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.     

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.     

The medial border of the tibial tuberosity as an auxiliary tool for tibial component rotational alignment during total knee arthroplasty (TKA)

Purpose

The objective of this study was to quantify the amount of ensuing internal rotation of the tibial component when positioned along the medial border of the tibial tubercle, thus establishing a reproducible intraoperative reference for tibial component rotational alignment during total knee arthroplasty (TKA).

Methods

The angle formed from the tibial geometric centre to the intersection of both lines from the middle of the tibial tuberosity and its medial border was measured in 50 patients. The geometric centre was determined on an axial CT slice at 10 mm below the lateral tibial plateau and transposed to a slice at the level of the most prominent part of the tibial tuberosity. Similar measurements were taken in 25 patients after TKA, in order to simulate the intraoperative appearance of the tibia after making its proximal resection.

Results

This angle was found to be similar (n.s.) in normal and post-TKA tibiae [median 20.4° (range 15°–24°) vs. 20.7° (range 16°–25°), respectively]. In 89.3 % of the patients, the angle ranged from 17° to 24°. No statistical difference (p n.s.) was found between women and men in both normal [median ?20.7° (range 16°–25°) vs. 19.9° (range 15°–24°)] and post-TKA tibiae [median 21.4° (range 19°–24°) vs. 20° (range 16°–25°)].

Conclusion

This study found that in 90 % of the patients, the medial border of the tibial tuberosity is internally rotated 17°–24° in relation to the line connecting the middle of the tuberosity to the tibial geometric centre. Since this anatomical landmark may be more easily identifiable intraoperatively than the commonly used “medial 1/3”, it can provide a better quantitative reference point and help surgeons achieve a more accurate tibial implant rotational position.

Level of evidence

Cohort and case control studies, Level III.

     

High tibial open wedge osteotomy below the tibial tubercle: clinical and radiographic results

Purpose

The purpose of this study was to evaluate the clinical and radiographic results of open wedge HTO below the tubercle for genu varum in relatively young patients.

Methods

Thirty-seven knees in 19 patients with genu varum treated by open wedge HTO below the tubercle between 2001 and 2008 were retrospectively studied. Median follow-up was 36 months (12–108), and median patient age at the time of surgery was 26 years (16–45). Clinical results were evaluated using Lysholm knee scores and Hospital for Special Surgery knee scores. Satisfaction with the results of surgery (0–10 points) was subjectively evaluated using operative scar (1–5 points) and leg shape (1–5 points) results at follow-up. Radiographic evaluations were made using: (1) tibiofemoral angles, (2) mechanical axis deviations, (3) varus-valgus inclinations of the tibial plateau, (4) tibial slopes, and (5) Insall-Savati and (6) Blackburne-Peel ratios.

Results

All but one patient achieved radiographic healing and union at the osteotomy site at an average of 3 months postoperatively. Average Lysholm knee score improved from 89.4 ± 8.7 preoperatively to 98.6 ± 2.5 at final follow-up (P = 0.0001), and mean HSS score improved from 91.1 ± 5.6 preoperatively to 98.5 ± 2.0 at final follow-up (P = 0.0001). Mean patient satisfaction score at final follow-up was 8.6 ± 1.0, and mean tibiofemoral angle increased from ?1.6° preoperatively to 7.7° at final follow-up (P < 0.0001). The point where the mechanical axis crosses the tibial plateau also shifted significantly from 15.0% preoperatively to 50.6% at final follow-up (P = 0.0002). However, mean posterior tibial slope did not change significantly (9.7° preoperatively and 8.7° at final follow-up; P = NS), and neither did patella heights as measured by Insall-Savati and Blackburne-Peel ratios.

Conclusion

Both functional assessment and radiographic measures indicated that HTO below the tibial tubercle leads to significant improvements in radiographic parameters and knee function without changes in patellar height or posterior tibial slope. The results obtained support the hypotheses that opening wedge HTO below the tibial tubercle should be recommended in relatively young patients with genu varum.

Level of evidence

Therapeutic study, 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.     

Intraoperative anthropometric measurements of tibial morphology: comparisons with the dimensions of current tibial implants

Purposes

This study analyzed morphological differences in the resected proximal tibial surfaces of Chinese males and females undergoing total knee arthroplasty (TKA) and compared the measurements with the dimensions of five currently used tibial implants.

Methods

The mediolateral (ML), middle anteroposterior (AP), medial anteroposterior (MAP), and lateral anteroposterior (LAP) dimensions of the resected tibial surfaces of 976 Chinese TKA knees (177 male, 799 female) were measured. The ML/AP ratio of every knee was calculated. These morphological data were compared with the dimensions of five currently used tibial implants.

Results

The ML, AP, MAP, and LAP dimensions of the resected proximal tibias showed significant differences according to gender. Compared with currently used tibial implants, the smaller implants showed tibial ML undersizing and the larger implants showed tibial ML overhang. The ML/AP aspect ratio progressively decreased with increasing AP dimension in the resected proximal tibias, which contrasts with the relatively constant or increased (NexGen) aspect ratio in currently used tibial implants. Males showed a higher ML/AP aspect ratio than females for a given AP dimension. This indicates that for an implant with a given AP dimension, the tibial ML dimension tends to be undersized in males and to overhang in females.

Conclusion

The results of this study may provide fundamental data for designing suitable tibial implants for use in the Chinese population, especially for design of gender-specific prostheses.

Level of evidence

II.     

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.     

Medial femoral head border is a reliable and reproducible reference for axis determination for femoral component of unicompartmental knee arthroplasty

Purpose

The femoral component should be implanted parallel to the mechanical axis in unicompartmental knee arthroplasty. It was hypothesised that a line between medial femoral condyle centres and medial border of femoral head will be parallel to the mechanical axis; this study set out to examine this hypothesis.

Methods

One hundred X-rays in fifty patients were included for this study. Long-leg standing X-rays including hip and ankle with patellae facing forwards were obtained. On these films, we measured the angle, α, between mechanical axis and the line between the femoral head centre and knee centre (medial mechanical axis), and the angle, β, between the medial mechanical axis and a line between medial femoral condyle and femoral head centre.

Results

The average value of α was 0.1 ± 0.5° and the average value of β 3.0° ± 0.3°. These data indicate that mechanical axis and medial mechanical axis are virtually parallel to each other.

Conclusion

As medial femoral head border is easily identified fluoroscopically, it is a reliable landmark for orientating the femoral component of medial UKA.

Level of evidence

Case series with no comparison group, Level IV.     

Accurate alignment and high function after kinematically aligned TKA performed with generic instruments

Purpose

Performing kinematically aligned total knee arthroplasty (TKA) with generic instruments is less costly than patient-specific instrumentation; however, the alignment and function with this new technique are unknown.

Methods

One hundred and one consecutive patients (101 knees) treated with kinematically aligned TKA, implanted with use of generic instruments, were prospectively followed. The medial collateral ligament was not released. The lateral collateral ligament was released in the 17 % of patients with a fixed valgus deformity. Six measures of alignment were categorized from a scanogram of the extremity, an axial scan of the knee, and an intraoperative measurement. Both the Oxford Knee and WOMAC? scores were assessed as function. High function was a mean Oxford Knee score >41.

Results

The frequency that patients were categorized as in-range was 93 % for the mechanical alignment of the limb (0° ± 3°), 94 % for the joint line (?3° ± 3°), 57 % for the anatomic axis of the knee (?2.5° ± ?7.4° valgus), 4 % for the varus–valgus rotation of the tibial component (≤0° valgus), 98 % for the rotation of the tibial component with respect to the femoral component (0° ± 10°), and 94 % for the intraoperative change in the anterior–posterior distance of the tibia with respect to the femur at 90° of flexion (0 ± 2 mm). The mean OKS score was 42, and WOMAC? score was 89. For each alignment, the function was the same for patients categorized as an outlier or in-range.

Conclusions

The authors prefer the use of generic instruments to perform kinematically aligned TKA in place of mechanically aligned TKA because five of six alignments were accurate and because high function was restored regardless of whether patients had an alignment categorized as an outlier or in-range.

Level of evidence

IV.     

Opening wedge high tibial osteotomy: plate position and biomechanics of the medial tibial plateau

Purpose

To ascertain whether changing position and size of the spacer may modify the load and displacement of the tibial plateau when performing an opening wedge high tibial osteotomy.

Methods

Fifteen sawbones tibia models were used. In the axial plane, the anterior, medial, and posterior thirds of the tibial plateau were marked, and the medial and posterior thirds were called “point 1” and “point 2”, respectively. A 7.5-mm-stainless steel indenter was used to apply the load over these two points: the load applied to point 1 simulated the load to that site when the knee was extended, and the load to point 2 simulated the load to the same area when the knee was flexed. Maximum load (N) and displacement (mm) were calculated.

Results

The system was shown to withstand higher loads with less displacement when the plate was posterior than it could do with the plate in the middle position. Significant differences were also found when comparing the anterior and middle position of the plate with the greatest displacement when the plate was anterior. The differences were increased when comparing the anterior and posterior positions of the plate. No statistical differences (n.s.) were found when using different spacers. The maximum stiffness was achieved if the plate was posterior and in point 1 indenter position, in which the force vector stands on the points of the lateral and medial supports (Fμ = 198.8 ± 61.5 N). The lowest stiffness was observed when the plate was anterior, and the force was applied to point 2 (Fμ = 29.7 ± 5.1 N).

Conclusions

Application of the plate in a more posterior position provides greater stability.     

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.     

Coronal tibial anteromedial tunnel location has minimal effect on knee biomechanics

Purpose

Studies have found anatomic variation in the coronal position of the insertion site of anteromedial (AM) bundle of the anterior cruciate ligament (ACL) on the tibia, which can lead to questions about tunnel placement during ACL reconstruction. The purpose of this study was to determine how mediolateral placement of the tibial AM graft tunnel in double-bundle ACL reconstructions affects knee biomechanics.

Methods

Two different types of double-bundle ACL reconstructions were performed. The AM tibial tunnel was placed at either the medial or lateral portion of tibial AM footprint. Nine cadaveric knees were tested with the robotic/universal force-moment sensor system with the use of (1) an 89.0-N anterior tibial load at full extension (FE), 30°, 60° and 90° of knee flexion and (2) a combined 7.0-Nm valgus torque and 5.0-Nm internal tibial rotation torque at FE, 15°, 30°and 45° of knee flexion.

Results

Both medial (2.6?±?1.2 mm) and lateral (1.6?±?0.9 mm) double-bundle reconstructions reduced the anterior tibial translation (ATT) to less than the intact value (3.9?±?0.7 mm) at FE. At all other flexion angles, there was no significant different in ATT between the intact knee and the reconstructions. At FE, the ATT for the medial AM reconstruction was different from that of the lateral AM construction and closer to the intact ACL value.

Conclusion

The coronal tibial placement of the AM tunnel had only a slight effect on knee biomechanics. In patients with differing AM bundle coronal positions, the AM tibial tunnel can be placed anatomically at the native insertion site.

     

Use of a gyroscope sensor to quantify tibial motions during a pivot shift test

Purpose

The purpose of this preliminary study was to evaluate the use of a gyroscope sensor to record rotations of the tibia about its long axis during a clinical pivot shift examination.

Methods

Ten patients with a unilateral ACL injury were tested under anaesthesia prior to surgery. Each ankle was placed in neutral position, wrapped and stabilized with athletic tape, and a small aluminium plate was taped to the bottom of the foot. A data recovery module was attached to the bottom of each plate using a swivel bracket that allowed alignment of the gyro axis with the long axis of the tibia. The module contained a triaxial gyroscope, battery and circuitry for wireless data broadcast to a laptop computer. Ten pivot shift tests were performed on both knees, and the surgeon’s clinical grading of the pivot shift was noted for each limb. Mean values (10 trials) of peak tibial rotational velocity and integrated tibial rotation were compared between knees for each patient during the pivot shift reduction event (external tibial rotation during knee flexion).

Results

Five patients (50 %) had significantly greater tibial rotation in their injured knee, four showed no difference between knees, and one had significantly greater rotation in the normal knee (p < 0.05). Seven patients (70 %) showed greater peak rotational velocity in their injured knee, and three had no difference between the knees (p < 0.05). Correlations of rotation and rotational velocity with clinical pivot shift grade were weak (r ² = 0.09 and 0.19, respectively).

Conclusions

Foot gyroscope measurements did not correctly identify the injured limb in all patients. Peak rotational velocity during the reduction event was a better indicator of ACL deficiency than the integrated rotation. If this technology is to be more useful clinically, gyroscope data may have to be combined with accelerometer data, perhaps with sensors mounted on both the tibia and femur.

Level of evidence

Diagnostic case–control study, Level III.     

Medial tibial pain pressure threshold algometry in runners

Purpose

Pressure algometry (PA) may provide an objective and standardised tool in assessing palpation pain over the tibia. The purpose of this study was to analyse the intra-rater repeatability of PA and to determine whether tibial tenderness in healthy runners differ from runners with medial tibial stress syndrome (MTSS).

Methods

Pressure algometry was performed on 20 asymptomatic runners (40 legs) and 9 MTSS patients (14 symptomatic legs) at standardised locations along the medial border of the tibia. Intra-rater reliability was assessed in 10 randomly selected asymptomatic runners through repeated measurements 2 weeks later.

Results

Intra-rater reliability was moderate to excellent (ICC 0.53–0.90) in asymptomatic runners. Pain pressure threshold (PPT) was significantly reduced at 2/9–5/9 of the distance from the medial malleolus to the medial tibial condyle (p = 0.002–0.022). There was evidence of a statistically significant association between both height and weight, and PPT from the 3/9 (r = 0.416, p = 0.008) to 7/9 (r = 0.334, p = 0.035) and 3/9 (r = 0.448, p = 0.004) to 6/9 (r = 0.337, p = 0.034) area, respectively. In both MTSS patients and healthy runners, there was evidence of lower PPT in females compared to males (p = 0.0001–0.049) and a negative association between age and PPT (p = 0.001–0.033). MTSS patients had significantly lower PPT at the 3/9 site (p = 0.048) compared to asymptomatic runners.

Conclusion

Pain pressure threshold algometry can be incorporated into MTSS clinical assessment to objectively assess pain and monitor progress. The presence of reduced medial tibial PPT in asymptomatic runners suggests that clinicians may not need to await resolution of medial tibia tenderness before allowing return to sport in MTSS patients.

Level of evidence

III.     

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.     

Influence of soft tissues on the proximal bony tibial slope measured with two-dimensional MRI

Purpose

Despite increasing interest in the functional anatomy of the menisci, little information is available regarding the relationship between the tibial slope and the menisci. It was hypothesized that the meniscus would reduce the differences in slope between the medial and lateral compartments and would mitigate the effects of age and gender on the tibial slope.

Methods

MRI sagittal images from 101 patients were used in this study. The angle between a line tangent to the medial and lateral tibial bony slope and the proximal tibial anatomical axis was measured on sagittal MRI images (bony slope). The angle between the tangent line to the highest point of the anterior and posterior horn of the meniscus and the proximal tibial anatomical axis was also determined (soft tissue slope). The measurements were carried out twice by two observers. The influence of gender and age on these parameters was analysed.

Results

Repeated measures analysis of variance showed good inter- and intra-observer reliability for both bony and soft tissue slope (ICC (0.87–0.93) and (0.91–0.97) for inter- and intra-observer reliability, respectively). In both compartments, the soft tissue significantly reduced the tibial slope towards the horizontal plane. In addition, the soft tissue slope was significantly more horizontal in the lateral compartment compared to the medial compartment (p < 0.01). These differences were not influenced by age or gender.

Conclusion

The menisci of the knee generate a more horizontal tibial slope when measured on MRI. The soft tissue slope is more horizontal in the lateral compartment of the knee compared to the medial compartment.

Level of evidence

Diagnostic, Level III.     

Patellofemoral kinematics during deep knee flexion after total knee replacement: a computational simulation

Purpose

Actions requiring deep knee flexion, such as kneeling and squatting, are challenging to perform after total knee replacement (TKR), though many manufactures emphasize that their knee prostheses could safely achieve high flexion. Little is known about the patellofemoral kinematics during deep flexion. This study aimed to track the movement of the patella during kneeling and squatting through dynamic computational simulation.

Methods

A validated knee model was used to analyse the patellar kinematics after TKR, including shifting, tilting and rotation. The data were captured from full extension to 135° of knee flexion. For kneeling, an anterior force of 500 N was applied perpendicularly on the tibial tubercle as the knee flexed from 90° to 135°. For squatting, a ground reaction force was applied through the tibia from full extension to 135° of flexion.

Results

This study found that patellar shifting and rotation in kneeling were similar to those while squatting. However, during kneeling, the patella had a greater medial tilt and showed signs of abrupt patellar tilt owning to an external force being concentrated on the tibial tubercle.

Conclusions

In terms of squatting and kneeling movements, the latter is a more strenuous action for the patellofemoral joint after TKR due to the high forces acting on the tibial tubercle. It is suggested that overweight patients or those requiring high flexion should try to avoid kneeling to reduce the risk of the polyethylene wear. Further modification of trochlear geometry may be required to accommodate abrupt changes in patellar tilting.

Level of evidence

II.     

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.     

Variations in kinematics and function following patellar stabilization including tibial tuberosity realignment

Purpose

The current study was performed to characterize the influence of patellar stabilization procedures on patellofemoral and tibiofemoral dynamic motion.

Methods

Six knees were evaluated pre-operatively and 1 year or longer following stabilization via tibial tuberosity realignment, with simultaneous medial patellofemoral ligament reconstruction performed for five knees. Knees were imaged during extension against gravity using a dynamic CT scanner. Models representing each knee at several positions of extension were reconstructed from the images. Local coordinate systems were created within one femur, patella and tibia for each knee, with shape matching of the bones used to transfer the coordinate axes to the other models. The patellar lateral shift and tilt and tibial external rotation were quantified based on the reference axes and interpolated to flexion angles from 5° to 40°. Pre-operative and post-operative data were compared with the paired t tests.

Results

Surgical realignment significantly decreased the average patellar lateral shift and tilt at low flexion angles. At 5°, surgical realignment decreased the average lateral shift from 15.5 (6.3) to 8.5 (4.7) mm and decreased the average lateral tilt from 20.8 (9.4)° to 13.8 (6.4)°. The changes were statistically significant (p < 0.05) at 5° and 10° of flexion, as well as 20° for lateral shift. The average tibial external rotation also increased significantly at 30° and 40° following surgery.

Conclusion

Patellar stabilization including a component of tuberosity realignment reduces patellar lateral shift and tilt at low flexion angles, but the long-term influence of increased tibial external rotation on tibiofemoral function is currently unknown.

Level of evidence

Prospective comparative study, Level II.     

Different changes in slope between the medial and lateral tibial plateau after open-wedge high tibial osteotomy

Purpose

In contrast to radiographic measurements, MRI provides multiple slices of the knee joint in the sagittal plane, making it possible to assess the medial and lateral tibial slope separately. The purpose of this study is to investigate the effect of medial open-wedge high tibial osteotomy (MOWHTO) on bony and meniscal slope in the medial and lateral tibiofemoral compartments. It was hypothesised that greater changes on the medial tibial plateau would be observed compared with the lateral one.

Methods

A retrospective analysis of prospectively collected data was performed on pre- and post-operative MRIs from 21 patients (17 men and 4 women; age 52 ± 9 years). Inclusion criteria were varus alignment, medial compartment osteoarthritis and election for a primary MOWHTO. Each patient had a preoperative and a post-operative high-resolution MRI (3Tesla, Magnetom Trio, Siemens AG) at an average follow-up of 2.1 years. A previously published method was used to measure bony and meniscal slope for each compartment. The difference between pre- and post-operative tibial slope for both compartments was calculated and associated with the amount of frontal correction.

Results

There was a significant increase in bony tibial slope in both compartments following MOWHTO. When a change in bony tibial slope was detected in an individual patient, the change was larger in the medial compartment, with the average change also significantly greater (p < 0.01) in the medial compartment (2.4° ± 1.3°) compared with the lateral compartment (0.9° ± 1.1°). There was also a significant increase (p < 0.01) in the lateral tibial meniscal slope of 0.9° ± 1.4°, which was equivalent to the change in the bony lateral slope. The amount of frontal correction was not significantly associated with the amount of change in slope.

Conclusions

The results suggest that the modification of the bony slope is larger in the medial compartment after MOWHTO, which is likely related to the location of the hinge on the lateral tibial cortex. These findings suggest that consideration of the medial and lateral tibial slope intra-operatively could be important to identify the optimal location of the hinge. However, further studies are required before recommending any modification to the surgical technique, as the potential clinical consequences of tibial slope alterations remain unknown.

Level of evidence

IV.