Medial-Pivot Design Improved Knee Symptoms From Anteroposterior Instability in Early-Range Flexion and Resolved Anterior Knee Pain in Revision Total Knee Arthroplasty.

BACKGROUND: Instability can lead to poor functional results after tricompartmental total knee arthroplasty (TKA). We identified a group of patients who appeared to have anteroposterior (AP) instability in early-range flexion (ie, 20 to 30° range) associated with anterior knee pain and feelings of instability. The purpose of this study was to assess the clinical results in terms of stability and anterior knee pain after revision TKA with a medial-pivot implant and to assess the effect of the implant positioning used in the revision technique. METHODS: There were 45 patients (45 knees) evaluated retrospectively to assess standing lower extremity alignment and functional results by generating a knee stability score after revision TKA with medial pivot implant design. RESULTS: Revision TKA using the medial-pivot TKA lowered the joint line by 3.6 millimeters (mm) (P < .001) and positioned the tibia anteriorly by 3.5 mm (P < .001) on radiographic measurements as compared with results after primary TKA. Moreover, medial pivot revision TKA improved AP stability by a 56-point change in score (P < .001). CONCLUSION: Revision TKA using a medial pivot design improved AP stability and anterior knee pain after failed primary procedures.

The Quadriceps Vector is Most Parallel to the Spherical Axis With Minimal Difference for Gender or Ethnicity.

BACKGROUND: The extensor mechanism may be the key to kinematic alignment of total knee arthroplasty. The purpose of this study was to determine any differences in the direction of the quadriceps vector based on gender or ethnicity and to determine which anatomically derived alignment axis is closest to the quadriceps vector. METHODS: Computed tomography scans and patient records for 14 Caucasians (9 men and 5 women) and 40 Japanese (19 men and 21 women) were evaluated. Three axes of alignment-anatomic, mechanical, and spherical-were identified, measured, and compared to the quadriceps vector in each case. Principal component analysis was used to determine the quadriceps vector by using 3-dimensional models of muscles on computed tomography scans. RESULTS: No statistically significant differences in the orientation of the quadriceps vector were found based on gender or ethnicity, and the quadriceps vector was most closely aligned with the spherical axis. CONCLUSION: Because the quadriceps is the primary knee extensor, the spherical axis therefore may be a ubiquitous guide to alignment of the arthroplasty knee based on motion.

High Risk of Failure With Bimodular Femoral Components in THA.

BACKGROUND: The bimodular femoral neck implant (modularity in the neck section and prosthetic head) offers several implant advantages to the surgeon performing THAs, however, there have been reports of failure of bimodular femoral implants involving neck fractures or adverse tissue reaction to metal debris. We aimed to assess the results of the bimodular implants used in the THAs we performed. QUESTIONS/PURPOSES: We asked: (1) What is the survivorship of the PROFEMUR(®) bimodular femoral neck stems? (2) What are the modes of failure of this bimodular femoral neck implant? (3) What are the major risk factors for the major modes of failure of this device? METHODS: Between 2003 and 2009, we used one family of bimodular femoral neck stems for all primary THAs (PROFEMUR(®) Z and PROFEMUR(®) E). During this period, 277 THAs (in 242 patients) were performed with these implants. One hundred seventy were done with the bimodular PROFEMUR(®) E (all are accounted for here), and when that implant was suspected of having a high risk of failure, the bimodular PROFEMUR(®) Z was used instead. One hundred seven THAs were performed using this implant (all are accounted for in this study). All bearing combinations, including metal-on-metal, metal-on-polyethylene, and ceramic-on-ceramic, are included here. Data for the cohort included patient demographics, BMI, implant dimensions, type of articular surface, length of followup, and C-reactive protein serum level. We assessed survivorship of the two stems using Kaplan-Meier curves and determined the frequency of the different modes of stem failure. For each of the major modes of failure, we performed binary logistic regression to identify associated risk factors. RESULTS: Survivorship of the stems, using aseptic revision as the endpoint, was 85% for the patients with the PROFEMUR(®) E stems with a mean followup of 50 months (range, 1-125 months) and 85% for the PROFEMUR(®) Z with a mean followup of 50 months (range, 1-125 months)(95% CI, 74-87 months). The most common modes of failure were loosening (9% for the PROFEMUR(®) E), neck fracture (6% for the PROFEMUR(®) Z and 0.6% for the PROFEMUR(®) E), metallosis (1%), and periprosthetic fracture (1%). Only the bimodular PROFEMUR(®) E was associated with femoral stem loosening (odds ratio [OR] =1.1; 95% CI, 1.04-1.140; p = 0.032). Larger head (OR = 3.2; 95% CI, 0.7-14; p = 0.096), BMI (OR = 1.19; 95% CI, 1-1.4; p = 0.038) and total offset (OR = 1.83; 95% CI, 1.13-2.9; p = 0.039) were associated with neck fracture. CONCLUSION: Bimodular neck junctions may be potentiated by long neck lengths, greater offset, and larger head diameters. These factors may contribute to bimodular neck failure by creating a larger moment about the neck's insertion in the stem. The PROFEMUR(®) E implant is associated with high periprosthetic loosening. Based on our experience we cannot recommend the use of bimodular femoral neck implants. LEVEL OF EVIDENCE: Level III, therapeutic study.

Midterm clinical and radiographic results of the medial pivot total knee system.

PURPOSE: The ADVANCE® Medial Pivot Knee System was designed with a highly congruent medial compartment and a less conforming lateral compartment to more closely mimic the kinematics of the normal knee. The purpose of this study was to evaluate the midterm clinical and radiographic outcomes of this total knee arthroplasty (TKA) system. METHODS: Between January 1998 and December 2006, 421 primary TKAs were performed in 373 subjects using this system and a surgical technique that resects the posterior cruciate ligament. Of these, 365 TKAs in 320 subjects were available for a follow-up visit occurring at a mean of 5.3 years. Subjects were evaluated using Knee Society Scores, range of motion, and radiographic review. RESULTS: The average Knee Society clinical score was 95.5 at final follow-up, with 358 (98%) TKAs having excellent or good results. Range of motion increased from a preoperative mean of 115 to 119° at final follow-up. Component survivorship, excluding revisions for infection or trauma, was 96.6% at five years. CONCLUSIONS: This study demonstrates subjects implanted with the ADVANCE® Medial Pivot Knee System achieved satisfactory clinical and radiographic midterm outcomes.

Assessment of a medial pivot total knee arthroplasty design in a cadaveric knee extension test model.

A total knee has been designed to mimic less-compliant medial and more-compliant lateral behavior. In vivo testing compared open-kinematic chain behaviors of cadaver knees in their normal state and after implantation of the knee prosthesis. Specimen's limbs were computed tomography scanned, and infrared arrays on tibia and femur were registered to bone markers. Motion of the joint and quadriceps force were reported from 90° flexion to full extension. Less medial and more lateral anterior-posterior motion was seen in both the intact and the implanted knees. Tibiofemoral rotation and translation were similar in direction but were reduced in magnitude for the prosthetic knees. Quadriceps force, defined as that applied force required to extend the knee, required after implantation was variable between specimens but not statistically different from the intact condition. The prosthesis tested exhibits kinematic behavior similar to that in their normal state, with no difference in quadriceps force required for extension.

Kneeling is safe for patients implanted with medial-pivot total knee arthroplasty designs.

Nine ADVANCE (Wright Medical Technology, Arlington, TN)) Medial-Pivot (MP) and 9 ADVANCE Double-High total knee arthroplasties were analyzed under radiographic surveillance at standing, mid kneeling, and full kneeling. In vivo tibiofemoral contact positions were obtained using the 3- to 2-dimensional image registration technique. The contact in Double-High knee was always more posterior than that in the MP knee presumably because of the presence of the posterior cruciate ligament. The contact positions in both the designs moved anterior from standing to mid kneeling, moved posterior from mid kneeling to full kneeling, and remained within the intended articulation range of the implants. This study indicates that kneeling is safe in MP total knee arthroplasty even in the absence of a cam-post or posterior cruciate ligament.

Total hip arthroplasty modular neck failure.

The use of modular components in total hip arthroplasty has increased in popularity. The advantages of modularity in hip arthroplasty include improved visualization during acetabular revision and restoration of proper hip biomechanics. Disadvantages include disassociation of components, failure at modular junctions, corrosion, and the generation of metal ions and debris. We present 2 cases that demonstrate the potential for modular neck fracture, requiring subsequent revision of well-fixed components.

The rationale for a total knee implant that confers anteroposterior stability throughout range of motion.

The topic at hand in this series of presentations concerns the design of total knee prostheses. This presentation concerns the rationale for an implant to confer anteroposterior stability without the need for a central "cam and post" mechanism, as is common in posterior cruciate-substituting total knee arthroplasty prostheses.

Kinematics of the human knee using an open chain cadaver model.

There continues to be controversy about the kinematics of the human knee. This study used seven knees from cadavers moved by pulling on the quadriceps tendon in an open chain fashion using video motion analysis to determine the instantaneous helical axis of movement. Computed tomography scans of the specimens allowed the axes to be related to condyles. The parameter beta was defined by the relationship of the helical axis to the center of the condyle (pure spinning motion) and the contact point of the condyle on the tibia (pure rolling motion). Axes above the center of the condyle represent countertranslation, those between the center and the contact point combined spinning and rolling, and those below represent concordant translation. If the motion of the knee is guided by the crossed four-bar link then this model, that allows the knee to 'seek its own path' throughout the range of motion, should show the rollback that commonly is thought to be an important feature of knee motion. The results of this study show that the medial side of the knee stays stable in spinning kinematics whereas the lateral side has a rolling motion in full flexion progressing to a spinning motion in midflexion and counter-translation near full extension. The kinematics that would be expected from rollback were not observed.

Fluoroscopic analyses of cruciate-retaining and medial pivot knee implants.

Contemporary posterior cruciate-retaining total knee designs have provided pain relief and improved knee function but have failed to reproduce the kinematics and stability of the normal nonarthritic knee. The Medial Pivot total knee design features a near constant radius of curvature of the femoral component. The tibial surface is highly congruent and asymmetric, permitting a medial pivot motion during knee flexion. The purpose of the current study was to analyze and compare the gait kinematics of the Sigma posterior cruciate-retaining total knee implant, the Advance Traditional posterior cruciate-retaining total knee implant, and the Advance Medial Pivot knee implant using fluoroscopic analysis. In vivo kinematics were determined for 15 clinically successful total knee arthroplasties. Five knee implants were evaluated from each group. The authors analyzed the kinematics of knee motion during the stance phase of gait for each patient. On average, subjects with the Medial Pivot knee implant had a medial pivot motion. Both posterior cruciateretaining designs had a paradoxical roll forward of the tibia on femur during knee flexion and had greater excursion of both condyles during knee flexion than the medial pivot design. Nine of 10 of the posterior cruciate-retaining designs had condylar lift-off averaging 1.7 mm whereas only one Medial Pivot knee implant had condylar lift-off measuring 1.1 mm.

Time-dependent circumferential deformation of cortical bone upon internal radial loading.

Short and long duration tests were conducted on hollow femoral bone cylinders to study the circumferential (hoop) creep response of cortical bone subjected to an intramedullary radial load. It was hypothesized that there is a stress threshold above which nonlinear creep effects dominate the mechanical response and below which the response is primarily determined by linear viscoelastic material properties. The results indicate that a hoop stress threshold exists for cortical bone, where creep strain, creep strain rate and residual strain exhibited linear behavior at low hoop stress and nonlinear behavior above the hoop stress threshold. A power-law relationship was used to describe creep strain as a function of hoop stress and time and damage morphology was assessed.

Well-fixed acetabular component retention or replacement: the whys and the wherefores.

Occasionally the adult reconstructive surgeon is faced with a well-fixed acetabular component that is associated with an arthroplasty problem that ordinarily would require removal and replacement of the cup. Removal of a well-fixed cup is associated with considerable morbidity in bone loss, particularly in the medial wall of the acetabulum. In such a situation, retention of the cup with exchange only of the polyethylene liner may be possible. As preparation for a prospective study, I informally reviewed my experience of cup retention or replacement in revision total hip arthroplasty. An algorithm for retaining or revising a well-fixed acetabular component is presented here.

The response of rabbit patellar tendons after autologous blood injection.

PURPOSE: Blood is a rich source of growth factors that can stimulate fibrocyte migration and help induce neovascular ingrowth. These properties may be able to stimulate a healing response in chronic degeneration of a tendon (tendonosis). The purpose of this study was to assess the biomechanical and histological effects of autologous blood injection on animal tendons. METHODS: New Zealand white rabbit left side patellar tendons were injected with 0.15 cc of autologous blood. We then compared the mechanical properties and histology to the normal right patellar tendon at 6 and 12 wk. RESULTS: At 6 and 12 wk after the injection, there were no differences in the histology compared with normal tendon tissue, and there were no significant changes in tendon stiffness. Biomechanically, the tendons were not damaged at 6 wk after the injection. By 12 wk, tendons that were injected with blood were significantly (P < 0.014) stronger. CONCLUSION: We found that injecting blood directly into normal tendons appears safe. Further evaluation of this technique would appear indicated.