A Novel Classification System For Metatarsal-Sesamoid Arthritis 

Are you choosing the right bunion correction procedure for your patients? Classification and subsequent procedure selection methods for HAV have traditionally been based on a two-dimensional framework. The anteroposterior (AP) radiograph defines the severity of hallux valgus only in the transverse plane using the hallux valgus angle (HVA), intermetatarsal angle (IMA), hallux interphalangeal angle (HIA) and proximal articular set angle (PASA).¹ Rotational deformities of the sesamoid complex in the coronal plane have attracted less attention in literature.

The sesamoid complex functions as an important component of the first MTP joint. The tibial and fibular sesamoid bones lie within the tendons of the flexor hallucis brevis (FHB) to provide mechanical advantage and stability at the first MTP joint. The complex also serves an important function during weight bearing, as the sesamoids aid in redistribution of weight to reduce load and cushion the first metatarsal head.² 

Both sesamoids embed in the plantar plate on the plantar aspect of the joint capsule. Each small bone has a hyaline articulation with the plantar aspect of the first metatarsal head on either side of an intersesamoidal ridge, called the crista. The central portion of the plantar plate, located between the sesamoids, is the intersesamoidal ligament. This gap between the sesamoids allows for passage and protection of the long flexor tendon as it travels distally to its insertion on the hallux. The tibial and fibular sesamoid anchor to the proximal phalanx and metatarsal via thickenings of the joint capsule, referred to as the medial and lateral sesamoid phalangeal ligament and the medal and lateral metatarsosesamoid ligament. Additionally, the tibial sesamoid provides a distal attachment for the abductor hallucis tendon and the fibular sesamoid serves as the attachment of the adductor hallucis and fibers of the transverse intermetatarsal ligament.^1,2

As deformity progresses in hallux valgus and the first metatarsal moves medially, the sesamoids are pulled laterally and erode the intersesamoidal ridge of the head of the first metatarsal, disrupting the intrinsic stability of the complex. As the complex becomes increasingly unstable, the medial soft tissues attenuate and the lateral soft tissues contract, which increases the lateral deforming forces and further worsens the hallux valgus deformity.³ The migration of the sesamoids also causes them to function out of their respective grooves and increase bony contact with the intersesamoidal ridge and the head of the metatarsal.

Hardy and Clapham’s classification system was developed to assess displacement of the sesamoids on an AP radiograph.⁴ However, this system evaluates the amount of shift of the tibial sesamoid in relation to the first metatarsal, but does not give insight into the degenerative changes occurring as the sesamoids move out of their respective grooves and come into contact with the intersesamoidal ridge. Classic radiographic signs of sesamoid arthritis include: joint space narrowing; subchondral sclerosis; hypertrophied sesamoids; and crista flattening. These features are difficult to observe on AP radiograph, supporting the practice of regularly ordering a sesamoid axial view when working up a patient for hallux valgus and possible surgical intervention.⁵   

Research shows the recurrence rate for hallux valgus deformities ranges from 25 to 78 percent, and it is becoming clear that lack of attention to the first metatarsal-sesamoid complex is one of the greatest risk factors for recurrence and predictors of patient satisfaction.⁶ Largey and colleagues evaluated the first MTP joint in patients undergoing correction of hallux valgus and found a positive correlation between overall American Orthopaedic Foot and Ankle Society (AOFAS) score and absence of sesamoid arthritis.⁷ Additionally, Tsai and team concluded suboptimal outcomes following hallux valgus correction could be attributed to arthritic changes at the articulation of the sesamoids and metatarsal head.⁸ 

Our Findings On A New Way To Look At Metatarsal-Sesamoid Arthritis

We conducted a retrospective, radiographic study to formulate a classification system for metatarsal-sesamoid arthritis (MSA) in order to demonstrate the importance of obtaining sesamoid axial radiographs and to consider arthritic change of the sesamoids when determining hallux valgus procedure selection. Subjects included 71 patients with a diagnosis of hallux valgus seen at Phoenix Foot and Ankle Institute between January 1, 2020 and January 1, 2021. Patient selection was based on a hallux valgus ICD-10 diagnosis (M20.11 and M20.12) along with a record of standard three radiographic views of the foot and a sesamoid axial view. We measured the intermetatarsal (IM) angle, hallux valgus angle (HVA) and tibial sesamoid position (TSP) using anteroposterior (AP) radiographs. We also utilized these radiographs to determine the presence and grade of hallux rigidus based on the Coughlin Shurnas classification system. Sesamoid-axial views were used to measure the tibial sesamoid distance to the first metatarsal, the fibular sesamoid distance to the first metatarsal, the distance between the sesamoids, and the size of the tibial and fibular sesamoid. This view also allowed for analysis of the crista shape (flat versus rounded) and the sesamoid axial tibial sesamoid position as classified by Yildirim and colleagues.⁹ We calculated means and medians of each measurement for the sample population and T-tests assuming unequal variances determined significant values between signs of arthritic change. Additionally, we assessed correlations between radiographic measurements using Pearson’s correlation coefficient(r). Using these findings, we devised a four-grade novel classification system. 

Figure 1: Our four-grade novel classification system for metatarsal-sesamoid arthritis 

The results of this study indicated that patients with a tibial sesamoid position of 5 on AP radiographs had significantly decreased tibial metatarsal-sesamoid joint space when compared to other tibial sesamoid positions. Patients with a tibial sesamoid position of 5 on AP radiographs also had significantly larger tibial sesamoids than patients with other tibial sesamoid positions. In addition, we found patients with a flattened crista had significantly decreased space between the tibial and fibular sesamoids.

While these positive correlations are very important findings, it may be the measurements that showed poor correlation that serve as key discoveries in this study. There was very poor correlation between metatarsal-sesamoid joint space narrowing with both worsening IM angle and HAV angles. In our observation, this poor correlation serves as an indicator that surgeons cannot rule out the presence or severity of sesamoid arthritis based on IM and HAV angles alone, necessitating the need for appropriate sesamoid-axial radiographs. These radiographic findings, coupled with appropriate clinical symptoms, are evolving surgeon procedure selection in complex hallux valgus deformities. Future research will be necessary to assess surgical outcomes with this classification system. 

Sesamoid function is pivotal to procedure selection, and we do believe as we sift through our Monday morning schedules and review radiographs, that we should pay more attention to a sesamoid axial radiographic view and the arthritic condition of the sesamoids that can worsen, typically unbeknownst, over time.

Jessica Katzer is a 4th year podiatric medical student at the Arizona College of Podiatric Medicine at Midwestern University. She can be reached at jessica.katzer@midwestern.edu

Kayla Vanden Hoek is a 4th year podiatric medical student at the Arizona College of Podiatric Medicine at Midwestern University. She can be reached at kayla.weber@midwestern.edu 

Jonathan Yazhari is a 4th year podiatric medical student at the Arizona College of Podiatric Medicine at Midwestern University. He can be reached at jonathan.yazhari@midwestern.edu

Dr. McAlister is a fellowship-trained foot and ankle surgeon. He is in private practice and is the founder of the Phoenix Foot and Ankle Institute. (www.phoenixfai.com) One can reach Dr. McAlister at jeff.mcalister@phoenixfai.com.

References 

1. Mann RA, Coughlin MJ. Hallux valgus--etiology, anatomy, treatment and surgical considerations. Clin Orthop Relat Res. 1981;(157):31-41.

2. Sims AL, Kurup HV. Painful sesamoid of the great toe. World J Orthop. 2014;5(2):146-150. 

3. Catanese D, Popowitz D, Gladstein AZ. Measuring sesamoid position in hallux valgus: when is the sesamoid axial view necessary? Foot Ankle Spec. 2014;7(6):457-459. 

4. Hardy RH, Clapham JC. Observations on hallux valgus; based on a controlled series. J Bone Joint Surg Br. 1951;33-B(3):376-391. 

5. Katsui R, Samoto N, Taniguchi A, et al. Relationship between displacement and degenerative changes of the sesamoids in hallux valgus. Foot Ankle Int. 2016;37:1303-1309. 

6. Jeuken RM, Schotanus MGM, Kort NP, Deenik A, Jong B, Hendrickx RPM. Long-term follow-up of a randomized controlled trial comparing scarf to chevron osteotomy in hallux valgus correction. Foot Ankle Int. 2016;37(7):687-695.

7. Largey A, Canovas F, Roussanne Y, Hebrard W, Bonnel F. Degenerative cartilage changes in metatarsosesamoidal joint and Scarf procedure results for hallux valgus: a prospective study of 100 cases[in French]. Rev Chir Orthop Reparatrice Appar Mot. 2008;94:685-692. 

8. Tsai J, Daniel JN, McDonald EL, Pedowitz DI, Rogero RG, Shakked RJ, Nicholson KJ, Raikin SM. High prevalence of degenerative changes at the metatarsal head sesamoid articulation found during hallux valgus correction surgery. Foot Ankle Spec. 2020:1938640020912135. 

9. 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. 2005;26(3):247-250.