Lesser Toes Deformities

Barbara Piclet-Legré

Véronique Darcel

♦ INTRODUCTION

Minimally invasive, percutaneous foot and ankle surgery techniques derive from and borrow the general principles of traditional open surgery. Percutaneous surgical techniques are particularly suitable for correcting lesser toes deformities because they allow targeted tendon, capsular, and bone procedures to be performed “à la carte” according to the different types of deformities and their reducibility. The polymorphism of lesser toes deformities has long been an obstacle to the reliable and reproducible classification schemes.

Physiopathology

Toe deformities usually develop from a disharmony in the musculotendinous balance between the extrinsic and intrinsic muscles of the foot.

As a reminder, the extensors act only on the 1° phalanx (P1) by the suspender effect of the fibro-aponeurotic structure with the extensor sling’s transversely oriented fibers (this extensor sling is also called transverse or quadrilateral lamina) and the extensor wing’s obliquely oriented fibers; the flexors act on the 2° and 3° phalanges (P2 and P3); the balance between these different tendons is restored only by the interossei and lumbricals (often atrophied in the sedentary) muscles (Tables 12.1 and 12.2).

Passive stabilization of the metatarsophalangeal (MTP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints is ensured by the collateral ligaments, the joint capsule, and the plantar plate. Any lesion of these structures may cause or aggravate the deformity.¹,²

Many hypothesize that a mechanical overload of the joints linked to a retraction of the gastrocnemius, a pathology of the rear, midfoot, or forefoot gradually causes the deformities.

Among the risk factors, female sex, older age, and a high body mass index have been identified³,⁴ as well as genetic factors⁵ and unsuitable footwear, particularly in the elderly.⁶

Deformities may also be due to central or peripheral neurological disease such as stroke or Charcot-Marie-Tooth disease or rheumatic conditions such as rheumatoid arthritis that may destroy the stabilizing elements of the joint. Iatrogenic and posttraumatic deformities are also caused by malunion, compartment syndrome, or lesion of the tendon apparatus. Harnessing syndrome, due to the presence of an anastomotic slip between the flexor hallucis longus and the flexor digitorum longus (FDL), can cause deformation of the lateral toes in flexion when the first ray is shortened.

Classification of Lesser Toes Deformities

Referenced publications use nonstandardized descriptive international names such as “claw toe,” “mallet toe,” “hammer toe,” “curly toe,” or “cross over toe.” A Dutch study showed clearly insufficient concordance for the definition of “hammer toe” (24%), “claw toe” (9%), and “mallet toe” (the better with 70%) using as reference the definitions of Coughlin and Mann.⁷

The French Association of Foot Surgery Classification (AFCP)

Almost 10 years ago, the senior author proposed an exhaustive systematic clinical classification deformities of the lesser toes at The French Association of Foot Surgery (Association Française de Chirurgie du Pied) spring congress in Lille, France, in 2013. This morphological classification was validated in 2018 and published by Lintz et al.⁸ for the second toe. It describes the position of each joint of the toe from proximal to distal in relation to the anatomical
reference position. Deformities in the sagittal plane take precedence over deformities in the horizontal plane. Each toe is described by its number (from 2 to 5) then by three letters, one for each joint. In the sagittal plane, the position of the segment of the joint is denoted “e” for extension, “n” for neutral, or “f” for flexion (Table 12.3). If there is no deformity in the sagittal plane (ie, the position of the joint is classified as “n”), the deformity in the horizontal plane can be taken into account. It is denoted “m” for medial, “n” for neutral, or “l” for lateral (Table 12.4).

Table 12.1 Global Action of Extrinsic and Intrinsic Pull on the MTP Joints and IP Joints

	Extrinsic	Intrinsic
MTP joints	Extension	Flexion
IP joints	Flexion	Extension
IP, Interphalangeal; MTP, metatarsophalangeal.

Table 12.2 Specific Action of the EDL and EDB Tendons on the MTP, PIP, and DIP Joints

	EDL and EDB	FDL	FDB	Interosseous Lumbricals	Plantar Fascia
MTP joints	Extension/sling wing			Flexion	Flexion
PIP joints	Extension		Flexion	Extension
DIP joints	Extension	Flexion		Extension
DIP, distal interphalangeal; EDB, extensor digitorum brevis; EDL, extensor digitorum longus; FDB, flexor digitorum brevis; FDL, flexor digitorum longus; MTP, metatarsophalangeal; PIP, proximal interphalangeal.

The classification in the only one for which inter- and intra-observer reproducibility and speed have been evaluated (˜30 seconds) on second toe deformities.

However, it does not provide information on reducibility, pulp support, joint stability, and radiological characteristics.

This classification may easily be applied to the other toes.

Figures 12.1 to 12.6 illustrate examples of the use of the classification.

An additional category of “pulp support score” was added in 2021. It translates the quality of pulp support into passive and active during the foot examination⁹ (Table 12.5).

♦ INDICATIONS AND CONTRAINDICATIONS

Indications and contraindications depend on the vascularity of the toe, the goals of the patient, and the overall flexibility of the toe. In an active infection, any surgical intervention other than amputation may be contraindicated. Poor vascularization of the foot may result in delayed bony and softtissue healing, and in some cases devascularization of the toe with toe loss. Rigid deformities treated with soft-tissue procedures alone may result in recurrence or worsening deformity. Maintaining patient expectations and careful anatomical understanding will result in better outcomes overall. Other limitations will be exposed in the description below. Meticulous postoperative care is paramount in the first 6 weeks after surgery; if the patient cannot commit to this, surgery may be contraindicated.

Table 12.3 AFCP Classification of Lesser Toes Deformities

Sagittal Deformity
MTP	e	n	f
PIP	e	n	f
DIP	e	n	f
We proceed in the same way for the PIP and the DIP. AFCP, French Association of Foot Surgery; DIP, distal interphalangeal; MTP, metatarsophalangeal; PIP, proximal interphalangeal.

♦ PATIENT HISTORY AND PHYSICAL EXAMINATION

What are the decision criteria for a correcting toe deformity?

Analysis of the Functional Impact of the Deformation

The functional impact of pain in the feet on quality of life has been demonstrated as quite significant with an SF-36

score being reduced on the physical, social functioning, and mental health components.³ In the older population, deformities of the lesser toes are associated with an increased risk of falling (67%).¹⁰ The most frequent complaint of toe deformity is the dorsal contact with the shoe, though other complaints such as excess pulp pressure or a metatarsalgia by vertical pressure on the metatarsal head are common.

Table 12.4 When There Is No Sagittal Deformity (Segment of the Joint in Neutral Position [n]), the Deformity in the Horizontal Plane Can Be Taken Into Account and Denoted “m” When the Segment is Deflected Medially and “l” When Deflected Laterally

Horizontal Deformity
MTP n	m	l
PIP n	m	l
DIP n	m	l
DIP, distal interphalangeal; MTP, metatarsophalangeal; PIP, proximal interphalangeal.

Figure 12.1 2efn deformity according to the French Association of Foot Surgery classification, equivalent of “claw toe.”

Figure 12.2 2efe deformity according to the French Association of Foot Surgery classification.

Figure 12.3 2nfn deformity according to the French Association of Foot Surgery equivalent classification of “hammer toe.”

Figure 12.4 2nff deformity according to French Association of Foot Surgery classification equivalent classification to “mallet toe.”

Figure 12.5 2lfn and 3eff according to French Association of Foot Surgery classification.

Pulp Pressure Quality

Pulp pressure can be assessed in weight bearing by the “paper pull-out test” (the patient’s ability to hold a sheet of paper on the ground using toe pressure against pull-out) or on the AFCP lesser toe classification of pulp pressure previously described.⁹

Reducibility

The authors test the reducibility of each joint according to the AFCP classification.

One can use the push-off test to qualify the deformation as reducible, semireducible, or nonreducible. In non-weight bearing, the examiner presses under the metatarsal head in question. The deformation is reducible when this support completely corrects the deformation.

Figure 12.6 4nmn deformity according to French Association of Foot Surgery classification.

The terms used are flexible (f), semirigid (sr), or rigid (r).

In neurological feet, it is not uncommon for the deformity to be reducible in equinus and for an fff (flexible MTP, PIP, DIP) deformity to be observed in dorsal flexion, which testifies to the retraction of the flexors.

The authors usually add reducibility and etiology to the classification description; the reducibility is noted after the description of the deformity of the toe: flexible (f), semirigid (sr), rigid (r) and the cause is noted before: rhumatismal (rh), posttraumatic (pt), neurological (nr), iatrogenic (ic).

If the authors use these descriptors, for instance, they can write (rh)2nfn(r), (pt)3nln(f), or (nr)2345nff(sr) to describe deformities.

Metatarsophalangeal Instability

The evaluate the plantar plate, palpate the MTP and using the drawer test or Lachman test¹¹: the foot being off-loaded, the metatarsal head is held between the thumb and index finger, and, with the other hand, move the toe upward; the drawer is positive when the toe subluxates, indicating a lesion of the plantar plate.

Table 12.5 The Score for Each Toe Is 0 When the Pulp Support Is Normal, 1 When Support Is Present Only With Active Flexion, and 2 in the Absence of Support in Passive and Active

Score	State
0	Pulp support at rest, reinforced with active flexion
1	Pulp support only with active flexion (no support passive)
2	Absence of any pulp support on the ground (absence of active and passive support)

Figure 12.7 “V” sign meaning 2nd MTP (MTP2) synovitis.

At the synovitis stage, the “V” sign is the first seen on clinical examination. Under weight bearing with bare feet, there is an abnormal gap between the affected toe and its neighbor¹² (Figure 12.7).

♦ IMAGING STUDIES

Standard Radiograph

Weight-bearing foot radiographs are useful to analyze phalanx bone morphology and look for osteoarthritic degeneration of the joints. Joint deformities, such as an MTP subluxation or dislocation, may lead to a superposition of the joint spaces of the toes on the standard incidences. Centered or zoomed shots are sometimes necessary. Radiographs also highlight other foot morphology affecting the toes, such as pes cavus or prior traumatic deformity.

Ultrasound

In the hands of a skilled user, ultrasound is extremely helpful in examining the plantar plate¹³ as it is dynamic and has the best resolution among all the imaging modalities.

A rupture is noted as a partial- or full-thickness hypoechoic area of the plate, most often distal and lateral with variable propagation proximally and medially. The second ray is most often affected. Toe dorsiflexion improves visualization of lesions. Indirect plantar signs such as phalangeal avulsion and effusion of the flexor tendon sheath in contact with the plate can be visualized. On the dorsal side, ultrasound detects joint synovitis and phalangeal subluxation at the preradiographic stage. The limits of ultrasound are the thickened hyperkeratosis of the anterior pad for the plantar cuts and the fixed and irreducible hyperextension of the MTP for the dorsal cuts.¹⁴

MRI

MRI has a sensitivity of 96% and a specificity of 95% in the diagnosis of plantar plate lesions.

The lesions usually appear as a discontinuity of the plate in hypersignal T2, which extends toward the base of P1.¹⁵ A trap image is the central and distal pseudodefect of the plantar plate, which causes a physiological T2 hypersignal.

MRI is superior to ultrasound and radiography in the diagnosis of synovitis and subchondral bone changes in arthropathies. It is the reference examination in the differential diagnosis, particularly in the diagnosis of nonmechanical pathologies.¹⁴

♦ PREOPERATIVE PLANNING AND PREPARATION

Nonsurgical options should be attempted first, although their level of scientific evidence is low.

Physiotherapy for stretching the gastrocnemius muscles or strengthening the intrinsic “foot sheathing” is prescribed depending on the etiology. The osteopathic technique of strain counterstrain, advocated by Masson,¹⁶ acts on the abnormal shortening of the tissues at the level of the deformity responsible for the restriction of movement. Intra-articular steroid injection can be proposed in case of synovitis without lesion of the plantar plate, which is essential to seek.¹⁵ Beware of the risk of plantar plate rupture¹⁷ because it will promote joint instability.

SURGICAL TECHNIQUE

What Surgery Apart From Treating the Cause?

Studies on surgical treatments are mostly level 4 (retrospective case series). In all cases, treating the cause of the deformities allows better results. For instance, in this case, the lengthening of the medial gastrocnemius was necessary in association with the percutaneous gestures of the deformed toes to correct deformity (Figure 12.8). The analysis of the deformity according to the morphological classification of the AFCP⁸ aided by the pulp score⁹ makes it possible to target the surgical indication. The choice of technique is made from proximal to distal, and the deformity is corrected sequentially at the level of the MTP, then of the PIP, and finally of the DIP if necessary.

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