Saturday, November 30, 2013

Hemiarthroplasty (including hemiarthroplasty with biological resurfacing)

1. Description - a surgical procedure in which the humeral articular surface is replaced without attention to the glenoid side of the joint. A humeral hemiarthroplasty is not the same as a ream and run.

In the hemiathroplasty the rough humeral joint surface (see below)

is replaced with a smooth metal surface (see below).

The humeral head prosthesis is connected to a stem (titanium alloy) the tapered body of which fits inside the humerus.

2. Indications - In glenohumeral arthritis, both sides of the joint are affected so that either a ream and run or a total shoulder arthroplasty is usually used in conjunction with the humeral joint surface replacement. However, in certain circumstances a hemiarthroplasty alone may be considered: (1) the diagnosis is avascular necrosis and the glenoid joint surface is unaffected; (2) diagnosis is dysplasia and there is insufficient glenoid bone stock for a glenoid arthroplasty, (3) the diagnosis is osteoarthritis, but the glenoid is smooth and congruent with the humeral head, (4) the shoulder is so tight that a glenoid component cannot be inserted properly; (5) there is concern about the status of the rotator cuff (a special humeral hemiarthroplasty prosthesis is available for the management of cuff tear arthropathy when pseudo paralysis is not present); (6) there is concern about low grade infection (an uncemented non-ingrowth hemiarthroplasty is safer to revise that a total shoulder arthroplasty).

3. Technique

The important consideration in a humeral hemiarthroplasty is that the diameter of curvature of the prosthetic humeral head needs to match or slightly exceed that of the native humeral head that it replaces. This is because the glenoid shape is not altered by the procedure.

The exposure and the humeral hemiarthroplasty

An important aspect of our technique is fixation of the humeral component without cement, without bony ingrowth, and without weakening the humeral shaft by removing bone from its inner endosteal surface. The fixation must recognize that the endosteal anatomy is variable. The inside of the humerus (arm bone) may be cylindrical or tapered.

The inside of the humerus changes in shape as one moves down the shaft.

Trying to fit a prosthesis by reaming the inside of the bone may substantially weaken it.

Trying to force a tight fit risks fracture.

We find that the safest method for securing the stem within the humeral canal is to use impaction grafting with bone harvested from the arthritic humeral head (which is removed at the time of surgery) to conform the inner surface of the bone to the prosthesis. Some have likened this fitting of the patient's bone the prosthesis to the fitting of the traveler to the bed by the inn keeper Procrustes.

As a result, the tapered stem is securely fixed with a biological press fit that safely distributes the load from the prosthesis to the humerus.

Antibiotics after joint replacement

4. Rehabilitation - The most important aspect of the post operative rehab program is preventing stiffness - using the exercises shown here. Of particular concern is the subscapularis.

Once the range of motion is well established and after 6 weeks, we usually start early strengthening and the traction three.

5. Results - The results of hemiarthroplasty depend on the diagnosis for which the procedure is performed - as mentioned under 'indications', it is often performed in unusual circumstances.  Hemiarthroplasty has been combined with meniscal allograft or with soft tissue interposition ("biological resurfacing"), but the addition of the interposition does not seem to improve the results.

6. Complications - the possible risks of hemiarthroplasty include stiffness, pain, infection, fracture and glenoid wear. If stiffness and pain are persistent at six weeks after surgery, a gentle manipulation under anesthesia with complete muscle relaxation is often helpful. If stiffness is present months after the procedure, a surgical soft tissue release is an option. Infection is uncommon after this procedure, especially if advanced prophylactic antibiotics (Ceftriaxone and Vancomycin) are used before and for a day after surgery. Fractures are extremely rare with the impaction bone grafting technique. Glenoid wear is a particular risk when the quality of the bone is poor or when the glenoid surface is not congruent with the humeral prosthesis.

Some surgeons have attempted to combine the hemiarthroplasty with biological resurfacing of the glenoid. This procedure has fallen into disfavor. 

**To see more of the Shoulder Arthritis Book, click here.**