Abstract
Background: The 1-incision and 2-incision techniques are commonly used methods to repair a distal biceps rupture, and they differ in the location of reinsertion of tendon into bone.
Hypothesis: The native distal biceps brachii tendon inserts on the posterior-ulnar aspect of the bicipital tuberosity, which functions as a cam, increasing the tendon's moment arm during its principal action of forearm supination. Repair of the distal biceps tendon to the anterior aspect of the tuberosity compromises forearm supination due to absence of the bicipital tuberosity's cam effect.
Study Design: Controlled laboratory study.
Methods: Eleven matched pairs of fresh-frozen cadaveric upper extremities were prepared for repair of the distal biceps tendon using either anterior or posterior reattachment with transosseous suture fixation. Specimens were tested on a materials testing machine with intact distal biceps insertion and after repair. A load cell at the distal radial-ulnar joint measured resultant elbow flexion and forearm supination torque produced by 100-N force applied to the proximal aspect of the tendon.
Results: Although there was a trend (P = .104) toward loss of supination torque with the anterior reconstruction method, no significant differences in torque (0.80 vs 0.89 N·m) or flexion force (11.87 vs 12.07 N) were found between the anterior and posterior reconstruction techniques.
Conclusion: There is no statistically significant difference in flexion force or supination torque between the anterior and posterior reconstruction techniques.
Clinical Relevance: This study supports existing limited clinical data suggesting no functional differences exist between 2 common repair methods. Further biomechanical and clinical investigations directly comparing the results of distal biceps tendon repairs made to the anterior aspect versus the posterior aspect of the tuberosity are necessary to definitely determine if differences exist in resultant elbow flexion and forearm supination functions.
The function of the biceps brachii includes elbow flexion and forearm supination. Considering that the distal biceps tendon wraps around the bicipital tuberosity and inserts on its posterior aspect (Figures 1 and 2), it appears that the tuberosity may function as a cam. In the same fashion that the patella improves the function of the extensor mechanism by increasing the distance of the line of pull to the axis of rotation of the knee, the bicipital tuberosity may function by altering the distance of the tendon in relation to the axis of rotation of the radius. It is well known that supination function, to a greater degree than flexion function, is severely compromised by rupture of the distal biceps tendon.2,4,13,14 Acute anatomical repair can restore both functions to normal or near-normal levels.2,3,6,7,9,14
Dissection of embalmed left upper extremity human cadaveric specimen showing anatomical insertion of distal biceps tendon on posterior-ulnar aspect of bicipital tuberosity.
Anteroposterior (A) and cross section (B) of the normal biceps insertion.
Different methods of distal biceps tendon repair have evolved over the past century.1,3,5,7,10,11,15,16 Current methods generally fall into 1 of 2 categories: 1-incision repair techniques in which the ruptured tendon is reattached to the anterior aspect of the tuberosity (Figure 3) or 2-incision repair techniques in which the tendon is reattached more closely to its true anatomical insertion on the posterior aspect of the tuberosity (Figure 4). Although proponents of particular repair techniques have cited specific advantages in terms of surgical exposure, ease of tendon reattachment, and rates of complications, excellent clinical and functional results have been reported in studies of both repair methods.1,3,5,7,8,10,11,15,16
Anteroposterior (A) and cross section (B) of the biceps attachment after 1-incision technique.
Anteroposterior (A) and cross section (B) of the biceps attachment after 2-incision technique.
Given the anatomical considerations outlined above, we hypothesized that repair of the distal biceps tendon to the anterior aspect of the tuberosity would compromise the resultant supination function compared with repair to the posterior aspect of the tuberosity and compared with the intact tendon state due to loss of the “cam” effect. To our knowledge, no previous study has directly compared the functional results of these 2 methods of repair of the ruptured distal biceps tendon. The purpose of this biomechanical study was to use a cadaveric model to perform this comparison in a controlled laboratory setting.
Methods
Eleven matched pairs of fresh-frozen upper extremity cadaveric specimens were thawed to room temperature and dissected, preserving the distal biceps tendon and its insertion, the elbow joint capsule, and the distal radioulnar joint soft tissue complex. Specimens were tested in pairs. One specimen in each pair (anterior group) was first tested with its distal biceps tendon intact and again after an anterior repair, whereas the contralateral specimen (posterior group) was tested intact and again after posterior repair.
Each specimen was mounted in the testing apparatus with 4-point fixation of the humerus (Figure 5). The forearm bones were fixed in full supination using a 0.625 K-wire. With the elbow at a 90° starting angle and a load cell placed at the level of the distal radioulnar joint, a 100-N force was applied to the proximal biceps tendon. The resultant elbow flexion force (newtons) was recorded by the materials testing machine (MTS, Minneapolis, Minn). To determine forearm supination torque (newton-meters), the forearm pin was removed, and the ulna was fixed to the testing apparatus at a 90° angle to the humerus. The forearm was placed at a neutral starting position, and a quarter-inch Steinman pin was inserted through the distal radius parallel to the load cell. The 100-N force was again applied to the proximal biceps tendon and a resultant supination force (newtons) produced by the Steinman pin onto the load cell. This value was multiplied by the distance (meters) from the center of the distal radius to the center of the load cell to calculate torque (newton-meters).
Testing apparatus and measurement of elbow flexion force (newtons) resultant to a 100-N force applied to the proximal biceps tendon in left upper extremity specimen.
With the same specimen still fixed within the testing apparatus, the distal biceps tendon was then sharply excised from its insertion and prepared with a No. 5 Ethibond whipstitch. The tendon was then repaired to the bicipital tuberosity by 1 of 2 methods. Repair to the anterior aspect of the tuberosity was performed by the method described by Kaeding et al 7 (anterior group). With the forearm in maximum supination, the cortex of the anterior-ulnar tuberosity was lightly burred. Two parallel eyelet guide pins were drilled through the tuberosity from anterior to posterior, angled approximately 25° proximal. The suture was pulled through the tuberosity and tied securely over the posterior cortical bridge. This repaired specimen was then tested by the same protocol described above. The repair site was observed for signs of tendon wear, suture fixation failure, or loss of tendon-bone apposition.
The testing sequence was then repeated in the contralateral specimen. After testing the intact specimen, the distal biceps tendon was repaired to the posterior aspect of the tuberosity using the modified Boyd-Anderson technique (posterior group). With the forearm fully pronated, a bur was used to excavate the posterior tuberosity, and 2 small drill holes were placed on the radial side. The tendon was passed between the forearm bones and drawn into the defect by pulling the sutures through the drill holes. The sutures were tied over a cortical bone bridge, and testing was performed.
An analysis of covariance was performed to determine if significant differences existed between the anterior group and the posterior group for both elbow flexion and forearm supination. Each model included the intact measurement for each sample. Two surgeons performed all of the procedures (4 pairs and 7 pairs), so a variable for surgeon was tested in each model to account for any variability or difference because of surgeon.
Results
The results summarized in Table 1 reveal that no significant differences were found between the 2 groups with adjustments for the intact measurement for elbow flexion (anterior group, 11.87 N; posterior group, 12.07 N;P= .691) or supination force (anterior group, 5.00 N; posterior group, 6.02 N; P = .111). The adjusted anterior group showed a trend toward loss of supination torque (0.80 N·m) compared with the adjusted posterior group (0.89 Nm), although this did not reach significance (P = .104). The intact measurement for each sample did not differ in the cadaveric upper extremities between the 2 groups. The surgeon variable was significant only when comparing supination force. However, the difference in the adjusted means of supination force was not significant between the 2 groups when it was adjusted for by the intact measurement alone or when both intact measurement and surgeon were added. Because of this, the surgeon variable was not included in the model.
Summary Statistics and Comparison of Continuous Variables
Each outcome was adjusted for the intact measurement.
A power analysis based on a Student 2-sample t test of the adjusted means revealed that in a future study, 86 specimens per group would be necessary to detect a significant difference in the adjusted means and SDs as seen in supination force in our data, with an α of .05 and 80% power. This is a conservative estimate, and the power would increase slightly if a linear model with significant covariates were used.
Grossly, there were no tendon ruptures during testing in either the intact or repaired states. The repaired tendons showed no compromise in suture fixation or in tendon-to-bone apposition during the testing.
Discussion
Rupture of the distal biceps tendon causes impairments in elbow flexion and forearm supination functions that are unacceptable to most physically active patients.2,4,13,14 Surgical treatment is generally advised to restore these functions. Methods described as “anatomical” involve reattachment of the distal biceps tendon directly to the bicipital tuberosity and have been shown in several studies to restore both flexion and supination functions.1,3,4,6,9,14,15 Previous studies, however, have included both 1-incision and 2-incision techniques within the classification of an anatomical repair. 15 On the basis of the anatomy of the distal biceps tendon insertion and in support of our hypothesis, we believe that 1-incision and 2-incision techniques are not equally anatomical and therefore should be considered separately. The purpose of this study was to determine if repair of the ruptured distal biceps tendon to the anterior aspect of the tuberosity, as accomplished with a 1-incision technique, would compromise the resultant forearm supination torque compared with repair to the posterior aspect of the tuberosity adjusted for the intact tendon state.
Historically, anatomical repair of the distal biceps tendon through an anterior approach required extensive soft tissue dissection within the cubital fossa.5,8,12 This was associated with several complications, including radial and median nerve injuries.5,8 In 1961, Boyd and Anderson 5 described their classic 2-incision technique. This minimized the amount of anterior dissection, thereby decreasing the risk of nerve injury, although other complications including heterotopic ossification and radial-ulnar synostosis occurred as a result of extensive soft tissue dissection on the posterior aspect of the elbow. 5 Modifications of this 2-incision technique have reduced these risks while enabling anatomical reattachment of the distal biceps tendon to the posterior aspect of the tuberosity.1,7,10,11,16 Clinical results have generally been excellent, and several studies using isokinetic testing methods have reported full or near-full restoration of elbow flexion and forearm supination functions.1,6,7,10,11,14,16
More recently, several authors have advocated 1-incision techniques.1,10,11 Using suture anchors or different types of pull-through suture fixation, the ruptured distal biceps tendon is reattached directly to the anterior aspect of the bicipital tuberosity. Several retrospective studies have reported few complications and generally excellent clinical results. Only 2 studies, however, included isokinetic testing for resultant elbow flexion and forearm supination functions.1,9 Although their results were comparable with those after traditional 2-incision repairs, there is insufficient evidence to determine that 1-incision and 2-incision repair techniques equally restore elbow flexion and, most important, forearm supination functions. Although suture anchors may be used more commonly in clinical practice for a 1-incision repair, our technique of tying a knot over a bony bridge as described above should not alter the biomechanical results as the insertion site would be identical, without introducing confounding variables such as anchor breakage and pullout.
To our knowledge, this is the first biomechanical study to investigate different methods of distal biceps tendon repair for the effect on elbow flexion and forearm supination functions. The results support our null hypothesis, showing no significant differences for either elbow flexion force or forearm supination torque resultant to a 100-N force applied to the intact, anterior repaired, or posterior repaired distal biceps tendon. We were able to show a trend toward loss of supination force, although this did not reach significance. Intuitively, this corresponds with the anatomy of the distal biceps tendon insertion and the function of the bicipital tuberosity as a cam mechanism to increase supination function. A power analysis revealed that an excessive number of cadaveric specimens would be required for the small difference to reach significance. If such a cam function does exist in vivo, then either our testing methods were insensitive to detect any difference between repairs made to the anterior aspect of the tuberosity and to those made to the more anatomical insertion on the posterior aspect of the tuberosity or current anatomical repair methods may negate/minimize the cam effect. In either case, we believe any difference that may exist would be too small to be clinically relevant. Because of the small number of cadaveric specimens available, we did not randomize for patient handedness, nor did we stratify results based on skeletal age. We are unaware of any literature that relates bicipital tuberosity characteristics (size, location, etc) to handedness or age, although if there is significant variation, this may be relevant.
Further biomechanical and clinical investigations directly comparing the results of distal biceps tendon repairs made to the anterior aspect versus the posterior aspect of the tuberosity are necessary to definitely determine if differences exist in resultant elbow flexion and forearm supination functions. In addition, biomechanical factors should not be the sole consideration of the surgeon. Familiarity with the surgical technique as well as complication rates of each should also be considered.
This initial biomechanical study supports existing limited clinical data to suggest that there are no significant functional differences between these 2 common repair methods. This information may add support to those surgeons preferring a 1-incision technique—that although the distal biceps is reattached anterior to its true anatomical insertion, a significant loss of supination function does not seem to occur.