Sunday, May 31, 2015

Shoulder joint replacement - the glenoid

Accurate preparation of the glenoid surface for a ream and run or for the glenoid component of a total shoulder glenoid component requires excellent exposure. In either case the exposure needs to allow reaming of the face of the glenoid to a single concavity. Rather than using a guide wire in an attempt to guide the glenoid reaming to a theorectical orientation, we use a nubbed glenoid reamer placed in a central drill hole – a technique that enables the orientation of the reamer to be adjusted so that a concentric concavity is achieved with minimal bone removal. The insertion of the reamer is facilitated by using a humeral head retractor as a ‘shoehorn’ which is removed once the reamer is in place.

Ream and Run

The goal of the glenoid aspect of the ream and run is to concentrically and conservatively ream the glenoid face so that glenohumeral stability and the contact area for distribution of the humeral load to the glenoid are optimized. The glenoid is exposed by an extralabral capsular release, i.e. leaving the labrum attached to the glenoid to help preserve its contribution to the depth of the socket. When the shoulder is symmetrically tight and without posterior erosion, a 360-degree extralabral capsular release is performed. When the shoulder is tight anteriorly and the humeral head is posteriorly subluxated, the extralabral release is limited to the anterior capsule. Any remaining articular cartilage is curetted from the face of the glenoid. Frequently, the removal of the remaining anterior cartilage reveals a biconcavity of the bony surface in which case the ridge between these concavities is burred to facilitate reaming. The center of the glenoid is identified and burred to center the drill for the nub of the reamer.

It is emphasized that the reaming of the glenoid face is very conservative – only enough bone is removed to establish a single glenoid concavity. In that there is are no holes made in the glenoid surface for component fixation, less bone is removed with the ream and run than for a total shoulder arthroplasty. The angle of glenoid reaming is adjusted to preserve as much glenoid subchondral bone as possible. The adequacy of the glenoid bone preparation is checked by inserting a round back glenoid trial component and ensuring that it does not rock even when eccentric loads are applied to the rim. The humeral head diameter of curvature is chosen to be 2 mm less than that of the reamed glenoid surface. In most cases we pair a reamed glenoid diameter of curvature of 58 mm with a humeral head prosthesis of 56 mm diameter of curvature, yielding a 2mm diametral mismatch.

Total Shoulder

As for the ream and run procedure, the goals for total shoulder arthroplasty include establishing maximal stability and maximal contact area for distribution of the humeral load to the glenoid. In addition, the procedure needs to achieve support of the prosthetic glenoid by precisely contouring the bone supporting it as well as secure and durable fixation of the component to the underlying bone. In that glenoid bone stock is a most precious commodity when performing shoulder arthroplasty and in that excessive reaming has been associated with increasing rates of glenoid component failure, preservation of glenoid bone is a high priority. Both bone preservation and the quality of fixation are enhanced by the precise drilling of the holes for peg fixation of a glenoid component rather than the less precise preparation for a keeled component. This precision has the additional benefit of minimizing the amount of cement used, reducing the risk of thermal damage.

In contrast to the ream and run technique, in total shoulder arthroplasty, the glenoid is exposed by excising the labrum from the bony glenoid, removing any tissue that may interfere with complete glenoid component seating. As in the case of the ream and run procedure, if the preoperative axillary view shows posterior humeral head subluxation, the inferior glenohumeral capsule is left intact.

The size of the glenoid component is determined using round back glenoid trials. The center of the glenoid face is marked and a burr hole is made at this point to guide the drill for the reamer. The angle of glenoid reaming is adjusted to preserve as much glenoid subchondral bone as possible. Glenoid bone is preserved by orienting the reaming and the component along the glenoid axis rather than the scapular axis. Reaming is always started by hand; power is used very sparingly except in hard bone. Appropriate positioning of retractors facilitates this reaming. In that the goal of reaming is to conservatively establish a single glenoid concavity, it is important to check the progress of reaming frequently so that the reamer does not inadvertently remove more bone than necessary. The adequacy of the glenoid bone preparation is checked by inserting the round back glenoid trial component and ensuring that it does not rock even when eccentric loads are applied to the rim.

After the hole for the central peg is drilled, the peripheral drill guide is inserted into the central peg hole and set firmly on the reamed glenoid surface to precisely guide the drilling of the additional holes for the peripheral pegs. The drill guide needs to be oriented to take maximal advantage of the available glenoid bone; care must be taken to assure that the drill guide sits flush on the reamed glenoid surface so that the hole position will match the position of the component pegs. After each peripheral hole is drilled, a derotation peg is placed in it to maintain alignment of the guide while the subsequent holes are completed and to make sure that the hole is of the proper depth. Each hole is checked to determine whether it penetrates the scapula.

After irrigation with antibiotic containing saline solution, the holes are cleaned and dried with a spray of sterile CO2 gas removing all tissue and fluid from the holes so that the injected cement will directly contact bone without interposed fluid or the blood clot that results from the use of thrombin. It is apparent that neither fluid nor clot will turn into bone or cement, so the presence of either will compromise the quality of fixation.

Unpenetrated holes are pressurized with a syringe. Penetrating holes are cemented, but the cement is not pressurized. The use of a carbon dioxide gas spray and cement pressurization has essentially eliminated the problem of postoperative radiolucent lines


No cement is placed on the bony face of the glenoid; if the back of the glenoid component matches the prepared bony face, there is no advantage to an interposed layer of cement, which could fail and become displaced and consequently leave the glenoid component relatively unsupported as shown below.

While some surgeons have been concerned about avoiding penetration of the holes for glenoid fixation, glenoid perforation does not appear to affect the clinical outcome of total shoulder arthroplasty. It is evident, however, that penetration is more likely in severely pathological glenoids that have substantial medial or posterior bone erosion and for this reason, rather than the penetration itself, shoulder arthroplasty may be less successful in cases of particularly severe arthritic deformity.

Reamed bone retrieved during the glenoid preparation (reaming and drilling) is used to create a bone paste that is interposed between the flutes of the central anchor peg to help facilitate bone tissue integration. The glenoid component is firmly impacted into position, assuring that its posterior aspect is completely seated on bone by sliding a finger over the back of the component to feel the bone that should lie immediately beneath. The joint space is checked to assure that no bits of cement or bone remain. From the time the glenoid component is in place, it is important to prevent the humerus from dislodging it by the ‘bottle cap’ mechanism; we use a broad flat retractor to safely deliver the proximal humerus into the wound after the glenoid has been implanted.

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 run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

See the countries from which our readers come on this post.