Effect of rotator interval closure on glenohumeral stability and motion: a cadaveric study

The effect of rotator interval closure, which is performed as an adjunct to arthroscopic stabilization of the shoulder, has not been clarified. Fourteen fresh-frozen cadaveric shoulders were used. The position of the humeral head was measured using an electromagnetic tracking device with the capsule intact, sectioned, and imbricated between the superior glenohumeral ligament and the subscapularis tendon (SGHL/SSC closure) or between the superior and middle glenohumeral ligaments (SGHL/MGHL closure). The direction of translational loads (10, 20, and 30 N) and arm positions were (1) anterior, posterior, and inferior loads in adduction; (2) anterior load in abduction/external rotation in the scapular plane; and (3) anterior load in abduction/external rotation in the coronal plane. The range of motion was measured using a goniometer under a constant force. Both methods reduced anterior translation in adduction. Only SGHL/MGHL closure reduced anterior translation in abduction/external rotation in the scapular plane and posterior translation in adduction. Both methods reduced the range of external rotation and horizontal abduction. Rotator interval closure is expected to reduce remnant anterior/posterior instability and thereby improve the clinical outcomes of arthroscopic stabilization procedures.     

盂肱韧带维持肩关节前方稳定性生物力学研究

目的研究盂肱韧带(glenohumeral ligament,GHL)对维持肩关节前方静力性稳定结构的作用。方法取自愿捐赠新鲜男性成人肩关节上肢标本15只,制成肩关节-骨韧带标本,随机分为A、B、C、D及E组(n=3),根据选择性切断试验不同,再分为A1～A4、B1～B3、C1～C2、D1～D2、E1～E2各亚组。A1～A4组分别为肩关节骨-韧带标本完整组、盂肱上韧带(superior GHL,SGHL)损伤组、SGHL/盂肱中韧带(middle GHL,MGHL)损伤组及SGHL/MGHL/盂肱下韧带(inferior GHL,IGHL)损伤组;B1～B3组分别为肩关节骨-韧带标本完整组、MGHL损伤组、MGHL/IGHL损伤组;C1～C2组分别为肩关节骨-韧带标本完整组、盂肱下韧带前束(IGHL-anterior band,IGHL-AB)损伤组;D1～D2组分别为肩关节骨-韧带标本完整组、盂肱下韧带后束(IGHL-posterior band,IGHL-PB)损伤组;E1～E2分别为肩关节骨-韧带标本完整组、IGHL损伤组。在50N后前方负荷作用下,分别在肩关节外展0、45、90°时,测量各组标本负荷-位移曲线,评价盂肱韧带对维持肩关节前方稳定的作用。结果A1组完整肩关节外展0、45、90°平均位移很小,为15.00±4.99mm;A2组为16.85±4.26mm;A3组为19.59±2.83mm,外展90°位移A3组与A1、A2组比较差异有统计学意义(P<0.05);A4组肩关节稳定性最差,平均位移22.34±5.70mm。B2组肩关节稳定性无明显下降;B3组肩关节稳定性在外展45、90°时很差。C2组在外展45°和90°时稳定性很差,平均位移分别为23.19±4.58mm和15.32±1.30mm,与A1组比较差异有统计学意义(P<0.05)。D2组对肩关节前方稳定性影响不大,平均位移17.30±4.93mm。E2组与C2组相似,平均位移20.26±4.75mm。结论GHL是重要的肩关节前方静力性稳定结构,SGHL对肩关节前方稳定性无明显影响,MGHL和IGHL共同维持肩关节的前方稳定性,以IGHL作用最明显。     

Normal variations of the glenohumeral ligament complex: an anatomic study for arthroscopic bankart repair

PurposeThe purpose of this study was to evaluate the prevalence and morphologic characteristics of normal variations in the glenohumeral ligament complex (GHLC).Type of studyAnatomic study in cadavers.MethodsWe investigated 84 cadaver shoulders and recorded visualization of the superior glenohumeral ligament (SGHL), middle glenohumeral ligament (MGHL), and anterior band of the inferior glenohumeral ligament (AIGHL). In cases with an AIGHL, we noted the location of its origin with respect to the anterior glenoid in terms of a clock face as in a right shoulder. If an MGHL was present, the site of its glenoid attachment was recorded. The presence of a cord-like MGHL, the Buford complex, and a sublabral foramen was also investigated.ResultsOf these, 79 (94.1%) manifested an SGHL, 53 (63.1%) an MGHL, and 76 (90.5%) an AIGHL. The AIGHL originated in an area located between the 2- and 5-o’clock position; in 11 (14.5%), the origin was at the 2-o’clock position; in 49 (64.5%) at the 3-o’clock position; in 11 (14.5%), the 4-o’clock position; and in 5 (6.5%) at the 5-o’clock position. Two common variations in the attachment of the MGHL were seen; 30 of 53 MGHL (56.6%) originated from the labrum separate from the origin of the SGHL, and 23 (43.4%) from the labrum at the origin of the SGHL. Of the 84 specimens, 15 (17.9%) manifested a cord-like MGHL, and one (1.2%) the Buford complex. None of the specimens had a sublabral foramen, a finding that requires further investigation.ConclusionsOur results suggest that the Buford complex is a rare variant of the GHLC, and the cord-like MGHL appears to be a relatively common normal variant.Clinical relevanceThe present study provides useful information concerning normal variations of the GHLC to arthroscopists considering Bankart repair.     

Functional study of glenohumeral ligaments

BackgroundThe glenohumeral ligaments are passive stabilising anatomical structures of the shoulder which, in synergy with the other active and passive stabilising structures, enable joint movement and cohesion. The purpose of this study is to analyse the isolated and synergic function of the glenohumeral ligaments by using a tetrapolar detection system with computer analysis.MethodsIn a study performed on cadavers after anatomical dissection, detector electrodes were positioned on the individual ligaments and recordings were made of bioelectric impedance and, consequently, the resistance, which is an indicator of the state of tension or relaxation of the ligamentous complex. Predefined positions of the upper limb were adopted—neutral adduction, adduction with external rotation, abduction at 45° with neutral and external rotation, and abduction at 90° with neutral and external rotation.ResultsThe superior glenohumeral ligament is important in stabilisation of the glenohumeral joint in adduction and external rotation. The middle glenohumeral ligament is an important stabilising structure in the positions of adduction and external rotation and abduction up to 45° in external rotation. The resistance, and therefore tension, of the inferior glenohumeral ligament, which is negligible in positions of neutral adduction and adduction in external rotation, increases in value for angles between 45° and 90°, indicating the important stabilising function of this ligament in those positions.ConclusionOur experimental study on cadavers, which involved evaluating the resistance of the glenohumeral ligaments by means of tetrapolar detection and computer analysis of the results, contributes to our knowledge of the functional activity of the anterior portion of the joint capsule.     

Management of the subscapularis contracture during shoulder arthroplasty for primary glenohumeral arthritis

Aim To evaluate the safety and effectiveness of a particular subscapularis release in shoulder arthroplasty for primary glenohumeral arthritis. Materials and methods Twenty-eight patients (19F, 9M) underwent shoulder arthroplasty for primary glenohumeral arthritis. Preoperative average Constant Score (CS) was 31.2 points (range 14–52), active anterior elevation (AAE) 92° (30–100°) and active external rotation (AER) 11° (−40 to 20°). During arthroplasty for subscapularis contracture, patients underwent subscapularis release freeing the superior tubular tendon (STT) with a section of the coracohumeral ligament (CHL) and the superior glenohumeral ligament (SGHL) and a deep release consisting of a section of the middle glenohumeral ligament (MGHL), very close to the glenoid labrum, and the inferior glenohumeral ligament (IGHL). An anatomic study was performed on 13 cadavers, verifying the structure of subscapularis tendon and its relationship with the capsule, the surrounding ligaments and the axillary nerve. Moreover, after having placed traction sutures on the subscapularis tendon, its lengthening was measured after STT release alone and after STT and deep release. The complete absence of neurological and vascular lesions was also verified. Results Average follow-up: 2.9 years. Postoperative mean CS was 70.5 (p〈0.005), with an absolute gain of 39.1. AAE increased from 92° to 142° (p=0.001) while AER increased from 8° to 48° (p=0.002). At the last follow-up, 19 patients (67.8%) were very satisfied, 5 patients (17.8%) were satisfied, 3 patients (10.7%) partially satisfied and 1 patient (3.5%) unsatisfied. In the anatomic control, the average lengthening of subscapularis tendon was 0.9 cm after STT release alone and 2.5 cm after STT and deep release. No vascular and neurological lesions were observed. Conclusions The subscapularis release during shoulder arthroplasty is extremely important to obtain the proper balance between anterior and posterior soft tissues and to achieve an optimal range of motion and joint stability. An adequate anatomical dissection could give good tendon mobilisation and lengthening, necessary for a good repair, and lead to a recovery of the range of motion, particularly for external rotation.     

Dynamic capsuloligamentous anatomy of the glenohumeral joint

Though many anatomic and biomechanical studies have been performed to elucidate capsuloligamentous anatomy of the glenohumeral joint, no previous studies have evaluated capsuloligamentous anatomy during rotator cuff contraction. The purpose of this study was to define and document the orientation and interrelationship between the glenohumeral ligaments during simulated rotator cuff contraction. Six fresh cadaveric shoulders were arthroscoped to document and grade ligamentous anatomy. The superior and middle glenohumeral ligaments and the anterior and posterior bands of the inferior glenohumeral ligament complex were labeled by an arthroscopicassisted technique with a linked metallic bead system. Shoulders were then placed onto an experimental apparatus that simulated rotator cuff function through computer-controlled servo-hydrolic actuators attached to the rotator cuff and biceps by a clamp and cable-and-pulley system. Simulated rotator cuff action and manual placement allowed shoulders to be placed into three positions of rotation (neutral, internal, and external) in three positions of scapular plane abduction (0°, 45°, 90°). Anteroposterior and axillary lateral plane radiographs were taken in each position to document orientation of all four ligaments. Both the superior and middle glenohumeral ligaments were maximally lengthened in 0° and 45° abduction and external rotation and appeared to shorten in all positions of abduction. The anterior and posterior bands of the inferior glenohumeral ligament complex maintained a cruciate orientation in all positions of abduction in the anteroposterior plane, except at 90° abduction and external rotation, where they are parallel. This cruciate orientation is due to the different location of the glenoid origin and humeral insertion of each band and may allow reciprocal tightening of each during rotation. The glenohumeral capsule is composed of discreet ligaments that undergo large charges in orientation during rotation. The superior and middle glenohumeral ligaments appear to complement the inferior glenohumeral ligaments, with the former tightening in adduction and the latter tightening in abduction. This relationship permits the large range of motion normally seen in the glenohumeral joint.     

The effect of radiofrequency thermal capsulorrhaphy on glenohumeral translation, rotation, and volume

The purpose of this study is to evaluate the effects of radiofrequency (RF) thermal capsulorrhaphy on the kinematic properties of the glenohumeral joint as determined by changes in resistance to multidirectional translational forces, alteration in the range of internal and external rotation, and changes in glenohumeral joint volume. Nonablative RF thermal energy was used to contract the glenohumeral joint capsule in 6 cadaveric shoulders. Measurements of translation were made after application of a 30-N load in anterior, posterior, and inferior directions. The maximum arc of internal and external rotation after application of a 1-N-m moment was also determined for vented specimens before and after thermal capsulorrhaphy. The percent reduction in glenohumeral capsular volume was measured by use of a saline solution injection-aspiration technique. Capsular shrinkage resulted in reductions in anterior, posterior, and inferior translation. The largest percent reductions in anterior translation were seen in external rotation at 45 degrees (48%, P <.05) and 90 degrees (41%, P <.05) abduction. For inferior translation, the largest percent reductions were seen in internal rotation at 45 degrees (40%, P <.05) and 90 degrees (45%, P <.05) abduction. Reductions in posterior translation were noted in internal rotation at 45 degrees (27%, P <.05) and 90 degrees (26%, P <.05) abduction. Other changes in translation were observed but were not statistically significant. The maximum arc of humeral rotation was reduced by a mean of 14 degrees at 45 degrees abduction and 9 degrees at 90 degrees abduction. The mean percent reduction in capsular volume for all shoulders was 37% (range, 8%-50%). This could not be correlated with percent reductions in translation and rotation. This study demonstrated the significant effect of RF thermal capsulorrhaphy in reducing glenohumeral multidirectional translation and volume with only a small loss of rotation in cadaveric shoulders.     

关节镜下盂肱关节前方松解对原发性冻结肩的早期疗效

目的观察应用关节镜进行关节囊前方松解术对原发性冻结肩的治疗效果。 方法2015年3月至2017年3月陕西省人民医院收治的60例原发性冻结肩患者,所有患者经术前MRI检查或术中探查确诊,排除由其余肩部疾病(骨折、肩峰撞击、肩袖损伤、钙化性肌腱炎)引起的继发性冻结肩,所有患者应用关节镜行盂肱关节前方松解术。采集术前及术后的疼痛视觉评分(VAS)、Constant评分、复旦大学肩关节功能评分系统(FUSS),应用单因素重复测量方差分析对结果进行统计学分析评估,对肩关节各方向的被动活动度应用配对t检验方法进行统计学分析。 结果所有患者术后均未出现腋神经损伤或肩关节不稳等并发症。与术前相比,术后12周时患者的VAS评分[(0.7±0.6)vs (8.1±0.7),F ＝38.01]、Constant评分[(93.9±3.0)vs (34.2±3.4),F ＝121.42]及FUSS评分[(93.8±1.3)vs (40.1±2.2),F ＝220.09]差异有统计学意义(均为P <0.01);同时,与术前相比,患肩被动外展[(152±13)° vs (74±9)°,t ＝37.678]、前屈[(156±12)° vs (60±10)°,t ＝46.469]、体侧外旋[(66±11)° vs (8±3)°,t ＝37.762]及内旋在术后12周时明显改善(均为P <0.01)。 结论应用关节镜对盂肱关节囊前方结构进行彻底松解,可有效改善原发性冻结肩患者肩关节功能。     

Glenohumeral movement patterns after puncture of the joint capsule: An experimental study

In on experimental series comprising 22 shoulder specimens obtained at autopsy, we investigated the influence of an intact capsule on glenohumeral stability. Puncture of the capsule resulted in significant glenohumeral translation in unloaded and loaded specimens during shoulder abduction. A maximum of 16.6 mm of distal translation was observed at 20° of abduction. Concomitant with this translation the humerus spontaneously rotated externally, with a maximum rotation of 15.8° at 50° of abduction. After venting the capsule, anterior and posterior translation and external rotation were increased significantly. Maximum total increase in anteroposterior translation was 14 mm at 30° of abduction. The external rotation was increased up to 7.1° at 40° of abduction. These findings indicate that studies evaluating glenohumeral instability are compromised unless the translations resulting from capsular venting ore corrected. Evaluation of shoulder stability should be performed before violation of the intraarticular pressure mechanisms.     

Release of the coracoacromial ligament can lead to glenohumeral laxity: a biomechanical study

The purpose of this study was to determine change in glenohumeral joint translation after release of the coracoacromial ligament. Six fresh, frozen unpaired glenohumeral joints were tested in a neutral position and at 30 degrees internal and 30 degrees external rotation of the humerus at 0 degrees, 30 degrees, and 60 degrees of abduction on a custom glenohumeral joint translation testing apparatus. A joint compression load of 20 N was simulated; then a 15-N load was applied to the humerus in anterior, posterior, superior, and inferior directions, and translations on the glenoid were measured with an electromagnetic tracking device. The tests were then repeated after a 1.5-cm section of the coracoacromial ligament was released from the acromion. A multivariate analysis of variance was used for statistical analyses with a P value of.05 as the level of significance. At 0 degrees and 30 degrees of abduction, release of the coracoacromial ligament resulted in a significant increase in glenohumeral joint translations, in both the anterior and inferior directions. In addition, the differences in translation between before and after the release of the coracoacromial ligament decreased in all directions as glenohumeral abduction increased, and they were not significant at 60 degrees of abduction in any of the rotations. The results of this study suggest that the coracoacromial ligament has a role in static restraint of the glenohumeral joint. It provides a suspension function and may restrain anterior and inferior translations through an interaction with the coracohumeral ligament. Although this is a biomechanical study without simulation of the shoulder muscles, it indicates that the coracoacromial ligament contributes to glenohumeral stability. Caution should be exercised in the release of the coracoacromial ligament in those with rotator cuff pain associated with glenohumeral instability.     

Multidirectional kinematics of the glenohumeral joint during simulated simple translation tests: impact on clinical diagnoses.

At the end ranges of motion, the glenohumeral capsule limits translation of the humeral head in multiple directions. Since the 6-degree of freedom kinematics of clinical tests are commonly utilized to diagnose shoulder injuries, the objective of this study was to determine the magnitude and repeatability of glenohumeral joint kinematics during a simulated simple anteroposterior translation test in the anterior and posterior directions. A magnetic tracking system was used to determine the kinematics of the humerus with respect to the scapula in eight cadaveric shoulders. At 60 degrees of glenohumeral abduction and 0 degrees of flexion/extension, a clinician applied anterior and posterior loads to the humerus at 0 degrees, 30 degrees, and 60 degrees of external rotation until a manual maximum (simulating a simple translation test) was achieved. Prior to each test, the reference position of the humerus shifted posteriorly 1.8+/-2.0 and 4.1+/-3.8 mm at 30 degrees and 60 degrees of external rotation, respectively. Anterior translation decreased significantly (p < 0.05) from 18.2+/-5.3 mm at 0 degrees of external rotation to 15.5+/-5.1 and 9.9+/-5.5 mm at 30 degrees and 60 degrees, respectively. However, no significant differences were detected between the posterior translations of 13.4+/-6.4, 17.1+/-5.0, and 15.8+/-6.0 mm at 0 degrees, 30 degrees, and 60 degrees of external rotation, respectively. Coupled translations (perpendicular to the direction of loading) at 0 degrees (6.1+/-4.0 and 3.8+/-2.9 mm), 30 degrees (4.7+/-2.7 and 5.9+/-3.1 mm), and 60 degrees (2.3+/-2.3 and 5.0+/-3.5 mm) of external rotation were in the inferior direction in both the anterior and posterior directions, respectively. Based on the data obtained, performing a simulated simple translation test should result in coupled inferior translations and anterior translations that are a function of external rotation. The low standard deviations demonstrate that the observed translations should be repeatable. Furthermore, capsular stretching or injury to the anterior-inferior region of the capsule should be detectable during clinical examination if excessive coupled translations exist or no posterior shift of the reference position with external rotation is noted.     

Superoinferior translation in the intact and vented glenohumeral joint

The purpose of this investigation was to measure inferior translation in the intact and vented shoulder in different positions of abduction and rotation. Fifteen shoulders from adult cadavers were tested before and after venting of the joint capsule on an apparatus that permitted unconstrained translation when a 50 N inferior force was applied to the humeral shaft. The greatest inferior translation in the intact shoulder occurred at 45° abduction in neutral rotation. Venting the capsule significantly increased inferior translation in all positions but 45° abduction, and the greatest effect was seen at 0° glenohumeral abduction in neutral rotation. The so-called "sulcus sign" is the result of intraarficular vacuum effect and capsular laxity. Venting the capsule results in a significant increase in inferior translation. This is an important effect to consider during procedures for repairing instability of the shoulder, because failure to appreciate the normal "play" in inferior glenohumeral translation might lead the surgeon to believe that perceived laxity represents actual instability.     

Arthroscopic glenohumeral folds and microscopic glenohumeral ligaments: the fasciculus obliquus is the missing link

This study tested the hypotheses that the folds in the inferior glenohumeral capsule appear at the borders and crossings of the underlying capsular ligaments and that embalming may result in misinterpretation of these folds as ligaments. The inferior capsular structures in 80 unembalmed cadaver shoulders were compared with 24 embalmed shoulders. During arthroscopy and dissection, an anteroinferior fold was more prominently seen in internal rotation and was almost obliterated in external rotation. A posteroinferior fold appeared in external rotation and almost disappeared in internal rotation. During dissection, the anteroinferior fold developed at the border of the anterior band of the inferior glenohumeral ligament (ABIGHL) and where this ligament crossed with the fasciculus obliquus (FO). Several patterns of crossing of the ABIGHL and the FO were seen that determined the folding-unfolding mechanism of the anteroinferior fold and the appearance of possible synovial recesses. The axillary part of the IGHL is formed by the FO on the glenoid side and by the ABIGHL on the humeral side. The posteroinferior fold was determined by the posterior band of the IGHL. The folds in the embalmed specimens did not necessarily correspond with the underlying fibrous structure of the capsule. The folds and recesses observed during arthroscopy indicate the underlying capsular ligaments but are not the ligaments themselves. The IGHL complex is formed by its anterior and posterior bands and also by the FO. Both findings are important during shoulder instability procedures because the ligaments need to be restored to their appropriate anatomy and tension. Because the FO may also be involved, Bankart-type surgery may have to reach far inferiorly. Midsubstance capsular shift procedures also need to incorporate this ligament.     

Effect of joint compression on inferior stability of the glenohumeral joint

To determine the relative importance of negative intraarticular pressure, capsular tension, and joint compression on inferior stability of the glenohumeral joint we studied 17 fresh, normal adult cadaver shoulders using a "3 degrees of freedom" shoulder test apparatus. Translations were measured in intact and vented shoulders while a 50-N superior and inferior directed force was applied to the shoulder. Three different joint compressive loads (22 N, 111 N, 222 N) were applied externally. Tests were performed in 3 positions of humeral abduction in the scapular plane (0 degree, 45 degrees, 90 degrees) and in 3 positions of rotation (neutral, maximal internal, and maximal external). After tests of the intact and vented shoulder, the glenohumeral ligaments were sectioned and tests were repeated. With minimal joint compression of 22 N, negative intraarticular pressure and capsular tension limited translation of the humeral head on the glenoid. Increasing the joint compressive load to 111 N resulted in a reduction of mean inferior translation from 11.0 mm to 2.0 mm at 0 degree abduction, from 21.5 mm to 1.4 mm at 45 degrees abduction, and from 4.5 mm to 1.2 mm at 90 degrees abduction. With a compressive load of 111 N, venting the capsule or sectioning of glenohumeral ligaments had no effect on inferior stability. Clinical relevance: Glenohumeral joint compression through muscle contraction provides stability against inferior translation of the humeral head, and this effect is more important than negative intraarticular pressure or ligament tension.     

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.     

In Vivo Knee Kinematics for a Cruciate Sacrificing Total Knee Arthroplasty Having Both a Symmetrical Femoral and Tibial Component

BackgroundEarly total knee arthroplasty (TKA) designs were symmetrical, but lead to complications due to over-constraint leading to loosening and poor flexion. Next-generation TKAs have been designed to include asymmetry, pertaining to the trochlear groove, femoral condylar shapes, and/or the tibial component. More recently, an advanced posterior cruciate sacrificing (PCS) TKA was designed to include both a symmetrical femoral component with a patented V-shaped trochlear groove and a symmetrical tibial component with an ultracongruent insert, in an attempt to reduce inventory costs. Because previous PCS TKA designs produced variable results, the objective of this study is to determine and evaluate the in vivo kinematics for subjects implanted with this symmetrical TKA.MethodsTwenty-one subjects, implanted with symmetrical PCS fixed-bearing TKA, were asked to perform a weight-bearing deep knee bend (DKB) while under fluoroscopic surveillance. A 3-dimensional to 2-dimensional registration technique was used to determine each subject’s anteroposterior translation of lateral and medial femoral condyles as well as tibiofemoral axial rotation and their weight-bearing knee flexion.ResultsDuring the DKB, the average active maximum weight-bearing flexion was 111.7° ± 13.3°. On average, from full extension to maximum knee flexion, subjects experienced −2.5 ± 2.0 mm of posterior femoral rollback of the lateral condyle and 2.5 ± 2.2 mm of medial condyle motion in the anterior direction. This medial condyle motion was consistent for the majority of the subjects, with the lateral condyle exhibiting rollback from 0° to 60° of flexion and then experienced an average anterior motion of 0.3 mm from 60° to 90° of knee flexion. On average, the subjects in this study experienced 6.6°± 3.3° of axial rotation, with most of the rotation occurring in early flexion, averaging 4.9°.ConclusionAlthough subjects in this study were implanted with a symmetrical PCS TKA, they did experience femoral rollback of the lateral condyle and a normal-like pattern of axial rotation, although less in magnitude than the normal knee. The normal axial rotation pattern occurred because the lateral condyle rolled in the posterior direction, while the medial condyle moved in the anterior direction. Interestingly, the magnitude of posterior femoral rollback and axial rotation for subjects in this study was similar in magnitude reported in previous studies pertaining to asymmetrical TKA designs. It is proposed that more patients be analyzed having this TKA implanted by other surgeons.     

Micromotion and Migration of Cementless Tibial Trays Under Functional Loading Conditions

BackgroundThe outcome of cementless total knee arthroplasty (TKA) relies on successful bony ingrowth into the implant surfaces. Failures due to aseptic loosening are still reported, especially in younger and more active patients. The objective of this study is to quantify the micromotion of a commercially available design of cementless tibial tray under loading conditions simulating walking and stair descent.MethodA commercially available design of cementless total knee arthroplasty was implanted in 7 cadaveric knees which were preconditioned with 500 cycles of 0°-100° flexion under a vertical load of 1050 N in a custom-built, multiaxial functional activity simulator. This was followed by application of the peak forces and moments occurring during walking and stair descent. During each loading procedure, 3-dimensional motion at the bone-prosthesis interface was measured using digital image correlation.ResultsThe tray migrated 101 ± 25 μm on average during preconditioning, which was dominated by rotation in the sagittal plane (92% of total migration), combined with posterior translation (28%) and minimal rotation in the transverse plane (14%). The migration varied 2.7-fold (61-167 μm) between the 6 measurement zones. Stair descent produced significantly higher total micromotion than walking in zone #5 (62 ± 9 vs 51 ± 10 μm, P < .05) and zone #6 (68 ± 17 vs 37 ± 10 μm, P < .05). In addition, during stair descent, the tray exhibited significantly more tilting (anterior zones: 31 ± 17 vs ?16 ± 20 μm, P < .05; posterior zones: ?60 ± 8 vs ?40 ± 7 μm, P < .05) and more anteroposterior displacement in the anterior zones (?25 ± 3 vs ?13 ± 2 μm, P < .05) when compared to walking.ConclusionThe relative motion at the bone-prosthesis interface varied substantially around the periphery of the cementless tray. Under the loading conditions evaluated, the tray primarily underwent a rocking motion in the sagittal plane. Compared with walking, stair descent produced significantly more micromotion, especially in the posterior zones.     

Effect of the neck-shaft angle on stability in the onlay type of reverse shoulder arthroplasty: a cadaveric study

BackgroundAlthough reverse shoulder arthroplasty (RSA) has been indicated for treating patients suffering from cuff tear arthropathy, instability is a severe complication. The relationship between the humeral neck-shaft angle and joint stability in RSA as well as the clinical effect of subscapularis tendon repair on postoperative stability after RSA remain controversial. This study is primarily aimed to investigate the relationship between humeral neck-shaft angle and stability using the onlay type of RSA with preserved shoulder girdle muscles using fresh frozen cadavers. Moreover, we aimed to investigate the effect of subscapularis tendon repair after RSA placement.MethodsAn onlay type RSA of not-lateralized glenosphere in a massive rotator cuff tear model with preserved shoulder component muscles was placed on 7 fresh frozen cadavers, and traction tests were performed to dislocate by changing the neck-shaft angle of the stem to 135°, 145°, and 155°. The anterior dislocation force (DF) was evaluated in 6 patterns as follows: 2 patterns at 30° and 60° of abduction and 3 patterns at 30° of internal rotation, in neutral rotation, and 30° of external rotation. DF was recorded at neck-shaft angles of 135°, 145°, and 155° and with and without subscapularis tendon repair.ResultsAt 30° abduction, DF was significantly higher at a neck-shaft angle of 155° regardless of the rotational position (P < .05), and at abduction 60°, there was no difference in DF according to any rotational position and any neck-shaft angle. Regardless of the neck-shaft angle, the DF was significantly higher at 60° abduction than at 30° abduction (P < .05). Furthermore, the DF was significantly higher with subscapularis tendon repair (P < .01).ConclusionOur results showed some relationship between humeral neck-shaft angle and stability in the onlay type of RSA with preserved shoulder component muscles using fresh frozen cadavers. Moreover, a neck-shaft angle of 155° showed the highest anterior DF among neck-shaft angles of 135° and 145° at 30° abduction, and there was no difference at abduction 60° among any neck-shaft angle. Furthermore, subscapularis tendon repair also contributed to anterior stability.     

In vivo articular cartilage contact at the glenohumeral joint: preliminary report

BACKGROUND: Little is known about normal in vivo mechanics of the glenohumeral joint. Such an understanding would have significant implications for treating disease conditions that disrupt shoulder function. The objective of this study was to determine articular contact locations between the glenoid and humeral articular surfaces in normal subjects during shoulder abduction with neutral, internal, and external rotations. We hypothesized that glenohumeral articular contact is not perfectly centered and is variable in normal subjects tested under physiological loading conditions. METHODS: Orthogonal fluoroscopic images and magnetic resonance image-based computer models were used to characterize the centroids of articular cartilage contact of the glenohumeral joint at various static, actively stabilized abduction and rotation positions in five healthy shoulders. The shoulder was investigated at 0 degrees , 45 degrees , and 90 degrees abduction with neutral rotation and then at 90 degrees abduction combined with active maximal external rotation and active maximal internal rotation. RESULTS: For all the investigated positions, the centroid of contact on the glenoid surface for each individual, on average, was more than 5 mm away from the geometric center of the glenoid articular surface. Intersubject variation of the centroid of articular contact on the glenoid surface was observed with each investigated position, and 90 degrees abduction with maximal internal rotation showed the least variability. On the humeral head surface, the centroids of contact were located at the superomedial quarter for all investigated positions, except in two subjects' positions at 0 degrees abduction, neutral rotation. CONCLUSIONS: The data showed that the in vivo glenohumeral contact locations were variable among subjects, but in all individuals they were not at the center of the glenoid and humeral head surfaces. This confirms that "ball-in-socket" kinematics do not govern normal shoulder function. These insights into glenohumeral articular contact may be relevant to an appreciation of the consequences of pathology such as rotator cuff disease and instability.