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Biomedical subjects

D M Kohn

Publications and source records attributed to D M Kohn.

7 recordsLinked to original sources
PubMed2000

Chondral lesions after arthroscopic meniscus repair using meniscus arrows.

Meniscus repair using bioabsorbable devices has become popular in the last few years. Good clinical results have been reported and few complications have been published. This report describes the case of a 37-year-old male patient with a lateral meniscus repair using 4 Meniscus Arrows (Bionx Implants, Blue Bell, PA). Postoperatively, repeated episodes of intra-articular effusions have occurred. A second-look arthroscopy 8 months after the reconstruction showed that the meniscus tear had not healed and revealed the presence of chondral damage corresponding to the location of the arrows in the posterior area of the lateral femoral condyle. Surgeons using the Meniscus Arrow should be aware of this possible postoperative complication.

Absorbable Implants↗
PubMed1999

Ligament graft initial fixation strength using biodegradable interference screws.

The objective of this study was to evaluate the initial fixation strength of three types of biodegradable interference screws [an Endo Fix, 7 x 25 mm polyglycolic acid, non-self-tapping (Acufex); a biodegradable interference screw, 7 x 23 mm poly-L-lactic acid, self-tapping (Arthrex); a Bioscrew, 7 x 25 mm poly-L-lactic acid, self-tapping (Linvatec)] in comparison to a titanium interference screw (Linvatec, 7 x 25 mm) in anterior cruciate ligament reconstruction using a bone-patellar tendon-bone graft. Porcine lower limbs were used. To control for specimen related bias, bone mineral density of each tibia was measured. All specimens were loaded to failure. Failure mode was determined by visual analysis. The maximum load to failure [mean (SD)] was 785 (87) N (titanium screw), 555 (60) N (Acufex), 592 (211) N (Arthrex), and 844 N (Linvatec). The primary fixation strength of the titanium screw and the Linvatec screw was significantly higher (p < 0.05) than the primary fixation strength of the Arthrex screw and the Acufex screw. There was no difference in bone mineral density between the groups. With respect to primary fixation strength, all biodegradable screws were strong enough to allow accelerated rehabilitation. From this point of view the biodegradable screws may be a reasonable alternative to titanium interference screws.

Absorbable Implants↗
PubMed1999

Resulting tensile forces in the human bone-patellar tendon-bone graft: direct force measurement in vitro.

The objective of this study was to measure the resultant force in the human bone-patellar tendon-bone graft after reconstruction of the anterior cruciate ligament under various conditions in vitro. Seven fresh-frozen cadaver lower extremities were used. Force measurement was made with a quartz force transducer mounted in a specially designed load cell. The effect of passive extension movement, quadriceps pull, varus torque, and valgus torque on the resultant force in the ligament were investigated. Passive extension of the joint generated a rapid increase of force in the graft between 30 degrees and 0 degrees of flexion, reaching its maximum (128+/-25 N) at full extension. When quadriceps pull was applied to extend the joint, resultant force increased at 50 degrees of flexion and reached its maximum (219+/-25 N) at full extension. Additional resistance applied to the level of the ankle joint generated an additional load of the graft. Increase of forces in the ligament resulted from both varus and valgus applied moments.

Aged↗
PubMedDate not supplied

Cortical versus cancellous interference fixation for bone-patellar tendon-bone grafts.

The objective of this study was to evaluate the initial fixation strength of a metal interference screw (9 x 25 mm; Arthrex, Naples, FL) with respect to its position relative to the bone plug in anterior cruciate ligament reconstruction using a bone-patellar tendon-bone graft. Porcine lower limbs were used. In group 1 (n = 20) the screw was placed adjacent to the cortex of the bone plug. In group 2 (n = 20) the screw was placed between the cancellous surfaces of the tibial tunnel and the bone plug. Specimens were loaded to failure using an universal material testing machine. Failure mode was defined by visual analysis of the specimens after loading. Primary fixation strength was not significantly different for both groups. Maximum force was 779 +/- 179 N (group 1, cortical side) and 743 +/- 143 N (group 2, cancellous side). There was a difference in failure modes. In group 1, testing resulted predominantly in tendon ruptures and bone plug fractures (70%). In group 2, bone plug pullouts were predominant (75%). From these data we conclude that the position of the screw relative to the bone plug influences failure mode but not the initial fixation strength.

Animals↗
PubMedDate not supplied

Cyclic testing of meniscal sutures.

Suturing the meniscus has become a standard procedure for repairable tears. Studies investigating the outcome of meniscal sutures report a considerable rate of failures. Regarding the indications, which have been extended to the avascular zones, and regarding some accelerated rehabilitation protocols, the need for further in vitro investigations has become obvious. The aim of this study was to compare different meniscal suture types (vertical and horizontal mattress sutures) and materials (absorbable monofilament PDS 2-0, and nonabsorbable braided Ethibond 2-0 [Ethicon, Somerville, NJ]) under standard and cyclic loading conditions. Testing was performed on medial porcine menisci. In group A, specimens were tested to failure at a cross-head speed of 50 mm/minute. In group B, cyclic testing (100 cycles) was performed first within different load intervals (5 to 20 N and 5 to 40 N). Finally, the specimens were loaded until failure. In both groups, the failure loads were recorded and the failure modes were analyzed. In group A, there was no difference between suture type or suture material, with a mean failure load of 60 N. The failure modes were significantly different for vertical (100% suture failure) and horizontal sutures (50% suture failure) (P <.0001). In group B, 13% of the sutures failed under cyclic loading (7 with 40-N load, 1 with 20-N load). The gap of the sutured tear that appeared within the first load cycles was broader in horizontal sutures (P <.001). During the first cycles, the thread cut through the meniscus tissue and disappeared from the surface (partial tissue failure). There was no difference according to suture material. The ultimate failure loads after cyclic loading did not differ from the values of group A. These results show that meniscal sutures may fail under repetitive loading conditions and that a gap appears between the meniscal margins within the first loading cycles irrespective of the suture type and suture material used. The appearance of the gap and suture disappearance on the meniscal surface because of partial tissue failures (which were more pronounced in the horizontal sutures) confirmed the superior resistance of meniscal tissue to vertical sutures.

Animals↗
PubMedDate not supplied

Comparison of initial fixation strength between biodegradable and metallic interference screws and a press-fit fixation technique in a porcine model.

The objective of this study was to evaluate the initial fixation strength of a biodegradable interference screw compared with press-fit fixation and a titanium interference screw in anterior cruciate ligament reconstruction using a bone-patellar tendon-bone graft. Porcine lower limbs were used. The specimens underwent 500 loading cycles between 60 and 250 N. This corresponds to loads in the graft during aggressive rehabilitation. Thereafter, intact specimens were loaded to failure. Failure mode was defined by visual analysis. Under cyclic loads none of the interference screw fixations failed. In the press-fit group (angle between load axis and tunnel axis 80 degrees), five specimens failed. The mean maximal load to failure was 945 N (+/- 87) for the titanium screw, 797 N (+/- 60) for the biodegradable screw, and 708 N (+/- 211) for the five press-fit specimens that did not fail during cyclic loading. With respect to primary fixation strength, biodegradable screws are a reasonable alternative to titanium interference screws. The press-fit fixation did not provide a secure fixation in all cases. Five press-fit specimens failed under cyclic loads comparable with those seen under conditions of accelerated rehabilitation.

Absorbable Implants↗