A 45-year-old right-handed woman presented with bilateral numbness within her median innervated areas of both hands. She had been diagnosed with bilateral carpal tunnel syndrome (CTS) a year prior to the visit, with positive nerve conduction studies and clinical examinations indicating CTS of a moderate degree on her right side and lesser degree on her left side. She subsequently underwent endoscopic carpal tunnel release (ECTR) of her right hand. Postoperatively, she has experienced a reduction in the nocturnal paresthesias of her right hand, but 9 months after ECTR she still complains of numbness at the tips of her thumb, index, and long fingers. She holds an office job, and also owns horses and works frequently in the stables. In addition to her persistent numbness, she complains of right hand weakness and lack of endurance, both while working at the computer and during everyday chores and manual work. She still has occasional nocturnal paresthesias in her left hand. She has no history of diabetes or thyroid disease, she is normotensive, not obese, and a nonsmoker.
Since the failure rate of surgical CTS is approximately 10 to 20%, it is important to ask the following questions when investigating a patient with residual median nerve problems:
• Was the surgery done correctly (complete/incomplete release)?
• Was the diagnosis correct?
• Was the nerve healthy enough to recover from surgery?
The right hand is examined with a small transverse scar at the level of the volar wrist crease (▶Fig. 21.1). The scar is pale, has healed uneventfully, and without hyperesthesia or hyperkeratosis. There is no sweating of the skin in the palm of the hand, nor hyperemia and thus no suspected pain syndrome. There is no visible swelling over the carpal tunnel or visible wasting of the thenar muscles.
When testing the patient for possible residual CTS, Tinel’s test was negative over her right and operated carpal tunnel, and positive over her nonoperated left carpal tunnel. Similarly, Phalen’s and Durkan’s tests were negative on her right, operated, side but positive on her left.
Using manual muscle testing to screen for proximal median nerve involvement, she was found to be weak when testing her right flexor carpi radialis (FCR), flexor pollicis longus (FPL), and flexor digitorum communis II (FDP II; ▶Video 21.1).
Scratch collapse test (SCT) was found to be positive over the median nerve at the level of the right lacertus fibrosus (LF), with pain upon compression at the same level (▶Video 21.1).
The findings of (1) weakness of proximal median nerve innervated muscles, (2) positive SCT, and (3) pain over the median nerve at the level of the LF indicate that the patient is suffering from a proximal median nerve entrapment, so-called lacertus syndrome.
Ultrasound (US) is a valuable tool to investigate the potentially failed (or untreated) CTS. Using a transverse view and a nerve examination program, the median nerve can be readily identified proximal to the volar wrist crease.
The patient had a normal median nerve US appearance on the operated right side, with a slightly elliptical nerve without hyperechogenicity (▶Fig. 21.2a). Contrarily, on her left side, where she has clinical symptoms of CTS, the median nerve was found to be enlarged in diameter and cross-sectional area, as well as hyperechogenic, indicating endoneurial edema (▶Fig. 21.2b).
Fig. 21.1 General appearance of the hand. Arrow points to the scar from the endoscopic carpal tunnel release.
Fig. 21.2 (a) Transverse ultrasound view of the carpal tunnel, showing the median nerve with a normal appearance and a diameter of 0.52 cm. (b) Ultrasound appearance in the same patient, symptomatic carpal tunnel. Note the hyperechogenicity of the median nerve as well as increased diameter, 0.63 cm.
Fig. 21.3 Anatomy of proximal median nerve entrapments. (a) In the lacertus syndrome, an entrapment of the median nerve occurs at the level of the lacertus fibrosus, resulting in weakness in the flexor carpi radials, flexor pollicis longs and the deep flexor of the index finger. During surgery, the lacertus should be completely transected. (b) In the event of a concomitant superficialis syndrome, the median nerve is additionally compressed at the arch of the flexor digitorum superficialis (FDS) with resulting weakness in the FDS IV and sometimes paresthesias in the median nerve distribution in the hand. In this instance, a release of the FDS arch also needs to be completed during surgery.