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.     

In vivo 3D kinematics of normal forearms: Analysis of dynamic forearm rotation

Background

Forearm rotation is an indispensable activity of daily living and comprises complex motions with rotational and translational components. It is thought that changes in these motions with injury or disease may affect diagnostic indices. Several studies have assessed in vivo forearm kinematics with static conditions, but dynamic forearm kinematics have not yet been reported. The purpose of this study was to analyze forearm kinematics during dynamic rotation using radiographic 3D–2D registration methods.

Methods

Ten forearms of five healthy males with the mean age of 37 years old were enrolled. Lateral fluoroscopic images were taken during forearm rotation from maximum supination to maximum pronation with their elbows flexed to approximately 45°. Geometric bone models were created from CT scans of the humerus, the radius and the ulna. Three-dimensional kinematics were determined using 3D–2D model registration techniques with the images and models, and the arc of axial rotation of the radius, volar/dorsal translation of the ulna at the distal radioulnar joint and rotation axis of forearm were computed.

Findings

The radial rotation arc was 157°. The ulna translated 3.9 mm (SD 1.5 mm) dorsally during activity. The rotation axis of the forearm passed through the center of the radial head and the ulnar head at the 1.9 mm (SD 0.7 mm) posterior from its geometric centroid.

Interpretation

The posteriorly deviated rotation axis at the ulnar head may result in the ulnar head translating dorsally during pronation. These data provide a basis for objective assessment of pathological forearm function.     

How much can carpus rotate axially? An in vivo study

BACKGROUND: Supination and pronation movements occur primarily at the forearm though are possible at the wrist joint too. The axial rotation of the wrist also called the radiometacarpal rotation has been quantified but for its passive range which may never occur during the day-to-day routine activities. It is normally not possible for the wrist joint to rotate axially in an active manner. However, voluntary effort to rotate the forearm while keeping the hand fixed on a custom designed device is able to provide active rotation of the wrist which occurs in a manner similar to that occurring during the daily routine activities. METHODS: The present study measured axial rotation of the wrist in 20 asymptomatic volunteers who had axial CT done of their wrist with elbow in 10-30 degrees flexion and forearm positioned parallel to the long axis of the table with thumb pointing up towards the roof. The examination was repeated twice while the subject actively tried to supinate and pronate the forearm against the fixed hand and the metacarpals using maximum voluntary effort on a custom designed positioning device. FINDINGS: The mean radiometacarpal supination and pronation were 17.15 degrees (SD 7.9) and 17.0 degrees (SD 10) respectively. The movement was found to occur predominantly at midcarpal joint with radiocarpal joint contributing only 18% to supination and 31% to pronation. INTERPRETATION: The radiometacarpal rotation has a crucial bearing in the development of the wrist prostheses. The design of the prostheses should consider accommodating axial movements that occur in the carpus during the activities of daily living.     

Mechanism of limitation of pronation/supination of the forearm in geometric models of deformities of the forearm bones

OBJECTIVE: To clarify the mechanism of limitation of pronation/supination of the forearm associated with the angular deformity of the forearm bones and narrowing of the interosseous space. DESIGN: A three-dimensional geometric model of the forearm bones with the interosseous membrane and its axial section were used. BACKGROUND: Limitation of pronation/supination associated with the deformity of the forearm bones is one of the significant problems encountered in the treatment of the forearm fracture. Elucidation of its mechanism is important for its prevention and treatment. METHODS: In the axial section, the effects of the positional relationship between the axis of pronation/supination and the forearm bones on the range of pronation/supination was studied using analytic geometry in each model with non-narrowing or narrowing of the interosseous space. Subsequently, in the three-dimensional model each forearm bone with the same angular deformity, the direction and magnitude of the angular deformity which would lead to limitation of pronation/supination were calculated using analytic geometry. Each parameter of the models was obtained by the radiographic measurements of the normal forearms. RESULTS: When the axis of the pronation/supination passed through the interosseous region (less than 2 cm radioulnarly and 0.8 cm anteroposteriorly) in the model of the axial section without narrowing of the interosseous space, more than 40 degrees of pronation and supination were possible. When the axis deviated from this region, significant loss of pronation/supination was observed associated with restriction by the interosseous membrane rather than impingement. Furthermore, the area of this region decreased according to narrowing of the interosseous space with shortening of the interosseous membrane. In the three-dimensional model, the direction and magnitude of the angular deformity which would lead to significant loss of pronation/supination was more than 14 degrees radially, 7 degrees ulnarly, 5 degrees anteriorly, 4 degrees posteriorly. CONCLUSIONS: The positional relationship between the axis of pronation/supination and the forearm bones with the interosseous membrane may play an important role regarding pronation/supination of the forearm. RELEVANCE: Evaluation of the bone deformities based on understanding this mechanism of limitation of pronation/supination would lead to an appropriate treatment of malunion of the forearm bones.     

Geometrical adaptation in ulna and radius of cerebral palsy patients: Measures and consequences

Background

The presence of significant forearm bone torsion might affect planning and evaluating treatment regimes in cerebral palsy patients. We aimed to evaluate the influence of longstanding wrist flexion, ulnar deviation, and forearm pronation due to spasticity on the bone geometries of radius and ulna. Furthermore, we aimed to model the hypothetical influence of these deformities on potential maximal moment balance for forearm rotation.

Methods

Geometrical measures were determined in hemiplegic cerebral palsy patients (n = 5) and healthy controls (n = 5). Bilateral differences between the spastic arm and the unaffected side were compared to bilateral differences between the dominant and non-dominant side in the healthy controls. Hypothetical effects of bone torsion on potential maximal forearm rotation moment were calculated using an existing anatomical muscle model.

Findings

Patients showed significantly smaller (radius: 41.6%; ulna: 32.9%) and shorter (radius: 9.1%; ulna: 8.4%) forearm bones in the non-dominant arm than in the dominant arm compared to controls (radius: 2.4%; ulna 2.5% and radius: 1.5%; ulna: 1.0% respectively). Furthermore, patients showed a significantly higher torsion angle difference (radius: 24.1°; ulna: 26.2°) in both forearm bones between arms than controls (radius: 2.0°; ulna 1.0°). The model predicted an approximate decrease of 30% of potential maximal supination moment as a consequence of bone torsion.

Interpretation

Torsion in the bones of the spastic forearm is likely to influence potential maximal moment balance and thus forearm rotation function. In clinical practice, bone torsion should be considered when evaluating movement limitations especially in children with longstanding spasticity of the upper extremity.     

In-vivo kinematic analysis of forearm rotation using helical axis analysis

Background

Controversy still exists regarding the location and nature (static or dynamic) of the forearm joint axis. This might be due to inconsistent results from in-vitro data and less precise methods of analysis. We present the first in-vivo kinematic analysis of normal forearm joint rotation described by helical axis analysis.

Methods

Data obtained from computed tomography images of both forearms of five healthy volunteers was used to calculate finite helical axis parameters from transformation matrices. Four positions were analyzed: maximum pronation, maximum supination, 60° pronation, and 60° supination. Kinematic analysis focused on the motion of the radius around the ulna.

Findings

The forearm axis as defined by finite helical axis extended from the radial head between its kinematic center and the proximal radioulnar joint, to the dorsal region of the ulnar head at the distal radioulnar joint. The axis was found to be variable.

Interpretations

Helical axis analysis has precisely defined the nature and location of the forearm axis. This new information of forearm kinematics defined by finite helical analysis, may be useful in implant design, and in guiding surgeons in their reconstruction of instabilities of the distal and proximal radioulnar joint.     

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.     

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.     

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.     

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.     

桡骨骨折术后前臂旋转功能障碍的预防及康复

目的探讨桡骨骨折术后前臂旋转功能障碍的康复。方法报道桡骨骨折术后前臂旋转功能障碍的53例患者。结果术后随访2～7年。前臂的旋前/旋后分别由治疗前的平均23.47°/34.42°改善到治疗后的平均66.59°/78.56°（P<0.01）。病程<2个月的早期康复者,其旋转功能恢复程度比病程>2个月的晚期康复者疗效明显（P<0.01）。结论桡骨骨折术后要积极预防和康复前臂旋转功能障碍,且康复时间越早越好。     

Modulation of excitability in the cerebral cortex projecting to upper extremity muscles by rotational positioning of the forearm

The forearm rotation changes sensory inputs to the central nervous system, thereby providing orientation of the hand for grasping an object. Electrical activities of the muscles, induced by transcranial magnetic stimulation to the brain, i.e., motor evoked potentials (MEPs), are used for estimation of the excitability of motor neurons in the brain and spinal cord. It is well known that rotational positioning of the forearm influences MEPs of forearm muscles through modulation of excitability in the central nervous system. In the present study, we investigated whether such a posture-dependent change of MEPs could be found in upper arm and intrinsic hand muscles at three different rotational forearm positions: the most internal (pronation), neutral, and most external (supination) positions of rotation. MEPs were simultaneously recorded from the four muscles, biceps brachii (BB), triceps brachii (TB), abductor digiti minimi (ADM), and abductor pollicis brevis (AbPB). MEP amplitudes and latencies in BB, TB and ADM were significantly larger and shorter, respectively, in supination compared to the values in other positions. By contrast, MEP of AbPB in supination was lower in amplitude and longer in latency. Importantly, muscle lengths of TB, ADM and AbPB are constant in any rotational forearm positions, excluding the possibility of the muscle-length dependent change of spinal reflex. Therefore, these results might be attributable to the posture-dependent modulation of the motor cortex activity for the upper limb. The motor cortex probably changes the control strategy for the upper limb muscles in accordance with the sensory input from the forearm.     

The effect of torsional moments on the posterolateral rotatory stability of a lateral ligament deficient elbow: An in vitro biomechanical investigation

BackgroundClinical tests for posterolateral rotatory instability of the elbow apply external torsional moments to the forearm; however, biomechanical studies of lateral collateral ligament injuries and their surgical repair, reconstruction and rehabilitation have primarily relied on varus gravity loading to quantify instability.The aim of this investigation was to determine the effect of torsional moments on the posterolateral rotatory instability of the lateral ligament deficient elbow.MethodsSix cadaveric arms were tested in an elbow motion simulator with the arm in the varus position. A threaded outrigger was inserted on the dorsal aspect of the proximal ulna to suspend 400 g, 600 g, and 800 g of weight to allow torsional moments of 0.12, 0.18, and 0.23 Nm respectively on the ulna. An injured model was created by sectioning of the common extensor origin, and the lateral collateral ligament.FindingsDuring simulated active flexion with the arm in varus, the injured model resulted in a significant increase in external rotation of the ulnohumeral articulation with the forearm both pronated and supinated (pronation: P = .021; supination: P = .015). The application of torsional moments to the lateral ligament deficient elbow resulted in a significant increase in the posterolateral rotatory instability of the elbow.InterpretationThis investigation demonstrates that the application of even small amounts of external torsional moments on the forearm with the arm in the varus position increases the rotational instability of the lateral ligament deficient elbow. During clinical examination for posterolateral rotatory instability and biomechanical studies of lateral ligament injury, the application of external torsion to the forearm should be considered to detect subtle instability.Level of evidenceBasic Science Study.     

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.     

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.     

A wearable tremor-suppression orthosis

The Viscous Beam is a wearable tremor-suppression orthosis that applies viscous resistance to motion of the wrist in flexion and extension. The orthosis reduces tremor amplitude and is small enough to be worn under the sleeve of a shirt. Hand and forearm cuffs couple the damper to the user. The cuffs permit full thumb and finger motion, wrist flexion and extension, and forearm pronation and supination. Damping is provided by a constrained-layer-damping (CLD) system, distinct in that it can damp large rotary deflections through a small bending radius. A bending-plate transmission linearly converts wrist extension/flexion to rectilinear translation within the damper. Bending deformation of two plates held a fixed distance apart within the transmission results in relative displacement along the lengths of the plates. A viscous fluid incorporated between the plates provides shear damping. Silicone fluids with viscosities as high as 10 million centistokes (cS) and shear layers as thin as 0.76 mm have been tested. With these parameter values, damping constants as high as 2.0x10(-3) N-m/(degrees/s) have been measured. This testing was conducted with strain rates as high as 4,580 degrees/s. The elastic stiffness of this beam was measured to be 4.1x10(-2) N-m/degrees.     

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.     

Do flexion/extension postures affect the in vivo passive lumbar spine response to applied axial twist moments?

BACKGROUND: The injury potential and mechanical effects of combining axial rotation with non-neutral flexion/extension postures in vivo remains poorly understood, despite being identified as a risk factor in epidemiological and in vitro studies. The purpose of this experiment was to quantify the passive axial twist motion of the lumbar spine in various postures, and to assess whether non-neutral flexion/extension postures cause a detectable change in the range of twist motion and/or spine rotational stiffness. METHODS: Ten healthy male participants were passively rotated three times from a neutral and six flexed/extended starting postures (maximum-, mid-, mild-), while the moment-angle relationships were measured. The upper body was fixed to an adjustable rigid harness and the lower body was fixed to a cradle that rested on a frictionless table, thereby isolating the lumbar spine. FINDINGS: The lumbar spine stiffness and rotational range of motion were modulated by the different flexion/extension postures. The average maximum rotational stiffness values were smallest in maximum-flexion (81.0%, SD 16.6), and largest in maximum-/mid-extension postures at 125.4% (SD 24.4, P<0.0001) of the neutral stiffness magnitude. The axial twist angle was significantly different for each posture (P<0.0001), with 13.8% (SD 8.9) greater rotation in the maximum-flexion and 23.8% (SD 7.8) less rotation in the maximum-extension posture. The lateral bend coupled motion with axial twist was significantly different (P<0.0001) between the maximum-flexion (11.4 degrees , SD 6.3), mid-flexion/maximum-extension/mid-extension (6.5 degrees , SD 4.5), and mid-extension/mild-flexion/mild-extension postures (4.4 degrees , SD 3.8). INTERPRETATION: The lumbar spine stiffness and rotational range were modified by flexed-extended postures. The postural mechanism observed may be due to a change in the initial distance separating the facets prior to rotation. This information will be useful in determining spine rotational injury mechanisms through comparison with in vitro literature and for patient positioning during diagnostic tests.     

老年人桡骨远端骨折治疗后腕关节屈伸及旋转活动的Meta分析

背景：目前老年桡骨远端骨折是否需切开复位钢板内固定以恢复影像学上的解剖复位还存在争议。目的：对老年人桡骨远端骨折手术与非手术治疗的疗效进行系统评价。 方法：计算机检索 PubMed,Springer 以及万方等数据库,手工检索相关的中英文骨科杂志。收集所有对手术与非手术治疗老年人桡骨远端骨折疗效进行比较的文献。利用Cochrane协作网提供的RevMan5.0软件进行统计学分析。 结果与结论：共纳入符合标准的文献6篇,其中随机对照研究2篇,回顾性队列研究4篇。Meta分析结果显示：两组腕关节背伸活动度[MD=-0.87,95% CI（-3.31,1.58）, P=0.49],屈曲活动度[MD=-2.79,95%CI（-6.47,0.88）,P=0.14],旋前活动度[MD=-0.08,95%CI（-1.49,1.64）,P=0.92],旋后活动度[MD=-0.7,95%CI（-3.52,2.12）,P=0.63]以及并发症的发生[MD=1.35,95%CI（0.71,2.56）,P=0.36]差异均无显著性意义;手术组桡骨长度更接近于正常的解剖长度[MD=2.46,95% CI（1.78,3.15）,P 〈0.01];手术组尺倾角[MD=3.73,95%CI（2.97,4.48）,P〈0.00001]以及掌倾角[MD=6.81,95%CI（3.72,9.90）,P〈0.0001]更接近于正常的解剖角度。两组患肢腕关节屈伸,旋前旋后活动度以及并发症的发生差异均无显著性意义,而手术组解剖复位程度明显优于非手术组。     

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.