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Lateral Sesamoid Position Relative to the Second Metatarsal in Feet With and Without Hallux Valgus: A Prospective Study
The Journal of Foot & Ankle Surgery xxx (2015) 1–4
Contents lists available at ScienceDirect
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Original Research
Lateral Sesamoid Position Relative to the Second Metatarsal in Feet With and Without Hallux Valgus: A Prospective Study Xiang Geng, PhD 1, Chao Zhang, MD 2, Xin Ma, MD 3, Xu Wang, MD 4, Jiazhang Huang, MD 2, Jian Xu, PhD 1, Chen Wang, MD 1 1
Resident, Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai, China Attending Physician, Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai, China Professor, Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai, China 4 Associate Professor, Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai, China 2 3
a r t i c l e i n f o
a b s t r a c t
Level of Evidence: 4
We sought to determine whether hallux valgus displaces the sesamoid bones laterally away from a stationary first metatarsal or whether the first metatarsal head is displaced medially from the stationary sesamoids, which remain in position relative to the rest of the forefoot. We reviewed weightbearing radiographs in the dorsal plantar view of 128 consecutive patients (149 feet) seen over 2 months in 2014. Of these, 82 feet (55%) had a hallux valgus angle of >15 (hallux valgus group) and 67 feet (45%) had an angle of no more than 15 (control group). We measured the absolute distances from the center of the lateral sesamoid and the first metatarsal head to the long axis of the second metatarsal. Next, the relative distances, defined as the ratio of these 2 absolute distances to the length of the second metatarsal, were calculated to adjust for foot size. Both the absolute and the relative distances from the center of the first metatarsal head to the second metatarsal differed significantly between the 2 groups and correlated positively with the hallux valgus angle and first intermetatarsal angle. However, neither the absolute nor the relative distance to the lateral sesamoid bone differed significantly between the groups, nor did they correlate with either of the 2 angles. Thus, despite medial shifting of the first metatarsal in hallux valgus, the lateral sesamoid retains its relationship to the second metatarsal in transverse plane. Its apparent lateral movement is a radiographic misinterpretation. Awareness of this misinterpretation should improve the success of corrective surgery. Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: dorsal plantar radiographs hallux valgus second metatarsal sesamoid subluxation
Two sesamoid bones are nearly always present at the first metatarsophalangeal joint. They lie on either side of the flexor halluces longus and are connected by an interosseous ligament, although congenital absence of the medial sesamoid has been infrequently reported (1). Sesamoid subluxation away from the head of the first metatarsal is commonly found in feet with hallux valgus (HV) and is important in disease progression and the potential for recurrent deformity (2–4). Many studies have investigated the relative location and articulation between the sesamoids and the first metatarsal (4–10). However, not knowing the actual location of the sesamoids with respect to the rest of the forefoot can confuse corrective operations for HV. For example,
Financial Disclosure: This work was supported by the National Natural Science Foundation of China (Grant 81171670). Conflict of Interest: None reported. X. Geng and C. Zhang contributed equally to this report. Address correspondence to: Xin Ma, MD, Department of Orthopedics, Huashan Hospital, Fudan University, 12 Middle Wulumuqi Road, Shanghai 200040, China. E-mail address: [email protected] (X. Ma).
the question remains whether the sesamoids should be pulled medially to restore their relationship with the first metatarsal head or the first metatarsal head should be pulled back to the sesamoids. Many investigators have also proposed that, in reality, the subluxation is caused by the first metatarsal head drifting medially away from the sesamoidsdthat is, the sesamoids actually maintain their position (11–18). However, few to date have systematically investigated the actual relationship between the lateral sesamoid and the second metatarsal in feet with different hallux valgus angles (HVAs) or intermetatarsal angles (IMAs), but this relationship is also instructive for corrective operations. For example, should only the ligament between the sesamoids and the first metatarsal head be released, or should the soft tissue connecting with lateral metatarsals also be cut. We sought to determine whether the lateral sesamoid actually moves laterally in HV or whether its apparent lateral movement is a radiographic misinterpretation. Thus, we compared, in a prospective cohort study, the position of the lateral sesamoid bone and the first metatarsal head relative to the second metatarsal on weightbearing dorsal plantar (DP) radiographs of feet with and without HV. We also
1067-2516/$ - see front matter Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2015.08.023
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X. Geng et al. / The Journal of Foot & Ankle Surgery xxx (2015) 1–4
correlated these distances with the HVA and first IMA to determine whether the position of the sesamoids was associated with HV. Patients and Methods Patients The institutional review board of our hospital approved the study. All patients gave written informed consent to participate. All the patients who had attended our outpatient department for HV or other foot problems from August 1 to September 30, 2014 were eligible for the study to achieve the estimated sample size. Patients <20 years old and those with foot deformities, infection, or a history of trauma or surgery were excluded. After the purpose of the research was explained and informed consent obtained, standard weightbearing DP radiographs were taken of the affected feet, with the central beam inclined at 15 from the coronal plane and targeted at the midtarsal joints. The tube-to-cassette distance was 1 m. Feet with an HVA of >15 were classified as having an HV deformity, and those with an angle of no more than 15 were classified as controls. Because we merely obtained conventional DP radiographs, HV in our study was defined only according to the transverse plane deformity. Measurements Measurements were mainly taken using the CentricityÒ Web, version 3.0, digital viewing system (GE Healthcare, Cleveland, OH) by the first author (X.G.). The HVA was measured between the long axes of the first metatarsal bone and the proximal phalanx, and the IMA was measured between the long axes of the first and second metatarsal (Fig) (19). All these lines should be the mechanical axes as defined by Paley and
Tetsworth (20). In brief, the axis of the proximal phalanx was drawn through the center of the proximal articular surface and the center of the distal end of the diaphysis. The axis of the second metatarsal was drawn from the center of the distal articular surface to the center of the proximal end of the diaphysis. Finally, the first metatarsal axis was drawn to connect the center of the first metatarsal head and the center of the first metatarsal base, as described by Miller (21). We believe this method is the most precise and least-biased method of identifying the axis of the first metatarsal (22). The lateral sesamoid position (LSP) relative to the second metatarsal in the present study was defined as the shortest distance from the center of the lateral sesamoid to the axis of the second metatarsal (Fig.). The position of the first metatarsal (M1P) was defined as the shortest distance from the center of the first metatarsal head to the axis of the second metatarsal. To adjust for differences in foot size, the deviation coefficient for the lateral sesamoid (LSDC) and the deviation coefficient for the first metatarsal (M1DC), respectively, were defined as follows: LSDC ¼ LSP=LM2 and M1 DC ¼ M1 P=LM2 where LM2 is the length of the longitudinal line of the second metatarsal.
Measurement Reliability Ten feet were selected without known bias, and the HVA, IMA, LSP, M1P, and LM2 were measured twice, 1 week apart by the same author (X.G.) to determine the intrarater reliability. Next, 2 independent authors (C.Z., J.X.) measured the HVA, IMA, LSP, M1P, and LM2 to determine the interrater reliability. The intraclass correlation coefficients were calculated for both intrarater and interrater reliability (23).
Statistical Analysis The measurements of the LSP, M1P, LSDC, M1DC, and LM2 were compared between feet with and without HV using the Student t test. The linear relationships between the LSP, M1P, LSDC, or M1DC and the HVA or IMA were assessed using Pearson’s correlation coefficients. All data conformed to the assumptions of the tests used to analyze them. Alpha was set at 0.05, and all tests were 2-tailed. The data were analyzed using the SPSS, version 21.0 statistical software package (IBM Corp., Armonk, NY) by 1 of us (C.W.).
Results Demographic Information Of the 128 enrolled patients (149 feet), 82 feet (55%) (from 63 females [77%] and 19 males [23%]) had HV. Their median age was 56.5 (range 20 to 81) years. The remaining 67 feet (45%) (from 43 females [64%] and 24 males [36%]) did not have HV and constituted the control group. Their median age was 53 (range 20 to 72) years. The groups did not differ in age or sex (p ¼ .56 and p ¼ .09, respectively). Measurements and Reliability
Fig. Measurements to locate the sesamoid bones in relationship to the other bones of the foot. Line A is the axis of the first phalanx; line B, the length of the second metatarsal; line C, the distance from the first metatarsal head to the long axis of the second metatarsal; line D, the distance between the center of the lateral sesamoid bone and the axis of the second metatarsal; line E, the axis of the first metatarsal; and line F, the axis of the second metatarsal. The hallux valgus angle is the arc between lines A and E, and the intermetatarsal angle is the arc between lines E and F.
The intrarater and interrater reliability was excellent (Table 1). Both the absolute deviation of the first metatarsal from the second metatarsal (i.e., M1P) and the ratio calculated to control for foot size variation (i.e., M1DC) exhibited significant differences between the HV and non-HV groups (Table 2). Both values were increased in feet with HV, indicating movement of the first metatarsal away from the second. In addition, both the larger absolute distance (i.e., M1P) and the ratio (i.e., M1DC) correlated with larger HVA and IMA measurements (M1P to HVA, r ¼ 0.52, p < .001; M1P to IMA, r ¼ 0.68, p < .001; M1DC to HVA, r ¼ 0.60, p < .001; and M1DC to IMA, r ¼ 0.75, p < .001). More importantly, neither the absolute distance from the lateral sesamoid to the second metatarsal (i.e., LSP) nor the ratio calculated to normalize the foot size variation (i.e., LSDC) differed significantly between the 2 groups. Both values showed no increase in feet with HV, indicating the lateral sesamoid was stationary relative to the second metatarsal. Furthermore, neither the LSP nor the LSDC correlated with the HVA and IMA measurements (LSP to HVA, r ¼ 0.08, p ¼ .33; LSP to IMA, r ¼ 0.09, p ¼ .25; LSDC to HVA, r ¼ 0.18, p ¼ .13; and LSDC to IMA, r ¼ 0.18, p ¼ .12).
X. Geng et al. / The Journal of Foot & Ankle Surgery xxx (2015) 1–4
Table 1 Reliability of measurements in a study of sesamoid subluxation in hallux valgus (n ¼ 10 measurements for each variable) Measurement
Interrater Correlation
Intrarater Correlation
Hallux valgus angle Intermetatarsal angle Position of the lateral sesamoid* Position of the first metatarsal heady Length of the second metatarsal
0.97 0.92 0.87 0.90 0.96
0.98 0.92 0.89 0.91 0.98
* Distance between the center of the lateral sesamoid bone and the axis of the second metatarsal. y Distance between the center of the first metatarsal head and the axis of the second metatarsal.
Discussion The sesamoid bones are an integral part of the function of the first metatarsophalangeal joint. However, they appear on radiographs to be laterally displaced relative to the first metatarsal head in feet with HV. Because of the relationship between the sesamoids and the first metatarsal, different methods of staging the extent of sesamoid subluxation have been investigated using either DP or tangential radiographic views (6–8,10). However, because HV is a comprehensive deformity involving the entire forefoot (24), these studies could not correctly locate the sesamoids with respect to the rest of the forefoot in HV. This can lead to misconceptions about the causes of HV and to confusion during surgery. Describing the relationship between the sesamoids and the lateral metatarsals systematically and mathematically can help characterize the deformity from the pure first ray to more rays. Given that the second metatarsal is nearest to the sesamoids and often represents the axis of the forefoot, we chose the second metatarsal shaft as the reference landmark in our study. We investigated the position of the center of the lateral sesamoid and the first metatarsal head in HV in relation to this landmark. Several studies have found that weightbearing tangential radiographs seem to be better for assessing sesamoid subluxation, because metatarsal rotation can alter the perceived displacement between the sesamoids and the first metatarsal on DP radiographs (7–9,25). However, none of these studies have shown that it tends to alter the relationship between the sesamoids and lateral metatarsals. In contrast, the need to dorsiflex the metatarsophalangeal joint in the tangential view can markedly change the position of the sesamoids (26). Therefore, we chose the
Table 2 Measurements in feet with and without hallux valgus Measurement
Hallux Valgus Group (n ¼ 82)
Control Group (n ¼ 67)
p Value
HVA ( ) IMA ( ) LSP* (mm) M1Py (mm) LM2 (mm) LSDC M1DC
26.8 8.4 (15.2 to 49.8) 9.6 3.1 (4.6 to 17.9) 15.2 1.9 (11.3 to 20.5) 24.6 3.1 (18.9 to 33.9) 64.2 4.6 (54.1 to 81.9) 0.24 0.03 (0.16 to 0.31) 0.38 0.05 (0.30 to 0.55)
11.2 3.2 (3.1 to 15.0) 6.5 2.1 (2.2 to 10.4) 15.0 1.9 (10.8 to 18.8) 23.2 1.7 (18.4 to 26.7) 65.4 5.6 (55.7 to 83.4) 0.23 0.03 (0.15 to 0.30) 0.36 0.03 (0.29 to 0.43)
<.001 <.001 .54 .001 .18 .16 <.001
Abbreviations: HVA, hallux valgus angle; IMA, intermetatarsal angle; LM2, length of second metatarsal; LSDC, deviation coefficient for lateral sesamoid (calculated as LSP/ LM2); LSP, lateral sesamoid position; M1DC, deviation coefficient for first metatarsal (calculated as M1P/LM2); M1P, first metatarsal head position. Data presented as mean standard deviation (range). * Distance between the center of the lateral sesamoid bone and the axis of the second metatarsal. y Distance between the center of the first metatarsal head and the axis of the second metatarsal.
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conventional DP radiographic view to avoid this problem and to make measuring the HVA and IMA more convenient. Although sesamoid subluxation often occurs in HV, in our study, the distance between the lateral sesamoid and the second metatarsal shaft was not significantly larger in the HV group than in the control group and did not correlate with either the HVA or the IMA. In contrast, in the HV group, the first metatarsal head was significantly farther from the second metatarsal shaft than it was in the feet without HV. Also, this increased distance correlated positively with the HVA and IMA. Moreover, the relative distances of these landmarks (the deviation coefficients for the lateral sesamoid and the first metatarsal [i.e., LSDC and M1DC], respectively) showed the same relationship as the absolute distance between these landmarks (LSP and M1P). These are possibly more objective measures because they accommodate differences in foot size. Our data have shown that the sesamoids retain their relationship to the second metatarsal in HV. In contrast, the medial shifting of the first metatarsal creates what has been termed “sesamoid subluxation.” However, although this phenomenon has been reported by multiple investigators (11–18), few have empirically verified it using a prospective study, especially from the aspect of the relationship between the lateral sesamoid and lateral metatarsals in feet with and without HV. Saragas and Becker (15) found no significant difference in the distance from the lateral border of the lateral sesamoid to the second metatarsal axis in feet with and without HV. However, they did not assess its correlation with conventional angles, such as HVA and IMA, nor did they calculate the relative distance to adjust for different foot sizes (15). Finally, they measured from the outermost border of the sesamoid. However, we believe that does not indicate the general location of the lateral sesamoid accurately, because we observed irregular protrusions on the lateral border of the sesamoid in some of the feet. Huang et al (16) demonstrated that the sesamoids location in HV feet do not change relative to the second metatarsal after surgical correction. However, they also chose the lateral border of the lateral sesamoid as the landmark, and they did not compare the sesamoid location between feet with and without HV (16). Furthermore, we believe that the pre- and postoperative locations of the sesamoids could be influenced by the surgical procedure itself, or even by the surgeon performing the procedure. Judge et al (17) and Ramdass and Meyr (18) chose the medial sesamoid and second metatarsal as landmarks in HV feet and reported that the distance did not change in the transverse and frontal planes postoperatively. However, considering that the congenital absence of the medial sesamoid is more common (1), measurements of its location might not be feasible in some patients. Also, this distance is larger than that between the lateral sesamoid and the second metatarsal; thus, we believe the former is a less-sensitive measure of the sesamoid location and could hide minor differences. When correcting HV, by extension, the first metatarsal should be brought back on top of the sesamoids and not vice versa. Distal soft tissue procedures are usually required; however, to date, different surgeons have released different tissues (27). In contrast, our study has demonstrated that the lateral sesamoid is almost stationary in the transverse plane; thus, we have deduced that the soft tissue connecting the sesamoids with the lateral metatarsals, including the deep metatarsal ligament and the insertion of the adductor hallucis muscle on the lateral sesamoid, should be left intact. The present study had several shortcomings. First, HV is a triplanar deformity; however, DP radiographs can only show the displacement in the transverse plane. Second, the present study only compared normal and preoperative HV feet and did not include the
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postoperative follow-up data. Therefore, computed tomography scans with 3-dimensional measurements (28) would be a better method. Also, pre- and postoperative comparisons would be valuable additions to future studies. In conclusion, the apparent lateral movement of the sesamoid in HV feet is a radiographic misinterpretation. Thus, the sesamoids retain their relationship to the second metatarsal, and the medial drifting of the first metatarsal, not the lateral migration of the sesamoids, is what leads to the subluxation between the first metatarsal and the sesamoids. Also, although the subluxation of the sesamoids that laterally displace them from the first metatarsal head exists, “sesamoid subluxation” is a relative description. In reality, “metatarsal subluxation” can better describe both the subluxation of the metatarsal–sesamoid joint and the misalignment of the first metatarsophalangeal joint. References 1. Day F, Jones PC, Gilbert CL. Congenital absence of the tibial sesamoid. J Am Podiatr Med Assoc 92:153–154, 2002. 2. Jahss MH. The sesamoids of the hallux. Clin Orthop Relat Res 157:88–97, 1981. 3. Wooster M, Davies B, Catanzariti A. Effect of sesamoid position on long-term results of hallux abducto valgus surgery. J Foot Surg 29:543–550, 1990. 4. Coughlin MJ. Hallux valgus. J Bone Joint Surg Am 78:932–966, 1996. 5. Hardy RH, Clapham JC. Observations on hallux valgus: based on a controlled series. J Bone Joint Surg Br 33-B:376–391, 1951. 6. Agrawal Y, Desai A, Mehta J. Lateral sesamoid position in hallux valgus: correlation with the conventional radiological assessment. Foot Ankle Surg 17:308–311, 2011. 7. Talbot KD, Saltzman CL. Assessing sesamoid subluxation: how good is the AP radiograph? Foot Ankle Int 19:547–554, 1998. 8. Kuwano T, Nagamine R, Sakaki K, Urabe K, Iwamoto Y. New radiographic analysis of sesamoid rotation in hallux valgus: comparison with conventional evaluation methods. Foot Ankle Int 23:811–817, 2002. 9. Dayton P, Feilmeier M, Kauwe M, Holmes C, McArdle A, Coleman N. Observed changes in radiographic measurements of the first ray after frontal and transverse plane rotation of the hallux: does the hallux drive the metatarsal in a bunion deformity? J Foot Ankle Surg 53:584–587, 2014. 10. Mortier JP, Bernard JL, Maestro M. Axial rotation of the first metatarsal head in a normal population and hallux valgus patients. Orthop Traumatol Surg Res 98:677– 683, 2012.
11. Mann RA, Coughlin MJ. Hallux valgusdetiology, anatomy, treatment and surgical considerations. Clin Orthop Relat Res 157:31–41, 1981. 12. Alvarez R, Haddad RJ, Gould N, Trevino S. The simple bunion: anatomy at the metatarsophalangeal joint of the great toe. Foot Ankle 4:229–240, 1984. 13. Vanderwilde R, Staheli LT, Chew DE, Malagon V. Measurements on radiographs of the foot in normal infants and children. J Bone Joint Surg Am 70:407–415, 1988. 14. Jahss MH. Disorders of the hallux and first ray. In: Disorders of the Foot and Ankle: Medical Surgical Management, pp. 943–1106, edited by MH Jahss, WB Saunders, Philadelphia, 1991. 15. Saragas NP, Becker PJ. Comparative radiographic analysis of parameters in feet with and without hallux valgus. Foot Ankle Int 16:139–143, 1995. 16. Huang EH, Charlton TP, Ajayi S, Thordarson DB. Effect of various hallux valgus reconstruction on sesamoid location: a radiographic study. Foot Ankle Int 34:99– 103, 2013. 17. Judge MS, LaPointe S, Yu GV, Shook JE, Taylor RP. The effect of hallux abducto valgus surgery on the sesamoid apparatus position. J Am Podiatr Med Assoc 89:551–559, 1999. 18. Ramdass R, Meyr AJ. The multiplanar effect of first metatarsal osteotomy on sesamoid position. J Foot Ankle Surg 49:63–67, 2010. 19. Chhaya SA, Brawner M, Hobbs P, Chhaya N, Garcia G, Loredo R. Understanding hallux valgus deformity: what the surgeon wants to know from the conventional radiograph. Curr Probl Diagn Radiol 37:127–137, 2008. 20. Paley D, Tetsworth K. Mechanical axis deviation of the lower limbs: preoperative planning of uniapical angular deformities of the tibia or femur. Clin Orthop Relat Res 280:48–64, 1992. 21. Miller JW. Distal first metatarsal displacement osteotomy: its place in the schema of bunion surgery. J Bone Joint Surg Am 56:923–931, 1974. 22. Srivastava S, Chockalingam N, El Fakhri T. Radiographic measurements of hallux angles: a review of current techniques. Foot (Edinb) 20:27–31, 2010. 23. Shrout PE. Measurement reliability and agreement in psychiatry. Stat Methods Med Res 7:301–317, 1998. 24. Wen J, Ding Q, Yu Z, Sun W, Wang Q, Wei K. Adaptive changes of foot pressure in hallux valgus patients. Gait Posture 36:344–349, 2012. 25. Suzuki J, Tanaka Y, Takaoka T, Kadono K, Takakura Y. Axial radiographic evaluation in hallux valgus: evaluation of the transverse arch in the forefoot. J Orthop Sci 9:446–451, 2004. 26. Yildirim Y, Cabukoglu C, Erol B, Esemenli T. Effect of metatarsophalangeal joint position on the reliability of the tangential sesamoid view in determining sesamoid position. Foot Ankle Int 26:247–250, 2005. 27. Schneider W. Distal soft tissue procedure in hallux valgus surgery: biomechanical background and technique. Int Orthop 37:1669–1675, 2013. 28. Collan L, Kankare JA, Mattila K. The biomechanics of the first metatarsal bone in hallux valgus: a preliminary study utilizing a weight bearing extremity CT. Foot Ankle Surg 19:155–161, 2013.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Original Research
Lateral Sesamoid Position Relative to the Second Metatarsal in Feet With and Without Hallux Valgus: A Prospective Study Xiang Geng, PhD 1, Chao Zhang, MD 2, Xin Ma, MD 3, Xu Wang, MD 4, Jiazhang Huang, MD 2, Jian Xu, PhD 1, Chen Wang, MD 1 1
Resident, Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai, China Attending Physician, Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai, China Professor, Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai, China 4 Associate Professor, Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai, China 2 3
a r t i c l e i n f o
a b s t r a c t
Level of Evidence: 4
We sought to determine whether hallux valgus displaces the sesamoid bones laterally away from a stationary first metatarsal or whether the first metatarsal head is displaced medially from the stationary sesamoids, which remain in position relative to the rest of the forefoot. We reviewed weightbearing radiographs in the dorsal plantar view of 128 consecutive patients (149 feet) seen over 2 months in 2014. Of these, 82 feet (55%) had a hallux valgus angle of >15 (hallux valgus group) and 67 feet (45%) had an angle of no more than 15 (control group). We measured the absolute distances from the center of the lateral sesamoid and the first metatarsal head to the long axis of the second metatarsal. Next, the relative distances, defined as the ratio of these 2 absolute distances to the length of the second metatarsal, were calculated to adjust for foot size. Both the absolute and the relative distances from the center of the first metatarsal head to the second metatarsal differed significantly between the 2 groups and correlated positively with the hallux valgus angle and first intermetatarsal angle. However, neither the absolute nor the relative distance to the lateral sesamoid bone differed significantly between the groups, nor did they correlate with either of the 2 angles. Thus, despite medial shifting of the first metatarsal in hallux valgus, the lateral sesamoid retains its relationship to the second metatarsal in transverse plane. Its apparent lateral movement is a radiographic misinterpretation. Awareness of this misinterpretation should improve the success of corrective surgery. Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: dorsal plantar radiographs hallux valgus second metatarsal sesamoid subluxation
Two sesamoid bones are nearly always present at the first metatarsophalangeal joint. They lie on either side of the flexor halluces longus and are connected by an interosseous ligament, although congenital absence of the medial sesamoid has been infrequently reported (1). Sesamoid subluxation away from the head of the first metatarsal is commonly found in feet with hallux valgus (HV) and is important in disease progression and the potential for recurrent deformity (2–4). Many studies have investigated the relative location and articulation between the sesamoids and the first metatarsal (4–10). However, not knowing the actual location of the sesamoids with respect to the rest of the forefoot can confuse corrective operations for HV. For example,
Financial Disclosure: This work was supported by the National Natural Science Foundation of China (Grant 81171670). Conflict of Interest: None reported. X. Geng and C. Zhang contributed equally to this report. Address correspondence to: Xin Ma, MD, Department of Orthopedics, Huashan Hospital, Fudan University, 12 Middle Wulumuqi Road, Shanghai 200040, China. E-mail address: [email protected] (X. Ma).
the question remains whether the sesamoids should be pulled medially to restore their relationship with the first metatarsal head or the first metatarsal head should be pulled back to the sesamoids. Many investigators have also proposed that, in reality, the subluxation is caused by the first metatarsal head drifting medially away from the sesamoidsdthat is, the sesamoids actually maintain their position (11–18). However, few to date have systematically investigated the actual relationship between the lateral sesamoid and the second metatarsal in feet with different hallux valgus angles (HVAs) or intermetatarsal angles (IMAs), but this relationship is also instructive for corrective operations. For example, should only the ligament between the sesamoids and the first metatarsal head be released, or should the soft tissue connecting with lateral metatarsals also be cut. We sought to determine whether the lateral sesamoid actually moves laterally in HV or whether its apparent lateral movement is a radiographic misinterpretation. Thus, we compared, in a prospective cohort study, the position of the lateral sesamoid bone and the first metatarsal head relative to the second metatarsal on weightbearing dorsal plantar (DP) radiographs of feet with and without HV. We also
1067-2516/$ - see front matter Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2015.08.023
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correlated these distances with the HVA and first IMA to determine whether the position of the sesamoids was associated with HV. Patients and Methods Patients The institutional review board of our hospital approved the study. All patients gave written informed consent to participate. All the patients who had attended our outpatient department for HV or other foot problems from August 1 to September 30, 2014 were eligible for the study to achieve the estimated sample size. Patients <20 years old and those with foot deformities, infection, or a history of trauma or surgery were excluded. After the purpose of the research was explained and informed consent obtained, standard weightbearing DP radiographs were taken of the affected feet, with the central beam inclined at 15 from the coronal plane and targeted at the midtarsal joints. The tube-to-cassette distance was 1 m. Feet with an HVA of >15 were classified as having an HV deformity, and those with an angle of no more than 15 were classified as controls. Because we merely obtained conventional DP radiographs, HV in our study was defined only according to the transverse plane deformity. Measurements Measurements were mainly taken using the CentricityÒ Web, version 3.0, digital viewing system (GE Healthcare, Cleveland, OH) by the first author (X.G.). The HVA was measured between the long axes of the first metatarsal bone and the proximal phalanx, and the IMA was measured between the long axes of the first and second metatarsal (Fig) (19). All these lines should be the mechanical axes as defined by Paley and
Tetsworth (20). In brief, the axis of the proximal phalanx was drawn through the center of the proximal articular surface and the center of the distal end of the diaphysis. The axis of the second metatarsal was drawn from the center of the distal articular surface to the center of the proximal end of the diaphysis. Finally, the first metatarsal axis was drawn to connect the center of the first metatarsal head and the center of the first metatarsal base, as described by Miller (21). We believe this method is the most precise and least-biased method of identifying the axis of the first metatarsal (22). The lateral sesamoid position (LSP) relative to the second metatarsal in the present study was defined as the shortest distance from the center of the lateral sesamoid to the axis of the second metatarsal (Fig.). The position of the first metatarsal (M1P) was defined as the shortest distance from the center of the first metatarsal head to the axis of the second metatarsal. To adjust for differences in foot size, the deviation coefficient for the lateral sesamoid (LSDC) and the deviation coefficient for the first metatarsal (M1DC), respectively, were defined as follows: LSDC ¼ LSP=LM2 and M1 DC ¼ M1 P=LM2 where LM2 is the length of the longitudinal line of the second metatarsal.
Measurement Reliability Ten feet were selected without known bias, and the HVA, IMA, LSP, M1P, and LM2 were measured twice, 1 week apart by the same author (X.G.) to determine the intrarater reliability. Next, 2 independent authors (C.Z., J.X.) measured the HVA, IMA, LSP, M1P, and LM2 to determine the interrater reliability. The intraclass correlation coefficients were calculated for both intrarater and interrater reliability (23).
Statistical Analysis The measurements of the LSP, M1P, LSDC, M1DC, and LM2 were compared between feet with and without HV using the Student t test. The linear relationships between the LSP, M1P, LSDC, or M1DC and the HVA or IMA were assessed using Pearson’s correlation coefficients. All data conformed to the assumptions of the tests used to analyze them. Alpha was set at 0.05, and all tests were 2-tailed. The data were analyzed using the SPSS, version 21.0 statistical software package (IBM Corp., Armonk, NY) by 1 of us (C.W.).
Results Demographic Information Of the 128 enrolled patients (149 feet), 82 feet (55%) (from 63 females [77%] and 19 males [23%]) had HV. Their median age was 56.5 (range 20 to 81) years. The remaining 67 feet (45%) (from 43 females [64%] and 24 males [36%]) did not have HV and constituted the control group. Their median age was 53 (range 20 to 72) years. The groups did not differ in age or sex (p ¼ .56 and p ¼ .09, respectively). Measurements and Reliability
Fig. Measurements to locate the sesamoid bones in relationship to the other bones of the foot. Line A is the axis of the first phalanx; line B, the length of the second metatarsal; line C, the distance from the first metatarsal head to the long axis of the second metatarsal; line D, the distance between the center of the lateral sesamoid bone and the axis of the second metatarsal; line E, the axis of the first metatarsal; and line F, the axis of the second metatarsal. The hallux valgus angle is the arc between lines A and E, and the intermetatarsal angle is the arc between lines E and F.
The intrarater and interrater reliability was excellent (Table 1). Both the absolute deviation of the first metatarsal from the second metatarsal (i.e., M1P) and the ratio calculated to control for foot size variation (i.e., M1DC) exhibited significant differences between the HV and non-HV groups (Table 2). Both values were increased in feet with HV, indicating movement of the first metatarsal away from the second. In addition, both the larger absolute distance (i.e., M1P) and the ratio (i.e., M1DC) correlated with larger HVA and IMA measurements (M1P to HVA, r ¼ 0.52, p < .001; M1P to IMA, r ¼ 0.68, p < .001; M1DC to HVA, r ¼ 0.60, p < .001; and M1DC to IMA, r ¼ 0.75, p < .001). More importantly, neither the absolute distance from the lateral sesamoid to the second metatarsal (i.e., LSP) nor the ratio calculated to normalize the foot size variation (i.e., LSDC) differed significantly between the 2 groups. Both values showed no increase in feet with HV, indicating the lateral sesamoid was stationary relative to the second metatarsal. Furthermore, neither the LSP nor the LSDC correlated with the HVA and IMA measurements (LSP to HVA, r ¼ 0.08, p ¼ .33; LSP to IMA, r ¼ 0.09, p ¼ .25; LSDC to HVA, r ¼ 0.18, p ¼ .13; and LSDC to IMA, r ¼ 0.18, p ¼ .12).
X. Geng et al. / The Journal of Foot & Ankle Surgery xxx (2015) 1–4
Table 1 Reliability of measurements in a study of sesamoid subluxation in hallux valgus (n ¼ 10 measurements for each variable) Measurement
Interrater Correlation
Intrarater Correlation
Hallux valgus angle Intermetatarsal angle Position of the lateral sesamoid* Position of the first metatarsal heady Length of the second metatarsal
0.97 0.92 0.87 0.90 0.96
0.98 0.92 0.89 0.91 0.98
* Distance between the center of the lateral sesamoid bone and the axis of the second metatarsal. y Distance between the center of the first metatarsal head and the axis of the second metatarsal.
Discussion The sesamoid bones are an integral part of the function of the first metatarsophalangeal joint. However, they appear on radiographs to be laterally displaced relative to the first metatarsal head in feet with HV. Because of the relationship between the sesamoids and the first metatarsal, different methods of staging the extent of sesamoid subluxation have been investigated using either DP or tangential radiographic views (6–8,10). However, because HV is a comprehensive deformity involving the entire forefoot (24), these studies could not correctly locate the sesamoids with respect to the rest of the forefoot in HV. This can lead to misconceptions about the causes of HV and to confusion during surgery. Describing the relationship between the sesamoids and the lateral metatarsals systematically and mathematically can help characterize the deformity from the pure first ray to more rays. Given that the second metatarsal is nearest to the sesamoids and often represents the axis of the forefoot, we chose the second metatarsal shaft as the reference landmark in our study. We investigated the position of the center of the lateral sesamoid and the first metatarsal head in HV in relation to this landmark. Several studies have found that weightbearing tangential radiographs seem to be better for assessing sesamoid subluxation, because metatarsal rotation can alter the perceived displacement between the sesamoids and the first metatarsal on DP radiographs (7–9,25). However, none of these studies have shown that it tends to alter the relationship between the sesamoids and lateral metatarsals. In contrast, the need to dorsiflex the metatarsophalangeal joint in the tangential view can markedly change the position of the sesamoids (26). Therefore, we chose the
Table 2 Measurements in feet with and without hallux valgus Measurement
Hallux Valgus Group (n ¼ 82)
Control Group (n ¼ 67)
p Value
HVA ( ) IMA ( ) LSP* (mm) M1Py (mm) LM2 (mm) LSDC M1DC
26.8 8.4 (15.2 to 49.8) 9.6 3.1 (4.6 to 17.9) 15.2 1.9 (11.3 to 20.5) 24.6 3.1 (18.9 to 33.9) 64.2 4.6 (54.1 to 81.9) 0.24 0.03 (0.16 to 0.31) 0.38 0.05 (0.30 to 0.55)
11.2 3.2 (3.1 to 15.0) 6.5 2.1 (2.2 to 10.4) 15.0 1.9 (10.8 to 18.8) 23.2 1.7 (18.4 to 26.7) 65.4 5.6 (55.7 to 83.4) 0.23 0.03 (0.15 to 0.30) 0.36 0.03 (0.29 to 0.43)
<.001 <.001 .54 .001 .18 .16 <.001
Abbreviations: HVA, hallux valgus angle; IMA, intermetatarsal angle; LM2, length of second metatarsal; LSDC, deviation coefficient for lateral sesamoid (calculated as LSP/ LM2); LSP, lateral sesamoid position; M1DC, deviation coefficient for first metatarsal (calculated as M1P/LM2); M1P, first metatarsal head position. Data presented as mean standard deviation (range). * Distance between the center of the lateral sesamoid bone and the axis of the second metatarsal. y Distance between the center of the first metatarsal head and the axis of the second metatarsal.
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conventional DP radiographic view to avoid this problem and to make measuring the HVA and IMA more convenient. Although sesamoid subluxation often occurs in HV, in our study, the distance between the lateral sesamoid and the second metatarsal shaft was not significantly larger in the HV group than in the control group and did not correlate with either the HVA or the IMA. In contrast, in the HV group, the first metatarsal head was significantly farther from the second metatarsal shaft than it was in the feet without HV. Also, this increased distance correlated positively with the HVA and IMA. Moreover, the relative distances of these landmarks (the deviation coefficients for the lateral sesamoid and the first metatarsal [i.e., LSDC and M1DC], respectively) showed the same relationship as the absolute distance between these landmarks (LSP and M1P). These are possibly more objective measures because they accommodate differences in foot size. Our data have shown that the sesamoids retain their relationship to the second metatarsal in HV. In contrast, the medial shifting of the first metatarsal creates what has been termed “sesamoid subluxation.” However, although this phenomenon has been reported by multiple investigators (11–18), few have empirically verified it using a prospective study, especially from the aspect of the relationship between the lateral sesamoid and lateral metatarsals in feet with and without HV. Saragas and Becker (15) found no significant difference in the distance from the lateral border of the lateral sesamoid to the second metatarsal axis in feet with and without HV. However, they did not assess its correlation with conventional angles, such as HVA and IMA, nor did they calculate the relative distance to adjust for different foot sizes (15). Finally, they measured from the outermost border of the sesamoid. However, we believe that does not indicate the general location of the lateral sesamoid accurately, because we observed irregular protrusions on the lateral border of the sesamoid in some of the feet. Huang et al (16) demonstrated that the sesamoids location in HV feet do not change relative to the second metatarsal after surgical correction. However, they also chose the lateral border of the lateral sesamoid as the landmark, and they did not compare the sesamoid location between feet with and without HV (16). Furthermore, we believe that the pre- and postoperative locations of the sesamoids could be influenced by the surgical procedure itself, or even by the surgeon performing the procedure. Judge et al (17) and Ramdass and Meyr (18) chose the medial sesamoid and second metatarsal as landmarks in HV feet and reported that the distance did not change in the transverse and frontal planes postoperatively. However, considering that the congenital absence of the medial sesamoid is more common (1), measurements of its location might not be feasible in some patients. Also, this distance is larger than that between the lateral sesamoid and the second metatarsal; thus, we believe the former is a less-sensitive measure of the sesamoid location and could hide minor differences. When correcting HV, by extension, the first metatarsal should be brought back on top of the sesamoids and not vice versa. Distal soft tissue procedures are usually required; however, to date, different surgeons have released different tissues (27). In contrast, our study has demonstrated that the lateral sesamoid is almost stationary in the transverse plane; thus, we have deduced that the soft tissue connecting the sesamoids with the lateral metatarsals, including the deep metatarsal ligament and the insertion of the adductor hallucis muscle on the lateral sesamoid, should be left intact. The present study had several shortcomings. First, HV is a triplanar deformity; however, DP radiographs can only show the displacement in the transverse plane. Second, the present study only compared normal and preoperative HV feet and did not include the
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postoperative follow-up data. Therefore, computed tomography scans with 3-dimensional measurements (28) would be a better method. Also, pre- and postoperative comparisons would be valuable additions to future studies. In conclusion, the apparent lateral movement of the sesamoid in HV feet is a radiographic misinterpretation. Thus, the sesamoids retain their relationship to the second metatarsal, and the medial drifting of the first metatarsal, not the lateral migration of the sesamoids, is what leads to the subluxation between the first metatarsal and the sesamoids. Also, although the subluxation of the sesamoids that laterally displace them from the first metatarsal head exists, “sesamoid subluxation” is a relative description. In reality, “metatarsal subluxation” can better describe both the subluxation of the metatarsal–sesamoid joint and the misalignment of the first metatarsophalangeal joint. References 1. Day F, Jones PC, Gilbert CL. Congenital absence of the tibial sesamoid. J Am Podiatr Med Assoc 92:153–154, 2002. 2. Jahss MH. The sesamoids of the hallux. Clin Orthop Relat Res 157:88–97, 1981. 3. Wooster M, Davies B, Catanzariti A. Effect of sesamoid position on long-term results of hallux abducto valgus surgery. J Foot Surg 29:543–550, 1990. 4. Coughlin MJ. Hallux valgus. J Bone Joint Surg Am 78:932–966, 1996. 5. Hardy RH, Clapham JC. Observations on hallux valgus: based on a controlled series. J Bone Joint Surg Br 33-B:376–391, 1951. 6. Agrawal Y, Desai A, Mehta J. Lateral sesamoid position in hallux valgus: correlation with the conventional radiological assessment. Foot Ankle Surg 17:308–311, 2011. 7. Talbot KD, Saltzman CL. Assessing sesamoid subluxation: how good is the AP radiograph? Foot Ankle Int 19:547–554, 1998. 8. Kuwano T, Nagamine R, Sakaki K, Urabe K, Iwamoto Y. New radiographic analysis of sesamoid rotation in hallux valgus: comparison with conventional evaluation methods. Foot Ankle Int 23:811–817, 2002. 9. Dayton P, Feilmeier M, Kauwe M, Holmes C, McArdle A, Coleman N. Observed changes in radiographic measurements of the first ray after frontal and transverse plane rotation of the hallux: does the hallux drive the metatarsal in a bunion deformity? J Foot Ankle Surg 53:584–587, 2014. 10. Mortier JP, Bernard JL, Maestro M. Axial rotation of the first metatarsal head in a normal population and hallux valgus patients. Orthop Traumatol Surg Res 98:677– 683, 2012.
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