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Is There A Gap Between Biomechanics Knowledge And New Trends In Bunion Surgery?
Recent trends in foot and ankle surgery suggest a disconnect between current knowledge of biomechanics and selection of surgical procedures to correct hallux abductovalgus (HAV) deformity. One only has to look at the current issue of Podiatry Today, where two respected podiatric surgeons offer insights into their own protocols for performing a “triplane” Lapidus procedure to correct hallux abuctovalgus.1,2 Collectively, the two articles provide excellent pearls for performing a Lapidus procedure while offering sound advice for optimal postoperative management. However, these two articles seem to suggest that a Lapidus procedure which includes correction of a perceived “pronation” deformity at the first metatarsocuneiform joint is now the standard of care in the podiatric profession. This raises concern, as the premise for surgical de-rotation of the first metatarsal into the direction of inversion at the first metatarsocuneiform joint in HAV correction continues to be unfounded, in my opinion. Furthermore, the discussion by DiDomenico and colleagues2 regarding the concept of first ray “hypermobility” as a deciding factor in selection of the Lapidus procedure requires some clarification based upon current biomechanics research.
Where Should We Focus Correction Of “Pronation” In Hallux Abductovalgus Deformity?
The first metatarsal is not pronated in isolation in HAV deformity. Rather, the entire first ray is everted in patients with HAV deformity.3 Kimura showed that the talonavicular joint, not the first metatarsocuneiform joint, is everted in patients with HAV deformity.4 Shibuya and coworkers identified that whole foot pronation is a significant risk factor for HAV deformity.5 They warned that isolated de-rotation of the first metatarsal fails to address the true location of pronation deformity in HAV patients.6
As Kimura’s study showed, the first metatarsocuneiform joint is already fully rotated into inversion in HAV patients.4 Further rotation of this joint into the direction of inversion makes no sense, in my opinion. Addressing pronation of joints located proximal to the first metatarsocuneiform joint with additional surgical procedures or with foot orthotic therapy may improve long term outcomes of HAV surgery, although this premise has yet to be proven with quality studies.
How Do We Detect First Ray Hypermobility And How Can We Correct It?
Foot and ankle surgeons continue to rely on static measures of first ray mobility in patients when deciding whether osteotomy or fusion is necessary for correction of HAV deformity.7-11 However, these static tests do not predict actual stiffness or stability of the first ray segment during dynamic gait.12 Static standing radiographs which measure first metatarsus primus elevatus (MPE) do not predict first ray hypermobility, hallux valgus or hallux rigidus.13 In fact, MPE deformity increases as severity of hallux rigidus increases suggesting that this radiographic finding is a result, not the cause of the pathology.13,14
The role of first ray “hypermobility” and hallux abductovalgus deformity continues to be misunderstood. The long-standing notion that sagittal plane first ray hypermobility causes HAV deformity has yet to be proven. Furthermore, there is convincing evidence that loss of sagittal plane stability of the first ray is a result, not the cause of HAV deformity.
In HAV deformity, excessive dorsal mobility of the first ray occurs from loss of the shielding effect of the FHL, the plantar aponeurosis and the deep transverse metatarsal ligament from ground reaction forces as the first metatarsal displaces medially from the sesamoid envelope. Rush and co-workers demonstrated that, when the intermetatarsal angle is corrected with an osteotomy of the first metatarsal, a 26 percent increase in stiffness and resistance to dorsiflexion of the first ray will occur.15 The authors concluded that hypermobility of the first ray could be corrected with osteotomy of the first metatarsal without the need for fusion of the first metatarsocuneiform joint.
In a cadaveric study of HAV specimens, Coughlin and team noted a 50 percent reduction in dorsal excursion of the first ray when the first metatarsal was realigned with a proximal crescentic osteotomy.16 In a follow up clinical study, Coughlin et al prospectively studied 103 patients with HAV deformity.17 First ray mobility measured pre-operative was 7.2 mm and diminished to 4.5 mm with after realignment of the first metatarsal with proximal crescentic osteotomy. Mobility of the first ray correlated with magnitude of metarsus primus varus deformity.17 Doty and Couglin reviewed the results of all studies of mobility of the first ray in HAV deformity and also looked at their own studies showing disappearance of “hypermobility” after the first metatarsal was re-aligned with osteotomy alone.18
They concluded:
“While the metatarsocuneiform joint is critical to the development of hallux valgus, it is for different reasons than those envisioned by Lapidus and others. These historical theories were based on unreliable methods by which to quantify mobility. Metatarsocuneiform joint mobility may be necessary for a hallux valgus deformity to develop; however, “hypermobility” may not be the cause but rather the result of a hallux valgus deformity.”18
At What Joint Does First Ray Hypermobility Occur?
In the sagittal plane, motion occurring during gait at the medial naviculocuneiform joint is twice that of the motion occurring at the first metatarsocuneiform joint.19 This dispels the myth that the first metatarsal medial cuneiform joint is the primary contributor to “hypermobility” of the first ray in many foot pathologies. In fact, kinematic studies verify that the first metatarsocuneiform joint moves less in all directions than any other joint of the foot.19,20
However, excessive transverse plane mobility of the first metatarsocuneiform joint has been identified in patients with HAV deformity compared to healthy controls.4,21 DiDomenico and colleagues noted this, which certainly justifies their opinion that the Lapidus procedure is the best option to control hypermobility in HAV patients.2 As shown in the studies by Rush and Coughlin, correcting transverse plane alignment of the first metatarsal in HAV surgery is the critical step in reducing sagittal plane hypermobility.15-17
Triplane HAV Surgical Options: Where Are The Head-To-Head Comparisons?
There may be merit in addressing a pronated or everted position of the first metatarsal when performing HAV surgery. Ideally, medial column pronation is best corrected at the specific joint from which it originates, i.e the talonavicular joint. However, an indirect correction of pronation of the first metatarsal with a de-rotational Lapidus procedure or even a first metatarsal osteotomy might provide benefit over conventional HAV surgery. Unfortunately, there are no long-term comparative studies which can answer this question.
In terms of solving first ray hypermobility associated with HAV deformity, there is one high quality comparative study which provides compelling insight. In 2004, Faber and associates published the results of a Level 1 randomized, prospective blinded study of 101 feet treated with either a distal (Hohmann) osteotomy of the first metatarsal or a Lapidus procedure to treat HAV deformity.22 They published this initial study after a two-year follow up of the patients and subsequently published a nine-year follow up of the same patients.23 When comparing outcomes, there was no difference between the two surgical procedures in terms of radiologic or clinical measures. When comparing the preoperative and postoperative measures of first ray mobility, both the Hohmann osteotomy and the Lapidus procedure gave similar outcomes.
The researchers concluded:
“This study does not support the theory that a hallux valgus deformity in a patient with a clinically assessed hypermobile TMTJ-1 joint requires fusion of the first tarso-metatarsal joint.”23
In Conclusion
I believe that based on my experience and the evidence cited above that the elimination of sessions devoted to biomechanics at podiatric surgical conferences has led to a gap in understanding of the pathomechanics of the very disorders which are being discussed from the podium. The pending reduction of biomechanics case volume from podiatric residency training further illustrates a lack of respect for the requirement of current knowledge in biomechanics when planning and performing foot and ankle surgery.
Dr. Richie is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is a Fellow and Past President of the American Academy of Podiatric Sports Medicine. Dr. Richie is a Fellow of the American College of Foot and Ankle Surgeons, and the American Academy of Podiatric Sports Medicine. Dr. Richie is the author of a new book titled "Pathomechanics of Common Foot Disorders," which is available from Springer at https://www.springer.com/us/book/9783030542009 .
References
1. DiDomenico L, Spingola HD, Cameron J. Emphasizing the role of sagittal plane reduction in the Lapidus procedure. Podiatry Today. 2021;34(9):18-22.
2. Miller JR, Capuzzi MJ, Siwy T. One group's postoperative protocol for triplane bunion correction. Podiatry Today. Available at: https://www.hmpgloballearningnetwork.com/site/podiatry/blog/one-groups-postoperative-protocol-triplane-bunion-correction . Published September 2, 2021. Accessed September 14, 2021.
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