Background: The hamstring tendon graft has become increasingly popular in anterior cruciate ligament (ACL) reconstruction because of low donor-site morbidity. However, the tibial fixation is considered difficult, partly because of low tibial mineral bone density. Therefore, we tested whether preparation of the tibial tunnel with compaction by serial dilation provided a stronger anchorage of the graft-fixation-device complex compared to traditional extraction drilling of the tibial tunnel.
Prior to and during these investigations we became aware that the knee laxity measurements using the Telos Stress Device (TSD) and radio stereometric analysis (RSA) were difficult to reproduce. We therefore designed a new standardized protocol (NSP) on how to apply the TSD aimed at ensuring (1) a reliable positioning of the TSD on the patients` extremity that would result in (2) precise knee laxity measurements.
Matherials and methods
Study 1: In twenty bovine tibiae, the bone tunnels were created with either extraction drilling (group ED) or compaction by serial dilation (group SD). Twenty bovine digital extensor tendons were fixated in the bone tunnel with an Intrafix device. The graft-fixation-device complexes were mounted in a hydraulic test machine. The fixation strength was evaluated after cyclic loading.
Study 2: Part study 1: One investigator followed the official company instructions on how to apply the TSD. Another investigator followed the NSP. The TSD was applied to the knee of 30 healthy persons. Double measurements were carried out. The position of the stress arms of the TSD was marked following each measurement. The reliability of each protocol was calculated as the difference in length between the first and second markings.
Part study 2:The NSP for the TSD was then used in a clinical study. Thirty-five patients underwent ACL reconstruction. Double measurements of knee laxity by RSA were performed at a 3-month follow-up.
Study 3: 40 patients (22 males and 18 females) undergoing ACL reconstruction were randomized to either extraction drilling (group ED) or compaction by serial dilation (group SD) of the tibial tunnel. The hamstring graft was anchored with a Retrobutton® and a supplementary interference screw (Arthrex®) in the femur and a Delta interference screw (Arthrex®) in the tibia. Tantalum beads were placed in both the proximal part of the tibia and distal part of the femur. Beads were placed in the hamstring graft at the fixation sites as well. RSA were performed post-operatively and again after 6, 12 and 24 weeks. The ACL-reconstructed knee was stressed with a TSD. Migration of the tantalum markers in the graft was measured in reference to the bone markers in the tibia and femur. Knee laxity was assessed at every follow by measuring the relation of the tibial bone markers to the femoral bone markers in both the anterior and the posterior stress position.
Results
Study 1: The difference between group SD and the group ED ranged from a mean slippage of 0 mm at 70-220 N, to a mean slippage of 0.1 mm at 70-520 N. We found no significant difference in slippage of the graft-fixation-device complex after 1600 cycles.
Study 2: Part study 1: The precision of positioning the stress arms of the TSD was improved at all marking sites using the NSP compared with the original company instructions. Part study 2: The double measurements of the knee laxity in the clinical study using the NSP resulted in a mean difference of 0.0 mm and a prediction interval of ±5.2 mm.
Study 3: Six patients (3 males and 3 females) were excluded during follow-up, which resulted in 17 patients in group ED (mean age: 32.5 years (range: 20 – 50)) and 17 patients in group SD (mean age: 32.0 years (range: 20 – 49)). The mean migration of the graft at the tibial fixation site after 3 months was 1.3 (sd 0.6) mm, in group ED and 0.8 (sd 0.5) mm in group (P = 0.02). The knee laxity after 3 months was 13.0 (sd 4.0) mm in group ED and 10.9 (sd 3.1) mm in group SD (P=0.09).
Conclusion:
Study 1 failed to show a significant difference between group SD and group ED. In contrast study 3 found a significant smaller mean migration of the hamstring graft at the tibial fixation site in group SD compared to group ED. No significant difference in stress radiographic knee laxity was found between the 2 groups.
Even though the NSP improved the positioning of the TSD on the patients’ extremities, the combination of the TSD and RSA was not able to provide acceptable knee laxity measurements in a clinical setting compared with other devices on the market.
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