Early revision for component malrotation in total knee arthroplasty

Midterm results for revision total knee arthroplasty for component malrotation

INTRODUCTION

Accurate positioning of components in total knee arthroplasty (TKA) is essential to a satisfactory outcome. Significant malrotation may lead to chronic pain, stiffness, and dysfunction. This study aims to quantify improvements in functional outcomes following revision surgery for malrotation of either one or both components in TKA versus revision for aseptic loosening.

METHODS

This was a retrospective review of TKAs that matched and compared the two-year functional outcomes of the malrotation group to a functionally similar aseptic loosening group. Functional outcomes were compared between groups using Short Form (SF-12), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), and Knee Society Functional Score (KSFS). Student t-tests and chi-squared or Fisher's tests were used for statistical analysis.

RESULTS

Of the patients revised, 24 had malrotation and 57 had aseptic loosening. A total of 16 femoral and 17 tibial components were revised for malrotation. All 16 femoral components were internally malrotated (mean -4.8 ± 4.1 degrees; range, -0.5 to -16.6). Of the tibial components, 15 were internally malrotated, (mean -9.5 ± 6.6 degrees; range, -2.2 to -23.5) and 2 were externally malrotated (mean 4.6 ± 2.1 degrees; range, 3.1 to 6.0). All functional outcome measures significantly improved comparably within both groups preoperatively to 24 months postoperatively. At 24 months, functional outcome measures were comparable between the groups and WOMAC function scores were significantly higher in the malrotation group.

CONCLUSION

Revision TKA for malrotation can yield clinically and statistically significant functional improvements, similar in magnitude to those seen following revision TKA for aseptic loosening.

LEVEL OF EVIDENCE

Level III.

Curve-on-curve technique does not improve tibial coverage in total knee arthroplasty in comparison to tibial tuberosity technique with use of anatomical implants: randomized controlled trial

INTRODUCTION

During the last years, main attention while performing total knee replacement was paid to femoral component alignment; however, there is still lack of studies concerning tibial baseplate rotational alignment, especially in terms of anatomical designs of knee prosthesis. Some recent studies proved that tibial baseplate malrotation might be a cause of knee pain and patients' dissatisfaction. The aim of this study was to compare tibial component rotation and its coverage on the tibial plateau achieved with curve-on-curve and tibial tuberosity techniques (t-t technique) with use of anatomic knee designs with asymmetric tibial baseplate.

MATERIALS AND METHODS

A total of 88 patients were randomly assigned in a 1:1 ratio to undergo total knee arthroplasty with use of the PERSONA PS (Zimmer Biomet) knee design with an asymmetric baseplate. The rotation of the tibial component was assessed and performed with two different techniques: curve-on-curve technique and tibial tuberosity technique. Tibial component rotation was measured on computed tomography (CT) scans using the method suggested by Benazzo et al. and designed for asymmetrical implants. For the measurement of the tibial bone coverage, the component surface area was outlined and measured on a proper CT section, then the tibial cut surface area was outlined and measured on a section just below the cement level. Pre- and post-operative range of motion was measured by another independent researcher 12 months post-operatively during follow-up visit.

RESULTS

There was a statistically significant difference between both groups in median value of tibial rotation angle: 7° (interquartile range (IQR) = 0-12) in curve-on-curve technique group vs 2° (IQR-1-7) in tibial tuberosity technique group, probability value (p) = 0.0041, with values above 0 meaning external rotation of the component. There was no statistically significant difference between both groups in terms of range of motion (ROM) with average values of 124.3° ± 13.0° for curve-on-curve technique and 125.6° ± 12.8° for t-t technique with p = 0.45. There was a statistically insignificant difference between both groups in terms of coverage percentage in slight favor for curve-on-curve technique (85.9 ± 4.2 vs 84.5 ± 4.8, p = 0.17).

CONCLUSION

In this study, no difference between the groups in terms of tibial bone coverage and range of motion was proved, even though both techniques differed significantly with values of tibial rotation. Future studies should be focused on influence of specific values of tibial rotation on patient-reported outcomes and survivorship of anatomic knee implants.

Internal Rotation, Varus, and Anterior Femoral Component Malalignments Adversely Affect Patellofemoral Joint Kinematics in Patellofemoral Arthroplasty

Background

Patellofemoral arthroplasty (PFA) is reported to provide nearly normal PF joint kinematics but only with adequate surgical techniques. This study evaluated the effects of various femoral component settings on patellar component biomechanics.

Methods

A dynamic musculoskeletal computer simulation analyzed normal knee and standard PFA models, as well as 8 femoral component malposition models: 5° internal or external rotation, 5° valgus or varus, 5° extension or flexion, and 3-mm or 5-mm anterior positioning. Mediolateral patellar translation, lateral patellar tilt, and contact force and stress at the PF joint were measured in each model during gait.

Results

The patella in the standard PFA model was shifted up to 5.0 mm laterally near heel off and was tilted up to 3.0° laterally at heel strike compared to the normal knee model. The patella in the external rotation model translated more laterally in the direction of the femoral component setting than in the standard model. However, in the internal rotation and varus alignment models, the patellar lateral shift occurred largely in the opposite direction of the femoral component setting. The patella in most models was tilted in the same direction as the femoral component setting. The PF contact force was increased, especially in the anterior femoral position models, by up to 30 MPa compared with 20 MPa in the standard model.

Conclusions

Internal rotation, varus, and anterior femoral component settings during PFA should be avoided to reduce postoperative complications, whereas external rotation might be appropriate only for cases with lateral patellar instability.

Component Rotation in Well-Functioning, Gap-Balanced Total Knee Arthroplasty without Navigation

INTRODUCTION

Malalignment of total knee arthroplasty (TKA) components is a potential cause of clinical failure following TKA. Since the goal of a gap-balancing (GB) technique is equal flexion and extension gaps secondary to soft-tissue balancing, and not necessarily component alignment, variation in component placement may exist. Our purpose was (1) to evaluate precision of component alignment in well-functioning GB TKAs performed without the aid of navigation using computed tomographic (CT) evaluation and (2) to determine any relationship between femoral version and/or tibial torsion and TKA component positioning.

METHODS

There were 93 well-functioning TKAs performed with an extension gap first GB technique with a minimum 2-year follow-up evaluated using CT to assess component rotational alignment, as well as osseous femoral version and tibial torsion. Femoral and tibial rotational alignment was assessed by previously described methods.

RESULTS

The mean Knee Society Score was 185.7 ± 21.7. Mean range of motion was 128.5 ± 7.8°. Femoral postero-condylar axis (relative to the transepicondylar axis) values ranged from -8.3 to 4.1° with a mean of -0.78 ± 2.7° (internal rotation). Mean tibial rotation was 17.2 ± 7.9° internal rotation relative to the tibial tubercle. No correlation was found between native femoral version and femoral component rotational alignment (Pearson's correlation coefficient, r, 0.007). Weak correlation was found between native tibial torsion and tibial component alignment (r = 0.24).

CONCLUSIONS

Despite being only a secondary objective with the GB technique, most components evaluated were within the desired range of rotation. Alignment was not influenced by native osseous rotational geometry.

Management of patella maltracking after total knee arthroplasty: a systematic review

PURPOSE

Patella maltracking is among the most frequent causes of poor outcomes and early failure after total knee arthroplasty (TKA), with an incidence that ranges from 1 to 20%. Even if there is agreement between authors regarding the preoperative and intraoperative management of patella maltracking in TKA, less clear are postoperative conducts. The purpose of this systematic review is to summarize and compare surgical techniques used to treat patella maltracking after TKA.

METHODS

A systematic review of the literature was performed with a primary search on Medline through PubMed. The PRISMA 2009 flowchart and checklist were used to edit the review. Screened studies had to provide clinical, functional and radiological results and complications of the proposed treatment to be included in the review.

RESULTS

A total of 21 articles were finally included. Three main types of surgical procedures and other minor techniques have been identified to manage patella maltracking after TKA. The choice of the proper technique to use in the specific case depends on several factors, first of all the malpositioning of the prosthetic components.

CONCLUSION

Patella maltracking after TKA represents a frequent and challenging problem for orthopedic surgeons. Treatments described in the literature are often able to correct an abnormal patellar tracking; nevertheless, authors report variable percentages of residual knee pain and dissatisfaction in re-treated patients. Therefore, it would be desirable to prevent the maltracking condition at the time of primary arthroplasty, using proper surgical precautions.

Different rotational alignment of tibial component should be selected for varied tibial tubercle locations in total knee arthroplasty

PURPOSE

The main purpose of this study was to identify how the accuracy of the tibial rotation reference axes varied in populations with different tibial tubercle locations. We hypothesized that the accuracy of the axes of tibial rotation would be affected by the changes of tibial tubercle locations.

METHODS

Surgical epicondylar axis (SEA), medial third of the patellar tendon (1/3MPT), medial third of the tibial tuberosity (1/3MTT), medial border of the tibial tuberosity (MTT) and Akagi line were drawn. The angle between SEA and horizontal line with the angle between the four tibial rotation axes and the horizontal line was compared by T test. Then, the correlation between TTTG with the angles between the four axes and SEA vertical lines was analyzed. The TTTG was divided into three subgroups (TTTG < 10 mm, 10 mm ≤ TTTG < 15 mm, TTTG ≥ 15 mm), then t test was performed for the angles between the vertical lines of the SEA and the four rotation axes of the tibia in each group.

RESULTS

Among the four tibial rotation axes, only the difference between MTT and the line perpendicular to SEA had no statistical significance (NS.). The four tibial rotational axes were all positively correlated with TTTG (p < 0.001). When TTTG ≥ 15 mm, Akagi line was 2.5° ± 6.9°internally rotated to the line perpendicular to SEA, while the 1/3MPT and MTT was 0.9° ± 5.3°and 1.3° ± 5.9°externally rotated to the line perpendicular to the SEA when TTTG < 10 mm and 10 mm ≤ TTTG < 15 mm, respectively.

CONCLUSIONS

MTT showed the best consistency with SEA. TT-TG had a significant positive correlation with all four tibial rotational axes. In patients with TTTG < 10 mm, 10 mm ≤ TTTG < 15 mm and TTTG ≥ 15 mm, the 1/3MPT, MTT and Akagi line demonstrated good alignment consistency with SEA, respectively.

A new robotically assisted technique can improve outcomes of total knee arthroplasty comparing to an imageless navigation system

BACKGROUND

Robotic assisted total knee arthroplasty (RTKA) has shown improved knee alignment and reduced radiographic outliers. However, there remains debate on functional outcomes and patient-reported outcomes (PROMs). This study compares the 1-year clinical outcomes of a new imageless robotically assisted technique (ROSA Knee System, Zimmer Biomet, Warsaw, IN) with an imageless navigated procedure (NTKA, iAssist Knee, Zimmer, Warsaw, IN).

METHODS

The study is a retrospective analysis of prospectively collected data that compared the functional outcomes and PROMs of 50 imageless RTKA with 47 imageless NTKA at 1-year follow-up. Baseline characteristics, intraoperative and postoperative information were collected including complications, revisions, Knee Society Score (KSS), Knee injury and Osteoarthritis Outcome Score (KOOS) score, and Forgotten Joint Score (FJS-12). Radiographic analysis of preoperative and postoperative images evaluating hip-knee-ankle (HKA) angle was performed.

RESULTS

There was no difference regarding baseline characteristics between the groups. Mean operative time was significantly longer in the RTKA group (122 min vs. 97 min; p < 0.0001). Significant differences were reported for the "Pain" (85 [RTKA] vs 79.1 [NTKA]; p = 0.0283) subsection of the KOOS score. In addition, RTKA was associated with higher maximum range of motion (119.4° vs. 107.1°; p < 0.0001) and better mean improvement of the arc of motion by 11.67° (23.02° vs. 11.36°; p < 0.0001). No significant differences were noted for other subsections of KOOS, KSS, FJS-12, complications, or limb alignment at 1-year follow-up.

CONCLUSIONS

Imageless RTKA was associated with longer surgical time, better pain perception and improved ROM at 12-month follow-up compared with NTKA. No significant differences were reported on other PROMs, complication rates and radiographic outcomes.

LEVEL OF EVIDENCE

III.

Revision for coronal malalignment will improve functional outcome up to 5 years postoperatively

PURPOSE

Revision of a total knee arthroplasty (TKA) for the diagnosis of malalignment is widely performed. However, very little is known about the functional outcome in revision TKA surgery for malalignment. The aim of this study was to assess the functional outcome and to identify factors influencing the functional outcome of patients who have had a revision of a TKA for the diagnosis of malalignment at 5 years follow-up.

METHODS

All patients with a revision of a TKA for malalignment as the primary reason were selected from a prospective database. The diagnosis of symptomatic malalignment was made by the surgeon and quantified by radiologic examination. Functional outcome was scored by the functional score of the Knee Society Clinical Rating System (fKSS) at 0, 12, 24 and 60 months. Multiple imputation for missing data and multivariable analysis were performed to identify factors influencing functional outcome.

RESULTS

After selection, 105 patients (age: 65.1 ± 9.1 years, gender M:F 30:75) were eligible for outcome analysis. Functional outcome significantly improved from the preoperative (fKSS: 44.1 ± 22.0) to 5 years postoperative (64.7 ± 24.0, p < 0.001) time frames. Higher degree of coronal deviation, younger age and lower preoperative KSS were found to be strongest positive influencing factors for the change in fKSS.

CONCLUSION

Revision of TKA for malalignment appears to be an effective treatment to improve functional outcome up to 5 years postoperatively. Higher degree of coronal deviation, younger age and lower preoperative KSS are the strongest contributing factors for functional improvement.

LEVEL OF EVIDENCE

Level III; Therapeutic prospective cohort study.

No Benefit to Sensor-guided Balancing Compared With Freehand Balancing in TKA: A Randomized Controlled Trial

BACKGROUND

Soft tissue balancing in TKA has traditionally relied on surgeons' subjective tactile feedback. Although sensor-guided balancing devices have been proposed to provide more objective feedback, it is unclear whether their use improves patient outcomes.

QUESTIONS/PURPOSES

We conducted a randomized controlled trial (RCT) comparing freehand balancing with the use of a sensor-guided balancing device and evaluated (1) knee ROM, (2) patient-reported outcome measures (PROMs) (SF-12, WOMAC, and Knee Society Functional Scores [KSFS]), and (3) various surgical and hospital parameters (such as operative time, length of stay [LOS], and surgical complications) at a minimum of 2 years of follow-up.

METHODS

A total of 152 patients scheduled for primary TKA were recruited and provided informed consent to participate in this this study. Of these, 22 patients were excluded preoperatively, intraoperatively, or postoperatively due to patient request, surgery cancellation, anatomical exclusion criteria determined during surgery, technical issues with the sensor device, or loss to follow-up. After the minimum 2-year follow-up was accounted for, there were 63 sensor-guided and 67 freehand patients, for a total of 130 patients undergoing primary TKA for osteoarthritis. The procedures were performed by one of three fellowship-trained arthroplasty surgeons (RPS, HJC, JAG) and were randomized to either soft tissue balancing via a freehand technique or with a sensor-guided balancing device at one institution from December 2017 to December 2018. There was no difference in the mean age (72 ± 8 years versus 70 ± 9 years, mean difference 2; p = 0.11), BMI (30 ± 6 kg/m 2 versus 29 ± 6 kg/m 2 , mean difference 1; p = 0.83), gender (79% women versus 70% women; p = 0.22), and American Society of Anesthesiology score (2 ± 1 versus 2 ± 1, mean difference 0; p = 0.92) between the sensor-guided and freehand groups, respectively. For both groups, soft tissue balancing was performed after all bony cuts were completed and trial components inserted, with the primary difference in technique being the ability to quantify the intercompartmental balance using the trial tibial insert embedded with a wireless sensor in the sensor-guided cohort. Implant manufacturers were not standardized. Primary outcomes were knee ROM and PROMs at 3 months, 1 year, and 2 years. Secondary outcomes included pain level evaluated by the VAS, opioid consumption, inpatient physical therapy performance, LOS, discharge disposition, surgical complications, and reoperations.

RESULTS

There was no difference in the mean knee ROM at 3 months, 1 year, and 2 years postoperatively between the sensor-guided cohort (113° ± 11°, 119° ± 13°, and 116° ± 12°, respectively) and the freehand cohort (116° ± 13° [p = 0.36], 117° ± 13° [p = 0.41], and 117° ± 12° [p = 0.87], respectively). There was no difference in SF-12 physical, SF-12 mental, WOMAC pain, WOMAC stiffness, WOMAC function, and KSFS scores between the cohorts at 3 months, 1 year, and 2 years postoperatively. The mean operative time in the sensor-guided cohort was longer than that in the freehand cohort (107 ± 0.02 versus 84 ± 0.04 minutes, mean difference = 23 minutes; p = 0.008), but there were no differences in LOS, physical therapy performance, VAS pain scores, opioid consumption, discharge disposition, surgical complications, or percentages of patients in each group who underwent reoperation.

CONCLUSION

This RCT demonstrated that at 2 years postoperatively, the use of a sensor-balancing device for soft tissue balancing in TKA did not confer any additional benefit in terms of knee ROM, PROMs, and clinical outcomes. Given the significantly increased operative time and costs associated with the use of a sensor-balancing device, we recommend against its routine use in clinical practice by experienced surgeons.

LEVEL OF EVIDENCE

Level I, therapeutic study.

Staging Bilateral Total Knee Arthroplasties Reduces Alignment Outliers

BACKGROUND

Patients frequently present with bilateral symptomatic knee osteoarthritis and request simultaneous total knee arthroplasties (TKAs). Technical differences between simultaneous and staged TKAs could affect clinical and radiographic outcomes. We hypothesized that staged TKAs would have fewer mechanical alignment outliers than simultaneous TKAs.

METHODS

We reviewed 87 simultaneous and 72 staged TKAs with at least 2 years of follow-up. Radiographic assessment was done using standing long leg and lateral radiographs of the knee. Coronal and sagittal measurements were performed by 4 blinded observers on 2 separate occasions with an intraobserver agreement of 0.95 and interobserver of 0.92.

RESULTS

The first simultaneous knee had no difference in the probability of establishing the mechanical axis outside 3° of neutral (45%) compared to the first staged knee (54%, P = .337). However, the second simultaneous knee (49%) was more likely to establish the axis outside mechanical neutral compared to the second staged knee (28%; odds ratio 2.54, confidence interval 1.31-4.94, P = .006). There was an increased risk of deep venous thrombosis with staged TKA (odds ratio 2.96, confidence interval 1.28-6.84, P = .011), but other perioperative complication rates were not significantly different. There were no clinically significant differences in range of motion or Knee Society Score.

CONCLUSION

There is a significantly increased risk of establishing the second knee outside mechanical neutral during a simultaneous TKA compared to staged bilateral TKAs, possibly related to a number of surgeon-related and system-related factors. The impact on clinical outcomes and radiographic loosening may become significant in long-term follow-up.

CT measures of femoral and tibial version and rotational position of femoral and tibial components of knee replacements: limitations in reliability and suitability for routine clinical practice

OBJECTIVES

Rotational malalignment of knee replacements as measured on CT is understood to be associated with poor outcomes. The aim of this study is to measure the inter-rater and intra-rater reliability of measures of femoral and tibial version in the native arthritic knee and postoperative TKR component position using CT.

METHODS

Eighty patients underwent CT of the knee before and after total knee replacement. Preoperative femoral and tibial version and component rotation were independently measured by two musculoskeletal radiologists.

RESULTS

Mean differences between and within raters were small (< 1.6°). Maximum 95% limits of agreement for inter-rater and intra-rater comparisons were 8.1° and 7.6° for preoperative femoral version, 9.0° and 7.9° for postoperative femoral rotation, 26.0° and 20.5° for preoperative tibial version, and 24.9° and 23.6° for postoperative tibial rotation respectively. Postoperative ICCs varied from 0.68 to 0.81 (lower 95% CI:0.55-0.72) for both intra- and inter-rater comparisons. Preoperative ICCs were lower: 0.55-0.75 (lower 95% CI:0.40-0.65).

CONCLUSION

The lower 95% confidence level for ICC of version and rotational measurements using the Berger protocol of TKRs on CT are all less than 0.73 and that the normal range of differences between observers is up to 9° for the femoral component and 26° for the tibial component. This suggests that CT measurements derived from the Berger protocol may not be consistent enough for clinical practice.

KEY POINTS

• CT is commonly used to measure the rotational profile of knee replacements in symptomatic patients using the Berger protocol. • The limits of agreement for both femoral and tibial component rotation are wide even for experienced observers. • CT measurements of the rotation of knee arthroplasty are not reliable enough for routine clinical use.

The personalized Berger method is usable to solve the problem of tibial rotation

Purpose

The revision of any total knee replacement is carried out in a significant number of cases, due to the excessive internal rotation of the tibial component. The goal was to develop a personalized method, using only the geometric parameters of the tibia, without the femoral guidelines, to calculate the postoperative rotational position of tibial component malrotation within a tolerable error threshold in every case.

Methods

Preoperative CT scans of eighty-five osteoarthritic knees were examined by three independent medical doctors twice over 7 weeks.

The geometric centre of the tibia was produced by the ellipse annotation drawn 8 mm below the tibial plateau, the sagittal and frontal axes of the ellipse were transposed to the slice of the tibial tuberosity. With the usage of several guide lines, a right triangle was drawn within which the personalized Berger angle was calculated.

Results

A very good intra-observer (0.89-0.925) and inter-observer (0.874) intra-class correlation coefficient (ICC) was achieved. Even if the average of the personalized Berger values were similar to the original 18° (18.32° in our case), only 70.6% of the patients are between the clinically tolerable thresholds (12.2° and 23.8°).

Conclusion

The method, measured on the preoperative CT scans, is capable of calculating the required correction during the planning of revision arthroplasties which are necessary due to the tibial component malrotation. The personalized Berger angle isn’t altered during arthroplasty, this way it determines which one of the anterior reference points of the tibia (medial 1/3 or the tip of the tibial tuberosity, medial border or 1/6 or 1/3 or the centre of the patellar tendon) can be used during the positioning of the tibial component.

Level of evidence

Level II, Diagnostic Study (Methodological Study).

Accelerometer-based, hand-held navigation for improved knee alignment in total knee arthroplasty: An observational study

BACKGROUND

Malalignment in total knee arthroplasty has been associated with poor implant longevity and clinical outcomes. The aim of this study was to investigate the accuracy of accelerometer-based navigation in restoring the mechanical axis.

METHODS

106 primary total knee arthroplasties performed during February 2016 to September 2017 at a tertiary care centre in India were enrolled in this observational study. We noted the intra-op tourniquet time. Two separate blinded observers measured the preoperative mechanical axis and the post operative radiological results (mechanical axis, coronal and sagittal alignment of femoral and tibial components) and the mean value was taken as final data. Interclass correlation was done to look for variability between the two observers.

RESULTS

The mean pre operative mechanical axis was 13.74 ± 10.44. The mean tourniquet time was 53.14 ± 7.42 min 91.5% (96/106) knees were within ±3° of neutral mechanical axis with a mean of 1.00° ± 2.68°. The femoral and tibial components with coronal alignment within ±3° perpendicular to the mechanical axis were 93.39% (99/106) and 89.62% (95/106) respectively. In the sagittal plane 89.62% of the femoral components and 87.73% of the tibial components were within ±3° perpendicular to the axis of tibia.

CONCLUSION

The Accelerometer based portable navigation system effectively reduces the coronal and sagittal alignment outliers in total knee arthroplasty and has no role in rotational alignment of components.

The Impact of a Gap Balancing or Measured Resection Surgical Technique on Posterior Condylar Offset and Patient-Reported Outcome Measures

Background

To increase total knee arthroplasty procedure satisfaction, surgeons are exploring improvements in surgical technique. The impact of gap balancing or measured resection approach on posterior condylar offset (PCO) is not well understood.

Methods

We reviewed the clinical and radiographic results of 498 unilateral posterior stabilized total knee arthroplasties. Radiographs were assessed to measure the primary endpoints of anterior-posterior width, PCO, and anterior condylar offset. Clinical outcome measures were used to assess patient improvement measures. Multiple linear regression analyses were performed to determine the clinical factors related to our primary endpoints.

Results

No significant difference was observed between groups in anterior-posterior width (P = .24) and PCO (P = .78). Significant positive correlations were observed between postoperative PCO and knee range of motion (r = 0.12, P = .04) and total Knee Society Scores (r = 0.14, P = .02).

Conclusion

No impact of surgical technique on PCO was observed. Correlations were observed between postoperative PCO and the functional subscore and total Knee Society Score. All patients reported clinical improvements at 1 year postoperatively.

Influence of posterior tibial slope on three-dimensional femorotibial alignment under weight-bearing conditions in healthy Japanese elderly people

BACKGROUND

Assessment of three-dimensional (3D) femorotibial alignment is essential for successful knee osteoarthritis treatment in the elderly. The complex morphology of the posterior tibial slope (PTS) might have an influence on sagittal and rotational alignment and the positional relationship between the femur and tibia in the anterior-posterior (AP) direction under weight-bearing conditions.

OBJECTIVE

This study aimed to clarify the association between the PTS and 3D femorotibial alignment under weight-bearing conditions in healthy Japanese elderly individuals.

METHODS

We investigated the 3D femorotibial alignment of 110 lower extremities of 55 healthy individuals (26 women, 29 men, mean age: 70 ± 6 years). Using our previously reported 3D-to-2D image registration technique, we evaluated the 3D hip-knee-ankle angle (3DHKA) in the sagittal plane, rotational alignment, and the distance between the femoral and tibial origins in the AP direction (tibial AP position) as femorotibial alignment parameters under weight-bearing conditions. We assessed the medial and lateral PTS and their angular difference (PTS difference) as PTS parameters. Stepwise multiple linear regression analysis was performed using PTS parameters and other possible confounders (age, sex, height, and weight) as the independent variables and femorotibial alignment parameters as the dependent variable.

RESULTS

Weight (𝛽 = 0.393, p < 0.001) and lateral PTS (𝛽 = 0.298, p < 0.001) were the predictors associated with 3DHKA in the sagittal plane. Lateral PTS (𝛽 = 0.304, p = 0.001) was the only predictor associated with the tibial AP position. Sex (𝛽 = -0.282, p = 0.002) and PTS difference (𝛽 = -0.231, p = 0.012) were associated with rotational alignment.

CONCLUSIONS

We found that a steeper lateral PTS resulted in a more flexed knee and anterior tibia. The PTS difference was positively correlated with tibial external rotation. Our data could be used as the standard reference for realignment surgery to ensure PTS is appropriately maintained.

Minimum Five Years Follow-Up of Total Knee Arthroplasty Using Morphometric Implants in Patients With Osteoarthritis

BACKGROUND

The use of morphometric implants in total knee arthroplasty (TKA) has shown better early clinical outcomes compared to conventional implants. The primary objective of this study is to evaluate the functional outcome and the implant survivorship of a morphometric TKA at a minimum of 5 years of follow-up.

METHODS

From May 2012 to June 2015, all patients undergoing primary TKA with a single design of morphometric posterior-stabilized prosthesis (Persona; Zimmer) in a prospective observational single-center study were evaluated. The Knee Society Scoring System (KSS) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) were completed preoperatively, 1, 3, and 5 years postoperatively. Kaplan-Meier was used to calculate survivorship of the implants. The average follow-up was 75 months.

RESULTS

In total, 237 TKAs were performed in 235 patients with a mean age of 73 years (49-90). The KSS Knee Score increased from 44.7 (13-64) preoperatively to 93.6 (71-100), the KSS Function Score from 45.8 (17-69) to 92.2 (51-98), and the KSS Satisfaction Score from 26.6 (16-51) to 41 (35-55) at 5 years of follow-up. Similarly, for the KOOS score, a significant improvement of all the subscales was observed at 5 years of follow-up. Implant survival without reoperation at 5 years of follow up was 98.72% (95% confidence interval 0.95-1.00).

CONCLUSION

This is the first study demonstrating that significant improvements of the functional scores with good survivorship can be achieved at a minimum of 5 years of follow-up with TKA using morphometric implants.

Increased external rotation of the osteoarthritic knee joint according to the genu varum deformity

PURPOSE

To evaluate the rotational profile of the lower extremity using computed tomography (CT) in accordance with the degree of varus deformity in medial condyle-affected knee joint osteoarthritis (OA).

METHODS

This retrospective study included 1036 patients (872 lower extremities) with end-stage knee OA. The coronal alignment of the lower extremity was measured using standing anteroposterior radiography. The CT parameters of femoral anteversion and tibial torsion were assessed in relation to the knee joint. The axes were the femoral neck axis; the distal femoral axis, which was composed of the anterior trochlear axis, the clinical transepicondylar axis, and the posterior condylar axis; the axis of the proximal tibial condyles; and the bimalleolar axis.

RESULTS

There was a tendency for increased external rotation of the knee joint parameters in relation to the hip and ankle joints as varus deformity of the lower extremity increased. The relative external rotational deformity of the knee joint in relation to the hip joint had a positive value with a good correlation. The relative external rotational deformity of the knee joint in relation to the ankle joint also demonstrated a positive value with a good correlation.

CONCLUSION

The distal femur and proximal tibia (knee joint) tended to rotate externally in relation to the hip and ankle joint, respectively, as the degree of varus deformity increased. This study identified the relationship between lower extremity varus deformity and rotational deformity of knee joints with OA.

LEVEL OF EVIDENCE

III.

The Functionality of a Novel Robotic Surgical Assistant for Total Knee Arthroplasty: A Case Series

Conventional total knee arthroplasty and soft tissue balancing is based on a subjective unquantified assessment, which can lead to imperfect balancing and poor patient outcomes. Five case studies were used to present the functionality of a novel robotic system in allowing intraoperative adjustments based on objective measures for several primary total knee arthroplasty cases. The robotic system allows the surgeon to drive every step of the case, turning the subjective nature of conventional knee replacement into a more objective and scientific approach for restoration of alignment, gap balancing, joint space restoration, femoral rotation, and Q-angle restoration. The robotic system allowed precise intraoperative adjustments, as demonstrated by these cases, and is a promising step towards more personalized total knee arthroplasty made possible by utilizing real-time objective measures.

Reliability of Imageless Computer-Assisted Navigation for Femoral Rotational Alignment in Total Knee Arthroplasty

Introduction:

The aim of this study was to evaluate the reliability of the femoral component rotation on intra-operative data recorded in a computer-assisted navigation system (CAN-FRA) compared with the post-operative femoral component rotation observed on computed tomography (CT-FRA).

Material and method:

Computer-assisted total knee arthroplasty (TKA) or primary osteoarthritis of the knee was performed in 51 knees in 36 patients with a mean age of 69.51 years. All procedures were performed by a single surgeon using the same implant design. The intraclass correlation coefficient (ICC) was used to compare the intra-operative CAN-FRA with the post-operative CT-FRA. The angle between the anatomical epicondylar axis and the posterior condylar axis of the implant (CT-FRA) was measured at two separate timepoints by three observers who were blinded to the intra-operative CAN-FRA. Internal rotation was defined as rotation in the negative direction, while external rotation was defined as positive.

Results:

The mean intra-operative CAN-FRA was 0.1° ± 2.8° (range -5.0° to 5.5°). The mean post-operative CT-FRA was -1.3° ± 2.1° (range -4.6° to 4.4°). The mean difference between the CAN-FRA and the CT-FRA was -1.3° ± 2.2° (range -7.9° to 2.4°). The respective ICC values for the three observers were 0.92, 0.94, and 0.93, while the respective intra-observer coefficients were 0.91, 0.85, and 0.90. The ICC for the intra-operative CAN-FRA versus the post-operative CT-FRA was 0.71.

Conclusion:

This study shows that using a computer-assisted navigation system in TKA achieves reliable results and helps to achieve optimal positioning of the femoral component and rotation alignment correction.

A new technique for determining the rotational alignment of the tibial component during total knee arthroplasty

BACKGROUND

We evaluated the effectiveness of our new technique "Range of motion-anatomical (ROM-A) technique" which is the combination of the self-positioning technique "Range of motion (ROM) technique" and the anatomical landmarks technique in determining the tibial component (TC) rotation alignment in total knee arthroplasty (TKA) using a navigation system.

METHODS

This retrospective study included 103 knees who underwent TKA. The ROM-A technique was consisted of two steps. First, the TC was set and marked by the ROM technique in knee extension. Second, the TC was set according to the marking in the knee flexion and the component rotational angle relative to the anatomical tibial anteroposterior (AP) axis was adjusted between 0° and 10° external rotation using the navigation system. The rotational angle of TC relative to the anatomical AP axis was measured using postoperative computed tomography. Moreover, the hypothetical rotational angle of the TC in the ROM technique was calculated only from the intraoperative difference between the two techniques.

RESULTS

The actual rotational angle by the ROM-A technique was externally rotated 3.0°, and the rotational outlier occurred in 3.0%. A significant difference in outlier rate was observed between the two techniques (p = 0.03). The hypothetical rotational angle of TC determined by the ROM technique (the first step only in the ROM-A technique) was externally rotated 4.6° and the TC rotational outlier (difference to AP axis: >10°) occurred in 11.7%.

CONCLUSION

Using the ROM-A technique, the TC was finally fixed in almost all targeted rotational positions, and this technique could reduce the anatomical rotational outlier compared with the ROM technique.

Preoperative tibiofemoral rotational alignment is a risk factor for component rotational mismatch in total knee arthroplasty

BACKGROUND

Rotational mismatch between the femoral and tibial components is reported to be a risk factor for unsuccessful total knee arthroplasty (TKA). However, the rotational mismatch can still occur even when each component is aligned within the desired angle. Therefore, there may be other unknown factors. This study aims to investigate a risk factor for component rotational mismatch in TKA. The authors hypothesized a significant correlation between the rotational mismatch angle and not only the rotational alignments of components, but also the preoperative tibiofemoral rotation angle.

METHOD

This retrospective cohort study included 79 knees who underwent TKA. Computed tomography images were obtained preoperatively and 2 weeks after surgery for the component positional measurement. The postoperative component rotational mismatch angle between the tibial and femoral components and the rotational alignment of each tibial and femoral component to anatomical axes was evaluated. In addition, the preoperative rotational angle between the tibia and femur bones and patients' demographics were also investigated. The correlation between the postoperative component rotational mismatch angle and perioperative variables was analyzed to identify risk factors for component rotational mismatch.

RESULTS

The mean component rotational mismatch angle was 1.8° of internal rotation of the tibial component relative to the femoral component, and the angle ranged from 11.3° of internal rotation to 7.3° of external rotation of the tibial component. Multivariate regression analysis showed that the preoperative rotational alignment between the tibia and femur and the rotational alignment of each component were influential factors in the postoperative component rotational mismatch angle.

CONCLUSION

The preoperative tibiofemoral rotational alignment and the rotational alignment of each tibial and femoral component and are risk factors for the postoperative component rotational mismatch in TKA.

Functionally Oriented Alignment of the Lower Extremity Reflecting the Direction of Gait for Healthy Elderly, Knee Osteoarthritis, and Total Knee Arthroplasty Subjects

Purpose

The objective of this study was to evaluate the functional lower extremity alignment based on both position and motion [functionally oriented alignment (FOA)] of the knee in healthy elderly, varus osteoarthritis (OA), and total knee arthroplasty (TKA) subjects.

Methods

This study evaluated 87 knees in 24 healthy elderly (72 ± 5 years), 39 varus OA (72 ± 6 years), and 24 TKA (75 ± 4 years) subjects. A 3D assessment system was used on 3D models and biplanar long-leg radiographs with the toe angle reflecting gait direction, by applying a 3D-to-2D image registration technique. In the world coordinate system, the y-, z-, and x-axes were defined as gait direction, gravity direction, and the cross product of y- and z-axes, respectively. The parameters were: (a) coronal inclination, sagittal inclination, and transverse direction of the femur and tibia relative to the ground and (b) the difference between the yz-plane of the world coordinate system (functional plane) and the yz-plane of the femoral or tibial coordinate system (anatomical plane).

Results

The femur had more medial and posterior inclination and the tibia had more lateral and anterior inclination in osteoarthritic knees as compared to healthy knees, and TKA knees had inclinations similar to healthy knees. Rotation was similar or different in the anatomical and functional planes among the subjects with the healthy, knee OA, and TKA.

Conclusions

The association between the anatomical and functional planes and the position of each bone relative to gravity varied depending on the condition of the knees.

Level of Evidence: Level of III

Why Reintervention After Total Knee Arthroplasty Fails? A Consecutive Cohort of 1170 Surgeries

BACKGROUND

The aim of this study was to analyze why contemporary reintervention after total knee arthroplasty (RiTKA) fails.

METHODS

Between January 2006 and December 2010, from a multicenter cohort of 1170 RiTKAs, we assessed all failures of RiTKA requiring additional surgery. All indications for the index reintervention were included. The minimum follow-up period was 3 years.

RESULTS

A total of 192 (16.4%) patients required additional surgery after RiTKA (re-reintervention). The mean follow-up period was 7.7 years. Mean age was 69.2 years. The mean time to re-reintervention was 9.6 months with 90.1% of rTKA failure occurring within the first two years. Infection was the main cause of new surgery after RiTKA (47.9%; n = 92/192). Other causes included extensor mechanism pathology (14.6%), stiffness (13.5%), pain (6.8%), aseptic loosening (5.2%), laxity (5.2%), periprosthetic fracture (3.6%), and wound pathology (3.1%). In four groups, the main indication for re-reintervention was recurrence of the pathology leading to the first reintervention: RiTKA for infection (59/355, 16.6%, P < .05), stiffness (18/174, 10.3%, P < .05), extensor mechanism failure (9/167, 5.4%, P < .05), and RiTKA for pain (4/137, 2.9%, P = .003). Global survival curve analysis found 87.9% survivorship without re-reintervention at one year and 83% at eight years.

CONCLUSION

Contemporary RiTKA failures mainly occur in the first two postoperative years. Infection is the main cause of failure in RiTKA. Recurrence of the initial pathology occurs in four groups of RiTKA and is the main indication for re-reintervention in these groups; infection (16.6%), stiffness (10.3%), extensor mechanism failure (5.4%), and pain (2.9%).

How to predict early clinical outcomes and evaluate the quality of primary total knee arthroplasty: a new scoring system based on lower-extremity angles of alignment

Background

A method that can accurately predict the outcome of surgery can give patients timely feedback. In addition, to some extent, an objective evaluation method can help the surgeon quickly summarize the patient’s surgical experience and lessen dependence on the long wait for follow-up results. However, there was still no precise tool to predict clinical outcomes of total knee arthroplasty (TKA). This study aimed to develop a scoring system to predict clinical results of TKA and then grade the quality of TKA.

Methods

We retrospectively reviewed 98 primary TKAs performed between April 2013 and March 2017 to determine predictors of clinical outcomes among lower-extremity angles of alignment. Applying multivariable linear-regression analysis, we built Models (i) and (ii) to predict detailed clinical outcomes which were evaluated using the Knee Society Score (KSS). Multivariable logistic-regression analysis was used to establish Model (iii) to predict probability of getting a good clinical outcome (PGGCO) which was evaluated by Knee Injury and Osteoarthritis Outcome Score (KOOS) score. Finally, we designed a new scoring system consisting of 3 prediction models and presented a method of grading TKA quality. Thirty primary TKAs between April and December 2017 were enrolled for external validation.

Results

We set up a scoring system consisting of 3 models. The interpretations of Model (i) and (ii) were good (R² = 0.756 and 0.764, respectively). Model (iii) displayed good discrimination, with an area under the curve (AUC) of 0.936, and good calibration according to the calibration curve. Quality of surgery was stratified as follows: “A” = PGGCO ≥0.8, “B” = PGGCO ≤0.6 but < 0.8, and “C” = PGGCO < 0.6. The scoring system performed well in external validation.

Conclusions

This study first developed a validated, evidence-based scoring system based on lower-extremity angles of alignment to predict early clinical outcomes and to objectively evaluate the quality of TKA.

The tibial lateral axis is a novel extraarticular landmark for detection of the tibial anteroposterior axis

PURPOSE

Although the tibial rotation axis is significant in knee arthroplasty, no reliable extraarticular landmark has been proposed. We hypothesized that the tibial lateral axis (TLA), a tangential line of the lateral tibial surface, is perpendicular to the surgical epicondylar axis (SEA) and compared it to other existing landmarks by 3D-CT.

METHODS

Fifty legs in 25 consecutive patients were studied. Using their preoperative CT, the TLAs were identified on slices at 10-50% of the total length of the tibia and the measured differences of angles against the line perpendicular to the SEA (the tibial AP axis) were calculated. The differences between the SEA and the femoral and tibial posterior condylar axis, Akagi's line and the line between the medial intercondylar spine and the medial border of the patellar tendon (sAP line)(intraarticular), the ankle axis, and the transmalleolar axis (extraarticular) were also calculated and compared.

RESULTS

The mean values of TLA at 10%, 20%, 30% were virtually parallel to the SEA (0.97° ± 4.84°, 0.02° ± 4.61°, 1.10° ± 4.97°, respectively). They were equivalent to existing intraarticular landmarks and superior to existing extraarticular landmarks, and these levels corresponded to the tip to the lower end of the tibial tubercle (at 10.8% and 17.0% of total tibial length).

CONCLUSION

The proximal TLAs can be an extraarticular bony landmark that indicates the line perpendicular to the SEA. A prospective study is needed to prove the validity and accuracy of the axes clinically.

An optimization method for implantation parameters of individualized TKA tibial prosthesis based on finite element analysis and orthogonal experimental design

Background

Individualized and accurate implantation of a tibial prosthesis during total knee arthroplasty (TKA) can assist in uniformly distributing the load and reducing the polyethylene wear to obtain a long-term prosthetic survival rate, but individualized and accurate implantation of a tibial prosthesis during TKA remains challenging. The purpose of this study was to optimize and individualize the positioning parameters of a tibial prosthesis to improve its accurate implantation using a new method of finite element analysis in combination with orthogonal experimental design.

Methods

Ten finite element models of TKA knee joint were developed to optimize the implantation parameters (varus angle, posterior slope angle, and external rotation angle) of tibial prosthesis to reduce the peak value of the contact pressure on the polyethylene liner according to the method of finite element analysis in combination with orthogonal experimental design. The influence of implantation parameters on the peak value of the contact pressure on the polyethylene liner was evaluated based on a range analysis in orthogonal experimental design.

Results

The optimal implantation parameters for tibial prosthesis included 0° varus, 1° posterior slope, and 4° external rotation. Under these conditions, the peak value of the contact pressure on the polyethylene liner remained the smallest (16.37 MPa). Among the three parameters that affect the peak value of the contact pressure, the varus angle had the greatest effect (range = 6.70), followed by the posterior slope angle (range = 2.36), and the external rotation angle (range = 2.15).

Conclusions

The optimization method based on finite element analysis and orthogonal experimental design can guide the accurate implantation of the tibial prosthesis, reducing the peak value of the contact pressure on the polyethylene liner. This method provides new insights into the TKA preoperative plan and biomechanical decision-making for accurately implanting TKA prosthesis.

Optimal rotational positioning of tibial component in total knee arthroplasty: determined by linker surgical technique using a high definition CT

INTRODUCTION

The rotational alignment of femoral and tibial components is an important determinant of the success of Total Knee Arthroplasty (TKA). The optimal rotational position of the tibial component is still unclear. The purpose of this study was (1) to determine the pre-operative S-TEA (surgical-transepicondylar axis) derived tibialanteroposterior (AP) axis angle and postoperative tibial component axis angle using a "Bird's eye" high-definition CT image in TKA performed by Linker surgical technique; (2) to determine the femorotibial mismatch angle; and (3) to determine the optimal tibial component rotation in a well-aligned femoral and tibial components.

MATERIALS AND METHODS

55 knees in 49 osteoarthritis patients who underwent primary TKA by Linker surgical technique were evaluated. Preoperative tibial AP axis angle, and the postoperative tibial component axis angle were measured. Rotational mismatch between femoral and tibial components was also measured.

RESULTS

The mean angle of the pre-operative tibial AP axis was 17.8° ± 4.0°, ranging from 4.3° to 25.4°. The mean angle of the post-operative tibial component axis was 16.2° ± 4.9°, ranging from 3.8° to 25.2°. The mean postoperative tibial component axis line was at 14.2% ± 11.9%.

CONCLUSION

Because of the variability of pre-operative S-TEA derived tibial AP axis angle, the tibial component axis angle was also variable among the knees, but the two angles bore a strong correlation to each other. Based on our results, the optimal axis of the tibial component passes about halfway through the medial edge and medial one-third of the tibial tuberosity.

LEVEL OF EVIDENCE

Level II.

One-Stage Total Knee Arthroplasty Plus Corrective Osteotomy for Osteoarthritis Associated With Severe Extra-articular Deformity

The mainstay for treatment of articular deformity caused by advanced tricompartmental osteoarthritis of the knee is total knee arthroplasty. When this is also associated with an extra-articular deformity, this also must be compensated or corrected. In this scenario, it is essential to achieve an optimal mechanical situation by restoring the anatomical and mechanical limb axes and an adequate soft-tissue balance. These premises are necessary to relieve pain and achieve satisfactory functionality and implant survival over time. A reconstructive single-stage technique is proposed for patients with knee osteoarthritis amenable to arthroplasty and a severe extra-articular deformity, aiming at addressing both problems simultaneously.

Femoral Component Malrotation Produces Quadriceps Weakness and Impaired Ambulatory Function following Total Knee Arthroplasty: Results of a Forward-Dynamic Computer Model

Proper placement of the prosthetic components is believed to be an important factor in successful total knee arthroplasty (TKA). Implant positioning errors have been associated with postoperative pain, suboptimal function, and inferior patient-reported outcome measures. The purpose of this study was to investigate the biomechanical effects of femoral component malrotation on quadriceps function and normal ambulation. For the investigation, publicly available data were used to create a validated forward-dynamic, patient-specific computer model. The incorporated data included medical imaging, gait laboratory measurements, knee loading information, electromyographic data, strength testing, and information from the surgical procedure. The ideal femoral component rotation was set to the surgical transepicondylar axis and walking simulations were subsequently performed with increasing degrees of internal and external rotation of the femoral component. The muscle force outputs were then recorded for the quadriceps musculature as a whole, as well as for the individual constituent muscles. The quadriceps work requirements during walking were then calculated for the different rotational simulations. The highest forces generated by the quadriceps were seen during single-limb stance phase as increasing degrees of femoral internal rotation produced proportional increases in quadriceps force requirements. The individual muscles of the quadriceps displayed different sensitivities to the rotational variations introduced into the simulations with the vastus lateralis showing the greatest changes with rotational positioning. Increasing degrees of internal rotation of femoral component were also seen to demand increasing quadriceps work to support normal ambulation. In conclusion, internal malrotation of the femoral component during TKA produces a mechanically disadvantaged state which is characterized by greater required quadriceps forces (especially the vastus lateralis) and greater quadriceps work to support normal ambulation.

Measuring Tibial Component Rotation Following Total Knee Arthroplasty: What Is the Best Method?

BACKGROUND

Tibial component malrotation is associated with pain, stiffness, and altered patellofemoral kinematics in total knee arthroplasty (TKA). However, measuring tibial component rotation following TKA is difficult. Proposed protocols utilizing computed tomography (CT) lack validity and can be time-consuming. This study aimed to (1) compare the reproducibility of the Berger (two-dimensional CT) and Mayo (three-dimensional CT) protocols and (2) validate a simple measurement technique using an anatomical distance on two-dimensional axial CT-the Center of the Tibial tray to the tip of the Tibial Tubercle (CTTT).

METHODS

Rotational alignment of 70 TKA patients was evaluated by 3 independent observers using the Berger, Mayo, and CTTT protocols. The inter-rater and intra-rater interclass correlation coefficients, mean difference between measurements, and the mean measurement times were calculated.

RESULTS

The intra-rater reliability for all 3 protocols was rated as "very good" (Mayo 0.96, Berger 0.85, and CTTT 0.85). The inter-rater reliability for the Mayo and the Berger method was rated as "very good" (0.87 and 0.83, respectively), and the CTTT was rated as "good" (0.79). Comparing the CTTT to the Mayo method produced an r² value of 0.73 with 92% of CTTT measurements ≤6 mm having <9° of tibial component internal rotation and 93% of patients with a CTTT ≥10 mm having ≥9° internal rotation.

CONCLUSION

Three-dimensional CT is the gold standard for measuring tibial component rotational alignment. The CTTT has the strongest correlation to the Mayo method and can be reliably used as a rapid screening tool.

Improved Range of Motion and Patient-Reported Outcome Scores With Fixed-Bearing Revision Total Knee Arthroplasty for Suboptimal Axial Implant Rotation

BACKGROUND

Suboptimal implant rotation has consequences with respect to knee kinematics and clinical outcomes. We evaluated the functional outcomes of revision total knee arthroplasty (TKA) for poor axial implant rotation.

METHODS

We retrospectively reviewed 42 TKAs undergoing aseptic revision for poor axial implant rotation. We assessed improvements in Knee Society Score (KSS) and final range of motion (ROM). Subgroup analyses were performed for preoperative instability and stiffness, as well as the number of components revised and level of implant constraint used.

RESULTS

Revision for poor axial rotation in isolation improved KSS from 52 ± 22 to 84 ± 25 (P < .001), and flexion increased from 105 ± 21° to 115 ± 13° (P = .001). Revision in the setting of instability significantly improved the KSS (P < .001) but did not affect ROM (P = .172). Revision in the setting of stiffness significantly improved both KSS (P < .001) and ROM (P = .002). There was no statistically significant difference between the postoperative KSS (P = .889) and final knee flexion (P = .629) with single- or both-component revision TKA for isolated poor axial rotation or between the postoperative KSS (P = .956) and final knee flexion (P = .541) with or without the use of higher constraint during revision TKA for isolated poor axial rotation.

CONCLUSION

Revision TKA for poor axial alignment improves clinical outcomes scores and functional ROM.

A new landmark for measuring tibial component rotation after total knee arthroplasty

BACKGROUND

Existing methods for assessment of total knee arthroplasty (TKA) component rotation on computed tomography (CT) scans are complex, especially in relation to the tibial component. Anecdotal evidence from our practice pointed towards a potential new landmark. The study aims were to check the prevalence of this landmark, define tibial component rotation in relation to it and demonstrate its reliability.

METHODS

Two hundred and eleven CTs undertaken following TKA were reviewed for presence of the landmark. A protocol to measure tibial component rotation in relation to this landmark was developed and the rotation measured using this method and Berger's protocol. Thirty one of the 211 CT scans were measured twice by two observers. Reliability was calculated using the Intraclass Correlation Coefficient (ICC).

RESULTS

The new landmark of a flat area on the lateral cortex of the tibia inferior to the tibial component was identified on all scans. Median tibial component rotation measured using our protocol was 0.0° ± 5.4° and -9.2° ± 5.5° using Berger's protocol. Intra-observer reliability with the new method was excellent (ICCs of 0.899 and 0.871) and inter-observer reliability was good (ICCs of 0.734 and 0.836).

CONCLUSIONS

The new landmark had a very high prevalence and could be used to define tibial component rotation. This measurement of tibial component rotation had acceptable reliability. This landmark has potential for use in the radiological assessment of tibial component rotation following TKA. Further work is required to determine its relationship to anatomical structures and symptoms of tibial component mal-rotation.

In vivo kinematics and ligamentous function of the knee during weight-bearing flexion: an investigation on mid-range flexion of the knee

PURPOSE

To investigate the in vivo femoral condyle motion and synergistic function of the ACL/PCL along the weight-bearing knee flexion.

METHODS

Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging technique during a single-legged lunge (0°-120°). The medial and lateral femoral condyle translation and rotation (measured using geometric center axis-GCA), and the length changes of the ACL/PCL were analyzed at: low (0°-30°), mid-range (30°-90°) and high (90°-120°) flexion of the knee.

RESULTS

At low flexion (0°-30°), the strains of the ACL and the posterior-medial bundle of the PCL decreased. The medial condyle showed anterior translation and lateral condyle posterior translation, accompanied with a sharp increase in external GCA rotation (internal tibial rotation). As the knee continued flexion in mid-range (30°-90°), both ACL and PCL were slack (with negative strain values). The medial condyle moved anteriorly before 60° of flexion and then posteriorly, accompanied with a slow increase of GCA rotation. As the knee flexed in high flexion (90°-120°), only the PCL had increasingly strains. Both medial and lateral condyles moved posteriorly with a rather constant GCA rotation.

CONCLUSIONS

The ACL and PCL were shown to play a reciprocal and synergistic role during knee flexion. Mid-range reciprocal anterior-posterior femoral translation or laxity corresponds to minimal constraints of the ACL and PCL, and may represent a natural motion character of normal knees. The data could be used as a valuable reference when managing the mid-range "instability" and enhancing high flexion capability of the knee after TKAs.

LEVEL OF EVIDENCE

Level IV.

Rotational component alignment in patient-specific total knee arthroplasty compared with conventional cutting instrument

BACKGROUND

Although many studies investigated the accuracy of customized cutting block (CCB), the data on rotational alignment are still lacking. The study aimed to assess whether CCB improved the component rotational position compared with conventional cutting instrument (CCI) using computed tomography scanning.

METHODS

Eighty-six of 102 total knee arthroplasties from the previous randomized study were analyzed. The outcomes were rotational position of the femoral and tibial components, frequency of outliers and intra-class correlation coefficient.

RESULTS

The mean femoral component rotation was not different between CCB versus CCI: 0.9° ± 0.8° versus 1.1° ± 1.1° (P = 0.29). Both groups had similar outlier frequencies: 2% (CCB) versus 2% (CCI) (P = 0.74). CCB had nearly 1° less mean tibial component deviation compared with CCI (P < 0.001): (1) dorsal tangent reference (DTR): 0.7° ± 0.8° versus 1.5° ± 1.0°, and (2) tibial trans-epicondylar reference (TTR): 0.5° ± 0.9° versus 1.4° ± 1.1°. Outlier frequencies were similar: (1) DTR: 0% CCB versus 5% CCI (P = 0.24), and (2) TTR: 5% in CCB versus 12% CCI (P = 0.20). Measurements based on tibial tubercle showed that CCB had ~ 1.4° less mean tibial component deviation compared with CCI: 0.3° ± 1.4° versus 1.7° ± 1.6° (P < 0.001) with a corresponding, less frequency of outliers: 0% versus 19% (P = 0.002). However, there was poor intra-observer reproducibility (0.61).

CONCLUSIONS

CCB did not improve femoral component rotational alignment compared with CCI nor affect outlier frequency, but it marginally improved the accuracy of tibial rotational alignment. The tibial tubercle reference point had poor intra-observer reproducibility.

Influence of tibial component rotation on short-term clinical outcomes in Oxford mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

Malposition of tibial components is an important factor for complications in unicompartmental knee arthroplasty (UKA), but the direct relationship between clinical outcomes and position of tibial component remains unknown. We aimed to investigate whether tibial component rotation in the axial plane could affect clinical outcomes after UKA.

METHODS

A total of 50 patients with anteromedial osteoarthritis of the knee underwent Oxford mobile-bearing UKA in this study. Patient-derived clinical scores using the Oxford Knee Score (OKS) and the functional activities of Knee Society Score (KSSF) were assessed preoperatively, and then after one year and two years following surgery. Postoperative tibial component rotation angles using two reference lines in the axial plane were assessed using three-dimensional computed tomography two weeks postoperatively. External rotation of the tibial component relative to each reference line was considered a positive value. We analysed the sequential change of the OKS and KSSF using repeated measures analysis of variance (P < 0.05). The effects of tibial component rotation on the OKS and KSSF were analysed using linear regression analysis.

RESULTS

OKS and KSSF showed significant recovery between the preoperative and one-year postoperative period. Rotation angles of tibial components had significant negative correlations with the recovery of the OKS in the two years following UKA.

CONCLUSIONS

Tibial component rotation played an important role in improving clinical outcomes during the two years following Oxford mobile-bearing UKA. A trend towards poor outcome was observed when the tibial component was placed at a higher angle of external rotation.

LEVEL OF EVIDENCE

III.

The flexion space is more reliably balanced when using the transepicondylar axis as compared to the posterior condylar line

PURPOSE

The purpose of this study was to evaluate the differences in flexion space balance when the femoral component is implanted parallel to the surgical transepicondylar axis (TEA) or with 3° of external rotation from the posterior condylar line (PoCoLi). It was hypothesized that implantation parallel to the TEA will produce a more reliably balanced flexion space.

METHODS

Forty-eight consecutive patients with a varus deformity were prospectively randomized to undergo total knee arthroplasty with a femoral component implanted parallel the TEA, or with 3° of external rotation from the PoCoLi. The posterior condylar angle (PCA) was measured. Intraoperative load measurements were taken at 10°, 45°, and 90° of flexion.

RESULTS

The PCA was similar between groups (TEA group: 4.2° ± 1.5° and PoCoLi group: 4.0° ± 1.3°; n.s.). The mean difference in load values between the medial and lateral compartments was significantly lower in the TEA group than in the PoCoLi group at the 45 (0 ± 8 vs. 9 ± 13 lbs; respectively, p = 0.008) and 90° flexion angles (1 ± 9 vs. 10 ± 15 lbs; respectively, p = 0.01). The PoCoLi group had a linear increase in the difference of load values between the medial and lateral compartments with increasing magnitude of the posterior condylar angle (45°, p = 0.0013; 90°, p = 0.0006), but this was not observed in the TEA group.

CONCLUSION

Femoral component implantation parallel to the TEA resulted in a more balanced flexion gap as compared to implantation at 3° of external rotation from the PoCoLi. The intraoperative use of the TEA rather than the PoCoLi to set femoral component rotation may provide a more balanced flexion space and decrease the need for extensive soft tissue releases.

LEVEL OF EVIDENCE

II.

Morphometric Tibial Implant Decreases Posterior Overhang Rate and Improves Clinical Outcomes: Results of a Prospective, Matched Controlled Study

BACKGROUND

Tibial implant's positioning in total knee arthroplasty (TKA) requires a compromise between implant's rotation and bone coverage. We hypothesized that morphometric tibial trays (MTTs) would improve implant positioning and clinical outcomes as compared with symmetrical tibial trays.

METHODS

Thirty-three patients were included prospectively according to the following criteria: age from 18 to 85 years, body mass index <35 kg/m², and posterostabilized cemented TKA performed for primary arthritis. Patients were matched for age, gender, body mass index, and preoperative international knee society (IKS) scoring system and Knee Injury and Osteoarthritis Outcome Score (KOOS) pain score, in a 1:1 fashion with patients from a prospectively collected database receiving a symmetrical tibial tray TKA. Tibial implant's rotation, bone coverage, and the percentage of patients with a posterior overhang (PO) >3 mm were assessed using computerized tomography. The IKS and the KOOS were compared at 3-year follow-up.

RESULTS

Bone coverage (90% vs 88%, P = .07) and rotation (mean difference 0.7 ± 3°; P = .69) were not different between the 2 groups. The percentage of patient with a PO was lower in the morphologic group (2/33 vs 14/33, P = .01, odds ratio = 10.3 [2.12-50.24]). Functional scores were superior in the morphometric group: IKS (mean difference 20 ± 21 points; P = .0005), mainly due to a difference in the IKS pain subscore (mean difference 11 ± 15 points; P = .0002). According to the multivariate analysis, an MTT had a positive, independent effect on IKS pain (P = .006) and KOOS pain subscores (P = .03) at the last follow-up.

CONCLUSION

The use of an MTT in TKA did not modify the tibial implant position in the axial plane; however, it decreased implant's posterior overhang and improved functional scores. The clinical improvement was mainly found on pain scores.

Optimization of parameters for femoral component implantation during TKA using finite element analysis and orthogonal array testing

Background

Individualized and accurate implantation of a femoral component during total knee arthroplasty (TKA) is essential in achieving equal distribution of intra-articular stress and long-term survival of the prosthesis. However, individualized component implantation remains challenging. This study aimed to optimize and individualize the positioning parameters of a femoral component in order to facilitate its accurate implantation.

Methods

Using computer-simulated TKA, the positioning parameters of a femoral component were optimized individually by finite element analysis in combination with orthogonal array testing. Flexion angle, valgus angle, and external rotation angle were optimized in order to reduce the peak value of the pressure on the polyethylene liner of the prosthesis.

Results

The optimal implantation parameters of the femoral component were as follows: 1° flexion, 5° valgus angle, and 4° external rotation. Under these conditions, the peak value of the pressure on the polyethylene liner surface was minimized to 16.46 MPa. Among the three parameters, the external rotation angle had the greatest effect on the pressure, followed by the valgus angle and the flexion angle.

Conclusion

Finite element analysis in combination with orthogonal array testing can optimize the implantation parameters of a femoral component for TKA. This approach would possibly reduce the wear of the polyethylene liner and prolong the survival of the TKA prosthesis, due to its capacity to minimize stress. This technique represents a new method for preoperative optimization of the implantation parameters that can achieve the best possible TKA outcome.

Extrinsic Factors as Component Positions to Bone and Intrinsic Factors Affecting Postoperative Rotational Limb Alignment in Total Knee Arthroplasty

BACKGROUND

This study aimed to identify the factors affecting postoperative rotational limb alignment of the tibia relative to the femur. We hypothesized that not only component positions but also several intrinsic factors were associated with postoperative rotational limb alignment.

METHODS

This study included 99 knees (90 women and 9 men) with a mean age of 77 ± 6 years. A three-dimensional (3D) assessment system was applied under weight-bearing conditions to biplanar long-leg radiographs using 3D-to-2D image registration technique. The evaluation parameters were (1) component position; (2) preoperative and postoperative coronal, sagittal, and rotational limb alignment; (3) preoperative bony deformity, including femoral torsion, condylar twist angle, and tibial torsion; and (4) preoperative and postoperative range of motion (ROM).

RESULTS

In multiple linear regression analysis using a stepwise procedure, postoperative rotational limb alignment was associated with the following: (1) rotation of the component position (tibia: β = 0.371, P < .0001; femur: β = -0.327, P < .0001), (2) preoperative rotational limb alignment (β = 0.253, P = .001), (3) postoperative flexion angle (β = 0.195, P = .007), and (4) tibial torsion (β = 0.193, P = .010).

CONCLUSION

In addition to component positions, the intrinsic factors, such as preoperative rotational limb alignment, ROM, and tibial torsion, affected postoperative rotational limb alignment. On a premise of correct component positions, the intrinsic factors that can be controlled by surgeons should be taken care. In particular, ROM is necessary to be improved within the possible range to acquire better postoperative rotational limb alignment.

Tibiofemoral rotational alignment affects flexion angles in navigated posterior-stabilized total knee arthroplasty

PURPOSE

To investigate the tibiofemoral rotational profiles during navigated posterior-stabilized (PS) total knee arthroplasty (TKA) and investigate the effect on post-operative maximum flexion angles.

METHODS

Twenty-five subjects, treated with navigated PS TKA, were enrolled, and the effect of posterior cruciate ligament (PCL) resection and component implantation on tibiofemoral rotational kinematics was statistically evaluated. Then, the effect of rotational alignment changes on the post-operative maximum angles was retrospectively examined in 96 subjects using the multiple regression analysis.

RESULTS

Tibial internal rotation was significantly increased in full extension (p < 0.01 and <0.001, respectively) and at 60° and 90° flexion (p < 0.05) after PCL resection, which further increased after implantation, compared with that before resection. The amount of tibial internal rotation from 90° flexion to maximum flexion was significantly decreased after PCL resection and implantation, compared with that before resection (p < 0.05). The internal changes in the rotational alignment were independent factors for the minimal improvement in the post-operative maximum flexion angles (R ² = 0.078, p = 0.0067).

CONCLUSION

PCL resection changed the tibial rotational alignment and decreased the amount of tibial internal rotation. The implantation of PS components further increased the internal rotational alignment and could not compensate for the tibiofemoral rotation. Finally, the internal changes in rotational alignment affected the improvement of the maximum flexion angles, suggesting that rotational alignment is an important factor for improving post-operative maximum flexion angles.

LEVEL OF EVIDENCE

II.

Experience Influences the Agreement and Reliability of Tibial Component Positioning in Total Knee Arthroplasty

BACKGROUND

Poor rotation of the tibial component is associated with unfavorable total knee arthroplasty outcomes. Some surgeons utilize the tibial tubercle (TT method), while others utilize the femoral cam (Box method) as a rotational landmark during total knee arthroplasty. Our purpose is to determine the reproducibility of 2 methods for establishing intra-operative tibial component rotation, while also comparing the effect of level of training.

METHODS

Twelve surgeons positioned and sized a symmetric tibial component on 7 cadaver knees. Surgeons were allowed to utilize their preferred method for establishing tibial component rotation. Seven surgeons selected the TT method, 4 utilized the Box method, and 1 used both methods depending on the specimen. Repeat measurements were completed by each surgeon after a rest period. The differences between tibial tray positions were assessed using computer-assisted optoelectronic measurements. Intra-class correlation coefficients were calculated to determine inter-observer agreement (IOA) and intra-rater reliability (IRR).

RESULTS

Overall, both the Box method and the TT method demonstrated high IRR for tibial component rotation. Experienced surgeons were more consistent at establishing component rotation regardless of technique. Trainees were more consistent when utilizing the Box method (IRR 0.96, IOA 0.94) than the TT method (IRR 0.71, IOA 0.72).

CONCLUSION

Surgeon experience influences the agreement and reliability of tibial component position. For less experienced surgeons, the Box method was more effective than the TT method for consistently reproducing tibial component rotation.

Unexplained pain following total knee arthroplasty: Is rotational malalignment the problem?

BACKGROUND

Malrotation of tibial and femoral components is a potential source of pain following total knee arthroplasty (TKA). This study aimed to 1) compare component rotation in TKA patients with unexplained pain versus a control group with well-functioning TKAs and 2) investigate the relationship between TKA component rotation and pain.

METHODS

Seventy one patients with unexplained pain after primary TKA were compared to a control cohort of 41 well functioning TKA patients. Both groups underwent post-operative computed tomography (CT) scans to assess component rotation. Findings were compared between the painful and control TKA groups.

RESULTS

We found no difference in femoral component rotation between the painful and control groups (mean 0.6° vs 1.0° external rotation (ER), p=0.4), and no difference in tibial component rotation (mean 11.2° vs 9.5° internal rotation (IR), p=0.3). Also, there was no difference in combined mal-rotation (tibial+femoral rotation) between the groups (mean 10.5° vs 8.5°IR, p=0.25). Fifty-nine percent of patients in the painful group had tibial component rotation >9°IR vs 49% in the control group.

CONCLUSION

In the largest study yet on component rotation after TKA, we found no difference in the incidence of tibial, femoral, or combined component mal-rotation in painful versus well-functioning TKAs. Tibial component IR relative to the junction of the medial to middle thirds of the tibial tubercle appears to be common in patients with well-functioning TKAs. The significance of slight tibial IR should be interpreted with caution when evaluating the painful TKA. Level III retrospective case-control study.

The comparison of femoral component rotation in the total knee arthroplasty

Introduction Background: Optimal femoral component rotation in total knee arthroplasty (TKA) is crucial to establish a balanced knee reconstruction. Unbalanced knees can lead to instability, patellofemoral problems, persistent pain, stiffness, and generally poorer outcomes including early failure. There are several methods to achieve the femoral component rotation such as balanced gap technique, measured resection technique, and bone landmarks such as transepicondylar line (TEA) and Whiteside line. The purpose of this study was to compare the balan ced gap technique with the TEA technique.

Materials and Methods: This randomised prospective study compares the femoral component rotation obtained with the use of balanced gap technique and the TEA, as well as compares the differences due to preoperative knee desaxations. The study includes 50 knees, 19 with neutral alignment, 22 with varus, and 9 with valgus desaxation. The femoral component rotation was measured postoperatively on photodocumentation taken after determining the TEA and balanced gap technique line peroperatively. These lines were compared to the posterior femoral condyles obtaining the degree of rotation. In case of transepicondylar line it is condylar twist angle (CTA) and in case of ligament balancer rotation axis it is ligament balancer angle (LBA).

Results: The statistically significant differences in femoral component rotation using the techniques mentioned above as well as differences in individual knee desaxations were observed. The average LBA was 3.42 degrees and average CTA 3.58 in neutral knees group, but in the varus knees the average CTA value was 2.27 degrees and LBA value was 1.05 degrees. The average CTA value in patients with valgus desaxation is 4.78 degrees and LBA value is 5.22 degrees. According to Tukey Post Hoc test a statistically significant difference in LBA value is between neutral and varus knees with a significance level of p = 0.000022 and the most significant difference between varus and valgus knees with a significance level of p = 0.000011.

Conclusion: The statistically significant differences in femoral component rotation using the techniques mentioned above as well as differences in individual knee desaxations were observed.

No influence of femoral component rotation by the lateral femoral posterior condylar cartilage remnant technique on clinical outcomes in navigation-assisted TKA

PURPOSE

To investigate whether cartilage thickness in the lateral femoral posterior condyle affects the femoral rotation angles on navigation and clinical outcomes of navigation-assisted total knee arthroplasty (TKA).

METHODS

This is a prospective randomized study of navigation-assisted TKA. Fifty cases underwent TKA without removal of the lateral posterior femoral cartilage (Group 1), and 56 cases underwent TKA with removal of the lateral posterior femoral cartilage (Group 2). The femoral rotation was evaluated using CT and compared with navigation values. The angle between the clinical transepicondylar axis and posterior condylar axis measured on CT was defined as the femoral rotation angle on CT. Elevation of the joint line and patellar measurements were also evaluated.

RESULTS

The clinical outcomes were not statistically different in the two groups. The radiographic measurements were not statistically different except femoral rotation angle on navigation. The mean femoral rotation angle of navigation was 4.0° ± 2.2° without cartilage removal and 5.1° ± 2.5° with cartilage removal. The reliability and validity were high between the femoral rotation angle on navigation in the cartilage removal group and that on CT, but there were no differences in clinical outcomes between the two groups.

CONCLUSION

There was little effect of navigation-assisted TKA on radiographic and clinical outcomes, although femoral rotational differences were caused by the lateral femoral posterior condylar cartilage. Although the rotational differences due to cartilage would be within the clinical safety margin, surgeons should consider that difference during TKA.

LEVEL OF EVIDENCE

Lower quality randomized trial (no masking), Level II.

[Anterior knee pain after total knee arthroplasty : Causes, diagnosis and treatment]

BACKGROUND

Anterior knee pain is one of the most common complications after total knee arthroplasty. An incidence of up to 30 % has been reported in peer-reviewed studies.

TARGET

The purpose of this study was to systematically review the literature and to identify determinants that have been analyzed with regard to anterior knee pain.

CAUSES

Patient- and knee-specific characteristics, prosthetic designs and operative techniques are addressed as well as functional and neurologic determinants. Instability, increased contact pressure in the patellofemoral joint and patella maltracking due to malrotation of components, offset errors, ligament insufficiencies or patella baja are mechanical reasons for anterior knee pain. Functional causes include pathologic gait patterns, quadriceps imbalance and dynamic valgus. They have to be differentiated from infectious and inflammatory causes as well as soft tissue impingement, arthrofibrosis and neurologic diseases.

TREATMENT

A differentiated treatment algorithm is recommended. Often conservative treatment options exist, however, particularly with most mechanical causes revision surgery is necessary.

Reproducibility and Precision of CT Scans to Evaluate Tibial Component Rotation

BACKGROUND

Component rotation likely plays a greater role on the survivorship and outcomes of total knee arthroplasties than is currently known. Our goal was to evaluate the precision, interobserver reliability, and intrarater reliability of tibial component rotation as measured by computed tomography (CT) scan, regardless of measurement technique.

METHODS

Three fellowship-trained, academic arthroplasty surgeons independently measured tibial component rotation on CT scans of 62 total knee arthroplasties using their methods of choice. Measurements were repeated at least 2 weeks after the initial measurement. The precision of the measurements was assessed using a formal 8-step protocol as the gold standard. Intraclass correlation coefficients (ICCs) were calculated to evaluate precision, interobserver agreement, and intrarater reliability RESULTS: The interobserver agreement between the 3 surgeons for tibial component rotation was also moderate (ICC = 0.52). The intrarater reliability of tibial rotation was excellent (ICC = 0.81). Comparison of surgeons' measurement to a validated gold standard revealed only moderate precision for tibial component rotation (ICC = 0.64).

CONCLUSION

Practicing surgeons measuring tibial rotation were internally consistent, but failed to demonstrate satisfactory precision and interobserver agreement. We support the adoption of standardized criteria for the measurement of tibial component rotation on CT scans.

Femoral rotation in total knee arthroplasty: a comparison of patient individualized jigs with gap balancing in relation to anatomic landmarks

PURPOSE

The purpose of our study was to compare the accuracy of the rotational position of the femoral component in total knee arthroplasty aligned with patient individualized jigs (PSJ) to a gap balancing technique (GBT).

METHODS

A consecutive series of 21 osteoarthritic patients were treated with 22 cruciate-retaining total knee prostheses. During surgery, the rotation of the femoral component pinholes was recorded for all knees using PSJ and GBT and transferred to computer tomograms (CT). The rotational differences between PSJ and GBT relative to the transepicondylar axis were analysed.

RESULTS

The medium rotation of the femoral component pinholes was 1.3° ± 5.1° (min = -6.3°; max = 14.4°) for PSJ and 0.1 ± 1.4° (min = -1.6°; max = 3.4°) for GBT. Outliers of more than 3° were found more frequently with PSJ in 12 cases but only in one for GBT.

CONCLUSION

Based on our study, we would not recommend relying intra-operatively solely on the CT-based PSJ without the option to adjust or control femoral rotation.

LEVEL OF EVIDENCE

II.

The medial border of the tibial tuberosity as an auxiliary tool for tibial component rotational alignment during total knee arthroplasty (TKA)

PURPOSE

The objective of this study was to quantify the amount of ensuing internal rotation of the tibial component when positioned along the medial border of the tibial tubercle, thus establishing a reproducible intraoperative reference for tibial component rotational alignment during total knee arthroplasty (TKA).

METHODS

The angle formed from the tibial geometric centre to the intersection of both lines from the middle of the tibial tuberosity and its medial border was measured in 50 patients. The geometric centre was determined on an axial CT slice at 10 mm below the lateral tibial plateau and transposed to a slice at the level of the most prominent part of the tibial tuberosity. Similar measurements were taken in 25 patients after TKA, in order to simulate the intraoperative appearance of the tibia after making its proximal resection.

RESULTS

This angle was found to be similar (n.s.) in normal and post-TKA tibiae [median 20.4° (range 15°-24°) vs. 20.7° (range 16°-25°), respectively]. In 89.3 % of the patients, the angle ranged from 17° to 24°. No statistical difference (p n.s.) was found between women and men in both normal [median -20.7° (range 16°-25°) vs. 19.9° (range 15°-24°)] and post-TKA tibiae [median 21.4° (range 19°-24°) vs. 20° (range 16°-25°)].

CONCLUSION

This study found that in 90 % of the patients, the medial border of the tibial tuberosity is internally rotated 17°-24° in relation to the line connecting the middle of the tuberosity to the tibial geometric centre. Since this anatomical landmark may be more easily identifiable intraoperatively than the commonly used "medial 1/3", it can provide a better quantitative reference point and help surgeons achieve a more accurate tibial implant rotational position.

LEVEL OF EVIDENCE

Cohort and case control studies, Level III.

Does Maximal External Tibial Component Rotation Influence Tibiofemoral Load Distribution in the Primary Knee Arthroplasty Setting: A Comparison of Neutral vs Maximal Anatomical External Rotatory States

BACKGROUND

Tibial component rotation at time of knee arthroplasty can influence conformity, load transmission across the polyethylene surface, and perhaps ultimately determined survivorship. Optimal tibial component rotation on the cut surface is reliant on standard per operative manual stressing. This subjective assessment aims to balance constraint and stability of the articulation through a full arc of movement.

METHODS

Using a cadaveric model, computer navigation and under defined, previously validated loaded conditions mimicking the in vivo setting, the influence of maximal tibial component external rotation compared with the neutral state was examined for changes in laxity and tibiofemoral continuous load using 3D displacement measurement and an orthosensor continuous load sensor implanted within the polyethylene spacer in a simulated single radius total knee arthroplasty.

RESULTS

No significant difference was found throughout arc of motion (0-115 degrees of flexion) for maximal varus and/or valgus or rotatory laxity between the 2 states. The neutral state achieved equivalence for mediolateral load distribution at each point of flexion. We have found that external rotation of the tibial component increased medial compartment load in comparison with the neutral position. Compared with the neutral state, external rotation consistently effected a marginal, but not significant reduction in lateral load under similar loading conditions. The effects were most pronounced in midflexion.

CONCLUSION

On the basis of these findings, we would advocate for the midtibial tubercle point to determine tibial component rotation and caution against component external rotation.