Distal radius fractures are the most common upper extremity injury, and are increasingly being treated surgically with pre-contoured volar-locking plates. These plates are favored for their low-profile template while allowing for rigid anatomic fixation of distal radius fractures. The geometry of the distal radius is extremely complex, and little evidence within the medical literature suggests that current implant designs are anatomically accurate. The main objective of this study is to determine if anatomic alignment of the distal radii corresponds accurately with modern volar-locking plate designs. Additionally, this study will examine sex-linked differences in morphology of the distal radius.

Segmented CT models of ten female cadaver (mean age, 88.7 ± 4.57 years, range, 82 – 97) arms, and ten male cadaver (mean age, 86 ± 3.59 years, range, 81 – 91) arms were created. Micro CT models were obtained for the DePuy Synthes 2.4mm Extra-articular (EA) Volar Distal Radius Plate (4-hole and 5-hole head), and 2.4mm LCP Volar Column (VC) Distal Radius Plate (8-hole and 9-hole head). Plates were placed onto the distal radii models in a 3D visualization software by a fellowship-trained orthopaedic hand surgeon. The percent contact, volar cortical angle (VCA), border and overlap of the watershed line (WSL) were measured.

Both sexes showed an increase in the average VCA measure from medial to lateral columns which was statistically significant. Female VCA ranged from 28 – 36 degrees, and 38 – 45 degrees for males. WSL overlap ranged from 0 – 34.7629% for all specimens without any statistical significance. The average border distance for females was 2.58571 mm, compared to 3.52411 mm for males, with EA plates having a larger border than VC plates. The border distances had statistically significant differences between the plate types, and was approaching significance between sexes. Lastly, a maximum percent contact of 21.966 % was observed in specimen F4 at a 0.3 mm threshold. No statistical significance between plate or sex populations was observed.

This study investigated the incoherency between the volar cortical angle of the distal radius, and the pre-contoured angle of volar locking plates. It was hypothesized that if the VCA measures between plate and bone were unequal then there would be an increase in watershed line overlap, and decrease in percent contact between the surfaces. Our results agreed with literature, indicating that the VCA of bone was larger than that of the EA and VC pre-contoured plates examined in this study.

With distal radius fracture incidences and prevalence on the rise for elderly female patients, it is a necessity that volar locking plates be re-designed to factor in anatomical features of individual patients with a particular focus on sex differences. New designs should focus on providing smaller head sizes that are more accurately tailored to the natural contours of the volar distal radius. It is recommended that future studies incorporate expertise from multiple surgeons to diversify and further understand plate placement strategies.

The role of anconeus in elbow stability has been a long-standing debate. Anatomical and electromyographic studies have suggested a potential role as a stabilizer. However, to our knowledge, no clinical or biomechanical studies have investigated its role in improving the stability of a lateral collateral ligament (LCL) deficient elbow.

Seven cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. An LCL injured model was created by sectioning of the common extensor origin, and the LCL. The anconeus tendon and its aponeurosis were sutured in a Krackow fashion and tensioned to 10N and 20N through a transosseous tunnel at its origin. Varus-valgus angles and ulnohumeral rotations were recorded using an electromagnetic tracking system during simulated active elbow flexion with the forearm pronated and supinated. During active motion, the injured model resulted in a significant increase in varus angulation (5.3°±2.9°, P=.0001 pronation, 3.5°±3.4°, P=.001 supination) and external rotation (ER) (8.6°±5.8°, P=.001 pronation, 7.1°±6.1°, P=.003 supination) of the ulnohumeral articulation compared to the control state (varus angle −2.8°±3.4° pronation, −3.3°±3.2° supination, ER angle 2.1°±5.6° pronation, 1.6°±5.8° supination).

Tensioning of the anconeus significantly decreased the varus angulation (−1.2°±4.5°, P=.006 for 10N in pronation, −3.9°±4°, P=.0001 for 20N in pronation, −4.3°±4°, P=.0001 for 10N in supination, −5.3°±4.2°, P=.0001 for 20N in supination) and ER angle (2.6°±4.5°, P=.008 for 10N in pronation, 0.3°±5°, P=.0001 for 20N in pronation, 0.1°±5.3°, P=.0001 for 10N in supination, −0.8°±5.3°, P=.0001 for 20N in supination) of the injured elbow. Comparing anconeus tensioning to the control state, there was no significant difference in varus-valgus angulation except with anconeus tensioning to 20N with the forearm in supination which resulted in less varus angulation (P=1 for 10N in pronation, P=.267 for 20N in pronation, P=.604 for 10N in supination, P=.030 for 20N in supination). Although there were statistically significant differences in ulnohumeral rotation between anconeus tensioning and the control state (except with anconeus tensioning to 10N with the forearm in pronation which was not significantly different), anconeus tensioning resulted in decreased external rotation angle compared to the control state (P=1 for 10N in pronation, P=.020 for 20N in pronation, P=.033 for 10N in supination, P=.001 for 20N in supination).

In the highly unstable varus elbow orientation, anconeus tensioning restores the in vitro stability of an LCL deficient elbow during simulated active motion with the forearm in both pronation and supination. Interestingly, there was a significant difference in varus-valgus angulation between 20N anconeus tensioning with the forearm supinated and the control state, with less varus angulation for the anconeus tensioning which suggests that loads less than 20N is sufficient to restore varus stability during active motion with the forearm supinated. Similarly, the significant difference observed in ulnohumeral rotation between anconeus tensioning and the control state suggests that lesser degrees of anconeus tensioning would be sufficient to restore the posterolateral instability of an LCL deficient elbow. These results may have several clinical implications such as a potential role for anconeus strengthening in managing symptomatic lateral elbow instability.

Previous biomechanical studies of lateral collateral ligament (LCL) injuries and their surgical repair, reconstruction and rehabilitation have primarily relied on gravity effects with the arm in the varus position. The application of torsional moments to the forearm manually in the laboratory is not reproducible, hence studies to date likely do not represent forces encountered clinically.

The aim of this investigation was to develop a new biomechanical testing model to quantify posterolateral stability of the elbow using an in vitro elbow motion simulator.

Six cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. A threaded screw was then inserted on the dorsal aspect of the proximal ulna and a weight hanger was used to suspend 400g, 600g, and 800g of weight from the screw head to allow torsional moments to be applied to the ulna. An LCL injured (LCLI) model was created by sectioning of the common extensor origin, and the LCL. Ulnohumeral rotation was recorded using an electromagnetic tracking system during simulated active and passive elbow flexion with the forearm pronated and supinated. A repeated measures analysis of variance was performed to compare elbow states (intact, LCLI, and LCLI with 400g, 600g, and 800g of weight).

During active motion, there was a significant difference between different elbow states (P=.001 pronation, P=.0001 supination). Post hoc analysis showed that the addition of weights did not significantly increase the external rotation (ER) of the ulnohumeral articulation (10°±7°, P=.268 400g, 10.5°±7.1°, P=.156 600g, 11°±7.2°, P=.111 800g) compared to the LCLI state (8.4°±6.4°) with the forearm pronated. However, with the forearm supinated, the addition of 800g of weight significantly increased the ER (9.2°±5.9°, P=.038) compared to the LCLI state (5.9°±5.5°) and the addition of 400g and 600g of weights approached significance (8.2°±5.7°, P=.083 400g, 8.7°±5.9°, P=.054 600g).

During passive motion, there was a significant difference between different elbow states (P=.0001 pronation, P=.0001 supination). Post hoc analysis showed that the addition of 600g and 800g but not 400g resulted in a significant increase in ER of the ulnohumeral articulation (9.3°±7.8°, P=.103 400g, 11.2°±6.2°, P=.004 600g, 12.7°±6.8°, P=.006 800g) compared to the LCLI state (3.7°±5.4°) with the forearm pronated. With the forearm supinated, the addition of 400g, 600g, and 800g significantly increased the ER (11.7°±6.7°, P=.031 400g, 13.5°±6.8°, P=.019 600g, 14.9°±6.9°, P=.024 800g) compared to the LCLI state (4.3°±6.6°).

This investigation confirms a novel biomechanical testing model for studying PLRI. Moreover, it demonstrates that the application of even small amounts of torsional moment on the forearm with the arm in the varus position exacerbates the rotational instability seen with the LCL deficient elbow. The effect of torsional loading was significantly worse with the forearm supinated and during passive elbow motion. This new model allows for a more provocative testing of elbow stability after LCL repair or reconstruction. Furthermore, this model will allow for smaller sample sizes to be used while still demonstrating clinically significant differences. Future biomechanical studies evaluating LCL injuries and their repair and rehabilitation should consider using this testing protocol.

Hinged elbow orthoses (HEO) are often used to allow protected motion of the unstable elbow. However, biomechanical studies have not shown HEO to improve the stability of a lateral collateral ligament (LCL) deficient elbow. This lack of effectiveness may be due to the straight hinge of current HEO designs which do not account for the native carrying angle of the elbow. The aim of this study was to determine the effectiveness of a custom-designed HEO with adjustable valgus angulation on stabilizing the LCL deficient elbow.

Eight cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. An LCL injured (LCLI) model was created by sectioning of the common extensor origin, and the LCL. The adjustable HEO was secured to the arm and its effect with 0°, 10°, and 20° (BR00, BR10, BR20) of valgus angulation was investigated. Varus-valgus angles and ulnohumeral rotations were recorded using an electromagnetic tracking system during simulated active elbow flexion with the forearm pronated and supinated. We examined 5 elbow states, intact, LCLI, BR00, BR10, BR20.

There were significant differences in varus and ER angulation between different elbow states with the forearm both pronated and supinated (P=0 for all). The LCLI state with or without the brace resulted in significant increases in varus angulation and ER of the ulnohumeral articulation compared to the intact state (P 0.05). The difference between each of the brace angles and the LCLI state ranged from 1.1° to 2.4° for varus angulation and 0.5° to 1.6° for ER.

Although there was a trend toward decreasing varus and external rotation angulation of the ulnohumeral articulation with the application of this adjustable HEO, none of the brace angles examined in this biomechanical investigation was able to fully restore the stability of the LCL deficient elbow. This lack of stabilizing effect may be due to the weight of the brace exerting unintentional varus and torsional forces on the unstable elbow. Previous investigations have shown that the varus arm position is highly unstable in the LCL deficient elbow. Our results demonstrate that application of an HEO with an adjustable carrying angle does not sufficiently stabilize the LCL deficient elbow in this highly unstable position and varus arm position should continue to be avoided in the rehabilitation programs of an LCL deficient elbow.

Distal radius fractures are the most common upper extremity fracture. The incidence is significantly higher in elderly females with osteoporotic bone. When surgery is indicated, volar locking plates (VLPs) allow for rigid fixation particularly in comminuted fractures with poor bone quality. Although numerous studies have shown the importance of plate placement to avoid soft tissue complications associated with volar plate fixation, there has been little evidence on the anatomic fit of current VLPs. Moreover, the effect of gender differences in distal radius morphology on anatomic fitting of VLPs has not been studied. The aim of this study was to evaluate the gender difference in distal radius morphology and the accuracy of the fit of a current VLP to CT-based distal radius models.

Segmented CT models of ten female (mean age, 89 ± 5 years), and ten male (mean age, 86 ± 4 years) cadaveric wrists were obtained. Micro-CT models of the DePuy-Synthes 4-hole extra-articular (EA) and 8-hole volar column (VC) distal radius VLPs were created. A 3D visualization software was used to simulate appropriate plate placement on to the distal radius models by a fellowship-trained hand surgeon. Volar cortical angles (VCA) of the medial, middle and lateral portion of the distal radius were measured and compared between genders. The accuracy of the fit of the two VLP designs were quantified using the percentage of the watershed line (WSL) overlapped by the plate (WSL overlap), the distance between the WSL and the most distal aspect of the posterior plate (prominence distance) and the percentage of contact between the plate and bone.

There were statistically significant gender differences in medial, middle and lateral VCAs (p=.003 medial, p=.0001 middle, p=.002 lateral). VCA ranged from 28° to 36° in females and from 38° to 45° in males. The WSL overlap did not show statistically significant gender differences (male: 5.9%, female: 13.6%, p=.174). However, the difference in prominence distance between different genders approached statistical significance (male: 3.5mm, female: 2.6mm, p=.087). Contact mapping between the plate and bone did not demonstrate a perfect contact in any of our specimens. Thus, contact measurements were categorized into 0.1mm, 0.2mm, and 0.3mm threshold contacts. There were no statistically significant gender differences in any of the threshold categories (0.1mm: p=.84, 0.2mm: p=.97, 0.3mm: p=.99).

Our results confirm that there are gender differences in distal radius morphology. Current plate designs incorporate a VCA of 25° which does not match the native VCA of the distal radius in males or females. Although the difference in prominence distance approached statistical significance, there were no statistically significant gender differences in the WSL overlap or the contact threshold values. This lack of statistical significance may be related to the small sample size. This study proposes novel methods of assessing the anatomic fit of current VLPs in a 3D CT-based model that may be used in future studies with a larger sample size. Moreover, this study demonstrated the importance of considering gender differences in distal radius morphology in the design of future generations of implants.