Osso buco is the traditional name in United States. Elsewhere, butchers sell the same piece — or a close cousin — under a different name.
Anatomically adjacent — tortuguita is on the upper rear leg, osso buco is the cross-cut shank below it. Both are slow-cook working muscles with significant connective tissue.
Both bone-in cross-cut braising cuts rich in marrow and collagen; osso buco gives a similar gelatinous sauce with more meat per portion.