Fig. 5.1
(a) Classic AP angles: 1 metatarsal 1–2 angle(IM angle), 2 hallux valgus angle, 3 distal metatarsal angle (proximal articular set angle), 4 distal articular set angle, 5 metatarsus adductus angle, 6 joint congruency, 7 tibial sesamoid position [7], 8 hallux interphalangeus. (b) Lateral projection angles: 1 Meary’s angle, bisection of talus and first metatarsal; 2 Seiberg index, lines parallel to dorsum of first and second metatarsals
Distal metatarsal articular angle (DMAA) or proximal articular set angle (PASA) is commonly discussed in association with HAV. There is a growing body of data suggesting that this measurement may be a radiographic artifact rather than a true deformity of the distal metatarsal surface. Coughlin and Freund [10] analyzed the intraobserver and interobserver reliability of radiographic assessments of hallux valgus. Their study validated the reliability of the hallux valgus angle and metatarsal 1–2 angles ; however, they questioned the reliability of the distal metatarsal angle (DMAA) . The common radiographic findings in hallux valgus was found to be the hallux valgus angle, metatarsal 1–2 angle, and sesamoid subluxation in the literature review by Coughlin and Jones [11]. This was later supported by Lee et al. in 2012 [12] who concluded that the hallux valgus angle had the highest reliability and the DMAA, the lowest among intraobserver and intraobserver reliability. However, they did observe that the DMAA did correlate with sesamoid rotation angle. Coughlin and Carlson [13] described angular osteotomies for hallux abducto valgus associated with increased metatarsal 1–2 angle, distal metatarsal angle, and proximal phalangeal articular angle. This at times incorporated a “triple” osteotomy of the first metatarsal base, first metatarsal head, and proximal phalanx.
Richardson et al. [14] described the DMAA (PASA) anatomically and how it varies with hallux valgus deformities. Vittletoe et al. [15] stated that the PASA measurement was unreliable. In 1993, Martin [16] found that the preoperative PASA observe rarely correlated with intraoperative findings. In 2002, Chi et al. [17] questioned the relevance of the DMA and offered that the rotation of the hallux may influence the measurement. Robison et al. [18] found that the linear correlation the DMAA correlated with the amount of frontal plane rotation of the first metatarsal. Dayton et al. [19] found that a reduction of PASA of 18.7° occurred after a tarsometatarsal arthrodesis was performed with frontal plane correction also correlating the measured PASA changes to frontal plane rotation. Jastifer et al. [20] compared radiographic DMAA versus anatomic and found only a 66% correlation. They believed that it was an important factor as it correlated with severity of hallux valgus. As a point of clarification on terminology, the distal metatarsal angle (DMAA) and proximal articular set angle (PASA) are indeed the same measurement and have been used interchangeably to define the metatarsal articular surface angulation. It is clear from analysis of the available literature that the reliability and clinical importance of the distal metatarsal angle is suspect. This is likely because radiographic DMAA/PASA assessment is a two-dimensional observation and is seen to change with the three-dimensional position of the first ray. Additionally, the presence of articular surface angular deformity has not been confirmed by intraoperative observation. The concept of joint congruency was identified by Piggot in 1960 [21]. Joints were classified as either congruous, deviated, or subluxated depending where joint lines intersected from the first metatarsal head and base of the proximal phalanx. This has been associated with adaptation of the joint surfaces which has common sense appeal but has not been shown to occur. It is not clear what the true effect of congruency has on the HAV deformity, and it is interesting to consider the possible effect frontal plane rotation has on this transverse plane radiographic measurement. Taking into consideration the serious questions that exist regarding DMAA/PASA and the changes that are seen with multiplane position, this often quoted radiographic finding may very well be an artifact driven by planar orientation.
Multiple researchers have associated the medial cuneiform shape with the possible etiology and progression of metatarsus primus adductus. In 1960 Lapidus [22] described an angular deviation of the medial cuneiform that has been call “atavistic.” This cuneiform shape finding was associated as a possible cause for development of hallux valgus deformity [23]. Vyas et al. in 2010 [24] found that the medial cuneiform obliquity angle was not related to juvenile hallux valgus. Conversely, Burns and Mecham in 2014 [25] pointed out that many theories of hallux valgus have suggested pathology at the metatarsal cuneiform joint; however, not all joint types with hallux valgus had abnormal shaped joints. This was substantiated by Doty et al. [26] who found that the first metatarsal cuneiform mobility was not related to joint shape or medial inclination angle. Saragas and Becker also confirmed that there was no relationship with the first metatarsal cuneiform angle and hallux valgus [27]. Additionally, Hatch et al. [28] found an inverse relationship to the joint obliquity and severity of hallux valgus and concluded that the joint obliquity was a poor indicator of the hallux abducto valgus deformity.
Sagittal Plane Evaluations
Over the past five decades, there has been substantial controversy regarding sagittal plane malalignment and instability of the first ray. Dietze et al. [29] described that in eight patients with “instability,” there was a correlation of increased intermetatarsal angle and increased dorsiflexion of the first ray. King et al. [30] described the metatarsal medial cuneiform angle (MMCA) and identified a correlation of increased angle associated with hallux valgus. Roukis and Landsman in 2003 [31] summarized in their literature review that there was no consensus for first ray range of motion. Standard sagittal plane assessment is usually performed by evaluation of Meary’s and the Seiberg index and indicated in Fig. 5.1b. This has correlation to sagittal plane range of motion as described by Samimi et al. [32]. Any plantar gapping at the first metatarsal cuneiform joint is also noted (metatarsal medial cuneiform angle) as described by King et al. [30]. They concluded that the pathology of HAV be evaluated by biplanar radiographs evaluating the entire foot complex and not just the forefoot deformities. With regards to clarity, sagittal plane instability is one of the most controversial topics with regard to evaluation and management of HAV.
Sesamoid Position
Another common radiographic measurement recommended for staging of HAV deformity and selecting corrective procedures is the transverse plane tibial sesamoid position (TSP) . Like other radiographic measurements discussed, the evidence describing the role sesamoid position plays in the development and correction of HAV has undergone an evolution. While a majority of authors state that sesamoid realignment is critical to overall hallux abducto valgus repair success, the challenge has been in the understanding of the mechanics [7, 33, 34]. In 1951 Hardy and Clapham [35] described the tibial sesamoid position from one to seven with seven being the most severe deformity of hallux valgus (Fig. 5.2). Early studies focus more on the AP radiographic view. Saragas and Becker [27] pointed out that the sesamoids are fixed and the metatarsal is the component that moves with increased severity. Additionally, Woo et al. in 2015 [36] substantiated that the lateral sesamoid release in surgical repair of hallux abducto valgus alone did not affect sesamoid position. Geng et al. [37] pointed out that the lateral sesamoid doesn’t change position relative to the second metatarsal confirming Saragas and Becker’s earlier study. Meyer [9] noted that a TSP of one was not observed in their “normal” population calling into question what we define as normal with regard to sesamoid station. A major concern with assessing TSP is whether what we see on the AP radiograph and use to define sesamoid subluxation is indeed accurate. Talbot and Saltzman [38] stated the AP radiographic view doesn’t correlate with the axial views. Similar to the medial sesamoid parameters of observed lateral sesamoid position has also been discussed [39, 40]. The effect of metatarsal eversion on the perceived sesamoid subluxation has been widely discussed in the past several years and cannot be discounted.
Kuwano [41] identified sesamoid rotation on axial views and described a sesamoid rotation angle. Further studies have elucidated the importance of frontal plane rotation of the metatarsal and subsequent sesamoid rotation. Dayton et al. [42] observed in their cadaveric study that frontal plane rotation correlated with changes in tibial sesamoid position (TSP) and IM angle. This was also corroborated by DiDomenico et al. in 2014 [43]. The identification of frontal plane rotation of the first metatarsal dates back to DJ Morton [44] and Mizuno et al. [45]. Authors have stressed the importance of getting axial radiographs to assess rotation of the sesamoids [46, 47]. The axial view in conjunction with the AP and LAT radiographic views provide a 3D representation of the first metatarsal and first ray position. Standardization of this view is important as there are many variables. Yildirim et al. [48] illustrated that the amount of dorsiflexion of the first metatarsal-phalangeal joint can affect the sesamoid position. They found that the more dorsiflexion of the joint, the greater tendency to have the sesamoids reduce under the metatarsal head. This was agreed upon by other researchers utilizing computerized tomography (CT) studies [48, 49]. The study by Lamo-Espinosa et al. advocated that the best position to evaluate the sesamoids would be at neutral position with no induced dorsiflexion by CT imaging. Kim et al. in 2015 [50] studied with a semi weight-bearing CT 19 ft without hallux valgus and 166 with hallux valgus. They identified rotation of the metatarsal as the alpha angle (Fig. 5.3). Based upon their findings, they categorized four different groups with hallux valgus sesamoid positions. This incorporated either plus or minus rotation of the first metatarsal (P+, P-) and plus or minus subluxation of the sesamoids (S+ S−) (Fig. 5.4). The class of P-S- was found in 2.4% of the hallux valgus group. P− S+ was present in 12.7%. P + S− was found in 25.9% and P + S+ was found in 61.4%. Total pronation was found in 87.3% and sesamoid subluxation was exhibited in 71.7%. Ideally neutral position CT studies should be evaluated in all patients with hallux abductovalgus. At the very least the evaluation of the sesamoid complex should be done with axial (coronal) radiographic views. Because of the variability discussed, further standardization of this method needs to be performed in the future.
Critique of Standard Assessments
As can be seen by review of the studies presented, traditional radiographic assessments of hallux abducto valgus have been frequently criticized in literature and have little scientific validation. Of all the angular measurements that have traditionally evolved, the only ones that have held up to critical analysis in recent literature and have proven reliable are the hallux valgus angle, metatarsal 1–2 angle (also known as intermetatarsal angle (IMA) , and the sesamoid position. Even attempts at augmentation with computerized assessments have failed. Various authors have questioned the intra- and interobserver reliability of standard manual radiographic assessment [51–53]. Computerized augmentation of measurements has been advocated as more reliable than manual methods [54–56]. Panchbhavi and Trevino [57] recommended computer-assisted radiographs measuring the width of the forefoot pre- and postsurgery. Ege et al. [58] advocated the use of iphone® software for evaluation of the HVA, IMA, and DMAA. Whatever the method, there is still a lack of interobserver reliability of these measurements. Certainly, more studies are needed to further delineate the pathomechanics of HAV.
The Effect of CORA on Our Understanding of the Deformity
The center of rotation angulation (CORA) as described by Paley [59] identifies the apex of the deformity. This may be done by means of the anatomic axis or mechanical axis. The anatomic axis is the bisection of the mid-diaphyseal osseous segments. This traditionally is the way the intermetatarsal angle (metatarsal 1–2 angle) is evaluated. Ortiz et al. [60] described an “angle to be corrected” utilizing the anatomic axis of the first metatarsal and the “predicted” anatomic axis. The mechanical axis is the line connecting the midpoint of the joint articular surfaces of the segment. Dayton et al. [61] identified the anatomic axis of the first ray to be the first metatarsal cuneiform joint (Fig. 5.5). The angular correction axis (ACA) is the chosen point of the surgical correction. If the ACA does not correlate with the CORA, then secondary deformities may occur. The anatomic CORA of the first ray is at the first metatarsal cuneiform joint. This was substantiated by Tanaka et al. [62] in their mapping study of hallux valgus.
The mechanical axis of the first ray may also be evaluated. This has range from the spherical midpoint (Mose Sphere) as advocated by Coughlin et al. [63] to the evaluation of hallux abducto valgus by the mechanical axis of the first ray by LaPorta et al. [64]. Even though that this evaluation hasn’t yet been validated, they found that the normal mechanical axis of the medial column and the mechanical axis of the first ray to be 11°.
One major issue in the assessment of postoperative repair of hallux valgus is the inaccuracies of using dual measurements. Hardy and Clapham [35] described the angle formed by the axis of the first and second metatarsals as an indicator for hallux valgus severity. Even though this is frequently utilized and attempted, there are many errors in this process [63]. One must keep in mind Paley’s deformity of correction principles to assess pre- and postoperative results. A common error is to identify preoperative anatomic metatarsal 1–2 angles and compare result with postoperative mechanical axis angles (Fig. 5.6a, b, c). Smith et al. [65] reported that the postoperative IM angles didn’t improve much after distal metatarsal procedures. With distal metatarsal procedures, Coughlin et al. recommended using a center of head technique with a Mose sphere [63]. The effect that this measurement technique has on postoperative results is discussed in further detail in chapter seven.
Fig. 5.6
(a) Preoperative AP assessment with IM angle of 17º. (b) Post operative AP assessment using the mechanical axis. IM angle is 4.7º. (c) Post operative AP assessment of anatomic axis of 9.6º. Clearly, the method utilized will change the perceived results of correction
Weight-Bearing CT Scanning
Two-dimensional studies have provided some insight into the pathology of hallux abducto valgus [66–68]. We must further look into the three-dimensional structure and kinematics of the first ray and it’s components. Historically we have gained some insight into the 3D nature of the deformity by comparing multiplane radiographic views. These relationships are being clarified with the advent of weight-bearing and semi-weight-bearing CT scanning. Scranton and Rutkowski’s study utilized axial sesamoid views to observe the position of the metatarsal [66]. They found feet with bunions had a mean of 14.5° of metatarsal pronation (eversion) versus the normal group having 3.1° of eversion. Mortier et al. [67] also used the axial views and found an average of 12.7° eversion of the metatarsal in the hallux abducto valgus group. Further support for the presence of first metatarsal rotation was identified on two-dimensional radiographs by Okuda et al. [69]. They found that the rounding of the lateral head of the first metatarsal was indicative of first metatarsal pronation/eversion. This was later confirmed by the study of Yamaguchi et al. in 2015 [70]. Additionally, the lateral bowing of the first metatarsal was thought to be a radiographic artifact caused by eversion of the first metatarsal segment making it appear more curved and present with cortical thickening [71].
Three-dimensional computed tomography (CT) has evolved to provide more insight into the pathomechanics of hallux valgus. More recently with the aid of technologic advances, Collan et al. [72] reported on the use of weight-bearing 3-D CT evaluating patients with hallux valgus [10] to a control group [7]. While not found to be statistically significant, they found that the amount of first metatarsal rotation of the hallux valgus group was 8° everted versus the control group of 2°. They found that the cuneiform was rotated into valgus to a greater degree than the first metatarsal although they were both rotated. One methodological issue that may confuse their findings is the fact that while the scans were taken weight bearing, the patient was in single-leg stance, not in functional angle and base of gait. This fact alters the overall kinematic relationships because in single-leg stance, the weight-bearing extremity is externally rotated inducing supination of the foot. Geng et al. [73] found that the medial cuneiform was more everted than the first metatarsal in the hallux valgus group. Their study utilized weight-bearing CT. Kim et al. in 2015 [50] utilized semi weight-bearing CT in their study of 19 control feet versus 166 ft with hallux valgus. They found a high incidence of first metatarsal pronation of 87.3% in the hallux valgus group. The amount of pronation averaged 15.8°. Their study also supported the findings by Smith et al. [65] regarding the amount sesamoid subluxation from the first metatarsal head stages 0–3. Lamo-Espinosa et al. [49] found in normal subjects (no HV deformity) that the CT appearance of the sesamoids was zero according to the classification of Yildirim et al. [48]. Katsui et al. [74] discussed a direct correlation of sesamoid displacement with increased severity of hallux valgus and arthritic changes. Kimura et al. [75] studied 10 ft with hallux valgus and ten normal feet with a simulated weight-bearing CT using 3-D computer analysis. They supported Geng et al. findings of increased valgus rotation of the medial cuneiform in hallux valgus patients. They also found that the navicular was more in a valgus position, while the first metatarsal relative to the cuneiform was slightly inverted in the hallux valgus group.
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