Percutaneous Talonavicular Fusion Technique With the Shannon Burr

The talonavicular (TN) joint, a ball-and-socket joint, is formed by the articulation between the head of the talus and the posterior aspect of the navicular.1,3 As an essential link between the hindfoot and midfoot, the talonavicular joint allows for controlled movements of the hindfoot and has the greatest range of motion of the triple joint complex.2,3 Etiologies of TN joint pathology include trauma, inflammatory conditions, idiopathic degeneration, and acquired flat foot deformity.1,3,4 Correction of end-stage deformity is typically managed surgically through arthrodesis of the involved joint, most commonly performed as part of a double or triple arthrodesis.1,3 Despite the loss of range of motion at the TN joint, these arthrodesis procedures ultimately restore and maintain physiologic hindfoot alignment.2,3 Surgical fixation of the TN joint is traditionally performed through an open approach with dorsal and/or medial incisions.2 Historically, patient outcomes are generally satisfactory, but postoperative nonunion remains a concern with rates ranging widely among previous literature.1 Also, wound healing and skin bridge formation are complications of the open approach. The primary modifiable risk factors associated with nonunion are inadequate joint preparation and improper fixation techniques.1,2 Continual advancements in minimally invasive surgery now include percutaneous approaches, which offer a presumed reduction in surgical trauma allowing for fewer wound healing complications, earlier functional recovery, and reduced morbidity. Previous literature investigating minimally invasive approaches has also detailed the use of medial and dorsal portal sites for TN fusion.5 Our original study examined both the challenges and potential of utilizing a Shannon burr for percutaneous TN joint preparation in 9 cadavers.5 The inherent curved nature of the TN joint to be prepared by a straight burr warranted investigation. The results of this study were used to identify the anatomical structures most at risk and the considerations that must be taken to avoid injury to adjacent structures. The identified structures most at risk for contact were seen to be those most adjacent to both the dorsal and medial portal sites. Building upon our previous cadaveric investigation of this technique, the present study uses the published selection of portals, recommendations for dissection, and an understanding of anatomical variations to demonstrate an intraoperative percutaneous approach to TN fusion. TECHNIQUE The patient is a 57-year-old female who presented to the clinic with a rigid flat foot deformity, end-stage posterior tibial tendon dysfunction, and midfoot arthritis. She had failed physical therapy, immobilization, and bracing and had used shoe inserts to no avail. She met the indications for triple arthrodesis, naviculocuneiform fusion, Lapidus procedure, and percutaneous Achilles tendon lengthening. Percutaneous talonavicular fusion was used to help maintain the soft tissue envelope, minimize incision size, and due to surgeon preference. Preoperative weight-bearing films were obtained (Fig. 1A, B). A video illustrating the percutaneous TN fusion is available for viewing (see Video, Supplemental Digital Content 1, https://links.lww.com/TIO/A86 which demonstrates the described procedure). The patient was positioned supine on the operating table with the operative extremity on a surgical bump for improved visualization and a triangle under the knee to improve the plantigrade position of the foot for the operation and accessibility of a large C-arm (Fig. 1C, D). A thigh tourniquet was applied to the operative extremity. The extremity was prepped and draped in the usual sterile manner. The tourniquet was inflated in concordance with the patient’s blood pressure. Surface anatomy landmarks, including the anterior talus, navicular, cuneiform, and metatarsal, were identified with a skin marker using fluoroscopy whereas extensor hallucis longus (EHL) was identified by palpation (Fig. 1E, F). The medial portal site was identified and labeled approximately 1 cm dorsal to the posterior tibialis (PT) tendon’s insertion on the navicular whereas the dorsal portal was identified and labeled between the tibialis anterior (TA) and EHL tendons (Fig. 1G). Both portal sites were confirmed by fluoroscopy.FIGURE 1: Patient preparation. A and B, Preoperative weight-bearing x-rays. C and D, Patient positioning. E and F, Surface anatomy and incision location. G, Portal incisions.Next, a 0.3 cm incision was made at each portal site using an 11-blade scalpel. Blunt dissection was carried out using a curved hemostat (Fig. 2A). A curved periosteal elevator was used to gently elevate the capsule from the joint at the dorsal and medial portal sites (Fig. 2B). Starting from the medial portal, under fluoroscopy, a 2 × 19.5 mm straight Shannon burr was used to prepare the joint (Fig. 2G). A 2 × 13 mm straight burr can also be used for joint preparation. The burr was continuously irrigated with small amounts of saline to prevent thermal damage to the bone surface and skin. Care was taken to prevent the burr from contacting the skin. This step was repeated at the dorsal portal, and the burr was alternated repeatedly between both sites (Fig. 2C–F). When the TN joint has been loosened, a pin distractor can be utilized to prepare the deeper parts of the joint until the operating surgeon is comfortable with the procedure. Both sites were irrigated copiously to ensure excess cartilage removal. The smallest available digital osteotome or a small curved curette can be used to ensure appropriate joint preparation and remove any remaining cartilage or sclerotic bone (Fig. 3A). Adequate joint preparation was confirmed with fluoroscopy (Fig. 3B, C).FIGURE 2: Joint preparation. A, Curved hemostat used for blunt dissection down to joint. B, Curved periosteal elevator used to free joint capsule. C and D, Shannon burr in dorsal portal site. E and F, Shannon burr in medial portal. G, 2.0 × 19.5 mm Shannon burr used in procedure.FIGURE 3: Joint fusion. A, Small digital osteotome used to confirm joint preparation. B and C, Final joint preparation. D and E, K wire insertion. F and G, Final screw construct. H and I, 3-month radiographs.The type and configuration of fixation and screws are up to the surgeon’s discretion and hardware availability. In this specific procedure, under fluoroscopic guidance, 2 threaded 0.045” Kirschner (K) wires were percutaneously inserted across the talonavicular joint, 1 superior and one 2 to 3 mm inferior in a diverging manner. One positional K wire was inserted to maintain rotation while inserting the screws (Fig. 3D, E). A depth gauge was used to measure screw size, and the proximal cortex was tapped for increased compression. A cannulated 4.0 partially threaded screw 2 to 3 mm larger than the measured size was first inserted over the inferior K wire and tightened for compression. Then, a 5.0 headless fully threaded cannulated screw was inserted over the superior K wire and tightened (Fig. 3F, G). All incisions were subsequently irrigated. Subcutaneous tissue was reapproximated using 4-0 Monocryl and skin was closed using 3-0 nylon horizontal mattress sutures. A sterile dressing was then applied and the patient was placed in an AO splint. The patient was seen in the clinic at the 2-week mark for radiographs, incision check, and suture removal. They are placed in a short-leg, non-weight-bearing cast at this time until 6 weeks postoperatively followed by partial weight-bearing to full-weight-bearing in a boot. The patient will be seen at 3, 6, and 12 months postoperatively. Three-month weight-bearing radiographs were obtained and are presented in Fig. 3H, I. EXPECTED OUTCOMES Percutaneous preparation of the TN joint can decrease operative time and allow for smaller incisions to be utilized for TN fusion. The use of the Shannon burr helps to protect the surrounding soft tissue and neurovasculature. This technique can potentially reduce healing time while still allowing safe and meticulous joint preparation and fusion under fluoroscopic guidance. COMPLICATIONS As described in our cadaveric study, potential complications associated with a percutaneous approach to the talonavicular joint may include damage to surrounding structures.5 The TA tendon and saphenous vein were each contacted once without damage and the EHL tendon was contacted 3 times without damage while performing the approach in 9 cadavers, highlighting the relative safety of the approach. However, the superficial and deep peroneal nerves (SPN and DPN) were each contacted and damaged one time. With these results in mind, careful blunt dissection at each portal site and gentle periosteal elevation at the joint can mitigate the risk of damage to adjacent structures. The risk of thermal damage to the skin and tissues can be mitigated by ensuring copious irrigation is utilized while preparing joint surfaces. If at any point there is concern for tendon or nerve injury, the procedure should be converted to an open procedure to appropriately identify and repair the structures as needed. Inadequate joint surface preparation is another possible consequence of the percutaneous approach. Using imaging software to analyze the percutaneously prepared surface area of the TN joint in cadavers, the distal talus and proximal navicular had 82.5% and 80.9% joint preparation, respectively, showing excellent total surface area of prepared joint surfaces.5 Inadequate visualization and poor joint preparation can predispose patients to nonunion. To assist in preparing the joint, a pin distractor can be used to improve access to the joint once it has been loosened. Adequate irrigation is required to remove loose pieces of cartilage that might impede joint fusion. Ensuring proper depth under fluoroscopy is pertinent so as to not invade into the calcaneus or cuboid bones. If the surgeon is not confident in the extent or quality of joint preparation using this minimally invasive technique, the incisions should be expanded to allow full TN joint visualization. In this patient’s case, only the TN joint was prepared with the Shannon burr due to the surgeon’s comfort and previous surgical experience. In conclusion, percutaneous TN fusion is a promising technique that can be used in an isolated TN fusion or in combination with other foot and ankle procedures. The procedure can maintain the soft tissue envelope and possibly preserve the vascularity, potentially increasing the chances of union and reducing operative time.