A Novel Option for Thumb Reconstruction
Investigators from Stockholm, Sweden, recently published a long-term follow-up study on 13 patients with thumb amputations who underwent a two-stage reconstruction. First, they implant a metal receptacle into the bony remnant and anticipate bone ingrowth into the fixture. On an average of 3 months later, the skin on the end of the amputation stump is thinned to stimulate skin healing directly to the bone. Then an abutment screw is pressed through the skin into the fixture to provide an exposed metallic post to which a custom cosmetic prosthesis is attached. implantation of a metallic implant into their bony remnant.
The investigators started using this procedure in 1990 using custom-designed experimental implants in three patients. Beginning in 2004, they have used a standardized implant in an additional 10 patients and now report on follow-up as long as 25 years (average 9.5 years). The researchers considered failure as removal of the fixture, and at regular follow-up appointments measured DASH scores, pinch and grip strengths, monofilament threshold sensory testing, and the Sollerman standardized hand function test.
Two patients died from unrelated causes during the course of the study. Four were non users. Two of these had their implants removed because of loosening, one had a deep infection which required hardware removal, and one patient decided not to use any prosthesis after a year. Five other patients have had seven superficial infections around the skin openings, and all were treated successfully with antibiotics and local wound care.
There were eight mechanical complications in the three original patients treated with the custom-designed implants before 2005. These included bending or breakage of the percutaneous post, and all were successfully treated with post replacement. No mechanical complications were noted for the patients who received the standardized implant beginning in 2005. For both types of implant, no failures have occurred after the first year, with the longest follow-up being 25 years.
For the seven patients who were available for functional testing, they used their prostheses every day for 8 – 24 hours. The average grip, tip pinch, and key pinch strengths were 70%, 66%, and 71% of the unaffected hand, respectively. The mean value of all scores from the Sollerman hand function test was 76 out of a possible 80 points. All patients were able to feel touch on their prostheses. One patient could detect the 2.83 (.08 gram) S-W monofilament, one could detect the 3.61 (.22 gram) monofilament, two had protective sensation, and three others could feel deep pressure.
DISCUSSION Function of the cosmetic prosthesis fixed to the thumb remnant through an osseointegrated fixture and percutaneous post parallels function following a toe-to-thumb transfer. All of the prosthetic users regained at least some sensibility, evidence for osseoperception, that has been observed previously in individuals receiving dental or extremity osseointegrated prostheses. The mechanism for this perception is uncertain. The sensibility present in the osseointegrated prostheses provides a distinct advantage over an ordinary hand prosthesis, where the user has no tactile feedback and instead has to rely on visual clues. The procedures of fixture and post placement are markedly easier than toe-to-thumb transfer and do not incapacitate the foot. Infections can be problematic with the percutaneous post, but most have been managed successfully with preservation of the implants. Since the investigators implemented standard implant components and a strict rehabilitation program in 2005, they have had 100% success for the six patients with average follow-up of seven years (longest ten years).
COMMENT The concept of leaving a metallic implant sticking through the skin for years is counterintuitive. The investigators’ success in recent cases stems from their experience in gaining osteointegration of the implant and stabile, non-mobile skin surrounding the post. Clearly, this is not a commonly used method of thumb reconstruction but certainly has its merits in terms of simplicity compared to toe transfer and the restoration of at least some sensibility compared to standard prosthetic fitting. It is a procedure that all hand care specialists should be aware of when discussing reconstruction options with patients who are missing thumbs.