The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis

Tibia-first, gap-balanced patient-specific alignment restores bony phenotypes and joint line obliquity in a great majority of varus and straight knees and normalises valgus and severe varus deformities

PURPOSE

The present study focuses on testing the capability of a restricted tibia-first, gap-balanced patient-specific alignment technique (PSA) to restore bony morphology and phenotypes.

METHODS

Three-hundred and sixty-seven patients were treated with navigated total knee arthroplasty and tibia-first gap-balanced PSA technique. Boundaries for medial proximal tibial angle were 86°-92°, mechanical lateral distal femoral angle 86°-92°, and hip-knee-ankle angle 175°-183°. Knees were classified by coronal plane alignment of the knee (CPAK), with subsequent analyses comparing pre- and postoperative distributions. Phenotype classification within CPAK groups assessed pre- and postoperative distributions.

RESULTS

Preoperatively, the largest CPAK group was type II (30.8%), followed by type I (20.5%) and type V (17.8%). Postoperatively, type II remained the largest group (39%), followed by type V (30%). All groups with varus/valgus deformities (I, III, IV and VI) became smaller. While in straight legs (II, IV), the CPAK was restored in more than 70%-75%, in varus groups (I, IV) in 40%-50% and in valgus (III and VI) in 5%-18%. The joint line obliquity remained the same in the majority of knees (straight >75%; varus 63%-80%; valgus VI 95%), with the exception of CPAK III (40%). The phenotype analysis showed for straight legs a phenotype restoration of 85%, for varus 94% and for valgus 37%. Joint line convergence angle was reduced significantly in all groups from 1.8°-4.3° preoperatively to 0.6°-1.2° postoperatively.

CONCLUSION

PSA restores bony phenotypes and joint line obliquity in the majority of straight and varus knees, while most of the valgus and extreme varus knees are normalised.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

A new tibial insert design with ball-in-socket medial conformity and posterior cruciate ligament retention closely restores native knee tibial rotation after unrestricted kinematic alignment

PURPOSE

In total knee arthroplasty (TKA) with posterior cruciate ligament (PCL) retention, the medial and lateral insert conformity that restores in vivo native (i.e., healthy) knee tibial rotation and high function without causing stiffness is unknown. The purpose was to determine whether a ball-in-socket (B-in-S) medially conforming (MC) and flat lateral insert implanted with unrestricted kinematic alignment (KA) TKA and PCL retention restores tibial rotation to native.

METHODS

One group of 25 patients underwent unrestricted KA TKA with manual instruments. Another group of 25 patients had native knees. Single-plane fluoroscopy imaged each knee while patients performed step-up and chair rise activities. Following 3D model-to-2D image registration, anterior-posterior (A-P) positions of the femoral condyles were determined. Changes in A-P positions with flexion were used to determine tibial rotation.

RESULTS

At maximum flexion, mean tibial rotations of KA TKA knees were comparable to native knees (Step up: 12.3° ± 4.4° vs. 13.1° ± 12.0°, p = 0.783; Chair Rise: 12.7° ± 6.2° vs. 12.6° ± 9.5º, p = 0.941). However, paths of rotation differed in that screw home motion was less evident in KA TKA knees. At 8 months follow-up, the median Forgotten Joint Score was 69 points (range 65 to 85), the median Oxford Knee Score was 43 points (range 40 to 46), and mean knee flexion was 127º ± 8°.

CONCLUSIONS

The ball-in-socket medial, flat lateral insert and PCL retention implanted with unrestricted KA TKA restored in vivo native knee tibial rotation at maximum flexion for each activity and high function without stiffness. Providing high A-P stability, this implant design might benefit patients desiring to return to demanding work and recreational activities.

LEVEL OF EVIDENCE

Therapeutic - Level II.

Alignment strategy for different types of varus knee with generic instruments: Mechanical alignment or kinematic alignment?

OBJECTIVE

A thorough examination of the available approaches is crucial to comprehensively understand the variance among the alignment strategies employed in total knee arthroplasty (TKA). In this study, we assessed the functional outcomes during the perioperative and postoperative periods of TKA in patients using generic instruments with varus knee to compare the mechanical alignment (MA) and kinematic alignment (KA) procedures.

METHODS

A total of 127 patients from the First Affiliated Hospital of Wannan Medical College who had undergone unilateral TKA between November 2019 and April 2021 were included. The patients with varus knee deformity were categorized into two groups [type I (n = 64) and type IV (n = 63)] based on the modified coronal plane alignment of the knee (mCPAK) classification. The type I and IV groups were further subdivided into MA (n = 30 and n = 32) and KA subgroups (n = 34 and n = 21), respectively. The clinical information collected included sex, surgical side, age, body mass index, and perioperative data [including operation time, intraoperative blood loss, length of hospital stay, and the American Society of Anesthesiologists (ASA) classification]. All patients were monitored for 12 months post-surgery to evaluate the recovery of knee joint function. During this period, the Knee Disability and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR) and the active range of motion (AROM) and visual analog scale (VAS) pain scores were compared at different time points, i.e., before the operation and 6 weeks, 6 months, and 12 months post-operation. Additionally, the patients' subjective experiences were assessed at 6 and 12 months post-surgery using Forgotten Joint Score Knee (FJS-12 Knee), while complications were recorded throughout the monitoring period.

RESULTS

No significant variances were observed in ASA classification, operation duration, blood loss volume during surgery, and hospital stay length between the patients who underwent KA TKA and those who received MA TKA (P > 0.05). During the initial 6 weeks post-operation, the KA group exhibited a significantly reduced average VAS pain score (P < 0.05), with no such differences at 6 months and 1 year after the surgery (P > 0.05). Furthermore, the KA group had significantly higher scores on the KOOS JR at 6 weeks, 6 months, and 1 year following the surgery (P < 0.05). Moreover, the AROM score of the KA group significantly improved only at 6 weeks after the surgery (P < 0.05); however, no prominent differences were found at 6 months and 1 year after the operation (P > 0.05). The KA cohort also exhibited a significant increase in FJS-12 Knee at 1 year following the operation (P < 0.05), whereas no such difference was detected at 6 months following the surgery (P > 0.05). Thus, compared to the MA method, the KA procedure provided pain relief and improved active motion range within 6 weeks after the surgery in patients undergoing TKA. Further, the KOOS JR exhibited significant increases at 6 weeks, 6 months, and 1 year while the FJS-12 Knee demonstrated a significant increase at 1 year after the KA TKA procedure.

CONCLUSION

Therefore, our study results suggest that the KA approach can be considered in patients using generic instruments with varus alignment of the knee, particularly those with mCPAK type I and IV varus knees, to help improve patient satisfaction.

Comparable accuracy of femoral joint line reconstruction in different kinematic and functional alignment techniques

PURPOSE

A key part of kinematic alignment (KA) and functional alignment (FA) is to restore the natural femoral joint line, in particular the medial joint line. KA is known to reproduce the femoral joint line accurately; however, direct comparisons with other surgical techniques such as FA are currently lacking. The purpose of this study was to evaluate differences of alignment parameters in KA and FA techniques with a special focus given to the femoral joint line.

METHODS

We performed a retrospective radiological analysis of pre- and postoperative long leg radiographs of 221 consecutive patients with varus or neutral leg alignment, who underwent primary total knee arthroplasty (TKA) procedures from 2018 to 2020. Patients were assigned to one of four groups: (1) FA: image-based robotic-assisted TKA, (2) FA: imageless robotic-assisted TKA, (3): restricted KA: 3D cutting block-assisted (patient-specific instruments, PSI) TKA, (4): unrestricted KA: calipered technique. Patients' radiographs were (re)-analyzed for overall limb alignment, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), as well as medial and lateral femoral joint line alteration. Statistical significance was determined using unpaired t testing (FA vs. KA group) and one-way ANOVA (subgroup analyses).

RESULTS

Comparisons of KA vs. FA, as well as individual subgroups of KA and FA did not show any differences in the accuracy of medial joint line reconstruction (< 2 mm, p = 0.384, p = 0.744, respectively) and LDFA alteration (< 2°, p = 0.997, 0.921, respectively). Correction of MPTA (3.4° vs. 2.2°) and lateral femoral joint line (2.1 mm vs. 1.5 mm) was higher for FA and FA subgroups compared to KA and KA subgroups (both p < 0.001).

CONCLUSION

Kinematic and functional alignments showed a comparable accuracy in reconstruction of the medial femoral joint line and femoral joint line orientation. Increased correction of MPTA and lateral femoral joint line was recorded with FA techniques.

LEVEL OF EVIDENCE

III.

SF-36 physical function and general health domains are independent predictors of acute hospital length of stay after hip fracture surgery

OBJECTIVE

The demographics and co-morbidities of individuals may impact healthcare consumption, but it is less understood how premorbid physical and mental function may influence these effects. The aim of this study is to determine patient's pre-fracture quality of life and mobility affect acute hospital burden in the management of hip fracture, using length of stay (LOS) as a proxy for healthcare resource.

MATERIALS AND METHODS

This is a retrospective study which investigated hip fracture patients who underwent surgery over the period of 2017-2020. Variables collected include LOS, age, gender, race, marital status, payer type, ASA score, time to surgery (TTS), type of surgery, fracture type, POD1 mobilization, discharge disposition, pre-fracture SF-36, EQ-5D and Parker mobility score (PMS) based on patient's recollection on admission. These variables were correlated with LOS using binary logistic regression on SAS.

RESULTS

There were 1045 patients, and mean age was 79.5 + 8.57 (range 60-105) years with an average LOS 13.64 + 10.0 days (range 2-114). On univariate analysis, PMS, EQ-5D and all domains of SF-36 except bodily pain (BP), emotional role and mental health were associated significantly with LOS. Amongst the QOL and PMS scores, only the domains of SF-36 Physical Function (PF) (OR = 0.993, p = 0.0068) and General Health perception (GH) (OR 0.992, p = 0.0230) remained significant on the multivariate model.

CONCLUSION

Our study showed that poor premorbid scores of SF36 PF and GH are independent factors associated with longer LOS in hip fracture patients after surgery, regardless of fracture type, age and ASA status. Hence, premorbid SF36 PF and GH can be used to identify patients that are at risk of prolonged hospital stay and employ targeted strategies to facilitate rehabilitation and discharge planning.

Alignment philosophy influences trochlea recreation in total knee arthroplasty: a comparative study using image-based robotic technology

PURPOSE

The ability of kinematic alignment (KA) to consistently restore trochlea anatomy in total knee arthroplasty (TKA) is unknown despite recreation of constitutional anatomy being its rationale for use. The purpose of this study was to assess if alignment choice in TKA effects the ability to restore the native trochlea groove.

METHODS

One hundred and twenty-two consecutive patients undergoing robotic-assisted TKA using the MAKO image-based robotic platform had simulated femoral components placed according to kinematic, mechanical and functional alignment principals. Implant position and trochlea restoration between groups were compared. Restoration was assessed by shift (medial-lateral) and depth relative to the native groove from three consistent points; full extension (0°), mid-flexion (30°-40°) and deep flexion (70°-80°).

RESULTS

Three hundred and sixty-six alignment options were analysed. Femoral alignment was significantly different between groups. Of KA, 13.1% compared to 3.3% of FA plans were outside safe coronal boundaries. The trochlear groove was translated the most by MA compared to KA and FA (full extension, MA 7.84 ± 1.99 mm lateral to the native groove, KA 6.40 ± 2.43 mm and FA 6.88 ± 1.74 mm, p ≤ 0.001). In full extension, FA most closely restored the trochlear groove depth in all three positions of flexion.

CONCLUSION

Alignment philosophy led to significant differences in trochlea groove recreation. A kinematically placed femoral component led to positioning considered unsafe in over 13% of cases. A functionally placed femoral component most closely restored trochlea depth in all three positions of flexion.

Which Asymmetric Tibial Component Is Optimally Designed for Calipered Kinematically Aligned Total Knee Arthroplasty?

Calipered kinematically aligned (KA) total knee arthroplasty (TKA) restores the patient's prearthritic joint lines and sets internal-external rotation of the tibial component parallel to the flexion-extension (FE) plane, which is not a mechanical alignment (MA) target. Two asymmetric tibial components designed for MA set the tibial component to either a femoral component (FC) target or a tibial tubercle (TT) target. The study determined the optimal asymmetric tibial component to use with KA as the one with smaller IE deviation from the MA target, greater coverage of tibial resection, and lower incidence of cortical overhang. The study included 40 patients treated with bilateral calipered KA TKA with different asymmetric tibial components in opposite knees. A best-fit of a kinematic tibial template to the tibial resection set the template's slot parallel to the knee's FE plane. Each asymmetric tibial component's anterior-posterior (AP) axis was set parallel to the slot. Computer tomography analysis determined the IE deviation (-internal/+ external) of each tibial component from its MA target, tibial resection coverage by the baseplate and insert, and incidence of cortical overhang. The patient-reported Forgotten Joint Score (FJS) and Oxford Knee Score (OKS) determined outcomes. The mean IE deviation from the MA target was 2 degrees external for the FC-target asymmetric tibial component and -8 degrees internal for the TT-target asymmetric tibial component (p < 0.001). Tibial resection coverage by the baseplate (insert) was 88% (84%) for the FC target and 84% (79%) for the TT target (p < 0.001 for baseplate and insert). The FC target insert covered 3 mm more of the posterolateral resection (p < 0.001). Posteromedial coverage was comparable. The incidence of cortical overhang was 2.5% for each baseplate. There was no difference in FJS and OKS. When performing calipered KA, the more optimal design was the asymmetric tibial component with the FC target because of the smaller deviation from its MA target and the greater coverage of the tibial resection by the baseplate and insert.

Negligible effect of surgeon experience on the accuracy and time to perform unrestricted caliper verified kinematically aligned TKA with manual instruments

PURPOSE

Surgeons performing total knee arthroplasty (TKA) are interested in the accuracy and time it takes to make the four femoral resections that determine the setting of the femoral component. A method for quantifying the error of each resection is the thickness, measured by a caliper, minus the femoral target. The present study tested the hypothesis that the mean deviation of the resection from the femoral target, the percentage of resections with a deviation of ± 0.5, 1.0, 1.5, and 2.0 mm, and the time to complete the femoral cuts were not different between experienced (E) and less-experienced (LE) surgeons performing unrestricted caliper verified kinematically aligned (KA) TKA with manual instruments.

METHODS

This study analyzed intraoperative verification worksheets from 203 patients treated by ten E surgeons and 58 patients treated by four LE surgeons. The worksheet recorded (1) the thickness of the femoral target for the distal medial (DM), distal lateral (DL), posterior medial (PM), and posterior lateral (PL) resections and the caliper thickness of the resections with a resolution of 0.5 mm, and (2) the time to complete them. The most accurate resection has a mean difference ± standard deviation of 0 ± 0.0 mm.

RESULTS

The accuracy of the 1044 initial resections (261 patients) was significantly closer to the femoral target for E vs. the LE surgeons: 0.0 ± 0.4 vs. - 0.3 ± 0.5 for the DM, 0.0 ± 0.5 vs. - 0.4 ± 0.6 for the DL, - 0.1 ± 0.5 vs. - 0.2 ± 0.5 PM, and - 0.1 ± 0.5 vs. - 0.4 ± 0.6 for the PL resections (p ≤ 0.0248). E surgeons completed the femoral resections in 12 min; 5 min faster than LE surgeons (p < 0.0001).

CONCLUSIONS

Because the mean difference in femoral resections with manual instruments for E vs. LE surgeons was < 0.5 mm which is within the caliper's resolution, differences in accuracy were not clinically relevant. Surgeons exploring other alignment options and robotic, navigation, and patient-specific instrumentation might find these values helpful when deciding to change.

LEVEL OF EVIDENCE

III; case-control study.

A Best-Fit of an Anatomic Tibial Baseplate Closely Parallels the Flexion-Extension Plane and Covers a High Percentage of the Proximal Tibia

There are no reports of in vivo internal-external (I-E) rotational alignment and coverage of the proximal tibia after performing a best-fit method of an anatomically designed and asymmetrically shaped tibial baseplate during calipered kinematically aligned (KA) total knee arthroplasty (TKA). We hypothesized that a best-fit plane sets the anterior-posterior (A-P) axis of the anatomic baseplate closely parallel to the flexion-extension (F-E) plane of the knee and covers a high percentage of the proximal tibia. A total of 145 consecutive primary TKAs were prospectively collected. The calipered KA method and verification checks set the positions and orientations of the components without ligament release in all knees without restrictions on the preoperative deformities. A best-fit method selected one of six trials of anatomic baseplates that maximized coverage and set I-E rotation parallel to and within the cortical edge of the proximal tibia. The angle between the transverse axes of the components (i.e., the deviation of the A-P axis of the anatomic baseplate from the F-E plane of the native knee) and the cross-sectional area (CSA) of the proximal tibia were measured on postoperative computerized tomographic scans. The mean deviation of the anatomic baseplate from the F-E plane was 2-degree external ± 5 degrees. The mean coverage of the proximal tibia was 87 ± 6% (CSA of baseplate from the manufacturer/CSA of proximal tibia × 100). The anatomic baseplate and best-fit method adequately set I-E rotation of the baseplate closely parallel to the F-E plane of the knee and cover a high percentage of the proximal tibia.

Clinical and Radiological Changes of Ankle in Knee Osteoarthritis With Varus After Total Knee Arthroplasty: A Systematic Review

Background: Arthritis with severe varus deformity remains a challenge in total knee arthroplasty (TKA). Until recently, surgeons aimed at a neutral lower limb alignment when performing a TKA. However, the impact of TKA on the ankle joint has been ignored. Therefore, we conducted a systematic review to assess the clinical and radiological changes in the ankle joint after TKA on knees with severe varus deformity. Methods: A systematic search was conducted in four English (PubMed, Embase, Cochrane Library, and Web of Science) and four Chinese (CBM, VIP, CNKI, and Wan Fang Database) databases. Screening of literature and extraction of data were independently performed by two researchers. The modified methodological index for non-randomized studies (MINORS) was used to assess the quality. Results: A total of eight studies were eligible, namely, four prospective and four retrospective studies. TKA resulted in a negative clinical effect in the ankle joint in patients with ankle osteoarthritis. Seven studies reported changes in the mechanical tibiofemoral angle, and four studies reported radiological changes in the hindfoot. The mean score of the MINORS was 9.8 out of eight (9-11). Conclusion: As a result of the correction of the knee osteoarthritis with severe varus deformity following mechanically aligned TKA, the radiological malalignment of the ankle joint was improved. However, some patients experience increased ankle pain after undergoing TKA, especially, if there was a residual knee varus deformity, a stiff hindfoot with varus deformity, or ankle arthritis.

Analysis of Gender Differences in the Rotational Alignment of the Distal Femur in Kinematically Aligned and Mechanically Aligned Total Knee Arthroplasty

To compare the angle between the external rotation references of the femoral components in the axial plane by gender and lower limb alignment in Korean patients with osteoarthritis (OA). Magnetic resonance (MR) images of 1273 patients were imported into a modeling software and segmented to develop three-dimensional femoral bony and cartilaginous models. The surgical transepicondylar axis (sTEA), posterior condylar axis (PCA), the kinematically aligned axis (KAA), and anteroposterior axis were used as rotational references in the axial plane for mechanically aligned (MA) TKA. The relationship among axes were investigated. Among 1273 patients, 942 were female and 331 were male. According to lower limb alignment, the varus and valgus knee groups comprised 848 and 425 patients, respectively. All measurements, except PCA-sTEA, differed significantly between men and women; all measurements, except PCA-sTEA, did not differ significantly between the varus and valgus knee groups. In elderly Korean patients with OA, rotational alignment of the distal femur showed gender differences, but no differences were seen according to lower limb alignment. The concern for malrotation of femoral components during kinematically aligned TKA is less in Koreans than in Caucasians and relatively less in women than in men. In MA TKA, malrotation of the femoral components can be avoided by setting different rotational alignments for the genders.

Patient satisfaction following total knee arthroplasty using restricted kinematic alignment

AIMS

Alternative alignment concepts, including kinematic and restricted kinematic, have been introduced to help improve clinical outcomes following total knee arthroplasty (TKA). The purpose of this study was to evaluate the clinical results, along with patient satisfaction, following TKA using the concept of restricted kinematic alignment.

METHODS

A total of 121 consecutive TKAs performed between 11 February 2018 to 11 June 2019 with preoperative varus deformity were reviewed at minimum one-year follow-up. Three knees were excluded due to severe preoperative varus deformity greater than 15°, and a further three due to requiring revision surgery, leaving 109 patients and 115 knees to undergo primary TKA using the concept of restricted kinematic alignment with advanced technology. Patients were stratified into three groups based on the preoperative limb varus deformity: Group A with 1° to 5° varus (43 knees); Group B between 6° and 10° varus (56 knees); and Group C with varus greater than 10° (16 knees). This study group was compared with a matched cohort of 115 TKAs and 115 patients using a neutral mechanical alignment target with manual instruments performed from 24 October 2016 to 14 January 2019.

RESULTS

Mean overall patient satisfaction for the entire cohort was 4.7 (SE 0.1) on a 5-point Likert scale, with 93% being either very satisfied or satisfied compared with a Likert of 4.3 and patient satisfaction of 81% in the mechanical alignment group (p < 0.001 and p < 0.006 respectively). At mean follow-up of 17 months (11 to 27), the mean overall Likert, Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, Western Ontario and McMaster Universities Osteoarthritis Index, Forgotten Joint Score, and Knee Society Knee and Function Scores were significantly better in the kinematic group than in the neutral mechanical alignment group. The most common complication in both groups was contracture requiring manipulation under anaesthesia, involving seven knees (6.1%) in the kinematic group and nine knees (7.8%) in the mechanical alignment group.

CONCLUSION

With the advent of advanced technology, and the ability to obtain accurate bone cuts, the target limb alignment, and soft-tissue balance within millimetres, using a restricted kinematic alignment concept demonstrated excellent patient satisfaction following primary TKA. Longer-term analysis is required as to the durability of this method. Cite this article: Bone Joint J 2021;103-B(6 Supple A):59-66.

Measured Resection Techniques Do Not Align to the Cylindrical Axis in Kinematic Total Knee Arthroplasty

Background

There has been increasing interest with improved functional results in kinematically aligned total knee arthroplasty. Kinematic alignment seeks to replicate the rotational axes of the individual knee. The femoral component can either be aligned to the estimated prearthritic distal and posterior joint lines via a measured-resection technique or by aligning to the cylindrical axis (CA). The CA is calculated using three-dimensional imaging and defined as a line equidistant from the medial and lateral condylar surfaces from 15° to 115° flexion. This study investigates whether these 2 techniques lead to similar alignment angles in the coronal plane.

Materials and Methods

One hundred three knees undergoing total knee arthroplasty were assessed using a computed tomography-based protocol. The image-based cylindrical axis coronal angle (CAA) was calculated, and the distal condylar coronal angle (DCA) was calculated to simulate a caliper measured resection technique. A computed tomographic planning software program was used to measure the offset from the distal-most extent of the calculated cylinder to the distal-most aspect of the condyles.

Results

The DCA measured 3.3° valgus (standard deviation 2.4°) and the CAA 1.8° valgus (standard deviation 2.1°). The mean difference in offset from CAA radius to DCA from the medial condyle and the lateral condyle was 2.85 mm and 1.51 mm, respectively, increasing valgus predilection.

Conclusions

Caliper measured resection kinematically aligned techniques will position the femoral component in a significantly more valgus position than when aligning to the CA of the knee. This is due to an increased offset of the distal femoral articulation from the most distal aspect of the cylinder on the medial side of the knee.

What you need to know about kinematic alignment for total knee arthroplasty

This lecture outlines the various alignment philosophies for total knee arthroplasty (TKA). It is logical that our desire to improve clinical outcomes for TKA involves a more personalized and physiological implantation process that preserves each patient's anatomical features. We will take a deep dive into the kinematic alignment concept by describing its rationale, surgical steps and results. Kinematic implantation of TKA can be done reliably at a low cost and appears to achieve acceptable implant biomechanics. While its short-term clinical results are encouraging, it must be evaluated further. The thresholds for acceptable alignment (indications for restricted kinematic alignment) still need to be specified. LEVEL OF EVIDENCE: V; Expert opinion.

A cruciate-retaining implant can treat both knees of most windswept deformities when performed with calipered kinematically aligned TKA

PURPOSE

Surgeons performing total knee arthroplasty (TKA) on the osteoarthritic valgus deformity often use a posterior stabilized (PS) and semi-constrained implants to substitute for the release of a contracted posterior cruciate ligament (PCL) instead of a cruciate retaining (CR) implant. Calipered kinematic alignment (KA) strives to retain the PCL and use a CR implant. The aim of this study of the windswept deformity was to determine whether the level of implant constraint, outcome scores, and alignment after bilateral calipered KA TKA are different between a pair of knees with a varus and valgus deformity in the same patient.

METHODS

A review of a prospectively collected database identified all patients with a windswept deformity treated with bilateral TKA (n = 19) out of 2430 consecutive primary TKAs performed between 2014 and 2019. Operative reports determined the level of implant constraint. Patient response to the Forgotten Joint Score (FJS) and Oxford Knee Score (OKS) assessed outcomes at a mean follow-up of 2.3 years. Postoperative alignment was measured on an A-P computer tomographic scanogram of the limb.

RESULTS

CR implants were used in 15 of 19 (79%) valgus deformities and 17 of 19 (89%) of varus deformities (n.s.). No knees required a semi-constrained implant. There was no difference in the median postoperative FJS and OKS (n.s.), and a 1° or less difference in the mean postoperative distal lateral femoral angle (p = 0.005) and proximal medial tibial angle (n.s.) between the paired varus and valgus knee deformity.

CONCLUSION

Based on this small series, surgeons that use calipered KA TKA can expect to use CR implants in most patients with windswept deformity and achieve comparable outcome scores and alignment between the paired varus and valgus deformity.

LEVEL OF EVIDENCE

IV.

Outcomes in Patients with a Calipered Kinematically Aligned TKA That Already Had a Contralateral Mechanically Aligned TKA

Prior studies suggest kinematically aligned (KA) total knee arthroplasty (TKA) provides some clinical benefits. There are no reports of self-reported outcome measures in patients treated with a calipered KA TKA that already had a contralateral mechanically aligned (MA) TKA. We performed a retrospective study and asked the following questions: (1) Were you satisfied with your MA TKA when you were treated with the KA TKA? (2) What are the Forgotten Joint Scores (FJS) and Oxford Knee Scores (OKS) in each of your knees? (3) Do you favor one knee? and (4) Did one knee recover faster? From January 2013 to January 2017, 2,378 consecutive primary TKAs were performed of which all were treated with calipered KA that uses serial verification checks incorporating measurements of bone resections and positions to restore the prearthritic or native joint lines accurately. A records review identified patients with a prior primary MA TKA in the contralateral limb. Excluded were those with a history of fracture, osteotomy, infection, or revision knee surgery in either limb. In September 2018, 78 patients (57 females) with a mean age of 73 years (range, 50-91 years) completed a follow-up evaluation consisting of the FJS and OKS questionnaires and three anchor questions. A total of 83% of patients were satisfied with the MA TKA and 92% were satisfied with the KA TKA. The KA TKA had a 15 point higher median FJS and a comparable OKS to that of the MA TKA. Also, 56% of patients favored the KA TKA, and 8% favored the MA TKA. Seventy four percent of patients favored the recovery of the KA TKA, and 6% favored the recovery of the MA TKA. Accordingly, a patient considering a contralateral KA TKA can expect that more often than not the KA TKA will have a higher FJS, a similar OKS, be their favorite knee, and recover faster. Present study is therapeutic and reflects level IV evidence.

Deviations in femoral joint lines using calipered kinematically aligned TKA from virtually planned joint lines are small and do not affect clinical outcomes

PURPOSE

Kinematically aligned total knee arthroplasty (KA TKA) strives to restore the native distal and posterior joint lines of the femur. Because the joint lines of a virtually planned femoral component on the native femur can serve as surrogates of those of the native femur, the present study determined position and orientation deviations of the femoral joint lines following calipered KA TKA from virtually planned joint lines and whether these alignment deviations affect clinical outcomes. Our hypotheses were that the alignment deviations for most knees would be less than 2 mm and/or 2° and that larger alignment deviations would not be associated with lower clinical outcome scores.

METHODS

A review of lower extremity CT scanograms and CT scans of the knee identified 36 patients treated with calipered KA TKA in one limb and no other skeletal deformities in either limb. 3D models of the operated femur with the implanted femoral component and the native femur were created. The articular surfaces of a 3D model of the implanted femoral component in the TKA knee were shape-matched to the condyles of the native femur to create a virtual plan. The shape-matched femoral component served as a reference from which to determine alignment deviations of the femoral component implanted in the ipsilateral femur. The Forgotten Joint Score (FJS) and Oxford Knee Score (OKS) were obtained at an average of 20 months.

RESULTS

For proximal-distal and anterior-posterior positions and varus-valgus and internal-external orientations of the femoral component, the root mean square deviations from the planned joint lines ranged from 1.4 to 1.5 (mm or degrees). The mean differences ranged from - 0.1 to 0.2 (mm or degrees) indicating an absence of systematic alignment deviations. The proportion of knees with joint lines within ± 2 mm and ± 2° of the joint lines of virtually planned knees ranged from 83 to 92%. For the FJS and OKS, the median values were 79 (out of 100) and 45 (out of 48), respectively, and there were no significant correlations between deviations in the positions and orientations and either the FJS or the OKS.

CONCLUSION

Alignment deviations were bounded by 2 mm and 2° for most knees, which previous biomechanical studies have shown reduce the risks of stiffness, loss of extension, loss of flexion, and tibial compartment forces higher than those of the native knee. Moreover, because median FJS and OKS were relatively high, and because larger alignment deviations did not correlate with lower outcome scores, deviations did not affect clinical outcomes. These results validate calipered KA TKA as a surgical technique which closely restores the distal and posterior femoral joint lines to those planned and achieves concomitant high patient-reported outcome scores. Thus, surgeons can use the calipered KA TKA technique with confidence that the surgical alignment goal will be satisfied with sufficient accuracy that high patient-reported outcomes are achieved.

LEVEL OF EVIDENCE

III.

Combining kinematic alignment and medial stabilized design in total knee arthroplasty: Basic rationale and preliminary clinical evidences

Objective: kinematic alignment technique has been recently described as a new surgical procedure able to restore the patient specific physiological knee alignment; furthermore, new prosthesis, as medial stabilized (MS) third generation TKA, were designed to better reproduce the anatomical shape of the knee. In this prospective study, the authors evaluated early clinical improvement and radiological outcomes of patients having pre-operative small coronal limb deformity underwent TKA using a surgical technique combining a "restricted kinematic alignment" with medial stabilized polyethylene insert.

Methods

Fifteen consecutive patients (8 female and 7 male) scheduled for a total knee replacement have been enrolled for this study and treated using a modern third generation knee implant with a medial congruent tibial polyethylene. Clinical improvements have been assessed pre-operatively and at 6 and 12 months Follow up (FU) using the Oxford knee Score (OKS)( Ishikawa et al., Jun. 2015) 12 the Knee Society Score (KSS)( Pinskerova and et al., Aug. 2004) 13 and Forgotten Joint Score (FJS) as patient reported outcomes measurement system (PROMs). A radiological evaluation was made by a single physician at 6 months.

Results

Average improvement in OKS was from 20.2 (SD 5.5) pre-operatively to 41.3 (SD 2.1) at the final FU. KSS pain/motion improved with a mean score from 40.1 (SD 4.0) pre-op to 89.1 (SD 6.3) while KSS function improved with an average score from 51.0 (SD 6.2) pre-op to 81.8 (SD 8.4) showing good to excellent results in all the knee treated. The mean FJS at 6 months follow up was 75.1 (SD 4.2) improving to 79.3 (SD 3.3) at one year FU. Post-operative XR showing an average varus Hip-Knee-Ankle (HKA) angle of 178.8° (range from 176° to 182°, SD 2,3°); We found no statistically significant difference between pre-operative and post-operative HKA (p < 0,05).

Conclusion

The current authors assumed appropriate to combine a modern TKA implant designed replicating the anatomical shape of the native knee with a surgical technique able to better reproduce the physiological, patient specific, knee biomechanics. Our findings suggest that combining MS implant with KA technique may results in better short-term functional results, helping the patient to "forget" their replaced joint and restoring their pre-arthritic quality of life.

Short-term follow-up of kinematically vs. mechanically aligned total knee arthroplasty with medial pivot components: A case-control study

INTRODUCTION

The kinematic alignment (KA) technique for total knee arthroplasty (TKA) and the medial pivot (MP) component design are two options promoting a physiologic prosthetic knee kinematics when used in combination that could improve TKA outcomes. Case-control study is initiated to compare the 1-year radio-clinical outcomes between kinematic alignment medial pivot total knee arthroplasty (KA MP-TKAs) and mechanical alignment medial pivot total knee arthroplasty (MA MP-TKA). Goal of a study was to answer the following questions: Do KA MP-TKAs patients have improved functional outcomes compared to MA MP-TKAs patients? (Q1); Do prosthetic knee and lower limb alignments differ between KA and MA patients (Q2)? And does kinematic implantation of MP TKA has higher risk of reoperations and revisions (Q3)?

MATERIAL AND METHODS

A case-control study was carried out to compare the 1-year clinical and radiographic outcomes between 24 consecutive KA-TKA patients and 24 matched MA-TKA patients. All patients had implantation with manual instruments and a cemented medial pivot TKA with excision of the PCL. All data were collected prospectively, and outcome scores were patient reported.

RESULTS

KA patients had superior values in Forgotten Joint Score (FJS) at 1-year (KA 77 vs. MA 51) (p=0.05) follow-up. After one year KA patients scored better in objective section of the new Knee Society Score (KSS) (p=0.02), and in sport section of the Knee Osteoarthritis Outcome Score (KOOS) (p=0.01). Eleven out of 24 patients (46%) in KA group and 7/24 patients (29%) in MA group had limb alignment out of 180°±3°, whereas 17/24 (70%) of KA patients, and 14/24 (58%) of MA patients had orientation of tibial component with more than 3° of varus. No reoperation or revision occurred in either group.

DISCUSSION/CONCLUSION

The KA of MP TKA design seems to have a good efficacy at early-term, with some 1-year functional performance higher to the ones from MA MP TKAs. Further research is needed to define if those early results will last over time.

LEVEL OF EVIDENCE

III, case-controlled study.

Gap balancing versus measured resection for primary total knee arthroplasty: a meta-analysis study

INTRODUCTION

To achieve the most desirable post-operative results, operation techniques and procedures for total knee arthroplasty (TKA) are highly standardized. However, debates persist whether patients having undergone a gap balancing technique (GB) perform better than those having undergone measured resection (MR) technique. Therefore, a meta-analysis study was conducted to investigate advantages of GB compared to the MR. The focus of the present study was on clinical and functional scores, radiological measurements and further complications.

MATERIALS AND METHODS

The present meta-analysis was conducted according to the PRISMA checklist. In November 2019, literature search was performed. All clinical studies comparing measured resection technique versus gap balancing technique for primary total knee arthroplasty were considered for inclusion. Only articles reporting quantitative data under the outcomes of interest were eligible for inclusion. The methodological quality assessment and statistical analyses were performed through the Review Manager Software version 5.3 (The Cochrane Collaboration, Copenhagen).

RESULTS

Data from 25 clinical trials (2971 procedures) were collected. Patient baseline demonstrated a good comparability. No difference among the two cohorts was found in terms of SF-12 Mental and Physical, ROM, KSS, KSS Function, OKS, WOMAC. No difference was found in the alignment of mechanical axis and femoral rotation. During the knee motion, no difference was found between the medial and lateral gaps among the two techniques. The GB showed a significant elevated joint line (P < 0.0001), along with a longer duration of the operating time (P = 0.001). No differences were found in terms of revision surgery, aseptic loosening or prosthetic infections.

CONCLUSION

GB and MR achieve similar outcomes for TKA. In the GB group, a proximalisation of the joint line and extended operating time was detected. Regarding the additional outcomes of interest, the present analysis showed comparability between both groups, MR and GB.

Revision of total knee arthroplasty with the use of patient-specific instruments: an alternative surgical technique

INTRODUCTION

Accuracy in the placement of components in revision total knee arthroplasty (R-TKA) surgery is sometimes challenging. The applicability of patient‑specific instruments (PSI) in knee surgery has progressively expanded to types of surgery other than primary arthroplasty. Could this assistive technology be used to facilitate accurate R-TKA surgery? The aim of the current manuscript is to describe this new application of PSI for revision of TKA-to-TKA and to provide a step-by-step technical guideline for use.

AREAS COVERED

We will describe the application and a detailed description of PSI technology to TKA revision surgery, step-by-step, from CT images acquisition for preoperative planning and PSI blocks production to the surgery.

EXPERT COMMENTARY

The system can facilitate the accomplishment of the bony cuts for optimal implant placement and that can be useful in minimally altering the femoral and the tibial joint line. It is obvious that technology alone will not replace surgical skill and that accuracy of the system will also depend on the quality of the CT images and the ability of the software to prevent metal artifacts. Despite that, our initial results are promising and prove that the concept of applying PSI technology to the R-TKA surgery is feasible.

Impact of preoperative varus deformity on postoperative mechanical alignment and long-term results of "mechanical" aligned total knee arthroplasty

PURPOSE

Preoperative varus deformity may affect postoperative mechanical alignment and outcomes of total knee arthroplasty (TKA). In this study, we aimed to determine whether (1) greater degrees of preoperative varus deformity increase the incidence of varus-aligned TKAs and (2) residual varus alignment improves the long-term survival rate in TKAs with preoperative varus deformity.

METHODS

We retrospectively reviewed 905 primary TKAs for varus-type osteoarthritis from November 1998 to June 2009. The mean follow-up was 8.23 years (±3.47 years). We measured pre- and postoperative mechanical hip-knee-ankle axis angle (HKA) on full-length standing radiographs to assess the severity of preoperative varus deformities, defined as mild (0°<HKA≤5°), moderate (5°<HKA≤10°), severe (10°<HKA≤15°), and very severe (HKA>15°). Postoperative alignment was divided to four groups: valgus (HKA<-3°), neutral (-3°≤HKA≤3°), mild varus (3°<HKA≤6°), and severe varus (HKA>6°). We performed survival analysis in all cases for mechanical failure.

RESULTS

Varus-aligned TKAs increased proportionally to increasing preoperative varus deformity (p<0.001). The survival rate showed no significant difference according to the preoperative varus deformity (p=0.147). However, the survival time for postoperative neutral alignment (16.13±0.10 years, 95% CI 15.94-16.33 years) was longer than the survival time for mild varus (15.32±0.35 years, 95% CI 14.64-16.00 years) and severe varus (13.38±0.53 years, 95% CI 12.35-14.42 years) alignment (p<0.001).

CONCLUSION

Postoperative varus malalignment appears to increase proportionally to the severity of preoperative varus deformity. Also, postoperative neutral alignment results in longer TKA survival time than residual varus alignment.

LEVEL OF EVIDENCE

III, Retrospective comparative cohort study.

Kinematically aligned total knee arthroplasty reproduces more native rollback and laxity than mechanically aligned total knee arthroplasty: A matched pair cadaveric study

BACKGROUND

A growing body of evidence supports that kinematically aligned (KA) total knee arthroplasty (TKA) provides superior clinical outcomes and satisfaction than mechanically aligned (MA) TKA. In theory, KA TKA would restore knee kinematics closer to the native condition than MA TKA, but the current biomechanical evidence is lacking.

HYPOTHESIS

KA TKA would restore knee biomechanics to the native condition better than MA TKA.

METHODS

Seven pairs of cadavers were tested. For each pair, one knee was randomly assigned to KA TKA and the other to MA TKA. During KA TKA, the sizes of femur and tibia resections were equivalent to implant thickness to align with the patient-specific joint line. MA TKA was performed using conventional measured resection techniques. All specimens were mounted on a customized knee-testing system and digitized. Knee motions measured during flexion included rollback, axial tibiofemoral rotation, and laxities, specifically varus-valgus laxity, anterior-posterior translation, and internal-external rotation.

RESULTS

The pattern of knee motion following KA TKA was similar to the native knee. However, following MA TKA, both medial and lateral rollback and tibiofemoral axial rotation were decreased relative to those of the native knee. Valgus laxity was restored only after KA TKA, whereas varus laxity was restored only after MA TKA. Anterior translation was increased regardless of the alignment strategy. In addition, rotational laxities were restored after KA TKA, but external rotation laxity increased after MA TKA.

CONCLUSION

KA TKA restores femoral rollback and laxity to the native condition better than MA TKA. KA TKA may enhance functional performance and provide a more normal knee sensation.

LEVEL OF EVIDENCE

II, Controlled laboratory study.

Calipered Kinematically Aligned Total Knee Arthroplasty: An Accurate Technique That Improves Patient Outcomes and Implant Survival

Kinematic alignment performed with caliper measurements and verification checks accurately co-align the femoral and tibial components with the 3 axes and joint lines of the native knee without ligament release and without restrictions on the degree of preoperative varus, valgus, flexion, and extension deformities and the degree of postoperative correction. [Orthopedics. 2019; 42(3):126-135.].

Is There a Force Target That Predicts Early Patient-reported Outcomes After Kinematically Aligned TKA?

BACKGROUND

Four mechanical alignment force targets are used to predict early patient-reported outcomes and/or to indicate a balanced TKA. For surgeons who use kinematic alignment, there are no reported force targets. To date the usefulness of these mechanical alignment force targets with kinematic alignment has not been reported nor has a specific force target for kinematic alignment been identified.

QUESTIONS/PURPOSES

(1) Does hitting one of four mechanical alignment force targets proposed by Gustke, Jacobs, Meere, and Menghini determine whether a patient with a kinematically aligned TKA had better patient-reported Oxford Knee and WOMAC scores at 6 months? (2) Can a new force target be identified for kinematic alignment that determines whether the patient had a good/excellent Oxford Knee Score of ≥ 34 points (48 best, 0 worst)?

METHODS

Between July 2017 and November 2017, we performed 148 consecutive primary TKAs of which all were treated with kinematic alignment using 10 caliper measurements and verification checks. A total of 68 of the 148 (46%) TKAs performed during the study period had intraoperative measurements of medial and lateral tibial compartment forces during passive motion with an instrumented tibial insert and were evaluated in this retrospective study. Because the surgeon and surgical team were blinded from the display showing the compartment forces, there was no attempt to hit a mechanical alignment force target when balancing the knee. The Oxford Knee Score and WOMAC score measured patient-reported outcomes at 6 months postoperatively. For each mechanical alignment force target, a Wilcoxon rank-sum test determined whether patients who hit the target had better outcome scores than those who missed. An area under the curve (AUC) analysis tried to identify a new force target for kinematic alignment at full extension and 10°, 30°, 45°, 60°, 75°, and 90° of flexion that predicted whether patients had a good/excellent Oxford Knee Score, defined as a score of ≥ 34 points.

RESULTS

Patients who hit or missed each of the four mechanical alignment force targets did not have higher or lower Oxford Knee Scores and WOMAC scores at 6 months. Using the Gustke force target as a representative example, the Oxford Knee Score of 41 ± 6 and WOMAC score of 13 ± 11 for the 31 patients who hit the target were not different from the Oxford Knee Score of 39 ± 8 (p = 0.436) and WOMAC score of 17 ± 17 (p = 0.463) for the 37 patients who missed the target. The low observed AUCs (from 0.56 to 0.58) at each of these flexion angles failed to identify a new kinematic alignment force target associated with a good/excellent (≥ 34) Oxford Knee Score.

CONCLUSIONS

Tibial compartment forces comparable to those reported for the native knee and insufficient sensitivity of the Oxford Knee and WOMAC scores might explain why mechanical alignment force targets were not useful and a force target was not identified for kinematic alignment. Intraoperative sensors may allow surgeons to measure forces very precisely in the operating room, but that level of precision is not called for to achieve a good/excellent result after calipered kinematically aligned TKA, and so its use may simply add expense and time but does not improve the results from the patient's viewpoint.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Poor relationship between frontal tibiofemoral and trochlear anatomic parameters: Implications for designing a trochlea for kinematic alignment

BACKGROUND

The kinematic alignment (KA) technique for total knee arthroplasty (TKA) is an emerging implant positioning philosophy that aims to restore constitutional knee anatomy to improve knee kinematics. At present, the KA technique aims to reconstruct native femorotibial (FT) joint alignment, however there is still insufficient consideration towards the inter-individual trochlear anatomy variability. Poor trochlear restoration may compromise clinical outcomes. Our study aimed at assessing the anatomical relationship between the native trochlea and other FT anatomical parameters.

METHODS

Fifty-eight preoperative CT scans of low-grade knee arthritic patients were segmented to create 3D bone models. The FT and the PF anatomical parameters were measured using in-house software. Values were compared between different groups of lower limb and FT joint line (JL) orientation, and correlations between FT and PF anatomical parameters were assessed.

RESULTS

We were unable to detect any significant correlation between groove orientation (frontal and axial) or groove radius and either the hip-knee-ankle (HKA), or the lateral distal femoral (LDFA), or the medial proximal tibial (MPTA), or the FTJL-mechanical axis (FTJLMAA) Angles. When considering the correlation within sub-groups of limb or JL orientation, we only found a positive correlation (r = 0.464, p = 0.022) in the varus lower limb (HKA ≤ 180°) sub-group between groove frontal orientation and LDFA.

CONCLUSION

Our study shows that the determination of several limb, knee, and JL parameters is of poor value to predict individual trochlea anatomy. This raises the issue of how to improve femoral component design to achieve individualised FT and PF anatomical restoration with KATKA.

LEVEL OF EVIDENCE

Level 1 - computational study.

Kinematic alignment of current TKA implants does not restore the native trochlear anatomy

INTRODUCTION

Preserving constitutional patellofemoral anatomy, and thus producing physiological patellofemoral kinematics, could prevent patellofemoral complications and improve clinical outcomes after kinematically aligned TKA (KA TKA). Our study aims 1) to compare the native and prosthetic trochleae (planned or implanted), and 2) to estimate the safety of implanting a larger Persona^® femoral component size matching the proximal lateral trochlea facet height (flange area) in order to reduce the native articular surfaces understuffing generated by the prosthetic KA trochlea.

METHODS

Persona^® femoral component 3D model was virtually kinematically aligned on 3D bone-cartilage models of healthy knees by using a conventional KA technique (group 1, 36models, planned KA TKA) or an alternative KA technique (AT KA TKA) aiming to match the proximal (flange area) lateral facet height (10 models, planned AT KA TKA). Also, 13postoperative bone-implant (KA Persona^®) models were co-registered to the same coordinate geometry as their preoperative bone-cartilage models (group 2implanted KA TKA). In-house analysis software was used to compare native and prosthetic trochlea articular surfaces and medio-lateral implant overhangs for every group.

RESULTS

The planned and performed prosthetic trochleae were similar and valgus oriented (6.1 and 8.5, respectively), substantially proximally understuffed compared to the native trochlea. The AT KA TKAs shows a high rate of native trochlea surface overstuffing (70%, 90%, and 100% for lateral facet, groove, medial facet) and mediolateral implant overhang (60%). There was no overstuffing with conventional KA TKAs having their anterior femoral cut flush.

CONCLUSION

We found that with both the planned and implanted femoral components, the KA Persona^® trochlea was more valgus oriented and understuffed compared to the native trochlear anatomy. In addition, restoring the lateral trochlea facet height by increasing the femoral component size generated a high rate of trochlea overstuffing and mediolateral implant overhang. While restoring a native trochlea with KA TKA is not possible, the clinical impact of this is low, especially on PF complications. In current practice it is better to undersize the implants even if it does not restore the native anatomy. Longer follow-up is needed for KA TKAs performed with current implant, and the debate of developing new, more anatomic, implants specifically designed for KA technique is now opened.

LEVEL OF EVIDENCE

II, Laboratory controlled study.

Differences in trochlear parameters between native and prosthetic kinematically or mechanically aligned knees

INTRODUCTION

Kinematic (KA) and mechanical (MA) alignment techniques are two different philosophies of implant positioning that use the same TKA implants. This might generate differences in the resulting prosthetic trochleae parameters between the two techniques of alignment. Our study aim was to test the following hypotheses : (1) mechanically or kinematically aligned femoral implant understuffs the native trochlear articular surface and poorly restores the native groove orientation, and (2) the orientation of the prosthetic trochlear groove and trochlear fill are different between MA and KA.

METHODS

Three-dimensional models of the femur were made from segmentation of preoperative Magnetic Resonance Imaging scans (MRIs) of ten subjects with isolated medial tibiofemoral osteoarthritis. In-house planning and analysis software kinematically and mechanically aligned a modern cruciate retaining femoral component and determined differences in parameters of the trochlear fit between native and prosthetic trochleae, and between KA and MA prosthetic trochleae.

RESULTS

The MA prosthetic trochleae did not fill (understuffed) the entire length of the native medial facet and the proximal 70% of the native groove and lateral facet, and oriented the trochleae groove 8° more valgus than native. The KA prosthetic trochleae understuffed the proximal 70% of the native trochleae, and had a groove 6° more valgus than native. The KA trochleae understuffed the medial facet distally and oriented the groove 2° less valgus and 3° more internally rotated than the MA trochleae.

CONCLUSION

MA and KA prosthetic trochleae substantially understuff and create a prosthetic groove more valgus compared to native trochlear anatomy, and they also differed between each other regarding trochleae stuffing and groove alignment. Although randomized trials have not shown differences in patellofemoral complications between KA and MA, a femoral component designed specifically for KA that more closely restores the native trochlear anatomy might improve patient reported satisfaction and function.

LEVEL OF EVIDENCE

Level 2 controlled laboratory study.