1,720,986 research outputs found
Parametric Control of the Stiffness of Lumbar Segments
No full textTo clarify relations between kinematics and mechanics of lumbar spinal segments (L3/L4, L4/L5) versus thoracic T6/T7. Measurements of rotational angle-torque characteristics and migrations of the instantaneous helical axis (IHA) in cyclic segment motions; correlation of IHA-position and differential segment stiffness by applying theorem of Steiner. In neutral axial position of the thoracic segment (alpha = 0), IHA was found within central areas of the intervertebral disc. No change of axial IHA-positions by flexion/extension. In axial rotation IHA-migrations along wide arches from one joint to the other and S-shaped characteristics: strong dependence of IHA-migration and the differential stiffness on the degree of flexion/extension. In flexion/extension, J-shape of the characteristic and simultaneous anterior/posterior IHA-migration. Correlation of initial differential segment stiffness and IHA-position via theorem of Steiner. The following conclusions are obtained: 1. Non-linearity of the characteristics is hardly produced by the soft tissues but mainly by IHA-migration and IHA-tilting. 2. The segment stiffness in axial rotation is parametrically controlled via the degree of additional flexion/extension. 3. The autochthon muscles are able to control the segment stiffness in axial rotation via shifting the resulting force line in anterior/posterior direction without change of its amount about the factor 3-5
The upper ankle joint: Curvature morphology of the articulating surfaces and physiological function
No full textPurpose: The curvature morphology of the articulating surfaces determines the physiological movement pattern. We quantitatively examined the curvature morphology of the tibiotalar articulating surfaces and specified their geometric contact patterns. Methods: Geometrically equivalent cartographic nets were marked on the talar and tibial articulating surfaces of true-to-scale moldings of 20 human ankle joints (intervals of 5 mm) to relate corresponding articulating units of the surfaces. The corresponding contours of the net lines were compared, and the incongruity of articulating surfaces could thus be quantified locally. Results: All tibial sagittal net lines represented circular arcs. Along the sagittal talar net lines, the curvature radii increased medially from anterior to posterior but decreased laterally. Each net line could be approximated by three circular arcs. Examining these three parts of the talar net lines, the anterior sagittal curvature radii increased from medial to lateral, whereas the posterior radii decreased. The tibial and talar transversal net lines were congruent. The articulation surfaces showed a transversal contact line in every dorsal/plantar joint position. The degree of local congruity was solely ascertained by the incongruity of the corresponding sagittal net lines. The maximal degrees of congruity were found laterally for dorsal flexion, laterally/centrally for neutral joint position, and centrally/medially for plantar flexion. Conclusions: By the transversal line contact, the contact area is broadened over the articulating surfaces from lateral to medial. In dorsal flexion, compressive loads are mainly transferred by lateral/anterior zones and in plantar flexion by medial/posterior zones of the articulating surfaces. Reconstruction of the transversal contact line is essential
Wie sind die klinischen Ergebnisse operativ behandelter Talusfrakturen?
No full textOur study focuses to determine the medium-range results of function and radiological flndings of operatively treated fractures of the talus. Furthermore we had the intention to investigate risl-factors for posttraumatic arthrosis and necrosis of the talus. Material and Methods: We included all 41 patients (w/m: 13/28) operated between 19952000 with talus neck, corpus or dislocated fracture of the talus edge (open/closed: 11/30). Fractures were classified according to Hawkins: type 1: 6x, type II: 17x, type III: 7x, type IV: 3x, 8x dislocated peripheral fractures. 39x screw osteosynthesis, 2x K-wire fixation were done and 12 additive transfixation with fixateur externe. Score: AOFAS Ankle-Hindfoot-Scale, radiological assessment according to the Bargon score. 34 patients, mean age 35 years (12-60), were followed up clinically with an average of 4 years (24-72 months). Results: AOFAS Score: pain (40 points): circle divide 31 [10-40]; function (50 points): circle divide 39 [14-50]; alignement(10 points): circle divide 7 [0-10]; degree of arthritis due to the Bargon scale: 0 degrees: 5x, 1 degrees: 8x, 2 degrees: 7x, 3 degrees: 7x. Complications: 4x necrosis of margin of the wound, 1 deep infection, 5 necrosis of the talus bone. The severity of the fracture was I x type II according to Hawkins 3x type III and 1x type IV. 3 of the 5 patients who developed a talus necrosis had 2 degrees or 3 degrees soft tissue damage. One patient had an imminent compartment syndrome. One patient who suffered a polytrauma was operated six days post injury. Second operation: 1 Syme amputation due to necrosis of the talus subsequent to an infection. 4 x arthrodesis of the upper ankle joint and 5x arthrodesis of the subtalar joint due to posttraumatic arthritis. Conclusion: Primary screw osteosynthesis is the treatment of choice depending on the lesions of the soft-tissue and accompanied injuries in combination with a fixateur externe. Nevertheless the primary osteosynthesis is not able to prevent necrosis of the talus completely, that occurs in a frequency of 15%. Risk factors for a posttraumatic arthritis in addition to the type of fracture and the result of reconstruction are an accompanied soft tissue defect and local capsule-band complex with necessary temporary transfixation. Early plastic reconstruction of defects can reduce the time of immobilisation and allows motion therapy. The functional results are positive compared with the radiological results that showed arthritis in 70%
How do spinal segments move?
No full textPurpose: 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: 20-60 mm 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'/+30. 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. (C) 2009 Elsevier Ltd. All rights reserved
Total disc arthroplasties alter the characteristics of the instantaneous helical axis of the cervical functional spinal units C3/C4 and C5/C6 during flexion and extension in in vitro conditions
No full textTotal disc arthroplasty (TDA) increases the risk of adjacent segment disease (ASD). Kinematic analyses are necessary to compare the intact condition (IC) with alterations after TDA to develop better prostheses. A well-established 6D measuring apparatus (resolution < 2.4 μm; 400 positions/cycle) was used. Kinematics of the flexion and extension of 8 human cervical spine segments (cFSU) C3/C4 and C5/C6 (67.9 ± 13.2 y) were analyzed in the IC and after TDA (Bryan® Cervical Disc [B-TDA], Prestige LP® Cervical Disc [P-TDA]). The migration of the instantaneous helical axis (IHA) and the stiffness of the segments were calculated. Analyses demonstrated a stretched U-curved IHA migration in the sagittal plane. The IHA positions were significantly more cranial in cFSU C5/C6 than in C3/C4 in IC and after either TDA (IC: p < 0.001; B-TDA: p = 0.001; P-TDA: p = 0.045). In cFSU C3/C4 IHA positions shifted anteriocranially after either TDA (p < 0.001). In cFSU C5/C6, the IHA positions were significantly more anterocranial after B-TDA than in IC and after P-TDA (anterior: p < 0.001; cranial: p = 0.005). After B-TDA, the IHA migration path length was significantly longer in cFSU C3/C4 than in C5/C6 (p = 0.007) and longer than in IC in both cFSU (C3/C4: p = 0.047; C5/C6: p < 0.001). Stiffness was increased after both TDA. Various kinematic alterations were observed after both TDA. Increased translation and IHA position shifting after both TDA might indicate abnormal strain and a derogated benefit of TDA. These results imply the most abnormal strain after B-TDA. The lower cFSU might be more susceptible to alterations after TDA than the upper cFSU
Mathematical study on the guidance of the tibiofemoral joint as theoretical background for total knee replacements
No full textThe mathematical approach presented allows main features of kinematics and force transfer in the loaded natural tibiofemoral joint (TFJ) or in loaded knee endoprostheses with asymmetric condyles to be deduced from the spatial curvature morphology of the articulating surfaces. The mathematical considerations provide the theoretical background for the development of total knee replacements (TKR) which closely reproduce biomechanical features of the natural TFJ. The model demonstrates that in flexion/extension such kinematic features as centrodes or slip ratios can be implemented in distinct curvature designs of the contact trajectories in such a way that they conform to the kinematics of the natural TFJ in close approximation. Especially the natural roll back in the stance phase during gait can be reproduced. Any external compressive force system, applied to the TFJ or the TKR, produces two joint reaction forces which - when applying screw theory - represent a force wrench. It consists of a force featuring a distinct spatial location of its line and a torque parallel to it. The dependence of the geometrical configuration of the force wrench on flexion angle, lateral/medial distribution of the joint forces, and design of the slopes of the tuberculum intercondylare is calculated. The mathematical considerations give strong hints about TKR design and show how main biomechanical features of the natural TFJ can be reproduced
KNEE MOTION ANALYSIS OF THE NON-LOADED AND LOADED KNEE: A RE-LOOK AT ROLLING AND SLIDING
No full textMany studies of knee motion have been reported in the literature over more than 100 years. Of particular interest to the analysis presented here is the work of the Freeman group, who elegantly measured tibio-femoral kinematics in studies made on cadavers and the knees of living individuals using MRI, anatomical dissection and RSA. We examined and reevaluated the data collected by Freeman's group and suggest that their conclusion should be considered to be incorrect, since their methods of evaluation were oversimplified from the mathematical and physical perspectives. By applying appropriate methods, however, it is possible to show that the same data yield important insights into physiological knee kinematics and reveal that the rolling-sliding relationship depends on the degree of flexion and on joint load in the medial and lateral compartment, as well. In the initial range of flexion, a considerable amount of rolling was found to occur. Based on this analysis, it is possible to gain useful insights of value for the design of total knee replacements
A novel total knee replacement by rolling articulating surfaces. In vivo functional measurements and tests
No full textThe purposes of the paper were as follows: to show the fundamental functional differences between the natural knee and common total knee replacements (TKR), to describe the ideas on how main properties of the natural knee can be adopted by a novel TKR and to present some main biomechanical functions of this TKR. By analyzing the morphology of the articulating surfaces and the kinematics of the natural knee the design of the novel TKR was developed. The use was made of the test procedures established in vitro and of lateral X-ray photographs as well as fluoroscopy in vivo. The function of the novel TKR is comparable to that of the natural knee joint in terms of kinematics (roll/slide behaviour), loads of the articulating surfaces ( diminished shear loads), stability and leeway under external impacts, reduction of the load in the patellofemoral joint, and ligament balancing
Influence of Cyclops Syndrome after Anterior Cruciate Ligament Reconstruction on the Functional Outcome
No full textBackground: A review of recent reports concerning the functional Outcome after treatment for Cyclops syndrome can produce contradictory results. Therefore, the purpose of this study was to evaluate the functional outcome of our patients treated for Cyclops syndrome after anterior cruciate ligament reconstruction. Methods: Between 1998 and 2006 ten patients were followed for the occurrence of a Cyclops syndrome. The Lysholm score, Marshall score and Tegner activity score was used for clinical evaluation at final follow up; in addition, a subjective assessment of knee function and knee pain on a Visual analogue scale was registered. Knee stability was measured using the KT-1000 arthrometer. Results were compared with a control group of 24 uneventful ACL reconstructions. Results: Revision arthroscopy for symptomatic extension block was performed after a mean of 6.8 months. After a mean follow-up of 23 months after second surgery all patients' regained full range of motion. The mean Lysholm score and Marshall score was 85 and 41 after Cyclops syndrome and 92 and 46 for the control group. After Cyclops syndrome patients experienced a significantly increased ACL transplant laxity but no significant difference was found concerning patient's subjective rating of knee function and knee pain. Conclusion: Although patients Subjective rating of knee function and knee pain was nearly identical in both groups objective knee scores disclosed impaired knee function in our patients treated for Cyclops syndrome
Kinematics of cervical segments C5/C6 in axial rotation before and after total disc arthroplasty
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