The Medial Tibial Plateau Can Be Used as a Direct Anatomical Reference for the Posterior Tibial Slope in Medial Unicompartmental Knee Arthroplasty.

There has been no consensus about how to determine the individual posterior tibial slope (PTS) intraoperatively. The purpose of this study was to investigate whether the tibial plateau could be used as a reference for reproducing individual PTS during medial unicompartmental knee arthroplasty (UKA). Preoperative computed tomography (CT) data from 48 lower limbs for medial UKA were imported into a three-dimensional planning software. Digitally reconstructed radiographs were created from the CT data as the lateral knee plain radiographs and the radiographic PTS angle was measured. Then, the PTS angles on the medial one-quarter and the center of the MTP (» and ½ MTP, respectively), and that on the medial tibial eminence (TE) were measured on the sagittal multiplanar reconstruction image. Finally, 20 lateral knee radiographs with an arthroscopic probe placed on the » and the ½ MTP were obtained intraoperatively, and the angle between the axis of the probe and the tangent line of the plateau was measured. The mean radiographic PTS angle was 7.9 ± 3.0 degrees (range: 1.7-13.6 degrees). The mean PTS angles on the » MTP, the ½ MTP, and the TE were 8.1 ± 3.0 degrees (1.2-13.4 degrees), 9.1 ± 3.0 degrees (1.4-14.7 degrees), and 9.9 ± 3.1 degrees (3.1-15.7 degrees), respectively. The PTS angles on the » MTP and the ½ MTP were strongly correlated with the radiographic PTS angle (r =0.87 and 0.80, respectively, p < 0.001). A statistically significant difference was observed between the mean angle of the radiographic PTS and the PTS on the TE (p < 0.01). The mean angle between the axis of the probe and the tangent line of the tibial plateau was -0.4 ± 0.9 degrees (-2.3-1.3 degrees) on the » MTP and -0.1 ± 0.7 degrees (-1.5-1.2 degrees) on the ½ MTP, respectively. An area from the medial one-quarter to the center of the MTP could be used as an anatomical reference for the individual PTS.

Referencing the Tibial Plateau With a Probe Improves the Accuracy of the Posterior Slope in Medial Unicompartmental Knee Arthroplasty.

Background: There is currently no consensus on intraoperative references for determining the posterior tibial slope (PTS) in medial unicompartmental knee arthroplasty (UKA). The medial tibial plateau could serve as a direct reference for determining the native PTS through the placement of a hook probe in the anteroposterior direction of the medial tibial plateau. This study aimed to examine the accuracy of this new referencing method. Methods: We consecutively performed 55 medial UKAs using our new method (study group), and the preoperative and postoperative PTS on lateral knee radiographs were examined. These outcomes were then compared with those of consecutive 50 medial UKAs performed using the conventional method (control group), which immediately preceded the start of the use of the new method. Results: The correlation coefficient between the preoperative and postoperative PTS of the study group was larger than that of the control group (0.887 and 0.482, respectively). The mean implantation error of the PTS in the study group was smaller than that of the control group (-1.1° ± 1.3° and -3.0° ± 3.2°, respectively; P < .0001). The percentages of knees within 2° of implantation error were 73% and 34% in the study and control groups, respectively (P < .0001). The root mean square errors in the study and control groups were 1.7° and 4.3°, respectively. Conclusions: The direct referencing method with a probe can significantly improve the accuracy of tibial sagittal alignment.

Treatment of thigh abscess caused by retroperitoneal perforation of cecal cancer: A case report.

Introduction and importance: Iliopsoas and iliacus abscesses are caused by hematogenous and lymphatic infections and the spread of inflammation in neighboring organs. A small number of cases have been reported in which inflammation spread not only within the iliopsoas muscle but also to the thigh. Here we report a case of retroperitoneal infiltration and perforation of cecal cancer that caused extensive abscess formation from the iliacus muscle to the thigh. Case presentation: An 80-year-old man who had undergone chemotherapy for cecal cancer had abdominal pain and right thigh pain without any particular attraction. CT images showed extensive abscess formation from the iliacus muscle to the subcutaneous part of the thigh due to retroperitoneal infiltration and perforation of cecal cancer. Ileocecal resection, colostomy, and retroperitoneal abscess drainage were performed for perforation of cecal cancer and pelvic abscess. Although the thigh was initially drained by a small incision, the infection did not heal. Extensive debridement and drainage were required for all of the contaminated areas, and after all the infection was completely cured. Clinical discussion: The optimal treatment for an abscess that has spread from the inguinal region to the thigh is unclear. In this case, active debridement and drainage of the infected area were effective and should have been done early. Conclusion: We believed that debridement and drainage should have been performed from the time of the first surgery not only by the small incision drainage but also for all of the contaminated areas when the infection had been widespread.

A direct referencing method of the tibial plateau for the posterior tibial slope in medial unicompartmental knee arthroplasty.

PURPOSE: There is no consensus on intraoperative references for the posterior tibial slope (PTS) in medial unicompartmental knee arthroplasty (UKA). An arthroscopic hook probe placed on the medial second quarter of the medial tibial plateau (MTP) in an anteroposterior direction may be used as a direct anatomical reference for the PTS. The purpose of this study is to investigate the availability and accuracy of this method. METHODS: Marginal osteophyte formation and subchondral depression of the MTP and angles between the bony MTP and the cartilage MTP were retrospectively evaluated using preoperative sagittal MRI of 73 knees undergoing medial UKA. In another 36 knees, intraoperative lateral knee radiographs with the probe placed on the MTP were prospectively taken in addition to the preoperative MRI. Then, angles between the bony MTP and the probe axis and angles between the preoperative bony MTP and the postoperative implant MTP were measured. RESULTS: Among 73 knees, one knee with grade 4 osteoarthritis had a posterior osteophyte higher than the most prominent point of the cartilage MTP. No subchondral depression affected the direct reference of the MTP. The mean angle between the bony MTP and the cartilage MTP was -0.8° ± 0.7° (-2.6°-1.0°, n = 72), excluding one knee with a "high" osteophyte. The mean angle between the bony MTP and the probe axis on the intraoperative radiograph was -0.6° ± 0.4° (-1.7-0.0, n = 36). The mean angle between the pre- and postoperative MTP was -0.5° ± 1.5° (-2.9°-1.8°). The root-mean-square (RMS) error of these two PTS angles was 1.6° with this method. CONCLUSION: Cartilage remnants, osteophyte formation and subchondral bone depression do not affect the direct referencing method in almost all knees for which medial UKA is indicated. When the posterior "high" osteophyte of the MTP is noted on preoperative radiography, preoperative MRI or CT scan is recommended to confirm no "high" osteophyte on the medial second quarter. The accuracy of this method seems equal to that of robotic-assisted surgery (the RMS error in previous reports, 1.6°-1.9°).

Nontuberculous mycobacterial infection of the knee after arthrocentesis for idiopathic hemarthrosis: A case report.

INTRODUCTION: Nontuberculous mycobacterial (NTM) infections of the musculoskeletal system are uncommon. Such infections are typically acquired by direct inoculation after penetrating trauma, surgical procedures, or needle injections. There are no reported cases of NTM infection after arthrocentesis for idiopathic hemarthrosis of the knee. Here we report a case of NTM infection in the knee that developed after arthrocentesis for idiopathic hemarthrosis of the knee. PRESENTATION OF CASE: The patient was an 85-year-old woman who experienced swelling of the left knee. An arthrocentesis was carried out, and hemarthrosis was found. The patient was referred to our hospital for repeated recurrence of hematoma of the knee. Significant swelling was observed in the suprapatellar sac. Magnetic resonance imaging examination revealed a mass at the suprapatellar sac. Laboratory data showed elevation of inflammatory markers. Debridement was performed under arthroscopy and samples were collected for culture. Although routine microbiological cultures were negative, the patient continued to experience knee swelling and laboratory data showed high C-reactive protein levels. Therefore, open debridement was carried out. At 4 weeks after the first surgical treatment, intraoperative cultures yielded Mycobacterium intracellulare. At this point, we diagnosed septic arthritis of the knee due to NTM infection. The patient showed an excellent prognosis with three-drug medical treatment for 1 year. CONCLUSION: Clinically, diagnosis of septic arthritis due to NTM infection is not easy. Because selection of examination depends on clinical suspicion, NTM infections should be considered for patients with elevation of inflammatory markers after episodes of surgical procedures, and/or needle injections.

Referencing the substitute anteroposterior line of the tibia improves rotational alignment of the tibial component in medial unicompartmental knee arthroplasty.

BACKGROUND: There is no consensus regarding how best to determine the tibial rotational alignment in unicompartmental knee arthroplasty (UKA). The purpose of this study was to clarify whether using the substitute anteroposterior (sAP) line of the tibia, as has recently been proposed, can improve tibial rotation. METHODS: The study included 57 consecutive medial UKAs. From May 2015 to September 2016, 28 knees in 28 patients underwent UKA using the medial intercondylar ridge (MIR) line as the tibial anteroposterior (AP) reference (MIR group). From October 2016 to March 2018, 29 knees in 29 patients underwent UKA using the sAP line (sAP group). In both groups, the external rotation angle of the tibial component relative to a line perpendicular to the surgical epicondylar axis was measured using computed tomography-based three-dimensional preoperative planning software for TKA and UKA. RESULTS: The mean external rotation angles of the tibial component in the MIR and sAP groups were 5.2° ± 8.5° (range, -12.4° to 20.8°) and 0.7° ± 3.2° (range, -6.0° to 7.4°), respectively (unpaired t test, P = 0.014). The variation in the external rotation angle of the tibial component was significantly smaller in the sAP group than in the MIR group (F test, P < 0.0001), as was the number of the outliers with more than ±5° error (Fisher's exact test, P < 0.0001). CONCLUSIONS: The use of the sAP line as the AP reference could improve and stabilize the rotational orientation of the tibial component in UKA procedures.

Winged scapula following axillary thoracotomy with long thoracic nerve preservation.

Winged scapula is a rare condition caused by injuries to the long thoracic nerve (LTN) and accessory nerves. A 69-year-old man underwent surgery for right lung cancer. Video-assisted thoracic surgery was converted to axillary thoracotomy at the fourth intercostal space. The latissimus dorsi was protected, and the serratus anterior was divided on the side anterior to the LTN. Two months after discharge, he presented with difficulty in elevating his right arm and protrusion of the scapula from his back. Active forward flexion of the right shoulder was limited to 110° and abduction to 130°. He was diagnosed with winged scapula. After 6 months of occupational therapy, the symptoms improved. The LTN may have been overstretched or damaged by the electric scalpel. We recommend an increased awareness of the LTN, and to divide the serratus anterior at a site as far as possible from the LTN to avoid postoperative winged scapula.

Obliquity of tibial component after unicompartmental knee arthroplasty.

BACKGROUND: The native knee joint line is varus relative to the tibia and remains parallel to the floor during gait even with varus lower-limb alignment. We investigated the desired degree of frontal obliquity for positioning the tibial component during unicompartmental knee arthroplasty (UKA). METHODS: We retrospectively analyzed full-leg, standing, hip to ankle digital radiographs from 107 osteoarthritic knees. We measured the hip-knee-ankle (HKA) angle, the tibial joint-line orientation angle (JLOA), which indicates the angle of the joint line (tibial component) relative to the floor, and the medial proximal tibial angle (MPTA), which is the angle of the joint line (tibial component) relative to the tibial mechanical axis, before and after UKA in the coronal plane. RESULTS: The preoperative HKA angle (mean 7.3°, standard deviation (SD) 3.0) was significantly higher than the postoperative HKA angle (mean 3.4°, SD 3.0, P < 0.0001). The preoperative MPTA (mean 4.8°, SD 2.1) did not significantly differ from the postoperative MPTA (mean 4.5°, SD 3.0, P = 0.47). The mean postoperative JLOA was parallel to the floor (JLOA; 0.2°, SD 3.6). CONCLUSION: When the tibial component is positioned along the natural joint slope restoring pre-disease alignment of the overall lower limb in the coronal plane, the tibial component was positioned parallel to the floor. When UKA is indicated for the medial osteoarthritis patient, the surgeon should install the tibial component four to five degrees varus to the tibial mechanical axis to maintain joint-line parallelism.

Anteroposterior Rotational References of the Tibia for Medial Unicompartmental Knee Arthroplasty in Japanese Patients.

BACKGROUND: In unicompartmental knee arthroplasty (UKA), there is no consensus regarding how to determine the anteroposterior (AP) reference of the tibia. A number of surgeons in Japan perform the sagittal saw cut using the medial intercondylar ridge (MIR) of the tibia according to surgical manuals. However, there is no theoretical basis for this practice. METHODS: Preoperative computed tomography data from 32 lower limbs of 31 Japanese patients who received UKA were used. First, the angles between the surgical epicondylar axis and the MIR and the substitute AP (sAP) line connecting the medial border of the patellar tendon at the articular surface level and the medial intercondylar tubercle were measured. Next, the mediolateral (ML)/AP ratio of the tibial cut surface was measured when cut parallel to the MIR and sAP line. Finally, the ML/AP ratio of the tibial component was investigated in 4 contemporary UKA implants. RESULTS: The MIR and sAP line were externally rotated 94.9° ± 4.1° and 90.4° ± 3.6° relative to the surgical epicondylar axis, respectively. Compared with a cut parallel to the MIR, the mean ML/AP ratio of the cut surface was significantly larger, and the ML/AP ratio was closer to the ML/AP ratio of the components for a cut parallel to the sAP line. CONCLUSION: Obtaining the tibial AP orientation is one of the key steps not only in total knee arthroplasty but also in UKA. The sagittal cut referencing the sAP line provides better AP rotation and fitting of the tibia in UKA than referencing the MIR.

Location of the ankle center for total knee arthroplasty.

BACKGROUND: The purpose of this study was to investigate the ankle center position as determined from the malleoli for total knee arthroplasty (TKA). METHODS: We retrospectively analyzed computed tomography data from 102 patients with osteoarthritic knees. The tibial anteroposterior (AP) axis and transmalleolar axis (TMA) were used as rotational reference axes of the knee and ankle joint, respectively. With these axes, we regarded the offset distance from the intermalleolar midpoint as the position of the ankle center and investigated any angular osteotomy errors on the proximal tibia when the ankle center was assumed to the intermalleolar midpoint. RESULTS: The mean offset distances relative to the tibial AP axis were 1.8±0.9mm medial and 4.2±1.2mm anterior, and the distances relative to the TMA were 3.0±0.9 and 3.6±1.1mm in the coronal and sagittal planes, respectively. Mean angular osteotomy errors were 0.3±0.2° in the coronal plane and 0.8±0.2° in the sagittal plane. CONCLUSIONS: The ankle center was located around the intermalleolar midpoint. The position of the ankle center observed along the knee reference axis further approached the intermalleolar midpoint than when observed along the ankle reference axis in the coronal plane, but not in the sagittal plane. And the coronal angular osteotomy error was smaller than the sagittal error. Therefore, the intermalleolar midpoint in the coronal plane is a reliable landmark for the ankle center during TKA. However, surgeons should be cognizant of this sagittal angular error.

The Valgus Inclination of the Tibial Component Increases the Risk of Medial Tibial Condylar Fractures in Unicompartmental Knee Arthroplasty.

BACKGROUND: Medial tibial condylar fractures (MTCFs) are a rare but serious complication after unicompartmental knee arthroplasty. Although some surgical pitfalls have been reported for MTCFs, it is not clear whether the varus/valgus tibial inclination contributes to the risk of MTCFs. METHODS: We constructed a 3-dimensional finite elemental method model of the tibia with a medial component and assessed stress concentrations by changing the inclination from 6° varus to 6° valgus. Subsequently, we repeated the same procedure adding extended sagittal bone cuts of 2° and 10° in the posterior tibial cortex. Furthermore, we calculated the bone volume that supported the tibial component, which is considered to affect stress distribution in the medial tibial condyle. RESULTS: Stress concentrations were observed on the medial tibial metaphyseal cortices and on the anterior and posterior tibial cortices in the corner of cut surfaces in all models; moreover, the maximum principal stresses on the posterior cortex were larger than those on the anterior cortex. The extended sagittal bone cuts in the posterior tibial cortex increased the stresses further at these 3 sites. In the models with a 10° extended sagittal bone cut, the maximum principal stress on the posterior cortex increased as the tibial inclination changed from 6° varus to 6° valgus. The bone volume decreased as the inclination changed from varus to valgus. CONCLUSION: In this finite element method, the risk of MTCFs increases with increasing valgus inclination of the tibial component and with increased extension of the sagittal cut in the posterior tibial cortex.

Comparison of MRI- and CT-based patient-specific guides for total knee arthroplasty.

BACKGROUND: The patient-specific guide for total knee arthroplasty (TKA) is created from the data provided by magnetic resonance imaging (MRI) or computed tomography (CT) scans. It remains unknown which imaging technology is suitable for the patient-specific guide. The purpose of this study was to compare the accuracy of implant positioning and operative times between the two types of patient-specific guides for TKA. METHODS: Forty arthritic knees were divided into two treatment groups using MRI-based (PS-MRI group) or CT-based (PS-CT group) patient-specific guides in this prospective, comparative study. The guide in the PS-MRI group had a cutting slot, whereas that in the PS-CT group only had a pin locator. The operative times were compared between the two groups. The angular error and number of outliers (deviations >3°) of the implant position using pre- and postoperative CT were investigated in both groups. RESULTS: The mean operative time was significantly shorter in the PS-MRI group (109.2 ± 16.5 min) than in the PS-CT group (129.5 ± 19.4 min) (p<0.001). There were no significant differences in the accuracy of the implant position regarding the coronal, sagittal, and axial planes between the groups (p>0.05). CONCLUSIONS: To reduce the operative time, guides with additional functions, such as cutting and positioning, should be used. Both CT- and MRI-based-guides would result in the same accuracy in three planes but high inaccuracy in the sagittal plane. The use of patient-specific guide based on MRI might not be cost-effective. LEVEL OF EVIDENCE: level 2.

Enhanced pre-operative thrombolytic status is associated with the incidence of deep venous thrombosis in patients undergoing total knee arthroplasty.

BACKGROUND: Deep venous thrombosis (DVT), which is often associated with pulmonary embolism (PE), is a serious complication after total knee arthroplasty (TKA). In the present study, we examined the overall thrombotic and thrombolytic status using Global Thrombosis Test (GTT) in non-anticoagulated blood of patients undergoing TKA to develop the predictable marker for the incidence of DVT. METHODS: DVT was diagnosed using doppler ultrasonography a day after the surgery in 31 patients with osteoarthritis (n = 24), rheumatoid arthritis (n = 6) and ankylosing spondylitis (n = 1) by the well-trained operator. We measured overall thrombotic and thrombolytic status using GTT and other biomarkers, which is associated with blood coagulation and fibrinolysis, before and immediately after the surgery. RESULTS: Newly-generated DVT during the operation was detected in 11 of 31 patients (35.4%) 1 day after TKA. There were no differences in markers of coagulation (PT and APTT), platelet activity (platelet aggregation-induced by ADP and collagen) and fibrinolysis (FDP and D-dimer) between non-DVT and DVT group both before and after the surgery. Both Pre- and Post-operative GTT-occlusion times (OT), an index of platelet reactivity, were tended to be shorter, but not significant, in DVT group compared with non-DVT group. Pre-operative GTT-lysis time (LT), an index of thrombolytic activity, was significantly shorter in DVT group compared with non-DVT group, while there were no differences in post-operative value of this index between DVT group and non-DVT group, suggesting overall thrombolytic activity was enhanced in DVT group before surgery. CONCLUSIONS: Our data suggest that enhancement of pre-operative thrombolytic activity assessed by GTT may be a predictable marker for the incidence of DVT after TKA.

Influence of the sagittal reference axis on the femoral component size.

The sagittal reference axes used for setting of the femoral component vary according to surgical methods. The purpose of the study was to clarify the relation of the sagittal reference axis with the anteroposterior (AP) length of the distal femur at the time of determining the femoral component size. Fifty consecutive varus osteoarthritic knees with primary total knee arthroplasty were divided into two groups according to surgical methods (intramedullary and extramedullary groups) and were examined based on CT data. AP length of the distal femur changed nearly 0.6mm corresponding to each 1° flexion of the sagittal reference axis. The size of the femoral component in the intramedullary group was larger than that in the extramedullary group. The sagittal reference axis had an influence on the component size.

Tibia vara affects the aspect ratio of tibial resected surface in female Japanese patients undergoing TKA.

BACKGROUND: Tibia vara seen in Japanese patients reportedly influences the tibial component alignment when performing TKA. However, it is unclear whether tibia vara affects the component position and size selection. QUESTIONS/PURPOSES: We therefore determined (1) the amount of medial tibial bow, (2) whether the tibia vara influences the aspect ratio of the tibial resected surface in aligning the tibial component with the tibial shaft axis, and (3) whether currently available tibial components fit the shapes of resected proximal tibias in terms of aspect ratio. METHODS: We measured the tibia vara angle (TVA), proximal varus angle (PVA), and the mediolateral and middle AP dimensions of the resected surface using three-dimensional preoperative planning software in 90 knees of 74 female patients with varus osteoarthritis. We determined the correlations of the aspect ratio with TVA or PVA and compared the aspect ratios to those of five prosthesis designs. RESULTS: The mean TVA and PVA were 0.6° and 2.0°, respectively. The aspect ratio negatively correlated with both TVA and PVA (r = -0.53 and -0.55, respectively). The mean aspect ratio of the resected surface was 1.48 but gradually decreased with increasing AP dimension, whereas four of the five prostheses had a constant aspect ratio. CONCLUSIONS: The aspect ratio of resected tibial surface was inversely correlated to the degree of tibia vara, and currently available prosthesis designs do not fit well to the resected surface in terms of aspect ratio. CLINICAL RELEVANCE: The design of a tibial component with a smaller aspect ratio could be developed to obtain better bone coverage in Japanese patients.

Estimation of frontal alignment error of the extramedullary tibial guide on the bi-malleolar technique: a simulation study with magnetic resonance imaging.

PURPOSE: The bi-malleolar technique for the extramedullary tibial guide is a representative method for determining the ankle center in total knee arthroplasty (TKA). The purpose of this study is to estimate three-dimensionally the lateral errors (difference between the real ankle center and the bi-malleolar center) and the varus angular errors of this technique under the condition that the malleolar prominences were correctly identified. METHODS: Magnetic resonance images of 51 lower limbs from 51 healthy volunteers were analyzed. The lateral errors were measured, including or excluding the subcutaneous thickness, along the line perpendicular to the transmalleolar axis (TMA) or along the tibial anteroposterior (AP) axis. Furthermore, we evaluated the effects of the tibial torsion and the difference between the subcutaneous thicknesses on the malleoli on the lateral error. RESULTS: When including the skin, the mean lateral errors of the ankle center observed along the line perpendicular to the TMA and along the tibial AP axis were 3.7 ± 1.4mm and 1.2 ± 1.5mm, respectively. The mean angular errors were 0.6 ± 0.2° and 0.2 ± 0.3°, respectively. A significant correlation between the tibial torsion and the lateral error was noted when observed along the tibial AP axis. The difference between the subcutaneous thicknesses on the malleoli affected the lateral error. CONCLUSION: The errors were small enough to determine the mechanical axis of the tibia if the tibial guide could catch the bi-malleolar prominences of the ankle accurately and align along the tibial AP axis.

Increase in posterior tibial slope would result in correction loss in frontal plane after medial open-wedge high tibial osteotomy.

PURPOSE: The purpose of this study was to clarify the causes of the increase in the posterior tibial slope during open-wedge high tibial osteotomy (HTO) and to investigate whether its changes influenced the correction angle in frontal plane. METHODS: We retrospectively reviewed 20 patients (26 knees) treated with open-wedge HTO. They were divided into the following two groups. Group A consisted of the knees whose opening gaps were fixed using a spacer plate having the trapezoidal block with a 2° posterior slope. In Group B, anterior and posterior opening gaps were fixed separately. The posterior tibial slope and the hip-knee-ankle angle were measured based on CT data. The relationship between the correction rate in frontal plane and the changes of posterior tibial slope was investigated. RESULTS: Increase in the posterior tibial slope was 2.1 ± 2.5° in Group A and 0.2 ± 1.2° in Group B, which showed a statistical difference (P = 0.02). The difference between the hip-knee-ankle angles before and after operation was 5.2 ± 2.3° in Group A and 5.5 ± 2.5° in Group B. The correction rate was statistically correlated with the changes of posterior tibial slope (R = -0.55, P = 0.003). CONCLUSION: To avoid increase in the posterior tibial slope, the trapezoidal block with a only 2° posterior slope in a spacer plate was not sufficient, and it was necessary to fix anterior and posterior gaps separately. The correction angle in frontal plane had a trade-off relationship with the changes in posterior tibial slope. Thus, we thought that increase in the posterior tibial slope might result in correction loss. LEVEL OF EVIDENCE: Therapeutic study, Retrospective comparative study, Level III.

Effects of cartilage remnants of the posterior femoral condyles on femoral component rotation in varus knee osteoarthritis.

Preoperative planning of total knee arthroplasty (TKA) based on computerized tomography (CT) data can produce a femoral rotational error due to lack of information on the femoral cartilage thickness. The research question of this study is how much femoral rotational error is expected due to the cartilage remnants when using the posterior condylar angles (PCA, angle between the posterior condylar line and the surgical epicondylar axis (SEA)) on CT data. CT arthrography was performed for 35 consecutive varus osteoarthritic knees in 31 patients who underwent TKA, on which the cartilage thicknesses of the posterior femoral condyles were measured. The PCAs when including or excluding the cartilage remnants were also measured. The cartilage thicknesses of the medial and lateral posterior condyles averaged 0.39mm (SD=0.53) and 1.55mm (SD=0.26), respectively (p<0.0001). When the cartilage was included or excluded, the PCA averaged 2.2° (SD=1.5) and 3.3° (SD=1.5), respectively (p=0.002). The cartilage remnants in the posterior femoral condyles produced an average of 1.1° and a maximum of 2.1° of additional femoral external rotation when using CT data for the preoperative planning. CT scan measurements of femoral rotation are subject to error. Although this is said to be small and within the safety margin for setting the femoral component parallel to the trans-epicondylar axis, this difference should be considered by surgeons who use the posterior condylar axis, in order to avoid excessive external rotation of the femoral component.