Anthropometry of the medial tibial condyle to design the tibial component for unicondylar knee arthroplasty for the Korean population

Unicondylar knee arthroplasty (UKA) has gained popularity in the recent years for treating medial compartment osteoarthritis of the knee joint in the Asian population. There is little information about the anthropometry of the resected bony surfaces of the knee joint in these population groups for designing the appropriate size-matched UKA components. We studied the anthropometry of the resected medial tibial condyles in 50 male and 50 female Korean cadavers by using three-dimensional computer tomography. We measured the anteroposterior dimension, the mediolateral dimension at defined points and the condylar aspect ratio. These measurements were compared with similar dimensions of the tibial components from five conventionally used UKA designs. Statistical analysis was performed using Student’s t-test, Paired t-test and Pearson’s correlation coefficient. We found that three of the tibial component designs showed mediolateral overhang for the whole range of measured anteroposterior dimensions of the resected medial tibial condyles, whereas one of the designs (DePuy) showed mediolateral undersizing for the smaller AP dimensions and overhang for the larger AP dimensions of the resected medial tibial condyles. Another design (Smith and Nephew) showed mediolateral undersizing for the whole range of measured anteroposterior dimensions of the resected medial tibial condyle. We found a decrease in the condylar aspect ratio with increasing AP dimension for our cadaver population data. However, the majority of the conventional tibial prosthesis showed either a constant condylar aspect ratio or an increasing aspect ratio (DePuy) with the increasing AP dimension of the resected medial tibial condyle. Our study may provide guidelines for designing appropriate tibial UKA components for a majority of Asian sub-populations and encourage similar studies in other population groups. D. S. Kwak and S. Surendran contributed equally to this work.     

Relationship between the tibial anteroposterior axis and the surgical epicondylar axis in varus and valgus knees

Purpose

Proper rotational alignment in total knee arthroplasty (TKA) is essential for successful outcomes. The surgical epicondylar axis (SEA) has been frequently used to determine the femoral rotational alignment, and the anteroposterior (AP) axis of the tibia described in previous study has been introduced as a line perpendicular to the SEA in healthy knees. However, the rotational relationship between the distal femur and the proximal tibia would vary between normal and osteoarthritic knees, and a question remains whether the rotational relationship between the SEA and the AP axis of the tibia would be the same between normal and osteoarthritic knees. This study aims to determine whether the AP axis of the tibia is actually perpendicular to the SEA and useful for the tibial rotational alignment also in osteoarthritic knees.

Methods

Preoperative computed tomography scans on 25 varus and 25 valgus knees undergoing TKA were studied. The SEA and the AP axis of the tibia were identified using a three-dimensional software, and the angle between the line perpendicular to the projected SEA and the AP axis was measured.

Results

The AP axis of the tibia was 1.7° ± 4.3° and 2.0° ± 4.0° internally rotated relative to the line perpendicular to the SEA in the varus and valgus groups, respectively.

Conclusions

The AP axis of the tibia was, on average, perpendicular to the SEA in both varus and valgus knees. The AP axis would be useful for setting the tibial component with minimal rotational mismatch.

Level of evidence

IV.     

Anatomic tibial component design can increase tibial coverage and rotational alignment accuracy: a comparison of six contemporary designs

Purpose

The aim of this study was to comprehensively evaluate contemporary tibial component designs against global tibial anatomy. We hypothesized that anatomically designed tibial components offer increased morphological fit to the resected proximal tibia with increased alignment accuracy compared to symmetric and asymmetric designs.

Methods

Using a multi-ethnic bone dataset, six contemporary tibial component designs were investigated, including anatomic, asymmetric, and symmetric design types. Investigations included (1) measurement of component conformity to the resected tibia using a comprehensive set of size and shape metrics; (2) assessment of component coverage on the resected tibia while ensuring clinically acceptable levels of rotation and overhang; and (3) evaluation of the incidence and severity of component downsizing due to adherence to rotational alignment and overhang requirements, and the associated compromise in tibial coverage. Differences in coverage were statistically compared across designs and ethnicities, as well as between placements with or without enforcement of proper rotational alignment.

Results

Compared to non-anatomic designs investigated, the anatomic design exhibited better conformity to resected tibial morphology in size and shape, higher tibial coverage (92 % compared to 85–87 %), more cortical support (posteromedial region), lower incidence of downsizing (3 % compared to 39–60 %), and less compromise of tibial coverage (0.5 % compared to 4–6 %) when enforcing proper rotational alignment.

Conclusions

The anatomic design demonstrated meaningful increase in tibial coverage with accurate rotational alignment compared to symmetric and asymmetric designs, suggesting its potential for less intra-operative compromises and improved performance.

Level of evidence

III.     

Preoperative morphometric differences in the distal femur are based on skeletal size in Japanese patients undergoing total knee arthroplasty

Purpose

The objectives of this study were to measure the morphometric parameters of preoperative distal femurs to determine the differences by diagnosis and gender after accounting for skeletal size.

Methods

One-hundred and seventy-nine Japanese patients who underwent total knee arthroplasty (TKA) (25 males and 154 females) were assessed. The anteroposterior length (AP), mediolateral width (ML), aspect ratio (AR), surgical epicondylar axis (SEA) to posterior condylar axis (PCA) angle, and Whiteside to SEA angle were measured on preoperative computed tomography scans. The AP/ML, AR/ML, SEA/PCA, and Whiteside/PCA relationships were evaluated and compared by patient diagnosis and gender. The results were also compared with the sizes of 10 currently available TKA implants in Japan.

Results

The mean AP, ML, AR, SEA/PCA angle, and Whiteside/PCA angle were 58.8 mm, 64.7 mm, 0.91, external rotation (ER) 3.5°, and ER 1.6°, respectively. AP and AR each were significantly correlated with ML (p < 0.001). AP, ML, and AR were not significantly different between patients diagnosed with osteoarthritis and rheumatoid arthritis. AP/ML and AR/ML were significantly correlated within each diagnosis (p < 0.001), but the analysis of covariance showed no significant differences between the diagnoses. AP and ML were significantly longer (p < 0.001) in males (63.6, 72.7 mm) than in females (58.1, 63.4 mm), while AR was smaller in males (0.88 vs. 0.92), with significant correlations for AP/ML (male: p < 0.010, female: p < 0.001) and AR/ML (male: p = 0.002, female: p < 0.001) in each gender. However, the analysis of covariance showed no significant differences between gender in the AP/ML and AR/MR correlations. The AP/ML ratio of our data was similar to the size variations of the 10 TKA implants, but the AR/ML ratio was quite different from almost all the implants.

Conclusions

No differences in preoperative femur morphometry were found between patients with different diagnoses, but the gender difference in AR was related to the difference in skeletal size between males and females.

Level of evidence

Case series with no comparison groups, Level IV.     

Femoral and tibial insert downsizing increases the laxity envelope in TKA

Purpose

This study examines the effect of component downsizing in a modern total knee arthroplasty (TKA) system on the laxity envelope of the knee throughout flexion.

Methods

A robotic testing system was utilized to measure laxity envelopes in the implanted knee by in the anterior–posterior (AP), medial–lateral (ML), internal–external (IE) and varus–valgus (VV) directions. Five fresh-frozen cadavers were tested with a modern cruciate retaining TKA implantation, a 1-mm thinner polyethylene insert and a femoral component 2 mm smaller in the AP dimension.

Results

The downsized tibial insert was more lax throughout the flexion arc with up to 2.0 mm more laxity in the AP direction at full extension, a 43.8 % increase over the original implantation. A thinner insert consistently increased laxity throughout the arc of flexion in all degrees of freedom. Downsizing the femoral component resulted in 8.5 mm increase in AP laxity at 90°, a 73.9 % increase. In mid-flexion, downsizing the femur produced similar laxity values to the downsized insert in AP, ML, IE and VV directions.

Conclusion

Downsizing the TKA components had significant effects on laxity throughout flexion. Downsizing a femoral component 2 mm had an equivalent increase in laxity in mid-flexion as downsizing the tibial insert 1 mm. This study quantifies the importance of choosing the appropriate implant component size, having the appropriate size available and the effect of downsizing. The laxity of the implanted knee contributes to how the implant feels to the patient and ultimately the patient’s satisfaction with their new knee.     

Medial sixth of the patellar tendon at the tibial attachment is useful for the anterior reference in rotational alignment of the tibial component

Purpose

The anteroposterior (AP) axis connecting the middle of the posterior cruciate ligament to the medial border of the patellar tendon at its attachment has been introduced as a reproducible and reliable reference perpendicular to the surgical epicondylar axis in healthy knees. A recent literature has reported that the AP axis of the tibia is, on average, almost perpendicular to the surgical epicondylar axis also in varus and valgus knees and can be used as a tibial rotational reference to minimize the risk for rotational mismatch between the femoral and tibial components in total knee arthroplasty (TKA). However, it is difficult to identify the AP axis after tibial resection. The purpose of the current study was to determine a modified AP axis that runs parallel to the AP axis and passes through the centre of the cut surface in osteoarthritic knees.

Methods

Preoperative computed tomography scans on 30 varus and 30 valgus knees undergoing TKA were studied using a three-dimensional software. The modified AP axis that runs parallel to the AP axis and passes through the centre of the cut surface was drawn. We investigated where the modified AP axis crossed the patellar tendon at its tibial attachment.

Results

The modified AP axis passed through the medial 1/6 of the patellar tendon (4 mm from medial edge) at its attachment in both varus and valgus knees.

Conclusions

The AP axis of the tibia is useful as a tibial rotational reference in cutting the proximal tibia, but it is difficult to identify the AP axis after tibial resection. The clinical relevance of this study is that medial 1/6 of the patellar tendon at its attachment would be a useful landmark in aligning the tibial component.

Level of evidence

IV.     

Femoral sizing in total knee arthroplasty is rotation dependant

Purpose

The mismatch between the medio-lateral (ML) and the antero-posterior (AP) size of femoral components in total knee arthroplasty (TKA) has been linked to gender, ethnicity, morphotype and height differences in patients. The hypothesis of this study was that the AP size measurement of a femoral component increases with more external rotation in posterior referencing TKA.

Methods

During a 2-year period, 201 patients were included in this prospective study. The AP distance of the distal femur was measured with an AP sizer of the Vanguard (Biomet, Warsaw, US) knee system. This AP sizer allows to dial in external rotation by 1° increments and to determine the femoral size with an anterior boom. AP size was noted at 0°, 3° and 5° of external rotation and then compared for ML matching.

Results

Antero-posterior and corresponding ML sizes match perfectly for the Vanguard at 0° of external rotation and a central boom position on the anterior femoral surface. Then, the anterior boom was positioned on the antero-lateral cortex and the AP size increased a mean (SD) 1 (0.5) mm. With 3° of external rotation, the AP size increased a mean (SD) 2.3 (0.4) mm and for 5° a mean (SD) 3.8 (0.3) mm (P < 0.05). This increase in AP size resulted in ML overhang of 2.2 (1.2) mm for 3° and 4.8 (2.6) mm for 5° (P < 0.05).

Conclusions

Antero-posterior size measurement of the distal femur is determined by the anatomy of the anterior surface with a higher antero-lateral cortex and the amount of external rotation that is dialled in during surgery. Since these parameters vary case per case, the availability of narrow components offers more surgical options to the surgeon and its importance extends beyond the gender aspect allowing different amounts of external rotation to be used without ML overhang.

Level of evidence

II.     

Anatomic single-bundle ACL surgery: consequences of tibial tunnel diameter and drill-guide angle on tibial footprint coverage

Purpose

To investigate the consequences of differences in drill-guide angle and tibial tunnel diameter on the amount of tibial anatomical anterior cruciate ligament (ACL) footprint coverage and the risk of overhang of the tibial tunnel aperture over the edges of the native tibial ACL footprint.

Methods

Twenty fresh-frozen adult human knee specimens with a median age of 46 years were used for this study. Digital templates mimicking the ellipsoid aperture of tibial tunnels with a different drill-guide angle and a different diameter were designed. The centres of these templates were positioned over the geometric centre of the tibial ACL footprint. The amount of tibial ACL footprint coverage and overhang was calculated. Risk factors for overhang were determined. Footprint coverage and the risk of overhang were also compared between a lateral tibial tunnel and a classic antero-medial tibial tunnel.

Results

A larger tibial tunnel diameter and a smaller drill-guide angle both will create significant more footprint coverage and overhang. In 45 % of the knees, an overhang was created with a 10-mm diameter tibial tunnel with drill-guide angle 45°. Furthermore, a lateral tibial tunnel was found not to be at increased risk of overhang.

Conclusion

A larger tibial tunnel diameter and a smaller drill-guide angle both will increase the amount of footprint coverage. Inversely, larger tibial tunnel diameters and smaller drill-guide angles will increase the risk of overhang of the tibial tunnel aperture over the edges of the native tibial ACL footprint. A lateral tibial tunnel does not increase the risk of overhang.     

The use of a mono-fluted reamer results in decreased enlargement of the tibial tunnel when using a transtibial ACL reconstruction technique

Purpose

To evaluate whether femoral tunnel preparation using a mono-fluted reamer rather than an acorn reamer would result in less tibial tunnel deformation when using a transtibial technique for anterior cruciate ligament reconstruction.

Methods

Tibial and femoral tunnel preparation was performed in four matched pairs of cadaveric knees. The tibial tunnel was drilled using a standard acorn reamer. The femoral tunnel was prepared using a transtibial technique with a mono-fluted reamer, and then, the same femoral tunnel was re-reamed using an acorn reamer. The anterior–posterior (AP) and medial–lateral (ML) dimensions of the tibial tunnel were recorded after each reamer. We then compared the measurements following the use of each reamer using a paired two-sample t test.

Results

There was a significantly larger degree of tibial tunnel deformation following femoral tunnel preparation with the acorn reamer when compared with the mono-fluted reamer. The initial tibial tunnel measured 10.5 and 10.1 mm in the AP and ML dimensions, respectively. The resultant AP diameter of the tibial tunnel after femoral reaming was 16.7 mm (p < 0.001) for the acorn reamer compared with 11.6 mm (p < 0.001) for the mono-fluted reamer. The ML diameters were 11.3 mm (p = 0.003) versus 10.2 mm (p = 0.07) for the acorn and mono-fluted reamer, respectively.

Conclusion

The use of a mono-fluted reamer for femoral tunnel preparation results in less tibial tunnel deformation during transtibial reaming.     

Variability of the location of the tibial tubercle affects the rotational alignment of the tibial component in kinematically aligned total knee arthroplasty

Purpose

Our experience with computer plans of kinematically aligned total knee arthroplasty showed that the anteroposterior (AP) axis of the tibial component when viewed in an axial plane did not consistently intersect either the medial border or the medial 1/3 of the tibial tubercle. The purposes were (1) to determine the variability in the mediolateral location of the tibial tubercle with respect to the medial tibia on the magnetic resonance image (MRI) of the knee and (2) to determine whether the AP axis of the kinematically aligned tibial component intersects either the medial border or the medial 1/3 of the tibial tubercle.

Methods

One hundred and fifteen knees in 111 consecutive subjects treated with total knee arthroplasty were studied. The mediolateral location of the tibial tubercle was measured from a magnetic resonance image (MRI) of the knee. The distances between the AP axis of the tibial component and the medial border of the tibial tubercle and between the AP axis and the medial 1/3 of the tibial tubercle were measured from a computer plan of the reconstructed knee.

Results

On the MRI, the medial border of the tibial tubercle varied 15 mm from the medial border of the tibia. On the computer plan, the AP axis of the tibial component in an axial view of the tibia did not intersect either the medial border (p < 0.0001) or the medial 1/3 of the tibial tubercle (p < 0.0001). In 70 and 86 % of knees, the mediolateral distance of the AP axis of the tibial component was 2 mm or greater from the medial border of the tibial tubercle and the medial 1/3 of the tibial tubercle, respectively, which causes a clinically meaningful error in rotation of 5° or more.

Conclusions

Because the mediolateral location of the tibial tubercle varies, the medial border and medial 1/3 of the tibial tubercle are not reliable landmarks when the goal is to kinematically align the rotation of the tibial component on the tibia.

Level of evidence

IV.     

Relationship of native tibial plateau anatomy with stability testing in the anterior cruciate ligament-deficient knee

Purpose

Recent attention has been drawn to tibial plateau slope and depth with relation to both risk of anterior cruciate ligament (ACL) tear and kinematics in the cruciate-deficient knee. The purpose was to evaluate the relationship between native proximal tibial anatomy and knee kinematics in the anterior cruciate-deficient knee.

Methods

Twenty-two cadaveric knees underwent CT scanning to measure proximal tibia anatomy. Translation was measured during Lachman and mechanized pivot-shift tests on the intact knee and then after resection of the ACL. Pearson’s correlation was calculated to assess the relationship between tibial translation of the ACL-deficient knee and tibial plateau anatomic parameters.

Results

No significant correlation was found between ACL-deficient kinematic testing and tibial slope or depth (n.s.). Lateral compartment translation on Lachman and pivot-shift testing correlated with lateral compartment AP length (P?=?0.007 and P?=?0.033, respectively). The ratio of lateral AP length to medial AP length correlated with lateral compartment translation during the pivot shift (P?=?0.002).

Conclusion

There was a poor correlation between native tibial slope and kinematic testing. There were, however, increases in translation during pivot-shift and Lachman testing with increased AP length of the lateral compartment. In addition, the finding of increased pivot-shift magnitude when the lateral compartment was relatively wide in the AP plane compared to the medial compartment suggests that patients with a “dominant” lateral compartment may be prone to a greater magnitude of instability after ACL injury.     

Tibial base design and patient morphology affecting tibial coverage and rotational alignment after total knee arthroplasty

Purpose

To understand interactions between total knee arthroplasty tibial base design attributes, variations in tibial morphology, and the resulting tibial coverage and rotational alignment.

Methods

Tibial anthropometric measurements, including aspect ratio (medial–lateral width/anterior–posterior length) and tibial asymmetry, were taken for 14,791 total knee arthroplasty patients and compared with the ability of four different commercial tibial base designs to cover the resected plateau. The anthropometric measurements were also compared with the resulting tibial base rotation, which occurred when rotating the base to maximize coverage.

Results

All four tibial base designs resulted in similar coverage ranging from 80.2 (4.7) % to 83.8 (4.6) %. Mean tibial base rotation when placed to maximize coverage ranged from 3.7 (4.4)° (internal) to 3.8 (4.5)° (external) relative to the medial third of the tibial tubercle. More asymmetric tibiae and tibiae with a lower aspect ratios resulted in increased internal tibial base rotation.

Conclusions

The four tibial base designs assessed provided similar levels of tibial bone coverage across the patient population, despite different design features. Rotating the tibial base to maximize coverage did not significantly increase the tibial coverage, but induced variability in tibial base alignment. Certain tibial anthropometrics may predispose particular patients to internal tibial base mal-rotation.     

Does a conservative tibial cut in conventional total knee arthroplasty violate the deep medial collateral ligament?

Purpose

Based on the anatomy of the deep medial collateral ligament (MCL), it was hypothesized that at least part of its cross-sectional insertion area is jeopardized while performing a standard tibial cut in conventional total knee arthroplasty (TKA). The aim of this study was to determine whether it is anatomically possible to preserve the tibial deep MCL insertion during conventional TKA.

Methods

Thirty-three unpaired cadaveric knee specimens were used for this study. Knees with severe varus/valgus deformity or damage to the medial structures of the knee were excluded. In the first part of the study, the dimensions of the tibial insertion of the deep MCL and its relationship to the joint line were recorded. Next, the cross-sectional area of the deep MCL insertion was determined using calibrated digital photographic analysis. In the second part, the effect of a standard 9-mm 3° sloped tibial cut on the structural integrity of the deep MCL cross-sectional insertion area was determined using conventional instrumentation.

Results

The proximal border of the deep MCL insertion site on the tibia was located on average 4.7 ± 1.2 mm distally to the joint line. After performing a standard 9-mm 3° sloped tibial cut, on average 54 % of the deep MCL insertion area was resected. In 29 % of the cases, the deep MCL insertion area was completely excised.

Conclusion

The deep MCL cannot routinely be preserved in conventional TKA. The deep MCL insertion is at risk and may be jeopardized in case of a tibial cut 9 mm below the native joint line. As the deep MCL is a distinct medial stabilizer and plays an important role in rotational stability, this may have implications in future designs of both unicondylar and total knee arthroplasty, but further research is necessary.     

Lateral versus medial tibial plateau: morphometric analysis and adaptability with current tibial component design

The purpose of this study was to analyze the in vivo dimensions of each tibial plateau for planning of unicompartmental knee arthroplasty (UKA), and to compare the morphometric data to the dimensions of nine current designs of UKA tibial components. Thirty-seven knees (31 females and 6 males) operated on with UKA were studied. All patients were examined postoperatively using computed tomography (CT). There were 18 lateral and 19 medial UKAs. On the CT scan, each operated tibial plateau was measured in the transverse plane at the resection level, just below the full polyethylene tibial component. We measured the length of the anteroposterior (AP) cut as well as the maximal mediolateral dimension of the resected plateau (perpendicular to the AP cut). We compared the measurements with nine current UKA systems: Accuris (Smith and Nephew), Advance (Wright Medical), HLS Uni Evolution (Tornier), Miller-Galante and “ZUK” (Zimmer), Oxford and Oxford α (Biomet), Preservation (DePuy) and Unix (Stryker). There was good correlation between patient height and mediolateral dimension (r = 0.6), and between patient height and area of total tibial plateau (r = 0.7). The anteroposterior dimension was greater for the medial plateau (mean 50.8 mm, SD 3.3) than for the lateral plateau (mean 47.2 mm, SD 3.3). This difference was statistically significant (P = 0.0016). Some UKA implants are designed with an asymmetric femoral component, but none have an asymmetric tibial component. The present study suggests, however, that the shape of the medial tibial plateau differs from that of the lateral plateau. This difference can lead to mediolateral overhang for medial UKA, if the surgeon aims for optimal anteroposterior coverage.     

Rotation in total knee arthroplasty: no difference between patient-specific and conventional instrumentation

Purpose

It was our hypothesis that patient-specific instrumentation (PSI) can improve the accuracy of the rotational alignment in TKA based on the concept of the system and on the potential to clearly identify pre-operatively during planning the classical anatomical landmarks that serve as references to set-up the rotation both for the femur and tibia.

Materials and methods

In this prospective comparative randomized study, 40 patients (20 in each group) operated in our institution between September 2012 and January 2013 by the 2 senior authors were included. Randomization of patients into one of the two groups was done by the Hospital Informatics Department with the use of a systematic sampling method. All patients received the same cemented high-flex mobile bearing TKA. In the PSI group, implant position was compared to the planed position using previously validated dedicated software. The position of the implants (frontal and sagittal) was compared in the 2 groups on standard X-rays, and the rotational position was analysed on post-operative CT-scan.

Results

90 % of the patients add <2° or mm of difference between the planned position of the implants and the obtained position, except for the tibial rotation where the variations were much higher. Mean HKA was 179° (171–185) in the PSI group with 4 outliers (2 varus: 171° and 172°:184° and 185°) and 178.3° with 2 outliers (171° and 176°) in the control group. No difference was observed between the two groups concerning the frontal and sagittal position of the implants on the ML and AP X-rays. No significant difference of femoral rotation was observed between the two groups with a mean of 0.4° in the PSI group and 0.2° in the control group (p: n.s). Mean tibial rotation was 8° of internal rotation in the PSI group and 15° of internal rotation in the standard group (p: n.s).

Conclusion

Based on our results, we were unable to confirm our hypothesis as PSI cannot improve rotation in TKA. More work needs to be done to more clearly define the place of PSI in TKA, to keep on improving the accuracy of the system and to better define the individual targets in TKA in terms of frontal, sagittal and rotational positioning of the implant for each patient.

Level of evidence

Prospective comparative randomized study, Level II.     

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.     

Partial restoration of knee kinematics in severe valgus deformity using the medial-pivot total knee arthroplasty

Purpose

The objectives of the study were to examine knee kinematics in knees with severe valgus deformities and to compare pre- and post-operative knee kinematics for the same subjects implanted with medial-pivot total knee arthroplasty (TKA).

Methods

Seven subjects with severe valgus deformities due to osteoarthritis (OA) or rheumatoid arthritis (RA) were enrolled in the prospective study. Prior to TKA, three-dimensional (3D) kinematics were assessed by 3D to 2D registration technique using the image matching software ‘Knee Motion’, under in vivo, weight-bearing conditions. Postoperatively, each subject again performed the same motion under fluoroscopic surveillance.

Results

Preoperative kinematics demonstrated external rotation of tibias from extension to flexion, and small posterior femoral translations dominated in the medial condyle associated with anterior slides during partial range of motion. Postoperatively, these non-physiological tibial rotations were restored, and most subjects exhibited small internal rotations of tibias. On average, preoperative tibial internal rotation was ?4.7° ± 7.6° from full extension to maximum flexion, and the angle was 4.8° ± 3.1° postoperatively (p = 0.01). In addition, small amounts of posterior translation of the lateral condyle and anterior translation of the medial condyle were confirmed in most subjects postoperatively.

Conclusions

The study showed that the preoperative kinematic pattern established in severe valgus deformity was different from the physiological knee pattern. In addition, post-operative results suggest that the non-physiological kinematics were partially restored after TKA by using the prosthesis design even in the absence of the posterior cruciate ligament (PCL) and the cam–post mechanism.

Level of evidence

II.     

Partial resection of the PCL insertion site during tibial preparation in cruciate-retaining TKA

Purpose

Based on the anatomy of the tibial PCL insertion site, we hypothesized that at least part of it is damaged while performing a standard tibial cut in a PCL-retaining total knee replacement. The purpose of this study was to determine and quantify the amount of resection of the tibial PCL attachment with a 9 mm tibial cut with 3 degrees of posterior slope.

Methods

Twenty cadaver tibias were used. The borders of the PCL footprint were demarcated, and calibrated digital pictures were taken in order to determine the surface area. A standard tibial intramedullary guide was used to prepare and perform a tibial cut at a depth of 9 mm with 3 degrees posterior slope. After the tibial cut was made, a second digital picture was taken using the same methodology to measure the surface area of the remaining PCL insertion.

Results

The mean surface area of the intact tibial PCL footprint before the cut was 148.9 ± 25.8 mm² and after the tibial cut 47.1 ± 28.0 mm². On average, 68.8 ± 15.3 % of the surface area of the PCL insertion was removed.

Conclusion

The results of this study, therefore, indicate that the conventional technique for tibial preparation in cruciate-retaining total knee arthroplasty can result in damage or removal of a significant part of the tibial PCL insertion.     

Biomechanical analysis of the tibial tray design in TKA: comparison between modular and offset tibial trays

Purpose

The aim of this work was to develop a computational biomechanical study to compare the performance of tibial trays with different offsets for a total knee arthroplasty. The goal was to investigate whether the offset tibial tray shifts the bone stress distribution, influencing the clinical outcome.

Methods

Three geometric models were developed for the intact tibia bone: one considering a standard tibia case and the other two reproducing tibias with a medial or a lateral offset of the metaphysis. Appropriate prosthetic components were assembled in the bone for the aforementioned cases. The finite element method was used to obtain the mechanical stress distribution for the models, and the stress shielding effect due to the prosthesis was analysed.

Results

The obtained results revealed that the offset cases are subjected to higher stresses than the standard case. These values can be two times superior to the ones verified in a standard case. The stress shielding effect was confirmed along all the analysed paths, except near the stem’s end in some areas.

Conclusion

The higher stresses registered can originate lower clinical outcomes in the offset cases. These findings can be an important beginning to understand whether better bone stress distribution could be achieved in deformity correction with associated osteotomies instead of offsetting.