Multimodality imaging in shoulder arthroplasties Part 1: Biomechanics, indications, preoperative imaging, and types of arthroplasties – A pictorial review
How to cite this article: Sarvesvaran M, Thaker S, Srinivasan S, Brar RS, Bhatt R, Gupta H. Multimodality imaging in shoulder arthroplasties Part 1: Biomechanics, indications, preoperative imaging, and types of arthroplasties – A pictorial review. Indian J Musculoskelet Radiol 2021;3(1):24-9.
Shoulder biomechanics, shoulder arthroplasty indications and types and appropriate pre-operative imaging are discussed in part one of this two-part pictorial review. Shoulder biomechanics in severe osteoarthritis and following reverse shoulder arthroplasty are represented graphically, with discussion on the principles of reverse shoulder arthroplasty. Case examples are utilized to demonstrate the main indications for shoulder arthroplasty.
The decision of whether to proceed with arthroplasty and the arthroplasty type is heavily influenced by the pre-operative imaging. Factors for type of arthroplasty include arthroplasty indication, the integrity of the deltoid and rotator cuff musculature, and the amount of glenoid and humeral head bone stock. The key findings to look for and comment on across a range of imaging modalities are reviewed, using multiple cases including plain radiography, CT, ultrasound, and MRI. Examples of arthroplasty options are provided including humeral head resurfacing arthroplasty, hemiarthroplasty, anatomical total shoulder arthroplasty, and reverse total shoulder arthroplasty.
A good understanding of the above principles is crucial for the radiologist to interpret pre-operative imaging correctly and aid in surgical planning.
Shoulder arthroplasty remains the mainstay of surgical treatment for numerous indications after failure of conservative management of the painful shoulder with severely restricted movements. Musculoskeletal radiologists play a key role by strategic use of various imaging methods. This helps the orthopedic surgeon, by providing crucial pre- and peri-operative information and monitors post-operative patient progress including complications.
We have divided shoulder arthroplasty imaging into two parts for easier understanding. In the first part, we describe the biomechanics of the degenerated and implanted shoulder, discuss indications, and focus on appropriate pre-operative imaging. In part two, we revisit shoulder arthroplasty complications before introducing new perioperative concepts, including 3D-printed customized glenohumeral implants, pre- and intra-operative CT-guided navigation and emerging arthroplasty techniques. They minimize human error and arguably improve accuracy of implant placement, which in turn should benefit our patients.
While hemiarthroplasty and anatomical total shoulder arthroplasty (TSA) replicate anatomy and biomechanics of the normal shoulder joint, reverse TSA (RTSA) aims to reverse the glenohumeral anatomy to exploit the use of deltoid to provide the function of the deficient rotator cuff. Grammont, in 1985, has described four cardinal principles of RTSA: (1) Medialized center of rotation, (2) distalizing and therefore tensioning the deltoid onto the humerus, (3) stable center of rotation, and (4) a semi-constrained prosthesis with a larger arc of motion [Figure 1]. These principles have revolutionized prosthesis designs and widened indications for RTSA.
Shoulder arthroplasty indications are similar to those in other joints, including osteoarthritis, inflammatory arthropathy, and avascular necrosis of the humeral head. Indications unique to the shoulder joint are rotator cuff arthropathy, complex proximal humerus fractures, shoulder arthroplasty revisions, and bone tumors involving the proximal humerus.
For accurate assessment of glenohumeral osteoarthritis, a dedicated Grashey view is essential for accurate assessment of the joint space [Figure 2]. The classic osteoarthritis findings are non-uniform joint space loss, osteophytosis, subchondral cystic change, and subchondral sclerosis [Figure 3a]. Uniform joint space narrowing, central erosive changes and absence of marginal osteophytes, and subchondral changes are usually features of an inflammatory arthropathy [Figure 3b]. One should remember that end-stage inflammatory arthropathy can demonstrate overlapping imaging features with primary osteoarthritis. Proximal humeral head fractures, not suitable for open reduction and internal fixation, are considered for treatment with arthroplasty [Figure 4]. The Neer classification is used to characterize the fracture pattern. Neer type 3 and 4 fractures typically result in arthroplasty in patients requiring activity preservation, who have preserved deltoid and subscapularis function. Irreparable massive rotator cuff tears and associated severe rotator cuff arthropathy are also candidates for arthroplasty [Figure 5]. Revision arthroplasties are increasingly performed as the number of total shoulder arthroplasties is increasing. Indications for revision include primary procedures complicated by infection and superior prosthesis migration due to irreparable rotator cuff tears. Custom-designed prostheses can be utilized for malignant tumors of the humerus in highly specialized centers.
PRE-OPERATIVE IMAGING AND ITS UTILITY IN ARTHROPLASTY DECISION-MAKING
Radiography remains the first-line imaging method to confirm and categorize indications of shoulder arthroplasties. It can assess glenoid morphology and bony remodeling besides confirming the presence of degenerative disease [Figure 6]. Radiography has been superseded by the increasing use of CT. Furthermore, superior migration of the humeral head on radiographs or CT with a reduced acromiohumeral distance of <7 mm implies rotator cuff failure. In advanced cases of rotator cuff arthropathy, one can readily assess femoralization of the humeral head and acetabularization of the acromion undersurface [Figure 7].
CT remains a cornerstone imaging technique used in all pre-operative cases for evaluating subchondral changes, their location, the adequacy of glenoid bone stock, and glenoid version [Figure 8]. Modern shoulder arthroplasty planning software require CT scan as per their protocol. It assists the surgeon in determining operative suitability and use of appropriate implant and designing a targeting jig. CT is an essential part of 3D printing of tailored implants, with CT navigation now widely used by shoulder surgeons globally, further discussed in part 2.
Sonography allows for dynamic assessment of the rotator cuff integrity [Figure 9], tendinopathy, and tears [Figure 10] with increasing sensitivity and specificity approaching MRI. It can also play a key role in the preoperative imaging of rotator cuff arthropathy.
Besides establishing the diagnosis of shoulder osteoarthritis and rotator cuff tears, MRI is the best modality for assessing for atrophy and fatty infiltration of the rotator cuff [Figure 11]. Hence, the MRI has a prognostic value when used preoperatively and guide shoulder surgeons to choose the appropriate technique. Goutallier et al. classification is the most commonly used semi-quantitative classification system for fatty atrophy which relies on the muscle-to-fat ratio of primarily the supraspinatus and infraspinatus musculature [Figure 12].
Arthroplasty options, of increasing invasiveness, include humeral head resurfacing arthroplasty, hemiarthroplasty, anatomical TSA, and RTSA. The type of arthroplasty is typically guided by the indication and the integrity of the deltoid, rotator cuff, glenoid, and humeral head bone stock. For example, anatomical TSA requires a functional rotator cuff and adequate glenoid bone stock, whereas the RTSA only requires an intact deltoid. Hemiarthroplasty is best utilized in patients where an inadequate glenoid bone stock precludes an anatomical TSA, as long as the humeral bone stock is sufficient, and the rotator cuff musculature is intact. Humeral head resurfacing is primarily used in younger patients and is the least invasive arthroplasty option [Figure 13]. Its practice is declining with the emergence of better arthroplasty options. It provides an opportunity for subsequent revision surgery once humeral head resurfacing can no longer achieve optimum function and is usually revised with anatomical or RTSA depending on rotator cuff status.
Numerous shoulder arthroplasty options are available to treat a variety of advanced shoulder pathologies. Adequate understanding of shoulder biomechanics and their implications on surgical planning and postsurgical prognosis are critical for the musculoskeletal radiologist. It allows optimum utilization of pre-operative imaging to help surgeons manage the patient’s shoulder ailments in a timely and effective fashion.
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