Development of newer finger implant in Japan started with hinged Ceramic implant in early 1980’ and was abandoned its use in early stage (Doi 1984 and Minami 1988). Although silicone finger implant has been most popular, breakage of the implant, particle induced inflammation and implant subsidence continued to be the problems of the silicone implant. In turning to new century, there was another enthusiasm of developing new finger implant in Japan. Surface replacement was chosen for the PIP joints, however, most of design for the MP joint had constrained mechanism, including ball and socket joint with stem allows piston motion and semi-hinged joint with much freedom. Currently available finger implants in Japan will be discussed briefly. The author developed cement-less surface finger implants (Self Locking Finger Joint, SLFJ) for the MP (including thumb) and PIP. Characteristics of the implant include,(1) the joints anchor(stem) has tapered screw with two long legs which spread intramedullary allows fixation without cement and thus change the position during the operation for optimum collateral tension, (2) joint design that preserve collateral ligament and surface contour, (3) simultaneous replacements of both MP and PIP are possible. Over 500 joins in 200 patients have been operated during last seven years. Of 50 cases operated by author with minimum of 4 years follow up, 34 cases were available for evaluation. There were 98 joints: 72 MP, 12 PIP and 14 MP of the thumbs. Average follow up was 5 years and 5 months (4 years ~ 6 years and 6 months). Fixation of the joints anchor were stable, only three joints showed marked loosening. Breakage of the joint anchors was found in 7 MP and 2 PIP; 5 out of 9 breakage of the legs were occurred during the operation. In x-ray evaluation, about half of the joint anchors were found securely fixed to the bone within 2 years. Dislocations of the joints were found in 4 MP joints in 3 cases (3 were early dislocation and were found to be technical failure and one late dislocation) and 2 PIP joints (one early and one late dislocation). Five MP implants were removed because of progressive flexion contracture and 3 MP and 2 PIP were re-operated. Range of motion of ext/flex averaged −25/70 in MP and −20/65 in PIP.
Destruction and deformity in both PIP and MP joints are not uncommon and cause sever disabilities. Arthroolasty of the MP joint combined with arthrodesis of the PIP joint are the usual choice for this condition. Some motion in ulnar digits provides great benefits for rheumatoid patients. We report implant arthroplasty of the PIP joint and also simultaneous replacement of PIP and MP joint in same finger.
Twenty-five joints in 15 patients underwent PIP arthroplasty either with silicone or surface replacement implant. Twelve PIP joints in 6 patients used Silicone implant (6 Swanson and 6 Avanta) alone and mean follow up was 42(6–84) months. New cementless surface implant (Self Locking Finger Joint, SLFJ) were developed and clinically used for about 3 years. Because of the stem design, SLFJ are able to use both PIP and MP joint simultaneously or combined with silicone implant. Four PIP joints in 3 patients used SLFJ alone and 6 patients underwent both PIP and MP joint with implant simultaneously. Combination of SLFJ PIP and silicone MP was 4 finger in 2 hand, SLFJ PIP and SLFJ MP was 3 finger in 2 hand, silicone PIP and SLFJ MP was 3 finger in 2 patients and silicone PIP and silicone MP was 1 finger. Mean follow up for SLFJ in either PIP or MP was 18(4–37) months.
Average arc of the PIP with silicone implant alone was 38(10–50 ° and SLFJ alone was 55(45–60) °. One PIP SLFJ dislocates immediate after surgery and was converted silicone later on. Of 7 SLFJ with combined PIP and MP arthroplasties, 2 PIP lost motion completely, one PIP move only 15°, 4 PIP move 75 °in average. Four silicone PIP combined with MP arthroplasties move 45°in average. One PIP SLFJ had breakage in stem legs, which believed to occur during interaction of stem insertion from both side of the basal phalanx, and was seen at immediate post op X-ray. There was one instability in index replaced with SLFJ for sever Swan neck deformity and no infection. Patient satisfaction for simultaneous replacement in PIP and MP joint were excellent except one whose age was 72.
Stability of the PIP joint in index finger is important for pinch and PIP motion of ring and little fingers are required for grip motion. Although arthrodesis of the PIP joint were performed more often and functional improvement usually obtained compared to pre-operative condition, ulnar 2 digits better to preserve some motion in the PIP joint as long as there is a possibility, and especially for the young patients. The results of the simultaneous replacement in PIP and MP joint seems discourage, however, when considering the severity of the deformities of this series, there is a good chance in the future. We will improve implant design and surgical technique as well as post-operative therapy, and continue to challenge the simultaneous replacement of PIP and MP joint.
Although silicone finger implant has several disadvantages including loss of motion, implant breakage and osteolysis, Swanson or other silicone prosthesis are still most widely accepted in the world. Osseointegrated implant showed great improvement as for as stem fixation, however, still used silicone joint with high incidence of fracture. Cement-less surface type finger joint prosthesis has been developed and clinical trial has carried out. Ninety three joint replacement in 30 hands with mean follow up about 2 years are reported.
The endoprosthesis consists of 3 different parts; two titanium joint anchor (fixture) in proximal and distal, titanium joint head in proximal, and HMWDP joint socket in distal. The joint anchor has tapered self tapping screw in joint side surface and has two flat long legs attached toward canal side which spread and compressed to intramedural canal firmly by turning a locking screw within the joint anchor. Each joint component is fixed to the anchor within a square hole. The MP joint component has anatomical head but semiconstrained toward volar dislocation by deep dorsal roof shape of the joint socket. Each socket has 2 different thickness. Because of cement less joint fixture mechanism and design, this endoprosthesis system is able to preserve collateral ligament and adjust the tension of collateral ligament. Twenty-six patients (24 women and 3 men) with average age of 59. 8years(range 35–80 years) were operated. Four patients were operated in both hands. Total of 93 joints were operated in 30 hands, average 3. 1 joints in one hand (4 in 16, 3 in 5, 2 in 5 and 1 in 4).
Follow up averaged 23. 9 (range 14–37) months. The average arc of motion was 47(20–85) ° and extension lag was significantly improved in most cases. Ulnar deviation recurred moderately about 25%, and 2 cases complained pain with flexion contracture. There were 3 dislocations and 2 loosening with fracture of the leg.
Surface type endoprosthesis preserving surrounding soft tissue is the optimal design in large implant arthroplasties. This new finger joints prosthesis provided cement-less joint fixture mechanism and surface type design and preliminary results were satisfactory. Although further follow up and more cases are required, this finger joint prosthesis has proven to be a very good alternative to silicone implant replacement especially for the young patients.
