Improved accuracy of component alignment with the implementation of image-free navigation in total knee arthroplasty.

Accuracy of implant positioning and reconstruction of the mechanical leg axis are major requirements for achieving good long-term results in total knee arthroplasty (TKA). The purpose of the present study was to determine whether image-free computer navigation technology has the potential to improve the accuracy of component alignment in TKA cohorts of experienced surgeons immediately and constantly. One hundred patients with primary arthritis of the knee underwent the unilateral total knee arthroplasty. The cohort of 50 TKAs implanted with conventional instrumentation was directly followed by the cohort of the very first 50 computer-assisted TKAs. All surgeries were performed by two senior surgeons. All patients received the Zimmer NexGen total knee prosthesis (Zimmer Inc., Warsaw, IN, USA). There was no variability regarding surgeons or surgical technique, except for the use of the navigation system (StealthStation) Treon plus Medtronic Inc., Minnesota, MI, USA). Accuracy of implant positioning was measured on postoperative long-leg standing radiographs and standard lateral X-rays with regard to the valgus angle and the coronal and sagittal component angles. In addition, preoperative deformities of the mechanical leg axis, tourniquet time, age, and gender were correlated. Statistical analyses were performed using the SPSS 15.0 (SPSS Inc., Chicago, IL, USA) software package. Independent t-tests were used, with significance set at P < 0.05 (two-tailed) to compare differences in mean angular values and frontal mechanical alignment between the two cohorts. To compute the rate of optimally implanted prostheses between the two groups we used the chi(2) test. The average postoperative radiological frontal mechanical alignment was 1.88 degrees of varus (range 6.1 degrees of valgus-10.1 degrees of varus; SD 3.68 degrees ) in the conventional cohort and 0.28 degrees of varus (range 3.7 degrees -6.0 degrees of varus; SD 1.97 degrees ) in the navigated cohort. Including all criteria for optimal implant alignment, 16 cases (32%) in the conventional cohort and 31 cases (62%) in the navigated cohort have been implanted optimally. The average difference in tourniquet time was modest with additional 12.9 min in the navigated cohort compared to the conventional cohort. Our findings suggest that the experienced knee surgeons can improve immediately and constantly the accuracy of component orientation using an image-free computer-assisted navigation system in TKA. The computer-assisted technology has shown to be easy to use, safe, and efficient in routine knee replacement surgery. We believe that navigation is a key technology for various current and future surgical alignment topics and minimal-invasive lower limb surgery.

Biochemical, biomechanical and histological properties of osteoarthritic porcine knee cartilage: implications for osteochondral transplantation.

INTRODUCTION: Cartilage lesions of the knee joint are frequently observed during arthroscopy and when surgical intervention is required, osteochondral autograft procedures are an established method of treatment. Frequently lesions are located on the medial femoral condyle (MFC), and typical donor locations for osteochondral grafts include the medial and lateral patellar groove. This technique provides good results, even when the quality of cartilage transplanted from an osteoarthritic joint is doubtful. This study characterizes biological, biomechanical and histological properties of cartilage explants from the patellar groove harvested from osteoarthritic joints. MATERIALS AND METHODS: Cylindrical cartilage explants were harvested from the arthritic areas of the MFC as well as normal appearing regions of the medial and lateral patellar groove from porcine joints revealing various grades of osteoarthritis. Matrix synthesis rates were determined, and explants were investigated by mechanical testing and histology. RESULTS: Articular cartilage obtained from the typical donor areas of the medial and lateral patellar groove provided constant enhanced material properties, matrix synthesis rates and histological appearance compared to samples from the arthritic lesions of the MFC, even in joints with end-stage osteoarthritis of the MFC. No significant difference was found between patellar groove cartilage samples harvested from joints with different stages of osteoarthritis. CONCLUSION: Our findings demonstrate that healthy appearing cartilage from the patellar groove does not undergo significant alterations in material properties due to the arthritic milieu present in osteoarthritic joints. Accordingly these locations provide a source of functional tissue for transplant procedures even in joints with end-stage osteoarthritis.

Complications following internal fixation of unstable distal radius fracture with a palmar locking-plate.

OBJECTIVES: The increasing number of fixed-angle plate systems used to treat distal radius fractures carries with it the problem of determining the optimal fixation for unstable fractures. Our goal was to analyze the clinical and radiological outcomes of patients with displaced, unstable distal radius fractures treated with a palmar fixed-angle plate. DESIGN: Prospective protocol; multicenter clinical study; retrospective analysis. SETTING: Level 1 university trauma centers. PATIENTS: Over a mean 15-month period (range, 12 to 27 months), 141 consecutive patients were treated for an unstable dorsally displaced distal radius fracture of which 114 or 81% were followed for 1 year or longer. INTERVENTION: Open reduction and palmar internal fixation with a fixed-angle plate (2.4 mm LCP Distal Radius Plates; Synthes, Salzburg, Austria). Indication for surgical treatment was the inability to obtain or maintain fracture or articular alignment after initial closed reduction. MAIN OUTCOME MEASURES: In a follow-up period, which had to be longer than 12 months, objective and subjective functional results (active range of motion; strength; Disabilities of the Arm, Shoulder, and Hand (DASH) score; visual analog scale (VAS); Green and O'Brien Score) and radiographic assessment (palmar tilt, radial inclination, ulnar variance, fracture union) were assessed. Potentials for complications were given special attention. RESULTS: In the 114 patients followed for a minimum of 12 months, there were 21 men and 93 women with a mean age of 57 years (17 to 79 years). Fractures were classified according to the AO/ASIF classification system as type A2 (n = 39), A3 (n = 16), C1 (n = 24), C2 (n = 30), or C3 (n = 5). The modified Green and O'Brien Score revealed 31 excellent, 54 good, 23 fair, and 6 poor results. Active wrist motion averaged 54 degrees extension (82% as compared with the uninjured side) and 46 degrees flexion (72% as compared with the uninjured side). The average pronation was 81 degrees (95% as compared with the uninjured side), and the average supination was 82 degrees (95% as compared with the uninjured side). Mean grip strength at final follow-up was 70% of the uninjured side. Low residual pain values in the wrist were demonstrated: 81 patients (71%) were pain free, 17 patients (15%) had mild pain, 10 patients (9%) had moderate pain, and 6 patients (5%) had severe pain. The DASH score averaged 13 points (range, 0 to 39 points). Fracture union was achieved in all patients. A mean loss of palmar tilt of 3.4 degrees (range, 0 to 8 degrees), radial inclination of 0.4 degrees (range 0 to 2 degrees), and of the ulnar variance of 1.2 mm (range, 0 to 6 mm) was measured. The overall complication rate was 27% (31/114). The most frequent problems were flexor and extensor tendon irritation (57% of the total number of complications), including 2 ruptures of the flexor pollicis longus tendon, 2 ruptures of the extensor pollicis longus tendon, 4 cases of extensor tendon tenosynovitis, and 9 cases of flexor tendon tenosynovitis. Carpal tunnel syndrome was observed in 3 patients, and complex regional pain syndrome occurred in 5 patients. In 2 cases, loosening of a single screw was seen. Delayed fracture union occurred in 3 patients, and intraoperative intraarticular screw displacement was recognized in 1 patient. Neither clinical outcome nor complication rate were dependent on fracture type (intraarticular versus extraarticular). CONCLUSION: Fixation of unstable dorsally displaced distal radius fractures with a fixed angle plate provides sufficient stability with minimal loss of reduction. Nevertheless, very distal palmar plate position can interfere with the flexor tendon system, too long screws can penetrate the extensor compartments, and distal screws in comminuted fracture patterns can cut through the subchondral bone and penetrate into the radiocarpal joint. Mindful of these problems, we consider that the complex fracture pattern of an unstable distal radius fracture cannot be treated by a single plate system and approach.

Regional differences in prostaglandin E2 and nitric oxide production in the knee meniscus in response to dynamic compression.

Injury or loss of the knee meniscus is associated with altered joint stresses that lead to progressive joint degeneration. The goal of this study was to determine if dynamic mechanical compression influences the production of inflammatory mediators by meniscal cells. Dynamic compression increased prostaglandin E2 (PGE(2)) and nitric oxide (NO) production over a range of stress magnitudes (0.0125-0.5 MPa) in a manner that depended on stress magnitude and zone of tissue origin. Inner zone explants showed greater increases in PGE(2) and NO production as compared to outer zone explants. Meniscal tissue expressed NOS2 and NOS3 protein, but not NOS1. Mechanically induced NO production was blocked by NOS inhibitors, and the non-selective NOS inhibitor L-NMMA augmented PGE(2) production in the outer zone only. These findings suggest that the meniscus may serve as an intra-articular source of pro-inflammatory mediators, and that alterations in the magnitude or distribution of joint loading could significantly influence the production of these mediators in vivo.

Repair response of the inner and outer regions of the porcine meniscus in vitro.

BACKGROUND: The menisci are essential intra-articular structures that contribute to knee function, and meniscal injury or loss is associated with joint degeneration. Tears of the outer vascularized zone have a greater potential for repair than do tears in the inner avascular region. OBJECTIVE AND HYPOTHESIS: Develop an in vitro explant model to examine the hypothesis that differences exist in the intrinsic repair response between the outer and inner region of the meniscus. STUDY DESIGN: Controlled laboratory study. METHODS: Cylindrical explants were harvested from the outer one third and inner two thirds of medial porcine menisci. To simulate a full-thickness defect, a central core was removed and reinserted immediately. Explants were cultured for 2, 4, or 6 weeks, and meniscal healing was investigated using mechanical testing, histologic analysis, and fluorescence confocal microscopy. RESULTS: Over the 6-week culture period, meniscal explants exhibited migration of cells into the repair site, followed by increased tissue formation that bridged the interface. The repair strength increased significantly over time, with no differences between the 2 regions. CONCLUSION: The findings show that explants from the avascular inner zone and vascular outer zone of the meniscus exhibit similar healing potential and repair strength in vitro. CLINICAL RELEVANCE: These findings support the hypothesis that the regional differences in meniscal repair observed clinically are owed to the additional vascular supply of the outer meniscus rather than intrinsic differences between the extracellular matrix and cells from these 2 areas.

Biaxial strain effects on cells from the inner and outer regions of the meniscus.

During knee joint loading, the fibrocartilaginous menisci experience significant spatial variations in mechanical stimuli. Meniscus cells also exhibit significant variations in biosynthesis and gene expression depending on their location within the tissue. These metabolic patterns are consistent with a more chondrocytic phenotype for cells located within the avascular inner two-thirds compared with a more fibroblastic phenotype for cells within the vascularized outer periphery. The spatial distribution of cell biosynthesis and gene expression patterns within the meniscus suggest that cells may exhibit intrinsically different responses to mechanical stimuli. The objective of our study was to test for intrinsic differences in the responsiveness of these meniscus cell populations to an equivalent mechanical stimulus. Cellular biosynthesis and gene expression for extracellular matrix proteins in isolated inner and outer meniscus cells in monolayer were quantified following cyclic biaxial stretch. The results demonstrate that inner and outer meniscus cells exhibit significant differences in matrix biosynthesis and gene expression regardless of stretching condition. Both inner and outer meniscus cells responded to stretch with increased nitric oxide production and total protein synthesis. The results suggest that inner and outer meniscus cells may respond similarly to biaxial stretch in vitro with measures of biosynthesis and gene expression.

The effects of cyclic mechanical strain and tumor necrosis factor alpha on the response of cells of the meniscus.

OBJECTIVES: Cells of the knee meniscus respond to changes in their biochemical and biomechanical environments with alterations in the biosynthesis of matrix constituents and inflammatory mediators. Tumor necrosis factor alpha (TNF-alpha) is a pro-inflammatory cytokine that is involved in the pathogenesis of both osteoarthritis and rheumatoid arthritis, but its influence on meniscal physiology or mechanobiology is not fully understood. The objectives of this study were to examine the hypothesis that cyclic mechanical strain of meniscal cells modulates the biosynthesis of matrix macromolecules and pro-inflammatory mediators, and to determine if this response is altered by TNF-alpha. METHODS: Cells were isolated from the inner two-thirds of porcine medial menisci and subjected to biaxial tensile strain of 5-15% at a frequency of 0.5Hz. The synthesis of proteoglycan, protein, nitric oxide (NO), and prostaglandin E(2) were determined. RESULTS: Cyclic tensile strain increased the production of nitric oxide through the upregulation of nitric oxide synthase 2 (NOS2) and also increased synthesis rates of prostaglandin E(2), proteoglycan, and total protein in a manner that depended on strain magnitude. TNF-alpha increased the production of NO and total protein, but inhibited proteoglycan synthesis rates. TNF-alpha prevented the mechanical stimulation of proteoglycan synthesis, and this effect was not dependent on NOS2. CONCLUSIONS: These findings indicate that pro-inflammatory cytokines can modulate the responses of meniscal cells to mechanical signals, suggesting that both biomechanical and inflammatory factors could contribute to the progression of joint disease as a consequence of altered loading of the meniscus.