Chapter 6 – Forefoot Pathology




Chapter 6 Forefoot Pathology


Daniel Z. Goldbloom and John P. Negrine



Hallux Valgus



Introduction


Hallux valgus is a forefoot deformity comprised of lateral deviation of the great toe with medial deviation of the metatarsal head. This can occur with or without subluxation of the first metatarsophalangeal joint (MTPJ). The term was first introduced in the 1870s by Carl Heuter, a German surgeon. He recognized that the deformity was due to joint angulation, rather than simple enlargement.


The term “bunion” is derived from the Latin word bunio, meaning a turnip. The “turnip” describes the prominent medial eminence of the first MTPJ, and so hallux valgus is just one of the causes of a bunion. The management of hallux valgus has advanced significantly, as we have better understood the nature of the deformity and the biomechanical consequences of surgery.



Pathogenesis: Etiology, Epidemiology, and Pathophysiology


The prevalence of hallux valgus is unclear. It is probably around 2% in unshod populations, but is much higher in the shoe-wearing population1. Women comprise the majority of sufferers as they tend to wear narrow shoes with, or without, high heels. There are about nine women to every man presenting for surgical treatment of hallux valgus2.


The etiology is unclear. There is an underlying genetic basis, which is activated by lifestyle factors. In one study, a family history was documented in 94%2. Genetic factors that have been implicated, but are as yet unproven, can be divided into bone, joint, and soft tissue factors (Table 6.1)




Table 6.1 Genetic and lifestyle factors in the etiology of hallux valgus













Genetic factors Lifestyle factors



  • Rounded metatarsal head



  • Rounded first metatarsocunieform joint



  • Medial-facing first metatarsocuneiform joint



  • Single-faceted proximal first metatarsal articular surface



  • Lateral exostosis of the first metatarsal base



  • First metatarsal that is longer than the second metatarsal3



  • Calf tightness with ankle dorsiflexion <10°



  • Pes planus



  • First-ray hypermobility



  • Generalized ligamentous laxity




  • Narrow shoes



  • High heels



  • Excessive loading (e.g., ballet dancers)


Hallux valgus deformity has four components. These are not necessarily sequential4.




  1. 1. Valgus of the first MTPJ – always.



  2. 2. Metatarsus primus varus – nearly always.



  3. 3. Pronation of the proximal phalanx – often.



  4. 4. First metatarsal elevation – particularly in cases with a long first metatarsal.


In the normal foot, the first MTPJ is stabilized by static and dynamic structures, which normally prevent deformity. The static structures are the ligaments, capsule, and the crista of the first metatarsal head, and the dynamic structures are the musculotendinous structures.


In the development of hallux valgus the first structures to fail are the medial capsule and medial collateral ligament, which is essentially a thickening of the capsule. Failure of the medial structures leads to the first metatarsal moving into varus, metatarsus primus varus. The hallux moves into valgus. Figure 6.1 demonstrates, in the axial plane, how the deformity progresses.






(a) The normal alignment;





(b) as the metatarsal head moves medially the sesamoid mechanism remains and consequently appears to sublux laterally and superiorly. EHL: extensor hallucis longus; EHB: extensor hallucis brevis; FHL: flexor hallucis longus; LS: lateral sesamoid; MS: medial sesamoid.



Figure 6.1 An axial, cross-sectional view of the first metatarsophalangeal joint.


It is important to understand that it is the metatarsal head that moves medially, with the sesamoid mechanism remaining essentially unmoved. The medial and lateral sesamoids lie in the respective heads of flexor hallucis brevis (FHB) (Figure 6.2). In remaining in situ, the sesamoids sublux laterally and superiorly relative to the first metatarsal head. The subluxation of the sesamoids causes the crista of the first metatarsal head to become flattened, as a result of abrasion by the medial sesamoid. As a result of the pull of the adductor hallucis tendon on the inferior part of the base of the proximal phalanx, the great toe also pronates.





Figure 6.2 The sesamoid mechanism viewed from the plantar aspect. AbH: abductor hallucis; AdH: adductor hallucis; FHB: flexor hallucis brevis.


The abductor hallucis moves inferolaterally and loses its ability to abduct the hallux. It should be remembered that the ab/adduction of the toes is described relative to the second metatarsal longitudinal axis. The long and short flexor and extensor tendons also come to lie lateral to the joint, and their line of pull is no longer neutral, but as partial adductors. Thus in correcting hallux valgus the first metatarsal head is relocated over the sesamoids, rather than the sesamoids being relocated under the metatarsal.


The result of the hallux valgus deformity is to defunction the first ray, consequently overloading the lesser rays. This overload leads to lesser MTPJ instability and lesser toe deformities, such as clawing (Figure 6.3).





Figure 6.3 Bilateral hallux valgus, with secondary deformity of the lesser rays.



Classification


There are two important classification systems for hallux valgus. The first relates to severity (Table 6.2). This classification, for the most part, dictates surgical treatment. It relies on both the hallux valgus angle (HVA) and the intermetatarsal angle (IMA) (Figure 6.4).




Table 6.2 Classification of hallux valgus
































Hallux valgus angle (HVA) Intermetatarsal angle (IMA)
Normal <15° <9°
Mild <20° <11°
Moderate <40° <16°
Severe <50° <20°
Very severe >50° >20°




Figure 6.4 The radiological angles in hallux valgus. HVA: hallux valgus angle; IMA: intermetatarsal angle; DMAA: distal metatarsal articular angle.


The second classification depends on the congruency or incongruency of the MTP joint. This terminology is to some degree a misnomer, as an incongruent joint is in fact a joint that is subluxed. A congruent hallux valgus is one in which the distal metatarsal articular angle (DMAA) is increased, with the first metatarsal head being angulated laterally. Consequently the two joint surfaces are “congruent” (Figure 6.5a). Congruent hallux valgus is more likely to be associated with juvenile onset hallux valgus and is often seen in combination with conditions such as Down’s syndrome. The congruent joint is also more stable and the hallux valgus is less likely to progress. The incongruent hallux valgus (Figure 6.5b) is much commoner, is less stable, and more likely to progress.


Figure 6.5



(a) A congruent hallux valgus with an increased DMAA; the joint articulates congruously.





(b) An incongruent hallux valgus. Note the first MTP and sesamoid articulations are subluxed. The proximal phalanx is also rotated.



Clinical Presentation



History and Examination

Patients with hallux valgus usually present with pain and deformity. The pain has often been present for years. It can be localized to the “bunion,” or may be experienced more globally around the MTPJ. The patient is usually restricted in the style of shoes that can be worn. Metatarsalgia may also be reported with painful callosities under the lesser metatarsal heads; these are often called “transfer lesions.” There is also often dorsal pain and callosities over the proximal interphalangeal joints (PIPJs) of the second and third toes.


Some patients describe a progressive deformity of the second MTPJ, which initially becomes synovitic, with tenderness and swelling of the joint. The second toe then deforms and may eventually cross over the big toe.


In considering hallux valgus it is important to consider the forefoot as a whole, as rebalancing all of the aspects of forefoot deformity is important in treatment. For example, in treating a claw second toe in the presence of hallux valgus it is necessary to correct both the hallux and the second toe, indeed on occasions all of the toes may need to be addressed. Management of lesser toe deformity is discussed later in this chapter.


Generalized ligamentous laxity should be noted, for example by recording a Beighton score. Local examination of the first MTPJ should record: the severity of the valgus; pronation of the toe; correctability of the MTPJ deformity; pain on movement of the MTPJ; MTPJ range of movement – a stiff joint will remain so after correction; erythema and tenderness; and size of the medial eminence. A neurovascular examination should be recorded, in particular the dorsomedial branch of the superficial peroneal nerve should be examined, as sensation is often reduced at the time of presentation and reduced sensation postoperatively may not be the result of surgical damage.


While an assessment is made for tendo Achillis (TA) tightness, pes planus, and first ray hypermobility, the role of these features in hallux valgus is poorly understood.



Investigations

Weightbearing AP and lateral plain radiographs are the primary, and usually only, investigation. The HVA, IMA, and DMAA are measured. The DMAA, also known as the proximal articular set angle (PASA), is the angle between the articular surface of the first MTPJ and the longitudinal axis of the first metatarsal (Figure 6.4), It is normally less than 10°. A high DMAA is seen in congruent hallux valgus and will need to be corrected by surgery. The plain radiographs may also show MTPJ arthritis, lesser MTPJ subluxation or dislocation, and TMTJ arthritis.



Treatment


Non-surgical. The non-surgical management of hallux valgus is not corrective, it is supportive and consists of:




  • – accommodative shoes with a deep and wide toe box, which can be bought off the shelf, or customized



  • – a toe separator can decrease pressure on the medial capsule and also relieve pain between toes



  • – padding, with or without a cut out, can be used to offload pressure from a corn or callus.


Custom-made orthoses do not play a significant role and, at best, provide short-term symptomatic relief.


Surgical. There are over 130 procedures described for the management of hallux valgus, as such no single operation is a panacea.


The indication for surgery has long been pain, which may prevent the wearing of shoes. We believe the indication should be extended to include progressive and severe deformity. The severe deformity, if left untreated, affects the lesser rays and makes eventual surgical management more complex.


Bunionectomy with capsular plication has been shown to lead to recurrence and worsening of the deformity. It should not be undertaken for correction of hallux valgus. Surgically the HVA, DMAA, and IMA must be addressed. The aim of surgical treatment is to reduce the first metatarsal head over the sesamoids. Barouk described four components in correction of hallux valgus:




  1. 1. Distal soft tissue release



  2. 2. Osteotomy of the first metatarsal



  3. 3. Medial capsular plication



  4. 4. An Akin osteotomy to correct hallux valgus interphalangeus.


While not every patient needs all four of these components they should be considered in a stepwise fashion – for example, step four can be omitted if there is no hallux valgus interphalangeus. We will describe these steps in sequence.




  1. 1. A distal soft tissue release involves dividing the lateral structures, which prevent correction of the deformity. The adductor hallucis is released from its attachment to the lateral sesamoid. The lateral joint capsule, also known as the lateral sesamoid suspensory ligament, is released along the line of the sesamoid to allow the sesamoid to reduce under the head of the first metatarsal. Sectioning of the lateral collateral ligament is controversial. It allows a greater correction, particularly in cases of severe deformity, but also leads to a higher risk of hallux varus. As part of this procedure the medial capsule is opened and a bunionectomy, preserving the sulcus, is undertaken.



  2. 2. An osteotomy of the metatarsal may allow the head of the metatarsal to be translated laterally and reduce the IMA. First metatarsal osteotomies are classified as distal, shaft, or basal.


In cases of a congruent joint with a high DMAA, an extra element is required, with rotation of the articular surface medially. This can be achieved by a medial closing wedge osteotomy of the shaft or by adding medial rotation to a translational shaft osteotomy – we prefer the latter.


The choice of osteotomy is determined by the severity of the deformity:


Mild deformity can be managed with a soft tissue procedure combined with a distal or shaft osteotomy of the first metatarsal.


The chevron osteotomy (Figure 6.6) is a distal osteotomy in which a “V” shaped cut of the metatarsal is made. This allows lateral translation of the capital fragment. It is stable, but can be fixed. We use a 2 mm absorbable rod. The results are satisfactory for mild deformity. When combined with a lateral release its indications can be stretched without an increased incidence of avascular necrosis5.





Figure 6.6 A selection of first metatarsal osteotomy patterns.


Moderate to severe deformities can be managed with a number of techniques (Figure 6.6). Osteotomies can be classified as basal (e.g., basal chevron, crescentic) or shaft osteotomies (e.g., Scarf, Ludloff). In modern practice they are usually combined with a lateral release and offer a more powerful correction than distal osteotomy. Good results have been reported for all of the above osteotomies.


The Scarf osteotomy (Figure 6.7) is a shaft osteotomy. It is very versatile and can be used for mild, moderate, and severe deformities with success6. It has a large surface area, which almost eliminates the risk of non-union and has been shown to be a stronger construct than a proximal crescentic osteotomy7. It is a technically demanding procedure, but allows:




  • – the IMA to be reduced



  • – plantar translation of the metatarsal head



  • – slight shortening of the first ray



  • – medial rotation of the articular surface to correct the DMAA, should this be necessary.




  1. 3. Capsular plication is important, but not always necessary. In some cases the sesamoids lie under the metatarsal head following the lateral release and osteotomy. In these cases the capsule needs simple closure. In others the sesamoids remain laterally displaced, in which cases the capsule is plicated.



  2. 4. The Akin osteotomy is an extra-articular medial-closing wedge osteotomy of the base of the proximal phalanx. Although often used to augment a hallux valgus correction, we believe its true indication is for the case of hallux valgus interphalangeus, which often coexists with hallux valgus. The deformity is due to different articulation angles between the proximal and distal articular surfaces of the proximal phalanx. Many surgeons use an Akin osteotomy in 80% or so of cases, as the fourth stage of hallux valgus correction. The decision as to whether to add an Akin osteotomy on the table is a clinical one, based upon the appearance of the foot after completion of the first three stages.





Figure 6.7 Postoperative correction of hallux valgus following a Scarf osteotomy.


The more severe deformities, with a greater than 50° HVA, are more difficult to correct successfully with osteotomy. Arthrodesis of either the MTPJ or TMTJ is a safer option.


Fusion of the first TMTJ to correct hallux valgus is eponymously known as a Lapidus procedure. As well as severe deformity, other indications for a Lapidus type procedure are hallux valgus with TMT arthritis and TMTJ instability. The arthrodesis of the TMTJ includes excision of a laterally based wedge, to close the IMA. Distally the lateral soft tissue release, bunionectomy, and medial capsular plication are undertaken. The postoperative management requires six weeks of non-weight bearing to allow union. Reported satisfaction rates of the Lapidus procedure are generally lower than with osteotomies. Thus the majority of surgeons prefer to use an osteotomy as routine.


Arthrodesis of the first MTPJ will be discussed later in the chapter, in the section on hallux rigidus. Nevertheless it is worth noting that fusion of the first MTP leads to a reduction in the IMA.


Excisional arthroplasties in the form a Keller–Brandes, with excision of the basal half of the proximal phalanx, or a Mayo, with excision of the metatarsal head, have been used as a salvage for severe deformity with poor tissue quality, such as in rheumatoid arthritis. These procedures can lead to poor outcomes as they defunction the first ray, risking the development of transfer lesions to the lesser rays. They have largely been abandoned.


An algorithm for surgical decision making is shown in Table 6.3.




Table 6.3 An algorithm for surgical decision making in hallux valgus surgery





















Mild DSTR + distal or shaft osteotomy +/– Akin
Moderate DSTR + shaft osteotomy +/– Akin
Severe: Systemic disease – first MTPJ fusion
No systemic disease – DSTR + shaft or basal osteotomy +/– Akin
Very severe First MTPJ or TMTJ fusion


DSTR: distal soft tissue release.



Complications

The complications of hallux valgus surgery are commonly related to technical failure. It is important that the surgery is well planned, and the principles adhered to. Selection of the osteotomy is important.




  • If the first metatarsal is excessively shortened or elevated there is a risk that the lesser rays will be overloaded, and the patients develop painful callosities under the lesser metatarsal heads. In time the lesser toes will deform.



  • Stiffness can be a result of failure to shorten the first metatarsal and decompress the first MTP joint.



  • Recurrence of the hallux valgus may be the result of a failure of correction, or choosing a procedure of limited corrective power.



  • Hallux varus is usually resultant on being overly aggressive with corrective components – in particular the lateral release.


Avascular necrosis of the first metatarsal head has been reported, in particular with a chevron osteotomy. The blood supply of the metatarsal head has been well described8. On the lateral side, there are both dorsal and plantar networks of vessels from the continuation of the dorsalis pedis artery. They supply the metatarsal head via the capsule. Probably most important is the plantar plexus of vessels, which enter the head just proximal to the capsule. There is also a nutrient artery to the metatarsal shaft. Avascular necrosis is very rarely seen with a Scarf osteotomy, despite the routine performance of a lateral release. In a Scarf osteotomy much play is made on keeping the plantar blood supply to the metatarsal head intact. Thus we recommend keeping the inferior limb of a chevron osteotomy long, to maintain the plantar vascularity, if a lateral release is undertaken



Minimally Invasive Hallux Valgus Surgery

The advent of minimally invasive surgery in orthopedics has led to increasing numbers of correction options in hallux valgus9. The basics are similar in that a lateral release and distal osteotomy of the first metatarsal are performed. The difference is that the aims are achieved through percutaneous approaches with the use of a 2 to 3 mm diameter burr to perform the osteotomy. Large studies have been reported using various techniques. These techniques are technically demanding at the outset and, while they may become more popular, the important point to make is that one should not stray from the principles of deformity correction outlined above.



Bunionettes



Introduction


A bunionette is a deformity characterized by a prominence of the head of the fifth metatarsal. The overall incidence is difficult to determine, as many cases are asymptomatic, although they often present in joggers and Alpine skiers. The pressure of shoes causes pain from both bursitis and the formation of lateral or plantar keratoses. The female to male ratio may be as high as 9:110.


Coughlin’s classification11 is simple to use and helps to guide management (Figure 6.8). Type 1 can be due to a dumbbell-shaped head or a hypertrophied lateral condyle. Different studies show type 2 or 3 to be the most common.





Figure 6.8 The Coughlin classification of bunionettes. (From left to right) type 1: enlarged metatarsal head; type 2: lateral deviation of the metatarsal shaft; type 3: increased fourth–fifth intermetatarsal angle.



Presentation


The patient presents with pain over the lateral, dorsolateral, or plantar aspect of the fifth metatarsal head, with associated swelling and erythema. If chronic there may be a lateral or plantar lateral hyperkeratosis. The fifth toe is often medially deviated and there may be an associated claw or hammer deformity.


Pes planus is commonly associated with symptomatic bunionettes12. There are two reasons for this: firstly, the planus loads the lesser metatarsal heads; and, secondly, it leads to forefoot pronation, which causes apparent widening of the fifth metatarsal head.


The investigation of choice is an AP and lateral weightbearing plain radiograph. The AP view determines the type of deformity. As with hallux valgus the MTPJ angle and IMA are measured. The MTPJ angle is normally <14° and the IMA is <8°. The width of the metatarsal head should be <13 mm. These measurements are not as useful or reliable as they are in hallux valgus.



Treatment


Most cases are treated non-operatively with comfortable shoes to accommodate the toes. Padding can be used to relieve pressure. Hyperkeratoses can be trimmed. Orthoses with a medial arch support to reverse forefoot pronation and a cut-out to accommodate the prominence may be helpful.


Surgical treatment is reserved for cases that are refractory to non-operative management, usually with intractable keratotic lesions. There are over 30 different procedures described. The aim of surgery is to relieve pressure by narrowing the width of the forefoot and, in some cases, elevate the metatarsal head.


Lateral condylectomy is commonly suggested for a type 1 deformity. It reduces the width of the forefoot, but just as with bunionectomy for hallux valgus, the recurrence rate is high and there is an incidence of medial subluxation of the MTPJ. We do not recommend this procedure.


Resection of the entire head and increasing amounts of the shaft have been suggested for salvage, in conditions such as rheumatoid arthritis and infection with ulceration. Unfortunately resection can lead to unsatisfactory biomechanics and poor function postoperatively.


We prefer osteotomy for most bunionettes requiring surgery. Type 1 and mild to moderate type 2 conditions can be treated with a distal osteotomy. A Weil osteotomy13 is an extra-articular oblique cut of the metatarsal neck from dorsal distal to plantar proximal. Although it is more commonly used to shorten the metatarsal in cases of lesser MTPJ instability, in bunionettes the osteotomy can be used to translate the head medially to realign the fifth ray14. The osteotomy can be directed “uphill” from lateral to medial to offload the metatarsal head, in cases with plantar pressure.


The limitation of the Weil osteotomy is the width of the metatarsal. A larger deformity requires a proximal osteotomy. The tenuous blood supply to the watershed area at the proximal metaphyseal/diaphyseal junction is well described15, as it is thought to inhibit the Jones fracture healing. Therefore the “proximal” osteotomy has to be more distal than its first ray equivalent. A well described option is the “oblique sliding osteotomy.” It is similar to the Ludloff for the first ray (Figure 6.6) in that is a based around an oblique cut from dorsal proximal to plantar distal. The osteotomy is rotated to achieve correction. There is a real risk of inadequate fixation due to the width of the metatarsal. This can be offset by predrilling the screw hole. There is a paucity of studies on which to base surgical management of symptomatic bunionettes.



Hallux Rigidus


Hallux rigidus is the term used to denote the stiffness associated with osteoarthritis of the first MTPJ. It is present in 2.5% of the population aged over 50 years.



Etiology


Most cases arise spontaneously, although hallux rigidus has been associated with hallux valgus interphalangeus, a flat metatarsal head, a history of trauma, and female gender. Bilateral involvement is associated with a family history. Coughlin found no association with elevatus, first-ray hypermobility, a long first metatarsal, Achilles or gastrocnemius tendon tightness, abnormal foot posture, symptomatic hallux valgus, adolescent onset, shoes, or occupation16.



History and Examination


The diagnosis is made from history, physical examination, and x-rays. There is usually a history of pain in forced dorsiflexion, such as during toe off. Non-weightbearing pain implies advanced disease.


On examination there is a reduced range of motion, particularly in dorsiflexion. It is important to note whether there is pain in the midrange on passive movement, as this has implications for treatment. Pressure areas dorsally and sometimes medially may be present as a result of osteophyte formation. The same osteophytes can cause paresthesia if they lead to pressure on the dorsal cutaneous nerve.



Imaging and Classification


Weightbearing AP, lateral, and oblique foot radiographs will show the typical changes of osteoarthritis: joint space narrowing, subchondral sclerosis, subchondral cysts, and osteophytes. In the case of a normal radiograph, an MRI may be helpful to look for early changes.


Coughlin and Shurnas classified this condition into five stages, 0 to 417, which helps to guide management (Table 6.4).


Sep 15, 2020 | Posted by in ORTHOPEDIC | Comments Off on Chapter 6 – Forefoot Pathology
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