Effects of repetitive subfailure strains on the mechanical behavior of the inferior glenohumeral ligament

Correlation of knee laxity with alignment and repetitive physical activity in patients with knee osteoarthritis: A cross-sectional study

BACKGROUND

Malalignment, knee laxity, and repetitive physical activity are considered biomechanical risk factors for knee osteoarthritis (KOA), though the correlation among these factors is poorly understood. The purpose of this study was to elucidate the relationship between knee laxity and alignment, and to determine the effects of repetitive physical activity on knee laxity in patients with KOA.

METHODS

The study subjects were 68 patients with radiographic tibiofemoral KOA and 68 control subjects. Each participant underwent clinical evaluation, muscle strength test, radiography, and knee laxity test. Laxity was evaluated before and after repetitive stepping exercise using tri-axial accelerometer.

RESULTS

Mediolateral acceleration correlated (P < 0.01) with two coronal alignments (mechanical axis: hip-knee-ankle angle (HKA); and joint line convergent angle (JLCA)). Pearson correlation coefficient was small (r = 0.23-0.24) before but increased after stepping (r = 0.28-0.33). Increased mediolateral acceleration after stepping correlated with JLCA (r = 0.37, P < 0.001). There were significant differences in coronal alignments, gait speed, mediolateral acceleration, and accelerations in all directions between the control and KOA groups. Anteroposterior acceleration did not correlate with sagittal knee alignment. Multiple logistic regression analysis identified HKA/JLCA, and increased mediolateral acceleration after stepping as significant diagnostic predictors of KOA.

CONCLUSIONS

We found a direct relationship between knee laxity and alignment or repetitive physical activity. Repetitive stepping activity significantly increased mediolateral acceleration in KOA patients, compared with the control. Stepping increased the correlation between mediolateral acceleration and coronal alignment. In knees with large JLCA, repetitive stepping caused much larger mediolateral laxity.

Bench, Bar, and Ring Dips: Do Kinematics and Muscle Activity Differ?

The purpose of this study was to profile and compare the kinematics, using 3D motion capture, and muscle activation patterns, using surface electromyography (sEMG), of three common dip variations; the bench, bar, and ring dips. Thirteen experienced males performed four repetitions of each dip variation. For each participant, repetitions 2-4 were time-normalized and then averaged to produce a mean value for all kinematic and sEMG variables. The mean maximal joint angles and mean peak sEMG amplitudes were compared between each variation using a one-way ANOVA with repeated measures. Several significant differences (p < 0.05) between dip variations were observed in both kinematic and sEMG data. The bench dip predominantly targets the triceps brachii but requires greater shoulder extension range. The mean peak triceps brachii activation was 0.83 ± 0.34 mV on the bench, 1.04 ± 0.27 mV on the bar, and 1.05 ± 0.40 mV on the ring. The bar dip is an appropriate progression from the bench dip due to the higher peak muscle activations. The ring dip had similar peak activations to the bar dip, with three muscles increasing their activation intensities further. These findings have implications for practitioners prescribing the dip, particularly to exercisers with a history of shoulder pain and injury.

Characterizing the Mechanical and Viscoelastic Response of the Porcine Facet Joint Capsule Ligament in Response to a Simulated Impact

The facet capsule ligament (FCL) is a structure in the lumbar spine that constrains motions of the vertebrae. Subfailure loads can produce micro-damage resulting in increased laxity, decreased stiffness, and altered viscoelastic responses. Therefore, the purpose of this investigation was to determine the mechanical and viscoelastic properties of the FCL under various magnitudes of strain from control samples and samples that had been through an impact protocol. Two hundred FCL tissue samples were tested (20 Control & 180 Impacted). Impacted FCL tissue samples were obtained from functional spinal units that had been exposed to one of nine sub-failure impact conditions. All specimens underwent to following loading protocol: preconditioning with 5 cycles of 5% strain, followed by a 30 second rest period, 5 cycles of 10% strain and 1 cycle of 10% strain with a hold duration at 10% strain for 240 seconds (4 minutes). The same protocol followed for 30% and 50% strain. Measures of stiffness, hysteresis and force-relaxation were computed. No significant differences in stiffness were observed for impacted specimens in comparison to control. Impacted specimens from the 8g Flexed and 11g Flexed and Neutral conditions exhibited greater hysteresis during the cyclic-30% and cyclic-50% portion of the protocol in comparison to controls. In addition, specimens from the 8g and 11g Flexed conditions resulted in greater stress decay for the 50%-hold conditions. Results from this study demonstrate viscoelastic changes in FCL samples exposed to moderate and highspeed single impacts in a flexed posture.

Utilization of Internal Bracing in Elbow Medial UCL Stabilization: From Biomechanics to Clinical Application and Patient Outcomes

Ulnar collateral ligament (UCL) reconstruction has been successfully utilized to treat symptomatic UCL insufficiency in overhead athletes. Despite the overall success of the procedure, attempts have been made to improve upon the original technique with the goal of hastening return to sport. Most recently, there has been interest in repairing or reconstructing the native ligament with internal brace (IB) augmentation. Biomechanical cadaveric studies assessing UCL repair with IB augmentation have attempted to evaluate the efficacy of this treatment; however, the literature is seemingly divided on its benefit. Preliminary clinical studies suggest internal bracing may allow a faster return to sport than conventional techniques. The purpose of this review was to provide an analysis of the current evidence on IB augmentation in UCL repair of the elbow as it pertains to biomechanical advantages/disadvantages, reported surgical techniques, and clinical outcomes in comparison with traditional UCL reconstruction techniques.

Biaxial softening of isolated cerebral arteries following axial overstretch

Arteries play a critical role in carrying essential nutrients and oxygen throughout the brain; however, vessels can become damaged in traumatic brain injury (TBI), putting neural tissue at risk. Even in the absence of hemorrhage, large deformations can disrupt both the physiological and mechanical behavior of the cerebral vessels. Our group recently reported the effect of vessel overstretch on axial mechanics; however, that work did not address possible changes in circumferential mechanics that are critical to the regulation of blood flow. In order to address this in the present work, ovine middle cerebral arteries were isolated and overstretched axially to 10, 20, or 40% beyond the in vivo configuration. Results showed a statistically significant decrease in circumferential stiffness and strain energy, as well as an increase in vessel diameter following 40% overstretch (p < 0.05). These passive changes would lead to a decrease in vascular resistance and likely play a role in previous reports of cellular dysfunction. We anticipate that our findings will both increase understanding of vessel softening phenomena and also promote improved modeling of cerebrovascular mechanics following head trauma.

Fatigue exhaustion of the mitral valve tissue

Sudden failure and rupture of the tissue is a rare but serious short-term complication after the mitral valve surgical repair. Excessive cyclic loading on the suture line of the repair can progressively damage the surrounding tissue and finally cause tissue rupture. Moreover, mechanical over-tension, which occurs in a diseased mitral valve, gradually leads to tissue floppiness, mitral annular dilation, and leaflet rupture. In this work, the rupture mechanics of mitral valve is studied by characterizing the fracture toughness exhaustion of healthy tissue. Results of this study show that fracture toughness of the posterior mitral valve is lower than its anterior counterpart, indicating that posterior tissue is more prone to failure. Moreover, the decrease in fracture toughness by increasing the number of fatigue cycles shows that excessive mechanical loading leads to progressive failure and rupture of mitral valve tissue within a damage accumulative process.

Repeated High Rate Facet Capsular Stretch at Strains That are Below the Pain Threshold Induces Pain and Spinal Inflammation With Decreased Ligament Strength in the Rat

Repeated loading of ligamentous tissues during repetitive occupational and physical tasks even within physiological ranges of motion has been implicated in the development of pain and joint instability. The pathophysiological mechanisms of pain after repetitive joint loading are not understood. Within the cervical spine, excessive stretch of the facet joint and its capsular ligament has been implicated in the development of pain. Although a single facet joint distraction (FJD) at magnitudes simulating physiologic strains is insufficient to induce pain, it is unknown whether repeated stretching of the facet joint and ligament may produce pain. This study evaluated if repeated loading of the facet at physiologic nonpainful strains alters the capsular ligament's mechanical response and induces pain. Male rats underwent either two subthreshold facet joint distractions (STFJDs) or sham surgeries each separated by 2 days. Pain was measured before the procedure and for 7 days; capsular mechanics were measured during each distraction and under tension at tissue failure. Spinal glial activation was also assessed to probe potential pathophysiologic mechanisms responsible for pain. Capsular displacement significantly increased (p = 0.019) and capsular stiffness decreased (p = 0.008) during the second distraction compared to the first. Pain was also induced after the second distraction and was sustained at day 7 (p < 0.048). Repeated loading weakened the capsular ligament with lower vertebral displacement (p = 0.041) and peak force (p = 0.014) at tissue rupture. Spinal glial activation was also induced after repeated loading. Together, these mechanical, physiological, and neurological findings demonstrate that repeated loading of the facet joint even within physiologic ranges of motion can be sufficient to induce pain, spinal inflammation, and alter capsular mechanics similar to a more injurious loading exposure.

Mid-term to long-term outcome of the open Bankart repair for recurrent traumatic anterior dislocation of the shoulder

BACKGROUND

The purpose of this study was to assess the long-term outcome of the open Bankart repair for traumatic, recurrent anterior dislocation of the shoulder by evaluation of recurrence, range of motion, return to sports, arthritis, patient satisfaction, and outcome measures.

METHODS

Of 162 patients, 127 patients (mean age, 31 years) were evaluated at a mean follow-up of 17.1 years (5-24) after undergoing an open Bankart repair using suture anchors. An independent orthopedic surgeon obtained a history and examined each for range of motion. Radiographs for arthritis and osteolysis were obtained unless the patient refused. Questionnaires including return to sports and function as well as satisfaction and outcome measures were completed by all patients.

RESULTS

There was 1 recurrent dislocation (0.8%) and 1 recurrent subluxation (0.8%) but no pain or apprehension. All remaining shoulders were stable. Compared with the normal shoulder, there was statistical difference in external rotation in abduction and at the side as well as in internal rotation but not in forward elevation or abduction. However, no patient considered any measurable loss functionally significant. Of 107 patients who participated in sports, 98 returned to the sport; 7 of the remaining 9 discontinued for reasons other than the shoulder. There were 91 patients who agreed to radiography; 48 had normal findings, 34 had mild arthrosis, 9 had moderate arthrosis, and none had severe arthrosis. Mean postoperative outcome scores were as follows: American Shoulder and Elbow Surgeons, 93.53; Rowe, 91.41; and Western Ontario Shoulder Instability Index, 327.7. There were 125 patients who were satisfied and would undergo the procedure again.

CONCLUSION

The open Bankart procedure remains the standard by which other techniques can be measured for treatment of recurrent, traumatic anterior dislocation of the shoulder.

Using mouse models to investigate the pathophysiology, treatment, and prevention of post-traumatic osteoarthritis

Post-traumatic osteoarthritis (PTOA) is defined by its development after joint injury. Factors contributing to the risk of PTOA occurring, the rate of progression, and degree of associated disability in any individual, remain incompletely understood. What constitutes an "OA-inducing injury" is not defined. In line with advances in the traumatic brain injury field, we propose the scope of PTOA-inducing injuries be expanded to include not only those causing immediate structural damage and instability (Type I), but also those without initial instability/damage from moderate (Type II) or minor (Type III) loading severity. A review of the literature revealed this full spectrum of potential PTOA subtypes can be modeled in mice, with 27 Type I, 6 Type II, and 4 Type III models identified. Despite limitations due to cartilage anatomy, joint size, and bio-fluid availability, mice offer advantages as preclinical models to study PTOA, particularly genetically modified strains. Histopathology was the most common disease outcome, cartilage more frequently studied than bone or synovium, and meniscus and ligaments rarely evaluated. Other methods used to examine PTOA included gene expression, protein analysis, and imaging. Despite the major issues reported by patients being pain and biomechanical dysfunction, these were the least commonly measured outcomes in mouse models. Informative correlations of simultaneously measured disease outcomes in individual animals, was rarely done in any mouse PTOA model. This review has identified knowledge gaps that need to be addressed to increase understanding and improve prevention and management of PTOA. Preclinical mouse models play a critical role in these endeavors. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:424-439, 2017.

Load-induced changes in the diffusion tensor of ovine anulus fibrosus: A pilot MRI study

PURPOSE

To assess the feasibility of diffusion tensor imaging (DTI) for evaluating changes in anulus fibrosus (AF) microstructure following uniaxial compression.

MATERIALS AND METHODS

Six axially aligned samples of AF were obtained from a merino sheep disc; two each from the anterior, lateral, and posterior regions. The samples were mechanically loaded in axial compression during five cycles at a rate and maximum compressive strain that reflected physiological conditions. DTI was conducted at 7T for each sample before and after mechanical testing.

RESULTS

The mechanical response of all samples in unconfined compression was nonlinear. A stiffer response during the first loading cycle, compared to the remaining cycles, was observed. Change in diffusion parameters appeared to be region-dependent. The mean fractional anisotropy increased following mechanical testing. This was smallest in the lateral (2% and 9%) and largest in the anterior and posterior samples (17-25%). The mean average diffusivity remained relatively constant (<2%) after mechanical testing in the lateral and posterior samples, but increased (by 5%) in the anterior samples. The mean angle made by the principal eigenvector with the spine axis in the lateral samples was 73° and remained relatively constant (<2%) following mechanical testing. This angle was smaller in the anterior (55°) and posterior (47°) regions and increased by 6-16° following mechanical testing.

CONCLUSION

These preliminary results suggest that axial compression reorients the collagen fibers, such that they become more consistently aligned parallel to the plane of the endplates.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;45:1723-1735.

Fundamental biomechanics of the spine--What we have learned in the past 25 years and future directions

Since the publication of the 2nd edition of White and Panjabi׳s textbook, Clinical Biomechanics of the Spine in 1990, there has been considerable research on the biomechanics of the spine. The focus of this manuscript will be to review what we have learned in regards to the fundamentals of spine biomechanics. Topics addressed include the whole spine, the functional spinal unit, and the individual components of the spine (e.g. vertebra, intervertebral disc, spinal ligaments). In these broad categories, our understanding in 1990 is reviewed and the important knowledge or understanding gained through the subsequent 25 years of research is highlighted. Areas where our knowledge is lacking helps to identify promising topics for future research. In this manuscript, as in the White and Panjabi textbook, the emphasis is on experimental research using human material, either in vivo or in vitro. The insights gained from mathematical models and animal experimentation are included where other data are not available. This review is intended to celebrate the substantial gains that have been made in the field over these past 25 years and also to identify future research directions.

Quantification of strain induced damage in medial collateral ligaments

In the past years, there have been several experimental studies that aimed at quantifying the material properties of articular ligaments such as tangent modulus, tensile strength, and ultimate strain. Little has been done to describe their response to mechanical stimuli that lead to damage. The purpose of this experimental study was to characterize strain-induced damage in medial collateral ligaments (MCLs). Displacement-controlled tensile tests were performed on 30 MCLs harvested from Sprague Dawley rats. Each ligament was monotonically pulled to several increasing levels of displacement until complete failure occurred. The stress-strain data collected from the mechanical tests were analyzed to determine the onset of damage and its evolution. Unrecoverable changes such as increase in ligament's elongation at preload and decrease in the tangent modulus of the linear region of the stress-strain curves indicated the occurrence of damage. Interestingly, these changes were found to appear at two significantly different threshold strains (P&lt;0.05). The mean threshold strain that determined the increase in ligament's elongation at preload was found to be 2.84% (standard deviation (SD) = 1.29%) and the mean threshold strain that caused the decrease in the tangent modulus of the linear region was computed to be 5.51% (SD = 2.10%), respectively. The findings of this study suggest that the damage mechanisms associated with the increase in ligament's elongation at preload and decrease in the tangent modulus of the linear region in the stress-strain curves in MCLs are likely different.

Open Bankart repair for revision of failed prior stabilization: outcome analysis at a mean of more than 10 years

BACKGROUND

The purpose of this study was to analyze the outcome of open Bankart repair for failed stabilization surgery at a mean follow-up of >10 years.

MATERIALS AND METHODS

Thirty patients underwent revision open Bankart repair by a single surgeon for failed prior stabilization surgery, with a standard technique and postoperative rehabilitation. All patients were referred by other surgeons. Evaluation was by an independent examiner, at a mean follow-up of 10.2 years. Evaluation included a history, physical examination for range of motion, outcome scores, recurrence, return to athletics, and radiographic examination.

RESULTS

All cases had persistent Bankart and Hill-Sachs lesions. Failures included 14 patients with a failed single arthroscopic Bankart repair; 1 patient with 2 failed arthroscopic Bankart repairs; 1 patient with an arthroscopic failure and an open Bankart repair; 7 patients with failed open Bankart repairs; and 1 patient with a failed open Bankart repair, then a failed arthroscopic attempt. Two patients had had thermal capsulorrhaphy; 2 others had staple capsulorrhaphy, 1 with an open capsular shift and 1 after a failed arthroscopic Bankart repair, an open Bankart repair, and then a coracoid transfer. All arthroscopic Bankart repairs had anchors placed medial and superior on the glenoid neck. Mean motion loss compared with the normal contralateral side was as follows: elevation 1.15°, abduction 4.2°, external rotation at the side 3.2°, external rotation in abduction 5.1°, and internal rotation 0.6 vertebral levels (NS). No patient had an apprehension sign, pain, or instability. Of 23 who played sports, 22 resumed after. Outcomes scores were as follows: American Shoulder and Elbow Surgeons, 89.44; Rowe, 86.67; Western Ontario Shoulder Instability Index, 476.26. On radiographic examination, there were 13 normal radiographs and 7 with mild, 2 with moderate, and 0 with severe arthritic changes.

CONCLUSION

The open Bankart repair offers a reliable, consistently successful option for revision of failed stabilizations.

First-time anterior shoulder dislocations: should they be arthroscopically stabilised?

The glenohumeral joint is inherently unstable because the large humeral head articulates with the small shadow glenoid fossa. Traumatic anterior dislocation of the shoulder is a relatively common athletic injury, and the high frequency of recurrent instability in young athletes after shoulder dislocation is discouraging to both the patient and the treating physician. Management of primary traumatic shoulder dislocation remains controversial. Traditionally, treatment involves initial immobilisation for 4-6 weeks, followed by functional rehabilitation. However, in view of the high recurrence rates associated with this traditional approach, there has been an escalating interest in determining whether immediate surgical intervention can lower the rate of recurrent shoulder dislocation, improving the patient's quality of life. This review article aims to provide an overview of the nature and pathogenesis of first-time primary anterior shoulder dislocations, the widely accepted management modalities, and the efficacy of primary surgical intervention in first-time primary anterior shoulder dislocations.

Subfailure overstretch induces persistent changes in the passive mechanical response of cerebral arteries

Cerebral blood vessels are critical in maintaining the health of the brain, but their function can be disrupted by traumatic brain injury (TBI). Even in cases without hemorrhage, vessels are deformed with the surrounding brain tissue. This subfailure deformation could result in altered mechanical behavior. This study investigates the effect of overstretch on the passive behavior of isolated middle cerebral arteries (MCAs), with the hypothesis that axial stretch beyond the in vivo length alters this response. Twenty nine MCA sections from 11 ewes were tested. Vessels were subjected to a baseline test consisting of an axial stretch from a buckled state to 1.05* in vivo stretch (λIV) while pressurized at 13.3 kPa. Specimens were then subjected to a target level of axial overstretch between 1.05*λIV (λz = 1.15) and 1.52*λIV (λz = 1.63). Following overstretch, baseline tests were repeated immediately and then every 10 min, for 60 min, to investigate viscoelastic recovery. Injury was defined as an unrecoverable change in the passive mechanical response following overstretch. Finally, pressurized MCAs were pulled axially to failure. Post-overstretch response exhibited softening such that stress values at a given level of stretch were lower after injury. The observed softening also generally resulted in increased non-linearity of the stress-stretch curve, with toe region slope decreasing and large deformation slope increasing. There was no detectable change in reference configuration or failure values. As hypothesized, the magnitude of these alterations increased with overstretch severity, but only once overstretch exceeded 1.2*λIV (p < 0.001). These changes were persistent over 60 min. These changes may have significant implications in repeated TBI events and in increased susceptibility to stroke post-TBI.

Effects of simulated injury on the anteroinferior glenohumeral capsule

Glenohumeral dislocation results in permanent deformation (nonrecoverable strain) of the glenohumeral capsule which leads to increased range of motion and recurrent instability. Minimal research has examined the effects of injury on the biomechanical properties of the capsule which may contribute to poor patient outcome following repair procedures. The objective of this study was to determine the effect of simulated injury on the stiffness and material properties of the AB-IGHL during tensile deformation. Using a combined experimental and computational methodology, the stiffness and material properties of six AB-IGHL samples during tensile elongation were determined before and after simulated injury. The AB-IGHL was subjected to 12.7 ± 3.2 % maximum principal strain which resulted in 2.5 ± 0.9 % nonrecoverable strain. The linear region stiffness and modulus of stress-stretch curves between the normal (52.4 ± 30.0 N/mm, 39.1 ± 26.6 MPa) and injured (64.7 ± 21.3 N/mm, 73.5 ± 53.8 MPa) AB-IGHL increased significantly (p = 0.03, p = 0.04). These increases suggest that changes in the tissue microstructure exist following simulated injury. The injured tissue could contain more aligned collagen fibers and may not be able to support a normal range of joint motion. Collagen fiber kinematics during simulated injury will be examined in the future.

Management of mid-season traumatic anterior shoulder instability in athletes

Shoulder dislocation and subluxation injuries are common in young athletes and most frequently occur during the competitive season. Controversy exists regarding optimal treatment of an athlete with an in-season shoulder dislocation, and limited data are available to guide treatment. Rehabilitation may facilitate return to sport within 3 weeks, but return is complicated by a moderate risk of recurrence. Bracing may reduce the risk of recurrence, but it restricts motion and may not be tolerated in patients who must complete certain sport-specific tasks such as throwing. Surgical management of shoulder dislocation or subluxation with arthroscopic or open Bankart repair reduces the rate of recurrence; however, the athlete is unable to participate in sport for the remainder of the competitive season. When selecting a management option, the clinician must consider the natural history of shoulder instability, pathologic changes noted on examination and imaging, sport- and position-specific demands, duration of treatment, and the athlete's motivation.

Preconditioning is correlated with altered collagen fiber alignment in ligament

Although the mechanical phenomena associated with preconditioning are well-established, the underlying mechanisms responsible for this behavior are still not fully understood. Using quantitative polarized light imaging, this study assessed whether preconditioning alters the collagen fiber alignment of ligament tissue, and determined whether changes in fiber organization are associated with the reduced force and stiffness observed during loading. Collagen fiber alignment maps of facet capsular ligaments (n = 8) were generated before and after 30 cycles of cyclic tensile loading, and alignment vectors were correlated between the maps to identify altered fiber organization. The change in peak force and tangent stiffness between the 1st and 30th cycle were determined from the force-displacement response, and the principal strain field of the capsular ligament after preconditioning was calculated from the fiber alignment images. The decreases in peak ligament force and tangent stiffness between the 1st and 30th cycles of preconditioning were significantly correlated (R ≥ 0.976, p < 0.0001) with the change in correlation of fiber alignment vectors between maps. Furthermore, the decrease in ligament force was correlated with a rotation of the average fiber direction toward the direction of loading (R = -0.730; p = 0.0396). Decreases in peak force during loading and changes in fiber alignment after loading were correlated (p ≤ 0.0157) with the average principal strain of the unloaded ligament after preconditioning. Through the use of a vector correlation algorithm, this study quantifies detectable changes to the internal microstructure of soft tissue produced by preconditioning and demonstrates that the reorganization of the capsular ligament's collagen fiber network, in addition to the viscoelasticity of its components, contribute to how the mechanical properties of the tissue change during its preconditioning.

Arthroscopic Bankart repair combined with remplissage technique for the treatment of anterior shoulder instability with engaging Hill-Sachs lesion: a report of 49 cases with a minimum 2-year follow-up

BACKGROUND

Engaging Hill-Sachs lesions are known to be a risk factor for recurrence dislocation after arthroscopic repair in patients with anterior shoulder instability. For a large engaging Hill-Sachs lesion, arthroscopic remplissage is a solution.

HYPOTHESIS

Arthroscopic Bankart repair combined with the Hill-Sachs remplissage technique can achieve good results without significant impairment of shoulder function.

STUDY DESIGN

Case Series; Level of evidence, 4.

METHODS

Forty-nine consecutive patients who underwent arthroscopic Bankart repair and Hill-Sachs remplissage for anterior shoulder instability were followed up for a mean duration of 29.0 months (range, 24-35 months). There were 42 males and 7 females with a mean age of 28.4 years (range, 16.7-54.7 years). All patients had diagnosed traumatic unidirectional anterior shoulder instability with a bony lesion of glenoid and an engaging Hill-Sachs lesion. Physical examination, radiographs, and magnetic resonance imaging were performed during postoperative follow-up. The American Shoulder and Elbow Surgeons (ASES) score, Constant score, and Rowe score were used to evaluate shoulder function.

RESULTS

The active forward elevation increased a mean of 8.0° (range, -10° to 80°) postoperatively. However, the patients lost 1.9° (range, -40° to 30°) of external rotation to the side. Significant improvement was detected with regard to the ASES score (84.7 vs 96.0, P < .001), Constant score (93.3 vs 97.8, P = .005), and Rowe score (36.8 vs 89.8, P < .001).There were 1 redislocation, 2 subluxations, and 1 patient with a positive apprehension test; the overall failure rate was 8.2% (4 of 49). Successful healing of the infraspinatus tendon within the Hill-Sachs lesion was shown by magnetic resonance imaging.

CONCLUSION

Arthroscopic Bankart repair combined with Hill-Sachs remplissage can restore shoulder stability without significant impairment of shoulder function in patients with engaging Hill-Sachs lesions.

The effect of cyclic loading simulating oscillatory joint mobilization on the posterior capsule of the glenohumeral joint: a cadaveric study

STUDY DESIGN

Experimental laboratory design.

OBJECTIVES

To examine the effect of force and repetition during oscillatory joint mobilizations on the posterior capsule of the glenohumeral joint.

BACKGROUND

The optimal external force and frequency to be used during joint mobilization to elongate the posterior capsule of the glenohumeral joint has yet to be identified.

METHODS

Twenty-one posterior capsules were harvested from fresh-frozen shoulders. A cyclic loading test simulating oscillatory posterior joint mobilization on the shoulder specimens was performed with a material testing machine. The specimens were assigned to 3 different loading groups simulating joint mobilization in the toe (5 N), transition (20 N), and beginning of the linear regions (40 N) of the load displacement curve. Displacement of the humeral head at an applied load of 5 N was recorded at the 1st, 100th, 200th, 300th, 400th, 500th, and 600th cycles and at 1 hour after completion of the cyclic loading. Furthermore, stiffness was calculated after the 1st and 600th cycles and 1 hour after testing.

RESULTS

Humeral head displacement was significantly greater for the 100th to 600th cycle, compared to the 1st cycle, for all 3 loading groups. Significant increases in displacement and stiffness were observed between the 1st cycle and 1 hour after completion of the cyclic tests for both the 20-N and 40-N loading groups.

CONCLUSION

While oscillatory joint mobilization to a force of 5 N resulted in temporary elongation of the posterior capsule, mobilization to loads of 20 and 40 N resulted in sustained elongation of the capsule for up to 1 hour. Our findings also suggest that mobilization up to loads that represent the beginning of the linear region of the load displacement curve could be performed without serious damage to the posterior capsule.

Management of shoulder instability in in-season athletes

Although shoulder instability is common in young athletes, there are limited prospective data to guide treatment for competitive athletes who sustain a dislocation mid-season. The management of athletes during their competitive season requires an understanding of the natural history of shoulder instability, the specific needs of the injured athlete (eg, specific sport, player position), and the duration of treatment. Rehabilitation can enable an athlete with a shoulder dislocation to return to play within 3 weeks of injury. Bracing is an option, but it can result in restricted glenohumeral motion and thereby possibly affect performance. Surgical stabilization should be considered for the athlete with recurrent instability or inability to perform; however, this frequently results in the termination of the player's season. In this article, we review the available literature to help guide physicians treating athletes with shoulder instability.

The American Society of Shoulder and Elbow Therapists' consensus rehabilitation guideline for arthroscopic anterior capsulolabral repair of the shoulder

This manuscript describes the consensus rehabilitation guideline developed by the American Society of Shoulder and Elbow Therapists. The purpose of this guideline is to facilitate clinical decision making during the rehabilitation of patients following arthroscopic anterior capsulolabral repair of the shoulder. This guideline is centered on the principle of the gradual application of stress to the healing capsulolabral repair through appropriate integration of range of motion, strengthening, and shoulder girdle stabilization exercises during rehabilitation and daily activities. Components of this guideline include a 0- to 4-week period of absolute immobilization, a staged recovery of full range of motion over a 3-month period, a strengthening progression beginning at postoperative week 6, and a functional progression for return to athletic or demanding work activities between postoperative months 4 and 6. This document represents the first consensus rehabilitation guideline developed by a multidisciplinary society of international rehabilitation professionals specifically for the postoperative care of patients following arthroscopic anterior capsulolabral repair of the shoulder.

Characterization of the Fatigue Behavior of the Medial Collateral Ligament Utilizing Traditional and Novel Mechanical Variables for the Assessment of Damage Accumulation

Ligaments are regularly subjected to repetitive loading in vivo. Typically, mechanical studies focus on repetitive loading protocols of short duration, while those characterizing damage accumulation over a longer duration (i.e., fatigue studies) are lacking. The aims of this study were as follows: (a) to demonstrate that damage does accumulate in ligament tissue subjected to repetitive loading and (b) to evaluate existing and new methods for characterizing fatigue damage accumulation. It was hypothesized that ligaments would accumulate damage with repetitive loading as evidenced by failure at stresses well below ultimate tensile strength, creep curve discontinuities, and by reductions in stiffness during loading. Eight normal medial collateral ligaments from female New Zealand white rabbits were cycled in tension, between 0 MPa and 28 MPa, to failure or until 259,200 cycles, whichever came first. Medial collateral ligaments that did not fail were subsequently loaded to failure. Displacement rates (dlmax/dt) as well as primary, secondary, and tertiary creeps were monitored as indices of damage accumulation and impending mechanical failure. Additionally, the relative utilities of tangent, secant, and chord stiffness parameters were critically evaluated. Finally, new uses for the second derivative of force-displacement data were explored. Three out of eight ligaments failed during testing, demonstrating that ligaments can fail in fatigue under moderate tensile stress in vitro. The evaluation of displacement rates (dlmax/dt), as well as primary through tertiary creep patterns, were not well suited to predicting failure in normal ligaments until rupture was all but imminent. Tangent stiffness, which was calculated from a mathematically defined start of the “linear region,” was surprisingly constant throughout testing. Secant stiffness dropped in a predictable fashion, providing a global indicator of tissue stiffness, but did not provide any insight into fiber mechanics. Chord stiffness, on the other hand, appeared to be sensitive to fiber recruitment patterns. The second derivative of force-displacement data proved to be a useful means of (a) objectively defining the start of the linear region and (b) inferring changes in fiber recruitment patterns within ligament tissue. Tangent, secant, and chord stiffnesses highlight different attributes of ligament responses to loading; hence these parameters cannot be used interchangeably. Additionally, the second derivative of the force-displacement curve was introduced as a useful descriptive and analytical tool.

Relationships between total and non-recoverable strain fields in glenohumeral capsule during shoulder subluxation

Non-recoverable strain in the glenohumeral capsule is of prime clinical significance, but the factors that contribute to non-recoverable strain are largely unknown. This study examined the relationship between total and non-recoverable strain in the antero-inferior glenohumeral capsule using an experimental model. Maximum principal total strain alone explained up to 35% of the variance in non-recoverable strain. A multiple regression model, including variables for lateral position and specimen, explained 50% of the variance in non-recoverable strain. Both linear and quadratic terms for maximum principal total strain were significant predictors of non-recoverable strain. The correlation of total and non-recoverable strain directions exhibited a slope of nearly 1:1. The regression model showed that non-recoverable strain is likely to be low for small levels of total strain, and increase non-linearly with total strain. Non-recoverable strain tended to be higher closer to the glenoid, even when controlling for total strain. Minimum principal total strain was not a significant predictor of non-recoverable strain for the cases examined, indicating that the glenohumeral capsule may demonstrate uniaxial failure behavior even when loaded biaxially. These results are important toward prediction of non-recoverable strain in computational models of glenohumeral subluxation, as well as for theoretical models of ligament failure.

[Multidirectional shoulder instability. Nonoperative and operative treatment strategies]

Multidirectional shoulder instability (MDI) is characterized by symptomatic instability in at least two directions, often with a global hyperlaxity. The etiology is mostly atraumatic, with an acquired or congenital enlarged capsular volume or redundancy. Muscular imbalances and pathologic patterns of muscle recruitment and motion are also common findings. Traumatic onset of MDI is rare, although capsulolabral lesions can be found during surgery. Therapy aims at a normalization of muscle balance/weakness and motion patterns. If conservative treatment fails, arthroscopic capsular plication techniques, in combination with repair of labral and interval lesions, can accomplish results similar to those of classic open techniques but with reduced morbidity and invasiveness.

Treating the athlete with anterior shoulder instability

Acute traumatic anterior shoulder dislocation is a relatively common occurrence in the athletic population. Although the overall incidence of traumatic shoulder instability in the general population is only 1.7%, the incidence in a high physical-demand population is two-fold greater. Instability often becomes a recurrent pattern and jeopardizes athletic performance and participation. A thorough assessment and discussion with the patient with respect to treatment decision-making are critical in the management of anterior shoulder instability.

Subrupture tendon fatigue damage

The mechanical and microstructural bases of tendon fatigue, by which damage accumulates and contributes to degradation, are poorly understood. To investigate the tendon fatigue process, rat flexor digitorum longus tendons were cyclically loaded (1-16 N) until reaching one of three levels of fatigue damage, defined as peak clamp-to-clamp strain magnitudes representing key intervals in the fatigue life: i) Low (6.0%-7.0%); ii) Moderate (8.5%-9.5%); and iii) High (11.0%-12.0%). Stiffness, hysteresis, and clamp-to-clamp strain were assessed diagnostically (by cyclic loading at 1-8 N) before and after fatigue loading and following an unloaded recovery period to identify mechanical parameters as measures of damage. Results showed that tendon clamp-to-clamp strain increased from pre- to post-fatigue loading significantly and progressively with the fatigue damage level (p <or= 0.010). In contrast, changes in both stiffness and hysteresis were significant only at the High fatigue level (p <or= 0.043). Correlative microstructural analyses showed that Low level of fatigue was characterized by isolated, transverse patterns of kinked fiber deformations. At higher fatigue levels, tendons exhibited fiber dissociation and localized ruptures of the fibers. Histomorphometric analysis showed that damage area fraction increased significantly with fatigue level (p <or= 0.048). The current findings characterized the sequential, microstructural events that underlie the tendon fatigue process and indicate that tendon deformation can be used to accurately assess the progression of damage accumulation in tendons.

Effects of posterior-inferior capsular plications in range of motion in arthroscopic anterior Bankart repair: a prospective randomized clinical study

The effects of posterior plications associated with anterior shoulder instability surgery are still unclear both on shoulder range of motion (ROM) and on recurrence rate. The objective of this randomized study is to evaluate the influence of posterior-inferior plications, performed in association with repair of anterior Bankart lesion, on gleno-humeral (GH) range of motion. In a 24-month period, 40 patients were prospectively enrolled in this study. The criteria for inclusion were age between 17 and 40 years, traumatic unidirectional instability, no previous shoulder surgery, no more than three episodes of dislocation, no relevant glenoid bone deficiency, no clinical evidence of pathological anterior inferior laxity (measured with external rotation with the arm at the side inferior to 90 degrees and Gagey sign negative) and arthroscopic finding of isolated anterior Bankart lesion. A total of 20 patients (group A) were randomized to treat Bankart lesion using three bioadsorbable anchors loaded with a #2 braided polyester suture. In 20 randomized patients (group B) two posterior-inferior capsular plications performed with a #1 polidioxanone suture without any capsular shift were added to the same anterior capsulorraphy performed in group A. Postoperative rehabilitation protocol was the same for all 40 patients. Patients were examined preoperatively and at a 2-year follow-up by a single independent expert physician unaware of the surgical procedure. GH ROM, Constant, UCLA and ASES rating scores as well as recurrence of instability were recorded. At follow-up, forward flexion (FF) decreased by a mean value of 14.5 degrees (median -10 degrees ; range -5 degrees to -35 degrees ; P < 0.001) in group B and increased by a mean value of 3.5 degrees (median 0 degrees ; range -25 degrees to 40 degrees ; P < 0.312) in group A; external rotation with arm adducted (ER1) increased by a mean value of 1.8 degrees (median 0 degrees ; range -15 degrees to 30 degrees ; P < 0.924) in group B, and increased by a mean value of 2.6 degrees (median 2.5 degrees ; range -38 degrees to 40 degrees ; P < 0.610) in group A; external rotation with arm abducted at 90 degrees (ER2) decreased by a mean value of 2.9 degrees (median 0 degrees ; range: -20 degrees to 10 degrees ; P < 0.161) in group B and increased by a mean value of 0.7 degrees (median 0 degrees ; range -30 degrees to 25 degrees ; P < 0.837) in group A; the IR2 decreased by a mean value of 2.4 degrees (median -3.5 degrees ; range -15 degrees to 10 degrees ; P < 0.167) in group B and increased by a mean value of 2.2 degrees (median 0 degrees ; range -20 degrees to 30 degrees ; P < 0.456) in group A. The UCLA mean score gains by 43.1% (median 40; P < 0.001) relatively, and of 45.2% relatively (median 40; P < 0.001), respectively, in group B and A, ASES mean score relatively gains by 21.7% (median 21.2%; P < 0.001) in group B, and of 19.2% (median 18.9%; P < 0.001) in group A, and Constant mean score improves by 20.2% (median 16.5; P < 0.001) in group B, and 10.2% (median 8.4%; P < 0.001) in group A. Thus, the only statistical significant differences were the reduction of forward flexion in group B and the improvements of the scores in both groups. No recurrence of instability was found in the plicated group, while in the non-plicated group we had one traumatic recurrence. In conclusion, arthroscopic posterior-inferior plications associated with a Bankart lesion repair in a selected group of patients seem to reduce only FF, without any effect on rotation. A longer follow-up and a larger number of patients are needed to give definitive conclusions on the benefit to the recurrence rate.

Altered collagen fiber kinematics define the onset of localized ligament damage during loading

Detecting the initiation of mechanical injury to biological tissue, and not just its ultimate failure, is critical to a sensitive and specific characterization of tissue tolerance, development of quantitative relationships between macro- and microstructural tissue responses, and appropriate interpretation of physiological responses to loading. We have developed a novel methodological approach to detect the onset and spatial location of structural damage in collagenous soft tissue, before its visible rupture, via identification of atypical regional collagen fiber kinematics during loading. Our methods utilize high-speed quantitative polarized light imaging to identify the onset of tissue damage in ligament regions where mean collagen fiber rotation significantly deviates from its behavior during noninjurious loading. This technique was validated by its ability to predict the location of visible rupture ( P = 0.0009). This fiber rotation-based metric of damage identifies potential facet capsular ligament injury beginning well before rupture, at 51 ± 12% of the displacement required to produce tissue failure. Although traditional macroscale strain metrics fail to identify the location of microstructural damage, initial injury detection determined by altered fiber rotation was significantly correlated ( R = 0.757, P = 0.049) with tissue yield (defined by a decrease in stiffness), supporting the capabilities of this method. Damaged regions exhibited higher variance in fiber direction than undamaged regions ( P = 0.0412).

An analysis of capsular area in patients with anterior, posterior, and multidirectional shoulder instability

BACKGROUND

Although increased capsular volume has been implicated in shoulder instability, there is a paucity of clinical evidence to quantify the size of the capsule with specific instability conditions of the shoulder.

HYPOTHESIS

Shoulder capsular area, as measured by magnetic resonance arthrography, is increased with specific patterns of shoulder instability.

STUDY DESIGN

Cross-sectional study; Level of evidence, 4.

METHODS

During an 8-month period, all patients with a diagnosis of anterior (n = 19), posterior (n = 14), or multidirectional (n = 13) instability of the shoulder and who were assessed with a magnetic resonance arthrogram were reviewed. A group of 10 control patients without clinical instability were also identified. The magnetic resonance arthrograms of all groups were randomly mixed, and 5 reviewers recorded measures of capsular length and area and determined labral abnormalities. The magnetic resonance arthrogram measurements were compared between groups, and interobserver agreement was determined.

RESULTS

The cross-sectional area of the capsule was increased in patients with posterior (P = .017) or multidirectional instability (P = .021) versus controls, but not in patients with anterior instability. Additionally, the posteroinferior cross-sectional area was increased in patients with posterior (P = .001), multidirectional (P = .003), and anterior (P = .008) instability. In patients with a posterior labral tear, the mean axial (P = .043) and mean posteroinferior sagittal cross-sectional area (P = .011) was increased, but there were no differences in cross-sectional area for those with an anterior labral tear. The overall interobserver reliability was very good (correlation coefficient range, 0.68-0.94).

CONCLUSION

Our results reinforce the concept that capsular elongation and laxity, either preexisting or acquired, play a role in certain instability conditions of the shoulder. Additional work is needed to determine how to correlate surgical decision making with the cross-sectional area measurements demonstrated in this study.

Long-term outcome of acute versus chronic bony Bankart lesions managed arthroscopically

BACKGROUND

Acute bony Bankart lesions can be successfully treated with an arthroscopic approach to fix the avulsed bone fragment to the glenoid without grafting.

HYPOTHESIS

Chronic bony Bankart lesions with glenoid defects can be repaired arthroscopically in the same manner as acute lesions.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Over 6 years, 215 of 406 unstable shoulders were managed with an arthroscopic approach. A bony Bankart lesion was detected in 68 (31.6%); of these, 41 were operated on <3 months after the first dislocation (acute group) and 27 at a longer interval (chronic group). Preoperative evaluation was by radiography and computed tomography. A modified Bankart technique was used to repair the capsulolabral complex and fix the avulsed bone fragment to the healthy glenoid with suture anchors. Long-term follow-up data (at least 4 years) were available for 65 patients (41 acute and 24 chronic). Preoperative and postoperative Rowe scores were compared.

RESULTS

One patient from the acute group (2.4%) and 1 patient in the chronic group (4.2%) experienced traumatic redislocation. The mean postoperative Rowe scores increased, from 59 to 92 and from 43.5 to 61, respectively (both P < .001).

CONCLUSION

An arthroscopic procedure using suture anchors appears to enable successful treatment of acute bony Bankart lesions. Chronic lesions had less favorable outcomes.

Differences in scapular upward rotation between baseball pitchers and position players

BACKGROUND

Baseball pitchers have been reported to have an increased prevalence of shoulder injury compared with position players such as infielders and outfielders. Furthermore, insufficient scapular upward rotation has been empirically linked with several of these shoulder disorders. However, the difference in scapular upward rotation between pitchers and position players is not known.

HYPOTHESIS

Pitchers will have decreased scapular upward rotation of their dominant shoulders compared with position players.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Dominant shoulder scapular upward rotation was measured with the arm at rest and at 60 degrees , 90 degrees , and 120 degrees of humeral elevation among 15 professional baseball pitchers and 15 position players with no recent history of upper extremity injury.

RESULTS

Independent t tests showed pitchers have significantly less scapular upward rotation at 60 degrees (3.9 degrees , P = .011) and 90 degrees (4.4 degrees , P = .009) of humeral elevation compared with position players.

CONCLUSION

Baseball pitchers have less scapular upward rotation than do position players, specifically at humeral elevation angles of 60 degrees and 90 degrees .

CLINICAL RELEVANCE

This decrease in scapular upward rotation may compromise the integrity of the glenohumeral joint and place pitchers at an increased risk of developing shoulder injuries compared with position players. As such, pitchers may benefit from periscapular stretching and strengthening exercises to assist with increasing scapular upward rotation.

Use of a movement system impairment diagnosis for physical therapy in the management of a patient with shoulder pain

STUDY DESIGN

Case report.

BACKGROUND

Based on our assumption that subtle deviations in the precision of shoulder movement cause tissue injury, we have developed a set of movement-related diagnoses for shoulder problems. The purposes of this case report are to (1) illustrate the use of a movement system impairment (MSI) diagnosis in a patient with shoulder pain, (2) illustrate how the MSI diagnosis guided treatment prescription, and (3) describe the outcomes of treatment based on a MSI diagnosis for shoulder impingement.

CASE DESCRIPTION

The patient was a 46-year-old female with recurrent right-shoulder pain of 2 months' duration. Initially she reported that her pain was constant but varied in intensity and had increased gradually over time. Shoulder pain limited her ability to bicycle and perform reaching movements. The systematic clinical examination for assessing the patient's preferred alignment and movements included items related to pain, alignment, movement, muscle length, muscle strength, and function. Based on the examination, the MSI diagnosis was humeral anterior glide with scapular downward rotation. The treatment focused on correction of her shoulder alignment, functional movements, and associated impairments of muscle function. The patient was seen 4 times in 6 weeks.

OUTCOMES

The patient was pain free with all activities at 1 month and there was no recurrence of symptoms 3 years after the last physical therapy visit.

DISCUSSION

A MSI diagnosis of humeral anterior glide with scapular downward rotation guided physical therapy treatment and resulted in positive short- and long-term outcomes.

Glenohumeral internal rotation deficits in professional pitchers enrolled in an internal rotation stretching program

BACKGROUND

Repetitive throwing motion creates increased external rotation and decreased internal rotation in the glenohumeral joint. There is controversy regarding the contribution of osseous and soft tissue adaptations to these changes in rotation.

OBJECTIVE

To evaluate internal rotation deficits in the professional baseball thrower's shoulder and determine the impact of an internal rotation stretch program on that deficit.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Eighty-five male professional pitchers were evaluated in this study. Players were divided into 2 groups based on length of participation in an appropriate internal rotation stretch program. Data were collected on internal and external rotations and total range of motion in both dominant and nondominant arms using a goniometer. Internal rotation deficit (the lack of internal rotation relative to the opposite side) was calculated. Generalized comparative statistical tests were used.

RESULTS

Pitchers with 3 or more years in a stretch program (group 1) had greater internal rotation (74.3 degrees vs 54.3 degrees ) and greater total range of motion (217.0 degrees vs 194.2 degrees ) in dominant shoulders than did pitchers with less than 3 years (group 2). Total range of motion was greater in the dominant than in the nondominant arm for group 1. Internal rotation deficit in dominant arms was significantly greater for group 2 than for group 1. The analysis of dominant arm rotation relative to years in an internal rotation stretching program for pitchers in both groups showed a progressive increase in both internal rotation and total arc of motion with the number years in such a program plateauing after year 3.

CONCLUSION

The throwing motion shifts the total arc of motion toward external rotation and diminishes internal rotation. The increased external rotation may be attributable to increased humeral retroversion. The internal rotation deficit, however, is caused by soft tissue adaptations that can be addressed by consistent participation in a stretching program focused on internal rotation.

Cervical facet capsular ligament yield defines the threshold for injury and persistent joint-mediated neck pain

The cervical facet joint has been identified as a source of neck pain, and its capsular ligament is a likely candidate for injury during whiplash. Many studies have shown that the mechanical properties of ligaments can be altered by subfailure injury. However, the subfailure mechanical response of the facet capsular ligament has not been well defined, particularly in the context of physiology and pain. Therefore, the goal of this study was to quantify the structural mechanics of the cervical facet capsule and define the threshold for altered structural responses in this ligament during distraction. Tensile failure tests were preformed using isolated C6/C7 rat facet capsular ligaments (n=8); gross ligament failure, the occurrence of minor ruptures and ligament yield were measured. Gross failure occurred at 2.45+/-0.60 N and 0.92+/-0.17 mm. However, the yield point occurred at 1.68+/-0.56 N and 0.57+/-0.08 mm, which was significantly less than gross failure (p<0.001 for both measurements). Maximum principal strain in the capsule at yield was 80+/-24%. Energy to yield was 14.3+/-3.4% of the total energy for a complete tear of the ligament. Ligament yield point occurred at a distraction magnitude in which pain symptoms begin to appear in vivo in the rat. These mechanical findings provide insight into the relationship between gross structural failure and painful loading for the facet capsular ligament, which has not been previously defined for such neck injuries. Findings also present a framework for more in-depth methods to define the threshold for persistent pain and could enable extrapolation to the human response.

Arthroscopic management of traumatic anterior shoulder instability in collision athletes: analysis of 204 cases with a 4- to 9-year follow-up and results with the suture anchor technique

PURPOSE

The purpose of this study was to determine the effectiveness of arthroscopy in the selection of surgical procedure and treatment of both acute and recurrent traumatic anterior shoulder instability in rugby players by use of pre-established selection criteria. We describe the injury mechanisms, analyze the pathologic lesions and treatment indications based on surgical findings, and assess the results in patients treated with the arthroscopic suture anchor technique.

METHODS

From November 1996 to November 2001, 204 rugby players with acute or recurrent traumatic anterior instability underwent an initial arthroscopic examination. Criteria such as type of Bankart lesion, tissue quality, and presence of bony defects were evaluated and used to determine the method of stabilization: arthroscopy or open stabilization. Open surgery was indicated in patients with bone humeral deficiencies greater than one fourth of the articular humeral head, bone glenoid deficiencies greater than 25% of the glenoid extension, capsular laxity with poor tissue quality, and humeral avulsion of the glenohumeral ligament; all other patients underwent arthroscopic reconstruction via the bone suture anchor technique.

RESULTS

The mean follow-up was 5.9 years (range, 3.9 to 8.9 years). We performed arthroscopic stabilization in 39 cases of acute instability; only 1 case (2.5%) required the mini-open technique for reinsertion of humeral avulsion of the glenohumeral ligament. Of 158 cases of recurrent instability, 121 underwent arthroscopic stabilization, and 37 (23.4%) required reconstruction with open surgery. The main cause was bony deficiency (treated with the Latarjet procedure). The results of the arthroscopic reconstructions were evaluated by use of the Rowe scale and analyzed according to stability and range of motion. Good or excellent results were found in 94.9% of cases in the acute instability group and in 91.8% in the recurrent instability group, the poor results were due to instability recurrence. In the acute instability group there were 2 cases of recurrence (5.1%) while playing rugby. In the recurrent instability group there were 10 recurrences (8.3%).

CONCLUSIONS

Arthroscopic stabilization was possible in 97.5% of our patients with acute instability and 76.6% of patients with recurrent instability based on the selection criteria for this population. We were able to obtain excellent results in 90% of cases using the suture anchor technique in rugby players with our selection criteria.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Tensile cervical facet capsule ligament mechanics: failure and subfailure responses in the rat

Clinical, epidemiological, and biomechanical studies suggest the involvement of the cervical facet joint in neck pain. Mechanical studies have suggested the facet capsular ligament to be at risk for subfailure tensile injury during whiplash kinematics of the neck. Ligament mechanical properties can be altered by subfailure injury and such loading can induce cellular damage. However, at present, there is no clear understanding of the physiologic context of subfailure facet capsular ligament injury and mechanical implications for whiplash-related pain. Therefore, this study aimed to define a relationship between mechanical properties at failure and a subfailure condition associated with pain for tension in the rat cervical facet capsular ligament. Tensile failure studies of the C6/C7 rat cervical facet capsular ligament were performed using a customized vertebral distraction device. Force and displacement at failure were measured and stiffness and energy to failure were calculated. Vertebral motions and ligament deformations were tracked and maximum principal strains and their directions were calculated. Mean tensile force at failure (2.96 +/- 0.69 N) was significantly greater (p < 0.005) than force at subfailure (1.17 +/- 0.48 N). Mean ligament stiffness to failure was 0.75 +/- 0.27 N/mm. Maximum principal strain at failure (41.3 +/- 20.0%) was significantly higher (p = 0.003) than the corresponding subfailure value (23.1 +/- 9.3%). This study determined that failure and a subfailure painful condition were significantly different in ligament mechanics and findings provide preliminary insight into the relationship between mechanics and pain physiology for this ligament. Together with existing studies, these findings offer additional considerations for defining mechanical thresholds for painful injuries.

The inferior glenohumeral ligament: a correlative investigation

The inferior glenohumeral ligament (IGHL) was investigated by correlating the biomechanical properties, biochemical composition, and histologic morphology of its 3 anatomic regions (superior band, anterior axillary pouch, and posterior axillary pouch) in 8 human cadaveric shoulders. The overall biochemical composition of the IGHL appeared similar to other ligaments, with average water content of 80.9 +/- 2.5%, collagen content of 80.0 +/- 9.2%, and crosslinks of 0.715 +/- 0.13 mol/mol collagen. The proteoglycan content was highest in the superior band (2.73 +/- 0.7 mg/g dry weight) and may, in part, explain its viscoelastic behavior. Histologic analysis demonstrated longitudinally organized fiber bundles that were more uniform in the mid-substance but more interwoven and less uniformly oriented near the insertion sites. The superior band had the most pronounced fiber bundle interweaving, while crimping was more evident in the anterior axillary pouch. Elastin was identified in each of the regions. Tensile testing demonstrated a trend toward higher ultimate tensile stress (16.9 +/- 7.9 MPa) and tensile modulus (130.3 +/- 47.9 MPa) in the superior band compared to the axillary pouch. The mean ultimate tensile strain of the IGHL was 16.8 +/- 4.6%. These complex IGHL properties may help to explain its unique functions in stabilizing the shoulder in different arm positions and at different rates of loading, including the failure patterns seen clinically, as in Bankart lesions (insertion site) versus capsular stretching (ligament substance).

Anatomical glenoid reconstruction for recurrent anterior glenohumeral instability with glenoid deficiency using an autogenous tricortical iliac crest bone graft

BACKGROUND

Anterior shoulder instability associated with severe glenoid bone loss is rare, and little has been reported on this problem. Recent biomechanical and anatomical studies have suggested guidelines for bony reconstruction of the glenoid.

HYPOTHESIS

Anatomical glenoid reconstruction will restore stability in shoulders with recurrent anterior instability owing to glenoid bone loss.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Eleven cases of traumatic recurrent anterior instability that required bony reconstruction for severe anterior glenoid bone loss were reviewed. In all cases, the length of the anterior glenoid defect exceeded the maximum anteroposterior radius of the glenoid based on preoperative assessment by 3-dimensional CT scan. Surgical reconstruction was performed using an intra-articular tricortical iliac crest bone graft contoured to reestablish the concavity and width of the glenoid. The graft was fixed with cannulated screws in combination with an anterior-inferior capsular repair.

RESULTS

At mean follow-up of 33 months, the mean American Shoulder and Elbow Surgeons score was 94, compared with a preoperative score of 65. The University of California, Los Angeles score improved to 33 from 18. The Rowe score improved to 94 from a preoperative score of 28. The mean motion loss compared with the contralateral, normal shoulder was 7 degrees of flexion, 14 degrees of external rotation in abduction, and one spinous process level for internal rotation. All patients returned to preinjury levels of sport, and only 2 complained of mild pain with overhead sports activities. No patients reported any recurrent instability (dislocation or subluxation). The CT scans with 3-dimensional reconstructions obtained 4 to 6 months postoperatively demonstrated union of the bone graft with incorporation along the anterior glenoid rim and preservation of joint space.

CONCLUSION

Anatomical reconstruction of the glenoid with autogenous iliac crest bone graft for recurrent glenohumeral instability in the setting of bone deficiency is an effective form of treatment for this problem.

Mechanical damage to the intervertebral disc annulus fibrosus subjected to tensile loading

Damage of the annulus fibrosus is implicated in common spinal pathologies. The objective of this study was to obtain a quantitative relationship between both the number of cycles and the magnitude of tensile strain resulting in damage to the annulus fibrosus. Four rectangular tensile specimens oriented in the circumferential direction were harvested from the outer annulus of 8 bovine caudal discs (n = 32) and subjected to one of four tensile testing protocols: (i) ultimate tensile strain (UTS) test; (ii) baseline cyclic test with 4 series of 400 cycles of baseline cyclic loading (peak strain = 20% UTS); (iii & iv) acute and fatigue damage cyclic tests consisting of 4 x 400 cycles of baseline cyclic loading with intermittent loading to 1 and 100 cycles, respectively, with peak tensile strain of 40%, 60%, and 80% UTS. Normalized peak stress for all mechanically loaded specimens was reduced from 0.89 to 0.11 of the baseline control levels, and depended on the magnitude of damaging strain and number of cycles at that damaging strain. Baseline, acute, and fatigue protocols resulted in permanent deformation of 3.5%, 6.7% and 9.6% elongation, respectively. Damage to the laminate structure of the annulus in the absence of biochemical activity in this study was assessed using histology, transmission electron microscopy, and biochemical measurements and was most likely a result of separation of annulus layers (i.e., delamination). Permanent elongation and stress reduction in the annulus may manifest in the motion segment as sub-catastrophic damage including increased neutral zone, disc bulging, and loss of nucleus pulposus pressure. The preparation of rectangular tensile strip specimens required cutting of collagen fibers and may influence absolute values of results, however, it is not expected to affect the comparisons between loading groups or dose-response reported.

Thermal Damage Prediction for Collagenous Tissues Part I: A Clinically Relevant Numerical Simulation Incorporating Heating Rate Dependent Denaturation*

Subablative thermotherapy is frequently used for the treatment of joint instability related diseases. In this therapy, mechanically deformed collagenous tissues are thermally shrunk and the stability of the tissue is re-established. In this research, the thermal damage fields generated by three different clinical heating modalities (monopolar and bipolar radio frequency and Ho:YAG laser) are compared numerically using finite element analysis. The heating rate dependent denaturation characteristics of collagenous tissues are incorporated into the model using experimental data from in vitro experimentation with rabbit patellar tendons. It is shown that there are significant differences among the thermal damage profiles created by these modalities, explaining the main reason for the discrepancies reported in the literature in terms of the efficacy and safety of each modality. In the complementary paper, the accuracy of the model presented here is verified by in vitro experimentation with a model collagenous tissue and by quantifying the denaturation-induced birefringence change using Optical Coherence Tomography and Magnetic Resonance Imaging.

Pathomechanics of acquired shoulder instability: a basic science perspective

Normal asymptomatic glenohumeral motion is dependent on the coordinated function of dynamic and static stabilizers. Data from both selective sectioning studies of the capsuloligamentous components and tensile testing of the inferior glenohumeral ligament have provided important insights into the in situ function of these structures. However, little is known regarding the mechanism of microdamage accumulation in acquired shoulder instability. Recent findings suggest that cyclic subfailure loading of the inferior glenohumeral ligament may induce gradual stretching of the anteroinferior capsule, compromising its capacity to restrain excessive humeral translations. Further studies elucidating the mechanism of load transmission in the capsule during physiologic arm motion, as well as data on the intrinsic healing response of the capsular ligaments, are required to more fully characterize the pathoetiology of acquired shoulder instability.

Biomechanics of shoulder capsulorrhaphy procedures

Nonanatomic capsulorrhaphy procedures and reconstructions used to treat shoulder instability create mechanical alterations to the glenohumeral joint that lead to eventual arthrosis. Current capsulorrhaphy procedures have evolved toward restoring normal anatomy and have stimulated relevant anatomic research. Analysis of the subscapularis insertion has demonstrated a superior tendinous insertion and an inferior muscular insertion with the inferior glenohumeral capsule consistently located beneath the muscular insertion of the subscapularis. In addition, 2 types of inferior humeral capsular attachments have been identified. The anterior capsular insertion may bifurcate into a superior internal fold adjacent to the articular cartilage and an inferior external fold on the humeral surgical neck. Alternatively, the capsule may insert over a broad area on the surgical neck. Therefore, releasing the muscular portion of the subscapularis and both capsular folds or the entire broad capsular insertion enhances proper shifting of the capsule during laterally based capsulorrhaphy procedures. Biomechanical studies allow direct study of the different parameters involved in capsulorrhaphy procedures, and several recent studies have improved our understanding. Anterior tightening procedures such as the Putti-Platt or Magnuson-Stack procedure, as well as a tight Bankart repair, result in a loss of external rotation and maximum elevation. Furthermore, this type of operative intervention creates greater posterior joint loads and abnormal posteroinferior humeral head subluxation, leading to pain and arthrosis. Anatomic capsulorrhaphy procedures produce more normal joint mechanics. Current and future studies will evaluate new arthroscopic capsulorrhaphy techniques.

A Novel Application of the Principles of Linear Elastic Fracture Mechanics (LEFM) to the Fatigue Behavior of Tendon Tissue

Background: Experiments on the fatigue of tendons have shown that cyclic loading induces failure at stresses lower than the ultimate tensile strength (UTS) of the tendons. The number of cycles to failure Nf has been shown to be dependent upon the magnitude of the applied cyclic stress. Method of approach: Utilizing data collected by Schechtman (1995), we demonstrate that the principles of Linear Elastic Fracture Mechanics (LEFM) can be used to predict the fatigue behavior of tendons under cyclic loading for maximum stress levels that are higher than 10% of the ultimate tensile strength (UTS) of the tendon (the experimental results at 10% UTS did not fit with our equations). Conclusions: LEFM and other FM approaches may prove to be very valuable in advancing our understanding of damage accumulation in soft connective tissues.

Incremental and single trauma produce equivalent subfailure soft tissue injury of the cervical spine

BACKGROUND

Automotive collision simulations have been performed using either incremental or single trauma. In single trauma, a single impact is performed, while in incremental trauma, a series of impacts of increasing severity are executed. Equivalency of incremental and single trauma for soft tissue injury severity due to the final impact has not been established. Thus, the purpose of the present study was to investigate whether incremental and single trauma produced similar cervical spine subfailure injury severity due to simulated frontal impacts.

METHODS

Porcine cervical spine specimens (C2-T1) of the incremental trauma group were subjected to five frontal impacts (2, 3.5, 5, 6.5, 8 g), while single trauma specimens were subjected to a single impact (8 g). Flexibility tests were performed on specimens while intact and following each impact. Intact and post 8 g flexibility parameters were compared within incremental and single trauma groups and between groups.

FINDINGS

No significant differences (P < 0.05) were found between incremental and single trauma groups when either intact or post 8 g flexibility parameters were compared. Significant increases in flexibility parameters from intact to post 8 g were observed in both groups, indicating soft tissue injury.

INTERPRETATION

Incremental and single trauma produced equivalent subfailure cervical spine injury in simulated impacts, for the experimental conditions studied. This study may facilitate greater use of the incremental trauma protocol in future experimental designs.