Colin P. McDonald

The effect of anteromedial facet fractures of the coronoid and lateral collateral ligament injury on elbow stability and kinematics.

BACKGROUND It is postulated that fractures of the anteromedial facet of the coronoid process and avulsion of the lateral collateral ligament lead to posteromedial subluxation and arthritis of the elbow. It is not clear which injuries require internal fixation and whether repair of the lateral collateral ligament is sufficient. We hypothesized that increasing sizes and subtypes of anteromedial facet fractures cause increasing instability and that isolated lateral collateral ligament repair without fracture fixation would restore elbow stability in the presence of small subtype-I fractures. METHODS Ten fresh-frozen cadaveric arms from donors with a mean age of 66.3 years at the time of death were used in this biomechanical study. Passive elbow flexion was performed with the plane of flexion oriented horizontally to achieve varus and valgus gravitational loading. An in vitro unconstrained elbow-motion simulator was used to simulate active elbow flexion in the vertical position. Varus-valgus angle and internal-external rotational kinematics were recorded with use of an electromagnetic tracking system. Testing was repeated with the coronoid intact and with subtype-I, subtype-II, and subtype-III fractures. Instability was defined as an alteration in varus-valgus angle and/or in internal-external rotation of the elbow. All six coronoid states were tested with the lateral collateral ligament detached and after repair. RESULTS In the vertical position, the kinematics of subtype-I and subtype-II anteromedial coronoid fractures with the lateral collateral ligament repaired were similar to those of the intact elbow. In the varus position, the kinematics of 2.5-mm subtype-I fractures with the lateral collateral ligament repaired were similar to those of the intact elbow. However, 5-mm fractures demonstrated a mean (and standard deviation) of 6.2 degrees +/- 4.5 degrees of internal rotation compared with a mean of 3.3 degrees +/- 3.1 degrees of external rotation in the intact elbow (p < 0.05). In the varus position, subtype-II 2.5-mm fractures with the lateral collateral ligament repaired demonstrated increased internal rotation (mean, 7.0 degrees +/- 4.5 degrees; p < 0.005). Subtype-II 5-mm fractures demonstrated instability in both the varus and valgus positions (p < 0.05). Subtype-III fractures with the lateral collateral ligament repaired were unstable in all three testing positions (p < 0.05). CONCLUSIONS This study suggests that the size of the anteromedial coronoid fracture fragment affects elbow kinematics, particularly in varus stress. The size of an anteromedial coronoid fracture and the presence of concomitant ligament injuries may be important determinants of the need for open reduction and internal fixation.

Effect of coronal shear fractures of the distal humerus on elbow kinematics and stability

BACKGROUND Coronal shear fractures of the distal humerus can include some or all of the cartilaginous and bony surface. Fixation is preferred, but severe comminution, nonunion, and avascular necrosis may mandate excision. The amount of distal humerus that is safe to excise is unknown. This study examined the effect of excision of the capitellum and trochlea on elbow kinematics and stability with intact collateral ligaments. METHODS Eight cadaveric arms were mounted in an upper extremity joint testing system. Electromagnetic receivers on the radius and ulna enabled quantification of ulnohumeral and radiocapitellar kinematics. The distal humeral articular surface was sequentially excised to replicate clinically relevant coronal shear fractures, leaving the collateral ligaments undisturbed. The arms underwent simulated active flexion in vertical and valgus-loaded positions, and passive forearm rotation in the vertical position. RESULTS In the vertical position, sequential excision of the articular surface increased valgus angulation during active flexion (P < or = .04), and excision of the entire articular surface increased ulnar external rotation compared to the intact elbow (P < or = .02). In the valgus position, excisions involving the trochlea increased valgus angulation for active flexion (P < or = .04). The radial head moved distal, posterior, and medial on the capitellum with some or all of the trochlea excised (P < or = .02). DISCUSSION While the capitellum alone does not contribute to elbow stability, the trochlea has an important role. Excision of the trochlea resulted in multiplanar instability of the ulnohumeral and radiocapitellar joints. Therefore, excision of an irreparable capitellum fracture may be considered if collateral ligaments are intact, while excision of some or all of the trochlea may not.

Contribution of the Olecranon to Elbow Stability: An in Vitro Biomechanical Study

BACKGROUND The amount of the olecranon that can be removed without substantially affecting the kinematics and stability of the elbow is controversial. The purpose of this study was to determine the effect of serial resections of the olecranon on elbow kinematics and stability. METHODS Eight fresh, previously frozen cadaver arms were mounted in an in vitro motion simulator, and kinematic data were obtained with use of an electromagnetic tracking system for active and passive motion. Flexion was studied in the varus, valgus, horizontal, and dependent positions. Custom-written three-dimensional computer navigation software was utilized to guide serial resection of the olecranon in 12.5% increments from 0% to 100%. A traditional triceps advancement repair was performed following each resection. Flexion angle, amount of olecranon resection, and active and passive motion measurements were compared. RESULTS Serial resection of the olecranon resulted in a significant increase in varus-valgus angulation with the arm in the varus (p < 0.04) and valgus (p = 0.01) orientations. Ulnohumeral rotation significantly increased in the varus (p < 0.001) and valgus (p < 0.007) orientations. Angular (p = 0.02) and rotational (p < 0.001) kinematics were greater with passive compared with active motion. There was no difference in elbow kinematics following olecranon resection with the arm positioned in the horizontal and dependent positions. CONCLUSIONS Valgus-varus angulation and ulnohumeral rotation progressively increase with sequential excision of up to 75% of the olecranon. Elbow stability is progressively lost with sequential excision, with gross instability noted at resection of > or = 87.5% of the olecranon.

Effect of the Posterior Bundle of the Medial Collateral Ligament on Elbow Stability

PURPOSE The role of the posterior bundle of the medial collateral ligament in stability of the elbow remains poorly defined. The purpose of this study was to determine the effect of sectioning the posterior bundle of the medial collateral ligament on the stability of the elbow. METHODS Varus and valgus gravity-loaded passive motion and simulated active vertical motion were performed on 11 cadaveric arms using an in vitro elbow motion simulator. Varus/valgus angle and internal/external rotation of the ulna with respect to the humerus were recorded using an electromagnetic tracking system in varus, valgus, and vertical orientations. Testing was performed on the intact elbow and after sectioning of the posterior bundle of the medial collateral ligament. RESULTS With active flexion in the vertical position, the varus/valgus kinematics were unchanged after sectioning of the posterior bundle of the medial collateral ligament. However, in pronation, there was an increase in internal rotation after sectioning of the posterior bundle of the medial collateral ligament compared with that of the intact elbow. This rotational difference was not detected with the forearm in supination. During supinated passive flexion in the varus position, sectioning of the posterior bundle of the medial collateral ligament resulted in increased varus angulation at all flexion angles. In pronation, varus angulation and internal rotation both increased. In supination, sectioning of the posterior bundle of the medial collateral ligament had no effect on maximum varus-valgus laxity or maximum internal rotation. However, in pronation, the maximum varus-valgus laxity increased by 3.5 degrees (30%) and maximum internal rotation increased by 1.0 degrees (29%). CONCLUSIONS These results indicate that isolated sectioning of the posterior bundle of the medial collateral ligament causes a small increase in varus angulation and internal rotation during both passive varus and active vertical flexion. This study suggests that isolated sectioning of the posterior bundle of the medial collateral ligament may not be completely benign and may contribute to varus and rotation instability of the elbow. In patients with insufficiency of the posterior bundle of the medial collateral ligament, appropriate rehabilitation protocols (avoiding forearm pronation and shoulder abduction) should be followed when other injuries permit.

The influence of type II coronoid fractures, collateral ligament injuries, and surgical repair on the kinematics and stability of the elbow: An in vitro biomechanical study

PURPOSE This study determined whether elbow stability could be restored with open reduction and internal fixation (ORIF) of type II coronoid fractures and evaluated the role of collateral ligament repair. METHODS Passive varus and valgus and simulated active vertical motion were performed using an in vitro elbow motion simulator. Varus/valgus angle and internal/external rotation were measured with the coronoid intact, with 50% removed, and after ORIF. Testing was performed with the collateral ligaments detached and repaired. RESULTS Vertical: stability was normal when both the lateral collateral ligament (LCL) and medial collateral ligament (MCL) were repaired, irrespective of the coronoid state. Kinematics were altered with a repaired LCL, incompetent MCL, and type II coronoid fracture (P < .05). Varus: LCL repair restored coronal stability but did not restore internal rotation (P < .05). CONCLUSIONS These findings suggest that repair of type II coronoid fractures and injured collateral ligaments should be performed where possible. Over-tensioning the LCL, in the setting of MCL and coronoid deficiency, may contribute to instability.

Image-based navigation improves the positioning of the humeral component in total elbow arthroplasty.

HYPOTHESIS Implant alignment in total elbow arthroplasty (TEA) is a challenging and error-prone process using conventional techniques. Identification of the flexion-extension (FE) axis is further complicated for situations of bone loss. This study evaluated the accuracy of humeral component alignment in TEA. We hypothesized that an image-based navigation system would improve humeral component positioning, with navigational errors less than or approaching 2.0 mm and 2.0 degrees . MATERIALS AND METHODS Implantation of a modified commercial TEA humeral component was performed with and without navigation on 11 cadaveric distal humeri. Navigated alignment was based on positioning the humeral component with the aid of a computed tomography (CT)-based preoperative plan registered to landmarks on the distal humerus. Alignment was performed under 2 scenarios of bone quality: (1) an intact distal humerus, and (2) a distal humerus without articular landmarks. RESULTS Navigation significantly improved implant alignment accuracy (P < .001). Navigated implant alignment was 1.2 +/- 0.3 mm in translation and 1.3 degrees +/- 0.3 degrees in rotation for the intact scenario. For the bone loss scenario, navigated alignment error was 1.1 +/- 0.5 mm and 2.0 degrees +/- 1.3 degrees . Non-navigated alignment was 3.1 +/- 1.3 mm and 5.0 degrees +/- 3.8 degrees for the intact scenario and 3.0 +/- 1.6 mm and 12.2 degrees +/- 3.3 degrees for the bone loss scenario. DISCUSSION Image-based navigation improves the accuracy and reproducibility of humeral component placement in TEA. Implant alignment errors for the navigated alignments were below the target of 2.0 degrees and 2 mm that is considered standard for most navigation systems. Non-navigated implant alignment error was significantly greater for the bone loss scenario compared with the intact scenario. CONCLUSIONS Implant malalignment may increase the likelihood of early implant wear, instability, and loosening. Improved implant positioning will likely lead to fewer complications and greater prosthesis longevity.

A morphological analysis of the humeral capitellum with an interest in prosthesis design

INTRODUCTION Although interest in capitellar arthroplasty is increasing, the morphology of the capitellum has not been fully characterized. Our purpose was to quantify the anthropometric features of the capitellum with an interest in arthroplasty design. We hypothesized that the shape is more complex than originally believed, and cannot be accurately modeled as a spherical structure. METHODS Fifty cadaveric human elbows underwent helical computer tomography scans. After reconstruction and establishment of a coordinate system for the distal humerus, circle-fits were applied to each of the 1-mm-thick slices. Sagittal radii of curvature were calculated every 10° of flexion around each circle (0-130° of flexion). A single transverse radius was calculated at 60° of flexion. The surface of the capitellum was described by sagittal and transverse radii of curvature and the footprint by height and width. These pairs of parameters were correlated to determine their strength of association. RESULTS The average height was 23.2 ± 2.9 mm (range, 18.3-29.5), while the average width was 13.9 ± 2.3 (range, 9-19). The sagittal radius of curvature was 11.6 ± 1.4 mm (range, 8.7-14.8), and the transverse radius was 14.0 ± 3.0 mm (range, 9.6-20.9). Correlations of height and width and sagittal and transverse radii were significant (R = .547, .705) (P < .01). Sagittal and transverse radii and height and width were significantly different (P < .001 for each pair). CONCLUSION The capitellum does not have a spherical surface or a circular footprint. There is substantial variability in the relationship between the height and width, and between the surface radii, that may be difficult to replicate with an off-the-shelf implant.

Computer assisted surgery of the distal humerus can employ contralateral images for pre-operative planning, registration, and surgical intervention

BACKGROUND Bone loss at the distal humerus can lead to errors in the identification of the elbows flexion-extension axis. Referencing the anatomy of the contralateral (uninjured) elbow may prove beneficial in accurately defining this axis. The objective of this study was to compare distal humeral morphology between paired specimens and determine whether geometric differences exist. METHODS Medical CT images of 25 paired, dry cadaveric, distal humeri were acquired and a range of anatomic characteristics were measured, following registration of each pair to a common coordinate system. RESULTS The anthropometric features of the distal humerus were similar from side-to-side, with differences on the order of 1.0 degrees and 0.5 mm. CONCLUSIONS Preoperative imaging of the contralateral normal elbow may be employed in patients with peri-articular bone loss, where referencing anatomic landmarks of the injured side is not possible.

Development of an image-based technique to examine joint congruency at the elbow

Identifying joint contact in articular joints is important for both the biomechanical investigation of joint mechanics and the study of osteoarthritis. The purpose of this study is to develop a proximity mapping technique to non-invasively determine joint congruency, as a surrogate of joint contact. To illustrate the capabilities of this algorithm, a cadaveric upper extremity was positioned at varying degrees of elbow flexion. This technique was validated using a gold standard experimental casting technique. The pattern of the cast showed an excellent agreement with the generated proximity map using the inter-bone distance algorithm. The results from this study agree with the results of previous studies examining joint contact at the elbow both in the location and in the tracking of the joint contact throughout elbow flexion. Ultimately, this technique will lead to an increased understanding of the effect of malalignment and instability of the joint on contact mechanics.

Stem abutment affects alignment of the humeral component in computer-assisted elbow arthroplasty

OBJECTIVES AND HYPOTHESIS The humeral component in total elbow arthroplasty has limited geometric modularity, and the extent to which this affects accurate positioning is unknown. The objectives of this study were to (1) validate the accuracy of a computer-assisted implant alignment technique, and (2) identify variations in distal humeral morphology that affected computer-assisted implant alignment. This was achieved by implanting both an unmodified humeral component and an implant with a reduced stem using computer assistance. We hypothesized that implantation of a humeral component with a reduced stem length would be more accurate than implantation of the standard length stem. In addition, we hypothesized that the variation in flexion-extension (FE) varus-valgus angulation would significantly affect computer-assisted implant alignment. MATERIALS AND METHODS Computer-assisted alignment of the implant articulating axis with the humeral FE axis was performed on 13 cadaveric humeri for both the regular and modified humeral component. Navigation was based on alignment of the prosthesis with a preoperative plan and registration of this plan to the humerus. RESULTS Implant alignment was significantly improved for the reduced stem. Alignment error of the reduced stem averaged 1.3 ± 0.5 mm in translation and 1.2° ± 0.4° in rotation, compared with 1.9 ± 1.1 mm and 3.6° ± 2.1° for the regular stem. Humeral varus-valgus angulation significantly affected alignment of the unmodified stem. DISCUSSION A humeral component with a fixed valgus angulation cannot be accurately positioned in a consistent fashion without sacrificing alignment of the FE axis. Improved accuracy of implant placement can be achieved by introducing a family of humeral components, with 3 valgus angulations of 0°, 4° and 8°.