Arthroereisis (also referred to as arthrosis) is the limitation of excessive movement across a joint. Subtalar arthroereisis (STA) or extraosseous talotarsal stabilization (EOTTS) is designed to correct the excessive talar displacement and calcaneal eversion by placing an implant in the sinus tarsi, a canal located between the talus and the calcaneus.
Flexible flatfoot is a common disorder, anatomically described as excessive or abnormal pronation during weight bearing due to anterior and medial displacement of the talus. Flexible flatfoot may be congenital in nature, a result of cerebral palsy and other neuromuscular disorders, or may be acquired in adulthood due to posterior tibial tendon dysfunction, which in turn may be caused by trauma, overuse, and inflammatory disorders, among others. Symptoms include dull, aching and throbbing cramping pain, which in children may be described as growing pains. Conservative treatments include orthotics or shoe modifications. Additional symptoms include refusal to participate in athletics or walking long distances. Surgical approaches for painful flatfoot deformities include tendon transfers, osteotomy, and arthrodesis. Arthroereisis with a variety of implant designs has also been investigated.
STA has been performed for more than 50 years, with a variety of implants, designs, and compositions. The Maxwell-Brancheau Arthroereisis® (MBA) implant is the most frequently reported , although other devices such as the HyProCure®, STA-PEG® implant device and a Kalix® are also reported in the medical literature. The MBA implant is described as a reversible and easy to insert device with the additional advantage that it does not require bone cement. In children, insertion of the MBA implant is frequently offered as a stand-alone procedure, while adults often require adjunctive surgical procedures on bone and soft tissue to correct additional deformities.
A number of implants have received marketing clearance through the U.S. Food and Drug Administration’s (FDA) 510(k) pathway. For example, the HyProCure® Subtalar Implant System/Extra Osseos Fixation Device (GraMedica) received marketing clearance in 2004 (K042030, the SubFix™ arthroereisis implant (Memometal Technologies, Bruz, France) received FDA marketing clearance in 2010 (K093820) and the Arthrex ProStop Plus™ (Arthrex, Naples, FL) received marketing clearance in 2008 (K071456). The MBA implant (now owned by Integra LifeSciences Corp., Plainsboro, NJ) received FDA 510(k) marketing clearance in 1996, because it was substantially equivalent to products on the market prior to device regulation. According to the FDA summary, the primary indication for the subtalar MBA device is “as a spacer for stabilization of the subtalar joint. It is designed to block the anterior and inferior displacement of the talus, thus allowing normal subtalar joint motion but blocking excessive pronation and the resulting sequela”. (1) The MBA Resorb Implant® received 510(k) marketing clearance in 2005 (K051611). This implant employs the same basic mechanical features as the predicate MBA implant, but is composed of a material (poly l-lactic acid) that is resorbed by the body. Predicate devices include the Osteomed Talar-Fit™ (K031155), Nexa Orthopedics Subtalar Peg (K032902 and K033046), Arthroereisis Implant Talus of Vilex (TOV, K041289), Instrateck (K080280), and Wright Medical Smith Sta-Peg (K792670).