Abstract
Chronic Achilles tendon ruptures represent a surgical challenge, with multiple repair techniques described in the literature. These approaches are selected according to the extent of the defect, and procedures for larger defects are often associated with greater morbidity and technical complexity. The use of scar tissue interposition has been reported as a reconstructive option in chronic lesions. Building on this concept, we describe a technique that combines scar tissue interposition with reinforcement using flexor hallucis longus tendon transfer. This approach provides a moderately complex procedure that avoids the morbidity of more extensive reconstructions while restoring tendon continuity. The technique was performed in a patient with chronic Achilles rupture, achieving restoration of gait and functional recovery during follow-up. This method represents a feasible alternative for selected cases, expanding the surgical options available for chronic Achilles tendon reconstruction.
Introduction
Chronic Achilles tendon ruptures constitute one of the most complex challenges in orthopedic surgery because, when diagnosis is delayed, retracted and degenerated ends arise that prevent a tension-free primary repair.
Traditionally, the reconstruction of these lesions has been approached using autologous or allograft techniques, or another techniques like VY-type flap or lower edge flap, that implies big and bloody wounds, with the resulting donor-site morbidity and associated complications.
However, recent studies have shown that the scar tissue naturally interposed between the tendon stumps possesses a favorable histological composition characterized by the presence of fibroblasts and densely organized collagen fibers that confer properties similar to those of an intact tendon. Thus, a direct repair that takes advantage of this regenerative tissue has shown promising clinical and functional results in chronic Achilles tendon rupture reconstructions, as reported by Yasuda and colleagues in previous studies. ,
Understanding that, over time, this tissue can evolve into functional tendon material, it is important to consider the viability of direct repair by harnessing this regenerative tissue—achieving satisfactory functional outcomes and reducing the need for autologous grafts, more invasive techniques, or their reinforcement. It should be noted that the application of these techniques is not limited exclusively to the Achilles tendon. For example, Kim et al. (2021) reported reconstruction of a chronic extensor hallucis longus tendon rupture using interposed scar tissue, broadening the spectrum of this strategy’s application in repairing chronic tendinous lesions at different locations.
Similarly, innovations in the FHL “long harvest” technique, described by Bibbo (2022), have enabled obtaining sufficient tendon length to address extensive Achilles defects, ensuring adhesion to the muscle belly and restoration of plantar flexion function.
The flexor hallucis longus (FHL) tendon transfer has emerged as a dynamic and effective option in reconstructing large Achilles tendon defects. , Recent literature—including the series by Xu et al. and reports by Ozer et al. (2018)—has demonstrated significant improvements in functional scales (such as the AOFAS and ATRS), along with a low incidence of complications and high patient satisfaction, supporting the utility of this technique in chronic lesions with large defects.
Because this is a medical case report, the present document summarizes clearly and simply the results obtained from clinical examination, imaging studies, and other complementary tests, which have allowed us to justify our therapeutic choice for a chronic Achilles tendon rupture. Our strategy is based on exploiting the scar tissue that naturally forms between the damaged tendon ends—observed to assume, over time, functions similar to those of a healthy tendon. In addition, we used a transfer of the flexor hallucis longus tendon, a technique that helps recover foot movement and strength while avoiding more invasive procedures. Together, these measures aim to effectively restore Achilles tendon function, offering a safe alternative grounded in recent evidence and studies that have shown positive results in patients with similar chronic ruptures.
Case report
We present the case of a 57-year-old woman who experienced indirect trauma while walking, resulting in abrupt pain and gait limitation in her right lower limb. She was initially evaluated in the emergency department, where the injury was overlooked. With persistent symptoms at >12 weeks, she attended outpatient consultation.
On examination, she exhibited an altered gait with compromised plantar flexion of the affected limb, a palpable gap at the ankle, a positive Thompson test for Achilles tendon injury, and a positive Matles test. MRI of the ankle revealed a defect smaller than 5 cm ( Fig. 1 ), leading to the decision to reconstruct the chronic rupture via a modified flexor hallucis longus (FHL) transfer, following evidence-based guidelines , and using a single approach similar to that proposed by Abubeih et al.
Ankle MRI demonstrated an Achilles tendon defect measuring <5 cm.
This approach allowed direct assessment of the interposed tissue between the tendon stumps and FHL transfer with an interference screw, as described by Decarbo et al. Postoperatively, we implemented a modified functional rehabilitation protocol based on Willits et al. and detailed by Costa et al.
The protocol included an anterior splint in plantar flexion for three weeks. Upon completion, it was exchanged for a Walker boot with a 40 mm heel lift, reduced by 10 mm each week until a 10 mm heel raise remained. During this period, crutches were weaned progressively until week 6, after which physical therapy began.
Weekly outpatient follow-up assessed the surgical wound and reinforced postoperative instructions. On day 8, the wound was re-evaluated while the splint remained in place ( Fig. 2 ). At week 3, sutures and the anterior splint were removed, and weight-bearing in the Walker boot commenced ( Fig. 3 ). By week 6, scar healing, Matles and Thompson tests, and unassisted ambulation in the Walker boot were all satisfactory ( Fig. 4 ).
Evaluation with the splint followed by removal showed an adequate wound status and a negative Matles test.
“ Re -evaluation of the surgical wound was performed; sutures were removed, and the patient began ambulation with a walker boot.
Six weeks after surgery, the wound had completely healed, and clinical examination revealed a negative Matles test, consistent with preserved Achilles tendon function.
Surgical technique
Under general anesthesia and in the prone position, a thigh tourniquet was applied to avoid gastrocnemius-soleus complex fixation, which could hinder distal retraction of the proximal stump. After standard antiseptic preparation, a posterior longitudinal incision was made from lateral to medial. The paratenon was incised, tenolysis performed, and the Achilles tendon inspected, revealing interposed scar tissue that generated plantar flexion on the Thompson maneuver but with reduced power.
Fibrotic tissue was debrided while preserving proximal and distal fibrous flaps. After incising the deep fascia of the leg and retracting the posterior tibial neurovascular bundle, the FHL muscle belly and tendon were identified and isolated.
The FHL tendon was transected, and a medial calcaneal wall slot was created as distally as possible. A tendinous whipstitch was placed in the distal segment of the proximal FHL stump( Fig. 5 ). A tunnel was drilled through the posterior tuberosity of the calcaneus exiting plantarly, through which the FHL tendon was positioned. An interference screw was inserted to complete the FHL transfer as described by DeCarbo. ( Figs. 6 A , B ).
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