Comparison of Fracture Versus Radiolucent Table in the Treatment of Slipped Capital Femoral Epiphysis

Abstract

Purpose:

Compare slipped capital femoral epiphysis stabilized on fracture versus radiolucent table.

Methods:

Twenty unilateral stable mild slipped capital femoral epiphyses were stabilized in-situ with a single screw. Age, sex, side, body-mass index, type of table, anesthesia time, surgery time, fluoroscopy time, number of fluoroscopy images, preoperative/postoperative lateral head-shaft angle, and number of screw threads engaging the epiphysis were noted.

Results:

There were no differences in the measured parameters.

Conclusions:

Stabilization of mild slipped capital femoral epiphysis can be accomplished reliably and safely with the use of either a radiolucent or fracture table.

INTRODUCTION

The treatment goals of slipped capital femoral epiphysis (SCFE) are to stabilize the physis, achieve epiphysiodesis, and avoid complications. Successful proximal femoral physeal fusion without slip progression has been reported using a single centrally placed screw.^1,2 SCFE can be stabilized on either a fracture table or a radiolucent table. Lee and Chapman described in-situ fixation for slipped capital femoral epiphysis on a radiolucent operating table.³ The authors found the procedure to be easy and reliable.

The relationship between table selection, time required, and screw placement has been studied.⁴ Blasier et al. noted greater operating room and surgery times for the fracture versus the radiolucent table. The purpose of the current study was to compare the perioperative outcomes of unilateral mild stable slipped capital femoral epiphysis treated with in-situ single-screw fixation using either a radiolucent table or a fracture table.

METHODS

The medical records and radiographs of all children who underwent in-situ fixation of SCFE with a single cannulated screw at a single institution were reviewed. The medical records were reviewed for stability, sex, side, age at surgery, height, weight, surgery time, anesthesia time, fluoroscopy time, and number of fluoroscopic images taken. A patient who was able to walk with or without crutches was classified as having a stable SCFE.⁵ Frog-leg lateral radiographs were reviewed for the head-shaft angle, the number of threads engaging the epiphysis, and slip progression. The choice of surgical table was by surgeon preference. Only unilateral mild slips were included in order to have a similar population for comparison.

The lateral head-shaft angle was calculated according to the method described by Southwick.⁶ The value for the lateral head-shaft angle of the normal hip was subtracted from the head-shaft angle on the affected side to obtain the slip angle. A mild slip was defined as a difference in the head-shaft angle of less than 30 degrees; a moderate slip was a difference of 30-50 degrees; and a severe slip was a difference of more than 50 degrees.⁷

The number of threads was determined on the first postoperative frog-leg lateral radiograph as the most threads on either side of the screw contained within the epiphysis. The number of threads was recorded as either five, or more or less than five. Slip progression was based on the difference between pre- and post-operative lateral head-shaft angles. A difference of 10 degrees or more was considered slip progression.⁸

The body mass index (BMI) was calculated as [body wt in kg/(body ht in cm)²] x 10⁴.⁹ Chi square p-values were calculated on observed frequencies of nominal data. Analysis of variance (ANOVA) was performed on grouped continuous data. A p-value <0.05 was considered significant.

RESULTS

Forty-eight children were diagnosed with a stable slipped capital femoral epiphysis and treated with in-situ single-screw fixation. Of these 48 children, 20 were classified as having a mild unilateral stable slip, and comprise the study population. Eleven children were treated on a radiolucent table and nine children were treated on a fracture table. There were 13 males and seven females. There were 10 slips on the right side and 10 slips on the left side. Table 1 shows the patient data.

TABLE 1. Patient Data.

Pt. No.	Sex	Side	Age	BMI	Table	Anes. Time	Surgery Time	Preop head-shaft angle	Postop head-shaft angle	Fluoro time	Fluoro Images	Threads
1	F	L	10.4	31	Fracture	95	25	18	24	109	61	<5
2	F	R	9.75	30	Fracture	78	32	20	23	82	43	<5
3	M	L	10.3	32	Fracture	75	32	21	19	102	49	<5
4	M	R	12.2	38	Fracture	109	66	19	16	259	190	<5
5	F	R	12.1	25	Fracture	191	41	24	26	187	116	>5
6	M	L	14.8	26	Fracture	127	36	22	20	75.8	54	<5
7	F	R	9.5	31.6	Fracture	104	42	20	17	241	130	>5
8	M	R	12.9	37	Fracture	95	37	17	25	144	84	>5
9	F	L	11.1	37	Fracture	70	29	25	33	120	74	<5
10	M	L	11.5	22	Radioluc	163	33	28	31	251	124	<5
11	M	L	10.3	35	Radioluc	110	45	17	21	205	132	<5
12	F	L	10	29	Radioluc	65	29	27	26	78	58	<5
13	M	L	13.1	28	Radioluc	60	18	29	31	80.2	46	<5
14	M	L	13.5	36	Radioluc	60	20	23	24	100	78	<5
15	M	R	11.8	31	Radioluc	66	19	27	23	65.5	49	<5
16	M	R	11.1	30	Radioluc	66	20	25	33	101	88	>5
17	M	R	12.3	28	Radioluc	62	24	25	26	106	66	>5
18	F	R	10.6	24	Radioluc	125	58	19	14	254	145	<5
19	M	L	12.4	24	Radioluc	73	46	5	13	N/A	75	>5
20	M	R	11.5	25	Radioluc	35	20	18	15	120	56	>5

The mean age at surgery was 11.7 years ± 1.5 (range 9.5-14.8). The mean head-shaft angle on the preoperative frog-leg lateral radiographs was 21 degrees ± 5 (range 5-29). The mean BMI was 30.0 ± 4.9 (range 21.6-38.0). The mean anesthesia time was 91 minutes ± 38 (range 35-191). The mean surgery time was 33 minutes ± 13 (range 18-66). The mean number of fluoroscopic images was 86 ± 40 (range 43-190). The mean fluoroscopy time was 141 seconds ± 68 (range 66-259) (Table 2). The number of screw threads that engaged the femoral epiphysis on the first post-operative frog-leg lateral radiograph was five or greater in seven slips, and less than five in 13 slips.

TABLE 2. Selected Variables.

	Radiolucent table (mean)	Fracture Table (mean)	Outcome (p-value)
Age	11.7	11.7	0.97
BMI	28	32	0.11
Preoperative head-shaft angle (degrees)	22	21	0.57
Anesthesia time (minutes)	81	105	0.16
Surgery time (minutes)	30	38	0.21
Fluoroscopy time (seconds)	136	147	0.75
Fluoroscopic images	83	89	0.77

Table 2 shows the comparison of selected variables. There was no statistical difference between the radiolucent table group and the fracture table group for any of the measured outcomes. There was no statistical difference when comparing for side (right or left) and table (p=0.65). There were four left slips and five right slips that had surgery on the fracture table. There were six left slips and five right slips that had surgery on the radiolucent table. There was no statistical difference when comparing the sex of the patient and the table used (p=0.081). There were five females and four males that had surgery on the fracture table. There were two females and nine males that had surgery on the radiolucent table.

Analysis of table and the number of threads engaging the femoral epiphysis showed no statistical difference between the fracture and radiolucent table (p=0.89). Of those children that had surgery on the fracture table, three had five or more threads engaging the epiphysis and six had less than five threads. On the radiolucent table, four patients had five or more threads and seven had less than five threads engaging the epiphysis. There were no slips that progressed 10 degrees or more.

DISCUSSION

Both radiolucent and fracture tables have been used while performing in-situ single-screw fixation of SCFE. Aronson and Carlson, Ward et al., and Goodman et al. have all reported series in which a fracture table was utilized for in-situ single-screw fixation of SCFE.^1,2,10 An advantage of using a fracture table is that no further manipulation of the hip may be required once the patient is positioned. The procedure then involves placement of the screw under fluoroscopic guidance.

Lee and Chapman have previously described the technique of in-situ single-screw fixation using a radiolucent table.³ Proposed advantages of using a radiolucent table are a decrease in operating room time (because there is no need to transfer and set up the patient on the fracture table), better visualization of the lateral image, and the ability to perform bilateral procedures more easily. However, because fluoroscopic imaging is obtained with manipulation of the limb, there is the potential of guidewire breakage.¹¹

Blasier et al. compared the use of radiolucent and fracture tables.⁴ All patients were treated with single-screw fixation. Thirty-six patients were treated on a fracture table and 29 on a radiolucent table. Time on the table and time for surgery were significantly greater for the fracture table versus the radiolucent table. Mean operating room time on the fracture table (63 minutes) was greater than that on the radiolucent table (51 minutes). Mean surgery time for the fracture table (39 minutes) was greater than that for the radiolucent table (25 minutes). The authors felt that use of the radiolucent table was a useful alternative to use of the fracture table for fixation of SCFE. Although we noted a trend in increased times, our study did not confirm the significance reported by Blasier et al. Our slip population was restricted to stable unilateral mild SCFE. The study of Blasier et al. included slips with a range of slip angles (16-88 degrees) and 12 bilateral patients.

Slip progression following fixation for slipped capital femoral epiphysis has been previously evaluated.^8,12 Carney et al. retrospectively evaluated the progression of stable SCFE treated by single cannulated screw epiphysiodesis in-situ.⁸ The surgery was accomplished on either a radiolucent or a fracture table. Slip progression of more than 10 degrees occurred in 20% of cases and appeared to be inversely related to the number of threads crossing the physis. Placement of the screw with five threads engaging the epiphysis was suggested. The comparison of results following use of a radiolucent versus a fracture table was not performed, but provided motivation for this study. In the current series, there was no statistical difference between table groups with respect to the number of threads engaging the femoral epiphysis. When using the fracture table, 33% of screws had more than five threads engaging the epiphysis. When using the radiolucent table, 36% of screws had more than five threads engaging the epiphysis.

This study compared the perioperative outcomes of in-situ single-screw fixation of mild unilateral stable slipped capital femoral epiphysis using either a radiolucent or fracture table. There was no difference between the table groups with respect to age, side of slip, or BMI. The outcomes of anesthesia time, surgery time, fluoroscopic time, the number of fluoroscopic images taken, slip progression, and the number of threads engaging the epiphysis were not statistically different when comparing table groups. In-situ single-screw fixation of a unilateral stable slipped capital femoral epiphysis can be accomplished reliably and safely with the use of either a fracture or radiolucent table.