Normal functional range of motion of upper limb joints during performance of three feeding activities

This study was designed to quantify the range of upper limb joint motion required during the performance of a specific type of functional activity. Ten able-bodied men were studied as they performed three feeding tasks--eating with a spoon, eating with a fork, and drinking from a handled cup. Three shoulder joint rotations, one elbow joint rotation, one forearm joint rotation, and three wrist joint rotations were quantified simultaneously using a three-dimensional measurement system. It was found that the required ranges of motion for the feeding tasks were 5 degrees to 45 degrees shoulder flexion, 5 degrees to 35 degrees shoulder abduction, 5 degrees to 25 degrees shoulder internal rotation, 70 degrees to 130 degrees elbow flexion, from 40 degrees forearm pronation to 60 degrees forearm supination, from 10 degrees wrist flexion to 25 degrees wrist extension, and from 20 degrees wrist ulnar deviation to 5 degrees wrist radial deviation. Wrist rotation was also measured, but it was found to be negligible.     

The effect of the orientation of the radial head on the kinematics of the ulnohumeral joint and force transmission through the radiocapitellar joint

Background. The treatment of radial head fractures that are not amenable to an open reduction and internal fixation, remains to be a difficult issue. A potential problem with prosthetic replacement of the radial head is the shape of current radial head prostheses. The purpose of this study was to determine the effect of the shape of the radial head on kinematics and load transfer of the elbow. Methods. Kinematics of the elbow and radiocapitellar force transmission were measured in 6 fresh frozen upper extremities. The effect of radial head shape was tested by rotating the head 90 degrees , with a custom-made 'native' radial head prosthesis. 3-D spatial orientation of the ulna showed an average difference in ulnohumeral laxity, between the nominal and 90 degrees conditions, of 0.1 degrees throughout the arc of motion with neutral forearm rotation (maximum: 2 degrees ). Findings. We found an average difference in ulnar axial rotation, of 0.1 degrees (maximum: 1.9 degrees ). No differences showed statistical significance. Radiohumeral joint force was measured and maximally showed a 32 times increase of force in the altered shape conditions. Interpretation. Our results show that the kinematics of the elbow was not affected by altering the shape of the radial head, but it did adversely affect the forces in the radiohumeral joint. This could possibly generate degenerative changes in the elbow.     

Ligament fibre recruitment of the elbow joint during gravity-loaded passive motion: an experimental study

BACKGROUND: Knowledge of elbow collateral ligament length during passive motion is essential in understanding ligament physiology and pathology, such as tightness and instability. METHODS: Five anatomical unembalmed specimens were passively placed in six flexion positions together with three forearm rotations, using equipment with gravity as motion force. These 18 positions were recorded using CT-scan. Three-dimensional data of ligament insertions were obtained through anatomical millimetre sections. Ligament length was measured in each position. FINDINGS: In neutral rotation, the lateral collateral ligament was long between 0 degrees and 30 degrees as well as at 90 degrees, and short between about 60 degrees and 120 degrees of flexion. In pronation, it was long at about 0 degrees and between 60 degrees and 120 degrees, short at about 30 degrees of flexion. In supination, it was long at about 30 degrees and 90 degrees and short between 120 degrees and 150 degrees of flexion. In any forearm rotation, the highest length of the anterior bundle of the ulnar collateral ligament was measured at about 90 degrees, its smallest length between 120 degrees and 150 degrees of flexion, position at which the posterior bundle length was greatest. INTERPRETATION: At 60 degrees of flexion, the collateral ligaments were slackened in any forearm rotations. Forearm rotation plays an indirect role in the posterolateral stability of elbow as it changes length of the lateral collateral ligament. This ligament can be tested passively at 90 degrees of flexion in supination, the anterior bundle of the ulnar collateral ligament between 0 degrees and 30 degrees in neutral rotation and the posterior bundle between 120 degrees and 150 degrees in neutral rotation.     

Effect of various forearm axially rotated postures on elbow load and elbow flexion angle in one-armed arrest of a forward fall

Background

Falling onto the outstretched hand is a major cause of upper extremity injury. The overall objectives of this study were to develop an experimental model for elbow load during a simulated fall onto one-armed arrest using three different forearm axially rotated postures as alternative fall arrest strategies. Additionally, the relationship between the elbow flexion angle and different axially rotated postures were also investigated.

Methods

Fifteen healthy young male Taiwanese graduate students with an average age of 23 years were studied. Subjects performed a one-armed arrest of a 5 cm fall onto a force plate. Each subject fell onto the force plate with his forearm 45° axial externally rotated (ER), non-rotated (NR), and 45° axial internally rotated (IR) postures. Kinematics and kinetics of the upper extremity were calculated and analyzed by using laboratory-developed motion analysis procedures.

Findings

The valgus–varus shear forces in the ER group were 1.4 times greater than the NR group, and 2.7 times greater than the IR group. The elbow joint remained at almost full extension in the ER (3.9°) group, while elbow flexion angle was observed in the NR (24.6°) and IR (40.3°) groups.

Interpretation

A fall onto the outstretched hand with an externally rotated forearm should be avoided in order to reduce excessive valgus–varus shear force on the elbow joint. Knowledge of elbow kinematics and kinetics during a forward fall with various forearm axially rotated posture may be helpful in preventing injuries.     

The effect of forearm rotation on laxity and stability of the elbow

OBJECTIVE: The purpose of this study was to quantify the relationship between forearm rotation and valgus/varus laxity of the elbow joint over the range of elbow flexion. BACKGROUND: There is little known about the influence of forearm rotation on the laxity and stability of the elbow joint. The general opinion exists that forearm rotation does not significantly influence the laxity and stability of the elbow joint. METHODS: Nine fresh-frozen cadaver elbows were used. Passive elbow flexion with the forearm in neutral rotation and in 40 degrees and 80 degrees of pronation and supination was performed under valgus/varus loads: (1) in intact elbows; (2) after a lateral surgical approach (lateral epicondylar osteotomy of the distal humerus); (3) after release of the anterior bundle of the medial collateral ligament; and (4) after release of the anterior bundle of the medial collateral ligament plus radial head resection. Valgus/varus elbow laxity was quantified using an electromagnetic tracking device. RESULTS: There was a statistically significant effect (P < 0.05) of forearm rotation on valgus/varus laxity throughout the range of flexion. The laxity was always greater in pronation than in supination, regardless of the surgical approach or the integrity of the anterior bundle of the medial collateral ligament or radial head. CONCLUSIONS:Valgus/varus laxity of the elbow is forearm rotation-dependent. The potential role of this effect should be considered and controlled for in the design of studies examining laxity and stability of the elbow joint. RELEVANCE: The observation that forearm pronation increases valgus/varus laxity, particularly in medial collateral ligament deficient elbows, implies a possible additional factor in throwing kinematics that might put professional baseball pitchers at risk of medial collateral ligament injury due to chronic valgus overload. Our data indicate that forearm rotation should be considered during the clinical examination of elbow instability.     

Moment arms of forearm rotators

BACKGROUND: Rotation about a longitudinal axis of the forearm has been a matter of investigation for over 100 years. However, most studies were limited to only a few muscles and to their action in specific set positions of elbow and forearm rotation. This investigation aims at determining the moment arms of muscles that contribute to pronation and supination at three different angles of elbow flexion throughout the entire range of forearm rotation. METHODS: Muscle moment arms were derived from tendon excursions that were recorded on a full-size epoxy model of the radioulnar complex. The results were verified on a fresh cadaver specimen. FINDINGS: Moment arms of all major supinators exhibit peak values in 40-50 degrees of pronation, for all three positions of the elbow. These peak values vary with elbow position, the biceps muscle showing the highest dependency with its greatest moment arm in 90 degrees of elbow flexion. The pronators show a maximum of moment arm about the neutral position, with little dependency on elbow flexion. Brachioradialis brings the pronated, or supinated forearm into the neutral position. The bow of the radius is in function comparable to the 'throw' of a crankshaft, forming a greater lever arm between the point of insertion of the muscles and the axis of rotation of the radius. INTERPRETATION: The observations drawn from this study could be of eminent value in planning rotator muscle transplantation, in understanding functional disorders after injury, and in the physical treatment of forearm rotator muscle deficiency. Reconstruction of the physiological anatomical arrangement in the treatment of injuries is strongly recommended for restoration of function.     

Loading characteristics of females exhibiting excessive valgus moments during cutting

BACKGROUND: Excessive knee valgus moments are considered a risk factor for non-contact anterior cruciate ligament injuries in female athletes, however, little is known about the biomechanical factors that contribute to this loading pattern. The purpose of this study was to compare lower extremity kinematics, foot position and ground reaction forces between female soccer players who demonstrate normal frontal plane moments at the knee with those who demonstrate excessive frontal plane moments at the knee during a cutting maneuver. METHODS: Sixty-one female soccer players, 16 (2) years, participated. Three dimensional kinematics and ground reaction forces were recorded during a side-step cutting maneuver. Knee frontal plane moments were calculated with inverse dynamics equations and were used to classify subjects into normal (N=38) and excessive valgus moment (N=23) groups. FINDINGS: Data revealed that the subjects with excessive valgus moments demonstrated an initial loading pattern that included greater laterally directed ground reaction forces (P<0.001, effect size 1.51), increased hip abduction (P=0.002, effect size 0.79), increased hip internal rotation (P=0.008, effect size 0.71) and a more internally rotated foot progression angle (P=0.04, effect size 0.55). Taken together, these variables explained 49% of the variance in peak knee valgus moment (R=.698, P<0.001). INTERPRETATION: These results provide insight into potentially injurious loading strategies and support the premise that interventions designed to encourage loading of the lower extremity in a more neutral alignment may work to decrease frontal plane loading at the knee.     

Kinematics of the ulna during pronation and supination in a cadaver study: implications for elbow arthroplasty

OBJECTIVE: Aim of this study was to exactly describe and quantify kinematics of the ulna during pro- and supination. DESIGN: Biomechanical study in fresh frozen cadavers. BACKGROUND: A previous MRI study revealed a varus/valgus motion of the ulna averaging 7.1 degrees during pro-/supination. Axial rotation, however, could not be quantified. METHODS: Sixteen arms were examined in a new apparatus that fixed the humerus on a template and allowed forearm rotation. Motion of a Kirschner wire placed in the ulna was recorded in steps of 30 degrees by two perpendicularly arranged charge coupled device cameras during pro- and supination. RESULTS: From supination to pronation the ulna showed a semi-lunar evasive motion in the coronal and transverse plane with an initial varus shift, then a dorsal and finally a valgus shift. Motion in the coronal plane averaged 14.14 degrees (SD 4.78). Valgus angles of the ulna in 30 degrees, 60 degrees and 90 degrees pronation were significant (P<0.05) to each other and the neutral position. Varus angles of the ulna in 30 degrees, 60 degrees and 90 degrees supination (P<0.01) were significant to each other and the neutral position.A maximum ulnar axial pronation rotation of 3.2 degrees (SD 2 degrees ) was noted. Axial rotation angles of 90 degrees and 60 degrees of pronation were significant to each other and to the neutral position (P<0.05), respectively. CONCLUSIONS: To prevent increased stress on the bone-cement interface in elbow arthroplasty, a mean axial rotation of at least 3.2 degrees should be possible.     

The effect of the orientation of the noncircular radial head on elbow kinematics

OBJECTIVE: The objective of this study was to identify the effect of radial head shape and orientation on elbow kinematics in the otherwise intact elbow. DESIGN: Biomechanical study, analyzing simulated active motion of cadaveric arms. BACKGROUND: A discrepancy exists between the noncircular anatomy of the radial head and radial head prostheses. The effect of radial head shape is unknown. METHODS: Kinematic effects of radial head shape were tested in six fresh-frozen upper extremities. A custom-made native radial head prosthesis was used to simulate altered shape conditions, by rotating the radial head 90 degrees. Three-dimensional spatial orientation of the ulna was recorded, during simulated active motion. A three factor ANOVA was used to compare (a) nominal and 90 degrees oriented conditions, (b) throughout the flexion arc (c) in three forearm positions (P < 0.05). Post-hoc Tukey tests were done to assess significance. RESULTS: No significant effect of altering radial head shape was found on total ulnohumeral laxity and angulation during gravity valgus stress. We did find a significant effect on total ulnar axial rotation and rotation during gravity valgus stress. CONCLUSION: The outer shape of the radial head seems to change rotation of the ulna during flexion-extension in an otherwise intact elbow. RELEVANCE: The shape of the radial head effects intact elbow kinematics. Clinical importance of this finding is clear. If a sub-optimally placed radial head prosthesis were to be used in an otherwise intact elbow, the elbow could be at risk for early ulnohumeral arthritis.     

Effect of tibial tubercle elevation on biomechanics of the entire knee joint under muscle loads

BACKGROUND: Anterior elevation of the tibial tubercle, known as Maquet procedure, is performed to reduce excessive patellofemoral contact stresses in knee joints with patellofemoral osteoarthritis and anterior pain. Previous investigations, however, have entirely focused on the likely effect of tibial tubercle elevation procedure on biomechanics of contact at the patellofemoral joint with no attention what-so-ever to associated alterations in biomechanics of the tibiofemoral joint. METHODS: Using a validated 3D nonlinear finite element model of the entire knee joint, the effect of 1.25 cm and 2.5 cm tubercle elevations on the entire knee joint biomechanics was investigated under constant quadriceps load of 411 N alone or combined with hamstrings co-activation of 205.5 N under joint angles of 0-90 degrees. FINDINGS: Results confirm the effectiveness of this procedure in reducing patellofemoral contact forces, especially at smaller flexion angles. Maximum contact stress substantially decreased at full extension but increased at 90 degrees. Substantial effects of tuberosity elevation on tibial kinematics, cruciate ligament forces, tibiofemoral contact forces and extensor lever arm were found. The posterior cruciate ligament and tibiofemoral contact forces at larger flexion angles considerably increased whereas the anterior cruciate ligament and tibiofemoral contact forces at near full extension angles decreased. Overall, the extent of changes depended on the magnitude of anterior elevation, joint flexion angle and loading considered. INTERPRETATION: Biomechanics of the tibiofemoral joint were significantly influenced by tibial tubercle elevation. Current results advocate the need for an integral view of the entire knee joint in management of various joint disorders rather than a view in which each component is considered and treated in isolation with no due attention to perturbations caused and associated consequences.     

The effect of coronoid fractures on elbow kinematics and stability

BACKGROUND: Coronoid fractures often occur in the setting of more complex elbow trauma. Little is known about the influence of coronoid fracture size on elbow kinematics, particularly in the setting of concomitant ligament injuries. The purpose of this study was to determine the effect of coronoid fractures on elbow kinematics and stability in ligamentously intact and medial collateral ligament deficient elbows and to determine the effect of forearm position on elbow stability in the setting of coronoid fracture. METHODS: Eight cadaveric arms were tested during simulated active dependent elbow motion and gravity-loaded passive elbow motion. Kinematic data were collected from an electromagnetic tracking system. The protocol was performed in ligament origin repaired and medial collateral ligament deficient elbows with radial head arthroplasty. Testing was carried out with the coronoid intact, and with 10% (Type I), 50% (Type II), and 90% (Type III) removed. Varus-valgus angulation of the ulna relative to the humerus and maximum varus-valgus laxity were measured. FINDINGS: With repaired ligament origins and medial collateral ligament deficiency, there was increased varus angulation and increased maximum varus-valgus laxity following simulation of a Type II and Type III coronoid fracture. There was less kinematic change with the forearm in supination than in pronation. INTERPRETATION: Elbow kinematics are altered with increasing coronoid fracture size. Repair of Type II and Type III coronoid fractures as well as lateral ligament repair is recommended where possible. Forearm supination may be considered during rehabilitation following coronoid repair. Valgus elbow positioning should be avoided if the medial collateral ligament is not repaired.     

The influence of isolated femur and tibia rotations on patella cartilage stress: a sensitivity analysis

BackgroundTo determine the influence of femur and tibia rotations in the transverse and frontal planes on patella cartilage stress.MethodsPatella cartilage stress profiles of six healthy females were obtained during a squatting task using subject-specific finite element models of the patellofemoral joint (45° of knee flexion). Input parameters for the finite element model included joint geometry, quadriceps muscle forces, and weight-bearing patellofemoral joint kinematics. The femur and tibia of each model were then rotated to 2°, 4°, 6°, 8°, and 10° along their respective axes beyond that of the natural degree of rotation in weight-bearing. The process was repeated for internal rotation, external rotation, adduction, and abduction. Quasi-static loading simulations were performed to quantify average patella cartilage stress.FindingsIncremental femur internal rotation beyond that of the natural rotation resulted in progressively greater patella cartilage stress (41–77%), whereas incremental tibia internal rotation resulted in a decrease in patella cartilage stress (7–10%). Femur and tibia external rotation resulted in a mild increase in patella cartilage stress, but only at 10° (9%). Incremental femur adduction resulted in an increase in patella cartilage stress, but only at 10° (43%). Femur abduction and frontal plane tibia rotation in either direction had no influence on patella cartilage stress.InterpretationFemur internal rotation and adduction resulted in the greatest increases in patella cartilage stress. In contrast, tibia rotations in the transverse and frontal planes had minimal to no influence on patella cartilage stress. These results emphasize the need for clinicians to identify and correct faulty hip kinematics in persons with PFP.     

A minimally invasive method for the determination of force in the interosseous ligament

Objective. The objective was to develop and utilize a minimally invasive testing system to determine the force in the interosseous ligament under axial compressive loads across the range of motion of the human forearm.

Design. Eleven fresh frozen human cadaveric forearms were used (51–72 years).

Background. Current studies investigating interosseous ligament forces altered the structure of the forearm by implanting load cells into the radius and ulna. This may affect load transfer through the forearm. Little information was available on interosseous ligament function over the entire flexion range of the elbow.

Methods. A robotic joint testing system was used to apply a 100 N compressive load to the forearm and measure the resulting displacement. Each forearm was tested with no disruption of the bones and soft tissues of the forearm. The principle of superposition was used to calculate the forces in the interosseous ligament and was indirectly validated using fluoroscopy.

Results. The force in the interosseous ligament ranged from a minimum of 8 N in neutral forearm rotation at full extension to a maximum of 43 N in supination at 30° of flexion. The largest force was found in supination at all flexion angles.

Conclusions. The interosseous ligament is an important structure in the stability of the forearm. The force in the interosseous ligament depends on the elbow flexion angle and forearm rotation.Relevance

This study suggests that radial head fractures are best treated with the forearm in supination, since the interosseous ligament takes the largest load in this position. Complex injuries which have a poor prognosis, may require interosseous ligament reconstruction to improve clinical outcomes.     

The effect of radial head fracture size on radiocapitellar joint stability

OBJECTIVE: The purpose of this study was to determine the effect of radial head fracture size on radiocapitellar stability. DESIGN: Repeated measures using Instron materials testing machine. BACKGROUND: Radial head fractures are common injuries and controversy exists as to the optimal management of displaced wedge fractures. METHODS: Fractures were simulated in six fresh-frozen cadaveric radiocapitellar joints by removing sequential 20 degree wedges from the anterolateral aspect of each radial head until 140 degrees of the radial head was removed. Decreased shear load at the radial head during joint loading was used as an indicator of decreased stability at the radiocapitellar joint. Using a custom designed jig and employing a compressive joint load of 100 N, the maximum shear load at the radiocapitellar joint was measured at 30, 60, 90 and 120 degrees of elbow flexion. RESULTS: There was no difference in the shear load between the intact specimen and that with a 20 degree wedge removed at all flexion angles (P>0.05). Shear load decreased with each increase in wedge size between 20 and 120 degrees (P<0.05). After 120 degrees, one-third the diameter of the radial head, the shear load was always less than 0.8 N. CONCLUSIONS: This study demonstrated an inverse relationship between radiocapitellar joint stability and radial head fracture size. RELEVANCE: Small radial head fracture fragments are biomechanically significant. Therefore, the use of an arbitrary fragment size as an indication for surgery should be reconsidered, particularly if there is an associated ligamentous injury.     

Biomechanical evaluation of intra-articular and extra-articular procedures in anterior cruciate ligament reconstruction: a finite element analysis

BACKGROUND: Intra-articular techniques (single and double bundles) are the most widely used procedures for the anterior cruciate ligament reconstruction. Lemaire introduced in 1967 the extra-articular techniques, and combined intra-articular and extra-articular reconstruction, to better restore the stability of the knee. However, the effectiveness of these procedures (intra-articular, extra-articular combined or not with intra-articular) seems to be controversial. METHODS: In the present study, we developed numerical models of a knee joint to evaluate the effects of these different procedures on the kinematics and biomechanics of the knee during an internal rotation test. Six cases were simulated: intact anterior cruciate ligament, intra-articular reconstructed anterior cruciate ligament (single and double bundles), extra-articular reconstructed anterior cruciate ligament alone, and combination of extra- and intra-articular reconstructions. The loading condition was an internal tibial torque of 2 N m at 0 degrees, 15 degrees, 30 degrees and 45 degrees of knee flexion. Internal rotation of the tibia and forces within the grafts and the ligaments were calculated. FINDINGS: This study showed that both single and double bundles intra-articular reconstructions restore similar internal rotation control and biomechanics of the soft structures as the intact anterior cruciate ligament situation. On the other hand, our results indicate that extra-articular reconstruction reduces appreciably the internal rotation and modifies the charges distribution in the soft structures when compared to the intact anterior cruciate ligament. INTERPRETATION: The extra-articular procedure alters the kinematics of the knee, which might overconstraint the ligaments and the femorotibial joints, leading to the failure of the anterior cruciate ligament reconstruction.     

Lower extremity biomechanics during the landing of a stop-jump task

BACKGROUND: Literature shows that landing with great impact forces may be a risk factor for knee injuries. The purpose of this study was to examine the relationships among selected lower extremity kinematics and kinetics during the landing of a stop-jump task. METHODS: Landmark coordinates and ground reaction forces during a stop-jump task were collected. Lower extremity joint angles and resultants were reduced. Pearson correlation coefficients among selected lower extremity kinematics and kinetics were determined. FINDINGS: The hip flexion angular velocity at the initial foot contact had significant correlation with peak posterior and vertical ground reaction forces (r = -0.63, P < 0.001, r = -0.48, P < 0.001) during the landing of the stop-jump task. The knee flexion angular velocity at the initial foot contact also had significant correlation with peak posterior and vertical ground reaction force (r = -0.49, P < 0.001, r = -0.06, P < 0.001) during the landing of the stop-jump task. Peak proximal tibia anterior shear force and peak knee extension moment during landing of the stop-jump task had significantly correlation with the corresponding posterior and vertical ground reaction forces (r > 0.51, P < 0.001). INTERPRETATION: A large hip and knee flexion angles at the initial foot contact with the ground do not necessarily reduce the impact forces during the landing of the stop-jump task, but active hip and knee flexion motions do. Hip joint motion at the initial foot contact with the ground appears to be an important technical factor that affects anterior cruciate ligament loading during the landing of the stop-jump task.     

The influence of internal and external tibial rotation offsets on knee joint and ligament biomechanics during simulated athletic tasks

BackgroundFollowing anterior cruciate ligament injury and subsequent reconstruction transverse plane tibiofemoral rotation becomes underconstrained and overconstrained, respectively. Conflicting reports exist on how rotations influence loading at the knee. This investigation aimed to determine the mechanical effects of internal and external tibial rotation offsets on knee kinematics and ligament strains during in vitro simulations of in vivo recorded kinematics.MethodA 6-degree-of-freedom robotic manipulator arm was used to articulate 11 cadaveric tibiofemoral joint specimens through simulations of four athletic tasks produced from in vivo recorded kinematics. These simulations were then repeated with 4° tibial rotation offsets applied to the baseline joint orientation.FindingsRotational offsets had a significant effect on peak posterior force for female motion simulations (P < 0.01), peak lateral force for most simulated tasks (P < 0.01), and peak anterior force, internal torque, and flexion torque for sidestep cutting tasks (P ≤ 0.01). Rotational offsets did not exhibit statistically significant effects on peak anterior cruciate ligament strain (P > 0.05) or medial collateral ligament strain (P > 0.05) for any task.InterpretationTransverse plane rotational offsets comparable to those observed in anterior cruciate ligament deficient and reconstructed patients alter knee kinetics without significantly altering anterior cruciate ligament strain. As knee degeneration is attributed to abnormal knee loading profiles, altered transverse plane kinematics may contribute to this. However, altered transverse plane rotations likely play a limited role in anterior cruciate ligament injury risk as physiologic offsets failed to significantly influence anterior cruciate ligament strain during athletic tasks.     

Knee joint biomechanics in open-kinetic-chain flexion exercises

BACKGROUND: Different rehabilitation exercises such as open-kinetic-chain flexion and extension exercises are currently employed in non-operative and post-operative managements of joint disorders. The challenge is to strengthen the muscles and to restore the near-normal function of the joint while protecting its components (e.g., the reconstructed ligament) from excessive stresses. METHODS: Using a validated 3D nonlinear finite element model, the detailed biomechanics of the entire joint in open-kinetic-chain flexion exercises are investigated at 0 degrees, 30 degrees, 60 degrees and 90 degrees joint angles. Two loading cases are simulated; one with only the weight of the leg and the foot while the second considers also a moderate resistant force of 30 N acting at the ankle perpendicular to the tibia. FINDINGS: The addition of 30 N resistant force substantially increased the required hamstrings forces, forces in posterior cruciate and lateral collateral ligaments and joint contact forces/areas/stresses. INTERPRETATION: At post-anterior cruciate ligament reconstruction or injury period, the exercise could safely be employed to strengthen the hamstrings muscles without a risk to the anterior cruciate ligament. In contrast, at post-posterior cruciate/lateral collateral ligaments reconstructions or injuries, the open-kinetic-chain flexion exercise should be avoided under moderate to large flexion angles and resistant forces.     

Glenohumeral joint kinematics related to minor anterior instability of the shoulder at the end of the late preparatory phase of throwing.

OBJECTIVE: The first aim of this study was an approach to quantify the 3D kinematics of the glenohumeral joint referred to the joint surfaces. The method was used to study the glenohumeral patho-arthrokinematics related to minor anterior instability at the end of the late preparatory phase of throwing. STUDY DESIGN: Using a finite helical axis approach, arthrokinematics focused on: (i) the rotations and shift of the humeral head on the glenoid cavity, and (ii) the migration of contact of the articular surfaces. BACKGROUND: Controversy still exists whether the clinical syndrome called 'minor anterior glenohumeral instability' can be validly termed as an instability. METHODS: Helical CT-data of discrete shoulder positions were three-dimensionally reconstructed. Based on humeral and scapular sets of skeletal landmarks, rotation matrices and translation vectors were estimated and processed in glenohumeral finite helical axes. The finite helical axis parameters of rotation, shift and direction were related to a co-ordinate system embedded on the glenoid, whereas the position of the finite helical axis was related to the articulating surface of the humeral head. RESULTS: From 90 degrees abduction and 90 degrees external rotation to full cocking (90 degrees abduction with full external rotation and horizontal extension), the humeral head in the normal shoulders did not externally/internally rotate on the glenoid. In contrast, a large external rotation component was found in the minor unstable shoulders. The geometrical centre of the humeral head of the normal shoulders translated into a posteriorized position on the glenoid, whereas in minor anterior instability it translated centrally on the glenoid. CONCLUSIONS: Compared with in vitro biomechanical research which states that towards full cocking the anterior part of the inferior glenohumeral ligament limits anterior translation and external rotation of the humeral head on the glenoid, the results suggest in minor anterior instability a dysfunction of the anterior part of the inferior glenohumeral ligament. RELEVANCE: The results indicate that the so-called 'minor anterior glenohumeral instability syndrome' can validly be stated as an instability problem. The results also indicate that the glenohumeral joint does not move consistently as a ball-and-socket joint, meaning that the concave-convex rules for glenohumeral joint mobilization need 'evidence-based' adjustments.     

前交叉韧带损伤膝关节6个自由度静态加载体的稳定性

背景:由于膝关节的体外标本无法模拟膝关节的真实运动,而体内的运动测试又无法获得骨结构的运动信息,因而不能得到准确的膝关节稳定性数据,也就无法对膝关节损伤的早期诊断及防治措施进行深入的研究.目的:应用计算机三维重建技术、2D/3D图像配准技术及图像处理技术对前交叉韧带损伤膝关节6个自由度变化进行静态加载体内稳定性测试.方法:8例患者单侧膝关节前交叉韧带断裂而对侧正常,膝关节在屈曲0°,30°,60°和90°时分别进行134 N前加载.采集各角度相互垂直的2D图像,与3D CT图像在虚拟X射线投射系统进行2D/3D图像配准,还原膝关节不同角度时的股骨和胫骨相对3D位置关系,获得膝关节6个自由度数据.结果与结论:前交叉韧带断裂后胫骨前移均明显增加,在完全伸直(0°)时胫骨前移最小,胫骨前移在30°时达到最大;胫骨前移在60°和90°时逐渐减小,各角度间比较差异均有显著性意义(P=0.000).前交叉韧带断裂后,膝关节胫骨内旋、内移均较健侧增加(P=0.000).提示通过2D/3D图像配准技术可以实现对膝关节静态加载的体内稳定性分析;前交叉韧带损伤后膝关节前移、内旋和内移均明显增加.