Abstract
Background
The biceps brachii is the main forearm supinator, which is a direct consequence of its anatomic arrangement. The primary aim of distal biceps rupture is to restore supination strength and function. Cadaveric studies demonstrate that anatomic repairs significantly improve the supination moment when compared to more anterior repairs; however, this has not been tested in the clinical setting. The aim of this study was to compare biomechanical and clinical outcomes of an anatomic repair (Footprint), with a widely used transosseous technique (Endobutton).
Methods
Twenty-two patients were retrospectively identified from a clinical database (11 Footprint versus 11 Endobutton). Biomechanical performance of strength and endurance for flexion and supination was assessed using a validated isokinetic dynamometry protocol and clinical outcome scores (Quick Disabilities of the Arm, Shoulder and Hand Outcome Measure and the Mayo Elbow Performance Score) were collected for all patients.
Results
For supination, the Footprint group demonstrated a superior trend for all biomechanical parameters tested. This was statistically significant for mean peak torque, total work of maximal repetition and work in the last third of repetitive testing (p = 0.031, p = 0.036 and p = 0.048). For flexion, the Footprint group demonstrated a superior trend for all biomechanical parameters tested but this was only statistically significant for work in the last third of repetitive testing (p = 0.039). The clinical outcomes were good or excellent for all patients in both groups.
Conclusion
This study is the first to demonstrate that an anatomic Footprint repair restores superior biomechanical supination strength and endurance compared to a conventional Endobutton technique in a clinical setting. Both techniques, however, provide good or excellent clinical outcomes.
Keywords: Distal biceps, repair, elbow, Footprint, Endobutton, supination
Introduction
The biceps brachii is the primary forearm supinator and has a secondary role as an elbow flexor. These functional attributes are a direct consequence of its anatomy. The two distinct heads of the biceps are obvious at their origins but can also be defined individually at their insertion onto the radial tuberosity where they attach as a single functional unit.1 The footprint of the distal biceps attachment is at the apex of the bicipital tuberosity when viewed in the coronal plane. The tuberosity itself is offset ulnarly from the axis of the radius when the forearm is fully supinated, dorsally when the forearm is in neutral rotation and radially when the forearm is pronated.1,2 This anatomic relationship means that contraction of the biceps muscle creates a cam effect to produce supination of the radius.
If instead, the biceps is attached along the long axis of the radius, biceps contraction only produces a supination moment when the forearm is in a pronated position, as this is the only position where a more anterior attachment site will still be offset from the axis of the radius. In contrast, an anatomic attachment site will remain offset from the long axis throughout the arc of rotation3 (Figure 1). Hence the effect of an offset distal biceps attachment site is most pronounced when the forearm is in a neutral to fully supinated position.
Figure 1.
Illustrations demonstrating the moment arm of the repaired biceps tendon from the axis of the radius (dots), in a traditional Endobutton technique (a), and in the Footprint technique (b). In the fully supinated position, the Footprint technique creates a larger moment arm distance (d) and is thus likely to improve supination strength and endurance. Source: Image used with permission from Phadnis and Bain.4
Surgical fixation primarily aims to restore functional supination strength, therefore it would seem desirable to try and reproduce the native anatomic insertion of the biceps tendon to the radial tuberosity. Cadaveric biomechanical studies have demonstrated that an anatomic repair does improve the supination moment as compared to a more anterior repair, particularly when the forearm is in the supinated or neutral position.3
Distal biceps repair is performed through either a single or double incision approach using suture anchors, transosseous tunnels with cortical buttons or tunnels alone; interference screws or a combination of the above.5,6
Transosseous cortical button (TCB) fixation is popular as it can be performed through a single, discrete anterior incision and provides the greatest resistance to pull out when compared to other techniques.7,8 In this technique, the transosseous tunnel is created as close to the ulnar margin of the radial tuberosity as possible, in order to best restore the supination moment; however, this does not recreate the true footprint, so the supination torque is not optimized. There is also a risk of tunnel blowout, particularly if a large diameter docking hole is created. Directing the drill radially may minimize the risk of blowout but this drill angle places the posterior interosseous nerve (PIN) at greater risk.9
Alternative single incision transosseous techniques, which restore the native biceps footprint anatomy, have been described using transosseous tunnels alone or with a cortical button.4,10 In one of these studies, biomechanical testing was performed to assess the supination force of the repaired tendon as compared with the patient’s uninjured contralateral arm. The authors demonstrated no significant reduction in supination force except for peak supination torque at 60 degrees/s and the power of supination at 120 degrees/s.9
Both techniques have been shown to closely restore supination strength compared to the patient’s uninjured arm10,11 although there has been no clinical comparison between the two techniques.
The aim of this study was to investigate whether there was any difference in the biomechanically tested flexion and supination strength and/or clinical outcomes when comparing an anatomic single incision repair using a cortical button versus a standard TCB repair.
The null hypothesis was that there would be no difference in the biomechanical properties or patient-reported outcomes between each technique.
Methods
The Southern Adelaide Human Research Ethics Committee approved the study (Protocol number 42.15). All participants gave informed consent regarding the biomechanical testing.
Patients
A power analysis performed by Wittstein et al.12 when comparing isokinetic biceps performance in dominant and non-dominant arms found that five subjects were required to detect a significant difference in peak supination or flexion torque with 80% power and an alpha value of 0.05 (based on the mean and standard deviations described by Leighton et al.13).
On this basis, the aim was to test a minimum of five patients from each surgical technique group.
All procedures were performed by or under the direct supervision of the senior surgeon (GIB). The standard Endobutton technique7 was used for all consecutive patients up until December 2013. Following development of the Footprint technique,4 it became the preferred method of treating distal biceps ruptures.
This change of practice forms the basis for a clinical comparison between the two techniques.
Using a clinical database, 101 consecutive patients who had been treated surgically for a distal biceps tendon rupture at least one year prior to the study were retrospectively identified. Patients with non-acute tears, partial tears or tears requiring graft reconstruction were excluded.
Patients with any complications other than transient lateral cutaneous nerve palsies were excluded. Two patients in the Endobutton group were therefore excluded because of haematoma requiring re-operation for washout. One patient from the Footprint group had a double incision approach for suture retrieval and fixation during the early development of the technique, so was excluded. There were no re-tears or posterior interosseous nerve injuries in the whole series using either technique.
All remaining patients were invited to attend for assessment of patient-reported functional outcome and biomechanical performance testing.
Twenty-two patients (11 in each group) were suitable and available to be included in the study. All patients were male, and there was no significant difference in the age of patients in each group (Endobutton mean age 60 years (SD ± 10.9) versus Footprint mean age 54 years (SD ± 9.2), p = 0.08).
Eight-one per cent (9/11) had repair on the dominant arm in the Endobutton group and 54% (6/11) had repair on the dominant arm in the Footprint group (p = 0.093).
As a consequence of the change in practice during the clinical series, the delay until testing following surgery was significantly longer in the Endobutton group compared to the Footprint group (ET mean 5.29 years versus FT mean 1.99 years p = < 0.01).
None of the patients in either group had experienced any post-operative complications or re-operations.
Surgical techniques
Both techniques have been described in the literature but the salient points are outlined below.
Endobutton technique
A single anterior incision in the proximal forearm is made. The torn tendon end is retrieved, debrided and whip stitched using two number 2 Fibrewire (Arthrex, Naples, Florida, USA) sutures in a Krackow configuration from proximal to distal. The sutures are passed through an Endobutton (Smith and Nephew, UK) and the tendon is then whip stitched from distal to proximal such that the knots are tied proximally. After exposure of the tuberosity, a unicortical docking hole is created with a high-speed burr, the size of which is dependent on the patient’s tendon. A 4.5 mm drill hole is made through the dorsal cortex of the radius to allow passage of the Endobutton. Passage of the button is achieved using a straight needle or Beath pin with leading and trailing sutures placed in the peripheral holes of the Endobutton, so that the tendon is docked into the trough and the Endobutton lies against the dorsal cortex of the radial tuberosity.
Footprint technique
A single anterior incision is made in the proximal forearm. The torn tendon is retrieved outside the wound, debrided and whip stitched with two number 2 Fibrewire (Arthrex, Naples, Florida, USA) sutures from distal to proximal, then proximal to distal in a Krackow configuration such that four suture strands exit at the distal aspect of the tendon. Two 2.5 mm drill holes are created in the radius from anterior to posterior exiting on the posterior aspect of the radial tuberosity. A shuttling technique using an epidural needle and loop of monofilament suture is used to pass the fibrewire sutures from posterior to anterior through the drill holes. The tendon is reduced to the tuberosity by pulling on the sutures. This places the tendon on the surface of the tuberosity at its normal anatomic position. The four suture strands are passed individually through the four holes of an Endobutton and knots are tied to secure the repair with the Endobutton lying on the anterior surface of the proximal radius.
Rehabilitation
This was the same in both groups. The elbow was immobilized in a bulky bandage/plaster slab and sling for one week following surgery. Active range of motion was initiated thereafter with no heavy lifting or contact sports allowed for three months.
Outcome measures
Patient-reported outcome measures (PROMs) and clinical outcome
The Quick Disabilities of the Arm, Shoulder and Hand Outcome Measure (QuickDASH) and the Mayo Elbow Performance Score (MEPS) were collected for all patients on the same day as their biomechanical testing.
Biomechanical performance testing
Biomechanical performance was assessed using an isokinetic dynamometer (Biodex System 3 Dynamometer, Biodex Medical Systems Inc., Shirley, NY) and followed a previously published and validated testing protocol.14
Trial testing was performed on healthy volunteers prior to commencement of patient testing, in order to ensure correct and consistent use of the testing apparatus during the study. The dynamometer was calibrated in accordance with manufacturer’s instructions prior to testing each individual.
The testing was performed by three independent investigators, who were blinded to the surgical technique that had been performed.
No adjustment was made for hand dominance as the dominant and non-dominant arms have been shown to demonstrate similar peak torque and endurance for supination and flexion.12
The patients were first familiarized with the dynamometer and given time to practice trial repetitions until confident with the testing protocol.
Actual testing was commenced following a 1 min break after trial testing.
Supination was measured first in the non-operated arm followed by the operated arm. The dynamometer was then calibrated for flexion testing and this was done in the same order. Hence, the non-operated arm was used as an individual control for each patient.
During testing, the patient was asked to perform three maximum effort repetitions followed by a minute rest and then asked to perform 50 consecutive repetitions. Verbal encouragement was given throughout to maintain maximal effort.
Strength was evaluated using the value for peak torque in Newton meters (N m) generated during each test.
Endurance was evaluated using total work and work fatigue.
Total work is the sum of work (in Joules) for all repetitions performed during testing.
Work fatigue is the ratio of the difference expressed as a percentage between the work performed in the first third of repetitive testing to that performed during the last third.
A positive biomechanical performance difference between the two groups tested was defined as one where there was a statistically significant difference between the operated arm of the two groups but no statistically significant difference between the non-operated control arms for a given parameter of strength and endurance measured during testing. Hence, if there was a significant difference between the groups for both the operated and non-operated arms (control) this was not considered to be a statistically relevant difference.
Statistical analysis
Categorical variables and baseline demographic data are described by frequencies and percentages. Continuous variables are presented as means and standard deviations. The Student’s t-test (paired) was used to test for differences between the two groups with a significance level of <0.05 set for all analyses.
Results
Patient demographics
Table 1 summarizes the demographic characteristics of the patients in the two groups.
Table 1.
Patient demographic; hand dominance and operated side; time from intervention to follow-up.
| Endobutton repair | Footprint repair | ||||
|---|---|---|---|---|---|
| Age (years) | Dominant hand? (Dom/Non) and operated side | Days after repair to functional assessment | Age (years) | Dominant hand? (Dom/Non) and operated side | Days after repair to functional assessment |
| 68 | Dom – Right | 2157 | 46 | Dom – Right | 986 |
| 69 | Dom – Right | 1567 | 72 | Dom – Right | 1274 |
| 63 | Dom – Right | 2672 | 65 | Dom – Right | 682 |
| 48 | Dom – Right | 2427 | 54 | Dom – Right | 417 |
| 56 | Dom – Right | 1711 | 53 | Dom – Left | 559 |
| 50 | Dom – Right | 2333 | 44 | Non – Left | 731 |
| 72 | Dom – Right | 1641 | 47 | Non – Left | 735 |
| 60 | Dom – Right | 1649 | 57 | Non – Left | 1165 |
| 79 | Dom – Left | 1941 | 60 | Non – Left | 605 |
| 62 | Non – Left | 1482 | 59 | Dom – Right | 349 |
| 43 | Non – Left | 1662 | 43 | Non – Right | 489 |
PROMs/clinical outcome
The PROMs were good or excellent for all patients in both groups.
There was no significant difference in mean MEPS (Endobutton 97.3 versus Footprint 97.7, p = 0.852) or QuickDASH score (Endobutton 5.2 versus Footprint 5.0, p = 0.952) between the two groups. There was no correlation between the PROMs or clinical outcome scores and the biomechanical data. Table 2 summarizes the PROMs/clinical outcome for each group.
Table 2.
Patient-reported outcome measures (PROMs) and clinical outcome scores for Endobutton and Footprint repairs.
| Quick Disabilities of the Arm, Shoulder and Hand Outcome Measure (QuickDASH) | Mayo Elbow Performance Score (MEPS) | |||
|---|---|---|---|---|
| Repair technique | Endobutton repair | Footprint repair | Endobutton repair | Footprint repair |
| 0 | 4.5 | 100 | 100 | |
| 9.1 | 29.5 | 100 | 90 | |
| 2.3 | 4.5 | 100 | 100 | |
| 0 | 0 | 100 | 100 | |
| 4.5 | 0 | 100 | 100 | |
| 6.8 | 0 | 100 | 100 | |
| 27.3 | 0 | 80 | 100 | |
| 0 | 15.9 | 100 | 85 | |
| 0 | 0 | 95 | 100 | |
| 0 | 0 | 100 | 100 | |
| 6.8 | 0 | 95 | 100 | |
| Mean | 5.2 | 5.0 | 97.3 | 97.7 |
| Student’s t-test p-value | =0.952 | =0.852 | ||
Biomechanical performance outcomes
A significant difference between the groups was only considered relevant if a significant difference was seen between the groups for the operated arm but not for the control arm.
Flexion
For flexion, the Footprint group demonstrated a superior trend for all biomechanical parameters tested; however, the only parameter with a significant difference during testing was for mean work done in the last third of repetitive testing, which was greater in the operated arm of the Footprint group compared to the operated arm of the Endobutton group (Endobutton 293.2 J versus Footprint 386.2 J, p = 0.039).
There were no other significant biomechanical performance differences between the operated arms for the two groups for all other parameters measured during flexion testing.
Table 3 shows the results of biomechanical testing of flexion for both groups.
Table 3.
Biomechanical functional outcomes for flexion between Endobutton and Footprint repairs.
| Functional outcome measured | Arm (repaired or control) | Endobutton repair (mean average) | Footprint repair (mean average) | Student’s t-test (p-value) bold = p < 0.05 |
|---|---|---|---|---|
| Peak torque flexion (N m) | Repaired arm | 38.3 | 41.8 | 0.273 |
| Control arm | 37.4 | 40.9 | 0.223 | |
| Average peak torque flexion (N m) | Repaired arm | 25.1 | 28.6 | 0.194 |
| Control arm | 24.0 | 28.15 | 0.182 | |
| Work of maximal rep flexion (J) | Repaired arm | 44.8 | 53.7 | 0.096 |
| Control arm | 42.81 | 54.34 | 0.032 | |
| Total work of trial flexion (J) | Repaired arm | 1332.3 | 1739.6 | 0.028 |
| Control arm | 1303.5 | 1731.0 | 0.019 | |
| Work in first third flexion (J) | Repaired arm | 618.2 | 776.4 | 0.059 |
| Control arm | 561.5 | 769.43 | 0.014 | |
| Work in last third flexion (J) | Repaired arm | 293.2 | 386.2 | 0.039 |
| Control arm | 311.4 | 399.7 | 0.068 | |
| Work fatigue flexion (% of J; first versus last third) | Repaired arm | 48.0 | 50.1 | 0.375 |
| Control arm | 42.0 | 47.6 | 0.209 | |
| Average power flexion (W) | Repaired arm | 21.8 | 28.4 | 0.029 |
| Control arm | 20.8 | 27.9 | 0.021 |
Supination
For supination, the Footprint group demonstrated a superior trend for all biomechanical parameters tested. The parameters that showed a significant difference between the operated arms of the two groups were as follows:
A significantly greater mean peak torque of supination in the operated arm of the Footprint group compared to the Endobutton group (Endobutton 5.8 N m versus Footprint 7.6 N m, p = 0.031).
A significantly greater total work of maximal repetition of supination in the operated arm of the Footprint group compared to the Endobutton group (Endobutton 8.5 N m versus Footprint 12.0 N m, p = 0.036).
A significantly greater work in the last third repetitive testing of supination in the operated arm of the Footprint group compared to the Endobutton group (Endobutton 106.3 J versus Footprint 157.7 J, p = 0.048).
There were no other significant biomechanical performance differences between the operated arms for the two groups for all other parameters recorded during supination testing.
Table 4 shows the results of biomechanical testing of supination for both groups.
Table 4.
Biomechanical functional outcomes for supination between Endobutton and Footprint repairs.
| Functional outcome measured | Arm (repaired or control) | Endobutton repair (mean average) | Footprint repair (mean average) | Student’s t-test (p-value) bold = p < 0.05 |
|---|---|---|---|---|
| Peak torque supination (N m) | Repaired arm | 8.2 | 9.2 | 0.189 |
| Control arm | 8.5 | 9.2 | 0.294 | |
| Average peak torque supination (N m) | Repaired arm | 5.8 | 7.6 | 0.031 |
| Control arm | 5.8 | 6.6 | 0.159 | |
| Total work of maximal rep supination (J) | Repaired arm | 8.5 | 12.0 | 0.036 |
| Control arm | 10.46 | 12.1 | 0.186 | |
| Total work of trial supination (J) | Repaired arm | 342.6 | 493.1 | 0.051 |
| Control arm | 344.8 | 416.4 | 0.145 | |
| Work in first third supination (J) | Repaired arm | 121.0 | 169.2 | 0.051 |
| Control arm | 129.5 | 162.3 | 0.100 | |
| Work in last third supination (J) | Repaired arm | 106.3 | 157.7 | 0.048 |
| Control arm | 100.2 | 120.55 | 0.181 | |
| Work fatigue supination (% of J; first versus last third) | Repaired arm | 89.46 | 90.08 | 0.463 |
| Control arm | 77.40 | 75.18 | 0.323 | |
| Average power supination (W) | Repaired arm | 5.3 | 7.1 | 0.680 |
| Control arm | 4.9 | 5.7 | 0.197 |
Discussion
There is a substantial body of cadaveric, biomechanical and non-comparative data to suggest that an anatomic reconstruction of the distal biceps is likely to better restore supination force than a relatively non-anatomic anterior repair.1,2,10
This study directly compared the biomechanical and clinical outcomes of an anatomic distal biceps repair (Footprint group) with a widely used transosseous technique (Endobutton group) and in doing so, is the first study to assess the effect an anatomic distal biceps repair has on restoration of supination and flexion force in a comparative clinical study.
The results demonstrated superior biomechanical performance in the Footprint group for several of the measured parameters during supination testing (mean peak torque, total work of maximal repetition and work in the last third of supination). The findings related to supination torque suggest that the results seen in cadaveric testing are replicated in the clinical situation when a Footprint (anatomic) repair is performed, although not all parameters tested for supination showed a significant difference between the groups. In particular, there was no difference in the degree of fatigue seen during repetitive testing of the two repair techniques.
In this study, supination was tested through the full arc of rotation. It may have been of value to specifically measure supination strength from a neutral to fully supinated position specifically as this is the region in the rotation arc that is most likely to be influenced by an anatomic repair.3 In addition, fatigue may have been more apparent in this part of the rotation arc.
However, the testing methods used were based on a validated protocol and according to the manufacturer’s guidelines. Furthermore, to reduce bias and error, a period of trial testing was performed prior to commencement of the study and during the study, testing was performed by researchers who were blinded to the type of repair performed.
Both repair techniques adequately restored flexion strength compared to the control arms and there was no consistent superiority between the two types of repair with regard to flexion strength. We did not expect to see a difference in flexion strength; however, it was important to demonstrate that an anatomic repair does not compromise flexion strength. The similarity in flexion testing also suggests that the improved supination strength was an isolated effect from anatomic repair.
In this study, there was no difference in the patient-reported outcome scores between the two groups and all patients in both groups either had good or excellent outcomes. In addition, despite the advantage seen in relation to supination for the Footprint group, the conventional Endobutton repairs also restored supination strength to greater than 80% of the control arms in all parameters recorded. This is in keeping with the results reported by other authors.8,11
These findings raise the question as to whether the biomechanical advantage of an anatomic repair is a clinical improvement that can be perceived by patients. The PROMs scores in this study were good or excellent for both groups; however, it is possible that that the PROMs used are not sensitive enough to demonstrate these differences.
If therefore both techniques produce equivalent PROMs and an anatomic repair has been demonstrated to restore supination strength more effectively in cadaveric and now clinical testing, should the question be, ‘why not perform an anatomic repair’ as long as it can be done using a safe, reproducible technique. There were no serious complications (re-tear or PIN injury) in the Footprint group of the patients tested in this study or those in the larger series of the senior author. In another study reporting a very similar technique in 27 patients, there was only one re-rupture following a trauma and no PIN injuries.10 Hence, this single incision anatomic technique appears to fulfil the criteria for safety and reproducibility and may be preferable to surgeons who favour a single incision repair.
There are limitations to this study. First, there was no prospective randomization of patients as the two techniques were performed exclusively at different time points. Consequently, the follow-up period for the Footprint patients was shorter than for the Endobutton patients, although only patients with a minimum one-year follow-up were included. It might have been expected that with longer follow-up, the restoration of normal function and strength would be greater, as the patient would have had more time for rehabilitation and consolidation of the repair; however, the converse was seen – Footprint patients with a shorter post-operative time performed better with regard to supination strength. Another possible reason for this may have been because the Footprint group tended to be younger than the Endobutton group (also a reflection on the different follow-up time) even though there was no statistically significant difference between the groups according to age. To mediate this, the patient’s own un-operated arm was used as a control and a difference between the groups was only considered to be present when there was a significant difference between the repaired arms but not between the control arms.
There were only 11 patients in each group and whilst this was adequate according to the historical power analysis13 to show a biomechanical difference, it only represents around 20% of patients undergoing these procedures in the senior surgeon’s practice and it would always be preferable to test a larger group of patients. This is difficult to achieve in practice because of the willingness required by working age participants to retrospectively attend for testing which may be time consuming and inconvenient for them.
Conclusion
Clinical testing demonstrated that an anatomic single incision distal biceps repair restores superior supination torque compared to a conventional Endobutton technique. Both techniques have a low complication rate and provide equivalent good or excellent PROMs.
Acknowledgement
This article is based on work presented at the British Elbow & Shoulder Society conference as a free paper in June 2017.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Ethical Review and Patient Consent
The Southern Adelaide Human Research Ethics Committee approved the study (Protocol number 42.15).
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