Arnold ADIKRISHNA, Je Yeon KIM, Aashay L. KEKATPURE, Hyun-Joo LEE, Minjae KIM, In-Ho JEON

Dorsal apex curve of the proximal ulna

Objective: To analyze the apexes and angulations along the curvature in the posterior border of the proximal ulna-termed the "dorsal apex curve" (DAC)-using the computer-aided design software.Methods: Eight pairs of normal cadaveric ulnae were analyzed. The ulnar Cartesian coordinate system was standardized using a user-defined coordinate systems feature. DAC was defined by the best-fit curvature of serial apexes in the posterior border in axial cross-sections along the ulna, whereas the best-fit curvature was obtained using polynomials interpolation method. DAC apexes in three different planes were determined by calculating the second derivative value of curve function, and subsequently, DAC angulations were calculated. Statistical analysis was performed using analysis of variance with repeated measures with significance level set as 0.001.Results: The average ulnar length was 246±15 mm (224-274 mm). The average ratios of dorsal apex, varus apex, and edge point were 23±3% (17-27%), 33±4% (27-43%), and 10±1% (8-13%), respectively, relative to the ulnar length. The average amount of varus, dorsal, hook, and torsion angulation were 167±4° (157-172°), 176±1° (175-178°), 90±0°, and 31±10° (15-49°), respectively. We found no significant differences between left and right ulnae or between male and female ulnae.Conclusion: Dorsal apexes and angulations are important landmarks for surgeons when applying plates and attempting total elbow replacement surgery. This curve provides valuable information to medical manufacturers for modeling both plates and ulna components of artificial elbow joints.

___

Grechenig W, Clement H, Pichler W, Tesch NP, Win- disch G. The influence of lateral and anterior angulation of the proximal ulna on the treatment of a Monteggia frac- ture: an anatomical cadaver study. J Bone Joint Surg Br 2007;89:836-8.

Ring D, Jupiter JB, Simpson NS. Monteggia fractures in adults. J Bone Joint Surg Am 1998;80:1733-44.

Strauss EJ, Tejwani NC, Preston CF, Egol KA. The poste- rior Monteggia lesion with associated ulnohumeral insta- bility. J Bone Joint Surg Br 2006;88:84-9.

Duggal N, Dunning CE, Johnson JA, King GJ. The flat spot of the proximal ulna: a useful anatomic landmark in total elbow arthroplasty. J Shoulder Elbow Surg 2004;13:206-7.

Dumont CE, Pfirrmann CW, Ziegler D, Nagy L. Assess- ment of radial and ulnar torsion profiles with cross-sec- tional magnetic resonance imaging. A study of volunteers. J Bone Joint Surg Am 2006;88:1582-8.

Puchwein P, Schildhauer TA, Schöffmann S, Heidari N, Windisch G, Pichler W. Three-dimensional morphometry of the proximal ulna: a comparison to currently used ana- tomically preshaped ulna plates. J Shoulder Elbow Surg 2012;21:1018-23.

Rouleau DM, Canet F, Chapleau J, Petit Y, Sandman E, Faber KJ, et al. The influence of proximal ulnar morphol- ogy on elbow range of motion. J Shoulder Elbow Surg 2012;21:384-8.

Rouleau DM, Faber KJ, Athwal GS. The proximal ulna dorsal angulation: a radiographic study. J Shoulder Elbow Surg 2010;19:26-30.

Windisch G, Clement H, Grechenig W, Tesch NP, Pichler W. The anatomy of the proximal ulna. J Shoulder Elbow Surg 2007;16:661-6.

Yong WJ, Tan J, Adikrishna A, Lee HJ, Jung JW, Cho DW, et al. Morphometric analysis of the proximal ulna using three-dimensional computed tomography and computer- aided design: varus, dorsal, and torsion angulation. Surg Radiol Anat 2014;36:763-8.

Brownhill JR, Mozzon JB, Ferreira LM, Johnson JA, King GJ. Morphologic analysis of the proximal ulna with special interest in elbow implant sizing and alignment. J Shoulder Elbow Surg 2009;18:27-32.

Totlis T, Anastasopoulos N, Apostolidis S, Paraskevas G, Terzidis I, Natsis K. Proximal ulna morphometry: which are the "true" anatomical preshaped olecranon plates? Surg Radiol Anat 2014;36:1015-22.

Akpinar F, Aydinlioglu A, Tosun N, Tuncay I. Morphologic evaluation of the ulna. Acta Orthop Scand 2003;74:415-9.