Abstract
Background
After elbow fracture-dislocation, surgeons confront numerous treatment options in pursuing a stable joint for early motion. The relative contributions of the radial head and coronoid, in combination, to elbow stability have not been defined fully.
Questions/purposes
The purpose of this study was to evaluate the effect of an approximately 50% transverse coronoid fracture and fixation in the setting of an intact or resected radial head on coronal (varus/valgus) and axial (internal and external rotational) laxity in (1) gravity varus stress; and (2) gravity valgus stress models.
Methods
Kinematic data were collected on six fresh-frozen cadaveric upper extremities tested with passive motion throughout the flexion arc under varus and valgus gravity stress with lateral collateral ligaments reconstructed. Testing included coronoid fracture and osteosynthesis with and without a radial head.
Results
In the varus gravity stress model, fixation of the coronoid improved varus stability (fixed: 1.6° [95% confidence interval, 1.0–2.2], fractured: 5.6° [4.2–7.0], p < 0.001) and internal rotational stability (fixed: 1.8° [0.9–2.7], fractured: 5.4° [4.0–6.8], p < 0.001), but radial head fixation did not contribute to varus stability (intact head: 2.7° [1.3–4.1], resected head: 3.8° [2.3–5.3], p = 0.4) or rotational stability (intact: 2.7° [0.9–4.5], resected head: 3.9° [1.5–6.3], p = 0.4). With valgus stress, coronoid fixation improved valgus stability (fixed: 2.1° [1.0–3.1], fractured: 3.8° [1.8–5.8], p < 0.04) and external rotation stability (fixed: 0.8° [0.1–1.5], fractured: 2.1° [0.9–3.4], p < 0.04), but the radial head played a more important role in providing valgus stability (intact: 1.4° [0.8–2.0], resected head: 7.1° [3.5–10.7], p < 0.001).
Conclusions
Fixation of a 50% transverse coronoid fracture improves varus and internal rotatory laxity but is unlikely to meaningfully improve valgus or external rotation laxity. The radial head, on the other hand, is a stabilizer to resist valgus stress regardless of the status of the coronoid.
Clinical Relevance
Determination as to whether it is necessary to fix a coronoid fracture should be based on the stability of the elbow when tested with a varus load. The elbow may potentially be stable with fractures involving less than 50% of the coronoid. Under all circumstances, the radial head should be fixed or replaced to ensure valgus external rotatory stability.
Electronic supplementary material
The online version of this article (doi:10.1007/s11999-014-3477-1) contains supplementary material, which is available to authorized users.
Introduction
Elbow fracture-dislocations often involve fractures of both the radial head and the coronoid. On the basis of multiple studies and our own clinical experience, internal fixation and the fractured coronoid that involves more than 50% of its height is well accepted [1–4, 6, 8–10].
Although the importance of bone deficiency in these injuries has been carefully studied, the effect of osteosynthesis of the coronoid in the presence or absence of an intact radial head is clinically relevant and, to our knowledge, has not been previously investigated with an experimental model.
The purpose of this study was to evaluate the effect of an approximately 50% transverse coronoid fracture and fixation in the setting of an intact or resected radial head on coronal (varus/valgus) and axial (internal and external rotational) laxity in (1) gravity varus stress; and (2) gravity valgus stress models.
Materials and Methods
Specimen Preparation
Six fresh-frozen cadaver upper extremities were used for this study. The mean age of the donors was 72 years (range, 52–93 years). Three were right, and three were left-sided specimens from five males and one female donor. The arms were transected at the midhumerus. The humerus was cemented in an acrylic cylinder with polymethylmethacrylate and then mounted in a custom testing apparatus (Fig. 1).
Fig. 1.
Specimen prepared for experiment. The source and sensor of the tracking system are demonstrated. Muscle loading is simulated by weights across the flexor and extensor musculature.
The custom testing apparatus provided firm fixation of the specimen in the coronal plane but allowed full flexion and extension. Passive muscle loading was maintained with each experimental condition; nylon cords were firmly sutured to the biceps, brachialis, and triceps tendons. These were loaded with 2 kg, 2 kg, and 4 kg, respectively.
An electromagnetic tracking system (Polhemus Fastrak, Colchester, VT, USA) was used to record the kinematic data. Sensors were secured to the ulna and the humerus. Coordinate systems for the humerus and ulna were defined using standard anatomic landmarks [11]. The center of the humeral shaft, as defined by the centroid method, substituted for the center of glenohumeral rotation.
The elbow was moved passively from full extension to full flexion. The forearm was maintained in neutral position with respect to pronation-supination by holding the specimen gently at the wrist to control rotation. Five trials of flexion were performed to account for soft tissue conditioning with the last trial being selected for the data analysis.
Experimental Protocol
The same standardized protocol of experimental conditions was performed for each specimen. All tests were performed by the same two investigators (RUH, ML-P). The intact elbow was tested in three loading configurations: vertical (transepicondylar axis parallel to the floor), varus under gravity stress (transepicondylar axis perpendicular to the floor with the medial epicondyle down), and valgus under gravity stress (transepicondylar axis perpendicular to the floor with the lateral epicondyle down) (Fig. 1). We randomized the order of these positions through the protocol to minimize bias toward an effect of position.
Because in clinical practice the lateral collateral ligament (LCL) is nearly universally repaired or reconstructed, we chose not to include LCL injury as a variable in our experimental design. However, exposure through the lateral aspect of the elbow was required to perform the experiment. The lateral aspect of the elbow was exposed. The origin of the LCL and the overlying common extensor tendon fibers were detached in the same manner done clinically by using an osteotomy of the lateral epicondyle and supracondylar ridge of the humerus. We used a chevron-shaped osteotomy to increase the security of the subsequent repair of the LCL with one or two lag screws as is done clinically to fix the osteotomy. The elbow was then tested with the LCL and epicondyle intact and then after the ligament complex was detached and reattached. This step confirmed that repair of the osteotomy effectively restored nominal kinematics and stability, thus validating the technique (see Supplementary Fig. S1). All data are therefore reported as if the LCL was intact or reconstructed.
Using fluoroscopy, the coronoid process was predrilled for a 3.5-mm lag screw to provide later fixation with interfragmentary compression. The medial aspect of the elbow was exposed next.
The flexor mass was reflected from the epicondyle, exposing the capsule. The anterior limit of the anterior band of the medial collateral ligament (MCL) was carefully identified. A small Kirschner wire was placed from medial to lateral through the coronoid process to guide the plane of the coronoid osteotomy. The wire was placed such that the cut did not disrupt any of the MCL fibers but created a fragment of approximately 50% of the bony height of the coronoid. The goal of the coronoid osteotomy was to simulate a transverse Type II fracture (Fig. 2) [8].
Fig. 2.
Demonstration of the Type II coronoid fracture created anterior to the attachment of the collateral ligaments and consisting of approximately 50% of coronoid articular surface.
The elbow was tested both with the coronoid fractured and with the coronoid fixed. The next step consisted of removing the radial head. Testing was repeated with a coronoid fracture and synthesis with the LCL repaired with and without a radial head. In this study, we focus our analysis on the effect of the coronoid fracture with the radial head intact or resected during varus and valgus loading configurations.
At the conclusion of the testing protocol, the soft tissues were dissected from each specimen, which was then carefully photographed and measured, paying special attention to the relative articular areas of the radial head, whole coronoid, and fragment of the coronoid fractured. The transverse coronoid fractures were characterized by measuring the intraarticular surface area of the fracture fragment and remaining coronoid process. These areas were determined using high-quality digital photographs and a commercial digital photographic software package (Adobe Photoshop; Adobe Systems, San Jose, CA, USA). The average remaining area of the coronoid for our six specimens was 46% ± 6% (range, 42%–59%). This confirms that the fractures studied were transverse in nature and approximately 50% of the coronoid process.
Kinematic Analysis
Standard Cartesian coordinate systems for the humerus and ulna were defined by the digitization of anatomical landmarks [11]. Euler rotations were used to define flexion-extension angle (first Euler rotation), varus-valgus angle (second Euler rotation), and internal-external rotation angle (third Euler rotation).
To validate the methodology, we first compared kinematic parameters between the intact elbows and after reattachment of the LCL complex in the presence of the radial head to establish baseline conditions. Reattachment of the LCL complex in the presence of an intact radial head and coronoid did not result in changes to kinematic parameters from the intact elbow (see Supplementary Fig. S1). Therefore, the condition of the repaired LCL with an intact radial head and coronoid process was used throughout the study as the baseline condition of the elbow [1].
In this model, we specifically studied the effects of elbow injury and repair on angular and rotatory laxity during conditions of varus and valgus gravity loading. The vertical, unloaded condition was not included in the kinematic analysis. Varus-valgus laxity and internal-external rotational laxity were defined as the difference in the varus, valgus, and internal and external rotation angles of the gravity loading curves from the angles of the intact elbow measured at 60° of flexion. Hence, our four clinical simulated testing configurations as described previously (radial head intact, radial head resected, coronoid fractured, and coronoid fixed) are analyzed according to four kinematic parameters of interest: varus and internal rotation laxity with varus load and valgus and external rotatory laxity with valgus load.
Statistical Methods
Similar to previous studies, we observed that the greatest laxity of the elbow was in the midflexion range. The kinematic data obtained at 60º of flexion were chosen as representative of this behavior for the statistical analysis [7]. As has been observed by other authors, large variation existed between the kinematics of the specimens in this study. Therefore, two-way repeated-measures analysis of variance models were used with coronoid (two conditions) and radial head status (four conditions: intact, resected, monopolar replacement bipolar replacement) as the main effects for six specimens (48 observations per model) [7]. Tukey post hoc multiple comparisons were analyzed when a significant effect was observed in the model, and in this study, we consider only two of the radial head conditions (intact and resected). This strategy allows each specimen to serve as its own control, and large variations between specimens may not preclude statistically significant effects from being observed. Significance was defined as variations occurring by chance to occur with < 0.05 likelihood.
Results
In the varus gravity stress model, fixation of the coronoid improved varus and internal rotational stability, but radial head fixation did not contribute to stability. The mean varus angle laxity with the coronoid fractured was 5.6° (95% confidence interval [CI], 4.2–7.0) versus 1.6° (95% CI, 1.0–2.2) with the coronoid fixed (p < 0.0001). In the post hoc analysis, fixation of the coronoid with the radial head intact resulted in mean varus angle laxity of 1.1° (95% CI, 0–2.1) versus 4.4° (95% CI, 2.5–6.2) with the coronoid fractured (p = 0.2) (Fig. 3). Fixation of the coronoid with the radial head resected resulted in mean varus laxity of 2.1° (95% CI, 1.0–3.2) versus 5.5° (95% CI, 3.4–7.6) with the coronoid fractured (p = 0.1) (Fig. 3). Mean varus angle laxity with an intact radial head was 2.7° (95% CI, 1.3–4.1) versus 3.8° (95% CI, 2.3–5.3) after radial head resection (p = 0.4). The mean internal rotation angle laxity with the coronoid fractured was 5.4° (95% CI, 4.0–6.8) versus 1.8° (95% CI, 0.9–2.7) with the coronoid fixed (p < 0.0001). In the post hoc analysis, fixation of the coronoid with the radial head intact resulted in mean internal rotation angle laxity of 1.2° (95% CI, −0.2 to 2.5) versus 4.2° (95% CI, 1.2–7.3) with the coronoid fractured (p = 0.3) (Fig. 4). Fixation of the coronoid with the radial head resected resulted in mean internal rotation angle laxity of 2.2° (95% CI, −0.5 to 5.0) versus 5.6° (95% CI, 1.9–9.3) with the coronoid fractured (p = 0.3) (Fig. 4). Mean internal rotation angle laxity with an intact radial head was 2.7° (95% CI, 0.9–4.5) versus 3.9° (95% CI, 1.5–6.3) after radial head resection (p = 0.4).
Fig. 3.
Varus load and varus instability. The important role of the fractured and fixed coronoid is demonstrated under varus load.
Fig. 4.
With varus load, internal rotatory displacement is greatest in the absence of a radial head and simulated coronoid fracture. In this instance, the fixation of the coronoid fracture is the most important element in enhancing rotatory stability.
With valgus gravity stress, coronoid fixation improved valgus and external rotation stability slightly, but the radial head played a more important role in providing valgus stability. The mean valgus angle laxity with the coronoid fractured was 3.8° (95% CI, 1.8–5.8) versus 2.1° (95% CI, 1.0–3.1) with the coronoid fixed (p = 0.04). In the post hoc analysis, fixation of the coronoid with the radial head intact resulted in mean valgus angle laxity of 1.1° (95% CI, 0.3–1.9) versus 1.7° (95% CI, 0.7–2.6) with the coronoid fractured (p = 1.0). Fixation of the coronoid with the radial head resected resulted in mean valgus laxity of 5.1° (95% CI, 2.2–8.1) versus 9.1° (95% CI, 2.7–15.5) with the coronoid fractured (p = 0.2) (Fig. 5). Mean valgus angle laxity with an intact radial head was 1.4° (95% CI, 0.8–2.0) versus 7.1° (95% CI, 3.5–10.7) after radial head resection (p < 0.001). In the post hoc analysis, valgus laxity increased after resection of the radial head both with the coronoid fractured (mean, 1.7°; 95% CI, 0.7–2.6 to mean, 9.1°; 95% CI, 2.7–15.5; p < 0.001) and fixed (mean, 1.1°; 95% CI, 0.3–1.9 to mean, 5.1°; 95% CI, 2.2–8.1; p < 0.001) (Fig. 5). The mean external rotation angle laxity with the coronoid fractured was 2.1° (95% CI, 0.9–3.4) versus 0.8° (95% CI, 0.1–1.5) with the coronoid fixed (p = 0.04). In the post hoc analysis, fixation of the coronoid with the radial head intact resulted in mean external rotation angle laxity of 0.7° (95% CI, 0–1.4) versus 1.5° (95% CI, 0.8–2.1) with the coronoid fractured (p = 1.0) (Fig. 6). Fixation of the coronoid with the radial head resected resulted in mean external rotation angle laxity of 1.9° (95% CI, −0.3 to 4.0) versus 4.5° (95% CI, −0.1 to 9.2) with the coronoid fractured (p = 0.4) (Fig. 6). Mean external rotation angle laxity with an intact radial head was 1.1° (95% CI, 0.6–1.6) versus 3.2° (95% CI, 0.6–5.8) after radial head resection (p = 0.08).
Fig. 5.
Valgus load. The preeminent role of the radial head resisting valgus instability is demonstrated in this figure. Notice the relative insignificance of the coronoid fracture or its fixation.
Fig. 6.
External rotation deformity with valgus load again demonstrates the importance of the radial head. Slightly greater significance is demonstrated with coronoid fixation but this is minimal compared with the stabilizing effect of the radial head.
Discussion
Understanding the relative contributions of the articular elements of the elbow to stability is paramount in the decision-making process to treat elbow fracture-dislocations. The indications for coronoid fracture fixation continue to be debated, and the effect of coronoid deficiency on elbow stability may depend on the integrity of the remaining stabilizing structures. Repair of the LCL complex is now universally accepted in the surgical management of the so-called terrible triad [5]. Thus, we selected an experimental protocol with intact collateral ligaments. We aimed to describe the relative contributions to elbow stability of the intact radial head and a fracture affecting 50% of the coronoid as well as the effect of coronoid fracture fixation on restoring elbow stability.
We recognize that this biomechanical study had several limitations. Practical limits exist for the ability to test the large number of specimens that would be required to show statistical significance for small kinematic changes. Furthermore, our experimental protocol used repeated testing of these small numbers of specimens. However, small specimen number and repeated testing were accommodated by using statistical methods that allow for each elbow to serve as its own control. By showing the difference in these parameters, rather than absolute numbers, these concerns are mitigated to some extent. Next, we have chosen to analyze only a subset, as described previously, of the experimental conditions tested and modeled such that the effects of coronoid fixation and radial head resection can be clearly elucidated. This would seem reasonable because the ligaments are universally recognized to require repair; the status of and size of the coronoid fracture is the common clinical question. Finally, it should be recognized that the data presented here represent the elbow under the condition of simulated LCL repair. Our LCL-repaired condition consisted of lag screw fixation of the previously osteotomized LCL origin from the lateral epicondyle. Therefore, this repair technique did not simulate a clinical repair. However, like previous studies, our fixation did restore the kinematics to that of the intact elbow (see Supplementary Fig. S1) [1]. However, there were several strengths of the study. We were able to model a common clinical condition, transverse coronoid fractures of approximately 50% of the coronoid process, for which, at present, no clear management guidelines exist. To our knowledge, this is the first study to include varus-valgus and rotational kinematics data for transverse Type II coronoid fractures in terrible triad injuries before and after coronoid fracture fixation.
In the models for the injured elbow under varus gravity stress, there is a clear effect for coronoid fixation to improve both varus and internal rotation angular laxity, and we consider the effect size for varus (4.0° ± 0.6°) and internal rotation (3.6° ± 0.6°) angles to be of likely clinical significance. Although the post hoc comparisons with the radial head intact or resected did not reach statistical significance, this may be a Type II error because of the small sample size. This should be a subject of further investigation. On the other hand, the radial head offers no contribution to resist varus angulation or internal rotation during varus loading conditions. If the surgeon is in doubt about the stability of a coronoid fracture, examination of the elbow should assess elbow varus internal rotational stability under varus load. This may be attempted intraoperatively with the collateral ligaments temporarily stabilized.
In the models for the injured elbow under valgus gravity stress, the radial head is the dominant stabilizer (Figs. 5, 6), as has been demonstrated previously [6]. Similar to Pollock et al. [7], we found a very small but statistically significant effect of the coronoid under valgus load. Given the small effect sizes, fixation of a fracture involving 50% of the coronoid will likely have little additional effect on external rotation and valgus stability. This is consistent with the experimental observations of Jeon et al. [4]. In our model, the effects on elbow kinematics of transverse Type II coronoid fractures in conjunction with an absent radial head demonstrated the need for radial head restoration to resist valgus and external rotatory displacement. Thus, every effort should be made to reconstruct or replace the radial head in this setting. The relative stability of monopolar and bipolar radial head replacements in this setting is the subject of part two of this study.
Although this study investigates a difficult and complex injury, we have focused on the interaction of two components: status of a fractured and repaired 50% coronoid fracture and the presence or absence of a radial head. On the basis of this study, fixation of Type II coronoid fractures results in improved varus and internal rotatory stability of the elbow to near normal values. However, the determination of whether the coronoid must be fixed can be made after the radial head has been reliably fixed or replaced, the ligaments stabilized, and the elbow reexamined. Varus, internal rotatory instability should be specifically assessed. If stable, no fixation may be necessary; if unstable, then the coronoid must be fixed. Similarly, this study reinforces the essential requirement of a functional radiocapitellar joint to stabilize the elbow in valgus and external rotation.
Electronic supplementary material
Footnotes
Each author certifies that he or she, or a member of his or her immediate family, has no funding or commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request.
Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.
This work was performed at the Mayo Clinic, Rochester, MN, USA.
Contributor Information
Bernard F. Morrey, Email: morrey.bernard@mayo.edu.
Joaquin Sanchez-Sotelo, Email: sanchezsotelo.joaquin@mayo.edu.
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