1 Introduction

Restoration of knee kinematics remains a fundamental objective of total knee arthroplasty (TKA), with a goal of improving pain and function in end-stage osteoarthritis. Mechanical alignment (MA) has traditional been considered the gold standard approach, aiming to achieve a neutral mechanical axis through standardized bone resections and ligament balancing. ^1–4. While MA has been shown to yield reproducible radiographic and functional outcomes, several studies have shown it does not consistently reestablish patient specific native tibiofemoral motion patterns. This limitation has contributed to growing interest in kinematic alignment ^5–7.

Kinematic alignment (KA) attempts to restore native joint line and limb alignment, resurfacing the femur and tibia in a fashion that maintains native soft tissue and ligament tension, minimizing the need for extensive soft tissue release. The technique emphasizes native kinematics rather than a uniform neutral alignment. This personalized technique results in unique technical challenges, including adjustments in component sizing and orientation to accommodate patient specific morphology ^8–10. Despite this, studies have demonstrated KA as a non-inferior approach to TKA compared to MA in varus knees, showing comparable complication rates, improved range of motion, and achieving patient satisfaction.^2,11

Valgus knee deformities, which account for approximately 10% of TKA cases, present unique anatomical and biomechanical challenge, such as lateral cartilage loss and posterolateral tibial bone deficiency ^12–14. These features can complicate intraoperative balancing and have been associated with increased rates of instability and revision.¹⁵ Given this consideration, surgeons have favored MA in valgus knee arthroplasty, as KA remains controversial. Critics argue that leaving the knee in residual valgus may predispose to progressive medial instability and component maltracking.¹⁶ Advocates for KA argue that maintaining native knee anatomy and minimizing ligament release may achieve more physiologic kinematics, in turn improving functional recovery.¹⁷

The purpose of this study was to evaluate early radiographic correction, clinical outcomes, complications, and patient reported outcome measures following manual KA-TKA in patients with valgus knee deformity.

2 Methods

This retrospective cohort study (Level IV evidence) was conducted following institutional review board approval. Patient who underwent primary total knee arthroplasty using a manual kinematic alignment technique by a single surgeon at a single institution from January 1st, 2021, until January 1st, 2025, were identified using relevant CPT for primary TKA (27446) and ICD-10 codes for valgus knee (M21.06). Inclusion criteria included adult patients (≥18 years) with radiographically confirmed valgus knee deformity undergoing primary TKA. Exclusion criteria included revision arthroplasty, post-traumatic arthritis, reimplantation, conversion procedures, and knees requiring hinge constructs due to gross ligament insufficiency. Valgus alignment was assessed on standing short-leg anteroposterior radiographs using the anatomical femorotibial angle as a surrogate for mechanical alignment, given the absence of long leg films. Ranawat classification was assigned based on the magnitude of coronal deformity both preoperatively and postoperatively. All measurements were performed by a single observer and inter-observer reliability was not assessed. Valgus deformity was defined using measured coronal alignment on standardized radiographs, with inclusion based on the presence of valgus alignment rather than a single fixed angular cutoff. Valgus knee alignment was determined using preoperative reports and radiographic measurements. Short angle radiographic images were analyzed and measured.

All procedures were performed using a manual calipered kinematic alignment technique with the Attune knee system, in which bone resections are verified to match implant thickness within ±0.5 mm, restoring each patient's native joint line and limb alignment without routine ligament release.¹⁰ The distal femur and tibia were resurfaced to reproduce pre-arthritic anatomy, including native posterior tibial slope and constitutional coronal alignment, with soft-tissue preservation unless instability required constrained implantation.

Data collected included patient demographics including age at time of surgery, sex, ethnicity, race, BMI, height, weight, medical history. Operative data collected included procedure details, fixation method, implant manufacturer, pre and postoperative distal femoral and proximal tibial angles, and pre and postoperative Ranawat classifications. Fixation strategy (cemented vs cementless) was determined intraoperatively based on bone quality, age, BMI, and implant stability. Post-operative data was collected for one year following surgery and included complications including revision, readmission, re-operative data, length of hospital stay, and range of motion. PROMIS physical and mental and Knee Injury and Osteoarthritis Outcome Score – Joint Replacement (KOOS JR) scores were collected for 2 years following surgery.

3 Results

A total of 178 primary manual KA-TKAs were reviewed, of which 29 met valgus criteria. Twenty-five knees were included in the final analysis after excluding hinge constructs and incomplete follow-up. Hinge constructs were excluded due to advanced ligament insufficiency. Baseline demographic characteristics, including patient age, sex distribution, and BMI, are summarized in Table 1.

Clinical outcomes are summarized in Table 2. Hospital length of stay averaged approximately two days, and postoperative complications were infrequent, with only one periprosthetic fracture observed (4%). The patient sustaining a periprosthetic fracture had a preoperative valgus deformity of 4.3°, corrected to 3.5° postoperatively and subsequently required intramedullary nailing 11 days after surgery. Functional recovery was favorable, as reflected by postoperative range of motion exceeding 120° at one year in nearly all patients. Majority utilized cementless fixation, specifically 76% (19/25). Hinge cases were excluded in this analysis. No postoperative instability events requiring bracing, reoperation, or revision were observed.

Preoperative Ranawat classifications included 11 class I, 12 class II, and 2 class III; all patients were classified as Ranawat I postoperatively (25/25). The average valgus correction was 11.2° ± 6.2 preoperatively to 4.1° ± 2.3 postoperatively. Component angles showed a distal femoral angle of 81.5° ± 3.3° pre-op and 83.7° ± 3.7° post-op (mean change +2.2° ± 3.8°); the proximal tibial angle pre-op averaged 86.3° ± 2.9°, and the post-op “proximal tibial angle” averaged 87.0° ± 2.2° (mean change +0.7° ± 3.4°).

A total of 10 patient PROMIS and KOOS JR scores were included in the analysis, with 15 patient scores being excluded due to incomplete data collection, not meeting the 2-year data collection requirement (10/25, 40%). The mean preoperative KOOS JR was 45.1 ± 24.2, which improved postoperatively to 57.0 ± 17.5 at 6 weeks, 64.1 ± 20.4 at 3 months, 68.3 ± 17.6 at 6 months, 69.5 ± 26.4 at 1 year, and 70.1 ± 18.8 at 2 years. Statistically significant improvement was seen at 6 months (95% CI 0.22–46.3, p = 0.048) and 2 years (95% CI 1.6–48.5, p = 0.039). Improvements at 6 weeks, 3 months, and 1 year were not statistically significant when compared to preoperative measurements (p = 0.28, p = 0.13, p = 0.10, respectively). Mean preoperative PROMIS Physical score was 41.8 ± 9.6, improving to 45.7 ± 8.5 at 6 weeks, 48.3 ± 8.5 at 3 months, 50.2 ± 8.9 at 6 months, 49.1 ± 9.6 at 1 year, and 47.4 ± 9.0 at 2 years. Statistically significant improvement was seen at 3 months (95 % CI 1.8–11.3, p = 0.013) and 6 months (95 % CI 4.5–12.4, p < 0.001). Improvements at 6 weeks, 1 year, and 2 years were not statically significant (p = 0.077, p = 0.084, p = 0.084, respectively). Mean preoperative PROMIS mental score was 52.5 ± 11.0, with postoperative means of 53.1 ± 9.3 at 6 weeks, 52.4 ± 9.6 at 3 months, 53.5 ± 9.7 at 6 months, 52.6 ± 8.9 at 1 year, and 51.4 ± 11.0 at 2 years. There was no statistical significance found between any measurements (p > 0.05). Fifteen patients lacked complete 2-year PROM data due to loss to follow up, no patients were excluded due to requiring revision or reoperation (see Table 3).

4 Discussion

The purpose of this study was to investigate the kinematic alignment technique for total knee arthroplasty in valgus knees and to assess whether represents a feasible surgical approach in the patient population. In this retrospective cohort review (Level IV evidence) of 25 valgus knees, manual kinematic alignment resulted in correction to Ranawat class I postoperatively in all cases. Functional recovery was found in all patients, with an average ROM of 126.0° at one year and complication rates were low at 4%, consisting of a single periprosthetic fracture. Three knees requiring hinge constructs were excluded due to severe ligament insufficiency, highlighting that KA may not be appropriate for all valgus phenotypes. Patient-reported outcomes further demonstrated functional benefits, with significant improvements in both KOOS JR and PROMIS Physical scores. Because no mechanically aligned comparator group was included, conclusions relative to MA should be interpreted in context.

The optimal alignment strategy in TKA remains a debated topic. Critics of the KA approach argue that its aim to preserve native knee anatomy and soft tissue balance may increase the risk of postoperative instability, particularly in valgus knees, where posterolateral tibial bone loss and medial collateral ligament laxity may predispose patients to postoperative instability. Sterneder et al. propose that MA, paired with standardized lateral soft tissue release, should remain the gold standard. They report reproducible outcomes with MA, including a mean postoperative hip–knee–ankle angle of 0°, improved ROM, had low revision rates (1.1%), and favorable patient-reported outcome scores, even in severe valgus deformities exceeding 20°.¹⁶ Their central argument is that leaving a knee in residual valgus, a common outcome with KA, risks progressive medial instability.

In contrast, our study found that KA in select valgus knees can yield comparable short term clinical outcomes without evidence of early instability. Mean ROM exceeded 120.0°, complication rates were low (4%), and improvement was seen in patient-reported outcome scores (KOOS JR and PROMIS) extending up to two years postoperatively. These findings suggest that a properly executed KA technique does not inherently compromise early stability in valgus knee arthroplasty. Nevertheless, this study's limited follow-up and relatively small cohort warrant cautious interpretation.

KA has been shown to yield outcomes comparable to MA in the general TKA population. In a 13-year follow-up study, Dossett et al. compared kinematically and mechanically aligned TKAs, in 88 patients and found no significant difference in reoperation rates (P = 0.66). Furthermore, although not statistically significant, patient satisfaction favored KA, with 96% satisfied compared to 82% in the MA cohort.¹⁸ Our findings are consistent with these observations, demonstrating low overall complication rates and meaningful improvements in PROMs and KOOS-JR scores at up to two years of follow-up.

Our study's results further show that the kinematic alignment technique may be a option even in patients with valgus deformities. Almaawi et al. demonstrated that constraining alignment to a neutral mechanical axis may distort native knee anatomy. Specifically, they reported that MA required average corrections of 3.3° in the medial proximal tibial angle (MPTA) and 3.2° in the lateral distal femoral angle (LDFA), whereas KA required only minimal correction—0.5° and 0.3°, respectively.¹⁹ This statistically significant difference highlights how MA forces substantial deviation from patient-specific anatomy, whereas KA more closely reproduces native morphology. Yamamoto et al. further support the functional benefits of restoring native alignment; their study found that patients undergoing KA demonstrated significant improvements in clinical outcomes, reinforcing that KA is a reliable technique across diverse patient populations.²⁰

These findings align with our results, showing low complication rates and improved PROM and KOOS-JR scores up to two years of follow-up. Although KA has not been universally adopted, multiple studies have concluded that it is comparable—and in some cases more beneficial—than MA in terms of patient-reported outcomes and implant survival ^20–23. Current AAOS recommendations similarly report high-quality evidence indicating no difference in functional outcomes or complications between KA and MA. However, given the inherent variability in patient knee morphology and the importance of precise preoperative assessment, personalization should be considered when determining alignment strategy. Integrating advanced technologies such as computer-assisted measurements and patient-specific instrumentation may further optimize KA application. Future multicenter studies with larger sample sizes and long-term follow-up are needed to better define composite outcomes and determine which patient subgroups may benefit most from this alignment philosophy.

Finally, there are a few additional details to consider when implementing a manual calipered technique for kinematic knee arthroplasty. It is important to note that the goal is to restore a patient's pre-arthritic anatomy. Therefore, the goal is to typically leave only a small degree of valgus, typically 1-3 degrees of residual valgus in most cases. When considering each millimeter of bone or cartilage roughly represents one degree of limb alignment, these patients are often undergoing 5-7 degrees of correction which results in a nearly straight limb. Studies of normal limb alignment have shown that it is rare for a person to have more than 3 degrees of native valgus. While a central tenet of kinematic knee arthroplasty is that ligaments don't contract, it is recognized that they can stretch. Therefore, in knees with attenuated ligaments other techniques or implants should be considered. For example, 3 of 28 cases in this small series required a hinge due to an attenuated MCL, demonstrating that a kinematic technique cannot be universally applied. While in most patients a small degree of residual valgus is cosmetically acceptable, it is important to discuss this with the patient preoperatively, so they understand the goal is to restore pre-arthritic alignment rather than strictly straighten the limb. The final consideration should be the patellofemoral joint. It should be kept in mind that as the valgus position of the femoral component increases, the trochlea is “aimed” more medially, which has the potential for affecting early patellar capture.

5 Conclusion

This study evaluated the use of kinematic alignment in primary total knee arthroplasty in patients with valgus knee deformity, a deformity traditionally fixed with mechanical alignment. We found kinematic alignment demonstrated favorable clinical and functional outcomes, with low complication rates and significant improvements in range of motion and patient reported clinical outcomes. These findings suggest that kinematic alignment demonstrates acceptable early outcomes and low short-term complication rates in a select cohort of patients with valgus knee deformity. While these findings support the feasibility of manual kinematic alignment in select valgus knees, continued investigation may further refine and inform its application.

Guardian/patient's consent

Given that this was a retrospective chart review study, consent was not required. IRB approval was requested, and this study was deemed exempt. No personal identifying information was recorded during this study, and all reported data was de-identified.

Credit author statement credit author statement

Jakub Gocal: Conceptualization, investigation, Writing - Original Draft, Writing - Review and Editing. Margaret Grossman.: Data curation, Writing- Original draft preparation, Methodology, Formal Analysis. David St. Etienne Jr: Conceptualization, Writing - Original Draft. Pranav Krishnan: Conceptualization, Writing - Review and Editing, Supervision. Nicholas Brown: Conceptualization, Writing - Review and Editing, Supervision.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.