The influence of femoral rollback on patellofemoral contact loads in total knee arthroplasty.

Increasing femoral rollback in flexion is thought to reduce patellofemoral contact load in total knee arthroplasty (TKA). The objectives of this study were to quantify the dependence of patellar load on rollback and to assess the effectiveness of posterior cruciate ligament (PCL)-retaining, PCL-sacrificing, and PCL-substituting TKA types in generating rollback. Nine cadaver knees were tested in simulated squatting. Six TKAs that were expected to produce varying amounts of femoral rollback were evaluated: PCL-retaining TKA, PCL-sacrificing TKA, a commercially available PCL-substituting TKA, and 3 modified PCL-substituting TKAs in which the anteroposterior position of the tibial post was varied. Kinematics, quadriceps loads, and patellofemoral contact loads were recorded. Significant differences in rollback were observed in the 30 degrees to 90 degrees flexion range. PCL-sacrificing TKAs generated the least rollback. PCL-retaining TKAs produced greater rollback but had the most variability. PCL-substituting TKAs produced the greatest and most reproducible rollback. Moving the tibial post posteriorly further increased rollback. Increased rollback correlated with reduced patellar load (-2.2%/mm). Reductions in patellar load of 17.6% were observed. Quadriceps loads were reduced by increasing rollback but to a smaller degree (-0.9%/mm). Rollback primarily affects patellar load rather than quadriceps load or efficiency.

Bending stiffness, torsional stability, and insertion force of cementless femoral stems.

In cementless total hip arthroplasty, increased femoral stem flexibility and decreased fracture propensity are desirable characteristics. The slotting and tapering of the stem have been introduced to achieve this. These features should not, however, be allowed to interfere with the ability of the distal stem to provide initial mechanical stability, especially under rotation. This study was done to investigate the ability of slotted and tapered stem designs to reduce stiffness and insertion force while still maintaining adequate torsional strength. The torsional strength, maximum insertion force, and insertional work of straight, slotted, and taper stems were measured by inserting each type into rigid polyurethane foam and torque testing to failure. Bending stiffness of each stem design was calculated using numerical methods. When compared to a straight stem, a unislot stem has similar torsional strength, maximum insertional force, and work of insertion. The bending stiffness is decreased by 19% to 82% depending on the bending direction. A trislot design decreased torque strength by 29%, maximal insertion force by 36%, and work by 11%. Bending stiffness was decreased by 74% and was not dependent on bending direction. A 0.5-mm taper decreased torque strength by 11% and insertional work by 14%. No difference was seen in maximum insertional force. We conclude that the design features studied (slots and taper) are effective in decreasing stem stiffness and reducing fracture propensity.

Femoral stem insertion generates high bone cement pressurization.

Adequate bone cement pressurization is critical in obtaining optimal femoral cement mantles during total hip arthroplasty. Pressurization can be generated during insertion of the femoral stem into the cement-filled canal. This may be clinically useful in augmenting conventional cement gun pressurization. Two factors, which were expected to influence the amount of insertion-induced pressurization, are the cement's cure state (viscosity) at the time of insertion and the femoral stem profile. This study evaluated the effect of these factors on cement pressurization during stem insertion. Femoral stems were inserted at a controlled rate into a reusable, simulated femoral canal. Intramedullary pressures were monitored at four locations along the canal's medial midline. The intrusion factor quantity, which accounts for pressure magnitude, duration of pressurization, and cement viscosity, was developed to quantify pressurization. Stem insertion into late cure stage (high viscosity) cement resulted in significantly higher intramedullary pressures (as much as 187% higher) and intrusion factors (as much as 43% higher) as compared with early stage (low viscosity) cement. The highest pressures and intrusion factors were found in the distal canal. A tapered stem profile resulted in significantly higher pressures (as much as 65%) and higher intrusion factors (as much as 63%) than a straight stem.

Arthrodesis of the knee: experience with intramedullary nailing.

Knee arthrodesis using an intramedullary nail has gained acceptance as treatment in difficult cases such as infection after total knee arthroplasty (TKA), neuropathic joint, and obesity. A retrospective review of 22 cases treated at our institution using an intramedullary nail for knee arthrodesis was performed. Deep infection after primary (11) or revision (6) TKA was the most common indication for this procedure. A long intramedullary nail was used in 3 cases, a long nail with a proximal interlocking screw was used in 6 cases, and a customized nail with a valgus bend and a proximal interlocking screw was used in 11 cases. A modular knee fusion nail was used in 1 case. Successful fusion occurred in all cases, although 4 patients required additional surgery. Average operative blood loss was 748 mL, and average time to union was 7 months. Shortening of the extremity averaged 3.2 cm. Tibiofemoral alignment was improved by using a customized valgus nail (average, 3.1 valgus; range, 1-5) when compared with a straight nail (average, 0.2 valgus; range, 3 varus to 3 valgus). No patient developed infection in the hip or ankle region as a result of the long intramedullary nail. Intramedullary nailing is an excellent technique for knee arthrodesis in difficult cases. A customized proximal interlocking nail with 5 degrees to 7 degrees of valgus and 5 degrees of anterior angulation improves tibiofemoral alignment and is straightforward to insert or extract should it be necessary. Stability and pain relief are rapid, and the fusion rate is maximized.

The effect of patella preparation for total knee arthroplasty on patellar strain: a comparison of resurfacing versus inset implants.

This study was conceived to quantify variables in surgical technique that may lead to patellar fracture after total knee arthroplasty. Anterior surface strain on load-bearing cadaveric patellae was measured before and after patellar resurfacing or inset prosthesis placement. Variables studied were i) the type of prosthesis (resurfacing vs inset), ii) the depth of reaming or osteotomy during surface preparation, and iii) the overall thickness of the polyethylene/patella composite after implantation. Comparison of measured patellar surface strain patterns for the different prosthesis styles, which were implanted at varying depths, provided statistically significant data from which the following clinically relevant conclusions can be made: i) Patellar resurfacing is superior to inset prosthesis placement when comparing postoperative patellar strain (22% vs 28% increase in strain compared with preoperative values). ii) Osteotomy for patellar resurfacing is more tolerant to error by excess cutting than is reaming for inset prosthesis placement (25% vs 42% increase in strain with a 2-mm error). iii) If the ideal depth of cut or reaming is surpassed, attempts to re-create the original patellar thickness by using a thicker prosthesis are mechanically detrimental. Key words: patella, strain, resurfacing, complications.

Hip osteotomy arthroplasty: ten-year follow-up.

We previously reported the initial success of combined osteotomy and arthroplasty of the hip for arthritis with femoral deformity. This technique has gained acceptance. We now report, for the first time, the ten year clinical and radiographic results with histology of 2 specimen. The osteotomies healed and the proximal femoral segment remained viable. One of three patients is symptom free without subsequent operative treatment. One of three patients had revision for acetabular loosening at eight years and biopsy of the proximal femur showed the proximal femoral segment to be viable. One of three patients had loosening of a macrofit bipolar prosthesis which required revision to total hip replacement at five years. Histology revealed viability of the proximal femur. All three patients are doing well at ten year follow-up. Based on the results of this study and current knowledge, the technique of osteotomy and arthroplasty for hip arthritis associated with femoral deformity is effective when combined with current techniques of ingrowth femoral component of total hip arthroplasty.

The effect of surface coating of femoral prostheses implanted without cement: a 2- to 4-year follow-up study.

A randomized, concurrently controlled, prospective, single-blinded, multicenter study was done to evaluate the effect of proximal surface coating of a femoral prosthesis on clinical and radiographic results of cementless total hip arthroplasty (THA). The Profile femoral prosthesis (DePuy, Warsaw, IN), an anatomic titanium alloy stem, was used in one of three configurations: (1) smooth, (2) porous coated, or (3) hydroxyapatite (HA) coated. Ninety-one cases were enrolled in the study, with seven cases lost to follow-up and 79 cases available for clinical review with 24- to 48-month follow-up. The study shows that HA-coated stems performed as well, if not better than, porous-coated or smooth stems. Results show HA-costed stems with statistically superior total Harris hip scores (microHA = 96.0) than smooth stems (microS = 85.1) (Student's t-test, P = 0.004). This was primarily due to differences between the functional score of the two groups (microHA - 31.6; microS = 27.9, P = 0.003). Porous-coated stems were intermediate in performance (microPC = 89.8), with hip scores that were statistically indistinguishable from both smooth and HA-coated stems. Our data support the hypothesis that clinical differences exist and are attributable to the type of surface coating used for the cementless femoral components in THA.

One-stage revision of periprosthetic fractures around loose cemented total hip arthroplasty.

Fourteen cases of femoral fracture occurring about a loose cemented proximal femoral prosthesis are presented. All fractures occurred with relatively minor trauma, and significant preinjury osteolysis was present in all cases. Treatment consisted of immediate surgical revision of the loose femoral component using a long-stem noncemented component in conjunction with cerclage wiring. In most instances, morselized bone graft was used. Strut grafts were used in seven cases to improve stability. Two patients with extensive bone loss were unable to support a prosthesis and were treated with whole femoral allografts. Follow-up ranged from 24 to 84 months (mean, 49 months), except for one patient lost to follow-up at 12 months; evaluations consisted of Harris hip scores and radiographic analysis for fracture healing and implant stability. All fractures healed, and patient function increased dramatically. Postoperative Harris hip scores increased to an average of 74 points. Complications consisted of one postoperative fracture and four patients with femoral component loosening. No cases of component loosening were seen in the five cases in which components were designed for distal stability (four fully porous-coated, one fluted). Of the seven cases relying on proximal stability, two cases of early loosening and two cases of late loosening occurred. We recommend revision with long-stem, cementless implants in conjunction with cerclage wiring and strut grafts for the treatment of femoral fractures about loose cemented hip prostheses. Implant stability distal to the fracture is emphasized.

The transepicondylar axis approximates the optimal flexion axis of the knee.

The traditional understanding of knee kinematics holds that no single fixed axis of rotation exists in the knee. In contrast, a recent hypothesis suggests that knee kinematics are better described simply as two simultaneous rotations occurring about fixed axes. Knee flexion and extension occurs about an optimal flexion axis fixed in the femur, whereas tibial internal and external rotations occur about a longitudinal rotation axis fixed in the tibia. No other translations or rotations exist. This hypothesis has been tested. Tibiofemoral kinematics were measured for 15 cadaveric knees undergoing a realistic loadbearing activity (simulated squatting). An optimization technique was used to identify the locations of the optimal flexion and longitudinal rotation axes such that simultaneous rotations about them could best represent the measured kinematics. The optimal flexion axis was compared with the transepicondylar axis defined by bony landmarks. The longitudinal rotation axis was found to pass through the medial joint compartment. The optimal flexion axis passed through the centers of the posterior femoral condyles. No significant difference was found between the optimal flexion and transepicondylar axes. To an average accuracy of better than 3.4 mm in translation, and 2.9 degrees in orientation, knee kinematics were represented successfully by simple rotations about the optimal flexion and longitudinal rotation axes. The optimal flexion axis is fixed in the femur and can be considered the true flexion axis of the knee. The transepicondylar axis axis, which is identified easily by palpation, closely approximates the optimal flexion axis.

Knee kinematics in genesis total knee arthroplasty. A comparison of different tibial designs with and without posterior cruciate substitution in cadaveric specimens.

Knee joint kinematics after total knee arthroplasty (TKA) are not well understood. This study measured knee kinematics before and after TKA in six cadaveric specimens. Different tibial surface contours (standard, flat, and dished) and slopes (10 degrees and 15 degrees) with the posterior cruciate ligament (PCL) intact as well as a posterior-stabilized design were studied. The anteroposterior and proximal-distal displacements of the tibia relative to the femur were measured during active knee extension. For the standard design, it was possible to restore the normal position of the tibia relative to the femur at 90 degrees of flexion to within 2 mm; however, restoration of the tibiofemoral position was not achieved with the knee in the extended position. At 90 degrees of flexion, all of the TKA components resulted in a posteriorly positioned tibia compared with the normal knee. The standard, flat, and dished components shifted the tibia into a proximal position compared with the normal knee, while the 15 degrees and posterior-stabilized components shifted the tibia distally. With the knee in the extended position, the standard, flat, dished, and posterior-stabilized designs placed the tibia posteriorly and proximally compared with the normal position of the tibia relative to the femur. The 10 degrees and 15 degrees sloped components placed the tibia in a more anterior position. Of the PCL-retaining designs tested, the 10 degrees sloped tibial component produced the closest to normal knee kinematics. Overall, normal kinematic behavior of the knee was not restored after TKA.

Cementless hemispheric acetabular components. A 4- to 8-year follow-up report.

A retrospective radiographic analysis was performed on 71 cementless acetabular components followed from 4 to 8 years after surgery. A Harris-Galante (Zimmer, Warsaw, IN) cup was used in 46 cases and an Optifix (Smith & Nephew Richards, Memphis, TN) cup was used in 25 cases. There were 66 primary and 5 revision cases. Nonprogressive radiolucencies were common in both types of cups (64% of Optifix, 70% of Harris-Galante). Radiolucencies were almost exclusively less than or equal to 1 mm in width and were most common in zones 1 and 3. Ten cups had continuous but nonprogressive radiolucencies, none greater than 1 mm in all three zones. No radiolucent lines wider than 2 mm were seen in any case. Four cups had progressive radiolucency that stabilized. Radiolucency around fixation screws was seen in one case, and demonstrated stable ingrowth at revision surgery. No cases of osteolysis, screw breakage, migration, or loss of fixation surface occurred. A single case of a broken locking mechanism of a Harris-Galante cup 2 years after liner exchange is reported.

Posterior cruciate ligament strain biomechanics in total knee arthroplasty.

To evaluate the role of the posterior cruciate ligament in total knee arthroplasty, 8 normal whole-leg cadaveric legs were studied. Strain patterns of the posterior cruciate ligament were measured during active and passive knee flexion extension. Total knee arthroplasty was performed, and posterior cruciate ligament strain was measured again. The standard tibial insert was removed, and 3 additional tibial trays were used: flat, 10 degrees sloped, and 15 degrees sloped. The posterior cruciate ligament strain was recorded for each tibial insert. Total knee arthroplasty with a standard insert produced a large range of posterior cruciate ligament strain values (+/- 6%). Of the 8 specimens, 3 produced excessively taut posterior cruciate ligament strain, 3 were slack, and 2 returned strain to the baseline strain value. Changing the surface contour and slope of the tibial inserts did not produce any consistent change in the posterior cruciate ligament strain pattern. The ability of total knee arthroplasty to reproduce normal posterior cruciate ligament strain behavior has not been demonstrated.

Allograft-host mismatch in revision total hip replacement.

Mismatch between a structural femoral allograft and the distal host canal is a difficult problem in femoral reconstruction for revision of total hip replacement. A technique is presented that satisfactorily solves this problem and offers additional advantages over other allograft techniques, as illustrated in two cases.

Penetration of piperacillin-tazobactam into cancellous and cortical bone tissues.

The penetration characteristics of piperacillin-tazobactam into cortical and cancellous bone tissues were investigated in 10 patients undergoing total hip replacement. The concentration ratios of piperacillin/tazobactam were 9.4 +/- 1.8 in cancellous bone tissue and 8.0 +/- 2.2 in cortical bone tissue, which were close to the 8:1 ratio of drugs administered. The mean ratios of drug concentrations in bone and plasma for cancellous and cortical tissue were 23 and 18%, respectively, for piperacillin and 26 and 22%, respectively, for tazobactam. The concentrations of tazobactam achieved are sufficient to exert anti-beta-lactamase activity and supportive of clinical trials involving bone and joint infections, including those caused by beta-lactamase-producing pathogens.

Tibial plateau coverage in total knee arthroplasty.

Optimizing coverage of the resected tibial plateau is an important consideration in total knee arthroplasty. The tibial coverage of eight different tibial tray designs was examined in 35 resected tibial specimens. When no component overlap was permitted, the average tibial coverage of the different designs ranged from 76.4% to 80.8%. When the component was allowed slight overlap, a "surgical fit," the average coverage ranged from 78.5% to 85.5%. As a group, the six symmetric designs provided more coverage than the two asymmetric designs (p < 0.05). Areas of poor coverage were identified, and different tray geometries were compared. Asymmetric tibial components are thought to be more anatomic in nature and therefore cover the tibial plateau surface more completely than symmetric components. The results of this study do not support this, and in fact demonstrate that symmetric components can provide more coverage when compared with two asymmetric component designs.

Cementless hemispheric acetabular components. 2-4-year results.

A retrospective clinical and radiographic analysis was performed on 99 patients (106 hips) undergoing total hip arthroplasty with noncemented Harris-Galante (Zimmer, Warsaw, IN) or Optifix (Smith Nephew Richards, Memphis, TN) acetabular components. There were 94 primary and 12 revision procedures with a minimum follow-up period of 24 months (range, 24-52 months). The cups were evaluated for evidence of vertical and horizontal migration, as well as the presence of radiolucencies at the bone-implant interface. Age, sex, component inclination and medialization, cup coverage, and number of fixation screws used were examined to determine the influence of these factors on the incidence of cup migration or radiolucent line formation. A radiolucent line was present in at least one zone in 60% of the Harris-Galante and 45% of the Optifix cups. Progressive radiolucent lines were noted in two of the Optifix and three of the Harris-Galante components. Two Harris-Galante cups (1.9%) were revised. There were no Optifix cup migrations or evidence of instability in the Optifix or remaining Harris-Galante cups. Although there was a trend toward an increased incidence of radiolucencies in those cups lacking complete coverage, no statistically significant radiographic predictors for failure or impending failure could be determined from this short-term follow-up study. With the exception of the two revisions, all acetabular components performed well clinically over the study period.

Failure of the polyethylene liner leading to notching of the femoral component in bipolar prostheses.

Polyethylene wear is an increasingly recognized problem in joint replacement surgery. Three cases of polyethylene wear in bipolar hip prostheses are presented. Owing to failure of the polyethylene liner, impingement of the metal shell produced notching of the femoral component.

Operative treatment of distal femoral fractures proximal to total knee replacements.

Twenty fractures of the distal part of the femur proximal to a total knee replacement were treated operatively by members of the New England Trauma Study Group. Notching of the anterior aspect of the femoral cortex was associated with only two of these fractures, and none of the knee prostheses was loose at the time of the fracture. All twenty fractures were treated with open reduction and stable internal fixation, and the operation on fifteen fractures was supplemented with bone grafts. Every fracture healed, and eighteen healed after a mean of sixteen weeks (range, six to forty weeks). Union of the other two fractures was delayed, but repeat open reduction and internal fixation combined with autogenous bone-grafting resulted in union. After operative treatment, the patients returned to the level of activity that they had had before the fracture. The pre-existing tibiofemoral alignment and range of motion of the knee were also restored. At the time of follow-up, the average clinical rating of the Knee Society for all twenty knees had not decreased compared with the score before the fracture.

Prevention of longitudinal crack propagation around a femoral prosthesis: a study of cerclage wire fixation.

This study examined the effect of single versus triple-wrap cerclage fixation techniques in preventing propagation of a longitudinal fracture around a cementless femoral prosthesis. A proximal filling femoral component was implanted in 14 matched pairs of fresh-frozen bovine femora, following placement of a 45-mm longitudinal crack in the anteromedial cortical wall of the proximal femur. In one group of seven pairs, a single cerclage wire was applied to one specimen of each pair. A triple-wrap of a single cerclage wire was similarly placed in one specimen of each of the other seven pairs. All specimens were axially loaded on a materials testing system machine and the force required to propagate the fracture of the proximal femur was recorded. A triple-wrap cerclage technique required a significant increase in the force to propagate a proximal femur fracture around a non-cemented prosthesis when compared to a single cerclage wire.

Longitudinal crack propagation in bone around femoral prosthesis.

Intraoperative femoral fracture is a well-recognized technical complication of cementless total hip arthroplasty. This study was designed to establish an in vitro model for initiation and propagation of fractures of the proximal femur in cementless THA and to assess the effect of fracture fixation in the form of cerclage wiring and drilling a hole in the distal extent of the fracture line. Fourteen human anatomic femur specimens were studied. Longitudinal cracks were made and propagation was performed on a materials testing system machine. A drill hole at the tip of a longitudinal crack does not prevent crack propagation. However, cerclage wiring has a statistically significant effect (p less than 0.025) on the ability of the fractured femur to withstand increased load.