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Muscle moment arm defines the function of the muscle. To date, moment arms of the arm muscles at the glenohumeral joint using the tendon excursion method have not been reported. As the functions of these muscles at the shoulder joint are controversial, this study was undertaken to determine the moment arms of the long and short heads of the biceps (LHB, SHB), the coracobrachialis, and the long head of the triceps muscles. The moment arms were determined in 10 cadaveric shoulders by measuring the tendon excursion when the arm was rotated by 1 radian (57.3°) in 22 different motions. The LHB was a flexor, horizontal flexor, and abductor. The SHB and coracobrachialis were flexors, horizontal flexors, and adductors. The long head of the triceps was an extensor and adductor. Arm rotation significantly affected the function of the LHB only: it was an internal rotator in flexion and an external rotator in abduction. This study clarifies the individual function of the arm muscles at the glenohumeral joint.

Purpose Laboratory studies evaluating the importance of the stabilizing structures of the distal radioulnar joint (DRUJ) largely have been limited to static design. Clinically, dynamic loading seems to be an important component of DRUJ instability. This study was designed to evaluate the influence of dynamic loading on the stability of the DRUJ with foveal versus styloid triangular fibrocartilage complex (TFCC) disruptions in a laboratory setting. Methods Twelve fresh-frozen cadaveric upper-extremity specimens were tested using a dynamic simulator to study the contributions of the 2 ulnar insertions of the TFCC to the dynamic stability of the DRUJ. The specimens were tested in 3 loading conditions (no load, agonist loading, antagonist loading) in 3 different states of the TFCC (intact, foveal disruption, styloid disruption). Results Without load no significant differences were found for the different conditions of the TFCC. Under loaded conditions the foveal insertion had a greater effect on stability than did the styloid insertion. Under agonist loading significant differences were found during supinating and pronating motions. With antagonist loading a significant difference was found only during supination. Conclusions The study results support the clinical impression that dynamic loading is an important component of DRUJ instability and that disruption of the foveal TFCC insertion into the foveal region of the distal ulna can produce instability.

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. Paired 1-tailed Student's 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. Results Paired 1-tailed Student's 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.

This study examined the kinematic characteristics of the Pritchard ERS elbow-resurfacing system, with special attention paid to the effects of the radial head component. The kinematics between the ulna and humerus were assessed in 6 human cadaveric specimens by an electromagnetic tracking system throughout a full flexion/extension range of motion. The elbows were studied under 2 loading conditions, in 3 orientations (neutral, varus, and valgus), and under 4 surgical conditions. The varus/valgus and internal/external rotation laxities were used to assess the condition differences. Specifically, the maximum laxities throughout the extension motion were compared, as were the laxities at 40 degrees, 75 degrees, and 110 degrees of flexion. Both the varus/valgus and internal/external rotation laxities of the ulnohumeral joint increased after total elbow arthroplasty (TEA) implantation, with and without a radial head. This increase was most evident in the extension portion of the arc of motion. At 40 degrees of flexion, the varus/valgus laxity of the intact elbow was 4 degrees +/- 2 degrees versus 11 degrees +/- 8 degrees for a TEA with a radial head and 22 degrees +/- 11 degrees for a TEA without a radial head while the elbow was being subjected to compressive loads via the biceps, brachialis, and triceps. The kinematic data demonstrate a consistent increase in laxity with the Pritchard ERS TEA. They also indicate that a radial head component is necessary for optimal tracking and stability of the ERS arthroplasty.

Twelve fresh-frozen cadaveric occipitocervical specimens were randomized based on dual energy xray absorptiometry analysis of bone mineral density. The specimens were subjected to physiologic loads in a device that applied pure unconstrained flexion and extension, lateral bending, and axial rotational moments. The spines were tested intact and after major injury simulating transoral decompression of the dens. Biomechanical testing using pure moments with physiologic loads (< 1.5 N-m) was used to compare stability of posterior occipitocervical plates and screws, loop and cable construct, and new cervical rod and screw system. The injury created significantly less stiffness and greater range of motion and neutral zone at C1-C2 in flexion and extension and lateral bending and greater range of motion and neutral zone in axial rotation than the intact state. In lateral bending, the new rod construct had significantly lower mean values for range of motion than the loop and the plate construct. In axial rotation, the rod construct had a significantly higher mean value for stiffness than the other two devices and a significantly lower mean value for range of motion than the loop. The new rod-based instrumentation system for occipitocervical fixation is biomechanically equivalent or superior to a plate and screw construct and a rod and cable system.

Resection of the distal ulna (Darrach operation) and the ulnar head hemiresection interposition arthroplasty (Bowers procedure) are common methods of treating the arthrotic distal radioulnar joint (DRUJ). The purpose of this study was to evaluate the dynamic effects of both the Bowers operation and the resection of the distal ulna on radioulnar impingement and dorsal-palmar displacement and to compare their biomechanical performances. With a dynamic forearm simulator forearm rotation was performed with simultaneous loading of relevant muscles. Torque along the forearm axis was generated by simulated muscle action with loading of the 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. Resection of the distal ulna created a significant instability of the forearm with movement of the radius ulnarly. Anteroposterior translations in each loading condition could be detected as well but the magnitude of displacement was little and less predictable. The results of the Bowers operation demonstrated significantly less instability compared with the Darrach results. Our data demonstrates that the dynamic behavior of the Bowers procedure is superior to the mechanical performance of complete resection of the distal ulna.

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.

In order to perform cadaveric biomechanical studies of the human forearm and distal radio-ulnar joint, a dynamic simulator has been constructed. The device is based upon a Plexiglas frame, to which the ulna is secured in a vertical orientation and the humerus in a horizontal orientation. The hand is secured in a sliding bar linkage to a stepper-motor that is used to rotate the forearm. The tendons to be loaded are connected to pneumatic actuators that provide agonist and antagonist muscle loading resulting in torque along the forearm axis. The muscle loading profiles and magnitudes are programmable as a function of the pronation-supination position and direction. A magnetic tracking system is used to collect three-dimensional kinematics data of up to four segments, in conjunction with the muscle tendon loads, forearm torque and other prescribed experimental measures. All functions are under PC control using custom software written with LabVIEW (National Instruments, Austin, TX). For the DRUJ testing, the validity of the tendon loading protocol to produce physiologic torque/rotation patterns was verified using in vivo data. The relationship of individual muscle forces to forearm torque was determined by a cadaveric study.

Background: The optimum management of ligamentous injuries of the elbow is not known. Use of dynamic external fixators has been advocated to stabilize the joint while maintaining motion, but there are no published data to corroborate their efficacy. The purpose of this study was to test the hypothesis that a laterally applied unilateral dynamic external fixator is capable of stabilizing and restoring normal kinematics to elbows with varying degrees of soft-tissue injury. Methods: Six fresh-frozen cadaveric upper extremities, from donors who were an average of seventy-six years of age at the time of death, were tested in a custom apparatus with an electromagnetic tracking device to analyze the kinematic behavior. Testing began with an injury of either the lateral or the medial collateral ligament, which was followed by a second test with an injury to the ligament on the contralateral side of the joint. In each test, the varus-valgus displacement and the forearm rotatory displacement were measured through the arc of elbow flexion under three loading conditions (hand weight alone, hand weight plus 3.5 N, and hand weight plus 7 N). After each test (with each injury), a unilateral external fixator was applied from the lateral aspect of the elbow, and the same measurements were conducted under the three loading conditions across the elbow joint. Results: With varus stress testing, both after injury of the medial collateral ligament alone and after injury of the lateral collateral ligament and extensor mass alone, the laterally applied unilateral dynamic external fixator was capable of maintaining the displacements within the laxity envelope of an uninjured elbow. With valgus stress testing, after either lateral or medial ligamentous injury, the fixator was unable to maintain displacements within the normal laxity envelope when a 7-N load was applied to the elbow. When both medial and lateral injuries were present, the lateral fixator maintained varus displacement within normal limits, but valgus displacement was consistently maintained within normal limits only when no additional load was applied to the forearm. Conclusions: A lateral dynamic elbow external fixator is capable of maintaining varus displacements within normal limits in the presence of medial and lateral collateral ligament injuries and with a 7-N load added to the limb. However, valgus displacement is only consistently maintained within normal limits if no additional displacement force is added to the weight of the hand and forearm. The maintenance of valgus displacement is more sensitive to additional load and specifically to the extent of medial soft-tissue injury. Clinical Relevance: The use of external fixation of the elbow is growing in popularity. Yet, there is virtually no information with regard to the adequacy of various constructs in the context of specific pathological conditions. We demonstrated that a limited spectrum of soft-tissue injuries about the elbow can be adequately managed with a laterally applied half-pin fixator.

STUDY DESIGN Biomechanical comparison of 5 atlantoaxial posterior arthrodesis techniques. OBJECTIVE To assess the relative value of different posterior wire constructs when one or two transarticular screws are used. SUMMARY OF BACKGROUND DATA A combination of Gallie or Brooks techniques and 2 posterior transarticular screws has been shown to be effective for atlantoaxial arthrodesis. Anatomic constraints may preclude the insertion of a transarticular screw unilaterally or bilaterally. METHODS Ten adult human cadaveric upper cervical spine specimens were used. The specimens were tested intact, after odontoidectomy and transverse and capsular ligament section and after stabilization with each of the 5 techniques: Brooks-Jenkins cable fixation, Brooks-Jenkins with unilateral transarticular screw, Gallie posterior wire construct with unilateral transarticular screw, Brooks-Jenkins with bilateral screws, and Gallie with bilateral screws. Pure moments were applied in flexion-extension, lateral bending, and torsion within physiologic limits (

Background. The treatment of radial head fractures that are not amenable to an open reduction and internal fixation, remains to be a difficult issue. A potential problem with prosthetic replacement of the radial head is the shape of current radial head prostheses. The purpose of this study was to determine the effect of the shape of the radial head on kinematics and load transfer of the elbow. Methods. Kinematics of the elbow and radiocapitellar force transmission were measured in 6 fresh frozen upper extremities. The effect of radial head shape was tested by rotating the head 90 degrees , with a custom-made 'native' radial head prosthesis. 3-D spatial orientation of the ulna showed an average difference in ulnohumeral laxity, between the nominal and 90 degrees conditions, of 0.1 degrees throughout the arc of motion with neutral forearm rotation (maximum: 2 degrees ). Findings. We found an average difference in ulnar axial rotation, of 0.1 degrees (maximum: 1.9 degrees ). No differences showed statistical significance. Radiohumeral joint force was measured and maximally showed a 32 times increase of force in the altered shape conditions. Interpretation. Our results show that the kinematics of the elbow was not affected by altering the shape of the radial head, but it did adversely affect the forces in the radiohumeral joint. This could possibly generate degenerative changes in the elbow.

Details of the mechanical properties of hinged external fixators are essential to use the fixator properly in the clinical setting. A hinged external fixator (Dynamic Joint Distractor 2) was attached to the lateral side of 7 cadaveric elbows. Cantilever lateral bending tests were performed at 3 flexion angles in varus and valgus directions. Varied states of joint contact and axial loading were studied. Stiffness of the construct was calculated with uniaxial loading. Stiffness decreased with increased elbow flexion. Gap creation made the system less stiff. Axial loading made the system stiffer, especially in valgus testing. Stiffness in varus was approximately 4 times that in valgus. Lateral fixator application with half pins is most effective for protecting against varus-producing forces. When using the external fixator for unstable elbows, attention should be paid to the status of the articular surfaces and the integrity of the ligaments, and this should also be noted for elbow position during rehabilitation.

Comminuted radial head fractures can be treated with a radial head implant. The effects of lengthening (2.5 mm, 5 mm) and shortening (2.5 mm, 5 mm) of the radial neck, were compared to the nominal length in six human upper extremity cadavers. Total varus-vaigus laxity and ulnar rotation were recorded. We hypothesized that restoring the exact length of the radius is important to maintain normal kinematics in the elbow joint. Lengthening or shortening of more than 2.5 mm significantly changed elbow kinematics. Lengthening caused a significant decrease (p &LT; 0.001) in varus-valaus laxity, with the ulna tracking in varus and external rotation. Shortening caused a significant increase in varus-valgus laxity (p &LT; 0.001) and ulnar rotation (p &LT; 0.001). with the ulna tracking in valgus and internal rotation. Our study suggests that a restoration of radial length is important and that axial understuffing or overstuffing the radiohumeral joint by 2.5 mm or more, will alter elbow kinematics. &COPY; 2004 IPEM. Published by Elsevier Ltd. All rights reserved.

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° 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 ≥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. Clinical Relevance: Resection of the olecranon beyond the posteromedial osteophytic margin increases the strain in the anterior bundle of the medial collateral ligament, with the potential for a consequent ligament rupture. We advise resection of the osteophytes only.

Most radial head prostheses do not seem to be based on anatomic data. This may be due partly to the great variation of radial morphology. More importantly, few articles report on the dimensions of the radius. Authors have mainly studied dimensions of the radial head, with less emphasis to the relationship with the rest of the radius. Dimensions of, and relationship between, the proximal and the rest of the radius were measured on 27 fresh-frozen cadaveric upper extremities. Radial head, articulating surface, diaphysis, and distal radius were measured. Angles between the radial neck and diaphysis were defined and calculated. Axes of the distal and proximal radius were defined and radial torsion was calculated. Repeated measures were done by two observers in ten specimens. Inter- and intra-class correlation coefficients were very acceptable. Radial dimensions were found to be highly variable. Calculation of radial torsion showed the largest range. The average torsion was 54° (range = 23–78°). Radial length was 235 mm (range = 207–269 mm). Radial neck length was 13 mm (range = 9–19 mm). We found an average proximal diaphysis-neck angle of 17° (range = 6–28°). End to end-neck angle was 13° (range = 4–22°). Our findings indicate that even with a perfectly anatomical prosthesis, restoration of the anatomical situation can only be achieved when the implant is placed in the correct position. Instrumentation should be developed to allow accurate and reproducible implantation. The measurements we provide may aid this development. Clin. Anat. 17:564–569, 2004. © 2004 Wiley-Liss, Inc.

Objective. The objective of this study was to identify the effect of radial head shape and orientation on elbow kinematics in the otherwise intact elbow. Design. Biomechanical study, analyzing simulated active motion of cadaveric arms. Background. A discrepancy exists between the noncircular anatomy of the radial head and radial head prostheses. The effect of radial head shape is unknown. Methods. Kinematic effects of radial head shape were tested in six fresh-frozen upper extremities. A custom-made native radial head prosthesis was used to Simulate altered shape conditions, by rotating the radial head 90degrees. Three-dimensional spatial orientation of the ulna was recorded, during simulated active motion. A three factor ANOVA was used to compare (a) nominal and 90degrees oriented conditions, (b) throughout the flexion are (c) in three forearm positions (P < 0.05). Post-hoc Tukey tests were done to assess significance. Results. No significant effect of altering radial head shape was found on total ulnohumeral laxity and angulation during gravity valgus stress. We did find a significant effect on total ulnar axial rotation and rotation during gravity valgus stress. Conclusion. The outer shape of the radial head seems to change rotation of the ulna during flexion -extension in all otherwise intact elbow. Relevance The shape of the radial head effects intact elbow kinematics. Clinical importance of this finding is clear. If a sub-optimally placed radial head prosthesis were to be used in an otherwise intact elbow, the elbow could be at risk for early ulnohumeral arthritis. (C) 2004 Elsevier Ltd. All rights reserved.

Sixteen fresh-frozen spines from cadavers (C4-T1) were randomized on the basis of dual energy xray absorptiometry analysis of bone mineral density. The specimens were subjected to physiologic loads (

Background: The posteromedial aspect of the olecranon process is a site of impingement and subsequent osteophyte development in throwing athletes. Treatment with debridement, 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.

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.

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 degrees +/- 4.0 degrees greater than normal. Without the radial head component, however, significant kinematic disturbances and instabilities were seen. The varus and valgus displacements were 13.3 degrees +/- 5.5 degrees 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.

The most common method to treat the arthralgic distal radioulnar joint is resection of the entire ulnar head (Darrach procedure). Pain and weak grip strength usually manifest complications related to instability of the distal forearm. In an attempt to mechanically stabilize the distal forearm after ulnar head resection, an endoprosthesis was developed to replace the ulnar head after Darrach resection. The goals of this study were to evaluate the dynamic effects of the Darrach procedure on radioulnar convergence and the mechanical efficacy of implantation of an ulnar head endoprosthesis after Darrach resection. Cadaver forearms were rotated actively and passively and relevant muscles were loaded simultaneously with a dynamic PC-controlled forearm simulator. Resultant total forearm torque and 3-dimensional kinematics of the ulna, radius, and third metacarpal were recorded simultaneously in 7 fresh-frozen cadaver upper extremities. Comparisons were made between the intact state, after Darrach resection, and after implantation of ulnar head endoprosthesis. The Darrach resection created substantial forearm instability with movement of the radius ulnarly (0.92-0.38 cm vs intact state) and anteroposterior translation in each loading condition. Implantation of the ulnar head endoprosthesis effectively restored distal radioulnar joint stability by simulating the geometry of the ulnar head, further stabilized by attaching the triangular fibrocartilage complex. These laboratory data provide validity to implanting an ulnar head endoprosthesis to stabilize the distal forearm after Darrach resection.

Nine cadaver upper extremities were tested to evaluate the constraint properties of the dorsal and palmar radioulnar ligaments at their foveal and styloid attachments to the ulna. The specimens were tested by anterior and posterior displacement of the radius relative to the ulna with the forearm in pronation, supination, and neutral rotation. There were no statistically significant differences in the relative percent of constraint contribution of the styloid and foveal ligament insertions. In neutral forearm rotation total displacement after sectioning both ligament insertions tended to be larger in palmar than in dorsal displacement. A similar trend was observed with 60° forearm supination. In the pronated position, however, the trend was reversed with larger total displacement in dorsal displacement. (J Hand Surg 2002;27A:61-67. Copyright © 2002 by the American Society for Surgery of the Hand.)

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.

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° and 80° 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

To The Editor: I was interested in "Contribution of Monoblock and Bipolar Radial Head Prostheses to Valgus Stability of the Elbow" (2001;83:1829-34), by Pomianowski et al., who analyzed the stability of elbows with a deficient medial collateral ligament after a variety of treatments, including preservation, resection, or replacement of the radial head with different radial head prostheses. This cadaveric study, which proves the mechanical efficiency of radial head replacement and confirms some clinical observations, is a great contribution to the understanding of both the biomechanics and certain pathological conditions of the elbow. I have just a few methodological questions that pertain to the validity of the results presented by Pomianowski et al. The Judet bipolar prosthesis, …