Biomechanical Comparison of Two Surgical Repair Techniques of the Distal Biceps Tendon

Abstract

Purpose

This study aimed to characterize the relationship between the distal biceps tendon force and the supination and flexion rotations during the initiation phase and to compare the functional efficiency of anatomic versus nonanatomic repairs.

Methods

Seven matched pairs of fresh-frozen cadaver arms were dissected to expose the humerus and elbow while preserving the biceps brachii, elbow joint capsule, and distal radioulnar soft tissue complex. For each pair, the distal biceps tendon was severed with a scalpel and then repaired with bone tunnels placed at either the anterior (anatomic) or the posterior (nonanatomic) aspect of the bicipital tuberosity on the proximal radius. A supination test with 90° of elbow flexion and an unconstrained flexion test were conducted on a customized loading frame. The biceps tension was applied incrementally at 200 g per step, whereas the radius rotation was tracked with a 3-dimensional motion analysis system. The tendon force needed to produce a degree of supination or flexion was derived as the regression slope of the tendon force-radial rotation plots. A two-tailed paired t test was performed to compare the difference between the anatomic repair and the nonanatomic repair cadavers.

Results

Significantly greater tendon force was required to initiate the first 10° of supination with the elbow in flexion for the nonanatomic group compared with the anatomic group (1.04 ± 0.44 N/degree vs 0.68 ± 0.17 N/degree, P = .02). The average nonanatomic to anatomic ratio was 149% ± 38%. No difference existed between the two groups in the mean tendon force needed to produce the degree of flexion.

Conclusions

Our results show that anatomic repair is more efficient in producing supination than nonanatomic repair, but only when the elbow is in 90° of flexion. When the elbow joint is not constrained, the nonanatomic supination efficiency improved, and the difference between the techniques was not significant.

Clinical relevance

The present study added to the body of evidence in comparing anatomic versus nonanatomic repair of the distal biceps tendon and serves as a foundation for future biomechanical and clinical studies in this topic. Given no difference when the elbow joint was not constrained, one could argue that surgeon comfort and preference could guide which technique to use when addressing the distal biceps tendon tears. More studies will be needed to clearly define whether there will be a clinical difference between the two techniques.

The biceps brachii muscle functions as a strong supinator of the forearm and a weaker elbow flexor. The distal tendon of the biceps muscle has a particularly complex anatomy.^1,2 It contains short and long heads that externally rotate as they coalesce and attach to the ulnar side of the radial tuberosity. During this rotation, the medially located short head externally rotates and attaches in a more distal and radial position to the long head on the radial tuberosity.1, 2, 3 In turn, the radial tuberosity acts as a cam that increases biceps supination torque. Although rare, rupture of the distal biceps tendon can be devastating, decreasing supination and flexion strength by as much as 50% and 40%, respectively.4, 5, 6 Surgical repair is the mainstay treatment for avulsion, which usually yields excellent restoration of functionality.^4,6

Distal biceps tendon repairs are well studied in the literature, with numerous publications having been conducted on clinical outcomes and fixation methods.^7,8 Repairs typically use either a 1-incision or a 2-incision technique with varying types of fixation.^4,9, 10, 11 The 1-incision technique reattached the distal biceps tendon in a nonanatomic position located more anterior and radially than native anatomy. Meanwhile, the 2-incision technique externally rotates and reattached the tendon near its true anatomic site on the posterior aspect of the radial tuberosity. Proponents of either technique remark advantages in surgical exposure, ease of reattachment, surgical time, and complication rate; although, studies have shown no statistical differences in clinical outcomes of both techniques.^7,9,10,12,13 The choice to use 1- or 2-incision repairs has thus far been decided by the surgeon's comfort with the procedure. Despite no clinically significant differences, there are previous biomechanical studies that suggest possible functional differences in biceps brachii function between both surgical techniques. Specifically, supination may be affected because nonanatomic repairs in cadaveric arms were previously shown to generate less supination torque when in neutral and supinated starting positions.^14,15 However, no significant differences in flexion have been seen across both techniques so far.^14,16,17 Although most of these studies focused on the force generated during the movement phase, none, to our knowledge, has yet to describe the force required to initiate movements in both supination and flexion for both techniques.

The intent of this research was to characterize the relationship of the biceps tendon force with flexion and supination rotation during the rotation initiation phase. Our goal was to add to the growing body of research into functional differences between distal biceps tendon repair techniques. Given the anatomical differences between both techniques, we hypothesized that the 2-incision (anatomical) repair of the distal biceps tendon would result in less tendon force required to initiate supination and flexion as opposed to 1-incision (nonanatomical) repair. To research this, we conducted a study using matched pairs of fresh-frozen cadaveric arm specimens and assessed the biceps tendon loads required to initiate supination and flexion after anatomic and nonanatomic repairs.

Methods

Specimens preparations

Seven matched pairs of fresh-frozen cadaveric arm specimens from elderly donors (two men and five women, mean age: 77.6 years) were procured for the study. The specimens were transected approximately 5 cm proximal to the wrist and stored in sealed plastic bags at −20°C. Within each pair, specimens were assigned to receive either anatomic or nonanatomic repair. The apex of the bicipital tuberosity was used as the bisector separating the nonanatomic location from the anatomic location (Fig. 1). The humerus and elbow were dissected, preserving the distal biceps tendon, elbow joint capsule, and distal radioulnar soft tissue complex. The distal biceps tendon was first severed with a scalpel and then repaired with bone tunnels placed at one of the two aforementioned areas. The Krackow stitches with No.2 FiberWire sutures were used in the tendon, and the sutures were pulled through the bone tunnels and tied down on the other side of the cortex.

Figure 1.

Illustration of the anchoring locations of the two repair approaches. Top: anatomic repair with a posterior bone tunnel (shaded oval); the arm is placed in full supination to approach the posterior part of the radial tuberosity. Bottom: nonanatomic repair with an anterior bone tunnel. The area shaded in red shows the radial tuberosity, small blue dots used for suture passing and tying over a bone bridge.

Experimental protocols

Two sets of loading tests, a supination test and an unconstrained flexion test, were conducted on a customized loading frame (Fig. 2). The humerus was rigidly bolted to the frame in a vertical position. The elbow was kept in a 90° flexion position during the supination test by pining the distal ulna through its canal to a hole on an adjustable bracket. The flexion constraint was removed for the flexion test, and the distal ulna rested on top of the bracket. The long and short heads of the bicep tendon were sutured together (No. 2 FiberWire). The suture was then connected to a weight-pulley system for the application of tendon force along the anatomic line of biceps action. Another weight-pulley system was set up at the distal radius to apply a small counter-balance pronation torque (250 g weight for 0.075 Nm counter-torque). The biceps tension was created by applying force in a stepwise fashion increasing by 200 g (∼2 N) sequentially until it passed the point where the resulting supination torque overcame the pronation counter-torque for the supination test or 135° flexion was reached for the flexion test. Marker triads from a motion analysis system (Optotrak Certus) were attached to the distal radius to track its movement regarding the fixed humerus. Both tests started with the forearm in a maximum-pronated position upheld by the counter-torque. The forearm was constrained at 90° flexion throughout the supination test, whereas in the flexion test, the forearm started from a 90° flexion position supported by a point contact at the distal ulna. Each test was conducted three times, and the averaged data of the three trials were used for further analysis.

Figure 2.

Experimental setup.

Data analysis

Supination and flexion rotations of the radius were plotted against the applied tendon forces. To quantify the motion initiation response, the regression average of the tendon force needed to produce a degree of supination or flexion of the radius was derived, using data from the first 10° of primary rotation. The differences between the anatomic and nonanatomic repairs were compared using a two-tailed paired t test, with the level of statistical significance set at .05. The nonanatomic over anatomic ratio was also calculated for each pair.

Results

In the supination test with the elbow flexed at 90°, significantly greater tendon force is required to initiate the first 10° of supination for the nonanatomic group than that in the anatomic group (1.04 ± 0.44 N/degree vs 0.68 ± 0.17 N/degree, P = .02) (Fig. 3). The average nonanatomic to anatomic ratio was 149% ± 38%.

Figure 3.

The biceps tendon force required to initiate a degree of supination at 90° elbow flexion from individual pairs of nonanatomic and anatomic repairs.

In the unconstrained flexion test, the mean (SD) tendon force needed for the degree of flexion was 0.60 ± 0.24 N/degree and 0.44 ± 0.33 N/degree for the nonanatomic and anatomic, respectively. This difference was not statistically notbale (P = .09). The tendon force per degree of unconstrained supination accompanied by the flexion was 0.84 ± 0.24 N/degree and 0.68 ± 0.10 N/degree for the two respective groups (P = .13). Data from individual pairings are presented in Figure 4.

Figure 4.

The biceps tendon force required to initiate a degree of unconstrained flexion (left) and accompanied supination (right) from individual pairs of nonanatomic and anatomic repairs.

Discussion

Historically, distal biceps tendon repair is associated with several complications, including posterior interosseus nerve and lateral antebrachial cutaneous nerve injuries. These particular complications are more common with the single anterior incision technique.¹⁸ Furthermore, it is difficult to achieve anatomic repairs through the single-incision technique (the tendon is usually inserted on the anterior aspect of the tuberosity with this technique).¹¹ In 1961, Boyd and Anderson¹⁹ described their classic two-incision technique that minimized the amount of anterior dissection, thereby decreasing the risk of nerve injury. This technique also enables the anatomical reattachment of the distal biceps tendon to the posterior aspect of the tuberosity. However, other complications such as heterotopic ossification and radioulnar synostosis are increased because of extensive soft tissue dissection on the posterior aspect of the elbow with this technique.^11,18

A few studies have compared patients’ isometric strength in supination and flexion between the two techniques but with conflicting findings. In a retrospective review of 26 patients, with an average follow-up of 33 months, Johnson et al¹¹ found no statistically significant differences regarding flexion strength or endurance, supination strength or endurance, or complication rates between the single-incision and two-incision techniques. Another retrospective review of 37 acute patients after a 1-year follow-up reported a 20% greater improvement in supination torque with the two-incision technique over the one-incision technique.²⁰

Grewal et al²¹ conducted randomized clinical trials comparing 1-incision versus 2-incision (n = 47 and 44, respectively) and found that the 2-incision group had 10% better isometric flexion strength at the 24-month follow-up.

Previous biomechanical studies looking at the functional differences between anatomic and nonanatomic repairs have focused on isometric torque generated at the proximal radius in response to one specific level of tendon force.^14,16,22 The present study is novel in that it aimed to capture the relationship between tendon force and supination/flexion movement, specifically in the initiation phase of biceps function. We hypothesized that anatomical repair of the distal biceps tendon would result in less tendon force required to initiate supination as opposed to the nonanatomical repair. The results of this study partially support this hypothesis. Anatomic repairs have a more efficient initiation force for supination, but only when the elbow is flexed at 90°. When the elbow is unconstrained, there was no difference in the efficiency between both the groups. This finding may be explained by the previous functional studies demonstrating that the biceps brachii contributes the most toward supination torque when the elbow is flexed at 90°.²³ As the elbow approaches 0° or is less constrained, the biceps brachii contributes less toward supination as the supinator muscle supplies more force. Therefore, it is reasonable to assume that an anatomic repair of the distal biceps tendon has a more efficient supination at 90° of elbow flexion because of the native placement of the tendon on its insertion site. Nonanatomic repairs are likely not as efficient in producing supination because of the anterior placement on the radial tuberosity, resulting in a less efficient cam effect. These results are supported by previous evidence suggesting nonanatomic repair results in loss of supination.^14,15

Prud’homme-Foster et al¹⁴ compared the effect of anatomic and nonanatomic repairs on forearm supination torque, by testing eight fresh-frozen cadaver arms both before and after tendon resection and repair. All their anatomic repairs showed no difference compared with intact tendon measurements. When comparing anatomic and nonanatomic repairs, they found no differences in the supination torque when the forearm was in 45° of pronation. However, when the arm was in neutral rotation, they found that 15% less supination torque was generated by the nonanatomic repair. When the arm was tested in 45° of supination, they found that 40% less supination torque was generated in the nonanatomic repair.

Henry et al¹⁶ compared elbow flexion and forearm supination in eleven matched pairs of fresh-frozen cadavers after repair of the distal biceps tendon using either anterior (nonanatomic) or posterior (anatomic) reattachment with trans-osseous suture fixation. Although there was a trend toward loss of supination torque with the nonanatomic method (there was a nonsignificant 10% reduction in supination torque in the nonanatomic repair with the forearm fully pronated), they found no significant differences in torque or flexion force between the anterior and posterior reconstruction techniques.¹⁶

In comparison to the aforementioned studies, our study showed that the nonanatomic repair had a 49% deficiency over anatomic repair during supination initiation. These findings support the notion that more sufficient tendon wrapping around the tuberosity, as afforded by the anatomic repair, preserves the advantage of the cam effect for efficient supination function.¹⁴

Tendon placement on the bicipital tuberosity likely plays less of a role in generating flexion force than supination torque. It is also possible that this result is a consequence of the brachioradialis muscle providing most of the initiation force for elbow flexion, given the resting pronated position and thus increased slack in the distal biceps tendon.^24,25 Regardless, this finding is consistent with the current literature as previous functional studies on flexion strength have shown no difference between the two techniques.^14,16,17

It is important to note the limitations of our study. One major limitation is the advanced age of our cadavers. The average cadaver age of 77.6 years in this study may not be representative of the common population for distal biceps tendon ruptures, which usually occur in weightlifters around the ages of 40 to 50 years.²⁶ There is also a concern for the influence of dominant vs. nondominant extremities, as repair of the dominant extremities has previously been shown to maintain more strength compared with the nondominant one.²⁷ Although this was relatively mitigated through a random repair assignment for each arm, this effect is possibly more prevalent in our study due to a small sample size. This study also only focused on the pronated starting position of the forearm, whereas future studies could look at more neutral and supinated positions.

In conclusion, our results showed that anatomic repair is more efficient in initiating supination motion than nonanatomic repair, but only when the elbow is in 90° of flexion. When the elbow joint is not constrained, the supination efficiency of the nonanatomic repair improved and the difference between the two techniques was no longer significant. The two techniques are also not significantly different in initiating the flexion of the forearm. Although our results are limited by a small sample size and pronated-only starting position, our study adds to the body of evidence comparing anatomic versus nonanatomic repair of the distal biceps tendon. More biomechanical and clinical studies comparing the results of distal biceps tendon repairs through the anatomic and nonanatomic repair techniques are needed to definitively determine whether differences exist in the resultant forearm supination and elbow flexion functions. However, our study can serve as a foundation for future biomechanical and clinical studies on this topic. Given no difference when the elbow joint was not constrained, one could argue that surgeon comfort and preference could guide which technique to use when addressing distal biceps tendon tears. More clinical studies in this area will hopefully determine whether there is a clinical difference between the two techniques.