Intercalary Prosthesis in Reconstruction of Humeral Defects
Timothy A. Damron
Intercalary prostheses were designed for replacement of segmental defects in diaphyseal bone. They are most commonly used for humeral defects, although they are available for other sites on a custom basis. Although the initial design of the humeral intercalary prosthesis employed a male-female taper junction, the latest design is that of a modified lap joint.
INDICATIONS
Indications for the intercalary humeral prosthesis involve both the location of the bone lesion and the underlying diagnosis, the latter of which relates to expected survival. It is recommended that the tumor or segmental defect be in the location as defined by all of the criteria listed below. Furthermore, it is strongly recommended that these prostheses be limited to patients with limited life expectancy. Patients should generally have an estimated survival of at least 4 to 6 weeks to be able to live long enough to benefit from this procedure. Anticipated survival beyond a few years would suggest that consideration should be given to a more biological reconstruction that would have the potential to last longer.
Location within bone (ALL criteria advisable)
Segmental diaphyseal humeral defects 4 cm or greater
Rationale: The minimum size of the body portion of these prostheses is 5 cm. Often, even for 4-cm defects, the bone edges require some trimming back to solid margins, resulting in a 5-cm defect. Care should be taken not to overlengthen the arm by inserting a body section larger than the original defect, as this may result in neuropraxia.
Defect within middle third of humerus
Rationale: Middle third defects are more likely to have intact bone proximal and distal to accept a cemented intramedullary stem.
Five centimeter or more of intact remaining proximal and distal medullary canal
Rationale: Minimum off-the-shelf stem sizes are 5 cm. While standard stems may be trimmed to shorter lengths, this may compromise fixation.
Alternatives: For shorter defects, adequate treatment may be able to be achieved by shortening and internal fixation or by cementation of the defect with spanning internal fixation using either intramedullary nailing or plate and screw fixation.
Limited life expectancy (EITHER/OR)
Disseminated malignancy (metastatic disease or myeloma)
Rationale: Patients with disseminated disease have limited life expectancy and are less likely to outlive the prosthesis before complications such as aseptic loosening occur, as suggested by the premature
high rate of loosening observed with the latest version of this device at relatively short duration of follow-up.2
OR solitary metastatic carcinoma undergoing resection (renal or thyroid carcinoma)
Rationale: In these patients, life expectancy is unknown but often still limited. If they become long-term survivors, the reconstruction may require conversion to a potentially more long-lasting solution such as an intercalary allograft or vascularized fibular autograft with appropriate fixation.
TABLE 31.1 Contraindications | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||
CONTRAINDICATIONS
Contraindications also involve the location of the tumor and the patient’s life expectancy. Normal life expectancy should be considered a relative contraindication to the use of this device (Table 31.1). For patients who are anticipated to live for longer than a few years, consideration should be given to a more biological reconstruction, such as an intercalary diaphyseal allograft or autograft with spanning internal fixation. When allograft is not available or is not acceptable to the patient, vascularized fibular grafts have been used to reconstruct such deficits.
PREOPERATIVE PLANNING
Confirm diagnosis
Preoperative metastatic workup to search for likely primary and identify extent of disease
Total body bone scan
Computerized tomography of chest/abdomen/pelvis
Serum protein electrophoresis and urine protein electrophoresis to evaluate for multiple myeloma
Establish diagnosis of humeral lesion with tissue before proceeding with treatment
Preoperative needle biopsy
Intraoperative needle or open biopsy with frozen section
Assess extent of bone defect and remaining proximal and distal bone
Plain biplanar radiographs of entire humerus
Consider MRI or CT to assess extent of defect
Entertain alternative means of operative management
Consider alternatives to spacer
Internal fixation with bone cement or allograft to fill defect
Proximal or distal endoprosthetic device if closer to one end of humerus
Decide upon a backup plan
Ensure all equipment will be available
Primary plan: spacer implants, trials, insertion equipment, straight reamers, reamer driver, antibiotic loaded bone cement (author utilizes a pre-mixed Tobramycin containing PMMA), insertion tool of choice for bone cement (author utilizes a Toomey syringe)
Backup plan(s): internal fixation implants and insertion equipment, allograft, other prostheses (such as proximal humeral replacement for more proximal lesions or a total elbow distal humeral replacement for more distal lesions)
Consider pre-operative embolization
Consider for vascular malignancies (renal carcinoma, thyroid carcinoma, myeloma) if intralesional procedure planned
Not absolutely necessary if wide en bloc resection planned
TECHNIQUE
Positioning
Typically, the patient is positioned supine with the arm on an armboard in order to facilitate stability after resection of the involved segment. The author prefers a Jackson table or other equivalent vascular imaging table without metallic bars on the side that may impede fluoroscopic imaging. The patient may also be positioned far enough to the opposite side of the imaging table that no armboard is needed.
Landmarks
The landmarks of the shoulder, including the acromion, distal clavicle, coracoid, arm, and elbow should be identified and marked to facilitate accurate placement of the surgical incision.
Surgical Incision
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
