The prevalence of bilateral slipped capital femoral epiphysis has been reported to range between 40% and 80%1. This wide range may be related to the variability in the radiographic criteria used to evaluate the hips2, the duration of the follow-up period3, and the age of the patient at the time of diagnosis4. Bilateral slipped capital femoral epiphysis may present either as a primary bilateral slip (simultaneous slips) or as a later contralateral slip (subsequent slip). The reported frequency of a subsequent, contralateral slip during the remaining growth period has ranged between 25% and 40%5-7. There is controversy regarding the advisability of prophylactic pinning of the radiographically and clinically normal contralateral hip in patients with a unilateral slip. Proponents of prophylactic pinning have argued that slipped capital femoral epiphysis is a disease of the physes that places the patient at substantial risk for a subsequent, contralateral slip until physeal closure occurs1,6,8,9. Bilateral slipped capital femoral epiphysis was found in 67% of the patients in the study by Hägglund et al., who proposed prophylactic pinning of the contralateral hip in patients presenting with a unilateral slip3. Billing and Severin identified rates of bilaterality in patients with slipped capital femoral epiphysis of up to 80% when they were followed beyond maturity2. The subsequent slipped capital femoral epiphysis does not appear to have a benign natural history, as Hägglund et al. reported that 53% of second slips recognized during adolescence were associated with osteoarthritic changes during a period of long-term follow-up6. Jensen et al. reported mild osteoarthritis in one of nine hips in which a subsequent slip was detected during adolescence and severe osteoarthritis in two10.
Opponents of prophylactic pinning argue that the procedure is unnecessary in most cases10,11, and they have advocated close observation to detect a subsequent slip at an early phase, before it progresses to a more severe grade. The results on long-term follow-up of chronic slipped capital femoral epiphysis are favorable provided that displacement is mild and remains so. Castro et al. reported that, since the majority of the sequential slipped capital femoral epiphyses in their patients were detected and treated early, close follow-up rather than prophylactic pinning was more advisable11. However, if the prevalence of subsequent, contralateral slipping is high and if the outcome or complications associated with the subsequent slip are substantially greater than the risks of prophylactic pinning, then simultaneous pinning of the radiographically and clinically normal hip as well as the slipped capital femoral epiphysis may be appropriate. The treatment of slipped capital femoral epiphysis must be aimed at preventing a moderate or severe slip of the epiphysis and minimizing the risk of osteonecrosis and chondrolysis, which are the most serious complications3,12, as the long-term outcome of slipped capital femoral epiphysis is directly related to the slip severity13 and the presence or absence of osteonecrosis and chondrolysis14-16.
The purpose of the current study was to evaluate the risk of unfavorable results (osteonecrosis, chondrolysis, and a severe slip, which can lead to later degenerative arthritis) in a large series of contralateral slipped capital femoral epiphyses in children who initially presented with a unilateral slipped capital femoral epiphysis.
We performed a retrospective review of the records of all patients with a slipped capital femoral epiphysis treated between 1993 and 2003 at a single hospital. Patients who had an endocrine or metabolic disease, had simultaneous bilateral involvement, or had been treated elsewhere for an initial slip were excluded. A complete set of radiographs made at the time of presentation was a criterion for inclusion. Only children who initially had had a unilateral slip and had been followed for a minimum of twenty-four months or until skeletal maturity (defined as fourteen years old for girls and sixteen years old for boys) were included17 in the analysis for detection of a subsequent, contralateral slip.
In this study, the surgeons stabilized all slipped capital femoral epiphyses with either a single or a double 7.3-mm cannulated screw. The acute slips were stabilized with the patient either on a fracture table with the lower limb internally rotated or on a standard operating room table with the patella forward. Image intensification was used in all cases. In no case was a slipped capital femoral epiphysis reduced or manipulated. Any change in the position of the slipped capital femoral epiphysis occurred incidentally during the positioning of the patient. As the chronic slips did not move during treatment (presumably they were stable), the hip was positioned with the patella facing forward for ease of pinning under image intensification without manipulation. Postoperatively, all patients were instructed to use partial weight-bearing on the operatively treated lower limb for six weeks.
The medical records provided information on gender, age, and the chronicity of the slip. The chronicity was classified as acute, acute-on-chronic, or chronic. The slip was considered to be acute if the symptoms had been present for three weeks or less, acute-on-chronic if sudden acute pain had occurred after the symptoms had been present for more than three weeks, and chronic if the symptoms had been present for more than three weeks.
All preoperative and follow-up radiographs were reviewed to determine the grade of the slip and the presence or absence of complications (osteonecrosis and chondrolysis). The grade of the slip was defined as mild (<30°), moderate (30° to 50°), or severe (>50°) on the basis of the lateral head-shaft angle described by Southwick18.
Patients who had been followed for more than twelve months were included in the analysis to detect complications. Chondrolysis was defined as a decrease in the joint space to a width of =3 mm19, and radiographic evidence of osteonecrosis included collapse and sclerosis of the femoral head20.
The age of the patients as well as the grade and chronicity of the slips were compared among the unilateral slips, first-side (index) slips in the patients with a bilateral slip, and the subsequent, contralateral slips in those with a bilateral slip. Statistical analysis was performed with analysis of variance (for the age comparison) and the chi-square test (for the chronicity and grade comparisons). P values of 0.05 were considered to be significant.
The database of 520 patients diagnosed with slipped capital femoral epiphysis was initially evaluated. At the time of the primary admission, 331 patients had a unilateral slip and 189 had a bilateral slip. After exclusion of the patients with a unilateral slip who had been lost to follow-up, had not reached skeletal maturity at the time of the last radiograph, or had been followed for less than two years, 227 patients (147 boys and eighty girls) with a unilateral slipped capital femoral epiphysis remained; these patients had been followed for an average of 26.4 months. A subsequent slip developed in the contralateral hip of eighty-two of these patients (forty-eight boys and thirty-four girls). The slip in the contralateral hip was detected at a mean of 6.5 months (range, one to twenty-five months) after the time of the initial presentation (Figs. 1-A and 1-B). There were no documented cases of pin penetration into the hip joint at the time of surgery.
The average age at the time of the initial presentation was thirteen years (range, nine to sixteen years) for the patients with a unilateral slipped capital femoral epiphysis in whom a subsequent, contralateral slip did not develop and 11.2 years (range, seven to fifteen years) for those in whom a subsequent slip did develop. This difference was significant (p < 0.05).
In the group without a subsequent slip, thirty-six (25%) of the index unilateral slips were acute, seven (5%) were acute-on-chronic, and 102 (70%) were chronic, and none of these designations changed during the follow-up period. In the group with a subsequent, second-side slip, twenty-three (28%) of the index unilateral slips were acute, six (7%) were acute-on-chronic, and fifty-three (65%) were chronic. On the contralateral side, sixty-two subsequent slips (76%) were acute, three (4%) were acute-on-chronic, and seventeen (21%) were chronic. There was no difference with regard to chronicity between the unilateral slipped capital femoral epiphyses in the patients without a subsequent slip and the index slipped capital femoral epiphysis in the patients who did have a subsequent, contralateral slip; however, both differed with regard to chronicity from the subsequent, contralateral slips, which were more likely to be acute (p < 0.05). Unfortunately, insufficient data were available in the charts to classify the slipped capital femoral epiphyses as stable or unstable, terms that have been shown to correlate better with the risk of osteonecrosis than the older terms acute and chronic.
There were eighty-one (56%) mild, fifty-two (36%) moderate, and twelve (8%) severe unilateral slipped capital femoral epiphyses in the patients who did not have a subsequent slip. In the group that did have a subsequent slip, sixty-three (77%) of the index unilateral slips were mild, fourteen (17%) were moderate, and five (6%) were severe, whereas sixty-four (78%) of the subsequent, second-side slips were mild, ten (12%) were moderate, and eight (10%) were severe (Fig. 2). The grades of severity were similar between the index slipped capital femoral epiphyses and the subsequent, contralateral slips in the group with a subsequent slip; however, both differed with regard to the grades of severity from the unilateral slipped capital femoral epiphyses in the group without a subsequent slip (p < 0.05).
Of the patients in whom the unilateral slipped capital femoral epiphysis was not followed by a second slip, 114 had been followed for more than one year (average, 33.2 months). Thirteen (11%) of these 114 children had a major complication: osteonecrosis of the femoral head was identified in eleven and chondrolysis, in two. The average intervals between the operation and identification of osteonecrosis and chondrolysis were 170 days (range, fifteen to 377 days) and ninety-five days, respectively. Of the patients who had a subsequent, contralateral slipped capital femoral epiphysis (with an average age of 11.7 years at the time of the second slip), fifty-eight were followed for more than one year (average, thirty-two months) after diagnosis of the second slip. There were five complications (9%): one patient had osteonecrosis (Fig. 3), and four had chondrolysis. All of the patients in whom chondrolysis developed had a severe slip, and the patient in whom osteonecrosis developed had an unstable slip. The average interval between the operation and the development of chondrolysis was 119 days (range, forty-five to 194 days) in this group.
A poor outcome was identified in nineteen (23%) of the contralateral hips with later slipped capital femoral epiphysis, as determined by including all of those with a moderate or severe slip and/or established osteonecrosis or chondrolysis. A complication (osteonecrosis) developed in only one patient with a mild slip.