What Is the Normal Ulnar Bow in Adult Patients?

Abstract

Background Rotation of the forearm is a result of the complex interaction among the radius, ulna, and interosseous membrane. Although the radius is recognized as curved, the ulna is generally thought of as a “straight bone.” To better describe normal anatomy, which may lead to more successful anatomic fixation of forearm fractures, we aimed to apply a method of measuring the normal ulnar bow and determine the mean ulnar bow in adults. Questions/purposes (1) To what degree is the ulna bowed in the coronal and sagittal planes in normal adult forearms? (2) To what degree is the radius bowed in the coronal plane in normal adult forearms? Methods Radiographs of the forearms of adults taken during a 1-year period were initially obtained retrospectively. These radiographs were performed for various reasons, including forearm pain and routine radiographic follow-up. Radiographs were excluded if evidence of a fracture or post-fracture fixation was found, if a patient had missing AP or lateral images, or if a suboptimal technique was used. The coronal and sagittal bow of the ulna was measured with a method adapted from previous studies that assessed radial bow using AP and lateral radiographs, respectively. Similar measurements were made in the coronal plane for the radius. All measurements were performed independently by the four authors. There was excellent interobserver reliability for ulnar bow in the coronal and sagittal planes (interclass correlation coefficient = 0.96 and 0.97, respectively) and for radial bow in the coronal plane (interclass correlation coefficient = 0.90). Results The mean maximal coronal ulnar bow was 7 ± 2 mm and was located at 75% of the ulnar length, measured proximally to distally. The location of coronal bow was consistently distal to the radial bow location. The mean maximal sagittal ulnar bow was 6 ± 3 mm and was located at 39% of the ulnar length. The mean maximal coronal bow of the radius was 14 ± 2.0 mm and was 59% of the total length of the radius from proximal to distal. Conclusions The ulna is not a “straight bone,” as is commonly thought, but rather has a bow in both the coronal and sagittal planes. Clinical Relevance Knowledge of the standard ulnar bow may be pivotal to prevent malunion of the ulna during surgery. Future research using these data in preoperative planning may lead to changes in plate contouring and clinical outcomes in forearm fracture management.

Computer tomographic analysis of anatomic characteristics of the ulna – essential parameters for preshaped implants

“…We found an average ratio of the PUDA apex to the total ulnar length of 23.2% which is comparable to the CT-analysis from Yong et al (26.4%) [5]. Two recent studies investigated the anterior-posterior and lateral bow of the ulna bone and published slightly different results compared to the existing literature [26,27]. Especially the location of the ulna bows were described to be more distally than presumed previously [26,27].…”

“…Two recent studies investigated the anterior-posterior and lateral bow of the ulna bone and published slightly different results compared to the existing literature [26,27]. Especially the location of the ulna bows were described to be more distally than presumed previously [26,27]. It must be noted, that the comparison between different studies are impeded because of the different measurement methods.…”

Morphological symmetry of the radius and ulna—Can contralateral forearm bones utilize as a reliable template for the opposite side?

“…Length, volume, bowing and twisting differences of the bilateral forearm bones were investigated first, then regional shape differences were analyzed. In particular, many researchers have reported that the radius and ulna have characteristic natural bowing and twisting [28,[32][33][34][35][36]. Several studies reported that deformities of the forearm bone diaphysis can cause 50% to 60% restriction of forearm bone rotation [31,37].…”

“…Secondly, PSIs can be developed [8,9]. The radius and ulna, which have complex anatomical structures compared to other limb bones, are parallel long bones that have a natural bow [10][11][12][13]. The radius and ulna enable the execution of precise movements such as supination and pronation since the radius can pivot around the ulna [14].…”

3D Quantitative Measurement of the Coronoid Process and Proximal Ulna: A Chinese Adults-Based Morphometric Study

“…Therefore, the anatomic reduction and joint stability counting on implants cannot be overemphasized, and only in this way can the satisfactory functional outcome be recovered [5][6][7]. So, anatomic parameters of the elbow need to be acquired and analyzed to promote the classi cation and design of internal xation for fracture, while there were still a series of pitfalls in previous studies that could not fully elucidate the characteristics of these structures [6,[8][9][10][11].…”