Rotational alignment in total knee arthroplasty

Following the Anatomy of the Proximal Tibia With a Standard Anatomic Technique and the Use of an Asymmetrical Tibial Base Plate can Lead to a Mismatched Internal Components' Rotation in Mechanically Aligned Total Knee Arthroplasty

Background

Tibiofemoral components rotational congruency affects the total knee arthroplasty (TKA) success. The smart insert sensor (I-S) helps to establish tibial component rotation reciprocally to a fixed femoral rotation. We aimed (1) to validate the use of I-S as a possible tool to reach reproducible reciprocal femorotibial rotation (RftR) in TKA independently from anatomic landmarks, reducing outliers in combined and mismatched femorotibial rotation (CftR and MMftR, respectively) positioning and (2) to validate the "curve-on-curve" method for a specific type of asymmetrical tibial component.

Methods

From February 2018, we conducted a prospective case-control study including 106 patients undergoing TKA. Patients were divided into 2 groups based on the method used to establish tibial component rotation: with the I-S use (group A, n = 53) and with the standard "curve-on-curve" technique (group B, n = 53). Rotational alignment was calculated using the Berger protocol with postoperative computed tomography scanning. Alignment parameters measured were tibial and femoral component rotations (tR, fR), the CftR, the MMftR, and the RftR.

Results

Intraoperative rotation measured by I-S correlated the best with RftR (r = 0.84; P < .001) at the post-operative CT scanning. No significant differences were found between groups A and B regarding all types of rotation (fR: P = .774; tR: P = .467; CftR: P = .847) except for MMftR (P = .036) and RftR (P = .023). There were no outliers in group A but 27 and 12 outliers in group B for MMftR and CftR respectively (P < .001; P = .032).

Conclusions

The TKA components' rotation established using a smart I-S intraoperatively is ascribable to the RftR at postoperative computed tomography scan. The I-S helps reduce outliers in the CftR and MMftR. An asymmetrical tibial base plate implanted using the curve-on-curve technique does not create a neutral reciprocal femorotibial rotation significantly increasing the number of cases with mismatched femorotibial internal rotation.

Surgeon-Applied Stress and a Ligament Tensor Instrument Provide a Similar Assessment of Preresection Flexion Laxity During Robotic Total Knee Arthroplasty

Background

Robotic-assisted total knee arthroplasty (RA-TKA) allows surgeons to perform intraoperative soft tissue laxity assessments prior to bone resections and is used to alter resections to achieve gap balance. This study compared 2 techniques for flexion gap laxity assessment during RA-TKA.

Methods

A prospective study of 50 primary RA-TKAs performed by a single surgeon was conducted between February and October 2023. Following full exposure, anterior tibial dislocation, and osteophyte removal, maximal medial and lateral compartment flexion laxity was quantified to the nearest 0.5 mm by the robotic system using a dynamic, surgeon-applied stress (SURGEON). This data was used to plan a balanced flexion gap by adjusting the femoral component size, rotation, and anterior-posterior translation. Flexion laxity was quantified again after distal femoral and proximal tibial resections using a ligament tensor instrument (TENSOR). These new data were used to plan for the same desired flexion gap using the same variables. Paired-samples t-tests and a simple linear regression were used for analysis.

Results

Both methods produced near-identical recommendations for femoral component sizing (mean deviation 0.06 sizes, range -1 to +1 size; P = .569), rotation (deviation mean 1.0°, range -3.0° to +3.0°; P = .741), and anterior-posterior translation (deviation mean 0.13 mm, range -0.5 to +0.5 mm, P = .785). SURGEON femoral component rotation predicted TENSOR rotation (R2 = 0.157; 95% confidence interval = 0.124, 0.633; P = .004).

Conclusions

Assessing flexion laxity with a surgeon-applied stress vs a ligament tensor produced near-identical laxity data in RA-TKA, suggesting surgeons may comfortably choose either technique as a reliable method.

Level of Evidence

Level III.

Computer-Assisted Surgery in Total Knee Arthroplasty: Our Experience

Background

Total knee arthroplasty (TKA) is a reliable orthopedic procedure for knee osteoarthritis with long-term success rates of 90% after 15 years. Computer-assisted surgery (CAS) has been developed to improve the accuracy of the alignment and orientation of the components in TKA.

Methods

A prospective study involving 103 subjects who underwent CAS-TKA was conducted over a 3-year period. Subjects were assessed for pre- and post-operative varus and valgus deformity, BMI, comorbidities, and Knee Society Score (KSS). Outcome measures of post-operative KSS, post-operative alignment, and hospital stay were examined by Spearman correlation coefficients. Categorical outcomes of complication and secondary procedures were compared by chi-squared test and odds ratio.

Results

The study considered 103 TKA patients with a mean ± SD age of 63.7 ± 8.4 years (33-88 years). Unilateral knee replacement was performed on 56 patients (54.3%) and remaining 47 (45.6%) had simultaneous bilateral TKA. Forty (34.8%) patients were obese, and severe pre-operative deformity (> 15°) was observed in 47 (31.3%) patients. Mean coronal alignment of the knee joint was 91.33° (SD: 90.69° valgus-88.92° varus). The mean post-operative KSS noted in obese and non-obese subjects were 93.43 (84-98) and 94.76 (85-98) respectively. Post-operative KSS for knees with severe deformity was 94.08 (80-98), while it was 95.76 (83-98) in those with mild to moderate deformities.

Conclusion

The study confirms that navigation in CAS-TKA consistently achieved coronal alignment of the knee joint within ± 3°, irrespective of the patient BMI and degree of deformity.

Accuracy of Femoral Component External Rotation with all Burr Robotic Assisted Total Knee Arthroplasty

Introduction

External rotation of femoral component is controversial in Total knee arthroplasty (TKA). The aim of our study is to assess the precision of femoral component external rotation in Robotic Assisted All Burr TKA.

Materials and methods

This is a prospective study of 30 cases who underwent All Burr Robotic Assisted TKA at our institute, RNH hospital. Inclusion criteria were primary and secondary osteoarthritis of the knee and exclusion criteria were revision and partial knee replacement. On Navio robotic system femoral external rotation was planned as per medio-lateral flexion gap balancing and executed with burr. Post-operative CT scan was done in all patients to assess intra-operative planned femoral external rotation.

Results

Out of 30 cases, 20 were female and 10 were male. Mean age was 66.06±7.43 years. On Navio the planned external rotation of femoral component was 2.86±1.16. Average of femoral component external rotation on postoperative CT scan was 3.11±1.16. The mean deviation of achieved femoral component external rotation from planned external rotation was -0.24 to ±0.28. Only 37% patients required 3° external rotation. Correlation between planned and achieved femoral component external rotation was significant, positive and very strong as indicated by r=0.97 and p=0.0001.

Conclusion

All Burr Robotic Assisted TKA provides near accurate femoral component external rotation as planned on Navio with deviation of less than 0.3° between planned and achieved external rotation.

Is the Akagi Line a Reliable Landmark for Adjusting the Rotational Axis of the Tibial Component in Patients with Patellofemoral Instability?

Purpose

This study aimed to investigate whether the Akagi line is a reliable anatomic landmark for adjusting the rotational axis of the tibial component in patients with patellofemoral (PF) malalignment.

Materials and methods

This retrospective case-control study included 86 patients with PF instability and 129 controls. On the superimposed axial CT images, TT-TG, TT-PCL, nTT-TG, nTT-PCL, knee joint rotation, and the angle between the Akagi line and surgical transepicondylar axis (Akagi/sTEA angle) were measured. In addition, a modified Akagi line, drawn 1 cm medial to the patellar tendon attachment, was defined, and the angle between the new Akagi line and sTEA (mAkagi/sTEA angle) was also measured and compared between groups.

Results

There were 86 patients (47 females, 39 males) in the case group and 129 patients (56 females, 73 males) in the control group with a mean age of 35.7 ± 17.9 years and 41.1 ± 18.8 years, respectively (p < 0.001). Radiologic variables of PF alignment (TT-TG, TT-PCL, nTT-TG, nTT-PCL, and knee joint rotation) were significantly abnormal in the case group (p < 0.001 for all variables). The Akagi/sTEA angle was significantly higher in the case group, resulting in 89.5% external malrotation of the tibial component (> 10°). However, the tibial component was 96.5% aligned correctly (between 10° external and 3° internal rotation) in the control group. Using the modified Akagi line significantly improved the rotational alignment, and normal tibial rotation increased to 93.3% of the case group. The Akagi/sTEA angle strongly correlated with the knee rotation (rho: 0.735, p: 0.001), TT-TG (rho: 0.715, p: 0.001) and nTT-TG (rho: 0.783, p: 0.001). But the TT-PCL (rho: 0.459, p: 0.001) and nTT-PCL (rho: 0.589, p: 0.001) had a medium correlation.

Conclusions

The Akagi line might cause unacceptable external rotation of the tibial component in patients with PF malalignment. The use of the modified Akagi line described in this study may be a solution for the rotational mismatch between femoral and tibial components in TKA.

Level of evidence

Level III, retrospective case-control study.

CAPAbility: comparison of the JOURNEY II Bi-Cruciate Stabilised and GENESIS II total knee arthroplasty in performance and functional ability: protocol of a randomised controlled trial

Background

Osteoarthritis of the knee is a common condition that is expected to rise in the next two decades leading to an associated increase in total knee replacement (TKR) surgery. Although there is little debate regarding the safety and efficacy of modern TKR, up to 20% of patients report poor functional outcomes following surgery. This study will investigate the functional outcome of two TKRs; the JOURNEY II Bi-Cruciate Stabilised knee arthroplasty, a newer knee prosthesis designed to provide guided motion and improve knee kinematics by more closely approximating a normal knee, and the GENESIS II, a proven existing design.

Aim

To compare the change in Patient-reported Outcome Measures (PROMs) scores of the JOURNEY II BCS and the GENESIS II from pre-operation to 6 months post operation.

Methods

CAPAbility is a pragmatic, blinded, two-arm parallel, randomised controlled trial recruiting patients with primary osteoarthritis due to have unilateral TKR surgery across two UK hospitals. Eligible participants (n = 80) will be randomly allocated to receive either the JOURNEY II or the GENESIS II BCS knee prosthesis. Baseline measures will be taken prior to surgery. Patients will be followed at 1 week, 6 to 8 weeks and 6 months post-operatively. The primary outcome is the Oxford Knee Score (OKS) at 6 months post-operatively. Secondary outcomes include: other PROMs, biomechanical, radiological (computerised tomography, (CT)), clinical efficacy and safety outcomes. An embedded qualitative study will also investigate patients’ perspectives via interview pre and post surgery on variables known to affect the outcome of TKR surgery. A sub-sample (n = 30) will have additional in-depth interviews to explore the themes identified. The surgeons’ perspectives on the operation will be investigated by a group interview after all participants have undergone surgery.

Discussion

This trial will evaluate two generations of TKR using PROMS, kinematic and radiological analyses and qualitative outcomes from the patient perspective.

Trial registration

International Standard Randomised Controlled Trials Number Registration, ID: ISRCTN32315753. Registered on 12 December 2017.

Patient Variation Limits Use of Fixed References for Femoral Rotation Component Alignment in Total Knee Arthroplasty

BACKGROUND

Optimal rotational alignment of the femoral component is a common goal during total knee arthroplasty. The posterior condylar axis (PCA) is thought to be the most reproducible reference in surgery, while the transepicondylar axis (TEA) seems to better approximate the native kinematic flexion axis. This study sought to determine if rules based on patient gender or coronal alignment could allow reliable reproduction of the TEA from the PCA.

METHODS

Three-dimensional models based on preoperative computed tomography were made representing a patient's arthritic knee joint. The landmarks were defined and angular relationships determined.

RESULTS

The population group of 726 patients contained large anatomic variation. When applying the standard reference rule of 3° external rotation from the PCA, 36.9% of patients would have a rotational target greater than ±2° from their TEA. When applying the mean external rotation of the TEA from the PCA (1.85°) from this population, this proportion dropped to 26.0% of patients. The use of statistically significant gender and coronal alignment relationships to define the femoral rotation did not reduce the proportion of patients in ±2° error.

CONCLUSION

This study shows that gender and coronal alignment relationships to the TEA to PCA angle are not clinically significant as a quarter of patients would still have a target for rotation greater than ±2° from the TEA using these relationships. Superior tools for orienting rotational cuts directly to the TEA in surgery or preoperative identification of relevant patient-specific angles might capture the proportion of patients for whom standard reference angles are not appropriate.