Gross Appearances of the Posterior Cruciate Ligament Correlate With Its Histological Features but not With In Vivo Function in Cruciate-Retaining Total Knee Arthroplasty.

Background No study has evaluated whether the macroscopic appearance or histological features of the posterior cruciate ligament (PCL) affect the in vivo PCL function in cruciate-retaining (CR) total knee arthroplasty (TKA). The aim of this study is to elucidate the correlation between intraoperative gross appearances of the PCL and clinical parameters, their corresponding histological features, and the in vivo function. Methods The intraoperative gross appearances of the PCLs were evaluated; we also examined their correlations with clinical parameters, corresponding histological features, and the in vivo function in CR-TKA. Results There were significant correlations between intraoperative gross appearances of the PCL and that of the anterior cruciate ligament, the preoperative knee flexion angle, and the intercondylar notch stenosis. There was a significant correlation between the intraoperative gross appearance in the middle part and the corresponding histological features. However, there was no significant correlation between the intraoperative gross appearance or histological features and the PCL tension, amount of rollback, and maximum knee flexion angle. Conclusions The intraoperative gross appearance of the PCL correlated with clinical parameters. Also, there was a significant correlation between the intraoperative gross appearance in the middle part and the corresponding histological features; however, there was no correlation between the intraoperative gross appearance or histological features and the in vivo function.

Human Trials on the Prevention of Tunnel Widening by the Emdogain in Anterior Cruciate Ligament Reconstruction.

Background Although anterior cruciate ligament reconstruction (ACLR) is an established procedure, some problems remain, such as bone tunnel widening after ACLR. In animal studies, Emdogain (EMD) prevented tunnel widening by promoting tendon-bone healing. This study aimed to evaluate the effects of EMD on the prevention of tunnel widening after anterior cruciate ligament (ACL) injury in humans. Methods Nineteen patients who underwent ACLR were included. Seven patients in the EMD group were administered EMDs into the femoral tunnel during ACLR, while 12 patients in the control group were not administered EMDs. After surgery, at two and four weeks and three, six, and 12 months, femoral and tibial tunnel widening were evaluated on computed tomography images. Anteroposterior laxity and clinical scores such as the Lysholm score, the International Knee Documentation Committee (IKDC) subjective form, and the Knee Injury and Osteoarthritis Outcome Score (KOOS) were assessed before surgery and 12 months postoperatively. Results Tunnel widening on the femoral side was significantly smaller in the EMD group than in the control group at two weeks. However, there was no significant difference between the two groups at 12 months. There were no significant differences in anteroposterior laxity and clinical scores between the groups before and 12 months after surgery. Conclusion EMD administration into the bone tunnel did not prevent tunnel widening at 12 months after ACLR, although tunnel widening of the femoral tunnel was reduced by EMD administration in the early phase.

Inverted V-Shaped High Tibial Osteotomy Decreases the Posterior Tibial Slope More but Shortens the Tibia Less Than Closed-Wedge High Tibial Osteotomy.

PURPOSE: To assess the postoperative anatomical changes in the lower extremity after inverted V-shaped high tibial osteotomy (IVHTO) using 3-dimensional (3D) computed tomography (CT) bone models and compare those changes after closed-wedge high tibial osteotomy (CWHTO). METHODS: Preoperative and 3-week postoperative CT scanning of the lower extremity were obtained from patients who underwent IVHTO and CWHTO between October 2019 and March 2021. 3D CT bone models were reconstructed using ZedKnee software. The postoperative changes (Δ) in (1) posterior tibial slope (PTS), (2) knee rotation angle (KRA), (3) tibial torsional angle (TTA), (4) patella tilt (PT), (5) Insall-Salvati ratio (ISR), and (6) tibial length (TL) were compared between IVHTO and CWHTO. RESULTS: Thirty-seven knees (18 IVHTO and 19 CWHTO) in 34 patients were retrospectively enrolled in this study. ΔPTS at the medial and lateral tibial plateau in the IVHTO group (-6.5° and -5.0°) was larger compared with that in the CWHTO group (-3.3° and -2.0°; P = .024 and P = .002, respectively). No significant differences exist between the IVHTO and CWHTO groups in ΔKRA (0.8 ± 4.5° and -1.5 ± 6.5°; P = 0.631), ΔTTA (-3.9 ± 6.2° and -4.1 ± 7.3°; P = .951), ΔPT (-2.0 ± 4.8° and -0.6 ± 4.1°; P = .353), and ΔISR (0.0 and 0.0; P = .829). ΔTL in the IVHTO group (-1.6 ± 2.3 mm) was smaller compared with that in the CWHTO group (-4.1 ± 1.6 mm; P < .001). CONCLUSIONS: (1) The postoperative PTS in the IVHTO group was further decreased compared to the CWHTO group; (2) no significant differences in ΔKRA, ΔTTA, ΔPT, and ΔISR exist between the 2 groups; and (3) the ΔTL in the IVHTO group was significantly smaller compared with the CWHTO group. LEVEL OF EVIDENCE: Level III, retrospective cohort study.

Clinical outcomes of knee joint distraction combined with marrow stimulation procedures for patients with advanced knee osteoarthritis.

BACKGROUND: Knee joint distraction (KJD) has received much attention as a joint preserving surgery, especially in young patients with advanced knee osteoarthritis (OA). METHODS: This study included 16 patients with advanced knee OA who underwent KJD combined with marrow stimulating techniques and were followed up for more than 2 years. The patients' clinical scores, including the Japanese Orthopaedic Association (JOA) score, Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales, ROM, joint space width, and semiquantitative MRI were evaluated. The factors affecting clinical outcomes were analyzed. RESULTS: Postoperatively, the JOA score and the individual scores of the KOOS subscales improved significantly (JOA score: P = 0.0028, KOOS-symptoms: P = 0.0016, -pain: P = 0.0011, -ADL: P = 0.0009, -sports/recreation: P = 0.0144, and -QOL: P = 0.0034). Although the extension of the knee joint did not change throughout the follow-up period, flexion of the joint deteriorated at the time of device removal but recovered to the preoperative level at the final follow-up. Preoperative joint space width was 2.4 ± 2.0 mm and at the final follow-up, it increased to 3.3 ± 1.5 mm, showing statistically significant improvement (P = 0.034). The postoperative semiquantitative MRI score also improved significantly (from 6.0 ± 3.0 to 42.1 ± 28.7, P = 0.0001). A high BMI was associated with a poor clinical outcome. CONCLUSION: Although the effect of marrow stimulating techniques for cartilage repair was not well clarified and the complication rate was high, the clinical and radiographic outcomes showed significant improvement after KJD combined with marrow stimulating techniques in patients with advanced knee OA. However, we should be careful about suggesting this procedure in obese patients.

Association between medial meniscus extrusion under weight-bearing conditions and pain in early-stage knee osteoarthritis.

PURPOSE: This study aimed to investigate the association between the severity of medial meniscus extrusion (MME) under weight bearing and pain in patients with early-stage knee osteoarthritis (OA). METHODS: Twenty-eight patients with symptomatic early-stage knee OA (Kellgren and Lawrence grade ≤ 2) who visited our outpatient clinic between 2016 and 2018 were included in this cross-sectional study (mean age: 58.0 ± 11.6 years, female: n = 10). MME was evaluated under weight-bearing conditions using ultrasonography. Patients were divided into two groups according to the severity of MME under weight bearing: those with MME ≥ 3 mm were assigned to the severe group, whereas those with MME < 3 mm were assigned to the mild group. The knee injury osteoarthritis outcome score (KOOS) system was used to evaluate knee pain. The incidence of bone marrow lesions (BMLs) was evaluated using magnetic resonance images. RESULTS: The KOOS pain score was significantly lower in the severe group than in the mild group (P < 0.05). The incidence of BMLs was significantly higher in the severe group (69%) than in the mild group (7%) (P < 0.001). CONCLUSION: Patients with early-stage knee OA who have greater MME under weight-bearing have more intense knee pain and a higher incidence of BMLs.

Evaluation of the degenerative pattern of PCL in osteoarthritis patients using UTE-T2 mapping.

BACKGROUND: The posterior cruciate ligament (PCL) is one of the essential stabilizers of the knee joint and it was demonstrated that its degenerative change related to the knee osteoarthritis (OA). We aimed to evaluate signal of the PCL in OA patients in comparison with healthy young and elderly volunteers using the ultra-short echo timeenhanced (UTE)-T2∗ mapping, and to validate these findings with histology. METHODS: Thirty asymptomatic volunteers, 13 young people (younger group) and 17 elderly people (elder group), and 27 patients who had undergone total knee arthroplasty (OA group) were enrolled in this study. UTE-T2∗ maps of PCL were obtained from all participants. The PCL was divided into proximal, middle, and distal parts and the UTET2∗ values obtained from each part were compared among the groups. In OA group, the sacrificed PCLs were evaluated histologically in each part corresponding to the part of UTE-T2∗ maps and compared. RESULTS: The UTE-T2∗ values in OA group were significantly higher than those in other groups except in distal part. In elder group, the UTE-T2∗ values were significantly higher than those in younger group only in the proximal part. Moreover, in OA group, the UTE-T2∗ values in proximal and middle parts were significantly higher than those in distal part. There was a moderate correlation between the UTE-T2∗ values and histological scores. CONCLUSIONS: The specific signal intensity pattern of the PCL in patients with OA was demonstrated using UTE-T2∗ mapping, and these findings were related to histological degenerated status of the PCL.

The correlation between osteoarthritis stage and the effect of the lateral wedge insole for 3 months on medial meniscus extrusion in the knee joint.

BACKGROUND: Medial meniscus extrusion (MME) leads to symptomatic knee osteoarthritis (OA) due to increased mechanical stress. MME increases with weight-bearing, and the difference in MME between non-weight-bearing and weight-bearing status (ΔMME) is a factor that causes greater MME. The lateral wedge insole (LWI) is an ideal approach for decreasing the amount of ΔMME associated with the reduction of medial loading stress in the early stage of knee OA. However, the effect of the LWI for 3 months on the ΔMME and its response to OA stage have not been elucidated. OBJECTIVE: To investigate the effects of the LWI for 3 months on MME and the ΔMME in each stage of OA. METHODS: Participants were divided into three groups: no intervention with the LWI (control group; n = 9) and intervention with the LWI in early OA (early OA group: Kellgren-Lawrence (K/L) stage = 2, n = 17) and late OA (late OA group: K/L stage > 2, n = 13). MME was evaluated using ultrasound, and the ΔMME was obtained as the difference in MME from non-weight-bearing and weight-bearing conditions. These measurements were performed at two time points: the initial office visit as a baseline and post-3 months. RESULTS: The weight-bearing MME and ΔMME values post-3 months were significantly decreased compared with those at baseline in the early OA group but not in the control or late OA groups. CONCLUSIONS: The use of the LWI for 3 months decreased weight-bearing MME and ΔMME values, and its effectiveness was more pronounced in the early stage of knee OA.

Inversed V-shaped High Tibial Osteotomy for Severe Varus Deformity due to Blount Disease: A Case Report.

Introduction: Blount disease is a growth disorder of the medial proximal tibial physis causing a multi-planar deformity of the lower limb. Several types of surgical approaches have been described for the correction of angular deformity including external fixation, opened-/closed- wedge high tibial osteotomy (HTO), and tibial condylar valgus osteotomy. However, they are associated with various disadvantages such as limb length discrepancy, risk of infections, and delayed union at the osteotomy site, especially in cases of severe varus deformity. Case Report: We report a case of a 16-year-old boy with unilateral severe genu varum caused by Blount disease. Considering that the current case, the patient was severely obese and a highly active young boy with severe unilateral genu varum, with the epiphyseal line almost closed, and with no abnormalities with respect to the intra-articular anatomical structures, inverted V-shaped HTO was applied. After the treatment, the boy was not only able to perform his daily activities but was also able to participate in sports quite early. Although the required correction angle was quite large, inverted V-shaped HTO successfully corrects the deformity with minimal disadvantages. Conclusion: Inverted V-shaped HTO would be selected as one of the effective treatments for a severely obese, young, and highly active patient suffering from severe genu varum caused by Blount disease.

Increase in medial meniscal extrusion in the weight-bearing position observed on ultrasonography correlates with lateral thrust in early-stage knee osteoarthritis.

BACKGROUND: Lateral thrust is known to be risk factors for knee osteoarthritis progression. Medial meniscus extrusion is also known to be risk factors for knee osteoarthritis progression; moreover, the amount of change in medial meniscus extrusion from non-weight bearing to weight bearing is an important factor for the progression of knee osteoarthritis. This study aimed to investigate the correlation between lateral thrust and the change in medial meniscus extrusion. METHODS: In total, 44 knees from 44 patients (mean age, 68.9 years) with knee osteoarthritis were divided into two groups according to the Kellgren-Lawrence grade: early-stage osteoarthritis (Kellgren-Lawrence = 2) and severe osteoarthritis (Kellgren-Lawrence = 3 or 4). The lateral thrust during gait, represented as the lateral acceleration peak immediately after heel strike, was recorded by an inertial sensor. The amount of change in medial meniscus extrusion, which was the difference between weight-bearing (unipedal standing) and non-weight-bearing (supine) conditions, was evaluated using ultrasonography. RESULTS: The mean value of the lateral acceleration peak in the severe osteoarthritis group was higher than that of the early-stage osteoarthritis group (p < 0.05). The non-weight-bearing and weight-bearing medial meniscus extrusion in the severe OA group were significantly higher than those of the early-stage osteoarthritis group (p < 0.001). However, the amount of change in medial meniscus extrusion in severe osteoarthritis group was significantly lower than in the early-stage osteoarthritis group (p < 0.05). The amount of change in medial meniscus extrusion showed a significant correlation with the lateral acceleration peak in the early-stage osteoarthritis group (r = 0.56, p < 0.001). On the other hand, there was no significant correlation in the severe osteoarthritis group. CONCLUSION: The lateral thrust shows a positive correlation with the amount of change in medial meniscus extrusion by weight bearing in patients with early-stage knee osteoarthritis.

Histological Evaluation of Early-Phase Changes in the Osteochondral Unit After Microfracture in a Full-Thickness Cartilage Defect Rat Model.

BACKGROUND: The microfracture (MF) technique is an established surgical treatment for cartilage injury. However, the early-phase histological changes in full-thickness cartilage defects (FTCDs) after MF and the concomitant changes in the subchondral bone are still unknown. PURPOSE: To determine the early-phase histological changes in FTCD associated with subchondral bone remodeling after MF in rat model. STUDY DESIGN: Controlled laboratory study. METHODS: Rats were subjected to FTCD, followed by MF at the trochlear groove. For histological analysis, experiment and untreated control rats were sacrificed at 0, 1, 3, 7, 14, 28, and 56 days postoperatively (n = 6 knees per time point). Cartilage healing response was evaluated with the Pineda score. Osteoclast activity was evaluated by counting and locating the number of tartrate-resistant acid phosphatase (TRAP)-positive cells in the subchondral bone. MF hole diameter and bone mineral density in the subchondral bone were measured sequentially in 3 rats (n = 6 knees) by 3-dimensional µ-computed tomography. RESULTS: Pineda score showed no difference in cartilage response from day 0 to day 3 but a significant improvement from day 7 to day 56. Although the MF holes were filled with blood clots in all specimens, the defect sites were not. The number of TRAP-positive cells peaked at day 3, mostly accumulating around the deeper zone of the MF holes. Over time, the number of TRAP-positive cells decreased to preoperative levels, localizing around the aperture of the MF holes where there was active remodeling of the osteochondral unit. The MF hole diameter was largest at day 14, and most holes disappeared by day 28. Bone mineral density was also highest at day 14 and decreased to preoperative levels by day 56. CONCLUSION: Histological changes in the FTCD after MF were derived from endochondral ossification within the deeper zone of the MF holes. CLINICAL RELEVANCE: The absence of healing by blood clot in the FTCD should be noted by surgeons performing MF, and indications for MF should be carefully considered not only for maximizing the postoperative clinical outcome but also minimizing potential complications, such as formation of subchondral bone cysts or intralesional osteophytes.

Characteristic morphology of the proximal tibiofibular joint in patients with discoid lateral meniscus.

BACKGROUND: Patients with discoid lateral meniscus (DLM) are prone to meniscal injuries related to its shape and abnormal mobility. The anatomical joint inclination of the proximal tibiofibular joint (PTFJ) can also affect joint movement in knee motion. However, an association between PTFJ morphology and DLM remains unclear. The purpose of this study was to investigate the morphology of the PTFJ on MRI and how this differs between patients with and without DLM. MATERIALS AND METHODS: Fifty-eight patients with DLM and 58 age-matched controls (normal meniscus) were included in this study. Slices from preoperative MRI sagittal images that clearly showed the PTFJ were used for measurements. The angle between the PTFJ and the perpendicular line of the fibula axis was measured as the inclination angle, and patients were classified as horizontal-type (<20°) or oblique-type (>20°). The inclination angle was also compared among patients with open and closed epiphysis in both groups to assess the effect of age. RESULTS: Patients in the horizontal-type PTFJ group frequently had DLM. Before epiphyseal closure, most patients had a horizontal-type PTFJ, with or without DLM. However, in older patients with a closed epiphysis, most with a normal meniscus had an oblique-type PTFJ, and those with DLM retained the horizontal-type joint. CONCLUSION: The horizontal-type PTFJ was significantly associated with DLM, and patients with DLM tended to retain a horizontal-type PTFJ after epiphyseal closure. In contrast, in patients with a normal meniscus, the PTFJ may change from a horizontal-type to an oblique-type PTFJ in line with bone maturity.

Limitation of in-situ arthroscopic fixation for stable juvenile osteochondritis dissecans in the knee.

Current treatment algorithms for stable juvenile osteochondritis dissecans (JOCD) of the knee have not been established. For arthroscopically stable lesion, in-situ arthroscopic fixation with bioabsorbable pins was introduced as a more desirable approach because of less surgical morbidity and faster recovery. However, there is a paucity of literature that concludes on its efficacy. The aim of this study is to determine the efficacy and limitation of in-situ arthroscopic fixation on stable JOCD lesion in the knee. Ninety-six patients with 110 affected knees were reviewed. Subsequently, patients who underwent in-situ arthroscopic fixation for arthroscopically stable JOCD lesions were grouped for further analysis. Arthroscopic lesion stability was graded according to the Guhl's grading system from the surgical description of each lesion. The grade I and II were defined as 'stable' lesions. The lesion status was also evaluated with the MRI grading system described by Dipaola in preoperative images retrospectively. The grade I and II lesions were also defined as 'stable' and more than III as 'unstable'. Clinical outcomes were evaluated by the Lysholm score at the final office visit. If the patient had a revision surgery, the case was classified as a complete failure. There were 13 lesions in 13 patients with open physis treated with in-situ arthroscopic fixation using bioabsorbable pins. In this population, radiographical lesion status and the Lysholm score were significantly improved in 10 cases (preoperative: 77.5±11.2, postoperative: 98.9±3.1, P=0.002); however, we found three revision cases (failure rate, 23%). Of these revision cases, all lesions were graded as 'unstable' in MRI. In this series, the failure rate was 23% for in-situ arthroscopic fixation for arthroscopically stable JOCD lesion of the knee. Because of the potential risk for underestimation of lesion instability, we strongly suggest that this less invasive approach should be chosen with great care for the lesion that presents arthroscopically stable, but as unstable status on MRI. LEVEL OF EVIDENCE: Level IV, case series.

Effects of lateral wedge insole application on medial compartment knee osteoarthritis severity evaluated by ultrasound.

BACKGROUND: It is known that a lateral wedge insole (LWI) decreases medial loading stress in the knee. Medial meniscus pathology, such as a degenerative tear or a root tear, leading to malfunction and medial meniscus extrusion (MME), is a critical condition that leads to severe osteoarthritis (OA). However, the effect of LWI on MME is still unknown. The objective of this study was to investigate the effect of LWI use on MME in knee OA using ultrasonography. METHODS: Thirty-one knees from 18 patients with knee OA diagnosed radiographically were allocated to the OA group (mean age, 73.6years; sex M:F, 2:16). Twenty-two knees from 11 volunteers without knee OA were also enrolled as an age-matched control group. MME was evaluated using ultrasonography with the patients in three positions: supine, standing without LWI, and standing with LWI. RESULTS: In both groups, the mean values of the MME increased significantly when patients were in the standing position compared to the supine position. In the OA group, MME significantly decreased with LWI use. There was no significant difference in MME between use and non-use of an LWI in the control group. CONCLUSIONS: The LWI could significantly decrease MME in patients with knee OA.

Chondrocyte Cell-Sheet Transplantation for Treating Monoiodoacetate-Induced Arthritis in Rats.

Engineered cell sheets that are fabricated by using temperature-responsive culture dishes are now available in the clinical setting. Engineered chondrocyte cell sheets are used in clinical trials for treating focal articular cartilage defects. However, the efficacy of engineered chondrocyte cell sheets for treating diffusely degenerated articular cartilage remains unknown. In the present study, we assessed the utility of engineered chondrocyte cell sheets for treating diffusely degenerated articular cartilage in a monoiodoacetate (MIA)-induced arthritis animal model. At 1 and 3 weeks after intra-articular MIA injection into rat knees (1 w-MIA/3 w-MIA model), the degenerated cartilage at load-bearing area sized 1 × 3 mm was removed. Rats in each group were divided into three subgroups: Removal (R) group as control, Removal + Drilling (RD) group in which cartilage was removed followed by subchondral drilling, and Removal + Drilling + Sheet transplantation (RDS) group in which the removed cartilage area was covered with a 2 × 4 mm size of triple-layered chondrocyte cell sheet. In the histological assessment, the score of the RDS group in each model was significantly better than that of R and RD groups at 4 and 12 weeks, respectively, after the surgery. Our results demonstrated that the transplanted chondrocyte cell sheets improved cartilage repair even under such severe conditions as diffusely degenerated articular cartilage. Chondrocyte cell sheets appear to be useful as a treatment option for MIA-induced arthritis models.

Bilateral TKA for Charcot arthropathy associated with multiple levels of spinal canal stenoses: A case report and review of literature.

We report a case of an 84-year-old male with multiple levels of canal stenoses who are diagnosed as Charcot arthropathy of bilateral knees. Although he did not feel any pain, recurrence of joint fluid collection and severe instability prevented him from standing and walking. Deficit in superficial sensation and bathyesthesia below the level of Th10, and tendon reflexes of extremities were seen. Romberg test was positive. Laboratory data showed no abnormal findings. We performed bilateral TKA based on the diagnosis of Charcot arthropathy. At 3-year follow-up, there is no complaint about joint instability and collection of joint fluid.

Unique Anatomic Feature of the Posterior Cruciate Ligament in Knees Associated With Osteochondritis Dissecans.

BACKGROUND: Osteochondritis dissecans (OCD) of the knee is a disorder in juveniles and young adults; however, its etiology still remains unclear. For OCD at the medial femoral condyle (MFC), it is sometimes observed that the lesion has a connection with fibers of the posterior cruciate ligament (PCL). Although this could be important information related to the etiology of MFC OCD, there is no report examining an association between the MFC OCD and the PCL anatomy. PURPOSE: To investigate the anatomic features of knees associated with MFC OCD, focusing especially on the femoral attachment of the PCL, and to compare them with knees associated with lateral femoral condyle (LFC) OCD and non-OCD lesions. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: We retrospectively reviewed 39 patients (46 knees) with OCD lesions who had undergone surgical treatment. Using magnetic resonance imaging (MRI) scans, the PCL attachment at the lateral wall of the MFC was measured on the coronal sections, and the knee flexion angle was also measured on the sagittal sections. As with non-OCD knees, we reviewed and analyzed 25 knees with anterior cruciate ligament (ACL) injuries and 16 knees with meniscal injuries. RESULTS: MRIs revealed that the femoral PCL footprint was located in a significantly more distal position in the patients with MFC OCD compared with patients with LFC OCD and ACL and meniscal injuries. There was no significant difference in knee flexion angle among the 4 groups. CONCLUSION: The PCL in patients with MFC OCD attached more distally at the lateral aspect of the MFC compared with knees with LFC OCD and ACL and meniscal injuries.

Gap measurement in posterior-stabilized total knee arthroplasty with or without a trial femoral component.

PURPOSE: To investigate the effects of a trial femoral component on the intraoperative joint gap and intraoperative joint gap kinematics throughout the range of knee motion in minimally invasive surgery-total knee arthroplasty (MIS-TKA) with the gap technique. MATERIALS AND METHODS: A total of 103 patients [15 men (15 knees) and 89 women (89 knees)] aged 50-88 years (mean 74.8 years) who received MIS-TKA with the gap technique were included. The intraoperative joint gap differences (90° flexion gap distance minus 0° extension gap distance) with and without the trial femoral component were compared. Subsequently, the intraoperative joint gap kinematics at 0°, 45°, 90°, and 120° with the trial femoral component were investigated. RESULTS: The intraoperative component gap difference (4.4 ± 2.7 mm) was larger than the estimated joint gap difference (1.2 ± 1.9 mm) (p < 0.01). The mean intraoperative component gap distances at 0°, 45°, 90°, and 120° of knee flexion were 14.7 ± 2.6, 19.0 ± 3.2, 19.2 ± 3.4, and 16.6 ± 3.3 mm, respectively. The intraoperative component gap distance increased significantly from 0° extension to 90° of knee flexion (p < 0.01), and then decreased significantly toward deep knee flexion at 120° (p < 0.01). CONCLUSIONS: The trial femoral component influenced the intraoperative gap measurements, and increased the intraoperative gap difference. The joint gap kinematics with the trial femoral component were not constant throughout the range of knee motion, even if the appropriate joint gaps in extension and flexion were achieved. For acquisition of constant stability throughout the knee motion, the present results should be taken into account by surgeons performing MIS-TKA with the gap technique.