Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-3482-7
ELBOW
Biomechanical differences of the anterior and posterior bands of the ulnar collateral ligament of the elbow Timothy J. Jackson · Shelby E. Jarrell · Gregory J. Adamson · Kyung Chil Chung · Thay Q. Lee
Received: 6 March 2014 / Accepted: 11 December 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014
Abstract Purpose The main purpose of this study was to examine the functional characteristics of the anterior and posterior bands of the anterior bundle of the ulnar collateral ligament (UCL). Methods Six cadaveric elbows were tested using a digital tracking system to measure the strain in the anterior band and posterior band of the anterior bundle of the UCL throughout a flexion/extension arc. The specimens were then placed in an Instron materials testing machine and loaded to failure to determine yield load and ultimate load of the UCL. Results The posterior band showed a linear increase in strain with increasing degrees of elbow flexion while the anterior band showed minimal change in strain throughout. The bands showed similar strain at yield load and ultimate load, demonstrating similar intrinsic properties. Conclusion The anterior band of the anterior bundle of the UCL shows an isometric strain pattern through elbow range of motion, while the posterior band shows an increasing strain pattern in higher degrees of elbow flexion. Both bands show similar strain in a load to failure model, indicating insertion point, not intrinsic differences, of the bands determine the function of the anterior bundle of the UCL.
T. J. Jackson · S. E. Jarrell · G. J. Adamson (*) Congress Medical Associates, 800 South Raymond Ave, Pasadena, CA 91105, USA e-mail: [email protected] K. C. Chung · T. Q. Lee Orthopaedic Biomechanics Laboratory, VA Healthcare System, Long Beach, CA, USA T. Q. Lee University of California, Irvine, Irvine, CA, USA
This demonstrates a biomechanical rationale for UCL reconstructions using single point anatomical insertion points. Keywords Ulnar collateral ligament · Strain · Elbow flexion · Anterior band · Posterior band · Cadaveric study
Introduction As the major stabilizing structure of the medial elbow, the anterior bundle of the ulnar collateral ligament (UCL), and more specifically the anterior band of the anterior bundle, plays a critical role in the throwing motion for athletes [8]. The UCL functions as the predominant stabilizer to valgus stress as elucidated by Morrey et al. [10] and supported by multiple subsequent studies [3, 5, 11]. Overhead athletes can produce tremendous forces across the medial aspect of the elbow with throwing activities [2]. Micro-trauma to the anterior bundle of the UCL during the late cocking and acceleration phases can result in eventual tearing of the ligament, resulting in the loss of velocity and elbow pain [9]. The UCL of the elbow can be subdivided into three main structures: the anterior bundle, the posterior bundle and the transverse ligament. The anterior bundle has been demonstrated to be the main stabilizer to valgus force [5, 6]. The anterior bundle can be further subdivided into anterior and posterior bands. Studies in which the UCL is cut sequentially have shown that the anterior band of the anterior bundle is the key component in maintaining valgus stability [3]. Initially, it was thought that the anterior and posterior bands stabilized the elbow in a reciprocal fashion, with the anterior band tight in extension and the posterior band tight in flexion [10]. However, more recently, Ciccotti et al. [4] measured strain and did not show a reciprocal function for
13
the bands of the anterior bundle. The anterior band of the anterior bundle demonstrated little strain compared with the posterior band. It is unclear whether this difference in strain is related to intrinsic properties of the bands of the ligament or from their respective insertion points. The purpose of this study was to test the functional characteristics of the anterior bundle of the UCL, by measuring the strain pattern of the anterior and posterior bands of the anterior bundle, throughout a range of elbow flexion and during load to failure using a video tracking model. The hypothesis is that the anterior band of the anterior bundle will show minimal strain, while the posterior band will show increasing strain through the arc of elbow flexion and that this can be attributed to the anatomical location, not intrinsic properties of the bands of the ligament.
Materials and methods
Knee Surg Sports Traumatol Arthrosc
Fig. 1 Cadaveric dissection of the medial side of the elbow for specimen testing. Sutures were placed along the anterior and posterior bands of the UCL. These were used by the video tracking software to measure strain. The pins were placed in bone to record elbow flexion angle
Anatomical dissection Six fresh-frozen cadaveric elbow specimens with a median age at death of 67 years (range 50–83) were used. There were five male and one female specimen. The humerus was transected 15–20 cm above the humeral condyles. The distal forearm was pinned in neutral rotation and skin, subcutaneous tissues, and fat were removed from the entire specimen to the wrist. Dissection over the medial condyle was carried down to the underlying fascia. A longitudinal incision was carried out through the flexor/pronator mass overlying the UCL, and the muscle insertion was bluntly dissected off the ligament. Small retractors were then placed into the incision, keeping the flexor mass from contacting or obstructing the view of the UCL, through its arc of motion. The anterior and posterior borders were marked with 5-0 silk suture as shown in the photo (Fig. 1). The anterior UCL was marked at its origin, midpoint, and insertion on both the anterior and posterior borders, demarcating the anterior and posterior bands. These sutures were used as markers for video analysis. Biomechanical evaluation Two pins were placed in both the humerus and ulna, near the respective origin and insertion of the ligament, to serve as static markers throughout the arc of motion, in determining elbow flexion angle. The humerus was clamped to a static holding system with the epicondylar axis perpendicular to the baseplate of the mounting device with the UCL facing superiorly. Valgus torque was provided by the weight of the forearm. The elbows were preconditioned by manually flexing and extending the elbow through five
13
cycles prior to analysis. With the forearm held in neutral rotation, the elbow was manually taken through five range of motion cycles from maximum extension to maximum flexion and filmed with a digital video camera (Canon GL2, Canon USA, Lake Success, NY) aligned perpendicular to the UCL at 70° flexion. After testing throughout the elbow flexion/extension arc, load to failure testing was performed using an Instron materials testing machine (Instron Corp, Model #3365, Canton, MA, USA). All soft tissue was stripped from the humeri and forearms, with the exception of the anterior and posterior bands of the anterior bundle of the UCL. The lateral condyle and olecranon were resected with the use of an oscillating saw to prevent impingement of the surfaces during tensile testing. Specimens were then potted in PVC tubing using plaster of Paris and then mounted on the Instron testing device in 70° of elbow flexion. Each specimen was preloaded with 20 N for 10 s and then cycled through ten cycles of 20–60 N, to precondition the ligament. The UCL was then loaded to failure at 10 mm/min. Videos were analysed, and the markers were tracked using WINanalyze software (Mikromak, Berlin, Germany). The anterior and posterior band lengths and strain behaviour throughout the elbow flexion/extension arc and during load to failure were measured. The accuracy of this method was 0.15 mm; whereas the repeatability between multiple trials of elbow flexion/extension was 0.2 mm. The initial length of both the anterior and posterior bands was defined with the elbow at 70° of flexion. Seventy degrees was chosen as the initial reference length as this represents the middle of the normal range of motion of the elbow (0–140).
Knee Surg Sports Traumatol Arthrosc
IRB approval was waived by the Subcommittee on Human Studies at the VA Long Beach Health Care System as this is a cadaveric basic science study.
yield point and 23.5 ± 0.9 % at ultimate failure (Fig. 3). There was no statistically significant difference between the strains at yield point and ultimate load between the anterior and posterior bands of the anterior bundle.
Statistical analysis The three middle trials of flexion/extension were averaged together, and this average was averaged across the six specimens. Based on data from pilot testing of two specimens showing a 10 % difference in strain with elbow flexion/ extension between the anterior and posterior bands and a standard deviation of 6 %, a sample size of six specimens was needed to show a statistically significant difference with an alpha of 0.05 and a power of 0.8. A paired t test was used to compare the differences between anterior and posterior bands with a significance level of 0.05.
Results Figure 2 demonstrates the strain characteristics of the anterior and posterior bands of the anterior bundle of the UCL through an arc of motion between 40° and 100° of elbow flexion. The anterior band changed very little throughout the arc of motion, whereas the posterior band showed a linear increase in strain as elbow flexion increased. The crossover demonstrated at 70° of elbow flexion is because the reference length used to calculate strain was taken at 70° of flexion. For all specimens, the mean yield point for the anterior bundle of the UCL was 203.3 ± 30.3 N and the ultimate load was 293.1 ± 38.7 N. The anterior band of the anterior bundle showed a strain of 23.3 ± 0.9 % at the yield point and 23.6 ± 0.9 % at ultimate failure. The posterior band of the anterior bundle showed a strain of 22.9 ± 0.9 % at the
Discussion The most important finding of this study is the difference in strain patterns for the anterior and posterior bands of the UCL with no difference in the intrinsic properties. The anterior band showed no significant strain, while the posterior band demonstrated a significant amount of strain with elbow flexion. The similar tensile strength, as measured in the load to failure model, demonstrates the anatomical location of the insertions of the bands determines their function rather than the inherent properties of each band. These results reinforce the importance of anatomy as it relates to reconstructive procedures. Accurately reproducing the most relevant anatomical structures will lead to improved kinematics which can translate into high rates of long-term, successful clinical outcomes. Callaway et al. [3] found that sectioning the anterior band of the anterior bundle of the UCL reduced resistance to valgus loads at 30°, 60° and 90° of flexion and co-primary restraint at 120°. Posterior band sectioning alone did not affect valgus laxity. The posterior band was found to be a co-primary restraint at 120° and a secondary restraint at 30° and 90°. This and another study by Floris et al. [5] showed the anterior band to be the primary restraint to valgus laxity. The relationship between the bands was postulated by Callaway to be reciprocal in nature. The strain pattern demonstrated in this study suggest the anterior band maintained a static function while the posterior bands strain increased, suggesting its role in valgus stability is increased at higher flexion angles.
Fig. 2 Graph depicting the strain of the anterior and posterior bands at varying degrees of elbow flexion; *P
ELBOW
Biomechanical differences of the anterior and posterior bands of the ulnar collateral ligament of the elbow Timothy J. Jackson · Shelby E. Jarrell · Gregory J. Adamson · Kyung Chil Chung · Thay Q. Lee
Received: 6 March 2014 / Accepted: 11 December 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014
Abstract Purpose The main purpose of this study was to examine the functional characteristics of the anterior and posterior bands of the anterior bundle of the ulnar collateral ligament (UCL). Methods Six cadaveric elbows were tested using a digital tracking system to measure the strain in the anterior band and posterior band of the anterior bundle of the UCL throughout a flexion/extension arc. The specimens were then placed in an Instron materials testing machine and loaded to failure to determine yield load and ultimate load of the UCL. Results The posterior band showed a linear increase in strain with increasing degrees of elbow flexion while the anterior band showed minimal change in strain throughout. The bands showed similar strain at yield load and ultimate load, demonstrating similar intrinsic properties. Conclusion The anterior band of the anterior bundle of the UCL shows an isometric strain pattern through elbow range of motion, while the posterior band shows an increasing strain pattern in higher degrees of elbow flexion. Both bands show similar strain in a load to failure model, indicating insertion point, not intrinsic differences, of the bands determine the function of the anterior bundle of the UCL.
T. J. Jackson · S. E. Jarrell · G. J. Adamson (*) Congress Medical Associates, 800 South Raymond Ave, Pasadena, CA 91105, USA e-mail: [email protected] K. C. Chung · T. Q. Lee Orthopaedic Biomechanics Laboratory, VA Healthcare System, Long Beach, CA, USA T. Q. Lee University of California, Irvine, Irvine, CA, USA
This demonstrates a biomechanical rationale for UCL reconstructions using single point anatomical insertion points. Keywords Ulnar collateral ligament · Strain · Elbow flexion · Anterior band · Posterior band · Cadaveric study
Introduction As the major stabilizing structure of the medial elbow, the anterior bundle of the ulnar collateral ligament (UCL), and more specifically the anterior band of the anterior bundle, plays a critical role in the throwing motion for athletes [8]. The UCL functions as the predominant stabilizer to valgus stress as elucidated by Morrey et al. [10] and supported by multiple subsequent studies [3, 5, 11]. Overhead athletes can produce tremendous forces across the medial aspect of the elbow with throwing activities [2]. Micro-trauma to the anterior bundle of the UCL during the late cocking and acceleration phases can result in eventual tearing of the ligament, resulting in the loss of velocity and elbow pain [9]. The UCL of the elbow can be subdivided into three main structures: the anterior bundle, the posterior bundle and the transverse ligament. The anterior bundle has been demonstrated to be the main stabilizer to valgus force [5, 6]. The anterior bundle can be further subdivided into anterior and posterior bands. Studies in which the UCL is cut sequentially have shown that the anterior band of the anterior bundle is the key component in maintaining valgus stability [3]. Initially, it was thought that the anterior and posterior bands stabilized the elbow in a reciprocal fashion, with the anterior band tight in extension and the posterior band tight in flexion [10]. However, more recently, Ciccotti et al. [4] measured strain and did not show a reciprocal function for
13
the bands of the anterior bundle. The anterior band of the anterior bundle demonstrated little strain compared with the posterior band. It is unclear whether this difference in strain is related to intrinsic properties of the bands of the ligament or from their respective insertion points. The purpose of this study was to test the functional characteristics of the anterior bundle of the UCL, by measuring the strain pattern of the anterior and posterior bands of the anterior bundle, throughout a range of elbow flexion and during load to failure using a video tracking model. The hypothesis is that the anterior band of the anterior bundle will show minimal strain, while the posterior band will show increasing strain through the arc of elbow flexion and that this can be attributed to the anatomical location, not intrinsic properties of the bands of the ligament.
Materials and methods
Knee Surg Sports Traumatol Arthrosc
Fig. 1 Cadaveric dissection of the medial side of the elbow for specimen testing. Sutures were placed along the anterior and posterior bands of the UCL. These were used by the video tracking software to measure strain. The pins were placed in bone to record elbow flexion angle
Anatomical dissection Six fresh-frozen cadaveric elbow specimens with a median age at death of 67 years (range 50–83) were used. There were five male and one female specimen. The humerus was transected 15–20 cm above the humeral condyles. The distal forearm was pinned in neutral rotation and skin, subcutaneous tissues, and fat were removed from the entire specimen to the wrist. Dissection over the medial condyle was carried down to the underlying fascia. A longitudinal incision was carried out through the flexor/pronator mass overlying the UCL, and the muscle insertion was bluntly dissected off the ligament. Small retractors were then placed into the incision, keeping the flexor mass from contacting or obstructing the view of the UCL, through its arc of motion. The anterior and posterior borders were marked with 5-0 silk suture as shown in the photo (Fig. 1). The anterior UCL was marked at its origin, midpoint, and insertion on both the anterior and posterior borders, demarcating the anterior and posterior bands. These sutures were used as markers for video analysis. Biomechanical evaluation Two pins were placed in both the humerus and ulna, near the respective origin and insertion of the ligament, to serve as static markers throughout the arc of motion, in determining elbow flexion angle. The humerus was clamped to a static holding system with the epicondylar axis perpendicular to the baseplate of the mounting device with the UCL facing superiorly. Valgus torque was provided by the weight of the forearm. The elbows were preconditioned by manually flexing and extending the elbow through five
13
cycles prior to analysis. With the forearm held in neutral rotation, the elbow was manually taken through five range of motion cycles from maximum extension to maximum flexion and filmed with a digital video camera (Canon GL2, Canon USA, Lake Success, NY) aligned perpendicular to the UCL at 70° flexion. After testing throughout the elbow flexion/extension arc, load to failure testing was performed using an Instron materials testing machine (Instron Corp, Model #3365, Canton, MA, USA). All soft tissue was stripped from the humeri and forearms, with the exception of the anterior and posterior bands of the anterior bundle of the UCL. The lateral condyle and olecranon were resected with the use of an oscillating saw to prevent impingement of the surfaces during tensile testing. Specimens were then potted in PVC tubing using plaster of Paris and then mounted on the Instron testing device in 70° of elbow flexion. Each specimen was preloaded with 20 N for 10 s and then cycled through ten cycles of 20–60 N, to precondition the ligament. The UCL was then loaded to failure at 10 mm/min. Videos were analysed, and the markers were tracked using WINanalyze software (Mikromak, Berlin, Germany). The anterior and posterior band lengths and strain behaviour throughout the elbow flexion/extension arc and during load to failure were measured. The accuracy of this method was 0.15 mm; whereas the repeatability between multiple trials of elbow flexion/extension was 0.2 mm. The initial length of both the anterior and posterior bands was defined with the elbow at 70° of flexion. Seventy degrees was chosen as the initial reference length as this represents the middle of the normal range of motion of the elbow (0–140).
Knee Surg Sports Traumatol Arthrosc
IRB approval was waived by the Subcommittee on Human Studies at the VA Long Beach Health Care System as this is a cadaveric basic science study.
yield point and 23.5 ± 0.9 % at ultimate failure (Fig. 3). There was no statistically significant difference between the strains at yield point and ultimate load between the anterior and posterior bands of the anterior bundle.
Statistical analysis The three middle trials of flexion/extension were averaged together, and this average was averaged across the six specimens. Based on data from pilot testing of two specimens showing a 10 % difference in strain with elbow flexion/ extension between the anterior and posterior bands and a standard deviation of 6 %, a sample size of six specimens was needed to show a statistically significant difference with an alpha of 0.05 and a power of 0.8. A paired t test was used to compare the differences between anterior and posterior bands with a significance level of 0.05.
Results Figure 2 demonstrates the strain characteristics of the anterior and posterior bands of the anterior bundle of the UCL through an arc of motion between 40° and 100° of elbow flexion. The anterior band changed very little throughout the arc of motion, whereas the posterior band showed a linear increase in strain as elbow flexion increased. The crossover demonstrated at 70° of elbow flexion is because the reference length used to calculate strain was taken at 70° of flexion. For all specimens, the mean yield point for the anterior bundle of the UCL was 203.3 ± 30.3 N and the ultimate load was 293.1 ± 38.7 N. The anterior band of the anterior bundle showed a strain of 23.3 ± 0.9 % at the yield point and 23.6 ± 0.9 % at ultimate failure. The posterior band of the anterior bundle showed a strain of 22.9 ± 0.9 % at the
Discussion The most important finding of this study is the difference in strain patterns for the anterior and posterior bands of the UCL with no difference in the intrinsic properties. The anterior band showed no significant strain, while the posterior band demonstrated a significant amount of strain with elbow flexion. The similar tensile strength, as measured in the load to failure model, demonstrates the anatomical location of the insertions of the bands determines their function rather than the inherent properties of each band. These results reinforce the importance of anatomy as it relates to reconstructive procedures. Accurately reproducing the most relevant anatomical structures will lead to improved kinematics which can translate into high rates of long-term, successful clinical outcomes. Callaway et al. [3] found that sectioning the anterior band of the anterior bundle of the UCL reduced resistance to valgus loads at 30°, 60° and 90° of flexion and co-primary restraint at 120°. Posterior band sectioning alone did not affect valgus laxity. The posterior band was found to be a co-primary restraint at 120° and a secondary restraint at 30° and 90°. This and another study by Floris et al. [5] showed the anterior band to be the primary restraint to valgus laxity. The relationship between the bands was postulated by Callaway to be reciprocal in nature. The strain pattern demonstrated in this study suggest the anterior band maintained a static function while the posterior bands strain increased, suggesting its role in valgus stability is increased at higher flexion angles.
Fig. 2 Graph depicting the strain of the anterior and posterior bands at varying degrees of elbow flexion; *P
