A New Approach For Correcting Hammertoe Deformities

The advantages of lesser proximal interphalangeal joint arthrodesis in hammertoe surgery are numerous and well known. Arthrodesis is indicated in patients who have compromised intrinsic muscle function and are lacking both digital and metatarsophalangeal joint stability. Indeed, digital arthrodesis has always been an excellent procedure to consider if you fear reoccurrence of the hammertoe deformity due to biomechanical factors. Through the years, surgeons have employed several methods and devices to facilitate fusion across the lesser proximal interphalangeal joints (PIPJ) for stable hammertoe correction. This has ranged from the end to end anastomosis to the popular peg-in-hole arthrodesis of the proximal and middle phalanx. Fixation has included K-wire fixation (both buried and external), Reese screws, 26-gauge wire and absorbable fixation. I’ve also found that the Stayfuse implant (Zimmer/Pioneer Surgical) provides an excellent and simple method for approaching PIPJ arthrodesis for hammertoe correction in replacement of K-wire fixation. How Does It Work? The StayFuse implant is a two component (male/female) threaded system made of titanium. The threaded proximal (female) portion is the larger of the two and is fit to the medullary canal of the proximal phalanx after resection of the distal portion. You would fit the distal threaded (male) portion to the medullary canal of the middle phalanx after you’ve resected the base. The distal component has an elongated fluted stem with a thread profile at the end for its patented snap connection to the proximal phalangeal portion. Furthermore, there is a unique “Hex-Lock” design at the junction of the two components that prevents rotation of the bones. The two components have an array of sizes and diameters that you can use, depending upon the size of the phalanges. The different sized components are also color-coded so they’re easy to identify. The remainder of the instruments include: a universal driver handle that accepts a wide array of piloting; driver bits which you’ll need during the drilling/insertion portion of the surgery; an optional transfer template that helps to ensure good alignment of the piloting holes across the fusion site; probes; and a power attachment bit for the option of using power equipment. Initial Step-By-Step Tips The surgical procedure using the StayFuse implant is really based on a simple three-step approach: pre-drill, insert and snap together. Prior to the procedure, you should use preoperative X-rays and the Zimmer/ Pioneer Surgical OR template to determine the correct size of the implant components. The actual procedure itself is similar to performing an arthroplasty procedure of the proximal interphalangeal joint. Dissect carefully through the soft tissue structures, transect the extensor digitorum longus tendon and reflect it both proximally and distally. This allows for easy exposure of the base of the middle phalanx and the head of the proximal phalanx. Using a saw, resect these two structures perpendicular to the long axis of the bones. This creates two parallel planes perpendicular to the central canal of the associated bones. Then drill the holes into the middle and distal phalanx with the correct size drills. At this point, you should reconfirm toe length and alignment before proceeding. Then take the corresponding “prox” and “mid” components of the implant (as they are actually labeled in the set) and carefully screw them into their corresponding phalanx. The “hex” or hexagonal base of each component of the StayFuse implant should be flush with the bone. Snap together the “male” and “female” portions of the implant in a parallel fashion with moderate pressure while holding the toe in reduced position. You should examine the apposition of the arthrodesis site and probe it if necessary to confirm good alignment and approximation. You can use fluoroscopy to confirm implant position and reduction of the arthrodesis site. Irrigation, soft tissue and skin closure are the same as in an arthroplasty procedure. Understanding The Real ‘Pearls’ Of The Technique As far as pearls go in using the device, I feel one of the most crucial factors on whether the surgery is going to be successful or not happens prior to the first incision. The OR templates are a necessary tool for selecting the correct sizes of the components. You must take into account how much bone is going to be resected off both the middle and proximal phalanx. You must also confirm the threads of the two component system will engage some cortical bone internally. If not, you will get a “pistoning” effect of the implant in the soft medullary bone. This is very similar to what you could see with an internally buried threaded K-wire technique. This pistoning will not set things up well for an arthrodesis. Obviously, you would want to resect as little off the base of the middle phalanx as possible as this bone is already short. You also do not want to disrupt an abundant amount of intrinsic tendon attachments. You also don’t need to perform an aggressive resection of the head of the proximal phalanx. Resection of the head can be at, or just proximal to, the surgical neck of the bone. You only need to resect enough bone in order to distract the middle and proximal phalanx. This will give you clearance for the two component system to “snap” parallel into each other, as well as fully reduce the deformity at this joint level. Excessive shortening of the toes is discouraged. When implanting the two components in bone, be aware that forceful manipulation is unnecessary. The soft medullary canal is very receptive to gentle drilling and implantation. I personally have not needed the power attachment bit and feel the risk is too high for a split bone cortex. I have found it very useful to slightly countersink the hex components on either side of the arthrodesis site. The male and female components will still engage and this does create some excellent bony apposition. It is highly recommended to insert the proximal (female) component first for obvious reasons. The “mid” or male portion is difficult to work around if you are still drilling and inserting the proximal portion at the joint. When You Are Snapping The Device Together The final step of snapping the device together is one of the most critical to the success of the procedure. I recommend using sterile gauze during this step to avoid slippage of your fingers on the toe. You should distract the middle phalanx gently in order to align the two components axially. If the two components are not in alignment, you not only risk a poor apposition, but damage to the implant itself. You also need to be very persistent when applying significant pressure to get the device to engage. Strive for bone-to-bone contact. You will encounter several “alarming” ratcheting noises when compressing the components but this is normal. When the process is complete, you’ll hear a more “pronounced” snap but this just indicates that the components have completely seated themselves. Sometimes, you’ll need to slightly rotate the phalanges in order to obtain the full engagement of the “prox” and “mid” implant components. As your familiarity with the device increases, recognizing the final engagement of the implant becomes easier. You should confirm good bony apposition via visualization, probing and fluoroscopy. Final Thoughts Using the StayFuse implant gives you several advantages in comparison to other procedures. The three-step technique for implantation is very simple to perform, with minimal instrumentation. A range of diameters and lengths are available, depending on bone size. There is no disruption of the joints, proximal or distal, to the PIPJ. Employing the device enables you to provide a more stable union with added rotational stability. This improved fixation enhances the healing process. There is no post-op implant exposure, which eliminates pin tract infections. Without an external wire and when you compare it to traditional K-wire fixation, the implant improves patient comfort as well as patient perception and can reduce the prolonged need of a post-op shoe. If the situation arises, you do have the option of removing the device later via a “windowing” technique through the middle phalanx. The only real disadvantage I see with the device is the inability to concurrently stabilize across the metatarsophalangeal joint with pinning, if this was so desired for mechanical or structural reasons. In comparison to the other digital arthrodesis procedures performed, I have found the StayFuse implant to be an excellent device. It is coupled to a relatively simple implantation procedure and has had reproducible results. I have addressed digits two through four using the implant. (The fifth toe usually is best addressed with a simple arthroplasty at the PIPJ.) It is up to your discretion whether adjunctive soft tissue procedures (i.e. tenotomy, capsulotomy, etc.) are needed along with the StayFuse. I believe that using the implant leads to fewer complications, such as nonunions, pseudoarthroses, pin tract infections, pain and need for revisional surgeries. In particular, the appearance of a somewhat “bulbous” fused PIPJ — which you’ll often see with the “offset” arthrodesis of the peg-in-hole procedure — is well addressed with the StayFuse implant. Dr. Paul is in an orthopedic group practice, McLean County Orthopedics, Inc., and is in an orthopedic sports medicine practice, Sports Enhancement Center, Inc., in Bloomington, Ill. He is an Associate of the American College of Foot And Ankle Surgeons and is a team podiatrist for Illinois State University Athletics. Dr. Burks is a Fellow of the American College of Foot and Ankle Surgeons. He is board-certified in foot surgery. Dr. Burks practices in Little Rock, Arkansas. Editor’s Note: For a related article, see “The Top Eleven Pearls For Hammertoe Surgery” in the April 2002 issue at www.podiatrytoday.com.
 

References:

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