Originally I wanted to talk about hand and wrist approaches, which is the title of this JAAOS review article. However, the first section called “Innervation” brings up some good teaching points about advanced hand and wrist anatomy.
What I learned today
First, a reminder of the sensory innervation of the hand:
Superficial branch of the radial nerve (SBRN)
- Innervates the dorsoradial hand, dorsum of thumb and index fingers, radial aspect of long finger
- Divides into a few branches that are joined by the terminal branches of the lateral antebrachial cutaneous (LABC) nerveDorsal sensory branch of the ulnar nerve (DSBUN)
- Innervates the dorsum of the small and ring fingers, and the ulnar half of the long finger
- Converges with the SBRN near the base of the third MC. “Using the third carpometacarpal (CMC) joint as a reference, a proposed site for safe surgical incision lies just proximal to the joint, between 0.6 cm radial and 2 cm ulnar to the joint.”Palmar cutaneous branch of the median nerve
- Innervates the proximal thenar eminence
- Originates 5 cm proximal to the wrist crease and travels along the ulnar aspect of FCR sheath (in contrast, palmar branches of ulnar nerve originate distal to wrist crease)
It’s interesting because I’ve frequently seen images where the dorsal ring finger had the split innervation, instead of the dorsal long finger. I wonder what the rate of anatomic variability is. I’m sure it’s been published somewhere. I’m just too lazy to look.
Moving on.
In the digits, the neurovascular bundle travels in a triangular fibrous tunnel. The tunnel is formed from the Grayson and Cleland ligaments and the flexor tendon sheath. Great, more ligaments I’ve never heard of.
The Grayson ligaments lie volar to the neurovascular bundle while the Cleland ligaments pass dorsally. The Grayson ligaments also originate from the volar flexor sheath instead of the phalanges like the Cleland ligaments. Both structures insert into the skin, helping with stability during finger motion.
I guess I might as well point out the natatory ligament too. These are relevant to Dupuytren disease, where they contribute to webspace contractures. They merge with fibers of the spiral band, lateral digital sheet, and the superficial aspect of the flexor tendon sheath.
And finally, there’s Kaplan’s cardinal line.
The proper radial digital nerve to the index finger is at risk in the area where the thenar crease and the Kaplan cardinal line intersect.
The more I learn about anatomy, the more I feel is left to learn…
Sources
Catalano LW, Zlotolow DA, Purcelli Lafer M, Weidner Z, Barron OA. Surgical exposures of the wrist and hand. J Am Acad Orthop Surg. 2012 Jan;20(1):48-57. doi: 10.5435/JAAOS-20-01-048. PMID: 22207518.
Image: Ligaments of the Fingers
Cardoso R, Szabo RM. Wrist anatomy and surgical approaches. Orthop Clin North Am. 2007 Apr;38(2):127-48, v. doi: 10.1016/j.ocl.2007.02.010. PMID: 17560397.
Kovacs E, Battafarano, DF, Mathew SD, Diamond HS. Dupuytren Contracture. Medscape https://emedicine.medscape.com/article/329414-overview#a7