Analysis of Trends in Orthopedic Knee Surgery—Key Findings on Total and Unicompartmental Knee Arthroplasty from a Leading Journal

Abstract

Purpose: This review examines the recent literature on total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA) published in the Knee Surgery Sports Traumatology and Arthroscopy (KSSTA) journal in 2023. The aim was to identify key research themes, advancements, and global contributions to knee surgery research. Methods: Articles published in KSSTA in 2023 were identified through a structured database search using the term “knee OR TKA OR UKA”. Inclusion criteria focused on primary studies, reviews, and case reports in English related to TKA or UKA. Data were extracted and synthesized thematically to analyze research trends and gaps. Results: The search yielded to 75 articles, 63 focused on TKA and 12 on UKA. Most contributions originated from Europe, followed by Asia and North America. Robotic-assisted TKA emerged as a significant advancement, enhancing surgical precision but requiring further validation through extended follow-up studies. Personalized implants showed potential for improved outcomes, though cost-effectiveness remains a concern. In UKA, slight overcorrection during alignment was associated with better functional results. Conclusions: The literature in the 2023 KSSTA highlights journal-specific trends and innovations in knee surgery. While techniques like robotic TKA and personalized implants are promising, further research is essential to standardize protocols and evaluate long-term impacts, emphasizing the need for sustained research efforts in knee orthopedics.

1. Introduction

Knee surgery, particularly total knee arthroplasty (TKA), has seen significant advancements over the past decades due to innovations in biomaterials and personalized treatments. As the rate of knee osteoarthritis and related degenerative conditions continues to rise with aging populations, these developments have become critical in improving patient outcomes and reducing recovery time. This review focuses on the latest trends and key findings published in the Knee Surgery, Sports Traumatology and Arthroscopy (KSSTA) journal in the field of knee orthopedics, emphasizing the integration of advanced technologies and materials.

One of the key trends in knee surgery is the evolution of materials used in implants. Traditional metal and polyethylene components are now being supplemented by advanced materials like ceramics and cross-linked polyethylene, which have shown enhanced wear resistance and biocompatibility. These materials not only improve the longevity of knee implants but also reduce the incidence of osteolysis, a common cause of implant failure [1,2].

Robotic-assisted TKA has become a key innovation, offering enhanced precision in lower limb alignment and joint line orientation due to the high precise component placement [3]. Furthermore, the patient-specific instrumentation (PSI) also uses advanced preoperative imaging techniques to create customized cutting guides that allow surgeons to tailor procedures to the patient’s individual anatomy. PSI has demonstrated significant improvements in implant positioning, crucial for reducing wear and enhancing the long-term success of knee replacements. However, a recent meta-analysis comparing PSI with conventional surgery has shown no difference in improvement of PROM’s (Patient Reported Outcomes Measurement), complication rate, OR-time and transfusion rate [4,5,6].

In addition, after a call for action, a tremendous effort in the improvement of research methods in orthopedics has been undertaken in recent years [7]. The KSSTA journal published a series of papers facilitating the use of best available methods to ensure highest research standards [8,9,10,11,12].

In summary, the integration of advanced biomaterials, minimally invasive techniques, and personalized treatments in knee orthopedics is leading to improved patient outcomes. These innovations are helping to reduce recovery times, improve implant longevity, and enhance the precision of surgical interventions, ultimately offering a more tailored and effective approach to knee joint preservation and replacement. To provide further insights and consolidate the most recent findings published in 2023, this review was performed to offer a comprehensive overview of emerging and well-established journal-specific trends and innovations in knee orthopedic surgery.

2. Materials and Methods

The primary aim of this analysis was to identify and summarize new insights related to knee orthopedics and focused on knee arthroplasty that were published in the KSSTA journal. The review aimed to provide an overview of cutting-edge developments in the field by narratively assessing the relevant literature, categorizing it into distinct themes, and highlighting key findings that could influence clinical practice or future research.

This review was conducted in adherence to a structured protocol, which was registered and published on the Open Science Framework on 3 November 2024. The protocol can be accessed at https://osf.io/pdmb9/files/osfstorage (accessed on 3 November 2024).

The approach followed established guidelines for conducting narrative reviews [13,14]. Since this review exclusively examined studies available in the public domain, ethical approval was not applicable. Nonetheless, strict compliance with ethical standards for research reporting and synthesis was observed to ensure transparency, integrity, and accountability throughout the review process.

2.1. Search Strategy

To identify the literature, research was conducted within the KSSTA electronic database. The use the search string “knee OR TKA OR UKA” to comprehensively capture studies related to TKA or UKA surgery. The initial search was conducted on 21 October 2024. The final search was conducted on 3 November 2024, encompassing articles published from 1 January 2023 through 31 December 2023.

2.2. Inclusion and Exclusion Criteria

The review included all primary research articles, case reports, review papers, and clinical studies published in KSSTA within the specified timeframe that focus on TKA or UKA procedures. Only articles published in English were considered. Articles were excluded if they did not primarily address surgical procedures involving TKA or UKA or lack relevant clinical information. Furthermore, commentary pieces, editorials, and studies conducted on animal or cadaver models were not considered. Additionally, studies were excluded if the full-text article was not available. Any discrepancies between reviewers will be resolved through discussion and consensus.

2.3. Data Extraction

All identified research was uploaded to EndNote v.20 (Clarivate Analytics, Philadelphia, PA, USA). Key details were extracted from each study including authorship, publication date, country, study design, and primary findings. Since the broad search term “knee OR TKA OR UKA” yielded all knee-related studies, the retrieved articles were organized into subgroups and categorized in separate Excel spreadsheets.

2.4. Data Synthesis

Given the anticipated heterogeneity in the included studies, a narrative synthesis was employed to present the findings. Studies were organized thematically based on categories identified during data extraction, such as surgical techniques, robotic-assisted surgery, personalized surgery and rehabilitation outcomes. This thematic analysis highlighted trends, identified research gaps, and suggested directions for future investigation within the domain of TKA and UKA surgery.

3. Results

3.1. Results of Study Selection

All search records were initially compiled using EndNote v.20, (Clarivate Analytics, Philadelphia, PA, USA). The initial search using the term “Knee OR TKA OR UKA“ yielded 367 articles. These results were screened step-by-step, following the PRISMA [15] guidelines, as shown in Figure 1. In the first step, 95 studies were excluded due to their focus on the shoulder (n = 26), hip (n = 41), or other unrelated research (n = 28). In the second step, an additional 16 studies were excluded, leaving 256 studies extracted to excel spreadsheets. Of these, 63 were categorized as related to TKA and 12 to UKA.

3.2. Distribution of Published Studies

Figure 2 illustrates the distribution of studies published in 2023 within the KSSTA journal that focus on TKA and UKA. These studies are categorized by country and continent, highlighting global research activity in this field.

The data indicate that the USA is the leading contributor, with 10 studies (TKA n = 7, UKA n = 3), followed by Germany with 7 (TKA n = 6, UKA n = 1), and Belgium with 7 studies (TKA n = 7). This emphasizes North America’s significant role in TKA and UKA research.

Europe presents a diverse research landscape, with Germany, Belgium, France, Austria, Denmark, Italy, Switzerland, the Netherlands, Turkey, UK, Spain, and Sweden. With a total of 44 studies, Europe as a total is the most productive continent in TKA- and UKA-related research published in the KSSTA journal.

Asia also shows considerable research output, particularly from Japan, Republic of Korea, followed by China. This reflects the growing importance of Asia in the global scientific community, especially in the field of knee surgery and related studies.

Oceania are represented by Australia and New Zealand, respectively, though their contributions are notably smaller compared to the major research hubs in North America, Europe, and Asia.

Overall, Figure 2 highlights the global distribution of research activities related to the knee, indicating that the majority of studies are concentrated in Europe, Asia, and North America. This distribution underscores the leading role these regions play in advancing the field of knee surgery and related disciplines.

The main topics of publications in 2023 were lower limb alignment, gap balancing, robotic-assisted TKA, implant design, personalized TKA, and revision TKA and UKA.

3.3. TKA

3.3.1. Alignment and Gap Balancing

The alignment of the prosthesis significantly affects postoperative stability and function; however, there are no recommendations in the literature regarding the specific distraction force applied during the preparation of both the extension and flexion gap. One study [16] demonstrated that both kinematic and functional alignments (FA) achieve comparable accuracy in the lateral distal femoral angle (LDFA) alteration and reconstruction of the medial femoral joint line. However, functional alignment provides the advantage of better correction of the medial proximal tibial angle (MPTA) and the lateral femoral joint line, resulting in more stable joint conditions.

Additionally, the FA technique proved beneficial for improved ligament balance in the knee [17]. This method achieved the highest proportion of balanced knees across all groups studied, indicating that FA is an optimal strategy for ensuring a well-balanced knee prosthesis.

Kinematical alignment has been introduced by Howell at the beginning of the last decade aiming the reconstruction of the natural knee according to the pre-arthritis stage as close as possible. Nowadays, there are three different approaches to follow: the unrestricted, restricted, and reversed kinematic alignment. Unrestricted kinematic alignment (unKA-TKA) was compared to mechanical alignment (MA-TKA) in terms of deviation of the prosthetic trochlear angle (PTA) [18]. A medial deviation of the Q-angle of 6° valgus was reported when unKA-TKA was performed. This deviation adversely affected patellofemoral kinematics and resulted in decreased patient satisfaction, similar to a misaligned trochleoplasty. Most patients with un-KA-TKA had a PTA positioned medially to the quadriceps vector (QV), further compromising kinematics. A 17-point lower Forgotten Joint Score (FJS) was found when the PTA is orientated medially suggesting that the PTA should ideally be oriented laterally to the QV.

Restricted kinematic alignment (rKA) sets some boundaries in component placement, such as a varus orientation between 85 and 92°, for instance, and still replicates native knee anatomy better than adjusted mechanical alignment (aMA) [19]. Finally, iKA, in contrast, starts with the preparation of the tibia first and the cutting on the femoral side is adjusted in accordance [19]. Clinical studies comparing restricted with unKA are still missing. A study examined the distribution of functional knee phenotypes of Japanese populations undergoing TKA and investigated whether restricted kinematic alignment (rKA) achieves an anatomically neutral alignment. In 114 TKA cases, patients were classified into functional knee phenotypes based on preoperative and postoperative angles. Results indicated that rKA aligned the joint line more accurately parallel to the ground (72% within ±3°) compared to mechanical alignment (27%), although clinical outcomes were similar across all groups [20]. The accurate placement of femoral components is crucial. Research shows that aligning the distal medial and proximal medial femoral condyles within 1 mm of the patient’s pre-arthritic femoral joint surface can potentially lead to better outcomes in the FJS, OKS, and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) after one year [21]. This fine-tuning can significantly improve functional outcomes and minimize postoperative discomfort.

In addition to precise component placement, surgeons must consider the specific challenges of TKA in patients with posttraumatic osteoarthritis (PTOA). Studies demonstrate that functional outcomes and pain relief are generally inferior in PTOA patients compared to those with osteoarthritis. Complication rates are also higher in PTOA-TKA. Therefore, surgeons should thoroughly inform patients about the potential risks and differences in outcomes compared to TKA performed for osteoarthritis [22].

More recently another alignment strategy has been discussed, the so-called ground kinematically aligned technique introduced by Matsumoto et al. [23]. In this approach, alignment is achieved by simulating the femoral and tibial cut lines based on full-length standing coronal radiography of the lower limb, which includes the calcaneus to ensure a neutral relationship to the ground mechanical axis (MA). In this method, the femoral angle (FA) is first defined as the angle between the hip-to-knee MA and a line perpendicular to the femoral distal cut. For patients with varus osteoarthritic knees, the tibial proximal cut is then adjusted to match the femoral angle, compensating for the natural valgus or varus angles of the femur, while a navigation system measures the tibial angle (TA) from the ankle center. This approach aims to achieve a physiological alignment that closely replicates natural knee kinematics, providing an alternative to traditional kinematic alignment strategies.

Post-TKA gait is a crucial indicator of functionality. In one study [24], patients who received iKA exhibited a gait pattern two years postoperatively that more closely resembled that of healthy control subjects than those with aMA. This is attributed to the more precise restoration of native limb alignment by following the kinematical alignment concept, enabling a more physiological knee load distribution.

Additionally, soft-tissue balancing techniques such as the flexion-first balancing method have the potential to improve postoperative outcomes. This method resulted in greater mobility in deep flexion and higher knee injury and Osteoarthritis Outcome Score (KOOS) compared to the classical gap balancing technique [25]. This underscores the importance of balanced ligament status for successful postoperative knee mobility.

Soft-tissue balancing is crucial to optimizing knee stability and functionality after TKA. Proper intraoperative joint gaps and ligament balancing significantly correlates with better results in KOOS sub-score two years postoperatively [26]. In conclusion, joint gap balance appears to have a greater impact on postoperative outcomes than prosthesis alignment alone.

Posteromedial capsulotomy may be a valuable option to widen the medial femorotibial gap during knee extension [27]. This technique improves ligament balance in posterior-stabilized TKA, particularly when intraoperative narrowing of the medial component gap is observed.

Another important procedure for optimizing ligament balance is the partial or complete posterior capsular release (PCR). A study [28] demonstrated that both partial and complete PCR may help increase the medial component gap in extension and prevent joint gap mismatch. Specifically, in cases with an increased varus angle at 0° of flexion, partial PCR offers an effective way to correct biomechanical imbalances without negatively affecting knee function.

A study of patients with constitutional varus deformity showed that ligament balance using multiple needle puncturing (MNP), also called pie crust technique, is primarily determined by constitutional alignment rather than medial soft-tissue contractures. In particular, in patients with a larger medio-lateral gap difference in extension, a higher incidence of MNP was observed in the anterior and posterior fibers of the superficial medial collateral ligament (sMCL) [29]. These findings highlight the importance of precise soft-tissue balancing in patients with varus deformity.

In the context of medial-pivot TKA (MP-TKA), differences in strain patterns of the sMCL and lateral collateral ligament (LCL) were observed [30]. The sMCL showed increased tension at low to mid-flexion, while the LCL was more stressed at high flexion.

These findings suggest that medial stability combined with lateral flexibility is critical for good postoperative outcomes, and lateral relaxation at deep flexion should be avoided during soft-tissue balance.

Further investigation into ligament forces in BCR-TKA (bicruciate-retaining) showed that changes in ligament tension before and after surgery provide valuable information for optimizing ligament balance. This contributes to the development of strategies that facilitate the restoration of deep knee flexion and improve prosthesis design [31].

In a retrospective comparative study, 363 knees that underwent mechanically aligned TKA with a medially stabilizing technique were analyzed. Patients were divided into two groups: a “tight medial” group and a “balanced” group. Analysis of PROMs and radiographic assessments revealed no statistically significant differences between the groups. Furthermore, there was no significant variation in joint line distance observed between the cohorts [32].

Moreover, the variability in bone resection demonstrates that the choice of a specific alignment strategy should be made on an individual basis. Simulations show that modern orthopedic surgeons can avoid biomechanically inferior alignments through preoperative planning and restore the most natural knee alignment possible [33].

3.3.2. Robotic-Assisted Surgery in Primary TKA

A key argument for robotic-assisted TKA (raTKA) is its superior precision in implant position compared to conventional surgery. High precision in component alignment has been observed with both image-free hand navigation and CT-based robotic technology [34,35]. This accuracy is essential for achieving a long-term stable and functional alignment of the prosthesis, which needs to be still proven in the near future.

One study highlights that intraoperative alignment measurements using the MAKO™ system yield higher HKA values (3.2°) and greater residual varus deformity compared to postoperative full-leg radiographs (FLR) (1.4°). Additionally, the mechanical medial proximal tibial angle (mMPTA) was higher in preoperative FLRs than in CT images. These differences underscore the role of FLR in refining alignment assessment and preventing overcorrection in TKA for varus osteoarthritis [36].

The long-term clinical outcomes of raTKA remain unclear. Although patients with a robotic-assisted knee prosthesis showed improved FJS compared to conventional techniques after one year, this difference was no longer significant at the five-year mark. [37,38]. Specifically, robotic-assisted technology offers advantages in restoring the original anatomy and coronal alignment, although differences in clinical outcomes after two years of follow-up were not significant [39]. However, in the long term, it is expected that the more precise component placement may reduce the risk of aseptic loosening and revisions. Another advantage of raTKA is the ability to pursue different alignment strategies. Studies have shown that kinematic alignment can be more precisely achieved with robotic systems, leading to improved restoration of natural knee anatomy [39]. However, kinematic alignment has also been associated with excessive valgus and internal rotation of the femoral component in some cases, underlining the need for a more individualized approach in terms of planning and adjustments during surgery [40]. The boundaries for implant placement are not clear yet.

Despite its numerous advantages, raTKA presents some challenges, particularly during the adoption phase. Surgeons face a learning curve, and operation time will be longer compared to conventional surgery [41]. RaTKA has been shown to reduce operative time for surgeons with high case volumes, whereas it increases operative time for surgeons with lower case volumes. Interestingly, factors such as surgeon case volume and patient selection (e.g., non-obese, female patients) significantly influence these outcomes. [42]. High volume centers are, in general, specialized centers, providing an optimized treatment path, which also impacts on outcome.

Robotic systems not only offer more precise implantations but also facilitate the collection of important intraoperative data that can contribute to improving future procedures [43]. Nonetheless, we are still facing the early stages of robotic technology in arthroplasty, and there remains significant potential for further advancements. Personalized alignment and implant positioning provide promising avenues for optimizing outcomes following TKA. Artificial intelligence will help to identify the most optimal implant position for the patient, executed with the help of robotic-assisted surgery, which will be recommended to the surgeon, based on the phenotype, bone loss, and soft tissue envelope.

Computer-aided surgery (CAS) in TKA achieves more precise alignment. In one study, CAS-guided FA proved to be a reliable method for compensating for extreme bony morphologies and achieving a balanced knee, with soft-tissue release required in only 14.5% of patients [44]. This technique can reduce the need for invasive soft-tissue manipulations while still achieving optimal kinematic outcomes.

3.3.3. Implant Design

A key aspect of TKA is ligament balance, as it influences the stability and function of the knee joint postoperatively. The use of verasense sensor-assisted TKA did not lead to significant improvements in ROM, reoperation rates, or functional outcomes compared to manual balancing techniques [45]. However, sensor usage was associated with a lower rate of manipulations under anesthesia, underscoring the importance of precise measurement of ligament tensions and joint pressure for optimal outcomes.

Aside from the most frequently used PS and CR design in TKA, the medial pivot shift design has also gained popularity over the last years, aiming to better mimic natural knee kinematics. Medial pivot TKA, with or without the preservation of the PCL, result in similar clinical outcomes regarding ROM, patient-reported outcomes, and radiographic assessments after two years [46]. This suggests that both techniques are viable options, with the choice depending on individual anatomy and surgeon preference.

The importance of the PCL when using a medial pivot shift design was studied recently. A medial congruent-posterior cruciate ligament resected (MC-PCLX) group was compared with the medial congruent-posterior cruciate ligament retained (MC-PCL) group. The MC-PCLX group had a greater ROM; however, patient satisfaction was higher in the MC-PCL group. Additionally, gait analysis showed that the MC-PCL group experienced lower forefoot pressure when ascending a 30° incline, which more closely resembled normal gait patterns compared to the MC-PCLX group [47].

Similarly, when comparing posterior-stabilized and cruciate-substituting designs, clinical outcomes were comparable at six months, indicating that different approaches can lead to similar results [48]. Cruciate-retaining prostheses offer the advantage of eliminating the needs for a femoral box, potentially minimizing bone resection. Attention needs to be paid to the flexion gap when using the CR design in order to avoid overstuffing causing a reversed anterior translation of the femoral component during knee flexion.

Different prosthesis designs influence postoperative kinematic outcomes. When comparing fixed-bearing (FB) and mobile-bearing (MB) implants, both designs demonstrated stable kinematics, although their rotational movements and translations during the sit-to-stand test differed [49]. While FB prostheses showed a higher prevalence of a medial pivot mechanism, however, both designs led to similar clinical outcomes.

Cemented MB prostheses more notably reduced lateral polyethylene wear compared to FB prostheses, potentially increasing the longevity of the prosthesis [50]. However, longer follow-up is required to better understand the clinical significance of these wear patterns.

The question of whether to perform patella resurfacing during TKA remains a topic of debate. Studies have shown that patients with preoperative patellofemoral arthritis have a higher risk of postoperative anterior knee pain (AKP) if patella resurfacing is not performed [51,52]. In particular, for patients with advanced patellofemoral arthritis (Iwano stage 3 or 4), patella resurfacing during TKA is recommended to reduce the risk of reoperation and persistent AKP. Patella resurfacing in conjunction with or without lateral capsula release does not show any effect on AKP and functional outcomes [53]. This suggests that patella resurfacing alone is sufficient to reduce AKP, without the need for additional soft tissue intervention, providing patella mobility is preserved.

Studies show that patella scores two years postoperatively were better with the gap-balancing technique compared to the measured resection technique. Although the difference in patella scoring was small and clinically insignificant, both techniques effectively improved gait and functionality [54]. The gap-balancing technique demonstrated higher patella scores and greater external rotation of the femoral component, indicating its effectiveness in clinical practice. Furthermore, the estimated risk of requiring a TKA is approximately 5%, but the likelihood of undergoing TKA increases with the first five years following a tibial plateau fracture [54].

The use of antibiotic-loaded bone cement (ALBC) in TKA is considered a cost-effective practice, particularly in single-payer healthcare systems like Canada’s [55]. Despite potential cost increases, ALBC remains an economical choice to prevent infections and improve long-term prosthesis survival rates.

For patients requiring revision surgery after TKA, the 1.5-stage exchange arthroplasty offers an acceptable long-term survival rate [56]. The use of autoclaved femoral components and new polyethylene inserts proved effective in preventing aseptic loosening.

Reconstruction of the extensor mechanism allograft (EMA) following extensor apparatus injury during TKA demonstrated good functional outcomes [57]. Although septic revisions can impair knee function, no increased risk of reinjury or infection was observed. This technique provides a reliable option for restoring functionality after extensor mechanism damage.

3.3.4. Personalized TKA

The personalization of TKA aims to replicate the pre-osteoarthritic anatomy, laxity, and biomechanics of the knee as closely as possible. This approach often requires a departure from the traditional dogma of flush anterior femoral cuts to achieve individualized anatomical restoration of the anterior femoral compartment. The goal is to strike an optimal balance between clinical efficacy and economic sustainability [58]. A key role in this context is played by the constitutional sagittal alignment, which serves as the basis for personalization on the coronal plane. This alignment, based on healthy knee conditions, facilitates an individualized adjustment and can help create optimal biomechanical conditions [59].

Recent studies indicate that customized TKA approaches offer significant advantages. Among patients who received a personalized TKA combined with “personalized alignment”, the satisfaction rate after a follow-up period of at least two years was 94%. Additionally, 89% of patients met the PASS criteria for the Oxford Knee Score (OKS), and 85% for the FJS. These results surpass the published outcomes for off-the-shelf (OTS) TKA prostheses, suggesting that personalized approaches may tend to deliver better postoperative outcomes [60].

Both implant systems, customized individually made (CIM) and OTS-TKA, improved patients’ function, pain, and health-related quality of life. According to one study patients with CIM-TKA showed better results in demanding activities, as measured by High-Activity Arthroplasty Score [61]. These differences suggest that customized approaches may provide an additional advantage in performing demanding movements.

3.3.5. Revision TKA

Preoperative planning, especially for revision TKA (RTKA), is very important to better assess bony defects. The use of 3D-CT segmentation to predict tibial or femoral defects has proven superior to standard 2D radiography, as it allows for a more accurate estimation of defect volume. This technique helps to better anticipate intraoperative challenges and optimize surgical planning [62]. Such advancements in imaging technologies could support updated classification systems for RTKA in the future, helping the surgeon to choose the most appropriate implant and constraint.

One of the proven methods for addressing severe femoral and tibial metaphyseal bone defects in RTKA is the use of cones or sleeves. Cones provide reliable fixation and have been shown to be safe and effective. Studies indicate that TMC demonstrate excellent mid- to long-term clinical and radiological outcomes, with a promising 8-year survival rate for both the cones and the implant components [63]. This underscores the importance of this technology in successfully managing complex revision cases where conventional methods may not be sufficient. The long-term stability and biocompatibility of TMC make them a preferred choice in revision arthroplasty. The alternative to cones is the usage of sleeves. A meta-analysis revealed a higher incidence rate of intraoperative fracture when using sleeves. Postoperative fracture and infection occurred more often when using cones [64].

The need for revision following TKA can be triggered by various factors, such as bone defects, poor implant placement, infection, periprosthetic fractures, or arthrofibrosis. It has been shown that revisions due to arthrofibrosis can result in significant improvements in ROM, with patients reporting a mean ROM improvement of over 25 degrees, although PROMIS scores for physical function and pain indicated moderate functional impairment [65].

Interestingly, one study shows that patients with contralateral pes plano-valgus deformity have an increased risk of aseptic revision within four years after primary TKA. This foot deformity affects gait and kinematics and may thus be a risk factor for higher revision rates [66].

In terms of clinical outcomes, research indicates that patients treated at hospitals with differing in revision rates following primary TKA tend to achieve comparable clinical results. This finding suggests that revision rates alone may not be a reliable measure of clinical outcome after primary TKA [67]. Furthermore, a meta-analysis revealed that, when appropriately selected and indicated, both Condylar Constrained Knee (CCK) and Rotating Hinge Knee (RHK) prostheses provide similar survival rates and clinical outcomes in revision TKA [68].

3.3.6. Pre- and Postoperative Care

Patient expectations regarding the outcomes of TKA encompass both knee-related and general health aspects. Studies show that the fulfillment of these expectations is significantly correlated with patient satisfaction following surgery. Surgeons should, therefore, ensure that patients are well-informed about the realistic potential benefits and limitations of TKA to avoid unrealistic expectations and promote higher satisfaction [69]. Comprehensive preoperative education about realistic expectations has proven effective in improving pain management (as measured by the WOMAC pain score) and satisfaction more than one year after surgery. This effect was particularly pronounced in patients with higher central sensitization inventory (CSI) values [70].

Moreover, preoperative assessment is critical to the success of TKA. Studies indicate that the Clinical Frailty Scale (CFS) is a better predictor of postoperative complications and functional outcomes than the Modified Frailty Index (MFI) or Charlson Comorbidity Index (CCI). This emphasizes the need for a thorough evaluation of preoperative functional status to optimize the planning and management of TKA [71].

Patient optimism has a positive correlation with preoperative joint function and postoperative outcomes after TKA, whereas pessimism is associated with poorer results. Assessing general personality traits prior to surgery can help identify pessimistic patients who are at a higher risk of suboptimal postoperative outcomes. In such cases, cognitive-behavioral interventions may be beneficial in enhancing optimism and thus improving postoperative results [72].

Although patients using cryo-compression with Game Ready achieved notably greater knee extension during the first two weeks of intervention compared to those following the usual care protocol, this improvement was likely attributed to random variation. Beyond this period, no significant differences between the groups were observed, either during or after the intervention ended [73].

In terms of postoperative prevention of thromboembolic events, aspirin has been shown to be safe and effective, performing on par with the main anticoagulants used after TKA. This supports aspirin as a viable alternative for preventing complications [74].

3.4. Unicondylar Knee Arthropalsty (KA)

The outcomes and survival rates following medial UKA are influenced by several factors. Knees with restored pre-arthritic alignment, as well as those with relative overcorrection after medial UKA, demonstrate better mid-term outcomes and higher survival rates compared to knees with under correction of their pre-arthritic alignment. These findings support the practice of restoring or relatively overcorrecting the pre-arthritic alignment to achieve optimal results after medial UKA [75]. Specifically, residual varus axis alignment following medial UKA led to a significant improvement in functional knee scores two years postoperatively, with better return to sports and recreational activities compared to patients with postoperative neutral mechanical axis [76].

Either fixed or mobile bearing implants can be used. Clinically, there does not seem to be a difference; however, the size of wear particles differs between mobile and fixed bearing design.

A retrospective matched-pairs analysis compared fixed-bearing and mobile-bearing components in lateral UKA. The results indicated that the short- to mid-term survival rate was lower for the mobile-bearing group compared to the fixed-bearing group. Aside from this difference, both procedures demonstrated equivalent clinical outcomes. Therefore, the fixed-bearing design should be favored in treating isolated lateral osteoarthritis [77].

Long-term follow-up of patients who underwent three-dimensional image-based robotic-assisted UKA (raUKA) revealed high implant survival rates and good to excellent clinical outcomes over a period of at least ten years. However, unexplained pain was the most common reason for revisions following raUKA [78]. Factors influencing functional outcomes after medial UKA also include the precise alignment of the implants. Functional outcomes can be improved through correct coronal alignment. Minor clinical improvements were observed when the tibial implant was positioned closer to the preoperative tibial deformity rather than strictly restoring the Cartier angle [79]. Additionally, the risk of postoperative patellofemoral incongruence in patients with under correction of pre-arthritic coronal alignment was twice as high as in patients whose pre-arthritic alignment was restored or overcorrected. Interestingly, patellofemoral incongruence did not negatively impact functional outcomes, although mid-term Kujala scores were worse in this patient group [80].

Interestingly, it has been shown that biomarkers such as interleukin-6 (IL-6) and vascular endothelial growth factor A (VEGF-A) may play a role in predicting postoperative outcomes after UKA. Lower synovitis scores and higher IL-6 and VEGF-A levels were significantly associated with better outcomes after UKA. These insights may help in better identifying suitable candidates for UKA in clinical practice [81].

A study involving 1000 knees with anteromedial OA, treated with both preoperative and postoperative medial UKA, demonstrated that CPAK phenotype I had the highest prevalence preoperatively (45.0%). Postoperatively, CPAK phenotype II was most prevalent (53.3%). However, it was also observed that 45.1% of knees maintained their preoperative CPAK phenotype after medial UKA. The variation in CPAK phenotypes among patients with OA poses a significant challenge in the treatment of osteoarthritis using medial UKA [82].

Regarding revision rates and postoperative satisfaction, patients who underwent medial UKA revision due to unexplained pain had worse postoperative PROM scores compared to patients who were revised due to aseptic loosening. The likelihood of significant improvement after surgery was lower in these patients [83]. In a comparison of UKA and high tibial osteotomy (HTO) patients, UKA patients showed better OKS over time, as well as higher pain and satisfaction scores. However, these differences were below the established minimal clinically important differences, suggesting that HTO may represent an equivalent treatment option from the patient’s perspective in certain indications [84]. Interestingly, a research group from Denmark demonstrated in prospective multicenter cohort studies that patient-reported outcomes following primary knee arthroplasty were similar across hospitals with varying revision rates, despite differences in patient and implant selection. While radiographic classifications and surgical incidence were higher in the low-revision hospital, these variations did not align with typical revision risk factors. This indicates that differences in patient selection alone cannot fully explain the observed variation in revision rates. The findings imply that revision rates may be influenced more by thresholds and indications for revision surgery, rather than outcomes from primary procedures, highlighting the need for further investigation into these factors [67,85].

4. Discussion

The aim of this review was to summarize the current journal-specific trends in orthopedic knee surgery published in the Journal “Knee Surgery Sports Traumatology and Arthroscopy in 2023” related to TKA and UKA. The main findings of this review relate to the amount of papers per content, the focus of those papers, and the geographical distribution per content.

Geographical distribution shows that the European region seems to contribute most to the journal, with Germany, Belgium, France, and Italy being the dominant countries. This is not surprising taking the size of their orthopedic communities into account. Relevant contributions also come from the USA and three Asian countries—Japan, China, and the Republic of Korea—underlining their position in the field (Figure 1). Those findings are in line with findings from a trend analysis, showing a stable and growing contribution for Japan and the Republic of Korea and in increasing growth of contributions to the field from China [86].

The ongoing debate around modern TKA approaches highlights the complexity of optimizing alignment, surgical technique, and postoperative outcomes. Achieving optimal alignment is critical for prosthesis function and long-term joint stability. FA appears particularly promising, as it not only restores the medial and lateral joint lines but also improves ligament balance, and thereby enhancing biomechanical stability [16,17]. This is especially relevant for varus-aligned knees. However, the absence of detailed recommendations for the forces applied during gap balancing suggests a need for standardization in this area.

Van de Graaf et al. showed that FA leads to slight changes in coronal limb alignment without significantly affecting the native JLO. FA starts with a kinematic plan and achieves soft-tissue balance without major alteration of native joint anatomy. These results support the idea that both KA and FA preserve native knee anatomy, with FA offering the benefit of balanced gaps [87]. In an RCT, Young et al. reported that FA required significantly fewer soft-tissue releases than MA (only 16% vs. 65%). Despite this, PROMs at two years were similar between both groups. However, FA was associated with slightly higher KOOS subscale scores, suggesting some benefits in specific patient subgroups. Altogether, the recent evidence supports van de Graaf’s conclusion that FA improves intraoperative soft-tissue balance without leading to major differences in mid-term PROMs compared to MA [88].

One of the most notable innovations in TKA is the use of raTKA, which improves the precision of prosthetic component positioning. Robotic systems have demonstrated advantages particularly in restoring anatomical alignment and joint kinematics [34,35,37]. A recent meta-analysis focusing on the NAVIO system found improved alignment accuracy with robotic assistance, although short term complication rates and functional scores were similar to conventional TKA, indicating that improved radiographic results do not necessarily translate into clinical benefits at 1–2 years [89].

A large national database analysis by Maman et al. showed that raTKA was associated with fewer postoperative complications and shorter hospital stays compared to navigation-guided procedures, without increasing costs. This suggests that although both methods offer high precision, raTKA may provide slight advantages in perioperative outcomes [90].

Nevertheless, some studies report that functional improvements (e.g., FJS) may diminish over the long term, underscoring the need for extended follow-up to validate these benefits [37,38]. Despite this, robotic systems enable complex alignment strategies and patient specific adjustments. Challenges like prolonged surgical time and a steep learning curve depend on case volume and surgeon experience [41,42]. This is consistent with the findings from the NAVIO meta-analysis, which concluded that robotic assistance improves alignment but yields comparable short-term clinical outcomes. In other words, 2025 data confirm the 2023 conclusions—imageless raTKA enhances radiographic accuracy without altering short-term function [89].

Regarding ligament balancing and sensor-assisted techniques, current evidence suggests limited clinical benefits compared to manual techniques. For example, while the verasense sensor did not significantly improve range of motion or reoperation rates, it reduced the frequency of manipulation under anesthesia, highlighting the value of accurate ligament tension measurement [45]. Specific prosthetic techniques such as medial pivot designs and PCL retention allow for individualized approaches based on anatomy [46,47]. A meta-analysis by Vermue et al. found no significant differences in functional scores, ROM, complication rates, or revisions between PCL-retaining and PCL-sacrificing medial pivot TKAs. The results suggest that both strategies yield comparable outcomes and can be selected based on surgeon preference [91].

Personalization in TKA aims to replicate the pre-arthritic anatomy as closely as possible. Evidence indicates that personalized implant designs lead to better clinical outcomes and higher patient satisfaction compared to off-the-shelf prostheses [60,61]. Vogel et al. confirmed significantly improved functional outcomes at two years with customized TKA, with similarly high satisfaction levels. These findings reinforce the idea that patient-specific instrumentation and alignment offer clinical benefits equal to or exceeding standard approaches [92].

Kizaki et al. found that PSI does not lead to better PROMs, shorter surgery times, or fewer complications than conventional TKA. Although PSI may slightly reduce blood loss, this does not translate into lower transfusion rates [4]. Customized TKA can enhance function in demanding activities and provide anatomically accurate reconstruction, but the higher cost and increased planning complexity remain relevant limitations.

In revision TKA, accurate preoperative planning using advanced imaging like 3D-CT segmentation is crucial for evaluating bone defects. Techniques using metal cones and sleeves have yielded good mid- to long-term outcomes, especially in cases with severe bone loss [62,63]. Brenneis et al. used volumetric CT to quantify tibial defects and showed that preoperative defect size correlates with the need for cones or sleeves. These findings support the use of 3D imaging, which aligns well with intraoperative needs and enhances fixation planning more effectively than 2D methods [93].

Material selection plays an important role, as sleeves are associated with a higher risk of intraoperative fractures [64]. Zitsch et al. reported excellent outcomes for both cones and sleeves; at around 3.5 years of follow-up, survival was 96%, osseointegration 98%, and knee society scores were equivalent. There were no differences in aseptic survival rates. These results confirm Longo’s earlier findings that both methods are highly effective in managing tibial bone loss in revision TKA [94]. Reconstruction of the extensor mechanism has been shown to restore function after septic revision [57]. However, 237 such reconstructions were analyzed and reported only about 54% five-year survival, with many patients experiencing extensor lag or infection. They concluded that both allografts and synthetic meshes often result in persistent dysfunction and are frequently associated with complications. Together, the studies from 2023 and 2024 underline the challenges and often poor outcomes of these difficult cases [95].

Regarding patient outcomes, preoperative factors such as functional classification and psychological disposition are highly relevant. The CFS has been shown to be a strong predictor of complications and postoperative function [71]. In a randomized trial, Lee et al. demonstrated that patient education and expectation management improved satisfaction and pain scores at one year, though differences were less pronounced at two years. This suggests that educational interventions are especially beneficial in the early postoperative phase, particularly in patients with high levels of catastrophizing [96]. Moreover, patients with optimistic expectations tend to report better outcomes, supporting the use of psychological interventions in selected cases [72].

In UKA, mid-term outcomes and survival depend on pre-arthritic alignment and correction strategies. Slight overcorrection or restoration of the pre-arthritic alignment leads to better results than under-correction. Knees with residual varus alignment after UKA show better function and higher activity levels compared to those corrected to a neutral axis [76,77]. A 2025 study on the Oxford Domed Lateral implant reported only 74.8% ten-year survival due to dislocations and progression of arthritis. The authors recommend abandoning the mobile-bearing design in favor of fixed-bearing implants for lateral UKA [9].

Fixed-bearing designs are now preferred for lateral compartment OA due to higher mid-term survival, although functional outcomes remain similar [78]. Ruderman et al. reported 96.1% ten-year survival and 94% satisfaction for lateral raUKA, confirming excellent long-term results [97].

raUKA shows good long-term survival and outcomes, but unexplained pain remains a leading cause for revision [84]. Proper coronal alignment and implant positioning improve function. While overcorrection reduces the risk of patellofemoral incongruence, it may lower Kujala scores—though this does not appear to impact function significantly [80,81].

Emerging biomarkers such as IL-6 and VEGF-A might help predict outcomes in UKA. Higher values have been associated with improved postoperative results, offering potential for better patient selection [82]. Bayoumi et al. confirmed the phenotypic diversity in anteromedial OA, with 25 preoperative phenotypes reducing to 17 after UKA. These findings support the view that anteromedial OA encompasses a heterogeneous group with varying correction responses [98]. CPAK-based phenotyping before and after UKA shows that some patients retain their original phenotype, complicating predictions and standardization [83].

When comparing UKA and HTO, UKA patients report slightly better OKS and satisfaction scores. However, differences are marginal, indicating that HTO remains a valid option in selected cases [85]. Importantly, revisions for unexplained pain yield worse PROMs than revisions for aseptic loosening, highlighting the need for careful diagnostic evaluation [84]. A large registry study by Debopadhaya et al. reported that UKA is associated with fewer complications, shorter hospital stays, and a higher likelihood of outpatient surgery compared to HTO—especially relevant in young, active patients [99].

Multicenter cohort data suggest that institutional factors, such as revision thresholds, influence UKA revision rates independently of clinical outcomes. Consistent PROMs across hospitals with different revision policies imply that revision criteria may be more responsible for the differences than surgical performance itself [67,85]. This points to the importance of standardized revision criteria and further research into long-term UKA outcomes.

Recent studies confirm that medial UKA preserves native knee kinematics better than TKA. Copp et al., using dynamic video analysis, showed that TKA results in altered movement patterns (e.g., less varus, tibial internal rotation), while UKA patients retain more natural motion symmetry [100]. Finite element studies also indicate that TKA leads to 30% reduction in femoral bone strain, compared to only 4–8% for UKA or partial replacements [101].

New meta-analyses and RCTs showed little difference in survival or loosening rates between cemented and cementless TKA. Liu et al. analyzed 16 RCTs with 2358 patients and found no difference in infection, loosening, or revision. Only functional scores showed slight, time-dependent variation [102]. Zhao et al. confirmed that a new 3D-printed cementless TKA performs similarly to cemented systems after one year [103].

In UKA, cementless fixation has clear advantages. Za et al. summarized data from over 3500 UKAs and found excellent five- and ten-year survival (96% and 93.6%), fewer reoperations, and similar clinical scores [104]. Rahman et al. showed via radiographic analysis that tibial fixation is far better in cementless designs (55–81% vs. only 25% in cemented UKAs) [105]. These findings confirm that modern cementless implants—especially in UKA—offer excellent fixation and may even reduce bone pain.

Implant design significantly influences long-term outcomes. A retrospective analysis by Hariri et al. showed that fixed-bearing lateral UKAs had higher survival than mobile ones [77]. Fricka et al. reported similar findings for medial UKA, with fixed bearings showing slightly better five-year survival and fewer revisions [106]. Apostolopoulos et al. analyzed tibial components and found that all-polyethylene designs distribute stress more effectively than metal-backed components [107]. A meta-analysis also showed no survival advantage for expensive modular metal tibial trays. Altogether, recent data highlight the importance of implant coatings (e.g., microporous titanium, hydroxyapatite) and design (e.g., fixed vs. mobile, all-poly vs. metal) for integration and long-term success [105].

This narrative review has several limitations that may impact the generalization and robustness of its results and conclusion. The primary limitation is its exclusive focus on literature published in the KSSTA journal. While this targeted approach offers a concentrated perspective on contemporary research, it inherently excludes potentially relevant and influential studies from other journals. Consequently, the findings may lack comprehensiveness, and broader trends in the field could remain unexamined. This restriction to a single journal limits the ability to compare or contextualize the results within the wider body of orthopedic research.

Another significant limitation is the inclusion of only English-language studies. This introduces a potential language bias, as important findings published in non-English journals may have been overlooked.

Additionally, the review relies on narrative synthesis rather than a meta-analytical approach. While this allows for thematic exploration and the identification of research gaps, it does not provide the statistical rigor or quantitative assessment of effect sizes that are possible with meta-analysis. This may reduce the ability to draw strong, evidence-based conclusions and limits the reproducibility of the findings.

The search strategy also presents limitations. Although the use of a broad term like “knee OR TKA OR UKA“ aimed to capture all relevant studies on TKA or UKA surgery, it may have led to the inclusion of studies with varying relevance. The reliance on a single database further compounds the risk of incomplete literature retrieval, as studies indexed elsewhere may not have been considered.

Lastly, the review excluded certain types of articles, such as commentary pieces, editorials, and studies conducted on animal or cadaver models. While these exclusions aimed to maintain a focus on clinical relevance, they also may have overlooked valuable insights, particularly in preclinical innovations or expert opinions that could inform future research directions

5. Conclusions

This narrative review of the literature in the 2023 KSSTA on TKA and UKA highlights recent advancements and evolving journal-specific trends in knee surgery research. The review reveals significant contributions from Europe, Asia, and North America, with a focus on established techniques such as robotic-assisted surgery, functional alignment, and personalized implant designs. While robotic TKA shows promise in achieving precise anatomical alignments, further longitudinal studies are necessary to confirm sustained functional improvements. Personalized implant approaches have also demonstrated potential for improved patient satisfaction; however, economic and logistical challenges persist. For UKA, the studies underscore the benefits of slightly overcorrected alignment strategies for optimal function. To advance TKA and UKA outcomes, future research should prioritize standardized protocols, long-term follow-ups, and the integration of emerging biomarkers to better predict surgical success.