- Research article
- Open access
- Published:
Preserving coronal knee alignment of the knee (CPAK) in unicompartmental knee arthroplasty correlates with superior patient-reported outcomes
Knee Surgery & Related Research volume 36, Article number: 1 (2024)
Abstract
Background
The optimal alignment target for unicompartmental knee arthroplasty (UKA) remains controversial, and literature suggests that its impact on patient-reported outcome measures (PROMs) varies. The purpose of this study was to identify the relationship between changes in the coronal plane alignment of the knee (CPAK) and PROMs in patients who underwent UKA.
Methods
A retrospective analysis of 164 patients who underwent UKA was conducted. The types of CPAK types categorized into unchanged, minor (shift to an adjacent CPAK type, e.g., type I to II or type I to IV), and major changes (transitioning to a nearby diagonal CPAK type or two types across, such as type I to V or type I to III). PROMs were assessed preoperatively and 1 year postoperatively using the Hospital for Special Surgery (HSS) scores, Knee Society (KS) scores, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Forgotten Joint Scores (FJS). Comparison was performed between patients who experienced and who did not experience any changes in the CPAK.
Results
Patients with preserved native CPAK alignment demonstrated significantly superior 1 year postoperative outcomes, with higher HSS, KS knee, and WOMAC pain scores (p = 0.042, p = 0.009, and p = 0.048, respectively). Meanwhile, the degree of change in CPAK did not significantly influence the PROMs, and patients who experienced minor and major changes in the CPAK showed comparable outcomes.
Conclusion
Preserving the native CPAK in UKA procedures is important for achieving favorable clinical outcomes at 1 year postoperative. The extent of change in the CPAK type exerted a limited impact on PROMs, thus emphasizing the importance of change in alignment itself.
Introduction
Unicompartmental knee arthroplasty (UKA) is an effective surgical treatment for medial compartment osteoarthritis, and it offers advantages such as reduced surgical exposure, preservation of cartilage in unaffected knee compartments, retention of the cruciate ligaments, and biomechanics similar to the natural knee [1,2,3,4,5]. It is widely accepted that alignment affects the survivorship of UKA, but there is no consensus regarding the optimal alignment strategies for UKA [6,7,8,9,10].
Despite the endeavor to preserve native knee kinematics, UKA introduces alignment alterations through restoration of the joint space reduced by cartilage loss [11]. Conventional UKA adopts a mechanical alignment concept, aiming to achieve a neutral mechanical axis [12, 13]. This approach is based on the observation that 70% of the weight-bearing forces exert pressure on the medial compartment, and this load increases as varus alignment increases [14]. Consequently, undercorrection of varus alignment in medial UKA may result in early wear and failure of the polyethylene insert [15]. Meanwhile, recent studies have preferred a kinematic or pre-arthritic alignment strategy, involving resection of the femur and tibia to resemble their pre-arthritic state, with an aim to restore the joint to its state before cartilage degeneration [16, 17]. The normal alignment of the knee is naturally in slight varus [18]. In case of patients with constitutional varus alignment, uniform correction to neutral alignment may not be desirable [17].
The coronal plane alignment of the knee (CPAK) classification method determines a patient’s constitutional alignment by measuring the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) [19]. By determining the difference between the MPTA and LDFA and then summing them up, the resultant arithmetic hip–knee–ankle angle (aHKA) and joint line obliquity (JLO) can be classified into nine types. These categories include a range of aHKAs (varus, neutral, and valgus) and JLO (apex distal, neutral, and apex proximal) [19]. The principles of mechanical or kinematic alignment in UKA can potentially integrate with the CPAK, as UKA may change the type of CPAK, thus potentially influencing patient outcomes [20]. To the best of our knowledge, none of the studies have yet explored the clinical outcomes of patients who underwent UKA in relation to a shift in the CPAK classification.
Therefore, the purpose of this study was to evaluate the patient-reported outcome measures (PROMs) in patients who underwent UKA, by comparing those with changes in the CPAK phenotype with those who did not experience any changes in the CPAK phenotype. In addition, a subgroup analysis categorized patients into those with a minor shift to an adjacent CPAK type and those with major extensive transitions in CPAK type. The aim of this subgroup analysis was to identify potential differences in PROMs based on the extent of changes in the CPAK. We hypothesized that patients with any CPAK change would exhibit poorer outcomes than those without, and that major changes would lead to worse outcomes than minor ones.
Materials and methods
Data collection
This study was approved by the institutional review board (IRB) of the authors’ institute (IRB no. 2005-180-1126). The requirement of obtaining informed consent was waived due to the retrospective nature of the study. We conducted a retrospective review of patients who underwent medial UKA between January 2005 and December 2020, with a minimum 1 year postoperative follow-up. The selection criteria for UKA included patients with medial knee pain due to medial compartment osteoarthritis or osteonecrosis (over Kellgren and Lawrence grade 2), a coronal plane deformity of less than 15 degrees, a flexion contracture of less than 15 degrees, intact cartilage in the lateral compartment and patellofemoral joint as confirmed by magnetic resonance imaging (MRI), and an intact anterior cruciate ligament, also verified by MRI.
Patient demographic data, including age, sex, and body mass index (BMI), were collected. Preoperative and postoperative 1 year MPTA and LDFA values from long-leg radiographs were measured. The MPTA was defined as the angle between the proximal joint line and the tibial mechanical axis, while the LDFA was defined as the lateral angle between the distal joint line and the femoral mechanical axis. Postoperative measurements were adjusted due to radiopaque femoral and tibial implants, along with the radiolucent polyethylene insert. The postoperative MPTA was defined as the angle between the line from the distal end of the femoral component to the center of the lateral joint space and the tibial mechanical axis. The postoperative LDFA was defined as the lateral angle between the line from the distal end of the femoral component to the center of the lateral joint space and the femoral mechanical axis. (Fig. 1). As both the medial tibial and femoral cartilages, along with the subchondral bones, are resected during UKA, we used the distal end of the femoral component in the medial compartment as a reference point for both MPTA and LDFA. This point contacts the polyethylene insert, serving as a reliable reference. The CPAK type was categorized based on the classification by MacDessi et al., with types I through IX representing the nine alignment phenotypes [19]. The PROMs of patients who retained their CPAK classification after surgery and who experienced changes in the CPAK classification after surgery were compared. Additionally, a subgroup analysis was performed by categorizing patients who experienced a shift in the CPAK classification: those with minor changes (shift to an adjacent CPAK type, e.g., type I to II or type I to IV) and those with major changes (transitioning to a nearby diagonal CPAK type or two types across, such as type I to V or type I to III).
PROMs, including the Hospital for Special Surgery (HSS) scores [21], Knee Society (KS) scores (knee scores and function scores) [22], the Western Ontario and McMaster Universities Arthritis Index (WOMAC) [23], and the Forgotten Joint Scores (FJS) [24], were documented both preoperatively and at 1 year postoperatively. Complications that necessitated revision surgery were also recorded until the final follow-up of each patient.
Surgical protocol
All UKAs were performed by two experienced surgeons at a high-volume tertiary hospital. A medial mini-parapatellar arthrotomy was performed (10 cm), followed by osteophyte resection. Medial release was performed only for the deep medial collateral ligament. Tibial resection was carried out using extramedullary guides to achieve matched mediolateral declination and anteroposterior tibial slope. The target for tibial resection was set at a thickness of 4 mm to achieve a minimum gap of 8 mm. Mediolateral inclination was adjusted by manipulating the distal end position of the extramedullary guide. In instances where the preoperative MPTA exhibited valgus alignment, the resection was aligned with the native mediolateral declination, as previously mentioned. Notably, the maximum MPTA was 92 degrees in this study, and instances of valgus MPTA were rare. Distinct techniques for distal femoral resection were employed based on the implant used during surgery. For one approach, an intramedullary guide was used, and the distal femoral cut was determined by the valgus angle established on the basis of preoperative standing long-leg radiographs (MIS Miller/Galante, Zimmer, Warsaw, USA). The other technique utilized a spacer block to achieve well-balanced flexion and extension gaps (Sigma High Performance Partial Knee, DePuy Synthes, Warsaw, USA). All components were fixed with cement. Patients were encouraged to walk and perform range of motion exercises as tolerated on the day of surgery.
Statistical analysis
Statistical analysis was performed using Python 3.11.4. Categorical variables were evaluated using the chi-square method, while continuous variables were analyzed using the independent t-test and the one-way analysis of variance (ANOVA). Post hoc analysis was conducted using Tukey’s Honestly Significant Difference (HSD) method. Two blinded independent observers conducted radiographic measurements, and the intraclass correlation coefficient (ICC) was subsequently calculated to assess the level of agreement between measurements. A p-value below 0.05 was considered statistically significant.
Results
The demographic characteristics, preoperative data, and radiologic characteristics of patients included in this study are presented in Tables 1 and 2. During the study period, 173 patients were initially assessed for eligibility, and 9 patients were excluded due to missing follow-up records. Finally, 164 patients were included in the analysis. The ICC values for radiologic parameters were 0.943, 0.943, 0.779, and 0.888 for preoperative MPTA, preoperative LDFA, postoperative MPTA, and postoperative LDFA, respectively, and they indicated good agreement between measurements.
The presentation of preoperative and postoperative patient distribution of the CPAK types is depicted in Fig. 2. Among the patients who underwent UKA, 75 maintained their original CPAK type, whereas 89 experienced a change in the CPAK type. The transition of the CPAK type from preoperative to postoperative status is visualized through a heat map (Fig. 3).
The preoperative MPTA, LDFA, and HKA in patients who retained their CPAK type were 86.8 ± 1.9, 88.7 ± 2.1, and −6.0 ± 3.0 degrees, respectively. In contrast, those who experienced changes in their CPAK type had preoperative measures of 87.4 ± 1.9, 88.6 ± 1.6, and −6.2 ± 3.3 degrees, respectively. Comparisons of preoperative MPTA, LDFA, and HKA between the two groups showed no significant differences (p = 0.080, p = 0.627, p = 0.619, respectively).
A comparison of PROMs between patients who retained their original CPAK type and those who experienced alterations in the CPAK type is presented in Table 3. No significant differences were observed in preoperative PROMs between the two groups. However, postoperative PROMs, including the 1 year HSS score, KS knee score, and WOMAC pain score, were significantly superior in patients who did not experience any CPAK changes (p = 0.042, p = 0.009, and p = 0.048, respectively). Other scores also exhibited a tendency to favor patients who did not experience any CPAK changes, although these differences were not statistically significant. When subcategorizing the patients based on CPAK changes, 73 were classified into the minor CPAK change group, while 16 patients were categorized into the major CPAK change group. A statistically significant difference was observed in the 1 year KS knee score (p = 0.019), indicating superior outcomes in patients who did not experience any CPAK changes compared with those in the minor and major CPAK change groups (Table 4). Meanwhile, no significant difference was found between the minor and major CPAK change groups.
Throughout the study period, four patients required revision surgery. Among them, two underwent conversion to total knee arthroplasty due to tibial component loosening, which occurred at 82 months and 6 months postoperatively. Another patient required conversion to total knee arthroplasty due to a periprosthetic fracture of the proximal tibia resulting from a fall. Additionally, one patient developed periprosthetic infection 2 months after surgery and subsequently underwent arthroscopic debridement, without infection recurrence.
Discussion
The main findings of this study revealed a significant difference in postoperative 1 year PROMs among patients who underwent UKA, and superior outcomes were observed in patients who did not experience any change in the CPAK types. The degree of CPAK change, whether minor or major, did not show any significant difference or trend in PROMs.
In this study, we utilized the CPAK classification as a novel approach to determine the optimal alignment following UKA. To the best of the authors’ knowledge, this is the first investigation to assess PROMs based on CPAK changes following UKA. Notably, patients who did not experience any CPAK changes demonstrated significant improvements in the HSS scores, KS knee scores, and WOMAC pain scores. In addition, an overall favorable trend was observed in the PROMs in these patients, with the exception of the FJS. This may suggest that while patients are likely to experience a significant improvement of PROMs postoperatively, those with preserved CPAK types likely experience greater pain relief and improved functional outcomes. Likewise, deviation from the native alignment may result in relatively less improvement in discomfort, pain, and decreased function compared with maintaining the original alignment. These findings, in the clinical setting, may encourage the surgeons to prioritize the patient’s native alignment when performing UKA.
Another strength of this study is the detailed categorization of CPAK changes into unchanged, minor, and major change groups. Interestingly, the findings revealed that the degree of change in the CPAK did not influence PROMs, compared with the change in CPAK itself. The number of patients with major CPAK changes was less (16 patients) than that of patients with minor CPAK changes (73 patients). This difference may be attributed to the fact that the UKAs assessed in this study were not aimed at overcorrecting the coronal alignment.
The optimal alignment target for UKA has been extensively studied; however, it has yielded inconclusive results. Alignment targets can be classified into the following three categories: overcorrection (including valgus alignment), undercorrection, and alignment resembling the patient’s native state. Studies supporting neutral or overcorrected alignment, such as those by Collier et al. and Whiteside et al., associated postoperative valgus alignment with a reduced risk of revision, despite potential unfavorable PROMs with extreme valgus knee angulation [7, 13]. Bayoumi et al. found that relative overcorrection from pre-arthritic alignment yielded improved mid-term outcomes compared with relative undercorrection [25]. In contrast, several studies have reported against valgus overcorrection in medial UKA [26,27,28]. Hernigou et al. demonstrated that valgus overcorrection of the coronal alignment increased the risk of cartilage degeneration in the lateral knee compartment [27]. Price et al. found that lateral knee compartment arthritis was the primary cause of revision in medial UKAs [29]. Additionally, a simulation study by Sekiguchi et al. suggested that a 2° varus to neutral alignment in the coronal plane was preferable compared with varus exceeding 4° or valgus alignment [9].
The postoperative changes in CPAK following medial UKA can primarily be attributed to changes in the medial joint line. If the joint line remains unchanged, it is expected that CPAK would also remain consistent. However, several factors can lead to variations in the joint line. In cases where tibial resection is minimal, and the gap is adjusted through additional femoral resection, the medial joint line may elevate, resulting in changes in joint line obliquity from apex distal to either neutral or apex proximal. Conversely, excessive tibial resection may have the opposite effect. Additionally, correction of flexion contracture through soft tissue release or bone resection aimed at achieving an appropriate extension gap may also contribute to change in CPAK.
There are several limitations to this study. First, its retrospective nature and the relatively small sample size increased the risk for introducing selection bias. In addition, 1 year PROMs were used as the primary outcomes, and longer follow-up periods are needed to assess any postoperative complications, including implant longevity. Third, the absence of a standardized approach for measuring the postoperative MPTA and LDFA in patients who underwent UKA necessitated designation of the center of the lateral joint space as a landmark. Although this method can provide a foundation for future investigations, its application should be interpreted cautiously.
Conclusion
Preserving the native CPAK in UKA procedures is important for achieving favorable clinical outcomes at 1 year postoperative. The extent of change in the CPAK type exerted a limited impact on PROMs; thus, emphasizing the importance of change in alignment itself.
Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Abbreviations
- aHKA:
-
Arithmetic hip–knee–ankle angle
- CPAK:
-
Coronal plane alignment of the knee
- JLO:
-
Joint line obliquity
- LDFA:
-
Lateral distal femoral angle
- MPTA:
-
Medial proximal tibial angle
- PROM:
-
Patient-reported outcome measures
- UKA:
-
Unicompartmental knee arthroplasty
References
Yang KY, Wang MC, Yeo SJ, Lo NN (2003) Minimally invasive unicondylar versus total condylar knee arthroplasty–early results of a matched-pair comparison. Singapore Med J 44(11):559–562
Lombardi AV Jr, Berend KR, Walter CA, Aziz-Jacobo J, Cheney NA (2009) Is recovery faster for mobile-bearing unicompartmental than total knee arthroplasty? Clin Orthop Relat Res 467(6):1450–1457. https://doi.org/10.1007/s11999-009-0731-z
Lyons MC, MacDonald SJ, Somerville LE, Naudie DD, McCalden RW (2012) Unicompartmental versus total knee arthroplasty database analysis: is there a winner? Clin Orthop Relat Res 470(1):84–90. https://doi.org/10.1007/s11999-011-2144-z
Koh YG, Lee JA, Lee HY, Chun HJ, Kim HJ, Kang KT (2020) Anatomy-mimetic design preserves natural kinematics of knee joint in patient-specific mobile-bearing unicompartmental knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 28(5):1465–1472. https://doi.org/10.1007/s00167-019-05540-0
Kim TK, Mittal A, Meshram P, Kim WH, Choi SM (2021) Evidence-based surgical technique for medial unicompartmental knee arthroplasty. Knee Surg Relat Res 33(1):2. https://doi.org/10.1186/s43019-020-00084-x
Nie Y, Yu Q, Shen B (2021) Impact of tibial component coronal alignment on knee joint biomechanics following fixed-bearing unicompartmental knee arthroplasty: a finite element analysis. Orthop Surg 13(4):1423–1429. https://doi.org/10.1111/os.12927
Collier MB, Eickmann TH, Sukezaki F, McAuley JP, Engh GA (2006) Patient, implant, and alignment factors associated with revision of medial compartment unicondylar arthroplasty. J Arthroplasty 21(6 Suppl 2):108–115. https://doi.org/10.1016/j.arth.2006.04.012
Kleeblad LJ, van der List JP, Pearle AD, Fragomen AT, Rozbruch SR (2018) Predicting the feasibility of correcting mechanical axis in large varus deformities with unicompartmental knee arthroplasty. J Arthroplasty 33(2):372–378. https://doi.org/10.1016/j.arth.2017.09.052
Sekiguchi K, Nakamura S, Kuriyama S, Nishitani K, Ito H, Tanaka Y et al (2019) Effect of tibial component alignment on knee kinematics and ligament tension in medial unicompartmental knee arthroplasty. Bone Joint Res 8(3):126–135. https://doi.org/10.1302/2046-3758.83.Bjr-2018-0208.R2
Malhotra R, Gupta S, Gupta V, Manhas V (2021) Navigated unicompartmental knee arthroplasty: a different perspective. Clin Orthop Surg 13(4):491–498. https://doi.org/10.4055/cios20166
Nishida R, Hiranaka T, Kamenaga T, Hida Y, Fujishiro T, Okamoto K et al (2021) Impact of joint line orientation on clinical outcomes in bilateral Oxford mobile-bearing unicompartmental knee arthroplasty. Knee 28:186–193. https://doi.org/10.1016/j.knee.2020.11.018
Kennedy WR, White RP (1987) Unicompartmental arthroplasty of the knee. Postoperative alignment and its influence on overall results. Clin Orthop Relat Res 221:278–285
Whiteside LA (2005) Making your next unicompartmental knee arthroplasty last: three keys to success. J Arthroplasty 20(4 Suppl 2):2–3. https://doi.org/10.1016/j.arth.2005.03.029
Schipplein OD, Andriacchi TP (1991) Interaction between active and passive knee stabilizers during level walking. J Orthop Res 9(1):113–119. https://doi.org/10.1002/jor.1100090114
Barbadoro P, Ensini A, Leardini A, d’Amato M, Feliciangeli A, Timoncini A et al (2014) Tibial component alignment and risk of loosening in unicompartmental knee arthroplasty: a radiographic and radiostereometric study. Knee Surg Sports Traumatol Arthrosc 22(12):3157–3162. https://doi.org/10.1007/s00167-014-3147-6
Plancher KD, Brite JE, Briggs KK, Petterson SC (2022) Pre-arthritic/kinematic alignment in fixed-bearing medial unicompartmental knee arthroplasty results in return to activity at mean 10-year follow-up. J Bone Joint Surg Am 104(12):1081–1089. https://doi.org/10.2106/jbjs.21.00801
Vasso M, Del Regno C, D’Amelio A, Viggiano D, Corona K, Schiavone Panni A (2015) Minor varus alignment provides better results than neutral alignment in medial UKA. Knee 22(2):117–121. https://doi.org/10.1016/j.knee.2014.12.004
Luo CF (2004) Reference axes for reconstruction of the knee. Knee 11(4):251–257. https://doi.org/10.1016/j.knee.2004.03.003
MacDessi SJ, Griffiths-Jones W, Harris IA, Bellemans J, Chen DB (2021) Coronal Plane Alignment of the Knee (CPAK) classification. Bone Joint J 103-b(2):329–337. https://doi.org/10.1302/0301-620x.103b2.Bjj-2020-1050.R1
Sappey-Marinier E, Batailler C, Swan J, Schmidt A, Cheze L, MacDessi SJ et al (2022) Mechanical alignment for primary TKA may change both knee phenotype and joint line obliquity without influencing clinical outcomes: a study comparing restored and unrestored joint line obliquity. Knee Surg Sports Traumatol Arthrosc 30(8):2806–2814. https://doi.org/10.1007/s00167-021-06674-w
Insall JN, Ranawat CS, Aglietti P, Shine J (1976) A comparison of four models of total knee-replacement prostheses. J Bone Joint Surg Am 58(6):754–765
Kim SJ, Basur MS, Park CK, Chong S, Kang YG, Kim MJ et al (2017) Crosscultural adaptation and validation of the Korean version of the new knee society knee scoring system. Clin Orthop Relat Res 475(6):1629–1639. https://doi.org/10.1007/s11999-017-5307-8
Bae SC, Lee HS, Yun HR, Kim TH, Yoo DH, Kim SY (2001) Cross-cultural adaptation and validation of Korean Western Ontario and McMaster Universities (WOMAC) and Lequesne osteoarthritis indices for clinical research. Osteoarthritis Cartilage 9(8):746–750. https://doi.org/10.1053/joca.2001.0471
Lee J, Lim SH, Ro DH, Lee MC, Han HS (2021) Translation and validation of the Korean version of the forgotten joint score. Clin Orthop Surg 13(4):482–490. https://doi.org/10.4055/cios20213
Bayoumi T, Burger JA, Ruderman LV, van der List JP, Zuiderbaan HA, Kerkhoffs G et al (2023) Restoration or relative overcorrection of pre-arthritic coronal alignment leads to improved results following medial unicompartmental knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 31(9):3981–3991. https://doi.org/10.1007/s00167-023-07441-9
Mullaji AB, Shetty GM, Kanna R (2011) Postoperative limb alignment and its determinants after minimally invasive Oxford medial unicompartmental knee arthroplasty. J Arthroplasty 26(6):919–925. https://doi.org/10.1016/j.arth.2011.03.008
Hernigou P, Deschamps G (2004) Alignment influences wear in the knee after medial unicompartmental arthroplasty. Clin Orthop Relat Res 423:161–165. https://doi.org/10.1097/01.blo.0000128285.90459.12
Fisher DA, Watts M, Davis KE (2003) Implant position in knee surgery: a comparison of minimally invasive, open unicompartmental, and total knee arthroplasty. J Arthroplasty 18(7 Suppl 1):2–8. https://doi.org/10.1016/s0883-5403(03)00291-2
Price AJ, Waite JC, Svard U (2005) Long-term clinical results of the medial Oxford unicompartmental knee arthroplasty. Clin Orthop Relat Res 435:171–180. https://doi.org/10.1097/00003086-200506000-00024
Acknowledgements
Not applicable.
Funding
The authors declare that they did not receive any funding regarding this study.
Author information
Authors and Affiliations
Contributions
SEK: drafting, analysis, data interpretation, editing. KRY, JML: data collection, analysis, editing. MCL: data collection, performed surgery, writing, and editing. HSH: Conceived of concept, performed surgery, writing, and editing.
Corresponding author
Ethics declarations
Ethics approval and consent to participate
This study was approved by the institutional review board of Seoul National University Hospital. Informed consent was waived due to its retrospective nature.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Additional information
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
About this article
Cite this article
Kim, S.E., Yun, KR., Lee, J.M. et al. Preserving coronal knee alignment of the knee (CPAK) in unicompartmental knee arthroplasty correlates with superior patient-reported outcomes. Knee Surg & Relat Res 36, 1 (2024). https://doi.org/10.1186/s43019-023-00204-3
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/s43019-023-00204-3