Kinematics of the patellofemoral joint in total knee arthroplasty

Sagittal plane patellofemoral kinematics was determined for 81 subjects while performing a weight-bearing deep knee bend under fluoroscopic surveillance. Fourteen normal knees, 12 anterior cruciate ligament (ACL)-deficient knees, and 55 total knee arthroplasties (TKAs) were assessed. Of TKAs, 39 had resurfacing with a dome-shaped patella, 8 had resurfacing with an anatomic mobile-bearing patella, and 8 were unresurfaced. TKA patellae experienced more superior patellofemoral contact and higher patellar tilt angles compared with the normal knees and ACL-deficient knees (P <.05). Patellofemoral separation at 5 degrees (+/-3 degrees ) extension was seen in 86% cruciate-retaining and 44% cruciate-stabilized TKAs and 8% ACL-deficient knees but not in the normal knees or mobile-bearing TKAs (P <.05). The patellar kinematic patterns for subjects having a TKA were more variable than subjects having either a normal knee or an ACL-deficient knee. Kinematic abnormalities of the prosthetic patellofemoral joint may reduce the effective extensor moment after TKA.     

Explicit finite element simulation of eccentric loading in total knee replacement

In vivo kinematic data indicate that unicondylar or edge loading occurs during normal activities in well-aligned and malpositioned knee replacements. Using a validated explicit finite element model of a knee replacement, the effects of eccentric loading of a total knee replacement are simulated. Only minor variations were observed in the kinematics with a medial offset of the vertical load of as much as 15 mm (representing a medial:lateral loading ratio of 86:14), although the polyethylene stresses did increase by approximately 3 MPa throughout the stance phase of gait. There was a significant change in the kinematics and stresses when unicondylar loading occurred (95:5 medial:lateral loading ratio). Even for the unicondylar load case, contact always was maintained within the lateral compartment. This raises the question whether lift-off often observed in fluoroscopy studies really occurs. The model predicted regions of plastic deformation that closely resemble those observed in retrieved specimens of catastrophic wear. The explicit finite element model offers considerable insight into the kinematics and stresses generated by total knee replacement during different and varied loading conditions that occur during normal usage.     

Patello-femoral joint in total knee replacement

Total knee arthroplasty (TKA) surgery is a widely used treatment and has a high success rate. Despite its success, the patello-femoral articulation has been overlooked as a contributor to the successful outcome of TKA. Patello-femoral complications remain the leading cause of failed knee replacement, accounting for up to 10% of complications. To understand the concept of patellar mal-tracking, we explore the normal anatomy and biomechanics of the patello-femoral articulation, and review the surgical factors and complications related to patellar tracking, with an aim to discussing the concepts on how to avoid such complications. Surgeons should be aware of the frequent occurrence of abnormal patellar tracking, and should pay particular attention to the patello-femoral component of knee replacement surgery.     

Early results with a total patellofemoral joint replacement arthroplasty prosthesis

This report concerns a new prosthesis for total patellofemoral joint replacement. Patients severely disabled due to isolated patellofemoral arthritis in whom all other treatment options had been tried and failed, or were not indicated, became candidates for this surgery. Fifteen patients met these criteria and were followed an average of 3.75 years (range: 2.25-5.5 years). Using the Activities of Daily Living Scale, 14 of 15 patients (93%) had excellent (85%-100%) or good (75%-84%) results, and 1 was fair (65%-74%).     

Primary resection total knee arthroplasty for complicated fracture of the distal femur with an arthritic knee joint

Treatment of fractures of the distal end of the femur in an elderly patient is difficult. If the knee joint is arthritic, the problem is even greater. The reports of two patients with rheumatoid arthritis who sustained fractures of the distal end of the femur and underwent unconventional treatment with a resection total knee arthroplasty are presented.     

Navigation-assisted total knee arthroplasty for a knee with malunion of the distal femur

Conventional total knee arthroplasty (TKA) has been developed for several decades. However, very few previous reports describe TKA with less invasive modality for extra-articular angular deformity. Herein, we report a case of navigation-assisted TKA for severe osteoarthritis associated with malunited distal femoral fracture. Fourteen months after navigation TKA surgery, satisfactory alignment, diminished length discrepancy, and improved range of motion were noted. Our report reveals that navigation system without intramedullary reaming is a feasible and less invasive alternative for TKA surgery for complex arthritic knee disorders.     

Differences in patellofemoral contact stresses between mobile-bearing and fixed-bearing total knee arthroplasties: a dynamic in vitro measurement

Introduction  Anterior knee pain is one of the most common problems after total knee arthroplasty (TKA). Mobile-bearing designs should improve patella tracking with a reduced rate of patella tilt as well as reduced patellofemoral contact stresses and improve knee flexion. The aim of this dynamic in vitro investigation was to evaluate the changes of patellofemoral contact stresses after TKA using fixed and mobile-bearing designs. Materials and methods  Seven knee specimens were mounted into a knee simulator imitating an isokinetic extension of the knee. The patellofemoral contact was measured before and after tricompartimental TKA with fixed and mobile-bearing designs using pressure-sensitive films. Contact stresses were measured from 120° knee flexion to full extension with a simulated force of the quadriceps muscle up to 1,200 N. Additionally all measurements were performed with simulated co-contraction of the hamstrings muscles. Results  Fixed-bearing TKA increases patellofemoral contact stresses compared to physiologic conditions. After patella resurfacing, contact stresses increase even more. By changing the prosthesis design to mobile bearing, maximum contact stress was measured to be punctual higher than in fixed-bearing implants. In the interval between 0°–30° and 70°–105° of flexion, obviously lower pressures were evaluated for the mobile-bearing design. With cocontraction of the hamstrings, a lower contact stress of the mobile-bearing design was evident for the complete measurement of the knee extension. Conclusion  An increase of patellofemoral contact stresses after patellar resurfacing in TKA could be demonstrated. This outcome implicates a higher risk of patellofemoral complications. The mobile-bearing design showed evidently lower patellofemoral contact stresses than the fixed-bearing design.     

Osteolysis of the distal femur after total knee arthroplasty

An 11.1% incidence of femoral osteolysis (30 cases in 28 patients) was identified in a series of 271 primary total knee arthroplasties. Two minimally constrained total knee designs (Synatomic [Depuy, Warsaw, IN] and Porous-Coated Anatomic [PCA, Howmedica, Rutherford, NJ]) were used in this patient population. Femoral osteolysis was observed in 26 Synatomic and 4 PCA knees. The average follow-up period was 52 months (range, 24–96 months). Osteolytic lesions were identified radiographically, adjacent to the nonporous-coated (smooth) regions of the anterior and posterior flanges of the Synatomic and PCA femoral components. The average time to the diagnosis of femoral osteolysis was 31 months (range, 7–96 months). The average patient age at the time of primary total knee arthroplasty was 63 years (range, 43–83 years) and the average weight was 180 lb. (range, 107–278 lb.). Sixteen of the 30 cases were in men. All of the cases with femoral osteolysis had cementless implantation. Tissue specimens were obtained from the 18 cases requiring revision. Implants remained in situ an average of 66 months (range, 15–96 months) prior to revision. In 16 of the 18 cases revised, the femoral component was clinically and radiographically stable. Six of 18 cases were revised for severe osteolysis. The remaining 12 cases were revised for failed metal-backed patellae, failed cementless tibial fixation, or advanced polyethylene wear. Wear of the thin tibial inserts and patellar components were the two sources of particulate polyethylene. Polyethylene debris was observed in all tissue specimens. In cases with failed metal-backed patellae or impingement of the tibial locking pin-and-clip, fine metallic debris was also noted in tissue specimens. Microscopic evaluation of the osteolytic tissue revealed a florid histiocytic response with occasional giant cells. Intracellular submicron particulate polyethylene was identified with polarized light microscopy and oil-red-O staining techniques. In the study population, statistically significant factors associated with femoral osteolysis included male gender (P < .05), younger age (P < .05), increased patient weight (P < .05), positive tibial osteolysis (P < .001), osteoarthritis (P < .07), and length of time in situ (P < .001). In addition, patients with a Synatomic prosthesis were at increased risk for osteolysis compared to patients with a PCA device (P < .02). The authors postulate that histiocytic granuloma gained access to the proximal femur primarily via the unbonded interface between the smooth metal and bone.     

A comprehensive joint replacement program for total knee arthroplasty: a descriptive study

Background  

Total knee arthroplasty (TKA) is a commonly performed surgical procedure in the US. It is important to have a comprehensive inpatient TKA program which maximizes outcomes while minimizing adverse events. The purpose of this study was to describe a TKA program – the Joint Replacement Program (JRP) – and report post-surgical outcomes.     

Partial and total joint replacement in femur head necrosis

In literature, the results of hip arthroplasty in patients with avascular osteonecrosis of the femoral head vary. The main reason may be the nonhomogeneous patient groups concerning etiology of the femoral head necrosis (FHN). Analyzing the results of hip endoprosthesis in relation to the etiology of FHN leads to the assumption that steroid-induced FHN and FHN with underlying systemic bone diseases (renal osteodystrophy, sickle-cell hemoglobinopathy) have the highest loosening rates. Diseases with immunosuppressive medication and sickle-cell hemoglobinopathy have the highest risk of joint infection. Therefore etiology plays an important role in the long-term results of hip endoprostheses in FHN. Modern cement techniques of the second generation and new non-cemented total hip endoprostheses seem to have better results than older prostheses and cement techniques. We followed-up 52 non-cemented thrust plate prostheses in 45 patients with FHN, prospectively, for at least 2 years (3.7 +/- 1.6 years). The revision rate was 9.6% (two aseptic loosenings in one patient with renal osteodystrophy and one patient with alcohol abuse, as well as three late infections in one patient with alcohol abuse and two patients with renal osteodystrophy). Additionally, five prostheses showed radiologic lines of a minimum of 2 mm. Future studies with longer follow-up are needed to find out whether these prosthetic designs with proximal fixation of the femoral component preserving the diaphysial bone have advantages in young FHN patients.     

Results of total knee replacement for isolated patellofemoral arthritis: when not to perform a patellofemoral arthroplasty

Many procedures have been used to treat advanced isolated patellofemoral arthritis, with varying results. Patellofemoral arthroplasty (PFA) is a bone-conserving procedure that has shown short-term success but has relatively high revision rates. Total knee arthroplasty (TKA) has been recommended for treatment of this disease in patients who are older than 60 years of age. Recent literature indicates that PFA is most successful in patients who have isolated patellofemoral arthritis secondary to trochlear dysplasia or patellar fracture and in patients who are younger than 60 years; TKA is recommended for older patients who have primary or idiopathic isolated patellofemoral arthritis.     

Errors in the identification of the transepicondylar and anteroposterior axes of the distal femur in total knee replacement using minimally-invasive and conventional approaches: a cadaver study

We have investigated the errors in the identification of the transepicondylar axis and the anteroposterior axis between a minimally-invasive and a conventional approach in four fresh-frozen cadaver knees. The errors in aligning the femoral prosthesis were compared with the reference transepicondylar axis as established by CT. The error in the identification of the transepicondylar axis was significantly higher in the minimal approach (4.5 degrees of internal rotation, sd 4) than in the conventional approach (3 degrees of internal rotation, sd 4; p < 0.001). The errors in identifying the anteroposterior axis in the two approaches were 0 degrees (sd 5) and 1.8 degrees (sd 5) of internal rotation, respectively (p < 0.001).     

Stanmore total knee replacement versus internal fixation for supracondylar fractures of the distal femur in elderly patients

BACKGROUND: Supracondylar fractures of the femur in the elderly are difficult to treat. Total knee replacement is often not considered. The aim of this study was to compare the short to medium term outcome of fixation and total knee replacement in medically fit active elderly patients with no pre-existing arthritis in order to determine whether total knee replacement can be an alternative to internal fixation. PATIENTS AND METHODS: In this retrospective study, we included patients who were aged 75 or over with an ASA grade of two or less, walked independently before their injury, and sustained a type A or C supracondylar fracture. Four were treated with internal fixation and six with a cemented Stanmore knee replacement. Patients were reviewed clinically and radiographically a minimum of 6 months after surgery. RESULTS: The advantages of total knee replacement were a greater proportion of patients returned to independent walking, rehabilitation was more rapid, and knee flexion was better. The advantages of internal fixation were a decreased need of blood transfusion, a smaller proportion of patients reported knee pain at follow up, and a better mean Oxford knee score at follow up. Anaesthetic time and level of patient satisfaction at follow up were similar. There were no peri-operative deaths. CONCLUSION: In this preliminary study, total knee replacement was a reasonable alternative to internal fixation for the treatment of supracondylar fractures of the distal femur in elderly.     

Effects of a distal venting hole in the femur during total hip replacement

In 18 patients who underwent total hip replacement, the intramedullary pressure in the femur was measured during the insertion of the femoral prosthesis component. Half the patients had a pressure release hole (diameter 4.5 mm) drilled into the medullary canal at the distal end of the femur, the other half not. In the patients without a venting hole, the intramedullary pressure increased transiently to a median of 390mmHg during the insertion of the femoral stem, while those with a venting hole only showed an increase to 23mmHg. A drop in arterial oxygen tension of 2.2kPa and in thrombocytes of 51 x 10(9)/1 was found in those without a venting hole, while the corresponding values in those with a venting hole were 0.9kPa and 20 x 10(9)/1. Furthermore, a significant correlation was demonstrated between the increase in intramedullary pressure and the drop in oxygen tension and in blood platelets. No significant change in blood pressure was measured during operation in either group.