Extension gap needs more than 1-mm laxity after implantation to avoid post-operative flexion contracture in total knee arthroplasty

Medial soft tissue release is also related to the anterior stability of cruciate-retaining total knee arthroplasty: a cadaveric study

BACKGROUND

Medial soft tissue release is occasionally performed to achieve mediolateral ligament balance in total knee arthroplasty (TKA), whose sequential effect on mediolateral and anteroposterior stability remains unclear. This study aimed to quantitatively evaluate the difference in mediolateral and anteroposterior stability according to a sequential medial soft tissue release in TKA.

METHODS

Cruciate-retaining TKA was performed in six cadaveric knees. Medial and lateral joint gaps, varus-valgus angle, and tibial anterior and posterior translations relative to the femur with pulling and pushing forces, respectively, were measured. All measurements were performed at full extension and 45° and 90° flexion after release of the deep medial collateral ligament (MCL) (stage 1), the posteromedial capsule (stage 2), and the superficial MCL (stage 3). Mediolateral and anteroposterior stability were compared between stages, and correlations between mediolateral and anteroposterior stability were analyzed.

RESULTS

Medial joint gap significantly increased from stages 1 to 3 by 3.2 mm, 6.8 mm, and 7.2 mm at extension, 45° flexion, and 90° flexion, respectively, and from stages 2 to 3 by 3.5 mm at extension. Varus-valgus angle was varus at stage 2, which turned to valgus at stage 3 (-2.7° to 0.8°, -2.2° to 4.3°, and -5.5° to 2.5° at extension, 45° flexion, and 90° flexion, respectively). Anterior translation at 90° flexion significantly increased from stages 1 and 2 to stage 3 by 11.5 mm and 8.2 mm, respectively, which was significantly correlated with medial gap (r = 0.681) and varus-valgus angle (r = 0.495).

CONCLUSIONS

Medial soft tissue release also increased tibial anterior translation as well as medial joint gap, and medial joint gap and tibial anterior translation were significantly correlated. Surgeons should be careful not to create too large medial joint gap and tibial anterior translation in flexion by excessive medial release up to the superficial MCL for achieving an equal mediolateral joint gap in extension.

Establishing femoral component rotation using a dynamic tensioner does not improve patellar position after total knee replacement with use of anatomic implants: A case-control study

BACKGROUND

Anterior knee pain (AKP) is one of the reasons for dissatisfaction after total knee replacement (TKR). It may result from patellofemoral joint dysfunction, caused by improper rotation of implant components. The aim of this study was to analyze patella positioning in patients after standard measured resection TKR and TKR with a use of a dynamic tensioner, and to assess the frequency of AKP, range of motion (ROM), and patient-reported outcome measures 6 weeks and 3 months postoperatively.

METHODS

The study consisted of 127 patients who underwent TKR. Eighty-nine of them treated with use of the dynamic tensioner FUZION formed the study group; the remainder formed the control group. All participants received cemented PERSONA MC without patella resurfacing. All patients had a standard anteroposterior, lateral weight-bearing, long-leg view X-ray and computed tomography examination in 30° of knee flexion following the procedure.

RESULTS

There were no significant differences between the study and the control groups regarding: posterior condylar axis (PCA)-patella angle, surgical transepicondylar axis (sTEA)-patella angle, PCA-sTEA angle, deviation from 90° in PCA-patella, sTEA-patella and PCA-sTEA angles. No significant difference was found in a ratio of obtaining PCA-patella angle deviation of more than 3°. Regarding clinical parameters, statistically and questionablly clinically significant difference in favor of the Study Group was found in Forgotten Joint Score 6 weeks and 3 months post-operativley and ROM 6 weeks post-operatively. However, such difference was not found by analyzing ROM 3 months post-operatively, AKP and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores.

CONCLUSION

Compared with the standard 3° of femoral component external rotation, use of a dynamic tensioner does not allow for more accurate restoration of the patellar facet position with reference to the PCA.

Increased Posterior Condylar Offset Decreases the Extension Gap in Cases With Flexion Contracture in Modified Gap Technique Total Knee Arthroplasty

Purpose There have been no reports comparing the change in medial and lateral posterior condylar offset (PCO) and the extension gaps. The purpose of this study was to elucidate the relationship between the change in medial and lateral PCO and the extension gap in total knee arthroplasty (TKA). The hypothesis is that an increase in both medial and lateral PCO can be a factor for a decrease in the extension gap, especially in cases of flexion contracture. Methods This retrospective study included 63 patients with medial osteoarthritis who underwent mobile-bearing PS-TKA using the modified gap techniques. Patients consisted of seven men (seven knees) and 53 women (56 knees), with the mean age of 76 (range, 58-88) years. The patients with valgus knee and cruciate retaining TKA were excluded. The medial ΔPCO (ΔPCO defined as the amount of change of the PCO before the resection of the posterior condyle and after the implant setting), lateral ΔPCO, the rotation angle of the posterior condyle osteotomy, and the gap differences were evaluated. The data were compared among three groups（Group A: ΔPCO increase on both sides, Group B: ΔPCO increase on only one side, Group C: ΔPCO decrease on both sides. The gap differences were compared between the cases with flexion contracture of ≥ 15° and the cases with flexion contracture of < 15°. The correlations between the gap differences and flexion contracture were evaluated in each group. Results There was no gap difference evident in any group (P≥0.05). The gap difference in Groups A (P=0.0067) and group C (P=0.0484) was significantly larger in cases with flexion contracture of ≥ 15° compared to those with flexion contracture of < 15°. Conclusions There was no correlation between the change in PCO and the extension gap. However, there was an inverse correlation between the flexion contracture and extension gap in cases with increased medial and lateral PCO.

Management of fixed flexion contracture in primary total knee arthroplasty: recent systematic review

INTRODUCTION

This study aimed to systematically review the literature and identify the surgical management strategy for fixed flexion contracture in primary total knee arthroplasty (TKA) surgery, pre-, intra-, and post-operatively. Secondary endpoints were etiologies and factors favoring flexion contracture.

MATERIALS AND METHODS

Searches were carried out in November 2023 in several databases (Pubmed, Scopus, Cochrane, and Google Scholar) using the following keywords: "flexion contracture AND TKA", "fixed flexion deformity AND TKA", "posterior capsular release AND TKA", "posterior capsulotomy in TKA", "distal femoral resection AND TKA". Study quality was assessed using the STROBE checklist and the Downs and Black score. Data concerning factors or strategies leading to the development or prevention of flexion contracture after TKA were extracted from the text, figures, and tables of the included references. The effect of each predictive factor on flexion contracture after TKA was recorded.

RESULTS

Thirty-one studies were identified to meet the inclusion and exclusion criteria. These studies described a variety of preoperative and intraoperative factors that contribute to the development or correction of postoperative flexion contracture. The only clearly identified predictor of postoperative flexion contracture was preoperative flexion contracture. Intraoperative steps described to correct flexion contracture were: soft-tissue balancing (in posterior and medial compartments), distal femoral resection, flexion of the femoral component, and posterior condylar resection. However, no study has investigated these factors in a global model.

DISCUSSION

This review identified various pre-, intra-, and post-operative factors predictive of post-operative flexion contracture. In practice, these factors are likely to interact, and it is therefore crucial to further investigate them in a comprehensive model to develop an algorithm for the management of flexion contracture.

LEVEL OF EVIDENCE

IV.

Can a Total Knee System Providing 1 mm Increment of Polyethylene Insert Thickness Offer a Clinical Benefit?

Background and Objectives: The purpose of this study was to compare clinical outcomes and polyethylene (PE) insert thickness between total knee arthroplasty (TKA) systems providing 1 mm and 2 mm increments. Materials and Methods: In this randomized controlled trial, 50 patients (100 knees) undergoing same-day or staggered bilateral TKA were randomized to receive a TKA system providing 1 mm increments in one knee (1 mm group) and a TKA system providing 2 mm increments in the other knee (2 mm group). At 2 years postoperatively, Knee Society Score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, Forgotten Joint Score (FJS), range of motion (ROM), and insert thicknesses were compared between the groups. Results: A total of 47 patients (94 knees) participated in follow-up analysis. In each group, patient-reported outcomes improved significantly after TKA (all, p < 0.05). There were no significant differences in patient-reported outcomes. The mean ROM was not significantly different between groups at preoperative and 2-year points. The rate of postoperative flexion contracture ≥ 5° was 2.1% and 4.3%, and the rate of postoperative recurvatum ≥ 5° was 4.3% and 2.1% in the 1 mm group and 2 mm, respectively (all, p = 1.000). Mean insert thickness was significantly thinner in the 1 mm group than the 2 mm group (p = 0.001). The usage rate of a thick insert (≥14 mm) was 12.7% and 38.3% in the 1 mm group and 2 mm group (p = 0.005). Conclusions: The use of a TKA system providing 1 mm PE insert thickness increments offered no clinical benefit in terms of patient reported outcomes over systems with 2 mm increments at 2 years of follow-up. However, the TKA system with 1 mm increments showed significantly thinner PE insert usage. As a theoretical advantage of 1 mm increments has yet to be proven, the mid- to long-term effects of thinner PE insert usage must be determined.

Effect of mediolateral gap difference on postoperative outcomes in navigation-assisted total knee arthroplasty using an ultracongruent insert and the medial stabilising technique

PURPOSE

This study was aimed to compare the clinical, functional, and radiographic outcomes between symmetric and asymmetric extension and mediolateral gap balance after navigation-assisted (NA) total knee arthroplasty (TKA) using ultracongruent (UC) insets and the medial stabilising technique (MST).

METHODS

In all, 363 knees of 275 patients who underwent mechanical alignment-target NA TKA with MST between January 2015 and December 2017 were analysed. Patients were divided into balanced (extension mediolateral gap difference ≤ 2 mm) and tight medial (difference ≥ 3 mm) groups. Pre- and postoperative clinical, functional (range of motion, Western Ontario and McMaster University Osteoarthritis [WOMAC] index, Knee Society Knee Score [KSKS], and Knee Society Function Score [KSFS]) and radiographic (hip-knee-ankle [HKA] angle, femoral condylar offset, extension angle [a minus indicates hyperextension], and joint line distance) outcomes were compared between the groups. Student's t- or Chi-squared test was used to compare the outcomes.

RESULTS

Among the 363 knees analysed, 279 (77%) were assigned to the balanced group and 84 (23%) to the tight medial group. The preoperative HKA angle was significantly greater in the tight medial group than in the balanced group (9.7° ± 4.1° vs 14.3° ± 4.7°, P < 0.001). The postoperative WOMAC index, KSKS, and KSFS were similar between the groups. The change in the joint line distance was not significantly different (1.5 ± 3.7 vs 2.0 ± 3.3; n.s).

CONCLUSION

The clinical, functional, and radiographic outcomes, including joint line distance, were comparable between the tight medial and balanced group after mechanical alignment-targeted UC TKA with MST.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

An electronic force sensor accurately detects increased but not decreased soft tissue tension in total knee arthroplasty

BACKGROUND

Postoperative knee instability is a leading cause of revision total knee arthroplasty (TKA). This study used a commercially available insert-shaped electronic force sensor to measure joint loads and facilitate ligament balance adjustment, and assessed the ability of this sensor to detect increased or decreased soft tissue tension during primary TKA.

METHODS

Changes in medial and lateral tibiofemoral joint loads during knee flexion were evaluated with sensor thicknesses ranging from 10 to 16 mm using six varus osteoarthritis cadaver knees with intact medial collateral ligaments (MCLs), and the measurements were repeated after MCL resection. Correlations between joint loads and maximum knee extension angle were also evaluated. To validate the efficacy of the sensor, the values were compared with those obtained using a conventional tension device.

RESULTS

For MCL-intact knees in extension, the medial joint load increased with sensor thickness. The maximum knee extension angle decreased with sensor thickness (ρ = -0.4), resulting in extension restriction up to -20°. Knee flexion contracture was below 5° when the total tibiofemoral joint load was below a cut-off of 42 lb. After the MCL was resected, medial joint loads remained unchanged at low values, even with increased sensor thickness. In contrast, the tension device clearly detected an increased gap as the degree of tension decreased.

CONCLUSIONS

The electronic sensor identified increased joint loads associated with increased ligament tension, and could predict knee flexion contracture during TKA. However, unlike the tension device, it did not accurately detect excessively decreased ligament tension.

What is the Optimal Posterior Cruciate Ligament Tension to Achieve Patient Satisfaction in Cruciate-Retaining Total Knee Arthroplasty?

INTRODUCTION

Achieving adequate posterior cruciate ligament (PCL) tension is important during PCL-retaining total knee arthroplasty (CR-TKA), but the effect of PCL release on this tension is unpredictable. This study assessed the relationship between postoperative PCL laxity and patient satisfaction at a 2-year follow-up.

METHODS

There were 44 varus osteoarthritis knees undergoing CR-TKA included. The PCL tension was adjusted by resizing the femoral component and modifying the posterior tibial slope, without PCL release. Postoperative PCL laxity at 90° of knee flexion was defined as the difference in radiographic anterior-posterior tibial translation with or without an 80-Newton posterior load at the tibial tubercle measured using a load device. Four subgroups were defined according to the PCL laxity: laxity ≤0 mm (n = 5); 0 mm < laxity ≤2 mm (n = 19); 2 mm < laxity ≤4 mm (n = 10); and laxity >4 mm (n = 10). The effect of PCL laxity on the 2-year postoperative 2011 Knee Society Score was determined.

RESULTS

The femoral component was downsized in 27 of 44 knees, while the posterior tibia slope was increased in 6 of 44 knees, but no PCL was released intraoperatively. The 2011 Knee Society Score subscores improved significantly from preoperatively to postoperatively, and patients reported "neutral satisfaction" or better after 96% of operations. The mean PCL laxity was 2.3 mm on postoperative stress radiographs, and postoperative satisfaction scores were significantly highest in the subgroup with 2-4 mm laxity.

CONCLUSION

CR-TKA was successfully performed without PCL release. Moderate PCL laxity (2-4 mm) achieved excellent postoperative satisfaction.

Evaluation of the balance function before and after total knee arthroplasty using Berg balance scale

INTRODUCTION

The purpose of this study was to evaluate balance function before and after total knee arthroplasty (TKA) using Berg balance scale (BBS). The study also aimed to identify factors associated with balance impairment.

MATERIALS AND METHODS

Ninety-three knees in 90 patients were prospectively evaluated using their BBS scores, passive knee extension/flexion angles, Visual analogue scale for pain scores, hip-knee-ankle angles, and knee extensor/flexor muscle strengths before and after TKA. A total BBS score of less than 45 indicates an enhanced risk of multiple falls. Multivariate logistic regression models were performed to elucidate factors associated with post-operative BBS score.

RESULTS

A significant difference in mean pre- and post-operative BBS scores were noted (49.3 ± 6.4 vs. 52.2 ± 4.7) (p < 0.05). The percentage of pre- and post-operative BBS scores less than 45 were 20% and 10% (p < 0.05). Rheumatoid Arthritis (RA), lower pre-operative BBS score, and larger post-operative knee flexion contracture were significantly associated with lower post-operative BBS score (p < 0.01). The post-operative knee flexion contracture greater than 10° was significantly associated with substantially high odds of post-operative BBS scores less than 45 (Odds ratio 7.6; 95% confidential interval 1.69-34.17).

CONCLUSIONS

While TKA significantly improved BBS scores, 10% of the patients remained at a risk for multiple falls. RA, lower pre-operative BBS score, and post-operative knee flexion contracture greater than 10° retained balance impairment even after TKA.

The knee position at tourniquet inflation does not affect the gap balancing during total knee arthroplasty

INTRODUCTION

The relationship between gap balancing and clinical outcome of total knee arthroplasty (TKA) has been researched. Tourniquet is widely used by most surgeons; however, there are little quantitative data about the gap depending on the tourniquet usage. We aimed to investigate whether the knee position at tourniquet inflation affected the gap measurement intra-operatively.

METHODS

TKA was performed for 104 knees and the tourniquet was inflated with the knee at full flexion and extension. The gap was measured in each static knee flexion status (0°, 30°, 45°, 60°, 90°, 120°, and in full flexion) using a tensor. We measured the gap twice; under the tourniquet inflation and release. The gap difference at each static knee flexion status was calculated by subtracting the gap under release from that under inflation.

RESULTS

When the tourniquet was inflated with the knee at full flexion, the mean gap differences were < 1 mm and < 1° in each static knee flexion status. When the tourniquet was inflated with the knee at full extension, the mean gap differences were < 1 mm and < 1°, respectively. All values of the gap difference were minimum, and were not affected by the tourniquet, whether the knee position at the tourniquet inflation was flexed or extended.

CONCLUSIONS

We postulated that the knee position at tourniquet inflation would affect the gap, which was refuted by our results. This shows that we can measure the gap without considering the knee position at tourniquet inflation.

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.

Hyperextension following two different designs of fixed-bearing posterior-stabilized total knee arthroplasty

PURPOSE

Hyperextension after total knee arthroplasty (TKA) is related to worse functional outcomes. Among the reported predictive factors, it is unclear whether prosthesis design affects postoperative hyperextension. Hence, our objectives were to (1) compare time-dependent changes of the extension angle following multi-radius (MR) and single-radius (SR) TKA and (2) assess predictive factors for the hyperextension.

METHODS

In this study, consecutive 136 MR TKAs and consecutive 71 SR TKAs performed by a single surgeon were reviewed. The extension angle was evaluated by digitized full-extension lateral radiographs at preoperative, 3 months and at 1 and 2 years after TKA. A positive value was defined as hyperextension. A multiple regression analysis was used to determine predictive factors for the extension angle and the risk of hyperextension > 5°.

RESULTS

The postoperative extension angle of both groups gradually increased during the first 2 years and the SR group finally progressed with 4.04° greater extension than the MR group (p < 0.01). The incidence of hyperextension > 5° in the SR group was 18.3% and for the MR group, 7.4% (p = 0.02). However, the Oxford knee scores was nonsignificant different between the groups (p = 0.15). Preoperative extension angle, sagittal femoral component angle (SFA) and SR prosthesis were predictive factors for the extension angle at 2 years after TKA and were also associated with hyperextension > 5°.

CONCLUSIONS

The extension angle of the SR group became significantly more extended than that of the MR group during the first two years after TKA. Hence, ideal extension position immediately after SR TKA may be different from that of the MR TKA prosthesis. The preoperative extension angle, SFA and SR prosthesis were factors that were associated with postoperative hyperextension.

Gender-specific difference in the recurrence of flexion contracture after total knee arthroplasty

Background

Range of motion after total knee arthroplasty (TKA) can impact patients’ daily lives. Nevertheless, flexion contracture (FC) often recurs after TKA, even upon achieving full extension intraoperatively. This study aimed to evaluate the relationship among preoperative, intraoperative, and postoperative knee extension angles, and clarify the risk factor for postoperative FC.

Methods

One hundred forty-seven knees undergoing TKA using a navigation system were evaluated. We measured the pre- and postoperative (6 months after TKA) extension angles using a goniometer, and intraoperative (before and after TKA) extension angle using a navigation system; the correlation between these angles at each time point was evaluated.

Results

The mean preoperative, intraoperative (before and after TKA) and postoperative extension angles were -9.9°, -6.8°, -0.1°, and -2.0°. Regarding intraoperative extension angle after TKA, 58 knees showed ≤ 5° hyperextension and six knees showed > 5° hyperextension. At 6 months, no cases showed hyperextension and 105 knees showed full extension. The mean intraoperative extension angle after TKA in the postoperative full extension group was 0.4°. A significant correlation was found among extension angles at each point (p<0.01, respectively). However, the intraoperative extension angle after TKA correlated with the postoperative extension angle only in females. Contrarily, the recurrence rate of FC was significantly higher in males than in females (p<0.01).

Conclusion

Intraoperative extension angles significantly correlated with pre- and postoperative extension angles in TKA. Moreover, intraoperative mild (≤ 5°) hyperextension is acceptable for postoperative full extension. There was a gender-specific difference in correlation between intra- and postoperative knee extension angles.

Level of evidence

III.

Comparison of risk for postoperative hyperextension between cruciate retaining and posterior stabilized total knee arthroplasties

INTRODUCTION

The incidence of postoperative hyperextension and factors affecting hyperextension needs to be investigated separately for cruciate retaining (CR) and posterior stabilized (PS) total knee arthroplasties (TKAs), because the mechanism for preventing hyperextension is different according to the bearing design. The purpose of the study was to compare the incidence of postoperative hyperextension between CR and PS TKAs and analyze the factors affecting the postoperative hyperextension.

METHODS

Matched 213 CR and PS TKAs with Persona^® prosthesis were retrospectively reviewed. The preoperative demographics, clinical and radiographic knee condition, and pelvic incidence were similar between groups. Appropriate knee extension (0°-5°), confirmed with a goniometer, was achieved intraoperatively. The knee sagittal angle was radiographically measured preoperatively and at 2 years postoperative. The incidence of hyperextension (sagittal angle < - 5°) was investigated. The factors affecting the postoperative hyperextension were analyzed in terms of age, sex, preoperative mechanical axis, knee sagittal angle, postoperative posterior tibial slope (PTS), change of posterior femoral offset, and pelvic incidence.

RESULTS

The knee sagittal angle was not significantly different preoperatively between CR and PS TKAs. The postoperative knee sagittal angle was 2.9° in CR TKAs and 4.4° in PS TKAs (p = 0.004). The incidence of postoperative hyperextension was 11.7% (25/213) in CR TKAs and 4.2% (9/213) in PS TKAs (p = 0.007). The preoperative sagittal angle, postoperative PTS, and pelvic incidence were the significant factors affecting the postoperative hyperextension in CR TKAs (odds ratio 0.869, 2.205, and 1.045, respectively); the preoperative sagittal angle was only the significant factor in PS TKAs (odds ratio 0.857) CONCLUSIONS: Postoperative knee hyperextension occurred more frequently and was affected by more factors in CR TKAs than PS TKAs. Efforts to avoid hyperextension and closed observation are required in TKAs performed in patients with the risk factors.

LEVEL OF EVIDENCE

III.

Intraoperative physiological lateral laxity in extension and flexion for varus knees did not affect short-term clinical outcomes and patient satisfaction

PURPOSE

Medial release during total knee arthroplasty (TKA) is used to correct ligament imbalance in knees with varus deformity. However, questions remain on whether residual ligament imbalance would be related to inferior clinical results. The purposes of the present study were to measure the intraoperative joint gap and to evaluate the effect of intraoperative soft tissue condition on the new Knee Society Score (KSS 2011) at 2-year follow-up, without the maneuver of additional medial release to correct the asymmetrical gap balance.

METHODS

Varus-valgus gap angle and joint gap were measured using a tensor device without medial release for 100 knees with preoperative varus deformity. The knees were categorized according to the varus-valgus gap angle and the laxity. The preoperative and postoperative clinical outcomes using KSS 2011 were compared between the groups.

RESULTS

The average varus-valgus angles had a residual imbalance of 2.8° varus and 1.3° varus in extension and flexion, respectively. In comparison, according to varus-valgus joint gap angle and knee laxity in extension and flexion, no significant differences were found in postoperative range of motion and subscale of KSS 2011 among the groups.

CONCLUSION

Intraoperative asymmetrical joint gap and physiological laxity do not affect early clinical results after TKA.

LEVEL OF EVIDENCE

III.

Multi-radius posterior-stabilized mobile-bearing total knee arthroplasty partially produces in-vivo medial pivot during activity of daily living and high demanding motor task

PURPOSE

The purpose of the present study was to assess the kinematical behavior of a multi-radius posterior-stabilized (PS) mobile-bearing (MB) total knee arthroplasty (TKA) during an activity of daily living (Sit-To-Stand-STS) and a high demanding motor task (Deep-Knee-Lunge-DKL) using model-based dynamic RSA. We hypothesized the achievement of medial pivoting movement in both motor tasks due to the congruent geometry of the inlay with the femoral component, which should allow good stability of the medial compartment, and to the high magnitude of rotations guaranteed by the MB on the tibial side.

METHODS

Twenty-two randomly selected patients were recruited and prospectively evaluated. The PS MB cemented TKA was implanted with the standard technique (medial parapatellar approach, adjusted mechanical alignment). At minimum 9-month follow-up, patients were examined with model based Dynamic RSA developed in our Institute (BI-STAND DRX 2) during the execution of two motor tasks: STS and DKL. The motion parameters were evaluated using the Grood and Suntay decomposition and the low-point kinematics methods.

RESULTS

In the extension phase of DKL femur performed a greater antero posterior translation of 3.8 mm compared to STS between 0° and 20° of knee flexion (p < 0.05). Low-point analysis showed a medial pivoting movement in both motor tasks: in 62% of patients during STS and 48% during DKL. Varus-valgus rotations were lower than 1° during all the range-of-motion in both motor tasks without differences.

CONCLUSIONS

Medial pivot was partially produced by this multi-radius PS MB TKA with some differences during activity of daily living (STS) and high demanding motor task (DKL).

LEVEL OF EVIDENCE

IV.

Coronal and sagittal laxity affects clinical outcomes in posterior-stabilized total knee arthroplasty: assessment of well-functioning knees

PURPOSE

Both coronal and sagittal laxity of well-functioning knees after total knee arthroplasty (TKA) was examined, and the correlations between the joint laxity and the clinical outcomes were analyzed to clarify the adequate joint laxity for the prosthesis, and the relationship between the laxity and the outcomes.

METHODS

Forty well-functioning TKA knees with a high-flexion posterior-stabilized (PS) prosthesis were studied. All patients were diagnosed as having osteoarthritis with varus deformity and were followed up for 2 years or more. The coronal and sagittal laxity was assessed at extension and flexion, and the correlations between the joint laxity and the clinical outcomes were evaluated.

RESULTS

The varus and valgus laxity averaged 5.6 ± 1.8° and 3.6 ± 1.2° at 10° knee flexion, and 7.4 ± 5.1° and 3.6 ± 2.7° at 80° knee flexion, respectively, and the AP laxity at 30° and 75° knee flexion averaged 8.7 ± 3.6 mm and 6.6 ± 2.3 mm, respectively. Knee flexion angle correlated with the joint laxity, while the other outcomes including patient-reported pain and instability were adversely affected by the greater laxity.

CONCLUSIONS

This study exhibited the importance of consistent medial laxity both at extension and flexion, which averaged 3.6°. Care should be taken to maintain the medial stability and to obtain adequate laxity both at extension and flexion during surgery. A few degrees of medial tightness can be allowed to achieve excellent clinical results after TKA for preoperative varus knees.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

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.

Gradual change in knee extension following total knee arthroplasty using ultracongruent inserts

BACKGROUND

Total knee arthroplasty (TKA) using an ultracongruent (UC) insert is widely performed. Lack of the posterior cruciate ligament or post-cam mechanism is a concern in terms of range of motion. The flexion angle of UC TKA had been well investigated; however, natural history and correlation factors of the postoperative extension angle have not been well documented. This study aimed to investigate time-dependent changes in extension after TKA using UC inserts, and to evaluate factors that correlated with the postoperative extension angle.

METHODS

This study reviewed 388 gap-balanced UC TKAs (331 patients) without hyperextension at navigation and performed between November 2010 and December 2014. The extension angle (a positive number indicates hyperextension) was measured on full-extension lateral radiographs. The extension angles from five days post-operation to final follow-up were investigated. Factors correlated with the postoperative extension angle were evaluated using multiple regression analysis.

RESULTS

Mean follow-up duration was 46.2 months. Until two years, the extension angle gradually increased; mean angles at five days/six months/one year/two years/and final follow-up were: -9.2°/-2.6°/0.6°/1.0°/1.0°, respectively. Female sex (β = -0.15, P = 0.002) and pre-operative hyperextension (β = 0.31, P < 0.001) were associated with postoperative hyperextension deformity.

CONCLUSIONS

Following UC TKA, knees became gradually more extended until two years post-operation. Sex and pre-operative extension angle were predictive factors for the postoperative extension angle following UC TKA.

LEVEL OF EVIDENCE

Level 4, Case series.

Changes in postoperative extension angle after total knee arthroplasty: Effect of polyethylene insert thickness

BACKGROUND

Flexion contracture is a serious complication after total knee arthroplasty (TKA). Polyethylene insert (PE) thicker than the extension gap during surgery causes flexion contracture. The purpose of this study was to identify the changes over time in postoperative extension angle and the correlation between extension gap and PE thickness.

METHODS

Overall, 127 knees were analyzed to evaluate the changes in extension angle over time. "Gap difference" was defined as the distance obtained by subtracting the extension gap from the PE thickness. Patients were divided into four groups according to gap difference (0-3 or greater mm). We evaluated the correlation of gap difference and changes in postoperative extension angle over time.

RESULTS

The extension angles of all knees were -4.2 ± 3.9 (deg. mean ± s.d.) at surgery, -5.9 ± 5.7 at 3 months, -3.4 ± 5.4 at 6 months, and -1.3 ± 5.4 at 2 years. Gap difference was negatively correlated with the extension angle at surgery and at 2 years (r = 0.40, r = 0.36). The extension angles at 2 years in each group (groups 0, 1, 2, 3 or greater) were 2.0°±4.7°, -0.8°±5.3°, -3.4°±5.3°, -4.0°±4.1° (p < 0.05), respectively.

CONCLUSIONS

The extension angle became worse at 3 months compared to that at surgery (p = 0.01) and then improved until 2 years. The correlation between gap difference and extension angle was maintained at 2 years, and thicker PE caused flexion contracture even after 2 years. Hence, PE selection considering the extension gap is important.

Posterior capsular release is a biomechanically safe procedure to perform in total knee arthroplasty

PURPOSE

Surgeons may attempt to strip the posterior capsule from its femoral attachment to overcome flexion contracture in total knee arthroplasty (TKA); however, it is unclear if this impacts anterior-posterior (AP) laxity of the implanted knee. The aim of the study was to investigate the effect of posterior capsular release on AP laxity in TKA, and compare this to the restraint from the posterior cruciate ligament (PCL).

METHODS

Eight cadaveric knees were mounted in a six degree of freedom testing rig and tested at 0°, 30°, 60° and 90° flexion with ± 150 N AP force, with and without a 710 N axial compressive load. After the native knee was tested, a deep dished cruciate-retaining TKA was implanted and the tests were repeated. The PCL was then cut, followed by releasing the posterior capsule using a curved osteotome.

RESULTS

With 0 N axial load applied, cutting the PCL as well as releasing the posterior capsule significantly increased posterior laxity compared to the native knee at all flexion angles, and CR TKA states at 30°, 60° and 90° (p < 0.05). However, no significant increase in laxity was found between cutting the PCL and subsequent PostCap release (n.s.). In anterior drawer, there was a significant increase of 1.4 mm between cutting the PCL and PostCap release at 0°, but not at any other flexion angles (p = 0.021). When a 710 N axial load was applied, there was no significant difference in anterior or posterior translation across the different knee states (n.s.).

CONCLUSIONS

Posterior capsular release only caused a small change in AP laxity compared to cutting the PCL and, therefore, may not be considered detrimental to overall AP stability if performed during TKA surgery.

LEVEL OF EVIDENCE

Controlled laboratory study.

No detrimental effect of ligament balancing on functional outcome after total knee arthroplasty: a prospective cohort study on 129 mechanically aligned knees with 3 years' follow-up

Background and purpose - In the classical mechanical alignment technique, ligament balancing is considered a prerequisite for good function and endurance in total knee arthroplasty (TKA). However, it has been argued that ligament balancing may have a negative effect on knee function, and some authors advocate anatomic or kinematic alignment in order to reduce the extent of ligament releases. The effect of the trauma induced by ligament balancing on functional outcome is unknown; therefore, the aim of this study was to investigate this effect. Patients and methods - 129 knees (73 women) were investigated. Mean age was 69 years (42-82), and mean BMI was 29 (20-43). Preoperatively 103 knees had a varus deformity, 21 knees had valgus deformity, and 5 knees were neutral. The primary outcome measure was the Knee injury and Osteoarthritis Outcome Score (KOOS). Secondary outcome measures were the Oxford Knee Score (OKS) and patient satisfaction (VAS). All ligament releases were registered intraoperatively and outcome at 3 years' follow-up in knees with and without ligament balancing was compared Results - 86 knees were ligament balanced and 43 knees were not. Ligament-balanced varus knees had more preoperative deformity than varus knees without ligament balancing (p = 0.01). There were no statistically significant differences in outcomes between ligament-balanced and non-ligament-balanced knees at 3 years' follow-up. No correlation was found between increasing numbers of soft tissue structures released and outcome. Interpretation - We did not find any negative effect of the trauma induced by ligament balancing on knee function after 3 years.

Intraoperative medial joint laxity in flexion decreases patient satisfaction after total knee arthroplasty

INTRODUCTION

The relationship between postoperative tibiofemoral ligament balance and patient satisfaction in total knee arthroplasty (TKA) has been explored previously. However, the optimal intraoperative medial-lateral ligament balance during knee flexion in terms of postoperative patient satisfaction remains unknown. We evaluated the effect of intraoperative flexion instability on patient satisfaction after TKA.

MATERIALS AND METHODS

This study consisted of 46 knees with varus osteoarthritis undergoing TKA. Medial-lateral component gaps at 0° knee extension and 90° flexion were measured intraoperatively using a knee balancer. Differences in postoperative patient outcomes at 3 weeks and 1 year were compared between medially tight knees in 90° flexion with a medial component gap of < 4 mm and medially loose knees in 90° flexion with a gap of ≥ 4 mm. Outcomes were measured using the 2011 Knee Society Scoring System (2011 KS).

RESULTS

The median total 2011 KS score at 1 year postoperatively in the medially loose knees [median 97; interquartile range (IQR) 75-117] was significantly lower than that in the medially tight knees (median 128; IQR 104-139, P < 0.01), while preoperative and 3-week postoperative scores were similar. In addition, medial flexion gaps were not significantly associated with total 2011 KS scores before surgery or at 3 weeks postoperatively. However, at 1 year after surgery, medial component flexion gaps were negatively associated with the total 2011 KS score (R = - 0.42; P < 0.01) and the 2011 KS satisfaction subscale score (R = - 0.36; P = 0.01).

CONCLUSIONS

Excessive intraoperative medial joint laxity of ≥ 4 mm at 90° flexion progressively decreased patient satisfaction for 1 year. Since intraoperative medial laxity in flexion is likely to interfere with functional recovery after TKA, medial stabilization during TKA is important throughout knee flexion.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Factors affecting the incidence and management of fixed flexion deformity in total knee arthroplasty: A systematic review

PURPOSE

This study aimed to systematically review the literature and identify factors which would contribute to the intraoperative correction of FFD to frame a potential surgical algorithm or predictive model to guide intraoperative decision-making.

METHODS

Electronic searches of six databases were undertaken in April 2016 according to the PRISMA guidelines, and the reference lists of studies searched. Quality of studies was assessed using the STROBE checklist, and the Downs and Black Scores.

RESULTS

Twenty-five studies investigating 10, 679 knees were found to satisfy the inclusion and exclusion criteria. These studies described a variety of pre-operative and intra-operative factors which contribute to the development or correction of post-operative FFD. The only patient predictor of post-operative FFD was pre-operative FFD. The intra-operative steps described to correct FFD were: distal femoral resection, soft-tissue balancing (in the posterior and medial compartments), sagittal component flexion and posterior condylar offset. However, no studies investigated these in an integrated model.

CONCLUSION

This review has identified various pre-, intra- and post-operative factors predictive of post-operative FFD. In practice, these factors are likely to interact, and therefore further investigation in an integrated model is crucial to developing a statistically sound and reliable intraoperative algorithm for surgeons to follow when correcting fixed flexion deformity.

Influence of soft tissue balancing and distal femoral resection on flexion contracture in navigated total knee arthroplasty

PURPOSE

The purpose of this study was to evaluate the influence of intra-operative soft tissue balancing and distal femoral cutting on flexion contracture in navigated TKA.

METHODS

This was a prospective cohort study. Fifty-nine patients of primary navigation-assisted TKA were included with over 15° of flexion contracture and excluded valgus knees. Among the cases, 43 cases were performed with soft tissue balancing procedures only, and 16 cases were performed with soft tissue balancing and additional distal femoral bone cutting. The mean preoperative flexion contracture was 17.5° ± 2.7°. The angles of flexion contracture were recorded at each surgical step with navigation.

RESULTS

The mean difference in flexion contracture angle between initial angle and angle after medial release was 5.2° ± 2.8°. The mean difference in flexion contracture angle between medial release step and after posterior cruciate ligament (PCL) release was 2.5° ± 2.2°. The mean difference in flexion contracture angle between PCL release step and after routine bone cutting was 3.1° ± 3.2°. The mean difference in flexion contracture angle between after trial insertion and after posterior clearing procedure was 2.7° ± 1.9°. Among the cases, TKA with 2 mm additional bone cutting were performed in 16 cases. The mean difference in flexion contracture angle after additional femoral bone cutting was 4.8° ± 2.1°.

CONCLUSION

The medial release and 2 mm additional bone cutting could correct flexion contracture by 5°. The appropriate soft tissue balancing and bone cutting could correct flexion contracture intra-operatively up to 5° in each step.

LEVEL OF EVIDENCE

II.

Patient-related factors influence stiffness of the soft tissue complex during intraoperative gap balancing in cruciate-retaining total knee arthroplasty

PURPOSE

How much force is needed to pre-tension the ligaments during total knee arthroplasty? The goal of this study was to determine this force for extension and flexion, and for both compartments, and to identify predicting patient-related factors.

METHODS

Eighty patients [55 females, mean age 71 (SD 9.7)] were recruited and had a navigated cruciate-retaining total knee arthroplasty. Distraction of the medial and lateral compartments of the extension and flexion gap (90°) with an instrumented bi-compartmental double-spring tensioner took place after finishing the bone cuts. Applied forces and resulting gap distances were recorded by the navigation system, resulting in a force-elongation curve. Lines were fitted with the intersection defined as the stiffness transition point. The slopes (N/mm) represented the stiffness of the ligamentous complex. Linear multiple regression analysis was performed to identify predicting factors.

RESULTS

The amount of force at the stiffness transition point was on average 52.3 (CI₉₅ 50.7-53.9), 54.5 (CI₉₅ 52.7-56.3), 48.3 (CI₉₅ 46.2-50.2), and 59.3 (CI₉₅ 57.0-61.6) N for the medial and lateral extension and flexion gap, respectively, and varied considerably between patients. The force at the stiffness transition point was significantly different between extension and flexion and both compartments (P < 0.05). Stiffness of the ligaments statistically significantly helped to predict the amount of force at the stiffness transition point, as well as body mass index, gender, and varus-valgus alignment.

CONCLUSION

The amount of force at the stiffness transition point varies between 48 and 59 N, depending on flexion/extension and compartment. Patient-related factors influence the stiffness transition point and can help predict the stiffness transition point. When forces higher than 60 N are used for gap distraction, the ligamentous sleeve of the knee might be over-tensioned.

LEVEL OF EVIDENCE

Prognostic study, Level I-high-quality prospective cohort study with >80 % follow-up, and all patients enrolled at same time point in disease.

Effects of Cementing on Ligament Balance During Total Knee Arthroplasty

Complications related to joint imbalance may contribute to some of the most predominant modes of failure in total knee arthroplasty (TKA). These complications include instability, aseptic loosening, asymmetric component wear, and idiopathic pain. Fixation may represent a step that introduces unchecked variability into the procedure and may contribute to the incidence of joint imbalance-related complications. The ability to quantify in vivo loading in the medial and lateral compartments would allow for the ability to confirm balance after fixation and prior to wound closure. This retrospective study sought to capture any variability and imbalance associated with cementing technique. A total of 93 patients underwent sensor-assisted TKA. All patients were confirmed to have quantifiably balanced joints prior to cementation. After cementing and final component placement, the sensor was reinserted into the joint to capture any cementation-induced changes in loading. Imbalance was observed in 44% of patients after cementation. There was no difference in the proportion of imbalance due to surgeon experience (P=.456), cement type (P=.429), or knee system (P=.792). A majority of knees exhibited loading increase in the medial compartment. It was concluded that cementation technique contributes to a significant amount of balance-related variability at the fixation stage of the procedure. The use of the sensor in this study allowed for the correction of all instances of imbalance prior to closure. More objective methods of balance verification may be important for ensuring optimal surgical outcomes. [Orthopedics. 2017; 40(3):e455-e459.].

Decreased extension gap and valgus alignment after implantation of total knee prosthesis in primary varus knees

PURPOSE

It was hypothesised that implantation of a total knee prosthesis may change the size and shape of the joint gap. To test this hypothesis, a tensor device was used which was specifically designed to reproduce the conditions before and after implantation, including attachment of the polyethylene insert trial. This study aimed to compare the joint gaps before and after implantation of a total knee prosthesis using this new tensor device.

METHODS

A total of 259 primary varus knees were included in this study. Knees were exposed using a medial parapatellar approach, and the anterior and posterior cruciate ligaments were resected. After the trial reduction, the intraoperative joint gap kinematics was measured using the tensor device.

RESULTS

Implantation of a total knee prosthesis decreased the size of the extension joint gap and made it valgus, but did not influence the size or shape of the flexion joint gap.

CONCLUSIONS

The present findings suggest that the classical gap technique, which creates equal and rectangular extension and flexion joint gaps in the bone cutting surface, results in an imbalance between the extension and flexion joint gaps after implantation. To achieve equal and rectangular extension and flexion joint gaps after implantation, the prepared extension joint gap should be about 2 mm larger than the flexion joint gap and slightly varus before implantation in primary varus knees.

LEVEL OF EVIDENCE

Therapeutic study, Level II.

Capsular release around the intercondylar notch increases the extension gap in posterior-stabilized rotating-platform total knee arthroplasty

BACKGROUND

In posterior-stabilized (PS) total knee arthroplasty (TKA), various post-cam designs can be used. A larger cam of the femoral component may tighten the extension gap. Few studies have investigated the relationship between capsular release around the intercondylar notch and the extension gap. The aim of this study was to assess the effect of capsular release around the intercondylar notch on the extension gap.

METHODS

Forty-eight patients (54 knees) who underwent PS rotating-platform TKA (PFC Sigma RP-F) were enrolled retrospectively. We measured the extension gap with and without a femoral trial using a knee balancer, applying a joint distraction force of 44lb. When an intraoperative flexion contracture of >5° persisted, we performed a capsular release approximately 10mm cranial to the intercondylar notch. After full knee extension was achieved, the extension gap was measured again.

RESULTS

Thirty knees required capsular release. With a trial, the medial and lateral differences between the extension gaps before and after capsular release were 1.7mm (p<0.0001) and 2.3mm (p<0.0001), respectively. Without a trial, the gaps were enlarged by 0.4mm (p=0.0452) and 0.6mm (p=0.0215), respectively. Twenty-four knees did not require release. No significant differences were noted in the range of motion at one-year follow-up between the two cohorts.

CONCLUSIONS

With PS rotating-platform TKA, capsular release around the intercondylar notch is found to increase the extension gap and may prevent postoperative flexion contracture.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Assessing coronal laxity in extension and flexion at a minimum of 10 years after primary total knee arthroplasty

PURPOSE

Favourable long-term results after total knee arthroplasty (TKA) require appropriate soft tissue balance. However, the relationships between long-term results after TKA surgery and mediolateral laxities at extension and at 90° flexion remain unknown. This study therefore quantitatively assessed ligament balance at extension and at 90° knee flexion at least 10 years after primary TKA, as well as clarifying the relationships between long-term outcomes and mediolateral laxities.

METHODS

This study included 49 knees (19 CR type and 30 PS type) of 33 patients followed up for at least 10 years after TKA at our hospital. Plain radiographs were obtained with about 150 N of varus or valgus stress using a Telos arthrometer at extension. At 90° flexion, epicondylar views were obtained under a 1.5-kg load and with about 10 kg of varus or valgus stress.

RESULTS

Lateral laxity of about 5° was observed in both extension and flexion, with total laxities of varus and valgus stress each less than 10°. Postoperative clinical outcomes were good, with significant improvements in extension angle, femorotibial angle, and KSS, and no loosening in any knee.

CONCLUSIONS

Good long-term results of TKA can be obtained with a lateral laxity of about 5°, equivalent to that of healthy knees.

LEVEL OF EVIDENCE

III.

The influence of posterior tibial slope changes on joint gap and range of motion in unicompartmental knee arthroplasty

BACKGROUND

The effect of posterior slope on joint gap in unicompartmental knee arthroplasty (UKA) has yet to be quantified. The purpose of this study was to quantify the effect of the tibial slope on the joint component gap and postoperative range of motion in UKA.

METHODS

Forty consecutive patients were prospectively enrolled. The correlation between the tibial slope changes and the component gap, the component gap difference between flexion angles, the postoperative extension or flexion angles was examined. The correlation of joint looseness with tibial slope changes and postoperative extension angle was also examined.

RESULTS

Increased tibial slope positively correlated with the differences between the component gap at 90° and 10°, 120° and 10°, or 135° and 10° knee flexion angle. Although tibial slope change did not affect postoperative flexion angle, increased tibial slope reduced postoperative extension angle. Moreover, increased tibial slope resulted in decreased joint looseness during 10° of knee flexion and decreased joint looseness during 10° of knee flexion resulted in reduced postoperative extension angle.

CONCLUSIONS

Increased tibial slope resulted in tight component gap at knee extension compared with that at knee flexion. Furthermore, tight component gap at extension lead to decreased postoperative extension angle. These results indicate that an individual anatomical tibial slope should be considered when tibial sagittal osteotomy was performed and increasing tibial slope should be avoided to achieve full extension angle after UKA.

LEVEL OF EVIDENCE

II.

Ligament balancing in total knee arthroplasty-Medial stabilizing technique

Ligament balancing is one of the most important surgical techniques for successful total knee arthroplasty. It has traditionally been recommended that medial and lateral as well as flexion and extension gaps are equal. This article reviews the relevant literature and discusses the clinical importance of the aforementioned gaps. Current evidence indicates that achieving medial stability throughout the range of motion should be a high priority in ligament balancing in total knee arthroplasty. Finally, the medial stabilising surgical technique, which aims to achieve good medial stability in posterior cruciate-retaining total knee arthroplasty, is introduced.

Evaluation of spacer block technique using tensor device in unicompartmental knee arthroplasty

INTRODUCTION

Mobile-bearing unicompartmental knee arthroplasty (UKA) was designed so that flexion and extension gap adjustments could achieve isometric function of the ligaments throughout ROM to prevent complications. However, achieving accurate knee balancing using a spacer block technique remains difficult since determination of the thickness of the spacer block is determined according to the feeling of the individual surgeon's hand. The objective of the study was to investigate flexion and extension medial unicompartmental knee gap kinematics in mobile-bearing UKA and to reveal the accuracy of spacer block measurement technique using a gap tensor device.

MATERIALS AND METHODS

Mobile-bearing UKA was performed in 40 knees of 31 subjects using generally accepted spacer block technique so that the extension gap was made equal to the flexion gap. The extension and flexion gaps of the medial knee compartment were measured using the tensor device with 25, 50, 75, 100, 125, and 150 N of joint distraction force. The interplay gap was calculated by subtracting the thickness of the tibial prosthesis and the thickness of the selected size of bearing from the measured extension and flexion gaps. Medial compartmental joint interplay gap differences were compared among flexion and extension gaps.

RESULTS

The mean flexion interplay gap was 25 N: 0.5 mm, 50 N: 1.5 mm, 75 N: 2.4 mm, 100 N: 3.1 mm, 125 N: 3.6 mm, 150 N: 4.0 mm. The mean extension interplay gap was 25 N: -0.2 mm, 50 N: 0.81 mm, 75 N: 1.7 mm, 100 N: 2.5 mm, 125 N: 3.1 mm, 150 N: 3.5 mm. The measured extension gap was shown to be significantly smaller compared with the flexion gap at every joint distraction force (P < 0.01).

CONCLUSIONS

These results suggest that gap measurement using a spacer block in UKA has the potential risk that the resulting extension gap may be smaller than the flexion gap. Surgeons should adjust the flexion and extension gaps with caution to achieve good ligament function when performing mobile-bearing UKA.

Influence of Intraoperative Soft Tissue Balance on Postoperative Active Knee Extension in Posterior-Stabilized Total Knee Arthroplasty

We evaluated the influence of intraoperative soft tissue balance on postoperative active knee extension using Offset Repo-Tensor® among 73 varus osteoarthritic knees underwent primary posterior-stabilized total knee arthroplasty. The joint center gap between osteotomized surfaces and the component gap after femoral trial component placement were measured using a joint distraction force of 40lb. The active knee extension angle was measured 4weeks after surgery. The postoperative extension angle was not correlated with the joint center gap at 0°, but positively correlated with the component gap at 0°, and the joint looseness at 0° which was calculated by subtracting insert thickness from the component gap. Thus, intraoperative soft tissue measurement with femoral trial component placement would be useful to predict the postoperative knee extension angle.

Intraoperative ligament laxity influences functional outcome 1 year after total knee arthroplasty

PURPOSE

To find out if there is an association between ligament laxity measured intraoperatively and functional outcome 1 year after total knee arthroplasty (TKA).

METHODS

Medial and lateral ligament laxities were measured intraoperatively in extension and in 90° of flexion in 108 patients [122 knees; median age 70 (range 42-83) years]. Mechanical axes were measured preoperatively and at 1-year follow-up. Outcome measures were the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Knee Society Clinical Rating System, the Oxford Knee Score and patient satisfaction. The relationships between laxity and outcome scores were examined by median regression analyses.

RESULTS

Post-operative mechanical axis had a significant effect on the association between ligament laxity and KOOS. Therefore, the material was stratified on post-operative mechanical axis. In perfectly aligned and valgus-aligned TKAs, there was a negative correlation between medial laxity and all subscores in KOOS. The most important regression coefficient (β) was recorded for the effect of medial laxity in extension on activities of daily living (ADLs) (β = -7.32, p < 0.001), sport/recreation (β = -6.9, p = 0.017) and pain (β = -5.9, p = 0.006), and for the effect of medial laxity in flexion on ADLs (β = -3.11, p = 0.023) and sport/recreation (β = -4.18, p = 0.042).

CONCLUSIONS

In order to improve the functional results after TKA, orthopaedic surgeons should monitor ligament laxity and mechanical axis intraoperatively and avoid medial laxity more than 2 mm in extension and 3 mm in flexion in neutral and valgus-aligned knees.

LEVEL OF EVIDENCE

II.