Evaluation of soft-tissue balance during total knee arthroplasty

Assessment of knee collateral ligament stiffness by strain ultrasound elastography

BACKGROUND: Knowledge of the biomechanics of the normal collateral ligaments is important to secure optimal stability of the knee following injury. Various in vitro methods have been described in evaluating the biomechanics of these ligaments. However, a method of direct evaluation has not been reported. OBJECTIVE: To determine the stiffness characteristics of the collateral ligaments of the knee using strain ultrasound elastography. METHODS: Strain ultrasound elastography was performed on different components of the collateral ligaments in various angles of knee flexion in 18 healthy males (36 ligaments). We measured relative stiffness of the ligaments using strain ratio (SR = target tissue strain/reference strain). A lower strain ratio indicates higher relative stiffness. RESULTS: There was moderate to excellent intra- and inter-rater agreement for strain ratio measurements in all ligament portions. Strain ratios were lowest at 0° in all three ligaments, indicating high relative stiffness. In the superficial and deep medial collateral ligaments, the strain ratio increased with increasing knee flexion, whereas in the lateral collateral ligament, stiffness showed a tendency to fluctuate. CONCLUSION: Strain ultrasound elastography is a reliable tool for monitoring relative stiffness of the collateral ligaments of the knee and is easily applied to the routine clinical setting.

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.

Intraoperatively accurate limb alignment after opening wedge high tibial osteotomy can be lost by large knee joint line convergence angle during surgery

INTRODUCTION

The purpose of this study was to assess early postoperative loss of achieved correction and associated factors after opening wedge high tibial osteotomy (OWHTO).

MATERIALS AND METHODS

OWHTO was performed in 121 patients with osteoarthritis of the knee (mean age 66 years, 154 knees). Anteroposterior radiographs of the knee and full-length leg, and varus and valgus stress radiographs of the knee were taken, and the femorotibial angle (FTA), joint line convergence angle (JLCA), and medial proximal tibial angle (MPTA) were measured. The changes in the FTA, JLCA, and MPTA were defined as ΔFTA, ΔJLCA, and ΔMPTA.

RESULTS

The ΔFTA and ΔJLCA at postoperative 0-2 days were - 1.8 ± 1.2° and - 1.9 ± 1.4°, respectively. The ΔFTA, ΔJLCA and ΔMPTA at postoperative 1-12 months were 0.9 ± 1.3°, 0.2 ± 1.2° and - 0.8 ± 0.8°, respectively. A positive correlation was found between ΔFTA and ΔJLCA at postoperative 0-2 days (ρ = 0.642, P < 0.001) and at postoperative 1-12 months (ρ = 0.402, P < 0.001). A negative correlation was found between ΔFTA and ΔMPTA at postoperative 1-12 months (ρ = - 0.534, P < 0.001). A discrepancy in alignment represented by the FTA occurred in the supine radiographs between the day of surgery and postoperative 2 days. Multiple regression analysis suggested that postoperative JLCA on the day of surgery was the factor related to early postoperative change of the FTA.

CONCLUSIONS

This study demonstrated the early loss of achieved correction after OWHTO due to change of the JLCA, even if the accurate alignment is obtained intraoperatively.

Total knee arthroplasty with the least-constrained implant possible for type II valgus knee > 20°: a 3–14 years’ follow-up

Objective

To estimate the midterm outcome of primary total knee arthroplasty for severe valgus deformity using selective release of tight lateral structures and the least-constrained implant.

Methods

We performed total knee arthroplasty on 65 consecutive type II knees with valgus deformity> 20°. Surgery was done via a medial parapatellar approach. Conventional bone cutting was done with selective lateral soft tissue release, and the least-constrained total knee prosthesis possible was used. Posterior stabilized implants were employed in most knees, except for three knees that required the implantation of constrained condylar knee prostheses. The average duration of follow-up lasted for 10.5 years.

Results

Preoperatively, average valgus was 30.6°, and average range of motion was 43.7° (range, 0–80°). Postoperatively, average valgus was 7.3° and average range of motion was 110.6° (range, 80–130°). The lateral collateral ligament and iliotibial band were released in all knees, and release of the popliteus tendon was required in two knees. Stable flexion and extension gaps were achieved in most cases, except for two that had medial side instability. Follow-up showed that stability was maintained.

Conclusions

This surgical technique combined selective lateral soft tissue release with use of the least-constrained implant possible and was effective for severe valgus deformities of the knee, with good clinical results.

A surgical reduction technique for posterior cruciate ligament avulsion fracture in total knee arthroplasty: a comparison study

Background

Posterior cruciate ligament (PCL) avulsion fracture of the tibia is an uncommon but serious complication during primary cruciate-retaining total knee arthroplasty (TKA). The first objective of this report was to conduct a retrospective cohort study to investigate the incidence and potential risk factors of PCL avulsion fracture in primary cruciate-retaining TKA. The second objective was to assess the functional outcomes of the knee after reduction of PCL avulsion fracture.

Methods

From January 2014 to January 2016, 56 patients who experienced PCL avulsion fracture of the tibia in primary cruciate-retaining TKA were included in the study group. Patients in this group underwent reduction of avulsion fracture. In this period, we selected 224 patients (control group) for comparison. Patients in this group also underwent the same TKA, but no PCL avulsion fracture occurred. The range of motion of the knee and Knee Society Scores were assessed. The Forgotten Joint Score was used to analyze the ability to forget the joint. Differences were considered statistically significant at p < 0.05.

Results

In our series, the incidence of PCL avulsion fracture was 4.6%. There were no significant differences (p > 0.05) with regard to the preoperative or postoperative range of motion of the knee, final 4-year mean clinical score in the study and control groups 92.4 ± 2.7 and 93.6 ± 1.9, respectively, and mean functional scores of 85.1 ± 1.8 and 87.1 ± 1.2, respectively.

Conclusions

The incidence of PCL avulsion fracture of the tibia is relatively high. Older age and female gender were the two risk factors of fracture in primary cruciate-retaining TKA. Reduction of PCL avulsion fracture with a high-strength line can achieve good stability and function of the knee.

Increased valgus laxity in flexion with greater tibial resection depth following total knee arthroplasty

PURPOSE

Soft tissue balancing is of central importance to outcome following total knee arthroplasty (TKA). However, there are lack of data analysing the effect of tibial bone cut thickness on valgus laxity. A cadaveric study was undertaken to assess the biomechanical consequences of tibial resection depth on through range knee joint valgus stability. We aimed to establish a maximum tibial resection depth, beyond which medial collateral ligament balancing becomes challenging, and a constrained implant should be considered.

METHODS

Eleven cadaveric specimens were included for analysis. The biomechanical effects of increasing tibial resection were studied, with bone cuts made at 6, 10, 14, 18 and 24 mm from the lateral tibial articular surface. A computer navigation system was used to perform the tibial resection and to measure the valgus laxity resulting from a torque of 10 Nm. Measurements were taken in four knee positions: 0° or extension, 30°, 60° and 90° of flexion. Intra-observer reliability was assessed. A minimum sample size of eight cadavers was necessary. Statistical analysis was performed using a nonparametric Spearman's ranking correlation matrix at the different stages: in extension, at 30°, 60° and 90° of knee flexion. Significance was set at p < 0.05.

RESULTS

There was no macroscopic injury to the dMCL or sMCL in any of the specimens during tibial resection. There was no significant correlation found between the degree of valgus laxity and the thickness of the tibial cut with the knee in extension. There was a statistically significant correlation between valgus laxity and the thickness of the tibial cut in all other knee flexion positions: 30° (p < 0.0001), 60° (p < 0.001) and 90° (p < 0.0001). We identified greater than 5° of valgus laxity, at 90° of knee flexion, after a tibial resection of 14 mm.

CONCLUSION

Increased tibial resection depth is associated with significantly greater valgus laxity when tested in positions from 30° to 90° of flexion, despite stability in extension. Greater than 5° of laxity was identified with a tibial resection of 14 mm. When a tibial bone cut of 14 mm or greater is necessary, as may occur with severe preoperative coronal plane deformity, it is recommended to consider the use of a constrained knee prosthesis.

Biomechanics and wear comparison between mechanical and kinematic alignments in total knee arthroplasty

The uses of mechanical and kinematic alignments in total knee arthroplasty are under debate in recent clinical investigations. In this study, the differences in short-term biomechanics and long-term wear volume between mechanical and kinematic alignments in total knee arthroplasty were investigated, based on a subject-specific musculoskeletal multi-body dynamics model during walking gait simulation. An increase of 8.2% in the peak tibiofemoral medial contact force, a posterior contact translation by maximum 4.7 mm and a decrease of 5.5% in the wear volume after a 10-million-cycle simulation were predicted in the kinematic alignment, compared with the mechanical alignment. Nevertheless, the tibiofemoral contact mechanics, the range of motions and the long-term wear were not markedly different between mechanical and kinematic alignments. Furthermore, the mechanical alignment with a posterior tibial slope similar to that under the kinematic alignment was found to produce similar anterior-posterior translation and the range of motion, and an approximate wear volume, compared with the kinematic alignment. The ligament forces under the kinematic alignment were influenced markedly by as much as 25%, 50% and 77% for the medial collateral ligament, lateral collateral ligament and posterior cruciate ligament forces, respectively. And, a maximum increase of 40% for patellofemoral contact force was predicted under the kinematic alignment. These findings suggest that the kinematic alignment is an alternative alignment principle but no marked advantages in biomechanics and wear to the mechanical alignment. The adverse effects of the kinematic alignment on patella loading and soft tissue forces should be noticed.

Robotic Total Knee Arthroplasty with a Cruciate-Retaining Implant: A 10-Year Follow-up Study

Background

This study compared clinical and radiological results between robotic total knee arthroplasty (TKA) and conventional TKA with a cruciate-retaining implant at 10-year follow-up. The hypothesis was that robotic TKA would allow for more accurate leg alignment and component placement, and thus enhance clinical and radiological results and long-term survival rates.

Methods

A total of 113 primary TKAs performed using a cruciate-retaining implant in 102 patients from 2004 to 2007 were reviewed retrospectively. Of the 113 TKAs, 71 were robotic TKAs and 42 were conventional TKAs. Clinical outcomes (visual analogue scale pain score, Hospital for Special Surgery score, Western Ontario and McMaster University score, range of motion, and complications), radiological outcomes, and long-term survival rates were evaluated at a mean follow-up of 10 years.

Results

Clinical outcomes and long-term survival rates were similar between the two groups. Regarding the radiological outcomes, the robotic TKA group had significantly fewer postoperative leg alignment outliers (femoral coronal inclination, tibial coronal inclination, femoral sagittal inclination, tibial sagittal inclination, and mechanical axis) and fewer radiolucent lines than the conventional TKA group.

Conclusions

Both robotic and conventional TKAs resulted in good clinical outcomes and postoperative leg alignments. Robotic TKA appeared to reduce the incidence of leg alignment outliers and radiolucent lines compared to conventional TKA.

Effect of Soft Tissue Releases on Joint Space Opening in Total Knee Arthroplasty

BACKGROUND

The purpose of this study was to determine the gap achieved to the medial and lateral compartments following sectioning and release of the relevant soft tissues in preparation for a total knee arthroplasty.

METHODS

A custom-designed knee tensioner allowed the application of forces to the medial and lateral compartments of 12 cadaveric knee specimens. Loads of 100 N and 200 N were applied to each compartment, and the resulting displacement was measured in the following conditions: (1) All soft tissues intact, (2) an arthrotomy, (3) anterior cruciate ligament (ACL) sectioned, (4) posterior cruciate ligament (PCL) sectioned, and (5) release of the anterior aspect of the deep medial collateral ligament (MCL) fibers. Tensions were applied for all conditions from 90° to 0° of knee flexion in 30° increments.

RESULTS

No differences were found in medial or lateral displacement after the arthrotomy or releasing the ACL or PCL at either 100 N or 200 N. At the 100 N load application, there was a significant increase in gap width when the anterior portion of the deep MCL was released (7.49 mm) compared to the intact (5.28 mm) and arthrotomy (5.75 mm) conditions. With respect to the 200 N load application, there were statistically significant differences detected between the deep MCL fiber release (11.09 mm) and intact conditions (8.05 mm) and release of the deep MCL and arthrotomy conditions (8.77 mm).

CONCLUSION

The medial parapetellar arthrotomy, ACL and PCL sectioning did not result in medial or lateral displacement changes. The release of the anterior fibers of the deep MCL as part of the surgical exposure increased the medial gap magnitude.

Varus and valgus stress tests after total knee arthroplasty with and without anesthesia

INTRODUCTION

Retrospective studies demonstrated inadequate soft tissue balance is associated with the long-term outcome of total knee arthroplasty (TKA). However, most of these studies have evaluated the joint laxity only postoperatively without anesthesia. Therefore information about the effect of anesthesia on knee laxity is important for soft tissue balancing at the time of surgery. This study was conducted to determine how anesthesia affects the varus and valgus stress tests after TKA.

MATERIALS AND METHODS

A consecutive series of 26 patients undergoing staged bilateral TKA was evaluated. Varus and valgus laxity of the knee with the TKA implant was measured a few days before the contralateral TKA without anesthesia and again immediately after the contralateral TKA under spinal anesthesia.

RESULTS

The laxity was significantly increased from 3.0° to 3.6° (p = 0.005) and from 4.7° to 5.7° (p = 0.007) in medial and lateral side, respectively, when the stress tests were performed under anesthesia in comparison to the laxity measured without anesthesia. The major change in laxity (≥3°) was measured in 6 (23%) patients tested without anesthesia.

CONCLUSIONS

Anesthesia significantly influenced knee joint laxity after TKA. The findings of this study suggest that muscular forces impart a stabilizing force across the joint.

Total knee arthroplasty in valgus knees using minimally invasive medial-subvastus approach

BACKGROUND

An ideal approach for valgus knees must provide adequate exposure with minimal complications due to approach per se. Median parapatellar approach is most commonly used approach in TKA including valgus knees. A medial subvastus approach is seldom used for valgus knees and has definite advantages of maintaining extensor mechanism integrity and minimal effect on patellar tracking. The present study was conducted to evaluate outcomes of total knee arthroplasty (TKA) and efficacy of subvastus approach in valgus knees in terms of early functional recovery, limb alignment and complications.

MATERIALS AND METHODS

We retrospectively reviewed 112 knees with valgus deformity between January 2006 and December 2011. All patients were assessed postoperatively for pain using Visual Analog Scale (VAS) and quadriceps recovery in form of time to active straight leg raising (SLR) and staircase competency and clinical outcomes using American Knee Society (AKS) score and radiographic evaluation with average followup of 40 months (range 24-84 months).

RESULTS

The mean VAS on postoperative day (POD) 1 and POD2 at rest was 2.73 and 2.39, respectively and after mobilization was 3.28 and 3.08, respectively (P < 0.001). The quadriceps recovery was very early and 92 (86.7%) patients were able to do active SLR by POD1 with mean time of 21.98 h while reciprocal gait and staircase competency was possible at 43.05 h. The AKS and function score showed significant improvement from preoperative mean score of 39 and 36 to 91 and 79 (P < 0.001), respectively, and the mean range of motion increased from 102° preoperatively to 119° at recent followup (P < 0.001). The mean tibiofemoral valgus was corrected from preoperative 16° (range 10°-35°) to 5° (range 3°-9°) valgus (P < 0.001).

CONCLUSIONS

Mini-subvastus quadriceps approach provides adequate exposure and excellent early recovery for TKA in valgus knees, without increase in incidence of complications.

Intraoperative joint gaps and mediolateral balance affect postoperative knee kinematics in posterior-stabilized total knee arthroplasty

BACKGROUND

Adjusting joint gaps and establishing mediolateral (ML) soft tissue balance are considered essential interventions for better outcomes in total knee arthroplasty (TKA). However, the relationship between intraoperative laxity measurements and weightbearing knee kinematics has not been well explored. This study aimed to quantify the effect of intraoperative joint gaps and ML soft tissue balance on postoperative knee kinematics in posterior-stabilized (PS)-TKA.

METHODS

We investigated 44 knees in 34 patients who underwent primary PS-TKA by a single surgeon. The central joint gaps and ML tilting angles at 0°, 10°, 30°, 60°, 90°, 120° and 135° flexion were measured during surgery. At a minimum of two year follow-up, we analyzed in vivo kinematics of these knees and examined the influence of intraoperative measurements on postoperative kinematics.

RESULTS

Gap difference of knee flexion at 135° minus 0° was correlated with the total posterior translation of lateral femoral condyle (r=0.336, p=0.042) and femoral external rotation (r=0.488, p=0.002) during squatting, anteroposterior position of lateral femoral condyle (r=-0.510, p=0.001) and maximum knee flexion (r=0.355, p=0.031) in kneeling. Similar correlations were observed between deep flexion gap differences with respect to the 90° reference and postoperative knee kinematics. Well-balanced knees showed less anterior translation of medial femoral condyle in mid- to deep flexion, consistent femoral external rotation, and the most neutral valgus/varus rotation compared with unbalanced knees.

CONCLUSION

These findings indicate the importance of adequate intraoperative joint gaps in deep flexion and ML soft tissue balance throughout the range of motion.

Varus-valgus stress radiograph as a predictor for extensive medial release in total knee arthroplasty

PURPOSE

The purpose of this study was to identify the risk factors for predicting the reduction osteotomy as extensive medial release during total knee arthroplasty (TKA) using multivariate logistic regression.

METHODS

A total of 404 TKAs were enrolled and sorted into two groups according to the extent of medial release and then analysed for the statistical significance of various risk factors including age, gender, body mass index (BMI), pre-operative knee mechanical axis angle (KMAA), mechanical varus stress angle (MVrSA), mechanical valgus stress angle (MVgSA), and sum of the mechanical varus and valgus stress angles (SMVVA) with use of multivariate logistic regression analysis.

RESULTS

SMVVA to a more varus direction was found to be a significant risk factor for the reduction osteotomy (p < 0.0001, adjusted odds ratio (OR) = 2.705 with 95 % CI 2.126-3.443). KMAA and MVgSA to a more varus direction were also significant risk factors (p = 0.010, adjusted OR = 1.189 with 95 % CI 1.041-1.357, and p = 0.005, adjusted OR = 1.401 with 95 % CI 1.109-1.767). The other variables were not significant risk factors.

CONCLUSIONS

The overall results suggest that careful attention should be given to the need for extensive medial release and failure of the conventional soft tissue release technique during TKA in patients with a greater varus angle in the pre-operative SMVVA, MVgSA, and KMAA, especially with a greater varus SMVVA, which was the strongest predictor of reduction osteotomy.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

In vivo length change patterns of the medial and lateral collateral ligaments along the flexion path of the knee

PURPOSE

The knowledge of the function of the collateral ligaments-i.e., superficial medial collateral ligament (sMCL), deep medial collateral ligament (dMCL) and lateral collateral ligament (LCL)-in the entire range of knee flexion is important for soft tissue balance during total knee arthroplasty (TKA). The objective of this study was to investigate the length changes of different portions (anterior, middle and posterior) of the sMCL, dMCL and LCL during in vivo weightbearing flexion from full extension to maximal knee flexion.

METHODS

Using a dual fluoroscopic imaging system, eight healthy knees were imaged while performing a lunge from full extension to maximal flexion. The length changes of each portion of the collateral ligaments were measured along the flexion path of the knee.

RESULTS

All anterior portions of the collateral ligaments were shown to have increasing length with flexion except that of the sMCL, which showed a reduction in length at high flexion. The middle portions showed minimal change in lengths except that of the sMCL, which showed a consistent reduction in length with flexion. All posterior portions showed reduction in lengths with flexion.

CONCLUSIONS

These data indicated that every portion of the ligaments may play important roles in knee stability at different knee flexion range. The soft tissue releasing during TKA may need to consider the function of the ligament portions along the entire flexion path including maximum flexion.

LEVEL OF EVIDENCE

III.

No influence of coronal laxity and alignment on lift-off after well-balanced and aligned total knee arthroplasty

PURPOSE

In vivo fluoroscopic analyses have revealed the kinematics after total knee arthroplasty (TKA), including femoral condylar lift-off. This study asked whether differences in static varus-valgus laxity or coronal limb alignment after TKA affect lift-off under weight-bearing conditions. It was hypothesised that there is a correlation between coronal laxity or alignment and lift-off during walking.

METHODS

The current study analysed nineteen subjects undergoing cruciate-retaining TKA performed by the measured resection technique. The varus-valgus laxity at knee extension was measured using a 150 N stress radiograph. The mechanical axis was measured using a full-standing radiograph. Continuous radiological images were taken while the subject walked on a treadmill, and the images during single-leg stance were analysed to determine the lift-off using a 3D-to-2D image-to-model registration technique.

RESULTS

The average angle in varus/valgus stress was 6.8 ± 1.8°/6.6 ± 2.1°. No statistically significant differences were observed between the varus and valgus laxity. The average amount of lift-off was 0.7 ± 0.4 mm. The static varus-valgus laxity (n. s.) or the differences in the laxities (n. s.) on the stress radiograph did not influence lift-off. The weight-bearing ratio was achieved within the middle third of the knee in 90 % of subjects. Two outliers with valgus alignment (68 ± 1 %) demonstrated no significant difference in lift-off in comparison with the majority of the subjects (46 ± 9 %).

CONCLUSION

The static coronal laxity and alignment did not influence the lift-off under dynamic weight-bearing conditions after well-balanced and aligned cruciate-retaining TKA. Measured resection technique can produce sufficient coronal stability and alignment without significant lift-off during walking.

Gap measurement in posterior-stabilized total knee arthroplasty with or without a trial femoral component

PURPOSE

To investigate the effects of a trial femoral component on the intraoperative joint gap and intraoperative joint gap kinematics throughout the range of knee motion in minimally invasive surgery-total knee arthroplasty (MIS-TKA) with the gap technique.

MATERIALS AND METHODS

A total of 103 patients [15 men (15 knees) and 89 women (89 knees)] aged 50-88 years (mean 74.8 years) who received MIS-TKA with the gap technique were included. The intraoperative joint gap differences (90° flexion gap distance minus 0° extension gap distance) with and without the trial femoral component were compared. Subsequently, the intraoperative joint gap kinematics at 0°, 45°, 90°, and 120° with the trial femoral component were investigated.

RESULTS

The intraoperative component gap difference (4.4 ± 2.7 mm) was larger than the estimated joint gap difference (1.2 ± 1.9 mm) (p < 0.01). The mean intraoperative component gap distances at 0°, 45°, 90°, and 120° of knee flexion were 14.7 ± 2.6, 19.0 ± 3.2, 19.2 ± 3.4, and 16.6 ± 3.3 mm, respectively. The intraoperative component gap distance increased significantly from 0° extension to 90° of knee flexion (p < 0.01), and then decreased significantly toward deep knee flexion at 120° (p < 0.01).

CONCLUSIONS

The trial femoral component influenced the intraoperative gap measurements, and increased the intraoperative gap difference. The joint gap kinematics with the trial femoral component were not constant throughout the range of knee motion, even if the appropriate joint gaps in extension and flexion were achieved. For acquisition of constant stability throughout the knee motion, the present results should be taken into account by surgeons performing MIS-TKA with the gap technique.

Changes in Joint Gap Balances between Intra- and Postoperation in Total Knee Arthroplasty

Achieving correct soft tissue balance and preparing equal and rectangular extension and flexion joint gaps are crucial goals of TKA. Intraoperative gap balances would change postoperatively; however, changes in joint gap balances between pre- and postoperation remain unclear. To explore these changes associated with TKA, we prospectively investigated 21 posterior cruciate ligament retaining TKAs for varus knees. Intraoperative extension gap balance (iEGB) was 2.6 ± 2.0° varus versus postoperative extension gap balance (pEGB) of 0.77 ± 1.8° valgus (P < 0.01), while no significant difference between intraoperative flexion gap balance (iFGB) and postoperative flexion gap balance (pFGB) was observed. We also explored correlations between intraoperative and postoperative gap balances but found no significant correlations. These observations indicate that (i) surgeons should avoid excessive release of the medial soft tissue during TKA for varus knees and (ii) intraoperative gap balance may not be necessarily reflected on postoperative gap balance.

The use of navigation to achieve soft tissue balance in total knee arthroplasty - a randomised clinical study

BACKGROUND

Achieving soft tissue balance is an operative goal in total knee arthroplasty. This randomised, prospective study compared computer navigation to conventional techniques in achieving soft tissue balance.

METHODS

Forty one consecutive knee arthroplasties were randomised to either a non-navigated or navigated group. In the non-navigated group, balancing was carried out using surgeon judgement. In the navigated group, balancing was carried out using navigation software. In both groups, the navigation software was used as a measuring tool.

RESULTS

Balancing of the mediolateral extension gap was superior in the navigation group (p=0.001). No significant difference was found between the two groups in balancing the mediolateral flexion gap or in achieving equal flexion and extension gaps.

CONCLUSIONS

Computer navigation offered little advantage over experienced surgeon judgement in achieving soft tissue balance in knee replacement. However, the method employed in the navigated group did provide a reproducible and objective assessment of flexion and extension gaps and may therefore benefit surgeons in training.

LEVEL OF EVIDENCE

Level I, RCT.

Soft Tissue Balancing of Varus Arthritic Knee in Minimally Invasive Surgery Total Knee Arthroplasty: Comparison between Posterior Oblique Ligament Release and Superficial MCL Release

PURPOSE

To assess proper soft tissue balancing of the varus arthritic knee between posterior oblique ligament (POL) release group and superficial medial collateral ligament (SMCL) release group.

MATERIALS AND METHODS

This retrospective study was performed on 186 patients who underwent minimally invasive surgery (MIS) total knee arthroplasty (TKA) from January 2011 to December 2011. Eighty-three patients were in the group of SMCL release and 103 patients were in the POL release group. We intended to use a 10 mm polyethylene insert (PE) during TKA, and retrospectively compared the actual thickness of PE between POL release group and SMCL release group.

RESULTS

The mean PE thickness was 10.59±1.3 mm (range, 8 to 15 mm) in POL group and 11.88±1.8 mm (range, 10 to 18 mm) in SMCL group (p=0.001). We found a significant difference in the mean PE thickness between POL release group and SMCL release group.

CONCLUSIONS

POL and deep MCL releases in MIS-TKA would be beneficial for varus deformity correction in the osteoarthritic knee.

Intraoperative joint gaps affect postoperative range of motion in TKAs with posterior-stabilized prostheses

BACKGROUND

Joint gaps and mediolateral (ML) soft tissue balance have long been known to affect clinical scores and patient function after TKA, but the relationship between gaps and soft tissue balance remain poorly defined. If specific relationships exist between soft tissue tension and patient function, then objective targets could be established to assist surgeons in achieving more consistent postoperative knee function.

QUESTIONS/PURPOSES

By performing instrumented gap measurements during TKA, we sought to quantify the relationships between intraoperative soft tissue tension and clinical scores and patient function.

METHODS

We prospectively followed 57 patients with 63 primary TKAs with posterior-stabilized prostheses. Joint gaps and ML soft tissue balance were measured intraoperatively from 0° to 135° with the patella reduced after independent bone cuts and soft tissue releases. We determined the relationships between these intraoperative measurements and postoperative ROM and Knee Society scores at minimum 2-year followup.

RESULTS

Larger joint gaps at 120° and 135° flexion predicted larger postoperative knee flexion (r=0.296 and r=0.393, respectively), whereas larger gaps at 10° flexion predicted greater postoperative knee extension (r=0.285). Knees with rectangular joint gaps did not show better ROM or Knee Society scores compared with knees with trapezoidal joint gaps. In the range of normal surgical variation, neither joint gaps nor gap asymmetry affected the incidence of postoperative instability.

CONCLUSIONS

Avoiding small joint gaps in extension and in deep flexion should allow patients who undergo TKAs to obtain maximum ROM.

LEVEL OF EVIDENCE

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Lateral soft tissue laxity increases but medial laxity does not contract with varus deformity in total knee arthroplasty

BACKGROUND

In TKA, soft tissue balance (the joint gap) depends on the amount of resected bone and soft tissue release. Some studies report preoperative bony deformity correlates with soft tissue balance evaluated intraoperatively and that the medial tissues are contracted with varus deformity. However, these studies did not take into account the amount of resected bone and did not describe whether the soft tissue was tight or loose. Therefore, it remains unclear whether in varus deformity the soft tissues on the medial side are contracted.

QUESTIONS/PURPOSES

We compared (1) intraoperative joint gap, (2) amount of resected bone, and (3) intraoperative soft tissue laxity on the lateral and medial sides according to severity of preoperative varus deformity.

METHODS

We retrospectively reviewed 70 patients with osteoarthritis and varus deformities who underwent 90 TKAs. We retrospectively divided the 90 knees into three groups according to degree of preoperative alignment: mild varus group (<10°), moderate varus group (10°-20°), and severe varus group (>20°). To evaluate intraoperative soft tissue tension, we calculated the soft tissue gap by subtracting the thickness of the resected bone from the joint gaps on the medial and lateral sides, respectively. We then explored the relationship between the soft tissue gap and preoperative alignment.

RESULTS

The lateral soft tissue gap was larger in the severe varus group than in the mild and moderate varus groups. The medial soft tissue gap was larger in the severe varus group than in the mild varus group, but there were no differences in the medial joint gaps among the groups.

CONCLUSIONS

After the bone is resected, the soft tissue on the lateral side is more lax; however, the soft tissue on the medial side is not shorter with greater preoperative varus deformity.

Quantification of soft tissue balance in total knee arthroplasty using finite element analysis

Unbalanced contact force on the tibial component has been considered a factor leading to loosening of the implant and increased wear of the bearing surface in total knee arthroplasty. Because it has been reported that good alignment cannot guarantee successful clinical outcomes, the soft tissue balance should be checked together with the alignment. Finite element models of patients' lower extremities were developed to analyse the medial and lateral contact force distribution on the tibial insert. The distributions for four out of five patients were not balanced equally, even though the alignment angles were within a clinically acceptable range. Moreover, the distribution was improved by changing soft tissue release and ligament tightening for the specific case. Integration of the biomechanical modelling, image matching and finite element analysis techniques with the patient-specific properties and various dynamic loading would suggest a clinically relevant pre-operative planning for soft tissue balancing.

Robotic-assisted TKA reduces postoperative alignment outliers and improves gap balance compared to conventional TKA

BACKGROUND

Several studies have shown mechanical alignment influences the outcome of TKA. Robotic systems have been developed to improve the precision and accuracy of achieving component position and mechanical alignment.

QUESTIONS/PURPOSES

We determined whether robotic-assisted implantation for TKA (1) improved clinical outcome; (2) improved mechanical axis alignment and implant inclination in the coronal and sagittal planes; (3) improved the balance (flexion and extension gaps); and (4) reduced complications, postoperative drainage, and operative time when compared to conventionally implanted TKA over an intermediate-term (minimum 3-year) followup period.

METHODS

We prospectively randomized 100 patients who underwent unilateral TKA into one of two groups: 50 using a robotic-assisted procedure and 50 using conventional manual techniques. Outcome variables considered were postoperative ROM, WOMAC scores, Hospital for Special Surgery (HSS) knee scores, mechanical axis alignment, flexion/extension gap balance, complications, postoperative drainage, and operative time. Minimum followup was 41 months (mean, 65 months; range, 41-81 months).

RESULTS

There were no differences in postoperative ROM, WOMAC scores, and HSS knee scores. The robotic-assisted group resulted in no mechanical axis outliers (> ± 3° from neutral) compared to 24% in the conventional group. There were fewer robotic-assisted knees where the flexion gap exceeded the extension gap by 2 mm. The robotic-assisted procedures took an average of 25 minutes longer than the conventional procedures but had less postoperative blood drainage. There were no differences in complications between groups.

CONCLUSIONS

Robotic-assisted TKA appears to reduce the number of mechanical axis alignment outliers and improve the ability to achieve flexion-extension gap balance, without any differences in clinical scores or complications when compared to conventional manual techniques.

Total knee arthroplasty in severe valgus knee deformity: comparison of a standard medial parapatellar approach combined with tibial tubercle osteotomy

PURPOSE

Primary TKA in valgus knees with a deformity of more than ten degrees may prove challenging, since bone and soft tissue abnormalities make accurate axis restoration, component orientation and joint stability attainment a difficult task. The purpose of this study was to determine which approach is optimal in these patients, by comparing the standard medial parapatellar approach to a lateral parapatellar combined with a tibial tubercle osteotomy (TTO).

METHODS

Forty-four valgus knees--with an axis deviation ranging from 15 to 36 degrees (mean 24°)--were dealt with primary TKA and followed up for a minimum period of 7 years. Lateral parapatellar arthrotomy combined with TTO was performed in 22 individuals (Group A) and a standard medial parapatellar capsulotomy in the remaining patients (Group B). The International Knee Society System Score (IKSS) was used for clinical evaluation. Radiological assessment was performed yearly postoperatively using long films for assessment of the anatomical axis.

RESULTS

The postoperative IKSS scores showed no significant statistical difference between groups A and B (P < 0.05). In the alignment parameter, however, residual valgus deviation occurred in 9% of patients from Group A and in 32% from Group B. No late-onset instability was displayed.

CONCLUSION

Lateral parapatellar approach combined with TTO may prove highly beneficial in significant valgus deformities, as the anatomical axis is restored accurately and soft tissue release of the lateral contracted structures facilitated to an important extent.