Residual hip dysplasia: is there a place for hip shelf operation?

PURPOSE: After modern acetabular osteotomies were introduced, hip shelf operations have become much less commonly used. The aims of this study were to assess the short-term and long-term outcome of a modified Spitzy shelf procedure and to compare the results with those of periacetabular osteotomy (PAO). METHODS: In all, 44 patients (55 hips) with developmental dysplasia of the hip and residual dysplasia had a modified Spitzy shelf operation. Mean age at surgery was 13.2 years (8 to 22). Indication for surgery was a centre-edge angle < 20° with or without hip pain. Outcome was evaluated using duration of painless period and survival analysis with conversion to total hip arthroplasty (THA) as endpoints. RESULTS: Preoperative hip pain was present in 46% of the hips and was more common in patients ≥ 12 years at surgery (p < 0.001). One year postoperatively, 93% of the hips were painless. Analysis of pain in hips with more than ten years follow-up showed a mean postoperative painless period of 20.0 years (0 to 49). In all, 44 hips (80%) had undergone THA at a mean patient age of 50.5 years (37 to 63). Mean survival of the shelf procedure (time from operation to THA) was 39.3 years (21 to 55). CONCLUSIONS: The Spitzy operation had good short and long-term effects on hip pain and a 30-year survival (no THA) of 72% of the hips. These results compare favourably with those of PAO and indicate that there is still a place for the shelf procedure in older children and young adults.

Long-term outcome of closed reduction in late-detected hip dislocation: 60 patients aged six to 36 months at diagnosis followed to a mean age of 58 years.

PURPOSE: The aims of this study on late-detected developmental dislocation of the hip (DDH) were to assess the outcome in patients aged 55 to 60 years and to define prognostic factors. METHODS: The study included 60 patients (74 hips). Primary treatment was skin traction to obtain closed reduction, followed by hip spica plaster cast. There were 52 girls and eight boys with a mean age at reduction of 19.6 months (8 to 37). Criteria for good long-term outcome were no osteoarthritis (OA) or total hip arthroplasty (THA) and modified Harris Hip Score ≥ 80 points. RESULTS: The mean patient age at follow-up was 57.7 years (55 to 60). Good long-term clinical and radiographic outcome occurred in 39 of 73 hips (53%). In all, 24 hips (32%) had undergone THA at a mean patient age of 48.1 years (31 to 58). Survival analysis with conversion to THA as endpoint showed a reduction in survival from 100% at patient age 30 years to 62% at 58 years. Risk factors for poor outcome were age at reduction ≥ 1.5 years and residual dysplasia (Severin grades III/IV) at skeletal maturity. CONCLUSION: With a mean follow-up of patient age 58 years, the outcome of late-detected DDH, treated with traction and closed reduction, was satisfactory in more than half the hips. This indicates that the hip will probably last more than 50 years if risk factors like age at reduction ≥ 1.5 years, residual dysplasia and avascular necrosis are avoided.

Prognostic factors for long-term outcome of chronic slipped capital femoral epiphysis treated with fixation in situ.

PURPOSE: Predictive factors for long-term outcome after in situ fixation for chronic slipped capital femoral epiphysis (SCFE) have so far not been systematically analysed. The aims of this study were to define predictors for long-term outcome and to assess the association between initial grade of slipping and post-slip deformities. METHODS: We studied 51 patients (60 hips) with chronic SCFE treated with in situ fixation. There were 31 males and 20 females with a mean age of 12.9 years. The mean follow-up was 39.0 years (21.1 to 56.8). Post-slip deformity was defined as abnormal alpha (a) angles in anteroposterior (AP) and lateral radiographs; AP angle of 74° and lateral angle of 63° were used as cutoffs between normal and abnormal α-angles. Harris hip score (HHS) less than 85 points was classified as a poor clinical outcome and osteoarthritis was a poor radiographic outcome. RESULTS: The mean slip angle was 31.7° (12° to 77°). The mean AP α-angle was 67.4° (36° to 111°) and the mean lateral α-angle was 57.1° (22° to 104°). Post-slip deformities developed in almost one-third of hips with a mild degree of slipping and in about half the hips with more pronounced degrees of slipping. The long-term outcome was good in 40 hips (67%) and poor in 20 hips. A small AP α-angle was the only independent prognostic factor for a good combined clinical and radiographic outcome. CONCLUSION: Post-slip deformity, defined as an abnormally high AP α-angle, is the most important prognostic factor for poor long-term clinical and radiographic outcome in chronic SCFE treated with in situ fixation.

The outcome and prognostic factors in children with bilateral Perthes' disease: a prospective study of 40 children with follow-up over five years.

AIMS: The aims of this study were to describe the course of non-operatively managed, bilateral Perthes' disease, and to determine specific prognostic factors for the radiographic and clinical outcome. PATIENTS AND METHODS: We identified 40 children with a mean age of 5.9 years (1.8 to 13.5), who were managed non-operatively for bilateral Perthes' disease from our prospective, multicentre study of this condition, which included all children in Norway who were diagnosed with Perthes' disease in the five-year period between 1996 and 2000. All children were followed up for five years. The hips were classified according to the Catterall classification. A modified three-group Stulberg classification was used as an outcome measure, with a spherical femoral head being defined as a good outcome, an oval head as fair, and a flat femoral head as a poor outcome. RESULTS: Concurrent, simultaneous bilateral Perthes' disease was seen in 23 children and 17 had the sequential onset of bilateral disease. The mean delay in onset for the second hip in the latter group was 1.9 years (0.3 to 5.5). The five-year radiographic outcome was good in 30 (39%), fair in 25 (33%) and poor in 21 (28%) of the hips. The strongest predictors of poor outcome were > 50% necrosis of the femoral head, with odds ratio (OR) 19.6, and age at diagnosis > 6 years (OR 3.3). Other risk factors for poor outcome were the timing of the onset of disease, where children with the sequential onset of bilateral disease had a higher risk than those with the concurrent onset of bilateral disease (p = 0.021, chi-squared test). Following a diagnosis of Perthes' disease in one hip, there was a 5% chance of developing it in the contralateral hip. CONCLUSION: These results imply that we need to distinguish between children with concurrent onset and those with sequential onset of bilateral Perthes' disease, as the outcomes may be different. This has not been previously described. Children with concurrent onset of bilateral disease had a similar outcome to our previous series of those with unilateral disease, whereas children with sequential onset of bilateral disease had a worse prognosis. The increased risk of developing Perthes' disease in the contralateral hip in those with unilateral disease is important information for the child and parents.

The acetabulum in Perthes' disease: a prospective study of 123 children.

PURPOSE: We assessed the radiographic changes of the acetabulum during the course of Perthes' disease and investigated whether they were associated with femoral head sphericity 5 years after diagnosis. METHODS: We studied 123 children with unilateral Perthes' disease, femoral head necrosis more than 50 % and age at diagnosis 6 years or older. Pelvic radiographs were taken at onset, 1 year and 5 years after diagnosis. Sharp's angle, acetabular depth-to-width ratio (ADR) and lateral acetabular inclination were measured. RESULTS: Compared to the unaffected hips, the Perthes' hips developed significantly higher Sharp's angles (p < 0.001) and a higher proportion with an upward-sloping lateral acetabular margin (Perthes' hips: 49 %, unaffected hips 1 %). The mean ADR values were significantly lower on the affected side at all stages (p < 0.001). ADR values at diagnosis were associated with a more spherical femoral head at the 5-year follow-up [odds ratio (OR) 1.012, 95 % confidence interval (CI) 1.002-1.022, p = 0.016]. None of the other acetabular parameters were significantly associated with the femoral head shape 5 years after diagnosis. CONCLUSION: The acetabulum developed an increasingly dysplastic shape in the course of Perthes' disease. Early dysplastic changes of the acetabulum were not associated with a poor radiological outcome 5 years after diagnosis. Routine measurement and monitoring of acetabular changes in plain radiographs were of little prognostic value and can, therefore, hardly be recommended in clinical practice.

Dysplasia of the contralateral hip in patients with unilateral late-detected congenital dislocation of the hip: 50 years' follow-up of 48 patients.

The aim of this study was to investigate the incidence of dysplasia in the 'normal' contralateral hip in patients with unilateral developmental dislocation of the hip (DDH) and to evaluate the long-term prognosis of such hips. A total of 48 patients (40 girls and eight boys) were treated for late-detected unilateral DDH between 1958 and 1962. After preliminary skin traction, closed reduction was achieved at a mean age of 17.8 months (4 to 65) in all except one patient who needed open reduction. In 25 patients early derotation femoral osteotomy of the contralateral hip had been undertaken within three years of reduction, and later surgery in ten patients. Radiographs taken during childhood and adulthood were reviewed. The mean age of the patients was 50.9 years (43 to 55) at the time of the latest radiological review. In all, eight patients (17%) developed dysplasia of the contralateral hip, defined as a centre-edge (CE) angle < 20° during childhood or at skeletal maturity. Six of these patients underwent surgery to improve cover of the femoral head; the dysplasia improved in two after varus femoral osteotomy and in two after an acetabular shelf operation. During long-term follow-up the dysplasia deteriorated to subluxation in two patients (CE angles 4° and 5°, respectively) who both developed osteoarthritis (OA), and one of these underwent total hip replacement at the age of 49 years. In conclusion, the long-term prognosis for the contralateral hip was relatively good, as OA occurred in only two hips (4%) at a mean follow-up of 50 years. Regular review of the 'normal' side is indicated, and corrective surgery should be undertaken in those who develop subluxation.

Femoroacetabular impingement after slipped upper femoral epiphysis: the radiological diagnosis and clinical outcome at long-term follow-up.

Deformity after slipped upper femoral epiphysis (SUFE) can cause cam-type femoroacetabular impingement (FAI) and subsequent osteoarthritis (OA). However, there is little information regarding the radiological assessment and clinical consequences at long-term follow-up. We reviewed 36 patients (43 hips) previously treated by in situ fixation for SUFE with a mean follow-up of 37 years (21 to 50). Three observers measured the femoral head ratio (FHR), lateral femoral head ratio (LFHR), α-angle on anteroposterior (AP) and frog-leg lateral views, and anterior femoral head-neck offset ratio (OSR). A Harris hip score < 85 and/or radiologically diagnosed osteoarthritis (OA) was classified as a poor outcome. Patients with SUFE had significantly higher FHR, LFHR and α-angles and lower OSR than a control group of 22 subjects (35 hips) with radiologically normal hips. The interobserver agreement was less, with wider limits of agreement (LOA), in hips with previous SUFE than the control group. At long-term follow-up abnormal α-angles correlated with poor outcome, whereas FHR, LFHR and OSR did not. We conclude that persistent deformity with radiological cam FAI after SUFE is associated with poorer clinical and radiological long-term outcome. Although the radiological measurements had quite wide limits of agreement, they are useful for the diagnosis of post-slip deformities in clinical practice.

Prognostic factors and outcome of treatment in Perthes' disease: a prospective study of 368 patients with five-year follow-up.

This nationwide prospective study was designed to determine prognostic factors and evaluate the outcome of different treatments of Perthes' disease. A total of 28 hospitals in Norway were instructed to report all new cases of Perthes' disease over a period of five years and 425 patients were reported and followed for five years. Of these, 368 with unilateral disease were included in the present study. The hips were classified radiologically according to a modified two-group Catterall classification and the lateral pillar classification. A total of 358 patients (97%) attended the five-year follow-up, when a modified three-group Stulberg classification was used as a radiological outcome measure. For patients over six years of age at diagnosis and with more than 50% necrosis of the femoral head (152 patients), the surgeons at the different hospitals had chosen one of three methods of treatment: physiotherapy (55 patients), the Scottish Rite abduction orthosis (26), and proximal femoral varus osteotomy (71). Of these hips, 146 (96%) were available for the five-year follow-up. The strongest predictor of outcome was femoral head involvement of more or less than 50% (odds ratio (OR) = 7.76, 95% confidence interval (CI) 2.82 to 21.37), followed by age at diagnosis (OR = 0.98, 95% CI 0.92 to 0.99) and the lateral pillar classification (OR = 0.62, 95% CI 0.40 to 0.98). In children over six years at diagnosis with more than 50% of femoral head necrosis, proximal femoral varus osteotomy gave a significantly better outcome than orthosis (p = 0.001) or physiotherapy (p = 0.001). There was no significant difference between the physiotherapy and orthosis groups (p = 0.36), and we found no difference in outcome after any of the treatments in children under six years (p = 0.73). We recommend proximal femoral varus osteotomy in children aged six years and over at the time of diagnosis with hips having more than 50% femoral head necrosis. The abduction orthosis should be abandoned in Perthes' disease.

The epidemiology and aetiology of Perthes' disease in Norway. A nationwide study of 425 patients.

A nationwide study of Perthes' disease in Norway was undertaken over a five-year period from January 1996. There were 425 patients registered, which represents a mean annual incidence of 9.2 per 100 000 in subjects under 15 years of age, and an occurrence rate of 1:714 for the country as a whole. There were marked regional variations. The lowest incidence was found in the northern region (5.4 per 100 000 per year) and the highest in the central and western regions (10.8 and 11.3 per 100 000 per year, respectively). There was a trend towards a higher incidence in urban (9.5 per 100 000 per year) compared with rural areas (8.9 per 100 000 per year). The mean age at onset was 5.8 years (1.3 to 15.2) and the male:female ratio was 3.3:1. We compared 402 patients with a matched control group of non-affected children (n = 1 025 952) from the Norwegian Medical Birth Registry and analysed maternal data (age at delivery, parity, duration of pregnancy), birth length and weight, birth presentation, head circumference, ponderal index and the presence of congenital anomalies. Children with Perthes' disease were significantly shorter at birth and had an increased frequency of congenital anomalies. Applying Sartwell's log-normal model of incubation periods to the distribution of age at onset of Perthes' disease showed a good fit to the log-normal curve. Our findings point toward a single cause, either genetic or environmental, acting prenatally in the aetiology of Perthes' disease.

Universal or selective screening of the neonatal hip using ultrasound? A prospective, randomised trial of 15,529 newborn infants.

The aim of this study was to evaluate whether universal (all neonates) or selective (neonates belonging to the risk groups) ultrasound screening of the hips should be recommended at birth. We carried out a prospective, randomised trial between 1988 and 1992, including all newborn infants at our hospital. A total of 15 529 infants was randomised to either clinical screening and ultrasound examination of all hips or clinical screening of all hips and ultrasound examination only of those at risk. The effect of the screening was assessed by the rate of late detection of congenital or developmental hip dysplasia in the two groups. During follow-up of between six and 11 years, only one late-detected hip dysplasia was seen in the universal group, compared with five in the subjective group, representing a rate of 0.13 and 0.65 per 1,000, respectively. The difference in late detection between the two groups was not statistically significant (p = 0.22). When clinical screening is of high quality, as in our study, the effect of an additional ultrasound examination, measured as late-presenting hip dysplasia, is marginal. Under such circumstances, we consider that universal ultrasound screening is not necessary, but recommend selective ultrasound screening for neonates with abnormal or suspicious clinical findings and those with risk factors for hip dysplasia.

Good results after treatment with the Frejka pillow for hip dysplasia in newborns: a 3-year to 6-year follow-up study.

Because there is no consensus with regard to the efficiency of the Frejka pillow in the treatment of hip joint dysplasia in newborns, the aim of the present study was to evaluate our results with this device. During the 3-year period 1988 to 1990, the Frejka pillow was used in 108 newborns with clinically unstable hips verified by ultrasonography. There were three treatment failures (2.8%), defined as infants who needed additional treatment with an abduction splint or hip-spica cast. Avascular necrosis of the femoral head occurred in one patient (0.9%). At an age of 3 years to 6 years, 85 of the children attended a follow-up examination. An intoeing gait was observed in 17% and slightly reduced hip mobility in 20% of the patients. Compared with normal children, the patients had somewhat lower coverage of the femoral head by radiography, indicated by a lower centre-edge angle and a higher migration percentage, but the coverage was within the normal range in all cases. The mean anteversion angle was larger than that of normal children but only three patients had abnormally high anteversion angles. In conclusion, the results with the Frejka pillow were good, with few treatment failures and complications, and it is the most simple abduction device for the parents to handle. More rigid devices like the von Rosen splint seem to involve a slightly lower failure rate, but a higher risk of avascular necrosis. Therefore, we recommend the Frejka pillow when treatment is started within a few days of birth.

Treatment of scoliosis with spinal bracing in quadriplegic cerebral palsy.

To evaluate the clinical results of the treatment and to assess the factors that influenced the rate of scoliosis progression, a retrospective study of spinal orthosis in 86 patients with spastic quadriplegic cerebral palsy was performed. The mean age of the patients was 13.8 years (range 5 to 33 years). Their scoliotic deformities were treated with custom-moulded, polypropylene thoraco-lumbar-sacral orthoses. Cobb angles were measured on radiographs taken in a sitting position before treatment, in orthosis, and during follow-up. The mean initial Cobb angle was 68.4 degrees (range 25 to 131 degrees). The mean correction in orthosis was 25 degrees (range 3 to 60 degrees). Seventy-two patients had a follow-up period of more than 2 years. At the latest follow-up, average 6.3 years (range 2 to 14 years) after the start of treatment, the mean Cobb angle without orthosis was 93.1 degrees (range 40 to 145 degrees). The mean progression per year was 4.2 degrees (range -3 to 21 degrees). Linear multiple regression revealed that age and initial correction in orthosis were the only variables that significantly influenced the rate of progression. Twenty-two patients had no progression or progression <1.0 degrees per year. Correction in orthosis was the only variable that predicted progression <1.0 degrees per year in both age groups (<15 years and > or =15 years). Of the 57 patients who were still alive and had not undergone surgical fusion, 72% used their orthoses at a mean age of 22 years. Parents and caregivers expressed satisfaction with the use of orthosis, mainly because of improved sitting stability which gave better overall function.

The role of fluoroscopy in avoiding rotational deformity of treated femoral shaft fractures: an anatomical and clinical study.

In the first part of the study we examined the accuracy of femoral anteversion (AV) determined by fluoroscopy, simulating a method used in closed intramedullary femoral nailing. Twenty cadaveric femora were used. The condyles and posterior trochanteric area were resting on a horizontal table. The proximal femur was imaged using a C-arm image intensifier with horizontal X-ray beam at an angle of 30, 45, or 60 degrees to the long axis of the femoral shaft. To evaluate the reliability of the measurements, the real AV angle was determined by radiography. A small difference (mean 2 degrees ) was found between the real AV angle and the angle between the horizontal plane and the central head-neck axis (NH angle) as displayed by the image intensifier. In a separate clinical study, the NH angle was assessed and used as a guide to intraoperative rotational reduction in ten patients with femoral shaft fracture using the aforementioned method. Follow-up examinations of the AV angle showed that rotational deformities of clinical significance were avoided.

Reliability of ultrasonography in the follow-up of hip dysplasia in children above 2 years of age.

PURPOSE: The aim of the present study was to assess whether ultrasonography (US) was reliable in the follow-up of children above 2 years of age who had previously been treated for congenital or developmental hip dislocation or dysplasia (HD). MATERIAL AND METHODS: As part of the routine follow-up, we examined 53 children (106 hips), aged 2-12 years (mean 6 years). Using US, the coverage of the femoral head was assessed by the distance from the lateral tangent of the ossified femoral head to the lateral bony acetabular rim (lateral head distance, LHD). The corresponding distance was measured on radiographs (LHDR). The radiographic femoral head coverage was assessed by the migration percentage (MP) and the center-edge (CE) angle. RESULTS: We found a good accordance between sonographic LHD and the radiographic parameters MP and CE in all age groups, indicating that femoral head coverage was reliably assessed by US. There was also a high correlation between LHD and LHDR (r=0.85). All hips with subluxation were detected by US. In 11 hips that appeared normal on US, but with dysplasia or uncertain findings by radiography, the condition spontaneously normalized in 9 out of 9 examined hips with further follow-up. CONCLUSION: Because a reliable assessment of the hip is obtained, we recommend that US should be used as the primary imaging technique in the routine follow-up of children above 2 years of age with previous HD. Radiography should be omitted when US shows normal findings and is only needed when the US LHD is above the upper normal limit or the hip looks abnormal or suspicious by subjective evaluation.

The natural history of hip abnormalities detected by ultrasound in clinically normal newborns: a 6-8 year radiographic follow-up study of 93 children.

Ultrasound screening for hip dysplasia or dislocation has revealed a group of children with clinically normal hips, but with abnormal or suspicious ultrasound. During the 3-year period 1988-90, we found 170 children with this combination. We evaluated the natural history of these hips. 93 children were examined clinically and with standard radiography 6-8 years after birth. The center edge (CE) angle of Wiberg and migration percentage (MP) were measured on the radiographs. 87 children had not undergone any treatment, whereas treatment with an abduction orthosis had been initiated at approximately 4 months of age because of persisting dysplasia in 6 cases. All hips were radiographically normal at this follow-up. The mean CE value was 24 degrees (SD 6.5) and the mean MP was 13% (SD 5.2). 73 children had no complaints in their lower extremities, whereas 12 had intoeing gait, 1 had outtoeing gait, 2 had hip or knee pain, and 5 had other complaints not relevant to hip dysplasia. We conclude that infants with sonographically abnormal or suspicious hips, but with normal clinical findings, do not need immediate treatment because spontaneous resolution occurs in most of them. Postponement of treatment in the few with persistent dysplasia does not seem to affect the outcome.

The use of ultrasound in determining the initiation of treatment in instability of the hip in neonates.

We have evaluated the effect of the use of ultrasound in determining the initiation of treatment in neonatal instability of the hip. A total of 99 newborn infants (1.5% of all live births) with neonatal hip instability did not have treatment from birth, but were re-examined at eight to 15 days. In the 31 who had persisting clinical instability and ultrasound abnormality, treatment was then started with a Frejka pillow. The hips in the remaining 68 infants showed spontaneous clinical stabilisation and improvement of the ultrasound findings. Treatment was therefore withheld. There was a marked trend towards normal development in mildly unstable hips, whereas no hips with severe instability did so spontaneously. Further follow-up showed normal development in all the hips which had been treated, and in all except five of the 68 untreated infants. These five infants showed persistent hip dysplasia on both ultrasound and radiological examination at four to five months of age. Treatment with an abduction splint was then started and their hips developed normally. Ultrasound is very useful in deciding on treatment if the examiners have adequate experience with the method. Its use substantially reduces the rate of treatment. Spontaneous resolution occurred in more than half of the unstable hips. Since five of the untreated infants developed hip dysplasia a strict follow-up is essential to identify and treat these cases.

[Leg length inequality and rotational deformity after traction treatment of femoral shaft fractures in children]. / Beinlengdeforskjell og rotasjonsfeil etter strekkbehandling av femurskaftfraktur hos barn.

87 patients who experienced femoral shaft fracture at the age of two to 14 years were reviewed, on average, seven (three to 12) years after the injury occurred. Three methods of treatment had been used: Bryant skin traction, and skeletal traction using either the Weber table or the Braun frame. Patients two to three years of age at the time of injury had significantly less leg length inequality than those aged four to ten years. The reason was that in the youngest group, where which 16 out of 21 patients had been treated with skin traction, the effect of traction was less efficient and there was therefore a larger overlap of the fragments at fracture healing than in the older group, where all patients had had skeletal traction. Among ten to 14 year olds there was also less leg length inequality than among four to ten year olds. This was because of lack of growth stimulation in the oldest patients after fracture healing. The results indicate that an initial overlap of approximately 10 mm should be aimed at in patients under 11 years of age, whereas overlap should be avoided in older patients. Rotational deformity, defined as side difference in anteversion angle of 15 degrees or more, occurred in seven patients (8%), but none of them had any complaints. We conclude that traction treatment gives good results, with few complications. Over-growth remains a significant problem in children under 11 years of age.

[Femoral shortening osteotomy for chronic hip dislocation in patients with cerebral palsy]. / Forkortingsosteotomi av femur ved kronisk hofteluksasjon hos pasienter med cerebral parese.

Hip dislocation of several years duration in cerebral palsy needs treatment only if the patient has serious complaints. With the aim of reducing pain and problems with sitting function and perineal hygiene, we performed shortening osteotomy of the femur in 15 patients (12 girls and 3 boys) with spastic quadriplegia or diplegia at mean age of 14 (8-26) years. The patients were severely mentally and physically retarded, and only one patient had gait function, with support. A subtrochanteric shortening osteotomy of 3-5 cm was performed. The mean follow-up period was 5 (1-10) years. The symptomatic effect of the operation was good. The patients and parents were satisfied because the pain disappeared and the patients had less spasticity and stiffness. Complications were seen in two patients in the form of skin necrosis under both heels; this was caused by the plaster. Although reduction of the dislocation was not the aim of the surgery, radiographs at follow-up of 16 operated hips showed that five hips were reduced, whereas 11 hips remained subluxated or dislocated. We conclude that shortening osteotomy of the femur produces good symptomatic effects, probably due to reduction of the abnormally high muscle tension across the hip joint.