Using CAD (computer aided design) helped create and test a custom made mechanical replacement for the wrist before it was manufactured. The implant was created in a biocompatible metal alloy. Titanium 6Al4VELI was as the material of choice for the implant but a low carbon content stainless steel (316L) can be used. For the metal transformation a lathe, mill, drill and grinding equipment was used. The implant goes through a degreasing and passivation process that removes contamination of foreign materials while machining and then goes through a sterilization process. The titanium implant has an extension range of motion similar to the wrist, this emulates the normal joint angle of the wrist while standing, but has a reduced range of motion in flexion. This provides stability to the limb and allows the patient to move more naturally. A 7 years old female dog with bilateral osteoarthritis and osteosarcoma went through surgery for implant placement. The patient is prepared for surgery in the usual manner. The dorsal area of the wrist is incised carefully protecting vascular and nervous structures. The joint capsule is opened and almost all carpal bones except the accessory carpal bone are removed in order to fit the implant. Two main components make the implant work. A radial component that has a shaft proximally that fits inside the radial medullar canal and distally allows for a metacarpal component that consists of four pins that fit through metacarpal bones number II to V. Both components connect to provide a hinge movement wit a predefined range of motion. The artificial joint is a non cemented type and has a surface treatment to promote bone integration. The radial component has a blockade pin that goes through the radial cortex and fasten the component to the bone. This avoids the component to rotate allowing early use of the limb. Tools were made specifically for the correct placement of the implant. After surgery and six weeks convalescence the dog is allowed to walk. Surgery allowed the dog to walk almost normal after just three days. Because early walking can be a risk during recovery the dog should be restricted until bone ingrowth within the implant takes place. Once the implant is in place the articular capsule is closed followed by subcuticular tissue and skin. Broad spectrum antibiotics are given for seven days. Skin sutures are removed ten days after surgery. Rehabilitation follows surgery starting with controlled walking. Six weeks later the dog is allowed to walk unrestricted.
Conclusions: This is the first total wrist replacement made worldwide in dogs. It provides almost immediate use of the joints and can reestablish pain free movement for a better quality of life for the dog. Cementless implants can be used in small dogs but in larger breeds bone cement can help reduce recovery times. Custom made implants will ensure a trouble free tight fitting. Design of the implant can be improved but results at this stage are satisfactory. Implants provide a true alternative to treatment of wrist diseases.