Flexor Hallucis Longus Tendon Transfer for Achilles Reconstruction

35 Flexor Hallucis Longus Tendon Transfer for Achilles Reconstruction

Milap S. Patel, Mauricio P. Barbosa, and Anish R. Kadakia

Abstract

The use of tendon transfer to treat deficiency of a pathologic motor unit is a fundamental skill for the practicing orthopaedic surgeon. New concepts with regard to autograft/allograft reconstruction have been noted; however, the ability of a traditional tendon transfer to restore function is proven and effective. For reconstruction of the Achilles tendon, whether for chronic tendinosis or rupture, the transfer of the flexor hallucis longus to the calcaneus is a proven, effective, and reliable method to restore a patient’s ability to ambulate without significant difficulty or pain. Modern fixation techniques allow for a single posterior incision approach with decreased morbidity to the midfoot, with minimal functional loss of hallux plantar flexion strength for an overwhelming majority of patients. The use of the flexor hallucis longus is an excellent option for Achilles reconstruction, with good functional outcomes noted after 1 year. In the high-level athlete, however, consideration for graft reconstruction or use of the peroneal tendons may be considered to avoid the morbidity of the loss of hallux strength.

Keywords: flexor hallucis longus, Achilles tendinosis, Achilles reconstruction, tendon transfer

35.1 Indications and Pathology

• Flexor hallucis longus (FHL) transfer is indicated to reconstruct the Achilles tendon in its entirety, or augment an insufficient Achilles tendon.

• On rare occasions, FHL transfer can be utilized in the setting of an acute Achilles tendon rupture where primary repair is not possible. This is most common in the setting of an insertional rupture given that most noninsertional ruptures are amenable to nonoperative or operative repair.

• Chronic Achilles tendon ruptures are associated with contracture of the triceps surae with difficulty to obtain a direct repair in most settings. FHL tendon transfer is utilized to augment a reconstruction (V-Y, turndown, allograft) that both improves power and provides a new vascular bed.

• If reconstruction is not possible in chronic Achilles tendon rupture, then an FHL transfer in isolation can be performed with the understanding that a 20 to 30% functional loss of power will occur.¹

• Advanced insertional and noninsertional Achilles tendinosis that requires operative debridement of greater than 50% of the viable tendon may benefit from FHL augmentation.

35.1.1 Clinical Evaluation

• Clinical evaluation of Achilles pathology has been previously described in detail in chapters 32 to 34.

• Chronic Achilles tendon rupture results in insufficient plantar flexion power that significantly affects the ability to navigate inclines and stairs in addition to athletic activity. The greatest difficulty in activities of daily living may occur with descending stairs giving the inability of the Achilles to generate sufficient power to control the descent.

• Plantar flexion is present, but weak due to compensatory involvement from posterior tibial tendon (PTT), FHL, flexor digitorum longus (FDL), peroneus longus, and peroneus brevis (PB).

• Clinical evaluation for an intact and adequately strong FHL tendon is essential before choosing this tendon for a transfer. This is performed by evaluating interphalangeal flexion strength of the hallux with the ankle in flexion and extension. Palpation behind the ankle for tenderness is important to exclude an FHL tear or entrapment within the fibro-osseous tunnel.

35.1.2 Radiographic Evaluation

• A lateral weight-bearing radiograph of the ankle is important when evaluating Achilles tendon pathology.

Radiographs of the ankle may demonstrate avulsion of the Achilles tendon insertion.

Significant calcific tendinosis of the midsubstance or insertion of the tendon should alert the surgeon to the possible need for an FHL transfer.

In most cases, the radiograph will be nondiagnostic given the soft-tissue nature of Achilles tendon disorders.

• Magnetic resonance imaging (MRI) or ultrasound can provide added diagnostic value and localize level of the tear in the acute setting; however, this is not routinely required.

This can be used if there is concern about FHL tendon pathology or integrity.

In chronic/neglected Achilles rupture, MRI will provide further information regarding degree of gastrocnemius and soleus muscle fatty infiltration.

If a significant, greater than 50%, fatty infiltration is noted, isolated reconstruction of the Achilles without augmentation will be unlikely to achieve a satisfactory clinical outcome without an additional tendon transfer.

• In the setting of tendinosis, MRI is useful in analyzing the quality of the tendon. An FHL tendon transfer is beneficial where more than 50% of the Achilles is abnormal, given that this is predictive of the amount of tendon resection that will be required.

35.1.3 Nonoperative Options

• Nonoperative treatment options regarding the various Achilles pathology are explained in detail in Chapters 32 to 34.

35.1.4 Contraindications

• Athletic patients who rely on unaffected hallux motion such as ballerinas, soccer, or volleyball players may benefit from peroneal tendon augmentation instead of FHL transfer.²

• Four percent of patients will complain of constant balance loss and this should be discussed prior to surgery.³

35.2 Goals of Surgical Procedure

• Restore plantar flexion power to the affected lower extremity to enable functional ambulation.

• Improve plantar flexion power in the setting of a reconstruction of the Achilles tendon (V-Y, turndown, allograft) to enable high-impact activity.

35.3 Advantages of Surgical Procedure

• Strength.

The FHL is twice as strong as the FDL and is a stronger plantar flexor than the PB.

FHL is active during the same phase as triceps surae, which is helpful in maintaining normal ankle biomechanics.

• Anatomic location:

Proximity to the Achilles tendon making it convenient for harvesting and may be performed through a single incision.

• Vascular:

The large muscle belly may improve the overall environment for healing of the reconstructed Achilles tendon (V-Y, turndown, allograft).

• Viability:

FHL has a very low rate of intrinsic disease, making this a very reliable choice and resilient tendon transfer.

• Hypertrophy:

Clear data have demonstrated hypertrophy of the FHL muscle following tendon transfer, improving the overall function over time.⁴

35.4 Key Principles

• Prone position facilitates the harvest and transfer of the FHL; however, a supine approach with external rotation of the affected limb may also be performed if desired.

• Thorough understanding of the proximity of the tibial nerve immediately medial to the FHL is required to avoid iatrogenic injury.

35.5 Preoperative Planning and Patient Positioning

• Preoperative imaging to determine the relative amount of tendinosis or fatty atrophy (chronic rupture) should be performed to determine the likely need for an FHL transfer.

• Equipment:

Interference screw fixation is preferred for the single incision technique:

Appropriate reamers and interference screws should be available. A 6.5to 7.25-mm screw is commonly utilized.

Fluoroscopy:

Use of a large C-arm facilitates placement of the calcaneal bone tunnel and facilitates removal of any calcaneal spurs.

Fig. 35.1 Patient is positioned prone with a centrally placed incision. In cases of insertional disease, the incision must be carried distally in order to ensure removal of the insertional calcific spur.

• Positioning:

Patient lying prone with both feet just off the end of the surgical table facilitates the harvest and placement of the transfer.

If the patient cannot be placed prone, then the surgery can be performed supine with a beanbag or large bump used to externally rotate the affected leg. Placement of multiple blankets underneath the affected leg places the foot in a “figure 4” position, which improves the externally rotated position of the foot.

• This position may be preferred if a long harvest from the midfoot is chosen. However, given the modern fixation methods available, a long harvest is not required for most cases.

Regional anesthesia is preferred if possible.

Our preference is not to utilize a tourniquet in nearly all surgical cases. If a tourniquet is preferred, make sure to place a thigh tourniquet and have the tubing face posteriorly if placed while the patient is supine in order to prevent pressure-related skin problems. A calf tourniquet will limit full muscle mobilization and excursion and is therefore not advised.

Lower extremity is prepped and draped up to the knee.

35.6 Operative Technique

35.6.1 Surgical Approach

• Prone position:

A direct midline approach is made between the posterior tibial and peroneal artery angiosomes (Fig. 35.1).

• Supine:

A medially based incision is made 1 cm anterior to the posterior border of the Achilles tendon, with the dissection directed laterally.

35.6.2 Surgical Procedure: Posterior Ankle FHL Harvest

• Care should be taken to avoid creating large subcutaneous planes superficial to the crural fascia to minimize unnecessary soft-tissue trauma. The fascia is then incised allowing visualization of the Achilles tendon:

In the setting of tendinosis, adhesions may be present, obliterating the normal plane between the fascia and the Achilles tendon.