The Foot and Ankle Online Journal 5 (5): 1
Rupture of the flexor hallucis longus (FHL) tendon is rare in the absence of trauma and associated systemic disease. Rupture of FHL is also rare in hallux valgus corrective surgery. We present a case of FHL rupture after Akin osteotomy for hallux interphalangeus, a brief literature review and treatment options. We assert the benefit of exploration and primary repair of the FHL, especially if the rupture is distal to the knot of Henry. The aim of repair is to regain proprioceptive input from the joint and facilitate Metatarsophalangeal (MTP) joint plantarflexion.
Key Words: Hallux valgus, bunion, flexor hallucis longus (FHL), hallux interphalangeus, FHL tear, FHL rupture, Akin osteotomy
Accepted: April, 2012
Published: May, 2012
Flexor hallucis longus (FHL) rupture is commonly associated with trauma and occasionally systemic disease. Those patients with systemic disease, such as diabetes, lupus, gout, psoriatic arthritis, Systemic lupus erythematosus (SLE), kidney disease and Reiter’s disease are susceptible due to weakness within the tendon structure. Trauma can be direct open injury causing laceration to the plantar aspect of the foot resulting in injury to the FHL tendon, or closed injury commonly associated with overuse in athletes and ballet dancers. Due to its contribution to maintenance of the longitudinal arch, damage may lead to pes planus.
Rupture can occur at one or 3 sites or zones .
• Zone 1; just proximal to the FHL insertion, distal to the sesamoids
• Zone 2: the area between the sesamoids and the knot of Henry.
• Zone 3; proximal to the knot of Henry.
Treatment options for disruption of the FHL include non-operative, primary open end-end repair, tenodesis to the FDL, tenodesis of the distal FHL to the remnant of FHB tendon, tendon transfer using a slip of the FDL tendon IPJ fusion.
An otherwise fit and well 45 year-old female patient was seen six weeks post bilateral Akin osteotomies (Fig. 1). There were no reported complications at surgery but at review, she was unable to plantar-flex the right big toe, noticeable as she was able on the contralateral side. She had no neurological deficit. Her surgeon had recommended interphalangeal joint (IPJ) fusion. She was unconvinced by this and sought second opinion.
Figure 1 Post-operative radiograph of bilateral Akin osteotomies.
She was seen at eight weeks post-operation in a dedicated foot and ankle clinic where an ultrasound of her right foot was carried out. It suggested an intact flexor hallucis brevis (FHB) tendon and revealed a torn FHL tendon. The tendon distally appeared to extend to the base of the proximal phalanx which suggested the site of the rupture to be the base of the proximal phalanx, i.e., in close proximity to the akin osteotomy. She was counselled regarding the treatment options, namely non-operative, IPJ fusion or exploration with a view to repair of the torn tendon.
One of her main concerns was her inability to grip the floor with her toe and therefore non-operative management or fusion of the IPJ were unacceptable to her. She opted for exploration and repair and gave informed consent.
She underwent exploration and repair of the FHL tendon with re-alignment of the sesamoid mechanism of the big toe ten weeks post Akin osteotomy. A longitudinal lazy “S” incision was made in the plantar aspect of the right big toe, centred over the metatarsophalangeal (MTP) joint. The ruptured distal and proximal ends of FHL tendon were identified (Fig. 2). The flexor hallucis brevis tendon was found to be intact. The proximal tendon had retracted to the level of mid metatarsal. Following soft tissue release, the two ends of the FHL tendon were approximated and primarily repaired. Tendon transfer was not required.
Figure 2 Intra-operative identification of FHL Tendon.
The big toe was placed in a plaster of Paris with the toe flexed at the MTP Joint to reduce tension and kept initially for 2 weeks when her plaster was removed for wound check. The plaster was then reapplied for a further 2 weeks.
The FHL originates at the distal 2/3 of the posterior fibula, interosseous membrane and adjacent intermuscular septum within the deep compartment. It is supplied by the tibial nerve from branches of the S1/S2/L5 roots. The tendon passes through the posterior aspect of the fibro-osseous tunnel and plantar midfoot, known as the knot of Henry. It inserts on the plantar surface of the base of the distal phalanx of the greater hallux, passing between the medial and lateral sesamoid bones at the metatarsophalangeal joint. It passes beneath the sustentaculum in an oblique manner prior to inserting on the base of the distal phalanx.
The FHL flexes the great toe. It has a synergistic action with flexor hallucis brevis in assisting with plantar flexion of the foot at the ankle. In addition, it contributes to the distribution of forces at the plantar side of the forefoot and maintains the longitudinal arch of the foot along with the plantar fascia .
A search of the literature was carried out on Embase and PUBMED using the search strings 1) “FHL rupture” “Flexor hallucis longus rupture”, “FHL tear” “flexor hallucis longus tear” and 2) “akin osteotomy” “hallux valgus” “bunion”. The two search strings were also combined to ascertain whether there was literature pertaining to the two conditions concurrently.
Although the search returned a number of case reports and series pertaining to FHL rupture [3-18], there was only one case of rupture associated with hallux valgus surgery  found in the literature. They reported this as likely partial iatrogenic laceration at the time of surgery. Their patient was treated with surgical debridement of the distal stump of the FHL from under the first MTP joint and tenodesis of the proximal stump to the flexor digitorum longus (FDL) tendon.
FHL and FDL have interconnections in the foot, so if it is cut proximal to knot of Henry (where the tendons cross), then the FDL has a mass action with FHL. This has implications for harvesting the FHL for tendon reconstruction; if harvested at this site it is safe to sacrifice. However, if the tendon is ruptured distal to Knot of Henry, then plantar flexion will be deficient and may be unacceptable to patients. This suggests repair of FHL should be attempted.
A high percentage of FHL ruptures are associated with nerve injuries (50% of patients had distal nerve lacerations), but our patient had an isolated FHL rupture. She also continued to have no plantar flexion at the IP joint which is in keeping with the experience of most authors who assert that primary repair of distal injuries are associated with minimal postoperative IP joint motion.
Following repair of FHL, patients may experience restricted IP joint motion, contracture of the IP joint due to a tight FHL tendon for which Coghlan & Clarke  suggest a Z-lengthening of the FHL to achieve acceptable results.
A literature search confirmed the rarity of rupture of the FHL in the absence of systemic disease. The paucity of case reports regarding iatrogenic rupture of the FHL tendon at the time of hallux valgus corrective surgery could be due to rarity of the event or reluctance to report.
The FHL is at risk during hallux valgus surgery and care should be taken to remember to protect it during Akin osteotomy. The authors postulate that iatrogenic rupture of the FHL is more common than the literature reflects, and paucity of papers is influenced by reluctance to report If the FHL is cut during Akin osteotomy, treatment options are either non-operative, fusion of IPJ or repair. The benefits of plantarflexion of the MTP joint and proprioception input from the joint must be weighed against the morbidity of exploratory surgery and the inherent risks it carries.
This case illustrates repair of a cut FHL to be a viable alternative to fusion for treating this complication. Repair can result in some success in regaining plantar flexion of the MTP joint validating its consideration. Patients should be counselled that flexion at the IPJ is unlikely to occur, even after the surgery.
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Address Correspondence to: Mr. Pinak S. Ray, Foot and Ankle Surgical Unit, Barnet General Hospital, Barnet, London, UK, EN5 3DJ
1, 2 Foot and Ankle Surgical Unit, Barnet General Hospital, Barnet, London, UK, EN5 3DJ
© The Foot and Ankle Online Journal, 2012