The word "instability" refers to a situation with abnormal motion. In order to understand instability, one must first understand stability, or normal motion.
An example: a door opens and closes. This motion is the normal, stable motion for the door. If the hinges became loose and the door moved also downward to scrape the floor, or upward if lifted, that would represent abnormal motion or instability.
First, to review, here is the anatomy of the normal ankle ligaments:
Anterior (towards the front)
Talofibular (connects talus and fibula)
Calcaneofibular (connects talus and fibula)
Posterior (towards back side)
Talofibular (connects talus and fibula)
This view shows the same ligaments along with the peroneal tendons, which go behind the fibula, and help to evert the foot (move the ankle towards the little toe side).
Quite often, in cases of instability, these peroneal tendons are working overtime to keep the ankle joint in place. The extra stress on these tendons can lead to peroneal tendonitis.
When someone twists their ankle, the first ligaments to tear are the Anterior Talofibular, then the Calcaneofibular, usually in that order. The tear can be partial (grades I or II) or complete (grade III).
The "anterior drawer" test, pictured here, where the foot is pulled forward while stabilizing the leg, is used to check for injuries of the ankle ligaments. An abnormal test is indicated by a feeling of looseness noted by the examiner, with less of this looseness noted on the uninjured side.
Unless this test is done properly, with the patient at least momentarily relaxed, a complete ligament tear can be missed.
Lateral stress view of ankle, as noted on "anterior drawer" test, where the foot is pulled forward while stabilizing the leg, indicates that the talus is coming out of the ankle joint, thus demonstrating ankle instability (abnormal motion).
This view shows another situation where the ankle is pulled forward just as the xray picture is taken. You can see that the talus is approximately 50% dislocated towards the front and out of the ankle joint, indicating that the ligaments that normally would hold the talus in place are clearly not doing their job.
This AP or front view of the ankle with an inward twist also demonstrates the talus coming out of joint, which is an abnormal motion, thus indicating instability.
It is important to recognize complete tears in the acute (fresh) setting because often they can be treated with a walker boot very successfully.
For cases with chronic instability, usually surgery is required for the ankle to regain stability.
For considerations regarding stability surgery, the pertinent anatomy is illustrated above. The extensor retinaculum is like a belt loop, holding the tendons that extend or lift up the toes, down against the surface of the foot and ankle bones, instead of sticking up like the string on a bow (think of bow and arrow).
For the Brostrom type repair, the anterior talofibular ligament is reconstructed, either by suturing that ligament together, or reattaching it to the bone, and then the extensor retinaculum is also sutured to the front of the fibula for additional stability.
Sometimes, for more advanced cases, or where there has been previous ankle ligament surgery, a different procedure is needed which sacrifices part of one of the tendons, like the peroneal tendon, which is on the little toe (lateral) side of the foot. One of these procedures, the Watson Jones procedure, is illustrated below.
Another technique involves using a tendon from a cadaver, or sometimes harvested from elsewhere in the body, to reconstruct the ankle ligaments, mainly anterior talofibular, and calcaneofibular.
The tendon is anchored with a screw that resorbs over time.
In most cases, after surgical reconstruction, the recommendation is that you stay on crutched or use a walker, avoiding full weight on the operated leg, for six weeks after surgery. Since this procedure is elective, it is important to choose a time when you can comply with the limited weightbearing recommendation. Bearing weight too early can jeopardize the repair.
These options can be discussed more fully at the time of your consultation.