Pre-milling technique improves the accuracy of posterior femoral condyle cut and reduces the tibial recut in Oxford unicompartmental knee arthroplasty.

BACKGROUND: Recuts are sometimes needed in UKA because of inadequate posterior tibial cut thickness. We investigated the efficacy of a pre-milling technique (the first milling is done prior to the posterior condylar cut) in Oxford unicompartmental knee arthroplasty to enhance bone cut thickness and to minimize tibial recuts. PATIENTS AND METHODS: Between January 2021 and January 2023, a posterior condyle cut was made before milling in 213 knees in 152 patients (conventional group), while the pre-milling technique was used in 198 knees in 140 patients (pre-milling group). The thickness of the posterior condyle and the rate of tibial recuts were compared between the groups. RESULTS: The bone cut thickness was thinner in the conventional group than in the pre-milling group in small-size (4.7 mm ± 0.6 mm and 5.0 mm ± 0.6 mm, P = 0.0001) and in medium-size (5.1 mm ± 0.5 mm and 5.4 mm ± 0.5 mm, 0.0001) femoral components, whereas there was no difference in large-size femoral components. However, the thickness was still less than the component thickness (5.17 mm for small, 5.57 mm for medium and 6.17 mm for large) in both groups. Tibial recuts were more prevalent in the conventional group than in the pre-milling group (14 knees, 7%, 3 knees 2%, P = 0.002). CONCLUSIONS: The pre-milling technique was found to increase the bone cut thickness in small and medium femoral components, reducing the need for tibial recuts. Further research is warranted to optimize the pre-milling technique and to investigate its long-term impact on patient outcomes.

Current concept: personalized alignment total knee arthroplasty as a contrast to classical mechanical alignment total knee arthroplasty.

Mechanical alignment (MA) total knee arthroplasty (TKA), with neutral leg alignment, mechanical component alignment, and parallel gaps, has achieved good long-term survival. Patient satisfaction, however, is not always perfect. In contrast to the MA, which aims for an ideal goal for all patients, an alternative has been proposed: kinematic alignment (KA)-TKA. In KA, the articular surface is replicated using components aligning with the three kinematic axes. KA-TKA has been gaining popularity, and in addition to the true or calipered KA, various derivatives, such as restricted KA, soft-tissue respecting KA, and functional alignments, have been introduced. Moreover, the functional approach encompasses several sub-approaches. This somewhat complicated scenario has led to some confusion. Therefore, the terminology needs to be re-organized. The term "personalized alignment (PA)" has been used in contrast to the MA approach, including all approaches other than MA. The term "PA-TKA" should be used comprehensively instead of KA and it represents the recent trends in distinct and unique consideration of each individual case. In addition to a comparison between MA and KA, we suggest that evaluation should be conducted to decide which approach is the best for an individual patient within the "personalized alignment" concept.

Preoperative Arithmetic Hip-Knee-Ankle Angle as a Predictor of Postoperative Leg Alignment in Medial Oxford Unicompartmental Knee Arthroplasty.

Introduction This study aimed to evaluate whether the arithmetic hip-knee-ankle angle (aHKA) can be used to predict the postoperative HKA. Methods This study included 248 knees in 166 patients who underwent Oxford unicompartmental knee arthroplasty (UKA) between February 2021 and November 2022. Through preoperative and postoperative long-leg radiography, the medial proximal tibial angle (MPTA) and the lateral distal femoral angle (LDFA) were expressed as the deviation from the perpendicular line to the mechanical axes, and the mechanical HKA (mHKA) was defined as the angle between the femoral and tibial mechanical axes. Using the MPTA and LDFA, the arithmetic HKA (aHKA; MPTA + LDFA) and the joint line obliquity (JLO; MPTA - LDFA) were calculated, and the preoperative and postoperative values were compared. Results The preoperative aHKA and the postoperative mHKA values were similar (-0.38° ± 2.96°) and significantly smaller than the difference between the preoperative and postoperative mHKAs (4.58° ± 3.60°, P < 0.05). Meanwhile, the MPTA tended to be varus, and the LDFA tended to be valgus. Eventually, the JLO inclined more medially from -6.33° ± 3.42° preoperatively to -8.97° ± 3.92° postoperatively, representing a significant difference (P < 0.05). Conclusion The preoperative aHKA was similar to the postoperative mHKA. Therefore, it can be regarded as a predictor of postoperative leg alignment after Oxford UKA. Meanwhile, there was a medial incline of the joint line. Further investigation is required to evaluate the effect of such a joint line alteration.

Tibial Lateral Condyle Fracture After Cementless Oxford Unicompartmental Knee Arthroplasty (UKA): A Report of Four Cases.

Cementless unicompartmental knee arthroplasty (UKA) has a lower rate of radiolucency in postoperative follow-up than cemented UKA. However, the rate of tibial plateau fracture, one of the complications, has been reported to be higher in cementless UKA than in cemented UKA. We report four cases of postoperative tibial lateral condyle fractures after cementless Oxford UKA. Four patients underwent cementless Oxford UKA. Immediate postoperative radiography and CT showed no fracture lines. At five to six weeks postoperatively, MRI showed a fracture line from the intersection of the longitudinal and transverse tibial osteotomies through the lateral pinhole to the end of the lateral tibial diaphysis. At three months, bone union was observed without surgical treatments. Lateral tibial fracture after cementless Oxford UKA has a good clinical course without the need for surgical intervention. Medial fractures should thus be more actively prevented. MRI is useful for less symptomatic tibial lateral condyle fractures.

Prediction of Postoperative Range of Motion after Mobile-Bearing Medial Unicompartmental Knee Arthroplasty from the Preoperative Range of Motion and Other Preoperative Factors.

Postoperative flexion after unicompartmental knee arthroplasty might be predicted from the preoperative range of motion and other preoperative factors, but this has not been sufficiently investigated. Between 2013 and 2017, 198 patients (198 knees) underwent unilateral knee arthroplasty with medial mobile-bearing unicompartmental knee arthroplasty. Range of motion was measured preoperatively and at the time of final follow-up. To investigate the accuracy of the prediction of preoperative to postoperative gain or loss of the flexion angle, we performed receiver operating characteristic analysis. Logistic regression analysis was used to evaluate other predictive factors. Change in flexion angle was significantly strongly and negatively correlated with the preoperative flexion angle (R = - 0.688; 95% confidence interval: -0.755 to -0.607; p < 0.001). Preoperative flexion angle was suggested to be a significant predictor of gain or loss of the flexion angle with the area under the curve of 0.781; the cutoff value calculated using the Youden index was 140 degrees. Logistic regression analysis showed that in addition to the preoperative flexion angle of the operated side, the postoperative flexion range was significantly affected by the patient's height and by the preoperative flexion angle of the contralateral knee. If the preoperative flexion angle in Oxford mobile-bearing medial unicompartmental knee arthroplasty is <140 degrees, the postoperative flexion angle may be improved; if it exceeds 140 degrees, the postoperative flexion angle may worsen. This predictive ability is further improved by consideration of the patient's height and the range of motion on the contralateral side.

Caliper-Based Restricted Kinematic Alignment Total Knee Arthroplasty.

Restricted kinematic alignment total knee arthroplasty (rKA-TKA) is a reasonable selection for avoiding an extreme alignment that has been conceded to induce implant failure. However, computer-aided devices (CAS), such as navigation, robotics, and patient-specific instrumentation, are necessary to perform rKA-TKA. This paper reports on the surgical technique of kinematic alignment total knee arthroplasty (KA-TKA) using mechanical instruments. The lateral distal femoral angle (LDFA) and the medial proximal tibial angle (MPTA) are measured from preoperative long radiographs or CT of the lower limb, and the arithmetic hip-knee-ankle angle (aHKA) is calculated from the MPTA - LDFA. The predefined restriction boundaries are used to determine the osteotomy angle. In our practice, the LDFA is 85° to 93°, the MPTA is 85° to 90°, and the aHKA is 5° varus to 3° valgus. If correction of the femoral osteotomy is required, this can be achieved by changing the thickness of the paddle set on the distal articular surface or by adjusting the angle of the variable angle femoral cutting guide. For the tibia, the distal end of the extramedullary rod, with the proximal part placed in the center of the knee joint, should be adjusted so that it does not exceed the lateral malleolus. This limits the medial tilt of the osteotomy plane to within 5.5°. These techniques allow restricted KA to be performed with existing mechanical instruments without using CAS.

Varus placement of the tibial component reduces the potential risk of fracture with adequate bony coverage in the Oxford unicompartmental knee arthroplasty.

A short keel-cortex distance (KCD), especially to the posterior cortex, is a potential risk factor for tibial plateau fracture after Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study aimed to evaluate the effect of tibial component alignment in the coronal plane and tibial proximal morphology on the KCD. Included in this study were 51 patients scheduled for primary Oxford medial unicompartmental knee arthroplasty (UKA). The anterior and posterior KCD were preoperatively assessed using 3D simulation software with the component set perpendicular to the tibial mechanical axis (neutral), 3° valgus, 3° varus, and 6° varus, relative to neutral alignment. We evaluated the existence of overhanging medial tibial condyle where the medial eminence line, the line including the medial tibial eminence parallel to the tibial axis, passes outside of the tibial shaft. In all component alignments, patients with a medial overhanging condyle had significantly shorter posterior KCD than those without. In patients with a medial overhanging condyle, the posterior KCD significantly increased when the tibial component was placed in 3° varus (4.6 ± 1.5 mm, P = 0.003 vs neutral, P < 0.001 vs 3° valgus) and 6° varus (5.0 ± 1.4 mm, P < 0.001 vs neutral, P < 0.001 vs 3° valgus) compared with in neutral (3.5 ± 1.9 mm) or 3° valgus (2.8 ± 1.8 mm). In OUKA, varus implantation increased the KCD. This could potentially decrease the risk of fracture, even in knees with the overhanging medial condyle. Conversely, valgus implantation of the tibial component shortened the KCD, and should therefore be avoided.

Effects of Unrestricted Kinematically Aligned Total Knee Arthroplasty with a Modified Soft-Tissue Respecting Technique on the Deformity of Limb Alignment in Japanese Patients.

Background and Objectives: Unrestricted kinematic alignment total knee arthroplasty (KA-TKA) with a soft-tissue respecting technique (STRT) is a soft-tissue-dependent tibial resection entailing the restoration of the original soft-tissue tension using ligamentotaxis after resurfacing the femur, based on the concept of restoring the native or pre-osteoarthritis alignment in each patient. However, there is no consensus on the indications of unrestricted KA-TKA with the STRT. We modified the STRT, followed by an investigation of the effects of surgery on the postoperative hip-knee-ankle angle (HKAA). Materials and Methods: We retrospectively analyzed the clinical background data, including the preoperative and postoperative HKAA, of 87 patients who underwent unrestricted KA-TKA with the modified STRT. Univariate and multivariate analyses were performed to determine the factors affecting the postoperative HKAA. A receiver operating characteristic (ROC) curve was plotted to investigate the change in the cut-off values of preoperative HKAA with respect to the safe zone of the postoperative HKAA. We generated two regression models, the linear regression model and generalized additive model (GAM) using machine learning, to predict the postoperative HKAA. Results: Univariate and multivariate analyses revealed the preoperative HKAA as the factor most relevant to the postoperative HKAA. ROC analysis revealed that the preoperative HKAA exhibited a high predictive utility, with a cut-off value of -10°, when the safe range of postoperative HKAA was set at ±5°. The GAM was the superior machine learning model, indicating a non-linear association between the preoperative and postoperative HKAA. Patients with preoperative HKAAs ranging from -18° to 4° were more likely to fall within the ±5° safe range of the postoperative HKAA. Conclusions: The preoperative HKAA influences the postoperative HKAA in unrestricted KA-TKA with the modified STRT. Machine learning using the GAM may contribute to the selection of patients eligible for the surgical approach.

Restricted Kinematically Aligned Total Knee Arthroplasty Following Failed Oxford Unicompartmental Knee Arthroplasty.

In this report, we describe how to revise a failed Oxford unicompartmental knee arthroplasty to kinematically aligned total knee arthroplasty (TKA). Its benefits are the maintenance of the native joint line along with the avoidance of supplemental parts, such as metal augments and stems. This can be applied to patients whose medial tibial cortex is well preserved. The distal cutting plane and rotation alignment are decided before the removal of the femoral component. The tibial cutting plane is up to 12 mm below the lateral joint surface and the varus is up to 5° below the extramedullary rod. Eventually, the native joint line and alignment along with the soft tissue envelope can be well maintained, similar to the restricted kinematically aligned TKA.

A Muscle-Preserving Short Transverse Incision for Unicompartmental Knee Arthroplasty: A Technical Note.

We describe the use of a short transverse incision technique with muscle retention for unicompartmental knee arthroplasty (UKA). The incision is made transversely just above the joint line, followed by a detachment of subcutaneous soft tissue from the underlying capsule and fascia to create a mobile window. The fascia is incised along the medial border of the vastus medialis and the capsule of the suprapatellar pouch is incised laterally, preserving vastus medialis muscle. All procedures are performed within the mobile window while controlling the knee flexion angle. Following implantation, the capsule and fascia are anatomically repaired. This approach was used in 30 consecutive patients who underwent Oxford UKA, including one bi-unicompartmental knee arthroplasty without complications. Importantly, no patients had any disturbances of the infrapatellar branch of the saphenous nerve disturbances such as numbness, hyperesthesia, hypoesthesia, or neuroma pain. The transverse approach is thought to be a safe and feasible method for UKA.

Kinematically Aligned Oxford Unicompartmental Knee Arthroplasty Using the Microplasty Instrumentation System.

This technical note demonstrates kinematically aligned Oxford unicompartmental knee arthroplasty using the Microplasty instrumentation system with custom-made devices. The medial joint line is evaluated preoperatively; if it is aligned and parallel with the lateral joint line, they are considered to comprise the coronal knee joint line (CJL). In this case, the coronal inclination of a spoon gauge inserted into the medial joint space indicates the CJL. Otherwise, an accessory spoon is inserted and connected to the medial spoon to refer to the posterior condylar line, which is considered the CJL. The tibial cutting block is then connected without changing the inclination of the spoon and the coronal tilt of the tibial extramedullary rod is adjusted, which is implemented with a custom-made ankle yoke. The remainder of the steps is then identical to the conventional Microplasty procedure. This technique can imitate the cutting line to the CJL, which might be considered ideal from mechanical and kinematic perspectives.

Incomplete Screw Thread Engagement of Proximal Fragment: A Possible Failure Risk After Internal Fixation for Femoral Neck Fractures.

Background For successful internal fixation for femoral neck fracture, the sliding mechanism of the screw is important because it can induce inter-fragmental compression. The thread should penetrate the fracture line and be located within the proximal fragment. If screw thread engagement is incomplete and a part of the thread remains within the distal fragment, the screw sliding can be disturbed, potentially leading to fixation failure. We hypothesized that screw thread in the fracture is a risk of fixation failure. Methods We studied 133 hips that underwent internal fixation for femoral neck fracture using dual sliding and compression screws (DSCS) with 20 mm threads. The existence of incomplete thread engagement and fixation failure (cut out, perforation, pseudoarthrosis, or femoral neck shortening) were evaluated on anteroposterior hip radiography postoperatively. The distances from the thread end to the fracture line, screw head to the femoral head cortex, and femoral head diameter were measured to analyze their relationships with any incomplete thread engagement and fixation failure. Differences in evaluation data were assessed using Fisher's exact test, Student's t-test, and receiver operating characteristic (ROC) analysis. Results Forty-six cases had at least one screw with incomplete thread engagement, and the other 87 hips had a complete engagement. The failure rate in the group of hips with incomplete thread engagement was significantly higher (7/46, 15.2%) than that in the group of hips with complete thread engagement (3/87, 3.4%) (P = 0.032). Incomplete thread engagement was found in 59 out of 266 screws (22.2%), and a femoral head ≤ 43.9 mm in diameter was associated with an increased risk of incomplete thread engagement. Most incomplete thread engagement screws (81.4%) had < 5 mm thread length within the distal fragment. Conclusion A partially threaded screw is a significant risk of fixation failure after internal fixation for a femoral neck fracture. The smaller femoral head diameter increases the possibility of incomplete thread engagement. Shortening the thread length by 5 mm may help to avoid incomplete thread engagement.

Multicenter study on atypical femoral fractures in patients with bone metastases taking bone- modifying agents.

Bone-modifying agents (BMAs), with bone-resorptive inhibitory effects, such as zoledronic acid and denosumab, are widely used at higher doses for bone-related events caused by bone metastasis of malignant tumors. These drugs have been suggested to be associated with atypical femoral fractures (AFFs), and the relationship between BMAs and AFFs has attracted attention. To investigate the clinical features including bone union time of AFFs in patients administered BMA for bone metastasis, we conducted a retrospective multicenter study. Thirty AFFs from 19 patients were enrolled in this study. Thirteen patients had bilateral AFFs, and nineteen AFFs had prodromal symptoms. Eighteen AFFs underwent surgery after complete fracture, three failed to achieve bone union and required nonunion surgery, and 11 AFFs that achieved bone union had an average period until bone union of 16.2 months, which was much longer than that previously reported for ordinary AFFs. Seven patients discontinued the BMAs, but not due to AFFs. Stopping BMAs in patients with bone metastasis would make it difficult to secure their performance of activities of daily living, and AFF with BMA administration might require a longer time for union. Therefore, it would be important to prevent incomplete AFF from becoming complete AFF via prophylactic internal fixation.

Is simultaneous bilateral unicompartmental knee arthroplasty and total knee arthroplasty better than simultaneous bilateral total knee arthroplasty?

INTRODUCTION: This retrospective study aims to clarify if there are benefits of performing unicompartmental knee arthroplasty (UKA) on just one indicated side in patients who undergo simultaneous bilateral knee arthroplasty. MATERIALS AND METHODS: We compared 33 cases of simultaneous bilateral UKA/total knee arthroplasty (TKA) (S-UT) with 99 cases of simultaneous bilateral TKA (S-TT). Comparison included blood tests [C-reactive protein (CRP), albumin, and D-dimer], the incidence of deep vein thrombosis (DVT), range of motion (ROM), and clinical scores before and 1 year after surgery. RESULTS: Clinical scores were not significantly different between the groups. The postoperative flexion angle was significantly better in UKA sides. Blood tests showed that the S-UT had a significantly higher albumin value at 4 and 7 days after surgery. The CRP value at 4 and 7 days, and the D-dimer value at 7 and 14 days after surgery were significantly lower in the S-UT. The S-UT had significantly lower incidence of DVT. CONCLUSIONS: In cases of bilateral arthroplasty, if there is an indication on only one side, a better flexion angle can be obtained by UKA on that side, and with less surgical invasion. Moreover, the incidence of DVT is low, which is considered to be a benefit of performing UKA on just one side.

Mobile bearing orbit on the tibial component in Oxford unicompartmental knee arthroplasty.

PURPOSE: To evaluate the bearing orbit of the tibial component during extension-flexion motion in Oxford unicompartmental knee arthroplasty. MATERIALS AND METHODS: A total of 32 knees in 25 patients with medial osteoarthritis who underwent Oxford unicompartmental knee arthroplasty were evaluated. The distance between the vertical wall of the tibial component and the bearing (wall-bearing distance) and that between the anterior edge of the tibial component and the bearing (sagittal bearing position) were measured at 0°, 30°, 60°, 90° and 120° knee flexion with neutral tibial rotation (extension-flexion motion), and internal and external tibial rotation with 90° knee flexion (tibial rotation motion). A custom-made rounded trial bearing and caliper were used for this measurement. We calculated the wall-bearing distance, change in extension-flexion motion and tibial rotation motion. Wall-bearing distances and change in wall-bearing distance were compared using ANOVA or t-test. RESULTS: The wall-bearing distance was smallest at 60° and increased 1.0 ± 1.1 mm in knee extension and 1.1 ± 1.5 mm in knee flexion. The bearing moved posteriorly with knee flexion, and the sagittal bearing position increased by 8.1 ± 3.4 mm during extension-flexion motion. Consequently, the bearing moved in a rough C-shaped orbit of the tibial component. CONCLUSIONS: The mobile bearing moves in a rough C-shape and is mostly close to the vertical wall of the tibial component at 60°. The wall-bearing distance can change during extension-flexion motion and might be influenced by tibial component rotation. To avoid bearing separation from or contact with the vertical wall that may cause bearing dislocation, the wall-bearing distance should be evaluated before keel slot preparation.

Bearings can dislocate with smaller femoral components and thicker bearings in Oxford™ medial unicompartmental knee arthroplasty.

BACKGROUND: A mobile bearing can dislocate when joint laxity is larger than jumping height, the height difference between the bottom and the peak of the bearing (the highest point of the upper bearing surface on each side). Significant laxity due to improper gap balancing should therefore be avoided. However, once the bearing rotates vertically on the tibial component, the bearing can dislocate with smaller laxity than the jumping height. We mathematically calculated the required laxity for dislocation (RLD) and the required rotation of the bearing for dislocation (RRD). The current study addressed the question: 1) could the femoral component size and the bearing thickness affect the RLD and RRD? HYPOTHESIS: The femoral component size and the bearing thickness could affect the MLD and MRD. METHODS: The RLD and RRD were calculated using the bearing dimensions provided by the manufacturer with femoral component size, bearing thickness, and directions (anterior, posterior, and medial/lateral) as the variables on a two-dimensional basis. RESULTS: The RLD was 3.4 to 5.5mm in the anterior, 2.3 to 3.8mm in the posterior, and 1.4 to 2.4mm in the medial or lateral directions. The RLD decreased with a smaller femoral size or a thicker bearing. Similarly, the RRD decreased with a smaller femoral size or a thicker bearing thickness in all directions. CONCLUSIONS: Increased bearing thickness and decreased femoral component size deceased the RLD and RRD, which would relate to an increased risk of dislocation. Selecting the femoral component as large as possible and the bearing as thin as possible would therefore be helpful in the prevention of dislocation. LEVEL OF EVIDENCE: III; comparative computer simulation study.

Intraoperative avulsion fracture of the intercondylar eminence in Oxford mobile-bearing unicompartmental knee arthroplasty: Case report.

BACKGROUND: Unicompartmental knee arthroplasty (UKA) can provide good postoperative results and long term survival, but there may be complications. We present a rare case of avulsion fracture of the intercondylar eminence during UKA surgery. CASE PRESENTATION: An 88-year-old man had right-knee pain with anteromedial osteoarthritis. Oxford partial knee UKA (Zimmer Biomet, Warsaw, IN) was performed by the senior author by the under-vastus approach using Microplasty instruments. During the final check of the range of motion, an avulsion fracture of the intercondylar eminence occurred at the terminal extension. A 4.0 mm cannulated cancellous screw was inserted into the intercondylar eminence from just in front of the anterior cruciate ligament to the posterior tibial cortex. Six months postoperatively, bony fusion was confirmed by lateral radiography. Two years after the surgery, the patient was fully satisfied. The flexion angle was 125°, but still with an extension limit of 10°. DISCUSSION: Avulsion fracture of the intercondylar eminence can be caused by hyperextension and/or the ACL becoming tighter in full extension of the knee. In this patient, avulsion fracture also probably occurred due to increased tension of the ACL in the fully extended position. After making the horizontal cut, we inserted a thin metal plate to prevent deeper vertical cuts, but an excessive horizontal cut was a possible cause of the fracture. As treatment for avulsion fracture of the intercondylar eminence, fixation of the cannulated cancellous screw resulted in uneventful bone fusion. We recommend having a cannulated cancellous screw at hand for such complications and for other potential intraoperative problems, such as tibial plateau fracture. Further investigation into limited postoperative extension might be needed. CONCLUSION: Our patient had intraoperative avulsion fracture of the intercondylar eminence, a relatively rare complication of Oxford UKA which is probably caused by the extension being tight and/or an excessive horizontal cut. Having a cannulated cancellous screw at hand is advised, and attention should be paid to postoperative limit of extension.

Approximately 41% of knees have a looser gap in full extension than in 20° flexion after Oxford unicompartmental arthroplasty.

INTRODUCTION: In Oxford unicompartmental knee arthroplasty (OUKA), the flexion and extension gaps should be adjusted to prevent mobile-bearing dislocation. The extension gap is recommended to be evaluated in the 20° flexion position to avoid underestimation due to tension of the posterior capsule. However, we have become aware of a looser gap in full extension than in 20° flexion in some instances. MATERIALS AND METHODS: We retrospectively investigated 83 knees in 60 patients who underwent OUKA between January and June 2020. During surgery, the extension gaps were measured in both full extension and 20° flexion. The knees were classified into two groups: the gap was looser in full extension (0° group), and the gap was equal or looser in 20° flexion than in full extension (20° group). The hip-knee-ankle angle (HKAA), the lateral distal femoral angle (LDFA), the medial proximal tibia angle (MPTA), the posterior tibial slope angle (PTSA), and the last spigot size were also measured and compared between the groups. RESULTS: There was looseness in approximately 41% of knees (34 out of 83 knees) in full extension. In the knees in the 0° group, the last spigot size was significantly smaller (median 1 and 2, P < 0.01). However, there were no significant differences in the HKAA, MPTA, LDFA or PTSA between the groups. CONCLUSIONS: Approximately 41% of knees have a looser gap in full extension than in 20° flexion after OUKA. Further investigation is needed to better understand which extension gap should be used in such cases, and to find the contributing factors in loose full extension gap other than the size of the last spigot.

Trans patellar tendon sagittal tibial cut for lateral unicompartmental knee arthroplasty-location of the split- CT simulation study.

BACKGROUND: In lateral unicompartmental knee arthroplasty (UKA), a sagittal cut is often performed through the patellar tendon (PT). Although the approach is likely widely used, it has not been described in detail, especially regarding the site of the split. This study aimed to clarify where the split should be made. METHODS: This single-center retrospective cohort study included 49 consecutive patients and 51 knees with lateral osteoarthritis. Using preoperative computed tomography, we measured the distance from the medial edge of the PT to the intersection of the PT and the sagittal cutting line, defined as a line parallel to the Akagi's line and passing the tip of the lateral tibial spine. RESULTS: The sagittal cut line passed a mean of 45 ± 11% of the patellar tendon width from the PT medial edge. CONCLUSIONS: The tendon split should be made just medial to the center of the PT because it is where the sagittal cut line for lateral UKA passes.