Effects of posterior cruciate ligament resection on the tibiofemoral joint gap

Biomechanical effects of patellar positioning on intraoperative knee joint gap measurement in total knee arthroplasty

BACKGROUND

Balancing both the lateral/medial and extension/flexion joint gaps is a prerequisite for soft tissue balance in total knee arthroplasty. The purpose of this study was to quantify the effects of patellar positioning and quadriceps load during total knee arthroplasty on knee joint gap measurements.

METHODS

Eight fresh-frozen cadaveric knees ranging in age from 65 to 85 years old were used. Using a medial parapatellar approach, posterior cruciate ligament sacrificing total knee arthroplasty was performed. The specimens were mounted on a custom knee testing system that allowed the femur to be locked in position for knee extension or flexion. Patellar positions of eversion, reduction, and following repair of the arthrotomy were examined. The influence of quadriceps muscle load was investigated by varying the quadriceps load from 0 to 125N. The lateral and medial joint gaps, represented by the distance from the implanted femoral component surface to the cut tibia surface, were measured with 100N tibial distraction force using a 3D digitizer in both extension (0 degrees ) and flexion (90 degrees ).

FINDINGS

Both the medial and lateral joint gaps with patella eversion were significantly smaller than those with patellar reduction and arthrotomy repair (extension: all quadriceps loads, P<0.0002; flexion: quadriceps loads less than 75N, P<0.0002). In patella eversion, quadriceps loading decreased the lateral joint gap more than the medial joint gap in both extension and flexion; however, the effect was greater in knee flexion with significant differences seen at all quadriceps loads, whereas in extension significant differences were only seen for quadriceps loading of 75N and greater. Patella eversion also caused a lateral-posterior shift and external rotation of the tibia compared to the other conditions (P<0.005). With patella reduction and repair of the arthrotomy lower quadriceps loading decreased the extension gap significantly more than the flexion gap (P<0.01). Following repair of the arthrotomy higher quadriceps loading significantly decreased the flexion gap more than the extension gap (P<0.04).

INTERPRETATION

The patellar positioning and quadriceps muscle loading in total knee arthroplasty have a strong influence on intraoperative joint gap measurements.

Flexion-extension gaps balanced using navigation assistance in TKA

This study evaluated the accuracy of navigation for balancing soft tissue and flexion-extension gaps in primary total knee arthroplasty (TKA). We evaluated 112 knees treated with TKA using the gap technique and navigation system. Flexion-extension gaps were measured before femoral cutting (precutting gaps) and before prosthesis insertion (final gaps). Balanced precutting flexion-extension gaps were shown in 45 cases (40.2%), and balanced final flexion-extension gap was achieved in 105 cases (93.8%). Precutting tight extension gaps resulted from preoperative extension lag. We found TKA using the gap technique with navigation to be an effective means of achieving balanced flexion-extension gaps.

Effect of PCL on flexion-extension gaps and femoral component decision in TKA

This study was done to evaluate the change of medial-lateral gap in flexion and extension after posterior cruciate ligament (PCL) release in severely deformed knees and to determine how PCL release affects bone resection, rotation, and size of the femoral component and polyethylene thickness in converting to a PCL-sacrificed design. Thirty primary osteoarthritis patients with severe varus deformity or flexion contracture were enrolled. After releasing the PCL, the medial gap in extension increased by 1.2 mm, the lateral gap in extension increased by 0.3 mm, the medial gap in flexion increased by 4.5 mm, and the lateral gap in flexion increased by 3.4 mm. Compared with PCL-retained prostheses, the mean external rotation of the femoral component decreased by 1.6 degrees in the PCL-sacrificed type. Polyethylene thickness increased by 1.2 mm. In 12 cases, a larger femoral component was needed. In 8 knees, the size of the femoral component and the thickness of polyethylene did not change; however, posterior femoral resection could be decreased. In 8 knees, thicker polyethylene was planned with slightly increased distal femoral resection. After PCL cutting, flexion gap increased significantly compared with extension gap; however, correction of varus deformity was not significant. Conversion to PCL-sacrificed design resulted in a decrease in external rotation of the femoral component and increased the size of the femoral component or the thickness of the polyethylene insert.

Quantification of effect of sequential posteromedial release on flexion and extension gaps: a computer-assisted study in cadaveric knees

A novel sequence of posteromedial release consistent with surgical technique of total knee arthroplasty was performed in 15 cadaveric knees. Medial and lateral flexion and extension gaps were measured after each step of the release using a computed tomography-free computer navigation system. A spring-loaded distractor and a manual distractor were used to distract the joint. Posterior cruciate ligament release increased flexion more than extension gap; deep medial collateral ligament release had a negligible effect; semimembranosus release increased the flexion gap medially; reduction osteotomy increased medial flexion and extension gaps; superficial medial collateral ligament release increased medial joint gap more in flexion and caused severe instability. This sequence of release led to incremental and differential effects on flexion-extension gaps and has implications in correcting varus deformity.

Ligament tension in the ACL-deficient knee: assessment of medial and lateral gaps

Obtaining symmetric and balanced gaps under equilateral loads is a common goal in posterior cruciate ligament (PCL)-retaining and -sacrificing TKAs. Owing to limitations in existing surgical tensors, however, tensing knee ligaments with standardized and symmetric loads has been possible only with the patella subluxated or everted. We therefore determined the influences of (1) patellar eversion versus complete reduction, (2) PCL resection, and (3) load magnitude on gap symmetry and balance in the anterior cruciate ligament (ACL)-deficient knee. We used a novel computer-controlled tensioner to measure gaps in 10 cadavers with an applied force of 50 N, 75 N, and 100 N per side. Gap data were acquired at 0 masculine, 30 masculine, 60 masculine, 90 masculine, and 120 masculine flexion with the patella reduced and everted and with the PCL intact and resected. Everting the patella tightened the medial and lateral flexion gaps between 90 masculine and 120 masculine by 0.7 mm to 2.7 mm. PCL resection increased gaps from 30 degrees to 120 degrees by 1 mm to 3 mm. Increasing the force from 50 N to 100 N increased the mean gap by 0.5 mm. Everting the patella and resecting the PCL influenced gap balance and symmetry. Surgeons should be aware of how these conditions affect gaps during assessment and balancing.

The intra-operative joint gap in cruciate-retaining compared with posterior-stabilised total knee replacement

We have developed a new tensor for total knee replacements which is designed to assist with soft-tissue balancing throughout the full range of movement with a reduced patellofemoral joint. Using this tensor in 40 patients with osteoarthritis we compared the intra-operative joint gap in cruciate-retaining and posterior-stabilised total knee replacements at 0°, 10°, 45°, 90° and 135° of flexion, with the patella both everted and reduced.

While the measurement of the joint gap with a reduced patella in posterior-stabilised knees increased from extension to flexion, it remained constant for cruciate-retaining joints throughout a full range of movement. The joint gaps at deep knee flexion were significantly smaller for both types of prosthetic knee when the patellofemoral joint was reduced (p < 0.05).

Factors affecting flexion gap tightness in cruciate-retaining total knee arthroplasty

With the exception of flexion gap tightness, which is common in cruciate-retaining (CR) total knee arthroplasty (TKA), the risk factors of flexion gap tightness have not been described. This retrospective study characterized factors that are associated with flexion gap tightness in CR TKA. Data on 203 consecutive knees that underwent CR TKA were reviewed. The prevalence rate of flexion gap tightness was 21.1%. By logistic regression analysis after adjusting for age, preoperative flexion contracture, and referencing method used for femoral sizing, insufficient tibial slope remained a significant independent risk factor of flexion gap tightness. Although excessive tibial slope should be avoided, the findings of the present study demonstrate that the risk of flexion gap tightness can be reduced by increasing the tibial slope in CR TKA.

Evaluation of joint laxity against distal traction force upon flexion in cruciate-retaining and posterior-stabilized total knee arthroplasty

BACKGROUND

Several studies have reported varus-valgus stability in the extension position after total knee arthroplasty (TKA). However, few studies have evaluated joint laxity in the flexion position postoperatively. The purpose of the study was to evaluate joint laxity against distal traction force on flexion after cruciate-retaining and posterior-stabilized total knee arthroplasties.

METHODS

A total of 44 knees (22 knees cruciate-retaining, 22 knees posterior-stabilized) in 40 patients with osteoarthritis were tested in this study. The subjects were seated at a table and their knee joints were fixed at 80 degrees of flexion to avoid overlapping images of condyles and the femoral shaft. Tibial shafts were adjusted to be parallel to the radiographic films, and posteroanterior radiographs were obtained. Flexion stress tests were performed with a distal traction of 100 N at a neutral foot position. Radiographs were obtained at neutral and traction positions. The distance from the perpendicular line of the top of the polyethylene insert to the midpoint on the tangential line of the femoral condyle was measured (joint space distance) at each side.

RESULTS

In the flexion-neutral position, average joint space distances were 0.1 +/- 0.2 mm in cruciate-retaining (CR) TKA knees and 0.2 +/- 0.3 mm in posterior-stabilized (PS) TKA knees. With flexion-traction stress tests, the average joint space distances were 0.5 +/- 0. 5 mm in CR TKA knees 2.4 +/- 1.2 mm in PS TKA knees. Average changes of joint space distances between the two positions were 0.3 +/- 0.4 mm (CR TKA) and 2.2 +/- 1.5 mm (PS TKA). The changes in joint space distances between neutral and traction positions of PS TKA knees were significantly larger than those of CR TKA knees in flexion stress tests (P < 0.01).

CONCLUSION

The posterior cruciate ligament acted as a stabilizer against distal traction force in the CR-TKA knees. However, the laxity of PS-TKA knees against distal force differed among individual cases.

Surgical technique differences between posterior-substituting and cruciate-retaining total knee arthroplasty

Fundamental differences in implant design and the relative size of the flexion and extension spaces suggest that subtle, different surgical techniques should be used for cruciate-retaining and posterior-substituting total knee arthroplasties. Sacrificing the posterior cruciate ligament (PCL) selectively opens the flexion space approximately 2 mm more than the extension space, which accounts for some of the technical differences. When performing a cruciate-retaining knee, the key points are to avoid stiffness due to an extra tight flexion space caused by a tight PCL and to avoid flexion instability from overrelease of the PCL. When performing a posterior-substituting knee, the key points are to avoid flexion instability due to an extra large flexion space caused by PCL sacrifice and to avoid postoperative knee flexion contracture by underresection of the distal femur. For posterior-sacrificing knees, cam-post impingement is a potential problem and can be avoided by avoiding excessive femoral component flexion and tibial component slope.

Shape of the joint gap for 90 degrees and 120 degrees knee flexion after total knee arthroplasty

BACKGROUND

The joint gap is set rectangular at 90 degrees flexion during total knee arthroplasty (TKA). However, the condition of the joint gap in deep knee flexion is obscure.

METHODS

The method for obtaining a posteroanterior view radiograph of the knee at 90 degrees flexion (the epicondylar view) was modified, and a method to obtain an anteroposterior view radiograph at 120 degrees flexion (deep flexion view) was established. With this method, subjects lie on the radiography table with their thighs placed on a device so their lower legs hang down in neutral rotation with a 1.5-kg weight attached to the ankle. The joint gap angle and medial and lateral joint space widths were measured on epicondylar view and deep flexion view radiographs in 20 normal male subjects, 20 normal female subjects, and 20 subjects after TKA.

RESULTS

The joint gap was almost rectangular at two flexion angles in normal subjects. In the implanted knees, the gap angle was 1.4 degrees varus +/- 3.3 degrees (mean +/- standard deviation), and no significant difference was found between medial and lateral joint space widths at 90 degrees flexion. In contrast, the gap angle was 2.5 degrees varus +/- 2.5 degrees and the lateral joint space width was significantly wider than the medial joint space width at 120 degrees flexion (P < 0.001). The gap angle was more varus with a significant difference in the implanted knees than that in the normal subjects at 120 degrees flexion (P < 0.001).

CONCLUSIONS

The joint gap was trapezoidal with a wider lateral side at 120 degrees flexion even though it was almost rectangular at 90 degrees flexion after TKA.

Joint gap changes with patellar tendon strain and patellar position during TKA

Balancing of the joint gap in extension and flexion is a prerequisite for success of a total knee arthroplasty. The joint gap is influenced by patellar position. We therefore hypothesized the state of the knee extensor mechanism (including the patellar tendon) would influence the joint gap. In 20 knees undergoing posterior-stabilized type total knee arthroplasties, we measured the joint gap and the patellar tendon strain from 0 degrees to 135 degrees flexion with the femoral component in position. When the patella was reduced, the joint gap was decreased at 90 degrees and 135 degrees (by 1.9 mm and 5.5 mm, respectively) compared with the gap with the patella everted. The patellar tendon strain increased with knee flexion. Patellar tendon strain at 90 degrees flexion correlated with the joint gap difference with the patella in everted and reduced positions. This suggests that in addition to the collateral ligaments, the knee extensor mechanism may have an influence on the joint gap. Therefore, accounting for extensor mechanism tightness may be important in achieving the optimal joint gap balance during total knee arthroplasty.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Flexion gap preparation opens the extension gap in posterior cruciate ligament-retaining TKA

It has been reported that preparation of the flexion gap results in significant widening of the prepared extension gap in posterior stabilized (PS) total knee arthroplasty (TKA). To date, there is a paucity of data regarding cruciate ligament-retaining (CR) TKA. Changes in the extension gap caused by preparation of the flexion gap were measured in 42 varus osteoarthritic knees undergoing CR TKA. The extension gap was first prepared and then measured before and after preparation of the flexion gap. The extension gap increased significantly on both the medial and lateral sides (18.8-20.0 and 21.7-22.7 mm, respectively) (P < 0.01). Preparation of the flexion gap also resulted in significant widening of the extension gap on CR TKA. However, amount of extension gap increase in CR TKA was smaller than previous reports on PS TKA.

Function of posterior cruciate ligament bundles during in vivo knee flexion

BACKGROUND

The biomechanical functions of the anterolateral and posteromedial bundles of the posterior cruciate ligament over the range of flexion of the knee joint remain unclear.

HYPOTHESIS

The posterior cruciate ligament bundles have minimal length at low flexion angles and maximal length at high flexion angles.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Seven knees from normal, healthy subjects were scanned with magnetic resonance, and 3-dimensional models of the femur, tibia, and posterior cruciate ligament attachment sites were created. The lines connecting the centroids of the corresponding bundle attachment sites on the femur and tibia represented the anterolateral and posteromedial bundles of the posterior cruciate ligament. Each knee was imaged during weightbearing flexion (from 0 degrees to maximal flexion) using a dual-orthogonal fluoroscopic system. The length, elevation, deviation, and twist of the posterior cruciate ligament bundles were measured as a function of flexion.

RESULTS

The lengths of the anterolateral and posteromedial bundles increased with flexion from 0 degrees to 120 degrees and decreased beyond 120 degrees of flexion. The posteromedial bundle had a lower elevation angle than the anterolateral bundle beyond 60 degrees of flexion. The anterolateral bundle had a larger deviation angle than the posteromedial bundle beyond 75 degrees of flexion. The femoral attachment of the posterior cruciate ligament twisted externally with increasing flexion and reached a maximum of 86.4 degrees +/- 14.7 degrees at 135 degrees of flexion (P < .05).

CONCLUSION

These data suggest that there is no reciprocal function of the bundles with flexion, which is contrary to previous findings. The orientation of the anterolateral and posteromedial bundles suggests that at high flexion, the anterolateral bundle might play an important role in constraining the mediolateral translation, whereas the posteromedial bundle might play an important role in constraining the anteroposterior translation of the tibia.

CLINICAL RELEVANCE

These data provide a better understanding of the biomechanical function of the posterior cruciate ligament bundles and may help to improve the design of the 2-bundle reconstruction techniques of the ruptured posterior cruciate ligament.

Influence of intra-operative joint gap on post-operative flexion angle in osteoarthritis patients undergoing posterior-stabilized total knee arthroplasty

Recently, we developed a new tensor for total knee arthroplasty (TKA) procedures enabling soft tissue balance assessment throughout the range of motion while reproducing post-operative joint alignment with the patello-femoral (PF) joint reduced and the tibiofemoral joint aligned. Using the tensor with a computer-assisted navigation system, we investigated the relationship between various intra-operative joint gap values and their post-operative flexion angles. An increased value during the extension to flexion gap and a decreased value during the flexion to deep flexion gap with PF joint reduced, not everted, showed an inverse correlation with post-operative knee flexion angle, not pre-operative flexion angle. In conclusion, understanding the characteristics of joint gap kinematics in posterior-stabilized TKA under physiological and reproducible joint conditions may enable the prediction of the post-operative flexion angle and help to determine the appropriate intra-operative joint gap.

Preparation of the flexion gap affects the extension gap in total knee arthroplasty

Changes in the extension gap caused by the preparation of the flexion gap were measured in 50 varus osteoarthritic knees undergoing total knee arthroplasty. The extension gap was first prepared and then measured before and after preparation of the flexion gap. The extension gap increased significantly on both the medial and lateral sides (19.3 +/- 0.3 to 22.0 +/- 0.3 and 21.9 +/- 0.3 to 24.0 +/- 0.3 mm, respectively, mean +/- SE, both P < .0001). The increase was greater medially (P = .0014), and in the knees with more varus deformities (> or = 10 degrees, P = .0075). Thus, preparation of the flexion gap resulted in significant widening of the extension gap, especially on the medial side. The medial release should be stepwise and conservative to achieve adequate soft tissue balance.

Movement of the posterior cruciate ligament during knee flexion--MRI analysis

The movement of the posterior cruciate ligament (PCL) during flexion of the living knee is unknown. The purpose of the present study was to analyze the movement of the PCL using magnetic resonance imaging (MRI). The posterior cruciate ligaments in 20 normal knees were visualized using MRI from extension to deep flexion. Sagittal inclination relative to the longitudinal axis of the tibia was measured and analyzed with reference to the patellar tendon (PT) and the anterior cruciate ligament (ACL). Although the PCL was slack in extension, it straightened with anterior inclination (24.1+/-5.1 degrees ) at 90 degrees flexion. At active maximum flexion (129.2+/-8.1 degrees ), the ligament was almost parallel (3.9+/-7.4 degrees inclination) to the longitudinal axis of the tibia. At passive maximum flexion (158.8+/-5.8 degrees ), the inclination was reversed anteroposteriorly, measuring -23.0+/-6.7 degrees . The PCL and PT moved in a corresponding manner within 20 degrees of discrepancy. The results of this in vivo study of the PCL have clinical relevance to conservative therapy for PCL knee injuries. The results of this study could also be useful in PCL reconstruction surgery to determine the optimum graft position to allow maximum postoperative motion.

Changes in anteroposterior stability following total knee arthroplasty

This study evaluated the changes in anteroposterior stability at flexion and extension following posterior cruciate ligament (PCL)-retaining and PCL-substituting total knee arthroplasty (TKA), in comparison with normal knees. Altogether, 29 knees of 24 patients underwent either PCL-retaining ( n = 19) or PCL-substituting ( n = 10) TKA. Anteroposterior displacement was measured with a KT-2000 arthrometer preoperatively, 1 month after surgery, and again an average of 3 years after surgery. Anteroposterior stability at flexion and extension did not change following PCL-retaining TKA and was not significantly different from that of normal subjects, whereas anteroposterior stability increased following PCL-substituting TKA and was significantly greater than that of normal subjects an average of 3 years after surgery.

Step-by-step measurements of soft tissue balancing during total knee arthroplasty for patients with varus knees

Using a step-by-step procedure, we measured joint gap during surgery using a simple device with a torque meter in 45 osteoarthritis knee joints (43 patients) with varus deformity. The effects of specific cuts or releases of the anatomic portion on joint gaps were investigated. Each cut or release resulted in various increases in the medial gap from 1.2 to 3.8 mm on average. The final gap measurements averaged 24.1 mm medially and 27.6 mm laterally in extension, and 24.6 mm medially and 27.2 mm laterally in flexion. The results of the measurements showed that each step-by-step procedure had a tendency of gap increase. The results led us to measure soft tissue balancing in a step-by-step procedure during total knee arthroplasty.