Given the risks and patient concerns associated with K-wire fixation, these authors discuss the use of emerging hammertoe implants, absorbable pins and cannulated screws, and share a couple of illuminating case studies.

Hammertoe correction is one of the most frequently performed procedures for foot and ankle surgeons. Hammertoe digital deformity is characterized by an extension deformity at the metatarsophalangeal joint (MPJ) and a flexion deformity at the proximal interphalangeal joint.1,2

Digital deformity typically is associated with pain in the forefoot, difficulty fitting shoes and an unacceptable cosmetic appearance for the affected patients.2,3 Forefoot pain is typically attributed to hyperkeratotic skin lesions, callosities or ulcerations about the MPJ, the proximal interphalangeal joint and distal interphalangeal joints as well as nail deformities secondary to the curling of the digits.4 Loss of purchase of the digit overloads the MPJ as well as the surrounding digits, ultimately changing the gait pattern. This often advances other forefoot etiologies.

Treatment options are often guided by the patient’s discomfort as well as the reducibility of the affected digit. Conservative management of a fixed hammertoe includes shoe gear modification with a high and wide toe box, toe sleeves, a foam cushioning device, orthotics or offloading pads such as a metatarsal bar. However, if conservative management fails to alleviate symptoms, then surgical correction is warranted.

Surgical approaches for hammertoe correction are based on the surgeon’s preferred approach. We prefer the transverse elliptical incision over the proximal interphalangeal joint. One would perform a DuVries condylectomy on the head of the proximal phalanx. Using a rongeur, remove the cartilage of the base of the middle phalanx. Following this, the surgeon would implant the hardware under standard protocol.

K-Wires: A Fading Gold Standard For Hammertoe Repair?

K-wires have been the gold standard for hammertoe digital repair. Kirschner originally introduced K-wires to orthopedics in 1909, utilizing surgical grade stainless steel for the fixation of fractures. Taylor was the first surgeon to introduce K-wires for fixation of hammertoe repairs in 1940.5 Today, the most commonly used sizes for K-wire fixation in the foot and ankle are 0.9 mm (0.035 inch) to 1.6 mm (0.062 inch). The introduction of K-wire fixation for hammertoe correction was initially popular to help prevent flail toe, which is the most common complication secondary to excessive bone resection.1

Although K-wires are simplistic to use as fixation, they carry inherent risks such as pin tract infections, migration and breakage.3 Zingas and colleagues noted a 2.5 percent failure rate when they utilized 1.1 mm (0.045 inch) K-wire for fixation of the lesser digit hammertoe deformity.6 Reese and co-workers reported a rate of pin tract infections of as much as 18 percent in digital arthrodesis procedures with K-wire fixation.7 In a study by Caterini and colleagues, the average incidence of nonunion following proximal interphalangeal joint arthrodesis and fixation via intramedullary K-wire was about 20 percent.8

The biggest concerns our patients have about externally protruding K-wires are the anxiety with the removal of the K-wire in the office as well as accidental “trauma” within their home.

In recent years, there has been a move away from the percutaneous K-wire to other forms of fixation for digital correction in foot surgery. This has been spearheaded by the desire of the surgeon and patient alike to avoid the risks and pain of percutaneous fixation, and offer long-term internal stabilization of the corrected deformity. Today, there are at least five different implants commonly utilized by the foot and ankle surgeon. The implants that we will discuss include the Smart Toe (Stryker), StayFuse (Tornier) and Pro-Toe (Wright Medical Technologies). We’ll also discuss the use of absorbable pins such as Trim-It pins (Arthrex) and cannulated screws.

A Closer Look At Three Emerging Implants

The Smart Toe implant is a memory-based nitinol implant that compresses across the proximal interphalageal joint as it warms to the body’s temperature level. As a one-piece implant, there are no interconnecting parts, which allows for easy insertion.9 The newest generation comes in both a neutral and 10 degree plantarflexed implant, allowing for further correction of the digital deformity. The biggest drawback to this implant is the fact that it is a thermally reactive implant. As compression occurs, there is very little flexibility to change the position of the implant/digit if the surgeon does not approve of the initial correction.

The StayFuse implant is a two-piece interlocking titanium intramedullary implant the surgeon would use in the proximal interphalangeal joint. Both the proximal and distal aspect of the implant resemble a screw with threaded heads. The implant then snaps together giving the device its final construct. An advantage to this implant is that there is no violation of the distal interphalangeal joint and no exposed hardware, which decreases the risk of infection.10 We have noticed some complications in our practice if the device is not completely engaged at its interlocking mechanism, which has led to recurrence.

Pro-Toe is one of the newest implants released to the market. This implant has similar advantages and disadvantages to the Smart Toe and StayFuse. As a completely buried implant, the risk of digital infection is low. The proximal aspect of this device screws into the proximal phalanx. The surgeon broaches the middle phalanx and then impacts it onto the serrated distal flange, maintaining correction. This implant comes in both angulated (10 degrees) and non-angulated implants. The angle gives the surgeon the ability to position the digit in both a mechanically and cosmetically appropriate position during the procedure.

In our practice, we have had very successful outcomes utilizing this implant. The biggest advantage we have noticed so far is the absence of exposed hardware leading to decreased anxiety. We have also noted very little chronic swelling of the surgical digit.

How Effective Are Absorbable Pins?

Absorbable pins became a popular alternative to the traditional K-wire for the fixation of digital contractures. This is because this device’s functions are identical to the K-wire in its mechanical role. One can either cut and bury the absorbable pin within the proximal and middle phalanx, or drive the pin the entire length of the digit. Despite its mechanical strength, there is a flaw in the breaking point of this device. There was a common failure point of breakage as surgeons initially inserted the pin and drove it distally. Other possible flaws include production of sinus tracts with the potential for secondary bacterial infection within the digit.9

Konkel and colleagues found that complete bone union occurred in 38 of the 48 toes (73 percent).11 The authors noted no wound infection or toe swelling at final follow-up when using absorbable pin fixation.

Pertinent Pearls On Using Cannulated Screws For Fixation

Recently, surgeons have used small cannulated screws for fixation. Although this surgical procedure sacrifices the distal interphalangeal joint to treat the proximal interphalangeal joint, it significantly reduces the risks of residual toe angulation, mallet toe deformity and nonunion of the proximal interphalangeal joint. Cannulated screws also reduce postoperative shoe restrictions.

Disadvantages of this technique are the risks of having to perform a second operation related to persistent pain at the tip of the toe caused by the head of the screw as well as breakage.8 Another disadvantage is the lack of bone purchase in larger proximal phalanges. This may cause pistoning of the screw and/or backing out of the implant, which increases the amount of swelling present in the digit as well as an increase in the risk of infection.

We have also found that screw length can pose a significant problem. In a few cases, we have noted screw threads in either the distal interphalangeal joint or proximal interphalangeal joint distracting the joint. When this occurs, we leave the guide wire in place and drive the screw into the proximal aspect of the phalanx. Note that one should not drive these wires across the MPJ as there is a high risk of breakage due to the small diameter of the wire.

Case Study One: Percutaneous K-Wire Salvage In A Case Of Osteoporotic Bone

A healthy 56-year-old female underwent hammertoe correction of the second, third and fourth toes with MPJ release and capsular tendon balancing. Preoperatively, the surgeon and patient discussed fixation options and due to the patient’s desire to avoid percutaneous fixation, they selected an intramedullary option.

The surgeon used a transverse elliptical incision over the proximal interphalangeal joint of the second, third and fourth toes, and performed a condylectomy of the proximal phalanx. The bone was osteoporotic and quite soft in nature. The surgeon prepared the middle phalanx portion of the proximal interphalangeal joint and used a broach to prep the medullary canal.

The surgeon first inserted the intramedullary implant (in this case the Pro-Toe) into the proximal phalanx and then impacted the fin into the middle phalanx. Despite the rather poor bone quality, the medullary device captured well in the second and fourth toes. The middle phalanx on the third toe, however, would not retain the serrated fin in an acceptable fashion.

At this point, the options included “upsizing” the internal device (if available), converting to a cannulated screw from the tip of the toe or going to a percutaneous K-wire. The surgeon chose to utilize the K-wire because it would not sacrifice the distal interphalangeal joint like a screw would.

Unfortunately, at that time, an upsize of the medullary implant was not available. Though the patient was initially disappointed to have the percutaneous fixation, she understood the rationale and all three toes healed uneventfully.

Case Study Two: When There Is Post-Op Drift Of The Second Toe At The Proximal Interphalangeal Joint

A 46-year-old female previously had hammertoe correction via a condylectomy of the second proximal interphalangeal joint with percutaneous K-wire fixation. The initial procedure and postoperative course were unremarkable. Protected weightbearing occurred until K-wire removal at six weeks postoperatively. Gradually over a three-month period, the patient noted a drift of the second toe at the proximal interphalangeal joint laterally toward the third toe. The surgeon attempted conservative care but this ultimately failed to realign the toe.

Typically, pseudofibrosis at the arthroplasy site maintains stabilization of the toe following K-wire removal but this was not the case for this patient. In this case, with mobilization of the fibrosis, the toe destabilized at the proximal interphalangeal joint and a valgus deformity occurred. Surgical options included a repeat K-wire stabilization, a trans-distal interphalangeal/proximal interphalangeal screw or an intramedullary device. In this case, use of the Pro-Toe salvaged and stabilized the proximal interphalangeal joint deformity.

In Conclusion

As technology drives the world of foot and ankle surgery, there will be many more devices developed for the correction of digital deformity. Each of the aforementioned devices has its own pros and cons. However, the most important aspect in hammertoe correction is selecting the appropriate implant for each individual patient. Different implant usage will also vary according to the comfort level of the surgeon. As we proceed forward in practice, the role of K-wire fixation has decreased due to the obvious apparent risks these wires carry. However, K-wires do and always will have an appropriate place in the foot and ankle surgeon’s armamentarium for digital correction.

When we consider the evolution occurring with hammertoe correction and surgical implants, it is important to be comfortable with multiple devices and techniques. As with any surgical procedure, one must tailor implant selection to each patient’s specific individual anatomic constraints. Simply said, there may not be one hammertoe implant or fixation that covers every patient.

Dr. Hyer is a board-certified foot and ankle surgeon in Columbus, Ohio. He and his colleagues founded FootSourceMD.com to provide patients across the country with convenient access to reliable resources and products recommended by physicians. Dr. Hyer also contributes to medical education and research through frequent presentations and publications. He also serves on the editorial boards of the Journal of Foot and Ankle Surgery, and Foot and Ankle Specialist.

Dr. Scott is an Associate of the American College of Foot and Ankle Surgeons. He completed a comprehensive one-year advanced foot and ankle fellowship at The Orthopedic Foot and Ankle Center in Westerville, Ohio.

References

1. Coughlin MJ. Operative repair of the mallet toe deformity. Foot Ankle Int. 1995; 16(3):109-116.

2. Harmonson J, Harkless L. Operative procedures for the correction of hammertoe, claw toe, and mallet toe. Clin Podiatric Med Surg. 1996; 13(2):211-220.

3. Coughlin MJ, Mann RA, Saltzman CL. Surgery of the Foot and Ankle, Eighth Edition. Mosby, Philadelphia, 2007, pp. 389–390.

4. Alvine FG, Garvin KL. Peg and dowel fusion of the proximal interphalangeal joint. Foot Ankle. 1980; 1(2):90–94.

5. Taylor RG. An operative procedure for the treatment of hammertoe and claw-toe. J Bone Joint Surg. 1940; 22:607-609.

6. Zingas C, Katcherian DA, Wu KK. Kirschner wire breakage after surgery of the lesser toes. Foot Ankle Int. 1995; 16(8):504-509.

7. Reese AT, Stone NH, Young AB. Toe fusion using Kirschner wire: A study of the postoperative infection rate and related problems. JR Coll Surg Edinb. 1987; 32:158–163.

8. Caterini R, Farsetti P, Tarantino U, Potenza V, Ippolito E. Arthrodesis of the toe joints with an intramedullary cannulated screw for correction of hammertoe deformity. Foot Ankle Int. 2004; 25(4):256–261.

9. Roukis TS. A 1-piece shape-metal Nitinol intramedullary internal fixation device for arthrodesis of the proximal interphalangeal joint in neuropathic patients with Diabetes. Foot Ankle Spec. 2009; 2(3):130–134.

10. Ellington JK, Anderson RB, Davis WH, Cohen BE, Jones CP. Radiographic analysis of proximal interphalangeal joint arthrodesis with an intramedullary fusion device for lesser toe deformities. Foot Ankle Int. 2010; 31(5):372–376.

11. Konkel KF, Menger AG, Retzlaff SA. Hammer toe correction using an absorbable intramedullary pin. Foot Ankle Int. 2007; 28(8):916–920.

For further reading, see “Minimizing The Risk Of Failed Hammertoe Surgery” in the December 2010 issue of Podiatry Today.