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

The effect of suture fixation of type I coronoid fractures on the kinematics and stability of the elbow with and without medial collateral ligament repair

The objective of this study was to determine the effect of suture repair of type 1 coronoid fractures on elbow kinematics in ligamentously intact and medial collateral ligament (MCL)-deficient elbows. Cadaveric testing was performed in stable and MCL-deficient elbows with radial head arthroplasty and with the coronoid intact, with the coronoid fractured, and after suture repair. Ulna versus humerus angulation was measured during active motion. Varus and valgus motion pathways were measured during passive gravity-loaded flexion. With intact ligaments, there was a small increase in valgus angulation after a type 1 fracture that was not corrected with suture fixation. With MCL deficiency, there was no change in kinematics regardless of coronoid status. Type 1 coronoid fractures cause only small changes in elbow kinematics that are not corrected with suture repair. MCL repair, rather than type 1 coronoid fixation, should be considered if the elbow remains unstable after radial head repair or replacement and lateral ligament repair.

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.

The effect of radial head fracture size on elbow kinematics and stability

This study determined the effect of radial head fracture size and ligament injury on elbow kinematics. Eight cadaveric upper extremities were studied in an in vitro elbow simulator. Testing was performed with ligaments intact, with the medial collateral (MCL) or lateral collateral (LCL) ligament detached, and with both the MCL and LCL detached. Thirty degree wedges were sequentially removed from the anterolateral radial head up to 120 degrees . Valgus angulation and external rotation of the ulna relative to the humerus were determined for passive motion, active motion, and pivot shift testing with the arm in a vertical (dependent) orientation. Maximum varus-valgus laxity was calculated from measurements of varus and valgus angulation with the arm in horizontal gravity-loaded positions. No effect of increasing radial head fracture size was observed on valgus angulation during passive and active motion in the dependent position. In supination, external rotation increased with increasing fracture size during passive motion with LCL deficiency and both MCL and LCL deficiency. With intact ligaments, maximum varus-valgus laxity increased with increasing radial head fracture size. With ligament disruption, elbows were grossly unstable, and no effect of increasing radial head fracture size occurred. During pivot shift testing, performed with the ligaments intact, subtle instability was noted after resection of one-third of the radial head. In this in vitro biomechanical study, small subtle effects of radial head fracture size on elbow kinematics and stability were seen in both the ligament intact and ligament deficient elbows. These data suggest that fixation of displaced radial head fractures less than or equal to one-third of the articular diameter may have some biomechanical advantages; however, clinical correlation is required.

Kinematics and stability of the fractured and implant-reconstructed radial head

Controversy exists as to the optimal management of radial head fractures. Biomechanical studies have been conducted to quantify elbow stability for simulated wedge fractures, head excision, and head replacement, with and without the integrity of the collateral ligaments. Our in vitro studies have demonstrated that in the ligamentously intact elbow, kinematics and stability are slightly altered with simulated depressed wedge fractures up to 120 degrees of the radial head, markedly altered with head resection, and improved after radial head replacement. Radial head excision decreases elbow stability in the ligament-deficient elbow, and radial head replacement improves stability similar to that of the native radial head. The ligaments have the most marked influence on stability, particularly when the upper limb is positioned such that valgus and varus gravity loads are applied to the elbow. Whereas the radial head acts as a secondary stabilizer to the collateral ligaments with the arm in these positions, its relative role is greater when the arm is in the dependent position and elbow flexion is simulated, particularly in extension. Further studies are needed to elucidate the complex interaction of the radial head with the capitellum, the ulnohumeral joint, and the ligamentous structures for different activities of daily living.

Soft-tissue stabilizers of the elbow

Elbow stability is afforded by both static and dynamic structures. Static structures include the complex bony architecture and soft-tissue stabilizers. Knowledge of the anatomy and biomechanics of the stabilizers is important to understand, diagnose, and treat elbow instability. Bony anatomy, detailed elsewhere, contributes to the inherent stability of the elbow. The static soft-tissue stabilizers consist of the anterior and posterior joint capsule and both medial and lateral collateral ligament complexes. Additional stability is conferred by dynamic structures--the muscles crossing the elbow joint.

Coronal shear fractures of the distal humerus: the capitellum and trochlea

Fractures of the capitellum and trochlea are uncommon and multiple options have been advocated for the treatment of this injury. A single management technique has not emerged as the superior technique, and a complement of interventions is necessary to manage the continuum of injuries that can be observed. In general, open reduction and internal fixation is advocated for healthy and active patients with satisfactory bone quality to allow for the insertion of stable fixation. In the geriatric population, total elbow arthroplasty may emerge as the treatment of choice particularly for the more comminuted fracture patterns. Postoperative rehabilitation is important and is guided by fracture stability, ligament integrity, and the ability of the patient to cooperate with the treatment protocol. Gratifying results can be achieved in most patients with even the most complex injuries.

Rehabilitation of elbow trauma

The rehabilitation of elbow trauma presents numerous challenges. Involvement of the osseous structures, compromise of the ligamentous stability, and loss of the soft tissue excursion necessary for elbow motion and function require due consideration during the treatment of elbow joint injuries. Stiffness of the elbow joint following trauma is common. This stiffness is caused by extrinsic and intrinsic factors. Contractures of the elbow joint develop as a result of contractures of the joint capsule, ligamentous structures, musculotendinous structures, intra-articular adhesions,and ectopic ossification. Early mobilization and splinting of the elbow following injury, within a safe arc of elbow motion, makes the elbow joint more compliant to the rehabilitative techniques outlined. Understanding the details of elbow anatomy, biomechanics, trauma, and surgical procedures for repairing the osseous and the ligamentous structures thus are the key factors in rehabilitating the elbow joint successfully.

Management of comminuted radial head fractures with replacement arthroplasty

Radial head arthroplasty is indicated for displaced comminuted radial head fractures that cannot be managed reliably with open reduction and internal fixation and that have an associated elbow dislocation. Replacement also is indicated in patients with comminuted radial head fractures that have or are likely to have a disruption of the medial col-lateral, lateral collateral, or interosseous ligaments. Biomechanical studies have demonstrated that metallic implants restore elbow stability similar to the native radial head. The early and midterm clinical experience with metallic radial head arthroplasty has been encouraging relative to earlier reports with silicone devices. Newer modular designs incorporate improved sizing to better reproduce the anatomy of the proximal radius and are easier to insert intraoperatively.

The effect of radial head excision and arthroplasty on elbow kinematics and stability

BACKGROUND

Radial head fractures are common injuries. Comminuted radial head fractures often are treated with radial head excision with or without radial head arthroplasty. The purpose of the present study was to determine the effect of radial head excision and arthroplasty on the kinematics and stability of elbows with intact and disrupted ligaments. We hypothesized that elbow kinematics and stability would be (1) altered after radial head excision in elbows with intact and disrupted ligaments, (2) restored after radial head arthroplasty in elbows with intact ligaments, and (3) partially restored after radial head arthroplasty in elbows with disrupted ligaments.

METHODS

Eight cadaveric upper extremities were studied in an in vitro elbow simulator that employed computer-controlled actuators to govern tendon-loading. Testing was performed in stable, medial collateral ligament-deficient, and lateral collateral ligament-deficient elbows with the radial head intact, with the radial head excised, and after radial head arthroplasty. Valgus angulation and rotational kinematics were determined during passive and simulated active motion with the arm dependent. Maximum varus-valgus laxity was measured with the arm in a gravity-loaded position.

RESULTS

In specimens with intact ligaments, elbow kinematics were altered and varus-valgus laxity was increased after radial head excision and both were corrected after radial head arthroplasty. In specimens with disrupted ligaments, elbow kinematics were altered after radial head excision and were similar to those observed in specimens with a native radial head after radial head arthroplasty. Varus-valgus laxity was increased after ligament disruption and was further increased after radial head excision. Varus-valgus laxity was corrected after radial head arthroplasty and ligament repair; however, it was not corrected after radial head arthroplasty without ligament repair.

CONCLUSIONS

Radial head excision causes altered elbow kinematics and increased laxity. The kinematics and laxity of stable elbows after radial head arthroplasty are similar to those of elbows with a native radial head. However, radial head arthroplasty alone may be insufficient for the treatment of complex fractures that are associated with damage to the collateral ligaments as arthroplasty alone does not restore stability to elbows with ligament injuries.

The medial collateral ligament of the elbow is not isometric: an in vitro biomechanical study

BACKGROUND

The anterior bundle of the medial collateral ligament (AMCL) of the elbow has been shown to be the most important valgus stabilizer of the elbow. However, the isometry of this band has not been quantified.

HYPOTHESIS

Isometric fibers exist within the AMCL, and these fibers are located within its central region.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve cadaveric elbow specimens were mounted in a testing apparatus in a valgus gravity-loaded orientation. Passive supinated flexion was performed and the motion recorded using an electromagnetic tracking device. Hundreds of attachment points for the AMCL of the elbow were recorded on the medial epicondyle and ulna. The overall change in length between each point on the ulna to every humeral point, throughout the arc of motion, was quantified (DeltaL = Lmax - Lmin). The locations of the smallest DeltaL values were determined relative to the attachment site of the AMCL on the medial epicondyle.

RESULTS

True isometry was not found throughout the arc of flexion. The smallest DeltaL values averaged 2.8 +/- 1.2 mm (range: 0.7 mm to 5.2 mm). Isometric fibers do not exist within the AMCL; however, "nearly" isometric areas are located on the lateral aspect of the attachment site of the AMCL on the medial epicondyle, near the anatomic axis of rotation.

CONCLUSIONS

We postulate that these nearly isometric areas would be the most ideal location for graft attachment during reconstruction of the AMCL.

Application of screw displacement axes to quantify elbow instability

OBJECTIVES

To determine if screw displacement axis patterns describing elbow joint motion: (1) change after ligament transection in vitro; (2) can reflect subtle changes in stability as a function of forearm position; (3) can reflect dynamic stabilization of the ligament insufficient elbow provided by muscle activity.Design. An in vitro kinematic study of eighteen cadaveric specimens tested in a joint simulator.

BACKGROUND

In the elbow joint, screw displacement axes have been employed for proper positioning and design of endoprostheses. The effect of instability on screw displacement axes has not been previously reported.

METHODS

Passive and simulated active flexion, with the forearm maintained in both pronation and supination, was performed on eighteen intact and ligament insufficient elbows. Instability was produced by transection of the medial collateral or lateral collateral ligament complexes. Kinematics were recorded using an electromagnetic tracking device and analyzed with a repeated measures design.

RESULTS

During passive motion, division of either ligament caused deviation of screw displacement axes compared to the intact state (P<0.05). Transection of the medial/lateral collateral ligament generated greater instability with the forearm maintained in pronation/supination compared to supination/pronation (P<0.05). Muscle activation increased stability similar to the intact state (P>0.05).

CONCLUSIONS

These results are consistent with observations determined using traditional kinematic descriptors. Screw displacement axes can readily detect changes in stability due to ligament sectioning.

RELEVANCE

Clinicians can employ the screw displacement axis technique as a succinct descriptor of motion to readily detect elbow instability.

Variability and repeatability of the flexion axis at the ulnohumeral joint

Previous investigations have implemented screw displacement axes (SDAs) to define the elbow flexion axis for proper positioning of dynamic external fixators and endoprostheses. However, results across studies vary, which may be attributed to forearm position (pronation-supination) during elbow motion, or the mode of loading (active/passive) employed to generate flexion. Therefore, the aim of this study was to determine the influence of the flexion mode employed and forearm position on individual variation and repeatability of SDAs throughout elbow flexion. With the forearm pronated, the location of the average SDA was similar whether elbow flexion was generated actively or passively. In contrast, with the forearm supinated, the average SDA was 2.4 degrees and 1.4 degrees more valgus (p<0.001) and internally rotated (p<0.001), respectively, and positioned 1.6 and 0.8 mm further proximally (p=0.002) and anteriorly (p=0.005) relative to the capitellum, respectively, during active compared to passive flexion. During active flexion, the location of the average SDA was independent of forearm position. Conversely, during passive flexion, the average SDA angle was 3.4 degrees and 1.0 degrees more valgus (p<0.001) and internally rotated (p=0.009), respectively, and 1.7 and 0.7 mm more proximal (p<0.001) and anterior (p=0.001) relative to the capitellum, respectively, with the forearm held pronated rather than supinated. SDAs calculated throughout flexion deviated from the average SDA in both orientation and position, demonstrating that elbow flexion behaves similar to a loose hinge joint. These factors suggest that to encompass the location of all SDAs throughout flexion, and therefore properly mimic normal elbow joint motion, an endoprosthesis should be modeled similar to a "loose" rather than "pure" hinge joint. This would allow for dependencies of SDA angulation on forearm position and muscle activation, and slight freedom of movement to account for variances in SDA location. These factors should also be considered during soft-tissue reconstructions.