Is There an Optimal Position for First Metatarsophalangeal Joint Fusions?

The first metatarsophalangeal joint (MTPJ) fusion is a workhorse procedure that has evolved over time in its utility. The discovery of the usefulness of the first MTPJ fusion was initially unintentional. Several surgeons in the 1800s found that bony ankylosis of the first MTPJ after surgery produced a stiff, pain-free joint if positioned adequately.¹ Following these incidental occurrences, Wyeth first described MTPJ arthrodesis in 1887 and Clutton in 1894 for severe hallux valgus deformities.² From then on it became used for a variety of forefoot pathologies, most notably hallux rigidus.^1,2 By the 1950s McKeever routinely performed first MTPJ fusions, many with a dorsiflexory angle upwards of 35 degrees on females, during a time when many female patients were adamant about wearing high heels post-fusion. McKeever’s construct of choice was a stainless-steel screw with a washer inserted through the proximal phalanx and placed into the metatarsal shaft.²

Just as medicine evolved, so did trends in fixation. While Clutton originally fixated his arthrodesis with an ivory peg, with the rise of AO principles, a plethora of fixation options came to fruition.² Today, effective constructs range from sutures and wires to screws, plates, and staples in many combinations and positions, to even bioabsorbable fixation.³ In fact, recent advances in bioabsorbable fixation constructs present a significantly attractive option for first ray surgery, with newer iterations of magnesium or cortical bone–based screws replacing conventional titanium due to their increasingly stronger loading properties.⁴ That being said, biomechanically, the strongest construct is a dorsal locking plate and a lag screw, followed by non-locking plate and lag screw, screws alone, and plate alone.³

However, with the rise of rigid, stable constructs, studies show that excessive rigidity/stability does not always translate to positive clinical outcomes. Some researchers suggest a higher nonunion risk for rigid locking plates versus nonlocking plates in first MTPJ fusion for the treatment of hallux rigidus.³ This urges the notion that a degree of micromotion at the arthrodesis site optimizes union as opposed to excessive rigidity. Researchers recently published a study that a biplanar construct is advantageous in that it provides more stability at the first MTPJ than a rigid locking plate/lag screw combination while also maintaining adequate levels of micromotion at the arthrodesis site.⁵ This assumption extrapolates from studies on Lapidus constructs. A 2022 systematic review compared staples, crossing screws, and plate fixation for first MTPJ fusion using 250+ feet with an overall union rate of 95% or greater regardless of construct.⁶ This is also demonstrated in other systematic reviews by Roukis as well as Korim and colleagues.^7,8 Additionally, in Roukis’ study, symptomatic non-unions accounted for only 1.8% of total cases.⁷

This prompts the question: with overall high union rates, and only one-third of actual nonunions being symptomatic, at what point does fixation type become moot? In the authors’ opinion, more concerning is the rate of malunion (approximately 6% in Roukis’ systematic review).⁷

What is the Optimal Position of the First MTPJ?

First MTPJ fusions have treated a wide variety of pathology over the years. In addition to hallux valgus and hallux rigidus, it is useful for systemic arthritis, gout, revisional surgery, and neuromuscular conditions.⁹ Biomechanically these conditions and their resultant first ray deformities have a significant impact on the loadbearing status of the hallux and often cause secondary conditions like transfer metatarsalgia and lateral column overload.¹⁰ By properly realigning the hallux through first metatarsophalangeal joint fusion, one can restore the function of the first ray. A well-aligned first MTPJ arthrodesis reduces stresses on adjacent joints, improves stability of the first ray as the first ray lever arm is lengthened, increases ankle push off power, and reduces stride width.^11–14 With the clear impact that a well-corrected first ray has on gait, one can postulate that the position of the first MTPJ during arthrodesis is an extremely significant factor. Yet surprisingly, even with predictable, positive outcomes (ie, patient satisfaction rate over 90% across multiple studies⁹), there is no absolute, precise numerical value to quantify the most appropriate fusion position—only “ranges” in degrees, which in and of themselves prove to be impractical to assess in surgical practice without a protractor in the surgical tray.

The accepted “ranges” for acceptable fusion positions vary widely by author. Prominent researchers (studies with > 500 citations) claim an appropriate position of 10–15 degrees of valgus, 20–30 degrees of dorsiflexion, and neutral in the frontal plane.^15,16

However, there are 60+ other studies that each opine their own definitions on appropriate positions ranging anywhere from 0–40 degrees in both the sagittal and transverse planes.¹⁷ While opinions clearly differ on the acceptable fusion position, the biomechanical implications of deviations in each plane are readily apparent and described extensively in literature. Too much plantarflexion and frontal plane rotation can cause stress on the interphalangeal joint, while too much dorsiflexion can cause plantar first metatarsal head and sesamoid pain, shoe irritation, and propulsion issues during gait.¹⁸(Figure 1). Too much abduction in the transverse plane can cause second digit irritation, while an adducted hallux can cause excessive gapping between digits 1 and 2. This notion is also echoed by DeCarbo and colleagues, who feel the most appropriate position in the sagittal plane is “slightly off the floor” to avoid the above complications of sagittal malunion.⁵

Wagner more recently expanded on the position of the great toe by measuring toe-to-floor distance instead of degree of dorsiflexion.³ Although he agreed with a slight valgus angle, he mentioned that measuring an angle is near impossible intraoperatively. Furthermore, the point was made that the angle of dorsiflexion of the hallux during fusion can additionally have a wide variance depending on foot type—for example, a severe cavus foot with a plantarflexed first ray would require a much higher angular relationship between the hallux and first metatarsal. The value of this angle could easily potentially be greater than the aforementioned range of 20–30 degrees by Coughlin.¹⁹

Another example to illustrate this notion is that while a 15-degree angle between the hallux and first metatarsal in the sagittal plane might constitute an acceptable fusion position in a normal foot, this may either be too small an angle in severe cavus or too great an angle in severe planus foot structures. With a 15-degree dorsiflexory angle in a cavus foot structure, the patient may struggle significantly to achieve toe clearance or develop significant arthrosis and deformity of the interphalangeal joint due to stress. In a severe planus structure 15 degrees of dorsiflexion between the hallux and first metatarsal could induce sesamoiditis and reduce propulsion during gait. Because of this the recommendation arose for surgeons to perform toe-to-floor distance measurements instead. This method is independent of the first metatarsal declination angle, allowing it to be applied to all foot types.³  

Furthermore, this measurement is much more practical and quantifiable intraoperatively. This is the root of the problem in angular measures of hallux position. Appropriate angular positions are entirely dependent on extremely variable anatomic presentations. Therefore, in our opinion, the most practical measurement of the position of the hallux in first MTPJ fusions should be neutral in the frontal plane, 0–5mm from the floor, and a parallel relationship to the second digit under 2 conditions: that it does not induce a moderate-to-severe hallux abductus deformity, and that it avoids a varus angulation.

While we feel that this is the most appropriate approximation of the hallux, social, pathologic, and biomechanical aspects must be considered when choosing fusion position. As mentioned earlier from McKeever’s study, women wearing high heels can be fused in a high degree of dorsiflexion to accommodate for the shoe wear.² In hallux valgus patients with severe abductus deformities of the lesser digits, overcorrecting the hallux abductovalgus deformity can cause excessive gapping between toes 1 and 2.

Insights on Addressing Malunions

In Roukis’ meta-analysis/systematic review, malunions occurred in 6.1% of cases after first MTPJ arthrodesis.⁷ According to Roukis, dorsal malunions are statistically most common, occurring approximately in 87% of cases. However, this study did not mention how many were symptomatic. This is followed by valgus malunions.^20,21 Rarely, plantar malunions can occur.¹⁵ It has been said that fixation without a plate can cause dorsiflexory malunions of the toe of up to 40 degrees.²² That being said, use of a plate can also cause a dorsal malunion if too much dorsal bend is applied.²³ This may account for why dorsal malunions are most common.  

While still relatively rare, malunions can be addressed in various ways. Cullen and colleagues treated 2 dorsal malunions in their study with a dorsal opening wedge osteotomy.²⁴ Both patients reported subjective improvement not only in toe position, but the ability to wear shoe gear with no irritation.

In addition, other procedures used to address malunions include a plantar wedge osteotomy, crescentic osteotomy, or trapezoid osteotomy. Multiplanar malunions are often addressed with a through and through osteotomy to properly position the toe. Care must be taken not to overly shorten the toe with these as well as closing base osteotomies. If shortening occurs, the use of bone graft is applicable in that it restores length and anatomy of the first ray and in our opinion helps with real-estate for a dorsal plate. In our opinion, an additional important aspect of first metatarsophalangeal joint malunions is assessment of the interphalangeal joint. Many times, in the event of malunion, this joint may undergo adaptive changes due to altered stresses and biomechanics. This can have a significant impact on deformity correction, and it is our opinion that practitioners should take into consideration adaptive changes and deformities of the interphalangeal joint when addressing first MTPJ malunions (Figure 2).

While osteotomies can correct first MTPJ malunions, an option gaining popularity is fusion takedown and conversion to first MTPJ arthroplasty for unhappy patients. Both authors have performed fusion conversions to arthroplasties in practice with success (Figure 3, Figure 4, and Figure 5). Malunions, in particular plantar malunions, of first MTPJ arthrodesis increase stress across the interphalangeal joint. Re-establishing motion at the first MTPJ can therefore decrease stress across adjacent joints in the event of symptomatic malunion.²⁵ Furthermore, in our experience, medially or laterally based trapezoidal bone block resection prior to implant insertion can also help correct transverse malunions. A small 2023 case series documented a 30-point increase in AOFAS/H/MTP/IP scores in patients who were converted from first MTPJ fusion to arthroplasty.²⁶ These patients reported high Visual Analogue Scale foot and ankle scores of 95+ at 5 years. There are multiple other case studies documenting positive results in converting first MTPJ fusions to arthroplasty.^25,27

While this procedure is a viable option, we feel it is better for a patient with low physical demands. Additionally, the practitioner should consider soft tissue constraints when performing this procedure. Staged monorail distraction prior to implantation may be necessary to preserve soft tissue neurovasculature in patients who have significantly shortened first rays prior to revision.²⁵

In Conclusion

Although there are a range of values proposed in the literature for position of the great toe joint, the position of the hallux during arthrodesis must be made on a case-by-case basis using toe-to-floor distance and lesser digit relationship. Malalignment in any or all of the 3 planes can affect a patient’s daily activities, so both social and biomechanical factors must be taken into consideration to ensure the correction position of the first MTPJ and prevent complications such as a malunion. In the event of malunion, the surgeon must take into consideration the patient’s primary complaint, the degree and origin of the deformity, and its relationship to the surrounding structures of the foot. Only then can the appropriate plan be formulated.

Dr. Shaffer practices at Cascade Orthopedics & Sports Medicine Center in Hood River, OR.

Dr. Hoffler is a fellowship-trained foot and ankle surgeon practicing at The Centers of Advanced Orthopaedics, Orthopaedic Associates of Central Maryland Division in Baltimore, MD.

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