Injury to the Distal Motor Branch of the Ulnar Nerve From Thumb K-Wire Fixation

Abstract

We present a complication of trapeziectomy with hematoma distraction arthroplasty for thumb carpometacarpal joint arthritis in a 61-year-old female. Shortly after Kirschner (K)-wire removal at 5.5 weeks post-operatively, the patient noted weakness with thumb adduction. Electromyography and nerve conduction studies done at 3, 5, and 14 months post-operatively showed acute axonal ulnar neuropathy affecting the deep, distal motor branch of the left hand with subsequent partial recovery of function. We postulate that insertion of 1 of the 2 K-wires resulted in a third-degree transection injury to the deep motor branch of the ulnar nerve. To our knowledge, this complication has not been previously reported. We believe it is important for surgeons performing this procedure to be aware of this potential complication as it results in a significant functional disability for the patient.

Introduction

The trapeziometacarpal joint is the most common joint in the upper extremity requiring operative intervention for debilitating osteoarthritis (OA). ¹ The prevalence of thumb carpometacarpal (CMC) joint OA can be as high as 30% in post-menopausal women. ¹ Its high prevalence has been attributed to joint laxity, which may be the result of inherently high mobility in a joint reliant on ligamentous structures (anterior oblique and dorsoradial ligaments) for stability. ² Numerous surgical treatments have been described, ³ with surgery being indicated when non-operative management fails, leaving the patient disabled due to functional impairments or pain.

The temporary use of K-wire fixation to hold the metacarpal base to length has been described in many surgical techniques to treat basal joint OA. ⁴ We report a case of neuropathy involving the deep, distal motor branch of the ulnar nerve following trapeziectomy and hematoma distraction arthroplasty. To the best of our knowledge, this complication has not been previously reported and resulted in significant morbidity.

Case Presentation

A 61-year-old right-hand dominant female presented in February 2016 with CMC arthritis of her left thumb causing pain. Radiographic images revealed pantrapezial disease (Figure 1). Osteoarthritis was present in bilateral thumb CMC joints with superimposed erosive inflammatory arthritis of the interphalangeal joints stabilized on Plaquenil and Sulfasalazine. In addition, she has hypothyroidism and reflux disease. Previous surgeries include a remote right carpal tunnel release.

Figure 1.

Preoperative posterior–anterior X-ray view of left wrist demonstrating pantrapezial osteoarthritis.

In May 2016, she underwent left trapeziectomy and hematoma arthroplasty. The trapezium was sharply dissected and excised piecemeal with a rongeur. The thumb was positioned in abduction and two .062 K-wires were driven from the base of the first metacarpal through the second metacarpal percutaneously (Figure 2). The extensor pollicis brevis tendon was then tenodesed at the base of the first metacarpal to manage the associated metacarpophalangeal joint hyperextension. No intraoperative complications were noted. She was immobilized with a thumb spica splint with the interphalangeal joint free.

Figure 2.

Posterior–anterior (A) and lateral (B) X-ray views of the left hand with 2 crossed K-wires 5.5 weeks after trapeziectomy with distraction hematoma arthroplasty.

The K-wires were removed in clinic 5.5 weeks post-operatively and she began range of motion exercises. She reported excellent pain relief. At 9.5 weeks, she reported difficulty with adduction of the left thumb. Physical examination revealed decreased muscle bulk of the first dorsal webspace. She was referred for hand therapy and electromyography (EMG) studies, which revealed evidence of an acute axonal injury, affecting the deep distal motor branch of the left ulnar nerve (involving both the first dorsal interosseous [FDI] and adductor pollicis [AdP] muscles) with active denervation and no recruitable units (Table 1). The amplitude of the left FDI was reduced at 0.5 mV, compared to 13.9 mV on the unaffected hand.

Table 1.

Summary of Nerve Conduction and Electromyography Studies of the Left Hand Performed at 3, 5, and 14 Months Post-Operatively.^a

	3 Months (Laboratory A)					5 Months (Laboratory B)					14 Months (Laboratory A)
	Amp (mV)	Recruitment	Fib	PSW	Fasc	Amp (mV)	Recruitment	Fib	PSW	Fasc	Amp (mV)	Recruitment	Fib	PSW	Fasc
FDI	0.5 (13.9)	None	3+	3+	0	3.2 (12.3)	1-2 units	3+	2+	0	6.1 (9.9)	4-5 units	0	0	0
AdP	-	None	2+	2+	0	-	Reduced	3+	3+	0	-	-	-	-	-

Abbreviations: AdP, adductor pollicis muscle; Amp, amplitude; Fasc, fasciculations; FDI, first dorsal interosseous muscle; Fib, fibrillations; PSW, positive sharp waves.

^a(n) denotes non-affected hand.

At 5 months, she was seen for a second opinion and electrodiagnostic studies were repeated. She felt an improvement symptomatically but still complained of a weak pinch. Objectively, her Medical Research Council grade was 1/5 for AdP and 2/5 for FDI. The EMG studies demonstrated a 3.2 mV amplitude of the left FDI muscle. Although demonstrating mild improvement from the 0.5 mV 2 months prior, this change may be due to inter-laboratory variability. Repeat studies did show recruitment of 1 to 2 motor units when previously there was none in FDI or AdP.

At 14 months post-operation, she demonstrated grade 3+/5 strength in her left FDI, and 3/5 in the AdP, with a positive Froment sign. ⁵ The EMG studies showed a left ulnar response to FDI with an amplitude of 6.1 mV compared to the contralateral side of 9.9 mV. It should be noted that these studies and the electrodiagnostic studies from 3 months were performed by the same physician. Subjectively, the patient has roughly 60% strength compared to the non-affected side. She works in the medical profession and is still having difficulty with movements such as using nail clippers and removing caps from needles with the affected hand.

Discussion

We were unable to find previous reports of acute injury to the deep distal motor branch of the ulnar nerve following K-wire fixation for trapeziectomy with hematoma arthroplasty. The K-wire likely injured the distal deep motor ulnar nerve just proximal to the terminal branches that innervate the transverse head of the AdP and first interossei muscles. ⁶ This terminal branch point generally traverses the second metacarpal along its midpoint. We surmise that 1 of the 2 K-wires placed to maintain reduction (Figure 2) caused direct nerve injury during insertion.

Given the mechanism and time to recovery, this case most likely demonstrates a third-degree axonal injury, as described by Sunderland and MacKinnon. ^7,8 A third-degree axonal injury is consistent with our electrodiagnostic studies showing fibrillation in the muscles supplied by the deep motor branch of the ulnar nerve (Table 1). Recovery is usually incomplete and can take an extended amount of time due to scar tissue, axonal cross-shunting at the site of injury, and hypertrophy of recovered muscle fibers. ⁸ The patient was discouraged from pursuing early nerve exploration and tendon transfer surgeries at 6 months. In this isolated case, partial recovery was seen at 14 months, and therefore, early intervention was not necessary.

Though our literature search did not yield any similar cases, injury to the deep motor branch of the ulnar nerve is a significant complication. Management of Bennett and Rolando fractures could theoretically lead to similar injury, given the typical K-wire placement for fixation, though reports were not found. We did find cases of damage to the superficial radial nerve and median nerve by K-wire transection and migration, respectively. ^9,10 Given that K-wire fixation of the thumb is a common procedure, we hypothesize that this is an underreported complication.

This case report identifies another potential complication of K-wire use for temporary stabilization after trapeziectomy. Given previous patient reported and clinical outcomes showing little to no benefit of K-wire use versus simple trapeziectomy, we question if the use of K-wires is necessary after trapeziectomy for first basal joint OA. ⁴

Conclusion

While rare, surgeons performing K-wire fixation in the thumb should be aware of possible injury to the deep motor branch of the ulnar nerve. Injury to this nerve can lead to significant functional disability.