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Torsional Fracture of the Humerus after Subpectoral Biceps Tenodesis with an Interference Screw: A Biomechanical Cadaveric Study
Clinical Biomechanics 30 (2015) 915–920
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Torsional Fracture of the Humerus after Subpectoral Biceps Tenodesis with an Interference Screw: A Biomechanical Cadaveric Study David P. Beason a,⁎, Jay P. Shah b, James W. Duckett a, Patrick W. Jost a, Glenn S. Fleisig a, E. Lyle Cain Jr. a b
a
American Sports Medicine Institute, Birmingham, AL, USA Division of Orthopaedic Surgery, University of Alabama at Birmingham, Birmingham, AL, USA
a r t i c l e
i n f o
Article history: Received 10 February 2015 Accepted 20 July 2015 Keywords: Biceps tenodesis Biomechanical Torsion Spiral fracture Humerus Interference screw
a b s t r a c t Background: Humeral fracture following subpectoral biceps tenodesis has been previously reported; however, there are no published biomechanical studies reporting the resulting torsional strength of the humerus. Our purpose was to determine if there is an increased risk of humerus fracture after subpectoral biceps tenodesis with an interference screw and to determine if screw size is also a factor. We hypothesized that limbs receiving the procedure would have reduced failure torque and rotation under external rotation compared to untreated controls and that the larger screw size would result in inferior mechanical properties compared to the smaller. Methods: Twenty matched pairs of embalmed cadaveric humeri were subjected to subpectoral biceps tenodesis using either a 6.25 or 8.0 mm interference screw, with the untreated contralateral limb serving as a control. Each humerus was mechanically tested in torsional external rotation to failure. Findings: Maximum torque and rotation to failure were reduced in the tenodesis group compared to controls; however, there was no difference between screw sizes. When both screw sizes were combined into a single group, paired t-tests also showed similar differences. Interpretation: Based on our experiment, there is an increased risk for humerus spiral fracture when subjected to torsional external rotation after subpectoral biceps tenodesis with an interference screw compared to an intact humerus; however, there is not a significant difference between a 6.25 mm and 8.0 mm screw. Surgeons may elect to use alternative fixation methods in patients at high risk (e.g., overhead throwing athletes, etc.) for torsional loads and fracture. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Tendinosis of the long head of the biceps is a common and significant cause of pain in the shoulder (Friedman et al., 2008; Provencher et al., 2008). Controversy exists in the literature with respect to the ideal treatment of recalcitrant biceps tendinopathy. No consensus has been achieved with respect to tenotomy versus tenodesis, location of tenodesis, or method and/or size of tenodesis fixation (Elser et al., 2011; Khazzam et al., 2012; Mazzocca et al., 2005a,2005b; Millett et al., 2008; Nho et al., 2010b). The appropriate treatment takes into account many factors: patient age, level of function, associated shoulder pathology, and surgeon preference. Subpectoral biceps tenodesis has recently increased in popularity due to its simplicity, preservation of length-tension relationship, advantage of an interference screw, and low complication rate (Mazzocca et al., 2005a, 2008; Millett et al., 2008; Nho et al., 2010a; Provencher et al., 2008).
⁎ Corresponding author at: 833 St. Vincent’s Drive, Suite 205, Birmingham, AL 35205, United States. Tel.: +1 205 918 2116; fax: +1 205 918 2179. E-mail address: [email protected] (D.P. Beason).
http://dx.doi.org/10.1016/j.clinbiomech.2015.07.009 0268-0033/© 2015 Elsevier Ltd. All rights reserved.
Subpectoral biceps tenodesis with an interference screw has been shown to have a complication rate of 2% in a recent large clinical series with no cases of fracture reported (Nho et al., 2010a). Two additional outcomes studies also have not reported any fractures (Mazzocca et al., 2008; Millett et al., 2008); however, humeral fracture after subpectoral biceps tenodesis has been listed as a potential complication in several other case studies (Dein et al., 2014; Friedel et al., 1995; Gyulai, 1990; Provencher et al., 2008; Reiff et al., 2010; Sears et al., 2011). One study reported on two humerus fractures in healthy, active patients that occurred within six months of surgery using a technique similar to the current and previous studies (Sears et al., 2011). In both cases, the fracture included the cortical drill hole used for screw placement and occurred at 3 and 6 months post-operatively. Another reported proximal humerus fracture after keyhole biceps tenodesis 12 weeks after surgery in a 50 year-old female. Radiographs showed that the fracture involved the tenodesis drill hole (Reiff et al., 2010). Another reported humerus fracture of a 46year-old male baseball pitcher following open subpectoral biceps tenodesis with an 8-mm bioabsorbale interference screw. Again, radiographs indicated a spiral fracture through the drill site (Dein et al., 2014). At our institution, we have had two previously unreported cases of humeral fracture following biceps tenodesis within the previous two
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years. In one, a 56 year-old male, who had undergone open biceps tenodesis with a 6.25 x 15 mm polyether ether ketone (PEEK) interference screw, fell out of bed on the night of surgery. Radiographs revealed a proximal third spiral fracture of the humerus that involved the tenodesis interference screw hole (Fig. 1a). A second case involved a 42 year-old male who had undergone biceps tenodesis with 6.25 x 15 mm PEEK interference screw. After around one year, his left humerus was fractured (Fig. 1b) at the site of the tenodesis screw. Although the biomechanical properties of various methods of tenodesis have been previously studied (Arora et al., 2013; Buchholz et al., 2013; Golish et al., 2008; Mazzocca et al., 2005a; Sethi et al., 2013; Slabaugh et al., 2011; Tashjian and Henninger, 2013), only pullout strength has been evaluated. To our knowledge, there are no published studies reporting the torsional strength of bone after subpectoral biceps tenodesis with an interference screw. The purpose of the current study was to biomechanically determine the effect of subpectoral biceps tenodesis on the torsional fracture properties in matched pairs of cadaveric humeri with two different commercially available screw sizes. We hypothesized that limbs receiving the biceps tenodesis procedure would have reduced failure torque and rotation under external rotation compared to matched limbs not having received the procedure. Further, we hypothesized that the larger of the two screw sizes would result in inferior mechanical properties compared to the smaller screw size. 2. Methods 2.1. Surgical technique The subpectoral biceps tenodesis technique has previously been described (Mazzocca et al., 2005b). This technique was modified for a cadaveric study as follows. The study was performed on 20 matched pairs of embalmed human cadaveric humeri obtained from the University of Alabama at Birmingham Anatomical Donor Program as well as a commercial vendor (Science Care, Inc., Phoenix, AZ, USA). Each cadaver was randomized with respect to which side would comprise the study group, with the untreated contralateral side serving as a control. In addition, cadavers were randomly assigned either a 6.25 x 15 mm or 8.0 x 12 mm Bio-Tenodesis interference screw (Arthrex, Inc., Naples, FL, USA) (Table 1). After intra-articular tenotomy of the long head of the biceps, the pectoralis major tendon was palpated from the muscle belly to its insertion on the proximal humerus. On the medial aspect of the arm, a skin incision was made 1 cm superior to the inferior border of the pectoralis tendon and continued to 2 cm below the inferior border.
Table 1 Demographic data of cadaveric pairs by group. Data shown as means (standard deviations).
6.25 mm (n = 10) 8.00 mm (n = 10)
Age (years)
% Right Limb Tenodesis
% Male
76 (13) 72 (15)
60 50
30 30
The inferior border of the pectoralis tendon was identified and the muscle was retracted superiorly and laterally with an Army-Navy retractor. The proximal biceps tendon was palpable immediately posterior to the pectoralis muscle, and the tendon was easily pulled out of the surgical wound. Number 2 FiberWire (Arthrex, Inc., Naples, FL, USA) was passed through the tendon beginning at the musculotendinous junction and continued proximally for approximately 2 cm in Krackow fashion. The remaining proximal portion of the tendon was excised. A Homan retractor was placed laterally under the deltoid and a Chandler placed on the medial aspect of the humerus to retract the conjoined tendon and neurovascular structures. A guide wire was placed in the bicipital groove and a 6.5-mm or 8-mm reamer (for a 6.25 or 8 mm screw, respectively) was passed over the guide wire to create a bone tunnel in the anterior cortex as proximal as possible to the inferior border of the pectoralis tendon (Fig. 2a). Both limbs of the suture were passed through the screw and driver and snapped to the end of the driver (Fig. 2b). The driver was then placed into the bone tunnel and the screw was advanced over the tendon until it was flush with the anterior cortex. 2.2. Biomechanical testing Cadaver limbs were dissected of all soft tissue so that only the humerus and re-attached biceps tendon (for the tenodesis group) remained (Fig. 2c). The proximal humeral epiphyses were potted in polymethyl methacrylate (PMMA) using a custom test fixture, such that approximately 5 cm of the humeral diaphysis was left exposed between the PMMA and the tenodesis screw. The tenodesis site on the proximal diaphysis (or analogous location for the control group) was not obscured. Each specimen was then loaded into an MTS 858 MiniBionix servohydraulic axial/torsional test frame (MTS Systems Corp., Eden Prairie, MN, USA) and lowered into a second fixture where the distal humerus was also cemented in PMMA within the test frame setup (Fig. 3). This technique ensured precise alignment of the top
Fig. 1. Imaging examples of patients experiencing humeral shaft fracture following subpectoral biceps tenodesis (a,b).
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Fig. 2. Cadaver specimen (a,b) during and (c) following tenodesis and dissection.
and bottom fixtures and minimized the amount of unwanted loading (i.e., axial tension/compression and bending) in the system. As mentioned previously, no existing biomechanical study has investigated torsional properties of the humerus following biceps tenodesis, so a direct reference for the loading protocol was not available. All humeri were
tested in torsional external rotation at a rate of 1°/s until failure (i.e., humeral fracture), as described by Huff et al. (Huff et al., 2013) This rate was chosen in order to obtain quasistatic properties of the humerus that would allow for the most meaningful calculations of torsional stiffness and would present a clear transition from initial toe region to linear elastic behavior, which may not have been possible in a dynamic loading environment. Maximum torque, rotation to failure, torsional stiffness, and fracture mode were measured and recorded. Maximum torque and rotation to failure were defined as the torque and rotation at the point of ultimate failure of the bone. Torsional stiffness was calculated as the slope of the torque versus rotation curve within the linear region subsequent to the viscoelastic toe region and prior to a yield point. 2.3. Statistical analysis Data were evaluated for differences between treated and untreated limbs as well as between screw sizes. Initial comparisons were made using two-way analysis of variance (ANOVA) with repeated measures to compare between tenodesis and non-tenodesis limbs as well as between the two different screw sizes. If this analysis were to show no difference in the effect of the screw size, the data for screw sizes would be combined and compared between tenodesis and native properties using two-tailed paired t-tests. Significance for all analyses was defined at p ≤ 0.05. 3. Results
Fig. 3. Torsional test setup in the mechanical test frame. Both humeral epiphyses are potted in PMMA.
Humeri in the control (i.e., non-tenodesis) group fractured in primarily one of two modes. Some formed a spiral fracture extending most of the length of the diaphysis (Fig. 4a), while others experienced a catastrophic diaphyseal fracture in which the bone splintered into many fragments, leaving only the proximal and distal ends (Fig. 4b). Humeri receiving the tenodesis procedure fractured in a consistent pattern, with the majority of fractures (90%) occurring through the screw hole location (Fig. 4c). For the 6.25 mm screw group, biceps tenodesis resulted in a 41% reduction in maximum torque and a 53% reduction in rotation to failure compared to controls. For the 8 mm group, the analogous reductions were 32% and 43%. Two-way ANOVA with repeated measures showed a significant reduction in maximum torque and rotation to failure in the tenodesis group compared to controls; however, there was no significant difference for torsional stiffness (Table 2). Although pairwise comparisons from the ANOVA showed no significant difference between screw sizes for rotation to failure (p = 0.218) or torsional stiffness (p = 0.542), there was a non-significant trend (p = 0.0929) for the smaller size screw leading to reduced torsional strength (not
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Fig. 4. (a) Spiral fracture; (b) catastrophic diaphyseal fracture; (c) spiral fracture through tenodesis screw location.
shown in Table 2). It is worth noting an unpaired t-test between the only native limbs indicated that the maximum torque also trended toward being lower (p = 0.0668) in the native contralateral limbs in the 6.25 mm group compared to the 8 mm native limbs. Hence, the baseline bone quality in the 8 mm group may have been inherently higher. When combining the data for both screw sizes (both 6.25 mm and 8.0 mm), biceps tenodesis resulted in a 35% reduction in maximum torque and a 48% reduction in rotation to failure compared to controls. Paired t-tests for the combined screw sizes showed significant differences between tenodesis limbs and control limbs (Table 2, Fig. 5) for both maximum torque and rotation to failure. Torsional stiffness of the tenodesis group was not different from control for either screw size or combined (Table 2). 4. Discussion In this study, we have demonstrated a significant detrimental effect of subpectoral biceps tenodesis on humeral fracture torque and rotation in embalmed human cadavers; however, the size of interference screw did not significantly affect the torque or rotation to failure. This is the first study to evaluate the torsional strength of the humerus after
interference screw placement. Previous work investigating torsional properties of porcine femurs showed an approximately 23% reduction in failure torque with an open 4 mm defect compared to unaltered controls, but no difference when the defect was filled with a cortical screw (Ho et al., 2010). The significant reduction in maximum torque and rotation to failure seen in the tenodesis group suggests that the theoretical fracture risk caused by creating a stress riser in the humerus is a legitimate clinical concern during torsional loading in external rotation as in our study. In our study, humeral fracture involved the drill hole in 90% of the tenodesis group. The stress riser effect of bone drilling is well known, as is the increase in strength when using bioabsorbable filler. A previous study looking at transcortical holes in the absence of tenodesis concluded that a hole with a diameter 50% of the outer bone diameter reduced torsional strength by 60%, but also suggested that small transcortical holes have no significant effect on strength (Hipp et al., 1990). Another study evaluated the torsional strength of matched pairs of fibulas and found a 40% reduction in load to failure with a single 3.5 mm drill hole; (Johnson and Fallat, 1997) however, a different group determined that a cortical hole in rabbit femurs filled with a resorbable screw was significantly stronger when tested in torsion than matched controls with an empty hole
Table 2 Biceps tenodesis procedure significantly reduced humeral fracture torque and rotation to failure for both screw sizes. Data shown as means (standard deviations). p-values are for tenodesis compared to control, with two-way ANOVA comparing the two different screw sizes and the paired t-test comparing the combined results.
Tenodesis
Control
p-value Power
6.25 mm 8.00 mm Combined 6.25 mm 8.00 mm Combined 2-way ANOVA Paired t-test 2-way ANOVA Paired t-test
Max Torque (N-m)
Rotation to Failure (°)
Stiffness (N-m/°)
24.1 (19.2) 38.6 (22.9) 31.8 (21.9) 40.7 (13.5) 56.6 (20.7) 49.1 (19.0) 0.00000778 0.00000406 0.928 0.999
12.4 (6.78) 17.2 (7.75) 14.7 (7.45) 26.7 (12.2) 29.9 (6.64) 28.4 (9.45) 0.0000469 0.0000277 0.999 1.000
2.43 (1.75) 2.70 (1.38) 2.56 (1.53) 2.23 (1.09) 2.61 (1.43) 2.43 (1.26) 0.511 0.236 0.0991 0.0826
Fig. 5. Maximum torque and rotation to failure were significantly reduced (*) in the tenodesis limbs compared to matched controls.
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(Alford et al., 2007). Previous work using porcine femurs showed a significant decrease in torsional strength of femurs with a single 4 mm drill hole compared to unaltered controls. There were no differences between the same controls and femurs with a 4 mm hole filled with either a 4.5 mm cortical screw or plaster of paris (Ho et al., 2010). In the current study, we did not include a group with an unfilled drill hole, hence direct comparisons to previous studies which reported improved strength when filling the hole with a screw are difficult. Potential discrepancies between our findings of reduced properties with a drill hole filled with an interference screw and previous findings of properties similar to those of unaltered control limbs are possibly due to the fact that, in the current study involving biceps tenodesis, the biceps tendon was included as part of the material filling this hole along with the interference screw. In previous work not investigating biceps tenodesis, however, there was no soft tissue included between the screw or plaster and the drilled bone (Ho et al., 2010). Screw type may have an influence on late postoperative fracture risk. The bioabsorbable screws used in this study were composed of poly-L-lactic acid (PLLA), but the study evaluated only the time-zero failure properties of the humerus without adjusting for screw absorption. The resorption rate of PLLA screws in the humerus is unknown. One investigation concluded that PLLA ACL screws eventually disappear completely and that the tunnel is not filled with bone (Barber et al., 2008). A different study found that PLLA screws were intact and surrounded by a fibrous layer at 52 weeks with no obvious resorption (Walsh et al., 2007), while another showed approximately 60% reduction in PLLA screw volume at two years (Drogset et al., 2006). Yet another implied that a cortical defect forms at the location of the screw hole as screw degradation occurs, and may have contributed to the two fractures in their report. (Sears et al., 2011) It has been suggested using a non-absorbable screw may minimize the open-hole effect (Reiff et al., 2010). Previous research has reported the torque on the humerus during baseball pitching to be between 92 and 98 N-m (Fleisig et al., 2011a; Sabick et al., 2004; Urbin et al., 2013). The mean fracture torque of 49 N-m measured in the control limbs of the current study is appreciably lower than these functional values reported during pitching, but falls within the range of 46-53 N-m reported in previous studies of cadaveric native humeral torsion (Lin et al., 1998; Schopfer et al., 1994). The mean rotation to failure for the untreated group in our study was 28.4°. Functional measurements of humeral torsion angle during throwing are not available for comparison. One reason for the discrepancies seen between our experimental results and live throwing measurements could be related to the fact that in our study, the soft tissues were removed from the tested humeri as well as all joint attachments. As a result, there were no muscle contractions or other forces being applied by soft tissues. It is also worth noting that the reported measurements for baseball pitchers occur during the cocking phase of the pitching motion at an external rotation of approximately 1250°/s (Fleisig et al., 2011b), whereas our controlled mechanical torsion testing was conducted at 1°/s. Additionally, the mean age of the subjects in the current study (74 years) was much higher than the typical overhead throwing athlete due to the nature of availability of cadaveric specimens. One potential limitation to the current study is the use of formalinfixed, embalmed humeri as opposed to fresh-frozen specimens. Previous studies into the effects of formalin fixation on the biomechanical properties of bone have yielded mixed results. One recent study found similar results between fresh-frozen and embalmed cadaveric femurs in pullout and off-axis longitudinal compression tests (Topp et al., 2012). A different investigation found that short-term fixation (4 weeks or less) had no significant effect, whereas long-term fixation (8 weeks) was detrimental to the compressive material properties including elastic modulus (Ohman et al., 2008). Another recent study compared three different fixation techniques of human cortical bone and found that formalin fixation for six months did not decrease cortical bone elastic modulus in bending tests (Unger et al., 2010). Other work,
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however, has shown that even short-term fixation on the order of a few hours can adversely affect dynamic material properties of bovine bone; these adverse changes were not noted in quasistatic testing (Currey et al., 1995). It is difficult to speculate as to whether our torsional tests on embalmed humeri would have shown different results to freshfrozen humeri given differences in test methodologies and study design between our study and previous work by others. As mentioned above, our failure torque results fell within the range of previous humeral torsion studies (Lin et al., 1998; Schopfer et al., 1994), which used freshfrozen human cadaver bones. Another limitation of this study was the advanced age of the cadaveric specimens. The mean age for the combined groups was 74 years old. In our clinical practice, we typically do not perform this biceps tenodesis in patients over 70 years old; however, the age of our specimens is consistent with the those in other biomechanical studies involving biceps tenodesis (Golish et al., 2008; Mazzocca et al., 2005a). A related limitation is that no bone density measurements were made to be able to assess whether potential differences in bone density were a confounding factor to the torsional fracture properties reported here. As mentioned previously, however, our study was conducted in a paired fashion and randomized in terms of which limb received the tenodesis in an attempt to minimize the effect of discrepancies in bone quality between subjects and to avoid an arm-dominance bias within subjects. 5. Conclusions Our results demonstrated a significant reduction in maximum torque and rotation to failure in subpectoral biceps tenodesis with an interference screw, thus leading to an increased risk for humerus fracture in external rotation of cadaveric humeri. Based on our study design, we could not detect a significant difference between the 6.25 mm and 8 mm screw sizes. Future work will focus on investigating similar effects of biceps tenodesis using smaller holes and suture-only techniques. Acknowledgements For their significant contributions to this study, the authors would like to express their gratitude to Kyle Aune, Carrie Elzie, Tim Evans, Jonathan Freind, Monica Milanovich, Justin Silverman, Brian Walters, and Murphy Walters. This work was partially supported by Arthrex, Inc. (Naples, FL, USA) in the form of donation of the tenodesis screws and instrumentation used in the study. The sponsor had no role in the study design; collection, analysis and interpretation of data; writing of the report; or the decision to submit the article for publication. References Alford, J.W., Bradley, M.P., Fadale, P.D., Crisco, J.J., Moore, D.C., Ehrlich, M.G., 2007. Resorbable fillers reduce stress risers from empty screw holes. J. Trauma 63 (3), 647–654. http://dx.doi.org/10.1097/01.ta.0000221042.09862.ae (00005373-20070900000025 [pii]). Arora, A.S., Singh, A., Koonce, R.C., 2013. Biomechanical evaluation of a unicortical button versus interference screw for subpectoral biceps tenodesis. Arthroscopy 29 (4), 638–644. http://dx.doi.org/10.1016/j.arthro.2012.11.018 S0749-8063(12)01885-3 [pii]. Barber, F.A., Field, L.D., Ryu, R.K., 2008. Biceps tendon and superior labrum injuries: decision making. Instr. Course Lect. 57, 527–538. Buchholz, A., Martetschlager, F., Siebenlist, S., et al., 2013. Biomechanical comparison of intramedullary cortical button fixation and interference screw technique for subpectoral biceps tenodesis. Arthroscopy 29 (5), 845–853. http://dx.doi.org/10. 1016/j.arthro.2013.01.010 (S0749-8063(13)00020-0 [pii]). Currey, J.D., Brear, K., Zioupos, P., Reilly, G.C., 1995. Effect of formaldehyde fixation on some mechanical properties of bovine bone. Biomaterials 16 (16), 1267–1271 (0142961295981352 [pii]). Dein, E.J., Huri, G., Gordon, J.C., 2014. A Humerus Fracture in a Baseball Pitcher After Biceps Tenodesis. Am. J. Sports Med. 42 (4), 877–879. Drogset, J., Grøntvedt, T., Myhr, G., 2006. Magnetic resonance imaging analysis of bioabsorbable interference screws used for fixation of bone-patellar tendon-bone autografts in endoscopic reconstruction of the anterior cruciate ligament. Am. J. Sports Med. 34 (7), 1164–1169. http://dx.doi.org/10.1177/0363546505285384. Elser, F., Braun, S., Dewing, C.B., Giphart, J.E., Millett, P.J., 2011. Anatomy, function, injuries, and treatment of the long head of the biceps brachii tendon. Arthroscopy 27 (4),
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Nho, S.J., Reiff, S.N., Verma, N.N., Slabaugh, M.A., Mazzocca, A.D., Romeo, A.A., 2010a. Complications associated with subpectoral biceps tenodesis: low rates of incidence following surgery. J. Shoulder Elb. Surg. 19 (5), 764–768. http://dx.doi.org/10.1016/j. jse.2010.01.024 (S1058-2746(10)00047-9 [pii]). Nho, S.J., Strauss, E.J., Lenart, B.A., et al., 2010b. Long head of the biceps tendinopathy: diagnosis and management. J. Am. Acad. Orthop. Surg. 18 (11), 645–656 (18/11/645 [pii].). Ohman, C., Dall’Ara, E., Baleani, M., Van Sint Jan, S., Viceconti, M., 2008. The effects of embalming using a 4% formalin solution on the compressive mechanical properties of human cortical bone. Clin. Biomech. 23 (10), 1294–1298. http://dx.doi.org/10. 1016/j.clinbiomech.2008.07.007 (S0268-0033(08)00228-3 [pii]). Provencher, M.T., LeClere, L.E., Romeo, A.A., 2008. Subpectoral biceps tenodesis. Sport. Med. Arthrosc. 16 (3), 170–176. http://dx.doi.org/10.1097/JSA.0b013e3181824edf (00132585-200809000-00010 [pii]). Reiff, S.N., Nho, S.J., Romeo, A.A., 2010. Proximal humerus fracture after keyhole biceps tenodesis. Am. J. Orthop. 39 (7), E61–E63. Sabick, M.B., Torry, M.R., Kim, Y.-K., Hawkins, R.J., 2004. Humeral Torque in Professional Baseball Pitchers. Am. J. Sports Med. 32 (4), 892–898. http://dx.doi.org/10.1177/ 0363546503259354. Schopfer, A., Hearn, T., Malisano, L., Powell, J., Kellam, J., 1994. Comparison of torsional strength of humeral intramedullary nailing: a cadaveric study. J. Orthop. Trauma 8 (5), 414–421. Sears, B.W., Spencer, E.E., Getz, C.L., 2011. Humeral fracture following subpectoral biceps tenodesis in 2 active, healthy patients. J. Shoulder Elb. Surg. 20 (6), e7–e11. http://dx. doi.org/10.1016/j.jse.2011.02.020. Sethi, P.M., Rajaram, A., Beitzel, K., Hackett, T.R., Chowaniec, D.M., Mazzocca, A.D., 2013. Biomechanical performance of subpectoral biceps tenodesis: a comparison of interference screw fixation, cortical button fixation, and interference screw diameter. J. Shoulder Elb. Surg. 22 (4), 451–457. http://dx.doi.org/10.1016/j.jse.2012.03.016 (S1058-2746(12)00125-5 [pii]). Slabaugh, M.A., Frank, R.M., Van Thiel, G.S., et al., 2011. Biceps tenodesis with interference screw fixation: a biomechanical comparison of screw length and diameter. Arthroscopy 27 (2), 161–166. http://dx.doi.org/10.1016/j.arthro.2010.07.004 (S07498063(10)00677-8 [pii]). Tashjian, R.Z., Henninger, H.B., 2013. Biomechanical evaluation of subpectoral biceps tenodesis: dual suture anchor versus interference screw fixation. J. Shoulder Elb. Surg. 22 (10), 1408–1412. http://dx.doi.org/10.1016/j.jse.2012.12.039 (S10582746(13)00021-9 [pii]). Topp, T., Muller, T., Huss, S., et al., 2012. Embalmed and fresh frozen human bones in orthopedic cadaveric studies: which bone is authentic and feasible? Acta Orthop. 83 (5), 543–547. http://dx.doi.org/10.3109/17453674.2012.727079. Unger, S., Blauth, M., Schmoelz, W., 2010. Effects of three different preservation methods on the mechanical properties of human and bovine cortical bone. Bone 47 (6), 1048–1053. Urbin, M.A., Fleisig, G.S., Abebe, A., Andrews, J.R., 2013. Associations Between Timing in the Baseball Pitch and Shoulder Kinetics, Elbow Kinetics, and Ball Speed. Am. J. Sports Med. 41 (2), 336–342. http://dx.doi.org/10.1177/0363546512467952. Walsh, W., Cotton, N., Stephens, P., et al., 2007. Comparison of poly-l-lactide and polylactide carbonate interference screws in an ovine anterior cruciate ligament reconstruction model. Arthroscopy 23 (7), 757–765. http://dx.doi.org/10.1016/j. arthro.2007.01.030.
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Torsional Fracture of the Humerus after Subpectoral Biceps Tenodesis with an Interference Screw: A Biomechanical Cadaveric Study David P. Beason a,⁎, Jay P. Shah b, James W. Duckett a, Patrick W. Jost a, Glenn S. Fleisig a, E. Lyle Cain Jr. a b
a
American Sports Medicine Institute, Birmingham, AL, USA Division of Orthopaedic Surgery, University of Alabama at Birmingham, Birmingham, AL, USA
a r t i c l e
i n f o
Article history: Received 10 February 2015 Accepted 20 July 2015 Keywords: Biceps tenodesis Biomechanical Torsion Spiral fracture Humerus Interference screw
a b s t r a c t Background: Humeral fracture following subpectoral biceps tenodesis has been previously reported; however, there are no published biomechanical studies reporting the resulting torsional strength of the humerus. Our purpose was to determine if there is an increased risk of humerus fracture after subpectoral biceps tenodesis with an interference screw and to determine if screw size is also a factor. We hypothesized that limbs receiving the procedure would have reduced failure torque and rotation under external rotation compared to untreated controls and that the larger screw size would result in inferior mechanical properties compared to the smaller. Methods: Twenty matched pairs of embalmed cadaveric humeri were subjected to subpectoral biceps tenodesis using either a 6.25 or 8.0 mm interference screw, with the untreated contralateral limb serving as a control. Each humerus was mechanically tested in torsional external rotation to failure. Findings: Maximum torque and rotation to failure were reduced in the tenodesis group compared to controls; however, there was no difference between screw sizes. When both screw sizes were combined into a single group, paired t-tests also showed similar differences. Interpretation: Based on our experiment, there is an increased risk for humerus spiral fracture when subjected to torsional external rotation after subpectoral biceps tenodesis with an interference screw compared to an intact humerus; however, there is not a significant difference between a 6.25 mm and 8.0 mm screw. Surgeons may elect to use alternative fixation methods in patients at high risk (e.g., overhead throwing athletes, etc.) for torsional loads and fracture. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Tendinosis of the long head of the biceps is a common and significant cause of pain in the shoulder (Friedman et al., 2008; Provencher et al., 2008). Controversy exists in the literature with respect to the ideal treatment of recalcitrant biceps tendinopathy. No consensus has been achieved with respect to tenotomy versus tenodesis, location of tenodesis, or method and/or size of tenodesis fixation (Elser et al., 2011; Khazzam et al., 2012; Mazzocca et al., 2005a,2005b; Millett et al., 2008; Nho et al., 2010b). The appropriate treatment takes into account many factors: patient age, level of function, associated shoulder pathology, and surgeon preference. Subpectoral biceps tenodesis has recently increased in popularity due to its simplicity, preservation of length-tension relationship, advantage of an interference screw, and low complication rate (Mazzocca et al., 2005a, 2008; Millett et al., 2008; Nho et al., 2010a; Provencher et al., 2008).
⁎ Corresponding author at: 833 St. Vincent’s Drive, Suite 205, Birmingham, AL 35205, United States. Tel.: +1 205 918 2116; fax: +1 205 918 2179. E-mail address: [email protected] (D.P. Beason).
http://dx.doi.org/10.1016/j.clinbiomech.2015.07.009 0268-0033/© 2015 Elsevier Ltd. All rights reserved.
Subpectoral biceps tenodesis with an interference screw has been shown to have a complication rate of 2% in a recent large clinical series with no cases of fracture reported (Nho et al., 2010a). Two additional outcomes studies also have not reported any fractures (Mazzocca et al., 2008; Millett et al., 2008); however, humeral fracture after subpectoral biceps tenodesis has been listed as a potential complication in several other case studies (Dein et al., 2014; Friedel et al., 1995; Gyulai, 1990; Provencher et al., 2008; Reiff et al., 2010; Sears et al., 2011). One study reported on two humerus fractures in healthy, active patients that occurred within six months of surgery using a technique similar to the current and previous studies (Sears et al., 2011). In both cases, the fracture included the cortical drill hole used for screw placement and occurred at 3 and 6 months post-operatively. Another reported proximal humerus fracture after keyhole biceps tenodesis 12 weeks after surgery in a 50 year-old female. Radiographs showed that the fracture involved the tenodesis drill hole (Reiff et al., 2010). Another reported humerus fracture of a 46year-old male baseball pitcher following open subpectoral biceps tenodesis with an 8-mm bioabsorbale interference screw. Again, radiographs indicated a spiral fracture through the drill site (Dein et al., 2014). At our institution, we have had two previously unreported cases of humeral fracture following biceps tenodesis within the previous two
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years. In one, a 56 year-old male, who had undergone open biceps tenodesis with a 6.25 x 15 mm polyether ether ketone (PEEK) interference screw, fell out of bed on the night of surgery. Radiographs revealed a proximal third spiral fracture of the humerus that involved the tenodesis interference screw hole (Fig. 1a). A second case involved a 42 year-old male who had undergone biceps tenodesis with 6.25 x 15 mm PEEK interference screw. After around one year, his left humerus was fractured (Fig. 1b) at the site of the tenodesis screw. Although the biomechanical properties of various methods of tenodesis have been previously studied (Arora et al., 2013; Buchholz et al., 2013; Golish et al., 2008; Mazzocca et al., 2005a; Sethi et al., 2013; Slabaugh et al., 2011; Tashjian and Henninger, 2013), only pullout strength has been evaluated. To our knowledge, there are no published studies reporting the torsional strength of bone after subpectoral biceps tenodesis with an interference screw. The purpose of the current study was to biomechanically determine the effect of subpectoral biceps tenodesis on the torsional fracture properties in matched pairs of cadaveric humeri with two different commercially available screw sizes. We hypothesized that limbs receiving the biceps tenodesis procedure would have reduced failure torque and rotation under external rotation compared to matched limbs not having received the procedure. Further, we hypothesized that the larger of the two screw sizes would result in inferior mechanical properties compared to the smaller screw size. 2. Methods 2.1. Surgical technique The subpectoral biceps tenodesis technique has previously been described (Mazzocca et al., 2005b). This technique was modified for a cadaveric study as follows. The study was performed on 20 matched pairs of embalmed human cadaveric humeri obtained from the University of Alabama at Birmingham Anatomical Donor Program as well as a commercial vendor (Science Care, Inc., Phoenix, AZ, USA). Each cadaver was randomized with respect to which side would comprise the study group, with the untreated contralateral side serving as a control. In addition, cadavers were randomly assigned either a 6.25 x 15 mm or 8.0 x 12 mm Bio-Tenodesis interference screw (Arthrex, Inc., Naples, FL, USA) (Table 1). After intra-articular tenotomy of the long head of the biceps, the pectoralis major tendon was palpated from the muscle belly to its insertion on the proximal humerus. On the medial aspect of the arm, a skin incision was made 1 cm superior to the inferior border of the pectoralis tendon and continued to 2 cm below the inferior border.
Table 1 Demographic data of cadaveric pairs by group. Data shown as means (standard deviations).
6.25 mm (n = 10) 8.00 mm (n = 10)
Age (years)
% Right Limb Tenodesis
% Male
76 (13) 72 (15)
60 50
30 30
The inferior border of the pectoralis tendon was identified and the muscle was retracted superiorly and laterally with an Army-Navy retractor. The proximal biceps tendon was palpable immediately posterior to the pectoralis muscle, and the tendon was easily pulled out of the surgical wound. Number 2 FiberWire (Arthrex, Inc., Naples, FL, USA) was passed through the tendon beginning at the musculotendinous junction and continued proximally for approximately 2 cm in Krackow fashion. The remaining proximal portion of the tendon was excised. A Homan retractor was placed laterally under the deltoid and a Chandler placed on the medial aspect of the humerus to retract the conjoined tendon and neurovascular structures. A guide wire was placed in the bicipital groove and a 6.5-mm or 8-mm reamer (for a 6.25 or 8 mm screw, respectively) was passed over the guide wire to create a bone tunnel in the anterior cortex as proximal as possible to the inferior border of the pectoralis tendon (Fig. 2a). Both limbs of the suture were passed through the screw and driver and snapped to the end of the driver (Fig. 2b). The driver was then placed into the bone tunnel and the screw was advanced over the tendon until it was flush with the anterior cortex. 2.2. Biomechanical testing Cadaver limbs were dissected of all soft tissue so that only the humerus and re-attached biceps tendon (for the tenodesis group) remained (Fig. 2c). The proximal humeral epiphyses were potted in polymethyl methacrylate (PMMA) using a custom test fixture, such that approximately 5 cm of the humeral diaphysis was left exposed between the PMMA and the tenodesis screw. The tenodesis site on the proximal diaphysis (or analogous location for the control group) was not obscured. Each specimen was then loaded into an MTS 858 MiniBionix servohydraulic axial/torsional test frame (MTS Systems Corp., Eden Prairie, MN, USA) and lowered into a second fixture where the distal humerus was also cemented in PMMA within the test frame setup (Fig. 3). This technique ensured precise alignment of the top
Fig. 1. Imaging examples of patients experiencing humeral shaft fracture following subpectoral biceps tenodesis (a,b).
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Fig. 2. Cadaver specimen (a,b) during and (c) following tenodesis and dissection.
and bottom fixtures and minimized the amount of unwanted loading (i.e., axial tension/compression and bending) in the system. As mentioned previously, no existing biomechanical study has investigated torsional properties of the humerus following biceps tenodesis, so a direct reference for the loading protocol was not available. All humeri were
tested in torsional external rotation at a rate of 1°/s until failure (i.e., humeral fracture), as described by Huff et al. (Huff et al., 2013) This rate was chosen in order to obtain quasistatic properties of the humerus that would allow for the most meaningful calculations of torsional stiffness and would present a clear transition from initial toe region to linear elastic behavior, which may not have been possible in a dynamic loading environment. Maximum torque, rotation to failure, torsional stiffness, and fracture mode were measured and recorded. Maximum torque and rotation to failure were defined as the torque and rotation at the point of ultimate failure of the bone. Torsional stiffness was calculated as the slope of the torque versus rotation curve within the linear region subsequent to the viscoelastic toe region and prior to a yield point. 2.3. Statistical analysis Data were evaluated for differences between treated and untreated limbs as well as between screw sizes. Initial comparisons were made using two-way analysis of variance (ANOVA) with repeated measures to compare between tenodesis and non-tenodesis limbs as well as between the two different screw sizes. If this analysis were to show no difference in the effect of the screw size, the data for screw sizes would be combined and compared between tenodesis and native properties using two-tailed paired t-tests. Significance for all analyses was defined at p ≤ 0.05. 3. Results
Fig. 3. Torsional test setup in the mechanical test frame. Both humeral epiphyses are potted in PMMA.
Humeri in the control (i.e., non-tenodesis) group fractured in primarily one of two modes. Some formed a spiral fracture extending most of the length of the diaphysis (Fig. 4a), while others experienced a catastrophic diaphyseal fracture in which the bone splintered into many fragments, leaving only the proximal and distal ends (Fig. 4b). Humeri receiving the tenodesis procedure fractured in a consistent pattern, with the majority of fractures (90%) occurring through the screw hole location (Fig. 4c). For the 6.25 mm screw group, biceps tenodesis resulted in a 41% reduction in maximum torque and a 53% reduction in rotation to failure compared to controls. For the 8 mm group, the analogous reductions were 32% and 43%. Two-way ANOVA with repeated measures showed a significant reduction in maximum torque and rotation to failure in the tenodesis group compared to controls; however, there was no significant difference for torsional stiffness (Table 2). Although pairwise comparisons from the ANOVA showed no significant difference between screw sizes for rotation to failure (p = 0.218) or torsional stiffness (p = 0.542), there was a non-significant trend (p = 0.0929) for the smaller size screw leading to reduced torsional strength (not
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Fig. 4. (a) Spiral fracture; (b) catastrophic diaphyseal fracture; (c) spiral fracture through tenodesis screw location.
shown in Table 2). It is worth noting an unpaired t-test between the only native limbs indicated that the maximum torque also trended toward being lower (p = 0.0668) in the native contralateral limbs in the 6.25 mm group compared to the 8 mm native limbs. Hence, the baseline bone quality in the 8 mm group may have been inherently higher. When combining the data for both screw sizes (both 6.25 mm and 8.0 mm), biceps tenodesis resulted in a 35% reduction in maximum torque and a 48% reduction in rotation to failure compared to controls. Paired t-tests for the combined screw sizes showed significant differences between tenodesis limbs and control limbs (Table 2, Fig. 5) for both maximum torque and rotation to failure. Torsional stiffness of the tenodesis group was not different from control for either screw size or combined (Table 2). 4. Discussion In this study, we have demonstrated a significant detrimental effect of subpectoral biceps tenodesis on humeral fracture torque and rotation in embalmed human cadavers; however, the size of interference screw did not significantly affect the torque or rotation to failure. This is the first study to evaluate the torsional strength of the humerus after
interference screw placement. Previous work investigating torsional properties of porcine femurs showed an approximately 23% reduction in failure torque with an open 4 mm defect compared to unaltered controls, but no difference when the defect was filled with a cortical screw (Ho et al., 2010). The significant reduction in maximum torque and rotation to failure seen in the tenodesis group suggests that the theoretical fracture risk caused by creating a stress riser in the humerus is a legitimate clinical concern during torsional loading in external rotation as in our study. In our study, humeral fracture involved the drill hole in 90% of the tenodesis group. The stress riser effect of bone drilling is well known, as is the increase in strength when using bioabsorbable filler. A previous study looking at transcortical holes in the absence of tenodesis concluded that a hole with a diameter 50% of the outer bone diameter reduced torsional strength by 60%, but also suggested that small transcortical holes have no significant effect on strength (Hipp et al., 1990). Another study evaluated the torsional strength of matched pairs of fibulas and found a 40% reduction in load to failure with a single 3.5 mm drill hole; (Johnson and Fallat, 1997) however, a different group determined that a cortical hole in rabbit femurs filled with a resorbable screw was significantly stronger when tested in torsion than matched controls with an empty hole
Table 2 Biceps tenodesis procedure significantly reduced humeral fracture torque and rotation to failure for both screw sizes. Data shown as means (standard deviations). p-values are for tenodesis compared to control, with two-way ANOVA comparing the two different screw sizes and the paired t-test comparing the combined results.
Tenodesis
Control
p-value Power
6.25 mm 8.00 mm Combined 6.25 mm 8.00 mm Combined 2-way ANOVA Paired t-test 2-way ANOVA Paired t-test
Max Torque (N-m)
Rotation to Failure (°)
Stiffness (N-m/°)
24.1 (19.2) 38.6 (22.9) 31.8 (21.9) 40.7 (13.5) 56.6 (20.7) 49.1 (19.0) 0.00000778 0.00000406 0.928 0.999
12.4 (6.78) 17.2 (7.75) 14.7 (7.45) 26.7 (12.2) 29.9 (6.64) 28.4 (9.45) 0.0000469 0.0000277 0.999 1.000
2.43 (1.75) 2.70 (1.38) 2.56 (1.53) 2.23 (1.09) 2.61 (1.43) 2.43 (1.26) 0.511 0.236 0.0991 0.0826
Fig. 5. Maximum torque and rotation to failure were significantly reduced (*) in the tenodesis limbs compared to matched controls.
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(Alford et al., 2007). Previous work using porcine femurs showed a significant decrease in torsional strength of femurs with a single 4 mm drill hole compared to unaltered controls. There were no differences between the same controls and femurs with a 4 mm hole filled with either a 4.5 mm cortical screw or plaster of paris (Ho et al., 2010). In the current study, we did not include a group with an unfilled drill hole, hence direct comparisons to previous studies which reported improved strength when filling the hole with a screw are difficult. Potential discrepancies between our findings of reduced properties with a drill hole filled with an interference screw and previous findings of properties similar to those of unaltered control limbs are possibly due to the fact that, in the current study involving biceps tenodesis, the biceps tendon was included as part of the material filling this hole along with the interference screw. In previous work not investigating biceps tenodesis, however, there was no soft tissue included between the screw or plaster and the drilled bone (Ho et al., 2010). Screw type may have an influence on late postoperative fracture risk. The bioabsorbable screws used in this study were composed of poly-L-lactic acid (PLLA), but the study evaluated only the time-zero failure properties of the humerus without adjusting for screw absorption. The resorption rate of PLLA screws in the humerus is unknown. One investigation concluded that PLLA ACL screws eventually disappear completely and that the tunnel is not filled with bone (Barber et al., 2008). A different study found that PLLA screws were intact and surrounded by a fibrous layer at 52 weeks with no obvious resorption (Walsh et al., 2007), while another showed approximately 60% reduction in PLLA screw volume at two years (Drogset et al., 2006). Yet another implied that a cortical defect forms at the location of the screw hole as screw degradation occurs, and may have contributed to the two fractures in their report. (Sears et al., 2011) It has been suggested using a non-absorbable screw may minimize the open-hole effect (Reiff et al., 2010). Previous research has reported the torque on the humerus during baseball pitching to be between 92 and 98 N-m (Fleisig et al., 2011a; Sabick et al., 2004; Urbin et al., 2013). The mean fracture torque of 49 N-m measured in the control limbs of the current study is appreciably lower than these functional values reported during pitching, but falls within the range of 46-53 N-m reported in previous studies of cadaveric native humeral torsion (Lin et al., 1998; Schopfer et al., 1994). The mean rotation to failure for the untreated group in our study was 28.4°. Functional measurements of humeral torsion angle during throwing are not available for comparison. One reason for the discrepancies seen between our experimental results and live throwing measurements could be related to the fact that in our study, the soft tissues were removed from the tested humeri as well as all joint attachments. As a result, there were no muscle contractions or other forces being applied by soft tissues. It is also worth noting that the reported measurements for baseball pitchers occur during the cocking phase of the pitching motion at an external rotation of approximately 1250°/s (Fleisig et al., 2011b), whereas our controlled mechanical torsion testing was conducted at 1°/s. Additionally, the mean age of the subjects in the current study (74 years) was much higher than the typical overhead throwing athlete due to the nature of availability of cadaveric specimens. One potential limitation to the current study is the use of formalinfixed, embalmed humeri as opposed to fresh-frozen specimens. Previous studies into the effects of formalin fixation on the biomechanical properties of bone have yielded mixed results. One recent study found similar results between fresh-frozen and embalmed cadaveric femurs in pullout and off-axis longitudinal compression tests (Topp et al., 2012). A different investigation found that short-term fixation (4 weeks or less) had no significant effect, whereas long-term fixation (8 weeks) was detrimental to the compressive material properties including elastic modulus (Ohman et al., 2008). Another recent study compared three different fixation techniques of human cortical bone and found that formalin fixation for six months did not decrease cortical bone elastic modulus in bending tests (Unger et al., 2010). Other work,
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however, has shown that even short-term fixation on the order of a few hours can adversely affect dynamic material properties of bovine bone; these adverse changes were not noted in quasistatic testing (Currey et al., 1995). It is difficult to speculate as to whether our torsional tests on embalmed humeri would have shown different results to freshfrozen humeri given differences in test methodologies and study design between our study and previous work by others. As mentioned above, our failure torque results fell within the range of previous humeral torsion studies (Lin et al., 1998; Schopfer et al., 1994), which used freshfrozen human cadaver bones. Another limitation of this study was the advanced age of the cadaveric specimens. The mean age for the combined groups was 74 years old. In our clinical practice, we typically do not perform this biceps tenodesis in patients over 70 years old; however, the age of our specimens is consistent with the those in other biomechanical studies involving biceps tenodesis (Golish et al., 2008; Mazzocca et al., 2005a). A related limitation is that no bone density measurements were made to be able to assess whether potential differences in bone density were a confounding factor to the torsional fracture properties reported here. As mentioned previously, however, our study was conducted in a paired fashion and randomized in terms of which limb received the tenodesis in an attempt to minimize the effect of discrepancies in bone quality between subjects and to avoid an arm-dominance bias within subjects. 5. Conclusions Our results demonstrated a significant reduction in maximum torque and rotation to failure in subpectoral biceps tenodesis with an interference screw, thus leading to an increased risk for humerus fracture in external rotation of cadaveric humeri. Based on our study design, we could not detect a significant difference between the 6.25 mm and 8 mm screw sizes. Future work will focus on investigating similar effects of biceps tenodesis using smaller holes and suture-only techniques. Acknowledgements For their significant contributions to this study, the authors would like to express their gratitude to Kyle Aune, Carrie Elzie, Tim Evans, Jonathan Freind, Monica Milanovich, Justin Silverman, Brian Walters, and Murphy Walters. This work was partially supported by Arthrex, Inc. (Naples, FL, USA) in the form of donation of the tenodesis screws and instrumentation used in the study. The sponsor had no role in the study design; collection, analysis and interpretation of data; writing of the report; or the decision to submit the article for publication. References Alford, J.W., Bradley, M.P., Fadale, P.D., Crisco, J.J., Moore, D.C., Ehrlich, M.G., 2007. Resorbable fillers reduce stress risers from empty screw holes. J. Trauma 63 (3), 647–654. http://dx.doi.org/10.1097/01.ta.0000221042.09862.ae (00005373-20070900000025 [pii]). Arora, A.S., Singh, A., Koonce, R.C., 2013. Biomechanical evaluation of a unicortical button versus interference screw for subpectoral biceps tenodesis. Arthroscopy 29 (4), 638–644. http://dx.doi.org/10.1016/j.arthro.2012.11.018 S0749-8063(12)01885-3 [pii]. Barber, F.A., Field, L.D., Ryu, R.K., 2008. Biceps tendon and superior labrum injuries: decision making. Instr. Course Lect. 57, 527–538. Buchholz, A., Martetschlager, F., Siebenlist, S., et al., 2013. Biomechanical comparison of intramedullary cortical button fixation and interference screw technique for subpectoral biceps tenodesis. Arthroscopy 29 (5), 845–853. http://dx.doi.org/10. 1016/j.arthro.2013.01.010 (S0749-8063(13)00020-0 [pii]). Currey, J.D., Brear, K., Zioupos, P., Reilly, G.C., 1995. Effect of formaldehyde fixation on some mechanical properties of bovine bone. Biomaterials 16 (16), 1267–1271 (0142961295981352 [pii]). Dein, E.J., Huri, G., Gordon, J.C., 2014. A Humerus Fracture in a Baseball Pitcher After Biceps Tenodesis. Am. J. Sports Med. 42 (4), 877–879. Drogset, J., Grøntvedt, T., Myhr, G., 2006. Magnetic resonance imaging analysis of bioabsorbable interference screws used for fixation of bone-patellar tendon-bone autografts in endoscopic reconstruction of the anterior cruciate ligament. Am. J. Sports Med. 34 (7), 1164–1169. http://dx.doi.org/10.1177/0363546505285384. Elser, F., Braun, S., Dewing, C.B., Giphart, J.E., Millett, P.J., 2011. Anatomy, function, injuries, and treatment of the long head of the biceps brachii tendon. Arthroscopy 27 (4),
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