Abstract
We evaluated the prevalence of slipped capital femoral epiphysis in the contralateral hip of 169 children who had been managed with pinning in situ and thirty who had been managed with immobilization in a spica cast. Only children who had initially been seen with a unilateral slip and had been followed for a minimum of two years or until skeletal maturity were included in the study. The average duration of follow-up was 3.6 years (range, 0.5 to 9.5 years) for the group that had been managed with a cast and 2.8 years (range, 1.0 to 8.3 years) for the group that had been managed operatively. In sixty-one (36 per cent) of the 169 patients who had had operative treatment and two (7 per cent) of the thirty who had been managed with a spica cast, a slip subsequently developed in the contralateral hip; this difference was significant (p = 0.001). On the basis of these findings, we recommend that closer attention be paid to the potential development of a slip in the contralateral hip after pinning.
The prevalence of bilateral slipped capital femoral epiphysis has been reported to range between 25 and 40 per cent4, although the exact numbers of patients were not given. This wide range may be related to the variability in the roentgenographic criteria used to evaluate the hips, in the duration of follow-up, in the presence of symptoms in the contralateral hip, and in possible geographic or biological factors. It is believed that an unrecognized slip of the proximal femoral capital epiphysis may lead to future problems10.
Hägglund et al. followed 260 patients for sixteen to sixty-six years. Twenty-eight (27 per cent) of 104 patients who had a slip of the contralateral hip that had not been diagnosed during adolescence had roentgenographic evidence of early osteoarthrosis. The reported high prevalence of bilateral involvement has led some surgeons to recommend prophylactic pinning of the unaffected hip in patients who have a unilateral slip9,10. Other surgeons believe that the complications encountered with prophylactic pinning of a normal hip considerably outweigh the benefits6.
If the initial treatment of a unilateral slip alters the prevalence of a slip in the contralateral hip, and if there is a greater risk of osteoarthrotic changes developing in the presence of an unrecognized slip, then prophylactic pinning may be appropriate. We hypothesize that a change in the treatment of a unilateral slip might influence the prevalence of a late slip in the contralateral hip. The purpose of the current study was to evaluate the frequency of a slip in the contralateral hip after immobilization in a spica cast or pinning of a unilateral slip.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
†Shriners Hospital for Crippled Children, Philadelphia Unit, 8400 Roosevelt Boulevard, Philadelphia, Pennsylvania 19152.
‡Section of Orthopaedic Surgery, University of Michigan Hospitals and Clinics, 1500 East Medical Center Drive, Ann Arbor, Michigan 48109.
§Department of Orthopaedic Surgery, Saint Christopher's Hospital for Children, Front and Erie Streets, Philadelphia, Pennsylvania 19134.
We retrospectively reviewed the medical records of 199 children who had been managed for a unilateral slip between 1966 and 1989 at five different medical centers. Thirty hips were treated with immobilization in a spica cast and 169, with pinning. Only children who initially had a unilateral slip and had been followed for a minimum of two years or until skeletal maturity (which we defined as fourteen years old in girls and sixteen years old in boys) were included. At three centers, all patients were managed operatively: at one center, twenty-four of twenty-seven patients were managed with a hip-spica cast; and at one center, eight patients were managed operatively and six were managed with a cast. The average duration of follow-up was 3.6 years (range, 0.5 to 9.5 years) for the group that had been managed with a cast and 2.8 years (range, 1.0 to 8.3 years) for the group that had been managed with pinning.
Anteroposterior and frog-leg lateral roentgenograms were made for all patients. The slips were graded as mild, moderate, or severe. At two centers, the slip was classified as mild when the degree of displacement of the epiphysis seen on the frog-leg lateral roentgenogram was 0 to 33 per cent, moderate when it was 34 to 50 per cent, and severe when it was 51 per cent or more. At two centers, the slip was classified as mild when the lateral slip angle of Southwick was less than 30 degrees, moderate when it was 31 to 45 degrees, and severe when it was greater than 45 degrees. At the remaining center, a mild slip meant that the difference in the femoral head-shaft angle of Southwick between the two hips was less than 30 degrees; moderate, that it was 31 to 50 degrees; and severe, that it was more than 50 degrees.
The age, sex, and race of the patient; the chronicity of the slip; and the symptoms associated with the contralateral hip were recorded. The chronicity was classified as acute, acute-on-chronic, or chronic. The slip was considered 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.
The Pearson chi-square test was used to evaluate the difference in the frequency of late slips in the contralateral hip between the two groups. Differences in frequency that were related to age, sex, race, or chronicity could not be evaluated statistically because of the small number of patients who had been managed with a cast.
Thirty patients from two centers were managed with traction for four to ten days to relieve pain and spasm, followed by immobilization in a one and one-half spica cast. The patients were immobilized for ten to twelve weeks, with the exception of two patients who were immobilized for only eight weeks. Gentle range-of-motion and strengthening exercises1 were started after the cast had been removed. Two (7 per cent) of the thirty patients who had been managed with a cast had a late slip in the contralateral hip, twenty-four and thirty-four months after the initial slip.
Cannulated screws or pins were used to stabilize the slip in 169 patients. The patients used crutches without weight-bearing for one to three weeks, advancing to full weight-bearing as tolerated. Sixty-one (36 per cent) of the 169 patients who had been managed with pinning had a late slip in the contralateral hip. This prevalence was significantly increased compared with that for the group that had been managed with a cast (p = 0.001).
Treatment modality: Two of the twenty patients who had had a mild slip and had been managed with a spica cast had a late slip in the contralateral hip. The remaining ten patients who had been managed with a cast and who had had a moderate slip (nine patients) or a severe slip (one patient) did not have a subsequent slip in the contralateral hip. In the group that had been managed with pinning, forty-seven (44 per cent) of the 108 patients who had had a mild slip, eleven (30 per cent) of the thirty-seven who had had a moderate slip, and three (13 per cent) of the twenty-four who had had a severe slip had a late slip in the contralateral hip.
Chronicity of the slip: Of the thirty hips that had been immobilized in a spica cast, six had had an acute-on-chronic slip and twenty-four, a chronic slip. The two patients who later had a slip in the contralateral hip had initially had a chronic slip. Of the 169 patients who had been managed operatively, forty-two had had an acute slip; five, an acute-on-chronic slip; and 122, a chronic slip. A late slip of the contralateral hip developed in seventeen (40 per cent) of the forty-two patients who had had an acute slip, one of the five who had had an acute-on-chronic slip, and forty-three (35 per cent) of the 122 who had had a chronic slip.
Race: In the group that had been managed with a cast, one (4 per cent) of twenty-three white patients and one of five black patients had a late slip in the contralateral hip. Neither of the two Hispanic patients had such a slip. In the group that had been managed with pinning, twenty-seven (42 per cent) of sixty-five white patients, thirty-one (31 per cent) of 100 black patients, and three of four patients of other races had a late slip in the contralateral hip.
Sex: Two of the twenty boys and none of the ten girls who had been managed with a cast later had a slip in the contralateral hip. Forty-two (37 per cent) of the 114 boys and nineteen (35 per cent) of the fifty-five girls who had been managed with pinning later had a slip in the contralateral hip.
Age: At the time of the initial slip, the average age of the patients who were managed with a spica cast was 12.3 years (range, 8.0 to 17.5 years). In the two patients who subsequently had a slip in the contralateral hip, the initial slip had developed at the age of 11.5 years, compared with 12.4 years for the remainder of the group. The average age of the patients who were managed operatively was 12.9 years (range, 8.3 years to 17.1 years) at the time of detection of the initial slip. The average age of the patients who later had a slip in the contralateral hip was 12.5 years (range, 9.4 to 15.5 years) at the time of the initial presentation, compared with 13.1 years (range, 8.3 to 17.1 years) for the remainder of the group.
Grade of the contralateral slip: Of the two patients who had been managed with a cast and later had a slip in the contralateral hip, one had had a mild slip initially and the other, a moderate slip. Of the sixty-one patients who had been managed operatively and later had a slip in the contralateral hip, fifty (82 per cent) had had a mild slip; nine (15 per cent), a moderate slip; and two (3 per cent), a severe slip at the time of presentation.
At the two centers where the data were recorded, nineteen (49 per cent) of thirty-nine late slips in the contralateral hip were detected on follow-up roentgenograms without the patient reporting any symptoms. In the remaining twenty patients, the duration of the symptoms was one week to three months.
Several authors have documented the prevalence of slips in the contralateral hip in follow-up studies, but few have discussed the relationship between the type of treatment and the development of such a slip. Histopathological evidence that slipped capital femoral epiphysis is a chronic bilateral disease was obtained from the postmortem study of the hip of a girl who had died of a pulmonary embolus four days after pinning of a unilateral slip9. These changes included the appearance of clefts, disorganization of cartilage cells, central widening, loss of orientation, misalignment, and replacement of the normal perpendicular columns of chondrocytes on the unaffected side. These findings support the suspicion that slipped capital femoral epiphysis is a bilateral disease. However, it is likely that the slip was bilateral roentgenographically at the time of the initial slip but was undetected because it occurred at a very early stage of the disease.
The varied prevalence of bilaterality (25 to 40 per cent)4 that has been reported is probably due to the different criteria used to determine the presence of a slip in the contralateral hip. Many patients have bilateral slips that occur sequentially rather than concurrently. Hägglund et al. found that only twenty-three (14 per cent) of 159 patients who had bilateral slips had the slips concurrently, while Boyer et al. reported concurrent slips in eleven (39 per cent) of twenty-eight patients. In four reports on sequential slips in 153 patients (fifty-nine, fifty-five, fourteen, and twenty-five patients, respectively8,10,13,20), the time between the diagnosis of the first and second slips ranged from 0.8 to 1.3 years. Boyer et al. noted that, in nine of eleven patients who had sequential bilateral slips, the second slip occurred within twelve months after the first. Loder et al. found that, in thirty-eight of forty-one patients who had sequential bilateral slips, the second slip occurred within twenty-four months after the first. The second slip was noted between thirty-one and thirty-six months, between thirty-seven and forty-two months, and five years after the first slip in one patient each. On the basis of these reports, we believe that the duration of follow-up (at least two years or to skeletal maturity) in the current study was sufficient for most of the sequential slips to be diagnosed.
Billing and Severin used an imaging technique to evaluate remodeling of the femoral neck and found a slip bilaterally in fifty (79 per cent) of sixty-three patients. Hägglund et al. used fluoroscopy to record the position of the inferior border of the neck of the femur and estimated that three standard deviations below the normal predicted position of the femoral head indicated a slip. Using these criteria, they found a slip bilaterally in 159 (61 per cent) of 260 patients. They believed this figure to be an underestimation of the true prevalence because of their adherence to very strict criteria. In the current study, we identified the slips on standard anteroposterior and lateral roentgenograms.
The association between osteoarthrosis and slipped capital femoral epiphysis has not been well documented in the literature. Murray described a tilt deformity of the femoral head as characteristic of an old slip, which he noted in 40 per cent of his patients who had osteoarthrosis of the hip. Stulberg et al. examined seventy-five specimens obtained at the time of total hip replacement and reported that a third of them showed evidence of a previous slip. This figure was subsequently questioned by Resnick, who thought that the reported changes could be secondary to remodeling of the osteoarthrotic head. Jerre noted that, with a longer duration of follow-up and more severe degrees of slipping, there was a link between slipped capital femoral epiphysis and osteoarthrosis of the hip. Other studies have indicated that hips with a severe slip will have earlier and more severe degenerative changes5,18.
In the present review, we found no relationship between race and the development of a slip in the contralateral hip; however, the number of patients who had been managed with a cast was insufficient for statistical analysis. In a previous report of thirty-seven hips (thirty-two patients) that had been treated with immobilization in a spica cast (either unilaterally or bilaterally), we noted that one of five black patients and one of twenty-seven white patients had a slip in the contralateral hip1. This suggests that race might be an important variable, but the numbers in the two groups were too small to draw any conclusions. However, the current study did not show a similar trend; twenty-seven (42 per cent) of sixty-five white patients and thirty-one (31 per cent) of 100 black patients had sequential slips, indicating that race was not an influencing factor.
The major difference between the patients managed with a cast in the study by Meier et al. and those studied by us previously1 was race. Patients in the former study were primarily black and in the latter study, primarily white. Black patients, both boys and girls, had a higher prevalence of chondrolysis after immobilization in a cast1,16. Ingram et al. reported chondrolysis in seventeen (14 per cent) of 125 white patients and fifty-four (44 per cent) of 124 black patients. Of ninety-one hips in three studies1,15,16, twenty-four (three of twenty-nine in white boys, eleven of twenty-eight in black boys, ten of twenty in black girls, and none of fourteen in white girls) had chondrolysis after treatment with a cast.
Some authors still use immobilization in a spica cast for the treatment of slipped capital femoral epiphysis. In our previous study1, we used such treatment for thirty-seven hips that had a chronic slip and found progression of the slip in one hip after eight weeks. Narrowing of the joint space was seen in seven hips (19 per cent), and chondrolysis was noted in five of the seven. There were no complications specifically related to the cast. Meier et al. reported progression of the slip in three of seventeen hips after immobilization in a spica cast. These authors noted that two of the three hips did not have healing of the metaphyseal radiolucency, a criterion used in our earlier study1 to discontinue use of the cast. If they had used this criterion to document healing, progression would have occurred in only one hip, a finding consistent with other reports1.
In the current study, the initial method of treatment appeared to alter the prevalence of a slip in the contralateral hip. We do not necessarily recommend that all unilateral slips be treated with a cast but, rather, that closer attention be paid to the potential for the development of an asymptomatic slip in the contralateral hip and that alternative methods of postoperative management be considered carefully. Walking with crutches and a three-point gait will overload a potentially diseased contralateral hip that is at risk for a slip. This risk must be weighed against the risk of failure of pin fixation if weight-bearing is allowed on the affected side. Therefore, an alternative type of treatment that will not overload the hip—such as a period of immobilization after pinning in situ or the use of internal fixation that is strong enough to allow immediate full weight-bearing on the affected side—should be considered.
Prophylactic pinning would be an option if reliable predictors for the development of a slip on the contralateral side could be identified. A small pilot study7 showed that a retroverted head-neck angle, as measured on imaging studies of a roentgenographically normal hip, was predictive of a slip on the contralateral side in five of six patients. Fourteen patients who did not have a retroverted hip had no such slip. Imaging studies can also help to identify changes in the physis on the contralateral side before there is roentgenographic evidence of a slip, and this can aid in the determination of the need for operative treatment of the asymptomatic hip. A large prospective study is necessary to determine whether imaging studies of patients who have a unilateral slip would be helpful in predicting the development of a slip in the contralateral hip.
In the current study, the patients who had been managed with immobilization in a spica cast had a lower prevalence of a slip in the contralateral hip than did those who had been managed with pinning (two [7 per cent] of thirty compared with sixty-one [36 per cent] of 169). On the basis of these results, we recommend that the alternatives for treatment and for postoperative management of patients who have a unilateral slip be reassessed.
NOTE: The authors gratefully acknowledge Michael T. Busch, M.D., and W. Timothy Ward, M.D., for assistance with data collection; Michael Clancy, M.D., for contribution of patients; Elizabeth R. Gardner, P.T., for statistical analysis; and Carolyn Hendrix for preparation of the manuscript.
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