The consequences of not resurfacing the patella

Bilateral simultaneous total knee arthroplasty with and without patellar resurfacing. A prospective single surgeon series with a minimum follow-up of 7 years

BACKGROUND

Total knee arthroplasty (TKA) is the most effective treatment for end-stage adult knee osteoarthritis, but it has been reported that patient satisfaction may vary. A malfunction of the patellofemoral joint may produce anterior knee pain (AKP) for several reasons. While some surgeons systematically resurface the patella despite the risk of potential complications such as fracture, loosening, or wear of the patella, others prefer to preserve it to reduce AKP and revision rates. This study aimed to evaluate whether patellar resurfacing had better clinical and functional outcomes, complications, and revision rates in patients undergoing simultaneous bilateral total knee arthroplasty.

METHODS

We conducted a prospective cohort study, including patients who underwent bilateral simultaneous TKA in which the patella was replaced in one knee and preserved in the other, with a minimum follow-up of 7 years. We assessed clinical and functional outcomes with the Knee Society Score (KSS) and Visual Analogue Scale (VAS); complications and revision rates were also registered.

RESULTS

The final series consisted of 43 patients with 86 knee arthroplasties. After a mean of 7.6 years of follow-up, no significant differences were found regarding KSS (clinical: 82.8 ± 7.4 versus 83.2 ± 3.4, p = 0.92; functional 89.1 ± 8.2: versus 90.4 ± 6.8; p = 0.99), VAS (2.0 ± 0.9 versus 1.8 ± 1.0; p = 0.84), complications (10.5% versus 8.1%; p = 0.57), or revision rates (2.3% versus 2.3%; p = 0.99) when comparing patellar resurfacing versus retention.

CONCLUSION

In the context of total knee arthroplasty, patellar replacement did not demonstrate statistically significant differences concerning patellar retention in clinical nor functional outcomes, AKP, complications, or revision rates after a minimum of 7 years of follow-up.

Health-related quality of life after total knee arthroplasty and unicompartmental knee arthroplasty for unicompartmental osteoarthritis: A systematic review and meta-analysis

BACKGROUND

While previous research has demonstrated potential advantages of unicompartmental knee arthroplasty (UKA) over total knee arthroplasty (TKA), particularly in terms of clinical outcomes such as function and pain relief, the specific impact on health-related quality of life (HRQOL) remains unclear. This systematic review and meta-analysis aim to address this gap by comparing HRQOL outcomes between UKA and TKA, providing valuable insights for clinical decision-making.

METHODS

We conducted a literature search in the PubMed, Embase, Cochrane Controlled Register of Trials (CENTRAL), and Web of Science databases up to July 15, 2023. Eligible studies assessed HRQOL using EQ-5D, SF-36, or SF-12 and were assessed for methodological quality using the Newcastle-Ottawa Scale (NOS).

RESULTS

Seven eligible studies were included, comprising a total of 64,585 patients with 35,809 undergoing TKA and 28,776 undergoing UKA. Patient age ranged from 52.0 to 67.7 years with an average BMI ranging from 27.2 to 31.0 kg/m2. Follow-up periods ranged from 6 months to 10 years. Five studies (63,829 patients) that evaluated HRQOL using EQ-5D showed significantly better outcomes for UKA compared to TKA (MD -0.04, 95% CI -0.05 to -0.02). Two studies (756 patients) that evaluated HRQOL using SF-36 showed no significant difference between TKA and UKA. Five studies (63,286 patients) that evaluated functional outcomes using Oxford Knee Score (OKS) showed significantly better functional scores for UKA compared to TKA (MD -1.29, 95% CI -1.86 to -0.72). Four studies (24,570 patients) that reported patient satisfaction showed no statistically significant difference between TKA and UKA (MD 0.97, 95% CI 0.90 to 1.05). Further subgroup analysis did not affect the conclusions.

CONCLUSIONS

Our meta-analysis suggests that UKA is associated with better HRQOL and knee function, as well as similar patient satisfaction, compared to TKA for patients with unicompartmental osteoarthritis.

Anterior Knee Pain Following Primary Unilateral Total Knee Arthroplasty With Posterior-Stabilized Prosthesis and Patellar Resurfacing: Prevalence and Clinical Implications

BACKGROUND

Anterior knee pain following total knee arthroplasty (TKA) is associated with patient dissatisfaction. Factors related to postoperative anterior knee pain and its impact on patient outcomes are poorly understood. The following are the aims of this study: (1) to report the prevalence of anterior knee pain before and after TKA using a posterior-stabilized prosthesis with routine patellar resurfacing; (2) to investigate the association of preoperative clinical factors with the presence of anterior knee pain after TKA; and (3) to explore the association of postoperative anterior knee pain with postoperative self-reported function and quality of life.

METHODS

This retrospective study included 506 patients who had undergone elective primary unilateral TKA with a posterior-stabilized prosthesis and patellar resurfacing. Outcome measures prior to and 12 months after TKA included self-reported anterior knee pain, knee function, and quality of life.

RESULTS

Prevalence of anterior knee pain was 72% prior to and 15% following TKA. Patients who had preoperative anterior knee pain had twice the risk of experiencing anterior knee pain after TKA than patients who did not have preoperative anterior knee pain (risk ratio: 2.37, 95% CI 1.73-2.96). Greater severity of preoperative anterior knee pain and worse self-reported function were associated with the presence of postoperative anterior knee pain (rho = 0.15, P < .01; rho = 0.13, P < .01, respectively). Preoperative age, gender, and quality of life were not associated with postoperative anterior knee pain. Greater severity of postoperative anterior knee pain was associated with worse knee function at 12 months postoperative (rho = 0.49, P < .01).

CONCLUSION

One in 7 patients reported anterior knee pain 12 months following posterior-stabilized and patella-resurfaced TKA. The presence of preoperative anterior knee pain and worse self-reported function are associated with postoperative anterior knee pain.

Subchondral Bone Condition and Intraoperative Grading of Cartilage Degeneration Underneath Patella Unrelated to the Clinical Outcome after TKA with Unresurfaced Patella

The degree of cartilage degeneration assessed intraoperatively may not be sufficient as a criterion for patellar resurfacing in total knee arthroplasty (TKA). However, single-photon emission tomography/computed tomography (SPECT/CT) is useful for detecting osteoarthritic involvement deeper in the subchondral bone. The purpose of the study was to determine whether SPECT/CT reflected the cartilage lesion underneath the patella in patients with end-stage osteoarthritis (OA) and whether clinical outcomes after TKA without patellar resurfacing differed according to the severity of patellofemoral (PF) OA determined by visual assessment and SPECT/CT findings. This study included 206 knees which underwent TKA. The degree of cartilage degeneration was graded intraoperatively according to the International Cartilage Repair Society grading system. Subjects were classified into low and high uptake groups according to the degree of bone tracer uptake (BTU) on SPECT/CT in the PF joint. The Feller's patella score and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) were assessed preoperatively and postoperative 1 and 2 years. The increased BTU in the PF joint was associated with more severe degenerative cartilage changes underneath the patella (p < 0.001). The risk for the presence of denudated cartilage was greater in the high uptake group (odds ratio = 5.89). There was no association between clinical outcomes and visual grading of patellar cartilage degeneration or the degree of BTU on SPECT/CT. The visual assessment of the degree of cartilage degeneration underneath the patella and preoperative SPECT/CT evaluation of the PF joint were not predictive of clinical outcome after TKA with unresurfaced patella.

Patellar management during total knee arthroplasty: a review

The optimal management of the patella during total knee arthroplasty (TKA) remains controversial and surgeons tend to approach the patella with one of three general mindsets: always resurface the patella, never resurface the patella, or selectively resurface the patella based on specific patient or patellar criteria.

Studies comparing resurfacing and non-resurfacing of the patella during TKA have reported inconsistent and contradictory findings.

When resurfacing the patella is chosen, there are a number of available patellar component designs, materials, and techniques for cutting and fixation.

When patellar non-resurfacing is chosen, several alternatives are available, including patellar denervation, lateral retinacular release, and patelloplasty. Surgeons may choose to perform any of these alone, or together in some combination.

Prospective randomized studies are needed to better understand which patellar management techniques contribute to superior postoperative outcomes. Until then, this remains a controversial topic, and options for patellar management will need to be weighed on an individual basis per patient.

Cite this article: EFORT Open Rev 2021;6:861-871. DOI: 10.1302/2058-5241.6.200156

Patellar Fracture After Total Knee Arthroplasty With Retention: A Retrospective Analysis of 2954 Consecutive Cases

BACKGROUND

To the best of our knowledge, there have been no large case studies on patellar fracture after total knee arthroplasty (TKA) with patella retention.

METHODS

From 2005 to 2019, 2954 consecutive TKAs with patella retention were retrospectively reviewed. The incidence of patellar fracture was confirmed. Perioperative demographic factors associated with patellar fracture were compared between the nonpatellar fracture control (randomly selected after age and sex matching) and patellar fracture patient groups. To confirm the prognosis of identified patellar fractures, Hospital for Special Surgery knee score, union rates, and complications after treatment were evaluated. Treatment outcomes were compared as per the treatment method, and fracture type was classified by shape.

RESULTS

For primary TKAs with patella retention, patellar fracture occurred in 32 of 2883 cases (incidence 1.11%). When comparing the preoperative demographic factors between the patellar fracture and control groups, there was a significant difference in knee flexion of the affected limb. Twenty-three cases were treated nonoperatively, and nine cases were treated operatively. Of the 32 patellar fractures, 28 had confirmed union, and the HSS score at the latest follow-up increased significantly from the preoperative score. The only complication noted after treatment was nonunion in three cases. We found no significant differences in treatment results as per the treatment method and fracture type.

CONCLUSION

Patellar fracture after TKA with retained patella is infrequent, with relatively improved clinicoradiological results over those of patellar fracture after TKA with resurfaced patella reported in the literature. The improved results did not differ as per the treatment method and fracture type.

Development and validation of a robust patellar reference coordinate system for biomechanical and clinical studies

BACKGROUND

This study aimed to develop and validate a reference coordinate system for the human patella, based on the registration of bony landmarks on a computed tomography (CT) scan.

METHODS

Thirty-three native cadaveric specimens were scanned, and an observer marked a set of seven anatomical landmarks on each of them. Such markers were used to define the reference coordinate system. In order to validate its robustness, statistical distribution of the point registration was then studied. Afterwards, three different observers marked the anatomical landmarks on a sub-sample of six specimens and the intra-observer and inter-observer variability of the point registration was performed.

RESULTS

Results of this study showed the highest values to be 1.46 mm (intra) and 4.08 mm (inter), both observed for the patellar ridge top. The intra-class correlation coefficient (ICC) for inter-observer variability ranked higher than 0.8 for all the landmarks used for the identification of the reference frame, and ranged from 0.4-0.9 for other landmarks.

CONCLUSIONS

This study demonstrates low intra-observer and inter-observer variability in the CT registration of landmarks that define and validate a robust coordinate system of the patella that could be used to perform accurate biomechanical and clinical studies.

Patellar complications following total knee arthroplasty: a review of the current literature

Total knee arthroplasty is a common operation for treating patients with end-stage knee osteoarthritis and generally has a good outcome. There are several complications that may necessitate revision of the implants. Patella-related complications are difficult to treat, and their consequences impact the longevity of the implanted joint and functional outcomes. In this review, we explore the current literature on patellar complications in total knee arthroplasty and identify risk factors as well as strategies that can help in preventing these complications. We present pertinent findings relating to patellar complications. They can be classified into bony or soft tissue complications and include bone loss, aseptic loosening, periprosthetic fractures, patella fracture, patellar clunk syndrome, patellofemoral instability, extensor mechanism complications, maltracking, patella baja and malrotation. We conclude that patellar complications in total knee arthroplasty are common and have significant implications for the functional outcome of total knee arthroplasty. A high index of suspicion should be maintained in order to avoid them. Implant malpositioning and other forms of intraoperative technical error are the main cause of these complications, and therefore, primary prevention is crucial. When dealing with these established problems, a clear plan of action should be formulated in advance to allow appropriate management as well as anticipation of adverse outcomes.

The Challenge of Managing the "Third-Space" in Total Knee Arthroplasty: Review of Current Concepts

Total knee arthroplasty (TKA) is the best treatment for advanced knee osteoarthritis and it has proven to be durable and effective. Anterior knee pain (AKP) is still one of the most frequent complications after TKA, but sometimes no recognized macroscopic causes can be found. The correct treatment of patella is considered the key for a proper management of AKP. The inclusion of patellar resurfacing during TKA has been described as a potential method for the reduction of AKP. After surgeons started to resurface the patella, new complications emerged, such as component failure, instability, fracture, tendon rupture, and soft tissue impingement. Patelloplasty has been proposed as a good alternative to resurfacing but whether or not to resurface the patella is still a controversial topic in the literature. Therefore, patellofemoral joint is a complex critical aspect in TKA and choosing between the several options of treatment of patella could not be sufficient. In this review, evidence-based studies do not succeed in resolving this difficult argument. The accurate management of the so-called “third space” should include an accurate assessment of cartilage layers, balance of soft tissue, preoperative anterior tracking, and positioning of the femoral and tibial components. In fact, the selection of suitable implants and adherence to proper surgical technique are the fundamental principles for the success of TKA.

Total Knee Arthroplasty With Patellar Retention: The Severity of Patellofemoral Osteoarthritis Did Not Affect the Clinical and Radiographic Outcomes

BACKGROUND

The purpose of this study is to compare the clinical and radiographic outcomes of total knee arthroplasty (TKA) with patellar retention in accordance with the severity of patellofemoral arthritis.

METHODS

We retrospectively reviewed patients who underwent TKA with patellar retention using the NexGen LPS or LPS-flex system between September 2010 and May 2015. The radiographic severity of patellofemoral arthritis was categorized according to the Iwano classification system, and subjects were divided into mild (stage 0-I) and moderate to severe (stage II-IV) groups. Clinical outcomes were evaluated using the Hospital for Special Surgery score, Knee Society Score, function score, Western Ontario and McMaster Universities Osteoarthritis Index, and Feller score. Radiographic outcomes were assessed using the congruence angle, patellar tilt angle, and lateral patellar displacement. The minimum follow-up for clinical and radiographic evaluation was 2 years. Clinical and radiographic outcomes were compared between the 2 groups preoperatively and at the time of the last follow-up.

RESULTS

Four hundred seventy-four knees were enrolled and assigned to mild (n = 208) or moderate to severe (n = 266) groups. The preoperative Feller score was significantly lower in the moderate to severe group (P = .030), whereas the postoperative clinical and radiographic results did not differ significantly between the 2 groups.

CONCLUSION

Clinical and radiographic outcomes did not differ in accordance with the severity of patellofemoral arthritis after a minimum 2 years of follow-up of patients treated with TKA with patellar retention. Good outcomes were obtained with patellar retention in TKA, even in patients with advanced patellofemoral osteoarthritis.

Patella Resurfacing in Total Knee Arthroplasty: A Series of 1280 Patients at Midterm Follow-Up

BACKGROUND

The management of patella in total knee arthroplasty (TKA) is a controversial topic. The elevated risk of patellofemoral complications seems to support those who are not eager to perform such procedure. The aim of this study is to carry out a retrospective assessment of patients who underwent patellar resurfacing during TKA from 2004 to 2009.

METHODS

From January 1, 2004, to December 31, 2009, 1280 patients underwent TKA with patellar prosthesis implantation. Of them, 861 patients (639 women and 222 men with an average age of 67.7 ± 12.3 years) were available for a telephonic interview consisting of the questions included in the Knee Pain Score (KPS). Patients presenting KPS >36 and those subjected to reoperation were then evaluated clinically and radiologically.

RESULTS

Of the 861 patients included in the study, 801 showed a KPS <36. Among the remaining 60 patients, 33 had a KPS >36, while 27 had been reoperated at the target knee. In the former case, a decrease in normal Insall-Salvati index and patellar tilt values (from 1.08 to 1.02 and from 9.3 to 9.1, respectively) and average anatomic axis (from -2.6° to 1.1°) was found comparing preoperative with last follow-up evaluation. Only in 0.6% of the cases of reintervention, patellofemoral complications were found to be the cause.

CONCLUSION

This study conducted on a large and homogenous group of patients confirms a very low rate of complications related to patella resurfacing during TKA.

The predictive factors of secondary patellar resurfacing in computer-assisted total knee arthroplasty. A prospective cohort study

PURPOSE

The decision to resurface the patella during total knee arthroplasty (TKA) remains controversial. This prospective cohort study aimed to evaluate the outcome and survivorship of the native patella in computer-assisted TKA (CAS TKA) implanted for primary knee osteoarthritis, and to determine the predictive factors of secondary patellar resurfacing (SPR).

METHODS

A prospective cohort of 273 cementless ultra-congruent mobile-bearing CAS TKA implanted without patellar resurfacing was included in our total joint registry. Patients were evaluated with the International Knee Society (IKS) and Hospital for Special Surgery Patellar (HSSP) scores. Radiographic evaluation was focused on the patellofemoral (PF) compartment to assess: the patellar dysplasia (Wiberg classification), PF osteoarthritis (Iwano classification), femoral trochlear dysplasia (femoral sulcus angle), patellar maltracking (patellar tilt and lateralization), and patella height (Blackburne-Peel ratio).

RESULTS

At a six-year median follow-up, the CAS TKA survivorship using SPR as end-point was 95% (range, 91-99%). The IKS and HSSP improved significantly after SPR (p = 0.001 and 0.004, respectively). No significant difference in the IKS and HSSP was detected between TKA with native patella and SPR-TKA at latest follow-up. Importantly, four pre-operative radiographic PF parameters were significantly associated with SPR: higher stages of patellar dysplasia and PF osteoarthritis, and higher sulcus angle and patellar lateralization (hazard ratios = 5.1 to 11.6, p = 0.009 to 0.04).

CONCLUSION

When preserving the native patella, surgeons should be aware of pre-operative PF radiographic parameters that could influence the outcome and survivorship of CAS TKA leading to SPR. Particularly, evidence of PF dysplasia, osteoarthritis and maltracking should be determined pre-operatively to resurface the patella at the time of TKA.

LEVEL OF EVIDENCE

Therapeutic Level II (prospective cohort study).

Is Selectively Not Resurfacing the Patella an Acceptable Practice in Primary Total Knee Arthroplasty?

BACKGROUND

To resurface or not to resurface the patella remains a controversy in total knee arthroplasty (TKA). The purpose of this study was to assess the long-term outcomes associated with selectively not resurfacing the patella.

METHODS

This was a historical cohort study of 15,497 patients with 21,371 primary TKA procedures performed at a single institution between 1985 and 2010. The cohort included 402 (2%) knees with unresurfaced patellae and 20,969 knees with all-polyethylene patellae designs. Reasons for not resurfacing the patella were documented. Multivariable Cox regression analyses were used to estimate the risk of complications and revisions among procedures with unresurfaced patellae.

RESULTS

According to the surgeon, reasons for not resurfacing were normal cartilage (226, 56%), young patient (30, 8%), thin patella (53, 13%), and surgeons' choice (93, 23%). In age, sex, and calendar year-adjusted analyses, the risk of complications (hazard ratio [HR]: 1.25, 95% confidence interval [CI]: 1.06, 1.46) and all-cause revisions (HR: 1.39, 95% CI: 1.02, 1.89) were significantly higher after TKA with unresurfaced patellae. However, after adjusting for femoral component types and operative diagnoses, these associations were no longer significant. The only group with significantly worse outcomes were those with a thin patellae with increased risk of complications (HR: 2.66, 95% CI: 1.70, 4.17) and revisions (HR: 5.94, 95% CI: 2.35, 15.02). Yet, the excess risk in the thin patellae group was mainly due to infections, and not related to unresurfaced patellae.

CONCLUSION

Selectively not resurfacing the patella seemed to provide similar results compared with routine resurfacing.

In Vivo Three-Dimensional Patellar Mechanics: Normal Knees Compared with Domed and Anatomic Patellar Components

BACKGROUND

Patellofemoral complications are a major cause of revision surgery following total knee arthroplasty (TKA). High forces occurring at the patellofemoral articulation coupled with a small patellofemoral contact area pose substantial design challenges. In this study, the three-dimensional (3D) in vivo mechanics of domed and anatomically shaped patellar components were compared with those of native patellae.

METHODS

Ten normal knees, 10 treated with an LCS-PS (low contact stress-posterior stabilized) TKA (anatomically shaped patellar component), and 10 treated with a PFC Sigma RP-PS (press-fit condylar Sigma rotating platform-posterior stabilized) TKA (domed patellar component) were analyzed under fluoroscopic surveillance while the patient performed a weight-bearing deep knee bend from full knee extension to maximum knee flexion. Relevant bone geometries were segmented out from computed tomography (CT) scans, and computer-assisted-design (CAD) models of the implanted components were obtained from the manufacturer. Three-dimensional patellofemoral kinematics were obtained using a 3D-to-2D registration process. Contact mechanics were calculated using a distance map between the articulating patellar and femoral surfaces.

RESULTS

Both patellar component designs exhibited good rotational kinematics and tracked well within the femoral trochlea when compared with the normal patella. The contact areas in the TKA groups peaked at 60° of knee flexion (mean and standard deviation, 201 ± 63.4 mm for the LCS-PS group and 218 ± 95.4 mm for the Sigma RP-PS group), and the areas were substantially smaller than those previously reported for the normal patella. Contact points in the TKA groups stayed close to the center of the patellar components.

CONCLUSIONS

Both designs performed satisfactorily, although patellofemoral contact areas were reduced in comparison with those in the native patella.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Comparison of patellar resurfacing versus preservation in high flexion total knee arthroplasty

PURPOSE

Recently, high flexion design total knee arthroplasty (TKA) has been introduced to improve clinical outcomes. The purpose of this study is to compare the midterm outcomes between patellar resurfacing (PR) and patellar preservation (PP) in high flexion TKA.

METHODS

A total of 373 knees of primary TKAs were performed using high flexion design, 339 knees involved PR group and 34 knees involved PP group. After applying exclusion criteria, 1:3 matching was performed by the matching criteria. After matching, 69 knees in PR group and 23 knees in PP group remained. Radiographic outcomes, clinical outcomes, patients' satisfaction, ability and pain related to the high flexion activities were also evaluated.

RESULTS

There was no significant difference in radiograph measurements, KS function score and WOMAC score (n.s). However, PR group showed better outcomes in KS knee score (P = 0.001) and HSS score (P = 0.03). There was no significant difference in postoperative satisfaction and ability of high flexion activities between the groups, but the pain at the high flexion activities in PP group was worse than that in PR group.

CONCLUSION

In high flexion design of TKA, PR resulted in better midterm outcomes in regard to KS knee score, HSS score and knee pain related to the high flexion activities. The selective PR is recommended when performing primary TKA with high flexion design.

LEVEL OF EVIDENCE

IV.

Gender optimized patellar component designs are needed to better match female patellar anatomy

BACKGROUND

Avoidance of both over-resection of the native patella, and over-stuffing of the patello-femoral joint are advocated to reduce the risk of patellar complications following patellar resurfacing. Female gender, due to thinner native patella, and use of patellar prostheses from one specific manufacturer that were thicker for comparable diameters than the patellar prostheses from a second manufacturer were hypothesized to be risk factors for these undesirable technical outcomes.

METHODS

A retrospective review was undertaken of 803 consecutive knee replacements, performed by one surgeon, during which the same patellar resurfacing technique had been used, but with two different patellar implant designs.

RESULTS

Female gender, and use of one specific design of patella prostheses were associated with both increased risk of patellar over resection to ≤13mm residual patellar thickness, and creation of a patella construct that was thicker than the native patella (p<0.001).

CONCLUSIONS

Patellar prostheses design can contribute to compromises in surgical technique during patellar resurfacing in TKA in female patients with thinner patellae. Modifications to current patellar prosthesis dimensions may be considered to allow surgeons to more accurately resurface the thinner, native female patella.

LEVEL OF EVIDENCE

III.

Anterior knee pain after a total knee arthroplasty: What can cause this pain?

Total Knee Arthroplasty has been shown to be a successful procedure for treating patients with osteoarthritis, and yet approximately 5%-10% of patients experience residual pain, especially in the anterior part of the knee. Many theories have been proposed to explain the etiology of this anterior knee pain (AKP) but, despite improvements having been made, AKP remains a problem. AKP can be described as retropatellar or peripatellar pain, which limits patients in their everyday lives. Patients suffering from AKP experience difficulty in standing up from a chair, walking up and down stairs and riding a bicycle. The question asked was: “How can a ‘perfectly’ placed total knee arthroplasty (TKA) still be painful: what can cause this pain?”. To prevent AKP after TKA it is important to first identify the different anatomical structures that can cause this pain. Greater attention to and understanding of AKP should lead to significant pain relief and greater overall patient satisfaction after TKA. This article is a review of what pain is, how nerve signalling works and what is thought to cause Anterior Knee Pain after a Total Knee Arthroplasty.

Early PROMs following total knee arthroplasty--functional outcome dependent on patella resurfacing

Patella resurfacing during primary total knee arthroplasty (TKA) remains controversial. Variation in published results for patella resurfacing may potentially be explained by differences in design between TKA brands. We interrogated NJR-PROMs data to ascertain whether there is an early functional benefit to resurfacing the patella, both overall and for each of the five most popular primary knee designs through use of the Oxford Knee Score. A total of 8103 resurfaced TKAs and 15,290 nonresurfaced TKAs were studied. There was a large variation in the proportion of knees undergoing patella resurfacing by brand (Nexgen=16% versus Triathlon=52%). Patellar resurfacing did not significantly influence the magnitude of improvement in overall knee function or anterior knee-specific function irrespective of TKA brand or for cruciate retaining versus sacrificing designs.

Patellar resurfacing versus no resurfacing in two-stage revision of infected total knee arthroplasty

BACKGROUND

Cartilage debridement and staged reimplantation are the most common treatments for infected total knee arthroplasty (TKA). Very few studies have focused on the management of primarily non-resurfaced patellae in infected TKA. The purpose of this study was to compare the outcomes of patellar resurfacing and non-resurfacing in two-stage revision of infected TKA.

METHODS

This study involved a retrospective comparison of the reinfection rate and clinical outcomes of revision TKA patients managed with patellar resurfacing (22 patients, 23 knees) and patients managed without patellar resurfacing (26 patients) at a minimum two-year follow-up. The mean age in the resurfacing group was 69.4years old, and the mean age in the non-resurfacing group was 67.3years old. Three scales were used in the assessment: the Knee Society Score, Western Ontario and McMaster Universities Osteoarthritis Index, and the Anterior Knee Pain Scale.

RESULTS

Three knees had recurrent infections. All infections occurred in patients who had received patellar resurfacing. There were no significant differences between groups in clinical results and on the Anterior Knee Pain Scale. A lack of patellar resurfacing did not increase recurrence of infection and did not result in significant clinical differences compared to patellar resurfacing.

CONCLUSIONS

This study indicates that preservation of the original patellar bone is a feasible option for patellar management in revision of septic TKA.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Medium-term evaluation of total knee arthroplasty without patellar replacement

Objective

To mid-term evaluate patients who were submitted to total knee arthroplasty without patellar resurfacing.

Methods

It was realized a retrospective cross-sectional study of patients who were submitted to total knee arthroplasty without patellar resurfacing. In all patients clinical examination was done based on the protocol of the Knee Society Scoring System, which assessed pain, range of motion, stability, contraction, knee alignment and function, and radiological evaluation.

Results

A total of 36 patients were evaluated. Of these, 07 were operated only on left knee, 12 only on right knee and 17 were operated bilaterally, totaling 53 knees. Ages ranged from 26 to 84 years. Of the 53 knees evaluated, 33 (62.26%) had no pain. The maximum flexion range of motion averaged 104.7°. No knee had difficulty in active extension. As to the alignment for anatomical axis twelve knees (22.64%) showed deviation between 0° and 4° varus. Thirty-nine (75.49%) knees showed pace without restriction and the femorotibial angle ranged between 3° varus and 13° valgus with an average of 5° valgus. The patellar index ranged from 0.2 to 1.1.

Conclusion

Total knee arthroplasty whitout patellar resurfacing provides good results in mid-term evaluation.

The controversy of patellar resurfacing in total knee arthroplasty: Ibisne in medio tutissimus?

Early arthroplasty designs were associated with a high level of anterior knee pain as they failed to cater for the patello-femoral joint. Patellar resurfacing was heralded as the saviour safeguarding patient satisfaction and success but opinion on its necessity has since deeply divided the scientific community and has become synonymous to topics of religion or politics. Opponents of resurfacing contend that the native patella provides better patellar tracking, improved clinical function, and avoids implant-related complications, whilst proponents argue that patients have less pain, are overall more satisfied, and avert the need for secondary resurfacing. The question remains whether complications associated with patellar resurfacing including those arising from future component revision outweigh the somewhat increased incidence of anterior knee pain recorded in unresurfaced patients. The current scientific literature, which is often affected by methodological limitations and observer bias, remains confusing as it provides evidence in support of both sides of the argument, whilst blinded satisfaction studies comparing resurfaced and non-resurfaced knees generally reveal equivalent results. Even national arthroplasty register data show wide variations in the proportion of patellar resurfacing between countries that cannot be explained by cultural differences alone. Advocates who always resurface or never resurface indiscriminately expose the patella to a random choice. Selective resurfacing offers a compromise by providing a decision algorithm based on a propensity for improved clinical success, whilst avoiding potential complications associated with unnecessary resurfacing. Evidence regarding the validity of selection criteria, however, is missing, and the decision when to resurface is often based on intuitive reasoning. Our lack of understanding why, irrespective of pre-operative symptoms and patellar resurfacing, some patients may suffer pain following TKA and others may not have so far stifled our efforts to make the strategy of selective resurfacing succeed. We should hence devote our efforts in defining predictive criteria and indicators that will enable us to reliably identify those individuals who might benefit from a resurfacing procedure. Level of evidence V.

A randomized controlled trial comparing patellar retention versus patellar resurfacing in primary total knee arthroplasty: 5-10 year follow-up

Background

The primary purpose of this randomized controlled trial (RCT) was to compare knee-specific outcomes (stiffness, pain, function) between patellar retention and resurfacing up to 10 years after primary total knee arthroplasty (TKA). Secondarily, we compared re-operation rates.

Methods

38 subjects with non-inflammatory arthritis were randomized at primary TKA surgery to receive patellar resurfacing (n = 21; Resurfaced group) or to retain their native patella (n = 17; Non-resurfaced group). Evaluations were performed preoperatively, one, five and 10 years postoperatively by an evaluator who was blinded to group allocation. Self-reported knee-specific stiffness, pain and function, the primary outcomes, were measured by the Western Ontario McMaster Osteoarthritis Index (WOMAC). Revision rate was determined at each evaluation and through hospital record review.

Results

30 (88%) and 23 (72%) of available subjects completed the five and 10-year review respectively. Knee-specific scores continued to improve for both groups over the 10-years, despite diminishing overall health with no significant group differences seen. All revisions occurred within five years of surgery (three Non-resurfaced subjects; one Resurfaced subject) (p = 0.31). Two revisions in the Non-resurfaced group were due to persistent anterior knee pain.

Conclusions

We found no differences in knee-specific results between groups at 5–10 years postoperatively. The Non-resurfaced group had two revisions due to anterior knee pain similar to rates reported in other studies. Knee-specific results provide useful postoperative information and should be used in future studies comparing patellar management strategies.

ClinicalTrials.gov identifier

NCT01500252

[The third compartment in knee endoprosthetics: from denervation to replacement, which therapy is correct?]

Involvement of the patellofemoral compartment is common in osteoarthritis of the knee but to date there is no consensus as to the most appropriate approach concerning the patella. Both general non-selective resurfacing as well as selective or secondary resurfacing are currently accepted. However, despite abundant studies on the subject no clear conclusions can be drawn from the available evidence. There are arguments in favour of either approach. Accordingly, no strong evidence can be found to support peripatellar denervation. With the advent of new diagnostic modalities for the assessment of knee osteoarthritis, such as single photon emission computed tomography/CT (SPECT/CT), a more selective approach to patellar resurfacing with a potentially improved outcome might become possible.

Comparison of patellar retention versus resurfacing in LCS mobile-bearing total knee arthroplasty

PURPOSE

The aim of this retrospective study was to compare clinical outcomes of total knee arthroplasty (TKA) with and without patellar resurfacing using the Low Contact Stress (LCS) mobile-bearing prosthesis in 275 osteoarthritic knees (199 patients) after a minimum of 7 years of follow-up.

METHODS

Patients were divided into a patellar retention group (132 knees) and a resurfacing group (143 knees), with median follow-up durations of 7.8 years (range, 7-8.5 years) and 8.5 years (range, 7-10.6 years), respectively. The demographics of the two groups were otherwise matched. The patelloplasty was performed for patellar retention. Patients were evaluated by a blinded, independent observer using Feller's patellar score, the Knee Society score, patient satisfaction, patellar tilt, and lateral displacement.

RESULTS

Patellar resurfacing was not superior to retention with respect to any of the measured variables. Eight knees (6.1%) without and 6 (4.2%) with patellar resurfacing had anterior knee pain related to the patellofemoral joint (n.s.). The reoperation rate related to the patellofemoral joint was 0.8% (n = 1) in the retention group compared with 2.8% (n = 4) in the resurfacing group (n.s.). In the 35 patients who underwent bilateral TKA with patellar resurfacing on only one side, there were no significant differences between the two sides in subjective preference, clinical scores, or functional ability.

CONCLUSIONS

The clinical and radiographic outcomes of TKA with the LCS mobile-bearing prosthesis showed no significant difference between the two groups after a minimum of 7 years of follow-up. The findings in this study suggest that patellar retention with a patelloplasty may be viable as a routine procedure, even in knees with advanced patellofemoral arthritis, if soft tissue balancing and a patella-friendly prosthetic design are properly used.

LEVEL OF EVIDENCE

Therapeutic, retrospective, comparative study, Level III.

Patellar polyethylene spinout after low-contact stress, high-congruity, mobile-bearing patellofemoral arthroplasty

A low-contact stress, high-congruity, mobile-bearing patellofemoral joint arthroplasty decreases the contact force in the patellofemoral joint, theoretically reducing patellar polyethylene wear and increasing implant longevity. This article describes the case of a 47-year-old obese woman who presented with pain and loss of extension after a low-contact stress, high-congruity, mobile-bearing patellofemoral joint arthroplasty. Radiographs revealed dislocation (ie, spinout) of the patellar polyethylene. Patellar polyethylene spinout is a rare complication of metal-backed, mobile-bearing patellar resurfacing. Theoretically, patellar polyethylene spinout in low-contact stress, high-congruity, mobile-bearing patellofemoral arthroplasty is related to implant design and the placement of the metal base plate. Ultimately, the articulation of low-contact stress, high-congruity, mobile-bearing patellofemoral arthroplasty may be too congruent to resist the forces of the patellofemoral joint, particularly in patients who are obese, and the patellar rotation allowed by this articulation may not be sufficient for all patients. Should patellar spinout occur, replacement of the polyethylene is not sufficient to correct the problem; hence, revision of the patellar and trochlear components is required because it remains unclear whether failure is secondary to patellar or trochlear design deficiencies.

Revision surgery for patellofemoral problems: should we always resurface?

BACKGROUND

Routine patellar resurfacing performed at the time of knee arthroplasty is controversial, with some evidence of utility in both TKA (tricompartmental) and bicompartmental knee arthroplasty. However, whether one approach results in better implant survival remains unclear.

QUESTIONS/PURPOSES

We asked whether (1) routine patellar resurfacing in TKAs resulted in lower cumulative revision rates compared to bicompartmental knee arthroplasties, (2) patella-friendly implants resulted in lower cumulative revision rates than earlier designs, and (3) bicompartmental knee arthroplasties revised to TKAs had higher cumulative revision rates than primary TKAs.

PATIENTS AND METHODS

From a community-based joint registry, we identified 8135 patients treated with 9530 cemented, all-polyethylene patella TKAs and 627 bicompartmental knee arthroplasties without patellar resurfacing. We compared age, gender, year of index procedure, diagnosis, cruciate status, revision, and revision reason.

RESULTS

TKAs had a lower cumulative revision rate for patella-only revision than bicompartmental knee arthroplasties (0.8% versus 4.8%). Adjusting for age, bicompartmental knee arthroplasties were 6.9 times more likely to undergo patellar revision than TKAs. There was no difference in the cumulative revision rate for patella-only revisions between patella-friendly and earlier designs. The cumulative revision rate for any second revision after a patella-only revision was 12.7% for bicompartmental knee arthroplasties while that for primary TKAs was 6.3%.

CONCLUSIONS

Bicompartmental knee arthroplasties had higher revision rates than TKAs. Femoral component design did not influence the cumulative revision rate. Secondary patella resurfacing in a bicompartmental knee arthroplasty carried an increased revision risk compared to resurfacing at the time of index TKA. To reduce the probability of reoperation for patellofemoral problems, our data suggest the patella should be resurfaced at the time of index surgery.

Secondary patellar resurfacing in the treatment of patellofemoral pain after total knee arthroplasty

PURPOSE

This paper reports a prospective review of patients who, between 2004 and 2007, underwent secondary patellar resurfacing (SPR) due to anterior knee pain after a primary total knee arthroplasty (TKA). The aim was to evaluate the clinical outcomes obtained with the SPR and to compare them with radiological findings.

METHODS

A total of twenty-seven consecutive patients met the inclusion criteria. There were twenty-three (85%) women and four (15%) men with a median age of 70 years. The patients were evaluated before and after the surgery with the same functional scores and radiological parameters. Bone scintigraphy was also used in the assessment, and a CT-scan was performed in order to evaluate the femoral component rotation. The median time between TKA and SPR was 18 months.

RESULTS

With a median follow-up of 23 months, seventeen patients (63%) reported a clear subjective improvement after SPR, and patellofemoral scores (primary outcome measure), KSS and WOMAC (secondary outcome measures) showed a statistically significant improvement following the procedure. There were no significant changes after SPR in the Insall-Salvati ratio, the lateral patellar displacement or the lateral patellar tilt. The mean time between TKA and SPR had no statistically significant effect on outcome. The bone scintigraphy revealed increased patellar uptake in seven cases, but this was not related to subsequent improvement after SPR. Rotational computed tomography showed a median internal rotation of the femoral component of 1º. The complications observed were a patellar component loosening and an acute post-infection.

CONCLUSION

No clinical or radiological parameter was found to be related to the final outcome after SPR. There was a discrepancy between functional scale scores and the patient's subjective satisfaction.

Patellar resurfacing in total knee replacement: five-year clinical and economic results of a large randomized controlled trial

BACKGROUND

There is conflicting evidence regarding the merits of patellar resurfacing during total knee arthroplasty, as many of the previous randomized controlled trials have not been adequately powered.

METHODS

A pragmatic, multicenter, randomized controlled trial was initiated in 1999 in the United Kingdom. Within a partial factorial design, 1715 patients were randomly allocated to receive or not receive patellar resurfacing during total knee arthroplasty. The primary outcome measure was the Oxford Knee Score; secondary measures included the Short Form-12, the EuroQoL 5D, cost, cost-effectiveness, and the need for subsequent knee surgery.

RESULTS

The mean Oxford Knee Score was 35 points at five years postoperatively in both groups. There was no significant difference between the groups with respect to the mean Oxford Knee Score (difference, 0.59 point; 95% confidence interval, -0.58 to 1.76 points) or any other outcome measure at five years postoperatively. The outcome was not affected by whether the patella was domed or anatomic. There was no significant difference between the two groups with respect to the prevalence of knee-related readmission, of minor or intermediate reoperation, or of subsequent patella-related surgery. The total health care cost for the primary arthroplasty, subsequent monitoring, and any revision surgery did not differ significantly between the two groups.

CONCLUSIONS

In the largest randomized controlled trial of patellar resurfacing reported to date, the functional outcome, reoperation rate, and total health care cost five years after primary total knee arthroplasty were not significantly affected by the addition of patellar resurfacing to the surgical procedure.

The need for patellar resurfacing in total knee arthroplasty: a literature review

The controversy over whether or not to routinely resurface the patella during a total knee arthroplasty has persisted despite three decades of successful joint replacement procedures. Advocates for routine patellar resurfacing admit the occasional need for secondary patellar resurfacing and declare increased incidence of anterior knee pain in patients with non-resurfaced patellae as a cause for worry. Surgeons that leave the patella unresurfaced cite avoidance of complications that include patellar fracture, avascular necrosis, patellar tendon injury and instability. This review discusses the available literature on patellar resurfacing through an evidence-based analysis of randomized and pseudo-randomized controlled trials and published meta-analyses to date. The published literature seems to favour resurfacing the patellar routinely. Selective patellar resurfacing would be the ideal solution if sound pre-operative criteria could be established. So far, a method for accurately predicting which patients can avoid patellar resurfacing has not been found. Future research looking at patellar resurfacing should concentrate on developing criteria for selecting those patients that would benefit from patellar resurfacing and those that would do as well without resurfacing, and thus, limiting potential surgical complications.

Isolated resurfacing of the previously unresurfaced patella total knee arthroplasty

Postoperative anterior knee pain can be challenging after primary total knee arthroplasty. Isolated patellar resurfacing may provide symptomatic improvement in those patients with an unresurfaced patella. Seventeen isolated patellar resurfacing procedures were performed. Patient outcomes were evaluated using the Knee Society clinical and roentgenographic evaluation systems. Continued symptomatology and overall patient satisfaction were also analyzed. No revisions have been necessary at 47 months of follow-up. Overall, Knee Society knee scores and knee function scores significantly improved. Eight patients (53%) are asymptomatic and were satisfied with the procedure, whereas 7 patients (47%) continue to have anterior knee pain and are unsatisfied. Isolated patellar resurfacing for anterior knee pain in total knee arthroplasty with an unresurfaced patella has a low morbidity and revision rate but may not provide patients with predictable symptomatic improvement.

The outerbridge classification predicts the need for patellar resurfacing in TKA

Patellar resurfacing (PR) in total knee arthroplasty (TKA) is controversial. The Outerbridge classification of cartilage defects in the patella is commonly used in the literature. The purpose of this study was to determine if the Outerbridge classification can predict the need for PR as part of total knee arthroplasty. Between 1995 and 2000, we performed a prospective, randomized study of 500 TKAs. We carried out PR depending on the Outerbridge classification of the patella at the time of surgery. Patients with Outerbridge Grades I, II, and III formed Group A, whereas patients with Grade IV formed Group B. Within each group, resurfacing was completed on half of the patients. Group A had 328 patients (164 with PR, 164 without PR). In Group B, there were 172 patients (86 with PR, 86 without PR). An identical prosthetic design was used for both groups. The minimum followup was 5 years (average, 7.8 years) for both Group A and Group B. At the end of followup, we assessed the number of patients in each group that required secondary resurfacing as a result of patellofemoral pain. Patients in Group A required fewer revisions for PF pain. In Group A, only one patient required a secondary PR (0.6% rate), whereas in Group B, 10 patients needed PR (11.6% rate). In Group B, the risk of need of a patellar resurfacing was 21.5 times greater than in Group A. On the basis of these findings, we recommend PR in Outerbridge Grade IV patellae, but not in Grades I, II, and III.

LEVEL OF EVIDENCE

Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Resurfacing versus nonresurfacing the patella in total knee arthroplasty: a critical appraisal of the available evidence

A systematic literature search for evidences comparing treatment effect and harm of resurfacing versus nonresurfacing the patella in total knee arthroplasty was conducted and yielded five meta-analysis (MA), one systematic review (SR) and six randomized controlled trials not included in previous MAs/SR. The evidence suggests that patellar resurfacing would reduce the risk of anterior knee pain, as well as the risk of patella-related reoperation. Furthermore, patients not undergoing patella resurfacing would experience more knee pain during stair climbing and be less satisfied with surgery. No significant difference in range of motion can be expected with or without patellar resurfacing. Importantly, methodological limitations were observed in all retrieved studies and evidences about potential adverse events related to patellar resurfacing are presently undetermined.

Patella retention versus replacement in total knee arthroplasty; functional and clinimetric aspects

INTRODUCTION

Whether to resurface the patella or not in total knee arthroplasty still remains undecided. Classical scores and questionnaires might not be responsive or demanding enough. This study used two accelerometer based systems to study the hypothesis whether performance based tests are able to detect a difference in patients with or without a resurfaced patella.

METHOD

In this retrospective study 53 patients were included and divided into a resurfaced group (n = 31) and a non-resurfaced group (n = 22). Both groups were matched on age and longevity of follow up. Patients were clinically assessed using the Knee Society Score (KSS) at various time points. At final follow up patients were also assessed once using the Dynaport Knee Test and the Minimod Gait Test.

RESULTS

The Dynaport Knee Test showed a significant functional advantage for patients with a resurfaced patella [44 vs. 39.7 (P = 0.042)], whereas KSS and The Minimod were not significant (P values ranging from 0.07 to 0.75). Similar to other reports in literature, using the KSS, it was not possible to identify significant difference between patella resurfacing or retaining in total knee arthroplasty, however using a performance based test it was possible to determine significant difference. The found advantage of patella resurfacing may be less due to pain relief but due to a functional benefit during demanding motion tasks. This finding indicates that current measurement tools may not be accurate or specific enough to detect this difference. Therefore, we recommend complementing the classic evaluation tools with an objective functional test, when conducting a randomized trial to answer the indecision whether to resurface the patella or not.

Effect of an UHMWPE patellar component on stress fields in the patella: a finite element analysis

An increased stress in the patella due to the implantation of a patellar button may also be another potential source of pain in total knee arthroplasty patients. This study assessed the location inside the patella having largest stress change after implantation of an ultra high molecular polyethylene patella button. Finite elements models of the patellae before and after implantation of patellar button were created. Experimentally determined spring constants of muscles and ligaments, and patellofemoral contacting loads were applied to the models at 30 degrees , 60 degrees , and 90 degrees of knee flexion. The Von Mises stress of the intact patella decreased with increased knee flexion, while that of implanted patella increased. Also, the stress range in the implanted patella was 3-9 times higher than in the intact one. The highly stressed region of the intact patella moved proximally with higher knee flexion angles, while that of the implanted model stayed near the central anterior patella. At 90 degrees of knee flexion, the stress in the anterodistal patella increased considerably after implantation of a patella button so that the anterodistal patella may be susceptible to be painful source after the total knee replacement.

Predicting patellar failure after total knee arthroplasty

We identified patient and surgeon factors associated with patellar component failure in a series of 8530 TKAs performed in 5640 patients using the same posterior cruciate ligament-retaining TKA with all-polyethylene patellar components between January 1983 and December 2003. Patellar failure was defined as loosening, fracture, or patellar revision. All infections were excluded. Statistical analysis using Kaplan-Meier and Cox regression was used to determine the risk of patellar failure. Followup averaged 7.0 years (range, 2-22 years). Patellar component loosening occurred in 4.8% of TKAs (409 knees). Patellar fracture was identified in 5.2% of TKA (444 knees). Twenty-five patellae were revised (0.3%). TKA performed with a lateral release and patients with a body mass index of greater than 30 kg/m(2) were at the greatest risk of patellar loosening and fracture, respectively. Male gender, preoperative varus alignment of greater than 5 degrees , and large patellar component size also predicted a higher risk of patellar fracture. Medial patellar component position, tibial component thickness of greater than 12 mm, preoperative valgus alignment of 10 degrees or more, and preoperative flexion of 100 degrees or more predicted patellar loosening. An awareness of these factors that predict patellar failure after TKA may help determine the relative indications for TKA and influence surgical technique, especially when using this prosthesis.

LEVEL OF EVIDENCE

Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Total knee replacement with and without patellar resurfacing: a prospective, randomised trial using the profix total knee system

We have examined the differences in clinical outcome of total knee replacement (TKR) with and without patellar resurfacing in a prospective, randomised study of 181 osteoarthritic knees in 142 patients using the Profix total knee system which has a femoral component with features considered to be anatomical and a domed patellar implant. The procedures were carried out between February 1998 and November 2002. A total of 159 TKRs in 142 patients were available for review at a mean of four years (3 to 7). The patients and the clinical evaluator were blinded in this prospective study. Evaluation was undertaken annually by an independent observer using the knee pain scale and the Knee Society clinical rating system. Specific evaluation of anterior knee pain, stair-climbing and rising from a seated to a standing position was also undertaken. No benefit was shown of TKR with patellar resurfacing over that without resurfacing with respect to any of the measured outcomes. In 22 of 73 knees (30.1%) with and 18 of 86 knees (20.9%) without patellar resurfacing there was some degree of anterior knee pain (p = 0.183). No revisions related to the patellofemoral joint were performed in either group. Only one TKR in each group underwent a re-operation related to the patellofemoral joint. A significant association between knee flexion contracture and anterior knee pain was observed in those knees with patellar resurfacing (p = 0.006).

Patellar tracking during total knee arthroplasty: an in vitro feasibility study

Abnormal patellar tracking results in patello-femoral (PF) joint disorders and frequently in failure of total knee arthroplasty (TKA). It is fundamental to assess this tracking intra-operatively, i.e. since the implantation of the femoral and tibial components. The aim of this study was to assess the feasibility of three-dimensional anatomical-based patellar tracking intra-operatively in standard TKA. A surgical navigation system was utilized to test the new technique in-vitro. An original tracking device and a reference frame were designed and an articular convention for the description of PF joint kinematics was adopted. Six fresh-frozen amputated legs were analyzed with the new technique. Landmark digitations were used to define anatomical reference frames for the femur, tibia, and patella. Five trials of passive flexion were performed with 100 N force on the quadriceps, before and after standard knee arthroplasty. Patellar flexion, tilt, rotation and shift were calculated in addition to standard tibio-femoral (TF) joint kinematics. An intra-specimen repeatable path of motion over repetitions and a coupled path of motion throughout the flexion-extension cycle were observed in all intact knees, both at the TF and PF joints. Replication of the original PF motion in the intact knee was not fully accomplished in the replaced knee. These results revealed the feasibility and the necessity of patellar tracking during TKA. By monitoring intra-operatively also the PF kinematics, the surgeon has a more complete prediction of the performance of the final implant and therefore a valuable support for the most critical surgical decisions.

Patellofemoral instability after total knee arthroplasty

Despite advances in surgical technique and implant design, complications involving the extensor mechanism and patellofemoral joint after total knee arthroplasty (TKA) continue to be the most common cause of pain and the most commonly cited reason for revision TKA surgery. A thorough understanding of the etiologies of patellofemoral instability, careful preoperative planning, and meticulous surgical techniques will optimize clinical outcome. Evaluation of patellofemoral stability should begin in the operating room. Postoperatively, thorough history, physical examination, and dedicated radiographic studies should be obtained. Computed tomography scan is the most accurate and reliable way to assess component positioning. Treatment of patellofemoral instability is directed by its etiology. Revision of one or both components is indicated if malpositioning is present. If the components are determined to be in satisfactory positions, soft tissue procedures can be pursued. Future advancements in prosthetic design and the routine use of computer-assisted navigation systems will minimize patellofemoral instability.

LEVEL OF EVIDENCE

Therapeutic study, Level V (expert opinion). See the Guidelines for Authors for a complete description of levels of evidence.

Postoperative Imaging of the Knee

The knee is a frequently injured joint and, thus, a common focus of operative intervention. As operative techniques and imaging modalities evolve, radiologists must be aware of the expected postoperative appearance after knee surgeries that are performed commonly and also must be comfortable recognizing complications encountered commonly in the immediate and delayed postoperative period. Drawing on the large amount of attention this subject has received of late in the radiologic and orthopedic literature, this article reviews the knee surgeries performed most commonly and the expected normal and most frequently encountered abnormal postoperative imaging findings with an emphasis on MR imaging.