Total hip arthroplasty with the Secur-Fit and Secur-Fit plus femoral stem design a brief follow-up report at 5 to 10 years.

This report represents a 5- to 10-year follow-up of our initial 2- to 5-year data with this proximally hydroxyapatite-coated stem design (Secur-Fit, Stryker Orthopaedics, Mahwah, NJ). This is a retrospective review of a single surgeon's consecutive cases. A total of 105 cases were available for complete review. The average follow-up was 6.7 years (60-123 months). All stems achieved bony ingrowth. Harris hip score and Oxford hip score averaged to 91 and 17, respectively, with no differences seen between the 132 degrees and the 127 degrees stem designs. Leg length measurements were considered equal side-to-side differences of 7 mm or less in 87% of cases: 82% of standard- and 92% of high-offset cases (P < .05). Four cases of osteolysis were identified and occurred only in patients with an elevated rim liner, implicating neck-liner impingement. The stem design performed exceedingly well over the course of this study. Having a high-offset option aids the surgeon in proper leg length management.

Material properties of articular cartilage in the rabbit tibial plateau.

The material properties of articular cartilage in the rabbit tibial plateau were determined using biphasic indentation creep tests. Cartilage specimens from matched-pair hind limbs of rabbits approximately 4 months of age and greater than 12 months of age were tested on two locations within each compartment using a custom built materials testing apparatus. A three-way ANOVA was used to determine the effect of leg, compartment, and test location on the material properties (aggregate modulus, permeability, and Poisson's ratio) and thickness of the cartilage for each set of specimens. While no differences were observed in cartilage properties between the left and right legs, differences between compartments were found in each set of specimens. For cartilage from the adolescent group, values for aggregate modulus were 40% less in the medial compartment compared to the lateral compartment, while values for permeability and thickness were greater in the medial compartment compared to the lateral compartment (57% and 30%, respectively). Values for Poisson's ratio were 19% less in the medial compartment compared to the lateral compartment. There was also a strong trend for thickness to differ between test locations. Similar findings were observed for cartilage from the mature group with values for permeability and thickness being greater in the medial compartment compared to the lateral compartment (66% and 34%, respectively). Values for Poisson's ratio were 22% less in the medial compartment compared to the lateral compartment.

In vivo loads in the medial compartment of the rabbit knee.

BACKGROUND: The compressive loads produced in the medial compartment of a rabbit knee during hopping are unknown, and necessary for the development of an animal model to study unicompartmental osteoarthritis. METHODS: In an effort to obtain such data, a surgical procedure was developed to insert a pressure sensor into the medial tibial compartment of a New Zealand white rabbit knee joint, and an inactive sensor of the same thickness into the lateral tibial compartment. After the rabbits recovered from anesthesia, contact pressure was measured as the rabbits hopped. FINDINGS: The average peak pressure in the medial compartment was 60 N/cm2 (SD 16), a value that corresponds to 39% of the animals' body weight (range: 21-61%, SD 11%). INTERPRETATION: This is the first report of measured in vivo pressures associated with the load transmitted through the medial compartment of the skeletally mature New Zealand White rabbit, a model frequently used to study the progression of osteoarthritis.

Effects of increased chronic loading on articular cartilage material properties in the lapine tibio-femoral joint.

Methods of producing relevant and quantifiable load alterations in vivo with which to study load-induced cartilage degeneration analogous to osteoarthritis are limited. An animal model was used to investigate the effects of increased chronic loads on articular cartilage. Mature rabbits were randomized into one of three experimentally loaded groups and a fourth unoperated control group. A mechanical-loading device was skeletally fixed to the hind limb of animals in the loaded groups. Engaging the device resulted in an additional load of 0%, +22% or +44% body weight to the medial compartment of the experimental knee, while allowing normal joint function. Following a 12-week loading protocol, a creep-indentation test and needle probe test were used to determine the biphasic material properties and thickness of the cartilage at four locations of each femoral and tibial condyle of the experimental and contralateral limbs. Analyses of covariance were performed to compare outcome measures across the treatment groups. The effect of increased load was site and load-level specific with alterations of material properties and thickness most prominent in the posterior region of the medial compartment of the tibia. At this site, permeability increased 128% and thickness increased 28% in the +44% body weight group relative to the 0% body weight group. This model of altered chronic loading initiated changes in the material properties to the articular cartilage at the sites of increased load over 12-weeks that were consistent with early degenerative changes suggesting that increased tibio-femoral loading may be responsible for the alterations. This work begins to elucidate the chronic-load threshold and the time course of cartilage degeneration at different levels of altered loading.

Early revision for component malrotation in total knee arthroplasty.

Component malrotation may result in unsuccessful total knee arthroplasty. We asked whether revision improves function in patients with malrotated total knee arthroplasty components. We retrospectively reviewed 22 revision total knee arthroplasties performed for femoral and/or tibial component malrotation. Revision surgery was performed within 2 years of the primary arthroplasty in 81% of the cases (18 of 22) with the remainder within 5 years. Although all patients had pain, 32% of patients had associated instability and 36% of patients had poor range of motion. Average Knee Society Scores improved from 42 preoperatively to 77 postoperatively. Average Oxford Knee Scores improved from 38 preoperatively to 29 postoperatively. Although clinical and functional improvement was observed, these results are inferior to those for primary knee arthroplasty, and they emphasize the need for proper component rotational positioning during primary total knee arthroplasty. Internal component malrotation leads not only to patellofemoral problems, but also to difficulty in gap balancing and femoral component sizing, which may in turn lead to either poor range of motion or symptoms of knee instability.

Kneeling kinematics after total knee arthroplasty: anterior-posterior contact position of a standard and a high-flex tibial insert design.

Deep flexion activities including kneeling are desired by patients after total knee arthroplasty. This in vivo radiographic study sought to reveal the effect of tibial insert design on tibiofemoral kinematics during kneeling. One group of patients received standard posterior stabilized tibial inserts, whereas the other group received posterior stabilized tibial inserts (Flex inserts) that were designed to allow more flexion. The patients with the Flex inserts achieved greater range of motion without different tibiofemoral contact behavior.

A stem-allograft composite for femoral revision in total hip arthroplasty.

Femoral revision is difficult when the femoral canal exceeds 20 mm in diameter. For this subset of patients, we used a technique of cementing cortical allograft sleeves to a proximal ingrowth stem. The diameter of the allograft sleeves are matched to the diameter of the host femur. The stem-allograft construct provides initial stability with the opportunity for proximal bone ingrowth.

Femoral component sizing in total knee arthroplasty: size matched resection versus flexion space balancing.

Generally, 2 different methods are used to select femoral size. These can be termed "size-matched resection" and "flexion-space balancing." The purpose of this paper is to compare these 2 methods during 50 sequential total knee arthroplasty surgeries. The flexion-space-balancing method led to a smaller size selection than the size-matched-resection method in 28 (56%) knees. In the remaining 22 knees, the measurement methods led to the selection of the same size femoral component. The difference in measurement methods was significant (P<.05). The preoperative varus knees were more sensitive to the differences in measurement methods than the valgus knees (P<.05). A flexion space that is too small may adversely affect the clinical outcome of knee arthroplasty.

Tibial axis and patellar position relative to the femoral epicondylar axis during squatting.

A laboratory-based study was performed to describe the tibial axis and patellar position relative to the femoral epicondylar (FE) axis during squatting. During the squat, the angle between the tibial and FE axes averaged 90.5 degrees, and 66% of internal rotation of the tibia occurred before 15 degrees flexion. In the mid-sagittal plane of the femur, the patella followed a circular arc, and mediolateral patellar shift averaged 4.3 mm. These findings can be used as the basis for development of new total knee arthroplasty components that recreate normal patellofemoral kinematics, and may provide important guidelines for alignment of the tibial and femoral components. The perpendicular relationship between the tibial and the FE axes may be useful in locating the FE axis intraoperatively. The reduced mediolateral shift of the patella suggests that alignment of the femoral component with the FE axis will aid patellar tracking about a circular arc with small deviations in the medial-lateral direction.

Anatomic rotational relationships of the proximal tibia, distal femur, and patella: implications for rotational alignment in total knee arthroplasty.

The orientation of the femur, tibia, and patella are important considerations in total knee arthroplasty. Our goal was to describe the relationships between the femoral epicondylar (FE) axis, posterior femoral (PF) axis, posterior tibial (PT) axis, patellar (PAT) axis, and patellar ligament (PL). A secondary goal was to determine where the short axis of the tibial tray intersects the patellar ligament as a function of tibial component rotation. Thirty normal magnetic resonance imaging (MRI) scans were analyzed. Strong relationships were found between the FE and PAT axes (2 degrees +/- 3 degrees, r(2) = 0.73), and between the FE and PF axes (6 degrees +/- 2 degrees, r(2) = 0.77). When the tibial baseplate was aligned along the PT axis, 30% of the cases were in an ideal position. When the FE axis was used, 73% were ideal.

Tibiofemoral kinematic analysis of kneeling after total knee arthroplasty.

Some surgeons warn against kneeling after total knee arthroplasty (TKA), because limited clinical data exist. We describe the tibiofemoral contact position of TKA components during kneeling in vivo. Ten posterior-substituting (PS) and 10 cruciate-retaining (CR) designs were examined using a radiographic image-matching technique. Movement from standing to kneeling at 90 degrees produced different responses. CR knees translated anteriorly (medial, 4 +/- 4 mm; lateral, 2 +/- 6 mm). PS knees underwent little posterior translation (medial, 0.2 +/- 3 mm; lateral, 1 +/- 4 mm). Movement from 90 degrees to maximum flexion produced femoral posterior translation (CR medial, 5 +/- 4 mm; CR lateral, 5 +/- 4 mm; PS medial, 6 +/- 4 mm; PS lateral, 6 +/- 3 mm). The relationship between tibiofemoral contact position and flexion angle was more variable for CR (r2=.38) than for PS (r2=.64). Knee kinematics was similar to other deep-flexion weight-bearing activities.

Efforts to improve cementless femoral stems in THR: 2- to 5-year follow-up of a high-offset femoral stem with distal stem modification (Secur-Fit Plus).

A retrospective review of 81 sequential primary total hip arthroplasties using a cementless, high-offset femoral stem was performed. Follow-up was 24 to 60 months. The average age at the time of surgery was 54 years. The femoral bone types were: 36% Dorr A, 51% Dorr B, and 13% Dorr C. The mean postoperative Harris Hip Score was 95. The mean postoperative Oxford score was 17. Eighty-five percent had no clinical leg-length difference. All stems were radiographically stable. The stem features of hydroxyapatite coating on a rough circumferential titanium arc-deposit proximal surface in conjunction with distal flutes seem to provide immediate stability, making this implant clinically versatile. Potential benefits of increased offset include improved joint stability and avoidance of leg lengthening.