Sunday, May 31, 2015

Shoulder joint replacement - initial preparation of the humerus

The humeral head is exposed anteriorly by gentle external rotation and slight extension inserting a large flat retractor behind it. Special care is exercised in older patients and those with rheumatoid arthritis or other causes of fragile bone. Barriers to gentle external rotation may include an insufficiently released anterior capsule or blocking posterior osteophytes, such as that shown below.

If the humeral head cannot be safely dislocated anteriorly into the wound, we consider making a preliminary conservative humeral neck cut with the head in situ. Because of the often severely distorted anatomy of the arthritic humeral head, we do not use the estimated location of the anatomic humeral neck as a guide for the resection of the humeral head. Instead, the humeral osteotomy is oriented to the axis of the humeral canal as described below. Osteophytes are removed anteriorly, inferiorly and posteriorly.

With the proximal humerus exposed, the starting point is identified at the lateral aspect of the humeral head just behind the bicipital groove and close to the cuff insertion. A hole is burred at this point, the medullary canal is opened with a curette and then a 6 mm medullary reamer is inserted into the canal using a slight valgus bias. Successively larger reamers are used not as reamers per se but rather as sizers of the medullary canal, passing them down the canal until one begins to engage the distal endosteal cortex at the appropriate depth for the implant (“love at first bite”). When in position, the largest reamer that fits the canal defines the ‘orthopaedic axis’ of the humerus. The humeral head is resected in 30 degrees of retroversion at an angle of 45 degrees with the orthopaedic axis of the medullary canal using an oscillating saw. The cut plane passes just inside the rotator cuff insertion to the tuberosity under direct vision, assuring that the humeral articular surface is resected without damaging the cuff attachment superiorly or posteriorly 

No attempt is made to match the varus or valgus angulation of the native humerus.

The full circumference of the neck cut is inspected to assure that the osteophytes have been completely resected. Because access to posterior osteophytes may require substantial external rotation of the humerus placing tension on the median and musculocutaneous nerves, we try to assure that the arm not be maintained in this ‘danger’ position longer than 20 seconds or so at one time, especially in shoulders that have had internal rotation contractures preoperatively. When a humeral hemiarthroplasty alone or a cuff tear arthropathy prosthesis is planned, there is no change in the socket anatomy so it is important to measure and match the diameter of curvature of the resected head before it is converted to bone graft. 

With the proximal end of the humerus displaced medially into the joint, the rotator cuff is observed to establish its integrity. Consideration can be given to repairing a cuff defect if excellent quality cuff tissue can reach the tuberosity without undue tension when the arthroplasty components are in place and the arm is at the side. However, two potential downsides of cuff repair in this circumstance are recognized: (1) the tension of a rotator cuff repair may predispose to failure of the repair or shoulder tightness and (2) cuff repair requires a change in the postoperative rehabilitation from active to passive motion until the tendon has healed. Attempting a repair of tenuous cuff tissue may increase the risk of secondary cuff dysfunction. If it is elected to repair a cuff defect, this step is performed after the glenoid arthroplasty. If a substantial and irreparable rotator cuff tear is identified, the surgeon may consider the use of a cuff tear arthropathy prosthesis.

To avoid challenging the integrity of the proximal humerus during exposure for the glenoid arthroplasty, no further preparation of the humerus until after the work on the glenoid is complete.

Be sure to click on this link to the Shoulder Arthritis Book.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'