Gap Imbalance Research Articles

Propensity of the tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in Oxford unicompartmental knee arthroplasty: retrospective study.

A well-balanced joint gap is necessary in Oxford unicompartmental knee arthroplasty (OUKA) to prevent mobile-bearing dislocation. While the gaps between 20° (extension) and 100° (flexion) are precisely adjusted using the incremental mill system, there has been insufficient evaluation of gaps in other angles. We hypothesized that the gap is not always the same in other angles. This retrospective study aimed to evaluate the gap in full-extension (0°), mid-flexion (60°) and deep flexion (130°) for comparison with those in extension and flexion gaps. We evaluated 119 knees in 83 patients (51 females, 31 males, aged 71.9 years). The full-extension and mid-flexion gaps were compared with the extension gap, and the deep flexion gap was contrasted with the flexion gap. Each gap was classified into isometric, tight or loose, for evaluation of contributing factors. Although the full-extension gap tended to be isometric (45%), the mid-flexion tended to be tight (48%), whereas the deep-flexion was loose in most knees (84%) (P = 0.002). The tight mid-flexion and loose deep flexion gap pattern accounted for 44% of the total knees, especially so with smaller femoral components (P = 0.004). Our results highlight the propensity of tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in OUKA. Although the effect of such a minor gap imbalance is still unknown, the pattern was more prevalent in patients with smaller-sized femoral components. Use of a larger femoral component may equalize the gap throughout the motion arc.

Posterior tibial slope considered as an important addition to the CPAK classification system

IntroductionCoronal Plane Alignment of the Knee (CPAK), is an informative way to classify native knee alignment types, but does not consider posterior tibial slope, an important variable in knee kinematics. We hypothesized that tibial slope would have a significant effect on knee kinematics and warrant consideration in addition to the CPAK system. MethodsWe examined 335 adult patients with osteoarthritis receiving total knee arthroplasty. We measured the lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and posterior tibial slope angle (PTS). Knees were categorized into CPAK classes and subdivided into types ‘A’ (PTS 8°) or ‘B’ (PTS >8°). We recorded pre-and-post operative knee flexion, and extension/flexion gaps in all subjects. ResultsCPAK classes VII-IX were not seen. Classes I and II comprised a plurality of all knees. One-third of all knees were type B. CPAK classes III, IV, and VI had greater type B proportions, but this was not statistically significant. Type B knees had greater flexion both pre-op (p < .001) and post-op (p = .043); type A knees had greater flexion improvement pre-to-post operatively (p = .045). Type A knees had greater medial and lateral flexion-extension gap change pre-operatively (p = .021) and (p = .027), respectively. Type B knees had greater medial-lateral gap imbalance preoperatively in both flexion and extension. Discussion/conclusionOur results suggest that there are important pre and post-operative differences in medial and lateral femorotibial gap balance between type A and B knees that require consideration for intra-operative balancing. Differences in knee flexion further solidify that PTS is an important variable that affects kinematics before and after TKA. We propose the addition of PTS types A and B to the existing CPAK classes. This is an easy and logical way to create a comprehensive classification system in both coronal and sagittal planes that captures further differences in knee kinematics.

Functional alignment in total knee arthroplasty best achieves balanced gaps and minimal bone resections: an analysis comparing mechanical, kinematic and functional alignment strategies.

Key concepts in total knee arthroplasty include restoration of limb alignment and soft-tissue balance. Although differences in balance have been reported amongst mechanical alignment (MA), kinematic alignment (KA) and functional alignment (FA) techniques, it remains unclear whether there are differences in gap imbalance or resection thicknesses when comparing different constitutional alignment subgroups. MA (measured resection technique), KA (matched resections technique) and FA (technique based on the restricted KA boundaries) were compared in 116 consecutive patients undergoing 137 robotic-assisted cruciate-retaining total knee arthroplasties. The primary outcome was the proportion of balanced gaps (differential laxities ≤ 2mm) for extension, flexion, medial and lateral gap measurements. Manual pre-resection laxity measurements were obtained for MA and KA and manual post-resection measurements were obtained for FA in 10° and in 90° of knee flexion. Secondary outcomes were resection depths and implant alignment. All outcomes were analysed per constitutional coronal alignment and joint line obliquity subgroups. The proportions of balance in all four gap measurements were 54.7%, 66.4% and 96.5%, with MA, KA and FA, respectively. Across all constitutional alignment types, FA achieved the highest proportion of balance. MA resected the least amount of bone from the medial tibial plateau. KA had femoral components in most valgus and most internally rotated, tibial components in most varus and was the most bone-preserving for the posteromedial femoral condyle. FA had the most externally rotated femoral components and was most bone-preserving for the distal femoral resections. The study shows that implant alignment to the mechanical axis or joint line anatomy (equal resections) alone does not guarantee a balanced total knee arthroplasty. FA resulted in the highest proportion of balanced knees across all analysed subgroups. Future research will consider whether one alignment philosophy leads to superior outcomes for different constitutional alignment subgroups. Level II.

Mind the Gap: Alleviating Local Imbalance for Unsupervised Cross-Modality Medical Image Segmentation

Unsupervised cross-modality medical image adaptation aims to alleviate the severe domain gap between different imaging modalities without using the target domain label. A key in this campaign relies upon aligning the distributions of source and target domain. One common attempt is to enforce the global alignment between two domains, which, however, ignores the fatal local-imbalance domain gap problem, i.e., some local features with larger domain gap are harder to transfer. Recently, some methods conduct alignment focusing on local regions to improve the efficiency of model learning. While this operation may cause a deficiency of critical information from contexts. To tackle this limitation, we propose a novel strategy to alleviate the domain gap imbalance considering the characteristics of medical images, namely Global-Local Union Alignment. Specifically, a feature-disentanglement style-transfer module first synthesizes the target-like source images to reduce the global domain gap. Then, a local feature mask is integrated to reduce the 'inter-gap' for local features by prioritizing those discriminative features with larger domain gap. This combination of global and local alignment can precisely localize the crucial regions in segmentation target while preserving the overall semantic consistency. We conduct a series of experiments with two cross-modality adaptation tasks, i,e. cardiac substructure and abdominal multi-organ segmentation. Experimental results indicate that our method achieves state-of-the-art performance in both tasks.

Medial osteophyte resection width correlates with correction of the medio-lateral component gap imbalance during posterior-stabilized total knee arthroplasty

BackgroundThere is a lack of robust evidence for a correlation between the medial osteophyte resection and correction of the medio-lateral gap imbalance during total knee arthroplasty. The purpose of the present study was to quantify the effect of osteophyte resection on the medio-lateral component gap imbalance during posterior-stabilized total knee arthroplasty. MethodsForty-five cases of primary posterior-stabilized total knee arthroplasty using the measured resection technique with posterior-stabilized prosthesis for varus knee osteoarthritis were reviewed. Medial and lateral joint gaps at 0°, 10°, 45°, and 90° of flexion, and maximum flexion were measured intraoperatively before and after the osteophyte resection. The relationship between medial osteophyte resection width and change of joint varus angle and medial component gap were assessed using Pearson's correlation coefficient. FindingsMedial component gap and joint varus angle values at post medial osteophyte resection were significantly larger and lower than at pre-resection (Medial gap: pre 9.5 ± 1.8 mm, post 10.3 ± 1.8 mm, P < 0.001, Joint angle: pre 5.2 ± 2.9°, post 4.2 ± 2.9°, P < 0.001). There was no significant difference between pre and post medial osteophyte resection in lateral component gaps. Per each 1 mm of medial osteophyte resection width, increases of 0.13 mm medial component gap and 0.2° valgus were observed (Medial gap: r = 0.38, P < 0.001, Joint angle: r = 0.38, P < 0.001). InterpretationMedial osteophyte resection increases the medial component gap without lateral component gap increase, while decreasing the joint varus angle in primary posterior-stabilized total knee arthroplasty for varus knee osteoarthritis. Osteophyte resection width was found to correlate with correction of the medio-lateral component gap imbalance.

Predictive Gap-balancing Reduces the Extent of Soft-tissue Adjustment Required After Bony Resection in Robot-assisted Total Knee Arthroplasty—A Comparison With Simulated Measured Resection

BackgroundTo understand the extent and frequency of soft-tissue adjustment required to achieve mediolateral (ML) balance in measured resection (MR) vs gap-balancing (GB) total knee arthroplasty, this study compared ML balance and joint laxity throughout flexion between the 2 techniques. The precision of predictive GB in achieving ML balance and laxity was also assessed. MethodsTwo surgeons performed 95 robot-assisted GB total knee arthroplasties with predictive balancing, limiting tibial varus to 3° and adjusting femoral positioning to optimize balance. A robotic ligament tensioner measured joint laxity. Planned MR (pMR) was simulated by applying neutral tibial and femoral coronal resections and 3° of external femoral rotation. ML balance, laxity, component alignment, and resection depths were compared between planned GB (pGB) and pMR. ML balance and laxity were compared between pGB and final GB (fGB). ResultsThe proportion of knees with >2 mm of ML imbalance in flexion or extension ranged from 3% to 18% for pGB vs 50% to 53% for pMR (P < .001). Rates of ML imbalance >3 mm ranged from 0% to 9% for pGB and 30% to 38% for MR (P < .001). The mean pMR laxity was 1.9 mm tighter medially and 1.1 mm tighter laterally than pGB throughout flexion. The mean fGB laxity was greater than the mean pGB laxity by 0.5 mm medially and 1.2 mm laterally (P < .001). ConclusionMR led to tighter joints than GB, with ML gap imbalances >3 mm in 30% of knees. GB planning improved ML balance throughout flexion but increased femoral posterior rotation variability and bone resection compared to MR. fGB laxity was likely not clinically significantly different than pGB.

Rotating Hinge Revision Total Knee Arthroplasty for Severe Arthrofibrosis.

First, remove all soft-tissue and osseous sources of stiffness and adequately expose the knee, then remove all previous components. Create a stable and balanced extension gap, and, conversely, a relatively loose flexion gap, which allows for a substantial increase in range of motion. Then, in order to prevent instability in flexion, a rotating hinge prosthesis is utilized, which allows for appropriate kinematic motion despite gap imbalance. Additional steps to regain flexion include medial and lateral distal femoral partial condylectomies, as well as patellar component revision. The first line of treatment for stiffness following total knee arthroplasty is nonoperative and is mainly focused on physical therapy3. Manipulation under anesthesia can also be performed within the first 12 weeks postoperatively3. Surgical treatments can include arthroscopic debridement as well as open debridement with possible polyethylene liner exchange. If there is a mechanical cause for stiffness, then this should also be addressed surgically. For cases of arthrofibrosis without a clear mechanical etiology or for cases in which the above treatment has failed, complete revision of the femoral and tibial components should be considered3. An alternative option to the technique proposed here is to utilize a varus-valgus constrained implant. Revision with a hinged implant allows for a more aggressive approach to regaining motion, as compared with all other surgical alternatives. By revising all components, the surgeon is able to remove all sources of stiffness and reconstruct the knee until as much range of motion as possible is achieved. Unfortunately, even with balanced extension and flexion gaps, refractory stiffness is common. A solution for this residual stiffness is to unbalance the gaps and create a loose flexion gap. By doing so, the surgeon is advised to switch to a hinged implant to create a kinematically balanced knee. Any other revision implant, such as a varus-valgus constrained implant, would risk flexion instability. Several studies have examined the use of revision total knee arthroplasty with a hinged implant for arthrofibrosis and have showed substantial improvements in knee range of motion. Bingham et al. showed that the rotating hinge group had a 20° improvement in range of motion (p = 0.048)1. Hermans et al. found a 35.8° flexion gain in the hinge group compared with a 14.2° flexion gain in the varus-valgus constrained group (p = 0.0002)4. van Rensch et al. found a median gain of 45° of range of motion5. Patients should be aware that this procedure involving the use of a hinged implant has similar risks to other revision total knee arthroplasty procedures; specifically, there is a risk of recurrent arthrofibrosis as well as mechanical complications1,5. Achieve adequate exposure with a quadriceps snip.Perform a thorough synovectomy and debridement.Create a balanced extension gap with a relatively loose flexion gap.Distalize the joint line by resecting additional proximal tibia in cases of patella baja.Beware of refractory stiffness as a result of a scarred extensor mechanism.Consider revising the patellar component.Consider performing a partial condylectomy at the medial and lateral distal aspects of the femur. TKA = total knee arthroplastyAP = anteroposteriorCT = computed tomographyMRI = magnetic resonance imagingRHK = rotating hinge kneeNSAIDs = nonsteroidal anti-inflammatory drugs.

Equal bony resection of distal and posterior femur will lead to flexion/extension gap inequality in robot-assisted cruciate-retaining TKA.

Joint imbalance has become one of the main reasons for early revision after total knee arthroplasty (TKA) and it is directly related to the surgical technique. Therefore, a better understanding of how much bone has to be removed to obtain a balanced flexion/extension gap could improve current practice. The primary objective of this study was to analyse the amount of bone that needed to be removed from the distal and posterior femoral joint surfaces to obtain an equal flexion/extension gap in robot-assisted TKA. The second objective of this study was to evaluate whether the size of the knee joint influenced the amount of bony resection needed to achieve an equal flexion/extension gap in robot-assisted TKA. A retrospective analysis was performed on all patients receiving a robot-assisted TKA (Cruciate Retaining (n = 268)) by six surgeons from April 2018 to September 2019. The robot was used consecutively when available in all patients receiving Cruciate Retaining TKA. Gap assessment, bony resections, femoral implant size and hip-knee-ankle angle were evaluated with the robot. Femoral implant size was categorized into small (size 1-2), medium (size 3-5) and large (size 6-8). The difference between the posterior and distal resection needed to obtain equal flexion and extension gap was on average 2.0mm (SD 1.6) and 1.5mm (SD 2.2) for the medial and lateral compartment, respectively. The discrepancy was smaller in the large implant group compared to the small implant group (p < .05 medial and lateral) and medium implant group (p < .05 medial). Varus knees required a larger differential resection compared to neutral and valgus knees (only laterally) (medial compartment: p < .05 (varus-neutral), p = .051 (varus-valgus); lateral compartment: p < .05 (varus-neutral and varus-valgus). Removing an equal amount of bone from the distal and posterior femur will lead to flexion/extension gap imbalance in TKA. It was required to remove 1.5-2mm more bone from the posterior femur compared to the distal femur to equalize flexion and extension gap. This effect was size dependent: in larger knees, the discrepancy between the distal and posterior resections was smaller. IV.

Surgical procedures for the prevention of extension-flexion gap imbalance in total knee arthroplasty

The purpose of this study was to identify preoperative and intraoperative factors that influence extension-flexion gap imbalance in total knee arthroplasty (TKA). Ninety-three knees undergoing TKA with the modified gap balancing technique were included. Preoperative range of motion, intraoperative extension-flexion gap balance, thickness of the resected bone and radiological parameters were investigated. The preoperative flexion contracture, bone resection thickness in the medial proximal tibia, and the medial distal femur all correlated with the extension-flexion gap balance in TKA. Bone resection thickness in the medial proximal tibia and the medial distal femur were predictive of extension-flexion imbalance.

Medio-Lateral and Flexion-Extension Gap Imbalances in Mechanically Aligned Total Knee Arthroplasty Using Measured Resection Technique in Korean Patients: 3D Simulation.

Background: It is well known that the measured resection (MR) technique in mechanically aligned (MA) total knee arthroplasty (TKA) generates significant gap imbalances, but little is known about whether this applies to the knees of Asian patients. The aim of this study was to evaluate the medio-lateral and flexion-extension gap imbalances and to find the most optimal posterior femoral condyle resection method for operating on the knees of Asian patients. Methods: In total, 738 magnetic resonance imaging (MRI) scans of consecutive patients who underwent TKA were obtained. Four posterior femoral condylar resection methods were used: alignment by the surgical transepicondylar axis (TEA), Whiteside’s line (WSL), 3° external rotation to the posterior condylar axis (PCA), and flexion-extension axis (FEA). Results: For the medial compartments, there were significant differences between the flexion and extension gaps in the varus knee group in all four methods, but there were no differences between the flexion and extension gaps in the valgus knee group. For the lateral compartment, all the methods showed significant differences except for WSL of the valgus knee group and FEA of the varus knee group. Conclusions: In Asian patients, the use of the MA MR technique inevitably leads to medio-lateral or flexion-extension imbalances. Therefore, surgeons should consider which methods can minimize imbalances and choose the best method within the technically possible range.

Sensor-Assisted Total Knee Arthroplasty: A Narrative Review.

Wireless intraoperative load sensors have been used to improve the quality of soft-tissue balancing during total knee arthroplasty(TKA). Recent studies using the sensors have demonstrated reductions in gap imbalance, as well as early improvement of patient-reported clinical outcomes and low rates of arthrofibrosis. However, well-designed prospective studies are needed to determine whether the application of the sensor technology for TKA will have clinical benefits and improve the survival of prosthesis. Knowledge of the load-sensing technology (advantages and disadvantages, potential pitfalls, and future prediction) is crucial to apply this new TKA technique successfully. Herein, we conduct a narrative review of previous studies on this technique.

Quantitative and Qualitative Assessment of the Structural Convergence of the Economy in the Transition to Sustainable Development

At the present stage of the transition to sustainable development, when the share of a green economy in technologically advanced countries reaches one third of GDP, overcoming the structural crisis of the Russia is inseparable from reducing the technological gap and structural imbalances in the economy. These imbalances alienate Russia from ecologically and technologically advanced countries. Therefore, it is highly relevant to develop a methodology for assessing the structural convergence of the economy in the context of the transition to sustainable development, accompanied in developed countries by a new type of structural shift caused by the expansion of convergent technologies, the emergence of new principles of sectoral genesis and the formation of a green economy. The deepening of the divergent nature of Russian economy development was the result of a series of negative structural shifts that consolidated the dominance of extractive and resource-intensive industries, which threaten the final loss of technological identity, consolidation of the recessive trend and a lag in the transition to sustainable development. Therefore, today it is extremely important to formulate a methodology for assessing the structural convergence of Russian economy with technological and ecologically advanced countries, taking into account both quantitative and qualitative aspects.

Posterior tibial slope is a modifiable predictor of relatively large extension gaps in total knee arthroplasty for degenerative osteoarthritis.

During total knee arthroplasty (TKA) for osteoarthritis, the sagittal gap imbalance (SGI) with a relatively large extension gap is an important surgical challenge. We determined the predictors of SGI with a relatively large extension gap and evaluated the surgical outcomes of knees with SGI. 551 consecutive cases of primary TKA for osteoarthritis were retrospectively reviewed. The cohort was divided into two groups according to the SGI and statistically matched according to baseline characteristics via the inverse probability of treatment weighting method. Multiple linear and logistic regression analyses were performed to determine the predictors of sagittal gap difference (SGD) and SGI. Intergroup differences in clinical and radiological outcomes were analyzed. Of all the knees included, 8.5% (n = 45) presented with SGI with a relatively large extension gap and required femoral sagittal balancing to manage SGI. The hyperextension angle (HA), preoperative joint line convergence angle (JLCA), and the change in posterior tibial slope (PTS) significantly correlated to SGD and predicted SGI with a relatively large extension gap. SGI group showed significant changes in femoral posterior condylar offset and joint line height compared to those without SGI (1.48 vs -0.45, 1.37 vs -0.51, respectively). Postoperative ROM and knee society knee scores were lower in SGI group. Knees requiring sagittal balancing to manage SGI with a relatively large extension gap is not uncommon in TKA for osteoarthritic knees. The change in PTS is an independent and modifiable predictor of SGI.

Options and limitations of implant constraint

With an ever-increasing number of revisions, the surgeons will be faced with the dilemma of choosing the right implant for the revision knee. The soft tissue viability governs the choice of an implant at the time of revision. The selection ranges from the cruciate-retaining to the rotating/fixed hinge implants. The surgeon needs to plan preoperatively, but usually, the final decisions are made intraoperative. As determining the amount of constraint necessary can be challenging, we have tried to lay down a few pointers, which would help to make that choice. The posterior stabilized implants can manage most revision knees; in certain situations where they cannot accommodate the flexion-extension gap imbalance, a varus-valgus constrained implant should be used. The rotating hinge implants are used for severe instabilities or loss of soft tissue or bone around the knee. The use of a higher constraint implant has its consequences like reduced life span and reduced function. Thus it is crucial to use the least amount of constraint as necessary – however, as much as required.

Residual varus alignment can reduce joint awareness, restore joint parallelism, and preserve the soft tissue envelope during total knee arthroplasty for varus osteoarthritis.

The objectives were to compare the coronal joint configuration of the knee joints, coronal gap imbalances requiring substantial medial release, and patient-reported outcomes, including the forgotten joint score, between knees in which residual varus alignment was intentionally allowed according to an individualised lower limb analysis and those with mechanical alignment in total knee arthroplasty for varus osteoarthritis. Consecutive primary navigated total knee arthroplasty procedures for varus osteoarthritis were retrospectively reviewed. The study cohort was stratified based on whether residual varus alignment was intentionally allowed. Propensity-score matching was performed based on the baseline characteristics, including demographic characteristics, preoperative radiological measurements, and the Western Ontario and McMaster University Osteoarthritis Index (mechanical alignment group vs residual varus group). The patient-reported outcomes and coronal joint line orientation of the knee (relative to the ground) and ankle were evaluated. Coronal gap differences and coronal gap imbalances were analysed using intraoperative gap measurements. Relative to the ground and ankle, the postoperative knee joint line orientation slanted down laterally in the mechanical alignment group (-3.05˚ ± 1.62, relative to the ground; -2.65˚ ± 1.56, relative to the ankle joint), but was parallel in the residual varus group (-0.75˚ ± 1.59, relative to the ground; -0.95˚ ± 1.71, relative to the ankle joint). Coronal gap differences at extension and the proportion of coronal gap imbalances requiring substantial medial release were 1.27 ± 1.53 and 6% in the residual varus group and 2.32 ± 1.24 and 15% in the mechanical alignment group. Postoperatively, the residual varus group showed higher Western Ontario and McMaster University Osteoarthritis Index scores and total forgotten joint scores than the mechanical alignment group (6.97 ± 4.75 vs. 10.31 ± 5.74 and 56.42 ± 12.85 vs. 45.69 ± 14.49, respectively). Intentionally allowed residual varus alignment with individualised analysis of lower limb alignment restored the parallel joint line of the knees, preserved the soft tissue envelope, and reduced joint awareness after total knee arthroplasty for varus osteoarthritis. Therapeutic, Level III retrospective case-control study.

Selective medial release using multiple needle puncturing with a spacer block in situ for correcting severe varus deformity during total knee arthroplasty.

We aimed to establish a selective and sequential medial release technique using multiple needle puncturing (MNP) with a spacer block in situ in severe varus deformity during total knee arthroplasty (TKA) and to investigate its efficacy and safety. A total of 128 patients with a varus angle >15° were included. Patients were classified according to the tightness of extension and flexion (group 1, no tightness; group 2, extension; group 3, flexion; group 4, extension and flexion). When medial tightness was found on extension, the posterior clearing procedure, including release of the posterior capsule, posterior oblique ligament, and semimembranosus, was performed sequentially. When medial tightness was found on flexion, MNP using an 18-gauge needle with a spacer block in situ was performed at the anterior portion of the superficial MCL (aMCL). Clinical and radiological evaluations including stress radiographs were performed. Among 128 knees, 110 required medial release (posterior clearing procedure only in 44 [34.3%], MNP with a spacer block in situ at aMCL only in 38 [29.7%], posterior clearing procedure and MNP in 28 [21.9%]). The mediolateral gap imbalances on extension and/or flexion were significantly improved (p < 0.001 in all). There were no significant differences in clinical radiological outcomes among groups. Over-release, iatrogenic transection, and postoperative laxity on the stress radiographs were not observed. The selective and sequential technique using posterior clearing and/or MNP with a spacer block in situ can be a reliable option for managing medial tightness in severe varus deformity during primary TKA.

Evaluating the Sustainability of Public Debt in the Presence of Current and Fiscal Accounts Deficit in Developing Countries

We estimate the public debt sustainability for 53 developing countries divided into different regions using data from 1996 to 2017. Sustainability of public debt calculation is based on theoretically derived models with necessary and sufficient conditions. Current study empirically validates the importance of least evident saving-investment gap along with other variables in public debt sustainability issue. Findings show that current account, fiscal account and saving-investment gap imbalances cause unsustainable public debt for all different regions which is a matter of great concern for each region. Policy makers of the developing countries must bring policies to promote investment activities backed by saving not by debt.

Less gap imbalance with restricted kinematic alignment than with mechanically aligned total knee arthroplasty: simulations on 3-D bone models created from CT-scans

Background and purpose — Mechanical alignment techniques for total knee arthroplasty (TKA) introduce significant anatomic alteration and secondary ligament imbalances. We propose a restricted kinematic alignment (rKA) protocol to minimize these issues and improve TKA clinical outcomes.Patients and methods — rKA tibial and femoral bone resections were simulated on 1,000 knee CT scans from a database of patients undergoing TKA. rKA was defined by the following criteria: independent tibial and femoral cuts within 5° of the bone neutral mechanical axis, with a resulting HKA within 3° of neutral. Imbalances in the extension space, flexion space at 90°, medial compartment and lateral compartment were calculated and compared with measured resection mechanical alignment (MA) results. 2 MA techniques were simulated for rotation using the surgical transepicondylar axis (TEA) and 3° to the posterior condyles (PC).Results — Extension space imbalances ≥ 3 mm occurred in 33% of TKAs with MA technique versus 8.3% with rKA (p < 0.001). Similarly, more frequent flexion space imbalance ≥ 3mm was created by MA technique (TEA 34% or 3° PC 15%) versus rKA (6.4%, p < 0.001). Using MA with TEA or PC, there were only 49% and 63% of the knees respectively with < 3 mm of imbalance throughout the extension and flexion spaces and medial and lateral compartments versus 92% using rKA (p < 0.001).Interpretation — significantly fewer imbalances are created using rKA versus MA for TKA. rKA may be the best compromise, by helping the surgeon to preserve native knee ligament balance during TKA and avoid residual instability, whilst keeping the lower limb alignment within a safe range.

Epidemiology of Bearing Dislocations After Mobile-Bearing Unicompartmental Knee Arthroplasty: Multicenter Analysis of 67 Bearing Dislocations

BackgroundThis study investigated the epidemiology and causes of bearing dislocations following mobile-bearing unicompartmental knee arthroplasty (MUKA) and determined whether the incidence of primary bearing dislocations decreases as surgeon experience increases. MethodsWe retrospectively reviewed the bearing dislocations following MUKAs performed by 14 surgeons with variable experience levels. Causes of bearing dislocations were determined based on the surgical records, radiographs, and operator’s suggestion. Using a chi-squared test, the incidence of bearing dislocation was compared between the first 50, the second 50, and the next 100 unicompartmental knee arthroplasties (UKAs) of each surgeon's cohort. ResultsThere were 67 (3.6%) bearing dislocations from 1853 MUKAs. The mean time to bearing dislocations after index MUKAs was 33 months (range, 1-144 months); 55% of the bearing dislocations occurred within 2 years after the index MUKAs. Primary bearing dislocations (n = 58) were the most common, followed by secondary (n = 6) and traumatic dislocations (n = 3). There was no significant difference in the incidence of bearing dislocation between the first 50 and second 50 UKAs for each surgeon. Two surgeons showed a significant decrease in bearing dislocations in their second 100 UKAs, while the other surgeons did not show a difference between their first 100 and second 100 UKAs. ConclusionMost bearing dislocations after MUKAs were related to technical errors such as component malposition or gap imbalance. This study did not confirm that the incidence of bearing dislocations decreases as the number of cases increases. Level of EvidenceIV, Case series.

Total knee arthroplasty using hinge joints: Indications and results.

Possible indications for a rotating hinge or pure hinge implant in primary total knee arthroplasty (TKA) include collateral ligament insufficiency, severe varus or valgus deformity (> 20°) with relevant soft-tissue release, relevant bone loss, including insertions of collateral ligaments, gross flexion-extension gap imbalance, ankylosis and hyperlaxity.The use of hinged implants in primary TKA should be limited to the aforementioned selected indications, especially for elderly patients.Potential indications for a rotating hinge or pure hinge implant in revision TKA include infection, aseptic loosening, instability and bone loss.Rotating hinge knee implants have a 10-year survivorship in the range of 51% to 92.5%.Complication rates of rotating hinge knee implants are in the range of 9.2% to 63%, with infection and aseptic loosening as the most common complications.Although the results reported in the literature are inconsistent, clinical results generally depend on the implant design, appropriate technical use and adequate indications.Considering that the revision of implants with long cemented stems can be challenging, in the future it would be better to use shorter stems in modular versions of hinged knee implants.Cite this article: EFORT Open Rev 2019;4:121-132. DOI: 10.1302/2058-5241.4.180056