Slipped capital femoral epiphysis (SCFE) is a disorder of the adolescent hip that is characterized by posterior and inferior displacement of the capital femoral epiphysis on the metaphysis.1 This disorder is common in pediatric orthopedics, with an overall incidence of approximately 10 per 100,000 children in the United States.2 Tremendous variability is seen in the incidence of SCFE based on geographic location.2–7 This condition is seen more frequently in children of Hispanic, Polynesian, and African descent compared with the white population.2,8 The occurrence of SCFE is most common among adolescents age 12 to 13 years, and it is more common in boys and occurs at a younger age in girls.2,8,9 Most adolescents with SCFE are overweight, and in most cases the body mass index (BMI) is greater than the 95th percentile.9–11
Most patients with SCFE present with pain in the hip, groin, or knee and have restricted motion and a limp. Physical examination typically shows decreased abduction and internal rotation.1 Anteroposterior and frog-leg lateral radiographs of the pelvis are diagnostic. A common diagnostic measurement for identifying SCFE on radiographs is Klein's line, defined as a line drawn along the superior aspect of the femoral neck on the anteroposterior view. In the normal hip, the epiphysis projects superiorly to the drawn line. In patients with SCFE, the epiphysis is seen flush with or below the line.12 Unfortunately, reliance on this traditional radiographic measurement may lead to a missed diagnosis.13–15 Some authors have reported a missed diagnosis rate of as high as 60% with the use of Klein's line.14 Failure to recognize the diagnosis of SCFE can lead to progression of the slip and further risk of complications, such as avascular necrosis, decreased range of motion, impingement, and arthritis.13,14,16
The incidence of bilateral SCFE has been reported to be as low as 37% and as high as 60%.17,18 Approximately half of patients with bilateral disease initially present with bilateral hip involvement, and the rest progress to contralateral disease within approximately 18 months.18 Anecdotally, the authors noted occasional pinning of a presumed sequential slip that actually was present on presentation and was missed by the surgeon. This observation led the authors to ask how many of these sequential slips were truly sequential and not simply missed disease. The goal of this study was to describe the incidence of missed contralateral SCFE in patients treated for unilateral disease as well as to identify risk factors for missing these slips. The authors hypothesized that contralateral slips would be more often missed in patients with severe involvement of the treated side.
Materials and Methods
After institutional review board approval was obtained, a retrospective chart review was performed of all patients who underwent surgical treatment for sequential and bilateral SCFE at a single institution during an 18-year period. The Current Procedural Terminology code for the treatment of SCFE (27176) was used to identify patients who were eligible for inclusion in the study. Inclusion criteria included age younger than 18 years, orthogonal views of bilateral hips on initial presentation, and sequential pinning of bilateral hips on separate dates or bilateral pinning on the same day. Exclusion criteria included incomplete medical or radiographic records.
Basic demographic information for each patient was obtained from the medical record as documented at the time of diagnosis, including age, sex, race, height, weight, and medical comorbidities. If a patient presented with unilateral SCFE and contralateral SCFE developed subsequently, the time from initial presentation to the development of contralateral disease was recorded. Additional information obtained from the medical record included the attending surgeon, acuity, and chief complaint at the time of presentation. Radiographs from the date of presentation were reviewed for Risser and triradiate status, Klein's line, and severity of the treated slip. The severity of SCFE was determined by measuring the epiphyseal shaft angle.1 Slips were classified as mild (<30°), moderate (30°–50°), or severe (>50°).
Patients who underwent sequential pinning of bilateral hips on separate dates were identified and reviewed for the presence of bilateral SCFE on initial presentation. All radiographs that showed sequential slips were deidentified and reviewed by 3 pediatric orthopedists (B.C.S., R.D.B, B.M.R.), all of whom completed a 1-year fellowship in pediatric orthopedic surgery. The diagnosis of a contralateral slip was made when consensus was achieved by all 3 orthopedists. Descriptive characteristics are provided for the study population. Comparisons were made with Fisher's exact test, and P<.05 was considered significant.
The authors identified 413 patients who were surgically treated for SCFE. Of these, 311 underwent only 1 SCFE procedure. An additional 46 patients were excluded because of incomplete radiographs or other medical records. Of the records that were reviewed, 19 patients who were treated for bilateral SCFE and 37 patients who were treated for sequential involvement met the inclusion criteria. Table 1 shows the demographic features of the final study population of 56 patients. Study subjects were categorized as “correctly diagnosed” if bilateral SCFEs were pinned or if correct synchronous disease was treated with sequential pinning. Study subjects were categorized as “missed bilateral” if they were treated with sequential pinning when bilateral involvement on presentation was not recognized.
Characteristics of Study Population
Of the patients, 5 (8.9%) were found to have a missed contralateral slip at the time of initial presentation for the first surgical SCFE. These missed slips were recognized and pinned later. The other 51 (91.1%) patients were correctly diagnosed with either bilateral disease or synchronous slips.
No statistically significant differences were found between the correctly diagnosed group and the missed bilateral group when age, sex, race, and BMI were assessed (Table 1). Two trends were noted, however. The missed bilateral group tended to be younger, with a mean age of 10.8 years, compared with a mean age of 11.4 years in the correctly diagnosed group (P=.29). The missed bilateral group also tended to have a lower BMI of 24.6 kg/m2 compared with a BMI of 29.5 kg/m2 in the correctly diagnosed group (P=.15).
The Risser sign for all patients who had missed or sequential disease was 0. Triradiate status was classified as either open or closed. This status was evenly distributed between the correctly diagnosed and missed bilateral groups (Table 1). The average duration (range) of surgical fixation of sequential slips was 9.68 months (range, 1.38–24.0 months). The missed slips were pinned earlier on average than the correctly diagnosed slips (7.2 vs 10.2 months, respectively).
In the 5 missed contralateral slips, 2 were associated with mild operative hips and 3 with moderate operative slips (Table 2). Of the study subjects, 5 had severe slips, and all of these were in the correctly diagnosed group. Of the severe slips, 2 were in the sequential group and the rest were in the bilateral group. No statistically significant difference was noted between groups when this factor was assessed.
Severity of Primary Slip
Fellowship-trained pediatric orthopedic surgeons treated 54 of the 56 patients with bilateral SCFE. Both patients who were treated by orthopedic surgeons without pediatric training had missed bilateral SCFE. In contrast, of the 54 patients who were treated by pediatric orthopedic surgeons, only 3 (5.4%) had missed SCFE. Pediatric surgeons were more likely to identify bilateral disease at presentation compared with orthopedists without pediatric training (P=.0065; Table 3).
Trained in Pediatric Orthopedics
Of the 5 patients with missed contra-lateral slips, 3 (60%) had a positive finding for Klein's line, whereas none (0%) of the 32 patients with sequential slips had a positive finding. When these 2 groups were compared, a contralateral slip was more likely to be present if the contralateral hip had a positive finding for Klein's line (P=.0013). When correctly diagnosed bilateral disease was combined with correctly diagnosed sequential disease, however, no statistically significant difference was noted (P=1.00; Table 4).
Contralateral Klein's Line
In general pediatric orthopedic practice, SCFE is a commonly seen hip condition. As acute and unstable slips present in the emergency setting, requiring prompt treatment, the orthopedist on call must be familiar with this disease process as well. Bilateral disease is not uncommon, nor is sequential slippage.
In this cohort of 56 patients treated for SCFE, 43% were noted to have bilateral involvement. This is similar to previously reported rates of bilateral SCFE (range, 50%–60%).19 Patients in this study presented with sequential disease an average of 9.68 months after treatment of the initial slip, which is similar to previous reports.20
In this study, 5 (8.9%) patients were found to have a missed contralateral slip at the time of initial presentation and were treated at a later date. The authors noted that these patients tended to be younger (mean age, 10.8 vs 11.4 years) with a lower BMI (mean, 24.6 vs 29.5 kg/m2) compared with those patients correctly diagnosed. Slipped capital femoral epiphysis has been reported to occur most frequently among adolescents age 12 to 13 years, and most adolescents with SCFE are overweight, with a BMI greater than the 95th percentile.9–11 This study cohort appears to fit the “atypical” SCFE patient, who is younger and has a more normal BMI compared with the typical SCFE patient. The authors recommend increased vigilance when these patients present with supposed unilateral SCFE.
All of these patients were treated at a level 1 tertiary care children's hospital. In the earlier years of this study, orthopedic surgeons with and without pediatric training provided call coverage. The finding that missed contralateral slips were more commonly seen with treating surgeons without pediatric training (P=.0065) must be interpreted with caution. Although physicians without pediatric training missed 2 SCFEs, the pediatric-trained staff missed 3 slips. The pediatric-trained staff also treated the remainder of the cohort. This discrepancy may result in misleading results. Currently, all SCFEs are treated by pediatric-trained orthopedists at the authors' institution.
The utility of Klein's line as a diagnostic tool was also assessed. Some have questioned the use of Klein's line for radiographic evaluation of SCFE because of a high rate of missed SCFEs.13–15 A missed diagnosis rate of as high as 60% has been reported.14 In this series, Klein's line accurately identified only 60% of missed bilateral SCFEs. Although this did reach statistical significance on comparison of sequential disease with missed slips, no significant difference was noted when all patients correctly diagnosed were compared with those with missed disease. The authors recognize the false-negative rate of 40% in this cohort of missed SCFEs. They recommend that physicians use multiple methods to diagnose a SCFE and not rely solely on the finding of Klein's line.
The authors did not show a correlation between the severity of the slip and a missed contralateral slip. It was believed that severe slips can lead the observer to miss a subtle slip on the contralateral side. The authors included only 5 (10%) patients who had a severe slip, and in most patients the slip was mild (58%). One of the exclusion criteria was lack of orthogonal views of the bilateral hips. The severity of the slip was not measured for patients who were excluded from the study, and for this reason, the authors cannot comment on the relationship between slip severity and lack of appropriate radiographs in the exclusion group.
This study had some limitations. Because the study was retrospective, this analysis was inherently limited. The fellowship-trained pediatric orthopedists did not personally measure Southwick angles and did not remark on the status of Klein's line or the triradiate cartilage. These tasks were delegated to the other authors (A.W.S., J.R.K.). However, these authors met with the senior author (B.M.R.), a fellowship-trained pediatric orthopedist, to ensure that a standardized approach was used.1 The decision as to what actually constituted a slip was not specifically described. The reviewers were simply asked to follow their normal procedures to identify a slip. This approach was believed to be acceptable because all of the physicians who reviewed radiographs were fellowship-trained pediatric orthopedic surgeons who treat patients with SCFE regularly. Variability between observers was controlled by an adjudication process in which 3 of the authors reviewed the radiographs on 2 separate occasions and a contralateral hip was considered a missed slip only if a consensus was reached. It is possible that more slips could have been classified as missed. In addition, the number of patients included in this study was less than ideal. Previously discussed trends may have reached significance with greater power.
The authors described a subset of patients who were treated for SCFE and had missed contralateral disease with an incidence of 8.9%. The authors did not show a correlation between slip severity and missed contralateral slip. The patients with missed slips tended to be younger, with a normal BMI, although true statistical significance was not identified. Although Klein's line is a useful tool in the diagnosis of SCFE, a false-negative rate of 40% was observed. The authors recommend increased vigilance when an “atypical” patient with SCFE presents with supposed unilateral disease.
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Characteristics of Study Population
|Characteristic||Study Population (N=56)||Correctly Diagnosed (n=51)||Missed Bilateral (n=5)||P|
| Mean (SD)||11.4 (1.3)||11.4 (1.4)||10.8 (0.8)|
|Sex, No. (%)b||.39c|
| Male||33 (59)||31 (61)||2 (40)|
| Female||23 (41)||20 (39)||3 (60)|
|Race, No. (%)b||.44c|
| White||25 (45)||23 (45)||2 (40)|
| Hispanic||4 (7)||3 (6)||1 (20)|
| White non-Hispanic||27 (48)||25 (49)||2 (40)|
|Body mass index||.15a|
| Mean (SD), kg/m2||29.0 (6.5)||29.5 (6.4)||24.6 (6.4)|
| Range, kg/m2||13.8–52.9||18.8–52.9||13.8–28.6|
| Missing, No.||2||2||0|
|Risser sign, No. (%)d||.33a|
| Risser 0||46 (85.1)||41 (84)||5 (100)|
| Risser 1||3 (5.6)||3 (6)||0 (0)|
| Risser 3||3 (5.6)||3 (6)||0 (0)|
| Risser 4||2 (3.7)||2 (4)||0 (0)|
|Triradiates, No. (%)b||1.00c|
| Closed||23 (41)||21 (41)||2 (40)|
| Open||33 (59)||30 (59)||3 (60)|
Severity of Primary Slipa
|Study Population (N=56)||Correctly Diagnosed (n=51)||Missed Bilateral Slip (n=5)|
|Mild (<30°)||30 (57.7)||28 (59.6)||2 (40)|
|Moderate (30°–50°)||17 (32.7)||14 (29.8)||3 (60)|
|Severe (>50°)||5 (9.6)||5 (10.6)||0 (0)|
Trained in Pediatric Orthopedicsa
|Trained in Pediatric Orthopedics||No. (%)b|
|Study Population (N=56)||Correctly Diagnosed (n=51)||Missed Bilateral Slip (n=5)|
|No||2 (4)||0 (0)||2 (40)|
|Yes||54 (96)||51 (100)||3 (60)|
Contralateral Klein's Linea
|Klein's Line||No. (%)b|
|Study Population (N=56)||Correctly Diagnosed Bilateral Slip (n=19)||Missed Bilateral Slip (n=5)||Correctly Diagnosed Sequential Slip (n=32)|
|Negative||43 (80)||9 (53)||2 (40)||32 (100)|
|Positive||11 (20)||8 (47)||3 (60)||0 (0)|