Impact of Polyethylene Thickness on Clinical Outcomes and Survivorship in Medial Mobile-Bearing Unicondylar Knee Arthroplasty

BackgroundThe thickness of the polyethylene bearing in medial unicondylar knee arthroplasty (UKA) is determined by the depth of the tibial resection, degree of correctable deformity, and balance of the knee. The purpose of this study is to evaluate whether polyethylene thickness in medial mobile-bearing UKA impacts clinical outcomes and survivorship.MethodsA retrospective review from 2004 to 2017 identified patients who underwent a primary mobile-bearing medial UKA with 2-year minimum follow-up or revision. A total of 2305 patients (3030 knees) met inclusion criteria. Patients were divided in 2 groups: thin bearing (group 1): 3-mm or 4-mm bearing and thick bearing (group 2): ≥ 5 mm. The thin group consisted of 2640 knees (87%), whereas the thick group had 390 knees (13%). Preoperative and postoperative demographics, range of motion, Knee Society scores, complications, and reoperations were evaluated.ResultsMean follow-up was 5.2 years (range, 0.5 to 12.6). There was no significant difference between groups in postoperative range of motion or Knee Society scores (P > .05). Manipulations were performed in 1.3% of patients and not significantly different between groups. The all-cause revision rate for group 1 was 4.02% and group 2 was 4.58% (P = .6). Revision rates for tibial aseptic loosening were significantly higher in group 2 (1.8%) than those in group 1 (0.7%) (P = .04). There was no significant difference in failure rates between groups for tibial collapse or fracture, femoral aseptic loosening, arthritic progression, bearing dislocation, or other cause of revision.ConclusionThis study demonstrated that thicker bearings in medial UKA increased the risk of tibial aseptic loosening, but not all-cause failures or clinical outcomes.     

Relevance of the Tibial Slope on Functional Outcomes in ACL-Deficient and ACL Intact Fixed-Bearing Medial Unicompartmental Knee Arthroplasty

BackgroundExcessive posterior tibial slope in medial unicompartmental knee arthroplasty (UKA) has been implicated in early failure. The purpose of this study was to evaluate the relationship between preoperative posterior tibial slope and postoperative slope of the implant (PSI) on outcomes in patients with anterior cruciate ligament (ACL) intact and ACL-deficient knees after fixed-bearing medial UKA.MethodsPatients who underwent a medial UKA between 2002 and 2017 with a minimum 3-year follow-up were included. Preoperative posterior tibial slope and postoperative PSI were measured. Outcomes measures included Knee Injury and Osteoarthritis Outcomes Score (KOOS) subscales, Lysholm, and VR-12. Failure was defined as conversion to total knee arthroplasty.ResultsOf 241 knees undergoing UKA, 131 patients (70 women, 61 men; average age of 65 ± 10 years (average BMI of 27.9 ± 4) were included. For all patients, survivorship was 98% at 5 years and 96% at 10 years with a mean survival time for UKA was 15.2 years [95% CI: 14.6-15.7]. No failure had a PSI >7°. There were no superficial or deep infections. There were no significant differences in outcome scores between the ACL intact and the ACL-deficient group; therefore, the data were combined for analysis. At mean 8-year follow-up, KOOS pain scores were better in patients with PSI ≤7° (87 ± 16) than those with PSI >7° (81 ± 15). 76% of patients with PSI ≤7° reached the Patient Acceptable Symptom State for KOOS pain; whereas, 59% of patients with PSI >7° reached PASS for KOOS pain (P = .015).ConclusionPatients with postoperative posterior slope of the tibial implant >7° had significantly worse postoperative pain, without conversion to TKA, and with maintenance of high function. In ACL deficient and intact knees, nonrobotically-assisted, fixed-bearing medial UKA had a 96% survivorship at 10 years.     

Valgus Subsidence of the Tibial Component Caused by Tibial Component Malpositioning in Cementless Oxford Mobile-Bearing Unicompartmental Knee Arthroplasty

BackgroundValgus subsidence (VS) of the tibial component is a rare complication of unicompartmental knee arthroplasty (UKA), and surgeons might consider revision surgery. The present study aimed to identify the factors related to VS of the tibial component after cementless Oxford mobile-bearing UKA.MethodsThe study included 120 patients who underwent Oxford mobile-bearing UKA using a cementless tibial component in our center between September 2015 and September 2016. Six showed VS of >2° after surgery. Patients were stratified into 2 groups according to the occurrence of VS of the tibial component (VS group, n = 6; no-subsidence group, n = 114). Postoperative radiographic evaluations were conducted to assess the varus/valgus alignment, rotation, and mediolateral position of the tibial and femoral components. The Oxford Knee Score (OKS) was assessed at 3, 6, and 12 months postoperatively. Positional parameters and sequential change in OKS were compared between the two groups using unpaired t-test (P < .05, statistically significant).ResultsAt 3 months postoperatively, an average VS of 3.4° in the VS group was observed, with a significant decrease in OKS. VS was associated with a significantly more medial position and external rotation of the tibial component. After 3 months, VS stopped, and the OKS gradually improved without revision surgery.ConclusionsVS might be caused by the malpositioning of the tibial component. VS of the tibial component after UKA appears to stop, with simultaneous pain relief, even without revision after 3 months postoperatively.     

Unicompartmental Knee Arthroplasty Patients Have Lower Joint Awareness and Higher Function at 5 Years Compared to Total Knee Arthroplasties: A Matched Comparison

BackgroundThe purpose of this study was to evaluate postoperative outcomes at minimum 5-year follow-up in patients following unicompartmental knee arthroplasty (UKA) compared to a matched cohort of total knee arthroplasty (TKA) patients.MethodsPatients who had primarily medial compartment osteoarthritis (OA) who met criteria for medial UKA underwent TKA or medial UKA between 2014 and 2015 at a single institution, matched for age, sex, and body mass index. There were 127 UKAs in 120 patients and 118 TKAs in 116 patients included with minimum 5-year follow-up (range, 6 to 8). Mean age was 69 years (range, 59 to 79) and 71 years (range, 62 to 80) in the UKA and TKA groups, respectively (P = .049).ResultsPatients who underwent UKA had significantly higher mean (±SD) Forgotten Joint Scores (87 ± 20 versus 59 ± 34, P < .001); higher Knee Society Scores (88 ± 14 versus 75 ± 21, P < .001); and lower Numeric Pain Rating Scores (0.8 ± 1.6 versus 1.9 ± 2.2, P < .001). Survivorship free from all-cause revision was 96% (95% CI = 93%-99%) and 99% (95% CI = 97%-100%) at 5 years for TKA and UKA, respectively (P = .52). There were 8 both component revisions in the TKA group within 5 years from the date of surgery and 2 UKA conversions to TKA after 5-year follow-up.ConclusionPatients who have medial compartment OA and underwent UKA had significantly lower joint awareness, decreased pain, improved function, and higher satisfaction compared to matched TKA patients at minimum 5-year follow-up while maintaining excellent survivorship.     

Better Implant Positioning and Clinical Outcomes With a Morphometric Unicompartmental Knee Arthroplasty. Results of a Retrospective,Matched-Controlled Study

BackgroundDuring medial unicompartmental knee arthroplasty (UKA), tibial tray implantation requires compromise between bone coverage and rotational position. It was hypothesized that morphometric tibial tray (MTT) would improve implant positioning and subsequently clinical outcomes as compared to symmetric tibial tray (STT).MethodsA total of 106 patients who underwent medial UKA in our department between January 2017 and March 2018 were included matched on gender and age (53 in each group). Inclusion criteria were symptomatic medial femorotibial osteoarthritis, functional anterior cruciate ligament, primary arthritis, or osteonecrosis. Rotation of the tibial implant, tibial bone coverage, medial and posterior overhang were assessed with a postoperative computed tomography scan. The Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score Short Form (KOOS SF), and the quality of life score EuroQoL 5-Dimensions 3-Levels (EQ5D3L) were assessed at a minimum of 1-year follow-up.ResultsImplants of the STT group exhibited more external rotation (6.3° ± 4.02° vs 4.6° ± 3.59°; P = .04), and medial and posterior overhang >3 mm (35% vs 0% and 22% vs 0%; P < .0001) but no difference for tibial bone coverage (97.3% ± 11.35% vs 94.7% ± 10.89%; P = .23). Global KSS (188.6 ± 6.6 vs 175.2 ± 31.7; P < .01), KOOS SF (16.9 ± 6.1 vs 22.5 ± 11.8; P < .003), and EQ5D3L (1 ± 0.1 vs 0.9 ± 0.2; P < .001) were higher in MTT group. According to the multivariate analysis, MTT had a positive independent effect on the KSS, KOOS SF, and EQ5D3L.ConclusionThe use of an MTT in medial UKA allowed better implant positioning when decreasing the rate of overhang; superior short-term clinical outcomes were found as compared to STT.     

The Effect of Bone Quality on Tibial Component Migration in Medial Cemented Unicompartmental Knee Arthroplasty. A Prospective Cohort Study Using Dual X-Ray Absorptiometry and Radiostereometric Analysis

BackgroundPeriprosthetic bone mineral density (BMD) may influence implant fixation and subsequent loosening. Unicompartmental knee arthroplasty (UKA) restores normal knee kinematics and load distribution to the surrounding bone. We studied the influence of systemic and periprosthetic BMD of the proximal tibia on migration of the tibial component of cemented medial UKA.MethodsThe cohort was dichotomized into a normal BMD group (T-score ≥ −1; n = 37) and a low BMD group (T-score < −1; n = 28) according to World Health Organization criteria. BMD of the proximal tibia and migration of the tibial component were measured with dual X-ray absorptiometry scans and stereoradiographs with 2-year follow-up.ResultsPatients with normal systemic BMD had an 11% to15% higher BMD in all regions of interest (ROIs) compared to patients with low systemic BMD throughout follow-up. Over time, a decrease in periprosthetic BMD in ROI 1-3 was seen for both groups. The operated knees and contralateral knees showed a similar reduction in BMD in all ROIs between preoperative and 24 months.Between 12 and 24 months, the normal BMD group migrated (maximal total point motion) 0.03 mm (95% confidence interval, −0.01, 0.08) and the low BMD group migrated 0.02 mm (95% confidence interval, −0.03, 0.07). Migration over time was not influenced by change in periprosthetic BMD.ConclusionMigration of cemented medial tibial UKA was low until 24 months and was neither affected by preoperative systemic BMD nor affected by postoperative change in periprosthetic BMD. This suggests good long-term fixation despite an index difference in proximal tibial BMD.     

Titanium Niobium Nitride Mobile-Bearing Unicompartmental Knee Arthroplasty Results in Good to Excellent Clinical and Radiographic Outcomes in Metal Allergy Patients With Medial Knee Osteoarthritis

BackgroundThe main purpose of the present study was to analyze the clinical and radiological outcomes of patients with positive skin patch tests who underwent medial mobile-bearing titanium niobium nitride unicompartmental knee arthroplasty (UKA) during a mid-term follow-up.MethodsThirty-seven patients with positive skin patch tests were included in this prospective study. The clinical evaluation consisted of Oxford Knee Score and Knee Society Score (KSS) reports. Each patient was clinically evaluated the day before surgery (T₀) as well as at T₁ (11.9 ± 1.3 months) and during the final follow-up T₂ (67.2 ± 19.1 months). The positioning of the UKA was evaluated during the final follow-up using standardized radiographs (T₂: 67.2 ± 19.1 months).ResultsOxford and KSS ranged from a respective mean preoperative value of 23.0 ± 2.7 and 51.5 ± 5.0 to 42.1 ± 1.7 and 87.6 ± 2.2, respectively, at T₁ (P < .001) and to the final values of 45.0 ± 1.9 and 91.9 ± 3.4, respectively, at T₂ (P < .001 both vs T₁ and T₂). At T₂, the mean femoral angle was 7.0° ± 4.5°, mean tibial angle was 3.0° ± 2.1°, and mean tibial slope was 5.1° ± 3.2°. A significant difference was found between KSS and Oxford with ANOVA for repeated measures over time (P < .001). The Oxford and KSS scores showed significant improvements during each follow-up. No complications were found, and not a single patient required a revision surgery during the follow-up period.ConclusionThe hypoallergenic titanium niobium nitride mobile-bearing UKA showed comparable results to standard CoCr UKA regardless of the gender, age, BMI, and implant size of metal allergy patients with medial knee osteoarthritis. Careful patient selection processes and accurate medical histories played key roles in the choice of hypersensitivity-friendly implants.     

Alignment in Medial Fixed-Bearing Unicompartmental Knee Arthroplasty: The Limb Has a Leg Up on the Component

BackgroundTo assess how implant alignment affects unicompartmental knee arthroplasty (UKA) outcome, we compared tibial component alignment of well-functioning UKAs against 2 groups of failed UKAs, revised for progression of lateral compartment arthritis (“Progression”) and aseptic loosening (“Loosening”).MethodsWe identified 37 revisions for Progression and 61 revisions for Loosening from our prospective institutional database of 3351 medial fixed-bearing UKAs performed since 2000. Revision cohorts were matched on age, gender, body mass index, and postoperative range of motion with “Successful” unrevised UKAs with minimum 10-year follow-up and Knee Society Score ≥70. Tibial component coronal (TCA) and sagittal (TSA) plane alignment was measured on postoperative radiographs. Limb alignment was quantified by hip-knee-ankle (HKA) angle on long-leg radiographs. In addition to directly comparing groups, a multivariate logistic regression examined how limb and component alignments were associated with UKA revision.ResultsIn the Progression group, component alignment was similar to the matched successes (TCA 3.6° ± 3.5° varus vs 5.1° ± 3.5° varus, P = .07; TSA 8.4° ± 4.4° vs 8.8° ± 3.6°, P = .67), whereas HKA angle was significantly more valgus (0.3° ± 3.6° valgus vs 4.4° ± 2.6° varus, P < .001). Loosening group component alignment was also similar to the matched successes (TCA 6.1° ± 3.7° varus vs 5.9° ± 3.1° varus, P = .72; TSA 8.4° ± 4.6° vs 8.1° ± 3.9°, P = .68), and HKA was significantly more varus (6.1° ± 3.1° varus vs 4.0° ± 2.7° varus, P < .001). Using a multivariate logistic regression, HKA angle was the most significant factor associated with revision (P < .001).ConclusionIn this population of revised UKAs and long-term successes, limb alignment was a more important determinant of outcome than tibial component alignment.Level of EvidenceLevel III case-control study.     

Adequate Positioning of the Tibial Component Is Key to Avoiding Bearing Impingement in Oxford Unicompartmental Knee Arthroplasty

BackgroundBearing dislocation is a serious complication of unicompartmental knee arthroplasty (UKA) with the Oxford knee prosthesis equipped with a mobile bearing. We aimed to clarify the extent of intraoperative movement of the mobile bearing and its relationship with the positioning of prosthesis components in patients undergoing Oxford UKA.MethodsThis retrospective study included 50 patients (50 knees) who underwent Oxford UKA for anteromedial osteoarthritis or osteonecrosis of the knee. Intraoperative bearing movement was assessed at various angles of knee flexion (0°, 30°, 60°, 90°, and 120°). We stratified patients according to the extent of bearing movement posteriorly during intraoperative knee flexion, with or without contacting the lateral wall of the tibial component (with contact, 20 knees; without contact, 30 knees). Postoperative radiographic evaluations were conducted at 1 week postoperatively to assess the positional parameters of the tibial and femoral components (varus/valgus alignment, rotation, mediolateral position). Clinical evaluations were conducted at 1 year postoperatively (maximum flexion angle, Oxford Knee Score).ResultsAbnormal intraoperative movement of the mobile bearing resulting in contact with the lateral wall of the tibial component was associated with a significantly more medial position and external rotation of the tibial component, as well as poorer improvement in knee flexion angle at 1 year postoperatively.ConclusionIn Oxford UKA recipients, the bearing may impinge on the lateral wall of the tibial component during flexion above 60° if the tibial component is placed too medially or exhibits pronounced external rotation, which may limit knee function improvement postoperatively.     

High Failure Rates for Unicompartmental Knee Arthroplasty in Morbidly Obese Patients: A Two-Year Minimum Follow-Up Study

BackgroundSeveral recent studies have recommended offering unicompartmental knee arthroplasty (UKA) to all patients regardless of body mass index (BMI). The aim of this investigation was to evaluate the proposition that UKA can indeed be offered to the morbidly-obese and super-obese (morbidly-obese, BMI ≥ 40 kg/m²) without compromising results or survivorship.MethodsWe retrospectively reviewed mobile-bearing medial UKA procedures performed at our facility from January 2012 to May 2015 with a minimum of 2-year follow-up. The study cohort was divided into patients with morbid obesity (BMI ≥ 40 kg/m²) and those without morbid obesity (BMI < 40 kg/m²). A detailed medical record review was performed. Extracted outcome data included the frequency of (1) major revision procedures (components revised), (2) minor secondary procedures (components not revised), (3) infection procedures, and (4) recommendations for revision.ResultsWe found 152 patients (190 knees) who met criteria for inclusion. Mean follow-up duration was 3.4 years (range: 2.0-6.8 years). Major revision surgery occurred more frequently in the morbid-obesity UKA group (15.7% vs 3.0%, P < .01). Rates of minor secondary surgery and infection were comparable for both groups. Most failures in the morbid-obesity UKA group (85.7%) were due to disease progression involving other compartments or mobile-bearing instability.ConclusionWe found the rate of early major revision surgery in morbidly-obese patients undergoing UKA to be over 5-times greater than that of other patients. Failure was predominantly due to disease progression in other compartments or mobile-bearing instability. Further study is warranted and needed before expanding UKA indications to the morbidly-obese population.     

Mild Valgus Alignment After Lateral Unicompartmental Knee Arthroplasty Led to Lower Functional Results and Survivorship at Mean 8-Year Follow-Up

BackgroundIn medial unicompartmental knee arthroplasty (UKA), the best results and the highest survivorship are found by mild undercorrection of varus deformities. In lateral UKA, the desirable amount of valgus undercorrection has not yet been determined. The purposes of this study were to present the results of a consecutive series of lateral UKAs and to investigate the effect of postoperative limb alignment on them.MethodsA total of 161 lateral UKA were reviewed. Outcomes studied included range of motion (ROM), Knee Society Score (KSS), University of California Los Angeles Activity Score, Tegner Activity Scale, Forgotten Joint Score, visual analogue scale (VAS) for pain, and survivorship. Patients were divided into two groups according to postoperative alignment: group A (hip-knee-ankle ≥184°, 79 UKA) and group B (hip-knee-ankle <184°, 82 UKA).ResultsAt a mean follow-up of 8 years (range, 2-18), ROM (P < .01); KSS-C (P < .01); KSS-F (P < .01); VAS (P < .01) improved from baseline. No differences were noted in postoperative ROM, VAS, University of California Los Angeles, Tegner Activity Scale, and Forgotten Joint Score between groups. Group A showed higher postoperative clinical and functional KSS (P < .01) and higher survivorship (96.2 versus 91.5%, P = .01) than group B.ConclusionMild valgus alignment (3° or less) after lateral UKA is linked to lower clinical and functional scores and lower survivorship compared to moderate valgus (over 4°) at mean 8-year follow-up. More undercorrection of the coronal deformity in lateral UKA compared to medial UKA is desirable to get the best results.     

Diagnostic and Invasive Colonoscopy Are Not Risk Factors for Revision Surgery Due to Periprosthetic Joint Infection

BackgroundColonoscopy is routinely performed for colorectal cancer screening in patients who have a preexisting unicompartmental knee arthroplasty (UKA), total knee arthroplasty (TKA), or total hip arthroplasty (THA) prostheses. However, colonoscopy is theorized to provoke transient bacteremia, providing a potential nidus for periprosthetic joint infection. This study aimed to investigate the risk of aseptic and septic revision surgery in patients who underwent diagnostic colonoscopy or invasive colonoscopy within one year following UKA, TKA, or THA.MethodsA retrospective cohort analysis was performed using a national database. Patients were identified using Current Procedural Terminology. In total, 52,891 patients underwent UKA, 1,049,218 underwent TKA, and 526,296 underwent THA. Data were analyzed with univariate analysis preceding multivariable logistic regressions to investigate outcomes of interest at 2 and 3 years from the index procedure.ResultsDiagnostic colonoscopy resulted in no increase in odds of all-cause or septic revision surgery for any prostheses. At both time points, invasive colonoscopy resulted in lower odds of all-cause revision (P < .05) for patients with UKA, decreased odds of septic revision (P < .001) for patients with TKA, and decreased odds of both all-cause and septic revision (P < .05) for patients with THA.ConclusionOur results show that diagnostic colonoscopy was not a significant risk factor for revision following UKA, TKA, or THA. Paradoxically, invasive colonoscopy was protective against revision, even with very minimal use of antibiotic prophylaxis observed. This study addresses the theory that colonoscopy procedures may threaten an existing joint prosthesis via transient bacteremia and shows no increase in revision outcomes following colonoscopy.Level of EvidenceLevel III.     

Navigated Unicompartmental Knee Arthroplasty: A Different Perspective

BackgroudAnteromedial osteoarthritis is a recognized indication for unicompartmental knee arthroplasty (UKA). Favorable postoperative outcomes largely depend on proper patient selection, correct implant positioning, and limb alignment. Computer navigation has a proven value over conventional systems in reducing mechanical errors in total knee arthroplasty (TKA). However, the lack of strong evidence impedes the universal use of computer navigation technology in UKA. Therefore, this study was proposed to investigate the accuracy of component positioning and limb alignment in computer navigated UKA and to observe the role of navigation in proper patient selection.MethodsA total of 50 knees (38 patients) underwent computer navigated UKA between 2016 and 2018. All operations were performed by the senior surgeon using the same navigation system and implant type. The navigation system was used as a tool to aid patient selection: knees with preoperative residual varus > 5° on valgus stress and hyperextension > 10° were switched to navigated TKA. We measured the accuracy of component placement in sagittal and coronal planes on postoperative radiographs. Functional outcomes were also evaluated at the final follow-up (a minimum of 16 months).ResultsNine patients had tibia vara and 14 patients had preoperative hyperextension deformity. We observed coronal outliers for the tibial component in 12% knees and for the femoral component in 10% knees. We also observed sagittal outliers for the tibial component in 14% knees and for the femoral component in 6% knees. There was a significant improvement in the functional score at the final follow-up. On multiple linear regression, no difference was found in functional scores of knees with or without tibia vara (p = 0.16) and with or without hyperextension (p = 0.25).ConclusionsOur study further validates the role of computer navigation in desirable implant positioning and limb alignment. We encourage use of computer-assisted navigation as a tool for patient selection, as it allows intraoperative dynamic goniometry and provides real-time kinematic behavior of the knee to obviate pitfalls such as significant residual varus angulation and hyperextension that predispose early failure of UKA.     

Outcome of Revision Surgery for the Idiopathic Stiff Total Knee Arthroplasty

BackgroundIdiopathic stiff total knee arthroplasty (TKA) represents one of the most challenging subsets of the stiff TKA, as the etiology is unknown and there is no consensus on the most appropriate surgical treatment modality. Therefore, the aim of this study is to report on postoperative outcomes of revision surgery for idiopathic stiff TKA.MethodsWe retrospectively reviewed 189 consecutive patients (202 knees) who underwent revision TKA for stiffness: (1) 101 knees in the idiopathic stiffness cohort and (2) 88 in the non-idiopathic stiffness cohort. In the idiopathic stiffness cohort, 42 knees underwent isolated tibial insert exchange and 59 knees underwent component revision. Perioperative knee range of movement and complications were analyzed.ResultsThe overall revision surgery outcomes of the idiopathic stiffness cohort were worse than those of the non-idiopathic stiffness cohort with regard to maximum flexion (91.7° vs 100.1°, P = .02) and flexion range of motion (ROM) (87.6° vs 97.1°, P = .01). In the idiopathic stiffness cohort, isolated tibial insert exchange demonstrated greater maximum flexion (96.8° vs 88.4°, P = .06) and flexion ROM (93.2° vs 83.9°, P = .07). In terms of re-revision rates, the isolated tibial insert exchange idiopathic stiffness cohort demonstrated lower re-revision rates compared to the component revision idiopathic stiffness cohort (16.7% vs 31.0%, P = .01).ConclusionThis study demonstrates that the overall revision surgery outcome of idiopathic stiff TKA is worse than non-idiopathic TKA stiffness. In idiopathic stiffness cohorts, isolated tibial insert exchange was associated with lower re-revision rates than component revision, with similar efficacy in improving ROM, suggesting that isolated tibial insert exchange may be a preferred surgical treatment option in TKA patients with idiopathic stiffness.     

Prevalence of proximal tibia vara in Indonesian population with knee osteoarthritis

BackgroundProximal tibia vara has drawn interest since the concept of constitutional varus was introduced. Proximal tibia vara is a condition where the knee varus tilt the tibia condyle medially and shift the tibial articular surface medially. This condition affects medial proximal tibial angle measurements and the placement of the tibial implant in knee replacement surgery. Thus, it challenged the neutral knee arthroplasty alignment target because some people may present a proximal tibia vara. This study assesses the prevalence of the proximal tibia vara and the correlation to knee osteoarthritis grade.MethodsThis retrospective study was carried out from January 2021 to June 2021. Eighty-five limbs were included with the following inclusion criteria: knee osteoarthritis patients who received a long view lower extremity radiograph. The exclusions criteria were (1) patients who had undergone arthroplasty and lower extremity surgery before and (2) valgus knee deformity. The outcomes in this study were HKAA, MAD, TAD, MPTA, PTRP, LDFA, and PTS. Intraclass correlation (ICC) using two-way mixed was used to assess the reproducibility of the radiographic parameters. Multiple logistic regression was used to evaluate the correlation between knee osteoarthritis grade and radiographs parameters (MAD and TAD).ResultA total 85 limbs from 52 patients were assessed in this study. Proximal tibia vara was found in 18 knees (21%.). The logistic regression was performed to assess the correlation between the severity of the knee osteoarthritis and radiographic parameters (MAD, TAD, LDFA, and PTS) with an overall p-value < 0.001 and pseudo-R² = 0.29.ConclusionA significant portion of patients with knee osteoarthritis have proximal tibia vara, and it is a pre-existing condition. Since the pre-existing proximal tibia vara affects preoperative measurements, a long-standing lower extremity x-ray is recommended to be obtained as part of knee replacement preparation.     

What Is the Critical Tibial Resection Depth During Unicompartmental Knee Arthroplasty? A Biomechanical Study of Fracture Risk

BackgroundFracture after medial unicompartmental knee arthroplasty (UKA) is a rare complication. Biomechanical studies evaluating association between depth of resection and maximum load to failure are lacking. The purpose of this study is to establish the relationship between depth of resection of the medial tibial plateau and mean maximum load to failure.MethodsMedial tibial resections were performed from 2 to 10 mm in 25 standardized fourth-generation Sawbones composite tibias (Sawbones, Vashon Island, Washington). A metal-backed tibial component with a 9-mm polyethylene bearing was used (Stryker PKR). Tibias were mounted on a biomechanical testing apparatus (MTESTQuattro) and axially loaded cyclically 10 times per cycle and incrementally increased until failure occurred.ResultsLoad to failure was recorded in 25 proximal tibia model samples after medial UKA using sequential resections from 2 to 10 mm. Analysis of variance testing identified significant differences in mean maximum load to failure between groups (P = .0003). Analysis of regression models revealed a statistically significant fit of a quadratic model (R² = 0.59, P = .0001). The inflection point of this quadratic curve was identified at 5.82 mm, indicating that the maximum load to failure across experimental models in this study began to decline beyond a resection depth of 5.82 mm.ConclusionIn this biomechanical model, medial tibial resections beyond 5.82 mm produced a significantly lower mean load to failure using a quadratic curve model. Resections from 2 to 6 mm showed no significant differences in mean load to failure. Identification of the tibial resection depth at which the mean load to failure significantly decreases is clinically relevant as this depth may increase the risk of periprosthetic fracture after a medial UKA.     

Lower limb alignment in healthy Japanese adults

BackgroundKnowledge regarding the normal alignment of the lower limb is important when considering alignment for total knee arthroplasty. However, few studies have explored the lower limb alignment of healthy Japanese subjects.MethodsBetween July and October 2020, we performed whole leg standing radiography of 120 legs of 60 healthy adult Japanese volunteers aged <50 years in the closed-leg stance. The measurement parameters were hip knee ankle angle (positive for varus), percentage of constitutional varus (hip knee ankle angle ≥ 3°), mechanical axis deviation ratio, mechanical lateral distal femoral angle, medial proximal tibial angle, joint line convergence angle (positive for lateral opening), and tibial joint line angle (positive for medial inclination).ResultsThe mean measured values for all volunteers, men and women, were as follows: hip knee ankle angle (°), 2.3, 2.6, and 2.0; mechanical axis deviation ratio, 35.8, 35.6, and 36.9; mechanical lateral distal femoral angle (°), 86.7, 87.0, and 86.7; medial proximal tibial angle (°), 85.6, 85.0, and 86.2; joint line convergence angle (°), 0.6, 0.3, and 0.8; and tibial joint line angle (°), ?1.0, ?0.7, ?1.4, respectively. The percentage of constitutional varus was 35.8% overall, 35.8% in men and 35.3% in women. Only the medial proximal tibial angle was smaller in men than that in women (p = 0.003).ConclusionsThe mechanical lateral distal femoral and medial proximal tibial angles were smaller, hip knee ankle angle was larger, and percentage of constitutional varus was higher in Japanese subjects than those reported for subjects in other countries. Our findings improve the understanding of Japanese-specific alignments when considering alignment for lower limb surgery, especially, total knee arthroplasty.     

Satisfactory Outcomes of All-Poly Fixed Bearing Unicompartmental Knee Arthroplasty for Avascular Osteonecrosis Versus Osteoarthritis: A Comparative Study With 10 to 22 Years of Follow-up

BackgroundWhile good mid-term results for treating spontaneous knee osteonecrosis (SPONK) with unicompartmental knee arthroplasty (UKA) have been reported, concerns remain about implant survival at long-term. This study aimed to compare outcomes and survivorship of UKA for SPONK vs osteoarthritis at a minimum of 10 years.MethodsThis case-control study included medial UKA for femoral SPONK operated between 1996 and 2010 with a minimum 10-year follow-up (n = 47). Each case was matched with a medial UKA for osteoarthritis based on body mass index (BMI), gender, and age. Knee Society Score (KSS), complications and radiological (loosening) data were collected at the last follow-up. Kaplan-Meier survivorship analysis was performed using revision implant removal as endpoint.ResultsThe mean follow-up was 13.2 years (range 10 to 21 years). Mean age and BMI were 72.9 ± 8.4 years and 25.5 ± 3.6 Kg/m² in SPONK group. At last follow-up, knee and function KSS were 89.5 ± 12 and 79 ± 18 in SPONK group vs 90 ± 15 (P = .85) and 81.7 ± 17 (P = .47) in control group. Complications and radiological results showed no significant differences. The survival rate free from any revision was 85.1% at last follow-up in SPONK group and 93.6% in control group (P = .23). The leading cause for revision was aseptic tibial loosening (57.1%) in SPONK group. The 15-year survival estimate was 83% in SPONK group.ConclusionSatisfactory clinical outcomes at long-term after UKA for femoral SPONK were observed, similar to those after UKA for osteoarthritis, despite a higher risk of tibial loosening in the SPONK group. No symptomatic femoral loosening leading to a revision was observed.Level of EvidenceIV.     

The Functional Status of the ACL in Varus OA of the Knee: The Association With Varus Deformity and Coronal Tibiofemoral Subluxation

BackgroundThe present article analyzes the association of the functional anterior cruciate ligament (ACL) status and the overall varus deformity and coronal tibiofemoral subluxation (CTFS) in varus OA of the knee.MethodsOne hundred consecutive knees with varus OA in 84 patients were prospectively included. Knees were divided into two groups, in accordance with the ACL status (functionally sufficient or insufficient). All included patients were potential candidates for unicompartmental knee arthroplasty with predominantly medial compartment OA. Knees with Kellgren/Lawrence ≥ grade 3 in the lateral compartment were excluded leaving 79 knees to be included in this study. Mechanical varus deformity and CTFS were evaluated on AP radiographs and valgus stress radiographs, and compared between the two groups.ResultsKnees with a functionally insufficient ACL had significantly more varus deformity on hip-to-ankle AP standing radiographs (P = .001) and on valgus stress radiographs (P = .017). CTFS on AP standing radiographs was significantly higher (P = .045) in knees with a functionally insufficient ACL. Seventy-three percent (8/11) of the ACL-insufficient knees had a varus deformity of ≥10° and 64% (7/11) of ACL-insufficient knees had CTFS ≥ 6mm. By contrast, only one patient (2%, 1/41) with an insufficient ACL had< 10° varus deformity and a CTFS of < 6mm.ConclusionFunctional ACL insufficiency in osteoarthritic varus knees is associated with greater varus deformity and more advanced CTFS. Seventy-three percent of ACL-insufficient knees had a varus deformity of ≥10° and 64% of ACL-insufficient knees a CTFS of ≥ 6mm. In the work-up for medial unicompartmental knee arthroplasty, functional ACL insufficiency is likely in knees with varus deformity of ≥10° and CTFS of ≥ 6mm.     

Partial and Combined Partial Knee Arthroplasty: Greater Anterior-Posterior Stability Than Posterior Cruciate–Retaining Total Knee Arthroplasty

BackgroundLittle is known regarding anterior-posterior stability after anterior cruciate ligament–preserving partial (PKA) and combined partial knee arthroplasty (CPKA) compared to standard posterior cruciate–retaining total knee arthroplasty (TKA).MethodsThe anterior-posterior tibial translation of twenty-four cadaveric knees was measured, with optical tracking, while under 90N drawer with the knee flexed 0-90°. Knees were tested before and after PKA, CPKA (medial and lateral bicompartmental and bi-unicondylar), and then posterior cruciate–retaining TKA. The anterior-posterior tibial translations of the arthroplasty states, at each flexion angle, were compared to the native knee and each other with repeated measures analyses of variance and post-hoc t-tests.ResultsUnicompartmental and bicompartmental arthroplasty states had similar laxities to the native knee and to each other, with ≤1-mm differences throughout the flexion range (P ≥ .199). Bi-unicondylar arthroplasty resulted in 6- to 8-mm increase of anterior tibial translation at high flexion angles compared to the native knee (P ≤ .023 at 80-90°). Meanwhile, TKA exhibited increased laxity across all flexion angles, with increased anterior tibial translation of up to 18 ± 6 mm (P < .001) and increased posterior translation of up to 4 ± 2 mm (P < .001).ConclusionsIn a cadaveric study, anterior-posterior tibial translation did not differ from native laxity after PKA and CPKA. Posterior cruciate ligament–preserving TKA demonstrated increased laxity, particularly in anterior tibial translation.