Patrick J. Schimoler

The Importance of Preserving the Radial Tuberosity During Distal Biceps Repair

BACKGROUND The radial tuberosity contributes to the biceps supination moment arm and the elbow flexion moment. The purpose of our study was to compare the impact of a cortical bone trough versus an anatomic repair on measurements of the forearm supination moment arm and elbow flexion force efficiency. Our hypothesis was that a trough repair would decrease the tuberosity height, the native biceps supination moment arm, and elbow flexion force efficiency compared with an anatomic repair. METHODS The isometric supination moment arm and elbow flexion force efficiency were measured in ten matched pairs of cadaveric upper limbs. After testing, the geometry of the proximal aspect of the radius was reconstructed with use of stereophotogrammetry. All of the repair sites were three-dimensionally reconstructed to quantify the disturbance of the trough on native anatomy. The tuberosity distance was defined as the distance between the central axis of the radius and the centroid of the respective repair site. RESULTS Specimens with a trough repair had a 27% lower supination moment arm at 60° of supination (p = 0.036). There were no differences found for pronation or neutral forearm positioning (p > 0.235). Flexion force efficiency was not significantly different between the trough and anatomic repair groups. The average tuberosity distance was 11.0 ± 2.1 mm for the anatomic repairs and 8.3 ± 1.4 mm for the trough repairs (p = 0.003). The percentage of distance lost due to the trough was 25%. Furthermore, the supination moment arm in the supinated position was significantly correlated with the tuberosity distance. CONCLUSIONS The trough technique resulted in a significant decrease (p = 0.036) in the moment arm of a 60° supinated forearm and a significant reduction (p = 0.003) in radial tuberosity height. The loss of the supination moment arm was correlated with the decrease in tuberosity height, providing evidence that the radial protuberance acts as a mechanical cam. CLINICAL RELEVANCE The anterior protuberance of the radial tuberosity functions as a supination cam; therefore, consideration should be given to preserve its topographical anatomy during a distal biceps repair.

Validation of a Feedback-Controlled Elbow Simulator Design: Elbow Muscle Moment Arm Measurement

The Allegheny General Hospital (AGH) elbow simulator was designed to be a closed-loop physiologic simulator actuating movement in cadaveric elbow specimens via servoelectric motors that attach to the tendons of the biceps, brachialis, triceps, and pronator teres muscles. A physiologic elbow simulator should recreate the appropriate moment arms throughout the elbows range of motion. To validate this design goal, muscle moment arms were measured in three cadaver elbow specimens using the simulator. Flexion-extension moment arms of four muscles were measured at three different pronation/supination angles: fully pronated, fully supinated, and neutral; pronation-supination moment arms were measured at three different flexion-extension angles: 30 deg, 60 deg, and 90 deg. The tendon-displacement method was used in these measurements, in which the ratio of the change in musculotendon length to the change in joint angle was computed. The numeric results compared well with those previously reported; the biceps and pronator teres flexion-extension moment arms varied with pronation-supination position, and vice versa. This is one of the few reports of both flexion-extension and pronation-supination moment arms in the same specimens, and represents the first use of closed-loop feedback control in the AGH elbow simulator. The simulator is now ready for use in clinical studies such as in analyses of radial head replacement and medial ulnar collateral ligament repair. Copyright

Effects of camera switching on fine accuracy in a motion capture system.

When using optical motion capture systems, increasing the number of cameras improves the visibility. However, the software used to deal with the information fusion from multiple cameras may compromise the accuracy of the system due to camera dropout, which can vary with time. In cadaver studies of radial head motion, increasing the number of cameras used by the motion capture system seemed to decrease the accuracy of the measurements. This study investigates the cause. The hypothesis was that errors in position can be induced when markers are obscured from and then restored to a cameras viewable range, as can happen in biomechanical studies. Accuracy studies quantified the capabilities of the motion capture system with precision translation and rotation movements. To illustrate the effect that abrupt perceived changes in a markers position can have on the calculation of radial head travel, simulated motion experiments were performed. In these studies, random noise was added to simulated data, which obscured the resultant path of motion. Finally, camera-blocking experiments were performed in which precise movements were measured with a six-camera Vicon system and the errors between the actual and perceived motion were computed. During measurement, cameras were selectively blocked and restored to view. The maximum errors in translation and rotation were 3.7 mm and 0.837 deg, respectively. Repeated measures analysis of variance (ANOVAs) (alpha=0.05) confirmed that the camera-blocking influenced the results. Taken together, these results indicate that camera-switching can affect the observation of fine movements using a motion analysis system with a large number of cameras. One solution is to offer opportunity for user interaction in the software to choose the cameras used for each instant of time.

Comparing Biomechanical Properties, Repair Times, and Value of Common Core Flexor Tendon Repairs

Background: The aim of the study was to compare biomechanical strength, repair times, and repair values for zone II core flexor tendon repairs. Methods: A total of 75 fresh-frozen human cadaveric flexor tendons were harvested from the index through small finger and randomized into one of 5 repair groups: 4-stranded cross-stitch cruciate (4-0 polyester and 4-0 braided suture), 4-stranded double Pennington (2-0 knotless barbed suture), 4-stranded Pennington (4-0 double-stranded braided suture), and 6-stranded modified Lim-Tsai (4-0 looped braided suture). Repairs were measured in situ and their repair times were measured. Tendons were linearly loaded to failure and multiple biomechanical values were measured. The repair value was calculated based on operating room costs, repair times, and suture costs. Analysis of variance (ANOVA) and Tukey post hoc statistical analysis were used to compare repair data. Results: The braided cruciate was the strongest repair (P > .05) but the slowest (P > .05), and the 4-stranded Pennington using double-stranded suture was the fastest (P > .05) to perform. The total repair value was the highest for braided cruciate (P > .05) compared with all other repairs. Barbed suture did not outperform any repairs in any categories. Conclusions: The braided cruciate was the strongest of the tested flexor tendon repairs. The 2-mm gapping and maximum load to failure for this repair approached similar historical strength of other 6- and 8-stranded repairs. In this study, suture cost was negligible in the overall repair cost and should be not a determining factor in choosing a repair.

Measuring Moment Arms Using Closed-Loop Force Control With an Elbow Simulator

In search of a complete understanding of a joint’s function, one must understand both the anatomic parameters and how the brain controls the joint’s actuation. Accurate measurements of anatomical parameters are critical to non-linear biomechanical modeling and control and also to a clinical understanding of orthopaedic reconstruction. Likewise, new frontiers in the study of neuromuscular control contribute to our understanding of joint structure and function. One approach to study joint function is to use a joint simulator to actuate cadaver limbs. Towards the goals of understanding and improving human elbow joint control, a physiologic elbow joint simulator was previously constructed in our laboratory. It is the first elbow simulator to operate completely under closed-loop control. The closed-loop force control used to study joint mechanics permits measurement of moment arms in cadaveric elbow specimens. We hypothesized that the approach yields comparable results to previously-reported moment arm values.[1]Copyright

Control System for an Elbow Joint Motion Simulator

An elbow joint motion simulator provides the ability to derive various measures from cadaveric elbow specimens such as the kinematic effects of radial head prostheses and ligament strains. To ensure that the data collected is meaningful, the system must be able actuate the elbow through chosen displacements in a repeatable manner. A control system is developed in this thesis capable of performing this task. Linear positioners which create motion by applying loads through the brachialis, triceps, biceps, and pronator teres move the arm through flexion / extension or pronation / supination movements. Sensors measure loading and displacement states enabling the use of proportional-integral-derivative feedback control. Results indicate the systems capability. Suggestions for future work are given.

The optimal number and location of sutures in conduit-assisted primary digital nerve repair:

We evaluated the strength of conduit-assisted primary digital nerve repairs, with varying suture location and number, in 56 digital nerves from cadavers. Maximum load to failure was tested for the following seven repairs, designated by the number of epineurial sutures followed by the number of sutures at each end of the conduit: 4 (epineurial sutures)/0 (sutures at each end of conduit), 4/4, 4/2, 2/2, 0/4, 0/2, 0/1. The 4/4 repair (3.0 N) was significantly stronger than 4/0 (1.5 N), 2/2 (1.6 N), 0/4 (2.0 N), 0/2 (1.4 N) and 0/1 (1.1 N). Considering all repair types, there was a significant correlation between suture number and failure load, with the strongest repair having a total of 12 sutures, which is impractical. Reasonable repair options, which have two sutures at each end of the conduit and either two or no epineurial sutures, are as strong as a four-suture epineurial repair but have less sutures at the coaptation site.

Fibrin Glue Increases the Tensile Strength of Conduit-Assisted Primary Digital Nerve Repair

Background: An ideal peripheral nerve repair construct does not currently exist. Our primary goal was to determine whether fibrin glue adds to the tensile strength of conduit-assisted primary digital nerve repairs. Our secondary goal was to evaluate the impact of varying suture number and location on the tensile strength. Methods: Ninety cadaveric digital nerves were harvested and divided equally into the following repair groups: A (4/4), B (2/2), C (0/2), D (0/1), and E (0/0) with the first number referring to the number of sutures at the coaptation and the second number referring to the number of sutures at each proximal and distal end of the nerve-conduit junction. When fibrin glue was added, the group was labeled prime. The nerve specimens were transected and then repaired with 8-0 nylon suture and conduit. The tensile strength of the repairs was tested, and maximum failure load was determined. The results were analyzed with a 2-way analysis of variance. The Tukey post hoc test compared repair groups if the 2-way analysis of variance showed significance. Results: Both suture group and glue presence significantly affected the maximum failure load. Increasing the number of sutures increased the maximum failure load, and the presence of fibrin glue also increased the failure load. Conclusions: Fibrin glue was found to increase the strength of conduit-assisted primary digital nerve repairs. Furthermore, the number of sutures correlated to the strength of the repair. Fibrin glue may be added to a conduit-assisted primary digital nerve repair to maintain strength and allow fewer sutures at the primary coaptation site.

Quantification of Long Head of the Biceps Tendon Motion After Loop ‘N’ Tack Suprapectoral Biceps Tenodesis

Objectives: Lesions of the long head of the biceps are one of the most frequent causes of shoulder pain, and they can be successfully treated with biceps tenotomy or tenodesis. The advantage of a biceps tenodesis is avoiding the potential development of a cosmetic deformity (“Popeye sign”) or cramping muscle pain that can remain after tenotomy. Proponents of a subpectoral tenodesis believe that “groove pain” may remain a problem after suprapectoral tenodesis due to persistent motion of the biceps tendon within the bicipital groove. The objective of this study was to evaluate the motion of the biceps tendon within the bicipital groove before and after a suprapectoral tenodesis performed using the Loop ‘N’ Tack technique. Our hypothesis was that there would be minimal to no motion of the biceps tendon within the bicipital groove after the tenodesis. Methods: Six fresh-frozen cadaveric arms were obtained and dissected to expose the long head of biceps tendon and the bicipital groove from the transverse humeral ligament to the pectoralis major insertion. The scapula and ulna were affixed with inclinometers to measure motion in multiple planes. The biceps tendon and bicipital groove were marked with fiducials, which were tracked by two cameras focused on this region. The shoulder and elbow were taken through a full range of motion including scapular abduction, forward flexion, extension, internal rotation, and external rotation and elbow flexion and extension with a supinated, neutral, or pronated forearm. The translation of the biceps tendon was quantified as a function of scapular or forearm motion in each plane. A suprapectoral biceps tenodesis was then performed using the Loop ‘N’ Tack technique. The scapula and forearm were taken through the same motions, and the translation of the biceps tendon was quantified. A paired t-test was performed for each motion to determine if maximum biceps tendon translation in the bicipital groove was a function of tendon condition (native vs post-tenodesis). Results: There was minimal translation of the biceps tendon during elbow flexion and extension, both before and after tenodesis. There was significant translation of the biceps tendon in all planes of scapular motion in the native state, and the largest amount of translation was 20.73mm +/- 8.21mm during shoulder flexion and extension (Table 1). The translation of the biceps tendon after tenodesis was significantly reduced in every plane of scapular motion compared to the native state (p = 0.01 or p < 0.01 in all planes of motion). The largest amount of translation in any plane after tenodesis was 1.57mm +/- 0.98mm, which occured during shoulder flexion and extension (Table 1). Conclusion: In the native state, the translation of the biceps tendon within the bicipital groove ranges from 5.14mm - 20.73mm with scapular motion. There is statistically significant reduction in translation of the biceps tendon in all planes of scapular motion after the Loop ‘N’ Tack tenodesis (Figure 1), with a maximum translation of only 1.57mm. These data suggest that motion of the biceps tendon within the bicipital groove is essentially eliminated and should not be a cause of persistent pain. The Loop ‘N’ Tack biceps tenodesis is a simple, all-arthroscopic technique for patients with proximal biceps pathology. It is a viable alternative to subpectoral tenodesis, essentially eliminating all motion of the biceps tendon within the bicipital groove, and it should not lead to persistent “groove pain”. Table 1. Native Post-Tenodesis Results Average (mm) S.D. (mm) Average (mm) S.D. (mm) P-Value Elbow Flexion: Supination 1.85 1.66 0.56 0.37 0.15 Elbow Flexion: Neutral 1.73 1.43 0.83 0.64 0.30 Elbow Flexion: Pronation 3.03 1.55 0.72 0.24 0.01 Glenohumeral: Internal/External Rot. 9.37 1.70 1.32 0.78 <0.01 Glenohumeral: Flexion/Extension 20.73 8.21 1.57 0.98 <0.01 Glenohumeral: Full Flexion 10.32 2.60 0.75 0.47 <0.01 Glenohumeral: Abduction 5.14 2.67 1.26 1.17 0.01

Accuracy and Precision of a Control System for an Elbow Joint Simulator

Joint motion simulators (JMS’s) have been developed for many applications enabling the repeatable testing of prostheses, scientific investigations of joint mechanics and the study of surgical procedures.[1–4] Although Morrey has reported that radial head implants have lower post-operative satisfaction than other joint implants[5] and Dunning has examined several issues with radial heads, many problems remain.[6] It is therefore beneficial to develop a simulator capable of evaluating radial head implants. A robust simulator can also provide the ability to test soft tissue strains at the elbow and compare control schemes that may elucidate the body’s means of controlling multiaxial multimuscle systems.Copyright