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Neither Anterior nor Posterior Referencing Consistently Balances the Flexion Gap in Measured Resection TKA: A Computational Analysis
Abstract
Background:
Whether anterior referencing (AR) or posterior referencing (PR) produces a more balanced flexion gap in total knee arthroplasty (TKA) using measured resection remains controversial. Our goal was to compare AR and PR in terms of (1) medial and lateral gaps at full extension and 90° of flexion, and (2) maximum medial and lateral collateral ligament (MCL and LCL) forces in flexion.
Methods:
Computational models of 6 knees implanted with posterior-stabilized TKA were virtually positioned with both AR and PR techniques. The ligament properties were standardized to achieve a balanced knee at full extension. Medial-lateral gaps were measured in response to varus and valgus loading at full extension and 90° of flexion; MCL and LCL forces were estimated during passive flexion.
Results:
At full extension, the maximum difference in the medial-lateral gap for both AR and PR was <1 mm in all 6 knee models. However, in flexion, only 3 AR and 3 PR models produced a difference in medial-lateral gap <2 mm. During passive flexion, the maximum MCL force ranged from 2 N to 87 N in AR and from 17 N to 127 N in PR models. The LCL was unloaded at >25° of flexion in all models.
Conclusion:
In measured resection TKA, neither AR nor PR better balance the ligaments and produce symmetrical gaps in flexion. Alternative bone resection techniques and rotation alignment targets are needed to achieve more predictable knee balance.
... Yau [13] found that 56%,72% and 60% of femoral rotation exceeded the normal range when resection was performed using the TEA, PCA and AP, respectively. GB technique was proposed by Freeman and Install [14][15][16]. Based on the balance of soft tissue and ligament tension, the distal femoral flexion and extension resection are parallel to the tibial proximal platform. ...
Background
Total knee arthroplasty (TKA) is performed by gap balance (GB) and measured resection (MR) techniques for femoral rotation resection to achieve knee flexion balance and knee stability. It is still controversial to choose which technique is more advantageous. The purpose of this study was to compare the early clinical efficacy of GB and MR in TKA.
Methods
This study was a prospective randomized, double-blind controlled trial. From March 2018 to March 2019, 99 patients (99 knees) who underwent TKA at our institution were randomly treated with GB and MR. The cutting thickness of posterior condyle, radiographic findings, medial and lateral compartment pressure, gait analysis, and patients satisfaction were recorded.
Results
A total of 110 patients were enrolled for unilateral THA. Finally, 99 patients were included for analysis and comparison at 12 months follow-up. In GB group, the angle of Cutting Block to PCA was significantly lower than in the MR group (P<0.001) and the cutting thickness of the medial and lateral condyle was significantly higher than in the MR group (P<0.05). Medial compartment pressure was significantly higher than lateral compartment at 90° flexion and full flexion in MR (P<0.05). In GB group, Sagittal max knee flexion range and transversal knee rotation range was significantly was significantly larger than that in the MR group (P<0.05). In level of satisfaction at the most recent follow-up, there was no significant difference between the two groups (p>0.05).
Conclusion
In TKA, GB or MR techniques for femoral external resection has little effect on daily walking. However, the GB technique has advantages in early postoperative knee stability and knee flexion function improvement.
Background
Surgeons may resect additional distal femur during primary posterior stabilized (PS) total knee arthroplasty (TKA) to correct a flexion contracture. However, the resultant joint line elevation (JLE) increases midflexion laxity. We determined whether a mid-level constraint (MLC) insert reduced mid-flexion laxity after JLE.
Methods
Six computational knee models were developed using CT scans and average soft tissue properties yielding balanced extension gaps but with a 10° flexion contracture. Distal femoral resections of +2 and +4 mm were simulated with PS and MLC inserts. Varus-valgus (VV) ±10 Nm moments were applied at 30°, 45, and 60° of flexion. Coronal laxity (the sum of VV angulation) and coupled axial rotation (the sum of internal/external rotation) were measured and compared between insert models.
Results
At 30° of flexion, coronal laxities with the PS insert at the +2 and +4 mm resections averaged 7.9±0.6° and 11.3±0.6°, respectively, and decreased by 0.8° (p=0.06) and 1.0° (p=0.07), respectively, with the MLC insert. PS rotational laxities at the +2 and +4 mm resections averaged 11.1±3.9° and 12.5±4.6°, respectively, and decreased by 5.6° (p=0.01) and 7.1° (p=0.02), respectively, with the MLC insert. Similar patterns were observed at 45° and 60° of flexion.
Conclusions
With additional distal femoral resections to alleviate a flexion contracture, utilizing an MLC insert substantially reduced coupled axial rotation but had a minimal impact on coronal laxity compared to a PS insert. Efforts should be taken to avoid JLE in primary TKA as even MLC inserts may not mitigate coronal laxity.
Aims:
Surgeons commonly resect additional distal femur during primary total knee arthroplasty (TKA) to correct a flexion contracture, which leads to femoral joint line elevation. There is a paucity of data describing the effect of joint line elevation on mid-flexion stability and knee kinematics. Thus, the goal of this study was to quantify the effect of joint line elevation on mid-flexion laxity.
Methods:
Six computational knee models with cadaver-specific capsular and collateral ligament properties were implanted with a posterior-stabilized (PS) TKA. A 10° flexion contracture was created in each model to simulate a capsular contracture. Distal femoral resections of + 2 mm and + 4 mm were then simulated for each knee. The knee models were then extended under a standard moment. Subsequently, varus and valgus moments of 10 Nm were applied as the knee was flexed from 0° to 90° at baseline and repeated after each of the two distal resections. Coronal laxity (the sum of varus and valgus angulation with respective maximum moments) was measured throughout flexion.
Results:
With + 2 mm resection at 30° and 45° of flexion, mean coronal laxity increased by a mean of 3.1° (SD 0.18°) (p < 0.001) and 2.7° (SD 0.30°) (p < 0.001), respectively. With + 4 mm resection at 30° and 45° of flexion, mean coronal laxity increased by 6.5° (SD 0.56°) (p < 0.001) and 5.5° (SD 0.72°) (p < 0.001), respectively. Maximum increased coronal laxity for a + 4 mm resection occurred at a mean 15.7° (11° to 33°) of flexion with a mean increase of 7.8° (SD 0.2°) from baseline.
Conclusion:
With joint line elevation in primary PS TKA, coronal laxity peaks early (about 16°) with a maximum laxity of 8°. Surgeons should restore the joint line if possible; however, if joint line elevation is necessary, we recommend assessment of coronal laxity at 15° to 30° of knee flexion to assess for mid-flexion instability. Further in vivo studies are warranted to understand if this mid-flexion coronal laxity has negative clinical implications. Cite this article: Bone Joint J 2021;103-B(6 Supple A):87-93.
Objective:
The aim of this study was to compare the effect of Gap Balancing (GB) versus Measured Resection (MR) techniques on the early clinical and radiological results of Total Knee Arthroplasty (TKA).
Methods:
In this prospective study, 99 patients (99 knees) who underwent unilateral TKA between March 2018 and January 2019 were randomly allocated to one of two groups: The GP group, TKA with GB technique (19 male, 31 female; mean age = 55.9 ±16.5) and the MR group, TKA with MR technique (19 male, 30 female; mean age = 54.2 ± 18.7). Patients in both groups were comparable in terms of the demographic and clinical data. The angle of cutting block to PCA and Cutting Thickness of the Medial and Lateral Condyle (CTMC, CTLC) were intraoperatively measured. In radiographic analysis, Preoperative Mechanical Femorotibial Angle (Pre-mFTA), Postoperative Mechanical Femorotibial Angle (Post-mFTA), and joint line changes were examined. Femoral component Rotation Angle (FCRA) was also measured by computed tomography. In gait analysis, the spatiotemporal parameters (walking speed, step length, and single support time) and kinematics parameters (flexion angle, extension angle, and transversal rotation) were collected at 12 months postoperatively. Furthermore, Western Ontario and McMaster Universities Arthritis Index (WOMAC) were performed at 12 months after surgery.
Results:
CTMC and CTLC were both significantly higher in GB group than in the MR group (9.8±2.0 mm vs 8.5 ± 1.2 mm; 7.9 ± 1.8mm vs 6.8 ± 1.4mm; P = 0.001, P = 0.002, respectively). Angle of cutting block to PCA was statistically lower in GB group than in the MR group (1.7 ± 1.5° vs 3.1 ± 0.5 °; P < 0.001). FCRA is greater in the GB group compared to the MR group, but the difference did not reach statistical significance (1.2 ± 2.8 ° vs 0.7 ± 2.0 °; P > 0.05). Although post-mFTA significantly improved compared with pre-mFTA in both groups, no significant difference was observed in the changes of post-mFTA between the two groups (0.9 ± 1.7° vs 0.3 ± 1.8°, P > 0.05). No significant differences were determined between the two groups in spatiotemporal gait parameters including walking speed, step length, and single support time. The sagittal max knee flexion range was significantly larger in the GB group than in the MR group (49.27 ± 5.24 ° vs 45.99 ± 8.21 °, P < 0.05). The flexion range did not reach the level of the control group. There was no significant difference between the two groups in WOMAC at 12 months follow-up (P > 0.05).
Conclusion:
Evidence from this study has revealed GB and MR techniques have both little effect on early clinical results of TKA. Nonetheless, GB technique can provide better knee flexion in the early postoperative gait status compared with MR technique.
Level of evidence:
Level I, Therapeutic Study.
Preoperative flexion contracture is a risk factor for patients’ dissatisfaction following primary total knee arthroplasty (TKA). Previous studies utilizing navigation technology and cadaveric models attempted to identify surgical techniques to correct knees with flexion contracture and minimize undesirable outcomes such as knee instability. However, no consensus has emerged on a surgical strategy to treat this clinical condition. Therefore, the purpose of this study was to develop and evaluate a computational model of TKA with flexion contracture that can be used in developing optimal surgical strategies that restore knee extension and in understanding factors that cause negative outcomes. To that end, we developed six computational models of knees implanted with a posteriorly stabilized TKA using a measured resection technique. We incorporated tensions in the collateral ligaments representative of those achieved in TKA using reference data from a cadaveric experiment and determined tensions in the posterior capsule elements in knees with flexion contracture by simulating a passive extension exam. Subject-specific extension moments were calculated and used to evaluate the amount of knee extension that would be restored after incrementally resecting the distal femur. The models’ predictions of the extension angle after resecting the femur by 2 and 4 mm were within 1.2° (p ≥ 0.32) and 1.6° (p ≥ 0.25), respectively, compared to previous studies. Accordingly, the computational method presented in this study could be used to evaluate the mechanical impact of flexion contracture and its surgical treatment.
Measured resection is a common technique for obtaining symmetric flexion and extension gaps in posterior‐stabilized total knee arthroplasty (TKA). A known limitation of measured resection, however, is its reliance on osseous landmarks to guide bone resection and component alignment while ignoring the geometry of the surrounding soft tissues such as the medial collateral ligament (MCL), a possible reason for knee instability. To address this clinical concern, we introduce a new geometric proportion, the MCL ratio, which incorporates features of condylar geometry and MCL anterior fibers. The goal of this study was to determine whether the MCL ratio can predict the flexion gaps and to determine whether a range of MCL ratio corresponds to balanced gaps. Six computational knee models each implanted with posterior‐stabilized TKA were utilized. Medial and lateral gaps were measured in response to varus and valgus loads at extension and flexion. The MCL ratio was related to the measured gaps for each knee. We found that the MCL ratio was associated with the flexion gaps and had a stronger association with the medial gap (β=‐ 7.2 ±3.05, p<0.001) than with the lateral gap (β=3.9±7.26, p=0.04). In addition, an MCL ratio ranging between 1.1 and 1.25 corresponded to balanced flexion gaps in the six knee models. Future studies will focus on defining MCL ratio targets after accounting for variations in ligament properties in TKA patients. Our results suggest that the MCL ratio could help guide femoral bone resections in measured resection TKA, but further clinical validation is required.
This article is protected by copyright. All rights reserved.
Medial unicompartmental knee arthroplasty (UKA) is an accepted treatment for isolated medial osteoarthritis. However, using an improper thickness for the tibial component may contribute to early failure of the prosthesis or disease progression in the unreplaced lateral compartment. Little is known of the effect of insert thickness on both knee kinematics and ligament forces. Therefore, a computational model of the tibiofemoral joint was used to determine how non-conforming, fixed bearing medial UKA affects tibiofemoral kinematics and tension in the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) during passive knee flexion. Fixed bearing medial UKA could not maintain the medial pivoting that occurred in the intact knee from 0° to 30° of passive flexion. Abnormal anterior-posterior (AP) translations of the femoral condyles relative to the tibia delayed coupled internal tibial rotation, which occurred in the intact knee from 0° to 30° flexion, but occurred from 30° to 90° flexion following UKA. Increasing or decreasing tibial insert thickness following medial UKA also failed to restore the medial pivoting behavior of the intact knee despite modulating MCL and ACL forces. Reduced AP constraint in non-conforming medial UKA relative to the intact knee leads to abnormal condylar translations regardless of insert thickness even with intact cruciate and collateral ligaments. This finding suggests that the conformity of the medial compartment as driven by the medial meniscus and articular morphology plays an important role in controlling AP condylar translations in the intact tibiofemoral joint during passive flexion. This article is protected by copyright. All rights reserved.
Component rotation and anterior
- R L Barrack
- T Schrader
- A J Bertot
- M W Wolfe
- L Myers
Barrack RL, Schrader T, Bertot AJ, Wolfe MW, Myers L. Component rotation and anterior