What is a flexor hallucis longus (FHL) tendon transfer?
The flexor hallucis longus (FHL) tendon travels on the inner side of the ankle and foot. It is one of two tendons that flexes (bends) the big toe. A FHL tendon transfer is when this tendon is detached and repositioned onto the heel to strengthen or substitute a dysfunctional/ diseased Achilles tendon. The FHL tendon is a good substitute for the Achilles tendon as it is strong (eventually gaining up 75-80% Achilles tendon strength) and pulls in the same direction as the Achilles tendon. There is some loss of flexor power to the big toe but patients rarely notice a functional limitation from it.
When is this surgery considered?
A FHL tendon transfer is usually undertaken in the following scenarios:
If the Achilles tendon is torn, this is called an Achilles tendon rupture. If the injury is detected early, it can be treated using a boot or surgical repair. However, if the presentation following injury is delayed (more than 4 weeks), this is called a chronic Achilles tendon rupture. Boot therapy at this stage is unlikely to help and direct surgical repair may not be possible. In this scenario, an Achilles tendon reconstruction with FHL tendon transfer may be considered.
In some cases of severe Achilles tendinopathy (degeneration of tendon), a large section of the diseased tendon has to be excised to reduce pain. This weakens the Achilles tendon and may affect it's function. An FHL tendon transfer is used in this scenario to strengthen or replace the Achilles tendon.
How is the operation done?
You will be admitted on the day of operation. The operation takes about 1hour and is routinely done under a general anaesthetic. Occasionally a spinal anaesthetic may be considered. You will be able to go home the same day.
The operation is done through a single incision at the back of the ankle. The FHL tendon is identified and then detached at the back of the ankle. A tunnel is created in the heel bone and the FHL tendon is passed through this tunnel and secured in place using a non-metallic screw (see diagram below).
The wound is closed with a dissolvable stitch. Your ankle is protected in a plaster and you will be non-weight bearing on the operated leg for 2 weeks. At 2 weeks your stitch is trimmed and your ankle is secured in a boot with wedges for a further 4 weeks; at this stage, you will start weight-bearing on the operated leg. After 6 weeks, you will transition out of the boot and commence physiotherapy.
Diagram of FHL tendon transfer for Achilles disorders [Ref: www.arthrex.com/foot-ankle/fhl-tendon-transfer]
Aftercare and FAQs
It is important to keep the leg elevated as much as possible especially for the first 2 weeks. Your first clinic follow-up is usually 12 to 14 days after surgery.
Wound care – The plaster should be kept dry. At your first clinic appointment, wound inspection and suture removal would be undertaken.
Work - If you have a sedentary job you should be able to return to work within 2 weeks (if you can arrange safe transport). If your job is physical, you may need to stay off work until the boot is removed.
Recovery period – This procedure has a lengthy recovery and will take 12 to 18 months to achieve its maximum potential.
Driving - You will not be able to drive for 8 to10 weeks following surgery. However, if you drive an Automatic and it was your LEFT side that was operated on; then you may start short drives 2 weeks following surgery. It is advisable to check the terms of your car insurance to ensure your cover is valid, as some policies state that you must not drive for a specific time period after an operation.
Flying after surgery - It is generally recommended to wait at least six weeks to fly. It may be possible to fly on short-haul or domestic flights at an earlier time, but you should always check with your GP or surgeon. Always consult your doctor, your health insurance provider and the airline you are flying with before making your flight reservation.
What are the surgical risks?
Nerve damage — causing numbness and painful scar
Deep vein thrombosis (DVT) and pulmonary embolism (PE) – blood clots in the vein or lungs – to reduce this risk you would be prescribed heparin injections for a few weeks (unless contraindicated)
Rupture of the reconstruction
Prolonged swelling and stiffness
It is beyond the scope of this document to list rarer risks (less than one in a thousand) but I will be very happy to discuss any worries about specific concerns and also about any family history or your past health problems. If there is anything you do not understand or if you have any questions or concerns, please feel free to discuss them with me.
Research Articles on the Achilles tendon by Dev Mahadevan
Patient reported outcomes and satisfaction following single incision Flexor Hallucis Longus (FHL) augmentation for chronic Achilles tendon pathologies. Journal of Clinical Orthopaedics and Trauma 2021; 23: 101650
Current concepts review: Management of Achilles tendinopathy overview. Journal of Arthroscopy and Joint Surgery (JAJS). 2021 July; 8(3):216-221