Hammertoe surgery is not without its complications as reportedly 17 percent of patients are dissatisfied with their post-op results. Accordingly, these authors review key anatomical points and essential biomechanical considerations to help ensure appropriate procedure selection and favorable post-op outcomes.
While hammertoe surgery is a common procedure performed routinely around the country, it has unpredictable results. According to 2003 data from the Centers for Medicare and Medicaid Services, there are 300,000 hammertoe surgeries performed annually with over 50,000 patients unsatisfied with the results.1
This equates to approximately 17 percent of all hammertoe operations resulting in “unsatisfied” patients. Patients may complain their toes are too short, too long, too fat, too curved, too straight or too floppy.
Coughlin and colleagues conducted the largest hammertoe study with 118 toes on 67 patients.2 Patients underwent evaluation at an average of five years following proximal interphalangeal joint (PIPJ) fusion with Kirschner wire fixation. Fusion of the PIPJ occurred in 81 percent of cases and 84 percent attained subjective satisfactory results.
In a study of PIPJ arthrodesis, Lehman and Smith noted a 48 percent satisfaction rate without reservation with a peg-and-dowel technique.3 The rest were not completely satisfied with major reasons for postoperative dissatisfaction being toe angulation and incomplete relief of pain.
It is clear that something as “simple” as a toe has significantly mixed and unpredictable results. What can we do to improve patient satisfaction? How do we improve surgical outcomes?
First, it is imperative for foot and ankle surgeons to have a detailed understanding of digital anatomy as well as a solid conceptualization of the biomechanical forces acting on the digits. Perhaps the reason surgical outcomes are so unpredictable is not because the toes are so intricate or complicated, but is more due to a lack of an adequate physical exam. Without a thorough exam, one cannot identify the deforming forces and thus cannot appropriately plan surgery. It is essential to approach digital surgery with an attention to detail, an accurate knowledge of anatomic structures and how the biomechanical function and forces are transmitted and disrupted with surgical augmentation.
There are many functional considerations one must explore in order to develop accurate and appropriate surgical planning or salvage if hammertoe surgery fails. We have divided these into three simple categories: anatomy/physiology, biomechanics (tendon balancing and foot type) and deformity considerations (flexible versus rigid, subluxed versus dislocated). We present two cases of hammertoe deformity correction with discussion of these functional considerations.
A Pertinent Primer On Digital Anatomy And Physiology
A detailed understanding of digital anatomy is essential to understanding the biomechanical relationships and forces that act on the digit. This becomes the crux of hammertoe surgery. As we begin to manipulate and augment these biomechanical relationships, we will eliminate, neutralize or create new deforming forces, which may later translate to deformity.
Consider the four different surface planes of the anatomy: dorsal, plantar, medial and lateral. Then consider the orientation of how tendons cross these planes to conceptualize how the vector of force relates to movement through the digit. Where do the tendons cross the joints?
Dorsally, the tendon of the extensor digitorum longus (EDL) splits into three tendon slips with the central portion inserting on the base of the middle phalanx. The medial and lateral slips converge into the terminal tendon to insert together at the base of the distal phalanx. All of the tendon insertions are covered by the extensor expansion, a fibro-aponeurotic sling. This sling then wraps around the digit and inserts on the plantar aspect of the digit at the base of the proximal phalanx.
This is important to understand because the whole purpose of the EDL is to extend the metatarsophalangeal joint (MPJ). However, the long extensor does not actually have any dorsal attachment to the proximal phalanx. Rather, the long extensor works to extend the MPJ by suspending the proximal phalanx from its plantar insertions while directly acting to extend the PIPJ and the distal interphalangeal joint (DIPJ) with dorsal insertions.
Plantarly, the flexor digitorum longus (FDL) tendon inserts on the base of the distal phalanx and the flexor digitorum brevis (FDB) inserts on the base of the middle phalanx. Again, no insertions occur on the proximal phalanx that would directly plantarflex the MPJ. Ground reactive forces become an important passive stabilizer by pushing the proximal phalanx into extension and allowing the flexors to stabilize the digit by pushing it into the ground.
The plantar plate inserts on the base of the proximal phalanx and helps provide passive plantarflexion when the foot is loaded. For example, when the ground reactive forces push the MPJ up into extension, the plantar plate helps tether the proximal phalanx to the MPJ and thereby passively plantarflexes the MPJ.
Over time, the plantar plate begins to attenuate and it loses its tethering effects. As the ground pushes the proximal phalanx into extension, there is very little plantarflexory balance on the proximal phalanx. The long flexors therefore fire in an attempt to stabilize the digit and create a buckling effect through the small joints in the toe. This creates a hammertoe.
Medially, the lumbricalis and interosseous tendons travel along the same course, thereby providing a plantarflexory force at the MPJ, and continue dorsally to insert onto the extensor wing (lumbricalis) and extensor sling (interosseous). The lumbricalis and interosseous tendons thereby cross dorsal to the PIPJ joint axis, acting as an extensor of the PIPJ and DIPJ through the extensor expansion. The interosseous tendons course dorsal to the deep transverse metatarsal ligament while the lumbrical tendons originate plantar to the deep transverse metatarsal ligament.
The interossei are the only tendons located laterally. The collateral ligaments strengthen the MPJ capsule. The collateral ligaments are composed of two major structures. These structures are the phalangeal collateral ligament (PCL), which inserts onto the base of the proximal phalanx and the accessory collateral ligament (ACL), which inserts onto the plantar plate.4
When planning osteotomies, it is important to consider the orientation and placement of the cuts in order to optimize bone healing by increasing the apposition of the fusion interface. Metaphyseal bone will provide the largest surface area for fusion while also providing the best blood supply. You can also avoid excessive shortening by placing cuts through the metaphysis and not at the diaphysis (shaft) of the phalanx. Cuts through the phalangeal shaft increase nonunion rates and can lead to pseudoarthrosis and floppy toe.
Understanding The Biomechanics Of Hammertoe Deformities
It is important to ask yourself why the patient has a hammertoe deformity. Ask which digits are affected and why. A detailed physical exam with a full biomechanical exam including gait analysis is essential to identify the deforming forces, which one can then address sequentially with surgical planning. Important considerations for digital deformities include the following questions:
• Does the patient have an equinus and therefore extensor substitution that one needs to address?
• Is there flexor substitution or flexor stabilization?
• Is the foot hypermobile or is there an insufficient first ray?
• What is the overall foot architecture: flatfoot or cavus foot?
Predislocation syndrome is a common cause of dorsal subluxation and overlapping of the second digit. Predislocation syndrome is the result of chronic overloading to the second MPJ due to an insufficient first ray. When the weight of the body cannot transmit through the first ray during propulsion (either because of hypermobility or due to length discrepancies of the first metatarsal), the weight transmits/ transfers to the second MPJ.
This joint is not structurally designed to resist the combination of the ground reactive forces and body weight transmission, which occur during propulsion. Over time, this chronic hyperextensory force on the MPJ causes attenuation of the plantar plate. This can eventually lead to plantar plate rupture and dorsal subluxation of the second digit.
Perez and colleagues evaluated the role of the plantar plate and its function in passive plantarflexion of the digits.5 They concluded that the plantar plate provides a tethering of the proximal phalanx, which occurs with weightbearing. This creates passive plantarflexion of the digits through the windlass mechanism. This is an important consideration when performing any shortening osteotomy aimed to correct hammertoe deformity as shortening of the metatarsal will dampen the effects of the windlass mechanism (think of it as putting slack in the tethering line). This also helps explain why the most commonly cited complication of the Weil osteotomy is “floating toes.”6,7
Myerson and Jung examined the role of flexor to extensor tendon transfer for the treatment of metatarsophalangeal joint instability.8 They concluded that tendon balancing was an important consideration for hammertoe correction. They evaluated 59 patients for an average of 45 months postoperatively and found the second digit to be stable during stress manipulation in 78 percent of the patients studied.
However, only 42 percent of the study patients stated they were “very satisfied” with the remaining 58 percent of patients reporting residual pain, stiffness and dysfunction as the major causes of dissatisfaction.8 Thirty-seven percent had residual dorsiflexion contracture. The American Orthopaedic Foot and Ankle Society (AOFAS) functional scores averaged 82 points at the time of final follow-up. Interestingly, the study authors reported no statistical difference between patients who received FDL transfer with a shortening osteotomy (Weil) and those who only received a FDL transfer.
Bouche and Heit combined plantar plate repair with tendon transfer for chronic, severe, sagittal plane instability.9 The study authors reported a 100 percent satisfaction rate in 18 patients who had a minimum follow-up of one year. The average AOFAS score was 83, according to the study. The study authors concluded that the repair of the plantar plate was the key component in the combined approach that resulted in such success.
Assessing The Nature Of The Deformity And Determining Appropriate Surgical Goals
For patients with hammertoe deformities, there are a number of important considerations.
• Is the deformity flexible or fixed?
• What is the level of the deformity? Is it at the MPJ, the interphalangeal joint (IPJ), the DIPJ or a combination of the joints?
• Is fusion necessary?
• Is a straight toe desirable?
• How does one ensure toe purchase?
• Which toes should you fuse?
• How does one get a toe to fuse and what fixation devices — pins, bio-pins or screws — will you use?
• Are there other associated deformities, such as hallux rigidus or hallux abducto valgus, that contributed to or caused the hammertoe deformity?
It is important to consider the degree or severity of deformity. If the digit has been chronically dislocated, it will likely require not only some kind of tendon balancing and MPJ release but may also require a shortening osteotomy. Remember, the digit has been essentially shortened for a prolonged period of time while dislocated and will effectively lengthen following arthrodesis. Using a K-wire to reduce an unstable joint will only cause re-subluxation after pulling the pin. The K-wires do not correct deformity. They merely facilitate scarring of the soft tissues, primarily the MPJ capsule.
Always assess the correction with the foot both unloaded and loaded. What is the toe going to look like when the patient bears weight?
For revisional surgery, it is important to ask what went wrong with the index procedure. What deforming forces were not addressed? Ask if the surgeon under-addressed deformities or created any deformities.
For example, functionally, there is no difference between arthroplasty and arthrodesis. Procedure selection is predicated on the desired outcome or effect of the procedure. Strength will improve following fusion because the vector of force of the long flexor will transmit through the MPJ with improved plantarflexion of the digit. However, one has also changed the tendon balance relationships of the digit and provided the long flexor with a mechanical advantage that over time creates a new deformity: mallet toe. Performing an FDL transfer will prevent this new deformity from occurring while also providing tendon balancing of the digit.
Case Study One: When A Patient Presents With Medial Deviation Of The Second Digit And An Overlapping Toe
A patient presented with significant medial deviation of the second digit with a rigid, overlapping second toe. She underwent several procedures in order to address the various deforming forces.
First, the surgeon transected the extensor tendon at the level of the PIPJ and subsequently released the MPJ as the digit had been chronically dislocated dorsally with considerable soft tissue contractures about the MPJ. The surgeon completely released the medial joint capsule of the MPJ in order to address the significant medial deviation with transection of the medial collateral ligament.
Surgeons subsequently performed an arthrodesis at the PIPJ to provide a stable rigid lever and prevent recurrence of a rigid deformity. They employed two pin fixation to provide stability against rotation with one of the pins crossing the MPJ to allow the digit to scar down in a more anatomic position. However, in order to prevent dorsal migration of the digit upon removal of the pin and simultaneously prevent compensatory mallet toe deformity, the surgeon transferred the FDL tendon to the dorsal base of the proximal phalanx.
Subsequently, the surgeon reattached the extensor digitorum longus tendon (it had been previously transected at the level of the PIPJ and dissected out proximally) to the lateral aspect of the base of the proximal phalanx for lateral balancing.
The patient was completely satisfied three years postoperatively.
Case Study Two: When A Patient Presents With Predislocation Syndrome
A patient initially presented with symptoms of pain and dysfunction of the second toe that were consistent with predislocation syndrome. She had significant biomechanical pathologies that accounted for her deformity.
First and most importantly, she had insufficiency of the first ray with metatarsus primus elevatus and a subsequent functional hallux limitus. This prevented appropriate propulsion off the first ray with transfer to the second MPJ. She also had a gastroc equinus manifested by significant extensor substitution during gait analysis and flexor stabilization secondary to her compensatory pronated foot. This contributed to her symmetric hammertoe deformity of digits two through four with adductovarus deformity of the fifth digit.
She had a positive Lachman’s test of the second digit (a “pull up test” to evaluate for capsulitis), which was indicative of MPJ capsulitis and likely attenuation of the plantar plate. Her second digit had more dorsal subluxation clinically than her other hammertoes, which is also suggestive of plantar plate attenuation.
Accordingly, the surgical planning was based on addressing the deforming forces encountered in her biomechanical exam. The surgeons first performed first MPJ fusion with an endoscopic gastroc recession in order to provide a stable platform for propulsion during gait and eliminate the equinus deformity.
Subsequently, the surgeons performed a plantar plate repair of the second digit with extensor tendon transection at the level of the PIPJ with PIPJ arthrodesis. During the PIPJ arthrodesis, the surgeons transferred the FDL to the dorsal aspect of the proximal phalanx to provide tendon balancing. Next up was a standard arthrodesis of the third and fourth digits with transection of the EDL at the PIPJ with MPJ release. The surgeons subsequently performed a standard arthroplasty of the fifth digit with derotational skin plasty to remove the varus angulation.
The patient was completely satisfied with the results two years postoperatively.
Dr. Richey is a second-year resident with the Kaiser San Francisco Bay Area Foot and Ankle Residency Program at Kaiser Permanente Medical Center in San Francisco, Oakland and Walnut Creek, Calif.
Dr. Hamilton is a Fellow of the American College of Foot and Ankle Surgeons. He is a Staff Podiatric Surgeon and Attending Staff with the Kaiser San Francisco Bay Area Foot and Ankle Residency Program at the Kaiser Permanente Medical Centers in Oakland, Calif., San Francisco and Walnut Creek, Calif.
For further reading, see “How To Handle Complications Of Hammertoe Surgery” in the September 2005 issue of Podiatry Today or “Emerging Concepts In Hammertoe Surgery” in the September 2009 issue. Also see the Podiatry Today blog “Secrets To Navigating Hammertoe Surgery On The Fifth Toe” by William Fishco, DPM, at http://bit.ly/dkD76j .
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