The Hidden Disability Of Hallux Abductovalgus

Two recent studies validate an unforeseen risk of bunions which could cause catastrophic injury or even accidental death.^1,2 These studies contribute to a growing body of evidence that hallux abductovalgus (HAV) deformity is not simply a cosmetic concern, nor a minor annoyance. We now know that HAV deformity negatively affects balance and postural control, and several sources identify it as a significant risk factor for catastrophic falls.^1-8

The link between HAV deformity and fall risk first arose in a series of studies published by researchers at LaTrobe University in Australia.^3-8 These studies initially showed that foot deformities, such as hallux valgus and hammertoes, could affect balance and functional abilities in older people.^3-5 Two subsequent studies showed that patients with foot deformities reported more falls than those without foot deformities.^6,7 Then, a pivotal prospective study showed that specific foot problems such as hallux valgus, lesser toe deformities, and plantar calluses  increased the risk of multiple falls.⁸ Of all foot problems, HAV deformity has the highest prevalence in the patients with a history of multiple falls.^6-8

More recently, a group of researchers in Japan studied a group of 44 subjects (13 males, 31 females) with HAV deformity and compared them to a healthy group of 125 subjects without HAV.¹ Omae and coworkers used a force platform to measure static standing balance and postural sway in the study participants. The anterior-posterior postural sway was significantly greater in patients with HAV deformity by a magnitude of 20 percent. Furthermore, the magnitude of postural sway correlated with the severity of HAV deformity.¹ In other words, as the bunion deformity increases, one’s ability to stand upright and balance worsens.

In another recently published study, Shima and coworkers used various methods of measuring balance and postural control to study twenty patients with HAV deformity compared to twenty healthy controls.² Walking mobility, measured by the Timed Up and Go test (TUG), as well as functional balance, measured by the Berg Balance Scale (BBS), showed significant impairment in patients with HAV deformity.  Postural sway, measured with stabilometry, increased in patients with HAV deformity compared to healthy controls in all parameters tested. The researchers concluded that the study data supported the notion that patients with HAV deformity are at greater risk for catastrophic falls. Indeed, the subjects with HAV in this study showed a significantly increased fear of falling, as measured by the Falls Efficacy Scale (FES).²

How Does HAV Contribute To Fall Risk?

The mechanism by which HAV deformity may increase fall risk is multifactorial. The ability of a human to stand upright and ambulate with bipedal gait largely depends upon specialized features in the medial column of the foot not seen in other primates.⁹ The human foot is unique in that it has a longer, robust first metatarsal, abducted from the midline of the body to become more parallel to the long axis of the foot. This change in alignment of the first metatarsal brings the hallux into parallel alignment with the lesser digits. All these changes improve load-bearing capacity of the first ray and hallux during static stance and ambulation.¹⁰

In HAV deformity, medial displacement of the first metatarsal causes a loss of stiffness of the first ray, a condition commonly referred to as “hypermobility.”¹¹ The medial deviation of the first metatarsal in HAV deformity also compromises the primary stabilizers of the first metatarsophalangeal joint, which include the plantar aponeurosis and the flexor hallucis longus.¹² As a result, one can expect HAV deformity to reduce the load-bearing capacity of the first ray and compromise plantar purchase of the hallux. Both mechanisms potentially compromise balance and postural control.

Indeed, a prospective study by Mickle and colleagues validated that patients with HAV deformity have loss of plantarflexion strength of the hallux and also have an increased risk of traumatic falls.¹³ This study of 312 older individuals showed that hallux valgus and lesser toe deformity causes reduced plantarflexion strength of the toes, which increases the risk of falling in older people. In particular, hallux strength and the presence of lesser toe deformities were independent predictors of falls. Furthermore, individuals with hallux valgus and lesser toe deformities had weaker flexor muscles of the associated toes. The authors suggested that interventions focusing on exercises that strengthen the toe flexor muscles may be of benefit to prevent falls in elderly patients.¹³

Menz and coworkers underscored the importance of toe flexor strength through the development of a series of standardized tests for foot problems and correlated the results with the risk of falling in elderly patients in their prospective study.⁸ Two of these foot and ankle characteristics, toe plantarflexor weakness and disabling foot pain, significantly and independently associated with fall risk. This important study validated previous notions about the importance of toe grasping strength to maintain balance. This study also suggests that pain associated with foot deformities is also a risk factor for traumatic falls.⁸

Mickle and colleagues correlated foot pain, plantar pressure and fall risk in a prospective study of 162 community dwelling older adults.¹⁴ In this study, those who had a history of falls generated higher plantar pressures during gait and reported greater foot pain than those who had not fallen. The authors speculated that providing interventions for older individuals with foot pain and high plantar pressures may result in a reduced risk of falling.¹⁴ These interventions could include footwear with better cushioning under areas of high pressure, as well as podiatric care, which includes lesion debridement or orthotic treatment.

Foot pain in general is associated with an increased risk of falling.¹⁵ Pain can affect postural control and balance by limiting joint range of motion and interfering with proprioceptive input from joint mechanoreceptors.¹⁶ In the previously cited study published by Omae and team, subjects with HAV deformity had decreased lower leg muscle mass compared to healthy controls.⁷ It is possible that pain associated with joint subluxation or shoe pressure against the medial bunion in HAV deformity affects muscular activation of the foot and leg in a negative way which ultimately affects balance during standing and walking. This hypothesis warrants validation with further research.

Podiatric physicians can implement treatment interventions which can reduce risk of falling in patients with HAV deformity, as per a landmark study showing that a multifaceted, podiatry-based program reduced the incidence of falls in older adults by 36 percent over a 12-month period.¹⁷ This program incorporated several interventions which specifically address the mechanisms by which HAV deformity contributes to falls risk. Specifically, clinicians prescribed exercises to improve toe flexor strength and gave advice to improve the fit and function of footwear to accommodate deformity and reduce pain.¹⁷

It is tempting to assume that surgical correction could reduce the risk of traumatic falls posed by HAV deformity. Surprisingly, there are no studies that measure improvements of balance or postural control after HAV surgery or even after hammertoe surgery. Most scoring tools currently used to assess outcomes after HAV surgery do not include fear of falling as well as measures of balance and postural control.¹⁸ Future research should focus on measuring changes in balance and postural control after HAV surgery or digital surgery.

Final Thoughts

In conclusion, podiatric physicians should consider the significant global effects of HAV deformity which can negatively impact the health and well-being of their patients. It is clear that many patients with HAV deformity may be at risk for catastrophic falls. Patient education and implementation of simple interventions such as muscular strengthening and selection of appropriate footwear can go a long way to improve the quality of life of patients with HAV deformity.

Dr. Richie is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is a Fellow and Past President of the American Academy of Podiatric Sports Medicine. Dr. Richie is a Fellow of the American College of Foot and Ankle Surgeons, and the American Academy of Podiatric Sports Medicine. Dr. Richie is the author of a book titled "Pathomechanics of Common Foot Disorders," which is available from Springer at https://www.springer.com/us/book/9783030542009 .

References

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17. Spink MJ, Menz HB, Fotoohabadi MRf, et al. Effectiveness of a multifaceted podiatry intervention to prevent falls in community dwelling older people with disabling foot pain: randomized controlled trial. BMJ. 2011;342:d3411.

18. Hijji FY, Schneider AD, Pyper M,Laughlin RT.  The popularity of outcome measures in the foot and ankle literature. Foot Ankle Spec. 2020;13(1):58-68.