Daniel A. Oakes

A Biomechanical Comparison of Tibial Inlay and Tibial Tunnel Posterior Cruciate Ligament Reconstruction Techniques Graft Pretension and Knee Laxity

Background Most posterior cruciate ligament reconstruction techniques use a tibial bone tunnel, which results in an acute bend in the graft as it passes over the posterior portion of the tibial plateau. Hypothesis The tibial inlay technique will result in lower graft pretensions, less laxity, and less stretch-out after cyclic loading. Study Design Controlled laboratory study. Methods Graft pretensions necessary to restore normal laxity at 90° of knee flexion (laxity match pretension) and anteroposterior laxities at five knee flexion angles were recorded in 12 fresh-frozen knee specimens with bone-patellar tendon-bone posterior cruciate ligament graft reconstructions using both techniques and two femoral tunnel positions. Results When the graft was placed in a central femoral tunnel, the tibial tunnel reconstruction required an average 15.6 N greater laxity match pretension than the tibial inlay reconstruction. There were no significant differences in mean knee laxities between the tibial tunnel and tibial inlay techniques at any knee flexion angle; both reconstruction techniques restored mean knee laxity to within 1.6 mm of intact knee values over the entire flexion range. Conclusions There was no important advantage of one technique over the other with respect to the biomechanical parameters measured.

Biomechanical comparison of tibial inlay and tibial tunnel techniques for reconstruction of the posterior cruciate ligament. Analysis of graft forces.

Background: The tibial inlay technique of reconstruction of the posterior cruciate ligament offers potential advantages over the conventional transtibial tunnel technique, particularly with regard to the graft force levels that develop over a functional range of knee flexion. Abnormally high graft forces generated during rehabilitation activities could lead to stretch-out of the graft during the critical early healing period. The purpose of this study was to compare graft forces between these two techniques and with forces in the native posterior cruciate ligament. Methods: A load cell was installed at the femoral origin of the posterior cruciate ligament in twelve fresh-frozen cadaveric knees to measure resultant forces in the ligament during a series of knee loading tests. The posterior cruciate ligament was then excised, and the femoral ends of 10-mm-wide bone-patellar tendon-bone grafts were attached to the load cell to measure resultant forces in the grafts. For the tunnel reconstruction, the distal bone block of the graft was placed into a tibial tunnel and thin stainless-steel cables interwoven into the bone block were gripped in a split clamp attached to the anterior tibial cortex. With the inlay technique, the distal bone block was fixed in a tibial trough with use of a cortical bone screw with a washer and nut. The proximal ends of all grafts were pretensioned to a level of force that restored intact knee laxity at 90° of flexion, and loading tests were repeated. Results: There were no significant differences in mean graft forces between the two techniques under tibial loads consisting of 100 N of posterior tibial force, 5 N-m of varus and valgus moment, and 5 N-m of internal and external tibial torque. Mean graft forces with the tibial tunnel technique were approximately 10 to 20 N higher than those with the inlay technique with passive knee flexion beyond 95°. Mean graft forces with both reconstruction techniques were significantly higher than forces in the native posterior cruciate ligament with the knee flexed beyond approximately 90° for all but one mode of loading. Conclusions: In this cadaveric testing model, neither technique for reconstruction of the posterior cruciate ligament had a substantial advantage over the other with respect to generation of graft forces. Clinical Relevance: The relatively high graft forces (compared with the forces in the native posterior cruciate ligament) observed beyond 90° of knee flexion after reconstruction of the posterior cruciate ligament with either the tunnel or the inlay technique suggest that rehabilitation activities that involve loading of the knee while it is flexed beyond 90° (such as kneeling, squatting, or climbing high stairs) should be avoided in the early postoperative period.

An Evaluation of Human Demineralized Bone Matrices in a Rat Femoral Defect Model

The osteoconductive and osteoinductive potential of two human allogeneic demineralized bone matrix putties were compared in a critical-sized athymic rat femoral defect model. Defects were treated with (1) a demineralized bone matrix in a hyaluronic acid carrier, (2) a demineralized bone matrix in a glycerol carrier, (3) a hyaluronic acid carrier alone, or (4) with no implant. Radiographic examinations and histologic analyses were done at 4, 8, and 16 weeks postoperatively. Eight of the 48 defects treated with a demineralized bone matrix and none of the 36 surgical controls showed complete radiographic healing by 16 weeks and no statistically significant difference between the radiographic scores for the two demineralized bone matrix preparations was found. On histologic review, both preparations of demineralized bone matrix had passive remineralization. The largest foci of endochondral ossification were seen in limbs treated with a demineralized bone matrix in a hyaluronic acid carrier. The 8-mm rat femoral defect allows for stringent assessment of the osteoinductive potential of bone graft substitutes. Hyaluronic acid and glycerol are viable carriers for demineralized bone matrices. As both de-mineralized bone matrices tested provided an adequate osteoconductive matrix and showed some, although limited, osteoinductive capacity, these materials should be used in clinical practice only as bone graft extenders or enhancers.

Osteoinductive applications of regional gene therapy: ex vivo gene transfer.

Gene therapy represents the new frontier of medical science. Currently, there are no completely satisfactory treatment options for bone repair problems such as fracture nonunion, revision total joint arthroplasty, tumor resections, and fusions of the spine. Autogenous bone grafts, allograft implants, and prosthetic implants have been used to treat these problems. However, there are significant limitations associated with these methods including limited supply and limited osteogenic potential. Gene therapy, involving the manipulation of endogenous cells to generate specific proteins, offers a potential solution for these problems. By transferring genes into cells at a specific anatomic site, the osteoinductive properties of growth factors can be used at physiologic doses for a sustained period to facilitate a more significant healing response. Successful gene therapy involves four key steps: transduction, transcription, translation, and expression. To achieve gene transduction of a target cell, gene therapy models use vectors to enhance the entry and expression of exogenous deoxyribonucleic acid into the target cells nucleus. The transduction of a gene can be performed via either an ex vivo or an in vivo approach. Although there are many potential target cells for gene therapy, the specific anatomic site, the quality of the bone, and the soft-tissue envelope, will influence the selection of the target cells for regional gene therapy. Gene therapy vectors delivered to a treatment site in osteoconductive carriers have yielded promising results. Several investigators have shown exciting results using ex vivo and in vivo regional gene therapy in animal models. Comparative studies and human clinical trials have not yet been performed but are necessary to identify the optimal genes and dosages for each specific application of regional gene therapy. In the future, the treatment options for bone loss problems will represent a clinical continuum based on the anatomic site, the condition of the target tissue bed, and the desired duration of protein production.

Disappointing Short-Term Results With the DePuy ASR XL Metal-on-Metal Total Hip Arthroplasty

Outcomes of ultralarge-diameter femoral heads used in metal-on-metal (MOM) total hip arthroplasty (THA) are relatively unknown. This study reports on early failures of the ASR XL (Depuy, Warsaw, Ind) and assesses whether a correlation with cup positioning exists. A retrospective review of 70 consecutive MOM THAs with ultralarge-diameter femoral head and monoblock acetabular component was conducted. Minimum follow-up was 24 months. Of 70 THAs, 12 (17.1%) required revision within 3 years for pain (7), loosening (3), and squeaking (2). Three additional THAs noted squeaking, 2 noted grinding, and 3 additional hips had persistent pain. In total, 20 (28.6%) of 70 demonstrated implant dysfunction. Acetabular components for all symptomatic hips were in acceptable range of cup abduction and anteversion. The failures noted with this design do not correlate to cup placement. The high rate of implant dysfunction at early follow-up suggests serious concerns with the concept of MOM THA with an ultralarge-diameter femoral head paired with a monoblock acetabular cup.

Impaction Bone Grafting for Revision Hip Arthroplasty: Biology and Clinical Applications

&NA; Impaction bone grafting techniques are useful when the orthopaedic surgeon is faced with large cavitary acetabular defects or a large ectatic femoral metaphysis or diaphysis. Impaction bone grafting of the acetabulum involves packing of cavitary defects with compressed particulate graft, followed by insertion of either a cemented or cementless acetabular component. Impaction grafting of the femur involves retrograde filling of the femoral canal with impacted particulate graft, creating a neomedullary canal into which a cemented femoral stem can be placed. Use of the impaction allografting technique is appealing, especially in young patients, because of its potential to restore bone stock. The technically demanding nature of the procedure, the risk of complications, and the unknown long‐term fate of the impacted allograft highlight the need for ongoing assessment of this technique for revision total hip arthroplasties.

Injury to the anterior cruciate ligament during alpine skiing: a biomechanical analysis of tibial torque and knee flexion angle.

Background The anterior cruciate ligament has been shown to be particularly susceptible to injury during alpine skiing. Tibial torque is an important injury mechanism, especially when applied to a fully extended or fully flexed knee. Purpose We wanted to record the forces generated in the anterior cruciate ligament with application of tibial torque to cadaveric knees in different positions. Study Design Controlled laboratory study. Methods Thirty-seven fresh-frozen cadaveric knees were instrumented with a tibial load cell that measured resultant force in the anterior cruciate ligament while internal and external tibial torques were applied to the tibia at full extension, 90° of flexion, full flexion, and forced hyperflexion. Results At each knee flexion position, mean force generated by 10 N·m of internal tibial torque was significantly higher than the mean generated by 10 N·m of external tibial torque. Mean forces generated by tibial torque at 90° of flexion were relatively low. During flexion-extension without tibial torque applied mean forces were highest (193 N) when the knee was hyperflexed. Conclusions Application of internal tibial torque to a fully extended or fully flexed knee represents the most dangerous loading condition for injury from twisting falls during skiing. Clinical Relevance Understanding of the mechanisms of falls can be used to design better equipment and to better prevent or treat injury.

Biomechanical effects of femoral notchplasty in anterior cruciate ligament reconstruction

Notchplasty is frequently performed in conjunction with anterior cruciate ligament reconstruction. Bench loading tests were performed on 26 fresh-frozen knee specimens to measure excursion of a bone-patellar tendon-bone graft, anterior-posterior laxity of the knee, and graft forces before and after performing a 2-mm and a 4-mm notchplasty. The mean intraarticular pretension required to restore normal anterior-posterior laxity at 30° of flexion (laxity-matched pretension level) was 27 N before notchplasty, 48 N after 2-mm notchplasty, and 65 N after 4-mm notchplasty. The mean graft pretension decreased 53% and 58%, respectively, on completion of a loading test series involving anterior-posterior and constant tibial loading forces. Mean laxity increased 1.4 mm at full extension and decreased 1.8 mm at 90° of flexion after a 2-mm notchplasty. Mean graft forces increased markedly between 30° and 90° of passive flexion after notchplasty. Our results show that after a notchplasty, a higher level of graft pretension will be necessary to restore normal laxity at 30° of flexion. This increased level of pretension, combined with changes in graft excursion, produced dramatic increases in graft force when the knee was flexed to 90°. These relatively high forces would be detrimental to a remodeling graft and could lead to subsequent failure of the reconstruction.

Biomechanical effects of medial–lateral tibial tunnel placement in posterior cruciate ligament reconstruction

With most posterior cruciate (PCL) reconstruction techniques, the distal end of the graft is fixed within a tibial bone tunnel. Although a surgical goal is to locate this tunnel at the center of the PCLs tibial footprint, errors in medial–lateral tunnel placement of the tibial drill guide are possible because the position of the tip of the guide relative to the PCLs tibial footprint can be difficult to visualize from the standard arthroscopy portals. This study was designed to measure changes in knee laxity and graft forces resulting from mal‐position of the tibial tunnel medial and lateral to the center of the PCLs tibial insertion. Bone–patellar tendon–bone allografts were inserted into three separate tibial tunnels drilled into each of 10 fresh‐frozen knee specimens. Drilling the tibial tunnel 5 mm medial or lateral to the center of the PCLs tibial footprint had no significant effect on knee laxities: the graft pretension necessary to restore normal laxity at 90° of knee flexion (laxity match pretension) with the medial tunnel was 13.8 N (29%) greater than with the central tunnel. During passive knee flexion–extension, graft forces with the medial tibial tunnel were significantly higher than those with the central tunnel for flexion angles greater than 65° while graft forces with the central tibial tunnel were not significantly different than those with the lateral tibial tunnel. Graft forces with medial and lateral tunnels were not significantly different from those with a central tunnel for 100 N applied posterior tibial force, 5 N m applied varus and valgus moment, and 5 N m applied internal and external tibial torque. With the exception of slightly higher graft forces recorded with the medial tunnel beyond 65° of passive knee flexion, errors in medial–lateral placement of the tibial tunnel would not appear to have important effects on the biomechanical characteristics of the reconstructed knee.

The Effect of Femoral Tunnel Position on Graft Forces During Inlay Posterior Cruciate Ligament Reconstruction

Background The femoral tunnel may be positioned centrally or eccentrically within the posterior cruciate ligament footprint during a single-bundle posterior cruciate ligament reconstruction. Hypothesis After reconstruction, graft forces are significantly different from those of the native posterior cruciate ligament and are affected by the position of the femoral tunnel. Study Design Controlled laboratory study. Methods The resultant force in the native posterior cruciate ligament was measured in nine cadaveric knees as the knee was flexed from —5° to 120° of flexion. Posterior cruciate ligament reconstruction was performed with the femoral side of the graft positioned centrally and then offset 5 mm eccentric to the central position. Results Mean graft forces were not significantly different between eccentric and central tunnel positions during passive knee extension between 120° and 0° of flexion; at 5° of hyperextension, the eccentric position generated significantly lower graft forces. For both reconstruction techniques, mean graft forces were significantly higher than those for the native posterior cruciate ligament beyond approximately 90° of flexion, for 5 N·m internal and external tibial torque; 5 N·m varus and valgus moment. Conclusions Graft force reductions achieved with the eccentric femoral position appear to be relatively small compared with the forces expected during rehabilitation and activities of daily living. Clinical Relevance After posterior cruciate ligament graft reconstruction, rehabilitation activities that load the knee at high degrees of flexion should be avoided to limit excessive forces on the maturing graft.