Three-dimensional acromioclavicular joint motions during elevation of the arm

Using Dynamic Stereo X-ray Imaging for In Vivo Acromioclavicular Joint Kinematics Assessment: A Preliminary Investigation

Background

Acromioclavicular joint (ACJ) disruption occurs frequently in athletes engaged in contact sports. However, the current understanding of ACJ biomechanics during muscle-driven functional activities and the influence of different treatment approaches (eg, reconstruction surgery vs nonoperative methods) on ACJ kinematics and stability remains limited. The absence of precise in vivo biomechanical measurement modalities for scapular and clavicular kinematics contributes significantly to this lack of understanding.

Purposes/Hypothesis

The purposes of this study were to determine whether dynamic stereo x-ray (DSX) imaging can be used to evaluate the in vivo kinematics of the ACJ and to provide preliminary comparative data on ACJ kinematics, range of motion, and isometric strength of surgically reconstructed or nonoperatively treated ACJ shoulders and their uninjured contralateral shoulders. It was hypothesized that ACJ kinematics could be measured successfully using DSX and that surgically and nonoperatively treated shoulders would show abnormal 3-dimensional (3-D) ACJ kinematics compared with the uninjured contralateral.

Study Design

Controlled laboratory study.

Methods

In this cross-sectional study, 11 participants who had undergone unilateral ACJ reconstruction surgery and 3 patients who received nonoperative treatment were enrolled. ACJ kinematics were assessed during active forward flexion, scaption, and abduction through high-speed DSX imaging, complemented by 3-D bone models obtained via computed tomography (CT) scans. To gauge kinematic differences, a 1-dimensional statistical parametric mapping method was employed, which compared outcomes in the index limb to those in the uninjured counterpart. In addition, the range of motion and isometric strength at various abduction angles were analyzed, employing a repeated-measures analysis of variance to compare the affected and uninjured sides.

Results

Leveraging a combination of DSX imaging and patient-specific CT bone models, ACJ kinematics was measured successfully during movements along anatomic planes. Preliminary findings from this investigation revealed no detectable differences between the surgically reconstructed and uninjured sides in ACJ biomechanics, shoulder range of motion, and isometric strength outcomes. However, on average, the nonoperatively treated shoulders demonstrated increased internal rotation, upward rotation, and posterior tilting of the scapula relative to the clavicle (no statistical analyses were performed due to the small sample size).

Conclusion

DSX imaging is a promising tool for evaluating potential in vivo kinematic abnormalities in the ACJ during muscle-driven activities, laying the groundwork for further investigations in both ACJ-reconstructed and nonreconstructed patients. This study furnished essential data for conducting power analyses and designing future studies with an adequate sample size to investigate the impact of different treatment approaches on shoulder girdle mechanics.

Clinical Relevance

With its potential for accurately characterizing shoulder girdle kinematics post-ACJ injury, DSX imaging can offer valuable insights for future clinical studies, facilitating informed decisions regarding the short- and long-term impacts of treatment choices on shoulder health and function.

Finite element analysis of the treatment of a minimally invasive approach combined with a novel anatomical locking plate for scapular body fractures

BACKGROUND

The minimally invasive approach for the treatment of displaced scapular neck or body fractures has the advantages of less trauma and minimal muscle dissection. In clinical practice, the minimally invasive approach combined with an anatomical locking plate has been used to treat scapular body fractures. In addition, we have made minor modifications to the minimally invasive approach. However, the biomechanical study about the approach combined with an anatomical locking plate in treating scapular body fractures was limited.

METHODS

Finite element analysis (FEA) was used to conduct the biomechanical comparison between the anatomical locking plate (AP model) and reconstructive plate (RP model) in the treatment of scapular body fractures through the modified minimally invasive approach. A healthy male volunteer with no history of scapula or systemic diseases was recruited. High-resolution computed tomography images of his right scapula were obtained. Two scapula models were constructed and analyzed by the software of Mimics 21.0, Geomagic Wrap 2021, SolidWorks 2021, and ANSYS Workbench 2022, respectively.

RESULTS

Through static structural analysis, in terms of equivalent von Mises stress, equivalent elastic strain, and total deformation, the AP model exhibited superior safety characteristics, enhanced flexibility, and anticipated stability compared with the RP model. This was evidenced by lower maximum stress, lower maximum strain and displacement.

CONCLUSION

The minimally invasive approach combined with an anatomical locking plate for scapular body fractures had better biomechanical stability. The study provided a biomechanical basis to guide the clinical treatment of scapular body fractures.

Low acromial insufficiency fracture rate in reverse shoulder arthroplasty with distal clavicle excision

Background

This study investigated the rate of acromial insufficiency fractures (AIF) in patients undergoing reverse shoulder arthroplasty (RSA) with concomitant distal clavicle excision (DCE).

Methods

Patients who underwent primary RSA with DCE by a single surgeon from 2010 to 2021 were identified. Exclusion criteria included revision RSA, RSA for fracture, or cases utilizing an augmented baseplate or bone graft. AIF was defined as a radiographically proven acromion or scapular spine fracture. Pain without an identifiable fracture on imaging was defined as an acromial insufficiency reaction. Patient demographics, implant information, and radiograph measurements were compared between patients with and without acromial pathology.

Results

One hundred and seventy-five patients were included. Mean age was 72.8 years, and 67% of patients were female. There were 3/174 acromial insufficiency fractures (1.7%). AIF occurred at a mean of 9.3 months after surgery. Twelve patients had insufficiency reactions (6.9%). Patients with acromial pathology were more likely to be female (p = .003) and have a diagnosis of osteoporosis (p = .047) and inflammatory arthritis (p = .049). There was no significant difference between groups in terms of other factors.

Conclusion

The AIF rate in patients who underwent RSA with DCE was 1.7%. These findings suggest that DCE in the setting of RSA may have a protective role against AIF.

In Vivo Analysis of Acromioclavicular Kinematics and Distance During Multiplanar Humeral Elevation

BACKGROUND

Knowledge of acromioclavicular (AC) joint kinematics and distance may provide insight into the biomechanical function and development of new treatment methods. However, accurate data on in vivo AC kinematics and distance between the clavicle and acromion remain unknown.

PURPOSE/HYPOTHESIS

The purpose of this study was to investigate 3-dimensional AC kinematics and distance during arm elevation in abduction, scaption, and forward flexion in a healthy population. It was hypothesized that AC kinematics and distance would vary with the elevation angle and plane of the arm.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 19 shoulders of healthy participants were enrolled. AC kinematics and distance were investigated with a combined dual fluoroscopic imaging system and computed tomography. Rotation and translation of the AC joint were calculated. The AC distance was measured as the minimum distance between the medial border of the acromion and the articular surface of the distal clavicle (ASDC). The minimum distance point (MDP) ratio was defined as the length between the MDP and the posterior edge of the ASDC divided by the anterior-posterior length of the ASDC. AC kinematics and distance between different elevation planes and angles were compared.

RESULTS

Progressive internal rotation, upward rotation, and posterior tilt of the AC joint were observed in all elevation planes. The scapula rotated more upward relative to the clavicle in abduction than in scaption (P = .002) and flexion (P = .005). The arm elevation angle significantly affected translation of the AC joint. The acromion translated more laterally and more posteriorly in scaption than in abduction (P < .001). The AC distance decreased from the initial position to 75° in all planes and was significantly greater in flexion (P < .001). The MDP ratio significantly increased with the elevation angle (P < .001).

CONCLUSION

Progressive rotation and significant translation of the AC joint were observed in different elevation planes. The AC distance decreased with the elevation angle from the initial position to 75°. The minimum distance between the ASDC and the medial border of the acromion moved anteriorly as the shoulder elevation angle increased.

CLINICAL RELEVANCE

These results could serve as benchmark data for future studies aiming to improve the surgical treatment of AC joint abnormalities to restore optimal function.

Reversed total shoulder arthroplasty after acromioclavicular joint resection yields equivalent clinical results compared to a matched control group

INTRODUCTION

Reverse total shoulder arthroplasty (RTSA) is a well-establish procedure with increasing incidence. Depending on the medical history, many patients undergo multiple soft-tissue procedures before RTSA. The role of acromioclavicular pathology as well as the consequences of a distal clavicle resection (DCR) before RTSA has not been evaluated yet.

MATERIAL AND METHODS

A retrospective single-center review was performed on all patients undergoing primary RTSA with or without DCR with a minimum follow-up of 2 years. We compared patient-reported outcome measures (Constant score (CS), subjective shoulder values (SSV), and range of motion (ROM)) with a matched control group. The control group consisted of patients treated with a RTSA without DCR and matching was performed for age, sex, operating side, American Society of Anesthesiologists (ASA), body mass index (BMI), and indication. Surgical time and complication rate were recorded.

RESULTS

Thirty-nine patients with a mean follow-up of 63 months (SD 33) were enrolled in the study group. Mean age was 67 years (SD 7) with 44% male patients for both groups. The mean relative CS improved from 43% (SD 17) to 73% (SD 20) in the study group, and from 43% (18) to 73% (22) in the control group. The SSV improved from 29% (SD 17) to 63% (SD 29) in the study group, and from 28% (SD 16) to 69% (SD 26) in the control group (both n.s.). The postoperative ROM did not significantly differ between the two groups. Five patients in the study group and six in the control group had reoperations.

CONCLUSION

Patients who received a DCR before RTSA showed equivalent clinical outcomes compared to a match-control group with RTSA only. Surgical time was not different, and no complication related to the open DCR was observed in the study group. Therefore, we conclude that a prior DCR does not influence the postoperative outcome after RTSA.

LEVEL OF EVIDENCE

Level III: Retrospective comparative study.

Dynamic evaluation of the sternoclavicular and acromioclavicular joints using an upright four-dimensional computed tomography

In the analysis of the shoulder complex, the sequential changes occurring in the sternoclavicular and acromioclavicular joints during active shoulder motion are challenging to track. This study aimed to investigate the in vivo sternoclavicular and acromioclavicular joint motions during active elevation, including the sequential changes in these joint spaces using upright four-dimensional computed tomography (4DCT). Bilateral shoulders of 12 healthy volunteers upright 4DCT were obtained during active elevation similar to a "hands up" motion. The sternoclavicular and acromioclavicular rotation angles, joint distances, and closest points on the clavicle relative to the thorax and scapula were evaluated during 10°-140° of humerothoracic elevation. During humerothoracic elevation, the clavicle elevated, retracted, and rotated posteriorly relative to the thorax, whereas the scapula rotated upwardly, internally, and posteriorly relative to the clavicle. All the sternoclavicular and acromioclavicular joint rotation angles were significantly different at ≥ 30°-50° of humerothoracic elevation compared with 10° of humerothoracic elevation. The mean sternoclavicular and acromioclavicular joint distances were 2.2 ± 1.1 mm and 1.6 ± 0.9 mm, respectively. The closest points were located on the anteroinferior part of the medial and lateral clavicle in the sternoclavicular and acromioclavicular joints, respectively. Significant differences were observed in the acromioclavicular joint distance and anterior/posterior movements of the closest points in the sternoclavicular and acromioclavicular joints compared with 10° of humerothoracic elevation. Our sternoclavicular and acromioclavicular closest point results indicate that the impingement tends to occur at the anteroinferior part of the medial and lateral aspects of the clavicle and may be related to osteoarthritis.

Evaluation of the range of motion of scapulothoracic, acromioclavicular and sternoclavicular joints: State of the art

The scapulothoracic, acromioclavicular and sternoclavicular joints play a fundamental role in the shoulder function. Shoulder complex kinematics have been studied with different methods using: goniometers, 2 static radiographs, 3D motion analyzers (invasive or noninvasive) and digital inclinometers. Goniometers have been used traditionally to assess scapular rotation in relation to the thorax. The intrinsic limit of multiple static two-dimensional shoulder radiographs is the attempt of describing in two what is occurring in three dimensions. Technology innovations have led to the development of the 3D shoulder complex kinematics analysis ETS (Electromagnetic tracking systems) using sensors (invasive bone-pin markers or noninvasive skin surface marker) stitched to the scapula/clavicula, thorax, and humerus. Despite being uncomfortable, invasive 3D motion cortical pins analyzers still represent the current gold standard for tracking shoulder complex kinematics. Therefore, access to three-dimensional biomechanical instrumentations for collecting kinematic data represents an active problem for many physicians. A precise, easy to use and low-cost non-invasive method able to draw and analyze the kinematics of the shoulder complex has not been developed yet. Further researches are necessary to design a new non-invasive method able to draw and analyze the kinematics of the scapula and the whole shoulder complex, precisely.

The stress and strain pattern in the ligaments of the acromioclavicular joint using a quasi-static model

BACKGROUND

The precise role of the acromioclavicular and coracoclavicular ligaments during shoulder motion is unclear. We evaluate changes in the stress-strain distribution of the acromioclavicular joint's ligaments during different shoulder passive motion positions.

METHODS

A 3D acromioclavicular joint model was reconstructed. A constitutive hyperelastic model was used for the ligaments. The kinematics of the shoulder girdle was taken to simulate shoulder abduction (Motion 1) and horizontal adduction (Motion 2). A computer-generated quasi-static and non-linear finite element model was used to predict the 3D stress-strain distribution pattern of the acromioclavicular ligament and the coracoclavicular ligament complex.

FINDINGS

In motion 1, from 20 to 90° the peak von Mises stress was found in the conoid (4.14 MPa) and the anteroinferior bundle (2.46 MPa), while from 90 to 120° it was found in the conoid and the trapezoid. However, there were no significant differences between the mean stress values between anteroinferior bundle and trapezoid throughout the motion (p = 0.98). In Motion 2, from 20 to 80° the maximum equivalent elastic strain was found in the anteroinferior bundle (0.68 mm/mm) and the conoid (0.57 mm/mm), while from 80 to 100° it was higher in the conoid (0.88 mm/mm) than in the anteroinferior bundle (0.77 mm/mm).

INTERPRETATION

The coracoclavicular ligament complex demonstrated a high stress-strain concentration during simulated passive shoulder abduction. Additionally, it was shown that the acromioclavicular ligament plays an important role in joint restraint during passive horizontal adduction, changing the primary role with the trapezoid and conoid at different motion intervals.

3D measurement of clavicular and scapular orientations: The association with clinical characteristics and responsiveness to scapular repositioning in patients with neck pain

BACKGROUND

Clavicular and scapular orientations vary between neck pain patients as do clinical features and responses (changes in pain and rotation range) to scapular repositioning. Associations between these factors are unknown.

OBJECTIVES

To identify subgroups of neck pain patients based on three-dimensional (3D) measures of clavicular and scapular orientations and differences between subgroups in clinical characteristics and responses to scapular repositioning.

DESIGN

Cross-sectional study.

METHODS

Eligible participants were recruited as part of a larger study. The 3D clavicular and scapular orientations were analyzed on the more painful side of the neck using a hierarchical cluster analysis. Clinical characteristics were neck pain location, intensity, duration, disability and presence of headache. Responses to scapular repositioning were classified as "yes and no".

RESULTS

Fifty-eight participants (29 responsive; 29 non-responsive to scapular repositioning) participated in the study. Analysis identified two distinct subgroups: subgroup1 had greater clavicular retraction and scapular downward rotation (n = 26) and subgroup2 had greater clavicular elevation and scapular internal rotation and anterior tilt (n = 32). Headache and dominant pain in the upper neck were more frequent in subgroup 1 while dominant pain in the lower neck was frequent in subgroup 2 (p < 0.01). Most participants who responded positively to scapular repositioning (88.5%) were in subgroup1 and most non-responsive participants (81.2%) in subgroup2.

CONCLUSIONS

The 3D clavicular and scapular orientations identified two subgroups of neck pain patients. Participants with predominantly downward scapular rotation were distinguished by pain in the upper neck, presence of headache and a positive response to scapular repositioning.

Kinematic analysis of scapulothoracic movements in the shoulder girdle: a whole cadaver study

Background

Existing kinematic studies of the shoulder girdle focus on humerothoracic movements. Isolated scapulothoracic movements are also performed during daily activities and rehabilitation but kinematic values are lacking.

Methods

A kinematic analysis was performed in 14 cadaveric shoulders during protraction, retraction, and shrug. An optical navigation system was used to analyze sternoclavicular, scapulothoracic, and acromioclavicular motions.

Results

In the sternoclavicular joint, shrug and retraction caused a posterior clavicular rotation of 5° (standard deviation [SD] 6°) and 3° (SD 2°), while protraction induced an anterior rotation of 3° (SD 2°). Shrug caused a large clavicular elevation of 25° (SD 5°). Shrug and retraction caused an increase in retraction of 17° (SD 5°) and 9° (SD 2°). Protraction induced an increase of 10° (SD 2°) toward protraction. In the scapulothoracic joint, shrug induced an increase of 3° (SD 2°) in anterior scapular tilt, and a lateral rotation of 26° (SD 4°). Retraction caused a lateral rotation of 4° (SD 3°). Protraction caused an increase of 7° (SD 2°) in the scapular protraction position, while shrug and retraction demonstrated a decrease of 9° (SD 2°) and 6° (SD 5°). In the acromioclavicular joint, posterior tilting of the scapula compared to the clavicle increased 23° (SD 6°) during shrug, while during protraction an increase of only 4° (SD 3°) was seen. During shrug, relative lateral rotation increased 13° (SD 4°). The protraction movement decreased the relative protraction position with 3° (SD 2°).

Conclusion

This study provided normative kinematic values of scapulothoracic movements in the shoulder girdle.

Clavicular and scapular, but not spinal kinematics vary with scapular dyskinesis type during arm elevation and lowering in persons with neck pain

BACKGROUND

Scapular dyskinesis is often observed in patients with neck pain. However, it is unknown whether clavicular, scapular and spinal kinematics vary with different types of scapular dyskinesis during arm movement.

RESEARCH QUESTION

Are there differences in clavicular, scapular and spinal kinematics during unilateral arm elevation and lowering among neck pain patients presenting with (i) scapular winging, (ii) with dysrhythmia, (iii) with no scapular abnormality and (iv) healthy controls?

METHODS

Sixty participants with neck pain (20 in each group) and 20 asymptomatic controls were recruited. The 3D kinematic data were measured during unilateral arm elevation and lowering at 30°, 60°, 90°, and 120° in the scapular plane. A three-way mixed-effects ANOVA was used to determine the main effects (group, phase and angle) and the interactions between three independent variables on the kinematic data.

RESULTS

The neck pain group with scapular winging had decreased clavicular retraction and increased scapular internal rotation and anterior tilt compared to the other neck pain and control groups at all angles during both phases of arm movement (p < 0.01). The neck pain group with scapular dysrhythmia had decreased scapular upward rotation compared to all other groups (p < 0.01). Some alterations in the kinematics existed during the lowering phase compared to the raising phase for all groups (p < 0.05). Spinal kinematics were similar across all groups (p > 0.05).

SIGNIFICANCE

Specific patterns of clavicular and scapular kinematics were identified during arm movement relevant to the type of observed scapular dyskinesis in patients with neck pain. Such findings stand to inform more precise and relevant motor training in rehabilitation and improve understanding of the association between altered scapular kinematics and neck pain.

Shoulder structure and function: The impact of osteoarthritis and rehabilitation strategies

STUDY DESIGN

Invited review.

BACKGROUND

Shoulder osteoarthritis can result in significant functional deficits. To improve diagnosis and treatment, we must better understand the impact of osteoarthritis on shoulder biomechanics and the known mechanical benefits of currently available treatments.

PURPOSE

The purpose of this paper is to present up-to-date data on the effects of osteoarthritis and rehabilitation on the biomechanical parameters contributing to shoulder function. With this goal, we also reviewed the anatomy and the ranges of motion of the shoulder.

METHODS

A search of electronic databases was conducted. All study designs were included to inform this qualitative, narrative literature review.

RESULTS

This review describes the biomechanics of the shoulder, the impact of osteoarthritis on shoulder function, and the treatment of shoulder osteoarthritis with an emphasis on rehabilitation.

CONCLUSIONS

The shoulder is important for the completion of activities of daily living, and osteoarthritis of the shoulder can significantly reduce shoulder motion and arm function. Although shoulder rehabilitation is an integral treatment modality to improve pain and function in shoulder osteoarthritis, few high-quality studies have investigated the effects and benefits of shoulder physical and occupational therapies. To advance the fields of therapy and rehabilitation, future studies investigating the effects of therapy intensity, therapy duration, and the relative benefits of therapy subtypes on shoulder biomechanics and function are necessary.

Differences between Coracoclavicular, Acromioclavicular, or Combined Reconstruction Techniques on the Kinematics of the Shoulder Girdle

BACKGROUND

Although the coracoclavicular (CC) ligaments are classically reconstructed after acromioclavicular (AC) joint injuries, biomechanical studies over the past decade have indicated the importance of an additional reconstruction of the AC ligaments. To date, no kinematic study has investigated the kinematic differences between these reconstruction strategies.

PURPOSE

To evaluate the restoration of shoulder motion after an AC injury using a CC ligament, an AC ligament, or a combined reconstruction technique.

STUDY DESIGN

Controlled laboratory study.

METHODS

After creating a Rockwood grade V lesion in 14 cadaveric shoulders, the AC joint injury was treated with either a CC ligament reconstruction using a suspension device, an in situ AC ligament reconstruction using 2 coupled soft tissue anchors, or a combination of these 2 techniques. Joint motions were registered during humerothoracic elevation in the coronal plane and protraction in the intact shoulder in a Rockwood V lesion and after the 3 reconstruction strategies. An optical navigation system measured 3-dimensional rotation in the sternoclavicular and scapulothoracic joints, and both rotation and translation were analyzed in the AC joint.

RESULTS

In the sternoclavicular joint, the CC and combined reconstruction techniques adequately restored clavicular axial rotation, while the AC reconstruction technique showed a better correction of clavicular elevation. Scapulothoracic joint rotations were best restored by reconstructing the AC ligaments. In the AC joint, the relative tilting position and the lateral rotation of the scapula compared with the clavicle were best restored by the suspension device and combined reconstruction. The AC ligament reconstruction technique demonstrated a better restoration of the relative protracted position and resulted in a better correction of the translation of the scapula relative to the clavicle.

CONCLUSION

This study illustrates that there are kinematic differences between AC, CC, or combined ligament reconstruction strategies. Although each technique was able to restore different elements of the joint kinematics, none of the strategies completely restored the shoulder girdle to its preinjured state.

CLINICAL RELEVANCE

Humerothoracic movements after Rockwood V lesions are best restored using the CC reconstruction technique, and scapulothoracic movements are best restored using the AC ligament reconstruction technique.

Comparing exercises with and without electromyographic biofeedback in subacromial pain syndrome: A randomized controlled trial

BACKGROUND

Deficits in movement and muscle activation of scapulohumeral joint are related to Subacromial Pain Syndrome. Electromyography biofeedback during exercise may enhance muscle activation and coordination, and consequently improve pain and shoulder function.

METHODS

This study compared the effects of an exercise protocol with and without using electromyographic biofeedback on pain, function and movement of the shoulder complex in subjects with Subacromial Pain Syndrome. A total of 24 patients with subacromial pain (mean age = 46.2 + 8.1;18 women) were randomized to either therapeutic exercise or exercise plus biofeedback to the trapezius and serratus muscles. Pain and shoulder function were evaluated as the primary outcome and range of motion, muscle strength, electromyographic activity and scapulohumeral kinematics as secondary outcomes. The subjects underwent eight weeks of intervention and comparisons were made between groups in baseline, at 4 weeks, 8 weeks, and at 4 weeks post intervention.

FINDINGS

There were differences between groups for pain [mean difference = 1.5 (CI 0.3, 3.2) p = 0.01] at 8 weeks in the Exercise group and scapular upward rotation at 60° of arm elevation [mean difference = 13.9 (CI 0.9, 9.3), p = 0.006] in the Biofeedback group. There was no difference for the other variables of scapular kinematics as well as for shoulder function (DASH), muscle strength, range of motion and electromyographic variables.

INTERPRETATION

The addition of Biofeedback to the exercise protocol increased upward rotation of the scapula. However, the volunteers who performed only the Exercises had a better response in reducing pain.

Anteroinferior bundle of the acromioclavicular ligament plays a substantial role in the joint function during shoulder elevation and horizontal adduction: a finite element model

Background

Postoperative acromioclavicular (AC) ligament deficiency has been identified as a common cause of failure after isolated coracoclavicular reconstruction. The two-bundle arrangement of the acromioclavicular ligament has recently been reported in histological and anatomical research. In addition, a clear structural advantage of the superoposterior bundle (SPB) over the less consistent anteroinferior bundle (AIB) was also found. However, the current understanding of the function of the acromioclavicular ligament in joint stability is based on uniaxial bone loading experiments and sequential ligament sectioning. Consequently, these rigid biomechanics models do not reproduce the coupled physiological kinematics, neither in the normal joint nor in the postoperative condition. Therefore, our goal was to build a quasi-static finite element model to study the function of the acromioclavicular ligament based on its biomechanical performance patterns using the benefits of computational models.

Methods

A three-dimensional bone model is reconstructed using images from a healthy shoulder. The ligament structures were modeled according to the architecture and dimensions of the bone. The kinematics conditions for the shoulder girdle were determined after the osseous axes aligned to simulate the shoulder elevation in the coronal plane and horizontal adduction. Three patterns evaluated ligament function. The peak von Mises stress values were recorded using a clock model that identified the stress distribution. In addition, the variation in length and displacement of the ligament during shoulder motion were compared using a two-tailed hypotheses test. P values < 0.01 were considered statistically significant.

Results

The peak von Mises stress was consistently observed in the AIB at 2:30 in coronal elevation (4.06 MPa) and horizontal adduction (2.32 MPa). Except in the position 2:00, statistically significant higher deformations were identified in the two bundles during shoulder elevation. The highest ligament displacement was observed on the Y- and Z-axes.

Conclusions

The AIB has the primary role in restricting the acromioclavicular joint during shoulder motion, even though the two bundles of the AC ligament have a complementary mode of action. During horizontal adduction, the SPB appears to prevent anterior and superior translation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-02966-0.

Kinematic Alterations in the Shoulder Complex in Rockwood V Acromioclavicular Injuries During Humerothoracic and Scapulothoracic Movements: A Whole-Cadaver Study

BACKGROUND

Previous cadaveric kinematic studies on acromioclavicular injuries described mainly rotational differences during humerothoracic movements. Although isolated scapulothoracic movements are also often performed during activities of daily life and can be painful after acromioclavicular injuries, they have not been extensively studied. Further, the analysis of joint translations in kinematic studies has received little attention compared with biomechanical studies.

HYPOTHESIS

A kinematic analysis of joint motions in the intact shoulder versus a shoulder with Rockwood V injury would demonstrate a different pattern of kinematic alterations during humerothoracic and scapulothoracic movements.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A kinematic analysis was performed in 14 cadaveric shoulders during 3 humerothoracic passive movements (coronal and sagittal plane elevation and horizontal adduction) and 3 scapulothoracic passive movements (protraction, retraction, and shrug). An optical navigation system registered rotational motions in the sternoclavicular, scapulothoracic, and acromioclavicular joints in the intact and Rockwood V conditions. In the acromioclavicular joint, mediolateral, anteroposterior, and superoinferior translations were also analyzed.

RESULTS

In the Rockwood V condition, a significant increase in clavicular elevation in the sternoclavicular joint during both humerothoracic and scapulothoracic movements was demonstrated, whereas a significant decrease in posterior rotation of the clavicle occurred only during humerothoracic movements. In the scapulothoracic joint, the scapular position changed most significantly during protraction. In the acromioclavicular joint, the scapular tilting position was altered significantly during both humerothoracic and scapulothoracic movements, whereas the scapular rotational position changed only during coronal and sagittal plane elevation. The largest significant changes in the scapular protraction position were seen during protraction movement. Further, in the acromioclavicular joint there was a significant inferior translation of the scapula during all motions, a significant anterior translation during protraction and horizontal adduction, and a significant posterior translation during coronal plane elevation. Mediolaterally, the acromial end of the scapula slid further under the distal clavicle during protraction than during horizontal adduction.

CONCLUSION

Large kinematic differences were seen between the intact state and a Rockwood V lesion not only during humerothoracic movements but also during scapulothoracic movements in the cadaveric model. During humerothoracic movements, rotational differences were mainly caused by alterations in the clavicular position. In contrast, during protraction, the alterations in the scapular position were the dominant factor.

CLINICAL RELEVANCE

This study demonstrates that protraction induces larger kinematic alterations than horizontal adduction in acromioclavicular injuries and can therefore be included in both clinical examination and kinematic analyses to identify lesions more clearly.

Severe acromioclavicular joint osteoarthritis is associated with acromial stress fractures after reverse shoulder arthroplasty

Background

Little is known about the role of disorders of the acromioclavicular joint (ACJ) and how they relate to complications after reverse shoulder arthroplasty (RSA). The purpose of this study is to compare the severity of ACJ osteoarthritis in patients undergoing RSA with and without postoperative acromial and scapular spine fractures.

Methods

A retrospective review was performed to identify all patients who underwent primary RSA between 1/1/2007 and 10/31/2019 with a postoperative acromial or scapular spine stress fracture from a single institution. Patients who underwent RSA with a fracture were compared with an age-, sex-, and preoperative diagnosis-matched control group (1:4 controls) with a minimum 2-year follow-up. We compared demographics, medical comorbidities, and ACJ osteoarthritis between the 2 groups. Preoperative radiographs and 3-dimensional computed tomography scans were evaluated for ACJ osteoarthritis in all patients. The Petersson classification, a modified Petersson classification, location of the osteophytes, subchondral cysts, ACJ space, and size of the largest osteophyte were recorded and compared between the 2 groups.

Results

The study included 11 patients who underwent primary RSA (8 women and 3 men) with acromial (6) and scapular spine (5) fractures confirmed radiographically and 44 matched controls (average follow-up 3.1 vs. 4.3 years, P = .17). Average age at surgery was similar between study and control groups (69.6 vs. 70.0 years, P = .86). ACJ osteoarthritis with osteophytes larger than 2 mm was common and similar between the 2 groups (91% of patients with acromial fracture and 66% of controls, P = .15). There was no significant difference in the size or location of the ACJ osteophytes. The Petersson classification was similar between groups. However, the percentage of patients with subchondral ACJ cysts was higher in the fracture group (91% vs. 50%, P = .02), and the percentage of patients with large spanning or fused osteophytes was significantly higher in the fracture group (55% vs. 14%, P = .008).

Conclusion

Radiographic ACJ osteoarthritis is common in patients undergoing RSA. Severe ACJ osteoarthritis with completely spanning or fused osteophytes may predispose patients to acromial or scapular spine fractures after RSA.

Comparison of the effectiveness of novel intervention on restricted range of motion of shoulder in young healthy subjects

Objective

To evaluate the effectiveness of four novel and pragmatic interventions on the restricted range of motion (ROM) of shoulder joint in healthy subjects.

Methods

The study was conducted at Helping Hand Institute of Rehabilitation Sciences, Mansehra, in 6-months duration. This quasi-experimental study recruited 120 young subjects with an equal proportion of males and females for four novel intervention groups (n=30 each group) including pragmatic posterior capsular stretch, Serratus anterior stretch, rotator cuff facilitation and acromioclavicular joint mobilization. Study variables included measurement of Reaching up behind the back (RUBTB), Reaching down behind the neck (RDBTN), and shoulder range of motion (flexion, abduction, external rotation, internal rotation). The paired t-test was used for the change in pretest and posttest variables and the Kruskal Wallis test was used to compare the change in each group of interventions.

Results

All the variables improved significantly (p< 0.05) from their baseline scores for the interventions. The mean difference among the intervention groups for the variables was statistically significant (p<0.001) on the Kruskal Wallis test. Pragmatic posterior capsular stretch (PPCS) and serratus anterior stretch (SAS) improved the RUBTB and RDBTN more than the other interventions. Rotator cuff facilitation (RFC) improved shoulder rotation more than the rest of the intervention. Acromioclavicular joint mobilization (ACJM) was effective in improving the abduction and flexion ROM.

Conclusion

Pragmatic interventions are effective in improving shoulder ROM in young healthy adults and recommended for the trials on prevention and rehabilitation of shoulder pathologies.

Risk of Iatrogenic Axillary Nerve Injury During Acromioclavicular Joint Reconstruction

Anatomical reconstruction of the coracoclavicular ligaments involves drilling the base of the coracoid or looping a graft around it, placing the axillary nerve at risk for injury. Rockwood type V acromioclavicular (AC) separation injuries involve disruption of the AC joint capsule and coracoclavicular ligaments, resulting in inferomedial displacement of the scapulohumeral complex and alteration of the normal anatomical relations of the shoulder girdle structures. This study evaluated the effect of Rockwood type V AC separation on the anatomical relation of the axillary nerve to the coracoid base. Ten shoulders of 6 adult human cadavers were dissected to determine the dimensions of the coracoid. A digital caliper was used to measure the coracoclavicular distance and the minimal distance between the coracoid base and the axillary nerve. A Rockwood type V AC separation was created by transecting the AC joint capsule and coracoclavicular ligaments, and applying 15 kg of longitudinal tension to the upper extremity. Changes in the distance between the coracoid base and the axillary nerve were measured. Mean width, length, and thickness of the coracoid was 15.05±0.93 mm, 23.1±1.75 mm, and 11.88±1.33 mm, respectively. Mean distance between the coracoid base and the axillary nerve was 26.0±3.9 mm. After simulated Rockwood type V AC separation, mean distance was 22.0±3.4 mm; this difference was statistically significant (P=.0263; 95% CI, 2.0-5.9 mm). The axillary nerve is closer to the coracoid base during simulated Rockwood type V AC separation than previously reported in the orthopedic literature. Anatomical reconstruction of the coracoclavicular ligaments for Rockwood type V AC separation presents a higher risk for axillary nerve iatrogenic injury than previously reported. [Orthopedics. 2021;44(1):e68-e72.].

The recovery of reaching movement in breast cancer survivors: two different rehabilitative protocols in comparison

BACKGROUND

Breast cancer (BC) is the most common cancer in women in the developed world. The about the sequelae of surgery, especially in case of mastectomy or modified radical mastectomy is grown. Nowadays it is important choose appropriate exercise programs to allow recovery in "quantity" but also in "quality" of the movement of the operated upper limb.

AIM

The aim of this study was to verify whether specific exercises for the scapula may induce changes in fluidity of the reaching movement.

DESIGN

Randomized control-trial double-blind study.

SETTING

Exercise training laboratory and gait analysis laboratory.

POPULATION

Sixty-three breast cancer survivors were enrolled.

METHODS

Participants randomized to single rehabilitative treatment (ST), or to group rehabilitative treatment (GT). VAS, DASH and a biomechanical evaluation of upper limb were performed for each group before treatment (T0=baseline), at the end rehabilitative treatment (T1) and after three months of follow-up (T2).

RESULTS

Respect within group analysis, in the ST and in the GT, for VAS an improvement along evaluation times were observed, respectively at T0 to T1 and at T0 to T2 (P<0.001) without a statistically significant difference between groups. At the same, for the DASH, the results showed the same trend without a statistically significant difference between groups. For biomechanical parameters, at T2 velocity was statistically significantly greater in the ST than in the GT (P=0.029) in contrast with the duration, that was statistically significantly greater in the GT than in the ST (P=0.010).

CONCLUSIONS

Both protocols are effective in reducing pain and for functional recovery of the upper limb. The adoption of a non-intensive rehabilitation program should be implemented at least in the first year after the operation, with the adoption of specific myofascial exercises on the scapulo-thoracic joint with better results in the "qualitative" recovery of the achievement.

CLINICAL REHABILITATION IMPACT

Our study emphasizes the importance of rehabilitation in BC survivors after mastectomy, even during the course of radiotherapy and chemotherapy and the adoption of specific myofascial exercises on the scapulo-thoracic joint and specific exercises of muscular stretching on the pectoral muscle. Therefore, the proposed rehabilitation protocol must be "clipped" and "integrated" according to the specific objectives for each individual patient.

The Coupled Kinematics of Scapulothoracic Upward Rotation

BACKGROUND

Scapulothoracic upward rotation (UR) is an important shoulder complex motion allowing for a larger functional work space and improved glenohumeral muscle function. However, the kinematic mechanisms producing scapulothoracic UR remain unclear, limiting the understanding of normal and abnormal shoulder movements.

OBJECTIVE

The objective of this study was to identify the coupling relationships through which sternoclavicular and acromioclavicular joint motions contribute to scapulothoracic UR.

DESIGN

This was a cross-sectional observational study.

METHODS

Sixty participants were enrolled in this study; 30 had current shoulder pain, and 30 had no history of shoulder symptoms. Shoulder complex kinematics were quantified using single-plane fluoroscopy and 2D/3D shape matching and were described as finite helical displacements for 30-degree phases of humerothoracic elevation (30 degrees-60 degrees, 60 degrees-90 degrees, and 90 degrees-120 degrees). A coupling function was derived to estimate scapulothoracic UR from its component motions of acromioclavicular UR, sternoclavicular posterior rotation, and sternoclavicular elevation as a function of acromioclavicular internal rotation. The proportional contributions of each of the component motions were also calculated and compared between phases of humerothoracic elevation and groups.

RESULTS

Scapulothoracic UR displacement could be effectively predicted using the derived coupling function. During the 30- to 60-degree humerothoracic elevation phase, acromioclavicular UR accounted for 84.2% of scapulothoracic UR, whereas sternoclavicular posterior rotation and elevation each accounted for < 10%. During later phases, acromioclavicular UR and sternoclavicular posterior rotation each accounted for 32% to 42%, whereas sternoclavicular elevation accounted for < 11%.

LIMITATIONS

Error due to the tracking of sternoclavicular posterior rotation may have resulted in an underprediction of its proportional contribution and an overprediction of the proportional contribution of acromioclavicular UR.

CONCLUSIONS

Acromioclavicular UR and sternoclavicular posterior rotation are the predominant component motions of scapulothoracic UR. More research is needed to investigate how these coupling relationships are affected by muscle function and influenced by scapular dyskinesis.

Three-Dimensional Analysis of Scapular Kinematics During Arm Elevation in Baseball Players With Scapular Dyskinesis: Comparison of Dominant and Nondominant Arms

Background: The knowledge of 3-dimensional scapular kinematics is essential for understanding the pathological lesions of the shoulder and elbow in throwing athletes. Many studies about alterations of the resting scapular position, dynamic scapular motion, or scapular dyskinesis (SD) have been conducted, yet none of them have identified a consistent pattern of altered scapular kinematics in throwing athletes. Hypothesis/Purpose: To analyze the 3-dimensional scapular kinematics of dominant and nondominant arms in baseball players with a pathological condition of the shoulder or elbow. Study Design: Cross-sectional study. Methods: Bilateral scapular positions, consisting of upward rotation (UR), superior translation (ST), internal rotation (IR), protraction (PRO), and anterior tilting (AT) with an arm at rest and at 150° forward elevation, were measured among 319 baseball players with SD using 3-dimensional computed tomography. Angular values of scapula were compared between dominant and nondominant arms with statistical analysis. Level of Evidence: Level III, diagnostic study. Results: The scapular position of dominant arms showed significantly more AT, less ST at rest and more UR and IR and less ST, PRO, and AT at 150° full forward elevation compared with the nondominant arms. The magnitude of mean change of UR, IR, PRO, and AT during arm elevation increased significantly between the paired arms (P value: UR, ST, PRO, and AT: <.001 and IR: .001). Conclusion: When compared with the nondominant arms, UR, AT, and PRO with the arm at 150° forward elevation of dominant symptomatic arms in baseball players tilted toward positive compensation, whereas IR altered toward negative decompensation. In addition, the angular increment of the scapula increased significantly in dominant symptomatic arms compared with the nondominant arms.

Reconstruction of the Acromioclavicular Ligament Complex Using Dermal Allograft: A Biomechanical Analysis

PURPOSE

To analyze the posterior translational and rotational stability of the acromioclavicular (AC) joint following reconstruction of the superior acromioclavicular ligament complex (ACLC) using dermal allograft.

METHODS

Six fresh-frozen cadaveric shoulders were used (mean age of 65.3 ± 6.9 years). The resistance force against posterior translation (10 mm) and torque against posterior rotation (20°) was measured. Specimens were first tested with both the intact ACLC and coracoclavicular ligaments. The ACLC and coracoclavicular ligaments were then transected so simulate a Type III/V AC joint dislocation. Each specimen then underwent 3 testing conditions, performed in the following order: (1) ACLC patch reconstruction alone, (2) ACLC patch with an anatomic coracoclavicular reconstruction (ACCR) using semitendinosus allograft, and (3) the transected ACLC with an ACCR only. Differences in posterior translational and rotational torque across testing conditions were analyzed with a one-way repeated analysis of variance analysis.

RESULTS

Mean resistance against posterior translation in the intact condition was 65.76 ± 23.8 N. No significant difference found between the intact condition compared with specimens with the ACLC-patch only (44.2 ± 11.3 N, P = .06). The ACCR technique, when tested alone, had significantly less posterior translational resistance compared with the intact condition (38.5 ± 8.94 N, P = .008). ACLC patch in combination with an ACCR was closest in restoring native posterior translation (57.1 ± 19.2 N, P = .75). For rotational resistance, only the addition of the ACLC patch with an ACCR (0.51 ± 0.07 N-m) demonstrated similar torque compared with the intact joint (0.89 ± 0.5 N-m, P = .06).

CONCLUSIONS

The ACLC-patch plus ACCR technique was able to closest restore the percent of normal posterior translational and rotational stability.

CLINICAL RELEVANCE

Recurrent posterior instability of the AC joint is a potential complication after coracoclavicular reconstruction surgery. In the in vitro setting, this study demonstrated increased AC joint stability with the addition of an ACLC reconstruction using dermal allograft.

Three-dimensional scapular kinematics, shoulder outcome measures and quality of life following treatment for breast cancer - A case control study

BACKGROUND

There are no conclusive results concerning changes in scapular kinematics associated with upper limb dysfunctions after breast cancer surgery.

OBJECTIVE

To compare the three-dimensional (3-D) scapular kinematics during elevation of the arm between women after breast cancer surgery and controls. Shoulder range of motion (ROM), muscle strength, pain intensity, upper limb function, and quality of life were also assessed.

METHODS

Forty-two women were assigned to two groups (surgery group, n = 21; control group, n = 21). 3-D scapular kinematics was collected during elevation of the arm in the scapular plane. ROM was assessed using a digital inclinometer, muscle strength using a manual dynamometer, pain with the Visual Analogue Scale (VAS), upper limb function with the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire and quality of life with the 36-item Short-Form Health Survey (SF36).

RESULTS

The surgery group presented decreased scapular upward rotation at 120° of arm elevation in the scapular plane (p < .05; d = -0.88), decreased shoulder external rotation ROM and strength of shoulder abduction and external rotation when the affected side was compared to the non-affected side and control group. Moreover, the surgery group also reported higher pain, increased upper limb disability and poorer quality of life compared with healthy controls.

CONCLUSION

Scapular upward rotation seems to be decreased at 120° of arm elevation in women following breast cancer surgery. In addition, shoulder external rotation ROM, abduction strength, external rotation strength, function, and quality of life are also impaired in these women. They also experienced pain during the studied movements.

Therapeutic Interventions for Scapular Kinematics and Disability in Patients With Subacromial Impingement: A Systematic Review

CONTEXT

Impaired scapular kinematics are commonly reported in patients with subacromial impingement syndrome (SIS). Various therapeutic interventions designed to improve scapular kinematics and minimize pain and disability have been described in the literature. However, the short- and long-term benefits of these interventions are unclear.

OBJECTIVE

To determine the effects of specific short- and long-term therapeutic interventions on scapular kinematics and disability in patients with SIS.

DATA SOURCES

We searched PubMed, CINAHL, and SPORTDiscus databases from their origins to January 2018 using a combination of the key words scapular kinematics AND (shoulder dysfunction OR subacromial impingement) and conducted a manual search by reviewing the references of the identified papers.

STUDY SELECTION

Studies were included if (1) preintervention and postintervention measures were available; (2) patient-reported outcomes were reported; (3) scapular kinematics measures at 90° of ascending limb elevation in the scapular plane were included; (4) SIS was diagnosed in participants or participants self-reported symptoms of SIS; (5) they were original clinical studies published in English; and (6) the sample sizes, means, and measure of variability for each group were reported.

DATA EXTRACTION

Seven studies were found. Sample sizes, means, and standard deviations of scapular upward rotation, posterior tilt, and internal rotation at 90° of ascending limb elevation on the scapular plane and the Disabilities of the Arm, Shoulder and Hand scores were extracted.

DATA SYNTHESIS

Standardized mean differences between preintervention and postintervention measures with 95% confidence intervals (CIs) were calculated. We observed that the Disabilities of the Arm, Shoulder and Hand scores improved (mean difference = 0.85; 95% CI = 0.54, 1.16) but did not observe changes in scapular upward rotation (mean difference = -0.04; 95% CI = -0.31, 0.22), posterior tilt (mean difference = -0.09; 95% CI = -0.32, 0.15), or internal rotation (mean difference = 0.06; 95% CI = -0.19, 0.31).

CONCLUSIONS

The short- and long-term therapeutic interventions for SIS improved patient-reported outcomes but not scapular kinematics. The identified improvements in shoulder pain and function were not likely explained by changes in scapular kinematics.

Acromion Clavicular Joint Reconstruction with LARS Ligament in Acute Dislocation

BACKGROUND

The acromion clavicular joint dislocations are common injuries of the shoulder. The severity is dependent upon the degree of ligamentous injury. Surgical treatment is typically performed in higher grade acromioclavicular separation with several static and dynamic operative procedures with or without primary ligament replacement.

METHODS

47 patients with acute Rockwood type III, IV, and V injuries were treated surgically with LARS reconstruction. The success of technique was evaluated by radiographic outcomes for each patient at every follow-up visit (one, three, 12 months), while to assess pain reduction and clinical evaluation Visual Analogue scale score (VAS) and Constant-Murley score (CMA) was performed, respectively. An One Way Analysis of Variance (Kruskal-Wallis test), a multiple comparison Turket test, or a t-test (Mann-Whitney Rank Sum Test) were used when required.

RESULTS

Follow-up radiographs revealed maintenance of anatomical reduction in 41 patients, and no bone erosions has been identified. In short-term joint functional recovery has been observed. Indeed, after 12 months pain on the VAS-scale in all groups decreased significantly (P < 0.05), and the CMS revealed a significant overall improvement (P < 0.05).

CONCLUSION

These data demonstrate that the use of the LARS allows to provide stability to the joint and especially to ensure its natural elasticity, relieving pain and improving joint function already one month post-surgery.

Kinesiologic considerations for targeting activation of scapulothoracic muscles - part 2: trapezius

BACKGROUND

The trapezius is an extensive muscle subdivided into upper, middle, and lower parts. This muscle is a dominant stabilizer of the scapula, normally operating synergistically with other scapular muscles, most notably the serratus anterior. Altered activation, poor control, or reduced strength of the different parts of the trapezius have been linked with abnormal scapular movements, often associated with pain. Several exercises have been designed and studied that specifically target the different parts of the trapezius, with the goal of developing exercises that optimize scapular position and scapulohumeral rhythm that reduce pain and increase function.

METHODS

This paper describes the anatomy, kinesiology, and pathokinesiology of the trapezius as well as exercises that selectively target the activation of the different parts of this complex muscle.

CONCLUSIONS

This review provides the anatomy and kinesiology of the trapezius muscle with the underlying intention of understanding how this muscle contributes to the normal mechanics of the scapula as well as the entire shoulder region. This paper can guide the clinician with planning exercises that specifically target the different parts of the trapezius. It is recommended that this paper be read as a companion to another paper: Kinesiologic considerations for targeting activation of scapulothoracic muscles - part 1: serratus anterior.

Biomechanical Analysis of Superior and Anterior Precontoured Plate Fixation Techniques for Neer Type II-A Clavicle Fractures

OBJECTIVE

There are limited biomechanical data supporting the use of anterior or superior-lateral precontoured clavicle plates for the treatment of displaced Neer type II-A clavicle fractures. The objectives of this study were as follows: (a) compare noncontoured versus precontoured superior plating; (b) compare use of locking versus nonlocking screws in the lateral fragment for superior precontoured plates; and (c) compare superior versus anterior precontoured plates with locking lateral fragment screws.

METHODS

The following constructs were tested on a synthetic clavicle model simulating a Neer type II-A fracture: (a) superior precontoured plate with locking (SUP-L, n = 6); (b) superior precontoured plate with nonlocking (SUP-NL, n = 8); (c) anterior precontoured plate with locking (ANT-L, n = 7); and (d) superior noncontoured locking compression plate (SUP-LCP, n = 6). Constructs were subjected to cyclical cantilever loads. Construct stiffness and survival (cycles to failure) were documented. Mann-Whitney U tests were performed for group-wise statistical comparison (α = 0.05) of data.

RESULTS

The SUP-L construct was significantly stiffer than both SUP-LCP and ANT-L constructs (P < 0.02). The SUP-NL construct was stiffer than the SUP-L (P = 0.03) construct. Both SUP-L and ANT-L precontoured constructs survived longer than the noncontoured SUP-LCP construct (P < 0.022). The SUP-L construct survived longer than the SUP-NL (P = 0.013) and the ANT-L (P = 0.008) constructs.

CONCLUSIONS

Superior precontoured plates yielded biomechanically superior constructs compared with anterior precontoured and superior noncontoured plates. Using locking screws in the lateral fragment over nonlocking screws may improve overall superior precontoured plate construct survivability. However, our results were limited to a synthetic biomechanical model and require further investigation to establish a clinical correlation.

Biomechanical Analysis of Single-, Double-, and Triple-Bundle Configurations for Coracoclavicular Ligament Reconstruction Using Cortical Fixation Buttons With Suture Tapes: A Cadaveric Study

PURPOSE

To compare the acromioclavicular (AC) joint stability of single-bundle (SB), double-bundle with an anterolateral limb (DBa), double-bundle with a posterolateral limb (DBp), and triple-bundle (TB) coracoclavicular (CC) ligament reconstructions using cortical fixation buttons with suture tapes.

METHODS

Eight cadaveric shoulders were used. AC joint translation and rotational stability were tested for intact and following 4 different CC reconstruction techniques: SB, DBa, DBp, and TB configurations using cortical fixation buttons with suture tapes. For each reconstruction and native AC joint as control, anteroposterior (AP) and superoinferior translations were quantified using 10- and 15-N translational loads and anterior and posterior rotations were measured using 0.16- and 0.32-Nm rotational torque.

RESULTS

DBp reconstruction showed significantly better AP stability compared with SB and DBa reconstruction at 10 and 15 N (DBp: 4.1 ± 0.6 mm, SB: 7.8 ± 1.1 mm, P < .001; DBa: 6.5 ± 0.7 mm, P = .02 at 10 N; DBp: 5.5 ± 0.8 mm, SB: 10.1 ± 1.0 mm, P = .003; DBa: 9.1 ± 0.7 mm, P = .02 at 15 N). The degree of total rotation showed tendency to decrease according to increasing number of bundles; however, there were no significant differences (SB: 43.1 ± 9.2°, DBa: 37.9 ± 7.3°, DBp: 33.9 ± 6.8°, TB: 32.2 ± 6.6°, P = .37 at 0.32 Nm).

CONCLUSIONS

An additional posterolateral clavicular hole for CC ligament reconstruction using cortical fixation buttons with suture tapes resulted in better AP stability compared with SB reconstruction, whereas use of additional anterolateral clavicular hole did not show any improvement compared with SB reconstruction. Reconstruction using both anterolateral and posterolateral clavicular holes did not guarantee better stability compared with SB reconstruction. There was an increasing tendency of rotational stability with number of bundle increases, although they did not reach statistical difference.

CLINICAL RELEVANCE

When surgeons consider double-bundle CC ligament reconstruction using cortical fixation buttons with suture tapes, it is better to position the lateral clavicular hole posteriorly to restore AP stability.

A survey of human shoulder functional kinematic representations

In this survey, we review the field of human shoulder functional kinematic representations. The central question of this review is to evaluate whether the current approaches in shoulder kinematics can meet the high-reliability computational challenge. This challenge is posed by applications such as robot-assisted rehabilitation. Currently, the role of kinematic representations in such applications has been mostly overlooked. Therefore, we have systematically searched and summarised the existing literature on shoulder kinematics. The shoulder is an important functional joint, and its large range of motion (ROM) poses several mathematical and practical challenges. Frequently, in kinematic analysis, the role of the shoulder articulation is approximated to a ball-and-socket joint. Following the high-reliability computational challenge, our review challenges this inappropriate use of reductionism. Therefore, we propose that this challenge could be met by kinematic representations, that are redundant, that use an active interpretation and that emphasise on functional understanding.

Rater reliability and construct validity of a mobile application for posture analysis

[Purpose] Measurement of posture is important for those with a clinical diagnosis as well as researchers aiming to understand the impact of faulty postures on the development of musculoskeletal disorders. A reliable, cost-effective and low tech posture measure may be beneficial for research and clinical applications. The purpose of this study was to determine rater reliability and construct validity of a posture screening mobile application in healthy young adults. [Subjects and Methods] Pictures of subjects were taken in three standing positions. Two raters independently digitized the static standing posture image twice. The app calculated posture variables, including sagittal and coronal plane translations and angulations. Intra- and inter-rater reliability were calculated using the appropriate ICC models for complete agreement. Construct validity was determined through comparison of known groups using repeated measures ANOVA. [Results] Intra-rater reliability ranged from 0.71 to 0.99. Inter-rater reliability was good to excellent for all translations. ICCs were stronger for translations versus angulations. The construct validity analysis found that the app was able to detect the change in the four variables selected. [Conclusion] The posture mobile application has demonstrated strong rater reliability and preliminary evidence of construct validity. This application may have utility in clinical and research settings.

Validation of single-plane fluoroscopy and 2D/3D shape-matching for quantifying shoulder complex kinematics

Fluoroscopy and 2D/3D shape-matching has emerged as the standard for non-invasively quantifying kinematics. However, its accuracy has not been well established for the shoulder complex when using single-plane fluoroscopy. The purpose of this study was to determine the accuracy of single-plane fluoroscopy and 2D/3D shape-matching for quantifying full shoulder complex kinematics. Tantalum markers were implanted into the clavicle, humerus, and scapula of four cadaveric shoulders. Biplane radiographs were obtained with the shoulder in five humerothoracic elevation positions (arm at the side, 30°, 60°, 90°, maximum). Images from both systems were used to perform marker tracking, while only those images acquired with the primary fluoroscopy system were used to perform 2D/3D shape-matching. Kinematics errors due to shape-matching were calculated as the difference between marker tracking and 2D/3D shape-matching and expressed as root mean square (RMS) error, bias, and precision. Overall RMS errors for the glenohumeral joint ranged from 0.7 to 3.3° and 1.2 to 4.2 mm, while errors for the acromioclavicular joint ranged from 1.7 to 3.4°. Errors associated with shape-matching individual bones ranged from 1.2 to 3.2° for the humerus, 0.5 to 1.6° for the scapula, and 0.4 to 3.7° for the clavicle. The results of the study demonstrate that single-plane fluoroscopy and 2D/3D shape-matching can accurately quantify full shoulder complex kinematics in static positions.

Effects of short malunion of the clavicle on in vivo scapular kinematics

BACKGROUND

Short malunion of the clavicle after fracture can change scapular kinematics and alter clinical outcome. However, the effects of malunion on kinematics and outcomes remains poorly understood because there have been no in vivo studies measuring changes during active motion with malunion. This study aimed to measure and to compare in vivo 3-dimensional (3D) scapular kinematics between normal shoulders and shoulders with short malunion using 3D-2-dimensional model image registration techniques.

METHODS

Fifteen patients with clavicle fracture who had been treated conservatively were enrolled in this study. In these patients, the angle of scapular upward rotation, posterior tilting, and external rotation were compared between shoulders with short malunion and contralateral, normal shoulders. A 3D-2-dimensional model image registration technique was used to determine the 3D orientation of the scapula.

RESULTS

Scapular upward rotation increased following increase of the arm elevation angle and also showed a significant difference by arm elevation in both groups (P = .04). Posterior tilting of the scapula gradually increased as the arm abduction angle increased, and this varied significantly between groups (P = .01). Shoulders with short malunion also showed a more internally rotated position than the contralateral, normal shoulders between 100° and the maximum abduction angle (P = .04).

CONCLUSION

Our results suggest that clavicle shortening of >10% greatly affects scapular kinematics in vivo. Further studies will be needed to determine the clinical implications of short malunion of the clavicle.

Treatment of Symptomatic Acromioclavicular Joint Instability by a Docking Technique: Clinical Indications, Surgical Technique, and Outcomes

PURPOSE

To report functional and objective outcomes resulting from surgical treatment of patients with symptomatic type III through V acromioclavicular (AC) joint injury by use of a modification of the anatomic AC joint reconstruction developed by Carofino and Mazzocca.

METHODS

The study included all patients treated in 2009-2014 who presented with a history of direct trauma to the shoulder; deformity of the AC joint on clinical examination; radiographic findings that would classify the injury as a Rockwood type III, IV, or V injury; AC joint instability on clinical examination; and self-reported deficits of arm function on initial presentation, in whom a comprehensive and directed nonoperative program failed. The surgical procedure used an allograft with reinforcing internal sutures passed around the coracoid and through anatomically positioned clavicular holes for the coracoclavicular (CC) ligaments, used a docking technique for reconstruction of the superior AC ligaments, and included repair of the native AC ligaments. Outcomes were reported for patients with a minimum follow-up period of 1.5 years. Outcome measurements included dynamic-static stability evaluation and Disabilities of the Arm, Shoulder and Hand (DASH) scores.

RESULTS

The study included 15 patients with 15 affected shoulders. The postsurgical follow-up period averaged 3 years (range, 1.5-5 years). Postoperatively, one patient showed loss of reduction after a fall. All others showed 2-dimensional radiographic stability and 3-dimensional dynamic clinical stability. Static radiographic measurement of the CC distance at discharge averaged 0.93 cm compared with 2.7 cm on initial examination (P < .0001). Patient-reported outcomes at an average of 3 years' follow-up showed a DASH score of 13 compared with a preoperative DASH score of 51 (P < .0001).

CONCLUSIONS

This study confirms that anatomic CC ligament reconstruction and repair or reconstruction of the AC ligaments help restore arm function as shown by the patient-specific and clinical outcome metrics. These results were achieved by correction of the deformity, which in turn allowed for the obtainment of static and dynamic stability.

LEVEL OF EVIDENCE

Level IV.

Epidemiology of Acromioclavicular Joint Sprains in 25 National Collegiate Athletic Association Sports: 2009-2010 to 2014-2015 Academic Years

BACKGROUND

No previous studies have described the incidence of acromioclavicular (AC) joint injuries in a large sample of National Collegiate Athletic Association (NCAA) student-athletes. Such data are needed to understand the injury prevalence, mechanisms of injury, and recovery patterns in NCAA student-athletes.

PURPOSE

To describe the epidemiology of AC joint sprain injuries in 25 NCAA championship sports.

STUDY DESIGN

Descriptive epidemiology study.

METHODS

AC joint sprains were analyzed from the NCAA Injury Surveillance Program during the 2009-2010 to 2014-2015 academic years. AC joint sprain injury rates, rate ratios, and injury proportion ratios (IPRs) were reported with 95% CIs.

RESULTS

In the 25 NCAA sports examined during the 2009-2010 to 2014-2015 academic years, a total of 844 AC joint sprains were reported, for a rate of 1.72 per 10,000 athlete-exposures (AEs). The majority of AC joint sprains were reported in football (50.4%, n = 425). Most AC joint sprains occurred in competitions (66.0%, n = 557), and the competition rate was 8.58 times the practice rate (95% CI, 7.44-9.89). In sex-comparable sports (ie, soccer, basketball, ice hockey, lacrosse, baseball/softball, indoor track, outdoor track, cross-country, tennis, and swimming and diving), the AC joint sprain rate in men was 4.67 times that of women (95% CI, 3.56-6.14). Most AC joint sprains were caused by player contact (54.7%, n = 462), followed by surface contact (29.0%, n = 245). Of all AC joint sprains, 47.5% resulted in a time loss of <24 hours, and 5.9% were severe. In addition, 9.7% were recurrent, and only 1.0% required surgery. In sex-comparable sports, male athletes had a larger proportion of injuries due to player contact than did female athletes (IPR, 1.50; 95% CI, 1.06-2.13); female athletes had a larger proportion of injuries due to surface contact than male athletes (IPR, 1.55; 95% CI, 1.01-2.38). Also, compared with women, men had a larger proportion of AC joint sprains that were recurrent (IPR, 10.29; 95% CI, 1.45-72.90).

CONCLUSION

The highest rates of AC joint sprains occurred in men's football, ice hockey, and wrestling as well as women's ice hockey. Most AC joint sprains across all sports occurred because of a contact mechanism, particularly from player-player contact. Further research into the specific activities and exposures at the time of injury may lend a better understanding of the causation of these injuries and lead to appropriate interventions to decrease their incidence and severity.

Increased Upper Trapezius Muscle Stiffness in Overhead Athletes with Rotator Cuff Tendinopathy

Although excessive tension of the upper trapezius (UT) is thought to contribute to rotator cuff tendinopathy, no study examined UT tension in athletes with and without rotator cuff tendinopathy. Here we used UT shear modulus measured using ultrasound shear wave elastography as an index of muscle stiffness/tension. The aims of this study were twofold: 1) to determine whether the UT muscle shear modulus is altered in athletes with rotator cuff tendinopathy compared to asymptomatic athletes, and 2) to detect optimal cut-off points of UT shear modulus in identifying athletes with rotator cuff tendinopathy. Forty-three male volleyball players (17 asymptomatic and 26 with rotator cuff tendinopathy, mean age = 22.9±3.5 years) participated in the study. UT shear modulus was quantified during active arm holding at 30° and 60° of shoulder abduction and passive arm positioning at 0°, 30° and 60° of shoulder abduction. During the active tasks, the UT shear modulus was higher in athletes with rotator cuff tendinopathy than the asymptomatic athletes (p = 0.002), regardless the arm position. During the passive tasks, athletes with rotator cuff tendinopathy exhibited a higher UT shear modulus than asymptomatic athletes only at 0° of shoulder abduction (13.0±2.5 kPa vs 10.2±1.8 kPa, p = 0.001). When considering the active task, an optimal cut-off shear modulus of 12.0 kPa at 30° of shoulder abduction (sensitivity = 0.84, specificity = 0.57, AUC = 0.757, p = 0.008) and 9.5 kPa at 60° of shoulder abduction (sensitivity = 0.88, specificity = 0.67, AUC = 0.816, p = 0.002) was detected. When considering the passive task at 0° of shoulder abduction, a cut-off of 12.2 kPa was found (sensitivity = 0.73, AUC = 0.817, p = 0.001). Findings from the present study show that monitoring passive and active UT muscle shear modulus may provide important information for the prevention/rehabilitation of rotator cuff tendinopathy.

The biomechanical influence of the deltotrapezoid fascia on horizontal and vertical acromioclavicular joint stability

INTRODUCTION

Many studies have investigated the biomechanical influence of the acromioclavicular (AC) and coracoclavicular (CC) ligaments on the stability of the acromioclavicular joint (ACJ). It has been shown that augmentation of the CC ligaments alone can result in residual horizontal instability. Our hypothesis was that the DTF would have a significant stabilizing effect on horizontal ACJ stability.

MATERIALS AND METHODS

In a biomechanical in vitro study a sequential injury of the ACJ was created on eight shoulders from full body, which were placed in an upright sitting position. The translation and rotation of the clavicle were measured in relation to the acromion using an optical navigation system in various states during thoracic-humeral elevation, abduction, and horizontal adduction. The three states were: an intact shoulder, complete sectioning of the AC ligaments, and a circular lesion of the DTF.

RESULTS

Compared to the intact state we found a significant increase in anterior rotation of the clavicle of 1.11° (p = 0.012) and a tendency in lateral translation of 2.71 mm (p = 0.017) in relation to the acromion, with a combined lesion of AC ligaments and DTF. No significant differences were found between the intact state and the isolated dissected AC ligaments as well in adduction as elevation.

CONCLUSION

A combined lesion of the AC ligaments and the DTF resulted in a quantitatively small but significant increase in anterior rotation and a tendency in lateral translation of the clavicle in relation to the acromion. These differences were quantitatively small, so that the clinical relevance of the stabilization effect of combined AC ligaments and DTF injuries is questionable.

Distal radius fractures result in alterations in scapular kinematics: a three-dimensional motion analysis

BACKGROUND

Scapular motion is closely integrated with arm motion. Injury to a distal segment requires compensatory changes in the proximal segments leading to alterations in scapular motion. Since the effects of distal injuries on scapular kinematics remain unknown, in the present study we investigated the influences on scapular motion in patients with distal injuries.

METHODS

Sixteen subjects with a history of distal radius fracture and 20 asymptomatic healthy subjects (controls) participated in the study. Three-dimensional scapular and humeral kinematic data were collected on all 3 planes of shoulder elevation: frontal, sagittal, and scapular. All testing was performed in a single session; therefore, the sensors remained attached to the participants for all testing. The position and orientation data of the scapula at 30°, 60°, 90°, and 120° humerothoracic elevation and 120°, 90°, 60°, and 30° lowering were used for statistical comparisons. Independent samples t-test was used to compare the scapular internal/external rotation, upward/downward rotation, and anterior/posterior tilt between the affected side of subjects with a distal radius fracture and the dominant side of asymptomatic subjects at the same stage of humerothoracic elevation.

FINDINGS

Scapular internal rotation was significantly increased at 30° elevation (P=0.01), 90° elevation (P=0.03), and 30° lowering (P=0.03), and upward rotation was increased at 30° and 60° elevation (P<0.001) on the affected side during frontal plane elevation. Scapular upward rotation and anterior tilt were significantly increased during 30° lowering on both the scapular (P=0.002 and 0.02, respectively) and sagittal planes (P=0.01 and 0.02. respectively).

INTERPRETATION

Patients with distal radius fractures exhibit altered scapular kinematics, which may further contribute to the development of secondary musculoskeletal pathologies.

Comparison of 3-dimensional shoulder complex kinematics in individuals with and without shoulder pain, part 1: sternoclavicular, acromioclavicular, and scapulothoracic joints

STUDY DESIGN

Cross-sectional.

OBJECTIVES

To compare sternoclavicular, acromioclavicular, and scapulothoracic joint motion between symptomatic and asymptomatic individuals during shoulder motion performed in 3 planes of humerothoracic elevation.

BACKGROUND

Differences in scapulothoracic kinematics are associated with shoulder pain. Several studies have measured these differences using surface sensors, but the results of this technique may be affected by skin-motion artifact. Furthermore, previous studies have not included the simultaneous measurement of sternoclavicular and acromioclavicular joint motion.

METHODS

Transcortical bone pins were inserted into the clavicle, scapula, and humerus of 12 asymptomatic and 10 symptomatic individuals for direct, bone-fixed tracking using electromagnetic sensors. Angular positions for the sternoclavicular, acromioclavicular, and scapulothoracic joints were measured during shoulder flexion, abduction, and scapular plane abduction.

RESULTS

Differences between groups were found for sternoclavicular and scapulothoracic joint positions. Symptomatic individuals consistently demonstrated less sternoclavicular posterior rotation, regardless of angle, phase, or plane of shoulder motion. Symptomatic individuals also demonstrated less scapulothoracic upward rotation at 30° and 60° of humerothoracic elevation during shoulder abduction and scapular plane abduction.

CONCLUSION

The results of this study show that differences in shoulder complex kinematics exist between symptomatic and asymptomatic individuals. However, the magnitude of these differences was small, and the resulting clinical implications are not yet fully understood. The biomechanical coupling of the sternoclavicular and acromioclavicular joints requires further research to better understand scapulothoracic movement deviations and to improve manual therapy and exercise-based physical therapy interventions.

Dynamic comparison of segmentary scapulohumeral rhythm between athletes with and without impingement syndrome

Background:

Patients who have shoulder pain usually have compensatory or contributory deviation of shoulder motion during arm elevation. In the traditional scapulohumeral rhythm, the share of the acromioclavicular (AC) and the sternoclavicular (SC) joint movements and also the role of AC internal rotation angle are unknown.

Objectives:

The main purpose of this study was to measure and compare the segmentary scapulohumeral rhythm (SSHR) during scapular arm elevation at a steady rotational speed in athletes with and without impingement syndrome.

Patients and Methods:

Using a speedometer, the maximum speed of arm elevation was measured in 21 men in each of the involved and uninvolved groups. Using fluoroscopy on the dominant side, SSHR during scapular arm elevation at a rotational speed equal to 1/30 of maximum speed was compared between the two groups. The ratio of glenohumeral (GH) elevation angle to AC rotation angle in the scapular plane was considered as SSHR.

Results:

The maximum speed of arm elevation between the two groups was significantly different (P < 0.001). The rhythm of the involved group significantly exceeded the rhythm of the uninvolved group in a part of the first quarter range of the arm elevation. SSHR during arm elevation in the uninvolved group did not change significantly (P = 0.845); however, it decreased significantly in the involved group (P = 0.024).

Conclusions:

Speed differences between the two groups were probably due to the pain in some ranges of arm elevation. SSHR in the involved group probably changed in order to compensate downward rotation of the scapula in the resting position. Study of the AC upward rotation range can be misleading; therefore, the study of scapulohumeral rhythm is recommended.

A new description of scapulothoracic motion during arm movements in healthy subjects

The participation of scapula motion in arm movement is clinically well known and recent three dimensional (3D) analyses using kinematic techniques have confirmed its importance. Scapular motion relative to the thorax has a theoretical maximum of 6 degrees of freedom (DoF), resulting from rotations at both clavicular joints (3 rotational DoF each). However, most recent kinematic studies have only analysed the 3D rotations of the scapula relative to the thorax. In the present study, the 3D translations of the barycentre of the scapula were considered in order to complete the description of movement at the shoulder complex. Eight healthy subjects performed arm elevation in the sagittal and frontal planes, simulated activities of daily living (hair combing and back washing) and maximum voluntary scapula movement (forward and backward rolling). Measurements were recorded using a 6 DoF electromagnetic device and the acromial method of analysis was used. The results showed that 3D scapular rotations and translation of its barycentre were functionally consistent for all tasks. A principal component analysis (PCA) yielded three factors, explaining 97.6% of the variance. The first two factors (protraction and shrug, according to clinical descriptions) combined rotations and translations, consistent with the hypothesis that the scapula rolls over the curved thoracic surface. The third factor related to lateral-medial rotation, thus representing rotation in the plane tangential to the thorax. The PCA suggested that scapular motion can be described using these 3 DoF. This should be studied in a larger group of individuals, including patients with pathological conditions.

Scapular kinematics pre- and post-thoracic thrust manipulation in individuals with and without shoulder impingement symptoms: a randomized controlled study

STUDY DESIGN

Randomized controlled trial with immediate follow-up.

OBJECTIVES

To evaluate the immediate effects of a low-amplitude, high-velocity thrust thoracic spine manipulation (TSM) on pain and scapular kinematics during elevation and lowering of the arm in individuals with shoulder impingement syndrome (SIS). The secondary objective was to evaluate the immediate effects of TSM on scapular kinematics during elevation and lowering of the arm in individuals without symptoms.

BACKGROUND

Considering the regional interdependence among the shoulder and the thoracic and cervical spines, TSM may improve pain and function in individuals with SIS. Comparing individuals with SIS to those without shoulder pathology may provide information on the effects of TSM specifically in those with SIS.

METHODS

Fifty subjects (mean ± SD age, 31.8 ± 10.9 years) with SIS and 47 subjects (age, 25.8 ± 5.0 years) asymptomatic for shoulder dysfunction were randomly assigned to 1 of 2 interventions: TSM or a sham intervention. Scapular kinematics were analyzed during elevation and lowering of the arm in the sagittal plane, and a numeric pain rating scale was used to assess shoulder pain during arm movement at preintervention and postintervention.

RESULTS

For those in the SIS group, shoulder pain was reduced immediately after TSM and the sham intervention (mean ± SD preintervention, 2.9 ± 2.5; postintervention, 2.3 ± 2.5; P<.01; moderate effect size [Cohen d = 0.2]). Scapular internal rotation increased 0.5° ± 0.02° (P = .04; small effect size [Cohen d<0.1]) during elevation of the arm after TSM and sham intervention in the SIS group only. Subjects with and without SIS who received TSM and asymptomatic subjects who received the sham intervention had a significant increase (1.6° ± 2.7°) in scapular upward rotation postintervention (P<.05; small effect size [Cohen d<0.2]), which was not considered clinically significant. Scapular anterior tilt increased 1.0° ± 4.8° during elevation and lowering of the arm postmanipulation (P<.05; small effect size [Cohen d<0.2]) in the asymptomatic subjects who received TSM.

CONCLUSION

Shoulder pain in individuals with SIS immediately decreased after a TSM. The observed changes in scapular kinematics following TSM were not considered clinically important.

LEVEL OF EVIDENCE

Therapy, level 4. J Orthop Sports Phys Ther 2014;44(7):475-487. Epub 22 May 2014. doi:10.2519/jospt.2014.4760.

Revisit to scapular dyskinesis: three-dimensional wing computed tomography in prone position

BACKGROUND

Three-dimensional (3D) wing computed tomography (CT) showed a high inter-rater reliability in assessing scapular dyskinesis.

METHODS

The 330 scapular movements of 165 patients were classified into 4 types by 7 blinded observers. Then, 3D wing CT was performed with patients prone, and 4 blinded observers measured 5 angles, consisting of upward rotation (UR) superior translation (ST), anterior tilting (AT), protraction (PRO), and internal rotation (IR). The inter-rater reliability (IRR) of 2 methods was calculated, and cutoff values were determined for the 5 angles on the 3D wing CT images.

RESULTS

The IRR was 0.783 for the observational method of scapular dyskinesis and 0.981 for 3D wing CT in the prone position. UR and ST angles were significantly larger in type 3 more than in the other types (P < .001, P < .001), and the AT angle showed a similar pattern in type 1 (P < .001). The PRO angle was significantly larger in types 1, 2, and 3 more than in type 4 (P < .001, P < .001, P = .013), and the IR angle was significantly larger in type 2 more than in the other types (P < .001). The cutoff values of the 5 angles were UR, 117°; ST, 90°; AT, 8°; PRO, 99°; and IR, 51°. The UR angle showed a significant correlation with glenohumeral internal rotation deficit (odds ratio, 0.436; P = .029) and the IR angle with MDI (odds ratio, 8.947; P = .048).

CONCLUSION

The patients with a high UR angle showed a low rate of glenohumeral internal rotation deficit and those with a high IR angle had a high rate of the MDI in affected shoulder by the determinant of the cutoff value of the 5 angles.

LEVEL OF EVIDENCE

Level III, development of diagnostic criteria with nonconsecutive patients, diagnostic study.

Motion of the shoulder complex in individuals with isolated acromioclavicular osteoarthritis and associated with rotator cuff dysfunction: part 1 - Three-dimensional shoulder kinematics

This study described the three-dimensional shoulder motion during the arm elevation in individuals with isolated acromioclavicular osteoarthritis (ACO) and ACO associated with rotator cuff disease (RCD), as compared to controls. Seventy-four participants (ACO=23, ACO+RCD=25, Controls=26) took part of this study. Disability was assessed with the DASH, three-dimensional kinematics were collected during arm elevation in the sagittal and scapular planes, and pain was assessed with the 11-point numeric pain rating scale. For each kinematic variable and demographic variables, separate linear mixed-model 2-way ANOVAs were performed to compare groups. Both ACO groups had higher DASH and pain scores. At the scapulothoracic joint, the isolated ACO group had greater internal rotation than control, and the ACO+RCD group had greater upward rotation than both other groups. At the sternoclavicular joint, both groups with ACO had less retraction, and the isolated ACO group had less elevation and posterior rotation. At the acromioclavicular joint, the isolated ACO group had greater upward rotation, and both ACO groups had greater posterior tilting. Patients with ACO had altered shoulder kinematics, which may represent compensatory responses to reduce pain and facilitate arm motion during arm elevation and lowering.