Takayuki Muraki

Stabilizing mechanism in bone-grafting of a large glenoid defect.

BACKGROUNDnConventional wisdom suggests that the glenoid defect after a shoulder dislocation is anteroinferior. However, recent studies have found that the defect is located anteriorly. The purposes of this study were (1) to clarify the critical size of the anterior defect and (2) to demonstrate the stabilizing mechanism of bone-grafting.nnnMETHODSnThirteen cadaver shoulders were investigated. With use of a custom testing machine with a 50-N compression force, the peak translational force that was needed to move the humeral head and lateral humeral displacement were measured. The force was used to evaluate the joint stability. An osseous defect was created stepwise in 2-mm increments of the defect width. The bone graft was harvested from the coracoid process. The defect size was expressed as the estimated defect size divided by the measured glenoid length. Testing was performed with (1) the glenoid intact, (2) a simulated Bankart lesion, (3) the Bankart lesion repaired, (4) a 2-mm defect, (5) the Bankart lesion repaired, (6) the defect bone-grafted, (7) a 4-mm defect, (8) the Bankart lesion repaired, (9) the defect bone-grafted, (10) a 6-mm defect, (11) the Bankart lesion repaired, (12) the defect bone-grafted, (13) an 8-mm defect, (14) the Bankart lesion repaired, and (15) the defect bone-grafted.nnnRESULTSnForce and displacement decreased as the size of the osseous defect increased. The mean force after the formation of a defect of > or =6 mm (19% of the glenoid length) with the Bankart lesion repaired (22 +/- 7 N) was significantly decreased compared with the baseline force (52 +/- 11 N). Both the mean force (and standard deviation) and displacement returned to the levels of the intact condition (68 +/- 3 N and 2.6 +/- 0.4 mm, respectively) after bone-grafting (72 +/- 12 N and 2.7 +/- 0.3 mm, respectively).nnnCONCLUSIONSnAn osseous defect with a width that is > or =19% of the glenoid length remains unstable even after Bankart lesion repair. The stabilizing mechanism of bone-grafting was the restoration of the glenoid concavity.

The stabilizing mechanism of the Latarjet procedure: a cadaveric study.

BACKGROUNDnThe Latarjet procedure has been used commonly for extra-articular treatment of anterior glenohumeral joint instability. Recently, the technique also has been used as a bone-grafting procedure to repair large glenoid defects. The sling effect and the bone-block effect have been proposed as the stabilizing mechanisms of this procedure. The aim of this study was to determine the stabilizing mechanisms of this procedure.nnnMETHODSnEight fresh-frozen shoulders were prepared and tested with use of a custom testing machine instrumented with a load cell. With a 50-N axial force applied to the humerus, the humeral head was translated anteriorly. Translational force was measured at both the end-range and the mid-range arm positions, with the capsule intact, after creation of a Bankart lesion, after creation of a large glenoid defect, and after the Latarjet procedure with no load and then three different sets of loads applied to the subscapularis and conjoint tendons. Then, these two tendons were removed to observe the contribution of the sling effect to the stability. Finally, the sutures attaching the coracoacromial ligament to the capsular flap were removed in order to observe the effect of that attachment.nnnRESULTSnThe translational force, which decreased significantly after creation of a Bankart lesion or a large glenoid defect, returned to the intact-condition level after the Latarjet procedure was performed. At the end-range arm position, the contribution of the sling effect by the subscapularis and conjoint tendons was 76% to 77% as the load changed, and the remaining 23% to 24% was contributed by the suturing of the capsular flap. At the mid-range position, the contribution of the sling effect was 51% to 62%, and the remaining 38% to 49% was contributed by the reconstruction of the glenoid.nnnCONCLUSIONSnThe main stabilizing mechanism of the Latarjet procedure was the sling effect at both the end-range and the mid-range arm positions.nnnCLINICAL RELEVANCEnThe Latarjet procedure remains an effective procedure for restoring stability to an unstable glenohumeral joint, particularly when there is glenoid bone deficiency.

Effect of Posteroinferior Capsule Tightness on Contact Pressure and Area Beneath the Coracoacromial Arch During Pitching Motion

Background Tightness of the posteroinferior capsule is assumed to be the cause of internal rotation loss in baseball pitchers. Although the relationship between posterior capsule and subacromial impingement has been recognized, this relationship during the baseball-pitching motion is unclear. Hypothesis Contact pressure during baseball-pitching motion increases with posterior capsule tightness. Study Design Controlled laboratory study. Methods Eight fresh-frozen shoulders were used. The peak contact pressure and area on the coracoacromial arch were measured on a custom-designed shoulder experimental device capable of 6 degrees of freedom motion. Simultaneously, the sites of peak pressure on the coracoacromial arch and humerus were observed from various angles. The posteroinferior capsule tightness was simulated by plicating the capsule in the region from 6 to 8 oclock. The static testing positions correlated to the early cocking, late cocking, acceleration, deceleration, and follow-through phases of the pitching motion. Results The peak contact pressure during the follow-through phase (0.63 ± 0.50 MPa) significantly increased with posteroinferior capsule tightness (1.00 ± 0.65 MPa) (P = .014). Additionally, the contact area on the coracoacromial ligament during the follow-through phase (0.98 ± 0.67 cm2) significantly increased with posteroinferior capsule tightness (1.47 ± 0.91 cm 2) (P < .001). The site of the peak contact pressure did not change between the 2 conditions. Conclusion Our findings demonstrate that posteroinferior capsule tightness leads to higher contact pressure under the subacromial arch and increased contact area, particularly on the coracoacromial ligament during the follow-through phase. Clinical Relevance This tightness may affect risk of injury of the rotator cuff and its surrounding tissues by increasing subacromial contact during pitching.

Contact between the coracoacromial arch and the rotator cuff tendons in nonpathologic situations: A cadaveric study

HYPOTHESISnA recent ultrasound study has shown that impingement phenomenon was observed in healthy shoulders. We hypothesized that nonpathologic contact beneath the coracoacromial arch occurs in normal shoulders.nnnMATERIALS AND METHODSnSeven fresh-frozen cadaveric shoulders were studied. Each specimen was attached to a custom-designed shoulder-positioning device. A 22-N force was applied to the humeral head to keep it centered in the glenoid fossa. Contact pressure beneath the coracoacromial arch was measured by a flexible force sensor during flexion, abduction, internal and external rotation, extension, and horizontal abduction motions. Bending deformation of the coracoacromial ligament was measured by a linear variable differential transducer sensor. Data were recorded with the arm from 0 degrees to maximum range of motion with 10 degrees increments.nnnRESULTSnContact pressure with the coracoacromial ligament and acromion was not zero in the neutral position and increased during particular motions, such as flexion, abduction, horizontal abduction, and extension, whereas it was almost constant during internal and external rotation. Bending deformation of the coracoacromial ligament during flexion, abduction, and horizontal abduction motions was also shown to be greater than that during internal and external rotation.nnnDISCUSSIONnIt is possible that repetitive contact of the coracoacromial ligament may cause degenerative changes, and a ridge of proliferative acromial spurs may be the result of nonpathologic contact.nnnCONCLUSIONSnContact phenomenon of the coracoacromial arch was observed during all motions. Nonpathologic contact beneath the coracoacromial arch may be present in normal shoulders.

Impingement mechanisms of the Neer and Hawkins signs

HYPOTHESISnThe impingement mechanisms of the Neer and Hawkins sign remain unclear. In addition, there is still a lack of agreement regarding the arm rotation when performing the Neer sign.nnnMATERIALS AND METHODSnEight fresh frozen cadaveric shoulders were investigated. The specimens were attached to a shoulder-positioning device to which a compression force was applied. Subacromial contact pressure was measured with a flexible force sensor. The Neer sign was performed in three arm rotations (neutral, internal, and external).nnnRESULTSnThe contact sites of the coracoacromial arch side were common in both signs; however, those of the humeral head side were anatomically different: the supraspinatus tendon in the Neer sign and the subscapularis tendon in the Hawkins sign. The mean contact pressure in the Neer sign performed with the arm in internal rotation was greater than that in the Neer sign with the arm in other rotations.nnnDISCUSSIONnThe data from this study indicate that the Neer and Hawkins signs do not represent the same impingement mechanism. The contact sites on the humeral head side were anatomically different. Additionally, it was found that the maximum contact pressure for the Neer sign is with internal rotation of the arm.nnnLEVEL OF EVIDENCEnBasic Science Study.

Does the “bumper” created during Bankart repair contribute to shoulder stability?

BACKGROUNDnThe aim of this study was to determine the optimal repair configuration for anterior shoulder instability after a labral tear.nnnMATERIALS AND METHODSnNine fresh, frozen shoulders were used. With a 50-N axial force, the humeral head was translated anteriorly, and the translational force was measured. The measurement was performed with the capsule intact, after creating a Bankart lesion, and after the Bankart repair at 5 different positions: glenoid rim, glenoid surface-2 mm (on the glenoid surface 2 mm from the glenoid rim), glenoid surface-5 mm, scapular neck-2 mm (on the scapular neck 2 mm from the glenoid rim), and scapular neck-5 mm. Glenoid rim fixation was done with and without a bumper. The bumper was created by plicating the capsule to form a thickened mass of tissue.nnnRESULTSnThe translational force was restored to the intact level after the glenoid rim fixation. However, there was no significant difference in force after the Bankart repair with and without a bumper nor after the glenoid rim fixation and glenoid surface-2 mm. The force significantly decreased after scapular neck-2 mm and scapular neck-5 mm compared with the glenoid rim fixation.nnnCONCLUSIONnThe anchor fixation on the glenoid face does not increase the translational force compared with the glenoid rim placement, but the placement on the scapular neck decreases the translational force.

Effects of posterior capsule tightness on subacromial contact behavior during shoulder motions.

BACKGROUNDnAlthough posterior capsule tightness is believed to cause abnormal contact in the subacromial space, it is not clear whether this tightness changes the contact between the acromion and humeral head.nnnMATERIALS AND METHODSnNine fresh, frozen cadaveric shoulders were used to measure contact pressure on the coracoacromial arch during passive flexion, abduction, and internal and external rotation at 90° of elevation in the scapular plane, as well as horizontal adduction and abduction. The site where the peak contact pressure occurred was also observed. The posterior capsule in the region from 8 to 10 oclock in the right shoulder was plicated to simulate posterior capsule tightness.nnnRESULTSnPeak contact pressure significantly increased with the tightened posterior capsule during flexion. Although peak contact pressure on the coracoacromial ligament during internal rotation significantly increased after capsule tightening, there was no significant increase in pressure when considering the entire coracoacromial arch. The angle where the peak contact pressure occurred during flexion was not significantly far from the end range. The site of the peak contact pressure in 7 of 9 shoulders was on the lesser tuberosity during flexion, regardless of the posterior capsule tightness.nnnCONCLUSIONSnPosterior capsule tightness increased contact pressure mainly on the lesser tuberosity during flexion. The peak contact pressure occurred close to the end range of flexion, mainly on the lesser tuberosity. These findings are useful to understand the contribution of posterior capsule tightness to subacromial contact.

Measurement of stiffness changes in immobilized muscle using magnetic resonance elastography

BACKGROUNDnThe isolated evaluation of changes in muscle following immobilization and disuse is a challenge in living subjects. The purpose of this study was to determine whether magnetic resonance elastography is capable of detecting these changes.nnnMETHODSnAn animal model was created to produce a mild joint contracture following 42 days of one forelimb immobilization in a maximally flexed position with twice-daily passive exercise. Eight pairs of dog forelimbs were harvested. Magnetic resonance elastography scans were performed on the experimental limb in an extended elbow position with a torque of 0.6 N m. Scans of the contralateral limb were performed in two conditions, position matching and torque matching. Furthermore, wet weight, cross sectional area, resting muscle length, and range of elbow joint motion were measured.nnnFINDINGSnThe muscle from the experimental limb showed significant reduction in muscle mass, cross sectional area, slack length, and range of elbow motion. When comparing limbs in position matching condition, the muscle lengths were similar, and the experimental muscle had a significantly higher shear modulus (79.1 (SD 12.0)kPa) than the contralateral muscle (31.9 (SD 24.4)kPa). When comparing limbs in torque matching conditions, the muscle strains were similar, and the experimental muscle had a significantly lower shear modulus than the contralateral muscle (113.0 (SD 24.8)kPa).nnnINTERPRETATIONnThese findings suggest that following immobilization, magnetic resonance elastography has the potential to be used as a clinical tool to guide rehabilitation and as a research tool to study the loss of passive elastic components of muscle.

The Effect of Cyclic Loading Simulating Oscillatory Joint Mobilization on the Posterior Capsule of the Glenohumeral Joint: A Cadaveric Study

STUDY DESIGNnExperimental laboratory design.nnnOBJECTIVESnTo examine the effect of force and repetition during oscillatory joint mobilizations on the posterior capsule of the glenohumeral joint.nnnBACKGROUNDnThe optimal external force and frequency to be used during joint mobilization to elongate the posterior capsule of the glenohumeral joint has yet to be identified.nnnMETHODSnTwenty-one posterior capsules were harvested from fresh-frozen shoulders. A cyclic loading test simulating oscillatory posterior joint mobilization on the shoulder specimens was performed with a material testing machine. The specimens were assigned to 3 different loading groups simulating joint mobilization in the toe (5 N), transition (20 N), and beginning of the linear regions (40 N) of the load displacement curve. Displacement of the humeral head at an applied load of 5 N was recorded at the 1st, 100th, 200th, 300th, 400th, 500th, and 600th cycles and at 1 hour after completion of the cyclic loading. Furthermore, stiffness was calculated after the 1st and 600th cycles and 1 hour after testing.nnnRESULTSnHumeral head displacement was significantly greater for the 100th to 600th cycle, compared to the 1st cycle, for all 3 loading groups. Significant increases in displacement and stiffness were observed between the 1st cycle and 1 hour after completion of the cyclic tests for both the 20-N and 40-N loading groups.nnnCONCLUSIONnWhile oscillatory joint mobilization to a force of 5 N resulted in temporary elongation of the posterior capsule, mobilization to loads of 20 and 40 N resulted in sustained elongation of the capsule for up to 1 hour. Our findings also suggest that mobilization up to loads that represent the beginning of the linear region of the load displacement curve could be performed without serious damage to the posterior capsule.

Diagnosis of small partial-thickness rotator cuff tears using vibro-acoustography.

PurposeVibro-acoustography is a new imaging technique based on the dynamic radiation force of ultrasound. The purpose of this study was to apply this new imaging technique to the diagnosis of small partial-thickness rotator cuff tears and to determine how small of tears could be detected with this imaging technique.MethodsSeven supraspinatus tendons excised from embalmed cadavers were used. Three different sizes of partial-thickness bursal-sided tears (1, 3, and 5xa0mm3) were created in each specimen. The intersection of two co-focused ultrasound beams of slightly different frequency was swept across the intended imaging area. The acoustic emission data were collected and used to form and display a vibro-acoustography image of the tendon. Vibro-acoustography images were read by two orthopedic surgeons.ResultsThe rotator cuff tear could be detected by vibro-acoustography in all specimens. The diagnostic concordance rate was 90.5xa0% and the kappa coefficient value was 0.88, which resulted in a high concordance. The diagnostic concordance rate for the 1xa0mm tear was 71.3xa0%, which was low concordance (κxa0=xa00.481), whereas that for the 3 and 5xa0mm tears was 100xa0%.ConclusionsWe were able to detect a 3-mm tear by using vibro-acoustography. There is a possibility that this new imaging technique could become a useful imaging tool for the diagnosis of small partial-thickness rotator cuff tears.