Tarek A. Aly, MD, PhD; Osama A. Amin, MD, PhD
ORTHOPEDICS 2009; 32:817
It is hypothesized that the interruption of the blood supply is an important factor causing femoral head osteonecrosis in the early stages of Legg-Calvé-Perthes disease. Currently, treatment by containment is recommended to direct and guide remodeling of the softened femoral head as it evolves from fragmentation through ossification. The goal of this study was to show the results of arthrodiatasis to induce height recovery of the femoral head and to achieve true ambulatory nonweight-bearing containment.
Forty-two patients younger than 8 years with a diagnosis of Perthes’ disease were studied. Twenty-three patients (9 class B and 14 class C according to Herring’s classification) were treated with an articulated distraction technique and 19 patients (11 class B and 8 class C) were treated conservatively as a control group. Arthrodiatasis or articulated distraction of the hip combines off-loading of muscles and body forces with distraction of the joint space by means of an external fixator that crosses the hip joint. Radiologically, 21 patients (91%) had satisfactory results and 2 (9%) had unsatisfactory results. Clinically, the results were good in 21 patients (92%), fair in 1 (4%), and poor in 1 (4%). In patients treated conservatively, 14 patients (72%) had satisfactory results and 5 (28%) had unsatisfactory results. Clinically, 71% had good results, 17% had fair, and 12% had poor.
We conclude that hip joint containment by articulated arthrodiatasis (plus adductors and psoas minimal tenotomy surgery) is an effective method in the management of Perthes’ disease in patients younger than 8 years, classified B and C, and associated with a highly reduced range of abduction. Restoration of clinical abnormalities and satisfactory radiological parameters are achieved in high percentages.
It is hypothesized that the interruption of the blood supply is the important factor causing femoral head osteonecrosis in the early stages of Legg-Calvé-Perthes disease. It is likely due to >1 episode of infarction.1 In the advanced stages of the disease, subchondral fractures caused by mechanical stresses are expected to inhibit the revascularization of the head,2 creating a vicious cycle.3 Revascularization from the periphery is accompanied by resumption of ossification. At this precise stage, trauma produces a pathologic fracture that is followed by resorption of the underlying bone and eventual replacement by biologically plastic bone.4 The ischemic femoral head epiphysis cannot grow, but its articular cartilage can be nourished by the synovial fluid, and a mild synovitis may stimulate articular cartilage growth.1,5
The optimal treatment of Perthes’ disease continues to be a dilemma. Fortunately, most patients with Perthes’ disease require minimal or symptomatic treatment and have a relatively benign long-term prognosis.6 Treatment options vary from no treatment to undergoing nonoperative or operative treatments. Currently, treatment by containment is recommended to direct and guide remodeling of the softened femoral head as it evolves from fragmentation through ossification. Containment may be pursued with nonoperative means such as braces7-9 or operative methods such as femoral and acetabular osteotomies, or a combination of both.
The term “arthrodiatasis” was initially used to describe a technique involving articulated distraction of the hip joint that was developed by surgeons in Verona, Italy, and in use since 1979.10 The word is a composite from the Greek: arthro (joint), dia (through), and taxis (to stretch out). The technique was conceived as a conservative method of restoring joint function, based on awareness that under certain conditions, regeneration and repair of damaged articular cartilage can occur, at least to some extent. Judet and Judet11 have demonstrated this in animals.
The goal of this study was to show the results of arthrodiatasis to induce height recovery of the femoral head and to achieve true ambulatory nonweight-bearing containment.
Materials and Methods
From April 1999 to April 2005, 23 patients with a diagnosis of Perthes’ disease underwent distraction using an Orthofix external fixator (Verona, Italy). Seventeen boys and 6 girls were affected. The left hip was affected in 18 patients, while the right was affected in 5. No patient had any previous treatment. Mean patient age at the time of surgery was 6.8 years (range, 5-8 years; 9 patients were younger than 6 years). The main preoperative complaint was late afternoon pain and limping in all patients and severe limitation of abduction in 21 patients. The abduction of the affected hips ranged from -5° to 15° (average, 8.33°). For comparison, 19 patients of the same age group were treated conservatively with various methods as a control group.
Anteroposterior and lateral plain radiographs were taken of all patients, and arthrography was performed to assess the clinical stage of the disease. According to the lateral pillar classification of Herring et al,12 nine of the 23 hips treated with arthrodiatasis were class B and 14 were class C; 8 hips were Catterall group III and 15 were group IV. Surgery was performed during the stage of sclerosis in 8 patients and during the stage of fragmentation in 15 cases. For the conservatively treated group, 11 hips were class B and 8 class C; 12 hips were Catterall group III and 8 were group IV.
Surgery was performed with the patient under general anesthesia and placed supine on the operating table. The involved extremity, the iliac crest, and the groin were prepared free. Percutaneous adductor tenotomy was done, and psoas tendon recession was performed through a 3-cm anterior incision. Using the image intensifier, a perpendicular line was drawn from the shaft of the femur to the center of the femoral head. This was the line of the axis of flexion–extension of the hip.
A 2-mm guide wire was inserted from the lateral side toward the center of the femoral head. It should be parallel to the floor and perpendicular to the femur while held in the 15° abduction position. The Orthofix distractor device was applied onto the guide wire and reconstructed so that the central body had the hinged connection at one end. At the proximal end a T-clamp was attached to the ball joint, and at the distal end a longitudinal clamp was attached. The ball joint was adjusted to the proximal T-clamp to enable the pins to go into the supra-acetabular region, and 2 distal pins were inserted in the longitudinal portion of the clamp.
The hip was positioned in 15° of abduction to cover the majority of the femoral head, and the flexion–extension range of motion (ROM) of the hip was checked. The hip should easily move through an arc of motion.
Sterile dressings were applied, and no distraction was applied during surgery.
On postoperative day 2, patients were allowed to walk with full weight bearing on crutches. Flexion–extension exercises were performed, with careful attention to preserving knee ROM.
Distraction was started on postoperative day 2 at a range of 0.25 mm 4 times per day. Sagittal plane hip movement was encouraged by the addition of a hinge, but motion was restricted to 45° for fear of damaging the newly formed cartilage. After the patients’ parents were educated about pin site care and the rehabilitation program, the patients were discharged on postoperative day 7.
Distraction was continued until the Shenton-Menard line was radiographically overreduced by approximately 1 to 2 mm, controlling the continuity of reduction. Patients were allowed to walk without any restrictions. After the hip was reduced to the overcorrected Shenton’s line position, it was held in that position until the date of removal. The apparatus was left in place for 4 months. Clinical visits were twice per month for the first 2 months and once per month until fixator removal.
An arthrogram of the hip was obtained on the day of fixator removal for documentation of the reshaping of the femoral head. The other clue that the frame was ready for removal was that the lateral pillar had reossified. Resumption of weight bearing began on a gradual basis immediately after removal, and full weight bearing was achieved approximately 1 month after removal.
Evaluation of Results
The procedure was evaluated both clinically and radiographically. The clinical evaluation included the degree of pain, the extent of limping, and the hip motion for abduction and internal rotation.
The radiological evaluation depended on:
1. The center edge angle of Wiberg13: formed by a vertical line through the center of the femoral head and another line that begins at this point and extends to the outer edge of the acetabulum. Wenger et al13 reported that a center angle <20° might be considered pathological and indicative of defective acetabular covering (15°-19° fair result; <15° poor result) while an angle >25° are normal;
2. The thickness of the cartilage space of the affected hip (joint space) in relation to the healthy side;
3. The variation in the Mose concentric circles,14 which were used to detect the shape of the femoral head depending on both AP and lateral radiographs. This detection was done with a transparent plate containing a series of 28 concentric circles with a 2-mm difference in radius between every 2 successive circles (2 mm deviation is fair and >2 mm deviation is poor results). Ohashi et al15 described the head as spherical when the difference between the AP and lateral diameters is <2 mm, as ovoid when the difference is 2 to 6 mm, and as angular or flat when the difference is >6 mm;
4. The change in articulotrochanteric distance, which indicated a cephalic movement of the greater trochanter due to disturbed growth of the capital femoral epiphysis. The articulotrochanteric distance is measured as the distance between 2 parallel lines perpendicular to the axis of the shaft of the femur, 1 at the level of the tip of the greater trochanter and the other at the highest part of the ossified femoral head. The distance is recorded as positive if the tip of the greater trochanter is caudal to the highest part of the femoral head. An articulotrochanteric distance of ±5 mm has a significant effect on the patient (eg, positive Trendlenburg sign)16;
5. The congruity of Shenton’s line were evaluated; and
6. Classification of the deformity of the femoral head according to the criteria of Fulford et al,17 with AP, abduction, internal rotation, and true lateral view arthrography done for each patient. The head is considered to be spherical if there is no loss of contour in all 4 views, mildly deformed if there is loss of contour in 1 view, moderately deformed if there is loss of contour in 2 views, and severely deformed if loss of contour is evident in >3 views.
The result was rated good if there was a normal ROM and freedom from all symptoms and if radiographs revealed a round femoral head, well centered in the acetabulum, with no adaptive changes and no increase in the medial joint space.
The result was rated fair if the patient was asymptomatic but with a little restriction of motion (most commonly internal rotation), and if radiographically the head was round, somewhat broadened so as not to be fully contained within the acetabulum (<20% uncovered), and may have some adaptive acetabular changes provided the head remained round. There was always loss of epiphyseal height.
The result was rated poor if the patient always had a restricted ROM but did not always have symptoms; if radiographically the head was flattened, broad, irregular, and subluxated (>20%); and if adaptive changes were present in the acetabulurn and the medial joint space was always widened.
Results were tabulated and statistically analyzed with SPSS software (SPSS, Inc, Chicago, Illinois). Two types of statistics were done: descriptive statistics, eg, percentage, mean, and standard deviation; and analytic statistics, eg, Wilcoxon rank sum test, Kruskal-Wallis test, chi-square test, and Pearson correlation coefficient test (r test). AP value <.05 was considered statistically significant.
Twenty-three arthrodiatasis patients were followed for a mean of 76 months (range, 52-104 months) after fixator removal. The average duration of external fixation was 106 days (range, 65-125 days). Two patients had the fixator removed early, 1 at 90 days secondary to a pin tract infection and the other at 65 days secondary to hip infection following arthrography. Excluding the case of hip infection, the average duration of external fixation was 111 days (range, 90-125 days).
In evaluation of the clinical results, we used 3 parameters: pain, limping, and hip ROM. Surgery improved pain in all but 1 patient, who had a hip infection after arthrography throughout the follow-up period. At the end of follow-up, pain was completely relieved in 20 patients (87%), occasional pain was observed in 2 patients (9%), and mild pain in 1 patient (4%). Postoperative limping was seen in all patients while the fixator was in and shortly after the fixator was removed, because lengthening of the affected limb by an average of 1- to 1.5-cm. At final follow-up, limping disappeared in 22 patients (96%). Improvement of limp was observed in 1 patient (4%).
The average preoperative hip abduction was 8.33° (range, -5°-15°) and hip internal rotation was 7.22° (range, 0°-10°). The average postoperative hip abduction was 32.78° (range, 5°-45°) and internal rotation was 30.56° (range, 5°-40°). The overall average of increased abduction was 24.45° and internal rotation was 23.34° with a significant statistical difference between pre- and postoperative ranges (P<.007).
In the conservatively treated patients followed for a mean of 82 months (range, 64-112 months), pain improved in 15 (79%) and limping in 2 (10%). Hip ROM was limited in 6 patients (31%).
In the arthrodiatasis group, the femoral head was mildly deformed in 5 patients, moderately deformed in 14, and severely deformed in 4. Reshaping of the femoral head occurred in all patients on the date of frame removal, as evidenced by arthrography and the reossified lateral pillar. During the distraction phase, the femoral head will become osteoporotic, as will the femoral neck. Any dead bone in the femoral head will be seen as a white area. The lateral pillar begins to reossify approximately 4 to 6 weeks after applying the fixator.
The center edge angle of Wiberg improved postoperatively in comparison with the preoperative values, indicating improvement in the coverage of the femoral head. The average angle preoperatively was 22.6° (range, 16°-31°), while the average postoperative angle was 38.6° (range, 20°-48°) with a significant statistical difference between pre- and postoperative angles (P<.001). There is no statistical significant correlation between postoperative improved abduction and internal rotation with the center edge angle. The Shenton line became normal in all patients, which explains the disappearance of pain (Figures 1, 2).
The variation between the AP and lateral diameters of the femoral head was found <2 mm in 16 cases and 2 to 4 mm in 7 cases. This means that 16 femoral heads were spherical (70%) and 7 were ovoid (30%). The articulotrochanteric distance increased in 17 cases (Figure 2) and stayed the same in 6 cases. The cartilage space of the hip joint will also increase in all cases until the end of the follow-up period.
In the conservatively treated group, the center edge angle was 23.7° (range, 17°-33°), while the average postoperative angle was 29.3° (range, 19°-34°). The articulotrochanteric distance increased in 13 patients and stayed the same in 6 patients.
This study included 42 hips with Perthes’ disease. On a clinical and radiological basis, in the articulated distraction group 21 cases were satisfactory (91%) and 2 cases were unsatisfactory (9%). Clinically, the results can be evaluated as good in 21 patients (92%), fair in 1 (4%), and poor in 1. There was no statistical significant association between younger age and best prognosis. In the conservatively treated group, 14 patients were satisfactory (72%) and 5 were unsatisfactory (28%), and in overall results, 71% rated as good, 17% rated as fair, and 12% rated as poor.
One pin tract infection occurred that required early removal of the fixator. In another, hip infection following arthrography occurred and caused a poor result clinically.
Disagreement exists in assessing Perthes’ disease and its treatment. Indications for the treatment of Legg-Calvé-Perthes disease are based more on the personal experience of the surgeon rather than on scientific data.18
The goal of treatment of Legg-Calvé-Perthes disease is to achieve a painless and mobile hip and to minimize deformity of the hip joint, thereby delaying the onset of degenerative joint disease later in life. To progress the treatment of Perthes’ disease, patients at risk of significant deformity need to be identified at an early stage and offered treatment that is low risk but effective in preventing femoral head deformity.
Many treatment methods have been proposed to achieve this goal. In the past, hip motion exercises and nonweight bearing were popular; however, containment of the femoral head within the acetabulum and weight bearing is now preferred.19-22 The evidence that supports conservative treatment of children with Legg-Calvé-Perthes disease is not of high quality. No scientific evidence exists that conservative treatments modify Legg-Calvé-Perthes disease’s natural history. Containment, no containment, and simple symptomatic treatment have comparable effectiveness. Prolonged weight relief and/or containment treatments are associated with social and psychological problems.23
Petrie and Bitenc9 postulated that if one were able to maintain the entire femoral epiphysis within the acetabulum, the intra-articular pressure that would develop during ambulation would allow the femoral head to regenerate in a shape congruous to the acetabulum. Early motion allows dynamic molding of the femoral epiphysis to occur. The joint cartilage receives most of its nourishment from the surrounding tissues via imbibition. This process, dependent on the application and release of pressure, is facilitated by the intermittent motion and compression seen in ambulation.24
The importance of continuous passive motion in the regeneration of articular cartilage has been demonstrated using a rabbit model,11,25 where the animals subjected to intermittent active or continuous passive motion showed a reduced incidence of intra-articular adhesion formation compared with those in which the joint had been immobilized. Therefore, the treatment method that offers the advantages of both containment and early motion with weight bearing can solve the problem. The technique of arthrodiatasis was conceived as a conservative method of restoring joint function, based on awareness that under certain conditions, regeneration and repair of damaged articular cartilage can occur, at least to some extent. Distraction/arthrodiatasis performed gradually induces neovascularization in the tissues.8 The persistent joint-space widening after short-term distraction suggests repair of the articular cartilage, which may be related to clinical improvement. During transient loading of the distracted joint, as in walking, there is an intermittent increase in hydrostatic pressure.26-30 An explanation for the anabolic effect of intermittent hydrostatic pressure in vitro and during joint distraction may be an increase in the nutrition of the cartilage.31 Another advantage of distraction/arthrodiatasis is improving the moment arm of the hip abductors.
Clinical evaluation of treatment in Perthes’ disease is difficult. Most pediatric orthopedists would agree that most untreated patients with Perthes’ disease would heal with well-formed hip joints at maturity. However, certain risk factors may predispose to poor radiographic outcomes, resulting in controversy regarding the effectiveness of different treatment programs to improve on the disease’s natural history.3 The recognition that the risk of severe femoral head deformity can be assessed using Herring’s classification improves the ability to predict outcome in this age group and may become an important consideration in the formulation of future treatment protocols for children under 6 years old who present with Legg-Calvé-Perthes disease.
Kocaoglu et al,32 who used the Ilizarov technique for the treatment of Legg-Calvé-Perthes disease, reported that the low success rate of the technique does not justify the routine use. They insisted on ROM during the distraction phase through the use of a hinge. Therefore, the key to success of this procedure is maintaining and restoring hip ROM through distraction and exercises. This study reported 91% satisfactory results and 9% unsatisfactory. In our study, if the case with an unsatisfactory result because of hip infection following arthrography is excluded, the clinical outcome will be satisfactory in almost all patients. We attribute our best results over those of Kocaoglu et al32 to the addition of tenotomies to our maneuver. The iliopsoas tendon is a well-known cause for coxa saltans or snapping hip.33 Pressure of this muscle and its movements during hip flexion and extension and tightening of the hip adductors increase the intra-articular pressure, which affects the vascularization of the femoral head, especially in the rarefaction phase of the disease. Tenotomy for this muscle will eventually decreases the intra-articular pressure during the distraction phase and favors the condition for cartilage remodeling. Radiologically, an increase in the center edge angle may be attributed to increasing femoral head sphericity and stimulation of acetabular growth by supra-acetabular pins of the fixator.
In children presenting before 6 years of age, Perthes’ disease has been regarded as a benign disorder, and until recently, studies of outcome and the predictive value of Herring’s classification have tended to exclude this age group. Gent et al34 reported that, following a review of 127 cases of Perthes’ disease in children under 8, it became apparent that there were significant numbers of poor outcomes in children presenting younger than 6 years. They also mentioned that in children younger than 6 years, those classified as Herring C have 9 times the risk of a Stulberg IV deformity as those who are Herring A, and 6 times the risk for those who are Herring A or B. The risk of developing a Stulberg IV hip deformity from a Herring C lateral column collapse is only slightly less for children under 6 years than for older children, which means that young age is not a guarantee for a good result.
There was no statistically significant association between younger age and best prognosis. This is also mentioned in previous studies by Fabry et al35 and Rosenfeld et al.36 We believe that this is because all of our patients between 5 and 8 years were those in whom better outcomes were obtained when managed with containment methods.37 In terms of complications, we had 1 pin tract infection and 1 hip infection following arthrography. Therefore, we advocate the use of computed tomography instead. The rate of complication in this study was comparable to the study of Hau et al,38 which was 9%.
Some studies mention that group B hips in children who are younger than 8 years at the time of onset have favorable outcomes unrelated to treatment, whereas group C hips in children of all ages frequently have poor outcomes, which also appear to be unrelated to treatment.39 However, a more recent study by Rosenfeld et al36 to assess the natural history of this condition in this age group reviewed a large cohort of children who had received minimal treatment for the disease, and they reported that the prognosis for patients with the onset of Legg-Calvé-Perthes disease before 6 years (with Herring classification B or C) is favorable, with 80% having a good result. This result is much lower than our result using arthrodiatasis for the same age group.
Comparing our results with the literature is difficult, as few published reports exist using arthrodiatasis in the management of Perthes’ disease with a small number of patients and short follow-up periods. Most of authors agree that the optimum surgical treatment for Perthes’ disease has not been decided. In a study done by Segev et al,40 which included only 10 patients between 9 and 15 years, hip ROM was limited in most patients and limb shortening was present in 7, with the mean uncoverage percentage of the acetabulum approaching 40%. They concluded that this procedure should be regarded as a salvage procedure. Kitakoji et al,41 comparing results of femoral varus osteotomy and Salter innominate osteotomy, reported that there were no significant differences between the 2 groups. Kim et al,42 reporting the results of different containment methods performed in Japan, stated that the optimal treatment method for Perthes’ disease was not determined by their study, and that there were no differences in outcome among the hips with no treatment, those treated with bracing, and those treated with ROM therapy as described by Herring et al.43
Our study notes higher rates of acceptable results than would be expected compared with other methods. Is this method applicable to older age groups? Is it possible to change the natural history of Perthes’ disease? Long-term follow-up can answer these questions.
- Zahir A, Freeman MA. Cartilage changes following a single episode of infarction of the capital femoral epiphysis in the dog. J Bone Joint Surg Am. 1972; 54(1):125-136.
- Atsumi T, Kuroki Y, Yamano K. A microangiographic study of idiopathic osteonecrosis of the femoral head.Clin Orthop Relat Res.1989; (246):186-194.
- Noonan KJ, Price CT, Kupiszewski SJ, Pyevich M. Results of femoral varus osteotomy in children older than 9 years of age with Perthes disease. J Pediatr Orthop. 2001; 21(2):198-204.
- Salter RB. Legg-Perthes disease: the scientific basis for the methods of treatment and their indications.Clin Orthop Relat Res. 1980; (150):8-11.
- Ogata K, Whiteside LA. Barrier to material transfer at the bone-cartilage interface: measurement with hydrogen gas in vivo. Clin Orthop Relat Res. 1979; (145):273-276.
- McAndrew MP, Weinstein SL. A long-term follow-up of Legg-Calvé-Perthes disease. J Bone Joint Surg Am. 1984; 66(6):860-869.
- Curtis BH, Gunther SF, Gossling HR, Paul SW. Treatment for Legg-Perthes disease with the Newington ambulation-abduction brace. J Bone Joint Surg Am. 1974; 56(6):1135-1146.
- Harrison MH, Turner MH, Smith DN. Perthes’ disease. Treatment with the Birmingham splint. J Bone Joint Surg Br. 1982; 64(1):3-11.
- Petrie JG, Bitenc I. The abduction weight-bearing treatment in Legg-Perthes’ disease. J Bone Joint Surg Br. 1971; 53(1):54-62.
- Kucukkaya M, Kabukcuoglu Y, Ozturk I, Kuzgun U. Avascular necrosis of the femoral head in childhood: the results of treatment with articulated distraction method. J Pediatr Orthop. 2000; 20(6):722-728.
- Judet R, Judet T. The use of a hinge distraction apparatus after arthrolysis and arthroplasty [in French]. Rev Chir Orthop Reparatrice Appar Mot. 1978; 64(5):353-365.
- Herring JA, Neustadt JB, Williams JJ, Early JS, Browne RH. The lateral pillar classification of Legg-Calvé-Perthes disease. J Pediatr Orthop. 1992; 12(2):143-150.
- Wenger DR, Ward WT, Herring JA. Legg-Calvé-Perthes disease. J Bone Joint Surg Am. 1991; 73(5):778-788.
- Mose K. Methods of measuring in Legg-Calvé-Perthes disease with special regard to the prognosis. Clin Orthop Relat Res. 1980; (150):103-109.
- Ohashi H, Hirohashi K, Yamano Y. Factors influencing the outcome of Chiari pelvic osteotomy: a long-term follow-up. J Bone Joint Surg Br. 2000; 82(4):517-525.
- Leitch JM, Paterson DC, Foster BK. Growth disturbance in Legg-Calvé-Perthes disease and the consequences of surgical treatment. Clin Orthop Relat Res. 1991; (262):178-184.
- Fulford GE, Lunn PG, Macnicol MF. A prospective study of nonoperative and operative management for Perthes’ disease. J Pediatr Orthop. 1993; 13(3):281-285.
- Hefti F, Clarke NM. The management of Legg-Calvé-Perthes’ disease: is there a consensus? A study of clinical practice preferred by the members of the European Paediatric Orthopaedic Society. J Child Orthop. 2007; 1(1):19-25.
- Domzalski ME, Glutting J, Bowen JR, Littleton AG. Lateral acetabular growth stimulation following a labral support procedure in Legg-Calve-Perthes disease. J Bone Joint Surg Am. 2006; 88(7):1458-1466.
- Kacki W, Zarzycka M, Zarzycki D, et al. Comparison of radiological results of conservative and operative treatment by Salter osteotomy in severe cases of Perthes’ disease. Ortop Traumatol Rehabil. 2004; 6(6):740-747.
- Kolban M, Darczuk J, Chmielnicki M. Remodelling and congruency of the hip joint in children with Perthes’ disease treated with varus-derotation subtrochanteric osteotomy. Ortop Traumatol Rehabil. 2004; 6(6):697-704.
- Pietrzak S, Napiontek M, Kraiz S. The effect of the therapeutic approach on the course of Perthes’ disease and its outcome: Conservative vs. surgical treatment. Ortop Traumatol Rehabil. 2004; 6(6):751-757.
- Sinigaglia R, Bundy A, Okoro T, Gigante C, Turra S. Is conservative treatment really effective for Legg-Calvé-Perthes disease? A critical review of the literature. Chir Narzadow Ruchu Ortop Pol. 2007; 72(6):439-443.
- Wang L, Bowen JR, Puniak MA, Guille JT, Glutting J. An evaluation of various methods of treatment for Legg-Calvé-Perthes disease. Clin Orthop Relat Res. 1995; (314):225-233.
- Salter RB, Simmonds DF, Malcolm BW, Rumble EJ, MacMichael D, Clements ND. The biological effect of continuous passive motion on the healing of full-thickness defects in articular cartilage. An experimental investigation in the rabbit. J Bone Joint Surg Am. 1980; 62(8):1232-1251.
- Klein-Nulend J, Veldhuijzen JP, van de Stadt RJ, van Kampen GP, Kuijer R, Burger EH. Influence of intermittent compressive force on proteoglycan content in calcifying growth plate cartilage in vitro. J Biol Chem. 1987; 262(32):15490-15495.
- Lippiello L, Kaye C, Neumata T, Mankin HJ. In vitro metabolic response of articular cartilage segments to low levels of hydrostatic pressure. Connect Tissue Res. 1985; 13(2):99-107.
- van Kampen GP, Veldhuijzen JP, Kuijer R, van de Stadt RJ, Schipper CA. Cartilage response to mechanical force in high-density chondrocyte cultures. Arthritis Rheum. 1985; 28(4):419-424.
- van Valburg AA, van Roermund PM, Lammens J, et al. Can Ilizarov joint distraction delay the need for an arthrodesis of the ankle? A preliminary report. J Bone Joint Surg Br. 1995; 77(5):720-725.
- Veldhuijzen JP, Huisman AH, Vermeiden JP, Prahl-Andersen B. The growth of cartilage cells in vitro and the effect of intermittent compressive force. A histological evaluation. Connect Tissue Res. 1987; 16(2):187-196.
- Nimer E, Schneiderman R, Maroudas A. Diffusion and partition of solutes in cartilage under static load.Biophys Chem. 2003; 106(2):125-146.
- Kocaoglu M, Kilicoglu OI, Goksan SB, Cakmak M. Ilizarov fixator for treatment of Legg-Calvé-Perthes disease. J Pediatr Orthop B. 1999; 8(4):276-281.
- Hoskins JS, Burd TA, Allen WC. Surgical correction of internal coxa saltans: a 20-year consecutive study.Am J Sports Med. 2004; 32(4):998-1001.
- Gent E, Antapur P, Mehta RL, Sudheer VM, Clarke NM. Predicting the outcome of Legg-Calvé-Perthes’ disease in children under 6 years old. J Child Orthop. 2007; 1(1):27-32.
- Fabry K, Fabry G, Moens P. Legg-Calvé-Perthes disease in patients under 5 years of age does not always result in a good outcome. Personal experience and meta-analysis of the literature. J Pediatr Orthop B. 2003; 12(3):222-227.
- Rosenfeld SB, Herring JA, Chao JC. Legg-calve-perthes disease: a review of cases with onset before six years of age. J Bone Joint Surg Am. 2007; 89(12):2712-2722.
- Herring JA. The treatment of Legg-Calvé-Perthes disease. A critical review of the literature. J Bone Joint Surg Am. 1994; 76(3):448-458.
- Hau R, Dickens DR, Nattrass GR, O’Sullivan M, Torode IP, Graham HK. Which implant for proximal femoral osteotomy in children? A comparison of the AO (ASIF) 90 degree fixed-angle blade plate and the Richards intermediate hip screw. J Pediatr Orthop. 2000; 20(3):336-343.
- Herring JA, Kim HT, Browne R. Legg-Calve-Perthes disease. Part II: Prospective multicenter study of the effect of treatment on outcome. J Bone Joint Surg Am. 2004; 86(10):2121-2134.
- Segev E, Ezra E, Wientroub S, Yaniv M, Hayek S, Hemo Y. Treatment of severe late-onset Perthes’ disease with soft tissue release and articulated hip distraction: revisited at skeletal maturity. J Child Orthop. 2007; 1(4):229-235.
- Kitakoji T, Hattori T, Kitoh H, Katoh M, Ishiguro N. Which is a better method for Perthes’ disease: femoral varus or Salter osteotomy? Clin Orthop Relat Res. 2005; (430):163-170.
- Kim WC, Hiroshima K, Imaeda T. Multicenter study for Legg-Calvé-Perthes disease in Japan. J Orthop Sci. 2006; 11(4):333-341.
- Herring JA, Kim HT, Browne R. Legg-Calve-Perthes disease. Part I: Classification of radiographs with use of the modified lateral pillar and Stulberg classifications. J Bone Joint Surg Am. 2004; 86(10):2103-2120.
Drs Aly and Amin are from the Orthopedic Department, Tanta University Hospital, Tanta, Egypt.
Drs Aly and Amin have no relevant financial relationships to disclose.
Correspondence should be addressed to: Tarek A. Aly, MD, PhD, Orthopedic Department, Tanta University Hospital, 48th Sarwat St, Tanta, 31111, Egypt (firstname.lastname@example.org).