Estimation of accuracy of patient-specific musculoskeletal modelling: case study on a post polio residual paralysis subject.

For patients with patterns ranging out of anthropometric standard values, patient-specific musculoskeletal modelling becomes crucial for clinical diagnosis and follow-up. However, patient-specific modelling using imaging techniques and motion capture systems is mainly subject to experimental errors. The aim of this study was to quantify these experimental errors when performing a patient-specific musculoskeletal model. CT scan data were used to personalise the geometrical model and its inertial properties for a post polio residual paralysis subject. After having performed a gait-based experimental protocol, kinematics data were measured using a VICON motion capture system with six infrared cameras. The musculoskeletal model was computed using a direct/inverse algorithm (LifeMod software). A first source of errors was identified in the segmentation procedure in relation to the calculation of personalised inertial parameters. The second source of errors was subject related, as it depended on the reproducibility of performing the same type of gait. The impact of kinematics, kinetics and muscle forces resulting from the musculoskeletal modelling was quantified using relative errors and the absolute root mean square error. Concerning the segmentation procedure, we found that the kinematics results were not sensitive to the errors (relative error<1%). However, a strong influence was noted on the kinetics results (deviation up to 71%). Furthermore, the reproducibility error showed a significant influence (relative mean error varying from 5 to 30%). The present paper demonstrates that in patient-specific musculoskeletal modelling variations due to experimental errors derived from imaging techniques and motion capture need to be both identified and quantified. Therefore, the paper can be used as a guideline.

In vivo intersegmental motion of the cervical spine using an inverse kinematics procedure.

BACKGROUND: The main functions of the cervical spine are the stabilization and the orientation of the head. Pathologies are complex and difficult to diagnose. The first sign of the dysfunction is an abnormal intervertebral motion. It is the purpose of this feasibility study to determine the intersegmental motions and loading conditions of the cervical spine in vivo with standard clinical investigation methods. METHODS: We propose a new approach which merges full flexion-extension X-ray images, and continuous motion of the whole cervical spine obtained with a tracking motion system. These data were used as input for a subject-specific rigid body model of the cervical spine computed with the software MSC.Adams. This model simulates the cervical spine extension/flexion, the intervertebral motions are deduced using an inverse kinematics procedure. FINDINGS: Subject-specific rigid body models were computed from data of two subjects. The intersegmental motion and loading conditions were calculated. We found that the loading amplitudes depended on the intervertebral level, and that subject specific patterns were highlighted. We noticed an unsymmetrical behavior in flexion and extension. Furthermore intervertebral rotations were correlated with the global motion of the cervical spine. INTERPRETATION: A subject-specific rigid body model merged data from classical flexion-extension radiographs and noninvasive external motion capture. Our approach is based on inverse kinematics allowing the estimation of the intervertebral motion and mechanical behavior of the cervical spine in vivo, which gives valuable information concerning biomechanics of the cervical spine in vivo for cervical spine clinical investigation.

[Apophysitis of the iliac crest. A little known cause of low back pain and pelvic pain in children]. / L'apophysite de la crête iliaque: une cause méconnue de lombalgie et de douleurs du bassin chez l'enfant.

The authors describe an iliac osteochondrosis in 98 teenagers aged of 12 to 17 years, responsible for anterior, medial or posterior pains of pelvis and the lumbar zone, squaring with the period of ossification of the iliac crest. The spontaneous pain was revived by pressing a precise zone of the iliac crest. These pains have the usual characteristics of the pains of ossification of apophysis. The identification of the characteristics allows to avoid any further investigation which will have to be realised in case of doubt or modification of the evoluting symtomatology. It is to recognize this cause of pain so as not to attribute it to a regional morphological anomaly that may lead to excessive surgical indications. The evolution was constantly favourable after a few weeks delay. Only a momentary and adapted restriction of sporting activities is justified.

[Tendon surgery in equinovarus deformity of the foot in children and adolescents with cerebral palsy]. / La chirurgie tendineuse du pied varus équin de l'enfant et de l'adolescent infirme moteur d'origine cérébrale.

Fifty-eight children or adolescents with cerebral palsy who presented an equino varus deformity of the foot were operated on between the age of 4 to 21 by tibialis posterior tenotomy (23 cases), tibialis posterior transposition (18 cases), tibialis posterior (10 cases) or anterior (6 cases) transfer on the cuboid, with triceps lengthening (37 cases). 56 adolescents were reviewed, 45 had achieved their growth. The foot was painless and weight bearing improved. 15 failures were caused by overcorrection in valgus (7 cases, in 5 of which the tendon was transferred on the cuboid) or under correction and recurrence of the deformity (8 cases). A. walking E.M.G. was not made but a clinical examination of voluntary and automatic activity pre and post operatively in 30 cases, which showed that even after tibialis posterior tenotomy a new muscular activity can appear. We recommend this procedure in the varus deformity of the fore foot associated with triceps lengthening in equino varus deformity when the foot is flexible. When the foot is stiff or in cases of under correction and after 10 years, triple arthrodesis is recommended.

[A case of epiphyseal osteoid osteoma]. / Un cas d'ostéome ostéoïde épiphysaire.

The authors describe a case of osteoid osteoma developing in the lower femoral epiphysis of a 9-year-old child. It was close to the growth plate and was recognised with the aid of digital angiography and tomo-densitometry. It was removed by a surgical approach across the growth plate.

[Epiphyseal closure correction in children. Apropos of 18 cases]. / La désépiphysiodèse chez l'enfant. A propos de 18 cas.

The authors have performed 18 operative procedures to remove bony bridges across the growth plate in children. The causes of the formation of the bone bridge were many, including 10 after injury and 3 after infection. There were 9 good results and 9 failures. The causes of the failures were the extent of the bone bridge, sepsis as the causative lesion and technical errors during operation. The best results were obtained in cases where the bridge was peripheral, was easily approached and followed injury in young children. Extensive bridges located centrally had a poor prognosis. All the post-infective cases were failures.