First described in 1910 by three orthopaedic surgeons, Arthur Legg,1 Jacques Calvé,2 and George Perthes,3 Perthes disease consists of an ischemic necrosis of the growing proximal femoral epiphysis. This affects more boys than girls (ratio 5:1).4 The age of occurrence is between 4 and 8 yr, but it can occasionally occur in younger children and rarely older ones.5,6 Bilateral disease represents 8% to 24% of the cases.7,8
Pathogeny is an initial ischemic episode (necrosis stage), leading to bone resorption (fragmentation stage).9–11 This is followed by a repair of the bone (reconstruction stage), continued with a remodeling or healing stage.1–3,10 Opposite to other necroses of the femoral head (posttraumatic or post-infection) revascularization always occurs in Perthes disease.
Various theories have been advanced to explain the origin of the ischemic insult. Repeated microtrauma and coagulopathy are regularly mentioned as being responsible for Perthes disease.12–14 The role of endocrinopathy is controversial.15 Prematurity and passive nicotine exposure also have been mentioned.12,16 For some authors, many affected children are from low-income families.17 Environmental and ethnic factors are discussed in many studies.17–19
Various methods of treatment have been described,20–25 but all share the same goal: maintaining hip mobility and preventing head deformation and hip incongruity. Mobility is essential for the nutrition of the joint cartilage. Protecting joint congruency and keeping a spherical femoral head are crucial to delay the onset of degenerative joint disease in later adult life.25
Some authors recommend nonoperative treatment, including spica casting, immobilization, bed rest, traction, nonweightbearing, or bracing.20 Others advocate surgical methods, which are numerous and various: femoral varus osteotomy, pelvic osteotomy (Salter’s innominate osteotomy, Chiari’s osteotomy), combined osteotomies,21–23 and shelf acetabuloplasty.24,24
Many studies, based on the long-term consequences of Perthes disease, demonstrate that osteoarthritis is a frequent problem.26–28 The correction of subluxation is one of the keys to effective treatment. The shelf acetabuloplasty procedure may be performed to prevent the abutment of the femoral head against the superolateral margin of the acetabulum and improve the femoral head coverage.25
The purpose of this study was to review the radiographic results of hips treated with shelf acetabuloplasty and to compare these results with hips managed nonoperatively. The goal was to determine if operative treatment can improve the outcomes in children with severe disease.
MATERIALS AND METHODS
Agreement was obtained from the local ethical committee of the institution.
Patients and Choice of Treatment
Ninety-four children (102 hips) treated for Perthes disease between February 1982 and August 2014 were retrospectively reviewed with focus on the radiographic result. There were 79 boys and 15 girls. Fourteen patients with follow-up less than 2 yr were excluded from the series. Eighty patients (88 hips) were available for the study. Between 1982 and 2003 no patient was operated on with shelf acetabuloplasty and all were treated nonoperatively, except six patients treated by Chiari osteotomy. Conservative treatment consisted of relative rest; weight bearing was allowed in-house only and wheelchair was used outside the house. Sports was not allowed for 2 yr from the Perthes disease onset. Physiotherapy was prescribed once a week to maintain hip mobility. From December 2003 to February 2012, 47 hips have been operated on with shelf acetabuloplasty. The decision to treat operatively or nonoperatively was made according to the radiograph and from a pin-hole bone scan29–31 performed 3 mo after the Perthes disease onset. In the presence of head at risk signs or femoral head excentration, shelf acetabuloplaty was performed. In case of Conway-type B pathway, shelf acetabuloplasty was performed and in case of Conway-type A pathway nonoperative treatment was continued, except if the child was older than 8 yr (shelf surgery). Surgery was performed through a direct anterior approach. The shelf was harvested from the outer iliac wall. A slot was created in the acetabular edge, just above the capsule insertion. The capsule was partially reclined caudally to create the slot more caudally to avoid a too cephalad shelf placement, thus losing the effect of containment. The shelf was self-locking. Additional cancellous autologous bone chips were inserted above the first layer. Spica cast immobilization was applied for 4 postoperative weeks followed by a 4-week period of protected weight bearing with crutches.
To compare the effect of surgery on the result, a group of 47 operated patients (shelf group) was compared with another group of 41 children with Perthes who were treated nonoperatively (control group). The detailed clinical data of the two groups are summarized in Table 1.
For each affected hip, the Herring classification was applied at the time of the fragmentation stage.32–34 The lateral pillar height was expressed as a percentage of the normal side. In Herring group A, the lateral pillar’s height was intact, in group B, the lateral pillar’s height was more than 50%, and in group C, the lateral pillar’s height was less than 50%.
Head at Risk Signs
The four radiographic “head at risk” signs described by Catterall in 1971 were investigated.35 The first sign is the Gage sign, which corresponds to an osteoporotic area (radiolucent) on the lateral part of the epiphysis on anteroposterior view.36,37 The second one is a lateral calcification to the epiphysis, which means progressive collapse of the femoral head. The third one is a lateral head subluxation, which means a lack of congruency of the hip that compromises the hip development. The last sign is the horizontalization of the physeal slope. In addition, the fifth “head at risk” sign, which is the presence of metaphyseal cysts was also noted (Table 2).38
Stulberg Grading System
On the latest radiograph, the Stulberg’s grading system of the hip was applied.33,39,40 With this classification, five types of hips are defined on the radiograph at skeletal maturity (Table 3).
Radiographic Measurements (Figure 1)
Different radiographic measurements were realized at different times. For both groups (shelf and control), the first radiograph (at the time of diagnosis) and the radiograph at the latest follow-up were taken into account (Table 2). For the shelf group, radiographs obtained at the fourth postoperative week and 3 years postoperatively also were studied.
The different parameters evaluating the acetabulum were the acetabular depth (P), the acetabular height (H) and the Sharp angle (Sharp) (Figure 1A). Acetabular depth (P) was measured as the horizontal distance between the inferior tip of the teardrop and the lateral osseous edge of the acetabulum. Acetabular height (H) was the vertical distance between a line drawn horizontally from the inferior tip of the teardrop and the articular surface of the lateral osseous edge of the acetabulum. In the shelf group (Figure 1B), the shelf width was measured (S) and the total acetabular depth (P) was measured as the horizontal distance between the inferior tip of the teardrop and the lateral osseous edge of the shelf. The height of the shelf compared to the height of the primitive acetabulum also was measured (Hb, Hp). To avoid errors due to variation in radiographic magnification, all these measures were expressed as ratios of the affected hip to the normal side, giving the depth ratio and the height ratio. For the bilateral cases, we noted the evolution of these parameters on the successive radiographs.
The different parameters evaluating the femoral head (Figure 1C and D) were the shape (Mose’s circles), the head diameter (HD), the greater trochanter distance (GT), the migration index (MI) and the head excentration (Ex) (also called lateral subluxation or medial joint space). Using Mose’s circles26 on both anteroposterior and lateral hip views, the femoral head was considered spherical if the head contour was spherical and equal on both views, nonspherical if there was a difference greater than 2 mm between the radii on both views with the femoral head contour forming arcs of circles and flat if we noted more than 1 cm flattening on one view. The greater trochanter distance (GT) was measured on the anteroposterior view as the vertical distance between the top of the greater trochanter and a horizontal line from the articular surface of the lateral osseous edge of the acetabulum. The migration index (MI) represents the extent of uncovering of the femoral head in percentage. In case of a totally covered head after surgery, a negative value was given to express the overcoverage of the femoral head. The head excentration (EX) was the distance between a vertical line from the acetabulum and a line from the medial part of the femoral head. The head diameter, the greater trochanteric distance, the migration index and the head excentration were expressed as ratios of the affected hip to the normal side.
Bone Scan Assessment
Tc99m-bone scan (pin hole) allowed classifying the hips according to Conway.28–31 In the short pathway (Conway’s type A), the circumflex artery occlusion is of short duration and the vessel is rapidly functional allowing a sufficient perfusion of the femoral head. In the long pathway (type B), the occlusion is of long duration (complete obliteration) and a neovascularization develops through the growth plate. A bone scan was performed in 19 patients of the control group and in 31 of the shelf group.
IBM SPSS Statistics 20.0 was used. A significance level of α=0.05 was used. A Kolmogorov-Smirnov test was performed to test the normality of the sample. The unpaired t-test was used to compare the mean of the numerical variables of the two groups. For the categorical data, a chi-square was performed. To compare the numerical variables concerning the shelf at 4 wk postoperatively, 3 yr postoperatively, and at latest follow-up, ANOVA was performed followed by Bonferroni post-hoc test.
There were significantly more girls in the shelf group than in the control group (Table 1). No statistically significant difference was found between the two groups concerning side, bilateralism, or delay before diagnosis. The age at diagnosis was older in the shelf group than in the control group (Table 1). There were significantly more Herring type A and less Herring type C hips in the control group compared to the shelf group (Table 2). The “head at risk” signs were more frequently observed in the shelf group, but this difference was not significant, except for the Gage sign (Table 2). The mean age at the time of shelf acetabuloplasty procedure was 7.1 yr (range 3.2 to 15.3 yr).
Analysis of the Radiograph at the Time of Diagnosis (Table 2)
There were no significant differences between control and shelf groups in the acetabular depth ratio, in the acetabular height ratio, in the migration index, in the head diameter ratio, or in the greater trochanter distance ratio. There was a significant difference between the two groups in the head excentration ratio with more excentrated heads in the shelf group.
There were significantly more Conway type B patterns on bone scan in the shelf group compared to the control group (Table 2).
Analysis of the Radiograph at the Latest Follow-up (Table 3)
The mean follow-up was 6.3 yr (range 2.0 to 12.9 yr). The mean age at the latest follow-up was 11.3 yr and 11.7 yr for the control group and the shelf group, respectively, without significant difference.
There was a significantly better acetabular depth ratio (P) in the shelf group while the acetabular height (H) was not different. The head diameter ratio became significantly different between the two groups while the head excentration ratio did not. The greater trochanteric distance ratio was not different. The migration index was −5.3% in the shelf group (due to the overcoverage by the shelf), while it was 17.5% in the control group.
Stulberg’s classification at the latest follow-up showed no significant difference when we compared Stulberg 1 and 2 versus Stulberg 3 or 4, or if we compared Stulberg 1 to 3 versus Stulberg 4 between the two groups.
Analysis of Evolution of the Shelf Width in the Postoperative Period (Table 4)
The mean width of the shelf at 4 wk postoperatively was 18.0 mm. This width decreased to 12.5 mm at 3 yr postoperatively (P<0.0001) and to 11.8 mm at the latest follow-up (P<0.0001). The values at 3 yr and at the latest follow-up were not significantly different.
The mean migration index was 17.4% preoperatively and decreased to −27% at 4 wk postoperatively (P<000.1), to −2% at 3 yr postoperatively (P=0.002) and to −5% at the latest follow-up (P<0.0001). The difference was significant between the values at 4 wk postoperatively and at 3 yr postoperatively (P<0.0001) and at the latest follow-up (P<0.0001) but was not significant between the values at 3 yr postoperatively or at the latest follow-up. There was no difference between the shelf heights at 4 wk postoperatively, at 3 yr postoperatively, or at latest follow-up. The shelf height (Hb) related to the primitive acetabular height (Hp) decreased significantly from 9.0 mm at 4 wk postoperatively to 6.4 mm at the latest follow-up (P=0.027).
In the current study, we compared two groups with nearly similar clinical and radiographic characteristics at the time of the Perthes diagnosis. However, two differences were observed between the two groups. The mean age at diagnosis was older in the shelf group (6.1 vs. 4.7 yr) and there were more Herring C hips on the initial radiographs, suggesting a worse prognosis compared to the control group.29–30
The percentage of affected girls compared with boys was 19% considering the whole population of patients. There were more girls in the shelf group. Although girls have a shorter remodeling potential, it was shown that there was no significant difference in the outcome between boys and girls.4
Many studies contest the reproducibility and the reliability of Herring’s classification, but it has been shown to be the more reliable classification compared to Catterall or Salter-Thompson classifications.41,42 In addition, the Herring’s classification has the best prognostic value if correlated with the age of onset and the femoral head sphericity.29,43 The gage sign was significantly more present in the shelf group, giving a worse prognosis. It was shown that the horizontalization of the physeal slope has a very low prognostic value,44 and this sign was not taken into account in the present study.
The bone scan evaluation is of huge importance because it allows an earlier prognosis compared to radiography38–40 and can orient treatment earlier. There were more Conway B pathways in the shelf group, suggesting a worse prognosis in this group.
The radiographic parameters at the time of diagnosis were similar in both groups except for the excentration index (Ex), which was higher in the shelf group, also suggesting a worse prognosis.
Analysis of the immediate postoperative radiographs in the shelf group showed an increased femoral head coverage, resulting from a better acetabular depth and a better migration index. This persisted in the last radiographic analysis (Figure 2). The Sharp angle decreased significantly, and this difference also persisted on the last radiographs. A slight decrease of the shelf depth was observed with time compared to the immediate postoperative radiograph, while an overgrowth of the primitive acetabulum was observed. The primitive acetabular depth was increased at 3 yr postoperatively and then decreased but not in a significant way. These results suggest a lateral overgrowth of the acetabulum induced by the shelf procedure as stated by Domzalski et al.45 and more recently by Carsi et al.,46 but in these two studies there was no control group. In the present study, the acetabular depth ratio was significantly different between the two groups. The relative height of the shelf decreased, suggesting a remodeling effect. It was sometimes difficult to evaluate the true limit of the shelf in case of good fusion between shelf and acetabulum.
On the latest radiographs (Table 3), the femoral head diameter ratio and the acetabular depth ratio were significantly increased in the shelf group. Due to an acetabular overgrowth, the congruence of the joint was preserved. There was no difference between both groups concerning the acetabular height, the greater trochanteric distance, and the sphericity analysis of the femoral head with the Mose’s circles (Table 3). The excentration ratio was significantly increased in the shelf group but improved by comparison with the preoperative values.
Using Stulberg’s classification as a prognostic factor for osteoarthritis, there was no difference between both groups, even if there were initially worse prognostic factors in the shelf group (older patients, more Herring C, more Conway B, higher excentration ratio), suggesting a good effect of the procedure.
The shelf acetabuloplasty, when properly performed, increases the covering and decreases the lateral subluxation of the femoral head. The better coverage is due to both acetabular overgrowth and shelf coverage. Our results demonstrate that the shelf acetabuloplasty can improve the radiographic outcome of patients with severe Perthes disease and may be helpful to improve the hip acetabular and femoral radiographic parameters.
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