Weekly Case

Title : Case 642

Age / Sex : 75 / F


Chief complaint :



  • s/p reverse total shoulder arthroplasty, right (op. date: 2018-08-27)

  • abnormal findings on post-op. f/u images (2019-02-26)


What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : Hyo Jin Kim, Boramae Medical Center



Discussion


Answer:  acromion stress fracture (acromion fracture, type 2, in reverse total shoulder arthroplasty)


 


Findings: post-operative acromion stress fracture involving the anterior acromion posterior to the acromioclavicular joint


 


Differential Diagnosis: anterior dislocation, scapular notching…


 


Discussion: 


The reverse total shoulder arthroplasty, which reverses the ball and socket of the shoulder joint, was designed by Grammont et al in 1987 as a solution for pseudoparalysis and rotator cuff arthropathy. This design allows for the restoration of deltoid tension as the humeral prosthetic component depresses and medializes the center of rotation of the shoulder joint and lengthens its moment arm. When the deltoid contracts, the arm levers along the glenosphere, thereby facilitating abduction and elevation of the arm without an intact rotator cuff. An intact deltoid is therefore required for proper function of a reverse total shoulder arthroplasty.


Anterior dislocation is the most common early complication of reverse total shoulder arthroplasty, occurring in nearly 20% of patients, often without preceding trauma. A reverse arthroplasty dislocates anteriorly and superiorly along the axis of the deltoid muscle because of unopposed deltoid contraction. This is in contradistinction to anterior dislocation of the native shoulder, in which the humerus dislocates anteriorly and inferiorly.


Scapular notching is an exceedingly common complication of reverse total shoulder arthroplasty, occurring in 50%–96% of patients. On radiographs, bone resorption of the inferior scapular border is seen. This finding is likely related to medialization of the shoulder’s center of rotation, leading to repetitive contact between the humeral cup and the inferior scapular border during adduction. The severity of scapular notching can be described by using the four grades of the Sirveaux classification: grade 1, limited to pillar; grade 2, contacts lower glenosphere screw; grade 3, extends over the lower glenosphere screw; and grade 4, extends under the glenosphere base plate. Grade 1 and grade 2 scapular notching often stabilize and require no further treatment. Grade 3 and grade 4 scapular notching may undermine or loosen the glenosphere, sometimes requiring additional surgery.


Scapular spine and acromion fractures are complications unique to reverse total shoulder arthroplasty, with a reported prevalence of 5%–6.9%. These acromion fractures are divided into three types. Type 1 fractures involve the anterior acromion near or including the coracoacromial ligament footprint, tend to occur at the time of initial surgery, and often heal without intervention. Type 2 fractures involve the anterior acromion just posterior to the acromioclavicular joint. These fractures are thought to represent stress fractures of the acromion from restored abduction and elevation of the upper extremity exerting stress upon the acromion, which is often stiffened by adjacent acromioclavicular joint osteoarthritis. The radiologist should scrutinize the acromion in patients with a reverse arthroplasty for early signs of stress injury, including periosteal reaction and increased sclerosis. If radiographically occult, CT and bone scintigraphy may be helpful for diagnosis, especially in patients with focal pain. If untreated, type 2 fractures are at risk for displacement . Type 3 fractures involve the posterior acromion or scapular spine and are thought to arise from increased stress from the superior glenosphere screw.


 


References:


Shoulder arthroplasty, from indications to complications: what the radiologist needs to know. RadioGraphics 2016; 36:192-208


Classification of postoperative acromial fractures following reverse shoulder arthroplasty. J Bone Joint Surg Am 2013; 95:e104


 


 


To submit your answer, login first (for Korean radiologists) or send e-mail to balgundol@gmail.com (for non-Korean radiologists)

Correct Answer
Total applicants 19 Correct answers 10
Name Institution
김기욱 국군수도병원, 전문의
윤유성 순천향대 부천병원, 전문의
장민영 국민건강보험공단 일산병원, 전문의
강지희 서울대학교병원, 전문의
백승진 분당차병원, 전공의
김성진 365병원, 전문의
박병진 국군강릉병원, 전문의
고아라 전공의
김지은 서울대학교병원, 전문의
남태훈 분당서울대학교병원, 전문의
Semi-Correct Answer
Total applicants 19 Semi-Correct answers 3
최형인 군의관, 전문의
여현정 전문의
신재환 국군춘천병원, 전문의


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