Suboptimal patellofemoral alignment is associated with poor clinical outcome scores after primary total knee arthroplasty

Preoperative quadriceps malalignment is associated with poor outcomes after knee replacement which are avoided by external rotation of the femoral component

PURPOSE

Lateralisation of the proximal apex of the quadriceps tendon relative to the mechanical axis or external rotation relative to the femoral shaft can be accurately measured and is strongly associated with patella maltracking. The aim of this study was to first assess the association between preoperative quadriceps tendon alignment (QTA) and the patient-reported outcomes (PROMs) of total knee replacement, and second, determine the influence of component position on outcomes in patients with preoperative quadriceps tendon malalignment (QTM).

METHODS

A retrospective analysis of prospectively collected data was performed. All patients had preoperative and postoperative CT scans performed. PROMs were collected preoperatively and at 1 year postoperatively. QTA was measured by the quadriceps tendon axial angle (QTAx). The preoperative and postoperative coronal and axial alignment were measured. Femoral component rotation was measured relative to the preoperative posterior condyles.

RESULTS

Analysis was conducted on 388 cases and the mean preoperative QTAx was 6.2° externally rotated (standard deviation 12.0°). QTM (QTAx > 14°) was identified in 76 (19.8%) patients. The diagnosis of QTM was associated with reduced patient outcomes including Forgotten Joint Score (60.2 vs. 51.2, p = 0.008), EuroQol Visual Analogue Scale (81.3 vs. 75.7, p = 0.009), KOOS-12 (80.3 vs. 73.3, p = 0.001) and reduced PASS percentages for all KOOS subscales. In patients with preoperative QTM, femoral component external rotation >2° was associated with improved PROMs when compared to patients with <2° of femoral rotation. This included a clinically significant difference in the improvement of KOOS-12 (11.7 points, p = 0.013) and improved PASS percentages in all KOOS subscales. There was no association between coronal alignment or tibial axial alignment and outcomes.

CONCLUSIONS

Quadriceps malalignment is a common cause for poorer patient outcomes following total knee replacement. This can be avoided by externally rotating the femoral component to accommodate the deformity in the extensor mechanism.

LEVEL OF EVIDENCE

Level III, case-control study.

Individualised compared to off-the-shelf total knee arthroplasty results in lower and less variable patellar tilt

PURPOSE

The purpose of this study was to compare postoperative patellar tilt at 4 months follow-up in a consecutive series of randomised patients that received individualised or off-the-shelf (OTS) primary total knee arthroplasty (TKA). The hypothesis was that patellar tilt would be lower and less variable in patients who received individualised TKA compared to patients who received OTS TKA.

METHODS

A consecutive series of 385 patients randomised (1:1) to receive either OTS TKA or individualised TKA were analysed. Pre- and postoperative radiographs at 4 months were obtained of weight-bearing long leg, anterior-posterior and lateral knee views and a skyline view at 30° of flexion. Postoperative patellar tilt was measured between the anterior femoral line and patellar resection surface (β) and the anterior femoral line and mediolateral patellar axis (σ). Postoperative patellar tilt (absolute value) was compared between the individualised and OTS TKA groups based on preoperative phenotypes of their femoral mechanical angle, tibial mechanical angle and hip-knee-ankle angle. Variability in postoperative patellar tilt was compared using the 95% confidence intervals (CIs).

RESULTS

Comparisons of baseline patient characteristics revealed no difference between the individualised and OTS TKA groups. Comparison of absolute postoperative patellar tilt revealed significant differences between individualised and OTS TKA (|β|, 1.0° ± 1.0° and 2.5° ± 2.2°, respectively, p < 0.001; |σ|, 1.7° ± 1.6° and 2.8° ± 2.3°, respectively, p < 0.001). The 95% CI of postoperative patellar tilt (|β|) was narrower in patients that received individualised compared to OTS TKA (0.0° to 3.8° and 0.1° to 8.3°, respectively), irrespective of their preoperative phenotype.

CONCLUSION

Patients who underwent individualised TKA had lower and less variable postoperative patellar tilt than those with OTS TKA, irrespective of preoperative phenotype. Individualised TKA allows the decoupling of the tibiofemoral and patellofemoral joints, replicating anatomical trochlear orientation and improving patellar tilt, which could facilitate better clinical outcomes.

CLINICAL TRIAL REGISTRATION

This study constitutes a part of a larger registered randomised controlled trial comparing patient satisfaction following OTS versus individualised TKA (NCT04460989).

LEVEL OF EVIDENCE

Level II.

Preoperative Patello-femoral Alignment Affects Anterior Knee Pain After Primary Total Knee Arthroplasty Without Patellar Resurfacing

BACKGROUND

Anterior knee pain (AKP) after total knee arthroplasty (TKA) results in dissatisfaction with the surgical outcomes. This study aimed to investigate risk factors for AKP after TKA using radiographic assessments.

METHODS

This retrospective matched-pair, case-control study included 284 patients who underwent primary fixed-bearing, posterior-stabilized TKA from 2016 to 2020, with a minimum follow-up of 2 years. The inclusion criterion was varus osteoarthritis in the knees without patellar resurfacing. The exclusion criteria were the use of bone graft or metal block, valgus knees, and patellar resurfacing. The patellar tilt angle, lateral patello-femoral angle, length of the tibial tuberosity to the trochlear groove, hip-knee-ankle angle, patellar height, and trochlear dysplasia index were measured. Patients were divided into 2 groups according to the presence of AKP based on the Feller score (≤ 20 points) at a 2-year follow-up, then a 1:2 propensity matching was performed. Risk factors for AKP were identified through logistic regression analyses. A total of 135 patients were enrolled in this study after matching.

RESULTS

The preoperative patellar tilt angle, lateral patello-femoral angle, tibial tuberosity to the trochlear groove, and trochlear dysplasia index significantly differed between the groups (P < 0.05), but not the postoperative parameters (P > 0.05). The Western Ontario and McMaster Universities total score and Feller score were significantly different postoperatively. (P < 0.05) Logistic regression analyses revealed that the preoperative patellar tilt angle, preoperative trochlear dysplasia index, and preoperative lateral patellofemoral angle were significant risk factors.

CONCLUSIONS

Care should be exercised when performing TKA in patients who have a large patellar tilt angle, a small lateral patello-femoral angle, and a small trochlear dysplasia index preoperatively, as there can be an increased risk of postoperative AKP in TKA with unresurfaced patellae. Surgeons may consider counseling patients about their increased risk of AKP if these factors are present preoperatively.

LEVEL OF EVIDENCE

Ⅲ.

Robotic assessment of patella tracking in total knee arthroplasty

OBJECTIVES

Robotic tools have been developed to improve planning, accuracy and outcomes in total knee arthroplasty (TKA). The purpose of this study was to describe and illustrate a novel technique for assessing the patellofemoral (PFJ) in TKA using an imageless robotic platform.

METHODS

A consecutive series of 30 R-TKA was undertaken by a single surgeon utilising the described technique. A technique to dynamically assess the PFJ intra-operatively, pre- and post-implantation was developed. A full set of data from 9 cases was then collected and reviewed for analysis. A series of dynamic PFJ tracks collected intra-operatively pre- and post-implantation are presented. Furthermore, a full assessment of PFJ over and under-stuffing through a 90° arc of flexion is illustrated. Finally, a pre- and post-centre of rotation for the PFJ was defined and measured.

RESULTS

The described technique was defined over a series of 30 R-TKA using the described robotic platform. Nine cases were analysed to determine what data could be measured using the robotic platform. Intra-operative real-time data allowed a visual assessment of PFJ tracking through a range of motion of 0°-90° flexion pre- and post-implantation. PFJ over and under-stuffing was also assessed intra-operatively through a range of motion of 0°-90° flexion. Post-operative analysis allowed a more detailed study to be performed, including defining a pre- and post-implantation centre of rotation (COR) for the patella. Defining the COR allowed the definition of a patella plane. Furthermore, patella mediolateral shift in full extension, and end flexion could be measured.

CONCLUSION

Intra-operative assessment of the PFJ in TKA is challenging. Robotic tools have been developed to improve measurement, accuracy of delivery and outcomes in TKA. These tools can be adapted in novel ways to assess the PFJ, which may lead to further refinements in TKA techniques.

Transillumination method in total knee arthroplasty: new approach with old tools

PURPOSE

In this study, we evaluated the possibility of precise intraoperative localization of the lateral genicular arteries by an orthopaedic surgeon using the transillumination method.

METHODS

Twelve patients underwent cemented TKA with patella-friendly Zimmer Biomet NexGen Legacy Posterior Stabilized prostheses (without patellar resurfacing), seven right knees and five left knees. The mean age of patients in the study group was 66.636 ± 7.003 years. The minimal follow-up period was 13 months (mean-16.363 ± 2.5 months). Functional outcomes were assessed using Knee Society and a specific patellar questionnaire-Kujala Score. Intraoperative detection of insufficient patellar stability and/or patellar maltracking was based on the no-thumb technique. In pre- and postoperative period X-ray investigation, standard standing X-ray and Merchant view were used to evaluate implant position and patellofemoral congruency.

RESULTS

In this study, ten out of twelve knee joints (83.3%) had at least one artery visible by the proposed method in the lateral parapatellar area. Five out of ten knee joints had more than one artery that could be visualized and identified as an arterial vessel. Postoperative Knee Society Score showed significant improvement from a mean 51.181 ± 3.868 to a mean 88.727 ± 3.663. Mean hospital length of stay is 8.545 ± 1.863 days. X-ray assessment using standard anteroposterior, lateral, and Merchant skyline views showed appropriate implant positioning and patellofemoral congruency. The mean Kujala Score in the postoperative period (3 and 6 months) was 67.3 ± 6.75 and 75.6 ± 6.42, respectively.

CONCLUSIONS

Using the proposed transillumination method can help preserve the lateral blood supply to the patella and to avoid devascularized patella-related complications.

TRIAL REGISTRATION

Retrospectively registered on 5 of May 2023, Registration number - 3/3-1757.

Anatomic Patellar Design Has No Clinical Superiority Over Dome Patellar Design in Total Knee Arthroplasty: A Randomized Clinical Trial

BACKGROUND

Various patellar designs are used in total knee arthroplasty (TKA) for optimal management of patellofemoral pain. The aim of this study was to compare postoperative 2-year clinical outcomes of 3 patellar designs: medialized anatomic (MA), medialized dome (MD), and Gaussian dome (GD).

METHODS

In this randomized controlled trial, 153 patients undergoing primary TKA from 2015 to 2019 were enrolled. Patients were allocated to 3 groups (MA, MD, and GD). Demographic characteristics, clinical variables including knee flexion angle and patient-reported outcome measures (Kujala score, Knee Society Scores, the Hospital for Special Surgery score, and The Western Ontario and McMaster Universities Arthritis Index), and complications were collected. Radiologic parameters including Blackburne-Peel ratio and patellar tilt angle (PTA) were measured. A total of 139 patients who completed postoperative follow-up for 2 years were analyzed.

RESULTS

Knee flexion angle and patient-reported outcome measures did not statistically differ among the 3 groups (MA, MD, and GD). There were no extensor mechanism-related complications at any group. Group MA showed significantly higher mean values of postoperative PTA than group GD (0.1 ± 3.2 versus -1.8 ± 3.4, P = .011). Group GD (20.8%) had a tendency to have more outliers (over 5 degrees) in PTA than groups MA (10.6%) and MD (4.5%), although the differences were not statistically significant (P = .092).

CONCLUSION

Anatomic patellar design was not clinically superior over dome design in TKA, showing comparable results in terms of clinical scores, complications, and radiographic indices.

Association of patella alignment with cartilage relaxation times and self-reported symptoms in individuals with patellofemoral degeneration

To determine the cross-sectional and longitudinal associations of patella alignment with cartilage relaxation and patients' self-reported symptoms. Thirty participants with isolated patellofemoral joint (PFJ) degeneration (six males, 53.7 ± 9.3 years) and 24 controls (12 males, 47.6 ± 10.7 years) were included. Magnetic resonance assessment was performed to provide grading of structural abnormalities, cartilage relaxation times, and patella alignment. Self-reported symptoms were assessed using the self-administrated knee injury and osteoarthritis outcome score (KOOS). All participants were examined at baseline and 3 years. Statistical parametric mapping and Pearson partial correlation were used to evaluate the associations between patella alignment with cartilage relaxation times and self-reported symptoms, respectively. The analyses were performed between baseline (cross-sectional) as well as the baseline against 3 years (longitudinal). Results indicated that patella height and patella flexion were associated with T1ρ and T2 relaxation times at baseline (percentages of voxels showing significant correlation [PSV] = 10.1%-24.8%; mean correlations [R] = 0.34-0.36; mean p = 0.015-0.026). Furthermore, greater patella lateral alignment, lateral tilt, and lateral spin were associated with longer T2 times at 3 years (PSV = 11.0%-14.4%, R = 0.39-0.44, p = 0.017-0.028). Last, a higher patella was associated with a lower KOOS at baseline and at 3 years (R = -0.33 to -0.35). The study suggests that patella malalignment is a risk factor for worsening cartilage health, informing clinicians of a better rehabilitation program that targets PFJ degeneration.

Cemented Patellar Implant Malposition: A Non-Issue for the Painful Total Knee Arthroplasty

BACKGROUND

Non-optimal patellofemoral relationships may influence treatment decisions during revision total knee arthroplasty (TKA). We performed this study to determine whether patellar implant malposition or patellar tilt is associated with inferior patient-reported outcome scores or patient satisfaction after primary TKA.

METHODS

We identified 396 TKA patients (439 knees) from an institutional registry who had undergone patellar resurfacing, with preoperative and 6-week postoperative radiographs available, and patient-reported outcome measures (PROMs) completed at least 1 year after surgery (mean 505 days). Preoperative patient demographic characteristics, patient-reported expectations, National Institutes of Health - Patient Reported Outcomes Measurements Instrument Systems global health, Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, and University of California Los Angeles activity scores were compared between 60 TKAs performed with non-optimal patellofemoral relationships (36 patellar implant malposition, 24 patellar tilt) and 379 TKAs performed with optimal patellar implant placement.

RESULTS

There were no differences between the 2 cohorts regarding demographic features, preoperative radiographic disease severity, expectations, and PROMs; or postoperative tibiofemoral component alignment, PROMs, and patient-reported satisfaction (P = .48). Knee Injury and Osteoarthritis Outcome Score for Joint Replacement improved similarly (P = .62) for patients with optimal resurfacing (48.5-77.6 points) and non-optimal resurfacing (47.7-76.6 points). A similar proportion of optimal and suboptimal resurfaced patients reported being satisfied with their TKA (92.7% vs 88.1%, P = .29).

CONCLUSION

Although suboptimal patellofemoral relationships may prompt treatment considerations during revision TKA, the data obtained from this study do not suggest that patellar implant malposition or patellar tilt independently contribute to postoperative pain, functional limitation, or dissatisfaction.

LEVEL OF EVIDENCE

This is a level III, retrospective cohort study.

Midterm results of modern patellofemoral arthroplasty versus total knee arthroplasty for isolated patellofemoral arthritis: systematic review and meta-analysis of comparative studies

BACKGROUND

Both Patellofemoral Arthroplasty (PFA) and Total Knee Arthroplasty (TKA) are accepted surgical options for end-stage isolated patellofemoral osteoarthritis (PFOA). We performed a systematic review and meta-analysis to compare outcomes of PFA and TKA by evaluation of the patient-reported outcome measures (PROMs).

METHODS

We systematically identified publications reporting on patients that underwent either TKA or modern PFA for isolated PFOA. Meta-analysis software was used to screen for potential articles with at least two years' follow-up. Data were extracted and analysed for all PROMs operating time, postoperative inpatient time, complications and cost. We included five studies in our cumulative meta-analysis and reviewed them using Review Manager V.5.0. We computed the risk ratio as a measure of the treatment effect, taking into account heterogeneity. We used random-effect models.

RESULTS

No significant difference was found between both TKA and PFA in the context of operating time. No significant difference after five years' follow-up was found between the two treatment options in terms of UCLA score and patient satisfaction. PFA showed significant improvement in WOMAC score at five-year follow-up, less postoperative inpatient time, better cost-effectiveness and significantly less blood loss.

CONCLUSION

PFA seems to be a viable alternative to TKA for treatment of isolated PFOA in appropriately selected patients. PFA showed less postoperative inpatient time and blood loss with similar PROMs to the TKA. Moreover, it is an economically beneficial joint-preserving procedure.

Patellar Tracking in Total Knee Arthroplasty-Influence on Clinical and Functional Outcome

Anterior knee pain is a common problem after primary total knee arthroplasty (TKA). The aim of this study was to find parameters in patellar positioning which influence the clinical and functional outcome after TKA. Included were 59 patients who underwent TKA, of which three patients were treated bilaterally (n = 62 included knees). In a periodical follow-up of up to 5 years, each patient had to answer three questionnaires (HSS, WOMAC, SF-36) and underwent three radiographies of the knee (including merchant view) and a clinical examination, including Range Of Motion (ROM). All radiographs were evaluated by a single observer blinded to clinical data, who collected multiple parameters of sagittal and axial patellar alignment including newly developed methods for measuring patellar shift and tilt. Depending on the measurement results, three groups were built for each parameter and the influence on the outcome was determined. A lateral patellar tilt of more than 4° resulted in lower scores for both the HSS and WOMAC. The rarely investigated patellar facet angle showed a significantly inferior clinical and functional outcome in late follow-up of >24 months if lower than 142°, possibly due to progressive osteosclerotic changes of the patella caused by increased contact stress with corresponding patellar morphology. No significant difference was found for all other parameters. The newly developed method for measuring patellar shift has proven to be a valuable and easy instrument in the postoperative setting.

Patellar tilt does not affect patient reported outcomes after modern total knee arthroplasty

BACKGROUND

The focus of patella maltracking after total knee arthroplasty (TKA) has traditionally been on patella polyethylene damage and failure mechanisms rather than functional outcomes. The purpose of this study was to evaluate the effect of patellar tilt on patient reported outcomes (PROMS) after primary TKA performed with patellar resurfacing.

METHODS

A retrospective review using a single implant design was performed. Patella tilt was radiographically measured according to a standardized protocol. PROMS related to pain, function, and satisfaction were evaluated preoperatively and at minimum 1-year follow-up.

RESULTS

A total of 468 TKAs were included for analysis. Mean age and BMI were 64 years and 35 kg/m²; respectively while 63% of patients were female. The median follow-up period was 12.7 months. Overall, patellar tilt was corrected from a median of 5.0 degrees preoperatively to a median of 3.0 degrees postoperatively. Preoperative, postoperative, and the change in patellar tilt had no significant effects on PROMS at minimum 1-year follow-up (p ≥ 0.092). Satisfaction in knee function while getting out of bed was higher for patients with approximately the same patellar tilt before and after TKA compared to patients with an increase in lateral patellar tilt (95% vs 80%, p = 0.025).

CONCLUSIONS

The range of patellar tilt studied in this cohort had little to no effect on PROMS. However, suboptimal patellar tracking may potentiate edge loading of the polyethylene and contribute to implant damage in the long-term. These results are helpful to focus efforts on the tibiofemoral articulation as the predominant determinant of patient outcomes.

Intraoperative patellar maltracking and postoperative radiographic patellar malalignment were more frequent in cases of complete medial collateral ligament release in cruciate-retaining total knee arthroplasty

BACKGROUND

Patellar maltracking after total knee arthroplasty (TKA) can lead to significant patellofemoral complications such as anterior knee pain, increased component wear, and a higher risk of component loosening, patellar fracture, and instability. This study was to investigate the preoperative and operative variables that significantly affect patellar tracking after cruciate-retaining TKA.

METHODS

We studied 142 knee joints in patients who had undergone TKA: the knees were dichotomized based on postoperative patellar tracking, which was evaluated on patellar skyline, axial-projection radiographs: group 1, normal patellar tracking (lateral tilt ≤ 10° and displacement ≤ 3 mm) and group 2, patellar maltracking (lateral tilt > 10° or displacement > 3 mm). The patients' demographic data and clinical and radiographic measurements obtained before and after surgery were compared between the two groups.

RESULTS

Preoperative lateral patellar displacement was greater (4.1 ± 2.6 mm vs. 6.0 ± 3.5 mm), as was the frequency of medial collateral ligament (MCL) release (3/67 vs. 24/75) in group 2 than in group 1 (p < 0.001 and p < 0.001, respectively). The distal femur was cut in a greater degree of valgus in group 1 than in group 2. (6.3 ± 0.8° vs. 6.0 ± 0.8°) (p = 0.034).

CONCLUSIONS

Complete release of the MCL during surgery was associated with patellar maltracking (logistic regression: p = 0.005, odds ratio = 20.592). Surgeons should attend to patellar tracking during surgery in medially tight knees.

LEVEL OF EVIDENCE

Retrospective comparative study, level III.

Combined Total Knee Arthroplasty and Medial Patellofemoral Ligament Reconstruction for Chronic Patellar Dislocation and Severe Osteoarthritis

Chronic patellar dislocation in the setting of severe knee osteoarthritis is a rare clinical problem. Surgical management often consists of total knee arthroplasty combined with realignment of the extensor mechanism. Several techniques have been described to anatomically restore the extensor apparatus, and literature regarding this topic consists mainly of case reports. We describe a technique using combined medial patellofemoral ligament reconstruction using allograft tissue and total knee arthroplasty with patellar resurfacing for the treatment of chronic patellar dislocation and severe osteoarthritis.

Patellar facet ratio affects knee pain, stair climbing and stair descent after TKA without patellar resurfacing

PURPOSE

To determine whether knee pain or functional impairment after total knee arthroplasty (TKA) without patellar resurfacing are correlated with preoperative patellar morphology or postoperative patellar orientation. The hypotheses were that patellar shape, increased tilt and lateral displacement would be associated with pain and functional impairment.

METHODS

From a consecutive series of 152 knees that received a cemented postero-stabilized TKA, the Oxford Knee Score (OKS) and the Knee injury and Osteoarthritis Outcome Score (KOOS) were collected at a minimum follow-up of 12 months. Uni- and multi-variable linear regression analyses were performed to determine associations between the collected clinical scores and patient demographics and patellar morphology, measured from pre- and post-operative frontal, lateral and skyline view radiographs.

RESULTS

The OKS was 75 ± 23, whereas the KOOS pain, stair climbing, and descent were respectively 77 ± 24, 3.9 ± 1.1 and 3.8 ± 1.2. OKS was not associated with any radiographic outcomes, whereas KOOS pain was better for knees with larger medial patellar facets. The KOOS stair climbing and descent were also better for knees with larger medial patellar facets.

CONCLUSION

The findings of this study partly confirm the hypotheses that pain and functional impairments after TKA without patellar resurfacing are associated with patellar shape. No association was revealed between postoperative patellar orientation and function nor pain. Quantitative consideration of patellar congruency could therefore prevent pain and improve function after TKA without patellar resurfacing.

LEVEL OF EVIDENCE

Retrospective study, Level III.

Modern total knee arthroplasty designs do not reliably replicate anterior femoral morphology

PURPOSE

Biomechanical studies suggest that PF tracking is not reliably restored to physiological values in TKA despite surgical technique optimization. A clinical observation is that current TKA designs may not replicate anterior femoral offset. The aim was to examine the intraoperative resection thicknesses of the anterior femoral condyles during TKA and correlate these findings relative to modern prostheses.

METHODS

This was a retrospective analysis of 199 patients who underwent 233 TKAs using a single implant design with measured anterior femoral condylar resection thicknesses. The aim was to restore posterior condylar offset whilst minimizing overstuffing of the anterior compartment of the knee by choosing the smallest prosthesis to allow for the maximal anterior resection as close to the cortex without inducing notching. Prosthetic measurements from 7 commonly used TKAs were collected by analysis of 3D models of median sized explants.

RESULTS

An average of 7.9 mm (SD 2.5 mm, range 2-16.5 mm) and 11.5 mm (SD 2.5 mm, range 2-21 mm) was resected from the medial and lateral aspects of the anterior femur, respectively. The average anterior flange thickness for the prosthesis data set was 6.6 mm (SD 0.6 mm, range 6.1-7.9 mm) medially and 7.6 mm (SD 0.7 mm, range 6.8-9.0 mm) laterally. Comparison across patients who received the median prosthesis size of 5 (SD 1.3, range 2-8) was inadequately restored by 1.4 mm (p < 0.00001) medially and 3.4 mm (p < 0.00001) laterally.

CONCLUSION

Host anatomy is not routinely restored during TKA. The surgical teaching to aim for an anterior femoral osteotomy close to the anterior cortex will result in understuffing of the PFJ and based on current prosthesis designs, the risk of overstuffing is not as significant as once believed. Future prostheses and surgical techniques should aim to restore not only posterior femoral but also anterior femoral offset.

LEVEL OF EVIDENCE

IV, Case series.

Wiberg Type III patellae and J-sign during extension compromise outcomes of total knee arthroplasty without patellar resurfacing

BACKGROUND

Understanding the risk factors associated with postoperative pain and worse outcome can guide surgeons on whether primary patellar resurfacing is warranted during total knee arthroplasty (TKA). The purpose of this study was to determine whether clinical scores and pain after TKA without patellar resurfacing are correlated with patellar shape and postoperative patellar position and kinematics.

METHODS

Radiographs as well as anterior knee pain according to the Visual Analogue Scale (pVAS) were collected pre- and postoperatively for 100 knees aged 68 ± 7.7 years that received uncemented TKA without patellar resurfacing. At a minimum follow-up of 12 months the Forgotten Joint Score (FJS), the Oxford Knee Score (OKS) as well as the flexion range of motion and the presence of J-sign during active extension were recorded. Uni- and multivariable linear regression analyses were performed to determine associations between the collected clinical scores and patient demographic and radiographic data.

RESULTS

Postoperative OKS (79 ± 14.4) was worse for Wiberg Type III patellae (β = -11.4, P = .020, compared with Type II). Anterior pVAS (2 ± 2) was greater in knees with J-sign during extension (β = 2.8, P < .001). None of the other radiographic measurements (patellar tilt, congruence angle and lateral patellar displacement) were correlated with postoperative OKS or anterior pVAS.

CONCLUSION

Incongruent patellar shape (Wiberg Type III) is associated with worse clinical scores, and abnormal kinematics (J-sign) with increased pain after TKA without patellar resurfacing. The authors therefore recommend routine resurfacing for Wiberg Type III patellae, though further studies are required to confirm whether resurfacing truly improves clinical scores and pain in this subgroup.

Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty

Patellofemoral (PF) disorders are considered a major clinical complication after total knee replacement (TKR). Malpositioning and design of the patellar component impacts knee joint dynamics, implant fixation and wear propagation. However, only a limited number of studies have addressed the biomechanical impact of the patellar component on PF dynamics and their results have been discussed controversially. To address these issues, we implemented a musculoskeletal multibody simulation (MMBS) study for the systematical analysis of the patellar component’s thickness and positioning on PF contact forces and kinematics during dynamic squat motion with virtually implanted unconstrained cruciate-retaining (CR)-TKR. The patellar button thickness clearly increased the contact forces in the PF joint (up to 27%). Similarly, the PF contact forces were affected by superior–inferior positioning (up to 16%) and mediolateral positioning (up to 8%) of the patellar button. PF kinematics was mostly affected by the mediolateral positioning and the thickness of the patellar component. A medialization of 3 mm caused a lateral patellar shift by up to 2.7 mm and lateral patellar tilt by up to 1.6°. However, deviations in the rotational positioning of the patellar button had minor effects on PF dynamics. Aiming at an optimal intraoperative patellar component alignment, the orthopedic surgeon should pay close attention to the patellar component thickness in combination with its mediolateral and superior–inferior positioning on the retropatellar surface. Our generated MMBS model provides systematic and reproducible insight into the effects of patellar component positioning and design on PF dynamics and has the potential to serve as a preoperative analysis tool.

Preoperative patellofemoral anatomy affects failure rate after isolated patellofemoral inlay arthroplasty

PURPOSE

To analyze whether preoperative patellofemoral anatomy is associated with clinical improvement and failure rate after isolated patellofemoral arthroplasty (PFA) using a modern inlay-type trochlear implant.

METHODS

Prospectively collected 24 months data of patients treated with isolated inlay PFA (HemiCAP^® Wave, Arthrosurface, Franklin, MA, USA) between 2009 and 2016, and available digitalized preoperative imaging (plain radiographs in three planes and MRI) were retrospectively analyzed. All patients were evaluated using the WOMAC score, Lysholm score, and VAS pain. Patients revised to TKA or not achieving the minimal clinically important difference (MCID) for the total WOMAC score or VAS pain were considered failures. Preoperative imaging was analyzed regarding the following aspects: Tibiofemoral OA, patellofemoral OA, trochlear dysplasia (Dejour classification), patellar height (Insall-Salvati index [ISI]; Patellotrochlear index [PTI]), and position of the tibial tuberosity (TT-TG and TT-PCL distance).

RESULTS

A total of 41 patients (61% female) with a mean age of 48 ± 13 years could be included. Fifteen patients (37%) were considered failures, with 5 patients (12%) revised to TKA and 10 patients (24%) not achieving MCID for WOMAC total or VAS pain. Failures had a significantly higher ISI, and a significantly lower PTI. Furthermore, the proportion of patients with a pathologic ISI (> 1.2), a pathologic PTI (< 0.28), and without trochlear dysplasia were significantly higher in failures. Significantly greater improvements in clinical outcome scores were observed in patients with a higher preoperative grade of patellofemoral OA, ISI ≤ 1.2, PTI ≥ 0.28, TT-PCL distance ≤ 21 mm, and a dysplastic trochlea.

CONCLUSION

Preoperative patellofemoral anatomy is significantly associated with clinical improvement and failure rate after isolated inlay PFA. Less improvement and a higher failure rate must be expected in patients with patella alta (ISI > 1.2 and PTI < 0.28), absence of trochlear dysplasia, and a lateralized position of the tibial tuberosity (TT-PCL distance > 21 mm). Concomitant procedures such as tibial tuberosity transfer may, therefore, be considered in such patients.

LEVEL OF EVIDENCE

Level III, retrospective analysis of prospectively collected data.

Posterior condylar resections in total knee arthroplasty: current standard instruments do not restore femoral condylar anatomy

INTRODUCTION

Correct femoral rotational alignment in total knee arthroplasty (TKA) is important for femoropatellar knee kinematics as well as for the overall clinical success. The goal of the present study was to evaluate how accurately standard instruments of various manufacturers with specific rotational settings in posterior referencing restore the posterior femoral condylar anatomy and allow a rotational alignment which matches a particular anatomic rotational landmark on CT.

METHODS

The anatomical transepicondylar axis (aTEA) and the posterior condylar line (PCL) were identified and the angle formed by these two axes was measured on 100 consecutive CT scans of knees. A virtual posterior condylar resection was performed relative to the aTEA for femoral sizers of various manufacturers in different external rotations ranging from 3° to 7°. The resections of medial and lateral posterior condyle were calculated as well as the condylar twist angle (CTA) between PCL and aTEA.

RESULTS

The posterior condylar resection varied between 9 mm and 14 mm on the medial side and between 4 mm and 10.5 mm on the lateral side. The mean CTA was 5.5° of internal rotation (SD ± 1.9°). External femoral rotation resulted in increased resection of the medial posterior condyle and decreased resection of the lateral posterior condyle.

CONCLUSION

Femoral sizers using a posterior referencing technique increase, with rising external rotation, medial posterior condylar resection to an extent that may exceed the implant thickness in the majority of systems. Surgeons should be aware that current standard instruments do not restore the anatomy of the posterior medial and lateral condyle and do not align the femoral component parallel to the aTEA, which may result in internal rotation of a symmetric femoral component.