Assessment of Lateral Rotation Percentage and Rotational Deformity of the Elbow in Type 3 Supracondylar Humerus Fractures: A Biomechanical Study

Abstract

Background: Supracondylar humerus (SCH) fractures are the most common elbow fractures in children. Historically, displaced (Gartland type 3) SCH fractures have been treated with closed reduction and percutaneous pinning. Fluoroscopic imaging is used intraoperatively in order to assess adequate reduction of the fracture fragments before pinning. On lateral fluoroscopic and radiographic images, a lateral rotation percentage (LRP) can be estimated in order to assess rotational deformity. The purpose of this study was to determine the true rotational deformity of distal humerus fracture fragments in SCH fractures based upon the LRP using a clinically relevant laterally based pinning technique. Methods: In this study, a sawbones model was used to examine the correlation between calculated LRP and the true degree of rotational deformity with 3 of the most common extension-type SCH fracture types (low transverse, high transverse, and lateral oblique). Because fracture stability was not the focus of this study, a single pin was used to hold the construct and allow for fragment rotation along a fixed axis. In this study, 2 of the authors independently measured rotational deformity and compared this with LRP on fluoroscopic lateral imaging of a sawbones model at 0 to 45 degrees of rotational deformity. Results:The LRP of all 3 patterns demonstrated a near linear increase from 0 to 45 degrees with maximum LRP measured at 45 degrees for each of the 3 patterns. Univariate linear regression demonstrated an increase in LRP for the low transverse pattern of 2.02% for every degree of rotation deformity (R 2 = 0.97), 2.29% for the lateral oblique pattern (R 2 = 0.986), and 1.17% for the high transverse pattern (R 2 = 0.971). Maximum LRP was measured at 45 degrees for all 3 patterns with a mean of 53.5% for the high transverse pattern, 93.5% for the low transverse pattern, and 111.2% for the lateral oblique pattern. A higher LRP was measured with increasing degrees of rotational displacement in the low transverse and lateral oblique patterns for all degrees of rotational deformity compared to the high transverse pattern. Conclusion: There is a near linear correlation between the degree of malrotation and the LRP with more superior metaphyseal fracture patterns demonstrating a lower LRP than inferior fracture patterns. Clinical Relevance: Using our data one can estimate the degree of malrotation based on the LRP on radiographs in the clinical setting. Level of Evidence: Not applicable (basic-science article).

Assessment of Lateral Rotation Percentage and Rotational Deformity of the Elbow in Type 3 Supracondylar Humerus Fractures: A Biomechanical Study

“…Therefore, it is highly likely that the provided angles do not apply to the majority of intraoperative and postoperative scenarios, because we frequently accept some displacement, have varying wire positions and frequently do not get true lateral views in the clinic. Therefore, we do not think that Berdis et al’s1 data can be used reliably for the majority of fractures to estimate the true degree of malrotation, with it being hitherto unknown if any malrotation/LRP can be accepted, without affecting cosmesis and/or function.…”

“…Ryan et al4 reported that the AHL runs through the middle third of the capitellum in 100% of children 5 years of age and above but Berdis et al’s1 AHL runs through the front of the capitellum, indicating that the used bone model might not be an anatomic reproduction of a normal child’s humerus, which raises doubts about the reliability of the measured percentages.…”

“…We read with interest the recent publication by Berdis et al1 The authors1 stated that their lateral rotation percentages (LRP) do not apply if coronal or sagittal deformity exists but there are other factors which will also affect the measurements. Camp et al2 measured that the perceived Baumann angle increases with internal and decreases with external humeral rotation of the humerus if an anteroposterior radiograph is not taken as a true anteroposterior radiograph, with the perceived angle changing by ±1.6 degrees per 10 degrees change of rotation with the humerus parallel to the collector/cassette and by ±5 degrees per 10 degrees change of rotation with the humerus flexed 30 degrees.…”

“…We also assume that the LRP depends on the center of rotation and therefore on the position of the first K-wire at the level of the fracture and its direction, since this defines the axis of rotational displacement. We would like to ask Berdis et al1 why they inserted their K-wire with inclination in a posterior to anterior direction, stating that this makes their study as clinically relevant as possible by replicating standard intraoperative pin placement, despite this being the opposite to the anterior to posterior inclination recommended by Skaggs et al3 in accordance with normal anatomy? We would also like to ask the authors if they agree that their statement that “it should not matter if the arm is in internal or external rotation because it is a percentage” is a factual error, since on a true lateral view the perceived postero-anterior distance of the distal humeral fragment will be at its smallest and will increase with arm rotation in either direction in relation to the xray beam.…”

“…We assess intraoperative rotational malalignment by taking internal and external oblique elbow views, which show the alignment of the medial and lateral column, with our image intensifier machines not allowing to perform any measurements. Could Berdis et al1 explain how their measurements help with intraoperative decision making, as they stated in their discussion, since we generally do not accept malrotation, not using a specific LRP value as a decision guide?…”