肘关节内侧副韧带前束重建后肱桡关节的生物力学变化

目的通过比较肱桡关节在肘关节内侧副韧带(medial collateral-ligament,MCL)前束完整组与重建组的生物力学数据,评价通过界面螺钉固定人工肌腱重建MCL前束的疗效。方法本次实验选取人类肘关节作为标本,首先将标本分为对照组(前束完整组)及实验组(前束重建组),每组各20例,然后将压敏胶片(pressure sensitive film,PSF)放到肱桡关节内,当肘关节内侧副韧带前束处于不同屈曲角度(0°、30°、60°、90°)和不同状态(完整及重建)时分别测量肘关节外翻松弛度、肱骨小头与桡骨小头的接触面积及肱桡关节内的压强,数据应用SPSS 19.0统计软件进行分析。结果肘关节处于0°、30°、60°、90°时,肘关节外翻松弛度组内及组间比较差异无统计学意义(P0.05)。肘关节处于0°时,对照组和实验组的肱桡关节内压强均明显小于肘关节处于屈曲30°、60°、90°时关节内的压强(P0.05);肘关节处于30°、60°、90°时组内及组间肱桡关节内压强比较差异无统计学意义(P0.05)。前束完整组中,肘关节处于0°位时肱桡关节的受力面积最大(P0.05),两组其余各角度组内及组间比较差异均无统计学意义(P0.05)。结论在维持肘关节外翻稳定性方面,肘关节内侧副韧带前束的作用十分关键,使用人工肌腱重建肘关节内侧副韧带前束可以使肘关节内侧结构迅速恢复至正常状态,不但可以降低肱桡关节内压强,还可以增加肱桡关节接触面积,最终达到降低肱桡关节慢性损伤的发病率。     

肘关节内侧副韧带断裂对肱桡关节影响的生物力学研究

目的测量肘关节内侧副韧带(MCL)前束完整及断裂时在不同屈曲状态下肱桡关节的生物力学指标,探讨肘关节MCL前束对肱桡关节的生物力学影响。方法取人体肘关节标本,按是否切断肘关节MCL前束将标本分为对照组(MCL前束保留完整)及试验组(MCL前束被切断),分别测量2组标本在不同屈曲角度下(0°、30°、60°、90°)肱桡关节内平均压强和肱桡关节的接触面积。结果肘关节屈曲30°、60°时,试验组肱桡关节内平均压强大于对照组,肱桡关节接触面积小于对照组,差异有统计学意义(P0.05);而肘关节屈曲0°、90°时,2组肱桡关节内平均压强、肱桡关节接触面积差异无统计学意义(P0.05)。结论肘关节MCL前束在肘关节稳定中意义重大,其断裂后可导致肘关节内侧不稳定,造成肱桡关节内压强增大、关节接触面积减小。     

肘关节内侧副韧带前束损伤的生物力学研究

[目的]研究肘关节内侧副韧带(medial collateral-ligament,MCL)前束的生物力学作用,探讨肘关节内侧不稳定的发生机制。[方法]将人体肘关节尸体标本按照前束的完整程度分为3组:完整组、部分切断组、完全切断组,测量肘关节在不同屈曲角度下及不同程度前束损伤后关节松弛度(关节在极限以内的力或扭矩作用下的活动量或旋转[1])、肱尺关节平均压强和关节接触面积。[结果](1)前束完整组内外翻松弛度及全部切断组内平均压强和关节接触面积比较无统计学差异(P>0.05);(2)部分切断组及完全切断组外翻松弛度组内比较有统计学差异(P<0.05);前束完整组及前束部分切断组平均压强及接触面积组内比较均有统计学差异(P<0.05);(3)三组在关节松弛度、肱尺关节平均压强和关节接触面积的组间比较均存有统计学差异(P<0.05)。[结论](1)前束是肘关节内侧稳定的主要结构;(2)关节松弛度与关节内压强呈正相关关系,与关节接触面积呈负相关关系;(3)肘外翻应力试验应在屈肘>30°时进行,如外翻松弛度接近10°考虑MCL前束不完全断裂;如外翻松弛度达15°左右考虑MCL前束完全断裂;(4)前束部分损伤时是治疗肘内侧不稳的关键时期。     

单束重建与解剖双束重建治疗内侧副韧带Ⅲ级损伤的生物力学比较研究

目的比较单束重建与解剖双束重建治疗膝关节内侧副韧带(medial collateral ligament,MCL)Ⅲ级损伤后膝关节稳定性差异,为临床MCL损伤治疗提供生物力学参考。方法取自愿捐赠的成人新鲜膝关节标本9具,随机分为3组(n=3)。其中,正常MCL组仅行前交叉韧带(anterior cruciate ligament,ACL)离断并单束重建,保留完整MCL。单束重建组及双束重建组均离断ACL、MCL浅层(superficial MCL,sMCL)及后斜韧带(posterior oblique ligament,POL),制备MCLⅢ级损伤模型;ACL单束重建后,分别行sMCL单束重建、sMCL及POL解剖双束重建。采用生物材料动态力学试验机测量各组膝关节完全伸直位及屈曲不同角度时,胫骨前方移位距离(anterior tibial translation,ATT)、胫骨内旋角(internal rotation,IR)、胫骨外翻角(valgus rotation,VAL),以及内旋及外翻力矩作用下MCL及ACL受力情况。结果膝关节完全伸直位及屈曲15°、30°、45°、60°、90°位时,3组ATT差异均无统计学意义(P0.05)。单束重建组膝关节完全伸直位及屈曲15°位时IR及VAL,以及屈曲30°位时VAL,均明显大于双束重建组及正常MCL组(P0.05);双束重建组与正常MCL组差异均无统计学意义(P0.05)。膝关节完全伸直位及屈曲15°、30°位时,内旋、外翻力矩作用下,3组MCL及ACL受力差异均无统计学意义(P0.05)。结论相比单束重建,解剖双束重建治疗MCLⅢ级损伤可以更好地恢复膝关节的外翻及旋转稳定性。     

肘关节内侧副韧带前束的生物力学研究

尺侧副韧带(MCL)复合体为关节囊的增厚部分,由前束、后束及斜束构成.前束是肘关节内侧稳定的主要结构,临床上MCL损伤时应重点修复或重建MCL前束以稳定肘关节[1].我们采用压敏胶片对肘关节进行应力及受力面积的分析. 一、材料与方法 防腐保存的正常成人尸体的完整上肢标本12例,其中左、右各6例;男8例,女4例.采用长春试验机研究所生产生物力学试验机(CSS-44020型)及FUJIF-ILM超低压双片型压敏胶片在肘关节不同屈曲角度下承受150 N垂直压力及1.5 N/m外翻扭矩下的外翻松弛度[2].     

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。     

前后交叉韧带同时重建固定角度实验研究

目的探讨采用自体半腱肌肌腱同时重建前交叉韧带(anterior cruciate ligament,ACL)和后交叉韧带(posterior cruciate ligament,PCL)移植肌腱固定时膝关节屈曲最佳角度。方法清洁级6～8月龄新西兰大白兔24只,雌雄不限,体重(2.5±0.2)kg,根据重建韧带固定时膝关节屈曲角度不同,随机分为3组(n=8)。取双侧后肢半腱肌肌腱,同时重建右后肢PCL及ACL,并分别于膝关节屈曲90°(A组)、60°(B组)、30°(C组)位固定。术后观察实验动物一般情况;术后3个月时,采用空气栓塞法处死实验动物,取膝关节远、近端各10 cm长肢体,行伸屈等长实验、前后位移实验、膝关节内外旋转实验。结果实验动物均存活至实验完成。3组间ACL及PCL最大位移比较,差异均无统计学意义(P>0.05)。各组前、后方位移均<1 mm,提示前、后稳定性均良好;A组屈曲30°时前方位移及屈曲90°时后方位移均较C组大,差异均有统计学意义(P<0.05)。A组内、外旋转角度与C组比较,差异均有统计学意义(P<0.05);其余各组间比较,差异均无统计学意义(P>0.05)。结论同时重建兔ACL及PCL,以屈曲60°行韧带固定效果最佳。     

膨胀螺钉固定重建前交叉韧带的生物力学研究

背景:关节镜下重建前交叉韧带(ACL)的方法很多,且疗效较好。但目前尚无有关固定方法是否能提供坚强固定、恢复原有ACL生物力学特性的相关研究。目的:探讨股骨端膨胀界面螺钉固定腘绳肌腱移植重建ACL的生物力学。方法:取新鲜冰冻成人膝关节标本21具,采用4股腘绳肌腱移植重建ACL,股骨端分别使用膨胀界面螺钉(n=7)、可吸收界面螺钉(n=7)、金属界面螺钉(n=7)固定,测试循环载荷后位移、100 N位移、400 N位移、抗拉刚度、最大拔出载荷、失败模式以及肌腱切割程度等,并进行统计学分析。结果:循环载荷后位移:可吸收螺钉组<金属螺钉组<膨胀螺钉组,无统计学差异(P>0.05);最大拔出载荷:膨胀螺钉组>可吸收螺钉组>金属螺钉组,膨胀螺钉组与可吸收螺钉组比较无统计学差异(P>0.05),膨胀螺钉组与金属螺钉组比较有统计学差异(P<0.05);肌腱切割程度:膨胀螺钉切割伤最轻,可吸收螺钉次之,金属螺钉最重。结论:膨胀界面螺钉的最大拔出载荷、100 N位移、400 N位移以及抗拉刚度均超过普通界面螺钉,对移植肌腱损伤小,可以满足肌腱重建固定ACL的需要,并可实现单隧道ACL双束解剖重建。     

肘关节尺侧副韧带屈曲角度与负荷关系的生物力学研究

[目的]研究肘关节尺侧副韧带(UCL)在不同的肘关节屈曲角度时生物力学特性的变化.[方法]选取8对新鲜冰冻肘关节尸体标本,测量每个标本在前臂旋前、旋后、中立位时,肘关节不同被动屈曲角度下UCL的张力变化;测量UCL在肘关节不同屈曲角度下(30°、50°、70°、90°)外翻应力试验时失效载荷与屈曲角度的关系.[结果]肘关节在被动屈曲0°～57°时,对UCL前束的前带和后带均没有产生超过3%的张力,屈曲导致的张力改变对后带的影响有显著性(P＜0.01),对前带的影响无显著性(P=0.128).在57°以后,后带上的张力随着屈曲角度的增大而增加,在100°～130°左右的范围达到最大.前臂的旋转对韧带张力的影响无显著性.在肘关节屈曲90°时UCL断裂失效所需载荷最大,在屈曲30°时最小.UCL断裂好发部位为其前束肱骨内侧髁止点处.[结论]UCL损伤或者重建术后的固定角度应为肘关节屈曲＜57°,早期的康复锻炼肘关节屈曲0°～57°为安全范围.肘关节在屈曲90°时具有最高的外翻稳定性,可以减少UCL损伤机率.     

尺骨鹰嘴骨折不同程度骨量丢失对肘关节稳定性的影响

目的 探讨尺骨鹰嘴骨折时不同程度骨量丢失对肘关节稳定性的影响.方法 取10具20侧男性新鲜上技标本,在距尺骨鹰嘴尖部10 mm处向远端截骨,制备鹰嘴中部不同程度骨缺损,即骨量丢失模型,截骨分为4组,每组5侧上肢标本,即尺骨鹰嘴完整组、截除3mm组、截除6mm组、截除9 mm组,骨折断端予张力带内固定后,测量每组肘关节屈伸活动范围变化及肘关节在屈曲30°、60°、90°、120°时,前臂施加1.96 N·m扭距,肘关节内外翻角度的变化,同时观察肱尺关节关系.结果当尺骨鹰嘴截骨至3 mm时,肘关节的伸直活动开始受限;当尺骨鹰嘴截骨至6 mm时,CB片示肱尺关节出现不服贴,鹰嘴尖紧贴滑车关节面,滑车与鹰嘴之间间隙增大,肘关节的伸直活动明显受限;当尺骨鹰嘴截骨至9mm时,CR片示肘关节明显处于半脱位,滑车切迹的弧度基本消失.肘关节屈曲30°、60°、90°时,随截骨量增大肘外翻角度增大,当截骨量达到6 mm时外翻角度明显增大,差异有统计学意义(P＜0.05).而肘关节屈曲30°、60°、90°、120°时,内翻角度组间差异无统计学意义(P＞0.05).结论 尺骨鹰嘴中部截骨缩短达到6mm时,滑车切迹弧度发生改变,出现肘关节不稳定.临床对于尺骨鹰嘴中部粉碎性骨折如短缩不超过6 mm可单纯固定,否则应考虑原位植骨内固定.     

Stabilizers of capitellocondylar total elbow arthroplasty

The contribution of the medial and lateral collateral ligaments (MCL, LCL) and muscle forces to the kinematics and stability of the capitellocondylar total elbow arthroplasty was investigated in six fresh cadaveric elbows. The three-dimensional orientation of the ulna relative to the humerus was monitored with the use of an electromagnetic tracking device in neutral, valgus, and varus stress positions with (1) the ligaments intact, (2) LCL insufficiency obtained by osteotomizing the lateral epicondyle, (3) partial MCL insufficiency obtained by sectioning either the anterior or posterior bundle of the MCL, and (4) complete MCL insufficiency. Simulated muscle forces were applied as follows: (1) no load, (2) 1 kg each to the biceps and the brachialis and 2 kg to the triceps, and (3) 2 kg to the biceps and the brachialis and 4 kg to the triceps. The laxity was defined as the difference in valgus/varus orientation of the ulna in the valgus and varus stress positions. The laxity at 40°, 75°, and 110° elbow flexion was analyzed. The greatest laxity occurred with LCL insufficiency (40.7° ± 11.6°, average at three flexion angles) followed by that with MCL insufficiency (15.7° ± 9.9°), both of which were significantly larger than laxity with the intact ligaments (5.6° ± 2.5°). The laxity with the anterior bundle sectioned (12.0° ± 8.1°) was significantly greater than with the posterior bundle sectioned (3.3° ± 3.6°); thus the contribution of anterior bundle to stability was four times that of posterior bundle. Stabilizing effect of muscle loading was small in elbows with intact ligaments, whereas it was large with LCL or MCL insufficiency. Based on these data, we can see that the integrity of both the MCL and LCL is essential to maintain stability of this total elbow, the anterior bundle is a more important stabilizer than the posterior bundle, and the collateral ligaments seem to be the primary stabilizer and the musculature seems to be the secondary stabilizer. Careful implantation technique to preserve the collateral ligaments is required to obtain postoperative stability of this arthroplasty. Otherwise, routine exposure of the MCL and repair or reinforcement of the MCL, if deficient, may need to be considered during surgery.     

Single-strand ligament reconstruction of the medial collateral ligament restores valgus elbow stability

The purpose of this study was to determine the contribution of the central portion of the anterior bundle of the medial collateral ligament (MCL) to elbow stability and to evaluate the effectiveness of a single-strand MCL reconstruction in restoring elbow stability. Testing of 11 fresh-frozen upper extremities was first performed on the intact elbow and then with the capsule, flexor-pronator muscle group, posterior bundle, anterior or posterior band, and central band cut sequentially. Next, a single-strand reconstruction of the MCL was performed. The elbow was moved passively through a full arc of flexion in both varus and valgus gravity-loaded positions. Ulnar movement with respect to the humerus was analyzed by means of an electromagnetic tracking system. Maximum varus-valgus laxity throughout the arc of supinated flexion and pronated flexion was 6.6 degree plus minus 2.4 degree and 7.4 degree plus minus 2.0 degree, respectively, for the intact specimen, 34.2 degree plus minus 5.6 degree and 37.7 degree plus minus 11.8 degree for the specimen with all of the medial valgus elbow stabilizers cut, and 9.0 degree plus minus 2.5 degree and 10.5 degree plus minus 2.7 degree for the reconstructed specimen. Maximum varus-valgus laxity was not significantly different among any of the sectioning sequences until the central band was cut (P <.0001). There was no significant difference in maximum varus-valgus laxity between the intact and reconstructed elbows (P <.05). Our results demonstrate that the central band is an important valgus stabilizer of the elbow and that a simplified single-strand reconstruction is able to restore stability to the MCL-deficient elbow.     

A biomechanical study of stability of the elbow to valgus stress before and after reconstruction of the medial collateral ligament

The purpose of this study was to assess the stability of the elbow to valgus loads after reconstruction of the anterior bundle of the medial collateral ligament (MCL). The MCL in 14 human cadaveric elbows was exposed with a muscle-splitting approach. Each sample was secured in a materials test frame,5 N-m valgus moments were applied in 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion, and baseline stability was measured. This sequence was performed after the anterior bundle was sectioned and again after ligamentous reconstruction was done with the Jobe technique. At 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion, reconstruction reproduced an average of 99%, 102%, 97%, and 89%, respectively, of the stability of the intact ligament. The only significant difference between intact and reconstructed samples was at 120 degrees of flexion (P <.05). We concluded that this procedure reliably restores stability to a ruptured MCL throughout the flexion arc in the immediate postoperative period.     

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.     

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.     

尺骨鹰嘴部分切除对肘关节稳定性影响的研究

目的探讨尺骨鹰嘴尖部截骨短缩对肘关节稳定性的影响。方法取10具20侧男性新鲜上肢标本，随机分为四组，每组5侧标本，即尺骨鹰嘴完整组、截骨3mm组、截骨6mm组、截骨9mm组，截骨在尺骨鹰嘴尖部。每组分别在肘关节屈曲30°、60°、90°、120°时，前臂加1．96Nm力矩的情况下，测量外翻位肘外翻角度和内侧副韧带前束长度及内翻位肘内翻角度和桡侧尺副韧带长度。结果尺骨鹰嘴尖部截骨时，于同一肘关节屈曲位，随着尺骨鹰嘴尖部截骨量增大，肘关节内侧副韧带前束的长度逐渐变长，外翻角逐渐增大，当截骨量大于3mm上述变化差异显著，有统计学意义（P〈0．05）。结论尺骨鹰嘴尖部截骨量超过3mm时，肘关节出现不稳定。因此临床上当尺骨鹰嘴尖部严重粉碎性骨折片不超过3mm时，可予以手术切除，对肘关节稳定性影响不大，否则应给予修复重建。而对于尺骨鹰嘴尖部后内侧骨赘，建议仅切除骨赘或切除范围不超过正常鹰嘴尖部3mm。     

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

The purpose of this study was to determine the relative contribution of muscle activity and the effect of forearm position on the stability of the medial collateral ligament (MCL)-deficient elbow. Simulated active and passive elbow flexion with the forearm in both supination and pronation was performed using a custom elbow testing apparatus. Testing was first performed on intact specimens, then on MCL-deficient specimens. Elbow instability was quantified using an electromagnetic tracking device by measuring internal-external rotation and varus-valgus laxity of the ulna relative to the humerus. Compared with the intact elbow, transection of the MCL, with the arm in a vertical orientation, caused a significant increase in internal-external rotation during passive elbow flexion with the forearm in pronation, but forearm supination reduced this instability. Overall, following MCL transection the elbow was more stable with the forearm in supination than pronation during passive flexion. In the pronated forearm position simulated active flexion also reduced the instability detected during passive flexion, with the arm in a varus and valgus gravity-loaded orientation. The maximum varus-valgus laxity was significantly increased with MCL transection regardless of forearm position during passive flexion. We concluded that active mobilization of the elbow with the arm in vertical orientation during rehabilitation is safe in the setting of an MCL-deficient elbow with the forearm in a fully supinated and pronated position. Splinting and passive mobilization of the MCL-deficient elbow with the forearm in supination should minimize instability and valgus elbow stresses should be avoided throughout the rehabilitation period.     

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.