Effect of intraarticular pressure on glenohumeral kinematics during a simulated abduction motion: a cadaveric study.

BACKGROUND: The current understanding of glenohumeral joint stability is defined by active restrictions and passive stabilizers including naturally-occurring negative intraarticular pressure. Cadaveric specimens have been used to evaluate the role of intraarticular pressure on joint stability, although, while the shoulder's negative intraarticular pressure is universally acknowledged, it has been inconsistently accounted for. HYPOTHESIS: During continuous, passive humeral abduction, releasing the native intraarticular pressure increases joint translation, and restoring this pressure decreases joint translations. STUDY DESIGN: Descriptive Laboratory Study. METHODS: A validated shoulder testing system was used to passively abduct the humerus in the scapular plane and measure joint translations for seven (n = 7) cadaveric specimens. The pressure within the glenohumeral joint was measured via a 25-gauge needle during passive abduction of the arm, which was released and subsequently restored. During motion, the rotator cuff muscles were loaded using stepper motors in a force feedback loop and electromagnetic sensors were used to continuously measure the position of the humerus and scapula. Joint translation was defined according to the instant center of rotation of the glenohumeral head according to the recommendations by the International Society of Biomechanics. RESULTS: Area under the translation versus abduction angle curve suggests that releasing the pressure within the capsule results in significantly less posterior translation of the glenohumeral head as compared to intact (85-90˚, p < 0.05). Posterior and superior translations were reduced after 70˚ of abduction when the pressure within the joint was restored. CONCLUSION: With our testing system employing a smooth continuous passive motion, we were able to show that releasing intraarticular pressure does not have a major effect on the path of humeral head motion during glenohumeral abduction. However, both violating the capsule and restoring intraarticular pressure after releasing alter glenohumeral translations. Future studies should study the effect of simultaneous external rotation and abduction on the relationship between joint motion and IAP, especially in higher degrees of abduction. CLINICAL RELEVANCE: Thoroughly simulating the glenohumeral joint environment in the cadaveric setting may strengthen the conclusions that can be translated from this setting to the clinic.

Intraarticular injection of relaxin-2 alleviates shoulder arthrofibrosis.

Arthrofibrosis is a prevalent condition affecting greater than 5% of the general population and leads to a painful decrease in joint range of motion (ROM) and loss of independence due to pathologic accumulation of periarticular scar tissue. Current treatment options are limited in effectiveness and do not address the underlying cause of the condition: accumulation of fibrotic collagenous tissue. Herein, the naturally occurring peptide hormone relaxin-2 is administered for the treatment of adhesive capsulitis (frozen shoulder) and to restore glenohumeral ROM in shoulder arthrofibrosis. Recombinant human relaxin-2 down-regulates type I collagen and α smooth muscle actin production and increases intracellular cAMP concentration in human fibroblast-like synoviocytes, consistent with a mechanism of extracellular matrix degradation and remodeling. Pharmacokinetic profiling of a bolus administration into the glenohumeral joint space reveals the brief systemic and intraarticular (IA) half-lives of relaxin-2: 0.96 h and 0.62 h, respectively. Furthermore, using an established, immobilization murine model of shoulder arthrofibrosis, multiple IA injections of human relaxin-2 significantly improve ROM, returning it to baseline measurements collected before limb immobilization. This is in contrast to single IA (sIA) or multiple i.v. (mIV) injections of relaxin-2 with which the ROM remains constrained. The histological hallmarks of contracture (e.g., fibrotic adhesions and reduced joint space) are absent in the animals treated with multiple IA injections of relaxin-2 compared with the untreated control and the sIA- and mIV-treated animals. As these findings show, local delivery of relaxin-2 is an innovative treatment of shoulder arthrofibrosis.

Changes in Contact Area in Meniscus Horizontal Cleavage Tears Subjected to Repair and Resection.

PURPOSE: To assess the changes in tibiofemoral contact pressure and contact area in human knees with a horizontal cleavage tear before and after treatment. METHODS: Ten human cadaveric knees were tested. Pressure sensors were placed under the medial meniscus and the knees were loaded at twice the body weight for 20 cycles at 0°, 10°, and 20° of flexion. Contact area and pressure were recorded for the intact meniscus, the meniscus with a horizontal cleavage tear, after meniscal repair, after partial meniscectomy (single leaflet), and after subtotal meniscectomy (double leaflet). RESULTS: The presence of a horizontal cleavage tear significantly increased average peak contact pressure and reduced effective average tibiofemoral contact area at all flexion angles tested compared with the intact state (P < .03). There was approximately a 70% increase in contact pressure after creation of the horizontal cleavage tear. Repairing the horizontal cleavage tear restored peak contact pressures and areas to within 15% of baseline, statistically similar to the intact state at all angles tested (P < .05). Partial meniscectomy and subtotal meniscectomy significantly increased average peak contact pressure and reduced average contact area at all degrees of flexion compared with the intact state (P < .05). CONCLUSIONS: The presence of a horizontal cleavage tear in the medial meniscus causes a significant reduction in contact area and a significant elevation in contact pressure. These changes may accelerate joint degeneration. A suture-based repair of these horizontal cleavage tears returns the contact area and contact pressure to nearly normal, whereas both partial and subtotal meniscectomy lead to significant reductions in contact area and significant elevations in contact pressure within the knee. Repairing horizontal cleavage tears may lead to improved clinical outcomes by preserving meniscal tissue and the meniscal function. CLINICAL RELEVANCE: Understanding contact area and peak contact pressure resulting from differing strategies for treating horizontal cleavage tears will allow the surgeon to evaluate the best strategy for treating his or her patients who present with this meniscal pathology.

In vivo kinetic evaluation of an adhesive capsulitis model in rats.

BACKGROUND AND HYPOTHESIS: We hypothesized that extra-articular, internal fixation of the shoulder in rats would result in a subsequent decrease in rotational range of motion (ROM) and an increase in joint stiffness. We further hypothesized that residual kinematic changes would still be present at 8 weeks after immobilization. Extra-articular, internal fixation of the shoulder has been used to induce adhesive capsulitis in rats; however, the effects on in vivo kinematics have not been assessed. METHODS: Baseline measurements of rotational torque and ROM were acquired (n = 10 rats), and the left forelimb of each animal was immobilized with sutures passed between the scapula and the humeral shaft. After 8 weeks, the sutures were removed, and changes in kinematics and kinetics were longitudinally quantified in the follow-up period. Changes in stiffness, defined as the area under the angle-torque curve, were also quantified. RESULTS: Immediately after suture removal, there was a 63% decrease in total ROM compared with baseline (51° ± 10° vs. 136° ± 0°; P < .001). Similarly, total torque was found to increase 13.4 N.mm compared with baseline (22.6 ± 5.9 N.mm vs. 9.2 ± 2.6 N.mm; P = .002). Residual total ROM restrictions and an increased torque in internal rotation were still evident at 8 weeks of follow-up (113° ± 8° vs. 137° ± 0°, P < .001 and 3.5 ± 0.4 N.mm vs. 2.7 ± 0.7 N.mm, P = .036). Stiffness also increased after suture removal and at 8 weeks of follow-up compared with baseline. CONCLUSION: This animal model of adhesive capsulitis rendered lasting effects on in vivo kinematics of the shoulder.

A Paradigm Shift in Critical Care Infrastructure in Complex Settings: Evaluating an Ultraportable Operating Room to Improve Field Surgical Safety.

INTRODUCTION: Scarcity of operating rooms and personal protective equipment in far-forward field settings make surgical infections a potential concern for combat mortality and morbidity. Surgical and transport personnel also face infectious risks from bodily fluid exposures. Our study aimed to describe the serial, proof-of-concept testing of the SurgiBox technology: an inflatable sterile environment that addresses the aforementioned problems, fits on gurneys and backpacks, and drapes over incisions. MATERIALS AND METHODS: The SurgiBox environmental control unit and inflatable enclosure were optimized over five generations based on iterative feedback from stakeholders experienced in surgery in austere settings. The airflow system was developed by analytic modeling, verified through in silico modeling in SOLIDWORKS, and confirmed with prototype smoke-trail checking. Particulate counts evaluated the enclosure's ability to control and mitigate users' exposures to potentially infectious contaminants from the surgical field in various settings. SurgiBox enclosures were setup over a mannequin's torso, in a configuration and position for either thoracic or abdominal surgery. A particle counter was serially positioned in sternotomy and laparotomy positions, as well as bilateral flank positions. This setup was repeated with open ports exposing the enclosure to the external environment. To simulate stress scenarios, sampling was repeated with enclosure measurements during an increase in external particulate concentration. RESULTS: The airflow technology effectively kept contaminants away from the incision and maintained a pressure differential to reduce particle entry. Benchtop testing demonstrated that even when ports were opened or the external environment had high contaminant burden, the enclosed surgical field consistently registered 0 particle count in all positions. Time from kit opening to incision averaged 54.5 seconds, with the rate-limiting step being connecting the environmental control unit to the enclosure. The portable kit weighted 5.9 lbs. CONCLUSIONS: Analytic, in silico, and mechanical airflow modeling and benchtop testing have helped to quantify the SurgiBox system's reliability in creating and maintaining an operating room-quality surgical field within the enclosure as well as protecting the surgical team outside the enclosure. More recent and ongoing work has focused on specifying optimal use settings in the casualty chain of care, expanding support for circumferential procedures, automating airflow control, and accelerating system setup. SurgiBox's ultimate goal is to take timely, safe surgery to patients in even the most austere of settings.

Effect of rotator cuff muscle activation on glenohumeral kinematics: A cadaveric study.

Healthy shoulder function requires the coordination of the rotator cuff muscles to maintain the humeral head's position in the glenoid. While glenohumeral stability has been studied in various settings, few studies have characterized the effect of dynamic rotator cuff muscle loading on glenohumeral translation during shoulder motion. We hypothesize that dynamic rotator cuff muscle activation decreases joint translation during continuous passive abduction of the humerus in a cadaveric model of scapular plane glenohumeral abduction. The effect of different rotator cuff muscle activity on glenohumeral translation was assessed using a validated shoulder testing system. The Dynamic Load profile is a novel approach, based on musculoskeletal modeling of human subject motion. Passive humeral elevation in the scapular plane was applied via the testing system arm, while the rotator cuff muscles were activated according to the specified force profiles using stepper motors and a proportional control feedback loop. Glenohumeral translation was defined according to the International Society of Biomechanics. The Dynamic load profile minimized superior translation of the humeral head relative to the conventional loading profiles. The total magnitude of translation was not significantly different (0.805) among the loading profiles suggesting that the compressive forces from the rotator cuff primarily alter the direction of humeral head translation, not the magnitude. Rotator cuff muscle loading is an important element of cadaveric shoulder studies that must be considered to accurately simulate glenohumeral motion. A rotator cuff muscle activity profile based on human subject muscle activity reduces superior glenohumeral translation when compared to previous RC loading profiles.

Tendon lengthening after achilles tendon rupture-passive effects on the ankle joint in a cadaveric pilot study simulating weight bearing.

BACKGROUND: In recent years, primary Achilles tendon ruptures have increased due to the aging population's participation in physically demanding activities. These injuries commonly occur during recreational sports and frequently lead to a long-term reduction in activity despite treatment. Non-operative methods of treatment for Achilles tendon ruptures may result in the Achilles healing in a lengthened position compared to the pre-injury state. This study uses a cadaveric model that simulates static weight bearing to explore the effect of a lengthened Achilles tendon on ankle joint load distribution. METHODS: Five lower limb cadaveric specimens were placed on a custom jig, where a 334 N (75 lb) load was applied at the femoral head, and the foot was supported against a plate to simulate static double-leg stance. A pressure mapping sensor was inserted into the ankle joint. A percutaneous triple hemiresection tendo-Achilles lengthening procedure (Hoke procedure) was performed on each specimen to simulate tendon lengthening after conservative treatment. Contact pressure, peak pressure, and center-of-pressure were measured for native and tendon-lengthened conditions. RESULTS: Tendon rupture did not significantly alter average contact pressure, peak contact pressures, or center-of-pressure in the ankle joint compared with native tendon. CONCLUSION: Achilles lengthening does not significantly change contact pressures of the ankle joint in this model . This result suggests that the passive restraint on ankle joint translation imposed by the Achilles tendon is minimal without muscle activation.

Biomechanical properties of an intramedullary suture anchor fixation compared to tension band wiring in osteoporotic olecranon fractures- A cadaveric study.

INTRODUCTION: The aim of the study is to compare three different fixation techniques for transverse olecranon repair in cadaveric osteoporotic bone: (1) current recommended AO tension band technique with K-wire fixation; (2) Suture anchor fixation and (3) Polyester suture fixation. METHODS: Evaluated with bone densitometry, 7 osteoporotic human elbow specimens were included in the study. A transverse olecranon fracture was reduced anatomically and were fixated first using a K-wire tension band technique, second using two suture anchors, and third using polyester suture. Static simulations of the kinetics associated with active range of motion (AROM) and push up from a chair exercises were performed with cyclic loading using Instron hydraulic testing apparatus. Fracture displacement was measured using videographic analysis. Failure was defined as 2 mm fracture displacement. RESULTS: The biomechanical analysis found no statistical difference in displacements between the three fixation methods when testing AROM. In simulated push-up exercises, polyester suture fixation failed after 17 cycles and had significantly higher displacement compared to the other two methods. No difference between the K-Wire fixation versus Suture anchor fixation was observed, p = 0.162. CONCLUSION: Suture anchor fixation might be a viable surgical treatment option for osteoporotic transverse elbow fractures in geriatric patients.

Hyperflexion and Femoral Interference Screw Insertion in ACL Reconstruction.

BACKGROUND: In anatomic anterior cruciate ligament (ACL) reconstructions produced with flexible reamers and no knee hyperflexion, it is unknown whether knee hyperflexion is necessary for femoral interference screw insertion. PURPOSE: To compare femoral screw-graft divergence in anatomic ACL reconstructions with endoscopic interference screws placed without knee hyperflexion and with the use of flexible versus rigid screwdrivers. STUDY DESIGN: Controlled laboratory study. METHODS: Ten matched pairs of cadaveric knees had bone-tendon-bone graft ACL reconstructions with anatomic femoral tunnels. The knees were flexed to 90°. Femoral interference screws (7 × 20 mm) were placed in pairs of knees: in 1 knee with a flexible screwdriver and in the opposite knee with a rigid screwdriver. Graft-screw divergence was imaged with computed tomography scans and tested with cyclic and static biomechanical tests. RESULTS: The mean screw-graft divergence was 12.07° ± 4.04° with the rigid screwdriver and 10.68° ± 3.23° with the flexible screwdriver (P = .35). The cyclic tests with screws placed by a rigid screwdriver had a mean increase in displacement of 0.56 ± 0.20 mm. For screws placed with the flexible screwdriver, the mean increase in displacement was 0.58 ± 0.32 mm (P = .66). Yield load was 393.3 ± 95.1 N for screws placed by a rigid screwdriver and 408.2 ± 119.0 N for screws inserted with the flexible screwdriver (P = .78). Maximum load was 523.1 ± 88.7 N for screws placed by a rigid screwdriver and 467.1 ± 107.3 N for screws inserted with the flexible screwdriver (P = .09). CONCLUSION: With either a rigid or a flexible screwdriver, there were no significant effects on screw divergence or fixation strength. CLINICAL RELEVANCE: Knees can be kept at 90° during endoscopic femoral interference screw insertion. The use of a traditional rigid or flexible screwdriver will not affect screw-graft divergence or fixation strength.

Pressure Distribution in the Ankle and Subtalar Joint With Routine and Oversized Foot Orthoses.

BACKGROUND: Foot orthoses are used to treat many disorders that affect the lower limb. These assistive devices have the potential to alter the forces, load distribution, and orientation within various joints in the foot and ankle. This study attempts to quantify the effects of orthoses on the intra-articular force distribution of the ankle and subtalar joint using a cadaveric testing jig to simulate weight bearing. METHODS: Five lower-limb cadaveric specimens were placed on a custom jig, where a 334-N (75-lb) load was applied at the femoral head, and the foot was supported against a plate to simulate double-leg stance. Pressure-mapping sensors were inserted into the ankle and subtalar joint. Mean pressure, peak pressure, contact area, and center of force were measured in both the ankle and subtalar joints for barefoot and 2 medial foot orthosis conditions. The 2 orthosis conditions were performed using (1) a 1.5-cm-height wedge to simulate normal orthoses and (2) a 3-cm-height wedge to simulate oversized orthoses. RESULTS: The contact area experienced in the subtalar joint significantly decreased during 3-cm orthotic posting of the medial arch, but neither orthosis had a significant effect on the spatial mean pressure or peak pressure experienced in either joint. CONCLUSION: The use of an oversized orthosis could lead to a decrease in the contact area and alterations in the distribution of pressure within the subtalar joint. CLINICAL RELEVANCE: The use of inappropriate orthoses could negatively impact the force distribution in the lower limb.

Rat Model of Adhesive Capsulitis of the Shoulder.

This proposal aims to create an in vivo rat model of adhesive capsulitis for researching potential treatment options for this condition and other etiologies of comparable arthrofibrosis. The model includes extra-articular fixation of the shoulder in rats via scapular to humeral suturing, resulting in a secondary contracture without invading the intra-articular space and resulting in decreased rotational ROM and increased joint stiffness. We used 10 Sprague-Dawley rats for the purpose of this study. Baseline ROM measurements were taken before glenohumeral immobilization. The rats were subjected to 8 weeks of immobilization before the fixation sutures were removed and changes in ROM and joint stiffness were evaluated. To evaluate whether immobilization resulted in a significant reduction in ROM, changes in kinematics were calculated. ROM was measured at each time point in the follow-up period and was compared to the baseline internal and external ROM measurements. In order to evaluate the stiffness, joint kinetics were calculated by determining the differences in torque (text and tint ) needed to reach the initial external rotation of 60° and initial internal rotation of 80°. After the removal of the extra-articular suture fixation on follow-up day 0, we found a 63% decrease in total ROM compared to baseline. We observed continuous improvement until week 5 of follow-up, with the progress slowing down around a 19% restriction. On week 8 of follow-up, there was still an 18% restriction of ROM. Additionally, on follow-up day 0, we found the torque increased by 13.3 Nmm when compared to baseline. On week 8, the total torque was measured to be 1.4 ± 0.2 Nmm higher than initial measurements. This work introduces a rat model of shoulder adhesive capsulitis with lasting reduced ROM and increased stiffness.