Flexion Gap Balancing Research Articles

Different femoral rotation with navigated flexion-gap balanced or measured resection in total knee arthroplasty does not lead to different clinical outcomes.

Femoral rotation in total knee arthroplasty (TKA) is hypothesized to vary in the same knee depending on the method used to establish it. Thirty-eight patients who underwent TKA surgery using a measured resection technique (RT) were compared with 40 patients who underwent a flexion-gap balancing technique with computer-assisted (for navigation) surgery (FB-CAS) to assess clinical and radiographic alignment differences at two years postoperatively. In 36 of the 40 patients in the FB-CAS group, both methods were used. Intraoperatively, the transepicondylar femoral rotation (TEFR) in reference to the transepicondylar axis was established as the rotation that balanced the flexion gap. Once the TEFR was obtained, an analogous rotation as measured by a posterior reference femoral rotation (PRFR) cutting guide was determined. Femoral component rotation determined by the TEFR and PRFR methods differed in each of the knees. The median TEFR was 0.08°±0.6° (range - 1.5°, 1.5°), and the median PRFR was 0.06°±2.8° (range - 6°, 5°). The mean difference in the rotational alignment between the TEFR and PRFR techniques was 0.01° ± 3.1°. The 95% limits of agreement between the mean differences in measurements were between 6.2° external rotation and - 6.1° internal rotation. At 2 years postoperatively, we found no differences in the radiographic or clinical American Knee Society score between the two groups. Rotation of the femoral component in TKA can vary in the same knee depending on the surgical method used to establish it. This variation in femoral rotation is sufficiently small enough to have no apparent effect on the 2-year clinical outcome score. II.

Flexion gap stabilization by oversizing posterior condylar offset in deep-dished total knee replacement does not compromise flexion: A single-surgeon, retrospective, observational, mid-term series

IntroductionIn total knee replacement surgery, medio-lateral knee balancing is recognized as the key to achieving satisfactory functional results. But it may not be enough to stabilize the flexion gap using deep-dished implants. We achieved flexion gap balance by oversizing the femoral component, thus increasing the posterior condylar offset (PCO). The purpose of this study was to describe the applicability of this technique and to test whether it produced adverse effects on medium-term outcomes. We hypothesized that it would not compromise the results if used properly. We therefore asked: (1) at how many cases of flexion gap balance would require oversizing the femoral component; (2) if femoral components oversizing would modify the mid-term results as per forgotten joint score (FJS) scores and whether flexion gain would be comparable to patients in whom it was not increased. Materials and methodsNinety-four patients (120 knees) were operated between September 2009 and 2011 (age 68±9 years) using the cementless Hyperflex version of the Natural Knees (Zimmer, Warsaw, IN, USA). Postero stabilization was achieved using deep-dished inserts. The Gender configuration has provided narrow inserts to better adapt the female anatomy. A special navigation system measured the displacement of the lateral and medial femoro-tibial contact points with infra-millimetric precision. Adopting a tibial cut first, gap-balancing technique with anterior referencing, the decision to oversize the femoral component relied on the 90° flexion drawer test, which showed more than 6mm sagittal laxity before the femoral bone cuts. Eighty-one (105 knees) patients were reviewed with average 63±27-month follow-up. ResultsFemoral components were augmented by 1 size in 60 cases and by 2 sizes in 7 cases. At final review, knees with an oversized femoral component (60) achieved the same results as those implanted with a non-oversized femoral component (n=45) in terms of mean flexion gain (−5°±34 versus −4°±23, p=0.78), mean FJS (63±26 versus 61±23; p=0.56). ConclusionBalancing the Flexion gap by oversizing the femoral component did not compromise flexion range and functional results. Level of evidenceIV, Retrospective cohort study.

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.

Neither Anterior nor Posterior Referencing Consistently Balances the Flexion Gap in Measured Resection Total Knee Arthroplasty: A Computational Analysis

BackgroundWhether anterior referencing (AR) or posterior referencing (PR) produces a more balanced flexion gap in total knee arthroplasty (TKA) using measured resection remains controversial. Our goal was to compare AR and PR in terms of (1) medial and lateral gaps at full extension and 90° of flexion, and (2) maximum medial and lateral collateral ligament (MCL and LCL) forces in flexion. MethodsComputational models of 6 knees implanted with posterior-stabilized TKA were virtually positioned with both AR and PR techniques. The ligament properties were standardized to achieve a balanced knee at full extension. Medial-lateral gaps were measured in response to varus and valgus loading at full extension and 90° of flexion; MCL and LCL forces were estimated during passive flexion. ResultsAt full extension, the maximum difference in the medial-lateral gap for both AR and PR was <1 mm in all 6 knee models. However, in flexion, only 3 AR and 3 PR models produced a difference in medial-lateral gap <2 mm. During passive flexion, the maximum MCL force ranged from 2 N to 87 N in AR and from 17 N to 127 N in PR models. The LCL was unloaded at >25° of flexion in all models. ConclusionIn measured resection TKA, neither AR nor PR better balance the ligaments and produce symmetrical gaps in flexion. Alternative bone resection techniques and rotation alignment targets are needed to achieve more predictable knee balance.

The flexion space is more reliably balanced when using the transepicondylar axis as compared to the posterior condylar line.

The purpose of this study was to evaluate the differences in flexion space balance when the femoral component is implanted parallel to the surgical transepicondylar axis (TEA) or with 3° of external rotation from the posterior condylar line (PoCoLi). It was hypothesized that implantation parallel to the TEA will produce a more reliably balanced flexion space. Forty-eight consecutive patients with a varus deformity were prospectively randomized to undergo total knee arthroplasty with a femoral component implanted parallel the TEA, or with 3° of external rotation from the PoCoLi. The posterior condylar angle (PCA) was measured. Intraoperative load measurements were taken at 10°, 45°, and 90° of flexion. The PCA was similar between groups (TEA group: 4.2° ± 1.5° and PoCoLi group: 4.0° ± 1.3°; n.s.). The mean difference in load values between the medial and lateral compartments was significantly lower in the TEA group than in the PoCoLi group at the 45 (0 ± 8 vs. 9 ± 13lbs; respectively, p = 0.008) and 90° flexion angles (1 ± 9 vs. 10 ± 15lbs; respectively, p = 0.01). The PoCoLi group had a linear increase in the difference of load values between the medial and lateral compartments with increasing magnitude of the posterior condylar angle (45°, p = 0.0013; 90°, p = 0.0006), but this was not observed in the TEA group. Femoral component implantation parallel to the TEA resulted in a more balanced flexion gap as compared to implantation at 3° of external rotation from the PoCoLi. The intraoperative use of the TEA rather than the PoCoLi to set femoral component rotation may provide a more balanced flexion space and decrease the need for extensive soft tissue releases. II.

Effects of pre-operative measurement of proximal tibia varus angle on the prediction for condylar twist angle in total knee arthroplasty

Objective To assess the effects of pre-operative measurement of proximal tibia varus angle (PTA) on predicting condylar twist angle (CTA) in total knee arthroplasty (TKA). Methods The CT-scan of lower limb was performed in sixty-one health female volunteers aged 31.5 (18-38) years with 160 (153-170) cm heights from March 2016 to August 2016. The PTA, medial proximal tibial angle (MPTA) and CTA were determined. The PTA was defined between a line perpendicular to the mechanical axis of the tibia and the tangent on the internal tibial plateau. The MPTA was the medial angle between the mechanical axis of the tibia and the tangent on the internal tibial plateau. The CTA was the angle between the sTEA and the posterior condylar line. The correlations between these parameters were analyzed statistically by linear regression. Results The PTA, MPTA and CTA parameters were conformed to the normal distribution. The PTA was 2.30°±1.86°, ranged from 1.40° to 6.50°. The MPTA was 87.7°±1.86°, ranged from 83.50° to 88.60°. The CTA was 3.4°±1.27°, ranged from 0.50° to 5.80°. The linear regression analysis showed a strong positive correlation between the CTA and PTA in health female knees (r=0.58, P=0.048), while negative correlation was found between the CTA and MPTA in health female knees (r=-0.58, P=0.048). There were fifty-two (85.2%) volunteers with PTA that was more than 2° and less than 4°. Six (9.8%) volunteers had PTA less than 2°, while three (4.9%) had PTA more than 4°. There were eight (13.1%) volunteers with CTA less than 3°. Forty-three (70.5%) volunteers had CTA more than 3° and less than 4°. CTA more than 4° was found in ten volunteers (16.4%). Based on these above results, two formulas were demonstrated for predicting the CTA: CTA=2.52+0.395PTA, CTA=38.06-0.390MPTA. Conclusion The CTA can be predicted by calculating the PTA by CT-scan and standard long-leg standing radiographs before TKA. Using the present method could reduce the risk of femur component malrotation and the flexion gap balancing during TKA. Key words: Arthroplasty, replacement, knee; Femur; Rotation; Tomography

Revision Total Knee Arthroplasty Using a Constrained Condylar Knee Prosthesis Combined with a Posterior Stabilized Articular Surface.

Intraoperative assessment of valgus-varus stability is crucial for choosing articular surfaces with different levels of constraint. Legacy constrained condylar knee (CCK) prostheses are readily available to assemble and use with a CCK articular surface or a posterior stabilized (PS) articular surface in revision knee arthroplasty surgeries. We wanted to validate outcomes of revision total knee arthroplasty (TKA) using legacy CCK prostheses combined with a PS articular surface. Thirty-seven patients were enrolled and followed up for more than 2 years. Range of motion (ROM), the Knee Society score (KSS), the Knee Society functional score (KSS-F), and the Western Ontario and McMaster Universities Arthritis Index (WOMAC) were used to evaluate outcomes. Follow-up was a mean of 86.5 months (range: 28-152 months). The mean age of the participants was 69.8 years (range: 31-86 years). The mean ROM was 110.5 degrees, the KSS was 86.2 points, the KSS-F was 68.3 points, and the WOMAC score was 22.6 points. Seven participants had implant failures: five because of delayed infections and two because of posterior dislocations. In conclusion, revision TKA using a CCK prosthesis combined with a PS articular surface might provide satisfactory mid-term outcomes. Delayed infection was the most common cause of implant failure. Dislocation might occur in middle-old or older patients despite careful intraoperative examination of valgus-varus stability, extension-flexion gap balancing, and signs of recurvatum.

Anterior referencing versus posterior referencing in total knee arthroplasty: a prospective observational study

&lt;p class="abstract"&gt;&lt;strong&gt;Background:&lt;/strong&gt; Femoral component rotation in total knee arthroplasty (TKA) is essential for patella-femoral tracking, flexion gap balance and normal kinematic function of the knee. The two referencing techniques used for sizing and adjudging the femoral rotation are anterior referencing (AR) and posterior referencing (PR).The current study was designed so as to identify which referencing system determines the femoral rotation more accurately&lt;span lang="EN-IN"&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Methods:&lt;/strong&gt; This study involved 34 consecutive patients (22 females and 12 males) with 60 osteoarthritic knees (bilateral=26; unilateral =8) who satisfied the inclusion criteria. The trans-epicondylar axis, was taken as gold standard to adjudge the correct femoral rotation and was marked as E. The axis of rotation as per anterior instrumentation (A), and as per posterior instrumentation (P) were marked and compared as to which of the axis (A or P) was parallel to E.&lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Results:&lt;/strong&gt; A was always parallel to E, however P was parallel to E in 42 knees. In 18 knees (6 with valgoid deformity, 12 with hypertrophic osteoarthritis involving the medial femoral condyle), P and E tend to converge laterally, suggestive of excessive internal rotation&lt;span lang="EN-IN"&gt;. &lt;/span&gt;&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Conclusions:&lt;/strong&gt; Anterior referencing determines femoral rotation more accurately than posterior referencing for knees with severe valgoid deformity or those with hypertrophic osteoarthritis involving the overgrowth of medial femoral condyle&lt;span lang="EN-IN"&gt;.&lt;/span&gt;&lt;/p&gt;

Correcting Severe Varus Deformity Using Trial Components During Total Knee Arthroplasty

BackgroundExtensive medial soft tissue release may be necessary to correct severe varus deformity during total knee arthroplasty (TKA). However, this procedure may result in instability. Here, we describe a novel soft tissue balancing technique, which can minimize medial release in severe varus deformity during TKA. MethodsFifty knees (40 patients) with hip-knee-ankle angle of more than 20° of varus were corrected using this technique (group 1). After achieving flexion gap balancing by needle puncturing and spreading of the superficial medial collateral ligament, extension gap balancing was obtained by gradual extension with the trial components in place. After group 1 was set, a one-to-one patient-matched control group who had mild varus deformity was selected by propensity score matching (50 knees, 48 patients, group 2). At postoperative 1 year, mediolateral laxity was compared between the 2 groups using the stress radiographs. Clinical outcomes were also compared using the Knee Society Score and Western Ontario and McMaster Universities Osteoarthritis Index score. ResultsThere were no differences in mean medial and lateral laxities between groups 1 and 2 at 1 year after the operation (medial laxity: 2.3° ± 1.4° and 2.7° ± 1.3°, respectively, P = .310) (lateral laxity: 3.6° ± 1.7° and 3.2° ± 2.0°, respectively, P = .459). There were no significant differences in postoperative clinical scores and knee alignment. ConclusionOur technique of obtaining extension gap balancing using trial components led to safe and effective balancing by avoiding unnecessary extensive release in severe varus deformity during TKA.

Reduction Osteotomy vs Pie-Crust Technique as Possible Alternatives for Medial Release in Total Knee Arthroplasty and Compared in a Prospective Randomized Controlled Trial

BackgroundTo compare the gap change between the pie-crust technique and reduction osteotomy to determine their effects on flexion and extension gaps and their success rates in achieving ligament balancing during total knee arthroplasty. MethodsIn a prospective randomized controlled trial, 106 total knee arthroplasties were allocated to each group with 53 cases. If there was a narrow medial gap with an imbalance of ≥3 mm after the initial limited medial release, either reduction osteotomy or pie-crust technique was performed. The changes of extension and flexion medial gaps along with the success rate of mediolateral balancing were compared. ResultsThere was a significant difference in the change of medial gap in knee extension with mean changes of 3.5 ± 0.5 mm and 2.3 ± 0.8 mm in the reduction osteotomy and pie-crust groups, respectively (P < .001). For flexion gap, greater change was found in the pie-crust group compared with the reduction osteotomy group; the mean medial gap changes in knee flexion were 1.1 ± 0.5 mm and 2.3 ± 1.2 mm in the reduction osteotomy and pie-crust groups, respectively. The success rates were 90.6% and 67.9% in reduction osteotomy and pie-crust groups, respectively (P = .007). ConclusionAs an alternative medial release method, reduction osteotomy was more effective in extension gap balancing, and pie-crust technique was more effective in flexion gap balancing. The overall success rate of mediolateral ligament balancing was higher in the reduction osteotomy group than in the pie-crust group.

Rotational alignment of the femoral component in total knee arthroplasty.

We describe here various surgical options to obtain a correct rotational alignment of femoral component in total knee arthroplasty (TKA). The correct rotational alignment is the key point to obtain a rectangular balanced flexion gap as well to have a good patellar tracking. For that reason, rotation alignment largely affects postoperative kinematic results particularly during flexion.

Extension and flexion gap balancing and its correlation with alignment in navigated total knee arthroplasty.

Computer-assisted surgery was developed to improve the results of conventional total knee arthroplasty (TKA). The authors investigated the preoperative varus/valgus deformity influence on the production of balanced extension and flexion gaps using computer-assisted surgery. This study evaluated data from a prospective case series. A total of 132 patients (107 women and 25 men) underwent navigated TKA. Patients were divided into the following 3 groups according to the degree of the initial varus/valgus deformity: group 1, 0° to 3°; group 2, 3° to 9°; and group 3, greater than 9°. The final lower limb mechanical axis (LLMA) and the final flexion and extension gaps were measured. Knees exhibiting up to 3° of deviation on the frontal plane and a difference of up to 3 mm between the lateral and medial gaps were considered to be aligned and balanced, respectively. Average LLMA deviation decreased from 5.58° (± 4.80°) to 1.87° (± 1.66°). For knees with varus deviation, the percentage of balancing relative to the flexion gaps was 97.8% and that relative to the extension gap was 100% (P>.05). For knees with valgus deviation, the percentage of balancing relative to the flexion gaps was 95.1% and that relative to the extension gap was 97.6% (P>.05). Approximately 92% of the LLMA alignment was achieved in the group with varus deformity, whereas 71.4% was observed in the group with valgus deformity (P<.05). Computer-assisted TKA could attain proper flexion and extension balance regardless of coronal plane malalignment magnitude. Severe valgus and varus knees are more difficult to align using navigation. No difference was found in the balance of flexion or extension gaps in valgus or varus knees, independent of the severity.

Measured Resection Versus Gap Balancing for Total Knee Arthroplasty

The number of TKAs performed in the United States is expected to increase substantially in the next two decades [6]. Additionally, surgeons are performing TKAs in younger and more active patients. While many articles discuss the importance of radiographic alignment, soft-tissue balancing is essential to a successful TKA. There remains great controversy in how surgeons obtain correct alignment and soft-tissue tensioning. Some surgeons utilize a measured resection technique, while other surgeons favor a gap-balancing technique. As such, I have invited two internationally known orthopaedic surgeons to discuss these two approaches, both of which seek to achieve the same general goal — a well-aligned and well-balanced TKA. Bryan D. Springer MD is an attending joint replacement surgeon at the OrthoCarolina Hip and Knee Center in Charlotte, NC, USA, and a member of The Knee Society. Dr. Springer is the recipient of numerous Knee Society Awards, and has extensive experience with the gap-balancing technique. Sebastien Parratte MD, PhD is an attending joint replacement surgeon and assistant professor of orthopedic surgery at the University Hospital of Marseille in Marseille, France. Dr. Parratte likewise has received numerous Knee Society and Hip Society Awards, and has considerable experience with the measured resection technique. Matthew P. Abdel MD:What do you each see as the advantages of the gap-balancing or measured resection techniques, in terms of achieving ligament balance? Bryan D. Springer MD: Instability following TKA remains one of the most common modes of early failure. The gap-balancing technique is based on the progressive release of ligaments to create equal and symmetric flexion and extension gaps. It is imperative that one understands what structures affect extension, flexion, and both in order to create proper balance. One of the fundamental differences between the gap-balancing technique and measured resection technique lies in setting the rotation of the femoral component to achieve a symmetric flexion gap. Measured resection relies on arbitrary bony landmarks (surgical transepicondylar axis, posterior condylar axis, and anteroposterior (AP) axis of the femur) in order to set rotation. While bony landmarks may occasionally provide accurate rotation of the femoral component, one major disadvantage is the surgeon’s inability to accurately and reproducibly find them intraoperatively. Research has suggested there is wide variability in femoral component rotation when using bony landmarks, which leads to asymmetry of the flexion space and condylar lift off (Fig. 1) in flexion [3]. Open in a separate window Fig. 1 This schematic depicts condylar lift off that occurs when there is asymmetry of the flexion space. Published courtesy of Bryan D. Springer MD.

Changes in Joint Gap Balances between Intra- and Postoperation in Total Knee Arthroplasty

Achieving correct soft tissue balance and preparing equal and rectangular extension and flexion joint gaps are crucial goals of TKA. Intraoperative gap balances would change postoperatively; however, changes in joint gap balances between pre- and postoperation remain unclear. To explore these changes associated with TKA, we prospectively investigated 21 posterior cruciate ligament retaining TKAs for varus knees. Intraoperative extension gap balance (iEGB) was 2.6 ± 2.0° varus versus postoperative extension gap balance (pEGB) of 0.77 ± 1.8° valgus (P < 0.01), while no significant difference between intraoperative flexion gap balance (iFGB) and postoperative flexion gap balance (pFGB) was observed. We also explored correlations between intraoperative and postoperative gap balances but found no significant correlations. These observations indicate that (i) surgeons should avoid excessive release of the medial soft tissue during TKA for varus knees and (ii) intraoperative gap balance may not be necessarily reflected on postoperative gap balance.

Size measurement and flexion gap balancing in total knee arthroplasty—new benefits of the Attune™ system?

To the Editor, Although primary total knee arthroplasty (TKA) has been a procedure with high surgical success and various systems have revealed an outstanding long-term survival in recent decades [1], our patients still report knee pain or further problems in 20 % of cases [2, 3]. These cases are mostly caused by improper placement of the femoral shield or difficulties in balancing techniques [2, 3]. The Attune Total Knee Arthroplasty System (DePuy Synthes, Warsaw, IN) [4] was designed to address these cases by optimising guidance in femoral size measurement and flexion gap balancing using one single tool. The authors experienced benefits while measuring (1) flexion gap, (2) possible undercutting, and (3) cranio-caudal width of the femoral shield on the basis of the corresponding inlay in flexion in one surgical step. In addition, further narrow variants, minimising the medio-lateral width of the femoral shield, aid in more individual component placement as the system offers these options in four out of ten possible femoral sizes in contrast to one or no narrow variant (press fit condylar TKA or low-contact-stress TKA, DePuy Synthes, Warsaw, IN). After our initial experience as early users, we believe that the Attune TKA System offers an appropriate solution for the flexion gap balancing technique in individual total knee arthroplasty. However, the authors have initiated a prospective controlled outcome trial to conclusively testify this initial impression. With kind regards, Patrick Sadoghi, MD and Norbert Kastner, MD

Soft Tissue Releases Affect the Femoral Component Rotation Necessary to Create a Balanced Flexion Gap During Total Knee Arthroplasty

The structures that were released to balance the extension gap were recorded during 1500 consecutive TKA procedures, and the amount of femoral component external rotation (ER) necessary to balance the flexion gap was measured with a tensiometer. The amount of ER necessary to balance the flexion gap significantly decreased as more medial structures were released (1 structure=4.7°, 2=4.1°, 3=2.8°, 4 or more=1.1°, P<0.012), whereas significantly greater ER was necessary when three or more lateral structures were released (1 structure=5.3°, 2=5.5°, 3 or more=8.6°, P<0.03). Soft tissue releases affected the amount of femoral component ER necessary to balance the flexion gap, bringing into question the ability of techniques utilizing bony landmarks to properly align the femoral component in rotation.

Is adapted measured resection superior to gap-balancing in determining femoral component rotation in total knee replacement?

Obtaining a balanced flexion gap with correct femoral component rotation is one of the prerequisites for a successful outcome after total knee replacement (TKR). Different techniques for achieving this have been described. In this study we prospectively compared gap-balancing versus measured resection in terms of reliability and accuracy for femoral component rotation in 96 primary TKRs performed in 96 patients using the Journey system. In 48 patients (18 men and 30 women) with a mean age of 65 years (45 to 85) a tensor device was used to determine rotation. In the second group of 48 patients (14 men and 34 women) with a mean age of 64 years (41 to 86), an 'adapted' measured resection technique was used, taking into account the native rotational geometry of the femur as measured on a pre-operative CT scan. Both groups systematically reproduced a similar external rotation of the femoral component relative to the surgical transepicondylar axis: 2.4° (SD 2.5) in the gap-balancing group and 1.7° (SD 2.1) in the measured resection group (p = 0.134). Both gap-balancing and adapted measured resection techniques proved equally reliable and accurate in determining femoral component rotation after TKR. There was a tendency towards more external rotation in the gap-balancing group, but this difference was not statistically significant (p = 0.134). The number of outliers for our 'adapted' measured resection technique was much lower than reported in the literature.

Can we always trust in the computer? Adequate tibial alignment and flexion-gap balancing using personalised knee arthroplasty cutting blocks

To the Editor, Patient-individualised cutting blocks have drowned the market of total knee arthroplasty (TKA), promising not only faster but even easier surgical success after adequate planning [1–4]. The authors want to discuss how to adequately achieve and improve tibial alignment and flexion gap balancing using the patient individualised TruMatch total knee arthroplasty system (Johnson & Johnson, New Brunswick, NJ, USA). In case of straightforward surgery according to the TruMatch cutting blocks, the authors achieved excellent radiological and anatomical intraoperative results but faced significant flexion gap instability. Therefore, before performing the tibial cut using the TruMatch system the authors recommend double-checking the axis with the conventional alignment tower. In addition, the authors apply the femoral TruMatch cutting block and test its position with respect to adequate flexion gap balance and rotation using the Ranawat block [5]. After adjustment with the tibial alignment tower and the Ranawat block, not only appropriate cutting to the anterior femoral cortex, as measured using the TruMatch system, but also a well-balanced flexion gap can be achieved. We believe that surgeons should always double check patient-individualised cutting blocks using their conventional guides and hope that this letter will assist other knee surgeons in doing so. When using patient individualised cutting blocks, surgeons should avoid a straightforward application of these tools without critical verification, which might on the other hand counter the claimed time reduction.

Assessing the accuracy of bone resection by cutting blocks in patient-specific total knee replacements.

Introduction. The key to a successful total knee arthroplasty (TKA) is the restoration of the mechanical axis with balanced flexion and extension gaps. Patient-specific cutting block technique has been the latest development in total knee arthroplasty. This technique uses a magnetic resonance image (MRI) of the patient's symptomatic knee to create bone models and cutting jigs. This study was designed to evaluate the intraoperative accuracy of the patient-specific cutting block as compared to the preoperative template. Methods. Visionaire (Smith and Nephew, Genesis 2 Knee Arthroplasty) patient-specific TKA was used in all patients. An independent research officer was responsible for measuring all the resected articular surfaces of femur and tibia during surgery and compared it to the cutting block manufactured according to the preoperative template. Seven different measurements from each patient were obtained; four different measurements from the femur and three from the tibia were recorded. The differences between the actual resections made intraoperatively, as compared to the original pre-operative templates, were noted as the error. The surgical team was blinded to the measurements of the resections and the calculations of the errors. Results. Twenty-six Visionaire patient-specific TKA were included in the study. A total of 182 readings of bone resections made intraoperatively (seven for each patient). Eighty five percent of all collected readings were below the error margin of ≤1.5 mm. Size of resection had no effect on the error margin. All patients had satisfactory post-operative alignment, and at discharge all 26 patients achieved more than 90° of knee flexion. Conclusion. This observational study provides evidence that patient-specific TKA is comparable to other forms of TKA and may have some distinct advantages. In addition, we have shown that the cutting blocks are able to consistently deliver accurate cuts that are reproducible. We recommend intra-operative measurement of the bone resection and its comparison with the cutting block as a routine surgical step to confirm the MRI scan data, block placement, and instant validation of the bony resection before implant placement.

Comparison of Femoral Rotation in Total Knee Arthroplasty with Measured Resection Technique and Balanced Flexion Gap Technique

Purpose: Avoiding femoral malrotation has always been a technical challenge for orthopaedic surgeons in total knee arthroplasty. While modern surgical techniques have made the surgeon’s task easier, nevertheless it remains unclear which of the two most common techniquesthe measured resection or balanced flexion gap techniquesmore accurately restores femoral component rotation. This study aimed to compare the femoral rotation produced by these two surgical techniques and the relationship between the femoral rotation and coronal tibial alignments.This retrospective cohort study compared 20 posterior stabilized Anatomic Modular Knee (AMK), aligned using a measured resection technique to 20 mobile bearing Low Contact Stress knee (LCS) aligned using a balanced flexion gap referencing system. Long leg standing x-rays and CT scans of knees were used to measure rotation of the femoral component in the axial plane and tibial alignment in the coronal plane. Results: Average femoral component rotations were 2.98 (SD 3.21) degrees and 2.26 (SD 1.20) degrees for the AMK and LCS, respectively. Tibial component alignments were 0.66 (SD 1.94) degrees valgus and 0.4 (SD 1.09) degrees valgus for the AMK and LCS, respectively. These differences were not statistically significant. Conclusion: There were no statistically significant differences in femoral rotation between the two referencing systems. However, the balanced flexion gap method had a narrower range of implant rotational position. No statistically significant relationship was found between femoral rotation and tibial alignment in either system.