Hip disorders were found in 91 of the 17,141 patients (over all incidence 0.53%). The mean age of the patient group was 61.7 years (range: 21 to 86 years). Clinical and radiological findings led to a diagnosis of avascular necrosis in 70 patients and femur neck fracture in eight. Nine patients had hip dysplasia and/or subluxation, three had tumorous lesions (two had metastatic lesions; one had an expansile pelvic mass on MRI), and one patient had a marrow-infiltrating lesion of unknown etiology.

We divided the patients with hip disorders into three groups. Group I (23 patients; 25%) included patients whose symptoms were due predominantly to hip pathology (Figure 2). Patients with both hip and spine pathology (35 patients; 38.5%) were put in group II (Figure 3). Group III (33 patients; 36%) comprised patients whose symptoms were caused by spine pathology and whose hip disorders were incidental findings (Figure 4).

Twenty patients underwent hipoperations, 40 had spine surgery, and four had operations on hip and spine. The remaining patients have been managed by conservative therapy or clinical observation. Additional hip MRI (13 patients) and CT examinations (two patients) were performed for further evaluation.

DIAGNOSTIC PITFALLS

Several reports have described common musculoskeletal disorders that may mimic spinal pathology. Some are mentioned in studies of so- called hip - spine syndrome. ^5,6,8 In one study, 19 patients out of 35 (54%) were described as having simple hip-spine syndrome, that is, they had just one source of disability (either the hip or the spine) but pathologic changes were observed in both the hip and lumbar spine.⁵ Six (17%) had complex hip-spine syndrome and exhibited symptomatic changes in both the hip and spine. Changes in the lumbar spine were secondary to pathologic changes in hip, leading to the classification "secondary hipspine syndrome."

The source of pain was misdiagnosed in four patients (11.4%). Two patients with osteoarthritis of the hip were treated initially by laminectomy. Another two were referred for hip arthroplasty but received no symptomatic relief until undergoing lumbar spine treatment. The primary source of pain was hip disease in 24 patients (68.6%) and lumbar spine disease in 11 patients (31.4%). These results differ from our own findings (discussed above). This may be due to the authors' primary focus on hip disorders and the small patient sample.⁸

The major clinical symptoms originating from the hip are buttock, inguinal, and/or leg pain.⁷ Several reports also discuss groin pain associated with lower lumbar disc herniation .^{10- 12} The most common sites of involve ment appear to be L4-5 and L5-S1.¹⁰

We found many patients with abnormal signal intensity or morphology of the hip / proximal femur and referred them to an orthopedic surgeon. These patients were then reevaluated.

The major advantage of using coronal surgery is to reduce the cost of the study by avoiding the need for additional hip MR examinations. Coronal scout images may also help avoid a misdiagnosis. Elderly patients can have multiple comorbid diseases.

More than 1000 new spine MRI studies are performed in our hospital in a typical month. If the overall incidence of hip disorders detected on MRI is 0.53 %, as we have shown, then major coexistent hip disorders will be detected in five or more patients each month simply by modifying the spine MRI and carefully interpreting the results.

Some limitations of our investigation should be mentioned. The relatively poor resolution of the scout images meant that minor or detailed hip pathology could not be detected. It is also difficult to obtain scout images in patients with a severely distorted hip alignment or lumbosacral curve. Further investigation is needed to compare findings from plain-film x-rays, hip MRI, and surgery. Cases in which coronal scout images were negative but patients turned out to have significant hip pathology should also be followed. Coronal scout images will differ depending on the MRI equipment used and the patient's status, so several studies should be done before the proper images of the hip regions are obtained. The benefits of this approach will be realized only when radiologists become familiar with the technique.

In conclusion, misdiagnosis of major hip disorders can be avoided if images are interpreted carefully. This includes scout images from lumbar MRI spinal studies, which are useful for detecting coexistent hip pathology, as well as routine images.

Collaboration between radiologists, neurosurgeons, and orthopedic surgeons can also contribute to improved patient management.