Restricted kinematic alignment leads to uncompromised osseointegration of cementless total knee arthroplasty

Prediction of coronal alignment in robotic-assisted total knee arthroplasty with artificial intelligence

INTRODUCTION

Robotic-assisted technologies provide the ability to avoid soft tissue release by utilizing more accurate bony cuts during total knee arthroplasty (TKA). However, the ideal limb alignment is not yet established. The aim of this study was to predict postoperative Coronal Plane Alignment of the Knee (CPAK) using corresponding native bony measurements.

METHODS

This study analyzed a retrospective cohort of 530 primary robotic-assisted TKAs. Machine learning was utilized to predict appropriate target lateral distal femoral angles (LDFA) and medial proximal tibial angles (MPTA). Normalization of LDFA and MPTA alignments was performed using the min-max scaler operation on the training set with feature range [-1, 1] and repeated separately for the input and target distributions. A neural network of hidden dimensions (16, 8, 4) was trained via supervised learning to predict planned LDFA and MPTA values from preoperative LDFA and MPTA measurements.

RESULTS

The model converged after 104 epochs and batch size 4 with mean squared error ±1.82°. The model's regression agrees with the hypothesized change in preoperative to planned coronal alignment: valgus measurements are translated to neutral/aligned targets while varus alignments are translated to varus alignment of lesser severity. Evaluative statistics demonstrate this method for planning knee morphologies is significantly more accurate than making predictions about the mean (RMSE 1.440; R-squared 0.444; Nash Sutcliffe 0.579).

CONCLUSION

This study's model provides accurate predictions for target knee alignment morphologies. Future work is warranted to evaluate this method's usefulness for planning robotic TKA.

Early radiographic evaluation of an anatomic porous tantalum tibia: A prospective, multi-center, non-randomized clinical study

BACKGROUND

Excellent survival rates have been reported for total knee arthroplasty (TKA) performed with cementless porous metal tibial components. More data, however, is necessary to assess the survival and radiographic results of modular implants with anatomic designs. The purpose of this study was to investigate the early radiographic, survival, and clinical outcomes of a cementless tantalum metal tibial implant with a modular anatomic component.

METHODS

An early follow-up of a prospective, multi-center, non-randomized outcomes study of patients who received cementless tibial implants in primary TKA between 2018 and 2020 was performed. A total of 148 implants were available for review. Radiographs, the Forgotten Joint Score (FJS-12), Oxford Knee Score (OKS), patient satisfaction, and adverse events were collected for at least two-years post-operative. A minimum of two-years follow-up was available for 119 patients and evaluated for progressive radiolucent lines (RLLs).

RESULTS

The mean follow-up was 2.2 ± 0.6 years, and the two-year implant survival rate was 98.59% (95% C.I.: 94.46, 99.64) with no aseptic revisions during the follow-up period. Progressive tibial RLLs were present in 3.4% of patients at two-years follow-up, but were all less than 2 mm with all combined RLLs less than 4 mm. The FJS-12 and OKS all significantly (p < 0.0001) increased and exceeded their respective minimal clinical important differences, and 93% of patients were satisfied at two-years follow-up.

CONCLUSION

This study supports excellent survivorship, clinical and patient reported outcomes using cementless, fixed bearing TKA with minimal complications at early follow-up. Further follow-up is necessary to confirm the sustainability of the clinical outcomes and to evaluate mid- to long-term survivorship.

Comparison of Outcomes Between Functionally and Mechanically Aligned Total Knee Arthroplasty: Analysis of Parallelism to the Ground and Weight-Bearing Position of the Knee Using Hip-to-Calcaneus Radiographs

Background: The objective of this study was to compare the outcomes between patients undergoing mechanically aligned conventional total knee arthroplasty (MA-CTKA) and functionally aligned robotic-arm-assisted TKA (FA-RTKA). Methods: We reviewed a prospectively collected database of consecutive patients who underwent primary total knee arthroplasty (TKA) for knee osteoarthritis between June 2022 and May 2023. Patients were divided into two groups-MA-CTKA (n = 50) and FA-RTKA (n = 50)-based on the introduction of a robotic-arm-assisted system during the study period. The hip-knee-ankle (HKA) angle, joint line orientation angle (JLOA) relative to the floor, and weight-bearing line (WBL) ratio were evaluated using full-length standing hip-to-calcaneus radiographs to compare the conventional mechanical axis (MA) and the ground mechanical axis (GA) passing through the knee joint between the groups. Clinical outcomes were also compared between the two groups. Results: There were no significant differences in the postoperative HKA angle between the groups, due to discrepancies in the targeted alignment strategies (FA-RTKA: 2.0° vs. MA-CTKA: 0.5°; p = 0.001). The postoperative JLOA in the FA-RTKA group was more parallel to the floor, whereas the MA-CTKA group showed a downward angulation toward the lateral side (0.6° vs. -2.7°; p < 0.001). In the FA-RTKA group, the GA passed through a neutral position when accounting for the calcaneus, while the MA-CTKA group showed a more lateral GA position (48.8% vs. 53.8%; p = 0.001). No significant differences in clinical outcomes were shown between the FA-RTKA and MA-CTKA groups, with the FA-RTKA group demonstrating higher Forgotten Joint Scores and a greater range of motion (all p < 0.05). Conclusions: Functionally aligned TKA demonstrated improved joint line parallelism to the floor and more neutral weight-bearing alignment in the GA compared to mechanically aligned TKA. These findings indicate a more balanced load distribution across the knee, which may contribute to the superior clinical outcomes observed in the functionally aligned group.

Excellent results of restricted kinematic alignment total knee arthroplasty at a minimum of 10 years of follow-up

PURPOSE

While restricted kinematic alignment (rKA) total knee arthroplasty (TKA) with cemented implants has been shown to provide a similar survivorship rate to mechanical alignment (MA) in the short term, no studies have reported on the long-term survivorship and function.

METHODS

One hundred four consecutive cemented cruciate retaining TKAs implanted using computer navigation and following the rKA principles proposed by Vendittoli were reviewed at a minimum of 10 years after surgery. Implant revisions, reoperations and clinical outcomes were assessed using knee injury and osteoarthritis outcome score (KOOS), forgotten joint score (FJS), patients' satisfaction and joint perception questionnaires. Radiographs were analyzed to identify signs of osteolysis and implant loosening.

RESULTS

Implant survivorship was 99.0% at a mean follow-up of 11.3 years (range: 10.3-12.9) with one early revision for instability. Patients perceived their TKA as natural or artificial without limitation in 50.0% of cases, and 95.3% were satisfied or very satisfied with their TKA. The mean FJS was 67.6 (range: 0-100). The mean KOOS were as follows: pain 84.7 (range: 38-100), symptoms 85.5 (range: 46-100), function in daily activities 82.6 (range: 40-100), function in sport and recreation 35.2 (range: 0-100) and quality of life 79.1 (range: 0-100). No radiological evidence of implant aseptic loosening or osteolysis was identified.

CONCLUSION

Cemented TKA implanted with the rKA alignment protocol demonstrated excellent long-term implant survivorship and is a safe alternative to MA to improve patient function and satisfaction.

LEVEL OF EVIDENCE

Level IV, continuous case series with no comparison group.

Functional Alignment Achieved a More Balanced Knee After Robotic Arm-Assisted Total Knee Arthroplasty than Modified Kinematic Alignment

Background: The aim of this study was to evaluate the balance in extension and flexion achievable after total knee arthroplasty (TKA) using a modified kinematic alignment (KA) plan and the subsequent balance achievable after adjusting the component based on the functional alignment (FA) principle. Methods: This retrospective cohort study included 100 consecutive patients who underwent primary TKA for knee osteoarthritis through an image-based robotic system in a single center between October 2021 and February 2022. Whether modified KA or FA could achieve a balanced knee was evaluated by assessing the ligament balance in the medial and lateral compartments using a robotic system at extension and 90° flexion. Balance was defined as a difference of ≤2 mm between the compartments. Component positioning was adjusted within limits based on the functional positioning principles to achieve balance. Implant positioning and balance in extension and 90° flexion were compared between the modified KA plan (n = 100) and after FA adjustments (n = 100). Results: FA achieved significantly better balance in extension (FA, 99.0% vs. modified KA, 86.0%; p = 0.001) and flexion (98.0% vs. 43.0%; p < 0.001) than the modified KA plan. The mean difference in gap balance in extension (FA, 0.1 mm vs. modified KA, 0.6 mm; p = 0.001) and flexion (0.1 mm vs. 2.3 mm; p < 0.001) was also significant between the two techniques. The femoral component was positioned more externally rotated relative to the transepicondylar axis (FA, 2.5° vs. modified KA, 0.0°; p < 0.001) to obtain balanced targets. There were significant improvements in the patient-reported outcome measures between preoperative and postoperative assessments two years after TKA (all p < 0.05). Conclusions: FA consistently achieved superior balance in both extension and flexion following TKA compared with modified KA without altering the soft tissue envelope, leading to significant improvements in clinical outcomes at the two-year follow-up.

Novel technique for achieving the under-correction of native tibial varus in calipered restricted kinematically aligned total knee arthroplasty - A validation study

PURPOSE

Restricted kinematic alignment (rKA) TKA is relatively newer technique for achieving an overall under-corrected limb alignment. The present study aims to provide an easy and reproducible technique for achieving calipered rKA-TKA (crKA-TKA) using routine instrumentation.

METHOD

A prospective study was conducted including 30 patients (30 knees). All patients underwent crKA-TKA by the same surgeon. Pre-operatively all patients underwent long film standing radiographs, and coronal angles were measured to plan tibial bony cuts and the femoral axis angle (FAA) to restore tibial varus under correction and native distal femoral anatomy, respectively. Intra-operatively while taking tibial cuts, the alignment rod was noted to be always pointing towards the "third metatarsal" of the ipsilateral foot.

RESULTS

30 patients underwent total knee replacement with crKA technique. Angular corrections were satisfactory with all patients reaching the target MPTA of 87.48 ± 0.78 and LDFA of 90.301 ± 2.66 as planned, with an overall under-corrected limb alignment. HKA was achieved within a target of < ± 3 degrees of the native knee (3.56 ± 1.29). Post-operative radiological parameters were checked by two separate observers with excellent intra-class correlation coefficients.

CONCLUSION

The present study validates a novel intra-operative technique of confirming an under-corrected native tibial varus while performing crKA-TKA. The radiological outcomes of the study confirm that with careful pre-operative planning, coronal angular targets were easily achievable with very less outliers. Study further establishes that this method of calipered technique in rKA-TKA using routine digital templating software and standard instrumentations is an alternative method of executing rKA.

LEVEL OF EVIDENCE

IV, Prospective case series.

The Viability and Success of Noncemented Kinematic Total Knee Arthroplasty

BACKGROUND

The prevalence of noncemented total knee arthroplasty (TKA) is increasing as personalized knee alignment strategies deviate from implanting components on a strict mechanical axis. This retrospective study evaluated the outcomes of 74 consecutive noncemented unrestricted kinematic TKA procedures.

METHODS

This study included 74 consecutive noncemented kinematic TKAs performed by one surgeon at a tertiary academic medical center from 2021 to 2023. The technique used was unrestricted femur-first caliper kinematic TKA. The outcomes included revision, pain scores, and radiographic measurements.

RESULTS

Of the 74 procedures performed, there were no revisions or readmissions for problems related to TKA. The mean follow-up was 17.6 months, with 74% of patients being followed up for more than 1 year postoperatively. On the day of surgery, postoperative measurements showed that the average tibial mechanical, distal femoral, and anatomic tibiofemoral angles were 3.3°, 7.7°, and 5.8°, respectively. 5 knees were observed initially with signs of radiolucency, which all resolved by the most recent appointment. None of the knees was radiographically loose. Of the patients, 65%, 19%, and 16% reported no pain, minimal pain, and some pain, respectively, at the 6-week follow-up visit. This improved to 78%, 19%, and 3% at the most recent follow-up.

CONCLUSION

Combining kinematic alignment with noncemented fixation showed excellent clinical and radiographic outcomes with short-term survivorship. Although the use of both kinematic alignment and noncemented TKAs has been controversial, these early data suggest that noncemented kinematic TKA is safe and effective.

Cementless, Cruciate-Retaining Primary Total Knee Arthroplasty Using Conventional Instrumentation: Technical Pearls and Intraoperative Considerations

Background

Total knee arthroplasty (TKA) is commonly indicated for patients with severe tibiofemoral osteoarthritis in whom nonoperative treatment has failed. TKA is one of the most commonly performed orthopaedic surgical procedures in the United States and is associated with substantial improvements in pain, function, and quality of life1-3. The procedure may be performed with cemented, cementless, or hybrid cemented and cementless components4,5. Cementless TKA utilizing contemporary implant designs has been demonstrated to have excellent long-term survival and outcomes in patients who are appropriately indicated for this procedure5-8. The preference of the senior author is to perform this procedure with use of a cruciate-retaining implant design when feasible, and according to the principles of mechanical alignment to guide osseous resection. It should be noted that nearly all recent studies on outcomes following cementless TKA utilize traditional mechanical alignment7-9. Alternative alignment strategies, such as gap balancing and kinematic alignment, have not been as well studied in cementless TKA; however, preliminary short-term studies suggest comparable survivorship with restricted kinematic alignment and gap balancing compared with mechanical alignment in patients undergoing cementless TKA10,11.

Description

Our preferred surgical technique for cementless TKA begins with the patient in the supine position. A thigh tourniquet is applied, and a valgus post is set at the level of the tourniquet. A flexion pad is also placed at 90°, with a bar at 20°. After sterile skin preparation and draping, a time-out is conducted, and the tourniquet is raised. The surgeon makes a medial parapatellar incision, which begins from 1 cm medial to the medial edge of the patella, extending from the tibial tubercle to 2 fingers above the proximal pole of the patella, using a knife and with the knee at 90° of flexion. Scissors are then used to find the fat above the fascia and dissect distally in the same plane. A knife is used to perform a high vastus-splitting, medial parapatellar arthrotomy. Pickups and scissors are then used to perform a partial medial synovectomy, and electrocautery is used to perform a medial peel. As the procedure progresses further medial, the infrapatellar fat pad is excised, followed by the anterior femoral synovial tissue. The surgeon then cuts through the anterior cruciate ligament footprint and origin with the knee flexed before sawing through the tibial spines to decrease the height of the tibial bone block. To prepare the femur, a step drill is inserted into the femoral canal, and the intramedullary alignment guide is placed with the distal femoral cutting guide set to 5° of valgus. The distal femoral cutting guide is then pressed firmly against the distal femur, making sure that the medial side is touching bone, and threaded pins are inserted in the cutting guide under power. The distal femur is then precisely sectioned with use of an oscillating saw equipped with a 21 mm x 90 mm x 1.27-mm saw blade. The surgeon focuses on initiating the cut at the cortices before proceeding further, to avoid cortical blow-out. The resultant cut is meticulously assessed for uniformity and levelness, employing both the alignment rod and the distal cutting guide for verification. Following this assessment, the pins and guide are removed, and any remaining femoral condylar osteophytes are delicately excised with use of a rongeur. The surgeon uses the femoral sizing guide, measures the size of the femur, and double-checks rotation in preparation for the remaining distal femoral cuts. The holes are then drilled to set the rotation for the 4-in-1 cutting guide. When applying the 4-in-1 cutting guide, care is taken to align the guide with the drilled holes in order to avoid inadvertent malrotation. The secure fixation of the block is ensured through the judicious insertion of 2 threaded pins under power at full speed, followed by a more controlled, slower securing process to avoid stripping the threaded pins. Subsequently, the anterior cut is made with the oscillating saw, again with a focus on initiating the cut at the cortices before proceeding further. The posterior cuts are then made in a controlled manner, employing a gentle bouncing technique to facilitate tactile feedback, and keen attention is given to cutting both the medial and lateral cortices of each of the posterior condyles. The anterior chamfer and posterior chamfer are similarly osteotomized. Subsequently, the 4-in-1 cutting guide is gently removed. To complete this phase of the procedure, a curved osteotome and mallet are employed to delicately extract the resected posterior condyles and remove posterior osteophytes as needed. The concave side of the curved osteotome is used with precision to meticulously trace the contours of the condyles, ensuring a precise result. The surgeon places a bump under the knee and extends it to check the medial collateral ligament, quadriceps tendon, patellar tendon, and posterior cruciate ligament to ensure they are intact. To make the tibial cut, the extramedullary alignment guide is placed, and the height of the slot is set to the level of the subchondral bone, aligning the rotation and coronal axis with the 2nd metatarsal. The tibial slope is also set at this step, with the goal of the resection matching the patient's native tibial slope. Matching is usually achieved by visual inspection of the trajectory of the cutting jig, although the stylus can also be utilized to confirm the appropriate tibial slope. The tibial cut is then completed with use of an oscillating saw. A single-sided reciprocating saw is then used to cut perpendicular to the plateau in the medial compartment while making sure not to extend the cut into the unresected portion of the intact tibial plateau. After removal of the medial plateau fragment, a lamina spreader is placed in the medial compartment; this process is repeated with a second cut in a similar fashion in the lateral compartment to create a triangular bone block that fully preserves the insertion of the posterior cruciate ligament. The medial and lateral menisci are resected, and the gaps are checked with use of a spacer block and alignment rod. The surgeon then sizes the tibia and uses their index fingers to feel both medially and laterally for overhang. An alternative approach is to fully expose the tibia in flexion and to size the tibia under complete visualization of the tibial margins. The tibial trial is then pinned in place after ensuring appropriate external rotation and optimal tibial coverage without overhang. The femoral and tibial trial components are placed, and the surgeon tests 7 things: (1) overall varus-valgus alignment in full extension; (2) degree of extension (specifically noting any amount of recurvatum or flexion contracture); (3) flexion to gravity; (4) anteroposterior stability in flexion (using manual anterior-posterior translation of the tibia); (5) varus-valgus stability in extension, mid-flexion, and full flexion with use of a manual dynamic varus-valgus stress test; (6) patellar tracking; and (7) component rotation. At this point, if any of the above checkpoints are not within acceptable tolerances, additional ligamentous releases or cuts may be performed. After the surgeon is satisfied with the positioning and stability of the trial components, the tibial preparation is completed by seating the feet of the tibial bushing into the tray and drilling the tibia, then punching out the keel. The pins and the tray are removed, the retractors are taken out, and the knee is extended. The surgeon then performs a pulse lavage of the femur and tibia with normal saline solution. The final components are opened, attached to the inserters, and placed in plastic coverings. The final tibial baseplate is inserted and impacted, followed by the femoral component in a similar fashion. We ensure that no soft tissue is incarcerated under the components after impaction. A trial bearing is placed, and the knee is extended. The joint space is then bathed in approximately 500 mL of sterile 0.35% povidone-iodine solution, followed by pulsatile lavage with 1 L of sterile isotonic sodium chloride solution without antibiotics. Stability is then tested again, testing the (7) checkpoints previously discussed. At this point, the only modification that can be made is an increase or decrease in the polyethylene component. Our belief is that any additional changes that require removal or repositioning of the previously implanted cementless femoral and tibial components warrant modification to the cemented TKA. Once satisfied with the stability of the real implants and the trial tibial articular surface, the final polyethylene component is inserted. Finally, the tourniquet is released. The surgeon then irrigates the wound again and closes the arthrotomy and skin. Our preference is to utilize a knotless barbed suture for the arthrotomy closure, followed by 2-0 Vicryl (Ethicon) for subcutaneous closure and 2-0 monofilament knotless barbed suture for skin closure. Some surgeons may choose to utilize a non-barbed suture; however, the use of a barbed suture has been shown to be faster and equally as effective as a non-barbed suture in a large meta-analysis of patients undergoing TKA12. Before final closure, the peri-incisional iodophor-impregnated antimicrobial incise drape is peeled back, and sterile 10% povidone-iodine is applied to the skin surrounding the incision. After subcuticular closure, adhesive skin glue is applied, followed by a waterproof dressing with the knee in flexion.

Alternatives

There are numerous nonoperative treatments available for tibiofemoral osteoarthritis. According to the 2021 American Academy of Orthopaedic Surgeons Management of Osteoarthritis of the Knee (Non-Arthroplasty) Clinical Practice Guideline, these include bracing, nonsteroidal anti-inflammatory drugs, acetaminophen, supervised exercise, patient education, weight loss, and intra-articular corticosteroid injection, among others13. When nonoperative treatment has failed, surgical treatment is then indicated for patients who continue to have symptoms that interfere with quality of life. Surgical treatments for tibiofemoral osteoarthritis primarily include unicompartmental knee arthroplasty or TKA, although proximal tibial osteotomy can be performed in some select cases according to disease severity and patient age. Each of these treatments is supported by the recent 2022 American Academy of Orthopaedic Surgeons Management of Osteoarthritis of the Knee (Non-Arthroplasty) Clinical Practice Guideline.

Rationale

Historically, the initial generation of cementless TKA implant designs was associated with relatively high rates of failure and poor clinical outcomes when compared with cemented arthroplasty14,15. However, there has been a renewed interest in cementless TKA with modern implant designs that incorporate newer biomaterials and porous coatings, with several recent studies demonstrating equivalence to cemented components at short-term, mid-term, and in some studies long-term follow-up4,6-8. In a recent study, Kim et al. demonstrated 98% survival free from revision for aseptic loosening at 22 to 25 years postoperatively7. In addition to at least equivalent long-term functional outcomes compared with cemented TKA, across multiple studies4,7, several short-term benefits of cementless fixation have been reported, including decreased costs and the avoidance of complications associated with cement debris8,16,17. Additionally, because there is no need to mix cement, there is a reduced burden of staff training and the elimination of possible variables that may affect cement integrity, in turn leading to improved operative efficiency and shorter operative time8. Bone cement implantation syndrome (BCIS) has been reported in up to 28% of cases of cemented TKA, and has a substantial risk of morbidity and mortality16. Cement debris can also remain in the knee if not retrieved after cement curing and prior to closure17, which is believed to cause discomfort and polyethylene wear. This complication is also avoided when cementless implants are utilized. Additional factors leading to our preference for cementless TKA, when indicated, have not yet been proven in the literature but are intuitive concepts. For example, the lack of cement leads to easier removal of components during revision surgery, and preservation of bone stock is important for performing a successful revision TKA.

Expected Outcomes

Cementless TKA using modern implant designs has excellent long-term outcomes at up to 25 years. Kim et al. evaluated 261 patients who underwent bilateral simultaneous TKA with random assignment of cemented and cementless components in contralateral knees. In that study, the mean age was 63 years and the mean follow-up was 24 years. The authors found 98% survival without revision for aseptic loosening at 25 years7. Similar findings have also been shown in older patients. For example, in a 2022 study by Goh et al., 7-year survivorship of modern implant designs was 100%. In that study of patients >75 years old, 120 cementless TKAs were matched in a 1:3 ratio with TKAs using cemented implants of the same modern design. Ultimately, no difference was seen in final postoperative scores or improvement in scores at 2 years. Seven-year survivorship free from aseptic revision was 99.4% for patients with cemented implants and 100% for patients with cementless implants4.

Important Tips

When deciding to perform cementless TKA, we consider a variety of preoperative factors, such as a history of osteoporosis, preoperative radiographs showing areas of bone loss, and a history of conditions associated with low bone mineral density.Intraoperative factors can also be considered when deciding between cementless and cemented implants. For example, tactile feedback when sawing can help to determine if bone is hard and sclerotic, which we believe indicates a better candidate for cementless implants.○ Note that during tibial preparation in a varus knee, you will typically have substantial sclerosis of the medial tibial plateau and relative osteopenia in the lateral tibial plateau because of longstanding differences in joint loading. This pattern is reversed in valgus knees.○ In general, we believe that the decision regarding bone integrity should be made primarily on the basis of the non-sclerotic side.With use of the techniques described in the present article, we do not have a preoperative alignment threshold or knee range-of-motion criteria for cementless TKA. More research is needed, however, on the long-term outcomes of cementless TKA when utilizing personalized alignment strategies, which may dictate the placement of components in substantial varus or valgus relative to the anatomic axis.When utilizing keeled tibial implants, we recommend drilling in reverse to pack the walls of the drill hole with bone rather than milling it out, which we believe increases support for bone growth.If there is almost no resistance while drilling in reverse, we believe this to be a poor prognostic sign for cementless TKA, and cementing should be considered.When sizing the tibial baseplate, the goal is to maximize the size of the tibia to fit on top of the rim of cortical bone without overhanging. Undersizing may increase the potential for implant subsidence.Osseous cuts with cementless components need to be perfect. Dome-shaped cuts are at risk for rocking and/or toggling, which could contribute to loosening over time.All 4 quadrants of the tibia should be checked to confirm a flat surface.Soft tissues can get incarcerated under the implant, which is of particular concern for cementless implants as this could impair osseous ingrowth.During trialing, ensure that the trial is completely flush on bone, which is an additional check to guard against toggling and/or loosening.When impacting the femoral component, we recommend applying an extension force so that the weight of the inserter does not pull the component into flexion; however, excessive extension force could also cause a fracture.

Acronyms and Abbreviations

IV = intravenousAP = anteroposterior.

Cementless Total Knee Arthroplasty: Is it Safe in Demineralized Bone?

There is concern for cementless total knee arthroplasty (TKA) in patients with decreased bone mineral density (BMD) due to the potential increase in complications, namely failed in-growth or future aseptic loosening. Some data suggest that advances in cementless prostheses mitigate these risks; however this is not yet born out in long-term registry data. It is crucial to expand our understanding of the prevalence and etiology of osteoporosis in TKA patients, survivorship of cementless implants in decreased BMD, role of bone-modifying agents, indications and technical considerations for cementless TKA in patients with decreased BMD. The purpose of this study is to review current literature and expert opinion on such topics.

Comparison of Outcomes in Obese Patients after Total Knee Arthroplasty with Neutral or Mild Varus: A Retrospective Study with 8-Year Follow-Up

OBJECTIVES

Residual varus after total knee arthroplasty (TKA) can affect functional outcomes, which may worsen in the presence of obesity. However, no studies were found to compare the outcomes of obese patients involving postoperative residual mild varus or neutral. The aim of this study was to compare postoperative complications and prosthesis survival, and functional outcomes for knees of obese patients with neutral or mild varus after TKA.

METHODS

We retrospectively reviewed 188 consecutive obese patients (body mass index ≥30 kg/m2) at our hospital who underwent TKA due to varus knee osteoarthritis from January 2010 to December 2015. The mechanical hip-knee-ankle axis angle was measured in all patients at admission and discharge. Knee functions were retrospectively assessed based on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, Knee Society Knee Score (KS-KS), Knee Society Function Score (KS-FS), Forgotten Joint Score (FJS), and range of motion (ROM). Continuous data were compared between knees with neutral or mild varus alignment using analysis of Student's t test or variance or the Kruskal-Wallis test as appropriate. For multiple comparisons of outcomes, we used Bonferroni-Dunn method to adjust p-values. Categorical data were compared using the chi-squared test.

RESULTS

Of the 156 knees in 137 obese patients who completed follow-up for a mean of 8.32 ± 1.47 years, 97 knees were corrected from varus to neutral and 54 knees were kept in mild residual varus. Patients with mild varus knees had significantly WOMAC (8.25 ± 8.637 vs. 14.97 ± 14.193, p = 0.009) and better FJS (86.03 ± 15.607 vs. 70.22 ± 30.031, p = 0.002). The two types of knees did not differ significantly in KS-KS, KS-FS, or ROM. Although one patient with a neutral knee had to undergo revision surgery, there was no significant difference between two groups.

CONCLUSIONS

For obese patients with osteoarthritis, preservation of residual varus alignment after TKA can improve functional outcomes without compromising prosthesis survival.

Restricted kinematically aligned total knee arthroplasty with an anatomically designed implant can restore constitutional coronal lower limb alignment

PURPOSE

Restricted kinematically aligned total knee arthroplasty (rKA-TKA) may not restore the constitutional varus alignment in most patients with knee osteoarthritis. This study aimed to investigate (1) the extent to which constitutional lower limb alignment can be restored by rKA-TKA using an anatomically designed implant and (2) which lower limb alignment parameters are associated with patient-reported outcome measures (PROMs).

METHODS

This study included 60 patients who underwent rKA-TKA using an anatomically designed implant. Radiographic alignment parameters, including mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), coronal hip-knee-ankle angle (HKA), coronal joint line obliquity (JLO), posterior tibial slope (PTS), single-leg standing knee flexion angle (KFA), sagittal JLO, and arithmetic HKA (aHKA), were evaluated preoperatively and postoperatively. The Western Ontario and McMaster Universities Arthritis Index (WOMAC) was used for clinical evaluation.

RESULTS

The mLDFA, MPTA, and aHKA showed no significant differences before and after surgery. Coronal HKA and PTS have significantly changed from 8.1 ± 8.7° and 9.9 ± 8.6° preoperatively to 3.5 ± 3.1° and 2.5 ± 2.0° postoperatively, respectively (p < 0.001 for each comparison). The postoperative WOMAC total score was significantly correlated with the KFA (r = 0.4063, p = 0.0034) and sagittal JLO (r = -0.3435, p = 0.0157). Postoperative KFA is a causal factor for the increased postoperative WOMAC total score (r = 1.416, 95% confidence interval: 0.491-2.342, p = 0.003).

CONCLUSION

rKA-TKA using an anatomically designed implant can restore constitutional coronal lower limb alignment, while postoperative KFA and sagittal JLO were associated with poor PROMs. Care should be taken for the postoperative KFA because it is a risk factor for poor PROMs.

LEVEL OF EVIDENCE

Level III, case-control study.

Restricted kinematic alignment is clinically non-inferior to mechanical alignment in the short and mid-term: A systematic review

BACKGROUND

In recent years, kinematic alignment (KA) is becoming a valid alternative to mechanical alignment (MA) in total knee arthroplasty (TKA). However, to avoid early failures, the restricted kinematic alignment (rKA) approach has been developed to restore native knee kinematics without reproducing extreme knee phenotype. This systematic review aims to evaluate clinical and radiological outcomes between rKA and MA for TKA.

METHODS

A systematic literature search was conducted following PRISMA guidelines on Pubmed, Scopus and Cochrane Library. The following search string was adopted: (((restricted kinematic) AND (mechanical)) AND (alignment)) AND (knee). We included studies that analyzed rKA versus MA in terms of clinical outcomes and complications with a minimum of 6 months of follow up. The following rKA- and MA-related data were evaluated: patient-reported outcome scores (PROMs), radiographic analysis of lower limb alignment, and complications. Criteria from the Methodological Index for Non-Randomized Studies were used to assess the methodological quality of the articles.

RESULTS

This systematic review included seven clinical studies with a total of 892 knees (471 for MA group and 421 for rKA group, respectively). Overall, post-operative PROMs were similar between rKA and MA. Moreover, rKA reached better results regarding Forgotten Joint Score and post-operative patient satisfaction. Finally, no higher complication rate was observed with the rKA approach.

CONCLUSION

The rKA aims to restore native knee kinematics, avoiding extreme deformities. Clinical outcomes are not inferior or even better for rKA compared with MA, without increasing the risk of short-middle-term implant failure. However, there is a high heterogeneity regarding the 'restricted' protocols used.

Postoperative full leg radiographs exhibit less residual coronal varus deformity compared to intraoperative measurements in robotic arm-assisted total knee arthroplasty with the MAKO™ system

PURPOSE

Robotic arm-assisted total knee arthroplasty (raTKA), currently a major trend in knee arthroplasty, aims to improve the accuracy of implant positioning and limb alignment. However, it is unclear whether and to what extent manual radiographic and navigation measurements with the MAKO™ system correlate. Nonetheless, a high agreement would be crucial to reliably achieve the desired limb alignment.

METHODS

Thirty-six consecutive patients with osteoarthritis and a slight-to-moderate varus deformity undergoing raTKA were prospectively included in this study. Prior to surgery and at follow-up, a full leg radiograph (FLR) under weight-bearing conditions was performed. In addition, a computed tomography (CT) scan was conducted for preoperative planning. The hip-knee-ankle angle (HKA), mechanical lateral distal femur angle (mLDFA), mechanical medial proximal tibial angle (mMPTA) and joint line convergence angle (JLCA) were measured in the preoperative and follow-up FLR as well as in the CT scout (without weight-bearing) by three independent raters. Furthermore, the HKA was intraoperatively assessed with the MAKO™ system before and after raTKA.

RESULTS

Significantly higher HKA values were identified for intraoperative deformity assessment using the MAKO system compared to the preoperative FLR and CT scouts (p = 0.006; p = 0.05). Intraoperative assessment of the HKA with final implants showed a mean residual varus deformity of 3.2° ± 1.9°, whereas a significantly lower residual varus deformity of 1.4° ± 1.9° was identified in the postoperative FLR (p < 0.001). The mMPTA was significantly higher in the preoperative FLR than in the CT scouts (p < 0.001). Intraoperatively, the mMPTA was adjusted to a mean of 87.5° ± 0.9° with final implants, while significantly higher values were measured in postoperative FLRs (p < 0.001). Concerning the mLDFA, no significant differences could be identified.

CONCLUSION

The clinical importance of this study lies in the finding that there is a difference between residual varus deformity measured intraoperatively with the MAKO™ system and those measured in postoperative FLRs. This has implications for preoperative planning as well as intraoperative fine-tuning of the implant position during raTKA to avoid overcorrection of knees with slight-to-moderate varus osteoarthritis.

LEVEL OF EVIDENCE

Level IV.

A Randomized Controlled Trial of Kinematically and Mechanically Aligned Total Knee Arthroplasties: Long-Term Follow-Up

BACKGROUND

The optimal alignment technique for total knee arthroplasty (TKA) remains controversial. We previously reported 6-month and 2-year results of a randomized controlled trial comparing kinematically versus mechanically aligned TKA. In the present study, we report the mean 13-year (range, 12.6-14.4) follow-up results from this trial.

METHODS

The original cohort included 88 TKAs (44 kinematically aligned using patient-specific guides and 44 mechanically aligned using conventional instrumentation), performed from 2008 to 2009. After institutional review board approval, the health records of the original 88 patients were queried. Revisions, reoperations, and complications were recorded. There were 26 patients who died, leaving 62 patients for follow-up. Of these, 48 patients (77%) were successfully contacted via phone. Reoperations and complications were documented. Furthermore, a battery of patient-reported outcome measures (PROMs) (including Western Ontario and McMaster University Index, Oxford Knee Score, Knee Injury and Osteoarthritis Outcome Score Junior, Forgotten Joint Score, Modified-Single Assessment Numerical Evaluation, and patient satisfaction) were obtained.

RESULTS

Of the original 88 patients in the study, 15 patients had at least one reoperation (17%) and 5 patients had undergone complete revision surgery (6%). There was no difference between the 2 alignment methods for major and minor reoperations (P = .66). The kinematically aligned total knees self-reported a nonstatistically significant (P = .16) improved satisfaction (96% versus 82%), but no difference in other PROMs compared to mechanically aligned TKAs.

CONCLUSION

Kinematically aligned TKA demonstrates excellent mean 13-year results, comparable to mechanically aligned TKA with similar reoperations, complications, and PROMs.

Coronal alignment in total knee arthroplasty: a review

Total knee arthroplasty (TKA) alignment has recently become a hot topic in the orthopedics arthroplasty literature. Coronal plane alignment especially has gained increasing attention since it is considered a cornerstone for improved clinical outcomes. Various alignment techniques have been described, but none proved to be optimal and there is a lack of general consensus on which alignment provides best results. The aim of this narrative review is to describe the different types of coronal alignments in TKA, correctly defining the main principles and terms.

Clinical and Radiographic Outcomes of Inversed Restricted Kinematic Alignment Total Knee Arthroplasty by Asia Specific (Huang’s) Phenotypes, a Prospective Pilot Study

Inverse restricted kinematic alignment (irKA) was modified from restricted kinematic alignment for total knee arthroplasty (TKA). This prospective single-center study aimed to evaluate the outcomes of irKA-TKA on all knee subtypes classified by Asia specific (Huang’s) phenotypes. A total of 96 knees that underwent irKA-TKA at one hospital between January 2018 and June 2020 were included, with 15 knees classified in Type 1, nine in Type 2, 15 in Type 3, 47 in Type 4, and 10 in Type 5 by Huang’s phenotypes. Outcomes were knee alignment measures and patient-reported satisfaction evaluated by the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and traditional Chinese version of the Forgotten Joint Score-12 (FJS-12). Follow-up was one year. Type 4 knee was most significantly corrected in all angles by irKA-TKA, followed by Type 2 and 3 knees. Type 5 and 1 knee were only significantly corrected in some angles. The correlation between FJS-12 and WOMAC was good at 6 months (Pearson correlation coefficient (r) = 0.74) and moderate at 6 weeks, 3 months, and 12 months during follow-up (r = 0.37~0.47). FJS-12 and WOMAC displayed comparable hip–knee–ankle angle cut-off value (4.71° vs. 6.20°), sensitivity (70.49% vs. 67.19%), specificity (84.00% vs. 85.71%), and Youden index (54.49% vs. 52.90%) in prediction of good prognosis. In conclusion, irKA-TKA corrects knee alignment in all knee types with increasing satisfaction for one-year follow-up. Knees with presurgical varus deformity are most recommended for irKA-TKA. Both presurgical scores of the traditional Chinese version of FJS-12 and WOMAC predict the prognosis of irKA-TKA.

Computer Navigation Assisted Restricted Kinematic Alignment Improves Short-Term Outcomes in Total Knee Arthroplasty: An Ambispective Cohort Study

OBJECTIVES

Mechanical alignment (MA)-total knee arthroplasty (TKA) has been challenged due to the excessive soft tissue release and the evidence of the clinical outcomes of computer assisted navigation is still limited. The aim of this ambispective cohort study was to: (i) investigate whether computer assisted navigation is capable to achieve restricted kinematic alignment (rKA)-TKA; and (ii) compare the short-term outcomes between rKA-TKA and MA-TKA.

METHODS

We retrospectively included 41 patients diagnosed with osteoarthritis who received MA-TKA between April 2019 and January 2021 and 43 patients diagnosed with osteoarthritis who received rKA-TKA were included in the prospective cohort from January 2021 to September 2021. Demographical, peri-operative, and radiological data were collected and compared. Unpaired two-sample t-test for continuous variables and χ2 test for categorical variables were used to compare various measurements in two groups. The patient-reported outcome measures at baseline, 10 days (T1), and 6 months (T6) after surgery were statistically analyzed by generalized estimating equation (GEE) models.

RESULTS

Fourty-one patients (45 knees) and 43 patients (48 knees) were included in the MA and the rKA group respectively. Three constitutional knee phenotypes (II, I, IV) were the commonest in our population. Navigation improved the surgical accuracy (1.5° vs 3.5°, p < 0.001) and precision (interquartile range 4.0 vs 2.0, p < 0.001) in the rKA group than the MA group. The changes in Knee Injury and Osteoarthritis Outcome Score 12 (KOOS12), EuroQol five-dimension questionnaire (EQ5D) from baseline to T1 and T6 for patients with on-target rKA were larger than on-target MA counterparts (26.053 vs 18.607, P < 0.001(KOOS12, T1) , 0.457 vs 0.367 p < 0.001(EQ5D, T1) ; 51.017 vs 46.896, P = 0.023(KOOS12, T6) , 0.606 vs 0.565, P = 0.01(EQ5D, T6) ). Patients with on-target rKA had better Forgotten Joint Score (FJS) at T1 (54.126 vs 40.965, P = 0.002) compared with on-target MA counterparts.

CONCLUSIONS

Computer assisted navigation achieved the level of accuracy required by rKA-TKA. rKA-TKA offered significantly better short-term outcomes than MA-TKA.

Restricted kinematic alignment in primary total knee arthroplasty: A systematic review of radiographic and clinical data

Introduction

Kinematic alignment (KA) has increased in popularity in recent years, becoming a viable alternative to MA with encouraging short- and mid-term follow-up results. Recently, the concept of restricted kinematic alignment (rKA) has been developed to restore native knee kinematics better, avoiding failure of coronal alignment. This systematic review aims to examine whether rKA improves outcome scores (PROMs) compared with MA and to evaluate the radiographic analysis of the lower limb alignment and the causes of complications and reoperations with the rKA approach.

Methods

A systematic literature search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines on the Pubmed/Medline, Scopus, Cochrane Library, and Embase databases. The following key terms were used: "restricted kinematic alignment, rKA, kinematic alignment, primary total knee arthroplasty, primary total knee replacement, TKA rKA, and TKR rKA." The initial screening identified 328 studies. Each eligible article was evaluated according to the inclusion criteria: studies with levels of evidence (LoE) 1 to 4, written in English, published through May 2022, and involving human subjects. Criteria from the Methodological Index for Non-Randomized Studies (MINORS) were used to assess the methodological quality of the articles.

Results

Six clinical studies were included in this systematic review. The study was registered in the International Prospective Registry of Systematic Reviews (PROSPERO). A total of 574 knees were included. After excluding patients due to loss of follow-up or missing data, 475 knees were analyzed. The following rKA-related data were evaluated: patient-reported outcome scores (PROMs), radiographic analysis of the lower limb alignment, and causes of complications and reoperations.

Conclusions

The rKA is an improved concept for restoring native knee kinematics, avoiding excessive coronal varus/valgus alignment. It provides equivalent or slightly better PROMs than MA without increasing the risk of short-middle-term implant failure. Clinical studies with extended follow-up are needed to confirm this trend.

Excessive Sagittal Slope of the Tibia Component during Kinematic Alignment-Safety and Functionality at a Minimum 2-Year Follow-Up

The aim of this study was to assess the safety and functional outcomes of excessive sagittal alignment in the unrestricted kinematic alignment technique for total knee arthroplasty (TKA). A retrospective, single-center study was conducted between 2018 and 2020, including patients undergoing primary TKA with a minimum 2-year follow-up. EOS imaging conducted before and after surgery was reviewed for overall alignment, and a number of measurements were taken, including sagittal tibial slope and other tibia and femur component positioning. Patients were interviewed and asked to fill out several questionnaires including a visual analog scale, the Oxford Knee Score, and the Knee Injury and Osteoarthritis Outcome Score. Overall, 225 patients (66.7%) had a sagittal tibial slope angle above 5° (excessive) and 112 (33.3%) patients had an angle under 5° (moderate). A significant improvement in pain and function scores was observed in both groups following the surgery (p < 0.001). There were no significant differences between the moderate and excessive groups in the average VAS, OKS or the various subtypes of the KOOS score. However, there was a slight but significant difference in the number of patients achieving MCID in KOOS symptoms. There were no cases of early failure or loosening. Unrestricted KA and the excessive sagittal alignment of the tibial component seem to be reliable and safe in terms of restoring daily function and alleviating pain after a minimum of 2 years following the surgery.

Minimum 2-Year Radiographic and Clinical Outcomes of Unrestricted Kinematic Alignment Total Knee Arthroplasty in Patients with Excessive Varus of the Tibia Component

Kinematic alignment (KA) total knee arthroplasty (TKA) has gained much attention in recent years. However, debate remains on whether restrictions should be made on the tibia cut. The purpose of this study was to assess the safety and functional outcomes of excessive varus cuts. A single-center, retrospective analysis of consecutive patients undergoing TKA between 2018 and 2020 who had a minimum 2-year follow-up was conducted. EOS™ imaging conducted before and after surgery was analyzed for overall alignment, as well as for tibia and femur component positioning on the coronal planes. Patients were interviewed and asked to fill several questionnaires, including the visual analog score, Oxford knee score, and knee injury and osteoarthritis outcome score. Overall, 243 patients (71.9%) had a coronal tibial plate angle under 5° (moderate) and 95 patients (28.1%) had an angle above 5° (excessive). There were no significant differences between the moderate and excessive groups in patient-reported outcomes, nor were there differences in the number of patients achieving the minimal clinical difference. There were no cases of catastrophic failure or loosening. Unrestricted KA and excessive varus of the tibial component appears to be safe and efficient in relieving pain and restoring function for a minimum of 2 years following surgery.

Current concept of kinematic alignment total knee arthroplasty and its derivatives

The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA, the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered ‘alignment outliers’ in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients’ own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients’ own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal.

Osteoarthritic and non-osteoarthritic patients show comparable coronal knee joint line orientations in a cross-sectional study based on 3D reconstructed CT images

PURPOSE

Recently introduced total knee arthroplasty (TKA) alignment strategies aim to restore the pre-arthritic alignment of an individual patient. The native alignment of a patient can only be restored with detailed knowledge about the native and osteoarthritic alignment as well as differences between them. The first aim of this study was to assess the alignment of a large series of osteoarthritic (OA) knees and investigate whether femoral and tibial joint lines vary within patients with the same overall lower limb alignment. The secondary aim was to compare the alignment of OA patients to the previously published data of non-OA patients. This information could be useful for surgeons considering implementing one of the new alignment concepts.

MATERIAL

Coronal alignment parameters of 2692 knee OA patients were measured based on 3D reconstructed CT data using a validated planning software (Knee-PLAN^®, Symbios, Yverdon les Bains, Switzerland). Based on these measurements, patients' coronal alignment was phenotyped according to the functional knee phenotype concept. These phenotypes represent an alignment variation of either the overall alignment, the femoral joint line orientation or the tibial joint line orientation. Each phenotype is defined by a specific mean and covers a range of ± 1.5° from this mean. Mean values and distribution among the phenotypes are presented and compared between two populations (OA patients of this study and non-OA patients of a previously published study) as well as between HKA subgroups (varus, valgus and neutral) using t tests and Chi-square tests (p < 0.05).

RESULTS

Femoral and tibial joint lines varied within patients with the same overall lower limb alignment. A total of 162 functional knee phenotypes were found (119 males, 136 females and 94 mutual phenotypes). Mean values differed between the OA and non-OA population, but differences were small (< 2°) except for the overall alignment (e.g. HKA). The distribution of OA and non-OA patients among the phenotypes differed significantly, especially among the limb phenotypes.

CONCLUSION

Differences between OA and non-OA knees are small regarding coronal femoral and tibial joint line orientation. Femoral and tibial joint line orientation of osteoarthritic patients can, therefore, be used to estimate their native coronal alignment and plan an individualized knee alignment.

LEVEL OF CLINICAL EVIDENCE

III.

Joint line is restored in robotic-arm-assisted total knee arthroplasty performed with a tibia-based functional alignment

INTRODUCTION

Functional alignment (FA) in total knee arthroplasty (TKA) has been introduced to restore the native joint line obliquity, respect the joint line height and minimize the need of soft tissue releases. The purpose of this study was to assess the intraoperative joint line alignment and compare it with the preoperative epiphyseal orientation of the femur and tibia in patients undergoing robotic-arm-assisted (RA)-TKA using FA.

MATERIALS AND METHODS

This retrospective study included a consecutive series of patients undergoing RA-TKA between February 2019 and February 2021. The joint line orientation of the femur and tibia in the three-dimensions was calculated and classified on preoperative CT-scans and compared with the intraoperative implant alignment. The tibial cut was performed according to the tibial preoperative anatomy. The femoral cuts were fine-tuned based on tensioned soft tissues, aiming for balanced medial and lateral gaps in flexion and extension.

RESULTS

A total of 115 RA-TKAs were assessed. On average, the tibial component was placed at 1.8° varus (SD 1.3), while the femur was placed at 0.8° valgus (SD 2.2) and 0.6° external rotation (SD 2.6) relative to the surgical transepicondylar axis. Moderate to strong, statistically significant relationships were described between preoperative tibial coronal alignment and tibial cut orientation (r = 0.7, p < 0.0001), preoperative femoral orientation in the coronal and axial planes and intraoperative femoral cuts alignment (r = 0.7, p < 0.0001 and r = 0.5, p < 0.0001, respectively). One case (0.9%) of slight tibial component varus subsidence was reported 45-days post-operatively, but implant revision was not necessary.

CONCLUSIONS

The proposed robotic-assisted functional technique for TKA alignment, with a restricted tibial component coronal alignment, based on the preoperative phenotype and femoral component positioning as dictated by the soft tissues, provided joint line respecting resections. Further studies are needed to assess long-term implant survivorship, patient satisfaction and alignment-related failures.

Specific case consideration for implanting TKA with the Kinematic Alignment technique

The Kinematic Alignment (KA) technique for total knee arthroplasty (TKA) is an alternative surgical technique aiming to resurface knee articular surfaces.The restricted KA (rKA) technique for TKA applies boundaries to the KA technique in order to avoid reproducing extreme constitutional limb/knee anatomies.The vast majority of TKA cases are straightforward and can be performed with KA in a standard (unrestricted) fashion.There are some specific situations where performing KA TKA may be more challenging (complex KA TKA cases) and surgical technique adaptations should be included.To secure good clinical outcomes, complex KA TKA cases must be preoperatively recognized, and planned accordingly.The proposed classification system describes six specific issues that must be considered when aiming for a KA TKA implantation.Specific recommendations for each situation type should improve the reliability of the prosthetic implantation to the benefit of the patient.The proposed classification system could contribute to the adoption of a common language within our orthopaedic community that would ease inter-surgeon communication and could benefit the teaching of the KA technique. This proposed classification system is not exhaustive and will certainly be improved over time. Cite this article: EFORT Open Rev 2021;6:881-891. DOI: 10.1302/2058-5241.6.210042.

Restricted Kinematic Alignment, the Fundamentals, and Clinical Applications

Introduction: After a better understanding of normal knee anatomy and physiology, the Kinematic Alignment (KA) technique was introduced to improve clinical outcomes of total knee arthroplasty (TKA). The goal of the KA technique is to restore the pre-arthritic constitutional lower limb alignment of the patient. There is, however, a large range of normal knee anatomy. Unusual anatomies may be biomechanically inferior and affect TKA biomechanics and wear patterns. In 2011, the leading author proposed the restricted kinematic alignment (rKA) protocol, setting boundaries to KA for patients with an outlier or atypical knee anatomy. Material and Equipment: rKA aims to reproduce the constitutional knee anatomy of the patient within a safe range. Its fundamentals are based on sound comprehension of lower limb anatomy variation. There are five principles describing rKA: (1) Combined lower limb coronal orientation should be ± 3° of neutral; (2) Joint line orientation coronal alignment should be within ± 5° of neutral; (3) Natural knee's soft tissues tension/ laxities should be preserved/restored; (4) Femoral anatomy preservation is prioritized; (5) The unloaded/most intact knee compartment should be resurfaced and used as the pivot point when anatomical adjustment is required. An algorithm was developed to facilitate the decision-making. Methods: Since ~50% of patients will require anatomic modification to fit within rKA boundaries, rKA is ideally performed with patient-specific instrumentation (PSI), intra-operative computer navigation or robotic assistance. rKA surgical technique is presented in a stepwise manner, following the five principles in the algorithm. Results: rKA produced excellent mid-term clinical results in cemented or cementless TKA. Gait analysis showed that rKA TKA patients had gait patterns that were very close to a non-operated control group, and these kinematics differences translated into significantly better postoperative patient-reported scores than mechanical alignment (MA) TKA cases. Discussion: Aiming to improve the results of MA TKA, rKA protocol offers a satisfactory compromise that recreates patients' anatomy in most cases, omitting the need for extensive corrections and soft tissue releases that are often required with MA. Moreover, it precludes the reproduction of extreme anatomies seen with KA.

True Kinematic Alignment Is Applicable in 44% of Patients Applying Restrictive Indication Criteria-A Retrospective Analysis of 111 TKA Using Robotic Assistance

Introduction: Image-based robotic assistance appears to be a promising tool for individualizing alignment in total knee arthroplasty (TKA). The patient-specific model of the knee enables a preoperative 3D planning of component position. Adjustments to the individual soft-tissue situation can be done intraoperatively. Based on this, we have established a standardized workflow to implement the idea of kinematic alignment (KA) for robotic-assisted TKA. In addition, we have defined limits for its use. If these limits are reached, we switch to a restricted KA (rKA). The aim of the study was to evaluate (1) in what percentage of patients a true KA or an rKA is applicable, (2) whether there were differences regarding knee phenotypes, and (3) what the differences of philosophies in terms of component position, joint stability, and early patient outcome were. Methods: The study included a retrospective analysis of 111 robotic-assisted primary TKAs. Based on preoperative long leg standing radiographs, the patients were categorized into a varus, valgus, or neutral subgroup. Initially, all patients were planned for KA TKA. When the defined safe zone had been exceeded, adjustments to an rKA were made. Intraoperatively, the alignment of the components and joint gaps were recorded by robotic software. Results and conclusion: With our indication for TKA and the defined boundaries, “only” 44% of the patients were suitable for a true KA with no adjustments or soft tissue releases. In the varus group, it was about 70%, whereas it was 0% in the valgus group and 25% in the neutral alignment group. Thus, significant differences with regard to knee morphotypes were evident. In the KA group, a more physiological knee balance reconstructing the trapezoidal flexion gap (+2 mm on average laterally) was seen as well as a closer reconstruction of the surface anatomy and joint line in all dimensions compared to rKA. This resulted in a higher improvement in the collected outcome scores in favor of KA in the very early postoperative phase.