nerve transfer in AIN syndrome

1. JOURNAL CLUB
on
Outcomes of anterior interosseous
nerve transfer to restore intrinsic
muscle function after high ulnar
nerve injury

3. Introduction
• Ulnar nerve injuries have a 71% lower chance of motor recovery
when compared to the median nerve for similar injuries.
• Repair of a high ulnar nerve injury would not result in useful recovery
of intrinsic musculature in an adult.
• The likely reason for this is that the long re-innervation distance in a
mixed nerve would result in an irreversible collapse of the
intramuscular neural plexus, end plate degeneration, and muscle fibre
atrophy and fibrosis.
• This leaves the patient with a loss of dexterity, weakness of grip,
sensory loss, and a noticeable functional and aesthetic
“claw”deformity

4. • The “claw”posture becomes more obvious as the more proximal FDP re-
innervates and the unopposed action of the extrinsic flexors and
extensors causes hyperextension of the MCP joint with interphalangeal
joint flexion.

5. • Tendon transfers were historically used to rebalance the hand, but
they are physically limited by the principles of singular, linear
function, and struggle to emulate the natural, intricate multi-faceted
functionality of the intrinsics.

6. • Nerve transfers have been gaining popularity over the last 2 decades
for the treatment of high ulnar nerve injuries, repopulating the distal
endoneurial tubes with expendable donor axons, providing some
early muscle reinnervation.
• The most popular and practical of these is the anterior in- terosseus
nerve (AIN) to motor branch of the ulnar nerve (MUN) transfer.

7. Methods
• During the period of 2011–2018, 17 consecutive patients, who underwent
AIN to MUN nerve transfers for high ulnar nerve injuries, were evaluated.
• Inclusion criteria
All traumatic aetiology for ulnar nerve injury at the proximal forearm,
elbow, and above elbow levels
non-in-continuity lesions from oncological resection.
Traction injuries with at least a Sunderland grade IV with no intraoperative
stimulation across the ulnar nerve
• All patients that underwent distal AIN to MUN transfer for compression
and other in-continuity lesions were excluded.

8. ANALYSIS WAS DONE FOR:
• patient demographics
• Mechanism and level of injury
• Interval between injury and nerve transfer
• Nerve transfer techniques
• Time to recovery
• Follow up period
• Objective outcomes using the British Medical Research Council (BMRC)
motor strength grading for intrinsic musculature.

9. SURGICAL TECHNIQUE

12. Results
• In the 7-year study period, 16 patients (15 males and 1 female) met
the inclusion criteria as one patient was lost at follow-up
• Mean follow-up period : 17 months (range 12–18)
• Average age patients: 39.4 (range 19–77, SD = 19.7)
• The median delay between injury and the nerve transfer procedure
was 0.8 months

13. • Site of injuries were above the elbow in 5 cases (31.3%), at the level
of the elbow in 8 cases (50%) and at the proximal forearm level in 3
cases.
• Mechanism of injury included sharp transection of the nerve in 63.5%
of cases (10/16), blast injuries in 18.75% (3/16), 2 cases of traumatic
traction, and one case of a post traumatic neuroma resection which
was included as a full-thickness segment of the nerve was removed.

14. • There were three main techniques of nerve coaptation:
Conventional end-to-end (ETE) neurorrhaphy (7/16, 43.8%)
Hemi ETE where a few fascicles in the MUN were coapted to the terminal
AIN ETE (7/16, 13.8%)
Supercharged end-to-side (SETS) which is a true reverse end-to-side
(RETS) through an epineural window in the ulnar nerve motor branch.

15. • Five out of sixteen patients achieved MRC 4 and above (31%)
• 13/16 achieved MRC grade 3 or above (81%) recovery for intrinsic.
• One patient had residual clawing at 12 months follow-up, but was not
seen at 18 months.
• 3 patients (18.8%) had mild clawing at 18 months
• Of the twelve patients with no clawing, two had a positive Froment’s
test and two had a residual Wartenberg’s sign at 18 months.

16. • When looking at age in relation to outcomes very weak positive
correlation which was statistically insignificant (p-value = 0.64) was
noticed.
• There was a stronger positive correlation between the interval
between injury and nerve transfer , but this again was not significant (
p -value = 0.09).

17. • 12 studies were identified from similar published literature resulting in a
total of 102 patients including our series.
• All the studies employed the use of the AIN transfer to the MUN, either
alone or combined with a sensory transfer.

18. • Thirteen patients had injuries to the UN at the proximal forearm level,
37 were at the elbow, and 52 were in the arm or higher.
• The mean time to surgery for all patients was 5.17 months
• The average follow-up time was 20.72 months.

19. • Good outcomes (M3 or above) were obtained in 86% of patients and
of the 55 patients that had sensory transfers, and good outcomes (S3
+ or above) were obtained in 64% of patients.
• Although some of our patients had concurrent sensory nerve
transfers, the numbers were small and we did not include this as part
of our review.

20. Post-operative regimes
• The coaptation is completed without tension and adjacent joints are
put through a full ROM on the table.
• We usually use bulky dressings for the first 5–7 days with the addition
of a neutral wrist splint.
• After debulking of the dressing, a gentle range of movement exercises
is encouraged to facilitate nerve excursion and prevents subsequent
scarring.

21. Discussion
• In 1997 Wang and Zhu first described using the PQ branch of the AIN
to the MUN to restore intrinsic hand function for amputation injuries
at the wrist.
• Battiston used this technique specifically for high ulnar nerve injuries
and combining it with a distal sensory nerve transfer.

22. • The lack of correlation between delay to surgery and outcomes is not
all together unexpected as most of our nerve transfers were
performed acutely within a few days to months.

23. • A majority of our patients would receive FDP buddying along with the
nerve transfer which is a reliable method to improve grip strength.
• Other adjunctive procedures include correction of the Wartenberg’s
deformity and MCP joint capsulodesis with volar plate advancement

24. Study limitations
• Numbers of suitable cases are small and a large multicentre study
would be required.
• We did not review the sensory nerve transfers or look at sensory
outcomes in our patients
• Lack of patient reported outcome data being retrospective in nature.

25. CONCLUSION
• Distal nerve transfers provide a more functional and anatomical
reconstruction than tendon transfers.
• a recent survey of 62 surgeons from around the world showed 88%
used nerve transfers more frequently in the last 3 years.
• The AIN to motor branch nerve transfer proves to be a reliable
method of regaining intrinsic function in high ulnar nerve
• injuries with good motor recovery in 81.3% of our patients that
underwent the procedure, echoing other studies.
• research is needed to prove the efficacy of ETS neurorrhaphies and
the most effective technique for this.

26. • THANK YOU