Effectiveness of tendon transfers for massive rotator cuff tears: a simulation study

Individuals with rotator cuff tears unsuccessfully treated with exercise therapy have less inferiorly oriented net muscle forces during scapular plane abduction

Exercise therapy for individuals with rotator cuff tears fails in approximately 25.0 % of cases. One reason for failure of exercise therapy may be the inability to strengthen and balance the muscle forces crossing the glenohumeral joint that act to center the humeral head on the glenoid. The objective of the current study was to compare the magnitude and orientation of the net muscle force pre- and post-exercise therapy between subjects successfully and unsuccessfully (e.g. eventually underwent surgery) treated with a 12-week individualized exercise therapy program. Twelve computational musculoskeletal models (n = 6 successful, n = 6 unsuccessful) were developed in OpenSim (v4.0) that incorporated subject specific tear characteristics, muscle peak isometric force, in-vivo kinematics and bony morphology. The models were driven with experimental kinematics and the magnitude and orientation of the net muscle force was determined during scapular plane abduction at pre- and post-exercise therapy timepoints. Subjects unsuccessfully treated had less inferiorly oriented net muscle forces pre- and post-exercise therapy compared to subjects successfully treated (p = 0.039 & 0.045, respectively). No differences were observed in the magnitude of the net muscle force (p > 0.05). The current study developed novel computational musculoskeletal models with subject specific inputs capable of distinguishing between subjects successfully and unsuccessfully treated with exercise therapy. A less inferiorly oriented net muscle force in subjects unsuccessfully treated may increase the risk of superior migration leading to impingement. Adjustments to exercise therapy programs may be warranted to avoid surgery in subjects at risk of unsuccessful treatment.

Latarjet's muscular alterations increase glenohumeral joint stability: A theoretical study

The surgical Latarjet procedure aims to stabilise the glenohumeral joint following anterior dislocations. Despite restoring joint stability, the procedure introduces alterations of muscle paths which likely modify the shoulder dynamics. Currently, these altered muscular functions and their implications are unclear. Hence, this work aims to predict changes in muscle lever arms, muscle and joint forces following a Latarjet procedure by using a computational approach. Planar shoulder movements of ten participants were experimentally assessed. A validated upper-limb musculoskeletal model was utilised in two configurations, i.e., a baseline model, simulating normal joint, and a Latarjet model simulating its related muscular alterations. Muscle lever arms and differences in muscle and joint forces between models were derived from the experimental marker data and static optimisation technique. Lever arms of most altered muscles, hence their role, were substantially changed after Latarjet. Altered muscle forces varied by up to 15% of the body weight. Total glenohumeral joint force increased by up to 14% of the body weight after Latarjet, mostly due to increase in compression force. Our simulation indicated that the Latarjet muscular alterations lead to changes in the muscular recruitment and contribute to the stability of the glenohumeral joint by increasing compression force during planar motions.

Clinical outcomes in latissimus dorsi transfer single- versus double-incision technique

BACKGROUND/HYPOTHESIS

In patients with irreparable postero-superior rotator cuff lesions, a latissimus dorsi transfer (LDT) is performed. For this surgery, different techniques are used. In this study, we aim to compare the patient's functional outcome after treatment with modified L'Episcopo "single-incision" and modified Gerber "double-incision" technique for LDT.

METHODS

44 patients with irreparable postero-superior rotator cuff ruptures, refractory to physiotherapeutic treatment were included. 21 patients were treated using a modified L'Episcopo "single-incision", 23 patients with modified Gerber "double-incision" surgical approach. All patients had full-thickness tears of at least two complete tendons, and all had fully functioning deltoid and subscapularis muscles. Preoperatively, there were statistically significant differences between the two groups in all preoperative CMS sub-parameters except "power" and "pain". In the postoperative follow-up, a functional assessment using "Constant-Murley Score" (CMS) and "Age- and gender-related CMS" was conducted.

STUDY DESIGN

Retrospective-comparative trial.

LEVEL OF EVIDENCE III

RESULTS

There were no statistically significant differences between age, sex and time of follow-up between the two study groups (p > 0.05). The mean age was 59.2(± 6.3) years, and the mean follow-up time was 45.4(± 9.3) months for both groups taken together. Mean CMS improved for both groups together from 24.2 ± 8.2 points prior to surgery, to 62.8 ± 17.4 points after a mean follow-up time of 45.4 ± 9.3 months post surgery. The patients treated with "single-incision" surgery (n = 21) gained significantly (p < 0.001) more in CMS and all CMS-sub-scoring parameters except power and pain, compared to the patients treated with "double-incision" technique (n = 23).

CONCLUSION

This survey shows appealing post-operative functional outcome in patients with irreparable postero-superior rotator cuff lesions treated with two different techniques for LDT. We believe that the presentation of these methods and their results might encourage shoulder surgeons to implement these techniques. Especially the "single-incision" LDT surgery might be a more accustomed technique for many shoulder surgeons well trained in the deltopectoral approach.

Management of Failed Rotator Cuff Repairs: A Review

Failed rotator cuff repairs present a complex issue for treating surgeons. Many methods of management exist for this pathology including revision repair with biologic augmentation, repairs with allograft, tendon transfers, superior capsular reconstruction, balloon arthroplasty, bursal acromial reconstruction, and reverse total shoulder arthroplasty. This review discusses the current literature associated with these management options.

Shoulder kinematics and muscle activity following latissimus dorsi transfer for massive irreparable posterosuperior rotator cuff tears in shoulders with pseudoparalysis

BACKGROUND

The aim of this study was to evaluate the thoracohumeral (TH) and glenohumeral (GH) motion with muscle activity after latissimus dorsi transfer (LDT) in a shoulder with a massive irreparable posterosuperior rotator cuff tear (MIRT) and pseudoparalysis compared with the asymptomatic contralateral shoulder (ACS).

METHODS

We recruited and evaluated 13 patients after LDT in a shoulder with preoperative clinical pseudoparalysis and an MIRT on magnetic resonance imaging, with a minimum follow-up period of 1 year, and with a Hamada stage of 3 or less. Three-dimensional electromagnetic tracking was used to assess shoulder active range of motion in both the LDT shoulder and the ACS. The maximal active elevation of the shoulder (MAES) was assessed and consisted of forward flexion, scapular abduction, and abduction in the coronal plane. Maximal active internal rotation and external rotation were assessed separately. Surface electromyography (EMG) was performed to track activation of the latissimus dorsi (LD) and deltoid muscles during shoulder motion. EMG was scaled to its maximal isometric voluntary contraction recorded in specified strength tests.

RESULTS

In MAES, TH motion of the LDT shoulder was not significantly different from that of the ACS (F_1,12 = 1.174, P = .300) but the GH contribution was significantly lower in the LDT shoulder for all motions (F_1,12 = 11.230, P = .006). External rotation was significantly greater in the ACS (26° ± 10° in LDT shoulder vs. 42° ± 11° in ACS, P < .001). The LD percentage EMG maximum showed no significant difference between the LDT shoulder and ACS during MAES (F_1,11 = 0.005, P = .946). During maximal active external rotation of the shoulder, the LDT shoulder showed a higher percentage EMG maximum than the ACS (3.0% ± 2.9% for LDT shoulder vs. 1.2% ± 2.0% for ACS, P = .006).

CONCLUSIONS

TH motion improved after LDT in an MIRT with pseudoparalysis and was not different from the ACS except for external rotation. However, GH motion was significantly lower after LDT than in the ACS in active-elevation range of motion. The LD was active after LDT but not more than in the ACS except for active external rotation, which we did not consider relevant as the activity did not rise above 3% EMG maximum. The favorable clinical results of LDT do not seem to be related to a change in LD activation and might be explained by its effect in preventing proximal migration of the humeral head in active elevation.

Moment arms of the deltoid, infraspinatus and teres minor muscles for movements with high range of motion: A cadaveric study

BACKGROUND

Moment arms are an indicator of the role of the muscles in joint actuation. An excursion method is often used to calculate them, even though it provides 1D results. As shoulder movement occurs in three dimensions (combination of flexion, abduction and axial rotation), moment arms should be given in 3D. Our objective was to assess the 3D moment arms of the rotator cuff (infraspinatus and teres minor) and deltoid muscles for movements with high arm elevation.

METHODS

The 3D moment arms (components in plane of elevation, elevation and axial rotation) were assessed using a geometric method, enabling to calculate the moment arms in 3D, on five fresh post-mortem human shoulders. Movement with high range of motion were performed (including overhead movement). The humerus was elevated until it reaches its maximal posture in different elevation plane (flexion, scaption, abduction and elevation in a plane 30° posterior to frontal plane).

FINDINGS

We found that the anterior deltoid was a depressor and contributes to move the elevation plane anteriorly. The median deltoid was a great elevator and the posterior deltoid mostly acted in moving the elevation plane posteriorly. The infraspinatus and teres minor were the greatest external rotator of the shoulder. The position of the glenohumeral joint induces changes in the muscular moment arms. The maximal shoulder elevation was 144° (performed in the scapular plane).

INTERPRETATION

The knowledge of 3D moment arms for different arm elevations might help surgeons in planning tendon reconstructive surgery and help validate musculoskeletal models.

In-silico neuro musculoskeletal model reproduces the movement types obtained by spinal micro stimulation

BACKGROUND AND OBJECTIVES

Virtual patients and physiologies allow experimentation, design, and early-stage clinical trials in-silico. Virtual patient technology for human movement systems that encompasses musculoskeleton and its neural control are few and far in between. Our major goal is to create a neuro- musculoskeletal upper limb in-silico model, which is modular in architecture and generates movement as an emergent phenomenon out of a multiscale co-simulation of spinal cord neural control and musculoskeletal dynamics.

METHODS

The model is developed on the NEUROiD movement simulation platform that enables a co-simulation of popular neural simulator NEURON and the musculoskeletal simulator OpenSim. We further characterized and demonstrated the use of this model in generating a range of commonly observed upper limb movements by means of a spatio-temporal stimulation pattern delivered to the cervical spinal cord.

RESULTS

We were able to characterize the model based on proprioception (Ia, Ib and II fibers), afferent conduction delay and inital postures of the musculoskeletal system. A smooth movement was achieved in all the considered experiments. The generated movements in all degrees of freedom were reproduced in accordance with the previous experimental studies.

CONCLUSION

In this work, design and development of the upper limb model was described in a modular fashion, while reusing existing models and modules. We believe this work enables a first and small step towards an in-silico paradigms for understanding upper limb movement, disease pathology, medication, and rehabilitation.

Computational analysis of subscapularis tears and pectoralis major transfers on muscular activity

BACKGROUND

Pectoralis major is the most common muscle transfer procedure to restore joint function after subscapularis tears. Limited information is available on how the neuromuscular system adjusts to the new configuration, which could explain the mixed outcomes of the procedure. The purpose of this study is to assess how muscles activation patterns change after pectoralis major transfers and report their biomechanical implications.

METHODS

We compare how muscle activation change with subscapularis tears and after its treatment by pectoralis major transfers of the clavicular, sternal, or both these segments, during three activities of daily living and a computational musculoskeletal model of the shoulder.

FINDINGS

Our results indicate that subscapularis tears require a compensatory activation of the supraspinatus and is accompanied by a reduced co-contraction of the infraspinatus, both of which can be partially recovered after transfer. Furthermore, although the pectoralis major acts asynchronously to the subscapularis before the transfer, its activation pattern changes significantly after the transfer.

INTERPRETATION

The capability of a transferred muscle segment to activate similarly to the intact subscapularis is found to be dependent on the given motion. Differences in the activation patterns between intact subscapularis and the segments of pectoralis major may explain the difficulty in adapting psycho-motor patterns during the rehabilitation period. Thereby, rehabilitation programs could benefit from targeted training on specific motion and biofeedback programs. Finally, the condition of the anterior deltoid should be considered to improve joint function.

Treatment Options for Massive Irreparable Rotator Cuff Tears

PURPOSE OF REVIEW

Massive irreparable rotator cuff tears present a significant challenge to the orthopedic surgeon. No single treatment, particularly among joint-preserving options, has been shown to be superior. The purpose of this review is to discuss recent advances in the treatment of massive irreparable rotator cuff tears, including partial repair with and without graft augmentation, interposition grafts, superior capsule reconstruction, subacromial balloon spacers, tendon transfer, and reverse total shoulder arthroplasty. We will also offer guidance on surgical indications based on our clinical experience.

RECENT FINDINGS

Partial repair may offer reasonable clinical improvement for patients with lower preoperative function despite high re-tear rates. Additionally, several types of interposition grafts have shown promising short-term results and may outperform repair alone. Subacromial balloon spacers may lead to clinical improvement, especially in patients without glenohumeral osteoarthritis or pseudoparalysis, and recently received FDA approval for use in the USA. Superior capsule reconstruction is a technically demanding procedure that appears to produce excellent short-term results particularly when performed at high volume, but long-term studies in heterogeneous study groups are needed. Tendon transfers improve function by restoring force coupling in the shoulder, offering a promising option for younger patients. Reverse total shoulder arthroplasty (RTSA) is a reliable option for treatment of irreparable cuff tears in elderly patients with lower functional demands. Irreparable cuff tears remain a difficult condition to treat. Recommended treatment for younger patients without glenohumeral osteoarthritis is particularly controversial. For older patients with low-demand lifestyles and glenohumeral osteoarthritis, RTSA is an effective treatment option. For all discussed procedures, patient selection appears to play a critical role in clinical outcomes.

Sensitivity of Neuromechanical Predictions to Choice of Glenohumeral Stability Modeling Approach

Most upper-extremity musculoskeletal models represent the glenohumeral joint with an inherently stable ball-and-socket, but the physiological joint requires active muscle coordination for stability. The authors evaluated sensitivity of common predicted outcomes (instability, net glenohumeral reaction force, and rotator cuff activations) to different implementations of active stabilizing mechanisms (constraining net joint reaction direction and incorporating normalized surface electromyography [EMG]). Both EMG and reaction force constraints successfully reduced joint instability. For flexion, incorporating any normalized surface EMG data reduced predicted instability by 54.8%, whereas incorporating any force constraint reduced predicted instability by 43.1%. Other outcomes were sensitive to EMG constraints, but not to force constraints. For flexion, incorporating normalized surface EMG data increased predicted magnitudes of joint reaction force and rotator cuff activations by 28.7% and 88.4%, respectively. Force constraints had no influence on these predicted outcomes for all tasks evaluated. More restrictive EMG constraints also tended to overconstrain the model, making it challenging to accurately track input kinematics. Therefore, force constraints may be a more robust choice when representing stability.

Biomechanics of lower trapezius and latissimus dorsi transfers in rotator cuff-deficient shoulders

BACKGROUND

Irreparable posterosuperior rotator cuff tears cause pain and impaired shoulder function. Latissimus dorsi (LD) transfer has been proven to improve shoulder function, but lower trapezius (LT) transfer has recently been proposed as an alternative. This study aimed to compare the biomechanics of LD and LT transfers and how they are affected by different insertion sites.

METHODS

The Newcastle shoulder model was used to investigate the biomechanics of these 2 tendon transfers. Computed tomography data sets from 10 healthy subjects were used to customize the model, and virtual LD and LT transfers were performed on supraspinatus, infraspinatus, and teres minor insertion sites. Muscle moment arms and lengths were computed for abduction, forward flexion, and external rotation.

RESULTS

The LT yields greater abduction moment arms compared with the LD when it is transferred to the native supraspinatus and infraspinatus insertion sites. However, they become adductors when transferred to the native teres minor insertion. Both muscles show strong external rotation moment arms, except for the LT with a supraspinatus insertion. Resting muscle strains were 0.21 (±0.03), 0.12 (±0.02), and 0.06 (±0.03) for the LD and 0.70 (±0.15), 0.61 (±0.13), and 0.58 (±0.13) for the LT for the supraspinatus, infraspinatus, and teres minor insertions, respectively.

CONCLUSIONS

LT provided better abduction and external rotation moment arms when transferred to the infraspinatus insertion. LD performed better when transferred to the supraspinatus insertion. Overall, LT transfer showed a biomechanical advantage compared with LD transfer because of stronger abduction moment arms. However, significantly larger muscle strains after LT transfer necessitate a tendon allograft to prevent muscle overtensioning.

Arthroscopic-assisted latissimus dorsi transfer for massive rotator cuff tear: a systematic review

INTRODUCTION

This systematic review provides a comprehensive description of different surgical techniques for massive rotator cuff tears (MRCTs) using arthroscopic-assisted latissimus dorsi transfer (A-LDT), reporting clinical outcomes and complications.

SOURCES OF DATA

We searched the literature on Medline (PubMed), Web of Science and Scopus databases using the combined keywords 'latissimus dorsi', 'tendon', 'transfer', 'rotator cuff tears', 'shoulder' and 'arthroscopy' to identify articles published in English, Spanish, French and Italian. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was followed for the manuscript selection.

AREAS OF AGREEMENT

Ten studies (five retrospective and five prospective investigations), all published between 2014 and 2018, fulfilled our inclusion criteria, dealing with 348 (55.7% male) patients, with a mean age of 61.6 years (range 31-83).

AREAS OF CONTROVERSY

A-LDT is a technical demanding procedure. When compared with the open technique, it does not seem to provide significant subjective and objective clinical outcome improvements.

GROWING POINTS

A-LDT seems to yield lesser surgical complications and post-operative stiffness. Sparing the deltoid muscle belly could result in a more effective shoulder post-surgery function.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further comparative randomized controlled trials with longer follow-up are needed to clarify the potentially promising superiority of A-LDT.

The presence of a rotator cuff tear interferes with age-dependent muscle atrophy of intact shoulder muscles. An MRI study with 3 years' follow-up

Rotator cuff muscle atrophy is frequently studied, but it is unknown whether redistribution of mechanical load in the presence of a rotator cuff tear influence muscle atrophy that is observed in patients. We hypothesized that in the presence of a supraspinatus tear, redistribution of mechanical load towards teres minor and deltoid slows down atrophy of these muscles over time. In this retrospective observational study of 129 patients, we measured the cross-sectional surface-areas on MRI of shoulder muscles in an intact rotator cuff (n = 92) and in a supraspinatus-tear group (n = 37) with a mean follow-up of 3 ± 1.8 years. Mixed models were applied to evaluate changes in surface-area of the rotator cuff and deltoid with adjustments for age, sex and follow-up time. In patients with an intact rotator cuff, the mean surface-area of the teres minor decreased 6 mm²/year (95% CI 0.7-11.1, P = 0.026) and the mean deltoid surface-area decreased 75 mm²/year (95% CI 24.5-124.8, P = 0.004). The presence of a rotator cuff tear was associated with less reduction of teres minor and deltoid surface-area in patients <50 years, with an effect of a tear of 22 mm²/year (95% CI 1.7-41.7, P = 0.034) and 250 mm²/year (95% CI 75.8-424.3, P = 0.006), respectively. Whereas the surface-area of teres minor and deltoid decrease over time in patient with an intact rotator cuff, the decline in surface-area of these muscles was substantially less in the presence of a rotator cuff tear. Our findings indicate that atrophy may be reduced if an increase in mechanical load is exerted onto the muscle.

Teres major tendon transfer in the treatment of irreparable posterosuperior rotator cuff tears: long-term improvement of shoulder function and pain reduction at eight to 12 years’ follow-up

Aims

Since long-term outcome of teres major tendon transfer surgery for irreparable posterosuperior rotator cuff (RC) tears is largely unknown, the primary aim of this study was to evaluate the long-term outcome of the teres major transfer. We also aimed to report on the results of a cohort of patients with a similar indication for surgery that underwent a latissimus dorsi tendon transfer.

Patients and Methods

Patients and Methods In this prospective cohort study, we reported on the long-term results of 20 consecutive patients with a teres major tendon transfer for irreparable massive posterosuperior RC tears. Additionally, we reported on the results of the latissimus dorsi tendon transfer (n = 19). The mean age was 60 years (47 to 77). Outcomes included the Constant score (CS), and pain at rest and during movement using the Visual Analogue Scale (VAS).

Results

At a mean of ten years (8 to 12) following teres major transfer, the CS was still 23 points (95% confidence interval (CI) 14.6 to 30.9, p < 0.001) higher than preoperatively. VAS for pain at rest (21 mm, 95% CI 4.0 to 38.9, p = 0.016) and movement (31 mm, 95% CI 16.0 to 45.1, p < 0.001) were lower than preoperatively. We also found an increase in CS (32 points, 95% CI 23.4 to 40.2, p < 0.001) and reduction of pain (26 mm, 95% CI 9.9 to 41.8, p = 0.001) six years after latissimus dorsi transfer.

Conclusion

Teres major tendon transfer is a treatment option to gain shoulder function and reduce pain in patients with an irreparable posterosuperior RC tear at a mean follow-up of ten years. The teres major tendon might be a valuable alternative to the commonly performed latissimus dorsi tendon transfer in the treatment of irreparable posterosuperior RC tears. Cite this article: Bone Joint J 2018;100-B:309-17.

Modulation of shoulder muscle and joint function using a powered upper-limb exoskeleton

Robotic-assistive exoskeletons can enable frequent repetitive movements without the presence of a full-time therapist; however, human-machine interaction and the capacity of powered exoskeletons to attenuate shoulder muscle and joint loading is poorly understood. This study aimed to quantify shoulder muscle and joint force during assisted activities of daily living using a powered robotic upper limb exoskeleton (ArmeoPower, Hocoma). Six healthy male subjects performed abduction, flexion, horizontal flexion, reaching and nose touching activities. These tasks were repeated under two conditions: (i) the exoskeleton compensating only for its own weight, and (ii) the exoskeleton providing full upper limb gravity compensation (i.e., weightlessness). Muscle EMG, joint kinematics and joint torques were simultaneously recorded, and shoulder muscle and joint forces calculated using personalized musculoskeletal models of each subject's upper limb. The exoskeleton reduced peak joint torques, muscle forces and joint loading by up to 74.8% (0.113 Nm/kg), 88.8% (5.8%BW) and 68.4% (75.6%BW), respectively, with the degree of load attenuation strongly task dependent. The peak compressive, anterior and superior glenohumeral joint force during assisted nose touching was 36.4% (24.6%BW), 72.4% (13.1%BW) and 85.0% (17.2%BW) lower than that during unassisted nose touching, respectively. The present study showed that upper limb weight compensation using an assistive exoskeleton may increase glenohumeral joint stability, since deltoid muscle force, which is the primary contributor to superior glenohumeral joint shear, is attenuated; however, prominent exoskeleton interaction moments are required to position and control the upper limb in space, even under full gravity compensation conditions. The modeling framework and results may be useful in planning targeted upper limb robotic rehabilitation tasks.

Three-dimensional shoulder motion after teres major or latissimus dorsi tendon transfer for posterosuperior rotator cuff tears

BACKGROUND

Teres major (TM) transfer and latissimus dorsi (LD) transfer are essential treatment options in patients with posterosuperior rotator cuff (RC) tears. The purpose of this study was to quantify shoulder kinematics before and after TM transfer and LD transfer in posterosuperior RC tear patients.

METHODS

In this prospective cohort study, we quantitatively measured shoulder movements using an electromagnetic tracking device (Flock of Birds) preoperatively and 1 year after either TM (n = 13) or LD (n = 9) tendon transfer. Additional outcome measures included the Constant score (CS), patient-reported pain, and quantitative range of motion. Scapular kinematics were evaluated during arm abduction.

RESULTS

By use of a quantitative assessment, forward flexion (from 87° to 106°, P = .007), abduction (from 86° to 106°, P = .010), and external rotation in abduction (from 52° to 70°, P = .019) improved. Both transfers reduced pain (from 50 to 10 mm, P < .001), and the CS improved (from 37 to 62 points, P < .001). No significant differences in postoperative improvement in pain and function were found between TM and LD tendon transfers. The TM transfer group showed increased scapular lateral rotation compared with the LD transfer group (13°; 95% confidence interval [CI], 4.8° to 21.7°; P = .003). We were unable to detect differences between TM transfer and LD transfer in the change in protraction (3.2°; 95% CI, -6.3° to 12.8°; P = .489) and posterior tilt (3.5°; 95% CI, -3.5° to 10.5°; P = .313).

CONCLUSION

Tendon transfer surgery resulted in an overall improvement in CS, pain relief, and quantitative range of motion in the treatment of an irreparable posterosuperior RC tear. Scapular lateral rotation gradually increased after TM transfer, reminiscent of RC function, whereas such an increase was not observed after LD transfer.

The effect of a rotator cuff tear and its size on three-dimensional shoulder motion

BACKGROUND

Rotator cuff-disease is associated with changes in kinematics, but the effect of a rotator cuff-tear and its size on shoulder kinematics is still unknown in-vivo.

METHODS

In this cross-sectional study, glenohumeral and scapulothoracic kinematics of the affected shoulder were evaluated using electromagnetic motion analysis in 109 patients with 1) subacromial pain syndrome (n=34), 2) an isolated supraspinatus tear (n=21), and 3) a massive rotator cuff tear involving the supraspinatus and infraspinatus (n=54). Mixed models were applied for the comparisons of shoulder kinematics between the three groups during abduction and forward flexion.

FINDINGS

In the massive rotator cuff-tear group, we found reduced glenohumeral elevation compared to the subacromial pain syndrome (16°, 95% CI [10.5, 21.2], p<0.001) and the isolated supraspinatus tear group (10°, 95% CI [4.0, 16.7], p=0.002) at 110° abduction. Reduced glenohumeral elevation in massive rotator cuff tears coincides with an increase in scapulothoracic lateral rotation compared to subacromial pain syndrome (11°, 95% CI [6.5, 15.2], p<0.001) and supraspinatus tears (7°, 95% CI [1.8, 12.1], p=0.012). Comparable differences were observed for forward flexion. No differences in glenohumeral elevation were found between the subacromial pain syndrome and isolated supraspinatus tear group during arm elevation.

INTERPRETATION

The massive posterosuperior rotator cuff-tear group had substantially less glenohumeral elevation and more scapulothoracic lateral rotation compared to the other groups. These observations suggest that the infraspinatus is essential to preserve glenohumeral elevation in the presence of a supraspinatus tear. Shoulder kinematics are associated with rotator cuff-tear size and may have diagnostic potential.

Arthroscopic-Assisted Latissimus Dorsi Tendon Transfer for Massive, Irreparable Rotator Cuff Tears: Technique and Short-Term Follow-Up of Patients With Pseudoparalysis

PURPOSE

To describe a modified technique for arthroscopic-assisted transfer of the latissimus dorsi tendon in a selected group of patients with irreparable rotator cuff tears and pseudoparalysis and to evaluate its short-term results.

METHODS

Fifteen patients with irreparable rotator cuff tears and pseudoparalysis treated by arthroscopic-assisted latissimus dorsi tendon transfer were included. The mean patient age was 61.53 ± 6.24 years (range, 52-71 years). Patients were assessed with physical examination, University of California Los Angeles (UCLA) Score and Constant-Murley score, as well as visual analog scale score at a mean follow-up of 26.4 ± 2.58 months (range, 24-31 months).

RESULTS

At final follow-up, mean UCLA score increased to 27.47 ± 6.31 compared with the preoperative UCLA score of 6.53 ± 2.1 (P < .001). Constant-Murley score was 21 ± 7.41 and 59.73 ± 13.62 (P < .001), visual analog scale pain score was 7.47 ± 1.06 and 2.47 ± 0.91 (P < .001), active forward flexion was 58° ± 21.11° and 130° ± 30.05° (P < .001), active abduction was 51° ± 21.64° and 129.67° ± 25.45° (P < .001), and active external rotation was 13.33° ± 21.68° and 32° ± 18.03° (P < .001) preoperatively and postoperatively, respectively. Mean acromiohumeral distance was 3.13 ± 1.40 mm preoperatively, whereas it was 5.67 ± 1.67 mm postoperatively (P < .001). No significant complications requiring a revision surgery was observed during the final follow-up.

CONCLUSIONS

The modified technique of arthroscopic-assisted transfer of the latissimus dorsi tendon is a feasible, minimally invasive option for the surgical treatment of irreparable rotator cuff tears in a subset of patients with pseudoparalysis.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Latissimus Dorsi Transfer in Posterior Irreparable Rotator Cuff Tears

BACKGROUND

Massive rotator cuff tears pose a difficult and complex challenge even for the experienced surgeon; inability to repair these tears by conventional means designates them as irreparable, while management becomes quite taxing. Several operative options have been suggested for the management of such lesions with varying degrees of success, while it is imperative to match patient demands and expectations to the predicted outcome.

METHODS

Research articles are examined and key concepts are discussed, in order to provide an evidence based review of the available literature. The anatomy and pathomechanics along with the indications, contraindications and surgical techniques are reported.

RESULTS

Transfer of the Latissimus dorsi has been used with success to restore shoulder function in deficits of the posterior rotator cuff. Although it can be used in a variety of settings, the ideal patient for a Latissimus dorsi tendon transfer is a young and active individual, with no glenohumeral osteoarthritis that has a severe disability and weakness related to an irreparable posterior cuff tear.

CONCLUSION

Tendon transfers have proved to be a successful treatment option in salvaging this difficult problem, providing pain relief and restoring shoulder function. Despite the excellent functional outcomes and pain suppression following operation, a variety of factors may affect the outcome; thus making indications and preoperative assessment a valuable component.

Influence of fixation point of latissimus dorsi tendon transfer for irreparable rotator cuff tear on glenohumeral external rotation: A cadaver study

Latissimus dorsi tendon transfer is a surgical option for treating irreparable posterosuperior rotator cuff tears, notably when attempting to reconstruct active external rotation. We hypothesized that the positioning of the transfer's point of fixation would differ depending on the desired elbow-to-body external rotation or external rotation with the elbow abducted.

MATERIAL AND METHODS

Seven shoulders from four whole frozen cadavers were used. We created two systems to install the subject in a semi-seated position to allow external rotation elbow to body and the arm abducted 90°. Traction sutures were positioned on the latissimus dorsi muscle and a massive tear of the rotator cuff was created. We tested six different transfer positions. Muscle contraction of the latissimus dorsi was stimulated using 10-N and 20-N suspended weights.

RESULTS

The point of fixation of the latissimus dorsi on the humeral head had an influence on the elbow-to-body external rotation and with 90° abduction (P<0.001). The fixation point for a maximum external rotation with the elbow to the body was the anterolateral position (P<0.016). The fixation point for a maximum external rotation at 90° abduction was the position centered on the infraspinatus footprint (P<0.078).

CONCLUSION

The optimal point of fixation differs depending on whether external rotation is restored at 0° or 90° abduction.

LEVEL OF EVIDENCE

Fundamental study, anatomic study.

Subject-specific musculoskeletal modeling in the evaluation of shoulder muscle and joint function

Upper limb muscle force estimation using Hill-type muscle models depends on musculotendon parameter values, which cannot be readily measured non-invasively. Generic and scaled-generic parameters may be quickly and easily employed, but these approaches do not account for an individual subject's joint torque capacity. The objective of the present study was to develop a subject-specific experimental testing and modeling framework to evaluate shoulder muscle and joint function during activities of daily living, and to assess the capacity of generic and scaled-generic musculotendon parameters to predict muscle and joint function. Three-dimensional musculoskeletal models of the shoulders of 6 healthy subjects were developed to calculate muscle and glenohumeral joint loading during abduction, flexion, horizontal flexion, nose touching and reaching using subject-specific, scaled-generic and generic musculotendon parameters. Muscle and glenohumeral joint forces calculated using generic and scaled-generic models were significantly different to those of subject-specific models (p<0.05), and task dependent; however, scaled-generic model calculations of shoulder glenohumeral joint force demonstrated better agreement with those of subject-specific models during abduction and flexion. Muscles in generic musculoskeletal models operated further from the plateau of their force-length curves than those of scaled-generic and subject-specific models, while muscles in subject-specific models operated over a wider region of their force length curves than those of the generic or scaled-generic models, reflecting diversity of subject shoulder strength. The findings of this study suggest that generic and scaled-generic musculotendon parameters may not provide sufficient accuracy in prediction of shoulder muscle and joint loading when compared to models that employ subject-specific parameter-estimation approaches.

Surgical Simulations Based on Limited Quantitative Data: Understanding How Musculoskeletal Models Can Be Used to Predict Moment Arms and Guide Experimental Design

The utility of biomechanical models and simulations to examine clinical problems is currently limited by the need for extensive amounts of experimental data describing how a given procedure or disease affects the musculoskeletal system. Methods capable of predicting how individual biomechanical parameters are altered by surgery are necessary for the efficient development of surgical simulations. In this study, we evaluate to what extent models based on limited amounts of quantitative data can be used to predict how surgery influences muscle moment arms, a critical parameter that defines how muscle force is transformed into joint torque. We specifically examine proximal row carpectomy and scaphoid-excision four-corner fusion, two common surgeries to treat wrist osteoarthritis. Using models of these surgeries, which are based on limited data and many assumptions, we perform simulations to formulate a hypothesis regarding how these wrist surgeries influence muscle moment arms. Importantly, the hypothesis is based on analysis of only the primary wrist muscles. We then test the simulation-based hypothesis using a cadaveric experiment that measures moment arms of both the primary wrist and extrinsic thumb muscles. The measured moment arms of the primary wrist muscles are used to verify the hypothesis, while those of the extrinsic thumb muscles are used as cross-validation to test whether the hypothesis is generalizable. The moment arms estimated by the models and measured in the cadaveric experiment both indicate that a critical difference between the surgeries is how they alter radial-ulnar deviation versus flexion-extension moment arms at the wrist. Thus, our results demonstrate that models based on limited quantitative data can provide novel insights. This work also highlights that synergistically utilizing simulation and experimental methods can aid the design of experiments and make it possible to test the predictive limits of current computer simulation techniques.

Clinical outcome of latissimus dorsi tendon transfer and partial cuff repair in irreparable postero-superior rotator cuff tear

BACKGROUND AND PURPOSE

Irreparable rotator cuff tears are a common cause of pain in adult population, requiring in many cases a surgical treatment. Possible alternatives are debridement, partial repair, muscle transfers and joint replacement. We evaluated two groups of patients with irreparable rotator cuff tear treated surgically: one group received an arthroscopic-assisted latissimus dorsi tendon transfer (LDTT), and the other an arthroscopic rotator cuff partial repair. Aim of our study was to compare clinical results and quality of life in two groups of patients with massive irreparable rotator cuff tear: one receiving an arthroscopic LDTT and the other receiving an arthroscopic rotator cuff partial repair.

METHODS

Forty patients were assigned to two groups: 20 patients to group TT treated with LDTT and 20 patients to group PR treated with a partial repair. The average follow-up duration was 2.8 years (1-5, SD 3). Pre- and postoperative modified UCLA shoulder score, ROM, measurement of the strength and the rotator cuff quality of life (RC-QOL) were used to asses the outcome.

RESULTS

LDTT showed significative improvements when compared to partial repair in UCLA score results, strength and RC-QOL questionnaire. No differences were found between the groups in pain relief.

CONCLUSION

Both techniques are effective in reducing patients' symptoms. We believe that in younger, high-demanding patients with no or mild osteoarthritis, the LDTT represents a valid treatment option with better modified UCLA score improvement and strength at our follow-up.

Latissimus dorsi tendon transfer for irreparable postero-superior cuff tears: current concepts, indications, and recent advances

Latissimus dorsi tendon transfer is a method for surgical treatment of massive irreparable posterosuperior cuff tears. It partially restores active anteflexion, external rotation, and function of the shoulder but does not significantly increase strength of the shoulder. It is contraindicated in case of pseudoparalytic shoulder; associated irreparable subscapularis tear, deltoid palsy, and in case of associated osteoarthritis, as an isolated procedure. Results are inferior when performed as a secondary procedure compared with a primary procedure. However, latissimus dorsi tendon transfer is an attractive solution to improve shoulder mobility and function of young and non osteoarthritic patients whose previous surgical treatment of massive postero-superior irreparable rotator cuff tear failed. As a primary procedure, latissimus dorsi tendon transfer competes with debridement, biceps tenotomy, and partial cuff repair. In association with reverse shoulder arthroplasty, it restores active external rotation in osteoarthritic patients with active external rotation deficit. New arthroscopic assisted techniques might improve results in the future.

Latissimus dorsi tendon transfer for treatment of irreparable posterosuperior rotator cuff tears: long-term results at a minimum follow-up of ten years

BACKGROUND

Transfer of the latissimus dorsi tendon to the greater tuberosity of the humerus for treatment of an irreparable rotator cuff tear has been reported to yield good-to-excellent short to intermediate-term results in well-selected patients. The purpose of this study was to evaluate the long-term outcome of such transfers for irreparable posterosuperior rotator cuff tears to determine the durability of the results and to identify risk factors for an unfavorable outcome.

METHODS

Fifty-seven shoulders in fifty-five patients (seventeen women and thirty-eight men with a mean age of fifty-six years) were managed with latissimus dorsi tendon transfer. Final follow-up was performed at a mean of 147 months. Outcome measures included the Constant score and the Subjective Shoulder Value (SSV). Osteoarthritis, the acromiohumeral distance, and the so-called critical shoulder angle were assessed on standardized radiographs.

RESULTS

Forty-six shoulders in forty-four patients were available at the time of final follow-up. The mean SSV increased from 29% preoperatively to 70% at the time of final follow-up, the relative Constant score improved from 56% to 80%, and the pain score improved from 7 to 13 points (p < 0.0001 for all). Mean flexion increased from 118° to 132°, abduction increased from 112° to 123°, and external rotation increased from 18° to 33°. Mean abduction strength increased from 1.2 to 2.0 kg (p = 0.001). There was a slight but significant increase in osteoarthritic changes. Inferior results occurred in shoulders with insufficiency of the subscapularis muscle and fatty infiltration of the teres minor muscle. Superior functional results were observed in shoulders with a small postoperative critical shoulder angle.

CONCLUSIONS

Latissimus dorsi tendon transfer offered an effective treatment for irreparable posterosuperior rotator cuff tears, with substantial and durable improvements in shoulder function and pain relief. Shoulders with fatty infiltration of the teres minor muscle and insufficiency of the subscapularis muscle tended to have inferior results, as did those with a large critical shoulder angle.

LEVEL OF EVIDENCE

Therapeutic level IV. See Instructions for Authors for a complete description of levels of evidence.

Clinical applications of musculoskeletal modelling for the shoulder and upper limb

Musculoskeletal models have been developed to estimate internal loading on the human skeleton, which cannot directly be measured in vivo, from external measurements like kinematics and external forces. Such models of the shoulder and upper extremity have been used for a variety of purposes, ranging from understanding basic shoulder biomechanics to assisting in preoperative planning. In this review, we provide an overview of the most commonly used large-scale shoulder and upper extremity models and categorise the applications of these models according to the type of questions their users aimed to answer. We found that the most explored feature of a model is the possibility to predict the effect of a structural adaptation on functional outcome, for instance, to simulate a tendon transfer preoperatively. Recent studies have focused on minimising the mismatch in morphology between the model, often derived from cadaver studies, and the subject that is analysed. However, only a subset of the parameters that describe the model's geometry and, perhaps most importantly, the musculotendon properties can be obtained in vivo. Because most parameters are somehow interrelated, the others should be scaled to prevent inconsistencies in the model's structure, but it is not known exactly how. Although considerable effort is put into adding complexity to models, for example, by making them subject-specific, we have found little evidence of their superiority over current models. The current trend in development towards individualised, more complex models needs to be justified by demonstrating their ability to answer questions that cannot already be answered by existing models.

Musculoskeletal shoulder models: A technical review and proposals for research foci

Musculoskeletal shoulder models allow non-invasive prediction of parameters that cannot be measured, particularly the loading applied to morphological structures and neurological control. This insight improves treatment and avoidance of pathology and performance evaluation and optimisation. A lack of appropriate validation and knowledge of model parameters’ accuracy may cause reduced clinical success for these models. Instrumented implants have recently been used to validate musculoskeletal models, adding important information to the literature. This development along with increasing prevalence of shoulder models necessitates a fresh review of available models and their utility. The practical uses of models are described. Accuracy of model inputs, modelling techniques and model sensitivity is the main technical review undertaken. Collection and comparison of these parameters are vital to understanding disagreement between model outputs. Trends in shoulder modelling are highlighted: validation through instrumented prostheses, increasing openness and strictly constrained, optimised, measured kinematics. Future directions are recommended: validation through focus on model sub-sections, increased subject specificity with imaging techniques determining muscle and body segment parameters and through different scaling and kinematics optimisation approaches.

The influence of simulated rotator cuff tears on the risk for impingement in handbike and handrim wheelchair propulsion

BACKGROUND

Rotator cuff tears strongly affect the biomechanics of the shoulder joint in their role to regulate the joint contact force needed to prevent the joint from dislocation. The aim of this study was to investigate the influence of simulated progressed rotator cuff tears on the (in)stability of the glenohumeral joint and the risk for impingement during wheelchair and handbike propulsion.

METHODS

The Delft Shoulder and Elbow Model was used to calculate the magnitude of the glenohumeral joint reaction force and the objective function J, which is an indication of the effort needed to complete the task. Full-thickness tears were simulated by virtually removing muscles from the model.

FINDINGS

With larger cuff tears the joint reaction force was higher and more superiorly directed. Also extra muscle force was necessary to balance the external force such that the glenohumeral joint did not dislocate.

INTERPRETATION

A tear of only the supraspinatus leads only to a minor increase in muscle forces and a minor shift of the force on the glenoid, indicating that it is possible to function well with a torn supraspinatus muscle. A massive tear shifts the direction of the joint reaction force to the superior border of the glenoid, increasing the risk for impingement.

Biomechanical effect of latissimus dorsi tendon transfer for irreparable massive cuff tear

BACKGROUND

The purpose of this study was to determine the biomechanical effects of latissimus dorsi transfer in a cadaveric model of massive posterosuperior rotator cuff tear.

METHODS

Eight cadaveric shoulders were tested at 0°, 30°, and 60° of abduction in the scapular plane with anatomically based muscle loading. Humeral rotational range of motion and the amount of humeral rotation due to muscle loading were measured. Glenohumeral kinematics and contact characteristics were measured throughout the range of motion. After testing in the intact condition, the supraspinatus and infraspinatus were resected. The cuff tear was then repaired by latissimus dorsi transfer. Two muscle loading conditions were applied after latissimus transfer to simulate increased tension that may occur due to limited muscle excursion. A repeated-measures analysis of variance was used for statistical analysis.

RESULTS

The amount of internal rotation due to muscle loading and maximum internal rotation increased with massive cuff tear and was restored with latissimus transfer (P < .05). At maximum internal rotation, the humeral head apex shifted anteriorly, superiorly, and laterally at 0° of abduction after massive cuff tear (P < .05); this abnormal shift was corrected with latissimus transfer (P < .05). However, at 30° and 60° of abduction, latissimus transfer significantly altered kinematics (P < .05) and latissimus transfer with increased muscle loading increased contact pressure, especially at 60° of abduction.

CONCLUSION

Latissimus dorsi transfer is beneficial in restoring humeral internal/external rotational range of motion, the internal/external rotational balance of the humerus, and glenohumeral kinematics at 0° of abduction. However, latissimus dorsi transfer with simulated limited excursion may lead to an overcompensation that can further deteriorate normal biomechanics, especially at higher abduction angles.

Latissimus dorsi tendon transfer for irreparable rotator cuff tears: a modified technique using arthroscopy

Latissimus dorsi transfer is a well-established method for the treatment of posterosuperior massive irreparable rotator cuff tears. We propose using an arthroscopically assisted technique that avoids insult to the deltoid. With the patient in the lateral decubitus position, an L-shaped incision is made along the anterior belly of the latissimus muscle and then along the posterior axillary line. The latissimus and teres major are identified and separated. The tendon insertion of the latissimus is isolated, and a FiberWire traction suture (Arthrex, Naples, FL) is placed, facilitating dissection of the muscle to the thoracodorsal neurovascular pedicle and subsequent mobilization. The interval deep to the deltoid and superficial to the teres minor is developed into a subdeltoid tunnel for arthroscopic tendon transfer. The latissimus tendon is then transferred and stabilized arthroscopically to the lateral aspect of the infraspinatus and supraspinatus footprints by multiple suture anchors.

Infraspinatus/Teres minor transfer biceps in situ tenodesis procedure: initial results of a technique for massive cuff tears

Massive rotator cuff tears may not be primarily repairable with salvage options not necessarily providing acceptable results. Extrinsic tendon transfer is a significant undertaking with prolonged rehabilitation and variable outcome. A novel technique for the reconstruction of massive tears, not amenable to primary repair, by performing a transfer of the intrinsic posterior rotator cuff onto an intact, tenodesed long head of biceps tendon acting as a scaffold for the intrinsic transfer is described. The clinical results at short to medium term in 17 initial patients are presented. Encouraging results from this study suggest that this is a viable option for the management of massive rotator cuff tears with an intact posterior cuff with results equal or superior to other reconstructive techniques.

Latissimus dorsi tendon transfer for irreparable rotator cuff tears: a systematic review

BACKGROUND

Massive and irreparable posterior-superior rotator cuff tears present a difficult treatment problem. The purpose of this systematic review was to critically examine the outcomes of latissimus dorsi tendon transfers for the treatment of irreparable rotator cuff tears.

METHODS

A systematic review of the literature was performed via a search of electronic databases. Two reviewers independently assessed the methodological quality of, and extracted relevant data from, each included study. In cases in which the outcomes data were similar between studies, data were pooled for the purposes of generating summary outcomes through the use of frequency-weighted values.

RESULTS

Ten studies that fulfilled all inclusion and exclusion criteria were included. The frequency-weighted mean age was 58.7 years. Patients were followed for a frequency-weighted mean of 45.5 months (range, twenty-four to 126 months). Patients had a frequency-weighted mean adjusted Constant score of 45.9 preoperatively compared with 73.2 postoperatively (p < 0.001). The frequency-weighted mean active forward elevation improved from 101.9° preoperatively to 137.4° postoperatively (p < 0.001), and the frequency-weighted mean active external rotation improved from 16.8° to 26.7° (p < 0.001). Subscapularis muscle insufficiency, advanced teres minor muscle atrophy, and the need for revision surgery were correlated with poor functional outcomes in some studies.

CONCLUSIONS

Compiled data and frequency-weighted means demonstrated improvement in shoulder function, range of motion, strength, and pain relief after latissimus dorsi tendon transfer for irreparable rotator cuff tears. Patients and physicians should not expect an outcome of "normal" function or complete pain relief.

Personalized neuromusculoskeletal modeling to improve treatment of mobility impairments: a perspective from European research sites

Mobility impairments due to injury or disease have a significant impact on quality of life. Consequently, development of effective treatments to restore or replace lost function is an important societal challenge. In current clinical practice, a treatment plan is often selected from a standard menu of options rather than customized to the unique characteristics of the patient. Furthermore, the treatment selection process is normally based on subjective clinical experience rather than objective prediction of post-treatment function. The net result is treatment methods that are less effective than desired at restoring lost function. This paper discusses the possible use of personalized neuromusculoskeletal computer models to improve customization, objectivity, and ultimately effectiveness of treatments for mobility impairments. The discussion is based on information gathered from academic and industrial research sites throughout Europe, and both clinical and technical aspects of personalized neuromusculoskeletal modeling are explored. On the clinical front, we discuss the purpose and process of personalized neuromusculoskeletal modeling, the application of personalized models to clinical problems, and gaps in clinical application. On the technical front, we discuss current capabilities of personalized neuromusculoskeletal models along with technical gaps that limit future clinical application. We conclude by summarizing recommendations for future research efforts that would allow personalized neuromusculoskeletal models to make the greatest impact possible on treatment design for mobility impairments.

On validation of multibody musculoskeletal models

We review the opportunities to validate multibody musculoskeletal models in view of the current transition of musculoskeletal modelling from a research topic to a practical simulation tool in product design, healthcare and other important applications. This transition creates a new need for justification that the models are adequate representations of the systems they simulate. The need for a consistent terminology and established standards is identified and knowledge from fields with a more progressed state-of-the-art in verification and validation is introduced. A number of practical steps for improvement of the validation of multibody musculoskeletal models are pointed out and directions for future research in the field are proposed. It is hoped that a more structured approach to model validation can help to improve the credibility of musculoskeletal models.

Tendon fixation in arthroscopic latissimus dorsi transfer for irreparable posterosuperior cuff tears: an in vitro biomechanical comparison of interference screw and suture anchors

BACKGROUND

The fixation of the tendon to the bone remains a challenging problem in the latissimus dorsi tendon transfer for irreparable cuff tears and can lead to unsatisfactory results. A new arthroscopic method of tendon to bone fixation using an interference screw has been developed and the purpose of this study was to compare its biomechanical properties to the ones of a standard fixation technique with anchors.

METHODS

Six paired fresh frozen cadaveric human humeri were used. The freed latissimus dorsi tendon was randomly fixed to the humeral head with anchors or with interference screw after a tubularization procedure. Testing consisted to apply 200 cycles of tensile load on the latissimus dorsi tendon with maximal loads of 30 N and 60 N, followed by a load to failure test. The stiffness, displacements after cyclic loadings, ultimate load to failure, and site of failure were analysed.

FINDINGS

The stiffness was statistically higher for the tendons fixed with interference screws than for the ones fixed with anchors for both 30 N and 60 N loadings. Likewise, the relative bone/tendon displacements after cyclic loadings were lower with interference screws compared to anchors. Load to failure revealed no statistical difference between the two techniques.

INTERPRETATION

Compared to the standard anchor fixation, the interference screw fixation technique presents higher or similar biomechanical performance. These results should be completed by further biomechanical and clinical trials to confirm the interest of this new technique as an alternative in clinical use.

Development of a comprehensive musculoskeletal model of the shoulder and elbow

The Delft Shoulder and Elbow Model (DSEM), a musculoskeletal model of the shoulder and elbow has been extensively developed since its introduction in 1994. Extensions cover both model structures and anatomical data focusing on the addition of an elbow part and muscle architecture parameters. The model was also extended with a new inverse-dynamics optimization cost function and combined inverse-forward-dynamics models. This study is an update on the developments of the model over the last decade including a qualitative validation of the different simulation architectures available in the DSEM. To validate the model, a dynamic forward flexion motion was performed by one subject, of which the motion data and surface EMG-signals of 12 superficial muscles were measured. Patterns of the model-predicted relative muscle forces were compared with their normalized EMG-signals. Results showed relatively good agreement between forces and EMG (mean correlation coefficient of 0.66). However, for some cases, no force was predicted while EMG activity had been measured (false-negatives). The DSEM has been used and has the potential to be used in a variety of clinical and biomechanical applications.

Load on the shoulder complex during wheelchair propulsion and weight relief lifting

BACKGROUND

This study focuses on the relationship between overuse in association with wheelchair activities of daily living and risks for osteoarthrosis in the acromioclavicular and sternoclavicular joints. The aim is to quantify the joint moments and joint reaction forces in all three joints of the shoulder complex during wheelchair-related activities of daily living.

METHODS

A convenience sample of 17 subjects performed two tasks (wheelchair propulsion and weight relief lifting). Three-dimensional kinematics and kinetics were measured and position and force data were used as input for a musculoskeletal model of the arm and shoulder. Output variables of the model were the moments and the joint reaction forces on the sternoclavicular, acromioclavicular and glenohumeral joints.

FINDINGS

Moments on the sternoclavicular joint were higher than on the acromioclavicular and glenohumeral joint, but the joint reaction forces on the sternoclavicular and acromioclavicular joints were only one third of those on the glenohumeral joint (peak forces around 96N compared to 315N for wheelchair propulsion and around 330N compared to 1288N for weight relief lifting).

INTERPRETATION

Based on the results found in this study, net joint moments are likely a better measure to describe the load on the acromioclavicular and sternoclavicular joints due to the passive stabilization. Prospective studies on wheelchair overuse injuries should also look at the acromioclavicular and sternoclavicular joints since the load of wheelchair tasks might be a risk factor for osteoarthrosis in these joints.

A simulation analysis of the combined effects of muscle strength and surgical tensioning on lateral pinch force following brachioradialis to flexor pollicis longus transfer

Biomechanical simulations of tendon transfers performed following tetraplegia suggest that surgical tensioning influences clinical outcomes. However, previous studies have focused on the biomechanical properties of only the transferred muscle. We developed simulations of the tetraplegic upper limb following transfer of the brachioradialis (BR) to the flexor pollicis longus (FPL) to examine the influence of residual upper limb strength on predictions of post-operative transferred muscle function. Our simulations included the transfer, ECRB, ECRL, the three heads of the triceps, brachialis, and both heads of the biceps. Simulations were integrated with experimental data, including EMG and joint posture data collected from five individuals with tetraplegia and BR-FPL tendon transfers during maximal lateral pinch force exertions. Given a measured co-activation pattern for the non-paralyzed muscles in the tetraplegic upper limb, we computed the highest activation for the transferred BR for which neither the elbow nor the wrist flexor moment was larger than the respective joint extensor moment. In this context, the effects of surgical tensioning were evaluated by comparing the resulting pinch force produced at different muscle strength levels, including patient-specific scaling. Our simulations suggest that extensor muscle weakness in the tetraplegic limb limits the potential to augment total pinch force through surgical tensioning. Incorporating patient-specific muscle volume, EMG activity, joint posture, and strength measurements generated simulation results that were comparable to experimental results. Our study suggests that scaling models to the population of interest facilitates accurate simulation of post-operative outcomes, and carries utility for guiding and developing rehabilitation training protocols.

"What if": the use of biomechanical models for understanding and treating upper extremity musculoskeletal disorders

To aid understanding of the working of the upper extremity, several musculoskeletal models of the shoulder and arm have been developed. These models comprise the full shoulder girdle, which implies that the thoracohumeral link is formed by a scapular and clavicular segment. These models are based upon limited anatomical parameter sets and work on the assumption of a general control principle. Upper Extremity models have proven to be useful for different categories of applications, such as quantification of the load on musculoskeletal structures, or the evaluation of changes in the musculoskeletal structure on function and mechanical integrity ("what if" questions). Although these models are increasingly used, validation has long been a difficult issue. With the development of instrumented endoprostheses, a new method for model validation has come within reach. Up till now results have indicated that to obtain 'true' force values, models should be scaled, and should allow for cocontraction. Musculoskeletal models will be finding their way in education and in clinical decision making. On the longer run individualized models might become important for application to individual patients, although scaling will for some time remain a difficult issue.

Teres major muscle activation relates to clinical outcome in tendon transfer surgery

BACKGROUND

In massive rotator cuff tears a teres major (TMj) tendon transfer to the insertion of the supraspinatus (SSp) reverses its adduction moment arm into abduction which is supposed to be an adequate salvage procedure. Analysis of muscle function to find biomechanical ground of such success is scarce.

METHODS

We compared pre- and postoperative clinical outcome of TMj transfer, i.e. Range of Motion, pain, Constant Shoulder scores and arm force. TMj activation was evaluated in 14 patients suffering massive cuff tears using activation ratios to describe the desired 'in-phase' and undesired 'out-of-phase' contribution to the external arm moment. Additionally, we analyzed activation of the latissimus dorsi (LD) and the medial part of the deltoids (DE). The activation ratios were compared to controls and TMj activation ratios were related to clinical outcome.

FINDINGS

TMj tendon transfer improved arm function. Pre-operatively, we observed 'out-of-phase'abduction activation of TMj and LD. After transfer patients activated TMj according to its new anatomical position. 'Out-of-phase' LD abduction activation persisted. The clinical improvements coincided with changes in activation ratio of TMj.

INTERPRETATION

'Out-of-phase' TMj adductor activation is associated with compromised arm function in patients with irreparable cuff tears. After transfer, TMj is activated in correspondence with its new anatomical function, which was supportive for the improved arm function.

Numerical modelling of the shoulder for clinical applications

Research activity involving numerical models of the shoulder is dramatically increasing, driven by growing rates of injury and the need to better understand shoulder joint pathologies to develop therapeutic strategies. Based on the type of clinical question they can address, existing models can be broadly categorized into three groups: (i) rigid body models that can simulate kinematics, collisions between entities or wrapping of the muscles over the bones, and which have been used to investigate joint kinematics and ergonomics, and are often coupled with (ii) muscle force estimation techniques, consisting mainly of optimization methods and electromyography-driven models, to simulate muscular action and joint reaction forces to address issues in joint stability, muscular rehabilitation or muscle transfer, and (iii) deformable models that account for stress-strain distributions in the component structures to study articular degeneration, implant failure or muscle/tendon/bone integrity. The state of the art in numerical modelling of the shoulder is reviewed, and the advantages, limitations and potential clinical applications of these modelling approaches are critically discussed. This review concentrates primarily on muscle force estimation modelling, with emphasis on a novel muscle recruitment paradigm, compared with traditionally applied optimization methods. Finally, the necessary benchmarks for validating shoulder models, the emerging technologies that will enable further advances and the future challenges in the field are described.

Results of latissimus dorsi tendon transfer for irreparable cuff tears

Rupture of the supraspinatus and infraspinatus tendon (and teres minor) can cause loss of active external rotation (ER), entailing severe functional disability in daily activities. Latissimus dorsi tendon transfer (LDTT), proposed by Gerber in 1988, appears to be the best adapted solution in these cases of irreparable posterior and superior cuff tears. Between 2001 and 2004, 30 patients were operated on by the technique described by Gerber, with the transfer fixed anteriorly to the subscapularis tendon and laterally to the greater tuberosity by transosseous suture. One patient, subsequently requiring revision with a reversed prosthesis, was considered as a failure. Twenty-six patients were reviewed with a mean follow-up delay of 34+/-12 months. There were 14 men and 13 women. Mean age was 55.5 years (36 to 71 years). Preoperatively, active ER was symmetric in seven cases, loss of active ER was moderate with positive lag sign in five cases, significant with positive dropping sign in six cases, and severe in nine cases. Fatty muscular degeneration was present and significant in all cases for the infraspinatus muscle and in 14 cases for the teres minor muscle (associated with significant ER loss). Subjectively, 85% of the patients were very satisfied or satisfied and the Subjective Shoulder Value (SSV) was 68+/-17%. The pain score improved from 4.8+/-3 preoperatively to 12.2+/-2 postoperatively, strength from 3.7+/-2 kg to 4.2+/-1.8 kg, mean Constant score from 50+/-12 to 74+/-9, and Constant score adjusted for age and gender from 62+/-15% to 91+/-11%. Mean active ER gain was 7 degrees (-30 degrees to +50 degrees). The loss of active ER was aggravated in one case, unchanged in three, improved in nine and corrected in six. Hornblower sign was corrected in six cases and persisted in nine. Postoperatively, 8% of the patients were unable to eat and drink, compared to 64.7% preoperatively. The results of this series are comparable to those found in the literature for first-intention cases. LDTT restored active ER, but the results were incomplete and variable. Improvement was better in case of severe preoperative active ER deficit and insufficiency of the teres minor muscle. Recovery of strength was not observed in the present series. A narrow subacromial space and grade-3 Hamada classification had negative impact. In spite of an expected tenodesis effect, LDTT did not recenter the humeral head. LDTT compensates the deficient teres minor muscle rather than the infraspinatus muscle. The optimal indication for LDTT is irreparable superior and posterior rotator cuff rupture with loss of active ER associated with a deficient teres minor muscle. It is debatable whether LDTT is indicated in the absence of active motion deficiency: improvement was observed in these cases, but only in terms of subjective criteria.