Revision of an anatomic metal-backed glenoid component

Periprosthetic glenoid fractures in cases of metal-backed components occur due to polyethylene wear leading to loosening of the metal back, loss of substance of the glenoid, and then finally fatigue fractures.

Traumatic periprosthetic glenoid fractures around metal-backed components are very rare. More detail about the treatment of glenoid fractures is provided in the AO Surgery Reference Adult trauma Scapula module.

Preoperative planning should include the decision to consider:

• Revision to another anatomic implant
• Conversion to a reverse arthroplasty

An early sign of metal-backed component associated problems is joint space narrowing on x-rays due to polyethylene wear. In advanced stages there is metal-on-metal contact leading to metallosis and ultimately failure of the metal-backed component.

The amount of glenoid bone loss is of tremendous importance to the revision strategy.

Modern revision planning software makes it possible to quantify the glenoid defect.

Preoperative CT planning is mandatory when deciding on a strategy of metallic (including augmented designs) or bony reconstruction.

Rotator cuff integrity should be carefully evaluated preoperatively.

In addition, low-grade infection influences the decision-making process on whether a revision can be a one-stage or a two-stage procedure.

These principles are applicable for stemless, short, and standard stems.

Further details about prosthesis design can be found here.

The stemless configuration is shown in this description.

The standard patient position is the beach chair position with inclination of about 30°. An arm holder may be helpful but is not essential.

Intraoperative fluoroscopy can be helpful.

Patient positioning should be discussed with the anesthetist.

If augmentation or reinforcement of the glenoid fracture or defect is required, bone allograft may be utilized. Structural bulk allograft or morselized allograft are indicated for specific conditions of the glenoid.

If allograft is not available be prepared to take cortico-cancellous or cancellous graft from the iliac crest (autograft) as shown.

The procedure is done under perioperative antibiotics.

The standard approach used is the deltopectoral approach, which can easily be extended proximally and distally.

Previous incisions should be used if this approach was performed correctly during the primary operation. Do not hesitate to perform a new skin incision if the approach used in the primary was inaccurate.

Be prepared for extensive soft-tissue release and a more difficult subscapularis takedown technique before executing the arthrolysis needed to access the glenoid. Take biopsies for cultures.

In advanced chronic cases, severe metallosis may be present. A subtotal synovectomy is required in advanced stages.

Revision to an anatomic implant is very rare. However, it is possible to exchange the polyethylene component if the metal-back retention mechanism is intact.

Access and exposure of the glenoid is facilitated by humeral head removal. Remove the humeral head using standard instruments for the specific implant.

After exposing the glenoid, remove the polyethylene component, which is often worn out, and reimplant a new component into the existing metal base plate.

After placement of the glenoid component, a new humeral head is reinserted.

The humerus is reduced, and the subscapularis tendon is reattached.

The decision to carry out a revision to a reverse arthroplasty is based on a number of factors including:

• Status of the rotator cuff
• Shoulder function
• Patient age

Be prepared for extensive soft-tissue release and a more difficult subscapularis takedown technique before executing the arthrolysis needed to access the glenoid. Take biopsies for cultures.

Access and exposure of the glenoid is facilitated by humeral head removal. Remove the humeral head using standard instruments for the specific implant.

In this scenario the stem can be retained. The articular component is converted to a reverse after the glenoid is reconstructed.

In this scenario the stem must be removed.

Remove the humeral stem with the specific revision instruments for the arthroplasty.

Depending on the humeral component design, different strategies for implant extraction are available. More information on implant extraction is provided here.

After exposing the glenoid, remove the polyethylene component. Then evaluate the stability of the remaining metal back. In cases of a well-integrated and convertible component a glenosphere can be implanted.

If the component is loose and/or broken, remove the component, debride the remaining scapula bone, and evaluate the glenoid defect.

Management of the glenoid bone loss is closely related to the configuration of the remaining glenoid vault.

To facilitate stable fixation of a reverse baseplate, it may be necessary to reconstruct the glenoid vault using bone graft.

In cases of mild glenoid contained defects (Type 1 according to Gohlke) impaction bone grafting is performed and a reverse base plate is implanted.

The illustration on the left is a representative cross section of the glenoid vault shown in the right diagram.

In cases of large, contained defects (Type 2) a structural allograft or autograft is impacted followed by implantation of the base plate.

In non-contained defects with either anterior or posterior wall insufficiency (Type 3) a structural allograft or autograft is used and fixed with two or three screws.

In non-contained defects with severe medialization (Type 4) the same technique is applied.

The decision to perform a one versus two-stage base plate implantation depends on several factors:

• Initial size of the defect
• Primary stability of graft fixation
• Specific implant features
• Surgical experience

In all cases it is important to gain primary fixation in native bone. A reverse baseplate is shown with a central screw fixed into native bone with peripheral anti-rotation screws.

In Type 5 defects with loss of the glenoid vault bony reconstruction should always be performed as a two-stage operation.

Custom implants are often required.

Off-the-shelf augmented base plates may be used in isolation or with bony reconstruction to achieve optimized fixation to the scapula.

Customized implants are not uniformly available and evidence for their role remains to be established.

Advantages include:

• Single-stage procedure
• Personalized to the patient and structural defect
• Optimized function
• Durability
• Time zero structural support
• No risk of graft reabsorption

Disadvantages include

• Lack of availability
• Cost

A glenosphere is impacted on the baseplate.

In cases where a convertible stem has been used, the metaphyseal component including the polyethylene liner is impacted. In cases where the stem has had to be removed a new stem is implanted. The shoulder is then reduced.

The aftercare can be divided into four phases of healing:

• Inflammatory phase (week 1–3)
• Early repair phase (week 4–6)
• Late repair and early tissue remodeling phase (week 7–12)
• Remodeling and reintegration phase (week 13 onwards)

Full details on each phase can be found here.