External rotation stress imaging in syndesmotic injuries of the ankle: comparison of lateral radiography and radiostereometry in a cadaveric model

We compared the value of 7.5 Nm external rotation stress in diagnosing tibiofibular syndesmotic injuries of the ankle on lateral radiographs with radiostereometric analysis (RSA) in 10 cadaveric legs. After sectioning 2 ligaments, RSA showed an increase in posterior translation and external rotation of the fibula. This increase in posterior translation was smaller than the posterior displacement of the fibula on the lateral radiograph, and RSA showed mainly an increase in external rotation of the fibula that can not be measured on conventional radiographs. We conclude that instability of the syndesmosis in cadaveric ankles can be detected with 7.5 Nm external rotation stress RSA, but that external rotation stress lateral radiography is unreliable.     

Kinematics of the distal tibiofibular syndesmosis

In 11 healthy volunteers, the normal kinematics of the tibiofibular syndesmosis of the ankle during weight bearing and external rotation stress were compared to a nonweight-bearing neutral position by radiostereometry. We found very small rotations and displacements in this “normal” group, which indicated that the fibula is closely attached to the tibia, thereby preventing larger movements at the level of the ankle. We found no common kinematic pattern during weight bearing in the neutral position.

Application of a 7.5 Nm external rotation moment on the foot caused external rotation of the fibula between 2 and 5 degrees, medial translation between 0 and 2.5 mm and posterior displacement between 1.0 and 3.1 mm. These data can be used as normal reference values for studies of patients with suspected syndesmotic injuries.     

Kinematics of the distal tibiofibular syndesmosis

In 11 healthy volunteers, the normal kinematics of the tibiofibular syndesmosis of the ankle during weight bearing and external rotation stress were compared to a nonweight-bearing neutral position by radiostereometry. We found very small rotations and displacements in this “normal” group, which indicated that the fibula is closely attached to the tibia, thereby preventing larger movements at the level of the ankle. We found no common kinematic pattern during weight bearing in the neutral position.

Application of a 7.5 Nm external rotation moment on the foot caused external rotation of the fibula between 2 and 5 degrees, medial translation between 0 and 2.5 mm and posterior displacement between 1.0 and 3.1 mm. These data can be used as normal reference values for studies of patients with suspected syndesmotic injuries.     

Kinematics of the distal tibiofibular syndesmosis: radiostereometry in 11 normal ankles

In 11 healthy volunteers, the normal kinematics of the tibiofibular syndesmosis of the ankle during weight bearing and external rotation stress were compared to a nonweight-bearing neutral position by radiostereometry. We found very small rotations and displacements in this "normal" group, which indicated that the fibula is closely attached to the tibia, thereby preventing larger movements at the level of the ankle. We found no common kinematic pattern during weight bearing in the neutral position. Application of a 75 Nm external rotation moment on the foot caused external rotation of the fibula between 2 and 5 degrees, medial translation between 0 and 2.5 mm and posterior displacement between 1.0 and 3.1 mm. These data can be used as normal reference values for studies of patients with suspected syndesmotic injuries.     

Effects of ligament sectioning on the kinematics of the distal tibiofibular syndesmosis: a radiostereometric study of 10 cadaveric specimens based on presumed trauma mechanisms with suggestions for treatment

BACKGROUND: Syndesmotic injuries of the ankle without fractures can result from external rotation, abduction and dorsiflexion injuries. Kinematic studies of these trauma mechanisms have not been performed. We attempted to describe the kinematics of the tibiofibular joint in cadaveric specimens using radiostereometry after sequential ligament sectioning, and resulting from different trauma mechanisms and axial loading, in order to put forward treatment guidelines for the different types of syndesmotic injuries. METHODS: We assessed the kinematics of the distal tibiofibular joint in fresh-frozen cadaveric specimens using radiostereometry in the intact situation, and after alternating and sequential sectioning of the distal tibiofibular and anterior deltoid ligaments. To assess which of the known trauma mechanisms would create the largest displacements at the syndesmosis, the ankle was brought into the following positions under an axial load that was comparable to body weight (750 N): neutral, dorsiflexion, external rotation, abduction, and a combination of external rotation and abduction. RESULTS: In the neutral position, the largest displacements of the fibula consisted of external rotation and posterior translation. Loading of the ankle with 750 N did not apparently increase or decrease the displacements of the fibula, but gave a larger variety of displacements. In every position, sectioning of a ligament resulted in some fibular displacement. Sectioning of the anterior tibiofibular ligament (ATiFL) invariably resulted in external rotation of the fibula. Additional sectioning of the anterior part of the deltoid ligament (AD) gave a larger variety of displacements. In general, sectioning of the posterior tibiofibular ligament (PTiFL) gave the smallest displacements. Combined sectioning of the ATiFL and the PTiFL resulted in a larger variety of displacements in the neutral position. Sectioning of the AD together with the ATiFL and PTiFL resulted in tibiofibular displacements in the neutral situation exceeding the maximum values found in the intact situation, the most important being fibular external rotation. INTERPRETATION: Sectioning of the ATiFL results in mechanical instability of the syndesmosis. Of all trauma mechanisms, external rotation of the ankle resulted in the largest and most consistent displacements of the fibula relative to the tibia found at the syndesmosis. Based on our findings and the current literature, we recommend that patients with isolated PTiFL or AD injuries should be treated functionally when no other injuries are present. Patients with acute complete ATiFL ruptures, or combined ATiFL and AD ruptures should be treated with immobilization in a plaster. Patients with combined ruptures of the ATiFL, AD and PTiFL need to be treated with a syndesmotic screw.     

Biomechanical Analysis of Tibiofibular Syndesmosis Injury Fixation Methods: A Finite Element Analysis

The optimal treatment strategy after syndesmotic injuries is still controversial. In our study, we aimed to evaluate ideal fixation method in syndesmotic injury by using finite element analysis method. A 3D SolidWorks model file was created by taking computed tomography (CT) images of the area from the right foot base to the knee joint level of a healthy adult male. The intact model, injury model, and 8 different fixation models were created that 3.5 mm screw and suture-button were used in. The models were compared in terms of lateral fibular translation, posterior fibular translation and external rotation of fibula compared to tibia and stress values occurred on screws and suture-buttons. In the hybrid-1 model, lateral fibular translation and external fibular rotation values were obtained as close to the intact model. Von Mises stresses occurred in the screw (435.7 MPa) and suture-button (424.7 MPa) that used in hybrid-1 model was more than single screw at 4 cm model (316.8 MPa) and single suture-button at 2 cm model (160.7 MPa). In the Hybrid-1 model, the screw compensates for posterior fibular translation and external fibular rotation, while the suture-button compensates for lateral fibular translation. Also, the effect of the distal suture-button preventing diastasis in case of proximal screw failure, it was concluded that the hybrid-1 model can be used as a good treatment alternative in the surgical treatment of distal tibiofibular syndesmotic injuries.     

Effects of ligament sectioning on the kinematics of the distal tibiofibular syndesmosis: A radiostereometric study of 10 cadaveric specimens based on presumed trauma mechanisms with suggestions for treatment

Background?Syndesmotic injuries of the ankle without fractures can result from external rotation, abduction and dorsiflexion injuries. Kinematic studies of these trauma mechanisms have not been performed. We attempted to describe the kinematics of the tibiofibular joint in cadaveric specimens using radiostereometry after sequential ligament sectioning, and resulting from different trauma mechanisms and axial loading, in order to put forward treatment guidelines for the different types of syndesmotic injuries.

Methods?We assessed the kinematics of the distal tibiofibular joint in fresh–frozen cadaveric specimens using radiostereometry in the intact situation, and after alternating and sequential sectioning of the distal tibiofibular and anterior deltoid ligaments. To assess which of the known trauma mechanisms would create the largest displacements at the syndesmosis, the ankle was brought into the following positions under an axial load that was comparable to body weight (750?N): neutral, dorsiflexion, external rotation, abduction, and a combination of external rotation and abduction.

Results?In the neutral position, the largest displacements of the fibula consisted of external rotation and posterior translation. Loading of the ankle with 750?N did not apparently increase or decrease the displacements of the fibula, but gave a larger variety of displacements.

In every position, sectioning of a ligament resulted in some fibular displacement. Sectioning of the anterior tibiofibular ligament (ATiFL) invariably resulted in external rotation of the fibula. Additional sectioning of the anterior part of the deltoid ligament (AD) gave a larger variety of displacements. In general, sectioning of the posterior tibiofibular ligament (PTiFL) gave the smallest displacements. Combined sectioning of the ATiFL and the PTiFL resulted in a larger variety of displacements in the neutral position. Sectioning of the AD together with the ATiFL and PTiFL resulted in tibiofibular displacements in the neutral situation exceeding the maximum values found in the intact situation, the most important being fibular external rotation.

Interpretation?Sectioning of the ATiFL results in mechanical instability of the syndesmosis. Of all trauma mechanisms, external rotation of the ankle resulted in the largest and most consistent displacements of the fibula relative to the tibia found at the syndesmosis. Based on our findings and the current literature, we recommend that patients with isolated PTiFL or AD injuries should be treated functionally when no other injuries are present. Patients with acute complete ATiFL ruptures, or combined ATiFL and AD ruptures should be treated with immobilization in a plaster. Patients with combined ruptures of the ATiFL, AD and PTiFL need to be treated with a syndesmotic screw.     

Ankle joint contact loads and displacement in syndesmosis injuries repaired with Tightropes compared to screw fixation in a static model

BackgroundThe effect of syndesmotic fixation on restoration of pressure mechanics in the setting of a syndesmotic injury is largely unknown. The purpose of this study is to examine the contact mechanics of the tibiotalar joint following syndesmosis fixation with screws versus a flexible fixation device for complete syndesmotic injury.MethodsSix matched pairs of cadaveric below knee specimens were dissected and motion capture trackers were fixed to the tibia, fibula, and talus and a pressure sensor was placed in the tibiotalar joint. Each specimen was first tested intact with axial compressive load followed by external rotation while maintaining axial compression. Next, syndesmotic ligaments were sectioned and randomly assigned to repair with either two TightRopes® or two 3.5 mm cortical screws and the protocol was repeated. Mean contact pressure, peak pressure, reduction in contact area, translation of the center of pressure, and relative talar and fibular motion were calculated. Specimens were then cyclically loaded in external rotation and surviving specimens were loaded in external rotation to failure.ResultsNo differences in pressure measurements were observed between the intact and instrumented states during axial load. Mean contact presure relative to intact testing was increased in the screw group at 5 Nm and 7.5 Nm torque. Likewise, peak pressure was increased in the TightRope group at 7.5 Nm torque. There was no change in center of pressure in the TightRope group at any threshold; however, at every threshold tested there was significant medial and anterior translation in the screw group relative to the intact state.ConclusionEither screws or TightRope fixation is adequate with AL alone. With lower amounts of torque, the TightRope group appears to have contact and pressure mechanics that more closely match native mechanics.     

Does Humeral Component Lateralization in Reverse Shoulder Arthroplasty Affect Rotator Cuff Torque? Evaluation in a Cadaver Model

Background

Humeral component lateralization in reverse total shoulder arthroplasty (RTSA) may improve the biomechanical advantage of the rotator cuff, which could improve the torque generated by the rotator cuff and increase internal and external rotation of the shoulder.

Purpose

The purpose of this in vitro biomechanical study was to evaluate the effect of humeral component lateralization (or lateral offset) on the torque of the anterior and posterior rotator cuff.

Methods

Eight fresh-frozen cadaveric shoulders from eight separate donors (74 ± 8 years; six males, two females) were tested using an in vitro simulator. All shoulders were prescreened for soft tissue deficit and/or deformity before testing. A custom RTSA prosthesis was implanted that allowed five levels of humeral component lateralization (15, 20, 25, 30, 35 mm), which avoided restrictions imposed by commercially available designs. The torques exerted by the anterior and posterior rotator cuff were measured three times and then averaged for varying humeral lateralization, abduction angle (0°, 45°, 90°), and internal and external rotation (−60°, −30°, 0°, 30°, 60°). A three-way repeated measures ANOVA (abduction angle, humeral lateralization, internal rotation and external rotation angles) with a significance level of α = 0.05 was used for statistical analysis.

Results

Humeral lateralization only affected posterior rotator cuff torque at 0° abduction, where increasing humeral lateralization from 15 to 35 mm at 60° internal rotation decreased external rotation torque by 1.6 ± 0.4 Nm (95% CI, −0.07 −1.56 Nm; p = 0.06) from 4.0 ± 0.3 Nm to 2.4 ± 0.6 Nm, respectively, but at 60° external rotation increased external rotation torque by 2.2 ± 0.5 Nm (95% CI, −4.2 to −0.2 Nm; p = 0.029) from 6.2 ± 0.5 Nm to 8.3 ± 0.5 Nm, respectively. Anterior cuff torque was affected by humeral lateralization in more arm positions than the posterior cuff, where increasing humeral lateralization from 15 to 35 mm when at 60° internal rotation increased internal rotation torque at 0°, 45°, and 90° abduction by 3.2 ± 0.5 Nm (95% CI, 1.1–5.2 Nm; p = 0.004) from 6.6 ± 0.6 Nm to 9.7 ± 0.6 Nm, 4.0 ± 0.3 Nm (95% CI, 2.8-5.0 Nm; p < 0.001) from 1.7 ± 1.0 Nm to 5.6 ± 0.9 Nm, and 2.2 ± 0.2 Nm (95% CI, 1.4–2.9 Nm; p < 0.001) from 0.6 ± 0.6 Nm to 2.8 ± 0.6 Nm, respectively. In neutral internal and external rotation, increasing humeral lateral offset from 15 to 35 mm increased the internal rotation torque at 45˚ and 90˚ abduction by 1.5 ± 0.3 Nm (95% CI, 0.2–2.7 Nm; p = 0.02) and 1.3 ± 0.2 Nm (95% CI, 0.4–2.3 Nm; p < 0.001), respectively.

Conclusions

Humeral component lateralization improves rotator cuff torque.

Clinical Relevance

The results of this preliminary in vitro cadaveric study suggest that the lateral offset of the RTSA humeral component plays an important role in the torque generated by the anterior and posterior rotator cuff. However, further studies are needed before clinical application of these results. Increasing humeral offset may have adverse effects, such as the increased risk of implant modularity, increasing tension of the cuff and soft tissues, increased costs often associated with design modifications, and other possible as yet unforeseen negative consequences.

     

Two-View Gravity Stress Imaging Protocol for Nondisplaced Type II Supination External Rotation Ankle Fractures: Introducing the Gravity Stress Cross-Table Lateral View

Assessing ankle stability in nondisplaced Lauge-Hansen supination external rotation type II injuries requires stress imaging. Gravity stress mortise imaging is routinely used as an alternative to manual stress imaging to assess deltoid integrity with the goal of differentiating type II from type IV injuries in cases without a posterior or medial fracture. A type II injury with a nondisplaced fibula fracture is typically treated with cast immobilization, and a type IV injury is considered unstable and often requires operative repair. The present case series (two patients) highlights a standardized 2-view gravity stress imaging protocol and introduces the gravity stress cross-table lateral view. The gravity stress cross-table lateral view provides a more thorough evaluation of the posterior malleolus owing to the slight external rotation and posteriorly directed stress. External rotation also creates less bony overlap between the tibia and fibula, allowing for better visualization of the fibula fracture. Gravity stress imaging confirmed medial-sided injury in both cases, confirming the presence of supination external rotation type IV or bimalleolar equivalent fractures. Open reduction and internal fixation was performed, and both patients achieved radiographic union. No further treatment was required at 21 and 33 months postoperatively.     

Micromotion of the Souter-Strathclyde total elbow prosthesis in patients with rheumatoid arthritis

21 elbows in 18 patients with rheumatoid arthritis were treated with a Souter-Strathclyde total elbow prosthesis. 18 elbows were included in a radiostereometry (RSA) study. The aim of this clinical RSA study was to assess the three-dimensional micromotion pattern of the Souter-Strathclyde prosthesis, and thereby gain insight in the aseptic loosening process of this prosthesis. Implants were defined as at risk of aseptic loosening when the translation rate during the second postoperative year was more than 0.4 mm along one or more coordinate axes and/or the rate of rotation was more than 1° about one or more coordinate axes. Clinical examination revealed an increase in the range of motion and a marked reduction in pain. The RSA showed that 8 of 18 humeral components were at risk of aseptic loosening, although no signs of such loosening - defined as a complete radiolucent line of 2 mm or more - were found on the plain radiographs. In 7 humeral components, an anterior tilt about the transverse axis was seen that resulted in an anterior translation of the proximal tip and a posterior translation of the component's trochlea. Long-term studies of the Souter-Strathclyde prosthesis, have shown that this rotation is a specific pattern of failure in some implants. None of the ulnar components was at risk for aseptic loosening. Improvements in fixation of the Souter-Strathclyde total elbow arthroplasty should focus on the humeral component. At present, the lateral flange of the implant is enlarged to improve rotational stability about the transverse and longitudinal axes. The effect of this change in design on micromotion of the Souter-Strathclyde total elbow prosthesis will be studied in a randomized RSA study comparing the new design to the existing one.     

Micromotion of the Souter-Strathclyde total elbow prosthesis in patients with rheumatoid arthritis 21 elbows followed for 2 years

21 elbows in 18 patients with rheumatoid arthritis were treated with a Souter-Strathclyde total elbow prosthesis. 18 elbows were included in a radiostereometry (RSA) study. The aim of this clinical RSA study was to assess the three-dimensional micromotion pattern of the Souter-Strathclyde prosthesis, and thereby gain insight in the aseptic loosening process of this prosthesis. Implants were defined as at risk of aseptic loosening when the translation rate during the second postoperative year was more than 0.4 mm along one or more coordinate axes and/or the rate of rotation was more than 1 degrees about one or more coordinate axes. Clinical examination revealed an increase in the range of motion and a marked reduction in pain. The RSA showed that 8 of 18 humeral components were at risk of aseptic loosening, although no signs of such loosening-defined as a complete radiolucent line of 2 mm or more-were found on the plain radiographs. In 7 humeral components, an anterior tilt about the transverse axis was seen that resulted in an anterior translation of the proximal tip and a posterior translation of the component's trochlea. Long-term studies of the Souter-Strathclyde prosthesis, have shown that this rotation is a specific pattern of failure in some implants. None of the ulnar components was at risk for aseptic loosening. Improvements in fixation of the Souter-Strathclyde total elbow arthroplasty should focus on the humeral component. At present, the lateral flange of the implant is enlarged to improve rotational stability about the transverse and longitudinal axes. The effect of this change in design on micromotion of the Souter-Strathclyde total elbow prosthesis will be studied in a randomized RSA study comparing the new design to the existing one.     

The effect of tibiofemoral joint kinematics on patellofemoral contact pressures under simulated muscle loads.

Altered patellofemoral joint contact pressures are thought to contribute to patellofemoral joint symptoms. However, little is known about the relationship between tibiofemoral joint kinematics and patellofemoral joint contact pressures. The objective of this paper was to investigate the effect of tibiofemoral joint kinematics on patellofemoral joint pressures using an established in vitro robotic testing experimental setup. Eight cadaveric knee specimens were tested at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Tibiofemoral joint kinematics were measured by the robot and contact pressures by a TekScan pressure sensor. The isolated quadriceps loading caused anterior translation and internal rotation of the tibia up to 60 degrees of flexion and posterior translation and external rotation of the tibia beyond 60 degrees. The co-contraction of the hamstring muscles caused a posterior translation and external rotation of the tibia relative to the motion of the tibia under the quadriceps load. Correspondingly, the contact pressures were elevated significantly at all flexion angles. For example, at 60 degrees of flexion, the hamstrings co-contraction increased the posterior tibial translation by approximately 2.8 mm and external tibial rotation by approximately 3.6 degrees. The peak contact pressure increased from 1.4+/-0.8 to 1.7+/-1.0 MPa, a 15% increase. The elevated contact pressures after hamstrings co-contraction indicates an intrinsic relation between the tibiofemoral joint kinematics and the patellofemoral joint biomechanics. An increase in posterior tibial translation and external rotation is accompanied by an increase in contact pressure in the patellofemoral joint. These results imply that excessive strength conditioning with the hamstring muscles might not be beneficial to the patellofemoral joint. Knee pathology that causes an increase in tibial posterior translation and external rotation might contribute to degeneration of the patellofemoral joint. These results suggest that conservative treatment of posterior cruciate ligament injury should be reconsidered.     

A biomechanical evaluation of clinical stress tests for syndesmotic ankle instability

Displacement transducers were placed across the anterior and posterior tibiofibular ligaments of 17 fresh cadaver (78.4 +/- 6.7 years old at death) lower extremities. Displacements induced by various clinical tests (squeeze, fibula translation, Cotton, external rotation, and anterior drawer) were measured with the ankle ligaments intact and after sequential sectioning of the anterior tibiofibular ligament, anterior deltoid ligament, and posterior tibiofibular ligament. None of the syndesmotic stress tests could distinguish which ligaments were sectioned. Furthermore, the small displacements measured during the stress tests (with the exception of the external rotation test) suggest it is unlikely that the displacement induced in injured syndesmoses can be clinically differentiated from normal syndesmoses. Therefore, pain, rather than increased displacement, should be considered the outcome measure of these tests.     

S-Type Posterolateral Approach for Open Reduction and Internal Fixation of Pronation External Rotation Ankle Fractures: Improved Visualisation of the Posterior Joint and the Lateral Malleolus

Pronation external rotation (PER) fractures are unstable ankle fractures that require anatomically stable fixation. However, due to the long distance between the fibula and the posterior malleolus in PER IV, existing approaches may make it difficult for the fixation of the associated posterior joint and the lateral malleolus. We describe an S-type posterolateral approach for the open reduction and internal fixation of posterior malleolar fractures with an associated lateral malleolar fracture in PER IV.     

The effects of weight bearing on the distal tibiofibular syndesmosis: A study comparing weight bearing-CT with conventional CT

BackgroundSyndesmotic injures are common and weight bearing imaging studies are often advocated to assess disruption. Although studies have examined the anatomical relationship between the fibula and incisura, the effect of weight-bearing on the syndesmosis has not been well reported. We characterise the changes which occur at the syndesmosis during weight-bearing.MethodsIn this retrospective review we analysed the position of the fibula at the syndesmosis in a cohort of patients who underwent both non-weight-bearing and weight-bearing CT scans. The relative position of the fibula to the incisura was analysed to determine translation and rotation in the axial plane.Results26 patients were included. Comparison of measurements revealed statistically significant differences between groups which indicated that on weight-bearing the fibula translated laterally and posteriorly, and rotated externally with respect to the incisura.ConclusionsThis is the first study to measure the differences in position of the syndesmosis during weight-bearing in a population of patients that have undergone both weight bearing and non weight bearing CT. Our study confirms that weight-bearing results in lateral and posterior translation, and external rotation of the fibula in relation to the incisura and our findings should help in future studies looking at the effect of weight bearing on syndesmotic pathology.     

Clinical diagnosis of syndesmotic ankle instability: evaluation of stress tests behind the curtains

We studied the feasibility of clinical tests in the diagnosis of syndesmotic injury of the ankle. 9 investigators examined 12 persons twice, including 2 patients with an arthroscopically-confirmed syndesmotic injury. They sat behind a curtain that exposed only the lower legs. We found a statistically significant relation between the final arthroscopic diagnosis and the squeeze, fibula translation, Cotton, and external rotation tests as well as for limited dorsal flexion. None of the syndesmotic tests was uniformly positive in chronic syndesmotic injury. The external rotation test had the fewest false-positive results, the fibula translation test the most. The external rotation test had the smallest inter-observer variance. The physical diagnosis was missed in one fifth of all examinations. When in accordance with medical history and physical examination, positive stress tests should raise a high index of suspicion of syndesmotic instability. The final diagnosis of such instability, however, should be made by additional diagnostic imaging and/or arthroscopy.     

Clinical diagnosis of syndesmotic ankle instability: Evaluation of stress tests behind the curtains

We studied the feasibility of clinical tests in the diagnosis of syndesmotic injury of the ankle. 9 investigators examined 12 persons twice, including 2 patients with an arthroscopically-confirmed syndesmotic injury. They sat behind a curtain that exposed only the lower legs. We found a statistically significant relation between the final arthroscopic diagnosis and the squeeze, fibula translation, Cotton, and external rotation tests as well as for limited dorsal flexion. None of the syndesmotic tests was uniformly positive in chronic syndesmotic injury. The external rotation test had the fewest false-positive results, the fibula translation test the most. The external rotation test had the smallest inter-observer variance. The physical diagnosis was missed in one fifth of all examinations. When in accordance with medical history and physical examination, positive stress tests should raise a high index of suspicion of syndesmotic instability. The final diagnosis of such instability, however, should be made by additional diagnostic imaging and/or arthroscopy.     

Clinical diagnosis of syndesmotic ankle instability

We studied the feasibility of clinical tests in the diagnosis of syndesmotic injury of the ankle. 9 investigators examined 12 persons twice, including 2 patients with an arthroscopically-confirmed syndesmotic injury. They sat behind a curtain that exposed only the lower legs. We found a statistically significant relation between the final arthroscopic diagnosis and the squeeze, fibula translation, Cotton, and external rotation tests as well as for limited dorsal flexion. None of the syndesmotic tests was uniformly positive in chronic syndesmotic injury. The external rotation test had the fewest false-positive results, the fibula translation test the most. The external rotation test had the smallest inter-observer variance. The physical diagnosis was missed in one fifth of all examinations. When in accordance with medical history and physical examination, positive stress tests should raise a high index of suspicion of syndesmotic instability. The final diagnosis of such instability, however, should be made by additional diagnostic imaging and/or arthroscopy.     

Limits of movement in the human knee. Effect of sectioning the posterior cruciate ligament and posterolateral structures

We applied specific forces and moments to the knees of fifteen whole lower limbs of cadavera and measured, with a six degrees-of-freedom electrogoniometer, the position of the tibia at which the ligaments and the geometry of the joint limited motion. The limits were determined for anterior and posterior tibial translation, internal and external rotation, and varus and valgus angulation from zero to 90 degrees of flexion. The limits were measured in the intact knee and then the changes that occurred with removal of the posterior cruciate ligament, the lateral collateral ligament, the popliteus tendon at its femoral attachment, and the arcuate complex were measured. The cutting order was varied, allowing us to determine the changes in the limits that occurred when each structure was cut alone and the amount of motion of the joint that was required for each structure to become taut and to limit additional motion when the other supporting structures had been removed. Removal of only the posterior cruciate ligament increased the limit for posterior tibial translation, with no change in the limits for tibial rotation or varus and valgus angulation. The additional posterior translation was least at full extension and increased progressively, reaching 11.4 millimeters at 90 degrees of flexion. The progressive increase in posterior translation with flexion was apparently due to slackening of the posterior portion of the capsule, as the translation nearly doubled when the posterolateral structures subsequently were removed. Removal of only the posterolateral extra-articular restraints increased the amount of external rotation and varus angulation. The average increase in external rotation depended on the angle of flexion; it was greatest at 30 degrees of flexion and decreased with additional flexion. At 90 degrees of flexion, the intact posterior cruciate ligament limited the increase in external rotation to only 5.3 degrees, less than one-half of the 13.0-degree increase that occurred at 30 degrees of flexion. Subsequent removal of the posterior cruciate ligament markedly increased external rotation at 90 degrees of flexion, resulting in a total increase of 20.9 degrees. The limit for varus angulation was normal as long as the lateral collateral ligament was intact. When the lateral collateral ligament was cut, the limit increased 4.5 degrees (approximately 4.5 millimeters of additional joint opening) when the knee was partially flexed (to 15 degrees).(ABSTRACT TRUNCATED AT 400 WORDS)