Musculoskeletal shoulder models: A technical review and proposals for research foci

Musculoskeletal shoulder models allow non-invasive prediction of parameters that cannot be measured, particularly the loading applied to morphological structures and neurological control. This insight improves treatment and avoidance of pathology and performance evaluation and optimisation. A lack of appropriate validation and knowledge of model parameters’ accuracy may cause reduced clinical success for these models. Instrumented implants have recently been used to validate musculoskeletal models, adding important information to the literature. This development along with increasing prevalence of shoulder models necessitates a fresh review of available models and their utility. The practical uses of models are described. Accuracy of model inputs, modelling techniques and model sensitivity is the main technical review undertaken. Collection and comparison of these parameters are vital to understanding disagreement between model outputs. Trends in shoulder modelling are highlighted: validation through instrumented prostheses, increasing openness and strictly constrained, optimised, measured kinematics. Future directions are recommended: validation through focus on model sub-sections, increased subject specificity with imaging techniques determining muscle and body segment parameters and through different scaling and kinematics optimisation approaches.

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.

Specificity of clinical examinations for testing glenohumeral ligament integrity: a computational study

An accurate diagnosis of glenohumeral joint (GHJ) instability is essential for an effective surgical intervention. There is presently no known comprehensive algorithm of clinical tests for the confirmation of the functional integrity of glenohumeral ligaments (GHLs). A validated computational GHL strain analyser was applied to a set of GHJ kinematics data from the literature to simulate 57 different physiological clinical examination manoeuvres. An algorithm that integrates the GHL pre-straining activities at the toe region of the stress-strain curve was developed for the quantification of ligament loading from prevailing strains. This was used to upgrade the strain analyser and applied to produce a matrix of the various GHL loadings and sensitivities during the manoeuvres. The investigation magnified the likely impact of anatomical variations of GHL attachments as possible causes of misdiagnoses during clinical examinations of GHJ dysfunction. This can serve as an assistive guide to ascertain the functional condition of a specific GHL during symptomatic clinical examinations.