A Closer Look At The Single Screw Fixation Lapidus Procedure

The Lapidus bunionectomy provides stable, dependable reduction of hallux valgus and gives excellent stability to the medial column. A common sequela following bunionectomy is deformity recurrence. This procedure may provide the most stable platform to maintain excellent postoperative alignment of the first ray.   

There have been a variety of modifications to the Lapidus bunionectomy since its original description.¹ I will present a single screw fixation technique, which evolved because of my dissatisfaction with other fixation methods. Some years ago, I began to incorporate the fixation I used to reduce the first ray of Lisfranc fracture dislocations into Lapidus-type bunionectomies but with the elimination of the usual screw one would use from the medial cuneiform to the base of the second metatarsal.

I will discuss two techniques. One is a simple arthrodesis of the base of the first metatarsal to the medial cuneiform and the other technique involves using a bone graft with the redundant bone from the medial aspect of the first metatarsal head. Surgeons can use the bone graft if there is a concern of excess shortening of the first metatarsal with respect to the length of the second metatarsal.

Keys To Soft Tissue Dissection
Being mindful of the nerves, I begin my incision over the dorsal medial aspect of the medial cuneiform, extend it distally over the dorsal medial first metatarsal head and then extend it more at the hallux interphalangeal joint. This allows good visualization of ligamentous and bony structures. Then one frees the soft tissue and neurovascular bundle from the joint capsule medially and subsequently across the dorsal and lateral first metatarsophalangeal joint (MPJ).

Then create a capsulotomy in the first MPJ in the same plane as the skin incision. Free the medial capsule from the head of the first metatarsal with care to avoid buttonholing it. Take care to preserve the proximal attachment to the abductor hallucis muscle. If possible, avoid freeing up the dorsal capsule from the head of the first metatarsal head as this will prevent a possible complication of unintentional capsulodesis during the healing phase that may limit plantarflexion of the hallux.

Then resect the medial prominence. If one is to use this bone for graft, it is often easier to remove superficial fibrous tissue before removing the bone. The surgeon can easily transect a fibular collateral ligament from beneath the first metatarsal head with the tip of a #15 blade or Metzenbaum scissors. If a lateral release is needed, I recommend doing a partial release as hallux varus is a risk of lateral release with this particular procedure.

Performing A Proximal Osteotomy At The Fusion Site
For years, I used to struggle with a dorsal approach to resect the opposing joint articular cartilage at the first metatarsocuneiform joint. In my opinion, this approach is fraught with problems. I now exclusively use a medial approach. One would make an incision through the capsule dorsally and medially through the anterior slip of the tibialis anterior tendon, but leave the plantar ligaments intact. The proximal attachment of this tendon to the medial cuneiform will prevent the tendon from retracting proximally.

Going from medial to lateral with a wide sagittal saw blade or an osteotome, the surgeon can create a corrective wedge osteotomy to align the first and second metatarsal. In order to preserve length, I recommend distracting the joint slightly and leaving the most medial lip of the cartilage intact, working medially from this landmark. Due to the cartilage and bone needed to complete a completely corrective wedge, leaving this landmark intact will allow you to achieve full correction without creating excessive shortening.

After removing the desired amount of wedge, hold the first metatarsal in the desired position and advance a thin K-wire across the first metatarsal and cuneiform to hold it in that position for X-ray or fluoroscopy evaluation. Make adjustments in bone resection as needed, maintaining your landmark medially. After you are satisfied with the position, fixate with a single 4.5 mm cannulated screw.

What You Should Know About Single Screw Fixation
Using the guide K-wire in the 4.5 mm cannulated screw set, advance the K-wire from the dorsal lateral aspect of the first metatarsal just distal to the transition of the metaphysis to the diaphysis plantar medially to engage the plantar proximal medial aspect of the medial cuneiform. The medial cuneiform is wider at the plantar aspect. Ideally, the K-wire should exit at the plantar medial aspect of the medial cuneiform, just proximal to the articulation with the navicular. Radiographic evaluation confirms desired positioning.

Countersink the first metatarsal sufficiently to avoid stress risers and excess screw head prominence. Measure for proper screw length selection and then advance the screw to slight compression. Leave the temporary K-wire in place while advancing the screw as it will prevent the first metatarsal base from rotating the fixation screw. Then remove the original temporary K-wire for final screw tightening. This will allow good compression. Do not overcompress. Once you have achieved the desired compression across the Lapidus fusion site, remove all remaining K-wires.

If there are no half-threaded screws, over-drill over the K-wire just short of reaching the wedge resection site. In that case, advance a fully threaded 4.5 mm cannulated screw with good compression as I have described above. Then remove the guide K-wire. Excess compression will not improve results.

Combining Lapidus Bunionectomy With First MPJ Fusion In A Patient With Rheumatoid Arthritis
For a recent patient with a bunion and rheumatoid arthritis, I combined a single screw Lapidus bunionectomy for hallux valgus deformity reduction with fusion of the first MPJ. Ligamentous laxity from chronic inflammation around the MPJs is a common sequela in the rheumatoid foot and requires careful selection of the proper procedure to maintain good long-term results. In this case, I selected the single screw Lapidus bunionectomy with addition of the fusion of the first MPJ.

The pre-surgical X-rays demonstrated a significant deformity resulting in an extremely wide forefoot, which made shoe fitting difficult. Follow-up X-rays display excellent alignment and good weightbearing for the foot. The first MPJ fusion reduced the risk of gradual loss of alignment of the hallux on the first metatarsal. This allows for predictable long-term satisfaction with stable reduction and the ability to wear normal shoes. This patient also presented with a nonunion of the base of the second metatarsal. I purposely did not address this because of the increased stability of the fusion of the base of the first metatarsal and the cuneiform. This proved to be the right decision as the foot was unremarkable with respect to pain and swelling following full healing of the Lapidus.

Using A Bone Graft To Increase First Metatarsal Length
Before resecting the medial first metatarsal eminence, one should remove the fibrous periosteal and ligamentous tissue. Fashion the redundant bone to the approximate bone graft shape you wish to use at the fusion site of the base of the first metatarsal and the medial cuneiform. Resect the redundant bone with an osteotome or sagittal saw, and place it in sterile, normal saline on the back table. Use the aforementioned Lapidus wedge resection technique to remove the desired corrective wedge of bone at the first metatarsocuneiform joint.

Insert your bone graft at the fusion site and remodel it as needed for a good fit. Temporarily fixate the first metatarsal position parallel to the second metatarsal with a K-wire extending through the graft. Evaluate the position radiographically and fixate as I have discussed above. In regard to the K-wire extending through the bone graft, one may elect to leave it permanently in place by retracting it slightly, bending the distal tip and rotating it so the bent proud end is resting against the base of the metatarsal. This will allow for greater graft stability during consolidation.

Tighten the medial first MPJ capsule by removing what is necessary to balance it with the lateral capsule. One may accomplish this by using straight mosquito forceps from dorsal to plantar at the loose mid-portion of the capsule. Rotate the mosquito forceps to adjust for good alignment of the hallux on the first metatarsal. Excise the desired amount of medial capsule using the mosquito forceps as a guide. Plicate the MPJ capsule at the resection site with your non-absorbable suture of choice. Make sure the plication is strong and you are fully satisfied. Evaluate the foot to determine if you have achieved successful deformity reduction. Then complete deep tissue and integument closure.

In Conclusion
In my experience, I have found that the single screw Lapidus type bunionectomy results in satisfying and stable alignment, which resists recurrence of the hallux valgus deformity. This type of procedure provides greater support to the medial column and resistance to late-stage pronation. The single screw approach maintains excellent alignment and strong stability through the course of healing. As there is no fixation crossing other joints, the procedure maintains midtarsal mobility for excellent adaptation to walking surfaces.

The medial approach to the first metatarsocuneiform fusion site also provides a significant advantage to the conventional dorsal approach, which includes greater ease in creating smooth complete corrective wedge resection with minimal shortening. This approach provides predictable and much easier preparation at the fusion site for excellent alignment and rapid healing.

Dr. DuRussel is the Chief of Podiatry and the Acting Chief of Surgery at the Northern Navajo Medical Center in Farmington, NM.

Reference

1. Lapidus PW. The operative correction of the metatarsus primus varus in hallux valgus. Surg Gynecol Obstet. 1934;58:183–191.

For further reading, see “Emerging Concepts With Post-Lapidus Bunionectomy Weightbearing” in the September 2012 issue of Podiatry Today or “Why The Lapidus Bunionectomy Is The Best Procedure For Severe Bunions” in the December 2011 issue.

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