Harold E. Cates

Clicking and Squeaking: In Vivo Correlation of Sound and Separation for Different Bearing Surfaces

Fluoroscopy has proven to be an accurate method to determine in vivo motions1 and has enabled the extraction of accurate three-dimensional hip-joint kinematics unaffected by erroneous skin movements1,2. Previously, fluoroscopy was used to determine that the femoral head of a total hip prosthesis slides within the acetabular cup, leading to separation of certain aspects of the articular geometry3-5. This finding has often been referred to as hip separation, where there is a loss of contact area, leaving only edge contact. Although separation has been well documented, it has not been correlated to clinical complications nor has a more in-depth understanding of the cause and effect been developed. Another phenomenon observed primarily in total hip prostheses is the presence of squeaking. Mismatched ceramic couples6, acetabular component malposition7, and impingement8 have been proposed as factors in the development of squeaking. However, not all mismatched and malpositioned components lead to squeaking. Additionally, squeaking has been observed in properly matched and positioned implants and when no evidence of neck-to-rim impingement is present7,9,10. Audible squeaking of a hip replacement remains, therefore, a still unexplained phenomenon. The sliding motion within the acetabular cup, causing a total hip prosthesis to resemble a ball-and-socket joint, could lead to the induction of vibrational propagation across the interface of the femoral head and acetabular cup, possibly leading to audible interactions. It is further hypothesized that the “squeaking” sound, which mainly occurs in ceramic-on-ceramic total hip prostheses, may be due to separation of the femoral head. Fluoroscopy can facilitate the correlation of sound with three-dimensional movement, depict contact positions, and localize potential sound sources. This movement of the femoral head from the acetabular component and the impact conditions generated from sliding …

High-flexion TKA designs: what are their in vivo contact mechanics?

To accommodate for high flexion, new total knee arthroplasties (TKAs) have been designed. Unlike older designs which have been found to exhibit decreasing contact area with increasing flexion, we hypothesized the new designs would be associated with improved contact mechanics. We compared in vivo contact mechanics for 10 subjects having a fixed-bearing high-flexion posterior-stabilized (LPS-Flex) TKA and 10 subjects having a fixed-bearing high-flexion posterior cruciate-retaining (CR-Flex) TKA. All subjects performed deep knee bends to maximum flexion while under fluoroscopic surveillance. In vivo kinematics obtained using a three-dimensional to two-dimensional registration technique, were input into a three-dimensional inverse dynamic mathematical model to determine the contact forces. The contact areas and contact stresses were determined using a deformable contact model. The contact forces, contact areas, and contact stresses in both these implants increased with increasing flexion. The medial contact area in the LPS-Flex was higher than the CR-Flex for most of the flexion cycle. The lateral contact area was higher in the CR-Flex than the LPS-Flex in early and midflexion ranges. Although the lateral contact stresses were similar in both implants, the CR-Flex experienced higher medial contact stress than the LPS-Flex throughout flexion. However, both these implants were able to maintain sufficient contact area so the contact stress values were well below the yield strength of crosslinked polyethylene.

A non-invasive acoustic and vibration analysis technique for evaluation of hip joint conditions.

The performance evaluation of THA outcome is difficult and surgeons often use invasive methods to investigate effectiveness. A non-invasive acoustic and vibration analysis technique has recently been developed for more-in-depth evaluation of in vivo hip conditions. Gait kinematics, corresponding vibration and sound measurement of five THA subjects were analyzed post-operatively using video-fluoroscopy, sound and accelerometer measurements while walking on a treadmill. The sound sensor and a pair of tri-axial accelerometers, externally attached to the pelvic and femoral bone prominences, detected frequencies that are propagated through the femoral head and acetabular cup interactions. A data acquisition system was used to amplify the signal and filter out noise generated by undesired frequencies. In vivo kinematics and femoral head sliding quantified using video fluoroscopy were correlated to the sound and acceleration measurements. Distinct variations between the different subjects were identified. A correlation of sound and acceleration impulses with separation has been achieved. Although, in vivo sounds are quite variable in nature and all correlated well with the visual images. This is the first study to document and correlate visual and audible effects of THA under in-vivo conditions. This study has shown that the development of the acoustic and vibration technique provides a practical method and generates new possibilities for a better understanding of THA performance.

Stair ambulation biomechanics following total knee arthroplasty: a systematic review.

The purpose of this review was to summarize the biomechanical adaptations during stair ambulation that occur after total knee arthroplasty (TKA). Articles were identified by searching PubMed and Web of Science. During stair ascent, knee flexion angle at heel strike and walking velocity were reduced in TKA subjects compared to controls. Results of other variables were not consistent between studies. During stair descent only one study found any differences for knee moments in the sagittal and frontal plane between TKA subjects and controls. Other results during stair descent were not consistent between studies. Differences in methods can partially explain discrepancies between studies in this review. More studies with consistent and improved methods are needed in order to provide better understanding of stair ambulation following TKA.

Mechanically assisted taper corrosion in modular TKA.

The purpose of this study was to characterize the prevalence of taper damage in modular TKA components. One hundred ninety-eight modular components were revised after 3.9±4.2 years of implantation. Modular components were evaluated for fretting corrosion using a semi-quantitative 4-point scoring system. Design features and patient information were assessed as predictors of fretting corrosion damage. Mild-to-severe fretting corrosion (score ≥2) was observed in 94/101 tapers on the modular femoral components and 90/97 tapers on the modular tibial components. Mixed alloy pairs (p=0.03), taper design (p<0.001), and component type (p=0.02) were associated with taper corrosion. The results from this study supported the hypothesis that there is taper corrosion in TKA. However the clinical implications remain unclear.

Single Versus Multiple-Radii Cruciate-Retaining Total Knee Arthroplasty: An In Vivo Mobile Fluoroscopy Study

BACKGROUND Previous fluoroscopic studies, using static C-arm systems, have shown nonnormal kinematic patterns in cruciate-retaining (CR) total knee arthroplasty (TKA). This study compares in vivo the kinematic differences in subjects implanted with single sagittal radius (SR) vs multiradii (MR) CR TKA for various activities using a novel mobile fluoroscopic system. METHODS Using mobile fluoroscopy and 3D to 2D registration, tibiofemoral kinematics were analyzed for 25 subjects with an SR, symmetrical condylar CR TKA and 25 subjects with an MR, asymmetric condylar CR TKA for three dynamic weight-bearing activities: (1) deep knee bend (DKB), (2) walking up a ramp, and (3) walking down a ramp. RESULTS During DKB, from full extension to maximum knee flexion, the SR (-0.43 ± 3.43 mm) and MR (-1.00 ± 3.23 mm) groups experienced statistically similar anterior/posterior (AP) motion in the lateral condyle. The SR (3.51 ± 2.68 mm) group had significant anterior movement compared to the MR (-0.42 ± 2.20 mm) group in the medial condyle. This resulted in a significantly larger amount of normal axial rotation experienced by the SR (5.20 ± 3.93°) group compared to the MR (0.75 ± 5.12°) group. During ramp activities, the SR TKA consistently exhibited a significantly more posterior position of both condyles compared to the MR TKA. CONCLUSION Although the SR TKA exhibited larger amounts of axial rotation compared to the MR TKA in DKB, neither design exhibited weight-bearing kinematics as previously reported for the normal knee. Additional research on the normal knee for ramp activities is required to understand the importance of condylar position during these activities.

Knee Joint Loads and Surrounding Muscle Forces during Stair Ascent in Patients with Total Knee Replacement

Total knee replacement (TKR) is commonly used to correct end-stage knee osteoarthritis. Unfortunately, difficulty with stair climbing often persists and prolongs the challenges of TKR patents. Complete understanding of loading at the knee is of great interest in order to aid patient populations, implant manufacturers, rehabilitation, and future healthcare research. Musculoskeletal modeling and simulation approximates joint loading and corresponding muscle forces during a movement. The purpose of this study was to determine if knee joint loadings following TKR are recovered to the level of healthy individuals, and determine the differences in muscle forces causing those loadings. Data from five healthy and five TKR patients were selected for musculoskeletal simulation. Variables of interest included knee joint reaction forces (JRF) and the corresponding muscle forces. A paired samples t-test was used to detect differences between groups for each variable of interest (p<0.05). No differences were observed for peak joint compressive forces between groups. Some muscle force compensatory strategies appear to be present in both the loading and push-off phases. Evidence from knee extension moment and muscle forces during the loading response phase indicates the presence of deficits in TKR in quadriceps muscle force production during stair ascent. This result combined with greater flexor muscle forces resulted in similar compressive JRF during loading response between groups.

Influence of Total Knee Arthroplasty on Gait Mechanics of the Replaced and Non-Replaced Limb During Stair Negotiation

This study compared biomechanics during stair ascent in replaced and non-replaced limbs of total knee arthroplasty (TKA) patients with control limbs of healthy participants. Thirteen TKA patients and fifteen controls performed stair ascent. Replaced and non-replaced knees of TKA patients were less flexed at contact compared to controls. The loading response peak knee extension moment was greater in control and non-replaced knees compared with replaced. The push-off peak knee abduction moment was elevated in replaced limbs compared to controls. Loading and push-off peak hip abduction moments were greater in replaced limbs compared to controls. The push-off peak hip abduction moment was greater in non-replaced limbs compared to controls. Future rehabilitation protocols should consider the replaced knee and also the non-replaced knee and surrounding joints.

A COMPARISON OF DIFFERENT BEARING SURFACES DURING GAIT USING EXPERIMENTS AND MATHEMATICAL MODELING

INTRODUCTION Only few of the current evaluation techniques involve in vivo assessment leading to prediction of long-term use as well as appropriate comparison between the different materials and material combinations that are widely used in total hip arthroplasty (THA). Therefore, the objective of this study was to develop a load profile that better simulates the in vivo loading conditions of THA patients using in vivo fluoroscopic and mathematical modeling techniques and to compare implants with different baering surfaces. Initially, a mathematical model of the human extremity was derived to determine in vivo bearing surface and soft-tissue (muscles and ligaments) forces. Input for this model was obtained using fluoroscopy to determine in vivo hip motions. Tri-axial accelerometers were attached to the greater trochanter and the pelvis to determine propagating frequencies across the hip joint. METHODS Overall 20 subjects having non-cemented THA with variable bearing surface interfaces: ceramic-on-poly, metal-on-metal, metal-on-metal with polyethylene inner layer and metal-on-polyethylene are initially involved in the study. All the patients were judged as clinically successful (HHS> 90) and were analyzed under fluoroscopic surveillance while performing gait on a treadmill and on a force plate.