Expert Pearls For Treating Charcot-Marie-Tooth Disease
In examining the anterior muscle group, we noted +3/5 of the tibialis anterior and +5/5 of the extensor digitorum longus (EDL). The tibialis posterior, flexor digitorum longus and flexor hallucis longus were all +5/5. The exam of the affected foot revealed a rigidly plantarflexed first metatarsal lower than the heel. The other metatarsals with the ankle at 90 degrees were level to the heel. When we performed the Coleman block test, we noted that with the first metatarsal dropped out, the heel remained in a fixed varus position (see Figure 4).
We sent the patient to a neurologist, who confirmed the presumptive diagnosis of CMT HSN1. The EMG and NCV were consistent with demyelination and slow nerve conduction velocities. Preoperative radiographs indicated bisection of Meary’s angle at the first metatarsal medial cuneiform joint, indicating an anterior cavus variety with a visible bullet hole sign at the sinus tarsi. The dorsalis pedis view revealed a decrease of the talo-calcaneal angle along with metatarsus adductus (see Figure 5).
Pertinent Insights On The Stepwise Surgical Approach
Conservative care consisted of the use of high top boots. However, given the pattern of weakness and progression of deformity, we deemed it prudent to stabilize the peritalar complex via surgical intervention.
We employed a stepwise surgical approach. First, we performed a gastrocnemius recession to address the equinus contracture (see Figure 6). In the past, surgeons believed that posterior group lengthening with a cavus foot increased the deformity by allowing increased calcaneal declination. The current thinking is that with a tight posterior muscle group, the forefoot equinus is more pronounced. Achilles contracture further enhances varus stress secondary to a plantarflexed first ray and inverted heel alignment.4
We proceeded to address the rearfoot. A Coleman block test revealed a failure of the heel to come to a vertical position with the first metatarsal dropped out, indicating a rigid deformity. We addressed this with a Dwyer osteotomy and lateral translation (see Figure 7).
One would address the forefoot last. If there is no residual deformity, you don't need to do anything. When there is residual deformity, the surgeon can perform a peronus longus to peronus brevis transfer (see Figure 8). If continued plantarflexion persists, we advise a dorsiflexory wedge osteotomy of the first metatarsal, which we did in this case (see Figure 8). We then corrected the hallux malleus with an interphalangeal arthrodesis (see Figure 9). Realignment also helps relieve plantarflexion stress off the first metatarsal at the metatarsophalangeal level.
The management of cavus foot deformities secondary to Charcot Marie Tooth disease is complex and can be challenging. Understanding the etiology of the cavus foot, as well as the severity and rate of progression, is critical in determining the most effective surgical technique. Being a multiplanar musculoskeletal deformity, this condition requires a step-by-step surgical approach in order to address each component of the deformity (see Figure 10). The objectives of the surgery are to correct orthopedic deformities and stabilize and rebalance the muscles around the foot and ankle, ultimately providing pain relief with a more functional limb.