Does Residual Varus Alignment Cause Increasing Varus Laxity at a Minimum of Five Years After Total Knee Arthroplasty?

Comparison of Outcomes in Obese Patients after Total Knee Arthroplasty with Neutral or Mild Varus: A Retrospective Study with 8-Year Follow-Up

OBJECTIVES

Residual varus after total knee arthroplasty (TKA) can affect functional outcomes, which may worsen in the presence of obesity. However, no studies were found to compare the outcomes of obese patients involving postoperative residual mild varus or neutral. The aim of this study was to compare postoperative complications and prosthesis survival, and functional outcomes for knees of obese patients with neutral or mild varus after TKA.

METHODS

We retrospectively reviewed 188 consecutive obese patients (body mass index ≥30 kg/m2) at our hospital who underwent TKA due to varus knee osteoarthritis from January 2010 to December 2015. The mechanical hip-knee-ankle axis angle was measured in all patients at admission and discharge. Knee functions were retrospectively assessed based on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, Knee Society Knee Score (KS-KS), Knee Society Function Score (KS-FS), Forgotten Joint Score (FJS), and range of motion (ROM). Continuous data were compared between knees with neutral or mild varus alignment using analysis of Student's t test or variance or the Kruskal-Wallis test as appropriate. For multiple comparisons of outcomes, we used Bonferroni-Dunn method to adjust p-values. Categorical data were compared using the chi-squared test.

RESULTS

Of the 156 knees in 137 obese patients who completed follow-up for a mean of 8.32 ± 1.47 years, 97 knees were corrected from varus to neutral and 54 knees were kept in mild residual varus. Patients with mild varus knees had significantly WOMAC (8.25 ± 8.637 vs. 14.97 ± 14.193, p = 0.009) and better FJS (86.03 ± 15.607 vs. 70.22 ± 30.031, p = 0.002). The two types of knees did not differ significantly in KS-KS, KS-FS, or ROM. Although one patient with a neutral knee had to undergo revision surgery, there was no significant difference between two groups.

CONCLUSIONS

For obese patients with osteoarthritis, preservation of residual varus alignment after TKA can improve functional outcomes without compromising prosthesis survival.

Residual varus alignment after posterior-stabilized total knee arthroplasty limits medial soft tissue remodeling

BACKGROUND

Proper lower limb alignment and soft tissue balance are significant indicators to measure the success of total knee arthroplasty (TKA). Previous studies have confirmed that soft tissue relaxation around the knee after TKA will change over time; however, the relationship between lower limb alignment and soft tissue balance after TKA remains unclear. We studied (1) whether the change of soft tissue balance around the knee with time after posterior-stabilized (PS) TKA would affect the alignment of the lower limbs; (2) Whether the accuracy of lower limb alignment during PS TKA affects postoperative soft tissue remodeling.

METHODS

In this study, 100 patients were recruited after PS TKA. Among them, 50 patients with a hip knee ankle (HKA) angle of ≤  ± 3° were set as the neutral group, and 50 patients with an HKA angle of >  ± 3° were set as the deviation group. The imaging results measured the HKA angle before the operation as well as the HKA, varus, and valgus angles at 1, 3, 6, 12, and 24 months after TKA. Clinical assessment included range of motion (ROM), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Knee Society Score (KSS).

RESULTS

Eight people were excluded from the study. After the exclusion, the study enrolled 47 patients in the neutral group and 45 patients in the deviant group and were followed for up to 2 years. There was no statistical significance in mean varus angles as well as HKA angle changes during the follow-up phase of each groups (P > 0.05). The mean valgus angles of the patients in the neutral group group were 2.47°, 3.45°, 3.63°, 3.60° and 3.63°, and in the deviation group were 2.45° (P = 0.841), 2.88° (P < 0.001), 3.07° (P < 0.001), 3.06° (P < 0.001), and 3.10° (P < 0.001). ROM, WOMAC and KSS of the two groups were significantly improved after operation, with no difference between the two groups.

CONCLUSION

This study shows that whether the alignment is accurate or not in the early stage after TKA, the relaxation of the medial and lateral soft tissues of the knee joint change; however, this change will not significantly affect the alignment of the lower limbs. Postoperative residual varus deformity limits medial soft tissue remodeling.

LEVEL OF EVIDENCE

III.

Effect of total knee arthroplasty for valgus knee correction on clinical outcome and patellar position

PURPOSE

The purpose was to investigate the effect of different degrees of valgus deformity correction on patellar position and clinical outcome in patients with valgus knees after total knee arthroplasty (TKA).

METHODS

We retrospectively analyzed and followed 118 patients with valgus knees. Based on the post-operative hip-knee-ankle (HKA), patients were divided into three groups: neutral (±3°), mild (3-6°), and severe (> 6°). Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), range of motion (ROM), and Knee Society Score (KSS) were used to evaluate post-operative clinical efficacy. Also, the patellar tilt angle (ε-angle), congruence angle (θ-angle), and Insall-Salvati index (ISI) were used to represent the patellar position. Post-operative observation indicators included HKA, angle of the femur (α-angle), tibial angle (β-angle), femoral component flexion angle (γ-angle), and tibial component posterior slope angle (δ-angle).

RESULTS

All patients showed significant improvements in HKA, ROM, WOMAC, and KSS after operation (P < 0.001). Regarding patellar position, the ISI values decreased to varying degrees (P < 0.05). The patellar tilt angle was significantly increased in the severe valgus group compared to that in the mild valgus and neutral groups (P < 0.001). Univariate analysis showed that the degree of post-operative residual valgus was significantly affected by WOMAC, KSS, α-, ε-, and θ-angles.

CONCLUSION

Minor valgus undercorrection did not affect the short-term outcome after TKA; however, when the residual valgus angle was > 6°, the post-operative scores were significantly reduced. Inadequate valgus correction does not result in significant changes in patellar height but may increase the risk of poor patellar tracking.

Mid-Term Clinical and Radiological Results at a Tertiary Care Hospital in Türkiye: Is Residual Varus Really Important After Mechanically-Aligned Total Knee Arthroplasty?

INTRODUCTION

 Traditionally, in total knee arthroplasty (TKA), it is aimed to keep the mechanical axis of the lower extremity neutral (mechanical alignment: 3° varus-valgus in the coronal plane) to improve long-term outcomes. This study aimed to assess the mid-term radiological and clinical results of patients with postoperative residual varus (more than 3° of varus) after mechanically-aligned TKA.

METHODS

A total of 616 individuals who had undergone TKA for primary knee osteoarthritis between 2008 and 2013 in our tertiary care hospital were retrospectively examined. All TKAs were performed with the mechanical alignment strategy. For radiological evaluation, hip-knee-ankle (HKA) angle, knee alignment angle (KAA), mechanical medial proximal tibial angle (mMPTA), knee inclination (KI), joint line orientation angle relative to ground (JLOA-G), posterior tibial slope (PS), joint line convergence angle (JLCA) were measured. Besides, patients' latest radiographs were screened for any clue of aseptic loosening or mechanical failure. Knee Society Score (KSS) (knee and functional subgroups), and Lysholm, Oxford, and Tegner scores were used for clinical evaluation. In addition, knee flexion and extension limitations were assessed.

RESULTS

After applying the exclusion criteria, a minimum of five-year follow-up result of 110 patients was demonstrated. There were 101 females (92%) and nine males (8%). The mean follow-up time was 65.8 ± 6.3 months (range: 60.8-75.8 years). The mean age was 65.9 ± 7.7 years (range: 39 to 89 years). The preoperative mean mechanical axis angle of the lower extremity was 17.3° ± 7.8° (range: 13.4-43.9°), whereas it was 8.3° ± 3.6° (range: 3.2-19.8°) postoperatively. The preoperative mean flexion angle was 90.7° ± 23.8° (range: 40-130°), and the extension limitation was -2.5° ± 7.4° (range: -40-0°), whereas, postoperatively, they were 102.8° ± 15.4° (range from 40° to 150°) and -3.7° ± 7.5° (range from -40° to 0°), respectively. The latest follow-up's mean KSS knee subgroup was 67 ± 18.4 (range: 12-93), the mean KSS functional subgroup was 74 ± 23.6 (range: 20-100), the mean Lysholm score was 81.7 ± 15.7 (range:25-100), the mean Tegner score was 3.65 ± 0.99 (range: 1-5), the mean Oxford score was 37.4 ± 6.5 (range: 9-48). There was no patient with aseptic loosening or mechanical failure.

CONCLUSIONS

In the mid-term follow-up of patients with residual varus after mechanically-aligned TKA, satisfactory clinical and radiological results were obtained without aseptic loosening or implant failure.

The impact of postoperative inclination of the joint line on clinical outcomes in total knee arthroplasty using a prosthesis with anatomical geometry

The goal of this study was to investigate the impact of postoperative inclination of the joint line on clinical results after total knee arthroplasty (TKA) using a prosthesis with anatomical geometry. This study included 145 primary cruciate-retaining type of knee prosthesis with anatomical geometry. Three years postoperatively, clinical outcomes including the patient-reported outcomes (PROs) were recorded. Limb alignment was evaluated by the hip-knee-ankle (HKA) axis and inclination of the joint line was assessed by the joint line orientation angle (JLOA). Knees were divided into two groups according to the HKA: in-range (- 3 to 3°) and outlier group (< - 3° or > 3°) or the JLOA: in-range (2-4°) and outlier group (< 2° or > 4°), and clinical outcomes were compared between the groups. Postoperative Knee Society Function Score (KS-FS) was significantly higher in the HKA in-range group than the outlier group (p = 0.01). The Knee Society Knee Score and all subscales of the Knee injury Osteoarthritis Outcome Score were comparable between the groups. A multivariate analysis revealed a significant association between age at operation and postoperative KS-FS > of 80 points. Neither HKA in-range nor JLOA in-range were associated with the higher knee function. In conclusion, TKA-postoperative inclination of the joint line was not relevant to the short-term PROs. Treatment strategies that attempt to make joint line inclination in order to improve postoperative PROs should be avoided, and alignment goals such as kinematic alignment should be considered carefully.

Tibiofemoral lift-off and resulting laxity following total knee arthroplasty: Frequency in a series of 906 continuous cases and functional consequences at 4 years' follow-up in a case-control study

BACKGROUND

Tibiofemoral instability is one reason for early revision of total knee arthroplasty. It can be the consequence of tibiofemoral laxity, especially in the coronal plane with tibiofemoral lift-off. But does femoral condyle lift-off on conventional postoperative radiographs suggest the presence of laxity or potential instability? To our knowledge, this question has not yet been answered. This led us to conduct a retrospective study to evaluate (1) the frequency of lift-off on postoperative radiographs, (2) the relationship between lift-off and laxity in the short term and (3) the functional consequences of lift-off.

HYPOTHESIS

Postoperative lift-off is a rare event that is predictive of laxity.

METHODS

We carried out a single-center retrospective study using postoperative radiographs from patients who underwent primary total knee arthroplasty between 2014 and 2016. The sample consisted of 906 patients. Lift-off was defined as a tibiofemoral angle of 3° or more on immediate postoperative radiographs (day 0) that were non-weightbearing and had no stress applied. The functional outcomes were determined in the 17 patients identified as having lift-off who had been operated in the first year (2014) to ensure the follow-up was long enough. These patients were compared to 34 matched control patients who were operated the same year and chosen randomly among patients not having lift-off. The matching ratio was 2 controls to 1 case. Preoperative and surgical data were compiled from each patient's electronic medical record. Patients were evaluated at 4 years postoperatively using the subjective Oxford-48, objective HSS score, IKS score, overall patient satisfaction and stress radiographs of the knee. The cases of lift-off observed in 2014 (n=17) were paired with a control group of patients selected randomly during 2014.

RESULTS

The frequency of the lift-off event was 63/906 or 7%. The frequency was consistent over the three years studied: 7.1% in 2014 (19/269), 6.2% in 2015 (22/354) and 7.8% in 2016 (22/283). There was no significant difference between the two groups (17 with lift-off and 34 without) in the sex, age, body mass index and coronal plane deformity (preoperative HKA angle). At a mean follow-up of 4 years (range 12-49 months), the knees with postoperative lift-off had more laxity (p=0.002), particularly laxity when varus stress was applied (p=0.009). There were no other significant differences in the outcomes.

DISCUSSION

Immediate postoperative lift-off after total knee arthroplasty is not a rare event, with a 7% frequency in our study. While it reveals that laxity is present in the particular compartment, there is no evidence of functional consequences at 4 years' follow-up; however, a long-term assessment is required to verify this finding.

LEVEL OF EVIDENCE

III - case-control study.

Functional outcomes of residual varus alignment versus mechanical alignment in total knee arthroplasty for varus osteoarthritis: A preferred reporting items for systematic reviews and meta-analyses-compliant meta-analysis

BACKGROUND

One in five patients with mechanical alignment (MA) after total knee arthroplasty (TKA) was reportedly dissatisfied. As constitutional varus knees are common, restoring the patients' natural residual varus (RV) alignment is as an appealing alternative to neutral MA. This meta-analysis aimed to evaluate the effects of RV alignment on the functional outcomes compared with those of MA in TKA for the knees with varus osteoarthritis.

METHODS

The MEDLINE/PubMed, Cochrane Library, and EMBASE databases were comprehensively searched for papers comparing the effects of RV alignment and MA on the functional outcomes from the time of inception of the databases to July 2020. Studies comparing the functional outcomes in the knees subjected to TKA with RV alignment (case group) and MA (control group) were included. The Knee Society knee and functional scores (KSKS and KSFS, respectively), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), Oxford knee score (OKS), and forgotten joint score (FJS) were compared.

RESULTS

Seven studies were finally included; all studies showed a low risk of selection bias and provided detailed demographic data. The pooled mean difference in the KSKS (0.06, 95% confidence interval [CI]: -0.14 to 0.27; p = 0.55) and KSFS (0.08, 95% CI: -0.08 to 0.35; p = 0.56) between RV alignment and MA did not significantly differ. The pooled mean differences in the WOMAC (-0.25, 95% CI: -0.57 to 0.07; p = 0.12), OKS (0.06, 95% CI: -0.15 to 0.27; p = 0.56), and FJS (0.41, 95% CI: -0.18 to 1.00; p = 0.18) between the groups were not significant.

CONCLUSION

The beneficial effects of RV alignment on the functional outcomes are limited compared to those of MA in TKA for varus osteoarthritis to date. Currently, TKA with neutral MA should be considered as the gold standard.

Comparison of Outcomes After Total Knee Arthroplasty Involving Postoperative Neutral or Residual Mild Varus Alignment: A Systematic Review and Meta-analysis

Comparing mainly clinical and functional outcomes as well as prosthesis survival with neutral and residual mild varus alignment, we searched PubMed, Embase, Cochrane Library and Web of Science databases from 1 January 1974 to 18 December 2020 to identify studies comparing clinical and functional outcomes as well as prosthesis survival in the presence of different alignments after total knee arthroplasty (TKA) for varus knees. The included studies were assessed by two researchers according to the Newcastle–Ottawa Scale (NOS). Postoperative neutral alignment (0° ± 3°) was compared to residual mild varus (3°–6°) and residual severe varus (>6°). Meta‐analysis was performed using Review Manager 5.3. The odds ratios (OR) and mean differences (MD) were used to compare dichotomous and continuous variables. The fixed‐effect model and random‐effect model were used to meta‐analyze the data. Nine studies were included in the meta‐analysis with 1410 cases of postoperative neutral alignment, 564 of residual mild varus alignment and 175 of residual severe varus alignment following TKA, all of which were published after 2013. Three studies scored 7 points on the NOS, while the remaining studies scored 8 points, suggesting high quality. The pooled mean differences (MDs) of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score were 1.07 [95% confidence interval (CI) −1.06 to 3.20; P = 0.32; I² = 79%]. The meta‐analysis showed that neutral alignment and mild varus alignment were associated with similar the Oxford Knee Score (OKS), Knee Society Knee Score (KS‐KS), and Knee Society Function Score (KS‐FS), while neutral alignment was associated with lower Forgotten Joint Score (FJS) [mean difference −6.0, 95% confidence interval (CI) −9.37 to −2.64, P = 0.0005]. Neutral alignment was associated with higher KS‐KS than severe alignment (M 2.98, 95% CI 1.42 to 4.55, P = 0.0002; I² = 0%) as well as higher KS‐FS (M 8.20, 95% CI 4.58 to 11.82, P < 0.00001; I² = 0%). Neutral alignment was associated with similar rate of survival as mild varus alignment (95% CI 0.36 to 9.10; P = 0.48; I² = 65%) or severe varus alignment (95% CI 0.94 to 37.90; P = 0.06; I² = 61%). There was no statistical difference in others. Residual mild varus alignment after TKA may lead to similar or superior outcomes than neutral alignment in patients with preoperative varus knees, yet the available evidence appears to be insufficient to replace the current gold standard of neutral alignment. Severe varus alignment should be avoided.

Degree of coronal alignment correction can't predict knee function in total knee replacement

BACKGROUND

Whether neutral alignment brings better clinical outcomes is controversial. Consideration of the preoperative knee condition of patients and some limitations of previous studies, we suggested that other index may be more important than a generic target of 0° ± 3° of a neutral axis to reflect changes in coronal alignment after total knee replacement (TKR). The purpose of this study was to explore the relationship between alignment and functional outcome with a new grouping method and the concept of correction rate.

METHODS

The study included 358 knees, the mean follow-up period was 3.62 years. A new grouping method was adopted to divide patients into three groups based on the degree of correction of mechanical femoral-tibial angle (MFTA): under-correction (n = 128), neutral (n = 209) and over-correction (n = 21). Hospital for Special Surgery (HSS) score were compared among the 3 groups (ANOVA with or without LSD t-test). In addition, we also attempt to further explore whether the concept of correction rate can predict postoperative functional score (Simple linear correlation analysis).

RESULTS

HSS score showed significant improvement in all groups. There was no difference in HSS score (88.27 vs 88 vs 85.62) (p = 0.88) or incremental scores (26.23 vs 25.22 vs 22.88) (p = 0.25) based on the postoperative alignment category for the degree of correction of MFTA at the last follow-up. The correlational analyses also didn't show any positive results (r = -0.01 p = 0.95, r = -0.01 p = 0.97, r = 0.11 p = 0.15, r = 0.01 p = 0.90).

CONCLUSION

Categorization of optimal coronal alignment after TKR may be impractical. But we still believe that the concept of correction rate and new grouping method are worthy of research which can reflects the preoperative knee condition and the change of coronal alignment. Perhaps it can be better used in TKR in the future.

LEVEL OF EVIDENCE

III.

Clinical impact of component placement in manually instrumented total knee arthroplasty : a systematic review

AIMS

The goal of the current systematic review was to assess the impact of implant placement accuracy on outcomes following total knee arthroplasty (TKA).

METHODS

A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using the Ovid Medline, Embase, Cochrane Central, and Web of Science databases in order to assess the impact of the patient-reported outcomes measures (PROMs) and implant placement accuracy on outcomes following TKA. Studies assessing the impact of implant alignment, rotation, size, overhang, or condylar offset were included. Study quality was assessed, evidence was graded (one-star: no evidence, two-star: limited evidence, three-star: moderate evidence, four-star: strong evidence), and recommendations were made based on the available evidence.

RESULTS

A total of 49 studies were identified for inclusion. With respect to PROMs, there was two-star evidence in support of mechanical axis alignment (MAA), femorotibial angle (FTA), femoral coronal angle (FCA), tibial coronal angle (TCA), femoral sagittal angle (FSA), femoral rotation, tibial and combined rotation/mismatch, and implant size/overhang or offset on PROMs, and one-star evidence in support of tibial sagittal angle (TSA), impacting PROMs. With respect to survival, there was three- to four-star evidence in support FTA, FCA, TCA, and TSA, moderate evidence in support of femoral rotation, tibial and combined rotation/mismatch, and limited evidence in support of MAA, FSA, and implant size/overhang or offset impacting survival.

CONCLUSION

Overall, there is limited evidence to suggest that PROMs are impacted by the accuracy of implant placement, and malalignment does not appear to be a significant driver of the observed high rates of patient dissatisfaction following TKA. However, FTA, FCA, TCA, TSA, and implant rotation demonstrate a moderate-strong relationship with implant survival. Efforts should be made to improve the accuracy of these parameters in order to improve TKA survival. Cite this article: Bone Joint J 2021;103-B(9):1449-1456.

Reliability of stress radiography in the assessment of coronal laxity following total knee arthroplasty

BACKGROUND

Stress radiography is used in the valuation of soft tissue laxity following total knee arthroplasty (TKA). However, reliability and agreement is largely unknown.

METHODS

In this prospective reliability study, we included 15 participants with prior TKA. Standardized coronal stress radiographs were obtained in both extension and flexion and with both varus and valgus stress. All radiographs were repeated (test-retest). In extension the Telos stress device was used, and flexion radiographs were obtained using the epicondylar-view. Three independent raters measured angulation between femoral and tibial component from all radiographs. Reliability was assessed by intra-class correlation coefficient (ICC) and agreement visualized with Bland-Altman plots and by mean difference and limits of agreement (LOA).

RESULTS

Stress radiography in extension showed excellent reliability with ICC = 0.96 (0.95-0.98) and LOA of ±1.2°. Stress radiography at 80-90° of flexion showed good to excellent reliability when measuring medial laxity with ICC = 0.94 (0.89-0.97) and LOA of ±1.7°; however, when measuring lateral laxity the reliability was only moderate to good with ICC = 0.70 (0.51-0.84) and LOA of ±6.3°.

CONCLUSION

Stress radiography is clinically applicable and the methods described in this study provide excellent reliability for measurement of laxity in extension. The reliability of measurements in flexion is good to excellent when measuring medial laxity but only moderate to good when measuring lateral laxity.

Residual varus alignment after total knee arthroplasty increases knee adduction moment without improving patient function: A propensity score-matched cohort study

BACKGROUND

Targeting residual varus alignment in total knee arthroplasty may be functionally beneficial to preoperative varus patients.

METHODS

Bilateral TKA patients were enrolled. According to the postoperative hip-knee-ankle axis, patients were allocated into residual varus (3° ± 1°) alignment group or neutral (0° ± 1°) alignment group. Then, 1:2 propensity score matching was used to match preoperative variables. Finally, matched neutral (n = 45) and varus groups (n = 32) were followed-up for two years and compared. The primary outcome was the Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC). Secondary outcomes were range of motion (ROM), Knee Society knee score and function score, spatiotemporal gait parameters, dynamic alignment, knee flexion angle, knee adduction moment (KAM) and internal knee extension moment.

RESULTS

At two years after surgery, the mean difference of WOMAC score was 0.3 (95% CI, [-3.1, 3.7]) between the two groups. All secondary outcomes, except KAM and dynamic alignment, showed no significant difference between the two groups. Residual varus alignment group showed increased KAM and maximum KAM was 19% higher (P = 0.006).

CONCLUSIONS

Residual varus alignment showed no clinical benefits, and both groups of patients had a functionally identical knee gait biomechanics, except for increased KAM and varus alignment. The authors consider that even in patients with varus alignment, the first principle is still achieving neutral alignment, which is helpful for reducing the KAM.

LEVEL OF EVIDENCE

III, retrospective cohort study.

Over-voluming predicted by pre-operative planning in 24% of total knee arthroplasty

PURPOSE

Numerous studies demonstrated that prosthetic overhang and over-sizing cause pain and stiffness following total knee arthroplasty (TKA), but none considered volume changes within the joint capsule. This study was designed to investigate differences in volumes of resected bone compared to implanted components in TKA, and to determine the incidence and factors related to 'over-voluming'.

METHODS

Three-dimensional reconstructions were created from 100 magnetic resonance imaging scans taken to design patient-specific instruments for TKA. The preoperative simulations were used to calculate the volume ratio (VR) by dividing volume of planned components by that of planned bone resections. Uni- and multi-variable linear regressions were performed to determine associations between 'over-voluming' (VR > 1.0) and gender, implant size and version (standard versus narrow), osteophytes, resection levels, external rotation of the femoral component, hip-knee-ankle (HKA) angle, mechanical lateral distal femoral angle (mLDFA), and mechanical medial proximal tibial angle (mMPTA).

RESULTS

The overall implant/bone volume ratio was 0.91 ± 0.11 (range 0.63-1.16) with 'over-voluming' observed in 24 knees. Multi-variable regression confirmed over-voluming to be associated with lower mLDFA (OR 0.66; CI 0.45-0.93; p = 0.026) and extensive osteophytes (OR 0.14; CI 0.03-0.61; p = 0.014), but not HKA angle (OR 0.98; CI 0.76-1.26; p = n.s.).

CONCLUSIONS

Over-voluming was observed in 24% of knees, in which the implant volume exceeded the resected volume by up to 16%. Over-voluming was associated with intra-articular femoral valgus (low mLDFA), but not directly associated with tibial deformity (mMPTA) or HKA angle. Over-voluming could be associated with prosthetic overhang or excessive tensions within the joint capsule, and, therefore, contribute to unexplained pain and stiffness following TKA.

LEVEL OF EVIDENCE

IV, Retrospective cohort study.

Relationship between outcome scores and knee laxity following total knee arthroplasty: a systematic review

Background and purpose - Instability following primary total knee arthroplasty (TKA) is, according to all national registries, one of the major failure mechanisms leading to revision surgery. However, the range of soft-tissue laxity that favors both pain relief and optimal knee function following TKA remains unclear. We reviewed current evidence on the relationship between instrumented knee laxity measured postoperatively and outcome scores following primary TKA. Patients and methods - We conducted a systematic search of PubMed, Embase, and Cochrane databases to identify relevant studies, which were cross-referenced using Web of Science. Results - 14 eligible studies were identified; all were methodologically similar. Both sagittal and coronal laxity measurement were reported; 6 studies reported on measurement in both extension and flexion. In knee extension from 0° to 30° none of 11 studies could establish statistically significant association between laxity and outcome scores. In flexion from 60° to 90° 6 of 9 studies found statistically significant association. Favorable results were reported for posterior cruciate retaining (CR) knees with sagittal laxity between 5 and 10 mm at 75-80° and for knees with medial coronal laxity below 4° in 80-90° of flexion. Interpretation - In order to improve outcome following TKA careful measuring and adjusting of ligament laxity intraoperatively seems important. Future studies using newer outcome scores supplemented by performance-based scores may complement current evidence.