The impact of a rectangular or trapezoidal flexion gap on the femoral component rotation in TKA

Purpose  

The influence of soft tissue balancing on femoral component rotation in the gap technique remains unclear. The present study therefore compared the reliability of femoral component rotation determined by rectangular and trapezoidal gaps in total knee arthroplasty (TKA) using a navigation-assisted gap-balancing technique. The study also determined the correlation between femoral component rotation and gap measurement.     

Femoral component rotation in patients with leg axis deviation

Purpose  

Correct alignment of the rotation of the femoral component and the flexion gap after total knee arthroplasty is difficult in patients with preoperative leg axis deviation. Inaccuracy may result in problems with the patellofemoral joint and instability, in particular. We examined the influence of the preoperative leg axis on the rotation of the femoral component and the symmetry of the flexion gap after total knee arthroplasty using the tibial-cut-first technique.     

The effect of femoral component rotation on the kinematics of the tibiofemoral and patellofemoral joints after total knee arthroplasty

Purpose  

Complications after total knee arthroplasty (TKA) often involve the patellofemoral joint, and problems with patellar maltracking or lateral instability have sometimes been addressed by external rotation of the femoral component. This work sought to measure the changes of knee kinematics caused by TKA and then to optimise the restoration of both the patellofemoral and tibiofemoral joint kinematics, by variation of femoral component internal–external rotation.     

Kinematic analysis of the flexion axis for correct femoral component placement

Purpose  

This study evaluates a new method for intraoperative determination of femoral component rotation by a navigation system (flexion axis, FA) driven by joint stability over the range of motion.     

Significance of asymmetrical posteromedial and posterolateral femoral condylar chamfer cuts in total knee arthroplasty

Purpose

Orthopedic surgeons remove more bone from the posteromedial femoral condyle than the posterolateral condyle to achieve the desired femoral component rotation. Here, the correlation between the asymmetry of chamfer cuts and femoral component rotation in total knee arthroplasty was determined.

Methods

A model was built to simulate anterior chamfer cuts performed during total knee arthroplasty to measure posterior condylar offset. Right knee axial magnetic resonance imaging slices were examined from 280 consecutive patients (142 men, 138 women; mean age 31.4 ± 6.6 years). The anatomic and surgical transepicondylar axes, as well as the posterior condylar joint line, were drawn. Differences in the posteromedial and posterolateral offsets and the femoral rotation angles relative to the posterior joint line were measured.

Results

The mean surgical femoral rotation angle was 4.8° ± 1.2°, and the mean posterior condylar offset difference was 4.4 ± 1 mm, with a strong correlation (p < 0.0001; r = 0.803). There was no statistically significant difference between genders. Linear regression analyses revealed that a 0.8-mm difference between the anteroposterior dimensions of the medial and lateral posterior condylar offsets corresponded to 1° of femoral external rotation (p < 0.0001, R ² = 0.645).

Conclusion

The accuracy of the applied technique intra-operatively can be verified by correlating the asymmetry of posterior chamfer cuts with the achieved femoral component rotation, as determined by measuring the thicknesses of posterior chamfer cuts with a caliper. Technical errors can also be minimized by confirming the association between the femoral component rotation—as predicted by the posterior condylar offset difference—and the preoperatively measured femoral rotation angle.

Level of evidence

II.     

Length-change patterns of the collateral ligaments after total knee arthroplasty

Purpose

Total knee arthroplasty (TKA) is a procedure with function dependent upon correct tensioning of the soft-tissue constraints. The purpose of this study was to examine the length-change behaviour of the collateral ligaments during knee flexion–extension before and after TKA. The influence of differing degrees of internal-external rotation of the femoral component on slackening/tightening of the collateral ligaments during knee flexion was to be studied.

Methods

The length-change patterns of the collateral ligaments were measured in eight intact knees in vitro: sutures were passed along the ligaments and attached to displacement transducers. Measurements were repeated after TKA with the femoral component in neutral rotation, then with 5° internal and 5° external rotation.

Results

Both the MCL and LCL slackened during knee flexion from 0° to 110° flexion, at all stages of the experiment. In the native knee, the MCL slackened 2?mm, whilst the LCL slackened 7?mm. The MCL slackened a further 3?mm and the LCL a further 4?mm during flexion post-TKA. A 5° external rotation of the femoral component slackened the MCL 2?mm more and tightened the LCL by 2?mm. The opposite effects resulted from 5° internal rotation.

Conclusions

The collateral ligaments slackened more than normal following TKA, and these length changes were increased by femoral component rotation. External rotation of the femoral component to address patellar tracking may slacken the MCL and thus lead to valgus instability in the flexed knee.     

The effects of implantation of tibio-femoral components in hyperextension on kinematics of TKA

Purpose

Implantation of prosthetic tibio-femoral components in hyperextension is a well-established and effective procedure, but whether prosthetic orientation in the sagittal plane has any effects on the postoperative kinematics remains unclear. The purpose of this study is to explore how the aforementioned hyperextension affects knee kinematics.

Methods

Validated computational dynamic TKA models were established. Based on representative literatures and actual operation specifications, femoral and tibial components were assembled with 0° or 5° of hyperextension. Dynamic data, including the timing of cam-post engagement, anterioposterior femoral translation and tibial axial rotation coupling with knee flexion, were recorded for analysis.

Results

5° of femoral component hyperextension delayed cam-post engagement by an angle of 2°. Nevertheless, a 5° posterior slope of the tibial component resulted in a 38° delay in engagement. Comparing this with the femoral component at the same angle of hyperextension, the tibial component could more evidently assist in the prevention of paradoxical femoral anterior translation and the promotion of tibial internal rotation through early flexion.

Conclusion

Tibio-femoral components in hyperextension did significantly alter postoperative kinematics, especially for the tibial component. These results suggest that the degree of tibial posterior slope cutting should be more highly scrutinized intraoperatively.

Level of evidence

II.     

MRI morphometry, cartilage damage and impaired function in the follow-up after slipped capital femoral epiphysis

Objective  

To assess rotation deficits, asphericity of the femoral head and localisation of cartilage damage in the follow-up after slipped capital femoral epiphysis (SCFE).     

Patient-specific instrumentation improves tibial component rotation in TKA

Purpose

To compare the femoral and tibial components rotational alignment in total knee arthroplasty (TKA) performed either with conventional or with patient-specific instrumentation.

Methods

Forty-five patients underwent primary TKA and were prospectively randomized into two groups: 22 patients into the conventional instrumentation group (group A) and 23 patients into the Signature? patient-specific instrumentation group (group B). All patients underwent computed tomography of the operated knee in the first week after surgery to measure the components rotation.

Results

The femoral component rotation was 0.0° (?0.25, 1.0) in group A, and 0.0° (0.0, 1.0) in group B. The tibial component rotation was ?16.0° (?18.5, 11.8) in group A, and ?16.0° (?19.0, ?14.0) in group B. There were no significant differences between the two groups in tibial and femoral components rotation. The difference between the tibial component rotation and the neutral tibial rotation was similar in both groups [2.0° (?0.5, 6.3) in group A and 2.0° (?1.0, 4.0) in group B], but the dispersion around the median was different between the two groups. The amplitude of the difference between tibial rotation and neutral position was 27° (?13, 14) in group A and 9° (?3, 6) in group B.

Conclusions

There is a smaller chance of internal malrotation of the tibial component with the Signature? patient-specific instrumentation system, with less dispersion and amplitude of the tibial component rotation around the neutral position.

Level of evidence

II.     

Mechanical axis-derived femoral component rotation in extramedullary total knee arthroplasty: a comparison between femoral transverse axis and transepicondylar axis

Purpose  

Correct rotational alignment of the femoral component is paramount to the success of total knee arthroplasty, but debate continues as to which method is the most reliable. The purpose of this study was to evaluate mechanical axis-derived rotational axis of the femoral component using an extramedullary femoral alignment guide system.     

Less femoral lift-off and better femoral alignment in TKA using computer-assisted surgery

Purpose

A comparison has been made between navigation-assisted and conventional measured resection total knee arthroplasty (TKA), under the hypothesis that navigation assistance would improve the precision and consistency of component alignment and femoral component rotation.

Methods

The following radiographic parameters were measured: mechanical femorotibial angle, coronal and sagittal component angle, and femoral component rotation. Femoral condylar lift-off was checked by axial radiographs, and thresholds for outliers were set at 1.0 mm.

Results

Clinical results obtained using Knee Society and Hospital for Special Surgery systems were not statistically different. The mean mechanical femorotibial angle was 2.2° (SD: 0.9) in the conventional group and 1.7° (SD: 0.7) in navigation group (p = 0.001). The mean coronal femoral component angle was 89.2° (SD: 2.2) in conventional group and 90.4° (SD: 1.8) in navigation group (p = 0.006). The mean transepicondylar-posterior condylar axis angle was 1.7° (SD: 0.9) in conventional group and 1.2° (SD: 0.5) in navigation group (p = 0.008). Femoral condylar lift-off greater than 1 mm occurred more frequently (p = 0.000) in conventional group.

Conclusion

Coronal plane stability and precision of femoral component rotation were impacted by navigation system. The use of a navigation system with measured resection TKA can help optimize coronal stability and parallel component position.

Level of evidence

Retrospective case control study, Level IV.     

How to improve femoral component rotational alignment in computer-assisted TKA

Purpose

Although several anatomical landmarks have been proposed to obtain adequate femoral component alignment in total knee arthroplasty (TKA), there is still no consensus regarding the best way to correctly position the prosthetic component on the horizontal plane. A previous computed tomography (CT)-based study has demonstrated anatomical transepicondylar axis (aTEA) to be externally rotated relative to surgical transepicondylar axis (sTEA) of approximately 4.5°. In this study, it is described a new methodological approach to femoral component rotational positioning through the use of previously reported CT scan information and navigation.

Methods

Eight consecutive patients scheduled for navigated TKA were selected. Rotational placement of the femoral component was performed using navigation system. The femoral component was implanted setting 4.5° of internal rotation relative to the aTEA. Within 1 week from surgery, all patients underwent a CT scan, and the posterior condylar angle (PCA) was measured. A PCA of 0.0°, meaning component placement parallel to sTEA, was set as femoral rotational alignment target. Clinical evaluation was performed at a mean 14.3 months of follow-up with KOOS questionnaire.

Results

The mean PCA measured on post-operative CT images was 0.4° (SD 1.3°), meaning that the femoral component was averagely implanted with 0.4° of internal rotation relative to the sTEA. Seven out of eight cases (87.5 %) resulted to have within 1° deviation from the rotational alignment target. All patients but one reported good clinical results.

Conclusions

Relevant finding of the present study was that the use of navigation and aTEA as a reference demonstrated to be accurate to set up femoral component rotational positioning on the horizontal plane in TKA. Further study should be performed to confirm this conclusion.

Level of evidence

III.     

Computer-assisted surgery improves rotational positioning of the femoral component but not the tibial component in total knee arthroplasty

Purpose

Computer-assisted surgery (CAS) may facilitate better positioning of total knee arthroplasty (TKA) along the coronal and lateral axes; however, there are doubts as to its usefulness in the rotational plane.

Methods

This is a prospective study of 95 TKAs comparing two groups: the CAS group and the standard equipment group. The series comprises 95 cases. A radiography of the lower limb and computer tomographies (CTs) of the femoral condylar region, the proximal end of the tibia and the ankle were performed to measure rotational angulation. A month after TKA surgery, the radiography and the CTs were repeated to analyze the position of the prosthetic components in the rotational plane.

Results

In the coronal axis, both CAS and mechanical technique improved femoro-tibial alignment, but when there are preexisting deformities ≥4°, CAS obtains better results. A strong correlation (R = 0.94, p = 0.001) was observed between the mean rotational axis measured with CT in the tibial plateau and that measured from the axis of the ankle. The mean initial femoral rotation of the complete series was 6.7° and 2.7° at 1-month follow-up (p < 0.001). In the standard instrumentation group, the femoral rotation went from 6.8° to 2.3°, whereas in the CAS group the femoral rotation went from 6.5° to 3.1° (p = 0.039), which is very close to the ideal 3° angle of external rotation. Tibial rotation changed by 5.28° for the entire patient population, but no differences were found when comparing CAS and standard instrumentation.

Conclusion

CAS improves frontal alignment in TKA, especially in the presence of preoperative deformities. In the femoral component, navigation most closely replicated the ideal 3° external rotation of the femoral component, but tibial rotation did not differ when comparing CAS to standard instrumentation.

Level of evidence

II.     

How to assess femoral and tibial component rotation after total knee arthroplasty with computed tomography: a systematic review

Purpose

One of the most important factors leading to revision of total knee arthroplasties (TKA) is malrotation of femoral and/or tibial component. Rotation measurements performed on radiographs are limited and less reliable compared to 2D computed tomography (CT). Nowadays, 2D-CT and 3D-CT can be distinguished in measuring rotation of the TKA components. The aim of this systematic review is to determine the most reliable CT techniques in measuring rotation of the TKA components and to investigate possible cut-off points that can be used in the clinician’s decision for a possible revision of the TKA.

Methods

A search of PubMed, Embase, the Cochrane Central Register of Controlled Trials and Web of Science was performed up to April 2015. Final selections of 12 articles were used in this systematic review.

Results

3D-CT, compared to 2D-CT, is more reliable and shows a high level of intra- and interobserver reliability. Femoral component rotation is measured using the component’s posterior condylar line or inner pegs in relation to the epicondylar axis. Five different techniques were used to measure tibial component rotation. The posterior border of the tibial component in relationship to the geometric centre and tibial tubercle was most frequently used.

Conclusion

This systematic review shows a strong preference for 3D-CT to determine the component’s rotation following a TKA. The literature shows consensus on the reference points of the femoral component. In measurements of the tibial component, various techniques are used with similar results. No clear cut-off point for revision of malrotated TKA components can be stated because of limited evidence.

Level of evidence

III.

     

Are undesirable contact kinematics minimized after kinematically aligned total knee arthroplasty? An intersurgeon analysis of consecutive patients

Purpose

Tibiofemoral contact kinematics or knee implant motions have a direct influence on patient function and implant longevity and should be evaluated for any new alignment technique such as kinematically aligned total knee arthroplasty (TKA). Edge loading of the tibial liner and external rotation (reverse of normal) and adduction of the tibial component on the femoral component are undesirable contact kinematics that should be minimized. Accordingly, this study determined whether the overall prevalence of undesirable contact kinematics during standing, mid kneeling near 90 degrees and full kneeling with kinematically aligned TKA are minimal and not different between groups of consecutive patients treated by different surgeons.

Methods

Three surgeons were asked to perform cemented, kinematically aligned TKA with patient-specific guides in a consecutive series of patients with their preferred cruciate-retaining (CR) implant. In vivo tibiofemoral contact positions were obtained using a 3- to 2-dimensional image registration technique in 69 subjects (Vanguard CR–TKA N = 22, and Triathlon CR–TKA N = 47).

Results

Anterior or posterior edge loading of the tibial liner was not observed. The overall prevalence of external rotation of the tibial component on the femoral component of 6 % was low and not different between surgeons (n.s.). The overall prevalence of adduction of the tibial component on the femoral component of 4 % was low and not different between surgeons (n.s.).

Conclusions

Kinematically aligned TKA minimized the undesirable contact kinematics of edge loading of the tibial liner, and external rotation and adduction of the tibial component on the femoral component during standing and kneeling, which suggests an optimistic prognosis for durable long-term function.

Level of evidence

III.     

The anterior trochlear line as a reference for femoral component positioning in total knee arthroplasty

Purpose  

A new radiographic method using the anterior and posterior femoral condyles as a landmark to determine the rotational alignment of the femoral component in TKA had been developed.     

Radiologic measurement of lesser trochanter and its clinical significance in Chinese

Objective  

Femoral fracture is a major cause of morbidity and mortality in elderly persons. Surgery, the main choice of treatment of femoral fracture, may result in some complications severely affecting patients’ daily activities due to femoral malalignment. The lesser trochanter is an important anatomical structure of the femur which could be used as an anatomical landmark during and after operation to evaluate femoral alignment. To predict femoral rotational malalignment during surgery, the relationship between the height and width of the lesser trochanter and femoral rotation at different angles was investigated.     

The effects of limb alignment on anterior cruciate ligament graft tunnel positions estimated from plain radiographs

Purpose  

The aims of this study were (1) to evaluate the femoral tunnel position after anatomic double-bundle and nonanatomic single-bundle reconstruction; (2) to evaluate the influence of rotation of the femur caused by limb malalignment on measurements of the position of the femoral ACL tunnel aperture relative to Blumensaat’s line.     

Femoral rotation in total knee arthroplasty: a comparison of patient individualized jigs with gap balancing in relation to anatomic landmarks

Purpose

The purpose of our study was to compare the accuracy of the rotational position of the femoral component in total knee arthroplasty aligned with patient individualized jigs (PSJ) to a gap balancing technique (GBT).

Methods

A consecutive series of 21 osteoarthritic patients were treated with 22 cruciate-retaining total knee prostheses. During surgery, the rotation of the femoral component pinholes was recorded for all knees using PSJ and GBT and transferred to computer tomograms (CT). The rotational differences between PSJ and GBT relative to the transepicondylar axis were analysed.

Results

The medium rotation of the femoral component pinholes was 1.3° ± 5.1° (min = ?6.3°; max = 14.4°) for PSJ and 0.1 ± 1.4° (min = ?1.6°; max = 3.4°) for GBT. Outliers of more than 3° were found more frequently with PSJ in 12 cases but only in one for GBT.

Conclusion

Based on our study, we would not recommend relying intra-operatively solely on the CT-based PSJ without the option to adjust or control femoral rotation.

Level of evidence

II.

     

Rotational alignment of the distal femur: anthropometric measurements with CT-based patient-specific instruments planning show high variability of the posterior condylar angle

Purpose

Finding the anatomical landmarks used for correct femoral axial alignment can be difficult. The posterior condylar line (PCL) is probably the easiest to find during surgery. The aim of this study was to analyse whether a predetermined fixed angle referencing of the PCL could help find the surgical epicondylar axis (SEA) and this based on a large CT database with enough Caucasian diversity to be representable.

Methods

A total of 2,637 CT scans and 3D reconstructions from patients on four continents, executed for preoperative planning and creation of patient-specific instrumentation, were used to perform anthropometric measurements and to measure the posterior condylar angle (PCA) between the surgical epicondylar angle and the PCL.

Results

The mean (SD) PCA was 4° (1.4°) of external rotation. A significant correlation was found between more external rotation of the SEA and more proximal varus of the tibia or more distal valgus of the femur. For 59 % of the study population, 4° external rotation from the PCL would be the right amount of axial rotation to align the femoral component in line with the SEA. Nine per cent needs less, and 32 % needs more than 4° of axial rotation. On 105 (4 %) CT-based 3D models, external rotation between 7° and 11° was measured and 77 (73 %) of those cases were in varus or neutral alignment. In 132 patients, bilateral measurements were available and 94 (71 %) had rotation within 1° of the opposite side. This last finding underlines that there is even an intra-individual difference in distal femoral anatomy that can range from 1° to 5°.

Conclusions

This study was performed on a very large anthropometric CT and 3D models database and showed that there is a 41 % risk of malalignment if a fixed PCA referenced of the PCL is used in total knee arthroplasty. The clinical importance of this study is the observation that femoral axial anatomy is individual and also that it is determined by the tibial anatomy. A group of patients needs more than the average external rotation because they have more distal femoral valgus with dysplastic condyles or more proximal tibial varus with a bigger medial condyle.

Level of evidence

III.