Preoperative planning and approach selection

Issue: December 2004

ByWayne Z. Burkhead, MD

Wayne Z. Burkhead, MD,
is clinical professor, University of Texas Southwestern Medical School, W.B. Carrell Memorial Clinic, Dallas, Texas.

Before a patient enters the operating room, it is important for a surgeon to consider preoperative planning and approach selection when using a reverse prosthesis. With the Aequalis reverse prosthesis (TORNIER, St Ismier, France), which is approved by the Food and Drug Administration, surgeons are able to treat patients with rotator cuff tear arthropathy and failed shoulder arthroplasty in whom traditional shoulder replacements have failed to restore motion.

Patient selection

Before performing reverse prosthesis surgery, a surgeon must assess the patient and ask the following questions. Has an adequate trial of conservative treatment been given? Is the patient a candidate from an overall health standpoint and is balance a concern? Are the symptoms of pain severe and disabling enough to warrant surgical intervention? What resources does the patient have at home to help after surgery? These questions must be answered by the patient, the attending internist and by the surgeon before the surgery.

Preoperative planning

Shoulder surgery begins with careful preoperative planning. Preoperative high-quality radiographs, including the axillary view, are mandatory. If a surgeon is templating for a reverse prosthesis, then the glenosphere should always be templated on the axillary lateral view rather than on the anteroposterior view. The superior-inferior diameter of the glenoid is approximately 35 mm to 45 mm; however, a surgeon may see a narrower 25-mm range on the axillary lateral view. This has major implications in regard to the ability to achieve anterior and posterior screw fixation of the base plate.

For the humeral component, the anteroposterior external rotation view is an ideal view for templating. Preoperative external rotation should be 45º for accurate templating of the proximal humeral metaphyseal segment of the reverse prosthesis.

Templates are magnified to fit radiographic criteria, and surgeons must examine a number of parameters on the radiograph. The diaphyseal axis will help a surgeon determine the epiphyseal entry point. Templates will also help determine the size of the metaphysis and the glenosphere. The diameter and length of the stem can be determined, and the height of the humeral cut can be prepared, as well. The diaphyseal axis is not the same as the hinge point. The long axis of the diaphysis in the entry point into the humeral head is approximately 8 mm to 10 mm medial to the hinge point. When a surgeon is using the reverse osteotomy guide, the entry point must be made at that position and not at the hinge point.

There are two sizes of glenospheres and corresponding metaphyseal components — the 36-mm and the 42-mm component. The 36-mm component is used in 90% of patients in the European series. If a surgeon is using one size component in all surgeries, then some patients may be receiving an oversized component. The other parameters that a surgeon should assess include the height of the polyethylene and the possible need for a 9-mm metaphyseal spacer.

If a surgeon is using one size component in all surgeries, then some patients may be receiving an oversized component.

— Wayne Z. Burkhead, MD

A number of stem diameters are available, ranging from 6.5 mm to 15 mm in diameter and 100 mm to 210 mm in length. A 100-mm implant is most commonly used for primary replacement and a longer implant is chosen in special cases, such as revision arthroplasty, tumor reconstruction or periprosthetic fractures. The height of the humeral cut must also be considered. A surgeon has two options: The osteotomy guide creates a 155º cut below the epiphysis of the humerus, preserves bone stock and avoids excessive laxity, or a metaphyseal cortex is cut at the same angle. The latter is more aggressive and facilitates glenoid exposure.

A computed tomography (CT) scan is recommended to assess overall glenoid volume and bone quality. A surgeon can determine the entry point from the preoperative CT scan. Based on recent data from Frankle, a 10º to 15º angle of downward inclination is ideal. An experienced surgeon may choose a 10º angle on the glenoid component.

Skin incisions

A surgeon must also consider skin incisions. A number of skin incisions are used for shoulder surgery. The deltopectoral approach is where the incision follows the deltopectoral groove from the clavicle to the deltoid insertion. The skin incision that I prefer for the superolateral approach is when a finger is placed along the back of the clavicle and the incision is made along the finger. In difficult revision cases, a surgeon must be mentally and physically prepared to perform an extensile approach in which the deltoid is advanced and re-repaired. With this approach, a surgeon can offer the patient excellent results even in the face of failed cuff tear repair with deltoid dehiscence. Surgeons should be familiar with all approaches to the shoulder.

Surgical approaches

There are two basic surgical approaches for rotator cuff tear arthropathy — the deltopectoral approach and superolateral approach — each with associated benefits and risks. The deltopectoral approach is commonly used for arthroplasty and surgeons are familiar with the approach. Using this approach, it is easier for the surgeon to use a drill and tilt the glenoid sphere downward. There is limited risk to the axillary nerve. Drawbacks include difficulty exposing and preparing (reaming) the glenoid. The deltopectoral approach requires extensive capsulotomy for exposure and accurate placement of the glenoid. Also, the approach can be damaging to soft tissue (deltoid and subscapularis). Reduction is sometimes difficult with high deltoid tension. These downsides are compounded if the epiphyseal osteotomy is performed.

The superolateral approach is a direct approach along the glenoid axis. This approach respects the anterior-inferior soft tissues and allows for easy reduction. Exposure of the glenoid is facilitated by metadiaphyseal humeral osteotomy. When comparing series of patients done through this approach, the instability rate (0%) was lower than with a deltopectoral approach (5%). The difficulty associated with the superolateral approach is that it requires a paradigm shift. This approach is not used commonly for arthroplasty and makes tilting the glenoid sphere downward difficult. There is added risk to the axillary nerve, with an approach that splits the fibers of the deltoid muscle. This risk can be minimized by putting a stay suture 4 cm below the acromion and by taking more deltoid off of the clavicle to remove tension on the deltoid split laterally.

The superolateral approach is nonextensile to the humeral shaft and, therefore, as an isolated approach, it should not be used in revision and old trauma cases. A surgeon should, however, consider taking down part of the anterior deltoid when performing the deltopectoral approach for old trauma and revisions. Any time the deltoid is taken down, it must be accurately and anatomically repaired.

Infection

Douglas W. Jackson, MD: Infection around an implanted joint is a serious complication. If an infection develops, then the entire implanted joint may need to be removed to eradicate the infection. What are some pearls for confirming the diagnosis of infection?

Tom R. Norris, MD: No test is 100% accurate in confirming infection. A surgeon should always be suspicious of infection when performing revision surgery. In some situations, however, what may appear to be an infection is not. For example, I saw a patient in which the lucent area around the prosthesis was expanding. On a radiograph, it appeared to be an infection. However, an indium scan and differential bone scans showed that the patient had reactive tissue, not an infection.

Jackson: Are there approaches to prevent possible infections?

Andrew Green, MD: I aspirate patients preoperatively for a cell count and take a culture before I operate. If the cell count is elevated, then it is often due to an infection.

Jackson: What do you consider an elevated cell count?

Green: A cell count of 500 with no white cells in normal synovial fluid is a high index of suspicion. In terms of cultures, a surgeon should take multiple cultures because unusual bacteria exist around the shoulder. If multiple cultures are taken, then false positives can be eliminated. Then, surgeons must always take anaerobic cultures. Cultures should be observed for seven days because some bacteria will not grow in 48 hours, but rather in seven days.

Wayne Z. Burkhead, MD: Computed tomography arthrograms (CTA) are excellent preoperative tests for a patient with a painful arthroplasty. CTAs collect aerobic and anaerobic cultures simultaneously. A surgeon can evaluate the rotator cuff and the version of the components. CTA is the most important preoperative test that I perform on a patient who presents with a painful shoulder arthroplasty.

T. Bradley Edwards, MD: I also perform CTAs on patients and aspirate at the same time. If a patient has an infection and a surgeon debrides the patient, can the implant be reimplanted?

Burkhead: This is an organism- and patient host-specific decision. If the organism is gram-negative in a patient with diabetes who is on steroids for rheumatoid arthritis, then I would not reimplant the implant. I would perform a resection arthroplasty. However, if the patient is healthy and has a gram-positive organism, then I would reimplant.

Summary

Shoulder level and above function can be reliably restored in patients with rotator cuff tear arthropathy and failed hemiarthroplasty for fracture with a reverse prosthesis. Careful patient selection, accurate preoperative planning and the appropriate choice of approach will allow experienced and well-trained surgeons to safely add this new and important technology to their surgical armamentarium.