CHAPTER 43

Surgical Classification of theCavus Foot DeformityJobn A. Rucb, D.PM.

Historically, surgical repair of the cal,us foot defor-mity has been based on many different complicatedand confusing classification systems. Each individualexpert with an interest in the car,,us foot deformityhas attempted to make sense of the deformity fromhis own experience.

There is no single universal system for classfi-ing all car,.us deformities. Literally, each individualcalus deformity has unique components and com-binations of deformity. There are, however, cefiaingeneralities or broad groupings that can includemost of the car,.us deformities. The author willdescribe such a classification and correlate specificsurgical procedures to each category (Table 1).

Table 1

SURGICAL CI-{SSTUCAfl ONOF CAVUS DEFORMITIES

I. Mild FLE)(BLE FOREFOOT / DIGITAL-METAIARSOPHALANGEAT JOINT(anterior, global, flexible)

II. MOdCTAIC FT]NCTIONAT / BIOMECFIANICAIPlantarflexed First Metatarsal /Calcaneal Varus(anterior local-posterior)

m. Severe ADVANCED STRUCTURAI /FUNCTIONAI NEUROMUSCULARDISORDERS

Qlobal rigid, unstable)

MILD FLE)ilBLEFOREFOOT/DTGTTAL MPJ

The first or simplest category to define is a cavusfoot type where the deformity is primarilyrestricted to the metatarsaT, metatarsophalangeal,and digital segments of the foot (Fig. 1). A commondescription for this type of deformity wouldinclude the flexible forefoot equinus, where the

foot, in a resting attitude, demonstrates significantplantarflexion of the metatarsals and an associatedextension contracture of the metatarsophalangealjoints. This flexible deformity will commonlyreduce with stance or weight bearing. It is notuncommon to see this flexible forefoot equinus foottype reduced to a pes valgus foot-type with associ-ated hammefioe deformities upon weight bearing.The most comlnon complaint for this type of con-dition is metatarsalgia associated with thehypermobility and pTantar prominence of themetatarsal heads.

Figure 1. Forefoot equinus deformity with extensor contraction of thehallux and lesser digits.

As the patient ages and various levels of thedeformity become more fixed in their degree ofcontracture, severe dorsal luxation of the metalar-sophalangeal joint can occur, and may becomeresistant to reduction with weight bearing. This fixedextension contracture at the metatarsophalangealjoint is usually countered by severe contracture at

the interphalangeal joint level, and rigid, dorsallyluxated hammertoe deformities result.

Overpowering on the dorsal or extensor side

of the metatarsophalangeal joint will result in con-tracture of the extensor tendon apparatus, as wellas the extensor hood apparatus and other dorsaltissues about the metatarsophalangeal joint.

206 CHAPTER 43

Cornmon Surgical Procedures

The group of surgical procedures commonlyemployed in correction of the flexible forefootca\us deformities are focused around digital andmetatarsophalangeal joint pathology (Fig. 2A, 28),The specific procedures inciude:

1. Digital arthrodesis (hallux and lesser toe)

2. Metalarsophalangeal joint release (extensorhood release, extensor digitorum tendonlengthening)

3. Extensor tendon transfer techniques (Hibbs sus-pension, Jones suspension)

4. Biomechanical control

Figure 2A: Preoperative view- of a typical forefoot equinus deformity.

Figure 28: Postoperative view of a forefoot equinus deformity fol-lowing hallux and lesser digit interphalangeal arthrodesis, extensorhood release, and appropriate extensor tendon lengthening.

Figure l. Dorsoplantar radiograph clemonstrating ha1lux interpha-langeal joint fusion and proximal interphalangeal joint fusions ondigits 2, 3, 4 and arthroplasty with pinning of the 5th digit.

Digital Arthrodesis.The primary rationale for digital arthrodesis in theflexible forefoot cavus deformity is elimination ofthe retrograde buckling force at the level of themetatarsophalangeal joint (Fig. ,. Digitalarthrodesing procedures will correct the digitaldeformity, however, the primary mechanical influ-ence that is created on the foot is a reduction in theplantigrade pressure on the metatarsal head. Thiswill have a positive effect at reducing the forefootequinus, as well as allowing the extensor tendon tobe converted to a more effective dorsiflexor of theforefoot.

MPJ Release with Extensor Hood Release.

Long-standing forefoot equinus, although flexible,will result in progressive contracture of soft tissueson the dorsal side of the metatarsophalangeal joint.It is essential that these contractures be released inorder to accomplish an effective reduction of themetatarsophalangeal joint, and eliminate the retro-grade digital pressure on the metatarsal head.A fundamental technique employed beforerelease of dorsal metatarsophalangeal joint con-tracture includes the extensor hood release. Theexpansion fibers of the extensor hood leave theextensor tendon and progress medially and laler-ally to encase the metatarsal head and phalangealbase of the metatarsophalangeal joint. Contractureof this expansion will prevent reduction of theproximal phalanx to a plantigrade attitude or align-ment. The technique of extensor hood releaseentails a longitudinal incision along the medial andlateral aspect of the extensor tendon in order to

CHAPTER 43 207

release the extensor hood appara],lJs. The extensortendon is then mobilized and can be elevated fromthe metatarsophalangeal joint capsule. Followingthis release, a complete dorsal capsulotomy can beperformed. A sequential release of the metatarso-phalangeal joint may also include release of collateralligament structures, as well as the flexor apparatus.

Extensor Tendon Transfers: Jones TendonSuspensionThe Jones tendon suspension has been tradition-ally employed for equinus deformities of the firstmetalarsal with an associated cock-up deformity ofthe hallux. The purpose of the procedure is toeliminate the pull of the extensor hallucis longuson the hallux, and transfer its power into the firstmetatarsal in an attempt to dorsiflex the first ray.Equinus deformity of the first metatarsal and asso-ciated hallux malleus have a variety of differentetiologies. The specific cause of the deformity mustfirst be identified, and procedures should beselected to correct the specific imbalance. The

Jones suspension, in general, has been unsuccess-ful. Detachment of the extensor hallucis longustendon from the hallux, in most instances, leaves a

flail hallux which drags the ground during gait andmakes the application of socks and shoes difficultfor the patient. Arthrodesis of the interphalangeaijoint of the ha1lux is routine if the Jones suspensionis employed.

In addition, transfer of the EDL tendon intothe neck of the first metatarsal has not proven tobe an effective means for correction of the plan-tarflexed first metatarsal deformity.

In most instances, the combination deformityof flexible plantarflexed first metatarsal and halluxmalleus (cocked hallux) can be successfully cor-rected with a straight-forward arthrodesis of theinterphalangeal joint of the hallux, and appropriatehood release and metatarsophalangeal joint capsu-lotomy. If a more rigid deformity of the firstmetatarsal exists, then a dorsiflexory osteotomy is

the procedure of choice.

Extensor Tendon Transfers: Hibbs TendonSuspension

The Hibbs tendon suspension was a popular fore-foot procedure in the mid 7970s. The specific goals

of the procedure are similar to the Jones, which isto remove the deforming force of the EDL tendonson the digits, and transfer the tendons into themetatarsal region to act as a more effective dorsi-flexor of the forefoot. This procedure has fallen outof favor, as it tended to create more problems thanit corrected. Flail lesser digits, along with flexioncontractures of the distal interphalangeal joint,were common. No significant increase in dorsi-flexion of the flexible forefoot equinus wasappreciated.

The traditional PIPJ arthrodesis, along withappropriate muscle-tendon balancing on theextensor side of the joint, has been proven to bemore effective than the Hibbs tendon suspension.

MODERAIE FUNCTIONAL/BIOME CTIANI-ICAL PI-{NTARFLE)GD

FIRST METATARSAL/CALCATIEALVARUS CAVUS FOOT DEFORMITY

The next level of cavus deformity should be calledpodiatry's cavus foot. This deformity is veryfunctional in etiology and demonstrates classicpathologic biomechanics. The typical deformityconsists of a rigidly plantarflexed first metatarsaland associated varus angulation of the heel (Figs.

4A, 4B). The resultant supinatory function of thefoot produces the classic cavlts deformity with orwithout associated digital deformities.

Figure 44. Forefoot valgus created by rigid plantarflexed firstmetatarsal.

208 CHAPTER 43

Figure 48. Calcaneal varus associated with thebiomechanical car,-r:s foot deformity.

The specific etiology of this common ca\.usdisorder can include a yariet.r/ of early neurologicdisorders. The surgeon must take care to evaluatethe patient thoroughly and differentiate the idio-pathic condition or disorder from those withneuromuscular disease.

Comrnon Surgical ProceduresThe group of surgical procedures commonlyemployed in corection of the moderate category ofcar,us foot deformity include:

1. Dorsiflexory \Wedge Osteotomy, First Metatarsal

2. Dwyer Calcaneal Osteotomy

3. Functional Tendon Transfer TechniquesA. STAIT (Split Tibialis Anterior Tendon

Transfer)B. Peroneal Stop (Anastomosis)

Dorsiflexory Wedge Osteotomy (DFWO) of theFirst Metatatsal.Surgical correction of a rigidly plantarflexed firstme:;ilarsal is a relatively common procedure. Thestandard technique employed by members of thePodiatry Institute includes an oblique osteotomy withthe apex or hinge at the plantar/proximal aspect ofthe first metatarsal (Fig. 5). The osteotomy is obliqueddistaliy and flrated with one or two screws from dor-sal to plantar.

A technical pearl for fkation would include

Figure 5. Oblique dorsiflexory s.edge osteotomy of the firstmetatars2l.

the use of cortical screws. The partially threadedcancellous screw has a tendenry to glide along theinternal cofiex of the metatarsal and complicate thefixation process.

Dwyer Calcaneal OsteotomyCorrection of a rigid or tked heel varus is routineiyaccomplished with a Dwyer calcaneaT osteotomy.The technique is usually performed through a

culed lateral incision, with the calcaneal osteotomyin the mid or central portion of the posterior bodyor tuber of the calcaneus. Care must be taken toavoid violation of the subtalar joint or achilles inser-tion. Fkation is routinely performed with two lateralstaples (Fig. 6). The Coleman block test may behelpful to identify the need for the Dwyer, or torule-out those patients where there is adequateeversion range of motion within the subtalar joint.

Figure 6. Closure and fixation of a Dwyer calcaneal osteotomy.

CFIAPTER 43 209

STAff (Sptt Tibidis Anterior Tendon Transfer)Use of the split tibialis anterior tendon transferis an attempt to modify the foot attitudeduring the swing phase of gait. In many of the bio-mechanical car'.us deformities, the foot is observed inthe swing phase with a significantly adducted atti-tude. The STATT will effectively distributedorsiflexion through a yoke system or technique,and apply equal dorsiflexory power to the medialand lateral aspects of the foot. This will swing thefoot forward in a more even attitude and prepare itfor plantigrade foot contact. Elimination of excessiveadductus of the foot and/or varus at heel contact willreduce muscle compensation, which has promotedplantarflexion of the first metatarsal and heel varus.

Peroneal Stop (anastomosis)

This simple technique can decrease hyperactivity ofthe peroneus longus tendon. An overactive peroneuslongus can create a rigidly functioning plantarflexedfirst metatarsal. The peroneal stop technique is per-formed through alateral incision just proximal to thefibular malleoius. The foot is placed into a perpen-dicular attitude. The peroneus longus tendon is

pulled distally to relax tension on its muscle length,and the peroneus brevis is pulled proximally to sup-pofi the foot in a slightly evefied attitude. Thetendons are then sutured together, and create anequal balance of peroneal activity.

SEYERE ADVANCEDSTRUCTTIRAL/FLINCTIONAL

NEI]ROMUSfl-]IAR DISORDERS

The most complex and debilitating car,.urs deformitiesare grouped into this category (Fig 7). These are

severe car.rrs deformities of rearfoot and whole footinvolvement, and are usually associated with signifi-cant neuromuscular disease or imbalance. Commondisorders include Charcot-Marie-Tooth Disease, post-polio, and post-cerebrovascular accident.

Cornrnon Surgical Procedures

Triple afihrodesis is the mainstay for repair of thesesevere deformities. This surgicai procedure allowsfor realignment of severe deformity, and creation ofa stable plantigrade foot (Figs. BA, BB).

The Cole osteotomy can also be grouped in thiscategory, where the focus of the car.us defomity is

more midfoot in origin, and in cases where the rear-foot alignment is satisfactory and can be preserved.

Major tendon transfers are also commonlyemployed in these more severe deformities, andcommon procedures include the tibialis posteriortendon and peroneus longus tendon transfers.

Figure 7. Severe neurologic cal'us foot deformity

Figure 8A. Lateral radiograph of severe neurologic cal'r:s foot defor-mity, preoperative vieu'.

Figure 88. Postoperative view of same foot including triple arthrode-sis, dorsiflexory n-edge osteotomy of the first metatarsal and cligitalfusions. Other procedures included muscle tendon transfer such as

the tibialis postedor tendon transfer.