Effects of Resection of Posterior Condyles of Femur on Extension Gap of Knee Joint in Total Knee Arthroplasty

Background

When evaluating the effects of the preparation of the flexion gap on the extension gap in total knee arthroplasty (TKA), the effects of posterior condylar resection and osteophyte removal on the extension gap should be differentiated. Although the amount of osteophytes differs between patients, posterior condylar resection is a procedure that is routinely implemented in TKA. The aim of this study was to assess the effects of the resection of the posterior condyle of the femur on the extension gap in posterior-stabilized (PS) TKA.

The Effect of a Sagittal Cutting Error of the Distal Femur on the Flexion-Extension Gap Difference in Total Knee Arthroplasty

The aim of this study was to determine how much a distal femoral cutting error would affect the flexion-extension gap difference (flexion gap minus extension gap) in total knee arthroplasty (TKA). We evaluated 15 knees using a computer-simulation technique. Bone cutting errors of − 2°, 2° and 4° of extension were simulated in three TKA systems. A distal femoral cutting error of 2° of extension or flexion caused a change in the difference between the flexion and extension gaps of approximately two mm in all three TKA systems. Surgeons should recognize that distal femoral cutting errors have a significant effect on the flexion-extension gap difference in TKA and pay particular attention to the alignment of the distal cutting surface.     

Bone Mineral Density of the Femur in Autopsy Retrieved Total Knee Arthroplasties

Bone mineral density (BMD), as measured by DEXA, can vary depending on bone rotation and fat content of soft tissues. We performed DEXA measurements, under controlled positioning, on 24 autopsy-retrieved femora from patients who had fully functional and asymptomatic successful TKA to determine periprosthetic BMD changes and compared results to 24 normal cadaveric femora. In TKA specimens, BMD was affected by gender, preoperative diagnosis, and zone under analysis. The lowest mean BMD was in the anterior femoral condylar zone. Males had higher mean BMD at all zones while patients with preoperative diagnosis of osteoarthritis had higher BMD in the posterior condylar zone. The mean BMD in the anterior femoral condylar zone in TKA specimens was significantly lower than in normal specimens without arthroplasties, most likely due to stress shielding.     

Reduction in Bone Volume Resection with a Newer Posterior Stabilized Total Knee Arthroplasty Design

Background

Posterior stabilized total knee arthroplasty requires an intercondylar notch to accommodate the cam housing that articulates with the tibial post to create femoral rollback required for deep flexion. The volume of bone resected for the intercondylar notch varies with implant design, and newer designs may accommodate high flexion with less bone resection.

Questions/Purposes

This study aims to analyze the bone volume and density resected from the intercondylar notch for three posterior stabilized implants from a single company: a Posterior Stabilized (PS) system, a Hi-Flex system (HF), and a rounded new box-reamer (RB) system and to further assess whether the newer RB with a cylindrical cutting tool would preserve more native bone.

Materials and Methods

Using a computer model, the PS, HF, and RB femoral components were digitally implanted into CT scans of 19 cadaver femurs. Nine cadavers were fit with a size 4 implant, six with size 3, and four with a size 2. The volume of intercondylar bone resected digitally for femoral preparation was measured. Bone density was measured by CT scans in Hounsfield units (HU). A paired t test was used to compare the mean volume of bone resected for each implant.

Results

For the size 4 femurs, the newer RB design removed 8% less intercondylar bone than the PS design (7,832 ± 501 vs. 8,547 ± 377 mm³, p < 0.001) and 28% less bone than the HF design (7,832 ± 501 vs. 10,897 ± 444 mm³, p < 0.001). The average HU for size 4 femurs for RB design was 427 ± 72 (PS = 399 ± 69, p < 0.001; HF = 379 ± 66, p < 0.001). For the size 3 femurs, the RB design removed 12% less intercondylar bone than the PS (6,664 ± 786 vs. 7,516 ± 648 mm³, p < 0.001) and 27% less bone than the HF (6,664 ± 786 vs. 9,078 ± 713 mm³, p < 0.001). HU for size 3 femurs for the RB design was 452 ± 70 (PS = 422 ± 53, p < 0.1; HF = 410 ± 59, p < 0.01). For the size 2 femurs, the RB design removed 5% less intercondylar bone than the PS (5,730 ± 552 vs. 6,009 ± 472 mm³, p < 0.01) and 22% less bone than the HF (5,730 ± 552 vs. 7,380 ± 532 mm³, p < 0.001). HU for size 2 femurs for the RB design was 430 ± 48 (PS = 408 ± 55, p < 0.01; HF = 385 ± 56, p < 0.01).

Conclusions

The newer RB design removes less bone from the intercondylar notch than the classic PS and HF designs in all sizes tested. The bone-conserving cuts incorporated into this newer implant design appear to preserve native bone without compromising design objectives.

Electronic supplementary material

The online version of this article (doi:10.1007/s11420-013-9340-1) contains supplementary material, which is available to authorized users.     

Primary Versus Secondary Distal Femoral Arthroplasty for Treatment of Total Knee Arthroplasty Periprosthetic Femur Fractures

Current methods of fixing periprosthetic fractures after total knee arthroplasty (TKA) are variable, and include open reduction and internal fixation (ORIF) via plating, retrograde nailing, or revision using standard revision TKA components or a distal femoral arthroplasty (DFA). The purpose of this study is to compare patients who failed plating techniques requiring subsequent revision to DFA to patients who underwent primary DFA. Of the 13 patients (9.2%) who failed primary ORIF, causes included nonunion (53.8%), infection (30.8%), loosening (7.7%), and refracture (7.7%). There were significantly more surgical procedures for ORIF revision to DFA compared to primary DFA. Complications for patients who underwent primary reconstruction with DFAs included extensor mechanism disruption (8.3%), infection (5.6%), and dislocation (2.8%). Primary reconstruction via ORIF is beneficial for preserving bone stock, but primary DFA may be preferred in osteopenic patients, or those at high risk for nonunion.     

Posteriorly Offset Femoral Component to Restore Anteroposterior Position of the Distal Femur in Revision Total Knee Arthroplasty

This study is based on a radiographic analysis of 50 cadaveric femurs (26 males, 24 females). The position of a press-fit stemmed revision total knee arthroplasty femoral component was simulated with templates. A diaphyseal engaging stem was templated in 74% of the subjects (23 males, 14 females). Every diaphyseal engaging stem required the use of a posterior offset coupler to achieve engagement in the femoral isthmus. In 26% of femurs (3 males, 10 females), anterior bowing of the distal metaphysis prevented the use of a diaphyseal engaging stem. Our results suggest that males have less flexion of the distal femur than females and can be templated effectively with a diaphyseal engaging posteriorly offset stem, whereas a metaphyseal flexed stemmed component templates better in females.     

Effect of Total Knee Arthroplasty on Coronal Alignment of the Ankle Joint

BackgroundThe effect of total knee arthroplasty (TKA) on the ankle joint is not entirely clear. The purpose of this study is to assess postoperative changes in the coronal alignment of the ankle joint in patients undergoing TKA for various degrees of knee deformity.MethodsThis retrospective study included 107 patients who had undergone TKA for primary osteoarthritis. In all cases, preoperative coronal alignment deformity of the knee was corrected in an attempt to restore the native mechanical axis of the knee. Patients were stratified into 3 groups according to the degree of knee coronal alignment correction achieved intraoperatively: group 1 (<10° varus/valgus correction, n = 60), group 2 (≥10° varus correction, n = 30), and group 3 (≥10° valgus correction, n = 17). Knee/ankle alignment angles were measured on full-length, standing anteroposterior imaging preoperatively and postoperatively and included the following: hip-knee-ankle angle, tibial plafond inclination (TPI), talar inclination (TI), and tibiotalar tilt angle.ResultsSignificant changes in ankle alignment, specifically with regard to TPI (9.5° ± 6.9°, P < .01) and TI (8.8° ± 8.8°, P = .03) were noted in the ≥10° valgus correction group compared to the other 2 groups. Regardless of the degree of knee deformity correction, TKA did not lead to significant changes in the tibiotalar tilt angle.ConclusionA correction of ≥10° in a genu valgum deformity can affect ankle joint alignment, leading to alterations in TPI and TI. These findings need to be taken into consideration in assessing candidates for TKA as a possible cause of postoperative ankle pain.     

A Comparison of Variable Angle Versus Fixed Angle Distal Femoral Resection in Primary Total Knee Arthroplasty

This study assessed whether using a variable distal valgus resection angle improved post-operative coronal lower limb alignment in total knee arthroplasty (TKA). Two groups were compared: Fixed (n = 124), where a fixed distal valgus resection angle of 7° was used; Variable (n = 87), where the resection angle was adjusted to the measured femoral mechanical anatomical (FMA) angle of the patient. FMA and mechanical femoro-tibial (MFT) angles were measured on pre-operative and post-operative hip-knee-ankle radiographs. 85% of patients in the Variable group had a post-operative MFT angle within 0° ± 3°compared to 69% in the Fixed group (P = 0.006). The use of a fixed distal femoral resection angle for all patients is not appropriate. Setting the resection to an individual patient’s FMA angle can significantly improve the post-operative MFT angle.     

Total Knee Arthroplasty After Failed Distal Femoral Varus Osteotomy Using Selectively Stemmed Posterior Stabilized Components

The purpose of this study was to evaluate the outcomes of patients treated with total knee arthroplasty (TKA) for progression of arthritis after distal femoral varus osteotomy. Twenty-two consecutive distal femoral varus osteotomies converted to TKA were reviewed at a mean follow-up of 5 years (range, 2-14 years). Stemmed femoral or tibial components were used in 5 knees with poor bone quality, while the remaining 17 knees were treated with unstemmed components. The mean Knee Society knee and function scores in surviving knees were 91 points (range, 67-100 points) and 64 points (range, 50-70 points) respectively at final follow-up. Two patients underwent revision arthroplasty for polyethylene wear and component loosening at 8 and 11 years after the index arthroplasty, respectively. Standard components provide satisfactory stability in TKA after distal femoral varus osteotomy after appropriate ligamentous balancing, without the need for stemmed or highly constrained components in the majority of patients.     

Posterior Cruciate Ligament Resection Does Not Consistently Increase the Flexion Space in Contemporary Total Knee Arthroplasty

IntroductionIt is accepted dogma in total knee arthroplasty (TKA) that resecting the posterior cruciate ligament (PCL) increases the flexion-space by approximately 4mm. Unfortunately, this doctrine is based on historical studies of limited size with variable technique. The aim of this study was to determine the effect of PCL-resection on in vivo tibiofemoral joint space dimensions in a cohort of modern TKAs.MethodsTibiofemoral joint space measurements were made during 129 standardized TKAs by two arthroplasty surgeons. A medial parapatellar approach, computer navigation and provisional bone cuts were performed in all cases with particular attention to preserving PCL integrity. The tibiofemoral gap was measured with a calibrated tension device at extension, 45-degrees, and 90-degrees before and after complete PCL-resection.Results51% of patients were female (66/129) with mean age and BMI of 69.5 years and 34.2 kg/m², respectively. After PCL-resection, mean change in center joint space dimension increased 0.33mm at extension, 0.95mm at 45-degrees, and 1.71mm at 90-degrees (P < .001). The 90-degree flexion-space opened ≥4mm in only 10% of patients. Dividing the flexion-space change by femoral implant dimension to account for patient size, the flexion-space at 90-degrees significantly increased more in females compared to males (P = .020).ConclusionThe tibiofemoral joint space increased progressively from extension to mid-flexion through deep-flexion after PCL-resection, yet was substantially less than reported in historical studies. However, large variation in flexion-space opening was observed with some patients failing to increase the flexion-space whatsoever with PCL-resection. This runs counter to conventional TKA understanding and should be considered in modern surgical education.Level of EvidenceTherapeutic Level III.     

Joint Gap in Mid-Flexion Is Not a Predictor of Postoperative Flexion Angle After Total Knee Arthroplasty

Background

Postoperative knee flexion angle is one of the most important outcomes of total knee arthroplasty (TKA). Intraoperative ligament balancing may affect the postoperative range of motion of the knee. However, the relationship between intraoperative ligament balancing and postoperative flexion angle was still controversial. The purpose of this study was to determine whether intraoperative joint gap affects postoperative knee flexion angle or not.

Gap Balancing vs. Measured Resection Technique in Total Knee Arthroplasty

A goal of total knee arthroplasty is to obtain symmetric and balanced flexion and extension gaps. Controversy exists regarding the best surgical technique to utilize to obtain gap balance. Some favor the use of a measured resection technique in which bone landmarks, such as the transepicondylar, the anterior-posterior, or the posterior condylar axes are used to determine proper femoral component rotation and subsequent gap balance. Others favor a gap balancing technique in which the femoral component is positioned parallel to the resected proximal tibia with each collateral ligament equally tensioned to obtain a rectangular flexion gap. Two scientific studies have been performed comparing the two surgical techniques. The first utilized computer navigation and demonstrated a balanced and rectangular flexion gap was obtained much more frequently with use of a gap balanced technique. The second utilized in vivo video fluoroscopy and demonstrated a much high incidence of femoral condylar lift-off (instability) when a measured resection technique was used. In summary, the authors believe gap balancing techniques provide superior gap balance and function following total knee arthroplasty.     

Comparison of Gap Balancing vs Measured Resection Technique in Patients Undergoing Simultaneous Bilateral Total Knee Arthroplasty: One Technique per Knee

BackgroundTotal knee arthroplasty requires careful surgical technique to attain the goal of a well-aligned and symmetrically balanced knee. Soft tissue balance and correct femoral component rotation are paramount in achieving these goals. The two competing techniques to select femoral component rotation and soft tissue balance are the gap balance technique and the measured resection technique.MethodsWe performed a randomized, prospective study to compare the two techniques in patients undergoing simultaneous bilateral total knee arthroplasty, whereby one technique was performed in each knee. Fifty (50) subjects were enrolled into the study. The inclusion criteria were osteoarthritic varus knee deformities with similar deformities in both knees. Subjects were followed up for a minimum of two years.ResultsThe knees balanced via the gap balance technique had significantly more posterior medial bone removed from the femur than those knees balanced via the measured resection technique (P < .001). Knees in the gap balance group tended to require more medial knee releases in extension and tended to have smaller sized femoral components as a result of cutting more bone from the femur in flexion. The modular tibial polyethylene bearing tended to be thicker in the gap balance group. Despite these differences, average knee flexion and functional revised Oxford Knee Scores at 2-year follow-up were not statistically different.ConclusionAt 2-year follow-up, there were no differences between the function and scores using the two techniques. Long-term follow-up will be necessary to evaluate any differences in long-term durability.     

Bone Mineral Density in the Proximal Femur and Contralateral Knee After Total Knee Arthroplasty

Osteoarthrosis (OA) is often associated with pain and disability, which are relieved after total knee arthroplasty (TKA), but the nature of bone changes associated with OA is controversial. We examined preoperative hip and contralateral knee bone mineral density (BMD) in patients requiring TKA and monitored the BMD changes postoperatively. Sixty-nine patients, scheduled to have TKA for osteoarthrotic knees, had both hips and contralateral knee BMD measured by dual-energy X-ray absorptiometry (DXA) at the time of operation (baseline) and at 1 yr after operation. X-rays of the knee joints were also taken to evaluate the severity of OA. Preoperatively, 27% and 38% of the patients had total hip BMD Z-score more than 1 SD in the operated side and contralateral hips, respectively. In all regions of interest (ROI), the mean baseline BMD of the affected side proximal femur was significantly lower than that of the contralateral side (p < 0.0005-0.019). The severity of OA was not associated with BMD. During 1-yr follow-up, the postoperative knee status and the physical activity of the patients (AKS score) improved. However, neither the hip nor the nonoperated knee BMDs increased. Knee OA is associated with significantly lower BMD values in the affected side compared with the contralateral hip, and these levels remained similar or decreased during a 1-yr follow-up. We conclude that improved mobility after TKA does not improve the effects of preoperative disuse-associated bone loss in the short term.     

Five-Year Risk of Conversion to Total Knee Arthroplasty After Operatively Treated Periarticular Knee Fractures in Patients Over 40 Years of Age

BackgroundPeriarticular knee fractures present a significant challenge to minimize post-traumatic osteoarthritis. The purpose of this study is to compare the rates of conversion to total knee arthroplasty (TKA) for different periarticular knee fractures, investigate the rate of knee injections as a more rapid assessment of knee symptoms, and identify risk factors that lead to conversion to TKA following periarticular fractures.MethodsA comprehensive retrospective review of the Humana administrative claims database was performed. A total of 2813 patients greater than 40 years of age with diagnosis code for tibial plateau fracture or distal femur fracture linked to a Current Procedural Terminology code of open reduction internal fixation between 2007 and 2011 were evaluated. The rates of TKA and knee injections within 5 years were compared. Cox proportional hazards model was used to evaluate risk factors for conversion.ResultsOf 2813 periarticular fractures, the 5-year rate of conversion to TKA was 3.3%. The rate of conversion for tibial plateau fractures was significantly higher at 4.5% compared to 2.3% for distal femur fractures (P = .001). Tibial plateau fracture, obesity, and female gender were risk factors found to portend an increased risk of conversion to TKA with hazard ratios of 1.77, 1.69, and 1.88, respectively. The overall rate of knee injections was 12.8% with an average time to injection of 18.2 months after open reduction internal fixation.ConclusionThe rate of conversion to TKA for periarticular knee fractures overall was 3.3%, while the rate of knee injections within 5 years of surgery was 12.8%, suggesting a not insignificant minority of patients require treatment for symptomatic knee pain.Level of EvidenceTherapeutic Level III.     

The Use of Cementless Components Does Not Significantly Increase Procedural Costs in Total Knee Arthroplasty

BackgroundModern cementless total knee arthroplasty (TKA) designs have shown promising early clinical success; however, concerns exist regarding the higher cost of the cementless implants. The purpose of this study is to evaluate the total facility cost of cementless vs traditional cemented TKA along with the effect of cementless fixation on short-term outcomes.MethodsWe reviewed a consecutive series of patients between 2015 and 2017 who underwent either cementless or cemented primary TKA. Itemized facility costs were calculated for every procedure using a time-driven activity-based costing algorithm. Controlling for demographic variables and medical comorbidities, we performed a multivariate analysis to identify independent risk factors for facility costs following TKA. Short-term outcome metrics including complications, readmissions, and patient-reported outcomes were compared between groups.ResultsAmong the 2426 primary TKA patients in this study, 119 (4.91%) were performed using cementless implants. When compared to cemented TKA, cementless TKA patients had higher implant costs ($3047.80 vs $2808.73, P < .0001), but lower supply costs ($639.49 vs $815.57, P < .0001) and lower operating room personnel costs ($982.01 vs $1238.26, P < .0001). When controlling for confounding variables, cementless fixation did not have a significant effect on total facility cost or outcomes.ConclusionIn conclusion, the use of cementless TKA implants did not significantly increase total procedural costs when compared to traditional cemented TKA components at our institution. Our data suggest that the increased cost of a cementless implant is recouped through savings in cost of cement and supplies, as well as shorter operative times. The authors encourage investigators at other institutions to use the authors' methodology to evaluate (preferably in a prospective manner) whether the findings from this study can be corroborated.     

Migration and Inducible Displacement of the Bicruciate-Stabilized Total Knee Arthroplasty: A Randomized Controlled Trial of Gap Balancing and Measured Resection Techniques

BackgroundThe goal of this study is to investigate the migration and inducible displacement of a bicruciate-stabilized (BCS) total knee arthroplasty implanted using gap balancing (GB) or measured resection (MR) surgical techniques. We hypothesized equal migration and displacement between the techniques.MethodsThe study is a single-blinded, prospective, randomized controlled trial, with allocation of 71 patients to either GB or MR groups. Fifteen patients were withdrawn, resulting in 31 patients in the GB group and 25 in the MR group. Patients received the JOURNEY II? BCS implant. Migration and inducible displacement were evaluated using radiostereometric analysis and patient examinations were performed at a 2-week baseline, and at 6 weeks, 3 months, 6 months, 1 year, and 2 years postoperation.ResultsNo differences (P > .05) existed between GB and MR groups for any measurement of tibial or femoral migration. Both groups had tibial migrations below 0.5 mm from baseline to 6 months, and below 0.2 mm from both 6 months to 1 year and 1-2 years postoperation. No differences (P > .05) were found between GB and MR groups for inducible displacement.ConclusionNo differences were found in implant migration or inducible displacement between GB and MR groups. The BCS implant can be expected to have migration risks on par with industry standards and both surgical techniques are safe and effective options for implantation of this implant design.     

Contact Kinematic Differences Between Gap Balanced vs Measured Resection Techniques for Single Radius Posterior-Stabilized Total Knee Arthroplasty

Background

Measured resection (MR) and gap balancing (GB) are common surgical techniques for total knee arthroplasty (TKA). Controversy has arisen as each conceptually differs in how the knee is balanced through bone and soft tissue management. The objective of the present study was to compare both the frequency of condylar liftoff and the location of femorotibial contact from extension through midflexion between patients undergoing GB or MR TKA.