Introduction

Hammertoes are among the most common deformities of the forefoot. It results from an imbalance between the weak intrinsic muscles and the stronger extrinsic muscles surrounding the metatarsophalangeal joints (MTPJ) of the lesser digits. Hammertoe is a deformity that involves flexion at the interphalangeal joints (IPJ) and can be distinguished into categories including the classic hammertoe, mallet toe or claw toe. With the lesser digits being an important component in the balance of the foot, as well as in pressure distribution, deformities may lead to compensatory gait changes, distortions in cosmetics, callous formations, and pain. It is, therefore, important to know that there is a multitude of viable treatment options to consider. Treatments should first and foremost be centered around conservative measures such as wearing shoes with a wider toe box, toe pads, and the proper utilization of orthotics. If conservative management fails and pain persists with worsening deformity, the patient may benefit from surgical intervention. There are different types of characteristics of the deformities, and depending on its rigidity, the surgical approach will differ. A proper clinical evaluation of the patient is, therefore, of the utmost importance when aiming for long-term reduction of the deformity.

Anatomy

Deformities of the lesser digits result from an imbalance between the weak intrinsic muscles and the stronger extrinsic muscles. Any imbalance in these forces will favor the stronger extrinsic muscles and thus will result in an extended proximal phalanx and possible MTPJ hyperextension, as well as with a PIPJ and/or DIPJ flexion due to the long unopposed flexor.

• Extensor digitorum longus(EDL) primary function is in the swing phase of gait and functions to dorsiflex the foot. EDL tendon splits into four separate tendon slips as it courses across the ankle, with each one going to each of the lesser digits. Over the proximal phalanx, the tendon again divides into 3 slips, with the middle slip inserting into base of the middle phalanx, and the 2 lateral slips converting into a terminal tendon and inserting into the base of the distal phalanx.

• Extensor digitorum brevis(EDB) only has three slips and inserts into the fibrous expansion of EDL at the level of MTPJ of digits 2, 3, 4 forming what is called the extensor hood apparatus. Because of this unique anatomical construct, the pull of the EDL and EDB creates significant dorsiflexion of the MTPJ and minimal dorsiflexion power at the IPJ.

• Flexor digitorum longus(FDL) divides into 4 separate slips that insert onto the lesser digits distal phalanx and flex at the DIPJ, while FDB inserts onto the middle phalanx and flexes the PIPJ. With no flexor inserting into the proximal phalanx and working as an antagonist to the MPJ in an extended position, the force results in flexion in the PIP and DIP joints.

MTPJ instability is commonly found in patients with digital deformities. The structures providing stability to this joint include the plantar plate along with the accessory and proper collateral ligaments at the lateral and medial aspects of the joint. If these key ligamentous structures attenuate or rupture, it will lead to instability at the level of the MTPJ. Plantar plate ruptures may also lead to subluxation, and a collateral ligament injury may result in a medial or lateral drift with a potential valgus or varus rotation of the affected digit; this pathology leads to a 'cross-over deformity.'

The causes of hammertoe deformity are many and multifactorial, including congenital and acquired, with the most accepted factor and component being a biomechanical dysfunction. The etiology of deformities of the lesser digits includes:

• Neuromuscular conditions

• Diabetes

• Inflammatory arthropathies

• Ill-fitting shoes and high heels

• Intrinsic muscle imbalance

• Hallux valgus

• Long metatarsals

• Pes planus

To properly evaluate hammertoes, it is beneficial to retrieve diagnostic imaging.

Radiograph

The anterior-posterior, oblique, and lateral plain film radiographs are helpful in the evaluation of hammertoe deformities and should be taken with the patient being weight-bearing. It may be used to assess contractures, seeing into the medullary canal of the proximal phalanx is associated with hammertoe deformities, and this sign is called the "gun barrel." Imaging makes it further possible to evaluate the relative metatarsal lengths, identifying hallux valgus as well as metatarsus adductus by examining the overall forefoot alignment. This is particularly helpful during a pre-operative assessment. To determine the length of the hammertoe pre-operatively, a transverse line may be drawn on the radiograph from the tips of the distal phalanges of the adjacent digits on either side; a long toe would overlap this line.

Magnetic Resonance Imaging

Magnetic resonance imaging series may be helpful in the event that there is a suspicion for a plantar plate rupture. This kind of advanced diagnostic imaging may further help detect soft tissue or osseous pathologies such as avascular necrosis of the metatarsal head, with the second metatarsal being the most commonly affected, or defects of the cartilage. If the patient has a medical history with comorbidities such as diabetes, distal peripheral neuropathy, or peripheral vascular disease, noninvasive arterial studies may be warranted to assure healing assessment.

Hammertoe deformities can be extremely painful and can have a significant impact on a person’s quality of life. Surgical correction of hammertoe deformities is therefore among the most commonly performed surgical procedures performed on the forefoot.

Non-surgical Treatment

Before the surgical route is considered, conservative treatments are usually attempted. These treatments are concerned with relieving pressure dorsally over the involved PIPJ, plantarly to its metatarsal head as well as relieving the pressure to the tip of the involved toe. With lesser digit deformities, it is recommended that the patient begins using insoles or orthotics and shoes with a wide toe box to accommodate the deformities as well as to alleviate the pain that may present with the impingement of the digits. High heel shoes are not recommended due to the continued increased transfer of pressure to the forefoot. Padding or periodic shaving of the painful calluses may alleviate some of the patient’s discomfort, and strapping or taping the flexible deformities may improve some alignment. These modifications can be beneficial for managing forefoot disorders however none of these techniques are permanent solutions to the deformity.

Surgical Treatment

Once the flexion contractures start forming and becoming constant along with pain, surgical intervention may be indicated. Historically, this has been based on balancing out the forces from the extensors and the flexors by altering the relative lengths of the toe, including its osseous structures and its tendons. The distinction between flexible and rigid hammertoes, as well as the absence or presence of associated MTPJ deformity, will help to guide you to conservative care or to the best surgical intervention. Recent findings have shown that lesser toe surgery makes up 48% of forefoot surgeries with hammertoe surgery being the most common procedure.

Treatments must address and evaluate the deformity at all joints of the affected digit including DIPJ, PIPJ, and MTPJ. The most common surgical techniques employed to address the rigid or so-called fixed hammertoe deformities are PIPJ resection arthroplasty or PIPJ arthrodesis. For the correction of flexible hammertoes, soft tissue release is often used and this will maintain the structural stability of the toe.

If digital surgery is warranted and instability is noted at the MTPJ, this should be addressed as a concomitant procedure such as an osteotomy to address the affected metatarsal, and/or plantar plate repair. Plantar plate rupture may be diagnosed on physical examination by the Lachman test and is considered the most accurate clinical test for diagnosing MTPJ pathology. During the test, the metatarsal head should be stabilized while the proximal phalanx is displaced dorsally. If displacement is over 2 mm or 50% of the MTPJ, the test is positive indicating a plantar plate rupture or insufficiency. A dorsal medial deviation of the digit, often affecting the second toe, is commonly seen as an objective finding of MTPJ instability along with exquisite point tenderness just distal to MTPJ at the insertion of the plantar plate apparatus into the base of the proximal phalanx.

• PIPJ resection arthroplasty - Resection of the head of the proximal phalanx will shorten the distance from the origin to the insertion of the flexor digitorum longus and flexor digitorum brevis causing weakness. However, the extensors will not be weakened since their insertions are into the MTPJ via the extensor hood apparatus. This procedure is therefore most effective in treating flexor induced hammertoe deformities that are semirigid or rigid, as well as for elongated digits. Due to the loss of structural integrity, multiple arthroplasties should be avoided.

• PIPJ arthrodesis - The fusion of the PIPJ is an effective procedure for most deformities related to the digits. It is particularly useful and preferred when there are significant deforming forces, as well as when all or multiple digits are involved since it maintains the structural stability to the toes. The fusion converts the toe to a rigid lever arm, leading to FDL and FDB tendons now augmenting the intrinsic muscles providing plantarflexion stability at the MTPJ.

• Tendon transfers - Transferring the FDL and FDB tendons to the dorsal aspect of the proximal phalanx convert these tendons to plantar flexors of the MTPJ during weight-bearing in the same fashion as PIPJ arthrodesis. This procedure is indicated for flexible deformities. For the extensor tendon transfer, the EDL may be transferred to the metatarsal neck to eliminate the deforming force.

• Tenotomy - Another procedure indicated for flexible deformity is a flexor tenotomy performed at the PIPJ which effectively releases both the FDL and FDB. For mild, flexible extensor hammertoes the extensor tenotomy is indicated. The tenotomy must be performed proximal to the extensor hood apparatus to effectively release the pull. If the incision is made at the MTPJ, it requires a full capsulotomy.

• Weil Osteotomy - This is a distal oblique osteotomy resulting in a shortening of the metatarsal and is a procedure most commonly seen when addressing hammertoes or claw toes. It is often used to correct dislocations of the digits and angular deformities.

• Plantar Plate Repair - Commonly performed in conjunction with a Weil osteotomy. It is typically carried out through a dorsal approach where the injured or ruptured plantar plate is repaired using suture.

Enhancing Healthcare Team Outcomes

An interprofessional team that includes primary care physicians, podiatric surgeons, nurses, and physical therapists is the best approach for the management of hammertoe deformity. It may start as an initial visit to the primary care physician due to pain, swelling, or aesthetic concern. The diagnosis is made through a clinical examination, and radiographic imaging is helpful in evaluating the underlying structures and necessity for potential future surgical planning. However, conservative management should be considered as the primary approach. If proven ineffective, then the patient should get a referral to a surgeon and undergo a thorough surgical evaluation. If the patient undergoes surgery, post-operative protocol, including rehabilitation, should follow to maximize functionality; post-operative pain management with a focus on minimizing the opioid use should also be initiated. It is important for the patient to continue long term follow up to ensure the proper recovery timeline and milestones are being met.

Prognosis

Hammertoe deformity is a chronic progressive deformity. However, the overall prognosis of a hammertoe deformity is good. Once the patients have been evaluated, conservative management should be initiated. If functionality and pain do not improve, surgical intervention should be considered. Depending on the type of procedure, the technique used, and the surgeon’s preference, the postoperative recovery period differs. The standard post-op protocol usually includes partial weight-bearing with heel touch in a postoperative shoe for 2-6 weeks with the transition into a rigid athletic shoe. If the patient is a smoker or diabetic, the healing may take longer. Postoperative complications may arise depending on the surgical technique being used. Some of the more common post-surgical complications include infection, non-union, hematoma, numbness, and recurrence.

Rates of recurrence and revision surgery of digital deformities are relatively high and has been showing with rates ranging up to 10%. It has been found that the 2nd digit is more likely to fail relative to the third and the fourth. Patients that showed a greater transverse deformity pre-operatively is shown to experience a greater failure rate than if the deformity is mainly in the sagittal plane. Furthermore, performing concomitant surgery to address a deviated 1st MTPJ at the first ray has shown a decrease in hammertoe recurrence with nearly 50%. Recurrence may develop due to tight flexor tendon or due to inadequate bone resection, however care should be taken since excessive resection of bone may lead to a flail toe.

Complications

Hammertoes usually start out as mild deformities that progressively worsen over time, which can result in complications such as pain, gait imbalance, decreased quality of life, and skin changes like callouses, corns, and blisters. Surgical correction of the hammertoe deformity may lead to complications including but not limited to:

• Nonunion

• Malunion

• Avascular necrosis

• Metatarsalgia

• Malalignment

• Infection

• Numbness

• PIP joint instability (flail toe)

• Pain

• Recurrent deformity

• Stiffness

• Vascular impairment

• Chronic edema

• Mallet toe