This brief communication details a simple way of avoiding the ulnar neurovascular bundle when performing an elective routine open carpal tunnel decompression. The consequences of damaging this structure are paralysis of the small muscles of the hand, ulnar paraesthesia, and possible digital ischemia. The incision used by the senior author is a modification of the standard incision [from the ulnar border of the palmaris longus toward the midpoint of the ring finger (a more ulnar position)], the purpose of which is to reduce the likelihood of damaging the superficial palmar branch of the median nerve, which can cause palmar paraesthesia and a painful scar. This study was stimulated by the observation of the senior author that, using this incision, the ulnar artery is more commonly encountered in patients with small hands. If this is a true observation, then the risk of damaging the ulnar neurovascular bundle structures can be ameliorated by moving the modified incision radially in smaller hands, thereby reducing the procedure’s overall complication rate.
Over 6 months, all patients undergoing carpal tunnel decompression under the care of the senior author had preoperative measurements taken of hand volume (measured by water displacement) and length and wrist circumference (Fig. 1). The same described incision was used in all cases. The ulnar artery was not specifically identified by dissection intraoperatively, but if it was encountered in the process of dividing the subcutaneous fat and palmar ligament, then this fact was recorded.
Thirty patients (39 hands) took part. In 29 hands, the ulnar artery was not encountered and in 10 hands it was. The hands in which the ulnar artery were encountered were found to have, on average, wrist circumference/hand length ratios above 0.95; those hands in which it was not encountered had ratios, on average, below 0.95. This association achieved statistical significance (p < 0.0003).
In conclusion, the likelihood of encountering the ulnar neurovascular bundle in routine carpal tunnel decompression using the described incision can be determined by simply measuring the wrist circumference and hand length and calculating their ratio. Therefore, for trainees new to this procedure, we recommend using the described incision to avoid damaging the superficial palmar branch of the median nerve, except in instances where the patient has a wrist circumference/hand length ratio above 0.95. In these cases, the incision should be moved about 3 to 5 mm radially to reduce the risk of damage to the ulnar neurovascular bundle.
Richard H. J. Baker, M.R.C.S.
Katherine Gill, M.R.C.S.
Paul A Davey, F.R.C.S.(Orth.)
Department of Orthopaedics
Middlesex, United Kingdom
The authors declare no financial or other conflicts of interest.
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