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.     

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.     

Kinematically aligned TKA can align knee joint line to horizontal

Purpose

The joint line of the native knee is horizontal to the floor and perpendicular to the vertical weight-bearing axis of the patient in a bipedal stance. The purposes of this study were as follows: (1) to find out the distribution of the native joint line in a population of normal patients with normal knees; (2) to compare the native joint line orientation between patients receiving conventional mechanically aligned total knee arthroplasty (TKA), navigated mechanically aligned TKA, and kinematically aligned TKA; and (3) to determine which of the three TKA methods aligns the postoperative knee joint perpendicular to the weight-bearing axis of the limb in bipedal stance.

Methods

To determine the joint line orientation of a native knee, 50 full-length standing hip-to-ankle digital radiographs were obtained in 50 young, healthy individuals. The angle between knee joint line and the line parallel to the floor was measured and defined as joint line orientation angle (JLOA). JLOA was also measured prior to and after conventional mechanically aligned TKA (65 knees), mechanically aligned TKA using imageless navigation (65 knees), and kinematically aligned TKA (65 knees). The proportion of the knees similar to the native joint line was calculated for each group.

Results

The mean JLOA in healthy individuals was parallel to the floor (0.2° ± 1.1°). The pre-operative JLOA of all treatment groups slanted down to the lateral side. Postoperative JLOA slanted down to the lateral side in conventional mechanically aligned TKA (?3.3° ± 2.2°) and in navigation mechanically aligned TKA (?2.6° ± 1.8°), while it was horizontal to the floor in kinematically aligned TKA (0.6° ± 1.7°). Only 6.9 % of the conventional mechanically aligned TKA and 16.9 % of the navigation mechanically aligned TKA were within one SD of the mean JLOA of the native knee, while the proportion was significantly higher (50.8 %) in kinematically aligned TKA. The portion was statistically greater in mechanically aligned TKA group than the other two.

Conclusion

Postoperative joint line orientation after kinematically aligned TKA was more similar to that of native knees than that of mechanically aligned TKA and horizontal to the floor. Kinematically aligned TKA can restore pre-arthritic knee joint line orientation, while mechanically aligned TKA is inefficient in achieving the purpose even if navigation TKA is employed.

Level of evidence

III.

     

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 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.     

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.     

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 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.     

Increases in tibial force imbalance but not changes in tibiofemoral laxities are caused by varus–valgus malalignment of the femoral component in kinematically aligned TKA

Purpose

The purposes of this study were to quantify the increase in tibial force imbalance (i.e. magnitude of difference between medial and lateral tibial forces) and changes in laxities caused by 2° and 4° of varus–valgus (V–V) malalignment of the femoral component in kinematically aligned total knee arthroplasty (TKA) and use the results to detemine sensitivities to errors in making the distal femoral resections. Because V–V malalignment would introduce the greatest changes in the alignment of the articular surfaces at 0° flexion, the hypotheses were that the greatest increases in tibial force imbalance would occur at 0° flexion, that primarily V–V laxity would significantly change at this flexion angle, and that the tibial force imbalance would increase and laxities would change in proportion to the degree of V–V malalignment.

Methods

Kinematically aligned TKA was performed on ten human cadaveric knee specimens using disposable manual instruments without soft tissue release. One 3D-printed reference femoral component, with unmodified geometry, was aligned to restore the native distal and posterior femoral joint lines. Four 3D-printed femoral components, with modified geometry, introduced V–V malalignments of 2° and 4° from the reference component. Medial and lateral tibial forces were measured during passive knee flexion–extension between 0° to 120° using a custom tibial force sensor. Eight laxities were measured from 0° to 120° flexion using a six degree-of-freedom load application system.

Results

With the tibial component kinematically aligned, the increase in the tibial force imbalance from that of the reference component at 0° of flexion was sensitive to the degree of V–V malalignment of the femoral component. Sensitivities were 54 N/deg (medial tibial force increasing?>?lateral tibial force) (p?<?0.0024) and 44 N/deg (lateral tibial force increasing?>?medial tibial force) (p?<?0.0077) for varus and valgus malalignments, respectively. Varus–valgus malalignment did not significantly change varus, internal–external rotation, anterior–posterior, and compression–distraction laxities from 0° to 120° flexion. At only 30° of flexion, 4° of varus malalignment increased valgus laxity 1° (p?=?0.0014).

Conclusion

At 0° flexion, V–V malalignment of the femoral component caused the tibial force imbalance to increase significantly, whereas the laxities were relatively unaffected. Because tibial force imbalance has the potential to adversely affect patient-reported outcomes and satisfaction, surgeons should strive to limit errors in resecting the distal femoral condyles to within ±?0.5 mm which in turn limits the average increase in tibial force imbalance to 68 N. Because laxities were generally unaffected, instability resulting from large increases in laxity is not a clinical concern within the ±?4° range tested.

Level of evidence

Therapeutic, Level II.

     

Alignment does not influence cartilage T2 in asymptomatic knee joints

Purpose

To investigate whether the static knee alignment affects articular cartilage ultrastructures when measured using T2 relaxation among asymptomatic subjects.

Methods

Both knee joints (n = 96) of 48 asymptomatic volunteers (26 females, 22 males; 25.4 ± 1.7 years; no history of major knee trauma or surgery) were evaluated clinically (Lysholm, Tegner) and by MRI (hip–knee–ankle angle, standard knee protocol, T2 mapping). Group (n = 4) division was as follows: neutral (<1° varus/valgus), mild varus (2°–4° varus), severe varus (>4° varus) and valgus (2°–4° valgus) deformity with n = 12 subjects/group; n = 24 knees/group. Regions of interest (ROI) for T2 assessment were placed within full-thickness cartilage across the whole joint surface and were divided respecting compartmental as well as functional joint anatomy.

Results

Leg alignment was 0.7° ± 0.5° varus among neutral, 3.0° ± 0.6° varus among mild varus, 5.0° ± 1.1° varus among severe varus and 2.5° ± 0.7° valgus among valgus group subjects and thus significantly different. No differences between the groups emerged from clinical measures. No morphological pathology was detected in any knee joint. Global T2 values (42.3 ± 2.3; 37.7–47.9 ms) of ROIs placed within every knee joint per subject were not different between alignment groups or between genders, respectively.

Conclusion

Static frontal plane leg malalignment does not affect cartilage ultrastructure among young, asymptomatic individuals as measured by T2 quantitative imaging.

Level of evidence

Cross-sectional study, Level II-III.     

Is valgus unloader bracing effective in normally aligned individuals: implications for post-surgical protocols following cartilage restoration procedures

Purpose

Utilizing valgus unloader braces to reduce medial compartment loading in patients undergoing cartilage restoration procedures may be an alternative to non-weightbearing post-operative protocols in these patients. It was hypothesized that valgus unloader braces will reduce knee adduction moment during the stance phase in healthy subjects with normal knee alignment.

Methods

Gait analysis was performed on twelve adult subjects with normal knee alignment and no history of knee pathology. Subjects were fitted with an off-the-shelf adjustable valgus unloader brace and tested under five conditions: one with no brace and four with increasing valgus force applied by the brace. Frontal and sagittal plane knee angles and external moments were calculated during stance via inverse dynamics. Analyses of variance were used to assess the effect of the brace conditions on frontal and sagittal plane joint angles and moments.

Results

With increasing tension in the brace, peak frontal plane knee angle during stance shifted from 1.6° ± 4.2° varus without the brace to 4.1° ± 3.6° valgus with maximum brace tension (P = 0.02 compared with the no brace condition). Peak knee adduction moment and knee adduction impulse decreased with increasing brace tension (main effect of brace, P < 0.001). Gait velocity and sagittal plane knee biomechanics were minimally affected.

Conclusion

The use of these braces following a cartilage restoration procedure may provide adequate protection of the repair site without limiting the patient’s mobility.

Level of evidence

Therapeutic prospective comparative study, Level II.     

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.     

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Level of evidence

II.     

The minimally invasive far medial subvastus approach for total knee arthroplasty in valgus knees

Purpose

The lateral approach in the valgus knee asks for a lot of soft tissue releases during the arthrotomy. The hypothesis of this study was that the far medial subvastus approach could be used in valgus knees and would guarantee both functional and radiological good to excellent results.

Methods

This is a retrospective study on 78 patients (84 knees) undergoing primary total knee arthroplasty (TKA) for type I or II fixed valgus knees. The mean (SD) preoperative mechanical alignment was 187° (4°) HKA angle. Functional recovery, pain, tourniquet times, necessary soft tissue releases as well as radiological alignment were measured.

Results

The Knee Score improved significantly from 45 (10) to 90 (10) (P < 0.05) and the function score improved as well from 35 (20) to 85 (10) (P < 0.05). Flexion improved from 110° (10°) to 137° (8°). Hospital stay was 4 (1.2) days. Alignment was corrected to 181° (1.5°) HKA angle with a postoperative joint line shift of +2.8 (3.2) mm. No clinical instability, as evaluated by the senior author, or osteolytic lines was observed at minimal one-year radiological follow-up.

Conclusion

The far medial subvastus approach is an excellent approach to perform Krackow type I and II TKA with primary PS implants.

Level of evidence

IV.     

Patellar tilt and thickness do not influence postoperative flexion in a high-flex design total knee arthroplasty

Purpose

The purpose of this short-term study was to determine whether patellar thickness and tilt influence the postoperative flexion in a high-flex design total knee arthroplasty (TKA).

Methods

Between 2007 and 2009, 106 patients underwent surgery for TKA using rotating platform flex prosthesis (DePuy, Warsaw, Ind). All of them were suffering from end-stage osteoarthritis. All patients were evaluated preoperatively and at 12 months of follow-up. Maximum active, non-weight-bearing flexion was the primary outcome parameter. Standard standing antero-posterior and lateral weight-bearing radiographs were made. The patellofemoral joints were evaluated in skyline views taken with the knees at approximately 60° of flexion. Patellar thickness, patellar tilt, Caton–Deschamps indices and lower limb alignment were measured.

Results

The mean flexion observed before surgery was 125° ± 15° and after 1 year was 128° ± 13°. The mean patellar thickness preoperatively was 24.5 ± 2.9 and 25.8 ± 3.2 mm at 12 months after surgery. The mean patellar tilt before the procedure was 2.9° ± 4.1° and after 12 months of follow-up was ?0.8° ± 5.0°. The mean preoperative hip-knee-ankle was 2.6° ± 6.2°. No significant correlation was found between postoperative patellar tilt and thickness and postoperative flexion (n.s.).

Conclusions

Patellar tilt and thickness after TKA are factors that depend on the surgery. The resection of the patella can influence both patellar thickness and patellar tilt. By developing adequate surgical instruments, it would be possible to avoid the occurrence of an exaggerated patellar tilt or a major difference in patellar thickness. However, these two factors did not seem to influence the postoperative flexion in a high-flex design TKA, which can be seen as one of the most important outcome factors after TKA.

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.     

Intraoperative assessment of resected condyle thickness in total knee arthroplasty

Purpose

The purpose of this study was to assess the use of resected condyle thickness measurement, obtained with caliper, when verifying the accuracy of distal femoral bone resection in total knee arthroplasty.

Methods

Fifty-two total knee arthroplasties were performed to treat osteoarthritis with varus knee. The difference of caliper-measured thickness of resected medial and lateral femoral condyles after removal of cartilage from the lateral condyle was compared with radiographically measured values. The preoperative planned valgus cut angles and the postoperative femoral component valgus angles were compared.

Results

The difference of radiograph-measured thickness averaged 2.4 ± 2.2 mm and the difference of caliper-measured thickness averaged 2.0 ± 2.1 mm (r = 0.735, P < 0.001). The postoperative femoral component valgus angle averaged 4.8° ± 1.6° (range, 2.0°–7.6°). The difference between the valgus cut angle and femoral component valgus angle averaged ?0.3° ± 1.5°.

Conclusions

The confirmation of correspondence between the caliper-measured and radiographically measured thickness of resected condyles could verify the accuracy of distal femoral bone resection in total knee arthroplasty.

Level of evidence

III.     

Radiographic accuracy in TKA with a CT-based patient-specific cutting block technique

Purpose

Patient-specific instrumentation (PSI) technology for the implantation of total knee arthroplasty (TKA) has a rising interest in the orthopaedic community. Data of PSI are controversially discussed. The hypothesis of this paper is that the radiological accuracy of CT-based PSI is similar to the one of navigated TKA published in the literature.

Methods

Since 2010, all 301 consecutively performed PSI TKAs (GMK MyKnee©) were included in this study. The radiological assessment consisted in a preoperative and postoperative standard X-ray and long-standing X-ray. Changes from the planned to the definitively implanted component size were documented. Postoperative analysis included limb alignment and position of femoral and tibial components (for varus/valgus and flexion or tibial slope).

Results

The postoperative average hip–knee–ankle angle was 180.1° ± 2.0°. In the frontal plane a total of 12.4 % of outliers >3°, for the tibial components 4.1 % of outliers >3° and for the femoral components 4.8 % of outliers >3° were measured. A total of 12.3 % of outliers for posterior tibial slope and 9 % of outliers >3° for the femoral flexion were noted. 10.8 % of the 602 planned size components were adapted intraoperatively.

Conclusion

Although it is still unknown which limb axis is the correct one for the best clinical result, a technology providing the aimed axis in a most precise way should be chosen. Comparing the outcome of the current study with the data from the literature, there does not seem to be any difference compared to computer-assisted surgery.

Level of evidence

IV.     

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.     

A case series of lateral opening wedge high tibial osteotomy for valgus malalignment

Introduction

Lateral opening wedge high tibial osteotomy is a rarely employed surgical technique used for the treatment of lateral knee pain and degeneration in the setting of genu valgum. There exists little evidence of the suitability of this procedure for patients requiring osteotomies with a small correction.

Materials and methods

A case series of 23 patients (24 knees) undergoing lateral opening wedge high tibial osteotomy with a minimum follow-up of 2 years was performed between 2002 and 2008. A surgical technique avoiding the need for fibular osteotomy is described. Adverse events, patient-reported outcomes and radiographic measures of alignment were assessed at baseline, at 6 months postoperatively, and at time of final follow-up. A subgroup of 12 patients also underwent 3D gait analysis at the same time points.

Results

The mean follow-up was 52 months (±20.4). Statistically and clinically significant improvements were identified in the lower extremity functional scale [mean change (95 %CI) = 10 (2.4, 17.6)], and in the knee injury and osteoarthritis outcome score [mean change (95 %CI) = 10.9 (0.5, 21.4)]. Mechanical axis changed from 2.4 ± 2.4° valgus to 0 ± 2.6° varus (p<0.001), anatomical axis from 6.9 ± 2.8° to 4.7 ± 2.5° valgus (p < 0.001), with weight-bearing line offset changing from 60.2 ± 11.4 % to 49.5 ± 12.4 % (p < 0.001). Change in lateral tibial slope, from 6.5 ± 2.2° to 7.5 ± 2.3°, was very small and not statistically significant (n.s.). The peak knee adduction moment during gait significantly increased [mean change (95 %CI) = 0.72 %BW*Ht (0.42, 1.02), suggesting a medial shift in dynamic knee joint load. Two patients underwent total knee arthroplasty during the study period.

Conclusions

Lateral opening wedge high tibial osteotomy is a viable surgical option for patients with lateral knee pain and valgus malalignment requiring small degrees of correction.

Level of evidence

IV.