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What is hallux valgus (Bunion) deformity?
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| Clawed lesser toes: Often the second and third toes may gradually become curled up in association with worsening of the hallux valgus deformity due to mechanical reasons. |
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| Sesamoid bones: are the little bones within the tendons under the toe joint. They are similar in function as knee caps to the knees. |
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Hallux valgus is not only just a deformity of the big toe. It often eventually develops into a complex of misaligned bones in the forefoot. The most noticeable, but not the only, features of a typical hallux valgus deformity complex are the bunion, splayed forefoot and clawed lesser toes. The transverse metatarsal arch is almost always collapsed and producing the thick and painful callus under the middle of the forefoot. X-ray pictures would also reveal metatarsus primus varus deformity and dislocated sesamoid bones.
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Collapsed transverse metatarsal arch: While most people know about flat foot due to collapsing of the longitudinal arch on the inner side of the foot, there is also a transverse arch under the forefoot. It collapses as the result of metatarsus primus varus in hallux valgus deformity feet. |
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Thick and painful calluses: Due to abnormal pressure distributions in hallux valgus feet, thick and painful calluses can be developed under different parts of the forefoot. The principal and most painful callus is usually under the balls behind the second and third toes. This is related to the collapsed metatarsal transverse arch. After functional (vs. cosmetic) correction of the deformities the transverse arch should be restored and thus the callus disappears mostly if not entirely after bunion surgery. |
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How is hallux valgus (bunion) deformity developed?
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| First metatarsal bone: There are five long bones (metatarsals) behind the toes. |
The underlying cause of hallux valgus deformity is metatarsus primus varus. The cause-effect of these two deformities can be aptly expressed by the Chinese saying that "If a lower supporting column becomes tilted then the upper beam would become unleveled too." Metatarsus primus varus is the tilted lower column (first metatarsal bone) and hallux valgus is the misaligned upper beam (big toe). Therefore, hallux valgus is caused by leaning/tilting of the first metatarsal bone.
The development of hallux valgus deformity is started as soon as the first metatarsal bone starts to tilt (metatarsus primus varus) away from the second metatarsal bone. Once the first metatarsal bone starts to tilt towards the midline of the body (i.e.: away from the other metatarsal bones), the big toe will then be pulled over in the opposite direction by its tendons and muscles in the manner of a bow-string. The bunion deformity which forms the apex of the bow is created by the two tilting bones in opposite directions and it is actually the exposed first metatarsal head. This bow-string configuration can worsen gradually in time by additional deforming forces from even usual daily walking.
How is metatarsus primus varus developed?
| Metatarsus primus varus is developed when the first metatarsal bone is being forced away from the second metatarsal bone usually by forces exerted on it in daily walking activities, and additional abnormal forces from pronation of the foot and unhealthy shoes.
Some feet are particularly predisposed to such deformation due to inherent weakness/elasticity of the supporting soft tissues of the first metatarsal bone by heredity and greater flexibility among female population.
Tilting of the first metatarsal bone is considered the single most important underlying cause for bunion deformity. If possible, realignment of first metatarsal is always the primary objective in bunion surgery. Usually, once the tilting first metatarsal is corrected back to its normal alignment then the big toe will automatically be realigned by its own tendons due to resumption of their normal orientation in relation to the normalized first metatarsal alignment. |
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| Metatarsus primus varus: It means the first metatarsal bone tilts towards midline of the body. This change starts the domino effect of all other associated deformities in bunion foot. |
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| Pronation: is inward rolling of the foot and a form of flat foot. |
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| Unhealthy shoes: high heels, pointed and tight toe box |
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Who gets bunion (hallux valgus) deformity?
Up to 70-80% of people with bunion deformity have been reported to have a family history of the symptom. Their propensity and severity are greatly increased by wearing high heels and pointed shoes. Flat and pronated feet also increase their chance of developing bunions. Conversely, bunion (particularly metatarsus primus varus) causes flattening of a foot and increases flattening of a flat foot.
Is hallux valgus a cosmetic or function problem?
Feet with bunion deformity is obvious to everyone as being an unpleasant sight. However, it is unobvious to most observers and even some patients themselves that bunion deformity also represents a mechanical breakdown of the foot that is not only responsible for the pain experienced in the foot but also the leg and even low back. Bunion deformity actually represents a gradual collapsing process of several bonesˇ¦ alignment in the forefoot. At the same time the collective and interrelated function of these bones will deteriorate and finally alter the gait of the foot and leg. Consequently, bunion feet feel tired easily and can also lose balance in walking, in addition to having pain.
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