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.     

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.     

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.     

Biomechanical evaluation of a new reconstruction technique of the ulnar collateral ligament in the elbow with modified bone tunnel placement and interference screw fixation

Background

A new method for reconstruction of the anterior bundle of the ulnar collateral ligament using modified bone tunnel placement and interference screw fixation was developed to minimize operative dissection, improve graft tensioning, and reduce associated operative morbidities. The objective of this study was to compare varus–valgus laxity and failure properties of this new ulnar collateral ligament reconstruction to the intact ulnar collateral ligament.

Methods

Nine matched pairs of cadaveric upper extremities were used, the intact ulnar collateral ligament as the control for the load to failure properties and the contralateral arm for ulnar collateral ligament reconstruction. Varus–valgus laxity was measured at 30°, 50°, 70°, and 90° of elbow flexion for intact, ulnar collateral ligament transected, and ulnar collateral ligament reconstruction. Ulnar collateral ligament reconstruction was performed using a tendon graft passed through a bone tunnel and looped around the medial column of the humerus without dissection of the ulnar nerve. Distally, the graft was looped through a bone tunnel in the proximal ulna. Both ends were secured with interference screws. The specimens were loaded to failure at 50° of flexion at a rate of 30 deg/s. Repeated measures analysis of variance with a P value of 0.05 was used.

Findings

Elbow laxity significantly increased with ulnar collateral ligament transection. Following reconstruction, varus–valgus laxity at 30° and 50° of elbow flexion was completely restored to the intact state, only partially restored at 70°, and not changed at 90°. There was no significant difference between the yield and ultimate torques for the intact vs. reconstructed elbows. The angular displacement at yield and failure was significantly greater for the reconstructed elbows compared to the intact.

Interpretation

This reconstruction technique provides comparable strength to that of the native ligament. While stability was improved, failure occurred at greater angular displacement for the reconstructed limbs.     

The role of the brachialis muscle in elbow stability with collateral ligament injury: A biomechanical investigation

BackgroundThe brachialis muscle lies in close anatomic relation to the anterior capsule of the elbow joint. The contribution of the brachialis muscle to elbow stability has not yet been fully investigated. Therefore, the aim of this biomechanical in-vitro study was to analyze its influence on joint stability.MethodsNine fresh frozen cadaveric elbows were evaluated for stability against valgus and varus/posterolateral rotatory forces. Brachialis loading was measured indirectly using strain gauges. Three distinct scenarios were analyzed: A) with intact lateral ulnar and ulnar collateral ligaments B) with a ruptured lateral ulnar collateral ligament C) with ruptured lateral ulnar and ulnar collateral ligaments.FindingsIn all scenarios, an increased strain was observed under posterolateral rotatory/varus forces. The maximum measured strain occurred with elbow flexion of 30° and pronation of the forearm. The strain was significantly higher with dual-ligament rupture (mean - 210.5 μm/m; min. 97.8 μm/m; max. -310 μm/m; SD 107.8 μm/m; p = .034) compared to intact ligaments (mean − 106.9 μm/m; min. -32.51 μm/m, max. -287 μm/m; SD 100.2 μm/m) and single-ligament rupture (mean – 109.5 μm/m; min. - 96.7 μm/m; max - 130.4 μm/m; SD 18.2).InterpretationA strain of the brachialis muscle was observed under varus/posterolateral rotatory forces with a pronated forearm and the strain increased significantly in the event of a dual-ligament rupture. This suggests that the brachialis muscle may influence varus/posterolateral rotatory stability of the elbow. Hence, a concomitant tear of the brachialis muscle might result in pronounced instability following simple elbow dislocation.Level of evidenceBasic Science Study, Biomechanics.     

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.     

Stability of the unlinked Latitude total elbow prosthesis: A biomechanical in vitro analysis

BackgroundThe purpose of this study is to assess the valgus and varus laxity of the unlinked version of the Latitude total elbow prosthesis and the effects of radial head preservation or replacement.MethodsBiomechanical analysis of the valgus and varus laxity of the unlinked Latitude was performed in fourteen upper limb specimens in the following conditions: (1) native elbow, (2) native elbow after the surgical approach and closing all layers again, (3) elbow with humeral and ulnar component implanted, unlinked, with the native radial head preserved, (4) elbow with humeral and ulnar component implanted, unlinked, with the native radial excised, (5) elbow with humeral, ulnar, and radial head component implanted.FindingsAfter implantation of the Latitude total elbow prosthesis both the valgus and varus laxity slightly increase from mid to maximal flexion when compared to the native elbow after surgical approach. The unlinked Latitude total elbow prosthesis provides both valgus and varus stability in elbows with intact ligamentous constraints. With intact ligamentous constraints the radial head component only slightly contributes to the stability of the elbow after implantation of the unlinked Latitude total elbow prosthesis.InterpretationThe unlinked Latitude total elbow prosthesis provides both valgus and varus stability in elbows with intact ligamentous constraints. The radial head component contributes only slightly to the stability.     

Biomechanical comparison of lateral collateral ligament reconstruction with and without additional internal bracing using a three-dimensional elbow simulator

BackgroundAlthough an additional internal bracing significantly increases stability in a repair of the lateral ulnar collateral ligament, it remains unclear whether it also does in reconstruction. Aim of this study was to implement a three-dimensional elbow simulator for testing posterolateral rotatory instability. We hypothesized that (1) reconstruction with and without internal bracing is comparable in biomechanical properties, and (2) there would be higher load-to-failure with internal bracing.MethodsPosterolateral rotatory instability was tested by imitating the lateral pivot shift test in 16 elbows. Valgus and supination torques were simultaneously increased stepwise up to 1.2 Nm. Specimens were tested at 30°, 60°, 90°, and 120° elbow flexion with an intact lateral collateral ligament complex, dissected complex, and after reconstruction with or without internal bracing. Outcome measures included joint gapping, laxity, and load to failure.FindingsWith the implemented elbow simulator no significant difference was observed for gapping or laxity between both treatment groups. Comparing treatment and native ligament, gapping was reduced, especially with increased elbow flexion. Laxity was also reduced at some flexion angles. The mean load-to-failure was 8.1 ± 2.7 Nm without and 9.6 ± 3.6 Nm with internal bracing (P = 0.645).InterpretationBoth treatments were comparable in biomechanical properties but did not fully restore the native state. Although the additional augmentation of the LUCL reconstruction tends to increase the maximum load to failure, this difference was not statistically significant. Still, reconstruction with internal bracing seems to be a reasonable option in selected primary reconstructions. It could also be useful in revision reconstruction.     

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.     

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.     

内侧副韧带加强重建后桡骨小头切除治疗青年肘关节恐怖三联征患者疗效观察

目的报告应用侧副韧带修补重建并桡骨小头切除手术方式治疗青年肘关节恐怖三联征、桡骨小头粉碎骨折患者的疗效观察。方法自2005年11月至2009年10月,本院共收治肘关节三联征损伤3例。桡骨小头骨折按Mason法分类均为Ⅲ型。3例患者均行冠状突固定、肘内外侧副韧带、关节囊修补、内侧副韧带加强、重建并桡骨小头切除术,术后克氏针辅助固定肱尺关节于屈肘90°前臂旋转中立位,石膏固定3周,然后拔除克氏针,去除石膏,开始屈伸和旋转康复训练。结果3例患者均随访1年以上,骨折愈合,按照Broberg和Morrey的肘关节功能评分2例为良,1例为可。结论肘关节恐怖三联征伴有桡骨小头粉碎骨折的青年患者,韧带及关节囊的重建异常重要,桡骨小头置换应当审慎,在确保韧带重建满意的情况下切除桡骨小头并未造成肘关节明显功能障碍。     

Collateral ligament strains during knee joint laxity evaluation before and after TKA

Background

Passive knee stability is provided by the soft tissue envelope. There is consensus among orthopedic surgeons that good outcome in Total Knee Arthroplasty requires equal tension in the medial/lateral compartment of the knee joint, as well as equal tension in the flexion/extension gap. The purpose of this study was to quantify the ligament laxity in the normal non-arthritic knee before and after Posterior-Stabilized Total Knee Arthroplasty. We hypothesized that the Medial/Lateral Collateral Ligament shows minimal changes in length when measured directly by extensometers in the native human knee during varus/valgus laxity testing. We also hypothesized that due to differences in material properties and surface geometry, native laxity is difficult to reconstruct using a Posterior-Stabilized Total Knee.

Methods

Six specimens were used to perform this in vitro cadaver test using extensometers to provide numerical values for laxity and varus–valgus tilting in the frontal plane.

Findings

This study enabled a precise measurement of varus–valgus laxity as compared with the clinical assessment. The strains in both ligaments in the replaced knee were different from those in the native knee. Both ligaments were stretched in extension, in flexion the Medial Collateral Ligament tends to relax and the Lateral Collateral Ligament remains tight.

Interpretation

As material properties and surface geometry of the replaced knee add stiffness to the joint, we recommend to avoid overstuffing the joint, when using this type of Posterior-Stabilized Total Knee Arthroplasty, in order to obtain varus/valgus laxity close to the native joint.     

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.     

Elbow load during pushup at various forearm rotations

OBJECTIVE: Elbow joint loading was evaluated during pushup exercises at various forearm rotations. DESIGN: Subjects were asked to perform pushup in various forearm rotations: neutral, 90 degrees internal rotation, and 90 degrees external rotation. BACKGROUND: Training with pushup exercise is good for the muscles and joints of the upper extremities. However, excessive shear forces on the elbow might lead to injuries to either normal trainees or to handicapped people, especially for those who rely on elbow prosthesis. METHODS: The kinematics and kinetics of the elbow joint were investigated under various forearm rotations. RESULTS: The loading biomechanics of the elbow joint differed with various forearm rotations. It was noted that greater posterior and varus forces of the elbow are encountered with internal rotation of the hand position and, consequently, full forearm pronation. CONCLUSIONS: Pushup with hands in internally rotated position should be prevented so as to avoid excessive shear forces or moments. RELEVANCE: Knowledge of elbow kinematics and kinetics may be helpful in preventing injuries by reducing the elbow shear force with changes of forearm rotation.     

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.     

Anatomie des hinteren Kreuzbandes sowie der posterolateralen und posteromedialen Strukturen

The posterior cruciate ligament (PCL) is the strongest ligament of the human knee joint and the primary restraint against posterior tibial translation. It originates at the lateral wall of the medial femoral condyle and inserts into the posterior aspect of the tibial eminence approximately 10 mm below the joint surface. The quadriceps muscle is the functional agonist for the PCL, whereas the hamstrings act as an antagonist pulling the tibia back in 90° of flexion. There are two functional bundles: the strong anterolateral bundle which tightens in flexion and a thin posteromedial bundle which becomes tense in maximal flexion and in extension. The AL bundle originates in the superior aspect of the femoral PCL origin. Under arthroscopic visualization in 90° of flexion the PM bundle originates in the inferior aspect of the PCL origin. When the knee is extended the PM origin rotates backwards. The PM bundle inserts into the posterior aspect of the tibial insertion. The AL bundle inserts into the anterior aspect of the tibial insertion. When creating a tunnel for a PCL reconstruction one should be aware of the proximity of the nerves and vessels within the fossa poplitea. The PCL forms a functional unit with the posteromedial and posterolateral structures. The posteromedial structures are the medial collateral ligament, the posteromedial capsule with its muscular insertions (m. semimembranosus and m. gastrocnemius). The most important structures of the posterolateral corner are the fibular collateral ligament, the lateral m. gastrocnemius, the oblique popliteal ligament, the arcuate popliteal ligament, the popliteofibular ligament, and the tendon of the m. popliteus. The popliteofibular ligament has an important role for the passive stabilization against rotation. It is highly recommended that concomitant injuries of these structures be addressed when treating PCL injuries.     

Electromyographic study of the elbow flexors and extensors in a motion of forearm pronation/supination while maintaining elbow flexion in humans.

Activities of the elbow flexors (biceps brachii, BB; brachialis, B; brachioradialis, BR) and extensors (triceps brachii, TB) in a motion of forearm pronation/supination with maintenance of elbow flexion (PS-movement) in nine healthy human subjects were studied by electromyography (EMG). The subject performed the PS-movement slowly or quickly with or without a load extending the elbow. In the slow PS-movement, an increase and decrease of EMG activities during supination and pronation, respectively, were seen in BB and the reverse was in B. A clear increment of EMG activities in BB accompanied with a reduction of EMG activities in B and/or BR, and the reverse were often observed. The contraction level and gain with the forearm supine were higher and larger than those with the forearm prone, respectively, in BB and the reverse was in B and BR. In a series of the quick PS-movement, alternating increases of EMG activities between BB and the other flexors (B and BR) were seen. Since TB showed no EMG activities throughout the experiment, it is suggested that reciprocal contractions between BB and the other flexors, which produce a complementary force in flexion direction, enable motions of pronation/supination with maintenance of flexion. Contraction properties of the flexors were discussed.     

Influence of a mono-centric knee brace on the tension of the collateral ligaments in knee joints after sectioning of the anterior cruciate ligament--an in vitro study

OBJECTIVE: To analyze the influence of knee bracing on the tension of the medial and lateral collateral ligaments in anterior cruciate ligament deficiency. DESIGN: The tension of the collateral ligaments in anterior cruciate ligament deficient knees was measured with and without knee bracing using an in vitro model. BACKGROUND: Anterior cruciate ligament deficiency increases the tension in both collateral ligaments at the knee joint. Therefore knee braces should reduce that tension increase. However, that effect has never been proven quantitatively. METHODS: After anterior cruciate ligament-transection, the forces of the medial (anterior/posterior part) and lateral collateral ligament were measured in ten fresh human cadaver knees at 0 degrees, 20 degrees, 40 degrees, 60 degrees, 80 degrees and 100 degrees of flexion, with and without application of a mono-centric knee brace. To quantify the ligament forces, strain gauges were fixed at the bony origins of the ligaments. RESULTS: Bracing led to a significant decrease of ligament forces (20-100 degrees: P < 0.0001) in the anterior part of the medial collateral ligament in all joint positions. In the posterior aspect, this effect was observed only at 40 degrees (P < 0.0001) and 80 degrees (P = 0.001) of flexion. In the lateral collateral ligament, bracing caused a strain reduction from 60 degrees to 100 degrees of flexion (P < 0.0001). Therefore a flexion angle dependent effect of knee bracing on the strain was seen in the posterior aspect of the medial and in the lateral collateral ligament in anterior cruciate ligament deficient knee joints. CONCLUSIONS: Application of a mono-centric knee brace leads to a significant position dependent reduction of collateral ligament tension after anterior cruciate ligament-rupture.     

Biomechanik des hinteren Kreuzbandes und der hinteren Instabilität

The posterior cruciate ligament (PCL) is the primary restraint to posterior tibial translation. The different fibers of the PCL do not act isometrically. Indeed, the anterolateral bundle (AL) is tense in 90° of flexion, whereas the posteromedial bundle (PM) is tense in extension and in deep flexion angles beyond 120° of knee flexion. A functional agonist of the PCL is the quadriceps muscle. The ischiocrural muscles act as antagonists by pulling the tibia backwards in knee flexion. The PCL is supported by the posteromedial and posterolateral extra-articular structures. Posterolaterally, the lateral collateral ligament (LCL) is a restraint to varus forces. The popliteus muscle, in its function as an active internal rotator, supports the rotational stability of the knee. The most important passive stabilizer to external rotation is the popliteofibular ligament. Due to its isometric behavior, this ligament is a restraint to external rotation in different flexion angles. A deficiency of the posterolateral corner leads even in a straight axis to a functional varus deformity of the knee due to the lateral instability. This may be a reason for the high incidence of degenerative changes in the medial compartment. The posteromedial structures are restraints to the posterior tibial translation.