Introduction

Following the successful introduction of diagnostic and operative arthroscopy in the ankle, the techniques have been extended to the joints and tendons of the foot. In this chapter we describe these newer techniques, and their applications to conditions such as tarsal coalitions.

Subtalar Joint Arthroscopy

Diagnostic arthroscopy and arthroscopic surgery of the subtalar joint is a recent development, one of the earliest reports of subtalar arthroscopy was as recent as 1985. There are a number of reasons that this technique has not reached the same levels of popularity as arthroscopy of the ankle joint. The subtalar joint is a complex structure, into which it is relatively difficult to introduce an arthroscope. It is composed of a large posterior facet, which has close congruence. The posterior facet is separated from the middle and anterior facets by the sinus tarsi, which contains blood vessels, nerves, fat, and the talocalcaneal ligaments. Visualization and intervention can be challenging. On the other hand subtalar arthroscopy is a low-risk procedure and, with appropriate training, practice, and care, effective surgery can be undertaken¹.

Techniques

There are two main approaches to subtalar arthroscopy – posterior and sinus tarsi.

Posterior Arthroscopy

The posterior approaches to the subtalar joint are similar to the posterior approach to the ankle joint. The only difference is that the portals can be placed lower using the tip of the distal fibula as the reference level. Fluoroscopy can be helpful.

Sinus Tarsi Approach

Portals

The standard incisions are known as the anterolateral and the accessory anterolateral “sinus tarsi” portals. The anterolateral portal is situated immediately above the calcaneum at the angle of Gissane, beneath the lateral process of the talus, approximately 1 cm distal and 2 cm anterior to the tip of the fibula. The accessory anterolateral portal is positioned approximately 1.5 cm more distal, and 0.5 cm more dorsal. Each portal is checked before incision, by using a hypodermic needle to ensure the sinus tarsi is entered. Radiology can be used if in doubt. It is important to recognize that there is the potential for damage to both branches of the sural nerve and the lateral branch of the superficial peroneal nerve. Therefore the skin is incised with a knife and then round-ended scissors are used to separate the deep tissues until the sinus tarsi is entered. The separation is undertaken in the long axis of the foot. The scissors can then be rotated 90° and opened to spread the portals. Accessory portals can be established more posteriorly. These accessory posterior portals include the posterolateral portal from posterior ankle arthroscopy, and an accessory posterolateral portal, just posterior to the peroneal tendons. The accessory posterolateral portal does have a higher risk of damage to the sural nerve (Figure 13.1).

Figure 13.1 Portals for access to the subtalar joint. AL: anterolateral; AAL: accessory anterolateral; PL: posterolateral; APL: antero-posterolateral.

Standard Arthroscopic Tour

The arthroscope is inserted into the anterolateral portal and instruments into the accessory anterolateral portal. Initially the view may be obscured by the fat of the sinus tarsi. A 3.5 mm soft tissue resector is used to excise the fat adjacent to the arthroscope. Care is taken to leave the talocalcaneal ligaments undamaged. The initial area prepared is the anterior margin of the posterior facet of the subtalar joint, this is then extended into the lateral gutter, between the joint and the peroneal tendons. Swapping portals assists in visualization of the lateral gutter. Thus the anterolateral edge of the posterior facet is identified, and the foot gently moved to show the subtalar movement. Any osteophytes can then be removed using a small burr. A blunt periosteal elevator is then inserted into the joint, to open it for inspection. If chondral or osteochondral injuries are identified, the accessory posterolateral portal may be necessary to distract the joint, to allow debridement.

The tour then proceeds distally; any excess fat, synovitis, inflammatory tissue, or scarring is identified and removed. It is usually possible to bypass the talocalcaneal ligaments, leaving them intact to identify the middle facet, but they are removed for arthrodesis. The arthroscope is returned to the anterolateral portal and the resector to the accessory anterolateral portal allowing inspection of the anterior process of the calcaneum, the bifurcate ligament, the spring ligament, and the anterior facet of the subtalar joint. The head of the talus can be followed into the talonavicular joint, although soft tissue will need to be resected to clearly visualize the joint. It is possible to track along the anterior process of the calcaneum to identify the calcaneocuboid joint, and the quadrilateral point between the calcaneum, cuboid, navicular, and talus. This allows identification and treatment of osteophytes, loose bodies, un-united fractures, coalitions, and soft tissue pathologies (Figure 13.2).

Figure 13.2 Tour of the subtalar joint. PT: peroneal tendons; T: talus; C: calcaneus

Postoperatively, the wounds are closed with sutures or glue and adhesive tape. A wool and crepe compression bandage is applied for 48 hours. It is important to avoid hematoma and therefore intraoperative diathermy is used and postoperative elevation of the foot emphasized. The patient is advised to mobilize the foot and ankle, weight bearing as pain permits, in the ten days following surgery, and is then referred for progressive mobilization, guided by a physiotherapist.

Tarsal Coalitions

Tarsal coalitions may present in adolescence or adulthood. The history is of increasing, activity-related pain, stiffness, and recurrent instability. Tarsal coalitions are defined as either complete or incomplete. Complete tarsal coalitions have continuity of bony bridging, whereas a mixture of fibrous and cartilaginous tissue fills incomplete coalitions. The two most common tarsal coalitions are the calcaneonavicular and talocalcaneal. Both of these coalitions are amenable to arthroscopic resection.

Examination usually identifies a restriction of subtalar movement. Careful investigation is mandatory, with a full set of x-rays and either MRI or CT scanning. CT scanning, including 3D reconstruction, is particularly useful in defining talocalcaneal coalitions².

Resection of coalitions is usually considered when the symptoms are not improved with orthoses and rest in a cast. Extensive degenerative changes or a large talocalcaneal coalition are better treated by a subtalar or a triple arthrodesis. Preoperative valgus deformity will not improve following resection of the coalition, and may have to be separately addressed by calcaneal osteotomy, or even an arthroereisis implant.

Calcaneonavicular Coalition

A calcaneonavicular coalition bridges the gap from the anterior process of the calcaneum, across the quadrilateral point, to the lateral side of the navicular. It may be complete or incomplete. The coalition replaces the calcaneonavicular band of the bifurcate ligament. The rigidity of the coalition stiffens the movement of the hindfoot joint complex.

Resection can be undertaken arthroscopically³, through two sinus tarsi portals. The patient is positioned as for a subtalar arthroscopy. An anterolateral portal is established. A second accessory anterolateral portal is made slightly distal to the standard portal, over the calcaneonavicular coalition. The excision is performed with a 3.5 mm shaver and barrel burr. Adequacy of removal is assessed by direct vision (Figure 13.3) and by fluoroscopy. The excision must be wide and complete, and allow the restoration of hindfoot movement. This will help prevent re-calcification and recurrent formation of the coalition. The patient is mobilized early post-surgery.

Figure 13.3 Calcaneonavicular coalition: initial view (a) and at partial resection (b).

Good results from arthroscopic resection of calcaneonavicular coalitions have been reported, with few complications^4–5. The reported complications include hematoma formation, scar pain, infection, and damage to the branches of the sural or superficial peroneal nerves. Despite not using interposition grafting with fat or muscle, recurrent calcification or bony bridging is rare if the excision is adequate. Pain and stiffness can occur if there is established degenerative change in the talonavicular or subtalar joints, which has not been identified preoperatively.

Talocalcaneal Coalitions

Talocalcaneal coalitions once again may be complete or incomplete. Preoperative imaging is essential to determine the position, type, and extent of the coalition. Different shapes and extents of coalition can be identified on CT scanning, particularly with 3D reconstructions. The coalitions usually involve the middle facet, and may extend to a greater or lesser degree into the posterior facet. One particular type involves only the posterior medial aspect of the posterior facet and can require both sinus tarsi and posterior approaches for arthroscopic excision.

Smaller talocalcaneal coalitions, which are predominantly restricted to the middle facet with only limited extension into the posterior facet, are amenable to removal through a sinus tarsi approach (Figure 13.4). The positioning and portals are as for subtalar arthroscopy. Image intensification may be of assistance in guiding resection. The first step is to identify the limits of the coalition. Its extent into the posterior facet is noted, but also its extent into the anterior facet. Resections are undertaken using a combination of a 3.5 mm soft tissue resector and a 3.5 mm barrel burr. Care is required in the resection at the proximal end of the posterior facet, particularly where the FHL tendon is visualized, as this is in close proximity to the neurovascular bundle. Following adequate excision of the coalition, increased movements of the subtalar joint should be observed. The talocalcaneal ligaments can be released to enhance movement and correct deformity.

Figure 13.4 Talocalcaneal coalition – during resection.

When the coalition extends to the posteromedial aspect of the posterior facet, but is still sufficiently small to be resected, a combination of approaches can be used. The patient is positioned 45° prone, which permits both the sinus tarsi approach and the posterior approach to remove a peripheral coalition while preserving the joint surface and medial soft tissues. Wounds are closed in the standard manner.

General complications are similar to those listed for calcalaneonavicular resections. In addition, overaggressive resection into the soft tissues medial to the posterior facet can result in damage to the posterior tibial nerve. Poor selection of too extensive a tarsal coalition produces a large raw area of bony surface at the end of the procedure, which may lead to reformation of the coalition, or even the formation of a painful pseudarthrosis.

Studies have shown arthroscopic resection of talocalcaneal coalitions to be a feasible and effective technique⁶.

Posterior Subtalar Arthroscopy

Posterior subtalar arthroscopy can be used for excision of posteromedial talocalcaneal coalitions, which are a rare variant. The posterior approach can also be used to harvest the FHL for transfer in the salvage of late diagnosed tendo Achillis rupture in patients with poor quality soft tissues, or significant medical comorbidities. The patient is placed prone and the standard posteromedial and posterolateral portals are used.

Arthroscopic Subtalar Arthrodesis

In circumstances where the subtalar or transverse tarsal joints are degenerative and non-operative management of the pain has failed, the operation of choice is arthrodesis. Subtalar and hindfoot arthrodeses are also the mainstay of treatment for fixed deformity or deformity with degeneration.

Improvements in the internal fixation techniques used to stabilize the arthrodesis have resulted in improvements in the rates of union. Nevertheless there can be problems with the quality of the soft tissue envelope. This can be worsened by severe deformity where correction of the foot shape can lead to postoperative tension in the soft tissues on the concave side of the deformity. The tension can lead to wound breakdown, which can be complicated by infection, painful scar formation, and nerve dysfunction.

As arthroscopic ankle arthrodesis became established as an effective surgical technique, with high union rates and reduced complications, it was inevitable that subtalar arthroscopy would be considered and utilized for subtalar arthrodesis. The indications for arthroscopic subtalar arthrodesis are in situ fusion, or where correction of the rotational or angulatory deformities can be corrected by soft tissue releases and decortication alone. It is not indicated if there is a requirement for major bony excision or if there is significant bone loss requiring structural bone grafting, for example in the elevation of the talus after depressed calcaneal fractures. Similarly, if there are large cavities, which require extensive bone grafting, an arthroscopic technique should not be used.

There are a number of published reports of case series reviewing in situ arthroscopic subtalar arthrodeses, performed through a posterior approach^7–9, with usually an accessory sinus tarsi portal. Fusion rates are reported as being high, over 90%, but series numbers are low. We prefer the sinus tarsi approach for subtalar arthrodesis¹⁰. Using this approach, not only the posterior facet but the middle and anterior facets can be prepared, allowing a full decortication of the joint and therefore a greater correction of any rotary or angulatory deformity.

The patient is positioned as for subtalar arthroscopy, in the 45° semi-lateral, supine position. The standard sinus tarsi portals are created. The contents of the sinus tarsi, including the ligaments, can be removed for clear visualization and mobilization of the joint. A 4.5 mm soft tissue resector can be utilized for this purpose. Decortication is usually undertaken with a 4.5 mm barrel burr, starting at the anterior aspect of the posterior facet, and proceeding from the lateral side, posteriorly and medially. Once the medial side of the facet is reached, the decortication is completed from posterior to anterior, along the medial edge, with careful attention being made to identify the flexor hallucis longus tendon, which is an important landmark for the adjacent posterior neurovascular bundle. During decortication, prominent osteophytes and other pathologies, such as lateral process non-unions, may require removal. Similarly, tarsal coalitions may need to be removed from the middle facet, or from the medial side of the posterior facet. Once decortication of the posterior facet is complete, the middle and anterior facets are also decorticated. Care must be taken to avoid entering the talonavicular joint. Decortication allows considerable mobility, which allows the correction of deformity.

Apposition of the raw surfaces can be checked arthroscopically, and with fluoroscopy (Figure 13.5). Fixation is usually undertaken with one or two 6.5 mm cannulated titanium screws, inserted from the calcaneal tuberosity into the body and neck of the talus under radiological control. It is important to visually assess the alignment of the limb after the insertion of the cannulated guide wires to ensure correct heel alignment and rotation of the foot. Screws should have a short enough thread to allow compression.

Figure 13.5 The subtalar joint prepared (a) for introduction of screws (b).

Postoperatively the lower leg is immobilized in a backslab. The patient is advised to elevate the limb for the majority of the time for the first two weeks, to reduce swelling and the risk of a hematoma. At two weeks a below-knee cast is applied. Weight bearing is then permitted with the use of crutches. It is reasonable to utilize a removable boot, which can be removed to allow non-weightbearing active mobilization of the remaining joints. At 12 weeks following surgery, providing the patient can fully bear weight, with no pain on stressing the joint and x-rays showing no joint line lucency, the boot may be progressively discarded and rehabilitation continued.