A posterior-stabilized total knee arthroplasty shows condylar lift-off during deep knee bends

Tibiofemoral lift-off and resulting laxity following total knee arthroplasty: Frequency in a series of 906 continuous cases and functional consequences at 4 years' follow-up in a case-control study

BACKGROUND

Tibiofemoral instability is one reason for early revision of total knee arthroplasty. It can be the consequence of tibiofemoral laxity, especially in the coronal plane with tibiofemoral lift-off. But does femoral condyle lift-off on conventional postoperative radiographs suggest the presence of laxity or potential instability? To our knowledge, this question has not yet been answered. This led us to conduct a retrospective study to evaluate (1) the frequency of lift-off on postoperative radiographs, (2) the relationship between lift-off and laxity in the short term and (3) the functional consequences of lift-off.

HYPOTHESIS

Postoperative lift-off is a rare event that is predictive of laxity.

METHODS

We carried out a single-center retrospective study using postoperative radiographs from patients who underwent primary total knee arthroplasty between 2014 and 2016. The sample consisted of 906 patients. Lift-off was defined as a tibiofemoral angle of 3° or more on immediate postoperative radiographs (day 0) that were non-weightbearing and had no stress applied. The functional outcomes were determined in the 17 patients identified as having lift-off who had been operated in the first year (2014) to ensure the follow-up was long enough. These patients were compared to 34 matched control patients who were operated the same year and chosen randomly among patients not having lift-off. The matching ratio was 2 controls to 1 case. Preoperative and surgical data were compiled from each patient's electronic medical record. Patients were evaluated at 4 years postoperatively using the subjective Oxford-48, objective HSS score, IKS score, overall patient satisfaction and stress radiographs of the knee. The cases of lift-off observed in 2014 (n=17) were paired with a control group of patients selected randomly during 2014.

RESULTS

The frequency of the lift-off event was 63/906 or 7%. The frequency was consistent over the three years studied: 7.1% in 2014 (19/269), 6.2% in 2015 (22/354) and 7.8% in 2016 (22/283). There was no significant difference between the two groups (17 with lift-off and 34 without) in the sex, age, body mass index and coronal plane deformity (preoperative HKA angle). At a mean follow-up of 4 years (range 12-49 months), the knees with postoperative lift-off had more laxity (p=0.002), particularly laxity when varus stress was applied (p=0.009). There were no other significant differences in the outcomes.

DISCUSSION

Immediate postoperative lift-off after total knee arthroplasty is not a rare event, with a 7% frequency in our study. While it reveals that laxity is present in the particular compartment, there is no evidence of functional consequences at 4 years' follow-up; however, a long-term assessment is required to verify this finding.

LEVEL OF EVIDENCE

III - case-control study.

Valgus position of the femoral component causes abnormal kinematics in the presence of medial looseness in total knee arthroplasty: a computer simulation model of TKA for valgus knee osteoarthritis

PURPOSE

Total knee arthroplasty (TKA) for valgus knee osteoarthritis is challenging. Although overcorrection in TKA for valgus knee osteoarthritis is recommended, supportive data based on biomechanics have rarely been reported. The purpose of this study was to elucidate whether coronal rotation of the femoral compartment causes abnormal kinematics with or without medial looseness.

METHODS

Multi- and single-radius posterior-stabilised TKA implants were utilised in a computer simulation. A total of 4 mm of slack were provided in the medial collateral ligament (MCL) with varus or valgus position of the femoral component to simulate the context of valgus knee osteoarthritis. Kinematics during gait and squatting activities were evaluated in each condition.

RESULTS

During squatting, medial looseness and valgus replacement caused anterior translation of the medial femoral component in mid-flexion in the multi-radius implant. In the worst condition (7° valgus replacement with MCL looseness), there was rapid anterior translation in the multi-radius implant, and moderate anterior translation in the single-radius implant. Although medial looseness alone did not cause abnormal kinematics during gait, the worst condition exhibited an anterior translation to 4.9 mm in the multi-radius implant. This worst condition also exhibited a marked lift-off of 8.0 and 2.9 mm in the multi- and single-radius implants, respectively. Varus position caused little abnormal kinematics even with MCL looseness.

CONCLUSION

Valgus, not varus position of the femoral component caused abnormal kinematics with MCL looseness. To avoid valgus position, the safety target angle of femoral component would be slight varus rather than neutral in valgus knee OA.

Does lateral lift-off occur in static and dynamic activity in a medially spherical total knee arthroplasty? A pulsed-fluoroscopic investigation

Objectives

The medially spherical GMK Sphere (Medacta International AG, Castel San Pietro, Switzerland) total knee arthroplasty (TKA) was previously shown to accommodate lateral rollback while pivoting around a stable medial compartment, aiming to replicate native knee kinematics in which some coronal laxity, especially laterally, is also present. We assess coronal plane kinematics of the GMK Sphere and explore the occurrence and pattern of articular separation during static and dynamic activities.

Methods

Using pulsed fluoroscopy and image matching, the coronal kinematics and articular surface separation of 16 well-functioning TKAs were studied during weight-bearing and non-weight-bearing, static, and dynamic activities. The closest distances between the modelled articular surfaces were examined with respect to knee position, and proportions of joint poses exhibiting separation were computed.

Results

Overall, 1717 joint poses were analyzed. At a 1.0 mm detection threshold, 37 instances of surface separation were observed in the lateral compartment and four medially (p < 0.001). Separation was activity-dependent, both laterally and medially (p < 0.001), occurring more commonly during static deep flexion in the lateral compartment, and during static rotation in the medial compartment. Lateral separation occurred more frequently than medial during kneeling (7/14 lateral vs 1/14 medial; p = 0.031) and stepping (20/1022 lateral vs 0/1022 medial; p < 0.001). Separation varied significantly between individuals during dynamic activities.

Conclusion

No consistent association between closest distances of the articular surfaces and knee position was found during any activity. Lift-off was infrequent and depended on the activity performed and the individual knee. Lateral separation was consistent with the design rationale. Medial lift-off was rare and mostly in non-weight-bearing activities.

Cite this article: S. Key, G. Scott, J.G. Stammers, M. A. R. Freeman†, V. Pinskerova, R. E. Field, J. Skinner, S. A. Banks. Does lateral lift-off occur in static and dynamic activity in a medially spherical total knee arthroplasty? A pulsed-fluoroscopic investigation. Bone Joint Res 2019;8:207–215. DOI: 10.1302/2046-3758.85.BJR-2018-0237.R1.

Bi-cruciate substituting total knee arthroplasty provides varus-valgus stability throughout the midflexion range

BACKGROUND

Proper soft tissue balance is crucial for a successful clinical outcome after total knee arthroplasty (TKA). Bi-cruciate substituting (BCS)-TKA has been developed to more closely approximate normal knee characteristics. The purpose of the present study was to evaluate midflexion laxity before and after BCS-TKA using a navigation system, and assess the correlation between intraoperative laxity and the maximum flexion angle after surgery.

METHODS

Fifty-one knees in 46 patients with osteoarthritis replaced with BCS prosthesis were assessed. Manual mild passive internal-external rotational and varus-valgus stress was applied to the knees, and the maximum total laxity was measured automatically by a navigation system before and after TKA. The correlations with the range of motion (ROM) were evaluated using Spearman's correlation coefficients (ρ).

RESULTS

Internal-external stress assessment revealed no statistically significant difference at each flexion angle before and after BCS-TKA. In contrast, the varus-valgus stress assessment revealed that BCS-TKA had significantly decreased varus-valgus laxity from preoperative levels at 20-120° flexion angles. Furthermore, the maximum flexion angle at six months after surgery significantly correlated with the intraoperative laxity at deep flexion range.

CONCLUSION

BCS-TKA stabilized varus-valgus laxity to better than preoperative levels at midflexion range.

How does total knee replacement technique influence polyethylene wear?

In knee prostheses, wear is inherent to the tribology of the imperfectly congruent surfaces, one in chromium-cobalt alloy, the other in polyethylene. It is a multifactorial phenomenon, involving the properties of the respective materials and implant design, but also implant functioning, as determined by the implantation technique. There are still dark corners in the implantation charge book, especially concerning minimal insert thickness, the adjustment of tibiofemoral alignment and ligament balance. A review of the literature revealed consensus regarding minimal insert thickness (8mm), tibiofemoral alignment (to be kept within 5° on either side of the neutral axis) and ligament balance (identical collateral ligament tension in both extension and flexion spaces). Finer adjustment seems desirable. Tibiofemoral alignment is probably customizable according to individual patient morphology and weight. The rotational alignment of the components should allow harmonious patellar engagement. Classic ligament balance rules underestimate sagittal laxity, which needs checking to prevent paradoxical movement accelerating polymer delamination. Navigation techniques or specific ancillaries can help optimize implant component alignment. Control of sagittal laxity may require specific adaptation, notably in the flexion space. Improved implantation technique could postpone wear onset until beyond the 10th or even 20th postoperative year, barring material failure for other reasons.

No condylar lift-off occurs because of excessive lateral soft tissue laxity in neutrally aligned total knee arthroplasty: a computer simulation study

PURPOSE

Condylar lift-off can induce excessive polyethylene wear after total knee arthroplasty (TKA). A computer simulation was used to evaluate the influence of femoral varus alignment and lateral collateral ligament (LCL) laxity on lift-off after single-design TKA. It was hypothesised that proper ligament balancing and coronal alignment would prevent lift-off.

METHODS

The computer model in this study is a dynamic musculoskeletal program that simulates gait up to 60° of knee flexion. The lift-off phenomenon was defined as positive with an intercomponent distance of >2 mm. In neutrally aligned components in the coronal plane, the femoral and tibial components were set perpendicular to the femoral and tibial mechanical axis, respectively. The femoral coronal alignment was changed from neutral to 5° varus in 1° increments. Simultaneously, the LCL length was elongated from 0 to 5 mm in 1-mm increments to provide a model of pathological slack.

RESULTS

Within 2° of femoral varus alignment, lift-off did not occur even if the LCL was elongated by up to 5 mm. However, lift-off occurred easily in the stance phase in femoral varus alignments of >3° with slight LCL slack. The contact forces of the tibiofemoral joint were influenced more by femoral varus alignment than by LCL laxity.

CONCLUSIONS

Aiming for neutral alignment in severely varus knees makes it difficult to achieve appropriate ligament balance. Our study suggests that no lift-off occurs with excessive LCL laxity alone in a neutrally aligned TKA and therefore that varus alignment should be avoided to decrease lift-off after TKA.

LEVEL OF EVIDENCE

Case series, Level IV.

Active Flexion in Weight Bearing Better Correlates with Functional Outcomes of Total Knee Arthroplasty than Passive Flexion

PURPOSE

Correlations between maximum flexion and functional outcomes in total knee arthroplasty (TKA) patients are reportedly weak. We investigated whether there are differences between passive maximum flexion in nonweight bearing and other types of maximum flexion and whether the type of maximum flexion correlates with functional outcomes.

MATERIALS AND METHODS

A total of 210 patients (359 knees) underwent preoperative evaluation and postoperative follow-up evaluations (6, 12, and 24 months) for the assessment of clinical outcomes including maximum knee flexion. Maximum flexion was measured under five conditions: passive nonweight bearing, passive weight bearing, active nonweight bearing, and active weight bearing with or without arm support. Data were analyzed for relationships between passive maximum flexion in nonweight bearing by Pearson correlation analyses, and a variance comparison between measurement techniques via paired t test.

RESULTS

We observed substantial differences between passive maximum flexion in nonweight bearing and the other four maximum flexion types. At all time points, passive maximum flexion in nonweight bearing correlated poorly with active maximum flexion in weight bearing with or without arm support. Active maximum flexion in weight bearing better correlated with functional outcomes than the other maximum flexion types.

CONCLUSIONS

Our study suggests active maximum flexion in weight bearing should be reported together with passive maximum flexion in nonweight bearing in research on the knee motion arc after TKA.

Patients still wish for key improvements after total knee arthroplasty

Purpose

Our goals were to rigorously document and explore the interrelationships of various parameters in the aftermath of total knee arthroplasty (TKA), including patient characteristics, clinical scores, satisfaction levels, and patient-perceived improvements.

Materials and Methods

A questionnaire addressing sociodemographic factors, levels of satisfaction, and "wished-for" improvements was administered to 180 patients at least 1 year post primary TKA. Both satisfaction levels and wished-for improvements were assessed through nine paired parameters. Patients responded using an 11-point visual analogue scale (VAS) and the results were summarized as mean VAS score. Correlations between clinical scores and satisfaction levels and between satisfaction levels and desired improvements were analyzed.

Results

Patient satisfaction levels were only modest (mean score, 4-7) for eight of the nine parameters, including pain relief and restoration of daily living activities, the top two ranked parameters in wished-for improvement while high-flexion activity constituted the top source of discontent. Wished-for improvement was high in seven parameters, the top three being restoration of daily living activities, pain relief, and high-flexion activity. The effects of sociodemographic factors on satisfaction levels and wished-for improvement varied. Satisfaction levels correlated positively with functional outcomes, and satisfaction in pain relief and restoration of daily living activities correlated more often and most strongly with clinical scores.

Conclusions

Following TKA, patient satisfaction is not high for a number of issues, with improvements clearly needed in restoring daily living activities and relieving pain. Continued efforts to achieve better surgical outcomes should address patient-perceived shortcomings.

No influence of coronal laxity and alignment on lift-off after well-balanced and aligned total knee arthroplasty

PURPOSE

In vivo fluoroscopic analyses have revealed the kinematics after total knee arthroplasty (TKA), including femoral condylar lift-off. This study asked whether differences in static varus-valgus laxity or coronal limb alignment after TKA affect lift-off under weight-bearing conditions. It was hypothesised that there is a correlation between coronal laxity or alignment and lift-off during walking.

METHODS

The current study analysed nineteen subjects undergoing cruciate-retaining TKA performed by the measured resection technique. The varus-valgus laxity at knee extension was measured using a 150 N stress radiograph. The mechanical axis was measured using a full-standing radiograph. Continuous radiological images were taken while the subject walked on a treadmill, and the images during single-leg stance were analysed to determine the lift-off using a 3D-to-2D image-to-model registration technique.

RESULTS

The average angle in varus/valgus stress was 6.8 ± 1.8°/6.6 ± 2.1°. No statistically significant differences were observed between the varus and valgus laxity. The average amount of lift-off was 0.7 ± 0.4 mm. The static varus-valgus laxity (n. s.) or the differences in the laxities (n. s.) on the stress radiograph did not influence lift-off. The weight-bearing ratio was achieved within the middle third of the knee in 90 % of subjects. Two outliers with valgus alignment (68 ± 1 %) demonstrated no significant difference in lift-off in comparison with the majority of the subjects (46 ± 9 %).

CONCLUSION

The static coronal laxity and alignment did not influence the lift-off under dynamic weight-bearing conditions after well-balanced and aligned cruciate-retaining TKA. Measured resection technique can produce sufficient coronal stability and alignment without significant lift-off during walking.

In vivo femoro-tibial kinematic analysis of a tri-condylar total knee prosthesis

BACKGROUND

An alternative tri-condylar implant has been designed to incorporate necessary posterior stability without a post, but has not been evaluated. The purpose of the current study was to determine the in vivo three dimensional femoro-tibial kinematics of a tri-condylar implant during a weight bearing deep knee bend activity.

METHODS

Fluoroscopy based in vivo femoro-tibial kinematics of the tri-condylar implant was assessed for 66 knees during a deep knee bend activity, using a three dimensional to two dimensional model fitting approach.

FINDINGS

Average range of motion was 125.5° (standard deviation (SD)=20.5°) in sagittal plane, and 42 knees (63.6%) experienced at least 120° of weight-bearing knee flexion. The average amount of posterior femoral movement (PFM) was 8.7mm (SD=4.3mm) for the medial condyle and 11.2mm (SD=5.4mm) for the lateral condyle. PFM of the medial condyle was significantly smaller than that of the lateral condyle. The average amount of femoro-tibial axial rotation was 5.7° (SD=6.4°), and 56 knees (84.8%) experienced a normal axial rotation pattern. Condylar lift-off, mostly occurring in deep flexion range, was experienced in 16 knees (24.2%).

INTERPRETATION

Knees in the current study did achieve high weight-bearing flexion, more normal-like greater posterior femoral movement of lateral condyle than the medial condyle and a normal axial rotation pattern, albeit, less in magnitude than the normal knee.

3D in vivo femoro-tibial kinematics of tri-condylar total knee arthroplasty during kneeling activities

BACKGROUND

Kneeling position can serve as an important posture, providing stability and balance from a standing position to sitting on the floor or vice-versa. The purpose of the current study was to determine the kinematics during kneeling activities after subjects were implanted with a tri-condylar total knee arthroplasty.

MATERIALS AND METHODS

Kinematics was evaluated in 54 knees using fluoroscopy and a three-dimensional model fitting approach.

RESULTS

The average knee flexion at before contact status, at complete contact and at maximum flexion was 98.1±9.0°, 107.2±6.7°, and 139.6±12.3°, respectively. On average, there was no gross anterior displacement from before contact status to complete contact. Only slight posterior rollback motion of both condyles from complete contact to maximum flexion was observed. Three of 39 (7.7%) knees experienced anterior movement of both condyles more than 2mm from before contact status to complete contact. Reverse rotation pattern from before contact status to complete contact and then normal rotation pattern from complete contact to maximum flexion were observed. Condylar lift-off greater than 1.0 mm was observed in 45 knees (83.3%).

CONCLUSION

The presence of the ball-and-socket joint articulation provides sufficient antero-posterior stability in these designs to enable the patients to kneel safely without the incidence of any dislocation.

CLINICAL RELEVANCE

This study suggests a safe implant design for kneeling.

Retention versus sacrifice of the posterior cruciate ligament in total knee arthroplasty for treating osteoarthritis

BACKGROUND

The functional and clinical basis on which to choose whether or not to retain the posterior cruciate ligament during total knee arthroplasty surgery remained unclear after a Cochrane systematic review and meta-analysis in 2005, which contained eight clinical trials. Several new trials have been conducted since then. Hence, an update of the review was performed.

OBJECTIVES

Our aim was to assess the benefits and harms of retention compared to sacrifice of the posterior cruciate ligament in total knee arthroplasty in patients with osteoarthritis of the knee.

SEARCH METHODS

An extensive search was conducted in CENTRAL, MEDLINE (PubMed), EMBASE, Web of Science, CINAHL, Academic Search Premier, Current Contents Connect and Science Direct. All databases were searched, without any limitations, up to 6 December 2012. References of the articles were checked and citation tracking was performed.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials comparing retention with sacrifice of the posterior cruciate ligament in primary total knee arthroplasty in patients with osteoarthritis of the knee.

DATA COLLECTION AND ANALYSIS

Data were collected with a pre-developed form. Risk of bias was assessed independently by two authors (WV, LB). The level of evidence was graded using the GRADE approach. Meta-analysis was performed by pooling the results of the selected studies, when possible. Subgroup analyses were performed for posterior cruciate ligament retention versus sacrifice using the same total knee arthroplasty design, and for studies using a posterior cruciate ligament retaining or posterior stabilised design, and when sufficient studies were available subgroup analyses were performed for the same brand.

MAIN RESULTS

Seventeen randomised controlled trials (with 1810 patients and 2206 knees) were found, described in 18 articles. Ten of these were new studies compared to the previous Cochrane Review. One study from the original Cochrane review was excluded. Most new studies compared a posterior cruciate ligament retaining design with a posterior stabilised design, in which the posterior cruciate ligament is sacrificed (a posterior stabilised design has an insert with a central post which can engage on a femoral cam during flexion).The quality of evidence (graded with the GRADE approach) and the risk of bias were highly variable, ranging from moderate to low quality evidence and with unclear or low risk of bias for most domains, respectively.The performance outcome 'range of motion' was 2.4 ° higher in favour of posterior cruciate ligament sacrifice (118.3 ° versus 115.9 °; 95% confidence interval (CI) of the difference 0.13 to 4.67; P = 0.04), however the results were heterogeneous. On the item 'knee pain' as experienced by patients, meta-analysis could be performed on the Knee Society knee pain score; this score was 48.3 in both groups, yielding no difference between the groups. Implant survival rate could not be meta-analysed adequately since randomised controlled trials lack the longer term follow-up in order to evaluate implant survival. A total of four revisions in the cruciate-retention and four revisions in the cruciate-sacrifice group were found. The well-validated Western Ontario and McMaster Universities osteoarthritis index (WOMAC) total score was not statistically significantly different between the groups (16.6 points for cruciate-retention versus 15.0 points for cruciate-sacrifice). One study reported a patient satisfaction grade (7.7 points for cruciate-retention versus 7.9 points for cruciate-sacrifice on a scale from 0 to 10, 10 being completely satisfied) which did not differ statistically significantly. Complications were distributed equally between both groups. Only one study reported several re-operations other than revision surgery; that is patella luxations, surgical manipulation because of impaired flexion.The mean functional Knee Society Score was 2.3 points higher (81.2 versus 79.0 points; 95% CI of the difference 0.37 to 4.26; P = 0.02) in the posterior cruciate ligament sacrificing group. Results from the outcome Knee Society functional score were homogeneous. All other outcome measures (extension angle, knee pain, adverse effects, clinical questionnaire scores, Knee Society clinical scores, radiological rollback, radiolucencies, femorotibial angle and tibial slope) showed no statistically significant differences between the groups. In the subgroup analyses that allowed pooling of the results of the different studies, no homogeneous statistically significant differences were identified.

AUTHORS' CONCLUSIONS

The methodological quality and the quality of reporting of the studies were highly variable. With respect to range of motion, pain, clinical, and radiological outcomes, no clinically relevant differences were found between total knee arthroplasty with retention or sacrifice of the posterior cruciate ligament. Two statistically significant differences were found; range of motion was 2.4 ° higher in the posterior cruciate ligament sacrificing group, however results were heterogeneous; and the mean functional Knee Society Score was 2.3 points higher in the posterior cruciate ligament sacrificing group. These differences are clinically not relevant.

Articular cartilage of the posterior condyle can affect rotational alignment in total knee arthroplasty

PURPOSE

Rotational alignment is important for patellar tracking, ligament balance, and tibiofemoral congruity after total knee arthroplasty (TKA). The posterior condylar axis is often referred to as a rotational alignment landmark. However, articular cartilage wear localized only in the medial condyle might affect the accuracy of rotation, because surgical planning based on CT does not consider the cartilage thickness. The purpose of this study was to clarify whether the cartilage thickness of the posterior condyle affects rotational alignment after TKA.

METHODS

A total of 40 osteoarthritis patients waiting for TKA were recruited. MRI of axial sections was performed preoperatively. Scans were controlled to make the cross section perpendicular to the mechanical axis of the femur on the coronal plane and to the tangent line of the distal femur on the sagittal plane, so that the surgical section of the actual femur could be simulated. The condylar twist angle (CTA) was measured with and without articular cartilage. The cartilage thickness on the medial and lateral posterior condyles was surveyed in both MRI images and surgical specimens.

RESULTS

The CTA without cartilage (6.8 ± 2.0°) was significantly larger than the CTA with cartilage (5.2 ± 2.0°) (P < 0.01), and 12 knees (30%) demonstrated differences of more than 2 degrees. The cartilage depicted in MRI showed almost the same thickness as the actual specimens and was significantly thicker on the lateral condyles.

CONCLUSIONS

Surgical planning for TKA not considering articular cartilage might lead to the externally rotated malposition of the femoral implant.

LEVEL OF EVIDENCE

II.

Can Patellar Tendon Angle reveal sagittal kinematics in total knee arthroplasty?

The Patellar Tendon Angle is strongly correlated with both patello-femoral and tibio-femoral joint kinematics. Thus, the Patellar Tendon Angle might be regarded as a concise indicator of the antero-posterior translation of the femur with respect to the tibia. Twelve subjects, who had undergone total knee arthroplasty, were investigated by video-fluoroscopy during step-up/down. The kinematics at the replaced knee was reconstructed by means of 3D fluoroscopy. The Patellar Tendon Angle and the knee-flexion angle were measured on sagittal fluoroscopic images with software designed for the purpose. The slope of the linear trend of the Patellar Tendon Angle versus knee-flexion angle relationship correlated significantly with the mean (p = 0.001), most anterior (p = 0.001), and most posterior (p = 0.016) position reached by the femur over the tibia. The Patellar Tendon Angle versus knee-flexion angle relationship provides relevant information about the anterior or posterior positioning of the femur over the tibia, but it cannot be interpreted as quantification of the actual antero-posterior translation of the femur over the tibia.

Functional disabilities and satisfaction after total knee arthroplasty in female Asian patients

This study was conducted to investigate functional disabilities and patient satisfaction in Korean patients after total knee arthroplasty (TKA). Of 372 female patients who had undergone TKA with a follow-up longer than 12 months, 261 patients (70.2%) completed a questionnaire designed to evaluate functional disabilities, perceived importance, and patient satisfaction. The top 5 severe functional disabilities were difficulties in kneeling, squatting, sitting with legs crossed, sexual activity, and recreational activities. The top 5 in order of perceived importance were difficulties in walking, using a bathtub, working, recreation activities, and climbing stairs. Severities of functional disabilities were not found to be correlated with perceived importance. The 23 patients (8.8%) dissatisfied with their replaced knees had more severe functional disabilities than the patients satisfied for most activities. The dissatisfied patients tended to perceive functional disabilities in high-flexion activities to be more important than the satisfied.

Fluoroscopic and computed tomographic analysis of knee kinematics during very deep flexion after total knee arthroplasty

We examined the relative motion of femoral and tibial total knee arthroplasty components and the difference between 2 different tibial inserts (9 flat types and 7 dish types) in patients sitting in very deep flexion. X-ray, fluoroscopic examination, and computed tomography were used to analyze liftoff, and rotation. During seiza-style sitting, one knee (11%) with the flat insert lifted off on the medial side and 5 knees (71%) with the dish-type insert showed liftoff. The tibial internal rotation angles were 17.2 degrees +/- 4.1 degrees (flat type) and 11.7 degrees +/- 3.1 degrees (dish type) (P < .05). The flat type showed less liftoff at the medial side and more internal rotation. For very deep flexion, components that tolerate larger rotational freedom are favorable.

Modified gap-balancing technique in total knee arthroplasty: evaluation of the post-operative coronal laxity

It is unknown how intra-operative soft-tissue balance affects post-operative knee kinematics during different functional tasks. In order to clarify this relationship, the intra-operative varus-valgus balance and post-operative knee kinematics were compared for 17 patients who underwent total knee arthroplasty using a modified gap technique. The intra-operative balance was recorded with a tensor device, and in vivo knee kinematics of lunging, kneeling and non-weight-bearing knee extension were analyzed with 3D-to-2D model registration techniques. Femoral condylar separation from the tibial articular surface also was investigated. The post-operative varus-valgus angle in 90 degrees kneeling had a strong relationship with the intra-operative varus-valgus angle, while there was a weak relationship for the non-weight-bearing motion at 0 degrees and 90 degrees flexion. Articular surface separation was an uncommon observation, seen in 2.2% of images during non-weight-bearing motion and in none of the lunging or kneeling images. The modified gap technique appears effective providing stable knee arthroplasty kinematics during in vivo activities with minimal articular separation in non-weight-bearing motion.

In vivo adduction and reverse axial rotation (external) of the tibial component can be minimized

Mechanical alignment with conventional total knee arthroplasty (TKA) instruments often requires collateral ligament releases, which result in a high prevalence of adduction and reverse axial rotation (external rotation) of the tibial component during knee flexion with a variety of component designs. We used a radiographic image-matching technique to determine the contact kinematics during standing and kneeling at 90 degrees and maximum flexion in a series of 35 patients in which a new image-guided, custom cutting block system was used to kinematically align a cruciate-retaining prosthesis with the intent of restoring the 3 kinematic axes of the knee. The kinematically aligned prosthesis had a minimal prevalence of adduction (3%) and reverse axial rotation (8.5%). The anteroposterior contact positions of the lateral and medial femoral condyles did not edge load the tibial liner. The moderate association between abduction and internal rotation, the degree of knee flexion, and the contact position of the medial femoral condyle suggest that abduction was not a sign of lift-off of the medial femoral condyle, but the result of the medial femoral condyle moving up the anterior slope of the tibial liner. These more normal contact kinematics were achieved without release of the collateral ligaments or lateral retinaculum. In contrast to mechanical alignment with conventional surgical techniques, the use of kinematic alignment with custom-fit cutting guides and a cruciate-retaining, symmetric medial and lateral femoral-tibial bearing surface minimizes the undesirable consequences of adduction and reverse axial rotation (external rotation).

In vivo knee kinematics during high flexion after a posterior-substituting total knee arthroplasty

The objective of this study was to investigate biomechanics of TKA patients during high flexion. Six patients (seven knees) with a posterior-substituting TKA and weight-bearing flexion >130 degrees were included in the study. The six degree-of-freedom kinematics, tibiofemoral contact, and cam-post contact were measured during a deep knee bend using dual-plane fluoroscopy. The patients achieved average weight-bearing flexion of 139.5 +/- 4.5 degrees. Posterior femoral translation and internal tibial rotation increased steadily beyond 90 degrees flexion, and a sharp increase in varus rotation was noted at maximum flexion. Initial cam-post engagement was observed at 100.3 +/- 6.7 degrees flexion. Five knees had cam-post disengagement before maximum flexion. Lateral femoral condylar lift-off was found in five out of seven knees at maximum flexion, and medial condylar lift-off was found in one knee. Future studies should investigate if the kinematic characteristics of posterior-substituting TKA knees noted in this study are causative factors of high knee flexion.

Sensitivity of knee replacement contact calculations to kinematic measurement errors

The ability to measure in vivo knee kinematics accurately makes it tempting to calculate in vivo contact forces, pressures, and areas directly from kinematic data. However, the sensitivity of contact calculations to kinematic measurement errors has not been adequately investigated. To address this issue, we developed a series of sensitivity analyses derived from a validated in vivo computational simulation of gait. The simulation used an elastic foundation contact model to reproduce in vivo contact force, center of pressure, and fluoroscopic motion data collected from an instrumented knee replacement. Treating each degree of freedom (DOF) in the simulation as motion controlled, we first quantified how errors in measured relative pose of the implant components affected contact calculations. Pose variations of +/-0.1 mm or degree over the entire gait cycle changed maximum contact force, pressure, and area by 204, 100, and 117%, respectively. Larger variations of +/-0.5 mm or degree changed these same quantities by 1157, 108, and 578%, respectively. In both cases, the largest sensitivities were to errors in superior-inferior translation and varus-valgus rotation, with loss of contact occurring on one or both sides. We then quantified how switching the sensitive DOFs from motion to load control affected the sensitivity results. Pose variations of +/-0.5 mm or degree in the remaining DOFs changed maximum contact quantities by at most 3%. These results suggest that accuracy on the order of microns and milliradians is needed to estimate contact forces, pressures, and areas directly from in vivo kinematic measurements, and that use of load rather than motion control for the sensitive DOFs may improve the accuracy of in vivo contact calculations.

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.

5- to 9-year survivorship of single-radius, posterior-stabilized TKA

We studied 1030 consecutive cemented primary TKAs performed by the primary author (OMM) using a single-radius, posterior-stabilized total knee prosthesis with 5 years' minimum followup to determine whether an accelerated early failure rate was associated with this design. At 5 to 9.5 postoperative years, 32 knees had been revised at an average of 2.4 postoperative years (range, 0.1-8.2 years) because of infection (11), periprosthetic fracture (10), aseptic loosening (eight), stiffness (two), and late hemarthrosis (one). Four had only the tibial insert revised. One-half of all failures occurred within 1.5 years. The cases of aseptic loosening involved the femoral component in one patient, tibial component in five, and both components in two. With only seven patients (0.7%) having unknown outcomes, the overall failure rate was 4.9 per 1000 person-years for the study period. The Kaplan-Meier survivorship using any part of the prosthesis removed or revised for any reason as the end point was 95.8% (95% confidence interval, 93.7%-95.5%), and with aseptic loosening as the end point, it was 98.6% (95% confidence interval, 96.5%-99.4%). The midterm survivorship rates were comparable to those of other posterior-stabilized total condylar designs and are not suggestive of excessive risk of early failure.

LEVEL OF EVIDENCE

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