Abstract
Background There has been an increasing utilization of end-to-end (ETE) and reverse “supercharged” end-to-side (SETS) anterior interosseous nerve (AIN) to ulnar nerve transfers (NTs) for treatment of high ulnar nerve injury. This study aimed to review the potential indications for, and outcomes of, ETE and SETS AIN–ulnar NT.
Methods A literature review was performed, and 10 articles with 156 patients who had sufficient follow-up to evaluate functional outcomes were included. English studies were included if they reported the outcome of patients with ulnar nerve injuries treated with AIN to ulnar motor NT. Outcomes were analyzed based on the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire scores, grip and key pinch strength, and interosseous Medical Research Council–graded motor strength. Comparisons were made using the independent t -test and the chi-square test. No nerve graft control group was required for eligibility. Ulnar nerve injury types varied.
Results NT resulted in 77% of patients achieving M3+ recovery, 53.7 ± 19.8 lb grip strength recovery, 61 ± 21% key pinch recovery, and a mean DASH score of 33.4 ± 16. In this diverse group, NT resulted in significantly greater M3+ recovery and grip strength recovery measured in pounds than in the nerve graft/conventional treatment group, and ETE repairs had significantly better outcomes compared with SETS repairs for grip strength, key pinch strength, and DASH scores, but heterogeneity limits interpretation.
Conclusion ETE and SETS AIN–ulnar NTs produce significant restoration of ulnar nerve motor function for high ulnar nerve injuries. For ulnar nerve transection injuries at or above the elbow, ETE NT results in superior motor recovery compared with nerve grafting/conventional repair. However, further research is needed to determine the best treatment for other types of ulnar nerve injury and the role of SETS NT.
Keywords: anterior interosseous nerve, ulnar nerve, ulnar nerve injury, nerve transfer
Introduction
Ulnar nerve injury at any level can cause significant motor and sensory dysfunction. The resulting motor weakness can leave patients with claw deformities of the fourth and fifth fingers and diminished grip and pinch strength. 1 2 3 4 In an early study of ulnar nerve injury and repair, Gaul 5 found that grip strength is typically reduced to 10 to 50% of normal power and key pinch strength may be reduced to 20 to 50% of normal power after injury. Additionally, though motor function of the hand is more important than sensory function for quality of life, motor recovery is less reliable due to progressive motor endplate loss and muscular atrophy, 6 even despite early and well-performed microsurgical nerve repair. 6 7
Current ulnar nerve repair strategies include primary microsurgical repair, conduit-assisted repair, or reconstruction with an autograft or allograft. If the injury occurs around the level of the elbow, then transposition should be considered to minimize tension on the repair. However, proximal nerve repair and/or graft reconstructions are typically unpredictable 8 and have demonstrated consistently limited outcomes. 3 5 A study by Vastamäki et al 8 found that only 57 of 110 patients (51.8%) had clinically meaningful recovery, and the authors concluded that there was no benefit in ulnar nerve repair if the patient was older than 46 years, if the injury was more than 60 cm proximal from the middle finger tip, and if the graft was more than 7.5 cm in length. Subsequently, the traditional alternative to primary repair or reconstruction of high ulnar nerve lesions has been tendon transfers. 4 9 However, an alternative nerve reconstruction option that has been introduced is nerve transfers (NTs).
The benefit of NTs for high ulnar nerve lesions is that they allow for motor recovery prior to motor endplate loss and muscular atrophy. Two anterior interosseous nerve (AIN) NT methods have been introduced to reinnervate ulnar innervated intrinsic hand muscles. “End-to-end” (ETE) transfers require complete transection of the ulnar nerve motor fascicles, eliminating the possibility of recovering axons reaching the hand musculature, but they reproduce normal nerve continuity. In “supercharged end-to-side” (SETS) transfers, the end of the ulnar nerve is left intact and the terminal branch of the AIN is coapted to an epineural window in the motor fascicular group of the ulnar nerve distal to the nerve injury to augment nerve recovery. 10 11
Despite the potential of NTs for high ulnar nerve lesions, only limited studies of small sample sizes are currently available. Moreover, whether ETE or SETS is superior to the other is also not well understood. Therefore, a systematic review was undertaken to assess the effectiveness of ETE and SETS NT for the management of high ulnar nerve lesions.
Methods
Literature Search
A systematic search on PubMed and Ovid/Embase was conducted. The search was designed to identify all studies that investigated the outcomes of AIN–ulnar motor transfers in the context of ulnar neuropathy or ulnar nerve injury. Medical Subject Headings (MeSH) were used when possible. The search was conducted and completed on November 4, 2020, and there were no restrictions on publication date. Table 1 shows the search strategy used for each database.
Table 1. Systematic search strategies for PubMed, Ovid, and Embase.
| PubMed; Embase | Ovid (your journals@Ovid, journals@Ovid full text) |
|---|---|
| 1. Anterior interosseous nerve or AIN | 1. Anterior interosseous nerve or AIN |
| 2. Ulnar nerve or ulnar motor nerve | 2. Ulnar nerve or ulnar motor nerve |
| 3. Transfer or nerve transfer | 3. Transfer or nerve transfer |
| 4. Ulnar neuropathies or ulnar nerve paralysis | 4. Ulnar neuropathies or ulnar nerve paralysis |
| 5. Outcome or treatment or function or motor or clinical | 5. Outcome or treatment or function or motor or clinical |
| 6. 1 and 2 and 3 and 4 and 5 | 6. 1 and 2 and 3 and 4 and 5 |
| 7. Original articles and humans and remove duplicates (select for abstract) | |
| 8. 6 and 7 |
Study Selection and Eligibility
The Cochran's Collaboration PICOS (population, intervention, comparison, outcome, study design) method was used to define eligibility. English studies were included in this study if they reported the outcome of patients with ulnar nerve injuries (population) treated with AIN to ulnar motor NT (intervention). No nerve graft control group was required for eligibility.
Data Extraction
Studies were screened for the following demographics: age (years), injury type, and location. Preoperative functional measurements included Disabilities of the Arm, Shoulder, and Hand (DASH) score, grip strength (pound, kilogram, or percentage of unaffected side), key pinch (pound, kilogram, or percentage of unaffected side), presence of interosseous atrophy, and interosseous motor Medical Research Council (MRC) grade. Time between injury/onset of symptoms and surgery (preoperative time) and time from surgery to last recorded visit (follow-up time) were recorded. Postoperative measurements included DASH score, grip strength, key pinch, and interosseous motor MRC grade. Comparisons were made using the independent t -test and the chi-square test.
Results
Study Selection
Screening for eligibility and inclusion for analysis is shown by a Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram ( Fig. 1 ). The systematic literature search identified 192 articles; 10 additional articles were identified after reviewing their references, and 68 articles were removed as duplicates such that 134 unique articles remained. After further screening, 32 articles were eligible for full-text assessment. Ultimately, a total of 10 articles met inclusion criteria for qualitative analysis.
Fig. 1.
Flow diagram illustrating method of identifying articles for systematic analysis.
Patients
The 10 included studies yielded a total of 172 patients. Though 172 patients were included for preoperative analysis, only 156 patients were eligible for postoperative analysis as Davidge et al 12 lacked sufficient follow-up on 16 patients. The average age for all included patients was 44.7 years (ranging from 8 to 65 years). Injury information is displayed in Table 2 . The mean time between injury/onset of symptoms and surgery (preoperative time) was 8.8 ± 8.8 months, and the mean follow-up period (postoperative time) was 16.8 ± 7.4 months. The eligible studies are summarized in Table 3 . Three publications, Flores, 13 Baltzer et al, 14 and Sallam et al 15 performed concurrent retrospective analyses of control nerve graft 13 15 or “conventional management” 14 cohorts that were matched based on age, type of injury, and level of injury. Baltzer et al 14 defined their “conventional management” group as having either primary repair or reconstruction with nerve grafting for transection injuries or decompression for compression injuries. The three control cohorts, containing 61 patients, were combined and referred to as the control treatment group for this analysis. The injury types and locations for this control group are additionally shown in Table 2 .
Table 2. Injury type and location.
| ETE | SETS | Total NT | Control | |
|---|---|---|---|---|
| No. of patients (%) | No. of patients (%) | No. of patients (%) | No. of patients (%) | |
| Injury type | ||||
| Compression | 0 (0.0) | 66 (56.4) | 66 (40.2) | 6 (9.8) |
| Transection (or tissue loss) | 25 (53.2) | 16 (13.7) | 41 (25.0) | 35 (57.4) |
| Lesion-in-continuity | 15 (31.9) | 25 (21.4) | 40 (24.4) | 20 (32.8) |
| Other | 7 (14.9) | 10 (8.5) | 17 (10.4) | 0 (0.0) |
| Total | 47 | 117 | 164 | 61 |
| Injury location | ||||
| Proximal to elbow | 24 (43.6) | 24 (20.5) | 48 (27.9) | 19 (31.2) |
| Elbow | 26 (47.3) | 72 (61.5) | 98 (57.0) | 31 (50.8) |
| Distal to elbow | 5 (9.1) | 11 (9.4) | 16 (9.3) | 11 (18.0) |
| Multilevel/diffuse | 0 (0.0) | 10 (8.5) | 10 (5.8) | 0 (0.0) |
| Total | 55 | 117 | 172 | 61 |
Abbreviations: ETE, end-to-end; NT, nerve transfer; SETS, supercharged end-to-side.
Notes: Transection (or tissue loss) includes gunshot, sharp, or motor vehicle accident injury. Lesion-in-continuity includes closed or iatrogenic injuries.
Table 3. Summary of eligible publications' outcomes regarding ETE and reverse SETS nerve transfer and nerve grafts (when applicable).
| Study type | Procedure type (number of patients) | Outcomes evaluated | Preop timeMean in mo (SD) | Follow-up timeMean in mo (SD) | Summary results | |
|---|---|---|---|---|---|---|
| Battiston and Lanzetta 6 | Case series | ETE (7) With palmar cutaneous branch to ulnar sensory nerve for sensory function |
Injury type, injury location, preop atrophy, motor MRC grade, grip strength (% of normal), key pinch (% of normal) | 4.0 (1.9) | 29.1 (11.2) | - Signs of sensory/motor recovery present as soon as 12 wk - Best recovery in adolescent patient (M5) - MRC M4 or >: 85.7% - Grip strength, key pinch > 60%: 85.7% |
| Novak and Mackinnon 19 | Retrospective chart review | ETE (8) | Injury location, grip strength (lb), key pinch (lb) | 3 (3) | 18 (11) | - All patients had reinnervation of intrinsic muscles based on grip strength, key pinch - One patient required secondary tendon transfer - Grip strength improved from 8.8 ± 10.3 to 61.2 ± 27.8 lb - Key pinch improved from 2.2 ± 2 to 13.8 ± 6 lb |
| Delclaux et al 20 | Case report | ETE (1) With fourth, fifth digit sensory fascicles to posterior interosseous nerve for sensory function |
Injury type, injury location, preop atrophy, motor MRC grade | 18.0 | 18.0 | - MRC grade M3 |
| Flores 13 | Retrospective cohort | ETE (15) with ulnar sensory nerve to third common digital nerve for sensory function Graft (20) |
Injury type, injury location, motor MRC grade, grip strength (kg), postop DASH score | Transfer 7.1 (0.8) Graft 4.6 (3.8) |
Transfer 24.3 (15–38 range) Graft 28.2 (20–74 range) |
- Grip power significantly favored NT - NT group had longer preop time Transfer vs. graft data: - MRC M3/M4: 80 vs. 22% (Mann–Whitney's U -test, p = 0.028) - Grip strength: 31.3 ± 5.8 vs. 14.5 ± 7.2 kg (Mann–Whitney's U -test, p = 0.029) - DASH scores: 23.6 ± 6.7 vs. 34.2 ± 8.3 (Mann–Whitney's U -test, p = 0.031) |
| Sallam et al 15 | Retrospective cohort | ETE (24) With third web space sensory branch to superficial ulnar sensory branch and end-to-side transfer of dorsal ulnar cutaneous nerve to remaining sensory median nerve for sensory function Sural graft (28) |
Injury type, injury location, motor MRC grade, grip strength (lb), key pinch (lb) | Transfer 9.4 (6–18 range) Graft 7.8 (7–16 range) |
Transfer 28.6 (24–38) Graft 26.8 (24–36) |
- Motor recovery better with NT (chi-square, 4.16,
p
= 0.041)
- NT patients had more severe injury, greater length of gap (> 5 vs. 3–5 cm for graft) Transfer vs. graft data: - MRC M3 or >: 83.3 vs. 57.1% - Grip strength: 73.3 vs. 52.1% recovery - Key pinch: 73.0 vs. 54.1% recovery |
| Davidge et al 12 | Retrospective cohort | SETS (55 a ) | Injury type, injury location, preop atrophy, motor MRC grade, DASH score, grip strength (lb), key pinch (lb) | n/a | 8.0 (5.7) | - 15 patients had prior ulnar nerve surgery - Major predictor of poor intrinsic muscle recovery was absent preop compound muscle action potentials in ulnar nerve - Mean key pinch, grip strength, and DASH score all significantly improved - MRC grade 3+ improved from 15 to 70% of patients |
| Baltzer et al 14 | Retrospective matched cohort | SETS (13) Conventional management (primary repair, nerve graft or decompression) (13) |
Injury type, injury location, preop atrophy, grip strength, key pinch Functional recovery defined as at least two of the following improving: ability to flex at MCP joint w/o proximal joint flexion, abduction of index finger, ability to cross fingers, negative Froment's sign, return of intrinsic muscle bulk |
Transfer 4.4 (3.5) Conventional 1.5 (2.0) |
Transfer 13.5 (13) Conventional 39.0 (35) |
- Compression injuries had comparable return of function (both 67%) - Comparable grip strength (62 vs. 74%, p = 0.4), key pinch (52 vs. 67%, p = 0.2) Transfer vs. conventional data: - Intrinsic function recovery: 84 vs. 38% ( p < 0.05) - Function return following nerve transection: 85 vs. 14% ( p < 0.05) |
| Jarvie et al 17 | Case report | SETS (2) | Injury type, injury location, preop atrophy, motor MRC grade, DASH score | 4.0 | 12.0 | - DASH score improved by an average of 43.5 patients - Motor recovered by at least one MRC grade |
| Head et al 21 | Retrospective cohort | SETS (17) | Injury type, injury location, motor MRC grade | 17.6 (18.8) | 16.7 (8.5) | - Five patients underwent concomitant cubital tunnel release, and six had previous ulnar nerve surgeries - Median first dorsal interosseous motor MRC grade increased from 1 to 4 |
| Doherty et al 22 | Retrospective cohort | SETS (30) | Injury type, injury location, preop atrophy, motor MRC grade | n/a | 18.6 (7.7) | - 80% observed partial or complete resolution of clawing - 77% observed partial or complete resolution of intrinsic muscle wasting - MRC M3 or > 73% |
Abbreviations: DASH, Disabilities of the Arm, Shoulder, and Hand; ETE, end-to-end; MCP, metacarpophalangeal; MRC, Medical Research Council; NT, nerve transfer; postop, postoperative; preop, preoperative; SD, standard deviation; SETS, supercharged end-to-side; w/o, without.
Davidge et al had 55 patients initially but only 39 patients were eligible for follow-up analysis.
Demographics
The mean age of NT patients, 44.7 ± 14.7 years, was significantly older than the age of the control treatment group (31.3 ± 9.7 years, p < 0.001). Notably, the SETS treatment group was significantly older (50.5 ± 16.0 years) than both the ETE treatment group (32.6 ± 11.5, p < 0.001) and the control treatment group ( p < 0.001). None of the eligible publications focused specifically on the effect of age, though Battiston and Lanzetta 6 noted that their youngest patient, an 11 years old, had the best results with grade M5 strength. From the publications that reported gender, 62% (107/172) of patients were male.
Additional Procedures
A total of 25 patients (15%) underwent additional procedures to the injured upper extremity prior to NT. The most common procedure was neuroma excision (52%). Additionally, several patients required one or more procedures performed concurrently with NT, the most common being Guyon's canal decompression, flexor digitorum profundus tenodesis, primary anterior ulnar nerve transposition, and primary carpal tunnel release.
Preoperative and Postoperative Follow-up Time
The NT patients had significantly longer time to surgery (8.8 ± 8.8 months) than the control treatment group (5.4 ± 2.8 months, p = 0.001). There was no significant difference between the preoperative times for the ETE and SETS NT patients. Postoperatively, the ETE NTs and the control treatment patients both had significantly longer follow-up time (25.8 ± 6.8 and 29.9 ± 17.8 months, respectively) than the SETS NT patients (12.7 ± 7.7 months, p < 0.001).
Motor Recovery
Overall, of the patients with postoperative motor MRC grade outcome data, the 135 patients receiving NT, either by the ETE or SETS method, attained a significantly greater postoperative motor MRC grade than the 46 patients of the control treatment group (chi-square test, p < 0.001). Particularly, 77% of NT patients attained motor MRC grade M3 or higher, compared with only 39% of control patients ( p < 0.001) as shown in Fig. 2 . There was no significant difference in motor MRC grade outcome between ETE and SETS cases (chi-square test, p = 0.289).
Fig. 2.
Comparative postoperative outcomes for motor MRC grade, grip strength (percentage of unaffected side), and key pinch strength for each treatment group. MRC, Medical Research Council; SETS, supercharged end-to-side.
Grip strength proved more difficult to analyze as publications reported results in percentage of unaffected side and/or in pound or kilogram. When comparing by percentage of unaffected side, there was not a statistically significant difference between NT grip strength (65 ± 23%) and the control treatment group grip strength (59 ± 14%, p = 0.051). However, for the publications with grip strength measured in pound or kilogram, NT patients regained significantly more grip strength (53.7 ±19.8 lb of force) than the control group (32.0 ± 15.9 lb of force, p < 0.001) as shown in Fig. 3 . The SETS NT publications by Baltzer et al 14 and Davidge et al 12 found that patients regained approximately 61 ± 27% of strength of the unaffected side or 46.3 ± 20.2 lb of force. Comparatively, for those undergoing ETE NT, patients regained significantly greater grip strength with 73 ± 11% strength of unaffected side or 66.3 ± 19.1 lb of force, ( p = 0 . 009 and p < 0.001, respectively).
Fig. 3.
Comparative postoperative outcomes for DASH score and grip strength (pound of force) for each treatment group. DASH, Disabilities of the Arm, Shoulder, and Hand; SETS, supercharged end-to-side.
When comparing key pinch strength, it was found that only the ETE NT cohort had significantly greater recovery of strength (73 ± 12%) compared with control treatment group (58 ± 10%, p < 0.001). The ETE NT cohort also regained significant key pinch strength when compared with the SETS NT recovery (54 ± 25%, p < 0.001).
There was not a significant difference in DASH scores between the total NT group and the control treatment group (33.4 and 34.2, respectively, p = 0.769), but the ETE patients alone had a score of 24.3 that was significantly less than the control group ( p < 0.001). There was also a significant difference in the score of ETE patients versus the 36.9 score of SETS patients ( p < 0.001).
Discussion
In comparison to nerve grafting, NT has been reported to provide more rapid and consistent results. 1 2 It also avoids the restrictive scarring that occurs with muscle and tendon transfers and the biomechanical concerns of muscle transfer. 9 16 Overall, it appears that patients who undergo NT can expect signs of motor recovery within 3 to 6 months of their procedure. 6 12 14 17 Therefore, NT has utility in several circumstances, such as when there is a proximal injury, delay between the injury and surgery, excessive scarring, or significant loss of tissue, particularly when there is inadequate proximal nerve stump available. 1 2 9
Though NT has been classically considered only a revisional or “backup” procedure, 18 only a small percentage (15%) of eligible patients in this analysis had prior procedures to their affected upper extremity, while nearly half required at least one concurrent procedure during their NT. Though perhaps a reflection on study design, this may suggest a shift in attitude toward using NT as a primary management option.
Of the NT patients assessed in our review, the majority had either a compression injury (40%) or nerve transection (25%). An additional 24% had various lesions-in-continuity, which included traction or closed injuries. The most common location was at the elbow. The first of three controlled studies which compared NT with nerve grafts or conventional management was Flores. 13 He used ETE NT in 15 patients with either closed injuries-in-continuity or transection injuries at or above the elbow and compared the results to those of 20 matched patients who received nerve grafts. M3/M4 outcomes and handgrip strength measured in kilogram were significantly better in the NT group. Sallam et al 15 used ETE NT for 24 patients who had a postneuroma excision gap of more than 5 cm. This group was compared with a matched cohort of 26 patients who had complete transection injuries with a gap of less than 5 cm. who had received sural nerve grafts. They found that 83% of NT patients regained strength graded M3 or greater, compared with only 57% of the nerve graft patients (reported p < 0.05). Baltzer et al 14 analyzed the outcomes of 7 patients with transection injuries and 6 patients with compression injuries who received SETS NT compared with 13 matched patients who underwent conventional management by either primary repair, nerve grafting, or decompression. They found that SETS NT was significantly more efficacious for nerve transection injuries with an 85% recovery rate of intrinsic motor function compared with 14% for patients receiving conventional management (reported p = 0.03). In contrast, there was no difference between SETS and conventional management for compression injuries. These findings demonstrate that an ETE NT procedure is particularly effective in treating transection injuries at or above the elbow. The data for SETS NTs are not as robust, with one controlled study and a small number of patients. We could not complete an analysis of NTs for other specific types of ulnar nerve injuries due to lack of individually identified data.
This analysis confirms that NT cohorts have significantly better motor outcomes than control treatment cohorts. 13 14 15 18 Significantly better MRC motor grade outcomes and grip strength measured in pound were found in NT patients compared with control treatment groups. Although no significant difference was found between postoperative motor MRC grades of ETE and SETS patients, the ETE patients had significantly better outcomes for grip strength (73 ± 11 vs. 61 ± 27% of unaffected side, respectively, or 66.3 ± 19.1 vs. 46.3 ± 20.2 lb of force, respectively), key pinch strength (73 ± 12 vs. 54 ± 25% of unaffected side), and DASH scores (24.3 ± 7.0 vs. 36.9 ± 18.9). Only the ETE patients, and not the NT group as a whole, had significantly lower DASH scores than the control treatment group. These motor strength outcomes were most consistently reported but can only estimate intrinsic function recovery. 12 It is also important to note the context of these results and the study limitations. The SETS and ETE groups are not matched. The SETS patients were on average older than the ETE patients by 18 years and had shorter postoperative follow-up time, which could have diminished the potential motor outcomes. The two groups also differ in types of injuries. In addition, the lack of individual patient data from the included studies precluded performance of a true meta-analysis and thus limits the interpretation of the data. These limitations only further reinforce the need for additional studies on this topic.
We recommend that future studies compare ETE and SETS NT as initial surgery in specific injury types, report individual data, stratify patient groups for age, preoperative time, and level of injury, complete preoperative evaluations of MRC grade strength and key pinch strength both as a percentage of the unaffected side and in pound/kilogram, include the motor strength measurements as well as DASH questionnaire scores in the postoperative evaluation, and continue follow-up for at least 2 years.
Conclusion
Combining all of the available data, we conclude that AIN–ulnar NTs have the potential for some meaningful motor recovery for proximal ulnar nerve injuries. For ulnar nerve transection injuries at or above the elbow, ETE NT results in superior motor recovery compared with nerve grafting. However, more research is needed to determine the best treatment for other types of ulnar nerve injuries, including either advanced nerve compression or ulnar nerve injuries below the elbow, and the role that SETS NT may play in their management.
Acknowledgments
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Dr. Leandro Flores and Dr. Marco Lanzetta kindly provided individual data on 15 and 7 patients, respectively.
Funding Statement
Funding None.
Conflict of Interest None declared.
Statement of Informed Consent
This study uses published data and requires no informed consent.
Statement of Human and Animal Rights
No experimentation or procedures were performed on animals or humans during this study.
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