Anatomy of the Radial Collateral Ligament of the Index Metacarpophalangeal Joint

SCIENTIFIC ARTICLE

Anatomy of the Radial Collateral Ligament of the Index Metacarpophalangeal Joint Christopher J. Dy, MD, MSPH, Scott M. Tucker, MEng, Peter L. Kok, MD, Krystle A. Hearns, MA, Michelle Gerwin Carlson, MD

Purpose To describe the origin and insertion of the radial collateral ligament (RCL) of the index metacarpophalangeal (MP) joint, relative to the MP joint line and other landmarks readily discernible intraoperatively. Methods We dissected 17 fresh-frozen human cadaveric index fingers. We removed all overlying soft tissue from the MP joint except for the proper RCL. We dissected the RCL from its original insertion under loupe magnification while concurrently marking the ligamentous origin and insertion points. We measured distances of these points in relation to the bony landmarks (dorsal, articular, and volar surfaces) using digital photo analysis. The same observer recorded all measurements to reduce systematic error. Results The center of the metacarpal attachment of the RCL was located 5.4 ⫾ 1.1 mm from the dorsal border of the metacarpal, 8.0 ⫾ 2.2mm from the volar border of the metacarpal, and 10.3 ⫾ 3.2mm from the articular surface of the MP joint. The total width and height of the metacarpal origin site were 5.8 ⫾ 1.6 and 6.4 ⫾ 1.4 mm, respectively. The center of the proximal phalanx attachment of the RCL was located 6.8 ⫾ 1.4 mm from the dorsal border of the proximal phalanx, 5.7 ⫾ 0.9mm from the volar border of the proximal phalanx, and 4.4 ⫾ 0.8mm from the articular surface of the MP joint. The total width and height of the phalangeal origin site were 5.0 ⫾ 1.1 and 5.7 ⫾ 0.9 mm, respectively. Conclusions Our study defines the anatomic origin and insertion of the RCL of the index MP joint in relation to landmarks that are identifiable during surgery. Clinical relevance We believe this information will be useful to surgeons when repairing or reconstructing the RCL, allowing for recreation of normal RCL anatomy. (J Hand Surg 2013;38A:124–128. Copyright © 2013 by the American Society for Surgery of the Hand. All rights reserved.) Key words Radial collateral ligament, index finger, ligament, anatomy. acute injuries of the index finger metacarpophalangeal (MP) radial collateral ligament (RCL) should be promptly diagnosed and treated to avoid the potential long-term consequences of instability and decreased pinch strength.1 Primary repair of the acutely damaged

A

LTHOUGH NOT COMMONLY REPORTED,

From the Hospital for Special Surgery, New York, NY; and the Mayo Clinic, Rochester, MN.

or avulsed ligament is preferred.1–3 Delayed presentation and poor tissue quality can make primary repair difficult or impossible and ligament reconstruction necessary. Placement of the graft attachment sites at the origin and insertion of the native ligament restores stability4,5 and avoids compromising range of motion.6 No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.

TheinvestigationwasperformedintheBiomechanicsLaboratoryandtheBioskillsEducationLaboratory of the Hospital for Special Surgery. The authors thank Jennifer Hammann-Scala for her contribution to this project.

Correspondingauthor:MichelleG.Carlson,MD,HospitalforSpecialSurgery,523East72ndStreet, New York, NY 10021; e-mail: [email protected].

Received for publication August 10, 2012; accepted in revised form September 25, 2012.

0363-5023/13/38A01-0021$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2012.09.032

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FIGURE 1: Index finger specimen which has been dissected to expose the course and attachment sites of the proper RCL. (A), metacarpal head; (B) base of the proximal phalanx; asterisk, proper radial collateral ligament.

However, upon surgical exposure, the surgeon may encounter substantial scarring and obscuration of the ligament insertion sites, particularly after delayed treatment.4 There are no detailed descriptions of these attachments specifically for the proper RCL at the index MP joint. Previous descriptions of the anatomy of the proper portion of the index RCL have qualitatively described its bony origin along the dorsolateral tubercle of the metacarpal and its attachment along the proximal phalanx near the volar plate7,8 and demonstrated the dynamic nature of its length,7 but have not quantitatively described the locations of these attachments in relation to landmarks that are readily discernible during surgery. We performed cadaveric dissections to provide detailed, quantitative descriptions of the ligamentous attachment points of the proper RCL at the index MP joint. We placed emphasis on the location of these bony insertion sites relative to the dorsal, volar, and articular margins of the bone, landmarks that are easily visualized intraoperatively. This information can be used when determining graft insertion sites in the repair or reconstruction of the proper RCL of the index MP joint. MATERIALS AND METHODS We harvested 17 fresh-frozen cadaveric index finger specimens distal to the carpometacarpal joint from 13 male and 4 female donors with an average age of 53 years (range, 33– 64 y). We dissected away the overlying soft tissues to expose the MP joint and the RCL. We identified the accessory RCL and detached it from the metacarpal and volar plate, leaving only the proper RCL intact (Fig. 1). Using loupe magnification, we sharply divided the bony attachment sites of the proper RCL with a scalpel blade while tensioning the ligament

substance. We sequentially marked the entry points of the Sharpey fibers into the bone with an indelible marker (Fig. 2). The marker site was patted dry with gauze to prevent running or blurring of the marks. This was done for both the metacarpal and proximal phalanx attachments. We took measurements using digital calipers from the center of the attachments on the metacarpal and proximal phalanx, the edge of the attachment closest to the MP articular surface, the dorsal margin of the metacarpal insertion point, and the volar margin of the proximal phalanx to the immediately adjacent level of the MP articular surface and the dorsal and volar borders of the metacarpal and proximal phalanx (Fig. 3). We also measured the height and width of each ligamentous attachment site. We took high-resolution photographs of the specimens with a ruler in plane with the MP joint to calibrate for subsequent digital measurements. We took separate photographs of the metacarpal and proximal phalanx insertion sites to maximize visualization of the dorsal, volar, and articular surfaces of each bone. The same measurements taken with calipers were repeated with digital analysis software (Image J; NIH, Bethesda, MD). We calculated the area of each bony attachment site. The bony attachment sites were best fitted to an ellipse, and we used the center of this best-fit ellipse in the measurements. We employed the Pearson correlation test to evaluate the relationship between the manual caliper and digital photo measurements. Descriptive statistics were calculated for each measurement. RESULTS There was a strong correlation (r ⫽ 0.71; P ⬍ .001) between the caliper and digital measurements. Figures 3

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FIGURE 2: Index finger specimen in which the native RCL has been sharply excised from its bony attachments. The insertion points are marked and prepared for digital photo analysis. Arrowhead indicates metacarpal attachment of RCL; asterisk indicates proximal phalangeal attachment of RCL. This photograph was used for analysis of the RCL attachment to the metacarpal.

FIGURE 3: Measurements taken of the distances from the centers of the index RCL metacarpal and phalangeal attachment sites to the bony landmarks. The metacarpal head is to the left and the base of the proximal phalanx is to the right. Center of the origin at the metacarpal from the dorsal surface (A), articular surface (B), and volar surface (C). Center of the phalangeal insertion from the dorsal surface (D), articular surface (E), and volar surface (F).

and 4 show the digital measurements, which are reported in Table 1. The total height of the metacarpal was 14 mm, placing the center of the metacarpal RCL attachment 40% volar from the dorsal border of the metacarpal. The dorsal-most margin of the attachment site was 20% from the dorsal border of the metacarpal. The total height of the proximal phalanx was 12 mm, placing the center of the metacarpal RCL attachment 46% dorsal from the volar border of the proximal phalanx. The volar-most margin of the attachment site was 20% from the volar border of the proximal phalanx. DISCUSSION We have provided detailed definitions of the anatomy of the origin and insertion of the RCL at the index MP

joint. Appreciation for the importance of early diagnosis and treatment of injuries to the RCL of the index MP joint is growing.1 Acute primary repair of the index RCL is preferred,1–3 but in cases where diagnosis is delayed or attempts at nonoperative treatment have failed, the surgeon may encounter a ligament that cannot be repaired and ligament attachment sites that are obscured by scar. We have provided pragmatic information that allows the surgeon to replicate the anatomic origin and insertion of the RCL of the index MP joint by relying on the bony cortex, readily discernible during ligament reconstruction. Minami and colleagues7 performed an in-depth description of the anatomy of the RCL of the index MP joint and elegantly used biplanar radiography

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FIGURE 4: Measurements taken of the height and width of the index RCL metacarpal and phalangeal attachment sites and the distances from the edges of the ligamentous attachment sites to the bony landmarks. The metacarpal head is to the left and the base of the proximal phalanx is to the right. G, height of the metacarpal insertion point; H, width of the metacarpal insertion point; J, height of the phalangeal insertion point; K, width of the phalangeal insertion point; L, distance of dorsal aspect of the metacarpal origin from the dorsal edge of the metacarpal; M, distance of volar aspect of the phalangeal insertion from the volar edge of the phalanx; N; distance of distal-most margin of the metacarpal origin from the articular surface; P, distance of proximalmost margin of the phalangeal insertion from the articular surface.

to define the borders of the RCL’s bony attachments in 7 cadaveric specimens. After inserting metallic markers along the dorsal border of the metacarpal attachment and volar border of the proximal phalanx attachment, these borders were defined radiographically using a coordinate system for each bone centered on the sagittal and coronal axises. Because of differences in methodology, it is difficult to compare the quantitative measurements in our study with those in the study by Minami et al. Cursory evaluation of our results and the figures and text of their article show general agreement. Our study expands upon the work of Minami et al by marking the entirety of the ligamentous attachment point, which may explain our finding that the center of the metacarpal attachment tends to be more volar than previously described. The dorsal rim of the metacarpal attachment coincides with the dorsolateral tubercle; however, its center is 5.4 mm volar from the dorsal border of the metacarpal, or approximately 40% of the height of the metacarpal. In addition, the proximal phalanx insertion site of the index RCL may be more dorsal than previously thought. When viewed in the context of a complementary study using similar methods,9 the proximal phalanx insertion of the RCL of the index MP joint is positioned more dorsally than its counterpart at the thumb MP joint. The insertion of the RCL is 2.8 mm (or 29% of the bony height) from the volar surface of the thumb proximal phalanx9 but 5.7 mm (or 46% of the height) from the volar surface

of the index proximal phalanx. The relatively central positions in the sagittal plane of both the metacarpal and phalangeal attachments of the RCL may contribute to the clinical finding of greater laxity during ulnar deviation at the index MP joint compared with the thumb, particularly with the joint in extension. One specific limitation of our study is that we used an indelible marker to mark the footprint of the ligamentous insertion, introducing the possibility of ink bleeding onto adjacent tissue and altering the accuracy of our markings. We attempted to prevent this by carefully drying the ink after each application. Despite this limitation, we believe that our definition of the bony attachments of the index RCL is helpful to surgeons seeking to replicate the native orientation of the ligament. In a series of finger RCL reconstructions at the MP joint with long-term follow-up, Rierderer et al4 presented 20 cases reconstructed with tendon graft passed through the isometric attachment points. Graft fixation was achieved by suturing the proximal end to the dorsal interosseous fascia overlying the metacarpal and by suturing the distal end to the periosteal ridge at the origin of the A2 pulley. As mentioned in their analysis, Rierderer and colleagues thought that 3 of their reconstructions exhibited instability at 3 months, which they suspected resulted from poor fixation of the graft to bone. Because biomechanical testing has revealed both suture anchors and interference screws to have superior strength and stiffness compared with suture fixation through a bone tunnel,10 we believe that this mode of

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TABLE 1.

Anatomic Measurements

Mean (mm)

SD

Measurement Description

A

5.4

1.1

Center of origin at metacarpal from dorsal surface

B

10.3

3.2

Center of origin at metacarpal from articular surface

C

8.0

2.2

Center of origin at metacarpal from volar surface

D

6.8

1.4

Center of phalangeal insertion from dorsal surface

E

4.4

0.8

Center of phalangeal insertion from articular surface

F

5.7

0.9

Center of phalangeal insertion from volar surface

G

6.4

1.4

Height of metacarpal insertion point

H

5.8

1.6

Width of metacarpal insertion point

J

5.7

0.9

Height of phalangeal insertion point

K

5.0

1.1

Width of phalangeal insertion point

L

2.8

1.3

Distance of dorsal aspect of metacarpal origin from dorsal edge of metacarpal

M

2.5

0.8

Distance of volar aspect of phalangeal insertion from volar edge of phalanx

N

7.4

3.1

Distance of distal-most margin of metacarpal origin from articular surface

P

2.0

0.8

Distance of proximal-most margin of phalangeal insertion from articular surface

Measurements wee taken of the distances from the centers of the index RCL metacarpal and phalangeal attachment sites to the bony landmarks, height and width of attachment sites, and distances from the edges of the ligamentous attachment sites to the bony landmarks. Figures 3 and 4 show these measurements.

failure can be overcome with the use of modern implants. Rierderer et al emphasized the importance of recreating the anatomic path of the ligament to successfully reconstruct the RCL, and the pragmatic information we have provided will help the treating surgeon in following these recommendations. In our anatomic investigation, we found that the center of the metacarpal attachment of the RCL at the index MP joint is 5.4 mm from the dorsal surface of the metacarpal and 10.3 mm from the articular cartilage. The center of the phalangeal attachment is 5.7 mm from the volar surface of the proximal phalanx and 4.4 mm from the articular surface. REFERENCES 1. Gaston RG, Louri GM, Peljovich AE. Radial collateral ligament injury of the index metacarpophalangeal joint: an underreported but important injury. J Hand Surg Am. 2006;31(8):1355–1361. 2. Doyle JR, Atkinson RE. Rupture of the radial collateral ligament of the metacarpo-phalangeal joint of the index finger: a report of three cases. J Hand Surg Br. 1989;14(2):248 –250. 3. Kang L, Rosen A, Potter HG, Weiland AJ. Rupture of the radial collateral ligament of the index metacarpophalangeal joint: diagnosis and surgical treatment. J Hand Surg Am. 2007;32(6):789 –794. 4. Rierderer S, Nagy L, Buchler U. Chronic post-traumatic radial instability of the metacarpophalangeal joint of the index finger: long-term results of ligament reconstructions. J Hand Surg Br. 1998;23(4):503–506. 5. Hsieh Y-F, Draganich LF, Piotrowski GA, Mass DP. Effects of reconstructed radial collateral ligament on index finger mechanics. Clin Orthop Relat Res. 2000;(379):270 –282. 6. Bean CH, Tencer AF, Trumble TE. The effect of thumb metacarpophalangeal ulnar collateral ligament attachment site on joint range of motion: an in vitro study. J Hand Surg Am. 1999;24(2):283–287. 7. Minami A, An K-N, Cooney WP, Linscheid RL, Chao EYS. Ligamentous structures of the metacarpophalangeal joint: a quantitative anatomic study. J Orthop Res. 1984;1(4):361–368. 8. Rubin LE, Miki RA, Taksali S, Bernstein RA. Metacarpophalangeal collateral ligament reconstruction after band saw amputation: case report with review of MCP anatomy and injury. Iowa Orthop J. 2008;28:53–57. 9. Carlson MG, Warner KK, Meyers K, Hearns KA, Kok P. The anatomy of the thumb metacarpophalangeal ulnar and radial collateral ligaments. J Hand Surg Am. In press. 10. Lee SK, Kubiak EN, Liporace FA, Parisi DM, Iesaka K, Posner MA. Fixation of tendon grafts for collateral ligament reconstructions: a cadaveric biomechanical study. J Hand Surg Am. 2005;30(5):1051–1055.

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