Pre-Arthritic/Kinematic Alignment in Fixed-Bearing Medial Unicompartmental Knee Arthroplasty Results in Return to Activity at Mean 10-Year Follow-up

A controlled study of personalized versus standard osteotomy in medial unicompartmental knee osteoarthritis

PURPOSE

To compare the efficacy of personalized osteotomies with that of standard osteotomies in treating medial unicompartmental knee osteoarthritis.

METHODS

The clinical data of 96 patients who were diagnosed with unicompartmental knee osteoarthritis in our group between 2019 and 2023 were retrospectively analysed on the basis of preoperative and postoperative radiological measurements. The knee injury and osteoarthritis outcome score (KOOS), forgotten joint score (FJS), and Lysholm knee score scale (Lysholm) were used to assess the clinical outcome, and complications were observed and recorded.

RESULTS

According to the relevant criteria, 84 of 96 patients were included in this study. All patients were followed for a mean of 31 (range 22-55) months. Fifty-one patients underwent personalized osteotomy procedures, and thirty-three underwent standard osteotomy procedures. The postoperative KOOS Pain (P < 0.0001), KOOS Symptoms (P < 0.0001), KOOS ADL (P < 0.0001), KOOS Sport (P = 0.0023), KOOS QoL (P < 0.0001), Lysholm (P < 0.0001) and FJS (P < 0.0001) scores were higher than those in the standard osteotomy group. Nevertheless, postoperative extension (P = 0.2636) and postoperative flexion (P = 0.3554) were not significantly different.

CONCLUSION

This was a single-centre, retrospective, short follow-up study with several limitations. However, on the basis of the results of the present study, we believe that the function of the knee after medial unicompartmental knee arthroplasty (mUKA) is affected by the direction of tibial osteotomy. We believe that better clinical results may be obtained when the tibial implant is placed near the preoperative tibial deformity.

LEVEL OF EVIDENCE

Level IV; retrospective case series.

Gradual restoration of gait following unicompartmental knee arthroplasty: a prospective study

BACKGROUND

This study investigates the gait characteristics and clinical outcomes following Unicompartmental Knee Arthroplasty (UKA) to provide scientific evidence for optimizing postoperative rehabilitation and patient management.

METHODS

Between December 2022 and November 2023, 34 patients with unilateral medial compartment knee osteoarthritis (KOA) underwent UKA. Preoperative and postoperative videos of patients in standing, walking (side view), squatting, and supine knee-bending positions were captured using smartphones. Gait parameters including gait cycle, swing time, swing phase, stance time, stance phase, double support time, walking speed, step time, cadence, step length, stride length, stride width, active knee flexion angle, and maximum hip and knee flexion angles during squatting were analyzed using the MediaPipe framework for human pose estimation.

RESULTS

Postoperative WOMAC scores were significantly lower than preoperative scores (P < 0.001), while postoperative KSS scores were significantly higher than preoperative scores (P < 0.001).Compared to preoperatively, postoperative affected-side gait speed, step length, step width, and active knee flexion angle all increased (P < 0.05). Additionally, postoperative gait cycle time and double-limb support time were reduced compared to preoperative values (P < 0.05). Among the 17 patients who could perform squats preoperatively and postoperatively, the maximum knee flexion angle and hip flexion angle in the squat position increased from preoperative values of (96.41 ± 20.65)° and (113.77 ± 22.56)° to postoperative values of (110.15 ± 20.79)° and (124.84 ± 21.13)°.

CONCLUSIONS

UKA significantly enhances knee joint kinematics, facilitating the transition from basic to advanced functional activities.

Optimizing uni-compartmental knee arthroplasty: the impact of preoperative planning and arithmetic hip-knee-ankle angle

PURPOSE

The purpose of this study was to evaluate whether the combination of preoperative planning software combined with arithmetic hip-knee-ankle angle (aHKA) can help patients who underwent uni-compartmental knee arthroplasty (UKA) recover the constitutional alignment of the lower limb, obtain a better prosthetic position, and achieve better early patient-reported outcome measurements (PROMs).

METHODS

A total of 150 patients who underwent UKA (planning group: 50 patients using the preoperative planning software; conventional group: 100 patients using the conventional method) were included in the study. The aHKA was defined as 180° + mechanical medial proximal tibial angle (MPTA) - mechanical distal lateral femoral angle (LDFA). All patients in the planning group underwent UKA according to the planning software with the planned lower limb alignment of aHKA. All patients were divided into three groups: constitutional alignment group (postoperative HKA (post-HKA): aHKA ± 2.0°); overcorrection group (post-HKA > aHKA + 2.0°); under-correction group (post-HKA < aHKA - 2.0°). Comparisons between the planning and conventional groups were conducted: (1) the proportion of post-HKA restored to constitutional alignment group; (2) the postoperative prosthesis position parameter based on the guideline of the Oxford group; (3) the American Knee Society scores (KSS) at six months after surgery.

RESULTS

The proportion of the constitutional alignment group in the planning group was higher than that in the conventional group (86% vs. 66%) (p = 0.033). There was no significant difference in postoperative prosthesis position parameters between the two groups. No significant difference was found between the KSS clinical score (91.02 ± 4.20 vs. 90.61 ± 4.24) and KSS functional score (86.10 ± 7.23 vs. 84.30 ± 6.82) in six months after surgery between the planning and conventional groups.

CONCLUSION

Patients who underwent UKA using preoperative planning software in combination with aHKA were able to recover a higher proportion of the constitutional alignment than those with the conventional method. In addition, the planning group could achieve similar postoperative prosthesis position and short-term PROMs compared to the conventional group.

CLINICAL TRIAL NUMBER

Not applicable.

Optimal arithmetic hip-knee-ankle angle for performing prearthritic/kinematic alignment in unicompartmental knee arthroplasty

BACKGROUND

This study aimed to investigate whether arithmetic hip-knee-ankle angle (aHKA) can be a surrogate for valgus stress radiography (VSR). Furthermore, we investigated the optimal cutoff values for preoperative radiographic parameters, thereby validating the appropriate inclusion criteria for prearthritic/kinematic unicompartmental knee arthroplasty (prearthritic-UKA).

METHODS

We retrospectively analyzed 123 patients who underwent medial UKA. We measured the HKA on VSR, termed sHKA. The aHKA was calculated by subtracting the lateral distal femoral angle from the medial proximal tibial angle. Prearthritic-UKA was defined as a postoperative HKA angle within 3° of the aHKA. We divided the patients into the prearthritic-UKA and non-prearthritic-UKA groups. To assess whether the aHKA serves as a surrogate for VSR, Spearman's rank correlations were performed among the radiographic parameters. These radiographic parameters calculated the proper criteria for prearthritic-UKA using receiver operating characteristic (ROC) curve analysis and logistic regression analysis.

RESULTS

Overall, 59 patients were classified into the prearthritic-UKA group. The aHKA was larger than the sHKA and exhibited no significant correlation with the sHKA. ROC analysis revealed that the cutoff values of aHKA for detecting overcorrected UKA (i.e., postoperative HKA - aHKA >3°) was -5.0°. Similarly, the cutoff values for detecting undercorrected UKA (i.e., postoperative HKA - aHKA <-3°) were -3°. Logistic regression analysis revealed that the aHKA was significantly associated with prearthritic-UKA.

CONCLUSION

The aHKA was not identified as a surrogate for the sHKA. Comprehensive preoperative radiographic assessment, including both aHKA and VSR, is crucial for optimizing UKA outcomes and minimizing risks of misalignment.

Restoring coronal pre-arthritic alignment in mobile-bearing unicompartmental knee arthroplasty: mid- to long-term outcomes

BACKGROUND

Previous research suggests that restoring pre-arthritic alignment in fixed-bearing unicompartmental knee arthroplasty (UKA) can improve postoperative knee function. However, its applicability to mobile-bearing UKA remains unclear. This study evaluated whether patients who achieve pre-arthritic alignment following mobile-bearing UKA with the kinematic alignment technique experience superior postoperative knee function compared with those who do not.

METHODS

A retrospective analysis was conducted on 236 knee joints that underwent UKA using kinematic alignment techniques between May 2015 and November 2017. Of these, 222 knee joints met the inclusion criteria for the study. Postoperative outcomes were assessed, with pre-arthritic alignment determined using the arithmetic hip-knee-ankle angle (aHKAA). Postoperative alignment within ± 3° of the aHKAA was classified as pre-arthritic alignment. Patients were categorized into two groups: pre-aligned and non-pre-aligned. Final follow-up occurred in September 2024, and outcome measures included the visual analogue scale (VAS) score, Hospital for Special Surgery (HSS) score, and Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales for daily living, sports, and survivorship. Additionally, the percentage of patients meeting the patient-acceptable symptom state (PASS) criteria for KOOS-related subscales was recorded. Failure was defined as conversion to total knee arthroplasty.

RESULTS

Among the 222 knee joints analyzed, the average follow-up time was 8.65 years (range: 7-9 years), with an average implant survival time of 8.48 years and a total knee arthroplasty conversion rate of 2.7%. The 5-year survival rate was significantly higher in the pre-arthritically aligned group (99.4%) than in the non-pre-arthritically aligned group (92.5%) (p = 0.012). In total, 169 knees (76.13%) were classified as pre-arthritically aligned, while 53 knees (23.87%) were non-pre-arthritically aligned. postoperative VAS scores significantly improved from 6.90 ± 0.82 to 0.58 ± 0.56 (p < 0.001), and HSS scores increased from 56.3 ± 8.36 to 92.39 ± 4.54 (p < 0.001). Although no significant differences in postoperative VAS scores were observed between groups (p = 0.147), the pre-arthritically aligned group demonstrated significantly higher HSS scores and better KOOS subscale scores for daily living activities, sports, and quality of life than the non-pre-arthritically aligned group (all p < 0.01). The PASS ratio for KOOS subscales also indicated superior outcomes in the pre-arthritically aligned group.

CONCLUSION

Using the kinematic alignment technique for mobile-bearing UKA, knees that achieved pre-arthritic alignment demonstrated superior survivorship and subjective postoperative knee function compared with those that did not.

Severe Lateral Facet Patella Osteoarthritis Is Not Associated With Increased Failure at Mean 10 Years After Lateral Unicompartmental Knee Arthroplasty

BACKGROUND

The purpose of this study was to determine if severe lateral patella facet osteoarthritis was related to lower survivorship and poor patient-reported outcomes following fixed-bearing lateral unicompartmental knee arthroplasty (UKA).

METHODS

There were 61 patients who underwent a fixed-bearing, nonrobotically assisted, lateral UKA between May 7, 2003 and December 18, 2019 and met the inclusion criteria. The patello-femoral joint was examined intraoperatively for chondral damage prior to UKA implantation. Severe lateral facet patella osteoarthritis (LFPOA) was defined as Outerbridge grades 3 or 4 changes on the lateral facet. All patients completed subjective functional outcomes questionnaires and a clinical examination at a minimum of 4 years following UKA.

RESULTS

Severe LFPOA was identified in 28 (46%) patients. At a mean follow-up of 10.9 years, there were no statistically significant differences in any Knee Osteoarthritis Outcomes Score (KOOS) subscale or Kujala scores between patients who had and did not have severe LFPOA. There was no statistically significant difference in the percentage of patients who achieved Patient Acceptable Symptom State for the KOOS subscale scores between groups. Mean survival in patients who did not have severe LFPOA was 16.6 years (95% confidence interval, 15.4 to 17.7) compared to 18.9 years (95% confidence interval, 17.6 to 20.2) in patients who had severe LFPOA (P = 0.62).

CONCLUSIONS

Severe LFPOA did not result in lower survival or inferior functional outcomes compared to patients who did not have severe osteoarthritis at an average 10-year follow-up after fixed-bearing lateral UKA.

Fixed-Bearing Lateral Unicompartment Knee Arthroplasty in Degenerative ACL-Deficient and ACL-Intact Knees: A Matched Pair Analysis

BACKGROUND

Anterior cruciate ligament (ACL)-deficient knees are no longer considered a contra-indication for unicompartment knee arthroplasty (UKA). The purpose of this study was to determine if patients who had an ACL-deficient knee who underwent lateral UKA had similar mean 10-year outcomes compared to patients who had an ACL-intact knee and lateral UKA.

METHODS

Patients who underwent a lateral UKA with ACL deficiency by a single surgeon between 2004 and 2016 were identified. Preoperative magnetic resonance images were utilized to identify a torn or absent ACL in all knees. The absence of an ACL was confirmed during arthroscopy prior to UKA. Patients were matched 1:2 based on age and sex with patients who underwent lateral UKA with an ACL intact knee. The primary patient-reported outcome variable was survival without conversion to total knee arthroplasty. Secondary outcomes included Veterans Rand-12, the Lysholm score, the Knee Osteoarthritis Outcome Score activities of daily living subscale, and Sport subscale. A power analysis showed that 14 patients were needed to identify differences of 10 points on the Knee Osteoarthritis Outcome Score with a power of 80% (P = .05).

RESULTS

The cohort of patients who had an ACL-deficient lateral UKA included 4 men and 12 women (43 to 82 years of age). The matched control group included 32 patients. The mean age of both groups was 67 years (range, 43 to 85). There were 2 patients in the ACL-deficient group who failed. At 10 years, survivorship in the ACL-deficient group was 85%, while survival in the ACL-intact group was 100% (P = .035). At an average follow-up of 11 years (range, 4 to 19.6), there was no difference in outcome scores between ACL-deficient and ACL-intact patients.

CONCLUSION

Fixed-bearing lateral UKA in the ACL-deficient knee resulted in lower survival than patients who had an intact ACL. Patient-reported outcomes were similar in both groups. The ACL-deficient patient who wishes to undergo lateral UKA should be counseled on the lower survival.

LEVEL OF EVIDENCE

Level III. Retrospective cohort study.

Robotic-assisted medial unicompartmental knee arthroplasty restored prearthritic alignment and led to superior functional outcomes compared with conventional techniques

PURPOSE

Robotic-assisted medial unicompartmental knee arthroplasty (UKA) can ensure precise preoperative planning, minimise soft tissue damage and restore native coronal alignment. However, few studies have investigated how these advantages translate into differences in early postoperative outcomes. This study aimed to compare differences in early outcomes between conventional UKA (C-UKA) and robotic-assisted UKA (R-UKA).

METHODS

This retrospective study investigated two groups of patients who underwent medial UKA: C-UKA group (n = 35) and R-UKA group (n = 35). We assessed (1) serum indicators (hemoglobin, creatine kinase and C-reactive protein) and pain visual analogue scale (VAS) at postoperative days (PODs) 1, 2, 4 and 6; (2) radiologic parameters including joint line height change and arithmetic and mechanical hip-knee-ankle angle (aHKA and mHKA); (3) patient-reported outcomes including Knee Society Scores, Western Ontario and Mcmaster Universities Arthritis Index (WOMAC) and Forgotten Joint Score-12 (FJS-12) at 1-year follow-up.

RESULTS

Despite similar serum indicator results, pain VAS was lower in the R-UKA group than in the C-UKA group at PODs 2 (2.5 ± 1.3 vs. 3.6 ± 1.2, p = 0.02), 4 (2.4 ± 0.9 vs. 3.3 ± 1.0, p = 0.03) and 6 (1.9 ± 1.1 vs. 3.1 ± 1.1, p < 0.01). The joint line height change was significantly lower in the R-UKA group than in the C-UKA group (0.9 mm ± 0.6 mm vs. 2.0 mm ± 1.3 mm, p = 0.02). The equivalence test for preoperative aHKA and postoperative mHKA revealed equivalence in only the R-UKA group (p < 0.01). The R-UKA group showed better WOMAC and FJS-12 compared to C-UKA group at 1-year follow-up.

CONCLUSION

R-UKA led to lower pain VAS in the early postoperative period compared with C-UKA. Additionally, R-UKA effectively restored the joint line and prearthritic lower limb alignment, resulting in superior functional outcomes at 1-year follow-up compared with C-UKA.

LEVEL OF EVIDENCE

Level III.

Distinct knee phenotype variation: a comparative analysis of medial and lateral unicompartmental knee arthroplasty

PURPOSE

Lateral unicompartmental knee arthroplasty (UKA) is relatively less common than medial UKA. There has been no comparative analysis of the constitutional phenotypes of knees that underwent medial and lateral UKA. Therefore, this study aimed to compare the Coronal Plane Alignment of the Knee (CPAK) classification of knees that underwent medial and lateral UKA. Furthermore, the study analyzed whether CPAK phenotypes were maintained or altered after medial or lateral UKA.

METHODS

We retrospectively analyzed consecutive patients who underwent UKA. A radiological analysis was conducted using an EOS imaging system, and demographic data of patients undergoing UKA were collected. Performed measurements included the mechanical hip-knee-ankle angle (mHKA), lateral distal femur angle (LDFA), and medial proximal tibia angle (MPTA), which were analyzed both before and after UKA. The CPAK classification was used to classify knee alignment phenotypes.

RESULTS

A total of 310 knees of 244 patients were included in the study that underwent non-robotically assisted, fixed-bearing UKA (279 medial; 31 lateral). Preoperatively, the most common categories for knees were Type I (varus mechanical axis, 53.8%) in medial UKA and Type III (valgus alignment, 77.4%) in lateral UKA. Postoperatively, Type II (neutral mechanical axis) became the most common type for both groups, accounting for 34.1% in the medial UKA group and 25.8% in the lateral UKA group. Only 31.3% preserved their preoperative CPAK classification after the surgery (32.3% and 22.6%, respectively).

CONCLUSION

The CPAK classification differs significantly between knees that underwent medial and lateral UKA. While 31.3% of knees maintained their native knee phenotype, there is a tendency towards a neutrally aligned classification after surgery for both medial and lateral UKA. The CPAK classification optimizes preoperative categorization and may assist surgeons in tailoring personalized therapies to improve clinical outcomes.

LEVEL OF EVIDENCE

Level III.

A systematic comparative analysis of gait characteristics in patients undergoing total knee arthroplasty and unicompartmental knee arthroplasty: a review study

BACKGROUND

This study systematically reviews recent research comparing clinical outcomes and gait function changes in patients undergoing total knee arthroplasty (TKA) versus unicompartmental knee arthroplasty (UKA).

METHODS

A systematic search of the Web of Science, PubMed, and Embase databases was conducted, covering publications from January 2013 to September 2024, to identify studies evaluating changes in clinical scores and gait parameters in patients undergoing TKA or UKA. Following stringent selection criteria, data were synthesized from studies involving 171 TKA and 148 UKA patients, focusing on reported gait outcomes and aggregating findings for comprehensive analysis. Direct comparisons between TKA and UKA were performed to assess differences in clinical scores and gait parameters, aiming to elucidate the relative efficacy of each surgical approach and provide robust evidence for clinical decision-making.

RESULTS

Ten studies met the inclusion criteria for post-operative gait outcome comparisons between TKA and UKA, with seven studies also addressing clinical scores. One study reported greater improvement in WOMAC scores for the UKA group at 6 months post-operation (P < 0.05), while another found superior EQ-5D scores for UKA patients at 1 year post-surgery (P < 0.05). Conversely, five studies found no significant differences in clinical scores between groups at 1 year (P > 0.05). All ten studies assessed gait parameter recovery, with three studies showing no significant differences at 1 year (P > 0.05). However, seven studies identified superior gait recovery in the UKA group across various parameters, including walking speed, step and stride length, single support time, heel strike force, knee joint range of motion, knee flexion angles during different gait phases, peak knee adduction moment, peak tibial internal rotation moment, gait symmetry, and stride length symmetry (P < 0.05).

CONCLUSIONS

The analysis indicates that UKA offers certain advantages in post-operative gait improvements compared to TKA, though these do not translate into significant differences in conventional clinical scoring systems. To enhance the reliability and generalizability of these findings, future studies should involve larger-scale, prospective randomized controlled trials.

Unicompartmental Knee Arthroplasty: What is the optimal alignment correction to achieve success? The role of kinematic alignment

Unicompartmental knee arthroplasty (UKA) is in many ways the ultimate kinematic operation, as the express aim is to resurface the diseased side of the joint and restore pre-arthritic alignment and balance while maintaining integrity of both cruciate ligaments. An increasing body of knowledge relates the outcomes of UKA to pre-arthritic anatomy rather than an arbitrarily defined neutral. The Coronal Plane Alignment of the Knee (CPAK) classification provides a validated technique for calculating pre-arthritic limb alignment (the arithmetic hip-knee-ankle angle (aHKA)) and joint line obliquity (JLO) and will enable a greater understanding of the interactions between pre-arthritic anatomy, choice of prosthetic position and outcomes. When pre-arthritic alignment is not taken into consideration a post-operative limb alignment of mild to moderate varus for medial UKA and moderate valgus for lateral UKA appears to produce the best outcomes. When pre-arthritic anatomy is taken into account, superior results have been reported with restoration of pre-arthritic limb alignment and joint line obliquity. Restriction boundaries have yet to be clearly defined for tibial component coronal and hip-knee-ankle (HKA) angles when applying this new paradigm, but existing evidence would suggest a 6° varus limit for the tibial coronal angle may be a reasonable starting point. Lateral UKA has inherent differences in terms of tibial component positioning and ligament balance targets. Mobile bearing UKA demands a three-dimensional understanding of the effect of implant position on bearing stability. Modification of technique is necessary to produce anatomic tibia component angles with equipment designed for mechanical alignment. Robotic technology allows accurate understanding of pre-arthritic anatomy, precise reproduction of patient specific virtual planning, equally precise manipulation of soft tissue balance, and future research using these platforms is likely to further clarify in terms of ideal patient-specific component and limb alignment targets.

Fixed-bearing medial unicompartmental knee arthroplasty restores pre-arthritic coronal alignment and achieves satisfactory functional outcomes: a retrospective study

PURPOSE

This study aimed to (1) analyze the Coronal Plane Alignment of the Knee (CPAK) classification in patients undergoing unicompartmental knee arthroplasty (UKA), (2) assess whether UKA can restore pre-arthritic coronal alignment by utilizing the arithmetic hip-knee-ankle angle (aHKA), and (3) evaluate the relationship between patient-reported outcome measures (PROMs) and postoperative alignment following UKA.

METHODS

We retrospectively analyzed 152 consecutive patients who underwent fixed-bearing medial UKA. A radiological analysis was conducted using an EOS imaging system. Postoperative alignment was classified as neutral (varus ≤ 3°), mild varus (3° < varus ≤ 7°), or marked varus (varus > 7°) based on the mechanical hip-knee-ankle angle (mHKA). The aHKA was calculated and the CPAK classification was used to categorize knee phenotypes. The PROMs were obtained both before and after the surgery.

RESULTS

A total of 152 knees from 113 patients were included with a mean two-year follow-up. The mean difference between the postoperative mHKA and the estimated aHKA was 0.80° (90% CI 0.35 to 1.24; P = 0.003). Postoperatively, 63 (41.45%) of the 152 knees were in neutral group, 54 (35.53%) mild varus, and 35 (23.03%) marked varus. The neutrally aligned cohort did not exhibit significantly higher scores in range of motion, VAS, HSS, WOMAC, or FJS-12 scores compared to the mild or marked varus cohort (P = 0.205, 0.118, 0.076, 0.140, and 0.788, respectively) during the short-term follow-up.

CONCLUSION

Non-robotically assisted, fixed-bearing medial UKA can restore pre-arthritic coronal alignment and achieve satisfactory PROMs. Fixed-bearing medial UKA aims to restore the pre-arthritic alignment rather than achieving neutral mechanical alignment.

Small change in the arithmetic hip-knee-ankle angle during unicompartmental knee arthroplasty improves early postoperative functional outcomes

INTRODUCTION

The optimal lower-limb alignment after unicompartmental knee arthroplasty (UKA) remains controversial. This study aimed to investigate the optimal lower-limb alignment for functional improvement in the early post-UKA period. We hypothesized that a small change (Δ) in the arithmetic hip-knee-ankle (aHKA) angle during surgery would result in better postoperative knee function.

MATERIALS AND METHODS

This single-centered, retrospective study analyzed 91 patients (91 knees) who underwent UKA from April 2021 and December 2022. Preoperative and postoperative standing whole-leg radiographs were used to evaluate the mechanical HKA angle and aHKA angle. The aHKA angle was calculated from the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA). We defined restored aHKA angle as a postoperative aHKA angle within ± 3° of the preoperative aHKA angle. Functional improvement was evaluated using the preoperative and one-year postoperative Knee Society Scoring 2011 (KSS 2011). A multivariate regression analysis was performed to investigate the optimal lower-limb alignment for functional improvement.

RESULT

Postoperative restored aHKA angle (p = 0.020) was the only significant factor for improved KSS 2011 scores. Postoperative restored aHKA angle was obtained in 64 patients (70%). ΔMPTA (p < 0.001) and ΔLDFA (p = 0.037) were significant factors associated with a postoperative restored aHKA angle.

CONCLUSIONS

UKA restores the native knee, including resurfacing constitutional alignment and medial collateral ligament tension. Minimal change in the aHKA angle during UKA improves the functional outcomes of the knee during the early postoperative period, consistent with the minimally invasive surgical concept of UKA.

Predicting postoperative coronal alignment after fixed-bearing unicompartmental knee arthroplasty using a new morphological assessment method: the arithmetic hip-knee-ankle angle

PURPOSE

Only a few reports have been published so far on factors that predict postoperative coronal alignment after unicompartmental knee arthroplasty (UKA). The purpose of this study is to clarify the relationship between the arithmetic hip-knee-ankle angle (aHKA) and postoperative coronal alignment after medial fixed-bearing UKA.

METHODS

One hundred and one consecutive patients (125 knees) who underwent medial fixed-bearing UKA were assessed. Pre- and postoperative coronal HKA angles, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and the thickness of the tibial and femoral bone cut were measured. aHKA was calculated as 180° - LDFA + MPTA. Correlations between postoperative HKA angle and aHKA, LDFA, and MPTA were investigated by single regression analysis. After the patients were divided into three groups according to the postoperative HKA angle, i.e., HKA angle > 180°, 175° < HKA angle ≤ 180°, and HKA angle ≤ 175°, aHKA, LDFA, MPTA, preoperative HKA angle, and the thickness of the distal femoral as well as tibial bone cut were compared among the three groups.

RESULTS

aHKA and MPTA were positively correlated with postoperative HKA angle, while no correlation was found between postoperative HKA angle and LDFA. Among the three groups classified by postoperative HKA angle, significant differences were found in aHKA, MPTA, and preoperative HKA angle, while no significant difference was found in LDFA and the amount of distal femoral and tibial osteotomies.

CONCLUSIONS

aHKA was correlated with postoperative HKA angle after medial fixed-bearing UKA, which was probably due to the influence of MPTA.

The phenotypic diversity of anteromedial osteoarthritis before and after treatment with medial unicompartmental knee arthroplasty: A radiographic analysis of 1000 knees

PURPOSE

This study aimed to assess phenotypic variation in the coronal plane of knees with anteromedial osteoarthritis using the functional knee phenotype classification, before and after treatment with medial unicompartmental knee arthroplasty (UKA).

METHODS

The study comprised 1000 knees of 835 patients (45% females, 55% males, 90% Caucasian) who underwent medial UKA for anteromedial osteoarthritis. Pre and postoperative alignment was evaluated through the hip-knee-ankle angle (HKA), femoral mechanical angle (FMA), and tibial mechanical angle (TMA). Knees were classified according to the functional knee phenotype system which combines limb phenotype (HKA), and femoral and tibial knee phenotypes (FMA and TMA, respectively). Restoration of prearthritic coronal alignment following medial UKA was evaluated by phenotype.

RESULTS

Preoperatively, 76 distinct and 25 relevant (prevalence ≥1%) functional knee phenotypes were identified, of which VARHKA 6°VARFMA 3°NEUTMA 0° was the most common (9.4% of knees). The most prevalent limb phenotype, VARHKA 6°, comprised 15 distinct knee phenotypes (FMA and TMA combinations). Postoperatively, 58 distinct and 17 relevant functional knee phenotypes were observed, of which VARHKA 3°NEUFMA 0°NEUTMA 0° had the highest prevalence at 18.3%. Knees with combined tibial and femoral deformities were associated with a lower probability of restoration of prearthritic coronal alignment following medial UKA, compared to knees without extra-articular deformity, or knees with an isolated tibial or femoral deformity.

CONCLUSION

Phenotype analysis using the functional knee phenotype system demonstrated a wide diversity of coronal alignment phenotypes among knees with anteromedial osteoarthritis in a predominantly Caucasian population. Following medial UKA, a reduction from 25 preoperative to 17 postoperative relevant phenotypes was observed. Consideration of phenotypic variation can be of importance when aiming to restore prearthritic coronal alignment during medial UKA.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Preserving coronal knee alignment of the knee (CPAK) in unicompartmental knee arthroplasty correlates with superior patient-reported outcomes

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.

Knees with anteromedial osteoarthritis show a substantial phenotypic variation prior and following medial unicompartmental knee arthroplasty

PURPOSE

The primary aim of this study was to evaluate the phenotypic variation using the Coronal Plane Alignment of the Knee (CPAK) classification among 1000 knees with anteromedial osteoarthritis (OA) both prior to and following medial unicompartmental knee arthroplasty (UKA). The secondary aim of this study was to investigate whether knees maintained their preoperative CPAK phenotype and to evaluate the phenotypic alterations following medial UKA.

METHODS

The CPAK classification was used to analyze 1000 knees that underwent medial UKA as treatment for anteromedial OA. Knees were categorized into nine distinct CPAK phenotypes based on their arithmetic hip-knee-ankle angle (aHKA), which estimates the pre-arthritic alignment, and joint line obliquity (JLO), both pre- and postoperatively. Phenotypic variation was analyzed by sex and age, and the phenotypic alterations following medial UKA were evaluated by phenotype.

RESULTS

Preoperatively, CPAK phenotype I had the highest prevalence (45.0%). Among males, the preoperative prevalence of CPAK phenotype I was significantly higher compared to females (53.2% vs. 35.0%, respectively; p ≤ .001), whereas females exhibited a significantly higher occurrence of CPAK phenotype V compared to males (9.8% vs. 4.4%, respectively; p ≤ .015). Following medial UKA, CPAK phenotype II had the highest prevalence (53.3%). Overall, 45.1% of knees maintained their preoperative CPAK phenotype following medial UKA, which was most frequently observed among CPAK phenotype II (67.7%) and III (65.8%).

CONCLUSION

There is a substantial variation in CPAK phenotypes among knees with anteromedial OA, as well as following treatment with medial UKA. This variability challenges the assumption of uniform characteristics among knees with an identical wear pattern associated with anteromedial OA and emphasizes the complexity and variability of this specific form of OA.

LEVEL OF EVIDENCE

III, Retrospective cohort study.

Higher incidence of patellar incongruence after under correction of pre-arthritic coronal alignment following medial unicompartmental knee arthroplasty

PURPOSE

This study aimed to compare patellofemoral joint alignment of knees with restored pre-arthritic coronal alignment versus knees with under- or overcorrection from their pre-arthritic coronal alignment following medial unicompartmental knee arthroplasty (UKA) and evaluate the effect of patellofemoral joint alignment on patient-reported outcomes.

METHODS

A retrospective analysis of 517 knees following robotic-arm assisted medial UKA was conducted. Postoperative mechanical hip-knee-ankle angle (mHKA) was compared to estimated pre-arthritic coronal alignment, using the arithmetic hip-knee-ankle angle (aHKA). Knees were considered restored to the pre-arthritic coronal alignment if mHKA was within 2.0° of aHKA (Group 1). Non-restored knees were subdivided into > 2.0° over correction (Group 2), or > 2.0° under correction (Group 3) from the pre-arthritic coronal alignment. Patellar congruence and patellar tilt angles were compared between groups. The Kujala score and Knee Injury and Osteoarthritic Outcome Score for Joint Replacement (KOOS, JR) were analyzed by group. Continuous data was compared using analysis of variance or Kruskal-Wallis tests. Chi-squared tests were used to compare discrete variables. Logistic regressions were conducted to estimate the probability of postoperative patellofemoral malalignment.

RESULTS

Group 1 included 357 knees (69.1%), Group 2 included 57 knees (11.0%), and Group 3 included 57 knees (11.0%). The prevalence of postoperative abnormal patellar congruence (i.e. ≥ 17°) was higher in Group 3 at 40.4% (p = 0.009), with a higher odds ratio of having an abnormal patellar congruence angle (2.3, p = 0.01) compared to Group 1. The prevalence of postoperative abnormal patellar tilt (i.e. ≥ 14°) was comparable between groups (n.s.). At mean follow up of 4.4 ± 1.6 years, Kujala was worse in Group 3 (76.6 ± 17.4 compared to 84.0 ± 14.9 and 85.0 ± 14.4 in Groups 1 and 2, respectively; p = 0.006). Mean KOOS, JR outcomes were comparable among groups. No significantly inferior Kujala or KOOS, JR outcomes were observed in patients across all groups with abnormal patellar congruence or tilt angles.

CONCLUSION

Knees with under correction from their pre-arthritic coronal alignment following medial UKA were associated with a two-fold higher probability of having postoperative patellofemoral incongruence, as well as inferior mid-term Kujala scores compared to knees with restored pre-arthritic coronal alignment and knees with overcorrection from their pre-arthritic coronal alignment. Patellofemoral incongruence alone did not negatively impact functional outcome scores.

LEVEL OF EVIDENCE

IV, case series.

Restoration or relative overcorrection of pre-arthritic coronal alignment leads to improved results following medial unicompartmental knee arthroplasty

PURPOSE

A pre-arthritic alignment strategy for medial unicompartmental knee arthroplasty (UKA) aims to restore a patient's native lower limb alignment which may translate into improved outcomes. This study aimed to assess whether patients with pre-arthritically aligned knees versus patients with non-pre-arthritically aligned knees demonstrated improved mid-term outcomes and survivorship following medial UKA. The hypothesis was that pre-arthritic alignment in medial UKA would lead to better postoperative outcomes.

METHODS

A retrospective study of 537 robotic-assisted fixed-bearing medial UKA was conducted. During this procedure, the surgical goal was to restore pre-arthritic alignment guided by re-tensioning of the medial collateral ligament (MCL). For study purposes, coronal alignment was retrospectively evaluated using the mechanical hip-knee-ankle angle (mHKA). Pre-arthritic alignment was estimated through the arithmetic hip-knee-ankle (aHKA) algorithm. Knees were grouped according to the difference between postoperative mHKA and estimated pre-arthritic alignment (i.e., mHKA - aHKA) as Group 1 (pre-arthritically aligned: mHKA restored within 2.0° of the aHKA), Group 2 (mHKA > 2.0° overcorrected relative to the aHKA), or Group 3 (mHKA > 2.0° undercorrected relative to the aHKA). Outcomes included the Knee Injury and Osteoarthritic Outcome Score for Joint Replacement (KOOS, JR), Kujala, proportions of knees achieving the patient acceptable symptom state (PASS) for these scores, and survivorship. PASS thresholds for KOOS, JR and Kujala were determined using a receiver operating characteristic curve method.

RESULTS

A total of 369 knees were categorized as Group 1, 107 as Group 2, and 61 as Group 3. At 4.4 ± 1.6 years follow-up, mean KOOS, JR was comparable among groups, while Kujala was significantly worse in Group 3. The proportion of knees achieving the PASS for Kujala (76.5 points) was lower in Group 3 (n = 32; 59%) compared to Group 1 (n = 260; 74%) (p = 0.02). 5-year survivorship was higher in Group 1 and Group 2 (99% and 100%, respectively) compared to Group 3 (91%) (p = 0.04).

CONCLUSION

Pre-arthritically aligned knees and knees with relative overcorrection from their pre-arthritic alignment following medial UKA demonstrated improved mid-term outcomes and survivorship compared to knees with relative under correction from their pre-arthritic alignment. These results encourage restoring or relatively overcorrecting pre-arthritic alignment to optimize outcomes following medial UKA, and caution against under correction from the pre-arthritic alignment.

LEVEL OF EVIDENCE

IV, case series.

Intraoperative sensor technology quantifies inter-prosthesis pressure for predicting lower limb alignment after Oxford unicompartmental knee arthroplasty

Purpose: The aim of this study is to quantify inter-prosthetic pressures at different knee angles in Oxford unicompartmental knee arthroplasty (OUKA) and its correlation with postoperative lower limb alignment. Methods: This study included 101 patients (122 knees) who underwent OUKA from March 2022 to July 2022. The previously designed matrix flexible force sensor was used to measure the inter-prosthesis pressure of different knee joint angles during the UKA operation, and the force variation trend and gap balance difference were obtained. The correlation between inter-prosthesis pressure and postoperative lower limb alignment index including hip-knee-ankle angle (HKAA) and posterior tibial slope (PTS) was analyzed. The effect of PTS change (ΔPTS) on the inter-prosthesis pressure and the range of motion (ROM) of the knee joint was analyzed. Radiographic and short-term clinical outcomes of included patients were assessed. Results: The inter-prosthesis pressure of the different knee joint angles during the operation was not consistent. The mean inter-prosthesis pressure and gap balance difference were 73.68.28 ± 41.65N and 36.48 ± 20.58N. The inter-prosthesis pressure at 0° and 20° was positively correlated with postoperative HKAA (p < 0.001). ΔPTS was positively correlated with the pressure at the end of knee extension and negatively correlated with the pressure at the end of knee flexion (p < 0.001). The HKAA, ROM, degree of fixed knee flexion deformity, and knee society score of the included patients were significantly improved compared with those before the operation (p < 0.001). Conclusion: The inter-prosthesis pressure measured at the knee extension position can predict postoperative HKAA to some degree. Changes in PTS will affect the inter-prosthesis pressure at the end of flexion and end of knee extension, but this change is not related to the range of motion of the knee joint.

Robotic-assisted medial unicompartmental knee arthroplasty restores estimated pre-arthritic coronal limb alignment: A retrospective cohort study

BACKGROUND

Robotic-assisted medial unicompartmental knee arthroplasty (UKA) aims to restore pre-arthritic (constitutional) limb alignment, by re-tensioning of the medial collateral ligament (MCL). This study aimed to determine whether pre-arthritic coronal alignment was restored following robotic-assisted medial UKA in patients with medial compartment osteoarthritis.

METHOD

A retrospective study was undertaken, including 102 patients with a unilateral robotic-assisted medial UKA and a contralateral unaffected knee. Both the validated arithmetic hip-knee-ankle angle (aHKA) and alignment of the contralateral unaffected knee were used to estimate pre-arthritic alignment. The aHKA is a radiographic method to estimate the pre-arthritic mechanical hip-knee-ankle angle (mHKA). To verify restoration of pre-arthritic alignment, postoperative mHKA was compared to the aHKA. Additionally, postoperative mHKA, joint line congruence (JLCA), and knee joint line obliquity (KJLO) angles were compared between the operative and contralateral unaffected knee. Equivalence between postoperative and pre-arthritic alignment was assessed through the two-one-sided t-test (TOST), using equivalence margins of ±2.0°.

RESULTS

Postoperative mHKA was equivalent to the aHKA (mean difference -0.38°, 90% CI -0.69 to -0.07;p < .001), with 93 knees (91%) restored within 3.0° their aHKA. Postoperative mHKA, JLCA and KJLO were equivalent between the operative and contralateral unaffected knees, with mean differences of -0.65°, -0.65°, and -0.40°, respectively; all p < .001.

CONCLUSIONS

Postoperative and pre-arthritic coronal alignment were equivalent following robotic-assisted medial UKA, with 91% of knees restored within 3.0° of their pre-arthritic mechanical axis. These results demonstrate that both mechanical alignment and joint line congruence are restored by MCL re-tensioning in patients undergoing robotic-assisted medial UKA for medial compartment osteoarthritis.

The Lawrence D. Dorr Surgical Techniques & Technologies Award: Patient Acceptable Symptom State (PASS) in Medial and Lateral Unicompartmental Knee Arthroplasty: Does the Status of the ACL Impact Outcomes?

BACKGROUND

The aim of this study is to determine if there is a difference in the percentage of patients who reach Patient Acceptable Symptom State (PASS) when comparing anterior cruciate ligament (ACL)-deficient and ACL-intact knees following fixed-bearing medial and lateral unicompartmental knee arthroplasty (UKA).

METHODS

A consecutive series of 215 knees that underwent UKA (medial = 158, lateral = 57) were included in the study. The Knee Osteoarthritis Outcome Score functional score [KOOS activities of daily living (ADL)] and KOOS Sport were used as the primary outcome variables. A KOOS ADL PASS of 87.5 and KOOS Sport PASS of 43.8 were previously described for total knee arthroplasty (TKA). Failure was defined as conversion to TKA.

RESULTS

There were 157 in the ACL-intact group and 58 in the ACL-deficient group. Conversion to TKA was 3.7%. The failure rate in the ACL-deficient group was 5% (3/58) and 3% (5/157) in the ACL-intact group (P = .447). The mean survival for the entire group was 18.1 years (95% confidence interval 17.6-18.6). At 10 years, the survival was 94.3% (standard error = 0.028) in the ACL-deficient group and 97.6% (standard error = 0.014) in the ACL-intact group. At a mean 10 ± 3.5 years, with 93% follow-up, 83% in the ACL-deficient group and 80% in the ACL-intact group reached PASS for KOOS ADL (P = .218). For KOOS Sport, 85% of the ACL-deficient group compared to 81% in the ACL-intact group (P = .374) reached PASS.

CONCLUSION

The ACL-deficient cohort results were not significantly different compared to ACL-intact knees in both medial and lateral compartment UKA. Fixed-bearing medial and lateral UKA resulted in low failure rate and excellent long-term outcomes.