Determinants of patellar tracking in total knee arthroplasty

Internal rotational patellar resection and patella alta induced patellar maltracking in total knee arthroplasty: intraoperative measurement of the patellofemoral pressure

BACKGROUND

Anterior knee pain due to patellar maltracking following total knee arthroplasty (TKA) reduces patients' satisfaction. This study aimed to determine the patellofemoral pressure (PFP) in patients with favorable patellar tracking (FT) and impaired patellar tracking (IT) following TKA, the factors causing patellar maltracking, and the effect of lateral retinacular release (LRR) on patients with IT.

METHODS

Forty-four patients with varus knee osteoarthritis undergoing cruciate-retaining TKA were enrolled. After component implantation, patients with a separation of ≥ 2 mm of the patellar medial facet from the medial femoral trochlea throughout knee range of motion were classified into the IT group; meanwhile, the others were classified into the FT group. PFP was measured intraoperatively in three phases: (1) with the resurfaced patella (RP); (2) with the resurfaced patella and knee (RPK); and (3) when LRR was performed in IT (post-LRR). The PFPs at 0°, 90°, 120°, and 135° knee flexion were compared between FT and IT using the Mann-Whitney U test. Pairwise comparison of the PFP in IT between RPK and post-LRR was performed using the Wilcoxon signed-rank test. Correlations between PFP and pre- and postoperative radiographic parameters, such as hip-knee-ankle angle, lateral distal femoral angle, medial proximal tibial angle, anterior femoral offset, Insall-Salvati ratio (ISR), patellar tilt, and patellar resection angle (PRA), were evaluated using Spearman's rank correlation coefficients.

RESULTS

High lateral PFP in the knee flexion position led to patellar maltracking. Patients with IT (n = 24) had higher lateral and lower medial PFP than did patients with FT (n = 20) at 90°, 120°, and 135° knee flexion in RP and RPK. LRR in IT reduced the lateral PFP in the knee flexion position. PRA and ISR were correlated with the lateral PFP at no less than 90° in RP and RPK.

CONCLUSIONS

This study demonstrated that internal rotational patellar resection, which resulted in a thick medial patellar remnant and a thin lateral counterpart, and patella alta were the causative factors of high lateral PFP, which induced patellar maltracking after TKA. Surgeons should avoid internal rotational patellar resection to achieve FT and perform LRR in patients with patellar maltracking.

How to optimize patellar tracking in knee arthroplasty?

Good patellar tracking is needed for functionally successful total knee arthroplasty (TKA), and depends on several factors. The aim of the present Instructional Lecture is to identify the main factors and how to control them so as to optimize patellar tracking: more or less "patella-friendly" prosthetic trochlea design, requiring precise assessment and choice of model; patellar component design; type of tibial implant; surgical approach and management of peripatellar structures, and any lateral release; distal and posterior femoral bone cuts, determining femorotibial alignment, femoral component rotation and patellar height; tibial implant rotation with respect to the anterior tibial tubercle; patellar cut characteristics in resurfacing. In case of instability or patellar maltracking despite correct implant positioning, there are 2 main surgical techniques: medial patellofemoral ligament reconstruction, and anterior tibial tubercle medialization. To obtain optimal patellar tracking, correction of other factors should be associated: trochlear component design, distal and posterior femoral bone cuts, tibial implant positioning, patellar component shape and positioning, etc.

Cemented Patellar Implant Malposition: A Non-Issue for the Painful Total Knee Arthroplasty

BACKGROUND

Non-optimal patellofemoral relationships may influence treatment decisions during revision total knee arthroplasty (TKA). We performed this study to determine whether patellar implant malposition or patellar tilt is associated with inferior patient-reported outcome scores or patient satisfaction after primary TKA.

METHODS

We identified 396 TKA patients (439 knees) from an institutional registry who had undergone patellar resurfacing, with preoperative and 6-week postoperative radiographs available, and patient-reported outcome measures (PROMs) completed at least 1 year after surgery (mean 505 days). Preoperative patient demographic characteristics, patient-reported expectations, National Institutes of Health - Patient Reported Outcomes Measurements Instrument Systems global health, Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, and University of California Los Angeles activity scores were compared between 60 TKAs performed with non-optimal patellofemoral relationships (36 patellar implant malposition, 24 patellar tilt) and 379 TKAs performed with optimal patellar implant placement.

RESULTS

There were no differences between the 2 cohorts regarding demographic features, preoperative radiographic disease severity, expectations, and PROMs; or postoperative tibiofemoral component alignment, PROMs, and patient-reported satisfaction (P = .48). Knee Injury and Osteoarthritis Outcome Score for Joint Replacement improved similarly (P = .62) for patients with optimal resurfacing (48.5-77.6 points) and non-optimal resurfacing (47.7-76.6 points). A similar proportion of optimal and suboptimal resurfaced patients reported being satisfied with their TKA (92.7% vs 88.1%, P = .29).

CONCLUSION

Although suboptimal patellofemoral relationships may prompt treatment considerations during revision TKA, the data obtained from this study do not suggest that patellar implant malposition or patellar tilt independently contribute to postoperative pain, functional limitation, or dissatisfaction.

LEVEL OF EVIDENCE

This is a level III, retrospective cohort study.

An anatomo-functional implant positioning technique with robotic assistance for primary TKA allows the restoration of the native knee alignment and a natural functional ligament pattern, with a faster recovery at 6 months compared to an adjusted mechanical technique

PURPOSE

An anatomo-functional implant positioning (AFIP) technique in total knee arthroplasty (TKA) could restore physiological ligament balance (symmetric gap in extension, asymmetric gap in flexion). The purposes were to compare (1) ligament balancing in extension and flexion after TKA in the AFIP group, (2) TKA alignment, implant positioning and patellar tracking between AFIP and adjusted mechanical alignment (aMA) techniques, (3) clinical outcomes between both groups at 12 months.

METHODS

All robotic-assisted TKA with an AFIP technique were included (n = 40). Exclusion criteria were genu valgum (HKA angle > 183°), extra-articular deformity more than 10°, and patellar maltracking (high-grade J-sign). One control patient with a TKA implanted by an aMA technique was matched for each case, based on age, body mass index, sex, and knee alignment. Ligament balancing (medial and lateral gaps in millimeters) in full extension and at 90° of flexion after TKA in the AFIP group was assessed with the robotic system. TKA alignment (HKA angle), implants positioning (femoral and tibial coronal axis, tibial slope, joint-line orientation), patellar tracking (patellar tilt and translation) and the Knee Society Score (KSS) at 6 and 12 months were compared between both groups. The ligament balancing was compared using a t test for paired samples in the AFIP group. The radiographic measurements and KSS scores were compared between groups using a t test for independent samples.

RESULTS

In the AFIP group, there was no significant difference between the medial and lateral gap laxity in extension (NS). A significant opening of the lateral gap was observed in flexion compared to extension (mean: + 2.9 mm; p < 0.0001). The mean postoperative HKA angle was comparable between both groups (177.3° ± 2.1 in the AFIP group vs 176.8° ± 3.2; NS). In the AFIP group, the femoral anatomy was restored (90.9° ± 1.6) and the tibial varus was partially corrected (87.4° ± 1.8). The improvement of Knee and Function KSS at 6 months was better in the AFIP group (59.3 ± 11.9 and 51.7 ± 20, respectively, versus 49.3 ± 9.7 and 20.8 ± 13; p < 0.001).

CONCLUSION

The AFIP concept allowed the restoration of the native knee alignment and a natural functional ligament pattern. With a more physiological target for ligament balancing, the AFIP technique had equivalent clinical outcomes at 12 months compared to aMA, with a faster recovery.

LEVEL OF EVIDENCE

III retrospective therapeutic case control series.

Management of the Patella During Total Knee Arthroplasty

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The optimal management of the patella during total knee arthroplasty (TKA) remains a controversial topic with no consensus.

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Patellar management techniques during TKA include patellar retention or resurfacing with or without patellaplasty, as well as circumferential denervation and partial lateral facetectomy (PLF).

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Special considerations such as patient age, etiology of disease, implant design, and surgeon preference should be accounted for when determining optimal management.

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We recommend that most patellae be circumferentially denervated, regardless of whether they are resurfaced, as the potential benefits outweigh the small associated risks.

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Evidence demonstrates improved functional outcomes with the addition of PLF to nonresurfaced patellae. There is currently a paucity of evidence of this technique with respect to resurfaced patellae.

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Patellar resurfacing adds additional costs and health-care resources that should be considered in the decision-making process.

Patella resurfacing during total knee arthroplasty is cost-effective and has lower re-operation rates compared to non-resurfacing

BACKGROUND

The decision to resurface the patella as part of total knee arthroplasty may be influenced by the surgeon's preference, education, training, tradition and geographic location. Advocates for non-resurfacing or selectively resurfacing may claim no difference in patient reported outcomes, and that resurfacing is associated with increased risks such as extensor mechanism injury or malalignment, problems with the design of the patella component and technical issues intraoperatively.

AIMS

To critically examine factors that should be considered in addition to patient reported outcomes in the decision process of resurfacing or non-resurfacing of the patella in total knee arthroplasty.

METHOD

A comprehensive literature search was conducted to identify factors that may influence decision making in addition to knee specific patient reported outcome measures such as surgical risks, patient quality of life, procedure cost, re-operation rate, implant design, surgeons learning curve and the fate of remaining cartilage in native patellae.

RESULTS

Patient-reported outcomes are equivocal for resurfacing and non-resurfacing. Critical analysis of the available literature suggests that the complications of resurfacing the patella are historic, which is now lower with improved implant design and surgical technique. Routine resurfacing was cost-effective in the long term (potential saving £104 per case) and has lower rates of revision (absolute risk reduction 4%). Finally, surgical judgment in selective resurfacing was prone to errors.

CONCLUSION

Patella resurfacing and non-resurfacing had similar patient-reported outcomes. However, patella resurfacing was cost-effective and was associated with a lower rate of re-operation compared to non-resurfacing.

Early Patellofemoral Function of Medial Pivot Prostheses Compared with Posterior-Stabilized Prostheses for Unilateral Total Knee Arthroplasty

Objective

To systematically evaluate the patellofemoral joint design of medial pivot prosthesis, which incorporates a variety of “patella‐friendly” design features, by comparing clinical and radiographic results with another prosthesis.

Methods

All consecutive patients who underwent unilateral total knee arthroplasty (TKA) with medial pivot prosthesis (Group MP, 126 cases) between September 2016 and April 2018 were enrolled in this retrospective study. For each patient reviewed, a control patient was matched, according to age, gender, side, body mass index (BMI), preoperative range of motion (ROM), and operating period, who had received primary unilateral TKA with a conventional posterior‐stabilized prosthesis at the same period as the study group (Group PS, 126 cases). All patients underwent at least 1‐year follow‐up. At the preoperative and final follow‐up periods, data on the Knee Society Score (KSS) score, WOMAC score, Kujala score, and ROM were collected. Merchant views were taken with the knee flexion at 30°, 60°, and 90° to measure patella shift and tilt. Preoperative posterior condylar angle (PCA) was also measured. Postoperative complications, including anterior knee pain, maltracking, patellar clunk or crepitus (PCC), were evaluated.

Results

There were no significant differences in the demographics or clinical characteristics between the two groups. No statistically significant difference was identified in the KSS total score, including knee score and function score, or in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score between the two groups after the operation. We found statistically significant differences in the postoperative Kujala scores and the ROMs between the two groups. The mean Kujala score in group MP was better than in group PS (MP 77.16 ± 3.80 vs PS 75.97 ± 4.06, P < 0.05), while the ROM in group PS was significantly higher than in group MP (MP 122.24° ± 4.45° vs PS 123.78° ± 6.05°, P < 0.05). Simultaneously, the preoperative/postoperative Kujala score improvement in group MP was observed to be significantly larger than in group PS (MP 27.82 ± 5.31 vs PS 26.17 ± 4.89, P < 0.05), but the average ROM improvement in group PS was significantly greater than in group MP (MP 19.00° ±9.90° vs PS 21.57° ± 9.62°). In the 90° Merchant view, the mean patella tilt of group MP was statistically smaller than that of group PS (MP 4.21° ± 1.62° vs PS 4.74° ± 1.95°, P < 0.05), and the average patella tilt change in group MP was significantly greater than in group PS (MP –3.8° ± 1.43° vs PS –3.23° ± 1.33°, P < 0.05). Preoperative PCA did not show significant differences between the two groups. Two cases of PCC and three cases of anterior knee pain were noted in group MP, and nine cases and six cases, respectively, were observed in group PS. The incidence of PCC was significantly lower in group MP (1.6% vs 7.1%, P < 0.05). There was no significant difference in follow‐up time between the two groups.

Conclusion

The medial pivot prosthesis could achieve satisfactory outcomes with better patellofemoral performance attributed to its “patella‐friendly” design characteristics compared to the conventional posterior‐stabilized prosthesis.

Tibial Tubercle-Trochlear Groove Distance Influences Patellar Tilt After Total Knee Arthroplasty

BACKGROUND

Tibial tubercle-trochlear groove (TT-TG) distance is associated with a greater risk of recurrent patellar dislocation in young, active patients. However, the effect of TT-TG distance after total knee arthroplasty (TKA) has not been investigated. The purpose is to analyze the effect of TT-TG distance and component rotation on patellar tilt and patellar shift after TKA.

METHODS

After TKA, axial computed tomography scans and axial radiograph were taken in 115 consecutive knees. TT-TG distance was measured between the most anterior point of the tibial tuberosity and the deepest point of the femoral component relative to a line connecting the anterior condyles. Femoral and tibial component rotation was measured relative to the femoral and tibial rotational axis, respectively. Pearson correlation coefficients were calculated.

RESULTS

TT-TG distance had a significant correlation with patellar tilt in extension (R = 0.220, P = .018), patellar tilt in flexion (R = 0.438, P < .001), and patellar shift (R = 0.330, P < .001). Tibial component rotation had a significant correlation with patellar tilt in flexion (R = -0.251, P = .007) and patellar shift (R = -0.360, P < .001). Femoral component rotation had no significant correlations. Tibial component rotation had a significant correlation with TT-TG distance (R = -0.573, P < .001), whereas femoral component rotation had no correlation (P = .192).

CONCLUSION

TT-TG distance had a significant correlation with patellar tilt and patellar shift. Surgeons need to understand the factors affecting TT-TG distance and to pay attention to avoiding excessive TT-TG distance after TKA.

The evolution of patellofemoral prosthetic design in total knee arthroplasty: how far have we come?

Total knee arthroplasty (TKA) has evolved into a successful, cost-effective treatment for end-stage knee arthrosis.The patellofemoral articulation in TKA has largely been ignored during its development despite being an important determinant of outcome.New technologies still need further development to incorporate the patella in TKA surgical planning and operative technique.Alternative approaches to alignment in TKA will have a secondary impact on patellofemoral mechanics and possibly future implant designs.Technologies that assist with precise implant positioning may alter our understanding and overall practice of TKA. Cite this article: EFORT Open Rev 2019;4:503-512. DOI: 10.1302/2058-5241.4.180094.

Role of Anatomical Patella Replacement on Anterior Knee Pain

BACKGROUND

Anterior knee pain (AKP) remains a complex issue affecting patient satisfaction after total knee arthroplasty. Several radiographic parameters have been shown to be causative factors with various designs. The aim of this study is to evaluate the known radiographic parameters of AKP and clinical outcomes (ie, AKP) in the setting of a modern prosthesis with an anatomic patella button.

METHODS

Between July 2012 and December 2013, 90 total knee arthroplasties received 3 skyline views taken at 30°, 45°, and 60°. A patient-administered questionnaire was administered at 2-year follow-up to assess the incidence of AKP, painless noise, and satisfaction. Radiographs were analyzed for patellofemoral overstuffing, patellar tilt, and patellar displacement, and evaluated the patella resection angle.

RESULTS

On the patient-administered questionnaire, 10 (11.1%) patients reported AKP of a mild-to-moderate nature. Thirty-one had the best view at 30 Merchant views, 24 had best views at 45, and 35 had best views at 60. We found that patellar resection angle correlated with AKP (odds ratio 1.21, P = .044) and painless noise (odds ratio 1.22, P = .034). Patellar displacement and patellofemoral stuffing did not correlate with AKP or painless noise. No radiographic measurements correlated with changes in Knee Society Score pain or function scores or range of motion.

CONCLUSION

We found that a patellar resection angle correlated with the incidence of AKP and painless noise at 2-year follow-up. We failed to find any correlation with patellofemoral overstuffing, patellar displacement, or patellar tilt with clinical outcomes. We recommend the use of 3 Merchant views to fully evaluate the patellofemoral joint.

Association of Femoral Trochlear Dysplasia and Tibiofemoral Joint Morphology in Adolescent

BACKGROUND Trochlear dysplasia (TD) often leads to anatomic variations of the knee. Little is known about the association of TD and tibiofemoral joint morphology in adolescent. MATERIAL AND METHODS Computed tomography scans of 35 knees with TD and 55 knees with well-developed patella-femoral joint were analyzed randomly and retrospectively. Two researchers evaluated the posterior tibial slope (PTS), distal femoral rotation, proximal tibia varus angle, and femoral anteversion between the 2 groups. The independent Student's t-test was used to evaluate the statistical significance of variables. RESULTS The study group had a smaller lateral PTS (4.7±2.97) than the control group (6.96±3.05) (P<0.01), while the medial PTS showed consistent values between the control and the study group (non-significant). Patients with TD had smaller external rotation of the distal femur (2.69±0.93) compared to the control group (3.77±1.46) (P<0.01). In addition, the study group showed a bigger proximal tibia varus angle (4.46±1.09) compared to the control group (3.35±0.76) (P<0.01). The femoral anteversion in the study group (17.46±9.95) was increased compared to the control group (12.22±5.39) (P<0.01). The femoral anteversion and distal femoral rotation in patients with TD showed a positive correlation (r²=0.326; P<0.001). CONCLUSIONS Patients with TD had flatter lateral PTS compared to those without TD, but there were no differences in the medial PTS between the two groups. Patients with TD had smaller distal femoral rotation and bigger proximal tibia varus angle. The femoral anteversion in patients with TD was bigger than those without TD,and there was a positive correlation between the femoral anteversion and the external rotation of the distal femoral in the study group.

Prospective comparative study of intraoperative "Towel clip test" and "Vertical patella test" assessing lateral retinaculum tightness in patients undergoing TKA

BACKGROUND

Proper patellar tracking is one of the most important aspect of TKA to ensure good functional outcome. A patellar tracking problem noted intraoperatively serves as a warning sign and should prompt the surgeon to reassess position of each component. Various tests are there to assess lateral retinaculum tightness viz. "No thumb test", "Towel clip test". A new test "Vertical patella test" is described to assess lateral retinaculum tightness. A study was conducted to assess the effectiveness, correlation and validity of two techniques.

MATERIALS & METHODS

Patients >50 years of age and with diagnosis of Osteoarthritis knee having less than 30 varus and flexion deformity going in for primary TKA were selected with a sample size of 100 knees in a tertiary care centre. Revision cases or patients with flexion contracture more than 30, complex knee surgery; with pre existing patellar tilt were excluded from study.

RESULTS

Results of both tests were found to correlate in 75% of case with sensitivity of 96.65% and specificity of 75.00%. Kappa came out to be 0.634 which shows good agreement of vertical patella test and towel clip test. Result was computed using excel and SPSS and was found to be significant with p value< 0.05. Lateral retinaculum release was done in 8 knees.

CONCLUSIONS

Vertical patella test correlates with towel clip test, is easy to perform and saves time. The limitation of our study was small sample size.

Shape Analysis of the Patellar Bone Surface and Cutting Plane for Knee Replacement Surgery

Geometry of the patella (kneecap) remains poorly understood yet is highly relevant to performing the correct patellar cut to reduce pain and to improve function and satisfaction after knee replacement surgery. Although studies routinely refer to “parallel to the anterior surface” and “the patellar horizon,” a quantitative definition of these is lacking and significant variability exists between observers for this irregularly-shaped bone. A 2D-3D shape analysis technique was developed to determine the optimal device configuration for contacting the patellar surface. Axial and sagittal pseudo-X-rays were created from 18 computed tomography (CT) scans of cadaveric knees. Four expert surgeons reviewed three repetitions of the X-rays in randomized order, marking their desired cut plane and their estimate of the anterior surface. These 2D results were related back to the 3D model to create the desired plane. There was considerable variability in perceptions, with intra- and intersurgeon repeatability (standard deviations) ranging from 1.3° to 2.4°. The best configuration of contact points to achieve the desired cutting plane was three pegs centred on the patellar surface, two superior and one inferior, forming a 16 mm equilateral triangle. This configuration achieved predicted cut planes within 1° of the surgeon ranges on all 18 patellae. Implementing this, as was done in a subsequent prototype surgical device, should help improve the success and satisfaction of knee replacement surgery.

Influence of Total Knee Arthroplasty on Patellar Kinematics and Patellofemoral Pressure

BACKGROUND

Patellofemoral complications are one of the main problems after total knee arthroplasty (TKA). The design of the TKA component may affect the patellar biomechanics, which may be associated with this postoperative complication. The purpose of this study was to assess the influence of TKA and prosthesis designs on the patellar kinematics and patellofemoral pressure.

METHODS

Using fresh-frozen cadavers, we measured the patellofemoral pressure, patella offset, and patella tilt in the following 4 conditions: normal knee (patella replacement only), cruciate-retaining TKA, condylar-stabilizing TKA, and posterior-stabilized TKA.

RESULTS

The patellofemoral pressure increased significantly after the cruciate-retaining TKA and condylar-stabilizing TKA compared with the normal knee. The patella offset in the normal knee decreased with increasing knee flexion angles, while the patella offset in the TKA knees did not change significantly through the full range of motion. The amount of lateral patella tilt in the normal knee was significantly larger than the TKA knees in the full range of motion.

CONCLUSION

Although the femoral components are designed to reproduce an anatomical patellar tracking, the physiological patellar kinematics were not observed. Relatively high patellofemoral pressure and kinematic change after TKA may be associated with postoperative complications such as the anterior knee pain.

Influence of tibial rotation in total knee arthroplasty on knee kinematics and retropatellar pressure: an in vitro study

PURPOSE

Although continuous improvements have been made, there is still a considerable amount of unsatisfied patients after total knee arthroplasty (TKA). A main reason for this high percentage is anterior knee pain, which is supposed to be provoked by post-operative increased retropatellar peak pressure. Since rotational malalignment of the implant is believed to contribute to post-operative pain, the aim of this study was to examine the influence of tibial component rotation on knee kinematics and retropatellar pressure.

METHODS

Eight fresh-frozen knee specimens were tested in a weight-bearing knee rig after fixed-bearing TKA under a loaded squat from 20° to 120° of flexion. To examine tibial components with different rotations, special inlays with 3° internal rotation and 3° external rotation were produced and retropatellar pressure distribution was measured with a pressure-sensitive film. The kinematics of the patella and the femorotibial joint were recorded with an ultrasonic-based motion analysis system.

RESULTS

Retropatellar peak pressure decreased significantly from 3° internal rotation to neutral position and 3° external rotation of the tibial component (8.5 ± 2.3 vs. 8.2 ± 2.4 vs. 7.8 ± 2.5 MPa). Regarding knee kinematics femorotibial rotation and anterior-posterior translation, patella rotation and tilt were altered significantly, but relative changes remained minimal.

CONCLUSION

Changing tibial rotation revealed a high in vitro influence on retropatellar peak pressure. We recommend the rotational alignment of the tibial component to the medial third of the tibial tuberosity or even more externally beyond that point to avoid anterior knee pain after TKA.

The Effect of Patellar Thickness on Intraoperative Knee Flexion and Patellar Tracking in Patients With Arthrofibrosis Undergoing Total Knee Arthroplasty

BACKGROUND

We evaluated the intraoperative effect of patellar thickness on intraoperative passive knee flexion and patellar tracking during total knee arthroplasty (TKA) in patients with preoperative arthrofibrosis and compared them to patients with normal preoperative range of motion (ROM) documented in a prior study.

METHODS

Routine posterior cruciate ligament-retaining TKA was performed in a total of 34 knees, 23 with normal ROM and 11 with arthrofibrosis, defined as ≤100° of passive knee flexion against gravity under anesthesia. Once clinical balance and congruent patellar tracking were established, custom trial patellar components thicker than the standard trial by 2-mm increments (2-8 mm) were sequentially placed and trialed. Passive flexion against gravity was recorded using digital photograph goniometry. Gross mechanics of patellofemoral tracking were visually assessed.

RESULTS

On average, passive knee flexion decreased 2° for every 2-mm increment of patellar thickness (P < .0001), which was similar to patients with normal preoperative ROM. In addition, increased patellar thickness had no gross effect on patellar subluxation and tilt in patients with arthrofibrosis as well as those with normal ROM.

CONCLUSIONS

Patellar thickness had a modest effect on intraoperative passive flexion and no effect on patellar tracking in patients with arthrofibrosis undergoing TKA. There was no marked difference in intraoperative flexion and patellar tracking between patients with arthrofibrosis and patients with normal preoperative ROM.

Influence of the Rotational Alignment of the Femoral and Patellar Components on Patellar Tilt in Total Knee Arthroplasty

Purpose

The purpose of this study was to analyze the influence of rotational alignment of the femoral and patellar components on patellar tilt after total knee arthroplasty (TKA).

Materials and Methods

A total of 56 patients (76 knees) who underwent TKA using Advance Medial Pivot Knee system between May 2009 and April 2011 and were available for minimum 1-year follow-up were enrolled in this study. Whiteside's line and the transepicondylar line were used to determine the rotational alignment of the femoral component. Patella cut was aimed to be parallel to the anterior patellar cortex during surgery. Radiographic evaluation was performed using plain axial radiographs. The rotational alignment of the femoral component was measured as the angle between the anterior condylar axis and the surgical transepicondylar axis. The patellar resection angle was measured between the patellar resection axis and the anterior cortical line of the patella. Patellar tilt was evaluated to investigate the correlation with the rotation of the femoral component and patellar resection angle.

Results

The mean rotation of the femoral component was 0.42°±3.18° of internal rotation. The mean patellar resection angle was 1.82°±3.44°, indicating medial overresection. The mean patellar tilt was 6.12°±4.31° of lateral tilt. The rotational angle of the femoral component showed a negative correlation with patellar tilt in the linear regression analysis (p=0.749), but the patellar resection angle showed a positive correlation with patellar tilt (p<0.001).

Conclusions

Accurate patellar resection is recommended for proper patellar tracking in TKA.

Deep-dished highly congruent tibial insert in CR-TKA does not prevent patellar tendon angle increase and patellar anterior translation

PURPOSE

Starting from the hypothesis that a deep-dished highly congruent tibial insert in cruciate-retaining total knee arthroplasty would prevent the increase in patellar tendon angle and anterior patellar translation by reducing the paradoxical anterior femoral translation, the main purpose of the present study was to investigate the effect of this prosthesis design, and secondary to assess the clinical outcomes at 6-month follow-up.

METHODS

Twenty patients treated with cruciate-retaining total knee arthroplasty with navigation technique were enrolled and prospectively followed up at 6 months. The median value of age was 71 years (57-83). Before and after surgery, the following parameters were calculated: patellar tendon angle, anterior-posterior and medio-lateral patellar translation, patellar height and range of motion. All patients were assessed with the SF-36 Physical Functioning and the Knee injury and Osteoarthritis Outcome Score ADL scores.

RESULTS

Patellar tendon angle and anterior patellar translation significantly increased in post-operative conditions (p < 0.0001); a statistically significant medial patellar translation was found (p < 0.0001), while patellar height did not show any difference between pre- and post-operative conditions (n.s). A significant correlation was found between patellar tendon angle and anterior patellar translation and the clinical scores (p < 0.0417). There was a significant post-operative decrease (p < 0.0033) in the range of motion.

CONCLUSIONS

The present study failed to demonstrate that deep-dished highly congruent tibial insert prevents the anterior translation of the patella in cruciate-retaining total knee arthroplasty, thus causing inferior clinical scores. It provided useful information about the biomechanical role of the patella in total knee arthroplasty, allowing to choose the most appropriate surgical approach.

LEVEL OF EVIDENCE

Case series, Level IV.

Tibio-femoral and patello-femoral joint kinematics during navigated total knee arthroplasty with patellar resurfacing

PURPOSE

In total knee arthroplasty, surgical navigation systems provide tibio-femoral joint (TFJ) tracking for relevant bone preparation, disregarding the patello-femoral joint (PFJ). Therefore, the important intra-operative assessment of the effect of component positioning, including the patella, on the kinematics of these two joints is not available. The objective of this study is to explore in vivo whether accurate tracking of the patella can result in a more physiological TFJ and PFJ kinematics during surgery.

METHODS

Ten patients underwent navigated knee replacement with patellar resurfacing. A secondary system was used to track patellar motion and PFJ kinematics using a special tracker. Patellar resection plane position and orientation were recorded using an instrumented probe. During all surgical steps, PFJ kinematics was measured in addition to TFJ kinematics.

RESULTS

Abnormal PFJ motion patterns were observed pre-operatively at the impaired knee. Patellar resection plane orientation on sagittal and transverse planes of 3.9° ± 9.0° and 0.4° ± 4.1° was found. A good restoration of both TFJ and PFJ kinematics was observed in all replaced knees after resurfacing, in particular the rotations in the three anatomical planes and medio-lateral patellar translation.

CONCLUSIONS

Patella tracking results in nearly physiological TFJ and PFJ kinematics in navigated knee arthroplasty with resurfacing. The intra-operative availability also of PFJ kinematics can support the positioning not only of the patellar component in case of resurfacing, but also of femoral and tibial components.

The effect of femoral component design on patellar tracking in total knee arthroplasty: Genesis II prosthesis versus Vanguard prosthesis

INTRODUCTION

The Genesis II knee system incorporates 3° of external rotation into the femoral component and the femoral component is implanted in neutral rotation to the femur. The purpose of this study was to compare patellar tracking of the Genesis II knee system with that of the Vanguard knee system, in which the femoral component is routinely implanted in a 3° externally rotated position to the posterior condylar axis (PCA) of the femur.

MATERIALS AND METHODS

One hundred consecutive knees scheduled to undergo total knee arthroplasty (TKA) were enrolled. Fifty knees underwent TKA with the posterior-stabilized (PS) Genesis II prosthesis and 50 knees underwent TKA with the PS Vanguard prosthesis. Rotation of the femoral component was calculated by measuring the acute angle between the transepicondylar axis (TEA) and the PCA on axial computed tomography (CT) images. The postoperative patellar tilt and displacement were compared between groups. The range of motion and Knee Society scores were also compared.

RESULTS

Forty-eight knees in each group were followed up for 2 years. There was no difference in the angle between the PCA and the TEA on postoperative CT scans between the two designs. There was also no difference in patellar tracking between groups. Both the Genesis II and Vanguard knee systems showed good clinical results at 2 years postoperatively.

CONCLUSION

The patellar tracking of the Genesis II prosthesis was comparable to that of the Vanguard prosthesis.

LEVEL OF EVIDENCE

Prospective cohort study, Level II.

Kinematic differences between gender specific and traditional knee implants

In the ongoing debate about gender-specific (GS) vs. traditional knee implants, there is limited information about patella-specific outcomes. GS femoral component features should provide better patellar tracking, but techniques have not existed previously to test this accurately. Using novel computed tomography and radiography imaging protocols, 15 GS knees were compared to 10 traditional knees, for the 6 degrees of freedom of the patellofemoral and tibiofemoral joints throughout the range of motion, plus other geometric measures and quality of life (QOL). Significant differences were found for patellar medial/lateral shift, where the patella was shifted more laterally for the GS femoral component. Neither group demonstrated patellar maltracking. There were no other significant differences in this well-functioning group.

Robot-Assisted Navigation versus Computer-Assisted Navigation in Primary Total Knee Arthroplasty: Efficiency and Accuracy

Background. Since the introduction of robot-assisted navigation in primary total knee arthroplasty (TKA), there has been little research conducted examining the efficiency and accuracy of the system compared to computer-assisted navigation systems. Objective. To compare the efficiency and accuracy of Praxim robot-assisted navigation (RAN) and Stryker computer-assisted navigation (CAN) in primary TKA. Methods. This was a retrospective study consisting of 52 patients who underwent primary TKA utilizing RAN and 29 patients utilizing CAN. The primary outcome measure was navigation time. Secondary outcome measures included intraoperative final mechanical axis alignment, intraoperative robot-assisted bone cut accuracy, tourniquet time, and hospitalization length. Results. RAN navigation times were, on average, 9.0 minutes shorter compared to CAN after adjustment. The average absolute intraoperative malalignment was 0.5° less in the RAN procedures compared to the CAN procedures after adjustment. Patients in the RAN group tended to be discharged 0.6 days earlier compared to patients in the CAN group after adjustment. Conclusions. Among patients undergoing TKA, there was decreased navigation time, decreased final malalignment, and decreased hospitalization length associated with the use of RAN when compared to CAN independent of age, BMI, and pre-replacement alignment.

Isocentric 3-dimensional C-arm imaging of component alignments in total knee arthroplasty with potential intraoperative and postoperative applications

An intraoperative imaging tool for total knee arthroplasty could help avoid poor clinical outcomes related to malalignment. We investigated the feasibility of using isocentric (ISO-C) fluoroscopic imaging for this purpose. Three-dimensional ISO-C and computed tomographic (CT) images were acquired from 6 cadaveric specimens implanted with standard knee arthroplasty components and analyzed to determine rotational alignments. In comparison with standard CT measures, the ISO-C-based measures had overall accuracies (determined as root mean square error) of 0.8° and 1.3° and corresponding SDs of 1.3° and 1.4° for the femoral and tibial components, respectively. With ISO-C imaging, it is possible to measure rotational alignment in knee arthroplasty with accuracy and repeatability comparable with CT. Isocentric imaging has strong potential as an intraoperative tool to accurately align arthroplasty components.

Patellar tracking after total knee arthroplasty performed without lateral release

There is limited clinical data on patellar maltracking in patients who have undergone total knee arthroplasty (TKA) without lateral release. We performed a retrospective review of 191 consecutive TKAs performed by one surgeon through the subvastus approach without lateral release from 2007 to 2008. Radiographic measurements were made using the preoperative and postoperative 2 years radiographs. Multivariate logistic regression analysis was performed to determine the risk factors for patellar maltracking after TKA performed without lateral release. TKA resulted in increases in the patellar tilt and displacement (P<0.05). The presence of preoperative patellar tilt and displacement were predictive of postoperative patellar tilt and displacement in patients who underwent TKA through the subvastus approach without lateral release (P<0.05).

The effect of distal femur bony morphology on in vivo knee translational and rotational kinematics

PURPOSE

Tibio-femoral kinematics are clearly influenced by the bony morphology of the femur. Previous morphological studies have not directly evaluated relationships between morphology and knee kinematics. Therefore, the purpose of this study was to examine the relationship between distal femur bony morphology and in vivo knee kinematics during running. It was hypothesized that the posterior offset of the transcondylar axis would be related to the magnitude of anterior/posterior tibio-femoral translation and that the rotational angle of the transcondylar axis would be related to the magnitude of internal/external knee rotation.

METHODS

Seventeen contralateral (uninjured) knees of ACL-reconstructed patients were used. Distal femoral geometry was analyzed from 3D-CT data by determining the anteroposterior location (condyle offset ratio--COR) and rotational angle (condylar twist angle--CTA) of the femoral transcondylar axis. Six degree-of-freedom knee kinematics were obtained during running using a dynamic stereo radiograph system. Knee kinematics were correlated with the femoral morphologic measures (COR and CTA) to investigate the influence of femoral geometry on dynamic knee function.

RESULTS

Significant correlations were identified between distal femur morphology and knee kinematics. Anterior tibial translation was positively correlated with the condyle offset ratio (R(2) = 0.41, P < 0.01). Internal tibial rotation was positively correlated with the condylar twist angle (R(2) = 0.48, P < 0.01).

CONCLUSIONS

Correlations between knee kinematics and morphologic measures describing the position and orientation of the femoral transcondylar axis suggest that these specific measures are valuable for characterizing the influence of femur shape on dynamic knee function.

LEVEL OF EVIDENCE

III.

Identifying alignment parameters affecting implanted patellofemoral mechanics

Complications of the patellofemoral (PF) joint remain a common cause for revision of total knee replacements. PF complications, such as patellar maltracking, subluxation, and implant failure, have been linked to femoral and patellar component alignment. In this study, a dynamic finite element model of an implanted PF joint was applied in conjunction with a probabilistic simulation to establish relationships between alignment parameters and PF kinematics, contact mechanics, and internal stresses. Both traditional sensitivity analysis and a coupled probabilistic and principal component analysis approach were applied to characterize relationships between implant alignment and resulting joint mechanics. Critical alignment parameters, and combinations of parameters, affecting PF mechanics were identified for three patellar designs (dome, modified dome, and anatomic). Femoral internal-external (I-E) alignment was identified as a critical alignment factor for all component designs, influencing medial-lateral contact force and anterior-posterior translation. The anatomic design was sensitive to patellar flexion-extension (F-E) alignment, while the dome, as expected, was less influenced by rotational alignment, and more by translational position. The modified dome was sensitive to a combination of superior-inferior, F-E, and I-E alignments. Understanding the relationships and design-specific dependencies between alignment parameters can aid preoperative planning, and help focus instrumentation design on those alignment parameters of primary concern.

Computer-assisted patellar resection system: development and insights

Incorrect resection of the patella during total knee arthroplasty (TKA) can lead to anterior knee pain (AKP), patellar maltracking, patellofemoral impingement, patellar fracture, component loosening, and reduced range of motion. Computer-assisted surgery (CAS) systems for the tibia and femur improve cut accuracy, but no CAS system is available for patellar resection. We developed a system that included an optoelectronic localizer, marker arrays on the patella and instruments, and navigation software. Three users performed resections on artificial patellae mounted in a simulated surgical setup using five techniques (two CAS, three conventional), each repeated at least three times in randomized order. Computer-assisted patellar resection produced better or equal cut symmetry compared to conventional techniques, particularly superoinferiorly. Using CAS with a sawguide produced better results than using CAS freehand with an oscillating saw. This study showed the feasibility of computer-assisted patellar resection, which could lead to reduced pain and complications after TKA. The feedback provided could also make patellar CAS a valuable training tool.

The influence of patellar dislocation on the femoro-tibial loading during total knee arthroplasty

PURPOSE

Balancing the gap is essential in total knee arthroplasty (TKA). The purpose of this study was to quantify the influence of patellar position on femoro-tibial joint load in TKA. We hypothesized that resetting of the patella increased medial joint load and decreased lateral joint load.

METHODS

Our original tensor system was used during posterior-stabilized (PS) and cruciate-retaining (CR) total knee arthroplasty (TKA) using medial para-patellar approach (MPP) or sub-vastus approach (SV).

RESULTS

In PS-TKA, by resetting the patella, the ratios between medial and lateral compartments were not changed in both extension and flexion position using MPP and were significantly changed in flexion position using SV. In CR-TKA, by resetting the patella, the load of the lateral component decreased and the ratios between medial and lateral compartments were changed significantly in both extension and flexion position using SV.

CONCLUSION

It is important to be aware that, when performing CR-KA, the load of the lateral compartment will decrease by resetting the patella using SV.

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

PURPOSE

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).

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Patellofemoral kinematics in mobile-bearing and fixed-bearing posterior stabilised total knee replacements: a cadaveric study

PURPOSE

The aim was to compare the patellar kinematics in the normal knee, fixed-bearing (FB) and mobile-bearing total knee replacement (MB-TKR). The hypothesis that a mobile-bearing TKR has a more natural patellar movement was tested.

METHODS

Computer navigation was used to track the patella in nine whole lower extremities in the natural knee and in the same knee with a posterior stabilised FB-TKR and a posterior stabilised MB-TKR from 0° to 90° flexion. The form and position of the trochlea in the natural knee and the patellar groove of the TKR femoral component was also analysed.

RESULTS

There were no differences between the FB and MB-TKRs. But the patella in the TKRs at flexion angles of more than 50° had a more medial tilt compared to the natural knee. The patella of the natural knee tended to rotate externally with flexion, this was not seen in both TKR types. There were no significant differences in absolute mediolateral translation nor in translation relative to the patellar groove. During flexion, the patella lost contact with its groove earlier in the TKRs. The radius of the patellar groove of the femoral component was larger. The groove extended more superiorly and less far posteriorly, it was also positioned further laterally compared to the natural knee.

CONCLUSIONS

There are subtle kinematic differences in patellar tracking between the natural knee and a TKR presumably due to differences in the shape and position of the patellar groove. There are no kinematic differences in patellar movement between the FB- and MB-TKR.

Changes in patellar alignment after total knee arthroplasty

Although the results of total knee arthroplasty continue to improve, problems related to the patellofemoral joint remain significant. This study examined the factors affecting patellar alignment after total knee arthroplasty and subsequent changes in 56 knees during a postoperative period of 5.3 years. None of the knees examined displayed any clinical complications of the patellofemoral joint; no revision surgeries were necessary, with acceptable patellar alignment on average. The patellar resection angle had a strong influence on patellar alignment. Thinning of the patellar remnant on the medial side can increase postoperative lateral tilt, which leads to a need for lateral retinacular release. Although the changes in patellar alignment were minimal, the tendency that postoperative varus alignment resulted in patellar lateral tilt was observed. As postoperative femorotibial misalignment can lead to patellofemoral problems after total knee arthroplasty, surgeons need to pay scrupulous attention to femorotibial alignment and proper patellar preparation to decrease patellofemoral complications.

The effect of femoral component rotation on the extensor retinaculum of the knee

Malrotation of the femoral component may cause patellofemoral complications after total knee replacement (TKR). We hypothesized that femoral component malrotation would cause excessive lengthening of the retinacula. Retinacular length changes were measured by threading fine sutures along them and attaching these to the patella and to displacement transducers. The knee post-TKR was flexed-extended while the quadriceps were tensed, then the measurements repeated after rotating the femoral component 5 degrees internally and then 5 degrees externally. Internal rotation shortened the medial patellofemoral ligament (MPFL) significantly from 100 degrees to 0 degrees extension. External rotation lengthened the MPFL significantly from 90 degrees to 0 degrees extension. The transverse fibers of the lateral retinaculum showed no significant differences. The MPFL attaches directly from bone to bone, so it was lengthened directly by movement of the trochlea and patella, whereas the deep transverse fibers of the lateral retinaculum attach to the mobile iliotibial tract, so they were not lengthened directly.

Biomechanical consequences of patellar component medialization in total knee arthroplasty

The optimal amount of patellar component medialization in knee arthroplasty is unknown. We measured the impact, on patellofemoral kinematics and contact force distribution, of 0.0-, 2.5-, and 5.0-mm patellar component medialization in 7 cadaveric specimens implanted with knee arthroplasty components. The knees were flexed dynamically in a weight-bearing rig. Medialization led to lateral shift of the patellar bone, slight medial shift of the patellar component in the femoral groove, lateral tilt of the patella, reduced patellofemoral contact force in later flexion, and lateral shift of the center of pressure in early flexion. Effects on shift and tilt were proportional to the amount of medialization. As a result of this investigation, we recommend medializing the patellar component slightly-on the order of 2.5 mm.

The effect of patellar thickness changes on patellar tilt in total knee arthroplasty

We hypothesized that changes in patellar thickness following patellar resurfacing affect patellar tilt in total knee arthroplasty (TKA) patients. The study enrolled 272 TKAs and categorized them into four groups according to change in patellar thickness: (A) thinner by 1 mm or more, (B) equal or thinner by less than 1 mm, (C) thicker by 1 mm or less, and (D) thicker by more than 1 mm. Patellar tilt angle was measured postoperatively using Merchant radiography. There were no significant differences in postoperative patellar tilt among groups A, B, and C (n.s). However, the postoperative patellar tilting angle of group D was significantly higher than that of all other groups (P < 0.05). Postoperative patellar tilt increased when the postoperative patella was >1 mm thicker than the preoperative patella.

Finding and defining the ideal patellar resection plane in total knee arthroplasty

Asymmetric resection of the patella during total knee arthroplasty (TKA) correlates with anterior knee pain, bony impingement and patellar maltracking. Despite this, there is no consensus regarding the desired landmarks; the cut is often done freehand; and there has been no quantitative comparison of proposed resection planes. The objectives of this study were to: determine the intra- and inter-surgeon repeatability of two radiographic resection definitions (medial-divot, MD, and medial-lateral extents, MLE); calculate two additional definitions from the radiographic patellar circumferences (parallel to the anterior surface, ANT, and perpendicular to the anteroposterior tangent points, PERP); compare the clinical resection line to the previous four definitions before and after introducing the MD method clinically; and identify distinguishing features of patellae with better vs. worse resection angles. We hypothesized that the MD method would improve repeatability both radiographically and clinically, that the different radiographic definitions would produce comparable angles, and that we could identify distinguishing features. For the radiographic study, three surgeons drew lines on 40 preoperative X-rays plus 9 interspersed repetitions of 3 of these X-rays. For the clinical study, we compared the patellar resection angle for 20 patients immediately before and after implementing the new method. Given that the clinical goal is to have equal distances from the resection surface to the anterior surface, we compared all results to the ANT definition as the theoretically ideal definition. Confirming the first hypothesis, intra-surgeon repeatability (10 repetitions of 3 X-rays) and inter-surgeon repeatability (3 surgeons x 40 X-rays) were both significantly better using the new MD method compared to the MLE method (p<0.001). Contrary to the second hypothesis, clinical use of the MD method did not improve resection symmetry. Contrary to the third hypothesis, the PERP definition was significantly different from the other three definitions. In agreement with the fourth hypothesis, female patellae and more deformed patella had significantly greater asymmetry (p<0.001). Given the inherent variability shown in drawing the 'patellar horizon', we encourage researchers to draw the line several times and average the results when comparing tilt or the resection angle to this horizon. Based on the distinguishing characteristics of asymmetrically resurfaced patellae in our series, we recommend that clinicians be particularly careful when resecting laterally deformed patellae and the patellae of female patients.