6 Preoperative Assessment in Hallux Valgus DAVID M. LAPORTA THOMAS V. MELILLO VINCENT J. HETHERINGTON The goal of any bunion surgery is the elimination of tivity, and external environmental factors play a signifi- pain, restoration of a congruous metatarsophalangeal cant role in the development of hallux abducto valgus joint, realignment of the hallux into a rectus position, deformities. This belief persists despite historical stud- and preservation of joint motion. The best method for ies that demonstrate these are aggravating factors, not predicting a successful surgical result in hallux valgus primary pathologies. Hereditary factors are known to reconstruction is thorough preoperative planning. be causative only in that it is the foot type with its This helps ensure selection of the appropriate proce- associated biomechanical abnormalities that is inher- dure to attain these goals. Preoperative planning ited, not necessarily the resulting pathologic condition should include a thorough history as to the progres- known as hallux abducto valgus. sion of the deformity and an adequate clinical and radiographic examination. In addition, addressing the deformity by the choice of surgical procedures re- Biomechanical Etiology quires identifying its etiology and pathomechanics. The biomechanical etiology of hallux abducto valgus This chapter reviews and details pertinent features of has its origin in the rearfoot. The subtalar joint range the preoperative clinical and radiographic examina- of motion when excessive will most often lead to a tion. pronated foot. External factors such as limb rotations and equinus conditions tend to accelerate the patho- ETIOLOGY logic processes associated with hallux abducto valgus. The sequence of events usually commences when the The hallux abducto valgus deformity may result from a calcaneus everts beyond the vertical in an excessively variety of contributing factors. Proper historical and pronated foot. The resultant eversion unlocks the mid- clinical assessment of the patient in both a non-weight- tarsal joint, allowing the axes of the talonavicular and bearing and weight-bearing manner and a thorough calcaneocuboid joints to become parallel to each biomechanical evaluation, as well as an understanding other and resulting in an unstable midtarsal joint. This of the microscopic pathologies occurring in and instability, which persists during stance, allows for hy- around the first metatarsophalangeal joint, will ensure permobility of the first ray at the time it should be a more predictable surgical result by selection of the most stable for propulsion.1-3 appropriate procedure or procedures. At the same time, the soft tissue musculature around A historical review of the various etiologies shows the rearfoot and first ray become altered in the prona- that some still believe that shoe choice, excessive ac- ted foot. With calcaneal eversion, the pull of the flexor 107 108 HALLUX VALGUS AND FOREFOOT SURGERY hallucis brevis and longus are altered. In addition, placed on the medial side of the first metatarsophalan- with an unstable midtarsal joint the route of the pero- geal joint. The fibular sesamoidal ligament, con- neus longus muscle tendon is altered, thereby affect- versely, functionally shortens along with the other lat- ing the motion about the first ray. The peroneus eral soft tissue structures. The first metatarsal rotates longus muscle, coursing around the cuboid, normally slightly at the metatarsal cuneiform articulation. In a inserts into the base of the first metatarsal and the pronated foot, this slight rotation of the metatarsal al- medial cuneiform and stabilizes the complex at toe- lows for an inversion or varus rotation of the first off. In a pronated foot, the peroneus longus cannot metatarsal head relative to the sesamoids. The hallux perform this function, and the resultant muscular and now moves in the opposite direction of the first meta- biomechanical alteration results in a hypermobile first tarsal head, which accounts for the valgus or rotational ray.4-9 component of the deformity. As the amount of hallux With the preceding definition and an understanding eversion increases over time, the tibial, intersesa- of the mechanics of hypermobility of the first ray as an moidal, and fibular sesamoidal ligaments continue to etiology in hallux abducto valgus deformity, the first- adapt functionally to the deformity. The surgical im- ray axis and biomechanics of the subtalar and midtar- portance of the soft tissue adaptation lies in the fact sal joints can be discussed. The first ray possesses a that if valgus rotation of the hallux is a component of triplane axis that courses in an anterior, lateral, and the deformity and if transection of the fibular sesa- dorsal direction.3,10 Therefore, dorsiflexion of the first moidal ligament is not accomplished, there will still metatarsal will be accompanied by adduction and be some degree of valgus rotation left in the great toe. plantar flexion will be accompanied by abduction. With the advent of biomechanics and a more de- Motion about the first ray is dependent on the pero- tailed radiographic evaluation of the deformity, the neus longus muscle. As was previously discussed, the etiology in hallux abducto valgus deformity has be- peroneus longus muscle in turn is dependent on the come more refined and may be categorized as fol- stability of the midtarsal joint because it uses the cu- lows3 : boid as its fulcrum. From the cuboid this muscle courses anterior and dorsal to exert its stability on the 1. Hypermobility of the first ray first ray. The triplane stability exerted on the first ray 2. Instability of the midtarsal joint in normal biomechanics is one of plantarflexion, ab- 3. Calcaneal eversion beyond vertical duction, and a posterior pull. In normal gait therefore 4. Instability of the peroneus longus as the foot progresses from midstance into propul- sion, the supinating subtalar joint also locks the mid- tarsal joint; this ensures a stable lateral column of the Metatarsus Primus Varus foot and provides the peroneus longus muscle with an efficient fulcrum at the cuboid to exert a plantar, lat- The first metatarsal articulates proximally with the first eral, and posterior pull on the first ray. Consequently, cuneiform via their articular surfaces and strong liga- any pronatory influence that causes an unlocking of mentous support. As a result, any deviation or abnor- the midtarsal joint may result in metatarsus primus mality in this articulation can give rise to deformity. adductus over a period of time.3,5 Some of the terms used to describe this relationship Finally, it should be remembered that the first meta- between the first metatarsal and the cuneiform, as well tarsal head is firmly bound to the sesamoids by the as the relationship between the first metatarsal and the tibial and fibular sesamoidal ligaments.11,12 In the early second metatarsal, are metatarsus primus varus, meta- stage of hallux abducto valgus deformity, these two tarsus primus adductus, and an increased intermeta- ligaments firmly hold the sesamoids to the metatarsal tarsal angle. Quite often, and erroneously, these head. Therefore, the early radiographic view of the terms are used interchangeably. In reality, the term deformity is actually dorsiflexion, adduction, and in- metatarsus primus varus classically is used to describe version of the first metatarsal. As the deformity prog- a condition in which both medial and lateral cortices resses over time, the tibial sesamoidal ligament be- of the metatarsal are of equal length, but there is an comes functionally elongated as it adapts to stress increase in the measurable angle between the first and PREOPERATTVE ASSESSMENT IN HALLUX VALGUS 109 second metatarsal that is secondary to a deviation at Hardy and Clapman9 were the first to demonstrate that the first metatarsocuneiform joint. in younger patients it is an increase in the metatarsus Additionally, there exists a difference in the margins primus adductus of the first ray that initiates the trans- or sides of the cuneiform such that the lateral margin verse plane rotation of the great toe. Of 78 patients as compared to the medial margin of the first cunei- who developed adult hallux valgus deformity, it was a form is longer, causing an oblique angulation of the consistent finding that the initiating factor in the osse- first metatarsocuneiform joint. 13,14 The clinical and ra- ous structure was an increased intermetatarsal angle, diographic effect is an increased intermetatarsal angle which was later followed by the hallux moving away measurement on radiographs, and a pronounced first from the midline of the body. metatarsal medially on palpation. This type of cunei- form has often been termed atavistic and was origi- nally discussed by Lapidus15 in the surgical correction CLINICAL EVALUATION of hallux abductor valgus deformity. Klienberg in 193216 believed that such obliquity at the first metatar- The podiatric surgeon should never base the selection sophalangeal joint represented a medial cuneiform of a surgical procedure solely on any one set of find- that was an atavistic remnant of a period when the ings or evaluations. It is only after a thorough history hallux had a prehensile thumb-like function. and clinical examination in conjunction with assess- The alternative concept of an os intermetatarsum as ment of standardized radiographs that one may con- the proximate cause of a true metatarsus primus varus sider the appropriate surgical procedure that will was a poor attempt to explain its occurrence. Objec- yield the best long-term result. All too often the preop- tive studies by Wheeler17 failed to demonstrate the erative clinical examination of the deformity is limited correlation between the presence or absence of an os to the patient seated in the chair. It should be remem- intermetatarsum and the development of metatarsus bered that hallux abducto valgus is a dynamic propul- primus varus. sive phase deformity that obligates both non-weight- The radiographic diagnosis of metatarsus primus bearing and weight-bearing examination, as well as varus may be demonstrated by comparing the longitu- palpation and gait analysis.