SCIENTIFIC ARTICLE
A Biomechanical Comparison of 2 Hybrid Techniques for Elbow Ulnar Collateral Ligament Reconstruction Justin E. Chronister, MD, Randal P. Morris, BS, Clark R. Andersen, MS, William L. Buford, Jr, PhD, J. Michael Bennett, MD, Thomas L. Mehlhoff, MD Purpose To compare the valgus laxity and fixation strength of 2 hybrid techniques for elbow ulnar collateral ligament reconstructions. Methods Reflective markers were placed near the ligament attachments of the ulnar collateral ligament on the humerus and ulna of 12 fresh-frozen cadaveric upper extremities for tracking displacement with 4 motion analysis cameras. Valgus laxity testing was performed on the intact, disrupted ligament, and reconstructed elbows by applying a 3.0 Nm moment across the joint at 15 intervals throughout elbow motion from 0 to 120 . Two hybrid techniques for ulnar collateral ligament reconstruction were performed: a proximal docking method and a single-point distal fixation method. Failure testing was performed with the elbow at 90 by applying a cyclic valgus load 12 cm distal to the joint that we increased in 10-N intervals. Results Valgus laxity testing revealed no difference in ligament displacements between the 2 techniques over the entire range of elbow motion. Ligament displacement for the proximal docking hybrid technique was significantly higher than the intact at 0 and 15 of elbow flexion. Failure testing revealed no differences in ligament displacements or failure load between the 2 techniques. Conclusions Both the proximal docking and the single-point fixation hybrid reconstructions provided sufficient joint stability and strength compared to the intact elbows, with the exception of the proximal docking method at low flexion angles. The reconstructions were not significantly different with respect to valgus laxity or graft fixation displacement at failure. Clinical relevance The proximal docking and single-point fixation hybrids tested here are both viable surgical options with sufficient strength and valgus laxity mechanics, warranting clinical evaluation. (J Hand Surg Am. 2014;39(10):2033e2040. Copyright Ó 2014 by the American Society for Surgery of the Hand. All rights reserved.) Key words Elbow, biomechanics of ligament, ulnar collateral ligament, ligament reconstruction, valgus laxity.
T
HE ULNAR COLLATERAL LIGAMENT (UCL) of the elbow is susceptible to serious injury in high-performance overhead-throwing athletes. Extreme valgus stresses are generated during the late
From the Department of Orthopaedic Surgery and Rehabilitation, The University of Texas Medical Branch, Galveston; and the Fondren Orthopaedic Group, LLP, Houston, TX. Received for publication March 19, 2014; accepted in revised form July 21, 2014. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
cocking and early acceleration phases of throwing. Valgus moments on the elbow during a pitch have been estimated between 64 to 120 Nm,1e6 and the static demand on the UCL has been estimated at 32 Corresponding author: Randal P. Morris, BS, Department of Orthopaedic Surgery and Rehabilitation, The University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0165; e-mail: [email protected]. 0363-5023/14/3910-0023$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.07.040
Ó 2014 ASSH
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Nm.7e9 Within the functional range of 30 to 120 , the primary restraint against these stresses is the anterior bundle of the UCL.10e21 Repetitive stresses can lead to attenuation or disruption of stabilizing structures and result in elbow pain, instability, and reduced athletic performance.22e28 Before reconstruction efforts, this injury was often career-ending. Surgical reconstruction of the UCL was described by Jobe et al.29 They exposed the UCL by transection of the common flexor-pronator muscle group and transposed the ulnar nerve. A tendon graft pulled through 3 bone tunnels in the medial epicondyle and 2 in the sublime tubercle of the ulna created a figure-of-eight construct. Conway et al25 reported early results of this technique with 68% (38 of 56) returned to pre-injury sport levels, but 21% (12 of 56) had ulnar nerve complications. Smith et al30 later described a muscle-splitting approach, which preserved the dynamic stabilizing flexor-pronator group, thus making ulnar nerve transposition unnecessary. Thomson et al31 reported excellent results with this limited approach in 82% (27 of 33) of patients with 2-year follow-up, with all returning to their sport, and 5% (4 of 83) ulnar nerve complications overall. Rohrbough et al32 described docking 2 graft limbs in the humerus and tensioning them with suture over a humeral bone bridge. Results show 92% (33 of 36) returning to pre-injury levels and 6% (2 of 36) ulnar nerve complications.32e34 However, multiple bone tunnels at the sublime tubercle make restoring isometry difficult and increase the risk of ulnar stress fracture.35 Addressing these problems, Ahmad et al36 described a tenodesis screw technique that creates a more anatomic construct using single-point screw fixation in the humerus and ulna.37,38 A recently developed hybrid technique, the DANE TJ, uses proximal docking and a distal tenodesis screw. Favorable clinical outcomes have been reported,39 although there have also been concerns over high failure rates with the proximal docking suture fixation.40e42 Bennett et al43 recently described a technique, the TJ Hybrid, which combines looping the graft through smaller Jobe bone tunnels proximally rather than docking and single-point distal fixation with a tenodesis screw. The purpose of our study was to compare the valgus laxity and failure strength of these 2 hybrid UCL reconstruction methods in a pairwise, intactcontrol, mechanical design. The null hypothesis was that there would be no differences in joint laxity or strength between either 2 techniques or the intact condition. J Hand Surg Am.
MATERIALS AND METHODS Specimen preparation Twelve (6 pairs) fresh-frozen cadaveric upper extremities (mean age, 90 y; range, 72e101 y; 3 male, 3 female) were disarticulated at the shoulder. Skin and soft tissue were removed, leaving only the medial and lateral static elbow stabilizers and the elbow joint capsule. The palmaris longus was harvested from each specimen pair for UCL reconstruction; alternatively, paired fourth flexor digitorum superficialis were used for specimens lacking one or both palmaris longus tendons.40 All tendons were doubled over, passed through a 4.5-mm graft-sizing block, and kept in saline-soaked gauze throughout the study. Each humerus was sectioned 14 cm from the center of the elbow and potted in polymethylmethacrylate in metal boxes. To secure neutral rotation, where the greatest valgus laxity occurs,44 a 4.5-mm cortical screw was placed through the radius and ulna 7 cm from the elbow. A 7-mm diameter stainless steel metal rod was secured in the ulnar shaft. Small metal screws were placed into bone at the attachment sites of the anterior bundle of the UCL—one at the tip of the humeral epicondyle and one on the ulna in line with the insertion and 2.0 cm from the joint line. To track the 3-dimensional displacement of the UCL, spherical reflective optical markers (6.5-mm diameter) were glued to the screw heads. Ligament reconstructions Proximal docking hybrid: The matched pair specimens were randomized into 2 groups for UCL reconstruction, all performed by the same orthopedic surgeon. The proximal docking hybrid reconstruction performed was adapted from Dines et al39 and started with the ulnar bone tunnel centered on the UCL insertion site on the sublime tubercle. The surgeon started a guide pin 7 to 8 mm from the joint line on the lateral aspect of the ulna and angled it to a point just distal to the supinator crest, which resulted in a 3 mm margin between the articular surface and the tunnel after reaming. A cannulated reamer (Arthrex, Inc., Naples, FL) created a 5.5-mm tunnel to a depth of 15 to 17 mm without penetrating the lateral ulna. A 4.5-mm tunnel was drilled through the footprint of the origin of the UCL on the medial epicondyle, approximately 5 mm anterior from its inferior tip12,15,45 for a distance of 15 to 17 mm. The surgeon extended the tunnel through the posterior cortex using a 2.7-mm drill bit and sleeve. A second 2.7-mm tunnel was made starting anterior to the epicondylar ridge and drilled proximal to distal r
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FIGURE 1: The proximal docking hybrid technique for reconstruction of the UCL. This method uses a single biocomposite tenodesis interference screw on the ulna and suture docking across a 10-mm bone tunnel on the medial epicondyle.
FIGURE 2: The single-point fixation hybrid technique for reconstruction of the UCL. This method uses a single biocomposite tenodesis interference screw placed more distally on the ulna to secure the graft as it loops through a 10-mm bone tunnel on the medial epicondyle.
toward the original 4.5-mm tunnel, preserving a bone bridge of 10 mm between the 2 proximal tunnels.39 The tendon graft was folded onto itself sutured together with a locking Krackow stitch using 2-0 Fiberwire (Arthrex Inc., Naples, FL). A paddle driver with a 5.5 mm biocomposite interference screw (BioTenodesis Screw System, Arthrex, Inc., Naples, FL) secured the graft in the ulnar tunnel with 2 limbs of suture tied over the top of the screw to prevent slippage (36). With the elbow reduced, gentle varus stress was applied at 70 degrees of flexion (14, 41) and graft length estimated and marked. A locking Krackow stitch was tied in both free ends of the graft with 2-0 Fiberwire, cut to length, and passed through the medial epicondyle tunnels. While holding the reduction with manual tension on the graft, the elbow was cycled through its range of motion, and the sutures were secured over the epicondylar bone bridge to complete the reconstruction (Fig. 1).
A 5.5-mm tunnel was reamed to a depth of 15 to 17 mm without penetrating the lateral ulna. A 4.5-mm tunnel was drilled through the origin of the UCL on the medial epicondyle for a distance of 15 to 17 mm. The surgeon then extended the tunnel through the posterior cortex with a 3.2-mm drill bit and sleeve. A second 3.2-mm tunnel was made starting anterior to the epicondylar ridge and drilling proximal to distal toward the original 4.5-mm tunnel, preserving a 10-mm bone bridge between the 2 proximal tunnels. The graft was passed through the humeral tunnels leaving both ends exiting the isometric footprint on the medial epicondyle. The lengths of tendon ends were equalized, and the tendon graft was whipstitched with 2-0 Fiberwire. With the elbow reduced, a gentle varus stress was applied at 70 of flexion,14,41 and the graft was secured into the bottom of the ulnar tunnel using a paddle driver with a 5.5-mm biocomposite interference screw (BioTenodesis Screw System). A loop of 2-0 Fiberwire over the tendon graft was used to manually tension the graft during fixation and then tied to the whipstitch suture over the interference screw to complete the reconstruction (Fig. 2).
Single-point fixation hybrid: The second group underwent UCL reconstruction by the single-point fixation hybrid technique described by Bennett and Mehlhoff.43 A guide pin (Arthrex, Inc., Naples, FL) was placed into the sublime tubercle just distal to the insertion of the UCL, 13 to 15 mm from the joint on the lateral aspect of the ulna, along the medial ulnar ridge, and angled just distal to the supinator crest. The recommended placement of the guide pin is 5 mm distal to the anatomic insertion of the ligament so that after the tendon is compressed in the ulnar tunnel by the screw, the ligament will be at its isometric insertion point, 8 mm from the joint line.12 J Hand Surg Am.
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Valgus joint laxity testing Joint stability was evaluated by valgus laxity testing with methods similar to previous studies.36,40 The matched pair specimens were randomized for testing order, and each specimen was mounted horizontally r
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in a custom jig with the medial side oriented superiorly. A force gauge (IMADA, Inc., Northbrook, IL) was used to determine the weight of the forearm construct at a point 12 cm distal to the anatomic axis of rotation of the elbow. A total force of 25 N was then applied at this point by hanging the proper combination of weights to achieve a 3.0 Nm moment at the joint. The weights were applied for 30 seconds at randomized elbow flexion angle positions of 0 , 15 , 30 , 45 , 60 , 75 , 90 , 105 , and 120 . A fourcamera motion capture system (Motion Analysis Corp., Santa Rosa, CA), calibrated to a precision of 0.25 mm, recorded 3-dimensional displacement of the UCL between the optical markers at 120 Hz. After laxity testing for the intact condition, the ligament attachments of the UCL were released from the epicondyle and sublime tubercle and the protocol was repeated for the UCL deficient state. The protocol was repeated a final time after UCL reconstruction. The magnitude of the ligament displacement due to valgus force between the attachment sites was calculated as the square root of the sum of squared differences of the x, y, and z coordinates for each marker. Statistical analysis of the total displacement for all conditions (intact, cut, 2 reconstructions) consisted of mixed model analysis of variance with repeated measures, Tukey adjustment for multiple comparisons, and alpha set at .05.
FIGURE 3: Testing setup for UCL reconstruction failure using reflective markers and a 4-camera motion-tracking system.
the 2 reconstructions using paired t tests with alpha set at .05, and mode of failure was observed and recorded qualitatively. RESULTS Joint valgus laxity testing The valgus laxity data for all groups over all flexion angles tested are presented in Figure 4. The released ligament demonstrated increased valgus joint displacement when compared with the intact ligament, and this was statistically significant for all flexion angles (P < .04) except 90 . The single-point fixation hybrid reconstruction closely replicated the intact condition displacement throughout the range of motion, and no statistically significant differences were observed compared with the intact state. Although the proximal docking hybrid performed more closely to the intact state for higher flexion angles, it deviated significantly for 0 (P ¼ .01) and 15 (P ¼ .02) of flexion compared with the intact state. There were no statistical differences in joint displacements between the single-point fixation hybrid and the proximal docking hybrid over the flexion range.
Failure testing After UCL reconstruction, fixation strength was evaluated using methods similar to a previous study.37 The reconstructed forearms were potted with polymethylmethacrylate at the sectioned end to further secure the rod in the ulna and maintain neutral alignment. Specimens were mounted horizontally in a custom jig with the medial side oriented superiorly, and positioned in 90 of flexion. This orientation simulated the common throwing position in early acceleration,8,27 as suggested in previous biomechanical studies.8,11,26,35,37 Using an MTS 858 Mini-Bionics materials testing machine (MTS, Inc., Eden Prairie, MN), valgus loading was applied to the ulnar rod at a point 12 cm distal to the anatomic axis of rotation of the elbow via an eyelet swivel bearing to prevent axial loads through the forearm (Fig. 3). An initial cyclic load of 20 N was applied at a rate of 0.5 Hz for 200 cycles, producing a maximum moment of 2.4 Nm, and then increased in increments of 10 N for 200 cycles until ligament displacement reached 5.0 mm or complete failure occurred. The peak failure load interval, cycles to failure, failure stiffness, and mean displacement at each load were compared for J Hand Surg Am.
Failure testing Figure 5 shows the mean displacements for both techniques over the failure loading cycle. The singlepoint fixation hybrid sustained a higher average number of cycles before clinical failure than the proximal docking hybrid (802 584 vs 575 409), although not statistically significant (P ¼ .24). There was no statistical difference in the average peak loads to failure at 5.0 mm of ligament displacement between the proximal docking hybrid (47 N) and the single-point r
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FIGURE 4: Ulnar collateral ligament attachment site displacement over the flexion range of motion of the elbow for the intact, cut ligament, proximal docking hybrid reconstruction, and the single-point fixation hybrid reconstruction.
FIGURE 5: Mean displacement ( standard deviation) sustained by the proximal docking hybrid and single-point fixation hybrid UCL graft reconstructions over the course of load to failure testing.
fixation hybrid (58 N; P = .26). As shown in the figure, more single-point fixation hybrid specimens survived successive loading intervals and experienced less mean displacement at each load interval up to failure compared with the proximal docking hybrid, although there was no statistical significance (P > .44). The first load interval, 20 N, was the only load in which all 6 specimens for each reconstruction survived. Joint J Hand Surg Am.
stiffness during failure loading of the proximal docking hybrid (6.7 3.7 N/mm) and single point fixation hybrid (6.7 3.6 N/mm) reconstructions were near identical. The mode of failure observed for both UCL reconstructions was the clinical failure limit of 5 mm in displacement. No graft disruptions or tunnel or bone bridge failures were observed. Modes of failure for r
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the proximal docking hybrid included suture pulling out of the suture-ligament interface (5 of 6) and knot failure over the humeral bone bridge (1 of 6). Modes of failure for the single point fixation hybrid included intra-substance graft stretching (5 of 6) and partial graft-screw slippage (1 of 6). DISCUSSION Overall restoration of normal kinematics is critical to the throwing athlete, requiring resistance to valgus stress over a wide range of motion.8,11 Successful UCL reconstruction must restore valgus stability, normal kinematics, and sufficient load to failure strength, especially in the early rehabilitation period. The objective of this study was to characterize the biomechanical properties of 2 single-strand hybrid surgical UCL reconstruction techniques. Restoration of normal valgus laxity for the entire range of motion indicates accurate anatomic location of the bone tunnels. The anterior band of the UCL is tight from 25 to 90 of flexion, and the posterior band is tight between 90 and 125 .11,18,19 The most isometric portion is the central fibers between these bands.14,45 Single-stranded reconstructions have previously been shown to restore UCL kinematics.36e38,46 We observed a close restoration of native elbow valgus laxity for both reconstruction techniques. The single-point fixation hybrid closely replicated intact the valgus laxity profile throughout the flexion range with a deviation from intact displacements of about 2 mm. The proximal docking hybrid displacements deviated significantly from the intact at low flexion angles (0 and 15 ), and the valgus laxity profile approached the intact level at higher flexion angles. There was a similar trend found for docking hybrid techniques evaluated in other biomechanical studies35,46 and this could be secondary to more accurate isometric ulnar tunnel placement. The isometric deep middle portion of the UCL inserts on the most prominent portion of the sublime tubercle.45 In a cadaveric study, Dugas et al12 showed that this point is 7.8 2.0 mm from the ulna cartilage edge. After tenodesis with a screw, the tendon is compressed to the proximal edge of the tunnel. If the tunnel is centered over the most prominent point, this displacement may give a slightly more proximal insertion point than expected (Fig. 6). The singlepoint fixation hybrid technique places the ulnar starting point distal to the most prominent point (about 5 mm) bringing the proximal edge of the tunnel closer to the isometric point. This position also may account for the superficial anterior fibers, which J Hand Surg Am.
FIGURE 6: Attachment sites of the medial UCL showing (1) the origin on the medial epicondyle of the humerus and (2) the insertion on the sublime tubercle of the ulna, as described by Ochi.39 The ulnar insertion (3) was described by Dugas17 to be more distal than the sublime tubercle.
have been shown to be most important for lower flexion angles.12,14 Modified approaches to UCL reconstruction have aimed at improving the initial strength of reconstruction. Biomechanical studies of throwing have estimated angular velocity between 2,300 /s and 5,000 /s, with peak accelerations of 500,000 /s.8,11,23 This creates high valgus moments on the UCL estimated at 35 Nm during a pitch.6,8,23 The ultimate failure moment of the intact UCL has been estimated between 23 Nm and 34 Nm.9,36,47 Hectman et al9 found an ultimate failure of 23 Nm for the intact state, 13 Nm for a bone anchor, and 15 Nm for the Jobe technique. Paletta et al47 found the moment of failure to be 19 Nm for the intact and 14 Nm for multistranded docking reconstructions. Ahmad et al36 showed intact moments of 34 7 Nm, and 31 19 Nm for double interference screw reconstructions. Most biomechanical studies of reconstructions including ours were unable to recreate the strength of the intact ligament with lower peak moments at failure (6 Nm for the proximal docking hybrid, 7 Nm for the single-point fixation hybrid) than similar studies mentioned above. Average peak loads to failure for the proximal docking hybrid (47 N) and the single-point fixation hybrid (58 N) were comparable to those reported by Armstrong37 (53 N for docking, 53 N for EndoButton, 42 N for interference screw, and 33 N for figure of eight). Ahmad et al36 reported average stiffness values for UCL reconstructions using an interference screw of 20 13 N/mm, and Hurbanek et al40 reported comparable stiffness values for a docking reconstruction with an interference screw (15 6 N/mm). r
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The current study showed much lower joint stiffness for both reconstructions, which may be attributed to specimen age and different, albeit similar, testing methods. Finally, single-point fixation hybrid reconstructions failed primarily by mid substance graft stretching, whereas graftesuture interface pullout or slippage at the suture knot was observed for the proximal docking hybrid. This suggests that the weakest link may be the sutureegraft interface in docking constructs. Other studies have shown up to 100% failure rates for the docking technique at the suture-tendon, suture knot, or humeral bone bridge.35,41,42,47 The limitations of this study are those inherent to cadaveric studies, including advanced age of specimens, limited specimen number, evaluation only at time zero, and the inability to account for the effects of dynamic muscle stabilizers.6 The specimens used in this study were selected by availability, not via the results of an a priori power analysis. Thus, it is indeterminate whether differences in valgus laxity or failure strength would develop between the 2 techniques or their intact controls if the study had sufficient power or if more specimens were tested. For valgus laxity testing, using the greatest difference in displacement between the two reconstructions (15 of flexion), a minimum of 20 specimens would be needed to achieve 80% power at a significance level of .05. For failure displacement, at 20 N of applied load, the study would need 120 specimens to achieve 80% power. Clinically, postoperative healing and rehabilitation may result in higher maximum loads to failure for both techniques than the 3 Nm meter moments applied here for testing valgus laxity. Valgus orientation and increasing cyclic loads used during failure testing would likely be discouraged during an early rehabilitation regimen, as these represent a worst-case scenario. The results of this technique comparison reveal that the single-point fixation hybrid and proximal docking hybrid reconstructions both adequately restored valgus laxity to near intact levels, with the exception of the proximal docking hybrid at low flexion angles. There were also no differences in failure strength or stiffness between the 2 techniques. Clinical outcomes of the proximal docking hybrid have been reported,39 while further evaluation of the single point fixation hybrid is warranted.
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27. Jobe FW, Nuber G. Throwing injuries of the elbow. Clin Sports Med. 1986;5(4):621e636. 28. Miller CD, Savoie FH III. Valgus extension injuries of the elbow in the throwing athlete. J Am Acad Orthop Surg. 1994;2(5):261e269. 29. Jobe FW, Stark H, Lombardo SJ. Reconstruction of the ulnar collateral ligament in athletes. J Bone Joint Surg Am. 1986;68(8): 1158e1163. 30. Smith GR, Altchek DW, Pagnani MJ, Keeley JR. A muscle-splitting approach to the ulnar collateral ligament of the elbow. Neuroanatomy and operative technique. Am J Sports Med. 1996;24(5):575e580. 31. Thompson WH, Jobe FW, Yocum LA, Pink MM. Ulnar collateral ligament reconstruction in athletes: muscle-splitting approach without transposition of the ulnar nerve. J Shoulder Elbow Surg. 2001;10(2):152e157. 32. Rohrbough JT, Altchek DW, Hyman J, Williams RJ III, Botts JD. Medical collateral ligament reconstruction of the elbow using the docking technique. Am J Sports Med. 2002;30(4):541e548. 33. Dodson CC, Thomas A, Dines JS, Nho SJ, Williams RJ III, Altchek DW. Medial ulnar collateral ligament reconstruction of the elbow in throwing athletes. Am J Sports Med. 2006;34(12): 1926e1932. 34. Koh JL, Schafer MF, Keuter G, Hsu JE. Ulnar collateral ligament reconstruction in elite throwing athletes. Arthroscopy. 2006;22(11): 1187e1191. 35. Ciccotti MG, Siegler S, Kuri JA II, Thinnes JH, Murphy DJ IV. Comparison of the biomechanical profile of the intact ulnar collateral ligament with the modified Jobe and the docking reconstructed elbow: an in vitro study. Am J Sports Med. 2009;37(5): 974e981. 36. Ahmad CS, Lee TQ, Elattrache NS. Biomechanical evaluation of a new elbow ulnar collateral ligament reconstruction with interference screw fixation. Am J Sports Med. 2003;31(3):332e337. 37. Armstrong AD, Dunning CE, Ferreira LM, Faber KJ, Johnson JA, King GJ. A biomechanical comparison of four reconstruction techniques for the medial collateral ligament deficient elbow. J Shoulder Elbow Surg. 2005;14(2):207e215.
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A Biomechanical Comparison of 2 Hybrid Techniques for Elbow Ulnar Collateral Ligament Reconstruction Justin E. Chronister, MD, Randal P. Morris, BS, Clark R. Andersen, MS, William L. Buford, Jr, PhD, J. Michael Bennett, MD, Thomas L. Mehlhoff, MD Purpose To compare the valgus laxity and fixation strength of 2 hybrid techniques for elbow ulnar collateral ligament reconstructions. Methods Reflective markers were placed near the ligament attachments of the ulnar collateral ligament on the humerus and ulna of 12 fresh-frozen cadaveric upper extremities for tracking displacement with 4 motion analysis cameras. Valgus laxity testing was performed on the intact, disrupted ligament, and reconstructed elbows by applying a 3.0 Nm moment across the joint at 15 intervals throughout elbow motion from 0 to 120 . Two hybrid techniques for ulnar collateral ligament reconstruction were performed: a proximal docking method and a single-point distal fixation method. Failure testing was performed with the elbow at 90 by applying a cyclic valgus load 12 cm distal to the joint that we increased in 10-N intervals. Results Valgus laxity testing revealed no difference in ligament displacements between the 2 techniques over the entire range of elbow motion. Ligament displacement for the proximal docking hybrid technique was significantly higher than the intact at 0 and 15 of elbow flexion. Failure testing revealed no differences in ligament displacements or failure load between the 2 techniques. Conclusions Both the proximal docking and the single-point fixation hybrid reconstructions provided sufficient joint stability and strength compared to the intact elbows, with the exception of the proximal docking method at low flexion angles. The reconstructions were not significantly different with respect to valgus laxity or graft fixation displacement at failure. Clinical relevance The proximal docking and single-point fixation hybrids tested here are both viable surgical options with sufficient strength and valgus laxity mechanics, warranting clinical evaluation. (J Hand Surg Am. 2014;39(10):2033e2040. Copyright Ó 2014 by the American Society for Surgery of the Hand. All rights reserved.) Key words Elbow, biomechanics of ligament, ulnar collateral ligament, ligament reconstruction, valgus laxity.
T
HE ULNAR COLLATERAL LIGAMENT (UCL) of the elbow is susceptible to serious injury in high-performance overhead-throwing athletes. Extreme valgus stresses are generated during the late
From the Department of Orthopaedic Surgery and Rehabilitation, The University of Texas Medical Branch, Galveston; and the Fondren Orthopaedic Group, LLP, Houston, TX. Received for publication March 19, 2014; accepted in revised form July 21, 2014. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
cocking and early acceleration phases of throwing. Valgus moments on the elbow during a pitch have been estimated between 64 to 120 Nm,1e6 and the static demand on the UCL has been estimated at 32 Corresponding author: Randal P. Morris, BS, Department of Orthopaedic Surgery and Rehabilitation, The University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0165; e-mail: [email protected]. 0363-5023/14/3910-0023$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.07.040
Ó 2014 ASSH
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Nm.7e9 Within the functional range of 30 to 120 , the primary restraint against these stresses is the anterior bundle of the UCL.10e21 Repetitive stresses can lead to attenuation or disruption of stabilizing structures and result in elbow pain, instability, and reduced athletic performance.22e28 Before reconstruction efforts, this injury was often career-ending. Surgical reconstruction of the UCL was described by Jobe et al.29 They exposed the UCL by transection of the common flexor-pronator muscle group and transposed the ulnar nerve. A tendon graft pulled through 3 bone tunnels in the medial epicondyle and 2 in the sublime tubercle of the ulna created a figure-of-eight construct. Conway et al25 reported early results of this technique with 68% (38 of 56) returned to pre-injury sport levels, but 21% (12 of 56) had ulnar nerve complications. Smith et al30 later described a muscle-splitting approach, which preserved the dynamic stabilizing flexor-pronator group, thus making ulnar nerve transposition unnecessary. Thomson et al31 reported excellent results with this limited approach in 82% (27 of 33) of patients with 2-year follow-up, with all returning to their sport, and 5% (4 of 83) ulnar nerve complications overall. Rohrbough et al32 described docking 2 graft limbs in the humerus and tensioning them with suture over a humeral bone bridge. Results show 92% (33 of 36) returning to pre-injury levels and 6% (2 of 36) ulnar nerve complications.32e34 However, multiple bone tunnels at the sublime tubercle make restoring isometry difficult and increase the risk of ulnar stress fracture.35 Addressing these problems, Ahmad et al36 described a tenodesis screw technique that creates a more anatomic construct using single-point screw fixation in the humerus and ulna.37,38 A recently developed hybrid technique, the DANE TJ, uses proximal docking and a distal tenodesis screw. Favorable clinical outcomes have been reported,39 although there have also been concerns over high failure rates with the proximal docking suture fixation.40e42 Bennett et al43 recently described a technique, the TJ Hybrid, which combines looping the graft through smaller Jobe bone tunnels proximally rather than docking and single-point distal fixation with a tenodesis screw. The purpose of our study was to compare the valgus laxity and failure strength of these 2 hybrid UCL reconstruction methods in a pairwise, intactcontrol, mechanical design. The null hypothesis was that there would be no differences in joint laxity or strength between either 2 techniques or the intact condition. J Hand Surg Am.
MATERIALS AND METHODS Specimen preparation Twelve (6 pairs) fresh-frozen cadaveric upper extremities (mean age, 90 y; range, 72e101 y; 3 male, 3 female) were disarticulated at the shoulder. Skin and soft tissue were removed, leaving only the medial and lateral static elbow stabilizers and the elbow joint capsule. The palmaris longus was harvested from each specimen pair for UCL reconstruction; alternatively, paired fourth flexor digitorum superficialis were used for specimens lacking one or both palmaris longus tendons.40 All tendons were doubled over, passed through a 4.5-mm graft-sizing block, and kept in saline-soaked gauze throughout the study. Each humerus was sectioned 14 cm from the center of the elbow and potted in polymethylmethacrylate in metal boxes. To secure neutral rotation, where the greatest valgus laxity occurs,44 a 4.5-mm cortical screw was placed through the radius and ulna 7 cm from the elbow. A 7-mm diameter stainless steel metal rod was secured in the ulnar shaft. Small metal screws were placed into bone at the attachment sites of the anterior bundle of the UCL—one at the tip of the humeral epicondyle and one on the ulna in line with the insertion and 2.0 cm from the joint line. To track the 3-dimensional displacement of the UCL, spherical reflective optical markers (6.5-mm diameter) were glued to the screw heads. Ligament reconstructions Proximal docking hybrid: The matched pair specimens were randomized into 2 groups for UCL reconstruction, all performed by the same orthopedic surgeon. The proximal docking hybrid reconstruction performed was adapted from Dines et al39 and started with the ulnar bone tunnel centered on the UCL insertion site on the sublime tubercle. The surgeon started a guide pin 7 to 8 mm from the joint line on the lateral aspect of the ulna and angled it to a point just distal to the supinator crest, which resulted in a 3 mm margin between the articular surface and the tunnel after reaming. A cannulated reamer (Arthrex, Inc., Naples, FL) created a 5.5-mm tunnel to a depth of 15 to 17 mm without penetrating the lateral ulna. A 4.5-mm tunnel was drilled through the footprint of the origin of the UCL on the medial epicondyle, approximately 5 mm anterior from its inferior tip12,15,45 for a distance of 15 to 17 mm. The surgeon extended the tunnel through the posterior cortex using a 2.7-mm drill bit and sleeve. A second 2.7-mm tunnel was made starting anterior to the epicondylar ridge and drilled proximal to distal r
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FIGURE 1: The proximal docking hybrid technique for reconstruction of the UCL. This method uses a single biocomposite tenodesis interference screw on the ulna and suture docking across a 10-mm bone tunnel on the medial epicondyle.
FIGURE 2: The single-point fixation hybrid technique for reconstruction of the UCL. This method uses a single biocomposite tenodesis interference screw placed more distally on the ulna to secure the graft as it loops through a 10-mm bone tunnel on the medial epicondyle.
toward the original 4.5-mm tunnel, preserving a bone bridge of 10 mm between the 2 proximal tunnels.39 The tendon graft was folded onto itself sutured together with a locking Krackow stitch using 2-0 Fiberwire (Arthrex Inc., Naples, FL). A paddle driver with a 5.5 mm biocomposite interference screw (BioTenodesis Screw System, Arthrex, Inc., Naples, FL) secured the graft in the ulnar tunnel with 2 limbs of suture tied over the top of the screw to prevent slippage (36). With the elbow reduced, gentle varus stress was applied at 70 degrees of flexion (14, 41) and graft length estimated and marked. A locking Krackow stitch was tied in both free ends of the graft with 2-0 Fiberwire, cut to length, and passed through the medial epicondyle tunnels. While holding the reduction with manual tension on the graft, the elbow was cycled through its range of motion, and the sutures were secured over the epicondylar bone bridge to complete the reconstruction (Fig. 1).
A 5.5-mm tunnel was reamed to a depth of 15 to 17 mm without penetrating the lateral ulna. A 4.5-mm tunnel was drilled through the origin of the UCL on the medial epicondyle for a distance of 15 to 17 mm. The surgeon then extended the tunnel through the posterior cortex with a 3.2-mm drill bit and sleeve. A second 3.2-mm tunnel was made starting anterior to the epicondylar ridge and drilling proximal to distal toward the original 4.5-mm tunnel, preserving a 10-mm bone bridge between the 2 proximal tunnels. The graft was passed through the humeral tunnels leaving both ends exiting the isometric footprint on the medial epicondyle. The lengths of tendon ends were equalized, and the tendon graft was whipstitched with 2-0 Fiberwire. With the elbow reduced, a gentle varus stress was applied at 70 of flexion,14,41 and the graft was secured into the bottom of the ulnar tunnel using a paddle driver with a 5.5-mm biocomposite interference screw (BioTenodesis Screw System). A loop of 2-0 Fiberwire over the tendon graft was used to manually tension the graft during fixation and then tied to the whipstitch suture over the interference screw to complete the reconstruction (Fig. 2).
Single-point fixation hybrid: The second group underwent UCL reconstruction by the single-point fixation hybrid technique described by Bennett and Mehlhoff.43 A guide pin (Arthrex, Inc., Naples, FL) was placed into the sublime tubercle just distal to the insertion of the UCL, 13 to 15 mm from the joint on the lateral aspect of the ulna, along the medial ulnar ridge, and angled just distal to the supinator crest. The recommended placement of the guide pin is 5 mm distal to the anatomic insertion of the ligament so that after the tendon is compressed in the ulnar tunnel by the screw, the ligament will be at its isometric insertion point, 8 mm from the joint line.12 J Hand Surg Am.
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Valgus joint laxity testing Joint stability was evaluated by valgus laxity testing with methods similar to previous studies.36,40 The matched pair specimens were randomized for testing order, and each specimen was mounted horizontally r
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in a custom jig with the medial side oriented superiorly. A force gauge (IMADA, Inc., Northbrook, IL) was used to determine the weight of the forearm construct at a point 12 cm distal to the anatomic axis of rotation of the elbow. A total force of 25 N was then applied at this point by hanging the proper combination of weights to achieve a 3.0 Nm moment at the joint. The weights were applied for 30 seconds at randomized elbow flexion angle positions of 0 , 15 , 30 , 45 , 60 , 75 , 90 , 105 , and 120 . A fourcamera motion capture system (Motion Analysis Corp., Santa Rosa, CA), calibrated to a precision of 0.25 mm, recorded 3-dimensional displacement of the UCL between the optical markers at 120 Hz. After laxity testing for the intact condition, the ligament attachments of the UCL were released from the epicondyle and sublime tubercle and the protocol was repeated for the UCL deficient state. The protocol was repeated a final time after UCL reconstruction. The magnitude of the ligament displacement due to valgus force between the attachment sites was calculated as the square root of the sum of squared differences of the x, y, and z coordinates for each marker. Statistical analysis of the total displacement for all conditions (intact, cut, 2 reconstructions) consisted of mixed model analysis of variance with repeated measures, Tukey adjustment for multiple comparisons, and alpha set at .05.
FIGURE 3: Testing setup for UCL reconstruction failure using reflective markers and a 4-camera motion-tracking system.
the 2 reconstructions using paired t tests with alpha set at .05, and mode of failure was observed and recorded qualitatively. RESULTS Joint valgus laxity testing The valgus laxity data for all groups over all flexion angles tested are presented in Figure 4. The released ligament demonstrated increased valgus joint displacement when compared with the intact ligament, and this was statistically significant for all flexion angles (P < .04) except 90 . The single-point fixation hybrid reconstruction closely replicated the intact condition displacement throughout the range of motion, and no statistically significant differences were observed compared with the intact state. Although the proximal docking hybrid performed more closely to the intact state for higher flexion angles, it deviated significantly for 0 (P ¼ .01) and 15 (P ¼ .02) of flexion compared with the intact state. There were no statistical differences in joint displacements between the single-point fixation hybrid and the proximal docking hybrid over the flexion range.
Failure testing After UCL reconstruction, fixation strength was evaluated using methods similar to a previous study.37 The reconstructed forearms were potted with polymethylmethacrylate at the sectioned end to further secure the rod in the ulna and maintain neutral alignment. Specimens were mounted horizontally in a custom jig with the medial side oriented superiorly, and positioned in 90 of flexion. This orientation simulated the common throwing position in early acceleration,8,27 as suggested in previous biomechanical studies.8,11,26,35,37 Using an MTS 858 Mini-Bionics materials testing machine (MTS, Inc., Eden Prairie, MN), valgus loading was applied to the ulnar rod at a point 12 cm distal to the anatomic axis of rotation of the elbow via an eyelet swivel bearing to prevent axial loads through the forearm (Fig. 3). An initial cyclic load of 20 N was applied at a rate of 0.5 Hz for 200 cycles, producing a maximum moment of 2.4 Nm, and then increased in increments of 10 N for 200 cycles until ligament displacement reached 5.0 mm or complete failure occurred. The peak failure load interval, cycles to failure, failure stiffness, and mean displacement at each load were compared for J Hand Surg Am.
Failure testing Figure 5 shows the mean displacements for both techniques over the failure loading cycle. The singlepoint fixation hybrid sustained a higher average number of cycles before clinical failure than the proximal docking hybrid (802 584 vs 575 409), although not statistically significant (P ¼ .24). There was no statistical difference in the average peak loads to failure at 5.0 mm of ligament displacement between the proximal docking hybrid (47 N) and the single-point r
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FIGURE 4: Ulnar collateral ligament attachment site displacement over the flexion range of motion of the elbow for the intact, cut ligament, proximal docking hybrid reconstruction, and the single-point fixation hybrid reconstruction.
FIGURE 5: Mean displacement ( standard deviation) sustained by the proximal docking hybrid and single-point fixation hybrid UCL graft reconstructions over the course of load to failure testing.
fixation hybrid (58 N; P = .26). As shown in the figure, more single-point fixation hybrid specimens survived successive loading intervals and experienced less mean displacement at each load interval up to failure compared with the proximal docking hybrid, although there was no statistical significance (P > .44). The first load interval, 20 N, was the only load in which all 6 specimens for each reconstruction survived. Joint J Hand Surg Am.
stiffness during failure loading of the proximal docking hybrid (6.7 3.7 N/mm) and single point fixation hybrid (6.7 3.6 N/mm) reconstructions were near identical. The mode of failure observed for both UCL reconstructions was the clinical failure limit of 5 mm in displacement. No graft disruptions or tunnel or bone bridge failures were observed. Modes of failure for r
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the proximal docking hybrid included suture pulling out of the suture-ligament interface (5 of 6) and knot failure over the humeral bone bridge (1 of 6). Modes of failure for the single point fixation hybrid included intra-substance graft stretching (5 of 6) and partial graft-screw slippage (1 of 6). DISCUSSION Overall restoration of normal kinematics is critical to the throwing athlete, requiring resistance to valgus stress over a wide range of motion.8,11 Successful UCL reconstruction must restore valgus stability, normal kinematics, and sufficient load to failure strength, especially in the early rehabilitation period. The objective of this study was to characterize the biomechanical properties of 2 single-strand hybrid surgical UCL reconstruction techniques. Restoration of normal valgus laxity for the entire range of motion indicates accurate anatomic location of the bone tunnels. The anterior band of the UCL is tight from 25 to 90 of flexion, and the posterior band is tight between 90 and 125 .11,18,19 The most isometric portion is the central fibers between these bands.14,45 Single-stranded reconstructions have previously been shown to restore UCL kinematics.36e38,46 We observed a close restoration of native elbow valgus laxity for both reconstruction techniques. The single-point fixation hybrid closely replicated intact the valgus laxity profile throughout the flexion range with a deviation from intact displacements of about 2 mm. The proximal docking hybrid displacements deviated significantly from the intact at low flexion angles (0 and 15 ), and the valgus laxity profile approached the intact level at higher flexion angles. There was a similar trend found for docking hybrid techniques evaluated in other biomechanical studies35,46 and this could be secondary to more accurate isometric ulnar tunnel placement. The isometric deep middle portion of the UCL inserts on the most prominent portion of the sublime tubercle.45 In a cadaveric study, Dugas et al12 showed that this point is 7.8 2.0 mm from the ulna cartilage edge. After tenodesis with a screw, the tendon is compressed to the proximal edge of the tunnel. If the tunnel is centered over the most prominent point, this displacement may give a slightly more proximal insertion point than expected (Fig. 6). The singlepoint fixation hybrid technique places the ulnar starting point distal to the most prominent point (about 5 mm) bringing the proximal edge of the tunnel closer to the isometric point. This position also may account for the superficial anterior fibers, which J Hand Surg Am.
FIGURE 6: Attachment sites of the medial UCL showing (1) the origin on the medial epicondyle of the humerus and (2) the insertion on the sublime tubercle of the ulna, as described by Ochi.39 The ulnar insertion (3) was described by Dugas17 to be more distal than the sublime tubercle.
have been shown to be most important for lower flexion angles.12,14 Modified approaches to UCL reconstruction have aimed at improving the initial strength of reconstruction. Biomechanical studies of throwing have estimated angular velocity between 2,300 /s and 5,000 /s, with peak accelerations of 500,000 /s.8,11,23 This creates high valgus moments on the UCL estimated at 35 Nm during a pitch.6,8,23 The ultimate failure moment of the intact UCL has been estimated between 23 Nm and 34 Nm.9,36,47 Hectman et al9 found an ultimate failure of 23 Nm for the intact state, 13 Nm for a bone anchor, and 15 Nm for the Jobe technique. Paletta et al47 found the moment of failure to be 19 Nm for the intact and 14 Nm for multistranded docking reconstructions. Ahmad et al36 showed intact moments of 34 7 Nm, and 31 19 Nm for double interference screw reconstructions. Most biomechanical studies of reconstructions including ours were unable to recreate the strength of the intact ligament with lower peak moments at failure (6 Nm for the proximal docking hybrid, 7 Nm for the single-point fixation hybrid) than similar studies mentioned above. Average peak loads to failure for the proximal docking hybrid (47 N) and the single-point fixation hybrid (58 N) were comparable to those reported by Armstrong37 (53 N for docking, 53 N for EndoButton, 42 N for interference screw, and 33 N for figure of eight). Ahmad et al36 reported average stiffness values for UCL reconstructions using an interference screw of 20 13 N/mm, and Hurbanek et al40 reported comparable stiffness values for a docking reconstruction with an interference screw (15 6 N/mm). r
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The current study showed much lower joint stiffness for both reconstructions, which may be attributed to specimen age and different, albeit similar, testing methods. Finally, single-point fixation hybrid reconstructions failed primarily by mid substance graft stretching, whereas graftesuture interface pullout or slippage at the suture knot was observed for the proximal docking hybrid. This suggests that the weakest link may be the sutureegraft interface in docking constructs. Other studies have shown up to 100% failure rates for the docking technique at the suture-tendon, suture knot, or humeral bone bridge.35,41,42,47 The limitations of this study are those inherent to cadaveric studies, including advanced age of specimens, limited specimen number, evaluation only at time zero, and the inability to account for the effects of dynamic muscle stabilizers.6 The specimens used in this study were selected by availability, not via the results of an a priori power analysis. Thus, it is indeterminate whether differences in valgus laxity or failure strength would develop between the 2 techniques or their intact controls if the study had sufficient power or if more specimens were tested. For valgus laxity testing, using the greatest difference in displacement between the two reconstructions (15 of flexion), a minimum of 20 specimens would be needed to achieve 80% power at a significance level of .05. For failure displacement, at 20 N of applied load, the study would need 120 specimens to achieve 80% power. Clinically, postoperative healing and rehabilitation may result in higher maximum loads to failure for both techniques than the 3 Nm meter moments applied here for testing valgus laxity. Valgus orientation and increasing cyclic loads used during failure testing would likely be discouraged during an early rehabilitation regimen, as these represent a worst-case scenario. The results of this technique comparison reveal that the single-point fixation hybrid and proximal docking hybrid reconstructions both adequately restored valgus laxity to near intact levels, with the exception of the proximal docking hybrid at low flexion angles. There were also no differences in failure strength or stiffness between the 2 techniques. Clinical outcomes of the proximal docking hybrid have been reported,39 while further evaluation of the single point fixation hybrid is warranted.
2. Feltner ME, Dapena J. Dynamics of the shoulder and elbow joints of the throwing arm during a baseball pitch. Int J Sport Biomechan. 1986;2(4):235e259. 3. Morrey BF, Tanaka S, An KN. Valgus stability of the elbow. A definition of primary and secondary constraints. Clin Orthop Relat Res. 1991;265:187e195. 4. Pappas AM, Zawacki RM, Sullivan TJ. Biomechanics of baseball pitching. A preliminary report. Am J Sports Med. 1985;13(4): 216e222. 5. Tullos HS, King JW. Throwing mechanism in sports. Orthop Clin North Am. 1973;4(3):709e720. 6. Werner SL, Fleisig GS, Dillman CJ, Andrews JR. Biomechanics of the elbow during baseball pitching. J Orthop Sports Phys Ther. 1993;17(6):274e278. 7. Azar FM, Andrews JR, Wilk KE, Groh D. Operative treatment of ulnar collateral ligament injuries of the elbow in athletes. Am J Sports Med. 2000;28(1):16e23. 8. Fleisig GS, Andrews JR, Dillman CJ, Escamilla RF. Kinetics of baseball pitching with implications about injury mechanisms. Am J Sports Med. 1995;23(2):233e239. 9. Hechtman KS, Tjin-A-Tsoi EW, Zvijac JE, Uribe JW, Latta LL. Biomechanics of a less invasive procedure for reconstruction of the ulnar collateral ligament of the elbow. Am J Sports Med. 1998;26(5):620e624. 10. Cain EL, Dugas JR, Wolf RS, Andrews JR. Elbow injuries in throwing athletes: A current concepts review. Am J Sports Med. 2003;31(4):621e635. 11. Callaway GH, Field LD, Deng XH, Torzilli PA, O’Brien SJ, Altchek DW, et al. Biomechanical evaluation of the medial collateral ligament of the elbow. J Bone Joint Surg Am. 1997;79(8):1223e1231. 12. Dugas JR, Ostrander RV, Cain EL, Kingsley D, Andrews JR. Anatomy of the anterior bundle of the ulnar collateral ligament. J Shoulder Elbow Surg. 2007;16(5):657e660. 13. Field LD, Callaway GH, O’Brien SJ, Altchek DW. Arthroscopic assessment of the medial collateral ligament complex. Am J Sports Med. 1995;23(4):396e400. 14. Floris S, Olsen BS, Dalstra M, Søjbjerg JO, Sneppen O. The medial collateral ligament of the elbow joint: Anatomy and kinematics. J Shoulder Elbow Surg. 1998;7(4):345e351. 15. Fuss FK. The ulnar collateral ligament of the human elbow joint. Anatomy, function, and biomechanics. J Anat. 1991;175:203e212. 16. Hotchkiss RN, Weiland AJ. Valgus stability of the elbow. J Orthop Res. 1987;5(3):372e377. 17. Morrey BF, An KN. Functional anatomy of the ligaments of the elbow. Clin Orthop Relat Res. 1985;201:84e90. 18. Regan WD, Korinek SL, Morrey BF, An KN. Biomechanical study of ligaments around the elbow joint. Clin Orthop Relat Res. 1991;271:170e179. 19. Schwab GH, Bennett JB, Woods GW, Tullos HS. Biomechanics of elbow instability: the role of the medial collateral ligament. Clin Orthop Relat Res. 1980;146:42e52. 20. Sojbjerg JO, Ovesen J, Nielsen S. Experimental elbow instability after transection of the medial collateral ligament. Clin Orthop Relat Res. 1987;218:186e190. 21. Timmerman LA, Andrews JR. Histology and arthroscopic anatomy of the ulnar collateral ligament of the elbow. Am J Sports Med. 1994;22(5):667e673. 22. Ahmad CS, ElAttrache NS. Elbow valgus instability in the throwing athlete. J Am Acad Orthop Surg. 2006;14(12):693e700. 23. Andrews JR, Timmerman LA. Outcome of elbow surgery in professional baseball players. Am J Sports Med. 1995;23(4):407e413. 24. Bennett JB, Green MS, Tullos HS. Surgical management of chronic medial elbow instability. Clin Orthop Relat Res. 1992;278:62e68. 25. Conway JE, Jobe FW, Glousman RE, Pink M. Medial instability of the elbow in throwing athletes. Treatment by repair or reconstruction of the ulnar collateral ligament. J Bone Joint Surg Am. 1992;74(1):67e83. 26. Eygendaal D, Olsen BS, Jensen SL, Seki A, Söjbjerg JO. Kinematics of partial and total ruptures of the medial collateral ligament of the elbow. J Shoulder Elbow Surg. 1999;8(6):612e616.
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38. Armstrong AD, Dunning CE, Faber KJ, Johnson JA, King GJ. Single strand ligament reconstruction of the medial collateral ligament restores valgus elbow stability. J Shoulder Elbow Surg. 2002;11(1):65e77. 39. Dines JS, ElAttrache NS, Conway JE, Smith W, Ahmad CS. Clinical outcomes of the proximal docking hybrid technique to treat ulnar collateral ligament insufficiency of the elbow. Am J Sports Med. 2007;35(12):2039e2044. 40. Hurbanek JG, Anderson K, Crabtree S, Karnes GJ. Biomechanical comparison of the docking technique with and without humeral bioabsorbable interference screw fixation. Am J Sports Med. 2009;37(3):526e533. 41. McAdams TR, Lee AT, Centeno J, Giori NJ, Lindsey DP. Two ulnar collateral ligament reconstruction methods: the docking technique versus bioabsorbable interference screw fixation. A biomechanical evaluation with cyclic loading. J Shoulder Elbow Surg. 2007;16(2): 224e228. 42. Ruland RT, Hogan CJ, Randall CJ, Richards A, Belkoff SM. Biomechanical comparison of ulnar collateral ligament reconstruction techniques. Am J Sports Med. 2008;36(8):1565e1570. 43. Bennett JM, Mehlhoff TL. Reconstruction of the medial collateral ligament of the elbow. J Hand Surg. 2009;34(9):1729e1733. 44. Safran MR, McGarry MH, Shin S, Han S, Lee TQ. Effects of elbow flexion and forearm rotation on valgus laxity of the elbow. J Bone Joint Surg Am. 2005;87(9):2065e2074. 45. Ochi N, Ogura T, Hashizume H, Shigeyama Y, Senda M, Inoue H. Anatomic relation between the medial collateral ligament of the elbow and the humero-ulnar joint axis. J Shoulder Elbow Surg. 1999;8(1):6e10. 46. Morgan RJ, Starman JS, Habet NA, Peindl RD, Bankston LS Jr, D’Alessandro DD, et al. A biomechanical evaluation of ulnar collateral ligament reconstruction using a novel technique for ulnarsided fixation. Am J Sports Med. 2010;38(7):1448e1455. 47. Paletta GA, Klepps SJ, Difelice GS, Allen T, Brodt MD, Burns ME, et al. Biomechanical evaluation of 2 techniques for ulnar collateral ligament reconstruction of the elbow. Am J Sports Med. 2006;34(10): 1599e1603.
27. Jobe FW, Nuber G. Throwing injuries of the elbow. Clin Sports Med. 1986;5(4):621e636. 28. Miller CD, Savoie FH III. Valgus extension injuries of the elbow in the throwing athlete. J Am Acad Orthop Surg. 1994;2(5):261e269. 29. Jobe FW, Stark H, Lombardo SJ. Reconstruction of the ulnar collateral ligament in athletes. J Bone Joint Surg Am. 1986;68(8): 1158e1163. 30. Smith GR, Altchek DW, Pagnani MJ, Keeley JR. A muscle-splitting approach to the ulnar collateral ligament of the elbow. Neuroanatomy and operative technique. Am J Sports Med. 1996;24(5):575e580. 31. Thompson WH, Jobe FW, Yocum LA, Pink MM. Ulnar collateral ligament reconstruction in athletes: muscle-splitting approach without transposition of the ulnar nerve. J Shoulder Elbow Surg. 2001;10(2):152e157. 32. Rohrbough JT, Altchek DW, Hyman J, Williams RJ III, Botts JD. Medical collateral ligament reconstruction of the elbow using the docking technique. Am J Sports Med. 2002;30(4):541e548. 33. Dodson CC, Thomas A, Dines JS, Nho SJ, Williams RJ III, Altchek DW. Medial ulnar collateral ligament reconstruction of the elbow in throwing athletes. Am J Sports Med. 2006;34(12): 1926e1932. 34. Koh JL, Schafer MF, Keuter G, Hsu JE. Ulnar collateral ligament reconstruction in elite throwing athletes. Arthroscopy. 2006;22(11): 1187e1191. 35. Ciccotti MG, Siegler S, Kuri JA II, Thinnes JH, Murphy DJ IV. Comparison of the biomechanical profile of the intact ulnar collateral ligament with the modified Jobe and the docking reconstructed elbow: an in vitro study. Am J Sports Med. 2009;37(5): 974e981. 36. Ahmad CS, Lee TQ, Elattrache NS. Biomechanical evaluation of a new elbow ulnar collateral ligament reconstruction with interference screw fixation. Am J Sports Med. 2003;31(3):332e337. 37. Armstrong AD, Dunning CE, Ferreira LM, Faber KJ, Johnson JA, King GJ. A biomechanical comparison of four reconstruction techniques for the medial collateral ligament deficient elbow. J Shoulder Elbow Surg. 2005;14(2):207e215.
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