Purpose <p>Forefoot deformities in rheumatoid arthritis (RA) cause painful plantar callosities and severely impair quality of life. Although resection arthroplasty has historically been the standard surgical treatment, it sacrifices metatarsophalangeal (MTP) joint function. This review describes Combination Metatarsal Osteotomies for Shortening (CMOS), a joint-preserving surgical technique of Japanese origin, and presents its concept, indications, surgical technique, and clinical outcomes.</p> Methods <p>CMOS combines three types of proximal metatarsal shortening osteotomies tailored to the anatomical characteristics of each metatarsal: a modified Lapidus procedure for the first metatarsal, proximal oblique shortening osteotomy for the second to fourth metatarsals, and diaphyseal oblique shortening osteotomy (modified Coughlin procedure) for the fifth metatarsal.</p> Results <p>Proximal shortening osteotomy simultaneously achieves shortening and elevation of the metatarsal head, relieving soft tissue tension around the MTP joint and facilitating joint reduction without extensive soft tissue release. Long-term follow-up studies have confirmed maintenance of correction and preservation of joint function. A review of the international literature reveals that the vast majority of publications on joint-preserving surgery for RA forefoot deformity originate from Japan, with the corresponding author’s 2010 publication serving as the foundation for subsequent research by numerous Japanese investigators.</p> Conclusion <p>CMOS is an effective joint-preserving procedure that restores both function and appearance in RA patients with forefoot deformity, and represents a central technique in a field where Japan continues to lead the world.</p>