Patellofemoral kinematics during deep knee flexion after total knee replacement: a computational simulation

Purpose

Actions requiring deep knee flexion, such as kneeling and squatting, are challenging to perform after total knee replacement (TKR), though many manufactures emphasize that their knee prostheses could safely achieve high flexion. Little is known about the patellofemoral kinematics during deep flexion. This study aimed to track the movement of the patella during kneeling and squatting through dynamic computational simulation.

Methods

A validated knee model was used to analyse the patellar kinematics after TKR, including shifting, tilting and rotation. The data were captured from full extension to 135° of knee flexion. For kneeling, an anterior force of 500 N was applied perpendicularly on the tibial tubercle as the knee flexed from 90° to 135°. For squatting, a ground reaction force was applied through the tibia from full extension to 135° of flexion.

Results

This study found that patellar shifting and rotation in kneeling were similar to those while squatting. However, during kneeling, the patella had a greater medial tilt and showed signs of abrupt patellar tilt owning to an external force being concentrated on the tibial tubercle.

Conclusions

In terms of squatting and kneeling movements, the latter is a more strenuous action for the patellofemoral joint after TKR due to the high forces acting on the tibial tubercle. It is suggested that overweight patients or those requiring high flexion should try to avoid kneeling to reduce the risk of the polyethylene wear. Further modification of trochlear geometry may be required to accommodate abrupt changes in patellar tilting.

Level of evidence

II.     

Patellofemoral kinematics in mobile-bearing and fixed-bearing posterior stabilised total knee replacements: a cadaveric study

Purpose  

The aim was to compare the patellar kinematics in the normal knee, fixed-bearing (FB) and mobile-bearing total knee replacement (MB-TKR). The hypothesis that a mobile-bearing TKR has a more natural patellar movement was tested.     

Femoral component rotation after balanced gap total knee replacement is not a predictor for postoperative patella position

Purpose  

Femoral component rotation is believed to be one of the factors influencing patellar tracking behavior. With the balanced gap implantation technique, the rotation of the femoral component can vary as it is guided by the ligaments. This study investigated whether femoral component rotation influenced patella position after primary total knee replacement (TKR).     

Determinants of anterior knee pain following total knee replacement: a systematic review

Purpose

Anterior knee pain (AKP) following total knee replacement (TKR) is both prevalent and clinically relevant. The purpose of this study was to systematically review the peer-reviewed literature, and to identify and assess the different modifiable and non-modifiable determinants that may be associated with the development of AKP in patients following primary TKR.

Methods

A systematic computerized database search (Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, and Google Scholar) was performed in January 2012. The quality of the studies was assessed using the GRADE approach.

Results

A total of 54 articles met the inclusion criteria. Variables that have been researched with regard to the prevalence of AKP include patient and knee-specific characteristics, prosthetic design, operative technique, treatment of the patella, and time of assessment. A weak correlation with AKP was found for specific retained presurgery gait patterns. A weak recommendation can be given for the use of femoral components with a posterior centre of rotation, resection of Hoffa’s fat pad, patellar rim electrocautery, and preventing combined component internal rotation. The correlation between postsurgical AKP and the degree of patellar cartilage wear, tibial component bearing strategies, and patellar resurfacing is inconclusive. Due to substantial heterogeneity of the included studies, no meta-analysis was performed.

Conclusions

No single variable is likely to explain the differences in the reported rates of AKP, although variables leading to abnormal patellofemoral joint loading appear to be of special significance.

Level of evidence

III.     

A multivariate statistical ranking of clinical and gait measures before and after total knee replacement

The purpose of this study was to assess the use of a multivariate statistical method to rank clinical and gait variables, thus describing a ranking of patient dysfunction prior to and following total knee replacement (TKR) surgery. Twenty end-stage knee osteoarthritis (KOA) subjects scheduled for TKR and 20 healthy controls performed level walking and stair ascent twice: pre- (P1) and 6 months post-surgery (P2). Clinical and gait measures were entered into a principle component analysis (PCA) to determine orthogonal principle components (PCs). The PCs were entered into a discriminant function analysis to determine the best predictors of group membership. The PCA extracted three PCs for both the P1 and P2 data sets. Three orthogonal dimensions were formed: “knee dysfunction”, “gait dysfunction”, and “stair ascent dysfunction”. For P1 the “knee dysfunction” dimension composed of both subjective and objective measures, best discriminated between end-stage knee osteoarthritis patients and controls. For P2, the “stair ascent dysfunction” dimension best discriminated between 6 months post-TKR patients and controls. The results of this study suggest that a multivariate statistical method provides a clinically relevant ranking of patient dysfunction prior to and following TKR. This ranking of dysfunction could serve to identify rehabilitation priorities.     

Multilobulated popliteal cyst after a failed total knee arthroplasty

Popliteal cyst is a rare finding after total knee arthroplasty (TKA), but when present, it might indicate a malfunction of the TKA related to generation of wear-particles, or loosening. We present a case of a multilobulated popliteal cyst developing in a patient 8 years after primary TKA. The cyst was associated with a mechanical prosthetic loosening. The primary complaint of the patient was pain in the posterior region of the knee. A two-stage procedure consisting of cyst excision at first, followed after 5 months by a revision TKA was performed. Intraoperatively, a darkish, multilobulated cyst with a well-defined thick wall filled with fluid containing polyethylene debris, communicating with the knee joint was found. After 3 years of follow-up, the patient was satisfied and walked without the support of a cane. The patient presented a satisfactory knee range of motion. Clinical, radiological and ultrasound investigations ruled out popliteal cyst recurrence. A dissecting popliteal cyst associated with a failed TKA should be excised because it contains polyethylene debris that constitutes an induced factor for prosthetic loosening. A two-stage procedure with quite a long time in-between, as presented in this paper, can be a useful alternative to manage such a problem, in particular in very old patients associated with other medical problems.     

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.     

Imaging patellar complications after knee arthroplasty

The purpose of this study is to describe complications affecting the patella in patients with total or partial knee arthroplasty. We respectively analysed plain-film radiographs, as well as ultrasound images when acquired, in a consecutive series of 1272 patients. The mean interval from knee replacement to patellar complications was 5 years and 7 months (range, 5 months to 14 years). The complications described include fracture, instability, dislocation or luxation, necrosis of the patella, infection of the patella, erosion of the patella, patellar impingement on the prosthesis and patellar or quadricipital tendon tear. We discuss the pathological imaging findings in the patella and their differential diagnosis after knee arthroplasty. Patellar complications after knee arthroplasty are uncommon but often potentially serious.     

预存式自体输血在全膝关节置换术中运用的临床研究

目的探讨预存式自体输血在全膝关节置换术中的临床应用。方法自2006年9月～2008年6月,对35例单侧全膝关节置换手术患者进行预存自体输血。采血前、采血后第4天以及术后第3天检测血红蛋白（HGB）、红细胞（RBC）、红细胞压积（HCT）。结果预存自体血量（411．43±136．71）ml,所有患者均依靠回输预存自体血顺利度过围手术期,无1例需异体输血,未发生与预存自体输血相关的并发症。结论预存式自体输血简便、经济、安全、有效,全膝关节置换手术患者可依靠预存白体输血安全度过围手术期。     

Incarcerated patellar tendon in Hoffa fracture: an unusual cause of irreducible knee dislocation

Irreducible knee dislocation due to incarcerated soft tissue structures in associated fractures is extremely uncommon. We report a case of irreducible, closed dislocation of the knee secondary to incarcerated patellar tendon in a Hoffa fracture (unicondylar fracture of femur in the coronal plane) with associated communited fracture of patella and disruption of both cruciates. We treated this case initially with open reduction and internal fixation of fracture and repair of the patellar tendon. During the total followup period of eighteen months, the patient had restricted joint range of motion with no joint instability despite aggressive physiotherapy and further surgical intervention. The prognosis of such complex knee injuries with combination of ligamentous injuries and associated fractures is much worse when compared to either injuries alone.     

Changes in patellar alignment after total knee arthroplasty

Although the results of total knee arthroplasty continue to improve, problems related to the patellofemoral joint remain significant. This study examined the factors affecting patellar alignment after total knee arthroplasty and subsequent changes in 56 knees during a postoperative period of 5.3 years. None of the knees examined displayed any clinical complications of the patellofemoral joint; no revision surgeries were necessary, with acceptable patellar alignment on average. The patellar resection angle had a strong influence on patellar alignment. Thinning of the patellar remnant on the medial side can increase postoperative lateral tilt, which leads to a need for lateral retinacular release. Although the changes in patellar alignment were minimal, the tendency that postoperative varus alignment resulted in patellar lateral tilt was observed. As postoperative femorotibial misalignment can lead to patellofemoral problems after total knee arthroplasty, surgeons need to pay scrupulous attention to femorotibial alignment and proper patellar preparation to decrease patellofemoral complications.     

High-demand motor tasks are more sensitive to detect persisting alterations in muscle activation following total knee replacement

Knee osteoarthritis is one of the most frequent indications for total knee replacement (TKR). Unfortunately, many patients still have difficulties during daily life activities after TKR. As the underlying causes of these difficulties are still not fully understood, especially with regard to the role of aberrant muscle activation profiles, the purpose of this study was to examine to what extent muscle activation patterns return to normal after TKR. Furthermore, we aimed to further discuss remaining differences by linking them to pre- and post-operative measurements of the knee and hip kinetics and kinematics during multiple functional motor tasks.Therefore, muscle activity, kinetics and kinematics of knee and hip were measured and analyzed in seven patients during a number of functional tasks by using electromyography and three-dimensional motion analysis. Measurements were performed one week before and one year after surgery. Results were compared to seven matched healthy controls. The analyzed functional tasks included walking at self-selected speed, walking followed by a crossover and a sidestep turn, step descent and ascent.This study suggested that, while muscle activation profiles in patients one year after TKR did return to normal during walking, this was not the case during more demanding motor tasks. These findings may have direct implications for the design of future rehabilitation programs in order to result in faster recovery and ultimately more functional patients after TKR.     

Radiophosphate uptake in asymptomatic knee arthroplasty

The utility of radiophosphate bone scanning in the detection of complications following total knee replacement (TKR) is not yet fully established. A difficulty associated with the use of bone scanning is the persistent increased uptake seen around the prosthetic joint long after surgery, despite the absence of symptoms. In order to better characterize the time course of radiophosphate uptake, bone scans obtained 1 mo-12 yr after surgery were analyzed in 30 asymptomatic patients with 37 TKR. Uptake was graded 0-4+ in the femoral and tibial components. Scans of 18 implants were obtained 1 yr or less after surgery (Group 1), and 19 were obtained greater than 1 yr after surgery (Group 2). Mean uptake scores were as follows: femoral component Group 1 = 3.0 +/- 1.1; Group 2 = 1.8 +/- 0.9 (p less than 0.05); tibial component Group 1 = 3.2 +/- 0.8; Group 2 = 2.6 +/- 1.1 (not significant). Persistent increased uptake, particularly in the tibial component, reflects mechanical stresses peculiar to knee prostheses, and tends to undermine confidence in diagnosing loosening on the basis of a single study.     

Surgical complications of the patellofemoral articulation

The complications associated with surgery on the extensor mechanism of the knee were reviewed. These complications may be avoided by being mindful of the importance of patient selection, establishing specific diagnoses, and then carrying out proper surgical procedures. Also reviewed were the complications associated with the extensor mechanism in total knee arthroplasty. Patellofemoral complications are the most common complications of total knee arthroplasty. The importance of precise surgical technique in aligning the extensor mechanism was emphasized. Caution is probably advisable in the use of metal-backed patellar components for the time being. Lastly, the relatively rare, but important, complications of reflex sympathetic dystrophy, infrapatellar contracture syndrome, and patella infra were reviewed.     

Increased patellofemoral pressure after TKA: an in vitro study

Purpose

Considering the discrepant results of the recent biomechanical studies, the purpose of this study was to simulate dynamic muscle-loaded knee flexion with a large number of specimens and to analyse the influence of total knee arthroplasty (TKA) without and with patellar resurfacing on the patellofemoral pressure distribution.

Methods

In 22 cadaver knee specimens, dynamic muscle-loaded knee flexion (15°–90°) was simulated with a specially developed knee simulator applying variable muscle forces on the quadriceps muscles to maintain a constant ankle force. Patellofemoral pressures were measured with flexible, pressure-sensitive sensor foils (TEKSCAN) and patellofemoral offset with an ultrasound motion-tracking system (ZEBRIS). Measurements were taken on the native knee, after total knee arthroplasty and after patellar resurfacing. Correct positioning of the patellar implant was examined radiologically.

Results

The maximal patellofemoral peak pressure partly increased from the native knee to the knee with TKA with intact patella (35°–90°, p < 0.012) and highly increased (twofold to threefold) after patellar resurfacing (20°–90°, p < 0.001). Concurrently, the patellofemoral contact area decreased and changed from a wide area distribution in the native knee, to a punctate area after TKA with intact patella and a line-shaped area after patellar resurfacing. Patellar resurfacing led to no increase in patellar thickness and patellofemoral offset.

Conclusions

Despite correct implantation of the patellar implants and largely unchanged patellofemoral offset, a highly significant increase in pressure after patellar resurfacing was measured. Therefore, from a biomechanical point of view, the preservation of the native patella seems reasonable if there is no higher grade patellar cartilage damage.     

Assessment of posterior stability in total knee replacement by stress radiographs

The aim of this study was to assess the posterior stability of two different designs of total knee replacement (TKR) with deep-dished mobile bearing (MB) implants using stress X-rays. In a prospective non-randomized consecutive study, 34 patients with primary osteoarthritis of the knee underwent TKR. In group A (17 knees), they received a MB insert with a Duracon prosthesis and in group B (18 knees), a Genesis prosthesis. In all cases the posterior cruciate ligament (PCL) was resected. All patients had pre- and post-operative kneeling X-rays and were clinically evaluated with the Knee Society Score. Measurements on the radiographs were taken by tracing a line along the posterior cortex of the tibia and then measuring the perpendicular distance to a point marked at the posterior corner of Blumensaat's line. The average follow up was 10.7 months for group A and 5.4 months for group B. No statistical difference could be found in terms of clinical results and pre- and post-operative kneeling X-rays between the two groups. In each group, all knees demonstrated a significant posterior tibial translation postoperatively compare to their pre-operative status (p<0.0001). There are advantages in resecting the PCL in TKR: mobile flexion gap, correction of fixed deformity, more flexibility to adjust the joint line. The use of a deep dished polyethylene (PE) insert provides stability and use of MB insert reduces PE wear whilst retaining congruity. Two designs of deep-dished MB inserts showed significant posterior tibial translation on stress X-rays. It remains to be determined what amount of laxity is optimal for clinical function and polyethylene longevity.     

Popliteal artery–tibial plateau relationship before and after total knee replacement: a prospective ultrasound study

It seems to be a general belief that knee flexion releases the tension on the popliteal artery (PA) and displaces it posteriorly. Furthermore, there are opinions suggesting that previous surgery may result in fibrosis and rigidity of the vessels in the posterior knee region, which can lead to tethering of the PA, bringing it closer to the posterior tibia and making it more vulnerable during revision knee surgery. The aim of this study was to assess the distance between the PA and the tibial plateau in extension and flexion of the knee before and after surgery with total knee replacement (TKR). We studied 40 consecutive patients who were about to undergo TKR. The distance between the PA and tibial plateau was measured by ultrasound bilaterally in full knee extension without quadriceps contraction and in 90° knee flexion, both preoperatively and 15 weeks postoperatively. The mean preoperative distances in flexion and in extension were 7 mm (3–12) and 8 mm (4–13), respectively (p < 0.05). Postoperatively, the distances were significantly increased both in flexion, 9 mm (4–14) (p < 0.001) and in extension 9 mm (3–15) (p < 0.01). Assessment of the contralateral legs where 14 previously had been operated with TKR showed no significant difference either between flexion and extension or between pre- and postoperative measurements. In conclusions, knee flexion does not increase the distance between the artery and the proximal tibia in this osteoarthritis patient group. At 15 weeks post-TKR, there was an increased distance from the PA to the posterior tibia and assessment of the contralateral knee where previous TKR had been performed showed equal distance to the ipsi-lateral preoperative knee, suggesting that the postoperative changes at 15 weeks were due to capsular swelling.     

Patellar resection during total knee arthroplasty: effect on bone strain and fracture risk

Patellae in small knees, or after severe patellar erosion, may be vulnerable to fracture after resection during arthroplasty. The patellar remnant may be thin, while the polyethylene component has a standard thickness. Anterior patellar bone strain was measured in cadaver knees loaded via the quadriceps, from 0 to 90° flexion, with the patella intact, and after resections to 16, 13 and 11 mm thick and replacement by an 8-mm-thick polyethylene component. Strain increased significantly with knee flexion with constant 500 N quadriceps tension. Resection caused significant changes from intact values in knee flexion and extension and no significant effect at 30° flexion. In flexion, bending caused the anterior surface to become more convex, with high tensile bone strains. In extension, resection caused negative anterior strains, representing bending in the opposite direction, with large tensile strains on the cut posterior surface. For normal activities, such as rising from a chair (1.8 kN quadriceps tension) the patella appears safe against fracture with a minimal resection to 16 mm thick. An eroded patella resected to 11 mm thickness may be at risk of fracture with that loading.     

A new measurement technique for the tibiofemoral contact point in normal knees and knees with TKR

Flexion gap instability after cruciate retaining TKR allows paradoxical anterior movement of the femur during flexion. The tibiofemoral contact point (CP) moves anteriorly and produces a decrease in the lever arm of the extensor apparatus. This can provoke patellofemoral, tibiofemoral-joint pain and instability for the patient. In order to quantify the amount of paradoxical motion on a 90° flexion radiograph of the knee, the average normal CP of the natural knee should be known. There are no known CP measurement methods suited for natural knees and knees with TKR that can be applied in daily practice, and only estimations for the CP position have been made. Therefore, a CP measurement technique on lateral radiographs that can be applied to natural knees and knees with a TKR has been developed. The reproducibility of this method was assessed. It was then used to determine the normal range of the CP in natural knees. The medial contact point in the natural knee in 90° of flexion was determined to be at 68% (±6.6%) of the AP diameter of the tibia measured below the tibia-plateau simulating a bone resection with TKR. This reproducible CP measurement method can be used clinically to evaluate the CP after knee prosthesis and also in patients with suspected ligament lesions.     

Patellar fractures after total knee replacement

OBJECTIVE: The objective of our study was to describe the patterns of patellar fracture after total knee replacement and assess their clinical significance. MATERIALS AND METHODS: A retrospective review of patellar fractures after total knee replacement was performed. Seventeen cases were identified over a 10-year period. Radiographs, radiology reports, medical records, and operative notes were reviewed and analyzed. The clinical analysis included the time to fracture, the patient's symptoms and signs, whether the extensor mechanism was disrupted, and the treatment administered for the fracture. The radiographic analysis included fracture pattern, displacement, patellar position, presence of patellar osteonecrosis, and presence of soft-tissue abnormality. RESULTS: The incidence of patellar fractures after total knee replacement was 1.14%. The mean time from total knee replacement to patellar fracture was 17.5 months. Nine fractures were asymptomatic and identified on routine follow-up radiographs. The patterns of fracture were diverse: Transverse (n = 6), comminuted (n = 2), vertical (n = 5), and avulsion (n =4) fractures were seen. Thirteen fractures were displaced. Patellar osteonecrosis was suspected in four fractures, and three fractures were associated with disruption of the quadriceps tendons. Thirteen fractures were treated nonoperatively, and four were treated surgically. CONCLUSION: Patellar fractures are an uncommon, but important, complication after total knee replacement. Radiologists should be familiar with the imaging features of these fractures and their clinical significance.