Contact stresses with an unresurfaced patella in total knee arthroplasty: the effect of femoral component design

Compressive contact stresses between the patella and the anterior femur were measured with a digital electronic sensor before and after total knee arthroplasty (TKA) in 10 cadaver knee specimens. Contact stresses were measured first in normal knees, then after TKA with the Insall-Burstein Total Condylar, Miller Galante II, Ortholoc II, Porous Coated Anatomic, and Profix knee prostheses implanted without resurfacing the patella. The Insall-Burstein, Miller-Galante II, and Ortholoc II prostheses had significantly higher contact stresses than the normal knee throughout the flexion arc. The Porous Coated Anatomic, which has a smooth patellar groove, maintained contact area as in the normal knee and did not have significantly higher contact stresses at flexion angles <90 degrees. At flexion angles > or =105 degrees, patellofemoral contact occurred in two small areas as the patella encountered the intercondylar notch in all components except the Profix. The Profix maintained full contact and low compressive stresses throughout the full flexion arc because of its posteriorly extended patellar groove. Design features of the patellofemoral portion of TKA components are important factors that affect contact stresses in the patellofemoral joint. These features likely will affect the clinical results of TKA with an unresurfaced patella.     

Effect of femoral component designs on the contact and tracking characteristics of the unresurfaced patella in total knee arthroplasty.

OBJECTIVES: To determine the effect of 5 different femoral components used in total knee arthroplasty (TKA) on the contact area and tracking characteristics of the nonresurfaced patella and to identify any design features that might adversely affect these characteristics. DESIGN: An in-vitro study. SETTING: The biomechanics laboratory, Department of Mechanical Engineering, McGill University, Montreal. SPECIMENS: Six fresh-frozen cadaveric knee-joint specimens. INTERVENTIONS: An unconstrained quadriceps simulator was used to apply the conditions of static lifting to the specimens first in their normal state and then sequentially implanted with femoral and tibial components of various designs (Miller/Galante II, Anatomic Modular Knee [AMK] System, Whiteside Ortholoc Modular, press-fit condylar and Insall-Burstein II). OUTCOME MEASURES: Patellar 3-dimensional tracking characteristics, determined by using a 6 degrees-of-freedom electromechanical goniometer attached directly to the patella, and patellar contact pressure measurements, obtained using low-range Fuji Prescale film. RESULTS: Articulation of the normal patella on a prosthetic femoral component resulted in alterations in the normal patellofemoral contact and tracking characteristics. The exact departure depended on the design of the prosthetic trochlea. Although all of the selected prostheses demonstrated satisfactory contact characteristics near extension, marked alterations occurred at higher flexion angles. With 90 degrees or more of flexion, there was incompatibility between the geometries of the prosthetic notch of 2 femoral designs (AMK and PFC) and the normal knee. CONCLUSION: The design of the prosthetic femoral component must be taken into account when determining whether or not to resurface the patella at the time of TKA.     

股骨假体设计对保留髌骨全膝关节置换术后膝前痛的影响

目的探讨不同股骨假体设计对保留髌骨全膝关节置换术(totalkneearthroplasty,TKA)后膝前痛发生率及疼痛程度的影响。方法2002年1月15日～2月15日间,门诊共随访保留髌骨TKA后患者44例59膝,所有手术均于1998年10月～2001年10月间施行,术前诊断均为骨关节炎,术后随访3～40个月,平均19.1个月。依据目前较普遍认同的标准:股骨假体髌骨滑槽的深度、宽度、是否对称,髌骨滑槽的延伸范围,股骨假体前方向远端移行是否平滑等将股骨假体分为“髌骨友好”与“髌骨不友好”两组。病例排除的标准:(1)膝关节屈曲小于80°者;(2)X线影像提示存在股骨假体屈曲大于3°、股骨前方皮质切迹(notching)、髌骨高位或低位等外科操作失误者。按美国膝关节学会评分方法及患者自我感觉对疼痛发生率及疼痛程度进行量化分析。结果入选的40例51膝分属上述两组,“髌骨友好”组21膝,术后膝前痛评分平均为1.58(0～8)分;“髌骨不友好”组30膝,术后膝前痛评分平均为3.32(0～6)分,两组之间差异有非常显著性意义(t=4.642,P<0.01)。“髌骨友好”与“髌骨不友好”两组无膝前痛患者构成比分别为64%与9%,两组之间差异有非常显著性意义(χ2=15.457,P<0.01)。结论股骨假体设计的不同会直接影响保留髌骨TKA术后膝前痛的发生率及疼痛程度,行保留髌骨TKA     

Effect of femoral component design on patellofemoral crepitance and patella clunk syndrome after posterior-stabilized total knee arthroplasty

The purpose of this study was to determine if recent changes to the femoral component of a particular posterior-stabilized total knee prosthesis would affect the incidence of postoperative patellofemoral crepitance and patella clunk syndrome. One hundred eight total knee arthroplasties were performed with the conventional design; 136 were performed after the femoral component was changed. Complications were compared between the groups with an average follow-up of 17.7 months and 12.4 months, respectively. Thirteen knees with the conventional design (12%) were found to have patellofemoral complications; no complications were noted with the new design (P < .0001). Femoral components with a deep trochlear groove and smooth transition of the intercondylar box appear to better accommodate any peripatellar fibrous nodule that may form after total knee arthroplasty.     

Effect of rotational malposition of the femoral component on knee stability kinematics after total knee arthroplasty

Excessive external rotation of the femoral component can cause an abnormally tight popliteus tendon complex, which induces loss of rotational laxity of the knee in the late phase of knee flexion after total knee arthroplasty. This study evaluated the effect of popliteus tendon release on rotational and varus—valgus laxity of implanted knees with an excessively externally rotated femoral component. Rotational and varus—valgus laxity was measured with a knee kinematics testing device before and after total knee arthroplasty. External rotational positions of the femoral component of 5° and 8° were compared, and the effects of popliteus tendon release on rotational and varus—valgus laxity were evaluated. To further investigate this question, the effect of a conforming articular design was compared with that of a flat tibial surface. External rotational position of 5° did not change rotational or varus—valgus laxity of the knee. With an 8° external rotational position, however, external rotational laxity significantly decreased in knees with a conforming surface at angles of 30°, 45°, 60°, and 90°. After popliteus tendon release, external rotational laxity significantly improved at 90° flexion and was identical to that of the normal knee. Internal rotational range was similar before and after popliteus tendon release. Popliteus tendon release did not affect the varus—valgus laxity (stability) with either articular surface.     

Optimizing femoral component rotation in total knee arthroplasty.

Femoral component rotation is important in total knee arthroplasty to optimize patellofemoral and tibiofemoral kinematics. More recently, the epicondylar axis has been cited as the definitive landmark for femoral component rotation. However, there are few studies to support the validity of this rotational landmark and its effect on the patellofemoral and tibiofemoral articulations. In the current study, a total knee arthroplasty was done in 11 knees from cadavers. The knees were tested with various femoral component rotations from 5 degrees internal rotation to 5 degrees external rotation referenced to the epicondylar axis and to the posterior femoral condyles. Each knee acted as its own internal control. The knees were actively ranged from 0 degrees to 100 degrees by a force on the quadriceps tendon in an Oxford knee simulator. Three-dimensional kinematics of all three components were measured whereas a multiaxial transducer imbedded in the patella measured patellofemoral forces. Femoral component rotation parallel to the epicondylar axis resulted in the most normal patellar tracking and minimized patellofemoral shear forces early in flexion. This optimal rotation also minimized tibiofemoral wear motions. These beneficial effects of femoral rotation were less reproducibly related to the posterior condyles. Rotating the femoral component either internal or external to the epicondylar axis worsened knee function by increasing tibiofemoral wear motion and significantly worsening patellar tracking with increased shear forces early in flexion. Based on the current study, the femoral component should be rotationally aligned parallel to the epicondylar axis to avoid patellofemoral and tibiofemoral complications.     

The effects of femoral component design on the patello-femoral joint in a PS total knee arthroplasty

Introduction

Anterior knee pain following TKA performed utilizing the PFC Sigma system still represents a cause of failure. The purpose of this study was to evaluate whether or not a recent change in the femoral design (PFC Sigma PS) had a positive impact on the patello-femoral complication rate.

Materials and methods

A consecutive series of 100 TKA using the PFC Sigma PS system was followed prospectively for a minimum of 3 years. All patellae were replaced and a standard lateral release was never performed. Radiographic analysis following the Knee Society Score (KSS) included antero-posterior weight-bearing, lateral and bilateral axial radiographs. TKA rotational alignment was recorded at the final follow-up in 30 consecutive knees by performing a CT evaluation.

Results

Good to excellent clinical results according to the KSS were achieved in 94 % of the knees. Survival without need of reoperation for any reason was 98 % at 3 years minimum follow-up; two reoperations were done for removal of fibromatous intra-articular tissue (“Clunk syndrome”). There were no revisions for septic or aseptic loosening of the components. The mean ROM improved from 104° preoperatively to 115° (97°–132°) postoperatively: postoperative flexion was 120° or more in 58 % of the knees. Severe anterior knee pain was present in 9 % of patients. Radiographic evaluation showed 90 knees with a tibio-femoral anatomical axis between 8° and 2° of valgus (±3° from the intraoperative goal). CT evaluation of 30 consecutive knees showed that the femoral component positioning in relationship to the trans-epicondylar axis had only 2.80° of external rotation (±2.10°) with respect to a planned external rotation of 3°. This difference was statistically significant.

Conclusions

Although the PFC Sigma PS system provides good and predictable results for tricompartmental arthritis of the knee, anterior mechanism complications still represent a reason for dissatisfaction in a substantial group of patients.     

Early failure of the femoral component in unicompartmental knee arthroplasty

Unicompartmental knee arthroplasty has been proposed as treatment for unicompartmental arthritis. Overall, results have been satisfactory, with occasional failures of tibial component fixaton. Short-term loosening of the femoral components in unicompartmental knee arthroplasty that required revision to total knee arthroplasty is reported. All patients presented with pain and instability of the knee, with loosening confirmed radiographically and at revision surgery. The Porous-Coated Anatomic femoral component (Howmedica, Rutherford, NJ) was biomechanically tested after being implanted in cadaver limbs. Cyclic loading in flexion and extension under physiologic loads resulted in implant failure. The model of failure was rocking in the sagittal plane, which corresponds to the clinical findings. The femoral implant design consists of an angled bone-implant interface with straight arms, which causes shear at the bone-prosthesis interface and ultimate toggling and failure. A femoral component with a curved bone implant interface did not loosen under identical biomechanical testing in paired knees. It was concluded that the Porous-Coated Anatomic femoral component has an unacceptably high early clinical loosening rate, confirmed by comparative biomechanical testing.     

Rotational malalignment of the femoral component in total knee arthroplasty

Ligamentous balancing is a crucial part of total knee arthroplasty. To ensure proper kinematics, balance must be achieved in flexion and extension. Failure to do so may result in limited range of motion, premature polyethylene wear, or patellofemoral tracking problems. Balancing in extension is dependent on the type and extent of correctional ligamentous release. Flexion balance is dependent on proper femoral rotation. There are two methods to determine femoral rotation. In the classic method, the knee is tensed in flexion after ligamentous release in extension. The anteroposterior cut then is made parallel to the cut tibial surface. Alternatively, the anteroposterior cut can be based off fixed femoral landmarks. The purpose of the current study was to determine the variance between balancing the flexion gap with the classic method versus the technique of using fixed femoral landmarks to determine rotation. One hundred consecutive posterior stabilized knee arthroplasties were performed using the classic method. The resected posterior condyles in each case were measured. The actual difference between the resected condyles using the classic method was compared with the calculated difference of resected bone using bony landmarks to determine rotation. A variance analysis then was performed. Compared with classically balanced knees, rotational errors of at least 3 degrees occurred in 45 % of patients when rotation was determined from fixed bony landmarks. These patients had trapezoidal rather than rectangular flexion gaps. Such errors may have implications regarding polyethylene wear, range of motion, and long-term clinical results.     

Fracture of femoral component in a resurfacing total knee arthroplasty

We present a case of an unusual complication after a resurfacing total knee arthroplasty. Fracture of the uncemented porous-coated femoral component occurred 4 years after its implantation. The mechanical axis was restored and collateral ligament balance was achieved at the primary procedure. At revision, the femoral component was found fractured at the junction of the trochlea with the medial condyle, anteriorly to the medial peg. A thin layer of fibrous tissue was interposed between bone and metal under the fracture area. Metallurgical analysis of the fractured component revealed fatigue failure but no structural defect. Lack of bony support and excessive cyclic loading led to fracture of the implant.     

Fracture of the femoral component in unicompartmental total knee arthroplasty

A fracture of the anterior flange of a femoral component in a unicompartmental knee has been seen. This was thought to be due to lack of bony support leading to cantilever bend. The solution would seem to be to add a metal web to strengthen that area of the femoral component.     

全膝关节置换术股骨假体旋转力线研究进展

股骨假体旋转力线是影响全膝关节置换术预后的极其重要环节.以哪条轴线作为术中参照轴才能够最大程度地保证股骨假体旋转轴线对位准确,目前仍存有争议.该文就全膝关节置换术中各种股骨假体旋转定位参照轴的可靠性等作一综述.     

Role of abrasion of the femoral component in revision knee arthroplasty

We carried out 60 revision procedures for failed porous coated anatomic total knee replacements in 54 patients, which were divided into two groups. The 14 knees in group I had a well-fixed femoral component at surgery which was retained, and in the 46 knees in group II both tibial and femoral components were loose and were revised using a variety of implants. Our review comprised clinical and radiological assessment. A total of 13 knees required a second revision. Six (42%) in group I failed very early (mean 2.1 years) when compared with seven (15%) in group II (mean 6.8 years). Failure was due to wear of the polyethylene insert by the abraded, retained femoral component (crude odds ratio 4.07; 95% CI 1.07 to 15.5). We recommend a complete change of primary bearing surfaces at the time of revision of an uncemented total knee replacement in order to prevent early wear of polyethylene.     

Computed tomographic evaluation of femoral component rotation in total knee arthroplasty

Background:

Optimal femoral component rotational alignment in total knee arthroplasty (TKA) is crucial to establish a balanced knee reconstruction. Unbalanced knees can lead to instability, patellofemoral problems, persistent pain, stiffness, and generally poorer outcomes including early failure. Intraoperative techniques to achieve this optimal femoral component rotation include the use of the transepicondylar axis (TEA), the posterior-condylar-cut-parallel-to-the-tibial-cut (PCCPTC) technique and the anteroposterior axis technique (Whiteside''s line). The purpose of this study was to compare the PCCPTC technique to the TEA technique using computed tomography (CT) scans to assess femoral component rotational alignment.

Materials and Methods:

This study used postoperative CT scans to compare the degree of femoral component rotation obtained with the use of PCCPTC technique and the TEA. The femoral component rotation of 30 TKA was measured on postoperative CT scans the angle of deviation between the two lines radiographic trans-epicondylar axis (rTEA) and femoral prosthesis posterior condylar line (FPPCL) was determined. This angle represented the rotation of the femoral component relative to the true rTEA.

Results:

The degree of rotation measured 2.67 ± 1.11 degrees in the PCCPTC group and 5.60 ± 1.64 degrees in the TEA group.

Conclusion:

The use of the TEA technique for determining rotational alignment in TKR results in excessive external rotation of the femoral component compared to the PCCPTC technique.     

Sagittal plane positioning of the femoral component in total knee arthroplasty

The authors evaluated 623 total knee arthroplasties to determine the relationship between sagittal plane position of the femoral component and the final range of motion of the prosthetic knee. Two different prostheses were evaluated (Posterior Cruciate Condylar and A.G.C.) radiographically and functionally. Variation in sagittal plane position ranged from 20 degrees flexion to 20 degrees extension. No correlation between the sagittal plane position of the femoral component in either prosthesis and the final knee range of motion could be found. Sagittal plane femoral component position in the prostheses studied did not affect final range of motion when component position was between 20 degrees flexion and 20 degrees of extension.     

Intraoperative assessment of femoral component rotational alignment in total knee arthroplasty

Poor clinical results following total knee arthroplasty like flexion gap instability or anterior knee pain may be related to femoral component rotational malalignment. The transepicondylar axis has been recommended as a landmark to consistently recreate a balanced flexion gap. However, the reproducibility to identify the transepicondylar axis intraoperatively is low. In this feasibility study we wanted to find out whether fluoroscopy-based CT scans obtained by a motorized mobile C-arm (Iso C 3D) may be useful to asses the transepicondylar axis intraoperatively. Following the femoral resections the Iso C 3D was used intraoperatively in ten knees with mild to severe deformities. On multiplanar reconstructions of the distal femur the clinical epicondylar axis as well as the angle to the posterior cut (condylar twist angle) could be easily measured. The scanning time was 40 s and the extra time needed for the whole setup about five to ten minutes. The Iso C 3D was helpful to intraoperatively identify the transepicondylar axis and the condylar twist angle, especially in cases with severe deformity or dysplasia when standard landmarks are difficult to determine. Florian Geiger and Dominik Parsch contributed equally to this article.     

The influence of femoral component design in the elimination of patellar clunk in posterior-stabilized total knee arthroplasty

Patellar clunk occurs after posterior-stabilized total knee arthroplasty and is believed to be a design-related complication. This study was undertaken to define the incidence of patellar clunk with an optimized third-generation, posterior-stabilized prosthesis. One hundred ninety three patients with 238 knees were evaluated at a minimum of 2 years after primary total knee arthroplasty with a cemented, NexGen Legacy Posterior-Stabilized prosthesis (Zimmer, Warsaw, Ind). The mean follow-up was 48 months (range, 24-72 months). No patient manifested symptoms of patellar clunk or underwent surgery for any patello-femoral problem. These results support prior evidence that femoral component design is the primary cause of patellar clunk and that modifications incorporated into this third-generation, posterior-stabilized prosthesis has eliminated the problem.