Hyperpronation – The Role of Subtalar Arthroereisis

The alignment of the osseous structures of the foot determines the stability or instability of the foundation of the body. The talus plays a critical role in transferring the forces from the leg through the foot and onto the weight-bearing surface below. The motion of the talus on the calcaneus is determined by the articular facets of this complex as well as by the supporting soft-tissue structures. Pronation and supination are terms commonly used to describe the normal motion between the talus and calcaneus.

Overpronation describes a pathological condition in which there is excessive pronation. A more correct term would be hyperpronation, meaning excessive pronatory motion. The musculoskeletal kinetic chain is a series of links joined together as joints and, as the adage goes, the chain is only as strong as the weakest link. Instability of the talus on the calcaneus will lead to instability in other parts of the kinetic chain. Hyperpronation has been named one of the most common causes of orthopaedic pathological conditions. ¹

The sinus tarsi is a naturally occurring space in between the talus and calcaneus. It is formed by a groove on the undersurface of the talus and upper part of the calcaneus. This opening is angled from anterior–lateral–distal to posterior–medial–proximal. There is a good reason for this orientation, as the normal transfer of the weight of the body starts posterior–lateral and ends anterior–medial. The sinus tarsi serves as a fulcrum point between the transfer of the superincumbent weight of the body posteriorly to the calcaneus and anteriorly to the rest of the foot. In a ‘balanced’ hind-foot that has the normal amount of pronation and supination, this transfer of forces occurs without any excessive strain to the supporting tissues (see Figure 1A); however, if there is an imbalance within the subtalar joint complex, partial to full obliteration of the sinus tarsi occurs² (see Figure 1B). Finally, an excessive force will be placed on the supporting tissues, leading to excess pronation of the foot with each step taken.

The goal of treatment is to eliminate the cause and not just to address the symptoms. Clark pointed out: “In seeking to correct any angle of deformity, the logical place to make the change, from a mechanical point of view, is as near the angle of deviation as possible”.³ Modalities to stabilise the hind-foot have included both internal and external methods. The real aetiology is the slipping of the talus off the calcaneus leading to partial to full obliteration of the sinus tarsi. This is an internal deformity; therefore, external treatment methods are less effective. Numerous techniques for stabilising the subtalar joint complex have been introduced, many of which have not stood the test of time and have fallen by the wayside. The traditional mainstay of these internal stabilisation procedures primarily consisted of an arthrodesis; however, long-term results produced mixed degrees of satisfaction, with a high rate of arthritis in adjacent joints.^4–8

Due to the limitations of external treatment modalities, such as braces, splints, custom-moulded arch supports and the overly aggressive osseous procedures and their negative secondary conditions, the challenge was to develop a more reasonable solution. The apex of deformity in an excessively pronating foot occurs within the subtalar joint complex, specifically within the sinus tarsi. There are also many disadvantages with osseous arthrodesis procedures, including a long recovery time compared with arthroereisis, potential complications such as non-union and a prolonged period of non-weight-bearing and partial weight-bearing. The more aggressive rear foot reconstruction is usually reserved for extreme cases of flat foot.

The term arthroereisis is not commonly known in the medical community. It is the combination of ‘arthro-’, meaning joint, and ‘-ereisis’, which is a Greek word meaning pushing, lifting or raising up; ⁹ when combined, arthroereisis means the pushing, lifting or raising up of a joint. Unfortunately, many physicians have wrongly defined this term as joint-limiting, which implies that it is a procedure that will limit normal motion. However, the reality is that normal motion should still occur and only the excessive motion is limited. This procedure should be thought of as a joint-motion-restoring procedure.