How many anchors to use in arthroscopic Bankart repairs? A biomechanical study of postage-stamp glenoid fractures.

BACKGROUND: Deciding how many anchors to use in a Bankart repair is challenging because of the desire to enhance stability while avoiding a postage-stamp fracture of the glenoid rim. METHODS: This controlled laboratory study investigated load to fracture of the anterior glenoid rim after drilling holes of varying number and diameter and inserting anchors of 2 different types and sizes, with and without perforation of the medial cortex of the glenoid, creating postage-stamp fractures using a metallic humeral head that was compressed against the anterior glenoid rim. A destructive model with a servohydraulic load frame was used to test 46 synthetic scapulae with compressive strength and elastic modulus similar to that of a human glenoid. Load to fracture of the intact glenoid was compared with groups with a varying number of anchor holes of different diameters, with anchors of different sizes and types, and with anchors perforating or not perforating the glenoid medial cortex. The percentage of force to fracture an intact specimen was used to identify relative risk of fracture: low risk >75%, moderate risk 75%-50%, and high risk <50% of intact load. RESULTS: The load to fracture of intact glenoids was 1276 ± 42 N. Loads decreased linearly as the number of holes drilled on the glenoid rim increased. Compared with the 1.6-mm group, the 3.0-mm group had significantly lower glenoid rim strength in specimens with 4, 5, and 7 holes (P = .013, .032, and .045, respectively). All-suture anchors in 1.6-mm holes did not alter the glenoid rim strength, and up to 5 anchors were associated with low risk of fracture. Load to fracture was significantly higher with 3.0-mm rigid core bioabsorbable anchors with 4 anchors (1081 ± 6 N) compared with the 4-hole condition (838 ± 107 N; P = .033). Perforating the glenoid medial cortex with five 1.6-mm anchors significantly weakened the glenoid rim to 58% of intact (P = .012). Perforating the medial cortex weakened the glenoid rim to 52% and 42% (P < .001 for both) of intact in the 3.0-mm 4-anchor and 5-anchor constructions, constituting moderate and high risk of fracture, respectively. CONCLUSION: Up to five 1.6-mm all-suture anchors and four 3.0-mm bioabsorbable rigid-core anchors were associated with low risk of fracture of the glenoid rim. Smaller diameter all-suture anchors best preserved structural integrity of the glenoid rim, whereas tunnel enlargement and perforation of the glenoid medial cortex were associated with moderate or high risk of a postage-stamp fracture.

Incidental Pulmonary Nodules Found on Shoulder Arthroplasty Preoperative CT Scans.

With current emphasis on preoperative templating of anatomical and reverse shoulder arthroplasty (aTSA and rTSA, respectively), patients often receive thin slice (<1.0 mm) computerized tomography (CT) scans of the operative shoulder, which includes about two-thirds of the ipsilateral lung. The purpose of this study is to evaluate the prevalence and management of incidentally detected pulmonary nodules on preoperative CT scans for shoulder arthroplasty. In this single-center retrospective study, we queried records of aTSA and rTSA patients from 2015 to 2020 who received preoperative CT imaging of the shoulder. Compared to patients with negative CT findings, there were significantly more females (63.8% vs. 46.4%; P = .011), COPD (13.0% vs. 4.7%; P = .015), and asthma (18.8% vs. 6.9%; P = .003) among the patients with incidental nodules on CT. Binary logistic regression confirmed that female sex (odds ratio = 2.00; 95% CI = 1.04 to 3.88; P = .037), COPD history (OR = 3.02; 95% CI = 1.05 to 8.65; P = .040), and asthma history (OR = 3.17; 95% CI = 1.30 to 7.77; P = .011) were significantly associated with an incidental nodule finding. Incidental pulmonary nodules found on shoulder arthroplasty preoperative CT scans are often low risk in size with low risk of malignancy, and do not require further workup. This study may provide guidance to orthopedic surgeons on how to manage patients with incidental pulmonary nodules to increase chances of early cancer detection, avoid unnecessary referrals, reduce potentially harmful radiation exposure of serial CT scans, and improve cost efficiency.

Long head of biceps transfer to augment Bankart repair in chronic anterior shoulder instability with and without subcritical bone loss: a biomechanical study.

BACKGROUND: Treating recurrent anterior shoulder instability in participants in collision sports, patients with capsulolabral defects, and patients with bipolar bone loss remains challenging. The study purpose was to investigate the effect of long head of the biceps transfer (LHBT) on load-to-dislocation biomechanics in a repetitive serial shoulder dislocation cadaveric model comparing LHBT with the Latarjet and Bankart procedures-the first-line treatment methods for chronic traumatic anterior shoulder instability with and without anterior glenoid bone loss, respectively. METHODS: In this controlled laboratory study, 8 fresh-frozen cadaveric shoulders with different conditions were dislocated in sequence using a custom test frame. The muscle loading configuration simulated the arm in the apprehension position, and biceps loads of 20 N and 40 N were used for the static glenohumeral position analysis to evaluate the sling effect. Sequential experimental conditions consisted of the intact state, second and third dislocations, chronic instability, Bankart repair, first LHBT, subcritical glenoid bone loss, second LHBT, and Latarjet procedure. RESULTS: The pectoralis major and joint reaction loads to dislocation sequentially decreased with serial dislocations in all specimens, with the lowest value in the subcritical glenoid bone defect condition. In the setting of chronic instability, the pectoralis load to dislocation was significantly higher with the Bankart repair (P = .031) and LHBT (P < .001), at 71% and 85% of the intact value, respectively. Direct comparison of the pectoralis load to dislocation favored LHBT over Bankart repair (P = .015). In the subcritical defect scenario, LHBT did not significantly increase the load to dislocate, and the Latarjet procedure demonstrated a higher load to dislocate than LHBT (P < .001). All 3 surgical procedures tested significantly increased the angle of horizontal abduction at the time of dislocation and restored the glenohumeral position to closer to the intact state. Doubling the biceps load leveraged the sling effect, pulling the humeral head farther posterior-superiorly, but this was not enough to overcome the effect of a 20% subcritical glenoid bone defect. CONCLUSIONS: In a serial dislocation model, LHBT effectively stabilized the glenohumeral joint in a simulated chronic instability scenario, increasing the pectoralis major load-to-dislocate and glenohumeral joint reaction force components at the time of dislocation and restoring relative glenohumeral positioning to close to the intact state. The Latarjet procedure outperformed LHBT in stabilizing shoulders in the 20% subcritical glenoid bone defect condition.

Dermal allograft superior capsule reconstruction biomechanics and kinematics.

PURPOSE: To investigate the effect of a dermal allograft superior capsule reconstruction (SCR) on kinematics and joint pressure biomechanics immediately after simulated superior irreparable rotator cuff tear. METHODS: This controlled laboratory study tested 8 fresh-frozen cadaveric shoulders using a custom test frame. Balanced loading configuration centered the humeral head on the glenoid, and unbalanced load created a force pulling the head toward the acromion. Experimental conditions included the intact rotator cuff, irreparable supraspinatus tear (ISST), and dermal allograft SCR. A digital sensor measured glenohumeral and subacromial contact pressure maps, and a microscribe measured the acromion-humeral distance. RESULTS: Glenohumeral contact pressure of ISST was 175% (295 ± 44 kPa; P = .018) of the intact rotator cuff value (169 ± 10 kPa) at 0° in the balanced condition and 176% (P = .048) of intact at 30°. SCR decreased glenohumeral contact pressure to 110% (185 ± 27 kPa; P = .044) of intact at 0° and to 95% (P = .034) at 30°. Unbalanced ISST contact pressure was 146% (365 ± 23 kPa; P = .009) of intact (250 ± 24 kPa) at 0° and 122% (P = .045) at 60°. SCR decreased contact pressures to 110% (274 ± 21 kPa; P = .039) of intact at 0° and to 89% (P = .003) at 60°. ISST increased superior migration of the humeral head, decreasing the acromion-humeral distance by 3.0 ± 0.6 mm (P = .006) in the unbalanced condition at 0°. SCR increased the acromion-humeral distance to a value similar to that of the intact cuff (P = .003). SCR significantly lowered subacromial pressures in the unbalanced condition. CONCLUSIONS: In an irreparable supraspinatus tear model, the dermal allograft SCR showed competency in stabilizing the glenohumeral joint, decreasing glenohumeral and subacromial contact pressures, and increasing the acromion-humeral distance.

Altered Glenohumeral Biomechanics in Proximal Humeral Fracture Malunion.

INTRODUCTION: There is little biomechanical evidence to support the traditional guideline that 45° represents acceptable proximal humerus deformity. We evaluated glenohumeral contact pressure (GP) and area, subacromial contact pressure, and joint abduction to assess biomechanical changes with different proximal humerus deformities. METHODS: Fifteen fresh-frozen cadaver shoulders were used. Intact specimens were tested on a custom dynamic shoulder frame. Subsequently, a surgical neck fracture was made in each specimen and fixed using a custom dual hinge plate for fixation of 15°, 30°, and 45° deformities in varus, valgus, antecurvatum, retrocurvatum, and combined varus-antecurvatum and valgus-retrocurvatum. Specimens were then retested. RESULTS: Compared with the intact state, GP was markedly lower with all levels of varus and varus-antecurvatum deformity. Valgus and combined valgus-retrocurvatum deformity of 45° led to notable increases in GP compared with the intact state. Varus deformities of 30° and 45° caused significant increases in subacromial pressures and limited abduction markedly from 60° to 54.2° and 44.6° (P < 0.001). DISCUSSION: Varus and antecurvatum proximal humerus deformities as small as 15° were associated with notable alterations in glenohumeral joint mechanics. With valgus and retrocurvatum deformity, statistically significant joint alterations occurred only at higher deformity levels.

Foot fat pad: Characterization by mesenchymal stromal cells in rats.

Foot fat pad (FFP) is a highly functionalized fat depot of great significance for weight bearing in the foot. Mesenchymal stromal cells (MSCs) in subcutaneous adipose tissues are widely studied for regenerative potentials. MSCs in FFP, which may contribute to the physiological and pathological conditions of the foot, have not been characterized. In this study, MSCs were isolated from FFP (designated as MSCs-ffp) and subcutaneous adipose tissue (designated as MSCs-sub) from rats. The cell surface markers, proliferation, and efficiency of colony formation were compared between MSCs-ffp and MSCs-sub. In addition, MSCs-ffp were induced for osteogenic, chondrogenic, and adipogenic differentiation. The tri-lineage differentiation potentials were compared between MSCs-ffp and MSCs-sub by the expression of Runx2, Sox9, and proliferator-activated receptor gamma (PPAR-γ), respectively, using quantitative polymerized chain reaction. The expression of elastin and associated genes by MSCs-ffp were also evaluated. MSCs-ffp, like MSCs-sub, expressed CD44, CD73, and CD90. MSCs-ffp and MSCs-sub proliferated at similar rates but MSCs-ffp formed more colonies than MSCs-sub. MSCs-ffp were capable of differentiating into osteogenic, chondrogenic, and adipogenic lineages. Under the conditions of osteogenic and adipogenic differentiation, MSCs-sub expressed more Runx2 and PPAR-γ, respectively, than MSCs-ffp. The undifferentiated MSCs-ffp upregulated the expression of fibulin-5. In conclusion, MSCs-ffp shared common biology with MSCs-sub but were more efficient in colony formation, less adipogenic and osteogenic, and participated in elastogenesis. The unique features of MSCs-ffp may relate to their roles in the physiological functions of FFP.

Association between shoulder coracoacromial arch morphology and anterior instability of the shoulder.

BACKGROUND: Glenohumeral instability is a common condition of the shoulder. Glenoid bone loss and humeral head bone loss are well recognized as risk factors for recurrent instability. There are few studies in the literature that examine the role of coracoacromial arch anatomy in the pathogenesis of glenohumeral instability. Previous reports found an association between posterior acromial coverage (PAC) and posterior instability. We hypothesize that coracoacromial arch anatomy is related to anterior shoulder instability. METHODS: In this retrospective cohort study, 50 patients with unidirectional anterior shoulder instability were matched to a control group of 50 glenohumeral arthritis patients without any history of shoulder instability. Radiographic measurements of the coracoacromial arch anatomy were made: shoulder arch angle, scapular Y angle, anterior coracoid tilt (ACT), posterior acromial tilt, anterior acromial coverage angle, PAC angle, coracoid height, posterior acromial height, and critical shoulder angle were determined using standard lateral scapular and anteroposterior radiographs. RESULTS: Logistic regression analyses found a significant association between the presence of anterior instability and flatter coracoacromial arch angles (mean, 124.1°) vs. the arthritis control group (mean, 120.6°) (odds ratios [OR] = 1.113; 95% confidence interval [CI] = 1.039-1.191; P = .002). There was a significant association between anterior instability and ACT (OR = 1.144; 95% CI = 1.053-1.243; P = .001), whereas a negative association was found between anterior instability and PAC (OR = 0.909; 95% CI = 0.853-0.969; P = .004) and posterior acromial tilt (OR = 0.878; 95% CI = 0.773-0.998; P = .046). Lower critical shoulder angle values were associated with the arthritis group (28.2° vs. 33.9°) (OR = 1.555; 95% CI = 1.202-2.012; P = .001). CONCLUSIONS: Shoulder coracoacromial arch morphology may play a role in the stability of the shoulder joint and development of recurrent anterior instability. Shoulders with a decreased shoulder arch angle, a less contained and flatter coracoacromial arch and larger ACT, were associated with anterior instability. This study identifies the shoulder coracoacromial arch angle and anterior coracoid tile angles as risk factors for anterior shoulder instability. Our findings suggest that measuring these angles may help orthopedic surgeons understand the risk of anterior instability and analyze risk factors to improve clinical decision making.

Rotator Cuff Injuries in Tennis Players.

PURPOSE OF REVIEW: This review presents epidemiology, etiology, management, and surgical outcomes of rotator cuff injuries in tennis players. RECENT FINDINGS: Rotator cuff injuries in tennis players are usually progressive overuse injuries ranging from partial-thickness articular- or bursal-sided tears to full-thickness tears. Most injuries are partial-thickness articular-sided tears, while full-thickness tears tend to occur in older-aged players. The serve is the most energy-demanding motion in the sport, and it accounts for 45 to 60% of all strokes performed in a tennis match, putting the shoulder at increased risk of overuse injury and rotator cuff tears. Studies have shown deficits in shoulder range of motion and scapular dyskinesia to occur even acutely after a tennis match. First-line treatment for rotator cuff injuries in any overhead athlete consists of conservative non-operative management with appropriate rest, anti-inflammatory drugs, followed by a specific rehabilitation program. Operative treatment is usually reserved for older-aged players and to those who fail to return to play after conservative measures. Surgical options include rotator cuff debridement with or without tendon repair, biceps tenodesis, and labral procedures. Unlike rotator cuff repairs in the general population, repairs in the elite tennis athlete have less than ideal rates of return to sport to the same level of performance. Rotator cuff injuries are a common cause of pain and dysfunction in tennis players and other overhead athletes. The etiology of rotator cuff tears in tennis players is multifactorial and usually results from microtrauma and internal impingement in the younger athlete leading to partial tearing and degenerative full-thickness tears in older players. Surgical treatment is pursued in athletes who are still symptomatic despite an extensive course of non-operative treatment as outcomes with regard to returning to sport to the same pre-injury level are modest at best. Debridement alone is usually preferred over rotator cuff repairs for partial tears in younger players due to potential over-constraining of the shoulder joint and decreased rates of return to sport after rotator cuff repairs.

Synthetic coracoclavicular ligament vs. coracoclavicular suspensory construct for treatment of acromioclavicular dislocation: a biomechanical study.

BACKGROUND: A synthetic ligament (LockDown, Worcestershire, England) has become available to treat complete acromioclavicular dislocation with promising clinical results and potential benefit to avoid postoperative loss of reduction. We investigated the biomechanics of this synthetic ligament in a simulated immediate postoperative rehabilitation setting, hypothesizing that the synthetic ligament would demonstrate less superior coracoclavicular displacement to cyclic loading and higher ultimate load-to-failure values than a coracoclavicular suspensory construct. METHODS: Seven matched-pair cadaveric shoulders (mean age at time of death, 79 years) were loaded cyclically and to failure. One specimen in each pair was randomly assigned to the synthetic ligament or coracoclavicular suspensory construct. Superiorly directed 70-N cyclic loading for 3000 cycles at 1.0 Hz was applied through the clavicle in a fixed scapula simulating physiologic states during immediate postoperative rehabilitation, followed by a load-to-failure test at 120 mm/min. RESULTS: After 3000 cycles, the superior displacement of the clavicle in the synthetic ligament (9.2 ± 1.1 mm) was 225% greater than in the coracoclavicular suspensory construct (2.8 ± 0.4 mm, 95% confidence interval [CI] 3.4, 8.3; P < .001). Average stiffness of the synthetic ligament (32.8 N/mm) was 60% lower than that of the coracoclavicular suspensory construct (81.9 N/mm, 95% CI 43.3, 54.9; P < .001). Ultimate load-to-failure of the synthetic ligament was 23% (95% CI 37.9, 301.5; P = .016) lower than the coracoclavicular suspensory construct (580.5 ± 85.1 N and 750.2 ± 135.5 N, respectively). CONCLUSION: In a simulated immediate postoperative cadaveric model, the synthetic ligament demonstrated poorer biomechanics than the coracoclavicular suspensory construct. These findings suggest that a coracoclavicular suspensory construct may be preferable to a synthetic ligament if early rehabilitation is intended.

Biomechanics of Biodegradable Subacromial Balloon Spacer for Irreparable Superior Rotator Cuff Tears: Study of a Cadaveric Model.

BACKGROUND: A subacromial balloon spacer is an option to treat irreparable rotator cuff tears. We hypothesized that the balloon would restore glenohumeral contact pressure, the acromion-humeral interval, and deltoid load to intact values after a simulated irreparable supraspinatus tear in a cadaveric model. METHODS: Fourteen cadaveric shoulders (mean age at the time of death, 67.9 years) were tested using a custom test frame. In this frame, glenohumeral contact pressure, the acromion-humeral interval, and deltoid load were measured using a digital sensor, a MicroScribe, and a spring scale, respectively. Test conditions included the intact shoulder, a small supraspinatus tear, supraspinatus repair, repair plus balloon, an irreparable supraspinatus tear (rotator cable-insufficient), and an irreparable tear plus balloon. Load was applied in a simulated neutral arm position (balanced) and active shoulder abduction (unbalanced). RESULTS: When the balloon was inflated over the irreparable supraspinatus tear in the balanced condition, glenohumeral contact pressure increased by 122% (p = 0.006) compared with that for the irreparable tear at 0° of abduction and by 94% (p = 0.046) at 60°. In the unbalanced condition, pressure decreased in the irreparable tear condition after the balloon was inflated, restoring pressure to close to that in the intact state. The balloon did not restore glenohumeral contact area to that in the intact shoulder in either the balanced or the unbalanced condition. The irreparable tear displaced the humeral head superiorly in the unbalanced condition, decreasing the acromion-humeral interval. The balloon moved the head inferiorly by a mean (and standard error of the mean) of 6.2 ± 1.3 mm (p < 0.001) at 0° of abduction, 4.4 ± 1.3 mm (p < 0.001) at 30°, and 3.0 ± 0.8 mm (p < 0.001) at 60°. The balloon increased the deltoid load after an irreparable tear by 8.2% (p = 0.022) at 0°, 12.6% (p = 0.002) at 30°, and 11.1% (p = 0.008) at 60°. CONCLUSIONS: In a cadaveric model of an irreparable supraspinatus tear, a balloon spacer restored intact-state glenohumeral contact pressures at most abduction angles, lowered the humeral head, and increased deltoid load at postoperative time 0. CLINICAL RELEVANCE: This study supports further investigation of the balloon spacer in comparative clinical studies of surgical options for irreparable rotator cuff tears, with clinically relevant evaluation measures and observation periods.