Intra-articular remodelling of hamstring tendon grafts after anterior cruciate ligament reconstruction.

PURPOSE: A summary is provided on the existing knowledge about the specific healing phases of the intra-articular hamstring tendon graft used for ACL reconstruction. Differences between human and animal in vivo studies are explained, and implications for the postoperative time period are laid out. METHODS: A systematic review of the existing literature was performed on the topic of tendon remodelling of hamstring grafts in ACL reconstruction using Medline database. Publications between 1982 and 2012 were included. Special focus was directed on in vivo human and animal studies analysing intra-articular free tendon graft remodelling. RESULTS: Animal and human in vitro and vivo researches have demonstrated three characteristic stages of graft healing after ACL reconstruction: an early graft healing phase with central graft necrosis and hypocellularity and no detectable revascularization of the graft tissue, followed by a phase of proliferation, the time of most intensive remodelling and revascularization and finally, a ligamentization phase with characteristic restructuring of the graft towards the properties of the intact ACL. However, a full restoration of either the biological or biomechanical properties of the intact ACL is not achieved. CONCLUSION: Significant knowledge on human cruciate ligament remodelling has been added in the understanding of the processes during the course of graft healing. Most importantly, the remodelling process in humans is prolonged compared to animal studies. While today´s rehabilitation protocols are often extrapolated from findings of animal in vivo healing studies, current findings of human in vivo healing studies might require new post-operative regimens following hamstring ACL reconstruction.

Remodelling of human hamstring autografts after anterior cruciate ligament reconstruction.

PURPOSE: Histological analysis of the remodelling process of human hamstring tendon (HT) grafts after standardized anterior cruciate ligament reconstruction (ACLR) with an accelerated rehabilitation protocol. METHODS: Sixty-seven patients underwent retrieval of mid-substance biopsies after clinically successful hamstring autograft ACLR. Samples were allocated to one of three groups depending on the time point of retrieval: group 1 (6-12 months; n = 15), group 2 (13-24 months; n = 16) and group 3 (>24 months; n = 11). Biopsies from native HT (n = 17) and ACL (n = 8) served as controls. Cellular density, vascular density and myofibroblast density and collagen fibril alignment were analysed by haematoxylin-eosin, Masson-Goldner-Trichrom and immunohistochemical staining protocols. RESULTS: Compared with native HT (330.4/mm²), total cell number was increased in groups 1-3 (Group 1 = 482.0/mm² (P = 0.036); group 2 = 850.9/mm² (P = 0.005); and group 3 = 595.6/mm² (P = 0.043). There were no significant differences between the groups for vessel density. Myofibroblast density was higher in group 2 (199.6/mm²) compared with native HT (1.9/mm², P = 0.014). Collagen orientation was irregular up to 12 months. Thereafter, collagen orientation became more regular, adapting to, but not fully restoring, the appearance of the intact ACL. For the first 12 months, cells were predominantly ovoid. Ensuing cell morphology changed to spindle shaped in group 2 and predominantly narrow long cells over 24 months. CONCLUSION: Human hamstring grafts showed typical stages of graft remodelling, which was not complete up to 2 years after ACLR. The remodelling process in humans was prolonged compared with the results obtained in several animal studies. LEVEL OF EVIDENCE: Case-control study, Level III.

Remodeling of ACL allografts is inhibited by peracetic acid sterilization.

Sterilization of allografts for anterior cruciate ligament (ACL) reconstruction has become an important prerequisite to prevent disease transmission. However, current sterilization techniques impair the biological or mechanical properties of such treated grafts. Peracetic acid (PAA) has been successfully used to sterilize bone allografts without these disadvantages and does not impair the mechanical properties of soft tissue grafts in vitro. We asked whether PAA sterilization would influence recellularization, restoration of crimp length and pattern, and revascularization of ACL grafts during early healing. We used an in vivo sheep model for open ACL reconstruction. We also correlated the histologic findings with the restoration of anteroposterior stability and structural properties during load-to-failure testing. PAA slowed remodeling activity at 6 and 12 weeks compared to nonsterilized allografts and autografts. The mechanical properties of PAA grafts were also reduced compared to these control groups at both time points. We conclude PAA sterilization currently should not be used to sterilize soft tissue grafts typically used in ACL reconstruction.

Fresh-frozen free-tendon allografts versus autografts in anterior cruciate ligament reconstruction: delayed remodeling and inferior mechanical function during long-term healing in sheep.

PURPOSE: The objective of this study was to investigate the biologic healing and restoration of the mechanical function of a free soft tissue autograft and compare these to an identical nonsterilized fresh frozen allograft for anterior cruciate ligament (ACL) reconstruction in an in vivo sheep model. METHODS: Forty-eight merino sheep received either an allograft or autograft ACL reconstruction with a long flexor tendon. Each group was analyzed at 6, 12, and 52 weeks for descriptive analysis of histologic changes and quantitative analysis of recellularization, revascularization, and mechanical function. RESULTS: Recellularization and revascularization was significantly delayed at 6 and 12 weeks of healing, while at 52 weeks, differences had become less distinct. Overall remodeling had not been completed compared to the intact ACL. Significantly lower structural and mechanical properties and anterior-posterior laxity were found at 52 weeks for allografts, with no differences at the early healing time points. CONCLUSIONS: Allograft remodeling is delayed in ACL reconstruction and resulted in reduced long-term stability and mechanical function compared to autologous ACL reconstruction. CLINICAL RELEVANCE: Caution should be used with early full-weight bearing after allograft ACL reconstruction, because remodeling is delayed and long-term stability might be affected. Clinical studies should be warranted to examine the impact of varying rehabilitation protocols on long-term outcome.

Arthroscopic medial retinacular repair after patellar dislocation with and without underlying trochlear dysplasia: a preliminary report.

PURPOSE: This study was undertaken to evaluate the influence of underlying trochlear dysplasia (TD) on clinical outcomes of arthroscopic medial retinacular repair. METHODS: Between January 2000 and October 2004, a total of 91 patients underwent arthroscopic medial retinacular repair. Inclusion criteria for this study included an arthroscopic medial retinacular repair, a follow-up time of 12 months, and trochlear grading based on axial computed tomography (CT) scans (n = 48). TD, if present, was graded as types A through D, and patients were separated into group I (no or low-grade type A TD) and group II (types B through D TD). Redislocation was recorded, and Tegner, Lysholm, and International Knee Documentation Committee (IKDC) scores were determined. RESULTS: No or grade A TD was detected in 26 knees (group I), and TD of grade B or C was found in 22 knees (group II). Type D TD was not observed. At a follow-up time of 12 months, 4 redislocations had been noted, all belonging to group II. Neither the Tegner nor the Lysholm score reached preinjury levels, but in a comparison with preoperative status, we could find a significant increase in all scores in both groups. Group I reached a significantly better postoperative outcome than was attained by group II. CONCLUSIONS: Arthroscopic repair of the medial retinaculum is an effective technique by which patellofemoral instability can be addressed when normal or nearly normal trochlear geometry is present. In patients with underlying TD, patellofemoral stability cannot be completely restored, and clinical results are less successful. Precise preoperative radiologic determination of trochlear geometry may help the clinician to predict short-term outcomes in patients with patellofemoral instability. LEVEL OF EVIDENCE: Level III, retrospective comparative therapeutic study.

Stress radiography to measure posterior cruciate ligament insufficiency: a comparison of five different techniques.

Stress radiography presents the golden standard to quantify posterior laxity in posterior cruciate ligament (PCL) insufficiency. Several different techniques are currently available, but comparative data are insufficient. Different stress radiographic techniques result in different values for posterior laxity. Comparative controlled clinical study was designed. Prior to PCL reconstruction 30 patients underwent a series of stress radiographs: Telos device, hamstring contraction, kneeling view, gravity view, and an axial view. Posterior displacement, side-to-side difference (SSD), condyle rotation, required time, and pain were measured. Posterior displacement was: Telos 12.7 +/- 3 mm (SSD 10.6 +/- 3.1 mm), hamstring contraction 11.2 +/- 3.2 mm (SSD 8.5 +/- 3.4 mm), kneeling 14.4 +/- 3.8 mm (SSD 10.2 +/- 3.5 mm), gravity view 10.5 +/- 2.8 mm (SSD 9.1 +/- 2.4 mm), and axial view 19.4 +/- 6.9 mm (SSD 8.5 +/- 4.1 mm). In comparison to Telos the hamstring contraction, gravity, and the axial view underestimated the SSD by approximately 2 mm. Telos and kneeling caused significantly more pain than all other techniques (P < 0.001). The axial view was fastest (115 s, P < 0.001) and Telos longest (305 s, P < 0.001), respectively. Telos indicated the lowest rotational error with a significant difference between kneeling and gravity (P < 0.003). In contrast to Telos as the golden standard, hamstring contraction, gravity, and axial view underestimated the SSD. Kneeling and Telos are comparable with respect to SSD and pain. Although kneeling indicates a greater rotational error than Telos, it seems to be a reliable alternative for quantifying posterior tibial displacement in a more simple and fast way.

A model of soft-tissue graft anterior cruciate ligament reconstruction in sheep.

INTRODUCTION: Since there is to our knowledge no clinically valid and reproducible animal model of soft-tissue anterior cruciate ligament (ACL) reconstruction currently available, we developed one in sheep, in terms of graft suitability, postsurgical recovery, and knee stability. MATERIALS AND METHODS: To find a suitable graft, anatomical dissections of the hind limbs of 7 sheep were performed. After a pilot study in 3 sheep, we reconstructed the ACL with an ipsilateral, longitudinally split, superficial digital flexor tendon autograft and anatomic graft fixation in 42 sheep (study 1) and with a full, superficial digital flexor tendon autograft and extracortical graft fixation in 48 sheep (study 2). Follow-up examinations ranged from 6 to 104 weeks (study 1) and 3 to 24 weeks (study 2). RESULTS: All animals tolerated the graft harvest well and returned to physiological movement after about 4 weeks. Only 1 out of 93 ACL reconstructions failed. At final follow-up, the anteroposterior (AP) drawer displacement in both studies had almost regained the value of the intact contralateral knee. Maximum load-to-failure improved over time in both studies but was significantly lower at all time points compared with the intact ACL and the graft tissues. Tensile stress was significantly lower at final follow-up in both studies compared with the intact ACL and graft tissues. It attained 43.3% of the intact ACL and 58.3% of the graft tissue in study 1 and 28.9% and 22.8% in study 2, respectively. CONCLUSION: The flexor tendon is suitable, and sheep appear to be an appropriate animal model for soft-tissue graft ACL reconstruction. They tolerate the graft harvest well and quickly return to full weight-bearing and physiological movement. Their knees become stable without showing signs of macroscopically evident osteoarthritis.

Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: The impact of fixation level and fixation method under cyclic loading.

PURPOSE: To mechanically test different reconstruction techniques of the anterior cruciate ligament (ACL) under incremental cyclic loading and to evaluate the impact of the level and method of graft fixation on tensile properties of each technique. TYPE OF STUDY: In vitro biomechanical study. METHODS: Four hamstring and 1 patellar tendon reconstruction techniques were performed on 40 young to middle-aged human cadaveric knees (average age, 39 years). An anterior drawer with increasing loads of 20 N increments was applied at 30 degree of knee flexion. Anatomic, direct interference screw fixation was tested in 2 hamstring and in the patellar tendon groups. Nonanatomic (extracortical) graft anchorage was tested in the remaining 2 hamstring groups with indirect graft fixations on both sides and the combination of indirect tibial and direct femoral fixation. Structural properties were determined throughout the cyclic loading test. RESULTS: The more anatomic reconstruction techniques provided significantly higher structural properties and smaller loss of fixation compared with nonanatomic, extracortical fixation, with indirect repair on both fixation sites resulting in the lowest structural properties. The tibial fixation site was the weakest link in all of the anatomic reconstructions. Patellar tendon fixation with attached bone blocks in both bone tunnels significantly improved construct stiffness and decreased graft slippage. CONCLUSIONS: The results of this study suggest that anatomic fixation should be preferred for anchorage of hamstring tendons and linkage materials should be avoided. Direct soft-tissue fixation with interference screws still allows considerable graft slippage, which can be limited by using a bone block or application of a backup or hybrid fixation, especially on the tibial fixation site.