Anatomy and biomechanics of the patellofemoral joint: physiological conditions and changes after total knee arthroplasty

The patellofemoral joint constitutes a complex anatomical and functional entity. The tensile force of the quadriceps femoris muscle is transmitted through the patella and patellar ligament onto the tibial tuberosity. This particular three-dimensional arrangement increases the torsional moment acting on the knee joint. Dynamic alignment of the patella is determined by trochlear geometry and is supported by active muscular and passive connective tissue stabilizers. In addition to the retinaculum of the patella, the medial patellofemoral ligament is attracting increasing clinical attention. Multidirectional motion of the patella is closely connected to retropatellar pressure distribution which can be modulated by moving the patellar ligament insertion. Implantation of a knee endoprosthesis changes the joint surface geometry and consequently patella kinematics and retropatellar pressure distribution. Finite element analysis provides the possibility to assess retropatellar pressure distribution before and after implantation of prostheses.     

Patellofemoral contact zones in knee endoprostheses

Failures after total knee arthroplasty often are caused by problems of the patellofemoral articulation. We investigated 10 different femoral components and 12 different patellar implants. The size of the patellofemoral contact areas was evaluated by pressure sensitive films every 10 degrees up to 90 degrees of flexion. The forces of the quadriceps muscle and the patella ligament were measured by force transducers. The compressive forces acting between patella and gliding grove were calculated. The geometry of the components and forces was documented. The retropatellar contact areas are specific for each prosthesis. The patterns of displacement are similar for some groups of prostheses. The absolute size of the contact areas and their size relative total surface of the patellar implant is very small. This induces high local pressure of the polyethylene.     

Pathomechanics of the femoropatellar joint following total knee arthroplasty

Persistent discomfort in the femoropatellar joint is still one of the most disappointing aspects following total knee arthroplasty (TKA). Especially, TKA without patellofemoral replacement has a significant incidence of patellofemoral problems with a frequency between 5% and 45%. Pathomechanical factors in the development of retropatellar problems are loss of patellar thickness and retropatellar erosions. In 157 TKAs using Gschwend, Scheier, B?hler (GSB) joints without patellar resurfacing, pathomechanically postoperative vertical patellar malposition appeared to be the main cause of dysfunction. In many cases, the implantation technique leads to an artificial form of patella alta. This altered knee anatomy results in pathologic biomechanics, thus leading to reduced function. The combination of altered anatomy and reduced function leads to extensive patellar destruction and ultimately to intractable retropatellar pain.     

Lowering of the patella secondary to anterior advancement of the tibial tubercle for the patellofemoral pain syndrome

From a series of 72 patients treated with anterior advancement of the tibial tubercle for patellofemoral pain syndrome, secondary lowering of the patella was noted in eight. In all eight patients the results were poor following surgery, with severe disabling retro- and peripatellar pain and atrophy of the quadriceps muscle. We describe this complication and illustrate and discuss the biomechanical consequences. The shortening of the patellar ligament and lever arm of the ligament were determined from radiographs of the knee joints before and after surgery. A theoretical analysis was made of the compressive force in the patellofemoral joint in one of these patients. The Insall-Salvati index decreased from 0.88-1.25 (mean 1.07) preoperatively to 0.54-0.78 (mean 0.70) at follow-up, 1.0-2.5 years post-operatively. The lowering of the patella was correlated to a reduction of the lever arm of the patellar ligament in seven patients. The mechanism behind the lowering of the patella is obscure, but the reduced lever arm of the patellar ligament will increase the compressive force in the patellofemoral joint, and this might be one explanation of the poor results. Impaired congruity of the patellofemoral joint, increased tension in the patellar ligament, and increased pressure against the quadriceps tendon are other possible explanations.     

Lowering of the patella secondary to anterior advancement of the tibial tubercle for the patellofemoral pain syndrome

Summary From a series of 72 patients treated with anterior advancement of the tibial tubercle for patellofemoral pain syndrome, secondary lowering of the patella was noted in eight. In all eight patients the results were poor following surgery, with severe disabling retro- and peripatellar pain and atrophy of the quadriceps muscle. We describe this complication and illustrate and discuss the biomechanical consequences. The shortening of the patellar ligament and lever arm of the ligament were determined from radiographs of the knee joints before and after surgery. A theoretical analysis was made of the compressive force in the patellofemoral joint in one of these patients. The Insall-Salvati index decreased from 0.88–1.25 (mean 1.07) preoperatively to 0.54–0.78 (mean 0.70) at follow-up, 1.0–2.5 years postoperatively. The lowering of the patella was correlated to a reduction of the lever arm of the patellar ligament in seven patients. The mechanism behind the lowering of the patella is obscure, but the reduced lever arm of the patellar ligament will increase the compressive force in the patellofemoral joint, and this might be one explanation of the poor results. Impaired congruity of the patellofemoral joint, increased tension in the patellar ligament, and increased pressure against the quadriceps tendon are other possible explanations.     

Biomechanics of the patellofemoral joint and its clinical relevance

An analysis of the patellofemoral joint based on experimental determinations of pressure distributions on the patellar cartilage and vectorial calculations is presented. The extension torque of all quadriceps muscles is similar. The force transmitted to the patella by the retinacula is small in all knee positions. Because the rigid patella has its own lever arms and tendon insertions at different heights, the forces on patellar and quadriceps tendons are unequal. The small patellar contact areas change according to flexion and are dependent on quadriceps force. Retropatellar pressure is thereby limited and becomes independent of flexion angle. By virtue of the direct force transmission of the quadriceps tendon to the femur, the increase in the retropatellar force is strongly limited beyond 70 degrees. The lateral-to-medial ratio of contact areas, pressing forces, cartilage areas, and bone mass is always 1.6:1, whereas the mean pressure is the same on both facets. The osseous form of the patella does not allow identification of dysplasia because cartilage compensates for apparent incongruence, especially about the medial ridge. This permits the rigid patella to adapt itself to very different abutments. Its individual form results from functional adaptation and does not explain chondromalacia. The ventralization of the tibial tuberosity does not alter retropatellar loading. The mediodistal transfer results in a high increase of pressure on both facets.     

内侧髌股韧带重建联合胫骨结节移位和关节镜下外侧支持带松解术治疗持久性髌骨脱位

目的观察内侧髌股韧带重建联合胫骨结节移位和关节镜下外侧支持带松解术治疗持久性髌骨脱位的效果。方法对6例持久性髌骨脱位患者的10个膝关节行内侧髌股韧带重建联合胫骨结节移位和关节镜下髌骨外侧支持带松解术。手术前后采用Lysholm膝关节功能评价表和Kujala评分表进行评估,并通过CT观测手术前后髌骨外移度。结果 6例均获随访,时间24～36(29±7.21)个月。Lysholm评分术前为47.10分±10.31分,术后24个月为83.11分±5.21分,差异有统计学意义(P<0.05);Kujala评分术前为41.26分±13.36分,术后24个月为82.33分±5.31分,差异有统计学意义(P<0.05)。患膝运动能力均较术前明显改善。髌骨外移度术前为35.61 mm±5.37 mm,术后为4.30mm±1.13mm,差异有统计学意义(P<0.05)。结论内侧髌股韧带重建联合胫骨结节移位和关节镜下髌骨外侧支持带松解术能够有效纠正持久性髌骨外侧脱位,缓解症状,恢复膝关节功能。     

Effects of retinacular release and tibial tubercle elevation in patellofemoral degenerative joint disease

Release of the patellar retinaculum and tibial tubercle elevation have both been advocated for the treatment of patellofemoral degeneration. Questions remain, however, regarding the magnitude and predictability of such effects in diseased joints. Using cadaver knee joints exhibiting a range of patellofemoral cartilage degeneration, we investigated the effects on joint contact pressures on release of the patellar retinaculum, followed by tibial tubercle elevations of 1.25 and 2.5 cm. Retinacular release failed to alter the joint-loading parameters significantly. Tibial tubercle elevation reduced the patello-femoral joint contact area and contact force, but failed to cause a consistent change in contact pressure. Tibial tubercle elevation also caused a migration of the joint contact area superolaterally on the retropatellar surface. This migration occurred in conjunction with ventral tilting of the inferior pole of the patella as the tubercle was elevated, suggesting that significant changes in joint kinematics may result from this procedure.     

Patellaluxationen

Dislocation of the patella represents a frequent knee problem in childhood and adolescence. There are traumatic, recurrent, habitual and chronic forms. Many anatomical variations, which promote patellar dislocation, are known. The first traumatic dislocation is primarily treated conservatively with the exception of concomitant osteochondral fragments or very large soft tissue damage which justify surgical interventions. Recurrent, habitual and chronic dislocations are best cured surgically by vastus medialis advancement, reconstruction of the medial patellofemoral ligament, strengthening of the medial retinaculum together with a lateral release and by fixation of the patella using tendon grafts or medialisation of the insertion of the patellar ligament. To improve the femoropatellar groove by trochleoplasty is a different surgical concept. The long-term results following medialisation of the patellar ligament insertion or trochleoplasty are good with regards to patellar stability but mediocre in terms of avoiding degenerative changes in the patellofemoral joint.     

The influence of patellar resurfacing on patellar kinetics and retropatellar contact characteristics

Background

Femoropatellar complications are one of the most common problems after total knee arthroplasty (TKA). However, the question of whether to resurface the patella remains controversial. Therefore, we evaluated the kinetics and the retropatellar contact characteristics of patella resurfacing with fixed and gliding surfaces.

Methods

Eight Thiel-embalmed cadaver knees were tested—first intact, then after TKA without patellar resurfacing, and finally with additional patellar resurfacing—while flexing the knee from 0° to 100°. We tested a fixed as well as a gliding patella surface. During the examination, quadriceps and hamstring forces were applied. The retropatellar pressure was determined with a special patella sensor, and the patellar kinetics were measured using an optical three-dimensional motion analysis system.

Results

Resurfacing the patella caused a significant increase in retropatellar pressure and a significant decrease in retropatellar contact area. Using a fixed patella, the retropatellar pressure nearly quadrupled in higher flexion compared to the native patella. Furthermore, the lateral movement of the patella increased after TKA, especially after additional patellar resurfacing.

Conclusions

Resurfacing the patella routinely is not advised. When osteoarthritis of the patella is found, the gliding patella should be preferred.     

Why do orthopaedic surgeons ignore the medial patellofemoral ligament?

The medial patellofemoral ligament (MPFL) is a condensation of the medial capsule of the knee joint. In the past two decades dissection studies have shown that it extends from the superomedial border of the patella to the femoral epicondyle, at or immediately above the adductor tubercle. MRI and operative studies have revealed that it is almost invariably damaged by lateral patellofemoral dislocation. Current surgical management of such dislocations may involve imbricating the torn medial capsule and parapatellar retinaculum back onto the medial border of the patella. If the medial patellofemoral ligament is torn at or near the femoral attachment, as the latest MRI and operative studies demonstrate it frequently is, then this medial reefing procedure will not be successful in restoring normal anatomy and function. Here we review the anatomy and function of the MPFL, its role in patellar dislocation and as well as surgical treatment for patellar dislocation.     

Spontaneous ruptures of the extensor system of the knee following joint replacement in patients with rheumatoid arthritis

Spontaneous ruptures of the quadriceps tendon and the patellar ligament following total knee arthroplasty in two patients with rheumatoid arthritis are reported. Degenerative and steroid-induced changes of tendinous tissue, circulation problems as well as mechanical changes to the patellofemoral joint by resurfacing the patella are discussed being possible causes of these complications of the extensor mechanism of the knee.     

Medial patellofemoral ligament reconstruction: a novel approach

Recurrent patellar instability is common, and multiple procedures have been described for its treatment. Medial patellofemoral ligament reconstruction can be successful in patients who have an incompetent medial patellofemoral ligament or who have failed medial patellofemoral ligament repair and present with recurrent patellar instability. This article describes a novel approach to medial patellofemoral ligament reconstruction using a folded hamstring allograft with a new knotless suture anchor and bio-interference screw fixation. The principal advantage of this construct is the ability to definitively fix the medial patellofemoral ligament soft-tissue graft on the femur and provisionally fix the graft to the patella while assessing for reasonable medial patellofemoral ligament isometry throughout the arc of knee motion.     

复发性髌骨脱位治疗中内侧髌股韧带重建术的研究进展

复发性髌骨脱位是引起青少年膝关节功能障碍的常见疾病,其定义为髌骨脱位发生两次及两次以上,是一种骨科及运动医学临床常见的疾病。复发性髌骨脱位的病因有很多,但归根结底,髌骨在活动中所处的异常力学环境是引起不稳的根本原因。研究发现内侧髌股韧带被认为是限制髌骨向外脱位最重要的软组织结构,因而重建内侧髌股韧带对成功治疗复发性髌骨脱位起着重要的作用。但复发性髌骨脱位往往是一个多因素引起的临床问题,除了纠正软组织的异常外,骨性结构的异常也是一个不容忽视的问题。本文对近年来对内侧髌股韧带的解剖、生物力学、手术技巧、治疗结果及术后并发症的研究情况进行了综述。     

Patellar tracking and patellofemoral geometry in deep knee flexion.

Patellar tracking and femoral condylar geometry in deep knee flexion were evaluated using magnetic resonance imaging. The patellar tilting angle, patellar shift, and patellar anteroposterior translation from 0 degrees to 135 degrees flexion were measured. The depth of the femoral condylar articular surface and the curvature of the femoral condylar articular surface also were measured at 135 degrees flexion. The patella shifted laterally, tilted medially, and sank deeply into the intercondylar notch during deep knee flexion. The articular surface of the lateral condyle, existing deep within the intercondylar notch, began to curve steeply at a point farther from the center of the intercondylar notch than did the medial condyle. The geometry of the femoral condyle is adequate to fit the patellar geometry. Results of the current study suggest that the geometry of the lateral femoral condyle allows the patella to track smoothly with a larger patellofemoral contact area and less patellofemoral pressure during deep flexion.     

传统与改良Elmslie-Trillat术治疗髌骨不稳定的生物力学比较

目的 评价传统与改良Elmslie-Trillat术治疗髌骨不稳定的生物力学特性,为改良Elmslie-Trillat术治疗髌骨不稳定提供生物力学依据.方法 先对12具新鲜冰冻成人尸体膝关节完整标本(完整膝关节组,12具)进行生物力学测试测量髌骨移位距离,切断内侧髌股韧带制成髌骨不稳定模型(髌骨不稳定模型组,12具)后再测量髌骨移位距离,然后随机再分为2组(传统Elmslie-Trillat术组及改良Elmslie-Trillat术组,每组6具标本)分别采用传统和改良Elmslie-Trillat术矫正.膝关节屈曲30°位固定胫骨及股骨端,将标本安装在MTS-858实验机上,通过髌骨中心外侧施加20 N的载荷,测量髌骨移位距离.结果 完整膝关节组、髌骨不稳定模型组、传统Elmslie-Trillat术组及改良Elmslie-Trillat术组的髌骨外侧移位距离平均分别为(6.2±0.6)、(11.3±0.9)、(6.4±0.8)、(6.7±0.8)mm,4组外侧减内侧移位距离平均分别为(-1.5±0.5)、(3.5±0.4)、(-1.4±1.0)、(-1.3±1.0)mm.髌骨不稳定模型组的外侧移位距离和外侧减内侧移位距离分别与其他3组比较,差异均有统计学意义(P＜0.05);完整膝关节组、传统Elmslie-Trillat术组及改良Elmslie-Trillat术组的外侧移位距离和外侧减内侧移位距离比较差异均无统计学意义(P＞0.05).结论 内侧髌股韧带是髌骨的主要稳定因素.与传统Elmslie-Trillat术比较,改良Elmslie-Trillat术同样能改善髌骨异常力线,减少相同应力下的髌骨位移.

Abstract：

Objective To evaluate the biomechanical performance of the modified Elmslie-Trillat procedure in the treatment of patellar instability as compared with traditional Elmslie-Trillat procedure.Methods Twelve fresh frozen cadaveric specimens of intact knee joint were used in this study.First biomechanical measurements were performed to compare the patellar displacements between the intact knee joints and models of patellar instability which were made by cutting the medial patellofemoral ligaments.Next the models of patellar instability were randomized into 2 groups for treatments with traditional and modified Elmslie-Trillat procedures respectively.After the tibiofemoral joint was held at 30 degrees of flexion, a load of 20 N was applied to the lateral center of the patella.The patellar displacements were measured with transducers in an Instron Testing System.Results The lateral patellar displacement was respectively 6.2 ±0.6 mm, 11.3 ± 0.9 mm, 6.4 ± 0.8 mm and 6.7 ± 0.8 mm and the lateral minus medial patellar displacement was respectively - 1.5 ± 0.5 mm, 3.5 ± 0.4 mm, - 1.4 ± 1.0 mm and - 1.3 ± 1.0 mm for the 4 groups of intact knee joint, patellar instability, traditional Elmslie-Trillat procedure treatment and modified Elmslie-Trillat procedure treatment.There were significant differences in both of the patellar displacements between the patellar instability group and the other 3 groups ( P ＜ 0.05).There was no significant difference in both of the patellar displacements among the 3 groups of intact knee joint, traditional Elmslie-Trillat procedure treatment and modified Elmslie-Trillat procedure treatment ( P ＞ 0.05 ).Conclusion Since the medial patellofemoral ligament is a main stable factor for patella, patellar abnormal traction can be improved and patellar displacement can be reduced under the same loading by both modified and traditional Elmslie-Trillat procedures.     

自体中1／3髌韧带重建前十字韧带术后膝关节内并发症的探讨

目的探讨应用自体中1/3髌韧带移植重建前十字韧带术后膝关节内有关的并发症及其发病机制。方法1994年1月～1997年11月 ,对18例前十字韧带断裂的患者采用关节镜或小切口关节切开术 ,完成自体中1/3髌韧带移植重建前十字韧带。术后平均随访2年 ,对所有病例进行临床检查 ,确定膝关节疼痛部位 ,检查膝关节活动度及稳定性 ,并利用膝关节屈曲90°的侧位X线片测量髌韧带长度。结果随访18例患者 ,17例术后膝关节存在触发性或功能性疼痛 ,膝关节疼痛常位于髌股关节、髌骨下极、髌韧带供区及胫骨结节部位。8例患者术后患膝活动度有不同程度受限。6例患者髌韧带发生不同程度的短缩 ,平均短缩2.8mm。4例患者髌股关节间隙变窄。两种术式以上并发症的发生率及严重程度差异无显著性意义。结论应用自体中1/3髌韧带重建前十字韧带不仅应注意疼痛等并发症的发生 ,还应关注髌韧带供区及髌股关节并发症的发生 ,重视其发病的病理基础。髌韧带中1/3缺损可引起髌韧带短缩及髌股关节退变。     

髌股疼痛综合征病因与治疗的研究进展

髌股疼痛综合征(patellofemoral pain syndrome,PFPS)是导致膝关节疼痛最为常见的疾病之一。目前无特异性诊断措施,影像学检查无软骨、韧带及软组织损伤表现时方可考虑诊断为髌股疼痛综合征。其病因包括各种解剖结构异常导致的髌骨运动轨迹异常,如髌骨位置异常、Q角增大及足过度外翻等,股四头肌失衡和臀肌功能异常等下肢肌肉功能异常同样在髌股疼痛综合征的发生发展中起重要作用。目前存在多种治疗方式,股四头肌锻炼和臀外展肌锻炼目的在于改善髌骨动态稳定性;肌效贴和髌支具主要通过改善髌骨轨迹,减轻髌股关节面间的压力;足矫形垫主要用于伴有足外翻的患者;在保守治疗无效后,可考虑进行膝关节镜下松解髌骨外侧支持带术。由于髌股疼痛综合征为多种病因综合作用而致病,同时采用多种治疗方式有助于提高治疗效果。     

Posterior cruciate ligament rupture alters in vitro knee kinematics

Isolated posterior cruciate ligament injuries usually are treated nonoperatively, although some patients remain symptomatic, and degenerative changes within the patellofemoral joint and the medial compartment of the tibiofemoral joint have been seen in followup studies. In vitro simulation of knee squatting was done to quantify the influence of the posterior cruciate ligament on tibiofemoral and patellofemoral kinematics. For five knee specimens, knee kinematics were measured before and after sectioning the posterior cruciate ligament, and compared using a Wilcoxon signed rank test. The only kinematic parameters that changed significantly after sectioning the posterior cruciate ligament were the tibial posterior translation and patellar flexion. The posterior translation of the tibia increased significantly between 25 degrees and 90 degrees flexion. The average increase in the posterior translation exceeded 10 mm at 90 degrees flexion. The patellar flexion increased significantly from 30 degrees to 90 degrees flexion. The average patellar flexion increase peaked at 4.4 degrees at 45 degrees flexion. Increased tibial translation could adversely influence joint stability. Increased patellar flexion could increase the patellofemoral joint pressure, especially at the inferior pole, leading to degenerative changes within the patellofemoral joint.