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 degrees 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 degrees +/- 5.6 degrees). Less laxity was seen following release of the medial collateral ligament alone (6.8 degrees +/- 3.4 degrees), and the least laxity was seen in the intact state (3.4 degrees +/- 1.6 degrees). 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.     

Kinematics of partial and total ruptures of the medial collateral ligament of the elbow

In this study the kinematics of partial and total ruptures of the medial collateral ligament of the elbow are investigated. After selective transection of the medial collateral ligament of 8 osteoligamentous intact elbow preparations was performed, 3-dimensional measurements of angular displacement, increase in medial joint opening, and translation of the radial head were examined during application of relevant stress. Increase in joint opening was significant only after complete transection of the anterior part of the medial collateral ligament was performed. The joint opening was detected during valgus and internal rotatory stress only. After partial transection of the anterior bundle of the medial collateral ligament was performed, there was an elbow laxity to valgus and internal rotatory force, which became significant after transection of 100% of the anterior bundle of the medial collateral ligament and was maximum between 70 degrees to 90 degrees of flexion. No radial head movement was seen after partial or total transection of the anterior bundle of the medial collateral ligament was performed. In conclusion, this study indicates that valgus or internal rotatory elbow instability should be evaluated at 70 degrees to 90 degrees of flexion. Detection of partial ruptures in the anterior bundle of the medial collateral ligament based on medial joint opening and increased valgus movement is impossible.     

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.     

重建肘关节外翻稳定性的生物力学研究

目的　评价肘关节桡骨头 (radial head,RH)切除、尺侧副韧带 (medial collateral ligament,MCL )损伤以及 RH假体置换、MCL重建后的外翻稳定性。　方法　新鲜成人尸体上肢标本 12侧 ,制成肘关节“骨 -韧带”标本 ,在2 N· m的外翻力矩作用下 ,分别在肘关节 0°、30°、6 0°、90°和 12 0°伸屈时 ,测量肘关节外翻松弛度 :1完整肘关节(n=12 ) ;2 MCL切断 (n=6 ) ;3RH切除 (n=6 ) ;4 MCL切断 +RH切除 (n=12 ) ;5 RH假体置换 (n=6 ) ;6 MCL重建(n=6 ) ;7RH假体置换 +MCL重建 (n=12 )。用 SPSS 10 .0统计软件包作方差分析 ,比较各组的外翻稳定性。　结果　完整肘关节的平均外翻松弛度最小 ;RH切除后 ,外翻松弛度增大 ;单纯 MCL切断 ,外翻松弛度大于单纯 RH切除 (P<0 .0 1) ;MCL切断 +RH切除 ,外翻稳定性最差 ;行 RH假体置换 ,对稳定性有改善 ;MCL重建与完整 MCL差异无统计学意义 (P>0 .0 5 ) ;RH假体置换同时重建 MCL ,效果最好。　结论　 MCL是抵抗肘关节外翻应力最主要的因素 ,RH是次要因素。在重建肘关节的外翻稳定性方面 ,MCL的重建比 RH的假体置换更重要。在无条件行 RH假体置换时 ,修复MCL是较好的手术方式。     

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 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.     

Kinematics and functional characteristics of the Pritchard ERS unlinked total elbow arthroplasty

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.     

Role of collateral ligaments in the GSB-linked total elbow prosthesis.

The GSB III elbow prosthesis is a loose-hinged type of elbow implant. The introduction of such hinged elbow arthroplasty expanded the indications for elbow replacement to patients with more deficient bone and ligaments. The purpose of this study was to compare the kinematics and stability of the GSB III elbow prosthesis with that of the normal elbow and to investigate the role of the collateral ligaments in the kinematics and the stability of the GSB III total elbow prosthesis in an in vitro model. The results could show a semiconstrained kinematic pattern of the GSB III implant. The mean laxity for varus/valgus stress of the implant without collateral ligament support was significantly greater for all flexion angles when compared with intact elbows (mean, 12.7 degrees versus 5.4 degrees ) and with elbows treated with a standard implantation technique (mean, 9.5 degrees ). The release of the collateral ligaments increased the already observed varus shift after standard implantation of a GSB III elbow prosthesis. The laxity measured without collateral ligaments during loaded movement reached the maximum varus/valgus laxity of the GSB III prosthesis of 12 degrees degrees. The study confirms the role of the collateral ligaments in stabilizing the GSB III elbow prosthesis. Missing collateral ligaments may overload the implant-cement-bone interface and may be one factor contributing to early aseptic loosening of this device.     

Valgus stability of the elbow. A definition of primary and secondary constraints

The stabilizing structures of the elbow that resist valgus stress were studied with a tracking device in a model simulating active motion and muscle activity. By varying the order of serial release of the medial collateral ligament complex and removal of the radial head, each structure's contribution to valgus stability against the effect of gravity was determined. In the otherwise intact elbow, absence of the radial head does not significantly alter the three-dimensional characteristics of motion in the elbow joint. Isolated medial collateral release, on the other hand, causes increases in abduction rotation of about 6 degrees-8 degrees in magnitude. Releasing both structures results in gross abduction laxity and elbow subluxation. This study defines the medial collateral ligament (MCL) as the primary constraint of the elbow joint to valgus stress and the radial head as a secondary constraint. This definition facilitates the proper management of patients with radial head fractures and MCL disruption. The comminuted radial head fracture uncomplicated by MCL insufficiency should be treated by excision without the need for an implant and without concern of altering the normal kinematics of the elbow.     

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.     

Radial head fracture in the medial collateral ligament deficient elbow; biomechanical comparison of fixation, replacement and excision in human cadavers

A widely used clinical recommendation is that in the presence of medial collateral ligament injuries, two-part radial head fractures should be fixed rather than excising or replacing the radial head. Direct biomechanical data comparing fracture fixation, radial head replacement and excision in a human cadaveric elbow model, have not been previously described. Such comparison is clinically important as with the increasing availability of radial head implants and promising follow up results, the role of radial head replacement in fracture management may have to be redefined. In this study, five fresh cadaveric elbows had radial head fracture creation and medial collateral ligament division, fracture fixation, radial head replacement and excision. Valgus and varus laxity were determined using an electromagnetic tracking system. Radial head replacement leads to a similar valgus (P=0.80) [corrected] laxity as compared to radial head fixation. Radial head excision resulted in a significantly greater valgus laxity as compared to radial head fixation (P=0.02) or replacement (P=0.03). Both radial head excision and replacement led to a greater varus laxity as compared to fixation. Our results suggest that in the elbow with medial collateral ligament injury and two-part radial head fracture, fixation is overall biomechanically superior as compared to replacement and excision.     

Stability after medial collateral ligament release in total knee arthroplasty.

Six knees from cadavers were tested for change in stability after release of the medial collateral ligament with posterior cruciate-retaining and substituting total knee replacements. Load deformation curves of the joint were recorded in full extension and 30 degrees, 60 degrees, and 90 degrees flexion under a 10 N-m varus and valgus torque, 1.5 N-m internal and external rotational torque, and a 35 N anterior and posterior force to test stability in each knee. The intact specimen and posterior cruciate ligament-retaining total joint replacement were tested for baseline comparisons. The superficial medial collateral ligament was released, followed by release of the posterior cruciate ligament. The knee then was converted to a posterior-stabilized implant. After medial collateral ligament release, valgus laxity was statistically significantly greater at 30 degrees, 60 degrees, and 90 degrees flexion after posterior cruciate ligament sacrifice than it was when the posterior cruciate ligament was retained. The posterior-stabilizing post added little to varus and valgus stability. Small, but significant, differences were seen in internal and external rotation before and after posterior cruciate ligament sacrifice. The posterior-stabilized total knee arthroplasty was even more rotationally constrained in full extension than the knee with intact medial collateral ligament and posterior cruciate ligament.     

Fractures of the capitellum

Forty intact cadaver elbows were studied to determine the contribution of the capitellum to elbow stability. With the elbow at 10 degrees of flexion, valgus motion of the elbow after capitellum excision demonstrated a minimal increase. Although some increase in valgus motion did occur after capitellum excision and radial head resection it was not until the ulnar collateral ligament was released that a severe valgus deformity was produced. In addition, isolated capitellum excisions occurring with release of the medial collateral ligament produced severe valgus motion, demonstrating the importance of medial structures to elbow stability. The cadaver study suggests excision of the capitellum in the otherwise intact elbow has little effect on valgus motion. Over the past 15 years, 17 patients with fractures of the capitellum were treated. Followup at greater than 1 year utilizing various treatment modalities is reported. Although closed reduction gave the best result, acceptable results were also obtained by open reduction and internal fixation and excision. Our clinical findings corroborated the cadaver findings in that valgus instability of the elbow only occurred when fracture of the capitellum was associated with medial ligament injuries.     

Laxity of the elbow after experimental excision of the radial head and division of the medial collateral ligament. Efficacy of ligament repair and radial head prosthetic replacement: a cadaver study

We studied the stabilising effect of prosthetic replacement of the radial head and repair of the medial collateral ligament (MCL) after excision of the radial head and section of the MCL in five cadaver elbows. Division of the MCL increased valgus angulation (mean 3.9 +/- 1.5 degrees) and internal rotatory laxity (mean 5.3 +/- 2.0 degrees). Subsequent excision of the radial head allowed additional valgus (mean 11.1 +/- 7.3 degrees) and internal rotatory laxity (mean 5.7 +/- 3.9 degrees). Isolated replacement of the radial head reduced valgus laxity to the level before excision of the head, while internal rotatory laxity was still greater (2.8 +/- 2.1 degrees). Isolated repair of the MCL corrected internal rotatory laxity, but a slight increase in valgus laxity remained (mean 0.7 +/- 0.6 degrees). Combined replacement of the head and repair of the MCL restored stability completely. We conclude that the radial head is a constraint secondary to the MCL for both valgus displacement and internal rotation. Isolated repair of the ligament is superior to isolated prosthetic replacement and may be sufficient to restore valgus and internal rotatory stability after excision of the radial head in MCL-deficient elbows.     

Experimental elbow instability after transection of the medial collateral ligament

In 12 osteoligamentous autopsy elbow preparations, the stability of the elbow was independent of the collateral ligament with flexion of less than 20 degrees and greater than 120 degrees. The anterior part of the collateral medial ligament was the prime stabilizer of the elbow in this range of motion, i.e., the flexion range of function. The maximum valgus and internal rotatory instability after transection of the medial collateral ligament, 20.2 degrees and 21.0 degrees, respectively, were found at elbow flexions from 60 degrees to 70 degrees. Selective repair or reconstruction of the anterior part of the elbow medial collateral ligament may prove to be effective in the treatment of acute or chronic elbow instability.     

Single-strand reconstruction of the lateral ulnar collateral ligament restores varus and posterolateral rotatory stability of the elbow

Because of a lack of biomechanical studies of lateral elbow ligament reconstruction in the literature, the initial stability afforded by 3 different techniques of lateral ulnar collateral ligament reconstruction was evaluated in 8 cadaveric elbows. The arm was mounted in a testing apparatus, and passive flexion was performed with the arm in varus and valgus orientations. A pivot shift test was performed with the arm in the vertical orientation. An electromagnetic tracking device was used to quantify motion pathways. After intact testing, each specimen underwent sectioning of the radial collateral and lateral ulnar collateral ligaments from the lateral epicondyle. Reconstruction of the lateral ulnar collateral ligament was performed in a randomized sequence, consisting of proximal single-strand, distal single-strand, and double-strand tendon grafts. Division of the radial collateral and lateral ulnar collateral ligaments from the lateral epicondyle caused a significant decrease in rotational stability when the pivot shift test was being performed (P <.0001). Varus-valgus stability also decreased after transection of the radial collateral and lateral ulnar collateral ligaments (P <.0001). Reconstruction of the lateral ulnar collateral ligament restored elbow stability to that of the intact state. There was no significant difference in stability between the single- and double-strand repair techniques (P >.05). This study demonstrates that both single- and double-strand reconstructions restore varus and posterolateral elbow stability and may be considered appropriate reconstructive procedures in patients with symptomatic insufficiency of the lateral ligaments of the elbow.     

Effects of elbow flexion and forearm rotation on valgus laxity of the elbow

BACKGROUND: Clinical evaluation of valgus elbow laxity is difficult. The optimum position of elbow flexion and forearm rotation with which to identify valgus laxity in a patient with an injury of the ulnar collateral ligament of the elbow has not been determined. The purpose of the present study was to determine the effect of forearm rotation and elbow flexion on valgus elbow laxity. METHODS: Twelve intact cadaveric upper extremities were studied with a custom elbow-testing device. Laxity was measured with the forearm in pronation, supination, and neutral rotation at 30 degrees, 50 degrees, and 70 degrees of elbow flexion with use of 2 Nm of valgus torque. Testing was conducted with the ulnar collateral ligament intact, with the joint vented, after cutting of the anterior half (six specimens) or posterior half (six specimens) of the anterior oblique ligament of the ulnar collateral ligament, and after complete sectioning of the anterior oblique ligament. Laxity was measured in degrees of valgus angulation in different positions of elbow flexion and forearm rotation. RESULTS: There were no significant differences in valgus laxity with respect to elbow flexion within each condition. Overall, for both groups of specimens (i.e., specimens in which the anterior or posterior half of the anterior oblique ligament was cut), neutral forearm rotation resulted in greater valgus laxity than pronation or supination did (p < 0.05). Transection of the anterior half of the anterior oblique ligament did not significantly increase valgus laxity; however, transection of the posterior half resulted in increased valgus laxity in some positions. Full transection of the anterior oblique ligament significantly increased valgus laxity in all positions (p < 0.05). CONCLUSIONS: The results of this in vitro cadaveric study demonstrated that forearm rotation had a significant effect on varus-valgus laxity. Laxity was always greatest in neutral forearm rotation throughout the ranges of elbow flexion and the various surgical conditions. CLINICAL RELEVANCE: The information obtained from the present study suggests that forearm rotation affects varus-valgus elbow laxity. Additional investigation is warranted to determine if forearm rotation should be considered in the evaluation and treatment of ulnar collateral ligament injuries of the elbow joint.     

Valgus stability of the elbow

The valgus stabilizers of the elbow have been identified anatomically, but their relative importance has not been quantified. The purpose of this study was to analyze the acute changes of the torque-displacement curve to valgus stress following (a) section of the posterior portion of the medial collateral ligament; (b) excision of the radial head; (c) prosthetic replacement of the radial head; and (d) excision of the anterior portion of the medical collateral ligament. Thirty cadaver specimens underwent load-displacement testing in three positions: 0 degrees, 45 degrees, and 90 degrees of flexion. The anterior portion of the medial collateral ligament was the primary stabilizer of the elbow to valgus stress. The relative contribution of the posterior ligament was minimal. After excision of the radial head alone, the slope of the load-displacement curve decreased an average of 30%. Silicone rubber radial head replacement did not significantly improve the stability to valgus stress after radial head excision.     

Ligamentous stabilizers against posterolateral rotatory instability of the elbow.

BACKGROUND: The lateral ulnar collateral ligament, the entire lateral collateral ligament complex, and the overlying extensor muscles have all been suggested as key stabilizers against posterolateral rotatory instability of the elbow. The purpose of this investigation was to determine whether either an intact radial collateral ligament alone or an intact lateral ulnar collateral ligament alone is sufficient to prevent posterolateral rotatory instability when the annular ligament is intact. METHODS: Sequential sectioning of the radial collateral and lateral ulnar collateral ligaments was performed in twelve fresh-frozen cadaveric upper extremities. At each stage of the sectioning protocol, a pivot shift test was performed with the arm in a vertical position. Passive elbow flexion was performed with the forearm maintained in either pronation or supination and the arm in the varus and valgus gravity-loaded orientations. An electromagnetic tracking device was used to quantify the internal-external rotation and varus-valgus angulation of the ulna with respect to the humerus. RESULTS: Compared with the intact elbow, no differences in the magnitude of internal-external rotation or maximum varus-valgus laxity of the ulna were detected with only the radial collateral or lateral ulnar collateral ligament intact (p > 0.05). However, once the entire lateral collateral ligament was transected, significant increases in internal-external rotation (p = 0.0007) and maximum varus-valgus laxity (p < 0.0001) were measured. None of the pivot shift tests had a clinically positive result until the entire lateral collateral ligament was sectioned. CONCLUSIONS: This study suggests that, when the annular ligament is intact, either the radial collateral ligament or the lateral ulnar collateral ligament can be transected without inducing posterolateral rotatory instability of the elbow.     

Elbow joint laxity after experimental radial head excision and lateral collateral ligament rupture: efficacy of prosthetic replacement and ligament repair

The objectives of this experimental study were to investigate the effect of radial head excision and lateral collateral ligament (LCL) division on elbow joint laxity and to determine the efficacy of radial head prosthetic replacement and LCL repair. Valgus, varus, internal rotation, and external rotation of the ulna were measured during passive flexion-extension and application of a 0.75-Nm torque in 6 intact cadaveric elbows and after (1) either excision of the radial head or division of the LCL, (2) removal of both constraints, (3) isolated radial head prosthetic replacement, (4) isolated LCL repair, and (5) radial head replacement combined with LCL repair. Isolated radial head excision increased varus (mean, 4.8 degrees) and external rotatory laxity (mean, 7.1 degrees), as did isolated LCL division (mean, 14.1 degrees for varus; mean, 14.7 degrees for external rotation). After removal of both constraints, varus and external rotatory laxities were increased by 19.0 degrees and 20.1 degrees, respectively, compared with the intact specimens. Isolated radial head replacement reduced mean varus laxity to 14.6 degrees and mean external rotatory laxity to 14.8 degrees. Isolated LCL repair normalized varus laxity but resulted in a 2.9 degrees increase in external rotatory laxity. The combined procedures restored laxity completely. The radial head is a constraint to varus and external rotation in the elbow joint, functioning by maintaining tension in the LCL. Still, removal of both constraints induces severe laxity, and in this case, prosthetic replacement may substitute for the constraining capacity of the native radial head. The combination of LCL repair and radial head replacement restores laxity completely, but an isolated LCL repair performs almost as well, probably by compensating for the ligamentous tension lost from radial head excision.     

Muscle forces and pronation stabilize the lateral ligament deficient elbow.

The influence of muscle activity and forearm position on the stability of the lateral collateral ligament deficient elbow was investigated in vitro, using a custom testing apparatus to simulate active and passive elbow flexion. Rotation of the ulna relative to the humerus was measured before and after sectioning of the joint capsule, and the radial and lateral ulnar collateral ligaments from the lateral epicondyle. Gross instability was present after lateral collateral ligament transection during passive elbow flexion with the arm in the varus orientation. In the vertical orientation during passive elbow flexion, stability of the lateral collateral ligament deficient elbow was similar to the intact elbow with the forearm held in pronation, but not similar to the intact elbow when maintained in supination. This instability with the forearm supinated was reduced significantly when simulated active flexion was done. The stabilizing effect of muscle activity suggests physical therapy of the lateral collateral ligament deficient elbow should focus on active rather than passive mobilization, while avoiding shoulder abduction to minimize varus elbow stress. Passive mobilization should be done with the forearm maintained in pronation.