One of the most painful injuries one can endure is an achilles tendon rupture. Achilles tendon injuries can be difficult to manage, especially when the tendon is severely damaged or ruptured for an extended period. When direct repair is not possible due to poor tissue quality or a large defect, a neighoring tendon called the flexor hallucis longus (FHL) tendon transfer surgery offers a strong, reliable reconstructive option. The FHL tendon, which normally flexes the big toe, is repurposed to reinforce or replace the Achilles tendon, restoring ankle strength, function, and mobility.
How Common It Is and Who Gets It?
Chronic Achilles tendon ruptures are relatively uncommon, accounting for approximately 10–25% of all Achilles tendon injuries. They often develop when an acute rupture is missed or inadequately treated. The condition is most prevalent in middle aged or older adults, especially men aged 40 to 60, who experience a sudden increase in activity or return to sports after a period of inactivity. Individuals with metabolic conditions such as diabetes, obesity, or chronic corticosteroid use are also at greater risk of tendon degeneration and delayed healing. Flexor hallucis longus tendon transfer is typically used in these chronic or neglected cases, representing about 5–10% of surgical Achilles tendon reconstructions.
Why It Happens – Causes
Chronic Achilles tendon rupture occurs when the tendon fibers degenerate or fail to heal properly after an initial injury. Over time, scar tissue replaces normal tendon fibers, leading to weakness and elongation. The tendon retracts, creating a large gap that cannot be bridged by direct repair. Repetitive microtrauma, delayed treatment, or systemic illnesses further compromise tendon strength.
How the Body Part Normally Works?
The Achilles tendon connects the calf muscles (gastrocnemius and soleus) to the heel bone (calcaneus), enabling plantarflexion (moving ankle down) the motion required for walking, running, and jumping. The FHL muscle lies deep in the posterior leg and originates from the fibula, running behind the ankle and along the underside of the foot to insert into the distal phalanx of the big toe. The FHL tendon aids in toe flexion and ankle stabilization. Because of its strength, length, and close proximity to the Achilles, it can be safely transferred to reconstruct the ruptured tendon.
What You Might Feel – Symptoms
Patients with chronic Achilles rupture often report:
- Weakness or inability to push off when walking.
- Difficulty climbing stairs or standing on tiptoe.
- Swelling, tenderness, or a palpable gap above the heel.
- Altered gait or limping.
If untreated, chronic cases lead to muscle atrophy, poor movement, and pain in other joints.
How Doctors Find the Problem?
Diagnosis combines clinical evaluation with imaging:
- Physical exam: Reveals weakness, indentation in the Achilles region, and a positive Thompson test (absence of plantarflexion when squeezing the calf).
- Ultrasound: Identifies tendon discontinuity and scar tissue.
- MRI: Defines the extent of the rupture, degree of tendon retraction, and tissue quality.
- X-rays: May show calcification or bone spurs near the tendon insertion.
Imaging helps determine whether direct repair or tendon transfer is appropriate.
Recovery and What to Expect After Treatment
After surgery, the ankle is immobilized in a downward position using a cast or boot for 4–6 weeks. Weight-bearing is avoided during this period. Physical therapy begins around 6–8 weeks, progressing to strengthening and balance exercises. Most patients resume normal walking within 3 months and return to higher-impact activities within 6–12 months.
Possible Risks or Side Effects
- Infection or delayed wound healing.
- Weakness in big toe flexion (usually mild and without functional impact).
- Scar tenderness or stiffness.
- Rarely, re-rupture or tendon elongation.
- Deep vein thrombosis or nerve irritation.
Long-Term Outlook
FHL tendon transfer provides excellent long-term outcomes, with significant improvements in pain, strength, and mobility. Studies show average AOFAS ankle-hindfoot scores above 90, indicating high function and satisfaction. Most patients experience minimal loss of toe strength and can return to normal daily activities or recreational sports.
Out-of-Pocket Costs
Medicare
CPT Code 27691 – Flexor Hallucis Longus (FHL) Tendon Transfer: $175.25
Medicare Part B typically covers 80% of the approved cost for this procedure once your annual deductible has been met, leaving you responsible for the remaining 20%. Supplemental Insurance plans such as Medigap, AARP, or Blue Cross Blue Shield generally cover that remaining 20%, minimizing or eliminating out-of-pocket expenses for Medicare-approved procedures. These plans coordinate with Medicare to fill the coverage gap and reduce the patient’s financial responsibility.
If you have Secondary Insurance such as TRICARE, an Employer-Based Plan, or Veterans Health Administration coverage, it acts as a secondary payer. These plans usually cover any remaining balance, including coinsurance or small deductibles, which typically range between $100 and $300 depending on your plan and provider network.
Workers’ Compensation
If your FHL tendon transfer is required due to a work-related injury, Workers’ Compensation will cover all related medical expenses, including surgery, postoperative care, and rehabilitation. You will not have any out-of-pocket expenses, as the employer’s insurance carrier directly covers all approved costs.
No-Fault Insurance
If your FHL tendon injury or surgery is related to an automobile accident, No-Fault Insurance will typically cover the full cost of your treatment, including surgery and recovery. The only potential out-of-pocket expense may be a small deductible or co-payment, depending on your insurance policy.
Example
Michael Johnson underwent an FHL tendon transfer (CPT 27691) to restore strength and stability in his ankle after a chronic injury. His estimated Medicare out-of-pocket cost was $175.25. Since Michael had supplemental coverage through AARP Medigap, his remaining balance was fully covered, leaving him with no out-of-pocket expenses for the surgery.
Frequently Asked Questions (FAQ)
Q. How long does it take to recover from FHL Tendon Transfer surgery?
A. Recovery involves avoiding weight-bearing for several weeks, followed by gradual rehabilitation. Most patients regain full function within several months, though full recovery may take up to a year.
Q. Can I walk immediately after FHL Tendon Transfer surgery?
A. No, you will need to rest the foot and avoid putting weight on it for several weeks. After that, gradual weight-bearing and physical therapy will help restore function.
Q. Is physical therapy necessary after FHL Tendon Transfer?
A. Yes, physical therapy is essential to help restore strength, flexibility, and proper mobility to the foot and ankle after surgery.
Q. Who is a good candidate for FHL Tendon Transfer?
A. This procedure is ideal for patients with chronic Achilles tendon ruptures who have not had successful outcomes with other treatments, particularly when the tendon is too damaged to repair using traditional methods.
Q. What is the long-term outcome of FHL Tendon Transfer?
A. Most patients experience significant improvements in function, with many able to return to normal activities. However, the long-term success depends on the patient’s adherence to rehabilitation and recovery protocols.
Q. Will I need to wear a boot or cast after surgery?
A. Yes, you will likely need to wear a walking boot or cast for several weeks to protect the foot and allow the tendon to heal properly.
Summary and Takeaway
Flexor Hallucis Longus tendon transfer is a highly effective surgical solution for chronic Achilles tendon ruptures when direct repair is not feasible. It restores plantarflexion strength, enables normal gait, and provides long-term durability. With proper rehabilitation and follow-up, most patients regain near-normal function with minimal complications.
For me, FHL tendon transfer is only to be used when the Achilles tendon is too damaged or weak to heal well on its own. Instead of trying to repair bad tissue, the goal is to reinforce it with a stronger tendon nearby so the ankle can become stable and functional again. This is usually for more severe or long standing Achilles problems.
My surgical philosophy is to keep the repair strong and reliable while protecting as much normal function as possible. After surgery, healing and rehab are very important because strength and balance take time to come back. The goal is to help patients walk more normally again with less pain and better push off strength.
Clinical Insight & Recent Findings
A recent open-access study by Meter et al. (2022) describes an advanced technique for treating chronic or revision Achilles tendon ruptures, particularly when there is a large tendon gap or poor tissue quality. The authors combined flexor hallucis longus (FHL) tendon transfer with a posterior tibial tendon (PTT) allograft to reconstruct an 8.5 cm Achilles tendon defect.
This dual-tendon approach provided a stable repair while maintaining natural foot mechanics. The FHL tendon was anchored through the heel bone using an Endobutton system, while the PTT allograft bridged the remaining gap between the proximal and distal Achilles stumps. Postoperative care included non-weightbearing for four weeks followed by gradual rehabilitation. The technique’s main advantage lies in preserving native anatomy and improving tendon strength in complex revision cases.
According to the authors, this method offers surgeons a reliable reconstructive option that reduces the risk of re-rupture and restores functional mobility. (“Study on combining FHL tendon transfer with posterior tibial tendon graft for Achilles tendon repair – see PubMed.“)
Activity and Lifestyle Modifications
After surgery, start with low-impact activities like cycling and swimming before resuming running or jumping. Maintain flexibility and strength in the calf and ankle to prevent re-injury.
