Thumb Spica Splint Causing New Web Space Numbness
A 47-year-old dental hygienist with thumb carpometacarpal osteoarthritis has been fitted with a new custom-molded thumb spica splint. She wears it during hygiene appointments and at night. After two days she reports numbness and tingling over the first dorsal web space and the radial dorsum of the thumb. The symptoms began after she tightened the Velcro strap to keep the splint from slipping during a long procedure. The splint has a firm edge over the radial styloid, and the strap crosses the dorsal forearm just proximal to the wrist. There is no swelling, no color change, and no weakness. CMC grind is positive, and the thumb base is tender. She is afraid the splint is damaging the joint and wants to stop wearing it.
1. How would you evaluate the fit of the splint and distinguish radial sensory nerve compression from worsening CMC joint pain?
Read the worked answer
I would inspect and palpate the splint edges, especially over the radial styloid and the first dorsal web space, because the superficial radial nerve is vulnerable there. I would check the strap tension and ask the patient to reproduce the symptoms by tightening the strap, then release it and see whether the numbness changes. I would test light touch and two-point discrimination in the radial nerve distribution and compare with the other side. I would also assess whether the symptoms are provoked by splint wear and relieved by removal. CMC pain would be located at the thumb base, provoked by pinch, grasp, or CMC grind, and would not typically cause numbness in the web space. The new onset after strap tightening, the firm edge over the radial styloid, and the sensory distribution point to compression rather than joint deterioration. I would still document CMC tenderness and pinch pain so the two problems are not conflated.
2. What modifications would you make, and what instructions would you give before she resumes splint use?
Read the worked answer
I would relieve pressure over the radial styloid by flaring or padding the edge, reduce the strap tension, and reposition the strap so it does not cross a bony prominence or the dorsal radial sensory branch. I would check that the splint supports the CMC joint without pressing into the web space. If the splint cannot be adjusted without pressure, I would remake or choose a different prefabricated design. I would give a wear schedule with short initial trials and ask her to remove the splint if numbness returns. I would explain that the goal is immobilization of the painful CMC joint, not tight compression, and that a splint should not create new neurological symptoms. I would have her demonstrate donning and doffing and strap tightening. I would schedule a follow-up within a few days to recheck sensation and fit, and I would document the modification and her response.
3. What would make you stop splinting altogether and refer her for further evaluation?
Read the worked answer
I would stop splinting and refer if the numbness persists after the splint is removed and the pressure is relieved, if sensory loss becomes objective or spreads beyond the radial nerve distribution, or if weakness or pain out of proportion develops. Persistent symptoms would warrant surgeon or physician review to rule out a more proximal radial nerve problem or another cause. I would also refer if the CMC pain is not controlled by a well-fitted splint and an appropriate exercise program, because she may need injection, further imaging, or surgical consultation. The key distinction is between a fit problem that resolves with modification and a neurological deficit that does not. I would not keep adjusting a splint while sensory symptoms are progressive.