How To Master Talonavicular Fusions

   The talonavicular joint arthrodesis has been utilized for a variety of pathologies of the foot. Instability and subluxation of the rearfoot in adult acquired pes valgus is the most common reason for rearfoot fusion. Congenital deformities, neuromuscular diseases and arthritic conditions, whether they are from an inflammatory arthritis, osteoarthritis or posttraumatic causes, are less common pathologies that would require fusion of the talonavicular joint.1    In a rigid rearfoot deformity, such as a multiplanar deformity with heel valgus, forefoot abduction and/or forefoot varus, there is little substitute for a triple arthrodesis. However, when there is a flexible peritalar subluxation and one can manually reduce the deformity, there is the opinion that a single joint fusion of the talonavicular joint can stabilize the foot just as well as a triple arthrodesis.2 Compared to a triple arthrodesis, the talonavicular joint arthrodesis can ultimately reduce morbidity, time in the operating room and lower the incidence of complications. It may also provide some flexibility to the rearfoot.

Adult-Acquired Flatfoot: When Is A Talonavicular Fusion Appropriate?

   There are many different surgical approaches for the adult acquired flatfoot. One way is not necessarily better than another as long as one uses sound principles to evaluate and plan the reconstruction.    I analyze flatfoot and divide it into three regions. The first area includes the posterior musculature. Using the Silverskiold test as a guide, one should determine whether to perform a gastrocnemius recession or a tendo-Achilles lengthening. Surgeons should then proceed to address the hindfoot position. If it is rigid, consider either a fusion procedure or a calcaneal osteotomy. If it is flexible, then one can consider subtalar arthroeresis. One would rarely perform a subtalar arthroroesis without doing additional procedures to address the forefoot.    Finally, compare the position of the forefoot to the rearfoot. If there is varus and/or abduction, consider medial column procedures including fusions or osteotomies (i.e. cotton osteotomy). When both rearfoot and forefoot components are flexible, performing a talonavicular joint arthrodesis may be a good option. Certainly, many combinations may occur as all flatfoot deformities are different. Using a systematic approach to evaluate each segment, one can choose appropriate procedures with confidence.    When choosing the talonavicular joint fusion for a completely flexible flatfoot, one can often do it as a solo procedure. I choose not to perform a joint resection with a saw. I prefer to maintain the ball and socket anatomy of the fusion site, using a combination of osteotomes and bone curettes. One can use the curettes to scrape cartilage off the navicular “cup” and employ the osteotomes to chisel cartilage off the talar head. By doing this, one can “dial in” the exact position in the transverse plane (reducing abduction) and frontal plane (reducing forefoot varus). Resecting too much bone with a saw at the fusion site can make it difficult to get a good approximation of bone without a bone graft. Moreover, it is difficult to obtain multiplanar correction with flat surfaces from a saw cut. Ultimately, with more wedging and sculpting, increased bone loss leads to a more difficult approximation.

A Stepwise Approach To Surgical Technique

   Prior to surgery, scrub the lower extremity, prep and drape it in the usual sterile fashion. One can perform this procedure under a local with IV sedation without a tourniquet or opt for a general anesthetic with a thigh tourniquet according to your preference    If a posterior lengthening is necessary, surgeons should perform this prior to the fusion. One should map out the anatomic landmarks including the medial malleolus, tibialis anterior tendon and the navicular tuberosity.    Place the incision midway between the medial malleolus and the tibialis anterior tendon. Start the incision at the ankle joint and carry it distally to the naviculocuneiform joint. The critical part of the soft tissue dissection is handling the medial marginal vein, which one will always encounter. After making the skin incision, the superficial fascia will have small superficial veins, which can be bovied. The deeper layer of the subcutaneous tissue contains the medial marginal vein (great saphenous). Once you have isolated the medial marginal vein, clamp the tributaries running medial and lateral, and proceed to cut and hand-tie them. If possible, ligate the medial tributaries to allow for dorsal retraction of the vein. Once the vein is retracted, use a sponge to clear away any residual subcutaneous tissue.    Palpating with forceps, one can appreciate the bony landmarks, tibia, talus and the navicular tuberosity. Proceed to use a scalpel to open the talonavicular joint by making an incision in line with the skin incision. You will see that the capsule is loosely attached to the talar neck, but firmly attached to the navicular. One can easily obtain adequate exposure of the talonavicular joint by releasing the dorsal talonavicular ligaments and releasing the posterior tibial tendon/spring ligament tissues on the inferior aspect of the navicular tuberosity.    The easiest way to get good exposure dorsally is to take a freer or key elevator and pass it over the dorsal neck of the talus. In this area, the tissue is loosely attached. Prying the elevator upward will expose the tight attachment of the dorsal capsule and ligaments. Proceed to use a scalpel to hug the bone and dissect away tight dorsal tissues in order to allow for adequate exposure. The large dorsal flap of tissue will include the neurovascular structures, tendons, etc. Using your index finger, you should be able to palpate the entire talar neck and dorsal navicular bone. One can easily visualize the joint at this time and, if necessary, can release the dorsal talonavicular ligaments. If the exposure is inadequate, then one will struggle opening the joint.    Utilize a baby laminar spreader to open the joint. One may need to use a key elevator or freer elevator in order to allow the laminar spreader into the joint. Another method to help with opening the joint is to use a saw or osteotome to remove the cartilage cap off the talar head. This will provide room to allow the retractor to fit in the joint. However, surgeons should be careful not to take too much bone with this method. One can also utilize a joint distractor to open the joint.    Utilize manual instrumentation to remove cartilage, exposing the subchondral bone. Preserve the ball and socket fit to allow for ease of positioning the forefoot on the rearfoot. Fenestrate the subchondral bone with a 2.0-mm drill or a 0.062 K-wire. Leave the subchondral bone intact as this increases the strength of the fusion construct. One will notice a longer time to fusion when comparing fusion preparation leaving subchondral bone versus raw cancellous bone margins. However, I have not had any difficulty in achieving fusions by preserving the subchondral bone.    Obtain positioning by holding the calcaneus neutral to the leg with one hand. (This usually requires supination of the heel.) With the other hand, “dial in” the forefoot to reduce forefoot abduction and/or varus. Generally, the medial column is plantarflexed, which causes the navicular to plantarflex and the talus to dorsiflex. While an assistant holds the forefoot, proceed to obtain temporary fixation by inserting two 0.062 K-wires from the navicular into the talus, making sure to avoid the subtalar joint.    Under fluoroscopic imaging, inspect the fusion site. In critical evaluation, one should inspect the position of the talus on the navicular. The joint should be congruous on the AP view. The lateral view will enable you to evaluate temporary fixation and ensure the talus is in good position. Usually, with flatfoot surgery, one will see some dorsiflexion of the talus on the navicular.

Achieving Final Fixation And Closure

   One may typically achieve final fixation with partially threaded cancellous bone screws 4.0 mm or larger. These screws will replace the temporary fixation if one removes one wire at a time and inserts an appropriate screw in standard AO fashion. The typical screw length used is 40 mm. Surgeons may also use bone staples. However, I prefer using bone staples to augment screw fixation rather than using staple fixation alone.    Proceed to perform layer closure. A drain is rarely necessary. If using a tourniquet, deflate it after closing the capsule and deep fascia. One may ligate any bleeders prior to subcutaneous tissue closure. Proceed to apply a modified Jones compression dressing and posterior splint.

Pertinent Postoperative Considerations

   The post-op protocol includes non-weightbearing immobilization for six to eight weeks or until X-rays reveal consolidation at the fusion site. The first postoperative checkup is in one week. After removing the sutures/skin staples, have the patient wear a below knee cast that will remain on until he or she is ready to transition into a CAM walker. I do not change the cast unless I suspect a problem. After the patient achieves radiographic fusion, dispense a CAM walker for full weightbearing and prescribe aggressive rehabilitation by a physical therapist. The return to regular shoes is usually eight to 10 weeks after the procedure, depending on the patient’s swelling and pain tolerance.    Following surgery, complications with the talonavicular joint arthrodesis are similar to complications with any fusion surgery. These include nonunion, delayed union, malunion, infection and deep vein thrombosis secondary to cast immobilization. Despite a comprehensive preoperative consultation, patients are sometimes bothered by the feeling of a “stiff” foot and have trouble adjusting to it. One should also explain to patients that rehabilitation may take six months to a year, especially if they undergo a posterior muscle lengthening.    Patients will often have transient lateral column pain. This occurs shortly after they begin ambulating and it usually lasts for a month or two. Sometimes a cortisone injection is necessary but the pain is usually self-limiting.    Another major concern and possible long-term complication is neighboring joint arthrosis. Fortunately, the talonavicular joint arthrodesis preserves some motion in the hindfoot and, in that respect, may be more forgiving than a triple arthrodesis. Certainly the ankle joint is the most critical joint that one needs to preserve. A non-essential joint, such as the first metatarsocuneiform joint, is less of a concern. A fusion of the first metatarsocuneiform joint would not alter foot biomechanics as an ankle fusion would.

How To Avoid Common Surgical Pitfalls

   Remember that the inclusion criteria for a talonavicular joint arthrodesis is limited and it is important to sidestep common surgical mistakes. The most common mistake is trying to use this procedure for a semi-rigid or rigid hindfoot. The end result will be a fusion in an unacceptable position, which will lead to dysfunction and probable compensatory arthritic changes. In addition, not addressing ankle equinus will lead to failure. Remember, once one has realigned the hindfoot, the talus dorsiflexes and this can unmask equinus that may not have been that obvious on the physical exam. That is why clinicians should supinate the foot when assessing for equinus. Otherwise, what appears to be dorsiflexion of the ankle is actually pronation of the foot.    One should also evaluate other joints in the medial column for “faulting” or arthrosis. For example, if the patient has flexible peritalar subluxation and plantar insufficiency of the naviculocuneiform joint, then a talonavicular joint fusion alone may cause more breakdown at the naviculocuneiform joint. In another scenario, if there is arthrosis of the first metatarsocuneiform joint or naviculocuneiform joint, not addressing those problems will lead to failure of pain reduction. Therefore, one may need to include other fusions in the medial column.    Finally, there is no substitute for good joint preparation and rigid fixation. I prefer internal fixation unless the case involves a revision of a nonunion or for Charcot reconstruction. In such cases, I usually employ external fixation. When using internal fixation, using two screws is preferable over one screw or one screw with a bone staple. In the delayed unions or nonunions I have experienced, most involved using one screw (6.5 mm) or one screw (4.0 mm) and a compression staple.    In a triple arthrodesis, one screw fixation for the talonavicular joint is adequate because of the inherent stability of the other two joints being fused. However, in a single joint talonavicular fusion, there are rotary forces that cannot be shielded as in a triple arthrodesis. That torque is what can lead to fixation failure and/or nonunion in an inadequate fixation construct.    Nonunions are not common unless technical errors such as poor joint preparation and/or inadequate fixation occur. Certainly, other non-technical factors that may be causation for a nonunion can include smoking, non-compliance and/or certain systemic diseases.

In Conclusion

   The talonavicular arthrodesis has secured its place in flatfoot surgery with predictable results. For flexible peritalar subluxation, the talonavicular joint arthrodesis provides structural repositioning of the foot and adds stability necessary for walking. In vitro studies have shown that the talonavicular joint is the “key” joint in the triple joint hindfoot complex.3-5 A successful fusion of the talonavicular joint will reduce hindfoot motion to approximately 4 degrees of frontal plane motion as proven in an in vivo study by Fishco and Cornwall.6    In posterior tibial tendon dysfunction, in which there is a frank tendon rupture, or in late stages of intratendinous tearing, soft tissue augmentation with the flexor digitorum longus tendon may not hold up in the long run. Moreover, it is difficult to obtain structural correction with a tendon augmentation. Often, pain is resolved, but the flatfoot deformity is still present. The talonavicular joint arthrodesis may be a better choice in that population group. Certainly, one should avoid fusions of essential joints in the foot if possible. However, in the right patient, a well-positioned fusion can increase stability and improve function of the foot. Dr. Fishco is board-certified in foot surgery and reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. He is a teaching faculty member of the Phoenix Baptist Residency Program and is in private practice in Phoenix. He is also a faculty member of the Podiatry Institute.
 

References:

1. Chen C, Huang P, Chen T, et al: Isolated talonavicular arthrodesis for talonavicular arthritis. Foot & Ankle Intl 22 :633, 2001.
2. Mothershed RA, Stapp MD, Smith TF: Talonavicular arthrodesis for correction of posterior tibial tendon dysfunction. Clin Pod Med Surg 3, 1999.
3. Astion D, Deland JT, Otis JC, et al: Motion of the hindfoot after simulated arthrodesis. J Bone & Jt Surg 79A:241, 1997.
4. Gellman H, Lenihan M, Halikis N, et al: Selective tarsal arthrodesis: An in vitro analysis of the effect on foot motion. Foot & Ankle 8:127, 2087.
5. Wulker N, Stukenborg C, Savory KM, et al: Hindfoot motion after isolated and combined arthrodeses: measurements in anatomic specimens. Foot & Ankle Intl 21:921, 2000.
6. Fishco WD, Cornwall MW: Gait analysis after talonavicular joint fusion: 2 case reports. J Foot Ankle Surg 43(3), 241-7, 2004.