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Dorsoradial forearm and hand pain was historically considered difficult to treat surgically due to a particular susceptibility of the radial sensory nerve (RSN) to injury and/or compression. A nerve block, if it were done at all, was directed at the region of the anatomic snuff box to block the RSN in an effort to provide diagnostic information as to the pain etiology. Even for patients with pain relief following a diagnostic block, resecting the RSN often proved unsuccessful in fully relieving pain. The solution to successful treatment of this refractory pain problem was the realization that the RSN is not the sole source of sensory innervation to the dorsoradial wrist. In fact, in 75% of people the lateral antebrachial cutaneous nerve (LABCN) dermatome overlaps the RSN with other nerves, such as the dorsal ulnar cutaneous nerve and even the posterior antebrachial cutaneous nerves, occasionally providing sensory innervation to the same area. With this more refined understanding of the cutaneous neuroanatomy of the wrist, the diagnostic nerve block algorithm was expanded to include selective blockage of more than just the RSN. In contemporary practice, identification of the exact nerves responsible for pain signal generation informs surgical decision-making for palliative neurolysis or neurectomy. This approach offers a systematic and repeatable method to inform the diagnosis and treatment of dorsoradial forearm and wrist pain.
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Disclosures for this Article
Dawn M. LaPorte, MD, has no relevant conflicts of interest to disclose.
All authors of this journal-based CME activity have no relevant conflicts of interest to disclose. In the printed or PDF version of this article, author affiliations can be found at the bottom of the first page.
Dawn M. LaPorte, MD, has no relevant conflicts of interest to disclose. The editorial and education staff involved with this journal-based CME activity has no relevant conflicts of interest to disclose.
Upon completion of this CME activity, the learner will understand:
The nerve anatomy and differential diagnosis for dorsal radial forearm and hand pain.
The indications and technique for nerve blocks to identify the peripheral nerve source for dorsal radial wrist pain.
Treatment options and surgical technique for addressing dorsal radial cutaneous pain.
Deadline: Each examination purchased in 2021 must be completed by January 31, 2022, to be eligible for CME. A certificate will be issued upon completion of the activity. Estimated time to complete each JHS CME activity is up to one hour.
Entering hand surgery in 1978, as the senior author (A.L.D.) did, it was clear that dorsoradial forearm and wrist pain was a recurring problem. The leaders in the field, including Presidents of the American Society for Surgery of the Hand and directors of major hand surgery training centers around the world, reported cutaneous pain from injury to the RSN as a vexing clinical issue with inconsistent outcomes from surgical treatment.
It appeared this susceptibility of the RSN to injury and the subsequent difficulty with operative intervention was due to the nerve’s fixation as it exited the deep fascia binding the brachioradialis (BR) tendon to the extensor carpi radialis longus. This proximal binding limited the RSN’s excursion with ulnar wrist flexion, which is the cause of the pain that Wartenberg
Surgeons interpreted this anatomic reality to imply that whatever surgical treatment was applied to an injured RSN, a neurolysis in the forearm also would be required.
Once it became clear that a neuroma sent spontaneous pain signals and that the neuroma must be resected, it then was demonstrated that implanting the proximal end of the nerve into an adjacent muscle would prevent neuroma formation in a nonhuman primate model.
The notion that a transected nerve ending required special handling in local tissue provided surgeons a crucial technical advancement.
The final piece to the dorsoradial cutaneous pain puzzle was the realization that resecting a painful RSN neuroma was failing to give relief because another, overlapping nerve was still present, and it too was injured. This nerve was shown to be the LABCN in most cases.
By dissecting 53 cadavers and making observations in 41 patients, it was demonstrated that 75% of people have either partial or complete overlap of the LABCN and the RSN. Recently, these observations have been confirmed and other nerves, such as the dorsal ulnar cutaneous nerve, have been implicated as well.
Using this knowledge of anatomy, an improved strategy consisting of differential nerve blocks followed by muscular implantation of the RSN, LABCN, or both was developed. A small retrospective cohort of patients was reported in 1986 as part of a larger series that included other nerves as well.
There were 11 patients that had just the RSN involved and 15 that required both nerves to be removed; 88% of patients reported good to excellent relief of pain at a mean of 33 months after surgery. In 1987, a larger, retrospective cohort of 52 patients found that 12 patients had just the RSN as the source of pain, 3 had just the LABCN as the source of pain, and 37 had both nerves involved.
In the first of these reports, which studied 51 patients, only 5 reported good subjective improvement of pain after surgery. Seven patients reported an unchanged status after surgery, and in 1 case the pain was even worse after the surgical intervention.
Neither of these 2 reports included resecting the LABCN as part of the first surgical approach to their patients. Therefore, it would seem appropriate to review the technical details that give the highest chance of relieving a patient of their dorsoradial cutaneous pain.
The RSN’s origin from the radial nerve in the forearm is consistent, occurring at the division of the posterior interosseous nerve. The RSN then travels deep to the BR muscle, exiting through the fascia that joins the brachioradialis tendon to the tendon of the extensor carpi radialis longus, which is the site of common entrapment of the RSN.
classical description, in 1918, based upon 1,000 cadaver dissections, is the basis for the common description of the RSN innervating from the thumb dorsum to the radial side of the ring finger dorsally, with the rest of the dorsum being supplied by the dorsal cutaneous branch of the ulnar nerve. In the next year, Learmonth
The LABCN’s origin from the musculocutaneous nerve is constant, and it exits laterally from its passage between the biceps brachii and the brachialis. The LABCN travels beneath the lacertus fibrosus to enter the forearm adjacent to the cephalic vein, and may have a proximal division as it continues into the forearm as 2 separate nerves.
There are 3 distinct aspects to doing a nerve block to identify the peripheral nerve source of a painful scar or skin territory (Table 1). This is crucial for accurately diagnosing neuropathic dorsoradial wrist pain.
Table 1Technical Points for Successful Surgical Treatment of Dorsoradial Cutaneous Pain
Block the RSN over the dorsoradial forearm just volar to BR insertion, at the Tinel sign.
Block the LABCN over the volar, midforearm at the Tinel sign.
Implant each nerve in a separate tunnel in the proximal BR muscle, away from the BR tendon.
Extend the elbow at the time of nerve implantation into muscle.
Release lacertus fibrosis to prevent kinking/compression of LABCN.
Check that the palmar cutaneous branch of the median nerve is not involved in pain.
Check that the posterior cutaneous nerve of the forearm is not involved in pain.
First, this is a diagnostic block, and the patient must have pain prior to the block, preferably greater than 8 on a numerical rating scale, so that a decrease of at least 3 units can be identified. Inject 5 mL of the solution adjacent to, and not into, the nerve so that a nerve injection injury is not caused. Inject with either 1% Xylocaine (Lidocaine) or 0.5% Marcaine (Bupivacaine), with or without epinephrine. The location for the RSN is just lateral to the insertion of the BR tendon into the radius. The location for the LABCN is adjacent to the cephalic vein in the midforearm (Fig. 2).
Second, 5 minutes after the injection of the RSN, determine by moving touch which area of skin has gone numb. This should correspond with a known RSN skin territory. If nothing went numb, inject another 5 mL of anesthetic, and return in 5 minutes to repeat this skin testing.
Third, once a skin territory has become numb, assess the effect of this numbness on the patient’s perceived pain by obtaining a second numerical rating. Even if the pain reduction is greater than 5 units, if pain is still present, repeat this sequence of block steps for the LABCN.
If pain persists after a block of the RSN and the LABCN, and the pain is volar, consider the pain as coming from the palmar cutaneous branch of the median nerve. To effectively block this nerve, subcutaneously inject 5 mL at a point 5 cm proximal to the wrist and just ulnar to the palmaris longus tendon. It is common for the thumb, index, and middle fingers and half the ring finger to go numb for a while too.
If pain persists after the RSN and LABCN block and the pain is dorsal, consider the posterior cutaneous nerve of the forearm as the source of pain. To perform an isolated block of this nerve, trace a line from the lateral humeral epicondyle to the lateral intermuscular septum and identify the area 2 to 3 cm proximal to the epicondyle.
Inject local anesthetic deep to the fascia and evaluate for dorsal forearm numbness. Ultrasound guidance may be helpful to guide injection, though we find that this modality is only needed occasionally.
Finally, a note of caution: check the thumb pulp after the blocks. In some people, the RSN can innervate part of the thumb pulp. It is better to know this before resecting the RSN, as anesthesia in this area could be debilitating compared to the dorsal hand. We have never seen this variation.
In the earliest approach to treating dorsoradial cutaneous pain, distal and proximal incisions were routinely made for the purpose of identifying both the neuromas and the healthy, proximal segment of the nerves in question. This technique was thought to be necessary to insure identification of the involved nerves. More contemporary anatomical knowledge has led us to develop a single proximal incision surgical plan, which is our standard practice. If for any reason there is confusion in the forearm about finding the RSN deep to the BR or the LABCN in the forearm, then the distal incision can always be made and the distal branches identified. At that point, gentle traction will identify the proximal branches unambiguously.
Resecting the distal neuroma(s)
The necessity of resecting the neuroma if that same nerve is going to be divided proximally remains unclear experimentally or clinically. In other words, there is the possibility that collateral sprouting might reinnervate the remaining distal neuroma and permit reestablishment of a pain signal, but this has never been reported conclusively. Certainly, there can be no complaint made about excising the distal neuroma routinely, but we have not found that necessary. It is our standard practice to use intraoperative electrical stimulation to be sure the RSN is not the posterior interosseous nerve and that the palmar cutaneous branch of the median nerve is not the median nerve itself.
Implanting nerve into muscle
Implanting the proximal nerve into muscle is done in order to prevent recurrence of the neuroma. This is a time-tested method, sometimes referred to as transposing the nerve into muscle. A recent meta-analysis confirms the effectiveness of this approach in treating a peripheral neuroma in the extremity.
An error made during this implantation is to choose a site too close to the musculotendinous junction, as there is insufficient muscle bulk in this location. The nerve should be implanted proximally in the BR muscle belly, taking care not to injure the posterior interosseous nerve. The implantation site should be proximal to this motor nerve. No suturing is required. Another error is to do this portion of the surgery with the elbow flexed. The elbow must be extended. If the nerve is implanted with the elbow flexed, subsequent elbow extension may transmit a traction force upon the implanted nerve, which may either cause the nerve to pull out or be a source of recurrent pain. A final error can be made if the lacertus fibrosis is not released. The deep fascia superficial to the LABCN must be released from the forearm proximal to the antecubital fossa to prevent entrapment of the LABCN, which is a notable source of pain with elbow extension.
Other treatment approaches
There are several recently described techniques that may also be beneficial for the treatment of symptomatic neuromas and warrant discussion. The first is a new technique that offers an extension of the above-described muscular implantation of free nerve ends. Known as the vascularized, denervated muscle target and first reported by Tuffaha et al,
this option involves creation of a small, islandized muscle flap adjacent to the nerve terminus. Once the pedicled muscle flap is created, care is taken to ensure there is no component of the residual muscle’s motor innervation entering the flap. This new muscular construct is then wrapped around the nerve end, encasing it in a manner that provides the protection of the muscular implantation technique but also the benefit of enhanced direct neurotization potential, owing to the denervated nature of the muscle bulk. Another option, similar to the vascularized, denervated muscle target, is the regenerative peripheral nerve interface. First introduced by Urbanchek et al,
the regenerative peripheral nerve interface is a denervated, free-muscle graft. We do not regularly employ this technique due to the nonvascularized nature of the free-muscle graft and the consequential concern for muscle graft necrosis.
The final surgical approach to discuss is targeted motor reinnervation (TMR). Targeted motor reinnervation involves resection of the terminal neuroma and coaptation of the free nerve end to a motor nerve branch; recent high-quality studies have demonstrated a clear palliative effect.
This is not our preferred approach for 2 reasons: (1) from a technical standpoint, there is a limited quantity of expendable muscle in the distal forearm, so it may be difficult or impossible to transfer injured nerves to useful motor branches, and (2) from a more theoretical standpoint, the caliber of injured nerves at this level of the forearm is often much larger than the available motor branches with which to perform TMR, introducing the possibility of neuroma formation at the coaptation site owing to axonal escape.
A soft dressing is applied, as we have found the posterior slab dressing to be unnecessarily cumbersome and restrictive. We encourage gentle elbow range of motion and unrestricted hand use immediately after surgery. The dressing is removed on postoperative day 7 and sutures are removed on postoperative day 14.
Rehabilitation and long-term outcome
Most often, no rehabilitation is required. A substantial proportion of patients appreciate the decrease in pain immediately after surgery. There is a minority of patients who may develop allodynia at the junction of the dermatomes of the resected nerves and those persistent, unaltered nerves. This is accounted for by the physiology of the intact cutaneous nerve adjacent to the original area of pain. These nerves will be stimulated by the nerve growth factor released from the surviving Schwann cells of the distal RSN/LABCN. This will cause sprouting of the intact adjacent nerves into the denervated territory, causing it to shrink over time but also occasionally leading to allodynia.
This process goes on from about the second week to the eighth week. This can be treated by various desensitization techniques.
Dorsoradial wrist pain represents a challenging clinical entity to accurately diagnose. A systematic approach to a diagnostic workup, followed by appropriately targeted surgical treatment of affected nerves, is a reliable way to maximize the chance of successful pain relief.