Francesco Cenni

Geometrical changes of knee ligaments and patellar tendon during passive flexion.

Patterns of fibre elongation and orientation for the cruciate and collateral ligaments of the human knee joint and for the patellar tendon have not yet been established in three-dimensions. These patterns are essential for understanding thoroughly the contribution of these soft tissues to joint function and of value in surgical treatments for a more conscious assessment of the knee status. Measurements from 10 normal cadaver knees are here reported using an accurate surgical navigation system and consistent anatomical references, over a large flexion arc, and according to current recommended conventions. The contours of relevant sub-bundles were digitised over the corresponding origins and insertions on the bones. Representative fibres were calculated as the straight line segments joining the centroids of these attachment areas. The most isometric fibre was also taken as that whose attachment points were at the minimum change in length over the flexion arc. Changes in length and orientation of these fibres were reported versus the flexion angle. A good general repeatability of intra- and inter-specimens was found. Isometric fibres were found in the locations reported in the literature. During knee flexion, ligament sub-bundles slacken in the anterior cruciate ligament, and in the medial and lateral collateral ligaments, whereas they tighten in the posterior cruciate ligament. In each cruciate ligament the two compounding sub-bundles have different extents for the change in fibre length, and also bend differently from each other on both tibial planes. In the collateral ligaments and patellar tendon all fibres bend posteriorly. Patellar tendon underwent complex changes in length and orientation, on both the tibial sagittal and frontal planes. For the first time thorough and consistent patterns of geometrical changes are provided for the main knee ligaments and tendons after careful fibre mapping.

Kinematics of the three components of a total ankle replacement: in vivo fluoroscopic analysis.

Background: Careful kinematic analysis of ankle joints with newly developed prostheses should be carried out to assess the actual performance in vivo. This study analyzed the pattern of motion of the three components of a ligament-compatible ankle replacement, developed to replicate normal joint kinematics. Materials and Methods Twelve patients treated with this design were analyzed at 6, 12, and 24 months followup. A series of images were acquired by videofluoroscopy at extremes of the range of motion, and during flexion/extension against gravity and stair-climbing/descending. Three-dimensional positions and orientations of the tibial and talar metal components and of the polyethylene mobile-bearing were obtained from the images by a standard shape-matching procedure. Motion between the three components was calculated and descriptively analyzed. Results Large tibiotalar joint mobility of the replaced ankle was observed in all three anatomical planes, particularly in the sagittal. In flexion/extension against gravity, the mean range of flexion was 17.6, 17.7, and 16.2 degrees, respectively, over the three followups. The inclination angle of the mean axis of joint rotation was 3.7 degrees down and lateral in the frontal plane and 4.7 degrees posterior and lateral in the transverse plane, similar to those in the normal ankle. The corresponding antero-posterior translation of the meniscal-bearing with respect to the tibia was 3.3, 3.3, and 3.2 mm, with statistically significant correlation with joint flexion. Conclusion Physiological motion can be achieved in ligament-compatible ankle joint replacements. The considerable antero-posterior bearing-to-tibial motion and its coupling with flexion support the main original claims of this design. Level of Evidence: IV, Case Series

Functional performance of a total ankle replacement: thorough assessment by combining gait and fluoroscopic analyses

BACKGROUND A thorough assessment of patients after total ankle replacement during activity of daily living can provide complete evidence of restored function in the overall lower limbs and replaced ankle. This study analyzes how far a possible restoration of physiological mobility in the replaced ankle can also improve the function of the whole locomotor apparatus. METHODS Twenty patients implanted with an original three-part ankle prosthesis were analyzed 12 months after surgery during stair climbing and descending. Standard gait analysis and motion tracking of the components by three-dimensional fluoroscopic analysis were performed on the same day using an established protocol and technique, respectively. FINDINGS Nearly physiological ankle kinematic, kinetic and electromyography patterns were observed in the contralateral side in both motor activities, whereas these patterns were observed only during stair climbing in the operated side. Particularly, the mean ranges of flexion at the replaced ankle were 13° and 17° during stair climbing and descending, respectively. Corresponding 2.1 and 3.1mm antero/posterior meniscal-to-tibial translations were correlated with flexion between the two metal components (p<0.05). In addition, a larger tibiotalar flexion revealed by fluoroscopic analysis resulted in a physiological hip and knee moment. INTERPRETATION The local and global functional performances of these patients were satisfactory, especially during stair climbing. These might be associated to the recovery of physiological kinematics at the replaced ankle, as also shown by the consistent antero/posterior motion of the meniscal bearing, according to the original concepts of this ankle replacement design.

The reliability and validity of a clinical 3D freehand ultrasound system

BACKGROUND AND OBJECTIVE Acquiring large anatomical volumes in a feasible manner is useful for clinical decision-making. A relatively new technique called 3D freehand ultrasonography is capable of this by combining a conventional 2D ultrasonography system. Currently, a thorough analysis of this technique is lacking, as the analyses are dependent on the software implementation details and the choice of measurement systems. Therefore this study starts by making this implementation available under the form of an open-source software library to perform 3D freehand ultrasonography. Following that, reliability and validity analyses of extracting volumes and lengths will be carried out using two independent motion-tracking systems. METHODS A PC-based ultrasonography device and two optical motion-tracking systems were used for data acquisition. An in-house software library called Py3DFreeHandUS was developed to reconstruct (off-line) the corresponding data into one 3D data set. Reliability and validity analyses of the entire experimental set-up were performed by estimating the volumes and lengths of ground truth objects. Ten water-filled balloons and six cross-wires were used. Repeat measurements were also performed by two experienced operators. RESULTS The software library Py3DFreeHandUS is available online, along with the relevant documentation. The reliability analyses showed high intra- and inter-operator intra-class correlation coefficient results for both volumes and lengths. The accuracy analysis revealed a discrepancy in all cases of around 3%, which corresponded to 3 ml and 1 mm for volume and length measurements, respectively. Similar results were found for both of the motion-tracking systems. CONCLUSIONS The undertaken analyses for estimating volume and lengths acquired with 3D freehand ultrasonography demonstrated reliable design measurements and suitable performance for applications that do not require sub-mm and -ml accuracy.

Three-dimensional implant position and orientation after total knee replacement performed with patient-specific instrumentation systems

Patient‐specific instrumentation systems are entering into clinical practice in total knee replacement, but validation tests have yet to determine the accuracy of replicating computer‐based plans during surgery. We performed a fluoroscopic analysis to assess the final implant location with respect to the corresponding preoperative plan. Forty‐four patients were analyzed after using a patient‐specific system based on CT and MRI. Computer aided design implant models and models of the femur and tibia bone portions, as for the preoperative plans, were provided by the manufacturers. Two orthogonal fluoroscopic images of each knee were taken after surgery for pseudo‐biplane imaging; 3D component locations with respect to the corresponding bones were estimated by a shape‐matching technique. Assuming that the corresponding values at the preoperative plan were equal to zero, discrepancies were taken as an indication of accuracy for the systems. A repeatability test revealed that the technique was reliable within 1 mm and 1°. The maximum discrepancies for all the patients for the femoral component were 5.9 mm in a proximo‐distal direction and 4.2° in flexion. Good matching was found between final implantations and preoperative plans with mean discrepancies smaller than 3.1 mm and 1.9°.

Estimating medial gastrocnemius muscle volume in children with spastic cerebral palsy: a cross-sectional investigation

This cross‐sectional investigation evaluates the reliability of estimating medial gastrocnemius anatomical cross‐sectional area (aCSA) in typically developing and spastic cerebral palsy (SCP) cohorts. It verifies whether muscle volume estimations based on aCSA improve when aCSA is multiplied by muscle–tendon unit (MTU) or muscle length, and whether the resulting errors in volume estimations are smaller than changes after intervention.

Reliability of a clinical 3D freehand ultrasound technique: Analyses on healthy and pathological muscles

BACKGROUND AND OBJECTIVE 3D freehand Ultrasonography is a medical imaging technique that can be used to measure muscle and tendon morphological and structural properties, including volume, lengths and echo-intensity. These properties are clinically relevant in neurological disorders such as spastic cerebral palsy to monitor disease progression and evaluate the effect of treatment. This study presents a methodology for extracting these parameters along with a clinical reliability analysis for the data acquisition and processing. METHODS The medial gastrocnemius muscles and Achilles tendon of 10 typically developing children and 10 children with spastic cerebral palsy were assessed. An open-source in-house software library developed in Python (Py3DFreeHandUS) was used to reconstruct, into one 3D data set, the data simultaneously acquired from an US machine and a motion tracking system. US images were manually segmented and linearly interpolated by means of a new simplified approach which involved sequentially decreasing the total number of images used for muscle border segmentation from 100% to 5%. Acquisition and processing reliability was defined based on repeated measures from different data processers and from different data acquirers, respectively. RESULTS When only 10% of the US images were outlined, there was an average underestimation of muscle volume of 1.1% and 1.6% with respect the computation of all the available images, for the typically developing and spastic cerebral palsy groups, respectively. For both groups, the reliability was higher for data processing than for data acquisition. High inter-class correlation coefficient values were found for processing and acquisition reliability, with worst case values of 0.89 and 0.61, respectively. The standard error of measurement, expressed as a percentage of the average volumes, was smaller than 2.6 ml (4.8%) in all cases. CONCLUSIONS The present analysis demonstrates the effectiveness of applying 3D freehand ultrasonography in a clinical setting for analysing healthy and pathological paediatric muscle.

Achilles tendon moment arm length is smaller in children with cerebral palsy than in typically developing children

When studying muscle and whole-body function in children with cerebral palsy (CP), knowledge about both internal and external moment arms is essential since they determine the mechanical advantage of a muscle over an external force. Here we asked if Achilles tendon moment arm (MAAT) length is different in children with CP and age-matched typically developing (TD) children, and if MAAT can be predicted from anthropometric measurements. Sixteen children with CP (age: 10y 7m±3y, 7 hemiplegia, 12 diplegia, GMFCS level: I (11) and II (8)) and twenty TD children (age: 10y 6m±3y) participated in this case-control study. MAAT was calculated at 20° plantarflexion by differentiating calcaneus displacement with respect to ankle angle. Seven anthropometric variables were measured and related to MAAT. We found normalized MAAT to be 15% (∼7mm) smaller in children with CP compared to TD children (p=0.003). MAAT could be predicted by all anthropometric measurements with tibia length explaining 79% and 72% of variance in children with CP and TD children, respectively. Our findings have important implications for clinical decision making since MAAT influences the mechanical advantage about the ankle, which contributes to movement function and is manipulated surgically.

Can in Vivo Medial Gastrocnemius Muscle–Tendon Unit Lengths be Reliably Estimated by Two Ultrasonography Methods? A Within-Session Analysis

A clinically feasible method to reliably estimate muscle-tendon unit (MTU) lengths could provide essential diagnostic and treatment planning information. A 3-D freehand ultrasound (3-DfUS) method was previously validated for extracting in vivo medial gastrocnemius (MG) lengths, although the processing time can be considered substantial for the clinical environment. This investigation analyzed a quicker and simpler method using the US transducer as a spatial pointer (US-PaP), where the within-session reliability of extracting the muscle-tendon unit (MTU) and tendon lengths are estimated. MG MTU lengths were extracted in a group of 14 healthy adults using both 3-DfUS and US-PaP. Two consecutive acquisitions were performed per participant, and the data processed by two researchers independently. The intra-class correlation coefficients were above 0.97, and the standard error of measurements below 3.6 mm (1.5%). This investigation proposes that the simplified US-PaP method is a viable alternative for estimating MG MTU lengths.

Medial Gastrocnemius Muscle–Tendon Junction and Fascicle Lengthening across the Range of Motion Analyzed in 2-D and 3-D Ultrasound Images

Ultrasound imaging modalities offer a clinically viable method to visualize musculoskeletal structures. However, proper data comparison between investigations is compromised because of a lack of measurement error documentation and method standardization. This investigation analyzes the reliability and validity of extracting medial gastrocnemius belly and fascicle lengths and pennation angles in different ankle joint positions, across the full range of motion, in a cohort of 11 children with spastic cerebral palsy and 11 typically developed children. Each of these parameters was extracted from two consecutive acquisitions, using both 2-D and 3-D ultrasound images. The findings suggest that the muscle tendon junction extraction in 2-D images can be a suitable parameter for analyzing medial gastrocnemius muscle length in typically developed children and children with spastic cerebral palsy, although averaging over multiple measurements is recommended to reduce variability. More caution should be taken when performing analyses based on fascicle length.