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A normal hip joint is made up of the acetabulum and the head of the femur. However, a significant component is the round ligament, which determines the position of the femoral head in the acetabulum. It is surrounded by a fibrous capsule (Figure 1.).

Dislocation of the hip joint is one of the most common injuries encountered in clinical practice - up to 90% of all dislocations. It involves rupture of the round ligament and the most common dislocation is a dorsally anterior dislocation (Figure 2).

Symptoms

The injury generates very severe pain. The characteristic symptom of this injury is a non weight bearing hind limb, raised above the ground and may even appear to be shorter compared to the other limb.

Diagnosis and treatment

The diagnosis of hip dislocation is obtained on the basis of a clinical examination and palpation, determining the anatomy of the joint, the way the limb is held, the level of pain. The final diagnosis is confirmed by radiographs. For treatment, it is crucial to reduce the hip joint as soon as possible, meaning getting the bones back where they properly belong.

Severe trauma that causes the dislocation of the hip joint leads to a strong inflammatory reaction, swelling, hematomas, inflammatory reactions, as well as muscle contracture and filling the acetabulum with fragments of surrounding tissue, blood clots. Very often this makes it difficult to reduce the dislocation.

If the dislocation cannot be reduced, the grinding of the femoral head with the edge of the acetabulum leads to irreversible changes in the destruction of the joint and inability to use the limb.

The most popular method of treating an irreparably dislocated hip joint is Femoral Head Osteotomy (FHO). This method involves amputating the head and neck of the femur and bringing the acetabulum into a connective-tissue fusion with the proximal femoral epiphysis.

The Toggle Pin method is an alternative to femoral head amputation. It involves surgical reduction and fixation of the femoral head in the anatomical position using a special implant that mimics the work of the round ligament. The surgical technique involves the creation of a tunnel running subcondylar along the axis of the neck to the site of attachment of the round ligament on the femoral head (Figure 3).
It is necessary to use specialized tools which allow correct measurements and determination of tensions.

When performed correctly, the procedure leads to restoration of the correct biomechanics of the hip (Fig. 4 & Fig. 5). The effect of the procedure is visible immediately after the animal wakes up and the recovery period is several weeks shorter compared to the FHO procedure. The Toggle Pin method is limited to patients without hip dysplasia.

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.