Polyethylene damage and knee kinematics after total knee arthroplasty.

This study characterizes the relationship between in vivo knee kinematics and polyethylene damage by combining fluoroscopic analysis of tibiofemoral contact during dynamic activities and implant retrieval analysis in the same patients. Six patients (eight knees) underwent posterior cruciate ligament-retaining total knee arthroplasty. All patients participated in fluoroscopic analysis during a stair-rise and descent activity and treadmill gait an average of 18 months after arthroplasty, and articular contact was measured. Subsequently, all polyethylene tibial inserts were retrieved after an average of 26 months in vivo function: three at autopsy and five at revision. There was a statistically significant correlation between the damage location on the retrieved inserts and the articular contact location measured fluoroscopically during the activities. The femoral contact and polyethylene damage occurred predominantly on the posterior half of the tibial articular surface, and the damage pattern was largest in the compartment with the greatest range of in vivo femoral contact for each patient. This study showed that in vivo fluoroscopic analysis can predict the damage location on the polyethylene articular surface.

A new technique for removing noncemented acetabular components in revision total hip arthroplasty.

Removal of noncemented acetabular components during revision surgery can be a time-consuming technical challenge, resulting in exacerbation of defects and compromised bone stock. These factors are deleterious to reconstructive efforts and can compromise clinical results. A technique is described that can accomplish timely removal of noncemented acetabular components. The advantages of this technique include no further weakening of the remaining structural supports, minimal bone loss, avoidance of intrapelvic perforations, and reduction in operative time.

Wear patterns on tibial plateaus from varus and valgus osteoarthritic knees.

The size and location of articular cartilage wear was assessed on 106 varus and 37 valgus osteoarthritic tibial plateaus resected during total knee arthroplasty. Anterior cruciate ligament integrity was assessed intraoperatively, and calibrated digital images were used to measure the wear patterns. Complete anterior cruciate ligament deficiency was seen in 25% of the varus and 24% of the valgus knees. Wear patterns on anterior cruciate ligament intact and attenuated varus tibial plateaus occurred in the middle to anterior aspect of the medial plateau. Anterior cruciate ligament deficient varus plateaus had significantly larger wear areas located more posterior on the medial plateau. In contrast, anterior cruciate ligament intact and deficient valgus tibial plateaus had wear located posterior to the center of the lateral plateau. Anterior cruciate ligament integrity is a discrete feature of advanced osteoarthritis that strongly influences the articular wear patterns. The anterior cruciate ligament deficient wear patterns show a wear mechanism that is consistent with the posterior femoral subluxation and posterior tibiofemoral contact observed after acute anterior cruciate ligament rupture. These observations provide insight into the altered knee mechanics that exist in osteoarthritic knees and the resulting mechanical factors that contribute to degenerative changes.

In vivo kinematics of cruciate-retaining and -substituting knee arthroplasties.

A fluoroscopic measurement technique has been used to provide detailed three-dimensional kinematic assessment of knee arthroplasty function during a step-up activity. Three groups of knee arthroplasty subjects with excellent clinical outcomes and similar ranges of motion were evaluated. Each group received different prosthetic components and surgical treatments of the posterior cruciate ligament (PCL). Group 1 had relatively flat articular surfaces with retention of the bony insertion of the PCL, group 2 had similar articular geometry but recessed the PCL without retaining the bony insertion, and group 3 had prostheses with greater sagittal conformity and post/cam substitution of the sacrificed PCL. Although none of the knees exhibited normal knee kinematics, the ranges of axial rotation and condylar translation for group 1 were similar to ranges previously reported for normal and anterior cruciate-deficient knees. Axial rotations and condylar translations decreased when the PCL was surgically recessed or substituted. The smallest kinematic ranges were observed in group 3. The results indicate that both prosthetic component selection and surgical technique have a significant effect on prosthetic knee kinematics during functional activities.

Wear analysis of a retrieved hip implant with titanium nitride coating.

There is increasing interest in using surface modification technology to improve the wear properties of titanium alloy and limit articular surface wear of metal and polyethylene components. This report details the in vivo wear performance of titanium nitride coating on a retrieved hip implant obtained postmortem from a low demand patient 1 year after total hip arthroplasty. Analysis of the well-functioning implant revealed that wear debris can originate from a titanium nitride coated femoral head, as delaminated surface asperities, and manifest as adhesive wear on the articular surface. The wear observed on this implant indicates that rigorous testing and evaluation of titanium nitride coating technology should be conducted prior to widespread use on total joint implants.

Accurate measurement of three-dimensional knee replacement kinematics using single-plane fluoroscopy.

A simple extension of a previously reported object recognition technique has been used to implement a six-degree-of-freedom position/orientation estimator for the measurement of knee replacement motion from two-dimensional (2-D) fluoroscopic images. Computer modeling studies and controlled mechanical tests were performed to assess the accuracy of the technique. The results indicate that knee rotations can be measured with an accuracy of approximately one degree and that sagittal plane translations can be measured with an accuracy of approximately 0.5 mm. The measurement technique is uniquely well suited for performing dynamic kinematic measurements on individuals with knee replacements, and for performing comparative studies among subjects with different designs of knee replacements.

Failure of a well-fixed bone-ingrown titanium hip prosthesis.

A cementless titanium femoral stem was revised 5 years after implantation because of acute pain and progressive osteolysis. Substantial amounts of titanium and polyethylene wear debris were found in the surrounding tissues. Multiple sources of this debris were found as well as detachment of titanium fiber-mesh pads from the body of the femoral stem.

Knee kinematics and kinetics during locomotor activities of daily living in subjects with knee arthroplasty and in healthy control subjects.

BACKGROUND AND PURPOSE: Knee kinematics and kinetics have not been quantitatively studied during gait, stair negotiation, and rising from a chair in the same subjects, either among healthy control subjects or among subjects with knee joint impairments. Despite this paucity of data, rehabilitation goals often include achieving a specific peak knee torque at a specific, fixed angular velocity. SUBJECTS: We compared the kinematic and kinetic performance of the knees in 15 subjects (19 knees) who had undergone knee arthroplasty (KA group) and 11 healthy subjects (22 knees) who served as a control group. The KA group subjects ranged in age from 61 to 78 years, and the control group subjects ranged in age from 26 to 88 years. The KA group subjects had had knee osteoarthritis, were > or = 1 year postsurgery, and were considered fully rehabilitated. METHODS: All subjects were analyzed during barefoot paced walking, stair ascent and descent, and arising from a chair. RESULTS: Compared with the control subjects, the KA group subjects had significantly different knee sagittal range of motion, angular velocities, and maximum knee moments during loaded knee extension. Vertical ground reactions did not differ significantly between groups. Both groups' maximum extension angular velocity exceeded 350 degrees/s during the swing phase of gait, but the maximum loaded extension velocity averaged only 140 degrees/s (during rising from a chair). Maximum knee flexion moments were approximately 10 to 15 N.m/%BW (knee moments normalized to percentage of body weight in newtons). CONCLUSION AND DISCUSSION: We concluded that locomotor ADLs demand relatively slow loaded angular velocities and low knee torques, a factor that should be considered in knee postarthroplasty exercise prescription.

In vivo acetabular contact pressures during rehabilitation, Part I: Acute phase.

The authors conducted a two-part study to compare in vivo acetabular contact pressures during the acute and postacute phases of rehabilitation. This report compares in vivo acetabular contact pressures generated during selected "inpatient" rehabilitation activities and their relationship to pain, range of motion, and other clinical indicators. A pressure-instrumented Moore-type endoprosthesis was implanted in a 73-year-old woman who had sustained a femoral neck fracture. Acetabular contact pressures during the first 2 weeks after surgery were rank-ordered. Clinical data, including range of motion, manual muscle test grade, use of pain medication, and independence in gait, were collected simultaneously. Acetabular pressures did not follow the predicted rank order corresponding to the commonly prescribed temporal order of inpatient rehabilitation activities. Isometric hip extension and active hip flexion generated the highest pressures of all the studied activities, including those measured during gait activities. Isometric exercises, therefore, may not be entirely benign preparation for ambulatory activity. Clinical data did not correspond with peak pressure data, suggesting that observed responses to rehabilitation may not be dependable criteria for progressing the acute hip rehabilitation protocol. We discuss applications for rehabilitation programs based on hip contact pressure data as an initial attempt to formulate more defensible rehabilitation approaches for patients with acutely painful hips.

In vivo acetabular contact pressures during rehabilitation, Part II: Postacute phase.

The authors conducted a two-part study to compare in vivo acetabular contact pressures during the acute and postacute phases of rehabilitation in a single subject with a pressure-instrumented femoral prosthesis. This report compares six common hip rehabilitation activities for resultant in vivo hip pressure magnitudes during the first 5 years after discharge from an acute care hospital. These activities were full, partial, touch-down, and non-weight-bearing ambulation and isometric hip abduction and straight-leg-raising exercises. A pressure-instrumented femoral endoprosthesis implanted in a 73-year-old woman who had sustained a femoral neck fracture provided data for the activities. The activities were rank ordered and compared over time according to peak pressure magnitude. Prescribed weight bearing and exercise type were not good predictors of hip peak pressures in this patient. Maximum pressures occurred by 1 year postdischarge for most activities, with a tendency to stabilize or decline thereafter. Resisted isometric hip abduction exercise demonstrated the most variation over time. The results suggest that hip pressures may be limited by controlling muscle force and movement velocity during postoperative hip rehabilitation activities.

Unicompartmental knee replacement: a comparison of constrained and unconstrained designs.

Seventy-six patients who had eighty-seven unicompartmental knee replacements were followed for an average of fifty-three months (range, two to twelve years). The operation was on the medial side in eighty-two knees and on the lateral side in five. Fifty replacements were unconstrained and thirty-seven were constrained. Of the fifty knees that had an unconstrained replacement, forty-nine (98 per cent) had a good or excellent result, compared with only twenty-six (70 per cent) of the knees that had a constrained replacement; the difference is significant (p = 0.0007). No knee that had an unconstrained replacement had a poor result, compared with nine (24 per cent) of the knees that had a constrained replacement (p = 0.0009). Four (8 per cent) of the fifty knees that had an unconstrained replacement later had a revision total knee arthroplasty, compared with ten (27 per cent) of the thirty-seven knees that had a constrained replacement; the difference is significant (p = 0.04). Noteworthy degenerative changes in the opposite compartment occurred in only one of the eighty-seven knees (a knee in which an unconstrained prosthesis had been inserted).

Trunk kinematics during locomotor activities.

We investigated upper-body (ie, trunk) angular kinematics (motions) during gait, stair climbing and descending, and rising from a chair in two reference frames--relative to the pelvis and to room coordinates. Bilateral kinematic data were collected from 11 healthy subjects (6 female, 5 male), who were 27 to 88 years of age (mean = 58.9, SD = 17.9). During stair climbing, maximum trunk flexion relative to the room was at least double that during stair descending and gait. Arising from a chair required the most trunk flexion/extension range of motion (ROM) but the least abduction/adduction and medial/lateral (internal/external) rotation. Trunk ROM during gait was small (mean less than or equal to 12 degrees) and consistent with previous literature. Trunk range of motion relative to the room during stair climbing and descending was greater than trunk ROM during gait in all planes. The pelvis and trunk rotate in the transverse plane in greater synchrony during stair descending (mean = 8.1 degrees, SD = 5.6 degrees) than during gait (mean = 12.0 degrees, SD = 4.2 degrees). For all activities, trunk frontal and sagittal ROM relative to the pelvis was greater than that relative to the room coordinates. This finding suggests that trunk/pelvis coordination may be used to reduce potentially destabilizing anti-gravity trunk motions during daily activities. We conclude that upper-body kinematics relative to both pelvis and gravity during daily activities are important to locomotor control and should be considered in future studies of patients with locomotor disabilities.

Prevention of deep vein thrombosis after total knee arthroplasty. Coumadin versus pneumatic calf compression.

The rate of deep vein thrombosis (DVT) after total knee arthroplasty (TKA) without prophylaxis has been reported as high as 84%. Coumadin anticoagulation and pneumatic calf compression (PCC) boots are two current therapies that have been thought to be effective in reducing this high rate of DVT. To investigate these two methods, a nonrandomized prospective study was designed. The first group involved treating 48 consecutive knee arthroplasties with a regimen of coumadin anticoagulation. The second group involved 81 consecutive knee arthroplasties treated with sequential PCC boots. Bilateral lower extremity venography was performed between the eighth and tenth hospital postoperative days. The overall incidence of DVT in the coumadin group was 33%, with 29% having calf thrombi and 6% having thigh thrombi. The overall incidence of DVT in the boot group was 31%, with 27% having calf thrombi and 6% having thigh thrombi. In both groups, there were no treatment-related complications. Cost analysis of the administration of each type of therapy showed coumadin to be approximately 50% more expensive than PCC boots. Although coumadin and PCC boot therapy are safe and effective in reducing the incidence of DVT after TKA, there are economic factors that make the latter a more favorable option.

Vitallium-mold arthroplasty of the knee. A case report with 30-year follow-up study.

A case was reviewed of a 52-year-old woman who underwent vitallium-mold arthroplasty of the right knee in 1958. After more than 30 years her Hospital for Special Surgery knee score continued to show an excellent rating. The anatomic-designed implant, made of cobalt-chrome material and inserted cementless, appears to have withstood the test of time in the knee.

A relationship between stem orientation and function following total hip arthroplasty.

A retrospective gait analysis of patients with cemented Charnley-Mueller total hip arthroplasties was conducted to determine if functional differences exist between patients with femoral stems placed in varus and valgus orientations. Twenty patients and ten normals were studied using gait analysis to quantify joint motion and moments during level walking. In addition, a radiographic analysis of stem placement and mechanics of the reconstructed hip was performed on the total hip patients. All patients selected for the study had excellent clinical results on the basis of a score of 95 or better on the Harris hip rating form. The patients were divided into two subgroupings on the basis of stem orientation. A valgus group was defined as having a valgus stem orientation relative to the femoral shaft, with the femoral head-shaft offset shortened by 5 mm or greater compared to the contralateral unoperated hip, while the varus group was defined on the basis of having a varus stem orientation relative to the femoral shaft, with the femoral head-shaft offset restored to normal or greater than normal. A difference in gait was found between the varus and valgus patient groupings. The varus group had abnormal gait characteristics in the range of hip motion, the flexion-extension moments at the hip, and stride length. The patients in the valgus group had statistically normal gait. The differences in the gait characteristics were interpreted as an attempt to alter forces on the hip joint for patients in the varus group. These alterations were possibly an early indication of a subtle adaptation in patients with varus-placed femoral stems since, historically, a greater percentage of the patients in this configuration, retrospectively, go on to mechanical failures.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of age on dynamics of rising from a chair.

This article describes the sit-to-stand movement in nine healthy elderly adults, ages 61 to 74 years, and compares peak joint angles, torques, and velocities of 11 body segments with data collected from nine young women, ages 25 to 36 years. The subjects in this study rose from a chair under a controlled protocol. An optoelectronic system, two force plates, and two computers were used for data collection and processing. The data are described in relationship to three phases of the task previously described for the young subjects' data. Percentages of difference were calculated for the torques and the velocities. Independent t tests were conducted on maximum angles achieved and total joint excursions. Consistency between groups was demonstrated in the duration of each phase, as well as the body kinematics and kinetics occurring within each phase. There was little difference in maximum torques or velocities. Maximum angles of head-to-trunk extension, head-to-ground flexion, head-to-trunk excursion, and trunk-to-pelvis flexion were significantly different between groups. The differences in head position demonstrated between these two groups may have clinical implications for loss of balance during this task in older patients.

Exercise and gait effects on in vivo hip contact pressures.

Virtually all hip rehabilitation programs include exercise for muscle force development. The specific effects of various exercise modes on the hip joint itself are unknown. We will report on the effects of common exercise modalities on in vivo hip pressures. Four years prior to data collection, a pressure-instrumented Austin-Moore-type endoprosthesis was implanted in an otherwise healthy 73-year-old woman with a traumatic right hip fracture. Hip pressures during various experimental maneuvers were recorded periodically over a 5-year period. We compared measurements of peak pressure and rate of pressure rise obtained during gait with those obtained during isokinetic, isometric, and isotonic lower-limb exercises. Maximal exercise generated greater peak pressures than did gait, and tripling the angular velocity during exercise roughly tripled the rate of pressure rise. Torque production and resultant in vivo hip pressures varied directly during all experiments. Peak pressures and rate of pressure rise apparently can be controlled by varying the subject's exertion. The results reported are from a single subject; therefore, little generalizability is possible for these data. We suggest, however, that articular pressures may be important to rehabilitation planning; these data provide a direct insight into this potentially important exercise prescription consideration.

Mechanics of a constrained chair-rise.

A sit-to-stand task is analyzed by a method which estimates the segmental and whole body center of mass (CoM) kinematics and kinetics using bilateral whole body kinematic data from nine healthy young female subjects. The sit-to-stand, or chair-rise, task is constrained with regard to chair height, pace, initial lower limb position and arm use. The chair-rise maneuver is divided into four phases; (1) the flexion momentum phase; (2) the momentum transfer phase; (3) the vertical extension phase; and (4) the stabilization phase; the first three are examined in detail here. The momentum transfer phase, which immediately follows lift-off from the seat of the chair, is the most dynamic portion of the event, demanding a high degree of coordination. This maneuver is analyzed in order to determine if trunk movement is used only to position the body center of gravity or if the trunk motion generates momentum which is important during the brief but critical period of dynamic equilibrium immediately following lift-off from the chair. Our evidence points to the latter case and indicates that inter-segmental momentum transfer is possible during this period.