Patellar Cut and Composite Thickness: The Influence on Postoperative Motion and Complications in Total Knee Arthroplasty

Isolated patellofemoral arthroplasty-surgical technique and tips: current concepts

Successful patellofemoral arthroplasty (PFA) requires appropriate patient selection, correct implant positioning and attention to surgical technique. Whilst the original concept and rationale offered an attractive surgical option for patients with isolated patellofemoral arthritis, early results were disappointing and consequently many surgeons became reluctant to offer it. With newer-generation designs, outcomes have been more promising. However, attention to surgical technique remains an integral component to a successful outcome, with results being unforgiving when surgical errors are made. This paper explores the key components of the surgical technique in PFA, including implant design, patient selection and tips to avoid common mistakes.

Mechanical complications after total knee arthroplasty

INTRODUCTION

With the increasing demand for total knee arthroplasty (TKA) and the burden of revision TKA on the healthcare system, as well as the quality of life implications for patients, it is extremely important for surgeons to be able to anticipate and prevent TKA mechanical complications. Surgeons must be familiar with the different causes and mechanisms of TKA complications so that they can properly treat patients with failed TKAs and better avoid these complications.

AREAS COVERED

This review addresses TKA mechanical complications and provides context for the topic. A detailed review of surgical factors, implant factors, and patient factors that contribute to mechanical complications after TKA is provided. All of the literature cited in this review was gathered from the PubMed online database using different keywords based on the section of the manuscript.

EXPERT OPINION

As surgeons and engineers solve certain issues in TKA, new challenges will inevitably arise. We must continue to push forward and innovate from both a surgical technique and implant design perspective.

No difference between resurfaced and non-resurfaced patellae with a modern prosthesis design: a prospective randomized study of 250 total knee arthroplasties

PURPOSE

Despite numerous well-conducted studies and meta-analyses, the management of the patella during total knee arthroplasty (TKA) remains controversial. The aim of our study was to compare the clinical and radiological outcomes between patients with and without patellar resurfacing and to determine the influence of resurfacing on patellar tracking with a "patella-friendly" prosthesis.

METHODS

A single-centered prospective randomized controlled study was performed between April 2017 and November 2018. Two hundred and forty-five consecutive patients (250 knees) scheduled for TKA were randomized for patellar resurfacing or patella non-resurfacing. All patients received the same total knee prosthesis and were evaluated clinically and radiologically, including the International Knee Society Score (KSS knee and function), Forgotten Joint Score (FJS), anterior knee pain (AKP), pain when climbing stairs, patellar tilt, and patellar translation.

RESULTS

Two hundred and twenty-nine knees were available for clinical evaluation and 221 knees for radiographic analysis. The revision rate for patellofemoral cause was 3.1% (7 cases) with no difference between the groups (p = 0.217). There was no difference in survival rate between patellar resurfacing (88.3%) and non-resurfacing (85.3%) after 24 months (p = 0.599). There were no differences in KSS functional component (p = 0.599), KSS knee component (p = 0.396), FJS (p = 0.798), and AKP (p = 0.688) at a mean follow-up of 18 months. There was twice as much stair pain for the non-resurfacing group (17.1% versus 8.5%) (p = 0.043). There was patellar tilt in 43% of resurfaced knees (n = 50/116) versus 29% in non-resurfaced knees (n = 30/105) (p = 0.025); however, there was more patellar translation in the non-resurfaced group (21.0% versus 7.8%) (p < 0.001). There were no specific complications attributed to the patellar resurfacing procedure. There were four secondary patellar resurfacing procedures (3.6%) in the non-resurfaced group after a mean of 10 ± 7 months (1-17) postoperatively.

CONCLUSION

There is no superiority of patellar resurfacing or non-resurfacing in terms of clinical or radiological outcomes at mid-term. Secondary patellar resurfacing is rare. There is not enough evidence to recommend systematic patellar resurfacing with a "patella-friendly" prosthesis.

The patellofemoral morphology and the normal predicted value of tibial tuberosity-trochlear groove distance in the Chinese population

Background

Our objective was to obtain normal patellofemoral measurements to analyse sex and individual differences. In addition, the absolute values and indices of tibial tuberosity-trochlear groove (TT-TG) distances are still controversial in clinical application. A better method to enable precise prediction is still needed.

Methods

Seventy-eight knees of 78 participants without knee pathologies were included in this cross-sectional study. A CT scan was conducted for all participants and three-dimensional knee models were constructed using Mimics and SolidWorks software. We measured and analysed 19 parameters including the TT-TG distance and dimensions and shapes of the patella, femur, tibia, and trochlea. LASSO regression was used to predict the normal TT-TG distances.

Results

The dimensional parameters, TT-TG distance, and femoral aspect ratio of the men were significantly larger than those of women (all p values < 0.05). However, after controlling for the bias from age, height, and weight, there were no significant differences in TT-TG distances and anterior-posterior dimensions between the sexes (all p values > 0.05). The Pearson correlation coefficients between the anterior femoral offset and other indexes were consistently below 0.3, indicating no relationship or a weak relationship. Similar results were observed for the sulcus angle and the Wiberg index. Using LASSO regression, we obtained four parameters to predict the TT-TG distance (R² = 0.5612, p < 0.01) to achieve the optimal accuracy and convenience.

Conclusions

Normative data of patellofemoral morphology were provided for the Chinese population. The anterior-posterior dimensions of the women were thicker than those of men for the same medial-lateral dimensions. More attention should be paid to not only sex differences but also individual differences, especially the anterior condyle and trochlea. In addition, this study provided a new method to predict TT-TG distances accurately.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04454-8.

Influence of Patella thickness on Patellofemoral pressure in total knee Arthroplasty

BACKGROUND

Patellofemoral complications are one of the major issues after total knee arthroplasty (TKA). Excessive patellofemoral joint pressure is associated with complications after TKA surgery, and the amount of patellar osteotomy has a direct effect on patellofemoral joint pressure. The purpose of this study was to evaluate the influence of patella thickness on patellofemoral pressure in TKA.

METHODS

Five freshly frozen cadavers were operated with a custom-made Stryker posterior stabilizing type knee joint prosthesis. Patellofemoral joint pressure was measured using a pressure sensor, with the knee joint flexed from 90 to 110 degrees, and with patellar thickness of - 2 mm to + 4 mm.

RESULTS

Increasing or decreasing patellar thickness significantly increased or decreased patellofemoral pressure. Regarding knee flexion angle, patellofemoral pressure increased with increasing patellar thickness at all flexion angles, but the pressure increase was greatest at 90 degrees of knee flexion and smallest at 110 degrees.

CONCLUSIONS

The amount of patellar osteotomy influences the patellofemoral pressure. Surgeons should avoid increasing patella thickness, since the resulting increased patellofemoral pressure may reduce knee joint function.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

LEVEL OF EVIDENCE

IV, Case series.

Systematic review of the etiology behind patellar clunk syndrome

BACKGROUND

Total knee arthroplasty is one of the most successful operations performed worldwide today. Patellar clunk syndrome (PCS) is a postoperative complication that arises due to the development of a fibrous nodule along the undersurface of the quadriceps tendon. The current literature on PCS has not yet come to a consensus regarding its etiology. To date, this is the first study that analyzes the existing literature on PCS in order to generate a conclusion regarding its etiology. It is hypothesized that prosthesis design is the main component behind the development of PCS.

AIM

To determine the etiology of PCS and its association with pre and post-operative characteristics of the prosthesis and native knee.

METHODS

We conducted a systematic review according to the PRISMA guidelines by searching through PubMed, Cochrane, and Google Scholar from May-July 2018 for cases of PCS using search MeSH terms “patella OR patellar” AND “clunk” OR “catch” OR “crepitus”. The search included case series and clinical trials and excluded review articles, yielding 30 articles from the original search and 3 additional articles from reference lists. We extracted data upon the outcomes in patients afflicted with PCS to determine the etiology of PCS. We performed additional bias assessments to validate our search algorithm and results.

RESULTS

Prosthesis design was the metric most frequently implicated in the incidence of PCS, though several other metrics were contributory toward its pathogenesis. Later prosthetic designs incorporate a reduced intercondylar box ratio and box width to reduce contact between the proximal patellar pole and the intercondylar box, thereby reducing incidence of PCS.

CONCLUSION

The etiology of PCS is multifactorial, owing to the growing metrics that have associations with its incidence. This conclusion is validated by the significance of prosthesis design as the most likely parameter involved in developing PCS since different prosthesis designs are often the result of different parameters. Future studies should be directed at isolating individual prosthetic parameters of prosthesis designs in order to determine what permutation of parameters is most closely associated with the development of PCS.

A greater reduction in the distal femoral anterior condyle improves flexion after total knee arthroplasty in patients with osteoarthritis

BACKGROUND

The effect of an anterior condylar height (ACH) change after total knee arthroplasty (TKA) is not well-known. The effect of an ACH change was evaluated on postoperative knee flexion, New Knee Society Scores (2011KSS), and patellofemoral contact force.

METHODS

The study included 101 knees that underwent TKA. The medial or lateral ACH was measured using pre-operative and postoperative computed tomography. Pearson correlation between the change in ACH and knee flexion was calculated. The determinant of the change in flexion was evaluated using multivariable linear regression. The association between ACH and 2011KSS was assessed. Using the cases with the three highest and three lowest pre-operative medial ACHs, computer simulation was performed to detect the changes in patellofemoral contact forces.

RESULTS

A postoperative reduction in ACH correlated with increased flexion at one year (medial ACH, R = 0.58; lateral ACH, R = 0.48). On multivariable linear regression, reductions in medial ACH (β = 1.7, P < 0.001) and pre-operative flexion (β = -0.3, P < 0.001) were associated with increased flexion. A decrease in ACH was associated with improvements in advanced activities (medial, R² = 0.06; lateral, R² = 0.08) in 2011KSS. On computer simulation, all three cases with reduced and increased medial ACHs showed decreased and increased patellofemoral contact forces, respectively.

CONCLUSIONS

A change in ACH was an independent predictor of knee flexion after TKA. Greater reduction in ACH was associated with improved flexion after TKA, whereas an increase in postoperative ACH may be a risk factor for flexion loss.

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.

Total knee arthroplasty in osteogenesis imperfecta

Osteogenesis imperfecta is a genetic disease resulting in abnormal collagen formation, with multiple clinical manifestations. Advancements in medical and surgical treatments have prolonged the life expectancy of these patients in recent decades. As a result, orthopedic surgeons are likely to be faced with the challenge of performing arthroplasty in these patients on a more frequent basis. Here, we describe a patient with osteogenesis imperfecta and subsequent severe osteoarthritis prompting primary total knee arthroplasty. This rare case presents an opportunity to explore special considerations unique to this patient population, including comorbid bone defects, the need for using extramedullary guides, careful alignment of prostheses to accommodate abnormalities in limb axes, and equipment utilization.

Patellar complications after total knee arthroplasty

Patellar complications are a source of poor total knee arthroplasty (TKA) outcomes that can require re-operation or prosthetic revision. Complications can occur with or without patellar resurfacing. The objective of this work is to answer six questions. (1) Have risk factors been identified, and can they help to prevent patellar complications? Patellar complications are associated with valgus, obesity, lateral retinacular release, and a thin patella. Selecting a prosthetic trochlea that will ensure proper patellar tracking is important. Resurfacing is an option if patellar thickness is greater than 12mm. (2) What is the best management of patellar fracture? The answer depends on two factors: (a) is the extensor apparatus disrupted? and (b) is the patellar implant loose? When either factor is present, revision surgery is needed (extensor apparatus reconstruction, prosthetic implant removal). When neither factor is present, non-operative treatment is the rule. (3) What is the best management of patellar instability? Rotational malalignment should be sought. In the event of femoral and/or tibial rotational malalignment, revision surgery should be considered. If not performed, options consist of medial patello-femoral ligament reconstruction and/or medialization tibial tuberosity osteotomy. (4) What is the best management of patellar clunk syndrome? When physiotherapy fails, arthroscopic resection can be considered. Recurrence can be treated by open resection, despite the higher risk of complications with this method. (5) What is the best management of anterior knee pain? The patient should be evaluated for causes amenable to treatment (fracture, instability, clunk, osteonecrosis, bony impingement on the prosthetic trochlea). If patellar resurfacing was performed, loosening should be considered. Otherwise, secondary resurfacing is appropriate only after convincingly ruling out other causes of pain. A painstaking evaluation is mandatory before repeat surgery for anterior knee pain: surgery is not in order in the 10% to 15% of cases that have no identifiable explanation. (6) What can be done to treat patellar defects? Available options include re-implantation (with bone grafting, cement, a biconvex implant, or a metallic frame), bone grafting without re-implantation, patellar reconstruction, patellectomy (best avoided due to the resulting loss of strength), osteotomy, and extensor apparatus allograft reconstruction. LEVEL OF EVIDENCE: V, expert opinion.

Safety and Efficacy of 6.2 mm Patellar Button in Resurfacing Less than 20 mm Thin Patella: A Matched Pair Analysis

Purpose

Restoring the native patellar thickness after patellar resurfacing provides optimal function of the knee after arthroplasty and minimises complications related to the patellofemoral articulation. The aim of this study was to assess the usefulness of a thin patellar button (6.2 mm) in patients with a patella thickness of less than 20 mm during total knee arthroplasty.

Materials and Methods

This is a retrospective case control study. A total of 54 female patients with an intraoperative patellar thickness of <20 mm, resurfaced with a patellar button of 6.2 mm in thickness were identified (group 1). They were matched with 54 patients with a patellar thickness of 20–23 mm, resurfaced with a patellar button of 8 mm (group 2), based on age, sex, body mass index, and deformity. A clinical and radiological evaluation was done at a minimum 2-year follow-up.

Results

The preoperative mean patellar thickness was 18.94±1.07 mm and was restored to 19.06±0.79 mm in group 1, as compared to 21.63±0.99 mm and 21.72±0.99 mm in group 2. The mean postoperative range of motion was 122.22°±9.25° in group 1 and 123.52°±8.72° in group 2 (p=0.13). No patellar bone or button related complications were observed in any patient in either group.

Conclusions

The 6.2 mm thin patella is useful to restore the native thickness in patients with a patellar thickness of less than 20 mm without risk of button fracture, loosening or overstuffing.