The unpredictable material properties of bioabsorbable PLC interference screws and their adverse effects in ACL reconstruction surgery

The aim of this study was to look at the clinical outcome of polylactide carbonate (PLC) interference screws in knee ligament reconstruction surgery. We prospectively followed up 59 patients who underwent primary hamstring anterior cruciate ligament (ACL) reconstructions using PLC (Calaxo screw; Smith and Nephew, Andover, MA) screws to secure the graft in the tibial tunnel. The average age was 34 years (range 17–55 years, SD 8.93). Twenty-three (39%) patients presented with complications [synovitis in 15% (nine) patients, prominent tibial swelling in 34% (20) patients and both in seven patients]. In comparison, similar complications were not seen in two groups of 59 age and sex matched patients in whom PLLA (Bio RCI; Smith and Nephew, Andover, MA) screws or Titanium (RCI; Smith and Nephew, Andover, MA) screws were used by the same surgeon. The problems encountered in the PLC screw group did not adversely affect knee stability. Six patients underwent exploration of the tibial tunnel site. A sterile white cheesy substance was removed, leaving an empty tibial tunnel. The ACL graft was found to be well attached to tibial tunnel in all cases. The PLC screw diameter, surface area or tibial tunnel diameter did not have any correlation to the occurrence of complications. Two patients required multiple washouts, one of whom developed a deep infection. The degradation of PLC screws does not follow the gradual and controlled pattern demonstrated in the ovine model. The unpredictable screw degradation, and the reaction to it can lead to serious clinical consequences.     

Comparison of the bioabsorbable and metal screw fixation after ACL reconstruction with a hamstring autograft in MRI and clinical outcome: a prospective randomized study

There has never been an MRI study of tunnel widening comparing bioabsorbable to metal screw fixation in autologous hamstring anterior cruciate ligament (ACL) reconstruction. We randomized 62 patients to hamstring ACL reconstruction with either a bioabsorbable (n = 31) or metal screw (n = 31) fixation. The evaluation methods were clinical examination, KT-1000 arthrometric measurement, the International Knee Documentation Committee and Lysholm scores, and MRI. There were no differences between the groups preoperatively. Fifty-five patients (89%) were available at a minimum of 2-year follow-up (range 24–36 months). There was tunnel widening in both groups, but the increase was significantly greater in the AP dimension of the femoral tunnel in the bioabsorbable screw group compared to metal group (P = 0.01). The tibial tunnels showed no intergroup difference. Ninety-four percent of the knees were normal or nearly normal according to the IKDC scores and the average Lysholm score was 91 with no intergroup difference. The follow-up AP tibial tunnel diameter was smaller with normal knee laxity compared to abnormal knee laxity. The graft failure rate in the bioabsorbable screw group was 23% (7/31 patients) and 6% (2/31 patients) in the metal screw group. The use of bioabsorbable screws resulted in more femoral tunnel widening, and more graft failures compared to metal screws. The tunnel widening in the tibia was associated with the knee laxity (P = 0.02).     

A prospective evaluation of tunnel enlargement in anterior cruciate ligament reconstruction with hamstrings: extracortical versus anatomical fixation

Changes in the femoral and tibial bone tunnel were studied prospectively after arthroscopic ACL reconstruction with quadruple hamstring autograft. To determine whether tunnel enlargement can be decreased by fixing the graft close to the joint line having a stiffer fixation construct we compared "anatomical" (one absorbable interference screw femorally, and bicortical fixation with two absorbable interference screws tibially) and extracortical fixation techniques (Endobutton femorally, and two no. 6 Ethibond sutures over a suture washer tibially). Over a 2-year period we evaluated 60 patients clinically (IKDC scale, Cincinnati Knee Score, KT-1000) and radiographically (confirmed by MRI). The operated knee was radiographed immediately postoperatively and 6 and 24 months postoperatively. The femoral and tibial bone tunnel diameter was measured on anteroposterior and lateral images, and the tunnel area was calculated and compared to the initial area calculated from the perioperative drill size. In the "anatomical" group the immediately postoperative bone tunnel area was 75% larger than the initial tunnel area, after 6 months it was increased another 31%, and between 6 and 24 months it remained basically unchanged. In the "extracortical" group there was no significant enlargement immediately postoperatively, but after 6 months it was 65% larger than the initial area of drill and graft size, and between 6 and 24 months it decreased to 47%. There was no correlation between the amount of tunnel enlargement and clinical scores or KT-1000 measurement. Arthroscopic ACL reconstruction with quadruple hamstring autograft is associated with bone tunnel enlargement. Using a purely extracortical fixation technique thus significantly increased the tibial and femoral tunnel area during the first 6 postoperative months, while it decreased slightly thereafter. The insertion of large interference screws apparently not only compresses the graft in the bone tunnel but also significantly enlarges the bone tunnel itself. The immediate enlargement at the time of the operation is followed by a reduced further enlargement at 6 months and then stabilization. Tunnel widening did not influence clinical outcome over a 2-year period.     

Magnetic resonance imaging analysis of bioabsorbable interference screws used for fixation of bone-patellar tendon-bone autografts in endoscopic reconstruction of the anterior cruciate ligament

BACKGROUND: Metal interference screws can cause problems if revision is needed and can interfere with magnetic resonance imaging. Bioabsorbable screws have been developed to prevent these problems, but the rate of resorption and integration is not well understood. HYPOTHESIS: Poly-L-lactic acid interference screws will be resorbed 2 years after anterior cruciate ligament reconstruction. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: The study group consisted of 19 patients with isolated anterior cruciate ligament ruptures reconstructed with bone-patellar tendon-bone autografts fixed with poly-L-lactic acid interference screws using an endoscopic technique. Magnetic resonance imaging was used to evaluate resorption of the screws, bony integration of the screws, and integration of the bone blocks after 2 years. RESULTS: At 2 years, the mean reduction in the volume of the femoral screws was 64% and of the tibial screw was 63%. Bony integration of the femoral bone block was considered good in 17 patients and fair in 2 patients. Integration of the tibial bone block was considered good in 16 patients and fair in 1 patient who demonstrated widening of the tibial tunnel. Osteolysis around the screws was seen in 3 patients in the femur and none in the tibia. CONCLUSION: The mean reduction in volume of the poly-L-lactic acid screws as measured by magnetic resonance imaging after 2 years was approximately two thirds. The integration of the bone blocks was considered good in 90% of the patients. Osteolysis around the screws was visible in 16% of the patients. CLINICAL RELEVANCE: Two years after ACL reconstruction using poly-L-lactic acid interference screws, the surgeon can expect to find approximately one third of the volume of the screw remaining in the bone tunnels.     

Magnetic resonance imaging appearance of anterior cruciate ligament reconstruction using Calaxo screws

Bioabsorbable interference screws are commonly used to secure the graft during anterior cruciate ligament (ACL) reconstruction, in part because they result in less image degradation on subsequent magnetic resonance imaging (MRI). However, some bioabsorbable screws are associated with abnormalities on MRI examination not reported with metallic interference screws. We describe a finding on knee MRI examination after ACL reconstruction using a polylactide carbonate (PLC) bioabsorbable screw that we believe to be previously unreported with any other bioabsorbable screws. The finding raised suspicion of hemorrhage or infection, neither of which were present clinically. Analysis of tissue from the tibial tunnel suggested an explanation for the MRI finding: calcite crystals. An additional five patients with knee MRI examinations after ACL reconstruction using a PLC screw were reviewed and correlated with clinical findings with four having similar imaging abnormalities present. The PLC (Calaxo screw, Smith and Nephew, Andover, MA) screw used in these patients has been recalled in the United States and Europe by the manufacturer after a greater than expected incidence of adverse reactions, and legal action may be pending.     

Tibial tunnel widening after anterior cruciate ligament reconstructions with hamstring tendons using Rigidfix femoral fixation and Intrafix tibial fixation

The purpose of this study was to evaluate tibial tunnel widening prospectively after anterior cruciate ligament (ACL) reconstruction with hamstring tendon grafts using Rigidfix (DePuy Mitek, Raynham, MA) femoral fixation and Intrafix (DePuy Mitek) tibial fixation. Fifty-six consecutive patients who underwent ACL reconstruction with a minimum of 2 years’ postoperative evaluation were reviewed. On the anterior–posterior (AP) and lateral radiographs, the diameter of the tibial tunnel was measured at proximal, middle, and distal positions, and the shape of the tibial tunnels were classified. Tunnel widening was defined as widening of greater than 2 mm. Group I was defined as cases with no tunnel widening, and group II was defined as cases with tunnel widening. Postoperative laxity evaluations were performed using Lachman test, pivot-shift test, and instrumented laxity testing using the KT-1000 arthrometer. On the AP radiographs, the average diameter of the tibial tunnel increased 8.8% at 6 months and 8.5% at 12 months postoperatively compared to the immediate postoperative day. On the lateral radiographs, the average diameter of the tibial tunnel increased 7.2% at 6 months and 8.1% at 12 months year postoperatively compared to the immediate postoperative day. The tunnel shape evaluation revealed predominantly linear type in 53 patients (95%). Group I was 42 patients (75%), and group II was 14 (25%). The average KT-1000 measurement was 1.0 ± 1.8 mm in group I and 2.1 ± 2.8 mm in group II (n.s.). The Lachman and pivot-shift tests showed no significant differences between the two groups. In conclusion, hamstring ACL reconstruction using Rigidfix and Intrafix fixation showed less widening of the tibial tunnels than observed in previously published studies.     

MRI in ACL reconstructive surgery with PDLLA bioabsorbable interference screws: evaluation of degradation and osteointegration processes of bioabsorbable screws

PURPOSE: Anterior cruciate ligament (ACL) reconstructive surgery has seen significant progress since bioabsorbable interference screws have replaced synthetic metallic screws for ligament graft fixation within the femoral and tibial osseous tunnel. Our study compared the MR images of patients who underwent ACL reconstruction using bioabsorbable interference screws with those of patients who underwent ACL reconstruction using metallic screws to evaluate the MR aspects of degradation and osteointegration processes of bioabsorbable interference screws post-operatively. MATERIALS AND METHODS: Between September 1999 and December 2002 we performed MRI on 40 patients who underwent arthroscopic ACL reconstruction with patellar tendon auto-graft using PDLLA bioabsorbable screws in 35 cases and metallic screws in 5 cases. After surgery, all patients underwent an intensive rehabilitation programme along with clinical evaluation using the standard knee ligament evaluation form of the International Knee Documentation Committee (IKDC) and radiological examinations. MR studies were performed 1, 2 and 3 years post-operatively using a 0.5-Tesla MR scanner with T1- and T2*-weighted and STIR sequences. RESULTS: Thirty-three patients were clinically classified as group A IKDC (full return to sports activity) and 7 patients as group B IKDC. No foreign-body reaction was found in patients treated with bioabsorbable interference screws, both from a clinical point of view and from laboratory exams. Ferromagnetic artefacts were found in all patients treated with metallic interference screws. In patients with bioabsorbable interference screws, degradation of the screws and absence of significant artefacts allowed correct evaluation of the signal of the reconstructed ligament throughout its length, the osseous tunnels and the joint cavity. In 34 of 35 patients with bioabsorbable interference screws, the screw could not be detected due to complete degradation. In 8, 12 and 4 cases, a small cyst-like formation due to screw hydrolysis was present at the screw site within 1, 2 and 3 years from surgery respectively. Only in 4 cases was the process of osteointegration of the screw and bone plug complete 3 years after the operation, with consequent restoration of bone morphology. DISCUSSION AND CONCLUSIONS: The use of bioabsorbable interference screws is a valuable alternative to synthetic metallic fixation implants as the absence of artefacts allows correct post-operative MR follow-up. MRI is the only technique able to visualize all the portions of the transplant and to evaluate the healing process. Bioabsorbable interference screws usually degrade within one year. However, full osteointegration requires a long time and may not be complete 3 years after surgery. The presence of cyst-like formations at the screw site has to be regarded as a normal feature of the screw degradation process. Therefore, the use of bioabsorbable interference screws is recommended as it enables MR follow-up of the knee after ACL reconstruction.     

Polymer-hydroxyapatite composite versus polymer interference screws in anterior cruciate ligament reconstruction in a large animal model

The aim of the study was to assess the hard tissue response of a composite hydroxyapatite/poly L-lactic acid (HA/PLLA) interference screw for anterior cruciate ligament (ACL) reconstruction compared to a standard PLLA screw. Twelve skeletally mature rams underwent unilateral ACL reconstruction using an autologous bone-patellar tendon graft. Each animal received either two test HA/PLLA interference screws or two control PLLA interference screws. Animals were sacrificed at 6 and 12 months post-implantation and the operated knees excised. Undecalcified sections of the screw and surrounding tissues were cut from resin embedded samples and stained; sections were approximately parallel to the longitudinal axis of the screws. A quantitative assessment of bone formation between each screw type (PLLA vs. HA/PLLA) and adjacent tissue in both the tibia and femur was undertaken using automated image analysis (KS400, Zeiss, UK). The inflammatory response of each screw type was assessed by histological evaluation. New bone formation along the perimeter of the screw threads was statistically significantly higher with the HA/PLLA than the PLLA alone. The inflammatory response as assessed semi-quantitatively by histologically determining the number of inflammatory cells present in the tissue adjacent to the implant, was higher for PLLA than HA/PLLA. Significantly increased new bone formation and decreased inflammatory cells were observed in vivo with the composite screw in comparison with the standard polymer. A novel HA/PLLA composite biomaterial in the form of an interference screw demonstrated an improved hard-tissue response compared to PLLA in a large animal ACL reconstruction. This study determined the differences in the tissue response between PLLA and a composite material of HA/PLLA. The improved tissue related outcomes observed in vivo, may be of benefit clinically in ACL reconstruction.     

Intraarticular migration of a broken biodegradable interference screw after anterior cruciate ligament reconstruction

Poly-l-lactic acid biodegradable screws have been used effectively for graft fixation in anterior cruciate ligament (ACL) reconstruction. The overall complication rate associated with the use of this implant is low, although some authors reported complications, such as osteolysis and aseptic effusion of the knee joint. We report a case of a 29-year-old female patient with a failure of a biodegradable interference screw at 22 months after ACL reconstruction using bone–patellar tendon–bone graft. In this illustrated case, the screw broke and migrated into the knee joint. In addition, we performed a detailed review of the medical literature from 1990–2005 to identify possible causes of biodegradable screw failures. We identified six published cases of bioabsorbable interference screw failure with migration into the knee joint. Several authors have reported small diameter of the screw, poor bone quality, bone resorption, and screw divergence as potential causes for intraarticular migration of metallic interference screws. With regard to bioscrews, no specific risk factors for screw breakage and intraarticular migration have been reported. ACL reconstruction with the use of bioabsorbable interference screws for fixation is considered to be reliable. However, we need to be aware of potential problems associated with the use of this implant. Early recognition of bioscrew failure may prevent associated morbidities, such as subsequent cartilage damage.     

Pullout strength of tibial graft fixation in anterior cruciate ligament replacement with a patellar tendon graft: interference screw versus staple fixation in human knees

The endoscopic single incision technique for anterior cruciate ligament (ACL) reconstruction with a femoral half-tunnel may lead to a graft/tunnel mismatch and subsequent protrusion of the block from the tibial tunnel. The typical tibial fixation with an interference screw is not possible in these cases. Fixation with staples in a bony groove inferior to the tunnel outlet can be used as an alternative technique. Current literature does not provide biomechanical data of either fixation technique in a human model. This study was performed to evaluate the primary biomechanical parameters of this technique compared with a standard interference screw fixation of the block. Fifty-five fresh-frozen relatively young (mean age 44 years) human cadaver knee joints were used. Grafts were harvested from the patellar tendon midportion with bone blocks of 25 mm length and 9 mm width. A 10-mm tibial tunnel was drilled from the anteromedial cortex to the center of the tibial insertion of the ACL. Three different sizes of interference screws (7 × 30, 9 × 20, 9 × 30 mm) were chosen as a standard control procedure (n = 40). For tibial bone-block fixation the graft was placed through the tunnel, and the screw was then inserted on the cancellous or the cortical surface, respectively. Fifteen knees were treated by staple fixation. A groove was created inferior to the tunnel outlet with a chisel. The bone block was fixed in this groove with two barbed stainless steel staples. Tensile testing in both groups was carried out under an axial load parallel to the tibial tunnel in a Zwick testing machine with a velocity of 1 mm/s. Dislocation of the graft and stiffness were calculated at 175 N load. Maximum load to failure using interference screws varied between 506 and 758 N. Load to failure using staples was 588 N. Dislocation of the graft ranged between 3.8 and 4.7 mm for interference screw fixation and was 4.7 mm for staples. Stiffness calculated at 175 N load was significantly higher in staple fixation. With either fixation technique, the recorded failure loads were sufficient to withstand the graft loads which are to be expected during the rehabilitation period. Staple fixation of the bone block outside of the tunnel resulted in a fixation strength comparable to interference screw fixation. Received: 2 September 1996 Accepted: 30 January 1997     

A new bicortical tibial fixation technique in anterior cruciate ligament reconstruction with quadruple hamstring graft

We report a prospective series of 101 patients receiving a four-strand semitendinosus-gracilis autograft for anterior cruciate ligament reconstruction using a new bicortical tibial fixation technique with bioabsorbable interference screws. Patients (average age 32 years) were operated on between November 1997 and Mai 1998, and follow-up was at least 12 months postoperatively. The evaluation consisted of history, clinical examination, IKDC score, Cincinnati Knee Score, KT-1000 testing, standardized radiography and magnetic resonance imaging. One hundred patients were available for follow-up. There were two traumatic reruptures 6 and 11 months postoperatively. By IKDC score 87 patients were in groups A and B, 12 in group C, and 2 with a rerupture in group D. Mean Cincinnati Knee Score was 82 (range 46–100), KT-1000 manual maximum at follow-up showed an average difference of 1.7 mm between the sides. Full extension was rapidly achieved in all cases, and flexion averaged 135°. Considering the enlargement caused by the bioabsorbable interference screws, the incidence of tunnel widening was 6.6% on the femoral side and 1.7% on the tibial side. Tunnel widening did not affect the clinical results. Three patients experienced an effusion after more than 6 months postoperatively. There was one infection, which settled without functional impairment after early arthroscopic lavage and intravenous antibiotics. Otherwise no complications occurred. The described technique for anterior cruciate ligament reconstruction combines the advantage of anatomical graft position with sufficient graft fixation. A short intra-articular graft construct with a strong tendon to bone interface was created. Clinically, 87% of patients had a normal or nearly normal IKDC score at follow-up. Magnetic resonance imaging revealed a considerable increase in tunnel area caused by the insertion of the interference screws. On the other hand, the development of a “fibrous interzone” between the graft and the bone tunnel was prevented in most cases. At short-term follow-up the bicortical tibial fixation proved to be efficient even with an aggressive rehabilitation program. Received: 26 November 1999 Accepted: 5 March 2000     

Failure load of patellar tendon grafts at the femoral side: 10- versus 20-mm-bone blocks

The aim of the study was to investigate whether use of short bone blocks is safe in anterior cruciate ligament (ACL) reconstruction. Our hypothesis was that the smaller 10-mm-length bone blocks will fail at lower loads than 20-mm-bone blocks. Ten paired human cadaver knees were randomly assigned to the 10- or 20-mm group (group 1 and 2) and underwent bone–patellar tendon–bone femoral fixation with interference screw. Tensile tests were performed using a tensile testing machine (Instron). Stiffness, failure load and failure mode were recorded. Median stiffness was 72 N/mm (16–103) for 10-mm-bone blocks and 91 N/mm (40–130) for 20-mm-bone blocks. Median failure loads were 402 N (87–546) for 10-mm-long bone block and 456 N (163–636) for 20-mm-bone blocks. There was no statistically significant difference between groups (P = 0.35). All bone–patellar tendon–bone grafts were pulled out of the femoral tunnel with interference screw, due to slippage. We concluded that a 10-mm-long bone block was not significantly weaker than a 20-mm-long bone block. Failure loads of a 10-mm-bone block exceeded loading values at passive and active extension of the knee under normal conditions. Ten millimetre bone blocks offered sufficient fixation strength in ACL reconstruction.     

Initial fixation strength of a hybrid technique for femoral ACL graft fixation

Aperture fixation with interference screws matching the diameter of the tunnel is associated with the risk of graft laceration and graft rotation. A hybrid fixation technique (extracortical and aperture fixation) with undersized interference screws provides a higher fixation strength when compared to an aperture fixation using only a screw matching the size of the tunnel and also reduces the risk of graft laceration. This research is an experimental laboratory study. We evaluated the initial fixation strength at time-zero of an extracortical-, a hybrid- and an aperture fixation in ACL reconstruction using extracortical buttons and different sized interference screws in porcine knees. The tests were performed using a single cycle and cyclic loading protocol. Analysis of yield load, maximum load and stiffness in the single cycle loading test showed no statistically significant differences for hybrid fixation with a 1 mm undersized screw and aperture fixation with a screw matching the size of the tunnel. Cyclic loading tests showed a statistically significant difference between hybrid and aperture fixation. The use of an undersized screw alone in aperture fixation resulted in insufficient fixation strength. The initial fixation strength of the hybrid technique with undersized screws is higher compared to an interference screw fixation alone. The hybrid fixation technique is an alternative for ACL graft fixation.     

The mid- to long-term results of the anterior cruciate ligament reconstruction with hamstring tendons using Transfix technique

In this study, mid to long-term results of anterior cruciate ligament reconstruction with hamstring tendons and Transfix technique were evaluated. Anterior cruciate ligament (ACL) reconstruction with four-strand hamstring tendon was performed with Transfix technique on 271 (198 males, 73 females; mean age 25.7; 17–52) patients with anterior cruciate ligament ruptures. The patients were followed up with clinical examination, Lysholm and Tegner activity scales, IKDC scoring system, KT-1000 test and radiological examination. The mean follow-up period was 82 (48–100) months; 204 (75%) patients had no subjective complaints. According to the KT-1000 test, only 14 (5%) patients had more than 5 mm laxity postoperatively, whereas, 161 (59%) patients had more than 5 mm laxity preoperatively. In addition to this, only 19 (7%) patients had Lysholm scores less than 80 postoperatively, whereas 154 (57%) patients scored less than 80 preoperatively. When compared with Tegner activity scale, 189 (70%) patients scored <6 preoperatively and only 24 (8%) postoperatively; 78 (29%) patients scored D preoperatively and only 5 (2%) patients scored D postoperatively on the basis of the IKDC scoring system. Our functional results were found to be satisfactory in more than 90% of patients. Commonly seen problems in ACL reconstruction such as inaccurate graft placement and tunnel widening were found to be consistent with the values in relevant literature. However, we demonstrated that the functional results and the stability of the knee were not related with tunnel widening. This study concludes that the reconstruction of ACL with hamstring tendons and the Transfix technique is reasonably successful, safe and causes low morbidity. Furthermore, we believe that proper graft preparation, accurate tunnel placement, notch-plasty, fixation and rehabilitation program are all as important as the choice of graft and fixation material.     

Tunnel widening following anterior cruciate ligament reconstruction using hamstring autograft: a comparison between double cross-pin and suspensory graft fixation

Femoral and tibial tunnel widening following ACL reconstruction using hamstring autograft has been described. Greater tunnel widening has been reported with suspensory fixation systems. We hypothesized that greater tunnel widening will be observed in patients whose hamstring autograft was fixated using a cortical, suspensory system, compared to double cross-pin fixation on the femur. We performed clinical and radiographic evaluation on 46 patients at minimum 2 years after primary ACL reconstruction. We measured subjective and objective outcomes including KT-1000 and AP, lateral radiographs. A musculoskeletal radiologist, independent of the surgical team, measured tunnel width, while correcting for magnification, at the widest point and at 1 cm away from tibial and femoral tunnel apertures. Patients in the suspensory graft fixation group exhibited significantly greater absolute change and greater percent change in femoral tunnel diameter compared to patients with double cross-pin fixation (P ≤ 0.05). This difference was noted on both AP and lateral radiographs and at both measurement sites. There was no significant difference between groups for tibial tunnel widening, IKDC subjective scores or KT-1000 side to side differences. There was significantly more femoral tunnel widening associated with the use of the endobutton suspensory fixation system compared to the use of double cross-pins for fixation within the tunnel.     

Tibial tunnel enlargement after anterior cruciate ligament reconstruction by autogenous bone-patellar tendon-bone graft

This retrospective study was designed to evaluate changes in the diameter of the tibial tunnel over time following the reconstruction of the anterior cruciate ligament (ACL) with a bone-patellar tendon-bone autograft in 44 patients. The changes in the geometry of the bone tunnels were measured radiographically during the immediate postoperative period and at time intervals between 3 and 36 months after surgery. The dimensions at 1 year were correlated with the 1-year clinical results. The distance between the sclerotic margins of the tibial tunnel was measured at the distal tunnel exis on the medial tibial cortex, in the middle of the tunnel, and proximally at the level of the joint line. The dimensions were calculated by using a magnification factor determined by reference to the interference screw of known diameter located within the tunnel. The position of the centre of the tibial tunnel with regard to Blumensaat's line was also measured. The average tunnel diameter at the proximal tibial exit increased from 12±1.9 mm (mean ± standard deviation) postoperatively to 14±2.2 mm at 3 months. The average proximal tunnel diameter did not significantly change from 3 months to 2 years, and then decreased to 13±2.4 mm at 3 years. At 1 year, most of the patterns of osteolysis were of the cone type (57%), followed by the cavity type (40%) and line type (3%). The degree of osteolysis was not related to the tibial tunnel position with respect to Blumensaat's line. There was no correlation between the changes in tunnel diameter and either the IKDC score or the residual joint laxity measured by a KT-1000 arthrometer. The aetiology of tunnel enlargement is currently unknown. Possible factors responsible for bone resorption include micromotion of the graft relative to the tunnel wall, leading to an inflammatory response in the tunnel, or stress shielding of the tunnel wall proximal to the interference screw.     

Fixation strength of a novel bioabsorbable expansion bolt for patellar tendon bone graft fixation: an experimental study in calf tibial bone

This biomechanical study compares the initial fixation strength of a novel bioabsorbable two-shell expansion bolt (EB) with that of a well-established interference-screw technique in bone–patellar tendon–bone (BPTB) reconstruction in a calf model. Thirty tibia plateaus (age 5–6 months) were assigned to three groups: In groups I and II, trapezoidal bone plugs of BPTB grafts were fixed with bioabsorbable poly-L-lactide interference screws (8×23 mm) or titanium interference screws (8×25 mm) respectively. In group III, semicircular grafts were fixed using bioabsorbable poly-D, L-lactide expansion bolts (5.8/8.7×10×35 mm). The tensile axis was parallel to the bone tunnel, and the construction was loaded until failure applying a displacement rate of 1 mm per second. In group II the mean ultimate loads to failure (713 N±218 N) were found to be significantly higher than those of groups I (487 N±205 N) and III (510 N±133 N). Measurement of stiffness showed 45 N/mm±13.3 in group I, 58 N/mm±17.4 in group II and 46 N/mm±6.9 in group III, and did not demonstrate significant differences. We found a correlation between insertion torque and wedge insertion force and ultimate loads to failure in all groups ( r =0.53 in group I, r =0.54 in group II, and r =0.57 in group III). Cross-section planes of bone tunnel increased by 51%, 30% and 31% respectively, following insertion of screws or expansion of bolts ( p <0.05). We conclude that ACL graft fixation by means of the presented expansion bolt demonstrates a fixation strength similar to the established bioabsorbable screw fixation, and is a reasonable alternative fixation method, especially since some of the specific pitfalls of screw fixation can be avoided.     

Soft tissue graft interference fit fixation: observations on graft insertion site healing and tunnel remodeling 2 years after ACL reconstruction in sheep

Using soft tissue grafts for anterior cruciate ligament (ACL) reconstruction, insertion site healing plays a crucial role in the long-term fate of the graft. It has been shown in an experimental animal study that using a soft tissue graft and anatomic graft fixation, a direct ligamentous insertion alike the native ACL developed 24 weeks postoperatively. Yet there are no reports on the long-term insertion site healing of anatomically fixed soft tissue grafts. The objective of this study was to evaluate graft insertion site healing, the intra-tunnel fate of the graft and its osseous replacement 2 years after ACL reconstruction in sheep. The left ACLs of six sheep were replaced by an autologous flexor tendon split graft and anatomically fixed with biodegradable poly-(d, l-lactide) interference screws. Animals received polychromic sequential labeling at different points in time to determine bone apposition per period. For evaluation of the insertion site healing and intra-tunnel changes, MRI scans were taken in vivo. Following sacrifice, radiographic imaging, conventional histology and fluorescence microscopy was undertaken. Most of the specimens showed a wide direct ligamentous insertion. It showed patterns alike the direct ligament insertion seen in intact ACLs. The intra-tunnel part of the graft had completely lost its tendon-like structure and in two cases, it was separated from the graft insertion by a thick bony layer. The biodegradable interference screw was fully degraded in all specimens. Ossification of the former drill tunnels was intense, showing only partial-length tunnel remnants in one femoral and three tibial specimens. As the graft heals to the joint surface and the aperture site is closed with soft tissue, mechanical stress of the intra-tunnel part of the graft is eliminated and the bone tunnel is protected from synovial fluid, resulting in osseous bridging of the tunnel aperture site, accelerated intra-tunnel graft resorption and its osseous replacement.     

Tunnel enlargement after anterior cruciate ligament reconstruction in patients with post-operative septic arthritis

Tunnel enlargement is a frequent issue after ACL reconstruction and the “synovial bathing effect” is thought to be among the biological factors contributing to this phenomenon. Since the amount and the pressure of the synovial fluid inside the knee joint are higher and the length of its presence is longer in patients with post-operative septic arthritis after ACL reconstruction, we reviewed the tunnel enlargement in these cases in order to better evaluate this phenomenon in such a hostile environment. The null hypothesis of this study was that the highly represented phenomenon of the “synovial bathing effect” that occurs in an infected ACL reconstruction would not affect the amount of post-operative tunnel widening. A case-control study was done. At a mean follow up of 10 months (range 9–11 months) eight patients with septic arthritis following ACL reconstruction (group A) were radiologically reviewed using a CT scan and the diameters of femoral and tibial tunnels were measured. The results were compared with a control group (B) of uncomplicated ACL reconstruction cases operated by the same surgeon using the same technique. Although patients of Group A experienced a bigger amount of tunnel enlargement than patients of group B both on femoral (9.53 ± 1.07 vs. 9.35 ± 1.52 mm) and tibial side (10.07 ± 1.3 vs. 9.92 ± 0.74 mm), no clinical or statistically significant differences were detected between the groups (P > 0.05). No significant tunnel enlargement could be detected in patients of group A when compared with patients of group B. This seems to minimize the role of biological factors contributing to tunnel widening.     

MRI analysis of tibial position of the anterior cruciate ligament

This study aimed to establish normal values for the position of the native anterior cruciate ligament (ACL) insertion on the tibia to assist in the evaluation of tunnel placement after primary ACL reconstruction or prior to revision surgery. One hundred consecutive MRI studies performed on patients with a mean age of 29 years (range 20–35) from a single MRI facility were reviewed. Patients with prior surgery, significant osteoarthritis, acute ACL injury, or evidence of ACL reconstruction were excluded. Using digital image software, measurements were taken of anterior-most and posterior-most portions of the ACL insertion on the tibia. Depth of the tibia was also measured from the anterior edge of the tibial plateau to the posterior edge at the origin of the posterior cruciate ligament. The anterior insertion of the native ACL was located at a mean of 14 ± 3 mm (28 ± 5%) from the anterior tibial articular margin; the posterior portion of the ACL was located at a mean of 31 ± 4 mm (63 ± 6%). The tibial insertion of the ACL is located between 28 and 63% of the total anterior–posterior depth of the tibia. The results from this study are clinically relevant as they provide the clinician with baseline data to describe the position of the tibial footprint of the native ACL on sagittal MR imaging. Further, this data can be used as a guide to evaluate tibial tunnel position prior to primary ACL reconstruction, revision ACL surgery, or in ACL-reconstructed patients who continue to experience pain, instability, or dysfunction postoperatively.