Sabir Ismaily

Backside Wear of Polyethylene Tibial Inserts: Mechanism and Magnitude of Material Loss

BACKGROUND Wear of the underside of modular tibial inserts (backside wear) in total knee replacements has been reported by several authors. Although, for some implant designs, this phenomenon seems to contribute to osteolysis, the actual volume of material lost through wear of the backside surface has not been quantified. This study describes the results of computerized measurements of tibial inserts of one design known to be associated with a high prevalence of backside wear in situ. METHODS A series of retrieved total knee components of one design were examined. The duration of implantation of the retrieved components ranged from thirty-six to 146 months. Laser surface profilometry and computer-aided design software were used to develop individual three-dimensional models of each worn, retrieved tibial insert to compare with scanned unused inserts. Volumetric subtraction of both models revealed the material lost because of backside wear. RESULTS Worn and unworn areas on the backside surface were easily identified by stereomicroscopy and laser profilometry. The computer reconstructions showed that, in all retrievals, all unworn surfaces on the nonarticulating surface lay in one plane. The average volume (and standard deviation) of the material lost because of backside wear was 925 +/- 637 mm(3) (range, 197 to 2720 mm(3)). On the basis of the time in situ for each implant, the average volumetric wear rate was 138 +/- 95 mm(3)/yr. CONCLUSIONS The predicted volume of material removed because of backside wear is substantial and may be sufficient to induce osteolysis. Our results suggest that peg-like protrusions are not generated by the extrusion of polyethylene into screw-holes within the base-plate but by abrasion of the underside of the bearing insert, leaving the protruding pegs as the only remnants of the original surface.

Comparison of 2 femoral tunnel locations in anatomic single-bundle anterior cruciate ligament reconstruction: A biomechanical study

PURPOSE To evaluate knee stability after anterior cruciate ligament (ACL) reconstruction using 2 modern clinically relevant single-bundle constructs. METHODS Two arthroscopic ACL reconstructions were performed on 6 fresh-frozen human cadaveric knees using bone-patellar tendon-bone autografts. The tibial tunnel was centered in the anatomic tibial footprint. The femoral tunnel was reamed through the anteromedial (AM) portal and centered alternately in either the AM portion of the femoral footprint (center-AM) or the center of the femoral footprint (center-center). Two external loading conditions were applied: (1) a 134-N anterior tibial load and (2) a 10-Nm valgus load combined with a 5-Nm internal tibial torque. Resulting kinematics were determined under 4 conditions: (1) ACL intact, (2) ACL deficient, (3) center-AM reconstruction, and (4) center-center reconstruction. RESULTS In response to anterior tibial loading, anterior translation was similar in the ACL-intact knee and the 2 reconstructions at 0° to 60° of flexion but was greater in the reconstructed specimens at 90°. In response to the complex rotatory load, internal tibial rotation (ITR) at 30° of flexion was slightly greater in center-AM knees compared with ACL-intact knees (11.0° ± 0.6° v 10.5° ± 0.6°, P = .03). At other angles tested, ITR in both reconstructions was similar to the ACL-intact knee (P > .05). When we compared the 2 reconstruction alternatives, however, center-center knees exhibited greater resistance to ITR at all angles (P < .05). CONCLUSION Anatomic single-bundle ACL reconstruction performed with the femoral tunnel placed through the AM portal restores translational and rotational knee stability to an extent that closely approximates the ACL-intact condition. When compared with the AM femoral tunnel position, a femoral tunnel positioned in the anatomic center of the femoral origin of the ACL may further improve rotatory stability without sacrificing anterior stability. CLINICAL RELEVANCE This study provides additional biomechanical evidence in support of anatomic single-bundle ACL reconstruction with tunnels positioned in the center of the femoral and tibial footprints.

Backside Wear of Modular Ultra-High Molecular Weight Polyethylene Tibial Inserts

BACKGROUND The capture mechanisms of modular tibial total knee components may allow relative micromotion between the insert and the base-plate, leading to wear at the nonarticulating (backside) surface. Although retrieved components often display laxity in the capture mechanism in the unloaded condition, the magnitude of the relative motion that actually occurs under physiologic conditions has not been determined. This study was performed to assess the impact of different modes of knee-loading on the relative micromotion between the insert and the base-plate and the relationship between the duration that the implant had been in situ and the severity of backside wear. METHODS Twenty-one posterior-stabilized total knee replacements of one common design (Insall-Burstein II) were retrieved at one to 100 months after implantation. The extent and severity of backside wear was graded with use of stereomicroscopy. All components were soaked in a bath (of physiologic saline solution at 37 degrees C for four days prior to reassembly. The relative micromotion between the insert and the base-plate of each specimen was measured in vitro in two different conditions: with no axial load and with a combination of loads and torques simulating the stance phase of gait. RESULTS The capture mechanism laxity between the insert and the tibial base-plate in the unloaded condition was approximately eight times larger than the micromotion measured during simulated gait. The capture mechanism laxity allowed a mean (and standard deviation) of 618 +/- 226 micro m of total relative micromotion compared with 103 +/- 54 micro m of relative micromotion during the gait cycle. Under both loading conditions, the predominant direction of interface motion was medial-lateral. No correlation was found between the magnitude of capture mechanism laxity and the relative micromotion measured during simulated gait (p = 0.11). Larger polyethylene protrusions on the backside surface did not correlate with less micromotion (p = 0.48) or with capture mechanism laxity (p = 0.06). CONCLUSIONS For the implant design that was studied, capture mechanism laxity between the modular insert and the base-plate in the unloaded condition was an order of magnitude larger than and not indicative of the micromotion that occurred during simulated physiologic loading. In addition, polyethylene protrusions into the screw-holes of tibial base-plates did not seat or lock the insert in place and reduce relative motion. CLINICAL RELEVANCE While some clearance between the insert and the base-plate is required to allow assembly of modular tibial components at the time of surgery, the amount of relative interface motion during a functional activity such as normal gait, which can produce potentially damaging wear debris, is unknown. However, the compressive forces applied to the articular surface during a functional activity may substantially reduce micromotion between the insert and the base-plate relative to the unloaded condition.

The Flexion-Extension Axis of the Knee and its Relationship to the Rotational Orientation of the Tibial Plateau

We measured the optimal rotational alignment of the tibial component with respect to anatomic landmarks. Kinematic data were collected from functional maneuvers simulated in 20 cadaveric knees mounted in a joint simulator. The axis of knee motion was calculated for squatting and lunging activities over the interval of 30° to 90° of knee flexion. We then examined the accuracy and variability of 5 different anatomic axes in predicting the direction of knee motion. No one landmark guaranteed correct alignment of the tibial component and most predictors were highly variable (range, 6°-21°). The most accurate indicators were the medial third of the tibial tubercle (average error: squatting: 3.5° external rotation; lunging: 9.5°), and the medial-lateral axis of the resected tibial surface (6.7° and 1.1° internal rotation). The correct alignment of the tibial component can be best achieved by splitting the difference between these landmarks to eliminate placement of the component in excessive external and excessive internal rotation.

Development of a mandibular motion simulator for total joint replacement.

PURPOSE The purpose of this study was to develop a motion simulator capable of recreating and recording the full range of mandibular motions in a cadaveric preparation for an intact temporomandibular joint (TMJ) and after total joint replacement. MATERIAL AND METHODS A human cadaver head was used. Two sets of tracking balls were attached to the forehead and mandible, respectively. Computed tomographic (CT) scan was performed and 3-dimensional CT models of the skull were generated. The cadaver head was then dissected to attach the muscle activation cables and mounted onto the TMJ simulator. Realistic jaw motions were generated through the application of the following muscle forces: lateral pterygoid muscle, suprahyoid depressors (geniohyoid, mylohyoid, and digastric muscles), and elevator muscles. To simulate muscle contraction, cables were inserted into the mandible at the center area of each muscles attachment. To provide a minimum mouth closing force at the initial position, the elevator muscles were combined at the anterior mandible. During mandibular movement, each motion was recorded using a high-resolution laser scanner. The right TMJ of the same head was reconstructed with a total TMJ prosthesis. The same forces were applied and the jaw motions were recorded again. CT scan was performed and 3-dimensional CT models of the skull with TMJ prosthesis were generated. RESULTS Mandibular motions, before and after TMJ replacement, with and without lateral pterygoid muscle reattachment, were re-created in a cadaveric preparation. The laser-scanned data during the mandibular motion were used to drive 3-dimensional CT models. A movie for each mandibular motion was subsequently created for motion path analysis. Compared with mandibular motion before TMJ replacement, mandibular lateral and protrusive motions after TMJ replacement, with and without lateral pterygoid muscle reattachment, were greatly limited. The jaw motion recorded before total joint replacement was applied to the mandibular and prostheses models after total TMJ replacement. The condylar component was observed sinking into the fossa during jaw motion. CONCLUSION A motion simulator capable of re-creating and recording full range of mandibular motions in a cadaveric preparation has been developed. It can be used to simulate mandibular motions for the intact TMJ and total joint prosthesis, and to re-create and record their full range of mandibular motions. In addition, the full range of the recorded motion can be re-created as motion images in a computer. These images can be used for motion path analysis and to study the causation of limited range of motion after total joint replacement and strategies for improvement.

MRI study of the capitate, lunate, and lunate fossa with relevance to proximal row carpectomy.

PURPOSE To study the articular morphology (radius of curvature), (diameter, depth, circularity, and percent of circle) of the capitate, proximal lunate, and the lunate fossa of the distal radius using both magnetic resonance imaging (MRI) scans and plain radiographs. The correlation between plain radiographs and MRI scans for these measurements will also be assessed. METHODS Twenty MRI scans and 17 sets of radiographs of asymptomatic volunteers were evaluated. Standardized surface landmarks were digitized and measured in both the sagittal and coronal planes. The parameters of interest were calculated from the digitized data using specialized software. RESULTS Using MRI data, we determined the radius of curvature of the capitate to be only 37% +/- 10 of the lunate fossa of the distal radius on the coronal (anteroposterior) view and to be 57% +/- 10 on the sagittal (lateral) view. In both planes, the proximal lunate had a significantly larger diameter and radius of curvature than did the capitate. The ratio of the radius of curvature of the proximal capitate to the proximal lunate on the coronal projection ranged from .366 to .811, and on the sagittal projection the values ranged from .46 to .71. Plain radiographs were not sufficiently accurate to determine the radius of curvature ratio of the capitate to the lunate or to the lunate fossa of the distal radius on the coronal view based on a comparison with MRI data. Plain radiography did not correlate with MRI for most clinically relevant parameters. CONCLUSIONS The articular morphology of the capitate does not closely correspond with that of the lunate fossa when compared with the proximal lunate articular surface. Based on observed variations in capitate morphology and the potential for associated alterations in joint contact forces after proximal row carpectomy, preoperative MRI may facilitate the selection of patients with more favorable capitate morphology.

Anteroposterior Knee Stability During Stair Descent

This study examined the influence of tibio-femoral conformity on anteroposterior (AP) knee stability during stair descent, particularly with a dished cruciate sacrificing (CS) design. A joint simulator simulated stair descent of cadaveric knees. Tibio-femoral displacement was measured. Knees were tested in intact, ACL-deficient, and TKA with cruciate-retaining (CR), CS and posterior-stabilizing (PS) inserts. Loading during stair descent simulation caused femur displacement anteriorly prior to quadriceps contraction. Quadriceps contraction reestablished the initial femoral AP position. During simulated stair descent, AP stability was restored using PS, CR or CS inserts with an intact PCL. The CS design without the PCL did not provide AP stability. Increasing quadriceps force to restore AP stability may explain the clinical findings of pain and fatigue experienced by some patients after TKA.

Quantifying and Predicting Surgeon Work Effort for Primary and Revision Total Knee Arthroplasty

BACKGROUND The objectives of this study were to quantify increased utilization of resources in revision total knee arthroplasty (TKA) compared with primary TKA, determine preoperative factors that predict outcome measures, and compare Medicare reimbursement for each procedure. METHODS Seventy-eight revision TKA patients were compared with 80 primary TKA patients. Outcomes measured were surgical time, estimated blood loss, length of stay, and complications. RESULTS Revision TKA showed 49% increased surgical time compared with primary TKA. Estimated blood loss was increased 91%. Tibial and femoral bone loss was associated with increased surgical time as was use of longer stemmed tibial components. Average Medicare hospital payment increased 29% (

Hypothermia in Total Joint Arthroplasty: A Wake-Up Call

13,464 for primary,

Is digital photography an accurate and precise method for measuring range of motion of the hip and knee

17,331 for revision). Average physician reimbursement represented a 36% increase. Relative value units were increased to 31%. CONCLUSION There was substantial increase in work effort not commensurate with current Medicare reimbursement, which may limit patient access to revision TKA.