Verification of biomechanical factors of gait related to medial knee loading in patients 6 Months after total knee arthroplasty.

Background: The knee adduction moment (KAM) is considered an index for estimating the knee mechanical load, and increased KAM peak and KAM impulse are related to increased medial knee load and progression of knee joint degeneration. We aimed to verify the biomechanical factors of gait related to medial knee loading in patients 6 months after TKA. Methods: Thirty-nine women who underwent TKA were enrolled. A three-dimensional gait analysis was performed 6 months postoperatively to generate data on the lower limb joint angle, moment, and power at the backward component (braking phase) and forward component (propulsion phase) peaks of the ground reaction force. Medial knee loading was evaluated using the time-integrated value of KAM during the stance period (KAM impulse). The higher the value of the KAM impulse, the higher the medial knee joint load. The relationships between the KAM impulse and the data for biomechanical factors were evaluated using partial correlation analysis with gait speed as a control factor. Results: In the braking phase, the KAM impulse positively correlated with the knee adduction angle (r = 0.377) and negatively correlated with the toe-out angle (r = -0.355). The KAM impulse positively correlated with the knee adduction angle (r = 0.402), the hip flexion moment (r = 0.335), and the hip adduction moment (r = 0.565) and negatively correlated with the toe-out angle (r = -0.357) in the propulsive phase. Conclusion: The KAM impulse 6 months after TKA was related to the knee adduction angle, hip flexion moment, hip adduction moment, and toe-out angle. These findings may provide fundamental data for controlling variable medial knee joint load after TKA and implementing patient management strategies to ensure implant durability.

Postoperative femoral component rotation using posterior condylar referencing is difficult to predict preoperatively in total knee arthroplasty.

BACKGROUND: Many modern total knee arthroplasty (TKA) systems use posterior condylar axis (PCA) to derive the surgical trans-epicondylar axis (sTEA), which is widely regarded as the gold standard for femoral component rotation. However, the previous imaging studies showed that cartilage remnants can alter component rotation. We therefore conducted this study to determine how the postoperative femoral component rotation deviated from the preoperative plan using three-dimensional (3D) computed tomography (CT) which does not consider cartilage thickness. METHODS: A total of 123 knees of 97 consecutive osteoarthritis patients who underwent the same primary TKA system using PCA reference guide were included. External rotation was set at 3°or 5° according to the preoperative 3D CT plan. The number of varus knees (hip-knee-ankle (HKA) angle >5° varus) and valgus knees (HKA >5° valgus) were 100 and 5, respectively. The deviation from the preoperative plan was measured using overlapping pre- and postoperative 3D CT images. RESULTS: The mean (standard deviation, range) deviation from the preoperative plan in varus group, external rotation setting of 3°, 5° in varus group and valgus group were 1.3° (1.9°, -2.6° - 7.3°), 1.0° (1.6°, -2.5° - 4.8°), 3.3° (2.3°, -1.2° - 7.3°), and -0.8° (0.8°, -2.0°-0.0°), respectively. No correlation was found between the deviation from the plan and the preoperative HKA angle in varus group (R = 0.15, P = 0.15). CONCLUSIONS: The effect of asymmetric cartilage wear for rotation in the present study was supposed to be approximately 1° as mean value, but it can vary widely from patient to patient.

Early postoperative relationship between patient-reported outcome measures and gait biomechanical factors after total hip arthroplasty.

BACKGROUND: Patient-reported outcome measures (PROMs) have recently been considered as indicating clinical outcomes after total hip arthroplasty (THA). Although various factors are reportedly associated with post-THA and PROMs, the relationship with gait parameters, which are objective assessment factors after THA, remains unclear. RESEARCH QUESTION: What is the relationship between PROMs and gait biomechanical factors four weeks after THA? METHODS: Forty-five patients (six men and 39 women) who underwent THA were included. Three-dimensional gait analysis was performed four weeks post-THA; joint angle, internal moment, and power of the lower extremity at the first and second peaks of the vertical component of the floor reaction force were assessed for the operated side. PROMs were evaluated using the Japanese Orthopedic Association Hip Disease Evaluation Questionnaire (JHEQ). The relationship between the JHEQ score and extracted gait parameters was analyzed using gender and gait speed as control factors. RESULTS: For the JHEQ sub-domain, movement was positively correlated with the internal knee extension moment values at the first peak (r = 0.347). There was no significant correlation between JHEQ and the internal hip abduction moment value at the first peak. Mental status was negatively correlated with the hip flexion angle value at the second peak (r = -0.373), and positively correlated with the hip flexion moment value (r = 0.348). Total JHEQ scores and mental status were negatively correlated with the power of hip flexion value at the second peaks, respectively (r = -0.316, -0.444). SIGNIFICANCE: The results of this study may provide recovery guidelines to be used as an index for gait assessment in the early post-THA period. Further studies are needed to verify whether gait parameters can improve PROMs in the early post-THA period.

False malalignment after computer-navigated total knee arthroplasty.

BACKGROUND: Although computer navigation has improved component alignment in total knee arthroplasty (TKA), radiographic outliers are reported with a wide range in literature even using this technique. We hypothesized that the postoperative malalignment after computer-navigated TKA was partially derived from the inherent problems with two-dimensional (2D) measurement such as inaccuracies in measurement due to the knee position during the radiographic examination and the direction of the X-ray beam. We therefore conducted this study to determine how often knees with malalignment on 2D imaging were truly mal-aligned on three-dimensional (3D) reconstructed imaging. METHODS: Sixty-two computer-navigated primary TKAs performed in 47 patients were included in this study. In all cases, a weight-bearing long-leg radiograph was obtained after TKA. 3D measurements were performed for outliers 2° or more in coronal alignment of the femoral or tibial component. RESULTS: For the 18 femoral mal-aligned components on 2D imaging, eight (44.4%) were not truly mal-aligned on 3D imaging (P = 0.0014). For the eight tibial mal-aligned components on 2D imaging, all knees (100%) were not truly mal-aligned on 3D imaging (P < 0.0001). CONCLUSIONS: A considerable number of the false malalignments were included on 2D measurement. Postoperative component alignment in the computer-navigated TKA might be much better than previously reported.

Relationships between early postoperative gait biomechanical factors and patient-reported outcome measures 6 months after total knee arthroplasty.

BACKGROUND: This study was focused on the gait parameters of the knee extensor and hip abductor muscle groups, which are believed to contribute to knee joint function improvement in early postoperative TKA. The associations between patient-reported outcome measures (PROMs) 6 months after total knee arthroplasty (TKA) and the early postoperative internal knee extension moment, knee extension negative joint power, and internal hip abduction moment while walking were investigated. METHODS: Twenty-one patients who underwent primary TKA for knee osteoarthritis were included. Three weeks after TKA, gait at a comfortable speed was measured by three-dimensional motion analysis. The lower limb joint angle, internal joint moment, and joint power parameters on the operated side while standing were calculated. The PROMs 6 months after TKA were assessed using the Japanese Knee Osteoarthritis Measure (JKOM). The relationship between each gait biomechanical parameter and the JKOM was determined. RESULTS: The maximum internal knee extension moment and maximum knee extension negative joint power during the early stance showed moderate negative correlations with the JKOM scores. The maximum internal hip abduction moment was not correlated with the JKOM scores. The maximum internal hip extension moment during the early stance and internal hip flexion moment during the late stance showed moderate negative correlations with the total JKOM scores. CONCLUSION: The early postoperative internal knee extension moment, maximum knee extension negative joint power, and internal hip extension and flexion moment are associated with patient PROMs 6 months after TKA.

Intra- and interobserver reliability and agreement in three-dimensional computed tomography measurements of component positions after total knee arthroplasty.

BACKGROUND: Accurate evaluation of the postoperative position of total knee arthroplasty (TKA) components is crucial in the analysis of the association of alignments with clinical outcomes. The aim of this study was to investigate the reliability of measurements of component positions after TKA using three-dimensional computed tomography (3D-CT) reconstruction. METHODS: Two independent orthopedic surgeons (an attending surgeon and a fellow) examined 30 knees after primary TKA. The coronal, sagittal, and rotational positions of the femoral and tibial components were measured twice at an interval of six weeks on 3D-CT images reconstructed using ZedKnee software. Mean intra- and interobserver differences of measured angles were calculated, and the intra- and interobserver reliability was determined using intraclass correlation coefficients (ICCs), with agreement assessed by Bland-Altman analysis. RESULTS: The mean intraobserver difference between alignment measurements for femoral and tibial components was <2° (range 0.23-1.17°) and the mean interobserver difference was <1° (range 0.22-0.97°). The intra- and interobserver ICCs were >0.8 for all component positions. The only systematic bias found in the intra- and interobserver agreements occurred for the sagittal position of the femoral component. CONCLUSION: Three-dimensional-CT measurements of component positions after TKA showed good intra- and interobserver reliability for the femoral and tibial components in coronal, sagittal and rotational positions. The intra- and interobserver agreements were favorable for all but the sagittal position of the femur. These results suggest that 3D-CT can be used to evaluate the alignment of all TKA components except for the sagittal position of the femur.

Preoperative planned distance between the skin surface and the guide rod provides accurate posterior tibial slope in total knee arthroplasty.

BACKGROUND: Although sagittal tibial alignment in total knee arthroplasty (TKA) is important, no landmark exists to achieve reproducible slope. It is theoretically demonstrated that the preoperative planned distance between the skin surface and the rod can be a useful guide for the tibial slope in the previous imaging study. We conducted this retrospective study to confirm whether the results of the study are repeatable in an intra-operative situation. METHODS: Fifty-five consecutive TKAs using the distance from the extramedullary cutting guide rod to the skin surface as a reference guide for the tibial slope were performed and tibial component positioning was compared with 55 knees performed using the accelerometer-based portable navigation. The tibial component alignment was evaluated with a computed tomography (CT)-based three-dimensional (3D) software. RESULTS: The absolute mean deviation from the targeted slope in the proposed method was significantly smaller than the portable navigation (1.0° and 1.7°, respectively, p = 0.0025). The outlier rate beyond 3° was 0% in the proposed technique (16.4% in the portable navigation, p = 0.0014). CONCLUSIONS: The preoperative planned distance between the skin surface and the guide rod is a useful technique to provide accurate posterior tibial slope in TKA.

An accelerometer-based navigation did not improve the femoral component positioning compared to a modified conventional technique of pre-operatively planned placement of intramedullary rod in total knee arthroplasty.

INTRODUCTION: Although the most commonly used method of femoral component alignment in total knee arthroplasty (TKA) is intramedullary (IM) guides, this method demonstrated a limited degree of accuracy. Because of the femoral anterior bowing, the tip of the guide rod will impinge on the anterior cortex if a long rod is inserted. We hypothesized that the pre-operative planned insertion depth of the rod could increase the accuracy of the femoral component positioning in conventional TKA (modified conventional technique). Accelerometer-based, portable navigation device has been postulated to have better accuracy than conventional TKA in component positioning. The purpose of this study was to compare the post-operative femoral component alignment of TKA using the modified conventional technique with the accelerometer-based navigation. MATERIALS AND METHODS: Fifty-five knees underwent TKA using the modified conventional technique and femoral component positioning was compared with 55 knees performed using the accelerometer-based navigation device. The femoral component alignment was evaluated with a CT-based three-dimensional software. RESULTS: The mean absolute deviation from targeted alignment in the sagittal plane was significantly less in the modified conventional cohort than in the accelerometer-based navigation cohort (1.1° vs 2.6°, P < 0.001). In the modified conventional cohort, 96.4% had an alignment within 3° of a targeted angle in the coronal plane (vs 89.1% with the accelerometer-based navigation, P = 0.14), and 96.4% in the sagittal plane (vs 74.5% with the accelerometer-based navigation, P < 0.001). CONCLUSION: The modified conventional technique is a simple and equal to or more accurate method than the accelerometer-based navigation in positioning the femoral component in TKA at a mid-volume hospital.

Residual medial tightness in extension is corrected spontaneously after total knee arthroplasty in varus knees.

PURPOSE: Although soft tissue balancing is considered important for successful total knee arthroplasty (TKA), it is unclear whether the laxity and balance achieved intraoperatively change postoperatively. A recent study demonstrated anaesthesia significantly influenced knee joint laxity after TKA; however, there has been no comparison of the varus-valgus laxity immediately after TKA and in the postoperative period under the same anesthetic conditions. Therefore, quantitative stress arthrometric studies were conducted under identical conditions to identify changes in coronal ligament laxity after TKA spontaneously. METHODS: A consecutive series of 28 knees with varus of more than 5° in 28 patients undergoing staged bilateral TKAs was prospectively evaluated. Postoperative varus-valgus laxity was measured immediately after surgery, with the patient still under spinal anaesthesia; and again at the time of the contralateral TKA, again under anaesthesia. The mean time between the first and second operations was 9.7 ± 7.3 months. RESULTS: Mean medial laxity significantly changed from 2.4° ± 1.6° just after the first operation under anaesthesia to 3.8° ± 1.4° just after contralateral TKA under anaesthesia (p < 0.001), but no significant change occurred in lateral laxity (5.6° ± 2.4° just after the first operation and 5.7° ± 2.1° after contralateral TKA, n.s.). Significant negative correlations were identified between laxity immediately after surgery and the amount of laxity change on both the medial (R = - 0.63, p < 0.001) and lateral sides (R = - 0.53, p < 0.001). CONCLUSION: Spontaneous soft tissue correction occurs after TKA. The findings from this study provides a rationale that it is not necessary for surgeons to perform the medial soft tissue release until the soft tissue tension is equalized on both the medial and lateral sides which has the risk of excessive release leading to instability. In situations where the surgeon is confronted with a knee that becomes too tight or too loose depending on the insert thickness, it is recommended to choose the thicker insert with the understanding that the knee will initially have a slightly tighter medial compartment that will loosen over time. The results of this study provide technical considerations that can help a surgeon achieve adequate postoperative stability. LEVEL OF EVIDENCE: IV.

Case-related factors affecting cutting errors of the proximal tibia in total knee arthroplasty assessed by computer navigation.

PURPOSE: The aim of this study was to determine factors that contribute to bone cutting errors of conventional instrumentation for tibial resection in total knee arthroplasty (TKA) as assessed by an image-free navigation system. The hypothesis is that preoperative varus alignment is a significant contributory factor to tibial bone cutting errors. METHODS: This was a prospective study of a consecutive series of 72 TKAs. The amount of the tibial first-cut errors with reference to the planned cutting plane in both coronal and sagittal planes was measured by an image-free computer navigation system. Multiple regression models were developed with the amount of tibial cutting error in the coronal and sagittal planes as dependent variables and sex, age, disease, height, body mass index, preoperative alignment, patellar height (Insall-Salvati ratio) and preoperative flexion angle as independent variables. RESULTS: Multiple regression analysis showed that sex (male gender) (R = 0.25 p = 0.047) and preoperative varus alignment (R = 0.42, p = 0.001) were positively associated with varus tibial cutting errors in the coronal plane. In the sagittal plane, none of the independent variables was significant. CONCLUSION: When performing TKA in varus deformity, careful confirmation of the bone cutting surface should be performed to avoid varus alignment. The results of this study suggest technical considerations that can help a surgeon achieve more accurate component placement. LEVEL OF EVIDENCE: IV.

Revision Total Hip Arthroplasty Using a Cementless Cup Supporter and Iliac Autograft: A Minimum of 15-Year Follow-Up.

BACKGROUND: Bone deficiency in revision total hip arthroplasty is a surgical challenge. The Murata-Chiba cup supporter (MC support ring) is an acetabular component supporter for a cementless porous-coated cup. The purpose of this study is to examine the clinical and radiographic outcomes of reconstruction of acetabular bone deficiency using iliac autografts supported by an MC support ring in a revision setting with minimum 15-year follow-up. METHODS: Fifty-nine consecutive revision total hip arthroplasties (57 patients) using the MC support ring were followed for a minimum of 15 years. Nine hips had American Academy of Orthopaedic Surgeons type II deficiency and 24 had type III defects of the acetabulum. Clinical outcomes were evaluated using the Harris hip score. Radiographic evaluation included assessment for loosening and bone graft incorporation. Kaplan-Meier survival analysis was performed. RESULTS: At a minimum 15-year follow-up (mean, 17.6 years), 32 patients (33 hips) were alive, 17 patients (18 hips) were deceased, and 8 patients (8 hips) were lost to follow-up. The mean Harris hip score improved from 44.3 to 77.2 at final follow-up. Four hips required reoperation due to deep infection (2 hips) and liner dissociation (2 hips), but no acetabular components were revised for aseptic loosening. Incorporation of the bone graft occurred in all cases. One unrevised patient had radiographic failure. Survivorship at 15 years with re-revision or radiographic failure as the end point was 90.6% (95% confidence interval, 83.0%-98.8%). CONCLUSION: The reconstruction of acetabular bone deficiency using autografts supported by an MC support ring provided satisfactory clinical and radiological results at 17.6 years postoperatively.

The rectangular flexion gap is associated with an increased knee flexion angle in a cruciate-sacrificing rotating platform mobile-bearing total knee arthroplasty.

BACKGROUND: The knee flexion angle after a total knee arthroplasty is an important indicator of clinical outcome. However, there is little appropriate information about the correlation between the ligament balancing and knee flexion angle after total knee arthroplasty. The purpose of this study was to investigate the effect of the ligamentous balance in extension and flexion on knee flexion angle one year after posterior cruciate ligament sacrificing rotating platform total knee arthroplasty. METHODS: Eighty-five total knee arthroplasties in 71 patients were investigated in this study. The postoperative knee flexion angle and the percentage of improvement in the balanced group in which the difference between varus and valgus was less than 2° and the unbalanced group in extension and the rectangular group in which the asymmetry of the flexion gap was within 2° and the trapezoidal group in flexion were compared. The factors affecting postoperative knee flexion angle were also investigated in a forced entry multiple regression analysis. RESULTS: The mean flexion angle improved significantly from 116.2° to 122.5° in the rectangular group. By contrast, in the trapezoidal group, no significant improvement was seen (from 115.5° to 117.4°). The statistically significant difference was found between the rectangular and trapezoidal group in flexion in terms of the improvement of the knee flexion angle while there was no difference between the balanced and unbalanced group in extension. The multiple regression analysis showed that the asymmetry of the flexion gap was a predictor of the postoperative knee flexion angle. CONCLUSIONS: Asymmetric flexion gap affected negatively the postoperative knee flexion angle after posterior cruciate ligament sacrificing rotating platform total knee arthroplasty. A gap balancing technique is recommended for this type of implant.

The distance from the extramedullary cutting guide rod to the skin surface as a reference guide for the tibial slope in total knee arthroplasty.

BACKGROUND: Although sagittal tibial alignment in total knee arthroplasty (TKA) is important, no landmarks exist to achieve a reproducible slope. The purpose of this study was to evaluate the clinical usefulness of the distance from the guide rod to the skin surface for the tibial slope in TKA. METHODS: Computer simulation studies were performed on 100 consecutive knees scheduled for TKA. The angle between the line connecting the most anterior point of the predicted tibial cut surface and the skin surface 20 cm distal to the predicted cut surface (Line S) and the mechanical axis (MA) of the tibia in the sagittal plane was measured. RESULTS: The mean (±SD) absolute angle difference between the Line S and the MA was 0.9°±0.7°. The Line S was almost parallel to the MA in the sagittal plane (95% and 99% within two degrees and three degrees of deviation from MA, respectively). CONCLUSION: The guide rod orientation is a surrogate for the tibial cut slope because the targeted posterior slope is usually built into the cutting block and ensuring the rod is parallel to the MA in the sagittal plane is recommended. Therefore the distance between the skin surface and the rod can be a useful guide for the tibial slope. LEVEL OF EVIDENCE: II.

Varus and valgus stress tests after total knee arthroplasty with and without anesthesia.

INTRODUCTION: Retrospective studies demonstrated inadequate soft tissue balance is associated with the long-term outcome of total knee arthroplasty (TKA). However, most of these studies have evaluated the joint laxity only postoperatively without anesthesia. Therefore information about the effect of anesthesia on knee laxity is important for soft tissue balancing at the time of surgery. This study was conducted to determine how anesthesia affects the varus and valgus stress tests after TKA. MATERIALS AND METHODS: A consecutive series of 26 patients undergoing staged bilateral TKA was evaluated. Varus and valgus laxity of the knee with the TKA implant was measured a few days before the contralateral TKA without anesthesia and again immediately after the contralateral TKA under spinal anesthesia. RESULTS: The laxity was significantly increased from 3.0° to 3.6° (p = 0.005) and from 4.7° to 5.7° (p = 0.007) in medial and lateral side, respectively, when the stress tests were performed under anesthesia in comparison to the laxity measured without anesthesia. The major change in laxity (≥3°) was measured in 6 (23%) patients tested without anesthesia. CONCLUSIONS: Anesthesia significantly influenced knee joint laxity after TKA. The findings of this study suggest that muscular forces impart a stabilizing force across the joint.

A Useful Anatomical Reference Guide for Stem Anteversion during Total Hip Arthroplasty in the Dysplastic Hip.

Computed tomography scans of 50 dysplastic hips were obtained and reconstructed using preoperative planning software for total hip arthroplasty. The anteversion of the stem implanted parallel to the line connecting the trochanteric fossa and the middle of the medial cortex of the femoral neck (T line) was measured. The cutting heights of 5mm and 10mm above the lesser trochanter were simulated. The mean difference of the anteversion of the stem using the T line and the native femoral anteversion was 2.7° (95% CI: 1.0°-4.5°) and 3.5° (95% CI: 1.5°-5.5°) at cutting heights of 5mm and 10mm respectively. An anteversion using a T line is compatible with native femoral anteversion even in developmental dysplasia of the hip.

Accuracy of the second metatarsal as a landmark for the extramedullary tibial cutting guide in total knee arthroplasty.

PURPOSE: The purpose of this study was to evaluate the accuracy of the second metatarsal (MT2) as a landmark for proximal tibial cutting in total knee arthroplasty (TKA). It was hypothesized that the accuracy of the MT2 is not high, especially in rheumatoid arthritis (RA) patients whose foot joints are apt to be involved. METHODS: Computer simulation studies on 48 RA knees and 45 osteoarthritis (OA) knees were performed. The deviations from the mechanical axis (MA) of the tibia when the guide rod was pointed toward the base of the MT2 or the distal part of the MT2 were measured. RESULTS: The mean deviation from MA was 0.8° ± 2.1° valgus (range 8.1°-6.3° valgus) and 1.2° ± 2.9° valgus (range 11.6°-7.9° valgus) at the base of the MT2, and at the distal part of the MT2, respectively. The outlier rate when using the base of the MT2 was lower than when using the distal part of the MT2 (12.9 vs 32.3%, p = 0.0032). The outlier rate was equivalent in OA and RA patients (n.s.). However, foot involvement in RA patients demonstrated a trend toward significance (base of MT2 p = 0.078, distal part of MT2 p = 0.068). CONCLUSIONS: The major clinical relevance was to raise caution about using the MT2. Surgeons should aim toward the base of the MT2, but avoid using it in RA patients with foot involvement. The accuracy of the MT2 is not high and it should be used only to supplement other landmarks. LEVEL OF EVIDENCE: II.

The T-line as an intraoperative landmark for reproducing the native femoral anteversion during hip arthroplasty.

INTRODUCTION: Three-dimensional computed tomographic (CT)-based preoperative planning for total hip arthroplasty (THA) enabled us to evaluate the cut surface of the femoral neck osteotomy. When we planned the stem placement in 20° of anteversion, we noticed that the line connecting the trochanteric fossa and the middle of the medial cortex of the femoral neck (T line) was coincident with the component torsion in many cases. We attempted to evaluate the accuracy of the T line for reproducing the native femoral anteversion during THA comparing it with the midcortical line, the reference guide previously reported by Suh. MATERIALS AND METHODS: The institutional review board allowed a retrospective review of CT images of 100 normal hip joints. We performed virtual THA using the non-anatomic straight stem at three different cutting heights of 5, 10, or 15 mm above the lesser trochanter. The anteversion of the stem implanted parallel to the T line or midcortical line was measured. RESULTS: The mean difference of the stem anteversion using the T line and the native femoral anteversion was -0.77º (95 % CI: -1.92º to 0.38º), 0.69º (95 % CI: -0.42º to 1.79º) and 3.38º (95 % CI: 2.29º-4.46º) at cutting heights of 5, 10 and 15 mm, respectively. Using the midcortical line, stems tended to retroversion. CONCLUSIONS: Aligning the stem parallel to the T line on the cut surface provides a good reproduction of the femoral anteversion. The T line can be an useful intraoperative reference guide for the anteversion of the femoral component in THA for patients without severe hip deformity.

The tibial crest as a practical useful landmark in total knee arthroplasty.

BACKGROUND: The middle one-third of the tibial crest in the coronal plane and the fibula in the sagittal plane are known as landmarks for extramedullary guides in total knee arthroplasty (TKA). However, there are few foundational anatomic studies about them. We conducted this study to confirm whether these landmarks are reliable. METHODS: We evaluated 100 Japanese knees using 3D imaging software. We examined our data for correlations between the angle of deviation from the mechanical axis and patient-specific factors (i.e. hip-knee-ankle angle, tibial length, tibial bowing, and tibial torsion) to determine whether there are any individual factors affecting their reliability. RESULTS: The mean angles between each of the axes defined by the fibula and the tibial crest with the mechanical axis were 2.9°±0.6° of valgus and 0.7°±0.9° of varus in the coronal plane and 2.2°±0.8° of posterior and 3.6°±1.0° of anterior inclination in the sagittal plane. The middle one-third of the tibial crest (TCL) was revealed as a useful landmark, especially in female patients, who possess TCLs that were within 3° of the tibial mechanical axis in the coronal plane. There were no patient-specific factors strongly affecting reliability of these landmarks. CONCLUSIONS: We can use these landmarks even if the patient has tibial bowing or severe varus deformity. Although not considering soft tissue thickness, our study demonstrated that the tibial crest in the coronal and sagittal planes could be useful guidelines in performing TKAs. LEVEL OF EVIDENCE: II.

The effect of rotational fixation error of the tibial cutting guide and the distance between the guide and the bone on the tibial osteotomy in total knee arthroplasty.

Computed tomography based computer simulation studies were made on fifty consecutive patients with osteoarthritis scheduled for TKA. Proximal tibial cutting was simulated with the cutting guide placed at different rotational errors (-10°, 0°, 10° and 20° of internal rotation) and different distances (4 cm and 8 cm) between the alignment rod and the bone. Only ten degrees of rotation error with 8 cm of distance resulted in over 3° of varus or valgus tibial cut. Our study demonstrated that rotational mismatch between the proximal and distal part of the tibia should be avoided and the distance between the alignment rod and the bone should be as short as possible to achieve proper tibial alignment.