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The impact of ulnar collateral ligament tear and reconstruction on contact pressures in the lateral compartment of the elbow
J Shoulder Elbow Surg (2011) 20, 226-233
www.elsevier.com/locate/ymse
The impact of ulnar collateral ligament tear and reconstruction on contact pressures in the lateral compartment of the elbow John P. Duggan Jr., MDa,*, Uche C. Osadebe, BAb, Jerry W. Alexander, BSb, Philip C. Noble, PhDc, David M. Lintner, MDd a
St. David’s Hospital Round Rock, Round Rock, TX, USA Institute of Orthopedic Research and Education, Houston, TX, USA c Barnhart Department of Orthopedic Surgery, Baylor College of Medicine, Houston, TX, USA d The Methodist Hospital, Houston, TX, USA b
Hypothesis: Complete ulnar collateral ligament (UCL) injury increases articular pressure and reduces contact area compared with the normal intact UCL. UCL reconstruction restores the contact area and contact pressure observed in the native joint. Materials and methods: Six male cadaveric elbows were mounted on a custom jig capable of simulating the 2 critical phases of the throwing motion during pitching. A contact sensor was placed through an anterior arthrotomy into the radiocapitellar joint. Each specimen then underwent valgus loading at 1.75 and 5.25 Nm of torque with the biceps, brachialis, and triceps under axial load in each testing condition. Results: The average valgus laxity in the intact elbow at 90 was 3.7 0.6 at the 5.25 Nm level of torque, which doubled after transection. The reconstruction group demonstrated less laxity (2.4 0.4 ) and reduced valgus angulation of the ulna at 5.25 Nm of torque. The transected UCL condition showed peak contact pressure 67% higher compared with the native ligament group at 5.25 Nm of torque. The reconstructed group increased peak articular cartilage pressures by 33% from the native ligament. At 5.25 Nm of torque for the 90 flexion phase, the transected UCL condition showed an average contact pressure of 84% greater than that of the native ligament group. Reconstruction of the UCL restored average articular pressures to within 20% of intact values at 90 . Conclusion: UCL injury increases radiocapitellar contact pressures and reduces resistance of the elbow to valgus loading. Contact pressures and valgus laxity can be improved with UCL reconstruction. Discussion: Taken as a whole, the peak pressure data indicate that the reconstruction restores valgus stability and lateral contact pressures to nearly normal levels under the conditions tested. Because the 90 position is the clinically significant position, these laboratory data support the clinical success of the docking procedure. Level of evidence: Basic Science Study. Ó 2011 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: UCL tear; UCL reconstruction; radiocapitellar contact pressures; elbow; biomechanics; ulnar collateral ligament
*Reprint requests: John Patrick Duggan Jr, MD, St. David’s Hospital Round Rock, 2400 Round Rock Ave, Round Rock, TX 78681. E-mail address: [email protected] (J.P. Duggan Jr.).
Adaptive and maladaptive changes of the elbow are commonly observed in the overhead throwing athlete.22,42 Historically, two-thirds of baseball pitchers have radiographic
1058-2746/$ - see front matter Ó 2011 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2010.09.011
Impact of UCL tear and reconstruction evidence of elbow arthritis.42 Recently, Cheung et al10 listed overhead throwing as 1 of 3 risk factors for primary osteoarthritis of the elbow. The biomechanical demands of the pitching motion have been demonstrated in a number of studies.* These publications have shown that the valgus torque developed during pitching reaches levels approaching the failure load of the ulnar collateral ligament (UCL) at the point of maximal external rotation of the throwing elbow. The lateral column must provide varus counter torque to resist the valgus torque of the throwing motion. When the arm is at 90 , the resistance to valgus torque is provided by the UCL and the flexor pronator mass. The ulnohumeral articulation does not contribute to the resistance to valgus torque. At the 30 position the ulnohumeral joint does contribute resistance to valgus torqe.15 Fleisig et al15 stated that the compressive force generated between the radial head and capitellum is approximately 500 N. With repetitive application, loads of this magnitude may ultimately lead to arthritis, osteochondritis dissecans (OCD), and loose body formation, forcing pitchers to retire from baseball.4,8,15 Before the advent of successful surgical reconstruction, most injuries of the UCL in the throwing athlete were career-ending.34,43 But recently, clinical studies consistently report a high rate of athletes returning to play after UCL reconstruction.8,13,17,20,30,32,35,41 Despite these clinical observations, little is known about the pathomechanics of degenerative joint disease of the elbow and its relationship to the integrity of the UCL, especially in athletes. To our knowledge, no known studies compare contact area and pressure distribution of the lateral compartment of the elbow under valgus loading in the intact, UCL transected, and reconstructed states. The purpose of this study was to better understand the relationship between each of these factors. We hypothesized that a complete UCL injury would reduce the contact area between the radius and the capitellum, leading to increased articular pressures. Conversely, we hypothesized that reconstruction of the UCL using the docking technique would restore the contact area and articular pressures observed in the native joint.
Materials and methods Institutional Review Board approval was not required for this study.
Specimen preparation Six individual male frozen upper extremities (unpaired, 3 left, 3 right) were obtained for this study from the Texas State Anatomic Board. The average age of donors at death was 37.7 years (range, 2549 years). No specimens had evidence of previous elbow surgery or ligamentous insufficiency. No cartilage, bone, or soft tissue abnormalities were seen during specimen preparation or testing. ) References 1,2,3,5,7,15,16,18,21,23-25,29,33,39,41,43,44
227 Each arm was thawed and transected at its midpoint of the brachium with all skin and muscle preserved distal to the transection. A large intramedullary rod with 2 transverse interlocking screws was cemented into the humeral canal of each specimen. The accessory lateral approach was performed in concord with Kocher’s flexor carpi ulnaris/anconeus interval.19 The lateral UCL was identified. The capsule was incised posterior to and in line with the lateral UCL. Each specimen was confirmed to not demonstrate posterolateral rotatory instability pattern. An accessory posterior portal was made percutaneously along the lateral border of the olecranon into the radiocapitellar joint. Shuttle sutures were placed in each of the capsulotomies to allow the medial and lateral corner of the sensors to be passed into the radiocapitellar joint. With the biceps, triceps, brachialis, and forearm unloaded, the thin sensor was passed into the radiocapitellar joint by gentle traction of the medial and lateral sutures and by flexion and extension of the forearm. With forearm traction and the respective muscles loaded, the sensor was securely fastened within the radiocapitellar joint and to the skin for further reinforcement. As a final check, multiple fixed points on both sensors and screws were placed above the capitellum before and after each valgus torque to confirm no sensor movement would occur during testing. The anterior approach to the elbow was performed using a ‘‘boat race’’ incision over the anterolateral elbow. The brachioradialis and biceps were retracted laterally while the flexor pronator mass was retracted medially. A vertical anterior capsulotomy was made without violating the annular ligament. The sensor was then placed into the lateral compartment after retracting the lateral soft tissue and capsule, as described above. Next, 5-mm stainless-steel threaded half pins (APEX, Stryker, Mahwah, NJ) were inserted into the radius and the ulna, respectively. These pins were independent and allowed rotation of the radius about the ulna. The forearm was not transfixed. These 2 pins connected the specimen to a custom loading jig that was mounted in a biaxial mechanical testing machine (MTS, Eden Prairie, MN). The loading jig consisted of two 155-mm full circular rings with each individual half pin connected to the frame using individual rancho cubes (Smith and Nephew, Memphis, TN). Adjustment of the rancho cubes on the circular ring allowed for adjustment of the pronation and supination of the forearm. A small external fixator was also attached to pins inserted into the distal radius and the second metacarpal to control flexion/extension and radial/ulnar deviation of the wrist. Fiberwire Krackow sutures (Arthrex, Naples, FL) were placed in the biceps, brachialis, and triceps and were attached to free hanging weights of 20, 20, and 40 N, respectively.21 The loading ratio was consistent with the validated simulated motion and joint compression system previously described by Kamineni et al.21 Adjustment of the testing base controlled the flexion of the elbow, while adjustment of the custom jig controlled forearm rotation, wrist extension, and radial deviation to simulate the joint positions of the two critical phases of throwing: the late cocking/ early acceleration phase and the release phase.
Testing protocol Each specimen was preconditioned before testing with the standard application of 25 cycles at 1.75 Nm of valgus torque with loading of the biceps, brachialis, and triceps. The 1.75-Nm load was chosen because this value corresponded to the 5% load to
228 failure for the UCL. The cycle count was chosen based on the viscoelastic creep of the tendon, similar to the preconditioning of an anterior cruciate ligament graft. A pressure transducer (Tekscan, South Boston, MA) was calibrated, prepared, and inserted into the joint with the aid of passing sutures. The valgus inclination of the ulna with respect to the humerus was monitored with an electronic tilt meter (Seika N4 inclinometer, Rieker Inc, Aston, PA) attached to the forearm loading frame. A load cell (SSM-2050; Interface Inc., Scottsdale, AZ) measured the force applied by the MTS actuator, and the point of application of the applied force with respect to the elbow was measured with a 3D digitizer (Immersion Microscibe, San Jose, CA) for calculation of the applied moment. The point of load application was through the middle of the double ring construct after the pins were connected to the circular frames through the rancho connectors. We measured the distance, then applied the desired force to equal the torque required. We were able to effectively calculate the moment arm and apply a known valgus torque to the joint. One half-pin was placed in the ulna and radius, respectively, with the forearm not transfixed. The pin to the ulna was placed first. The pin to the radius was then placed using the circular double frame as a visual guide for the appropriate separation distance. The double circular frame was connected to the MTS machine with a machined bushing that allowed the machine to transmit the force to the specimen through the pins in solely the varus/valgus plane. Specimen rotation was not allowed. The point of load application was thus determined by the placement of the ulnar pin, which was generally in the middle of the forearm. The moment arm was calculated by using a fixed point above both the capitellum and the proximal ulnar ring, adding half the distance between the frames, and subtracting the joint space distance of the radiocapitellar joint. With the moment arm directly calculated by the 3D digitizer, and the 5% and 15% load to failure torques desired, the MTS machine applied the appropriate force for the torque. The specimen was mounted into a valgus-loading position through the humeral intramedullary rod and the custom elbow jig, allowing the valgus moment to be the sole degree of freedom. Each elbow was placed in 30 and 90 of flexion during loading by fixing the setup as shown in Figure 1. The orientation of the extremity during the late cocking/early acceleration phase of the pitching activity was simulated by setting the elbow at 90 of flexion, the forearm at 4 of pronation, wrist extension at 40 , and ulnar deviation at 5 . Pronation and supination was controlled by the double ring. The release phase was simulated by setting the elbow at 30 of flexion, the forearm at 24 of pronation, the wrist extension at neutral, and 20 of ulnar deviation (Table I).44 With the aid of passing sutures introduced through the posterolateral incision, the sensor was positioned within the unloaded radiocapitellar joint through the anterolateral approach and securely attached to the skin (Fig. 2). The proximal muscles of the elbow joint were then loaded. Measurements of the intact ligament state were taken at the starting position, during 1.75 Nm of torque, and during 5.25 Nm of torque for both of the simulated phases of throwing; 1.75 and 5.25 Nm were chosen to represent 5% and 15% of reported failure torque of the UCL. These values were similar to previous biomechanical reports on UCL and UCL reconstruction.y After each loading condition, 3 fixed points of the lateral distal humerus and 3 fixed points on the pressure transducer
y
References 1,2,5,9,18,21,23,24,28,29,31,33,36,38
J.P. Duggan Jr. et al.
Figure 1 Photograph shows the side view of the experimental setup at 90 simulating the late cocking/early acceleration phase. were digitized to ensure that the transducer was accurately and reproducibly positioned with respect to anatomic landmarks. Each of 6 specimens was subjected to 2 levels of applied torque (1.75 and 5.25 Nm) after being placed in positions simulating the late cocking/early acceleration phase and the release phases of throwing. These loading conditions were applied to each intact specimen and then repeated after transection and reconstruction of the UCL (described below). The UCL was transected by a flexor carpi ulnaris splitting approach. The muscle was bluntly elevated with a Cobb elevator and the anterior bundle was identified. The anterior bundle of the UCL was then transected sharply off its origin and split along the line of its fibers past the sublime tubercle. The docking reconstruction was performed with a fresh frozen nonirradiated gracilis allograft tendon supplied by the Musculoskeletal Transplant Foundation. A single gracilis allograft was thawed immediately before each individual reconstruction. It was prepared with locking whip stitches in each end with No. 2 Orthocord (Mitek, Norwood, Mass) and maximally tensioned on a standard anterior cruciate ligament graft board (Mitek) The docking modification of the Jobe technique was performed as described by Smith et al.36 Two converging 3.2-mm holes were made approximately 1 cm from the articular surface and 1 cm apart on the sublime tubercle of the ulna. A 4.5-mm drill was used on the origin of the UCL on the medial epicondyle. Starting anterior to the medial intermuscular septum, two 2.0-mm holes were drilled in the medial epicondyle. The holes were separated by a 1-cm bony bridge and converged onto the 4.5-mm socket located at the anatomic origin. The graft was weaved through the ulnar tunnels. Its posterior limb was docked into the humeral socket, and the remaining anterior limb was trimmed to the correct length and docked into the humeral socket. The reconstruction was then tensioned to manual maximum and tied over the bony bridge at 90 of elbow flexion during maximal manual varus loading. Next, the split native UCL ligament was reapproximated by 3 figure-of-eight No. 2 Orthocord sutures passed through the reconstructed anterior and posterior limbs. The flexor carpi ulnaris fascia was also repaired with No. 2 figure-of-eight Orthocord sutures. The skin layer was closed with a running Prolene suture (Ethicon, Somerville, NJ) in a baseball stitch pattern.
Impact of UCL tear and reconstruction
229
Table I Experiment parameters used during late cocking/ early acceleration phase and release phase simulation conditions Late cocking/early
Degrees
Acceleration Phase Elbow Flexion Forearm Pronation Wrist Extension Ulnar deviation
90 4 40 5
Release phase Elbow flexion Forearm pronation Wrist extension Ulnar deviation
30 24 0 20
UCL
Starting
Intact
1.75 5.25 1.75 5.25 1.75 5.25 1.75 5.25 1.75 5.25 1.75 5.25
Transected Reconstructed Intact Transected Reconstructed
Nm Nm Nm Nm Nm Nm Nm Nm Nm Nm Nm Nm
3.62 2.76 when the torque was increased to 5.25 Nm. After resection of the UCL, there was virtually no increase in laxity at the lower torque level vs a 120% increase at 5.25 Nm (7.99 4.28 vs 3.62 2.76 ; P ¼ .0261). After reconstruction of the UCL, the valgus angulation of the ulna was 0.49 1.18 with application of 1.75 Nm of torque, and 3.71 1.81 with 5.25 Nm (Table II). In 90 of flexion, the valgus inclination of the intact specimens averaged 1.35 1.15 under the action of 1.75 Nm of valgus torque and 3.67 1.57 when the torque was increased to 5.25 Nm. After resection of the UCL, these values increased slightly at 1.75 Nm (1.8 1.28 ), and were more than doubled at 5.25 Nm. After reconstruction of the UCL, the valgus angulation of the ulnar was only 0.3 0.26 with application of 1.75 Nm of torque and 2.4 0.99 with 5.25 Nm. These results indicate that with the application of low valgus moments, the reconstructive procedure consistently overtightened the elbow by approximately 1 of valgus laxity in the 30 and 90 positions. At 5.25 Nm of torque, elbow laxity was restored to normal values in the 30 simulation but was reduced by approximately 1 at 90 .
Radiocapitellar contact area
Figure 2 Photograph shows the rear view of the experimental setup at 90 simulating the late cocking/early acceleration phase.
Data analysis Each contour map illustrating the distribution of articular pressures was analyzed with specialized software to determine the contact area, peak contact pressure, average contact pressure, and peak force in the radiocapitellar joint. All data derived from the transected and reconstructed specimens were normalized with respect to the initial runs performed in the intact condition only. The contact area, peak contact pressure, average contact pressure, and valgus laxity underwent statistical analysis using a repeated measure analysis of variance and a Fisher protected least significant difference post hoc test to determine if there were significant differences between the groups. Statistical significance was determined at value of P < .05.
Results Valgus stiffness In 30 of flexion, the intact elbows opened an average of 1.1 1.09 with application of 1.75 Nm of torque and
Before the application of the valgus moment, the contact area of the intact radiocapitellar articulation averaged 117 103 mm2 at 30 and 98 46 mm2 at 90 . When loaded with a valgus torque of 1.75 Nm, the average contact area remained essentially constant during the simulation of the release phase (30 : 118 84 mm2) but increased by 30% in the late cocking phase (90 : 158 69 mm2; P ¼.0024). With application of 5.25 Nm of torque, the contact area increased by 34% at 30 (128 44 mm2) but remained essentially constant at 90 (e7%; 120 31 mm2; P ¼ .095; Table III). Once the UCL was transected, there was no significant change in the articular contact area before valgus loading at 30 or 90 (P ¼ .515 and P ¼ .940, respectively). The same response was observed with the application of 1.75 Nm of torque at 30 and 90 . At the higher torque level, the transected specimens did not show the normal physiologic response of the elbow in increasing the area of contact between the radius and the capitellum. Although the intact specimens increased the area of contact by 20% to 30% in both 30 and 90 of flexion, the contact areas of the transected specimens averaged 15% less than the same elbows in the intact state. Surgical reconstruction of the UCL increased the area of radiocapitellar contact to within 10% of intact values under each of the conditions evaluated, with the exception of the higher torque loading in the 30 flexed position. In this latter case, the contact area after reconstruction of the UCL was similar to values measured after ligament resection (130 25 vs 135 65 mm2) and was only 83% of the original intact values (158 69 vs 130 25 mm2).
230
J.P. Duggan Jr. et al.
Table II
Joint laxity in degrees Intact
1.75 Nm valgus 30 position 90 position 5.25 Nm valgus 30 position 90 position )
torque 1.11 1.35 torque 3.62 3.67
Sectioned 1.09 1.35 1.18 1.15 1.81 1.28
Average contact pressure (MPa)
Reconstructed 0.49 1.18 0.33 0.26
2.76 7.99 4.28) 3.71 1.81 1.57 8.38 1.85 2.43 0.99
P < .05 (statistically different from intact condition).
Table III
Intact Unloaded 30 position 90 position 1.75 Nm valgus 30 position 90 position 5.25 Nm valgus 30 position 90 position
0.31 0.24 torque 0.37 0.32 torque 0.47 0.58
Sectioned
Reconstructed
0.28 0.15
0.32 0.30 0.28 0.15
0.34 0.21 0.28 0.13
0.31 0.14
0.44 0.47 0.44 0.28
0.46 0.47 0.37 0.19
0.37 0.28
0.74 0.62 1.07 0.76
0.72 0.52 0.69 0.43
Average contact area (mm2) Intact
Unloaded 30 position 90 position 1.75 Nm valgus 30 position 90 position 5.25 Nm valgus 30 position 90 position )
Table IV
117.3 98.7 torque 117.8 128.5 torque 157.5 120.0
Sectioned
Reconstructed
103.9 108.2 96.0 113.2 14.0 46.9 97.0 32.5 95.0 57.7 84.1 44.1
115.8 85.2 117.3 85.2 93.0 43.3 118.3 46.7
69.7) 135.7 65.6 129.5 24.9 31.8 103.2 43.1 120.7 21.3
P < .05 (statistically different from intact condition).
Table V
Peak contact pressure (MPa) Intact
Unloaded 30 position 90 position 1.75 Nm valgus 30 position 90 position 5.25 Nm valgus 30 position 90 position
0.86 0.56 torque 1.13 0.87 torque 1.55 1.75
Sectioned
Reconstructed
0.87 0.42
0.78 0.86 0.79 0.60
0.90 0.76 0.62 0.41
1.11 0.43
1.21 1.50 1.33 1.08
1.16 1.50 1.11 0.74
1.34 1.04
2.24 2.24 2.92 2.26
2.11 2.03 2.32 1.71
Articular contact pressures In the intact elbow, average radiocapitellar contact pressures ranged from 0.3 to 1.1 MPa under the conditions examined. With the joint unloaded, the average contact pressure was only 0.31 0.28 MPa at 30 of flexion and 0.24 0.15 MPa at 90 . The addition of the valgus torque increased these values by an average of 25% at 1.75 Nm (30 : 0.37 0.31 MPa; 90 : 0.32 0.14 MPa) and 91% at 5.25 Nm (30 : 0.47 0.37 MPa; 90 : 0.58 0.28 MPa; Table IV). Because the articular pressure distribution was not uniform, peak pressures were typically 2 to 3 times average values. In the 30 position, peak contact pressures averaged 0.86 0.87 MPa unloaded, 1.13 1.11 MPa with 1.75 Nm valgus torque, and 1.55 1.34 MPa when the torque was increased to 5.25 Nm. Compared with the 30 position, peak pressures were approximately 30% lower unloaded and with 1.75 Nm valgus torque, and 13% greater at 5.25 Nm (Table V). After transection of the ulnar collateral ligament, average articular pressures were virtually unchanged from intact values when tested in the 30 position. With 1.75 Nm of valgus torque, peak pressures did not change significantly from intact levels, but increased by 45% under 5.25 Nm of torque (P ¼ .199). Conversely, average pressures in the 90 position were higher after ligament transection, with a 17% increase at the unloaded state to an 84% increase at 5.25 Nm of valgus torque. Similarly, peak pressures were increased by 41%, 53%, and 67% during the unloaded conditions, 1.75 Nm of torque, and 5.25 Nm of
torque, respectively. Under the last of these conditions, the peak pressure averaged 2.92 2.26 MPa, almost 6 times intact values (0.56 0.42 MPa). Reconstruction of the UCL restored average articular pressures to within 20% of intact values in the 90 position for all 3 conditions tested. In the 30 position, reconstructed specimens exhibited a 10% increase in average contact pressure in the unloaded state, 24% with 1.75 Nm of valgus torque, and 53% at 5.25 Nm of torque. Similarly, peak pressures were restored to intact values when the joint was unloaded and with the application of low torque (1.75 Nm) in the 30 position. At the higher torque (5.25 Nm), peak pressures increased 36% to 2.11 2.03 MPa in the 30 position (P ¼ .346). Valgus loading of the reconstructed specimens in the 90 position increased peak pressures by 28% at 1.75 Nm (1.11 0.74 vs 0.87 0.43 MPa; P ¼ .157) and by 33% at 5.25 Nm (1.75 1.04 vs 2.32 1.71 MPa; P ¼ .131).
Discussion Ahmad et al2 recently demonstrated changes in articular contact between the ulnar and the posteromedial olecranon during valgus loading in the presence of partial and complete insufficiency of the medial UCL. Other research has demonstrated that changes in structure and biomechanics of the forearm and elbow occur with radial shortening, transection of the interosseus membrane, and as
Impact of UCL tear and reconstruction a consequence of the Sauve-Kapandji procedure, leading to changes in loading of the radiocapitellar joint with axial loading.12,26,28,37,40 Given the recognized mechanism of valgus extensions overload on the posterior medial olecranon and the radiocapitellar joint during pitching, we sought to evaluate the effect of UCL insufficiency and reconstruction on pressures across the radiocapitellar joint. Eckstein et al14 have stated that contact pressures within the elbow become more uniform with increasing loads. They hypothesized that the anatomic incongruity that is observed in the unloaded elbow is overcome with the application of physiologic loads as the elbow becomes more congruous with flexion.14 This would serve as a mechanism for limiting contact pressures through increasing the contact area of the radiocapitellar joint with valgus loading. This hypothesis is confirmed by the measurements of the present study performed in intact specimens before transection of the UCL. For this reason, we chose to measure contact pressure and area under an axially loaded elbow. Many studies have investigated the effects of forearm position on the radiocapitellar joint in the presence of valgus laxity.9,29,36 Safran et al36 recently reported that the elbow has greater valgus laxity at neutral rotation. Previously, Morrey et al27 reported that the greatest force transmission occurred when the forearm was in a pronated position. In general, forearm pronation allows the greatest changes in contact pressure distribution with the axially loaded elbow.21,27,36 Rather than focus on adding multiple forearm rotations for our biomechanical testing, we chose to control the forearm rotation for the 2 flexion angles tested relevant to the 2 critical phases of throwing. The positions of the elbow, forearm, and wrist at the 2 critical phases of throwing were selected based on the research of Zheng et al.44 During the late cocking/acceleration phase of throwing where most UCL injuries occur, the elbow is oriented in 90 of flexion. The second critical phase is terminal deceleration when elbow flexion is typically 30 . To control for passive muscle tension, as defined by Safran et al,36 and its ultimate effect on articular contact pressure and area, the corresponding simulated forearm rotation, wrist flexion/extension, and radial/ulnar deviation at 30 and 90 of elbow flexion were set. Currently, there are several methods of UCL reconstruction, principally the Jobe and docking techniques.1,18,20,35,39,41 Of these, biomechanical testing has demonstrated that the docking technique provides the greatest resistance to valgus loading before mechanical failure.29 Paletta et al29 reported that the docking procedure (14.3 Nm) was nearly twice as strong as the Jobe technique (8.9 Nm) but was weaker than the native ligament (18.8 Nm). Both surgical reconstructions have multiple cadaveric biomechanical studies describing their efficacy in restoring valgus laxity but also clinical success, with a high rate of return to play.5,13,27,29,31,32,35,41 Because of the greater strength and ease of tensioning of the docking
231 technique compared with the Jobe technique, this is the senior author’s (D.L.) preferred method of UCL reconstruction in practice. Thus, we chose to test the docking technique in the present study. The strengths of our study include the young age of the specimens, the use of allografts to control graft size, and the simulation of critical phases of pitching through adjustment of loading and the orientation of the elbow, forearm, and wrist. The use of a flexible membrane pressure transducer also enabled reliable measurements to be recorded of the contact area and the peak and mean contact pressure of the radiocapitellar joint without the limitations inherent in the interpretation of dye transfer methods (Fuji film) or methods that necessitate disarticulation of the elbow joint.31 Multiple cadaveric biomechical studies use specimens stripped of all soft tissue or elbows without the distal radioulnar joint. This soft tissue dissection did not excise or transect any primary or secondary stabilizers about the elbow. Despite these controls, dissection might affect the pressure measurements. The main limitation of this study is its small sample size. Another possible limitation is the lack of simulating loading of the flexor-pronator mass during testing, similar to Park et al.31 The short-term clinical goal of UCL reconstruction is to allow a high-level throwing athlete to return to his or her previous level of competition. The surgical goal of UCL reconstruction is to restore the passive restraint to valgus torque seen on the UCL at the late cocking/early acceleration phase of throwing. The ultimate goal of UCL reconstruction is to allow an overhead athlete to return to the preinjury level with a painless stable ligament to valgus torque, but also to prevent any long-term degenerative changes about the elbow as is historically seen in throwers. Many clinical reports declare a high rate of return to play after UCL reconstruction. Cadaveric biomechanical studies report that valgus laxity is restored after UCL reconstruction. Contact pressures in other joints are related to increased articular degeneration; there are no previous studies reporting on the pressures or contact area in the radiocapitellar joint due to valgus loading with the UCL intact, transected, and reconstructed. In this analysis, the mean valgus stiffness of the reconstruction at 90 flexion state did not differ statistically from the intact ligament state and was slightly tighter than the native state (P ¼ .16). Comparing the laxity data at the 30 flexion state confirms these grafts are not truly isometric. The stability was not as consistently restored at 30 as at 90 . This is expected, because the reconstructions were tensioned to the manual maximum at 90 of elbow flexion. The differences in laxity and contact pressure could be because the native UCL is not truly isometric and as a result may have combined with the less olecranon engagement in the posteromedial trochlea at 30 , allowing more laxity as the elbow approaches extension.2,6,21
232 Despite evidence that UCL reconstruction restores valgus laxity to normal, we see that it also increases the peak contact pressure by 26% on average, thus only improving peak pressures compared with the transected group but not completely restoring radiocapitellar pressures to normal at the higher torque. There was no significant difference between the intact and reconstructed stages. Taken as a whole, the peak pressure data indicate that the reconstruction restores valgus stability and lateral contact pressures to nearly normal levels under the conditions tested. Because the 90 position is the clinically significant position, these laboratory data support the clinical success of the docking procedure. At the 30 elbow position, the average contact pressure for the reconstructed condition is 123% greater than the intact, whereas the transected group is 64% greater than the intact. At the 90 elbow position, the average contact pressure for the reconstructed condition is 18% greater than the intact, whereas the transected group is 84% greater than the intact. Contrary to our hypothesis, the contact area between the radius and the capitellum did not change significantly from the intact state over the 2 levels of torque at the 90 flexion position. Given the limited number of specimens, it is unclear if there is an overall trend in the contact area data. Because the torques performed were only 5% and 15% of load to failure, it is possible that a higher level of torque could result in a change in contact areas. The peak pressures measured in this study were not dangerous as single episodes. The study by Clements et al11 found 6 MPa of pressure during repetitive motion was detrimental to chondrocytes. However, our model applies compressive forces less than those calculated in other studies as occurring in the lateral compartment during actual throwing. We project that at load-to-failure levels that are routinely seen by pitches, the peak contact pressures in the radiocapitellar joint exceed the 6 MPa chondrocyte cell viability threshold. It is the repetitive application of these elevated forces to the lateral compartment in the ligament deficient state that is of concern for causing ongoing degeneration of the lateral compartment. These forces can be minimized through UCL reconstruction. During the act of throwing the baseball, the shoulder externally rotates rapidly and makes a sudden transition to internal rotation as cocking transitions to acceleration. It is at this moment of direction reversal when the maximal valgus torque is applied to the elbow. This load is shared almost 50:50 by tension in the medial soft tissues and compression on the lateral column of the normal elbow. If the UCL is lax or incompetent, by definition less tension is borne medially and more compressive load is shifted to the articular surfaces of the radiocapitellar joint to negate this valgus torque. Reconstructing the UCL is an attempt to normalize the tension in the medial tissues during this valgus load and thus decrease pain and normalize the forces seen laterally and medially.
J.P. Duggan Jr. et al. It is unclear if UCL laxity is directly related to the development of OCD in the thrower’s elbow. Osteochondritis is more likely in the younger thrower, but UCL reconstruction is not typically thought to be appropriate in this age group, rendering moot the issue of UCL laxity. In the younger skeletally immature thrower with OCD, the UCL should be evaluated, and if significant laxity is suspected, consideration should be given to restricting throwing until UCL reconstruction can be safely considered. In reality, patients at this age are typically prohibited from throwing due to their articular lesion regardless of the status of the UCL. However, in the throwers with early OCD of an age where UCL reconstruction may be appropriate, the UCL should be thoroughly evaluated and considered for reconstruction.
Conclusions Under the conditions tested, deficiency of the UCL increases valgus laxity of the elbow joint with associated increases in the average and peak contact pressures in the radiocapitellar joint. Reconstruction of the UCL significantly corrects the radiocapitellar contact pressures as well as the valgus laxity.
Acknowledgments We acknowledge the material support provided by Breg, the Musculoskeletal Transplant Foundation, David Laws, Shawn Manning, and Travis Bryan. We also acknowledge the assistance of Matthew Thompson in the preparation of this manuscript.
Disclaimer The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Ahmad CS, Lee TQ, ElAttrache NS. Biomechanical evaluation of a new ulnar collateral ligament reconstruction technique with interference screw fixation. Am J Sports Med 2003;31:332-7. 2. Ahmad CS, Park MC, ElAttrache NS. Elbow medial ulnar collateral ligament insufficiency alters posteromedial olecranon contact. Am J Sports Med 2004;32:1607-12. doi:10.1177/0363546503263149 3. Alcid JG, Ahmad CS, Lee TQ. Elbow anatomy and structural biomechanics. Clin Sports Med 2004;23:503-17. doi:10.1016/j.csm. 2004.06.008
Impact of UCL tear and reconstruction 4. Andrews JR. Bony injuries about the elbow in the throwing athlete. Instr Course Lect 1985;34:323-31. 5. Armstrong AD, Dunning CE, Ferreira LM, Faber K, Johnson J, King G, et al. A biomechanical comparison of four reconstruction techniques for the medial collateral ligament-deficient elbow. J Shoulder Elbow Surg 2005;14:207-15. doi:10.1016/j.jse.2004.06.006 6. Armstrong AD, Ferreira LM, Dunning CE, Johnson JA, King GJW. The medial collateral ligament of the elbow is not isometric. Am J Sports Med 2004;32:85-90. doi:10.1177/0363546503258886 7. Atwater AE. Biomechanics of overarm throwing movements and of throwing injuries. Exerc Sport Sci Rev 1979;7:43-85. doi:10.1249/ 00003677-197900070-00004 8. 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;28:16-23. 9. Callaway GH, Field LD, Deng XH, Torzilli PA, O’Brien SJ, Altcheck DW, et al. Biomechanical evaluation of the medial collateral ligament of the elbow. J Bone Joint Surgery Am 1997;79:1223-31. 10. Cheung EV, Adams R, Morrey BF. Primary osteoarthritis of the elbow: current treatment options. J Am Acad Orthop Surg 2008;16:77-87. 11. Clements KM, Bee ZC, Crossingham GV, Adams MA, Sharif M. How severe must repetitive loading be to kill chondrocytes in articular cartilage? Osteoarthritis Cartilage 2001;9:499-507. doi:10.1053/joca. 2000.0417 12. Diab M, Poston JM, Huber P, Tencer FH. The biomechanical effect of radial shortening on the radiocapitellar articulation. J Bone Joint Surg Br 2005;87:879-83. doi:10.1302/0301-620X.87B6.15543 13. Dodson CC, Thomas A, Dines JS, Nho SJ, Williams RJ, Altchek DW. Medial ulnar collateral ligament reconstruction of the elbow in throwing athletes. Am J Sports Med 2006;34:1928-32. doi:10.1177/ 0363546506290988 14. Eckstein F, Lohe F, Schulte E, Muller-Gerbl M, Milz S, Putz R. Physiological incongruity of the humero-ulnar joint: a functional principle of optimized stress distribution acting on articulating surfaces? Anat Embryol (Berl) 1993;188:449-55. doi:10.1007/ BF00190139 15. Flesig GS, Andrews JR, Dillman CJ. Kinetics of baseball pitching with implications about injury mechanisms. Am J Sports Med 1995; 23:233-9. doi:10.1177/036354659502300218 16. Fornalski S, Gupta R, Lee TQ. Anatomy and biomechanics of the elbow joint. Tech Hand Up Extrem Surg 2003;7:168-78. doi:10.1097/ 00130911-200312000-00008 17. Gibson BW, Webner D, Huffman R, Sennett BJ. Ulnar collateral ligament reconstruction in major league baseball pitchers. Am J Sports Med 2007;35:575-81. doi:10.1177/0363546506296737 18. 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;26:620-4. 19. Hoppenfeld S, deBoer P. Surgical exposures in orthopaedics. The anatomic approach. Philadelphia: J.B. Lippincott; 1984. p. 97-101. 20. Jobe FW, Stark H, Lombardo SJ. Reconstruction of the ulnar collateral ligament in athletes. J Bone Joint Surg Am 1986;68:1158-63. 21. Kamineni S, ElAttrache NS, O’Driscoll SW, Ahmad CS, Hirohara H, Neale PG, et al. Medial collateral ligament strain with partial posteromedial olecranon resection. A biomechanical study. J Bone Joint Surgery 2004;86:2424-30. 22. King JW, Brelsford JH, Tullos HS. Analysis of the pitching arm of the professional baseball pitchers. Clin Orthop 1969;67:116. doi:10.1097/ 00003086-196911000-00018 23. Large TM, Coley ER, Peindl RD, Fleischli JE. A biomechanical comparison of 2 ulnar collateral ligament reconstruction techniques. Arthroscopy 2007;23:141-50. doi:10.1016/j.arthro.2006.09.004 24. Loftice J, Fleisig GS, Zheng N, Andrews JR. Biomechanics of the elbow in sports. Clin Sports Med 2004;4:519-30. doi:10.1016/j.csm. 2004.06.003
233 25. Morrey BF, An KN. Articular and ligamentous contributions to the stability of the elbow joint. Am J Sports Med 1983;11:315-9. doi:10. 1177/036354658301100506 26. Morrey BF, An KN, Stormont TJ. Force transmission through the radial head. J Bone Joint Surg 1988;70:250-6. 27. Mullen DJ, Goradia VK, Parks BG, Matthews LS. A biomechanical study of stability of the elbow to valgus stress before and after reconstruction of the medial collateral ligament. J Shoulder Elbow Surg 2002;11:259-64. doi:10.1067/mse.2002.122622 28. Ofuchi S, Takahashi K, Yamagata M, Rokkaku T, Moriya H, Hara T. Pressure distribution in the humeroradial joint and force transmission to the capitellum during rotation of the forearm: effects of the SauveKapandji procedure and incision of the interosseous membrane. J Orthop Sci 2001;6:33-8. doi:10.1007/s007760170022 29. Paletta GA, Klepps SJ, Difelice GS, Allen T, Brodt M, Burns M, et al. Biomechanical evaluation of 2 techniques for ulnar collateral ligament reconstruction of the elbow. Am J Sports Med 2006;34:1599-603. doi: 10.1177/0363546506289340 30. Paletta GA, Wright RW. The modified docking procedure for elbow ulnar collateral ligament reconstruction. 2-year follow-up in elite throwers. Am J Sports Med 2006;34:1594-8. doi:10.1177/ 0363546506289884 31. Park MC, Ahmad CS. Dynamic contributions of the flexor-pronator mass to elbow valgus stability. J Bone Joint Surg Am 2004;86:2268-74. 32. Petty DH, Andrews JR, Fleisig GS, Cain EL. Ulnar collateral ligament reconstruction in high school baseball players. Am J Sports Med 2004; 32:1158-64. doi:10.1177/0363546503262166 33. Regan WD, Korinek SL, Morrey BF, An KN. Biomechanical study of ligaments around the elbow joint. Clin Orthop 1991;271:170-9. doi:10. 1097/00003086-199110000-00023 34. Rettig AC, Sherril C, Snead DS, Mendler JC, Mieling P. Nonoperative treatment of ulnar collateral ligament injuries in throwing athletes. Am J Sports Med 2001;29:15-7. 35. Rohrbough JT, Altcheck DW, Hyman J, Williams RJ, Botts JD. Medial collateral ligament reconstruction of the elbow using the docking technique. Am J Sports Med 2002;30:541-8. 36. 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;87:2065-74. doi:10.2106/JBJS.D.02045 37. Shepard MF, Markolf KL, Dunbar AM. The effects of partial and total interosseus membrane transaction on load sharing in the cadaver forearm. J Orthop Res 2001;19:587-92. doi:10.1016/S0736-0266(00) 00059-0 38. Sojbjerg JO, Ovesen J, Nielson S. Experimental elbow instability after transection of the medial collateral ligament. Clin Orthop Relat Res 1987;218:186-90. 39. 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;24:575-80. doi:10.1177/036354659602400503 40. Takatori K, Hashizume H, Wake H, Inoue H, Nagayama N. Analysis of stress distribution in the humeroradial joint. J Orthop Sci 2002;7: 650-7. doi:10.1007/s007760200116 41. Thompson WH, Jobe FW, Yocum LA, Pink MM. Ulnar collateral ligament reconstruction in throwing athletes: muscle-splitting approach without transposition of the ulnar nerve. J Shoulder Elbow Surg 2001;10:152-7. doi:10.1067/mse.2001.112881 42. Tullos HS, King JW. Throwing mechanism in sports. Orthop Clin North Am 1973;4:709-20. 43. Whitely R. Baseball throwing mechanics as they relate to pathology and performance: a review. J Sports Sci Med 2007;6:1-20. 44. Zheng N, Fleisig GS, Barrentine SW, Andrew JR. Biomechanics of pitching. In: Hung GK, Pallis JM, editors. Biomedical engineering principles in sports. New York: Kluwer Academic/Plenum Publishers; 2004. p. 209-56.
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The impact of ulnar collateral ligament tear and reconstruction on contact pressures in the lateral compartment of the elbow John P. Duggan Jr., MDa,*, Uche C. Osadebe, BAb, Jerry W. Alexander, BSb, Philip C. Noble, PhDc, David M. Lintner, MDd a
St. David’s Hospital Round Rock, Round Rock, TX, USA Institute of Orthopedic Research and Education, Houston, TX, USA c Barnhart Department of Orthopedic Surgery, Baylor College of Medicine, Houston, TX, USA d The Methodist Hospital, Houston, TX, USA b
Hypothesis: Complete ulnar collateral ligament (UCL) injury increases articular pressure and reduces contact area compared with the normal intact UCL. UCL reconstruction restores the contact area and contact pressure observed in the native joint. Materials and methods: Six male cadaveric elbows were mounted on a custom jig capable of simulating the 2 critical phases of the throwing motion during pitching. A contact sensor was placed through an anterior arthrotomy into the radiocapitellar joint. Each specimen then underwent valgus loading at 1.75 and 5.25 Nm of torque with the biceps, brachialis, and triceps under axial load in each testing condition. Results: The average valgus laxity in the intact elbow at 90 was 3.7 0.6 at the 5.25 Nm level of torque, which doubled after transection. The reconstruction group demonstrated less laxity (2.4 0.4 ) and reduced valgus angulation of the ulna at 5.25 Nm of torque. The transected UCL condition showed peak contact pressure 67% higher compared with the native ligament group at 5.25 Nm of torque. The reconstructed group increased peak articular cartilage pressures by 33% from the native ligament. At 5.25 Nm of torque for the 90 flexion phase, the transected UCL condition showed an average contact pressure of 84% greater than that of the native ligament group. Reconstruction of the UCL restored average articular pressures to within 20% of intact values at 90 . Conclusion: UCL injury increases radiocapitellar contact pressures and reduces resistance of the elbow to valgus loading. Contact pressures and valgus laxity can be improved with UCL reconstruction. Discussion: Taken as a whole, the peak pressure data indicate that the reconstruction restores valgus stability and lateral contact pressures to nearly normal levels under the conditions tested. Because the 90 position is the clinically significant position, these laboratory data support the clinical success of the docking procedure. Level of evidence: Basic Science Study. Ó 2011 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: UCL tear; UCL reconstruction; radiocapitellar contact pressures; elbow; biomechanics; ulnar collateral ligament
*Reprint requests: John Patrick Duggan Jr, MD, St. David’s Hospital Round Rock, 2400 Round Rock Ave, Round Rock, TX 78681. E-mail address: [email protected] (J.P. Duggan Jr.).
Adaptive and maladaptive changes of the elbow are commonly observed in the overhead throwing athlete.22,42 Historically, two-thirds of baseball pitchers have radiographic
1058-2746/$ - see front matter Ó 2011 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2010.09.011
Impact of UCL tear and reconstruction evidence of elbow arthritis.42 Recently, Cheung et al10 listed overhead throwing as 1 of 3 risk factors for primary osteoarthritis of the elbow. The biomechanical demands of the pitching motion have been demonstrated in a number of studies.* These publications have shown that the valgus torque developed during pitching reaches levels approaching the failure load of the ulnar collateral ligament (UCL) at the point of maximal external rotation of the throwing elbow. The lateral column must provide varus counter torque to resist the valgus torque of the throwing motion. When the arm is at 90 , the resistance to valgus torque is provided by the UCL and the flexor pronator mass. The ulnohumeral articulation does not contribute to the resistance to valgus torque. At the 30 position the ulnohumeral joint does contribute resistance to valgus torqe.15 Fleisig et al15 stated that the compressive force generated between the radial head and capitellum is approximately 500 N. With repetitive application, loads of this magnitude may ultimately lead to arthritis, osteochondritis dissecans (OCD), and loose body formation, forcing pitchers to retire from baseball.4,8,15 Before the advent of successful surgical reconstruction, most injuries of the UCL in the throwing athlete were career-ending.34,43 But recently, clinical studies consistently report a high rate of athletes returning to play after UCL reconstruction.8,13,17,20,30,32,35,41 Despite these clinical observations, little is known about the pathomechanics of degenerative joint disease of the elbow and its relationship to the integrity of the UCL, especially in athletes. To our knowledge, no known studies compare contact area and pressure distribution of the lateral compartment of the elbow under valgus loading in the intact, UCL transected, and reconstructed states. The purpose of this study was to better understand the relationship between each of these factors. We hypothesized that a complete UCL injury would reduce the contact area between the radius and the capitellum, leading to increased articular pressures. Conversely, we hypothesized that reconstruction of the UCL using the docking technique would restore the contact area and articular pressures observed in the native joint.
Materials and methods Institutional Review Board approval was not required for this study.
Specimen preparation Six individual male frozen upper extremities (unpaired, 3 left, 3 right) were obtained for this study from the Texas State Anatomic Board. The average age of donors at death was 37.7 years (range, 2549 years). No specimens had evidence of previous elbow surgery or ligamentous insufficiency. No cartilage, bone, or soft tissue abnormalities were seen during specimen preparation or testing. ) References 1,2,3,5,7,15,16,18,21,23-25,29,33,39,41,43,44
227 Each arm was thawed and transected at its midpoint of the brachium with all skin and muscle preserved distal to the transection. A large intramedullary rod with 2 transverse interlocking screws was cemented into the humeral canal of each specimen. The accessory lateral approach was performed in concord with Kocher’s flexor carpi ulnaris/anconeus interval.19 The lateral UCL was identified. The capsule was incised posterior to and in line with the lateral UCL. Each specimen was confirmed to not demonstrate posterolateral rotatory instability pattern. An accessory posterior portal was made percutaneously along the lateral border of the olecranon into the radiocapitellar joint. Shuttle sutures were placed in each of the capsulotomies to allow the medial and lateral corner of the sensors to be passed into the radiocapitellar joint. With the biceps, triceps, brachialis, and forearm unloaded, the thin sensor was passed into the radiocapitellar joint by gentle traction of the medial and lateral sutures and by flexion and extension of the forearm. With forearm traction and the respective muscles loaded, the sensor was securely fastened within the radiocapitellar joint and to the skin for further reinforcement. As a final check, multiple fixed points on both sensors and screws were placed above the capitellum before and after each valgus torque to confirm no sensor movement would occur during testing. The anterior approach to the elbow was performed using a ‘‘boat race’’ incision over the anterolateral elbow. The brachioradialis and biceps were retracted laterally while the flexor pronator mass was retracted medially. A vertical anterior capsulotomy was made without violating the annular ligament. The sensor was then placed into the lateral compartment after retracting the lateral soft tissue and capsule, as described above. Next, 5-mm stainless-steel threaded half pins (APEX, Stryker, Mahwah, NJ) were inserted into the radius and the ulna, respectively. These pins were independent and allowed rotation of the radius about the ulna. The forearm was not transfixed. These 2 pins connected the specimen to a custom loading jig that was mounted in a biaxial mechanical testing machine (MTS, Eden Prairie, MN). The loading jig consisted of two 155-mm full circular rings with each individual half pin connected to the frame using individual rancho cubes (Smith and Nephew, Memphis, TN). Adjustment of the rancho cubes on the circular ring allowed for adjustment of the pronation and supination of the forearm. A small external fixator was also attached to pins inserted into the distal radius and the second metacarpal to control flexion/extension and radial/ulnar deviation of the wrist. Fiberwire Krackow sutures (Arthrex, Naples, FL) were placed in the biceps, brachialis, and triceps and were attached to free hanging weights of 20, 20, and 40 N, respectively.21 The loading ratio was consistent with the validated simulated motion and joint compression system previously described by Kamineni et al.21 Adjustment of the testing base controlled the flexion of the elbow, while adjustment of the custom jig controlled forearm rotation, wrist extension, and radial deviation to simulate the joint positions of the two critical phases of throwing: the late cocking/ early acceleration phase and the release phase.
Testing protocol Each specimen was preconditioned before testing with the standard application of 25 cycles at 1.75 Nm of valgus torque with loading of the biceps, brachialis, and triceps. The 1.75-Nm load was chosen because this value corresponded to the 5% load to
228 failure for the UCL. The cycle count was chosen based on the viscoelastic creep of the tendon, similar to the preconditioning of an anterior cruciate ligament graft. A pressure transducer (Tekscan, South Boston, MA) was calibrated, prepared, and inserted into the joint with the aid of passing sutures. The valgus inclination of the ulna with respect to the humerus was monitored with an electronic tilt meter (Seika N4 inclinometer, Rieker Inc, Aston, PA) attached to the forearm loading frame. A load cell (SSM-2050; Interface Inc., Scottsdale, AZ) measured the force applied by the MTS actuator, and the point of application of the applied force with respect to the elbow was measured with a 3D digitizer (Immersion Microscibe, San Jose, CA) for calculation of the applied moment. The point of load application was through the middle of the double ring construct after the pins were connected to the circular frames through the rancho connectors. We measured the distance, then applied the desired force to equal the torque required. We were able to effectively calculate the moment arm and apply a known valgus torque to the joint. One half-pin was placed in the ulna and radius, respectively, with the forearm not transfixed. The pin to the ulna was placed first. The pin to the radius was then placed using the circular double frame as a visual guide for the appropriate separation distance. The double circular frame was connected to the MTS machine with a machined bushing that allowed the machine to transmit the force to the specimen through the pins in solely the varus/valgus plane. Specimen rotation was not allowed. The point of load application was thus determined by the placement of the ulnar pin, which was generally in the middle of the forearm. The moment arm was calculated by using a fixed point above both the capitellum and the proximal ulnar ring, adding half the distance between the frames, and subtracting the joint space distance of the radiocapitellar joint. With the moment arm directly calculated by the 3D digitizer, and the 5% and 15% load to failure torques desired, the MTS machine applied the appropriate force for the torque. The specimen was mounted into a valgus-loading position through the humeral intramedullary rod and the custom elbow jig, allowing the valgus moment to be the sole degree of freedom. Each elbow was placed in 30 and 90 of flexion during loading by fixing the setup as shown in Figure 1. The orientation of the extremity during the late cocking/early acceleration phase of the pitching activity was simulated by setting the elbow at 90 of flexion, the forearm at 4 of pronation, wrist extension at 40 , and ulnar deviation at 5 . Pronation and supination was controlled by the double ring. The release phase was simulated by setting the elbow at 30 of flexion, the forearm at 24 of pronation, the wrist extension at neutral, and 20 of ulnar deviation (Table I).44 With the aid of passing sutures introduced through the posterolateral incision, the sensor was positioned within the unloaded radiocapitellar joint through the anterolateral approach and securely attached to the skin (Fig. 2). The proximal muscles of the elbow joint were then loaded. Measurements of the intact ligament state were taken at the starting position, during 1.75 Nm of torque, and during 5.25 Nm of torque for both of the simulated phases of throwing; 1.75 and 5.25 Nm were chosen to represent 5% and 15% of reported failure torque of the UCL. These values were similar to previous biomechanical reports on UCL and UCL reconstruction.y After each loading condition, 3 fixed points of the lateral distal humerus and 3 fixed points on the pressure transducer
y
References 1,2,5,9,18,21,23,24,28,29,31,33,36,38
J.P. Duggan Jr. et al.
Figure 1 Photograph shows the side view of the experimental setup at 90 simulating the late cocking/early acceleration phase. were digitized to ensure that the transducer was accurately and reproducibly positioned with respect to anatomic landmarks. Each of 6 specimens was subjected to 2 levels of applied torque (1.75 and 5.25 Nm) after being placed in positions simulating the late cocking/early acceleration phase and the release phases of throwing. These loading conditions were applied to each intact specimen and then repeated after transection and reconstruction of the UCL (described below). The UCL was transected by a flexor carpi ulnaris splitting approach. The muscle was bluntly elevated with a Cobb elevator and the anterior bundle was identified. The anterior bundle of the UCL was then transected sharply off its origin and split along the line of its fibers past the sublime tubercle. The docking reconstruction was performed with a fresh frozen nonirradiated gracilis allograft tendon supplied by the Musculoskeletal Transplant Foundation. A single gracilis allograft was thawed immediately before each individual reconstruction. It was prepared with locking whip stitches in each end with No. 2 Orthocord (Mitek, Norwood, Mass) and maximally tensioned on a standard anterior cruciate ligament graft board (Mitek) The docking modification of the Jobe technique was performed as described by Smith et al.36 Two converging 3.2-mm holes were made approximately 1 cm from the articular surface and 1 cm apart on the sublime tubercle of the ulna. A 4.5-mm drill was used on the origin of the UCL on the medial epicondyle. Starting anterior to the medial intermuscular septum, two 2.0-mm holes were drilled in the medial epicondyle. The holes were separated by a 1-cm bony bridge and converged onto the 4.5-mm socket located at the anatomic origin. The graft was weaved through the ulnar tunnels. Its posterior limb was docked into the humeral socket, and the remaining anterior limb was trimmed to the correct length and docked into the humeral socket. The reconstruction was then tensioned to manual maximum and tied over the bony bridge at 90 of elbow flexion during maximal manual varus loading. Next, the split native UCL ligament was reapproximated by 3 figure-of-eight No. 2 Orthocord sutures passed through the reconstructed anterior and posterior limbs. The flexor carpi ulnaris fascia was also repaired with No. 2 figure-of-eight Orthocord sutures. The skin layer was closed with a running Prolene suture (Ethicon, Somerville, NJ) in a baseball stitch pattern.
Impact of UCL tear and reconstruction
229
Table I Experiment parameters used during late cocking/ early acceleration phase and release phase simulation conditions Late cocking/early
Degrees
Acceleration Phase Elbow Flexion Forearm Pronation Wrist Extension Ulnar deviation
90 4 40 5
Release phase Elbow flexion Forearm pronation Wrist extension Ulnar deviation
30 24 0 20
UCL
Starting
Intact
1.75 5.25 1.75 5.25 1.75 5.25 1.75 5.25 1.75 5.25 1.75 5.25
Transected Reconstructed Intact Transected Reconstructed
Nm Nm Nm Nm Nm Nm Nm Nm Nm Nm Nm Nm
3.62 2.76 when the torque was increased to 5.25 Nm. After resection of the UCL, there was virtually no increase in laxity at the lower torque level vs a 120% increase at 5.25 Nm (7.99 4.28 vs 3.62 2.76 ; P ¼ .0261). After reconstruction of the UCL, the valgus angulation of the ulna was 0.49 1.18 with application of 1.75 Nm of torque, and 3.71 1.81 with 5.25 Nm (Table II). In 90 of flexion, the valgus inclination of the intact specimens averaged 1.35 1.15 under the action of 1.75 Nm of valgus torque and 3.67 1.57 when the torque was increased to 5.25 Nm. After resection of the UCL, these values increased slightly at 1.75 Nm (1.8 1.28 ), and were more than doubled at 5.25 Nm. After reconstruction of the UCL, the valgus angulation of the ulnar was only 0.3 0.26 with application of 1.75 Nm of torque and 2.4 0.99 with 5.25 Nm. These results indicate that with the application of low valgus moments, the reconstructive procedure consistently overtightened the elbow by approximately 1 of valgus laxity in the 30 and 90 positions. At 5.25 Nm of torque, elbow laxity was restored to normal values in the 30 simulation but was reduced by approximately 1 at 90 .
Radiocapitellar contact area
Figure 2 Photograph shows the rear view of the experimental setup at 90 simulating the late cocking/early acceleration phase.
Data analysis Each contour map illustrating the distribution of articular pressures was analyzed with specialized software to determine the contact area, peak contact pressure, average contact pressure, and peak force in the radiocapitellar joint. All data derived from the transected and reconstructed specimens were normalized with respect to the initial runs performed in the intact condition only. The contact area, peak contact pressure, average contact pressure, and valgus laxity underwent statistical analysis using a repeated measure analysis of variance and a Fisher protected least significant difference post hoc test to determine if there were significant differences between the groups. Statistical significance was determined at value of P < .05.
Results Valgus stiffness In 30 of flexion, the intact elbows opened an average of 1.1 1.09 with application of 1.75 Nm of torque and
Before the application of the valgus moment, the contact area of the intact radiocapitellar articulation averaged 117 103 mm2 at 30 and 98 46 mm2 at 90 . When loaded with a valgus torque of 1.75 Nm, the average contact area remained essentially constant during the simulation of the release phase (30 : 118 84 mm2) but increased by 30% in the late cocking phase (90 : 158 69 mm2; P ¼.0024). With application of 5.25 Nm of torque, the contact area increased by 34% at 30 (128 44 mm2) but remained essentially constant at 90 (e7%; 120 31 mm2; P ¼ .095; Table III). Once the UCL was transected, there was no significant change in the articular contact area before valgus loading at 30 or 90 (P ¼ .515 and P ¼ .940, respectively). The same response was observed with the application of 1.75 Nm of torque at 30 and 90 . At the higher torque level, the transected specimens did not show the normal physiologic response of the elbow in increasing the area of contact between the radius and the capitellum. Although the intact specimens increased the area of contact by 20% to 30% in both 30 and 90 of flexion, the contact areas of the transected specimens averaged 15% less than the same elbows in the intact state. Surgical reconstruction of the UCL increased the area of radiocapitellar contact to within 10% of intact values under each of the conditions evaluated, with the exception of the higher torque loading in the 30 flexed position. In this latter case, the contact area after reconstruction of the UCL was similar to values measured after ligament resection (130 25 vs 135 65 mm2) and was only 83% of the original intact values (158 69 vs 130 25 mm2).
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Table II
Joint laxity in degrees Intact
1.75 Nm valgus 30 position 90 position 5.25 Nm valgus 30 position 90 position )
torque 1.11 1.35 torque 3.62 3.67
Sectioned 1.09 1.35 1.18 1.15 1.81 1.28
Average contact pressure (MPa)
Reconstructed 0.49 1.18 0.33 0.26
2.76 7.99 4.28) 3.71 1.81 1.57 8.38 1.85 2.43 0.99
P < .05 (statistically different from intact condition).
Table III
Intact Unloaded 30 position 90 position 1.75 Nm valgus 30 position 90 position 5.25 Nm valgus 30 position 90 position
0.31 0.24 torque 0.37 0.32 torque 0.47 0.58
Sectioned
Reconstructed
0.28 0.15
0.32 0.30 0.28 0.15
0.34 0.21 0.28 0.13
0.31 0.14
0.44 0.47 0.44 0.28
0.46 0.47 0.37 0.19
0.37 0.28
0.74 0.62 1.07 0.76
0.72 0.52 0.69 0.43
Average contact area (mm2) Intact
Unloaded 30 position 90 position 1.75 Nm valgus 30 position 90 position 5.25 Nm valgus 30 position 90 position )
Table IV
117.3 98.7 torque 117.8 128.5 torque 157.5 120.0
Sectioned
Reconstructed
103.9 108.2 96.0 113.2 14.0 46.9 97.0 32.5 95.0 57.7 84.1 44.1
115.8 85.2 117.3 85.2 93.0 43.3 118.3 46.7
69.7) 135.7 65.6 129.5 24.9 31.8 103.2 43.1 120.7 21.3
P < .05 (statistically different from intact condition).
Table V
Peak contact pressure (MPa) Intact
Unloaded 30 position 90 position 1.75 Nm valgus 30 position 90 position 5.25 Nm valgus 30 position 90 position
0.86 0.56 torque 1.13 0.87 torque 1.55 1.75
Sectioned
Reconstructed
0.87 0.42
0.78 0.86 0.79 0.60
0.90 0.76 0.62 0.41
1.11 0.43
1.21 1.50 1.33 1.08
1.16 1.50 1.11 0.74
1.34 1.04
2.24 2.24 2.92 2.26
2.11 2.03 2.32 1.71
Articular contact pressures In the intact elbow, average radiocapitellar contact pressures ranged from 0.3 to 1.1 MPa under the conditions examined. With the joint unloaded, the average contact pressure was only 0.31 0.28 MPa at 30 of flexion and 0.24 0.15 MPa at 90 . The addition of the valgus torque increased these values by an average of 25% at 1.75 Nm (30 : 0.37 0.31 MPa; 90 : 0.32 0.14 MPa) and 91% at 5.25 Nm (30 : 0.47 0.37 MPa; 90 : 0.58 0.28 MPa; Table IV). Because the articular pressure distribution was not uniform, peak pressures were typically 2 to 3 times average values. In the 30 position, peak contact pressures averaged 0.86 0.87 MPa unloaded, 1.13 1.11 MPa with 1.75 Nm valgus torque, and 1.55 1.34 MPa when the torque was increased to 5.25 Nm. Compared with the 30 position, peak pressures were approximately 30% lower unloaded and with 1.75 Nm valgus torque, and 13% greater at 5.25 Nm (Table V). After transection of the ulnar collateral ligament, average articular pressures were virtually unchanged from intact values when tested in the 30 position. With 1.75 Nm of valgus torque, peak pressures did not change significantly from intact levels, but increased by 45% under 5.25 Nm of torque (P ¼ .199). Conversely, average pressures in the 90 position were higher after ligament transection, with a 17% increase at the unloaded state to an 84% increase at 5.25 Nm of valgus torque. Similarly, peak pressures were increased by 41%, 53%, and 67% during the unloaded conditions, 1.75 Nm of torque, and 5.25 Nm of
torque, respectively. Under the last of these conditions, the peak pressure averaged 2.92 2.26 MPa, almost 6 times intact values (0.56 0.42 MPa). Reconstruction of the UCL restored average articular pressures to within 20% of intact values in the 90 position for all 3 conditions tested. In the 30 position, reconstructed specimens exhibited a 10% increase in average contact pressure in the unloaded state, 24% with 1.75 Nm of valgus torque, and 53% at 5.25 Nm of torque. Similarly, peak pressures were restored to intact values when the joint was unloaded and with the application of low torque (1.75 Nm) in the 30 position. At the higher torque (5.25 Nm), peak pressures increased 36% to 2.11 2.03 MPa in the 30 position (P ¼ .346). Valgus loading of the reconstructed specimens in the 90 position increased peak pressures by 28% at 1.75 Nm (1.11 0.74 vs 0.87 0.43 MPa; P ¼ .157) and by 33% at 5.25 Nm (1.75 1.04 vs 2.32 1.71 MPa; P ¼ .131).
Discussion Ahmad et al2 recently demonstrated changes in articular contact between the ulnar and the posteromedial olecranon during valgus loading in the presence of partial and complete insufficiency of the medial UCL. Other research has demonstrated that changes in structure and biomechanics of the forearm and elbow occur with radial shortening, transection of the interosseus membrane, and as
Impact of UCL tear and reconstruction a consequence of the Sauve-Kapandji procedure, leading to changes in loading of the radiocapitellar joint with axial loading.12,26,28,37,40 Given the recognized mechanism of valgus extensions overload on the posterior medial olecranon and the radiocapitellar joint during pitching, we sought to evaluate the effect of UCL insufficiency and reconstruction on pressures across the radiocapitellar joint. Eckstein et al14 have stated that contact pressures within the elbow become more uniform with increasing loads. They hypothesized that the anatomic incongruity that is observed in the unloaded elbow is overcome with the application of physiologic loads as the elbow becomes more congruous with flexion.14 This would serve as a mechanism for limiting contact pressures through increasing the contact area of the radiocapitellar joint with valgus loading. This hypothesis is confirmed by the measurements of the present study performed in intact specimens before transection of the UCL. For this reason, we chose to measure contact pressure and area under an axially loaded elbow. Many studies have investigated the effects of forearm position on the radiocapitellar joint in the presence of valgus laxity.9,29,36 Safran et al36 recently reported that the elbow has greater valgus laxity at neutral rotation. Previously, Morrey et al27 reported that the greatest force transmission occurred when the forearm was in a pronated position. In general, forearm pronation allows the greatest changes in contact pressure distribution with the axially loaded elbow.21,27,36 Rather than focus on adding multiple forearm rotations for our biomechanical testing, we chose to control the forearm rotation for the 2 flexion angles tested relevant to the 2 critical phases of throwing. The positions of the elbow, forearm, and wrist at the 2 critical phases of throwing were selected based on the research of Zheng et al.44 During the late cocking/acceleration phase of throwing where most UCL injuries occur, the elbow is oriented in 90 of flexion. The second critical phase is terminal deceleration when elbow flexion is typically 30 . To control for passive muscle tension, as defined by Safran et al,36 and its ultimate effect on articular contact pressure and area, the corresponding simulated forearm rotation, wrist flexion/extension, and radial/ulnar deviation at 30 and 90 of elbow flexion were set. Currently, there are several methods of UCL reconstruction, principally the Jobe and docking techniques.1,18,20,35,39,41 Of these, biomechanical testing has demonstrated that the docking technique provides the greatest resistance to valgus loading before mechanical failure.29 Paletta et al29 reported that the docking procedure (14.3 Nm) was nearly twice as strong as the Jobe technique (8.9 Nm) but was weaker than the native ligament (18.8 Nm). Both surgical reconstructions have multiple cadaveric biomechanical studies describing their efficacy in restoring valgus laxity but also clinical success, with a high rate of return to play.5,13,27,29,31,32,35,41 Because of the greater strength and ease of tensioning of the docking
231 technique compared with the Jobe technique, this is the senior author’s (D.L.) preferred method of UCL reconstruction in practice. Thus, we chose to test the docking technique in the present study. The strengths of our study include the young age of the specimens, the use of allografts to control graft size, and the simulation of critical phases of pitching through adjustment of loading and the orientation of the elbow, forearm, and wrist. The use of a flexible membrane pressure transducer also enabled reliable measurements to be recorded of the contact area and the peak and mean contact pressure of the radiocapitellar joint without the limitations inherent in the interpretation of dye transfer methods (Fuji film) or methods that necessitate disarticulation of the elbow joint.31 Multiple cadaveric biomechical studies use specimens stripped of all soft tissue or elbows without the distal radioulnar joint. This soft tissue dissection did not excise or transect any primary or secondary stabilizers about the elbow. Despite these controls, dissection might affect the pressure measurements. The main limitation of this study is its small sample size. Another possible limitation is the lack of simulating loading of the flexor-pronator mass during testing, similar to Park et al.31 The short-term clinical goal of UCL reconstruction is to allow a high-level throwing athlete to return to his or her previous level of competition. The surgical goal of UCL reconstruction is to restore the passive restraint to valgus torque seen on the UCL at the late cocking/early acceleration phase of throwing. The ultimate goal of UCL reconstruction is to allow an overhead athlete to return to the preinjury level with a painless stable ligament to valgus torque, but also to prevent any long-term degenerative changes about the elbow as is historically seen in throwers. Many clinical reports declare a high rate of return to play after UCL reconstruction. Cadaveric biomechanical studies report that valgus laxity is restored after UCL reconstruction. Contact pressures in other joints are related to increased articular degeneration; there are no previous studies reporting on the pressures or contact area in the radiocapitellar joint due to valgus loading with the UCL intact, transected, and reconstructed. In this analysis, the mean valgus stiffness of the reconstruction at 90 flexion state did not differ statistically from the intact ligament state and was slightly tighter than the native state (P ¼ .16). Comparing the laxity data at the 30 flexion state confirms these grafts are not truly isometric. The stability was not as consistently restored at 30 as at 90 . This is expected, because the reconstructions were tensioned to the manual maximum at 90 of elbow flexion. The differences in laxity and contact pressure could be because the native UCL is not truly isometric and as a result may have combined with the less olecranon engagement in the posteromedial trochlea at 30 , allowing more laxity as the elbow approaches extension.2,6,21
232 Despite evidence that UCL reconstruction restores valgus laxity to normal, we see that it also increases the peak contact pressure by 26% on average, thus only improving peak pressures compared with the transected group but not completely restoring radiocapitellar pressures to normal at the higher torque. There was no significant difference between the intact and reconstructed stages. Taken as a whole, the peak pressure data indicate that the reconstruction restores valgus stability and lateral contact pressures to nearly normal levels under the conditions tested. Because the 90 position is the clinically significant position, these laboratory data support the clinical success of the docking procedure. At the 30 elbow position, the average contact pressure for the reconstructed condition is 123% greater than the intact, whereas the transected group is 64% greater than the intact. At the 90 elbow position, the average contact pressure for the reconstructed condition is 18% greater than the intact, whereas the transected group is 84% greater than the intact. Contrary to our hypothesis, the contact area between the radius and the capitellum did not change significantly from the intact state over the 2 levels of torque at the 90 flexion position. Given the limited number of specimens, it is unclear if there is an overall trend in the contact area data. Because the torques performed were only 5% and 15% of load to failure, it is possible that a higher level of torque could result in a change in contact areas. The peak pressures measured in this study were not dangerous as single episodes. The study by Clements et al11 found 6 MPa of pressure during repetitive motion was detrimental to chondrocytes. However, our model applies compressive forces less than those calculated in other studies as occurring in the lateral compartment during actual throwing. We project that at load-to-failure levels that are routinely seen by pitches, the peak contact pressures in the radiocapitellar joint exceed the 6 MPa chondrocyte cell viability threshold. It is the repetitive application of these elevated forces to the lateral compartment in the ligament deficient state that is of concern for causing ongoing degeneration of the lateral compartment. These forces can be minimized through UCL reconstruction. During the act of throwing the baseball, the shoulder externally rotates rapidly and makes a sudden transition to internal rotation as cocking transitions to acceleration. It is at this moment of direction reversal when the maximal valgus torque is applied to the elbow. This load is shared almost 50:50 by tension in the medial soft tissues and compression on the lateral column of the normal elbow. If the UCL is lax or incompetent, by definition less tension is borne medially and more compressive load is shifted to the articular surfaces of the radiocapitellar joint to negate this valgus torque. Reconstructing the UCL is an attempt to normalize the tension in the medial tissues during this valgus load and thus decrease pain and normalize the forces seen laterally and medially.
J.P. Duggan Jr. et al. It is unclear if UCL laxity is directly related to the development of OCD in the thrower’s elbow. Osteochondritis is more likely in the younger thrower, but UCL reconstruction is not typically thought to be appropriate in this age group, rendering moot the issue of UCL laxity. In the younger skeletally immature thrower with OCD, the UCL should be evaluated, and if significant laxity is suspected, consideration should be given to restricting throwing until UCL reconstruction can be safely considered. In reality, patients at this age are typically prohibited from throwing due to their articular lesion regardless of the status of the UCL. However, in the throwers with early OCD of an age where UCL reconstruction may be appropriate, the UCL should be thoroughly evaluated and considered for reconstruction.
Conclusions Under the conditions tested, deficiency of the UCL increases valgus laxity of the elbow joint with associated increases in the average and peak contact pressures in the radiocapitellar joint. Reconstruction of the UCL significantly corrects the radiocapitellar contact pressures as well as the valgus laxity.
Acknowledgments We acknowledge the material support provided by Breg, the Musculoskeletal Transplant Foundation, David Laws, Shawn Manning, and Travis Bryan. We also acknowledge the assistance of Matthew Thompson in the preparation of this manuscript.
Disclaimer The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Ahmad CS, Lee TQ, ElAttrache NS. Biomechanical evaluation of a new ulnar collateral ligament reconstruction technique with interference screw fixation. Am J Sports Med 2003;31:332-7. 2. Ahmad CS, Park MC, ElAttrache NS. Elbow medial ulnar collateral ligament insufficiency alters posteromedial olecranon contact. Am J Sports Med 2004;32:1607-12. doi:10.1177/0363546503263149 3. Alcid JG, Ahmad CS, Lee TQ. Elbow anatomy and structural biomechanics. Clin Sports Med 2004;23:503-17. doi:10.1016/j.csm. 2004.06.008
Impact of UCL tear and reconstruction 4. Andrews JR. Bony injuries about the elbow in the throwing athlete. Instr Course Lect 1985;34:323-31. 5. Armstrong AD, Dunning CE, Ferreira LM, Faber K, Johnson J, King G, et al. A biomechanical comparison of four reconstruction techniques for the medial collateral ligament-deficient elbow. J Shoulder Elbow Surg 2005;14:207-15. doi:10.1016/j.jse.2004.06.006 6. Armstrong AD, Ferreira LM, Dunning CE, Johnson JA, King GJW. The medial collateral ligament of the elbow is not isometric. Am J Sports Med 2004;32:85-90. doi:10.1177/0363546503258886 7. Atwater AE. Biomechanics of overarm throwing movements and of throwing injuries. Exerc Sport Sci Rev 1979;7:43-85. doi:10.1249/ 00003677-197900070-00004 8. 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;28:16-23. 9. Callaway GH, Field LD, Deng XH, Torzilli PA, O’Brien SJ, Altcheck DW, et al. Biomechanical evaluation of the medial collateral ligament of the elbow. J Bone Joint Surgery Am 1997;79:1223-31. 10. Cheung EV, Adams R, Morrey BF. Primary osteoarthritis of the elbow: current treatment options. J Am Acad Orthop Surg 2008;16:77-87. 11. Clements KM, Bee ZC, Crossingham GV, Adams MA, Sharif M. How severe must repetitive loading be to kill chondrocytes in articular cartilage? Osteoarthritis Cartilage 2001;9:499-507. doi:10.1053/joca. 2000.0417 12. Diab M, Poston JM, Huber P, Tencer FH. The biomechanical effect of radial shortening on the radiocapitellar articulation. J Bone Joint Surg Br 2005;87:879-83. doi:10.1302/0301-620X.87B6.15543 13. Dodson CC, Thomas A, Dines JS, Nho SJ, Williams RJ, Altchek DW. Medial ulnar collateral ligament reconstruction of the elbow in throwing athletes. Am J Sports Med 2006;34:1928-32. doi:10.1177/ 0363546506290988 14. Eckstein F, Lohe F, Schulte E, Muller-Gerbl M, Milz S, Putz R. Physiological incongruity of the humero-ulnar joint: a functional principle of optimized stress distribution acting on articulating surfaces? Anat Embryol (Berl) 1993;188:449-55. doi:10.1007/ BF00190139 15. Flesig GS, Andrews JR, Dillman CJ. Kinetics of baseball pitching with implications about injury mechanisms. Am J Sports Med 1995; 23:233-9. doi:10.1177/036354659502300218 16. Fornalski S, Gupta R, Lee TQ. Anatomy and biomechanics of the elbow joint. Tech Hand Up Extrem Surg 2003;7:168-78. doi:10.1097/ 00130911-200312000-00008 17. Gibson BW, Webner D, Huffman R, Sennett BJ. Ulnar collateral ligament reconstruction in major league baseball pitchers. Am J Sports Med 2007;35:575-81. doi:10.1177/0363546506296737 18. 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;26:620-4. 19. Hoppenfeld S, deBoer P. Surgical exposures in orthopaedics. The anatomic approach. Philadelphia: J.B. Lippincott; 1984. p. 97-101. 20. Jobe FW, Stark H, Lombardo SJ. Reconstruction of the ulnar collateral ligament in athletes. J Bone Joint Surg Am 1986;68:1158-63. 21. Kamineni S, ElAttrache NS, O’Driscoll SW, Ahmad CS, Hirohara H, Neale PG, et al. Medial collateral ligament strain with partial posteromedial olecranon resection. A biomechanical study. J Bone Joint Surgery 2004;86:2424-30. 22. King JW, Brelsford JH, Tullos HS. Analysis of the pitching arm of the professional baseball pitchers. Clin Orthop 1969;67:116. doi:10.1097/ 00003086-196911000-00018 23. Large TM, Coley ER, Peindl RD, Fleischli JE. A biomechanical comparison of 2 ulnar collateral ligament reconstruction techniques. Arthroscopy 2007;23:141-50. doi:10.1016/j.arthro.2006.09.004 24. Loftice J, Fleisig GS, Zheng N, Andrews JR. Biomechanics of the elbow in sports. Clin Sports Med 2004;4:519-30. doi:10.1016/j.csm. 2004.06.003
233 25. Morrey BF, An KN. Articular and ligamentous contributions to the stability of the elbow joint. Am J Sports Med 1983;11:315-9. doi:10. 1177/036354658301100506 26. Morrey BF, An KN, Stormont TJ. Force transmission through the radial head. J Bone Joint Surg 1988;70:250-6. 27. Mullen DJ, Goradia VK, Parks BG, Matthews LS. A biomechanical study of stability of the elbow to valgus stress before and after reconstruction of the medial collateral ligament. J Shoulder Elbow Surg 2002;11:259-64. doi:10.1067/mse.2002.122622 28. Ofuchi S, Takahashi K, Yamagata M, Rokkaku T, Moriya H, Hara T. Pressure distribution in the humeroradial joint and force transmission to the capitellum during rotation of the forearm: effects of the SauveKapandji procedure and incision of the interosseous membrane. J Orthop Sci 2001;6:33-8. doi:10.1007/s007760170022 29. Paletta GA, Klepps SJ, Difelice GS, Allen T, Brodt M, Burns M, et al. Biomechanical evaluation of 2 techniques for ulnar collateral ligament reconstruction of the elbow. Am J Sports Med 2006;34:1599-603. doi: 10.1177/0363546506289340 30. Paletta GA, Wright RW. The modified docking procedure for elbow ulnar collateral ligament reconstruction. 2-year follow-up in elite throwers. Am J Sports Med 2006;34:1594-8. doi:10.1177/ 0363546506289884 31. Park MC, Ahmad CS. Dynamic contributions of the flexor-pronator mass to elbow valgus stability. J Bone Joint Surg Am 2004;86:2268-74. 32. Petty DH, Andrews JR, Fleisig GS, Cain EL. Ulnar collateral ligament reconstruction in high school baseball players. Am J Sports Med 2004; 32:1158-64. doi:10.1177/0363546503262166 33. Regan WD, Korinek SL, Morrey BF, An KN. Biomechanical study of ligaments around the elbow joint. Clin Orthop 1991;271:170-9. doi:10. 1097/00003086-199110000-00023 34. Rettig AC, Sherril C, Snead DS, Mendler JC, Mieling P. Nonoperative treatment of ulnar collateral ligament injuries in throwing athletes. Am J Sports Med 2001;29:15-7. 35. Rohrbough JT, Altcheck DW, Hyman J, Williams RJ, Botts JD. Medial collateral ligament reconstruction of the elbow using the docking technique. Am J Sports Med 2002;30:541-8. 36. 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;87:2065-74. doi:10.2106/JBJS.D.02045 37. Shepard MF, Markolf KL, Dunbar AM. The effects of partial and total interosseus membrane transaction on load sharing in the cadaver forearm. J Orthop Res 2001;19:587-92. doi:10.1016/S0736-0266(00) 00059-0 38. Sojbjerg JO, Ovesen J, Nielson S. Experimental elbow instability after transection of the medial collateral ligament. Clin Orthop Relat Res 1987;218:186-90. 39. 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;24:575-80. doi:10.1177/036354659602400503 40. Takatori K, Hashizume H, Wake H, Inoue H, Nagayama N. Analysis of stress distribution in the humeroradial joint. J Orthop Sci 2002;7: 650-7. doi:10.1007/s007760200116 41. Thompson WH, Jobe FW, Yocum LA, Pink MM. Ulnar collateral ligament reconstruction in throwing athletes: muscle-splitting approach without transposition of the ulnar nerve. J Shoulder Elbow Surg 2001;10:152-7. doi:10.1067/mse.2001.112881 42. Tullos HS, King JW. Throwing mechanism in sports. Orthop Clin North Am 1973;4:709-20. 43. Whitely R. Baseball throwing mechanics as they relate to pathology and performance: a review. J Sports Sci Med 2007;6:1-20. 44. Zheng N, Fleisig GS, Barrentine SW, Andrew JR. Biomechanics of pitching. In: Hung GK, Pallis JM, editors. Biomedical engineering principles in sports. New York: Kluwer Academic/Plenum Publishers; 2004. p. 209-56.