Gradual change in knee extension following total knee arthroplasty using ultracongruent inserts

BackgroundTotal knee arthroplasty (TKA) using an ultracongruent (UC) insert is widely performed. Lack of the posterior cruciate ligament or post-cam mechanism is a concern in terms of range of motion. The flexion angle of UC TKA had been well investigated; however, natural history and correlation factors of the postoperative extension angle have not been well documented. This study aimed to investigate time-dependent changes in extension after TKA using UC inserts, and to evaluate factors that correlated with the postoperative extension angle.MethodsThis study reviewed 388 gap-balanced UC TKAs (331 patients) without hyperextension at navigation and performed between November 2010 and December 2014. The extension angle (a positive number indicates hyperextension) was measured on full-extension lateral radiographs. The extension angles from five days post-operation to final follow-up were investigated. Factors correlated with the postoperative extension angle were evaluated using multiple regression analysis.ResultsMean follow-up duration was 46.2 months. Until two years, the extension angle gradually increased; mean angles at five days/six months/one year/two years/and final follow-up were: ? 9.2°/? 2.6°/0.6°/1.0°/1.0°, respectively. Female sex (β = ? 0.15, P = 0.002) and pre-operative hyperextension (β = 0.31, P < 0.001) were associated with postoperative hyperextension deformity.ConclusionsFollowing UC TKA, knees became gradually more extended until two years post-operation. Sex and pre-operative extension angle were predictive factors for the postoperative extension angle following UC TKA.Level of evidenceLevel 4, Case series.     

Different targets of mechanical alignment do not improve knee outcomes after TKA

BackgroundAccurate alignment is a basic principle of TKA surgery, but achieving alignment within this target may not translate into superior outcomes after surgery.PurposeTo assess if neutral TKA mechanical alignment was associated with superior knee outcomes and to examine the effect of various aspects of pre-operative and post-operative alignment on knee function.MethodsAnalysis of a database of 444 TKA patients between June 2009 and October 2016. Knee outcomes (WOMAC, AKSS and knee range of motion) were collected before surgery and during follow-up at a minimum of six months.ResultsAnalysis included 444 TKA patients (62% female, mean age 66 years, mean follow-up 23 months). Deformity varied from 21° varus (mean = 7.9, SD = 2.8) to 17° valgus deformity (mean = 7.7, SD = 2.8). Pre-operatively, 101 (23%) knees were in native neutral mechanical alignment, while 278 (63%) were in varus and 65 (15%) were in valgus. Post-operatively, a group of 365 (82%) TKA were found to be in neutral mechanical alignment and a group of 79 (18%) TKA were noted to be ‘Outliers’ (17 [4%] TKA > 3° varus and 62 [14%] TKA > 3° valgus alignment). Restoration of the target of alignment of 0 ± 3° or 0 ± 1°, did not have better functional outcomes scores, range of motion or prosthesis longevity than those in the outlier range.ConclusionNeutral TKA alignment did not appear to be a significant contributing factor to the improvement in knee function in short-medium term follow-up.     

Patellar tendon reconstruction with hamstring autograft for the treatment of chronic irreparable patellar tendon injuries

BackgroundPatellar tendon injuries not amenable to primary repair present a challenging problem for surgeons and patients alike. No standard surgical technique exists for these injuries and few studies report outcomes after surgical treatment.MethodsA retrospective analysis was conducted for patients undergoing surgical treatment for irreparable patellar tendon tears. Patients were treated with an indirect tendon reconstruction technique using high-strength suture to set initial patellar height and hamstring autograft for biologic augmentation. Patients who underwent this procedure between 2012 and 2018 and met minimum two-year follow-up with completion of all outcome measurements including KOOS, PROMIS, VAS pain and satisfaction scores were included.ResultsEleven patients met inclusion criteria. Ten of eleven patients (91%) had intact repairs and final patient outcomes were collected at a mean of 54.9 ± 23.1 months after surgery. Only one patient experienced extensor lag at final follow-up (p < 0.001). The preoperative Caton–Dechamps ratio was 1.77 ± 0.58, which decreased to 0.98 ± 0.25 after surgery (p < 0.001). The mean postoperative KOOS ADL score was 61.5. The mean postoperative PROMIS Global Mental and Physical Health scores were 46.9 ± 8.7 and 42.0 ± 9.8. Post-operative mean VAS satisfaction score was 5.6 ± 3.4.ConclusionsPatellar tendon reconstruction with autologous hamstring tendon graft and suture augmentation allows for acceptable outcomes in the setting of patellar tendon disruption with segmental defects when direct repair is not possible.     

Experience-optimised fast track improves outcomes and decreases complications in total knee arthroplasty

PurposeThe aim of this study was to describe an advanced total knee arthroplasty (TKA) fast-track programme and determine discharge parameters during hospitalisation, as well as patient satisfaction, outcomes and complications within the first 12 months after surgery.MethodsThis prospective study was based on patients selected consecutively for primary elective TKA, undergoing surgery between 2014 and 2017 in an established fast-track setting.Hospitalisation-related parameters were collected: demographics, body mass index (BMI), surgical time, ischaemia time, haemoglobin values, blood transfusions, length of stay, weight-bearing and stair-climbing time, opioid administration, preoperative and discharge loss of extension and maximum active flexion of the knee, visual analogue scale (VAS), 12-month follow-up satisfaction rate and range of motion, any complications, hospital re-admission and re-operation within the first 12 months. Differences were determined using t-tests.ResultsA total of 704 total knee replacements implanted in 481 patients were included in the study and 223 patients had a bilateral TKA. Their mean age was 69.8 years (range 57–88 years).At the 12-month follow-up, 623 patients (88.5%) reported being satisfied or very satisfied and 15 (2.1%) were dissatisfied with their TKA, mean active flexion and loss of extension were 104.4° and 2.3°, respectively. A total of 15 complications occurred (two percent): five painful knees, three knee stiffness, three haematomas, two infections, one hospital re-admission and one deep venous thrombosis. No cases of pulmonary embolism and death related to surgery were reported.ConclusionThe study reports on an advanced fast-track programme for TKA with a low incidence of surgery- and hospitalisation-related issues and complications and without any severe adverse events during the first year.On average, the fast-track programme had a short length of stay, an early recovery of weight-bearing, knee mobility, pain control and a high satisfaction rate, accompanied with an acceptable 12 month range of motion.     

Long-term results of revision total knee arthroplasty using a rotating hinge implant

BackgroundRotating hinge implants are commonly used in revision total knee arthroplasty (TKA) in the setting of significant ligamentous instability or bone deficiency. These highly constrained implants have been associated with variable clinical outcomes and uncertain long-term survivorship. The aim of this study is to establish long-term functional outcomes, radiographic results, and survivorship after revision TKA with a rotating hinge implant.MethodThis is a retrospective study of prospectively collected data of 41 consecutive patients undergoing revision TKA with rotating hinge components and minimum 10-years follow-up. The study included 22 females (53.7%) and 19 males (46.3%) with a mean age of 66.6 ± 8.5 years. Clinical outcomes recorded included the Oxford Knee Score (OKS) preoperatively and at latest follow-up. Range of motion, implant survivorship, and complications were also recorded. Predefined radiological outcomes were obtained using plain radiographs.ResultsThere was a significant improvement in OKS after revision TKA with a rotating hinge implant compared to preoperative scores (40.7 ± 4.2 vs. 21.4 ± 4.9 respectively, p < 0.001). At latest follow-up, mean range of motion was 111.5° ± 9.3° and mean overall limb alignment was 0.2° ± 2.0° varus. Implant survivorship at minimum 10-year follow-up was 90.2%. Radiographic lucent lines were observed in 14 patients (34.1%).ConclusionRevision TKA with a rotating hinge implant leads to satisfactory clinical outcomes and very good implant survivorship at long-term follow-up. Surgeons should have a low threshold to use these versatile implants in complex revision knee arthroplasty.     

Reconstruction of the extensor mechanism augmented with reverse transferred iliotibial band after proximal tibia tumor resection and mega-prosthetic replacement

BackgroundThe optimal procedure for functional reconstruction of the extensor mechanism after proximal tibia mega-prosthetic replacement remains unclear.MethodsSince 2006, 14 consecutive patients with aggressive bone tumors in the proximal tibia who underwent mega-prosthetic replacement were prospectively treated with reconstruction of the extensor mechanism using an ipsilateral iliotibial band. The surgical procedure consisted of wrapping the reversed iliotibial band around the tibia component, firmly suturing it to the remaining patellar tendon and tibialis anterior fascia, and covering it with a muscle flap. At the last follow up, the function was assessed based on extensor lag, active flexion of the knee, and Musculoskeletal Tumor Society score. Patellar height was measured with the Insall–Salvati ratio (ISR) preoperatively, postoperatively, and at the last follow up.ResultsAt the last follow up, the extensor lag and active flexion in 14 patients averaged 2.5° and 86°, respectively. Musculoskeletal Tumor Society score could be obtained in nine surviving patients at the last follow up and was a mean of 20.7 points. The mean ISR preoperatively, postoperatively, and at the last follow up was 1.04, 0.75, and 0.89, respectively. The extensor lag was not associated with the ISR value at any points, while reduced active flexion significantly correlated with a low ISR at the last follow up (P = 0.015). Four patients underwent additional surgeries due to postoperative infection, but none required eventual revision or amputation.ConclusionThe extensor mechanism reconstruction with the reverse transferred iliotibial band for mega-prosthetic replacement after proximal tibia resection yielded reliable outcomes with functional benefit to stabilize active knee extension.     

Can total knee arthroplasty restore the correlation between radiographic mechanical axis angle and dynamic coronal plane alignment during gait?

BackgroundTotal knee arthroplasty (TKA) is the treatment of choice for end-stage knee osteoarthritis. Postoperative static knee alignment has been recognized as a key component of successful surgery. A correction toward the kinematics of a native knee is expected after TKA, with an aim for neutral mechanical alignment. The evolution of frontal plane knee kinematics is not well understood.MethodsNineteen patients awaiting TKA were recruited. Three-dimensional knee kinematics during treadmill gait were assessed pre-operatively, 12 months after surgery, and compared to a control group of 17 asymptomatic participants.ResultsMean radiographic mechanical alignment was corrected from 5.4° ± 5.0 (Standard Deviation) varus pre-operatively to 0.1° ± 2.0 (Standard Deviation) valgus postoperatively (P = 0.002). Mean stance coronal plane alignment decreased from 6.7° ± 4.0 (Standard Deviation) varus per-operatively to 2.1° ± 3.8 (Standard Deviation) postoperatively (P = 0.001). Correlation between radiographic mechanical axis angle and dynamic frontal plane alignment during gait, before and after surgery, was weak (pre-operative R = 0.41; postoperative R = 0.13) compared to control (R = 0.88). In the sagittal plane, TKA patients maintained their pre-operative stiff knee gait adaptation. Postoperative transverse plane kinematics suggested restoration of external tibial rotation during swing after TKA compared to control (Pre-operative 3.1°, postoperative 6.8°, control 7.1°, P = 0.05).ConclusionThe lack of correlation between static and dynamic alignment suggests that static radiographic coronal alignment of the knee does not accurately predict dynamic behavior. In the sagittal plane, pre-operative gait adaptations were still present 12 months after surgery, supporting the need for a functional assessment to guide postoperative rehabilitation following TKA.     

No difference in the anteroposterior stability between the GRADIUS and multi-radius designs in total knee arthroplasty

BackgroundThis retrospective study aimed to compare stability and clinical and radiological outcomes of total knee arthroplasty (TKA) for the GRADIUS and multi-radius femoral designs after minimum of two-year follow-up.MethodsA total of 142 patients who underwent TKA using ATTUNE posterior stabilized (PS) implants (68 patients, GRADIUS group) or Persona PS implants (74 patients, multi-radius group) for degenerative osteoarthritis were included. After an average of 2-year follow-up, the anteroposterior (AP) stability at 30°, 60°, and 90° was measured using KT 2000 device and compared between the two groups. The clinical outcome measurements included range of motion (ROM) of the knee, patient-reported outcomes and anterior knee pain (AKP). For the clinical evaluation of mid-flexion instability, pain was evaluated using the visual analog scale (VAS) score recorded during climbing up or going down stairs. The radiolucent lines on knee radiographs obtained at final follow-up were evaluated and compared between two groups.ResultsThe average AP stability at 30° knee flexion was 5.7 mm in the GRADIUS group and 5.9 mm in the multi-radius group; however, the difference was not significant. The AP stability at 60° and 90° knee flexion was also similar in both groups. There were no significant differences in the ROM, patient-reported outcomes at follow-up, incidence of AKP and VAS scores between the two groups. There were no differences in the incidence of radiolucency around the components between the two groups.ConclusionThe GRADIUS design did not show any advantage with respect to the stability or clinical outcomes compared with the multi-radius design in TKA.     

Combined quadriceps lengthening (using an external ring fixator) and patellar tendon reconstruction (using a tendoachilles allograft) in a case of chronic patellar tendon rupture: A case report

BackgroundPatellar tendon rupture is an infrequent and debilitating condition, which if left untreated, is complicated by quadriceps contracture and patella alta. This results in reduced function of the knee extensor mechanism including extension lag, reduced range of motion (ROM), chronic knee pain, and frequent falls. Early primary repair has good results in most cases and is performed by opposing and suturing the tendon ends. However, when there is a delay between rupture and repair or in case of a re-rupture, primary repair techniques may not work due to retraction of the extensor mechanism. Several treatment modalities have been proposed in such cases, but there is no clear consensus.MethodologyWe present the case of a 39-year-old male with chronic rupture of patellar tendon that was reconstructed with a two-stage technique. In the first stage, a ring-fixator was applied to stretch the quadriceps muscle and the second stage consisted of reconstruction of the patellar tendon with a tendoachilles allograft. This procedure was performed in two stages five weeks apart and almost four years after the initial injury.ResultsResults were excellent at three years' follow-up with the patient achieving full extension, a ROM of 0–110° and 85% quadriceps strength. There was significant improvement in his pain, mobility and quadriceps bulk.ConclusionTo our knowledge, this treatment has not previously been described in the literature. We present this case as a proven treatment option for treatment of chronic patellar tendon injuries with extensor mechanism shortening.     

Mobile-bearing total knee arthroplasty: More rotation is evident during more demanding tasks

BackgroundSome reports showed few but significant more axial femorotibial rotation in favor of mobile-bearing (MB) versus fixed-bearing (FB) total knee arthroplasty (TKA), mostly during knee bend fluoroscopic studies. The goal of the current study was to submit MB and FB groups of TKA patients to a turning activity, in which additional rotation was to be expected.MethodsTwo consecutive cohorts of patients after TKA (10 FB and 11 MB knees in a total of 18 patients) were assessed using motion analysis five year postoperatively, while performing gait and sit-to-walk (STW) movements with and without turning steps.ResultsMean range of rotation in the FB group increased from 9.7° during gait, to 11.7° during STW straight, and to 14.3° during STW turning. Mean range of rotation in the MB group increased from 13.4° during gait to 21.0° during STW straight, and stayed at 21.1° during STW turning.ConclusionsToo many uncontrolled variables in the current study hinder a meaningful discrimination of MB from FB TKA rotation. However, the study does illustrate how more demanding task loads could be helpful in exploring the geometric constraints of TKA variants.Level of EvidenceLevel III, therapeutic study.     

Reconstruction of knee extensor with patellar tendon autograft following intraoperative radiotherapy

BackgroundPatellar tendon autograft after intraoperative extracorporeal radiotherapy has been used for reconstruction of the extensor mechanism following limb-sparing wide tumor resection around the knee. The purpose of this study was to determine the clinical outcome of this reconstruction technique.MethodsWe retrospectively reviewed six consecutive patients with peripatellar tendon and proximal tibial sarcoma who underwent reconstruction of the knee extensor mechanism. The resection area was planned to be contained with the patellar tendon in order to obtain a wide margin. First, the patella was osteotomized at the midline, and the inferior half of patella, patellar tendon, and tibial tuberosity were excised en bloc. The resected segments were devitalized with intraoperative extracorporeal radiotherapy and reimplanted into the original site. A follow-up evaluation included an assessment of the range of motion, extensor lag, the International Society of Limb Salvage score, and complications.ResultsSix patients were followed up for 121–270 months. One patient underwent an additional reconstruction with total knee arthroplasty due to a collapse of the tibial subchondral bone. A supracondylar fracture of the femur occurred in two patients, and a delayed union of the osteosynthesis site of the tibial shaft was observed in one patient. At the latest follow up, extensor lag had a median of five degrees, and International Society of Limb Salvage scores had a median of 83%. No local recurrence or rupture of the patellar tendon was observed.ConclusionsReconstruction of the knee extensor mechanism using a patellar tendon treated with intraoperative radiotherapy is a reliable and successful method.     

Residual varus alignment after total knee arthroplasty increases knee adduction moment without improving patient function: A propensity score-matched cohort study

BackgroundTargeting residual varus alignment in total knee arthroplasty may be functionally beneficial to preoperative varus patients.MethodsBilateral TKA patients were enrolled. According to the postoperative hip-knee-ankle axis, patients were allocated into residual varus (3° ± 1°) alignment group or neutral (0° ± 1°) alignment group. Then, 1:2 propensity score matching was used to match preoperative variables. Finally, matched neutral (n = 45) and varus groups (n = 32) were followed-up for two years and compared. The primary outcome was the Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC). Secondary outcomes were range of motion (ROM), Knee Society knee score and function score, spatiotemporal gait parameters, dynamic alignment, knee flexion angle, knee adduction moment (KAM) and internal knee extension moment.ResultsAt two years after surgery, the mean difference of WOMAC score was 0.3 (95% CI, [? 3.1, 3.7]) between the two groups. All secondary outcomes, except KAM and dynamic alignment, showed no significant difference between the two groups. Residual varus alignment group showed increased KAM and maximum KAM was 19% higher (P = 0.006).ConclusionsResidual varus alignment showed no clinical benefits, and both groups of patients had a functionally identical knee gait biomechanics, except for increased KAM and varus alignment. The authors consider that even in patients with varus alignment, the first principle is still achieving neutral alignment, which is helpful for reducing the KAM.Level of evidenceIII, retrospective cohort study.     

The results of patellar stainless steel wire extensor mechanism reconstruction in proximal tibial tumour excision mega-prosthesis surgeries for proximal tibial sarcomas

BackgroundExtensor mechanism function after a proximal tibial tumour excision is the major determining factor for the limb function. However, problems of extensor lag, delayed healing and poor functional outcomes exist with the previous methods of its reconstruction. We describe a novel technique of using a patellar stainless steel (SS) wire to reconstruct the extensor apparatus of the knee in non-porous coated implants and examine the functional outcome and associated complications.MethodsThis was a retrospective analytical interventional study. Twenty-six patients operated between 2011 and 2019 were included. Extensor lag measured at 6 months and 12 months postoperative, total range of motion at 12 months and Musculoskeletal Tumor Society (MSTS) score at the final visit were retrieved. Complications that occurred during the follow up period were noted. Patellar position was measured using comparative patellar-position-ratio.ResultsMean extensor lag at 6 months was 18.5° which improved to 8.7° at 12 months. Patellar malposition and deep infection were found to be the causes of poor functional outcome. A patellar-position-ratio between 0.9 and 1.1 led to a well-functioning extensor apparatus. Four patients underwent above-knee amputations. Deep infection and amputations reduced the MSTS score. An SS wire give way after 6 months did not affect the extensor power. A medial gastrocnemius flap reduced the infection rates.ConclusionPatellar SS wiring is an effective technique for reconstructing the knee extensor apparatus following a proximal tibial tumour excision mega-prosthesis. Proper position of the SS wire prevents wire-related complications. For a well-functioning extensor apparatus, use of a gastrocnemius flap cover intra-operatively is pertinent along with lack of infection for a pain-free, stable and mobile limb.     

Medial patellofemoral ligament reconstruction with autologous gracilis tendon: Clinical and radiological outcomes at a mean 6 years of follow up

BackgroundThe medial patellofemoral ligament (MPFL) is considered the primary soft tissue restrain to lateral translation of the patella during the first 15–30 degrees of knee flexion. The primary restraint thereafter is the slope of the lateral wall of the trochlea. A plenty of procedures are described in literature for MPFL reconstruction with different types of graft, angle of knee flexion for fixation and rehabilitation protocols. In this study we used MPFL reconstruction with doubled autologous gracilis tendon with the Schottle’s technique. The aim of our study is to evaluate outcomes at medium-long term follow up of MPFL reconstruction.MethodsPatients who underwent arthroscopic MPFL reconstruction for recurrent patellar dislocation were followed up for a minimum of 2 to 10 years. Patient-reported outcomes including the Kujala, Visual Analogue Scale (VAS) score were collected preoperatively and postoperatively. Clinical complications such as loss of ROM, recurrent sub-luxation or dislocation were recorded.ResultsA total of 38 patients with recurrent patellar dislocation were treated with MPFL reconstruction and data were available for final follow up (mean 72.3 months, SD 33.6). Mean age at time of surgery was 23.4 (SD 7.8). Mean number of dislocations before surgery was 7.1 (SD 10.5). Recurrent dislocations were not observed in any of the patients treated at last follow-up. Significant clinical improvements were also noted with Kujala and VAS score. Patellar tilt angle decreased significantly from pre to post-operative.ConclusionOur study demonstrated that MPFL reconstruction with patellar suture anchors fixation using autologous gracilis tendon is an effective, safe and reliable method for treating recurrent patellar dislocation.     

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

BackgroundAccurate 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.MethodsTwo 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.ResultsThe 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.ConclusionThree-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.     

Association of knee flexion angle after posterior-stabilized total knee arthroplasty with postoperative tibial external position relative to the femur and the extent of tibial internal rotation from knee extension to flexion

BackgroundThis study evaluated the relationship between preoperative and postoperative knee kinematics, moreover, investigated tibial rotational position and the extent of tibial internal rotation from knee extension to flexion as factors to obtain significant knee flexion after total knee arthroplasty (TKA).MethodsFifty-four patients (60 knees total; 15 males, 16 knees; 39 females, 44 knees) who underwent posterior-stabilized TKA using a navigation system were included. Intraoperative knee kinematics involving tibial rotational position relative to the femur and the extent of tibial internal rotation were examined at two time points: 1) after landmarks registration (pre-TKA) and 2) after skin closure (post-TKA). The relationship between the knee flexion angle at one year postoperatively and intraoperative tibial rotational position, or the extent of tibial rotation among several knee flexion angles calculated with a navigation system were investigated.ResultsThe postoperative knee flexion angle was positively associated with the preoperative flexion angle and intraoperative knee kinematics at post-TKA involving tibial external position relative to the femur at knee extension and the extent of tibial internal rotation from extension to 90° of flexion or to maximum flexion. There was a positive relationship between the extent of tibial internal rotation at pre-TKA and that at post-TKA.ConclusionsThe intraoperative kinematics of the extent of tibial internal rotation at post-TKA was influenced by that at pre-TKA. The greater external position of the tibia relative to the femur at knee extension and the greater extent of tibial internal rotation at post-TKA might lead to good knee flexion angle.     

Is postoperative flexion angle genuinely better in unicompartmental knee arthroplasty than in total knee arthroplasty? A comparison between the knees in the same patients

BackgroundThe aim of this retrospective study was to clarify if unicompartmental knee arthroplasty (UKA) can acquire a greater postoperative flexion angle than total knee arthroplasty (TKA) in the same individuals after adjusting for the preoperative flexion angle and if the preoperative flexion angle correlates with the change in flexion postoperatively.MethodsThirty-five patients between 2011 and 2017 who had undergone simultaneous TKA on one knee and UKA on the other knee were included in the study. Range of motion was measured preoperatively and at one year after the surgery. The relationship between the pre- and postoperative flexion angles was evaluated.ResultsUKA can acquire approximately 10° greater flexion postoperatively when compared to TKA, even after adjustment for the preoperative flexion angle. The preoperative flexion angle is strongly and negatively correlated with the change in flexion angle in both the TKA and UKA knees. A preoperative knee with a smaller flexion angle will gain greater flexion postoperatively, whereas a preoperative knee with a greater flexion angle tends to lose flexion angle. The thresholds of gain/loss are estimated as 123° and 135° in TKA and UKA knees, respectively.ConclusionsThese results provide an evidence that the UKA can acquire a greater postoperative flexion angle than the TKA and valuable information for patients who demand a deep postoperative flexion angle.     

Intraoperative assessment of midflexion laxity in total knee prosthesis

BackgroundSoft-tissue balancing of the knee is fundamental to the success of a total knee arthroplasty (TKA). In posterior-stabilized TKA, there is no stabilizer of the anterior–posterior translation in the midflexion range in which the cam-post mechanism does not engage yet. Therefore, instability in the midflexion range is suspected to occur in posterior-stabilized TKA. The purpose of this study was to measure the joint gap throughout a full range of motion and to analyze the joint gap laxity in the midflexion range after implantation of a mobile-bearing posterior-stabilized total knee prosthesis.MethodsJoint gap kinematics in 259 knees with varus osteoarthritis were measured during TKAs using a tensor device with the same shape of a total knee prosthesis of the same design was used. After the implantation of a mobile-bearing posterior-stabilized prosthesis and the reduction of the patellofemoral joint, the joint gap was measured at 0°, 30°, 60°, 90°, 120°, and 145° of flexion.ResultsThe center size of the joint gap was tight in extension and deep flexion and loose at midflexion ranges, especially at 30° of flexion (p < 0.001). The symmetry of the joint gap was varus at 0° and 145° of flexion (p < 0.001).ConclusionsOur results showed the joint gap laxity in the midflexion range after the implantation of a mobile-bearing posterior-stabilized prosthesis. Our new tensor device, which can attach the polyethylene insert trial, will provide the important information about the joint gap kinematics after implantation of total knee prostheses.Level of evidenceIV.