Surgical tips, tricks for performing minimally invasive bunion surgery
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Hallux valgus is a common foot deformity that often leads to altered joint mechanics, progressive pain and dysfunction. Approximately one in five adults aged 18 to 65 years are affected by this condition, with a higher prevalence in women.
Although the etiology of this complex pathology is poorly understood, the progressive forefoot deformity is often characterized by medial deviation of the first ray with lateral deviation and pronation of the hallux (Figure 1). Despite a multitude of published surgical techniques and outcome studies, there is no consensus on the ideal surgical treatment option.
Source: Justin C. Haghverdian, MD; and Andrew R. Hsu, MD
Surgical options are generally directed by the severity of the deformity and the presence of associated conditions, such as midfoot arthritis and/or instability and hallux metatarsophalangeal (MTP) joint arthritis. For mild deformities, distal metatarsal osteotomies are typically performed, while moderate to severe deformities often necessitate proximal metatarsal osteotomies, MTP fusion or tarsometatarsal (TMT) fusion (Lapidus). Conventional surgical techniques may require extensive open skin incisions, soft tissue dissection and intra-articular exposure that can lead to increased postoperative pain, swelling and wound complications. Recently, there has been significant growing interest in the use of minimally invasive (MIS) techniques in hallux valgus correction to reduce pain, improve function and shorten recovery times.
MIS bunion correction typically involves a large-shift transverse distal first metatarsal osteotomy performed in a percutaneous fashion with a low-speed, high-torque burr cooled with a saline drip (MIS Console, Arthrex Inc.). Fixation is performed with percutaneously placed fully threaded 3.5-mm/4-mm non-compression beveled-tip screws. The distal osteotomy is often combined with a percutaneous medial-closing wedge osteotomy (Akin) of the hallux proximal phalanx fixed with a 2.5-mm fully threaded compression screw. There is a steep learning curve involved with many MIS foot and ankle procedures, with a case volume of 20 to 40 often cited as a critical number to become proficient. In this article, we present surgical tips and tricks for performing MIS bunion surgery to assist surgeons as they incorporate this procedure into their practice.
Surgical technique
The patient is brought to the OR and placed in the supine position on a regular radiolucent table. A small bump is placed under the hip of the operative extremity, but the foot is left in a small amount of external rotation to allow for later guidewire and screw placement along the proximal aspect of the first metatarsal. A nonsterile tourniquet is applied at the level of the thigh. The extremity is positioned over a foam leg ramp hanging off the end of the bed. The operative extremity is then prepped and draped in the usual sterile fashion. A bump is placed behind the ankle and the foot is left off the end of the bed to avoid interference in later guidewire placement. The mini C-arm image intensifier is wrapped in several layers of Coban so that the foot can rest on the C-arm without moving.
Under X-ray guidance, the long axis of the first metatarsal is identified and marked out with a surgical marker (Figure 2). Next, a 5-mm stab incision using an 11-blade knife or Beaver blade is made over the medial aspect of the first metatarsal neck in location of the planned transverse osteotomy just proximal to the level of the sesamoids. Subperiosteal dissection is performed over the dorsal and plantar aspects of the metatarsal neck with a small periosteal elevator. A 2-mm by 13-mm straight burr is introduced percutaneously at the level of the osteotomy site and then carried bicortically around a central pivot joint following the same transverse orientation (Figure 3). The osteotomy site is confirmed to be complete and mobile using a small freer placed across the osteotomy. Next, a small, curved hemostat is placed in the medullary canal of the metatarsal and used to laterally translate the capital fragment until appropriate sesamoid coverage is obtained. Alternatively, the hemostat can be placed along the lateral aspect of the metatarsal for greater leverage and lateral shift. Translation is often 50% to 100% of the width of the first metatarsal (Figure 4).
Once lateral translation is achieved, the capital fragment is manually supinated into a neutral position and then held using a 1.6-mm K-wire inserted across the capital fragment into the second metatarsal (Figure 5). Next, a 1.1-mm guidewire is inserted proximally free hand or using a targeting jig. The wire is inserted as proximal as possible, hugging the medial aspect of the foot to obtain the correct trajectory into the lateral aspect of the capital fragment with bicortical fixation (Figure 6). Placing the wire too distally can reduce fixation strength by creating too large of a distal lever arm on the screw and not leave sufficient room for placement of two parallel screws. It is important to confirm on lateral X-ray that the osteotomy is not translated dorsal or plantar and that the guidewire starts just below midline in the metatarsal and ends up in the center of the metatarsal head distally (Figures 7 and 8).
A second 1.1-mm guidewire is then inserted distal to the proximal wire in a parallel fashion using a targeting jig (Figures 9 and 10). Once screw lengths are measured, it is helpful to drive the guidewires out of the end of the skin distally and clamp these with a small hemostat so that the wires do not accidentally back out during subsequent drilling and screw insertion. Next, the wires are over-drilled and two fully threaded screws are placed over the wires across the osteotomy site. To increase stability, the proximal screw is placed first bicortically prior to the placement of the second screw into the capital fragment. Our preference is to use two 3.5-mm fully threaded, headless non-compression screws with beveled tips to secure the osteotomy site (Figure 11).
The proximal screw is deliberately placed in proximal bone, out of bone and back into the bone to achieve purchase in the lateral aspect of the capital fragment. The bicortical fixation without soft tissue disruption of the lateral periosteum secures the osteotomy and permits bony remodeling laterally, which is seen on follow-up radiographs. We have not seen any nonunions across the lateral aspect of the osteotomy site if the screws are bicortical and in the correct orientation. Screw lengths are carefully measured to obtain as much length and bony fixation as possible. The screws are turned so that the obliquely oriented bevel of the screw head is flush with the medial cortex. Previously used non-MIS-specific screws would often protrude from the medial cortex and could cause hardware irritation against the medial soft tissues. Alternatively, 4-mm screws can also be used depending on patient size and fixation needs.
Attention is then turned to the proximal phalanx medial closing wedge Akin osteotomy. We typically perform a MIS Akin osteotomy in conjunction with our MIS distal osteotomy to ensure appropriate bunion correction because no soft tissue reconstruction is performed. A separate 5-mm stab incision is made over the medial aspect of the hallux proximal phalanx. A 2-mm burr is used percutaneously to osteotomize the proximal phalanx while preserving the lateral cortex of the proximal phalanx (Figure 11). The closing wedge osteotomy is then compressed and fixed using a 2.5-mm fully threaded, headless compression screw (Figure 12).
The remaining medial prominence of the proximal fragment is addressed by introducing the 2-mm burr through the original distal osteotomy site and shaving down the bone until the prominence is no longer palpable (Figure 13). Alternatively, the medial shelf can be osteotomized using the burr and pushed into the medullary canal as bone graft.
Final radiographs demonstrate hallux valgus correction and secure screw fixation (Figures 14 and 15). The five separate stab incisions are then irrigated and closed with 4-0 nylon sutures (Figures 16 and 17). A sterile soft bunion dressing is placed over the incisions.
Postoperative protocol
Postoperatively, patients are made weight-bearing as tolerated in a tall, controlled ankle movement boot or hard-sole postoperative shoe for 2 to 4 weeks. Sutures are removed at 2 weeks, and patients are then transitioned to regular athletic shoes around 4 weeks as individual pain and swelling allow. Impact activities are allowed at 10 to 12 weeks after surgery depending on radiographic evidence of healing. The main advantages we have found of MIS bunion surgery are the ability to shorten soft tissue recovery time and allow for early weight-bearing and significantly faster return to regular shoes.
Conclusion
There is a continually growing interest in the use of MIS techniques in foot and ankle surgery. From common forefoot conditions to deformities of the hindfoot and fusion procedures, MIS in foot and ankle shows considerable promise. With specialized saline-irrigated low-speed, high-torque burrs; targeting jigs; and specialized implants, osteotomies can be reproducibly created and secured using small incisions with minimal soft tissue dissection.
A recent systematic review by Tyler Gonzalez, MD, MBA, and colleagues in 2023 demonstrated that, in the 17 studies reviewed, the use of MIS techniques with a burr for hallux valgus deformity resulted in appropriate correction of the hallux valgus, intermetatarsal and distal metatarsal articular angles. The results showed an overall complication rate of 16.6%, recurrence rate of 2.2%, nerve injury of 2.4%, infection of 1.1% and nonunion of 0.4%. While the results of recurrence, nerve injury, infection and nonunion are similar to open techniques at the present time, the authors hypothesized that the higher overall complication rate was due to hardware irritation, which may be minimized with newer-generation implants, such as beveled screw tips.
Overall, when performed correctly and in the appropriately selected patient, we have found MIS bunion surgery to be reliable, reproducible and with significantly decreased pain and improved recovery time for patients with minimal complications. We believe the learning curve associated with the procedure to be approximately 20 cases. The learning curve can be significantly helped with careful planning and meticulous attention paid to the key steps of the procedure described in this article.
Technical tips
- Position the patient with the foot off the end of the bed, in slight external rotation, bump behind the ankle and foot securely resting on the mini C-arm image intensifier wrapped in Coban to minimize motion of the foot during the case.
- Mark out the planned osteotomy site, lateral axis of the first metatarsal and entry point and trajectory of the proximal screw prior to making any incisions.
- Carefully observe radiographs while creating the transverse osteotomy to ensure that it is straight and complete.
- Use a curved hemostat intramedullary or along the lateral metatarsal cortex to laterally translate the capital fragment until the sesamoids are covered. Supinate the hallux after the shift and then secure the capital fragment to the second metatarsal with an accessory K-wire.
- Ensure that the proximal screw starts as proximal as possible on anteroposterior view, starts slightly below midline on lateral view, is bicortical and is centered in the metatarsal head without translation of the osteotomy.
- Most MIS distal osteotomy cases require a combined percutaneous proximal phalanx Akin osteotomy with screw fixation to achieve long-lasting bony correction.
- Carefully shave down the remaining medial metatarsal bony ledge or osteotomize it and push it into the medullary canal with a freer.
- References:
- Gonzalez T, et al. Foot Ankle Orthop. 2023;doi:10.1177/24730114221151069.
- Lausé GE, et al. J Am Acad Orthop Surg. 2023;doi:10.5435/JAAOS-D-22-00608.
- Noback PC, et al. Foot Ankle Orthop. 2018;doi:10.1177/2473011418800239.
- Ray JJ, et al. Foot Ankle Orthop. 2019;doi:10.1177/2473011419838500.
- Shi GG, et al. J Am Acad Orthop Surg. 2020;doi:10.5435/JAAOS-D-19-00324.
- For more information:
- Justin C. Haghverdian, MD, and Andrew R. Hsu, MD, can be reached at the department of orthopedic surgery at the University of California-Irvine in Orange, California. Hsu’s email: hsuar@uci.edu.
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