Joint line position change in primary total knee arthroplasty: a radiographic analysis comparing conventional and robotic techniques

PURPOSE

Joint line (JL) position change in total knee arthroplasty (TKA) may alter knee biomechanics and impact function. The purpose of this study was to compare the change in JL position between robotic-assisted TKA (RA-TKA) and conventional TKA (C-TKA).

METHODS

A retrospective, radiographic analysis was conducted of patients who underwent RA-TKA and C-TKA to compare JL position change. JL position was measured in consecutive RA-TKAs and C-TKAs performed by four fellowship-trained arthroplasty surgeons. Statistical analysis was done utilizing t-tests and Mann Whitney U tests, with statistical significance being defined as a p value < 0.05.

RESULTS

Six hundred total RA-TKAs and 400 total C-TKAs were included in the analysis. There were no significant differences in patient baseline characteristics such as body mass index, range of motion, and tibiofemoral coronal alignment. RA-TKAs were associated with an average of 0.04 (2.2) mm JL position change, and C-TKAs were associated with an average 0.5 (3.2) mm JL position change (p = 0.030). There were inter-surgeon differences when comparing the change in JL position for RA-TKAs and C-TKAs between the four participating surgeons.

CONCLUSION

RA-TKA leads to better preservation of the JL position than C-TKA, and this seems to be dependent on the arthroplasty surgeon's preferences and techniques during TKA. Whether this statistically significant difference is clinically relevant needs to be further investigated.

Maintenance of the joint line and posterior condylar offset are the most notable variables for successful outcomes of revision total knee arthroplasty

INTRODUCTION

Controversy regarding which variables should be prioritized for better outcomes in revision total knee arthroplasty (RTKA) exists. This study aimed to comprehensively analyze the variables affecting RTKA outcomes.

MATERIALS AND METHODS

We retrospectively identified 87 RTKAs in 82 patients who were performed between March 2014 and February 2020. Range of motion (ROM), including flexion contracture (FC) and further flexion (FF), was analyzed according to the covariates. The covariates included mode of failure, joint line position, anteroposterior (AP) position, rotational alignment of the femoral component, and patellofemoral alignment. The differences between the final follow-up values of each RTKA variable and those of the native knee were evaluated. The clinical outcomes were evaluated.

RESULTS

No significant differences were observed between the joint line positions of the RTKA and native knees. The patellar and AP positions of the femoral component were restored to pre-TKA values. The femoral component had an external rotation of 2.78° compared with the native knee. In multivariable stepwise regression analysis, restoration of the adductor tubercle joint line and posterior condylar offset (PCO) were significant variables affecting ROM. Septic RTKA (33 knees) resulted in poor FF outcomes (p = 0.030) and Western Ontario and McMaster Universities Osteoarthritis Index stiffness (WOMAC S) scores (p < 0.001), compared with aseptic RTKA (54 knees).

CONCLUSIONS

Restoration of the joint line position and PCO are crucial factors for improved ROM in RTKA. Joint line elevation in RTKA resulted in worse ROM than joint line lowering. In addition, RTKA due to septic failure had inferior ROM and WOMAC S scores compared with RTKA due to aseptic failure.

LEVEL OF EVIDENCE

Level III, cohort study.

[Effect of prosthetic joint line installation height errors on insert wear in unicompartmental knee arthroplasty]

The clinical performance and failure issues are significantly influenced by prosthetic malposition in unicompartmental knee arthroplasty (UKA). Uncertainty exists about the impact of the prosthetic joint line height in UKA on tibial insert wear. In this study, we combined the UKA musculoskeletal multibody dynamics model, finite element model and wear model to investigate the effects of seven joint line height cases of fixed UKA implant on postoperative insert contact mechanics, cumulative sliding distance, linear wear depth and volumetric wear. As the elevation of the joint line height in UKA, the medial contact force and the joint anterior-posterior translation during swing phase were increased, and further the maximum von Mises stress, contact stress, linear wear depth, cumulative sliding distance, and the volumetric wear also were increased. Furthermore, the wear area of the insert gradually shifted from the middle region to the rear. Compared to 0 mm joint line height, the maximum linear wear depth and volumetric wear were decreased by 7.9% and 6.8% at -2 mm joint line height, and by 23.7% and 20.6% at -6 mm joint line height, the maximum linear wear depth and volumetric wear increased by 10.7% and 5.9% at +2 mm joint line height, and by 24.1% and 35.7% at +6 mm joint line height, respectively. UKA prosthetic joint line installation errors can significantly affect the wear life of the polyethylene inserted articular surfaces. Therefore, it is conservatively recommended that clinicians limit intraoperative UKA joint line height errors to -2-+2 mm.

Comparable accuracy of femoral joint line reconstruction in different kinematic and functional alignment techniques

PURPOSE

A key part of kinematic alignment (KA) and functional alignment (FA) is to restore the natural femoral joint line, in particular the medial joint line. KA is known to reproduce the femoral joint line accurately; however, direct comparisons with other surgical techniques such as FA are currently lacking. The purpose of this study was to evaluate differences of alignment parameters in KA and FA techniques with a special focus given to the femoral joint line.

METHODS

We performed a retrospective radiological analysis of pre- and postoperative long leg radiographs of 221 consecutive patients with varus or neutral leg alignment, who underwent primary total knee arthroplasty (TKA) procedures from 2018 to 2020. Patients were assigned to one of four groups: (1) FA: image-based robotic-assisted TKA, (2) FA: imageless robotic-assisted TKA, (3): restricted KA: 3D cutting block-assisted (patient-specific instruments, PSI) TKA, (4): unrestricted KA: calipered technique. Patients' radiographs were (re)-analyzed for overall limb alignment, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), as well as medial and lateral femoral joint line alteration. Statistical significance was determined using unpaired t testing (FA vs. KA group) and one-way ANOVA (subgroup analyses).

RESULTS

Comparisons of KA vs. FA, as well as individual subgroups of KA and FA did not show any differences in the accuracy of medial joint line reconstruction (< 2 mm, p = 0.384, p = 0.744, respectively) and LDFA alteration (< 2°, p = 0.997, 0.921, respectively). Correction of MPTA (3.4° vs. 2.2°) and lateral femoral joint line (2.1 mm vs. 1.5 mm) was higher for FA and FA subgroups compared to KA and KA subgroups (both p < 0.001).

CONCLUSION

Kinematic and functional alignments showed a comparable accuracy in reconstruction of the medial femoral joint line and femoral joint line orientation. Increased correction of MPTA and lateral femoral joint line was recorded with FA techniques.

LEVEL OF EVIDENCE

III.

Kinematically Aligned Oxford Unicompartmental Knee Arthroplasty Using the Microplasty Instrumentation System

This technical note demonstrates kinematically aligned Oxford unicompartmental knee arthroplasty using the Microplasty instrumentation system with custom-made devices. The medial joint line is evaluated preoperatively; if it is aligned and parallel with the lateral joint line, they are considered to comprise the coronal knee joint line (CJL). In this case, the coronal inclination of a spoon gauge inserted into the medial joint space indicates the CJL. Otherwise, an accessory spoon is inserted and connected to the medial spoon to refer to the posterior condylar line, which is considered the CJL. The tibial cutting block is then connected without changing the inclination of the spoon and the coronal tilt of the tibial extramedullary rod is adjusted, which is implemented with a custom-made ankle yoke. The remainder of the steps is then identical to the conventional Microplasty procedure. This technique can imitate the cutting line to the CJL, which might be considered ideal from mechanical and kinematic perspectives.

Identification of the joint line in revision total knee arthroplasty using a multiple linear regression model: a cadaveric study

INTRODUCTION

The results of revision total knee arthroplasty (rTKA) may be compromised by excessive joint line (JL) elevation. It is critical but challenging in reestablishing the JL in rTKA. Previous studies have confirmed that, biomechanically and clinically, JL elevation should not exceed 4 mm. Image-based studies described several approaches to locate the JL intraoperatively, however magnification errors could occur. In this cadaveric study, we aim to define an accurate and reliable method to determine the JL.

MATERIALS AND METHODS

Thirteen male and eleven female cadavers were used, with an average age of death being 48.3 years. The transepicondylar width (TEW), the distance from the medial (MEJL) and lateral (LEJL) epicondyle, adductor tubercle (ATJL), fibular head (FHJL) and tibial tubercle (TTJL) to the JL were measured in 48 knees. Intra- and interobserver reliability and validity were tested prior to any additional analysis. Pearson correlation and linear regression analysis were used to examine the correlations between landmark-JL distances (LEJL, MEJL, ATJL, FHJL and TTJL) and the TEW, and to further derive models for intraoperative JL determination. The accuracy of different models, quantified by errors between estimated and measured landmark-JL distances, was compared using the Friedman and post hoc Dunn tests.

RESULTS

The intra- and inter-observer measurements for TEW, MEJL, LEJL, ATJL, TTJL and FHJL did not differ significantly (p > 0.05). Between genders, significant differences were found on TEW, MEJL, LEJL, ATJL, FHJL and TTJL (p < 0.05). There was no association between TEW and either FHJL or TTJL (p > 0.05), while ATJL, MEJL, and LEJL were found to be correlated with TEW (p < 0.05). Six models were derived: (1) MEJL = 0.37*TEW (r = 0.384), (2) LEJL = 0.28*TEW (r = 0.380), (3) ATJL = 0.47*TEW (r = 0.608), (4) MEJL = 0.413*TEW - 4.197 (R² = 0.473), (5) LEJL = 0.236*TEW + 3.373 (R² = 0.326), (6) ATJL = 0.455*TEW + 1.440 (R² = 0.556). Errors were defined as deviations between estimated and actual landmark-JL distances. The mean absolute value of the errors, created by Model 1-6 was 3.18 ± 2.25, 2.53 ± 2.15, 2.64 ± 2.2, 1.85 ± 1.61, 1.60 ± 1.59 and 1.71 ± 1.5, respectively. The error could be limited to 4 mm in 72.9%, 83.3%, 72.9%, 87.5%, 87.5%, and 93.8% of the cases by referencing Model 1-6, respectively.

CONCLUSION

Compared to previous image-based measurements, the current cadaveric study most closely resembles a realistic view of intraoperative settings and could circumvents magnification errors. We recommend using Model 6, the JL can be best estimated by referencing the AT and the ATJL can be calculated as ATJL (mm) = 0.455*TEW (mm) + 1.440 (mm).

Effect of joint line orientation parameters on initial bone resection in mechanically aligned total knee arthroplasty: a retrospective clinicoradiological correlation study

BACKGROUND

Discrepancies in bone resection between the medial and lateral compartments are very common in total knee arthroplasty (TKA) when mechanical alignment (MA) is used. The purpose of this study was to explore whether and how joint line orientation affects the initial bone resection in mechanically aligned TKA.

METHODS

A total of 194 patients (225 knees) diagnosed with osteoarthritis (OA) were included. Virtual bone resection was conducted in the coronal view using full-length weight-bearing radiographs according to the technical requirements of MA, and the reliability of the virtual resection was verified via intraoperative caliper measurements. Correlation and regression analyses were conducted between the initial bone resection within the extension gap (EG) and various parameters, including the hip-knee-ankle (HKA) angle, mechanical lateral distal femoral angle (mLDFA), joint line congruence angle (JLCA), and medial proximal tibial angle (MPTA). Moreover, the correlation between intraoperative bone resection adjustments and joint line orientation parameters was also investigated.

RESULTS

All knees in the current case series were artificially divided into 4 subgroups: subgroup 1, containing 148 varus knees (65.8%) with valgus femurs; subgroup 2, containing 48 varus knees (21.3%) with varus femurs; subgroup 3, containing 17 valgus knees (7.6%) with varus tibias; and subgroup 4, containing 12 valgus knees (5.3%) with valgus tibias. In subgroup 1, the mLDFA and MPTA were positively correlated with the initial bone resection with regression coefficients of 0.670 and 0.089, respectively. Moreover, in all varus knees, intraoperative bone resection adjustments were negatively correlated with mLDFA and MPTA, with categorical regression coefficients of -0.426 and - 0.230, respectively.

CONCLUSION

When MA-TKAs are performed in varus knees with valgus femurs, the initial bone resection within the EG is mainly positively correlated with mLDFA, while the intraoperative bone resection adjustment is significantly correlated with mLDFA and MPTA in all varus knees.

A novel approach for joint line restoration in revision total ankle arthroplasty based on the three-dimensional registration of the contralateral tibia and fibula

PURPOSE

The use of total ankle arthroplasty (TAA) is increasing over time, as so will the need for revision TAAs in the future. Restoration of the ankle joint line (JL) in revision TAA is often difficult due to severe bone loss. This study analyzed the accuracy of a three-dimensional (3D) registration of the contralateral tibia and fibula to restore the ankle joint line (JL) and reported side-to-side differences of anatomical landmarks.

METHODS

3D triangular surface models of 96 paired lower legs underwent a surface registration algorithm for superimposition of the mirrored contralateral lower leg onto the original lower leg to approximate the original ankle JL using a proximal, middle and distal segment. Distances of the distal fibular tip, anterior and posterior medial colliculus to the JL were measured and absolute side-to-side differences reported. Anterior lateral distal tibial angle (ADTA) and lateral distal tibial angle (LDTA) were measured.

RESULTS

Mean JL approximation was most accurate for the distal segment (0.1 ± 1.4 mm (range: -3.4 to 2.8 mm)) and middle segment (0.1 ± 1.2 mm (range: -2.8 to 2.5 mm)) compared to the proximal segment (-0.2 ± 1.6 mm (range: -3.0 to 4.9 mm)) (p = 0.007). Distance of the distal fibular tip, the anterior, and posterior medial colliculus to the JL, ADTA and LDTA yielded no significant side-to-side differences (n.s.).

CONCLUSION

3D registration of the contralateral tibia and fibula reliably approximated the original ankle JL. The contralateral distal fibular tip, anterior and posterior medial colliculi, ADTA and LDTA can be used reliably for the planning of revision TAA with small side-to-side differences reported.

LEVEL OF EVIDENCE

IV.

Better accuracy and implant survival in medial imageless robotic-assisted unicompartmental knee arthroplasty compared to conventional unicompartmental knee arthroplasty: two- to eleven-year follow-up of three hundred fifty-six consecutive knees

PURPOSE

Implant malpositioning, joint line (JL) lowering, and malalignment have been identified as risk factors for implant failure in unicompartmental knee arthroplasty (UKA). The aims of this study were to compare the accuracy of implant positioning in robotic-assisted UKA versus conventional UKA in a large cohort and examine the correlation with implant survival at mid-term follow-up.

METHODS

This retrospective study included 356 medial UKAs from 2011 to 2019. The radiological measurements performed were coronal positioning of tibial implant according to Cartier angle (Δ Cartier), posterior tibial slope (PTS), residual hip-knee-ankle (HKA), and JL restoration. Outliers were defined as follows: post-operative HKA < 175° or > 180°, Δ Cartier > 3° or <  - 3°, JL change ≥ 2 mm, and PTS < 2° or > 8°. The survival probability was reported at the last follow-up.

RESULTS

Out of the 356 knees included, 159 underwent conventional UKA (44.5%) and 197 (55.5%) robotic-assisted UKA. The mean follow-up was 61.3 months ± 24.0. Robotic UKA was associated with better accuracy compared to conventional UKA in relation to HKA (67% vs 56%, p = 0.023), JL restoration (70% vs 44%, p < 0.0001), PTS (83% vs 55%, p < 0.0001), and tibial varus restoration (65% vs 55%, p = 0.049). Implant survival in the robotic group was found to be superior at the last follow-up (96.4% versus 87.3% at 9 years, p = 0.004).

CONCLUSION

Robotic assistance in patients undergoing medial UKA was associated with better accuracy compared to conventional UKA with respect to tibial implant positioning, post-operative limb alignment, and JL restoration. This was translated in improved survival at mid-term follow-up favouring the robotic group.

Adopting the Joint Line Theory for Bone Resection in Cruciate-Retaining Total Knee Arthroplasty to Prevent Flexion Gap Tightness

BACKGROUND

During a conventional measured resection using the posterior reference method for total knee arthroplasty (TKA) in varus knees, proximal tibia is resected from the lateral joint surface for the same thickness as the implant. Distal femur is resected from the worn medial surface for the same thickness as the implant. Posterior femur is resected using the posterior reference method with an external rotation for appropriate degrees. In this situation, although the joint line of the tibia is leveled to the height of lateral joint surface, the posterior joint line of the femur is leveled to the center of medial and lateral posterior condyle, which is a few millimeters lower than the lateral posterior condyle. This discrepancy between the proximal tibia-posterior femoral joint line causes a tight flexion gap in cruciate-retaining TKA. Therefore, downsizing of the femur is necessary to adjust the posterior joint line to the level of the lateral condyle.

PERSPECTIVES

To avoid this circumstance, the postoperative joint line should be leveled to the center of the original medial and lateral joint surface. Proximal tibia is resected from the lateral joint surface 1 mm to 2 mm thicker than the implant. Distal femur is resected from the worn medial surface 1 mm to 2 mm thinner than the implant. Posterior femur is resected using the posterior reference method with an external rotation for appropriate degrees. In this situation, all the joint lines are leveled to the center of the medial and lateral joint surface. Otherwise, use of an anatomically shaped implant with a physiologic joint line is another option to avoid joint line discrepancy.

CONCLUSIONS

Adopting joint line theory for bone resection can prevent the flexion gap tightness that likely occurs in cruciate-retaining TKA.

Robotic-assisted TKA leads to a better prosthesis alignment and a better joint line restoration as compared to conventional TKA: a prospective randomized controlled trial

PURPOSE

Correct positioning and alignment of the prosthesis is a very important factor for durability of prosthesis and implant survival which is improved with the use of technology in total knee arthroplasty. However, the long-term functional outcomes and survivorship are unclear. For this study, it was hypothesized that mechanical axis alignment of lower limb, post-operative joint line restoration, femoral and tibial component alignment is more accurate with the new handheld semi-active robotic-assisted TKA.

METHOD

From April-2019 to March-2020, 60 patients with unilateral knee osteoarthritis who underwent total knee arthroplasties were included in this prospective randomised controlled study. Computer generated randomization was used. Study included 48 female patients and 12 male patients. Pre-operative and post-operative radiographic measurements were done and compared between the two groups.

RESULTS

There was a significant difference between two groups with respect to mechanical axis deviation, joint line deviation and coronal alignment of femoral and tibial prosthesis. Mechanical axis deviation > 3° was seen in eight cases (28.5%) in C-TKA group compared to one case (3.1%) in RA-TKA (p 0.019). Joint line deviation of 3.5 mm was noted in C-TKA group as compared to 0.9 mm in RA-TKA group (p < 0.001) which was statistically significant. However, whether this difference of 2.6 mm of joint line elevation between C-TKA and RA-TKA leads to any difference in clinical outcome in terms of knee kinematics and knee flexion needs to be investigated with further studies. Clinically restoring normal joint line is important for improved knee function after primary TKA. No significant difference was noted in femoral component rotation on post-operative computed tomography (CT) scan.

CONCLUSION

The novel imageless, handheld semi-autonomous robotic system for TKA is highly accurate with respect to component positioning in coronal plane and mechanical alignment as compared to conventional TKA. Joint line is elevated in conventional TKA but is accurately restored using the robotic-assisted TKA which may lead to better patellofemoral kinematics.

LEVEL OF EVIDENCE

I.

Tibial joint line orientation has no effect on joint awareness after mechanically aligned total knee arthroplasty

PURPOSE

Joint line orientation (JLO) plays an important role in total knee arthroplasty (TKA), but its influence on patient-reported outcomes (PROs) is unclear. The purpose of this study was to examine JLO impact as measured by the forgotten joint score (FJS-12). The hypothesis was that restoring the joint line (JL) parallel to the floor would influence joint awareness favorably, i.e., allow the patient to forget about the joint in daily living.

METHODS

All computer-navigated primary TKAs using a cemented, cruciate-retaining (CR) design implanted between January 2018 and September 2019 were reviewed in this retrospective single-center analysis. Primary endpoints were: clinical [range of motion (ROM)], and patient-reported (FJS-12) and radiographical outcomes [tibia joint line angle (TJLA), hip knee axis (HKA), mechanical medial proximal tibia angle (mMPTA) as well as mechanical lateral distal femoral angle (mLDFA)].

RESULTS

Seventy-six patients (mean age: 70.3 ± 9.7 years, mean BMI: 29.7 ± 5.2 kg/m²) were included. Postoperative ROM averaged 118.7 ± 9.6°. The mean FJS-12 improved from 16.4 ± 15.3 (preoperatively) to 89.4 ± 16.9 (1-year follow-up; p < 0.001). Clinical outcomes and PROs did not correlate with JLO (p = n.s.). Cluster analysis using six measures revealed that a medially opened TJLA was associated with significantly better postoperative FJS-12.

CONCLUSION

Tibial JLO was found to have no effect on PROs. Considering the JLO in the coronal plane alone probably has questionable clinical relevance. Lower limb alignment should be assessed in all three planes and correlated with the clinical outcome.

LEVEL OF CLINICAL EVIDENCE

Level IV.

The epicondylar ratio can be reliably determined in both computed tomography and X-ray

PURPOSE

One of the key factors to the successful revision of total knee arthroplasty (rTKA) is the reconstruction of the joint line, which can be determined using the epicondylar ratio (ER). The measurement is established in X-ray and MRI. However, it is not known whether computed tomography (CT) allows a more reliable determination. The objective was to assess the reliability of the ER in CT and to determine the correlation between the ER in CT and a.p. X-ray of the knee.

METHODS

The ER was determined on X-ray and CT images of a consecutive series of 107 patients, who underwent rTKA. Measurements were made by two blinded observes, one measured twice. The inter- and intraobserver agreement, as well as the correlation between the two methods, were quantified with the Intraclass Correlation Coefficient.

RESULTS

The average lateral ER was 0.32 (± 0.04) in X-ray and 0.32 (± 0.04) in CT. On the medial side, the average ER was 0.34 (± 0.04) in X-ray and 0.35 (± 0.04) in CT. The interobserver agreement for the same imaging modality was lateral 0.81 and medial 0.81 in X-ray as well as lateral 0.74 and medial 0.85 in CT. The correlation between the two methods was lateral 0.81 and medial 0.79.

CONCLUSIONS

The ER can be reliably determined in X-ray and CT. Measurements of the two image modalities correlate. Prior to rTKA, the sole use of the X-ray is possible.

Joint line is restored in robotic-arm-assisted total knee arthroplasty performed with a tibia-based functional alignment

INTRODUCTION

Functional alignment (FA) in total knee arthroplasty (TKA) has been introduced to restore the native joint line obliquity, respect the joint line height and minimize the need of soft tissue releases. The purpose of this study was to assess the intraoperative joint line alignment and compare it with the preoperative epiphyseal orientation of the femur and tibia in patients undergoing robotic-arm-assisted (RA)-TKA using FA.

MATERIALS AND METHODS

This retrospective study included a consecutive series of patients undergoing RA-TKA between February 2019 and February 2021. The joint line orientation of the femur and tibia in the three-dimensions was calculated and classified on preoperative CT-scans and compared with the intraoperative implant alignment. The tibial cut was performed according to the tibial preoperative anatomy. The femoral cuts were fine-tuned based on tensioned soft tissues, aiming for balanced medial and lateral gaps in flexion and extension.

RESULTS

A total of 115 RA-TKAs were assessed. On average, the tibial component was placed at 1.8° varus (SD 1.3), while the femur was placed at 0.8° valgus (SD 2.2) and 0.6° external rotation (SD 2.6) relative to the surgical transepicondylar axis. Moderate to strong, statistically significant relationships were described between preoperative tibial coronal alignment and tibial cut orientation (r = 0.7, p < 0.0001), preoperative femoral orientation in the coronal and axial planes and intraoperative femoral cuts alignment (r = 0.7, p < 0.0001 and r = 0.5, p < 0.0001, respectively). One case (0.9%) of slight tibial component varus subsidence was reported 45-days post-operatively, but implant revision was not necessary.

CONCLUSIONS

The proposed robotic-assisted functional technique for TKA alignment, with a restricted tibial component coronal alignment, based on the preoperative phenotype and femoral component positioning as dictated by the soft tissues, provided joint line respecting resections. Further studies are needed to assess long-term implant survivorship, patient satisfaction and alignment-related failures.

A randomized controlled trial comparing functional outcomes for navigated kinematically aligned total knee arthroplasty versus navigated mechanically aligned total knee arthroplasty : the MaKKRO trial

Aims

Nearly 99,000 total knee arthroplasties (TKAs) are performed in UK annually. Despite plenty of research, the satisfaction rate of this surgery is around 80%. One of the important intraoperative factors affecting the outcome is alignment. The relationship between joint obliquity and functional outcomes is not well understood. Therefore, a study is required to investigate and compare the effects of two types of alignment (mechanical and kinematic) on functional outcomes and range of motion.

Methods

The aim of the study is to compare navigated kinematically aligned TKAs (KA TKAs) with navigated mechanically aligned TKA (MA TKA) in terms of function and ROM. We aim to recruit a total of 96 patients in the trial. The patients will be recruited from clinics of various consultants working in the trust after screening them for eligibility criteria and obtaining their informed consent to participate in this study. Randomization will be done prior to surgery by a software. The primary outcome measure will be the Knee injury and Osteoarthritis Outcome Score The secondary outcome measures include Oxford Knee Score, ROM, EuroQol five-dimension questionnaire, EuroQol visual analogue scale, 12-Item Short-Form Health Survey (SF-12), and Forgotten Joint Score. The scores will be calculated preoperatively and then at six weeks, six months, and one year after surgery. The scores will undergo a statistical analysis.

Discussion

There is no clear evidence on the best alignment for a knee arthroplasty. This randomized controlled trial will test the null hypothesis that navigated KA TKAs do not perform better than navigated MA TKAs.

Cite this article: Bone Jt Open 2021;2(11):945–950.

Accuracy of joint line restoration based on three-dimensional registration of the contralateral tibial tuberosity and the fibular tip

Purpose

To assess a novel method of three-dimensional (3D) joint line (JL) restoration based on the contralateral tibia and fibula.

Methods

3D triangular surface models were generated from computed tomographic data of 96 paired lower legs (48 cadavers) without signs of pathology. Three segments of the tibia and fibula, excluding the tibia plateau, were defined (tibia, fibula, tibial tuberosity (TT) and fibular tip). A surface registration algorithm was used to superimpose the mirrored contralateral model onto the original model. JL approximation and absolute mean errors for each segment registration were measured and its relationship to gender, height, weight and tibia and fibula length side-to-side differences analyzed. Fibular tip to JL distance was measured and analyzed.

Results

Mean JL approximation did not yield significant differences among the three segments. Mean absolute JL error was highest for the tibia 1.4 ± 1.4 mm (range: 0 to 6.0 mm) and decreased for the fibula 0.8 ± 1.0 mm (range: 0 to 3.7 mm) and for TT and fibular tip segment 0.7 ± 0.6 (range: 0 to 2.4 mm) (p = 0.03). Mean absolute JL error of the TT and fibular tip segment was independent of gender, height, weight and tibia and fibula length side-to-side differences. Mean fibular tip to JL distance was 11.9 ± 3.4 mm (range: 3.4 to 22.1 mm) with a mean absolute side-to-side difference of 1.6 ± 1.1 mm (range: 0 to 5.3 mm).

Conclusion

3D registration of the contralateral tibia and fibula reliably approximated the original JL. The registration of, TT and fibular tip, as robust anatomical landmarks, improved the accuracy of JL restoration independent of tibia and fibula length side-to-side differences.

Level of evidence

IV

Balance and constraint in revision TKR: A classification for instability management

Instability is an increasingly common cause and symptom of failure of Total Knee Arthroplasty (TKA). Patients seek 'Functional Stability', which is the sum of both a balanced joint and, if necessary, mechanical constraint. The objective of this paper is to classify the different types of TKA instability and their causes. Based on this classification, the authors give methodical recommendations for instability management.

Instability classification

Instability in revision TKA can be classified into 3 types based on the management of bone loss and ligamentous deficiency which directs the level of constraint required to achieve functional stability.

Type 1

Bone deficiency: Revision with restoration of joint line and rebuilding the bony anatomy results in a balanced joint. No increased constraint is needed.

Type 2

Ligament and soft tissue deficiency: Requires increased constraint to overcome instability.

Type 3

Composite (Total) deficiency: (combined Type 1 and 2).The multiple causes of instability are outlined for each Instability type along with an algorithm for restoring the joint line and adding titrated constraint to restore functional stability.

An accurate method for locating the joint line during revision total knee arthroplasty: A radiologic study in the Chinese population

BACKGROUND

The systems for precisely locating the joint line during primary and revision total knee arthroplasty are still controversial, and they should be better evaluated in the Chinese population.

METHODS

A total of 451 standard anteroposterior knee radiographs from 451 healthy Chinese people (283 males and 168 females, the average age of 33.26 years, range 20-50 years) were included to measure the femoral width (FW) and the distances from the adductor tubercle (AT), the medial epicondyle (ME), the lateral epicondyle (LE), and the fibular head (FH) to the joint line (JL). Correlation between FW and distances from landmarks to the joint line was evaluated using Pearson correlation coefficient, and the ratios of ATJL, MEJL, LEJL, FHJL to FW were calculated.

RESULTS

The average distances from the AT, the ME, the LE, the FH to the JL were 49.4 ± 5.0 mm, 28.3 ± 3.1 mm, 26.9 ± 2.9 mm, 20.0 ± 4.0 mm, respectively. An excellent linear correlation was found between FW and the distance from AT to the joint line (R = 0.836, R² = 0.698); it was more reliable than the LE (R = 0.686, R² = 0.471) and the ME (R = 0.672, R² = 0.452). The average ratios of ATJL/FW, MEJL/FW, LEJL/FW were 0.553, 0.317, and 0.302, respectively. There were significant differences between our results and the studies based on the Western people.

CONCLUSION

The AT can be used as a reliable landmark to locate the JL precisely by the formula (ATJL = 0.548 × FW in males; ATJL = 0.562 × FW in females) in the Chinese population. The LE and ME can be the second choices. Moreover, it may be better to use ratios from the research based on the same race.

3D-surface scan based validated new measurement technique of femoral joint line reconstruction in total knee arthroplasty

Purpose

This study aimed to validate a new joint line measurement technique in total knee arthroplasty for separated assessment of the medial and lateral femoral joint line alteration with 3D-surface scan technology. Separate assessment of the medial and lateral joint line alteration may improve TKA alignment assessment regarding to joint line restoration in kinematic alignment and use of robotic-assisted TKA surgery.

Methods

The medial and lateral joint line difference after TKA implantation on an artificial bone model was analyzed and compared with a 3D-scan and full femoral radiographs pre- and postoperatively. Radiographic analysis included the perpendicular distance between the most distal point of the medial and lateral condyle and the reproduced preoperative lateral distal femoral angle (LDFA). For evaluation of validity and reliability, radiographs were captured initially with true anteroposterior view and subsequently with combined flexion and rotation malpositioning. Reliability of the introduced measurement technique in between three observers was tested with intraclass correlation coefficient (ICC).

Results

Radiographic measurement showed a mean difference of 0.9 mm on the medial side and 0.6 mm on the lateral side when compared to the 3D-surface scan measurement. The reliability of measurement accuracy was ≤ 1 mm in x-rays with < 10° flexion error regardless to malrotation in these images. The ICC test showed very good reliability for the medial joint line evaluation and good reliability for lateral joint line evaluation (ICC 0.92, ICC 0.86 respectively).

Conclusion

The new introduced joint line measurement method showed a sufficient reliability, accuracy and precision. It provides separated information about medial and lateral joint line alteration in TKA surgery in absolute values.

Level of evidence

V - Experimental Study

Medial joint space width and convergence angle change with time after medial opening-wedge high tibial osteotomy

BACKGROUND

Although the medial joint space width (MJSW) is commonly used for radiographic evaluation of knee osteoarthritis, the changes in knee joint space width (JSW) during weight bearing after medial opening-wedge high tibial osteotomy (MOWHTO) remain unclear. This study aimed to depict how medial and lateral JSWs and convergence angles change gradually after MOWHTO.

METHODS

We retrospectively followed up 81 MOWHTO cases for over 45 months on average. Pre- and postoperative mechanical axes were recorded. The JSWs and convergence angles were measured preoperatively, immediately postoperatively, and 3-6, 9-12, and 21-24 months postoperatively. Patient-reported outcomes were measured using a visual analogue scale (VAS).

RESULTS

The mean mechanical femoral-tibial angle improved from 8.1° varus to 2.4° valgus. At the aforementioned times, the respective mean values of MJSW were 2.6, 3.5, 3.8, 4.0, and 4.2 mm; mean convergence angles were 4.8°, 2.9°, 2.2°, 2.1°, and 1.9°; and the mean VAS scores were 7.2, 7.8, 4.8, 1.4, and 1.3. The MJSW continued to increase significantly in the first year postoperatively and then plateaued for a minimum of 2 years follow up after MOWHTO. The convergence angle decreased significantly in the first 6 months postoperatively and was then maintained.

CONCLUSIONS

The MJSW, convergence angle, and VAS scores continued to improve through weight bearing during the first year after MOWHTO and were maintained for at least 2 years. Thus, JSW measurement may be an easy and representative way of radiographically monitoring the effect of MOWHTO.

Joint line elevation is not associated with mid-flexion laxity in patients with varus osteoarthritis after total knee arthroplasty

PURPOSE

Previous cadaver studies showed that the additional bone cuts in the distal and posterior femur and joint line elevation resulted in laxity at mid-flexion after total knee arthroplasty (TKA). However, these results are not always applicable to TKA candidates because the related studies used cadaver knees with no osteoarthritis. It was hypothesized that the joint line elevation results in mid-flexion laxity after TKA in patients with knee osteoarthritis. The purpose of this study was to analyze the relationship between joint line elevation and mid-flexion laxity in patients with knee osteoarthritis.

METHODS

30 knees with varus osteoarthritis undergoing TKA were evaluated. Two femoral trial component models were prepared: (1) normal model with a thickness of the distal and posterior femoral components of 9 mm, and (2) 2-mm joint line elevation model with a thickness of the distal and posterior femoral components of 9 - 2 = 7 mm. This 2-mm joint line elevation model simulated an additional bone cut in the distal and posterior femur, and joint line elevation, without an additional bone cut. The femoral trial component models were set before implantation and measured the joint gap kinematics using a tensor device through the full knee range of motion.

RESULTS

The differences in joint gap change from 30° to 90° were not statistically significant between the two models. However, the joint line elevation model decreased the joint gap laxity at 120° (p = 0.02) and at 145° (p = 0.01).

CONCLUSIONS

This study showed that a 2-mm joint line elevation was not associated with mid-flexion laxity in patients with varus osteoarthritis in the knee. The results of this study differed from the results in previous cadaver studies.

LEVEL OF EVIDENCE

Therapeutic study, level II, prospective comparative study.

Effect of additional distal femoral resection on flexion deformity in posterior-stabilized total knee arthroplasty

PURPOSE

Flexion deformity after total knee arthroplasty (TKA) is associated with poor function and dissatisfaction and should, therefore, be avoided. In the case of preoperative flexion deformity, an increased distal resection of the femur may be necessary. The degree of resection required has only been determined for cruciate-retaining (CR) prostheses to date and varies considerably from study to study. Although, for many surgeons, the algorithm for the treatment of a flexion deformity includes the resection of the posterior cruciate ligament (PCL) before additional distal resection, the degree of resection necessary for posterior-stabilized (PS)-type prostheses is not known.

METHODS

Fifty consecutive patients (50 knees) who were due to undergo navigated TKA were included in this prospective study. At the end of the operation, the flexion deformity resulting from different sizes of distal femoral augmentations on the trial implants (0-8.5 mm) was determined using the navigation system.

RESULTS

A linear relationship of 2.2° ± 0.3° flexion deformity per mm distal femoral augmentation was found. This was not dependent on age, sex, the preoperative coronal alignment, or the preoperative flexion deformity.

CONCLUSIONS

In conclusion, after the removal of posterior osteophytes and posterior capsule release, around 5 mm of the distal femur must be further resected in the case of 10° flexion deformity and 9 mm in the case of 20° flexion deformity.

LEVEL OF EVIDENCE

II (Prospective cohort study).

Flexion First Balancer: description of new technique in TKA to reproduce joint line and pre-disease mechanical alignment

A considerable proportion of patients (19%) are dissatisfied after total knee arthroplasty (TKA). Possible factors contributing to this dissatisfaction are decreased posterior condylar offset (PCO) with subsequent joint line elevation, leading to mid-flexion instability. Secondly, the pre-disease mechanical alignment is changed into a neutral alignment. The Flexion First Balancer was developed to avoid these problems. This technique aims to maintain MCL isometry by restoring medial PCO and medial joint line to its pre-disease level. Also, to reconstruct the pre-disease mechanical alignment by adjusting the distal femoral angle. In this study we provide a detailed technical overview of the Flexion First Balancer technique.

Medial stabilizing technique preserves anatomical joint line and increases range of motion compared with the gap-balancing technique in navigated total knee arthroplasty

BACKGROUND

Medial compartment stability is important in total knee arthroplasty. The medial stabilizing technique (MST) has been proposed to achieve medial stability without excessive medial soft tissue release in total knee arthroplasty. Herein, we compare the MST and the gap-balancing technique (GBT) in navigated total knee arthroplasty.

METHODS

We retrospectively analyzed 70 patients with varus knee osteoarthritis who underwent primary total knee arthroplasty using the navigation system. They were divided into MST (n = 39) and GBT (n = 31) groups. We assessed intraoperative navigation data, radiographic data, and insert thickness. Preoperative and postoperative joint line changes were measured. We also assessed range of motion and clinical instability before and after total knee arthroplasty. These parameters were statistically compared between the groups.

RESULTS

Compared with the GBT group, medial extension gaps were significantly smaller in the MST group (P = 0.008). The gap difference between medial and lateral extension was significantly greater in the MST group (P = 0.018). Other navigation data showed no significant differences. Insert thickness and joint line changes were significantly lower in the MST group (P = 0.001, P = 0.018, respectively). Postoperative range of motion was significantly greater in the MST group (P = 0.032). There was no objective or subjective knee instability in either group.

CONCLUSION

The MST could avoid knee joint line changes and might increase postoperative range of motion. Although the MST permitted a discrepancy between medial and lateral gaps, no patients felt knee instability. The MST might improve the results of total knee arthroplasty.

The adductor tubercle can be a radiographic landmark for joint line position determination: an anatomic-radiographic correlation study

Background

The adductor tubercle (AT) has been used intraoperatively as a landmark to evaluate the joint line position in knee arthroplasty. The purpose of this study was to determine whether the AT could be clearly identified on radiographic imaging as well as if the AT to joint line distance could be accurately measured for use as a radiographic landmark.

Methods

The distance from the AT to the joint line was measured on each of 78 knees during total knee arthroplasty. Next, the AT was marked with a metal marker for radiographic analysis. On the postoperative radiograph, the location of the AT was determined by tracing the metal marker. Subsequently, the radiographic joint line distance (RJLD) was measured and compared with the intraoperative joint line distance (IJLD) to test the agreement of the measurements.

Results

Location analysis indicated that the inflection point on the radiographic contour of the distal femur was the predicted location for the AT. The mean IJLD was 45 ± 3 mm and the RJLD was 45 ± 4 mm. The intraclass correlation coefficient was used to evaluate the inter-rater reliability between the two methods; that coefficient was 0.751, indicating good agreement between them. Measurements on the radiograph were comparable to the intraoperative measurements of the operated knees.

Conclusions

In addition to being an intraoperative landmark, the AT may also be an eligible radiographic landmark for analyzing joint line level. The RJLD measurement may be obtained to plan the joint line position in knees with significant bone loss preoperatively and to follow up the results of surgery postoperatively.

Adequate joint line restoration and good preliminary clinical outcomes after total knee arthroplasty using the Flexion First Balancer technique

INTRODUCTION

Up to 20% of patients are dissatisfied after total knee arthroplasty (TKA). Factors which could possibly contribute to this dissatisfaction are a decreased posterior condylar offset (PCO) and subsequent joint line elevation which leads to mid-flexion instability. The Flexion First Balancer (FFB) technique aims to adequately restore the medial PCO and thereby reconstruct the medial native joint line to its pre-disease height.

METHODS

A retrospective cohort of 59 patients operated using the FFB technique was analyzed and matched with a historic measured resection (MR) cohort of 59 patients. Groups were matched for age, gender, BMI and ASA classification. Joint line and PCO changes as well as patient reported outcome measurement scores (PROMs) were evaluated at one year [1.0 - 1.6] postoperatively.

RESULTS

Radiographic evaluation revealed no changes in joint line height in the FFB group, whereas an elevation in joint line was seen in the MR group (p = 0.002). The PCO increased after surgery in both group without any statistically significant differences. Evaluation of PROMs found no differences between the two groups for total OKS and KOOS scores, nor in re-operation or complication rates.

CONCLUSION

The FFB technique seems to be a safe technique to use in TKA and reconstructs the pre-disease joint line in contrast to the MR technique. The clinical outcomes were comparable between both groups.

Phenotyping the knee in young non-osteoarthritic knees shows a wide distribution of femoral and tibial coronal alignment

PURPOSE

There is a lack of knowledge about the joint line orientation of the femur and tibia in non-osteoarthritic knees. The primary purpose of the present study was to evaluate the orientation of the joint lines in native non-osteoarthritic knees using 3D-reconstructed CT scans. The secondary purpose was to identify knee phenotypes to combine the information of the femoral and tibial alignment.

METHODS

A total of 308 non-osteoarthritic knees of 160 patients (male to female ratio = 102:58, mean age ± standard deviation 30 ± 7 years (16-44 years) were retrospectively included from our registry. All patients received CT of the knee according to the Imperial Knee Protocol. The orientation of the femoral and tibial joint line was measured in relation to their mechanical axis (femoral mechanical angle, FMA, and tibial mechanical angle, TMA) using a commercially planning software (KneePLAN 3D, Symbios, Yverdon les Bains, Switzerland). The values of FMA and TMA were compared between males and females. Descriptive statistics, such as means, ranges, and measures of variance (e.g. standard deviations), were presented. Based on these results, phenotypes were introduced for the femur and tibia. These phenotypes, based on FMA and TMA values, consist of a mean value and cover a range of ± 1.5° from this mean (3° increments). The distribution of femoral and tibial phenotypes, and their combinations (knee phenotypes) were calculated for the total group and for both genders.

RESULTS

The overall mean FMA ± standard deviation (SD) was 93.4° ± 2.0° and values ranged from 87.9° varus to 100° valgus. The overall mean TMA ± SD was 87.2° ± 2.4° with a range of 81.3° varus to 94.6° valgus. FMA and TMA showed significant gender differences (p < 0.01). Females showed more valgus alignment than males. The most common femoral phenotype was neutral in both genders. The most common tibial phenotype was neutral in the male knees (62.8%) and valgus (41.6%) in the female knees. In males, the most frequent combination (knee phenotype) was a neutral phenotype in the femur and a neutral phenotype in the tibia (25.6%). In females, it was a neutral femoral phenotype and a valgus tibial phenotype (28.3%).

CONCLUSION

3D-reconstructed CT scans confirmed the great variability of the joint line orientation in non-osteoarthritic knees. The introduced femoral and tibial phenotypes enable the evaluation of the femoral and tibial alignment together (knee phenotypes). The variability of knee phenotypes found in this young non-osteoarthritic population clearly shows the need for a more individualized approach in TKA.

LEVEL OF EVIDENCE

III.

The negative effect of joint line elevation after total knee arthroplasty on outcome

PURPOSE

Total knee arthroplasty (TKA) is widely used as a treatment for knee osteoarthritis. However, still up to 20% of the patients are dissatisfied. Joint line elevation after TKA might be a contributing factor as it alters knee kinematics. The aim of this study was to investigate the effect of joint line elevation on outcome.

METHODS

A systematic review of the literature was performed to select studies that reported on joint line alterations after primary or revision TKA and outcome. Studies with comparable outcome parameters were included in a correlation analysis.

RESULTS

In total, 396 studies were identified, of which 27 met the inclusion criteria. 8 studies could be included in the correlation analysis. Mean joint line elevation after primary TKA was 3.0 mm and after revision TKA this was 3.6 mm. A statistically significant negative correlation was found between joint line elevation and the postoperative Knee Society Score (KSS) function score (ρ = - 0.496, p < 0.001). In a pooled analysis, the maintained joint line revision TKA group had statistically significant better postoperative KSS total scores compared to an elevated joint line group (p < 0.001).

CONCLUSION

In this systematic review, a negative correlation between joint line elevation and outcome was found. Furthermore, revision TKAs with a maintained joint line have statistically significant better postoperative KSS scores compared to an elevated joint line group. To achieve optimal outcome after TKA, restoration of the joint line is one of the parameters that should be pursued and introduced elevation should not exceed 4 mm.

LEVEL OF EVIDENCE

IV.

Are contemporary femoral components sizing and design likely to affect functional results in TKA? A mathematical model of an implanted knee to predict knee forces

PURPOSE

This study is aimed to investigate the effects of the choice of femoral and tibial components on several mechanical outputs that might be associated with total knee replacement surgery outcomes using a validated computational model: the Kansas knee simulator.

METHODS

Two models from the same range of implants were taken into account: Model 1, the femoral component fitted the femoral epiphysis, with physiological positioning of the articulating surface using a 10-mm-thick tibial component, and in Model 2, the femoral component was 4 mm smaller than in Model 1, and a 14-mm-thick tibial component was used with a similar tibial resection and the tibio-femoral joint line was 4 mm more proximal to compensate the increased posterior bone resection and maintain proper soft-tissue tension in flexion. Changes in reaction forces and contact pressures between the components, changes in extensor muscle forces and changes in patello-femoral joint kinematics during walking gait have been studied.

RESULTS

While the computational model predicted that most kinematic and kinetic outputs, including tibio-femoral and patello-femoral joint motions, contact forces, pressures and areas, were similar for Model 1 and Model 2, and a dramatic difference has been found in the extensor muscle forces necessary to flex and extend the knee. To reproduce the same knee motion with a knee reconstructed as in Model 2, a patient would need to generate approximately 40% greater extensor muscle force throughout the gait cycle in order to do so.

CONCLUSION

As a consequence of such a large increase in the extensor muscle force, the knee motions would probably be compromised and, subsequently, a patient with a knee reconstructed as in Model 2 would be less likely to be able to reproduce normal knee function and therefore more likely to report poor outcome.

Medial joint line elevation of the tibia measured during surgery has a significant correlation with the limb alignment changes following medial unicompartmental knee arthroplasty

PURPOSE

This study aimed to determine the correlation between the change in joint line height calculated from the resected bone and insert thickness during surgery and the change in limb alignment following unicompartmental knee arthroplasty (UKA). It was hypothesized that joint line elevation is correlated with the change in limb alignment.

METHODS

A total of 74 consecutive patients diagnosed with either isolated medial compartmental osteoarthritis (38 patients) or spontaneous osteonecrosis of the knee (36 patients) were included. The thickness of the proximal tibial and distal femoral bony cuts was measured during surgery; using these values, the medial joint line elevation of the tibia (MJLET) and medial joint line reduction of the femur (MJLRF) were defined. The correlation between the amount of change in the hip-knee-ankle (HKA) angle before and after surgery (δHKA) and the thickness of the tibial insert (TI), MJLET, or MJLRF were evaluated.

RESULTS

The mean values of δHKA, TI, MJLET, and MJLRF were 5.0° ± 2.6°, 8.5 ± 0.8, 4.4 ± 1.3, and 0.0 ± 1.1 mm, respectively. The δHKA had a significant, but weak-positive correlation with the TI (P = 0.02), and moderate-positive correlation with MJLET (P < 0.001). However, no correlation was observed between δHKA and MJLRF.

CONCLUSIONS

The MJLET measured during surgery had a significant moderate-positive correlation with the change in limb alignment following medial UKA. For clinical relevance, the surgeon can predict postoperative limb alignment after UKA by considering, intraoperatively, both the insert thickness and the depth of resection at the proximal tibia thus minimizing technical error to obtain an optimal alignment after UKA.

LEVEL OF EVIDENCE

Diagnostic study, level II.

The epicondylar ratio can be reliably used on X-ray of the knee to determine the joint line

PURPOSE

The epicondylar ratio (ER) is used to restore the individual joint line (JL), especially in revision total knee arthroplasty. It was first described in magnetic resonance imaging (MRI) but is usually applied to a.p. radiographs of the knee for preoperative planning. The objective of the current study was to define reliable landmarks in MRI and X-ray images of the knee, which allow comparison of the image modalities. Furthermore, the correlation of the measured ER in MRI and X-rays of the knee was calculated.

METHODS

A consecutive series of 87 patients who underwent an arthroscopical intervention of the knee were included into the present study. The lateral epicondyle was defined as the most lateral and distal prominence. On the medial side, the measurement was aligned to the epicondylar sulcus. The medial and lateral ER were calculated by dividing the perpendicular distance from the JL to the epicondyle by the transepicondylar distance. One observer determined the ER twice to calculate the intramethod intraobserver agreement, and a second observer obtained the intramethod interobserer agreement. The ER obtained from X-ray and MRI was compared to calculate the intermethod correlation.

RESULTS

The average lateral ER was 0.29 on X-ray versus 0.28 on MRI. The average medial ER was 0.33 and 0.33, respectively. Intramethod agreement ranged from 0.66 to 0.88 and intermethod correlation from 0.49 to 0.57.

CONCLUSIONS

The ER can be determined reliably on MRI and X-ray images of the knee. The correlation of the ER in MRI and X-ray is fair.

The medial tibial joint line elevation over 5 mm restrained the improvement of knee extension angle in unicompartmental knee arthroplasty

PURPOSE

The purpose of this study was to examine the relationship between medial tibial joint line elevation and the improvement of range of motion (ROM) in unicompartmental knee arthroplasty (UKA). The hypothesis was that limited elevation of tibial joint line will improve knee range of motion in UKA.

METHODS

Forty-six consecutive medial UKAs were enrolled in this study. Medial tibial joint line elevation was defined as the polyethylene insert and tibial tray thickness minus the tibial osteotomy and sawblade thickness. Positive values indicated an elevation of the tibial joint line. A component gap between the femoral trial prosthesis and the medial tibial osteotomy surface was also examined. Joint loosening was also calculated based on the joint component gap minus insert and tibial tray thickness. The correlation of the medial tibial joint line elevation with joint looseness and postoperative range of motion were analyzed.

RESULTS

The mean medial tibial joint line elevation was 4.9 ± 1.1 mm. The medial tibial joint line elevation reduced the improvement of knee extension (R = - 0.43, p < 0.01). The medial tibial joint line elevation was also correlated with reduced loosening of the joint knee extension (R = - 0.42, p < 0.01). This, in turn, resulted in limited improvement of the knee extension angle. Moreover, joint line elevation under 5 mm significantly improved knee extension angle compared to joint line elevation over 5 mm.

CONCLUSIONS

The medial joint line elevation of the tibia in UKA reduced the improvement of knee extension angle, due to a reduced joint looseness at knee extension. A tibial joint line elevation greater than 5 mm in UKA should be avoided to prevent postoperative flexion contracture. For the clinical relevance, this study clarified that the medial joint line of the tibia is an important factor to prevent postoperative flexion contracture in UKA.

LEVEL OF EVIDENCE

II.

Effect of joint line preservation on mobile-type bearing unicompartmental knee arthroplasty: finite element analysis

In this study, we performed a virtual mobile-bearing unicompartmental knee arthroplasty (UKA) on the contact pressure in the tibial insert and articular cartilage by using finite element (FE) analysis to understand clinical observations and elaborate on the potential risks associated with a joint line preservation such as wear on tibial insert and osteoarthritis on other compartment. Neutral position of the knee joint was defined in 0 mm joint line, and contact pressure between tibial insert and articular cartilage varies with respect to changes of joint line. Therefore, evaluation of contact pressure may provide the degree of joint line preservation. The FE model for the joint line was developed using a perpendicular projection line from the medial tibial plateau to the anatomical axis. Seven FE models for joint lines in cases corresponding to ± 6, ± 4, ± 2, and 0 mm were modeled and analyzed in normal level walking conditions. The maximum contact pressure on the superior and inferior surfaces of the polyethylene insert increased when the joint line became positive while the maximum contact pressure on the articular cartilage increased when the joint line became negative. The increase in the maximum contact pressure in the positive joint line exceeded that in the negative joint line, and this lead to an unsymmetrical maximum contact pressure distribution with respect to the joint line from a 0 reference. The joint line elevation was sensitive to increases or decreases in maximum contact pressures in the mobile-bearing UKA. The findings of the study determined that postoperative joint line preservation is important in mobile-type bearing UKA.

The tibial growth plate as a predictor of the original tibial plateau joint line as a reference for kinematically aligned total knee arthroplasty

Background

Restoration of the natural joint line is a cornerstone for kinematically aligned total knee arthroplasty (TKA). The purpose of this study was to investigate the relative orientation of the tibial growth plate (GP) with respect to the tibial plateau (TP) for possible application in predicting natural joint line for knees with highly advanced osteoarthritis patient at the time of kinematically aligned TKA.

Methods

Images from computed tomography (CT) of 27 normal knees (9 males, 18 females; mean age, 31.6 years) were studied. Geometry of the GP was extracted from CT images, and its moment-of-inertia axes were calculated for the whole GP and the medial and lateral halves. Angular orientations of each GP axis with respect to the TP plane were measured in anatomical coordinates.

Results

The TP and GP planes were oriented in 2.3 ± 1.8° of varus and 1.1 ± 1.9° of valgus relative to the tibial mechanical axis, respectively. With respect to the TP plane, the whole GP plane was inclined in 3.4 ± 1.5° of valgus. Orientation of the GP plane differed drastically between medial and lateral halves. The medial GP was in 4.9 ± 2.9° of varus and 1.8 ± 2.5° of anterior inclination, and the lateral half was in 10.4 ± 2.4° of valgus and 18.6 ± 4.0° of anterior inclination relative to the TP.

Conclusions

Angular orientation of the original TP plane can be predicted in reference to the GP plane and may provide reasonable guidance for the target bone resection angle of the tibia in kinematically aligned TKA.

Improved joint-line restitution in unicompartmental knee arthroplasty using a robotic-assisted surgical technique

PURPOSE

Joint-line restitution is one objective of unicompartmental knee arthroplasty (UKA). However, the joint line is often lowered when resurfacing femoral implants are used. The aim of this study was to compare the joint-line height in UKA performed by robotic-assisted and conventional techniques.

METHODS

This retrospective case-control study compared two matched groups of patients receiving a resurfacing UKA between 2013 and 2016 by either a robotic-assisted (n = 40) or conventional (n = 40) technique. Each group comprised 27 women and 13 menm wuth a mean age of 69 and 68 years, respectively. Indications for surgery were osteoarthritis (n = 35) and condylar osteonecrosis (n = 5). Two validated radiologic measurement methods were used to assess joint-line height.

RESULTS

Forty UKA (23 medial and 17 lateral) were analysed in each group. Restitution of joint-line height was significantly improved in the robotic-assisted group compared than the control group: +1.4 mm ±2.6 vs +4.7 mm ± 2.4 (p < 0.05) as assessed using method 1, and +1.5 mm ±2.3 vs +4.6 mm ±2.5 (p < 0.05) as assessed using method 2.

CONCLUSIONS

Restitution of joint-line height in resurfacing UKA can be improved with robotic-assisted surgery. Improvement in clinical outcome measures must be demonstrated with long-term studies.

The intercondylar notch ceiling: an accurate reference for distal femoral resection in total knee arthroplasty for severely degenerated varus knees

PURPOSE

To measure the distance from the intercondylar ceiling to the lowest point of the medial and lateral femoral condyles in a healthy population so to obtain a clearly discernible and accurate landmark for proper distal femoral resection during total knee arthroplasty (TKA).

METHODS

Three-dimensional models of the lower extremities of 100 healthy Chinese subjects were constructed using computed tomography scans. The distance between the distal surface of the medial femoral condyle and the intercondylar notch ceiling, in the direction of the femoral mechanical axis, was measured.

RESULTS

The mean distance from the distal surface of the medial femoral condyle to the intercondylar notch ceiling was 9.1 ± 1.4 and 8.2 ± 1.4 mm in male and female subjects, respectively. Interestingly, this distance did not differ significantly with varying sizes of the distal femur.

CONCLUSIONS

The intercondylar notch ceiling could be used as an accurate landmark to determine the proper distal femoral resection level during TKA. For the clinical relevance, the distal femoral bone cut should be at the level of the intercondylar notch ceiling when using the most of the current TKA prosthesis systems.

An anatomical study of the proximal aspect of the medial femoral condyle to define the proximal-distal condylar length

Objective:

Despite its possible role in knee arthroplasty, the proximal-distal condylar length (PDCL) of the femur has never been reported in the literature. We conducted an anatomic study of the proximal aspect of the medial femoral condyle to propose a method for measuring the PDCL.

Materials and Methods:

Inspection of dried bone specimens was carried out to assure the most proximal condylar margin (MPCM) as the eligible starting point to measure the PDCL. Simulation surgery was performed on seven pairs of cadaveric knees to verify the clinical application of measuring the PDCL after locating the MPCM. Interobserver reliability of this procedure was also analyzed.

Results:

Observation of the bone specimens showed that the MPCM is a concavity formed by the junction of the distal end of the supracondylar ridge and the proximal margin of the medial condyle. This anatomically distinctive structure made the MPCM an unambiguous landmark. The cadaveric simulation surgical dissection demonstrated that the MPCM is easily accessed in a surgical setting, making the measurement of the PDCL plausible. The intraclass correlation coefficient was 0.78, indicating good interobserver reliability for this technique.

Conclusion:

This study has suggested that the PDCL can be measured based on the MPCM in a surgical setting. PDCL measurement might be useful in joint line position management, selection of femoral component sizes, and other applications related to the proximal-distal dimension of the knee. Further investigation is required.

Changes of posterior condylar offset results in midflexion instability in single-radius total knee arthroplasty

INTRODUCTION

There is no algorithm for the management of joint stability in midflexion up to now. Change in the joint line (JL) is considered to be the primary cause, although it only determines the extension gap. The purpose of this study was to determine the influence of the posterior condylar offsets (PCO), which defines the flexion gap, on midflexion instability.

MATERIALS AND METHODS

Forty-two knee joints (38 patients) were included in this study, patients undergoing navigated total knee arthroplasty due to primary osteoarthritis of the knee. Changes in the JL and the PCO were determined from the navigation data. A gap tensioning device was used to determine the width of the joint gap at -5°, 0°, 30° and 60° intraoperatively.

RESULTS

Within a range between 5 mm proximalization and 2 mm distalization, the JL had no influence on stability in midflexion. In contrast to this, both an increase and a decrease in PCO led to midflexion instability (R = 0.361, p = 0.019). In 16 cases (38%), the PCO was changed by more than 2 mm. This led to a midflexion instability of more than 2 mm in seven of these cases (44%).

CONCLUSIONS

Whereas the joint line can be displaced by up to 5 mm without measurable changes in joint stability, reconstruction of the posterior offset within a tight range of 2 mm is necessary to avoid midflexion instability.

“Meniscal” scar as a landmark for the joint line in revision total knee replacement

AIM

To determine whether tissue identified at the joint line was actually remnant “meniscal” scar tissue or not.

METHODS

Nine patients undergoing revision knee surgery following informed consent had meniscal scar tissue sent to the histology department for analyses. All revisions were performed where joint line had been raised or lowered at earlier surgery. Although preoperative radiographic evaluations suggested that the joint line had been altered, intraoperatively there was scar tissue at the level of the recreated joint line. This scar tissue has traditionally been described as meniscal scar, and to identify the origins of this tissue, samples were sent for histological analyses. The tissue samples were stored in formalin, and embedded and sectioned before undergoing histochemical staining. All samples underwent macroscopic and microscopic examination by a histopathologist who was blind to the study aims. The specific features that were examined included tissue organisation, surface and central composition, cellular distribution including histiocytes, nuclear ratio and vasculature. Atypical and malignant features, inflammation and degeneration were specifically looked for. A statistical review of the study was performed by a biomedical statistician.

RESULTS

The histological findings for the nine patients showing the macroscopic and microscopic findings, and the conclusion are outlined in a Table. The histological analyses were reviewed to determine whether the tissue samples were likely to be meniscal scar tissue. The response was yes (2, 22%), no (6, 67%) and maybe (1, 11%) based on the conclusions. The results were “yes” when on macroscopy, firm cream tissue was identified. In these two “yes” samples, microscopic analyses showed organised fibrous tissue with focal degenerative areas with laminated pattern associated with histiocytes peripherally but no inflammation. The “no” samples were assessed macroscopically and microscopically and were deemed to have appearances representing fibrous synovial tissue and features in keeping with degenerate scar tissue or connective tissue. One sample was indeterminate and microscopically contained fibro-collagenous tissue with synovial hyperplasia. It also contained some degenerate hyalinised tissue that may represent cartilage, but the appearances were not specific.

CONCLUSION

Based on our pilot study, we recommend reliance on a number of markers to identify the joint line as outlined above, and to exercise caution in using the “meniscal” scar.

An unambiguous technique for locating the adductor tubercle and using it to identify the joint line

BACKGROUND

If the adductor tubercle could be accurately located, it would be a useful landmark for identifying the joint line during knee arthroplasty. This study aimed to develop an intraoperative technique to improve its locating accuracy.

METHODS

Evaluation of bone specimens and cadaveric knees revealed that the proximal slope of the adductor tubercle (PSAT) turns from the medial surface vertically into the superior surface of the medial condyle, which forms a distinctive edge. This provided an ideal landmark that could be unambiguously engaged using a tipped instrument. Using the PSAT as a reference point, we measured the distance to the joint line (the proximal-distal condylar length; PDCL) in eight pairs of cadaveric knees, and evaluated the inter-observer variability. Next, we measured 120 knees undergoing total knee arthroplasty to test this technique in a normal population. Finally, we divided each PDCL by the respective anterior-posterior condylar length (APCL) to create a ratio that could predict the PDCL regardless of knee size.

RESULTS

The intra-class correlation coefficient (ICC) was 0.86 for the cadaveric measurements. The mean PDCL from the operated knees was 46mm (coefficient of variance (CV): eight percent). The mean PDCL/APCL ratio was 0.77 (CV: six percent). The high ICC and low CV indicated that using the PSAT was a reliable technique.

CONCLUSION

The PSAT is an ideal surgical landmark. The tipped instrument engagement technique with it may help to unambiguously locate the adductor tubercle in order to identify the joint line during knee arthroplasty.

The adductor tubercle: an important landmark to determine the joint line level in revision total knee arthroplasty

PURPOSE

The restoration of the physiological femoro-tibial joint line (JL) is important to obtain a good outcome in revision total knee arthroplasty (RTKA). However, its assessment is challenging. The ratio of the distance between the adductor tubercle (AT) JL (ATJL) and the trans-epicondylar femoral width (FW) was proposed as a reliable method. The purpose of this study was to check whether this ratio is a reliable tool to restore the prosthetic JL height in challenging prosthetic revision cases.

METHODS

Twenty-one patients (mean age 65.8 years) were recruited. During surgery, FW was measured and ATJL distance was calculated using 0.53 (SD 0.03) as the ratio. After implant positioning, the obtained ATJL line was measured to verify the accuracy of the surgical procedure. Thirteen patients presented a healthy contralateral knee: a comparative radiograph examination was performed to verify the appropriateness of the restored JL height.

RESULTS

The intra-operatively calculated ATJL was not significantly different with respect to the measured ATJL obtained after prosthetic component implantation. The comparative analysis between the restored JL and the JL of the contralateral not operated knee was also not statistically significant, thus confirming the appropriateness of the restored JL height.

CONCLUSIONS

This study shows that the method which uses an AT to JL distance/FW ratio to determine the JL level, previously applied in primary TKA, is valid when using intra-operatively acquired measurements in RTKA. This is clinically relevant since it represents a reliable tool which helps surgeons to restore the JL level in challenging prosthetic revision cases.

LEVEL OF EVIDENCE

Case series, Level IV.

Change in collateral ligament length and tibiofemoral movement following joint line variation in TKA

PURPOSE

The primary intent of total knee arthroplasty is the restoration of normal knee kinematics, with ligamentous constraint being a key influential factor. Displacement of the joint line may lead to alterations in ligament attachment sites relative to knee flexion axis and variance of ligamentous constraints on tibiofemoral movement. This study aimed to investigate collaterals strains and tibiofemoral kinematics with different joint line levels.

METHODS

A previously validated knee model was employed to analyse the change in length of the collateral ligaments and tibiofemoral motion during knee flexion. The models shifted the joint line by 3 and 5 mm both proximally and distally from the anatomical level. The data were captured from full extension to flexion 135°.

RESULTS

The elevated joint line revealed a relative increase in distance between ligament attachments for both collateral ligaments in comparison with the anatomical model. Also, tibiofemoral movement decreased with an elevation in the joint line. Conversely, lowering the joint line led to a significant decrease in distance between ligament attachments, but greater tibiofemoral motion.

CONCLUSION

Elevation of the joint line would strengthen the capacity of collateral ligaments for knee motion constraint, whereas a distally shifted joint line might have the advantage of improving tibiofemoral movement by slackening the collaterals. It implies that surgeons can appropriately change the joint line position in accordance with patient's requirement or collateral tensions. A lowered joint line level may improve knee kinematics, whereas joint line elevation could be useful to maintain knee stability.

LEVEL OF EVIDENCE

V.

The medial and lateral epicondyle as a reliable landmark for intra-operative joint line determination in revision knee arthroplasty

Objectives

The purpose of this study was to develop an accurate, reliable and easily applicable method for determining the anatomical location of the joint line during revision knee arthroplasty.

Methods

The transepicondylar width (TEW), the perpendicular distance between the medial and lateral epicondyles and the distal articular surfaces (DMAD, DLAD) and the distance between the medial and lateral epicondyles and the posterior articular surfaces (PMAD, DLAD) were measured in 40 knees from 20 formalin-fixed adult cadavers (11 male and nine female; mean age at death 56.9 years, sd 9.4; 34 to 69). The ratios of the DMAD, PMAD, DLAD and PLAD to TEW were calculated.

Results

The mean TEW, DMAD, PMAD, DLAD and PLAD were 82.76 mm (standard deviation (sd) 7.74), 28.95 mm (sd 3.3), 28.57 mm (sd 3), 23.97 mm (sd 3.27) and 24.42 mm (sd 3.14), respectively. The ratios between the TEW and the articular distances (DMAD/TEW, DLAD/TEW, PMAD/TEW and PLAD/TEW) were calculated and their means were 0.35 (sd 0.02), 0.34 (sd 0.02), 0.28 (sd 0.03) and 0.29 (sd 0.03), respectively.

Conclusion

This method provides a simple, reproducible and reliable technique enabling accurate anatomical joint line restoration during revision total knee arthroplasty.

Cite this article: B. Ozkurt, T. Sen, D. Cankaya, S. Kendir, K. Basarır, Y. Tabak. The medial and lateral epicondyle as a reliable landmark for intra-operative joint line determination in revision knee arthroplasty. Bone Joint Res 2016;5:280–286. DOI: 10.1302/2046-3758.57.BJR-2016-0002.R1.

Joint line level in revision total knee replacement: assessment and functional results with an average of seven years follow-up

INTRODUCTION

It has been shown that the distance between the joint line (JL) and the fibular head is constant in both knees in a given individual. We analysed the influence of the JL level difference between the revised knee and the native knee from the functional outcomes after TKR revision.

METHODS

This multicentre study assessed retrospectively a consecutive series of 177 revised total knee replacements. Patients with contralateral knees that had undergone previous major surgery or trauma were excluded. The JL level difference between both knees was measured on Knee's AP standing X-rays and compared to the KSS Knee and Function scores at the final follow-up.

RESULTS

Eighty-five cases were analysed at a mean of seven years follow-up. There was a significant increase in KSS Knee and Function scores after surgery. The average elevation of the JL was 2.2 mm (s.d. 2.66 mm) compared with the healthy contralateral knee. When the JL was elevated more than 4 mm this correlated with a decreased KSS Function score and decreased post-operative knee flexion.

CONCLUSIONS

Poorer functional results are significantly associated with an elevation in the JL compared to the contralateral healthy knee. In those patients with a suitable contralateral knee the JL level to restore can be assessed by the distance between the femoral condyle and the apex of the fibular head of the contralateral knee.

Joint line and patellar height restoration after revision total knee arthroplasty

BACKGROUND

Restoration of proper joint line (JL) position and patellar height in revision total knee arthroplasty (TKA) is essential in the recovery of knee function and kinematics. We determined whether the JL position and patellar height could be restored in patients undergoing septic and aseptic revision TKA.

MATERIALS AND METHODS

We retrospectively reviewed 70 patients (74 knees) who had revision TKA between September 2004 and December 2010. Forty seven knees had a two stage revision for infected TKA and 27 knees for aseptic failure. The JL position, patellar height and patellar tendon (PT) length were measured and compared between primary TKA and post revision. The clinical scores including a hospital for special surgery (HSS), Knee Society Score (KSS), Western Ontario and McMaster Universities (WOMAC) and range of motion (ROM) were compared.

RESULTS

The overall JL increased from 17.51 mm to 18.37 mm post revision, the Insall-Salvati (IS) ratio declined from 0.98 to 0.92, and the PT length declined from 42.92 mm to 39.45 mm. 9 of the 21 patellar baja knees improved to normal patellar height. After revision, the JL in the septic group (17.02 mm) was significantly lower than the aseptic group (20.74 mm). The changes of the JL position and IS ratio in the septic group were significantly larger than the aseptic groups (P < 0.05). JL position had a positive correlation to the IS ratio and PT length post revision. The knee function scores including HSS, KSS, WOMAC scores, and ROM all improved post revision compared to pre revision (P < 0.05), and the septic group had a lower knee function compared to the aseptic group. JL position and IS ratio post revision had no correlation to the HSS, KSS, WOMAC scores, and ROM.

CONCLUSIONS

JL position can be sufficiently restored with appropriate distal femoral augment reconstruction after revision TKA, but the patellar height cannot be well improved, especially in the septic revision with obvious PT contracture. No correlation was found between the JL position and patellar height to the knee function post revision TKA.

Joint line restoration during revision total knee arthroplasty: an accurate and reliable method

During revision total knee arthroplasty, the joint line is frequently malpositioned, due to the disappearance of the anatomical landmarks following previous interventions. This leads to decreased clinical outcome and increased risk of re-intervention. Many methods have been proposed to restore the joint line, but none of them has shown itself to be reliable. We describe an accurate and precise method to localize the exact position of the joint line which guarantees a better clinical knee score. The adductor tubercle (AT) is recognized to be the most reliable landmark used to localize the knee joint line (JL). The distance from the AT to the JL on antero-posterior radiographs (ATJL) and the femoral diameter (FD) on true lateral views were measured on 200 randomly selected normal knees. These measurements were tested for intra- and inter-observer differences. Then, the relationship between these two measurements was studied. A significant correlation and linear regression between FD and ATJL was found (p < 0.001), making the adductor tubercle a valid landmark to accurately position the prosthetic joint within 4 mm from the normal position. No significant difference was noted in the intra and inter-observer measurements (F test not significant). Sex was found to be an intervening variable (p ˂ 0.001). The correlation and regression between ATJL and FD had to be adjusted accordingly. Once the ATJL was determined preoperatively, the JL level is found during surgery by using a caliper that is held on the easily palpable AT. Knowing the femoral diameter, we can easily locate the joint line level surgically, using the adductor tubercle as a landmark. This method leads to better clinical outcomes and a reduced risk of re-intervention following revision total knee arthroplasty.

Assessing joint line positions by means of the contralateral knee: a new approach for planning knee revision surgery?

PURPOSE

Reconstructing the natural joint line in knee revision surgery improves clinical and functional outcome but may be challenging when both cartilage and bone were removed during previous operations. Assessing joint lines (JLs) by means of bony landmarks is inadvisable because of large variations in human anatomy. Because of the inherent symmetry of the human body, we hypothesised that JLs may be directly assessed by measuring the distances from the bony landmarks to the JL of the contralateral knee by means of radiographic images.

METHODS

Using scaled weight-bearing radiographs in anteroposterior view of both knees, two independent observers measured the distances from the fibular head, the medial and lateral epicondyle, and the adductor tubercle to the JL. A two-sided p value of ≤0.05 was considered statistically significant.

RESULTS

Two hundred knees of 100 patients (50 men and 50 women) were examined. For the fibular head, the mean difference between the treated and the control knee was 0.0 mm with narrow confidence limits ranging from -1.1 to 1.1.

CONCLUSION

As a new assessment method, we have suggested to assess the JL by means of radiographs of the contralateral knee. The most precise parameter was found to be the distance between the fibular head and the JL. The level of arthritis, age, gender, visibility of the landmarks, and misalignment did not influence measurement accuracy. This parameter is the first tibia-related landmark for assessing the JL, which advantageously corresponds to the tibia-first technique in revision surgery.

LEVEL OF EVIDENCE

Diagnostic Study, Level II.

A method for assessing joint line shift post knee arthroplasty considering the preoperative joint space

BACKGROUND

Accurate comparison of outcomes regarding various surgical options in knee arthroplasty can benefit from an improved method for joint line analysis that takes into account the preoperative joint space.

METHODS

This article describes a new preoperative-based registration method that measures changes in the joint line by overlaying the 3D models of the bones with implants using preoperative CT along with preoperative and postoperative biplanar radiography. The method was tested on six cadaveric specimens for measuring alteration to the medial and lateral joint lines in extension and flexion.

RESULTS

The joint line shift, when measured using the new method, was in the range of -0.2 to 1.3 mm on average (SD=1.3 to 3.8 mm, for medial and lateral, in flexion and extension positions). This was significantly different (p≤0.01) from the results of a previous postoperative-based registration method which did not account for the cartilage thickness in calculating alterations of the joint line (mean=3.9 to 6.8mm, SD=1.2 to 4.3 mm).

CONCLUSION

These results further highlight the importance of considering the preoperative joint space in analyzing the joint line, and demonstrate the utility of the newly introduced method for accurate assessment of changes in the joint line after arthroplasty.

CLINICAL RELEVANCE

The introduced method provides accurate means for investigating joint line alterations in relation to different surgical techniques and the subsequent biomechanical effects after knee arthroplasty.