A flexor tenotomy is a soft tissue release that is indicated only in flexible toe deformities [12]. It is rarely performed as an isolated procedure in the adult except in patients with diabetes and peripheral neuropathy that have flexible toe deformities with or without ulceration. However, it has been supported after a PIPJ arthrodesis has been performed and a subsequent flexible DIPJ contracture occurs [13]. Nevertheless, it has been advocated in children or the elderly where larger surgical procedures cannot be performed [11, 14–16]. In a case study by Ross et al., he performed a flexor tenotomy on 188 curly or hammertoes in 62 pediatric patients with a 95% success rate. He concluded that in pediatric patients with solely a flexion contracture as the cause of the hammertoe, a flexor tenotomy is an effective procedure [14].

Moreover, a systematic review from Scott et al. in the Journal of Foot and Ankle Research in 2016 examined the effectiveness of percutaneous flexor tenotomies for the management and prevention of recurrence in diabetic toe ulcers. The only documented literature was case series designs with a total of 250 flexor tenotomies performed in 163 patients. They found good healing rates at 92–100% with recurrence rates ranging from 0 to 18% at 2 months follow-up. The authors concluded that better level of evidence is needed to confirm if a flexor tenotomy is a reliable procedure to prevent and/or heal distal toe ulcerations with flexible soft tissue contractures. The current evidence does show low recurrence rates and postoperative complications with reasonably high healing rates [16].

A flexor tenotomy is performed through a small medial, lateral, or plantar percutaneous or open digital incision; the flexor digitorum longus (FDL) tendon is released at the DIPJ or the PIPJ depending on the location of the contracture [17]. Some surgeons advocate transecting the flexor digitorum brevis (FDB) tendon as well [18]. The release of the flexor tendon contracture allows the toe to assume a more neutral position decreasing pressure at the distal aspect of the toe [16] (Fig. 7.2).

As with other foot and ankle surgeries, absolute contraindications include acute or chronic infection and vascular compromise. Relative contraindications for a flexor tenotomy include the nondiabetic adult patient and rigid deformities without ancillary procedures being performed [11].

Also, there is a loading phenomenon created when a tenotomy is performed which causes the load to transfer to a neighboring tendon which can cause increased pressure to adjacent digits. This is because the four long flexors and extensors to the lesser digits start from a shared muscle belly. Thus, when one tendon is transected, each of the residual tendons will have one-third greater power. To decrease the loading phenomenon, perform a tendon lengthening or tenotomy on the remaining digits to prevent transfer lesions [11].

A flexor to extensor tendon transfer is rarely performed as an isolated procedure but rather an adjunct to a broader flexible hammertoe correction. This includes sequential releases beginning with the dorsal skin incision, then an extensor tenotomy or lengthening, dorsal capsulotomy, and collateral ligament release. If additional stabilization and correction are required, then a flexor to extensor transfer could be added to achieve further plantarflexory influence at the MPJ. Conversely, a flexor to extensor tendon transfer could be added to a rigid deformity after a PIPJ arthroplasty/arthrodesis with or without a shortening metatarsal osteotomy to help stabilize the MPJ [19]. The transfer of the FDL to the extensor tendons theoretically changes the FDL into an intrinsic muscle which causes dorsiflexion of the DIPJ/PIPJ with plantarflexion at the MPJ [6]. Transfer of the FDL and FDB tendons into the dorsal expansion of the extensor tendons was first described by Girdlestone in 1947 [20]. Taylor, in 1951, also performed the same surgery in 68 patients. He reported 86% of the patients had good results [21]. There are many different techniques reported for the flexor to extensor tendon transfer, but the author prefers a technique recently described by Easley. They perform the operation with two separate plantar transverse incisions and one dorsal longitudinal incision. The more proximal plantar incision is placed along the proximal skin crease and the more distal plantar incision at the DIPJ. The FDL tendon is identified in between the slips of the FDB tendon and held under traction with a hemostat. Through the second more distal incision, the FDL tendon is released from its insertion into the distal phalanx. Next, the FDL tendon is dissected out of the more proximal incision and split longitudinally into two slips. A central longitudinal dorsal incision over the PIPJ is created. The incision is normally already extended over the MPJ as a release of the MPJ is usually previously been performed. A hemostat is passed from dorsal to plantar through the slips of the FDB tendon , and the corresponding slips of the FDL tendon are transferred dorsally to the proximal phalanx. The slips are then sutured over the proximal phalanx within the extensor tendons [19] (Fig. 7.3).

The most recent meta-analysis in 2012 examined 17 articles which included 515 FDL tendon transfers with a mean ± SD follow-up of 54.21 ± 20.64 months. The total overall patient satisfaction after FDL tendon transfer was 86.7% (95% confidence interval, 81.7%–90.5%) [22].

As with any foot and ankle surgeries, absolute contraindications include acute or chronic infection and vascular compromise. Relative contraindications for a flexor to extensor tendon transfer consist of an FDL tendon transfer as the principal procedure of a rigid lesser toe deformity [6, 11].

PIPJ stiffness has reported to be the highest complication when performing a flexor to extensor tendon transfer with one study reporting up to 60% of the cases had residual stiffness [23]. Furthermore, stiffness in patients with flexible hammertoe deformities is one of the chief causes for complaints postoperatively [24]. It is imperative to discuss with patients preoperatively that the operated lesser toe will not curl postoperatively and will feel stiff, but the deformity should be resolved. Recurrence of the lesser toe deformity has been described as high as 20% [19]. Swelling and numbness can also occur but usually resolve over time [2].

Recurrence of the deformity is relatively low after flexor to extensor tendon transfer but can be due to many different factors including but not limited to failure of the transfer, preoperative stiffness not sufficiently assessed, neurologic conditions, undue dorsal soft tissue scarring, or insufficient tautness of the transfer [19]. To help prevent recurrence and/or a floating toe when performing the FDL transfer, the toe should be held down at 20° of plantarflexion at the MPJ and the ankle at 90°. Moreover, if the FDL transfer is being utilized for stabilization of the MPJ, then perform the transfer toward the base of the proximal phalanx to achieve additional plantarflexory control over the MPJ. Conversely, if the FDL transfer is being performed to better stabilize the PIPJ, then the FDL tendons should be sutured toward the head of the proximal phalanx to attain added plantarflexion of the PIPJ.

Loss of blood supply to the toe can occur due to traction of the neurovascular bundle or compression due to the transfer. Deflation of the tourniquet before closure can help assess blood flow to the toe and allow much easier dissection to confirm the neurovascular bundle is not compressed if this is required. Other measures to help increase blood flow to a toe that may be compromised include applying warm gauze; removing , bending, or adjusting the K-wire; lowering the patient’s leg; dorsiflexing the toe at the MPJ; injecting lidocaine around the neurovascular bundle; applying of nitropaste and heat lamps; or simply waiting [7, 19].