Use of an Abductor Pollicis Brevis Tendon Slip for Reconstruction of the Radial Collateral Ligament of the Thumb Metacarpophalangeal Joint: An Anatomical Investigation

Abstract

Background

Reconstruction of the radial collateral ligament (RCL) of the thumb metacarpophalangeal (MP) joint is commonly performed for chronic injuries. This study aims to evaluate the anatomical feasibility and reliability of using the abductor pollicis brevis (APB) tendon to reconstruct the RCL.

Methods

Ten cadaver arms were dissected to evaluate the relationship between insertions of the RCL and APB. A slip of the APB was divided from tendon and reflected proximally. The dissected tendon was deemed sufficient for reconstruction if it could be reflected to the footprint of the RCL origin. The size of the dissected APB slip was then compared with that of the RCL.

Results

The dissected slip of the APB could be fully reflected proximally to the RCL origin in all specimens. The APB insertion was also found to be closely approximated to the RCL insertion, averaging 2.1 mm distal and 1.8 mm dorsal. Significant differences existed between the lengths (P < .001) of the APB slip and RCL, with no significant difference in widths (P = .051).

Conclusions

A sufficient APB tendon slip can be obtained to reliably reconstruct the RCL of the thumb MP. The location of the APB insertion closely approximates the RCL insertion.

Introduction

Treatment of chronic high-grade injuries of the radial collateral ligament (RCL) of the thumb metacarpophalangeal (MP) joint is commonly performed through reconstruction of the RCL.^1,2 Multiple reconstruction techniques have been described, including both free tendon grafting^2,3 and local tissue reconstruction.^4-6 One previously described method of local tissue reconstruction uses a slip of the abductor pollicis brevis (APB) tendon to reconstruct the RCL. ⁵ In contrast to previously described techniques of APB advancement to provide additional dynamic stability, this technique does not require release of the APB from its insertion site, and use of the tendon slip creates static stability, mirroring the action of the RCL.^4,7 Unlike free tendon grafting, this technique offers the ability to reconstruct the RCL without harvesting a separate tendon.

Although the use of an APB slip has previously been described in the literature, this study aims to more fully evaluate the local anatomy and feasibility of the technique. As such, we evaluated the reliability of obtaining a sufficiently sized APB tendon slip for reconstruction, and we compared the size of the tendon slip with the native ligament. We also quantified the anatomical relationship of the APB and RCL insertion sites.

Methods

We dissected 10 fresh-frozen cadaver arms under loupe magnification. A direct lateral incision was made over the radial aspect of the thumb MP. Dissection was carried down bluntly to the level of the APB aponeurosis. The aponeurosis was then incised sharply near the extensor pollicis longus tendon to expose the APB tendon. The tendon was easily identified in all cadavers and was sharply incised longitudinally to create a half-slip of tendon, which roughly approximated the width of the RCL while maintaining the continuity of the tendon. The radial half of the divided APB tendon was then proximally incised sharply at the musculotendinous junction (Figure 1). Once the tendon slip had been defined, the deep side of the tendon was released bluntly from the underlying muscle. For the purposes of this study, the remaining APB tendon was then released distally from its insertion to increase visualization of the collateral ligaments and proximal phalanx. This exposed the MP capsule, which was then sharply incised at the dorsal border of the RCL and dissected from the ligaments to improve visualization. Once the exposure was completed, the dissected slip of APB was then reflected proximally to overlie the RCL origin. If the reflected slip was able to fully cover the extent of the RCL origin proximally, it was determined to be of sufficient length for reconstruction. (Figure 2)

Figure 1.

Demonstration of the abductor pollicis brevis tendon slip (black asterisk) following its division from the remaining abductor pollicis brevis tendon (white asterisk).

Figure 2.

A demonstration of the dissected abductor pollicis slip (arrow) overlying an intact radial collateral ligament (RCL) (denoted by asterisk).

Note. The tendon slip is clearly able to be reflected proximally to the origin of the RCL. The metacarpal is denoted by “MC,” and the proximal phalanx is denoted by “P1.”

The collateral ligament and the APB slip were then dissected sharply from their insertion points on the proximal phalanx. Throughout the dissection, the insertion points of the ligament and tendon slip were marked with a permanent marker to precisely define the area of origin. The center points of insertions were then determined visually, which have been shown to correlate closely with digital photo analysis. ⁸ Measurements were then taken from the center of insertion points to both the volar cortex of the proximal phalanx and the articular surface. Finally, the length and width of the resected RCL and abductor pollicis slip were measured. All measurements included in this study were made with a digital caliper.

Statistical Considerations

Ninety-five percent confidence intervals for all measurement values are presented using a Student t distribution. Paired 2-sample t test was used for all statistical comparisons with a significance level of P ≤ .05.

Results

A sufficiently sized APB slip was isolated for RCL reconstruction in all cadavers. On average, the APB inserted 4.5 mm (±0.7 mm) from the articular surface of the proximal phalanx and 5.1 mm (±0.6 mm) from the volar cortex. The RCL inserted an average of 2.4 mm (±0.7 mm) from the articular surface and 3.3 mm (±0.6 mm) from the volar cortex of the proximal phalanx. The APB tendon slip inserted a mean of 2.1 mm (±0.6 mm) distal and 1.8 mm (±0.9 mm) dorsal to the insertion of the RCL. (Figure 3)

Figure 3.

Insertional relationship between the insertion of the abductor pollicis (arrow) and the radial collateral ligament (asterisk).

Note. The metacarpal is denoted by “MC,” and the proximal phalanx is denoted by “P1.”

The mean length of the RCL was 10.1 mm (±0.9 mm), and the mean width was 5.5 mm (±0.7 mm). The mean length of the dissected APB slip was 27.2 mm (±3.2 mm), and the mean width was 4.3 mm (±0.7 mm). There was a statistically significant difference between the lengths (P < .001) of the RCL and APB slip. However, the difference between the widths of the RCL and APB slip was not statistically significant (P = .051)

Discussion

Many authors advocate for the reconstruction or local soft tissue advancement in the surgical treatment of chronic RCL injuries with a variety of techniques described. This is largely due to the concern for attenuation of the ligament and an inability to achieve satisfactory restoration of stability with primary ligament repair. Durham et al ⁹ described attenuation of the RCL in 8 (75%) of 12 patients with greater than 2 months of instability. In contrast, Posner and Retaillaud ¹⁰ noted ligament attenuation requiring free tendon reconstruction in only 33% of chronic RCL injuries treated surgically. The location of the injury to the RCL may contribute to the need for additional stability beyond direct repair. Coyle ¹¹ showed reliable pain relief and reconstitution of joint stability with soft tissue advancement and bony reattachment with a supplementary intra-articular pinning of the MP joint in patients with RCL tears adjacent to either the proximal phalanx or the metacarpal head. However, 7 (16%) of the 45 patients with RCL tears were described as having a midsubstance tear that was not amenable to direct reattachment and were treated with free tendon reconstruction or abductor pollicis advancement.

Previously published outcomes of RCL reconstruction have shown largely successful results. Catalano et al ² showed restoration of pinch and grip strength in 10 patients with chronic RCL injuries treated with reconstruction, resulting in 8 excellent results and 2 good results. However, MP motion was 59% of the MP motion on the contralateral side following reconstruction. Durham et al ⁹ showed restoration of stability following treatment for chronic RCL injuries with a variety of techniques. Postoperatively, no injured thumbs demonstrated ulnar laxity, but there was a significant decrease in MP range of motion (ROM). Camp et al ⁷ performed APB advancement to treat chronic RCL instability in 8 patients and found restoration of functional stability in all patients. Reduced MP ROM was present in 4 (50%) patients, but the authors noted it did not result in loss of function.

Our study demonstrates this technique is an anatomically reliable and feasible method of RCL reconstruction. The APB slip was sufficiently sized for reconstruction in all specimens while leaving a large portion of the APB tendon undisturbed, which should prevent any functional deficit resulting from the use of the tendon. In addition, no significant statistical differences were found between the widths of the RCL and the APB slip. A statistically significant difference (P < .001) was found between the lengths of the APB slip and RCL, which suggests use of a shorter APB slip would be sufficient for reconstruction. Our results support previously published data describing the location of RCL insertion. ⁸ In addition, they show a close anatomical relationship between insertions of the RCL and the APB slip, with the ABP inserting 2.1 mm (±0.6 mm) distal and 1.8 mm (±0.9 mm) dorsal to the insertion of the RCL on average.

Surgical treatment of chronic RCL instability has shown reliably good results, but decreases in joint motion are commonly reported.^2,7,9 Nonanatomical reconstruction has been hypothesized to contribute to postoperative loss of motion. ¹² Although no definitive evaluation of nonanatomical reconstruction of the RCL has shown that it leads to loss of motion, there is biomechanical evidence suggesting that nonanatomical ulnar collateral ligament (UCL) reconstruction of the thumb MP can decrease motion. In that study, Bean et al ¹³ found a decrease in flexion from 56° to 47° and a decrease in radial deviation from 18° to 10° when the insertion of the UCL was placed 2 mm distal to the native insertion of the ligament. When the insertion was moved 2 mm dorsally, no significant change in MP ROM was found. Although it is unknown whether a similar effect would be seen with nonanatomical RCL reconstruction, it would imply that using an APB slip, which inserts an average of 2.1 mm distal to the RCL, could lead to a slight decrease in flexion. This theoretical biomechanical effect is supported by the clinical results of RCL reconstruction, with an APB slip reported by Iba et al ⁵ demonstrating a 6° decrease in flexion postoperatively.

Iba et al ⁵ presented a series of 8 patients treated for chronic RCL injury with reconstruction using a half-slip of the APB tendon at an average of 51 months of follow-up. All patients had previously been treated with thumb spica splinting for acute RCL injury for 3 or 4 weeks. Following a course of nonoperative treatment, all patients continued to have significant limitations in their activities in addition to pain, and surgery was performed at a range of 31 to 360 days after the initial injury. Intraoperatively, the joint was not stabilized with an intraarticular wire, and the patients were placed in a thumb spica splint for 4 weeks following surgery. The authors showed reliably good results at an average of 51 months of follow-up. All patients were symptom-free, and the MP joint was stable to ulnar-directed stress postoperatively. In addition, all patients were able to fully return to preinjury activities and sports within 6 months of surgery. A 6° decrease in joint flexion was noted, but there was no change in thumb interphalangeal joint motion or MP extension. Postoperative pinch strength was found to be 167% of preoperative pinch strength, and grip strength was found to be 112% of preoperative grip strength at final follow-up. In addition, the average Disabilities of the Arm, Shoulder, and Hand score postoperatively was 2.

As an anatomically reasonable technique that eliminates the need for free tendon harvest, we believe this is a reasonable technique deserving further investigation. In addition, previously published clinical results have been promising. At this time, results of this technique have only been published in 1 series, and there are no published studies evaluating the strength of the reconstruction or its effect on ROM. As such, further clinical and laboratory investigation would be helpful to further define its utility prior to widespread adoption.