Femoral neck fracture after removal of the standard gamma interlocking nail: a cadaveric study to determine factors influencing the biomechanical properties of the proximal femur.

We retrospectively analyzed 1334 patients who were implanted standard gamma interlocking nails (SGN) to stabilize trochanteric femoral fractures over the years 1992-1998. Reoperation to remove the nails was performed in 37 patients, in 9 of them purely because of pain. Three out of these 9 patients with removed SGN suffered femoral neck fractures in the early postoperative course after having been mobilized to full weight-bearing capacity. This complication was not observed with other implant systems and, considering the notoriously high complication rate of femoral neck fractures, severely reduces the value of the SGN concept per se. These findings in combination with other known shortcomings of SGNs prompted us to conduct an experimental study on the fracture force of excavated femurs addressing the hypothesis that the specific design of the SGN is responsible for the occurrence of fatigue fractures of the femoral neck. Eighteen matched pairs of fresh human cadaveric proximal femurs, which were treated by insertion and removal of (i) SGNs or (ii) dynamic hip screws (DHS) or (iii) by excavation in the absence of an implant, were subjected to incremental loading cycles and compared to the untreated contralateral femurs. Overall, the fracture force was found to be significantly lower among the treated than among the untreated bones. However, the fracture force required after removal of the DHS system was still significantly higher than for SGN or excavation alone. In this way, our findings demonstrate that removing relatively big implants such as SGN can cause serious complications such as femoral neck fractures. We therefore recommend to leave this type of device in place even after fracture healing except in cases of deep and chronic infection.

Comparison of femoral and tibial pullout forces in bone-patellar tendon-bone anterior cruciate ligament reconstructions with a new interference fixation device.

Interference screws have become the standard method for fixing bone-patellar tendon-bone (BPTB) grafts. To avoid the inherent pitfalls and complications of interference screws, a 28-mm long and from 5 to 7 mm spreadable metal bolt with nontapping threads was developed for this study. The technical applicability and biomechanical characteristics of this new BPTB interference fixation device were investigated by dissection or tensile testing of 48 cadaveric knee specimens from young donors. No problems occurred with respect to bone plug anchoring during insertion of the spreading bolts. The clinically important linear load was 920+/-283 N for the femoral and 635+/-247 N for the tibial fixation site. Bone plug pullout was the mode of failure in all specimens. The results of this study indicate that the spreading bolt is a reasonable alternative to interference screws.

Load sharing in augmented anterior cruciate ligament repair: a mathematical analysis based on in vitro measurements.

OBJECTIVE: To quantify the stress on a reinserted anterior cruciate ligament (ACL) we studied the load sharing between the ACL and a 3.7 mm polyethylene terephthalate (PET) band in 10 knees of fresh human cadavers. DESIGN: The load sharing between the Marshall sutures-ACL complex and the PET band and between the ACL and the PET band was calculated by means of a mathematical model. BACKGROUND: Augmentation of a reinserted ACL with a synthetic band is an accepted treatment for a ruptured ACL. METHODS: After transsecting the ACL at its femoral origin and reinserting it with four sutures using the Marshall technique we augmented it with the PET band. The augmentation device was inserted by the through-the-condyle (TTC) procedure and attached without preload to the femoral and the tibial condyle with 4 mm staples. Then the length of the ACL, the lengths of the Marshall sutures, the partial lengths and the angles between the different directions, and the adherence-friction force of the PET band were measured. RESULTS: In the beginning the Marshall sutures-ACL complex takes over 40% of an externally applied load and the PET band 60%. After the hypothetical ACL healing phase the PET band takes over 27% and the ACL 73% of the load. CONCLUSIONS: An external force of 40 N acting on the knee will therefore lead to an elongation of the Marshall sutures-ACL complex and result in movement of the proximal end of the ACL away from the femoral condyle of at least 0.5 mm, which is highly undesirable in the early postoperative healing phase.

[Alloplastic augmented femoral reinserted anterior cruciate liganent. Value of 2 channel augmentation for postoperative rehabilitation]. / Alloplastisch augmentiertes femoral reinseriertes vorderes kreuzband. Bedeutung der zweikanalaugmentation fuer die postoperative rehabilitation.

The rupture of the anterior cruciate ligament (ACL) near its femoral origin is a common injury of the knee and can lead to lesions of the meniscus due to instability and to early gonarthrosis. One procedure applied in current orthopaedic practice to prevent such impairment of knee joint function is ACL repair reinforced with a synthetic intraarticular ligament. In this study we used twelve knees of cadavers and after sectioning the ACL in each repaired it according the Marshall technique with USP 1 PDS II sutures. We augmented the repair in each case with a 3-mm PET (Trevira hochfest) band inserted by the through-the-condyle (TTC) procedure and attached without preload to the femoral and tibial condyle with a 4-mm staple. We then measured the length of the ACL, the length of the Marshall sutures-ACL complex, the partial lengths, and the deviation angles and adherence-friction force of the 3-mm PET augmentation device, and applied the law of Hooke to calculate the load-sharing between the USP 1 PDS II sutures-ACL complex and the 3-mm PET band and between the ACL and the 3-mm PET band, respectively. We also evaluated the load on the femoral and the tibial fixation of the augmentation device. The results showed that the 3-mm PET band took over 60% of an externally applied load on the knee during the hypothetic period of ACL healing and 27% of the force acting on the knee thereafter. It was calculated that a maximum of 75% of the load taken over by the augmentation device was at the tibial staple and only up to 45% of the force at the femoral one. With due consideration for the requirement for absolute protection ("stress shielding") of the healing ACL but also for the aim of early postoperative accelerated functional rehabilitation without casts, splints or other restrictions of joint movement, we believe that a pretensioned 3-mm PET band is the best choice, since augmentation without preload cannot fulfil these requirements.