Increased in vivo patellofemoral loading after total knee arthroplasty in resurfaced patellae

Preoperative patellar bone marrow lesions with full thickness cartilage defects correlate with residual anterior knee pain in total knee arthroplasty without patellar resurfacing

PURPOSE

Residual anterior knee pain is one of the most common problems after total knee arthroplasty (TKA). However, the contributing factors affecting postoperative anterior knee pain (AKP) remain poorly understood. This study aimed to evaluate the effect of preoperative patellar bone marrow lesions (BMLs) and patellar cartilage defects on postoperative AKP after patellar non-resurfacing TKA.

METHODS

This retrospective study included 336 patients who underwent unilateral TKA without patella resurfacing. All patients underwent preoperative magnetic resonance imaging (MRI) to assess the presence of BMLs and the degree of cartilage defects in the patella. Patients were categorized into four groups according to the presence of BMLs (with or without BMLs) and the degree of cartilage defects (with or without full thickness cartilage defects). The Kujala Anterior Knee Pain Scale (AKPS) and the Hospital for Special Surgery Knee Rating Scale (HSS) scores at 2 years after TKA were compared among the groups.

RESULTS

Preoperative BMLs in the patella were found in 132 (39.3%) of 336 cases. Among the four groups, the group with both BMLs and full-thickness cartilage defects demonstrated significantly lower AKPS compared to the other groups at 2 years after TKA (p < 0.01), but no significant difference was shown in the HSS scores, between these groups. There were no significant differences in either AKPS or HSS scores among the other three patient groups.

CONCLUSIONS

The presence of preoperative BMLs with full-thickness cartilage defects in the patella was associated with worse postoperative AKP after TKA without patella resurfacing. Patella resurfacing should be considered in this patient group to minimize the risk of developing residual AKP after TKA.

LEVEL OF EVIDENCE

III.

Alignment changes after open-wedge high tibial osteotomy result in offloading in the patellofemoral joint: a SPECT/CT analysis

PURPOSE

The patellofemoral (PF) joint may be adversely affected by medial open-wedge high tibial osteotomy (OWHTO). This study aimed to evaluate the PF compartmental changes using combined single-photon emission computed tomography (SPECT) and conventional computed tomography (CT) after OWHTO to provide clinical guidance regarding the PF joint pressure and force.

METHODS

Patients with medial osteoarthritis and varus malalignment > 5° were treated using OWHTO. Patients with a minimum 2-year follow-up were included in the study. The patellar positions were evaluated based on the radiographic parameters. The changes in chondral lesions during second-look arthroscopic examination were evaluated, and the PF joint arthritis grade was recorded on patellar Merchant radiographs using Kellgren-Lawrence classification. The PF compartmental changes according to SPECT/CT analysis after OWHTO were evaluated in all patients. The scintigraphic uptake was graded on four scales. Patients were divided into improved and unimproved groups according to the PF compartmental grade using the SPECT/CT uptake grading system.

RESULTS

At a mean follow-up period of 47.0 months (range 25-74 months), the mean mechanical femorotibial angle changed significantly from varus 6.3° (range 5-12°) to valgus 2.6° (range 0-8°); p < 0.001) postoperatively. The radiological parameters presenting patellar positions, including the tibial slope, patellar convergence angle, and lateral tilt angle, did not change significantly between the preoperative values and the 2-year follow-up values. The mean patellar height significantly decreased (0.07 ± 0.14, p = 0.001 according to the Blackburn-Peel index and 0.32 ± 0.23, p < 0.001 using the modified Insall-Salvati ratio). The average tibial tubercle to trochlear groove (TT-TG) distance significantly decreased from 14.1 to 12.2 mm (p < 0.001). The Q angle also significantly decreased from 9.8^o to 7.7^o (p = 0.008). Chondral lesions of the patella and trochlear groove revealed significant deterioration; at 2 years after OWHTO, the arthritic grades of the PF joints worsened significantly, as determined by radiography (p = 0.007). Scintigraphic uptake in the PF joint was significantly lower (from 2 to 1) at 2 years postoperatively compared to that immediately after the index operation (p < 0.001). Only 4 of 56 (7.1%) patients showed increased uptake. Comparison between the improved and unimproved groups according to scintigraphic uptake changes revealed that the changes in the cartilage status on the patellar undersurface and TT-TG distance were the most significant predictive factors of increased scintigraphic uptake in the PF joint after OWHTO.

CONCLUSION

Alignment correction by OWHTO result in PF compartment offloading and should be considered when identifying the surgical indications for OWHTO.

LEVEL OF EVIDENCE

Therapeutic, Level IV.

Under-correction of preoperative varus alignment does not lead to a difference in in-vivo bone loading in 3D-SPECT/CT compared to neutral alignment

BACKGROUND

The aim was to investigate the correlation of bone tracer uptake (BTU) in SPECT/CT and changes in coronal knee alignment after total knee arthroplasty (TKA). We questioned if undercorrection of preoperative varus alignment leads to a difference in BTU compared to neutral alignment.

METHODS

Consecutive 66 patients who received SPECT/CT before and after TKA were retrospectively included. Adjusted mechanical alignment was the alignment target. The alignment of the knee was measured on 3D-CT by selecting standardized landmarks. Maximum (mean ± SD) and relative BTU (ratio to the reference) were recorded using a previously validated localization scheme (p < 0.05).

RESULTS

In the native group, 20 knees were aligned (30.3%) in valgus (HKA > 181.5°), 12 (18.2%) in neutral (178.5°-181.5°) and 34 (51.5%) in varus (HKA < 178°). Overall TKA changed the alignment towards neutral. 48.5% remained in the same groups, whereas 50% of native valgus and 33% of varus knees changed to neutral after TKA. In native varus alignment mean BTU was significantly higher in some medial tibial and femoral regions (fem1ia (p = 0.010), fem1ip (p = 0.002), tib1a.mid (p = 0.005), tib1a.tray (p = 0.000), tib1p.tray (p = 0.000)); in native valgus alignment mean BTU was higher in the corresponding lateral tibial and femoral regions (fem2ip (p = 0.001), tib2a.tray (p = 0.011), tib2p.tray (p = 0.002)). After TKA, a significant decrease in femoral and tibial BTU (femoral preoperative BTU 1.64 +/-0.69; femoral postoperative BTU 0.95 +/-0.42; p = 0.000// tibial preoperative BTU 1.65 +/- 0.93; tibial postoperative BTU 1.16 +/- 0.48; p = 0.000) and an increase in patellar BTU was observed (p = 0.025). Native varus alignment correlated with a higher medial BTU decrease medially. Undercorrection of preoperative varus alignment showed no higher BTU after TKA.

CONCLUSION

Preoperative varus alignment correlated with a higher decrease in BTU in specific femoral and tibial medial regions. Preoperative valgus alignment correlated with a higher decrease in the corresponding lateral regions. Undercorrection of preoperative varus alignment did not lead to higher bone loading reflected by BTU after TKA.

The patellofemoral morphology and the normal predicted value of tibial tuberosity-trochlear groove distance in the Chinese population

Background

Our objective was to obtain normal patellofemoral measurements to analyse sex and individual differences. In addition, the absolute values and indices of tibial tuberosity-trochlear groove (TT-TG) distances are still controversial in clinical application. A better method to enable precise prediction is still needed.

Methods

Seventy-eight knees of 78 participants without knee pathologies were included in this cross-sectional study. A CT scan was conducted for all participants and three-dimensional knee models were constructed using Mimics and SolidWorks software. We measured and analysed 19 parameters including the TT-TG distance and dimensions and shapes of the patella, femur, tibia, and trochlea. LASSO regression was used to predict the normal TT-TG distances.

Results

The dimensional parameters, TT-TG distance, and femoral aspect ratio of the men were significantly larger than those of women (all p values < 0.05). However, after controlling for the bias from age, height, and weight, there were no significant differences in TT-TG distances and anterior-posterior dimensions between the sexes (all p values > 0.05). The Pearson correlation coefficients between the anterior femoral offset and other indexes were consistently below 0.3, indicating no relationship or a weak relationship. Similar results were observed for the sulcus angle and the Wiberg index. Using LASSO regression, we obtained four parameters to predict the TT-TG distance (R² = 0.5612, p < 0.01) to achieve the optimal accuracy and convenience.

Conclusions

Normative data of patellofemoral morphology were provided for the Chinese population. The anterior-posterior dimensions of the women were thicker than those of men for the same medial-lateral dimensions. More attention should be paid to not only sex differences but also individual differences, especially the anterior condyle and trochlea. In addition, this study provided a new method to predict TT-TG distances accurately.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04454-8.

The Patellar Resurfacing in Total Knee Prosthesis: Indications for Bone Stock and Patellar Morphology

The patellar resurfacing is still a controversial and unresolved problem. The choice to use the patellar resurfacing in the total knee prosthesis (TKP) is decided by the surgeon's experience; he analyzes the thickness, the shape, consumption of the surface and he chooses the use of patellar resurfacing or to limit itself to cheiloplasty, denervation, or often to the release of the lateral wing ligament. He also assesses the metabolic state of the bone linked to Osteoporosis and the potential fragility of the joint and kneecap in particular. Bone loss after total knee arthroplasty (TKP) may lead to periprosthetic fractures that are associated with significant costs (morbidity, economic, etc.) and pose a challenge to operative fixation. The literature doesn't express a definitive judgment on the two options, since the results can be overlapped on average. Each option has advantages and disadvantages to be considered in the overall balance of the patellar operation. In reality, however, this technical choice requires more consolidated decision-making criteria so as to minimize the incidence of post-surgical femoral-patellar pain syndrome, the second cause of failure, which frequently leads to revision of the implant. The balance between experience and evidence can be a compromise in the choice of surgery. The experience documented in the literature must identify the parameters capable of constructing an algorithm aimed not only at the secondary resurfacing rate, but at the overall clinical evaluation. This has implications also for the rehabilitation of these patients after surgery.

Modern total knee arthroplasty designs do not reliably replicate anterior femoral morphology

PURPOSE

Biomechanical studies suggest that PF tracking is not reliably restored to physiological values in TKA despite surgical technique optimization. A clinical observation is that current TKA designs may not replicate anterior femoral offset. The aim was to examine the intraoperative resection thicknesses of the anterior femoral condyles during TKA and correlate these findings relative to modern prostheses.

METHODS

This was a retrospective analysis of 199 patients who underwent 233 TKAs using a single implant design with measured anterior femoral condylar resection thicknesses. The aim was to restore posterior condylar offset whilst minimizing overstuffing of the anterior compartment of the knee by choosing the smallest prosthesis to allow for the maximal anterior resection as close to the cortex without inducing notching. Prosthetic measurements from 7 commonly used TKAs were collected by analysis of 3D models of median sized explants.

RESULTS

An average of 7.9 mm (SD 2.5 mm, range 2-16.5 mm) and 11.5 mm (SD 2.5 mm, range 2-21 mm) was resected from the medial and lateral aspects of the anterior femur, respectively. The average anterior flange thickness for the prosthesis data set was 6.6 mm (SD 0.6 mm, range 6.1-7.9 mm) medially and 7.6 mm (SD 0.7 mm, range 6.8-9.0 mm) laterally. Comparison across patients who received the median prosthesis size of 5 (SD 1.3, range 2-8) was inadequately restored by 1.4 mm (p < 0.00001) medially and 3.4 mm (p < 0.00001) laterally.

CONCLUSION

Host anatomy is not routinely restored during TKA. The surgical teaching to aim for an anterior femoral osteotomy close to the anterior cortex will result in understuffing of the PFJ and based on current prosthesis designs, the risk of overstuffing is not as significant as once believed. Future prostheses and surgical techniques should aim to restore not only posterior femoral but also anterior femoral offset.

LEVEL OF EVIDENCE

IV, Case series.

Increased focal bone tracer uptake at the popliteus muscle origin in primary TKA compared with revision TKA

OBJECTIVE

The purpose of the study was to investigate if the TKA design (cruciate retaining (CR), posterior stabilized (PS), revision prostheses) had an influence on the bone tracer uptake (BTU) pattern at the origin of the popliteus muscle.

MATERIALS AND METHODS

A total of 92 knees (male:female = 46:46) which had undergone prior TKA were included in this retrospective study, comprising the following 3 groups: (i) CR primary TKA (n = 45); (ii) PS primary TKA (n = 24); (iii) revision TKA (n = 23). All patients received a SPECT/CT after TKA surgery. SPECT/CT images were reviewed for the presence of BTU in the lateral femoral condyle (origin of the popliteus muscle) by two observers using Syngo.via software (Siemens Healthcare, Erlangen, Germany). The observers recorded the BTU pattern qualitatively in the lateral femoral condyle as either (i) absent; (ii) present and diffuse; and (iii) present and focal in the region of the popliteus muscle origin.

RESULTS

In patients with a CR and PS design, focal increased BTU at the origin of the popliteus muscle was found in 80.0% and 83.3% respectively. Diffuse BTU was the predominant finding in patients with revision TKA (60.9%). The patterns of BTU did not show significant differences between the CR and the PS design. However, patterns of BTU differed significantly between primary TKA designs and revision TKA (p < 0.001).

CONCLUSION

Differences in patterns of BTU at the popliteus muscle origin between primary TKA and revision prosthesis may be the result of decreased insertional tensile forces of the popliteus muscle after revision surgery due to increased stability provided by the revision design.

Bone SPECT/CT has excellent sensitivity and specificity for diagnosis of loosening and patellofemoral problems after total knee arthroplasty

PURPOSE

The primary purpose of this retrospective study with prospectively collected data was to evaluate the clinical value of SPECT/CT, in particular its impact on clinical diagnosis and patient management, in patients with pain, stiffness, or swelling after primary total knee arthroplasty (TKA). The secondary purpose was to determine the sensitivity and the specificity of SPECT/CT for different pathologies such as loosening and patellofemoral overloading.

METHODS

A retrospective analysis was carried out on 214 knees in 202 consecutive patients (mean age 69 ± 11 years) with persistent or recurrent knee pain after TKA. All patients underwent clinical examination, standardised radiographs, and 99mTc-hydroxymethane diphosphonate (HDP) SPECT/CT as part of a routine diagnostic algorithm. The diagnoses before and after SPECT/CT and final treatment were recorded. TKA component position was routinely measured on 3D-reconstructed images. Intensity and anatomical distribution of bone tracer uptake were determined.

RESULTS

SPECT/CT changed the clinical diagnosis and final treatment in 139/214 (65%) knees. In 117 (54.7%) out of 214 patients, revision surgery was proposed following SPECT/CT. Early onset of pain was significantly (p = 0.011) correlated with tibiofemoral stress pattern in SPECT/CT. A total of 86 knees (40.2%) were surgically revised using semi-constrained or fully constrained TKA. In 35 patients, a secondary patellar resurfacing was performed. SPECT/CT showed the clinical diagnosis to be incorrect for suspicion of tibial component loosening in 56 patients (26.2%), femoral component loosening in 53 patients (24.8%), and patellofemoral overloading/progressive patellofemoral osteoarthritis in 26 patients (12.1%) and provided different underlying causes of persistent knee pain after TKA. Likewise, SPECT/CT identified tibial component loosening in 8 patients (3.7%), femoral component loosening in 4 patients (1.9%), and patellofemoral OA in 71 patients (33.2%) without prior clinical suspected diagnosis. The sensitivity and specificity of SPECT/CT for detection of patellofemoral OA was 96.5% and 96.2%, respectively. The sensitivity and specificity for detection of tibial component loosening was 96.0% and 100%, respectively. The sensitivity and specificity for detection of femoral component loosening was 95.0% and 100%, respectively.

CONCLUSION

The diagnostic benefits of SPECT/CT in the challenging and complex cohort of patients with pain after primary TKA have been proven. The excellent sensitivity and specificity for detection of tibial or femoral component loosening and diagnosis of patellofemoral OA have been surgically confirmed. Due to the benefits in establishing the correct diagnosis, SPECT/CT should be implemented as part of the routine diagnostic algorithm for patients with pain after primary TKA.

LEVEL OF EVIDENCE

II.

Are modern knee outcomes scores appropriate for evaluating patellofemoral degeneration in osteoarthritis? Evaluation of the ceiling and floor effects in knee outcomes scores

INTRODUCTION

Patellofemoral (PF) degeneration plays an important role in knee function in the context of osteoarthritis. A specific evaluation of PF symptoms is needed to better understand the initial functional status of the knee before surgery. The aim of this study was to assess the validity of patient-related outcome measures (PROMs) for knee scores and PF scores in knee osteoarthritis.

HYPOTHESIS

PF scores are more reliable for evaluating anterior knee pain than global knee scores in the context of PF degeneration in osteoarthritis.

MATERIAL AND METHODS

We performed a prospective single-center study of continuous patients included between January 2017 and January 2018 in our surgical department for total knee arthroplasty (TKA) for primary knee osteoarthritis. The analysis used global knee PROMs (KOOS and new IKS) and PF-specific PROMs (HSS Patella score, Kujala score and Lille score). Floor and ceiling effects were determined for each score based on tibiofemoral and PF degeneration on radiographic views; it was considered significant when greater than 15%.

RESULTS

We included 114 TKA procedures in 113 consecutive patients. According to the Iwano classification, no significant floor or ceiling effect was found for the PF preoperative scores (0-12%). The KOOS ADL and QOL scores were particularly affected by the ceiling and floor effects, whatever the patellofemoral degeneration (23-88%). In cases of severe PF degeneration (Iwano grade 3 and 4), no significant differences in the distribution of the functional scores were found.

DISCUSSION

Modern knee outcome scores used to evaluate knee function do not monitor PF degeneration and related symptoms in the context of knee osteoarthritis according to the Iwano classification. PF scores do not have a floor and ceiling effects even if the severity of the PF degeneration is difficult to identify preoperatively. Physicians should be aware of this effect on the preoperative functional evaluation before TKA.

LEVEL OF EVIDENCE

III, comparative prospective study.

TKA design-integrated trochlea groove rotation reduces patellofemoral pressure

PURPOSE

Total knee arthroplasty (TKA) leaves 11-25% of the patients unsatisfied, and patellofemoral joint pain is one cause. This study aimed to compare the differences between kinematics and load transfer in the same knee with axial internal/external rotation of the femoral component (CoRo) versus a separate axial internal/external trochlear groove rotation (TrRo) which is included in the TKA trochlea design.

METHODS

A validated weight-bearing finite element model with modifications of the TKA axial femoral component rotation (CoRo) and a modified trochlear rotation (TrRo) was calculated and analysed.

RESULTS

Compared to the neutrally implanted TKA at 105° of flexion, a 6° external rotation of the trochlear groove reduced the retropatellar stress by 7%, whereas a 3° internal trochlear groove rotation increased the retropatellar stress by 7%. With femoral component rotation, the tibia inlay stress of 6.7 MPa at 60° of flexion was two times higher both with a 3° internal component rotation and a 6° external rotation.

CONCLUSION

These results demonstrate in the tested TKA design that a trochlear groove rotation can reduce retropatellar stress. Additionally, during the TKA operation, the surgeon should be aware of the significant influence of axial femoral component rotation on mechanical inlay stress during flexion and of the fact that even small changes in the patellofemoral joint may influence the tibiofemoral joint. These results support that an external rotation of the femoral component should be preferred in TKA to avoid anterior knee pain. Furthermore, new developed TKA designs should integrate an externally rotated trochlea groove.

Kinematically aligned total knee arthroplasty reproduces native patellofemoral biomechanics during deep knee flexion

PURPOSE

The implant positioning for kinematically aligned total knee arthroplasty (TKA) differs fundamentally from conventional mechanically aligned TKA. This difference may affect patellofemoral (PF) biomechanics after TKA. This cadaveric study tested the hypothesis that kinematically aligned TKA would restore PF biomechanics to the native condition better than mechanically aligned TKA.

METHODS

Seven pairs (14 knees) of fresh-frozen cadavers were tested. All specimens were mounted on a customized knee-testing system and digitized using a Microscribe 3DLX instrument (Revware Inc., Raleigh, NC, USA) to measure patellar kinematics in terms of patellar varus/valgus rotation, medial/lateral position, flexion/extension rotation and proximal/distal position at knee flexion angles of 0°, 30°, 60°, 90°, and 120°. The medial and lateral PF joint contact pressure distributions at 120° of knee flexion were measured using a K-scan system (Tekscan Inc., Boston, MA, USA). All patellae remained unresurfaced. For each pair, one knee was randomly assigned to kinematically aligned TKA and the other to mechanically aligned TKA performed using the conventional measured resection technique. During kinematically aligned TKA, the amount of femur and tibia resected was equivalent to implant thickness to maintain the patient-specific joint line. All patellar kinematics were measured and compared between the native condition and after surgery.

RESULTS

The patellae of mechanically aligned TKA rotated more valgus and was positioned more laterally compared with those of kinematically aligned TKA at knee flexion angles ≥ 90°. Neither the patellar flexion/extension rotation nor the proximal/distal position differed between either prosthetic knee design and the native knee at all flexion angles. The contact pressure distribution between the medial and lateral PF joint after kinematically aligned TKA were similar to those of the native knee, while the lateral PF joint contact pressure after mechanically aligned TKA was higher than that of the native knee (p = 0.038).

CONCLUSIONS

Kinematically aligned TKA better restores patellar kinematics and PF contact pressure distribution to the native condition than mechanically aligned TKA during deep knee flexion. These findings provide clues to understand why kinematically aligned TKA is associated with less anterior knee pain and better PF functional performance compared to mechanically aligned TKA. Patients undergoing kinematically aligned TKA may experience a more normal feeling during deep knee flexion activities.

Flexed femoral component improves kinematics and biomechanical effect in posterior stabilized total knee arthroplasty

PURPOSE

The kinematics and biomechanics of the knee joint are important in ensuring patient satisfaction and functional ability after total knee arthroplasty (TKA). There has been no study on knee joint mechanics with regard to the sagittal alignment of the femoral component. The objective of this study is to determine the extent of the impact of the femoral component's sagittal alignment on kinematics and biomechanics.

METHODS

A validated computational TKA model was used. The femoral component was simulated at - 3°, 0°, 5°, and 7° of flexion in the sagittal plane. This study evaluated the tibiofemoral (TF) joint kinematics, contact point, quadriceps force, and contact stress on the patellofemoral (PF) joint under a deep-knee-bend condition.

RESULTS

The kinematics of the TF joint in the posterior direction increased with the flexion of the femoral component position. For all tasks, the overall posterior locations of the TF contact points were observed in the medial and lateral compartments as the femoral component flexion angle increased. The quadriceps force and contact stress on the PF joint decreased with the femoral component flexion.

CONCLUSION

This study found that the femoral component sagittal position is an important factor in knee joint mechanics. In this study, the flexion of femoral component showed a stable reconstruction of the knee extensors' mechanism. Surgeons may consider neutral-to-mild flexed femoral component position, without concerns of anterior notching of the femoral cortex.

Patients undergoing total knee arthroplasty using a contemporary patella-friendly implant are unaware of any differences due to patellar resurfacing

PURPOSE

Anterior knee pain after total knee arthroplasty (TKA) is often unexplained, spurring ongoing debates on the need for patellar resurfacing. It was hypothesized that a contemporary patella-friendly implant would restore patellofemoral kinematics more physiologically than outdated implants and that there would be no perceived or clinically demonstrable differences due to resurfacing of patella (RP).

METHODS

This prospective bilateral randomized study was undertaken in 49 patients scheduled for the same-day bilateral TKAs. One knee was subjected at random to RP while withholding RP on the opposing side (non-RP). A recently approved single-radius femoral prosthesis featuring a deep, elongate trochlear groove with lateral tilt and a high lateral flange was implanted bilaterally in all patients. Mean follow-up duration was 5 years. Group comparisons were based on patient-reported outcomes [anterior knee pain, Forgotten Joint Score (FJS), and side preference], physician-rated results [Feller patellofemoral (PF) score], radiographic patellar position, patella-related complications, and need for reoperation.

RESULTS

There were no differences in midterm rates of anterior knee pain (RP 8%; non-RP 4%; n.s.), FJS (all n.s.), or side preference (RP 47%; non-RP 45%; n.s.), nor did the groups differ by Feller PF score (all n.s.) or radiographic patellar position (all n.s.). No secondary resurfacings of non-RP or RP revisions were required.

CONCLUSIONS

Patients were incapable of distinguishing whether RP was done, casting doubt on its benefits. Surgeons may thus forego RP during TKA when using contemporary patella-friendly TKA implants.

LEVEL OF EVIDENCE

Therapeutic study, Level I.

Good correlation between bone tracer uptake in SPECT/CT and intraoperative findings of chondral lesions graded with the ICRS scoring

The question if bone tracer uptake in SPECT/CT reflects the intraoperative cartilage status of the knee is still unanswered. In this study, thirty-three consecutive patients (male:female = 11:22; mean age ± standard deviation 61 ± 15) with bi- or tri-compartmental knee osteoarthritis who underwent SPECT/CT before total knee arthroplasty (TKA) were collected. The knee was graded in eleven different anatomical regions. In each region, the maximal relative bone tracer uptake (mrBTU) was measured twice by two observers with a six weeks interval. The intraclass correlation coefficients (ICC) showed excellent correlations and mean values were used. Intraoperatively every region was assessed with the macroscopic International Cartilage Repair Society (ICRS) scoring. A factorial analysis and a non-parametrical Spearman's correlation were calculated among the 11 knee regions on both mrBTU and ICRS scores and significant correlations were seen between regions belonging to the same knee compartment (p < 0.05). A non-parametrical Spearman's correlation was also performed to investigate the correlation between rmBTU in SPECT/CT and intraoperative ICRS cartilage grading. Significant correlations were seen on the medial compartment, on the proximal femoral trochlea and on the medial patellar facet (p < 0.05). A significant correlation between SPECT/CT and intraoperative findings was so demonstrated in several regions. The low accuracy of the macroscopic ICRS scoring system on grade I-II lesions could have affected the missing correlations on the lateral compartment since the selected presented mainly a varus gonarthrosis. The use of an objective measure as the rmBTU could overcome the limit of the subjectivity of MRI findings in early osteoarthritis. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:522-528, 2019.

Suboptimal patellofemoral alignment is associated with poor clinical outcome scores after primary total knee arthroplasty

BACKGROUND

Proper patellofemoral alignment is an important goal in total knee arthroplasty (TKA). Acceptable patellar alignment is defined as patellar tilt less than or equal to 5° and patellar displacement less than or equal to 5 mm. Previous studies reported an incidence of post-operative patellar malalignment in TKA from 7 to 35%. However, correlation between patellar malalignment and clinical outcome after TKA remains unclear. The purpose of the present study was to evaluate the effect of patellar tilt and displacement on the clinical outcome of TKA.

METHODS

A retrospective review of 138 primary TKAs with a minimum of 2 year follow-up is reported. Pre-operative and post-operative mechanical axis, patellar tilting angle and patellar displacement were measured. Clinical outcomes were evaluated by the knee functional scores including the Knee Society Score (KSS), Knee injury and Osteoarthritis Outcome Score (KOOS), and Western Ontario McMaster University Osteoarthritis Index (WOMAC) at final follow-up.

RESULTS

Forty-two (30%) primary TKAs had suboptimal patellofemoral alignment with a patellar tilt angle greater than 5° or lateral patellar displacement of more than 5 mm. There was no statistical difference in pre-operative mechanical axis, pre-operative patellar tilt angle, or pre-operative lateral patellar displacement between the primary TKAs with proper patellofemoral alignment and those with suboptimal alignment. Patients with post-operative patellar tilt or displacement had clinically significant reductions in KSS, KOOS, and WOMAC when compared with patients without post-operative patellar tilt or displacement. The odds of having a fair or poor post-operative result, an odds ratio of 3.4 (95% CI 1.6-7.2) for KSS, 6.4 (95% CI 2.9-14.2) for KOOS, and 5.9 (95% CI 2.6-13.5) for WOMAC, were associated with suboptimal patellofemoral alignment.

CONCLUSION

Establishing proper patellofemoral alignment remains an essential goal of primary TKA. There is a strong association between suboptimal post-operative patellofemoral alignment and poor clinical outcome scores after primary TKA.

Bloodpool SPECT as part of bone SPECT/CT in painful total knee arthroplasty (TKA): validation and potential biomarker of prosthesis biomechanics

PURPOSE

To compare bloodpool SPECT with planar imaging in bone SPECT/CT of painful total knee arthroplasty (TKA) with respect to inter-rater agreement, confidence, prosthesis outcome, and biomechanical functioning.

METHODS

Retrospective study of bloodpool SPECT and planar control images. Four raters used the validated Bruderholz scheme and a 5-point scale to grade uptake. Inter-rater agreement and overall confidence scores were calculated. Variable cluster analysis was performed to identify patterns of uptake, and associations between patterns and prosthesis outcome and biomechanical functioning were examined.

RESULTS

In all, 55 knees in 43 patients were analyzed (median follow-up 17 months; revision rate 21.8%). SPECT significantly improved inter-rater agreement in 24% of regions (all P < 0.05) and overall confidence by 20% (P < 0.001). Regional uptake cluster analysis showed improved antero-posterior separation with SPECT, and distinct patterns associated with prosthesis survival in lateral femoral (P = 0.041) and medial tibial (P < 0.001) regions. The prognostic value of SPECT outperformed planar imaging for tibial (P < 0.001), patellar (P = 0.009), and synovial (P = 0.040) assessment. Internal femoral malrotation resulted in increased uptake in posteromedial (P = 0.042) and anterolateral (P = 0.016) femoral, and lateral patellar (P = 0.011) regions. Internal tibial malrotation increased uptake in posterolateral (P = 0.026) and posteromedial tibial (P = 0.005), and medial patellar regions (P = 0.004). Bloodpool SPECT improved the prognostic value of late-phase SPECT/CT for the assessment of the medial tibial region.

CONCLUSIONS

Bloodpool SPECT outperforms planar assessment of painful TKAs and the identification of distinct uptake patterns make it a potentially clinically relevant biomarker of prosthesis survival and biomechanical functioning.

Evaluation of the Effect of the Sulcus Angle and Lateral to Medial Facet Ratio of the Patellar Groove on Patella Tracking in Aging Subjects with Stable Knee Joint

Purpose

To determine whether the sulcus angle and the lateral to medial facet ratio correlate with patella lateral displacement and tilt in patients without patella instability.

Methods

Computed tomography images of the lower limb of 64 patients without known arthropathy were collected. Three-dimensional models of the lower limb with a unified coordinate system were rebuilt by using Mimics software. The sulcus angle, lateral to medial facet ratio, lateral trochlear inclination of the patellar groove, tibial tuberosity-trochlear groove (TT-TG) distance, bisect offset index, and lateral tilt of the patella were measured. Pearson's correlation test was used to determine the relationship between the aforementioned parameters.

Results

Data from 51 patients were analyzed. The sulcus angle was negatively correlated with lateral tilt inclination (p < 0.001, r = 0.8406) and positively correlated with the bisect offset index (p = 0.003, r = 0.634) and patellar tilt (p = 0.03, r = 0.551); the lateral to medial facet ratio was positively correlated with TT-TG distance (p = 0.003, r = 0.643) and bisect offset index (p = 0.026, r = 0.559).

Conclusion

The sulcus angle and lateral to medial facet ratio of the patellar groove can influence patella tracking in patients with stable knee joints.