Jan Willem Louwerens MD PhD, orthopaedic surgeon, St. Maartenskliniek, Nijmegen, NL
Huub van der Heide MD PhD, orthopaedic surgeon, Leiden University Medical Center, NL
The combination of muscle weakness, deformity and sensory neuropathy causes problems with regard to sports/running, balance/stability, walking, standing, footwear, all dependent on severity of involvement. It follows that there is no standard treatment of deformity of the foot and that treatment should be individualized.
In general, treatment should be geared towards improving stability and function and slowing down the progression of foot deformities by corrective and supportive measures. Important factors in both conservative and surgical treatment are the flexibility of the foot and the status of the muscles. Based on physical examination a rough distinction between three grades of deformity is introduced.
Non-operative treatment includes muscle stretching and exercise, night splints, ankle-foot orthotics, shoe modifications and orthopaedic shoes. The more deformity and the less motor and sensory control, the more extensive the conservative measures. It is a challenge to treat fixed equinus and unstable hindfoot varus deformity conservatively. Weight, appearance and possible inhibition of propriocepsis are negative aspects of the treatment with the, often high, orthopaedic shoes.
From a surgical point of view, a variety of soft tissue releases, tendon transfers and non-articular osteotomies have been advocated and are most useful for correction of flexible deformity. Whether these procedures restore function and help prevent or delay the need for more extensive bony procedures is a matter of scientific research. In our experience with these procedures, the patients, in general, are improved as far as posture, stability and footwear are concerned. The results concerning restoration of normal biomechanics and total function are less evident. In case of severe deformities, these are succesfully corrected using a corrective triple arthrodesis of the tarsus in combination with 1st ray osteotomy and soft tissue procedures.
1. Conservative treatment HMSN foot
According to literature it is possible to determine a neuromuscular disorder as cause of cavus deformity in 60% of the patients. Nagai et al. found in a cohort of 149 patients with bilateral cavovarus deformity, regardless of family history a probability of HMSN of 78%. This implicates that we are commonly not only treating a patient with a foot deformity, but we are treating a patient with a neuromuscular disease accompanied by a foot deformity. It is often the combination of loss of control (impaired sensory feedback), loss of muscle strength and foot deformity which impairs the patients. With progress of muscle weakness patients complain about instability, loss of balance and control. Pain is associated with the amount of deformity and is not the primary problem, although there are patients that suffer neuropathic pain. Typically, the patients at first complain about problems during walking in darkness because under these circumstances they are no longer capable of using visual substitution. Clinically this can easily be tested by asking the patient to stand or walk with the eyes closed. The combination of loss of motor control, loss of joint function, and deformity incapacitates the patient to maintain balance, firstly in the horizontal plane, and finally in the sagittal plane. With fixed equinus in the ankle joint the patient will present with recurvation at the knee. The more loss of peripheral balance the more the patient will have to maintain balance at the level of the hip joint. Wines et al. analysed 104 feet in children with HMSN and found about 70% cavovarus feet, 20% planovalgus and 10% normal; in 45% they found symmetrical involvement. In their series they only operated on cavovarus deformities and performed more soft-tissues procedures in younger children, progressing to more bony procedures in older children.
Goals of the conservative treatment are to produce as much plantigrade weightbearing as possible and to enhance control/balance.
The conservative measures are completely depended on the clinical presentation. The most important factor is the amount of flexibility. A flexible foot and deformity in no more than one plane will need minor or no conservative measures. One might prescribe a ‘low cavus insole’ and with mild flexible clawing of the toes a ‘metatarsal pad’. For practical reasons it seems sensible to distinguish between the ‘pure cavus foot’ and the ‘cavovarus foot’. Conservative measures in the first case are easier applied because the foot needs no or minor adjustments in the horizontal plane. A rigid deformity with clawtoes requires the following:
· insole that supports the arch of the foot (no correction)
· metatarsal pad depending if the toes are flexible (in case of equinus this is pointless)
· plantar surface metatarsal heads cushioned
· if a metatarsal bar is prescribed in order to treat metatarsalgia then the heel must be rised
· toe space enlarged
· sufficient width and length
In the conservative treatment of the cavovarus feet, which is the case in the majority of patients, the largest group being patients with Charcot-Marie-Tooth disease, we differentiate between 3 grades.
These are the patients with a rather mild deformity and reasonable muscle control. They will present with deepening of the first ray which produces a forefoot cavus deformity. As soon as this is a fixed pronation deformity of the forefoot this will enhance varus of the hindfoot. In these patients the hindfoot is still flexible and can be corrected to a sufficient neutral position. Often the foot is broad. There will be clawing of the hallux and lesser toes.
· insole that provides enough depth for the deepened medial bal of the first ray. The forefoot will be in pronation thus the torsion around the longitudinal arch of the foot will enhance the hindfoot the be positioned in neutral.
· consider a ‘low cavus insole’ that stretches the foot.
· consider metatarsal pad
· concealed rocker bar (placed slightly back)
· reinforced heel counter (extended lateral and medial)
· lateral stiffening of the shoe
· buffer heel
· shoelacing for proper fit around the hindfoot.
In these patients no full correction of the hindfoot is possible. The cavus is more pronounced and the clawtoes also. Weakness of peroneals and dorsiflexors might result in a dropfoot. The hindfoot varus can be quite unstable.
· the basics of the insole are the same as mentioned for grade 1, however, the use of a ‘low cavus insole’ is now useless and the use of a metatarsal pad may also be pointless.
· plantar surface metatarsal heads cushioned
· support counter ankle stiffener (lateral and medial)
· in case of peroneal nerve paralysis a high stiffener will be needed
· shoe bottom stiffened (at least laterally)
· consider rocker/metatarsal bar
· toe space enlarged
· sufficient width and length.
The patients in this group present with a structural pes (equino-) cavovarus. One must accept the deformity as it is. Very little passive correction ( a.o. lateral wedging under the foorfoot) can be applied or none. Goals are to keep the hindfoot and ankle in neutral as best possible.
· insole conform grade 2
· high ankle stiffener (aproximately 18 cm). This can be without or with a stiffened tongue reducing the ankle motion, respectively, yes or no.
· such a high stiffener with a peroneal spring is also called a “Berlin stiffener”.
· metatarsal bar and buffer heel.
In case of patients with sensory feedback problems it is important to realize that they need quite a period of time (3-4 weeks) to adapt to new custom made shoes. This will be the case after each adaption.
Another problem that might arise is the complaint of a patient that has received high stiffened shoes or orthotic device that he or she experiences a loss of balance. This seems to be due to the immobilisation of the ankle joint, therewith also compromising the ankle-mechanism which plays an important role for maintaining balance.
These shoes are heavy (considering the patients are paralytic) and particularly adolescents find them ‘ugly’. More and more patients consider this treatment to be poorly acceptable.
Finally, it is argued that immobilisation of the feet in these therapeutic shoes has an adverse effect. The use might cause a gradual loss of function of the lower leg muscles and loss of the motor and balance control, because the shoes take over part of these functions. Thus the patients become more depending on the shoes.
It seems very strange that although this conservative treatment has been applied for many decades, maybe even more than a century, no controlled or prospective studies to evaluate the results of these measures have been performed.
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2. Surgical treatment of the cavus foot
Checklist for decision making:
1. Has the patient been examined by the neurologist. What is the diagnosis: CMT, tethered cord, a tumor in the spinal cord, post polio, M. Friedreich, multiple sclerosis, progressive muscle disease (etc.), or can no cause be found?
2. Is the deformity flexible or not? Are we dealing with a forefoot cavus, only, or is the hindfoot varus fixed, also? Does the tarsus come back to neutral? Is the equinus correctable passively? How is the ankle function? How does the patient react when the Coleman lateral blocktest is applied (Paulos et al. 1980; Azmaipairashvili 2005)? Are the claw toes flexible, yes or no?
3. Do deforming forces exist that can be transferred to a site where they can augment paralysed muscles? How strong are these muscles? Will the patient gain or loose by transfer of this muscle-tendon(s)? Do not forget that the muscle looses a significant amount of its strength due to the transfer. On the 5 grade scale, after transposition, the muscle force lessens round 2 grades. So, transposition of a muscle with strength less than 4/5 is most often not useful, unless the goal is that the transferred tendon acts as a tenodesis (maintaining a position passively).
4. Order and examine weight-bearing AP and lateral radiographs of both the foot AND the ankle joint.
5. Treatment should be individualised. Patient (parents) expectations, age, educational level, profession, play a role together with all the findings with physical and radiographic examination.
A good review of the literature has been written by Holmes en Hansen (1993). From a biomechanical point of view it seems advisable to restore the muscular imbalance in an earlier stage of the disease (Roper en Tibrewal, 1989). However, as long strong scientific evidence is still lacking our advice will be based on empirical/ more or less personal experience.
Soft tissue procedures
(1) A Steindler release of the fascia plantaris is a procedure long time propagated. It might be the first step for a still flexible deepened first ray. However, in this stage of the disease no or conservative treatment is sufficient. As soon as the forefoot cavus is not correctable the deformity in case of HMSN is predominantly caused by deepening of the first ray and not as much in the lesser rays. A cavovarus results. In these cases, when chosen for operative treatment, a basal dorsiflexing wedge osteotomy of MT1 and is necessary claw hallux correction will suffice. There is NO need to combine this with a fasciotomy.
(2) Transfer of the peroneus longus tendon to the peroneus brevis tendon eliminates the deforming plantarflexing force on the base of the first metatarsal and augments eversion strength.
(3) Transfer of the long toe (hallux and lesser rays) extensor-tendons to the peroneus tertius eliminates deforming force on the toes (stops recruitment) and augments dorsiflexion and eversion of the foot. The EHL can be placed on to the anterior tibial tendon and EDL on peroneus tertius.
(4) Hereafter, in case of (progressive) clawing of the toes one will have to transfer the toe flexors to the dorsum of the proximal phalanx (the extensor) in order to correct the deformity and establish muscle balance. In severe cases and in elderly the flexor tendons are simply severed. In case of extension contracture in the MP joints the extensor digitorum brevis tendons are cut and transfered to the distal ends of the extensor digitorum longus tendons (after 3) together with capsulotomy of the MTP joints. The MTP joints are released and in case the plantar fatpad has been dislocated a complete release of all soft tissues (volar plate and capsule) which have become attached to the metatarsal heads is indicated. Repositioning of the plantar fat pad in it’s original position under the metatarsal head is essential in treating the metatarsalgia which is caused by clawing of the toes with contracture at the MTP joints. This is analogues to the situation in the treatment of claw toe deformity in patients with Rheumatoid arthritis (van der Heide and Louwerens 2010). PIP fusion or resection are performed correcting the positon of the small toes and by shortening of the toes reposition at the MTP joints is facilitated.
(5) In case of fixed flexion deformity at the IP joint of the hallux an IP fusion is performed. When the IP joint is flexible transfer of the flexor hallucis longus tendon to the base of the proximal phalanx can be considered.
(6) Lengthening of Tendon Achilles in case of fixed equinus (and often the varus tendency increases due to this position). Watch out in cases with severe paralysis (loss of strength of the upper leg muscles) not to eliminate the only still remaining force that helps the patient to stand.
(7) Consider transfer of tibialis posterior to the foot-dorsiflexors in case of a flexible varus deformity + strong deforming tibialis posterior function + loss/severe weakness of dorsifexion strength. If the tarsus has a fixed varus deformity + strong deforming PTT + dropfoot, then the transfer can be combined with triple arthrodesis. Be aware of collaps of the medial arc in patients with valgus tendency and severe loss of muscle strength. Wagenaar and Louwerens (2007) described a technique in which the transferred posterior tibial tendon can be inserted proximal to the extensor retinaculum, which makes the transfer easier with comparable results. There is a tendency to advise transfer of the PTT in near all cases operated on in our clinic.
(8) Consider, in a flexible foot, transfer of tibialis anterior (split) in case of loss of eversion strength and varus tendency in the non weight bearing phase of walking. However the muscle must be strong (which is not the case in most HMSN patients).
(1) Dorsiflexing dorsal wedge osteotomy (OT) in case of fixed deepened first ray. Take care not to cause a transfer metatarsalgia under the second ray.
(2) When a mild varus of the hindfoot persists after correction of the forefoot cavus one should consider a Dwyer OT of the calcaneum.
(3) The above-mentioned procedures are combined with soft tissue procedures when appropriate.
(4) In case of a pure cavus deformity due to a very steep calcaneus (high calcaneal pitch) one might consider a Samilson-type OT of the calcaneus. Extensive release at the plantar aspect of the calcaneus is necessary in order to move the tuber calcaneus upwards. In my opinion this procedure is contraindicated in case of varus deformity, because with lowering of the arch the already existing increase of pressure along the lateral aspect of the foot will tend to increase even more.
(5) Triple arthrodesis remains a very powerful method to correct and stabilise the hindfoot. Two incision technique is advised in order to achieve a correct reposition of the foot in relation to the talus. Using the correct technique (see: triple arthrodesis operative method) this can be done with no or minor resection of bone. The talus is moved as medially as possible and more downward, while the foot is moved in a dorsal and lateral direction in relation to the talus. When the hindfoot is realigned very often the pronation results in further deepening of the first ray. Therefore, particularly in all HMSN patients, the triple arthrodesis is very often combined with dorsiflexing OT of MT1. Of course often soft tissue (particularly ATL and PTT) and other procedures as described above are performed if appropriate. In case the position of the talus within the ankle mortise should be accepted as it is (degenerative ankle joint in equinus position) or there is severe cavus then this technique is supplemented with Lambrinudi type bony wedge excision.
(6) In case of severe cavus, without varus deformity (for instance post polio), the apex of the curve is often oriented just distally from Chopart’s line. A correction is then performed by removing a dorsal wedge of bone (Cole OT).
(7) With the apex even more distally one might consider OT in the midfoot/ at the base of the metatarsal bones (Japas OT). In my experience this procedure is difficult because it is not easy to perform the osteotomies such wise that the metatarsal heads remain in the same level.
Results of surgical management
As for the conservative management, literature about the results of surgical intervention are sparse. Johnson et al. described only a small case series with 3 patients, they showed that patients had an improved function, a plantigrade foot and decreased pain. Most articles combine different diseases or have a short follow up. Leeuwesteijn et al. (2010) described a series of 33 patients with a flexible cavovarus foot, all due to HMSN, treated surgically, 80 to 90 percent of all patients were satisfied and were able to walk barefeet. The follow-up ranged form 1 to more then 10 years and the mean age at the time of operation was 28 years, but a substantial amount were adolescents.
Between 1997 and 2007, in the St Maartenskliniek triple arthrodesis was performed on 31 patients suffering of foot deformity as a result of HMSN (Leeuwesteijn et al. 2009). The validated Foot Function Index (FFI) (range 100-0, best score 0) was used to measure pain and impairment prospectively. Evaluation consisted of physical examination with assessment of early and late complications. The AOFAS-score, VAS-score for patients’ satisfaction and a QUOTE (Quality Of care Through the patients’ Eyes) questionnaire were used retrospectively. Mean follow-up time was 4.4 years. The FFI-score for pain improved from a mean 30.4% to a mean 16.7% (p=0.001). The lower the score the better. The mean score for disability did not improve; 20 patients significantly improved in function, however 11 patients significantly worsened. Mean postoperative AOFAS score was 74 points (range 48-94, best score 94 points). According to the QUOTE questionnaire, 77% of the patients was satisfied about the correction of the deformity, 63% could walk barefoot again and pressure callosities diminished in 84%. Mean patients’ overall satisfaction (VAS-scale) was 80%. Triple arthrodesis offers pain reduction with high patients’ satisfaction in these patients. Correction of foot deformity seems to have no certain effect with regard to improvement of function. Function is probably more related to the severity of the CMT.
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