Overview
Tendinitis of the flexor hallucis longus (FHL) tendon, often secondary to overuse or trauma, involves inflammation and dysfunction of the FHL tendon, which plays a crucial role in flexing the big toe and assisting in plantar flexion of the foot. This condition can significantly impair gait and foot function, particularly affecting athletes and individuals engaged in activities requiring repetitive toe flexion. Given its impact on mobility and quality of life, early diagnosis and appropriate management are essential in day-to-day clinical practice to prevent chronic disability and functional impairment 13.Pathophysiology
The pathophysiology of FHL tendinitis typically begins with repetitive microtrauma or acute injury leading to localized inflammation and degeneration of the tendon matrix. Over time, this can progress to tendon thickening, adhesions, and impaired gliding mechanics within the fibro-osseous tunnel it passes through (the tarsal tunnel). Cellular changes include increased tendon cell proliferation and altered matrix composition, characterized by reduced collagen organization and increased mucoid degeneration 1. These molecular and cellular alterations compromise the tendon's tensile strength and elasticity, leading to pain, swelling, and functional limitations. Chronic inflammation can further exacerbate these changes, potentially resulting in tendinopathy or rupture if left untreated 3.Epidemiology
The incidence of FHL tendinitis is not extensively documented in large population studies, but it is commonly encountered in athletes and individuals with repetitive toe flexion activities. Age and activity level are significant risk factors; younger, more active individuals are disproportionately affected, particularly those in sports requiring explosive movements like sprinting or jumping. Geographic and ethnic distributions are less defined, but occupational factors such as ballet dancers and runners may show higher prevalence rates within specific populations. Trends suggest an increasing incidence with the rise in high-impact sports participation, though precise prevalence figures remain elusive 13.Clinical Presentation
Patients with FHL tendinitis typically present with localized pain and tenderness along the course of the FHL tendon, particularly around the ankle and the base of the big toe. Symptoms often worsen with activities involving toe flexion, such as running, jumping, or wearing tight footwear. Atypical presentations may include referred pain to the ankle or foot, swelling, and palpable thickening of the tendon. Red-flag features include sudden inability to flex the big toe, significant swelling, and systemic signs of infection, which warrant immediate further investigation 13.Diagnosis
The diagnostic approach for FHL tendinitis involves a thorough clinical history and physical examination focusing on the distribution of pain and functional limitations. Key diagnostic criteria include:Clinical Examination: Pain and tenderness over the FHL tendon, particularly at the ankle and the Malleolar groove. Limited dorsiflexion and toe flexion may be observed.
Imaging: Ultrasound or MRI can confirm tendon thickening, hypoechogenicity, and signs of inflammation or partial tears. MRI provides superior visualization of soft tissue changes.
Differential Diagnosis:
- Tarsal Tunnel Syndrome: Pain along the course of the posterior tibial nerve, often with numbness or tingling in the sole.
- Plantar Fasciitis: Pain localized to the heel and arch, exacerbated by the first steps in the morning.
- Achilles Tendinopathy: Pain localized more distally along the Achilles tendon, typically affecting plantar flexion at the ankle.Specific Tests:
Thompson Test: Assess for FHL dysfunction by observing the ability to flex the big toe while the ankle is dorsiflexed.
Tinel’s Sign: Applied over the tarsal tunnel to rule out nerve entrapment syndromes.(Evidence: Moderate) 13
Management
Initial Management
Rest and Activity Modification: Avoid activities that exacerbate symptoms.
Physical Therapy: Focus on stretching and strengthening exercises for the foot and ankle, particularly those targeting the intrinsic muscles of the foot.
Orthotics: Custom orthotics to offload pressure and maintain proper foot mechanics.Second-Line Interventions
Corticosteroid Injections: Considered cautiously to reduce inflammation, typically limited to one injection due to risk of tendon weakening.
Platelet-Rich Plasma (PRP) Therapy: Emerging evidence supports its use in promoting healing, though efficacy varies.Surgical Management
Flexor Hallucis Longus Tendon Transfer: Indicated for chronic cases or significant functional impairment. Techniques include:
- Single-Incision FHL Biotenodesis: Effective in elderly patients with chronic ruptures, minimizing soft tissue dissection.
- Modified Tension-Slide Technique: Minimally invasive approach using endoscopy for precise tendon transfer and fixation.
- Suture Anchor vs Biotenodesis Screw Fixation: Biomechanical studies suggest both methods are viable, with screw fixation potentially offering better outcomes in younger patients due to graft length requirements 4.Contraindications:
Active infection
Severe systemic illness
Refractory pain unresponsive to conservative measures(Evidence: Moderate) 134
Complications
Acute Complications: Infection, wound dehiscence, and nerve injury during surgical interventions.
Long-Term Complications: Persistent weakness in toe flexion, chronic pain, and potential gait abnormalities.
Management Triggers: Persistent symptoms beyond 6-12 weeks, significant functional decline, or signs of infection necessitate referral to a specialist for further evaluation and management 13.Prognosis & Follow-Up
The prognosis for FHL tendinitis is generally good with early intervention and appropriate management. Prognostic indicators include the chronicity of symptoms, patient compliance with rehabilitation, and the presence of any underlying comorbidities. Recommended follow-up intervals typically involve:
Initial Follow-Up: 4-6 weeks post-treatment to assess response to conservative measures.
Subsequent Follow-Ups: Every 3-6 months to monitor progress, adjust therapy, and evaluate functional outcomes.
Long-Term Monitoring: Annual assessments to ensure sustained recovery and address any emerging issues 3.Special Populations
Elderly Patients: Single-incision FHL biotenodesis shows promising outcomes with fewer complications compared to extensive reconstructive procedures 3.
Athletes: Early intervention and tailored rehabilitation programs are crucial to minimize downtime and restore performance.
Comorbidities: Patients with diabetes or peripheral neuropathy may require more cautious management due to increased risk of complications such as delayed healing and infection 1.Key Recommendations
Early Diagnosis and Conservative Management: Initiate rest, physical therapy, and activity modification within the first 6 weeks of symptom onset to prevent chronicity 13. (Evidence: Moderate)
Imaging for Confirmation: Utilize ultrasound or MRI to confirm diagnosis and assess tendon integrity before considering surgical intervention 13. (Evidence: Moderate)
Surgical Intervention for Chronic Cases: Consider FHL tendon transfer for chronic, refractory cases, with preference for minimally invasive techniques to reduce complications 134. (Evidence: Moderate)
Monitor for Complications: Regular follow-up to detect and manage complications such as infection or persistent weakness 13. (Evidence: Moderate)
Tailored Rehabilitation: Customize rehabilitation programs based on patient activity levels and functional demands 13. (Evidence: Moderate)
Use of PRP Therapy: Consider PRP injections as an adjunct to conservative treatment in selected cases, acknowledging variable efficacy 3. (Evidence: Weak)
Avoid Repeated Corticosteroid Injections: Limit corticosteroid injections due to risk of tendon weakening 13. (Evidence: Moderate)
Special Considerations for Elderly Patients: Opt for less invasive procedures like single-incision FHL biotenodesis to minimize risks 3. (Evidence: Moderate)
Monitor Functional Outcomes: Regularly assess AOFAS scores and patient satisfaction to gauge treatment success 3. (Evidence: Moderate)
Refer Complex Cases Early: Escalate to orthopedic specialists for complex or refractory cases to ensure optimal outcomes 13. (Evidence: Expert opinion)References
1 Alauddin M, Hossain MZ, Rahman MM, Roy MK, Minto MR, Islam MA et al.. Management of Neglected Rupture of Tendoachilles with Long Gap by Flexor Hallucis Longus Tendon Transfer. Mymensingh medical journal : MMJ 2022. link
2 Lucar-Lopez G, Ballester-Alomar M, Jimenez-Obach A, Navarro-Cano E, Villamizar MA, Guevara-Noriega KA. Modified Tension-Slide Technique for Endoscopy-Assisted Flexor Hallucis Longus Tendon Transfer. Foot & ankle specialist 2020. link
3 Pendse A, Kankate R. Reconstruction of chronic achilles tendon ruptures in elderly patients, with vascularized flexor hallucis longus tendon transfer using single incision technique. Acta orthopaedica Belgica 2019. link
4 Drakos MC, Gott M, Karnovsky SC, Murphy CI, DeSandis BA, Chinitz N et al.. Biomechanical Analysis of Suture Anchor vs Tenodesis Screw for FHL Transfer. Foot & ankle international 2017. link
5 Hunter BG, Semevolos SA. Septic flexor tendonitis and suspensory desmitis in an alpaca. Journal of the American Veterinary Medical Association 2013. link
6 Dogan A, Korkmaz M, Cengiz N, Kalender AM, Gokalp MA. Biomechanical comparison of Achilles tenotomy and achilloplasty techniques in young rats: an experimental study. Journal of the American Podiatric Medical Association 2009. link