Functional description

The type of ligamental rupture depends on the direction, speed and force which occur on the ligament or its attachments to the cartilage or bone.

The x-ray can only show the injury when the ligament rupture is located at the bone and contains an avulsion. Normally, ligamental rupture can be demonstrated by a stress x-ray. In this case, imaging shows an extreme position of the joint, which diagnoses an opening or subluxation. For each joint there are routine methods, which allow us to have an examination standardization for diagnosis.
A proper functional diagnostic examination is subject to consideration of all biomechanically relevant joint stabilizing factors, which are:

1. The specific anatomy of the joint
2. The muscles
3. The capsular ligamental structures

For proper assessment of the ligament, point 1 and 2 are taken into account by positioning the patient such that his muscles are relaxed and the stress on the ligament cannot be reduced by the nature of the joint anatomy.

The design of the Telos equipment allows for correct anatomical positioning and proper equipmenet alignment to obtain the anatomical demonstration desired. Any muscular compensation is visible on the electronic display and may also be detected by manually examining the muscles for tension.

Before you take a stress x-ray, native x-rays are taken in two different planes to rule out a fracture of the bone, if clinically suspected. In such cases, a stress x-ray should not be taken.
The most common ligamental injuries are those of the anterior ankle joint ligaments (fibular side), mostly caused by supination trauma. Injuries of the medial ligaments by pronation trauma occur rather rarely and are mostly accompanied by a fracture of the fibula.
The anterior ankle joint consists of the distal ends of the two bones of the lower leg (tibia and fibula), and one tarsal bone, the talus. The anterior ankle joint is a hinge articulation, equipped with collateral ligaments. These ligaments are characterized by their fanlike attachments which split up into several parts fixed at different points on the tarsus.

Therefore, one ligament is always tense to stabilize the ankle irrespective of the position in which the lower leg and the foot move.

 

The Telos stress device enables you to examine each ligament separately

We recommend to start with the examination of the anterior talofibular ligament, since during the typical supination trauma this ligament is normally ruptured first and since the examination is less strenuous for the patient. 

Ligamentum fibulo-talare The anterior talofibular ligament is checked by lateral x-rays, taken in subluxation position of the talus in ventral direction (drawer: the heel is fixed and pressure is applied on the tibia). Due to this positioning, the foot is in its natural plantar flexion (tension of the anterior talofibular ligament), characterized by the origin of the ventral tibial condyle being shifted towards the vertex of the trochlea of the talus. Stabilization is thus reduced by the joint anatomy.

While applying pressure, the foot turns slightly inwards the tibia outwards (only possible if the knee and the joint is flexed by at least 30°) around the center of motion of the deltoid ligament which also attaches to the talus.


cruciate ligament, rupture of the cruciate ligament This x-ray should only be taken 1 minute after starting to apply pressure, since the talus slides only slowly in a ventral direction so that it takes about that time to achieve the required position for correct findings.

X-rays of the calcaneofibular ligament are taken in a-p position to measure the opening angle between tibia and talus.

The recommended positioning places the foot in 90° position to the tibia (tension of the calcaneofibular
ligament). Flexion of the knee joint results in a rectangular position of tibia and calcaneus, so that the dorsally tapered talus is firmly fixed in the malleolar furca. With a simple tilting motion the talus could get jammed in the furca. This problem is avoided by the design of the foot holding device. The heel is placed excentrically to the pivot of the foot holding device which, besides the tilting motion, performs an additional movement in tensile direction, thus pulling the talus out of the furca over the pivot of the deltoid ligament.

Moreover, flexion of the knee joint prevents a pain-relieving hip turning motion of the patient.
The pressure load applied in all stress examinations should be 15 daN. This empiric value is internationally accepted. Studies performed under fluroscopic control have shown that the joint may already open at values between 6 daN and 7 daN, if the ligament to be examined is ruptured. A higher pressure load than 15 daN is not advisable, since it leads to an increasing pain-induced muscular reaction force of the patient.

In case an x-ray is not taken with the recommended pressure load, the actually used load value should be recorded on the x-ray for the attending physician in order to avoid a false diagnosis. Comparative x-rays of the counterside must be taken under the same load as applied on the trauma side.

When mounting the equipment, please follow the schematic drawings showing the top views. It is important to mount each accessory as depicted.

Examination of the collateral ligaments of the knee in sedentary position results in the desired flexion of 15° to 20°. The angle may be increased up to 30° by altering the pad height. In case the knee shall be examined in extension, we recommend to position the patient supine and to use a pad support for the heel.

The design of the stress device also allows for an internal or external rotation of the tibia to examine the cruciate ligaments of the knee. This examination has one disadvantage: In order to maintain the rotational position the person performing the examination has to stay in the room during the x-ray and is therefore exposed to indirect radiation.

 
German | English