Shortening of the First Ray With Hallux Valgus Correction

 How Short Is Too Short?

There’s more than one way to shoe a horse. Likewise, there is more than one way to shorten the first ray with operative correction of moderate to severe hallux valgus deformity. Some find shortening necessary for adequate correction, though a major concern is an excessive amount of shortening and the potential associated consequences. The perceived shortening that comes with each procedure may impact procedural selection. It has been well described in the literature that following most first metatarsal osteotomies and or first tarsometatarsal fusions, there is an associated shortening.¹

We know and accept the risk of this shortening when it comes to bunion correction, but how short is too short? Is there a threshold or degree of shortening we must look to avoid in order to prevent any significant sequela? In our observation, the Lapidus procedure is often discussed when concerns for significant shortening arise. How does associated shortening with the Lapidus procedure compare with some of the other often utilized distal and midshaft osteotomies? In this piece, we hope to shed more light on this commonly encountered problem.

A Closer Look at Common Bunion Surgeries

Though there are over 130 procedures described for bunion correction, we will focus on what we feel are the so-called “workhorse” procedures in our investigation of first ray shortening. To start, how much first ray shortening can we expect with distal metatarsal osteotomies? Concrete and conclusive data is limited. Tóth et al recently reported on this issue, finding that subcapital first metatarsal osteotomies shortened the first ray on average by 3.8 +/- 1.8 mm.¹ Though the authors did not quantify a clinically significant amount of shortening, they concluded there was a high correlation between shortening and transfer metatarsalgia of rays 2 through 4.

Working our way proximally, the scarf osteotomy is another commonly utilized procedure for hallux valgus deformity correction. Similar concerns arise with shaft osteotomies when compared to distally based procedures. What is the expected amount of shortening?

Recent publications have tackled this question and findings are somewhat more conclusive than distal osteotomies. One hundred six patients undergoing a scarf osteotomy were assessed by Lenz et al.² Shortening of the first metatarsal was evaluated using three previously described methods. There was significant shortening independent of the method used. The average absolute and relative shortening was measured at 1.7 mm and 2.5%, respectively.

Using similar radiographic assessment tools, Suh et al found statistically significant shortening of the first metatarsal following the Scarf procedure.³ In this study 2 different groups of patients were described—those who developed transfer metatarsalgia and those who did not. In those who did, 9 percent of their 123 patients, there was an average shortening of 4 mm. The control group without metatarsalgia had an average shortening of 2.5 mm. We will discuss in subsequent sections the associated consequences of first ray shortening.

The Lapidus procedure has gained increased popularity in recent years as foot and ankle surgeons have focused on the ability to correct the bunion deformity at the apex with 3-dimensional correction. More so than most first ray procedures, the Lapidus has been criticized for the fact that it can lead to excessive and undue shortening, especially when planal resection is involved. Studies investigating associated shortening with planar cuts have found average shortening from 3.1mm to 7.5mm, quite a variable range.⁴ In comparison, studies investigating associated shortening with manual joint preparation found a range from 0.86 to 5.0mm.⁴ Some have argued that manual prep when it comes to joint arthrodesis is often inadequate and may lead to an increased incidence of nonunion.⁵

Searching for a Happy Medium

Where is the happy medium when it comes to shortening and adequate preparation? This is still very much a hot topic in the foot and ankle space. As of late, we have observed cut guides/systems for controlled planal resection of joint surfaces developed and implemented with increasing popularity. The goals in our observation seem to be 3-fold: correcting a suspected tri-plane deformity, limiting shortening, and achieving an adequate preparation for successful fusion.

Hatch and colleagues recently investigated first ray shortening with the Lapiplasty system (Treace Medical Concepts) on 35 patients. Average bone loss or shortening on the AP radiographic measurements was found to be 3.1mm and 2.4mm in the sagittal plane. These measurements would be on the lower end of the shortening range found in the literature. No patients were found to have transfer metatarsalgia, though there was only a 6-month follow-up.⁴

Through our literature review on this topic, it is apparent additional considerations should be made when evaluating and measuring the shortening of the first ray. There have been several techniques described and used to measure shortening but none have been universally accepted as the standard. Traditionally, AP radiographs have been used to measure preoperative to postoperative changes in the relative length of the first and second metatarsals. Postoperative changes in the sagittal plane correction can skew measurements if the final correction deviates in the sagittal plane. This is especially true with the Lapidus bunion correction. When evaluating shortening and its associated complications, one should be aware relative shortening may be affected by the changes in the sagittal plane and there is no agreed-upon radiographic standard.

Is There a Sequela of Shortening?

It is common for patients with HAV to have plantar pain at the lesser metatarsophalangeal joints (MTPJ). This pain is not necessarily due to the short first ray, but rather abnormal first ray mechanics and first ray insufficiency leading to pathologic load transfer to the lesser rays. There is well-documented literature indicating a relationship between iatrogenic shortening of the first metatarsal and postoperative metatarsalgia.^1,2,6-8

Iatrogenic shortening of the first metatarsal after hallux valgus correction is also thought to contribute to functional insufficiency of the first ray. During the stance phase, the whole sole of the foot should contact the ground. Iatrogenic first metatarsal shortening decreases first ray contact with the ground, causing an overload of the lesser metatarsals throughout the gait cycle. This unbalanced metatarsal length may also cause soft tissue stress to the plantar-distal lesser MTPJs during the push-off phase of the gait cycle.³

Transfer metatarsalgia is often manifested clinically by the presence of plantar callosities of the lesser metatarsal heads. Nakagawa et al evaluated 4 radiographic parameters associated with hallux valgus deformity. They found that relative metatarsal length (RML) was most significantly associated with the incidence of plantar callosities, highlighting the dermatologic manifestations of a functionally short first ray.⁷

Suh et al reported that 54.5% of patients with transfer metatarsalgia following the scarf osteotomy had plantar callosities, all located below the second metatarsal head. Subjectively, transfer metatarsalgia pain has been commonly reported more during ambulation and less during static standing.³

Insights on the Amount of Clinically Relevant Shortening

Although it is widely accepted that excessive shortening of the first metatarsal should be avoided because of the risk of transfer metatarsalgia, the exact amount of shortening that can be tolerated is difficult to define. As mentioned above, there is no gold standard method to measure metatarsal length. Different radiographic projections can alter angles, causing difficulty when establishing a precise and reproducible method of measuring metatarsal length.^2,9,10

Despite the inherent variability in metatarsal length assessment, the “acceptable” amount of first ray shortening has frequently been investigated. Carr and Boyd were among the first to describe this concept, and argued that the degree of the first metatarsal shortening in the treatment of hallux valgus should not exceed 4 mm.⁸ Nakagawa et al evaluated postoperative first metatarsal length following biplane interlocking osteotomies for HAV correction. Using Nilsonne/Morton’s method of relative metatarsal length (RML), they concluded that RML of −3 mm predicted postoperative metatarsalgia with a specificity of 88% and a sensitivity of 85%.⁷

Larger degrees of shortening have been described after hallux valgus correction, as Klosok et al reported an average shortening of the first metatarsal by 10 mm and Pouliart et al reported an average shortening of 8.5 mm postoperatively.^11,12 Interestingly, none of these studies found any correlation between the amount of shortening and the incidence of transfer metatarsalgia.

Such variability in shortening and associated transfer metatarsalgia have suggested that various factors apart from the metatarsal length may also alter the forefoot biomechanics. Elevation of the first metatarsal, subluxation of sesamoids, and hypermobility of the first metatarsal-cuneiform joint are all thought to contribute to the development of transfer metatarsalgia.

Geng et al conducted a biomechanical simulation study to investigate the relationship between first metatarsal shortening and plantar forefoot loading to determine how much shortening of the first metatarsal could be allowed, without the confounding factors of in vivo studies.¹³ They concluded that if the sagittal plane alignment of the distal first metatarsal head remains unchanged, lesser metatarsal loading will not change until the first metatarsal shortening exceeds 6 mm. Secondarily, the authors stated that more shortening might be allowed if its distal first metatarsal is plantarflexed.¹³ These findings all highlight the overall importance of the first metatarsal head sagittal plane alignment during HAV correction.

How Do We Avoid Shortening?

With this information in mind, we ask ourselves how surgeons avoid first ray shortening during HAV correction while some degree of shortening is inherent to every procedure.

Although there is no gold standard for the measurement of metatarsal length, the authors recommend utilizing a consistent method for measuring the metatarsal parabola. We believe that measuring RML using Nilsonne/Morton’s method with standard AP radiographs is reasonably quick, easy to perform intraoperatively under fluoroscopy, and useful in daily practice. Figure 1 illustrates Nilsonne/Morton’s method of metatarsal length assessment. Admittedly, this method of evaluation has inherent flaws. Length measurements may change based on the radiographic tube angle. Potential variations in the sagittal plane alignment before and after surgical correction may also lead to the inconsistent length measurement. It is important to remember that when the first ray is dorsiflexed, it measures longer when compared to the second in an AP radiograph. Keeping in mind that there has not been a change in absolute metatarsal length, but rather a change of projection on radiographs.⁴

In regard to the Lapidus procedure, shortening can be minimized by a method of joint preparation. Ellington et al demonstrated that first tarsometatarsal joint (TMTJ) preparation by curettage produced on average 2.9 mm of shortening while planar resection can shorten up to 7.5 mm.¹⁴ Many authors describe successfully utilizing joint curettage rather than planar cuts for first TMTJ to preserve the length of the first ray. Prissel et al demonstrated that joint preparation with curettage preserves the length of the first-ray while allowing a complete reduction in deformity and high union rates.¹⁵ The surgeons at our institution choose to utilize either an exclusively curettage technique, or a hybrid technique of curettage of the first metatarsal base and planar resection of the first cuneiform. This technique is intended to ensure the preservation of the first ray length while still achieving appropriate deformity reduction.

The first ray is composed of multiple joints spanning from the talonavicular joint to the interphalangeal joint of the hallux. Although the literature reflects shortening of the ray as a limitation of certain procedures and advises against techniques that produce shortening, many authors feel that 3-dimensional realignment of the first ray has a more dramatic effect on preserving normal first ray function than the length of the first metatarsal alone.^4,16 These findings align with the concept of restoring sagittal plane alignment of the first metatarsal, which we believe is just as important as preventing loss of first metatarsal length when restoring forefoot biomechanics and preventing transfer metatarsalgia (Figure 2).

Although prophylactic lesser metatarsal shortening osteotomies have been employed to maintain the metatarsal parabola during HAV correction, the authors are hesitant to perform this procedure prophylactically. This is especially true when performing a first tarsometatarsal arthrodesis for HAV correction. A study by King et al demonstrated a reduction of pressure under the second metatarsal head successful load-sharing following Lapidus arthrodesis for bunion correction.¹⁷ Because a reliable and reproducible metatarsal measurement method is currently lacking, there is no current threshold to support additional shortening osteotomies in the presence of transfer metatarsalgia.²

Unfortunately, it is difficult to identify patients who might develop metatarsalgia postoperatively. There continues to be emerging literature to challenge the concept of metatarsalgia resulting from first ray shortening alone. A missing correlation between metatarsal length and peak pressure under the lesser metatarsal heads has confirmed that first metatarsal length alone does not appear to be the only parameter in restoring forefoot biomechanics and preventing transfer metatarsalgia.

In Conclusion

Surgeons should aim to minimize first ray shortening during HAV correction, while also restoring appropriate sagittal plane alignment of the first metatarsal. We look forward to future advanced imaging techniques such as 3-dimensional CT analysis that may shed light on the true significance of metatarsal length relationships following HAV correction, to ultimately help surgeons better understand and treat transfer metatarsalgia associated with first ray insufficiency.

Dr. Hill is a second-year resident at the Grant Medical Center Foot and Ankle Residency Program.

Dr. Stone is a third-year resident at the Grant Medical Center Foot and Ankle Residency Program.

Dr. Barron is a board certified foot and reconstructive rearfoot/ankle surgeon. He practices at Gentle Foot Care—A Division of Ohio Foot & Ankle Specialists. He is the Podiatry Division Chief at Doctors Hospital in Columbus, OH, and is the Assistant Director of Research to the Grant Medical Center Foot and Ankle Residency Program.

References
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