A Closer Look At Surgical Correction Of Ankle Instability

Ankle instability can be due to ligamentous pathology, structural abnormalities and/or a lack of dynamic support in the ankle. This author addresses surgery for the unstable ankle, offering surgical pearls for primary repair, arthroscopic repair and secondary repair.

Out of the nearly 25,000 lateral ankle sprains that occur each day, almost 55 percent will go untreated.¹ When one renders treatment, the protocols are variable and at times of questionable efficacy. Of the three lateral collateral ligaments, the anterior talofibular ligament is the most commonly injured. This is an isolated injury in the good majority of reported lateral ankle sprains. Injuries range from a mere stretching of the ligament resulting in little to no disability or instability to a complete tear of one or more of the lateral collateral ligaments with significant disability and loss of stability.

Estimates on the incidence of chronic ankle instability range between 3 to 35 percent.² The main predisposing factor to chronic ankle instability is at least one sprain.³ Some have suggested that there is no correlation between the severity of sprain and the development of chronic ankle instability.⁴ The absence of treatment is likely a common pathway. However, even in those who are treated, instability may develop. In even the most ideal of situations, patients may experience both subjective and objective instability for up to one year.⁴ More accurate assessments place the period of vulnerability at about six weeks to three months. Surgery is indicated when patients continue to have disability and instability despite immobilization and dynamic/functional rehabilitation.

Key Considerations In Surgical Planning
A systematic and algorithmic workup of chronic ankle instability will result in satisfying and reproducible outcomes. Further, this will greatly minimize the likelihood of overlooking critical pieces of the puzzle and falling victim to common surgical pitfalls. One must understand that instability is a compound problem with not only ligamentous pathology but also potential dysfunction or failure of the dynamic support of the ankle as well as structural abnormalities.  

Common coexisting problems include peroneal tendon dysfunction, a cavus foot type, intraarticular pathology, syndesmotic instability, subtalar instability and suprapedal deformity.  

Peroneal tendon dysfunction. This involves weakness, pain and/or disability due to tears, dislocation syndrome or neuromuscular conditions. In neuromuscular situations, the posterior tibial tendon can often be a deforming force and one must address it as it could lead to failure of an otherwise well performed reconstruction.

Cavus foot type. These deformities can be flexible or rigid, intrinsic (actual joint malalignment or structural derangement) or extrinsic (peroneal longus overdrive). The deformity may be isolated to the forefoot, the hindfoot or be a combination of both.⁵ Failure to address associated deformity is one of the most common causes of a failed ankle instability surgery.

Intraarticular pathology. The avoidance of pain results in dysfunction. This includes post-traumatic synovitis or arthrofibrosis, osteochondral defects of the talus and/or tibia, exostoses and loose bodies.

Syndesmotic instability. Often overlooked, chronic syndesmotic instability is likely more common than one might appreciate. This can result in similar symptoms and have the same negative long-term effects as lateral collateral ligament instability.

Subtalar instability. Subtalar instability can be difficult to differentiate from lateral ankle instability. Diagnostic injections and stress examinations can be helpful. However, many stabilization procedures will secondarily stabilize the subtalar joint.

Suprapedal deformity. Although such conditions are rare, one should consider malunion or congenital deformities of the tibia and/or fibula, and surgically correct them if distal compensation is incomplete.

What Is The Role Of Arthroscopy In Ankle Instability Surgery?
Researchers estimate that one will find intra-articular pathology during arthroscopy in more than 90 percent of instability cases.^6,7 For this reason, one should incorporate arthroscopy into the surgical plan for most ankle stabilizations. Routine arthroscopic evaluation allows a complete assessment of the chrondral surface and the repair of any defects. The medial gutter and posterior ankle can be harbors of painful pathology, and one can address this without an accessory arthrotomy.

Debride post-traumatic synovitis and/or arthrofibrosis, and remove any loose bodies and/or exostoses. One should routinely evaluate the distal syndesmosis. A hook or Cotton test can uncover instability. However, the ability to place and rotate a 2 mm probe between the tibia and fibula is diagnostic of clinically significant instability and warrants surgical repair.

When incorporating arthroscopy into surgical ankle stabilization, there are some pearls to keep in mind.
• Mark out the fibula prior to joint insufflation.
• Avoid prolonged arthroscopy. Too much fluid insufflation will obscure and distort the anatomy and make dissection difficult.
• Utilize a posterior-lateral egress portal (18-gauge spinal needle) to limit fluid extravasation into the surrounding soft tissue.

Addressing Primary Repair Of Unstable Ankles
A full understanding of the degree of ligament pathology will ultimately determine which the surgeon chooses. The following are useful guidelines that should provide reproducible and satisfactory outcomes.
Exclusive anterior talofibular ligament pathology is the most common surgical situation. One can usually address this with a primary repair of the anterior talofibular ligament. The most common procedure is the Brostrom. The Gould modification allows a more robust and durable repair as well as stabilization of the subtalar joint.^8,9

The use of anchors is quite popular and a preference of the surgeon. However, anchors will be essential if there is a paucity of soft tissues on either the talar and/or fibular side of the construct. Augmentation with a secondary anchor (InternalBrace, Arthrex) may allow accelerated rehabilitation but should not be a substitute for poor technique in the primary repair. In addition, there is a nuance to use of this secondary anchor and with inexperienced hands, the use of this modality could potentially result in a repair that is too rigid.

Here are some surgical tips to keep in mind when performing primary repair of unstable ankles.
• During soft tissue dissection, avoid undermining over the anterior lateral ankle. It is unnecessary and increases the likelihood of a nerve entrapment, which is extremely difficult to resolve.
• In an arthroscopy, the anterior-lateral portal aids in arthrotomy placement.
• After making the arthrotomy, create a periosteal flap on the anterior border of the fibula.
• Decorticate the anterior border of the fibula to provide a bleeding cancellous surface for soft tissue adhesion. This will also aid in proper visualization if you are using anchors.
• Place anchors at 90 degrees to the proposed line of stress.
• Divide the inferior extensor retinaculum from the capsule/anterior talofibular ligament after making the arthrotomy.
• Place the suture line in the same orientation with the anterior talofibular ligament.
• A “pants over vest” suture technique brings the capsular/anterior talofibular ligament flap against the decorticated fibula. Place the entire suture line before tying the knots. This will aid in visualization.
• Then bring the inferior extensor retinaculum up and secure it to the remaining periosteal flap.

One can also use a modified Brostrom-Gould procedure in the setting of combined anterior talofibular and calcaneofibular ligament pathology. It is possible to employ anchors or fibular drill holes to get a secure repair of the calcaneofibular ligament as the periosteum of the fibula can be thin in this area.

Here some slight modifications to the surgical approach to consider.
• An incision that goes midline along the lateral malleolus and curves anteriorly toward the midpoint of the sinus tarsi can be quite useful. It allows good visualization of the peroneal tendons as well as the anterior talofibular ligament and calcaneofibular ligament. It also goes in line with most of the cutaneous nerves.
• Carry the arthrotomy down to the distal tip of the fibula and retract the peroneal tendons to access the calcaneofibular ligament. Bear in mind that the peroneal tendons are right at the tip of the fibula and are easily damaged.

What You Should Know About Arthroscopic Primary Repair
Arthroscopic primary repair is gaining attention with advances in technology. The advantage can be a limited incisional approach, which is appealing. However, experience with traditional open repairs is a must before graduating to this approach. It requires sound arthroscopic skills and a good assistant. Early results suggest good outcomes with a minimum of complications.^10,11

Here are a few surgical pearls to enhance results with arthroscopic primary repair.
• Mark out the fibula and the presumed location of the inferior extensor retinaculum prior to joint insufflation, which will represent the proposed exit site for sutures and placement of the suture line.
• Beware the communicating branch between the sural and intermediate dorsal cutaneous nerves.
• One must clean out the lateral gutter arthroscopically in its entirety to avoid incarceration of useless tissue in the repair.
• Decorticate the anterior fibula as you would in an open repair.
• One can ensure proper anchor placement by placing the anchor guide pins in the proposed fibular sites and confirming it with fluoroscopy.

A Guide To Secondary Repair And Revision
The literature is clear that primary anterior talofibular ligament repairs are reliable and durable.^12-15 When a primary repair fails, it is absolutely essential to determine why. One should first consider the aforementioned coexisting pathologies. An unrecognized or undercorrected cavus is the most common cause for failure. In addition, collagen disorders such as Ehlers-Danlos syndrome are rare enough that physicians’ experience with them is limited. These cases require utilization of non-native tissue or material to replace the ligaments or they will fail.  

Utilize secondary repair primarily if there is a catastrophic failure of the native ligaments, which one can determine by stress radiographs (positive anterior drawer and inversion stress exams), magnetic resonance imaging (MRI) or intraoperatively. Some surgeons prefer this as their procedure of choice. However, failure can make revision challenging as what would have been the salvage procedure has already been utilized.

An “anatomic repair” as Coughlin described has gained wide appeal.¹⁶ Although this approach is still technically demanding, the use of Bio-Tenodesis Screws (Arthrex) provides reproducible and easier fixation than traditional bone tunnels. There are no studies to suggest if allograft or autograft is better, and their use is a matter of personal preference. The most common allografts are the peroneal longus or semitendinosus. A slip of the peroneal brevis is the most commonly used autograft based on its proximity and ease of retrieval. However, there is reasonable criticism that this is the primary dynamic stabilizer of the lateral ankle and that perhaps one should utilize the peroneal longus.

Here are a few surgical tips to consider with “anatomic repair.”
• The incisional approach should allow easy visualization of the talar neck/body intersection, fibula, peroneal tendons and calcaneal insertion of the calcaneofibular ligament.
• If one uses an allograft, pre-tensioning the graft can remove creep and unintended slack in the graft.
• The path of the graft should be in line with the anterior talofibular and calcaneofibular ligaments and the insertion points on the talus and calcaneus at the native insertion of the ligament.
• When passing the graft through the fibula, set the tension at the fibula with either a Bio-Tenodesis screw or sew the graft to the periosteum. This allows greater control of the overall tension of the repair.
• Avoid over-tensioning the repair. There should be a “physiologic” range of motion of the ankle and subtalar joint. Bio-Tenodesis screws allow one to make adjustments.  

How To Proceed When There Is Coexisting Pathology
Peroneal tendons. If there is a high-grade tear (more than 50 percent of the tendon diameter) of the peroneal longus or brevis, debridement and tenodesis are recommended.¹⁷ If planning an anatomic repair, one can utilize the debrided portion of the tendon as a graft. If subluxation repair requires a fibular osteotomy, take care with the additional use of anchors to avoid iatrogenic fracture. If the posterior tibial tendon is dominant, consider a posterior tendon transfer through the interosseous membrane. If the peroneal tendons are beyond repair, one can utilize a flexor hallucis longus transfer.18

Cavus foot type. The Coleman block test is invaluable to determine the apex of deformity. If there is a flexible plantarflexed first ray but a varus thrust in gait, one must repair this. If it is due to peroneal longus overdrive, employ a peroneal stop procedure. If the first ray deformity is structural, a first tarsal metatarsal fusion instead of a dorsiflexory wedge osteotomy may provide more predictable correction without the risk of second ray overload. Research has shown that a combination of a wedge and transposition calcaneal osteotomy provides the greatest correction.¹⁹ The incision placement for this osteotomy must be at least 2.5 cm from the incision for the ligament repair to avoid vascular compromise to the soft tissue.²⁰

In Conclusion
Surgical repair of lateral ankle instability requires a firm grasp of the biomechanics of the ankle and foot. A comprehensive and systematic evaluation of the patient will help avoid common pitfalls. There are no shortcuts and one must address all contributing pathology either at the time of the index surgery or first in a planned staged repair. An understanding of the advantages and intention of technology will guide prudent use, avoid over-reliance and maintain sound surgical technique. A rational and evidence-based rehabilitation protocol is crucial for durable, functional and reproducible outcomes.

Dr. Gentile is in private practice at Northwest Extremity Specialists in Portland, Ore. He is an attending surgeon/teacher for the Legacy/Kaiser Portland Hospital’s Podiatric Surgical Residency Program.

References

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