The effect of radial head prosthesis diameter on posterolateral rotatory instability of the elbow

Relationship between measurements of ipsilateral capitellum and prosthetic radial head size

Background

Selecting the correct size of head component is challenging in radial head arthroplasty, particularly in comminuted fractures. This study aimed to investigate the relationship between measurements of the ipsilateral capitellum and the prosthetic radial head size, which may be used to predict the size of the radial head prosthesis preoperatively.

Methods

Our study enrolled all patients who underwent radial head arthroplasty at Beijing Jishuitan Hospital. Demographic, injury-related and radiographic data were collected. The prosthetic radial head size was recorded from the surgical notes. Three-dimensional models of preoperative CT scans were reconstructed, on which the lateral capitellar diameter, the capitellar width and the width between the capitellum and trochlea were measured. The correlations between measurements of the ipsilateral capitellum and the prosthetic radial head size were evaluated, and linear regression equations were established.

Results

The study enrolled 37 patients, with an average age of 42.8 ± 11.5 years and a male–female ratio of 20:17. The median diameter of the radial head prostheses was 22 (20, 22) mm. The average lateral capitellar diameter was 20.71 ± 1.93 mm, the mean capitellar width was 14.90 ± 1.40 mm, and the mean width between the capitellum and trochlea was 19.29 ± 1.78 mm. The lateral capitellar diameter (R = 0.820, P < 0.001), the capitellar width (R = 0.726, P < 0.001) and the width between the capitellum and trochlea (R = 0.626, P < 0.001) were significantly positively correlated with the size of the radial head prosthesis. The linear regression equation between the lateral capitellar diameter and the size of the radial head prosthesis was calculated and defined as follows: D = 7.44 + 0.67*d (D: diameter of radial head prosthesis; d: lateral capitellar diameter; and adjusted R2 = 0.719, P < 0.001).

Conclusions

There are positive correlations between the anatomical parameters of the ipsilateral capitellum and the prosthetic radial head size. The lateral capitellar diameter can be measured on three-dimensional CT preoperatively to predict the size of the radial head prosthesis intraoperatively.

Optimal Prosthesis Sizing for Radial Head Arthroplasty: A Review of Current Evidence and Guidelines

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Radial head arthroplasty is a viable surgical option when a radial head fracture cannot be reconstructed. Radial head arthroplasty provides a load-bearing articular structure against the capitellum in unstable fractured elbows.

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Studies have emphasized the importance of choosing the correct implant size to replicate the native radial head anatomy, citing various consequences of improperly sized radial head prostheses. Overstuffing of the radiocapitellar joint, or lengthening of the radius, has been extensively studied because of its detrimental effects on elbow biomechanics, but other types of improper sizing also have negative consequences.

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In the setting of severe fracture-dislocation or revision surgery, anatomic landmarks that are useful for prosthesis sizing often are missing. Various methods have been described to provide guidance for the accurate sizing of a prosthetic radial head; a retrieved radial head, the proximal edge of the lesser sigmoid notch, the radiocapitellar synovial fold, and the ulnohumeral joint space all represent useful references.

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Intraoperative radiographic examination is an important step while assessing implant size, including the height of the prosthetic radial head.

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Since no single method is perfect on its own, the surgeon should combine as many reference measures as possible, both before and during the procedure, for accurate prosthesis sizing in order to achieve successful outcomes.