Patellar Button Research Articles

Outcome after total knee arthroplasty with or without patellar resurfacing

Background: Anterior knee pain is one of the most important nagging factors following ‘total knee arthroplasty’. It requires adequate redressal to avoid patient dissatisfaction, undue psychological stresses and inflated costs due to readmission and reoperation. Aims: To assess the functional outcome prospectively in total knee arthroplasty with or without patellar resurfacing. Materials and Methods: A prospective randomised study involving 25 patients undergoing bilateral total knee arthroplasty (TKA) was carried out to study the outcome after TKA with patellar resurfacing (group I) and without patellar resurfacing (group II). The onlay surgical technique was used for patellar preparation, and a cemented all-polyethylene dome-shaped patellar button with three pegs was used for implantation. The Knee Society Score (KSS), Knee Functional Score (KFS) and visual analogue score were used for clinical assessment. Results: All outcomes were assessed after 1 year of follow-up in both the groups. There was a statistically significant difference between the group I and group II knees in the mean pain score (P < 0.001), 47.8 and 41.2, respectively, in the visual analogue score (P = 0.002), 0.76 and 1.56, respectively, and the mean KSS (P < 0.001), 90.28 and 84.16, respectively. However, there was no difference in the mean pre-operative and post-operative KFS between the two groups (P = 1.000), 45.00 (standard deviation [SD] ± 12.22) and 88.72 (SD ± 10.33), respectively. There was no statistical difference in the complication rates between the two groups. Conclusions: There is a significant improvement in anterior knee pain after patella resurfacing resulting in higher patient satisfaction.

Development of application and surgical technique of total knee arthroplasties: a systematic comparative analysis using worldwide registers

PurposeThe aim was to compare total knee arthroplasty (TKA) between countries with regard to epidemiologic data and surgical technique by the use of worldwide registers and compare findings with a previous report after one decade.MethodsA systematic search was carried out in November 2022 and compared to previous reports from 2010. We extracted data regarding implanted TKAs, patients’ age distribution, procedure types, fixation and revision rates. After identification of 28 national arthroplasty registers, 8of them, namely Australia, Canada, Denmark, England and Wales, New Zealand, Norway, Scotland and Sweden, offered sufficient data and were included in final analysis.ResultsA large variation was found in the annual number of implantations per 100,000 inhabitants with a range from 77 to 210.2 (mean 132.8). The fixation type varied strongly as well, e.g. over 95% of totally cemented TKAs in Sweden versus 61.2% cemented fixation in Denmark. Another significant difference was the use of patellar resurfacing in TKA, ranging from 47.3% (Canada) using a patellar button in TKA to less than 5% (Sweden). Within the period of one decade, the mean overall number of annual implantations increased (10%), whilst relative number of revisions decreased, the use of cemented TKA decreased from 87 to 74%, and the use of patella button remained largely inhomogeneous.ConclusionComparison of arthroplasty registers revealed large differences regarding the annual number of primary TKAs per inhabitant as well as primary TKA procedure types with an increase of annual implantations, decrease of relative number of revisions, and a decrease of the use of cemented systems over the period of one decade.

Patella component diameters of 38 mm and up might be associated with higher revision rates after patella resurfacing

PurposePatellar resurfacing is considered the standard of care for total knee arthroplasty in the USA. Complications of patella resurfacing include aseptic loosening or patella fractures and can threaten the integrity of the extensor mechanism. The goal of this study was to report on patella button revision rates in posterior stabilized total knee arthroplasty.Material and methodsBetween 01/2010 and 08/2016 patella buttons were implanted in 1056 patients (267 men and 550 women) as part of a posterior stabilized total knee arthroplasty.ResultsOf 1056 cases, 35 cases (14 women, 15 men, 5 bilateral, 3.3%) showed early loosening at a mean 52.5 months postoperatively. Patella components of 38 mm or larger diameters showed a significantly higher loosening rate than the 29, 32, 35 mm buttons (p < 0.01). Mean BMI of patients identified with aseptic loosening was 31.7 kg/m2, mean age at time of revision surgery was 63.3 years. All of the patients with loosening of the patella button required revision surgery; in 33 cases an exchange of the button was performed, in two cases a removal of the button and patellar bone grafting was indicated. No complications occurred after revision surgery.ConclusionThe current study reports a 3.3% patella loosening rate during this mid-term follow-up. Size 38 mm and larger patella components showed a significantly higher revision rate than smaller buttons and the authors advise caution when using large diameter patella components.

Patella height influences patellofemoral contact and kinematics following cruciate-retaining total knee replacement.

The role of patella height is discussed controversially in total knee arthroplasty (TKA). Therefore, this computational study aims to systematically analyze the biomechanical effect of different patella heights on patellofemoral (PF) forces and kinematics after cruciate-retaining (CR) TKA. We implemented a CR bicondylar TKA with a dome patellar button in a validated dynamic musculoskeletal multibody model of a male human knee joint. Retropatellar dynamics (contact force [N], shear force [N], patellar shift [mm], tilt [°], and rotation [°]) were evaluated during dual-limb squat motion (flexion from 0° to 90°) with simulated active muscle forces and the effects of different patella heights (Blackburne-Peel [BP] ratio of 0.39, 0.49, 0.65, 0.85, 1.01, and 1.1 were systematically examined). As active knee flexion increased, PF contact force also increased. Patella alta (BP = 1.1) resulted in higher PF contact forces compared to normal patella height (BP = 0.65) by up to 16%. Contrarily, patella baja was associated with decreased PF forces by 7%. Compared to patella baja (BP = 0.39), patella alta (BP = 1.1) considerably increased the contact force by up to 25%. Different patellar heights mainly affected PF shear forces during early knee flexion. Concerning PF kinematics, patella alta (BP = 1.1) yielded a greater lateral tilt of more than 4° and higher patellar rotation by up to 3° during deep knee flexion, compared to normal patella height (BP = 0.65). Our computational study indicates that patella alta is associated with the highest PF contact and shear force after the implantation of a CR bicondylar TKA. This should be considered in PF disorders following TKA.

Isolated effects of patellar resurfacing in total knee arthroplasty and their relation to native patellar geometry

The isolated effects of patellar resurfacing on patellar kinematics are rarely investigated. Nonetheless, knowing more about these effects could help to enhance present understanding of the emergence of kinematic improvements or deteriorations associated with patellar resurfacing. The aim of this study was to isolate the effects of patellar resurfacing from a multi-stage in vitro study, where kinematics after total knee arthroplasty before and after patellar resurfacing were recorded. Additionally, the influence of the native patellar geometry on these effects was analysed. Eight fresh frozen specimens were tested successively with different implant configurations on an already established weight bearing knee rig. The patello-femoral kinematics were thereby measured using an ultrasonic measurement system and its relation to the native patellar geometries was analysed. After patellar resurfacing, the specimen showed a significantly medialized patellar shift. This medialization of the patellar tracking was significantly correlated to the lateral facet angle of the native patella. The patellar shift after patellar resurfacing is highly influenced by the position of the patellar button and the native lateral patellar facet angle. As a result, the ideal medio-lateral position of the patellar component is affected by the geometry of the native patella.

Inlay Patellofemoral Arthroplasty: A Readily Reproducible Technique

Background: Patients with recalcitrant anterior knee pain and isolated patellofemoral osteoarthritis (PFOA) may benefit from patellofemoral arthroplasty. Arthroplasty with an inlay implant may be beneficial given recreation of native biomechanics and potentially avoiding anterior overstuffing. Indications: Patellofemoral arthroplasty is indicated in patients with anterior knee pain from isolated PFOA in patients with neutral alignment and intact menisci and ligaments. To highlight these indications, we present a 32-year-old female with severe anterior knee pain from PFOA, not resolved by conservative measures. Preoperative imaging demonstrated full-thickness chondral loss of the lateral patellar facet and trochlea, with neutral alignment and no significant trochlear dysplasia. Technique Description: This technique utilized the HemiCap Wave Implant manufactured by Anika Therapeutics (Franklin, MA, USA). A standard midline approach and medial parapatellar arthrotomy is performed. The patella is everted, and the trochlea is exposed. A guide pin is placed perpendicular to the trochlear bony surface and centrally in the defect. The pin is advanced, and the surrounding area is reamed. A guide block is placed over the pin in the trochlea and over-reamed. The area is prepared and centrally drilled, then tapped. A taper post is implanted. The trochlear implant is then secured to the taper post with an impactor and mallet. On the patellar side, a guide pin is placed in the center of the patella. Consideration is given to medialization of the button to decrease Q-angle. The patella is reamed to the diameter of an appropriately sized patellar button. A trial button is used to ensure satisfactory tracking. A real patellar implant is then cemented into place. Standard closure is performed. Results: Overall outcomes following inlay patellofemoral arthroplasty have been positive, with up to 89% of patients engaging in sports at 2 years status post surgery and 83% survival free of total knee arthroplasty at 5 years postoperatively. Discussion/Conclusion: Patellofemoral arthroplasty can provide good satisfaction and high rates of return to sport in patients with symptomatic, isolated patellofemoral arthritis. The surgical technique video presented provides reproducible steps, tips, and tricks for performing this procedure.

Fracture Risk With Patella Resurfacing During Total Knee Arthroplasty After Anterior Cruciate Ligament Reconstruction Using Bone-Patella-Bone Autograft: A Biomechanical Analysis.

BackgroundAnterior cruciate ligament (ACL) tears are common injuries. Ipsilateral bone patellar tendon bone (BPTB) autograft has been frequently used for ACL reconstructions. A large percentage of patients who sustain ACL ruptures develop early osteoarthritis and require total knee arthroplasty (TKA). When patients with previous BPTB autograft for an ACL tear undergo TKA, there may be an increased risk of fracture after patellar resurfacing.MethodsThere were 20 artificial Sawbones and 10 cadaveric patellae resurfaced. To simulate the presence of a previous BPTB autograft, a bone plug was removed from the anterior surface of the patellae and was resurfaced with a cemented patellar button. Biomechanical testing was performed to determine the compressive load to fracture of patellae with and without previous BPTB autograft.ResultsThe average maximum load to failure for the artificial Sawbones patellae without a previous BPTB autograft was 4551.40 N ± 753.12 compared with 2855.39 N ± 531.46 with a previous BPTB autograft (P < .001). The average maximum load to failure for the cadaveric patellae without a previous BPTB autograft was 7256.37 N ± 1473.97 compared with 5232.22 N ± 475.04 with a previous BPTB autograft (P = .021).ConclusionsThe results demonstrate a significantly lower maximum load to failure of a resurfaced patella in the presence of a previous BPTB autograft. This can be used to aid in the decision of whether to resurface the patellae in these patients and to educate patients that the presence of a previous BPTB autograft may be an increased risk factor for patella fracture after TKA.

Patellar button compatibility in the conversion of Patellofemoral Arthroplasty to a Total Knee Arthroplasty: A review of the contemporary literature.

Compared to total knee arthroplasty (TKA), patellofemoral arthroplasty (PFA) is a far less commonly performed operation. However, in carefully selected cohorts, PFA continues to be an appropriate treatment option for end-stage isolated patellofemoral joint osteoarthritis. In the later situation whereby a PFA is considered for conversion to a TKA - often due to disease progression - uncertainty remains regarding optimal management of the in situ patellar button. This review of the contemporary literature aimed to provide a summary of the current evidence to support surgeon decision-making, by evaluating the compatibility, efficacy, and survivorship of retained versus revised patellar buttons in PFA-to-TKA conversion. Specific focus was paid to implant design and technical considerations during revision, plus post-operative patient-reported outcomes and modes of secondary patellar component failure. A review of the Embase, Cochrane and PubMed databases was performed following PRISMA search principles. This investigation highlights that the fate of patellar buttons in PFA-to-TKA conversion has previously been poorly studied, with scant publication data available. Most reports have been of singular cases or small cohort series. Larger formal RCTs and level 1 evidence are lacking. The findings herein suggest that surgeons can confidently retain well-fixed, undamaged, dome-shaped all-polyethylene patellar buttons in the conversion of a PFA to TKA with the expectation of acceptable mid-term performance and survivorship, as long as congruent tracking with the new tibiofemoral components is achieved. This result is likely translatable to the majority of contemporary, all-polyethylene, dome-shaped patellar buttons, even with manufacturer mismatch.

A validated outcome categorization of the knee society score for total knee arthroplasty.

To determine cutoff values for the Knee Society Scores (KSS) indicative of a categorical scale of medium-term outcomes. One hundred and fifty-five patients who underwent primary cruciate-retaining TKA with a patellar button for osteoarthritis at a single-centre were assessed prospectively by the KSS and short-form Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) simultaneously at the 3-year follow-up. A validated categorization of the WOMAC score was used as a standard. The area under the curve (AUC) of receiver-operating characteristic (ROC) was used to assess the discriminative analysis accuracy of the, and the Youden index estimated the optimal cutoff point. For the KSS-knee score, the cutoff for an excellent outcome was 90.3 (AUC 0.75, 95% CI 0.71-0.78), 76.6 (AUC 76.6, 95% CI 0.70-076) for good, 64.8 (AUC 0.76, 95% CI 0.72-0.79) for fair, and < 64.8 (AUC 0.69, 95% CI 0.67-0.73) for poor. For the KSS-function score, the cutoff values were 85.2 (AUC 0.71, 95% CI 0.69-0.75), 73.1 (AUC 0.72, 95% CI, 0.70-0.76), 55.7 (AUC 0.70, 95% CI 0.71-0.74), and < 55.7 (AUC 0.68, 95% CI 0.66-0.72), respectively. A KSS-knee score ≥ of 90 was considered an excellent outcome, 77 good, 65 fair, and < 65 poor. For the KSS-function, those values are 85, 73, 56 and < 56, respectively. The treatment outcome's judgement may be clearer for the surgeon concerning a particular patient when using cutoff values for the scoring system employed, such as those determined in the present study. II.

Conforming patellar button design improves outcome of total knee arthroplasty

BackgroundPatellar resurfacing is commonly performed during total knee arthroplasty (TKA), and the patellar button design can vary within a TKA implant. Implant design is known to affect patella kinematics, contact mechanics, and ultimately the outcome of TKA. The aim of this study was to compare the patient-reported outcomes of TKA with either a conforming (CP) or medialized dome (MD) patellar component. MethodsThe study was a prospective cohort study of 100 TKAs performed between December 2015 and August 2017. We compared a consecutive series of 50 TKA subjects with a CP, with the previous 50 TKA subjects with an MD patella. The primary outcome measure was difference in Knee Injury and Osteoarthritis Score (KOOS) at 12 months. Other patient-reported outcome measures included EQ5D as a general health measure, and patient satisfaction. ResultsThere was no significant difference in baseline characteristics, KOOS, or EQ5D between the two groups. At 12 months, the CP Group had a higher mean KOOS function score (87 vs. 80, P = 0.04), and greater patient satisfaction (98% vs. 82% satisfied, P = 0.009) compared with the MD group. The CP Group had significantly lower frequency of pain with level walking, less difficulty with stairs, and lower mean EQ5D mobility at 12 months compared with the MD group. ConclusionsTKA performed using a conforming patella has superior results over a medialized dome patellar component for KOOS function, patient satisfaction, walking pain, stair performance, and mobility at 12 months postoperatively. The differences observed with the change in patellar design may be unique to this prosthesis.

Patellar Tracking in Revision Total Knee Arthroplasty: Does Retaining a Patella From a Different Implant System Matter?

BackgroundPatellar maltracking is a potential surgical complication following total knee arthroplasty (TKA) and can result in anterior knee pain, recurrent patellar dislocation, and damage to the medial patellar soft tissue stabilizers. Data remain unclear as to whether the patellar button should be revised during a revision TKA (rTKA) if changing the component implant system. Our study examines whether retaining the original patellar button during an rTKA using a different implant system affects patellar tracking. MethodsA retrospective cohort study of rTKA patients between August 2011 and June 2019 was performed at an urban, tertiary referral center. Patients were divided into 2 cohorts depending on whether their retained patella from their primary TKA was of the same (SIM) or different implant manufacturer (DIM) as the revision system used. Radiographic measurements were performed on preoperative and postoperative knee radiographs and differences were compared between the 2 groups. Baseline demographic data were also collected. ResultsOf the 293 consecutive, aseptic rTKA cases identified, 122 underwent revision in the SIM cohort and 171 in the DIM cohort. There were no demographic differences between the groups. No statistical significance was calculated for differences in preoperative and postoperative patellar tilt or Insall-Salvati ratio between the groups. The DIM group was found to have more lateral patellar translation (−0.01 ± 6.09 vs 2.68 ± 7.61 mm, P = .001). However, when calculating differences in the magnitude of the translation (thereby removing differences due to laterality), no difference was observed (0.06 ± 3.69 vs 0.52 ± 4.95 mm, P = .394). ConclusionNo clinically significant differences in patellar tracking were observed when the original patellar component was retained and a different revision implant system was used. Given the inherent risks of bone loss and fracture with patellar component revision, surgeons performing rTKA may retain the primary patella if it is well fixed and can still expect appropriate patellar tracking regardless of the revision implant system used. Level of EvidenceIII, Retrospective cohort study.

Actualización en osteonecrosis y fractura de rótula tras prótesis total de rodilla.

Periprosthetic patella fractures are much more common in knee prostheses in which the patella has been replaced. The aetiology of periprosthetic patella fractures has a traumatic origin in 12% of cases and atraumatic secondary to avascular necrosis in the remaining 88%. Peri-implant fractures, in which the patella has been replaced and the implant is stable with an integral extensor mechanism, resolve with conservative treatment. In cases of stable implant, with a displaced fracture of the upper or lower pole of the patella, the implant is left in situ and the extensor apparatus is repaired according to standard techniques. If there is disruption of the extensor apparatus with an unstable implant, the patellar button should be removed and continuity of the extensor apparatus repaired with a patellectomy. In these cases, internal fixation with wire cerclages is discouraged. In cases where the extensor mechanism is intact and the implant is unstable, the removal of the patellar button is sufficient. The risk of infection after surgery for a periprosthetic patella fracture is high.

Cementless Tritanium Baseplate Total Knee Arthroplasty: Survivorship and Outcomes at 5-Year Minimum Follow-Up.

Newer generation cementless total knee arthroplasty (TKA) designs have provided stronger osteointegration between the implant and bone. Despite excellent survivorship and outcomes with cemented TKAs, areas of concern within the bone-cement interface remain a concern and necessitate studies on alternative constructs. This study assesses: (1) implant survivorship; (2) clinical outcomes; and (3) complications with radiographic outcomes at a 5-year minimum follow-up of cementless highly porous titanium-coated baseplates in TKAs. Part of this study has been reported. We retrospectively reviewed a prospectively collected database at a single high-volume institution between July 1, 2013 and June 30, 2014 for patients who underwent a primary TKA using cementless highly porous titanium-coated baseplate implants. Patients were evaluated clinically at postoperative follow-up visits at a minimum of 5 years. To calculate the survivorship, Kaplan-Meier analysis was performed to determine all-cause, aseptic, and septic implant survivorship at each final follow-up for all patients. A total of 228 TKAs were performed and followed for a minimum of 5 years (range, 5-6 years). As of the latest follow-up, one case of septic loosening of the patellar button and one case of patellar dislodgment secondary to physical manipulation were recorded and revised. Overall, the cohort displayed implant survivorship of 99.5% at 5-year minimum follow-up. Improvements were seen in both Knee Society pain and function scores and were 37 points (range, 17-60 points) and 28 points (range, 15-47 points), respectively. The mean improvement in flexion was 17.8 (range, -20 to 40 degrees) and mean improvement in extension was -5.5 (range, -30 to 5 degrees). Cementless TKAs serve as strong alternative choice to cemented TKAs. Although cemented fixation is commonly known as the gold standard, results of this study confirm the findings of previous investigations on the survivorship of cementless TKA implants. Therefore, patients who undergo primary TKA with a cementless tritanium baseplate can expect excellent clinical outcomes at a 5-year minimum follow-up.

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.

Patellar Resurfacing Does Not Improve Clinical Outcome in Patients with Symptomatic Tricompartmental Knee Osteoarthritis. An RCT Study of 40 Patients Receiving Primary Cruciate Retaining Total Knee Arthroplasty.

There is some evidence that patellofemoral (PF) joint osteoarthritis (OA) causes anterior knee pain (AKP) after total knee arthroplasty (TKA). We hypothesized that patellar resurfacing in primary TKA for patients with symptomatic tricompartmental knee OA yields better clinical results after 2 years than non-resurfacing. A single center randomized controlled clinical trial comparing 40 patients receiving 42 cruciate retaining TKAs with (n = 21) or without patellar resurfacing (n = 21) was conducted. Primary outcome was the specific PF joint score HSS Baldini and secondary outcomes were the Knee Society Score (KSS) and the Knee Osteoarthritis Outcome Scale (KOOS). After 2 years no significant differences between both groups and between the groups in time for HSS Baldini, KSS, and KOOS were found. HSS Baldini score improved significantly after 6 weeks in both groups (p < 0.001) and did not improve in time afterward. At final follow-up the HSS Baldini mean score improved from a preoperative mean of 39 to 88 (difference of 49 points; p < 0.001)) for without patellar resurfacing group, and from a preoperative mean of 37 to 81 for patellar resurfacing group (difference of 47 points; p < 0.001). One patient in the patellar resurfacing group underwent a soft tissue re-alignment procedure because of patellar subluxation. Two patients in without patellar resurfacing group received secondary patellar button placement. Patellar resurfacing in primary TKA for patients with symptomatic tricompartmental OA has no beneficial effect over non-resurfacing and seems unnecessary. A special PF joint outcome measurement tool (HSS Baldini) and common knee scores showed no better knee function or AKP outcomes for with patellar resurfacing over without patellar resurfacing group in time and after 2 years of follow-up.

Design, Construction, and Early Results of a Formal Local Revision Knee Arthroplasty Registry.

National registries for primary and revision knee arthroplasty in Australia, New Zealand, and Europe have been successful in ensuring quality control and providing information to drive crucial research. However, they face challenges in delivering the granularity of data useful at a local hospital level. Our aim was to address these challenges by designing and initiating a local revision knee arthroplasty registry and combining the data with national figures to better evaluate the types of revisions undertaken, and improve patient outcomes and care. All revision knee arthroplasty cases in our center were analyzed from April 2014 to December 2015 using our standardized diagnostic algorithm. Information such as reason and type of revision was collected. Results were compared with Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) data. Primary outcome was comparison against our center's historical data between January 1999 and December 2013 and secondary outcome was comparison against national data prior to and after our intervention. Between April 2014 and December 2015, our center performed 35 revision knee arthroplasties. When compared with our center's historical data, we observed lower rates of revision knee arthroplasties due to "pain" (14.2 vs. 36.7%) with corresponding lower rates of patella button only revision (8.6 vs. 39.2%). Compared with national data before our intervention, we had lower revision rates from infection (14.2 vs. 22.3%) and loosening/lysis (11.4 vs. 29.2%). We undertook more minor revisions (45.7 vs. 30.5%) and similar total revisions (25.7 vs. 25.3%). Similar trends were seen in comparison to national data after our intervention. Our study shows that a local registry can be designed and successfully implemented for revision knee arthroplasty surgery. Data can be easily compared with historic and current hospital and national registry data trends to assess quality and robustness of revision arthroplasty programs. Our early results suggest our center has succeeded in reducing incidences of major revisions, complications, and the risk of re-revision surgery. This will improve the quality of our service with a significant cost reduction for our local health care budget.

The Effect of Patellar Button Placement on Gait and Patellar Stresses Following Total Knee Arthroplasty

In total knee arthroplasty with patellar resurfacing, surgeons are often faced with a choice of where to position the patellar button. Patellar button positioning has been studied in relation to patellar tracking and risk of subluxation. Consequently, medial placement has been recommended. However, postoperative gait and risk of periprosthetic complications have not been thoroughly addressed in relation to patellar button positioning.

Biomechanical analysis of a changed posterior condylar offset under deep knee bend loading in cruciate-retaining total knee arthroplasty.

The conservation of the joint anatomy is an important factor in total knee arthroplasty (TKA). The restoration of the femoral posterior condylar offset (PCO) has been well known to influence the clinical outcome after TKA. The purpose of this study was to determine the mechanism of PCO in finite element models with conservation of subject anatomy and different PCO of ±1, ±2, ±3mm in posterior direction using posterior cruciate ligament-retaining TKA. Using a computational simulation, we investigated the influence of the changes in PCO on the contact stress in the polyethylene (PE) insert and patellar button, on the forces on the collateral and posterior cruciate ligament, and on the quadriceps muscle and patellar tendon forces. The computational simulation loading condition was deep knee bend. The contact stresses on the PE insert increased, whereas those on the patellar button decreased as posterior condylar offset translated to the posterior direction. The forces exerted on the posterior cruciate ligament and collateral ligaments increased as PCO translated to the posterior direction. The translation of PCO in the anterior direction, in an equivalent flexion angle, required a greater quadriceps muscle force. Translations of the PCO in the posterior and anterior directions resulted in negative effects in the PE insert and ligament, and the quadriceps muscle force, respectively. Our findings suggest that orthopaedic surgeons should be careful with regard to the intraoperative conservation of PCO, because an excessive change in PCO may lead to quadriceps weakness and an increase in posterior cruciate ligament tension.

Kinematic Alignment in Cruciate Retaining Implants Improves the Biomechanical Function in Total Knee Arthroplasty during Gait and Deep Knee Bend.

Kinematic alignment (KA), which co-aligns the rotational axes of the components with three kinematic axes of the knee by aligning the components to the prearthritic joint lines, has been a recently introduced surgical technique. However, whether KA and cruciate retaining (CR) implants provide better biomechanical function during activities than mechanical alignment (MA) in posterior stabilized (PS) implants is unclear. We evaluated the biomechanical functions during the stance phase gait and deep knee bend, with a computer simulation and measured forces in the medial and lateral collateral ligaments and medial and lateral contact stresses in the polyethylene insert and patellar button. The forces on the medial collateral ligament in KA were lower than those in MA in both CR and PS TKA in the stance phase gait and deep knee bend conditions, whereas those on the lateral collateral ligament did not show any difference between the two surgical alignment techniques in the stance phase gait condition. The maximum contact stresses on the medial PE inserts in KA were lower than those in MA in both CR and PS TKA in the stance phase gait and deep knee bend conditions. However, the maximum contact stresses on the lateral PE inserts and the patellar button did not differ between MA and KA. The biomechanical function was superior in KA TKA than in MA TKA, and KA was more effective in CR TKA. This comparison could be used as a reference by surgeons to reduce the failure rates by using KA TKA instead of MA TKA.

Early outcomes of an anatomic trochlear-cutting patellofemoral arthroplasty: patient selection is key.

The purpose of this study was to report outcomes of a recent anatomic trochlear-cutting patellofemoral arthroplasty (PFA) system at > 3years. The hypothesis was that its functional scores and revision rates would be at least equivalent to those reported for other 'trochlear-cutting' implants in the literature. Twenty-eight consecutive patients that had received PFA using the same anatomic trochlear-cutting implant (KneeTech PFJ, Corin-Tornier, Montbonnot, France) with a dome-shaped patellar button and had systematic lateral facetectomy without lateral release were enrolled. Radiographic parameters collected pre-operatively included: trochlear dysplasia type and patellar height, TT-TG, patellar tilt and shape. Clinical scores collected pre-operatively and at > 3years included: Oxford Knee Score (OKS) and Knee Society Score (KSS). The initial cohort comprised 23 women (82%) and five men (18%), aged 63.3 ± 14.7years, of which 23 had trochlear dysplasia (82%). One patient (4%) could not be reached, and three (11%) were revised to TKA due to arthritic progression, aged 77, 80 and 83years at index operation, only one of which had trochlear dysplasia (type A). At final follow-up, none of the remaining 24 patients had complications; their OKS was 35.0 ± 10.3 and KSS symptoms and function were 19.8 ± 5.0 and 71.7 ± 13.6. The anatomic trochlear-cutting PFA granted satisfactory scores and prevented mechanical complications, but the high incidence of early revisions, all due to spread of arthritis hence to improper patient selection. PFA should be restricted to patients with trochlear dysplasia, in whom arthritis was triggered by patellar instability and maltracking rather than degenerative or age-related diseases. Retrospective case series, Level IV.