Keywords index metacarpophalangeal joint - radial collateral ligament - ligamentous plasty
Introduction
Injuries to the radial collateral ligament (RCL) of the index finger are scarcely reported in the literature,[1 ]
[2 ] and that makes some authors regard these injuries as underreported.[3 ]
[4 ] This fact may explain why there are more reports on the treatment of chronic injuries to this ligament[5 ]
[6 ] than on acute injuries.[2 ]
The most commonly proposed treatment for these chronic injuries at the metacarpophalangeal joints is by means of a free tendon graft,[7 ] mainly the palmaris longus.
Other methods described used the volar plate[8 ] or the abductor pollicis,[9 ] but the latter is indicated for the thumb.
Concerning the strength of the plasties, those fixed with interferential screws are considered the most resistant.[10 ]
[11 ]
For determining the insertion point of the plasty in the head of the metacarpal, we took as references anatomical studies that described the proximal insertion of the ligament, close to the articular surface for the accessory ligament, and also the thickness and the level of its distal insertion at the base of the phalanx and volar plate ([Fig. 1 ]).[12 ]
Fig. 1 The two zones of insertion of the studied structures. The most volar and proximal correspond to the distal insertion of the radial collateral ligament (RCL), and the other, to the first dorsal interosseous muscle (FDIM).
Based on all these concepts and on a previous report that proposed the use of a part of the tendon of the first dorsal interosseous muscle (FDIM) for the repair of a chronic injury of the RCL of the index finger,[13 ] we started an anatomical study to confirm the reliability of the technique regarding the length of the RCL and the tendinous portion of the FDIM.
Methods
For the study, we selected ten hands from ten specimens that were cryopreserved and thawed at room temperature for dissection. The study was performed under the ethical rules of the Department of Anatomy of our university.
Five hands were of women; their ages ranged from 46 to 96 years (mean: 72.8 years), and 8 of them were right hands.
The radial side of the hand was dissected through a dorsal midline incision from the proximal interphalangeal joint to the proximal third of the metacarpal, and then, two rectangular flaps were created at each side and opened in a book fashion, reaching the tendon sheath on both sides, taking care not to injure the interosseous and the lumbrical tendon. The extensor mechanism was opened through a longitudinal incision and, both sagittal bands were opened carefully until the tendon of the first dorsal interosseous muscle (FDIM) was drawn into the field.
The capsule was opened dorsally and resected until the most dorsal fibers of the radial collateral ligament (RCL) appeared.
At that point, dissection was performed to individualize the two portions of the FDIM. The most dorsal one is the planned for the study as, in previous dissections, was found to possess the longest portion of tendon ([Fig. 2 ]).
Fig. 2 The two portions of the first dorsal interosseous muscle (FDIM) were separated close to its insertion point.
The tendon of the FDIM crossed over the ligament for reaching its point of insertion at the base of the proximal phalanx that was situated distally and dorsally, to the RCL ([Figs. 3 ] and [4 ]).
Fig. 3 The tendon of the first dorsal interosseous muscle (FDIM) is separated from the radial collateral ligament (RCL). The tendon of the FDIM crosses almost perpendicularly and superficially the fibers of the RCL.
Fig. 4 Insertion of the first dorsal interosseous muscle (FDIM) at the base of the first phalanx. The radial collateral ligament (RCL) has been resected. The dorsal part of the FDIM tendon has been cut and distally reflected to show its point of insertion. The points of the distal insertion of the RCL are marked with stars, and a portion of the volar plate can also be seen (dotted line).
In five specimens, we measured the length of the RCL in situ. In all specimens, the measurement was taken after detaching the ligament from the metacarpal neck and from the volar plate and the base of the phalanx. We took the measurements of the longest and most superficial fibers of the ligament.
Then, we looked for the dorsal tendon of the FDIM and cut it at a point where we could see enough tendon fibers to reattaching it to the metacarpal, and also leaving enough tendon fibers in the proximal stump to suture it to the volar portion of the FDIM in order not to lose power ([Fig. 5 ]). The measurements were taken by two investigators independently with a conventional ruler calibrated in millimeters.
Fig. 5 The sufficient length of the dorsal tendon of the first dorsal interosseous muscle (FDIM) can be observed.
Results
The length of the FDIM distal tendon ranged from 20 to 40 mm (mean: 25 mm). The length of the RCL ranged from 14 to 24 mm (mean: 18.2 mm). In each specimen, the difference in length between both structures was always greater than than 2 mm (ranging from 2 to 16 mm), and the tendon of the FDIM was longer than the RCL. ([Table 1 ])
Table 1
Specimen
Gender
Age
RCL (mm)
FIDM (mm)
Difference (mm)
1
Male
77
18
20
2
2
Female
70
14
22
8
3
Male
96
15
25
10
4
Male
46
18
20
2
5
Female
77
18
20
2
6
Female
69
19
30
11
7
Male
87
24
40
16
8
Female
68
21
30
9
9
Female
84
17
21
4
10
Male
54
18
22
4
Mean
72.8
18.2
25
6.8
Discussion
From these results, we may deduce that when we leave the distal part of the tendon inserted at the base of the phalanx, any conventional bone anchor or tenodesis system can be used for the reattachment in the head of the metacarpal.
Although the tendon is not as thick as the RCL, we think that this technique can be used for the reinforcement of any repair or plasty.
The advantages of this plasty are that the direction of the fibers is very similar to those of the RCL, and its point of insertion at the base of the phalanx is “side by side”. The remaining part of the muscle retains enough tendon fibers to be attached to the tendon of the volar part of the muscle in order not to lose power, as previously reported.[13 ]
Nevertheless, this simple technique allows surgeons to perform a plasty of the RCL without additional incisions, and prevents them from sacrificing any other tendon for the same purpose, as they are in the same field. The maintenance of its distal insertion may also have a positive role in the revascularization of the repaired area.
Conclusions
This is a simple technique that can be used in every case. The difference in length of the tendon of the FDIM is enough to allow reinsertion by means of any anchoring system. The proximal part of the tendon must be sutured to the rest of the FDIM in order not to lose strength. This technique shortens the surgical time, as no other field is necessary for obtaining a tendon graft.
