Lateral Arthroscopic Subtalar Arthrodesis for Talocalcaneal Coalition: Surgical Technique

Tarsal coalition in adults

Adult tarsal coalition consists in abnormal union of two or more tarsal bones. Reported incidence ranges between 1 and 13%. It is generally a congenital condition, due to dominant autosomal chromosome disorder, but with some acquired forms following trauma or inflammatory pathology. Poorly specific clinical signs and the difficulty of screening on conventional X-ray may lead to diagnostic failure. The present review of tarsal coalition addresses the following questions: how to define tarsal coalition? How to diagnose it? How to treat it? And what results can be expected? There are 3 types of tarsal coalition, according to the type of tissue between the united bones: bony in pure synostosis, cartilaginous in synchondrosis, and fibrous in syndesmosis. Location varies; the most frequent forms are talocalcaneal (TC) and calcaneonavicular (CN), accounting for more than 90% of cases. Cuneonavicular, intercuneal and cuboideonavicular locations are much rarer, at less than 10%. Tarsal coalition is classically painful, often with valgus spastic flatfoot in young adults. The pain is caused by the biomechanical disturbance induced by the bone, cartilage or fibrous bridges which partially or completely hinder hindfoot and/or midfoot motion. Conventional imaging, with weight-bearing X-ray and CT, is standard practice. Weight-bearing CT is increasingly the gold standard, displaying abnormalities in 3 dimensions. Functional imaging on MRI and tomoscintigraphy assess direct and indirect joint impact at the affected and neighboring joint lines. Non-operative treatment can be proposed, with orthoses, rehabilitation and/or injections. But surgery is the most frequent option: either resection of the bony, cartilaginous or fibrous constructs to restore optimally normal anatomy, or arthrodesis in the affected joint line or the entire joint. Surgery can be open, arthroscopic or percutaneous, depending on the severity of the biomechanical impact on the affected and neighboring joints. Resecting the abnormality is the standard practice in all locations if it affects less than 50% of the talocalcaneal joint line and there is no osteoarthritis to impair the functional outcome. Otherwise, fusion is required. Level of evidence: V; expert opinion.

Defining the Structures at Risk and an Anatomical Safe Zone for Percutaneous Antegrade Subtalar Joint Fixation With a Single Screw: A Cadaveric Study

Percutaneous antegrade (anterior to posterior) fixation for subtalar joint (STJ) arthrodesis offers various intraoperative and biomechanical advantages. Currently, the entry point for percutaneous antegrade STJ screw fixation is not clearly described and variable. To our knowledge, there are no publications that evaluate anatomic structures at risk or define an anatomically safe entry point for this fixation. The aim of this investigation was to define an anatomically safe and reproducible entry point for percutaneous antegrade STJ arthrodesis fixation, while also describing anatomic structures at risk when undertaking this method of fixation. We hypothesized that percutaneous single screw antegrade STJ fixation would encroach upon named anatomic structures in more than one cadaveric specimen. Ten cadaver limbs were used in this investigation. A percutaneous guidewire was inserted 5 mm lateral to the tibialis anterior tendon. The midpoint of the talar neck served as the sagittal plane starting point, as seen on the lateral fluoroscopic view. A cannulated 6.5-mm headed screw was inserted antegrade through the STJ into the calcaneus. Each specimen was dissected to assess the distance from the screw to nearby anatomic structures and distance from the tibialis anterior tendon to named structures. Our hypothesis was found to be incorrect, as 0/10 screws invaded neurovascular or tendinous structures. The dorsalis pedis artery and deep peroneal nerve were on average 12.1 ± 2.79 mm and 12.2 ± 2.82 mm lateral to the screw, respectively. These findings are clinically relevant and ultimately allow us to define an anatomic safe starting point for percutaneous antegrade STJ single screw fixation.