Fracture at the stem-condylar junction of a modular femoral prosthesis in a varus-valgus constrained total knee arthroplasty.

UNLABELLED: We present a rare case of fracture of the modular femoral component in a varus-valgus constrained total knee arthroplasty (TKA) prosthesis which occurred 2 years after implantation. Both femoral and tibial components underwent a second revision using a constrained hinged TKA. Laboratory analysis revealed insufficient metaphyseal bone stock in association with inadequate cement mantle incorporation which made implant fixation solely reliant on the intramedullary stem construct. It was therefore hypothesized that high repetitive stresses over the junction of the modular component led to the fracture. LEVEL OF EVIDENCE: Case report, Level IV.

Total knee arthroplasty in severe valgus knee deformity: comparison of a standard medial parapatellar approach combined with tibial tubercle osteotomy.

PURPOSE: Primary TKA in valgus knees with a deformity of more than ten degrees may prove challenging, since bone and soft tissue abnormalities make accurate axis restoration, component orientation and joint stability attainment a difficult task. The purpose of this study was to determine which approach is optimal in these patients, by comparing the standard medial parapatellar approach to a lateral parapatellar combined with a tibial tubercle osteotomy (TTO). METHODS: Forty-four valgus knees--with an axis deviation ranging from 15 to 36 degrees (mean 24°)--were dealt with primary TKA and followed up for a minimum period of 7 years. Lateral parapatellar arthrotomy combined with TTO was performed in 22 individuals (Group A) and a standard medial parapatellar capsulotomy in the remaining patients (Group B). The International Knee Society System Score (IKSS) was used for clinical evaluation. Radiological assessment was performed yearly postoperatively using long films for assessment of the anatomical axis. RESULTS: The postoperative IKSS scores showed no significant statistical difference between groups A and B (P < 0.05). In the alignment parameter, however, residual valgus deviation occurred in 9% of patients from Group A and in 32% from Group B. No late-onset instability was displayed. CONCLUSION: Lateral parapatellar approach combined with TTO may prove highly beneficial in significant valgus deformities, as the anatomical axis is restored accurately and soft tissue release of the lateral contracted structures facilitated to an important extent.

Fixed versus mobile bearing knee arthroplasty: a review of kinematics and results.

There are several total knee arthroplasty designs available with wide variation in features. The long-term results of total knee replacement with a fixed bearing design have shown a high degree of clinical success. However, implant loosening and polyethylene wear became recognized as long-term causes of late failure. Mobile bearing knee replacements were designed to create a durable surface articulation by using a polyethylene insert that articulates with a metallic femoral component and a metallic tibial tray. The purpose of this article is to review clinical and basic scientific studies comparing the clinical results, the biomechanical features, and the kinematic patterns of fixed versus mobile bearing knee designs. Beside the fact that in vitro kinematic studies have shown reduced polyethylene wear in mobile bearings due to increased implant conformity and reduced polyethylene contact stresses, which should hypothetically prolong polyethylene life, various independent studies for both mobile bearing and fixed bearing prostheses have documented results that are comparable in terms of survival and performance.

Kinematic and Kinetic Waveform Changes of the Knee Joint Following a Mobile Bearing Total Knee Arthroplasty-Gait Analysis and Single Step Ascent.

The objective of this study is to analyze the kinetic and kinematic changes of the osteoarthritic knee after a mobile bearing total knee arthroplasty. Kinematic and kinetic gait analysis of level walking was performed in 15 patients (eight female and seven male) with knee ostoarthritis. All patients were free of any neurological diseases that could affect their normal gait. Mean age was 68.6 ± 5.2 years, mean height 159.8 ± 6.9 cm, and mean weight was 78.5 ± 10.1 kg. Full body gait analysis was performed using the BioKin three-dimensional (3D) motion analysis system preoperatively and 9 months after total knee arthroplasty. A single-step ascending kinetic analysis and a plantar pressure distribution analysis were also performed in all patients. An increased average cadence (mean 99.39 step/min preoperatively and 104.64 step/min postoperatively; p = 0.152), step length (0.44 m preoperatively and 0.52 m postoperatively; p < 0.001), stride length (0.89 m preoperatively and 1.0 m postoperatively; p < 0.007), and walking velocity (0.73 m/sec preoperatively and 0.90 m/sec postoperatively; p = 0.005) were noted postoperatively and postoperatively. A decrease in the stance duration percentage and the knee adduction moment was also reported postoperatively. All patients showed a significant improvement of knee kinetics and kinematics after a mobile bearing total knee arthroplasty. Statistically significant differences were found in the step length, stride length, and walk velocity postoperatively. The knee adduction moment was also significantly reduced. Further research is warranted to determine the clinical relevance of these findings. This study is a prospective comparative one and reflects level II evidence.

Total knee arthroplasty in severe valgus deformity: interest of combining a lateral approach with a tibial tubercle osteotomy.

INTRODUCTION: Among the patients requiring total knee arthroplasty (TKA), approximately 10-15% presents with a valgus deformity (VD). Severely deformed valgus knees represent a surgical challenge. The purpose of this study is to evaluate the results of TKA in grade II and III valgus knee deformities (Ranawat classification), focusing on axis correction, by using a lateral parapatellar capsulotomy combined with tibial tubercle osteotomy. HYPOTHESIS: The lateral approach in combination with a tibial tuberosity osteotomy is highly beneficial in the treatment of severe valgus knees in patients undergoing primary TKA, for correction of anatomical axis. PATIENTS AND METHODS: Between January 1995 and December 2001, 33 patients with severe VD, grade II and III, were treated with TKA by one surgeon. Twenty-six patients (19 male, seven female) with mean age of 72 years (57-79) were dealt with a resurfacing posterior stabilized design; whereas in seven cases, a constrained type implant was used. These seven patients were excluded from the study. Two more patients were lost for follow-up and were also excluded. The axis deviation of the remaining 24 patients ranged from 15 to 35 degrees, (average 23°). A lateral parapatellar arthrotomy, in combination with tibial tubercle osteotomy was used. Patients' clinical evaluation - using the International Knee Society (IKS) score - with simultaneous radiological assessment was performed yearly after the operation; and for a mean follow-up time of 11.5 years (8 to 15 years). RESULTS: The mean IKS score improved from 44 points (34 to 52) preoperatively, to 91 points (68 to 100) postoperatively, at the last follow-up. In terms of alignment parameter, only two knees had a residual valgus deviation greater than 7° (ideal range : 3-7°). One knee exhibited a 9° valgus, and another one 10°, according to anatomical axis measurments. In one case, there was a 5mm proximal migration of the osteotomised tuberosity fragment, due to breakage of the screw. However, the final outcome was not affected. There were no cases of tibial tubercle's non-union; neither of delayed instability. CONCLUSION: The lateral approach is a useful approach in the treatment of severe valgus knee deformity in patients undergoing primary TKA. Anatomical axis restoration is facilitated, as the contracted structures are easily accessed and, in severe cases, the patellar alignment may be achieved by displacing the osteotomised tubercle. However, careful fixation of the tuberosity is mandatory. LEVEL OF EVIDENCE: Level IV, prospective study of case series.