Search PubMed⌕ Search

Biomedical subjects

Jack Farr

Publications and source records attributed to Jack Farr.

11 recordsLinked to original sources
PubMed2006

Tibiofemoral contact mechanics after serial medial meniscectomies in the human cadaveric knee.

BACKGROUND: There is no consensus regarding the extent of meniscectomy leading to deleterious effects on tibiofemoral contact mechanics. HYPOTHESIS: The meniscus aids in optimizing tibiofemoral contact mechanics, increasing contact area, and decreasing contact stress. STUDY DESIGN: Controlled laboratory study. METHODS: Twelve fresh-frozen human cadaveric knees each underwent 15 separate testing conditions-5 serial 20-mm posterior medial meniscectomy conditions (intact, 50% radial width, 75% radial width, segmental, and total meniscectomy) at 3 flexion angles (0 degrees , 30 degrees , and 60 degrees )-under an 1800-N axial load. Tekscan sensors were used to measure total force and medial force, contact area, mean contact stress, and peak contact stress. RESULTS: All posterior medial meniscectomy conditions resulted in significantly decreased contact areas and increased mean and peak contact stresses compared with the intact state (P < .05). The changes in contact mechanics after segmental and total posterior medial meniscectomies were not statistically different (P > .05). Incremental changes in contact area and mean contact stress increased as more peripheral portions of the medial meniscus were removed, whereas peak contact stresses exhibited similar incremental changes throughout all meniscectomy conditions. CONCLUSIONS: The meniscus is a crucial load-bearing structure, optimizing contact area and minimizing contact stress. Loss of hoop tension (ie, segmental meniscectomy) is equivalent to total meniscectomy in load-bearing terms. The peripheral portion of the medial meniscus provides a greater contribution to increasing contact areas and decreasing mean contact stresses than does the central portion, whereas peak contact stresses increase proportionally to the amount of meniscus removed. CLINICAL RELEVANCE: Because the degree of meniscectomy leading to clinically significant outcomes is unknown, a prudent strategy is to preserve the greatest amount of meniscus possible.

Adult↗
PubMed2006

Evaluation of small intestinal submucosa grafts for meniscal regeneration in a clinically relevant posterior meniscectomy model in dogs.

Large meniscal defects are a common problem for which treatment options are limited. Successful meniscal regeneration has been achieved by using grafts of small intestinal submucosa in posterior, vascular meniscal defects in a dog model. This study investigates the long-term effects of a tibial tunnel fixation technique and a clinically based meniscectomy defect on meniscal regeneration using this model. Eight mongrel dogs underwent medial arthrotomy and partial meniscectomy. The dogs were divided into groups based on defect treatment: small intestinal submucosa (n = 4) or meniscectomy (n = 4). Dogs were scored for lameness by subjective scoring postoperatively, sacrificed at 6 months, and assessed for articular cartilage damage, gross and histologic appearance of the operated meniscus, amount of new tissue in the defect, and relative compressive stiffness of articular cartilage. Dogs in the meniscectomy group were significantly (P = .002) more lame than dogs treated with small intestinal submucosa. Small intestinal submucosa-treated joints had significantly (P = .01) less articular cartilage damage than meniscectomy joints. Small intestinal submucosa meniscal implants resulted in production of meniscal-like replacement tissue, which was consistently superior to meniscectomy in amount, type, and integration of new tissue, chondroprotection, and limb function during the study period. Small intestinal submucosa implants may be useful for treatment of large posterior vascular meniscal defects in humans. The tibial tunnel technique used for fixation may have clinical advantages and therefore warrants further investigation.

Animals↗
PubMed2006

Treatment of chondral defects in the patellofemoral joint.

Patellofemoral disease is one of the most controversial management issues in orthopedic surgery. Nonoperative management as a prerequisite first line treatment is successful in the majority of cases. However, a small subset of patients with persistent pain after adequate rehabilitation will be potential candidates for surgical intervention. Careful assessment of the underlying pathomechanics is critical for a successful outcome; these include malalignment of the extensor mechanism, trochlear dysplasia, soft-tissue imbalance, and chondral damage. As the pathology is multifactorial, the planning and treatment must be multifaceted. With careful patient selection, the options of titrated limited lateral release, restoration of MPFL function, tibial tubercle osteotomy, cartilage repair, and patellofemoral resurfacing provide improved functionality and pain relief for the young patient suffering from patellofemoral pain.

Algorithms↗
PubMed2006

Response surface optimization for joint contact model evaluation.

When optimization is used to evaluate a joint contact model's ability to reproduce experimental measurements, the high computational cost of repeated contact analysis can be a limiting factor. This paper presents a computationally-efficient response surface optimization methodology to address this limitation. Quadratic response surfaces were fit to contact quantities (contact force, maximum pressure, average pressure, and contact area) predicted by a discrete element contact model of the tibiofemoral joint for various combinations of material modulus and relative bone pose (i.e., position and orientation). The response surfaces were then used as surrogates for costly contact analyses in optimizations that minimized differences between measured and predicted contact quantities. The methodology was evaluated theoretically using six sets of synthetic (i.e., computer-generated) contact data, and practically using one set of experimental contact data. For the synthetic cases, the response surface optimizations recovered all contact quantities to within 3.4% error. For the experimental case, they matched all contact quantities to within 6.3% error except for maximum contact pressure, which was in error by up to 50%. Response surface optimization provides rapid evaluation of joint contact models within a limited range of relative bone poses and can help identify potential weaknesses in contact model formulation and/or experimental data quality.

Bone Screws↗
PubMed2006

Pulsed electrical stimulation in patients with osteoarthritis of the knee: follow up in 288 patients who had failed non-operative therapy.

BACKGROUND: Optimized pulsed electrical stimulation (PES) regulates chondrocyte genes, enhances production of cartilage matrix materials, and inhibits production of matrix catabolic factors. METHODS: This prospective, cohort study examined the use of a PES device in treatment of knee osteoarthritis (OA) in patients who had failed non-operative therapy. Primary outcome measures were patient and physician global evaluation, and patient assessment of knee pain. RESULTS: This study included 288 (95 men, 193 women) patients who used the device from 16 to more than 600 days (mean: 889 hours). Improvement in all efficacy variables (p < 0.001) occurred. A dose-response relationship between effect size and hours of usage was observed as cumulative time increased to more than 750 hours. Improvement in patient or physician global occurred in 59.0% of patients who used it less than 750 hours, and for 73.0% of those who used it more than 750 hours. An economic analysis of a sub-group of patients showed that 45.3% reduced nonsteroidal anti-inflammatory drug (NSAID) use by 50.0% or more. CONCLUSIONS: A highly optimized PES device successfully attenuated knee OA symptoms in patients who had failed non-surgical therapy. Less than 250 hours of therapy provided relief, but improvement increased in a dose-response manner after 750 hours of cumulative use.

Adult↗
PubMed2005

Trochlear contact pressures after anteromedialization of the tibial tubercle.

BACKGROUND: Anteromedialization is recommended for cartilage restoration of patellofemoral defects, with the presumption that it decreases contact pressures across the trochlea. No study has evaluated pressures on the trochlear side of the patellofemoral joint after anteromedialization of the tibial tubercle. HYPOTHESIS: Anteromedialization of the tibial tubercle decreases contact pressure across the trochlea. STUDY DESIGN: Controlled laboratory study. METHODS: Ten cadaveric knees were tested by placing an electroresistive pressure sensor on the femoral side of the patellofemoral joint. A validated model of nonweightbearing resisted extension was simulated by loading the extensor mechanism at 89.1 N and 178.2 N. Knees were tested 3 times per load at 30 degrees , 60 degrees , 90 degrees , and 105 degrees . The center of force and pressure across the patellofemoral articulation were compared before and after a reproducible and consistent anteromedialization. RESULTS: The mean center of force shifted medially after anteromedialization at 89.1 N and 178.2 N. At 89.1 N, the mean total contact pressure decreased significantly (P < .05) at all angles, and at 178.2 N, it decreased significantly at 30 degrees , 60 degrees , and 90 degrees of knee flexion. The mean lateral trochlear contact pressure decreased significantly (P < .05) at all flexion angles at both 89.1 N and 178.2 N. The mean central trochlear contact pressure decreased significantly (P < .05) at 30 degrees with the 89.1-N and 178.2-N loads but increased significantly (P < .05) at 90 degrees with the 89.1-N load. The mean medial trochlear contact pressure increased significantly (P < .05) at all flexion angles at 89.1 N and 178.2 N. CONCLUSION: Anteromedialization shifts the contact force to the medial trochlea and decreases the mean total contact pressure. CLINICAL RELEVANCE: Anteromedialization decreases the mean total contact pressure while shifting contact pressure toward the medial trochlea. This study suggests that anteromedialization is appropriate for unloading the lateral trochlea. However, this procedure appears to have minimal benefit on central chondral defects, and it may actually increase the load in patients with medial defects.

Adult↗
PubMed2005

A prospective randomized comparison of bioabsorbable and titanium anterior cruciate ligament interference screws.

PURPOSE: To compare the Phantom bioabsorbable polymer interference screw (DePuy, Warsaw, IN) with a titanium metal interference screw when used in fixation of femoral and tibial bone blocks in central third bone-patellar tendon-bone autograft anterior cruciate ligament (ACL) reconstructions. TYPE OF STUDY: Multicentered prospective randomized study. METHODS: Two surgeons performed primary ACL reconstructions at different locations. Preoperatively, the patients were randomly assigned. One group received a titanium cannulated interference screw. The second group received the cannulated poly-L-lactic bioabsorbable Phantom screw. Data included subjective evaluation of activity level and International Knee Documentation Committee scores. Objective measures were made using the KT-1000 arthrometer (MedMetric, San Diego, CA), range of motion, presence of effusions, and complications intraoperatively or postoperatively. Measurements were made at 1 year and 2 years. Radiographic evaluation was carried out at least 2 years from the initial surgical date and interpreted by 2 independent orthopaedic surgeons. RESULTS: At the 1-year follow-up (N = 97), pain was reported more during moderate activity in the Phantom screw group (6) compared with the titanium screw group (0) (P = .03). No statistical difference between range of motion (P = .45), activity level (P = .83), swelling with activity (P = .95), partial (P = .13) or full (P = .31) giving way, knee effusions (P = .33), or KT-1000 side-to-side difference (P = .53) were found. At the 2-year follow-up (N = 65), more subjects (18) in the Phantom interference screw group reported activity levels in the strenuous category compared with those in the titanium interference screws (7) group (P = .02). No differences were reported with respect to pain (P = .97), effusion (P = .17), partial (P = .28) or full (P = .27) giving way, swelling with activity (P = .21), range of motion ( P = .64), or KT-1000 side-to-side difference (P = .96). Radiographic inspection showed no change in bone plug position, osteolysis, adverse effect, or complication caused by the bioabsorbable material. Some evidence of tunnel widening was seen in both groups. CONCLUSIONS: Use of a poly-L-lactic bioabsorbable interference screw can provide clinical results equal to that of a metal interference screw for fixation of a central third bone-patellar tendon-bone graft in ACL reconstruction. LEVEL OF EVIDENCE: Level II, therapeutic.

Absorbable Implants↗
PubMed2004

Allograft interference screw fixation in meniscus transplantation.

Allograft meniscus transplantation is indicated to restore proper knee biomechanics and prevent subsequent articular degeneration in patients with a meniscus-deficient knee. A variety of techniques for fixation of meniscal transplants exist, with some techniques using soft-tissue fixation of the meniscal horns and others using bony fixation. The authors present a technique of meniscus transplantation using a tibial slot with allograft interference screw fixation. We have had excellent early results with this technique and believe that a cortical allograft interference screw reliably maintains the anatomic position of the meniscal attachments that are critical to the biomechanics and functional outcome of meniscus transplantation.

Arthroscopy↗