In vivo anteroposterior femorotibial translation of total knee arthroplasty: a multicenter analysis

Sensitivity of knee soft-tissues to surgical technique in total knee arthroplasty

Restricted range of motion and excessive laxity are both potential complications of total knee arthroplasty (TKA). During TKA surgery, the surgeon is frequently faced with the question of how tightly to implant the prosthesis. The most common method of altering implantation tightness is to vary the thickness of the polyethylene inlay after the bone cuts have been made and the trial components inserted. We have sought to quantify how altering the polyethylene thickness may affect post-operative soft tissue tension for a range of prosthetic designs. Four different prosthetic designs were implanted into fresh-frozen cadaveric knee joints. All four designs were implanted in the standard manner, with a 100 Newton distraction force used to set soft tissue balance. The tibiofemoral force was then recorded at 15° intervals throughout the passive flexion range. After the standard implantation of each prosthesis, the tibial component was raised or lowered to mimic increasing and decreasing the polyethylene thickness by 2mm and the force measurements repeated. Tibiofemoral force in extension correlated with implantation tightness for all prosthesis designs. Between 15° and 90° of knee flexion, all four designs were insensitive to changes in implantation tightness. Beyond 90° the effect was more notable in rotating platform mobile-bearing and cruciate-retaining prostheses than in posterior-stabilised mobile-bearing designs. The findings of this research may be useful in assisting surgical decision-making during the implantation of TKA prostheses.

Mobile-bearing total knee arthroplasty: a meta-analysis

An extensive database search was completed to perform a meta-analysis of outcomes of mobile-bearing total knee arthroplasty. Nineteen manuscripts encompassing 3506 total knee arthroplasty met criteria for analysis (average follow-up, 8.6 years). Data were subdivided based on design type and included rotating platform, meniscal bearing, and anterior-posterior glide-rotation subgroups. Fifteen-year survivorship of rotating platform designs (96.4%) was greater than meniscal bearing implants (86.5%). Mean component loosening (0.33%) and bearing instability (<1%) for all subgroups were uncommon. Implants placed prior to 1995 exhibited higher rates of bearing complications (1.6% vs 0.1%). Excellent results were obtained with mobile-bearing TKA over 2 decades. Loosening and bearing instability were uncommon. Bearing complications lessened after 1995, possibly secondary to improved surgical technique.

High flexion total knee arthroplasty - mid-term follow up of 5 years

Because of demographic changes, ever greater demands are made of knee replacement systems by patients and surgeons. To meet these demands, knee joint systems with increased flexion are currently being marketed. The main hypothesis of the present study was to evaluate the functional outcome of a high flexion TKA in amid-term follow up. 75 consecutive patients (29 men and 46 women) who had primary arthritis of the knee with similar deformity and range of motion undergo TKA using a NexGen Cr Flex mobile.

Knee Society knee and functional scores and range of motion were assessed.

The follow-up duration was 5 years. There was a highly significant improvement in comparison to the preoperative status (p<0.005). The maximum flexion was 122° in mean and the mean KSS was 167 (SD: 21) at final follow up. Despite positive results in the first 5 postoperative years, the NexGen Cr Flex mobile TKA shows no advantages with regard to ROM and KSS compared to the recent literature. Long-term studies are needed to determine a superiority of high flexion knee implants versus traditional TKA´s.

Patients prefer a bicruciate-retaining or the medial pivot total knee prosthesis

Four-hundred forty patients underwent staged bilateral total knee arthroplasty using a different prosthesis on each side. Prostheses used were anterior-posterior cruciate-retaining (ACL-PCL), posterior cruciate-retaining (PCL), Medial Pivot (MP), posterior cruciate-substituting (PS), and mobile bearing (MB). At the 2-year evaluation, we asked "Which is your better knee overall?" Responses were as follows: 89.1% preferred the ACL-PCL to the PS and 76.2% preferred the MP to the PS. The ACL-PCL and the MP were preferred equally. The MP was preferred over the PCL by 76.0%, and 61.4% preferred the MP over the MB. The PS and PCL were preferred equally. Range of motion, pain relief, alignment, and stability did not vary significantly by prosthesis used. Patients with bilateral total knee arthroplasties preferred retention of both cruciates with use of the ACL-PCL prosthesis or substituting with an MP prosthesis.

Kinematics of medial osteoarthritic knees before and after posterior cruciate ligament retaining total knee arthroplasty

Total knee arthroplasty (TKA) is a widely accepted surgical procedure for the treatment of patients with end-stage osteoarthritis (OA). However, the function of the knee is not always fully recovered after TKA. We used a dual fluoroscopic imaging system to evaluate the in vivo kinematics of the knee with medial compartment OA before and after a posterior cruciate ligament-retaining TKA (PCR-TKA) during weight-bearing knee flexion, and compared the results to those of normal knees. The OA knees displayed similar internal/external tibial rotation to normal knees. However, the OA knees had less overall posterior femoral translation relative to the tibia between 0° and 105° flexion and more varus knee rotation between 0° and 45° flexion, than in the normal knees. Additionally, in the OA knees the femur was located more medially than in the normal knees, particularly between 30° and 60° flexion. After PCR-TKA, the knee kinematics were not restored to normal. The overall internal tibial rotation and posterior femoral translation between 0° and 105° knee flexion were dramatically reduced. Additionally, PCR-TKA introduced an abnormal anterior femoral translation during early knee flexion, and the femur was located lateral to the tibia throughout weight-bearing flexion. The data help understand the biomechanical functions of the knee with medial compartment OA before and after contemporary PCR-TKA. They may also be useful for improvement of future prostheses designs and surgical techniques in treatment of knees with end-stage OA.

In vivo normal knee kinematics: is ethnicity or gender an influencing factor?

BACKGROUND

In vivo studies have suggested Caucasians achieve lower average knee flexion than non-Western populations. Some previous studies have also suggested gender may influence condylar AP translation and axial rotation, while others report an absence of such an influence.

QUESTIONS/PURPOSES

We determined whether different ethnic and gender groups residing in the United States had different knee translations and rotations.

METHODS

Three-dimensional knee rotations and translations were determined for 72 healthy subjects (24 Caucasian men, 24 Caucasian women, 13 Japanese men, 11 Japanese women) from full extension to maximum flexion using a fluoroscopic technique, under in vivo, weightbearing conditions.

RESULTS

Although we observed substantial variability in all groups, small differences between groups were found, especially in deep flexion. Japanese women and men and Caucasian women achieved higher maximum flexion (153°, 151°, and 152°, respectively) than Caucasian men (146°). External rotation was higher for these three groups than for Caucasian men. The medial condyle remained more anterior for Caucasian women and all Japanese subjects than for Caucasian men, possibly leading to greater axial rotation and flexion, observed for these three groups.

CONCLUSION

We identified small differences in maximum flexion between genders and ethnic groups. While no differences were identified in the lateral condyle translation, the medial condyle remained more stationary and more anterior for the groups that achieved highest (and similar) maximum flexion. Therefore, it may be important for future implant designs to incorporate these characteristics, such that only the lateral condyle experiences greater posterior femoral rollback, while the medial condyle remains more stationary throughout flexion.

Primary resection of the posterior cruciate ligament does not produce a gap mismatch in the navigated gap technique

Treatment of the posterior cruciate ligament (PCL) is a matter of continued controversy in total knee arthroplasty. By using so-called cruciate ligament-substituting implant designs, retention and resection of the PCL produce equivalent clinical results. However, it remains unclear whether primary resection of the PCL leads to relevant instabilities of the flexion gap. Especially when the increasingly popular navigated gap technique is used, this would result in a nonanatomic size selection and positioning of the femoral component and thus compromise the clinical outcome. The objective of this retrospective study was therefore to determine whether the navigated gap technique leads to a mismatch of the flexion and extension gap in primary routine resection of the PCL. In 92 patients consecutively enrolled in this study (92 knees), the flexion and extension gap were determined and documented after tibial resection, using the navigated gap technique navigation system (OrthoPilot 4.0; B. Braun Aesculap, Tuttlingen, Germany). The flexion gap was 10.4 ± 2.6 (2.5-19.5) mm; the extension gap was 10.4 ± 2.4 (5.5-17.5) mm. The individual difference was normally distributed around 0.0 ± 2.9 (-7 to 7) mm. In the navigated gap technique, primary routine resection of the PCL does not lead to a mismatch of the flexion and extension gap, so that a systematic nonanatomic resection of the femur can be ruled out.

In vivo comparison of knee kinematics before and after high-flexion posterior cruciate-retaining total knee arthroplasty

The objectives of this study were to compare preoperative and postoperative knee kinematics for subjects implanted with flexion-enhanced posterior cruciate-retaining total knee arthroplasty during deep flexion and to examine flexion performance of the prosthesis design. Three-dimensional kinematics was analyzed by fluoroscopic examinations of subjects using a single-plane model-image registration technique. Preoperatively, knee kinematics demonstrated small posterior femoral translation and limited axial rotation. These motions differed significantly from patterns previously reported for normal knees. Postoperatively, flexion performance was maintained, averaging 130 degrees , and kinematic patterns were similar to preoperative patterns. Although total knee arthroplasty can reduce pain and maintain functional performance, it appears that the characteristics of varus arthritic knee mechanics persist after arthroplasty.

Cruciate-retaining TKA using a third-generation system with a four-pegged tibial component: a minimum 10-year followup note

BACKGROUND

A third-generation TKA system was designed to address problems encountered with earlier designs including a high rate of patellofemoral complications. At a minimum of 5 years, we previously reported survivorship of 98.7% using revision for any reason as the endpoint for a cohort that includes the patients described in this report. That cohort was unique in that a tibial component that uses four short pegs for fixation was used in a subset of patients undergoing cruciate-retaining TKA and the tibial and femoral components were precoated with polymethylmethacrylate.

QUESTIONS/PURPOSES

We now report the survival rate, postoperative function, complications, radiographic loosening, and osteolysis at a minimum of 10 years postoperatively.

PATIENTS AND METHODS

We retrospectively reviewed 161 patients who underwent 179 TKAs. The patella was resurfaced in all cases and all components were cemented. Patients were evaluated clinically and radiographically for evidence of component loosening and osteolysis. Forty of the 161 patients (with 44 TKAs) had died and eight patients (nine knees) were lost to followup. For the remaining 113 patients (126 knees), the minimum followup was 10 years (mean, 11.7 years; range, 10.0-13.9 years).

RESULTS

Survivorship at a minimum of 10 years postoperatively using revision for any reason and revision for aseptic loosening were 97.7% and 100%, respectively. Three knees were revised: one for infection, one for periprosthetic fracture, and one for postoperative arthrofibrosis. There were no reoperations for patellar component maltracking, wear or loosening, tibiofemoral polyethylene wear, osteolysis, or aseptic loosening. Hospital for Special Surgery scores improved from a mean of 47.7 (range, 23-78) preoperatively to 85.4 (range, 33-100).

CONCLUSIONS

This cruciate-retaining design had a low risk of implant failure or revision and the design changes eliminated the patellar failures seen with earlier iterations at up to 10 years.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Physical examination and in vivo kinematics in two posterior cruciate ligament retaining total knee arthroplasty designs

The aim of this study was to investigate anteroposterior instability in the CKS and the PFC total knee arthroplasty (TKA) designs. Physical examinations, including VAS, IKS and WOMAC were performed in combination with a detailed fluoroscopic measurement technique for three-dimensional kinematic assessment of TKA design function. Anteroposterior instability rated with the IKS was not significantly different (p=0.34), but patients with a CKS design showed more limitations according to the WOMAC joint stiffness total score, and for items regarding higher flexion activities in the WOMAC score for knee disability. Kinematic analyses showed that the CKS design tended to have more anterior sliding of the femur on the tibia during mid- and deep flexion activities. The sliding distance was larger at the medial than at the lateral side. This phenomenon has also been described for posterior cruciate ligament deficient knees. Furthermore, the CKS design showed a significantly lower range of tibial rotation (p<0.05) from maximum extension to maximum flexion during deep knee bend activities. Kinematic differences can be ascribed to posterior cruciate ligament deficiency/laxity or differences in TKA designs.

Comparative study of intraoperative knee flexion with three different TKR designs

INTRODUCTION

Substantial flexion after total knee arthroplasty (TKA) is required for certain categories of patients who wish to squat or kneel in their daily life. Many factors influence this postoperative flexion, including the prosthesis design. It is therefore valuable to in vivo analyze these factors on three knee prosthesis designs through a study of their intraoperative flexion.

HYPOTHESIS

The posterior-stabilized (PS) knee prostheses provide better intraoperative flexion than the ultracongruent (UC) model. Of the currently available PS models, the high-flexion ones have better intraoperative flexion than standard models. Our main focus endpoint was the intraoperative flexion achieved, before soft-tissues closure, during TKA surgical procedure.

PATIENTS AND METHODS

This was a controlled study. Seventy-two osteoarthritic knees requiring TKA were included to compare three selected prosthesis models: the SAL ultracongruent and two PS models (the standard LPS and the LPS Flex). This was a single-operator study, with patients divided into three homogenous, comparable groups, in which intraoperative measurement of flexion was performed using computer-assisted navigation. Statistical analysis allowed comparison of the three models.

RESULTS

Intraoperatively, after prosthesis implantation, before soft-tissues closure, the mean flexion of the LPS-Flex was 134 degrees versus 124 degrees for the SAL (p=0.0004); the mean flexion of the standard LPS model was 130 degrees versus 124 degrees for the SAL (p=0.14); the PS Flex model showed no significant difference (p=0.26) in flexion (134 degrees) compared to the standard model (130 degrees). The SAL ultracongruent model seemed to be a factor reducing the intraoperative flexion by 8 degrees compared to the PS models (p<10(-4)).

DISCUSSION

In this study, the PS designs (standard or Flex) provided better intraoperative flexion than the SAL ultracongruent design. However, the LPS Prosthesis did not demonstrate superiority over the standard LPS Prosthesis.

LEVEL OF EVIDENCE

Level III, low-power prospective study.

Functional performance with a single-radius femoral design total knee arthroplasty

BACKGROUND

Better muscular recovery of the extensor mechanism after TKA is claimed by femoral designs based on a sagittal single radius.

QUESTIONS/PURPOSES

We aimed to compare postoperative knee performance through the Knee Society scores, flexor and extensor muscle function, stability, and gait of a series of patients receiving a posterior stabilized, cemented TKA, with a single-radius femoral design.

METHODS

We compared a series of patients treated with a single-radius femoral design TKA to a simultaneous series of patients receiving a multiradius femoral design. Both groups were similar in demographics and preoperative Knee Society scores. The clinical pathways were identical. Outcome assessment included Knee Society scores, isokinetic assessment, stabilometry, and gait cycle analysis.

RESULTS

We observed higher functional Knee Society scores (86.6 +/- 1.89 versus 80.3 +/- 1.90), fewer physiotherapy sessions (19.9 +/- 4.65 versus 22.2 +/- 3.34), and less time with two crutches (3.5 +/- 1.2 versus 5.2 +/- 1.04 weeks) for patients receiving the single-radius design. Isokinetic evaluation showed decreased flexion peak torque (40.3 +/- 7.9 versus 48.7 +/- 9.6), increased extension peak torque (77.2 +/- 16.1 versus 69.1 +/- 14.4), and lower flexor/extensor ratio (0.5 +/- 0.08 versus 0.7 +/- 0.1) in patients with the single-radius design. Stabilometry showing less relative oscillation, and gait cycle indirectly confirmed better support in the limb with the single-radius design.

CONCLUSIONS

The studied single-radius femoral design showed better functional short-term outcome and better extensor performance.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

In vivo kinematics after a cruciate-substituting TKA

Patterns of motion in the native knee show substantial variability. Guided motion prosthetic designs offer stability but may limit natural variability. To assess these limits, we therefore determined the in vivo kinematic patterns for patients having a cruciate-substituting TKA of one design and determined the intersurgeon variability associated with a guided-motion prosthetic design. Three-dimensional femorotibial contact positions were evaluated for 86 TKAs in 80 subjects from three different surgeons using fluoroscopy during a weightbearing deep knee bend. The average posterior femoral rollback of the medial and lateral condyles for all TKAs from full extension to maximum flexion was -14.0 mm and -23.0 mm, respectively. The average axial tibiofemoral rotation from full extension to maximum flexion for all TKAs was 10.8 degrees. The average weightbearing range of motion (ROM) was 109 degrees (range, 60 degrees-150 degrees; standard deviation, 18.7 degrees). Overall, the TKA showed axial rotation patterns similar to those of the normal knee, although less in magnitude. Surgeon-to-surgeon comparison revealed dissimilarities, showing the surgical technique and soft tissue handling influence kinematics in a guided-motion prosthetic design.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

The Mark Coventry Award: Articular contact estimation in TKA using in vivo kinematics and finite element analysis

In vivo fluoroscopy is a well-known technique to analyze joint kinematics of the replaced knee. With this method, however, the contact areas between femoral and tibial components, fundamental for monitoring wear and validating design concepts, are hard to identify. We developed and tested a novel technique to assess condylar and post-cam contacts in TKA. The technique uses in vivo motion data of the replaced knee from standard fluoroscopy as input for finite element models of the prosthesis components. In these models, tibiofemoral contact patterns at the condyles and post-cam articulations were calculated during various activities. To test for feasibility, the technique was applied to a bicruciate posterior-stabilized prosthesis. Sensitivity of the finite element analysis, validation of the technique, and in vivo tests were performed. To test for potential in the clinical setting, five patients were preliminarily analyzed during chair rising-sitting, stair climbing, and step up-down. For each task and patient, the condylar contact points and contact line rotation were calculated. The results were repeatable and consistent with corresponding calculations from traditional fluoroscopic analysis. Specifically, natural knee kinematics, which shows rolling back and screw home, seemed replicated in all motor tasks. Post-cam contact was observed on both the anterior and posterior faces. Anterior contact is limited to flexion angle close to extension; posterior contact occurs in deeper flexion but is dependent on the motor task. The data suggest the proposed technique provides reliable information to analyze post-cam contacts.

Gap balancing versus measured resection technique for total knee arthroplasty

Multiple differing surgical techniques are currently utilized to perform total knee arthroplasty (TKA). We compared knee arthroplasties performed using either a measured resection or gap balancing technique to determine if either operative technique provides superior coronal plane stability as measured by assessment of the incidence and magnitude of femoral condylar lift-off. We performed 40 TKA using a measured resection technique (20 PCL-retaining and 20 PCL-substituting) and 20 PCL-substituting TKA were implanted using gap balancing. All subjects were analyzed fluoroscopically while performing a deep knee bend. The incidence of coronal instability (femoral condylar lift-off) was then determined using a 3-D model fitting technique. The incidence of lift-off greater than 0.75 mm was 80% (maximum, 2.9 mm) and 70% (maximum, 2.5 mm) for the PCL-retaining and substituting TKA groups performed using measured resection versus 35% (maximum, 0.88 mm) for the gap-balanced group. Lift-off greater than 1 mm occurred in 60% and 45% of the PCL-retaining and -substituting TKA using measured resection versus none in the gap-balanced group. Rotation of the femoral component using a gap balancing technique resulted in better coronal stability which we suggest will improve functional performance and reduce polyethylene wear.

Assessment of tibiofemoral position in total knee arthroplasty using the active flexion lateral radiograph

This study is a retrospective comparative cohort radiographic analysis of 114 consecutive patients who underwent posterior cruciate retaining (PCR) total knee arthroplasty (TKA), medial and patellofemoral compartment bicruciate retaining arthroplasty (BCR), or bicruciate substituting (BCS) TKA. In an effort to obtain a quantitative measurement of both anteroposterior (AP) tibiofemoral position and active knee flexion we have routinely taken post-operative lateral radiographs in a position of maximal active flexion. Passive range of motion (PRoM) after TKA was significantly greater than pre-operative passive range of motion for each cohort (p<0.001). When comparing post-operative active range of motion (ARoM) to PRoM, there was a statistically significant difference within the PCR and BCR cohorts (p<0.001 and p<0.005, respectively), while none was detected in the BCS group (p=0.09). The mean rollback of PCR was -1.2 mm, BCR was -3.3 mm and BCS was -12.0 mm. The mean rollback of all three groups was similar to measurements reported from previous fluoroscopic historical control data. Our findings indicate that tibiofemoral AP translation during knee flexion can be assessed on an active flexion lateral knee radiograph and provide additional information that is not available from a routine lateral radiograph.

Quadriceps force in relation of intrinsic anteroposterior stability of TKA design

PURPOSE

Decreased quadriceps strength and fatigue is suspected to be one of the contributing factors for anterior knee pain and malfunction after total knee arthroplasty (TKA). The purpose of this in vitro study was to investigate the amount of quadriceps force required to extend the knee isokinetically after TKA in dependence of different prosthesis designs and the state of the posterior cruciate ligament (PCL).

MATERIALS AND METHODS

Eight fresh frozen human knee specimens underwent testing in a kinematic device simulating an isokinetic knee extension cycle from 120° of flexion to full extension. The quadriceps force was measured after implantation of a cruciate retaining (CR) TKA (Genesis II, Smith&Nephew, Memphis, TN, USA) applying a conventional CR (11 mm) and a highly conforming (deep dished, DD) polyethylene (PE) inlay consecutively before and after resection of the PCL. Finally, tests were repeated with a posterior-stabilized (PS) design.

RESULTS

Simulating a physiological knee extension, no significant differences in the average quadriceps force were detected between the cruciate preserving inlays (CR 1,146.57 ± 88.04 N, DD 1,150.19 ± 97.54 N, P = 0.86) as long as the PCL was intact. After resection of the PCL, the required quadriceps force increased significantly for both designs (CR 1,203.17 ± 91.51 N, P < 0.01 and DD 1,191.88 ± 80.07 N, P < 0.03). After implantation of the posterior stabilized femoral component quad force decreased to its initial levels with forces significantly lower compared to the PCL deficient knees provided with a CR or DD (PS 1,130.91 ± 107.88 N, P < 0.01) inlay. With a deficient PCL there were no statistical differences for the DD design in comparison with CR in mean quad forces (CR 1,203.17 ± 91.51 N vs. DD 1,191.88 ± 80.07 N, P = 0.50) nor in peak forces (CR 1,729.44 ± 161.86 N, DD 1,688.66 ± 123.18 N, P = 0.17).

DISCUSSION

At intact PCL peak quad forces and mean forces beyond 70° of flexion could be shown to be significantly lower with a PS TKA design in comparison with cruciate preserving designs such as CR and DD. In the PCL deficient knee quad forces with a highly conforming implant (DD) and CR were significantly higher than with a PS TKA. The use of PS implants in all PCL deficient knees seems to be advisable

Biomechanical analysis of posterior cruciate ligament retaining high-flexion total knee arthroplasty

BACKGROUND

High-flexion knee replacements have been developed to accommodate a large range of flexion (>120 degrees ) after total knee arthroplasty. Both posterior cruciate ligament retaining and sacrificing high-flexion knee designs have been marketed. The main objective of this study was to evaluate the biomechanical performance of a cruciate-retaining high-flexion knee replacement. Furthermore, the mechanical behaviour of this high-flexion knee replacement was compared to both a cruciate-retaining conventional and a posterior-stabilized high-flexion knee replacement.

METHODS

A finite element prosthetic knee model was developed to analyze the mechanical performance of the knee designs evaluated in this study. Polyethylene stresses and the amount of femoral rollback were studied during a squatting movement (flexion <or=150 degrees).

FINDINGS

During deep knee flexion, the cruciate-retaining high-flexion design demonstrated a lower peak tibio-femoral contact stress (74.7 MPa) than the cruciate-retaining conventional design (96.5 MPa). The posterior-stabilized high-flexion design showed the lowest peak tibio-femoral contact stress at the condylar articulation (54.2 MPa), although the post was loaded higher (77.4 MPa). The knee designs analyzed in this study produced a similar amount of femoral rollback during normal knee flexion (flexion > 120 degrees), whereas the cruciate-retaining designs showed a paradoxical anterior movement of the femoral condyles during high-flexion (flexion>120 degrees).

INTERPRETATION

The current study demonstrates a cruciate-retaining high-flexion knee replacement produces a lower prosthetic load than a conventional cruciate-retaining replacement during deep knee flexion. Compared to a posterior-stabilized high-flexion design, the cruciate-retaining high-flexion design demonstrated an equivalent prosthetic loading along with an inferior amount of femoral rollback in the high-flexion range. Posterior cruciate ligament balancing is an important surgical aim for high-flexion knee arthroplasty.

The effect of geometry of the tibial polyethylene insert on the tibiofemoral contact kinematics in Advance Medial Pivot total knee arthroplasty

BACKGROUND

In modern total knee arthroplasty (TKA), it is important to reproduce both medial pivot motion and posterior femoral rollback to obtain greater postoperative knee flexion. Several studies have reported the factors affecting knee motion and range of motion after TKA. The purpose of this study was to evaluate the effect of the tibial insert geometry on the tibiofemoral contact kinematics, especially focusing on the medial pivot motion and posterior femoral rollback.

METHODS

Seven cadaveric knees were replaced with the Advance Medial Pivot TKA, and two different geometries of polyethylene tibial insert, the standard medial pivot design (MP-design) and double high design (DH-design), were biomechanically compared. Four experimental configurations were evaluated in each specimen in this order: (1) the MP-design with posterior cruciate ligament (PCL) retaining, (2) the DH-design with PCL retaining, (3) the MP-design with PCL sacrificing, and (4) the DH-design with PCL sacrificing.

RESULTS

Under the PCL-retaining condition, both designs showed no medial pivot but bicondylar femoral rollback more than 60 degrees of knee flexion. In the MP-design, tibiofemoral contact point (estimated contact point, ECP) of the medial compartment was located on the posterior lip of the ball-insocket structure while demonstrating greater than 120 degrees of knee flexion. The posterior translation was also the same in both designs. On the other hand, ECP of the MP-design and the DH-design showed only medial pivot pattern under the PCL-sacrificing condition. In the DH-design, ECP of the lateral compartment showed paradoxical anterior translation from 0 degrees to 60 degrees of knee flexion. Total posterior translation was significantly greater in the lateral compartment than that in the medial compartment.

CONCLUSIONS

The results of this study suggest that in this type of TKA system the ball-in-socket geometry in the MP-design has an advantage for reproducing medial pivot motion in the PCL-sacrificing condition, and the flexion path structure in the DH-design is considered to be both effective and safe for femoral rollback in the PCL-retaining condition. However, neither design is sufficient to reproduce medial pivot motion and posterior femoral rollback. Therefore, a different design of tibial insert is needed for more physiological kinematics after TKA.

Posterior stabilized TKA reduce patellofemoral contact pressure compared with cruciate retaining TKA in vitro

Increased patellofemoral contact pressure was described after total knee arthroplasty (TKA). Aim of this in vitro study was to compare the influence of a posterior stabilized (PS) design in comparison to a cruciate retaining (CR) design on patellofemoral contact pressure. Patellofemoral area contact pressure, peak contact pressure and the centre of pressure motion were determined in eight fresh frozen human cadaveric specimens using a Tekscan sensor (K-Scan 4000). A robotic knee simulator was used simulating an isokinetic knee extension cycle from 120 degrees of flexion to full extension. All knees were tested in a first test cycle after implantation of a CR design and in a second test cycle after replacement by a PS design, both using a 11 mm PE inlay (Genesis II, Smith & Nephew, Memphis, TN, USA). The patella remained unresurfaced. A paired sampled t test to compare mean values (significance, P < or = 0.05) was used for statistical analysis. After implantation of the PS design, average patellofemoral area contact pressure was significantly lower (P < or = 0.006) compared with the CR design (PS: 3.58 +/- 1.25 MPa; CR: 4.31 +/- 1.40 MPa). Accordingly, average patellofemoral peak contact pressure decreased significantly (P < or = 0.02) with the PS design (6.12 +/- 2.37 MPa) in comparison with the CR design (7.17 +/- 2.41 MPa). On average, the centre of pressure motion was more physiological with the PS design compared to the CR design over the complete extension cycle. However, this was not significant. In conclusion, the data suggest less patellofemoral contact pressure of a posterior stabilized TKA design in comparison to a cruciate retaining design.

Effect of posterior condylar offset on cruciate-retaining mobile TKA

The objective of this article was to evaluate the effect of the change of posterior condylar offset to range of motion (ROM) and clinical results after computer-assisted cruciate-retaining mobile-bearing total knee arthroplasty (TKA). A total of 111 knees underwent cruciate-retaining mobile-bearing TKAs under computer-assisted navigation from January 2005 to September 2007. All cases were primary osteoarthritis and had <15 degrees of valgus or varus deformity. We divided patients into 4 groups according to change of posterior condylar offset, which was measured by postoperative minus preoperative posterior condylar offset (group 1: <-2 mm; group 2: -2-0 mm; group 3: 0-+2 mm; group 4: >2 mm). Preoperative age, thigh girth, body mass index, flexion contracture, further flexion, Hospital for Special Surgery (HSS) score, Knee Society (KS) knee score, and KS functional score did not show significant difference between groups. The measured change of posterior condylar offset ranged from +3.70 to -3.95 mm with a mean value of -1.67 mm. Postoperatively, there were no statistical differences between each group on flexion contracture (P=.522), further flexion (P=.442), HSS score (P=.116), KS knee score (P=.479), or KS functional score (P=.578). We could find no significant difference between ROM or clinical results with computer-assisted cruciate-retaining mobile-bearing TKAs in the comparison of groups according to changes of posterior condylar offset.

In vivo determination of kinematics for subjects having a Zimmer Unicompartmental High Flex Knee System

The objective of this study was to determine the in vivo kinematics during weight-bearing and non-weight-bearing activities for subjects with a unicompartmental knee arthroplasty (UKA) designed for high flexion and implanted with minimally invasive techniques. A total of 30 UKAs implanted in 18 patients were analyzed. All patients were implanted with a medial Zimmer Unicompartmental High Flex Knee System (Zimmer Inc, Warsaw, Ind). Under fluoroscopic surveillance, each patient performed weight-bearing deep knee bend, normal gait, and passive flexion. The kinematics of the medial UKA was determined using a 3-dimensional model registration technique. On average, the implant experienced posterior femoral rollback and normal axial rotation during flexion. However, the kinematic patterns for each patient were not consistent, and the variability was high during flexion and stance phase of gait.

Tibiofemoral kinematic analysis of knee flexion for a medial pivot knee

The performance of total knee arthroplasty in deeply flexed postures is of increasing concern as the procedure is performed on younger, more physically active and more culturally diverse populations. Several implant design factors, including tibiofemoral conformity, tibial slope and posterior condylar geometry have been shown directly to affect deep flexion performance. The goal of this study was to evaluate the kinematics of a fixed-bearing, asymmetric, medial rotation arthroplasty design in moderate and deep flexion. Thirteen study participants (15 knees) with a medial rotation knee arthroplasty were observed performing a weight-bearing lunge activity to maximum comfortable flexion and kneeling on a padded bench from 90 degrees to maximum comfortable flexion using lateral fluoroscopy. Subjects averaged 74 years of age and nine were female. At maximum weight-bearing flexion, the knees exhibited 115 degrees of implant flexion (102 degrees-125 degrees) and 7 degrees (-3 degrees to 12 degrees) of tibial internal rotation. The medial and lateral condylar translated posteriorly by 2 and 5 mm, respectively. At maximum kneeling flexion, the knees exhibited 119 degrees of implant flexion (101 degrees-139 degrees ) and 5 degrees (-2 degrees to 14 degrees) of tibial internal rotation. The lateral condyle translated posteriorly by 11 mm. The medial rotation knee exhibited motion patterns similar to those observed in the normal knee, but less tibial rotation. The medially conforming articulation beneficially controls femoral AP position in deep flexion, in patients who require such motion as part of their lifestyle.

2009 Marshall Urist Young Investigator Award: how often do patients with high-flex total knee arthroplasty use high flexion?

Although high-flexion TKA designs aim to safely accommodate deep flexion, it is unknown how often patients use deep flexion outside the laboratory. We used a validated smart-activity monitor to document the prevalence of knee flexion greater than 90 degrees in 20 consecutive patients (21 knees) who had high-flexion TKAs, at a minimum of 2 years' followup. Patients wore the device continuously for a mean of 35.7 +/- 0.5 hours. The 21 knees flexed more than 90 degrees for an average of 10 +/- 3.8 minutes (0.5%). Activities performed with flexion greater than 90 degrees were, on average, 70% in single-limb stance, 12% moving from sitting to standing, 8% walking, 7% moving from standing to reclining, 2% stepping, 0.9% moving from lying to standing, and 0.1% running. Eight knees flexed greater than 120 degrees for an average of 2.2 minutes (range, 0.2-15 minutes), or 0.1% of the testing time. Activities performed with flexion greater than 120 degrees were, on average, 90% in single-limb stance, 6% moving from sitting to standing, 3% walking, 0.6% moving from standing to reclining, 0.3% stepping, and 0.1% moving from lying to standing. Peak flexion used at any time during testing was, on average, 84% +/- 11% of maximum postoperative flexion (125 degrees +/- 12 degrees). These patients rarely used deep flexion.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Mobile bearing knee kinematics change over time. A fluoroscopic study in rheumatoid arthritis patients

BACKGROUND

In a previous fluoroscopy study the motion of a mobile bearing total knee prosthesis was evaluated. That study showed that the axial rotation of the insert was limited. Three possible explanations are given for the limited rotation: low conformity between the femoral component and insert, the fixed anterior position of the insert-tibia pivot point leading to impingement and fibrous tissue formation. While the effect of the conformity on the axial rotation will not change over time, the effect of impingement and fibrous tissue is likely to increase, and thereby further decreasing the axial rotation.

METHODS

In order to accurately assess changes in axial rotation over time in a mobile bearing total knee prosthesis rheumatoid arthritis patient group, patients were evaluated 8 months and 3 years postoperatively using fluoroscopy.

FINDINGS

In comparison with the 8 months evaluation, the rotation of the femoral component (range: -10.8 degrees to 2.8 degrees) and the insert (range: -5.9 degrees to 1.4 degrees) were further limited at 3 years (respectively, -5.9 degrees to 4.9 degrees and -2.8 degrees to 5.4 degrees). Patterns of axial rotation for the femoral component and insert varied considerably between the trials within patients while at the 8 months evaluation no significant difference within patients was observed.

INTERPRETATION

This study shows the importance of re-evaluating knee kinematics over time. The axial rotation of both the femoral component as the insert decreased over time, indicating a kinematic change caused by intrinsic factors. The decline in rotation of the insert could be explained by increased impingement and the formation of fibrous tissue.

Intraoperative evaluation of total knee replacement: kinematic assessment with a navigation system

Interest in the kinematics of reconstructed knees has increased since it was shown that the alteration of knee motion could lead to abnormal wear and damage to soft tissues. We performed intraoperative kinematic measurements using a navigation system to study knee kinematics before and after posterior substituting rotating platform total knee arthroplasty (TKA). We verified intraoperatively (1) if varus/valgus (VV) laxity and anterior/posterior (AP) laxity were restored after TKA; (2) if TKA induced abnormal femoral rollback; and (3) how tibial axial rotation was influenced by TKA throughout the range of flexion. We found that TKA improved alignment in preoperative osteoarthritic varus knees which became neutral after surgery and maintained a neutral alignment in neutral knees. The VV stability at 0 degrees was restored while AP laxity at 90 degrees significantly increased after TKA. Following TKA, the femur had an abnormal anterior translation up to 60 degrees of flexion, followed by a small rollback of 12 +/- 5 mm. TKA influenced the tibia rotation pattern during flexion, but not the total amount of internal/external rotation throughout whole range of flexion, which was preserved after TKA (6 degrees +/- 5 degrees ). This study showed that the protocol proposed might be useful to adjust knee stability at time zero and that knee kinematic outcome during total knee replacement can be monitored by a navigation system.

Range of motion in total knee arthroplasty: a prospective comparison of high-flexion and standard cruciate-retaining designs

BACKGROUND

Range of motion after a total knee arthroplasty is an important indicator of clinical outcome. Recently, a high-flexion posterior cruciate ligament-retaining knee prosthesis was designed to allow greater flexion after total knee arthroplasty. The purpose of this study was to compare range of motion and functional outcomes in patients who received either a high-flexion cruciate-retaining or a standard cruciate-retaining knee replacement.

METHODS

Fifty knees that had a total knee arthroplasty with a high-flexion design and fifty that had a total knee arthroplasty with a standard design were included in this study and were followed prospectively for a minimum of two years. The arcs of maximal non-weight-bearing passive flexion and weight-bearing flexion were measured, and the number of knees that allowed the patients to kneel and sit cross-legged in comfort was determined. In addition, the functional outcomes in these two groups were assessed with use of the Hospital for Special Surgery and Western Ontario and McMaster Universities Osteoarthritis Index scores.

RESULTS

At the time of the final follow-up, the average maximal non-weight-bearing flexion was 135.3 degrees for the knees in the high-flexion group and 134.3 degrees for the knees in the standard group; the difference was not significant. Moreover, no significant difference was found between the groups in terms of weight-bearing flexion (124.8 degrees in the high-flexion group and 123.7 degrees in the standard group) and the number of knees that allowed kneeling and sitting cross-legged. The average Hospital for Special Surgery knee score was 94.4 points in the high-flexion group and 92.4 points in the standard group; the difference was not significant. The Western Ontario and McMaster Universities Osteoarthritis Index scores also showed no significant difference between the groups.

CONCLUSIONS

For knees managed with a cruciate-retaining total knee arthroplasty, those that had the high-flexion design and those that had the standard design were found to have a similar range of motion under both non-weight-bearing and weight-bearing conditions. Moreover, no significant difference was found in terms of the other functional outcomes examined.

In vivo kinematic determination of total knee arthroplasty from squatting to standing

This study analyzed three dimensional (3D) in vivo kinematic data from the squatting to standing position for 18 Japanese subjects (18 knees) implanted with either Legacy((R)) Posterior Stabilized (LPS) Flex Fixed Bearing TKA or LPS Flex Mobile Bearing TKA. Under weight-bearing conditions, for all patients, the average roll-forward motions for the medial and lateral condyles were 4.0+/-3.6 mm and 6.3+/-3.4 mm, and the average external axial rotation was 3.1 degrees +/-4.1 degrees . For both groups, the weight-bearing range-of-motion (ROM) (110.7 degrees +/-12.7 degrees ) was less than pre (127.2+/-15.5 degrees ) and post (135.6+/-5.4 degrees ) operative non-weight bearing ROM. As hypothesized, the incidence, average and maximum lift off for the squatting to standing activity were much less than those of deep knee bend (DKB), and condylar motions and kinematics were opposite that of the DKB. There was little statistical difference of their kinematic patterns during this activity between the LPS fixed and mobile TKA implants.

Patella retention versus replacement in total knee arthroplasty; functional and clinimetric aspects

INTRODUCTION

Whether to resurface the patella or not in total knee arthroplasty still remains undecided. Classical scores and questionnaires might not be responsive or demanding enough. This study used two accelerometer based systems to study the hypothesis whether performance based tests are able to detect a difference in patients with or without a resurfaced patella.

METHOD

In this retrospective study 53 patients were included and divided into a resurfaced group (n = 31) and a non-resurfaced group (n = 22). Both groups were matched on age and longevity of follow up. Patients were clinically assessed using the Knee Society Score (KSS) at various time points. At final follow up patients were also assessed once using the Dynaport Knee Test and the Minimod Gait Test.

RESULTS

The Dynaport Knee Test showed a significant functional advantage for patients with a resurfaced patella [44 vs. 39.7 (P = 0.042)], whereas KSS and The Minimod were not significant (P values ranging from 0.07 to 0.75). Similar to other reports in literature, using the KSS, it was not possible to identify significant difference between patella resurfacing or retaining in total knee arthroplasty, however using a performance based test it was possible to determine significant difference. The found advantage of patella resurfacing may be less due to pain relief but due to a functional benefit during demanding motion tasks. This finding indicates that current measurement tools may not be accurate or specific enough to detect this difference. Therefore, we recommend complementing the classic evaluation tools with an objective functional test, when conducting a randomized trial to answer the indecision whether to resurface the patella or not.

The INDUS knee prosthesis - Prospective multicentric trial of a posteriorly stabilized high-flex design: 2 years follow-up

BACKGROUND

The anatomical and morphological differences and high-flexion daily activities in the Asian population have since ever prompted for development of customized knee replacement systems. INDUS knee system has advantages both of high-flex designs and is developed by keeping the anatomical variations of the native population in mind. The purpose of this study is to analyze the 2-year follow-up results using the INDUS prosthesis.

MATERIALS AND METHODS

Two hundred and ninety-seven knees in 276 patients were prospectively analyzed. There were 65 men (72 knees) and 211 (225 knees) women with a mean age of 64.56 years. Two hundred and forty-five knees had primary osteoarthritis, 48 knees had rheumatoid arthritis, and four knees had post-traumatic arthritis. Clinical parameters, including the Knee Society scores (knee score and function score), range of motion, post-operative anterior knee pain, and complications were recorded. Pre- and post-operative serial radiographs were analyzed for limb alignment, component positioning, and evidence of loosening.

RESULTS

The patients were followed-up for an average of 2.59 years (range, 2-3.3 years). The mean knee score and the mean function score were significantly improved from a pre-operative value of 39.4 points and 46.7 points to a post-operative value of 87 points and 86 points, respectively (P value <0.05). Two hundred and thirty four knees had no anterior knee pain while 63 knees had mild to moderate pain, but none of the patients requested any intervention for the same. Of the 276 patients (297 knees), 79 knees had flexion above 140 degrees , 167 had a flexion range of 130-140 degrees , 27 had a flexion range of 100-130 degrees , and 24 knees had a flexion < 100 degrees , with the mean range of movement being 132.9 degrees . Improvements in the range of movement were retained over time and a total of 205 patients (224 knees, 75.7%) could squat or sit cross-legged at the final follow-up. The mean tibiofemoral angle was 8.5 degrees +/-6.9 degrees of varus pre-operatively and 5.4 degrees +/-2.2 degrees of valgus (3-7 degrees of valgus) at the final follow-up, with no loss of alignment noted in any case. One knee underwent revision for late infection while another knee had periprosthetic supracondylar fracture treated with plate fixation.

CONCLUSIONS

Use of the INDUS knee prosthesis has a favorable short-term outcome, with a mean range of 135 degrees flexion and excellent knee scores.

The effect of oxidative aging on the wear performance of highly crosslinked polyethylene knee inserts under conditions of severe malalignment

First-generation crosslinked polyethylene developed for total hip arthroplasty has not gained wide acceptance for knee arthroplasty because of the increased potential for failure under high stresses and the increased risk for oxidative damage caused by free radicals. Sequentially crosslinked polyethylene (SQXL) is a second-generation crosslinked polyethylene that is reported to reduce the level of free radicals and preserve mechanical properties. Three groups of ultrahigh molecular weight polyethylene inserts were wear tested after artificial aging as per ASTM F2003: gamma-irradiated in air (GA-aged), sequentially crosslinked (SQXL-aged), and electron-beam irradiated and remelted (EBeam-aged). Inserts were tested in an AMTI knee wear simulator under malalignment conditions that were two standard deviations from the mean reported for computer-navigated and conventionally aligned techniques. GA-aged inserts delaminated by 500,000 cycles, and were severely damaged after 1 million cycles. None of the highly crosslinked inserts (SQXL-aged or EBeam-aged) delaminated or showed any signs of severe wear. Mean wear rate for GA-aged inserts was 124.6 +/- 49.4 mg/million cycles. Mean wear rates for SQXL-aged and EBeam-aged inserts were significantly lower (1.74 +/- 0.3 and 4.72 +/- 0.7, respectively). These results support the low levels of free radicals and preservation of mechanical properties reported in second-generation crosslinked ultrahigh molecular weight polyethylene.

Knee range of motion during the first two years after use of posterior cruciate-stabilizing or posterior cruciate-retaining total knee prostheses. A randomized clinical trial

BACKGROUND

The impact of posterior cruciate ligament-substituting and posterior cruciate ligament-retaining devices on the range of motion of the knee following primary total knee arthroplasty is unclear. The primary objective of our study was to compare the range of motion of the knee over the first two postoperative years between subjects who had received the ligament-substituting design and those who had received the ligament-retaining design. Secondarily, pain, function, and health-related quality of life were compared between the two groups.

METHODS

We undertook a prospective randomized study of 100 patients with noninflammatory osteoarthritis who were undergoing primary total knee arthroplasty. Patients were randomized at the time of surgery to receive one of the two study prosthesis designs. They were evaluated preoperatively, at the time of hospital discharge, at three months postoperatively, and at up to two years postoperatively by a physical therapist who was blinded to the group allocation. Active knee flexion and extension, measured with a goniometer, were the primary outcome measures. Self-reported pain, function, and health-related quality of life were measured with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the RAND 36-Item Health Survey (RAND-36). Complications and revision rates were determined through hospital record review and at each patient evaluation.

RESULTS

Eighty percent (seventy-eight) of the ninety-eight available patients returned for the final assessment. At two years postoperatively, the mean difference between the groups with regard to knee flexion was 0.03 degrees (95% confidence interval, -5.9 degrees to 6.0 degrees ) and the mean difference in knee extension was 1.0 degrees (95% confidence interval, -0.36 degrees to 2.4 degrees ). Ninety-one (93%) of the ninety-eight available patients completed questionnaires at the time of the final assessment. The two treatment groups had similar pain, function, and quality-of-life scores and complication rates. One subject in the cruciate-retaining group required revision, secondary to a deep joint infection, and one subject in the cruciate-substituting group required manipulation to address poor knee flexion.

CONCLUSIONS

Overall, the two treatment groups had a similar range of motion of the knee over the initial two-year postoperative time period. A satisfactory range of motion was achieved by three months postoperatively and was maintained at the final assessment.

In vivo kinematics of the salto total ankle prosthesis

BACKGROUND

Recent technological advancements in total ankle arthroplasty (TAA) have included the introduction of the mobile bearing concept. This bearing has several advantages, but researchers have questioned whether or not increased mobility sacrifices joint stability or durability of the implant. The present study evaluated the kinematics of this type of prosthesis implanted in patients.

MATERIALS AND METHODS

Fluoroscopy and 3D-to-2D registration techniques were used to determine the in vivo kinematics for 20 TAA subjects performing two activities: gait and step-up. The motion of the prostheses was described in terms of clinical rotations and as rotation about the helical (screw) axis. Then, the anterior-posterior translation and axial rotation of the mobile bearing insert were determined.

RESULTS

Among the clinical rotations, the dorsi-/plantarflexion was the most dominant, revealing the greatest pattern change and the largest magnitude. During gait, the orientation of the prosthetic components changed smoothly from plantarflexion to dorsiflexion. The average range of this motion was 9.2 degrees. For step-up activity, the range was 8.0 degrees. However, between 33% and 66% of stance phase, the talar component's orientation changed from dorsiflexion to plantarflexion. The average absolute range of anterior-posterior translation of the mobile bearing insert was 1.5 mm and 2.3 mm for gait and step-up, respectively.

CONCLUSION

These measured translations were relatively small and may suggest that the rotational portion of the motion was more dominant than translational and provided sufficient mobility.

Posterior cruciate ligament removal contributes to abnormal knee motion during posterior stabilized total knee arthroplasty

Abnormal anterior translation of the femur on the tibia has been observed in mid flexion (20-60 degrees ) following posterior stabilized total knee arthroplasty. The underlying biomechanical causes of this abnormal motion remain unknown. The purpose of this study was to isolate the effects of posterior cruciate ligament removal on knee motion after total knee arthroplasty. We posed two questions: Does removing the posterior cruciate ligament introduce abnormal anterior femoral translation? Does implanting a posterior stabilized prosthesis change the kinematics from the cruciate deficient case? Using a navigation system, we measured passive knee kinematics of ten male osteoarthritic patients during surgery after initial exposure, after removing the anterior cruciate ligament, after removing the posterior cruciate ligament, and after implanting the prosthesis. Passively flexing and extending the knee, we calculated anterior femoral translation and the flexion angle at which femoral rollback began. Removing the posterior cruciate ligament doubled anterior translation (from 5.1 +/- 4.3 mm to 10.4 +/- 5.1 mm) and increased the flexion angle at which femoral rollback began (from 31.2 +/- 9.6 degrees to 49.3 +/- 7.3 degrees). Implanting the prosthesis increased the amount of anterior translation (to 16.1 +/- 4.4 mm), and did not change the flexion angle at which femoral rollback began. Abnormal anterior translation was observed in low and mid flexion (0-60 degrees) after removing the posterior cruciate ligament, and normal motion was not restored by the posterior stabilized prosthesis.

Evaluation of impingement of the anterior tibial post during gait in a posteriorly-stabilised total knee replacement

Mechanical failure because of wear or fracture of the polyethylene tibial post in posteriorly-stabilised total knee replacements has been extensively described. In this study of 12 patients with a clinically and radiologically successful NexGen LPS posteriorly-stabilised prosthesis impingement of the anterior tibial post was evaluated in vivo in three dimensions during gait using radiologically-based image-matching techniques. Impingement was observed in all images of the patients during the stance phase, although the NexGen LPS was designed to accommodate 14 degrees of hyperextension of the component before impingement occurred. Impingement arises as a result of posterior translation of the femur during the stance phase. Further attention must therefore be given to the configuration of the anterior portion of the femoral component and the polyethylene post when designing posteriorly-stabilised total knee replacements.

High-flexion total knee arthroplasty

High-flexion total knee arthroplasty is considered flexion beyond 125 degrees . Certain activities and a number of workplace demands benefit from this greater range of motion. Some cultures and religions place more emphasis on deep knee flexion. Important patient factors include preoperative motion, body mass index, and previous knee surgery. Component design modifications focus on lengthening the radius of curvature through the posterior condyles, increasing the posterior condylar offset, recessing the tibial insert, lengthening the trochlear groove, and altering the cam-post design. These changes allow increased femoral rollback, translation, and thus clearance in deep flexion. Surgical techniques focus on soft tissue balancing, component sizing and position, removal of impinging osteophytes, and reestablishment of the flexion gap. A number of outcome studies have demonstrated benefits for high flexion after standard total knee and high-flexion designs.

The NexGen LPS-flex to the knee prosthesis at a minimum of three years

We carried out a prospective study to assess the clinical outcome, complications and survival of the NexGen Legacy posterior-stabilised-Flex total knee replacement (TKR) in a consecutive series of 278 knees between May 2003 and February 2005. Mean follow-up for 259 TKRs (98.2%) was 3.8 years (3.0 to 4.8). Annual follow-up showed improvement in the Knee Society scores (paired t-test, p < 0.05). At the last follow-up, the mean maximum flexion was 135° (110° to 150°). Two knees showed radiolucent lines, but revision was not required because the patients were asymptomatic. Revision was required in one case because of infection, but there were no prosthesis-related revisions. There were no other complications. The estimated survival rate at four years with revision for any reason and prosthesis-related problems was 99.6% and 100%, respectively.

This relatively large study indicates that the legacy posterior stabilised-Flex design provides excellent short-term outcome but warrants ongoing evaluation to confirm the long-term durability and functioning of the implant.

In vivo comparison of knee kinematics for subjects having either a posterior stabilized or cruciate retaining high-flexion total knee arthroplasty

The objective of this study was to determine the in vivo kinematics for subjects having either a fixed posterior stabilized (PS) or cruciate retaining (CR) high-flexion total knee arthroplasty (TKA). Three-dimensional kinematics from full extension to maximum flexion were determined for 30 subjects (15 PS, 15 CR) using fluoroscopy. On average, the PS subjects demonstrated 112 degrees of weight-bearing (WB) flexion, -6.4 mm of posterior femoral rollback, and 2.9 degrees of axial rotation. The CR subjects averaged 117 degrees of WB flexion, -4.9 mm of posterior femoral rollback, and 4.8 degrees of axial rotation. Posterior femoral rollback of the lateral condyle occurred for all PS TKAs and in 93% of the CR TKAs. Only 2 subjects in each group experienced greater than 1.0 mm of condylar lift-off. Subjects in both TKA groups demonstrated excellent WB ranges of motion and kinematic patterns similar to the normal knee, but less in magnitude.

Revision total knee arthroplasty

Revision total knee arthroplasty presents numerous technical challenges and decisions for the operating surgeon. Preoperative planning includes critically reviewing radiographs and ordering necessary equipment, including prosthetic components, extraction devices, and bone graft materials. In some cases, surgical exposure requires the use of extensile exposure techniques. Component removal is facilitated by the use of appropriate tools (eg, specialized osteotomes) as well as by the patience to ensure preservation of host bone. Bone loss is managed with bone grafts or prosthetic augmentation. Attention to balancing the flexion and extension gaps is essential to avoid problems with instability as well as excessively constrained prosthetic components. Intramedullary stem extensions improve long-term clinical results. Intraoperative extensor mechanism complications can be avoided with meticulous surgical technique; late complications may require surgical intervention.

The early radiological follow-up of a medial rotational design of total knee arthroplasty

The objective of this study was to investigate the hypothesis that the increased constraint of a medial rotational knee promotes earlier loosening of the prosthesis. All patients with a Freeman-Samuelson 1000 knee arthroplasty (medial pivot design), (group 1), or a Freeman-Samuelson Modular knee arthroplasty, (group 2), with a minimum follow-up of 2 years (mean follow-up 4 years) were identified from our unit's arthroplasty database, and matched as closely as possible for age, length of follow-up and pre-operative diagnosis. Standardised anteroposterior and lateral radiographs were analysed for component migration and radiolucent lines as recommended by the Knee Society. There were 48 knees in each group. There were no failures in group 2. There was one failure requiring revision of the tibial component in group 1. There was no significant difference in overall radiolucent line scores between the two groups (p=0.66, at 5 years). Progressive radiolucent lines were detected in similar numbers of patients in both groups (FS1000 8/48, FSM 7/48, p=0.84). Our early radiological survey suggests that the increased constraint of the medial pivot knee prosthesis does not result in an increased incidence of radiographic loosening.

The assessment of intraoperative prosthetic knee range of motion using two methods

The commonly used standard goniometer has been shown to underestimate knee flexion. Computer-assisted navigation for total knee arthroplasty offers itself as an alternative method to quantify knee flexion. The goal of our study was to determine the reliability of each instrument in measuring intraoperative range of motion during total knee arthroplasty. We prospectively performed intraoperative measurements using both methods on 99 knees. We assessed the variability between the 2 devices and the confounding effect of body mass index. The mean difference between the goniometric and navigation measurements was significant for flexion, extension, and range of motion. Increasing body mass index accentuated this difference. The goniometric method underestimated flexion measurements as compared to navigation, especially in patients with high body mass index. Our study confirms that navigation is a reliable tool for performing in vivo assessment of range of motion.

Magnetic resonance image analysis of meniscal translation and tibio-menisco-femoral contact in deep knee flexion

The purpose of this study was to clarify meniscal displacement and cartilage-meniscus contact behavior in a full extension position and a deep knee flexion position. We also studied whether the meniscal translation pattern correlated with the tibiofemoral cartilage contact kinematics. Magnetic resonance (MR) images were acquired at both positions for 10 subjects using a conventional MR scanner. Subjects achieved a flexion angle averaging 139 degrees +/- 3 degrees. Both medial and lateral menisci translated posteriorly on the tibial plateau during deep knee flexion. The posterior translation of the lateral meniscus (8.2 +/- 3.2 mm) was greater than the medial (3.3 +/- 1.5 mm). This difference was correlated with the difference in tibiofemoral contact kinematics between medial and lateral compartments. Contact areas in deep flexion were approximately 75% those at full extension. In addition, the percentage of area in contact with menisci increased significantly due to deep flexion. Our results related to meniscal translation and tibio-menisco-femoral contact in deep knee flexion, in combination with information about force and pressure in the knee, may lead to a better understanding of the mechanism of meniscal degeneration and osteoarthritis associated with prolonged kneeling and squatting.

Patient function after a posterior stabilizing total knee arthroplasty: cam-post engagement and knee kinematics

Even though posterior substituting total knee arthroplasty has been widely used in surgery, how the cam-post mechanism (posterior substituting mechanism) affects knee joint kinematics and function in patients is not known. The objective of the present study was to investigate posterior femoral translation, internal tibial rotation, tibiofemoral contact, and cam-post engagement of total knee arthroplasty patients during in vivo weight-bearing flexion. Twenty-four knees with a PS TKA were investigated while performing a single leg weight-bearing lunge from full extension to maximum flexion as images were recorded using a dual fluoroscopic system. The in vivo knee position at each targeted flexion angle was reproduced using 3D TKA models and the fluoroscopic images. The kinematics of the knee was measured from the series of the total knee arthroplasty models. The cam-post engagement was determined when the surface model of the femoral cam overlapped with that of the tibial post. The mean maximum flexion angle for all the subjects was 112.5 +/- 13.1 degrees . The mean flexion angle where cam-post engagement was observed was 91.1 +/- 10.9 degrees . The femur moved anteriorly from 0 degrees to 30 degrees and posteriorly through the rest of the flexion range. The internal tibial rotation increased approximately 6 degrees from full extension to 90 degrees of flexion and decreased slightly with further flexion. Both the medial and lateral contact point moved posteriorly from 0 degrees to 30 degrees , remained relatively constant from 30 degrees to 90 degrees , and then moved further posterior from 90 degrees to maximum flexion. The in vivo cam-post engagement corresponded to increased posterior translation and reduced internal tibial rotation at high flexion of the posterior substituting total knee arthroplasty. The initial cam-post engagement was also mildly correlated with the maximum flexion angle of the knee (R = 0.51, p = 0.019). A later cam-post engagement might indicate an environment conducive to greater flexion. If the factors that affect cam-post engagement timing can be established, proper manipulation of those factors may improve the function of the knee after posterior substituting total knee arthroplasty.

Quadriceps force during knee extension after non-hinged and hinged TKA: an in vitro study

BACKGROUND AND PURPOSE

Problems during knee extension, due to kinematic alterations, are not uncommon after total knee arthroplasty. Hinged prostheses provide higher stability than non-hinged designs and may minimize these alterations. Thus, in this in vitro study we investigated the quadriceps force required to extend the knee during an isokinetic extension cycle generating a constant extension moment after non-hinged and hinged total knee arthroplasty.

METHODS

Human knee specimens were tested in a kinematic knee simulator under physiological conditions, after implantation of two types of non-hinged cruciate retaining prosthesis (Gemini; Link, Germany and Interax I.S.A.; Stryker, Ireland) and a hinged prosthesis (Rotations-Knie; Link, Germany). During simulation of an extension cycle from 120 degrees knee flexion to full extension, the change in quadriceps force to produce the constant extension moment of 31 Nm was dynamically measured using a load cell attached to the quadriceps tendon.

RESULTS

After implantation of the non-hinged pros-theses, there was no alteration in maximum quadriceps force in knee flexion compared to physiological conditions, but alteration occurred at lower flexion angle (p=0.002) and increased up to 1,257 (SD 273) N (p=0.04) in knee extension. Following implantation of the hinged prosthesis, there was no alteration in quadriceps extension force in flexion but it decreased to 690 (SD 81) N (p=0.003) in extension.

INTERPRETATION

Hinged knee prostheses restore the quadriceps lever arm in knee flexion and improve the lever arm in knee extension due to higher constraint and knee joint stability. This would offer a potential advantage for patients with weak quadriceps strength by making it easier to stabilize the knee in full extension during walking.

In vivo determination of total knee arthroplasty kinematics: a multicenter analysis of an asymmetrical posterior cruciate retaining total knee arthroplasty

The objective of this study was to determine if consistent posterior femoral rollback of an asymmetrical posterior cruciate retaining (PCR) total knee arthroplasty was mostly influenced by the implant design, surgical technique, or presence of a well-functioning posterior cruciate ligament (PCL). Three-dimensional femorotibial kinematics was determined for 80 subjects implanted by 3 surgeons, and each subject was evaluated under fluoroscopic surveillance during a deep knee bend. All subjects in this present study having an intact PCL had a well-functioning PCR knee and experienced normal kinematic patterns, although less in magnitude than the normal knee. In addition, a surprising finding was that, on average, subjects without a PCL still achieved posterior femoral rollback from full extension to maximum knee flexion. The findings in this study revealed that implant design did contribute to the normal kinematics demonstrated by subjects having this asymmetrical PCR total knee arthroplasty.

Factors affecting anteroposterior instability following cruciate-retaining total knee arthroplasty in patients with rheumatoid arthritis

Controversy persists concerning around posterior cruciate ligament (PCL) retention in total knee arthroplasty (TKA) for patients with rheumatoid arthritis (RA). This study investigated factors affecting anteroposterior (AP) instability following cruciate-retaining (CR)-TKA. In a consecutive series of 70 knees from 52 RA patients, total displacement (TD) was measured using a KT-2000 arthrometer before and after CR-TKA under anesthesia, and changes in TD were defined as DeltaTD. TD was also measured under anesthesia in 65 knees from 48 RA patients at a mean of 7.5 years after CR-TKA. Mean postoperative TD was 9.4+/-0.95 mm, representing an increase of about 1.5-1.8 mm compared to preoperative TD, and possibly reflecting resection of the anterior cruciate ligament. Correlation analysis revealed significant negative correlations between DeltaTD and both preoperative flexion angle (r=-0.67, p<0.001) and preoperative extension angle (r=-0.63, p<0.001), suggesting that TD in knees with flexion contracture increased postoperatively. At medium-term follow-up, no patients displayed AP instability, and mean TD was 8.3+/-0.48 mm. A significant correlation was found between TD and permissible flexion angle (r=0.61, p<0.001). These results indicate that TD is basically maintained during the course of CR-TKA in RA, but may be slightly affected by factors other than the PCL itself.