Patrice Tétreault

Glenoid version and rotator cuff tears

The purpose of this study was to determine the relationship between rotator cuff (RC) tear and the orientation of the glenoid. Ninety‐six shoulders (94 patients) that underwent open RC repair were grouped according to the type of tear. We measured on MRI the acromio–glenoid angle (AG) and the supraspinatus fossa glenoid angle on the anterior–posterior (SGAP) and axial (SGAX) views. RC patients had a smaller AG angle (76 ± 7° vs. 86 ± 10°) and a larger SGAP angle (112 ± 6° vs. 102 ± 7°) compared to controls (p < 0.001). We also found a highly significant difference (p < 0.001) in glenoid version measured by SGAX between anterior cuff tears (–5 ± 4°) and posterior cuff tears (3 ± 3°). Furthermore, we identified an association between RC tear and the orientation of the glenoid relative to the axis of the supraspinatus fossa. Greater retroversion is predictive of an anterior cuff injury and greater anteversion is predictive of a posterior cuff injury.

Perioperative Interscalene Block Versus Intra-Articular Injection of Local Anesthetics for Postoperative Analgesia in Shoulder Surgery

Background and Objectives: Up to 70% of patients report moderate to severe pain after shoulder surgery, which can compromise early rehabilitation and functional recuperation. Postoperative shoulder pain control is improved with both interscalene block and intra‐articular local anesthetic injection. The present study hypothesized that perioperative interscalene analgesia would offer pain control superior to perioperative intra‐articular local anesthetics over the first 24 hours after surgery. Methods: Sixty patients undergoing shoulder surgery were randomly assigned to 1 of 2 groups: group IS had interscalene block with catheter installation, while group IA received intra‐articular local anesthetic, also with catheter installation. All patients received 3 local anesthetic injections: 0.25 mL/kg of 2% lidocaine with epinephrine 2.5 &mgr;g/mL immediately before and after surgery, and 0.25 mL/kg of 0.5% bupivacaine with epinephrine 2.5 &mgr;g/mL 1 hour after the end of surgery, after which the catheters were removed, and no further local anesthetics were administered. Postoperative pain at rest was evaluated in the postanesthesia care unit (PACU), 3 hours, 6 hours and 24 hours after surgery. The area under the 24 hour pain over time curve was calculated. Hydromorphone consumption in the PACU and over 24 hours was recorded. Results: Pain scores (IS: 0.4 ± 2 vs. IA: 4 ± 3, P < .0001) and opioid consumption (IS: 0.7 mg ± 1.4 vs. IA: 1.5 mg ± 1.2, P = .02) were significantly higher in the PACU for group IA. However, neither the mean pain scores over the first day after surgery (IS: 5 ± 2 vs. IA: 5 ± 3; P = .4) nor 24‐hour opioid consumption (IS: 4.4 mg ± 2.8 vs. IA: 4.2 mg ± 2.6; P = .4) were significantly higher in group IA. Conclusions: PACU measurements of immediate postoperative pain and narcotic consumption favor perioperative interscalene analgesia over intra‐articular analgesia. This benefit does not translate into lower overall pain for the first 24 hours after surgery.

Improvements in measuring shoulder joint kinematics.

For many clinical applications it is necessary to non-invasively determine shoulder motion during dynamic movements, and in such cases skin markers are favoured. However, as skin markers may not accurately track the underlying bone motion the methods currently used must be refined. Furthermore, to determine the motion of the shoulder a model is required to relate the obtained marker trajectories to the shoulder kinematics. In Wu et al. (2005) the International Society of Biomechanics (ISB) proposed a shoulder model based on the position of bony landmarks. A limitation of the ISB recommendations is that the reference positions of the shoulder joints are not standardized. The aims of this research project were to develop a method to accurately determine shoulder kinematics using skin markers, and to investigate the effect of introduction of a standardized reference configuration. Fifteen subjects, free from shoulder pathology, performed arm elevations while skin marker trajectories were tracked. Shoulder kinematics were reconstructed using a chain model and extended Kalman filter. The results revealed significant differences between the kinematics obtained with and without introduction of the reference configuration. The curves of joint angle tended towards 0° for 0° of humerus elevation when the reference configuration was introduced. In conclusion, the shoulder kinematics obtained with introduction of the reference configuration were found to be easier to interpret than those obtained without introduction of the reference configuration.

Influence of the medial offset of the proximal humerus on the glenohumeral destabilising forces during arm elevation: a numerical sensitivity study

This study assessed the influence of the medial offset of the proximal humerus on the glenohumeral destabilising forces during arm elevation in the plane of the scapula, using the AnyBody Modeling System. The variability of the medial offset was covered using literature data (minimum, 0 mm; average, 7 mm and maximum, 14 mm). The following parameters were studied: moment arm (MA; middle deltoid), muscle activity and stability ratios. The minimum offset decreased the MA of the middle deltoid ( − 11%), increased its activation (+18%) and its superior destabilising action (+40%). The maximum offset had an opposite effect (+9%, − 30% and − 30%). The stabilising action of the rotator cuff was not affected. Varying the medial offset seems to have an influence on the destabilising action of the middle deltoid. The AnyBody simulation tool appears to be promising in establishing links between shoulder morphology and stability.

Electromyographic activity in the immobilized shoulder musculature during ipsilateral elbow, wrist, and finger movements while wearing a shoulder orthosis

BACKGROUND Shoulder immobilization after rotator cuff surgery is usually prescribed to protect the repaired tendons; however, shoulder orthoses often also immobilize the elbow and wrist joints. There is insufficient evidence to support that elbow and wrist movements can affect repair integrity by highly activating the rotator cuff muscles. The aim of this study was to quantify the electromyographic activity of immobilized shoulder muscles during elbow, wrist, and finger movements. METHODS Fifteen shoulder muscles of the dominant limb of 14 healthy subjects were evaluated by use of electromyography with 11 surface electrodes and 4 fine-wire electrodes in the rotator cuff muscles. While wearing a custom orthosis, the subjects completed tests involving elbow, wrist, and finger movements of the ipsilateral limb. The peak activity of each muscle was normalized to maximum voluntary contraction (percent MVC) and averaged across the subjects. RESULTS Rotator cuff muscles were activated to less than 10% MVC in both slow and fast elbow flexions. The mean peak activations of all muscles during wrist and finger movements were less than 5% MVC. In daily activities such as writing, typing, clicking a computer mouse, and holding a box or bag, rotator cuff muscle activity did not exceed 11% MVC, but sudden movements such as grasping a bottle could show higher levels of activity, which in some individuals exceeded 20% MVC. CONCLUSION Elbow, wrist, and finger movements could minimally activate the rotator cuff muscles when the shoulder is immobilized with an orthosis.

Optimal shoulder immobilization postures following surgical repair of rotator cuff tears: a simulation analysis.

BACKGROUND There is a high incidence of retear following surgical repair of rotator cuff tears. Postoperative shoulder immobilization is commonly prescribed to protect the repair; but there is no consensus on the best immobilization postures. METHODS A generic musculoskeletal model of the shoulder was used to simulate postoperative immobilization of full thickness rotator cuff tears involving the supraspinatus only and the supraspinatus concomitantly with the infraspinatus or subscapularis. Optimal immobilization postures, which simultaneously minimized the stresses in the repaired tendons and the angle of humerus elevation, were obtained. RESULTS For isolated supraspinatus tears, elevation of the humerus in planes close to the scapular plane was suggested. When the infraspinatus was also involved, planes posterior to the scapular plane were suggested; while, if the subscapularis was also involved, planes anterior to the scapular plane and internal rotation were suggested. The required thoracohumeral elevation angles ranged from 58° to 109°, depending on the tear length and the muscles involved. The optimal postures reduced the stresses in the repaired tendons by between 29% and 90%. CONCLUSION Prescription of immobilization posture for a patient should be based on the conditions of the tear repaired. Appropriate choice of immobilization posture will reduce the stress in the repair, and as such has the potential to reduce retear rates.

Analysis of humeral head displacements from sequences of biplanar X-rays: repeatability study and preliminary results in healthy subjects

This work presents an accurate method to measure gleno-humeral translations in a controlled pseudo-kinematic environment. Low-dose biplanar X-rays were acquired from nine healthy subjects at three elevations of the arm in the scapular plane. On each set of images, shoulder bony landmarks were manually located in 3D using a dedicated software. Intra-observer and inter-observer repeatability of landmark identification, as well as humeral head center (GH) translations, were studied. Repeatability for the identification of GH in the global coordinate system (CS) was good with 95% confidence intervals (CIs) ranging from 0.57 to 2.25 mm. Scapular landmark CIs ranged from 0.80 to 12 mm. Gleno-humeral translations of small amplitude ( < 6 mm) were detected in seven out of nine subjects. The results obtained here confirm that calibrated low-dose stereo-radiography is a promising tool for the functional analysis of the shoulder.

Adaptation of the AnyBody™ Musculoskeletal Shoulder Model to the Nonconforming Total Shoulder Arthroplasty Context.

Current musculoskeletal inverse dynamics shoulder models have two limitations to use in the context of nonconforming total shoulder arthroplasty (NC-TSA). First, the ball and socket glenohumeral (GH) joint simplification avoids any humeral head translations. Second, there is no contact at the GH joint to compute the contact area and the center of pressure (COP) between the two components of NC-TSA. In this paper, we adapted the AnyBody™ shoulder model by introducing humeral head translations and contact between the two components of an NC-TSA. Abduction in the scapular plane was considered. The main objective of this study was to adapt the AnyBody™ shoulder model to a NC-TSA context and to compare the results of our model (translations, COP, contact area, GH joint reaction forces (GH-JRFs), and muscular forces) with previous numerical, experimental, and clinical studies. Humeral head translations and contact were successfully introduced in our adapted shoulder model with strong support for our findings by previous studies.

Electromyographic activity in the shoulder musculature during resistance training exercises of the ipsilateral upper limb while wearing a shoulder orthosis

BACKGROUND Resistance training is usually postponed until 3 months after rotator cuff surgery to prevent the damaging effects of high muscle stress on the repaired tendon. After upper limb immobilization, noninjured muscles as well as the repaired muscles are affected by long-term inactivity. Exercises with minimal cuff activity may be appropriate in the early postoperative period, so we aimed to quantify the effect of resistance exercises on the muscle activity of a semi-immobilized upper limb. METHOD Fifteen shoulder muscles of the dominant limb of 14 healthy subjects were evaluated by electromyography, with 11 surface electrodes and 4 fine-wire electrodes in the rotator cuff muscles. While wearing an orthosis, the subjects completed resistance tests including elbow and wrist flexion/extension with 3 loads, maximal squeezing, and shoulder adduction against 3 different foams. The peak activity of each muscle was normalized to maximal voluntary contraction (% MVC). RESULTS Shoulder muscles were activated less than 20% MVC during elbow and wrist flexion/extension with 2-lb (907-g) and 4-lb (1814-g) loads. In the maximal squeezing test, rotator cuff activity exceeded 20% MVC in some cases. During shoulder adduction tests, subscapularis, latissimus dorsi, triceps, and pectoralis major had the highest activation levels; supraspinatus and infraspinatus were minimally activated. CONCLUSION Supported elbow and wrist flexion/extension in the horizontal plane, with weights of up to 4 lb (1814 g), minimally activates the rotator cuff muscles while potentially preventing muscle disuse of other upper limb musculature. Resisted shoulder adduction cannot be considered safe for all rotator cuff injuries. LEVEL OF EVIDENCE Basic science study, electromyography

Mechanical analysis of cuff tear arthropathy during multiplanar elevation with the AnyBody shoulder model

BACKGROUND This numerical study analysed the mechanics of cuff tear arthropathy with the AnyBody shoulder model. METHODS The model simulated three frequent characteristics of cuff tear arthropathy: A supero-posterior massive rotator cuff tear, a proximal and static migration of the humeral head, and a contact between the humeral head and the scapula (glenoid & acromion) with friction. The mechanics of the cuff tear arthropathy with and without friction were studied by analysing: the mechanics of the deltoid (i.e. length & strength), the gleno-humeral and acromio-humeral contact forces, the friction moment, and the maximum elevation angle. Elevations in the frontal, scapular and sagittal planes were simulated. FINDINGS Compared to an intact condition, the cuff tear arthropathy model without friction estimated a deltoid strength of -18% (frontal=-13%, scapular=-17%, sagittal=-25%), a gleno-humeral contact force of -34% (frontal=-60%, scapular=-46%, sagittal=+5%), estimated an acromio-humeral contact force of 240 N (frontal=213 N, scapular=184 N, sagittal=324 N) and a maximum elevation angle of 77° (frontal=80°, scapular=87°, sagittal=65°). Contact friction enhanced this behaviour, decreasing even more the gleno-humeral contact force and the maximum elevation angle, while increasing the acromio-humeral contact force. INTERPRETATION This novel cuff tear arthropathy model suggests that friction and plane of elevation greatly influence the mechanics of the shoulder with cuff tear arthropathy. It also shows that the AnyBody simulation tool may be useful to study musculoskeletal pathologies and not only normal conditions.