Patella tracking and patella contact pressure in modular patellofemoral arthroplasty: a biomechanical in vitro analysis

A finite element analysis of patellofemoral joint biomechanics: Exploring potential causes of postoperative anterior knee pain following unicompartmental knee arthroplasty

Purpose

Anterior knee pain is a common complication following unicompartmental knee arthroplasty (UKA). This study aimed to elucidate the mechanism of anterior knee pain after UKA by examining the biomechanical characteristics of the patellofemoral joint.

Methods

This study employs the finite element analysis method. A healthy model of the right lower limb was created using CT scans of an intact right lower limb from a healthy woman. Based on this model, a preoperative pathological model was generated by removing the meniscus and part of the articular cartilage. The UKA prosthesis was then applied to this model with five different bearing thicknesses: 5 mm, 7 mm, 10 mm, 11 mm, and 13 mm. To simulate various degrees of knee joint flexion, the femur was rotated relative to the knee joint's rotational axis, producing lower limb models at flexion angles of 0°, 30°, 60°, 90°, and 120°. We applied a constant force from the center of the femoral head to the center of the ankle joint to simulate lower limb loading during squatting. The simulations were conducted using Ansys 17.0.

Results

Both overstuffing and understuffing increased the peak stress on the patellar cartilage, with overstuffing having a more pronounced effect. Compared to healthy and balanced models, overstuffed and understuffed models exhibited abnormal stress distribution and stress concentration in the patellar cartilage during knee flexion.

Conclusion

Overstuffing and understuffing lead to residual varus or valgus deformities after UKA, causing mechanical abnormalities in the patellofemoral joint. These abnormalities, characterized by irregular stress distribution and excessive stress, result in cartilage damage, exacerbate wear in the patellofemoral joint and consequently lead to the occurrence of anterior knee pain.

Current status of bicompartmental arthroplasty

BACKGROUND

Bicompartmental arthroplasty (BCA) serves as a less invasive alternative to total knee arthroplasty. This review aims to present the current status of BCA. BODY: Recent literature on BCA was reviewed and synthesized from the perspectives of function, radiological assessment, patient satisfaction, survival rate, patellar tracking, satisfaction survey, and revision rate.

CONCLUSION

BCA is beneficial for patients with bicompartmental arthritis and those suffering from deterioration in other compartments after unicompartmental knee arthroplasty (UKA). Compared to total knee arthroplasty, BCA reduces trauma, accelerates recovery, and improves sports ability. While BCA is evolving towards a more exciting future, more clinical studies are warranted to exploit its potential and validate its efficacy, eventually improving outcomes and patient satisfaction.

[The combination of partial knee arthroplasties in knee osteoarthritis with an intact anterior cruciate ligament - a future model?]

BACKGROUND

Preserving both cruciate ligaments in knee prosthetics enables approximately physiological joint kinematics. In this way, faster rehabilitation and a higher return-to-sports rate can be achieved. Accordingly, there are considerations to preserve both cruciate ligaments by combining two partial prostheses in the case of symptomatic bicompartmental (BiCom) knee osteoarthritis.

METHODS

This article summarizes the literature on BiCom arthroplasty and describes our own experiences from 54 consecutive cases with robotic-assisted technology.

RESULTS

According to current data, BiCom arthroplasty shows good clinical results, without being able to demonstrate a clear advantage over conventional TKA. The revision risk is slightly increased in the short-term interval, which could be positively addressed with robotic-assistance. The disadvantages are the increased implant costs and the risk of subsequent osteoarthritis. Accordingly, patients who may potentially take advantage of this treatment must be critically selected.

The Influence of Patello-Femoral Overstuffing After Modular Unlinked Bicompartmental Knee Arthroplasty (BiKA) for Medial Tibio-Femoral and Patello-Femoral Osteoarthritis of the Knee

BACKGROUND

The factors affecting results after bicompartmental knee arthroplasty (BiKA) have not been fully elucidated. This major ligament-preserving procedure may be more susceptible to overstuffing of the patello-femoral (PF) joint than the major ligament-sacrificing total knee arthroplasty. Currently, we investigated the effect of PF overstuffing after BiKA on its clinical outcome.

METHODS

There were 71 patients (74 knees) who underwent modular unlinked BiKA at our clinic who had a follow-up of 5 to 9 years. Final follow-up results were assessed by evaluating knee range of motion, the 2011 Knee Society Score (2011KSS), Japanese Knee Osteoarthritis Measure, and radiological findings. The degree of postoperative PF overstuffing was evaluated by computed tomography and magnetic resonance images for 55 knees, and the correlation between the degree of overstuffing and postoperative clinical results were examined.

RESULTS

Overall clinical results improved significantly after surgery without any revision cases. The X-ray measurements showed the improved coronal alignments and the appropriate implant installation angles. Higher degree of postoperative PF overstuffing caused by insufficient amount of osteotomy on the anterior surface of the femur correlated with worse postoperative total 2011KSS at 2 years after surgery (Spearman's rank correlation coefficient (rs) = -0.387, P = .004), as opposed to no correlation at the time of the final follow-up (Spearman's rank correlation coefficient = 0.068, P = .623).

CONCLUSION

Modular unlinked BiKA provided patients with a high level of satisfaction and functional improvement over 5 to 9 years postoperatively. However, because PF overstuffing affects initial patient satisfaction, the amount of osteotomy should be determined carefully during the surgery.

The lack of retropatellar resurfacing at index surgery is significantly associated with failure in patients following patellofemoral inlay arthroplasty: a multi-center study of more than 260 patients

PURPOSE

To evaluate the clinical outcomes of patients with a minimum 2-year follow-up following contemporary patellofemoral inlay arthroplasty (PFIA) and to identify potential risk factors for failure in a multi-center study.

METHODS

All patients who underwent implantation of PFIA between 09/2009 and 11/2016 at 11 specialized orthopedic referral centers were enrolled in the study and were evaluated retrospectively at a minimum 2-year follow-up. Clinical outcomes included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Tegner Scale, the visual analogue scale (VAS) for pain, and subjective patient satisfaction. Pre- and perioperative risk factors were compared among failures and non-failures to determine potential risk factors.

RESULTS

A total of 263 patients (85% follow-up rate) could be enrolled. The mean age at the time of index surgery was 49 ± 12 years with a mean postoperative follow-up of 45 ± 18 months. The overall failure rate was 11% (28 patients), of which 18% (5 patients) were patients with patella resurfacing at index surgery and 82% (23 patients) were patients without initial patella resurfacing. At final follow-up, 93% of the patients who did not fail were satisfied with the procedure with a mean transformed WOMAC Score of 84.5 ± 14.5 points, a mean KOOS Score of 73.3 ± 17.1 points, a mean Tegner Score of 3.4 ± 1.4 points and a mean VAS pain of 2.4 ± 2.0 points. An increased BMI was significantly correlated with a worse postoperative outcome. Concomitant procedures addressing patellofemoral instability or malalignment, the lack of patellofemoral resurfacing at the index surgery and a high BMI were significantly correlated with failure in our patient cohort.

CONCLUSION

Patellofemoral inlay arthroplasty shows high patient satisfaction with good functional outcomes at short-term follow-up and thus can be considered a viable treatment option in young patients suffering from isolated patellofemoral arthritis. Patellar resurfacing at index surgery is recommended to decrease the risk of failure.

LEVEL OF EVIDENCE

Retrospective case series, Level IV.

[When nothing else works: patellofemoral joint arthroplasty]

Patellofemoral joint replacement is the best treatment option available for isolated patellofemoral arthritis. Especially young patients should be operated on with bone-sparing techniques that also preserve the soft tissues, since these patients are very likely to be revised at some point in their lifetime. Correct patient selection is important for the success of surgery and should include a meticulous clinical examination and imaging. Special attention should be paid to additional pathologies that may also need to be addressed. For the trochlea, there are two different options for treatment with the inlay and onlay system. The retropatellar surface should be replaced. Patellofemoral joint replacement is still rarely performed, so treatment in specialised centres is recommended. National joint registry data show high revision rates, while data from centres show promising results.

[Patellofemoral inlay implants-an innovation in patellofemoral joint arthroplasty?]

Isolated arthrosis of the patellofemoral joint is a rare and complex disease. After conservative therapy has been exhausted, the orthopedist has various soft-tissue and bone reconstructive procedures as well as cartilage regenerative procedures at his hands. In cases of failed or unsatisfactory therapy, patellofemoral arthroplasty continues to be controversially discussed as an alternative therapy. A closer look at these studies reveals promising results with the correct indication and patient selection. The different prosthesis designs provide good postoperative results while considering general and specific risks. The current generation of patellofemoral inlay prostheses shows high patient satisfaction with significant improvements in knee function and pain relief in mid-term outcomes. However, a relatively high revision rate must be considered.

Patella alta and patellar subluxation might lead to early failure with inlay patello-femoral joint arthroplasty

PURPOSE

With the growing interest in resurfacing procedures, several new implants have been recently introduced for isolated patello-femoral joint arthroplasty (PFA). However, not much data are available for these new techniques or about the right indications for each type of implant.

METHODS

Out of a retrospective cohort of 20 inlay PFA, 11 PFA with an elevated Insall-Salvati index and an increased patello-femoral congruence angle showed an initial satisfactory result, but presented thereafter with recurrent pain and "clunk" phenomena. They were all revised after a median time of 25 months (range 8-28 months) into an onlay technique PFA and analyzed for their failure mode and revision technique.

RESULTS

Clinical symptoms such as clunking, as well as abraded areas craniolateral of the inlay implant found intraoperatively, were the main observations of this study. The modified Insall-Salvati index (mISI) was significantly higher in the revised knees compared to the unrevised (median 1.8 versus 1.6; p = 0.041). VAS and KSS significantly improved after revision (median VAS reduction in pain of 4.0 points, median KSS improvement of 20.0 points; p < 0.05).

CONCLUSION

Patients with high-normal patellar height index or patella alta, as well as a craniolateral type of arthritis with additional lateralization, should be considered contra-indicated for an inlay technique PFA. They could be considered for a PFA system reaching further proximal into the distal femur. An onlay PFA can be an option for early revision of failed inlay implants. The clinical relevance of this study is that patella alta and patellar subluxation are more difficult to adjust for with an inlay PFJ component.

LEVEL OF EVIDENCE

Level IV.

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

BACKGROUND

Proper patellofemoral alignment is an important goal in total knee arthroplasty (TKA). Acceptable patellar alignment is defined as patellar tilt less than or equal to 5° and patellar displacement less than or equal to 5 mm. Previous studies reported an incidence of post-operative patellar malalignment in TKA from 7 to 35%. However, correlation between patellar malalignment and clinical outcome after TKA remains unclear. The purpose of the present study was to evaluate the effect of patellar tilt and displacement on the clinical outcome of TKA.

METHODS

A retrospective review of 138 primary TKAs with a minimum of 2 year follow-up is reported. Pre-operative and post-operative mechanical axis, patellar tilting angle and patellar displacement were measured. Clinical outcomes were evaluated by the knee functional scores including the Knee Society Score (KSS), Knee injury and Osteoarthritis Outcome Score (KOOS), and Western Ontario McMaster University Osteoarthritis Index (WOMAC) at final follow-up.

RESULTS

Forty-two (30%) primary TKAs had suboptimal patellofemoral alignment with a patellar tilt angle greater than 5° or lateral patellar displacement of more than 5 mm. There was no statistical difference in pre-operative mechanical axis, pre-operative patellar tilt angle, or pre-operative lateral patellar displacement between the primary TKAs with proper patellofemoral alignment and those with suboptimal alignment. Patients with post-operative patellar tilt or displacement had clinically significant reductions in KSS, KOOS, and WOMAC when compared with patients without post-operative patellar tilt or displacement. The odds of having a fair or poor post-operative result, an odds ratio of 3.4 (95% CI 1.6-7.2) for KSS, 6.4 (95% CI 2.9-14.2) for KOOS, and 5.9 (95% CI 2.6-13.5) for WOMAC, were associated with suboptimal patellofemoral alignment.

CONCLUSION

Establishing proper patellofemoral alignment remains an essential goal of primary TKA. There is a strong association between suboptimal post-operative patellofemoral alignment and poor clinical outcome scores after primary TKA.

A lateral retinacular release during total knee arthroplasty changes femorotibial kinematics: an in vitro study

INTRODUCTION

Lateral retinacular release (LRR) is a common procedure during total knee arthroplasty (TKA), especially if patellar maltracking is observed intraoperatively. The impact of LRR on patellofemoral kinematics is well-examined, but the influence on femorotibial kinematics requires more elucidation. Therefore, the aim of this study was to evaluate the effects of LRR on femorotibial kinematics in vitro.

MATERIALS AND METHODS

A fixed bearing TKA was implanted in six human knee specimens. Femorotibial kinematics were measured dynamically through the use of a custom-constructed knee rig which flexes the knee from 20° to 120° under weight bearing conditions. Measurements were performed before and after LRR. LRR was performed completely including transection of synovium, retinaculum and tractus fibers. For the registration of tibiofemoral kinematics a 3-dimensional-ultrasound-based motion analysis system was used.

RESULTS

LRR revealed a significant reduction of femoral rollback at the lateral compartment (9.4 ± 5.0 vs 7.8 ± 9.4 mm; p < 0.01), whereas the present decrease of femoral rollback at the medial compartment was not significant (3.4 ± 4.7 vs 2.3 ± 5.9 mm; p = 0.34). Accordingly, LRR significantly reduced internal rotation of the tibia (0.8°; p < 0.01).

CONCLUSION

The results suggest that LRR significantly decreases lateral femoral rollback as well as internal rotation of the tibia, probably by changing the tension of the iliotibial band. When performing a LRR in clinical routine, surgeons should be aware of altering not only patellofemoral kinematics but also the femorotibial kinematics.

Reduced joint-awareness in bicruciate-retaining total knee arthroplasty compared to cruciate-sacrificing total knee arthroplasty

PURPOSE

There is rising impact of patient-reported outcome (PRO) measurement in joint arthroplasty over the past years. Bicruciate-retaining implants have shown more physiologic knee kinematics and provide superior proprioceptive capacities. The aim of this study was to evaluate if the functional properties of this new implant design lead to improved PRO results after total knee arthroplasty (TKA).

METHODS

This prospective, controlled trial compares PRO of bicruciate-retaining total knee arthroplasty (BCR-TKA) to unicondylar knee arthroplasty (UKA) and standard posterior-stabilized total knee arthroplasty (PS-TKA). We evaluated 102 patients (34 patients in each group) 18 months postoperatively after knee arthroplasty. Primary outcome measure was the Forgotten Joint Score (FJS).

RESULTS

The BCR-group showed the same level of joint awareness as the UKA-group (p = 0.999). The second control group of PS-TKA patients had a lower mean score value in the FJS compared to the BCR-group (p = 0.035) and UKA-group (p = 0.031). There was no correlation of age, gender, body mass index (BMI) and the FJS. No relevant floor- or ceiling effects occurred.

CONCLUSIONS

This study found reduced joint awareness for BCR-TKA compared to a standard total knee arthroplasty. The score values of the BCR-group were equal to the UKA-group. Further prospective, randomized studies to investigate long-term survivorship of bicruciate-retaining implants are needed.

LEVEL OF EVIDENCE

Level II.