A technique for measurement and description of three-dimensional six degree-of-freedom motion of a body joint with an application to the human spine

Non-invasive quantitative assessment of induced component displacement can safely and accurately diagnose tibial component loosening in patients: A prospective diagnostic study

PURPOSE

Aseptic loosening often requires major, expensive and invasive revision surgery. Current diagnostic modalities merely show indirect signs of loosening. A recent proof of concept study proposed a non-invasive technique for the quantitative and visual assessment of implant movement as a diagnostic aid for tibial component loosening. The primary research question addressed is whether this novel diagnostic modality can safely and effectively aid the diagnosis of aseptic loosening.

METHODS

This clinical study included patients suspected of aseptic total knee arthroplasty (TKA) loosening listed for revision surgery and asymptomatic patients. Safety was evaluated using a numerical rating scale (NRS) for discomfort and by registration of adverse events. Feasibility was assessed by recording the duration and ease of the procedure. Intra- and interrater reliability were evaluated. In symptomatic patients, diagnostic accuracy metrics were evaluated with intra-operative assessment as a reference test.

RESULTS

In total, 34 symptomatic and 38 asymptomatic knees with a TKA were analysed. The median NRS for discomfort during loading was 6 (interquartile range [IQR]: 3.75-7.00) in symptomatic patients and 2 (IQR: 1.00-3.00) in asymptomatic patients. No adverse events were reported. The majority of users found the use of the loading device easy. The median time spent in the computed tomography room was 9 min (IQR: 8.00-11.00). Excellent to good intra- and interrater reliabilities were achieved. Diagnostic accuracy analysis resulted in a sensitivity of 0.91 (95% confidence interval [CI]: 0.72-0.97) and a specificity of 0.72 (95% CI: 0.43-0.90).

CONCLUSIONS

The proposed diagnostic method is safe, feasible, reliable and accurate in aiding the diagnosis of aseptic tibial component loosening.

LEVEL OF EVIDENCE

Level II.

Human in vivo midtarsal and subtalar joint kinematics during walking, running and hopping

The interaction among joints of the midtarsal complex and subtalar joint is important for locomotor function; however, its complexity poses substantial challenges in quantifying the joints' motions. We determine the mobility of these joints across locomotion tasks and investigate the influence of individual talus morphology on their motion. Using highly accurate biplanar videoradiography, three-dimensional bone kinematics were captured during walking, running and hopping. We calculated the axis of rotation of the midtarsal complex and subtalar joint for the landing and push-off phases. A comparison was made between these rotation axes and the morphological subtalar axis. Measurement included total rotation about and the orientation of the rotation axes in the direction of the subtalar joint and its deviation via spatial angles for both phases. The rotation axes of all three bones relative to the talus closely align with the morphological subtalar axis. This suggests that the midtarsal and subtalar joints' motions might be described by one commonly oriented axis. Despite having such an axis, the location of the axes and ranges of motion differed among the bones. Our results provide a novel perspective of healthy foot function across different sagittal plane-dominant locomotion tasks underscoring the importance of quantifying midtarsal complex and subtalar motion while accounting for an individual's talus morphology.

Primary stability of the Activ L® intervertebral disc prosthesis in cadaver bone and comparison of the keel and spike anchoring concept

Background

High primary stability is the key prerequisite for safe osseointegration of cementless intervertebral disc prostheses. The aim of our study was to determine the primary stability of intervertebral disc prostheses with two different anchoring concepts – keel and spike anchoring.

Methods

Ten ActivL intervertebral disc prostheses (5 x keel anchoring, 5 x spike anchoring) implanted in human cadaver lumbar spine specimens were tested in a spine movement simulator. Axial load flexion, extension, left and right bending and axial rotation motions were applied on the lumbar spine specimens through a defined three-dimensional movement program following ISO 2631 and ISO/CD 18192-1.3 standards. Tri-dimensional micromotions of the implants were measured for both anchor types and compared using Student’s T-test for significance after calculating 95 % confidence intervals.

Results

In the transverse axis, the keel anchoring concept showed statistically significant (p < 0.05) lower mean values of micromotions compared to the spike anchoring concept. The highest micromotion values for both types were observed in the longitudinal axis. In no case the threshold of 200 micrometers was exceeded.

Conclusions

Both fixation systems fulfill the required criteria of primary stability. Independent of the selected anchorage type an immediate postoperative active mobilization doesn’t compromise the stability of the prostheses.

Optical motion capture accuracy is task-dependent in assessing wrist motion

Optical motion capture (OMC) systems are commonly used to capture in-vivo three-dimensional joint kinematics. However, the skin-based markers may not reflect the underlying bone movement, a source of error known as soft tissue artifact (STA). This study examined STA during wrist motion by evaluating the agreement between OMC and biplanar videoradiography (BVR). Nine subjects completed 7 different wrist motion tasks: doorknob rotation to capture supination and pronation, radial-ulnar deviation, flexion-extension, circumduction, hammering, and pitcher pouring. BVR and OMC captured the motion simultaneously. Wrist kinematics were quantified using helical motion parameters of rotation and translation, and Bland-Altman analysis quantified the mean difference (bias) and 95% limit of agreement (LOA). The rotational bias of doorknob pronation, a median bias of -4.9°, was significantly larger than the flexion-extension (0.7°, p < 0.05) and radial-ulnar deviation (1.8°, p < 0.01) tasks. The rotational LOA range was significantly smaller in the flexion-extension task (5.9°) compared to pitcher (11.6°, p < 0.05) and doorknob pronation (17.9°, p < 0.05) tasks. The translation bias did not differ between tasks. The translation LOA range was significantly larger in circumduction (9.8°) compared to the radial-ulnar deviation (6.3°, p < 0.05) and pitcher (3.4°, p < 0.05) tasks. While OMC technology has a wide-range of successful applications, we demonstrated it has relatively poor agreement with BVR in tracking wrist motion, and that the agreement depends on the nature and direction of wrist motion.

Effect of Number of Digits on Human Precision Manipulation Workspaces

Precision manipulation, or moving small objects held in the fingertips, is likely the most heavily utilized class of dexterous within-hand manipulation and adds greatly to the capabilities of the human hand. This article focuses on studying the effects of varying the number of digits used on the resulting manipulation abilities, in terms of translational workspaces and rotational ranges, by manipulating two circular objects, 50 mm and 80 mm in diameter. In general, as the number of digits in contact with the object increases, the results show a significant reduction in precision manipulation workspace range for four of the six translation and rotation directions and no significant change in the other two, suggesting that for these particular metrics, more fingers result in a reduction in performance. Furthermore, while two digits results in the largest workspaces for five of the six translation and rotation axes, the lack of ability to control rotation in the distal-proximal direction suggests that three digits may be more desirable for overall precision manipulation dexterity.

Surgical Outcomes of Extraforaminal Microdiskectomy by Midline Incision for Far-Lateral Lumbar Disk Herniation

BACKGROUND

 Far-lateral lumbar disk herniation (FLDH) is defined as a disk herniation located laterally to the medial wall of the pedicle. The aim of our study is to describe the extraforaminal microdiskectomy by midline incision for FLDH, which does not include laminotomy-partial facetectomy, and to evaluate mid-term surgical outcomes.

METHODS

 107 patients who underwent surgery for FLDH by midline incision for the first time between 2012 and 2017 were included in our study. The assessment of neurological status of the patients was done by physical examination, preoperative Oswestry Disability Index (ODI), Visual Analog Scala (VAS) scores, and magnetic resonance images. They were then followed-up postoperatively and at 12 months with VAS and ODI tests.

RESULT

 58 (54.2%) patients were male and 49 (45.8%) were female. The mean age at the time of surgery was 55.0 ± 8.6 years. The mean ODI scale score was 32.4 ± 6.2 preoperatively, 11.4 ± 2.1 early postoperatively, and 9.7 ± 2.2 in late postoperative follow-up (statistically significant, p = 0.001). The average VAS was 7.51 ± 1.1 preoperatively, 2.74 ± 0.7 early postoperatively, and 0.68 ± 0.08 in late postoperative follow-up (statistically significant, p = 0.001). The average operative time was 41 ± 7 (37 to 58) minutes.

CONCLUSIONS

 The extraforaminal microdiskectomy without laminotomy by midline incision is a minimally invasive approach for FLDH. Our technique allows a sufficient and safe decompression of the neural structures, and thus results in a significant reduction of the symptoms and disability.

Isolated unstable burst fractures of the fifth lumbar vertebra: functional and radiological outcome after posterior stabilization with reconstruction of the anterior column: About 6 cases and literature review

INTRODUCTION

L5 burst fractures represent a small percentage of all spine fractures. Treatment strategy has not yet been standardized. Anatomical features and their biomechanical characteristics create fracture patterns which differ from those at the thoracolumbar junction. The objective of this study was to evaluate L5 burst fracture surgical treatment outcomes after posterior stabilization and reconstruction of the anterior column.

PATIENTS AND METHODS

Six patients with fifth lumbar isolated unstable burst fractures were analyzed. Medical records, radiographs, and clinical scores were obtained. The results were evaluated based on restoration of vertebral body height, spinal lordosis/kyphosis, canal compromise and sagittal alignment at several phases of treatment.

RESULTS

No patient showed neurologic deterioration, regardless of treatment. The median preoperative anterior vertebral height was 41mm and postoperative was 48mm. The median preoperative kyphotic angle as measured by Cobb angle (local and regional) was 21.5 degrees and 33 degrees which improved respectively by 7.5 and 5.5 degrees following instrumentation. The median amount of backward protrusion of bony fragment into the canal was measured at 67% preoperatively and at 35% postoperatively. There were no pseudarthrosis and anterior arthrodesis solid fusion was visible in all cases. There were a sagittal alignment restoration. At one year of follow up, fusion was obtained in all the cases, all patients had minimal to moderate disability using Oswestry Disability Index. The ability to return to work revealed a good-to-excellent long-term result.

DISCUSSION

The results of treatment of 5th lumbar unstable burst fractures with posterior stabilization and reconstruction of the anterior column show benefit on durable functional outcome, spine stabilization and radiologic parameters.

LEVEL OF EVIDENCE

IV, retrospective study.

Proximal-distal shift of the center of rotation in a total wrist arthroplasty is more than twice of the healthy wrist

Reproduction of healthy wrist biomechanics should minimize the abnormal joint forces that could potentially result in the failure of a total wrist arthroplasty (TWA). To date, the in vivo kinematics of TWA have not been measured and it is unknown if TWA preserves healthy wrist kinematics. Therefore, the purpose of this in vivo study was to determine the center of rotation (COR) for a current TWA design and to compare its location to the healthy wrist. The wrist COR for six patients with TWA and 10 healthy subjects were calculated using biplane videoradiography as the subjects performed various range-of-motion and functional tasks that included coupled wrist motions. An open-source registration software, Autoscoper, was used for model-based tracking and kinematics analysis. It was demonstrated that the COR was located near the centers of curvatures of the carpal component for the anatomical motions of flexion-extension and radial-ulnar deviation. When compared to healthy wrists, the COR of TWAs was located more distal in both pure radial deviation (P < .0001) and pure ulnar deviation (P = .07), while there was no difference in its location in pure flexion or extension (P = .99). Across all coupled motions, the TWA's COR shifted more than two times that of the healthy wrists in the proximal-distal direction (17.1 vs 7.2 mm). We postulate that the mismatch in the COR location and behavior may be associated with increased loading of the TWA components, leading to an increase in the risk of component and/or interface failure.

Influence of the windlass mechanism on arch-spring mechanics during dynamic foot arch deformation

The function of the human foot is described dichotomously as a compliant structure during mid-stance and a stiff lever during push-off. The arch-spring and the windlass mechanisms, respectively, describe each of these behaviours; however, their interaction has not been quantified to date. We hypothesized that by engaging the windlass mechanism with metatarsophalangeal joint (MTPJ) dorsiflexion, we would observe stiffening of the arch and reduced energy absorption and dissipation during dynamic compressions of the foot. Using a custom apparatus, the MTPJ angle was fixed at 30 degrees of plantarflexion, neutral or 30 degrees of dorsiflexion for nine participants, with the shank positioned similarly to the end of mid-stance. The arch was compressed at two speeds, with the faster speed comparable to walking around 1.5 m s^-1 Six cameras captured the compression and elongation of the arch, along with other kinematic variables, synchronously with the ground reaction force. Combining these measures, we computed the energy absorbed, returned and dissipated in the arch. Contrary to our hypothesis, when the windlass mechanism was engaged, the arch elongated more, and absorbed and dissipated more energy than when it was not engaged. This engagement of the windlass altered the rotational axis of the mid-foot, which probably oriented the arch-spanning structures closer to their resting length, increasing their compliance. This study provides novel evidence for an interplay between the windlass and arch-spring mechanisms that aids in regulation of energy storage within the foot.

An improved stiffness matrix model of the functional spinal unit for application to an improved understanding of pathological changes

The stiffness matrix is a useful way to describe the mechanical behaviour of the functional spinal unit, which is defined as the superior and inferior vertebrae, capsules and ligaments. This usefulness is extended by means of the concept of the "balance point". The balance point is the load application point where the coupling coefficients of the stiffness matrix are minimized. Theoretical considerations are used to demonstrate that the stiffness matrix varies with load point location and thus a single stiffness matrix does not fully characterize the motion segment as well as to derive the stiffness matrix at any one specified point from the stiffness matrix at some other specified point. Special characteristics of the stiffness matrix obtained by loading through the "balance point" were shown. Some possible advantages derived from mechanical testing using the "balance point" concept are discussed. This study validates an improved stiffness matrix model that enhances the understanding of pathological changes by setting the gold standard of the behaviour of a normal functional spinal unit.

Differences in the Rotation Axes of the Scapholunate Joint During Flexion-Extension and Radial-Ulnar Deviation Motions

PURPOSE

To determine the location of the rotation axis between the scaphoid and the lunate (SL-axis) during wrist flexion-extension (FE) and radial-ulnar deviation (RUD).

METHODS

An established and publicly available digital database of wrist bone anatomy and carpal kinematics of 30 healthy volunteers (15 males and 15 females) in up to 8 different positions was used to study the SL-axis. Using the combinations of positions from wrist FE and RUD, the helical axis of motion of the scaphoid relative to the lunate was calculated for each trial in an anatomical coordinate system embedded in the lunate. The differences in location and orientation between each individual axis and the average axis were used to quantify variation in axis orientation. Variation in the axis location was computed as the distance from the closest point on the rotation axis to the centroid of the lunate.

RESULTS

The variation in axis orientation of the rotation axis for wrist FE and RUD were 84.3° and 83.5°, respectively. The mean distances of each rotation axis from the centroid of the lunate for FE and RUD were 5.7 ± 3.2 mm, and 5.0 ± 3.6 mm, respectively.

CONCLUSIONS

Based on the evaluation of this dataset, we demonstrated that the rotation axis of the scaphoid relative to the lunate is highly variable across subjects and positions during both FE and RUD motions. The range of locations and variation in axis orientations in this data set of 30 wrists shows that there is very likely no single location for the SL-axis.

CLINICAL RELEVANCE

Scapholunate interosseous ligament reconstruction methods focused on re-creating a standard SL-axis may not restore what is more likely to be a variable anatomical axis and normal kinematics of the scaphoid and lunate.

A four-dimensional-CT study of in vivo scapholunate rotation axes: possible implications for scapholunate ligament reconstruction

Additional fixation of the palmar scapholunate interosseous ligament has been advocated to improve the long-term results of dorsal scapholunate interosseous ligament reconstruction. To investigate the validity of this approach, we determined normal scapholunate motion patterns and calculated the location of the scapholunate rotation axis. We hypothesized that the optimal location of the scapholunate interosseous ligament insertion could be determined from the scapholunate rotation axis. Four-dimensional computerized tomography was used to study the wrist motion in 21 healthy participants. During flexion-extension motions, the scaphoid rotates 38° (SD 0.6°) relative to the lunate; the rotation axis intersects the dorsal ridge of the proximal pole of the scaphoid and the dorsal ridge of the lunate. Minimal scapholunate motion is present during radioulnar deviation. Since the scapholunate rotation axis runs through the dorsal proximal pole of the scaphoid, this is probably the optimal location for attaching the scapholunate ligament during reconstructive surgery.

Analysis of forearm rotational motion using biplane fluoroscopic intensity-based 2D-3D matching

Measuring three-dimensional (3D) forearm rotational motion is difficult. We aimed to develop and validate a new method for analyzing 3D forearm rotational motion. We proposed biplane fluoroscopic intensity-based 2D-3D matching, which employs automatic registration processing using the evolutionary optimization strategy. Biplane fluoroscopy was conducted for forearm rotation at 12.5 frames per second along with computed tomography (CT) at one static position. An arm phantom was embedded with eight stainless steel spheres (diameter, 1.5 mm), and forearm rotational motion measurements using the proposed method were compared with those using radiostereometric analysis, which is considered the ground truth. As for the time resolution analysis, we measured radiohumeral joint motion in a patient with posterolateral rotatory instability and compared the 2D-3D matching method with the simulated multiple CT method, which uses CTs at multiple positions and interpolates between the positions. Rotation errors of the radius and ulna between these two methods were 0.31 ± 0.35° and 0.32 ± 0.33°, respectively, translation errors were 0.43 ± 0.35 mm and 0.29 ± 0.25 mm, respectively. Although the 2D-3D method could detect joint dislocation, the multiple CT method could not detect quick motion during joint dislocation. The proposed method enabled high temporal- and spatial-resolution motion analyses with low radiation exposure. Moreover, it enabled the detection of a sudden motion, such as joint dislocation, and may contribute to 3D motion analysis, including joint dislocation, which currently cannot be analyzed using conventional methods.

Off-axis response due to mechanical coupling across all six degrees of freedom in the human disc

The kinematics of the intervertebral disc are defined by six degrees of freedom (DOF): three translations (Tz: axial compression, Tx: lateral shear, and Ty: anterior-posterior shear) and three rotations (Rz: torsion, Rx: flexion-extension, and Ry: lateral bending). There is some evidence that the six DOFs are mechanically coupled, such that loading in one DOF affects the mechanics of the other five "off-axis" DOFs, however, most studies have not controlled and/or measured all six DOFs simultaneously. Additionally, the relationships between disc geometry and disc mechanics are important for evaluation of data from different sized donor and patient discs. The objectives of this study were to quantify the mechanical behavior of the intervertebral disc in all six degrees of freedom (DOFs), measure the coupling between the applied motion in each DOF with the resulting off-axis motions, and test the hypothesis that disc geometry influences these mechanical behaviors. All off-axis displacements and rotations were significantly correlated with the applied DOF and were of similar magnitude as physiologically relevant motion, confirming that off-axis coupling is an important mechanical response. Interestingly, there were pairs of DOFs that were especially strongly coupled: lateral shear (Tx) and lateral bending (Ry), anterior-posterior shear (Ty) and flexion-extension (Rx), and compression (Tz) and torsion (Rz). Large off-axis shears may contribute to injury risk in bending and flexion. In addition, the disc responded to shear (Tx, Ty) and rotational loading (Rx, Ry, and Rz) by increasing in disc height in order to maintain the applied compressive load. Quantifying these mechanical behaviors across all six DOF are critical for designing and testing disc therapies, such as implants and tissue engineered constructs, and also for validating finite element models.

Three-dimensional kinematics of the lunate, hamate, capitate and triquetrum with type 1 or 2 lunate morphology

The purpose of this study was to investigate the differences in three-dimensional carpal kinematics between type 1 and 2 lunates. We studied 15 instances of wrist flexion to extension (nine type 1, six type 2), 13 of radial to ulnar deviation (seven type 1, six type 2), and 12 of dart-throwing motion (six each of type 1 and 2) in 25 normal participants based on imaging with computerized tomography. Mean proximal translation of the distal articular midpoint of the triquetrum relative to type 2 lunates during wrist radioulnar deviation was 2.9 mm (standard deviation (SD) 0.7), which was significantly greater than for type 1 lunates, 1.6 mm (SD 0.6). The hamate contacted the lunate in ulnar deviation and ulnar flexion of wrists with type 2 lunates but not with type 1. We conclude that the four-corner kinematics of the wrist joint are different between type 1 and 2 lunates.

Does Wrist Laxity Influence Three-Dimensional Carpal Bone Motion?

Previous two-dimensional (2D) studies have shown that there is a spectrum of carpal mechanics that varies between row-type motion and column-type motion as a function of wrist laxity. More recent three-dimensional (3D) studies have suggested instead that carpal bone motion is consistent across individuals. The purpose of this study was to use 3D methods to determine whether carpal kinematics differ between stiffer wrists and wrists with higher laxity. Wrist laxity was quantified using a goniometer in ten subjects by measuring passive wrist flexion-extension (FE) range of motion (ROM). In vivo kinematics of subjects' scaphoid and lunate with respect to the radius were computed from computed tomography (CT) volume images in wrist radial and ulnar deviation positions. Scaphoid and lunate motion was defined as "column-type" if the bones flexed and extended during wrist radial-ulnar deviation (RUD), and "row-type" if the bones radial-ulnar deviated during wrist RUD. We found that through wrist RUD, the scaphoid primarily flexed and extended, but the scaphoids of subjects with decreased laxity had a larger component of RUD (R2 = 0.48, P < 0.05). We also determined that the posture of the scaphoid in the neutral wrist position predicts wrist radial deviation (RD) ROM (R2 = 0.46, P < 0.05). These results suggest that ligament laxity plays a role in affecting carpal bone motion of the proximal row throughout radial and ulnar deviation motions; however, other factors such as bone position may also affect motion. By developing a better understanding of normal carpal kinematics and how they are affected, this will help physicians provide patient-specific approaches to different wrist pathologies.

Symphyseal fixation in open book injuries cannot fully compensate anterior SI joint injury-A biomechanical study in a two-leg alternating load model

INTRODUCTION

In open book injuries type Tile B1.1 or B1.2 also classified as APC II (anteroposterior compression), it remains controversial, if a fixation of the anterior ring provides sufficient stability or a fixation of the posterior ring should be included. Therefore the relative motion at the sacroiliac joint was quantified in a two-leg alternating load biomechanical pelvis model in the intact, the injured and the restored pelvis.

METHODS

Fresh-frozen intact (I) pelvises (n = 6) were subjected to a non-destructive cyclic test under sinosuidal axial two-leg alternating load with progressively increasing amplitude. Afterwards an open book injury (J) including the anterior ligament complex of the left sacroiliac joint, the sacrospinal and sacrotuberal ligaments (Tile B1.1) was created and the specimens were retested. Finally, the symphysis was stabilized with a modular fixation system (1-, 2- or 4-rod configuration) (R) and specimens were cyclically retested. Relative motion at the sacroiliac joint was captured at both sacroiliac joints by motion tracking system at two load levels of 170 N and 340 N during all tests.

RESULTS

Relative sacroiliac joint movements at both load levels were significantly higher in the J-state compared to the I-state, excluding superoinferior translational movement. With exception of the anteroposterior translational movement at 340N, the relative sacroiliac joint movements after each of the three reconstructions (1-, 2-, 4-rod fixation) were significantly smaller compared to the J-state and did not differ significantly to the I-state, but stayed above the values of the latter. Relative movements did not differ significantly in a direct comparison between the 1-rod, 2-rod and 4-rod fixations.

CONCLUSION

Symphyseal locked plating significantly reduces relative movement of the sacroiliac joint in open book injuries type Tile B1.1 or B1.2 (APC II) but cannot fully restore the situation of the intact sacroiliac joint.

Minimizing the Translation Error in the Application of an Oblique Single-Cut Rotation Osteotomy: Where to Cut?

OBJECTIVE

An oblique single cut rotation osteotomy enables correcting angular bone alignment in the coronal, sagittal, and transverse planes, with just a single oblique osteotomy, and by rotating one bone segment in the osteotomy plane. However, translational malalignment is likely to exist if the bone is curved or deformed and the location of the oblique osteotomy is not obvious.

METHODS

In this paper, we investigate how translational malalignment depends on the osteotomy location. We further propose and evaluate by simulation in 3-D, a method that minimizes translational malalignment by varying the osteotomy location and by sliding the distal bone segment with respect to the proximal bone segment within the oblique osteotomy plane. The method is finally compared to what three surgeons achieve by manually selecting the osteotomy location in 3-D virtual space without planning in-plane translations.

RESULTS

The minimization method optimized for length better than the surgeons did, by 3.2 mm on average, range (0.1, 9.4) mm, in 82% of the cases. A better translation in the axial plane was achieved by 4.1 mm on average, range (0.3, 14.4) mm, in 77% of the cases.

CONCLUSION

The proposed method generally performs better than subjectively choosing an osteotomy position along the bone axis.

SIGNIFICANCE

The proposed method is considered a valuable tool for future alignment planning of an oblique single-cut rotation osteotomy since it helps minimizing translational malalignment.

La TC con carico assiale nella instabilità del rachide lombo-sacrale

La diagnosi di instabilità del rachide lombo-sacrale è, a tutt'oggi, fondamentalmente clinica.

Anche le più sofisticate tecniche di diagnostica radiologica consentono infatti solo una valutazione statica di questa entità nosologica (che, per definizione si manifesta durante la deambulazione e con la stazione eretta) la cui definizione dinamica è campo pressochè esclusivo della radiologia convenzionale. Presentiamo i risultati di uno studio condotto attraverso l'uso di uno strumento originale progettato per sviluppare un carico assiale variabile e riproducibile in un paziente supino: il Compressore assiale. Con questo strumento, compatibile con l'esecuzione di esami TC, sono stati valutati 24 pazienti con forte sospetto clinico-radiologico di instabilità lombare.

La metodica di studio, denominata Axial Loaded - Computed Tomography (AL-CT) si basa sull'acquisizione successiva di esami TC basali e con carico assiale (AL), che vengono poi comparati. Il confronto avviene sia sulle scansioni assiali che su immagini ricostruite su piani sagittali e con «rendering» tridimensionale (3D-TC). La valutazione comparativa prevede sia l'uso di immagini statiche che l'organizzazione in sequenze cine (cine AL-CT) delle immagini 2D e 3D ottenute. Tutti i procedimenti di rielaborazione sono indispensabili nella valutazione dei risultati.

I risultati mostrano con chiarezza reperti (numerosi e spesso simultanei) a carico di tutte le component le unità funzionali spinali; fra questi meritano una segnalazione: l'incremento o la accentuazione di protrusioni discali sotto carico; la scomparsa del vacuum discale e/o intraarticolare durante la compressione («segno del vacuum»); l'accentuazione della listesi sotto carico; la ottimale ed originale visualizzazione dell' ipermobilità delle faccette articolari.

Proponiamo AL-CT e cine AL-CT come metodiche di scelta nello studio dell'instabilità lombare.

The effect of six degree of freedom loading sequence on the in-vitro compressive properties of human lumbar spine segments

The complex, direction-dependent, poro-viscoelastic properties of the intervertebral disc (disc) suggest that investigations of the six degree of freedom (6DOF) behaviour may be susceptible to inter-test variation in mechanical response if the disc does not return to initial conditions between loading directions. No studies have quantified the effects of sequential multi-directional loading on the consistency of the compressive response of the disc throughout a 6DOF testing protocol. Therefore, the objective of this study was to determine the effect of 6DOF loading on the compressive properties (stiffness and phase angle) of human discs, as evaluated by a reference compression test performed after each single DOF test. Fourteen intact human functional spinal units (FSU) were tested in each of ±6DOFs (shear directions followed by bending and compression) across four orders of magnitude loading frequencies (0.001-1Hz), followed by reference compression tests while subjected to physiological preload, hydration, and body temperature conditions in a hexapod robot. Repeated measures ANOVA revealed significant within-subjects effects between the reference compression tests for modulus (p<0.001), stiffness (p<0.001), and phase angle (p=0.008). Significant post-hoc pairwise comparisons were initially seen between the control and other reference compression tests for stiffness and modulus after the shear DOFs, however, no significant differences were present after the final reference compression test compared to control. More pronounced effects were seen for stiffness in comparison to modulus and phase angle. These effects may be due to three potentials factors, which include the sequence of testing, the cohort of degenerative specimens, and/or cumulative creep due to the constant application of a follower load. While the sequence of test directions was chosen to minimise the biphasic effect, there may be other sequences, which could result in minimal changes in compressive properties.

Functional Evaluation of the Lumbar Spine with Axial Loaded Computed Tomography (AL-CT) and Cine AL-CT

This study reports a personal experience in the functional study of the lumbar spine with original diagnostic techniques called Axial Loaded Computed Tomography (AL-CT) and Cine AL-CT, based on the use of the Axial Loader, a device that develops a variable and reproducible axial load in a supine patient during computed tomography or magnetic resonance investigation3,4.

We built a non ferromagnetic, X-ray transparent bed (the Axial Loader), with double blocking rests for shoulders and feet, that can be used during CT and MR spine studies. The inferior block is a platform that moves continuously in a longitudinal direction, with a micrometric mechanism. A dynamometer placed between the inferior platform and the patient's feet can measure the load applied.

We studied 75 patients, with a clinical and diagnostic suspicion of lumbar spine instability. The examinations were performed on a conventional CT unit (GE Sytec 3000, General Electric, Milwaukee) with a “volumetric” approach to the lumbar spine.

In conclusion, AL-CT and Cine AL-CT is currently the only diagnostic modality that can give dynamic information on the differents UFSs in all their components in one mildy invasive, easily reproducible diagnostic examination.

The Envelope of Physiological Motion of the First Carpometacarpal Joint

Much of the hand's functional capacity is due to the versatility of the motions at the thumb carpometacarpal (CMC) joint, which are presently incompletely defined. The aim of this study was to develop a mathematical model to completely describe the envelope of physiological motion of the thumb CMC joint and then to examine if there were differences in the kinematic envelope between women and men. In vivo kinematics of the first metacarpal with respect to the trapezium were computed from computed tomography (CT) volume images of 44 subjects (20M, 24F, 40.3 ± 17.7 yr) with no signs of CMC joint pathology. Kinematics of the first metacarpal were described with respect to the trapezium using helical axis of motion (HAM) variables and then modeled with discrete Fourier analysis. Each HAM variable was fit in a cyclic domain as a function of screw axis orientation in the trapezial articular plane; the RMSE of the fits was 14.5 deg, 1.4 mm, and 0.8 mm for the elevation, location, and translation, respectively. After normalizing for the larger bone size in men, no differences in the kinematic variables between sexes could be identified. Analysis of the kinematic data also revealed notable coupling of the primary rotations of the thumb with translation and internal and external rotations. This study advances our basic understanding of thumb CMC joint function and provides a complete description of the CMC joint for incorporation into future models of hand function. From a clinical perspective, our findings provide a basis for evaluating CMC pathology, especially the mechanically mediated aspects of osteoarthritis (OA), and should be used to inform artificial joint design, where accurate replication of kinematics is essential for long-term success.

A new dynamic six degrees of freedom disc-loading simulator allows to provoke disc damage and herniation

Purpose

The cause of disc herniation is not well understood yet. It is assumed that heavy lifting and extreme postures can cause small injuries starting either in the inner anulus or from the outside close to the endplate. Such injuries are accumulated over years until its structure is weakened and finally a single loading event leads to a sudden failure of the last few intact lamellae. This paper describes a novel, custom-developed dynamic 6-DOF disc-loading simulator that allows complex loading to provoke such disc damage and herniations.

Methods

The machine’s axes are driven by six independent servomotors providing high loads (10 kN axial compression, 2 kN shear, 100 Nm torque) up to 5 Hz. A positional accuracy test was conducted to validate the machine. Subsequently, initial experiments with lumbar ovine motion segments under complex loading were performed. After testing, the discs were examined in an ultra-high field MRI (11.7 T). A three-dimensional reconstruction was performed to visualise the internal disc lesions.

Results

Validation tests demonstrated positioning with an accuracy of ≤0.08°/≤0.026 mm at 0.5 Hz and ≤0.27°/≤0.048 mm at 3.0 Hz with amplitudes of ±17°/±2 mm. Typical failure patterns and herniations could be provoked with complex asymmetrical loading protocols. Loading with axial compression, flexion, lateral bending and torsion lead in 8 specimens to 4 herniated discs, two protrusions and two delaminations. All disc failures occurred in the posterior region of the disc.

Conclusion

This new dynamic disc-loading simulator has proven to be able to apply complex motion combinations and allows to create artificial lesions in the disc with complex loading protocols. The aim of further tests is to better understand the mechanisms by which disc failure occurs at the microstructural level under different loading conditions. Visualisation with ultra-high field MRI at different time points is a promising method to investigate the gradual development of such lesions, which may finally lead to disc failure. These kinds of experiments will help to better investigate the mechanical failure of discs to provide new insights into the initiation of intervertebral disc herniation. This device will also serve for many other applications in spine biomechanics research.

Precision of image-based registration for intraoperative navigation in the presence of metal artifacts: Application to corrective osteotomy surgery

Navigation for corrective osteotomy surgery requires patient-to-image registration. When registration is based on intraoperative 3-D cone-beam CT (CBCT) imaging, metal landmarks may be used that deteriorate image quality. This study investigates whether metal artifacts influence the precision of image-to-patient registration, either with or without intermediate user intervention during the registration procedure, in an application for corrective osteotomy of the distal radius. A series of 3-D CBCT scans is made of a cadaver arm with and without metal landmarks. Metal artifact reduction (MAR) based on inpainting techniques is used to improve 3-D CBCT images hampered by metal artifacts. This provides three sets of images (with metal, with MAR, and without metal), which enable investigating the differences in precision of intraoperative registration. Gray-level based point-to-image registration showed a better correlation coefficient if intraoperative images with MAR are used, indicating a better image similarity. The precision of registration without intermediate user intervention during the registration procedure, expressed as the residual angulation and displacement error after repetitive registration was very low and showed no improvement when MAR was used. By adding intermediate user intervention to the registration procedure however, precision was very high but was not affected by the presence of metal artifacts in the specific application.

Validation of a Novel Spine Test Machine

A novel spine test machine was developed for physiological loading of spinal segments. It can be used in conjunction with external motion-capture systems (EMCS) to measure angular displacement, but can also measure in-plane rotations directly, though the inherent error is unknown. This study quantified error inherent in the displacement measurement of the machine. Synthetic specimens representative of cadaveric spinal specimens were tested. Machine displacement was compared to EMCS displacement. The maximum machine displacement error was <2 deg for lumbar and thoracic specimens. The authors suggest that researchers use EMCS in conjunction with the test machine when high accuracy measurements are required.

In Vivo kinematics of the trapeziometacarpal joint during thumb extension-flexion and abduction-adduction

PURPOSE

The primary aim of this study was to determine whether the in vivo kinematics of the trapeziometacarpal (TMC) joint differ as a function of age and sex during thumb extension-flexion (Ex-Fl) and abduction-adduction (Ab-Ad) motions.

METHODS

The hands and wrists of 44 subjects (10 men and 11 women with ages 18-35 y and 10 men and 13 women with ages 40-75 y) with no symptoms or signs of TMC joint pathology were imaged with computed tomography during thumb extension, flexion, abduction, and adduction. The kinematics of the TMC joint were computed and compared across direction, age, and sex.

RESULTS

We found no significant effects of age or sex, after normalizing for size, in any of the kinematic parameters. The Ex-Fl and Ab-Ad rotation axes did not intersect, and both were oriented obliquely to the saddle-shaped anatomy of the TMC articulation. The Ex-Fl axis was located in the trapezium and the Ab-Ad axis was located in the metacarpal. Metacarpal translation and internal rotation occurred primarily during Ex-Fl.

CONCLUSIONS

Our findings indicate that normal TMC joint kinematics are similar in males and females, regardless of age, and that the primary rotation axes are nonorthogonal and nonintersecting. In contrast to previous studies, we found Ex-Fl and Ab-Ad to be coupled with internal-external rotation and translation. Specifically, internal rotation and ulnar translation were coupled with flexion, indicating a potential stabilizing screw-home mechanism.

CLINICAL RELEVANCE

The treatment of TMC pathology and arthroplasty design require a detailed and accurate understanding of TMC function. This study confirms the complexity of TMC kinematics and describes metacarpal translation coupled with internal rotation during Ex-Fl, which may explain some of the limitations of current treatment strategies and should help improve implant designs.

In vivo three-dimensional intervertebral kinematics of the subaxial cervical spine during seated axial rotation and lateral bending via a fluoroscopy-to-CT registration approach

Accurate measurement of the coupled intervertebral motions is helpful for understanding the etiology and diagnosis of relevant diseases, and for assessing the subsequent treatment. No study has reported the in vivo, dynamic and three-dimensional (3D) intervertebral motion of the cervical spine during active axial rotation (AR) and lateral bending (LB) in the sitting position. The current study fills the gap by measuring the coupled intervertebral motions of the subaxial cervical spine in ten asymptomatic young adults in an upright sitting position during active head LB and AR using a volumetric model-based 2D-to-3D registration method via biplane fluoroscopy. Subject-specific models of the individual vertebrae were derived from each subject's CT data and were registered to the fluoroscopic images for determining the 3D poses of the subaxial vertebrae that were used to obtain the intervertebral kinematics. The averaged ranges of motion to one side (ROM) during AR at C3/C4, C4/C5, C5/C6, and C6/C7 were 4.2°, 4.6°, 3.0° and 1.3°, respectively. The corresponding values were 6.4°, 5.2°, 6.1° and 6.1° during LB. Intervertebral LB (ILB) played an important role in both AR and LB tasks of the cervical spine, experiencing greater ROM than intervertebral AR (IAR) (ratio of coupled motion (IAR/ILB): 0.23-0.75 in LB, 0.34-0.95 in AR). Compared to the AR task, the ranges of ILB during the LB task were significantly greater at C5/6 (p=0.008) and C6/7 (p=0.001) but the range of IAR was significantly smaller at C4/5 (p=0.02), leading to significantly smaller ratios of coupled motions at C4/5 (p=0.0013), C5/6 (p<0.001) and C6/7 (p=0.0037). The observed coupling characteristics of the intervertebral kinematics were different from those in previous studies under discrete static conditions in a supine position without weight-bearing, suggesting that the testing conditions likely affect the kinematics of the subaxial cervical spine. While C1 and C2 were not included owing to technical limitations, the current results nonetheless provide baseline data of the intervertebral motion of the subaxial cervical spine in asymptomatic young subjects under physiological conditions, which may be helpful for further investigations into spine biomechanics.

Batting cage performance of wood and nonwood youth baseball bats

The purpose of this study was to examine the batting cage performance of wood and nonwood baseball bats used at the youth level. Three wood and ten nonwood bats were swung by 22 male players (13 to 18 years old) in a batting cage equipped with a 3-dimensional motion capture (300 Hz) system. Batted ball speeds were compared using a one-way ANOVA and bat swing speeds were analyzed as a function of bat moment of inertia by linear regression. Batted ball speeds were significantly faster for three nonwood bat models (P<.001), significantly slower for one nonwood model, and not different for six nonwood bats when compared with wood bats. Bat impact speed significantly (P<.05) decreased with increasing bat moment of inertia for the 13-, 14-, and 15-year-old groups, but not for the other age groups. Ball-bat coefficients of restitution (BBCOR) for all nonwood were greater than for wood, but this factor alone did not correlate with bat performance. Our findings indicate that increases in BBCOR and swing speed were not associated with faster batted ball speeds for the bats studied whose moment of inertia was substantially less than that of a wood bat of similar length.

Surgical accuracy in identifying the elbow rotation axis on fluoroscopic images

PURPOSE

To assess the accuracy of surgeons in identifying elbow rotation axis (RA) on fluoroscopic images and to measure the interobserver variability.

METHODS

Five healthy subjects underwent 3-dimensional computed tomography (CT) analysis of their nondominant elbow. Real-time rotation software enabled surgeons to approximate the elbow RA on CT-reconstructed fluoroscopy, which was repeated twice with different starting positions to increase the number of observations. The surgeons used anatomical landmarks of choice. Analysis of variance (ANOVA) was used to determine structural error differences between surgeons, and intraclass correlation coefficients (ICCs) were used to determine the corresponding interobserver variability.

RESULTS

Eight subspecialty-trained trauma surgeons (P.K., N.W.L.S., V.M.d.J., P.J., G.M.K., R.W.P., T.S., B.A.v.D.) participated and attempted to identify the RA on reconstructed fluoroscopy. A total of 15 RA definitions on 5 elbows were recorded per surgeon. The surgeons had a mean rotational error of 5° (range, < 1°-13°) and mean translational error of 1 mm (range, < 1-8 mm), compared with the true elbow RA as measured by the 3-dimensional CT analysis. The ANOVA showed structural differences between surgeons in rotational and translational errors, indicating that some surgeons consistently had more accurately identified the elbow RA than others. The ICC was 0.12 for rotational error and 0.10 for translational error, indicating a large interobserver variability.

CONCLUSIONS

We show in this in vivo study that identification of the elbow RA on fluoroscopy is associated with substantial rotational errors and large inconsistencies among surgeons. Implementation of standardized anatomical landmarks is required to improve surgeons' accuracy. These landmarks should preferably take into account both the coronal and the sagittal planes, using the orientation of the capitellum and trochlea as well as the posterior distal humeral cortex.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic II.

Influence of flexible fixation for open book injury after pelvic trauma--a biomechanical study

BACKGROUND

Implant loosening is frequently detected after fixation of open book injuries. Though many authors do not see this as a complication, it is often the reason for hardware removal or reinstrumentation in the case of remaining instability. We hypothesized that the flexibility of the implant has an influence on loosening and thus on failure of the construct.

METHODS

We used 6 fresh-frozen pelvic specimens and tested them with our recently introduced test setup for two-leg alternate loading. We subjected them to a non-destructive quasi-static test in the intact condition followed by a non-destructive cyclic test under axial sinusoidal loading with progressive amplitude. Afterwards we simulated an open book injury and performed fixation with three different configurations of a modular fixation system (1-, 2- or 4-rod configuration) in randomized order. Subsequently, the specimens were subjected to 3 cyclic tests with the same loading protocol as previously defined. Finally, each construct was cyclically tested to failure keeping the final rod configuration.

FINDINGS

We detected significantly greater mobility after 1-rod-fixation and no significant differences after 2-rod or 4-rod-fixation compared to the intact symphysis condition. In the destructive test series the 4-rod-fixation failed first followed by the 1-rod-fixation. The 2-rod-fixation sustained almost 3 times as many load cycles prior to failure as the 4-rod-fixation, whereas the 1-rod-fixation sustained twice as many cycles as the 4-rod-fixation.

INTERPRETATION

In conclusion, flexible fixation of the ruptured pubic symphysis in human specimens shows superior behavior with respect to load bearing capacity and ability to withstand cyclic loading compared to stiff constructs.

Three-dimensional motion analysis of the cervical spine for comparison of anterior cervical decompression and fusion versus artificial disc replacement in 17 patients

Object

Cervical arthroplasty with an artificial disc (AD) has emerged as an alternative to anterior cervical discectomy and fusion (ACDF) for the management of cervical spondylosis. This study aims to provide 3D motion analysis data comparing patients after ACDF and AD replacement.

Methods

Ten patients who underwent C5–6 ACDF and 7 who underwent C5–6 AD replacement were enrolled. Using biplanar fluoroscopy and a model-based track technique (accurate up to 0.6 mm and 0.6°), motion analysis of axial rotation and flexion-extension of the neck was performed. Three nonoperative segments (C3–4, C4–5, and C6–7) were assessed for both intervertebral rotation (coronal, sagittal, and axial planes) and facet shear (anteroposterior and mediolateral).

Results

There was no difference in total neck motion comparing ACDF and AD replacement for neck extension (43.3° ± 10.2° vs 44.3° ± 12.6°, p = 0.866) and rotation (36.0° ± 6.5° vs 38.2° ± 9.3°, p = 0.576). For extension, when measured as a percentage of total neck motion, there was a greater amount of rotation at the nonoperated segments in the ACDF group than in the AD group (p = 0.003). When comparing specific motion segments, greater normalized rotation was seen in the ACDF group at C3–4 (33.2% ± 4.9% vs 26.8% ± 6.6%, p = 0.036) and C6–7 (28.5% ± 6.7% vs 20.5% ± 5.5%, p = 0.009) but not at C4–5 (33.5% ± 6.4% vs 31.8% ± 4.0%, p = 0.562). For neck rotation, greater rotation was observed at the nonoperative segments in the ACDF group than in the AD group (p = 0.024), but the differences between individual segments did not reach significance (p ≥ 0.146). Increased mediolateral facet shear was seen on neck extension with ACDF versus AD replacement (p = 0.008). Comparing each segment, C3–4 (0.9 ± 0.5 mm vs 0.4 ± 0.1 mm, p = 0.039) and C4–5 (1.0 ± 0.4 mm vs 0.5 ± 0.2 mm, p = 0.022) showed increased shear while C6–7 (1.0 ± 0.4 mm vs 1.0 ± 0.5 mm, p = 0.767) did not.

Conclusions

This study illustrates increased motion at nonoperative segments in patients who have undergone ACDF compared with those who have undergone AD replacement. Further studies will be required to examine whether these changes contribute to adjacent-segment disease.

Arthroscopic debridement in the treatment of patients with osteoarthritis of the elbow, based on computer simulation

We retrospectively assessed the value of identifying impinging osteophytes using dynamic computer simulation of CT scans of the elbow in assisting their arthroscopic removal in patients with osteoarthritis of the elbow. A total of 20 patients were treated (19 men and one woman, mean age 38 years (19 to 55)) and followed for a mean of 25 months (24 to 29). We located the impinging osteophytes dynamically using computerised three-dimensional models of the elbow based on CT data in three positions of flexion of the elbow. These were then removed arthroscopically and a capsular release was performed.

The mean loss of extension improved from 23° (10° to 45°) pre-operatively to 9° (0° to 25°) post-operatively, and the mean flexion improved from 121° (80° to 140°) pre-operatively to 130° (110° to 145°) post-operatively. The mean Mayo Elbow Performance Score improved from 62 (30 to 85) to 95 (70 to 100) post-operatively. All patients had pain in the elbow pre-operatively which disappeared or decreased post-operatively. According to their Mayo scores, 14 patients had an excellent clinical outcome and six a good outcome; 15 were very satisfied and five were satisfied with their post-operative outcome.

We recommend this technique in the surgical management of patients with osteoarthritis of the elbow.

Cite this article: Bone Joint J 2014;96-B:237–41.

Two-leg alternate loading model--a different approach to biomechanical investigations of fixation methods of the injured pelvic ring with focus on the pubic symphysis

The dorsal component of the pelvic ring is considered to be the most essential element for the stability of the pelvic ring. None of the current biomechanical set-ups include the effect of shear stresses by alternating loads that the pelvic ring has to withstand during walking. We hypothesize that a biomechanical test set-up with two-leg alternate loading will lead to stress imitation at the pubic symphysis that are more similar to existing strains than other test set-ups, and would, therefore, be more adequate for biomechanical testing of fixation methods. A new biomechanical two-leg standing test set-up with an alternate pelvic loading was constructed and was validated with six human pelvises from fresh frozen cadavers. Three-dimensional motion tracking was performed. The specimens were subjected to a non-destructive quasi-static test and a non-destructive cyclic test with progressive load amplitude from 170 N to 340 N over 1000 cycles. The initial rotational 'range of motion' and 'mean displacement' around the vertical axis for a pre-load of 170 N was about 0.3° and 0.2°, respectively, increasing by 0.1-0.2° at a load of 340 N. The rotation around the vertical axis and the translation along the frontal horizontal axis confirmed the stability of the pubic symphysis. The rate of ascend of displacements decreased, once the rotation reached 1° or the translation reached 1mm. The current biomechanical test set-up was compared with previous clinical findings, and the method was found valid for measuring inter-segmentary movements at the pubic symphysis.

The six degrees of freedom motion of the human head, spine, and pelvis in a frontal impact

OBJECTIVE

The goal of this study is to characterize the in situ 6-degree-of-freedom kinematics of the head, 3 vertebrae (T1, T8, and L2), and the pelvis in a 40 km/h frontal impact.

METHODS

Three postmortem human surrogates (PMHS) were exposed to a deceleration of 15 g over 125 ms and the motion of selected anatomical structures (head, T1, T8, L2, and pelvis) was tracked at 1000 Hz using an optoelectric stereophotogrammetric system. Displacements of the analyzed structures are reported in the sagittal and the transverse planes. Rotations of the structures are described using the finite helical axis of the motion.

RESULTS

Anterior displacements were 530.5 ± 39.4 mm (head), 434.7 ± 20.0 mm (T1), 353.3 ± 29.6 mm (T8), 219.9 ± 19.3 mm (L2), and 78.9 ± 22.1 mm (pelvis). The ratio between peak anterior and lateral displacement was up to 19 percent (T1) and 26 percent (head). Magnitudes of the rotation of the head (69.9 ± 1.5°), lumbar (66.5 ± 9.1°), and pelvis (63.8 ± 11.8°) were greater than that of the thoracic vertebrae (T1: 49.1 ± 7.8°; T8: 47.7 ± 6.3°). Thoracic vertebrae exhibited a complex rotation behavior caused by the asymmetric loading of the shoulder belt. Rotation of the lumbar vertebra and pelvis occurred primarily within the sagittal plane (flexion).

CONCLUSION

Despite the predominance of the sagittal motion of the occupant in a pure (12 o'clock) frontal impact, the asymmetry of belt loading induced other relevant displacements and rotations of the head and thoracic spine. Attempts to model occupant kinematics in a frontal impact should consider these results to biofidelically describe the interaction of the torso with the belt.

Three-dimensional analysis of cervical spine segmental motion in rotation

INTRODUCTION

The movements of the cervical spine during head rotation are too complicated to measure using conventional radiography or computed tomography (CT) techniques. In this study, we measure three-dimensional segmental motion of cervical spine rotation in vivo using a non-invasive measurement technique.

MATERIAL AND METHODS

Sixteen healthy volunteers underwent three-dimensional CT of the cervical spine during head rotation. Occiput (Oc) - T1 reconstructions were created of volunteers in each of 3 positions: supine and maximum left and right rotations of the head with respect to the bosom. Segmental motions were calculated using Euler angles and volume merge methods in three major planes.

RESULTS

Mean maximum axial rotation of the cervical spine to one side was 1.6° to 38.5° at each level. Coupled lateral bending opposite to lateral bending was observed in the upper cervical levels, while in the subaxial cervical levels, it was observed in the same direction as axial rotation. Coupled extension was observed in the cervical levels of C5-T1, while coupled flexion was observed in the cervical levels of Oc-C5.

CONCLUSIONS

The three-dimensional cervical segmental motions in rotation were accurately measured with the non-invasive measure. These findings will be helpful as the basis for understanding cervical spine movement in rotation and abnormal conditions. The presented data also provide baseline segmental motions for the design of prostheses for the cervical spine.

Does total disc arthroplasty in C3/C4-segments change the kinematic features of axial rotation?

We analyze how kinematic properties of C3/C4-segments are modified after total disc arthroplasty (TDA) with PRESTIGE(®) and BRYAN(®) Cervical Discs. The measurements were focused on small ranges of axial rotation (<0.8°) in order to investigate physiologic rotations, which frequently occur in vivo. Eight human segments were stimulated by triangularly varying, axially directed torque. By using a 6D-measuring device with high resolution the response of segmental motion was characterised by the instantaneous helical axis (IHA). Position, direction, and migration rate of the IHA were measured before and after TDA. External parameters: constant axially directed pre-load, constant flexional/extensional and lateral-flexional pre-torque. The applied axial torque and IHA-direction did not run parallel. The IHA-direction was found to be rotated backwards and largely independent of the rotational angle, amount of axial pre-load, size of pre-torque, and TDA. In the intact segments pre-flexion/extension hardly influenced IHA-positions. After TDA, IHA-position was shifted backwards significantly (BRYAN-TDA: ≈8mm; PRESTIGE-TDA: ≈6mm) and in some segments laterally as well. Furthermore it was significantly shifted ventrally by pre-flexion and dorsally by pre-extension. The rate of lateral IHA-migration increased significantly after BRYAN-TDA during rightward or leftward rotations. In conclusion after the TDA the IHA-positions shifted backwards with significant increase in variability of the IHA-positions after the BRYAN-TDA more than in PRESTIGE-TDA. The TDA-procedure altered the segment kinematics considerably. TDA causes additional translations of the vertebrae, which superimpose the kinematics of the adjacent levels. The occurrence of adjacent level disease (ALD) is not excluded after the TDA for kinematical reasons.

Kinematic changes in elbow osteoarthritis: in vivo and 3-dimensional analysis using computed tomographic data

PURPOSE

To investigate in vivo 3-dimensional kinematics in elbow osteoarthritis. We hypothesized that normal kinematics is preserved in an osteoarthritic elbow with a normal radiocapitellar joint (OAN). Conversely, we hypothesized that an osteoarthritic elbow with radiocapitellar degenerative changes (OAD) would show an abnormal kinematics pattern. Furthermore, the differences in osteophyte formation between groups may affect elbow kinematics.

METHODS

We examined 7 normal elbows, 7 OAN elbows, and 9 OAD elbows. We investigated 3-dimensional kinematics using computed tomography registration techniques. The osteophyte location was determined using 3-dimensional bone models generated from computed tomography data.

RESULTS

The kinematics is different in OAN and OAD elbows. In the OAN group, the ulna changed by 11° from a valgus to a varus position during elbow flexion and demonstrated a 4° change in the axis of elbow motion, similar to that in normal elbows. Osteophytes formed medially on the olecranon fossa. In the OAD group, the ulna changed by 4° varus during flexion from the 90° position, but only by 2° valgus during elbow extension from 90°. The change in the axis of elbow motion was 9°. Additional osteophytes formed on the anteromedial and lateral trochlea, lateral olecranon fossa, and medial olecranon of the ulnotrochlear joint, and on the radiocapitellar joint.

CONCLUSIONS

Normal kinematics was preserved in the OAN group. The OAD group demonstrated marked changes in the direction of elbow motion in the extension range, and the valgus motion pattern during extension was decreased.

CLINICAL RELEVANCE

The results of the current study provide a good starting point for further research into the nature of arthritic progression in the elbow joint and the role of debridement arthroplasty.

In vivo three-dimensional kinematics of the cervical spine during maximal axial rotation

The cervical spine exhibits considerable mobility, especially in axial rotation. Axial rotation exerts stress on anatomical structures, such as the vertebral artery which is commonly assessed during clinical examination. The literature is rather sparse concerning the in vivo three-dimensional segmental kinematics of the cervical spine. This study aimed at investigating the three-dimensional kinematics of the cervical spine during maximal passive head rotation with special emphasis on coupled motion. Twenty healthy volunteers participated in this study. Low-dose CT scans were conducted in neutral and in maximum axial rotation positions. Each separated vertebra was segmented semi automatically in these two positions. The finite helical-axis method was used to describe 3D motion between discrete positions. The mean (±SD) maximum magnitude of axial rotation between C0 and C1 was 2.5 ± 1.0° coupled with lateral flexion to the opposite side (5.0 ± 3.0°) and extension (12.0 ± 4.5°). At the C1-C2 level, the mean axial rotation was 37.5 ± 6.0° associated with lateral flexion to the opposite side (2.5 ± 6.0°) and extension (4.0 ± 6.0°). For the lower levels, axial rotation was found to be maximal at C4-C5 level (5.5 ± 1.0°) coupled with lateral flexion to the same side (-4.0 ± 2.5°). Extension was associated at levels C2-C3, C3-C4 and C4-C5, whereas flexion occurred between C5-C6 and C6-C7. Coupled lateral flexion occurred to the opposite side at the upper cervical spine and to the same side at the lower cervical spine.

In vivo and 3-dimensional functional anatomy of the anterior bundle of the medial collateral ligament of the elbow

BACKGROUND

Although the anterior bundle of the medial collateral ligament (AMCL) is a critical stabilizer of the elbow joint, little information exists on in vivo and 3-dimensional functional anatomy of the AMCL. The purposes of this study were to investigate in vivo changes in the length of the AMCL during elbow flexion and to clarify the 3-dimensional functional anatomy of the AMCL.

METHODS

We created 3-dimensional models of the AMCL and bones from computed tomography data of 4 healthy elbows in 5 different elbow positions. The AMCL was subdivided into 9 ligaments. We calculated changes in lengths of ligaments during flexion and related ligament origins to the axis of rotation of the elbow joint.

RESULTS

There were 4 uniquely configured isometric ligaments, where their origins aligned broadly along the course of the axis of rotation in the coronal plane. The medially originating ligaments inserted on the posterior portion of the tubercle of the coronoid process, whereas the laterally originating ligaments inserted on its anterior portion. There were 5 non-isometric ligaments, 3 of which had origins proximal to the axis and became taut only in extension and the other 2 having origins distal to the axis and becoming taut only in flexion.

CONCLUSIONS

Isometric ligaments within the AMCL do not originate from a narrow area; rather, they originate from a broader area that extends more medially in the coronal plane than previously thought, which explains how the AMCL reconciles isometricity and robustness. The proximal and distal ligaments act as checkreins that work only at the limits of elbow motion.

Adjacent level effects of bi level disc replacement, bi level fusion and disc replacement plus fusion in cervical spine--a finite element based study

BACKGROUND

Studies delineating the adjacent level effect of single level disc replacement systems have been reported in literature. The aim of this study was to compare the adjacent level biomechanics of bi-level disc replacement, bi-level fusion and a construct having adjoining level disc replacement and fusion system.

METHODS

In total, biomechanics of four models- intact, bi level disc replacement, bi level fusion and fusion plus disc replacement at adjoining levels- was studied to gain insight into the effects of various instrumentation systems on cranial and caudal adjacent levels using finite element analysis (73.6N+varying moment).

FINDINGS

The bi-level fusion models are more than twice as stiff as compared to the intact model during flexion-extension, lateral bending and axial rotation. Bi-level disc replacement model required moments lower than intact model (1.5Nm). Fusion plus disc replacement model required moment 10-25% more than intact model, except in extension. Adjacent level motions, facet loads and endplate stresses increased substantially in the bi-level fusion model. On the other hand, adjacent level motions, facet loads and endplate stresses were similar to intact for the bi-level disc replacement model. For the fusion plus disc replacement model, adjacent level motions, facet loads and endplate stresses were closer to intact model rather than the bi-level fusion model, except in extension.

INTERPRETATION

Based on our finite element analysis, fusion plus disc replacement procedure has less severe biomechanical effects on adjacent levels when compared to bi-level fusion procedure. Bi-level disc replacement procedure did not have any adverse mechanical effects on adjacent levels.

PREDICTION OF BIOMECHANICAL CHARACTERISTICS OF INTACT AND INJURED LOWER THORACIC SPINE SEGMENT UNDER DIFFERENT LOADS

In this study, the biomechanical roles of disc nucleus and ligaments of human lower thoracic spine (T10–T12) under different loads were investigated using finite element (FE) method. The T10–T12 FE model was developed and validated against the published results. The FE model was then modified accordingly to simulate the injured conditions of nucleus, ligaments and facets and loaded under different configurations to analyze the segmental gross responses and the stress distribution around the annulus circumference. The high first-principal stress of annulus at the posterolateral region has an important role on the disc annulus's tear and a flexion moment causes a high first-principal stress at posterolateral region, despite of the existence of ligaments. The study also shows that decompression in intervertebral discs can reduce the dilatation of annulus tears by 18% around the posterolateral regions of disc annulus. The disc nucleus and the posterior ligaments have important roles in resisting compression and flexion loads, respectively. The investigations in this paper not only supplement experimental research but are also helpful in the understandings of biomechanics of lower thoracic spine.

Spinal kinematics and facet load transmission after total disc replacement

STUDY DESIGN

In vitro human cadaveric biomechanical study.

OBJECTIVE

The objectives were to determine the effect of total disc replacement (TDR) on kinematics, especially range of motion (ROM), helical axis of motion (HAM), and facet joint contact force.

SUMMARY OF BACKGROUND DATA

Ball-and-socket type artificial discs are designed to mimic normal motion, but the biomechanical effect on kinematics has not been thoroughly clarified.

METHODS

Fourteen human cadaveric L4-L5 units were tested before and after TDR. In 7 specimens, facet contact forces were directly measured with thin-film piezoresistive load transducers inserted in the facet joints. In the other 7 specimens, the facet joint capsules were kept intact. Moments (±7.5 Nm) were applied in flexion/extension, lateral bending, and axial rotation motion, with and without an axial compressive preload of 400 N. Three-dimensional motion was recorded, and each angular ROM and HAM were calculated.

RESULTS

Without axial compressive preload, the TDR did not produce significant differences in ROMs in all cases. However, under compressive preload, the TDR produced significantly larger ROMs for flexion (4.0° and 8.7°) and lateral bending (2.4° and 5.6°) (intact state and TDR, respectively). The TDR did not alter the HAM significantly except the location in lateral bending without compressive preload and the orientation in flexion/extension against horizontal plane. The location of HAM was slightly shifted caudally by the compressive preload in intact and TDR states. Despite the increased ROMs, the facet contact forces were not significantly altered by the TDR either with or without compressive preload (26 N and 27 N in extension, 41 N and 41 N in lateral bending, 117 N and 126 N in axial rotation).

CONCLUSION

TDR using a ball-and-socket type artificial disc significantly increased ROM under axial load and maintained the HAM with similar facet contact forces to the intact state.

Studying primate carpal kinematics in three dimensions using a computed-tomography-based markerless registration method

The functional morphology of the wrist pertains to a number of important questions in primate evolutionary biology, including that of hominins. Reconstructing locomotor and manipulative capabilities of the wrist in extinct species requires a detailed understanding of wrist biomechanics in extant primates and the relationship between carpal form and function. The kinematics of carpal movement, and the role individual joints play in providing mobility and stability of the wrist, is central to such efforts. However, there have been few detailed biomechanical studies of the nonhuman primate wrist. This is largely because of the complexity of wrist morphology and the considerable technical challenges involved in tracking the movements of the many small bones that compose the carpus. The purpose of this article is to introduce and outline a method adapted from human clinical studies of three-dimensional (3D) carpal kinematics for use in a comparative context. The method employs computed tomography of primate cadaver forelimbs in increments throughout the wrist's range of motion, coupled with markerless registration of 3D polygon models based on inertial properties of each bone. The 3D kinematic principles involved in extracting motion axis parameters that describe bone movement are reviewed. In addition, a set of anatomically based coordinate systems embedded in the radius, capitate, hamate, lunate, and scaphoid is presented for the benefit of other primate functional morphologists interested in studying carpal kinematics. Finally, a brief demonstration of how the application of these methods can elucidate the mechanics of the wrist in primates illustrates the closer-packing of carpals in chimpanzees than in orangutans, which may help to stabilize the midcarpus and produce a more rigid wrist beneficial for efficient hand posturing during knuckle-walking locomotion.

How do spinal segments move?

PURPOSE

To study and clarify the kinematics of spinal segments following cyclic torques causing axial rotation (T(z) (t)), lateral-flexion (T(x) (t)), flexion/extension (T(y) (t)).

METHODS

A 6D--Measurement of location, alignment, and migration of the instantaneous helical axis (IHA) as a function of rotational angle in cervical, thoracic, and lumbar segments subjected to axially directed preloads.

RESULTS

IHA retained an almost constant alignment, but migrated along distinct centrodes. THORACIC SEGMENTS: IHA was almost parallel to T(z) (t), T(x) (t), or T(y) (t), stationary for T(x) (t) or T(y) (t), and migrating for T(z) (t) along dorsally opened bows. IHA locations hardly depended on the position or size of axial preload. LUMBAR SEGMENTS: IHA was also almost parallel to T(z) (t), T(x) (t), or T(y) (t). In axial rotation IHA-migration along wide, ventrally or dorsally bent bows depending on segmental flexional/extensional status. Distances covered: 20-60mm. In lateral-flexion: IHA-migration to the left/right joint and vice versa. In flexion/extension IHA-migration from the facets to the centre of the disc. CERVICAL SEGMENTS: In flexion/flexion IHA was almost stationary for and parallel to T(y) (t). In axial rotation or lateral-flexion IHA intersected T(z) (t)/T(x) (t) under approximately -30 degrees /+30 degrees.

CONCLUSIONS

Generally joints alternate in guidance. Lumbar segments: in axial rotation and lateral-flexion parametrical control of IHA-position and IHA-migration by axial preload position. Cervical segments: kinematical coupling between axial rotation and lateral-flexion. The IHA-migration guided by the joints should be taken into account in the design of non-fusion implants. FE-calculations of spinal mechanics and kinematics should be based on detailed data of curvature morphology of the articulating surfaces of the joint facets.

Three-dimensional in vivo kinematics of the subtalar joint during dorsi-plantarflexion and inversion-eversion

BACKGROUND

It is difficult to determine the kinematics of the subtalar joint because of its anatomical and functional complexity. The purpose of the study was to clarify the 3D kinematics of the subtalar joint in vivo.

MATERIALS AND METHODS

Subjects were four healthy female volunteers. Magnetic resonance imaging (MRI) sequences were acquired in seven positions during dorsi-plantarflexion (DPF) and in 10 positions during inversion-eversion (IE) at intervals of 10 degrees. MRI data of the talus and calcaneus in the neutral position were superimposed on images of the other positions using voxel-based registration, and relative motions and axes of rotation were visualized and quantitatively calculated.

RESULTS

The calcaneus always rotated from dorsolateral to medioplantar during DPF and IE, and the motion plane was very similar to that of the entire foot in IE. The axes of rotation of the calcaneus relative to the talus during DPF and IE had a very close spatial relationship, running obliquely from antero-dorso-medial to postero-planto-lateral and penetrating the talar neck. The rotation angle around each of these calcaneal axes tended to be greater in IE (20 degrees +/- 2 degrees) than in DPF (16 degrees +/- 3 degrees). In DPF, motion of the calcaneus relative to the talus occurred predominantly around maximum dorsiflexion and plantarflexion, with little movement observed at intermediate positions. During IE, the calcaneus exhibited uninterrupted motion related to foot movement.

CONCLUSION

The subtalar joint is essentially a uniaxial joint with a motion plane almost identical to that of IE of the entire foot.

CLINICAL RELEVANCE

Knowledge of normal subtalar kinematics may be helpful when evaluating pathologic conditions.

Does trochanteric step osteotomy provide greater stability than classic slide osteotomy? A preliminary study

The use of a trochanteric slide osteotomy needs a partial weightbearing period to allow safe healing of the osteotomy. We compared the initial rigidity of fixation of the trochanteric slide osteotomy with that of a newly developed technique, the trochanteric step osteotomy. The slide and step osteotomies were tested on six bilateral pairs of cadaveric femora with cyclic shear load of constant amplitude for 100 cycles in both a superior direction to represent standing and 60 degrees of hip flexion to represent a squat stance. Translational and rotational migration and cyclic amplitude were measured with an optoelectronic camera system. During superior loading, translational migration of the slide osteotomy was greater than for the step osteotomy (slide median, 1.7 mm; step median, 0.3 mm), but rotational migration was not (slide median, 1.9 degrees; step median, 0.2 degrees ). Translational amplitude was greater for the slide osteotomy in the superior direction (median slide, 0.3 mm; median step, 0.16 mm), but not in rotational amplitude. Similar trends in migration and amplitude were observed for the squat loading configuration. The data suggest the trochanteric step osteotomy is a more stable construct than the commonly performed slide osteotomy.