Development of a pneumatic tensioning device for gap measurement during total knee arthroplasty

Joint gap produced by manual stress is dependent on the surgeon's experience and is smaller in flexion in robotic-assisted total knee arthroplasty

PURPOSE

This study aimed to retrospectively investigate (1) the reproducibility of gap measurements by manual stress using the Z-shaped retractor depending on the surgeon's experience with this maneuver and (2) the consistency of the gap distraction force produced by manual stress throughout the range of motion (ROM) in the robotic-assisted total knee arthroplasty (TKA). It was hypothesized that the joint gap produced by manual stress is not reproducible depending on the surgeon's experience, and the distraction force applied by manual stress throughout the ROM is not constant.

METHODS

Medial and lateral joint gaps were obtained throughout the ROM by manual stress or a tensioner by two surgeons with different levels of experience in robotic-assisted TKA. The association between the differences in gap measurement by the two surgeons and the preoperative radiographic parameters, including the hip-knee-ankle (HKA) angle and absolute and relative varus/valgus laxities were analyzed.

RESULTS

The experienced surgeon produced significantly greater gaps than the inexperienced surgeon from 0° to 100° flexion, with a mean difference of 0.35 ± 0.12 mm in the medial gap (p < 0.0001), and from 10° to 120° flexion with a mean difference of 0.57 ± 0.13 mm in the lateral gap (p < 0.0001). The tensioner produced a significantly greater medial gap from 70° to 110° flexion with a mean difference of 0.32 ± 0.01 mm in the medial gap (p < 0.0001) and from 0° to 110° flexion with a mean difference of 1.12 ± 0.26 mm in the lateral gap (p < 0.0001). The differences in gap distance by manual stress between experienced and inexperienced surgeons were moderately correlated with the HKA angle in the lateral gap (r = 0.40, p = 0.01). The gap differences due to manual stress and a tensioner showed moderate negative correlation with the HKA angle in the medial gap (r = - 0.50, p = 0.001) and weak negative correlation with the absolute valgus laxity in the lateral gap (r = - 0.35, p = 0.03).

CONCLUSIONS

The joint distraction force by manual stress may differ depending on the surgeon's experience and tended to be smaller in deep flexion; therefore, the flexion gap may be underestimated. Surgeons should determine implant positioning considering gap balance by manual stress, taking into account these characteristics of the manual stress maneuver.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Impact of Component Alignment and Soft Tissue Release on 2-Year Outcomes in Total Knee Arthroplasty

BACKGROUND

The objective of this study was to investigate the impact of alignment and soft tissue release on patient outcomes following total knee arthroplasty (TKA).

METHODS

In a multicenter study, soft tissue releases during TKA were prospectively documented in 330 robotic-assisted TKAs. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were captured postoperatively. Delphi analysis was used to determine inlier and outlier component alignment boundaries: Tibia Coronal (TC): ±3°, Femur Coronal (FC): ±3°, Femoral Axial (FA): 3°Int-6°Ext, Hip-Knee-Ankle (HKA): 3°Val-4°Var, and Tibiofemoral Axial (TFA): 3°Int-6°Ext. Kruskal-Wallis analysis of variance tests were used to compare groups.

RESULTS

No significant differences were found between any individual or grouped inlier and outlier alignment criterion and KOOS at any timepoint. Outlier alignment frequencies were: TC: 0%, FC: 12%, FA: 8%, HKA: 9%, TFA: 8%, and Any: 23%. Soft tissue releases were performed in 18% of cases. Knees with soft tissue releases reported significantly worse KOOS scores at: 6M: Symptoms (80.0 versus 75.3, P = .03), activities of daily living (ADL) (86.2 versus 80.8, P = .030), quality of life (70.1 versus 60.9, P = .008), 12M ADL (90.0 versus 85.1, P = .023), and 24M ADL (91.9 versus 87.2, P = .016). A higher proportion of patients achieved Minimal Clinically Important Difference for pain at 6 months for those having no releases versus released (92.3% versus 81.0%, P = .021). No significant associations were found between preoperative deformity and preoperative or postoperative KOOS.

CONCLUSION

The addition of soft tissue releases after bony cuts is associated with worse KOOS scores out to 2 years and was more prevalent in knees with worse deformity, while no such association was found for alignment.

New Technologies in Knee Arthroplasty: Current Concepts

Total knee arthroplasty (TKA) is an effective treatment for severe osteoarthritis. Despite good survival rates, up to 20% of TKA patients remain dissatisfied. Recently, promising new technologies have been developed in knee arthroplasty, and could improve the functional outcomes. The aim of this paper was to present some new technologies in TKA, their current concepts, their advantages, and limitations. The patient-specific instrumentations can allow an improvement of implant positioning and limb alignment, but no difference is found for functional outcomes. The customized implants are conceived to reproduce the native knee anatomy and to reproduce its biomechanics. The sensors have to aim to give objective data on ligaments balancing during TKA. Few studies are published on the results at mid-term of these two devices currently. The accelerometers are smart tools developed to improve the TKA alignment. Their benefits remain yet controversial. The robotic-assisted systems allow an accurate and reproducible bone preparation due to a robotic interface, with a 3D surgical planning, based on preoperative 3D imaging or not. This promising system, nevertheless, has some limits. The new technologies in TKA are very attractive and have constantly evolved. Nevertheless, some limitations persist and could be improved by artificial intelligence and predictive modeling.

Load imbalances existed as determined by a sensor after conventional gap balancing with a tensiometer in total knee arthroplasty

PURPOSE

To evaluate intercompartmental load intraoperatively with a sensor after conventional gap balancing with a tensiometer during total knee arthroplasty (TKA).

METHODS

Fifty sensor-assisted TKA procedures were performed prospectively between August and September 2018 with a cruciate-retaining prosthesis. After applying a modified measured resection technique, conventional balancing between resected surfaces was achieved. The equal and rectangular flexion-extension gaps were confirmed using a tensiometer at 90° and 5°-7° (due to posterior tibial slope) of knee flexion. Then, the load distribution was evaluated intraoperatively with a sensor placed on trial implants in the positions of knee flexion (90° flexion) and extension (10° flexion).

RESULTS

The proportion of coronal load imbalance (medial load - lateral load ≥  ± 15 lb) was 56% in extension and 32% in flexion (p = 0.023). The proportion of sagittal load imbalance (extension load - flexion load ≥  ± 15 lb) was 36% in the medial compartment and 4% in the lateral compartment (p < 0.001). An additional procedure for load balancing was performed in 74% of knees.

CONCLUSIONS

Coronal and sagittal load imbalances existed as determined by the sensor even after the achievement of appropriate conventional gap balance. The additional rebalancing procedure was performed for balanced loads in 74% of the knees after conventional balancing. The use of an intraoperative load sensor offers the advantage of direct evaluation of the load on TKA implants.

LEVEL OF EVIDENCE

IV.

New mobile-bearing TKA with unique ball and socket post-cam mechanism offers similar function and stability with better prosthesis fit and gap balancing compared to an established fixed-bearing prosthesis

PURPOSE

A mobile-bearing (MB) posterior-stabilized total knee arthroplasty (TKA) system with ball and socket post-cam mechanism has been developed with the aims of better prosthesis fit and enhanced stability. However, the data are limited to compare its clinical outcomes with an already established fixed-bearing (FB) implant design.

METHODS

This is a prospective randomized study comparing 260 patients in the MB group and 133 patients in FB group with a minimum 2 years of follow-up. Intraoperative variables, post-operative functional outcomes and incidence of adverse events were compared.

RESULTS

MB group showed better prosthesis fit as the incidence of over-hang of femoral component at junction (medial: 1% vs. 5% and lateral: 2% vs 4%, p < 0.001) and trochlea (medial: 2% vs 30%, p = 0.042 and lateral: 13% vs 21%, p = 0.015) was less than FB group. MB group also showed better gap balancing as the incidence of medio-lateral gap difference more than 2 mm was less in flexion (2.3% vs. 16%, p < 0.001) and extension (3.1% vs. 9.8%, p = 0.005). Post-operative functional outcomes and incidence of adverse events showed no difference between the two groups at 2 years.

CONCLUSIONS

New MB design offers similar functional outcomes and stability along with better intraoperative prosthesis fit and gap balancing compared to an established fixed-bearing design. Hence, this new MB design could be an alternative prosthesis of choice for posterior-stabilized TKA.

LEVEL OF EVIDENCE

I.

What is a balanced knee replacement?

For multifactorial reasons an estimated 20% of patients remain unsatisfied after total knee arthroplasty (TKA).

Appropriate tension of the soft tissue envelope encompassing the knee is important in total knee arthroplasty and soft tissue imbalance contributes to several of the foremost reasons for revision TKA, including instability, stiffness and aseptic loosening.

There is debate in the literature surrounding the optimum way to achieve balancing of a total knee arthroplasty and there is also a lack of an accepted definition of what a balanced knee replacement is.

It may be intuitive to use the native knee as a model for balancing; however, there are many difficulties with translating this into a successful prosthesis.

One of the foundations of TKA, as described by Insall, was that although the native knee has more weight transmitted through the medial compartment this was to be avoided in a TKA as it would lead to uneven wear and early failure. There is a focus on achieving symmetrical tension and pressure and subsequent ‘balance’ in TKA, but the evidence from cadaveric studies is that the native knee is not symmetrically balanced.

As we are currently trying to design an implant that is not based on its anatomical counterpart, is it possible to create a truly balanced prosthesis or to even to define what that balance is? The authors have reviewed the current evidence surrounding TKA balancing and its relationship with the native knee.

Cite this article: EFORT Open Rev 2018;3:614-619. DOI: 10.1302/2058-5241.3.180008.

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.

Outcome in total knee arthroplasty with a medial-lateral balanced versus unbalanced gap

PURPOSE

To evaluate the clinical outcome in 108 total knee arthroplasty (TKA) patients with a medial-lateral balanced versus unbalanced gap after a mean follow-up of 34 months.

METHODS

64 women and 44 men (mean age, 69.5 years) underwent computer-assisted TKA for osteoarthritis using a cemented fixed-bearing cruciate-retaining prosthesis. The medial-lateral gap difference (measured with the prosthesis in situ and the patella reduced) was balanced (≤2 mm) in 81 patients and unbalanced (>2 mm) in 27 patients. After a mean follow-up of 34 months, patients were assessed using the Western Ontario and McMaster Universities Arthritis Index (WOMAC) questionnaire for pain, stiffness, and physical function. Scores were normalised to 0% (worst) to 100% (best).

RESULTS

The balanced and unbalanced gap groups were comparable in terms of age, severity of osteoarthritis, and proportion of pre- and post-operative mechanical alignment. Compared with the balanced gap group, the unbalanced gap group had a larger medial-lateral extension gap difference (0.75±0.57 vs. 2.02±1.15 mm, p=0.001) and medial-lateral flexion gap difference (0.79±0.63 vs. 2.98±2.13 mm, p=0.001) and lower normalised total WOMAC score (84.9±18 vs. 74.8±20.8, p=0.017).

CONCLUSION

WOMAC score is better in TKAs with a medial-lateral balanced (<2 mm) gap.

Comparison of soft tissue balancing, femoral component rotation, and joint line change between the gap balancing and measured resection techniques in primary total knee arthroplasty: A meta-analysis

BACKGROUND

This meta-analysis was designed to compare the accuracy of soft tissue balancing and femoral component rotation as well as change in joint line positions, between the measured resection and gap balancing techniques in primary total knee arthroplasty.

METHODS

Studies were included in the meta-analysis if they compared soft tissue balancing and/or radiologic outcomes in patients who underwent total knee arthroplasty with the gap balancing and measured resection techniques. Comparisons included differences in flexion/extension, medial/lateral flexion, and medial/lateral extension gaps (LEGs), femoral component rotation, and change in joint line positions. Finally, 8 studies identified via electronic (MEDLINE, EMBASE, and the Cochrane Library) and manual searches were included. All 8 studies showed a low risk of selection bias and provided detailed demographic data. There was some inherent heterogeneity due to uncontrolled bias, because all included studies were observational comparison studies.

RESULTS

The pooled mean difference in gap differences between the gap balancing and measured resection techniques did not differ significantly (-0.09 mm, 95% confidence interval [CI]: -0.40 to +0.21 mm; P = 0.55), except that the medial/LEG difference was 0.58 mm greater for measured resection than gap balancing (95% CI: -1.01 to -0.15 mm; P = 0.008). Conversely, the pooled mean difference in femoral component external rotation (0.77°, 95% CI: 0.18° to 1.35°; P = 0.01) and joint line change (1.17 mm, 95% CI: 0.82 to 1.52 mm; P < 0.001) were significantly greater for the gap balancing than the measured resection technique.

CONCLUSION

The gap balancing and measured resection techniques showed similar soft tissue balancing, except for medial/LEG difference. However, the femoral component was more externally rotated and the joint line was more elevated with gap balancing than measured resection. These differences were minimal (around 1 mm or 1°) and therefore may have little effect on the biomechanics of the knee joint. This suggests that the gap balancing and measured resection techniques are not mutually exclusive.

Flexion and extension gaps created by the navigation-assisted gap technique show small acceptable mismatches and close mutual correlations

PURPOSE

The aim of this study was to investigate the mechanism underlying the development of gap differences in total knee arthroplasty using the navigation-assisted gap technique and to assess whether these gap differences have statistical significance.

METHODS

Ninety-two patients (105 knees) implanted with cruciate-retaining prostheses using the navigation-assisted gap balancing technique were prospectively analysed. Medial extension and flexion gaps and lateral extension and flexion gaps were measured at full extension and at 90° of flexion. Repeated measures analysis of variance was used to compare the mean values of these four gaps. The correlation coefficient between each pair of gaps was assessed using Pearson's correlation analysis.

RESULTS

Mean intra-operative medial and lateral extension gaps were 20.6 ± 2.1 and 21.7 ± 2.2 mm, respectively, and mean intra-operative medial and lateral flexion gaps were 21.6 ± 2.7 and 22.1 ± 2.5 mm, respectively. The pairs of gaps differed significantly (P < 0.05 each), except for the difference between the medial flexion and lateral extension gaps (n.s.). All four gaps were significantly correlated with each other, with the highest correlation between the medial and lateral flexion gaps (r = 0.890, P < 0.001) and the lowest between the medial flexion and lateral extension gaps (r = 0.701, P < 0.001).

CONCLUSION

Medial and lateral flexion and extension gaps created using the navigation-assisted gap technique differed significantly, although the differences between them were <2 mm, and the gaps were closely correlated.

CLINICAL RELEVANCE

These narrow ranges of statistically acceptable gap differences and the strong correlations between gaps should be considered by surgeons, as should the risks of soft tissue over-release or unintentional increases in extension or flexion gap after preparation of the other gap.

Can we define envelope of laxity during navigated knee arthroplasty?

PURPOSE

Functional outcomes after knee arthroplasty (TKA) remain poor. The ability to restore the soft tissue envelope intraoperatively may improve such outcomes. The aim of this study was to extend the scope of computer navigation as a tool to quantifying the envelope of laxity during subjective stress testing preoperatively and to quantify the effects of knee replacement and how it changes as a result of ligamentous failure.

METHODS

Loaded cadaveric legs were mounted on a purpose-built rig. Envelope of laxity was measured in 3 degrees of freedom using computer navigation. Knees were subjectively stressed in varus/valgus, internal/external rotation and anterior draw. This was performed preoperatively, during TKA and after sequential sectioning of ligaments. Real-time data were recorded at 0°, 30°, 60° and 90° of flexion. Mixed effect modelling was used to quantify the effects of intervention on degree of laxity.

RESULTS

In all cases, there was an increase in laxity with increasing flexion or ligament sectioning. Operator and movement cycle had no effect. Insertion of a TKA showed increased stability within the joint, especially in internal/external rotation and anterior drawer. Once the PCL and popliteus were cut, the implant only maintained some rotatory stability; thereafter, the soft tissue envelope failed.

CONCLUSIONS

This work has shown a novel way by which computer navigation can be used to analyse soft tissue behaviour during TKA beyond the coronal plane and throughout range of motion. Despite subjective stress testing, our results show reproducible patterns of soft tissue behaviour-in particular a wide range of mid-flexion excursion. It also quantifies the limits within which a cruciate-retaining TKR can maintain knee stability. This functionality may guide the surgeon in identifying and/or preventing soft tissue imbalances intra-operatively, improving functional results.