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.     

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.     

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.     

The orientation of the surgical epicondylar axis varies in varus and non-varus knees in the coronal plane

Purpose

To investigate the orientations of the surgical epicondylar axis (SEA) of varus and non-varus knees in the coronal plane.

Methods

One-hundred and sixty-two knees from 81 Chinese patients undergoing total knee arthroplasty (TKA) were retrospectively investigated. The angle between the medial side of the femoral mechanical axis and the SEA (MA-SEA), as well as the physiological valgus angle, was measured in the coronal plane using three-dimensional reconstruction. The joint line angle (JLA) and hip-knee-ankle angle (HKAA) were measured in long-leg weight-bearing radiographs. The mean of each parameter was compared between the varus (HKAA < 177.0°) and the non-varus knees (HKAA ≥ 177.0°) using an independent t test. Linear regression was used to assess the correlation between MA-SEA with JLA and HKAA.

Results

A total of 42 non-varus knees (6 valgus and 36 neutral knees) and 98 varus knees were measured, as 22 knees were abandoned due to unrecognizable bony landmarks. The mean MA-SEA and JLA were significantly larger in non-varus knees (both, p < 0.01). The mean physiological valgus angle was 5.9 ± 1.0° for Chinese TKA patients and was significantly larger in varus knees (p < 0.01). There was a strong positive correlation between the MA-SEA and JLA (R ² = 0.35, p < 0.05).

Conclusions

There were significant differences in the orientation of the SEA between varus and non-varus knees, which was strongly correlated with the orientation of the femoral joint line. These findings will enhance the current knowledge of knee anatomy and should prove useful for coronal alignment in TKA.

Level of evidence

III.

     

Patellar height modification after high tibial osteotomy by either medial opening-wedge or lateral closing-wedge osteotomies

Purpose

High valgus tibial osteotomy is used to treat medial femoro-tibial osteoarthritis. Changes in patellar height due to high valgus tibial osteotomy can cause technical difficulties during subsequent knee arthroplasty. The primary objective of this study was to assess the hypothesis that patellar height decreases after opening-wedge osteotomy and increases after closing-wedge osteotomy. The secondary objective was to assess whether frontal axis correction and tibial slope modification correlated with patellar height changes.

Methods

A multicentre, prospective, comparative, observational, non-randomised study was conducted in consecutive patients undergoing isolated high valgus tibial osteotomy according to standard practice in each of the ten study centres. Patellar height was assessed based on the Caton-Deschamps index.

Results

Of 321 included patients, 224 underwent opening-wedge and 97 closing-wedge osteotomy. Patellar height did not change significantly after closing-wedge osteotomy (1.07 ± 0.2 pre-operatively and 1.0 ± 0.19 postoperatively). Patellar height decreased significantly after opening-wedge osteotomy (from 0.98 ± 0.19 to 0.88 ± 0.21, p < 0.0001, mean decrease 9 ± 22 %). Patellar height decreased by more than 20 % in 49 (28 %) patients after opening-wedge osteotomy. The patellar height decrease after opening-wedge osteotomy correlated significantly with axis correction magnitude and tibial slope change.

Conclusion

Our results support routine baseline measurement of patellar height before high valgus tibial osteotomy and posterior positioning of the opening wedge to limit the tibial slope change in patients requiring major axis correction by opening-wedge osteotomy.

Level of evidence

Prospective cohort study, Level II.     

Varus femoral and tibial coronal alignments result in different kinematics and kinetics after total knee arthroplasty

Purpose

Abnormal knee motion under various conditions has been described after total knee arthroplasty (TKA). However, differences in kinematics and kinetics of knees with varus femoral versus varus tibial alignment have not been evaluated. It was hypothesized that varus femoral and tibial alignments have the same impact on knee motion.

Methods

A musculoskeletal computer simulation was used. Femoral and tibial alignment in the coronal plane was each varied from neutral to 5° of varus in 1° increments. Lift-off, defined as an intercomponent distance of >2 mm, and tibiofemoral contact forces were evaluated during gait up to 60° of knee flexion. Knee kinematics and contact stresses were also examined during squat, with up to 130° of knee flexion.

Results

During gait, lift-off occurred readily with more than 3° of varus tibial alignment and slight lateral joint laxity. In contrast, lift-off did not occur with varus femoral or tibial alignment of up to 5° during squat. Peak medial contact forces with varus femoral alignment were approximately twice those observed with varus tibial alignment. The lowest points of the femoral condyles moved internally with varus femoral alignment, contrary to the kinematics with neutral or varus tibial alignment. On the other hand, there was femoral medial sliding and edge loading against the tibia in mid-flexion with varus tibial alignment.

Conclusion

Varus femoral alignment affects the non-physiological rotational movement of the tibiofemoral joint, whereas varus tibial alignment causes medial–lateral instability during mid-flexion. Varus femoral and tibial alignments might lead to post-TKA discomfort and unreliability.

     

Femoral bone and cartilage wear is predictable at 0° and 90° in the osteoarthritic knee treated with total knee arthroplasty

Purpose

Kinematically aligned total knee arthroplasty (TKA) positions the femoral component at the natural angle and level of the distal (0°) and posterior (90°) joint line. This technique applies referencing guides at 0° and 90° that are adjusted to compensate for wear and kerf and perform resections equal in thickness to the femoral component. Knowing whether femoral bone and cartilage wear is predictable would assist in establishing general guidelines for adjusting the resection level of these two referencing guides. This study tests the hypothesis that femoral bone and cartilage wear is predictable at 0° and 90° in the varus and valgus osteoarthritic knee treated with TKA.

Methods

The study consists of 205 patients and 208 knees with Kellgren–Lawrence Grade 3 or 4 osteoarthritis and treated with a TKA. Each knee had a narrow slice (2 mm) preoperative 1.5 tesla magnetic resonance image in the sagittal plane. Femoral bone and cartilage wear at 0° and 90° was computed from best-fit circles superimposed on the peripheral boundary of the subchondral bone on the medial and lateral femoral condyles.

Results

Overall, 99.5 % of knees had minimal bone wear (<1 mm) at 0° and 90°. In the 74 % (154 of 208) of knees with a varus deformity, 92 % at 0° and 2 % at 90° had >1 mm cartilage wear on the medial femoral condyle. In the 26 % (54 of 208) of knees with a valgus deformity, 78 % at 0° and 55 % at 90° had ≥1 mm cartilage wear on the lateral femoral condyle.

Conclusions

As a general guideline, adjustment for femoral bone wear is rarely required when performing kinematically aligned TKA. Most osteoarthritic knees require adjustment of the distal referencing guide to compensate for cartilage wear on the medial femoral condyle in the varus knee and the lateral femoral condyle in the valgus knee. Adjustment of the posterior referencing guide is required in about half of valgus osteoarthritic knees to compensate for lateral cartilage wear at 90°. Knowing that bone wear is rare and cartilage wear is predictable in varus and valgus Kellgren–Lawrence Grade 3 or 4 osteoarthritic knees helps establish general guidelines for adjusting the distal and posterior femoral referencing guides to restore the natural angle and level of the femoral joint lines when performing kinematically aligned TKA with generic instruments.

Level of evidence

IV.     

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.     

Revision total knee arthroplasty with varus–valgus constrained prosthesis versus posterior stabilized prosthesis

Purpose

The aims of this retrospective study were to provide the basis for the choice of prosthesis in revision total knee arthroplasty (TKA) and to evaluate the outcome with varus–valgus constrained prosthesis compared with posterior stabilized (PS) prosthesis.

Methods

One hundred and five patients (121 knees) received revision TKA; of which thirty-seven patients (42 knees) received PS prosthesis and sixty-eight patients (79 knees) received varus–valgus constrained prosthesis. The mean follow-up duration was 64.8 ± 31.5 months and 63.2 ± 28.1 months in the PS and varus–valgus constrained groups, respectively. The criterion of prosthesis choice was a subjective laxity assessed by the surgeon intraoperatively. A multivariate analysis was performed to evaluate the preoperative factors in the choice of the prosthesis.

Results

The grade of femoral bone defect was the only factor that affected the choice of prosthesis. Clinical results improved significantly in both groups after surgery. There were no significant differences in clinical results between the two groups. Complication rates were 9.5 % in the PS group and 10.1 % in the varus–valgus constrained group, and the Kaplan–Meier survivorship analysis revealed 8-year component survival rates of 83.1 and 93.0 % in the PS and varus–valgus constrained groups, respectively.

Conclusions

Femoral bone defect is an important factor to be considered in the choice of prosthesis for revision TKA. The varus–valgus constrained prosthesis showed an outcome similar to that of the PS prosthesis. For clinical relevance, varus–valgus constrained prosthesis is recommended in revision TKA when the PS prosthesis seems unsuitable for the management of instability.

Level of evidence

III.     

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.     

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.     

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.     

Incidence and radiologic predictor of postoperative patellar instability after Fulkerson procedure of the tibial tuberosity for recurrent patellar dislocation

Purpose

Excellent results of anteromedialization of the tibial tuberosity for recurrent patellar dislocation have been reported; however, the contribution of the preoperative anatomic factors to postoperative patellar instability has not been well established. The purpose of this study was to investigate the mid-term results and the incidence of postoperative patellar instability after Fulkerson procedure for recurrent patella dislocation, and to determine the radiologic predictor of the postoperative patellar instability.

Methods

Sixty-two knees of 41 patients underwent Fulkerson procedure with or without lateral retinacular release for recurrent patellar dislocation and were followed-up for 85–155 months. Predisposing anatomic factors for recurrent patellar dislocation were evaluated preoperatively, including valgus knee alignment (femorotibial angle), patella alta (Insall–Salvati ratio), trochlear dysplasia (trochlear depth), lateral patellar displacement (congruence angle) and lateral malposition of the tibial tuberosity (tibial tuberosity-trochlear groove distance). The relationship between the measurements of anatomic factors and postoperative patellar instability, which was defined by the patellar re-dislocation or residual apprehension after surgery, was analyzed.

Results

The Fulkerson score and the Kujala score were significantly improved from the median of 65 (35–80) points and 68 (36–82) points preoperatively to 95 (60–100) points and 92 (57–100) points at the final follow-up, respectively. Three knees (4.8%) experienced postoperative patellar re-dislocation and 4 knees (6.5%) showed the positive apprehension sign at the final follow-up. The statistical analysis showed that the postoperative patellar instability correlated with only patella alta.

Conclusion

Patella alta was the only predictor of postoperative patellar instability after Fulkerson procedure. These results indicated that isolated Fulkerson procedure should not be indicated for recurrent patellar dislocation with severe patella alta.

Level of evidence

Case–control study, Level III.     

Patella infera or patellar tendon adherence after high tibial osteotomy

Purpose

Alterations in patellar height after high tibial osteotomy are found in many instances. Fibrosis of the tendon is implicated as the cause of the mechanism of patella lowering. This study aimed to determine the relationship between the position of the patella and the histopathological findings at the patellar tendon after high tibial osteotomy.

Methods

Nineteen knees in seventeen patients who were consecutively hospitalised for implant extraction are studied. All of the patients had previously undergone closing wedge osteotomy by the same surgeon at the same department. The median follow-up time is 15 months (range: 11–35). Five patients who all underwent high tibial osteotomy at the same time are also included in the study as a control group for histopathological evaluation. All of the patients are evaluated radiologically, patellar tendon biopsies are taken during the operation, and histopathological analyses are performed.

Results

The shortening of the patellar tendon is statistically significant (P < 0.05). The severity of the vascularisation, inflammation, and fibrotic change observed at the distal part of the tendon is evident. However, there is no statistically significant correlation between these findings and the degree of shortening.

Conclusions

The shortening of the tendon occurs as a result of adherence in the distal part of the tendon. It would appear that it is this shortening that causes the difficulties encountered during arthroplasty surgery of osteotomy patients, and not patella infera.

Level of evidence

Retrospective study, Level II.     

Effects of four different surgical approaches on intra-operative joint gap in posterior-stabilized total knee arthroplasty

Purpose

The effects of surgical approaches and patellar positions on joint gap measurement during total knee arthroplasty (TKA) remain unclear. We hypothesized that joint gap changes with different knee flexion angles would not be consistent within four different approaches and two different patellar positions.

Methods

This study enrolled 80 knees undergoing posterior-stabilized TKA. For 60 varus knees, parapatellar, midvastus, and subvastus approaches were used in 20 knees each. For 20 valgus knees, a lateral subvastus approach was used. Component gap length and inclination were measured intra-operatively using a specific tensor device under 40 lb with the patella reduced or shifted laterally, at 0°, 45°, 90°, and 135° of knee flexion.

Results

Mean gap lengths at 45° and 90° of knee flexion were significantly larger with the parapatellar approach than with midvastus or lateral subvastus approaches (P < 0.05). Regarding gap inclination, varus angle increased linearly through the entire arc of flexion in all four approaches. When the patella was shifted laterally, gap lengths at 45°, 90°, and 135° were significantly reduced compared with those for the patella reduced in the subvastus approach, whereas gap length was constant in the parapatellar approach, regardless of patellar position.

Conclusion

Joint gap kinematics was not consistent within four different approaches and two different patellar positions. Relatively large gaps at 45° and 90° were unique features for the parapatellar approach. Surgeons should be aware that the flexion gap is reduced when the patella is shifted laterally in vastus medialis-preserving approaches such as the subvastus approach.

Level of evidence

II.     

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.     

Monoplanar versus biplanar medial open-wedge proximal tibial osteotomy for varus gonarthrosis: a comparison of clinical and radiological outcomes

Purpose

We compared clinical and radiological results of two proximal tibial osteotomy (PTO) techniques: monoplanar medial open-wedge osteotomy and biplanar retrotubercle medial open-wedge osteotomy, stabilised by a wedged plate.

Methods

We evaluated 88 knees in 78 patients. Monoplanar medial open-wedge PTO was performed on 56 knees in 50 patients with a mean age of 55 ± 9 years. Biplanar retrotubercle medial open-wedge PTO was performed on 32 knees in 28 patients with a mean age of 57 ± 7 years. Mean follow-up periods were 40.6 ± 7 months for the monoplanar PTO group and 38 ± 5 months for the biplanar retrotubercle PTO group. Clinical outcome was evaluated using the hospital for special surgery scoring system, and radiological outcome was evaluated by the measurements of femorotibial angle (FTA), patellar height and tibial slope changes.

Results

In both groups, post-operative HSS scores increased significantly. No significant difference was found between groups in FTA alteration, but the FTA decreased significantly in both groups. Patellar index ratios decreased significantly in the monoplanar PTO group (Insall-Salvati Index by 0.07, Blackburne-Peel Index by 0.07), but not in the biplanar retrotubercle PTO group. Tibial slopes were increased significantly in the monoplanar PTO group, but not in the retrotubercle PTO group.

Conclusions

Biplanar retrotubercle medial open-wedge osteotomy and monoplanar medial open-wedge osteotomy are both clinically effective for the treatment for varus gonarthrosis. Retrotubercle osteotomy also prevents patella infera and tibial slope changes radiologically.

Level of evidence

Therapeutic study, prospective comparative study, Level 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.     

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.     

Accuracy of the second metatarsal as a landmark for the extramedullary tibial cutting guide in total knee arthroplasty

Purpose

The purpose of this study was to evaluate the accuracy of the second metatarsal (MT2) as a landmark for proximal tibial cutting in total knee arthroplasty (TKA). It was hypothesized that the accuracy of the MT2 is not high, especially in rheumatoid arthritis (RA) patients whose foot joints are apt to be involved.

Methods

Computer simulation studies on 48 RA knees and 45 osteoarthritis (OA) knees were performed. The deviations from the mechanical axis (MA) of the tibia when the guide rod was pointed toward the base of the MT2 or the distal part of the MT2 were measured.

Results

The mean deviation from MA was 0.8° ± 2.1° valgus (range 8.1°–6.3° valgus) and 1.2° ± 2.9° valgus (range 11.6°–7.9° valgus) at the base of the MT2, and at the distal part of the MT2, respectively. The outlier rate when using the base of the MT2 was lower than when using the distal part of the MT2 (12.9 vs 32.3 %, p = 0.0032). The outlier rate was equivalent in OA and RA patients (n.s.). However, foot involvement in RA patients demonstrated a trend toward significance (base of MT2 p = 0.078, distal part of MT2 p = 0.068).

Conclusions

The major clinical relevance was to raise caution about using the MT2. Surgeons should aim toward the base of the MT2, but avoid using it in RA patients with foot involvement. The accuracy of the MT2 is not high and it should be used only to supplement other landmarks.

Level of evidence

II.