The theory of bunion pathogenesis and proper treatment has been very much discussed in the orthopedic literature. The wealth of information related to the surgical treatment of bunions has been modeled into what we often refer to as treatment procedures and principles. These procedures and principles are intended to ensure a uniform approach to the treatment of symptomatic bunions, but the variety of approaches to the treatment of bunions makes them a formality. The pathogenesis, examination, and treatment of bunions are described here in a single presentation that considers all perspectives. In addition, bunion is a complex deformity, and our understanding of it may be incomplete. Surgical treatment of bunions can be difficult. The notion that surgical treatment of bunions is evolving is a false argument, and today we can only say with certainty that the surgical approach remains variable. The established treatment process is unanimously accepted, but it is recommended here that the surgical capital treatment of bunions should be individualized for the particular patient.
I. Historical review and etiology
Bunion, a word derived from the Latin Bunion, meaning bighead, is a term that does not clearly define the disease. To our knowledge, the first person to publish Hallux valgus was Carl Hueter in 1870. bunion (Hallux valgus) is a progressive disease that develops due to poor shoe fit. There is support for this idea, but there is insufficient evidence that ill-fitting shoes are a causative factor for bunions. On the contrary, the observation that many people do not develop bunions despite wearing ill-fitting shoes for many years suggests an inadequate definition of bunion predisposing factors. Other studies have reported the onset of bunions in individuals who do not wear shoes, suggesting that congenital factors are a predisposing factor. Adolescent and male feet are not compressed by pointed shoes but develop bunions, suggesting the presence of congenital factors. The association of bunions with female gender has also been proposed as a common predisposing factor for bunions. The exact etiology of bunions remains unclear and may be a function of multiple factors. However, there is a tendency for bunions to worsen over time, which seems to be related to repetitive stress on the 1st metatarsophalangeal joint.
II. Pathogenesis
1. Anatomical factors
In people without bunions, the alignment of the bunion-metatarsophalangeal joint is.
(1) symmetrical alignment of the joint surface of the proximal end of the 1st phalanx with the joint surface of the 1st metatarsal head in the case of repetitive joint stress during the gait cycle.
(2) The position of the distal articular surface of the 1st metatarsophalangeal joint has a normal physiological position in relation to the axis of the 1st metatarsal stem.
(3) Stable and balanced soft tissue around the 1st metatarsophalangeal joint.
(4) A stable 1st metatarsocuneiform joint. There are no muscles or tendon junctions on the first metatarsal head, so changes in these physiologic factors can cause a bunion to occur.
The bunion is repeatedly pushed into a valgus position by forces, especially during weight bearing and walking, which ultimately results in valgus of the 1st metatarsophalangeal joint. The aggregation of ground reaction forces and the force of muscle activity cause the medial joint capsule to become weak, the lateral joint capsule and bunion tendon to contract, and the subsequent medial displacement of the 1st metatarsal head (creating a bunion).
Ground reaction forces may play a role in the gradual formation of the bunion. The forefoot is subjected to ground reaction forces greater than its weight with each step it takes. As these forces are transmitted across the metatarsal weakness of the bunion, the 1st metatarsal toe moves through physiological mobility. If the forces are transmitted to the medial metatarsal aspect of the bunion, these structures restrict the medial aspect of the 1st metatarsophalangeal joint and subsequently become weak. In this one model, any factor that acts on the medial aspect of the bunion and causes weight-bearing asymmetry can trigger a bunion. Narrow shoes and laxity of the 1st metatarsophalangeal joint can produce this type of situation.
Muscle forces that change through the 1st metatarsophalangeal joint also play a role in the development of bunion deformity. If the pulling forces of the medially active structures, especially the bunion tendon, are directed towards the metatarsal plane, then the forces against the bunion retractors are lost. The extensor hallucis longus (EHL) and flexor hallucis longus (FHL) will gradually become a group of forces acting on the lateral aspect of the joint. The metatarsal tendon membrane (strand mechanism) also shifts laterally, as does the short thumb flexor tendon. These contraction forces cause the ridge under the head of the 1st metatarsal to fail to maintain the correct trajectory of the seed bone. The force of the muscle across the metatarsophalangeal joint becomes the force that makes the bunion deformed.
2. A number of other factors are also involved in bunion formation, including
(1) flat feet.
(2) laxity of the 1st metatarsocuneiform joint.
(3) The relationship between the morphology of the 1st metatarsal head and the proximal phalanx.
(4) lesions of the medial joint capsule.
Flatfoot and bunion
Flat feet can cause bunions due to forefoot abduction, which causes an increase in nonphysiological stress on the medial aspect of the metatarsal side of the bunion when lifting the heel. The correlation between flat feet and bunions is controversial. Some authors have suggested that patients with flat feet are more likely to develop bunions than those with normal arches. But other people’s studies do not support this idea. This series of controversies are Level III to V evidence criteria, i.e., Level I evidence, is not sufficient to decide right from wrong on the issue of flat feet versus bunions.
1st metatarsocuneiform joint laxity
Mobility of the 1st metatarsocuneiform joint (TMT) can be observed in the sagittal or cross-sectional plane. The prevalence of medial column hypermobility in bunion patients remains controversial. Theoretically, laxity can cause bunions to occur in two ways. First, dorsal subluxation of the 1st metatarsal beyond the physiological range can cause a flatfoot-like morphology, increasing forefoot abduction and causing nonphysiological weight bearing on the medial side of the bunion during heel lift. Second, a more than physiologic range of medial subluxation of the 1st metatarsal increases the angle between the 1st and 2nd metatarsals and promotes the appearance of metatarsal inversion. The foot and ankle surgeon still holds the view, popularized by Morton, that laxity of the 1st metatarsal cuneiform joint or poor stability of the medial column of the foot is responsible for the appearance of bunions and causes pain, and Lapidus himself supports this view and proposes surgical treatment with a 1st metatarsal cuneiform joint fusion. However, this theory is convincing, but there is no evidence to support such a correlation, and in fact, other researchers have found that 1st metatarsal cuneiform joint laxity is not directly associated with bunions. There is insufficient evidence (Level Ⅲ to V) and no positive or negative studies to determine the relationship between 1st metatarsophalangeal joint laxity and bunion (Level I).
Characteristics of the 1st metatarsal head
A “square” or flat 1st metatarsophalangeal joint resists the forces of valgus and limits the development of bunions; in contrast, a rounded or concentric metatarsophalangeal joint is prone to bunions when valgus stresses continue to act on the bunion. To the best of our knowledge, it remains to be seen whether the shape of the metatarsal head contributes to bunions, and there is no evidence to support a correlation between metatarsal head shape and bunions.
Distal metatarsal articular surface angle (DMAA)
There may be a situation in which the 1st metatarsal and proximal phalangeal bunion joints are aligned and symmetrical, indicating that the patient is congenitally predisposed to bunions.
III. Clinical presentation
1. Medical history
Not all bunion patients are symptomatic. In addition to the obvious cosmetic deformity, patients will have pain caused by shoe wear, especially when wearing pointed shoes. Common complaints include pain at the medial prominence and pain with movement of the 1st metatarsophalangeal joint. There may also be pain in the 2nd metatarsophalangeal joint, which may be located under the 2nd metatarsal head, and sometimes the 2nd toe is impinged by the bunion. To determine the pain associated with the bunion, the physician should pay attention to the shoe restrictions and the limitation of movement caused by the deformity.
2. Physical examination
The severity of the bunion deformity, and the degree of flatfoot should be examined under weight. To observe the shoe fit, the doctor should pay attention to the contour of the patient’s foot for comparison with the shoe contour. In the patient’s sitting position, check for medial pain, 1st metatarsophalangeal joint movement, and 1st metatarsocuneiform joint laxity. Restricted movement of the 1st metatarsophalangeal joint, possibly with friction sounds, should alert the patient to possible degeneration of the 1st metatarsophalangeal joint.
There is no clear definition of normal 1st metatarsocuneiform joint mobility, and although there are many ways to examine 1st metatarsocuneiform joint mobility, hypermobility of the 1st metatarsal row is a controversial finding and difficult to diagnose. the Klaue meter can be used to measure 1st metatarsal row mobility, but it is not particularly useful in the outpatient setting. The clinical examination, which cannot be adequately performed for TMT, may only examine the mobility of the medial metatarsal row. The physician examines the 2nd metatarsophalangeal joint for synovitis, excessive metatarsal weight bearing, or 2nd toe deformity, which are also often associated with bunions.
3.Imaging
Proper examination of bunions requires weight-bearing frontal and lateral full foot x-rays. The angles are measured on these films and these angular relationships determine the degree of bone and joint deformity in the bunion. Other conditions, such as instability, arthrosis or poor alignment of joints elsewhere in the foot, or signs of vascular, neurological or systemic disease should also be noted. The oblique position of the foot can assist in examining these, but it is not used to measure parameters such as angles and is therefore not routinely taken. A weight-bearing seed bone image can be helpful in preoperative planning. The seed bone can show a lateral displacement in the weight-bearing orthostatic position, while the normal foot seed bone is located within the corresponding articular surface.
4. Imaging measurements of bunion patients
Parameters of the bunion deformity in the orthostatic position can help to have a basic judgment of the deformity. The bunion angle (HVA), defined as the angle between the axis of the 1st metatarsal stem and the axis of the proximal phalanx stem, is used to indicate the degree of deformity of the 1st metatarsophalangeal joint. Some authors consider the maximum limit of the normal bunion angle to be 15 degrees. The intermetatarsal interval angle (IMA), refers to the angle formed by the axis of the 1st and 2nd metatarsal trunks. This angle represents the degree of inversion of the metatarsals. The upper limit of normal is 9 degrees. Interphalangeal joint angle, the angle formed between the distal and proximal phalangeal axes of the bunion. The angle represents the degree of interphalangeal valgus (HVI) of the bunion. The upper limit of normal is 10 degrees. Distal articular surface angle (DMAA) evaluates the angular relationship between the articular surface of the metatarsal head and the 1st metatarsal trunk. The upper limit of normal is 10 degrees.
5. Radiographic measurements suggesting the presence of so-called laxity
Hyperplasia of the 2nd metatarsal trunk, medial orientation of the 1st metatarsal cuneiform joint, and tilting of the 1st metatarsal cuneiform joint are all considered to be indirectly indicative of overactivity of the 1st metatarsal row. Hyperplasia of the 2nd metatarsal tuberosity, especially in the medial cortex, is a sign of laxity of the 1st metatarsal row. There are no studies available to demonstrate that imaging changes in the 2nd metatarsal are associated with hyperactivity, however, one study found a marginal correlation between IMA and TMT joint dorsal mobility in patients with bunions. A medial orientation of the 1st metatarsocuneiform joint has also been suggested as a sign of hypermobility.
6. Severity
Imaging measurements of HVA and IMA can define the degree of bunion deformity. Operators usually use these results to select different surgical procedures. Bunions are defined as mild, moderate and severe. The HVA in the grading is relatively consistent (mild, less than 30 degrees; moderate, 30 to 40 degrees; and severe, greater than 40 degrees), whereas the IMA has variations in the grading (mild, less than 10 or 15 degrees; moderate, 10 to 15 degrees; and severe, greater than 15 or 20 degrees). We believe that these measures are more arbitrary in terms of grading, and recently, there is no evidence to support that absolute imaging measures can be used for bunion severity definition.
7. Non-surgical treatment
Non-surgical treatment of bunions can relieve symptoms and avoid causing complications that arise with surgical treatment. To ensure that non-surgical treatment of bunions is targeted, patients need to determine what the patient’s unique complaints are. Pain is usually not the primary symptom, but rather aesthetic problems, or difficulty wearing shoes, are often the main complaint. Because of the time required to recover from bunion surgery and the potential for complications, surgical treatment is not always necessary.
Pain can be relieved by changing shoes or changing the way you move. Wearing a pair of shoes with a wide foreshortening can be effective in reducing pain, and thick padding on the medial bony prominence or modifying the width of the shoe medially can also be effective. However, non-surgical treatment cannot change the bunion deformity, and only successful surgery can improve functional problems.