Unravelling the Etiology of Shoulder Osteoarthritis
Unravelling the Etiology of Shoulder Osteoarthritis
Osteoarthritis (OA) is a progressive disease resulting from the degradation of synovial joint
 articular cartilage over time.

 The hallmark symptom is diffuse aching and progressive pain made worse with activity. Loss of
 range of motion and compromised function inevitably follow. This degenerative disease can
 affect the shoulder joint. When symptoms become refractory to conservative treatment such as
 anti-inflammatory medication, steroid injections, activity modification or physical therapy;
 surgery (total or reverse shoulder arthroplasty) may be considered.

 Idiopathic shoulder OA is typically characterized by posterior subluxation of the humeral
 head upon the glenoid and posterior bone loss. An imbalance in the application of forces
 applied to the proximal humerus by the posterior and anterior rotator cuff muscles has been
 postulated to be the leading cause of idiopathic shoulder OA. However, there is only
 preliminary evidence to support this theory and the etiology of this pattern of deformity is
 unknown. The theory the posterior humeral head subluxation is a precursor to OA is only
 supported by very low-level evidence and no longitudinal studies have been conducted. As a
 result, the cause and natural history of shoulder OA remains unknown.

 Research into this area is urgently needed to generate knowledge that will inform future
 treatments aimed at modifying and slowing the progression of shoulder OA and to reduce the
 need for shoulder replacement therapy.

 The aim of this project is to develop an understanding of the pathophysiology of shoulder OA.
Purpose: The aim of this project is to develop an understanding of the pathophysiology of
 shoulder OA. This project will recruit two groups of 30 participants, (60 participants in
 total) and follow them over a period of 5-years.

 Group 1- Participants with posterior subluxation of the humeral head and show early signs of
 degeneration in their shoulder 'disease group' Group 2- Participants with posterior
 subluxation of the humeral head and show no signs of degeneration 'control/healthy' group

 Hypotheses: The investigators hypothesize that there are several factors that contribute to
 the development of shoulder OA. Uncovering those pathways will lead to more targeted therapy.
 (1) The posterior rotator cuff muscles (infraspinatus/teres minor) apply relatively greater
 force than the anterior (subscapularis) cuff; an imbalance in the force couple occurs and the
 humeral head translates posteriorly on the glenoid; progressive posterior subluxation of the
 humeral head occurs and degeneration of the glenoid and humeral head cartilage follow. (2)
 Posterior subluxation of the humeral head is associated with progressive cartilage
 proteoglycan loss. (3) Pre-morbid glenoid morphology including increased retroversion is
 associated with the development of shoulder OA.

 Participant Involvement: The following will be completed with participants: T1Rho Magnetic
 Resonance Imaging (MRI), quantitative Computed Tomography (qCT), functional and motion
 analysis at baseline, year 2 and year 4 in the 'affected' shoulder in both groups 1 and 2.
 These tests will also be conducted on the asymptomatic, contralateral shoulder in Group 1
 participants at baseline and year 4. The finite element model validation will be performed in
 years 2 and 3, and participant-specific finite element analysis (which has no active
 participant involvement) will occur in years 3 to 5. Overall study analysis will occur in
 year 5. This project will be done in two-parts. The first part will consist of six
 participants; assuming further funding is obtained, part two of the study will proceed. The
 second part of the project will be based on successfully obtaining funds to continue the
 remainder of the study recruitment (54 participants) and testing. As pilot data is urgently
 needed to secure granting funds to support this overall project, the investigators will
 commence with recruiting the first 6 participants. Once further funds are secured, the
 remaining portion (recruitment of 54 participants) of the project will continue.

 Objectives: (1) Determine whether patients with posterior humeral head subluxation have an
 imbalance between the posterior and anterior rotator cuff muscles. Objective 1 will be
 assessed through T1Rho MRI, and functional testing/motion analysis.

 (2) Determine whether patients with static posterior subluxation of the humeral head are at
 risk of degenerative changes (i.e. proteoglycan loss). Objective 2 will be assessed through
 T1Rho MRI and qCT scans.

 (3) Determine which joint factors are associated with progression of OA. This will be
 assessed using qCT scans and finite element model analysis.

 Clinical Relevance: The cause is shoulder OA is unknown, and the burden and costs associated
 with this degenerative disease are increasing with our aging population. Research in this
 area is urgently needed to generate knowledge which will inform future treatments which may
 modify and slow the progression of shoulder OA, and to reduce the need for shoulder
 replacement therapy.
Inclusion Criteria:

 -  Adults <60 years of age

 -  Posterior humeral head subluxation >55% (determined from imaging)

 Exclusion Criteria:

 -  >60 years of age

 -  History of shoulder instability

 -  History of shoulder trauma including fracture

 -  Neurological disorders of the upper limb

 -  Imaging evidence of humeral head or glenoid bony deformity

 -  Rotator cuff pathology

 -  Labral pathology

 -  Pre-existing joint deformity (OA) cases greater than grade I (as per Samilson and
 Prieto)