Considering the Risks of Lesser Metatarsalgia in Hallux Valgus Surgery

It's never as simple as it appears with the human body, especially when it comes to surgical biomechanics of the foot. First ray insufficiency-induced lesser metatarsalgia is a prime example. Unfortunately, the increasing popularity of the Lapidus procedure, combined with industry-driven cut-guides for first metatarsal-cuneiform joint arthrodesis, produces a result that violates metatarsal parabola evidence-based guidelines, in my observation. The argument I hear to the contrary is that plantarflexing the first ray compensates, but in my experience those same individuals do not show their weight-bearing lateral X-rays.

I am not here to bash the Lapidus procedure. I perform more than most but less than some. In my opinion, the same thoughts apply to the Austin bunionectomy, the Scarf bunionectomy, or a minimal incision procedure. The issue is first metatarsal shortening and the subsequent need to shorten the second metatarsal "prophylactically." I don't dislike lesser metatarsal osteotomies, I flat-out hate them. However, I contend that most of the time the second metatarsal is not truly a "long metatarsal."

So how much first metatarsal shortening is too much, and can you overcome the shortening with plantarflexion? Is it just a geometry equation? Were Maestro and his colleagues¹ correct that the foot morphotype is very precise and anything that violates the "harmonious curve" will result in a pathologic situation? Or is it not as black and white as it appears and substantially more nuanced? Buckle up. To arrive at a genuinely evidence-based answer is kind of like going on a long car trip with the late Hunter S. Thompson…a wild ride, but we will have fun getting there.

It begins with first ray biomechanics and Christensen and colleagues' landmark research published as a series of articles from the late 1990s and early 2000s.^2-6 The peroneus longus eccentrically contracts during the second rocker of gait to evert the medial column of the foot into the central column of the foot, converting the foot from a mobile adaptor to a rigid lever.^2-7 Additionally, the peroneus longus creates a supinatory moment on the hindfoot to enhance the stability of the foot as it goes into the third rocker of gait. During the third rocker of gait, the plantar fascia, via the Windlass mechanism, becomes the primary arch augmenter in the sagittal plane and a static stabilizer of the medial column of the foot due to the leverage generated through the sesamoids and the larger arc of curvature of the first metatarsal head.^2-9 The posterior tibial tendon is the primary arch augmenter in the transverse plane and functions in conjunction with the intrinsic muscles via the plantar fascia by eccentrically contracting during the second rocker of gait to also stabilize the medial arch.⁹

With adduction of the first metatarsal, lateral deviation of the hallux, and then frontal plane rotation of the first metatarsal and hallux follow.^3,7,11 The ultimate result is the sesamoids become displaced, resulting in destabilization of the first ray.^3,7,11 This sequence of events negatively impacts the Windlass mechanism's function, and hypermobility ensues.³ The result is a lateral shift of pressure to the second and possibly the third metatarsal.^3,7,11  On top of all of that, metatarsus primus adductus functions a short first metatarsal causing further contributing to the first ray insufficiency induced lesser metatarsalgia.^8,11 Additionally, the presence of hypermobility in conjunction with hallux abducto valgus compared to controls without deformity is well documented and must become part of the overall treatment consideration.¹³   Segmental realignment of the first metatarsal improves this situation by relatively plantarflexing the first metatarsal by 26 percent. Still, the plantar fascia must be competent to allow the Windlass mechanism to do its magic.³

To further complicate matters, equinus can rear its ugly head and throw a wrench into the mix. Continued loading of the gastrocsoleal complex results in the peroneus longus becoming ineffective.^6,8,10 Conversion of the foot from a mobile adapter to rigid lever faulters and instability to the first ray ensues. In addition, distal compensation for equinus to allow the body to move over the planted foot results in a breakdown of the medial arch at the navicular-cuneiform joint with an elevation of the first ray.⁶ Also, as the center of pressure moves distally and laterally, a tightening of the gastrocsoleal complex produces a multiplying effect of second ray and possibly third ray overload.¹²

Of course, there is even more when it comes to the surgical biomechanics of first ray insufficiency induced lesser metatarsalgia. The subtalar axis lies lateral to the first ray and medial to the lesser metatarsals.⁷ The first metatarsal produces a supinatory moment, and lesser metatarsals create a pronatory moment due to reactive ground forces.⁷ In the presence of hypermobility, the supinatory moment of the first ray is diminished. The first ray can lack hypermobility and be functionally insufficient if the Windlass mechanism is compromised, producing a similar consequence.⁷ The importance of clinical evaluation of Windlass function via the Windlass activation test as part of a biomechanical examination.⁷

Several authors confirm the importance of the ± 2mm firstsecond ray relationship.^14-18 Unfortunately, the problem is not as simple as the geometrical relationships described by Maestro et al.^1,19 The evolution to lesser rat symptomatology due to first ray insufficiency is more directly related to load transfer.¹⁹ Geng and colleagues demonstrated via finite element modeling a load transfer increase of 55 percent significantly increases the risk for development of metatarsalgia.²⁰ In a subsequent article, the same authors found shortening the first metatarsal by 6mm put the second ray in the at risk category due to an increased load transfer of 54.83 percent.²¹ Additionally, the authors found plantarflexion of the first metatarsal could potentially offset some the load transfer and recommended this approach with significant shortening.²¹

Aggregated data from in vivo studies for hallux abducto valgus surgical correction (different types of procedures including Austin, Lapidus, Scarf, and midshaft osteotomy, for example) and the potential development of lesser metatarsalgia fall somewhere between a maximum 4-6mm of first ray shortening.^22-26 First metatarsal-cuneiform joint cartilaginous surfaces account for approximately 1-3mm of the first ray length and figure into the overall equation.^27,28 Cut guides for first metatarsal-cuneiform arthrodesis may take more bone than the parameters set forth by this aggregated data and place the patient at increased risk. Sagittal plane position was critical for the Lapidus procedure in mitigating post-op lesser metatarsalgia.^25-26 Sagittal plane alignment can be challenging with the Lapidus procedure and less than ideal position is problematic.Like Rush and colleagues’ findings, correction of hallux abducto valgus may indirectly treat pre-op metatarsalgia.^3,22

In seeking an answer to the question, “how much shortening is okay with hallux abducto valgus surgical correction?” My thought based on the literature is that 4 to 6mm of shortening is acceptable with the following caveats:

1. If the patient has equinus, treat it surgically as well.

2. Know the starting point firstsecond ray relationship. If it is outside the ± 2mm relationship this must be considered in your preoperative planning.

3. Think of the foot as columns, know the relationship between the medial, central, and lateral columns preoperatively. If the central column is too long relative to the lateral and medial columns, adjust your preoperative plan accordingly. It is rare for this situation to occur, and lesser metatarsal osteotomies should be required infrequently.

4. Consider the hindfoot and address any hindfoot deformities either concomitantly or as a staged procedure.

Despite our best efforts, lesser metatarsalgia may still occur. Educate and inform patients pre-operatively about the risk. If it does occur, take a comprehensive approach to treatment. This topic, as much as any topic in the foot and ankle sector, demonstrates symbiotic relationship between biomechanics and surgery.

Disclosure: Dr. DeHeer discloses that he is a speaker for Paragon 28 and a consultant for and stock owner in SUTUREGARD Medical Inc., the manufacturer of HEMIGARD^®.

Dr. DeHeer is the Residency Director of the St. Vincent Hospital Podiatry Program in Indianapolis. He is a Fellow of the American College of Foot and Ankle Surgeons, a Fellow of the American Society of Podiatric Surgeons, a Fellow of the American College of Foot and Ankle Pediatrics, a Fellow of the Royal College of Physicians and Surgeons of Glasgow, and a Diplomate of the American Board of Podiatric Surgery. Dr. DeHeer is a Partner with Upperline Health and the Medical Director of Upperline Health Indiana.

References

1. Maestro M, Besse J-L, Ragusa M, Berthonnaud E. Forefoot morphotype study and planning method for forefoot osteotomy. Foot Ankle Clin. 2003;8(4):695-710.

2. Johnson CH, Christensen JC. Biomechanics of the first ray part I. The effects of peroneus longus function: A three-dimensional kinematic study on a cadaver model. J Foot Ankle Surg. 1999;38(5):313-321.

3. Rush SM, Christensen JC, Johnson CH. Biomechanics of the first ray. Part II: metatarsus primus varus as a cause of hypermobility. A three-dimensional kinematic analysis in a cadaver model. J Foot Ankle Surg. 2000;39(2):68-77.

4. Bierman RA, Christensen JC, Johnson CH. Biomechanics of the first ray. Part III. Consequences of Lapidus arthrodesis on peroneus longus function: a three-dimensional kinematic analysis in a cadaver model. J Foot Ankle Surg. 2001;40(3):125-131.

5. Roling BA, Christensen JC, Johnson CH. Biomechanics of the first ray. Part IV: the effect of selected medial column arthrodeses. A three-dimensional kinematic analysis in a cadaver model. J Foot Ankle Surg. 2002;41(5):278-285.

6. Johnson CH, Christensen JC. Biomechanics of the first ray part V: The effect of equinus deformity: A 3-dimensional kinematic study on a cadaver model. J Foot Ankle Surg. 2005;44(2):114-120.

7. Christensen JC, Jennings MM. Normal and abnormal function of the first ray. Clin Podiatr Med Surg. 2009;26(3):355-371.

8. Thordarson DB, Schmotzer H, Chon J, Peters J. Dynamic support of the human longitudinal arch. A biomechanical evaluation. Clin Orthop Rel Res. 1995;316:165-172.

9. Mayich DJ, Novak A, Vena D, Daniels TR, Brodsky JW. Gait analysis in orthopedic foot and ankle surgery—topical review, part 1: principles and uses of gait analysis. Foot Ankle Int. 2014;35(1):80-90.

10. Besse, J-L. Metatarsalgia. Orthop Traumatol Surg Res. 2017;103(1):S29-S39.

11. Perera AM, Mason L, Stephens MM. The pathogenesis of hallux valgus. J Bone Joint Surg. 2011;93(17):1650-1661.

12. Cheung JT-M, Zhang M, An K-N. Effect of Achilles tendon loading on plantar fascia tension in the standing foot. Clin Biomech. 2006;21(2):194-203.

13. Shibuya N, Roukis TS, Jupiter DC. Mobility of the first ray in patients with or without hallux valgus deformity: systematic review and meta-analysis. J Foot Ankle Surg. 2017;56(5):1070-1075.

14. Domínguez-Maldonado G, Munuera-Martinez PV, Castillo-Lopez JM, Ramos-Ortega J, Albornoz-Cabello M. Normal values of metatarsal parabola arch in male and female feet. ScientificWorldJournal 2014;2014:505736.

15. Harris RI, Beath T. Report 15th Army Foot Survey. National Research Council of Canada, Ottawa. 1947:1-268.

16. Harris RI, Beath T. The short first metatarsal: its incidence and clinical significance. J Bone Joint Surg. 1949;31(3):553-565.

17. Hardy RH, Clapham JCR. Observations on hallux valgus. J Bone Joint Surg Br. 1951;33(3):376-391.

18. Laporta G, Melillo T, Olinsky D. X-ray evaluation of hallux abducto valgus deformity. J Am Podiatr Med Assoc. 1974;64(8):544-566.

19. García-Aznar JM, Bayod J, Rosas A, et al. Load transfer mechanism for different metatarsal geometries: a finite element study. J Biomech Eng. 2009;131(2):021011.

20. Geng X, Huang D, Wang X, et al. Loading pattern of postoperative hallux valgus feet with and without transfer metatarsalgia: a case control study. J Orthop Surg Res. 2017;12(1):1-7.

21. Geng X, Shi J, Chen W, et al. Impact of first metatarsal shortening on forefoot loading pattern: a finite element model study. BMC Musculoskelet Disord. 2019;20(1):1-9.

22. Nakagawa S, Fukushi J-I, Nakagawa T, Mizu-Uchi H, Iwamoto Y. Association of metatarsalgia after hallux valgus correction with relative first metatarsal length. Foot Ankle Int. 2016;37(6):582-588.

23. Ahn J, Lee HS, Seo JH, Kim JY. Second metatarsal transfer lesions due to first metatarsal shortening after distal chevron metatarsal osteotomy for hallux valgus. Foot Ankle Int. 2016;37(6):589-595.

24. Suh JW, Jang H-S, Park H-W. Iatrogenic second transfer metatarsalgia and the first metatarsal shortening and elevation after Scarf osteotomy. Foot Ankle Surg. 2021. DOI: 10.1016j.fas.2021.11.005 

25. Greeff W, Strydom A, Saragas NP, Faria Ferrao PN. Radiographic assessment of relative first metatarsal length following modified Lapidus procedure. Foot Ankle Int. 2020;41(8):972-977.

26. Busch A, Wegner A, Haversath M, Brandenberger D, Jager M, Beck S. First ray alignment in Lapidus arthrodesis–Effect on plantar pressure distribution and the occurrence of metatarsalgia. Foot (Edinb). 2020;45:101686.

27. Boffeli TJ, Hyllengren SB. Can we abandon saw wedge resection in Lapidus fusion? A comparative study of joint preparation techniques regarding correction of deformity, union rate, and preservation of first ray length. J Foot Ankle Surg. 2019;58(6):1118-1124. 

28. Dahlgren N, et al. First tarsometatarsal fusion using saw preparation vs. standard preparation of the joint: A cadaver study. Foot Ankle Surg. 2020;26(6):703-707.