Press-fit Fixation Research Articles

Tibiale Press-fit-Fixierungen von Beugesehnen zur Rekonstruktion des vorderen Kreuzbandes

Press-fit fixation of hamstring tendon autografts for anterior cruciate ligament reconstruction is an interesting technique because no hardware is necessary. This study compares the biomechanical properties of press-fit fixations to an interference screw fixation. Twenty-eight human cadaveric knees were used for hamstring tendon explantation. An additional bone block was harvested from the tibia. We used 28 porcine femora for graft fixation. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclic loading were investigated. The maximum load to failure was 970±83N for the press-fit tape fixation (T), 572±151N for the bone bridge fixation (TS), 544±109N for the interference screw fixation (I), 402±77N for the press-fit suture fixation (S) and 290±74N for the bone block fixation technique (F). The T fixation had a significantly better maximum load to failure compared to all other techniques (p<0.001). This study demonstrates that a tibial press-fit technique which uses an additional bone block has better maximum load to failure results compared to a simple interference screw fixation.

Proximal Femoral Allograft for Major Segmental Femoral Bone Loss: A Systematic Literature Review

As the indications for total hip arthroplasty increase, the prevalence of extensive proximal femoral bone loss will increase as a consequence of massive osteolysis, stress shielding and multiple revisions. Proximal femoral bone stock deficiency provides a major challenge for revision hip arthroplasty and is likely to account for a significant future caseload. Various surgical techniques have been advocated included impaction allografting, distal press-fit fixation and massive endoprosthetic reconstruction. This review article provides a systematic review of the current literature to assess the outcome of revision hip arthroplasty using allograft to reconstruction massive proximal femoral bone loss.

Anterior Cruciate Ligament Reconstruction With Semitendinosus and Gracilis Tendon Grafts Using a Pressfit Fixation Without Hardware

A new technique for anterior cruciate ligament reconstruction with anatomic placement of the grafts and with pressfit fixation close to the point of insertion using hamstring grafts has been developed. The advantages of this technique are: small diameter of the tunnel corresponds to the smallest dia

Reverse hybrid total hip arthroplasty in select patients

Abstract Purpose To report the result of cemented cups and cementless stems (reverse hybrid) in 17 total hip arthroplasties (THAs). Methods From January 2003 to January 2008, 17 hips (17 patients) received reverse hybrid THAs and were included in this study. The mean patient age was 70 years (range, 52–81 years). The reasons for a reverse hybrid THA were an acetabulum too small to accommodate a metal shell, a severely osteoporotic acetabulum with thin subchondral bone, in which press-fit and screw fixation of the metal shell was deemed unstable, irradiation arthritis, and sequelae of sepsis, while the proximal femoral canal is normally shaped for a press-fit stem. Demographic data, surgical techniques, reasons for surgery, Harris hip score, and complications were reported. Results The average Harris hip score was 84.4 (range, 48–100) points at an average follow-up of 40.1 months (range, 24–73 months). One patient had a Vancouver type 2B fracture and received reoperation with open reduction. The patient had a 3-cm subsidence of the stem and thigh pain at follow-up. Another patient had an asymptomatic 1.5-cm subsidence of the stem. No loosening, migration, or progressive radiolucent lines around the cup were noted in any patient. Conclusion Reverse hybrid THA was associated with good clinical and radiographic results of the cemented cups in patients with the four selection criteria. It is noteworthy that one periprosthetic femoral fracture and one asymptomatic stem subsidence occurred. The lower average hip score with reverse hybrid THA than with ordinary THA is attributable to major comorbidities in the patients.

Arthroskopische Rekonstruktion des vorderen Kreuzbandes in Press-fit-Technik

Problems related to the use of interference screws for fixation of bone-patellar tendon-bone grafts for anterior cruciate ligament (ACL) replacement have led to increasing interest in press-fit techniques. Most of the described techniques use press-fit fixation on either the femoral or tibial side. Therefore an arthroscopic technique was developed which achieves bone-patellar tendon-bone graft fixation by press-fit on both sides without the need for supplemental fixation material. The first consecutive 40 patients were examined clinically with a KT-1000 arthrometer and radiologically after a mean of 28.7 months (range 20-40 months) postoperatively. The mean difference in side-to-side laxity was 1.3 mm (SD 2.2 mm) and the results according to the International Knee Documentation Committee (IKDC) score were as follows: 7 A, 28 B, 5 C, 0 D. The presented press-fit technique avoids all complications related to the use of interference screws. It achieves primary stable fixation of the bone-patellar tendon-bone graft thereby allowing early functional rehabilitation. However, fixation strength depends on bone quality and the arthroscopic procedure is demanding. The results showed reliable stabilization of the operated knees.

Fremdmaterialfreie Rekonstruktion des vorderen Kreuzbandes mit autologer Quadrizepssehne

Reconstruction of the anterior cruciate ligament (ACL) is a widely used procedure, but up to now no results have been published on an implant-free technique using a quadriceps tendon autograft and press-fit fixation. A total of 112 patients with primary rupture of the anterior cruciate ligament were included in a prospective case control study and 106 patients could be evaluated postoperatively after a mean of 12.4 months (range 12-14 months). The patients showed good to excellent results according to the Lysholm score in 81% and the International Knee Documentation Committee (IKDC) score in 86% of cases. Furthermore the anterior-posterior translation was less than 3 mm in 83% of the patients by testing with the KT-1000 arthrometer. Neither tunnel widening nor an increase of radiological joint degeneration was recorded by radiological examination. Reconstruction of the ACL with an autologous quadriceps tendon and an implant-free technique yielded good results compared to established operative methods in the short-term and should be consistently followed-up for long-term confirmation.

Biomechanical characterization of double-bundle femoral press-fit fixation techniques

Press-fit fixation of patellar tendon bone anterior cruciate ligament autografts is an interesting technique because no hardware is necessary. To date, no biomechanical data exist describing an implant-free double-bundle press-fit procedure. The purpose of this study was to characterize the biomechanical properties of three double-bundle press-fit fixations. In a controlled laboratory study, the patellar-, quadriceps- and hamstring tendons of 10 human cadavers (age: 49.2±18.5years) were used. An inside out press-fit fixation with a knot in the semitendinosus and gracilis tendons (SG) combined with an additional bone block, with two quadriceps tendon bone block grafts (QU) was compared with press-fit fixation of two bone patellar tendon bone block (PT) grafts in 30 porcine femora. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were investigated. The maximum load to failure was 703±136N for SG fixation, 632±130N for QU and 656±127N for PT fixation. Stiffness of the constructs averaged 138±26N/mm for SG, 159±74N/mm for QU, and 154±50N/mm for PT fixation. Elongation during initial cyclical loading was 1.2±1.4mm for SG, 2.0±1.4mm for QU, and 1.0±0.6mm for PT (significantly larger for PT and QU between the first 5 cycles compared with cycles 15-20th, P<0.01). All investigated double-bundle fixation techniques were equal in terms of maximum load to failure, stiffness, and elongation. Unlike with single-bundle press-fit fixation techniques that have been published, no difference was observed between pure tendon combined with an additional bone block and tendon bone grafts. All techniques exhibited larger elongation during initial cyclical loading. All three press-fit fixation techniques that were investigated exhibit comparable biomechanical properties. Preconditioning of the constructs is critical.

Biomechanische Analyse der Press-fit-Fixierung von Kreuzbandtransplantaten

Press-fit fixation of anterior cruciate ligament autografts is an interesting technique because no hardware is necessary. A total of 168 cadaveric human patellar, quadriceps and hamstring tendons (average age 49.2 +/- 18.5 years) were used and 15 different fixation methods were tested. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were compared. Some techniques showed comparable biomechanical qualities to interference screw fixation. All investigated double bundle fixation techniques were equal in terms of maximum load to failure, stiffness and elongation. All techniques exhibited greater elongation during initial cyclical loading. Some of the press-fit fixation techniques investigated exhibited comparable biomechanical properties and preconditioning of the constructs is critical. Press-fit fixation enhances tendon to bone contact at the entry of the bone tunnel to the joint.

Fremdmaterialfreie vordere Kreuzbandplastik mit der Patellasehne in Press-fit-Doppelbündeltechnik

Anterior cruciate ligament (ACL) reconstruction using autologous tendons (BTB patellar tendon, hamstrings, quadriceps tendon) in an implant-free fixation technique is becoming more and more popular due to biological and economical reasons. In 1987 an implant-free press-fit fixation technique of a BTB graft from the medial side of the patellar tendon (via mini-arthrotomy) was introduced and first published during the 4th ESKA Conference 1990 in Stockholm. Special emphasis is given to the anatomical orientation of the BTB graft. During the inside-out femoral press-fit fixation the bone-ligament margin of the graft is placed directly into the femoral insertion line of the natural ACL adapting its double-bundle structure. The graft is fixed by press-fit within the tibial metaphysis and its ligamentous part is secured in the metaphysis by harvested cancellous bone blocks driven into the joint line from the outside. The postoperative regime includes weight-bearing as tolerated and free motion. Out of 159 patients 95 could be seen for follow-up after an average of 10.7 years. The final IKDC knee score revealed 22.1% in group A (very good) and 62.1% in group B (good). The Tegner activity level was 6.8 preinjury and 6.0 postoperatively. The average KT 1,000 side-to-side difference was 1.8 mm. Subjectively no patient complained of instability and 99% of the patients could kneel on hard ground with minimal or no complaints. ACL revision surgery due to graft failure was not necessary in any of the patients. Advantages of the described procedure are a narrow anatomical orientation including the double bundle structure of the ACL, rapid graft incorporation by bone-to-bone healing, lack of bone resorption at the graft-host interface, decreased donor site morbidity, cost-effectiveness and ease of possible revision surgery.

Standardized Reconstruction of Acetabular Bone Defects Using the Cranial Socket System

Management of primary or secondary acetabular bone loss (D'Antonio type I-IV ). Implantation and stable fixation using a cementless, cranially extended oval press-fit cup to restore painless joint function and loading capacity. Septic or aseptic loosening of the acetabular component after total hip arthroplasty. Acetabular bone loss after tumor resection. Primary acetabular bone defects in developmental dysplasia of the hip. Persistent deep infection. Bone defects including the parts of the iliac bone adjoining the sacrum (fixation of the stem in the ilium is not possible any more). Complete exposure of the acetabular defect using a standard approach. Removal of the loose cup. Excision of soft and granulation tissue from the acetabular ground and the rim. Reaming of the acetabulum with sequentially larger hemispheric reamers until an adequate bony bed is created for the insertion of the cranial socket. Eccentric cranial sockets without a craniolateral flap are preferable for use in type I and II defects with teardrop lysis mostly involving the craniolateral acetabulum, if a trihedral press-fit fixation can be achieved. Supplementary screw fixation through the acetabular ground, is possible. If a type III defect is present, the authors recommend the use of cranial sockets with an anatomic flap in order to increase primary stability by supplementary screw fixation. This is especially recommended for the management of deficiencies in the medial or posterior wall. If there is pelvic discontinuity (type IV), adequate acetabular reconstruction with primary stability of the component can only be achieved by a supplementary intramedullary structured stem fixed in the dorsal part of the ilium. Partial loading of the operated limb with 10 kg for a period of 6-12 weeks. Then increased loading with 10 kg per week. Thrombosis prophylaxis until full weight bearing. Physiotherapy and gait training. A total of 50 cup revisions using the ESKA cranial socket system were clinically and radiologically analyzed with an average follow-up of 65.7+/-28.5 months (26-123 months). Defects were classified according to D'Antonio. There were 21 type II, 23 type III, and six type IV defects. The Harris Hip Score increased from 40 preoperatively to 68.3 points postoperatively. Four patients had recurrent hip dislocation requiring replacement of the inlay. In four cases of aseptic loosening, the acetabular component had to be revised. With revision of the acetabular component as an endpoint, implant survival was 92% after an average of 5.4 years.

Implant-free press-fit fixation for bone–patellar tendon–bone ACL reconstruction: 10-year results

The aim of this study is to determine the outcome of anterior cruciate ligament (ACL) reconstruction without foreign material with patellar tendon bone graft in the fixation with bone dowels near the native insertion. Between 1998 and 1999, 189 patients were operated with ACL reconstruction with BTB patellar tendon graft. In a prospective study, 148 (78%) (91M, 57F) patients could be seen for a mean follow-up of 10.3 years. All had foreign material-free press-fit and a bottom-to-top (BTT) fixation in 120 degrees knee flexion. All patients were evaluated with detailed history, clinical examinations, radiographic examination with weight bearing which could be compared to the time of surgery in 64 (43%) patients. Laxity testing was performed in Lachman position with the Rolimeter and pivot shift. All patients were graded according to the IKDC and Tegner activity score. 87% of the patients achieved an IKDC score of A/B. The subjective IKDC score was A/B in 94.6% of the subjects. The average side-to-side difference was 1.42 +/- 0.88 mm for the Lachman test, 97% of the patients were rated between 0 and 2 mm. The pivot-shift test was negative in 90% and was observed with a glide in 7% of the patients. Radiological joint space narrowing was found in the medial compartment in 8 (12.4%) cases, and laterally in 9 (14.1%) cases. All these patients had partial or total meniscus resections. The patello-femoral joint space was reduced in 21 (23%) cases. The Tegner activity score changed from 6.9 pre-injury to 5.0 at the 10-year follow-up. The implant-free fixation of the graft with bone dowels and BTT implantation has good and excellent results after 10 years in more than 80% of the patients. Loss of the meniscus is a main factor contributing to osteoarthritis. Advantages of patellar tendon bone press-fit fixation include anatomical positioning and fast bone-to-bone healing, ease for revision surgery and cost effectiveness.

Zementfreie Hüftendoprothetik: eine aktuelle Übersicht / Cementless total hip arthroplasty: a review

The purpose of total hip replacement (THR) is the restoration of a painless functioning hip joint with the main focus on the biomechanical properties. Advances in surgical techniques and biomaterial properties currently allow predictable surgical results in most patients. Despite the overwhelming success of this surgical procedure, the debate continues surrounding the optimal choice of implants and fixation. Femoral and acetabular implants with varying geometries and fixation methods are currently available. Problems inherent with acrylic bone cement, however, have encouraged surgeons to use alternative surfaces to allow biologic fixation. Optimal primary and secondary fixation of cementless hip stems is a precondition for long-term stability. Important criteria to achieve primary stability are good rotational and axial stability by press-fit fixation. The objective of the cementless secondary fixation is the biological integration of the implant by bony ingrowth. Nevertheless, current investigations show excellent results of cementless fixation even in older patients with reduced osseous quality. The main advantages of cementless fixation include biological integration, reduced duration of surgery, no tissue damage by cement polymerization and reduction of intraoperative embolisms. In comparison to cemented THR both, cementless sockets and stems provide good long-term results.

Biodegradable Screw versus a Press-Fit Bone Plug Fixation for Hamstring Anterior Cruciate Ligament Reconstruction

Background Press-fit fixation of a tendon graft has been advocated to achieve tendon-to-bone healing. Hypothesis Fixation of hamstring tendon grafts with a porous bone scaffold limits bone tunnel enlargement compared with a biodegradable interference screw fixation. Study Design Randomized controlled trial; Level of evidence, 1. Methods Between 2005 and 2006, 20 patients (17 men, 3 women) with a primary reconstruction of the anterior cruciate ligament (ACL) were enrolled in this study. Patients were randomized to obtain graft fixation in the tibial tunnel either by means of an interference screw (I) or a press-fit fixation with a porous bone cylinder (P). At 3 months after surgery, a computed tomography (CT) scan of the knee was performed, and tunnel enlargement was analyzed in the coronal and sagittal planes for the proximal, middle, and distal thirds of the tunnel. After 6 months and 1 and 2 years, radiographs of the knee in the sagittal and coronal plane were analyzed for bone tunnel widening. The International Knee Documentation Committee (IKDC), Tegner, and Lysholm scores of both groups were compared after 1 and 2 years. Results The bone tunnel enlargement determined by CT was 106.9% ± 10.9% for group P and 121.9% ± 9.0% for group I (P < .02) in the anteroposterior (AP) plane and 102.8% ± 15.2% versus 121.5% ± 10.1% in the coronal plane (P < .01). The IKDC, Tegner, and Lysholm scores improved in both groups from preoperatively to postoperatively without significant differences between the 2 groups. There was a trend to higher knee stability in group P after 3 months (0.6 ± 1.4 mm vs 1.8 ± 1.5 mm; P = .08). Conclusion Both interference screw and a press-fit fixation lead to a high number of good or very good outcomes after ACL reconstruction. Tibial press-fit fixation decreases the amount of proximal bone tunnel enlargement.

Die Rekonstruktion der Kahnbeinpseudarthrose mit avaskulärem proximalen Fragment mit freiem mikrovaskulär gestielten Beckenkammtransplantat

The goal of the procedure is osseous healing of the scaphoid in an anatomic position and replacement of necrotic bone at the site of the scaphoid nonunion by a vascularized iliac bone graft. Scaphoid nonunion with necrotic fragment in SNAC (scaphoid nonunion advanced collapse) < 1. Nonunion following previous surgery. Pattern of advanced carpal collapse (SNAC > 1). Malformation, disease or previous injury of the vascular system. Poor compliance. Reduced general health. Principles of the surgical technique according to Pechlaner et al.: harvesting of a corticocancellous bone graft from the anterior iliac crest with a nutrient vascular bundle from the deep circumflex iliac artery, debridement of the necrotic scaphoid, press-fit fixation of the tailored graft, pin fixation, and microvascular anastomosis to the radial artery. Fixation in an upper-arm cast for 4 weeks, followed by lower-arm cast fixation including the thumb to the interphalangeal joint until week 12. Physiotherapy. Wrist splinting in patients enforced to heavy manual load. The described procedure has been practiced at the own institution since 1985 and evaluated in different studies. Using a free vascularized iliac bone graft, union could be achieved in 85% of patients with avascular scaphoid nonunion and in 80% with avascular proximal pole nonunion. The nonunion can be bridged in 93% following failed previous scaphoid screw fixation.

Ten-year follow-up of the non-porous Allofit cementless acetabular component

Cementless acetabular fixation has demonstrated superior long-term durability in total hip replacement, but most series have studied implants with porous metal surfaces. We retrospectively evaluated the results of 100 consecutive patients undergoing total hip replacement where a non-porous Allofit component was used for primary press-fit fixation. This implant is titanium alloy, grit-blasted, with a macrostructure of forged teeth and has a biradial shape. A total of 81 patients (82 hips) were evaluated at final follow-up at a mean of 10.1 years (8.9 to 11.9). The Harris Hip Score improved from a mean 53 points (23 to 73) pre-operatively to a mean of 96 points (78 to 100) at final review. The osseointegration of all acetabular components was radiologically evaluated with no evidence of loosening. The survival rate with revision of the component as the endpoint was 97.5% (95% confidence interval 94 to 100) after 11.9 years. Radiolucency was found in one DeLee-Charnley zone in four acetabular components. None of the implants required revision for aseptic loosening. Two patients were treated for infection, one requiring a two-stage revision of the implant. One femoral stem was revised for osteolysis due to the production of metal wear debris, but the acetabular shell did not require revision. This study demonstrates that a non-porous titanium acetabular component with adjunct surface fixation offers an alternative to standard porous-coated implants.

Anterior Cruciate Ligament Reconstruction With and Without Computer Navigation: A Clinical and Magnetic Resonance Imaging Evaluation 2 Years After Surgery

The purpose of this study was to evaluate the benefits of computer navigation on tunnel placement during anterior cruciate ligament reconstruction. A prospective, randomized, controlled study comparing computer navigation with manual operation was performed between December 2003 and April 2004. We assigned 20 patients to the computer navigation group and 20 patients to the manual navigation group. Surgery was performed by use of a patellar tendon autograft with press-fit fixation. A lateral radiograph of the knee at maximum extension was used to determine the exact position of the tibial tunnel at 4 days postoperatively. Outcomes were evaluated with International Knee Documentation Committee 2000, Tegner, and Lysholm scoring. There was an additional magnetic resonance imaging (MRI) evaluation of tunnel placement and graft quality at the most recent follow-up, approximately 24 months after surgery. The postoperative radiographs and 2-year postoperative MRI scans showed no differences between groups for tibial or femoral tunnel placement. In both groups the mean tibial tunnel placement was 46% of the maximal diameter of the tibia. There were no significant differences between groups for objective and subjective outcomes scoring. Although some qualitative differences existed between groups with respect to MRI graft appearance at 2 years, this had no correlation with overall results. No significant differences were found between computer-assisted and manually navigated anterior cruciate ligament reconstruction with regard to tunnel placement and clinical results at a mean of 2 years postoperatively. Level I, randomized, single-blinded, controlled trial.

Langzeitergebnisse der zementfreien konischen Balgrist-Spreizpfanne – Vergleichsanalyse zur Alloclassic-Schraubpfanne

The press-fit fixation of the conical Balgrist expansion cup (Allo Pro, Baar, Schweiz) is realised by the help of a (titanium alloy) split ring and a metal-backed inlay. The results and fixation principles of the cement-free Balgrist hip socket are analysed within a clinical and radiological long-time study and compared with those of the conical Zweymüller-Alloclassic CFS (Zimmer-GmbH, Winterthur, Schweiz) screw cup for a concluding evaluation. Between 1993 and 2003, 277 Balgrist hip sockets and between 1994 and 2000 130 Alloclassic-Zweymüller screw cups were performed consecutively in 364 patients considering similar indications with an average age of 54.6 years and 51.9 years, respectively. The clinical investigation was carried out with the Harris hip score (HHS). Radiological evaluation included a manual migration analysis according to Sutherland et al., Nunn et al. and Effenberger et al.; radiolucent lines were registered according to the zones of DeLee and Charnley. The survival rate of both cups was calculated on the basis of the Kaplan-Meier and the life-table analyses. Besides 4 (1.4%) aseptic loosenings, 5 Balgrist cups (1.8%) had to be replaced because of infection and another 1 (0.8%) because of persisting pain. Three Balgrist sockets (1.1%) showed a migration > 2 mm. In the Alloclassic group 1 cup (0.8%) was considered as being migrated, another cup (0.8%) had to be replaced due to infection. Considering aseptic loosening and radiological migration as an end point, the cumulative survival of the Balgrist cup at 13 years was 97.3%, that of the Zweymüller-Alloclassic cup at 10 years was 99.2%. In comparison with the Alloclassic group, the Balgrist hip sockets showed increased radiolucent lines of zone 1 (p < 0.001), without any effects on the survival time or the clinical result however. Both cups resulted in good to excellent clinical results in the HHS (91 points). The long-term analysis of the Balgrist hip socket proved that the concept of the retightening conical expansion cup leads to good clinical results and fulfils the minimum survival rate of 95% at 10 years as demanded by Delaunay and Kapandji. The good results obtained with the aid of this concept are comparable to those of the Alloclassic screwing cup.

Posterior cruciate ligament reconstruction with allogenic achilles tendon under arthroscopy in 19 cases

Objective To evaluate the method and its effect of posterior cruciate ligament (PCL) reconstruction with allogenic achilles tendon under arthroscopy.Methods We reviewed ninteen patients who were underwent arthroscopic PCL reconstruction using the allogenic achilles tendon from January 2004 to January 2008.A special technique was allowed for the standardized harvest of cylindrical calcaneus bone,ensuring adequate press-fit fixation within the femoral and tibial tunnels,and the function of the knee joint was assessed according to the Lysholm score.Results Ninteen patients were followed up.Before operation,the mean Lysholm score was 61 points (54～69 points).Twelve months later after operation,the score was 92 points (76～95 points).The excellent and good results were obtained in 89%.Conclusion Our study indicates that arthroscopic PCL reconstruction with allogenic achilles tendon can effectively improve the stability of the knee joint.It is important to achieve favorable result that the precise position is taken in the femoral and tibial tunnels in operation,and systematic rehabilitation training is performed after operation. Key words: Posterior cruciate ligament injuries; Arthroscopy methods; Tendons transplantation

Tension Degradation of Anterior Cruciate Ligament Grafts With Dynamic Flexion-Extension Loading: A Biomechanical Model in Porcine Knees

This study investigates the influence of various femoral anterior cruciate ligament graft fixation methods on the amount of tension degradation and the initial fixation strength after cyclic flexion-extension loading in a porcine knee model. One hundred twenty porcine digital extensor tendons, used as 4-stranded free tendon grafts, were fixated within porcine femoral bone tunnels by use of extracortical button, cross-pin, or interference screw fixation. One hundred twenty porcine patellar tendon-bone grafts were fixated by use of cross-pin, interference screw, or press-fit fixation. Each femur-graft complex was submitted to cyclic flexion-extension loading for 1,000 cycles throughout different loading ranges, and the total loss of tension was determined. After cyclic testing, the grafts were loaded to failure, and the data were compared with a pullout series without cyclic loading. Tension degradation after 1,000 cycles of flexion-extension loading averaged 62.6% +/- 10.0% in free tendon grafts and 48.9% +/- 13.35% in patellar tendon-bone grafts. There was no influence of the loading range on the total amount of tension degradation. The total amount of tension degradation was the highest with interference screw fixation of free tendon and patellar tendon-bone grafts. Despite excessive loss of tension, the initial fixation strength of the femur-graft complex was not reduced. The method of femoral graft fixation significantly influenced tension degradation during dynamic flexion-extension loading. Femoral graft fixation methods that secure the graft close to the tunnel entrance and that displace the graft substance from the center of the bone tunnel show the largest amount of tension degradation during cyclic flexion-extension loading. The graft substance, not the fixation site, was the weakest link of the graft complex within this investigation. We believe that the graft fixation method should be considered when aiming to improve the precision of femoral graft placement in anterior cruciate ligament reconstruction.

Microporous Pure β–Tricalcium Phosphate Implants for Press-Fit Fixation of Anterior Cruciate Ligament Grafts: Strength and Healing in a Sheep Model

A sheep study was conducted to test a press-fit technique using microporous pure beta-tricalcium phosphate (beta-TCP) dowels for fixation of the anterior cruciate ligament (ACL) graft. Microporous (5 mum) cylindrical plugs of beta-TCP (diameter, 7 mm; length, 25 mm) with interconnecting pores were used. The material featured a novel configuration of structure and surface geometry. Implants were tested by use of press-fit fixation of ACL grafts with and without bone blocks in 42 sheep over a period of 24 weeks. Biomechanical, radiologic, histologic, and immunohistochemical evaluations were performed. In load-to-failure tests at 6, 12, and 24 weeks after surgery, the intra-articular graft always failed, not the fixation. Grafts showed bony fixation in the tunnel at 6 weeks and primary healing at the junction of the tunnel and joint after 24 weeks. Tricalcium phosphate was resorbed and simultaneously replaced by bone. Remodeling was still incomplete at 24 weeks. In the sheep model microporous beta-TCP implants used with press-fit fixation of ACL grafts permit early functional rehabilitation. After 6 weeks, the graft is fixed by woven bone or bony integration. Implanted microporous tricalcium phosphate is resorbed and replaced by bone. In a sheep model we showed that primary healing of ACL grafts with resorption and bony replacement of the fixating implant can be achieved by means of press-fit fixation with pure beta-TCP.