- For reconstruction of the elbow after tumor resection in the distal humerus, modular prosthetic systems are typically used that require preparation of the ulnar canal, into which an appropriately sized ulnar stem component is placed
- Even careful preoperative review of lateral radiographs can result in overestimating the minimal canal size when selecting the ulnar component, which predisposes the patient to complications
- This retrospective study evaluated the normal population variation of the proximal ulna dorsal angulation (PUDA) on lateral elbow radiographs; these radiographs were used to template two commonly used modular total elbow systems
- The curved ulnar stem of the Modular Universal Tumor and Revision System was a limiting factor in the ability of templated elbows with PUDA ≥5° to accommodate the ulnar component
- When the Solar Elbow System was templated, elbows with PUDA >10° more frequently required either a smaller stem length or stem diameter
For reconstruction of the elbow after tumor resection in the distal humerus, modular prosthetic systems are typically used instead of total elbow systems. The commonly used modular systems require preparation of the ulnar canal into which an appropriately sized ulnar stem component is placed.
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Unfortunately, scant data is available about the bony anatomy of the proximal ulna for use in preoperative planning. Moreover, the ulnar cortex is relatively thin, and even careful preoperative review of lateral radiographs can result in overestimating the minimal canal size when selecting the ulnar component, which predisposes the patient to complications.
Caleb M. Yeung, MD, clinical orthopaedic surgery resident, Santiago Lozano-Calderon, MD, PhD, surgeon in the Orthopaedic Oncology Service at Massachusetts General Hospital, and colleagues have found that the proximal ulna dorsal angulation (PUDA), a measurement easily obtained from radiographs, can predict the proper size of the ulnar stem component in preoperative templating. PUDA measurements may also be useful when templating software is unavailable. The data appear in the Journal of the American Academy of Orthopaedic Surgeons: Global Research and Reviews.
The researchers reviewed lateral elbow radiographs of 514 adults who had no pathology, previous fracture or reconstruction of the ulna. On each radiograph, three researchers measured the PUDA twice, three months apart. The PUDA was defined as the angle formed by the intersection of lines drawn parallel to the non-articulating outer cortex of the olecranon and the dorsal diaphyseal cortex of the ulna.
Patients were stratified into PUDA groups of <5°, 5°–10° and >10°. The researchers randomly selected 221 of the same radiographs, at least 30 from each angle group. Using the TraumaCad software system, they templated two commonly used modular total elbow systems:
- Modular Universal Tumor and Revision System (MUTARS) by Implantcast, which comes in one size and has a curved ulnar stem
- Solar Elbow System (SES) by Stryker, which comes in small, standard and large sizes, and offers three straight ulnar stem lengths (63 mm, 53 mm and 50 mm)
- The MUTARS implant fit 97% of elbows with PUDA <5° and 92% of those with PUDA ≥5° (difference not statistically significant)
- The largest SES combination fit 100% of elbows with PUDA ≤10° vs. 93% of those with PUDA >10° (P=0.03)
- Elbows accommodating the MUTARS implant had a smaller median PUDA than elbows in which the MUTARS implant did not fit (5.4° vs. 5.8°; difference not statistically significant)
- Elbows into which the largest SES combination fit had a smaller median PUDA than elbows that accommodated smaller SES combinations (5.4° vs. 11.7°, P=0.03)
Multivariate analysis showed that demographic variables (age, sex, race, weight, height and body mass index) did not substantially contribute to the variance between patients in the PUDA measurement. Thus, preoperative measurement of the PUDA on lateral elbow radiographs is necessary for selecting an ulnar stem component size.
- When either modular system is used, the careful prosthetic selection is especially important for elbows with PUDA ≥5°, where a smaller ulnar stem should be considered
- For patients with PUDA ≥5°, alternatives to the MUTARS implant should be considered because the curved ulnar stem may not fit
- When the SES is used, elbows with PUDA >10° may require either a smaller stem length or smaller stem diameter
- In elbows with larger values for PUDA measurement, an osteotomy of the proximal olecranon may be warranted to permit a more straightforward insertion trajectory of the stem into the ulnar diaphysis
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