Historically, upon the discovery and subsequent validation of a surgical treatment’s efficacy for a particular disease, the ultimate goal for surgeons has been to perform the procedure while inflicting minimal harm to the patient. Minimally invasive surgery (MIS) emerges as a paradigm shift, offering substantial benefits such as diminished wound complications and expedited recovery, primarily through the reduction of surgical incisions.^1-3) This evolving trend towards MIS across various orthopaedic foot conditions marks a significant progression and represents a considerable challenge encountered by orthopaedic surgeons specializing in foot procedures.

In the field of foot surgery, MIS can essentially be delineated into two principal frameworks: the traditional approach, which utilizes arthroscopy or endoscopy to manage intra- or extra-articular conditions and tendon disorders, and a novel methodology that involves the execution of diverse bone and joint surgeries employing the Shannon burr (Fig. 1). This latter tool, which has achieved global acclaim since the mid-2010s, was initially designed for dental surgeries involving the excavation, perforation, and cutting of bone fragments. Despite its widespread application in various forefoot procedures, including the correction of hallux valgus, the utilization of MIS in midfoot and hindfoot procedures remains relatively underexplored.

Figure 1. Shannon burr set used in the surgical procedure. The set includes various sizes and types of burrs designed for precise cutting and shaping during minimally invasive surgeries.

Therefore, this study seeks to exclusively focus on and conduct a comprehensive review of bone and joint surgeries performed using the Shannon burr within the MIS framework, specifically targeting the midfoot and hindfoot regions. This comprehensive review aims to examine the current application of MIS techniques for various foot conditions, identify key factors for achieving optimal surgical outcomes, highlight anatomical considerations critical for minimizing complications, and provide forward-looking recommendations for future research in this field.

There is a scarcity of published studies on MIS for the midfoot. The midfoot is composed of multiple tarsal bones forming numerous joints, making deformity correction in minimally invasive manner challenging as it often requires simultaneous surgery on multiple joints. Current literature on MIS for the midfoot includes cases with Charcot neuroarthropathy-related deformities. Charcot neuroarthropathy is a disabling and progressive disease characterized by peripheral neuropathy caused by hyperglycemia, oxidative stress, adipose toxicity, elevated inflammatory markers, and the accumulation of advanced glycation end products.⁴⁾ When it affects the midfoot, most patients develop a rocker bottom deformity, increasing the risk of ulcers and osteomyelitis.⁵⁾ Even with surgical intervention, poor wound healing, nonunion, infection, and the risk of amputation contribute to the understandable caution toward this patient group.⁶⁾

Mateen et al.⁴⁾ reported favorable outcomes using a Shannon burr for multiple joint preparation, followed by intramedullary beaming device fixation and selective external fixation in patients with Charcot midfoot. They noted that this approach resulted in fewer complications and similar outcomes compared to the open approach.⁷⁾ Similarly, Miller⁵⁾ described a technique using Ø2×20-mm and Ø3×20-mm Shannon burrs to perform a triplanar closing wedge osteotomy with intramedullary beaming device fixation in midfoot Charcot patients. In addition, percutaneous Achilles tendon lengthening or gastrocnemius recession can aid in achieving a plantigrade position of the calcaneus. Miller⁵⁾ emphasized that the initial percutaneous incision should be located at the apex of the deformity. The surgical sequence is critical, with reduction and fixation of the middle and medial columns using beams and bolts, followed by assessment of the lateral column. In cases of rocker-bottom deformity, it is advantageous to stabilize the beam by crossing from the fifth and/or fourth metatarsal to the calcaneus through the cuboid.

Although the number of published studies remains limited, making direct comparison of incidence rates challenging, postoperative complications in MIS, similar to those in open surgery, include nonunion, hardware failure, loss of correction maintenance, infection, and, in severe cases, subsequent amputation.⁵⁾ Mateen et al.⁷⁾ reported that MIS demonstrated a comparable correctional power to open surgery in the reconstruction of midfoot Charcot neuroarthropathy. However, regarding postoperative complications, they noted that MIS was more frequently associated with pin-site infections that did not require further operative intervention, whereas open surgery had a higher incidence of plantar wound breakdown and asymptomatic nonunion. For surgeons, midfoot Charcot cases are particularly challenging due to the high complication rates. Therefore, if the safety of MIS in terms of these complications can be established, it could significantly advance the field. More research involving a larger cohort of patients and long-term follow-up is needed to substantiate these preliminary findings.

1. Hindfoot malalignment

Traditionally, the surgical treatment for hindfoot malalignment has focused on addressing valgus and varus malalignments in the coronal plane. The former is often associated with pes planus deformity, commonly related to posterior tibial tendon dysfunction, while the latter is typically accompanied by pes cavus deformity. A representative surgical technique for addressing hindfoot valgus malalignment is the medial displacement calcaneal osteotomy (MDCO), which offers several advantages, including reducing plantar fascia strain, decreasing the load on the medial longitudinal arch, and mitigating the flattening effect of the Achilles tendon on the medial longitudinal arch.⁸⁾ Conventional MDCO generally involves making a skin incision along an imaginary osteotomy line on the lateral heel, performing an oblique calcaneal osteotomy, and then medially displacing the posterior fragment by 1 cm, followed by fixation of the osteotomy site using screws or plates. Numerous postoperative complications associated with conventional MDCO have been reported in the literature.^9,10) These include wound healing issues, such as delayed healing or wound dehiscence. Neurovascular injury, including damage to the sural nerve or lateral calcaneal artery, can occur during the osteotomy or hardware placement. Over- or under-correction of the deformity can lead to residual malalignment or new biomechanical imbalances. Additionally, postoperative stiffness or pain in the hindfoot may persist despite appropriate healing. Lastly, hardware-related problems, such as prominence or irritation of the implants, may necessitate hardware removal.

MIS-MDCO was attempted relatively early, around the same time the MICA procedure for hallux valgus was introduced. Kheir et al.¹¹⁾ described the MIS-MDCO method in a series of 30 cases, reporting 100% union at the osteotomy site. Subsequent investigations by various researchers have reviewed MIS-MDCO, concluding that it offers higher patient satisfaction and a lower complication rate compared to conventional open MDCO.^12-18) A recent systematic review¹⁹⁾ also reached similar conclusions but noted that the quality of the studies conducted thus far is generally poor, with a high risk of bias.

When performing MIS-MDCO, a critical consideration for the surgeon is that the osteotomy area is relatively large to be completed using only a Shannon burr after the stab incision. This can lead to deviations in the osteotomy line from the preoperative plan, and the high-speed rotation of the Shannon burr increases the risk of skin burn injuries at the incision site. To address these issues, Guyton²⁰⁾ introduced a technique using a jig to maintain a consistent osteotomy line during burring. Similarly, Lee et al.²¹⁾ proposed a method involving the insertion of a reference Kirschner wire into the subcutaneous tissue along the osteotomy line. Regarding surgery-related neurovascular injuries, most studies to date have reported no sural nerve injuries. In addition, a cadaveric study by Durston et al.²²⁾ indicated that the nerve transection effect of the Shannon burr is minimal and that, as long as the quadratus plantae muscle maintains its normal anatomy, the MIS-MDCO procedure is safe from neurovascular damage. In nearly all studies, the osteotomy site was secured by one or two 5.0- or 6.5-mm cannulated screws fixed across the osteotomy line from the calcaneal tuberosity. However, as postoperative screw head irritation symptoms can occur, the use of headless screws or the intramedullary fixation of a blade plate²³⁾ might be considered as alternative methods.

The surgical treatment for hindfoot varus malalignment involves a skin incision and osteotomy similar to MDCO, followed by lateral displacement of the posterior fragment or performing a lateral closing wedge osteotomy. In this procedure, a lateral cortex-based wedge is removed, and the osteotomy site is closed. Although MIS-lateral displacement calcaneal osteotomy is theoretically feasible, it has not been widely reported, and lateral closing wedge osteotomy is not recommended due to the risk of sural nerve injury and technical difficulties.²⁰⁾

Given that the calcaneus has a sufficient vascular supply, the risk of nonunion at the osteotomy site is relatively lower compared to other long bones.^24,25) Based on this fact, the clear advantage of MIS-MDCO is the ability to achieve significant outcomes with small incisions, warranting further research in this area.

2. Achilles tendinopathy with Haglund deformity

Insertional Achilles tendinopathy is a common cause of intractable heel pain. This condition is often associated with Haglund deformity and retrocalcaneal bursitis. Haglund deformity refers to a bony prominence at the posterosuperior area of the calcaneal tuberosity near the Achilles tendon insertion site.²⁶⁾ This prominence can cause inflammation and longitudinal tears in the Achilles tendon due to friction.^27-29) When conservative treatment fails, surgical options such as Haglund deformity resection combined with Achilles tendon debridement may be considered. Numerous studies have reported on minimally invasive Haglund resection (calcaneoplasty),^30-32) Achilles tendon reattachment,^33-35) or flexor hallucis longus transfer³⁶⁾ through endoscopy. Additionally, dorsal closing wedge osteotomy^37-41) has been developed to reposition the Haglund deformity anteroinferiorly, preventing direct friction with the Achilles tendon and thus sparing it from damage. The dorsal closing wedge osteotomy was first introduced by Zadek,³⁷⁾ and Keck and Kelly³⁸⁾ modified this technique to remove a bone wedge from the posterior calcaneus. They placed the apex of the osteotomy just posterior to the weight-bearing point of the plantar calcaneal tubercle, whereas Zadek³⁷⁾ positioned it in the middle of the inferior surface of the calcaneal body. Typically, dorsal closing wedge osteotomy requires a lateral heel incision proportional to the size of the wedge to be removed. However, MIS-dorsal closing wedge osteotomy has been recently reported. Vernois et al.⁴²⁾ presented a MIS technique using a Ø3×20-mm Shannon burr. Nordio et al.⁴³⁾ reported that in 26 patients who underwent MIS-dorsal closing wedge osteotomy, the foot function index score improved from 65 to 8, and the visual analog scale score improved from 9 to 1, with a mean follow-up of 12 months, in a case series conducted without a control group. Choi and Suh⁴⁴⁾ attempted a similar technique using Ø2×20-mm Shannon burr (Fig. 2), achieving early clinical improvement compared to open calcaneoplasty. The final clinical scores showed no statistically significant differences between the two groups; however, at 6 months postoperatively, the clinical scores were significantly higher in the group that underwent the MIS procedure. In the MIS group, there was one case of fixation loss requiring revision surgery with cerclage wiring. However, no instances of superficial or deep infection, operation-related sural nerve injury, nonunion, or malunion were observed. Compared with previous osteotomies,^37,38,42) the major difference in their technique⁴⁴⁾ was the location of the osteotomy apex. They placed the apex on the calcaneal tuberosity, 1 cm inferior to the Achilles tendon insertion site whereas previous techniques maintained the apex on the plantar side of the calcaneal body as they believe that grinding a large dorsally based wedge using a Shannon burr carries a significant risk of sural nerve injury. They also noted that their technique involves grinding the bone at the osteotomy site, which may produce substantial bone debris. This debris could potentially contribute to postoperative pain or serve as a source of wound infection. Therefore, thorough irrigation is necessary to remove the remaining bone debris. Furthermore, due to the substantial amount of bone that needs to be ground, attempting to perform the entire procedure through a minimal incision increases the risk of skin burn. This, in turn, could lead to postoperative wound complications. Therefore, slightly increasing the incision size may be a more beneficial approach. While various MIS techniques have been introduced in this field, open calcaneoplasty can still be performed with a relatively small incision. Consequently, surgeons who have not surpassed the learning curve may be reluctant to choose endoscopic calcaneoplasty. In contrast, MIS-dorsal closing wedge osteotomy has the distinct advantage of avoiding surgical damage to the Achilles tendon insertion site, making it a viable option. However, due to the lack of long-term follow-up studies with a large number of patients, a cautious approach is recommended.

Figure 2. Minimally invasive calcaneal osteotomy for Haglund deformity. Minimally invasive dorsal closing wedge calcaneal osteotomy with cannulated screw fixation may serve as an excellent alternative to open surgery for managing intractable insertional Achilles tendinopathy associated with Haglund deformity.

This review aimed to provide a comprehensive synthesis of the current advancements in minimally invasive bone and joint surgeries using the Shannon burr for various midfoot and hindfoot conditions. The midfoot conditions included Charcot neuroarthropathy, while the hindfoot conditions encompassed hindfoot malalignment and the management of intractable insertional Achilles tendinopathy associated with Haglund deformity. We analyzed the distinctive characteristics of each surgical technique and examined potential avenues for future innovation in this domain. Furthermore, the review emphasized critical considerations that surgeons must address to ensure optimal outcomes and improve patient satisfaction. Successful surgical intervention transcends the mere adoption of MIS techniques; it necessitates meticulous patient selection based on clear indications and the execution of procedures within the surgeon’s area of expertise. We aspire for this review to serve as a valuable resource in advancing the knowledge and expertise of practitioners in this rapidly evolving field.

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