The Effects of Latarjet Reconstruction on Glenohumeral Kinematics in the Presence of Combined Bony Defects: A Cadaveric Model.

BACKGROUND: Recurrent glenohumeral instability is often a result of underlying bony defects in the glenoid and/or humeral head. Anterior glenoid augmentation with a coracoid bone block (ie, Latarjet procedure) has been recommended for glenoid bone loss in the face of recurrent instability. However, no study has investigated the effect of Latarjet augmentation in the setting of both glenoid and humeral head defects (Hill-Sachs defects). PURPOSE: To evaluate the glenohumeral kinematics of the Latarjet procedure in the presence of combined bony defects. STUDY DESIGN: Controlled laboratory study. METHODS: Eighteen fresh-frozen cadaveric specimens void of all surrounding soft tissue were tested at all combinations of glenohumeral abduction (ABD) angles of 20°, 40°, and 60° and 3 external rotation (ER) levels of 0°, 40°, and 80°. Each experiment comprised anterior dislocation by translating the glenoid under a 50-N medial load applied on the humerus, simulating the static load of soft tissue. The primary outcome measurement was defined as the percentage of intact translation (normalized distance to dislocation). Specimens were tested in an intact condition (no defect), with different combinations of defects, and with Latarjet augmentation. The Latarjet procedure was performed for 20% and 30% glenoid defects by transferring the specimen's coracoid process anterior to the glenoid so that it was flush with the articulating surface. RESULTS: Results depended on the position of the arm. At 20° of ABD and 0° of ER, a 20% glenoid defect decreased the percentage of intact translation regardless of the humeral head defect size (P ≤ .0001). In this same setting, Latarjet reconstruction restored translation to dislocation greater than the native intact joint for all sizes of humeral head defects. At 60° of ABD and 80° of ER, a 20% glenoid defect led to an overall decrease in translation to dislocation with increasing humeral head defects. While Latarjet augmentation resulted in increased translation to dislocation for all humeral head defect sizes, it was not able to restore translation greater than the native intact joint for large humeral head defects (31% and 44%); the normalized percentages of intact translation to dislocation were 65% and 30%, respectively. CONCLUSION: These results demonstrate that some degree of translation can be regained for combined bony glenoid and humeral head defects with the Latarjet procedure. However, for humeral defects larger than 31%, the rotational effect of the humeral head defect led to persistent decreased translation and to dislocation despite glenoid augmentation. Thus, directly addressing the humeral defect to restore the articular surface should be considered in these cases. CLINICAL RELEVANCE: This study provides a critical value limit for combined anterior glenoid bone loss and humeral head defects. While this is a biomechanical study, the results indicate that in patients with humeral head defects greater than 31%, additional humeral-sided surgery may be needed.

Stability of the Glenohumeral Joint With Combined Humeral Head and Glenoid Defects: A Cadaveric Study.

BACKGROUND: Shoulders with recurrent anterior instability often have combined bony defects of the humeral head and glenoid. Previous studies have looked at only isolated humeral head or glenoid defects. PURPOSE/HYPOTHESIS: The aim of this study was to define the relationship of combined humeral head and glenoid defects on anterior shoulder instability. Combined bony defects will lead to increased instability compared with an isolated defect, and the "critical" size of humeral head and glenoid defects that need to be addressed to restore stability will be smaller when combined rather than isolated. STUDY DESIGN: Controlled laboratory study. METHODS: Eighteen shoulder specimens were tested at 60° of glenohumeral abduction and 80° of glenohumeral external rotation. Humeral head defect sizes included 6%, 19%, 31%, and 44% of the humeral head diameter. Glenoid defect sizes included 10%, 20%, and 30% of the glenoid width. Outcome measures included percentage of intact stability ratio (%ISR; the stability ratio for a given trial divided by the stability ratio in the intact state for that specimen) and percentage of intact translation (%IT; the distance to dislocation for a given trial divided by the distance to dislocation in the intact state for that specimen). RESULTS: The decrease in %ISR reached statistical significance for humeral head defects of 44%, for glenoid defects of 30%, and for a combined 19% humeral head defect with a 20% glenoid defect (65% mean %ISR). The decrease in %IT reached statistical significance for humeral head defects ≥31%, for glenoid defects ≥20%, and for a combined 19% humeral head defect with a 10% glenoid defect (69% mean %IT). CONCLUSION: In shoulders with combined humeral head and glenoid defects, bony reconstruction may be indicated for humeral head defects as small as 19% of the humeral head diameter and glenoid defects as small as 10% to 20% of the glenoid width, especially if the glenoid defect produces a significant loss of glenoid concavity depth. CLINICAL RELEVANCE: In shoulders with combined humeral head and glenoid defects, bony reconstruction may be indicated for defect sizes smaller than would be indicated for either defect found in isolation.

The Reduction in Stability From Combined Humeral Head and Glenoid Bony Defects Is Influenced by Arm Position.

BACKGROUND: Combined defects of the glenoid and humeral head are often a cause for recurrent shoulder instability. PURPOSE/HYPOTHESIS: The aim of this study was to evaluate the influence of combined bony lesions on shoulder instability through varying glenohumeral positions. The hypothesis was that instability due to combined defects would be magnified with increasing abduction and external rotation. STUDY DESIGN: Controlled laboratory study. METHODS: Eighteen cadaveric shoulders were tested. Experiments were performed at combinations of glenohumeral abduction angles of 20°, 40°, and 60° and external rotations of 0°, 40°, and 80°. The various glenoid defect sizes created were 10%, 20%, and 30% of the glenoid width. Four humeral head defects were created based on humeral head diameter (6%, 19%, 31%, and 44%). Each experiment consisted of translating the glenoid in a posterior direction to simulate an anterior dislocation under a 50-N load. The instability was measured as a percentage of intact translation (ie, loss in translational distance normalized to the no-defect condition). RESULTS: At 20° of abduction, instability increased from 100% to 85%, 70%, and 43% with increasing glenoid defect sizes of 10%, 20% and 30%, respectively, with a 6% humeral head defect. However, at a functional arm position of apprehension, these values were significantly decreased (P < .05) for humeral head defect sizes of 19%, 31%, and 44%, with translation values of 49%, 27%, and 2%, respectively. CONCLUSION: A humeral defect leads to rotational instability with the arm rotated into a functional position rather than a resting position. However, a significant glenoid defect can lead to loss of translation independent of changes in arm position. Combined defects as large as 44% of humeral head and 20% glenoid did not show instability at 20° of abduction and neutral position; however, defects as small as 19% humeral defect and 10% glenoid defect led to significant instability in the position of apprehension. CLINICAL RELEVANCE: Instability at lower levels of abduction and external rotation clinically indicates larger bony defects and may need to be directly addressed, depending on the patient's age and function.

A novel lunar bed rest analogue.

INTRODUCTION: Humans will eventually return to the Moon and thus there is a need for a ground-based analogue to enable the study of physiological adaptations to lunar gravity. An important unanswered question is whether or not living on the lunar surface will provide adequate loading of the musculoskeletal system to prevent or attenuate the bone loss that is seen in microgravity. Previous simulations have involved tilting subjects to an approximately 9.5 degrees angle to achieve a lunar gravity component parallel to the long-axis of the body. However, subjects in these earlier simulations were not weight-bearing, and thus these protocols did not provide an analogue for load on the musculoskeletal system. METHODS: We present a novel analogue which includes the capability to simulate standing and sitting in a lunar loading environment. A bed oriented at a 9.5 degrees angle was mounted on six linear bearings and was free to travel with one degree of freedom along rails. This allowed approximately 1/6 body weight loading of the feet during standing. "Lunar" sitting was also successfully simulated. RESULTS: A feasibility study demonstrated that the analogue was tolerated by subjects for 6 d of continuous bed rest and that the reaction forces at the feet during periods of standing were a reasonable simulation of lunar standing. During the 6 d, mean change in the volume of the quadriceps muscles was -1.6% +/- 1.7%. DISCUSSION: The proposed analogue would appear to be an acceptable simulation of lunar gravity and deserves further exploration in studies of longer duration.

An ambulatory biomechanical data collection system for use in space: design and validation.

INTRODUCTION: Loss in bone mineral density and muscle strength in astronauts following long-duration spaceflight have been well documented, but the altered force and movement environments in microgravity which may contribute to these changes have not been well characterized. This paper describes the instrumentation, software, and data collection procedures developed for the "Foot" experiment that was conducted on the International Space Station (ISS) to provide insight into the biomechanics of daily activity in a microgravity environment. METHODS: The instrumentation used for data collection included the Ambulatory Data Acquisition System (ADAS), ADAS electromyography (EMG) modules, the Joint Excursion System, and the Total Force-Foot Ground interface system, which were all integrated into a specially designed Lower Extremity Monitoring Suit. There were 14 total channels of data that were collected at sampling rates between 8 Hz and 1024 Hz, including 7 channels of EMG, 4 channels of joint angle data, 2 channels of in-shoe ground reaction force, and a marker channel for event recording. Data were typically collected for between 6.5 and 11.8 h of activity during 4 d on Earth and 4-7 d in flight. RESULTS: Exemplar data sets collected preflight on astronauts in 1 g to validate the instrumentation are presented. DISCUSSION: We conclude that the system provides valid and useful biomechanical information on long-term activity. The analysis of data collected on-orbit using the system described here will be presented in a series of future papers characterizing the biomechanics of astronaut activity during complete working days on the Earth and on the ISS.