Arthroscopic Assessment of Syndesmotic Instability in the Sagittal Plane in a Cadaveric Model.

BACKGROUND: Syndesmotic instability is multidirectional, occurring in the coronal, sagittal, and rotational planes. Despite the multitude of studies examining such instability in the coronal plane, other studies have highlighted that syndesmotic instability may instead be more evident in the sagittal plane. The aim of this study was to arthroscopically assess the degree of syndesmotic ligamentous injury necessary to precipitate fibular translation in the sagittal plane. METHODS: Twenty-one above-knee cadaveric specimens underwent arthroscopic evaluation of the syndesmosis, first with all syndesmotic and ankle ligaments intact and subsequently with sequential sectioning of the anterior inferior tibiofibular ligament (AITFL), the interosseous ligament (IOL), the posterior inferior tibiofibular ligament (PITFL), and deltoid ligament (DL). In all scenarios, an anterior to posterior (AP) and a posterior to anterior (PA) fibular translation test were performed under a 100-N applied force. AP and PA sagittal plane translation of the distal fibula relative to the fixed tibial incisura was arthroscopically measured. RESULTS: Compared with the intact ligamentous state, there was no difference in sagittal fibular translation when only 1 or 2 ligaments were transected. After transection of all the syndesmotic ligaments (AITFL, IOL, and PITFL) or after partial transection of the syndesmotic ligaments (AITFL, IOL) alongside the DL, fibular translation in the sagittal plane significantly increased as compared with the intact state (P values ranging from .041 to <.001). The optimal cutoff point to distinguish stable from unstable injuries was equal to 2 mm of fibular translation for the total sum of AP and PA translation (sensitivity 77.5%; specificity 88.9%). CONCLUSION: Syndesmotic instability appears in the sagittal plane after injury to all 3 syndesmotic ligaments or after partial syndesmotic injury with concomitant deltoid ligament injury in this cadaveric model. The optimal cutoff point to arthroscopically distinguish stable from unstable injuries was 2 mm of total fibular translation. CLINICAL RELEVANCE: These data can help surgeons arthroscopically distinguish between stable syndesmotic injuries and unstable ones that require syndesmotic stabilization.

Role of the Deltoid Ligament in Syndesmotic Instability.

BACKGROUND: The deltoid ligament (DL) is the principal ligamentous stabilizer of the medial ankle joint. Little is known, however, about the contribution of the DL toward stabilizing the syndesmosis. The aim of this study was to arthroscopically evaluate whether the DL contributes to syndesmotic stability in the coronal plane. METHODS: Eight above-knee cadaveric specimens were used in this study. A lateral hook test was performed by applying 100 N of lateral force to the fibula in the intact state and after sequential transection of the DL, anterior-inferior tibiofibular ligament (AITFL), interosseous ligament (IOL), and posterior-inferior tibiofibular ligament (PITFL). At each stage, distal tibiofibular diastasis was measured arthroscopically at both the anterior and posterior third of the incisura and compared to stress measurements of the intact syndesmosis. Measurements were performed using probes ranging from 0.1 to 6.0 mm, with 0.1-mm increments. RESULTS: There was no significant increase in diastasis at either the anterior or posterior third of the tibiofibular articulation after isolated DL disruption, nor when combined with AITFL transection. In contrast, a significant increase in diastasis was observed following additional disruption of the IOL (anterior and posterior third diastasis, P= .012 and .026, respectively), and after transection of all 3 syndesmotic ligaments (anterior and posterior third diastasis, P=.001 and .001, respectively). CONCLUSION: When evaluating the syndesmosis arthroscopically in a cadaveric model under lateral stress, neither isolated disruption of the DL nor combined DL and AITFL injuries destabilized the syndesmosis in the coronal plane. In contrast, the syndesmosis became unstable if the DL was injured in conjunction with partial syndesmotic disruption that included the AITFL and IOL. CLINICAL RELEVANCE: Disruption of the DL appeared to destabilize the syndesmosis in the coronal plane when associated with partial disruption of the syndesmosis (AITFL and IOL).

The effect of ankle distraction on arthroscopic evaluation of syndesmotic instability: A cadaveric study.

BACKGROUND: To assist with visualization, orthopaedic surgeons often apply ankle distraction during arthroscopic procedures. The study aimed to investigate whether ankle distraction suppresses fibular motion in cadaveric specimens with an unstable syndesmotic injury. METHODS: Fourteen fresh-frozen above knee specimens underwent arthroscopic assessment with 1) intact ligaments, 2) after sectioning of the anterior inferior tibiofibular ligament, the interosseous ligament, and the posterior inferior tibiofibular ligament, and 3) after sectioning of the deep and superficial deltoid ligament. In all scenarios, the lateral hook test, anterior-posterior hook test, and posterior-anterior hook test were applied. Each test was performed with and without ankle distraction. Coronal plane anterior and posterior tibiofibular diastasis as well as sagittal plane tibiofibular translation due to the applied load were arthroscopically measured. FINDINGS: Tibiofibular diastasis in the coronal plane, as measured at both the anterior and posterior third of the incisura, was found to be significantly less when ankle distraction was applied, as compared to arthroscopic evaluation in the absence of distraction. In contrast, measurement of sagittal plane tibiofibular translation was not affected by ankle distraction. INTERPRETATION: Since arthroscopic findings of syndesmotic instability are subtle the differential values of the syndesmotic measurements taken on and off distraction are clinically relevant. To optimally assess syndesmotic instability one should evaluate the syndesmosis without distraction or focus on fibular motion in the sagittal plane when distraction is required.

Arthroscopically measured syndesmotic stability after screw vs. suture button fixation in a cadaveric model.

BACKGROUND: Appropriate management of ankle syndesmotic instability is needed to prevent the development of complications. Previous biomechanical studies have evaluated movement of the fibula after screw or suture button fixations with different results, most likely being caused by variations in experimental setups that did not mirror the in vivo clinical setting. This study aimed to arthroscopically compare in a cadaveric model the stability of syndesmotic fixation with either a suture button or syndesmotic screw. METHODS: Eight fresh matched pairs of human ankle cadaver specimens (above knee) underwent arthroscopic assessment with (1) intact ligaments, (2) after complete disruption, and (3) after repair with either a quadracortical syndesmotic screw or suture button construct. In every stage, four loading conditions were considered under 100N of direct force: 1) unstressed, 2) lateral hook test, 3) anterior to posterior (AP) translation test, and 4) posterior to anterior (PA) translation test. Coronal plane tibiofibular diastasis, as well as sagittal plane tibiofibular translation, were arthroscopically measured. RESULTS: Coronal plane anterior and posterior tibiofibular diastasis and sagittal plane tibiofibular translation were measured using probes of increasing diameters. Following screw fixation, syndesmotic stability was similar to the uninjured syndesmosis in the coronal plane (anterior, median 0.0mm [IQR 0.0-0.3] vs. 0.3mm [IQR 0.2-0.3]; p=0.57; posterior, median 0.1mm [IQR 0.0-0.4] vs. 0.2mm [IQR 0.1-0.3]; p=1.0) but more rigid in the sagittal plane (median 0.0mm [IQR 0.0-0.1] vs. 1.0mm [IQR 0.4-1.5]; p=0.012). Repairing the unstable syndesmosis with a suture button construct resulted in coronal plane stability similar to the uninjured syndesmosis (anterior, median 0.2mm [IQR 0.1-0.3] vs. 0.2mm [IQR 0.1-0.3]; p=0.48; posterior, median 0.2mm [IQR 0.1-0.3] vs. 0.3mm [IQR 0.1-0.5]; p=0.44). However, sagittal plane fibular motion remained unstable as compared to the uninjured syndesmosis (median 2.2mm [IQR 1.6-2.6] vs. 0.8mm [IQR 0.4-1.3]; p=0.012). CONCLUSION: Current fixation methods for syndesmotic disruption maintain coronal plane fibular stability. Screw and suture button constructs, however, respectively resulted in greater or insufficient constraint to fibular motion in the sagittal plane as compared to the intact syndesmotic ligament. These findings suggest that neither traditional screw nor suture button fixations optimally stabilize the syndesmosis, which may have implications for postoperative care and clinical outcomes.

A biomechanic comparison of an internal radiocarpal-spanning 2.4-mm locking plate and external fixation in a model of distal radius fractures.

PURPOSE: To compare the biomechanic stability of distal radius fracture fixation with a new internal radiocarpal-spanning 2.4-mm locking plate, which acts as an internal distal radius fixator, versus a standard distal radius external fixator. The number of locking screws necessary for adequate fracture fixation was also assessed. METHODS: Ten cadaveric specimens were mounted in a loading fixture with cables attached to the 2 flexor and 3 extensor wrist tendons. A 1-cm osteotomy was created to simulate an unstable distal radius fracture. The radiocarpal-spanning locking plate was fixed to the radius and index metacarpal with 4 screws proximally and 4 distally. The specimen was incrementally loaded through the tendons. Motion at the fracture site was determined. Screws were sequentially removed from the construct, the specimen was again incrementally loaded, and fracture motion was measured. The fixation was then changed to an external fixator, and the loading tests were repeated. RESULTS: Fracture fixation with the radiocarpal-spanning 2.4-mm locking plate was significantly more stable with 4 screws proximally and 4 screws distally (4 x 4) and with the 3 x 3 configuration than with the external fixator in both flexion and extension. The 4 x 4 screw configuration was not significantly different from the 3 x 3 screw configuration. The 4 x 4 screw configuration was significantly more stable than the 2 x 2 and 1 x 1 screw configurations in both flexion and extension. All internal fixator configurations and the external fixator showed more fracture displacement at increasingly higher loads. CONCLUSIONS: Fracture fixation with the new internal radiocarpal-spanning 2.4-mm locking plate is more stable than with a standard distal radius external fixator. Only three 2.4-mm locking screws proximally and three 2.4-mm locking screws distally are required for adequate fixation of the locking spanning plate.