Navigational predictors in determining the necessity for collateral ligament release in total knee replacement

Correction of Varus Alignment with Peripheral Osteophyte Removal during Total Knee Arthroplasty: An Assessment with Computer Navigation

Techniques for symmetrical balancing in flexion and extension have been described; however, the ideal technique is unclear. This study aimed to clarify whether resection of peripheral osteophytes could restore neutral hip-knee-ankle (HKA) angle of varus deformity of arthritic knees. Data from 90 varus arthritic knees that had undergone total knee arthroplasty (TKA) using a nonimage-based navigation system were analyzed. The change in the coronal mechanical axis, while applying manual valgus stress at extension and 90 degrees of knee flexion, was recorded after the following sequential procedures: (1) anterior cruciate ligament (ACL) sectioning, (2) subperiosteal stripping of the deep medial collateral ligament (MCL) from the underlying osteophytes on the medial tibia, and (3) complete removal of peripheral osteophytes from the proximal medial tibia and distal medial femoral condyle. Repeated measures of analysis of variance (ANOVA) were performed to compare the varus angle among each step, and a post hoc analysis by paired t-test was utilized to compare the parameters between baseline and each step. The varus alignment with valgus stress at extension and 90 degrees of flexion (mean: 6.0 ± 3.6 and 5.2 ± 3.9 degrees of varus, respectively) was significantly corrected to a near-neutral mechanical axis (mean: 0.9 ± 2.4 and 1.4 ± 4.2 degrees of varus, respectively) after peripheral osteophyte resection (p < 0.01, both). In many cases, varus deformity of arthritic knees could be corrected to near-neutral HKA angle by applying manual valgus stress after complete peripheral osteophyte resection. These procedures could facilitate soft tissue balancing in TKA, minimizing the risk of overrelease of the medial soft tissues.

Less soft tissue release in total knee arthroplasty for anteromedial compared to posteromedial knee osteoarthritis

In total knee arthroplasty (TKA), the aim of achieving a mechanically straight leg axis as well as symmetrical and equally wide gaps has become established as the gold standard in terms of surgical technique. In contrast to TKA unicompartmental knee arthroplasty (UKA) is performed in anteromedial osteoarthritis (AMOA) and does not normally require releases. This raises the hypothesis whether the type of osteoarthritis (AMOA vs. posteromedial osteoarthritis (PMOA)) determines the requirement for soft tissue releases in TKA.In this retrospective study, 114 patients with medial osteoarthritis of the knee who had been treated with a navigated total knee replacement were consecutively included. On the basis of the preoperative lateral radiographs, the patients were divided into two groups: AMOA and PMOA. The incidence and the extent of releases performed were recorded using the navigation records.Patient-specific data (gender, age) did not differ between the groups (NS). Knees with AMOA presented an overall varus alignment of 5.3 ± 3.5°, knees with PMOA 8.0 ± 4.0° (p < 0.001). 30 cases (44%) had to be released in the AMOA group, compared with 33 cases (72%) in the PMOA group (p = 0.004). In the case of medial release, the extension gap increased 3.3 ± 2.4 mm in the AMOA compared to 5.3 ± 3.7 mm in the PMOA group (p = 0.006). The medial flexion gap was released 2.2 ± 2.6 mm in the AMOA and 2.9 ± 3.0 mm in the PMOA group (p = 0.008).To achieve a neutral mechanical alignment, a release has to be performed due to asymmetry of the extension gap more often if PMOA is present than in AMOA. Surgeons should be prepared to perform more frequent and extensive medial releases in PMOA. Higher constrained implants should be available in case of unintended over release in PMOA.

Assessing the Role of Minimal Medial Tissue Release during Navigation-Assisted Varus Total Knee Arthroplasty Based on the Degree of Preoperative Varus Deformity

We assessed the impact of a minimal medial soft-tissue release with complete peripheral osteophyte removal on the ability to attain manual preresection deformity correction during navigation-assisted total knee arthroplasty (TKA) for varus osteoarthritis. We included 131 TKAs for 109 patients with medial compartment predominant osteoarthritis. The steps for achieving minimal medial soft-tissue release were performed as follows: (1) elevation of a periosteal sleeve to 5-mm distal to the joint line and (2) complete removal of peripheral osteophytes. The evaluation criteria of this study were as follows: (1) age, (2) height, (3) weight, (4) body mass index (BMI), (5) sex, (6) the preoperative femorotibial mechanical angle in the neutral position before medial release and (7) the mechanical angle in maximum manual valgus stress after the two-step medial-release procedure (measured on the navigation screens). Multiple regression analysis of the criteria was performed to determine the degree of varus deformity that allowed neutral alignment but required extensive medial release. The femorotibial mechanical angle in the neutral position before medial release and sex correlated with the mechanical angle in maximum manual valgus stress on the navigation screen after medial release (r = 0.72, p < 0.001). Based on the regression formula, the maximum degree of preoperative varus deformity that allowed neutral alignment by the minimum medial-release procedure was 5.3 degrees for males and 9.1 degrees for females. The magnitude of deformity which has an impact on the ability to correct varus deformity (by minimal soft-tissue release and complete osteophyte removal) was clarified. If the preoperative degree of varus deformity was within 5.3 degrees for males and 9.1 degrees for females, an extensive medial release was not required to obtain neutral alignment.

Is Standing Coronal Long-Leg Alignment View Effective in Predicting the Extent of Medial Soft Tissue Release in Varus Deformity during Total Knee Arthroplasty?

The aim of this study was to assess the predictive value of the femoral intermechanical-anatomical angle (IMA), mechanical lateral distal femoral angle (mLDFA), medial proximal tibia angle (MPTA), femorotibial or varus angle (VA), and joint line convergence angle (CA) in predicting the stage of the medial collateral ligament (MCL) during total knee arthroplasty (TKA) of varus knee. We evaluated 229 patients with osteoarthritic varus knee who underwent primary TKA, prospectively. They were categorized in three groups based on the extent of medial soft tissue release that performed during TKA Group 1, osteophytes removal and release of the deep MCL and posteromedial capsule (stage 1); Group 2, the release of the semimembranosus (stage 2); and Group 3, release of the superficial MCL (stage 3) and/or the pes anserinus (stage 4). We evaluated the preoperative standing coronal hip-knee-ankle alignment view to assessing the possible correlations between the knee angles and extent of soft tissue release. A significant difference was observed between the three groups in terms of preoperative VA, CA, and MPTA by using the Kruskal-Wallis test. The extent of medial release increased with increasing VA and CA as well as decreasing MPTA in preoperative long-leg standing radiographs. Finally, a patient with a preoperative VA larger than 19, CA larger than 6, or MPTA smaller than 81 would need a stage 3 or 4 of MCL release. The overall results showed that the VA and MPTA could be useful in predicting the extent of medial soft tissue release during TKA of varus knee.

Arithmetic hip-knee-ankle angle and stressed hip-knee-ankle angle: equivalent methods for estimating constitutional lower limb alignment in kinematically aligned total knee arthroplasty

PURPOSE

Kinematically aligned total knee arthroplasty (KA TKA) relies on precise determination of constitutional alignment to set resection targets. The arithmetic hip-knee-ankle angle (aHKA) is a radiographic method to estimate constitutional alignment following onset of arthritis. Intraoperatively, constitutional alignment may also be approximated using navigation-based angular measurements of deformity correction, termed the stressed HKA (sHKA). This study aimed to investigate the relationship between these methods of estimating constitutional alignment to better understand their utility in KA TKA.

METHODS

A radiological and intraoperative computer-assisted navigation study was undertaken comparing measurements of the aHKA using radiographs and computed tomography (CT-aHKA) to the sHKA in 88 TKAs meeting the inclusion criteria. The primary outcome was the difference in the paired means between the three methods to determine constitutional alignment (aHKA, CT-aHKA, sHKA). Secondary outcomes included testing agreement across measurements using Bland-Altman plots and analysis of subgroup differences based on different patterns of compartmental arthritis.

RESULTS

There were no statistically significant differences between any paired comparison or across groups (aHKA vs. sHKA: 0.1°, p = 0.817; aHKA vs. CT-aHKA: 0.3°, p = 0.643; CT-aHKA vs. sHKA: 0.2°, p = 0.722; ANOVA, p = 0.845). Bland-Altman plots were consistent with good agreement for all comparisons, with approximately 95% of values within limits of agreement. There was no difference in the three paired comparisons (aHKA, CT-aHKA, and sHKA) for knees with medial compartment arthritis. However, these findings were not replicated in knees with lateral compartment arthritis.

CONCLUSIONS

There was no significant difference between the arithmetic HKA (whether obtained using CT or radiographs) and the stressed HKA in this analysis. These findings further validate the preoperative arithmetic method and support use of the intraoperative stressed HKA as techniques to restore constitutional lower limb alignment in KA TKA.

LEVEL OF EVIDENCE

III.

Can the need for soft tissue release in total knee replacement be predicted pre-operatively? A study based on surgical navigation

Introduction

In complex and deformed knees, soft tissue release (STR) is required to obtain symmetry in the femorotibial gap. The objective of this study was to attempt to predict the need for soft tissue release using surgical navigation in total knee replacement (TKR).

Methods

Prospective and non-randomized study. One hundred thirty knees. At the start of navigation, an attempt was made to correct the femorotibial mechanical axis by applying force to the medial or lateral side of the knee (varus-valgus stress angle test). A gap balanced technique with computer-assisted surgery (CAS) was performed in all cases. The ligaments were tensioned, and using CAS visualization and control, progressive STR was performed in the medial or lateral side until a symmetry of the femorotibial gap was achieved.

Results

Eighty-two patients had a varus axis ≥ 3° and 38 had a valgus axis (P < 0.001). STR was performed under navigation control in 38.5% of cases, lateral release (LR) in 12 cases, and medial release (MR) in 38 cases. After performing the varus-valgus stress angle test (VVSAT), the axis of 0° could be restored at some point during the manoeuvre in 28 cases. STR was required in 44.6% of varus cases and 27% of valgus cases (P = 0.05). A significant relationship was found between the previous deformity and the need for MR (P < 0.001) or LR (P = 0.001). STR was more common in male patients (P = 0.002) and as obesity increased.

Conclusion

This study shows that pre-operative factors favouring the need to perform STR in a TKR implant can be defined.

Navigation Improves the Survival Rate of Mobile-Bearing Total Knee Arthroplasty by Severe Preoperative Coronal Deformity: A Propensity Matched Case-Control Comparative Study

The primary hypothesis of this study was that the survival rate over 10 years of total knee arthroplasties (TKAs) implanted with a navigation system was superior to that of TKAs implanted with a conventional technique. The secondary hypothesis was that the severity of the initial coronal deformity had a negative influence on the survival rate. A national, multicentric, retrospective study was performed in France, including eight university or private centers with high volumes in knee surgery. Cases operated on with either a conventional (control group) or a navigated (study group) technique were matched after calculating the propensity score using the logistic regression technique. All patients were contacted after 10 years or more to determine the survival of the TKA. The need for date and cause of revision were noted. The primary end point of the study was the occurrence of a revision for any mechanical reason. Survival curves were calculated using the Kaplan-Meier's technique, with the primary criterion as end point. The influence of the implantation technique was analyzed by a log-rank test at a 5% level of significance. The influence of severity of the preoperative coronal deformity was analyzed using the same technique. A total of 513 cases were included in each group. The survival rates after 13 years were 96.5% in the study group and 92.9% in the control group (not significant). There was no significant difference between both groups for the survival rates after 13 years for small deformity (96.0 vs. 97.0%), but the difference was significant for large deformity (97.0 vs. 89.0%, p = 0.04). The results suggest that the use of a navigation system, allowing a more consistent correction of the preoperative coronal deformity, thus allows a better long-term prosthetic survival in cases with a large initial coronal deformity. A navigation system should be routinely used in cases of initial coronal deformity greater than or equal to 10 degrees, as conventional techniques do not routinely provide satisfactory axial correction in these difficult cases.

Mechanical alignment changes during flexion in total knee arthroplasty without affecting clinical outcomes

BACKGROUND

Primary aim of this study is to investigate if Hip-Knee-Ankle angle, measured in the coronal plane, changes with knee flexion after total knee arthroplasty. The secondary aim is to assess the relationship between Hip-Knee-Ankle during knee flexion and clinical outcome at mid-term follow up.

METHODS

334 computer assisted total knee arthroplasties were retrospectively evaluated. A total of 233 patients were available for assessment of clinical outcomes at last follow up (mean 35 months). Hip-Knee-Ankle angle at different degrees of knee flexion and components' alignment were recorded intraoperatively.

FINDINGS

Patients were stratified based on the preoperative alignment: 202 varus knees, 99 neutral knees, and 33 valgus knees. In the varus knee group, 146 patients (89%) maintained a neutral overall limb alignment when flexed to 20°, 118 (72%) remained neutrally aligned at 45° and 92 (54%) at 90°. In valgus knee group, 26 (90%) remained neutrally aligned at 20°, 22 (75%) at 45° and 16 (55%) at 90°. In neutrally-aligned knee group, 88 (96%) remained neutrally aligned at 20°, 73 (79%) at 45° and 61 (66%) at 90°. Femoral component external rotation was correlated with varus alignment in flexion. Good outcomes were reported in 181 (78%) cases, fair results in 28 (12%) cases, poor results in 24 (10%) of cases. Poor results were not correlated to Hip-Knee-Ankle angle at different knee flexion angles.

INTERPRETATION

This study demonstrates that intraoperative Hip-Knee-Ankle angle changes as the knee moves into deeper flexion. However, neutral Hip-Knee-Ankle through the range of motion does not correlate with superior outcomes.

Kinematic alignment is bone and soft tissue preserving compared to mechanical alignment in total knee arthroplasty

BACKGROUND

Kinematically aligned (KA) total knee arthroplasty (TKA) has emerged as an alternative approach to the intraoperative alignment targets of mechanically aligned (MA) TKA. While the clinical outcomes of the two philosophies have been investigated, further investigation is required to quantify exactly how the two philosophies differ in their approach to correcting the deformities encountered in osteoarthritic knees such as fixed flexion deformities (FFD) and coronal malalignment. The aim of this paper was to compare MA and KA philosophies in TKA in terms of the intra-operative correction of FFD and coronal malalignment and quantify the way in which each philosophy achieves a well-balanced knee that can reach full extension.

METHODS

A retrospective review of prospective data collected from 210 consecutive TKAs performed by a single surgeon between March 2015 and May 2017 was undertaken. MA and KA cases were compared in terms of pre-operative patient deformity and characteristics, intraoperative steps taken to correct FFD (including bony resections, soft tissue releases and components used) and postoperative alignment achieved.

RESULTS

One hundred twenty MA and 90 KA TKAs were analysed. There was no significant difference in terms of patient age, gender and preoperative coronal and sagittal deformity between the two cohorts. KA TKAs were able to achieve the same degree of sagittal correction as MA TKAs with less total bony resection (16.7 mm vs. 18.9 mm, p < 0.0001), less soft tissue releases (10% vs. 49.2%, p < 0.0001). This was achieved with a difference in component alignment. The femur was in more valgus (-2.5 vs. -0.03°, p < 0.0001), the tibia in more varus (2.3 vs. 0.3°, p < 0.0001), and the overall alignment slightly more varus in the KA group (1.1 vs. 0.4°, p = 0.007), without significant difference in the proportion of patients within three degrees of a neutral axis.

CONCLUSION

This study shows that using a kinematic alignment philosophy in total knee arthroplasty results in the achievement of extension range-of-motion and soft tissue balance goals with less bone resection and less soft tissue release. This allows for bone stock preservation and minimization of trauma due to soft tissue release. Further study is required to correlate these results with patient reported outcomes and determine their clinical significance.

LEVEL OF EVIDENCE

III - retrospective cohort study.

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.

Lower limb alignment and laxity measures before, during and after total knee arthroplasty: A prospective cohort study

BACKGROUND

This study compared knee alignment and laxity in patients before, during and after total knee arthroplasty, using methodologically similar procedures, with an aim to help inform pre-operative planning.

METHODS

Eighteen male and 13 female patients were recruited, mean age 66years (51-82) and mean body mass index of 33 (23-43). All were assessed pre- and postoperatively using a non-invasive infrared position capture system and all underwent total knee arthroplasty using a navigation system. Knee kinematic data were collected and comparisons made between preoperative clinical and intraoperative measurements for osteoarthritic knees, and between postoperative clinical and intraoperative measurements for prosthetic knees.

FINDINGS

There was no difference in unstressed coronal mechanical femoral-tibial angles for either osteoarthritic or prosthetic knees. However, for sagittal alignment the knees were in greater extension intraoperatively (osteoarthritic 5.2° p<0.001, prosthetic 7.2° p<0.001). For osteoarthritic knees, both varus and valgus stress manoeuvres had greater angular displacements intraoperatively by a mean value of 1.5° for varus (p=0.002) and 1.6° for valgus (p<0.001). For prosthetic knees, only valgus angular displacement was greater intraoperatively (0.9°, p=0.002).

INTERPRETATION

Surgeons performing total knee arthroplasties should be aware of potential differences in alignment and laxity measured under different conditions to facilitate more accurate operative planning and follow-up.

Assessment of knee alignment with varus and valgus force through the range of flexion with non-invasive navigation

In image-free total knee arthroplasty (TKA) navigation, infra-red markers are attached to bony landmarks to provide kinematic data intra-operatively, with the aim of improving the precision of implant placement. In non-invasive navigation, infra-red markers are attached to the skin surface, with recent evidence suggesting that this can give repeatable measurements of lower limb mechanical alignment. The aim of our study was to evaluate the use of a non-invasive navigation system in the assessment of mechanical alignment with applied coronal force through the range of flexion. A previously validated non-invasive system (Physiopilot™) was tested on 23 volunteers with healthy knees. Two users performed two registrations of the software workflow on each participant's right and left knees. A force was manually applied to the end-point of varus and valgus knee laxity and the measured change in mechanical alignment was recorded. Force was applied with the knee positioned in increments of flexion from 0 to 90°. In keeping with previous studies, satisfactory values of coefficient of repeatability (CR) of 1.55 and 1.33 were found for intra-observer repeatability in measurement of supine mechanical femoro-tibial angle (MFTA) in extension, with a good inter-observer correlation of intraclass correlation coefficient (ICC) .72. However, when flexion was introduced, intra-observer and inter-observer reliability fell out with acceptable limits. Therefore, the trial did not support use of the Physiopilot™ system as a measure of MFTA when flexion is introduced. It was felt that learning-curve, soft tissue artefacts and lack of force standardisation equipment may have accounted for significant levels of error, with further studies required to address these issues.

Hereditary bilateral genu recurvatum: Case report of a family

BACKGROUND

Genu recurvatum is a rare condition in children and adolescents. The origin can be osseous, ligamentous and mixed.

METHODS

We describe for the first time a family inclusive two brothers and their mother with hereditary bilateral genu recurvatum of unknown etiology. The possible underlying pathology and treatment are discussed.

RESULTS

The underlying pathology of the early closure of the apophysis of the tibial tuberosity remained unclear. The mother was never treated, one of the brothers received a tibial osteotomy as a young adult. Both patients developed end-stage osteoarthritis of both knees which was successfully treated by a bilateral computer-navigated TKA. At seven to eight years after implantation in the older brother (left and right knee, respectively) and three to four years after implantation in the younger brother (right and left knee, respectively), the Visual Analogue Scale (VAS) pain score on a 0 to 100 scale was 0 of both brothers, the EQ-5D health status was 80 (scale of 0 to 100), the satisfaction was 10 (scale of 10) of both brothers. The Knee Injury and Osteoarthritis Outcome Score (KOOS) function of the younger brother of 75 (scale 0 to 100) and of the older brother 100. The KOOS sport of the younger brother was 10 (scale 0 to 100), whereas that of the older brother 85.

CONCLUSIONS

Hereditary bilateral genu recurvatum with end-stage osteoarthritis can be successfully treated with computer-navigated TKAs; however, impingement of the patella on the proximal tibia and the position of the tibial keel are of concern.

Dynamic knee behaviour: does the knee deformity change as it is flexed-an assessment and classification with computer navigation

PURPOSE

The aim of this study was to assess the kinematics of arthritic knees prior to TKA. The hypothesis was that the arthritic knee follows distinct patterns with regard to deformity in coronal plane as it flexes from extended position.

METHOD

Data from 585 consecutive arthritic knees that had undergone TKA using two non-image-based navigation systems were included in the study. Coronal plane alignment given by the femoro-tibial mechanical angle (FTMA) was recorded in extension, 30°, 60°, 90° and maximum flexion prior to making any bony cuts or ligamentous releases.

RESULTS

Complete data were available for 512 (87.5 %) of arthritic knees. It was found that pre-implant arthritic knees behaved in different distinct patterns from full extension to 90° flexion. These patterns in FTMA from extension through to 90° of flexion were classified into 4 major types (1, 2, 3, and 4) and 8 subgroups (1A, 1B, 2A, 2B, 3, 4A, 4B, 4C) for varus and valgus knees. Beyond 90° of flexion, there were no distinct or consistent patterns. There were differences between varus and valgus knee deformities not only in overall numbers (73.8 % varus vs. 21.1 % valgus) but also in kinematic behaviour. Only 14.1 % of total knees had a consistent deformity (Type 1A) which remained the same throughout the range of flexion. 14.1 % knees actually become opposite deformity as the knee flexes; thus, varus becomes valgus and valgus becomes varus as the knee flexes (Type 3 and 4C).

CONCLUSION

This study has observed and categorised distinct patterns which arthritic knees follow in the coronal plane as it flexes. This dynamic change during flexion will have bearing on collateral releases that are traditionally done based on deformity in extension or 90° flexion mainly. This may be the underlying cause of flexion instability especially for Types 3 and 4C knees if collateral soft tissue release is done based on deformity in extension. Full significance of this remains unknown and will need further investigation.

LEVEL OF EVIDENCE

III.

Measuring the effect of femoral malrotation on knee joint biomechanics for total knee arthroplasty using computational simulation

Objectives

Malrotation of the femoral component can result in post-operative complications in total knee arthroplasty (TKA), including patellar maltracking. Therefore, we used computational simulation to investigate the influence of femoral malrotation on contact stresses on the polyethylene (PE) insert and on the patellar button as well as on the forces on the collateral ligaments.

Materials and Methods

Validated finite element (FE) models, for internal and external malrotations from 0° to 10° with regard to the neutral position, were developed to evaluate the effect of malrotation on the femoral component in TKA. Femoral malrotation in TKA on the knee joint was simulated in walking stance-phase gait and squat loading conditions.

Results

Contact stress on the medial side of the PE insert increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. There was an opposite trend in the lateral side of the PE insert case. Contact stress on the patellar button increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. In particular, contact stress on the patellar button increased by 98% with internal malrotation of 10° in the squat loading condition. The force on the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) increased with internal and external femoral malrotations, respectively.

Conclusions

These findings provide support for orthopaedic surgeons to determine a more accurate femoral component alignment in order to reduce post-operative PE problems.

Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, C. Baek, S. H. Jung, K. K. Park. Measuring the effect of femoral malrotation on knee joint biomechanics for total knee arthroplasty using computational simulation. Bone Joint Res 2016;5:552–559. DOI: 10.1302/2046-3758.511.BJR-2016-0107.R1.

Optimal Number of Fixation Pins for Dedicated Mini Jig Cutting Guides During Navigated Total Knee Arthroplasty

PURPOSE

The optimal number of fixation pins for minimally invasive cutting guides in computer-navigated arthroplasty has not been determined. The authors hypothesized that more fixation pins will lead to greater mechanical stability and more accurate resections.

MATERIALS AND METHOD

12 bovine knee joints were divided into three groups with differing numbers of fixation pins. The ASM [Stryker] knee navigation system was utilized to perform resections, and accuracy of alignment and posterior slope was measured. Comparison was performed between the groups to calculate average differences between predicted and actual resection with differing number of pins.

RESULTS

The difference between actual and predicted values showed a trend toward diminishing with a greater number of fixation pins. The mean difference in coronal alignment of predicted versus actual resection was 0.75° for two fixation pins, 0.5° for three pins and 1° for four fixation pins. Similarly, the difference between posterior slope was 2.75°, 2°, and 1°, respectively.

CONCLUSION

This study reveals a trend toward greater accuracy of resections with more fixation pins. Further investigation may be beneficial.

Lack of evidence to support present medial release methods in total knee arthroplasty

PURPOSE

The aim of this review was to identify a reliable sequential medial release protocol for restoration of soft tissue balance in total knee arthroplasty of the varus osteoarthritic knee and to allow for improved intraoperative decision-making.

METHOD

Current medial release sequences and applicability based upon pre-operative deformity have been reviewed. Furthermore, risks associated with over release, and the necessity of medial release, are discussed.

RESULTS

The different medial release sequences are discussed in relation to pre-operative deformity, along with potential complications associated with medial release. It was found that release sequences may include the deep and superficial components of the medial collateral ligament, the posteromedial capsule, the posterior oblique ligament, the pes anserinus (pes A), and tendons of the semimembranosus and medial gastrocnemius muscle. The sequences described were found to vary substantially between studies, and very few studies had systematically quantified the effect of each release on balance.

CONCLUSION

While medial release is the standard intraoperative mode of balancing, there is a lack of evidence to support current methods. The correct method for defining intraoperatively the sequence, extent and magnitude of releases required remains ill-defined. It could be argued that the classic extensive medial release may be unnecessary and may be associated with iatrogenic injury to the pes A and saphenous nerve, instability and abnormal knee kinematics. Minimal medial release may allow for improved soft tissue balancing leading ultimately to improved functional outcome.

LEVEL OF EVIDENCE

V (expert opinion).

Non-invasive quantification of lower limb mechanical alignment in flexion

OBJECTIVE

Non-invasive navigation techniques have recently been developed to determine mechanical femorotibial alignment (MFTA) in extension. The primary aim of this study was to evaluate the precision and accuracy of an image-free navigation system with new software designed to provide multiple kinematic measurements of the knee. The secondary aim was to test two types of strap material used to attach optical trackers to the lower limb.

METHODS

Seventy-two registrations were carried out on 6 intact embalmed cadaveric specimens (mean age: 77.8 ± 12 years). A validated fabric strap, bone screws and novel rubber strap were used to secure the passive tracker baseplate for four full experiments with each knee. The MFTA angle was measured under the conditions of no applied stress, valgus stress, and varus stress. These measurements were carried out at full extension and at 30°, 40°, 50° and 60° of flexion. Intraclass correlation coefficients, repeatability coefficients, and limits of agreement (LOA) were used to convey precision and agreement in measuring MFTA with respect to each of the independent variables, i.e., degree of flexion, applied coronal stress, and method of tracker fixation. Based on the current literature, a repeatability coefficient and LOA of ≤ 3° were deemed acceptable.

RESULTS

The mean fixed flexion for the 6 specimens was 12.8° (range: 6-20°). The mean repeatability coefficient measuring MFTA in extension with screws or fabric strapping of the baseplate was ≤ 2°, compared to 2.3° using rubber strapping. When flexing the knee, MFTA measurements taken using screws or fabric straps remained precise (repeatability coefficient ≤ 3°) throughout the tested range of flexion (12.8-60°); however, using rubber straps, the repeatability coefficient was >3° beyond 50° flexion. In general, applying a varus/valgus stress while measuring MFTA decreased precision beyond 40° flexion. Using fabric strapping, excellent repeatability (coefficient ≤ 2°) was observed until 40° flexion; however, beyond 50° flexion, the repeatability coefficient was >3°. As was the case with precision, agreement between the invasive and non-invasive systems was satisfactory in extension and worsened with flexion. Mean limits of agreement between the invasive and non-invasive system using fabric strapping to assess MFTA were 3° (range: 2.3-3.8°) with no stress applied and 3.9° (range: 2.8-5.2°) with varus and valgus stress. Using rubber strapping, the corresponding values were 4.4° (range: 2.8-8.5°) with no stress applied, 5.5° (range: 3.3-9.0°) with varus stress, and 5.6° (range: 3.3-11.9°) with valgus stress.

DISCUSSION

Acceptable precision and accuracy may be possible when measuring knee kinematics in early flexion using a non-invasive system; however, we do not believe passive trackers should be mounted with rubber strapping such as was used in this study. Flexing the knee appears to decrease the precision and accuracy of the system. The functions of this new software using image-free navigation technology have many potential clinical applications, including assessment of bony and soft tissue deformity, pre-operative planning, and post-operative evaluation, as well as in further pure research comparing kinematics of the normal and pathological knee.

Unified quantification of variation in passive knee joint constraint

The interrelationship that exists between multiple degrees of freedom to produce a net constraint across the range of passive motion of the knee is not fully understood. Manual joint laxity assessments were performed on 28 cadaveric specimens and used to develop a unified description of the passive laxity envelope that incorporated multiple degrees of freedom into a single analysis using radial basis functions. The unified envelopes were then included in a principal component analysis to identify the primary modes of variation. The first three modes of variation constituted 82% of the variation. The first principal component (36.5% explained variation) correlated with changes to the relationship between varus-valgus and internal-external rotation and had the largest impact on internal-external laxity. The second principal component (27.2% explained variation) correlated with a shift in the internal-external envelope. The third principal component (18.3% explained variation) correlated with a shift in the varus-valgus envelope and a change in varus-valgus laxity. This research presents a novel methodology for quantifying complex changes to passive knee constraint, which may be used as a means for objectively scoring joint laxity and evaluating complex relationships between degrees of freedom in a single analysis.

Smart instrumentation for determination of ligament stiffness and ligament balance in total knee arthroplasty

Ligament balance is an important and subjective task performed during total knee arthroplasty (TKA) procedure. For this reason, it is desirable to develop instruments to quantitatively assess the soft-tissue balance since excessive imbalance can accelerate prosthesis wear and lead to early surgical revision. The instrumented distractor proposed in this study can assist surgeons on performing ligament balance by measuring the distraction gap and applied load. Also the device allows the determination of the ligament stiffness which can contribute a better understanding of the intrinsic mechanical behavior of the knee joint. Instrumentation of the device involved the use of hall-sensors for measuring the distractor displacement and strain gauges to transduce the force. The sensors were calibrated and tested to demonstrate their suitability for surgical use. Results show the distraction gap can be measured reliably with 0.1mm accuracy and the distractive loads could be assessed with an accuracy in the range of 4N. These characteristics are consistent with those have been proposed, in this work, for a device that could assist on performing ligament balance while permitting surgeons evaluation based on his experience. Preliminary results from in vitro tests were in accordance with expected stiffness values for medial collateral ligament (MCL) and lateral collateral ligament (LCL).

Computer-assisted measurements of coronal knee joint laxity in vitro are related to low-stress behavior rather than structural properties of the collateral ligaments

The relationship between coronal knee laxity and the restraining properties of the collateral ligaments remains unknown. This study investigated correlations between the structural properties of the collateral ligaments and stress angles used in computer-assisted total knee arthroplasty (TKA), measured with an optically based navigation system. Ten fresh-frozen cadaveric knees (mean age: 81 ± 11 years) were dissected to leave the menisci, cruciate ligaments, posterior joint capsule and collateral ligaments. The resected femur and tibia were rigidly secured within a test system which permitted kinematic registration of the knee using a commercially available image-free navigation system. Frontal plane knee alignment and varus-valgus stress angles were acquired. The force applied during varus-valgus testing was quantified. Medial and lateral bone-collateral ligament-bone specimens were then prepared, mounted within a uni-axial materials testing machine, and extended to failure. Force and displacement data were used to calculate the principal structural properties of the ligaments. The mean varus laxity was 4 ± 1° and the mean valgus laxity was 4 ± 2°. The corresponding mean manual force applied was 10 ± 3 N and 11 ± 4 N, respectively. While measures of knee laxity were independent of the ultimate tensile strength and stiffness of the collateral ligaments, there was a significant correlation between the force applied during stress testing and the instantaneous stiffness of the medial (r = 0.91, p = 0.001) and lateral (r = 0.68, p = 0.04) collateral ligaments. These findings suggest that clinicians may perceive a rate of change of ligament stiffness as the end-point during assessment of collateral knee laxity.

Columbus navigated TKA system: clinical and radiological results at a minimum of 5 years with survivorship analysis

The major factors that determine a favorable long-term clinical and functional outcome after conventional total knee arthroplasty (TKA) include correct implant positioning and restoration of the mechanical axis with soft tissue balancing to reduce aseptic failure; hence, the need for further developmental strategies that improve the accuracy and reproducibility of the surgical technique remains paramount for contemporary navigation research. Not all navigation systems are the same. The literature published thus far on mid-term results of navigated TKA relies on software that has no step-by-step soft tissue balancing with the tibia-first technique. The results are equivalent to those of conventional TKA.Therefore, the current authors conducted a minimum 5-year follow-up of a soft tissue-based navigated TKA system with the goal of soft tissue balancing. They analyzed intraoperative alignment and range of motion measurements, functional outcomes, radiographic assessment, and survival rates of high-flexion, high-conformity unresurfaced patella TKAs. The results at 5 years revealed a component revision rate of 0% compared with other nonnavigated TKAs (2.8% revision rate). The authors achieved a well-balanced TKA with a 0°±2° mechanical axis and an improved range of motion from 95° preoperatively to 110° postoperatively.

Computer-assisted total knee replacement in patients with arthritis and a recurvatum deformity

We retrospectively reviewed the records of 1150 computer-assisted total knee replacements and analysed the clinical and radiological outcomes of 45 knees that had arthritis with a pre-operative recurvatum deformity. The mean pre-operative hyperextension deformity of 11° (6° to 15°), as measured by navigation at the start of the operation, improved to a mean flexion deformity of 3.1° (0° to 7°) post-operatively. A total of 41 knees (91%) were managed using inserts ≤ 12.5 mm thick, and none had mediolateral laxity > 2 mm from a mechanical axis of 0° at the end of the surgery. At a mean follow-up of 26.4 months (13 to 48) there was significant improvement in the mean Knee Society, Oxford knee and Western Ontario and McMaster Universities Osteoarthritis Index scores compared with the pre-operative values. The mean knee flexion improved from 105° (80° to 125°) pre-operatively to 131° (120° to 145°), and none of the limbs had recurrent recurvatum. These early results show that total knee replacement using computer navigation and an algorithmic approach for arthritic knees with a recurvatum deformity can give excellent radiological and functional outcomes without recurrent deformity.

Standardising the clinical assessment of coronal knee laxity

Clinical laxity tests are used for assessing knee ligament injuries and for soft tissue balancing in total knee arthroplasty. This study reports the development and validation of a quantitative technique of assessing collateral knee laxity through accurate measurement of potential variables during routine clinical examination. The hypothesis was that standardisation of a clinical stress test would result in a repeatable range of laxity measurements.

Non-invasive infrared tracking technology with kinematic registration of joint centres gave real-time measurement of both coronal and sagittal mechanical tibiofemoral alignment. Knee flexion, moment arm and magnitude of the applied force were all measured and standardised. Three clinicians then performed six knee laxity examinations on a single volunteer using a target moment of 18 Nm.

Standardised laxity measurements had small standard deviations (within 1.1°) for each clinician and similar mean values between clinicians, with the valgus laxity assessment (mean of 3°) being slightly more consistent than varus (means of 4° or 5°).

The manual technique of coronal knee laxity assessment was successfully quantified and standardised, leading to a narrow range of measurements (within the accuracy of the measurement system). Minimising the subjective variables of clinical examination could improve current knowledge of soft tissue knee behaviour.

Clinical Outcomes After Computer-assisted Versus Conventional Total Knee Arthroplasty

The purpose of this study was to determine whether the use of computer-assisted surgery can improve the clinical results in total knee arthroplasty (TKA) compared with conventional methods of TKA.A literature search of PubMed (1966 to August 2011), CENTRAL (Cochrane Controlled Trials Register; issue 3, 2011), and EMBASE (1984 to August 2011) was conducted. Randomized, controlled trials detecting the clinical outcomes of TKA with or without the use of computer-assisted surgery were identified. A meta-analysis of these clinical trials was then performed. Twenty-one articles were included in the meta-analysis. The results confirmed that operative time was significantly increased with the use of computer-assisted TKA (mean standard difference, 14.68; 95% confidence interval [CI], 11.74 to 17.62; P<.00001], whereas no significant difference existed between the 2 groups regarding the total operative blood loss (mean standard difference, -54.38; 95% CI, -119.76 to 11.00; P=.10). As for other clinical outcomes, including the Knee Society Score (mean standard difference, 4.47; 95% CI, -1.05 to 9.99; P=.36) and range of motion (mean standard difference, 1.38; 95% CI, -1.43 to 4.18; P=.34), the use of computer-assisted TKA did not help to improve function recovery postoperatively.

Enlarged post-operative posterior condyle tightens extension gap in total knee arthroplasty

We investigated whether the extension gap in total knee replacement (TKR) would be changed when the femoral component was inserted. The extension gap was measured with and without the femoral component in place in 80 patients with varus osteoarthritis undergoing posterior-stabilised TKR. The effect of a post-operative increase in the size of the femoral posterior condyles was also evaluated. The results showed that placement of the femoral component significantly reduced the medial and lateral extension gaps by means of 1.0 mm and 0.9 mm, respectively (p < 0.0001). The extension gap was reduced when a larger femoral component was selected relative to the thickness of the resected posterior condyle. When the post-operative posterior lateral condyle was larger than that pre-operatively, 17 of 41 knees (41%) showed a decrease in the extension gap of > 2.0 mm. When a specially made femoral trial component with a posterior condyle enlarged by 4 mm was tested, the medial and lateral extension gaps decreased further by means of 2.1 mm and 2.8 mm, respectively.

If the thickness of the posterior condyle is expected to be larger than that pre-operatively, it should be recognised that the extension gap is likely to be altered. This should be taken into consideration when preparing the extension gap.

NAVIGATION IN TOTAL KNEE ARTHROPLASTY

Navigation was the most significant advance in instrumentation for total knee arthroplasty over the last decade. It provides surgeons with a precision tool for carrying out surgery, with the possibility of intraoperative simulation and objective control over various anatomical and surgical parameters and references. Since the first systems, which were basically used to control the alignment of bone cutting referenced to the mechanical axis of the lower limb, many other surgical steps have been incorporated, such as component rotation, ligament balancing and arranging the symmetry of flexion and extension spaces, among others. Its efficacy as a precision tool with an effective capacity for promoting better alignment of the lower-limb axis has been widely proven in the literature, but the real value of optimized alignment and the impact of navigation on clinical results and the longevity of arthroplasty have yet to be established.

Functional outcome after computer-assisted versus conventional total knee arthroplasty: a randomized controlled study

Despite the frequent use of computer-assisted total knee arthroplasty (TKA) and better radiological results for coronal alignment reported in many studies, there is still no evidence of improved clinical outcomes when compared to conventional TKA. We compared alignment after navigated TKA and conventional TKA in 80 randomized patients. Seventy three patients were available for physical and radiological examination at 20 month after surgery. Both groups showed similar Knee Society Score results, with medians of 89 points (navigated 49-95 points, conventional 48-95 points, n.s.) in the Knee Score and 70 points (navigated 45-100 points, conventional 40-100 points, n.s.) in the Function Score. The median improvement in the Knee Society Knee Score was 45 points (-3 to 88 points) in the navigated group and 35 points (-13 to 62 points) in the conventional group (P = 0.03), and the Knee Society Function Score improvement was 15 points (-10 to 50 points) in the navigated group versus 10 points (-10 to 50 points) in the conventional group (n.s.). The current health state at follow-up using the EuroQuol questionnaire was similar in both groups, with medians of 67 points in the navigated group and 65 points in the conventional group. This investigation did show slightly greater functional improvement at short-term follow-up in the navigated TKA group. Longer follow-up will be required to assess the possible benefit of computer-assisted navigation.

The effect of femoral component rotation on the extensor retinaculum of the knee

Malrotation of the femoral component may cause patellofemoral complications after total knee replacement (TKR). We hypothesized that femoral component malrotation would cause excessive lengthening of the retinacula. Retinacular length changes were measured by threading fine sutures along them and attaching these to the patella and to displacement transducers. The knee post-TKR was flexed-extended while the quadriceps were tensed, then the measurements repeated after rotating the femoral component 5 degrees internally and then 5 degrees externally. Internal rotation shortened the medial patellofemoral ligament (MPFL) significantly from 100 degrees to 0 degrees extension. External rotation lengthened the MPFL significantly from 90 degrees to 0 degrees extension. The transverse fibers of the lateral retinaculum showed no significant differences. The MPFL attaches directly from bone to bone, so it was lengthened directly by movement of the trochlea and patella, whereas the deep transverse fibers of the lateral retinaculum attach to the mobile iliotibial tract, so they were not lengthened directly.