Background:

In anterior approaches for total hip arthroplasty (THA), the femoral part of the procedure requires the release of the capsule from the greater trochanter. However, it is unknown whether any other tendons of the short external rotator muscles are also damaged during capsular release procedures. The aim of this cadaveric study was to identify the bony landmarks on the greater trochanter, which indicate the individual short external rotator muscle insertions.

Shoulder girdles of 20 cadavers (68–94yrs) were harvested. The anterior (ACHA) and posterior circumflex humeral arteries (PCHA) were injected with ink and the extra and intraosseous courses of the dyed vasculature dissected through the soft tissues and bone to the osteotendinous junctions of the rotator cuff. The ink injection and bone dissection method was newly developed for the study.

Rates of cross-over at the osteotendinous juntion were 75% in the supraspinatus, 67% in subscapularis, 33% in infraspinatus and 20% in teres minor. The supraspinatus and subscapularis insertions were vascularised by the arcuate artery, a branch of the ACHA. The insertions of the infraspinatus and teres minor were supplied by an unnamed terminal branch of the PCHA.

The insertions of the rotator cuff receive an arterial supply across their OTJ's in 50% of cases. This may explain observed rates of AVN in comminuted proximal humeral fractures. The terminal branch of the PCHA supplying the infraspinatus and teres minor insertions was named the “Posterolateral Artery”. Finally, the new method employed for this study which allowed for direct visualisation of intraosseous vasculature, will enhance our understanding of skeletal vascular anatomy and have clinical applications in orthopaedic and reconstructive surgery.

Purpose

Current coronoid fracture classification systems are based on fragment size and configuration using plain radiographs and/or CT. During surgery, coronoid fracture fragments appear much larger than anticipated because cartilage is radiolucent and therefore not taken into account with preoperative imaging. The purpose of this study was to quantify the articular cartilage thickness of the coronoid process, with reference to coronoid fracture classifications.

Anatomic studies have demonstrated that bipolar glenoid and humeral bone loss have a cumulative impact on shoulder instability, and that these defects may engage in functional positions depending on their size, location, and orientation, potentially resulting in failure of stabilisation procedures. Determining which lesions pose a risk for engagement remains a challenge, with Itoi's 3DCT based glenoid track method and arthroscopic assessment being the accepted approaches at this time. The purpose of this study was to investigate the interaction of humeral and glenoid bone defects on shoulder engagement in a cadaveric model. Two alternative approaches to predicting engagement were evaluated; 1) CT scanning the shoulder in abduction and external rotation 2) measurement of Bankart lesion width and a novel parameter, the intact anterior articular angle (IAAA), on conventional 2D multi-plane reformats. Hill-Sachs and Bony Bankart defects of varying size were created in 12 cadaveric upper limbs, producing 45 bipolar defect combinations. The shoulders were assessed for engagement using cone beam CT in various positions of function, from 30 to 90 degrees of both abduction and external rotation. The humeral and glenoid defects were characterised by measurement of their size, location, and orientation. The abduction external rotation scan and 2D IAAA approaches were compared to the glenoid track method for predicting engagement. Engagement was predicted by Itoi's glenoid track method in 24 of 45 specimens (53%). The abduction external rotation CT scan performed at 60 degrees of glenohumeral abduction (corresponding to 90 degrees of abduction relative to the trunk) and 90 degrees of external rotation predicted engagement accurately in 43 of 45 specimens (96%), with sensitivity and specificity of 92% and 100% respectively. A logistic model based on Bankart width and IAAA provided a prediction accuracy of 89% with sensitivity and specificity of 91% and 87%. Inter-rater agreement was excellent (Kappa = 1) for classification of engagement on the abduction external rotation CT, and good (intraclass correlation = 0.73) for measurement of IAAA. Bipolar lesions at risk for engagement can be identified using an abduction external rotation CT scan at 60 degrees of glenohumeral abduction and 90 degrees of external rotation, or by performing 2D measurements of Bankart width and IAAA on conventional CT multi-plane reformats. This information will be useful for peri-operative decision making around surgical techniques for shoulder stabilisation in the setting of bipolar bone defects

Metal-on-metal (MOM) and ceramic-on-metal (COM) studies in total hip arthroplasty (THA) documented adverse wear termed “edge loading”. Laboratory simulations necessitated cups steeply inclined to produce edge- loading, whereby cup rims could attenuate the normal wear patterns. Size of cup wear-pattern was therefore key in defining edge-loading. From prior simulator studies (‘Anatomic’ test: ISO-14242), we could demonstrate a linear relationship between size of cup wear-patterns and MOM diameters, cup wear-areas decreasing from 18% to 8%. However, retrieval studies (COM/ MOM) showed cup wear-patterns in vivo were much larger, typically covering 50–55% cup surfaces (Clarke 2013: Koper 2015). In prior MOM Anatomic simulator study (head oscillating, cup fixed), we noted areas worn on 60mm heads and cups averaging 1,668mm2 and 442mm2, respectively (Bowsher 2009). Thus, ratio ×3.77 described distributed area worn on heads relative to focal area worn in cups. In the orbital simulator, the only way to achieve larger cup wear areas was to reverse the component positions, i.e. cups oscillating, heads fixed. The overall goal for this project was to develop an understanding of how such edge-loading affected adverse-wear performance of THA in simulators. 60mm MOM (DJO, Austin TX) were chosen comparable to our prior study (Bowsher 2009) and cups were mounted inverted (oscillating) under fixed heads. Adaptors were machined to incline cup faces at 17o and 27o and, with the simulator's +/−23° motion, they experienced 40oand 50o cyclic peak oscillations, respectively. The orbital simulator was identical to that of prior study as was the test protocol (Bowsher 2009). Wear patterns on components were assessed visually and microscopically, taped and colored red to aid photography. The 40° and 50° tests produced circular cup wear patterns that came progressively closer to the rims without actually producing edge-loading, creating average wear area of 1,663mm2. These proved identical to wear areas on heads (orbiting) in prior Anatomic test (1,668mm2). Using the hemispherical-area datum of 5,655mm2 for 60mm MOM, our test produced cup wear patterns with desired 29.4% coverage. The value of ISTA conferences is that by definition these bring new arthroplasty ideas and technologies to the forefront. The international guideline for simulators (ISO-14242) has proven useful for standard ‘Anatomic’ cup tests that do not require edge-loading conditions. However, ours is the 1st simulator study to; (i) predict the size of THA wear patterns, (ii) show that ratio of head: cup wear-areas average ×3.8 in favor of mobile component, and (iii) demonstrated cups can be run Inverted to produce more clinically-relevant wear patterns that in edge- loading studies. The new learning experience was that studies of edge-loading in THA cups need to consider the ‘Inverted’ test in order to simulate clinically relevant tribo-mechanical parameters. Compared to Anatomic test, the Inverted-cup test has the advantage of (iv) producing larger cup wear areas, (v) clinically-relevant attenuation of wear patterns at cup rim, and (vi) intermittent edge-loading (instead of constant loading) judged likely to apply to a larger patient population at risk