Hong et al.  showed that pelvic parameters (PI, SS and PT) in patients with achondroplasia are closely related to spinal parameters (thoracic kyphosis, LL and thoracic kyphosis) and that these relationships play an important role in achieving sagittal balance. In addition, the trunk of patients with achondroplasia tends to tilt backwards (mean AVS, − 22.2 mm) to compensate for lumbar hyperlordosis . However, the present study showed that preoperative forward tilting of VAS contributes more to persistent postoperative hip flexion contracture. The authors postulated the reasons why patients with preoperative stroke tilt forward may have a higher risk of pre-existing hip flexion contracture and quadriceps shortening before thigh lengthening. Patients with achondroplasia have unique pelvic and spinal structures. They show a basin in the shape of a champagne glass and has a front PT . With regard to the spine, kyphosis in the thoracum compound is very common in infants and most often disappears when the child begins to walk [2,3,4]. As kyphosis begins to improve, lumbosacral hyperlordosis may begin to progress. Therefore, the spinopelvical parameters of patients with achondroplasia differ from those of the average population: they are more likely to have higher thoracic kyphosis and LL, as well as lower PT and thoracic kyphosis [2,3,4]. As a result, patients with achondroplasia have a higher risk of developing hip flexion contracture than the average population. In fact, we have already shown that hip flexion contracture often occurs after thigh lengthening in patients with achondroplasia [11, 12].
After the operation, patients with persistent hip flexion contracture showed a significant change in spinal parameters, including an increase in SS and LL and a decrease in PT. In addition, most patients had knee stiffness, especially with flexion restriction. These results suggest that the quadriceps muscles, mainly the rectus femoris, may be the main cause of hip flexion contracture. Tension and stiffness of the quadriceps muscles induce an imbalance of muscle strength around the pelvis and compensatory anterior pelvic tilt, which sequentially leads to a significant increase in SS and lumbar hyperlordosis. In addition, it may eventually lead to worsening of perioperative hip flexion contracture in these patients . This could explain why all patients with persistent hip flexion contracture underwent soft tissue release, including intramuscular recession of the rectus femoris, and consequently recovered almost completely in the range of motion of the hip joint. In patients with hip flexion contracture, a hip stretching exercise in the supine position was performed under the direction of a well-trained physician. Patients have been asked to do their exercise 5 times a week for at least 1 hour, in addition, they tend to have a position in their sleep. Hip flexion contracture often occurs after thigh lengthening in patients with achondroplasia, but few studies have examined its development in these patients. The aim of this study was to analyse persistent hip flexion contracture in patients with achondroplasia who had undergone thigh lengthening and to identify contributing factors. Persistent hip flexion contracture developed in 13 (38%) of the 34 patients with achondroplasia after thigh lengthening.
Eight (62%) of these 13 patients showed simultaneous limitation of knee flexion. Excessive thigh elongation (odds ratio [OR], 1.450; 95% confidence interval [CI] 1.064 to 1.975; p = 0.019) and forward inclination of the vertical sagittal axis (OR, 1.062; 95% CI 1.001 to 1.127; p = 0.047) contributed to sustained hip flexion contracture. Burn-specific contractures are due to thermal damage due to vascular insufficiency or compression edema or pressure ulcer, which eventually leads to joint and myofascial deformities.22 Another consideration is that in 2016, Danish researchers published a comprehensive theory on how contracture develops under central motor lesions. They suggested that adapting the neuromuscular tendon-connective tissue complex to central motor injury with several other factors (neuronal activation, mismatch between bone and muscle growth, mechanotransduction, tension homeostasis, microvascularization, genetics, epigenetics) is key to the prevention and treatment of muscle contractures. In the case of hip contracture, the hip is in a partially bent position when the person tries to get up. The type of posture, unlike normal vertical posture, shifts the weight of the body before the hip, creating a moment of hip flexion. X-rays of a 10-year-old boy with achondroplasia who has persistent hip flexion contracture after thigh extension. a first X-ray of the patient.
The patient was simultaneously subjected to bilateral thigh lengthening to gain 11 cm (extension percentage of 42.9%). b Postoperative radiography, which shows an exacerbation of the horizontal sacrum with complications of lumbosacral hyperlordosis of hip flexion contracture and no significant contracture group were as follows. In the hip flexion contracture group, refraction developed in 8 patients after removal of the external fixator. They underwent external fixatic reapplication by intramedullary nailing with or without bone grafting. Two patients had varus angle deformity and underwent osteotomy for acute correction. One patient showed a superficial infection of the pin site that required treatment with oral antibiotics. In contrast, 7 cases of refraction and 1 case of varus angle deformation developed in the group without significant contracture; The method of treatment for each complication was the same as that of the hip flexion contracture group. In addition, one patient had a deep infection at the surgical site.