Radial Head Lag: A Possible Biomechanical Mechanism for Osteochondritis Dissecans of the Capitellum in Baseball Pitchers

Abstract

Background:

Osteochondritis dissecans (OCD) of the capitellum is common in throwing athletes and is believed to result from repetitive overloading on the radiocapitellar (RC) joint, although the cause and mechanism remain unclear. The torsional forces (moments) generated by the triceps during elbow extension pull only on the ulna; therefore, the radial head moves passively across the capitellum and is effectively “dragged along” by the ulna. Any laxity in the proximal radioulnar joint could lead to asynchronous motion between the radius and ulna, resulting in the radial head lagging behind the coronoid and possibly malarticulating with the capitellum during such motion.

Hypothesis:

Radial head motion on the capitellum lags behind ulnohumeral joint motion during simulated throwing.

Study Design:

Controlled laboratory study.

Methods:

A total of 8 cadaveric elbows were tested under simulated throwing, including active extension of the elbow generated by pulling of the triceps under valgus stress, as well as during passive extension under valgus stress to serve as a reference. Ulnohumeral motion was tracked using a video camera. Radial head motion was tracked using an intra-articular, thin-film pressure sensor mounted on the capitellum, and the longitudinal movement of the center of force (COF) of the radial head was measured. Radial head motion was compared between passive and active motion for each 10° of elbow extension from 90° to 20°.

Results:

Elbow motion during simulated active extension reached an angular velocity of 366 deg/s. Radial head motion during simulated active extension significantly lagged compared with its motion during passive extension at every elbow extension angle examined between 70° and 20° (P < .001). The maximal lag reached a mean of 4 mm (range, 2-7 mm). In other words, RC and ulnohumeral motion were asynchronous during simulated throwing.

Conclusion:

This study describes a novel phenomenon: motion of the radial head across the capitellum during rapid extension, such as in baseball pitching, lags behind that seen during passive elbow motion. According to a new proposed theory of OCD lesion development, this lag should result in RC incongruency and elevated shear forces on the capitellum due to edge loading.

Clinical Relevance:

We propose a new biomechanical explanation for OCD of the capitellum in baseball pitchers: radial head lag. Understanding this process is the first step in efforts to prevent this common injury.

Keywords

elbow baseball pitching osteochondritis dissecans

The exact mechanism causing osteochondritis dissecans (OCD) of the capitellum remains unclear, but repetitive trauma, and more precisely increased compression and shear forces (including valgus and/or axial forces) inside the radiocapitellar (RC) joint, is believed to play a predominant role.^7,15,16 Capitellar OCD lesions have been described in athletes of various sports, but they are most prevalent among young throwing athletes. Specifically, the highest incidence was reported in youth baseball pitchers, ranging between 1% and 7%.¹⁶ This increased incidence led to the hypothesis that OCD lesions are the result of overpitching or poor throwing mechanics.^5,8 Apart from participating in specific sports, there are no other significant risk factors for developing capitellar OCD lesions.

The pitching motion has been extensively studied and is commonly divided into 6 phases: windup, stride, arm cocking, acceleration, deceleration, and follow-through.³⁵ Previous studies have placed the “critical moment” for an elbow injury during the late arm cocking and early acceleration phase when maximal valgus torque is reached.⁸ In that moment, maximal compression forces in the lateral elbow would cause OCD lesions, and maximal distraction forces in the medial elbow would cause medial ligament injuries. However, these compression forces, and any other forces acting on the joint surfaces during pitching, have never been directly measured: all available information is extrapolated from motion data collected during in vivo studies or bone density studies implementing computed tomography osteoabsorptiometry to assess cumulative forces on joint surfaces.¹⁹ Although measuring the actual movements and forces inside the joint is of great interest, biomechanical studies that allow for such measurements by using cadaveric specimens are performed in a slow, controlled fashion, unable to re-create the conditions of a throwing motion.

After the cocking phase, the pitching motion includes extremely fast elbow extension during the acceleration phase.²³ As extension torque is exerted by the triceps essentially on the ulna through the triceps tendon attachment in the olecranon, the radius is extended only by its ligamentous and muscular attachments with the ulna. We hypothesized that during rapid elbow extension, radial head motion on the capitellum would lag behind ulnohumeral joint motion. To better understand this lag, one should think of the ulnohumeral joint as it extends from 90° to 0°, or one-fourth of a circle. Under normal conditions, ulnohumeral and RC motions are synchronous, and the radial head would travel on the capitellum a distance equal to one-fourth of a circle.

However, our hypothesis was that during rapid elbow extension, the radial head lags behind the coronoid so that as the ulnohumeral joint reaches 0° (full extension), the radial head will have traveled less than the expected one-fourth of a circle across the capitellar surface. Although not tested in this study, we believe that this lag of the radial head, if present, constitutes mild joint incongruence that increases compressive and shear forces inside the joint, contributing to the formation of OCD lesions and moving the critical moment for their formation from the late cocking phase to the acceleration phase of throwing.

Methods

After we obtained approval from the institutional biospecimen subcommittee, 8 fresh-frozen, cadaveric upper limbs, from the fingertip to the midhumerus, were thawed at room temperature overnight. Exclusion criteria for the specimens were (1) flexion contracture of >15° or a pronation-supination rotation arc of <140°, (2) radiological evidence of arthritis or a deformity, (3) ligament insufficiency detected by a physical examination, and (4) cartilage erosion to the subchondral bone (Outerbridge grade IV³⁰) of the capitellum or radial head. We did not discard specimens exhibiting shallow erosion, fibrillation, or fissuring (Outerbridge grades II-III) with normal joint contact. The specimen characteristics were as follows: all male, 6 right and 2 left, mean age of 84 years (range, 63-95 years), and mean body mass index of 27 (range, 24-31).

Specimen Preparation

The skin and subcutaneous fat were removed from the midhumerus to 5 cm distal to the elbow joint. The biceps, brachialis, triceps, and pronator teres muscle bellies were removed, and their tendon insertions were preserved and sutured using a 23-kg (50-lb) braided polyester line in a locking Krackow configuration. The common flexor and extensor humeral origins were preserved. The proximal humeral end of the specimen was then potted into a cylindrical fiberglass sleeve parallel to its long axis using polyurethane resin (Smooth-Cast 65D; Techno-Industrial Products) to fix the specimen within the testing machine.

To permit placement of the pressure transducer, the lateral two-thirds of the anterior capsule was excised from its proximal origin to the joint line, taking care not to damage the annular or lateral collateral ligament; the lateral half of the posterior capsule was excised; and the origin of the anconeus muscle was released, exposing the posterior capitellum (see Appendix Figure A1, available in the online version of this article).

Pressure Transducer

A thin-film pressure transducer (5051; Tekscan) with a saturation pressure of 8.3 MPa (84 kg/cm²) was prepared by trimming it to include 17 to 19 sensor columns, creating a sensing matrix width of 22 to 25 mm that covered the entire capitellum.^26,34 The use of these trimmed sensors was validated in a separate study and found to be suitable for the applications described here (Rotman et al; unpublished data, 2020). According to the manufacturer’s recommendations, after trimming, the sensor was sealed using a thin adhesive laminate covering to prevent moisture and dirt from entering the sensor.³² The sensors were preconditioned and calibrated on a custom-made pneumatic load frame using I-Scan software (Tekscan) as previously described.³ A total of 6 sequential loads were applied to the sensor, which was sandwiched between 2 layers of a 1.6-mm rubber membrane, which was in turn sandwiched between 2 polished aluminum plates. As it is recommended that sensors be calibrated under conditions that mimic those encountered during testing,²⁸ this rubber membrane–aluminum block calibration construct was chosen to mimic the cartilage–subchondral bone condition of the elbow joint. The calibration loads ranged from 100 to 600 N and were applied in increments of 100 N.

The trimmed sensor was inserted into the joint from anterior to posterior until the sensor covered the entire capitellum (Appendix Figure A1). The sensor was held in place by tying it to 2 screws located on the posterior surface of the lateral distal humerus outside the RC joint and wrapping the humerus and sensor with duct tape.

Specimen Mounting and Testing

Specimens were mounted in a custom testing machine with the humerus in 90° of forward flexion and 90° of external rotation; that is, the humerus was horizontal with the medial epicondyle upward and the transcondylar axis perpendicular to the floor such that the elbow was under constant valgus gravitational torque (Figure 1). An additional valgus moment of 1 N·m was created by attaching a 500-g weight to the forearm, 20 cm distal to the RC joint line. The sutures attached to the brachialis, biceps, and triceps tendons were connected to Airpel pneumatic pistons (Airpot) through pulleys. The brachialis, biceps, and triceps pulleys were set at 2, 3.5, and 2 cm away from the humeral axis, respectively.¹ The suture attached to the pronator teres tendon was connected to the pneumatic piston through an islet screw positioned on the origin of this muscle on the proximal part of the medial epicondyle.

The forearm was positioned and held in neutral rotation with a load of 25 to 30 N on the pronator teres tendon using the least load necessary. Loads were applied to the triceps, biceps, and brachialis tendons in a 2:1:1 ratio (50, 25, and 25 N, respectively) as previously described.³ The elbow was passively extended from 90° to 0° over a period of about 6 seconds by pulling on a wire attached to the wrist, keeping the wire perpendicular to the forearm to minimize extraneous forces on the elbow.

To prepare the elbow for simulated rapid active extension such as during throwing, the elbow was held at 90° of flexion while a much higher load was applied to the triceps using an 8:1:1 ratio (100, 12.5, and 12.5 N, respectively) on the triceps, biceps, and brachialis tendons. Then, the wire holding the wrist was released and the elbow permitted to rapidly extend. The muscle-loading ratios during simulated active extension were determined in a pilot study (data not shown). All the specimens were tested first with passive motion and then with simulated active motion.

Data Acquisition

Elbow motion data were collected at 30 Hz using a video camera positioned 1 m below the joint (Figure 1) through I-Scan software to allow synchronization between video and sensor data. The elbow angle in each frame was later measured using an on-screen goniometer. The maximal angular speed was calculated from the fastest motion captured within a period of 0.1 seconds (across 4 video frames). Center of force (COF) data were captured at a frequency of 100 Hz. During simulated rapid active extension, the difference in sampling frequency between the elbow angle measurement and COF measurement, combined with the rapid rate of elbow extension (>30 deg/s), resulted in several instances of COF data being present without a time-synchronized elbow angle. Therefore, the elbow angle and COF data were resampled using linear interpolation, with elbow angles sampled at integer degree values for all subsequent analyses. For the analysis of COF data, we used only anteroposterior (longitudinal) displacement of the COF. The starting point, which was located at the anterior part of the capitellum, was marked as y = 0 for each specimen, and increasing values indicate movement toward the posterior part of the capitellum. During passive motion, appearance artifacts at the end range of motion prevented us from utilizing the COF data at the extension end range. Therefore, we decided to use only data from 90° to 20°. During active motion, no such artifacts appeared, and data from the entire range of motion were used.

Statistical Analysis

For statistical analysis, the evaluation of the longitudinal movement of the COF was limited to the arc of motion between 90° and 20°. For active and passive motion, we calculated the average displacement of the COF for each 10° increment in elbow extension. The association between the degree of elbow extension and curvilinear movement of the COF across the capitellum was assessed separately for passive and active motion. The movement of the COF was compared between passive and active motion for each 10° of elbow extension. Data were modeled using analysis of variance. All data were analyzed using 1- or 2-factor repeated-measures analysis of variance with post hoc least squares means contrast and Bonferroni correction where appropriate. Power analysis revealed that a sample size of 8 would give an 80% chance of detecting a significant difference of 1.0 standard deviations with P≤ .05. Based on our current data, for example, this gave us an 80% chance with P≤ .05 to detect a statistically significant difference of 2 mm between the location of the COF of the radial head during passive and active motion at 20° of flexion. All presented data have been rounded to the nearest significant digit. Statistical analysis was performed using JMP (Version 14; SAS Institute).

Results

The mean time for the elbow to extend from 90° to full extension was 0.6 seconds (range, 0.5-0.8 seconds) during simulated rapid active motion. The mean maximal angular speed during active motion was 366 deg/s (range, 320-420 deg/s). Passive extension occurred over a mean of 6 seconds (range, 5-8 seconds).

When tracking of the COF over the capitellum was mapped (Figure 2), there was no apparent difference between active and passive extension in any given specimen (Figure 3). The total distance traveled by the COF was the same in passive and active motion: 12 mm in the longitudinal direction from anterior to posterior (range, 8-15 mm and 8-16 mm during passive and active motion testing, respectively), and 3 mm in the horizontal direction from lateral to medial (range, 2-6 mm and 1-6 mm during passive and active motion testing, respectively).

There was a significant delay in the movement of the COF over the capitellum between 90° and 20° during rapid active extension, designed to mimic throwing, compared with that seen during passive extension. At any given extension angle, the location of the COF of the radial head on the capitellum during simulated throwing lagged behind that observed during passive extension (Figure 3). While the COF moved posteriorly a mean of 1.5 ± 0.6 mm for each 10° of passive extension, the COF moved posteriorly only a mean of 1.0 ± 0.4 mm during simulated throwing (Table 1 and Figure 4). These differences were statistically significant for all active versus passive elbow angles between 70° and 20°. The discrepancy in the position of the COF of the radial head on the capitellum progressively increased throughout the arc of elbow extension from 90° to 20° (Figure 5). The mean maximal lag in each specimen was 4 mm (range, 2-7 mm) and was measured in 20° of flexion (the last observation) in 6 of the 8 specimens. Tracking of the COF during active extension eventually caught up to that seen in passive extension, with some of that motion occurring after the ulnohumeral joint reached full extension.

Table 1

Posterior Movement of the COF of the Radial Head ^a

Elbow Flexion	COF Displacement of RC Joint, mm		Lag Between Passiveand Active Motion, mm	P Value
Elbow Flexion	Passive Motion	Active Motion	Lag Between Passiveand Active Motion, mm	P Value
90°	0	0	0
80°	2	1	1	.18
70°	3	2	1	<.001 ^b
60°	5	3	2	<.001 ^b
50°	7	4	3	<.001 ^b
40°	8	5	3	<.001 ^b
30°	10	6	4	<.001 ^b
20°	11	7	4	<.001 ^b

Measurements rounded to the nearest millimeter. As the elbow extended, the location of the COF of the radial head on the capitellum during simulated throwing (active motion) lagged relative to the location of the COF of the radial head during passive motion. COF, center of force; RC, radiocapitellar.

Statistically significant result. A P value <.007 was considered significant according to the Bonferroni correction for multiple comparisons.

Discussion

The present study confirms that there is a lag in the movement of the radial head on the capitellum when comparing passive motion and simulated throwing. Such a lag has the potential to cause elevated contact pressures between the radial head and the capitellum, with resultant increased shear stresses in the subchondral bone during rapid elbow extension under valgus loading conditions, such as in baseball throwing.

This is a novel finding that we believe to be important in explaining the etiological mechanism responsible for OCD of the capitellum in baseball players. Repeated excessive shear stresses lead to cartilage damage^2,31 and to stress fractures in the subchondral bone,³² which can result in nonunion under continued exposure to such stresses. The current consensus is that OCD of the capitellum results from repeated compression and/or shear forces.^20,24 However, our understanding of the forces inside the joint is limited to indirect data from kinematic studies.^8,25 Although it is well established that valgus torque and compressive forces in the RC joint during pitching peak as the elbow is flexed at about 90° (late cocking), the elbow flexion angles at which shear stresses in the subchondral bone are maximal are not known.

Physiological shear stresses are generated in the subchondral bone during anatomic movement of the joint under normal compressive loads.³⁶ However, pathological shear stresses can occur if maltracking or abnormal motion of one joint surface with respect to another occurs, such as with subluxation. Our finding of asynchronous motion of the RC and ulnohumeral joints during rapid active elbow extension under valgus loading constitutes abnormal joint kinematics.

The reason for this radial head lag is that extension of the elbow is accomplished by the triceps pulling directly on the ulna. Nothing pulls directly on the radius to extend the elbow. Therefore, the radial head moves passively across the capitellum during elbow extension principally because of its ligamentous attachments to the ulna at the proximal radioulnar joint (PRUJ). Any laxity in the PRUJ would permit the radial head to translate anteriorly or posteriorly with respect to the ulna. During rapid extension, the radial head likely translates slightly anteriorly relative to the ulna. From our data, this PRUJ subluxation would be <1 mm as the elbow extends past 90° but would increase progressively to as much as 4 mm before ball release. Based on trigonometric analysis of the forearm, such a translation of the radial head would correspond with a 1° angular deviation in the long axis of the radius with respect to the long axis of the ulna from the wrist to the elbow. This degree of annular deviation would be quite conceivable in the forearm unit. It is also possible that translational displacement at the PRUJ is accompanied by some form of translational displacement at the distal radioulnar joint such that the radial head translates on the capitellum but remains congruent.

During radial head lag, the RC joint could either subluxate or may stay congruent but temporarily nonconcentric. The first possible mechanism is that the radial head subluxates anteriorly on the capitellum and contacts it only by its posterior rim (Figure 6B). A second possible mechanism is that the lag only causes the radial head to “drag” on the capitellum, decreasing contact to the trailing anterior rim (Figure 6C) and manifesting only as nonconcentricity. We believe the second option to be the actual mechanism, although this was not examined in this experiment. Support for this assumption comes from studies examining subchondral bone density distributions in the elbow, which reportedly reflect the cumulative force on a joint surface under actual loading conditions. Examinations of asymptomatic baseball pitchers, pitchers with symptomatic medial collateral ligament insufficiency,¹⁰ and pitchers with OCD lesions¹⁷ all showed higher bone density in the anterior rim of the radial head than the posterior rim, indicating higher cumulative forces in that area.

This radial head lag on the capitellum has important biomechanical implications both for RC contact and for shear stresses in the subchondral bone and radial head. Sahu et al²⁷ have shown that even mild RC subluxation can cause a significant increase in joint pressures, albeit using a posterior subluxation model. In a biomechanical study, they measured RC contact area and pressure at 30° of elbow flexion, under an axial load of 100 N and with progressive posterior subluxation. With only 2-mm posterior subluxation, the contact area decreased by 29%, and contact pressure increased by 33%. Subluxation of 4 mm caused a decrease of 57% in the contact area and a 133% increase in contact pressure. In the present study, the maximal gap measured was 4 mm, indicating a possible substantial decrease in contact area and increase in joint pressure. In most specimens in the present study, the lag increased gradually throughout the entire arc of motion; this maximal lag was measured in 6 of the 8 specimens in the final 20° of extension. Extrapolating these data to real pitching, this would put maximal subluxation around the ball release phase.

Baseball pitching is by far the most serious risk factor for capitellar OCD, and the prevalence of OCD lesions in young pitchers can exceed 3%.^14,22 If predominantly compressive forces were the culprit in OCD lesions, one would expect these lesions to appear mostly on the upper anterior surfaces of the capitellum,¹¹ where the compressive forces are greatest and the subchondral bone is the densest.¹⁰ By contrast, OCD lesions are typically seen on the anteroinferior surface of the capitellum,^4,12,13 where the radial head would be during the acceleration phase, suggesting that repeated trauma to the capitellum happens at a later stage of the pitching motion during the acceleration phase and possibly even around ball release, which occurs at 25° to 40° of elbow extension.³³

Combining the current knowledge about pitching kinematics with the results of the current study, we propose a possible etiological mechanism for the development of OCD. As the elbow extends during the explosive acceleration phase of pitching, subtle perturbations of RC tracking develop, leading to mild joint incongruities and reaching a maximum around ball release. This incongruency either (1) creates shear and compressive forces that, when applied repeatedly, are sufficient to result in OCD lesions, or (2) sets the stage for an interruption of the smooth motion of the joint surfaces during ball release possibly due to quick wrist flexion,²¹ temporary supination,¹⁸ or reactive forces from the ball itself. This interruption creates significant peak pressures because of the reduced contact area. It is important to note that this biomechanical study examined only the first part of this theory (the radial head lagging), but further studies are needed to prove that this lag creates excessive forces inside the joint.

The mean maximal angular speed created in the active motion setting was 366 deg/s, and this was achieved near the end of motion. Studies measuring the speed of elbow extension during baseball pitching have found that it reaches around 2000 deg/s in youth pitchers³³ and increases with age and experience.⁹ This explosive motion is the result of a complex kinetic chain²⁹ and probably could not be re-created in a laboratory setting by simply pulling on the triceps. However, as biomechanical studies thus far have almost exclusively been performed in a slow, controlled manner, this new method represents a significant leap forward in testing elbow motion. Performing future studies with this new technique, presumably with varying elbow motion speeds, may allow us to extrapolate measured values to a real pitching speed.

This study has some obvious limitations derived from its design as an in vitro biomechanical study, namely discrepancies between the tested model and real-life motion. Many forces acting on the RC joint during a real pitching movement were not re-created, such as the distracting centrifugal force arising from quick pelvic and torso rotation or the decreasing nature of the compressive force arising from the diminishing valgus torque through the acceleration phase. Also, the presence of the sensor inside the joint during the experiment may also affect joint contact dynamics. Even though these factors most probably influence RC biomechanics, we believe that the model used provided a method that was a sufficient first step toward consistently reproducing the real phenomenon. Other limitations follow. (1) We did not compare the surface area and contact pressure in the RC joint between the 2 settings to prove our hypothesis of reduced contact areas and increased contact pressures caused by radial head lag. Because the load extracted on the elbow flexors, which create compressive forces in the RC joint during most of the 0° to 90° range of motion, was different in the 2 settings of this experiment, such a comparison would not be valid under these conditions. Another study in which a similar load is extracted on the elbow flexors in the 2 settings is needed to measure and compare the contact area and pressure. (2) It was not possible to directly measure shear forces during this study. We hypothesized that radial head lag increases shear forces, and the reasoning was explained in the Discussion, but the sensor used cannot measure the actual shear forces in the joint. (3) The proximal anterolateral capsule that was excised to allow for sensor insertion might be a factor limiting anterior subluxation of the radial head in real life. However, we took great care not to harm the annular ligament, and it was confirmed that the radial head was covered anteriorly by the ligament-capsule complex at the beginning of the motion. (4) Trimming of the sensor caused the output pressure map to include only every second row, raising concerns about its use under such circumstances. We thoroughly evaluated its use under these circumstances (Rotman et al; unpublished data, 2020). According to the Tekscan website and email correspondence with the company, sensor trimming should not affect the reliability of the results. In any case, it would theoretically influence the force and pressure data and not the COF data. (5) The muscle load of the pronator teres was different between specimens, ranging from 15 to 30 N. However, this is likely the result of the different sizes of specimens used. (6) The present study did not consider the potential effect that any change in valgus stability might have on radial head lag. Valgus stability is critical during overhead throwing and is determined by a number of parameters including integrity of the ulnar collateral ligament as well as dynamic contraction of the flexor pronator mass. The RC joint is known to contribute to stability of the elbow through the phenomenon of concavity-compression,⁶ which relates radial head translation to compression force on the radial head. Static and dynamic valgus stability, or degrees of instability, would also affect less compressive forces on the radial head and therefore potentially affect radial head lag. (7) Although specimens with severe cartilage erosion were excluded, most specimens had mild degenerative changes of the articular surfaces, which may influence joint mechanics including the COF. (8) OCD lesions are most prevalent in children and adolescents. Our anatomic specimens were much older in age, and so there are some possible limitations in extrapolating information from older age specimens to apply to the younger skeleton of patients with this condition.

The strengths of the study include the experimental model that was developed specifically to allow for the first time the measurement of contact mechanics during rapid motion and the reliability of the results; that is, the lag was observed in all specimens in varying degrees.

In summary, this study describes a phenomenon that we refer to as “radial head lag” that occurs during rapid elbow extension under valgus loading conditions, such as in a baseball pitching motion. We believe that this lag constitutes mild joint incongruency with a potential for excessive shear stresses in the capitellar subchondral bone. We thus propose a new theory of OCD development during baseball pitching: During rapid elbow extension, the radial head lags behind the capitellum on which it articulates in a mildly incongruent manner, creating excess shear stresses in capitellar cartilage and subchondral bone.

Supplemental Material

sj-pdf-1-ajs-10.1177_03635465211033971 – Supplemental material for Radial Head Lag: A Possible Biomechanical Mechanism for Osteochondritis Dissecans of the Capitellum in Baseball Pitchers

Supplemental material, sj-pdf-1-ajs-10.1177_03635465211033971 for Radial Head Lag: A Possible Biomechanical Mechanism for Osteochondritis Dissecans of the Capitellum in Baseball Pitchers by Dani Rotman, Jae-Man Kwak, Jorge Rojas Lievano, Alexander Hooke, Christopher L. Camp, James S. Fitzsimmons and Shawn W. O’Driscoll in The American Journal of Sports Medicine

Footnotes

Submitted July 30, 2020; accepted April 21, 2021.

One or more of the authors has declared the following potential conflict of interest or source of funding: C.L.C. has received education support and nonconsulting fees from Arthrex. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

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