Lateral Flexion Gaps Research Articles

Effect of Posterior Cruciate Ligament Resection on Gap Balancing in Robot-assisted Total Knee Arthroplasty.

Retention or sacrifice of the posterior cruciate ligament (PCL) is one of the most controversial issues while performing total knee arthroplasty (TKA). This study aimed to evaluate the impact of PCL resection on flexion-extension gaps, femoral component rotation, and bone resection amounts during robot-assisted TKA. This prospective study included 40 patients with knee osteoarthritis who underwent robot-assisted posterior-stabilized (PS) TKA between September 2021 and February 2022. Of the patients, 75% were women (30/40) with a mean age and BMI of 72.6 years and 27.4 kg/m2, respectively. The guidance module and camera stand assembly were used to capture gaps before and after PCL resection. Measurements of femoral component rotation and bone resection amounts were made in cruciate-retaining (CR) TKA mode and PS-TKA mode. After PCL resection, the mean change in the medial and lateral compartments of flexion gaps increased by 2.0 and 0.6 mm, respectively (p < 0.001). Compared with the CR-TKA mode group, the bone resection amounts of the medial posterior condyle and the lateral posterior condyle in the PS-TKA mode group decreased by 2.0 ± 1.1 and 1.1 ± 1.1 mm, respectively, and the external rotation of the femoral prosthesis relative to the posterior condylar axis and trans-epicondylar line was reduced by 1.0° ± 1.3° and 1.2° ± 1.6°, respectively (p < 0.001). The release of the PCL did not affect the extension gap, but significantly increased the flexion gap. Moreover, the increases in the medial flexion gap were greater than those of the lateral flexion gap. After PCL resection, less external rotation of the femoral prosthesis and fewer bone cuts of the posterior femur were needed in PS-TKA.

Maintaining the Physiological Lateral Flexion Gap in the Kinematically Aligned TKA Does Not Compromise Clinical Outcomes at One-Year Follow-Up.

Background: Instability is a common cause of (total knee arthroplasty) TKA failure, which can be prevented by achieving proper gap balance during surgery. There is no consensus on the ideal gap balance in TKA, and different alignment philosophies result in varying soft-tissue tightness. Traditional TKA aims for symmetric compartment balance, while kinematic alignment (KA) restores anatomy and accepts asymmetric flexion gaps. This study evaluated the impact of these philosophies on the flexion gap balance and clinical outcomes. Methods: A retrospective review of 167 patients who received true or restricted KA robotic-assisted TKA with at least one year of follow-up was conducted. The groups were based on intraoperative flexion gap differences: symmetric (0-1 mm) (n = 94) and asymmetric (2-5 mm) (n = 73). Results: Preoperative demographics and postoperative clinical and functional scores were compared. Both groups were similar in demographics and preoperative scores. True KA alignment was more likely to result in an asymmetric flexion gap, while restricted KA produced symmetric gaps. Conclusions: The study found no adverse effects from the physiological asymmetric flexion gap, with clinical and functional outcomes comparable to symmetric gaps. A 5 mm difference between the medial and lateral gap width did not negatively impact the outcomes. True KA more frequently results in a physiological asymmetric flexion gap.

Functionally aligned total knee arthroplasty: A lateral flexion laxity up to 6 mm is safe!

Loose flexion gaps are associated with poor functional outcomes and instability in total knee arthroplasty (TKA). The effect of a trapezoidal flexion gap in a functionally aligned TKA remains unknown. The aim of this study was to investigate the effect of a larger lateral flexion gap in a robotic-assisted (RA), functionally aligned (FA) andcruciate-retaining (CR) TKA on clinical outcomes. Data from 527 TKA in 478 patients from 2018 to 2020 werecollected. All patients underwent an RA (MAKO, Stryker), FA andCR TKA. Gap measurements were collected intraoperatively. Patient-reported outcome measures (PROMs), pain Visual analogue score (VAS)and range of motion were collected postoperatively. Patients were also asked about the ease of stair ascent and descent and kneeling on a 5-point scale. The minimum follow-up was 2 years. Patients were stratified into three groups based on lateral flexion laxity. At 2 years postoperatively, the group with a looser gap (3-6 mm) had higher mean PROMs when compared with the group with a gap of 2-3 mm. There were no differences detected in any other outcomes at 2 years. A total of 70.9% of patients in the group with a 3-6 mm gap reported being able to walk down a flight of stairs 'easily', compared with 56.7% in the 2-3 mm group and 54% in the <2 mm group (p = 0.04). The study shows that a loose lateral flexion gap in functionally aligned CR TKA does not adversely affect outcomes in the short term. Level III, retrospective cohort study.

Tibia-first, gap-balanced patient-specific alignment technique achieves well-balanced gaps in 90% of cases by rebuilding bony anatomy within boundaries.

Patient-specific alignment (PSA) techniquetries to achieve balanced gaps and simultaneously rebuild the individual bony phenotype. The hypothesis was: PSA technique achieves balanced knees in a high percentage with more anatomical resections than adjusted mechanical alignment (AMA). Three hundred sixty-seven patients underwent navigated total knee arthroplasty (TKA) with a tibia-first gap-balanced PSA technique. Resection boundaries for medial proximal tibia angle (MPTA) of 86-92°, mechanical lateral distal femoral angle (mLDFA) of 86-92°, and hip-knee-ankle angle (HKA) of 175-185° were defined. Preoperative and intraoperative parameters of HKA, MPTA, mLDFA, and gap widths were recorded. Depending on the coronal deformity, the patients were divided into three groups: varus HKA < 178°; straight 178-182° and valgus HKA > 182°. The stability was analysed by assessing the difference between medial and lateral extension and flexion gaps as well as between flexion and extension gaps. All PSA measurements were compared with data from a previously published AMA series. PSA achieved balanced gaps in extension, flexion and between flexion/extension in over 90% of cases, being similar to AMA. In PSA, MPTA and mLDFA were restored within 1°, except in extreme varus (MPTA difference 2°) and valgus knees (mLDFA difference 3°). This was caused by the defined boundaries of the alignment technique. This individualised reconstruction led to significantly more anatomical resections of all tibia and femur resections. A tibia-first, gap-balanced PSA technique achieves balanced joints in more than 90% of cases. By maintaining preoperative MPTA and mLDFA to a high extent, far more anatomical resections, compared to AMA were performed. Future studies need to be conducted to investigate whether those promising intraoperative results correlate with postoperative patient outcomes and whether patients outside the 5° corridor have higher failure rates. Level III, retrospective cohort study.

Laxity, Balance, and Alignment of a Simulated Kinematic Alignment Total Knee Arthroplasty.

Kinematic alignment (KA) and related personalized alignment strategies in total knee arthroplasty (TKA) target restoration of native joint line obliquity and alignment. In practice, deviations from exact restoration of the prearthritic joint surface are tolerated for either the femur or tibia to achieve ligamentous balance. It remains unknown what laxity, balance, and alignment would result if a pure resurfacing of both femur and tibia were performed in a KA TKA technique. We used data from 382 robot-assisted TKA performed with a digital joint tensioner to simulate TKA with a pure resurfacing KA technique for both femur and tibia. All knees had the posterior cruciate ligament retained. Knees were subdivided into 4 groups based on preoperative coronal alignment: valgus, neutral, varus, and high varus. Medial and lateral laxity in extension and flexion, balance in extension and flexion, and coronal plane alignment were compared between groups using analysis of variance testing. In simulated pure resurfacing KA TKA across a range of preoperative coronal plane deformities, only 11%-31% of knees would have mediolateral extension ligament balance within ±1 mm, and 20%-41% would have a medial flexion gap that is looser than the lateral flexion gap. Over 45% of knees would have coronal hip-knee-ankle angle >3 degrees from mechanical neutral. In simulations of pure resurfacing KA TKA, there was wide variability in the resulting laxity and alignment outcomes. Most knees had alignment and balance outcomes outside of normally accepted ranges. Techniques that deviate from pure resurfacing in order to achieve balance appear favorable.

Large Osteophytes over 10 mm at Posterior Medial Femoral Condyle Can Lead to Asymmetric Extension Gap Following Bony Resection in Robotic Arm-Assisted Total Knee Arthroplasty with Pre-Resection Gap Balancing.

Robotic arm-assisted total knee arthroplasty (TKA) involves a pre-resection gap balancing technique to obtain the desired gap. However, the expected gap may change owing to the soft-tissue release effect of unreachable osteophytes. This study evaluated the effect of unreachable osteophytes of the posterior medial femoral condyle on gap changes following bony resection. We retrospectively analysed 129 robotic arm-assisted TKAs performed for varus knee osteoarthritis. Knees were classified according to the size of osteophytes on the posterior medial femoral condyle using preoperative computed tomography measurement. After the removal of reachable osteophytes, the robotic system measured pre- and post-resection medial extension (ME), lateral extension (LE), medial flexion (MF), and lateral flexion (LF) gaps. No extension gap changes were observed for 25 (19.4%), and no flexion gap changes were observed 41 (31.8%) knees, following bone cuts. ME, LE, MF, and LF gaps increased with the osteophyte size (p < 0.05). For osteophytes <10 mm, all the gaps increased symmetrically. However, for osteophytes >10 mm, the ME gap increased asymmetrically more than LE, MF, and LF gaps (p < 0.05). The gap changes due to bony resection were correlated to the osteophyte sizes of the posterior medial femoral condyle. Surgeons should plan a slightly tight medial extension gap to attain the desired gaps for >10 mm osteophytes.

Lateral joint tightness in flexion following cementless mobile-bearing total knee arthroplasty decreases patient-reported outcome measures and postoperative range of motion

PurposeThe purpose of this study was to clarify the association between clinical outcomes and the flexion joint gap following rotating concave–convex (Vanguard ROCC) total knee arthroplasty (TKA). MethodsThis consecutive retrospective series included 55 knees that underwent ROCC TKA. All the surgical procedures were performed using a spacer-based gap-balancing technique. To evaluate the medial and lateral flexion gaps, axial radiographs of the distal femur were obtained using the epicondylar view with a distraction force to the lower leg at 6 months postoperatively. Lateral joint tightness was defined as the lateral gap being greater than the medial gap. To evaluate clinical outcomes, patients were asked to complete patient-reported outcome measures (PROMs) questionnaires preoperatively and during at least 1 year of follow-up postoperatively. ResultsThe median follow-up duration was 24.0 months. Overall, 16.0% of patients had postoperative lateral joint tightness in flexion. The postoperative range of motion and PROMs were lower in patients with lateral joint tightness than in those with a balanced flexion gap or lateral joint laxity. No serious complications, including bearing dislocations, occurred during the observation period. ConclusionLateral joint tightness in flexion following ROCC TKA decreases PROMs and postoperative range of motion. Level of evidence4.

Gap Pattern in Valgus Knee: An Assessment with TKA Navigation

Background: Valgus knee is a challenge of ligament balance in total knee arthroplasty (TKA). A lateral release is often recommended to achieve symmetric extension gaps in valgus deformity, due to the traditional requirements of tight lateral gap. However, the gap pattern valgus osteoarthritis knee has not been studied. Materials and Methods: The present study was a retrospective study on navigated TKA with 89 valgus osteoarthritis knees. The gap measurement, bone cut, and component rotation values were collected from navigation and the data were analyzed. Results: Only 6.70% of valgus knees in the present series had a narrower lateral flexion gap than medial flexion gap and 7.90% had narrower lateral extension gap than medial extension gap. Conversely, most of valgus cases were seen in bigger lateral flexion gaps than medial flexion gaps at 76.4%. This was consistent with the extension gap patterns of 80.9%. The degree of valgus deformity positively correlated with all gaps, except for flexion lateral gap. The present study demonstrated a mean external rotation of 2.25±2.09° in the femoral component rotation and the degree of valgus deformity had no significant correlation with femoral rotation. Conclusion: The lateral distal femoral condyle hypoplasia might have more important role in the extension gap than the ligament tension. The lateral ligament might influence the lateral flexion gap more than the lateral femoral condyle deficiency. Lateral structural release for correction of valgus deformity during extension could lead to instability in flexion especially for gap patterns with a lateral flexion gap that is wider than the medial flexion gap. Keywords: Valgus knee; Navigated TKA; Gap pattern

Avoiding Lateral Laxity in Robotic Arm-Assisted Total Knee Arthroplasty-A Surgical Technique Describing a New Method of Gap Capture and Balancing Strategy.

Optimal flexion-extension gap balancing is an important factor in outcomes after total knee arthroplasty. Knees with varus deformities are commonly associated with a greater degree of lateral laxity both in extension and flexion. Residual lateral laxity could be encountered by surgeons during component trialling after robotic-assisted total knee arthroplasty (RATKA), necessitating additional medial soft tissue release for a thicker insert. This study describes a new technique of gap assessment during RATKA and we propose a functional alignment based balancing strategy to avoid residual lateral laxity. This surgical technique was prospectively employed in 105 patients undergoing primary MAKO® (Stryker, Kalamazoo, Michigan) RATKA for osteoarthritis of the knee with varus deformity, between January 2021 and July 2021. Patients included had an initial lateral extension laxity of more than 24mm. Surgical data points collected consisted of characterization of the laxity profile of the knee using the medial and lateral extension and flexion initial gap captures, final gap captures after dynamic balancing with a functional alignment strategy, and residual lateral extension gap laxity in millimeters at the end of implantation. The mean initial lateral extension gap was 25.76mm (standard deviation [SD]=1.47) and the mean lateral flexion gap was 24.4mm (SD=1.94). Balance was achieved in all the patients with a 9 or 11mm insert, with a mean residual lateral laxity of 0.51mm (SD=0.73, range 0-2mm). The majority of patients (n=66, 62.85%) had zero lateral laxity at the end of final implantation while 24 patients (22.8%) had 1mm of residual lateral laxity. Residual lateral joint laxity can be avoided consistently and predictably in RATKA cases with initial gap capture of up to 30mm in lateral extension and flexion with this new technique of gap capture and employing various steps of balancing strategy described.

Achieving functional alignment in total knee arthroplasty: early experience using a second-generation imageless semi-autonomous handheld robotic sculpting system.

In order to minimize errors during achieving the targeted alignment of the total knee arthroplasty (TKA) components, robotic-assisted surgery has been introduced with the aim to help surgeons to improve implant survival, clinical outcomes, and patient satisfaction. The primary goal of this paper is to highlight surgical tips and tricks on how to achieve functional alignment (FA) through intra-operative boney mapping, numeric gap, and alignment data, using the next generation of imageless robotic surgical systems. This retrospective case-series contains planned and achieved data on the FA and joint gap data obtained from 526 patients captured and assessed with use of a semi-autonomous imageless handheld robotic sculpting systems. All patients were operatedupon by two experienced TKA surgeons. The mean difference between planned and achieved alignment was 1.46° (≥ 7° varus group), 1.02° (< 7° varus group), 1.16° (< 7° valgus group), and 1.43° (≥ 7° valgus group). The mean observed planned and achieved extension and flexion gaps were below 1.47mm for medial extension gaps, 1.12mm for the lateral extension gaps, 1.4mm for the medial flexion gaps, and 1.16mm for the lateral flexion gaps. Analysis of these first cases highlights the capability of the next generation of imageless robotic-assisted total knee replacement using a semi-autonomous handheld robotic sculpting to maintain accuracy of the desired alignment. The system allows the surgeon to choose freely their own alignment philosophy while maintaining efficiency.

Mid-Term Outcomes of Navigation-Assisted Primary Total Knee Arthroplasty Using Adjusted Mechanical Alignment.

The adjusted mechanical alignment (aMA) technique is an extension of conventional mechanical alignment (MA), which has rarely been reported. The purpose of this study was to evaluate mid-term outcomes of navigation-assisted total knee arthroplasty (TKA) using aMA. This retrospective cohort study enrolled 63 consecutive patients (77 knees) who underwent navigation-assisted TKA using aMA between September 2017 and October 2019. Fifty-two consecutive patients (61 knees) who underwent TKA using MA during the same period were assessed as the controlled group. The demographic data and perioperative data were recorded. The parameters of resection and soft tissue balance including tibia resection angle, frontal femoral angle, axial femoral angle, joint line translation, medial and lateral gap in extension and flexion position were recorded. Radiographic parameters and functional scores including the Hospital for Special Surgery (HSS) score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, and Forgotten Joint Score-12 (FJS-12) were evaluated. Surgery-related complications were recorded. The average follow-up was 3.5 years, with a minimum of 2.4 years. The frontal femoral angle was 2.55° ± 1.08° in aMA group versus 0.26° ± 0.60° in MA group (p < 0.001). The axial femoral angle was 3.07° ± 2.23° external in aMA group versus 2.30° ± 1.70° in MA group (p=0.027). The lateral flexion gap was wider in the aMA group, with a mean of 0.71 mm more laxity (p=0.001). Postoperative coronal alignment was 177.03° ± 1.82° in aMA group versus 178.14° ± 1.69° in MA group (p < 0.001). The coronal femoral component angle was 92.62° ± 2.78° in aMA group versus 90.85° ± 2.01° in MA group (p < 0.001). Both aMA-TKA and MA-TKA achieved satisfactory mid-term clinical outcomes. However, the HSS scores at 1 month postoperatively were significantly higher using aMA than using MA (p < 0.001). Navigation-assisted TKA using aMA technique obtained satisfactory mid-term clinical outcomes. The aMA technique aims to produce a biomimetic wider lateral flexion-extension gap and minimize releases of soft tissues, which might be associated with better early clinical outcomes than MA technique.

Arthritic knees with more than 10° valgus can have soft-tissue imbalance in flexion

Valgus knees have inferior outcomes compared to varus knees. There is little data regarding soft-tissue balance in flexion which may influence outcome in valgus knees undergoing TKA. The purpose of this study was to evaluate whether there is imbalance between medial and lateral flexion gaps in valgus deformity. A secondary aim was to compare soft-tissue balance in knees with valgus deformity less than 10° with those exceeding 10°. The null hypothesis was that there was no soft-tissue imbalance in 90° of flexion irrespective of magnitude of deformity. 64 valgus knees (52 female and 12 male) with deformity from 0.5 to 27.5° (mean 188.77, SD 6.21) were studied in 54 patients (mean age 67.81 y, SD 8.69) undergoing navigated TKA. Medial and lateral gaps in extension and at 90° of flexion were compared (using Independent-samples t test) between knees with valgus < 10° with those > 10° using a validated dynamic method after resection of cruciates, menisci and osteophytes, and then after final trialling. Mean initial medial-lateral (ML) gap difference in extension was 2.63mm (SD 2.63) and 2.09mm (SD 3.78) in flexion, being tighter laterally. Initial ML gap differences in extension and flexion correlated with valgus deformity (R = - 0.514; p = 0.00001; R = - 0.325; p = 0.01, respectively). Initial ML gap differences in extension correlated with those in flexion (R = 0.42; p = 0.0005). Mean ML flexion and extension gap differences were 1.30mm (SD 3.67) and 1.26mm (SD 1.92) in knees with < 10° valgus, and 3.17mm (SD 3.71) and 4.29mm (SD 2.45) in those > 10° valgus; p values were 0.026 and < 0.001 respectively. The lateral flexion gap in valgus knees may be narrower than the medial flexion gap, especially in knees with > 10° deformity. This contrasts with native and varus knees, in which it exceeds the medial gap. This novel study indicates the need to identify valgus knees with lateral flexion gap tightness by distracting the posterior femoral condyles from the proximal tibia by dynamic stressing of the soft-tissues after resection of cruciates, menisci, and osteophytes, with the knee flexed to 90°. These findings, highlighting the need for restoring flexion gap balance, may improve the inferior outcomes in valgus knees. IV.

Tibiofemoral dynamic stressed gap laxities correlate with compartment load measurements in robotic arm-assisted total knee arthroplasty.

AimsIt is unknown whether gap laxities measured in robotic arm-assisted total knee arthroplasty (TKA) correlate to load sensor measurements. The aim of this study was to determine whether symmetry of the maximum medial and lateral gaps in extension and flexion was predictive of knee balance in extension and flexion respectively using different maximum thresholds of intercompartmental load difference (ICLD) to define balance.MethodsA prospective cohort study of 165 patients undergoing functionally-aligned TKA was performed (176 TKAs). With trial components in situ, medial and lateral extension and flexion gaps were measured using robotic navigation while applying valgus and varus forces. The ICLD between medial and lateral compartments was measured in extension and flexion with the load sensor. The null hypothesis was that stressed gap symmetry would not correlate directly with sensor-defined soft tissue balance.ResultsIn TKAs with a stressed medial-lateral gap difference of ≤1 mm, 147 (89%) had an ICLD of ≤15 lb in extension, and 112 (84%) had an ICLD of ≤ 15 lb in flexion; 157 (95%) had an ICLD ≤ 30 lb in extension, and 126 (94%) had an ICLD ≤ 30 lb in flexion; and 165 (100%) had an ICLD ≤ 60 lb in extension, and 133 (99%) had an ICLD ≤ 60 lb in flexion. With a 0 mm difference between the medial and lateral stressed gaps, 103 (91%) of TKA had an ICLD ≤ 15 lb in extension, decreasing to 155 (88%) when the difference between the medial and lateral stressed extension gaps increased to ± 3 mm. In flexion, 47 (77%) had an ICLD ≤ 15 lb with a medial-lateral gap difference of 0 mm, increasing to 147 (84%) at ± 3 mm.ConclusionThis study found a strong relationship between intercompartmental loads and gap symmetry in extension and flexion measured with prostheses in situ. The results suggest that ICLD and medial-lateral gap difference provide similar assessment of soft-tissue balance in robotic arm-assisted TKA.Cite this article: Bone Jt Open 2021;2(11):974–980.

A single type of varus knee does not exist: morphotyping and gap analysis in varus OA.

To achieve a higher level of satisfaction in patients having undergone Total Knee Arthroplasty (TKA), a more personalized approach has been discussed recently. It can be assumed that a more profound knowledge of bony morphology and ligamentous situation would be beneficial. While CT/MRI can give 3D information on bone morphology, the understanding of the ligamentous situation in different flexion angles is still incomplete. In this study, the dynamic gap widths of a large number of varus knees were assessed in various flexion angles, to find out whether all varus knees behave similar or have more individual soft tissue patterns. Additionally, it was investigated whether the amount of varus deformity or other patient factors have an effect on joint gap widths. A series of 1000 consecutive TKA patients, including their CAS data and patient records were analyzed. Joint gap widths in multiple flexion angles (0°, 30°, 60°, 90°) were measured in mm and differences between the joint gaps were compared. A "standard" varus knee was defined as follows: (1) Lateral extension gap greater than medial, (2) lateral flexion gap greater than medial, and (3) flexion gap greater than extension gap. The percentage of fulfillment was tested for each and all criteria. To measure the influence of varus deformity on gap width difference, three subgroups were formed based on the deformity. Data were analyzed at 0°, 30°, 60° and 90° flexion. The effect of patient factors (gender, BMI, age) on gap sizes was tested by performing subgroup analyses. Only 444 of 680 (65%) patients met all three varus knee criteria. The lateral extension gap (4.1mm) was significantly larger than the medial extension gap (0.6mm) in 657 (97%) patients and the gap difference highly correlated with the amount of varus deformity (r2 = 0.62). In all flexion positions, however, no correlation between gap differences and varus deformity existed. Women had significantly larger extension and flexion gaps. Age and BMI showed no significant effect on gap widths. Varus knees show a large inter-individual variability regarding gap widths and gap differences. The amount of varus deformity correlates highly with the medio-lateral gap difference in extension, but not in any flexion angle. As varus knees are not all alike, a uniform surgical technique will not treat all varus knees adequately and the individual gap sizes need to be analyzed and addressed accordingly with an individualized balancing technique. Which final balancing goal should be achieved needs to be analyzed in future studies. Level III.

Component placement accuracy in two generations of handheld robotics-assisted knee arthroplasty.

Total knee arthroplasty (TKA) is the gold standard for treatment of end-stage osteoarthritis. Previous studies have shown that successful outcomes following TKA depend on accurate implant alignment and soft tissue balancing. Robotic-assisted TKA have demonstrated improved accuracy in component placement and have been associated with better outcomes and patient satisfaction. This study aims to report on the execution accuracy of two generations of handheld robotic-assisted surgical systems. This was a retrospective analysis of TKA procedures with two sequential generations of the same handheld robotic-assisted surgical system. Intra-operative data captured included pre-operative limb deformity, limb axes, range of motion, kinematic balance, and the resulting plan for component placement in three-dimensional space. Patients were stratified based on their preoperative coronal lower limb mechanical alignment (> 3° varus, < 3° varus, < 3° valgus, and ≥ 3° valgus). Measurements of component placement (overall lower limb alignment, medial and lateral flexion gaps, and tibial and femoral resection depths) were assessed using descriptive statistics. A total of 435 patients were included and stratified based on preoperative lower limb alignment: 229 with ≥ 3° varus, 78 with varus < 3° and 58 with valgus < 3°, and 70 with valgus > 3°. The mean difference between planned and achieved alignment in the lower limb valgus patients was < 1° across all groups. Mean differences between planned and achieved medial flexion gap was higher in the > 3° subgroup in the varus patient cohort ([< 3°]: 1.15 ± 1.92 vs. [> 3°]: 1.90 ± 2.57); this value was higher in the < 3° subgroup for valgus patients ([< 3°]: 1.34 ± 1.83 vs. [> 3°]: 0.956 ± 1.65). Average resection depth ranged from 9.46 to 10.4mm in the posterior medial femur, 9.25 to 9.95mm in the posterior lateral femur, 7.45 to 8.79mm in the distal medial femur, 8.22 to 9.18mm in the distal lateral femur, 6.70 to 7.07mm in the medial tibial condyle and 6.40 to 7.19mm in the lateral tibial condyle. Non-inferiority testing demonstrated the newer generation is non-inferior to the older generation. Robotic-assisted knee replacement using handheld image-free systems is able to maintain accuracy of component placement. Further investigation of patient reported outcomes as well as long-term implant longevity are needed.

Is Flexion Gap Rectangular in Native Indian Knees? Results of an MRI Study.

The purpose of this study was to evaluate the flexion-gap of the native knees in the normal population and to assess any gender-specific variations in the flexion gap of the knees. A total of 50 normal asymptomatic volunteers with normal knee radiographs were selected for MRI of the knee. The left knee was scanned in an open MRI using a T1-weighted sequence. Imaging was performed in neutral, passive varus and valgus stress at 90° of knee flexion by placing custom-made blocks on a special board consecutively below the distal part of the leg. The study population consisted of 26 males and 24 females with a mean age of 25.77years. Under varus stress, the mean lateral flexion gap increased to 9.28 ± 1.53mm and under valgus stress, the mean medial flexion gap increased to 2.75 ± 1.22mm from neutral. The increase in the flexion gap on the lateral side was 5.28 ± 1.79mm, which was significantly higher compared to that on the medial side. In gender-specific analysis, the mean lateral flexion gap was 10.21mm in females and 8.46mm in males under varus stress. The findings of the study indicate that the lateral soft tissues are more lax compared to the medial soft tissue structures and this laxity is higher in females as compared to males. The study provides evidence of the existing physiological variations of these soft tissue structures resulting in a trapezoidal flexion gap in the native knees rather than the recommended rectangular gap.

Component gap measurement reflects the planned gap balance during total knee arthroplasty more accurately and reliably than bone surface gap measurement.

This study aimed to compare the reliability of two gap assessment methods (component and bone surface gap measurement vs. planned gap balance) and identify the contributors to component gaps other than planned gaps. The prospectively collected data for 122 consecutive primary total knee arthroplasties (TKAs; 114 patients). After femoral planning for gap balancing, the medial and lateral planned gaps were calculated (planned gap). The established medial extension and flexion gaps (MEG and MFG, respectively) and lateral extension and flexion gaps (LEG and LFG, respectively) were measured with and without the TKA components (bone surface and component gaps) at 0° and 90° flexion. The intraclass and Pearson correlation coefficients for each gap measurement method were assessed using planned gap values, and multiple linear regression analyses were performed to identify the contributors to component gaps. Compared with the bone surface gap measurement, the component gap measurement showed higher reliability and stronger correlation with the planned gap balance for each gap. The changes in the medial posterior femoral offset contributed to the MEG and LEG, whereas those in the joint line height contributed to the LEG. The changes in the hip-knee-ankle angle and lateral posterior femoral offset contributed to the LFG. Component gap measurements of the established gap more accurately and reliably reflect the planned gap balance than do bone surface gap measurements. The established gaps are affected by several factors other than femoral planning.

Systematic effects of femoral component rotation and tibial slope on the medial and lateral tibiofemoral flexion gaps in total knee arthroplasty

PurposeTo quantify the effects of the systematic internal and external femoral component rotations and tibial slope on the medial and lateral tibiofemoral gaps in total knee endoprostheses. MethodsNineteen knee cadaver specimens with an intact ligament apparatus were fixed in a custom frame, facilitating physiological flexion motion. Virtual total knee arthroplasty (TKA) was performed on three-dimensional models obtained from computed tomography ​scans (0° and 90° flexions) with systematically altered femur rotations and tibial slopes. ResultsBoth the femur rotation and the tibial slope influenced the medial and lateral tibiofemoral flexion gaps (p ​< ​0.001), and the effects differed between the medial and lateral sides (p ​< ​0.001). The medial tibiofemoral flexion gap increased by 2.90 ​± ​0.34 ​mm and decreased by 2.66 ​± ​0.26 ​mm for 7° external and internal femur component rotations, respectively (both with p ​< ​0.001). The lateral tibiofemoral flexion gap decreased by 3.11 ​± ​0.31 ​mm and increased by 3.29 ​± ​0.33 ​mm for 7° external and internal femur component rotations, respectively (both with p ​< ​0.001). ConclusionFor established surgical methods, we recommend a neutral femur rotation for a 0° tibial slope and a 3° external femur rotation for a tibial slope of 9–10°. The translational potential of this research shows that while the rotation of the femoral component in extension has no effect on the gap size, owing to the axis of rotation being perpendicular to the gap, for a 90° flexion, we not only observe differences in the gap size between the medial and lateral ​but also unequal differences on either side depending on the inward or outward rotation. The main reason for this is the position of the axis of rotation, which is not precisely half way between the lateral and medial contact points. The results show that rotation of the femoral component always creates an unbalanced flexion gap. The translational potential of this articleThe article points out the differences in the tibiofemoral gap in total knee endoprostheses due to the systematic internal and external femoral component rotation. While in lower leg extension there are no differences seen, in 90° knee-flexion there are unequal differences within the medial and lateral compartment that show a mathematical relationship towards the femoral compartment rotation which needs to be intraoperatively considered.

Posterior cruciate ligament resection in total knee arthroplasty: the effect on flexion-extension gaps, mediolateral laxity, and fixed flexion deformity.

The aim of this study was to assess the effect of posterior cruciate ligament (PCL) resection on flexion-extension gaps, mediolateral soft-tissue laxity, fixed flexion deformity (FFD), and limb alignment during posterior-stabilized (PS) total knee arthroplasty (TKA). This prospective study included 110 patients with symptomatic osteoarthritis of the knee undergoing primary robot-assisted PS TKA. All operations were performed by a single surgeon using a standard medial parapatellar approach. Optical motion capture technology with fixed femoral and tibial registration pins was used to assess gaps before and after PCL resection in extension and 90° knee flexion. Measurements were made after excision of the anterior cruciate ligament and prior to bone resection. There were 54 men (49.1%) and 56 women (50.9%) with a mean age of 68 years (sd 6.2) at the time of surgery. The mean preoperative hip-knee-ankle deformity was 4.1° varus (sd 3.4). PCL resection increased the mean flexion gap significantly more than the extension gap in the medial (2.4 mm (sd 1.5) vs 1.3 mm (sd 1.0); p < 0.001) and lateral (3.3 mm (sd 1.6) vs 1.2 mm (sd 0.9); p < 0.01) compartments. The mean gap differences after PCL resection created significant mediolateral laxity in flexion (gap difference: 1.1 mm (sd 2.5); p < 0.001) but not in extension (gap difference: 0.1 mm (sd 2.1); p = 0.51). PCL resection significantly improved the mean FFD (6.3° (sd 4.4) preoperatively vs 3.1° (sd 1.5) postoperatively; p < 0.001). There was a strong positive correlation between the preoperative FFD and change in FFD following PCL resection (Pearson's correlation coefficient = 0.81; p < 0.001). PCL resection did not significantly affect limb alignment (mean change in alignment: 0.2° valgus (sd 1.2); p = 0.60). PCL resection creates flexion-extension mismatch by increasing the flexion gap more than the extension gap. The increase in the lateral flexion gap is greater than the increase in the medial flexion gap, which creates mediolateral laxity in flexion. Improvements in FFD following PCL resection are dependent on the degree of deformity before PCL resection. Cite this article: Bone Joint J 2019;101-B:1230-1237.

The Role of Complete Posterior Cruciate Ligament Release in Flexion Gap Balancing for Total Knee Arthroplasty

BackgroundThe sequence of posterior cruciate ligament (PCL) release in posterior-substituting designs, when performing gap balancing in total knee arthroplasty (TKA), is variable. We hypothesize that early complete PCL release during knee exposure will change the flexion balance to result in a uniform medial-lateral flexion gap symmetry at the time of implant placement. MethodsTen cadaveric knees were prepared for TKA using standard medial parapatellar approach. Medial and lateral flexion gaps were measured in the conditions of intact, partial (50%) resection, and full resection of PCL. Measurements were performed with both surgical navigation and a caliper. Flexion gap distances were reported for medial and lateral compartments in the 3 PCL conditions. ResultsMedial flexion gap increased after only complete release of the PCL (mean 3.94-5.05 mm). The lateral flexion gap increased as well (mean 4.17-4.67 mm). Complete PCL release resulted in a statistically significant increase in medial flexion gap compared to intact (P = .013) and partially released (P = .012) specimens. No significant differences were noted in lateral flexion gap change. Notable change in medial versus lateral gap (flexion gap symmetry) relationship occurred after just partial PCL release (P = .018). ConclusionAmong the 3 PCL states, changes in flexion gap distance were most conspicuous in the medial compartment. This suggests gap balancing performed with incomplete PCL release will not accurately reflect gap distance after eventual PCL removal, thus supporting the hypothesis. It is recommended that the PCL should be released to the fullest extent possible before ligament tensioning for femoral component rotation in posterior-stabilized TKA.