Gap Balancing Technique Research Articles

Influence of Gap Balance on the Sagittal Movement of a Specific Mobile Bearing Floating Platform Design in Total Knee Arthroplasty

We analyzed 119 knees implanted with mobile bearing floating platform prostheses using the navigation-assisted gap balancing technique to analyze the relationship between intraoperative sagittal movement of floating platforms and soft tissue balancing. The 95 (79.8%) knees were classified into the positive rollback group (mean insert posterior rollback 5.86 ± 1.24 mm), and the remaining 24 (20.2%) into the negative rollback group. Lateral flexion gap (LFG) differed significantly between knees with positive and negative rollback (20.5 ± 1.7 mm vs 22.1 ± 1.7 mm, P = .021). Only LFG significantly influenced the occurrence of bearing sagittal movement. Sagittal translation of the insert occurred in about 80% of knees implanted with mobile bearing floating platforms in TKA, and was affected by flexion gaps, especially on the lateral side.

Mid-Term Outcomes of Floating Platform Mobile-Bearing Total Knee Arthroplasty Under Navigational Guidance With a Minimum 4-Year Follow-Up

We evaluated 106 knees that underwent primary total knee arthroplasty (TKA) with the navigation-assisted gap balancing technique using an e.-motion cruciate retaining floating platform (FP) mobile-bearing prosthesis to prospectively assess the survival of the e.-motion FP system after a minimum follow-up of 4 years. There was no evidence of any complications, including dissociation or breakage of the polyethylene liner or component loosening at last follow up (5.1 ± 0.6 years). Four knees, however, required re-operation, three for distal femoral fracture, and one for infection. The estimated 5-year prosthesis survival rates without revision for any reason and for prosthesis-associated problems were 96.2% and 100%, respectively. The e.-motion floating platform, with a cruciate retaining design under navigation guidance, demonstrated excellent clinical results and 5-year survival rate.

Functional Outcome after Computer-Assisted Total Knee Arthroplasty Using Measured Resection versus Gap Balancing Techniques: A Randomised Controlled Study

To compare the 2-year outcome of total knee arthroplasty (TKA) using the measured resection versus the gap balancing techniques. 21 men and 31 women aged 41 to 89 (mean, 73) years who underwent primary TKA by a single surgeon for osteoarthritis and had an American Society of Anesthesiologists I or II physical status were prospectively studied. Patients were randomised to undergo computer-assisted TKA using the measured resection technique (n=26) or the gap balancing technique (n=26). At the 2-year follow-up, patients were assessed by a single orthopaedic registrar blinded to the type of surgery using the Knee Society score (KSS), functional Knee Society score (FKSS), and revised Oxford Knee score (ROKS). In the measured resection group, the mean KSS, FKSS, and ROKS increased from 34.3, 48, and 21 to 85.9, 89.6, and 36.5, respectively. In the gap balancing group, the respective scores increased from 35.4, 50, and 22.5 to 89.1, 92.4, and 40.6. Postoperative increases in the respective scores were slightly better with the gap balancing technique; the respective p values were 0.46, 0.44, and 0.12. Improvements in the knee scores were comparable with the 2 techniques.

Rotational Alignment of the Femoral Component in Computer-Assisted Total Knee Arthroplasty

This study compared two Computer Assisted Surgery (CAS) methods in 212 total knee arthroplasties to evaluate the differences between anatomic landmark axes in determining rotational position of the femoral component. Overall, there were large variations between CAS defined component orientation using an optimized gap-balancing technique and component orientation using anatomic reference axes (range, 16º internal rotation to 16º external rotation). If based on anatomic landmarks, these large variations would have led to asymmetrical flexion gaps in up to 60% of the knees studied. Of the anatomic axes studied, the posterior condylar axis was the only axis not significantly different from CAS optimized orientation. If anatomic landmarks are used for femoral component rotation with either a conventional or a CAS technique, asymmetric trapezoidal flexion gaps may result.Key Words: total knee arthroplasty, balancing, component rotation, Computer Assisted Surgery

No difference between tibia-first and femur-first techniques in TKA using computer-assisted surgery

The measured resection technique and the gap-balancing technique are two philosophies used in total knee surgery. It is still unknown whether one or the other technique provides superior results when computer-assisted surgery is performed. We hypothesized that the gap-balancing technique improves joint stability because the technique relies primarily on the soft tissue. A prospective controlled study was performed in 116 patients using the tibia-first or femur-first technique. The Columbus(TM) total knee system and the Orthopilot(®) (Aesculap(®) AG, Tuttlingen, Germany) navigation system were used in all cases. Sixty-three patients were allocated to the femur-first technique (group F) and 53 patients to the tibial first technique (group T). The mean follow-up time was 11.4 ± 1.1 months. The KSS, KOOS and SF-36 were taken prior to surgery and at the time of follow-up for clinical assessment. Long-leg weight-bearing radiographs were performed to assess ligament alignment. Radiographs in varus and valgus stress were performed using the Telos(®)-Instrument (Telos(®) GmbH, Greisheim, Germany) under a force of 15 N at the time of follow-up for the assessment of medial-lateral stability. The nonparametric t test (Mann-Whitney U-test) was used in order to compare the ligament stability and the scores between group F and group T. The lateral joint space opening for groups F and T was 3.4° ± 1.4° and 3.9° ± 1.7°, respectively (n.s.), and the medial joint space opening for groups F and T was 4° ± 1.4° and 4.1° ± 1.7°, respectively (n.s.). The femorotibial mechanical axis for groups F and T revealed 1.4° ± 1.2° and 0.7° ± 2.0° of varus, respectively (p = 0.138). The clinical assessment showed significant improvement according to KSS, KOOS and SF-36 in all subscales. Neither of the sores showed significant differences between the two groups. The surgeon should use his/her preferred surgical technique providing the implantation is performed with computer assistance. It remains unclear whether the same findings will occur after conventional surgery. II.

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.

Computer guided restoration of joint line and femoral offset in cruciate substituting total knee arthroplasty

PurposeThis prospective study aimed to evaluate radiographically, change in joint line and femoral condylar offset with the optimized gap balancing technique in computer-assisted, primary, cruciate-substituting total knee arthroplasties (TKAs). MethodsOne hundred and twenty-nine consecutive computer-assisted TKAs were evaluated radiographically using pre- and postoperative full-length standing hip-to-ankle, antero-posterior and lateral radiographs to assess change in knee deformity, joint line height and posterior condylar offset. ResultsIn 49% of knees, there was a net decrease (mean 2.2mm, range 0.2–8.4mm) in joint line height postoperatively whereas 46.5% of knees had a net increase in joint line height (mean 2.5mm, range 0.2–11.2mm). In 93% of the knees, joint line was restored to within ±5mm of preoperative values. In 53% of knees, there was a net increase (mean 2.9mm, range 0.2–12mm) in posterior offset postoperatively whereas 40% of knees had a net decrease in posterior offset (mean 4.2mm, range 0.6–20mm). In 82% of knees, the posterior offset was restored within ±5mm of preoperative values. ConclusionsBased on radiographic evaluation in extension and at 30° flexion, the current study clearly demonstrates that joint line and posterior femoral condylar offset can be restored in the majority of computer-assisted, cruciate-substituting TKAs to within 5mm of their preoperative value. The optimized gap balancing feature of the computer software allows the surgeon to simulate the effect of simultaneously adjusting femoral component size, position and distal femoral resection level on joint line and posterior femoral offset. Level of EvidenceLevel II

Does a Modified Gap-balancing Technique Result in Medial-pivot Knee Kinematics in Cruciate-retaining Total Knee Arthroplasty?: A Pilot Study

Normal knee kinematics is characterized by posterior femorotibial rollback with tibial internal rotation and medial-pivot rotation in flexion. Cruciate-retaining TKAs (CR-TKAs) do not reproduce normal knee kinematics. We hypothesized a more anatomic reconstruction of the medial femoral condyle, simultaneously preserving the tension of the PCL and medial collateral ligament, resulted in (1) medial-pivot rotation and tibial internal rotation, (2) lateral femoral rollback, and (3) reduced liftoff. We compared 10 patients who underwent CR-TKA using the new technique at their 1-year followup to a matched control group of nine patients using a traditional gap-balancing technique at their 2- to 4-year followup. All patients received lateral radiographs in extension and flexion, which we utilized for three-dimensional implant matching to calculate tibial internal rotation, lateral rollback, and lateral liftoff in extension and flexion. The new gap-balancing technique resulted in a median of 3.5° tibial internal rotation with 2.7-mm rollback of the lateral femoral condyle relative to the medial condyle in flexion, which was different from the control group. We found no differences in liftoff between the groups. The new technique resulted in tibial internal rotation with flexion and lateral rollback comparing the lateral to the medial condyle in flexion, but no differences in condylar liftoff. These preliminary results were comparable to published kinematic results of an asymmetric CR-TKA or medial-pivot CR-TKA but not to symmetric CR-TKA.

Computer-assisted gap balancing technique improves outcome in total knee arthroplasty, compared with conventional measured resection technique

The objective of this prospective study was to compare the functional outcome of conventional measured resection technique and computer-assisted gap balancing technique in TKA. 140 patients were randomized into two groups. The conventional measured resection technique without computer navigation was performed in Group 1 and the computer-assisted gap balancing technique in Group 2. Range of motion, clinical laxity assessment with KT-1000 arthrometer, postoperative radiological films and various functional knee scores were documented at 6 months and 2 years. At 2 years, there were significantly more patients (five patients, 7%) in the Group 1 with flexion contractures of more than 5° (P = 0.05). There were significantly more outliers in the Group 1 (eight patients, 11%), who demonstrated anterior tibial translation >5 mm, than Group 2 (two patients, 3%) (P = 0.041). The total excursion at 20° was significantly higher in Group 1 at 6 months (P = 0.012) and after 2 years (P = 0.031). Group 2 was able to demonstrate significantly better limb alignment with fewer outliers (more than 3° varus/valgus) than Group 1. At 6-month follow-up, Group 2 demonstrated better outcomes in Function Score (P = 0.040) and Total Oxford Score (P = 0.031). At 2-year review, Group 2 had better outcome in the Total Oxford Score (0.030). Computer-assisted gap balancing technique was able to achieve more precise soft tissue balance and restoration of limb alignment with better knee scores as compared to the conventional measured resection technique in total knee arthroplasty.

Comparison of joint line position changes after primary bilateral total knee arthroplasty performed using the navigation-assisted measured gap resection or gap balancing techniques

This study aimed to compare the clinical and radiological results of navigation-assisted TKAs performed using the measured gap resection or the gap balancing technique in thirty patients who underwent bilateral primary TKAs. Sixty cases of navigation-assisted TKAs [30 TKAs performed using the measured gap resection technique (Group A) and 30 TKAs performed using the gap balancing technique (Group B)] were analyzed prospectively with minimum follow-up of 2 years. The joint line positions were measured using preoperative and postoperative weight-bearing anteroposterior and lateral radiographs. Clinical results were evaluated using knee scores and functional scores. No significant differences in knee scores or functional scores were observed. Polyethylene thickness and flexion/extension gaps were significantly larger in Group B (P < 0.05). The meaningful proximal shift of the joint line was shown in Group B (P < 0.05). The navigation-assisted TKA with measured gap resection technique could be a useful technique with regard to restoration of the joint line.

Gap balancing versus measured resection technique using a mobile-bearing prosthesis in computer-assisted surgery

Navigation has been developed to help surgeons install implants more accurately and reproducibly; at the same time, this tool is able to record quantitative information such as joint range of motion, laxity and kinematics intra-operatively. As for standard surgery, two strategies are possible to achieve either femoral component rotation or overall prosthetic alignment: a measured gap resection approach, in which bone landmarks are used to guide resections equal to the distal and posterior thickness of the femoral component, or a gap-balancing technique, in which equal collateral ligament tension in flexion and extension is tried to find before as a guide to final bone cuts. The purpose of this paper is to compare the two different methods in a 67 patients group submitted to the same procedure using mobile-bearing (MB) prosthesis in order to analyse the effect of both techniques on joint line maintenance, axial limb restoration and components position. The gap group (GG) consists of 31 patients in whom the arthroplasty was performed using a navigated gap-balancing technique. The measured group (MG) consists of 36 patients in whom a computer-assisted measured resection technique was used. The results of imaging and the number of outliers were not statistically different (P=0.56) for the mechanical axis and prosthetic positioning between the two groups. The gap technique showed a statistically significant alteration of the post-operative value when compared with the measured resection technique, (P=0.036). The mean elevation of the joint line was 4.09mm for the GG and 3.50mm in the MG.

Femoral component rotation after balanced gap total knee replacement is not a predictor for postoperative patella position

Femoral component rotation is believed to be one of the factors influencing patellar tracking behavior. With the balanced gap implantation technique, the rotation of the femoral component can vary as it is guided by the ligaments. This study investigated whether femoral component rotation influenced patella position after primary total knee replacement (TKR). In this prospective cohort study, a primary TKR was implanted in 49 patients using a balanced gap technique and a CT-free navigation system. Femoral component rotation was measured using the navigation data of the distal femur cut, referenced from the posterior condyles. At the 2-year follow-up, lateral patellar tilt and patellar displacement were measured on axial patella radiographs. Logistic regression analysis on femoral component rotation and preoperative patella position was conducted to identify predictors for postoperative patellar tilt and displacement. Femoral component rotation that varied between -3 and 12° exorotation was not a predictor for postoperative tilt and displacement. Only preoperative displacement significantly predicted patella displacement. Although the balanced gap implantation technique resulted in a wide inter-patient variability for femoral component rotation, this variable rotation was not found to be associated with abnormal patellar position. Preoperative displacement results in a higher risk at a postoperatively displaced patella. The balanced gap technique can safely be used without an elevated risk for patella malposition.

The impact of a rectangular or trapezoidal flexion gap on the femoral component rotation in TKA

The influence of soft tissue balancing on femoral component rotation in the gap technique remains unclear. The present study therefore compared the reliability of femoral component rotation determined by rectangular and trapezoidal gaps in total knee arthroplasty (TKA) using a navigation-assisted gap-balancing technique. The study also determined the correlation between femoral component rotation and gap measurement. This prospective study included 99 patients (108 knees) who underwent postoperative CT after TKA with the navigation-assisted gap-balancing technique. A trapezoidal flexion or extension gap was defined as a >3 mm difference between the medial and lateral sides in 90° flexion or extension. An outlier of femoral component rotation was defined as >3° deviation from the transepicondylar axis. Postoperative CT showed that the femoral component had a tendency to rotate externally, with a mean 1.88 ± 2.49° from the surgical transepicondylar axis. Outliers and mean values of femoral component rotation were similar in the trapezoidal and rectangular flexion/extension gap groups. The medial flexion gap (r = -0.49, P = 0.007) and flexion gap differences (r = -0.59, P = 0.027) showed statistically significant negative correlations with the femoral component rotation. Multiple linear regression analysis also showed that the femoral component rotation was independently related to the flexion gap difference (β = -0.27, P = 0.031). In the gap technique, the rotation of the femoral component is affected more by the flexion gap than by the extension gap. However, neither the trapezoidal nor rectangular flexion gap influenced femoral component rotation.

Gap Balancing Through Small Incisions: Competing Goals

Significant controversy exists in the literature regarding the pitfalls and benefits of minimally invasive total knee arthroplasty (TKA). Regardless, most surgeons today use smaller exposures than in previous years. Although more difficult, rigid adherence to classical gap balancing techniques can allow a surgeon to achieve ideal ligament and flexion/extension gap balance in TKA through a minimally invasive approach. There are certain groups of patients (obesity/medical comorbidities/vascular insufficiency) in whom small incision approaches should not be attempted due to increased risks of wound complications. Additionally, achievement of gap balance requires sequential and safe removal of bone starting with the patellar cut, followed by the distal femoral cut, then by the tibial cut, and concluding with completion of the femoral component cuts. Use of special instruments such as protective metal patellar buttons, medial to lateral distal femoral cutting blocks, and low profile spacer blocks can facilitate the surgical process. Accurate femoral component rotation is more difficult in minimally invasive approaches and must be carefully checked. A tight extensor mechanism in flexion can mislead the surgeon to place the femoral component in an internally rotated position. Furthermore, with limited visualization, surgeons must avoid overaggressive ligament releases early in the procedure prior to completion of bone cuts. However, with appropriate patient selection and a systematic approach to minimally invasive total knee arthroplasty, surgeons can continue to achieve ideal ligament balance with a more soft tissue friendly operation.

Effect of Balanced Gap Total Knee Arthroplasty on Intraoperative Laxities and Femoral Component Rotation

The gap technique could lead to undesirable rotation of the femoral component in some knees. Using a navigation system, femoral component external rotations and varus-valgus laxities at 0° and 90° of flexion were measured intraoperatively in 44 patients. Significant improvements were observed at a minimum follow-up of 4 years with regard to clinical and radiologic outcomes. The balanced gap technique in total knee arthroplasty provided good intraoperative alignments and laxities of knees at 0° and 90°. However, increased femoral component external rotation was found to be correlated with increased varus alignment at 90° of knee flexion. This study shows that excessive external rotation of the femoral component during flexion gap balancing using the balanced gap technique in total knee arthroplasty can be avoided by additional soft tissue balancing guided by navigation.

The Use of Navigation to Obtain Rectangular Flexion and Extension Gaps During Primary Total Knee Arthroplasty and Midterm Clinical Results

The authors evaluated 112 knees treated by total knee arthroplasty (TKA) using a navigation-assisted modified gap balancing technique. Initial mediolateral gap differences in extension and in 90° of flexion were measured after proximal tibia bone cutting. Final flexion and extension gaps were measured by checking distances under equal tension before prosthesis insertion. Amount of femoral bone cutting and external rotations of femoral components were found to depend on initial gaps. Patients with a final rectangular gap had greater knee flexion angles preoperatively and at 1 year after TKA. However, no differences were observed between the clinical and radiologic outcomes of knees with rectangular and nonrectangular gaps at 1 or 4 years after TKA. The study shows that the navigation-assisted modified gap balancing technique provides an effective means of achieving rectangular flexion and extension gaps during TKA.

Correction of axial and rotational alignment after medial and lateral releases during balanced gap TKA

Background and purpose Restoration of mechanical alignment after total knee arthroplasty can be achieved with ligament releases. Several previously described sequences and results achieved with cadaver knees, with measured resection implantation techniques, may not be applied to the balanced gap technique. We investigated the peroperative effect of stepwise soft tissue releases following the “tightest structure first” on leg axis in extension and femur rotation in flexion.Methods During PCL-retaining total knee arthroplasty (TKA), using a balanced gap technique in 54 patients we determined the effect of each ligament release using a navigation system while the knee was distracted with a tensor in extension and flexion. The effect on alignment in extension and on femoral rotation in flexion was measured for each release separately.Results In more than half of the patients, one or more ligament releases were necessary. Release of the posteromedial condyle led to a minor effect on leg axis in extension and femoral rotation in flexion, release of the superficial medial collateral ligament to a few degrees, mainly in extension. Release of the iliotibial tract led to a small correction of leg alignment in extension. There was no statistically significant difference in the alignment-correcting effect of a release dependent upon the sequence in which the structure was released.Interpretation In PCL-retaining TKA, a stepwise “tightest structure first” protocol for ligament releases in extension with the balanced gap technique results in effective, gradual, alignment correction in extension, and limited femoral rotating effects in flexion.

Modified gap-balancing technique in total knee arthroplasty: evaluation of the post-operative coronal laxity

It is unknown how intra-operative soft-tissue balance affects post-operative knee kinematics during different functional tasks. In order to clarify this relationship, the intra-operative varus-valgus balance and post-operative knee kinematics were compared for 17 patients who underwent total knee arthroplasty using a modified gap technique. The intra-operative balance was recorded with a tensor device, and in vivo knee kinematics of lunging, kneeling and non-weight-bearing knee extension were analyzed with 3D-to-2D model registration techniques. Femoral condylar separation from the tibial articular surface also was investigated. The post-operative varus-valgus angle in 90 degrees kneeling had a strong relationship with the intra-operative varus-valgus angle, while there was a weak relationship for the non-weight-bearing motion at 0 degrees and 90 degrees flexion. Articular surface separation was an uncommon observation, seen in 2.2% of images during non-weight-bearing motion and in none of the lunging or kneeling images. The modified gap technique appears effective providing stable knee arthroplasty kinematics during in vivo activities with minimal articular separation in non-weight-bearing motion.

Ligament releases do not lead to increased postoperative varus-valgus laxity in flexion and extension: a prospective clinical study in 49 TKR patients

This prospective study investigated whether ligament releases necessary during total knee replacement (TKR) led to a higher varus-valgus laxity during intraoperative examination after implantation of the prosthesis and after 6 months. The laxity values of TKR patients were also compared to healthy controls. Varus-valgus laxity was assessed intra- and postoperatively in extension and 70 degrees flexion in 49 patients undergoing TKR, implanted using a balanced gap technique. Knees were catalogued according to ligament releases performed during surgery. Postoperative varus-valgus laxity and laxity after 6 months had not increased following release of the posteromedial capsule, iliotibial tract, and the superficial medial collateral ligament. The obtained postoperative laxity compares well with a healthy equally aged control group. It can be concluded that the balanced gap technique results in stable knees and that releases can safely be performed to achieve neutral leg alignment without causing postoperative laxity.

Gap Balancing versus Measured Resection Technique for Total Knee Arthroplasty

Multiple differing surgical techniques are currently utilized to perform total knee arthroplasty (TKA). We compared knee arthroplasties performed using either a measured resection or gap balancing technique to determine if either operative technique provides superior coronal plane stability as measured by assessment of the incidence and magnitude of femoral condylar lift-off. We performed 40 TKA using a measured resection technique (20 PCL-retaining and 20 PCL-substituting) and 20 PCL-substituting TKA were implanted using gap balancing. All subjects were analyzed fluoroscopically while performing a deep knee bend. The incidence of coronal instability (femoral condylar lift-off) was then determined using a 3-D model fitting technique. The incidence of lift-off greater than 0.75 mm was 80% (maximum, 2.9 mm) and 70% (maximum, 2.5 mm) for the PCL-retaining and substituting TKA groups performed using measured resection versus 35% (maximum, 0.88 mm) for the gap-balanced group. Lift-off greater than 1 mm occurred in 60% and 45% of the PCL-retaining and -substituting TKA using measured resection versus none in the gap-balanced group. Rotation of the femoral component using a gap balancing technique resulted in better coronal stability which we suggest will improve functional performance and reduce polyethylene wear.