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

Improved Clinical Outcomes With Dynamic, Force-Controlled, Gap-Balancing in Posterior-Stabilized Total Knee Arthroplasty

BACKGROUND

Optimal soft-tissue management in total knee arthroplasty (TKA) may reduce symptomatic instability. We hypothesized that TKA outcomes using a computer-assisted dynamic ligament balancer that acquires medial and lateral gap sizes throughout the motion arc would show improved Knee Society Scores (KSS) compared to TKAs done with a traditional tensioner at 0 and 90°. We also sought to quantify the degree to which the planned femoral rotation chosen to optimize medio-lateral balance throughout the arc of motion deviated from the femoral rotation needed to achieve a rectangular flexion gap at 90° alone.

METHODS

Baseline demographics, clinical outcomes, KSSs, and femoral rotations were compared in 100 consecutive, computer-assisted TKAs done with the balancer (balancer group) to the immediately prior 100 consecutive computer-assisted TKAs done without the balancer (control group). Minimum follow-up was 13 months and all patients had osteoarthritis. Mean knee motion did not differ preoperatively (110.1 ± 13.6° balancer, 110.4 ± 12.5° control, P = .44) or postoperatively (119.1 ± 10.3° balancer, 118.8 ± 10.9° control, P = .42). Tourniquet times did not differ (93.1 ± 13.0 minutes balancer, 90.7 ± 13.0 minutes control, P = .13). Postoperative length of stay differed (40.2 ± 20.9 hours balancer, 49.0 ± 18.3 hours control, P = .0009). There were 14 readmissions (7 balancer, 7 control), 11 adverse events (4 balancer, 7 control), and 3 manipulations (1 balancer, 2 control). The cohorts were compared using Student's t-tests, Shapiro-Wilk normalities, Wilcoxon rank-sums, and multivariable logistic regression analyses.

RESULTS

Postoperative KSS improvements were higher in the balancer group (P < .0001). In multivariable regression analyses, the balancer group experienced 7 ± 2 point improvement in KSS Knee scores (P < .0001) and 4 ± 2 point improvement in KSS Function scores (P = .040) compared to the control group.

CONCLUSIONS

The statistically and clinically significant improvements in postoperative KSS demonstrated in the balancer cohort are likely driven by improved stability throughout the motion arc. Further study is warranted to evaluate replicability by non-design surgeons.

Preoperative Joint Distraction Imaging and Planning Protocol for Total Knee Arthroplasty

BACKGROUND

Current preoperative total knee arthroplasty (TKA) planning strategies are bone-referencing and do not consider the ligamentous profile of the knee. This study assessed the mean Hip-Knee-Ankle (HKA) angle of the planned Distracted Alignment (DA), an alignment output using a joint distraction radiology and planning protocol, which incorporates preoperative evaluation of ligament laxity.

METHODS

A retrospective study of 144 knees undergoing TKA was performed. Each patient received a preoperative computer tomograph scan, a weight-bearing antero-posterior knee radiograph, and distracted knee radiographs in extension and flexion. The imaging was used to develop a preoperative DA plan aiming for medio-lateral and extension-flexion space balance. The mean DA, weight-bearing, and arithmetic HKA angles were compared to each other, and to the HKA of a healthy nonarthritic population.

RESULTS

The mean weight-bearing, arithmetic, and planned DA HKA angles were 4.8° (interquartile range [IQR] 6.5°) varus, 0.4° (IQR 4.5°) varus, and 2.2° (IQR 4.0°) varus, respectively. This compares to a healthy adult HKA angle of 1.3° varus. The difference between the planned DA and arithmetic HKA angles was greater than 3° for 36% of the patients in the study population.

CONCLUSIONS

The planned DA HKA angle was fundamentally different from the arithmetic HKA angle, but comparable to a healthy population. Considering both hard and soft tissue information of the knee, we believe the planned DA resulting from the joint distraction radiology protocol allows for optimized preoperative surgical planning in TKA. This protocol has been shown to be clinically viable.

Gap Balancing Throughout the Arc of Motion with Navigated TKA and a Novel Force-Controlled Distractor: A Review of the First 273 Cases

BACKGROUND

This study evaluated the ability to achieve the targeted soft-tissue balance in terms of medio-lateral (ML) laxity and gap values when using a computer-assisted orthopedic surgery (CAOS) system featuring an intraarticular, force-controlled distractor and assessed learning curves associated with the adoption of this technology.

METHODS

The first 273 cases using this technology were reported without any exclusions comparing 1) final ML laxity and 2) final average gap to their pre-defined targets. For both parameters, the signed and unsigned differentials were reported. The linear mixed model was used to evaluate laxity curve differences between surgeons. A cumulative sum control chart (CUSUM) was applied to assess surgeon learning curves regarding surgical time.

RESULTS

Both the average signed ML laxity and gap differentials were neutral throughout the full arc of motion. Both the average unsigned ML laxity and gap differentials were linear. Signature of ML laxity and gap differential curves tended to be surgeon-specific. The CUSUM analyses of surgical times demonstrated either a short learning curve or the absence of a discernable learning pattern for surgeons.

CONCLUSION

Data from all users involved with the pilot release of the balancing device were considered to capture variability in familiarity with the technique and learning curve cases were included. A high ability to achieve targeted gap balance throughout the arc of motion using the proposed method was observed.

Patient-reported impairment following TKA is reduced when a computationally simulated predicted ideal alignment is achieved

PURPOSE

Joint dynamics following Total Knee Arthroplasty (TKA) may influence patient-reported outcome. Simulations allow many knee alignment approaches to a single patient to be considered prior to surgery. The simulated kinematics can be matched to patient-reported outcome to predict kinematic patterns most likely to give the best outcome. This study aims to validate one such previously developed algorithm based on a simulated deep knee bend (the Dynamic Knee Score, DKS).

METHODS

1074 TKA patients with pre- and post-operative Computerised Tomography (CT) scans and 12-month post-operative Knee Injury and Osteoarthritis Outcomes (KOOS) Scores were identified from the 360 Med Care Joint Registry. Landmarking and registration of implant position was performed on all CT scans, and each of the achieved TKAs was computationally simulated and received a predictive outcome score from the DKS. In addition, a set of potential alternative surgical plans which might have been followed were simulated. Comparison of patient-reported issues and DKS score was evaluated in a counter-factual study design.

RESULTS

Patient-reported impairment with the knee catching and squatting was shown to be 30% lower (p = 0.005) and 22% lower (p = 0.026) in patients where the best possible DKS result was the one surgically achieved. Similar findings were found relating attainment of the best tibial slope and posterior femoral resection DKS plans to patient-reported difficulty straightening the knee (40% less likely, p < 0.001) and descending stairs (35% less likely, p = 0.006).

CONCLUSION

The DKS has been shown to correlate with presence of patient-reported impairments post-TKA and the resultant algorithm can be applied in a pre-operative planning setting. Outcome optimization in the future may come from patient-specific selection of an alignment strategy and simulations may be a technological enabler of this trend.

LEVEL OF EVIDENCE

III (Retrospective Cohort Study).

Investigation of femoral condyle height changes during flexion of the knee: implication to gap balance in TKA surgery

BACKGROUND

Gap balance of the knee at 0° and 90° of flexion has been pursued in total knee arthroplasty (TKA) with the trans-epicondyle axis (TEA) as a reference. This study investigated the height changes of the tibiofemoral articulation and compared the data with the femoral condyle height changes measured using different flexion axes.

MATERIALS AND METHODS

Twenty healthy knees were investigated during an in vivo weightbearing flexion using a technique combining MRI and a dual fluoroscopic imaging system (DFIS). The tibiofemoral contact points and the femoral condyle heights [measured using: TEA, geometric center axis (GCA), and iso-height axis (IHA)] were determined at each flexion angle. The height changes of the articular contact points and the femoral condyles were compared along the flexion path.

RESULTS

The changes of the medial and lateral contact point heights were within 2.5 mm along the flexion path. The changes of the medial and lateral condyle heights were within 8.9 mm for TEA, within 4.2 mm for GCA and within 3.0 mm for IHA. The height changes measured by the contact points and IHA are similar (p > 0.05), and both are significantly smaller than those measured using the TEA and GCA (p < 0.05).

CONCLUSIONS

The TEA and GCA measured varying femoral condyle heights, but the IHA resulted in minimal condyle height changes and could better represent the articulation characteristics of the knee. The data suggested that the IHA could be used as an alternative reference to guide surgical preparation of gap balance along the knee flexion path during TKA surgeries.

Sensor Use in Cruciate-Retaining Total Knee Arthroplasty Compared with Posterior-Stabilized Total Knee Arthroplasty: Load Balancing and Posterior Femoral Rollback

The purpose was to investigate the proportion of severe load imbalance after appropriate conventional gap balancing and analyze the intraoperative kinematics after load balancing in cruciate-retaining (CR) and posterior-stabilized (PS) total knee arthroplasties (TKAs). In total, 45 sensor-assisted CR and 45 PS TKAs using NexGen prosthesis were prospectively evaluated. After appropriate conventional gap balancing, the loads at 10, 45, and 90 degrees of knee flexion were evaluated with a wireless load sensor placed in trial implants. The proportion of severe load imbalance (medial load-lateral load >75 lbs) was investigated. After load balancing, location of the femorotibial contact point was investigated at each flexion angle to analyze femorotibial kinematics. The proportion of the severe load imbalance was significantly higher in CR TKAs at the 10 degrees knee flexion (37.8 vs. 15.6%, p = 0.031). This proportion was higher in CR TKAs than in PS TKAs at the 45 and 90 degrees knee flexion angles, but without statistical significance (31.1 vs. 15.6%, p = 0.134 and 33.3 vs. 15.6%, p = 0.085, respectively). After load balancing, consistent posterior femoral rollback occurred in medial and lateral compartments during 90 degrees flexion in CR TKAs (p < 0.001), but not in PS TKAs. Medial pivot kinematics was not observed in both TKA designs. The sensor was more beneficial in CR TKAs for achieving appropriate load balancing and consistent posterior femoral rollback compared with PS TKAs. Further studies are required to identify target load distribution to restore ideal knee kinematics after TKA. This study shows level of evidence II.

Large flexion contracture angle predicts tight extension gap during navigational posterior stabilized-type total knee arthroplasty with the pre-cut technique: a retrospective study

Background

This study aimed to determine the predictors of tight extension gap (EG) compared with the flexion gap (FG) during navigational posterior stabilized-type total knee arthroplasty using the pre-cut technique.

Methods

Nineteen patients with tight EG (defined as FG-EG ≥2 mm after pre-cut; group T) and 84 patients with an approximately equal gap (defined as FG-EG = 0–1 mm after pre-cut; group E) were enrolled. Medial tibial slope angle, hip knee ankle angle, flexion contracture angle, and active maximum flexion angle were compared between the two groups.

Results

The multivariate logistic regression model indicated that the probability of tight EG increased with flexion contracture angle (odds ratio, 1.13; 95% confidence interval 1.05–1.20; P ≤ 0.001). According to the receiver operating characteristic analysis, the flexion contracture angle cut-off value associated with tight EG was 15.0° (sensitivity, 85%; specificity, 78%).

Conclusion

This study demonstrated that a large flexion contracture angle (cut-off 15.0°) was associated with tight EG after pre-cut osteotomy during posterior stabilized-type total knee arthroplasty. Awareness of this risk factor may help improve preoperative predictability of tight EGs and preparedness for additional procedures, such as soft tissue release or capsulotomy, to correct them.

Level of evidence

Level III.

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.

A tensor with a flat surface overestimates midflexion laxity in total knee arthroplasty: Comparison between a tensor with a flat-shaped surface and a tensor with an insert-shaped surface

BACKGROUND

Soft tissue balance is important for the success of total knee arthroplasty (TKA). Various types of tensors have been developed for the precise measurement of a gap. We hypothesized that the surface shape of the tensor that contacted the TKA component affected the gap measurement. This study aimed to compare the gaps obtained with flat and insert-shaped surface tensors.

METHODS

Two senior surgeons performed 95 TKAs (Vanguard-PS:55 knees; Persona-PS:40 knees). The joint gap was measured in each static knee flexion status (0°, 30°, 45°, 60°, 90°, 120°, and full flexion). We compared the gaps measured with a flat surface tensor and an insert-shape surface tensor. We defined a significant change as a gap difference of >1 mm with a statistical significance.

RESULTS

In Vanguard-PS, significant changes were observed at 30° and 45°. In Persona-PS, significant changes were observed at 30°, 45°, and 60°. In both implants, gaps measured with the flat tensor were larger than those measured with the insert tensor at approximately midflexion, and the significant changes disappeared in higher flexion position over midflexion.

CONCLUSIONS

The surface shape of the tensor affected the measurement of midflexion laxity in TKA. When measuring the gap with a flat tensor, the midflexion laxity was overestimated. A tensor with an insert-shaped surface should be used to measure the gap in TKA.

Consistent femoral external rotation during weight-bearing knee flexion is associated with better patient-reported pain and mediolateral balance after total knee arthroplasty

BACKGROUND

Normal knees generally show consistent femoral external rotation during knee flexion, although knees that have had total knee arthroplasty exhibit various rotational patterns with less rotational angle. This study aimed to determine whether consistent femoral external rotation during weight-bearing knee flexion after total knee arthroplasty is associated with better patient-reported outcomes and mediolateral joint balance.

METHODS

A total of 40 total knee arthroplasty knees with a high-flexion posterior-stabilized prosthesis were divided into two groups based on their axial rotational kinematic pattern during squatting activity, and the clinical results including patient-reported outcomes and joint laxity were compared between the consistent external rotation group (20 knees) and the inconsistent external rotation group (20 knees). The unpaired Student's t-test or Welch's test were used for group comparison, and Fisher's exact test was applied for categorical data.

FINDINGS

"Pain at rest" and "Pain at first gait in the morning" measured using a numerical rating scale (/10) were significantly lower in the consistent external rotation group compared with those in the inconsistent external rotation group. "Pain during gait on flat surface" tended to be lower in the consistent external rotation group. Medial stability was obtained in both groups with significantly greater lateral laxity in extension in the inconsistent external rotation group.

INTERPRETATION

Total knee arthroplasty knees with consistent femoral external rotation during weight-bearing knee flexion exhibited better patient-reported pain and mediolateral soft tissue balance. Surgical procedures that control the mediolateral balance with medial stability would induce consistent femoral external rotation and improve patient-reported pain.

The medial gap is a reliable indicator for intraoperative soft tissue balancing in posterior-stabilized total knee arthroplasty

BACKGROUND

Appropriate soft tissue balance and accurate alignment are important for successful total knee arthroplasty (TKA). However, the optimal technique for establishing and measuring soft tissue balancing remains unclear. The aim of this study was to analyze the intraoperative medial and lateral gap pattern using digital knee balancer in posterior-stabilized (PS) TKA.

METHODS

This study involved 55 patients with medial osteoarthritis who underwent a primary TKA using an image-free navigation system. The extension gap and the flexion gap at 90° knee flexion were assessed using an offset seesaw-type digital balancer. Continuous joint distraction force from 10 lb to 60 lb was applied. Medial gap, lateral gap, and varus angle were measured.

RESULTS

The medial bone gap difference between extension and flexion was constant regardless of the distraction force from 20 lb to 60 lb. The lateral bone gap was significantly greater than the medial bone gap in extension and flexion from 30 lb to 60 lb (P < 0.05). The varus angle changed depending on the distraction force, especially in flexion. The varus angle in flexion was significantly greater than that in extension from 40 lb to 60 lb (P < 0.05).

CONCLUSIONS

The medial bone gap is a reliable indicator unaffected by the distraction force during surgery and is useful for adjusting the medial gap in extension and flexion appropriately to ensure medial stability in PS-TKA. The digital knee balancer and navigation system support both precise gap assessment and surgery.

There are isoheight points that measure constant femoral condyle heights along the knee flexion path

PURPOSE

It is a challenge to evaluate the maintenance of medial and lateral soft tissue balance in total knee arthroplasty (TKA). This study aimed to determine the "isoheight" points and the "isoheight" axis (IHA) that can measure constant medial/lateral condyle heights during flexion of the knee, and compare the IHA with two major anatomical axes, the transepicondylar axis (TEA) and the geometric center axis (GCA).

METHODS

Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging system while performing a single-legged lunge (0°-120°). The isoheight points of the medial and lateral femoral condyles were defined as the locations with the least amount of changes in heights during the knee flexion; an IHA is the line connecting the medial and lateral isoheight points. The measured changes of the condyle heights using the IHA were compared with those measured using the TEA and GCA.

RESULTS

Overall, the IHA was posterior and distal to the TEA, and anterior to the GCA. The isoheight points measured condyle height changes within 1.2 ± 2.3 mm at the medial and 0.7 ± 3.3 mm at the lateral sides during the knee flexion. Between 0° and 45°, the condyle height changes measured using the GCA (medial: 3.0 ± 1.8 mm, lateral: 2.3 ± 2.0 mm) were significantly larger than those of the IHA and the TEA (p < 0.05). Between 90° and 120°, the changes of the condyle heights measured using the TEA (medial: 5.3 ± 1.8 mm, lateral: 3.3 ± 1.8 mm) were significantly larger than those of the IHA and GCA (p < 0.05).

CONCLUSION

There are isoheight points in the medial and lateral femoral condyles that can measure constant heights along the full range of knee flexion and could be used to formulate an "isoheight" axis (IHA) of the femur. The condyle height changes measured by the TEA and GCA were greater than the IHA measurements along the flexion path. These data could be used as a valuable reference to evaluate the condyle height changes after TKA surgeries and help achieve soft tissue balance and optimal knee kinematics along the flexion path.

LEVEL OF EVIDENCE

IV.

Influence of component design on in vivo tibiofemoral contact patterns during kneeling after total knee arthroplasty: a systematic review and meta-analysis

PURPOSE

Modern TKR prostheses are designed to restore healthy kinematics including high flexion. Kneeling is a demanding high-flexion activity. There have been many studies of kneeling kinematics using a plethora of implant designs but no comprehensive comparisons. Visualisation of contact patterns allows for quantification and comparison of knee kinematics. The aim of this systematic review was to determine whether there are any differences in the kinematics of kneeling as a function of TKR design.

METHODS

A search of the published literature identified 26 articles which were assessed for methodologic quality using the MINORS instrument. Contact patterns for different implant designs were compared at 90° and maximal flexion using quality-effects meta-analysis models.

RESULTS

Twenty-five different implants using six designs were reported. Most of the included studies had small-sample sizes, were non-consecutive, and did not have a direct comparison group. Only posterior-stabilised fixed-bearing and cruciate-retaining fixed-bearing designs had data for more than 200 participants. Meta-analyses revealed that bicruciate-stabilised fixed-bearing designs appeared to achieve more flexion and the cruciate-retaining rotating-platform design achieved the least, but both included single studies only. All designs demonstrated posterior-femoral translation and external rotation in kneeling, but posterior-stabilised designs were more posterior at maximal flexion when compared to cruciate retaining. However, the heterogeneity of the mean estimates was substantial, and therefore, firm conclusions about relative behaviour cannot be drawn.

CONCLUSION

The high heterogeneity may be due to a combination of variability in the kneeling activity and variations in implant geometry within each design category. There remains a need for a high-quality prospective comparative studies to directly compare designs using a common method.

LEVEL OF EVIDENCE

Systematic review and meta-analysis Level IV.

Rotational and varus-valgus laxity affects kinematics of the normal knee: A cadaveric study

PURPOSE

The aim of this study was to evaluate the relationship between soft tissue laxity and kinematics of the normal knee using a navigation system.

METHODS

Fifteen cadaveric knees from 11 fresh frozen whole-body specimens were included in this study. The navigation system automatically recorded the rotation angle of the tibia as the internal-external (IE) kinematics and the coronal alignment of the lower limb as the varus-valgus (VV) kinematics. These measurements were made with the joint in maximal extension, at 10° intervals from 0° to 120° of flexion, and at maximal flexion during passive knee motion. For evaluation of laxity, the examiner gently applied maximum manual IE and VV stress to the knee at 0°, 30°, 60°, and 90° of flexion.

RESULTS

The measurements showed almost perfect reliability. The mean correlation coefficient between the intraoperative tibial rotation angle and the intermediate angle of IE laxity was 0.82, while that between the coronal alignment of the lower limb and the intermediate angle of the VV laxity was 0.96. There was a statistically significant correlation between kinematics and laxity at all degrees of knee flexion.

CONCLUSION

The present study revealed that the rotation angle of the tibia was correlated to the intermediate angle of IE laxity at 0°, 30°, 60°, and 90° of knee flexion and the coronal alignment of the lower limb also correlated to the intermediate angle of VV laxity. These findings provide important reference data on soft tissue laxity and kinematics of the normal knee.

The effect of anterior cruciate ligament resection on knee biomechanics

AIMS

The objectives of this study were to assess the effect of anterior cruciate ligament (ACL) resection on flexion-extension gaps, mediolateral soft tissue laxity, maximum knee extension, and limb alignment during primary total knee arthroplasty (TKA).

METHODS

This prospective study included 140 patients with symptomatic knee osteoarthritis undergoing primary robotic-arm assisted TKA. All operative procedures were performed by a single surgeon using a standard medial parapatellar approach. Optical motion capture technology with fixed femoral and tibial registration pins was used to assess study outcomes pre- and post-ACL resection with knee extension and 90° knee flexion. This study included 76 males (54.3%) and 64 females (45.7%) with a mean age of 64.1 years (SD 6.8) at time of surgery. Mean preoperative hip-knee-ankle deformity was 6.1° varus (SD 4.6° varus).

RESULTS

ACL resection increased the mean extension gap significantly more than the flexion gap in the medial (mean 1.2 mm (SD 1.0) versus mean 0.2 mm (SD 0.7) respectively; p < 0.001) and lateral (mean 1.1 mm (SD 0.9) versus mean 0.2 mm (SD 0.6) respectively; p < 0.001) compartments. The mean gap differences following ACL resection did not create any significant mediolateral soft tissue laxity in extension (gap difference: mean 0.1 mm (SD 2.4); p = 0.89) or flexion (gap difference: mean 0.2 mm (SD 3.1); p = 0.40). ACL resection did not significantly affect maximum knee extension (change in maximum knee extension = mean 0.2° (SD 0.7°); p = 0.23) or fixed flexion deformity (mean 4.2° (SD 3.2°) pre-ACL release versus mean 3.9° (SD 3.7°) post-ACL release; p = 0.61). ACL resection did not significantly affect overall limb alignment (change in alignment = mean 0.2° valgus (SD 1.0° valgus; p = 0.11).

CONCLUSION

ACL resection creates flexion-extension mismatch by increasing the extension gap more than the flexion gap. However, gap differences following ACL resection do not create any mediolateral soft tissue laxity in extension or flexion. ACL resection does not affect maximum knee extension or overall limb alignment. Cite this article: Bone Joint J 2020;102-B(4):442-448.

Intraoperative manipulation for flexion contracture during total knee arthroplasty

BACKGROUND

Joint gap unbalancing during total knee arthroplasty (TKA) induces flexion contracture. Flexion contracture is one of the most serious complications of TKA. When flexion contracture is found during surgery, intraoperative manipulation is often empirically performed. We evaluated the effects of intraoperative manipulation on joint gap and postoperative flexion contracture.

MATERIALS AND METHODS

TKA was performed for 136 knees. Intraoperative manipulation was performed for flexion contracture in 61 knees. Joint gap changes before and after manipulation were measured at six positions from extension to 120° of flexion. Manipulation was not performed for 75 knees. The extension angle was measured radiographically immediately after surgery, at 3 months, and 6 months postoperatively. Extension angles with manipulation and without manipulation were compared.

RESULTS

Joint gap changes (mm) before and after manipulation were 0.1, 0.0, -0.2, -0.3, -0.1, and -0.3 at 0°, 30°, 45°, 60°, 90°, and 120° of flexion, respectively, indicating that manipulation could not change joint gaps significantly. Extension angles (°) with and without manipulation were -4.0 ± 4.6 and -3.8 ± 3.9 immediately after surgery, -5.3 ± 6.7 and -5.5 ± 6.2 at 3 months postoperatively, and -2.7 ± 6.0 and -3.8 ± 5.8 at 6 months postoperatively. No statistically significant difference existed between the values with or without manipulation during all periods.

CONCLUSION

Intraoperative manipulation does not enlarge the gap or resolve postoperative flexion contracture. Developing the new surgical technique is required to achieve perfect balance at TKA.

Posterior cruciate ligament resection in total knee arthroplasty: the effect on flexion-extension gaps, mediolateral laxity, and fixed flexion deformity

AIMS

The aim of this study was to assess the effect of posterior cruciate ligament (PCL) resection on flexion-extension gaps, mediolateral soft-tissue laxity, fixed flexion deformity (FFD), and limb alignment during posterior-stabilized (PS) total knee arthroplasty (TKA).

PATIENTS AND METHODS

This prospective study included 110 patients with symptomatic osteoarthritis of the knee undergoing primary robot-assisted PS TKA. All operations were performed by a single surgeon using a standard medial parapatellar approach. Optical motion capture technology with fixed femoral and tibial registration pins was used to assess gaps before and after PCL resection in extension and 90° knee flexion. Measurements were made after excision of the anterior cruciate ligament and prior to bone resection. There were 54 men (49.1%) and 56 women (50.9%) with a mean age of 68 years (sd 6.2) at the time of surgery. The mean preoperative hip-knee-ankle deformity was 4.1° varus (sd 3.4).

RESULTS

PCL resection increased the mean flexion gap significantly more than the extension gap in the medial (2.4 mm (sd 1.5) vs 1.3 mm (sd 1.0); p < 0.001) and lateral (3.3 mm (sd 1.6) vs 1.2 mm (sd 0.9); p < 0.01) compartments. The mean gap differences after PCL resection created significant mediolateral laxity in flexion (gap difference: 1.1 mm (sd 2.5); p < 0.001) but not in extension (gap difference: 0.1 mm (sd 2.1); p = 0.51). PCL resection significantly improved the mean FFD (6.3° (sd 4.4) preoperatively vs 3.1° (sd 1.5) postoperatively; p < 0.001). There was a strong positive correlation between the preoperative FFD and change in FFD following PCL resection (Pearson's correlation coefficient = 0.81; p < 0.001). PCL resection did not significantly affect limb alignment (mean change in alignment: 0.2° valgus (sd 1.2); p = 0.60).

CONCLUSION

PCL resection creates flexion-extension mismatch by increasing the flexion gap more than the extension gap. The increase in the lateral flexion gap is greater than the increase in the medial flexion gap, which creates mediolateral laxity in flexion. Improvements in FFD following PCL resection are dependent on the degree of deformity before PCL resection. Cite this article: Bone Joint J 2019;101-B:1230-1237.

Mediolateral coronal laxity does not correlate with knee range of motion after total knee arthroplasty

INTRODUCTION

It remains controversial whether coronal laxity after total knee arthroplasty (TKA) is a critical factor in determining clinical outcomes such as knee range of motion (ROM). The purpose of this study was to evaluate the correlation between postoperative ROM and coronal laxity, which was defined as the angular motion from the neutral, unloaded position to the loaded position, in patients with medial knee osteoarthritis undergoing TKA.

MATERIALS AND METHODS

Preoperative and 1-year postoperative coronal laxity were assessed using radiographs by applying a force of 150 N with an arthrometer. A consecutive series of 204 knees was examined. A knee was defined as clinically "balanced" when the difference between medial and lateral laxity was 3° or less. Active ROM was measured using a goniometer. Values were expressed as median values.

RESULTS

The ROM was 105° preoperatively and 110° postoperatively, with the correlation being weak (r = 0.372, p < 0.001) between the periods. The total laxity also revealed a weak correlation (r = 0.270, p < 0.001) between the periods. Preoperative laxity was significantly larger (4° vs. 3°) on the medial side (p < 0.001) and postoperative laxity was larger (4° vs. 3°) laterally (p = 0.001). There was no significant correlation between postoperative ROM and laxity pre- and postoperatively. Additionally, there were no differences in ROM between the balanced and unbalanced groups in the pre- and postoperative periods.

CONCLUSIONS

This study indicated that mediolateral coronal laxity in patients with an osteoarthritic knee did not correlate with knee ROM after TKA when 3°-4° of laxity in the medial and lateral orientations was maintained.

Impact of intraoperative adjustment method for increased flexion gap on knee kinematics after posterior cruciate ligament-sacrificing total knee arthroplasty

BACKGROUND

In general, the flexion gap is larger than the extension gap with posterior cruciate ligament-sacrificing total knee arthroplasty. Several methods compensate for an excessive flexion gap, but their effects are unknown. The purpose of this study was to compare three methods to compensate for an increased flexion gap.

METHODS

In this study, squatting in knees with excessive (4 mm) and moderate (2 mm) flexion gaps was simulated in a computer model. Differences in knee kinematics and kinetics with joint line elevation, setting the femoral component in flexion, and using a larger femoral component as compensatory methods were investigated.

FINDINGS

The rotational kinematics during flexion with setting the femoral component in flexion were opposite to those in the other models. Using a larger femoral component resulted in the most physiological motion. The peak anterior translation was 10 mm in the joint line elevation model compared with approximately 6 mm in the other models. In the joint line elevation model, patellofemoral contact stress was excessively increased at 90° of knee flexion. In contrast, tibiofemoral contact stress was higher during knee extension with setting the femoral component in flexion due to anterior impingement. There were few differences in the effect of the three compensatory methods with a moderate flexion gap.

INTERPRETATION

A larger femoral component should be used to compensate for an excessive flexion gap because it has less negative impact on posterior cruciate ligament-sacrificing total knee arthroplasty, whereas any compensation method might be acceptable for a moderate flexion gap.

How prosthetic design influences knee kinematics: a narrative review of tibiofemoral kinematics of healthy and joint-replaced knees

INTRODUCTION

To improve the total knee arthroplasty (TKA) prosthesis design, it is essential to study the kinematics of the tibiofemoral joint. Many studies have been conducted in this area; however, conflicting results and incomparable testing methods make it difficult to draw definitive conclusions or compare research from studies. The goal of this article is to introduce what is known about both healthy and prosthetic tibiofemoral joint kinematics.

AREAS COVERED

Healthy tibiofemoral joint kinematics are reviewed in vivo by different activities, and the kinematics of existing knee prosthetic design features are considered separately. These features include but are not limited to cruciate retaining, posterior cruciate substituting, mobile-bearing, and high flexion.

EXPERT COMMENTARY

The type of activity that is being performed has a great influence on the kinematics of healthy knees, and the influences of different TKA prosthetic design features on the kinematics are complex and varied. Moreover, the TKA postoperative functional performance is influenced by many factors, and prosthetic design is among them, but not the only one that defines the performance.

A load-measuring device can achieve fine-tuning of mediolateral load at knee arthroplasty but may lead to a more lax knee state

PURPOSE

A balanced knee arthroplasty should optimise survivorship and performance. Equilibration of medial and lateral femorotibial load requires guided judicious pericapsular ligament release. The null hypothesis was that there would be no difference between use of a tensiometer device and a remote load sensor final load transfer across the joint through functional arc of motion.

METHODS

A cadaveric study, using eight knees, was performed to define the impact of an established gap distraction device against load sensor-aimed soft tissue release in a TKA setting. Using validated measures of laxity in six degrees of freedom and true real-time load sensing four states were examined: native knee, TKA using spacer blocks (TKA), TKA with soft tissue release aided by a monogram tensiometer (TKA-T) and finally where load across the tibiofemoral articulation remains unbalanced final soft tissue release using a sensor device (TKA-OS).

RESULTS

The laxity pattern was equivalent for TKA-T and TKA-OS. However, in only four of these seven knees despite the tensiometer confirming equivalence of rectangular flexion-extension gap dimensions and centralisation of collateral ligament distraction, there remained a > 15lb medial to lateral load difference for at least one point of the flexion arc. This was corrected by further final soft tissue release guided by the OS sensor device in the final three knees.

CONCLUSION

Tensiometer-guided soft tissue release at two points of flexion failed to achieve balance for three out of seven knee arthroplasty procedures. Sensor technology guided final soft tissue balancing to equilibrate load across the joint through full arc of motion. This work argues for the role of continuous sensor readings to guide the soft tissue balancing during total knee arthroplasty.

In-vivo elongation of anterior and posterior cruciate ligament in bi-cruciate retaining total knee arthroplasty

Anterior and posterior cruciate ligament (ACL and PCL) sacrifice in contemporary total knee arthroplasty (TKA) has been considered a potential factor leading to abnormal knee kinematics. Bi-cruciate retaining (BCR) TKA design allows retention of both ACL and PCL. However, there is a limited data on the ACL/PCL in-vivo elongation characteristics of BCR TKA. The study aimed to evaluate and compare the in-vivo elongation patterns of ACL/PCL between BCR TKA and contralateral non-implanted knee and to explore potential factors leading to the changed elongation patterns between limbs. ACL/PCL elongations of both knees during sit-to-stand were measured in 29 unilateral BCR TKA patients using a validated dual fluoroscopic tracking technique. Joint gap changes of the BCR TKA knees relative to the contralateral knee were quantified. BCR TKA and the contralateral non-implanted knee exhibited similar ACL elongation at extension and clinical anterior knee laxity. However, BCR TKA showed significantly greater PCL elongation during flexion than the non-implanted knee. Variation of changed elongation was observed for both ACL and PCL, suggesting a heterogeneous restoration of normal ACL/PCL functions. A significant correlation was found between extension joint gap change and the change of ACL elongation, highlighting the importance of precise joint line restoration and soft tissue balancing during BCR TKA surgery. Our findings suggest that BCR TKA did not fully restore "near-normal" cruciate ligament elongation patterns and anteroposterior stability. Considerable heterogeneity remains in the retained ligament elongation patterns and warrants further investigations of multifactorial factors to optimize ACL/PCL functions in BCR TKA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3239-3246, 2018.

Posterior Reference Position Affects Intraoperative Kinematic and Soft Tissue Balance in Navigated Posterior-Stabilized Total Knee Arthroplasty

BACKGROUND

The importance of medial compartment stability is recognized in total knee arthroplasty (TKA). To manage the medial extension-flexion gap, the posterior reference position can be changed from conventional posterior center to posterior medial in measured resection techniques. This study aimed to compare the intraoperative soft tissue balance and rotational kinematics between the posterior medial and posterior center reference groups.

METHODS

We enrolled 57 consecutive patients with varus osteoarthritis undergoing posterior-stabilized (PS) TKA using an image-free navigation system. The detailed surgical plan in both groups and intraoperative kinematics were recorded using navigation, and soft tissue balance measured with an offset-type tensor was statistically compared between groups.

RESULTS

Patients were divided into the posterior center reference group (n = 32) and posterior medial reference group (n = 25). The posterior medial and posterior lateral condyles were significantly thicker in the posterior center reference group (P < .05). Although preoperative rotational kinematics were comparable between groups, the tibial rotational position was significantly more externally rotated in the posterior center reference group than in the posterior medial reference group at 45°, 60°, and 90° of flexion (P < .05). The varus angle and joint component gap were significantly smaller in the posterior medial reference group than in the posterior center reference group at 60° and 90° of flexion (P < .05).

CONCLUSION

The posterior reference position affects intraoperative kinematics and soft tissue balance in navigated PS TKA. Posterior medial reference PS TKA decreases the excessive tibial external rotation during midflexion and increases the flexion stability compared with conventional posterior center reference PS TKA.

Is "symmetric" gap balancing still the gold standard in primary total knee arthroplasty?

A rectangular and symmetrical gap in flexion as well as in extension is mandatory to achieve good outcomes and good long-term results in total knee arthroplasty (TKA) using classical designs. Recently, as showed in several fluoroscopic studies, different modern designs (medial congruent or sagittally stable implants) have been demonstrated to better reproduce the more physiological medial pivoting (MP) biomechanics of the normal knee when compared to classical postero-stabilized (PS) and cruciate-retaining (CR) designs. These modern designs, characterized by different level of conformity, might require adopting a different surgical technique in terms of soft tissue balancing technique for primary TKA. In such cases, the current authors suggest to reproduce a slightly asymmetric extension and flexion gaps with a tighter medial then lateral compartment to re-establish the MP kinematics of the normal knee.

Intraoperative Measurements and Tools to Assess Stability

Knee stability is the ability for the joint to maintain an appropriate functional position throughout its range of motion. Knee instability can be defined as excessive laxity during activities of daily living. Intraoperative knee laxity can be affected by implant design, alignment of components, and soft-tissue balancing. Soft-tissue balance is a major contributor to knee instability. Mechanical balancing instruments can be classified as spacer blocks or joint-distraction devices. Conventional wisdom favors rectangular and equal flexion-extension gaps. However, knee balance is elusive even with mechanical balancing instruments. First-generation electronic balancing devices are equivalent in concept to spacer blocks instrumented with force sensors. Second-generation electronic balancing devices are equivalent in concept to mechanical distraction devices instrumented with pressure and displacement sensors. Electronic ligament balancers can be useful in documenting intraoperative knee laxity for quantifiable correlation with postoperative outcomes, thus directly relating postoperative stability to surgical balance, and may predict outcomes and knee stability.

Intraoperative Manipulation for Flexion Contracture During Total Knee Arthroplasty

Joint gap balancing during total knee arthroplasty (TKA) is important for ensuring postoperative joint stability and range of motion. Although the joint gap should be balanced to ensure joint stability, it is not easy to achieve perfect balancing during TKA. In particular, relative extension gap shortening can induce flexion contracture. Intraoperative manipulation is often empirically performed. This study evaluated the tension required for this manipulation and investigated the influence of intraoperative manipulation on the joint gap in cadaveric knees. Total knee arthroplasty was performed in 6 cadaveric knees from whole body cadavers. Flexion contracture was induced using an insert that was 4 mm thicker than the extension gap, and intraoperative manipulation was performed. Study measurements included the changes in the joint gap after manipulation at 6 positions, with the knee bending from extension to 120° flexion, and the manipulation tension that was required to create a 4-mm increase in the gap. The manipulation tension needed to create a 4-mm increase in the extension gap was 303±17 N. The changes in the joint gap after manipulation were 0.4 mm, 0.6 mm, 0.2 mm, -0.2 mm, -0.4 mm, and -0.6 mm at 0°, 30°, 45°, 60°, 90°, and 120° flexion, respectively. Therefore, the joint gap was not significantly changed by the manipulation. Intraoperative manipulation does not resolve flexion contracture. Therefore, if flexion contracture occurs during TKA, treatment with additional bone cutting and soft tissue release is likely more appropriate than manipulation. [Orthopedics. 2016; 39(6):e1070-e1074.].