Beitrag der Syndesmosen und des Deltabandes zur Stabilit�t der Au�enkn�chelfraktur Typ Weber B

Abstract

The purpose of the present biomechanical investigation was to check the functional importance of the syndesmosis ligaments and of the deltoid ligament for ankle fracture type B according to the AO-Weber classification. We constructed a special fixation clamp, with 12 fresh and unembalmed lower legs being tested for lateral shift (mm) and ten for tibiotalar rotation. All specimens were exposed in the same neutral position. Transverse loads (F(y)) varied between 0 and 150 N, axial loads (F(z)) between 0, 300, 600 and 1,000 N and rotational loads (F(r)) between 2.4 and 4.9 Nm. All series were repeated according to supination-eversion (SE) injury patterns of the Lauge-Hansen classification. Syndesmotic ligaments and the fibula were incrementally sectioned from anterior to posterior. Type SE I consisted of an isolated incision of the anterior syndesmosis ligament. Type SE II had an additional oblique fracture of the fibula at the height of the tibiofibular syndesmosis. In type SE III injuries, in addition to the fibular fracture, a complete rupture of the syndesmosis ligaments was present, and for type SE IV lesions the deltoid ligaments were incised. The transverse load-displacement curve was s-shaped in all uninjured joints,with the highest gradient between 10 and 20 N with no axial compression. Without axial compression in cases of F(y)=25 N transverse loads, the mean talus translation was 0.51 mm. Following type II injuries, the average talus translation was 0.68 mm (not significant) and rose to an average of 0.95 mm ( P <0.01) in type III injuries. After additional incision of the deltoid ligaments, the ankle joint subluxed permanently when more than 5-10 N transverse loads were applied. Axial loads of 300 N or more resulted in a considerable reduction in talus translations, indicating increased stability and congruency within the joint complex. In this way, the vertical loading of the ankle joints always contributed to joint stability. The average internal tibiotalar rotation reached with a torque of 2.4 Nm was 3.52 degrees and with 4.9 Nm 5.15 degrees when no axial compression was applied. External rotation measured -6.36 degrees and -8.62 degrees, respectively. Following the experimental protocol, significant increases were noted for external rotation at SE II degrees injuries ( P =0.003) and for internal rotation at SE III degrees ( P =0.03) injuries. Our data support the proposition that the deltoid ligaments and the posterior syndesmosis play a key role in the stability of ankle fractures for supination-eversion injuries. If these structures remain intact, conservative and early functional treatment are recommended in patients with minimal (<2 mm) or no fracture displacement. This concept is confirmed by the literature dealing with clinical mid- and long-term follow-up studies.

The diagnosis and treatment of deltoid ligament lesions in supination–external rotation ankle fractures: a review

“…With the deep part still intact, only 4–7° of external rotation of the talus was possible [79, 108]. In the absence of a medial injury, a complete fibular osteotomy does not cause abnormal motion of the ankle [83, 111]. The ATTL together with the anterior talofibular ligament on the lateral side is thought to restrict forward translation of the talus.…”

Ungeplante Zweiteingriffe nach Frakturen des oberen Sprunggelenks

“…Den größten Anteil haben die instabilen Luxationstypen. Das größte biomechanische Problem ist hierbei die Fibulalänge, gefolgt vom tibiofibularen Syndesmosenkomplex[26]. Beide wer den durch komplexe Unfallbewegun gen in Kombination mit dem Delta band oder Innenknöchel verletzt[11].…”

Frakturen des oberen Sprunggelenks

“…Auch den medialen Strukturen (Innenknöchel, Deltaband) kommt eine wesentliche Funktion als primärer Stabilisator der Malleolengabel zu [10,32,45].…”

“…Bei stablilen infra-und transsyndesmalen Frakturen kann der Patient -nach Abschwellen der Weichteile -in einer supinationshemmenden Orthese unter Vollbelastung mobilisiert werden. In biomechanischen Versuchen konnte nachgewiesen werden, dass das obere Sprunggelenk eine erhebliche Stabilitätsreserve bei axialer Krafteinleitung aufweist, wenn eine Rotation oder Bewegung in der Frontalebene (Pronation/Supination) verhindert wird [45,48]. Die Orthese wird bis zum knöchernen Durchbau der Fraktur, also für 4-6 Wochen, getragen.…”