Introduction
Extension of the fingers and the thumb adds to prehension of the hand by increasing
its ability to open the hand for grasping larger objects. For restoration of the hand
function in radial nerve palsy, the triple-tendon transfer of pronator teres (PT)
to extensor carpi radialis brevis (ECRB), flexor carpi ulnaris (FCU)/flexor carpi
radialis to extensor digitorum communis (EDC), and palmaris longus (PL) to rerouted
extensor pollicis longus (EPL) has been recommended. Our results with this set of
triple-tendon transfers are satisfactory as described in the study by Latheef et al.[1] Rerouting of EPL volarly and transfer to the PL was described by Scuderi[2] to achieve a combined extension and abduction, describing excellent results. Over
the years, this has become the standard transfer for thumb extension. Brand in his
study of the clinical mechanics of the hand has concluded that the EPL is an extensor
and adductor at the carpometacarpal (CMC) joint and the extensor pollicis brevis (EPB)
is an extensor and abductor.[3] This is because the EPL is ulnar to the axis of the CMC joint and the EPB is radial
to the CMC joint axis ([Fig. 1]). Therefore, it is necessary to reroute EPL when it is used as a recipient for thumb
extension transfer ([Fig. 2]). The EPB, on the other hand, produces good opening of the first web by abduction
at the CMC joint by virtue of being radial to the CMC joint axis. However, the EPB
does not usually extend the interphalangeal (IP) joint. The described anatomical variation
of the EPB extending the thumb IP joint ([Fig. 3]), therefore, gives the “best combination” of movements for a single-thumb extensor
tendon, that is, abduction at the CMC joint, extension at the metacarpophalangeal
joint (MCPJ), and extension at the IP joint. We hypothesized that in such patients
(having an anatomical variation of EPB which is extending the IP joint of thumb) tendon
transfer to the EPB provides better results than a rerouted EPL transfer. Our study
aimed to evaluate the efficacy of such tendon transfers to the EPB.
Fig. 1 A clinical picture showing the surface marking of the extensor pollicis longus and
the extensor pollicis brevis with respect to the metacarpophalangeal and carpometacarpal
joints. The extensor pollicis longus being ulnar to the axis acts as an extensor and
adductor while the extensor pollicis brevis acts as an extensor and abductor (refer
text). APL, abductor pollicis longus; EPB, extensor pollicis brevis; EPL, extensor
pollicis longus.
Fig. 2 Line diagram showing the concept of rerouting of the extensor pollicis longus, the
extensor pollicis longus tendon is removed from its normal location (around the Lister’s
tubercle) and transferred to more radial direction (arrow) so that instead of working
as an extensor and adductor it can start working as an abductor and extensor at the
thumb joints.
Fig. 3 The representative diagram showing the anatomical variations in the insertion patterns
of the extensor pollicis brevis. (A) The standard distal attachment of the extensor pollicis brevis on to the dorsal base
of the proximal phalanx; (B) a distal attachment to the extensor hood; and (C) a distal attachment of a distinct extensor pollicis brevis tendon onto the dorsal
base of the distal phalanx (Alemohammad et al[10]).
In a patient with brachial plexus palsy, we chose FCU as a favorable donor for EDC
and EPL based on the motor profile. We planned to attach FCU to both EDC and EPL (split
FCU transfer). During intraoperative traction on the EPL, we noted an adduction movement
which could not be addressed by rerouting, as the donor tendon was reaching the EPL
from the ulnar side ([Fig. 4A]). Since the rerouting was not possible, we inspected the EPB. On applying traction
on the EPB, we noted good radial abduction and extension of the thumb ([Fig. 4B]). FCU was attached to EPB to get thumb extension. Relying on this outcome of abduction
and extension in this patient, we have performed this transfer in six patients.
Fig. 4 Intraoperative photograph showing the movement of the thumb on applying traction
to extensor pollicis longus (A) and extensor pollicis brevis tendon (B). One can note the thumb extension and adduction produced by traction on extensor
pollicis longus (A) and abduction and extension produced on applying traction to extensor pollicis brevis
(B).
Materials and Methods
This study is a retrospective analysis of six patients who underwent tendon transfer
for wrist and digital drop. Among these six patients, three patients had radial nerve
palsy and three patients had brachial plexus palsy. In these patients, transfer of
the donor tendon to the rerouted EPL was planned for the thumb extension. When EPB
was evaluated intraoperatively, it was found to extend the IP joint also ([Fig. 4B]). Therefore, in these patients, EPB was used as the recipient instead of a rerouted
EPL. In patients with radial nerve palsy after the PT to ECRB and FCU to EDC transfers
were completed, the PL was delivered into the dorsal forearm wound. With the thumb
held in extended and abducted position, the PL was weaved through EPB. In patients
with brachial plexus palsy, the PT to ECRB was done in one patient who had a strong
PT and in other two patients with paralyzed PT, we used flexor digitorum superficialis
(FDS) of middle finger to the ECRB for wrist extension. FCU, which was strong in all
these three patients, was transferred to EDC for finger extension (split FCU into
two cases). For the thumb extension, in one patient, FDS of ring finger was transferred
to EPB and other two cases, one slip of split FCU was transferred to the EPB and another
to the EDC ([Figs. 5A] and [B]). Postoperative mobilization was started after 4 weeks. Patients were allowed to
use their hand at 2-month post surgery.
Fig. 5 (A) Intraoperative photograph and (B) the line diagram showing the direction of split flexor carpi ulnaris transfer (hemostat
showing the direction) to reach the extensor pollicis brevis and the extensor digitorum
communis slips for insertion. EDC, extensor digitorum communis; EPB, extensor pollicis
brevis; FCU, flexor carpi ulnaris.
We evaluated these patients at a minimum of 6-month follow-up (range: 6 months–2 years)
for range of motion of the thumb, pinch strength, and outcomes by the Bincaz score
([Table 1]). We measured the radial extension of the thumb at the CMC joint, in the plane of
the palm, as the angle between the line along radial subcutaneous border of the first
metacarpal and the index finger ray ([Fig. 6A]). This was measured with the IP joint in extension, as a flexed IP joint reduces
the radial extension of the thumb. The palmar abduction was measured at the CMC joint
in the plane perpendicular to the flat palm, as the angle between the dorsal subcutaneous
border of the proximal phalanx of the thumb and the palmar border of the index ray
([Fig. 6B]). The Kapandji score was measured to assess any restriction in opposition of the
thumb. The strengths of pulp pinch and key pinch were measured using a pinch meter.
Table 1 Bincaz score for evaluation of the results of tendon transfer for wrist and
digital extension
|
Points
|
3
|
2
|
1
|
0
|
|
Abbreviation: MCP, metacarpophalangeal.
|
|
Wrist extension
|
|
>29 degrees
|
0–29 degrees
|
0
|
|
MCP joint extension
|
|
Full
|
Loss of extension < 100 degrees
|
Loss of extension > 100 degrees
|
|
First web space opening
|
|
>39 degrees
|
30–39 degrees
|
<30 degrees
|
|
Patient satisfaction
|
Excellent
|
Good
|
Fair
|
Poor
|
Fig. 6 (A) Clinical picture showing the measurement of the radial abduction and (B) the palmar abduction achieved after the tendon transfer procedure.
Results
At an average follow-up of 9 months (range: 6 months–
2 years), patients had average
radial extension of the thumb of 29.2 degrees and an average palmar abduction of 65.7
degrees. The mean key pinch was 4.9 kg and pulp pinch was 3.4kg. All patients had
a Kapandji score of 10 ([Table 2]). On evaluation with the Bincaz score, one patient had an excellent result, three
patients had good results, and two patients had fair results ([Fig. 7]).
Table 2 Patient details and the result achieved in our series
|
Serial number
|
Diagnosis
|
Type of transfer
|
Radial abduction (degree)
|
Palmar abduction (degree)
|
IPJ flexion (degree)
|
Key pinch
|
Pulp pinch
|
Kapandji’s score
|
|
Abbreviations: EPB, extensor pollicis brevis; FCU, flexor carpi ulnaris; FDS, flexor
digitorum superficialis; IPJ, interphalangeal joint; PL, palmaris longus.
|
|
1
|
Brachial plexus palsy (C5–C7)
|
FDS–EPB
|
30
|
60
|
60
|
5.0
|
3.0
|
10
|
|
2
|
Radial nerve palsy
|
PL–EPB
|
25
|
66
|
90
|
4.5
|
3.5
|
10
|
|
3
|
Radial nerve palsy
|
PL–EPB
|
30
|
70
|
68
|
4.5
|
3.0
|
10
|
|
4
|
Brachial plexus palsy (C5–C7)
|
FCU–EPB
|
35
|
68
|
70
|
5.0
|
3.6
|
10
|
|
5
|
Radial nerve palsy
|
PL–EPB
|
35
|
60
|
80
|
5.2
|
4.0
|
10
|
|
6
|
Brachial plexus palsy (C5–7)
|
FCU–EPB
|
20
|
70
|
85
|
5.3
|
3.0
|
10
|
|
Mean
|
29.2
|
65.7
|
75.5
|
4.9
|
3.4
|
10
|
Fig. 7 Clinical pictures showing good long-term results of the tendon transfer to extensor
pollicis brevis for thumb extension. (A) Shows good palmar
abduction achieved and (B) shows comfortable full opposition, indicating the suitable tension in the transfer
and restoration of good function.
Discussion
In radial nerve palsy, there is loss of extension of the wrist, fingers, and thumb.
These patients have difficulty in bringing the thumb out of the palm. The traditional
recipients have been ECRB, EDC, and EPL. The transfer of PL to rerouted EPL has been
performed routinely since its description by Scuderi.[2]
The thumb is brought out of the palm by three tendons, all supplied by radial nerve,
which act on the three joints. The abductor pollicis longus (APL) brings about movement
of the CMC joint, EPB primarily at the MCPJ and the EPL primarily at the IP joint,
and also MCPJ and CMC joint as it crosses these joints. EPL is chosen as a recipient
for tendon transfer in radial nerve palsy, since it traverses all the three joints.
APL and EPB are radial to the MCP and CMC joint axis, and they produce radial extension.
Whereas, EPL is ulnar to the axis of the thumb CMC joint; therefore, it produces adduction
movement of the thumb. Due to its ulnar vector across the CMC and MCPJs, it has to
be rerouted to act as an extensor and abductor. Rerouting is a standard part of radial
nerve tendon transfer since its description by Scuderi,[2] but it requires donor tendon to approach the thumb from the radial side. If split
FCU or FCU along with EDC is used as donor, then rerouting is technically not possible,
as these tendons would reach the thumb from the ulnar side. In such patients, the
results are poor as the thumb goes into extension and adduction rather than abduction
([Fig. 8]). Variations in the insertion of EPB, into the extensor hood or base of the distal
phalanx, have been described, leading the EPB to extend the IP joint also ([Fig. 3]). Since it is radial to the CMC and MCPJ axis, it should act as a better radial
extensor (abductor).
Fig. 8 Clinical picture of a patient with brachial plexus palsy who underwent flexor carpi
ulnaris transfer to extensor digitorum and extensor pollicis longus for finger and
thumb extension, respectively. Due to the paucity of donors, only flexor carpi ulnaris
was available and hence, it was used for both finger and thumb extension. Since the
flexor carpi ulnaris reaches dorsum from the ulnar side rerouting of the extensor
pollicis longus was not possible. The thumb extension achieved in this patient was
not good because the thumb had as adduction moment while extension.
The standard anatomical description of the EPB, found in the current anatomical textbooks,
describes its origin as the posterior surface of the radius and adjacent part of the
interosseous membrane, distal to the origin of the abductor APL. Its tendon is described
to insert into the posterior surface of the base of the proximal phalanx of the thumb
after passing under the extensor retinaculum.[4] The primary function of EPB has been described to cause extension of the MCPJ of
the thumb, with contributions to abduction of the thumb and carpus, as well as stabilizing
the MCPJ of the thumb, by integrating into the extensor hood.[5]
[6]
Dawson and Barton,[7] from their study of the EPB on 16 cadaveric hands, concluded that this standard
description does not reflect reality and that EPB tendon anatomy varies considerably
from the standard description, even between two hands of the same individual. The
EPB and APL are considered to differentiate from a common muscle mass and are found
as completely separate entities only in humans and gibbons.[7]
[8] This theory of a common origin for the EPB and APL is further supported by the fact
that, in certain cases, the EPB muscle is fused to a variable extent with the muscle
belly of the APL as documented by Kulshreshtha et al.[6] They also found the absence of a separate muscle belly in three hands (6.8%) of
a total of 44 cadaveric hands. They further describe the variations of insertion of
the EPB. They found that in 25% of the cases, the tendon was inserted wholly into
the base of proximal phalanx; in 2% of cases, the tendon was inserted exclusively
into the extensor hood, in 25% tendons were inserted partly into the base of the proximal
phalanx and partly into the extensor hood. Also, 27% tendons showed all of these attachments,
that is, partial attachment to the base of the proximal phalanx and to the extensor
hood, coupled with prolongation to the distal phalanx. Twenty percent tendons were
attached only to the extensor hood, whereas they were prolonged into a combined insertion
with the tendon of EPL into the distal phalanx. In these studies, there is no clear
description whether these variable insertions caused extension of the IP joint or
not. Brunelli and Brunelli,[5] in their study of the EPB in 52 cadaveric hands, reported that the tendon inserted
wholly into the extensor hood, in 69.2% of cases, insertion of the tendon partially
to the base of the proximal phalanx and extensor hood in 19.2% and base of the distal
phalanx direct insertions in four cases (7.5%).
In their study of anatomical variations in the first extensor compartment of the wrist,
Jackson et al[9] found 57 (19%) cases where the EPB had dual insertion with one slip into the proximal
phalanx and the other inserting to the EPL. They also found an additional 16 (5.3%)
cases where traction on the EPB tendon caused IP joint extension, but the dual insertion
was not demonstrated or the dissection was not completed. Alemohammad et al[10] in their study of 90 cadaveric wrists and 143 patients with De Quervain’s tenosynovitis,
found 21.1% of EPB in the cadavers to cause extension of the IP joint, and 39.2% of
the patients with De Quervain’s tenosynovitis to have EPB causing extension of the
IP joint.
Hence, these studies suggest that the incidence of the EPB extending the IP joint
also should be upward of 20% of the population. In our institute, on serially examining
the effect of EPB on the IP joint in 46 consecutive cases undergoing tendon transfer
in the region, we noted that in 16 patients (34.8%), the EPB was extending the IP
joint also. Hence, a similar proportion of radial nerve/brachial plexus palsy patients
(one third) is potential candidates for an EPB, in lieu of a rerouted EPL transfer.
Rerouting the EPL may not actually be possible for all patients. When the FCU is used
for both finger and thumb extension, the donor tendon comes from the ulnar aspect
of the thumb precluding volar radial shift of the EPL. Such a transfer may be necessary
in the absence of the PL or due to paucity of donors in brachial plexus palsy. Single-FCU
tendon transfers have also been described for high-radial nerve palsies and no rerouting
is possible if they are chosen.[11]
[12] In addition, the subcutaneous rerouting of the EPL tendon causes a bowstringing
on the volar aspect of the wrist which may not be cosmetically acceptable.
Ropars et al,[13] in their study of radial nerve tendon transfer in 15 patients, reported mean abduction
of the thumb as 54 degrees (range: 0–70 degrees) and opposition as 8.7 (range: 3–10)
points on Kapandji’s scale. When FCU was used as a single donor for both fingers and
thumb extension, Gousheh and Arasteh[11] reported thumb abduction of 38 degrees (range: 35–42 degrees) and Al-Qattan[14] reported thumb abduction of 55 degrees (range: 50–60 degrees) achieved in their
series. In our study, the mean palmar abduction was 65.7 degrees. The articles in
the literature do not specifically mention about radial abduction. However, our patients
had a radial abduction of 27.5 degrees. Altintas et al[15] reported the mean abduction of the thumb in their series as 46 degrees. Using Bincaz
score, Ropars et al[13] in their study of 15 patients found that 11 had excellent, two good, one fair, and
one bad result. Al-Qattan[14] reported the overall result as per the Bincaz scale was excellent in 12 patients
and good in the remaining three patients. In the present study, on evaluation with
the Bincaz score, one patient had an excellent result, three patients had good results,
and two patients had fair results ([Figs. 7A] and [B]). Both the patients with fair results were the cases of brachial plexus palsy with
limited donor options and overall upper limb weakness where the patients reported
their overall satisfaction of function as fair contributing to the “fair outcome”
on Bincaz’s scale with score of 5 ([Table 1]), but the improvement in thumb extension was good in them as indicated by the range
of thumb movements achieved in our series ([Table 2]).
Transfers to the EPB have been used earlier in spastic hands with thumb in palm deformity
patients who have weakness of the thumb extensors. Transfer to the EPB has been preferred
for a similar reason that it brings about thumb abduction and extension. Transfers
to the EPL may not correct thumb in palm deformity because of its adductor moment
to the thumb.[16]
[17]
Jackson et al,[9] in their study of the EPB variations, have speculated on a transfer to the EPB in
radial nerve palsy. They suggested traction on the EPB to check whether it extends
the IP joint before deciding on the final transfer. However, no such case reports
and results have since appeared in the literature. We followed a similar methodology
to find good results with use of the EPB as a recipient for thumb extension transfer
when it extends the IP joint as well. In patients with this favorable anatomical variation
(34.8%), the EPB insertion provides an acceptable alternative to rerouting the EPL.
In ulnar-sided donor transfers, such a transfer to the EPB is preferable to a transfer
to the “unrerouted” EPL. We recommend that the EPB action is evaluated in all cases
of thumb extension tendon transfer when rerouting is not possible; if found extending
the IP joint also, the EPB is a better recipient for the transfer for thumb extension.
There are few shortcomings of using the EPB as follows:
-
EPB may be very thin and muscular, not allowing good tendon to tendon opposition.
In such cases, it is better to transfer to EPL. We encountered this situation in two
cases.
-
Decision for transfer to EPB can be taken only after exploration.
-
If one does not find the favorable EPB anatomy and the available donor tendon is reaching
the thumb from the ulnar side which precludes rerouting, one could use the technique
described by Colantoni Woodside and Bindra[18] in which the EPL is divided proximally, withdrawn distally through a small incision
over the metacarpal, and then tunneled back through the first compartment in a retrograde
manner to get it in line with the EPB. It could then be sutured to the donor tendon.
-
Alternatively, one could divide the EPL from its distal insertion on the ulnar side
of the extensor apparatus, withdraw it proximally, and reroute it through the first
compartment and suture it on the radial side of the extensor apparatus at the MCPJ
to get the same effect.
Based on our observations from this study, we recommend to use EPB as a recipient
for the tendon transfers in which the donor tendon reaches the thumb from the ulnar
side provided EPB is found to extend the IP joint. In other cases, when the possibility
of EPL rerouting is present, the results achieved by transfer to EPB in this series
are comparable to the rerouted EPL transfer.
Conclusion
Extensor pollicis brevis (EPB) produces better thumb abduction and extension by virtue
of its radial vector as compared with the EPL which has a more ulnar vector necessitating
rerouting. The described anatomical variation of EPB extending the thumb interphalangeal
joint, therefore, gives the “best combination” of movements by a single-thumb extensor
tendon. Hence, in situations where EPL rerouting is not possible (as in cases where
the donor tendon needs to reach the thumb from the ulnar side, for example, split
flexor carpi ulnaris) transfer to the EPB, provided it is extending the thumb IPJ,
would produce better extension and abduction of the thumb than the transfer to the
‘un-rerouted’ EPL.
