Thumb hypoplasia modified Blauth III B is usually treated by pollicization or, less commonly, by toe transfer. Both procedures always result in the resection of a body part, but with good cosmesis and acceptable function. We describe an intermetacarpal I/II arthrodesis with autologous bone graft augmentation to lengthen and stabilize the loose thumb. Clinical data were collected from nine patients, median age at surgery 3 years 8 months, with more than 7 years of follow-up. The results showed a grip strength on the Jamar dynamometer of approximately 61% of the unoperated hand. The Quick-DASH score was 11. The reconstructed thumb was 0.8 cm thinner and 1.9 cm shorter. Overall satisfaction on the VAS, with an average of 1.5 out of 10, is excellent with a partially usable thumb on a hand with five rays. The described procedure is a reliable treatment option with satisfactory results. In addition, none of the patients lost pincer grip between the second and third digit, but their thumb gained new function. Especially in environments where physical integrity has a high value, thumb construction instead of replacement could be considered.