Effect of arthroscopic procedures on the acromioclavicular joint

The objective of the current study was to determine the effect of arthroscopic acromioplasty, and combined acromioplasty and distal clavicle resection on joint kinematics and in situ forces in response to an anterior, posterior, and superior load of 70 N. The loading conditions were applied to 10 fresh-frozen cadaveric shoulders using a robotic and universal force and moment sensor testing system. Translations in response to a posterior load increased by approximately 30% after combined acromioplasty and distal clavicle resection when compared with the intact and acromioplasty conditions. The in situ force in the trapezoid and conoid ligaments increased significantly from 13 +/- 15 N to 40 +/- 25 N and 13 +/- 13 N to 38 +/- 28 N, respectively, between the intact and combined acromioplasty and distal clavicle resection conditions during anterior loading. The results suggest that an arthroscopic acromioplasty alone does not significantly affect the mechanics of the acromioclavicular joint with these loading conditions. However, an acromioplasty combined with a distal clavicular resection does result in significant increases in joint motion and ligament forces. In some circumstances, such as after a previous joint separation, the increased forces in the coracoclavicular ligaments could result in additional damage to weak ligaments.     

In situ force distribution in the glenohumeral joint capsule during anterior-posterior loading.

Our objective was to examine the function of the glenohumeral capsule and ligaments during application of an anterior-posterior load by directly measuring the in situ force distribution in these structures as well as the compliance of the joint. We hypothesized that interaction between different regions of the capsule due to its continuous nature results in a complex force distribution throughout the glenohumeral joint capsule. A robotic/universal force-moment sensor testing system was utilized to determine the force distribution in the glenohumeral capsule and ligaments of intact shoulder specimens and the joint kinematics resulting from the application of external loads at four abduction angles. Our results suggest that the glenohumeral capsule carries no force when the humeral head is centered in the glenoid with the humerus in anatomic rotation. However, once an anterior-posterior load is applied to the joint, the glenohumeral ligaments carry force (during anterior loading, the superior glenohumeral-coracohumeral ligaments carried 26+/-16 N at 0 degrees and the anterior band of the inferior glenohumeral ligament carried 30+/-21 N at 90 degrees). Therefore, the patient's ability to use the arm with the humerus in anatomic rotation should not be limited following repair procedures for shoulder instability because the repaired capsuloligamentous structures should not carry force during this motion. Separation of the capsule into its components revealed that forces are being transmitted between each region and that the glenohumeral ligaments do not act as traditional ligaments that carry a pure tensile force along their length. The interrelationship of the glenohumeral ligaments forms the biomechanical basis for the capsular shift procedure. The compliance of the joint under our loading conditions indicates that the passive properties of the capsule provide little resistance to motion of the humerus during 10 mm of anterior or posterior translation with anatomic humeral rotation. Finally, this knowledge also enhances the understanding of arm positioning relative to the portion of the glenohumeral capsule that limits translation during examination under anesthesia.     

Biomechanical study of the ligamentous system of the acromioclavicular joint

The ligamentous structures of the acromioclavicular joint were studied by gross examination and quantitative measurement in twelve human cadaver specimens. Distances between insertions at various extreme positions of the clavicle were studied with the biplane radiographic technique. Ligamentous contributions to joint constraint under displacements were determined by performing load-displacement tests along with sequential sectioning of the ligaments. Twelve modes of joint displacement were examined. The acromioclavicular ligament acted as a primary constraint for posterior displacement of the clavicle and posterior axial rotation. The conoid ligament appeared to be more important than has been previously described. That ligament played a primary role in constraining anterior and superior rotation as well as anterior and superior displacement of the clavicle. The trapezoid ligament contributed less constraint to movement of the clavicle in both the horizontal and the vertical plane except when the clavicle moved in axial compression toward the acromion process. The various contributions of different ligaments to constraint changed not only with the direction of joint displacement but also with the amount of loading and displacement. For many directions of displacement, the acromioclavicular joint contributed a greater amount to constraint at smaller degrees of displacement, while the coracoclavicular ligaments, primarily the conoid ligament, contributed a greater amount of constraint with larger amounts of displacement.     

Joint compression alters the kinematics and loading patterns of the intact and capsule-transected AC joint.

High compressive loads are transmitted through the shoulder across the acromioclavicular (AC) joint to the axial skeleton during activities of daily living and can lead to early joint degeneration or instability. The objective of this study was to quantify the effect of joint compression on the biomechanics of the intact and capsule-transected AC joint during application of three loading conditions. A robotic/universal force-moment sensor testing system was utilized to apply an anterior, posterior or superior load of 70 N in combination with 10 or 70 N of joint compression to fresh-frozen cadaveric shoulders (n=12). The application of joint compression to the intact AC joint decreased the posterior translation in response to a posterior load (-6.6+/-2.5 vs -3.7+/-1.0 mm, p<0.05). Joint compression also decreased the in situ force in the superior AC capsule by 10 N while increasing the joint contact force by 20 N for all loading conditions (p<0.05). The application of joint compression to the capsule-transected AC joint significantly decreased the amount of posterior and superior translation during posterior (-12.7+/-6.1 vs -5.5+/-3.2 mm, p<0.05) and superior (5.3+/-2.9 vs 4.2+/-2.3 mm, p<0.05) loading, respectively, while significantly increasing the coupled translations (anterior-posterior, superior-inferior or proximal-distal) in all loading conditions (p<0.05). The joint contact force also significantly increased by 20 N for all loading conditions (p<0.05). This quantitative data suggests: (1) common surgical techniques such as distal clavicle resection, which initially reduce painful joint contact, may cause unusually high loads to be supported by the soft tissue structures at the AC joint; and (2) compressive loads transmitted across a capsule-transected AC joint could be concentrated over a smaller area due to the increased coupled motion and joint contact force.     

Arthroscopic anatomical reconstruction of the acromioclavicular joint

Traditional techniques for restoration of a separated acromioclavicular joint are afflicted with various complications and often lead to recurrent dislocation. Lately, anatomic as well as minimally-invasive repair techniques with major focus on restoration of the coracoclavicular ligaments have been described for acromioclavicular joint reconstruction. We present a technique for an arthroscopically-assisted anatomical acromioclavicular joint reconstruction by replacing the conoid and trapezoid separately with nonabsorbable sutures and titanium buttons.     

Biomechanical function of surgical procedures for acromioclavicular joint dislocations

PurposeSurgical procedures for treatment of acromioclavicular (AC) joint dislocation replace the coracoclavicular (CC) ligaments to minimize motion, allow scarring, and increase the subsequent stability of the joint. The purpose of this study was to evaluate the biomechanical function of the surgically repaired or reconstructed (CC Sling, Rockwood Screw [DePuy Orthopaedics, Warsaw, IN], and Coracoacromial [CA] Ligament Transfer Construct) AC joint after AC joint dislocation.Type of StudyA cadaver study using a convenience sample.MethodsTwelve cadaveric shoulders were tested using a robotic/UFS testing system. Three external loading conditions (anterior, posterior, or superior load of 70 N) were applied to intact and surgically repaired or reconstructed AC joint. The resulting kinematics of the AC joint and in situ forces in the CC ligaments or surgical constructs was determined.ResultsFor the CC Sling, anterior and posterior translation significantly increased by 110% and 330% in response to an anterior and posterior load, respectively. However, the posterior translation for the Rockwood Screw significantly decreased by 60%. Anterior, posterior, and superior translation for the CA Ligament Transfer Construct significantly increased by 110%, 360%, and 100%, respectively. The coupled translations also significantly increased for the CC Sling and CA Ligament Transfer Construct in response to all loading conditions. In contrast, the coupled translations for the Rockwood Screw tended to decrease. Furthermore, the in situ forces increased significantly for all 3 surgical constructs compared with the intact CC Ligaments in response to an anterior and posterior load.ConclusionsAt time zero, increases in the primary and coupled motion for the CC Sling and CA Ligament Transfer Construct could comprise the initial healing period prescribed for AC joint dislocation. Our findings also suggest that the Rockwood Screw provides a highly rigid fixation and may explain the complications frequently seen in clinical practice.Clinical RelevanceCurrent surgical procedures do not have the appropriate stiffness to restore the stability of the intact joint before healing. Therefore, our results may lead to the design and development of new repairs, reconstructions, and rehabilitation protocols for AC joint dislocation.     

The acromioclavicular capsule as a restraint to posterior translation of the clavicle: a biomechanical analysis

Excessive posterior translation of the residual clavicle after distal clavicle resection can be associated with significant postoperative pain. Although the acromioclavicular capsule has been identified as the primary restraint to translation of the clavicle along this axis, the individual contributions of the anterior, posterior, superior, and inferior components of the capsular ligament have not been established. The purpose of this study was to define the relative roles of the individual acromioclavicular capsular ligaments in preventing posterior translation of the distal clavicle in normal acromioclavicular joints in a human cadaver model. Six fresh-frozen human cadaveric acromioclavicular joints were mounted on a specially designed apparatus which, when attached to a standard servohydraulic materials testing device, allowed translation of the distal clavicle along the anteroposterior axis of the acromioclavicular joint (i.e., parallel to the articular surface). Resistance to posterior displacement was measured for standardized displacements in the normal specimens and after serial sectioning of each of the acromioclavicular ligaments was performed. Sectioning of the anterior and inferior capsular ligaments had no significant effect on posterior translation at the 5% significance level. However, sectioning of the superior and posterior ligaments had statistically significant effects (P < .05). These capsular structures contributed 56% +/- 23% (+/- SEM) and 25% +/- 16%, respectively, of the force required to achieve a given posterior displacement. To avoid excessive posterior translation of the clavicle after distal clavicle excision, surgical techniques that spare the posterior and superior acromioclavicular capsular ligaments should be used.     

The relation of the coracoclavicular ligament insertion to the acromioclavicular joint: a cadaver study of relevance to lateral clavicle resection

Resection of the lateral end of the clavicle is a common procedure for arthrosis of the acromioclavicular joint (AC-joint). However, no anatomical data on the distance between the insertions of the coracoclavicular ligaments and the AC-joint have been reported. In 36 cadaver shoulders (18 male), we studied the relation between the AC-joint and the insertions of the joint capsule, trapezoid and conoid ligaments. The distance from the AC-joint to the medial end of its capsule was, on average, 0.7 cm (0.4-0.9) cm in women and 0.8 (0.4-1.2) cm in men. In women, the trapezoid ligament began, on average, at 0.9 (0.4-1.6) cm and ended at 2.4 (2.0-2.8) cm and in men, it began at 1.1 (0.8-1.6) cm and ended at 2.9 (2.1-3.8) cm medial to the AC joint. The corresponding figures for the conoid ligament were 2.6 (2.0-3.7) cm and 4.7 (3.9-6.2) cm. A resection of 1 cm of the lateral clavicle detaches 8%, a resection of 2 cm 60% and a resection of 2.5 cm 90% of the trapezoid ligament. We recommend a maximum resection of 1 cm of the lateral clavicle because a resection of 2 cm or more may cause postoperative AC-joint instability and related pain.     

The relation of the coracoclavicular ligament insertion to the acromioclavicular jointA cadaver study of relevance to lateral clavicle resection

Resection of the lateral end of the clavicle is a common procedure for arthrosis of the acromioclavicular joint (AC-joint). However, no anatomical data on the distance between the insertions of the coracoclavicular ligaments and the AC-joint have been reported. In 36 cadaver shoulders (18 male), we studied the relation between the AC-joint and the insertions of the joint capsule, trapezoid and conoid ligaments. The distance from the AC-joint to the medial end of its capsule was, on average, 0.7 cm (0.4-0.9) cm in women and 0.8 (0.4-1.2) cm in men. In women, the trapezoid ligament began, on average, at 0.9 (0.4-1.6) cm and ended at 2.4 (2.0-2.8) cm and in men, it began at 1.1 (0.8-1.6) cm and ended at 2.9 (2.1-3.8) cm medial to the AC joint. The corresponding figures for the conoid ligament were 2.6 (2.0-3.7) cm and 4.7 (3.9-6.2) cm. A resection of 1 cm of the lateral clavicle detaches 8%, a resection of 2 cm 60% and a resection of 2.5 cm 90% of the trapezoid ligament. We recommend a maximum resection of 1 cm of the lateral clavicle because a resection of 2 cm or more may cause postoperative AC-joint instability and related pain.     

Arthroscopic Suprascapular Nerve Release at the Suprascapular Notch in a Cadaveric Model: An Anatomic Approach

Arthroscopic release of the suprascapular nerve at the suprascapular notch, to our knowledge, has rarely been described. The purpose of this study was to evaluate the feasibility and relevant anatomic landmarks in a cadaveric model that can be identified arthroscopically for reliable and reproducible arthroscopic release of the superior transverse scapular (STS) ligament. In 8 fresh-frozen cadaveric shoulders, arthroscopic release of the STS ligament was performed. The acromioclavicular joint is first identified while viewing through a posterior subacromial portal. The distal clavicle is then followed medially until the most lateral portion of the coracoclavicular (CC) ligaments (trapezoid ligament) is identified. The most medial margin of the CC ligaments (conoid ligament) is identified, and the trapezoid and conoid ligaments are dissected and identified individually. The conoid ligament is followed inferiorly and medially to the base of the coracoid. At the base of the coracoid, the confluence of the trapezoid and conoid ligaments (CC) and the STS ligament is identified. The STS ligament can be identified coursing horizontally across the field of view. The STS ligament may be incised by use of dissecting scissors through a lateral, accessory lateral, or accessory posterior portal, releasing the suprascapular nerve.     

MRI evaluation of coracoclavicular ligament injury in acromioclavicular joint separation

Backgrounds  

Acromioclavicular joint separation is divided into three types according to Tossy and six types according to Rockwood. However, the trapezoid and conoid ligaments that constitute the coracoclavicular ligaments are not detailed in these classifications. In this study, we investigated the location and degree of ligament injury in acromioclavicular joint separation by means of magnetic resonance (MR) images.     

喙锁韧带重建的解剖放射学研究

目的测量不同透视体位下喙锁韧带骨道走行的放射学参数，为临床喙锁韧带重建提供解剖学依据。 方法取22具防腐处理的成人肩关节标本，解剖测量喙锁韧带两部分（斜方韧带，锥状韧带）的走行方向、止点宽度及透视体位下成角。 结果斜方韧带锁骨侧足印宽度（26.2±1.2） mm，喙突侧（22.7±1.6）mm。锥状韧带锁骨侧足印宽度（24.6±1.4）mm，喙突侧（19.2±1.6）mm。影像学测量韧带的插入角度：肩胛骨正位与锥状韧带与锁骨长轴成角（81±4）°，斜方韧带成角（67±7）°。侧位成角：斜方韧带（83±3）°，锥状韧带（70±6）°。与外科标志的毗邻关系：斜方韧带与锥状韧带足印区长轴中心点在锁骨间距（21.9±4.8）mm，在喙突侧间距（15.7±1.6）mm。 结论锥状韧带及斜方韧带止点足印宽度较为恒定，斜方韧带插入角度有变异度较大，锥状韧带较为恒定。两韧带在锁骨及喙突上间距较小。在进行肩锁关节解剖重建时，可参照其解剖学特点。     

Ligamentous restraints to anterior and posterior translation of the sternoclavicular joint

This experiment was conducted to determine the primary ligamentous restraints to anterior and posterior translation of the sternoclavicular joint. Twenty-four unpaired cadaver specimens were mounted in a custom fixture. Anterior and posterior translations were measured under a sub-failure load in the intact specimen and again after transecting one randomly chosen ligament (anterior capsule, posterior capsule, interclavicular ligament, and costoclavicular ligament; n = 6 for each group). Cutting the posterior capsule resulted in significant increases in anterior translation and posterior translation. Cutting the anterior capsule produced significant increases in anterior translation. Cutting the costoclavicular and interclavicular ligaments had little effect on sternoclavicular joint translation. The posterior capsule is the most important restraint for anterior and posterior translation of the sternoclavicular joint. The anterior capsule is another important restraint for anterior translation. The costoclavicular and interclavicular ligaments have little effect on anterior or posterior translation of the sternoclavicular joint.     

肩锁关节解剖学研究和临床意义

目的研究肩锁关节骨性和静态稳定结构,为肩部手术提供详细形态学资料。方法对26例成人新鲜尸体标本进行解剖,观察肩锁关节解剖形态并测量相关骨性标志和韧带的形态学参数。结果锥状韧带和斜方韧带锁骨止点中心到锁骨远端距离分别为(43.67±6.30)mm和(25.25±3.06)mm,止点宽度分别为(16.92±4.25)mm和(10.33±1.32)mm。锥状韧带长度为(15.54±3.32)mm,角度为(-116.25±10.90)°;而斜方韧带长度为(9.63±2.28)mm,角度为(75.42±11.37)°。锥状韧带和斜方韧带喙突止点相距(8.96±3.00)mm,而锁骨止点距离(13.08±3.50)mm,两条韧带呈"V"形结构。结论本研究获得了肩锁关节及其周围组织的详细形态学参数,为该部位手术提供解剖学资料。进行锁骨远端手术时应避免损伤锥韧带和斜方韧带止点,切除锁骨远端应不超过10mm以避免损伤斜方韧带。行喙锁韧带重建时要注意重建其"V"形解剖结构,以更好恢复其生理功能。     

Arthroscopic Decompression of a Bony Suprascapular Foramen

Arthroscopic decompression of the suprascapular nerve by transection of the transverse scapular ligament has only recently been described. Arthroscopic decompression of a bony suprascapular notch foramen has not been previously reported. This article presents a case report and outlines an arthroscopic technique to safely decompress a bony suprascapular notch. In the subacromial space, a lateral portal is used for viewing and a posterior portal for instrumentation. The medial wall of the subacromial bursa located behind the acromioclavicular joint is debrided with the shaver facing laterally and superiorly. The posterior acromioclavicular artery is routinely coagulated. A superomedial portal is now established using spinal needle localization. A smooth 5.5-mm cannula is placed in this portal and the coracoclavicular ligaments (trapezoid and conoid) are followed to the coracoid. The smooth cannula serves nicely to sweep and retract the suprascapular artery and associated fibrofatty tissue from the field of view while allowing instrumentation and visualization of the suprascapular notch. The course of the suprascapular nerve and morphology of the notch is confirmed. A Kerrison punch rongeur, routinely used in spine surgery, is introduced through the superomedial portal and a notchplasty is performed safely, allowing decompression of the suprascapular nerve.     

Magnetic resonance imaging of the coracoclavicular ligaments: its role in defining pathoanatomy at the acromioclavicular joint

Four patients with acromioclavicular joint injuries (one type II, two type III, one type V), two patients without acromioclavicular joint injury, and a fresh-frozen cadaver underwent magnetic resonance imaging (MRI) and plain radiographs. The normal conoid and trapezoid ligaments were easily identified in the cadaver and the two uninjured patients. Magnetic resonance imaging revealed disruption of both coraclavicular ligaments in the three patients with type II and type III injuries. However, the patient with the type V injury had disruption of the trapezoid ligament alone. Thus, the grade of injury, as determined by the change in the coracoclavicular interval onplain radiography and defined by the Rockwood classification system, failed to correlate with the pathoanatomy seen on MRI in two of the four injured patients. These findings suggest that improvements in the classification of these injuries may be necessary.     

Contribution of the passive properties of the rotator cuff to glenohumeral stability during anterior-posterior loading.

The passive properties of the rotator cuff have been shown to provide some stability during anterior-posterior (AP) translation. However, the relative importance of the rotator cuff to joint stability remains unclear. The purpose of this study was to quantify the force contributions of the rotator cuff and of capsuloligamentous structures at the glenohumeral joint during AP loading. We hypothesized that the rotator cuff acts as a significant passive stabilizer of the glenohumeral joint and that its contribution to joint stability is comparable to the contribution made by the components of the glenohumeral capsule. A robotic/universal force-moment sensor testing system was used to determine both the multiple "degrees of freedom" joint motion and the in situ force carried by each soft tissue structure during application of an 89N AP load at 4 abduction angles. The percent contribution of the rotator cuff to the resisting force of the intact joint during AP loading was significantly greater during posterior loading (35% +/- 26%) than during anterior loading at 60 degrees of abduction (P < .05). The contribution of the rotator cuff (i.e., 29% +/- 16% at 30 degrees of abduction) was found to be significantly greater than the contributions of the capsule components during posterior loading at 30 degrees, 60 degrees, and 90 degrees of abduction (P < .05). However, no differences could be found between the respective contributions of the rotator cuff and the capsule components during anterior loading. The results support our hypothesis and suggest that passive tension in the rotator cuff plays a more significant role than other soft tissue structures in resisting posterior loads at the glenohumeral joint. The important role of the rotator cuff during posterior loading may be a result of the thin posterior joint capsule compared with the anterior capsule, which has several thickenings. This information increases our understanding of posterior stability at the glenohumeral joint during clinical laxity tests.     

Reduced anterior tibial translation associated with adaptive changes in the anterior cruciate ligament-deficient joint: goat model.

Adaptive changes in the menisci and adjacent posterior capsule were documented within anterior cruciate ligament-deficient knee (stifle) joints in the goat model. These physical changes in the menisci and capsule developed over time and were associated with reduction in the initial (time zero) abnormal anterior tibial translation following transection of the anterior cruciate ligament. At 50 N of applied force, the normal goat knee joint has a total anterior-posterior translation of 0.6+/-0.1 mm (+/- SEM) at 45 degrees of flexion and 0.3+/-0.1 mm at 90 degrees. The translation immediately after transection (time zero) with 50 N of force was 8.2+/-0.5 mm at 45 degrees and 4.9+/-0.9 mm at 90 degrees. Within 8 months after transection and at 50 N of force, the treated knees had reduced translation values of 5.3+/-0.6 mm at 45 degrees of flexion and 2.9+/-0.5 mm at 90 degrees, or 35 (p<0.001) and 40% reductions, respectively, compared with the values at time zero. Magnetic resonance images of the ligament-deficient stifle joints, as well as gross measurements and image analysis after dissection, consistently demonstrated increases in cross-sectional area and volume of the menisci compared with the contralateral controls. These secondary changes were most pronounced in the posterior portion of the medial menisci, and histologic evaluation demonstrated hypercellularity with the accumulation of poorly organized collagen, reduced safranin O staining (proteoglycan matrix synthesis), a thickened capsule and capsule attachment, and increased vascularity at the meniscal capsule interface.     

Biomechanical tests for type II SLAP lesions of the shoulder joint before and after arthroscopic repair

Superior labral anterior-to-posterior (SLAP) lesions can cause shoulder pain partly by causing glenohumeral instability. The purpose of this study was to examine the effect of a simulated type II SLAP lesion and subsequent repair on glenohumeral translation of the vented shoulder. In eight cadaver joints, a robotic/UFS testing system was used to measure joint translation by applying an anterior, posterior, or inferior load of 50 N to each shoulder. The "apprehension tests" for anterior and posterior instability were simulated by applying an anterior load of 50 N with an external rotation torque of 3 Nm or a posterior load of 50 N with an internal rotation torque of 3 Nm. Each loading condition was applied at 30 degrees and 60 degrees of glenohumeral abduction with a constant joint compressive load (44 N) to the intact, simulated SLAP lesion, and repaired shoulder. Repair of the type II SLAP was then performed by placing a Suretac through the labrum both anterior and posterior to the biceps anchor and testing was repeated. ANOVA was used to compare translation of the intact joint, the joint after the type II SLAP lesion had been simulated, and after repair. At 30 degrees of abduction, anterior translation of the intact vented shoulder joint from anterior loading was 18.7+/-8.5 mm and increased to 26.2+/-6.5 mm after simulation of the type II SLAP lesion ( p< or =0.05). The arthroscopic repair did not restore anterior translation (23.9+/-8.6 mm) to the same degree as the intact joint ( p> or =0.05). At 60 degrees of abduction, anterior translation of 16.6+/-9.6mm in the intact joint was not significantly increased at 19.4+/-10.1 after simulation of the type II SLAP lesion ( p=0.0527). AP loading also resulted in inferior translation. At 30 degrees of abduction it was 3.8+/-4.0 mm in the intact joint and increased to 8.5+/-5.4 mm after the type II SLAP lesion ( p< or =0.05. After repair the inferior translation decreased significantly to 6.7+/-5.3 mm ( p< or =0.05). Although inferior translations were less at 60 degrees of abduction, results were similar to those at 30 degrees after repair. There were no significant increases in translation after SI/AP combined external rotation torque or posterior-anterior combined internal rotation torque loading.In this study the repair of a type II SLAP lesion only partially restored translations to the same degree as an intact vented shoulder joint. Therefore, improved repair techniques or an anteroinferior capsulolabral procedure in addition to the type II SLAP lesion repair might be needed to restore normal joint function.