Design and validation of an unconstrained loading system to measure the envelope of motion in the rabbit knee joint

Large Animal Models for Anterior Cruciate Ligament Research

Large animal (non-rodent mammal) models are commonly used in ACL research, but no species is currently considered the gold standard. Important considerations when selecting a large animal model include anatomical differences, the natural course of ACL pathology in that species, and biomechanical differences between humans and the chosen model. This article summarizes recent reports related to anatomy, pathology, and biomechanics of the ACL for large animal species (dog, goat, sheep, pig, and rabbit) commonly used in ACL research. Each species has unique features and benefits as well as potential drawbacks, which are highlighted in this review. This information may be useful in the selection process when designing future studies.

Rehabilitation of the medial- and lateral collateral ligament-deficient elbow: an in vitro biomechanical study

DESIGN

In vitro biomechanical research using an elbow motion simulator.

INTRODUCTION

The optimal rehabilitation of elbow dislocations with medial collateral ligament (MCL) and lateral collateral ligament (LCL) injuries has not been defined.

PURPOSE

To determine a safe rehabilitation protocol for elbow dislocations with MCL and LCL injuries.

METHODS

Eight cadaveric elbows underwent simulated active and passive motions with the arm in multiple orientations. Varus-valgus angulation and internal-external rotation of the ulna relative to the humerus were quantified for the intact joint and with injured MCL and LCL.

RESULTS

Active motion with injured MCL and LCL in the horizontal and vertical orientations resulted in kinematics similar to the intact elbow, whereas passive motion resulted in significant kinematic alterations. Marked elbow instability was noted in the varus and valgus orientations using both active and passive motion.

CONCLUSIONS

Elbows with MCL and LCL injuries should be rehabilitated using active motion in the horizontal or vertical orientations.

LEVEL OF EVIDENCE

Basic science research.

Reconstruction of the coronoid using an extended prosthesis: an in vitro biomechanical study

BACKGROUND

When repair of comminuted coronoid fractures is not possible, prosthetic replacement may restore elbow stability. The purpose of this biomechanical study was to determine whether a coronoid implant with an extended tip would improve elbow stability compared with an anatomic prosthesis in the setting of collateral ligament insufficiency.

MATERIALS AND METHODS

Passive elbow extension was performed in 7 cadaveric arms in the varus and valgus positions and active and passive extension in the horizontal position by use of an elbow motion simulator. Varus-valgus laxity of the ulna relative to the humerus was quantified with a tracking system with a native coronoid, a 40% coronoid deficiency, an anatomic prosthesis, and an extended prosthesis, with the collateral ligaments sectioned and repaired.

RESULTS

Laxity significantly increased after a 40% coronoid deficiency with both repaired and sectioned collateral ligaments (P ≤ .01). With the ligaments repaired, there was no significant difference in laxity between the native coronoid, the anatomic implant, or the extended implant. Ligament sectioning alone produced severe instability, with a mean laxity of 42.75° ± 11.54° (P < .01). With insufficient ligaments, the anatomic prosthesis produced no change in laxity compared with the native coronoid, whereas the extended implant significantly reduced laxity by 21.56° ± 17.70° (P = .02).

CONCLUSIONS

An anatomic coronoid implant with ligament repair restores stability to the coronoid-deficient elbow to intact levels. In the setting of ligament insufficiency, an extended implant improves stability relative to an anatomic implant, but the elbow remains significantly less stable than an intact elbow. Studies are needed to evaluate the feasibility of these designs.

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.

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.

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 effect of coronoid fractures on elbow kinematics and stability

BACKGROUND

Coronoid fractures often occur in the setting of more complex elbow trauma. Little is known about the influence of coronoid fracture size on elbow kinematics, particularly in the setting of concomitant ligament injuries. The purpose of this study was to determine the effect of coronoid fractures on elbow kinematics and stability in ligamentously intact and medial collateral ligament deficient elbows and to determine the effect of forearm position on elbow stability in the setting of coronoid fracture.

METHODS

Eight cadaveric arms were tested during simulated active dependent elbow motion and gravity-loaded passive elbow motion. Kinematic data were collected from an electromagnetic tracking system. The protocol was performed in ligament origin repaired and medial collateral ligament deficient elbows with radial head arthroplasty. Testing was carried out with the coronoid intact, and with 10% (Type I), 50% (Type II), and 90% (Type III) removed. Varus-valgus angulation of the ulna relative to the humerus and maximum varus-valgus laxity were measured.

FINDINGS

With repaired ligament origins and medial collateral ligament deficiency, there was increased varus angulation and increased maximum varus-valgus laxity following simulation of a Type II and Type III coronoid fracture. There was less kinematic change with the forearm in supination than in pronation.

INTERPRETATION

Elbow kinematics are altered with increasing coronoid fracture size. Repair of Type II and Type III coronoid fractures as well as lateral ligament repair is recommended where possible. Forearm supination may be considered during rehabilitation following coronoid repair. Valgus elbow positioning should be avoided if the medial collateral ligament is not repaired.