Case of the Week #8: Ankle instability secondary to Charcot-Marie-Tooth Disease
Key learning points:
1) Charcot-Marie-Tooth (CMT) disease is, in its commonest form, an autosomal dominant genetic condition. It is characterised by demyelination and slowed nerve conduction velocity of certain muscles to the lower limb, usually affecting tibialis anterior, peroneus brevis and the intrinsic muscles of the foot resulting in a high arch and clawing of the toes. 2) Podiatrists and physiotherapists are often the first opportunity for diagnosis of this condition due to the issues with foot deformity, ankle instability and gait changes. These practitioners need to be aware of the signs and symptoms of this condition and consider the family history of Charcot-Marie-Tooth disease. 3) A multidisciplinary team approach is vital to successfully manage patients with complex musculoskeletal conditions, whether or not surgery is indicated.
Master R is a 15 year old skeletally mature adolescent with Charcot-Marie-Tooth (CMT) disease, also known as Hereditary Motor Sensory Neuropathy type 1. His father and brother also have the condition, and this number of positive family members is common given its autosomal dominant inheritance pattern. Master R had extensive involvement with a podiatrist, physiotherapist and orthotist who were experienced in complex paediatric neurological conditions. Master R was overloading his lateral ray resulting in fifth metatarsal stress reaction and pain over the lateral border of his foot. Non-operative interventions attempted included repeated callous debridement and an Ankle-Foot-Orthoses (AFO) through Peninsula Orthotics. Unfortunately Master R's deformity progressed as he went through his pre-pubescent growth spurt, and he developed an ulcer to the base of the fifth metatarsal. This healed with standard wound care management, but prompted a referral to Dr Touzell to discuss surgical intervention.
On examination, the lateral ulcer was healed. Master R had a bilateral cavovarus feet consistent with CMT. His hindfoot deformity partially corrected on Coleman block testing, where a block (or in this case, the Australian Orthopaedic Association Joint Registry Summary!) is inserted under the lateral ray, leaving the base of the first metatarsal off the block. By eliminating the weight bearing properties of the first ray, it is possible to assess how much of the deformity is forefoot driven.
Coleman block testing - note how the varus left hindfoot partially corrects when the first ray is plantarflexed standing on the book.
Master R had a high-stepping gait with the left worse than the right and a subtle foot drop. He inverted his ankle as he walked due to lack of peroneus brevis and tibialis anterior control. He had mild clawing of the toes, including the hallux. He was very tender to palpation around the fifth metatarsal base, but also the cuboid and lateral heel pad. There was extensive callousity consistent with chronic overloading of the fifth metatarsal base, but no active ulceration or infection. He was tender to palpation along the length of his peroneal tendons. He was just able to get to a plantargrade ankle due to his achilles contracture and Silverskiold's test was positive. A careful neurological examination was as follows:
Ankle eversion (peroneal tendons): 4/5
Ankle dorsiflexion (tibialis anterior): 4/5
Great toe dorsiflexion (extensor hallucis longus): 5/5
Ankle plantarflexion (tibialis posterior and calf musculature): 5/5
Great toe plantarflexion (flexor hallucis longus): 5/5
Sensation to his foot was normal. He had a mildly brisk achilles tendon reflex on the left compared to the right, and normal patella tendon reflexes bilaterally. Master R also had wasting of the interossei of the hands and the thenar eminence of the thumbs consistent with Charcot-Marie-Tooth disease. Dr Touzell had a long discussion with Master R and his parents. He had really exhausted his treatment options, so the option of a flexible cavovarus foot reconstruction was discussed. This procedure is a step-wise process, aiming to gradually correct the cavovarus foot deformity with each step, and reevaluate of the appearance of the foot intra-operatively after each step of the procedure. The intra-operative decision making can be difficult as the patient is anaesthetised without the ability to assess weight bearing or muscle tension.
The surgical plan was outlined for for Master R and his parents. We discussed the steps involved in the procedure, and that intra-operatively we would constantly reassess the shape of Master V's foot to determine the effectiveness of each soft tissue or bony procedure. A tibialis posterior tendon transfer and peroneus longus to brevis transfer was performed. A valgarising heel shift osteotomy and dorsiflexion osteotomy to the first metatarsal to correct his bony malalignment was also performed to support the soft tissue reconstruction.
Master V was placed in a backslab and was non-weight bearing for six weeks after the procedure. He was able to do non-weight bearing range of motion exercises two weeks after the operation after transition to a CAM boot. He had a small amount of wound slough over the lateral wound, but this healed with three weeks of dressings and close observation in our rooms. A six-week x-ray demonstrated complete union of the calcaneal and first metatarsal osteotomy sites with good correction of his varus and cavus (see x-ray below).
Master V was permitted to weight bear as tolerated in a CAM boot for a further six weeks. Clinical review twelve weeks post-operatively demonstrated excellent clinical correction (pre-operative picture on the left, post-operative picture on the right).
Six months post surgery, Master R is no longer using his orthotic or Ankle-Foot Orthosis and is back to walking without pain or development of callousities or ulcers. He is even to play casual soccer with his friends and has done some bushwalking without pain or instability.
We also felt the family had not utilised all the services that was available to Master R and made a successful application to NDIS for hand therapy given his progressive loss of fine motor function and appropriate footwear. Master R also felt self-conscious about his condition and difficulty keeping up with his peers. A referral for counselling was made to help give Master R some strategies to build resilience and help him mentally was also successful.
This case highlights the importance of a multi-disciplinary approach to management of chronic musculoskeletal conditions. Charcot-Marie-Tooth disease affects not only the feet, but the hands and entire lower limbs of severely affected patients. Our paediatric credentialed in-house podiatrist, Dr Alicia James PhD, was able to use her experience in NDIS funding applications to successfully apply for increase in funding which was then utilised by his regular podiatrist, orthotist and physiotherapist. We also have an excellent working relationship with his orthotist (Nick Muller from Peninsula Orthotics) and communicated throughout Master R's post-operative journey about adjustments required to accomodate the changing nature of Master R's gait pattern and foot shape. Communication between his physiotherapist and Dr Touzell meant his response to surgery and tendon transfers could be carefully monitored. Finally, we engaged his General Practitioner to help coordinate care and continue to support the rest of his family.