Patricia G. Neale

Detrimental Effects of Overstuffing or Understuffing with a Radial Head Replacement in the Medial Collateral-Ligament Deficient Elbow

BACKGROUND Comminuted radial head fractures associated with an injury of the medial collateral ligament can be treated with a radial head implant. We hypothesized that lengthening and shortening of the radial neck would alter the kinematics and the pressure through the radiocapitellar joint in the medial collateral ligament-deficient elbow. METHODS The effects of lengthening (2.5 and 5 mm) and shortening (2.5 and 5 mm) of the radial neck were assessed in six human cadaveric upper extremities in which the medial collateral ligament had been surgically released. The three-dimensional spatial orientation of the ulna was recorded during simulated active motion from extension to flexion. Total varus-valgus laxity and ulnar rotation were measured. Radiocapitellar joint pressure was assessed with use of pressure-sensitive film. RESULTS Radial neck lengthening or shortening of >/=2.5 mm significantly changed the kinematics in the medial collateral ligament-deficient elbow. Lengthening caused a significant decrease (p < 0.05) in varus-valgus laxity and ulnar rotation (p < 0.05), with the ulna tracking in varus and external rotation. Shortening caused a significant increase in varus-valgus laxity (p < 0.05) and ulnar rotation (p < 0.05), with the ulna tracking in valgus and internal rotation. The pressure on the radiocapitellar joint was significantly increased after 2.5 mm of lengthening. CONCLUSIONS This study suggests that accurate restoration of radial length is important and that axial understuffing or overstuffing of the radiohumeral joint by >/=2.5 mm alters both elbow kinematics and radiocapitellar pressure. CLINICAL RELEVANCE This in vitro cadaver study indicates that a radial head replacement should be performed with the same level of concern for accuracy and reproducibility of component position and orientation as is appropriate with any other prosthesis.

Contribution of monoblock and bipolar radial head prostheses to valgus stability of the elbow

Background: The purpose of this study was to evaluate the stabilizing effect of radial head replacement in cadaver elbows with a deficient medial collateral ligament. Methods: Passive elbow flexion with the forearm in neutral rotation and in 80° of pronation and supination was performed under valgus and varus loads (1) in intact elbows, (2) after a surgical approach (lateral epicondylar osteotomy of the distal part of the humerus), (3) after release of the anterior bundle of the medial collateral ligament, (4) after release of the anterior bundle of the medial collateral ligament and resection of the radial head, and (5) after subsequent replacement of the radial head with each of three different types of radial head prostheses (a Wright monoblock titanium implant, a KPS bipolar Vitallium [cobalt-chromium]-polyethylene implant, and a Judet bipolar Vitallium-polyethylene-Vitallium implant) in the same cadaver elbow. Total valgus elbow laxity was quantified with use of an electromagnetic tracking device. Results: The mean valgus laxity changed significantly (p < 0.001) as a factor of constraint alteration. The greatest laxity was observed after release of the medial collateral ligament together with resection of the radial head (11.1° ± 5.6°). Less laxity was seen following release of the medial collateral ligament alone (6.8° ± 3.4°), and the least laxity was seen in the intact state (3.4° ± 1.6°). Forearm rotation had a significant effect (p = 0.003) on valgus laxity throughout the range of flexion. The laxity was always greater in pronation than it was in neutral rotation or in supination. The mean valgus laxity values for the elbows with a deficient medial collateral ligament and an implant were significantly greater than those for the medial collateral ligament-deficient elbows before radial head resection (p < 0.05). The implants all performed similarly except in neutral forearm rotation, in which the elbow laxity associated with the Judet implant was significantly greater than that associated with the other two implants. Conclusions and Clinical Relevance: This study showed that a bipolar radial head prosthesis can be as effective as a solid monoblock prosthesis in restoring valgus stability in a medial collateral ligament-deficient elbow. However, none of the prostheses functioned as well as the native radial head, suggesting that open reduction and internal fixation to restore radial head anatomy is preferable to replacement when possible.

The noncircular shape of the radial head

PURPOSE The purpose of this study was to define the shape of the radial head by identifying the relationship between precisely defined axes of the radial head. METHODS An anatomic study was done to define the shape of the radial head and specifically the relationship between the long and the short axis. Twenty-seven cadaveric upper extremities were used. The x and y axes of the radial head were defined in relationship to the radial notch of the ulna, with the forearm in neutral position. Outer diameters of the x and y axis were measured. These were compared with the actual maximum and minimum diameters of the radial head. X and y diameters of the articulating surface of the radial head also were measured. RESULTS Paired 1-tailed Students t-tests were used to compare the x and y diameters of the radial head. Regression analysis of x and y diameters of the radial head was done to identify a correlation between these parameters.Paired 1-tailed Students t-tests showed a significant difference between X and Y diameters of the radial head. Regression analysis of x and y diameters of the radial head showed a strong correlation between these 2 axes. CONCLUSIONS The radial head is not round. A strong correlation exists between the x and y diameters of the radial head. The orientation of the long axis is perpendicular to the radial notch with the forearm in neutral rotation. This finding will make it possible to approach the anatomy of the radial head more closely when designing radial head prostheses. The definition of the axes can be used as a guide when implanting the radial head prosthesis.

Dynamic Stabilizing Function of the Deltoid Muscle in Shoulders with Anterior Instability

Background The stabilizing role of the deltoid muscle has not been extensively studied. Purpose To study the contribution of the deltoid muscle to anterior stability of the shoulder. Study Design Controlled laboratory study. Methods We used nine fresh cadaveric shoulders with the arm at 90° of abduction and 90° of external rotation. The position of the humeral head was monitored by an electromagnetic tracking device with 0 and 1.5 kg of anterior translation force; with 0, 1, 3, and 5 kg of force applied to each of the anterior, middle, and posterior portions of the deltoid muscle; and with the capsule intact, vented, and with a simulated Bankart lesion. Results With the capsule intact, anterior displacement was significantly reduced by application of load to the middle deltoid muscle. After the capsule was vented, load application to the anterior, middle, or posterior deltoid muscle significantly reduced anterior displacement. With a simulated Bankart lesion, effects of muscle loading were most apparent: anterior displacement was significantly reduced with loading of each muscle portion. Conclusion The deltoid muscle is an anterior stabilizer of the glenohumeral joint with the arm in abduction and external rotation. Clinical Relevance The stabilizing function of the deltoid muscle takes on more importance as the shoulder becomes unstable.

Medial collateral ligament strain with partial posteromedial olecranon resection. A biomechanical study.

BACKGROUND Partial resection of the posteromedial aspect of the olecranon in the treatment of valgus extension impingement osteophytosis is a well-described technique. It has been hypothesized that removal of the normal olecranon process, beyond the osteophytic margin, increases the strain in the anterior bundle of the medial collateral ligament. METHODS We used an electromagnetic tracking device to investigate the strain in the anterior bundle of the medial collateral ligament as a function of increasing applied torque and posteromedial resections of the olecranon in seven cadaveric elbows. Applied torques under valgus stress consisted of hand weight, hand weight plus 1.75 Nm, and hand weight plus 3.5 Nm. Resections were conducted in sequential 3-mm increments, from 0 to 9 mm. We measured changes in the length of the anterior and posterior bands of the anterior bundle of the medial collateral ligament with strain gauges. The strains of the two bands were averaged, and the average was reported. RESULTS The strain in the anterior bundle of the medial collateral ligament was found to increase with increasing flexion angle, valgus torque, and olecranon resection beyond 3 mm. In two elbows, the anterior bundle of the medial collateral ligament ruptured during testing following the 9-mm resection. There was a significant difference between the strain following the 6-mm resection and that following the 3-mm resection at 110 degrees of flexion with 3.5 Nm of added torque (p = 0.004). CONCLUSIONS In this in vitro cadaver study, an increase in flexion angle, an increase in valgus torque, and resection of > or =6 mm led to an increase in strain in the anterior bundle of the medial collateral ligament. The non-uniform change in strain related to 3 mm of resection suggests that resections of the posteromedial aspect of the olecranon of >3 mm may jeopardize the function of the anterior bundle.

The effect of forearm rotation on laxity and stability of the elbow

OBJECTIVE The purpose of this study was to quantify the relationship between forearm rotation and valgus/varus laxity of the elbow joint over the range of elbow flexion. BACKGROUND There is little known about the influence of forearm rotation on the laxity and stability of the elbow joint. The general opinion exists that forearm rotation does not significantly influence the laxity and stability of the elbow joint. METHODS Nine fresh-frozen cadaver elbows were used. Passive elbow flexion with the forearm in neutral rotation and in 40 degrees and 80 degrees of pronation and supination was performed under valgus/varus loads: (1) in intact elbows; (2) after a lateral surgical approach (lateral epicondylar osteotomy of the distal humerus); (3) after release of the anterior bundle of the medial collateral ligament; and (4) after release of the anterior bundle of the medial collateral ligament plus radial head resection. Valgus/varus elbow laxity was quantified using an electromagnetic tracking device. RESULTS There was a statistically significant effect (P < 0.05) of forearm rotation on valgus/varus laxity throughout the range of flexion. The laxity was always greater in pronation than in supination, regardless of the surgical approach or the integrity of the anterior bundle of the medial collateral ligament or radial head. CONCLUSIONS Valgus/varus laxity of the elbow is forearm rotation-dependent. The potential role of this effect should be considered and controlled for in the design of studies examining laxity and stability of the elbow joint. RELEVANCE The observation that forearm pronation increases valgus/varus laxity, particularly in medial collateral ligament deficient elbows, implies a possible additional factor in throwing kinematics that might put professional baseball pitchers at risk of medial collateral ligament injury due to chronic valgus overload. Our data indicate that forearm rotation should be considered during the clinical examination of elbow instability.

Partial Posteromedial Olecranon Resection: A Kinematic Study

Background: The posteromedial aspect of the olecranon process is a site of impingement and subsequent osteophyte development in throwing athletes. Treatment with débridement, with resection of osteophytes and varying amounts of normal olecranon bone, is common. We found no reports in the literature concerning the effects of resecting different amounts of normal bone from the posteromedial aspect of the olecranon. We hypothesized that excessive resection would increasingly alter elbow kinematics and that an optimum amount of olecranon resection could be identified.Methods: We investigated the kinematic effects of increasing valgus and varus torques and posteromedial olecranon resections, in twelve cadaveric elbows, with use of an electromagnetic tracking device. Two valgus and two varus torques were applied, and three sequential resections were performed in 3-mm steps from 0 mm to 9 mm. Statistical analyses included paired t tests, 95% confidence intervals, a one-factor analysis of variance with repeated measures, and a post hoc test when significance was established.Results: Sequential partial resection of the posteromedial aspect of the olecranon resulted in stepwise increases in valgus angulation with valgus torque. Clear differences were seen at each level of resection. A pattern of increased valgus angulation also was seen in association with increased valgus torque. Increased valgus torque resulted in a trend toward increased axial internal rotation of the ulna, whereas increased osseous resection resulted in a decrease in the absolute degree of internal rotation or, in some specimens, increased external rotation.Conclusions: Although no single critical amount of olecranon resection was identified, valgus angulation of the elbow increased in association with all resections, with a marked increase occurring in association with a 9-mm resection. Our findings challenge the rationale of removing any amount of normal olecranon bone in throwing athletes as doing so may increase strain on the medial collateral ligament. The implications for the professional throwing athlete are important, and we recommend that bone removal from the olecranon be limited to osteophytes, without the removal of normal bone.

Kinematic and torque-related effects of dorsally angulated distal radius fractures and the distal radial ulnar joint

PURPOSE The purpose of this study was to examine the torque required to achieve a full range of motion of the distal radioulnar joint (DRUJ) as a result of increasing dorsal angulation from simulated fractures of the distal radius. Based on this study the accepted amount of dorsal angulation of the distal radius can be determined. METHODS In 9 fresh cadaver limbs motion of the DRUJ was simulated by a custom motion and loading forearm device. The malunion model of the distal radius was controlled by a specially designed external fixation frame that provided control in 6 degrees of dorsal angulations (N, 0 degrees, 10 degrees, 20 degrees, 30 degrees, and 40 degrees ). The study included an intact and nonintact triangular fibrocartilage complex. RESULTS This study showed that torque across the DRUJ was affected by the degree of simulated malunion of the distal radius. With more than 30 degrees dorsal angulation the torque across the DRUJ was increased in both muscle loading and unloading conditions. Although significance was not noted, with resistive loading this study showed torque changes with as little as 10 degrees malunion of the distal radius. CONCLUSIONS We conclude that reduction of distal radius fractures to within 10 degrees of dorsal angulation is needed to allow patients to maintain full forearm and wrist rotation.

The dynamic radioulnar convergence of the Darrach procedure and the ulnar head hemiresection interposition arthroplasty: a biomechanical study.

Resection of the entire ulnar head (Darrach operation) and the hemiresection interposition arthroplasty are common methods of treating the arthritic distal radioulnar joint (DRUJ). Biomechnical investigation about both of these procedures is lacking. The purpose of this study was to evaluate the dynamic effects of both the hemiresection interposition arthroplasty and the Darrach procedure on radioulnar convergence and dorsal–palmar displacement and to compare their biomechanical behaviours. With a dynamic computer-controlled testing device, cadaveric forearm rotation was performed with simultaneous loading of relevant muscles. Torque along the forearm axis was generated by simulated muscle action through pneumoactuators attached to relevant tendons while the wrist was constrained to prescribed ranges of motion. The instability of the radius relative to the ulna was evaluated using displacement data of digitized landmarks in an ulnar coordinate system. Seven fresh-frozen cadaver upper extremities were used. The Darrach resection created an extreme instability of the forearm with movement of the radius ulnarly. Anteroposterior translations in each loading condition could also be detected, but the magnitude of displacement was small and less predictable. The results of the hemiresection interposition arthroplasty demonstrated significantly less instability compared with the Darrach results.

Importance of a radial head component in Sorbie unlinked total elbow arthroplasty.

The effects of a radial head component on total elbow arthroplasty kinematics and stability were evaluated using an anatomic design unlinked total elbow prosthesis. An electromagnetic tracking device recorded motion and varus and valgus displacements under various conditions in 10 cadaveric elbows. The motion patterns of the intact elbows and the Sorbie-Questor™ total elbow prostheses with a radial head component were similar, as both tended to have a valgus position in extension, varus at midflexion, and more valgus toward full flexion. Under conditions of simulated muscle loading, the maximum valgus and varus laxity of the elbow prosthesis was, on average, 8.6° ± 4.0° greater than normal. Without the radial head component, however, significant kinematic disturbances and instabilities were seen. The varus and valgus displacements were 13.3° ± 5.5° greater than the intact elbows. One total elbow arthroplasty without a radial head dislocated during testing. Increasing the muscle loading across the elbow significantly enhanced dynamic stability of the total elbow arthroplasties, especially in the extension half of elbow motion where instability is greatest. However, this dynamic enhancement of stability was seen only in those elbows in which the radial head component had been implanted. The radial head component is an important stabilizer, particularly in extension for this prosthesis, and possibly for other unlinked total elbow prostheses. Although instability of unlinked prostheses depends on the prosthetic design, the use of a radial head replacement may be an important factor in preventing such instability. Perhaps even more importantly, a radial head component balances the load distribution across the articulation, which could decrease stress on the ulnohumeral articulation and therefore possibly reduce polyethylene wear, osteolysis, and loosening.