Laboratory Studies
Generally, laboratory studies are not required for a routine assessment. However, if systemic or metabolic disease is suspected, the following studies can be of value in determining etiology or disease activity:
Radiography
Radiography continues to be the standard means by which to assess joint pathology and measure angular deformity. Other imaging studies usually do not help in determining the degree of deformity or in evaluating the condition of the joint. However, one possible adjunct study is radionuclide imaging [12] to rule out osteomyelitis if ulceration is present and if the radiographic findings are inconclusive.
Radiographic views
Weightbearing anteroposterior (AP), lateral oblique (LO), lateral (LAT), and sesamoid axial views should be obtained in the angle and base of gait (see the images below). Nonweightbearing radiographs may reveal the osseous relationships differently, causing an improper selection of surgical procedure. Weightbearing radiographs demonstrate the structural status of the foot.
Medial bony enlargement is more prominent on this lateral oblique projection than on other views.
The AP projection is used to determine the intermetatarsal angle (IMA), metatarsus adductus angle (MAA), hallux abductus angle (HAA), proximal articular set angle (PASA), and hallux abductus interphalangeus angle (HAIA), as well as the first metatarsal length, sesamoid position, condition of the first metatarsophalangeal (MTP) joint, bone stock, first metatarsal base, hallux rotation, and medial metatarsal head enlargement (see the images below).
The LAT projection is used to determine first metatarsal sagittal plane position and dorsal exostosis and/or osteophytes.
The LO projection is useful in evaluating bone stock and presence of dorsomedial exostosis. Because the bunion is located on the dorsomedial aspect of the metatarsal head, the prominence may be appreciated fully only in an oblique view.
In the sesamoid axial view, the sesamoids are observed for any lateral subluxation out of their respective grooves. As well, the crista is evaluated for erosion created by this subluxation. The joint sesamoid-metatarsal joint space is also examined for degenerative changes. [13]
Radiographic angular relations
Various angles, structures, and positions are assessed as listed below.
The normal IMA is 8-12° in a rectus foot and 8-10° in an adductus foot type. This angle is the relation between the longitudinal axis of the first and second metatarsals. If the angle is increased, the condition is termed metatarsus primus adductus. [14]
The normal MAA is less than 15°; more than 15° is considered adductus. This angle is the relation between the longitudinal axis of the lesser tarsus and the second metatarsal. This angle indicates whether the forefoot is in a rectus or adducted attitude in reference to the rearfoot. The rectus foot has an MAA of less than 15°. An angle larger than 15° causes the hallux valgus deformity to appear more severe than it actually is.
The normal upper limit for the HAA is 15-20°. This angle is the abduction of the longitudinal bisection of the proximal phalanx and first metatarsal; it is also known as the first-MTP angle. This is the primary method for quantification of the hallux abductus, either positional or structural.
The normal upper limit for the PASA is 7.5°. This is a measurement of the structural position of the first metatarsal head cartilage. It is used in determining whether the joint is congruent, deviated, or subluxated (see the image below).
The upper limit of normal for the distal articular set angle (DASA) is 7.5°. This angle detects structural abnormalities of the proximal phalanx base. Abnormalities may indicate the need for proximal phalanx osteotomies. The angle is determined by longitudinal bisection of the proximal phalanx of the hallux with reference to a line that connects the medial and lateral extents of the proximal phalangeal articular surface. The degree of abduction of the phalangeal bisection away from 90° determines this angle. [15]
Sesamoid positions 1-3 are normal, and the range is 1-7 (see the image below). In pathologic hallux valgus, the crista often is eroded as a result of the laterally deviated position of the sesamoids. The sesamoid position represents the degree of lateral subluxation of the sesamoid apparatus.
Tibial sesamoid position with bisection of first metatarsal. Positions 1-3 are normal. Positions 4-7 indicate erosion of crista and laterally track-bound, nonreducible hallux valgus.
The normal range for the first metatarsal declination angle is 15-30°. This angle is determined by bisection of the first metatarsal shaft in reference to the weightbearing surface. This is a useful evaluation for selection of a procedure that includes plantarflexion of the metatarsal in the sagittal plane.
The upper limit of normal for the hallux valgus interphalangeus angle (HVIA) is 10°. A larger angle indicates a structural deformity of either the proximal phalanx head or the distal phalanx base, which gives the hallux an abducted appearance that is occasionally confused with a hallux valgus deformity. Inability to detect an abnormal angle may lead the surgeon to overcorrect a hallux abductus. The angle of abduction is determined on an AP view from longitudinal bisection of the proximal phalanx compared with longitudinal bisection of the distal phalanx.
In a study aimed at assessing the intraobserver and interobserver reliability of radiographic methods used to measure the hallux valgus angle (HVA) and IMA and determining the most reliable method for making those measurements before and after a proximal crescentic osteotomy of the first metatarsal, Shima et al found the most reliable method to be one in which a line connected the centers of the first metatarsal head and the proximal articular surface of the first metatarsal to define the longitudinal axis of the first metatarsal. [16]
Radiologic pathology
Radiographs may be useful in evaluating the condition of the first MTP joint. Two main aspects should be evaluated.
The first aspect is the width and uniformity of the joint space (see the images below). Normally, the joint space appears uniform. An increase or irregularity is indicative of degenerative changes. Therefore, if the osteoarthritis is severe enough, a joint-destructive procedure should be entertained. [17]
The joint should also be evaluated for osteophytes at the articular margins. The normal joint is free of osteophytes. Osteophytes are yet another indication of the severity of degeneration.
Radiographic bone stock assessment
Radiography is an excellent method for determining the quality and density of bone. In general, bone density should be uniform and trabeculation should be fine. The head of the metatarsal should be evaluated for cysts. In the normal metatarsal head, cysts should not be observable. Cysts indicate structural adaptation of the bone to function and load, or systemic arthritis.
Severe osteopenia or cysts may preclude the use of various forms of internal fixation or osteotomy. Note any increased density of the second metatarsal, which indicates excessive forces on the second metatarsal due to instability of the first metatarsal. Stress fractures of the second metatarsal commonly occur in this setting (see the image below).
Large intermetatarsal angle and hallux abductovalgus deformity secondary to previous injury. Note increased cortical density of second, third, and fourth metatarsals.
Other radiographic findings
The hallux valgus, the medial eminence, and the soft tissue are evaluated as follows:
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Hallux valgus - No valgus rotation, as noted by the symmetrical concavity of the borders the medial and lateral shafts, should be evident. Asymmetry indicates the need for a procedure to the proximal phalanx to derotate the hallux
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Medial eminence - The normal metatarsal head is free from excessive bony proliferation; bony proliferation indicates an the imbalance of the joint with excessive medial tension
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Soft tissue - The soft tissues are evaluated for edema, bursae, calcification, or other signs of chronic inflammation
Staging
Root et al divided the pathomechanical development of hallux valgus into four stages as follows [18] :
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Stage 1 - Excessive pronation causes hypermobility of the first ray, causing the tibial sesamoid ligament to be stretched and the fibular sesamoid ligament to contract; lateral subluxation of the proximal phalanx occurs
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Stage 2 - Hallux abduction progresses, with the flexor hallucis longus (FHL) and flexor hallucis brevis (FHB) gaining lateral mechanical advantage
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Stage 3 - Further subluxation occurs at the first MTP joint, with formation of metatarsus primus adductus
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Stage 4 - The first MTP joint finally dislocates
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Rheumatoid arthritis. Note greater deformity of right foot (image left) versus left foot (image right).
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Rheumatoid arthritis. Note lateral deviation of hallux, cystic changes of metatarsal head, and hammertoe of lesser digits.
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Line of pull of extensor hallucis longus causing metatarsal to deviate medially and hallux to deviate laterally.
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Nonweightbearing foot. Note medial prominence, contracture of extensor hallucis longus, and callus on second digit.
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Nonweightbearing foot with range of motion being assessed of first ray, which is currently in neutral (neither plantarflexed or dorsiflexed) position.
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Lateral view of first metatarsophalangeal joint with ligaments of sesamoid complex.
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Plantar muscles that contribute to deforming forces.
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Anteroposterior and lateral radiographs, weightbearing views.
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Medial bony enlargement is more prominent on this lateral oblique projection than on other views.
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Template showing angular measurements.
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Another template showing increased angular relationships.
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Congruency of first metatarsophalangeal joint.
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Tibial sesamoid position with bisection of first metatarsal. Positions 1-3 are normal. Positions 4-7 indicate erosion of crista and laterally track-bound, nonreducible hallux valgus.
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Bunion deformity with minimal joint destruction.
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Bunion deformity with significant joint destruction.
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Large intermetatarsal angle and hallux abductovalgus deformity secondary to previous injury. Note increased cortical density of second, third, and fourth metatarsals.
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Algorithm for choosing surgical correction of hallux abductovalgus. Click image to enlarge.
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Hallux abductovalgus deformity.
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Postoperative radiograph obtained after head osteotomy.
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Preoperative radiograph.
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Postoperative radiograph shows Keller, or resectional, arthroplasty.
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Preoperative radiograph shows degenerative joint disease.
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Postoperative radiograph obtained after resectional arthroplasty and total joint implant placement.
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Preoperative template for implant placement.
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Preoperative radiograph shows arthrodesis.
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Postoperative radiograph show arthrodesis.
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Preoperative radiograph shows hypermobile first ray.
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Postoperative radiograph shows arthrodesis of first metatarsocuneiform.
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Lateral release sequence: (1) release of conjoined adductor hallucis tendon, (2) release of fibular sesamoid ligament, (3) tenotomy of lateral head of flexor hallucis brevis, and (4) excision of fibular sesamoid.
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Severe hammertoe deformity in second toe overlapping great toe with associated hallux valgus deformity.
