What are the Outcomes of Secondary Patella Resurfacing for Dissatisfaction Following Primary Knee Arthroplasty? A Systematic Review and Meta-Analysis of 604 Knees.

BACKGROUND: Secondary patella resurfacing is often performed for dissatisfaction following primary knee arthroplasty where the native patella was retained. The purpose of this meta-analysis was to evaluate outcomes of secondary patella resurfacing. METHODS: The systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Studies reporting on patients who underwent secondary patella resurfacing after previous primary knee arthroplasty with retention of the native patella were considered eligible. The risk of bias was assessed using the Methodological Index for Non-Randomized studies tool. A random-effects model and the inverse-variance weighting method was used for meta-analysis. There were sixteen retrospective studies including 604 knees (594 patients) with a mean follow up of 42 months (range, 2 to 197). RESULTS: An overall improvement in patient-reported outcomes (PROMs) was achieved in 53% of cases from pooled data available for 293 knees [95% Confidence Interval (CI) (0.44, 0.62), I2=68% - moderate heterogeneity]. The pooled proportion of patients satisfied with the procedure was 59% [95% CI (48, 68), I2 = 70% - moderate heterogeneity] in a sample size of 415. There was a minimal rate (2%) of complication incidence when performing secondary patella resurfacing and a pooled rate of revision surgery of 10%. CONCLUSIONS: An improvement in pain, satisfaction, and PROMs was achieved in slightly more than half of the patients following secondary patella resurfacing. However, studies lacked standardized objective selection criteria for the procedure and the available data was predominantly retrospective, with high heterogeneity and variation in outcome reporting.

Analysis of published evidence on minimally invasive total hip arthroplasty.

Minimally invasive surgery has become a popular method of total hip arthroplasty. This study reviewed the literature to determine the number and quality of scientific publications analyzing different types of minimally invasive surgery approaches. The miniposterior approach has been studied the most and to our knowledge is the only approach with good quality randomized control study evidence. The overall length of follow-up and quality of reports for minimally invasive total hip arthroplasty is low.

The role of axial compressive and quadriceps forces in noncontact anterior cruciate ligament injury: a cadaveric study.

BACKGROUND: Compressive and quadriceps forces have been associated with noncontact anterior cruciate ligament (ACL) injury. The purpose of this study was to quantify the relative importance of each load component during noncontact ACL injury. HYPOTHESIS: We hypothesized that the introduction of a quadriceps force lowers the axial compressive force threshold to produce ACL injury. STUDY DESIGN: Controlled laboratory study. METHODS: Six pairs of fresh-frozen cadaveric knees, flexed to 15°, were loaded with axial compression (group A) or compression with a quadriceps force (group B) until failure. All specimens underwent axial compressive loading under displacement control with a time to peak load of 50 msec. The initial displacement of the MTS actuator was 8 mm and was increased in 2-mm increments with successive tests until catastrophic damage of the joint occurred. Failure was determined by a combination of clinical specimen examination and force-displacement data analysis and by dissection and direct visualization after failure was recognized. Differences in failure load between groups were examined using a paired t test (significance, P ≤ .05). RESULTS: In group A, there were 2 isolated ACL injuries, 2 ACL ruptures combined with a tibial plateau fracture, and 2 isolated tibial plateau fractures. In group B, there were 5 isolated ACL ruptures and 1 tibial plateau fracture. There was a significant difference in the average failure load between groups A and B: 10 832 N (95% confidence interval [CI], 9743-11,604 N) and 6119 N (95% CI, 4335-7903 N), respectively. CONCLUSION: Isolated compressive forces displayed an ability to produce an ACL injury in this cadaveric model, but the addition of a quadriceps load significantly reduced the compressive force required for ACL injury. CLINICAL RELEVANCE: Compressive and quadriceps forces contribute to noncontact ACL injury and should be taken into account when developing ACL injury prevention programs and rehabilitation after ACL reconstruction.

Computer-assisted techniques versus conventional guides for component alignment in total knee arthroplasty: a randomized controlled trial.

BACKGROUND: Optimal alignment of the prosthesis in total knee arthroplasty results in improved patient outcomes. The goal of this study was to determine the most accurate technique for component alignment in total knee arthroplasty by comparing computer-assisted surgery with two conventional techniques involving use of an intramedullary guide for the femur and either an intramedullary or an extramedullary guide for the tibia. METHODS: One hundred and seven patients were randomized prior to surgery to one of three arms: computer-assisted surgery for both the femur and the tibia (the computer-assisted surgery group), intramedullary guides for both the femur and the tibia (the intramedullary guide group), and an intramedullary guide for the femur and an extramedullary guide for the tibia (the extramedullary guide group). Measurements of alignment on hip-to-ankle radiographs and computed tomography (CT) scans made three months after surgery were evaluated. The operative times and complications were compared among the three groups. RESULTS: The coronal tibiofemoral angle demonstrated, on average, less malalignment in the computer-assisted surgery group (1.91°) than in the extramedullary (3.22°) and intramedullary (2.59°) groups (p = 0.007). The coronal tibiofemoral angle was >3° of varus or valgus deviation in 19% (seven) of the thirty-six patients treated with computer-assisted surgery compared with 38% (thirteen) of the thirty-four in the extramedullary guide group and 36% (thirteen) of the thirty-six in the intramedullary guide group (p = 0.022). The increase in accuracy with computer-assisted surgery came at a cost of increased operative time. The operative time for the computer-assisted surgery group averaged 107 minutes compared with eighty-three and eighty minutes, respectively, for the surgery with the extramedullary and intramedullary guides (p < 0.0001). There was no significant difference in any of the outcomes between the intramedullary and extramedullary guide groups. CONCLUSIONS: This study provides evidence that the implant alignment with computer-assisted total knee arthroplasty, as measured with radiography and computed tomography, is significantly improved compared with that associated with conventional surgery with intramedullary or extramedullary guides. This finding adds to the body of evidence showing an improved radiographic outcome with computer-assisted surgery compared with that following conventional total knee arthroplasty.

Hybrid cone-beam tomographic reconstruction: incorporation of prior anatomical models to compensate for missing data.

We propose a method for improving the quality of cone-beam tomographic reconstruction done with a C-arm. C-arm scans frequently suffer from incomplete information due to image truncation, limited scan length, or other limitations. Our proposed "hybrid reconstruction" method injects information from a prior anatomical model, derived from a subject-specific computed tomography (CT) or from a statistical database (atlas), where the C-arm X-ray data is missing. This significantly reduces reconstruction artifacts with little loss of true information from the X-ray projections. The methods consist of constructing anatomical models, fast rendering of digitally reconstructed radiograph (DRR) projections of the models, rigid or deformable registration of the model and the X-ray images, and fusion of the DRR and X-ray projections, all prior to a conventional filtered back-projection algorithm. Our experiments, conducted with a mobile image intensifier C-arm, demonstrate visually and quantitatively the contribution of data fusion to image quality, which we assess through comparison to a "ground truth" CT. Importantly, we show that a significantly improved reconstruction can be obtained from a C-arm scan as short as 90° by complementing the observed projections with DRRs of two prior models, namely an atlas and a preoperative same-patient CT. The hybrid reconstruction principles are applicable to other types of C-arms as well.

The effect of cement placement on augmentation of the osteoporotic proximal femur.

Femoroplasty, the augmentation of the proximal femur, has been shown in biomechanical studies to increase the energy required to produce a fracture and therefore may reduce the risk of such injuries. The purpose of our study was to test the hypotheses that: (1) 15 mL of cement was sufficient to mechanically augment the proximal femur, (2) there was no difference in augmentation effect between cement placement in the intertrochanteric region and in the femoral neck, and (3) cement placement in the femoral neck would predispose the proximal femur to an intertrochanteric fracture, whereas trochanteric placement would result in subtrochanteric fractures. In each of 18 pairs of osteoporotic human cadaveric femora, 15 mL of polymethylmethacrylate bone cement was injected into the trochanteric or femoral neck region of 1 femur, and the noninjected femur was used as the control. The augmentation effect of femoroplasty was evaluated under simulated fall conditions using a materials testing machine. Multiple linear regressions incorporating random effects were used to check for associations between covariates (bone mineral density, cement location, and treatment) and the parameters of interest (stiffness, yield energy, yield load, ultimate load, and ultimate energy). Significance was set at P < .05. It was found that femoroplasty with 15 mL of cement did not significantly increase stiffness, yield energy, yield load, ultimate load, or ultimate energy relative to paired controls. There were no significant differences in parameters of interest or fracture patterns in specimens augmented in the femoral neck versus the trochanter. It was concluded that 15 mL of cement was not sufficient to augment the proximal femur and that there was no biomechanical advantage to the placement of cement within the femoral neck versus the trochanter.

Mechanical evaluation of a 4-mm cancellous "rescue" screw in osteoporotic cortical bone: a cadaveric study.

OBJECTIVES: Obtaining sufficient fracture fixation in osteoporotic bone is challenging. The purposes of the current study were (1) to compare the pullout strength of a 4-mm cancellous screw (cancellous screw group) with that of a 3.5-mm cortical screw (cortical screw group), and (2) to measure the pullout strength of a 4-mm cancellous screw placed as a rescue screw (rescue screw group) in a stripped 3.5-mm cortical screw (stripped screw group) hole while controlling for bone density and cortical thickness. METHODS: We inserted 4 screws, one from each experimental group, into 11 osteoporotic cadaveric radii, while recording the insertion torque. Radii were mounted on a servohydraulic testing machine, and each screw was pulled out at a rate of 5 mm/min. Pullout strength was recorded. The effects of cortical thickness (near, far, and total), bone density, insertion torque, and the experimental screw group (cortical, cancellous, stripped, and rescue screw groups) on pullout strength were analyzed using multiple linear regression with random effects. Statistical significance was set at P < 0.05. RESULTS: There was no significant difference in pullout strength between the cortical and cancellous screw groups. The rescue screw group had significantly less pullout strength than did the cortical and cancellous screws, and only partly increased pullout strength compared with stripped screws. Bone density significantly affected pullout strength, but insertion torque and cortical thickness were not significant covariates. CONCLUSIONS: There seems to be no advantage in using a cancellous screw over a cortical screw in bicortical fixation in osteoporotic bone. Although the rescue screw provided greater pullout strength than the stripped screw, it is unknown if the purchase it provides is clinically sufficient.

Biomechanical comparison of three methods of sacral fracture fixation in osteoporotic bone.

STUDY DESIGN: Biomechanical cadaveric bench study. OBJECTIVE: To measure motion at the fracture site in an osteoporotic cadaveric sacral insufficiency fracture model before and after fracture creation, after fixation (via 1 of 3 fixation techniques), and after cyclic loading and to compare those values with motion of the intact pelvis. SUMMARY OF BACKGROUND DATA: Sacral insufficiency fractures occur frequently in the elderly and pose treatment challenges. Screw fixation and sacroplasty have been proposed as possible treatments. There is little information about the stabilization provided by these treatments. METHODS: We potted 18 osteoporotic cadaveric pelves, mounted them on a materials testing machine, measured sacroiliac (SI) joint motion with a vertical load applied to the lumbar spine, and created simulated sacral insufficiency fractures. Then, we measured fracture site motion under load and repaired the fracture using 1 of 3 techniques: a unilateral SI screw, a bilateral SI screw, or sacroplasty. A vertical compressive load (10-350 N) was applied cyclically at 0.5 Hz to the lumbar spine of the repaired specimens for 5000 cycles. Kinematic analysis was conducted prefracture, postfracture, postrepair, and after cyclic loading. RESULTS: Postfracture, there was a significant increase in motion relative to the intact SI joint. After fixation, the average motion in all 3 groups was similar to that of the intact pelvis. After cyclical loading, motion increased in all groups. No significant differences were found between treatments. CONCLUSION: All 3 fixation methods resulted acutely in motion similar to that of the intact pelvis. Although motion increased as a function of cyclical loading, no significant differences were found between fixation methods. All 3 repair methods reduced fracture site motion, but clinical studies are needed to determine if each method relieves pain and provides sufficient fixation for fracture healing.

Biomechanical comparison of extensile exposures in total knee arthroplasty.

The "banana peel" exposure is a novel technique for knee joint exposure that consists of partially peeling the patellar tendon off the tibia, leaving the extensor mechanism intact distally and laterally. Although good clinical results have been reported with this technique with no disruption of the extensor mechanism, concerns exist that it could cause extensor lag, quadriceps weakness, or patellar tendon rupture. We compared the banana peel exposure repair to tibial tubercle osteotomy repair, which we chose as our benchmark procedure because much is known about its associated healing and rehabilitation protocols. In our study of 16 paired, fresh-frozen human knee specimens, the 2 techniques were used alternately for the right and left knees. To measure acute strength, 10 pairs were tested. The patella was clamped and pulled superiorly at 25 mm/min until failure. For cyclical testing (6 pairs), the knee was extended from 90 degrees of flexion to 0 degrees for 2000 cycles at 0.25 Hz while we monitored the distance between the inferior pole of the patella and the tibial diaphysis using a passive optical kinematic measuring system. Mean failure strengths of the banana peel and osteotomy groups were 2642+/-1104 N and 2123+/-562 N, respectively, suggesting that the banana peel repair is not weaker than the osteotomy repair. Neither group had a significant increase (via paired Student t test, P>.05) in the distance between the inferior pole of the patella and the tibial diaphysis, suggesting that neither exposure would result in extensor lag.

Enhancement of mobile C-arm cone-beam reconstruction using prior anatomical models.

We demonstrate an improvement to cone-beam tomographic imaging by using a prior anatomical model. A protocol for scanning and reconstruction has been designed and implemented for a conventional mobile C-arm: a 9 inch image-intensifier OEC-9600. Due to the narrow field of view (FOV), the reconstructed image contains strong truncation artifacts. We propose to improve the reconstructed images by fusing the observed x-ray data with computed projections of a prior 3D anatomical model, derived from a subject-specific CT or from a statistical database (atlas), and co-registered (3D/2D) to the x-rays.The prior model contains a description of geometry and radiodensity as a tetrahedral mesh shape and density polynomials, respectively. A CT-based model can be created by segmentation, meshing and polynomial fitting of the object's CT study. The statistical atlas is created through principal component analysis (PCA) of a collection of mesh instances deformably-registered (3D/3D) to patient datasets.The 3D/2D registration method optimizes a pixel-based similarity score (mutual information) between the observed x-rays and the prior. The transformation involves translation, rotation and shape deformation based on the atlas. After registration, the image intensities of observed and prior projections are matched and adjusted, and the two information sources are blended as inputs to a reconstruction algorithm.We demonstrate recostruction results of three cadaveric specimens, and the effect of fusing prior data to compensate for truncation. Further uses of hybrid reconstruction, such as compensation for the scan's limited arc length, are suggested for future research.