Occult fractures of the femoral neck

Diagnostics

Occult Fractures of the Femoral Neck EVELYN ALBA, MD, RUSH YOUNGBERG, Occuli fractures of the femoral neck can be subtle or even undetectable on plain radiographs. Yet, untreated, the morbidity of this fracture significantly increases. This report discusses the clinical and radiologic ffndings seen in occult fractures of the femoral neck. It also discusses the role of tomograms, bone scan, computed tomography, and magnetic resonance imaging in further delineating this entity. (Am J Emerg Med 1992; 1054-66. Copyright 0 1992 by W.9. Saunders Company)

Much has been written regarding occult femoral neck fractures; however, this condition continues to go unrecognized. False negative and unremarkable plain radiographs continue to mislead physicians, imparting a false sense of security. As a result, additional studies are not obtained and the diagnosis is not made. In this report, four cases of missed subcapital stress femoral neck fractures are presented. The role of follow-up examination in the symptomatic patient with initially negative radiographs is reviewed. CASE REPORTS Case No. 1 An 82-year-old male presented to a primary care clinic with increasing left hip pain following a fall 1 week prior. The patient reported that his left lower extremity collapsed once while walking. He denied any numbness or tingling. Physical examination revealed a left lower extremity with intact sensory and motor function, with tenderness over the left femoral lateral trochanter. Initial plain radiographs of the hip were interpreted as negative for fracture. The diagnosis at that time was inflammation of the hip secondary to trauma, and nonsteroidal antiinflammatory medications were prescribed. Rest, a four-point walker for ambulation, and physical therapy were recommended. The patient presented to the emergency department approximately 10 days later with increasing difftculty with ambulation secondary to severe pain which was maximal with weight-bearing. He denied weakness, numbness, or radiation of pain. The patient found himself unable to sleep secondary to the pain despite the prescribed medications. His examination was unchanged. Repeat radiographs demonstrated a displaced left subcapital femoral neck fracture.

From the Departments of Emergency Medicine and ‘Radiology, Madigan Army Medical Center, Ft Lewis, WA. Manuscript received April 8, 1991; revision accepted July 15, 1991. Address reprint requests to Dr Alba, Department of Emergency Medical Services, Fort Ord. CA 93941. Key Words: Femoral neck, fracture. Copyright 0 1992 by W.B. Saunders Company The opinions and ideas expressed in this report are those of the authors and not necessarily those of the US government, the Department of Defense, or Madigan Army Medical Center. 0735-8757/92/l OOl -0017$5.00/O 64

MD* The patient underwent a bipolar cemented hemiarthroplasty. He followed a gradually progressive physical therapy rehabilitation program and progressed to ambulation without assistance approximately 2 months after injury.

Case No. 2 A 65-year-old male presented to a primary care clinic with a 2-week history of gradually worsening right hip pain, which increased when getting up, lifting, and walking. He denied any history of trauma or arthritis. Physical examination demonstrated a nontender right hip, equivocal bilateral straight leg raising, stiff hamstrings, and a negative bilateral FABER test. (This is a maneuver used to assess possible hip injury. This involves flexion, abduction, and external rotation of the hip). The diagnosis of sciatica was made, and the treatment plan included aspirin and limitation of activity. One month later follow-up examination demonstrated negative straight leg raising bilaterally, 1-2 + right hip FABER, and negative plain radiographs. Nonsteroidal antiinflammatory medications were begun for the same diagnosis. Symptoms and examination remained unchanged for 2 months after the onset of symptoms. An orthopedic specialist was then consulted, and a probable hip stress fracture was diagnosed. Though repeat plain radiographs were negative, a bone scan was obtained which was read as abnormal. Magnetic resonance imaging (MRI) findings were consistent with either avascular necrosis of the hip or a stress fracture. TABLE 1. Recommended Algorithm for Diagnostic for Clinical Suspicion of Occult Hip Fractures Clinical Suspicion Without

of Occult

fracture

c Orthopedic consultation

Hip Fractures

With fracture

1 Bedrest; no weight-bearing: follow-up 1 week later with repeat plain films / Abnormal

Approach

Orthopedic

c consultation

\ Normai \ Asymptomatic 1 Return to usual activity

Symptomatic or positive examination 1 Tomograms / Negative

\ Positive

4 MRI v bone scan’

c Orthopedic consultation

* Use or bone scan based on availability, and cost considerations. Magnetic resonance imaging will demonstrate occult fractures within 24 hours and patient may be held in hospital in interim.*

ALBA AND YOUNGBERG

W OCCULT

FRACTURES

OF THE FEMORAL

65

NECK

FIGURE 1.

The patient was instructed to avoid strenuous activity and subsequently underwent total hip arthroplasty. His condition gradually improved with physical therapy.

Case No. 3 An 85-year-old female presented to the emergency department with right hip and knee pain after tripping on her carpet and falling the night before. Her pain had been decreasing since the injury and she had been walking with a cane since the incident. The physical examination demonstrated full range of motion of the right hip without crepitance, and no pain with movement. There was tenderness to palpation over the greater trochanter with ecchymosis in that area. The left knee was within normal limits. Plain radiographs were interpreted as normal. Tomograms, however, demonstrated an impacted fracture of the femoral neck. The patient was treated nonoperatively with bedrest, and nonsteroidal antiinflammatory medications. The patient’s symptoms gradually improved though some residual discomfort remained.

Case No. 4 A 21-year-old otherwise healthy white male was undergoing a rigorous physical training program. One day during his physical training exercises he began noting the onset of left hip pain, though he denied any specific injury. Initial radiographs were interpreted as normal.

Stress fracture of the femoral neck.

After I month of treatment with nonsteroidal antiinflammatory medications and instructions on limiting activity, the pain began to increase in severity. He complained of pain primarily climbing stairs and running, and at night. Follow-up examination demonstrated pain in his left hip, full range of motion, and only slight discomfort on maximal internal rotation without point tenderness, or swelling. The limb was neurovascularly intact. Plain radiographs at that time demonstrated a stress fracture extending three quarters across the femoral neck. The patient underwent prophylactic ORIF with resolution of pain and rapid return to normal activity. A bone scan I year later was negative.

DISCUSSION Occult fractures may be secondary secondary to stress. Stress fracture

to manifest

trauma

or

has been defined as a partial or incomplete fracture of bone due to the inability of bone to withstand nonviolent stress that is applied in a rhythmic subthreshold manner.’ Stress fractures occur in normal or abnormal bones that have been subjected to repeated traumas, which alone would not be sufficient to cause fracture. Fatigue fractures occur in normal bones subject to increased load. Insufftciency fractures result from loads applied to bone weakened by underlying disease such as os-

AMERICAN

JOURNAL

OF EMERGENCY

MEDICINE

n Volume 10, Number 1 n January 1992

FIGURE 2. True lateral of the femoral neck.

teoporosis, rheumatoid arthritis, osteomalacia, fibrous dysplasia, Paget’s disease, and radiation.’ Patients with nondisplaced fractures may complain of only slight pain in the groin or of referred pain along the medial side of the thigh to the knee.3 However, the complaints may vary depending on how long the fracture has been present and patient activity. Physical examination may vary from a normal examination, to an isolated antalgic limp, to pain on internal rotation caused by increased intracapsular pressure.* Plain radiographs may be normal. However, they should always be carefully examined for any evidence of nondisplaced or minimally displaced femoral neck fractures. Abnormalities that might be found include (1) shortening of the femoral neck, (2) disruption of the smooth cortical line from the inferior margin of the neck to the head, (3) the presence of a curvilinear, broad band of increased density that extends transversely across the femoral neck from its inferior surface, caused by impaction of the fragments, and (4) minimal, but definite, disruption of the superior cortex of the neck.4 Final interpretation should take into account that stress fractures of the hip may take 10 to 14 days to appear as a distinct radiolucent line* (Fig 1). When discussing plain radiographs, one must clearly distinguish which projections will best demonstrate pathology of the femoral neck. In addition to the anteroposterior radiograph, a true lateral will best define the full extent of the proximal femur. The true lateral is obtained with the patient supine and the injured lower extremity in full extension. The

opposite, uninvolved hip and knee are each flexed approximately 90” and the ipsilateral foot supported off the radiographic table by a low stool or box. The x-ray tube is then positioned so that the beam is parallel to the table top, with the central ray directed mediolaterally parallel to and in the same vertical plane as inguinal crease (groin). The cassette is firmly positioned against the flank between the iliac crest and the 12th rib on the injured side, perpendicular to the central ray. This beam cassette geometry results in the true lateral radiograph of the hip. The frog-leg lateral, on the other hand, is actually an oblique projection of the proximal portion of the femur obtained with the patient supine and femur abducted and externally rotated. The x-ray tube is vertically positioned with respect to the patient and the table and centered over the pubic symphysis. The resultant radiograph depicts the femoral in midposition between true anteroposterior and true lateral positions. Therefore it is not appropriate for evaluation of the femoral neck, since neither the femoral neck shaft angle nor the trochanters can be evaluated. In addition, much manipulation is required to obtain the radiograph and may conceivably cause the patient pain and further injury5 (Figs 2 and 3). Tomograms may be useful in delineating these subtle fractures and are often used as a supplemental study. Radionuelide scanning is frequently used to confirm the finding of stress fracture on plain radiographs. In addition, Deutsch et al’ reported four cases in which initially negative plain radiographs were positive for stress fractures by bone scan and MRI. One other patient demonstrated diffuse mildly in-

ALBA AND YOUNGBERG

W OCCULT

FRACTURES

OF THE FEMORAL

NECK

67

FIGURE 3. FI-0g leg lateral.

creased uptake by bone scan though MRI and tomograms were negative. That patient was treated conservatively with no evidence of fracture 3 months latere6 As is demonstrated by this case, limitations to this study, especially in the elderly, include the time interval between the onset of symptoms and the appearance of abnormal activity on the bone scan (sometimes up to 4 days), and the lack of specificity (areas of synovitis, arthritis, and degenerative joint disease may mimic fractures).6 In doubtful cases, computed tomography (CT) may be of value in the differential diagnosis of a bone lesion. The Journal of Computer Assisted Tomography established the spectrum of CT changes in a series of patients with established stress fractures. Somer et al determined CT to be of value in differentiating stress fractures from other lesions including malignant and benign bone tumors.’ Magnetic resonance imaging can provide critical information about the viability of the femoral head in patients with intracapsular fracture, which can have a direct impact on therapy. Magnetic resonance imaging was effective in assessing and further characterizing the precise anatomic extent of fractures in patients with equivocally abnormal initial radiographs. It appears more sensitive and specific in delineating fracture lines than either tomograms or bone scan6 Since MRI achieves no less specificity than CT scanning

in bone tumors and inflammatory diseases and achieves much more sensitivity regarding soft tissues, MRI seems to be the procedure of choice for a better delineation of the lesions. Because of potential hazards of ionizing radiation, especially in children, it is likely that additional CT imaging will not be indicated in most cases. CONCLUSION As emergency physicians, we are in a position to perform the initial evaluation of patients presenting with hip pain after trauma. We must therefore assure that a relatively uncomplicated condition such as a nondisplaced subcapital femoral neck fracture does not progress to a limbthreatening condition requiring more significant surgical intervention. The nondisplaced or minimally displaced fracture should be suspected in persons at risk for occult fractures as discussed above. When fracture is suspected based on epidemiology, mechanism of injury, history and physical examination, the patient should not be allowed to bear weight on the affected limb and bedrest should be considered, despite unremarkable plain films.* It would be a tragedy to see a treatable nondisplaced fracture progress to a displaced fracture or to aseptic necrosis of the hip. On return at 1 week with continued symptoms, not only

68

AMERICAN

JOURNAL

OF EMERGENCY

MEDICINE

n Volume

10, Number

1 n January

1992

FIGURE 4. Nondisplaced stress fracture which progressed to a displaced fracture.

should the physical examination be repeated, but plain films should also be repeated. A true lateral view must be included to fully evaluate the femoral neck. Tomography may be supportive, however bone scan would be quite helpful in further delineating the presence or absence of a fracture. If MRI is readily available or if there are equivocal results from previous studies, MRI should be strongly considered as the next definitive study of choice (see Table 1). REFERENCES 1. Murcia M, Brennan stress fractures. Skeletal

RE, et al: Computed Radio1 1982;8:193

tomography

of

2. Harris JH, Harris WH: Radiology of Emergency Medicine. pp 491-497 3. Lee JK, Yao L: Stress fractures: MR imaging. Radiology 1988;169:217-220 4. Hofmann A, Wyatt R, et al: Missed subcapital fractures. Ann Emerg Med 1984;13:951-955 5. Deutsch AL, Mink JH, Waxman AD: Occult fractures of the proximal femur: MR imaging. Radiology 1989;170:113-116 6. Berger PE, Ofstein RA, Jackson DW, et al: MRI demonstration of radiographically occult fractures: What have we been missing? Radiography 1989;9(3):407-436 7. Somer K, Meurman, Kalle OA: Computed tomography of stress fractures. J Comput Assist Tomogr 1982;6:109 8. Zlatkin MB: MR of the hips. MRI Video Update. Tampa, FL, Radiology Educational Symposia, Inc, 1991