Does the osteoarthritic shoulder have altered rotator cuff vectors with increasing glenoid deformity? An in silico analysis.

BACKGROUND: A transverse force couple (TFC) functional imbalance has been demonstrated in osteoarthritic shoulders by recent 3-dimensional (3D) muscle volumetric studies. Altered rotator cuff vectors may be an additional factor contributing to a muscle imbalance and the propagation of glenoid deformity. METHODS: Computed tomography images of 33 Walch type A and 60 Walch type B shoulders were evaluated. The 3D volumes of the entire subscapularis, supraspinatus, and infraspinatus-teres minor (ISP-Tm) and scapula were manually segmented. The volume masks and scapular landmarks were imported into MATLAB to create a coordinate system, enabling calculation of muscle force vectors. The direction of each muscle force vector was described in the transverse and vertical plane, calculated with respect to the glenoid. Each muscle vector was then resolved into compression and shear force across the glenoid face. The relationship between muscle force vectors, glenoid retroversion or inclination, compression/shear forces on the glenoid, and Walch type was determined using linear regression. RESULTS: In the transverse plane with all rotator cuff muscles combined, increasing retroversion was significantly associated with increasing posterior drag (P < .001). Type B glenoids had significantly more posterior drag than type A (P < .001). In the vertical plane for each individual muscle group and in combination, superior drag increases as superior inclination increases (P < .001). Analysis of individual muscle groups showed that the anterior thrust of ISP-Tm and supraspinatus switched to a posterior drag at 8° and 10° of retroversion respectively. The compression force on the glenoid face by ISP-Tm and supraspinatus did not change with increasing retroversion for type A shoulders (P = .592 and P = .715, respectively), but they did for type B shoulders (P < .001 for both). The glenoid shear force ratio in the transverse plane for the ISP-Tm and supraspinatus moved from anterior to posterior shear with increasing glenoid retroversion, crossing zero at 8° and 10° of retroversion, whereas the subscapularis exerted a posterior shear force for every retroversion angle. CONCLUSION: Increased glenoid retroversion is associated with increased posterior shear and decreased compression forces on the glenoid face, explaining some of the pathognomonic bone morphometrics that characterize the osteoarthritic shoulder. Although the subscapularis always maintains a posterior thrust, the ISP-Tm and supraspinatus together showed an inflection at 8° and 10° of retroversion, changing from an anterior thrust to a posterior drag. This finding highlights the importance that in anatomic TSA the rotator cuff functional balance might be better restored by correcting glenoid retroversion to less than 8°.

What Is the Most Reliable Method of Measuring Glenoid Bone Loss in Anterior Glenohumeral Instability? A Cadaveric Study Comparing Different Measurement Techniques for Glenoid Bone Loss.

BACKGROUND: Preoperative quantification of bone loss has a significant effect on surgical decision making and patient outcomes. Various measurement techniques for calculating glenoid bone loss have been proposed in the literature. To date, no studies have directly compared measurement techniques to determine which technique, if any, is the most reliable. PURPOSE/HYPOTHESIS: To identify the most consistent and accurate techniques for measuring glenoid bone loss in anterior glenohumeral instability. Our hypothesis was that linear measurement techniques would have lower consistency and accuracy than surface area and statistical shape model-based measurement techniques. STUDY DESIGN: Controlled laboratory study. METHODS: In 6 fresh-frozen human shoulders, 3 incremental bone defects were sequentially created resulting in a total of 18 glenoid bone defect samples. Analysis was conducted using 2D and 3D computed tomography (CT) en face images. A total of 6 observers (3 experienced and 3 with less experience) measured the bone defect of all samples with Horos imaging software using 5 common methods. The methods included 2 linear techniques (Shaha, Griffith), 2 surface techniques (Barchilon, PICO), and 1 statistical shape model formula (Giles). Intraclass correlation (ICC) using a consistency model was used to determine consistency between observers for each of the measurement methods. Paired t tests were used to calculate the accuracy of each measurement technique relative to physical measurement. RESULTS: For the more experienced observers, all methods indicated good consistency (ICC > 0.75; range, 0.75-0.88), except the Shaha method, which indicated moderate consistency (0.65 < ICC < 0.75; range, 0.65-0.74). Estimated consistency among the experienced observers was better for 2D than 3D images, although the differences were not significant (intervals contained 0). For less experienced observers, the Giles method in 2D had the highest estimated consistency (ICC, 0.88; 95% CI, 0.76-0.95), although Giles, Barchilon, Griffith, and PICO methods were not statistically different. Among less experienced observers, the 2D images using Barchilon and Giles methods had significantly higher consistency than the 3D images. Regarding accuracy, most of the methods statistically overestimated the actual physical measurements by a small amount (mean within 5%). The smallest bias was observed for the 2D Barchilon measurements, and the largest differences were observed for Giles and Griffith methods for both observer types. CONCLUSION: Glenoid bone loss calculation presents variability depending on the measurement technique, with different consistencies and accuracies. We recommend use of the Barchilon method by surgeons who frequently measure glenoid bone loss, because this method presents the best combined consistency and accuracy. However, for surgeons who measure glenoid bone loss occasionally, the most consistent method is the Giles method, although an adjustment for the overestimation bias may be required. CLINICAL RELEVANCE: The Barchilon method for measuring bone loss has the best combined consistency and accuracy for surgeons who frequently measure bone loss.

Does the Walch type B shoulder have a transverse force couple imbalance? A volumetric analysis of segmented rotator cuff muscles in osteoarthritic shoulders.

BACKGROUND: The etiology of the Walch type B shoulder remains unclear. We hypothesized that a scapulohumeral muscle imbalance, due to a disturbed transverse force couple (TFC) between the anterior and posterior rotator cuff muscles, may have a role in the pathogenesis of the type B morphology. The purpose of this study was to determine whether there is a TFC imbalance in the Walch type B shoulder using an imaging-based 3-dimensional (3D) volumetric and fatty infiltration assessment of segmented rotator cuff muscles. METHODS: Computed tomography images of 33 Walch type A and 60 Walch type B shoulders with the complete scapula and humerus including the distal humeral epicondyles were evaluated. The 3D volumes of the entire subscapularis, supraspinatus, and infraspinatus-teres minor (Infra-Tm) were manually segmented and analyzed. Additionally, anthropometric parameters including glenoid version, glenoid inclination, posterior humeral head subluxation, and humeral torsion were measured. The 3D muscle analysis was then compared with the anthropometric parameters using the Wilcoxon rank sum and Kruskal-Wallis tests. RESULTS: There were no significant differences (P > .200) in muscle volume ratios between the Infra-Tm and the subscapularis in Walch type A (0.93) and type B (0.96) shoulders. The fatty infiltration percentage ratio, however, was significantly greater in type B shoulders (0.94 vs. 0.75, P < .001). The Infra-Tm to subscapularis fatty infiltration percentage ratio was significantly larger in patients with >75% humeral head subluxation than in those with 60%-75% head subluxation (0.97 vs. 0.74, P < .001) and significantly larger in patients with >25° of retroversion than in those with <15° of retroversion (1.10 vs. 0.75, P = .004). The supraspinatus fatty infiltration percentage was significantly lower in Walch type B shoulders than type A shoulders (P = .004). Walch type A shoulders had mean humeral retrotorsion of 22° ± 10° whereas Walch type B shoulders had humeral retrotorsion of only 14° ± 9° relative to the epicondylar axis (P < .001). CONCLUSION: The TFC is in balance in the Walch type B shoulder in terms of 3D volumetric rotator cuff muscle analysis; however, the posterior rotator cuff does demonstrate increased fatty infiltration. Posterior humeral head subluxation and glenoid retroversion, which are pathognomonic of the Walch type B shoulder, may lead to a disturbance in the length-tension relationship of the posterior rotator cuff, causing fatty infiltration.

Does proximal porous coating in short-stem humeral arthroplasty reduce stress shielding?

CONTEXT: Short-stem humeral designs in shoulder arthroplasty have been introduced recently. A retrospective cohort study was conducted to determine if newer proximal porous titanium coating in humeral short stems produced clinical and radiologic improvements. METHOD: Short-stem humeral implants (Tornier Ascend, Wright Medical) were used in 46 anatomical total shoulder replacements from October 2012 to December 2015. Clinical and radiologic measures were analyzed at one- and two-year follow-up. RESULTS: Nineteen shoulders received earlier grit blasted stems (Ascend Monolithic), and 27 shoulders received the later stems with proximal titanium porous coating (Ascend Flex). At two-year follow-up, radiographic changes and stress shielding were similar. Medial cortical thinning were more frequently observed in Monolithic (18 of 19) compared to Flex stems (19 of 27) on the PA films, though this was not statistically significant (P = 0.061). Clinical outcome scores improved regardless of the stem type used and independent of the radiologic adaptations on plain films. One participant with the Ascend Flex developed glenoid component failure and rotator cuff tear and was subsequently revised. DISCUSSION: Clinical and radiological outcomes are similar in both short-stem designs. Proximal titanium porous coating may reduce medial calcar cortical thinning but it does not prevent it. KEY MESSAGE: When compared to similarly designed uncoated grit-blasted stems, proximally porous coated humeral short stems produced similar clinical and radiological results. The proximal titanium porous coating may reduce medial cortical thinning.

Axillary Nerve Position in Humeral Avulsions of the Glenohumeral Ligament.

BACKGROUND: The axillary nerve is at risk during repair of a humeral avulsion of the glenohumeral ligament (HAGL). PURPOSE: To measure the distance between the axillary nerve and the free edge of a HAGL lesion on preoperative magnetic resonance imaging (MRI) and compare these findings to the actual intraoperative distance measured during open HAGL repair. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 25 patients with anterior instability were diagnosed as having a HAGL lesion on MRI and proceeded to open repair. The proximity of the axillary nerve to the free edge of the HAGL lesion was measured intraoperatively at the 6-o'clock position relative to the glenoid face. Preoperative MRI was then used to measure the distance between the axillary nerve and the free edge of the HAGL lesion at the same position. Distances were compared using paired t tests and Bland-Altman analyses. RESULTS: The axillary nerve lay, on average, 5.60 ± 2.51 mm from the free edge of the HAGL lesion at the 6-o'clock position on preoperative MRI, while the mean actual intraoperative distance during open HAGL repair was 4.84 ± 2.56 mm, although this difference was not significant (P = .154). In 52% (13/25) of patients, the actual intraoperative distance of the axillary nerve to the free edge of the HAGL lesion was overestimated by preoperative MRI. In 36% (9/25), this overestimation of distance was greater than 2 mm. CONCLUSION: The observed overestimations, although not significant in this study, suggest a smaller safety margin than might be expected and hence a substantially higher risk for potential damage. We recommend that shoulder surgeons exercise caution in placing capsular sutures in the lateral edge when contemplating arthroscopic repair of HAGL lesions, as the proximity of the nerve to the free edge of the HAGL tear is small enough to be injured by arthroscopic suture-passing instruments.

Design, Modeling, and Evaluation of the Eddy Current Sensor Deeply Implanted in the Human Body.

Joint replacement surgeries have enabled motion for millions of people suffering from arthritis or grave injuries. However, over 10% of these surgeries are revision surgeries. We have first analyzed the data from the worldwide orthopedic registers and concluded that the micromotion of orthopedic implants is the major reason for revisions. Then, we propose the use of inductive eddy current sensors for in vivo micromotion detection of the order of tens of µ m. To design and evaluate its characteristics, we have developed efficient strategies for the accurate numerical simulation of eddy current sensors implanted in the human body. We present the response of the eddy current sensor as a function of its frequency and position based on the robust curve fit analysis. Sensitivity and Sensitivity Range parameters are defined for the present context and are evaluated. The proposed sensors are fabricated and tested in the bovine leg.

The influence of intraoperative factors and postoperative rehabilitation compliance on the integrity of the rotator cuff after arthroscopic repair.

BACKGROUND: The purpose of this study was to determine when cuff re-tear commonly occurs in the postoperative period and to investigate the clinical factors that might predispose to an early cuff re-tear. METHODS: All patients with rotator cuff (supraspinatus ± infraspinatus) tear that required arthroscopic repair during the period between June 1, 2010, and May 31, 2012, with completed serial ultrasound examinations at 6 weeks, 12 weeks, and 26 weeks postoperatively were included. Intraoperative findings were noted. Functional clinical outcomes were assessed by Constant score, Western Ontario Rotator Cuff Index, and Oxford score. Compliance of patients with postoperative rehabilitation was established. RESULTS: There were 127 cases; the mean age of patients was 60 years. Overall re-tear rate was 29.1%. The percentage of new re-tears was significantly higher in the first 12 weeks than in the second 12 weeks postoperatively (25.2% and 3.9%, respectively). The patient's postoperative compliance was a significant prognostic factor for re-tearing. Significant associations were also found between re-tear and primary tear size, tendon quality, repair tension, cuff retraction, and footprint coverage. Poor compliance of patients was highest (17.3%) during the second 6 weeks postoperatively. Better functional outcomes were noted in patients who had re-torn their cuffs at the 12-week period (Oxford mean scores, P = .04). CONCLUSIONS: Understanding of the predisposing factors will assist in predicting the prognosis of the repaired rotator cuff. Despite the progress of patients' functions postoperatively, an early significant improvement of the clinical outcome should be a warning sign to a surgeon that the patient's compliance may be suboptimal, resulting in an increased risk of the cuff's re-tearing.

Cerebral oxygenation using near-infrared spectroscopy in the beach-chair position during shoulder arthroscopy under general anesthesia.

PURPOSE: To examine the risks of shoulder arthroscopy in the beach-chair position (BCP) as opposed to the lateral decubitus position. The challenge during general anesthesia, particularly with the patient in the BCP, has been to ascertain the lower limit of blood pressure autoregulation, correctly measure mean arterial pressure, and adequately adjust parameters to maintain cerebral perfusion. There is increasing concern about the BCP and its association with intraoperative cerebral desaturation events (CDEs). Assessment of CDEs intraoperatively remains difficult; the emerging technology near-infrared spectroscopy (NIRS) may provide noninvasive, inexpensive, and continuous assessment of cerebral perfusion, offering an "early warning" system before irreversible cerebral ischemia occurs. METHODS: A systematic review was undertaken to determine the incidence of intraoperative CDEs as measured by NIRS and whether it is possible to risk stratify patients for intraoperative CDEs, specifically the degree of elevation in the BCP. RESULTS: Searching Medline, Embase, and the Cochrane Central Register of Controlled Trials from inception until December 30, 2013, we found 9 studies (N = 339) that met our search criteria. The Level of Evidence was III or IV. CONCLUSIONS: There remains a paucity of high-level data. The mean incidence of CDEs was 28.8%. We found a strong positive correlation between CDEs and degree of elevation in the BCP (P = .056). Emerging evidence (Level IV) suggests that we may be able to stratify patients on the basis of age, history of hypertension and stroke, body mass index, diabetes mellitus, obstructive sleep apnea, and height. The challenge remains, however, in defining the degree and duration of cerebral desaturation, as measured by NIRS, required to produce measureable neurocognitive decline postoperatively. LEVEL OF EVIDENCE: Level IV, systematic review of Level III and IV studies.

The effect of humeral avulsion of the glenohumeral ligaments and humeral repair site on joint laxity: a biomechanical study.

PURPOSE: The aims of this cadaveric study were to assess the effect of different sizes of humeral avulsion of the glenohumeral ligament (HAGL) lesions on joint laxity and to investigate any difference between repairs with anchors placed in a juxtachondral position and repairs with anchors placed in the humeral neck. METHODS: Glenohumeral specimens were tested on a shoulder laxity testing system with translations applied anteriorly up to 30 N, with the joint in 60° of glenohumeral abduction. Testing was conducted in neutral rotation and under 1-Nm external rotation for 5 specimen states: intact, medium HAGL lesion (4:30 to 5:30 clock-face position), large HAGL lesion (3:30 to 6:30 clock-face position), repair with juxtachondral suture anchors, and repair with humeral neck suture anchors. RESULTS: Significant increases in translation were observed between the intact and large HAGL lesion states for neutral rotation (1.46 mm [SD, 2.33 mm] at 30 N; P = .049) and external rotation (0.81 mm [SD, 0.72 mm] at 30 N; P = .005). Significant reductions in translation were also observed between the large HAGL lesion and humeral neck repair states for neutral rotation (-1.78 mm [SD, 2.23 mm] at 30 N; P = .022) and external rotation (-0.33 mm [SD, 0.37 mm] at 30 N; P = .015). CONCLUSIONS: Large HAGL lesions can increase the passive motion of the glenohumeral joint in both neutral and external rotation, although these differences are small and may be difficult to measure clinically. A repair using anchors placed in the humeral neck is more likely to restore the normal restraint to anterior translation than a juxtachondral repair. CLINICAL RELEVANCE: Medium HAGL lesions are unlikely to show significant increases in joint translation, and repair of large HAGL lesions should be achieved with anchors placed in the humeral neck if possible.

The effect on loop elongation and stress relaxation during longitudinal loading of FiberWire in shoulder arthroscopic knots.

PURPOSE: This study examined the viscoelastic properties of 6 common arthroscopic sliding knots (Tennessee slider, Roeder knot, SMC knot, Duncan loop, Weston knot, and Nicky's knot) with 3 reversing half-hitches on alternating posts, tied with No. 2 FiberWire (Arthrex, Naples, FL). Knot configuration was designed to simulate a double-row rotator cuff repair with suture bridges. METHODS: Constructs were loaded in 20-N increments to 100 N and held for 2 minutes to monitor the viscoelastic behavior in tension. Suture was also tested without tying a knot. RESULTS: Stress relaxation increased with loading but did not differ between knot configurations. Initial elongation was highest during the first loading to 20 N. Relaxation was greater for the Roeder knot at 20 N and for the Roeder and SMC knots at 80 N (P < .05) when compared with the loop with no knot. Elongation was greatest for the Roeder knot throughout all loads. This difference was significant at 60 N compared with the knotless loop. At 100 N, all knots showed greater elongation than the knotless loop (P < .05). Testing of suture, without any knots, accounted for more than 75% of the overall stress relaxation and loop elongation of the suture-knot construct. CONCLUSIONS: In our in vitro evaluation of the Tennessee slider, Roeder knot, SMC knot, Duncan loop, Weston knot, and Nicky's knot in a simulated suture bridge construct, knot configuration was not a variable that influenced elongation or stress relaxation. Overall response was primarily due to the suture itself. With the exception of the Roeder knot, relaxation was similar provided that a secure knot was formed at the time of original tying. CLINICAL RELEVANCE: With the evolution of surgical devices, the reliance on knots is decreasing. The results of this study suggest that using knotless techniques for securing the rotator cuff will not change the stress relaxation characteristics of the suture bridge.

Rugby Union on-field position and its relationship to shoulder injury leading to anterior reconstruction for instability.

Due to the unique demands of each position on the Rugby Union field, the likelihood of an athlete sustaining a dislocation of their shoulder joint that requires surgical reconstruction may be affected by their position on the field. 166 patients with 184 involved shoulders requiring anterior reconstruction following an on-field Rugby Union injury between January 1996 and September 2008 were analysed. The mean age at time of injury was 18 years with the mean age at time of surgery being 20 years. The most prevalent mechanism of injury was a tackle in 66.3% of players. Players were more likely to suffer injury to their non-dominant shoulder than their dominant side (McNemar's Test, p<0.001). Statistical analysis using chi-squared test of goodness of fit showed there was not a uniform risk of injury for all player positions. Positions with significantly different risk of injury were five-eighth (increased risk) and wing (reduced risk). Although we observed an increased risk in flankers and fullbacks, and a lower risk in second row, these results did not reach statistical significance after application of the Bonferroni correction. This information can be utilized by team staff to assist in pre-season conditioning as well as the development of improved muscle co-ordination programmes for the non-dominant shoulder, and planning a graduated return to sport by the player recovering from surgical reconstruction of the shoulder for instability.

Posterior shoulder instability secondary to reverse humeral avulsion of the glenohumeral ligament.

BACKGROUND: Posterior shoulder instability resulting from a disruption of the posterior capsular structures has been reported. We present the largest series of these injuries in the published literature, propose a definition and highlight the clinical presentation, radiological findings, and associated injuries. MATERIALS AND METHODS: A retrospective review of a single shoulder surgeons database was performed identifying posterior instability cases associated with disruption of the posterior capsule. Chart, radiological imaging, and intra-operative findings were reviewed. RESULTS: Nineteen patients were identified with an average age lower than the overall posterior instability group. All occurred via a traumatic mechanism, the most common being a forced cross-body adduction. The only consistent symptom was posterior joint line pain. MRI reporting was found to be only 50% sensitive, increased to 78.6% when reviewed by the treating surgeon. Associated injuries are common with 58% having a labral tear, 32% a SLAP lesion, 26% a reverse Bankart lesion, 21% a chondral injury, 21% rotator cuff injury, and 11% extension of the tear into the posterior band of the inferior glenohumeral ligament. DISCUSSION: Disruption of the posterior capsule is a rare cause of recurrent posterior instability. There are no specific symptoms that identify the injury, though a mechanism of forced cross-body adduction should raise suspicion. Identification of the injury requires specific attention to the posterior capsule on MRI, preferably performed with the arm in slight external rotation and routine visualization of the posterior capsule via viewing from the anterior portal.

Operative outcome of displaced medial-end clavicle fractures in adults.

The results following nonoperative treatment of displaced, medial end clavicle fractures is often unsatisfactory; but no study has yet reported the outcome of operative fixation of these fractures. This study reports the results of open reduction and internal fixation on displaced, medial end clavicle fractures, in five adult patients (aged 25-52 years, mean 43) including 1 patient with a nonunion. The mean follow-up was 3.3 years (8 months-10.3 years). All fractures had united clinically and radiologically. No complications occurred, and no revision surgery was required. VAS pain scores averaged 0.75 (0-2) at rest, 0.75 (0-2) for normal activities, and 1.0 (0-2) for heavy activities. The mean DASH score was 9.0 (0-17), and all patients were very satisfied with the results of surgery (VAS 10). All patients had a full range of motion of their shoulder at final follow-up and were able to return to pre-injury occupational and activity levels.