We report a first case of hallux rigidus successfully treated in an elderly patient by intra-articular infiltration of cross-linked hyaluronic acid (HA) 21 mg/mL with mannitol (Desirial Plus) and review the previous literature on the different compositions of HA infiltrative treatment applied to hallux rigidus. A 77-year-old female patient with moderate unilateral pain of 6 months of evolution and stiffness of the movement of the first metatarsophalangeal joint of the left foot, corresponding to grade 2 of the classification proposed by Coughlin and Shurnas. The objective of the study was to perform a pilot test to (a) evaluate the correct technique of intra-articular infiltration as well as (b) the use of a commercial cross-linked HA 21 mg/mL with mannitol, to a voluntary patient diagnosed with hallux rigidus. A single cross-linked HA infiltration is applied to the first metatarsophalangeal joint with an administered amount of 1 mL. The loaded dorsiflexion, the unloaded dorsiflexion, and the unloaded plantarflexion angles of the first metatarsophalangeal joint improved from 15°, 20°, and 10°, respectively, before injection to 45°, 52°, and 22°, respectively, at 14 days after injection. Moreover, these improvements maintained until the final follow-up (400 days). The intensity of pain, according to the visual analog scale, improved from 7 of 10 before the injection, passing through 4 of 10 at 14 days after the injection, to 1 of 10 at 60 days after the injection. Cross-linked HA 21 mg/mL with mannitol improves symptomatology, joint mobility of the first metatarsophalangeal joint, and quality of life in the patient with stiff hallux submitted to the pilot test. These effects have been maintained for more than 14 months.