Emerging Advances In Minimally Invasive Bunion Surgery

Bunion surgery is one of the most common surgeries in foot and ankle practices. With over 50 choices of surgical technique to choose from for bunion correction, it is somewhat difficult to decide and decipher which procedure is best for a patient. In general, procedures are divided into osteotomy and fusion-type techniques. Osteotomies are divided into head and base procedures. Fusion options mainly include the Lapidus procedure and, to a smaller degree, fusion of the first metatarsophalangeal joint.

In my experience, the most commonly utilized bunionectomy surgery is currently the head osteotomy technique. This technique, which surgeons commonly perform with a V- or L-type osteotomy of the metatarsal head, allows for a medial to lateral shift of the metatarsal head and correction of the metatarsal-sesamoid position. Rigid fixation with the use of screw(s) allows for immediate weightbearing and a fairly rapid return to shoes at four to six weeks post surgery.

So why would we change what seems to work? Is minimally invasive bunion surgery really any better?

Recognizing The Challenges Surrounding Open Osteotomies For Bunion Correction

An open osteotomy of the metatarsal head is not without risks. Common issues can include joint stiffness, scar tissue formation, hypertrophic scarring of the skin and deformity recurrence. While surgeons can often address these problems, the post-op recovery process can be difficult for patients. Bunion recurrence can be very problematic for patients and for a long time, the idea of bunion return was blamed on hypermobility of the first ray. However, there is a spectrum of hypermobility and no clear understanding of why some bunions reoccur and others do not. Hypermobility is a problem and, in my experience, it is best to treat moderate to severe cases with a Lapidus procedure. However, recurrence can also be an issue in mild to moderate cases and this is not always understood.

The current thinking surrounding bunion correction has emphasized frontal plane deformity correction in relation to bunion realignment. This idea deals with the fact that as the metatarsal head shifts medially in the transverse plane, it also rotates in the frontal plane. This rotation is difficult to correct with the common V- or L-type head osteotomy because it primarily allows a medial to lateral shift of the metatarsal.

In turn, this procedure does not completely deal with the need for frontal plane correction. When thinking about triplanar correction, with proper frontal plane realignment, one is positioning the metatarsal head over the sesamoids in such a way that the pull of the flexor and extensor tendons is more rectus, resulting in less medial or lateral pull on the great toe, and less chance of bunion recurrence.

Pertinent Considerations Regarding Minimally Invasive Bunion Surgery

The option of addressing frontal plane correction is one of the main advantages with minimally invasive bunion correction. One performs the osteotomy with a linear cut through the metatarsal, which allows triplanar correction of the metatarsal head over the sesamoids. The surgeon shifts the metatarsal head laterally, plantarly and rotates it in the frontal plane. This advantage allows for better realignment options and has been a major improvement in my practice for the correction of bunions.

A previous issue I had with minimally invasive bunion surgery was a lack of adequate internal fixation options. Previously, it was common to cut the metatarsal head and shift it laterally with pin fixation of the toe from the distal tip into the metatarsal body. However, this created a floating metatarsal head and resulted in some cases of non-union or malunion.

Fortunately, there have been significant advances in fixation for minimally invasive bunion surgery. One model of interest is large screw fixation from the metatarsal base into the head, usually with two screws. Alternately, surgeons may employ an internal plate and screw technique. While I have found both approaches to be solid options, my preference is placing the hardware through the small incision I use for the osteotomy instead of making two additional incisions solely for screw placement.

For this reason, I prefer internal plate fixation. These systems utilize an intermedullary plate that one press fits into the metatarsal shaft and then anchors with screws into the metatarsal body and head. The fixation is solid, stable, reproducible and allows for similar weightbearing and return to shoes as one would find in utilizing an open osteotomy with screw fixation. Currently, I am using the MiniBunion^™ Implant System (CrossRoads Extremity Systems), which was designed by Bradley Lamm, DPM, FACFAS.

Comparing The Minimally Invasive Bunionectomy To Open Techniques

So is minimally invasive bunion surgery better, worse or the same as an open osteotomy? My current philosophy is that the minimally invasive procedure offers the advantage of better correction of the bunion deformity in three planes. It also allows for sparing of the joint, less scar tissue and less stiffness post-surgery. Finally, the one cm incision size is both preferred by the patient and poses less risk of skin complications.

That being said, it is important to select bunion deformities that do not have arthritic changes requiring debridement as that is difficult to perform with this technique. It is also important to realize that a severely deviated toe may not be as easily to reduce with a minimally invasive technique in comparison to a metatarsal osteotomy and soft tissue release.

Keys To Achieving Successful Outcomes With Minimally Invasive Bunionectomy Procedures

Here are some tips that, in my opinion, may help with minimally invasive surgery choices. Begin with smaller bunions, which are easier to correct. Then  work your way up to larger intermetatarsal angles. When planning incision and osteotomy placement, do so with fluoroscopic guidance and keep in mind that the osteotomy should be proximal to the sesamoid complex. The more proximal the osteotomy, the larger the possible angular correction.

One can take the incision to bone with minimal dissection as long as you are making a medially-based incision between the dorsal and plantar neurovascular structures. Protect the dorsal and plantar tissue during the osteotomy and consider using a saw-less system such as that provided with the MiniBunion in order to help reduce the risk of bone necrosis.

When creating the osteotomy, it is important to do so parallel to the metatarsal shaft. Shift the metatarsal with a lateral push of the metatarsal head and a medial pull and rotation of the great toe. This will shift the metatarsal head laterally, plantarly and also align it in the frontal plane. Overcorrection of the frontal plane is preferred to undercorrection. Place a temporary pin and check your alignment. In my experience, the toe will often be rectus without the need for further soft tissue rebalancing.

If there is still lateral pull on the toe, perform a lateral release through a stab incision in the web space dorsally. If the lateral pull persists, consider further shift of the metatarsal or consider an imbrication of the medial capsule.  The MiniBunion system allows placement of an internal suture through the plate, which one can use to tighten the medial capsule. This is fairly easy to execute. Once you are satisfied with the correction, place your fixation and imbricate the capsule as necessary medially.

I prefer heel weightbearing for the first week to allow bone healing and decrease edema, but weightbearing is possible early in the post-op course.  I close my incision with buried absorbable suture and Steri-Strips or glue. There is no suture removal necessary. Patients can proceed to use shoes at about four to six weeks postoperatively depending on bone healing progress, which one can evaluate through serial radiographs.

In Conclusion

Overall, the minimally invasive bunion procedure has been a great addition in my practice. Patients love the lack of scar tissue, the small incision, the lack of swelling and rapid healing. I also prefer the lack of post-operative care necessary in comparison to open osteotomy procedures.

I suggest proceeding slowly and cautiously. Take a course or two to learn the ins and outs of your preferred fixation system and technique prior to performing these procedures routinely. Begin with a simpler bunion and work your way up to more difficult cases. With proper planning and case selection, the minimally invasive bunion procedure can be very successful and productive with positive outcomes for you and your patients.  n

Dr. Baravarian is an Assistant Clinical Professor at the UCLA School of Medicine. He is the Director and Fellowship Director at the University Foot and Ankle Institute in Los Angeles (https://www.footankleinstitute.com/podiatrist/dr-bob-baravarian). Dr. Baravarian has disclosed that he is an investor in CrossRoads Extremity Systems.