Background Monteggia fractures and Monteggia-like lesions result after severe trauma and have high complication rates. Preliminary biomechanical studies suggested a correlation between ulnar fracture localization and clinical result. Objectives Key objective was to evaluate whether the site of the ulnar fracture can be correlated to clinical outcome after open reduction and internal stabilization. Methods In a retrospective, monocentric study 35 patients who underwent surgical treatment after suffering a Monteggia injury or Monteggia-like lesion were included. Fractures were classified according to Bado and Jupiter, the site of the fracture location at the proximal ulna and regarding the potential accompanying ligamentary injury. In a follow-up examination validated patient-reported outcome measures and functional parameters were evaluated. Furthermore, treatment strategy and complications were analysed. Results Mean patient age was 51.9 years (± 18.0). 69% were females (n = 24). Follow-up took place after 50.5 months (± 22.1). Fractures were classified according to Bado (I:2, II:27, III:4, IV:2). Bado II-fractures were further classified according to Jupiter (A:7, B:16, C:3, D:1). Cases were divided into subgroups depending upon the distance of the ulnar fracture site in respect to its distal endpoint (A: < 7 cm and B: > 7 cm). Average overall MEPS was 84.1 (± 19.0). Oxford elbow score and DASH were 37.2 (± 10.5) and 20.4 (± 20.5). Average extension capability reached − 7° (± 7.5). Mean flexion was 134.8° (± 19.7). Average pain according to visual analogue scale was 1.6 (± 1.9). We found no differences between the subgroups regarding the PROMs. Subgroup A displayed a worse extension capability (p = 0.027) and patients were significantly older (p < 0.01). Comparing patients with and without fracture of the radial head, we observed no differences. Patients with an accompanying injury of the coronoid process displayed higher pain levels (p = 0.011), a worse functionality (p = 0.027) and overall lower scoring in PROM. Conclusion The presented results suggest that in Monteggia fractures and Monteggia-like lesions, the localization of the ulna fracture can give a hint for its postoperative outcome. However, we could not confirm the hypothesis of an increasing instability in ulnar fractures located further distally (high severity of the potential ligamentous injury). Intraarticular fractures or injuries with a close relation to the joint have a worse prognosis, especially if the coronoid process is injured. Trial registration Registration was done with ClinicalTrials.gov under NCT05325268.

Le cubitus proximal détient une courbe sagittale unique pour chaque individu, nommée « Proximal Ulna Dorsal Angulation (PUDA) ». Une reconstruction non-anatomique du cubitus proximal, suite à une fracture complexe peut engendrer une malunion, de l’arthrose et de l’instabilité. L’objectif de cette étude était d’évaluer la magnitude de malalignement au niveau de l’angulation proximale dorsale du cubitus qui causerait un malalignement radio-capitellaire, avec et sans un ligament annulaire intact. Afin d’atteindre cet objectif, une étude biomécanique fut conduite sur six spécimens frais congelés avec un simulateur de mouvement du coude. Des fractures simulées au niveau du PUDA, furent stabilisées avec une fixation interne dans cinq configurations différentes. Des images fluoroscopiques furent prises dans différentes positions du coude et de l’avant-bras, avec le ligament annulaire intact, puis relâché. Le déplacement de la tête radiale fut quantifié avec le ratio radio-capitellaire. Une interaction significative fut découverte entre les positions du coude, les angles de malalignement et l’intégrité du ligament annulaire. La subluxation de la tête radiale fut accentuée lors de la déchirure du ligament annulaire. Une augmentation de la subluxation antérieure de la tête radiale fut observée lorsque le malalignement était fixé en extension et lors de mouvements de flexion progressive du coude. D’autre part, un malalignement en flexion et une extension graduelle du coude occasionnait une subluxation postérieure. En conclusion, les résultats ont démontré l’importance d’une reconstruction anatomique du cubitus proximal, car un malalignement de 5 degrés engendre une subluxation de la tête radiale, surtout lors d’une déchirure du ligament annulaire. / It has been shown that the proximal ulna has a sagittal bow, named the Proximal Ulna Dorsal Angulation (PUDA), unique for each individual. Non-anatomic reconstruction of the proximal ulna following a complex injury may lead to malunion, arthrosis and instability, hence the importance of understanding its initial anatomy. The purpose of this study was to evaluate the magnitude of angular malalignement at the proximal ulna dorsal angulation that would lead to radiocapitellar malalignement, with and without an intact annular ligament. In order to achieve our goal, a biomechanical study was conducted on six fresh frozen specimens, with an elbow movement simulator. Simulated fractures at the PUDA were stabilized with internal fixation at five different angles. Then, fluoroscopic images were taken in different elbow and forearm positions, first with the annular ligament intact and then released. Radial head displacement was quantified with the Radio-Capitellar-Ratio (RCR). Overall, a significant interaction was found between elbow positions, angles of malalignement and annular ligament integrity. Radial head subluxation was emphasized when the annular ligament was ruptured. Moreover, anterior subluxation of the radial head increased as malalignement was fixed into extension and with progressive elbow flexion. Furthermore, posterior subluxation increased with malalignement into flexion and with elbow extension. In conclusion, our results demonstrate the importance of obtaining an anatomic reconstruction, specific for each individual’s unique proximal ulna dorsal angulation, following a proximal ulna fracture. Indeed, malalignment of 5 degrees can lead to abnormal tracking of the radial head, especially when associated with annular ligament tear.