HandLab Clinical Pearls

June 2021 No. 68

A Simplified Approach to Neuromuscular Reeducation After CMC Joint Arthroplasty

Karol S. Young OTD, OTR/L, CHT

 

Neuromuscular reeducation to improve movement patterns, coordination, and kinesthetic sense requires focused active exercise. To be effective such exercises must be executed correctly and repeated long enough to create lasting change in the motor cortex. The longer the maladapted motor pattern has been established, the more time and repetition is required for long-lasting change.

Therapy referrals following carpometacarpal (CMC) joint arthroplasty rarely include neuromuscular reeducation. When bony changes such as subluxation/dislocation of the thumb CMC joint have prevented a normal movement pattern, reconstructive surgery can restore the mechanical integrity, but changing the motor pattern must be part of the post-operative focus to obtain the ideal outcome.(1)

It is assumed by most that such motor reeducation must occur with active motion outside of an orthosis. This is an accurate assumption for those orthoses which immobilize the thumb CMC joint, but an orthosis that uses thenar muscle contraction to increase the pressure within the constraining, snugly fitting orthosis to stabilize the CMC joint is the ideal training environment. Because muscle action is essential, the orthosis becomes an integral part of the neuromuscular reeducation: it positions the thumb in the ideal posture so only the desired functional movement can occur. This means that every active motion within the orthosis becomes beneficial muscle reeducation.

Susan is a practical example of the use of neuromuscular reeducation following CMC arthroplasty, although she was referred to therapy later than ideal.

She was seen in therapy three weeks after surgery, having been fitted elsewhere with a custom orthosis for full time immobilization of the wrist and thumb CMC and metacarpophalangeal (MP) joints. Unfortunately, the orthosis held the thumb MP joint in hyperextension and the entire thumb in adduction. This custom orthosis was replaced with a Push® MetaGrip® orthosis to place the thumb CMC joint in the desirable posture of palmar abduction and extension, while allowing full wrist and thumb IP and MP joint motion.

Susan’s therapy referral included an additional week of immobilization. Although she could move her thumb CMC joint within a small mid-range while in the MetaGrip, this met the goal of continuing to protect the surgical reconstruction. Within the MetaGrip she could immediately use her thenar muscles to stabilize the CMC joint in the ideal posture (dynamic stabilization), thus beginning muscle retraining. (Although Susan was seen three weeks after surgery, patients who are referred earlier can be fitted with the orthosis as soon as the wound is stabilized, starting the muscle retraining while also protecting the reconstruction.)

While wearing the MetaGrip, Susan actively hyperextended her thumb MP joint (Image 1A). This was undoubtedly part of her pre-surgery motion pattern as she stated hyperextension had long been present prior to her surgery. A small dorsal thermoplastic block was custom molded to fit proximally under the MetaGrip and distally to extend over the proximal phalanx to block the MP joint in slight flexion and yet allow full MP and IP flexion. See Image 1B.

Figure 1A: Thumb MP hyperextension without blocking
Figure 1B: With dorsal block

Per the physician’s referral, at four weeks post-surgery active thumb flexion, extension, and opposition were begun out of the orthosis. But Susan was unable to complete these exercises without MP joint hyperextension, which in turn contributed to undesirable first metacarpal adduction. To ensure the exercises were done accurately, she performed them in the orthosis. Although this limited the range of motion of the CMC joint, it allowed the recruitment of the accurate muscles while the CMC joint was stabilized in mid-position. Limiting the range of motion is often desirable as this ensures maximum stability of the CMC joint.

Also beginning at four weeks, Susan began light activities of daily living such as brushing her teeth and writing while in the orthosis, and then she began performing the same activities out of the orthosis while focusing on maintaining a slightly flexed posture of the thumb MP and IP joints.

Figure 2: Performing isometric exercises with Push MetaGrip orthosis and custom fitted dorsal block.

Six weeks after surgery Susan began isometric exercises while still wearing the MetaGrip with the dorsal block. She was instructed to make a “C” with her thumb and index finger while gently transmitting force to her thumb tip with the IP and MP joints in slight flexion. A tennis ball was initially used to ensure support of the thumb (a useful cue to prevent collapse) and to provide proprioceptive feedback while performing the exercise (Figure 2). Susan progressed to doing the exercise in the orthosis without the MP block, while not allowing MP joint hyperextension. When she was able to maintain the MP flexion posture without the dorsal block, she progressed to doing the same exercises without the MetaGrip.

Figure 3: Susan’s thumb posture after neuromuscular reeducation

From 8 to 10 weeks post-surgery Susan began to wean herself from the orthosis while monitoring her thumb posture. Over the next two months she was able to maintain proper posture of her thumb during functional use of her hand, so she discontinued the orthosis. See Figure 3. She was instructed, however, to wear the MetaGrip whenever she was engaged in highly repetitive or resistive activities to protect the reconstruction from excessive forces.

Whether surgeons specifically include neuromuscular reeducation as part of their post-operative arthroplasty patient referral, we must analyze the nuances of motor function and determine how we can best focus on helping each patient regain the most stable motor pattern. We should consider use of a thumb CMC orthosis which allows active motion in the desired posture, so every active thumb motion contributes to desirable motor relearning.

 

1. Lundborg G. Brain plasticity and hand surgery: an overview. J Hand Surg Br 2000;3:242-52. doi: 10.1054/jhsb.1999.0339.

2. L. DeMott. Novel isometric exercises for the dynamic stability programs for thumb carpal metacarpal joint instability. J Hand Ther 2017;30:372-375.

 

Download Clinical Pearl No. 68, A Simplified Approach to Neuromuscular Reeducation After CMC Joint Arthroplasty, June 2021

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Disclaimer: BraceLab Clinical Pearls are intended to be an informal sharing of practical clinical ideas; not formal evidence-based conclusions of fact.

 
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