JBJS | Acute Slipped Capital Femoral Epiphysis. Review of Outcomes and Rates of Avascular Necrosis*†

The Journal of Bone & Joint Surgery, Volume 78, Issue 3

Articles | March 01, 1996

Acute Slipped Capital Femoral Epiphysis. Review of Outcomes and Rates of Avascular Necrosis*†

T. RATTEY, M.D., F.R.C.S.(C)‡; F. PIEHL, M.D.§; J. G. WRIGHT, M.D., M.P.H., F.R.C.S.(C)¶, TORONTO, ONTARIO, CANADA

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Investigation performed at The Hospital for Sick Children, Toronto

The Journal of Bone & Joint Surgery. 1996; 78:398-402

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Abstract

One hundred and forty-nine patients (208 hips) were managed for slipped capital femoral epiphysis at The Hospital for Sick Children in Toronto from 1980 through 1990. We retrospectively reviewed the records of twenty-four patients (twenty-six hips) who had an acute slipped capital femoral epiphysis to evaluate the outcome of treatment and possible risk factors for avascular necrosis associated with this condition. The patients were evaluated with the Iowa hip-scoring system, a physical examination, and anteroposterior and lateral radiographs. The severity of degenerative joint disease was assessed on the radiographs with use of the system described by Boyer et al.Eighteen slips were classified as grade 1; seven, as grade 2; and one, as grade 3, according to the system of Southwick. Twenty-three hips were treated with in situ pinning and three, with reduction and pinning. The mean duration of follow-up was 5.9 years (range, 2.1 to 12.8 years). Poor Iowa hip scores and more severe degenerative changes were related to the development of avascular necrosis and to the severity of the slip. Avascular necrosis developed in four hips (15 per cent), two of which had had a reduction. Multiple logistic regression analysis, which included all 150 slips (both acute and chronic) for which there was adequate follow-up, showed that the rate of avascular necrosis was related to both the severity and the acute nature of the slip.

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Introduction

Introduction | Materials and Methods | Results | Discussion | References

Few reports in the literature have dealt solely with acute slipped capital femoral epiphysis^{1,3,11,13,20,21,28}. Because acute slips are much less common than chronic slips, most authors have reported the results of a small number of patients who had an acute slip along with those of patients who had a chronic slip^{7-10,12,17,18,25}. Acute slipped capital femoral epiphysis, however, has a different prognosis than chronic slipped capital femoral epiphysis, and it has been suggested that acute slips are associated with higher rates of avascular necrosis^{7-9,13,17,23,24}. The rate of avascular necrosis in those studies ranged from zero of seven hips²⁴ to seven of eleven hips⁷. In what we believe to be the largest study to have dealt solely with acute slips, avascular necrosis developed in eight (18 per cent) of forty-four hips¹³.

In addition, an acute slip may be treated differently than a chronic slip because it is possible to perform a closed reduction of an acute slip before pinning. The role of reduction in this setting is controversial. The purpose of reduction is to prevent malunion, which may predispose the hip to late osteoarthrosis⁸. However, reduction has been reported to increase the risk of avascular necrosis, which has been associated with a poor outcome⁸.

The purposes of the present retrospective study were to evaluate the outcome of treatment of acute slipped capital femoral epiphysis and to assess the risk factors for avascular necrosis associated with this condition.

*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. Funds were received in total or partial support of the research or clinical study presented in this article. The funding source was a Medical Research Council Scholarship (J. G. W.).

†Read at the Annual Meeting of The Canadian Orthopaedic Association, Winnipeg, Manitoba, Canada, June 1994.

‡Orthopedic Center, 4801 South Congress Avenue, Lake Worth, Florida 33414. Please address requests for reprints to Dr. Rattey.

§Midlands Orthopaedic P.A., 1910 Blanding Street, Columbia, South Carolina 29201.

¶The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G-1X8, Canada.

†Read at the Annual Meeting of The Canadian Orthopaedic Association, Winnipeg, Manitoba, Canada, June 1994.

‡Orthopedic Center, 4801 South Congress Avenue, Lake Worth, Florida 33414. Please address requests for reprints to Dr. Rattey.

§Midlands Orthopaedic P.A., 1910 Blanding Street, Columbia, South Carolina 29201.

¶The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G-1X8, Canada.

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TABLE I DATA ON THE PATIENTS IN WHOM AVASCULAR NECROSIS DEVELOPED

*According to the system of Southwick²⁹.†Reduction was not attempted, but an increased slip angle was noted on postoperative radiographs.

Case	Age at Op. (Yrs.)	Durat. of Follow-up (Yrs.)	Grade of Slip*	Reduction Attempted	No. of Pins
3	12.4	4.7	2	No†	2
6	18.9	2.8	2	Yes	3
11	11.8	3.1	2	Yes	1
23	7.6	6.0	1	No	2

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TABLE I DATA ON THE PATIENTS IN WHOM AVASCULAR NECROSIS DEVELOPED

*According to the system of Southwick²⁹.†Reduction was not attempted, but an increased slip angle was noted on postoperative radiographs.

Case	Age at Op. (Yrs.)	Durat. of Follow-up (Yrs.)	Grade of Slip*	Reduction Attempted	No. of Pins
3	12.4	4.7	2	No†	2
6	18.9	2.8	2	Yes	3
11	11.8	3.1	2	Yes	1
23	7.6	6.0	1	No	2

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

One hundred and forty-nine patients (208 hips) were managed for slipped capital femoral epiphysis at The Hospital for Sick Children in Toronto from January 1980 through December 1990. Thirty patients (thirty-two hips) had an acute slip; this diagnosis was made if the patient had had pain or a limp for less than three weeks as well as radiographic evidence of an acute slip (no rounding off of the metaphyseal neck) at the time of the initial examination. No patient had a traumatic slip, defined as a slip resulting from a violent force that caused the epiphysis to separate from the femoral neck through a normal proximal femoral physis⁸. Six patients (six hips) who had not been followed clinically or radiographically for at least two years were excluded; thus, twenty-four patients (twenty-six hips) who had an acute slip formed the basis for the present study.

The medical records were reviewed for demographic data (the sex of the patient, the age of the patient at the time of the slip, and any associated medical conditions), the history of the slip (the duration of pain or a limp, any associated minor trauma, and the weight-bearing status of the patient at the time of presentation), and details regarding treatment (whether or not a reduction was performed, the method of reduction, the method of treatment [fixation with pins, femoral osteotomy, or immobilization in a hip-spica cast], and the number of pins used).

The patients returned for a clinical or radiographic evaluation, or both. The Iowa hip score was used to assess function⁶. A physical examination was used to assess gait, the range of motion of the hip, the lengths of the lower extremities, and the strength of the muscles about the hip.

The radiographs were reviewed by one of us (T. R.), as recommended in a previous study³⁰. The preoperative radiographs were evaluated to determine the percentage of slip and the slip angle as described by Southwick²⁹. The normal lateral head-shaft angle ranges from 0 to 25 degrees²⁹. In patients who had unilateral involvement, the slip angle was defined as the difference between the head-shaft angle on the side of the slip and that on the normal side²⁹. In patients who had bilateral involvement, the slip angle was defined as the head-shaft angle minus 10 degrees; because such patients do not have a normal hip that would permit measurement of the slip angle with use of the method just described, the head-shaft angle of the contralateral hip is given the mean value of 10 degrees¹⁵. The severity of the slip was defined as grade 1 if the slip angle was less than 30 degrees, grade 2 if it was 30 to 60 degrees, and grade 3 if it was more than 60 degrees⁶.

The postoperative radiographs were reviewed to determine the reduction achieved; the position of the pin or pins within the epiphysis; the distance from the tip of the pin or pins to the subchondral bone; and the presence of chondrolysis, avascular necrosis, or degenerative changes. Chondrolysis was defined as a cartilage space of three millimeters or less¹⁴. The severity of degenerative joint disease was graded according to the system described by Boyer et al.⁵: grade 0 indicated normal radiographic findings and no degenerative changes; grade I, one subchondral cyst or one osteophyte, no subchondral sclerosis, and a normal cartilage space; grade II, a few subchondral cysts and osteophytes, slight subchondral sclerosis, and slight narrowing of the cartilage space; and grade III, multiple subchondral cysts and osteophytes, marked subchondral sclerosis, and moderate narrowing or obliteration of the cartilage space.

The radiographs of patients who had a chronic slip and adequate follow-up also were reviewed to determine the presence of avascular necrosis. Data on these patients as well as on those who had an acute slip then were evaluated with use of multiple logistic regression analysis to determine factors possibly related to avascular necrosis. Of the initial 149 patients (208 hips), 108 patients (150 hips) had sufficient follow-up data for the multiple logistic regression analysis. Forty-two of these patients had a bilateral slip (two had a bilateral acute slip, ten had one acute and one chronic slip, and thirty had a bilateral chronic slip), and sixty-six had a unilateral slip (twelve had an acute slip and fifty-four had a chronic slip). Thus, data on 124 chronic slips and twenty-six acute slips were included in the multiple logistic regression analysis.

Statistical analysis was performed with use of unpaired two-tailed t tests, Fisher exact and chi-square tests, analysis of variance, and, as mentioned, multiple logistic regression analysis. Logistic regression analysis, which is the appropriate multivariate statistical method with which to determine the effect of multiple variables on a binary outcome (for example, the presence or absence of avascular necrosis), was used to evaluate the relationship between the risk of avascular necrosis and the type of the slip (acute or chronic), the severity of the slip (grade 1, 2, or 3), and the number of pins.

Results

Introduction | Materials and Methods | Results | Discussion | References

Nineteen patients (twenty-one hips) who had an acute slip were assessed clinically and radiographically, two patients (two hips) completed a telephone questionnaire and had a complete radiographic examination, and three patients (three hips) had only a radiographic examination. Eleven slips involved the right hip and fifteen, the left. Thirteen slips were in male patients and thirteen, in female patients. Twelve patients had unilateral involvement, and twelve had bilateral involvement. Of the twelve patients who had bilateral involvement, ten had an acute slip on one side and a chronic slip on the other (ten acute slips) and two had a bilateral acute slip (four acute slips). The mean age of the patients was 12.3 years (range, 7.6 to 18.9 years) at the time of the diagnosis and 18.2 years (range, 12.8 to 25.0 years) at the time of the follow-up evaluation. Thus, the mean duration of follow-up was 5.9 years (range, 2.1 to 12.8 years).

Eighteen slips were classified as grade 1; seven, as grade 2; and one, as grade 3, according to the system of Southwick²⁹. Three slips were treated with reduction and pinning: the first, a grade-3 slip, was reduced with traction and manipulation and fixed with one pin with the patient under general anesthesia; the second, a grade-2 slip, was reduced with the Leadbetter maneuver¹⁹ and fixed with three pins; and the third, also a grade-2 slip, was reduced preoperatively with slings and springs and fixed with one pin. The reduction of this last slip was confirmed on postoperative radiographs. The remaining eighteen grade-1 and five grade-2 acute slips were treated with in situ pinning. Two patients had associated medical problems due to residual panhypopituitarism after the removal of a craniopharyngioma.

Three pins were used for the in situ pinning of one grade-1 slip; two, for the pinning of three slips (two grade-1 slips and one grade-2 slip); and one, for the pinning of nineteen slips (fifteen grade-1 and four grade-2 slips). No slip continued to progress after in situ pinning.

Complications developed in five patients (five hips) after the treatment of the acute slip. Avascular necrosis developed in four patients (four hips; 15 per cent) (Table I), one of whom subsequently had a femoral osteotomy because of pain in the hip. Two of these four patients had had reduction and pinning of a grade-2 slip, and the other two (one of whom had had a grade-1 slip and one of whom had had a grade-2 slip) had had in situ pinning. An increased slip angle was noted on the immediate postoperative radiographs of the patient (Case 3) who had been managed with what had been thought to be in situ pinning of a grade-2 slip, suggesting that additional slippage had occurred before the insertion of the pins. The follow-up radiographs showed no further slippage. The fifth patient had marked residual deformity due to in situ pinning of a grade-3 slip and was managed with a flexion-valgus femoral osteotomy, with the femoral head and neck placed in valgus angulation and the distal segment of the femur placed in flexion through the site of the osteotomy, for realignment of the proximal part of the femur. Chondrolysis did not develop in any patient who had an acute slip.

The mean Iowa hip score for the twenty-four patients (twenty-six hips) who had acute slipped capital femoral epiphysis was 92 points (range, 72 to 100 points) at the most recent evaluation. The score was related to the severity of the slip (analysis of variance, p = 0.04), with the patients who had a more severe slip having a poorer score. The two patients (two hips) who had avascular necrosis and who returned for an examination had Iowa hip scores of 72 and 87 points. The other two such patients (two hips) did not return for clinical examination.

The mean internal rotation of the twenty-one hips (nineteen patients) that were examined clinically was 20 degrees. Only one hip, in which avascular necrosis had developed, had decreased external rotation. Two patients (two hips) had abduction of 30 degrees or less. Both patients had had a femoral osteotomy. One of the patients had had 30 degrees of abduction before the osteotomy, which was performed because of malunion, and the other had had 0 degrees of abduction before the osteotomy, which was performed because of avascular necrosis. One hip, in which avascular necrosis had developed, had a fixed flexion deformity of 20 degrees. Seven patients (eight hips) had a positive Trendelenburg sign at the time of the most recent examination.

The mean grade of degenerative joint disease, as assessed on radiographs according to the system of Boyer et al.⁵, was 0.6. The severity of the slip was associated with a poor radiographic grade at the time of the most recent follow-up (Fisher exact test; p = 0.0003). Patients who had worse radiographic grades had lower Iowa hip scores (unpaired t test; p = 0.009) and were more likely to have a positive Trendelenburg sign (Fisher exact test; p = 0.03).

Because of the small numbers of hips in which the slip had been reduced or had been fixed with more than one pin, the relationship (if any) between avascular necrosis and either reduction or the number of pins could not be examined statistically. Pins were placed in the anterolateral portion of the head in four hips; avascular necrosis developed in two (Cases 3 and 6) but not in the other two (Cases 5 and 10). More than one pin was used in five hips; avascular necrosis developed in three (Cases 3 [two pins], 6 [three pins], and 23 [two pins]) but not in the other two (Cases 8 [two pins] and 15 [three pins]). Only one of the hips in which avascular necrosis developed was in a patient who had a medical problem (a craniopharyngioma). Two of the twenty-two hips in which avascular necrosis did not develop were in a patient who had a medical problem (an intracranial tumor and hypothyroidism).

After adjusting for all factors with multiple logistic regression analysis, only the acute nature of the slip (p = 0.01) and the most severe (grade-3) slips (p = 0.004) were significantly related to an increased risk of avascular necrosis.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

The highest reported rate of avascular necrosis after the treatment of acute slipped capital femoral epiphysis has been seven of eleven hips⁷. To our knowledge, the largest study to have dealt solely with acute slips included forty-four hips, twenty-nine of which had been manipulated; avascular necrosis developed in eight of eleven hips in which the position of the capital femoral epiphysis had improved with manipulation¹³. Other series have been smaller^7-9,17,24. Suggested risk factors for avascular necrosis have included the location of pins in the epiphysis, the number of pins, the severity of the slip, and reduction of the slip^5,7,9,13,21. Placement of the pins in the anterolateral portion of the epiphysis has been reported to increase the risk of avascular necrosis^6,21,26 because of the location of the lateral epiphyseal arteries in that area⁷. The rates of complications and reoperation also have been reported to increase with the number of pins⁴. Karol et al.¹⁶ recommended fixation with a single screw in the treatment of slipped capital femoral epiphysis. In all of those reports, the relationship of each factor with the risk of avascular necrosis was examined in isolation. The possibility that severe slips may be more likely to be treated with reduction and with multiple pins may confound the association between each of these factors and the risk of avascular necrosis.

Canale⁶ reported that the rate of avascular necrosis was 20 per cent after closed reduction of slipped capital femoral epiphysis, 33 per cent after open reduction, and 2 per cent without reduction. However, he did not provide specific rates of avascular necrosis for acute slips. Koval et al.¹⁷ reported that avascular necrosis was associated with two of twelve acute slips: it was noted on the preoperative bone scan of one patient who had a grade-3 slip, and it developed in one other patient in whom a grade-3 slip had been treated with reduction with traction and with three pins. Carey et al.⁷ reported that avascular necrosis developed in seven of eleven hips after the treatment of an acute slipped capital femoral epiphysis; all seven hips had had a severe slip that had been reduced by means of gentle internal rotation of the lower limb. Avascular necrosis did not develop in any of the other four hips, in which a mild slip had been treated without reduction. Griffith¹³ reported that avascular necrosis developed in eight of eleven hips in which the position of the capital femoral epiphysis had improved after manipulative reduction of an acute slip, but he provided no details regarding the severity of the slips.

Other authors have suggested that gentle reduction with the patient under anesthesia is a safe method for the reduction of an acute slipped capital femoral epiphysis^5,26. Casey et al.⁹ thought that skin traction with slight medial (internal) rotation for three or four days preoperatively was the safest method. Canale⁶ reported an 18 per cent prevalence of avascular necrosis in patients who had not received operative treatment of an acute slipped capital femoral epiphysis and suggested that patients who do not receive any form of treatment are at risk for avascular necrosis. Nishiyama et al.²⁴ reported that avascular necrosis did not develop after closed reduction of seven acute slips, but they did not provide any data regarding the severity of the slips. Thus, the role of reduction in the treatment of acute slipped capital femoral epiphysis is controversial.

Discrepancies in the reported rates of avascular necrosis may be due to differences in the definition of an acute slip, in the type and rigor of the attempted reduction, and in the severity of the slips. First, the inclusion of traumatic slipped capital epiphysis⁸ in some studies but not in others may have affected the rates of avascular necrosis. Second, the forceful reduction of slipped capital femoral epiphysis may have led to an increased rate of avascular necrosis in some series. The failure to consider the severity of the slips may have confounded the association between reduction and the risk of avascular necrosis, as discussed previously.

In the present study, avascular necrosis occurred in association with four (15 per cent) of twenty-six acute slips. The patients who had a severe slip were more likely to have a closed reduction. When the entire group of slips (acute and chronic) was evaluated with use of multiple logistic regression analysis, which adjusts for the additive effect of the severity of the slip, only the severity of the slip and the acute nature of the slip were associated with an increased risk of avascular necrosis. Thus, the previously reported association of avascular necrosis with reduction of a slipped epiphysis may be due to the confounding effect of the severity of the slip, in that a patient who has a severe slip may be more likely to have a reduction. Although the numbers are too small for clinically valid statistical evaluation, we believe that a gentle reduction will not cause avascular necrosis and that the number and position of the pins probably do not contribute to the risk of avascular necrosis.

Avascular necrosis and the severity of the slip both appear to affect the outcome. Carney et al.⁸ evaluated patients forty-one years after the treatment of slipped capital femoral epiphysis and reported lower Iowa hip and radiographic scores in patients in whom avascular necrosis had developed. Although Aronson and Carlson² reported no association between the severity of the slip and the clinical result, the mean duration of follow-up in that study was only three years. In the present study, the Iowa hip score and the severity of the degenerative changes were related to the severity of the slip. This finding suggests that the severity of the slip, independent of the presence of avascular necrosis, may affect the outcome and that malunion of a slipped capital femoral epiphysis may have long-term consequences.

NOTE: The authors thank Derek Stephane for his assistance with the statistical analysis.

References

Introduction | Materials and Methods | Results | Discussion | References

Aadalen, R. J.; Weiner, D. S.; Hoyt, W.; and |and |Herndon, C. H.: Acute slipped capital femoral epiphysis. J. Bone and Joint Surg.,56-A: 1473-1487, Oct. 1974.56-A1473 1974

Aronson, D. D., and |and |Carlson, W. E.: Slipped capital femoral epiphysis. A prospective study of fixation with a single screw. J. Bone and Joint Surg.,74-A: 810-819, July 1992.74-A810 1992

Barash, H. L.; Galante, J. O.; and |and |Ray, R. D.: Acute slipped capital femoral epiphysis. A report of nine cases. Clin. Orthop.,79: 96-103, 1971.7996 1971 [PubMed][CrossRef]

Blanco, J. S.; Taylor, B.; and |and |Johnston, C. E., II: Comparison of single pin versus multiple pin fixation in treatment of slipped capital femoral epiphysis. J. Pediat. Orthop.,12: 384-389, 1992.12384 1992 [CrossRef]

Boyer, D. W.; Mickelson, M. R.; and |and |Ponseti, I. V.: Slipped capital femoral epiphysis. Long-term follow-up study of one hundred and twenty-one patients. J. Bone and Joint Surg.,63-A: 85-95, Jan. 1981.63-A85 1981

Canale, S. T.: Problems and complications of slipped capital femoral epiphysis. In Instructional Course Lectures, The American Academy of Orthopaedic Surgeons. Vol. 38, pp. 281-290. Park Ridge, Illinois, The American Academy of Orthopaedic Surgeons, 1989.

Carey, R. P. L.; Moran, P. L.; and |and |Cole, W. G.: The place of threaded pin fixation in the treatment of slipped upper femoral epiphysis. Clin. Orthop.,224: 45-51, 1987.22445 1987 [PubMed]

Carney, B. T.; Weinstein, S. L.; and |and |Noble, J.: Long-term follow-up of slipped capital femoral epiphysis. J. Bone and Joint Surg.,73-A: 667-674, June 1991.73-A667 1991

Casey, B. H.; Hamilton, H. W.; and |and |Bobechko, W. P.: Reduction of acutely slipped upper femoral epiphysis. J. Bone and Joint Surg.,54-B(4): 607-614, 1972.54-B(4)607 1972

Colton, C. L.: Slipped upper femoral epiphysis. In Recent Advances in Orthopaedics, edited by A. Catterall. Vol. 5, pp. 61-77. Edinburgh, Churchill Livingstone, 1987.

Fahey, J. J., and |and |O'Brien, E. T.: Acute slipped capital femoral epiphysis. Review of the literature and report of ten cases. J. Bone and Joint Surg.,47-A: 1105-1127, Sept. 1965.47-A1105 1965

Greenough, C. G.; Bromage, J. D.; and |and |Jackson, A. M.: Pinning of the slipped upper femoral epiphysis—a trouble-free procedure?. J. Pediat. Orthop.,5: 657-660, 1985.5657 1985 [CrossRef]

Griffith, M. J.: Acute slipping of the capital femoral epiphysis. In Proceedings of the British Orthopaedic Association. J. Bone and Joint Surg.,57-B(1): 113, 1975.57-B(1)113 1975

Ingram, A. J.; Clarke, M. S.; Clark, C. S., Jr.; and |and |Marshall, W. R.: Chondrolysis complicating slipped capital femoral epiphysis. Clin. Orthop.,165: 99-109, 1982.16599 1982 [PubMed]

Jones, J. R.; Paterson, D. C.; Hillier, T. M.; and |and |Foster, B. K.: Remodelling after pinning for slipped capital femoral epiphysis. J. Bone and Joint Surg.,72-B(4): 568-573, 1990.72-B(4)568 1990

Karol, L. A.; Doane, R. M.; Cornicelli, S. F.; Zak, P. A.; Haut, R. C.; and |and |Manoli, A., II: Single versus double screw fixation for treatment of slipped capital femoral epiphysis: a biomechanical analysis. J. Pediat. Orthop.,12: 741-745, 1992.12741 1992 [CrossRef]

Koval, K. J.; Lehman, W. B.; Rose, D.; Koval, R. P.; Grant, A.; and |and |Strongwater, A.: Treatment of slipped capital femoral epiphysis with a cannulated-screw technique. J. Bone and Joint Surg.,71-A: 1370-1377, Oct. 1989.71-A1370 1989

Kulick, R. G., and |and |Denton, J. R.: A retrospective study of 125 cases of slipped capital femoral epiphysis. Clin. Orthop.,162: 87-90, 1982.16287 1982 [PubMed]

Leadbetter, G. W.: A treatment for fracture of the neck of the femur. J. Bone and Joint Surg.,15: 931-940, Oct. 1933.15931 1933

Loder, R. T.; Richards, B. S.; Shapiro, P. S.; Reznick, L. R.; and |and |Aronson, D. D.: Acute slipped capital femoral epiphysis: the importance of physeal stabilty. J. Bone and Joint Surg.,75-A: 1134-1140, Aug. 1993.75-A1134 1993

Loyd, R. D., and |and |Evans, J. P.: Acute slipped capital femoral epiphysis. Southern Med. J.,68: 857-862, 1975.68857 1975 [PubMed][CrossRef]

Morrissy, R.: Principles of in situ fixation in chronic slipped capital femoral epiphysis. In Instructional Course Lectures, The American Academy of Orthopaedic Surgeons. Vol. 38, pp. 257-262. Park Ridge, Illinois, The American Academy of Orthopaedic Surgeons, 1989.

Morrissy, R. T.: Slipped capital femoral epiphysis. In Lovell and Winter's Pediatric Orthopaedics, edited by R. T. Morrissy. Ed. 3, p. 902. Philadelphia, J. B. Lippincott, 1990.

Nishiyama, K.; Sakamaki, T.; and |and |Ishii, Y.: Follow-up study of slipped capital femoral epiphysis. J. Pediat. Orthop.,9: 653-659, 1989.9653 1989 [CrossRef]

O'Beirne, J.; McLoughlin, R.; Dowling, F.; Fogarty, E.; and |and |Regan, R.: Slipped upper femoral epiphysis: internal fixation using single central pins. J. Pediat. Orthop.,9: 304-307, 1989.9304 1989 [CrossRef]

O'Brien, E. T., and |and |Fahey, J. J.: Remodeling of the femoral neck after in situ pinning for slipped capital femoral epiphysis. J. Bone and Joint Surg.,59-A: 62-68, Jan. 1977.59-A62 1977

Riley, P. M.; Weiner, D. S.; Gillespie, R.; and |and |Weiner, S. D.: Hazards of internal fixation in the treatment of slipped capital femoral epiphysis. J. Bone and Joint Surg.,72-A: 1500-1509, Dec. 1990.72-A1500 1990

Schein, A. J.: Acute severe slipped capital femoral epiphysis. Clin. Orthop.,51: 151-166, 1967.51151 1967 [PubMed]

Southwick, W. O.: Osteotomy through the lesser trochanter for slipped capital femoral epiphysis. J. Bone and Joint Surg.,49-A: 807-835, July 1967.49-A807 1967

Wright, J. G., and |and |Feinstein, A. R.: Improving the reliability of orthopaedic measurements. J. Bone and Joint Surg.,74-B(2): 287-291, 1992.74-B(2)287 1992

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TABLE I DATA ON THE PATIENTS IN WHOM AVASCULAR NECROSIS DEVELOPED

*According to the system of Southwick²⁹.†Reduction was not attempted, but an increased slip angle was noted on postoperative radiographs.

Case	Age at Op. (Yrs.)	Durat. of Follow-up (Yrs.)	Grade of Slip*	Reduction Attempted	No. of Pins
3	12.4	4.7	2	No†	2
6	18.9	2.8	2	Yes	3
11	11.8	3.1	2	Yes	1
23	7.6	6.0	1	No	2

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TABLE I DATA ON THE PATIENTS IN WHOM AVASCULAR NECROSIS DEVELOPED

*According to the system of Southwick²⁹.†Reduction was not attempted, but an increased slip angle was noted on postoperative radiographs.

Case	Age at Op. (Yrs.)	Durat. of Follow-up (Yrs.)	Grade of Slip*	Reduction Attempted	No. of Pins
3	12.4	4.7	2	No†	2
6	18.9	2.8	2	Yes	3
11	11.8	3.1	2	Yes	1
23	7.6	6.0	1	No	2