Another Perspective On First Metatarsal Rotation And The Lapidus Bunionectomy

There has been a lot of attention recently on the Lapidus procedure in regard to its ability to correct a hallux valgus deformity by addressing three planes of motion.

Physicians have traditionally ascertained the severity of a bunion deformity by measuring the first/second intermetatarsal angle on the AP radiographic view. Recent studies have suggested that the coronal plane rotation can improve the position of the deformity by placing the sesamoids back into a normal position under the head of the first metatarsal in their sesamoidal grooves.¹ Some have suggested that physicians are not measuring the position of the sesamoids in relation to the second metatarsal head. A recent review and comparison of AP and sesamoid radiographic views has showed poor agreement between the two and that the cause of sesamoid dislocation may be an eversion or valgus rotation of the first metatarsal.¹ 

I think this is a rather confusing topic, leading to disagreement among those discussing it. When I initially began performing the Lapidus procedure over 15 years ago, we did not focus on rotation of the first metatarsal. I do believe, however, that I was addressing this when I reduced the first/second intermetatarsal angle to correct the deformity.

While I do not disagree there is rotation of the first metatarsal in the coronal plane, I do feel there is only one way to reposition the first metatarsal. The base of the first metatarsal and medial cuneiform have reniform shapes and when matched up anatomically, this positions the first metatarsal back in its correct position in regard to the coronal plane. In other words, if you rotate the first metatarsal back to align it with the articular surface of the medial cuneiform, this should correct the first metatarsal’s coronal plane position. There should be no focus on the sesamoids while doing this.

In my experience, if you reduce the intermetatarsal angle and match the reniform shapes of the first metatarsal and medial cuneiform, the sesamoids will go back to where they should be anatomically. This should also correspond radiographically. In my experience, the sesamoids usually do go back to where they should be an overwhelming majority of the time. In rare instances when the sesamoids have not gone back, then it’s usually my reduction of the intermetatarsal angle that needs fixing or the joint surfaces need to be realigned.

If my reduction is good and the sesamoids are not perfect radiographically, I will leave them. Sometimes, C-arm positioning will create a false appearance of where the sesamoids are anatomically. If my angle is reduced and the foot looks good clinically, I do not focus on the sesamoids. I have never had patients complain that their sesamoids were not in perfect alignment but I have had unhappy patients when the intermetatarsal angle is not reduced enough to remove the “bump” and make the forefoot smaller.

I’m not saying the sesamoids aren’t important and don’t play a role. I just feel this new focus on rotating the first metatarsal to “line up” the sesamoids is misleading. Since radiographs are two-dimensional, you can rotate the first metatarsal and if your C-arm is slightly out of position, your sesamoids could look as if they are “under” the first metatarsal head when they are truly medial or lateral. I have had surgical cases (which I discussed in previous DPM Blogs with pictures) when I rotated the first metatarsal and the sesamoid crista was practically rotated dorsally and the C-arm image showed the sesamoid crista as appearing “anatomically correct” because they looked as if they were directly under the first metatarsal head. Only a true sesamoid axial radiograph will show this. This is something I do not see people doing or discussing intraoperatively.  

In conclusion, when it comes to rotating the first metatarsal during a Lapidus procedure, the focus should be on the metatarsocuneiform and not the sesamoid bones. There is only one way one should rotate the metatarsal and that is to line up the base of metatarsal with the corresponding articulated surface of the medial cuneiform.

Reference

1. Smith WB, Dayton P, Santrock RD, Hatch DJ. Understanding frontal plane correction in hallux valgus repair. Clin Podiatr Med Surg. 2018;35(1):27-36.