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.     

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.

     

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 the severity of preoperative varus deformity influence postoperative alignment in both conventional and computer-assisted total knee arthroplasty?

Purpose

The postoperative alignment was compared according to the severity of preoperative varus deformity in computer-assisted and conventional total knee arthroplasty (CAS-TKA).

Methods

The study reviewed 127 consecutive CAS-TKA and 236 conventional TKA, retrospectively. In CAS-TKA, 77 knees with a varus deformity ≤15.0° were classified in group CAS-A and 50 knees with a varus deformity >15.0° were classified in group CAS-B. In conventional groups, 204 knees with a varus deformity ≤15.0 were classified in group Conventional-A and 32 knees with a varus deformity >15.0° were classified in group Conventional-B. The postoperative mechanical axis (MA) was compared among groups CAS-A, CAS-B, Conventional-A and Conventional-B.

Results

The average postoperative MA was 0.7° varus in group CAS-A, 2.8° varus in group CAS-B, 1.1° varus in group Conventional-A and 3.2° varus in group Conventional-B (p < 0.001). The postoperative MA was within 3° in 81.8, 62.0, 58.8 and 37.5 % of group CAS-A, CAS-B, Conventional-A and Conventional-B, respectively.

Conclusions

The severity of preoperative varus deformity influences postoperative alignment despite using CAS. More careful correction of the alignment is required, especially in TKA performed on patients with a greater varus deformity.

Level of evidence

III.     

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.     

The difference between weight-bearing and non-weight-bearing alignment in patient-specific instrumentation planning

Purpose

Retrospective study to analyse the difference between weight-bearing and non-weight-bearing alignment in osteoarthritic knees planned for patient-specific instrumented (PSI) total knee arthroplasty (TKA). The aim of the study is to observe whether a difference in alignment can be linked to arthritis staging or zone mechanical axis.

Methods

Full-leg standing radiographs and non-weight-bearing MRI of the whole leg were compared for hip–knee–ankle (HKA) angle, measured according to Moreland criteria, in seventy osteoarthritic patients. Kellgren–Lawrence (KL) staging and classification according to zone mechanical axis with Kennedy zones was done.

Results

A mean preoperative HKA angle on standing radiographs of 176.4° ± 7.2° was measured compared to 176.4° ± 6.9° for the MRI whole-leg HKA angle. A difference of 0°–1° was observed in 54 % of patients when comparing the weight-bearing with the non-weight-bearing HKA angle. Twenty-three per cent had a difference of 2° and another 23 % a difference of 3° or more. In female patients, the dynamic load pattern of weight-bearing increases the HKA angle due to convex side soft tissue laxity both in varus and valgus knees. More important differences were observed in the KL stage 3 and 4 patients (P < 0.05) and with a load-bearing axis outside of the articular surface (P < 0.05).

Conclusion

Surgeons should be aware that there is a difference between weight-bearing and non-weight-bearing alignment in patients with Kellgren–Lawrence 3 and 4 with a load-bearing axis outside of the articular surface (Kennedy 0 or 1 or 5). According to this study, these changes seem related to the amount of articular wear and the load-bearing axis. This is important for the preoperative planning process in PSI-assisted TKA. More concave side ligamentous release or more constraint can be necessary than imagined based on the PSI alignment result. Full-leg standing radiographs should be performed for PSI-assisted TKAs to analyse the position of the load-bearing axis.

Level of evidence

IV.     

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

Purpose

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

Methods

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

Results

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

Conclusion

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

Level of evidence

IV.     

Hindfoot alignment at one year after total knee arthroplasty

Purpose

It has previously been found that valgus hindfoot alignment (HFA) improves 3 weeks following total knee arthroplasty (TKA) for varus knee osteoarthritis (OA). In the present study, HFA was evaluated prior to TKA, as well as 3 weeks and 1 year following TKA. Using these multiple evaluations, the chronological effects of TKA on HFA were investigated.

Methods

The study included 71 patients (73 legs) who underwent TKA for varus knee OA. Radiograph examinations of the entire limb and hindfoot were performed in the standing position prior to TKA, as well as 3 weeks and 1 year following TKA. The varus–valgus angle was used as an indicator of HFA in the coronal plane. Patients were divided into two groups according to the preoperative varus–valgus angle: a hindfoot varus group (varus–valgus angle <76°) and a hindfoot valgus group (varus–valgus angle ≥76°). The changes in the varus–valgus angle were evaluated and compared in both groups.

Results

In the hindfoot valgus group, the mean ± standard deviation varus–valgus angle significantly declined from 80.5 ± 3.1° prior to TKA to 78.6 ± 3.7° 3 weeks following TKA and 77.1 ± 2.7° 1 year following TKA. However, in the hindfoot varus group, the mean varus–valgus angle prior to TKA (72.7 ± 2.6°) did not differ significantly from the mean varus–valgus angles 3 weeks (72.3 ± 3.3°) or 1 year (73.5 ± 3.0°) following TKA.

Conclusions

HFA improved chronologically in legs with hindfoot valgus as a result of the alignment compensation ability of the hindfoot following TKA. However, no improvement was noted in legs with hindfoot varus because the alignment compensation ability of the hindfoot had been lost. The patients with hindfoot varus should be attended for ankle pain in the outpatient clinic after TKA.

Level of evidence

III.

     

The combined Whiteside’s and posterior condylar line as a reliable reference to describe axial distal femoral anatomy in patient-specific instrument planning

Purpose

Aligning the femoral component in the axial plane parallel to the surgical epicondylar axis (SEA) has been generally recommended. In this retrospective study on the axial anatomy of the distal femur, as determined by the patient-specific instruments (PSI) planning tool based on MRI and 3D reconstructions, the different rotational axes were compared. The purpose of this study was to compare the impact of posterior axial anatomy on anterior anatomy and to compare the different angles of rotation obtained by a PSI-planning engineer.

Methods

The preoperative planning of 77 PSI patients with a mean (SD) age of 65.6 (9.6) years undergoing primary total knee replacement for osteoarthritis was analysed for rotational anatomy of the distal femur. The angles between the posterior condylar line (PCL) and the SEA called posterior condylar angle (PCA), between Whiteside’s line and the SEA and finally between Whiteside’s line and the PCL, were retrieved from the PSI axial rotation planning screen.

Results

The mean (SD) PCA was 3.2° (1.4°). The mean (SD) angle between Whiteside’s line and the SEA was 91.4° (2.2°), and the mean (SD) angle between Whiteside’s line and the PCL was 94.5° (2.3°). No significant difference for this last rotational parameter was found in between varus and valgus knees.

Conclusion

Patient-specific instrument’s preoperative planning found consistent angles to describe the distal femoral anatomy as previously published in the literature. The angle between Whiteside’s line and the PCL as measured on PSI planning is a mean angle of 94.5° (2.3°) for both varus and valgus knees. Setting a fixed PCA of 5° of external rotation referenced of the PCL makes this planning repeatable during conventional surgery.

Level of evidence

Therapeutic study, Level III.     

The coronal alignment after medial unicompartmental knee arthroplasty can be predicted: usefulness of full-length valgus stress radiography for evaluating correctability

Purpose

We aimed to clarify whether the coronal alignment after medial unicompartmental knee arthroplasty (UKA) is predictable using preoperative full-length valgus stress radiography.

Methods

Thirty-seven consecutive patients with a mean age of 71.5 ± 7.0 years awaiting medial UKA were recruited. Full-length weight-bearing radiographs of the lower limbs were obtained pre- and postoperatively. Preoperative full-length valgus stress radiography in the supine position was also performed, and the transition of the hip-knee-ankle angle (HKAA) and the weight-bearing ratio were assessed. The tibia first cut technique was used, and the distal femur was cut parallel to the cutting surface of the proximal tibia during surgery.

Results

The mean postoperative HKAA was 2.0° ± 2.1° varus, and the mean weight-bearing ratio was 43.1 ± 7.7 %; each of these parameters demonstrated significantly strong correlations with the values on the preoperative valgus stress radiographs (p < 0.01), while the correlation between the postoperative alignment and the preoperative standing alignment without stress was moderate (p < 0.01). The postoperative alignment was slightly undercorrected compared to that observed on the valgus stress radiographs (p < 0.05), and no knees exhibited evident overcorrection compared to that on the valgus stress radiographs.

Conclusion

Preoperative valgus stress radiography is useful for evaluating the correctability of varus deformities and predicting the postoperative coronal alignment. For clinical relevance, performing preoperative valgus stress radiography would help to more precisely select patients and, when combined with the tibia first cut technique, aid in achieving the expected knee alignment and avoid severe undercorrection or overcorrection.

Level of evidence

Diagnostic study, Level II.     

The alignment of the knee joint in relationship to age and osteoarthritis

Introduction

The aim of the present study was to describe the changes in the axis of the knee joint in both radiologically osteoarthritic and non-osteoarthritic knees, on the basis of angles measurable in standardized clinical short knee radiographs, in a cross sectional study of an epidemiological cohort.

Design

From the third inclusion of the Copenhagen City Heart Study, 4,151 subjects were selected for standardized radiography of the knees. After censuring the inclusion, the resulting cohort was comprised of 3,488 individuals. Images were analyzed for radiological knee joint osteoarthritis (OA) and the anatomical femorotibial axis of the knee joint was measured.

Results

The prevalence of knee joint OA in males was 27.9 % and 27.5 %, for the left and right knees respectively. In females this was 32.8 % and 36.4 %. The mean knee joint angles were 4.11° in males; and 5.45° in females. A difference of 1.3° was found between the genders. In non-osteoarthritic knees the increase in valgus orientation in relationship to increasing age was found to be 0.03° and 0.04° per year, respectively, for males and females. Likewise, Kellgren and Lawrence found that OA was seen to influence a shift towards varus of 0.55°–0.76° per level of OA.

Conclusion

Stratification in accordance with morphological severity of OA documented a clear tendency for the axis of the diseased knees to depart from the mean, primarily in the direction of varus. In knees exhibiting no signs of radiographic osteoarthritis we found a significant relationship between increasing age and a shift in the anatomical axis in the direction of valgus.     

The shape and orientation of the trochlea run more parallel to the posterior condylar line than generally believed

Purpose

This study was set up to identify the native trochlear geometry and define its relationship with the rotational landmarks of the distal femur.

Methods

The rotational landmarks of the distal femur were analysed on CT-scans of 281 patients with end-stage knee osteoarthritis.

Results

The anterior trochlear line (ATL) was on average 4.3° (SD 3.3°) internally rotated relative to the surgical transepicondylar axis (sTEA). The ATL was on average 2.1° (SD 3.0°) internally rotated relative to the posterior condylar line (PCL). The relationship between the ATL and the sTEA was statistically different in the different coronal alignment groups (p = 0.004): 3.9° (SD 3.0°) in varus knees, 4.0° (SD 2.9°) in neutral knees and 5.4° (SD 3.8°) in valgus knees. The lateralisation of the trochlea, represented by the distance between the perpendicular to PCL and the perpendicular to the posterior parallel line to the sTEA, was on average 2.2 mm (SD 1.8 mm).

Conclusion

The ATL was on average 4.3° (SD 3.3°) internally rotated relative to the sTEA and 2.1° (SD 3.0°) internally rotated relative to the PCL. The ATL is more externally orientated in varus knees and more internally rotated in valgus knees. The trochlear groove is lateralised by only 2.2 mm when the femoral component is externally rotated.

Level of evidence

III.

     

The surgical epicondylar axis is a consistent reference of the distal femur in the coronal and axial planes

Purpose

Various rotational landmarks including the surgical epicondylar axis (SEA) are used for preoperative planning and intra-operative reference of total knee arthroplasty (TKA) in the axial plane. The aim of the study was to elucidate the relationships between the SEA and other femoral anatomical landmarks, including the mechanical axis, distal and posterior knee joints, the trochlear groove, and the anterior femoral condyle, in both the coronal and axial planes.

Methods

Angular and linear measurements were taken of sixty femora using Orthomap3D, which has a tool to analyse computed tomography image data that makes it possible to measure three-dimensional distances and angles precisely. The inter- and intra-observer reliabilities of these measurements were evaluated. Comparisons were made according to height, weight, body mass index, and gender.

Results

The angle between the mechanical axis and the SEA was 90.2° (95 % CI 90.0°–90.4°). There was a significant correlation for each linear measurement between the SEA and the distal/posterior knee joint line and for each linear measurement between the SEA and the anterior medial/lateral femoral condyle. A significant difference was observed between genders in the linear measurements. Significant correlations were found between height and weight and linear parameters.

Conclusion

Knowledge of the relationships between the SEA and other femoral anatomical landmarks is useful in preoperative planning, intra-operative landmark, and postoperative assessment of TKA. The SEA is a consistent parameter of femoral alignment in the coronal plane and a stable reference for femoral rotation in the axial plane.

Level of evidence

III.     

Preservation of the posterior cruciate ligament is not helpful in highly conforming mobile-bearing total knee arthroplasty: a randomized controlled study

Purpose

The purpose of this study is to investigate whether the preservation of the posterior cruciate ligament (PCL) can be helpful for improving kinematics and clinical outcome in highly conforming mobile-bearing total knee arthroplasty (TKA).

Methods

Ninety osteoarthritic knees were randomly allocated to either the PCL-preserving group or the PCL-sacrificing group. Passive kinematics was recorded with a navigation system immediately after implantation. Three parameters (anterior/posterior translation, varus/valgus rotation, and internal/external rotation) were analysed from 0° to 120° flexion.

Results

The PCL-preserving group (42 knees) had more varus rotation over 90° flexion (p < 0.05) and more anterior translation of the femur in all ranges of flexion (p < 0.05) than those in the PCL-sacrificing group (44 knees). There was no difference in the internal/external rotation (p > 0.05). The range of motion, functional scores, and radiographic results did not significantly differ between the two groups at the final follow-up. Three knees in the PCL-preserving group were revised: two presented with instability caused by traumatic attenuation of the PCL and one with subluxation of the insert due to a tight PCL.

Conclusion

The preservation of the PCL was not helpful for improving kinematics and clinical outcome in highly conforming mobile-bearing TKA.

Level of evidence

II.     

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.     

The accuracy of the extramedullary and intramedullary femoral alignment system in total knee arthroplasty for varus osteoarthritic knee

Purpose

The intramedullary (IM) femoral alignment system does not alway guarantee accuracy of the component position in the total knee arthroplasty (TKA). In some cases, the extramedullary (EM) femoral alignment system in total knee arthroplasty (TKA) is a useful alternative surgical option to adjust femoral component alignment. In the EM technique, accuracy of the femoral head center location is mandatory. The purpose of this prospective randomized study was to compare the alignment after TKA using two different femoral alignment systems.

Methods

From January 2009 to December 2009, 91 patients (106 knees) with osteoarthritis underwent TKA. The IM femoral alignment system was used in 50 TKAs, and the EM system was used in 56 TKAs. We measured the coronal, sagittal alignment of the femoral component, and overall alignment from full-length standing. Anteroposterior radiographs were taken 1 year after surgery.

Results

The overall limb alignment was 0.2° ± 1.9° varus in the EM group and 1.1° ± 1.9° valgus in the IM group (p = 0.001). The coronal alignment of the femoral component was 90.0° ± 1.1° in the EM group and 90.3° ± 1.2° in the IM group, not statistically different (n.s.). The sagittal alignment of the femoral component was 2.3° ± 1.7° in the EM group and 2.5° ± 1.0° in the IM group (n.s.). Clinically acceptable overall limb alignment was achieved in 91.1 % of EM group and 84.0 % of IM group (n.s.).

Conclusion

The present study suggests that by applying our EM technique that uses a newly designed mechanical axis marker system, the alignment of the femoral component and overall limb alignment is reliable and at least as accurate as the standard IM technique.

Level of evidence

I.     

The radiological outcomes of patient-specific instrumentation versus conventional total knee arthroplasty

Purpose

The aim of this study was to investigate the post-operative radiological outcomes of patient-specific instrumentation (PSI) surgery versus conventional total knee arthroplasty (TKA).

Methods

Sixty patients scheduled for a primary TKA were prospectively divided into PSI or conventional technique. Coronal and sagittal radiographic long limb films were taken post-operatively. The accepted values for normal alignment were 180° ± 3° for hip-knee-ankle angle; 90° ± 3° for coronal femoral component angle or coronal tibia component angle; 0° to 3° flexion for sagittal femoral component angle and 0° to 7° posterior slope for sagittal tibia component angle.

Results

For hip-knee-ankle angle, there were 21 % more outliers in the PSI group compared to the conventional group (p = 0.045). Most of these outliers had valgus deformity in the PSI group and varus deformity in the conventional group (p = 0.045). For implant placement, there was no difference in the proportion of outliers between the two groups. There was also no difference in the duration of surgery.

Conclusions

This study showed that PSI surgery is associated with a larger proportion of outliers for lower limb alignment. PSI surgery as an alternative to conventional TKA is not advisable.

Level of evidence

II.     

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Level of evidence

III.     

A morphometric study of normal and varus knees

Purpose

The aim of the study was to investigate varus and normal knee morphologies to identify differences that may affect knee replacement alignment or design for varus knees.

Methods

Computed tomography scans of varus and normal knees were analyzed, and geometric shapes, points and axes were fit to the femur and tibia independently. These points were then projected in the three anatomical planes to measure the variations between the two groups.

Results

In the femur, varus knees had less femoral anteversion (p < 0.0001) and a larger medial extension facet (p < 0.05) compared with normal knees. In the tibia, the tubercle was found to be externally rotated in varus knees (12°), with a significant increase in the coronal slope (p = 0.001) and the extension facet angle (p = 0.002).

Conclusions

The study highlighted the differences and similarities found between the two groups, which raises awareness on changes required during surgical intervention and component placement or design for a varus knee. This is particularly relevant for the design of patient-specific instrumentation and implants.

Levels of evidence

Diagnostic study, Level III.     

Slight undercorrection following total knee arthroplasty results in superior clinical outcomes in varus knees

Purpose

Restoration of correct alignment is one of the main objectives of total knee arthroplasty (TKA). However, the influence of residual malalignment on clinical and functional outcomes is currently uncertain. This study was therefore undertaken to ascertain its influence in patients undergoing TKA for varus osteoarthritis of the knee.

Methods

A cohort of 132 consecutive patients (143 knees) with pre-operative varus alignment was evaluated with a mean follow-up period of 7.2 years. Based upon the post-operative alignment, patients were stratified into three groups: neutral, mild varus, and severe varus. These groups were compared with respect to clinical and functional outcomes.

Results

All patients had post-operative improvements in Knee Society Score (KSS). Knees that were left in mild varus scored significantly better for the KSS and the Western Ontario and McMaster Universities Arthritis Index, compared with knees that were corrected to neutral and knees that were left in severe varus exceeding 6°. No revisions occurred in any of the groups at midterm follow-up.

Conclusion

The results of this study contradict the conventional assumption that correction to neutral mechanical alignment leads to the best outcome following TKA. Patients with pre-operative varus had better clinical and functional outcome scores if the alignment was left in mild varus, as compared with patients with an alignment correction to neutral.

Level of evidence

Therapeutic study, Level III.