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BackgroundMuscular forces drive proximal humeral fracture deformity, yet it is unknown if arm position can help mitigate such forces. Our hypothesis was that glenohumeral abduction and humeral internal rotation decrease the pull of the supraspinatus and subscapularis muscles, minimizing varus fracture deformity.MethodsA medial wedge osteotomy was performed in eight cadaveric shoulders to simulate a two-part fracture. The specimens were tested on a custom shoulder testing system. Humeral head varus was measured following physiologic muscle loading at neutral and 20° humeral internal rotation at both 0° and 20° glenohumeral abduction.ResultsThere was a significant decrease in varus deformity caused by the subscapularis (p

Background: Volar radiocarpal instability is often seen after loss of fixation of volar lunate facet fragments. The pathogenesis of post-traumatic volar radiocarpal instability is poorly understood. The purpose of this study was to determine if injury to the dorsal wrist extrinsic carpal ligaments contributes to volar radiocarpal instability. Methods: Six matched pairs of cadaveric upper extremities were tested using a dynamic hand testing system. In group 1, the intact wrist, the wrist with a volar lunate facet fracture, and the fractured wrist after 500 cycles of grip were tested. In group 2, in addition to the intact and fractured wrist, the fractured wrist with the dorsal extrinsic carpal ligaments cut and the fractured wrist with the dorsal extrinsic carpal ligaments cut after 500 cycles of grip were also tested. Volar-dorsal displacement of the lunate was measured from 45° wrist flexion to 45° wrist extension in 22.5° increments with the wrist flexors/extensors loaded for each condition. Results: Volar lunate translation did not significantly increase after the volar lunate facet fracture alone, and was not evident to a significant extent until the dorsal wrist extrinsic carpal ligaments were cut. Further instability of the lunate occurred after grip cycling only with the dorsal extrinsic capsular ligaments cut. Conclusions: Injury to the dorsal wrist extrinsic carpal ligaments exacerbates volar radiocarpal instability. Unrecognized dorsal sided injury may be a contributing factor to why stable fixation of volar lunate facet fragments remains problematic after volar plating of intra-articular distal radius fractures with displaced volar lunate facet fragments.

Study designBiomechanical, cadaveric study.ObjectivesTo compare the relative stiffness of unilateral C1 lateral mass-C2 intralaminar fixation to intact specimens and bilateral C1 lateral mass-C2 intralaminar constructs.MethodsThe biomechanical integrity of a unilateral C1 lateral mass-C2 intralaminar screw construct was compared to intact specimens and bilateral C1 lateral mass-C2 intralaminar screw constructs. Five human cadaveric specimens were used. Range of motion and stiffness were tested to determine the stiffness of the constructs.ResultsUnilateral fixation significantly decreased flexion/extension range of motion compared to intact (P < .001) but did not significantly affect axial rotation (P = .3) or bending range of motion (P = .3). There was a significant decrease in stiffness in extension for both unilateral and bilateral fixation techniques compared to intact (P = .04 and P = .03, respectively). There was also a significant decrease in stiffness for ipsilateral rotation for the unilateral construct compared to intact (P = .007) whereas the bilateral construct significantly increased ipsilateral rotation stiffness compared to both intact and unilateral fixation (P < .001).ConclusionBilateral constructs did show improved biomechanical properties compared to the unilateral constructs. However, unilateral C1-C2 fixation using a C1 lateral mass and C2 intralaminar screw-rod construct decreased range of motion and improved stiffness compared to the intact state with the exception of extension and ipsilateral rotation. Hence, a unilateral construct may be acceptable in clinical situations in which bilateral fixation is not possible, but an external orthosis may be necessary to achieve a fusion.

Background: The Latarjet procedure is increasingly being utilized for the treatment of glenoid bone loss and has a relatively high neurological complication rate. Understanding the position-dependent anatomy of the axillary nerve (AN) is crucial to preventing injuries. Purpose: To quantify the effects of changes in the shoulder position and degree of glenoid bone loss during the Latarjet procedure on the position of the AN. Study Design: Controlled laboratory study. Methods: A total of 10 cadaveric shoulders were dissected, leaving the tendons of the rotator cuff and deltoid for muscle loading. The 3-dimensional position of the AN was quantified relative to the inferior glenoid under 3 conditions: (1) intact shoulder, (2) Latarjet procedure with 15% bone loss, and (3) Latarjet procedure with 30% bone loss. Measurements were obtained at 0°, 30°, and 60° of glenohumeral abduction (equivalent to 0°, 45°, and 90° of shoulder abduction) and at 0°, 45°, and 90° of humeral external rotation (ER). Results: Abduction of the shoulder to 60° resulted in a posterior (9.5 ± 1.1 mm; P <.001), superior (3.0 ± 1.2 mm; P =.013), and lateral (19.1 ± 2.3 mm; P <.001) shift of the AN, and ER to 90° resulted in anterior translation (10.0 ± 1.2 mm; P <.001). Overall, ER increased the minimum AN-glenoid distance at 30° of abduction (14.9 ± 1.3 mm [0° of ER] vs 17.3 ± 1.5 mm [90° of ER]; P =.045). The Latarjet procedure with both 15 and 30% glenoid bone loss resulted in a superior and medial shift of the AN relative to the intact state. A decreased minimum AN-glenoid distance was seen after the Latarjet procedure with 30% bone loss at 60° abduction and 90° ER (17.7 ± 1.6 mm [intact] vs 13.9 ± 1.6 mm [30% bone loss]; P =.007), but no significant differences were seen after the Latarjet procedure with 15% bone loss. Conclusion: Abduction of the shoulder induced a superior, lateral, and posterior shift of the AN, and ER caused anterior translation. Interestingly, the Latarjet procedure, when performed on shoulders with extensive glenoid bone loss, significantly reduced the minimum AN-glenoid distance during shoulder abduction and ER. These novel findings imply that patients with substantial glenoid bone loss may be at a higher risk of AN injuries during critical portions of the procedure. Consequently, it is imperative that surgeons account for alterations in nerve anatomy during revision procedures. Clinical Relevance: This study attempts to improve understanding of the position-dependent effect of shoulder position and glenoid bone loss after the Latarjet procedure on AN anatomy. Improved knowledge of AN anatomy is crucial to preventing potentially devastating AN injuries during the Latarjet procedure. [ABSTRACT FROM AUTHOR]

Background: Designed to help treat pain and loss of function after rotator cuff repair, allograft spacer procedures utilize a graft to act as a spacer in the subacromial space, decreasing pain from impingement of the greater tuberosity on the acromion at the extremes of overhead motion. Purpose: To evaluate the biomechanical characteristics of secured versus unsecured tensor fascia lata allografts used in an allograft spacer procedure. Study Design: Controlled laboratory study. Methods: A total of 8 fresh-frozen cadaveric shoulder specimens were used. There were 4 conditions tested: (1) intact rotator cuff, (2) stage III rotator cuff tear (complete supraspinatus tendon and superior one-half of the infraspinatus tendon), (3) unsecured tensor fascia lata graft, and (4) secured tensor fascia lata graft. Both superior and posterior translation of the humeral head were calculated in each condition. A 4-cm × 5-cm × 6-mm tensor fascia lata graft was used in the subacromial space to act as a spacer. Grafts were secured at the lateral edge of the native rotator cuff footprint with 2 knotless anchors. Results: With unbalanced loading, both secured and unsecured grafts varied in their ability to limit superior and posterior translation at various rotation angles back to levels seen with intact rotator cuffs at 0° and 20° of abduction. During balanced loading, both unsecured and secured grafts limited superior and posterior translation more than those seen in the rotator cuff–deficient condition (P <.01) and similar to those seen in the intact condition (P >.05). The secured and unsecured grafts allowed similar amounts of translation at every position with both unbalanced and balanced loading (P >.05). Finally, total graft motion was <7 mm in all positions. Conclusion: Unsecured tensor fascia lata grafts were biomechanically equivalent to secured grafts when used during allograft spacer procedures. Clinical Relevance: While both grafts were successful at limiting superior and posterior translation of the humeral head during early range of motion, the unsecured graft represents a cheaper, easier option to utilize during allograft spacer procedures. [ABSTRACT FROM AUTHOR]