Nathalie Maurel

Kinematic analysis of the upper limb: a useful tool in children with cerebral palsy

Upper limb involvement in cerebral palsy is usually more complex than lower limb involvement. Each child has a specific brain lesion and the clinical pattern is highly variable. Current clinical methods of assessment do not fully evaluate the kinematic activity during simple activities of daily life. We defined an upper limb three-dimensional kinematic protocol in order to complete the clinical analysis of such patients and reproducibility tests are in progress. Data were presented for one of the patients studied and showed some important differences between the clinical analysis and the kinematic one. A three-dimensional upper limb motion analysis gives a more complete kinematic evaluation and should help better measure the results of treatments.

In vitro biomechanical analysis of glenoı̈ds before and after implantation of prosthetic components

Biomechanical investigations are yet necessary to better understand the origin of the glenoïd loosening which is the main reason for revision surgery. The aim of this study was to analyse the behaviour of cadaveric glenoïds before and after implantation of glenoïd prostheses. For that, we developed a new experimental protocol allowing measurement of bone strains and implants displacements under various loading cases. Ten pairs of fresh cadaveric scapulae were tested. Two kinds of loads were applied on the intact glenoïd: physiological loads corresponding to a 0-180 degrees abduction and anteflexion movements, and 500N loads. The glenoïds were then implanted with a keeled or pegged cemented polyethylene implant. The same previous 500N loads were then applied on the implanted glenoïds. Strains were measured using six strain gages placed on precise points around the peripheral cortex of the glenoïd. Displacements of implants under loading were measured using two CCD cameras. Maximum strains were obtained between 60 degrees and 120 degrees of abduction or anteflexion. They were located at the anterior and antero-superior parts of the glenoïd during abduction and at the posterior and postero-superior parts during anteflexion. Implantation of a prosthetic component generally seemed to increase strains, but tensile strains were decreased at the postero-inferior part with the antero-inferior loading point.Some differences were observed between the implants, but they have to be confirmed by further experiments. The great number of data obtained for intact scapulae could be used for a better understanding of glenoïd behaviour and for validation of finite element models.

Biomechanical Comparison of Locking Compression Plate and Limited Contact Dynamic Compression Plate Combined with an Intramedullary Rod in a Canine Femoral Fracture‐Gap Model

OBJECTIVE To compare the biomechanical properties of locking compression plate (LCP) and a limited contact dynamic compression plate combined with an intramedullary rod (LC-DCP-R) in a cadaveric, canine, femoral fracture-gap model. STUDY DESIGN In vitro biomechanical study; nonrandomized, complete block (dog). SAMPLE POPULATION Paired cadaveric canine femora (n = 10 dogs). METHODS Paired femurs with a mid-diaphyseal 20 mm gap were stabilized with either LCP or LC-DCP-R. Nondestructive testing up to 60% of body weight (BW) was followed by a continuous destructive test. Comparative structural properties, 3-dimensional (3D) interfragmentary motion, and plate linear strain were evaluated. Paired comparisons were made between LCP and LC-DCP-R. RESULTS Stiffness after nondestructive testing was significantly lower for LCP with a mean (95% confidence interval [CI]) of 61 N/mm (46-76) versus 89 N/mm (67-110) for LC-DCP-R (P = .0072). Ultimate load to failure was significantly lower for LCP with a median (interquartile range [IQR]) of 270 N (247-286) versus 371.5 (353-385) for LC-DCP-R (P = .002). Axial motion at 60% BW was significantly higher for LCP with a median (IQR) of 1.01 mm (0.71-1.26) versus 0.36 mm (0.20-0.49) for LC-DCP-R (P = .002). Shear motion was significantly higher for LCP with a median (IQR) of 1.18 (0.78-1.58) versus 0.72 mm (0.45-1.00) for LC-DCP-R (P = .018). Strain was significantly higher for mid-LCP surface with a mean (95%CI) at 60% BW of 979 μdef (579-1378) versus 583 μdef (365-801) at mid-LC-DCP-R surface (P = .0153). The elastic limit strain of the plates was not different and was reached at a mean (95%CI) load of 241 N (190-292) for LCP versus 290 N (245-336) for LC-DCP-R (P = .12). CONCLUSION The LC-DCP-R showed higher stiffness and resistance to failure, lower interfragmentary motion, and lower plate strain and stress compared to LCP.

Biomechanical comparison of 4.0-mm short-threaded cannulated screws and 4.0-mm short-threaded cancellous screws in a canine humeral condylar fracture model.

OBJECTIVE To compare biomechanical properties of a humeral condylar fracture model stabilized either with a 4.0-mm short-threaded cancellous screw (CCS) or with a 4.0-mm short-threaded cannulated screw (CNS). STUDY DESIGN In vitro biomechanical study. SAMPLE POPULATION Bilateral cadaveric canine humeri (n = 20). METHODS Fractures of the lateral portion of the humeral condyle were simulated by standardized osteotomies; 10 condyles were each stabilized with CCS and 10 with CNS. Axial compression load was applied to each specimen until failure and force-displacement curves generated. Testing data for each construct were determined and compared using either a Students paired t-test (quantitative data) or a χ(2) test (qualitative data) with statistical significance set at P < .05. RESULTS Yield load (elastic limit), ultimate load at failure, and displacements at loads corresponding to walk and trot were determined from each curve. Mean ± SD ultimate load at failure was significantly higher (P = .01) for CCS constructs (1261 ± 261 N) than for CNS constructs (1078 ± 231 N). Yield loads were not significantly different (P = .10) between construct types, and exceeded all expected loads supported by the humeral condyle at walk. The risk of having a yield load below the expected physiologic load at trot was not statistically higher with a CNS construct compared with a CCS construct (P = .26). CONCLUSION Humeral condylar fracture repaired either by a 4.0-mm cannulated screw or a 4.0-mm cancellous screw have comparable stability in this condylar fracture model.

Shoulder and elbow kinematics during the Mallet score in obstetrical brachial plexus palsy

Background: The physical signs of obstetrical brachial plexus palsy range from temporary upper‐limb dysfunction to a lifelong impairment and deformity in one arm. The aim of this study was to analyze the kinematics of the upper limb and to evaluate the contribution of glenohumeral and scapulothoracic joints of obstetrical brachial plexus palsy children. Methods: Six children participated in this study: 2 males and 4 females with a mean age of 11.7 years. Three patients had a C5, C6 lesion and 3 had a C5, C6, C7 lesion. They were asked to perform five tasks based on the Mallet scale and the kinematic data were collected using the Fastrak electromagnetic tracking device. Findings: The scapulothoracic protraction and posterior tilt were significantly increased in the involved limb during the hand to mouth task (p = 0.006 and p = 0.015 respectively). The scapulothoracic Protraction/glenohumeral Elevation ratio was significantly increased in the involved limb during the hand to neck task (p = 0.041) and the elevation task (p = 0.015). The ratios of scapulothoracic Tilt on the three glenohumeral excursion angles were significantly increased during the hand to mouth task (p ≤ 0.041). The scapulothoracic Mediolateral/glenohumeral Elevation ratio was significantly increased in the involved limb during the elevation task (p = 0.038). The glenohumeral elevation excursion was significantly decreased in the involved limb during the hand to neck task (p < 0.001) and the elevation task (p = 0.0003). Interpretation: This study gives us information about the greater contribution of the scapulothoracic joint to shoulder motion for affected arm of obstetrical brachial plexus palsy patients compared to their unaffected arm. Kinematic analysis could be useful in shoulder motion evaluation during the Mallet score and to evaluate outcomes after surgery. HighlightsDevelopment of a kinematic protocol based on Mallet score tasks for obstetrical brachial plexus palsy children.Application of this kinematic protocol to assess shoulder and elbow motion dysfunction in these patients.This kinematic protocol appeared as a valuable adjunct to clinical scales in management of such patients.Increased scapulothoracic protraction and posterior tilt in the involved limb during the hand to mouth task.Decreased glenohumeral elevation excursion in the involved limb during the hand to neck and elevation tasks.

Influence of prolonged immersion on the resistance of arthroscopy knots in biological media.

INTRODUCTION Biomechanical studies of arthroscopic knots have been performed on sutures that were tied manually and tested immediately after tying. We performed this study to evaluate the knot and the suture during the healing phase, which was not evaluated in these previous studies. Our hypothesis was that the biomechanics features of arthroscopic knots may change in relation to the duration of incubation in biological media simulating synovial fluid. Thus our goal was to study the influence of incubation for 30 days in biological media simulating body fluid using a device to standardize knot tying and allow comparison of arthroscopic sutures. MATERIALS AND METHODS Three Ultra-High Molecular Weight PolyEthylene (UHMPWE) sutures (Fiberwire, Orthocord and Maxbraid) were tested with a self-locking slip knot (SMC knot). Sixty identical knots were tied using a standardized device, and divided into two groups: the control group « D0 » and the group « D30 » where the knots were soaked in biological media simulating body fluid for 30 days. Cyclic loading tests were then performed on the knots in each group using a machine to define four variables: clinical failure, ultimate failure, knot slippage and the characteristics of failure. RESULTS There was no significant difference between the two groups for knot resistance at clinical failure or ultimate failure, without regard to the suture, (P<0.05). After cyclic loading, the most slippage occurred in the Orthocord (≈5.6mm) then the Maxbraid (≈3.55mm) and the Fiberwire (≈2.51mm). The only suture whose slippage was influenced by the duration of incubation was Orthocord. At clinical failure, the loop that slipped the most was the Orthocord suture (≈5.45mm) then the Fiberwire (≈4.8mm) and the Maxbraid (≈4.1mm). In the Orthocord and Maxbraid sutures, knot slippage after clinical failure significantly increased with the duration of suture incubation (P<0.05). The reason for failure was breakage from tearing of suture fibers in all cases. CONCLUSION Prolonged incubation of arthroscopic suture knots influences slippage, which could result in unsuccessful primary attachment of the tendon during the healing phase. LEVEL OF EVIDENCE Level IV. Biomechanical study.

De novo generation in an in vivo rat model and biomechanical characterization of autologous transplants for ligament and tendon reconstruction

Background: Surgical reconstruction of ligaments and tendons is frequently required in clinical practice. The commonly used autografts, allografts, or synthetic transplants present limitations in terms of availability, biocompatibility, cost, and mechanical properties that tissue bioengineering aims to overcome. It classically combines an exogenous extracellular matrix with cells, but this approach remains complex and expensive. Using a rat model, we tested a new bioengineering strategy for the in vivo and de novo generation of autologous grafts without the addition of extracellular matrix or cells, and analyzed their biomechanical and structural properties. Methods: A silicone perforated tubular implant (PTI) was designed and implanted in the spine of male Wistar rats to generate neo‐transplants. The tensile load to failure, stiffness, Young modulus, and ultrastructure of the generated tissue were determined at 6 and 12 weeks after surgery. The feasibility of using the transplant that was generated in the spine as an autograft for reconstruction of medial collateral ligaments (MCL) and Achilles tendons was also tested. Findings: Use of the PTI resulted in de novo transplant generation. Their median load to failure and Young modulus increased between 6 and 12 weeks (respectively 12 N vs 34 N and 48 MPa vs 178 MPa). At 12 weeks, the neo‐transplants exhibited collagen bundles (mainly type III) parallel to their longitudinal axis and elongated fibroblasts. Six weeks after their transfer to replace the MCL or the Achilles tendon, the transplants were still present, with their ends healed at their insertion point. Interpretation: This animal study is a first step in the design and validation of a new bioengineering strategy to develop autologous transplants for ligament and tendon reconstructions.