The ADM (Abduction Dorsiflexion Mechanism) is a modern dynamic ankle foot orthosis designed and manufactured by the English company C-Pro Direct. It keeps the foot in abduction and dorsiflexion position while the foot is relaxed (e.g. while the baby is asleep). When the child is active, a dynamic ADM mechanism based on two independently working rotating mechanisms allows the foot to move in any direction and mobilize it in the sub-talar joints and tibio-talar joints.
Who are AFO-ADM orthoses for?
AFO-ADM orthoses are not usually used as the first orthopedic device option for clubfoot patients in the Ponseti method. It is a foot abduction brace. However, there is a small group of patients for whom AFO-ADM orthoses can be used successfully:
- patients after clubfoot surgery;
- patients intolerant of the foot abduction brace to a very high degree (despite the necessary changes made to the setting of the external rotation or widht of the brace and the elimination of factors that may occur in children (disease, teething, growth / development spurts, etc.) as well as after eliminating the relapse);
- clubfoot patients with excessive hypermobility of the knee;
- older children who require constant foot abduction and dorsiflexion due to a primary neurological condition (e.g. spina bifida)
- children who have a problem with dropped feet as a result of paralysis.
The AFO-ADM brace consists of:
- AFO (sandal) constructed from soft, ultra-lightweight and comfortable EVA foam around a rigid core, making the orthosis more comfortable for the little patient;
- dynamic mechanism ADM attached to the footwear (AFO sandal) and embracing the calf that regulates the external rotation (STJ) and dorsiflexion (TTJ) of the foot through the use of two mechanisms with rotating springs. Each of the two springs of the mechanism has 3 degrees of stiffness: Soft / Standard / Strong;
- tongue setmade from flexible materials comfortably secures patients feet without compromising sub-talar or tibio-talar motions.
- depth gauge tool to check the right heel position inside the sandal (AFO).
The ADM is unilateral, which means that it is put on only on the side of the foot with the defect. If the foot defect is bilateral, it requires the use of two orthoses independently. This is an advantage of the AFO-ADM orthoses because the legs remain free and the feet are not connected with the brace as is the case with the foor abduction brace used in children with congenital clubfoot during Ponseti management.
The ADM does not require any adjustment!
How the AFO-ADM orthosis works?
The AFO-ADM orthosis is based on the functional anatomy of the foot and its kinematics in relation to the two main joints of the foot:
- tibiotalar jointTTJ - that is the ankles mortise (TTJ), which enables the foot to move upward (dorsiflexion) and move downward (plantar flexion);
- subtalar joint STJ - that is the ankle, which enables the foot to move inward (inversion) and move outward (eversion). Subtalar joint with talonavicular joint enables the adduction and abduction of the foot.
Springs, which are a component of the mechanism, apply precisely defined torsional forces to change the position of the foot in relation to the above-mentioned joints. Various spring options - Soft / Standard / Strong - provide torsional forces ranging from 70 to 1330 Nmm. The effect of these springs is to apply to the foot forces that abduct and flex the foot dorsally at the same time.
The AFO-ADM brace has an articulated mechanism adjusted to the dominant axis of the ankle joint:
- TTJ axis of ADM is aligned with the main axis of movement tibiotalar joint and is generally accepted to be 20 to 30 ° from the frontal plane and 8 ° from the transverse plane when the calf joint is in the neutral position. So upper mechanism - TTJ is responsible for the dorsal and plantar flexion of the foot.
- STJ axis of ADM is aligned with the main axis of movement subtalar joint and the mean dominant axis of this joint is generally taken to be 42 ° from the transverse plane and 16 ° from the sagittal plane. So the lower mechanism - STJ - is responsible for the adduction and abduction of the foot and inversion (varus) and eversion (valgus) of the hindfoot. So when the dynamic ADM is attached to the AFO (sandal), the foot is simultaneously abducted, dorsally flexed, and the calcaneus becomes valgus.
The AFO-ADM orthosis supports a range of motion:
- 45° plantarflexion to 30° dorsiflexion;
- 5° inversion (inwersji (heel varus) to 30° eversion (heel valgus).
In this way, the mechanism stretches the tendons and ligaments of the foot while allowing greater freedom of movement. It maintains a corrected foot position and a long duration low-intensity stretch to the tendons and ligaments of the foot and lower leg. Stretching is most effective when your baby is relaxed or asleep.
Most doctors agree that dorsiflexion should be at least 10° (readings can be made on the TTJ dial),
and abduction should be at least 15° strong> (can be read on the STJ dial).