Within the carpal bones, the scaphoid have a fundamental role as a connecting link between both rows and the forearm. It is characterized by presenting a dorsal and volar retrograde flow with little vascularization at the proximal pole level. For this reason, when faced with a fracture of this pole, there is a high percentage of patients who progress towards a delayed consolidation or non-union. The treatment and early diagnosis of an acute scaphoid fracture is essential for the prognostic and evolution. Untreated or incorrectly managed injuries will have long-term complications such as pseudoarthrosis, avascular necrosis or chronic carpal instability that will progressively lead to the development of osteoarthritis. In front of any of these acute injuries, an surgical procedure will be indicated, where primary osteosynthesis with or without vascularized grafts is recommended. Unfortunately, these techniques are not always successful and in the case of highly displaced fractures the risk of nonunion increases. The current solution that we have are salvage surgical techniques where we are forced to sacrifice or fuse other carpal bones, restricting joint range. Therefore, in the face of recalcitrant necrosis of the proximal navicular pole, in situations where primary surgical repair is impossible, or in cases of SNAC wrist grade I-II, we think that a practicable alternative would be to use a stabilized partial scaphoid arthroplasty, which allow to recover the previous joint situation, maintain the complete joint range, controlling pain and thus avoiding carpal collapse. In the last 70 years, several implants have been designed. However, all of them have ended up failing because of the material used, which generated a reaction with fibrosis and adhesions, or because have an instability problem, since not being stabilized with the mechanical stress forces of the hand, it ended up flexing and dislocating dorsal. Furthermore, many of these implants did not respect the complex anatomy of the scaphoid with the rest of the carpal bones. Our goal is to overcome the problems of the past and design an anatomical partial scaphoid prosthesis which adapts perfectly to the rest of the carpal bones with which to articulate. The implant will only replace the proximal two thirds of the scaphoid that are injured, an area where vascularization was poor, maintaining a remnant of distal bone with its insertions distal to the scapho-trapezium-trapezoid ligament. In this way, the implant will be stabilized distally to the bone remnant with a fixed anchor but will also have a hydroxyapatite-coated flat articular facet to facilitate biointegration. In the proximal pole, it will be fixed to the lunate bone with a ligamentous plasty that simulates a scapho-lunate neoligament of almost 360º, through transosseous tunnels, reproducing the anatomy of the carpus. After the prosthetic design and fabrication, the stability during flexion-extension movements of the wrist, radial and ulnar deviation and the combined movement of throwing darts using cameras, load cells and intraosseous markers will be validated experimentally. For this, 2 repeated tests are carried, first evaluating the healthy forearms without carpal pathology and later after the implantation of the stabilized partial prosthesis.
